www.elektor.com APRIL 2008 aus$ 12.90 -nz$ 15.50 -sar 84.95 -us$ 9.95

DigiButler - a Coldfire home automation server
Sweep Generator - with a Parallax SX28 micro
ATM18 AVR Board - ATmega88 building block

9 770268

45113 5

ft yv

II

[1

II

1

ft. 1

r. )1 T. fl r, riffc

aytar Catalogue OUT NOW
rder on-line at
electronics, co. uk/ catalogue

Automotive Kits

■ i

■l

I i.

Ignition System

KC-5442 £26.25 + post & packing
This advanced and versatile ignition system can be used on
both two & four stroke engines. The system can be used to
modify the factory ignition timing or as the basis for a
stand-alone ignition system with variable ignition timing,
electronic coil control and anti-knock sensing. Kit supplied
with PCB, diecast case and all electronic components.
Features include:

• Timing retard & advance over a wide range

• Suitable for single coil systems

• Dwell adjustment

• Single or dual mapping ranges

• Max & min RPM adjustment

• Optional knock sensing

• Optional coil driver

Knock Sensor

KC-5444 £5.00 + post & packing
Add this option to your KC-5442 Programmable High Energy
Ignition system and the unit will automatically retard the
ignition timing if knocking is detected. Ideal for high
performance cars running high octane fuel.

Requires a knock sensor which is
cheaply available from

most auto recyclers. Kit %■ : h* « ,

supplied with PCB, and
all electronic components.

Ignition Coil Driver

KC-5443 £13.00 + post & packing
Add this ignition coil driver to the KC-5442
Programmable Ignition System and you have a
complete stand-alone ignition system that will
trigger from a range of sources including points,
Hall Effect sensors, optical sensors, or the 5 volt
signal from the car's ECU. Kit includes PCB with
overlay and all specified components.

Be one of the
first to get our brand new
colour catalogue. It’s bursting
with over 800 new products, „ a?
all with PDS pricing and in «l

full colour.

Hand Controller

KC-5386 £25.95 + post & packing
This LCD hand controller is required during the
initial setting-up procedure. It plugs into the main
unit and can be used while the engine is either
running or stopped. Using this Hand Controller, you
can set all the initial parameters and also program
the ignition advance/retard curve. Kit supplied with
silk screened and machined case, PCB, LCD, and all
electronic components.

hi

Three Stage FM Transmitter

KJ-8750 £6.50 + post & packing
This is a Three-Stage radio transmitter that is so stable you
could use it as your personal radio station and broadcast all
over you house. Great for experiments in audio transmission.
Includes a mic, PCB with overlay and all other parts

• Requires 9V battery (not included)

• Instructions included in kit

How To Order

Post and Packing Charges

Order Value

Cost

Order Value

£200 -£499.99
£500+

Cost

£30

£40

£10 - £49.99 £5

£50 - £99.99 £10

£100 -£199.99 £20

Max weight 121b (5kg). Heavier parcels POA.

Minimum order £10.

Note: Products are despatched from Australia, so local
customs duty and taxes may apply.

How to order:

Phone: Call Australian Eastern Standard Time Mon-Fri
on 0800 032 7241. Fax: +61 28832 3118
Email: techstore@jaycarelectronics.co.uk
Post: 320 Victoria Rd, Rydalmere NSW 2116 Australia
Expect 10-14 days for air parcel delivery

Check out the Jaycar range in your FREE Catalogue - logon to

www.jaycarelectronics.co.uk/elektor

or check out the range at

www.jaycarelectronics.co.uk

More Projects

0800 032 7241

(Monday - Friday 09.00 to 17.30 GMT + 10 hours only)
For those who want to write: 320 Victoria Rd,
Rydalmere NSW 2116 AUSTRALIA

Variable Boost Kit
for Turbochargers

KC-5438 £6.00 + post & packing
It's a very simple circuit with only a few components
to modify the factory boost levels. It works by
intercepting the boost signal from the car's engine
management computer and modifying the duty cycle of
the solenoid signal. Kit supplied in short form with PCB
with overlay, and all specified electronic components.

Combine these
two kits to get the
most cost effective car
performance increase
on the market!

Fuel Cut
Defeat Kit

KC-5439 £6.00 + post & packing
This simple kit enables you to defeat the factory fuel
cut-out signal from your car's ECU and allows your
turbo charger to go beyond the typical 15-17psi factory
boost limit.

Note: Care should be taken
to ensure that the boost
level and fuel mixture
don’t reach unsafe
levels. Kit
includes PCB
with overlay,
and all electronic
components.

IOA iZV DC motor
Speed Controller

KC-5225 £7.75 + post & packing

Use this kit for controlling 12V DC motors in cars such
as fuel injection pumps, water/air intercoolers and
water injection on performance cars. You can also use it
for headlight dimming and for running 12VDC motors in
24V vehicles. The kit will control loads up to 10 amps,
although the addition of an extra MOSFET
transistor will double that
capacity to an amazing
20 amps.

• Kit includes PCB
plus all electronic
components to build
the 10A version.

I nucar

BitScope PC Oscilloscopes & Analyzers

DSO Test Instrument Software for BitScope Mixed Signal Oscilloscopes

4 Channel BitScope

2 Channel BitScope

Pocket Analyzer

Digital Storage Oscilloscope

Up to 4 analog channels using industry standard
probes or POD connected analog inputs.

Mixed Signal Oscilloscope

Capture and display up to 4 analog and 8 logic
channels with sophisticated cross-triggers.

Spectrum Analyzer

Integrated real-time spectrum analyzer for each
analog channel with concurrent waveform display.

Logic Analyzer

8 logic, External Trigger and special purpose
inputs to capture digital signals down to 25nS.

Data Recorder

Record anything DSO can capture. Supports
live data replay and display export.

Networking

Flexible network connectivity supporting
multi-scope operation, remote monitoring and
data acquisition.

BitScope DSO Software for Windows and Linux

BitScope DSO is fast and intuitive multi-channel test and measurement software for your
PC or notebook. Whether it's a digital scope, spectrum analyzer, mixed signal scope,
logic analyzer, waveform generator or data recorder, BitScope DSO supports them all.

Capture deep buffer one-shots or display waveforms live just like an analog scope.
Comprehensive test instrument integration means you can view the same data in
different ways simultaneously at the click of a button.

DSO may even be used stand-alone to share data with colleagues, students or
customers. Waveforms may be exported as portable image files or live captures replayed
on other PCs as if a BitScope was locally connected.

BitScope DSO supports all current BitScope models, auto-configures when it connects
and can manage multiple BitScopes concurrently. No manual setup is normally required.
Data export is available for use with third party software tools and BitScope's networked
data acquisition capabilities are fully supported.

Data Export

Export data with DSO using portable CSV files or
use libraries to build custom BitScope solutions.

www.bitscope .com

4/2008 - elektor

3

Spring time!

New initiatives at Elektor

I do hope spring is in the air when you
read this, because at the time of writing
I can only see hail and sleet from the
windows of Elektor House, and the wind
is howling in the chimneys. Elektor staff,
including myself, has just returned from
the Embedded 2008 show in Nurem-
berg, Germany. We were happy to see
not only representatives of small, large
and would-be companies active in the
microcontroller arena, but also a good
many readers of our publications. Long
time subscribers, occasional newsstand
buyers, newcomers... thanks for drop-
ping by and letting us know what you
like (and hate) about Elektor. Remark-
ably, none of our direct competitors had
a presence at the Embedded show, and
even the Circuit Cellar booth was empty.
Although the ATM1 8 and DigiButler
projects published in this issue were
developed well before the Embed-
ded 2008 show, it was good to meet
up with our contact persons at the
companies behind the initiatives and
discuss the progress. In the case of the
ATM1 8, a working quadrocopter could
be seen in action at the Elektor booth
(video on YouTube soon). DigiButler, our
open-source Coldfire home automation
server, was demonstrated on the impres-
sive Freescale stand.

It's difficult if not impossible to pinpoint
a single trend from this year's Embed-
ded show, but the buzzwords are
definitely C-to-hardware, open-source,
development kits, CAN, fabless com-
panies, core licensing and fun applica-
tions. Unfortunately, there was also a lot
of vapourware around.

Back to the world of discrete compo-
nents and (mostly) analogue design,

I guess publishing an audio power
amplifier using error correction can also
be ca lied an initiative on our part, if
only because the high-end audio scene
seems to have regurgitated conventional
feedback concepts for more years than I
care to remember. Elektor having a fine
reputation for high-end audio designs
that can be built at home, it's time for a
fresh, audacious, approach!

The concept of i-TRIXX — simple circuits
from the Elektor labs combined with
'geeks & gadgets' stuff supplied through
a free weekly newsletter — has proved
very successful in Germany and The
Netherlands over the past year or so,
and you may have seen a crop of i-TRIXX
circuits already in our December 2006
and 2007 issues. The English language
version of i-TRIXX was launched on 5
March — have a look at www.i-trixx.
com and play the quiz — I did badly.

Jan Buiting
Editor

lenor

electronics worldwide

Most solid state power amplifiers employ some form of global negative
feedback to reduce non-linearities and output impedance. In some cases,
designers exploit alternatives like feedforward to circumvent perceived
disadvantages of global negative feedback. The present design uses er-
ror correction as (re)defined by Malcolm Hawksford around 1984.

24

a Power Amplifier

56 Frequency Sweep Oscillator

This project
found its
origins in a
need to see
and measure
the frequency
response of
audio filters,
tone controls and
amplifiers in real
time. An SX28 mi-
crocontroller module from Paral-
lax turned out to be a really good means of implementing the circuit.

CONTENTS

a Coldfire 32-bit home
automation server (1)

Here's advanced, all open-sour-
ce hardware and PC software
that allows remote switching of
electrical loads across networks
including the biggest we know
- the Internet. The ingredients
from the Freescale/Elektor kit-
chen: 32-bit embedded techno-
logy, free software, a low-cost
kit for the hardware and free
software tools.

1 6 Elektor Internet Radio (EIR)

Nowadays you can access every Internet
radio programme in the world by receiving,
buffering and decompressing IP packages.

This is all very easy with the state-of-the-art hard-
ware described in this article. All open-source!

Volume 34
April 2008
no. 376

projects

16 Elektor Internet Radio (EIR)

24 paX- a Power Amplifier with
Error Correction

Dig i Butler - a Coldfire 32-bit
home automation server (1)

40 ATM 18 AVR Board

56 Frequency Sweep Oscilla-
tor

62 Keyboard goes Game
Controller

Lucky Dip

74 Design Tips:

Automatic aquarium feeder
Ultra-responsive peak detector

technology

48 Free, Open, Licentious

Designing Capacitive
Sensing Interfaces for
Home Appliances

68 Energy Conscious

73 Labtalk:

My microcontroller doesn't go...

info & market

6 Colophon

8 Mailbox

News & New Products

66 Review: (jC goes Analogue
(Cypress PSoC)

81 Elektor SHOP

Sneak Preview

infotainment

76 Hexadoku

77 Retronics:

Formant synthesizer (1977)

ELECTRONICS WORLDWIDE

elektor international media

Elektor International Media provides a multimedia and interactive platform for everyone interested in electronics.
From professionals passionate about their work to enthusiasts with professional ambitions.

From beginner to diehard, from student to lecturer. Information, education, inspiration and entertainment.

Analogue and digital; practical and theoretical; software and hardware.

--aasw**

Surround

■SjSftwJ're builds
1,1 'hardware

UK Uinveriity Courses

!«r IlWC'HKLr tlMI -<lr Crv^M.I

5 » .atalpn

Volume 34, Number 376, April 2008 ISSN 1 757-0875

Elektor Electronics aims at inspiring people to master electronics at any personal
level by presenting construction projects and spotting developments in electronics
and information technology.

Publishers: Elektor International Media, Regus Brentford,

1000 Great West Road, Brentford TW8 9HH, England. Tel. (+44) 208 261
4509, fax: (+44) 208 261 4447 www.elektor.com

The magazine is available from newsagents, bookshops and electronics retail
outlets, or on subscription.

Elektor is published 1 1 times a year with a double issue for July & August.

Elektor is also published in French, Spanish, German and Dutch. Together with franchised
editions the magazine is on circulation in more than 50 countries.

International Editor:

Wisse Hettinga (w.hettinga@elektor.nl)

Editor: Jan Buiting (editor@elektor.com)

International editorial staff: Harry Baggen, Thijs Beckers,
Ernst Krempelsauer, Jens Nickel, Guy Raedersdorf.

Design sta Antoine Authier (Head),

Ton Giesberts, Luc Lemmens, Jan Visser, Christian Vossen

Editorial secretariat: Hedwig Hennekens (secretariaat@elektor.nl)
Graphic design / DT Giel Dols, Mart Schroijen

Managing Director / Publisher: Paul Snakkers
Marketing: Carlo van Nistelrooy

Customer Services: Anouska van Ginkel

Subscriptions: Elektor International Media,

Regus Brentford, 1000 Great West Road, Brentford TW8 9HH, England.
Tel. (+44) 208 261 4509, fax: (+44) 208 261 4447
Internet: www.elektor.com

6

elektor - 4/2008

FPGA Course on CD-ROM

Modern technology for everyone

[3lektor

L_3shop

FPGAs have established a firm position in the modern elec-
tronics designer's toolkit. Until recently, these 'super com-
ponents' were practically reserved for specialists in high-tech
companies. That's all changed now, also because of the
Elektor FPGA module. The combination of the module and
the prototyping board is the perfect introduction to FPGAs.
The nine lessons on the courseware CD-ROM are a step by
step guide to the world of Field Programmable Gate Array
technology. Subjects covered include not just digital logic
and bus systems but also building an FPGA Webserver,
a 4-channel multimeter and a USB controller. The CD also
contains PCB layout files in pdf format, a Quartus manual,
project software and various supplementary instructions.

ISBN 978-90-538 1-225-9 • £14.50 • US$29.00

Free of chorcj®

FPGA product bundle*.

Order quickly and safe through WWW.el6ktor.com/shop

or use the Order Form near the end of the magazine

Email: subscriptions@elektor.com

Rates and terms are given on the Subscription Order Form

Head Office: Elektor International Media b.v.

P.0. Box 1 1 NL-61 1 4-ZG Susteren The Netherlands
Telephone: (+31 ) 46 4389444, Fax: (+31 ) 46 43701 61

Distribution: Seymour, 2 East Poultry Street, London EC1A, England
Telephone:+44 207 429 4073

UK Advertising Huson International Media, Cambridge House,
Gogmore Lone, Chertsey, Surrey KT1 6 9AP, England.

Telephone: +44 1932 564999, Fax: +44 1932 564998

Email: p.brady@husonmedia.com
Internet: www.husonmedia.com
Advertising rates and terms available on request.

International Advertising Frank van de Raadt, address as Head Office

Email: advertenties@elektor.nl

Advertising rates and terms available on request.

Copyright Notice

The circuits described in this magazine are for domestic use only. All drawings, photographs,
printed circuit board layouts, programmed integrated circuits, disks, CD-ROMs, software carri-
ers and article texts published in our books and magazines (other than third-party advertise-
ments) are copyright Segment, b.v. and may not be reproduced or transmitted in any form
or by any means, including photocopying, scanning an recording, in whole or in part without

prior written permission from the Publishers. Such written permission must also be obtained
before any part of this publication is stored in a retrieval system of any nature. Patent protec-
tion may exist in respect of circuits, devices, components etc. described in this magazine.
The Publisher does not accept responsibility for failing to identify such patent(s) or other
protection. The submission of designs or articles implies permission to the Publishers to alter
the text and design, and to use the contents in other Segment publications and activities. The
Publishers cannot guarantee to return any material submitted to them.

Disclaimer

Prices and descriptions of publication-related items subject to change.
Errors and omissions excluded.

© Elektor International Media B.V. 2008

Printed in the Netherlands

4/2008 - elektor

7

INFO & MARKET

MAILBOX

Early experiments with a radio and U-series valves

At the age of a secondary-school student (15), I received a ra-
dio from my grandparents. It had an attractive brown Bakelite
case with a loudspeaker at the rear and a small grille covered
with cloth. It was a fairly lightweight set, without a heavy built-
in mains transformer. The Bakelite case could be removed eas-
ily by loosening two screws at the rear. There were lamps in-
side: U-series valves with thin steel pins fitted in valve sockets. I
can still remember that one of them was a type UCH21 .

If I interchanged the positions of the valves, the radio
stopped working. Evidently they were different types
of valves... The filaments of all the valves were con-
nected in series, as I quickly discovered. If I pulled
out one of the valves, the filaments of the other valves
went dark. The high voltage was taken directly from
the (then 220 V) AC mains, and it was connected di-
rectly to the chassis. Safety was apparently not an is-
sue! With a bit of experimenting, at that time I already
found out that rectifying 220 V AC produces a much
higher DC voltage than 220 V! Only much later did I
really understand why.

With further experimenting, I also noticed that the
chassis was sometimes live'. That proved to be re-
lated to which way the power plug was plugged in.

With nail polish borrowed from my sister, I painted
a small line on the AC plug and socket. Then I could work
'safely' as long as the plug was the 'right way round' in the
socket (Ed.: older AC wall outlets in The Netherlands did not
have plug polarisation).

By twiddling the trimmers, I managed to shift and stretch the medi-
um-wave band so much that I could receive Scheveningen Radio

coastguard. After that it was impossible to make the tuning scale
correct again, but that didn't bother me.

The radio set proved to cause interference to the radio in the
sitting room. By experimenting, I found a sensitive point in
the radio. If you touched one of the components, a whistling
sound came from the other radio. Later I managed to connect
a crystal headphone to the radio and use it as a microphone.
The result could be heard a block away: the pirate transmit-
ter 'Grannie' was born! However, the neighbours were not
at all pleased, and the local policeman was equally
unhappy.

However, this problem was sorted out quite quickly. I
often experimented with the set while it was connected
to the AC mains. This involved operating the radio
while it was upside down on the table. At a certain
point I dropped a component in the radio, and with-
out thinking I tried to grab it. I received an enormous
electric shock, and my hand tore the wiring to pieces.
Most likely my muscles contracted due to the current
that flowed through my hand. The short circuit in the
radio caused the fuse to blow. That wasn't anything
special for my parents - my father knew how to repair
fuses with bit of wire on the outside of the porcelain
cartridge.

Looking back on this adventure, I realise how lucky
you can be with electricity. But I still keep saying, 'Don't try to
do it yourself this way!'

Kees de Groot (Netherlands)

This bit of electronics nostalgia will no doubt bring back fond
memories for many of our readers

E-blocks for vocational
secondary schools

Dear Editor — we want to
have students at a vocational
secondary school learn a pro-
gramming language that they
can ultimately use to control
devices or equipment via a PC
and an I/O module (possibly
separate).

We formerly used Pascal for
this, but it is now too old.

We presently have your
Flowcode, E-blocks, Visual
Basic, etc. What would you
recommend?

Edward Ransbury (UK)

The E-blocks and ECIO units
available from us are without
question a convenient and fun
way to let students get acquain-
ted with programming by using
Flowcode.

As E-blocks is a modular system ,
you can always expand it in or-
der to provide your students with
a constant stream of new chal-
lenges and let them discover
new areas of interest.

A large number of schools all

over Europe have now discover-
ed the benefits of the E-blocks
system for educational purposes
and are already using it.

Enclosure and heat sinks
for the Mugen final amp
Dear Elektor — how can I
obtain the heat sinks for the
Mugen hybrid amplifier de-
scribed in your October 207
issue?

Carl Hamlin (USA)

The enclosure used by the aut-
hor has integrated heat sinks on
the sides.

This enclosure comes from an
Italian companyand can be orde-
red here: www.modushop.biz/
ecommerce/cat079_l2.php2n= 1
Description: Pesante dissipante
03/300N 3U 10mm BLACK
The German company Schuro
can also supply a similar enclo-
sure that can be used with this
design. Have a look at:
www.schuro.de/preisl-gehaeuse.
htm

Mac programs

Dear Editor — in response to
your answer in the Mailbox
section of the February
2008issue of Elektor, I would
like to comment that the state-
ment that software for pro-
gramming microcontrollers is
not available for Mac OS X is
simply not true.

It is perfectly possible to
program AVR microcontrollers
under Mac OS X. There is a
lot of software available in
the open-source world, and
as Mac OS X is a Unix-based
system, in many cases it can
be used without modification.

I personally use the USBprog,
which was featured recently
in your magazine (October
2007), with my MacBook Pro
to program a variety of AVR
systems (AT2323, ATmegal6
and ATmega32).

The required software consists
of an assembler (AVRA) and a
programmer (avrdude), along
with a C complier, etc. as
necessary.

You can find all of them, ready

for direct use with Mac OS X,
at http://www.osx-avr.org.
There are various packages of
this sort in available, but I use
the above-mentioned programs
almost every day.

Finally, with regard to your
suggestion to install Windows
using Bootcamp, it is much less
expensive and more conven-
ient to install a Linux distribu-
tion (such as Ubuntu) on your
Bootcamp partition. Windows
XP is expensive, and it is not
popular among Mac users for
relatively irrational reasons.
Naturally, software such as
avrdude and avra can also be
used just as well under Linux.
Paul Boven (The
Netherlands)

Some programs don't work
right out of the box, but in
many cases there are pre-built
images available with good
installation guides. Although
you may not always have a
nice GUI environment for the
microprocessor, it is often
possible to configure Eclipse

8

elektor - 4/2008

Intel Unplugged 7 challenge

Dear Jan — I am a member of the group of students at the
Technical University of Delft in the Netherlands that partici-
pated in the Intel Challenge. And I am proud to say that we
received the Innovation Award, which you may have already
heard. Now I am busy writing a scientific paper on this.

In the November 2007 issue of Elektor, I saw that your had
also established a competition for the Intel Challenge. The
article in that issue included a table of measurements for
the energy profile of a laptop computer. We also performed
similar measurements, and for this reason I find the table
interesting for checking and comparison with our measure-
ments for the paper.

I would like to ask you exactly how these measurements were
made. The article includes all the usual information about the
configuration and specifications of the laptop, but I would
like to know where in the electrical path the measurements
were actually made. Were they made directly at the input to
the laptop, or ahead of the adapter? And was the battery
installed in the laptop, and if so, was it fully charged?

Ivo Roos (The Netherlands)

Antoine Authier, the head of our Elektor lab , is the best person
to answer this question:

To start with , my sincere congratulations to you for winning the
competition!

In order to measure the energy profile of the laptop computer
made available to us by Intel , we measured the voltage and the
current drawn by the laptop directly at the power connector of
the laptop (i.e. after the AC mains adapter). The battery was not
installed in the laptop for these measurements.

For your information , / should also say that:

- The computer hardware allows the backlight of the TFT screen
to be set to 8 different brightness levels , but we only made
measurements at the minimum and maximum levels.

- We used glxgear to activate and load the 3D GPU.

- Audio output via the built-in speakers was also active during
the measurements. We used three levels here: off (mute), half of
maximum volume , and maximum volume. The current consump-
tion only increased when signals with a strong bass content were
being reproduced.

- The basic application load consisted of running Open Office
and the GIMP on the laptop.

- The standard network application load consisted of constantly
sending a file (using the SCP protocol).

- Full CPU loading was achieved by reading a DVD and DivX
encoding.

Power (W)

(possibly with plugins) for the
microcontroller you want to
program, which means that
you do not have to create any
make files. In addition, much
of the tooling is open-source
and is maintained quite well
by an enthusiastic user commu-
nity (which can also provide a
lot of support).

Best wishes from a program-
ming OS X user!

Niels Langendorff
(Germany)

Dear Elektor — I have been a
Mac user for a long time now,
and I speak from experience
when I say that there is a
lot of software available for
programming microcontrollers
under Mac OS X.

This software supports the
8051 , Microchip, R8C, AVR
and ARM devices. If you
Google 'avr usb osx', you will
find the following links:
http://ccrma. Stanford.
edu/~matt/avr-osx.htm
http:// www.eecs. berkeley.
edu/ ~mseeman/ resources/

macmicro.html

http://chris.dwan.org/robot/

We are happy to pass these
comments on to Mr Pantott , who
asked the question last month ,
and of course to all other rea-
ders who use Mac systems.

Mai I Box Terms

• Publication of reader's orrespondence
is at the discretion of the Editor.

• Viewpoints expressed by
correspondents are not necessarily

those of the Editor or Publisher.

• Correspondence may be
translated or edited for length, clarity

and style.

• When replying to Mailbox

correspondence,
please quote Issue number.

• Please send your MailBox

correspondence to:

editor@elektor.com or
Elektor, The Editor,

1 000 Great West Road,
Brentford TW8 9HH , England.

Corrections & Updates

TV Surround Light

February 2008, p. 24-29, ref. 070487-1

In the parts list, the designations IC3 and IC4 should be inter-
changed. This does not affect the PCB or the circuit diagram.
All passive SMD parts are rectangular shape, footprint
SMD1206.

Of the ADC 1 1 75JM and ADC 1 1 75TC mentioned in the
article, only the -JM version is a discontinued part. The PCB
has been designed to accept both versions.

LED light bars are available from, among others, www.
reichelt.de (e.g. # LED 13,5RGB 3W).

Contrary to what is stated in the article text on page 28,
ready-built boards are not available through the Elektor Shop.

Digital Inspector

September 2007, p. 38-41, ref. 060092-1.

The circuit diagram erroneously shows XI as a 20 MHz
crystal. This should be 10 MHz as stated in the parts list.

MUGEN — a Hybrid Audio Amplifier

October 2007, p. 20-29, ref. 070069-1.

In the parts list, resistor R1 1 should be 1 8 kQ, not 1 8 Q.

This does not affect the circuit diagram, which shows the
correct value.

In the power supply schematic (Figure 3), the type code of
transformer T2 should be 78057, not 78075.

4/2008 - elektor

9

INFO & MARKET

NEWS & NEW PRODUCTS

Fanless System with Core Duo processor

New from BVM is the WPC-763,
an innovative l/O-rich fanless mi-
cro computer designed for applica-
tions such as digital signage, POS
terminals, kiosks, ATM, thin serv-
ers, in-vehicle displays, outdoor
entertainment, gaming, multime-
dia system and building automa-
tion; anywhere where 24/7 opera-
tion, low noise and protection from
dust are critical requirements.
Based on the Intel 945 GM and
ICH7M chipset, two versions are
available, either the Core Duo 2
GHz or Celeron M 1 .86GHz low
power processors. The systems ful-

ly support Vista in addition to Win-
dow XP and XP Embedded. With
six COM ports, a GPIO port for
data collection and unit manage-
ment, two USB 2.0 ports and an
LPT port, the I/O-rich unit is ready-

configured to accept the barcode
scanners, photo sensors, card
readers, limit switches, printer and
other peripherals required in POS
and kiosk applications without hav-
ing to install additional cards.

Power input is 1 2-28 VDC with ro-
bust on-board voltage conversions
that isolate the unit from voltage
spikes and current surges likely to
be encountered in automotive ap-
plications; an anti-vibration drive
bay provides protection from shock
and vibration. The watchdog timer
function automatically resets in the
event of a software crash to max-
imise system up-time in embedded
public applications.

www.bvmltd.co.uk

(071168-IV)

RF amplifiers From AR offer unique impedance-matching capabilities

Most RF amplifiers have a nominal
internal impedance of 50 ohms,
which is fine for most RF applica-
tions. But since more and more
low to mid-frequency RF applica-
tions are now characterized by
impedances other than the usual
50 ohms, AR RF/Microwave In-
strumentation has created a fam-
ily of RF power amplifiers that
can incorporate a variable output
impedance.

The A3 amplifiers feature an inter-
nal impedance transformer with se-
lectable output impedance values
of 12.5, 25, 50, 100, 200 and
400 ohms. An external impedance
transformer is also available for
applications requiring an extended
range from 8 - 2000 ohms.

The A3 family presently includes
three amplifiers: Model 800A3
(800 watts), Model 1500A3
(1500 watts), and Model 5000A3
(5000 watts). Each of the ampli-
fiers covers the 1 0 kHz to 3 MHz
frequency range.

The unique impedance-matching
capabilities along with the excel-
lent mismatch tolerance makes
the A3 series amplifiers extremely
well suited to the ever-changing
requirements of research & de-
velopment applications as well

as general purpose lab use.

A3 amplifiers are currently be-
ing used in applications for fluo-
rescent lighting, ultrasound, plas-
ma generation and testing, mass
spectrometers, piezoelectric crys-
tals, EMC, and a variety of low
to mid-frequency RF applications.
For other applications and more
information on impedance match-
ing, please see AR RF/Microwave
Application Note #47 - available
in the Application Notes section of
AR Information Resource Center on
the company's web site.

www.arww-rfmicro.com

www.emv.nl

(071168-1)

Pico Technology has released the lat-
est version of PicoScope 6. This ver-
sion is the first to support Pico's en-
tire range of USB PC Oscilloscopes,
and has a number of new features.

Owners of the high-performance
5000 Series scopes are already fa-
miliar with the improved layout and
advanced triggering options of Pico-
Scope 6. From now on, it will sup-

PicoScope 6 update

port all Pico oscilloscopes from the
entry-level 2000 Series, through the
general-purpose and high-precision
scopes of the 3000 Series, up to the
high-performance 5000 Series with
1 GS/s real-time sampling rate.

The most exciting new feature in
PicoScope 6 is resolution enhance-
ment. This filtering algorithm adds
up to four bits to the effective reso-
lution of a scope. For example, it
can boost the effective resolution of
a PicoScope 5203 or 5204 from
8 bits to 12 bits, and the 12-bit
PicoScope 3224 and 3424 high-
resolution scopes can now deliver
up to 16 effective bits. The resolu-
tion enhancement is selectable in
increments of 0.5 bit.

PicoScope 6 now has independ-
ent horizontal zoom, using a new
control that is easily accessed from
the toolbar to give precise control
over timebase magnification. The
familiar windowed zoom tool is
still there to allow quick inspection
of waveform details.

Finally, the text file export feature
has been improved so that text-for-
mat data files up to 1 million sam-
ples long can now be exported.
PicoScope 6.0.12 is available for
download now, free of charge,
from the Pico Technology website

www.picotech.com

(071168-11)

10

elektor - 4/2008

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PicoScope 5000 Series

250 MHz bandwidth

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o WiEh class-leading bandwidth, sampling rate, memory depth and an array of advanced high-end features, the
^ PicoScope 5000 PC Oscilloscopes give you the features and performance you need without any compromise.

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Advanced Triggers

In addition to the standard trippers the FitoScdpe 5000 senes comes its
standard with pulse width, window, dropout, delay, arid logic level triggering.

25Q MHs Spectrum Analyser
High-speed USB 2.0 Connection
A u tomati t Measurements

Arbitrary Waveform Generator

Del me your own waveforms or select Irom 13
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Technology

The P- coScope 30QO Series of oscilloscopes from Pico Tflthfioic.^y
indudfis general purpose ,ind h-igh resolution models: With M bil
resolution and 1% accuracy, the 10MHz PicoScope 3424 is .ihSe to detect
changes as small as (X0£4% (244ppm) - making it the Ideal A channel
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for general purpose and portable
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The Ftco!Scope 2000 series oscilloscopes
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to check out our full Bine of PC -based ^instruments or ca

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u

4/2008 - elektor

11

INFO & MARKET

NEWS & NEW PRODUCTS

QVGA for Microchip PIC24F/H micros

Microchip announces a QVGA
Graphics Solution for implement-
ing graphics display and control
in cost-sensitive applications. The
new, easy-to-use solution for PIC24
16-bit microcontrollers includes a
free, highly optimized graphics
library with source code; third-
party library support; and the new
Graphics PICtail™ Plus daughter
board.

The free Microchip graphics li-
brary supports rapid, low-risk de-
velopment using two- and three-di-
mensional objects, including text,
circles, rectangles, buttons, meters,
windows, progress bars and more,
along with images, animation, and
touch screen capabilities. In addi-
tion, Microchip's third-party part-
ners, Segger (www.segger.com)
and Ramtex (www.ramtex.dk), of-

fer compatible graphics libraries to
provide even greater flexibility.
Microchip's new Graphics PICtail
Plus daughter board is designed to
plug into the (Elektor) Explorer-16
development board and includes a
Thin Film Transistor (TFT) LCD mod-
ule that supports 320x240 (quar-
ter VGA) graphic resolution and
65,000 colours along with touch-
screen operation.

The new QVGA Graphics Solu-
tion supports any of Microchip's
existing PIC24F 16-bit microcon-
trollers, and will offer support for
future PIC24H 16-bit microcontrol-
lers, 16-bit dsPIC® digital signal
controllers, and the new 32-bit PIC-
32 MX microcontrollers.

The PIC24F family of devices pro-
vide a parallel master port inter-
face, 4-8 kB of RAM and 16-

128 kB of Flash
program memory,
offering maximum
flexibility in sup-
porting different
LCD panel options.

For example, using
a 28-pin PIC24F
microcontroller
can enable high
system perform-
ance, an extremely
small footprint and
reduced total sys-
tem cost.

The graphics li-
brary, application notes and ad-
ditional design resources are all
available from Microchip's website
today, and the Graphics PICtail
Plus daughter board can be pur-
chased from www.microchipdirect.

com. For further information visit
Microchip's website below.

www.microchip.com / graphics

(080073-1)

Compact 5.7-inch VGA TFT display with LED backlight

Hitachi Display
Products Group re-
cently launched the
TX14D14VM1 BAB
that brings VGA
resolution and a
40,000 hour LED
backlight to the
existing range of
compact 5.7 inch
LCD TFT displays.

The 640(w) x
480(h) VGA reso-
lution display de-
livers 262,000
colours while a contrast ratio of
350:1 and typical brightness of

350cd/m2 ensure clear, bright
images for all lighting conditions

and environments.
With module dimen-
sions of (w) 1 3 1 .0mm
x (h) 1 02 . 2 m m x
(d) 1 0.9mm the
TX14D14VM1 BAB
form factor is compat-
ible with the other com-
pact displays in the 5.7
inch range and features
an active matrix, trans-
missive TFT LCD dis-
play. A touchpanel ver-
sion of the display, the
TX1 4D1 4VM1 BPB, is
also available, making this prod-
uct ideal for a huge range of em-

bedded industrial solutions from
handheld data loggers to human-
machine interfaces.

Both product versions are avail-
able immediately via Hitachi Dis-
play Product Group's distribution
partners across Europe. Hitachi
Display Products Group is also
able to design and develop cus-
tomised display modules for spe-
cific customer requirements.

www.hitachi-displays-eu.com

(071 168-VII)

IP68 rated temperature sensors

One of the main problems with
temperature sensors is the ingress
of moisture which can seriously
affect the sensor performance —
the weakest point often being the
lead/sensor interface.

So ATC Semitec have developed
a range of TPE encapsulated sen-
sors where the leads and sensor
are made from the same material.
This creates a waterproof barrier
which is rated to IP68 and can op-
erate up to 105 °C.

These cost-effective sensors en-
sure absolute integrity when used

in outdoor locations (e.g. solar
panels) as well as in under-floor
heating and other HVAC applica-
tions. There are also other options
such as stiff lead versions and a
high temperature variant rated
tol50°C.

Double-insulated and rated to 4 kV,
these IP68 sensors offer complete
peace of mind in applications
where moisture ingress has previ-
ously been a problem.

http://www.atcsemitec.co.uk/

(080073-VI)

12

elektor - 4/2008

o

Soldering .co.uk

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Control Systems

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Microcontroller Development Tools

Robots & Accessories

Test Equipment

Similar boards available for 8051 , ARM, AVR, dsPIC and
PSoC, plus compatible add-on boards and compilers.

Other robot kits available based on 68HC1 1 , 8051 , AVR,
BASIC Stamp and PIC, plus large range of accessories.

The PoScope features
a logic analyser with
serial bus decoding,
oscilloscope, pattern
generator, spectrum
analyser, chart recorder
and square-wave/PWM
generator in one low-
cost instrument from
£79.

New range of high-specification logic analysers from
ZeroPlus now also available.

The PICPLC16B makes
an ideal platform for
developing and imple-
menting automation
applications with its 16
relay outputs, 16 opto-
isolated inputs and
Ethernet controller for
£99.

A wide range of microcontroller and PC-based control
boards and add-ons are also available.

Other training systems available for microcontroller and
electronics teaching.

The IDL-800 is a low-
cost digital circuit lab
incorporating a large
solderless breadboard,
DC power supply,
function generator, volt
meter and useful
switches and displays
for £199.

We stock prototyping products from breadboards to
advanced digital and analogue circuit labs.

Start experimenting
with robotics with the
Robo-Box 3.0 robot kit.
Contains everything
required to build wheel
and track-based robots
and carry out a large
range of fun experi-
ments from £79.

Designed specifically
for teaching about 8051
microcontrollers, the
NX-51 V2 incorporates
a useful range of I/O
devices and comes
complete with detailed
example programs for
£99.

Gain the best start with
PIC microcontrollers
with MikroElektronika’s
EasyPIC5 development
system. High-speed
USB PIC programmer,
in-circuit debugger and
plentiful I/O devices on
one board from £79.

4/2008 - elektor

13

INFO & MARKET

NEWS & NEW PRODUCTS

New PicoScope 2000 series scopes

Each new model in the PicoScope
2000 series is an oscilloscope,
spectrum analyser, signal genera-
tor and arbitrary waveform gener-
ator (AWG) all in one unit, mak-
ing it extremely versatile and eco-
nomical. Unbeaten for functionality

and price, with bandwidths up to
25 MHz and sampling rates up to
200 MS/s, the new scopes have
a compact footprint of 100 mm x
1 35 mm (3.93 in x 5.3 1 in), small
enough to fit easily into a laptop
or travel bag.

The new PicoScope 2000 se-
ries scopes have two BNC input
channels, a third BNC for a sig-
nal generator and arbitrary wave-
form generator output, and a USB
port. Power is taken directly from
the PC, and the scopes use the full
USB 2.0 bandwidth of 480 Mbps
to achieve rapid display updates
without compromising accuracy
and detail.

All PicoScope PC Oscilloscopes
are supported by the same fully
functional version of PicoScope
6 for Windows, which makes the
most of the PC's processing power,
storage, graphics and communica-
tions. The familiar Windows inter-
face and controls make the soft-
ware easy to learn and operate,
and convenient for everyday use.
PicoScope owners can download
software updates, feature exten-

sions and improvements that will
remain free of charge for the life-
time of the product. They can also
contact Pico's technical specialists
for support by web, email, phone
or Skype, at no extra charge.
PicoScope 6 can save data in a
range of formats including CSV
text, PNG and BMP images and
MATLAB binary files. Drivers and
examples are included for Lab-
VIEW, C, C++, Delphi and Visual
Basic for integration into custom
applications.

The new PicoScope 2203, 2204
and 2205 PC Oscilloscopes are
available from local distributors,
or direct from Pico Technology,
priced from £159 to £300 + VAT
and delivery.

www.picotech.com

(080073-11)

Rambus xdr (tm) memory architecture named 2008 Designvision winner

The International Engineering Con-
sortium (IEC) has chosen the Ram-
bus XDR (tm| memory architecture as
the winner in the 2008 DesignVi-
sion Awards category for Semi-
conductors and ICs (IP). The IEC
DesignVision Awards recognize
technologies, applications, prod-
ucts, and services judged to be
the most unique and beneficial to
the industry.

Rambus recently announced that
Toshiba has taken a license for
the XDR memory architecture for
its next-generation HDTV chipsets.
In addition, Qimonda has begun
shipping its first samples of XDR
DRAM, and Elpida has begun ship-
ping 4.8 GHz XDR memory, the
world's fastest production DRAM.
Key components enabling the

breakthrough performance of the
XDR memory architecture are:

- The XDR DRAM, a high-speed
memory 1C that turbo-charges
standard CMOS DRAM cores with
a high-speed interface capable of
4.0 GHz data rates providing up
to 8 GB/s of bandwidth with a sin-
gle device.

• The XIO controller 10 cell provid-
ing the same high-speed signaling
capability found on the DRAM, but
adding additional enhancements
like FlexPhase(tm) technology that
optimizes timing and eliminates the
need for trace length matching.

• The XMC memory controller, a
fully synthesizable logical memory
controller that is optimized to take
advantage of innovations like Dy-
namic Point-to-Point which provides

for capacity expansion while deliv-
ering the signal integrity benefits of
point-to-point signaling.

• The XCG clock generator provid-
ing the system clocks with four pro-
grammable outputs, guaranteed to

meet the clocking requirements for
the XIO and XDR DRAM devices.

www.rambus.com

(080073-IV)

SMS Electronics wins major deal

Nottingham based SMS Electron-
ics Ltd have secured a multi year
/ multimillion pound deal with
Siemens Enterprise Communica-

tions Limited to provide a range of
services including Field Repair Unit
support, Second user equipment
refurbishment, Recycling (WEEE)
and logistics. Under the terms of
the deal SMS will acquire the Sie-
mens Enterprise Communications
Limited current operations based
in Beeston Nottingham which will
be transferred to a new company
SMS Product Services Ltd.

SMS Product Services Ltd will be
located in 40,000 sq ft building
adjacent to the SMS Electronics
Ltd current facility and increases
the manufacturing floor space
available to SMS to a total of
1 10,000 sq ft. The additional
capacity is also required to ca-
ter for higher volumes from its ex-
isting customer base and recent
contract wins.

SMS Electronics Ltd. have a
long and successful relationship
with Siemens and have also se-
cured a further 5 year extension
to their current Manufacturing
agreement with Siemens Enter-
prise Communications Ltd.

www.smselectronics.co.uk

(080073-VIII)

14

elektor - 4/2008

Quarter-brick DC-DC converters

The Bel Power division of Bel Fuse
Inc. announced the ORQB-COU
Series of open-frame isolated DC-
DC converters. Housed in the in-
dustry standard !4 brick (2.28"
L x 1 .45" W) package, the low-
cost series provides up to 100 W
of output power from a nominal
48 V input. Notably featuring a
4-to-l input voltage range to ac-
commodate both a 24 V and 48 V
standard input voltage in the same
module, it is moreover engineered
with built-in input and output filter-
ing to further minimize part counts.
The highly reliable devices operate
at efficiencies up to 91% over an
ultra wide range of output voltages
extending from 1 .2 V to 12 V.
Bel's newest UL/cUL 60950-1
approved series may be confi-

dently specified for employment
in a broad array of distributed
power architecture applications
where space is limited, and over-

all weight is a factor. Among the
most common uses for these high
power density parts are in wire-
less networks, optical and access

networks, as well as in industrial
networks and equipment. Addition-
ally, their open-frame construction
makes them ideally suited for con-
vection-cooled environments.

The isolated DC-DC converters offer a
full complement of control and protec-
tion features that include differential
remote on/off, positive/negative re-
mote sense, input over-/ under-voltage
lockout, and over-temperature protec-
tion. Parts also offer output voltage
trim, current limit, and short circuit
protection. These devices switch at a
fixed frequency (285 kHz) and have
an operating temperature range of
-40 to +85 degrees C.

www.belfuse.com

(080073-III)

NanoBoards open up new hardware possibilities

Altium Limited has previewed
its extended range of deploy-
ment NanoBoards at DesignCon
2008 and will showcase the new
solution in Europe at Embedded
World 2008.

Altium's new deployment Nano-
Boards are standard, off-the-shelf
design solutions that offer great-
er design flexibility for electronics
designers. They can customize
these cases to their own require-
ments. And by using Altium's
Innovation Station electronics
designers can develop and test
device intelligence and transfer
that design into the deployment
NanoBoards for a complete and
marketable product.

Electronics designers can now,
regardless of background or ex-
pertise, deploy a design into final
hardware making the end prod-
uct immediately available.

The extended range of deploy-
ment NanoBoards features the
same mother board and choice
of daughter and peripheral
boards as the Altium Desktop
NanoBoard. Designers will have
the choice of using a deployment
NanoBoard as a final product,
or integrating their deployment
NanoBoards into larger systems
such as mechanical devices.
They will also be able to do semi-

custom hardware design using the
templates included with the Altium
Designer software.

The Modular Commercial Enclosure
system comprises basic units avail-
able in two sizes, a 1 .0 and a 0.5
module. They can be configured by
designers and come with a range
of interchangeable components for
an array of installation options.

The system is designed to support
the pluggable NanoBoard hard-
ware deployment platform and in-
cludes all of the templates, mount-
ing details and graphics specifica-
tions required to produce a fully
customised application. The stand-
ard enclosures accommodate a
mother board with a choice of
FPGA daughter boards and a
3.5 inch touch screen display. The
standard 0.5 module provides for

a maximum of two peripheral
boards while the 1 .0 module
supports up to four peripheral
boards.

Altium's range of deployment
NanoBoards will be available
later in 2008.

www.altium.com/Products /
NanoBoard/

(080073-V)

4/2008 - elektor

15

INTERNET RADIO

Listening to

programmes

Harald Kipp and Dr Thomas Scherer

In the good old days, you had to modulate audio signals onto an RF carrier so they could be received
and demodulated to produce something more or less audible. Nowadays things are different: audio
signals are compressed and put into IP packets that are Streamed', and you can access every Internet
radio programme in the world by receiving, buffering and decompressing these packages. This is all
very easy with the state-of-the-art hardware described in this article.

Internet radio is something quite spe-
cial: even the most sensitive short-
wave receiver cannot come close to
providing such a broad range of pro-
grammes, and the sound quality is
simply not comparable. As the ‘Inter-
net broadcasters’ that provide these
programmes do not have to pump se-
veral hundred kilowatts of RF energy
in the air (with the resulting ‘ electro -
smog’), this type of broadcasting ope-
ration is also quite economical for rela-
tively small target audiences.

We could say a lot more about the ad-
vantages of this new sort of radio (see
inset), but what’s more important is to
answer the question posed in the next
section.

Why not use a pure software solution?

First of all, we have to say that the-
re are several programs (WinAmp,
iTunes, VLC, etc.) that are available
entirely free of charge for all possible
operating systems and can be used
to listen to Internet radio. Every true
21st-century person has a PC, Mac or
Linux machine available somewhere,
so why should you spend money on a
non-virtual, physical device, and on top
of that build it yourself?

Well, for one thing the hardware plat-
form for a software radio consumes
electricity, and quite a lot for this pur-
pose. Anyone who spends a good deal
of time listening to radio programmes
with a PC is engaged in a very environ-
mentally unfriendly activity. The solu-

tion proposed here manages to do the
job with a power consumption of only
1 watt. If you use it 10 hours a day, the
savings in electricity costs alone (rela-
tive to using a gamer PC as a radio) are
enough to repay you investment within
six months.

For another thing, there are applica-
tions for which a PC is not such a cle-
ver solution, such as connection to a
stereo system. A DIY Internet radio ba-
sed on Open Source technology is easy
to extend and adapt to special require-
ments - and last but not least, the EIR
keeps on working when your PC hangs
or crashes .

Operating principle

As the EIR is a complex project that
uses state-of-the-art hardware, it is
impossible to deal adequately with all
relevant topics in a single article. For
this reason, the main objective of this
article is to describe the hardware and
tell you how to assemble it and put it
into service. You can find additional in-
formation in documents on the Elektor
website (www.elektor.com) and the
project website [1], and there will be
additional articles on this subject in fu-
ture issues.

As you probably already realise, an In-
ternet radio must receive, buffer and
decode data streams. This means that
one of its basic ingredients must be a
reasonable microcontroller. As already

mentioned in the last issue of Elektor
[3], an ARM7 MCU [4] can provide the
necessary processing power.

The basic architecture is shown in Fi-
gure 1. The MCU is shown in the up-
per middle of the diagram, and it has
access to a healthy 64 MB of SDRAM
- which is sufficient for the buffer and
quite a few ‘extras’. The MCU has room
for the firmware, and there is also 4 MB
of flash memory available for non-vola-
tile data storage. A real-time clock ba-
cked up by a Supercap allows the cir-
cuit to be used to implement an alarm
radio or other applications that depend
on knowing the current time. To avo-
id having to exploit the full capacity
of the ARM7 MCU, audio decoding is
handled by a VS1053 IC [5], which is
specifically designed for this purpose.
The EIR also provides a comfortable
selection of interfaces: beside the man-
datory Ethernet port (since the EIR has
to access the Internet somehow), the-
re is a USB programming interface for
downloading new firmware, a serial
port and a JTAG port (useful for de-
bugging), and three useful expansion
connectors at the port level.

To allow you to record broadcasts if
you so desire, there is also a slot for an
MMC/SD memory card.

General aspects

The incoming data streams are normal-
ly compressed to such an extent that
they can handle sampled stereo data,
which typically has a resolution of

16

elektor - 4/2008

Details

As you can see immediately from look-
ing at the schematic diagram in Fig-
ure 2, this is a complex design. For
this reason, the following description
is based on the functional blocks.

• Ethernet

Access to the Internet is via an Ether-
net connector with an integrated trans-
former and two LEDs. The green LED
lights up when data is being trans-
ferred, while the yellow LED indicates
that a connection is present. The Eth-
ernet traffic is handled by a special-
ised IC (IC10, a DM9000E). Buffer IC9

16 bits and a sampling rate of 44.1 kHz,
using a data transmission rate as low
as 192 kbit/s (or even less) instead of
the normal rate of around 1.4 Mbit/s.
This means that a buffer with a capa-
city of approximately 10 seconds can
be implemented with around 256 KB
of RAM. This may not sound like much
nowadays, but it is still quite a hefty
chunk of memory for a microcontroller.
If you want to be on the safe side and
also want to have room for Internet ni-
ceties and other ‘extras’, you can quik-
kly end up with 512 kB or more. The
ARM7 MCU selected for this design
supports SDRAM, so the EIR with its
64 MB of RAM does not suffer from any
shortage of memory.

devise upgrades
that support this capabili-

ty and other conceivable features.

In order to avoid constraining the form
of any possible extensions, no user in-
terface components (such as buttons
or a display) are incorporated in the
board. However, they can easily be
connected via the expansion connec-
tors. The EIR is intended to form the
basis for user-designed expansions,
and the firmware that comes with the
board is thus designed to be used via
an integrated website. However, the
firmware is completely open, so other
options are always possible.

We chose Nut/OS as the operating
system. It is quite accommodating in
comparison with Linux and can ma-
nage with less than 40 kB of memory.
All in all, the software needs around
200 kB of memory. A capacity of 1 MB
is ample for data storage. As the MCU
already has 512 kB of flash memory on
board for program data as well as an
abundance of RAM, there are no bot-
tlenecks. All of the software is Open
Source, except for the flash program-
ming software from Atmel.

Incidentally, the microcontroller has
sufficient processing power to allow
a second audio stream to be recorded
on the SD card while another stream is
playing. It will certainly not take very
long for the Open Source community to

5-24V

Power Supply

Reset

Button

MMC /
SD-Card

AT91SAM7SE512

64 MByte
SDRAM

4 MByte
DataFlash

RTC / SuperCap

DM9000E

Ethernet

USB

Device / Prog.

RS232

Expansion

Connector

JTAG

Connector

OLED

Touch Wheel
(later Upgrade)

Figure 1. Block diagram of the Elektor Internet Radio.

4/2008 - elektor

17

INTERNET RADIO

2a

Figure 2. As you can see immediately from the schematic diagram of the EIR, this is a sophisticated project.

18

elektor - 4/2008

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4/2008 - elektor

19

INTERNET RADIO

2c

+1V8 +3V3 +VREF +3V3

VX

©

+3V3

©

C61

10(j

C62

C63

C64

C65

+3V3

©

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C67

C68

C69

C70

10^i

5

7

24

31

6

14

19

C71

C72

38

43

45

C73

IC7

CVDD0

DGND0

CVDD1

DGND1

CVDD2

DGND2

CVDD3

DGND3

DGND4

IOVDD0

IOVDD1

IOGND

IOVDD2

AGND0

AVDD0

AGND1

AVDD1

AGND2

AVDD2

AGND3

VS1053C-L

POWER

4

16

20

21

22

35

37

40

41
47

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H 0Q

4x lOOn

L - 3x lOOn - J

3x lOOn - '

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©

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©

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C87

C88

C89

C90

10|i

C91

C92

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1

14

27

C93

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9

43

49

VDD

VSS

VDD

VSS

VDD

VSS

VDDQ

VSSQ

VDDQ

VSSQ

VDDQ

VSSQ

VDDQ

VSSQ

28

41

54

6

12

46

52

C94 MT48LC128M16A2

5 POWER

3x 1 0On -

4x lOOn

071081 -11C

allows the Wait input of the MCU to be
used by expansion circuitry.

• Audio decoder

Although the ARM7 would just be able
to handle decoding of MP3 or AAC data
in software, a dedicated IC such as IC7
considerably reduces the load on the
MCU, and it is specifically designed to
handle HE -AAC and even Ogg-Vorbis
data in addition to the usual MP3 ver-
sions. Logically enough, this also simpli-
fies the application software. We used
a pre-production sample from VLSI in
the prototypes. If you have trouble ob-
taining this IC, you can use the VS 1033
version (without Ogg Vorbis capability)
instead. Although the MCU has a 1.8-V
output for powering peripheral devic-
es, a separate 1.8-V voltage regulator
is provided for IC7 for reasons of stabil-
ity. If you use the VS 1033, R39 and R42
must be changed to 100 kQ because it
needs a 2.5-V supply voltage.

• Supplementary flash memory

It is necessary to store a large number
of operational settings for the radio,
and they must remain available even
after a power outage (especially the
station list). The internal flash memo-
ry of the MCU could be used for this
purpose, but writing data to it is cum-
bersome. To simplify the process, a se-
rial flash memory (IC5) is included in
the design. With a capacity of 4 MB, it
has room for extensive station lists and
even more.

• Power supply

To keep the power consumption of the
EIR as low as possible, it is powered
by a switch-mode supply built around
IC12. It provides around 5 watts of
power at 3.3 V with an input volt-
age in the range of 5-24 V. As the EIR
takes only 1 W for its own use, there
is enough left over for DIY hardware
extensions.

• Soldering

The EIR is built on a densely popu-
lated multilayer PCB with lots of tiny
SMD components (see Figures 3 and
4), with some of the IC pins spaced
only 0.5 mm apart. To avoid problems
with DIY assembly, Elektor can supply
a pre-assembled board with all SMDs
already fitted (with the VS 1053). All
you have to do is to fit the relatively
large components, which helps you
avoid pernicious assembly errors. For
the diehards, it is of course possible to
build the board yourself using the lay-
out artwork.

Functional test

For initial testing of the power supply,
the load on the 3.3-V side should be at
least several millamperes (do not use
it with no load). The voltage regula-
tor should start working with at input
voltage of at least 4 V and draw 50 to

20

elektor - 4/2008

150 mA, depending on the load. This
will drop to 30-50 mA at 24 V. If every-
thing is OK, LED1 will light up. After
the ICs are fitted, you can use an os-
cilloscope to check that the crystal is
working. If XI is oscillating, the MCU
should be ready for action.

The MCU comes with an on-board
boot loader that supports communica-
tion from and to the RAM and with the
flash memory as well as downloading
new firmware. The AT91-ISP.exe file
available from Atmel (see reference [6])
installs the program SAM-BA, which
runs under Windows. After installing
this program, connect the EIR to your
PC via the USB port. After the power
is switched on, Windows should se-
lect the appropriate driver automatical-
ly. Now you can start SAM-BA. Select
‘USB’ as the connection type and ‘AT-
91SAM7SE512-EK’ as the device (this
is largely compatible with the EIR).
You can download a simple testing
firmware program from the Elektor
website. With this firmware and an op-
erational MCU and serial interface, you
can check the other components, such
as the Ethernet port and the audio de-
coder. After downloading the firmware
to the MCU, you have to tell the EIR

nnn

Figure 3. The component layout of the EIR. To avoid assembly problems, a board with prefitted SMD components is available.

COMPONENT LIST

Resistors

R1 # R2 = 27a SMD 0402
R3 = 1 kQ5, SMD 0402
R4 / R5 / R28 / R45 = 1 kQ, SMD 0402
R6 / R23 / R32 / R33 / R36 / R38 = lOkQ, SMD
0402

R7,R8,R18,R35,R44 = 0Q, SMD 0402
R9,R1 0,R1 3,R20,R22,R34 = 100l<a SMD
0402

R1 1 ,R1 2,R1 6 = 1 0a SMD 0603
R1 4,R1 5,R43 = 22a SMD 0402
R1 7 = 1MQ, SMD 0402
R1 9,R2 1 = 470a SMD 0402
R24,R25,R29,R30 = 50Q 1%, SMD 0402
R26,R27 = lka SMD 1206
R31 = 6kU8 1%, SMD 0603
R37 = 1 6kQ5 1%, SMD 0603
R39 = 200kQ* 1%, SMD 0402
R40 = 1 80a SMD 1 206
R41 = lOkQ 1%, SMD 0402
R42 = 470kQ* 1%, SMD 0402
R46 = 1 5l<a SMD 0402
R47 = 22l<a SMD 0402
R48 = 22a array, CAY16
R49 = 100l<a array, CAY 16
R50 = 10l<a array, CAY16
R100-R106 = 0Q*, SMD 1206 (not
required)

* see text

Capacitors

(SMD ceramic 6.3V unless otherwise
indicated

Cl -C4,C1 6, Cl 9,C30,C31 ,C35,C42, C46-

C51 ,C53-C59,C62-C65,C67,C68,C6
9,C71,C72,C73, C75,C76,C77,C79-
C85,C87,C88,C89,C91-C97 = lOOnF,
SMD 0402

C5,C6,C9,C1 0,0 7,C20,C32,C33,C34 =
22pF, SMD 0402
C7,C38 = InF, SMD 0402
C8,C21 ,C22,C27,C28,C37,C1 00 = lOnF,
SMD 0402

Cl 1 -Cl 4 = 220pF, SMD 0402
Cl 5,C39,C44,C45,C52,C60,C61 ,C66,C70
,C74,C78,C86,C90 = 10jL/F # SMD 0805
Cl 8,C23,C29 = 47nF, SMD 0402
C24,C25,C26,C43 = IjL/F, SMD 0805
C36 = 0.1 F, Double Layer Cap
FG0H1 04Z1 35

C40,C41 = 1/iF 25V, SMD 1206
C98,C99 = 1 00/-/F 1 6V tantalum, SMD

Inductors

LI = DLW5BTN1 02SQ2 (Murata)

L2 = 10jL/H, MSS5131 (Coilcraft)

L3 = BLM31 A (Murata)

Semiconductors

D1,D2,D3,D5 = PMEG3005AEA (Philips)

D4 = SM6T24CA (STM)

IC1 = AT91 SAM7SE51 2-AU (Atmel)

IC2 = MAX3222ECWN (Maxim)

IC3, IC6, IC8 = BZA408B diode array

IC4 = MT48LC32M1 6A2

IC5 = AT45DB321 D-SU (Atmel)

IC7 = VS1053C-L (VLSI)*

IC9 = NC7WZ07P6X (Fairchild)

1C 10 = DM9000E (Davicom)

IC1 1 = PCF8563T (Philips)

1C 1 2 = LT1616 (Linear Technology)

1C 1 3 = LTC1 844ES5-SD (Linear Technology)

LED1 = KP-1 608URC, red, SMD 0603
(Kingbright)

Miscellaneous

XI = 18.432 MHz quartz crystal, SMD
HC49SM

X2 = 1 2.288 MHz quartz crystal, SMD
HC49SM

X3 = 25.000 MHz quartz crystal, SMD
HC49SM

X4 = 32.678 kHz quartz crystal, SMD
MC-146

FI = fuse, 0.5A, fast, with holder, SMD
OMNI-BLOK (Littelfuse)

K1 ,K2,K3 = 40-way SIL pinheader, lead
pitch 2.54mm

K4 = USB-B socket, AMP-787780

K5 = 9-way sub-D plug, angled pins, US
standard

K6 = 20-way boxheader, 2.54mm lead
pitch

K7 = SD-card socket, SMD, FPS009-2700
(Yamaichi)

K8,K9 = 3.5-mm stereo jack socket, SMD,
SJ1-3515 (CUI)

K10 = RJ-45 socket with Ethernet transfor-
mer and LEDs, SMD, RJLD-043TC (Taimag)

K12 = DC adaptor socket with 2-mm pin,
TDC-002-3

JP1 = 6-way 2-row pinheader with 2 jum-
pers, 2.54mm lead pitch

SI = pushbutton, SMD, LSH (Schurter)

PCB with pre-mounted SMD parts, Elektor
Shop # 071081-1

Project software, archive 071081-1 1 .zip;
free downloads from www.elektor.com

4/2008 - elektor

21

INTERNET RADIO

Figure 4. As you can see from the fully assembled prototype, DIY soldering isn't so easy here.

that it should boot from this firmware
when it restarts. To do so, select the
routine ‘Boot from Flash (GPNVM2)’
under ‘Scripts’ and click ‘Execute’.

Then close SAM-BA and press the Re-
set button. Now the EIR can commu-
nicate with the PC via the serial inter-
face and a null-modem cable (pin 2 & 3

Table 1. Expansion connector K1

Pin

Signal

Use

Pin

Signal

Use

1

PAO

Free

2

PA1

Free

3

PA2

Free

4

PA3

TWI SDA

5

PA4

TWI SCL

6

PA5

UARTO RxD via JP1

7

PA6

UARTO TxD via JP1

8

PA7

UARTO RTS

9

PA8

UARTO CTS

10

PA9

DBUG RxD via JP1

1 1

PA1 0

DBUGTxD via JP1

12

PA1 1

Data Flash Chip Select

13

PA1 2

SPI MISO

14

PA1 3

SPI MOSI

15

PA1 4

SPI SPCK

16

PA1 5

MMC Chip Select

17

PA1 6

MMC Clock

18

PA1 7

MMC Command

19

PA1 8

MMC DATO

20

PA1 9

MMC DAT1 via R7

21

PA20

MMC DAT 2 via R8

22

PA21

Free

23

PA22

Free

24

PA23

SDRAM DQMH

25

PA24

SDRAM A10

26

PA25

SDRAM CKE

27

PA26

SDRAM Chip Select

28

PA27

SDRAM WE

29

PA28

SDRAM CAS

30

PA29

SDRAM RAS

31

PA30

IRQ 1 , MP3 Interrupt

32

PA31

MP3 Command Select

33

Vref

ADC Reference

34

3.3V

Power

35

AD4

Analogue input (free)

36

AD5

Analogue input (free)

37

AD6

Analogue input (free)

38

AD7

Analogue input (free)

39

GND

Ground

40

GND

Ground

Figure 5. Screen shot of SAM-BA running under Windows 2000.

leads swapped), and you can use a ter-
minal emulator to send commands to
the EIR (we recommend TeraTerm [7]
for Windows or Miniterm for Linux, and
Macs have a built-in terminal utility).

Listening to the radio

Before you can start listening to the
radio, you have to delete the test
firmware from the EIR and install the
radio firmware. To allow new firmware
to be loaded, first connect pins 34 and
36 of connector K3 with a jumper, then
press Reset, and finally remove the
jumper. After this, the EIR will start
up again with the boot loader, and you
can use SAM-BA to download the ra-
dio firmware.

Now connect the EIR to your local net-
work via the Ethernet port (using a hub,
a switch, or an Internet router with sev-
eral ports) and connect the audio out-
put to a headphone or an amplifier.

If the LAN or the router you are using
has an active DHCP server, the EIR will
fetch a valid address and start playing
the programme from the default sta-
tion. If you prefer to use fixed IP ad-
dresses, proceed as follows. When you
install Nut/OS, a small utility called
‘Discover’ is installed on the PC, and
you can always use it to find the EIR
(see Figure 6) and then configure the
desired IP address. Enter the router ad-
dress under ‘Gateway’, as illustrated
in Figure 7. After this, you should be
able to listen to the radio (Figure 8)
with fixed IP addresses.

Prospects

As already mentioned several times, the
EIR is a completely open-ended concept.
The software and hardware (via the ex-

Figure 6. You can use this program (here running under Linux
KDF) to find the EIR even if its IP address is unknown.

22

elektor - 4/2008

Table 2. Expansion connector K2

Pin

Signal

Use

Pin

Signal

Use

1

PBO

SDRAM DQML

2

PB1

Free

3

PB2

Address Bus A2

4

PB3

Address Bus A3

5

PB4

Address Bus A4

6

PB5

Address Bus A5

7

PB6

Address Bus A6

8

PB7

Address Bus A7

9

PB8

Address Bus A8

10

PB9

Address Bus A9

1 1

PB1 0

Address Bus A1 0

12

PB1 1

Address Bus A1 1

13

PB1 2

Free

14

PB1 3

Address Bus A1 3

15

PB1 4

Address Bus A1 4

16

PB1 5

Free

17

PB1 6

SDRAM BAO

18

PB1 7

SDRAM BA1

19

PB1 8

Free

20

PB1 9

FIQ, RTC Interrupt

21

PB20

IRQO, Ethernet Interrupt

22

PB21

Free

23

PB22

DataFlash Chip Select

24

PB23

USB Monitor

25

PB24

Free

26

PB25

Free

27

PB26

Free

28

PB27

Free

29

PB28

Free

30

PB29

Free

31

PB30

MP3 Data Select

32

PB31

MP3 Hardware Reset

33

3.3 V

Power

34

3.3 V

Power

35

Not used

36

Not used

37

Not used

38

NRST

Hardware Reset

39

GND

Ground

40

GND

Ground

pansion connectors) can be extended as
desired, and you can certainly look for-
ward to seeing several articles on this
subject in future issues of Elektor.

With regard to software tools, source
code and further developments, you
should occasionally check the egnite
project website [1] to see what’s new.
There you will find source code and in-
stallation files for Windows, Linux and
OS X. You will also find links to devel-
opment environments and other Open
Source projects.

There are lots of possibilities. An obvi-
ous enhancement would be to add a
few buttons and an LCD display so the
EIR can be used as a convenient stand-
alone device instead of only via a Web
browser. And the memory card slot al-
most cries to be used for a supplemen-
tary MP3 player application.

( 071081 - 1 )

Internet radio

If you take a look on the Web, you'll be astounded to see that Google
presently finds more than 21 million hits for 'Internet radio', so it's obvi-
ously a hot topic. The first experiments with packet-based 'broadcasts'
were carried out as early as 1 993, at around the same time as the first
usable browser (NCSA Mosaic) and thus the dawn of the commercial
Internet era. Quite early on, 'real' radio stations started broadcasting
their programmes via Internet streaming in addition to conventional
radio waves. Today you can receive tens of thousands of radio pro-
grammes with an ordinary Internet connection. In addition to a pletho-
ra of highly diverse niche programmes, you can now access nearly all
public and commercial broadcasters.

The term 'streaming', which covers near-real-time transmission of time-
referenced data such as audio or video content, refers to data streams
that are as continuous as possible and require the originator to transmit
a separate stream for each client, which can generate an enormous

traffic volume and thus be a costly proposition if there are a lot of lis-
teners. To keep the data rates within acceptable bounds, a lossy com-
pression is usually used to compress the data before transmission, and
the data is subsequently decompressed by the receiver. This means that
an Internet radio receiver must incorporate a commonly used streaming
decoder, such as MP3, Ogg Vorbis or Real Audio, regardless of whether
it is purely software- based or uses dedicated hardware.

As it is not possible to guarantee a constant propagation delay for in-
dividual data packets with the HTTP and FTP protocols normally used
on the Internet, the receiver must also have a data buffer with sufficient
capacity, which delays reception by a few seconds and means that it is
only 'quasi live'. This makes fast zapping between stations impossible.
However, thanks to digitalisation this drawback is offset by stable audio
quality, extreme (worldwide!) range, and a truly fathomless diversity
of programmes. It is also possible to receive previously recorded pro-
grammes (missed broadcasts) by means of 'audio on demand', which
no conventional radio station can offer.

Table 3. Expansion connector K3

Pin

Signal

Use

Pin

Signal

Use

1

PCO

Data Bus DO

2

PCI

Data Bus D1

3

PC2

Data Bus D2

4

PC3

Data Bus D3

5

PC4

Data Bus D4

6

PC5

Data Bus D5

7

PC6

Data Bus D6

8

PC7

Data Bus D7

9

PC8

Data Bus D8

10

PC9

Data Bus D9

1 1

PC10

Data Bus D1 0

12

PCI 1

Data Bus D1 1

13

PCI 2

Data Bus D1 2

14

PCI 3

Data Bus D1 3

15

PCI 4

Data Bus D1 4

16

PCI 5

Data Bus D1 5

17

PCI 6

Bus NWAIT, Open Collector

18

PCI 7

Ethernet Hardware Reset

19

PCI 8

MMC Card Detect

20

PCI 9

MMC Write Protect

21

PC20

Free

22

PC2 1

Address/Data Bus NWE

23

PC22

Address/Data Bus NRD

24

PC23

Ethernet Chip Select

25

Not used

26

Not used

27

Not used

28

Not used

29

Not used

30

Not used

31

Not used

32

Not used

33

3.3 V

Power

34

3.3 V

Power

35

JTAGSEL

Boundary Scan Enable

36

ERASE

Firmware Erase

37

VI N

Unregulated 5-24 V via

R106

38

SHDN

Power Shutdown

39

GND

Ground

40

GND

Ground

References and
web links

[1] egnite project website:

www.ethernut.de/de/hardware/eir/

[2] Wikipedia article:

en.wikipedia.org/wiki/lnternet_radio

[3] Ethernut and the Kipp Family:

Elektor, March 2008, pp 18-21.

[4] ARM7 MCU data:

www.atmel.com/products/at91/

[5] VS1053 data:

www.vlsi.fi/products/vsl 053.html

[6] Link for AT91 -ISP.exe:

www.atmel.com/dyn/resources/prod_docu-
ments/lnstall%20AT91 -ISP%20vl . 1 0.exe

[7] Windows terminal emulator:

ttss h 2 . so u reef o rge.jp/

4/2008 - elektor

23

Jan Didden

Most solid state power amplifiers employ some form of global negative feedback to reduce non-
linearities and output impedance. In some cases, designers exploit alternatives like feedforward
to circumvent perceived disadvantages of global negative feedback. The present design uses error
correction as (re)defined by Malcolm Hawksford around 1984 [1].

In part 1 of this article the author dis-
cusses error correction for audio am-
plifiers and presents an audio output
stage based on error correction. Part 2
will extend the principle to the voltage
amplifier stage and present a complete
error correction power amplifier. In a
separate article next month the pro-
tection circuitry is discussed in more
detail.

Negative feedback is not negative

This is not an article against negative
feedback (nfb). Negative feedback, as
a general principle, is one of the most
powerful tools available to the designer
to build amplifiers that are transparent
to the signal they amplify. With that I
mean that they do not add anything to,
or subtract from, the input signal. In
reality, circuits are never ideal, but the
changes to the signal can be made so
small that inaudibility of the change is
pretty much guaranteed.

Negative feedback is also fully under-
stood, and although bad-sounding
feedback amplifiers are still being sold,
it is totally unnecessary. So, you may
ask, why bother with error correction

(ec)? For one thing, it is different; and
different roads to the same goal are
often enjoyable to travel and explore.
Secondly, although we will see that ec
is in many respects another face of nfb,
with similar advantages and disadvan-
tages, there are some interesting differ-
ences and different challenges leading
to better understanding of the process-
es inside any feedback amplifier.

What the H.ec?

Let’s start by narrowing down what
we mean by ec in the context of this
article. I refer specifically to Malcolm
Hawksford’ s paper referenced above.
I will use the term ‘H.ec’ to refer to Mr.
Hawksford topology, and ‘ec’ to refer in
general to error correction.

Figure 1 is the basic topology from that
paper. We see an amplifier block N, on
which the error correction will be ap-

Figure 1. Hawksford's general feedback/feedforward/error correction structure.

24

elektor - 4/2008

plied. The difference between the input
and output of that amplifier is either
added to the input via block ‘a’ (error
feedback), or to the output via block ‘b’
(error feedforward). All the summing
and differencing blocks have unity
gain (1 x ). Of course it is important that
the error correction signal is added in
just the right proportion to cancel the
original error. In this design I use the
correction via block ‘a’, added to the

input.

We will further
assume that the am
plifier block ‘N’ is an output
stage from an audio power ampli
her with a gain only just below 1.

The object here is to make this gain
exactly 1, independent of output load,
frequency and signal level. If we suc-
ceed, we will have an ideal output
stage. Of course we won’t get that far,

but as we
will see, we can
get pretty close.

We now get to our
conceptual circuit in
Figure 2. The output
stage we want to linearise is A’, with a
gain of ‘about 1’. In practice, most out-
put stage gains are anywhere between
0.92 and 0.98 depending on the topol-
ogy, loading, signal frequency etcet-
era. We see immediately that V c , the
signal that is fed back to the input, is
V out - V e , where V e is the effective in-
put signal to the output stage. We can
now calculate V e as

^e= Vin-^out-Ve)-

We also know that V e = V out /A , and
if we plug that into the former equa-
tion and rearrange terms, we get:

Figure 2. Error correction concept.

4/2008 - elektor

25

070987-13

Figure 3. Basic paX output stage.

What is significant here is
that the actual amplifier gain
A is no longer part of the
equation. Whatever the short-
comings, non-linearities or er-
rors of A, we got rid of all of
those. This is our ideal output
stage!

If you are familiar with practi-
cal audio amplifiers, you prob-
ably are feeling a bit uneasy
now. An ideal power stage?

That would be the first one
ever! And you are right — in
reality, we can’t make that
ideal.

The reason is that we as-
sumed that the summers in
Figure 2 are ideal summers,
without flaws. That cannot
be. Those summers consist of
passive and (most probably)
active devices that have their
own non-linearities, so the ba-
sic accuracy will not be ideal.

Their characteristics will also
vary with frequency, so the
correction accuracy will vary
with frequency. As the out-
put stage gain will also vary
with frequency and load, the
amount of correction required
will vary with frequency and
load, meaning that signal lev-
els in the summers vary with
frequency and load as well.

This further leads to accura-
cy limitations.

Nevertheless, it is possible
to greatly improve the performance of
the output stage with relative simple
means, as we will see.

Thermal memories

There was one other goal I had with
this amplifier. In most power amplifi-
ers, the thermal bias compensation is
obtained by mounting a tran-
sistor in the bias circuit on
the same heatsink as the out-
put devices. In that way, if the
output devices heat up and
start to draw more current,
the bias transistor also heats
up. That causes the bias volt-
age to decrease, and the ob-
ject is to dimension this ther-
mal feedback loop such that
the bias current in the output
devices remains stable with
temperature. But because it

takes time for the heatsink to heat and
cool and transfer this changing tem-
perature to the bias transistor, this
loop reacts relatively slowly at several
seconds or more.

The first time I read about this was
in an article by a French audio (not
fashion) designer authoring under the
pseudonym Hephaistos [2]. He realized

that the dissipation levels in
the output and driver devic-
es vary with signal output
levels, related to music level
variations, and that they are
much faster than the reac-
tion time of the thermal bias
compensation circuit. When
a high level signal burst ap-
pears, the devices’ biasing
point would shift, and would
return to the earlier state only
seconds after the high level
burst had disappeared. Such
a burst is too short for the
thermal feedback to adjust
the bias. A smaller signal af-
ter the burst would thus be
processed with different op-
erating conditions than be-
fore. He called this ‘thermal
distortion’.

In my design I wanted to get
rid of this problem as well.
Therefore I selected Sanken
STD03N and STD03P devices
for the output stage. These
are Darlingtons, with a bias
diode integrated on the tran-
sistor chip. By using this di-
ode in the bias circuit, it can
track thermal cycles in the
output devices instantane-
ously, thus hopefully elimi-
nating thermal distortion. Be-
cause it is a Darlington, any
(pre) driver dissipation would
also be low enough to avoid
memory distortion.

There’s one catch: the on-
chip sense diodes need to be run with
a specific current to make their thermal
bias changes in millivolts per degree,
equal to the V be changes of the driver
and output devices in millivolts per de-
gree. This requires a different bias cir-
cuit from the usual V be multiplier.

Error correction basics

Figure 3 shows the basic to-
pology of the output stage
without error correction. You
will notice the integrated bias
diodes in the output devices.
To get a precise matching be-
tween these diodes and the
output Darlington’s b-e junc-
tions, Sanken’s engineers
used a string of five Schottky
diodes in the P-device and
a single silicon diode in the
N-device.

Figure 4. Current Conveyor basics.

26

elektor - 4/2008

The datasheet specifies a bias cur-
rent of 2.5 mA through the diodes, and
this current is set by the current mirror
formed by Q19-Q20 and Q18-Q11. The
current is set with R44 and mirrored
into the diodes. To keep this current
stable, the supply voltage for the cur-
rent mirrors is regulated by zener di-
odes D 10-Dll to 15 V. The bias for the
zeners is coming from the main sup-
ply via R36-R37 and R35-R38. To keep
exactly that supply stable, the junc-
tion between those resistors is boot-
strapped from the output via C11-C12.
The result is that with varying output
signal levels, the zener diodes can al-
ways provide a constant supply volt-
age for the current mirrors.

The datasheet for the output devices
also specifies a quiescent current of
40 mA through the output Darlingtons
for best thermal tracking. Although the
diodes track the changes in the Dar-
lington V be quite well, the absolute val-
ue of the diode threshold values varies
from unit to unit. Thus, it is necessary
to be able to adjust it, and that is the
purpose of RV1. So, we should set RV1
for 40 mA through the output stage.
OK, so now we have a nice and stable
output stage, but we need to drive it
with a signal. That is done through R60
to the junction of R19-R20. Suppose
that the input signal goes positive: the
junction of R19-R20 goes positive so
there will be less current through R19.
Since the current coming out of the
collector of Q20 is fixed, there will be
more current into the base of the Dar-
lington and the output signal will also
go positive, following the input signal.
In this case there will also be more cur-
rent through R20 so less from the base
of the P-device.

This will work quite well for DC and
low frequencies and nominal, resistive
(8 ohms) loads, where the Darlingtons
have a very high gain and the current
mirrors are almost perfect. However,
with increasing frequency and increas-
ing load currents, the Darlingtons need
more input current, so capacitors C7
and C8 are added to bypass R19-R20
so the input source can directly drive
the output devices.

This output stage is quite simple, rea-
sonably linear and satisfies the require-
ment for accurate temperature track-
ing of the instantaneous output device
dissipation.

The next step is to wrap error correc-

tion around it. Because the stage has
no excess gain, you cannot use a glo-
bal nfb loop around it. The nfb loop that
normally includes the output stage of
a feedback amplifier of course relies on
the excess gain in the voltage amplify-
ing stage to work its distortion-reduc-
tion trick.

The Current Conveyor

For ec we need to derive the difference
between the input and output signal,
and add that difference to the input
signal, as shown in Figure 2.
Subtracting two signals that are of sim-
ilar level, and adding two signals that
are of similar level is trivial with opamp
circuits. We can use one opamp (S2) to
subtract V out from V e , and another (SI)
to add the resulting V c to V in . But in
the spirit of ec I didn’t want to use an
obvious high global feedback element
in this circuit.

After a lot of head scratching and many
Internet searches, I came up with the
idea to use a current conveyor [3]. The
basic circuit is shown in Figure 4a.
This is a very interesting circuit: basi-
cally, whatever you send into the Y ter-
minal comes out in opposite direction
from the Z terminal, which works as a
current source.

Hence the name current conveyor : the
current at the input is conveyed to the
output. This particular type is called a
second-generation conveyor, generally
shown as a ‘CCII’. Terminal X is a refer-
ence terminal for the current input, and
the voltage at Y will be kept the same
as that at X.

What is this good for? As an example
(Figure 4b), if you connect a signal to
Y via a resistor, you know that the cur-
rent into that resistor will be the signal
minus V x (remember, V Y = V x ). So the
current into Y is this voltage across the
resistor divided by the resistance. That
same current comes out of Z, so you
have now converted a signal level to a
current that can be converted back to
a signal via another resistor.

If the second resistor on Z is twice the
input resistor on Y, you have a gain of
2, without a feedback loop. You can set
the gain of this circuit with just two
resistor ratios, as shown in Figure 4b.
The nice thing here is that we can ac-
curately set a gain (or attenuation, if
that would be required) without hav-
ing to resort to nfb.

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4/2008 - elektor

27

IECTS

IJ ifl

A

!'■

f !

\

V J 4

\|

V

H/

1 /

1

How H.ec differs from Global Negative Feedback - or not.

Error correction works by feeding back (part of) the output signal to
the input of the amplifier. It has many similarities to a classical nega-
tive feedback loop. But how is it different?

Two sides of the same medal. Figure la is the basic H.ec topol-
ogy. You can identify two feedback loops: one positive feedback loop
via V e to V c and back to V e ; and a negative feedback loop from the
amplifier output to V c . That particular arrangement makes H.ec so in-
teresting. Let's assume that the output stage 'A' is ideal and has a per-
fect gain of 1 . In that case, the correction signal at V c is 0, because
there is no difference between V e and V out . We could just throw away
the whole error correction part. But if the gain A is just below 1 , V c is
a negative signal which is subtracted from V in and the effect is that V e
increases. This works as a positive feedback
loop. In the case where the gain A would be
larger than 1 , the signal at V c is a positive
signal, which will be subtracted from V jn to
decrease V e . In this case, the system works
as a negative feedback loop. So, what you
see is a combined feedback loop that can
act either as a positive or negative feedback
loop, or not at all, depending on the error
of the main amplifier block. It looks as if the
phase and level of the loop adjusts itself as
needed. The validity of treating a combined
feedback loop by 'summing' the individual
loop contributions has been established
by several researchers in the past. Gerald
Graeme, at the time analogue 1C develop-
ment manager of Burr-Brown, wrote several
articles about it [1 ].

How does this differ from a 'classical' nega-
tive feedback loop? We can take the two
feedback loops in H.ec apart as in Figure
lb. Error correction can be seen as a classi-
cal global nfb loop with a positive feedback
loop embedded. For comparison, Figure
lc shows the global nfb topology for a uni-
ty-gain amplifier.

Less complexity is better. In the classi-
cal case, the high loop gain, necessary for
negative feedback to reduce distortion, is
obtained by means of a high-gain (ideally
infinite-gain) forward amplifier block. In the
case of H.ec, this high forward gain is ob-
tained by a positive feedback loop, and the
forward amplifier block can have any open-

loop gain. To keep the task of a practical error correction circuit as
small as possible (and therefore optimise the ec circuit linearity), the
error signals should be minimal. For this, an open-loop gain equal
to the required closed-loop gain is best. That means that with H.ec,
similar results as with classical feedback can be reached with a much
simpler amplifier. In the case of a unity gain amplifier, just an emit-
ter follower would be sufficient, while in the classical case, even if we
wanted a closed-loop gain of 1 , we would still need a very high-gain
amplifier block. If nothing else, this leads to the practical advantage

Figure la, top, is the basic error correction topology. In Figure lb,
middle, the two feedback loops are separated. The two figures are
equivalent. Figure lc, bottom, is a classical global nfb amplifier.

that the forward amplifier can be much simpler. Of course, there is no
such thing as a free lunch (TANSTAFL): we have diverted some of the
complexity to the two summers that must be precise circuits to make
it all work. As always in audio engineering, the final advantage de-
pends on how smart you are at implementing the various circuit parts.

Less gain is better. There is another advantage to H.ec. When a
negative feedback amplifier clips, the feedback loop tries to make the
output following the input by increasing the input signal more and
more. But that output cannot increase beyond clipping, and as a re-
sult the amplifier is overdriven. This can be quite drastic: consider an
amp with a 1 V input signal and an open-loop gain of 60 dB (1000
times) and a closed-loop gain of 30 dB (30 times) that clips at 30 V out .

If the output signal is 30 V, the effective
input signal to the 60 dB gain amplifier

( v in - ^feedback) is 30 V divided by the open-
loop gain, or about 30 mV. If we overdrive
this amplifier by doubling the input signal
to 2 V, the feedback signal cannot increase
due to clipping. So the effective input sig-
nal to the 60 dB gain amplifier jumps from
30 mV to 1 V! (2 V input - 1 V feedback).
The clipping will become very hard, and
the output wave looks as a sine wave with
the tops sheared off. There is a danger of
heavy internal stage overdrive, and it is
possible that it takes some time, after the
clipping ends, until all internal stages are
returned to their stable operation point.
Many amplifiers will have measures to try
to avoid these conditions but it does add
to the complexity. With an H.ec amplifier,
the mechanism is similar. The error cor-
rection signal will increase and the input
signal to the amplifier block is increased in
an attempt to enable the output to follow
the input. But now the amplifier block is a
low-gain block, typically having a gain of
only the closed-loop gain, for example only
30 dB, instead of the very high open-loop
gain of 60 dB of the negative feedback
amplifier. As a result, clipping and internal
overdrive is not as hard. In my opinion, this
is an important advantage, which is shared
with valve amplifiers. Valved amps of mod-
erate power output can sound quite pleas-
ant, despite relatively high distortion fac-
tors, which is to a large extend caused by
their soft clipping characteristics. It is also
one of the reasons why very high power (300 W or more) solid state
amplifiers sound better than 50 W amps with the same distortion: the
high power amp clips far less than the low power amp, so the hard
clipping, which can make the sound so harsh, is greatly reduced.

[1 ] "Generalized opamp model simplifies analysis of complex feed-
back schemes" - Gerald G. Graeme, EDN, 1 5 April 1 993, pp. 1 75.

28

elektor - 4/2008

The current conveyer does not use glo-
bal feedback; it is an open-loop circuit.
As an aside, current conveyors consist
internally mainly of current mirrors;
and it can be argued that current mir-
rors use 100% local feedback. But we
won’t get into that discussion here!

There is our summer circuit: we will
use equal resistors for unity gain (1).

V c back to V e is realized with the con-
nection of Z to X in Figure 5.

So, at this point, we need to get practi-
cal: where do we find this CCII thing?
There are CCII’s around, often de-
signed in low-voltage CMOS IC tech-
nology, and mostly used in laboratories
in academic surroundings. They might
as well be made from ‘unobtanium’.

Figure 5. Output stage with error correction.

The error correction loop around my
output stage is shown in Figure 5. The
error between the input and the out-
put appears across R34 and develops a
current that is ‘conveyed’ to R25. This
adds the correction signal to the V in to
make the H.ec work as we discussed
before in Figure 2. The positive feed-
back loop in Figure 2 from V e through

But, interestingly, CCII’s are part and
parcel of current feedback opamps and
so-called ‘diamond transistors’.

Figure 6 shows the simplified dia-
gram of the internals of an AD844 cur-
rent feedback opamp. We recognise
the CCII terminals: pin 3 is the high-
impedance X terminal, pin 2 the low-

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4/2008 - elektor

29

PROJECTS

*

t

impedance current input Y and pin 5
labelled Tz is the current source output
Z. It is readily seen that whatever cur-
rent is injected into pin 2 (Y) comes out
at pin 5 (Z) but in opposite direction. It
seems this part has been custom de-
signed for us! Other similar parts are
Maxim’s MAX435 and MAX436 (now
obsolete) and TI’s OPA860, which su-
perseded the OPA660 and OPA2660.

We can use the input stage for the CCII
function, and the buffer to drive the
output stage to isolate the input sum-
mer from the output stage’s non-line-
ar input impedance. We see that the
current output terminal is already in-
ternally connected to the buffer input,
again, just what we need!

Figure 7 shows the full output stage
circuit, with component values. Note

Figure 7. Full unity-gain output stage with Hawksford error correction.

30

elektor - 4/2008

\

T

\ /

1

/

i

f

■

/

f

#

V

\

Jr

Figure 8. Output stage distortion curve without (top) and with (bottom) error correction. P out = 50 W into 8 Q.

that the amplifier input is at pin 5
of the AD844, not at pin 2 or pin 3 as
we would expect in a classical opamp
circuit. This is NOT an opamp circuit,
but I’m sure a lot of people will be con-
fused by this...

Putting it all together

This output stage has two pairs of
output devices. The design goal was

100 watts in 8 Q and 200 watts in 4 Q.
For a pure resistive load, one pair of de-
vices would have been sufficient. How-
ever, speakers are not purely resistive;
depending on the signal frequency
they can act capacitive or inductive,
especially if there is a complex cross-
over filter. This leads to phase shifts
between the output voltage and output
current, so you can get the situation
that the output voltage is negative,

Figure 9. Prototype amplifier module and output/protection board.

CL>

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DAC Board

The MCP4921 is a general
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ADC Board

12-bit analog-to-digital con-
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4/2008 - elektor

31

but that the current is coming from
the positive side (the N-device). The
N-device will have a quite large V ce ,
and the current it is allowed to source
is much smaller with a large V ce than
what you would think from the allow-
able dissipation.

Further details about the safe opera-
tion area of the output devices will be
given in a separate article next month.
Anyway, because of the dual output
devices, there is also an additional cur-
rent source to bias the thermal track-
ing diodes, as well as an extra bias ad-
just trimmer.

as the current conveyor will exhibit
phase shift. In a ‘classical’ feedback
amplifier, if the phase shift becomes
too large, it will turn the nfb into pfb
which, as we all know, will lead to in-
stability and even oscillations. In H.ec
this is also the case of course (it shares
many attributes with a feedback am-
plifier), so we need to roll off the loop
gain for higher frequencies, just as in
a classical nfb amplifier. C3 does just
that by decreasing the effective correc-
tion impedance (R25//C3) with increas-
ing frequency.

Also remember that this stage needs

output stage can perfectly stand on its
own when driven by a suitable voltage
amplifier (Vas) stage. So, let’s take a
break here; we’ll attack that Vas, and
the power supply, in the next instal-
ment and develop a full-fledged, high
quality audio power amp. Stay tuned.

( 070987 - 1 )

Literature and note

[1] Hawksford, M.J., 'Distortion correction
in audio power amplifiers', JAES, Vol. 29,

No. 1/2. pp. 27-30, Jan/Feb 1981.

[2] HephaTstos, 'Thermal Distortion - it exists,

_ / ■ ■ i v. jp 1

Iv \

Figuur 10. De opgebouwde versterker-module op z'n koellichaam.

There are a few extra components in
the circuit which we haven’t men-
tioned before.

R60 is a small resistor in series with
the AD844 buffer output stage. A large
part of the output drive goes via the
two capacitors C2 and C4 to bypass
the current mirrors. R60 isolates the
buffer output from capacitive loads en-
suring stability.

Another capacitor, C3, is placed across
R25. As the frequency increases, the
loop through the output stage as well

to be driven from a low impedance
source, because the source output im-
pedance forms part of the ec scaling
resistor R25.

Finally, there is the 6-pin connector J10
and some associated resistors. This is
the connection to the protection board
which we will discuss separately. It
provides the V ce and I c related infor-
mation of the output devices to the pro-
tection circuitry.

This output stage is pretty linear as at-
tested by the curves in Figure 8. The

I've seen it', L'Audiophile, no. 32, May 1984.
(Ed.: Hephaistos was the Greek god of fire,
metalworking, stonemasonry and the art of
sculpture)

[3] In the early 90's, an IC designer, Doug
Wadsworth, designed a current conveyor for
audio on his own money (PA630). The chip,
the 'Swift Current' chip, eventually found its
way into Wadia DACs. It is no longer availa-
ble for other parties, but I had bought some
from him and knew they were a well kept se-
cret for hi-end audio.

32

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33

HOME AUTOMATION SERVER

home automation server

Part 1: introduction and circuit descriptions

Richard Sumka (Freescale Semiconductor Inc.),
Luc Lemmens & Jan Buiting (Elektor)

This project employs a Freescale Coldfire micro and associated PC software
that allows remote switching of electrical loads across networks including the
biggest we know - the Internet. The ingredients from the Freescale/Elektor
kitchen: 32 -bit embedded technology, free software, a low-cost kit for the
hardware and free tools to expand the functionality of the server to your own
liking.ln the first instalment we describe the general structure of the server and
the optional Turbo BDM programmer for Coldfire devices.

Out for the night
and forgotten to
switch off the lights
at home, or the heat-
ing? This project

could be the solution, providing the
ability to control equipment remotely
over the Internet using a web browser
or WAP enabled phone.

Sure, that application alone may look

trivial considering the sheer power of
the microcontroller used but that’s also
the crux of the project: it’s expandable
and totally geared to open-source de-
velopment as we have made sure that

elektor - 4/2008

all resources are available either free
(software) or at low cost (hardware).

Networked home automation server

Connecting applications together is
fast becoming a necessity rather than
an option, especially where Ethernet
networking is concerned. This home
automation server using a Freescale
32-bit Coldfire device and Freescale
software allows remote switching of
loads across Ethernet networks and
the Internet. And with some ingenui-
ty, simple modifications allow the serv-
er to be used for remote sensing and
monitoring.

Crossing the internet
(and WAP gateways)

Web pages are transferred across the
Internet using HyperText Transport
Protocol (HTTP). HTTP is a request-
response protocol and can be used to
send any type of data including binary
data. The client - a web browser - re-
quests a web page from a web serv-
er and the web server responds with
the web page contents. Simple as that
may sound, there’s a lot of technology
behind it all!

As illustrated in Figure 1, DigiButler is
a mini web server that will happily sit
behind an Internet connected router.
Alternatively, it may be connected to
a local network or directly to a PC. For
most of this article we will describe
the connection as though it were be-
hind a router.

The unit will accept commands from,
and return data to, any Internet-con-
nected PC or WAP telephone that has
DigiButler’ s IP number. Password pro-
tection is also provided by the client
software.

About the MCF52231

The Freescale Coldfire MCF-
52231CAF60 in its LQFP80 case is a
member of the MCF5223x family of 32-
bit connectivity microcontrollers. Its
architecture is shown in Figure 2. The
two key features of the family are the
integrated 10/100 Mbit/s Fast Ethernet
Controller (FEC) and Ethernet Physi-
cal Layer (EPHY); in brief, everything
needed to get a single chip application
onto an Ethernet network. If you want
to delve really deep into this, there’s
a must-read article available from Eric
Gregory [1].

This device also has a CAN 2. OB con-
troller. CAN is commonly used as an

i Main specifications

i • 32-bit Coldfire MCF5223 1 microcontroller i

• Open-source project

i • C source code i

• Free CodeWarrior software development platform

1 • Doubles as a low-cost Coldfire development system 1

i • Connectivity: EtFiernet (RJ45), RS232, BDM, analogue, l 2 C, timers |

• 1 relay (on board) suitable for mains loads up to 2 A

i • Accessible tFirough Internet or WAP i

• Client software witFi password and username protection

i • TCP/IP and RTOS stack witFi HTTP, DHCP, UDP, ICM8 ARP support ■

i • Easy IP setup i

• Ideal for web-driven remote sensing and control

i • Kit of parts available from Elektor SFiop i

L — — — — J

Optional Additional Modules

Crypto

CAN

— r

BDM

PLL GPIO

"1

JTAG

4-ch., 32-bit
timer

4-ch. DMA

i i

> ; io/ioo ; |

Q. i FEC i O

1 i

4-ch., 16-bit
timer

l 2 C

UART

2-ch., PIT

QSPI

UART

4-ch., 8-ch.

PWM

2 x 4-ch., 12-bit
ADC

UART

RTC

32 KB

SRAM

i

O i ColdFire®

| i M2

w 1 Core

i

System

Integration

071101-14

Figure 2. MCF52231 'Coldfire' architecture (courtesy Freescale).

4/2008 - elektor

35

HOME AUTOMATION SERVER

MCF52231 - bits to remember

• 128 l<B of embedded Flash memory

• 32 kB of SRAM

• 60 MHz Coldfire V2 32-bit CPU

• Up to 56 bits of general purpose I/O

• Three UARTs

• Serial peripheral interface (QSPI)

• l 2 C bus interface

• Four 32-bit timer channels with DMA capability

• 4-channel, 1 6-bit timer for capture, compare and PWM

• 2-channel periodic interrupt timer

• 4-channel, 16-bit or 8-channel, 8-bit PWM generator

• Two 4-channel, 1 2-bit analogue-to-digital converters

• 4-channel DMA controller

• Up to 73 general-purpose I/Os

• PLL, watchdog, real time clock, range of reset sensors

• On chip background debug module (BDM)

• Single 3.3-volt supply

+3V3 ©-

<4

RN1

TMS
TDI/DSI '

RN3

RN2

HUH-

Cl

lOOn

7x 4k7

RSTI^

A

IRQ11

1 1 °

IriUf

1 1 6

1 1 6

iRQi

1 1

5x 10k

S2

\

RCON

TDO/DSO

SDA

1 b

SCL

l 6

TIN2

TIN3

1 8

IRQ4

7x 10k

RESET ,

IRQ .

FBI

VDDA BLM31PG601SN1 +3V3
© ©

C20 C21

4|i7

6V3

^C7 JciT

4p7

6V3

220n

FB2

BLM31PG601SN1

^TJCIS ^C9 ' ' ^C10 Jci 1 ^C12 Jc

^OOn^ToOn^Lon^ ;

MOOn

Q Q Q Q O
LU 111 111 LU LLI

■»” CM CM

X X Q

Q Q Q

Q Q >

> >

/

/

X

J12

SDA

GPTO

GPT2

o a

o o
o o

SCL

6 GPT1

\

8

DIGITAL

J11

\ AN1

\ AN3

\ AN6

AN4

O a
o o
o o
o o

ANO /

_AN2/

mjy

10

_AN5/

ANALOG

QSPLOUT
QSPI SCK
QSPI-CSO
SYNCA
SYNCB

31 Trot

S.IRQ4

29

\IRQ7

40

IRQ11

41

SDA

80

SCL

79

vgpto

78

VGPT1

77

\GPT2

76

VGPT3

75

V ANO

68

\ AN1

67

S. AN2

66

AN3

65

V AN4

61

S..AN5

62

S, AN6

63

\ AN7

64

IRQ11

U1

MCF52231

80-pin

LQFP

RSTO

RSTI

JTAG EN / ** \JTAG EN 12
48_

49_

55

46

JTAG EN
PHY VDDA
PHYVDDTX
PHYVDDRX
PHY RBIAS

a. <

</) c/> -J

CO CO oc

> > > XTAL

EXTAL

i- oi

X X i- 04

CO 10 CO CO

CO CO CO CO

> > > >

JP2

BDM_EN

C4

220n

C3

220n

C2

220n

R3

If)

CO

CM

1-

h-

M R5

CM

<

» — | 10M | — <

Y1 r

I

I

a

a

1

1

1

l

CO

C5

■ <

22p

i i

25MHz

50

51

53

54

ALLPST

8 TINO /

9 TIN1 /

13 TIN2 y

14 TIN3 /

7 ALLPST/

TRST

TDO/DSO

TDI/DSI

RCON

TMS

TCLK

PHY_VSSA

PHY_VSSTX

PHY_VSSRX

TEST

UTXD1

URXD1

UCTS1

URTS1

UTXD0

URXDO

UCTSO

URTSO

rsti U? RSTI/ KRSJL

_[RST/

5 TDO/DSO /

4 TDI/DSI / ^ALLPST

3 RCON /

™S/

tclk/

47

52

56

38

U2

LD29080

J3

-6

-o

□ M

500mA 1N4002

R14

C22

330p

16V

green

^C16 Jc

R8 R9

C17

220n

T1

16

15

14

SI

J2

11

10

RJ45

J1

R11 RIO R12 R13

S2

13

15

25

O O

o a
o o |- 26

10

12

14

BDM PORT

TRST

TDI/DSI

TDO/DSO

ALLPST

"N

JP1

BDM_SEL0

R2

R1

a

o

CM

T- ’

CM

J

tX

C143

lOOn

12

R15

D3

J14

D4

2 cm

R16

yellow

1

•

3

2

4-

©

Cl 44

lOOn

R176

Cl 45

II

II

lOOn

2

v+

C1 +

©

U4

Cl-

T1IN

TIOUT

RIOUT

RUN

R20UT

R2IN

T2IN

T20UT

C2+

MAX3232ESE

C2-

V

16

14

13

J13

X

15

Cl 47

It

lOOn

UART0

1N4148

R17

OMRON G6D
Q1

BC546B

T

071101 - 11

Figure 3. Schematic of the home automation server. The circuit has been designed for expandability — in fact it makes a great development system for Coldfire 32-bit microcontrollers.

36

elektor - 4/2008

industrial control serial data bus be-
cause of its suitability for use in real-
time communication environments
and its reliable operation in conditions
of harsh EMI. The MCF52231’s big-
ger brother the MCF52235 also has

Cryptographic Ac-

celeration Unit and
random number
generator for se-
cure hardware en-

cryption. Some of

the other important features of the

MCF52231 are listed in the inset.

Electronics

If we include the transistor and the
voltage regulator, there are four ac-
tive components in the circuit dia-
gram in Figure 3. Let’s take a tour of
the schematic.

ing is reduced.

J1 is the BDM (Background Debug
Mode) interface, allowing in-circuit
debugging of the application code
and Coldfire Flash memory erasing
and programming. The associated pro-

Everyone's encouraged to improve & extend the
DigiButler C code and let us know the results

grammer (for optional use) is described
further on.

RS232 port J13 is driven by the internal
UART of the Coldfire and voltage level
translation is provided by U4, the fa-
miliar MAX232. A regular RS232 cable
should be used to connect the port to a
PC, i.e. not a null-modem cable.
Pushbutton SI is the main Reset and
its activation will restart the applica-

Voltage regulator U2 steps the input
voltage down to provide the Coldfire
device with a stable 3.3 V, which is fur-
ther decoupled by lots of 100 nF and
220 nF SMD capacitors in key posi-
tions. The VDDA supply for U1 is also

derived from the

+ 3.3 V line and
has additional fil-
tering by ferrite

bead FBI and a

pair of low-volt-
age SMD 4.7 jliF capacitors, C20 and
C21. Clean as whistle!

Relay control

A key feature of the home automation
board is its capacity to control hard-
ware remotely via the Internet. The
ability to control mains voltage equip-
ment is especially interesting but re-

Elektor is again proud and glad to work together with Freescale
Semiconductor Inc. for the benefit of its readership. After the great
success of the 8-bit MC9S08 SpYder and Accelerometer articles in
March and April 2007 we now take a giant leap to a 32-bit embed-
ded system we hope will challenge and inspire the thousands of mi-
crocontroller fans among you. The effort is boosted by a kit of parts
we're selling at a low price for the DigiButler project.

Historically Freescale has successfully concentrated on the auto-
motive market for its microcontrollers and as a result has held a

leadership position there for many years. More recently however,
there has been a real push to significantly increase support to the
markets served by the distribution network. This increase for the
mass market also extends to students and enthusiasts and has led
Freescale to work with Elektor.

Interestingly, Freescale has also been asked by some of their largest
OEM customers to work with Elektor so that graduates coming into
industry are familiar with their products when they start their careers.

At the heart of the circuit sits the
Freescale MCF52231 Coldfire device
(Ul). The 10 or 100 Mbit/s 802.3 ready
Ethernet interface is provided by iso-
lation transformer T1 and the physical
RJ45 Ethernet connector J2.

Crystal Y1 (25 MHz) sets the clock fre-
quency of the Coldfire microcontroller.
This is multiplied up by the device’s
internal PLL to give a core clock fre-
quency of 60 MHz.

Eight 12-bit analogue inputs are avail-
able on connector Jll. These are rout-
ed directly to the ADC pins of the Cold-
fire. A further six of the Coldfire ’s dig-
ital input/outputs are available on J12.
All can be used as general-purpose I/O
and two may be configured to connect
to the I 2 C module in the microproces-
sor. The two I 2 C lines, SDA and SCL,
are fitted with 10 kQ pull-up resistors.
The I 2 C can operate at up to 100 kbps
with maximum I 2 C bus loading and
timing, and even faster if the bus load-

tion code. S2 is directly connected to
pin IRQ7 of the Coldfire, with a pull-up
to the +3.3 V supply, acts as a general
purpose pushbutton input. If you want
to ‘program it in’, feel free to do so!
Jumpers JP1 and JP2 on the board are
for programming purposes and will be
discussed in part 2.

It’s not shown in the circuit diagram,
but a large prototyping area on the
board gives the user lots of room for
experimentation and to expand the
board’s functionality.

Any low-cost regulated or unregulated
power adapter with an output voltage
of 5-8V DC at about 500 mA is suitable
for powering the circuit. This input mi-
nus the drop across D1 is used to sup-
ply relay RE1, which has a maximum
coil voltage rating of 8 V. As would be
expected for such a design, there is
reverse polarity (Dl) and over-current
protection (FI), and an LED (D2) to in-
dicate power on.

quires special precautions. As with
any life threatening voltages, safety
is paramount and there must be elec-
trical isolation between the low volt-
age of the board and any mains volt-
age. Isolation is provided by relay RE1
whose contacts can switch a 250 VAC,
2 A load, the current capacity being
limited by the width of the PCB tracks
from RE1 to connector J14. Yellow LED
D4 shows the relay on/off status.

DigiButler software

The project firmware is a modified ver-
sion of the Coldfire Lite HTTP server
software available free from Freescale
and described in Application notes
AN3455 [2] and AN3470 [3]. A wealth
of information covering the software
operation and including training pres-
entations can be found at [4] and [5]. In
this project, modifications have been
made to the Freescale software to pro-

4/2008 - elektor

37

HOME AUTOMATION SERVER

Yes, Milord

• The project is open-source with all C code available free for every-
one to alter, recompile and flash

• The hardware and software are designed for expansion and
experimenting

• You are working with real 32-bit embedded technology

• The project has been designed and tested in close cooperation with
Elektor labs

• The PCB in the kit comes with the micro programmed and SMD

parts pre-soldered

• The hardware is fun to build on a high-quality board with SMDs
p re -stuffed

• There is a large community of knowledgeable Freescale microcon-
troller users

• The CodeWarrior programming suite is free and easy to use

• East Kilbride is a wet & windy place

• There may well be several Coldfire micros in your new car

vide authentication using username
and password and to allow access
from WAP enabled phones and web
browsers. There are a large number of
code modules in the project and all are
written in ‘C’. As the microcontroller is
operating at a whopping 60 MHz there

is no need for any

assembly language
code. In the project
settings, 81 kB of
Flash memory has
been reserved for
code space and 45 kB of it for web
content. If code optimization Level 1
is used when building the project then
only 58 kB of code space is used —
give it a try!

The board implements an HTTP web
server using a free TCP/IP and real
time operating system stack from
Freescale. The term ‘stack’ is used as
the software is designed as one proto-
col stack on top of another, as shown in
Figure 4. For those interested in the in-
ternal workings of the stack, a browse
through the project source code will
show that the stack
supports DHCP, UDP,

ICMP and ARP proto-
cols in addition to TCP/

IP and HTTP
Thanks to lots of free
information being
available on Cold-
fire TCP/IP stack pro-
gramming, very little
knowledge of the code
operation is needed to
modify web pages and
access the board hard-
ware across the Inter-
net or a WAP phone.

by the ‘embedded’ underground com-
munity. Some members have actual-
ly developed low-cost alternatives to
Freescale’ s proprietary programming
and debugging systems for various mi-
crocontroller families, including the high-
end ones! In all cases, the concept of

TBLCF is optional, open-source,
USB and costs less than $10 to

has

BDM is used to access the micros. SpY-
der [6] is a BDM for MC9S08 micros.

A “Turbo BDM Light Coldfire Inter-
face” (TBLCF) for use with CodeWar-
rior was developed by Daniel Malik. It
is found on the Freescale 68K/Coldfire
Processors forum [7]. In good commu-
nity spirit Daniel released all relevant
material on his design into the free-
ware domain. If you master the art of
‘judicious sampling’, TBLCF should not
cost more than a tenner for parts.

An important point to mention is that
TBLCF is optional for the present

TBLCF: open-source
and optional

It’s heartening to see
that many Freescale mi-
cros have been adopted
with great enthusiasm

Freescale
Web Server

Freescale
Compile Time FFS

Freescale
Run-Time FFS

ColdFire TCP/IP Lite RTOS and Console

ColdFire TCP/IP Lite Mini-Socket TCP API

ColdFireTCP/IPJLite

TCP

ColdFire_TCP/IP_Lite

UDP

ColdFire_TCP/IP_Lite

ICMP

ColdFire_

TCP/IP_Lite IP Layer

ColdFire TCP/IP Lite FEC Driver

Freescale
Ethernet PHY

Freescale
Hardware API

FFS = Flash File

Figure 4. TCP/IP and RTOS stack implemented on the Coldfire micro.

project. The DigiButler board in the kit
supplied by Elektor contains a ready-
programmed MCF52231 micro that will
not normally require re-programming or
debugging. So, TBLCF is for advanced
users wishing to modify the DigiBut-
ler firmware — everyone is encouraged

to do so and show

the results.

Daniel Malik’s de-
scription of TBLCF
is exhaustive and
eminently present-
ed in free documents and even artwork
to make the PCB. There’s an associat-
ed DLL and a step-by-step software
installation guide. Here, we will limit
ourselves to a condensed circuit de-
scription referring to Figure 5, cour-
tesy Daniel.

TBLCF has USB connectivity to the PC.
The hardware has two main parts: the
MC68HC908JB16 MCU and the BDM
interface driver based on a 74VHC14
buffer. The ‘VHC14 is used to achieve
low-cost translation of BDM signals

with voltages anywhere
between 3.3 V and 5 V
to the 5 V logic of the
MCU. The VHC logic
accepts overvoltage
on inputs, however the
output voltage swing
is limited by the power
rail voltages. When the
74VHC14 is powered by
a 3.3 V source, resistors
R3 and R4 would not
be able to pull the sig-
nals above the 3.3 V rail
and would only inject
current into the pow-
er rail of the 74VHC14.
Alas, 3.3V is below the
minimum High level
input voltage of the
MC68HC908JB16 and
the circuit would not
be guaranteed to work.
Diodes D2 and D3 have

071101-15

38

elektor - 4/2008

been added to increase the high level
voltages. The better alternative, two
N-channel MOSFET transistors, would
increase the cost and complicate the
PCB layout.

The RSTO signal is brought to two dif-
ferent pins of the MCU. This is strictly
speaking not needed and a connection
to pin PTE1 would be sufficient. How-
ever connecting the signal to PTA6 as
well simplified the PCB design!

The ColdFire BDM connector has been
here for a long time. In the past, boards
usually contained a lot of components
and were fairly large. A 26- way con-
nector with 0.1” spacing was therefore
of a reasonable size. Size of boards is
however shrinking and the connector
is becoming too large for smaller appli-
cations. Two optional enhancements
have been made to the standard BDM
connector:

1. Where the 26-way connector is too
large you can use a 10-way subset
of the connector (pins 1 through 10).
The only signal which is then miss-
ing is TA (Transfer Acknowledge)
on pin 26, but this is only needed in
systems with external memory bus

where the debugger is configured
incorrectly and accesses an area for
which a TA is not generated (nei-
ther internally nor externally). So,
the probability that it will be needed
is quite low and the absence of the
signal can be compensated for by a
careful use of the debugger.

2. The RSTO signal has been added to
pin 1 of the connector, which was
so far unused. This enables the in-
terface to detect resets of the micro-
controller caused by, for example, the
COP/watchdog circuit or a user RE-
SET button.

Note that the above enhancements are
suggestions only and the interface will
happily operate even with the original
26- way connector. Pins 11 and 12 of the
26-way connector can be removed to
make the interface compatible with both
the 10-way and 26-way ribbon cables.

Next month

It is planned to have kits for the Digi-
Butler project available with the publi-
cation of the May 2008 issue of Elektor.
We then finish the article by discuss-

ing hardware assembly and test, net-
work connection, Ethernet setup and
creating and uploading web pages. For
advanced users, CodeWarrior-driven
compilation and reflashing of the MPU
is also discussed.

( 071101 - 1 )

References and
Internet Links

Note: documents also available from
the project web page:

www.elektor.com/digibutler_en

[1] ColdFire Ethernet, by Eric Gregori.

[2] www.freescale.com/files/microcontrollers/
doc/app_note/AN3455.pdf

[3] www.freescale.com/files/microcontrollers/
doc/app_note/AN3470.pdf

[4] www.freescale.com/webapp/sps/site/
homepage. jsp?nodeld = 01 62468rH3YTLC

[5] www.emgware.com/

[6] Attack of the SpYder,

Elektor Electronics March 2007.

[7] http://forums.freescale.com/freescale/
board/ message? board. id = CFCOMM&thread.
id = 624

VDD 10

MMSD4148

Figure 5. Circuit diagram of TBLCF, the open-source, optional debugger/programmer for Coldfire micros. TBLCF should not cost you more than $10 to build.

4/2008 - elektor

39

PROJECTS MICROCONTROLLERS

This new series of articles presents a tiny processor module based on
an ATmega88 microcontroller, ideal for use at the heart of any number
of different projects. We begin with a reaction time tester and quickly
move on to more advanced projects such as a precision weather station
and a 3D magnetometer. Our most ambitious and final project will use
the ATmega to provide autonomous control to a four-motor aircraft. Each application
example provides an easy-to-understand demonstration of how to work with AVR microcontrollers.

Elektor readers will already have seen
the ATmega8, ATmegal6 and AT-
mega32 used in real-world applica-
tions. In this series we will be using
the ATmega88, which is a small, light-
weight and powerful microcontroller
(see text box). In comparison to the
ATmega8, which is the same physi-
cal size, the device offers a higher
clock rate, up to six PWM outputs, and
many other extras to make life easier
for developers.

Our AVR projects centre around an
ATM18 microcontroller module fit-
ted with an ATmega88. To make the
unit universally useful, it has been de-
signed to be as small and lightweight
as possible. The printed circuit board
is tried and (thoroughly) tested: it is
based on a design that has been used
successfully for years in autonomous

aircraft made by Microdrones in Ger-
many, adapted to suit our particular
needs. Anyone who has seen one of
these four-propeller aircraft in opera-
tion (for example, at Embedded World
2008) will appreciate how important it
is to pack as much computing power
as possible into a tiny volume.

The project essentially consists of two
printed circuit boards. The first is the
ATM 18 microcontroller module, meas-
uring 18 mm square; the second is
the ATM 18 test board, which sports a
wide range of interfaces and which is
intended to be used to help with de-
velopment. Of course, surface-mount
technology is inevitable in a project
like this, and so manually populating
the boards is somewhat tricky. How-
ever, Elektor comes to the rescue with
ready-made modules and test boards:

only the connectors need to be sol-
dered manually. This has the advan-
tage that the connectors not required
for a particular application need not be
fitted. In some applications it is appro-
priate to connect the microcontroller
module directly to other printed circuit
boards or sensors, and so the module
is also available as a separate item so
that you can use a single test board to
develop a range of different projects
based on the module.

The ATM18 microcontroller module

The module takes the form of a carrier
board, similar in style to that featured
in the R8C project which will be famil-
iar to Elektor readers. We have used a
special thin material for the printed cir-
cuit board to keep the weight and over-
all size of the module to a minimum.

40

elektor - 4/2008

4

The ATM 18 Project on Computer .club

ATM18 was developed jointly by Elektor and Computer:club 2 (www.cczwei.de) with contri-
butions from Udo Jurss, the main developer of www.microdrones.de. Elektor is pleased to
support the project through articles in the magazine, ready-stuffed boards supplied through
the Elektor Shop, supplementary information, software downloads and the forum at www.
elektor.com.

Each month, the latest deveopments and applications of the ATM1 8 system are presented by
Wolfgang Rudolph of Computer:club 2 in a TV broadcast on the German NRW-TV network.
The boards and example programs from this article instalment can be seen in Broadcast
#9 of CC 2 -tv on 20 March 2 008, Some understanding of German required!

CC 2 -tv is also broadcast as a Livestream on the Internet at www.nrw.tv/home/cc2.

i CC 2 -tv Podcasts are available from www.cczwei.de and - a few days later - from i

i sevenlood.de. i

L____ __________ ______________

The TQFP32 version of the ATmega88
is used (the device is also available in
a 28-pin DIL package). Also featuring
on the board is a 16 MHz crystal and
the necessary SMD capacitors, and
two resistors. Measuring just 18 mm
square the unit is smaller than a post-
age stamp, and, once programmed,
it forms a self-contained autonomous
unit. For reasons of space, the head-
er connectors are laid out on a 2 mm
pitch; in very space-critical applica-
tions the headers can be replaced with
a cable soldered directly to the board.
Headers with a 2 mm pitch are reason-
ably widely available since they have
long been in common use in Japan.
Unfortunately, we cannot use stand-
ard perforated board with the mod-
ule, but of course we can use the test
board, which brings the signals out to
2.54 mm (0.1 inch) pitch box headers.

Experiments can then be performed
very simply using insulated wire
(0.8 mm) to connect the various inputs
and buttons.

Figure 1 shows the pinout of the AT-
mega88 and Figure 2 shows the pinout
of the module: the similarities (and the
differences) should be evident. A to-
tal of 32 pins is reduced to 29, as the
GND and VCC connections are repeat-
ed on the TQFP package. The connec-
tions required for in-system program-
ming (ISP) are made available in a
single row to simplify connection to a
programmer.

The crystal and a couple of capacitors
are located on the reverse of the mod-
ule (see Figure 3). This is all that is
needed to get the microcontroller run-
ning: see the circuit diagram in Fig-

ure 4. The analogue supply voltage
AVCC is derived from the main supply
via a filter comprising R1 and C3, and
there is a 10 kQ pull-up resistor (R2) on
the reset input.

The printed circuit board layout is
shown in Figure 5, with the 2 mm
pitch pin headers on all four sides
clearly visible. When these are fitted
to the board, they mate perfectly with
the corresponding sockets on the test
board.

When soldering these headers it is
important to ensure that they are
mounted exactly vertically: it is pos-
sible to use the test board as a jig to
simplify the job: mate the pin head-
ers with their corresponding sockets
on the test board and then place the
microcontroller module on top. This

4/2008 - elektor

41

MICROCONTROLLERS

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Figure 1. The pinout of the ATmega88 in a TQFP package.

Figure 2. Pinout of the ATM18 microcontroller module.

will keep everything at the correct an-
gle while soldering. Do a single pin on
each connector first, and then make a
thorough visual inspection, adjusting
the positions of the connectors if nec-
essary. When everything is in order the
remaining pins can be soldered.

The test board

This printed circuit board is of course
rather larger. It provides a wide range
of external interfaces as well as a pow-
er supply for the ATM18, providing
an easy way to experiment with the

r — — — — — — — — — — — — — — — — — - - n

ATM18 micro-
controller module

Quick data i

Microcontroller: ATmega88 1

Operating voltage: 2.7 V to 5 V i

Processor clock: 0 Hz to 20 MHz |

(typically 1 6.0 MHz) i

Current consumption: approximately i

1 8 mA (at 5 V and 1 6 MHz) i

Hardware features

Two 8-bit counter/timers (TimerO, i

Timer2) 1

One 1 6-bit counter/timer (Timerl ) i

One synchronous serial interface (SPI) i

One asynchronous serial interface
(UART) i

One two-wire interface (l 2 C)

One 10-bit A/D converter with 8 inputs
(ADCO to ADC7) |

One analogue comparator

Up to 23 digital I/O lines 1

L_ ___ __ ___ __ ___J

Figure 3. Top and bottom views of the ATIVI18 microcontroller

module.

module and connect extra hardware,
sensors, actuators and other bits and
pieces. The board measures 80 mm
by 50 mm and the mounting holes are
spaced at 72 mm and 44 mm.

Figure 6 is the circuit diagram of the
test board. IC1 is a type LM2594-5.0
step-down converter, which provides
a regulated supply voltage of 5 V for
the microcontroller and peripherals
from an input supply (on connector
Kl) of between 7 V and 16 V without
dissipating large amounts of power
as heat. Current demand is low, and
a simple mains adaptor can be used.
Battery power, using rechargeable or
dry cells, is also feasible. Diode D1
protects against accidental reverse
polarity connection of the power sup-
ply: a Schottky diode is used as it has
a lower forward voltage drop. The
regulated voltage, EXT + 5 V, is used
as the supply for the board if jump-
er JP6 is set to ‘EXT’, bridging pins
1 and 2. If JP6 is set to bridge pins 2
and 3 (‘USB’), the supply is obtained
from K2, the connector for the TTL-
level serial interface. If an FTDI TTL-
232R adaptor [1] is connected to K2,
the 5 V supply will be taken from the
connected PC via its USB port. The
adapter will be available from the
Elektor shop in the near future. There
is also a 3.3 V version of the adaptor,
which can equally well be used. The
selected supply voltage is available on
eight pins of connector K8. There are

42

elektor - 4/2008

r

i

AVR, ATtiny and ATmega

It was decided to use an Atmel ATmega microcontroller for this
project. This comprises an entire family of devices, with the main dif-
ference between individual devices being in their processing power.
The design is particularly flexible and modern and ideal for low-cost
implementations. The original AVR design was produced at the Nor-
wegian Institute of Technology in Trondheim before being bought by
Atmel. The AVR core is particularly small and can be implemented
in as few as 4000 gates. Atmel, the only manufacturer of processors
using this core, produces two series of devices: the ATtiny series and
the ATmega series. The AVR has a RISC (reduced instruction set com-
puter) architecture; traditional CISC (complex instruction set compu-
ter) architectures offer more powerful and sophisticated instructions,

but decoding such an instruction takes considerably longer than does
the decoding of a RISC instruction. Furthermore, a CISC processor
generally takes longer to respond to an interrupt request than a RISC
processor, impairing real-time performance.

All ICs in the AVR family are structured in essentially the same way,
differing only in the quantity of memory available and the number
and types of timers provided. Some also feature an A/D converter or
a UART (universal asynchronous receiver/transmitter) to provide a se-
rial interface on the chip.

The AVR was designed with the efficient execution of programs writ-
ten in high-level languages in mind. From the point of view of both
price and performance a RISC microcontroller of this type makes the
ideal basis for our projects.

also a further eight ground pins, giv-
ing a total of eight points from which
a supply can be obtained to power ex-
ternal devices. Six more ground pins
are available at K9.

Jumper JP2 is also concerned with
power supply options. If it is fitted,
the +5 V supply is used as the refer-
ence voltage for the A/D converters in
the microcontroller. A low-pass filter is
used here to smooth the reference volt-
age in the same way as the analogue
supply is filtered on the module board.

Together these filters ensure that the
reference used for A/D conversions is
stable and free of interference.

The TXD and RXD signals on K2 are
compatible with TTL levels and are
not inverted. If proper RS-232 levels are
required, an external interface device
(such as a MAX232) must be used. The
interface is designed for direct connec-
tion to an FTDI TTL-232R USB-to-serial
converter.

There is a total of four pushbuttons on
the test board (Figure 7). Switch SW1

is the reset button, allowing the mi-
crocontroller program to be restarted
at any time. SW2, SW3 and SW4 are
general-purpose buttons connected to
K12. They can be connected to the mi-
crocontroller’s I/O ports so that their
state can be determined by a suitably-
written program.

The test board also provides outputs,
a ULN2003 power output driver giving
seven high-current outputs on Kll.
Each open-collector output can sink up
to 500 mA, and so is capable of driv-

+5V

Figure 4. Circuit diagram of the ATJVll 8 microcontroller module.

Figure 5. Printed circuit board for the ATJVll 8 microcontroller

module.

COJVIPONENTS LIST

ATJVll 8 controller module

Resistors (SJVID 805)

ri = ion

R2 = 1 OkQ

Capacitors (SJVID 805)

Cl ,C2,C3 = 4^7 6.3 V (Farnell #
922-7857)

C4,C5 = 22pF

Semiconductors

IC1 = ATmega88 (TQFP32 case),

Atmel)

Miscellaneous

Q1 = 1 6MHz quartz crystal, SMD (7mm
x 5mm)

3x 8-way pinheader, 2mm lead pitch

lx 5-way pinheader, 2mm lead pitch

PCB, ref. 071035-1 (track layouts free
download from www.elektor.com)

PCB, ready populated with SMDs, test-
ed, including pinheaders, Elektor-Shop
# 071035-91

4/2008 - elektor

43

PROJECTS

MICROCONTROLLERS

ing motors and relays directly. Seven
LEDs (with current-limiting resistors)
are provided to show the states of the
output signals. The inputs to the power
driver IC are available on K10, allowing
them to be connected to any desired
port on the microcontroller as required
by the user or programmer.

One of the most important interfaces

on the board is ISP connector K7, used
for connection to a programmer. The
pinout is compatible with the six-pin
ISP connector on the STK500 as well as
Atmel’s ISP mkll. A less expensive op-
tion is the Elektor USB AVR program-
mer, compatible with the ISP mkll. This
design will appear in next month’s is-
sue, but the unit is already available

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Figure 6. Circuit diagram of the ATM18 test board.

in conjunction with the ATM 18 test
board. The USB AVR programmer is
based on the popular general-purpose
USBprog programmer published in the
October 2007 issue of Elektor. Another
alternative is to make a simple Pony-
Prog compatible connection directly to
the connector on the processor module
board.

The power supply and interface op-
tions are summarised in the accompa-
nying text boxes.

Rapid prototype

The ATM18 test board is fitted with
a large number of 2.54 mm pitch con-
nectors. These can be connected with-
out the need for a soldering iron: any
desired configuration can be realised
quickly and simply using lengths of
insulated wire with stripped ends.
Wire with a gauge of 0.8 mm is ideal:
with a few 8 cm lengths of such wire
to hand the necessary connections can
be made and changed as needed for
any desired application or experiment
(Figure 8). If connections to external
modules or devices are needed, a pin
header can be used along with a suit-
able length of ribbon cable.

Software

Udo Jiirss [2], the designer of the
ATM18 system, is a professional en-
gineer and normally uses professional
software tools. For the applications we
will be looking at, the IAR C compiler
fits the bill: it provides a powerful de-
velopment environment offering almost
every conceivable feature. As is so of-
ten the case with such powerful tools,
it is not always easy to use at first,
and there is a degree of ‘running in’ as
the programmer learns how to use the
compiler to the desired effect. Time- or
memory-limited demonstration ver-
sions of the compiler are available
from the IAR website download area
[3]. The latter version is adequate for
many applications. The ‘Kickstart Edi-
tion’ of IAR Embedded Workbench for
the Atmel microcontroller is not time
limited, but can only generate code up
to a maximum of 4 kbytes. A number
of questions must be answered on the
website before the software down-
load can begin. We have arranged for
a project file to be available for readers
to download from the Elektor website:
this greatly simplifies configuring the
IAR compiler. All programs that fea-
ture in this series are also available for
download as hex object files.

44

elektor - 4/2008

r

n

Power supply

Overview of the ATM18 test board

• External supply from 7 V to 16V DC (K1 ).

• Reverse polarity protection (Dl).

• Select between external and USB power (PWR_SEL, JP6).

• Selectable A/D converter (AREF, JP2).

• Low-loss 5 V switching voltage regulator (1C 1 ) .

• Eight connections for powering external modules (DEV_PWR, K8).

• Auxiliary connection point for external power (VI N, JP1 ).

• LED power indicator (LED1).

• Additional ground reference (MGND, K9).

• Current consumption: 9 mA at 1 2 V without ATM1 8 module,

27 mA with ATM1 8 module.

Users who prefer not to use C and a
sophisticated development environ-
ment can work with assembler or
BASCOM. BASCOM-AVR is a very ef-
ficient high-level language for the AVR
microcontroller, broadly comparable to
QBasic. Programs are very clear and
straightforward to write as complex

our applications. BASCOM-AVR runs
under Windows 95, 98, NT and XP and,
with minor restrictions, under the Wine
emulator on Linux platforms.

LED running light in BASCOM

Our first programming example with

(16 MHz) is given here in units of Hz;
the value is needed so that the delays
in the program have the correct tim-
ing. We have chosen to drive the LEDs
from port C, which is therefore config-
ured as an output. Finally a byte varia-
ble ‘Leds’ is declared, initialised to the
value 1 (corresponding to just the first

Figure 7. Printed circuit board for the ATM18 test board.

COMPONENTS LIST

ATM18 test board

Resistors (SMD 805)

R1 = 10Q

R2,R4,R6,R8 / R1 0-R1 3 = 330D

R3,R5,R7,R9 = lOkD

Capacitors

Cl ,C2,C3 = 47jL/F 16V (SMD7343-43,
Farnell # 498-762)

C4,C5,C6 = 4jL/F7 6.3 V (SMD 805, Far-
nell # 922-7857)

Inductors

LI = 100jL/H (SMD2220, Epcos #
B82442A1 1 04K)

Semiconductors

D1,D2 = MBRS130 (BYS10), D0214-AC
(Farnell # 995587)

LED1 = SMD0603-LED, green (Farnell #
852-9833)

LED2-LED8 = SMD0603 LED, red (Farnell
# 852-9868)

IC1 = LM2594-5.0, S08 (National
Semiconductor)

IC2 = ULN2003AD, SOI 6

Miscellaneous

K1 = mains adapter socket, PCB mount,
Lumberg NEB21 R (Farnell #121 7037)

K2 = SIL pinheader, 6-way, angled pins
K3 = SIL socket pinstrip, 7-way
K4 = SIL socket pinstrip, 8-way
K5 = SIL socket pinstrip, 9-way
K6 = SIL socket pinstrip, 5-way
K7 = double-row pinheader, 6-way,

K8 = double -row pinheader, 16-way
K9 = SIL pinheader, 5-way
K10 = SIL socket pinstrip, 7-way
K1 1 = SIL pinheader, 7-way
K12 = socket pinstrip, 3-way
JP1, JP2 = pinheader, 2-way
JP6 = pinheader, 3-way
SW1-SW4 = pushbutton, SPNO-B3S series,
Omron (Farnell # 1 18-1016)

PCB, ref. 071035-2, track layouts free
download from www.elektor.com
SMD-populated board and all parts, #
071035-92 from the Elektor Shop

commands save the programmer a
great deal of work. The demonstration
version of BASCOM can be download-
ed for free from the Internet [4]; again,
there is a 4 kByte code size limit, but
there are no functional limitations and
the system is perfectly adequate for

BASCOM-AVR is the now classic first
test of a new microcontroller system,
a LED running light. Note that the
program (Listing 1) must specify the
file m88def.dat; alternatively, the mi-
crocontroller type can be specified
in the options. The crystal frequency

LED being lit).

In the infinite loop (from ‘Do’ to ‘Loop’)
this single set bit is shifted left one
place at a time: this corresponds to a
repeated multiplication of the variable
by two: 1 becomes 2, 2 becomes 4 and
so on. In this way the program drives

Interfaces

Overview of ATM18 test board:

• ISP programming adaptor (ISP, K 7).

• USART for FTDI USB-serial converter or TTL-level serial interface
(USART, K2).

• Three uncommitted pushbuttons that can be connected as required

(SW1 , SW2, SW3, K12).

• Seven LEDs that can be connected as required (LED2 to LED8,

K10).

• Seven power outputs (maximum 500 mA) that can be connected as
required (K1 1 ).

• Reset button (SW1).

• Socket for ATM18 microcontroller module (K3, K4, K5, K6).

4/2008 - elektor

45

MICROCONTROLLERS

the outputs high one after the other.
After each change there is a delay of
100 ms.

To test the program we first have to
connect port C (six pins) to the inputs
of the ULN2003 LED driver (seven
pins). The lower six bits, PCO to PC5,
are used, and the seventh input to the
ULN2003 is left unconnected. If de-
sired, a bit from another port could be
used, or port D, which has eight pins,
could be used instead of port C.

Next we must flash the code into the
microcontroller. For this we need a suit-
able programmer such as the STK500
[5] or the Elektor USB AVR program-
mer mentioned above. If you wish (and
provided your PC has a parallel port)
you can also use a simple parallel port

programmer described in a free bonus
article available from the Elektor web-
site. An AVR ISP programming adaptor
for the PC serial port was described in
the ‘Mini ATMega Board’ article in the
May 2006 issue of Elektor.
Programming is carried out using the
AVR tools, within which the program-
mer itself is called up. It is essential to
select the correct device (ATmega88)
and to specify the generated hex ob-
ject file (LEDl.hex): see Figure 9.

The device must be programmed not
only with the desired code, but also
with the desired fuse settings. Partic-
ularly important is the configuration to
allow use of the crystal as clock source:
as delivered by the manufacturer the

Figure 8. Test board wired up ready for an experiment.

Figure 9. Programming the flash memory.

Web Links

[1 ] http://www.ftdichip.com/Products/Evaluati-
onKits/USB-Serial.htm

[2] http://www.microdrones.de

[3] http://www.iar.com

[4] http://www.mcselec.com/elektor.htm

[5] http://www.atmel.com

r — — — — — — — — — — — — — — — — — — — n

Listing 1

Running light (LEDl.hex) 1

' 7 LEDs on PortD

$regfile = "m88def.dat" i

$crystal = 16000000 1

Config Portd = Output
Dim Leds As Byte i

Leds = 1 1

Do i

Leds = Leds * 2 1

If Leds > 64 Then Leds = 1
Portd = Leds i

Waitms 100 1

Loop

L ___ __ ___ __ ___ J

device is configured to use its internal
oscillator with a divide-by-8 prescaler.
Figure 10 shows the correct fuse set-
tings (again using the STK500).

If the programming procedure has
been carried out correctly, the result is
exactly what one would expect from a
quick glance at the Basic program: the
LEDs light in turn from right to left at
the rate of one step every 100 ms.

A further example BASCOM program
is available for free from the project
page on the Elektor website, as is the
C project for the reaction time tester
mentioned at the start of this article,
which requires the IAR compiler.

(071035-1)

Figure 10. Configuring the AVR fuses.

57K50D |_J|_n|(x]

Pn ij rim -U0C3 ! i ii i.fii::-: ti h/-i n .“i I Bii.ii I Aulit

F EkI. CrrrtfalOae.; Frequency fiD-fiO MHz; Slait-up lime PWRDWN/RE
F Hut Crystal Osc.; Frequency 3.0-D.D Ml Iz: Slait-uplime r^WTlDWH/PlC
F Em Crj,malOse . Frequency 3 . D-G.0 MHz; Slait-Lp lime PVRDVvW/RE
F but UrMalUae,; Frequency 3U HU MHz; Slart up lime FAVHOWHVHb
r Fd rjjjjJril flsi : FrKqiKriy 3 ThFi fl MHz. : : il,nlij; i Iuiik Fy/RDVrffclVRF
F Em Drytial Dae.; Frequency fifi-0.0 MHz; Start-tip lime PwROVvW/RE
r but. Lrystal Uae.: Frequency HU HU MHz: Start up lime F’WHUWWVHt
I F kI FjjjjJrfl flxi : . FrHifirn^pfifF MH t. Stall -i i| i linn PV/FI IW/N^RF Fl
F Em CqjttalDse.; Frequency fiD- MHz; Startup rime PWfl DV/N^RE &

F Cm Crystallise..: frequency QD- MHz: Start up time lAvTl CWN/riC S
F E m Crystal Oic.; Frequency HD- MH z; Start-up rime FVlfl DWH^RE S
F E m Ety&lal Oac.; Frequency H D MHz; Start up dmc PWR DWN^RE S

F r ut r>juMrt1 (ljir. rrerjierwy (1 0- Ml Ir; Slnrt-up lime rWFI RWKiynr S

F E m Crystal Ose.; Frequency fi D- MH z; S tart-up rime PUffi DWFWRE S

ie b m Crystal Uac.; Frequency HU MH c; Start up dmc h'WH LMFJ^Hb S

V

th u) j

AutoVcnly
V Smart Warnings

Pi 1 ijmivi

V Killy

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Filramj fMiiji.iiniiTiy itimIk flKI
ricadiio (uses .. G^ro. OkDD. OkIT . OK'
Lezwinq prDqrammhq mode.. OK!

46

elektor - 4/2008

QUASAR

electronics

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Tel: 0870 241

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for all units: Ord

full details. S
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and control units we have

uitable PSU
445 £8.95

PC / Standalone Unipolar
Stepper Motor Driver

Drives any 5, 6 or 8-lead
unipolar stepper motor
rated up to 6 Amps max.

Provides speed and direc-
tion control. Operates in stand-alone or PC-
controlled mode. Up to six 3179 driver boards
can be connected to a single parallel port.
Supply: 9Vdc. PCB: 80x50mm.

Kit Order Code: 3179KT - £12.95
Assembled Order Code: AS3179 - £19.95

Bi-Polar Stepper Motor Driver

Drive any bi-polar stepper
motor using externally sup-
plied 5V levels for stepping
and direction control. These
usually come from software
running on a computer.

Supply: 8-30Vdc. PCB: 75x85mm.

Kit Order Code: 3158KT - £17.95
Assembled Order Code: AS3158 - £27.95

Bi-Directional DC Motor Controller (v2)

Controls the speed of
most common DC
motors (rated up to
32Vdc, 10A) in both
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verse direction. The
range of control is from fully OFF to fully ON
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Screw terminal block for connections.

Kit Order Code: 3166v2KT - £17.95
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DC Motor Speed Controller (100V/7.5A)

Control the speed of
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modulation output for
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Dimensions (mm): 60Wx100Lx60H.

Kit Order Code: 3067KT - £13.95
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lost items are available in kit form (KT suffix)
>r assembled ^nd ready for use (AS prefix).

8-Ch Serial Isolated I/O Relay Module

Computer controlled 8-
channel relay board. 5A
mains rated relay out-
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inputs. Useful in a vari-
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programming (using our new Windows inter-
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Kit Order Code: 3108KT - £54.95
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Computer Temperature Data Logger

4-channel temperature log-
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Continuously logs up to 4
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^ 200m+ from board. Wide

range ot tree software applications for stor-
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Kit Order Code: 3145KT - £17.95
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Additional DS1820 Sensors - £3.95 each

Rolling Code 4-Channel UHF Remote

State-of-the-Art. High security.

4 channels. Momentary or
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DTMF Telephone Relay Switcher

Call your phone num-
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Infrared RC Relay Board

Individually control 12 on-
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Toggle or momentary. 15m+
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4/2008 - elektor

47

TECHNOLOGY

OPEN SOURCE R&D

...the liberties of Open Innovation

Antoine Authier

The boom in the Internet and rapid evolution of communication techniques and tools have made
diffusion of knowledge and projects possible on a massive scale, and allowed work and discussion
communities to be created on a global level. New ways of publishing and distributing artistic or
technical creations, and contributing to collective projects or works have appeared. When these
activities take place within a framework of openness and exchange, we talk about Open Innovation.

open source

This is the case with projects like GNU,
Linux, Mozilla, Apache, The GIMP,
MySQL, Amarok, OpenOffice, YAMPR
or more recently OpenMoko - all re-
ferred to as Open Source software or
electronic designs.

Artists too are taking advantage of this

wave and these collaborative tools.
Take a look at the Wallpaper project
started by Alex Ciccius and The Sam-
buki Social Crew: 100 artists are cre-
ating a 100’ (approximately 32 m) long
banner that can be viewed on www.
thespacejockeys. com/ wallpaper.

The vast quantity of information avail-
able on this subject on the Internet is
not very user-friendly and is difficult to
summarize. The intention of this arti-
cle is to first give a few historical land-
marks and describe open innovation.
Then we’ll take a look at a few exam-
ples of the different modes of distribu-
tion and their viabilities.

We will of course highlight the special
character of electronic hardware and
describe the development process.
There’s no question here of patents or
copyright laws, so unfortunately we
won’t have the opportunity to discuss
the problematic local implementations
of EUCD (European Union Copyright
Directive). Maybe some other time. . .

Open Source

The Open Source movement arose in
the late seventies at Berkeley Univer-
sity in California, in a development
project for an operating system com-
patible with Unix, called BSD (Berkeley
Software Distribution). The publication
of the source code, with no restrictions
and for the purpose of sharing, allowed
this project to develop in a collabora-
tive manner. In the event of collabora-

tion on major projects, many contrib-
utors may be involved without their
necessarily having known each other
at the outset. They work with the same
aim in different locations around the
globe, and they occasionally organize
meetings to define the development
plan.

A little later, in 1983, Richard Stallman
created the Free Software Foundation
to provide a framework for the devel-
opment of GNU (famously explained
as ‘GNU is Not Unix’). Then he drew
up the GPL (General Public Licence) in
order to distribute the fruits of this la-
bour, ensure its durability, and launch
free software. The use of the ambigu-
ous word ‘free’ has caused a lot of mis-
understandings. A piece of ‘free’ soft-
ware isn’t necessarily ‘free of charge’;
it may be sold, though this is generally
not the case.

The co-operative development of the
Linux core, launched by a Finnish stu-
dent, then its incorporation into GNU
(whose operating system was slow in
coming), laid the foundations for this
form of open innovation. When it in-
volves mainly software, we talk about
open source.

There is no definitive definition of open
source, nor does it correspond to a par-
ticular software licence either. The
term ‘open source’ doesn’t even have
any inherent legal value in itself.

We should also dispel once and for all
the confusion between ‘free’ software
and ‘open source’ software often per-
petrated by the press.

48

elektor - 4/2008

Principal licences

The information published in this inset has no legal value. The sheer
amount of information in the licence documents is such that we have
to content ourselves with merely extracting a few relevant passages just
to give a taste of the subject. We have concentrated on the principal
licences used for distributing source code or electronics projects. Read-
ers interested in one particular licence or another will need to look up
the corresponding complete document. You will find the texts of these
various licences in their many revisions on the Internet via the links
available at http://www.elektor.com/UK_open-innovation or directly
from the FSF website.

• BSD licence (Berkeley Software Distribution) allows the document it
protects to be re-used, in whole or in part and without restriction, in a
public or proprietary work.

Unlike the public domain, it does however present a few constraints to
be respected when redistributing the document.

It also protects the names of the authors in derivative publications, and
releases them from any problems that might arise out of the use of the
work.

It is one of the least restrictive.

• GNU GPL licence (GNU General Public License) is certainly the most
stringent. It makes the publication of modifications obligatory to the
distribution of the software. It is based on the Copyleft principle, which
relinquishes reproduction rights to the community (as distinct from
Copyright).

However, a document published under GPL belongs in a very real
sense to its author, who will decide the appropriate licence for the dis-
tribution of later versions of the document, thereby enabling them to
change licences.

It has a viral character, as it contaminates (closed) projects in which it
is used.

A project published under GPL must be GPL as a whole.

This is certainly the oldest and most popular licence for free software.

• GNU LGPL licence (GNU Lesser General Public License), a toned-
down version of the previous one, allows association of code under a
GNU GPL licence that is totally free with a resource that is not. In this
way, it allows a piece of proprietary software to be written including
free resources. It applies principally to software libraries. It's only really
of very limited interest.

• MPL licence (Mozilla Public License) allows combining both proprie-

tary source code (normally unpublished) with free source code within a
single project. It then guarantees the openness of the code specified as
free. By virtue of its non-viral character, it is regarded by many as freer
than the GPL licence. It guarantees the authors that the open character
of their work will be preserved, without constraining other contributors
(current or future) to doing the same.

• Chronodegradable licences

The free distribution of the source code takes place in a delayed fash-
ion after marketing of the software - in principle when a new commer-
cial version is published. This is the case with ID Software, famous for
the success of 'Doom', its first 3D game, whose source code it decided
to publish at the end of its software's lifetime, thereby benefiting from
external contributions to the storyline.

• IBMPL licence (IBM Public Licence) - used by IBM for distributing cer-
tain of its source codes that are regarded as non-strategic - recog-
nized by the OSI.

It differs from the GPL in the way it handles managing and distributing
patents. It makes the software publisher and distributor responsible,
rather than the contributors.

• SCSL licence (Sun Community Source Licence) is the licence original-
ly used by SUN Microsystems for distributing its JAVA language.

It does not allow the opening up of the JAVA source code and so is not
regarded as 'open'. However, it does allow, on the one hand, acquisi-
tion, use, and free redistribution of the JAVA virtual machine (without
which it wouldn't be possible to interpret the code you write), and on
the other hand, distribution of free libraries, software, and tools written
in JAVA. Since 2005 SUN has introduced new licences in order to in-
crease its openness, though still without publishing its sources.

• Shared Source licence, set up by Microsoft in response to pressure
from the free software world, constitutes several licence contracts and
is reserved for Microsoft's largest commercial partners and certain in-
fluential institutions (universities, Chinese government, etc.) It mainly
lets them consult the source code and allows debugging. Very few
have the right to modify.

• Creative Commons licence is flexible and customizable. It offers four
distribution options: paternity, no commercial use, no modification,
share-alike of the original conditions, which can be combined to cre-
ate a specific distribution licence.

A refreshing, novel concept that is really starting to take off.

The OSI (open source initiative) open
source movement was created in 1998
to respond to the economic and tech-
nical realities and defend the freedom
of access to software source codes. In
a few points, it defined the conditions
for a piece of software to be described
as open source; what’s more, it has be-

come the official certification body for
open source and its diverse publica-
tion licences.

Advantages and disadvantages

In his document entitled ‘The Open
Source Dynamic’, Robert Visseur lists

the advantages and disadvantages of
open source. We thought it worthwhile
to sum these up here.

• Quality: the stability and perform-
ance of open source software like
Linux or FreeBSD.

• Reactivity: e.g. updates to software

4/2008 - elektor

49

TECHNOLOGY

OPEN SOURCE R&D

like Apache or Linux appear very
quickly.

• Durability: e.g. loyal users have re-
programmed old operating systems
like MS-DOS or CP/M.

• Cost.

• Freedom: independence from the
developers

• Competition: impossible for a monop-
oly to take place, by virtue of the source
code and communication standards.
Stimulates competition between com-
panies, as well as between nations!
With open source code, the software
can breathe freely and benefits from
the support of the entire community.
This goes hand-in-hand with the writ-
ing and development of real, open, re-
liable standards where everyone can
cast a critical eye.

• Protection of intellectual proper-
ty: the principal complaint of open
source’s adversaries is that secrecy
and fierce competition are vital to sus-
tain innovation. To which open source
partisans argue that the mixing of ide-
as and mutual and cross-fertilization
favour innovation much more than the
fact of appropriation.

• Finish: interfaces have a reputation
for being rustic

• Risk of divergence: e.g. BSD gradu-
ally split into three projects: FreeBSD
(the most widespread and the most
user-friendly, favouring performance),
OpenBSD (favouring security) and the
original branch, NetBSD (which favours
adaptation to hardware).

• Brand image: Linux is often poorly-
regarded by the hierarchy for profes-
sional use.

• Support: Documentation is some-
times lacking. The Wiki script, which
came out in the mid-90s and has been
made popular recently by the free en-
cyclopaedia Wikipedia, is attempting to
make up for some of these shortcom-
ings. It offers readers the opportuni-
ty to contribute to documentation on
line.

English is obligatory, despite some
laudable translation efforts.

Contributing to a project

Nothing could be simpler than contrib-
uting to an open source project. Con-
tact its author by e-mail or IM, express
yourself in the project forum, give your
opinion, add a page of documentation
or advice to the Wiki.

You can contribute on several lev-
els, from simple encouragement to a
small donation. Your general remarks

on features or the interface will be ap-
preciated, a bug report, comment, or
the review of the source code will be
welcomed. And if you have a literary
bent, don’t hesitate to participate in
the project documentation. If you want
to program, prove yourself by sending
patches (corrections, improvements)
and it won’t be long before you obtain
write access to the version manager
(CVS, sub version, and so on).

Launching a project

Launching a project is hardly any more
complicated. You have an idea, you
think it may be useful to a communi-
ty, you want to share it. If you aren’t a
natural webmaster, open an account at
www.sourceforge.net and publish your
project, distribute your sources and
your work. If you want to keep con-
trol of it and host your project website
yourself, while benefiting from certain
collaborative development tools, create

your community space with the help
of gforce. If not, then a simple website
will do...

Distributing a project

How can the author of free software
earn a living, or at least some money
from it? Prior to distributing the fruits
of your labours on the Internet or sim-
ply opening it up to the world, and in
order to be able to do so, it’s important
to define the legal framework for it that
will allow you to be recognized, to pro-
tect yourself against possible abusive
use, and to share it or not.

Distributing code, circuits, drawings,
photos, art, etc. freely and free of
charge, while still retaining paternity,
can be done by means of a licence (for
example, Creative Commons). The in-
set should help you choose a licence
appropriate to your needs, from the
fairly stringent open source (free soft-

ware) licence to the shared source one,
via various intermediate nuances.

If your aim is to make money, you’ll
need to conform, to a greater or lesser
extent, to the economic models, strat-
egy, and marketing that are usual prac-
tice in our societies. The OSI is work-
ing towards an economy for software
with no user licences but based on the
sale of services, hardware, and the
support needed for rapid deployment.
Several thousands of engineers in Eu-
rope are employed by way of this eco-
nomic model.

Open Hardware

The concept of open source hardware,
or ‘open hardware’, is not all that dif-
ferent. However, it is much easier to
copy a piece of software than to repro-
duce hardware, which requires more
advanced skills and knowledge.

Although the open source concept is
still quite fuzzy, it is however clearly
defined by its licences. The concept

FreeBSD

< 8 >

of open source hardware, on the other
hand, still does not have a definition
that is recognized around the world,
nor totally accepted.

In an article published in ‘Linux Today’
in 1999, Richard Stallman, founder of
the FSF (Free Software Foundation)
and author of the GPL (General Public
Licence), stated that the GPL licence
was not suitable for electronic circuits,
as they are difficult to modify or copy.
Most of the people involved consider
that the same applies to embedded
software (firmware), generally stored
in Flash memory, but in any event not
at all comparable with the volatility of
software in a computer’s RAM, at best
stored on hard disk.

Users of open source hardware must
be able to modify the hardware and
distribute it freely. This necessitates
making available all the circuits, along
with the source code of the compo-
nents, in particular the HDL (Hardware
Description Language) sources of the
hardware and the firmware (most often
written in C and assembler).

50

elektor - 4/2008

In an Elektor interview with Harald
Kipp in Elektor March 2008, the father
of the Ethernut said, rather tongue-
in-cheek, that “for many people, open
source is like communism, in the sense
that everyone can take from the com-
munity without paying anything. ” Kipp
added that certain developers also re-
gard open source as like communism,
but because they perceive the hierar-
chy as a dictatorship!

Indeed, we might be tempted to im-
agine that anarchy reigns in open
source, but that’s far from being the
case. The organization of open source
projects is built on a solid framework,
indeed highly hierarchical, most of the
time with the owner of the project as
incontestable master at the top of the
structure.

If he doesn’t like a contribution, he can
withdraw it without asking anyone’s
opinion. If it’s a developer he doesn’t
like, he can send them packing without
any other form of trial, and refuse any
contribution from them.

For small-scale projects, it’s also the
owner who decides when and which
version will be published.

Source codes are (in general) freely
redistributable, i.e. anybody can pro-
claim themselves a distributor of free
software (as long as the licence condi-
tions are obeyed). If part of the com-
munity, or an isolated (and frustrated)
developer, thinks they can do better,
they are free to take up the source
code and branch off into a new project.
This branching process is called ‘fork’
(from the name of the instruction in the
POSIX standard for duplicating a proc-
ess in C).

Openness of minds

It’s important for a company to gather
malfunction (bug) reports from its us-
ers. It may go even further and deploy
a public forum where all users can ex-
press themselves, criticize any defi-
ciencies in the architecture, or sing its
praises. This initiative can turn out to
be an uncomfortable one. Allowing an-
yone to freely study the quality of the

source code and the hardware design
in order to discuss it openly takes a de-
gree of courage, a lot of getting used
to, perseverance, and even a thick skin,
such is the extent to which the criti-
cism may turn out to be caustic.

The more judicious criticisms are vital
to enable projects to evolve efficiently.
Without the pressure of a critical exter-
nal viewpoint, most design defects will
survive the various states, will become
entrenched, and before long an initially
elegant concept can turn into a huge,
labyrinthine system like MS w****.

Throughout the project, whether in
soft- and/or hardware, you must be
careful to stay legal and avoid infring-
ing - intentionally or not - this or that
patent. Difficult as such infringements
are to detect in a ‘closed’ project, they
will come to light all the quicker in an
open project because the size and di-
versity of the community. So you’ll
need to take appropriate measures to
ensure the validity of the copyright for
each of the various contributions - no

small task!

The community spirit of open projects
occasionally forces developers to spot
such infringements and to take imme-
diate action.

At the present time, most open hard-
ware and firmware projects are dis-
tributed under a BSD licence - less re-
strictive than the GPL licence - which
allows, in particular, distribution of im-
proved firmware without distribution of
the corresponding source code. In this
way, companies retain control over the
publication of certain improvements,
while keeping others secret, to protect
the added value of the product.

Commercial contribution

So where is the interest for a compa-
ny in contributing to an open source
project, when this is not constrained
by a licence? Why would it run the
risk of one of its competitors possibly
profiting from its work? Doubtless to
benefit from the improvements of other
contributors, but also because it judg-
es that before its competitors catch up,

the benefits of openness will have ena-
bled it to establish a convincing lead,
thanks to better products, better serv-
ices, and quality that it knows is su-
perior - even if all the competitors are
using the same software.

Certain companies will also make ‘late
contributions’, initially keeping their
improvements secret and only pub-
lishing them once their product is well
launched (see an example of a chrono-
degradable licence in the inset).

We would like to thank Harald Kipp for
the interview he granted us.

To discover this fascinating world in
greater depth, come and have a browse
at the following address:

www. elektor. com/UK_open-innovation

To your keyboards - happy surfing, and
happy development!

Elektor is distributing this article un-
der the creative commons licence with
an explicit mention of its paternity, ex-
cluding all commercial use, and iden-
tical sharing of the original conditions
(share- alike). We are keen to open up
the source code of our publications,
and do so whenever possible. Certain
of our authors are still reluctant and un-
fortunately won’t give us their permis-
sion. It’s often a hard choice for Elektor
between refusing a very interesting
but closed publication, and publishing
it anyhow, to allow as many people as
possible to benefit from it - but with-
out the pleasure of sharing the source.
In the long term, openness pays.

( 070948 - 1 )

Web links

www.elektor.com/UK_open-innovation

www.fsf.org

www.fsf.org/campaigns

www.opensource.org

http://opencollector.org/Whyfree/

http://opencollector.org/Whyfree/vilbrandt.html

www.presence-pc.com/tests/

Le-Hardware-Open-Source-1 12

http://features.linuxtoday.com/news_story.
php3?ltsn= 1 999-06-22-005-05-NW-LF

4/2008 - elektor

51

Ryan Seguine (Cypress Semiconductor Corp.)

With all the excitement about capacitive sensing in the portable media player, laptop PC
and mobile handset markets, it is easy to forget that such interface technologies have been
actively designed into White Goods applications for years. Significant improvements in
sensing algorithms and control circuitry have expanded the suite of applications in which the
technology can be implemented.

Designers are seeing the value of capacitive sensing as
a mechanical button and membrane switch replacement
as well as discovering new, exciting applications such as
touchscreens and proximity sensors.

A capacitive sensor is constructed of a conductive pad, the
surrounding ground, and its connection to a controller. In
most applications, the conductive pad is a large copper
footprint and the surrounding ground is a poured fill. As il-
lustrated in Figure 1 , a native (parasitic) capacitance, C P ,
exists between these two objects. When a third conductive
object, such as a human finger, is brought into proximity

with the sensor, the capacitance of the system is increased
by the capacitance of that object, C F .

Methods to use

There are several methods for detecting the increase in ca-
pacitance caused by the addition of C F .

Field-effect measurement uses an AC voltage divider
between a sensor capacitor and a local reference capaci-
tor. Finger detection is achieved by monitoring the change

52

elektor - 4/2008

Interfaces for Home Appliances

The end of the switch as we know it?

in voltage on this divider. Field-effect sensing is a highly-
sensitive technique and robust with regard to environmental
conditions, however it is implemented with a single ASIC
per sensor and does not provide analogue functions.

Charge transfer uses a switched capacitor circuit and
a reference bus capacitance with repeated charge transfer
steps from the smaller sensor capacitor to the larger bus
capacitor. The voltage on the bus capacitor is proportional
to the sensor capacitance. The capacitance can be deter-
mined by measuring the voltage after a fixed number of
steps or by counting the number of steps necessary to reach
a threshold voltage. Charge transfer is a low impedance
sensing method giving it good noise immunity and is capa-
ble or supporting analogue features in capacitive sensors.
The direct connection to V DD requires a high-quality, dedi-
cated voltage regulator for the sensor controller.

A relaxation oscillator is a charge time measurement
where the charging ramp is determined by the current
source (usually fixed) and the sensor capacitance value.
Larger sensor capacitors yield longer ramp times, usually
measured with a PWM and a timer. The relaxation oscillator
is highly flexible and can be implemented in many standard
microcontrollers, however the high-impedance inputs can
make it susceptible to noise sources without firmware or
hardware modifications to filter out such interference.

Successive Approximation

The Successive Approximation method (patents applied for by
Cypress Semiconductor) implemented with the PSoC device
uses a capacitance to vo tage converter and single-slope ADC.
The capacitance measurement is achieved by converting the
capacitance to a voltage, storing this voltage on a capacitor,
and then by measuring the stored voltage using an adjust-
able current source. The low-impedance technique has high
immunity to interference and greater sensitivity and analogue
characteristics. The current source and the connection scheme
allow for more tolerance in voltage regulator quality.

The capacitance-to-voltage converter shown in Figure 2
is implemented with switched capacitor technology. The
circuitry brings the sensor capacitor to a voltage relative
to the capacitance of the sensor. The switched capacitor is
clocked by the PSoC's internal main oscillator.

The sensor capacitor is connected to the analogue MUX bus
and is charged via a programmable current output digital-
to-analogue converter (iDAC) also connected to the bus.
The charge on each bus is given by q = CV. Switch SW2
is opened and SW1 closed to bring the potential across
C x to zero and reducing the charge on the bus by a value
proportional to capacitance of the sensor capacitor. This
charge-discharge process is repeated so that the sensor
capacitor is a current load on the bus.

With the switched capacitor circuit running, the iDAC uses
a binary search to determine the value at which the voltage

on the bus remains constant. This voltage is a factor of the
switching frequency, the sensor capacitance and the iDAC
value (current). The bus also functions as a bypass capaci-
tor, stabilizing the resulting voltage. Additional capacitors
can be added to the bus and affect performance and tim-
ing of the circuit.

The following equations apply:

V x = [1 / (f ox x CJ] X / DAC

^BUS = ^REF ” Vx

The calculated iDAC value is then used to charge the bus
again and the time required to take the bus from an initial
voltage to the comparator threshold is measured. The initial
voltage with no finger present and therefore the charge time
is known. A finger on the sensor increases the value of C X/
decreasing the initial voltage and increasing the charge
time measurement — see Figure 3.

Building a Sensor: the options

Capacitive sensors have diverse forms and functions
and they can use a variety of media. Their implementa-
tion ranges from simple to complex. Also, application
requirements determine sensor construction and imple-
mentation details.

Figure 1.

Graphical representation
of the elementary
capacitances involved.

Figure 2.

Basic circuitry to implement
capacitive sensing
based on successive
approximation.

4/2008 - elektor

53

TECHNOLOGY

CAPSENSE DESIGN

Figure 3.

Charge time measurement.

Figure 4.

A slider control employing
capacitive sensing.

Figure 5.
Capacitive and other
sensors in various forms
can be used to implement
lots of user controls on
electronic equipment.

Buttons and sliders are most common. Buttons are large
conductive pads connected to the controller. Capacitance
is measured and compared against a series of thresholds.
Decisions can be made as digital outputs or with more ana-
logue characteristics for activation pressure or finger size.
Sliders are linear or radial arrays of conductive pads. Cen-
tre-of-mass algorithms determine the position of activation
to a resolution far greater than the number of pins used to
sense. Most often, simple capacitive sensors like buttons
and sliders are deposited onto a printed circuit board using
copper (Figure 4). Other substrates and deposition media
such as silver ink can be used, however.

Dynamic user interfaces use buttons or activation
regions that reconfigure in response to the display itself.
These displays are moving the user experience forward
by promoting more seamless and intuitive interaction. The
construction of these systems is somewhat more complex

that simple buttons or sliders. Projected capacitance touch-
screens use transparent conductive materials over a display.
The conductive surface is deposited onto a substrate such
as glass or PET film and connected to the control circuitry.
The substrate is then adhered to the overlay between the
overlay and the display. The position of the activation is
determined in the same way as a slider. Two sliders, one
for each axis are intertwined to provide complete coverage
of the display area. Activation is detected on both axes
and the position exported as x- and y-data. Because a pro-
jected capacitance touchscreen is behind an overlay, it is
protected from impact, flexion, and environmental factors
that plague traditional resistive touchscreens.

Proximity sensors are essentially large buttons. The ob-
ject of a proximity sensor is not to detect the exact position
of a conductive object; rather the presence. Since the de-
vice does not need to know exact position, the response
time may be slower (3-4 ms vs. 250 |js). The sensitivity of a
proximity sensor is much greater; 30 cm can be achieved
in a well constructed design. Since proximity sensors do not
need to be associated with any display graphic, their place-
ment on the device is more flexible. A copper ring around
the outside of the control circuit board or a wire behind
the overlay allow very basic, cost-effective construction of
a proximity sensor.

Home appliances and white goods

Usage of capacitive sensors is expanding. The sensors de-
scribed have created new opportunities for designers to
work with such flexible, durable and elegant design ele-
ments. Buttons are still used for basic menu navigation and
activation. However, analogue characteristics of buttons
that are not expensive potentiometers allow easier and less
expensive implementation of increased functionality and
safety features.

LG's model LA-N131 DR Air Cleaner (Figure 6) uses five
capacitive sensors for front panel display menu navigation
buttons. These buttons have allowed the designers to im-
plement a seamless chassis design while still realizing the
user interface. The capacitive buttons detect the presence
of a human finger through four millimetres of glass. The
control circuitry is located on the non-sensor side of a two-
layer printed circuit board. LG uses the PSoC Mixed-Signal
Array to control the sensors and output status to the main
device processor.

Proximity sensors allow for reactive backlighting for night-
time operation or for safety features requiring a larger acti-
vating element such as an adult hand or metal pot to engage
the range-top controls. Figure 5 shows how proximity sen-
sors, buttons, sliders and even touchscreens can be controlled
by a single processor using PSoC. Firmware routines allow
changes in state based on user inputs or host commands.

Putting It All Together

The PSoC Mixed-Signal Array allows designers to imple-
ment buttons, sliders, touchpads, touchscreens, proximity
sensors and any combination of all these in a single chip.
The pre-defined firmware development modules, reference
code and calibration tools make designing a capacitive
sensing application fast, easy and effective.

Pre-defined firmware development tools include device in-
terconnects, I/O drive modes and APIs. These are created
with only a few clicks of the mouse in the PSoC Designer or
PSoC Express development tools. Reference code provides
a starting point with basic functionality, but the open-source

54

elektor - 4/2008

nature of the PSoC solution allows for customization and
optimization for any project. Calibration tools accelerate
development by providing real-time feedback for capacitive
inputs. Adjust parameters, increase sensitivity, and calibrate
sensors individually through the calibration tool.

PSoC devices are more than just capacitive sensors. Analogue
and digital resources are available for a myriad of other ap-
plications [1]. Basic digital control is available on all PSoC
devices. Drive LEDs, communicate through l 2 C, SPI and other
media, and control a simple 8-bit PWM. Higher-function de-
vices are capable of more digital functions as well as basic
analogue. A single PSoC can be configured as a capacitive
sensing and a temperature meter or a voltage meter.

Create your capacitive sensing application

The PSoC Mixed Signal Array is a configurable array of
digital and analogue resources, flash memory and RAM, an
8-bit microcontroller, and several other features. These fea-
tures allow PSoC to implement innovative capacitive sens-
ing techniques in its CapSense portfolio. Use PSoC's intui-
tive development environment to configure and reconfigure
the device to meet design specifications and specification
changes. New sensing technologies exhibit improved sen-
sitivity and noise immunity, reduced power consumption,
and increased update rate.

(071137-1)

Web Links

[1] PSoC CapSense: www.cypress.com/capsense.

Figure 6.

Capsense is expected to
become an established
technology in home
appliances and 'white
goods' like this
(conspicuously red) air
cleaner from LG.

Advertisement

PCB House

4>Start from £30
^Prototype & Production
&No Min Order
^Fast Delivery

WWW.

elektor.

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4/2008 - elektor

55

TEST & MEASUREMENT

Frequency Response
Sweep Oscillator M

50 Hz - 100 kHz range using the
Parallax SX28 micro

This project found its origins in a need to see and measure the frequency response of audio filters, tone
controls and amplifiers in real time. An SX28 microcontroller module from Parallax turned out to be a
really good means of implementing the circuit.

The standard way of measuring fre-
quency response is to use a frequen-
cy generator with an oscilloscope or
(fast) AC voltmeter and then plot the
results on logarithmic graph paper.

This is time consuming especially
when dealing with voltage controlled

filters which vary their frequency re-
sponse with a control voltage.

The author developed this circuit as a
means of displaying the frequency re-
sponse of a circuit on a standard os-
cilloscope. The firmware for the micro-
controller core of the test instrument is
written in assembly language.

Pluses and specs

There are a number of benefits to using
this design:

1. The oscillator has two frequency
ranges:

• 100 Hz to 100 kHz. This allows for the

56

elektor - 4/2008

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X

R12

S6

F RANGE

+5V

O

K7

O

> *>

R1£
20k

C7

-ill-

lOOu
25 V

R18

<=>

120k

(

IC3 = AD822AN

IC3

©

see text

R13

IC1

HA78M05CKC

C6

lOOn

K2

3D*

K1

8 -15V

C2

lOOu

40V

1

0 ♦

C4

lOOn

C3

lOOn

Cl

lOu

40V

070951 - 11

Figure 1. Circuit diagram of the sweep oscillator. The heart of the circuit is a Parallax SX28AC/DP microcontroller module.

testing of audio, ultrasonic and infra-
red communication circuits.

• 50 Hz to 15 kHz. Primarily for higher
resolution audio testing.

2. As component values in the circuit
under test are changed, the change
in frequency response is instantly ob-
servable on an oscilloscope screen.
This makes it easier to show the differ-
ence in frequency response between
various types of filter such as low-
pass, high pass, bandpass and notch
filters. You can even see the difference
between filters with Butterworth and
Chebychev responses.

3. The display on the scope shows a
true logarithmic response and as such
volts per decade/octave measure-
ment can be taken directly from the
display.

4. There is a facility to show a frequen-
cy marker on a second channel of the
oscilloscope. A frequency counter (a
digital multimeter with a frequency
range is adequate) connected to the
Marker Frequency Output will then

show the frequency at that point, the
marker can be moved to any point
on the display. This enables the easy
measurement of the -3 dB roll off points
and Q (quality factor) of any filter.

5. There is a facility for switching be-
tween two different frequency sweeps
and altering the amplitude of the out-
put signal.

6. The output of the circuit is buffered
so that it will not affect the response of
the circuit under test. This means that
both passive and active (amplifying)
circuits can be tested.

Circuit operation

The circuit is very straightforward,
see the schematic in Figure 1. The
microcontroller (IC2) generates the
8-bit values that are then sent to the
R/2R-based ADC (analogue to dig-
ital converter) made from precision
(1%) resistors R7 through R30. A dual
precision operational amplifier type
AD822AN (IC3) provides the buffer-
ing needed in the circuit. A pot (PI)

and a changeover switch (S8) allow
the output signal level of the sweep
oscillator to be attenuated as re-
quired to match the sensitivity of the
circuit under test if it’s ‘active’. The
swept-frequency signal fed to the in-
put of the filter or circuit under test is
available on connector K2.

The SX28AC/DP micro is clocked at
50 MHz using ceramic oscillator XI.
The oscillator pins of the micro also
serve to program the device and
that’s done via K7, which also pro-
vides the necessary ground and +5 V
connections.

The micro may be reset by pressing
and releasing pushbutton S3.

The power supply is convention-
al, based on a 78M05 regulator (IC1)
with its usual set of decoupling ca-
pacitors for noise suppression on the
supply rails. The unstabilised DC in-
put voltage may be between 8 V and
about 15 V from a mains adaptor with
300 mA or so current capacity.

The microcontroller reads five push-
button switches (SI through S5) and

4/2008 - elektor

57

TEST & MEASUREMENT

Frequency Counter

Oscilloscope

mr

© ©

□

□

CD

CD

Channel

Trigger

n

© ©

©°

n

□

A m B

<o> <n>

<n>

□°

-A A

A

-Z-A— A-I-

i

Marker Marker Trigger

Out Display Out

Sweep Oscillator

To

Circuit

Under

Test

t>

Circuit

Under

Test

070951 -12

Figure 2. How to connect the sweep oscillator to the oscilloscope, the filter and the frequency counter.

Figure 3. Component mounting plan of the sweep oscillator board. True-scale copper track layout available as a free download from
www.elektor.com.

two on/off switches (S6 and S7) to de-
termine the operation and settings of
the sweep oscillator. The switches are
read on microcontroller port lines RB0-
RB3 and RA0/RA1.

The instrument supplies signals to the
oscilloscope and the frequency meter
via RB5/K4, RB6/K3 and RB7/K6 with
10 kQ resistors inserted to protect the
micro against short circuits. RB4/K5 is
provided for experimental purposes
and future expansion. The same ap-
plies to SX28 port pins RA2 and RA3.

Let's get connected

The functional connections to the cir-
cuit are shown in Figure 2 mainly for
those who have never used a sweep
oscillator. Although some experienced
users will be able to do without it and
derive everything from the scope im-
age, the frequency counter is extremely
useful as it allows you to see the mark-
er frequency instantly.

Software & hardware development

All the hard work is done by the pro-
gram (‘firmware’) running within the
SX28AC, a microcontroller developed
by Parallax Inc. and available direct
from them or through authorized dis-
tributors [1]. Like so many other Paral-
lax products (including their renowned
Basic Stamps and recently the Propel-
ler), the SX28 enjoys wide support
from Internet communities. The SX28
is cheap by any standard, and lots of
free software and documentation is
available on the web. Datasheets, com-
pilers, programming examples, simula-
tors, you name it and it can be found
— see [2] ‘for starters’.

In terms of hardware development
tools, the author used Parallax’s SX-
Key™ Rev. F (now an ‘End of Life’
product, to be replaced soon by a
USB equivalent). The software devel-
oped for the project was written using
SX-Key V3.10, also from Parallax. The
source code may be obtained as a free
download from the Elektor website, the
archive file number is 070951-11. zip.
We suggest you open it to be able to
follow the discussion below.

The main loop of the program outputs
a continuous sine wave using a direct
digital synthesis (DDS) algorithm to ac-
cess values in a sinewave lookup ta-
ble. This is a pretty standard method
for creating a sinewave. The clever
part comes by using an interrupt serv-

58

elektor - 4/2008

ice routine to alter the value which de-
termines the frequency in the DDS rou-
tine. A piece of the routine is shown
in Listing 1. There is a facility in this
program for two sweep tables. An ex-
ternal switch is read by the program
which then changes between the two
sets of tables.

Again, SX28 micros come as ‘blank’ ICs
so you have to do your own program-
ming. Fortunately, that’s easy using the
information found on the Parallax web-
site. If you want to delve into the intri-
cacies of SX28 programming, the pub-
lications [3] and [4] are sure to get you
hooked on the device. Best of all, A1
Williams’s writings on assembly code
programming are a free download!

Construction

Elektor Labs have designed a quality
printed circuit board for the project.
The component layout is shown in Fig-
ure 3. The copper track layout is avail-
able separately as a free download
from the Elektor website. It’s a pdf at
true scale you can print directly to a
laser printer to make an acetate trans-
parent or ‘direct to copper’ transfer for
PCB production on a budget.

IC sockets should be used for the SX-
28 AC micro and the AD822 opamp. The
SX28AC micro should be programmed,
of course, before it can be used in this
circuit (yes there are readers out there
inserting blank micros in Elektor cir-
cuits and complaining it don't work).
Populating the board should not
present problems as the layout is gen-
erous and no esoteric or extremely
small parts are used. Everyone with a
keen eye for detail, some patience and
reasonable soldering skills should be
able to pull this one off.

BNC sockets should be used for the
sweep oscillator analogue output (K2),
the Trigger output (K3), Marker Display
(K4) and Marker (K6). The BNC sock-
ets are connected to the pinheaders on
the PCB using short pieces of thin coax
like RG174. The braid of the coax cable
goes to Ground!

Operation

The operation of the device is straight-
forward. Connect up the circuit as
shown in Figure 2. Before switching on
the power to the sweep oscillator and
circuit under test, set the output ampli-
tude pot and the attenuator switch to

COMPONENTS LIST

Resistors

R1 = IkQ

R2-R6 / R9 / R1 1 ,R1 2,R1 3,R1 5,R1 7,R1 9,R20-
R23,R27,R29 = lOkD 1%

R7,R8,R1 0,R1 4,R1 6,R1 8,R24,R28,R30 =
20I<D 1%

R25 = 1MD
R26 = 1 10D
PI = 4k7 potentiometer

Capacitors

Cl = 10jL/F 40V radial
C2 = 1 00yL/F 40V radial
C3-C6 = lOOnF
C7 = 100jL/F 25V radial

Semiconductors

D1 = LED, 3mm, low current
IC1 = 7805

IC2 = SX28AC/DP (Parallax), programmed,
Elektor Shop # 070951-41
IC3 = AD822AN

Miscellaneous

S1-S5 = pushbutton, 1 make contact
S6,S7 = on/off switch, 1 contact
S8 = switch, 1 changeover contact
K2-K6 = BNC socket
K7 = 4-way SIL pinheader
XI = 50MHz ceramic resonator
SX28 source and hex files, free download #
070951 -1 1 .zip from www.elektor.com
PCB, ref. # 070951 -I from
www.thepcbshop.com

AmpK2): 4.50V

Ampl( 1): 3 .obV

00 Persist I Clear 1 0 Grid
_ J 1 Display I 21;:

Vectors

Vector

Persist

r -100;- 5.00'S/ Auto f[

Ample 2): 4.56V

AmpK 1): 4.56V

Amplt 2): 4,56V

oo Persist t Clear

00 Persist I Clear VO Grid
J I Display I 20."

Vectors

Vectors

Figure 4. "Scoped results obtained with the instrument, (a) active tone control circuit with bass boost switched on.
(b) The same, with treble boost switched on. (c) band pass filter, (d) low-pass filter.

Listing 1 . DDS frequency control

. start of 0.2ms interrupt routine

/

; MODE register points to sine table on entry
; Mode register must point to sine table on exit
/

; () Value fetched from table is added to frequency register

; This increases the frequency produced by the main output routine.
; At end of sweep everything is reset.

; () Marker Buttons are read

; () Marker frequency is updated

; () Marker pointer is updated

; () Trigger is generated

Interrupt

4/2008 - elektor

59

TEST & MEASUREMENT

their lowest levels, set the frequency
range switch (S6) to the desired posi-
tion (100 kHz or 15 kHz) and the scope
time base selection switch to the 5 ms
position.

The oscilloscope controls have to be
set to the following positions

• timebase: 5 ms per division;

• external trigger on falling (negative-
going) edge.

Connect the power to the circuit under
test (CUT) first and then switch on the
power to the sweep oscillator. Increase
the output amplitude level to provide
a usable display on the oscilloscope
screen without any clipping of the sig-
nal. You should also see the output of
the marker display on the second chan-
nel (‘2’ or ‘B’). Adjusting the position of
this marker using the four pushbutton
switches allows you to measure the
frequency at this position on the screen
using a frequency meter connected to
the marker output connector.

Should there be any problems getting
the output of the circuit under test
to display on the oscilloscope screen
(faulty CUT, faulty connections etc.)
then connect the output of the sweep
oscillator directly to channel 1 (or A’)
of the oscilloscope to check that eve-
rything is working properly.

There is an option for altering the time-
base setting for the 15 kHz frequen-
cy range on the sweep oscillator but
this is best left switched to the 5 ms
setting.

( 070951 - 1 )

Web Links and
Literature

m www. pa ra I lax. com

[2] www.parallax.com/Productlnfo/
Microcontrollers/SXProductDown loads/
tabid/460/Default.aspx

[3] Programming the SX Microcontroller:

A Complete Guide.

Gunther Daubach, published by Parallax.

[4] Beginning Assembly Language for the SX
Microcontroller. Al Williams

(free download from Parallax website)

; (not shown here: check frequency range switch; Fetch low and high frequen-
cy word; start of button reading routine; end of button reading routine)

. start of marker frequency output routine on rb.7

;: fetch current marker value

mov

M, Table pntr L

; 1 : Fetch low word

mov

W,MFreqT Pntr

/

iread

/

; M now contains

lower nibble of FreqM and

W contains FreqL

mov

MFreqL,W ;

mov

MFreqM,M ;

mov

M, Table pntr H

; 1 : Fetch high word

mov

W,MFreqT Pntr

/

iread

/

; M now contains

FreqH and W now contains

Higher nibble of FreqM

or

MFreqM,W ;

mov

MFreqH,M ;

; : marker frequency value now in MFreqH.MfreqM.MfreqL

/

end of frequency marker output routine

; start of

frequency marker display rb.5 (ch2 on oscilloscope)

;bttn figs. 4=0

no marker being displayed

so test counter

;bttn figs. 4=1

marker displayed so clear

marker

sb

Bttn Figs. 4

jmp

tst cntr

;bttn figs. 4=0

clrb

bttn Figs. 4

;bttn figs. 4=1

clrb

rb . 5

jmp

F M end

tst cntr

stc

mov

W, M_Cntr

; is M Cntr=MFreqT Pntr

mov

W,MFreqT Pntr-W

sz

jmp

F M end

,-no

setb

rb . 5

;yes

setb

bttn figs. 4

F M end

inc

M_Cntr

/

end of frequency marker display

/

--start of trigger section

. Output on rb.6

; toggle trigger output based on state of

FreqT Pntr. 7

sb

FreqT Pntr. 7

/

clrb

rb . 6

/

snb

FreqT Pntr. 7

/

setb

rb . 6

/

/

end of trigger section

mov

M, #sine>>8

,-point M to Sine table

mov

W,#%10000110

,-set RTCC interrupt

mov

! OPTION, W

/

/

G> L 1 G^ G> J\. GJ. G^ _L d j/ W _L G G^ 1 1

sb

ra . 1

; select time delay

jmp

: td sel 0

mov

Time dly,#delay 1

; ra . 1 is 1

jmp

: td sel e

: td sel 0

mov Time dly,#delay 2 ;ra.l

: td sel e

(end of fragment)

60

elektor - 4/2008

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MODDING & TWEAKING

Keyboard goes Game G

Abraham Vreugdenhil

As a hobbyist you may often be designing a game or an application for your computer. When you're
demonstrating your program or game at a computer fair it seems a shame that people have to use a
standard keyboard. It would be much better if their attention was drawn to your creation rather than
the computer.

There are various reasons for wanting
a Custom Input Device (CID). We can
think of the following two examples.
What about a pinball game on your
computer? When you’ve created a great
table or game using Visual Pinball [1],
there is nothing so annoying as having
to use the keyboard for the plunger and
flippers. You want to put your hands on
the sides of the table when using the
flippers and pull a plunger to launch
the ball. A computer keyboard is obvi-
ously not suitable for this.

Then there is the game of Rock, Paper,
Scissors [2], where two players have
to use their hands to show each other

a symbol for a rock, paper or a pair of
scissors. A rock beats a pair of scissors
because the rock blunts the scissors.
The scissors beat the paper because
the scissors cut the paper. And the
paper beats the rock because the pa-
per can wrap round the rock. Instead
of playing against another person you
can also play against the computer. In
that case it’s down to the computer
program to ‘guess’ what its human op-
ponent will do. From the Elektor web-
site [3] you can download this game.
You can use the following keys for your
selection: [r] for rock, [s] for scissors
and [p] for paper. This isn’t much fun,

however. It would be much more en-
joyable if you had a real rock, scissors
and paper that you had to hit to make
your choice. But how can we turn this
bash on a rock or a flipper button into
a computer signal? Read on!

Keyboard

To build your own Custom Input De-
vice we propose the following meth-
od. We’ll use a type of input that is
well known and used by everybody:
the keyboard. Inside each keyboard is
some electronics that converts a key-
matrix into a serial signal that can be

Get hold of an old keyboard with either a PS2 or USB connector.

Open it up to get at the internal electronics.

62

elektor - 4/2008

Build your own
Custom Input Device

PS2 or USB?

In principle there is no difference between the operation of PS2 and USB keyboards when they're used to make a Custom Input Device. What
could make a difference is if you connect a PS2 keyboard via a PS2 to USB converter to your PC or laptop. In games where timing is important,
such as pinball games, you may notice when a short delay occurs in the operation of the Custom Input Device. The question is if the delay is
caused by the PS2 to USB converter, the Visual Pinball program; or simply the PC you're working with or its graphics card.

It has to be said that the author has never found any delay to be a hindrance. The nice thing about USB is that you can connect more than one
device at the same time. So you can connect a standard keyboard for normal use, as well as your Custom Input Device. In theory you could con-
nect up to 1 27 devices to your computer via USB. The PS2 to USB converters will come in very handy here.

used by a computer. Instead of the
more than 100 keys that are in a typi-
cal keyboard we’ll only use those that
are required by the game and connect
those to the electronics. In our exam-
ple for Rock, Paper, Scissors it will only
be the [r], [p] and [s] keys.

First you need to find an old, surplus
keyboard and take it apart. After re-
moving the screws from the underside
we can prise the two halves apart.
This exposes a membrane that con-
sists of three layers. The outer layers
have tracks on them and the middle
layer keeps them apart. The top and
bottom layers are connected to a small

board of about 10 by 6 cm. This board
also has a cable with a PS2 or USB con-
nector at the end. The board should be
carefully removed from the keyboard,
with a note being made of the connec-
tions to the membrane. The two con-
nectors on the board for the membrane
connections usually consist of a small-
er one with about 8 pins and a larger
one with about 21 pins.

Key choices

Now we have to determine which con-
nections are used by a particular key.
We place the top of the keyboard onto

the membrane and look which contacts
are underneath the required key. Next
we can find out in two ways which
connections are used by this key. The
simplest is to follow the tracks from
the key to the connector. You’ll have to
look carefully and hope that you don’t
make a mistake. The second method
is more reliable from a technical point
of view. Use a multimeter, (who can do
without one these days) and put it to
its resistance setting. Put one probe
on the membrane contact underneath
the key and with the other test each
of the contacts that connect to the
board. When you see a low resistance

Behold the (simple) electronics (this can obviously look different if you have a different keyboard).

The two layers that make up the key matrix are used to determine the correct connections.

4/2008 - elektor

63

MODDING & TWEAKING

of about 60 to 120 Ohm you’ll know
you’ve found the right contact. All the
other contacts should return an infinite
resistance.

Once we’ve determined which con-
nection is used by the key on the layer
with the small connector, we have to
do the same thing for the layer with
the large connector. We’ve then found
the point in the matrix for that particu-
lar key.

Next we connect two wires to the con-
nections we’ve just found and connect
the other ends to our switch. With the
keyboard circuit connected to the com-
puter, a press of the switch causes the
appropriate keystroke to be detected
by the computer.

CID for Rock, Paper, Scissors

For the game of Rock, Paper, Scissors
we choose the [r], [p] and [s] keys
and connected them to some cables.
The other ends were connected to
three switches that were mounted
inside three wooden discs. The discs
are mounted on springs and can be
pressed down. When that happens
a switch closes. On top of the discs
we’ve placed images of a rock, paper
and scissors. The keyboard electronics
are actually fairly attractive to look at.
There is a real 40-pin Zilog processor
with a few peripheral parts. It would
be a pity to hide this circuit out of
sight. We’ve therefore put this board in
a hollow wooden disc and put a clear
plastic panel over the top. In that way
everybody can admire the simplicity of
the keyboard circuit and our Custom

Input Device.

CID voor Visual Pinball

In the program for Visual Pinball we
can specify which keys operate the
flippers and which key launches the
ball. We can also interrupt the game
with the Esc key. We could use the 1 or
3 key to start a new game, for example.
There is also a facility to assign keys to
nudge the table in various directions.
For all functions that we want to make
use of we determine the switch con-
nections on the keyboard circuit and
connect them to small switches. We’ve
used a sturdy, bash-proof plastic box
measuring 40 by 30 by 12 cm for our
Visual Pinball CID. When it’s placed
sideways on the table it feels comfort-
able with your hands on it. The two
pushbuttons that operate the flippers
are mounted on the sides of the case
to give a more realistic feel of a pin-
ball table.

The plunger is made from a wooden
knob mounted on the end of a 6mm
diameter metal rod. On this rod we
mount a ring that is normally pulled
against a switch (by an elastic band
for example), keeping it opened. When
we pull the plunger (to launch the ball)
the switch closes. And when we let go
of the plunger the switch opens again
and the ball is launched. In Visual Pin-
ball the time that the switch is closed
corresponds to the power of the launch.
A short time gives less power and a
long time gives more power.

This type of interaction between your
CID and the program adds a lot to the

enjoyment. If we use a projector to
display our Visual Pinball game on a
large screen and put the CID some dis-
tance away we can imagine that we’re
standing in front of a giant pinball ma-
chine. The show can begin!

( 070724 - 1 )

Web Links

m www.pinballnirvana.com/index.
php?name = UpDownload

[2] http://en. wikipedia.
org/wiki/Rock_Paper_Scissors

[3] www.elektor.com

This is all we'll use from the keyboard: the board with a cable and plug.

You only need a few switches to make a functional CID.

64

elektor - 4/2008

Keyboard electronics or microcontroller

Instead of using the electronics from a keyboard to build a CID you could also build all of the hardware and software yourself. We take an AVR
processor made by Atmel and use the BASCOM-AVR compiler, for example. This compiler includes the commands to simulate a serial PS2 key-
board. When we connect the switches of our CID to the inputs of the microcontroller then the rest of the electronics can be designed as we wish.
Next we assign a particular 'key value' to each contact and use the microcontroller to send it to the computer. This key value is used in our pro-
gram to perform a certain action.

There are advantages and disadvantages in designing and building the hardware and software yourself. The advantage in building a system
yourself with e.g. an AVR microprocessor is that you can make it very small. On an 8-pin microcontroller there are five pins available for I/O, but
three are required for the PS2 connection, leaving two for switches.

If we use a 20-pin controller then we have 1 5 I/O pins available. Taking away the connections required for PS2 leaves us with 1 2 pins for the
switches. Even with a 20-pin 1C the circuit can be made very compact.

The disadvantages of building the circuit yourself are the costs and time required. An AVR microcontroller still costs a few pounds and it will easily
take up a few evenings before everything works. On top of that you need a cable with a PS2 connector, so you would probably have to take that
from an old keyboard anyway. In that case you might as well use the internal electronics of the keyboard at the same time.

The only reason to build the electronics and software for a CID yourself is when it needs to be very small or in a particular shape. This will only be
the case when the look and size of your CID is very important to you.

Visual Pinball

Visual Pinball is a Visual Basic toolkit to create a pinball game on your computer. In
the program are many objects, such as bumpers, flippers or rollovers that have unique
properties and can react to various events. The method of programming, such as the
code for an event, is very similar to Visual Basic. For example, when a ball goes across
a rollover you could increase a counter (get points) or play a wav file. You can display
images on the table or the
backbox, etc. You could use
it to build a table based on
a real pinball game, but you
could also design a futuristic
game that in reality could
never be built.

A unique game, adapted for a particular theme or activity such as a Fancy Fair, can be
made to look very interesting with the help of Visual Pinball. On the Internet you can
find a wealth of information. A good place to start is this link [1]. From here you can
also download Visual Pinball 7.

w v nu a |

jJBjxi

;mnm MOtt, i - i<- Wot

With a few innovations (elastic band and positioning of the switches) the CID for the pinball table The 'controller' for the Rock, Paper, Scissors game is exposed to the world in all its glory,
is like the real thing.

4/2008 - elektor

65

REVIEW

PSOC

Cypress PSoC development kit

things. Cypress PSoCs combine a microcontroller

Paul Goossens

Your average embedded system will be primarily
composed of digital components. However,
analogue components are also necessary for
filtering and amplifying signals, among other

PSoC Firs'tTouch

1HE UUIMATESUB1EHKIT

Featuring PSoC Express

PSoC Expro«'“

PSoC Programmer

Uung Window* 2000/XP/Vhta

For more information about
Cypreii'* PSoC' F.olTovch
or softwore update* go to
www.cypreu com/FiriiTou<h

You can buy the CY3270:

PSoC First Touch' starter kit for around
£15 (25 euros). It provides a convenient way
to discover for yourself what the Cypress PSoCs have
to offer.

This development kit consists of two hardware modules, a
mini-CD, a Quick Start Guide, and a piece of wire (!). All
of this is packaged in a plastic box, which you can later
use as a handy storage container. The only thing that's
missing is a USB cable - otherwise the kit is complete and
ready to use.

What is PSoC?

The abbreviation PSoC stands for 'programmable system on
chip'. A variety of 1C makers use this designation. It usually
refers to a microcontroller with a large amount of memory
and peripheral functions. At Cypress, this name is used for
a rather different kind of 1C. Beside the microcontroller and
some peripheral functions, the Cypress PSoC incorporates
several analogue components.

These analogue components are configurable. You can thus
use them to build a wide variety of analogue amplifiers,
filters, modulators, and the like directly in the chip. These
blocks allow analogue circuits to be incorporated in an em-
bedded system along with the microcontroller, all in a single
chip. This reduces the total number of components required
for a given design.

with analogue functional blocks. A development
kit such as the CY3270 forms a good starting
point for rapid familiarisation with these ICs.

The inputs and outputs of these analogue blocks can be
connected to any desired pins of the 1C. This also
holds true for the digital peripheral components
of the chip. This makes designing the PCB layout
a lot easier.

Software

The included CD-ROM contains another important part of
the kit: the development software and programmer. Inciden-
tally, this software also runs under Windows Vista without
any problems. Unfortunately, the programming software
included on the CD does not work under Windows Vista.
However, a new version that does work with Vista is avail-
able on the Cypress website.

Hardware

The hardware in this kit consists of two parts. The first
part is the 'FTPC bridge', while the second part is the
expansion board.

The expansion board holds the PSoC - a CY2 1 434 - that is
used to test the provided examples. In addition, this board
has an RGB LED, a small speaker, and a thermistor.

The PCB also has a pair of copper strips and a connector
for inserting the wire included in the kit. The copper strips
can be used to make a touch button in combination with
the PSoC. The included wire, which extends as a sort of an-
tenna, can be used to build a proximity sensing circuit.

The FTPC bridge provides the communication link between
the expansion board and a PC. The USB interface on this
board makes connection to a PC easy. This allows the PSoC
on the expansion board to be programmed from the PC.
In addition, it acts as a USB to l 2 C bridge and as a USB to
SPI bridge. This simplifies debugging of applications that
use these interfaces.

66

elektor - 4/2008

The microcontroller can be programmed in C with this soft-
ware. There is also a built-in simulator. The special feature
of this software is the capability of configuring the analogue
blocks in the PSoC.

Witt this software, connecting various types of sensors is
very easy. The software also includes a large number of
predefined blocks that can be used to connect a wide vari-
ety of sensors directly to the 1C. The associated C routines
for reading these sensors are also included. You can even
display typical schematics for the various sensors on the
screen.

Constructing a circuit effectively amounts to dragging the
necessary analogue functions to the design. The properties
of these blocks can be adjusted as necessary with a few
mouse clicks.

Assessment

The Cypress CY3270 development kit provides a lot of
value for relatively little money. The hardware is simple but
functional, and the FTPC bridge can be used afterwards as
a programming interface for your own projects.
Experimenting on the basis of the supplied examples is a
pleasant way to spend your time, and it's bound to inspire
you to develop your own creative uses for these PSoCs. The
easy-to-use development software, along with the library of
handy routines and ready-made sensor interfaces, is espe-
cially convenient.

( 070950 - 1 )

Kit available from:

www.cypress.com/go/elektorFTK

Sample applications

The software is complemented by four sample applica-
tions for the expansion card. Using these examples, you
can quickly understand how to make a touch sensor
that operates on the capacitance principle. Using a
piece of wire as a proximity detector is also quite
easy, and it's fun to experiment with adaptations
of this design.

The light sensor and temperature sensor are also
used in the other two examples.

See your design in print!

Elektor Electronics (Publishing)
are looking for

Freelance Technical Authors/Designers

If you have

# an innovative or otherwise original design you would like to see in print

in Europe's largest magazine on practical electronics

# above average skills in designing electronic circuits

# experience in writing electronics-related software ^

# basic skills in complementing your design with an explanatory text

# a PC , email and Internet access for efficient communication with our in-house design staff;

then do not hesitate to contact us for exciting opportunities in getting your designs published on a regular basis.

Elektor Electronics
Jan Suiting f, Editor

P.O. Box 77, NL-6II4-ZG Susteren, The Netherlands, Fax: (+31) 46 4370161
Email: editor@elektor.com

4/2008 - elektor

Kaj Schulten

Sensible energy usage is always a good
idea. It is better for the environment
as well as your wallet. Standby settings
are now frowned upon and low-energy
light bulbs are becoming more popular. Power
management inside the PC is also becoming
more important. Certainly those heavy-duty game systems
that can consume over 500W can do with a critical look at power saving possibilities.

In the early days of the personal computer the system could
really only be in one of two states: on or off. Putting the
machine into standby so it could be restarted more quickly
was still unheard of then. There was also the fact that the
operating systems in use at that time (DOS and later OS/2
and Windows) weren't very good at doing several things
at the same time. It was better to keep the hardware ac-
tive all the time (it was well-known that the hard drives in
those days didn't like it if they were continuously turned on
and off again). But even then the motherboard manufactur-
ers were hard at work implementing the Advanced Power
Management (APM).

APM made it possible to enter a power-saving standby
mode via a time-out setting in the BIOS or by pressing a
Suspend/Resume button. On detecting this signal the hard-
ware switched into a power-saving mode.

transformation

With the advent of newer operating systems such as Win-
dows 95 it became possible to activate this standby mode
from within Windows and make better use of it. After all, if
the BIOS decides that a device can go into standby mode,
but the operating system can't handle that, then the result
will be chaos.

As it was, APM could never be used to its full potential.
Much of the functionality could only be used from within the
BIOS and was not accessible to the operating system. The
support left much to be desired and there were numerous
problems with Windows 95 and power management that
left many users feeling very frustrated.

Progress

The successor to APM is known as the Advanced Configura-
tion and Power Interface (ACPI). With ACPI it is the operat-
ing system that makes the decisions regarding the power

management. It can put certain parts of the computer into
a different state, saving energy. This happens according
to the preferences of the user and the programs running at
the time. A device that is not used can be turned off or put
into an idle state; this is something that can also apply to
the whole computer.

The ACPI gives the operating system direct control over the
power management and the so-called Plug and Play prop-
erties of the computer. You do of course need an operating
system that supports the ACPI. Every Windows version from
98SE and NT4 onwards has support for these features.

It was very different as far as the alternative operating sys-
tems were concerned. It wasn't that long ago when putting
a computer into hibernation would result in a crash and
then required thorough check of the hard drive.
Fortunately the open source community doesn't rest and
these days most versions of Linux and FreeBSD make it easy
to call the ACPI functions. This is actually quite an achieve-
ment since the full ACPI specification is in excess of 600
pages. If it had been left to Microsoft it would have been a
closed Windows-only specification.

How does it work?

So how does the ACPI work? It would be too much to go
through the complete specification, but in a nutshell the
ACPI has seven different states, with the power saving vary-
ing from none to maximum.

'GO' is the normal state in which the computer operates.
The operating system and programs run normally and the
processor carries out its instructions. In GO it is possible to
turn of a device temporarily while it isn't required and turn
it back on again afterwards. Examples are hard drives
and monitors that are turned off after a few minutes if they
haven't been used for that period.

'G1 ' is the sleep state. This state has four sub-states: 'SI ' to

68

elektor - 4/2008

Computing

Advanced Power Management

'S4'. They effectively determine how quickly the computer
can be brought out of its sleep state.

In SI the memory cache is cleared, but the processor(s)
and the memory remain powered up. The machine can be
brought back to its normal state very quickly. This is also
called the 'POS' state or Power On Standby.

52 is almost the same as SI . The only difference is that the
processor is powered down. The computer therefore takes
a little bit longer to wake up again.

53 is also called 'Suspend to RAM' in the BIOS. In the vari-
ous operating systems it's called something different again
('Sleep' in Vista and OS X, for example). The operating sys-
tem keeps the memory powered up and stores the system
state in it. Because of this the user can get back to work
quickly, since storing the system status in RAM requires little
effort and you can carry on working where you left off. It
takes about as long as powering up the monitor again.

54 is better known as Suspend To Disk, although the various
operating systems again use different descriptions. In OS
X it's called 'Safe Sleep' and in the assorted Windows ver-
sions it's known as 'Hibernate'. In this state the system state
is written to the hard drive. The biggest advantage of this is
that the computer can be fully turned off once all the infor-
mation has been written. This is in contrast with S3, where
you would lose all the information if there was a loss of
power, for example caused by an empty laptop battery.
G2 is also known as S5, but it is not a state that saves more
energy than S4, since several parts remain powered up.
In this state a press of a key on the keyboard or a signal
over the LAN (Wake On LAN) can restart the computer. In
this state you wouldn't be able to change parts either. This
can only be done safely and without the loss of data in the
G3 state.

G3 is the same as the mechanical off state. The operating
system and programs have all been fully shut down and the

hardware has been turned off, with just the Real Time Clock
(RTC) on the motherboard running from a small lithium bat-
tery. In this state it is completely safe to add or replace any
hardware. The computer will be in this state when there is
a loss of power and usually remains in it when power is
re-applied. In some BIOSes this can be changed so that
a system will automatically return to the GO state after a
power-cut, and restart.

From the G2 and G3 states there obviously has to be a
full boot-up procedure before the system becomes opera-
tional again.

The success or failure of this functionality obviously depends
on the support provided by the underlying hardware. If
certain functions are missing it is often impossible for the
operating system to implement some power saving func-
tions. When this is the case the state of the system is often
called the Legacy mode. The ACPI is not used in this mode
and the computer effectively operates in either GO (on) or
G3 (off) mode.

Choices

The preference of the author is to use the S4 state on his lap-
top, as that works well with both Linux and Windows. The
biggest disadvantage is the power up time. When restart-
ing from Suspend To Disk the system first has to go through
a complete POST (Power-On Self-Test) and then write back
the system state into the memory, which takes a while. But
as with many things in life, it's a matter of priorities: do you
want to quickly resume with your work or do you want to
save energy (from your laptop battery, for example).
Another function of ACPI is used very much in portable com-
puters; running the processor at a lower frequency than it
is made for reduces the power consumption, extending the
life of batteries. Intel calls this SpeedStep, and AMD uses
the terms PowerNow and Cool'n'Quiet.

( 070796 - 1 )

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4/2008 - elektor

69

DO IT YOURSELF

Lucky Dip

Design it yourself or copy from the Internet?

Thijs Beckers

Like it or loath it, the Internet offers a treasure trove of information. Countless pages magically appear on
your computer screen via this digital connection. You only need to know how to find what you're looking
for. But it's not always that easy. For the electronics enthusiast there are of course all sorts of circuits and
ideas waiting to be unearthed — the good, the bad and the ugly! We take a grab at what is on offer.

Do-it-yourself single-chip audio ampli-
fiers with a LM3886 or similar, the so-
called ‘Gainclones’ are quite familiar

liltfCtTBuic Schematics ti>r Hubby isLs

^ 1 ■ flil F.h i-t,. gi^ri+p

'LL LIT j - - -y.M I ■■ 1 L *-» ■ L 1 ... , ,

13 ■{’ r-iip

la 1 7*-i”

. j a. m p..«-

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be f 'lau «

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MM ’ w *r*w

3m fc> hii-a

m. ri i ji.

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igure 1. USB sound card.

F&r ths fiiii inn-;, rhii dieuit -.vai tl*tlgned by two aulhari. i.U laurler Gandfort eT

Burnaby in Bntlil'k C alumina Canada, and mysa-ir F2eas* inal a suit you JiH
Laurel's tfie. Hantfy Dandy Lim-s Cfrcuits. Tnfe page it also avairawe in
Ranch by clicking Mi ihe flag

igure 2 Simple intercom.

by now. So we won’t talk about those.
Perhaps a little less well-known, but
still a very popular do-it-yourself sub-
ject is the modification of CD players
manufactured by Marantz, specifical-
ly the CD-63 and the practically iden-
tical CD-67. These players have now
reached quite a respectable age and
can easily be obtained second hand. A
large group of audio fanatics [1] knows
how to improve this player, with a few
modifications, to a level approaching
that of high-end.

Audio

A famous website with all kinds of in-
teresting audio projects is Elliott Sound
Products [2]. But this is, of course, not
the only source for interesting audio
circuits. At [3], for example, we find a
nice circuit for a USB sound card (Fig-
ure 1). Building a simple sound card
that connects to the USB port doesn’t
require a university degree any more.
Using an IC such as the PCM2706 from
Texas Instruments you immediately
have a headphone amplifier, a digital
output (S/PDIF) and a hardware con-
trol panel for your media player, with-
out the need to install anything at all
when used with Windows XP or Ma-
cOS X. You can even download a PCB
layout for this from this website [3].

For at home...

...there are naturally also a diverse
range of interesting circuits to be
found. For example, this doorbell in-

tercom [4]. This handy circuit (see Fig-
ure 2) uses the speaker for reproduc-
ing as well as picking up sound. The
volume can be adjusted with a poten-
tiometer. A switch (indoors) is used
to switch the circuit between listening
and talking, so that 2 -way communica-
tion becomes possible. Very handy, of
course.

A somewhat older ‘gimmick’, but there-
fore not necessarily less entertaining,
is the lightning bulb [5]. With a simple
lamp, a piece of aluminium foil and a
high voltage power supply, built from
a car ignition coil, it appears that there
is an electrical storm inside the glass
envelope of the lamp (see Figure 3).
It remains fascinating to see how the
electrons work their way from one elec-
trode (the filament) through the gas in
the lamp to the other electrode (the
aluminium foil). Of course, You need to
watch out with these types of projects,
because they operate at a dangerously
high voltage of several kilovolts.

Another thing that would be nice to
have at home is a metal detector. In
this instructional video [6] you can see
how you can, in a few minutes, turn
a radio and a calculator into a simple
metal detector that you can use, for ex-
ample, to find wires or pipes in a wall.
The ‘circuit’ uses the clock frequency
of the pocket calculator.

fuC

Very popular as well is the Arduino de-
velopment board [7]. It is targeted at

70

elektor - 4/2008

Figure 3 Lightning bulb.

igure 4. Arduino board.

igure 5 Midi-drums.

artists, designers and hobbyists and
everyone who is interested in interac-
tive applications. These little boards
are usually based on an Atmel AT-
megal68 microprocessor (see Fig-
ure 4). There are quite a lot of these
open-source applications and the
number continues to grow. Examples
of projects that have been designed
with this mini board are drum pads
with a MIDI interface (Figure 5), an in-
teractive light system for a bridge and
a virtual fish tank.

Microprocessors always need to be
programmed of course. One of the
many AVR programmers that can be
found online is the one from electron-
ics-diy.com [8]. Together with the pro-
gram called PonyProg [9] it is very

straightforward to program hex files
in, for example, a 28-pin ATmega8. The
circuit is very compact and can be tidi-
ly housed inside the shell for the serial
connector (see Figure 6). Incidentally,
on the PonyProg website you will also
find a circuit for a programmer that is
suitable for connecting to a parallel
port.

PC

If you have poor reception of a WiFi
signal you will definitely have to watch
this video [10]. This explains how you
can make a better antenna for just a
few pennies. Just roll up your sleeves
for five minutes and you’re done!
“Finally a use for that old Windows
95 laptop”, that’s how this website

[11] announces the circuit (Figure 7).
With three ICs, a dual opamp and a
handful of components you can make
an excellent 12-bit data logger for
less than £ 10 (€ 14). A simple Qbasic
program does the rest. Qbasic.exe is
generally on the original Windows 95
CD (usually in the folder ‘oldmsdos’)
or alternatively can be downloaded
from [12]. It will probably work with
GWbasic as well.

Figure 6. AVR-programmer.

Web Links (also on the Elektor website)

[1] www.diyaudio.com

[2] http://sound.westhost.com

[3] http://electronics-diy.com/PCM2706_USB_Soundcard.php

[4] www.mitedu.freeserve.co.uk/Circuits/Audio/doorint.htm

[5] www.uoguelph.ca/~antoon/circ/hv/l-bulb/l-bulb.html

[6] www.instructables.com/id/HomeMade-Metal-Detector

[7] www.arduino.ee

[8] http://electronics-diy.com/avr_programmer.php

[9] www.lancos.com/prog.html

[10] www.metacafe.com/watch/837885/wifi_antenna_hack

[11] www.techlib.com/electronics/serialport.htm

[12] www.fluid.tue.nl/student/colleges/NLS/software.html

[13] www.x-robotics.com/hardware_ing.htm

[14] www. electronics- lab. com/projects/automotive/005/index.htm I

[15] www.electronics-lab.com

[1 6] http://home.hccnet.nI/e.vd.logt

[1 7] www.zen221 42.zen.co.uk/Circuits/Power/add-on.html
[18] www.belza.cz/hf/bug.htm

4/2008 - elektor

71

DO IT YOURSELF

Figure 7. 12-bit ADC.

Robotics

Activating a robot (or something else)
with a certain sound signal can be
done with this [13] circuit (Figure 8).
The IC compares the frequency of the
input signal with that from its own fre-
quency generator (adjustable with a
resistor and capacitor) and switches
its output low when they match. So
you can for example, by whistling at a
certain frequency have the robot carry
out a pre-programmed action (make it
come towards you, for instance).

Miscellaneous

A simple parking aid which uses an IR
LED and IR photo diode is explained
here [14]. Via the home page of this
website [15] and the accompanying
forum many more interesting projects
are waiting to be found.

What has brewing beer got to do with
electronics? We find the answer here
[16]. On this website we can see the
building and brewing process of Emile
van de Logt. A genuine PID control-
ler and control with PC software are

igure 8. Tone detector.

deployed for this brewing process

(Figure 9).

A handy circuit for limiting the inrush
current (Figure 10) of, for example, a
bench power supply can be found on
[17]. Very useful when turning a circuit
on for the very first time. The maximum
current is determined by 0.7/R2. This
can therefore be easily adjusted as
required.

With a very small and simple circuit
built around a single transistor (Fig-
ure 11) you can build a spy microphone
that can be received with an FM radio.
The website [18] is unfortunately in
Czech, but it is easy to understand the
circuit without the text. There is even
a PCB layout available, although it is
rather spacious for a spy microphone.

This was just a random selection of
the immense number of circuits on of-
fer. We hope that we have given you a
few ideas and in the event that your
own searches prove to be fruitless, you
can always visit the Elektor website for
more than 2,000 circuits on stock.

( 070955 - 1 )

Tha -second schematic has a couple of added feSluies. If you don'1 wart 1o use a
voftmeter on the eulptf - use an LEO Instead. IMhe output voltage falls - the LED
wilt dim or t riln-grtsh eannpletefy. This Is enough to lei you k now I hart Ihe load on
the output Is excessive.

Where the Current Limiter Is to be left unattended Ter any length of rime - say
during a soak-last - Ihe Bu=ei Is useful. Should a problem develop* - and the
output vaBage Tal by 2-volts or more - the circuit will sound the alarm.

Add-On Current Limiter

igure 10. Current limiter.

PIP Control Settings

Sample Time Ts
PID Kc parameter
PID T] parameter
PID Td parameter
LP-Fitter constant

X

5 Seconds

80 %rc

282 Seconds

30 Seconds

0 Seconds

Send PID Output signal to:
r Electrical Heating Element
r Non-modulating Gas-Burner
P Modulating Gas Burner

a-coefficient DAC value
b-coefficient DAC value

PID Controller Model

First ebrew PID controller
r l Jpdnted ebrew PTh controller
C Allen Bradley Logix 5550 Type A
• Allen Bradley Logix 5550 Type C

Time-switch Control
^ Off r On

—

f” Show PID Controller Debug Info

OK

Cancel

Help

1-2.04

232,05

Figure 9. PID controller for brewery.

72

elektor - 4/2008

LABTALK

TECHNOLOGY

My microcontroller

doesn't go...

It is impossible to imagine modem electronics without microcontrollers. What used to be done with
combinational or sequential logic is now done with a single 1C that runs a program that does exactly
what we want it to do. Or perhaps more accurately: should do exactly what we want it to do.

■ C:\Program Files\Microchip\MPASM Suite\startup.asm [~^~|[~n~][~x"|

org OxOOO

-

start clrwdt

*

clear watchdog timer

movlw

b 1 11010111 1 ;

assign prescaler, internal clock

*

and

divide by 256

see p. 106

option

SfcOVlW

0x00

*

set w = 0

tris

portB

*

port B is

output

cirf

portB

*

port B all low

go bsf portB, 0

*

RBO

* 1 , thus

LED on p. 28

call

delay

call

delay

bcf portB, 0

i

RBO

* 0 , thus

LED off

call

delay

call

delay

goto

go

*

repeat forever 1

delay cirf tmrO

; clear

TMRO, start counting 1

again btfss tmrO,

0

; if bit 0 s 1

goto

again

no, then

check again

btfss

tmrO,

1

*

if bit 1

» 1

goto

again

no, then

check again

btfss

tmrO,

2

}

if bit 2

« 1

goto

again

r

no, then

check again

btfss

tmrO,

3

*

if bit 3

- 1

goto

again

no, then

check again

bt f ss

tmrO,

4

*

if bit 4

» 1

goto

again

i

no, then

check again

btfss

tmrO,

S

i

if bit 5

* 1

Luc Lemmens

Particularly during the early de-
velopment phase of the hard-
ware and software, we often
run into perplexing problems.
The most frustrating of these is
when the microcontroller doesn't
do anything at all (or appears
not to do anything at all). With
older microcontrollers that have
external program memory an os-
cilloscope or logic probe could
often give an answer. A meas-
urement on the address or data
bus would give a quick indica-
tion whether the microcontroller
was 'awake' or not. But these
days all memory is integrated in
the 1C, in most cases, so only the
I/O ports can sometimes provide
consolation as to an indication of
any sign of life.

Fortunately (?) most controllers
still have an external oscillator,
so that we at least can check
whether the clock is running.
However, even this option isn't
available with many small micro-
controllers that have an internal
oscillator.

The simplest method to ensure
that the oscillator is running and
that the software, in principle,
should be able to work, is to in-
sert a short routine at the begin-
ning of the program that toggles
one of the port pins a few times.
Preferably a port pin that has an
LED connected to it, that gives
immediate visual feedback and
an oscilloscope is not required.
Don't make the program wait for
some external action (such as a
button press, reception of data
via the serial link, etc.), but just
do 'something' on any pin what-
soever. If there is still no indica-
tion of any activity (and assum-

ing that very basic checks like
measuring the power supply and
whether the reset line is at the
desired level have already been
done), there is a chance of ten
to one that something has gone
wrong during programming. The
configuration fuses of the micro-
controller are the main suspects.

As has been mentioned in an
earlier 'LabTalk' article, modern
microcontrollers have a number
of bits (fuses) that define the be-
haviour of the 1C. In the scope of
this article we first have to look
at the settings, if there are any,
for the oscillator (internal/exter-
nal, frequency range). If these
settings are wrong then in most
cases nothing happens at all.
The second suspect is — if
present — the watchdog timer

(WTD). If this has been turned on
when programming and the ap-
plication does not reset the timer,
the microcontroller will repeated-
ly be reset and often won't even
reach the actual program.

Number three is the setting for
the reset circuit. For example,
the reset signal for some micro-
controllers can be selected to be
internal or external. Consult the
datasheet for the controller and
check the remainder of the circuit
to determine the correct settings.
It can sometimes take a bit of
looking around in the program-
mer software to find where these
settings are hidden — as we al-
ready discussed in an earlier sto-
ry — sometimes they have differ-
ent names than what you would
expect. In final desperation you

could try all possible combina-
tions of the fuses in the hope that
one of them works. This sounds
very awkward, but it will unfor-
tunately be necessary at some
point! Fortunately, reprogram-
ming of a microcontroller is not
such a time consuming job these
days.

A simple start-up indication built
into the application saves a lot
of time and frustration — at this
point you know that the hard-
ware is functioning and that noth-
ing went wrong when program-
ming the memory and fuses. At a
later stage of development, you
could remove the start-up rou-
tine, but only do that if absolute-
ly necessary.

( 070101 - 1 )

4/2008 - elektor

73

DESIGN TIPS

Automatic aquarium feeder

Helmut Schaefer

People come in all shapes and
sizes and we all have our own
character. You probably know
people who are at their best
first thing in the morning while
others can only get things done
when they are burning the mid-
night oil. The feeding habits of
different fish species also show
variation; some (such as catfish)
are nocturnal feeders while oth-
ers feed during the day. Unless
your own body clock is
in sync with the fish in
your aquarium you will
not be providing them
with food when they
really need it.

The solution described
here is an automatic
fish food dispenser. On
the mechanical side the
apparatus consists of
an off-the-shelf DC mo-
tor and reduction gear
driving an external
gear train sandwiched
between two plates.

It is necessary for the
spacing between the
plates to be greater
than the thickness of
the fish food pellet (see
illustration).

A hole in the upper
plate is directly be-
neath a vertical tube
(or magazine) which
contains a stack of
food pellets. The hole
in the lower plate is
offset and the pellets
will eventually drop
through here into the
aquarium below. In between
these holes is the final cog in
the gear train which has a hole
made in it between the hub and
toothed edge of the wheel. The
hole must be slightly bigger than
the diameter of the food pellet.
When the hole is beneath the
column of pellets a single pellet
drops down into the hole in the
gearwheel. At each feed time
the pellet is swept around until it
passes over the hole in the low-
er plate where it drops through
and provides a tasty snack to
the fish waiting below. The pro-
totype uses a motor/gearbox
combination from Conrad Elec-

tronics (model catalogue, part
no. 242535) which operates on
3 to 6 V and produces an output
speed of 1 1 to 22 rpm. An exter-
nal set of gears provides a further
10:1 reduction. The final output
gear takes around 30 seconds
to complete one revolution and
the low operating speed helps to
avoid the possibility of a pellet
becoming jammed in the mecha-
nism. The frequency of feeding
is actually controlled by an ex-
ternal mains time-switch which

switches a mains adapter pow-
ering the whole feeding mecha-
nism. The electronics incorporat-
ed into the feeding mechanism
ensures that each time the feeder
is switched on it only dispenses a
single food pellet. Modern time-
switches can be programmed
to switch several times in every
24hr period and can have an
'on' time of one minute or less.
A small cam on the gear train
output shaft actuates a micro-
switch when a single revolution
is completed. This technique of
tuning the whole unit off in be-
tween switching times means
that the standby current (exclud-

ing time-switch consumption) is
zero. Another advantage is that
each time the circuit is powered
up it effectively performs a reset
so it is not possible for the circuit
to lock-up in an undefined state
which sometimes occurs in digital
circuits as a result of glitches and
mains-borne interference.

The central logic element in the
circuit is the TTL SN74LS76N J-K
flip flop. In addition to the syn-
chronous functions of this chip

(store, set, reset and toggle)
there are two asynchronous in-
puts namely 'preset' and 'clear'
which are both active-low on this
particular version of the flip flop.
When power is applied to the
circuit the preset input of 1C 1 A
is held low by the RC network
R6 and C4 which ensures that
the flip flop will always be set
(Q = 1) at power up. Transistor
T1 switches on and the motor be-
gins turning. A feeding cycle can
also be initiated by pressing the
manual pushbutton. When the
output gear wheel has complet-
ed one revolution and pushed a
pellet over the hole in the lower

plate a cam on the output shaft
activates a micro-switch. This will
ground the 'clear' input of IC1 B
and produce a negative going
signal to the clock input of flip
flop IC1 A which clocks the state
of the J input (0 V) through to the
Q output to turn off T1 and the
motor. The 'preset' and 'clear'
inputs of IC1 B are connected di-
rectly to the micro-switch output
to provide a debounce function
ensuring that a single clean clock
edge is provided to IC1 A. All the
other inputs of IC1 B re-
lated to synchronous
operation are unused
and tied to ground
(logical 0).

Capacitors C2 and C3
should both be ceramic
types and although res-
ervoir capacitor C 1 is
shown as a tantalum a
normal electrolytic type
can be substituted. The
motor together with the
circuit draws around
35 mA. A 50 mA fuse
(FI ) is included in the
supply to protect the
motor and transistor
should a food pellet
become jammed in
the mechanism and
stall the motor. A more
powerful motor can
be used in the design
but in this case it will
be necessary to re-
duce the value of R4
to give a greater drive
current and swap T1
for a power transistor.
The fuse rating will also
need to be beefed-up
to handle the increased current.

A tip when drilling the plates is
to start by making just two holes
through the plates and then fit-
ting two pins or bolts through the
holes to fix the plates together be-
fore drilling the remaining holes
that are common to both plates.
This ensures that the holes will be
properly aligned.

Although the design was devel-
oped for feeding fish it could
also be adapted fairly easily for
other applications that require a
programmable momentary me-
chanical operation.

( 060354 - 1 )

+5V

74

elektor - 4/2008

Ultra-responsive peak detector

Stephen Bernhoeft

The peak detector presented
here will respond to amplitude
changes of the input signal with-
in one-half of a cycle. Because
no 'bleed' resistor is required
on the output capacitor, droop
is only limited by the 'off' resist-
ance of a CMOS switch. Note
that circuit is more accurately
described as an amplitude
detector, as the output level
is equal to the average of the
absolute values of the positive
and negative amplitudes. For a
sinusoidal input waveform, this
corresponds to the peak detect
function.

Positive and negative peaks are
measured separately. Whilst the
positive peak is being acquired,
the negative peak is output,
or vice versa. At the time a
positive-going zero-crossing is
detected, the positive peak de-
tector is reset, and similarly for
negative signals.

There are two key subcircuits.
One is a peak detector, the
other is a zero-crossing detector
(ZCD). There are two instances
of each type, corresponding
to the two possible signs of the
input signal. Note that all detec-
tors (of both types) give a posi-
tive output.

When +ZCD goes high, this
causes a brief pulse to reset the
positive-peak detector. The reset
has no effect on Vqut/ since the
high level of the +ZCD means
that the negative peak detec-
tor is connected to Vqut this
time.

During this (positive) half of the
input cycle, the +peak detector
continuously registers the most
positive input signal to date until
such a time as it is reset.

Now consider what happens
over the negative-going excur-
sion of the input signal. Firstly,
+ZCD goes Low, then -ZCD
goes High. In the short interval
that both are Low, the output ca-

pacitor is isolated. When +ZCD
goes Low, Vqut is removed from
the negative peak detector out-
put, and because -ZCD is high,
Vqut is instead connected to the
positive peak detector output.
The negative peak detector
operates in the same way as
described above for the posi-
tive one, but because it sees an
inverted copy of V !N , it gives a
positive (absolute value) output,
as required.

The circuit shown is suitable
for low frequencies up to a few
kHz. The AD8534 is specified
as unity-gain stable for capaci-
tive loads of up to 10 nF. Em-
pirically, it was found that even
an ordinary opamp such as the
LMC6484 gave no problems
with ringing at Vqut; possibly
the 'on' resistance of the switch
in the 74HC4066 helped to iso-
late the output capacitor.

One speed restriction is the
width of the reset pulse. It would
be possible to use a monostable

instead of the RC network. In
order to allow short reset times,
the MOS switches used here to
short the peak detect capaci-
tors could be supplemented with
discrete, low R DS (on) NMOS
transistors, such as TN0200K. If
necessary, dedicated compara-
tors may be used for the ZCD
sections.

Current consumption could also
be reduced. Firstly, by swap-
ping the comparator inputs
around — the 'working' com-
parator inputs are high-imped-
ance. If this is done, be sure
to invert the BAT54 diodes as
well. Of course, now we have
an inverted output to the peak
detector, i.e.

VoUT = “VpEAK

Lastly, if desired the inverting
opamp stage may be amended
to use 100 kQ resistors.

( 060300 - 1 )

2/2008 - elektor

75

INFOTAINMENT

PUZZLE

M^YAHAkII Puzzle with cm
I I vAO\JUr\v4 electronics touch

Despite all new-fangled computer programs the simple pencil & rubber are the preferred tools for
solving our monthly Hexadoku puzzle. Add some good brain exercise and win one of the prizes: an E-
blocks Starter Kit Professional and three Elektor Shop vouchers.

The instructions for this puzzle are straightforward.

In the diagram composed of 1 6 x 1 6 boxes, enter numbers such
that all hexadecimal numbers 0 through F (that's 0-9 and A-F)
occur once only in each row, once in each column and in each
of the 4x4 boxes (marked by the thicker black lines).

A number of clues are given in the puzzle and these determine
the start situation.

All correct entries received for each month's puzzle go into a
draw for a main prize and three lesser prizes. All you need to
do is send us the numbers in the grey boxes. The puzzle is also
available as a free download from our website.

SOLVE HEXADOKU AND WIN!

We believe these prizes should encourage

all our readers to participate!

The competition is not open to employees of Elektor International Media,
its business partners and/or associated publishing houses.

worth £248.55

and three

Elektor SHOP
Vouchers worth
£35.00 each.

Correct solutions received enter a prize draw for an

E-blocks
Starter Kit
Professional

PARTICIPATE!

Please send your solution (the numbers in the grey boxes) by email to:

editor@elektor.com - Subject: hexadoku 4-2008 (please copy exactly).

Include with your solution: full name and street address.

Alternatively, by fax or post to: Elektor Hexadoku

Regus Brentford - 1000 Great West Road - Brentford TW8 9HH

United Kingdom - Fax (+44) 208 2614447

The closing date is 1 May 2008.

PRIZE WINNERS

The solution of the January 2008 puzzle is: 90467.

The E-blocks Starter Kit Professional goes to:

Richard Berends (UK).

An Elektor SHOP voucher worth £35.00 goes to:

Jos Hartman (CH), Mehmet Sukuroglu (TR); David Gill (UK).

Congratulations everybody!

E

A

9

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4

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76

elektor - 4/2008

RETRONICS

INFOTAINMENT

'Formant' is with-
out doubt one of the biggest
names from the Elektor his-
tory. The mega project goes
back a good thirty years,
was forgotten for about 25,
and now hails us through
Google and Ebay. Along
with Chorosynth, it is one of
the vintage instruments pre-
sented at the fabulous www.
synthmuseum.com [1] web-
site brought to you by Paula
Chase and Jay Williston.

The scene: it's 1970 and
'groovy' sounds are heard
from Robert A. Moog's syn-
thesizers like the one used
by bands like Yes and Emer-
son, Lake & Palmer.

The Moog synthesizer was
the defocto standard at the
time, with lots of more or
less electronically minded
musicians (or musically
minded electronics fans)
adapting and extending it all
the time to create their own
flavour of sound. The pitch
wheel in particular created
sound 'bends' that became
forever associated with the
Hippy age. For a nice his-
tory of 'The Mooq', see (and
hear) [2].

The Elektor Formant was origi-
nally designed by C. Chapman
and the project saw its first pub-
lication in the May 1 977 issue of
Elektor. In an attempt to jump
the Moog bandwagon it was
announced as "an instrument
of advanced specification that
bears comparison with many
commercially available synthe-
sisers, but at a fraction of the
cost". The article series ended
with part 1 0 (!) in the April 1 978
issue. Two Elektor editors, now
retired, recalled that the pub-
lications got immense acclaim
but failed to sell significant
numbers of the printed circuit
boards. That changed dramati-
cally, at first when the Formant
article series were bundled into
a book (1980), and a bit later
(1 981 -82) when M. Aigner pub-

lished follow-up articles (and a
book) describing what looks like
'Formant mk.ll' containing good-
ies like a Ring Modulator, Sample
& Hold, Phase Shifter, Envelope
Follower, Mixer, ADSR Controller,
VC-LFOs, and other highly desir-
able sound warping circuitry,
some based on Curtis ICs. By
contrast, the original Chapman

design, although comprehensive
by itself, is a conventional Moog-
style synth with a classic 1 V/
octave characteristic and all the
usual modules like VCO, VCF,
LFO (made from 3 LFOs), Noise,
ADSR, VCA, COM, RFM (not the
manual but Resonance Filter
Module) and a 24-dB VCF, not
forgetting a keyboard and inter-

[2] www.youtube.com/
watch ?v=TttYkC3NyjM

Formant was rack-able
consisting of circuit boards
vertically mounted on a
backplane with the controls
(pots, switches) in bright
colours on the front panel.
The instrument pictured
here is privately owned by
my colleague Jan Visser
from the Elektor labs who
put it at my disposal for
photography and sound
checking of course! The
wooden case was available
at the time from electronics
retailers advertising in the
magazine. It's an almost
fully loaded Formant com-
plete with a keyboard and
even a mini-oscilloscope to
check the waveforms. With
the current revival of sev-
enties things & sounds, I
reckon the instrument would
fetch some hard cash on
Ebay!

The smaller unit pictured
here is the Aigner version
with a modest complement
of dual VCO, VCF, Dual
ADSR, LFO and COM. This fine
sounding specimen was rescued
from the skip and is currently in
safe storage at Elektor House.
Reportedly the instrument was
played 'live' several times at
electronics exhibitions and shows
in France and Germany during
the mid 1 980s.

( 070937 - 1 )

Formant synthesizer (1977)

Jan Buiting

face and of course a power
supply — all DIY, built on
Elektor 'EPS' printed circuit
boards and taking almost
100 pages to describe in
great (albeit dry) detail in
the magazine.

Retronics free download:

Formant music synthesiser book

(2 nd edition 1982).

www. e I e kto r.com/ ret ro_f o r m a n t

Web Links

[1] www.synthmuseum.com/
elektor/eleformOl .html

Retronics is a monthly column covering vintage electronics including legendary Elektor designs. Contributions, suggestions and requests are
welcomed; please send an email to editor@elektor.com

4/2008 - elektor

77

ELEKTOR

SHOWCASE

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78

elektor - 4/2008

products and services directory

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analyzer, signal generator,
multimeter, sound meter,
distortion analyzer, LCR meter.
Free to download and try.

SHOWCASE YOUR COMPANY HERE

Elektor Electronics has a feature to help
customers promote their business,

Showcase - a permanent feature of the
magazine where you will be able to showcase
your products and services.

For just £220 + VAT (£20 per issue for
eleven issues) Elektor will publish your
company name, website address and a
30-word description
For £330 + VAT for the year (£30 per
issue for eleven issues) we will publish
the above plus run a 3cm deep full colour

image - e.g. a product shot, a screen shot
from your site, a company logo - your
choice

Places are limited and spaces will go on
a strictly first come, first served basis.
So-please fax back your order today!

_ n

I wish to promote my company, please book my space:

• Text insertion only for £220 + VAT • Text and photo for £330 + VAT

NAME: ORGANISATION:

JOB TITLE:

ADDRESS:

TEL:

PLEASE COMPLETE COUPON BELOW AND FAX BACK TO 00-44-(0)1932 564998

COMPANY NAME

WEB ADDRESS

30- WORD DESCRIPTION

4/2008 - elektor

79

BOOKS, CD-ROMs, KITS & MODULES

A world of electronics

Ml iQC'T etVnJn

ute m

wiA CD-KOW

iWT wi CO’HOfA

AH* tfttn

IfltiT if CD-ROM

Annual

Johrgong

Annee

Joorgong

yy litenBS***!
frt, 1 .i*im»Vi««U

f*S#tWi*P*W trwl

HO urrrtftT^^^

All articles published in 2007

from a sin

Elektor 2007

This CD-ROM contains all articles published in Elektor Volume 2007. Using the supplied
Adobe Reader program, articles are presented in the same layout as originally found in the
magazine. An extensive search machine is available to locate keywords in any article. The
installation program now allows Elektor year volume CD-ROMs you have available to be
copied to hard disk, so you do not have to eject and insert your CDs when searching in another
year volume. With this CD-ROM you can produce hard copy of PCB layouts at printer resolution,
adapt PCB layouts using your favourite graphics program, zoom in / out on selected PCB areas
and export circuit diagrams and illustrations to other programs.

Modern technology for everyone

FPGA Course
in 9 chapters

The nine lessons on this courseware
CD-ROM are a step by step guide to
the world of Field Programmable Gate
Array technology. Subjects covered
include not just digital logic and bus
systems but also building an FPGA
Webserver, a 4-channel multimeter and
a USB controller. The CD also contains
PCB layout files in pdf format, a Quar-
tus manual, project software and various
supplementary instructions.

978-90-5381 -225-9 • £14.50 • US$ 29.00

More than 68,000 components

Elektor's Components
Database 4

The program package consists of eight
databanks covering ICs, germanium
and silicon transistors, FETs, diodes,
thyristors, triacs and optocouplers.
A further eleven applications cover the
calculation of, for example, LED series
droppers, zener diode series resistors,
voltage regulators and AMVs. A col-
our band decoder is included for de-
termining resistor and inductor values.
ECD 4 gives instant access to data on
more than 68,000 components. All
databank applications are fully in-
teractive, allowing the user to add,
edit and complete component data.
This CD-ROM is a must-have for all
electronics enthusiasts.

ISBN 978-90-5381-218-1 • £16.90 • US$33.80

ISBN 978-90-5381-159-7 • £15.90 • US$ 31.80

J \ J

Prices and item descriptions subject to change. E. & O.E

80

elektor - 04/2008

r

Visual Basic

5.® iD m HT 1444

\

for

Electro mc«
Engineering

ApiillcalJons

5.0, 6.0, VBA, .NET, 2005

Visual Basic for Electronics
Engineering Applications

This book is targeted towards those peo-
ple that want to control existing or self-
built hardware from their computer. After
familiarizing yourself with Visual Basic, its
development environment and the tool-
set it offers are discussed in detail. Each
topic is accompanied by clear, ready to
run code, and where necessary, sche-
matics are provided that will get your
projects up to speed in no time.

476 pages • ISBN 978-0-905705-68-2
£29.00 • US$ 58.00

PIC Microcontrollers

Silent alarm, poetry box, night buzzer and more!

PIC Microcontrollers

This hands-on book covers a series of
exciting and fun projects with PIC micro-
controllers. You can built more than 50
projects for your own use. The clear ex-
planations, schematics, and pictures of
each project on a breadboard make this
a fun activity. You can also use it as a study
guide. The technical background infor-
mation in each project explains why the
project is set up the way it is, including the
use of datasheets. Even after you've built
all the projects it will still be a valuable
reference guide to keep next to your PC.

446 pages • ISBN 978-0-905705-70-5
£27.00 • US$ 54.00

Datalogger "deLuxe"

(March 2008)

We have had the pleasure of proposing
various data acquisition units over the last
few years. This Datalogger "deLuxe" is a
nice exercise in product development. It
actually utilises an SD card as the media
for data storage. The hardware design
is compact and that makes the firmware
and software features even more interes-
ting.

(March 2008)

An ECIO acts as the brains of this PLC
board that has relays, opto-isolators CAN
(!) connectivity and an LCD. All this I/O
capacity together with Flowcode allows
the board to act as a versatile, powerful
PLC for quite complex control and auto-
mation projects. The LCD module is used
to display ASCII characters to the user as
a means of troubleshooting during the
software development stage or for moni-
toring the system.

Kit of parts incl. PCB, programmed control-
ler and display

Art.# 070745-71 • £71.75 • US$ 143.50

More information on the
Elektor Website:

www.elektor.com

Elektor

Regus Brentford
1 000 Great West Road
Brentford
TW8 9HH
United Kingdom
Tel.: +44 20 8261 4509
Fax: +44 20 8261 4447
Email: sales@elektor.com

r^lektor

LZ3 shop

Kit of parts incl. PCB , EClO-module and all
other components

Art.# 070786-71 • £76.00 • US$ 152.00

C0 2 Measurement

(January 2008)

Carbon dioxide (C02) is not just a threat
to the environment, it is also an impor-
tant and often ignored factor in deter-
mining air quality in the office and at
home. Too high a concentration of C02
leads to feelings of tiredness, disturbs
concentration, and causes headaches.
The Elektor C02 meter makes it easy to
determine the concentration of carbon
dioxide in the air. A microcontroller
monitors the measured value and can
trigger an alarm or start up a ventila-
tion system when a preset threshold is
exceeded.

Kit of parts, PCB , Sensor PCB, ATtiny26 and
display

Art.# 070802-71 • £107.50 • US$215.00

04/2008 - elektor

81

PRODUCT SHORTLIST, BESTSELLERS

~\

April 2008 (No. 376) £ US$

Elektor Internet Radio (EIR)

071 081-71 .... PCB, SMD-populated 1 1 5.00 230.00

CC2-AYR-Board 1

071 035-91 .... PCB, partly populated, ATM1 8 Controller module 7.30 1 4.60

071 035-92 .... PCB, partly populated ATM1 8-Testboard 27.00 54.00

080083-71 ....SMD-populated board and all parts 23.50 47.00

Frequency Response Sweep Oscillator

070951-41 ....Programmed controller 5.40 10.80

March 2008 (No. 375)

Data Logger "deLuxe"

070745-1 PCB, bare 16.30 32.60

070745-41 ....Programmed controller 19.90 39.80

070745-71 ....Kit of parts (PCB, programmed controller and display) ....71 .75 143.50

The Secrets of I2C

070600-1 PCB, bare 13.60 32.60

070600-41 ....Programmed controller 19.90 39.80

Cylon Voice

070859-41 ....Programmed controller 4.70 9.40

ECIO PLC

070786-1 PCB, bare 16.30 32.60

70786-71 Kit of parts (PCB, EClO-module, all other components)....76.00 152.00

February 2008 (No. 374)

LEDBUS System

070459-1 PCB, power module

070459-2 PCB, central

070459-41 .... PIC1 2F638-I/SN, programmed (power module)
070459-42 .... ATmega32-l 6PC, programmed (central)

RGB LED Mood Lighting

070892-1 PCB, bare

070892-2 PCB, bare

070892-3 PCB, bare

Surround Light for PC Monitor

070491-1 PCB, bare

070491-2 PCB, bare

LED Ringflash

070612-1 PCB, bare

070612-41 .... PIC1 6F628, programmed

070612-81 ....Software on CD-ROM

TV Surround Light

070487-1 PCB, bare

070487-41 .... Programmed controller

070487-42 .... Programmed controller

070487-81 ....Software on CD-ROM

CAN Explorer

060201 -1 PCB, MCP2515 and MCP2551 SN

060201 -W Testing & Error Sources Manual

Thermometer / Thermostat

070852-11 ....Software

www.thePCBshop.com

www.thePCBshop.com

3.10 6.20

13.80 27.60

www.thePCBshop.com

www.thePCBshop.com

www.thePCBshop.com

21.50 43.00

5.00 10.00

www.thePCBshop.com

10.50 21.00

5.20 10.40

21.50 43.00

12.70 25.40

10.50 21.00

5.20 10.40

www.thePCBshop.com
www.elektor.com

www.elektor.com

January 2008 (No. 373)

C0 2 Measurement

070802-1 PCB. bare

14.40...

28.80

070802-41 .... Programmed controller ATtiny26

070802-71 .... Kit of parts, PCB, Sensor PCB, ATtiny26

7.20...

14.40

and display

107.50...

...215.00

070802-81 Software on CD-ROM

5.20...

10.40

Anti-Standby Switch

070797-1 PCB, bare

14.40...

28.80

070797-41 .... ATtiny25, programmed

Control for Energy-saving Lamps

5.20...

10.40

070638-71 .... PCB, FAN771 ON and 2.5mH coil

Versatile DC Power Meter

14.40...

28.80

070559-1 PCB, bare

9.30...

18.60

070559-41 .... Programmed controller ATmega8-l 6P

9.00...

18.00

/

Prices and item descriptions subject to change. E. & O.E

Bestsellers

mr hi* \

PIC Microcontrollers

1

ISBN 978-0-905705-70-5

£27.00..

...US$54.00

2

Visual BaSIC for Electronics Engineering Applications

ISBN 978-0-905705-68-2

£29.00..

...US$58.00

3

309 Circuits

ISBN 978-0-905705-69-9

£19.95..

...US$39.95

4

PC Interfaces under Windows

ISBN 978-0-905705-65-1

£27.25..

...US$54.50

Microcontroller Basics

ISBN 978-0-905705-67-5 £19.50. US$ 39.00

lektor 2007

ISBN 978-90-5381-218-1 £16.90. US$ 33.80

FPGA

ISBN 978-90-5381-218-1

£16.90. US$ 33.80

ISBN 978-90-5381-159-7 £15.90. US$31.80

USB Toolbox

ISBN 978-90-5381-2 1 2-9 £1 9.90. US$ 39.80

Ethernet Toolbox

ISBN 978-90-5381-2 1 4-3 £1 8.90. US$ 37.90

C0 2 Measurement

Art.# 070802-71 E107.50...USS 215.00

USB Flash Board

Art. # 070125-71 £36.20 USS 72.40

Datalogger "deLuxe"

Art. # 070745-71 E71.75...USS 143.50

ECIO PLC

Art. # 070786-71

.£76.00 USS 152.00

Reflow Solder Controller

Art. # 060234-91 E171.80...USS 343.60

M Ik

Order quickly and safe through

www.elektor.com/shop

or use the Order Form near the end
of the magazine!

Elektor

Regus Brentford
1000 Great West Road
Brentford TW8 9HH * United Kingdom
Tel. +44 20 8261 4509
Fax +44 20 8261 4447
Email: sales@elektor.com

82

elektor - 04/2008

“Elektor? If our teachers knew
just how easily some concepts
can be explained...”

- Daniel Judd, 23, student - . >

Electronics at all the right levels

Secure a head start in electronics

with a Student Subscription!*

Advantages to subscribers:

Students qualify for a discount of no less than 20 %
compared to the normal price of an annual subscription

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INFO & MARKET

SNEAK PREVIEW

I *h ru in- %t-

Measure it with the PC and the soundcard

Twenty-odd years ago, PCs were so slow no one dreamed of using them for live measurements. By contrast,
today's machines happily run RTA (Real Time Analysis) and FFT (Fast Fourier Transformation) maths as a
background task. Obviously the options for measurements depend strongly on the software used and that's
why we examined a range of relevant products on the market. Also, the quality of the measurements results
returned will be determined to a large extent by the sound card used; well it so happens that an Elektor test

was planned for these.

Frequency Counter with ATtiny 2313

Only a few low-cost function generators and signal generators we've seen have a frequency display and an accurate fre-
quency adjustment. The module we propose cancels both shortcomings. The core of the circuit is an ATtiny231 3 microcontrol-
ler and that's about it for special ICs! Frequencies up to 5 MHz can be measured (without a prescaler!) and the LCD can be
switched between MHz, kHz and Hz readout.

Mini-display-board with M16C

Graphic displays have become affordable to the extent they can now be incorporated into small series and one-off applica-
tions. However the programming of a graphic display is far more complex than that of a display supporting text only. A
mini controller board based on the Ml 6C microcontroller from Renesas comes to your rescue by incorporating not only a
Display-on-Glass module but also a Tiny Basic interpreter that greatly simplifies the creation of graphics by your programs.

RESERVE YOUR COPY NOW! The April 2008 issue goes on sale on Thursday 24 April 2008 (UK distribution only).

UK mainland subscribers will receive the magazine between 1 8 and 22 April 2008. Article titles and magazine contents subject to change, please check www.elektor.com.

NEWSAGENTS ORDER FORM

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All magazine articles back to volume 2000 are available online in pdf format. The article summary and parts list (if applicable)
can be instantly viewed to help you positively identify an article. Article related items are also shown, including software down-

be downloaded.

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In the Elektor Shop you'll find all other products sold by the
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■ Choose »n option ▼

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■t ©

TTT panels arc compat&e with Wide KG*

itgh-pawer nr module support. 2 igbee

PCIe peripheral controller provide* flc.iblc
connectivity option*

Taw »nd Measurement Product Cu>d*

Briery Fuel CnuQC

Download Elektor

. Elektor February 2008
Elektor s 2008 TcOruary Issue can
be downloaded 1 The downloadable
version not only saves you time
and money but alio offers ful last
search options.

[^P*P

Construction prop

•r

K-venti Vie it CKine

Elektor is organising a
study trip to Chine

on 12*2! April of this year
and you're welcome to join ual

Please enter »our email
address t

More ©

Bator* luOm rttmg Queiuont
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r*o seeoorn

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taplorar 18;

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rpGA

Hell . 09

from e kit

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84

elektor - 4/2008

Description

Price each

Qty.

Total i

Order Code

CD-ROM FPGA Course

£14.50

CD-ROM Elektor 2007

(323

£16.90

CD-ROM E CD 4 £15.90

PIC Microcontrollers £ 27.00

Data Logger “deLuxe” £ 71.75

Free Elektor Catalogue 2008

Prices and item descriptions subject to change.

The publishers reserve the right to change prices
without prior notification. Prices and item descriptions
shown here supersede those in previous issues. E. & O.E.

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use $ prices, and send the order form to:

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Credit card VISA and MasterCard can be processed by mail, email, web, fax and telephone. Online ordering through our website is
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COMPONENTS

Components for projects appearing in Elektor are usually available from certain advertisers in this magazine. If difficulties in the supply
of components are envisaged, a source will normally be advised in the article. Note, however, that the source(s) given is (are) not exclusive.

TERMS OF BUSINESS

Delivery Although every effort will be made to dispatch your order within 2-3 weeks from receipt of your instructions, we can not guarantee this
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If the goods are returned because of a mistake on our part, we will refund the return postage. Damaged goods Claims for damaged goods
must be received at our Brentford office within 10-days (UK); 14-days (Europe) or 21 -days (all other countries). Cancelled orders All cancelled
orders will be subject to a 10% handling charge with a minimum charge of £5.00. Patents Patent protection may exist in respect of circuits,
devices, components, and so on, described in our books and magazines. Elektor does not accept responsibility or liability for failing to identify
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Elektor shall not be liable in contract, tort, or otherwise, for any loss or damage suffered by the purchaser whatsoever or howsoever arising out of, or in
connexion with, the supply of goods or services by Elektor other than to supply goods as described or, at the option of Elektor, to refund the purchaser
any money paid in respect of the goods. Law Any question relating to the supply of goods and services
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September 2007

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five per cent) of the full subscription price or £7.50, whichever is the
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cannot be cancelled after they have run for six months or more.

January 2008

«k

%

PIC Microcoirtrol\ej;5

Hekla*

r^lektor

L.~ SHOP

%

PIC Microcontrollers

Silent alarm, RGB fader, poetry box,
night bifrzer ahd more!

This hands-on book covers a series of exciting and fun
projects with PIC microcontrollers. You can built more
than 50 projects for your own use. The clear explanations,
schematics, and pictures of each project on a breadboard
make this a fun activity. You can also use it as a study
guide. The technical background information in each
project explains why the project is set up the way it is,
including the use of datasheets. All software used in this
book can be downloaded for free, including all of the
source code, a program editor, and the JAL open source
programming language.

446 pages • ISBN 978-0-905705-70-5 • £27.00 • US$ 54.00

Elektor

Reg us Brentford
1 000 Great West Road
Brentford TW8 9HH
United Kingdom
Tel. +44 20 8261 4509

Order quickly and safe through WWW.elektor.COIn/shop

Index of Advertisers

Allendale Electronics Ltd www.pcb-soldering.co.uk 13

ATC Semitec Ltd, Showcase www.atcsemitec.co.uk 78

Avit Research, Showcase www.avitresearch.co.uk 78

Beijing Draco www.ezpcb.com 33

Beta Layout, Showcase www.pcb-pool.com 33, 78

Bitscope Designs www.bitscope.com 3

Bowood Electronics Ltd, Showcase www.bowood-electronics.co.uk 78

Byvac Electronics, Showcase www.byvac.co.uk 78

Decibit Co. Ltd, Showcase www.decibit.com 78

Designer Systems, Showcase www.designersystems.co.uk 78

EasyDAQ, Showcase www.easydaq.biz 78

Easysync, Showcase www.easysync.co.uk 78

Elnec, Showcase www.elnec.com 78

EMCelettronica Sri, Showcase www.emcelettronica.com 78

Euro circuits www.eurocircuits.com 69

First Technology Transfer Ltd, Showcase . . www.ftt.co.uk 78

FlexiPanel Ltd, Showcase www.flexipanel.com 78

FLYPCB www.flypcb.com 55

Future Technology Devices, Showcase. . . . www.ftdichip.com 78

Futurlec, Showcase www.futurlec.com 78

ILP Electronics Ltd, Showcase www.iipeiectronics.com 78

Jaycar Electronics www.jaycarelectronics.co.uk 2

Labcenter www.labcenter.com 88

London Electronics College, Showcase . . . www.lec.org.uk 78

Marchand Electronics Inc, Showcase

MikroElektronika

MQP Electronics, Showcase

New Wave Concepts, Showcase . . .

Newbury Electronics

Nurve Networks

Paltronix

SK Pang Electronics

Peak Electronic Design

Pico

Quasar Electronics

Radiometrix, Showcase

Robot Electronics, Showcase

Robotiq, Showcase

Showcase

Tsien (UK) Ltd, Showcase

Ultraleds, Showcase

USB Instruments, Showcase

Virtins Technology, Showcase

www.marchandelec.com 79

www.mikroe.com 27, 29, 31

www.mqp.com 79

www.new-wave-concepts.com 79

www.newburyelectronics. co.uk 55

www.xgamestation.com 55

www.paltronix.com 13

www.skpang.co.uk 33

www.peakelec.co.uk 33

www.picotech.com 11

www.quasarelectronics.com 47

www.radiometrix.com 79

www. robot-electronics, co.uk 79

www.robotiq.co.uk 79

78, 79

www.componentbin.com 79

www.ultraleds.co.uk 79

www.usb-instruments.com 79

www.virtins.com 79

Advertising space for the issue of 19 May 2008
may be reserved not later than 22 April 2008

with Huson International Media - Cambridge House - Gogmore Lane -
Chertsey, Surrey KT 1 6 9AP - England - Telephone 01 932 564 999 -
Fax 01932 564998 - e-mail: p.brady@husonmedia.com to whom all
correspondence, copy instructions and artwork should be addressed.

4/2008 - elektor

87

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