www.elektor.com
Cardiac
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onitor
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From known andunknown sources
More solar powered circuits
January 2011
AUS$ 14.50 - NZ$17.50 - SAR 102.95 £4.80
+ Energy Saving Tips
9
77
D268
45 1
66
Integrate Touch Sensing Quickly and Easily
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Touch Screen Controllers
• Fully processed touch coordinates
• Projected Capacitive technology
- Multi-touch enabling gestures
- Low cost MCU implementation
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& Microchip
The Microchip name and logo, the Microchip logo and PIC are registered trademarks and mTouch is a trademark of Microchip Technology Incorporated in the U.S.A. and other countries. All other trademarks mentioned herein are property of their
respective companies. © 2010, MicrochipTechnology Incorporated, All Rights Reserved. ME259BEng/08.10
Microcontrollers Digital Signal Analog Memory
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An energetic edition
If I may offer something to ponder or
muse over during the winter holiday
period, try “how much energy is wasted
trying to devise and publish ways to save
energy, or get it from sustainable sources
and/or free sources”. I’m sure this conun-
drum will keep you busy, amused, frus-
trated, curious, excited or even hyperac-
tive for quite a few days. Let’s hope it does
not cause anxiety; if so, “there’s solace in
the pages to follow”. Whatever direction
yourthinking, pencilling, calculating and
head scratching veers off, it’s a comforting
thought that you are not alone. When in
doubt, write to the editor.
In this edition, in line with our cel-
ebrated 2011 Publishing Plan (it’s on our
website!), we have a focus on all-things-
energy — to which I should add ‘ener-
getic’. In this edition we cover green
energy, energy harvesting (page 14),
tips to save energy (page 34, some for
a good laugh too), and best of all, free
energy (page 52).
A lot of energy also went into producing
the other articles in this edition, which
should present a nice mix of traditional
electronics, microcontrollers and design
ideas. The Nixie Tube Thermometer on
page 24 bridges 50 years in a single
project, happily marrying a 21st century
microcontroller and associated program-
ming techniques with tube technology
from the 1950s. The result is a project
that’s sure to draw attention when
placed on your desk or mantelpiece.
Although I do not recommend bypassing
your local physician if you’re curious to
know your heart condition or other ail-
ments, why not draw your personal elec-
trocardiogram (ECG) with our Zigbee’d
cardiac monitor (page 56) and send him
your personal ECG graphs by email. If you
suspect you’re too FAT — go to page 18.
Myopic in the dark? — page 62.
In closing I congratulate my colleagues
in Elektor’s Dutch department on
the 50th Anniversary of their edition.
Believe it or not, ‘Elektuur’ as it was
called at the time started out in 1961
and was the mother of all international
versions of the magazine, including this
the English one born 14 years later. No
‘Double Dutch’ mockery but a laurel on
the front cover of all Elektor editions.
Goed gedaan jochiesl
Jan Buiting, Editor
6 Colophon
Who’s who at Elektor magazine.
8 The PCB Prototyper
Spreads its Wings
9 News & New Products
A monthly roundup of all the latest in
electronics land.
12 mbed Has Landed!
Simon Ford’s monthly column on the
Elektor/NXP mbed challenge
14 Economical Energy Harvesting
Presenting several designs that enable
circuits to be powered from solar energy.
18 Thin FAT
An overview of open source FAT
file system libraries for embedded
applications.
24 Nixie Tube Thermometer
This is what you get from combining
a modern microcontroller with a truly
classic display.
28 Flight Data Recorder
A speed and velocity recorder for
model airplanes, based on our ATM18
microcontroller module.
34 Energy Saving Tips
Seventeen ways, some tongue in cheek,
to reduce your energy bill and decrease
your personal carbon footprint.
38 All-Soft-555
Two new software utilities allow an ATtiny
microcontroller to act like the celebrated
555 timer, with a few features added!
43 E-Labs Inside: Under Scrutiny:
TheXmega Board
A look at Mikroelektronika’s latest
development system for the Xmega
processor.
44 E-Labs Inside:
Spotted at Electronica 2010
Some remarkable products seen last
November at the world’s leading
exhibition on state of the art electronics.
4
12-2010 elektor
CONTENTS
Volume 37
January 2011
no. 409
24 Nixie Tube Thermometer
Nixie tubes have a special charm all of their own. The author’s Sputnik-style
digital clock using the tubes appeared earlier in Elektor, and many variations
on the theme have appeared on the Internet. This digital thermometer, which
uses just two tubes, is, well, a little bit different.
48 Low-cost Headphone Amplifier
There have of course been numerous designs for headphone amplifiers before
this one, either more or less successful and simpler or more elaborate. The de-
sign presented in this article is straightforward, sounds guite good and can be
built using well-established components.
J23
52 Free Energy
Pursuits to make devices move perpetually or to generate energy from nothing
still occupy the attention of many people. Is it truly possible to generate free
energy, or are we simply deceiving ourselves and others? Here we describe a
selection of interesting ideas and projects.
J V J v
56 Wireless ECC
Many devices are available for recording or visualising electrocardiogram (ECG)
signals. The circuit proposed here uses a wireless link as an elegant solution
to the problem of galvanic isolation, completely eliminating any hazard to the
subject.
45 E-Labs Inside: Here Comes the Bus!
We call on our readers to assist with the
development of the Elektor Bus.
48 Low-cost Headphone Amplifier
Guess what, it’s straightforward,
sounds good and consists of dead
standard parts only.
52 Free Energy
Is it truly possible to generate free energy,
or are we deceiving ourselves and others?
56 Wireless ECG
In this project Zigbee modules are used to
build a system for wireless monitoring of
cardiac signals.
62 Groping in the Dark
Here we try to find out if a webcam is
any good for converting into a night
vision camera.
64 Design Tips:
Opamp versus Comparator
These devices look very similar with their
+ and - labels at certain pins, but ....
66 Support Board for Arduino Nano
In this article, we’re proposing a
motherboard that was originally designed
for a robotics application, but which can
very well be used for other jobs too.
68 Three out of Two Ain’t Bad
Adding a tacho signal to a two-wire fan as
used in PCs.
72 Notch Filters for Intermediate Fre-
quencies
Two simple filters, one RC and one LC,
for suppressing noise in communication
receivers.
75 Hexadoku
Our monthly puzzle with an electronics
touch.
76 Retronics: Tandberg Model 5 &
Stereo Record Amplifier (ca. 1959)
Regular feature on electronics ‘odd &
ancient’. Series Editor: Jan Buiting
84 Coming Attractions
Next month in Elektor magazine.
elektor 12-2010
5
e ektor
international media bv
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.
w m mm > m
ANALOGUE • DIGITAL
MICROCONTROLLERS & EMBEDDED^
AUDIO • TEST & MEASUREMENT^
* nt tt r
Volume 37, Number 409, January 2011 ISSN 1757-0875
Elektor 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 11 times a year with a double issue for July & August.
Elektor is also published in French, Spanish, American
English, 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,
Eduardo Corral, Ernst Krempelsauer, Jens Nickel, Clemens Valens.
Design staff Christian Vossen (Head),
Ton Ciesberts, Luc Lemmens.Jan Visser.
Editorial secretariat:
Hedwig Hennekens (secretariaat@elektor.nl)
Graphic design / DTP: Ciel Dols, Mart Schroijen
Managing Director / Publisher: Paul Snakkers
Marketing: Carlo van Nistelrooy
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/subs
6
01-2011 elektor
Elektor PCB Prototyper
W^ > A professional PCB router
with optional extensions!
This compact, professional PCB router can produce
complete PCBs quickly and very accurately. This makes
the PCB Prototyper an ideal tool for independent
developers, electronics labs and educational institutions
that need to produce prototype circuits quickly.
The PCB Prototyper puts an end to waiting for boards from
a PCB fabricator - you can make your own PCB the same
day and get on with the job. In addition, the PCB Proto-
typer is able to do much more than just making PCBs.
A variety of extension options are available for other
tasks, and a range of accessories is already available.
Specifications
• Dimensions: 440 x 350 x 350 mm (WxDxH)
• Workspace: 220x1 50x40 mm (XxYxZ)
• Weight: approx. 35 kg (78 lbs)
• Supply voltage: 1 1 0-240 VAC, 50/60 Hz
• Integrated high-speed spindle motor;
maximum 40,000 rpm (adjustable)
• Integrated dust extraction (vacuum system
not included)
• USB port for connection to PC
• Includes user-friendly Windows-based
software with integrated PCB software
module
Ordering
The complete machine (including software) is
priced at € 3,500 / £3,1 00 / US $4,900 plus VAT.
The shipping charges for UK delivery are £70.
Customers in other countries, please enquire
at sales@elektor.com.
Further information and ordering at
www.elektor.comlpcbprototyper
Email: subscriptions@elektor.com
Rates and terms are given on the Subscription Order Form.
Head Office: Elektor International Media b.v.
P.O.Box ii NL-6114-ZC Susteren The Netherlands
Telephone: (+31) 46 4389444, Fax: (+31) 46 4370161
Distribution:
Seymour, 2 East Poultry Street, London ECiA, England
Telephone:+44 207 429 4073
UK Advertising:
Huson International Media, Cambridge House,
Cogmore Lane, Chertsey, Surrey KT16 9AP, England.
Telephone: +44 1932 564999, Fax: +44 1932 564998
Email: r.elgar@husonmedia.com
Internet: www.husonmedia.com
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
carriers and article texts published in our books and magazines
(other than third-party advertisements) are copyright Elektor
International Media b.v. and may not be reproduced or transmit-
ted in any form or by any means, including photocopying, scan-
ning an recording, in whole or in part without prior written per-
mission from the Publisher. Such written permission must also be
obtained before any part of this publication is stored in a retrieval
system of any nature. Patent protection 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 Publisher to alter the text and
design, and to use the contents in other Elektor International
Media publications and activities. The Publisher cannot guaran-
tee 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. 2010 Printed in the Netherlands
elektor 01-2011
7
ELEKTOR PCB PROTOTYPER
The PCB Prototyper Spreads Its Wings
By Harry Baggen (Elektor Netherlands Editorial)
Last month we published the first article on the new PCB Proto-
typer, a general-purpose PCB router whose relatively low price
compared to similar machines makes it suitable for users outside
the normal target group of schools and companies. Visitors to the
recent Elektor Live! event had an opportunity to see a prototype
of the machine and several PCBs produced by the machine. They
were all impressed by the quality of the routed PCBs, and more than
few hobbyists are probably already thinking about other ways to
use the machine for their own purposes (and how to explain this
to their spouse).
The PCB Prototyper is more than just a PCB router. As mentioned
in the previous article, it is designed to be easily adapted to other
tasks. This is reflected in the modular architecture of the mechani-
cal construction and the software.
Our first article prompted a variety of responses from readers who
saw a lot of potential applications in addition to those originally
envisaged by Colinbus and Elektor. However, some of these appli-
cations ran into problems due to the dimensions of the machine.
This had more to do with the space available under the Plexiglas
cover than with the size of the working area. As we explained last
month, the aim is to develop a machine that can do much more
than just produce high-quality routed PCBs. Users must be able to
adapt the machine and the software as desired in order to achieve
what is effectively a machine tailored to their specific needs. To
avoid unduly restricting the scope
of future extensions, the enclosure
has been modified to be somewhat
larger than originally planned. The
new outside dimensions are now
455 x 385 x 360 mm (1 8 x 1 5.2 x 1 4.2
inch) (B x D x H).
Along with the enlarged enclosure,
the Y axis has been extended slightly.
This does not relate to the area avail-
able for PCB routing or the size of
the work table, but instead to the
space that may be occupied by future
accessories. For instance, a camera
mounted on the multifunctional head
must be able to view the area acces-
sible to the multifunctional head itself
(in other words, the working area of
the engraving module). Originally this
was only possible with a very small
camera, but now the PCB Prototyper
can also be used with larger cameras,
such as those used for scientific pur-
poses. Now there is also more room
for fitting a laser or a scanner.
Thanks to input from our readers, the PCB Prototyper is now ready
for more than just numerous alternative applications. Several new
accessories have also been developed or are presently being devel-
oped. They will be described in more detail in a future issue of in
Elektor. Readers with interesting ideas or wishes are invited to con-
tact Colinbus or Elektor to make them known. The more we hear
from you, the better we can adapt the software and accessories to
the wishes of all users.
( 100869 -I)
For more information on the PCB Prototyper, visit
www.elektor.com/pcbprototyper
8
01-2011 elektor
NEWS & NEW PRODUCTS
Step-up DC-DC converter
features highest efficiency
austriamicrosystems has introduced the
AS1310, an ultra low quiescent current
hysteretic step-up DC-DC converter opti-
mized for light loads (60 mA) and the high-
est efficiency — up to 92 %. With 1 pA the
AS1 31 0 step-up converter also features the
industry’s lowest quiescent current, oper-
ates over a wide 0.7 V to 3.6 V battery sup-
ply, and provides output voltages between
1.8 V and 3.3 V. Even at loads as light as
1 00 pA, efficiency still reaches 85%, signifi-
AS 1 310 DC-DC Boost
Consuming Only IgA
cantly increasing battery life.
Since the supply voltage of many battery
powered applications is moving from 3 V to
1 .8 V, the AS1 31 0 boost DC-DC converter
was designed to be able to generate both;
many competitive DC-DC converters are not
able to do so. If the input voltage exceeds
the output voltage the device goes into a
feed-through mode and the input is directly
connected to the output voltage. The fea-
tures and performance oftheASI 310 boost
DC-DC converter make it very well suited
for single- and dual-cell powered devices,
including blood glucose meters, remote
controls, hearing aids, wireless mouse or
any light-load application. The AS1310
DC-DC converter is an especially good fit for
applications in which a lot of time is spent
in an idle mode and therefore draws only a
small current.
In order to save power the AS1 310 also fea-
tures a shutdown mode in which it draws
less than 100 nA. During shutdown, the
battery is disconnected from the output. In
addition, the AS1 31 0 step-up DC-DC con-
verter allows adjustable low battery detec-
tion. If the battery voltage decreases below
the threshold defined by two external resis-
tors, the output is pulled to logic low. This
signal is used to indicate ‘low battery’, so no
separate supervisory ICs are needed.
The AS1 31 0 boost DC-DC converter is avail-
able in a TDFN 8-pin 2x2 mm package and
operates over a temperature range of -40°C
to +85 9 C with a wide power supply range of
0.7 to 3.6 V.
www.austriamicrosystems.com (100820-I)
More applications for
Hameg HMP2000 series
Hameg’s HMP2000 series High Power Sup-
plies were improved by adding an impor-
tant feature: Channel 2, till now an aux-
iliary channel with 0-5. 5V output, was
upgraded to a full-grown 0-32 V channel.
This improves the universal applicabil-
ity significantly, also with regard to future
applications. The HMP2020 now features
two identical channels with 0-32V out-
put voltage, one delivering 1 0 A, the other
5 A. The HMP2030 now has three identical
channels with 0-32 V, 0-5 A outputs. Also
new are the LabView, CVI, and PLUG&PLAY
drivers for all types of the HMP series which
also includes the HMP4030 with three, and
the HMP4040 with four, identical 0-32 V /
i imi la !i ii — ■ - , , m ...
* 16,800 V 5,800 fl .-
5500 V 6.830 A
32 mv imn -
0-1 0 A channels. Hence all programming
systems and interfaces (USB, LAN, IEEE, and
RS-232) popular in the ATE world are now
being supported. The drivers are available
at no cost for downloading from the web
page below.
www.hameg.com/HMP 2030 (100820-I)
QuickUSB® Module
offers 20 megabytes/sec
transfer rates
Bitwise Systems, designers and manufac-
turers of custom embedded systems and
PC interface products, has announced the
availability of their QuickUSB Module that
makes adding Hi-speed USB 2.0 to new or
existing products fast and easy.
Under ordinary circumstances, imple-
menting a USB peripheral requires a func-
tional understanding of the USB protocol as
well as a considerable amount of firmware
and software development and stringent
compliance testing. The Bitwise Systems
QuickUSB Module provides a very-desirable
alternative for adding hi-speed USB 2.0 for
speeds as much as 40x faster than USB 1.1.
The QuickUSB® QUSB2 module makes
adding Hi-Speed USB 2.0 to new or existing
products fast and easy by integrating all the
hardware, firmware, and software needed
to implement a general-purpose USB end-
point into a simple plug-in module and
development library. The module may sim-
ply be used as a development station when
combined with the QuickUSB Adapter Board
or QuickUSB Evaluation Board. It may also
be designed as a plug-in module for new
products, or designed directly into new
products and licensed
using the QuickUSB iChipPack or QuickUSB
EEPROMs.
The QuickUSB module contains parallel and
serial hardware ports that are connected to
circuits within the peripheral. The QuickUSB
library included with the module provides
user-callable software functions that trans-
fer data to and from the hardware ports
over the USB. The designer then obtains
multiple ports of flexible, high-speed USB
connectivity without requiring a prior in-
depth knowledge of USB.
QuickUSB differs from other USB modules in
that it performs high-speed data transfers
of 20 megabytes/sec or more via its high-
speed parallel port. This makes QuickUSB
the idea interface for high-performance USB
peripherals such as FPGA, DSP or microcon-
troller based data acquisition systems.
The QuickUSB QUSB2 Module is a 2” x 1 . 5 ”
(50 x 38 mm) circuit board that implements
a bus-powered Hi-speed USB 2.0 endpoint
terminating in a single 80-pin target inter-
elektor 01-2011
9
NEWS & NEW PRODUCTS
face connector. The target interface con-
sists of:
One 8- or 1 6-bit high-speed parallel port
Up to five general-purpose 8-bit parallel I/O
ports
Two RS-232 ports
One I2C master port
One SPI master port
One FPGA configuration port (Altera PS or
XilinxSS)
2 KB of user-available, non-volatile memory
Software, libraries and drivers for Windows
32/64, Linux and Mac OS X
The QuickUSB Module, QUSB2 is priced at
$149.00 ea. It is available immediately in
small quantities.
www.quickusb.com (100820-MI)
DC/DC LED driver with 48
watts output power in
DIP24 package
With the release of AMLD-Z, Aimtec
launches via MSC Vertriebs GmbH the
third series in its line of DC/DC LED Drivers.
Offered in a DIP24 packages, the AMLD-Z
are feature rich LED drivers and meet the
rigorous demands for environment friendly
LED lighting solutions. From a wide (8:1)
input range of 7-60 VDC, the AMLD-Z series
of LED drivers provide constant output cur-
rents ranging from 1 50 to 1 000 mA, gener-
ating from 6 to 48 watts of power to main-
tain the constant colour and brightness that
is required by today’s most demanding LED
applications.
The new AMLD-Z series provides remote
ON/OFF control function in addition to
both PWM and analog voltage
dimming control
( 0 - 100 %).
Open and short
circuit protec-
tion works con-
tinuously until the
short circuit condi-
tion is resolved, pro-
tecting the converter,
the LED lights, and the converter’s input cir-
cuit from extremely high currents a short to
ground causes.
Boasting efficiencies as high as 97 %,
Aimtec’s LED drivers are designed to be
as reliable as the LEDs they drive, allowing
Parallax: Spinneret Web Server and Propeller Platform USB
The new Spinneret Web Server from Paral-
lax may be small — at less than 1 V 2 by 4 inches
— but it is a feature packed development plat-
form. The built-in MicroSD card socket and
real-time clock allow ample room for time-
stamped file and data storage, and the over-
sized EEPROM can store non-volatile data for
use when there is no MicroSD card present.
As an open-source hardware design, all design
including layout, schematics, and firmware —
are available under licenses that allow free dis-
tribution and reuse. This means that the Spin-
neret Web Server’s design can be incorporated into new applications royalty free and without a non-disclosure agreement.
The Spinneret Web Server is an Ethernet based development board for the Propeller microcontroller. Web page content, files, and logs
can be stored on a MicroSD card. The serial EEPROM has 32 KB for storing a Propeller program and 32 KB for non-volatile data storage,
independent of the MicroSD card. There is a real-time clock controller for time stamping files and events and a backup capacitorthat
will keep the clock running through extended power outages. There is a serial programming header and two auxiliary I/O connections,
one for level-shifted open collector communications over a three-pin data/power/ground cable, and a the second is a 1 2-pin socket
for direct 3.3 volt I/O connections. There are eight status LEDs on the PCB, plus two that are repeated on the Ethernet jack. One of the
status LEDs is user controllable and shares a line with a button that can be read under user control. A second button resets the Propel-
ler to reload the firmware from the EEPROM. Spinneret retails at $49.99.
Combining a 64 KB EEPROM, 5 MHz removable crystal, 1 .5 A power regulation, USB, and a microSD card slot on a compact, bread-
board and protoboard friendly module, the Propeller Platform USB is an easy-to-use development tool for the multicore Propeller
microcontroller. All 32 Propeller I/O are available via pin sockets, along with 5 V and 3.3 V regulated power.
Features include:
80 MHz 8-Core Parallax Propeller P8X32A with removable 5 MHz crystal
64 KB EEPROM for long-term program and data storage
5 V and 3.3 V 1 .5A ultra LDO voltage regulators accept 5.5 V minimum power input
USB-to-serial interface for loading and communication
2.1 mm center-positive barrel jack and screw terminal power connections
2.8” x 2.5” footprint with pin sockets to add additional Platform modules or connect to a breadboard.
microSD card slot connected to P0-P3.
The new Propeller Platform USB retails at $49.99. At www.Parallax.com, search “Propeller Platform.”
www.Parallax.com/go/spinneret (100820-V)
10
01-2011 elektor
them to be used at an operating temperature of -40 to +85 degrees
Celsius at full load for compatible with a wide range of LEDs applica-
tions from variety of manufacturers without the need for any exter-
nal components.
www.msc-ge.com (100821— IV)
Pololu: simple motor controllers
Pololu announces the release of its Simple Motor Controllers, a
line of motor drivers with enhanced capabilities that make basic
control of DC motors easy. With four sup-
ported high-level interfaces — USB
for direct connection to a com-
puter, TTL serial for use
with embedded sys-
tems, RC hobby servo
pulses for use as an RC-
controlled electronic speed
control (ESC), and analogue
voltages for use with a poten-
tiometer or analogue joystick-
-and a wide array of configurable
settings, these devices simplify con-
trolling motors in a variety of projects.
Units can be paired to enable mixed RC
or analogue control of differential-drive robots, and they can be
daisy-chained with additional Pololu servo and motor controllers
on a single serial line.
A free configuration program, available for Windows and Linux,
allows for quick controller configuration over USB (no more
dip switches or jumpers) and simplifies initial testing. Con-
troller features include: acceleration and deceleration limits to
decrease mechanical stress on the system, optional safety con-
trols to avoid unexpectedly powering the motor, a wizard for
automatic RC and analogue input calibration, and support for
limit switches.
The controller versions offer a wide operating voltage range up
to 5.5-40 V and continuous current ratings from 1 2 A up to 25 A,
which means they can deliver up to several hundred watts in a small
form factor. The unit prices are $39.95, $43.95, $54.95, and $59.95
for the Simple Motor Controller 1 8v1 5 (item #1 377), 24v1 2 (item
#1 379), 1 8v25 (item #1 381 ), and 24v23 (item #1 383), respectively.
www.pololu.com/smc (100820-VI)
IP67 wall mounted enclosures for harsh
environments
The new 1 555F range from Hammond Electronics is a family of rug-
ged IP67 sealed enclosures designed for wall mounting PCB-based
or DIN rail based equipment such as security components, control
equipment and radio repeaters used in harsh industrial environ-
ments or outdoor applications. Available in RAL 7035 light gray and
moulded in either general purpose ABS or flameproof polycarbon-
ate, the units have a number of innovative features that provide
excellent functionality. In use, the lid is secured to the wall or other
surface using the slots moulded
into the integral flanges. The
screws securing the lid to the
base are then inaccessible as
they are against the surface,
giving security against unau-
thorised tampering. For maxi-
mum security, the units can be
attached to the wall with tam-
per-resistant screws. Standoffs
are moulded into both the lid
and the base and, apart from
in the two smallest sizes, DIN
rail mounting tabs are also pro-
vided. The bottom of the base
features a moulded recess for a
membrane keyboard or label.
The initial six sizes range from 1 20 x 66 x 42mm to 1 59 x 91 x
62mm; all lids are fitted with captive M4 stainless steel screws that
engage with stainless steel inserts in the base, allowing repeti-
tive assembly and disassembly. Environmental sealing is achieved
through a tongue and groove design and a moulded silicon rubber
gasket; all fixings are outside the gasket seal.
www.hammondmfg.com (100820-VII)
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elektor 01-2011
11
NXP MBED DESIGN CHALLENGE
mbed Has Landed!
Question: What do you get when you land 75
engineers and boxes of all sorts of electronic
components together in a concrete UFO? Answer:
You get the biggest mbed hands-on workshop
we’ve ever attempted!
mbed
DESIGN
CHALLENGE
m
By Simon Ford (UK)
I just arrived back from a trip to Elektor Live!, a daylong Elektor event
in Eindhoven, The Netherlands. This was an excellent outing for
anyone interested in electronics, and it had the added attraction of
being held in the ‘Evoluon’ conference centre, which is an impressive
saucer-shaped building that was actually built as a Science Museum
by the Philips company in the 1 960s. It was certainly the first time
I’d ever been able to ask a taxi driver to “take us to the UFO.”
Our mission was to run a hands-on mbed workshop in the
morning. Whilst I had originally guessed 1 5 to 20 people might
sign up, the email I had received the week before confirmed
Elektor had closed applications on reaching 75 people. Yes, 75!
That beats any of our previous workshops by a large margin,
and as a result we spent much of the night before collecting
together as many electronics kits as we could get our hands on.
We arrived with all sorts of SparkFun Electronics breakout boards
(accelerometers, gyros, screens, sensors, trackballs, RFID readers,
etc.), mbed baseboards, and even some of the robots we used in
a recent ‘mbed Robot Racing’ event. We figured it was certainly
enough to keep people busy.
The workshop was a great success. We had an impressive
assortment of attendees, ranging from total novices to experts,
working with microcontrollers and electronics — all day, every
day! This was a great testament to our focus on tackling the
requirements of prototyping itself rather than catering to designers
with particular skill sets. We want mbed to be a useful tool for
novices and experts alike. Given the success, we’ll be looking to
run these events elsewhere. Tell us if one should be run near you!
While we were there, we bumped in to lots of people who were
already mbed users, and it turns out some of them have been
working on ideas for the NXP mbed Design Challenge 2010. I
managed to get a few of them to reveal what they were up to. If
their ideas are anything to go by, we should see a very interesting
and diverse range of entries for this competition. I’m really looking
forward to seeing people posting their results as these projects
come together.
For those of you who haven’t seen it yet, note that NXP
Semiconductors, Circuit Cellar , and Elektor launched the NXP
mbed Design Challenge in September 201 0. The challenge puts
up prizes for designers who share reference designs and building
blocks that can help other mbed users prototype even faster. After
all, the goal of fast innovation and invention is the real motivation
behind mbed. We asked ourselves: What can be done to get out
of the way and let innovators experiment quickly to invent future
applications for microcontrollers?
We want all sorts of entries. Examples include innovative ideas,
whacky applications, impressive engineering feats, and simple
solutions to real problems. These projects will demonstrate new
ideas and techniques. They’ll inspire other designers and influence
the development of future products, so everyone can do their bit to
help move the industry forward. And, if being part of this mission
isn’t motivation enough, take a look at the Circuit Cellar website to
see the prizes up for grabs!
The submission deadline is 1 pm EST on February 28, 201 1 . If you
have an mbed, be sure to obtain a Registration Number on the
Circuit Cellar a nd then get prototyping. With the rapid way in which
the mbed community is growing, there will be lots of people to help
you out along the way, so we hope the process will be good fun too.
Good luck!
(100873)
Simon Ford, co-creator of mbed, is a lifelong electronics and comput-
er engineer. He works at ARM, and before starting mbed was techni-
cal lead for the ARMv7/NEON architecture now found in most new
smartphones.
To enter the NXP mbed Design Challenge 2010, go to: www.circuitcellar.com/nxpmbeddesignchallenge/
12
01-2011 elektor
V
mbed
DESIGN
CHALLENGE
Start prototyping the
mbed way!
Redefine the way people build
prototypes! NXP and ARM/mbed
are challenging you to use the
mbed NXP LPC1768 prototyping
board and mbed online "Cloud"
compiler to develop an
innovative hardware- or
software-based application.
Succeed, and you could walk
away with part of a prize pool
worth $10,000!
Deadline for entries is
February 28, 201 1
Register for the challenge at
www.circuitcellar.com/nxpmbeddesignchallenge
NXP mbed Design Challenge empowered by:
mbed
ENERGY HARVESTING
Economical
Energy Harvesting
Every little bit helps
By Rolf Blijleven (Netherlands)
Alternative energy is a hot topic. In this article we
describe several options for powering circuits from
solar energy. As you can see, significant results
can be achieved with a modest investment and
a bit of sunlight. What’s more, once it works the
power is free.
In this article we show you several ways to power your circuits from
an alternative energy source instead of batteries or the AC power
grid. Here we focus on solar energy, but the methods described here
can certainly be used with other energy sources as well. As you can
see, quite respectable results can be obtained at a modest cost with
a clever combination of modern and less modern components.
Virtually all alternative energy sources have three practical
shortcomings: they are not
continuously available, or if they
are they do not supply a constant
amount of power, and the
available power is often too low
for direct use. The engineering
discipline that deals with these
problems (and finds solutions for
them) is called energy harvesting, which is the art of collecting
energy whenever a source provides some energy and storing the
collected energy until enough is available to be used for a practical
purpose. Energy harvesting is receiving more and more attention
in recent years, and rightly so.
The block diagram of an energy harvesting system is shown in
Figure 1 . A transducer is necessary to convert a particular form of
energy into electricity. The voltage must be raised to a usable level,
and the energy must be stored in a buffer. The energy level in the
buffer must be monitored to determine when enough is available.
At this point, it can be provided to the load - a circuit that does
something with the energy. This continues until the stored energy
is used up, after which the cycle begins again.
If you want to put this idea into practice immediately, a ready-to-use
kit is available from Texas Instruments (EZ-2500-SEH PI). It is based
on the Cymbet EnerChip EH solar energy harvesting module I 2 1 and
provides a complete platform for an autonomous domestic wireless
sensor system. This kit is primarily intended for rapid prototyping. If
you’d rather put something together yourself, read on...
Eternal energy
As already mentioned, we focus
on solar energy here, so the
transducer is a solar cell. We
looked for solar cells available
in the price range of 30 pounds/
euros. All manufacturers specify
the dimensions and the maximum voltage and current. If you
calculate the corresponding power figures (voltage times current
divided by the area in square centimetres), you will see that there is
a large spread — from slightly more than 2 W/cm 2 for a cell with an
area of just under 25 cm 2 to a hefty 1 2 W/cm 2 for a cell with nearly
the same size. If you also check the prices, you can see that the
higher-priced models are by no means always better. Accordingly,
it’s certainly worthwhile to shop around on the Web and do a bit
of maths.
The yield per unit of incident light (watt/lux) is only rarely specified,
which is a pity because this is an important parameter. From
measurements on a cell with a price of 4 euros we saw that the
significant results with a
modest investment
14
01-2011 elektor
ENERGY HARVESTING
figure of 200 mA at 1 V promised on the package was achieved only
with perpendicular illumination on a cloudless day. With subdued
artificial light or rainy weather, it amounted to no more than around
0.02 mA at 0.2 V.
Mind the gap
Most electronic components need at least 3 V to do anything useful,
and small motors typically need at least 5 V. The gap between what
a solar cell can deliver and what we need for practical use is thus
approximately 3 V or more. Of course, you can bridge this gap by
using a relatively large solar panel or connecting several cells in
series or parallel, which amounts to the same thing. However, other
solutions are also possible, which brings us to the second block in
the block diagram. Two options are described below.
The first is based on the Maxim MAXI 044 switched-capacitor voltage
converter 1C I 3 !. As illustrated in Figure 2a and 2b, it connects an
external capacitor C e alternately in parallel with the input voltage
V\ n and in reverse series with storage capacitor C s . The operating
current of the 1C is approximately 30 pA, which is 50 jiA less than its
predecessor, the ICL7660, with which it is fully pin compatible. The
circuit shown in Figure 3 doubles the voltage from the solar cell, and
with several MAXI 055s operating in cascade you can multiply the
input voltage even more (Figure 4). Here C e has a value of 1 0 pF and
C s is the storage device in the block diagram, which can be as large
as you wish. We have more to say about this shortly.
Retro technology
We weren’t satisfied with a minimum input voltage level of 1 .5 V. It
should actually be possible to harvest voltages lower than 1 V, and
preferably even lower than the transistor base-emitter threshold
voltage of 0.6 V. After a bit of detective work, we found the solution
shown in Figure 5. The principle is not new. It’s based on the work
of Cockroft and Walton in the 1 930s, with further refinements by
Dickson in the 1 970s, after whom this technique is named. The
Dickson charge pump is enjoying renewed interested in recent years
because it can be used (in a further improved form) as a separate
unit in an 1C to boost the supply voltage for the rest of the 1C to the
desired level Kl. However, it can also be implemented quite well with
discrete components.
Briefly, it works as follows (see Figure 4): X and X are anti-phase
clock signals. When X is low, the voltage at the first node is U in - V d ,
where V d is the forward voltage drop over the diode. When X goes
high, the voltage rises to \/ x + (V m - \/ d ), where \/ x is the amplitude
of the clock signal. This causes D2 to conduct until the voltage at
node 2 is \Z in + (V x - V d ) - V d . If you connect enough of these stages
in series, you can raise a low input voltage to any desired level. We
used an astable multivibrator (AMV) built from bipolar transistors
as the clock source. The result is shown in Figure 5. The necessary
component values can be calculated from the formula for the
output voltage:
f
Vout —Vin+N-
in
V x -
c
\
V
c + c,
-Vd-
out
{C + C s )-f c
-Vd
OSC J
Figure 1. Basic block diagram of an energy harvesting system.
Figure 2. Operating principle of voltage multiplication with a
switched capacitor. C e is connected to the supply voltage in
phase ‘a’ and in series with C s in phase ‘b’. The resulting output
voltage is -V { , so the total voltage between the input and the
output is doubled.
Figure 3. A MAXI 044 configured as a voltage doubler (a)
and as a voltage
elektor 01-2011
15
ENERGY HARVESTING
Figure 5. Voltage multiplication with an AMV and a Dickson charge
pump. Voltages as low as 200 mV can be harvested if the AMV is
built with germanium transistors.
In addition to \/ x , V d and V m , the terms of this formula are N (the
number of stages), C (the value of capacitors Cl , C2, etc.), C p (the
parasitic capacitance), / out (the output current), and f osc (the clock
frequency). For the enthusiasts, the derivation of this formula can
be found in reference Kl with a bit of searching.
v+
Figure 6. This circuit monitors the voltage of the storage buffer
(V+) and switches on the MOSFET when enough stored energy is
available.
Applied math
The formula clearly shows several things. Firstly, normal diodes with
a forward voltage drop (\/ d ) of 0.6 V have a highly detrimental effect
on the result, but this problem can mitigated by using Schottky
diodes, which have a forward voltage drop of only 0.2 V (or as little
as 75 mV at low current levels). Secondly, the parasitic capacitance
(C p ) of several dozen picofarads is hardly negligible. If the value of
Cis kept small, it takes less time for the pump to start filling up the
storage capacitor, but this also reduces the contribution of V x . As
V x is equal to the input voltage, it must be used economically. It is
therefore better to make C much larger than C p (for example, 1 00 pF
or 220 pF), so the ratio of C to C+ C p is nearly 1 . Thirdly, the effect of
the load current / out can be minimised by choosing a clock frequency
that is as high as possible.
With an AMV constructed using BC550C transistors, useful energy
can be harvested at voltages of around 0.6 V or more. Can we do
even better? On eBay we found type AC1 75 germanium transistors,
and with them the circuit starts working at around 200 mV (with
thanks to an idea from Vladimir Mitrovic published in the December
2009 edition of Elektor). And once the AMV starts working, it
continues to operate until the input voltage drops to approximately
80% of the level necessary to start working.
Storage space wanted
Encouraged by this result, we encountered the next challenge:
energy storage. To but it briefly, electrolytic capacitors need several
hours to charge, batteries need several days, and both lose most of
their charge overnight. An electrolytic capacitor is therefore better,
and the question is how big it should be.
The answer may be calculated from:
/ = Cxd\//dt
C = /xdt/dV
For example, if C s must supply a current of 1 mAand the voltage on
C s may drop from 5 V to 2.5 V in the process, we need an electrolytic
capacitor with a value of 0.8 mF (1 mA x 2 s x 2.5 V), so two 4700 jllF
capacitors connected in parallel are more than enough. Two
seconds may seem like a short time, but bear in mind that an ATtiny
(for example) can operate with as little as 200 pA and can certainly
do something useful in two seconds, such as reporting a reading in
a ZigBee network. Supercaps and other heavy-duty devices can be
used for more demanding tasks. Expensive? Not at all. We picked
up a 0.1 5-F device for about 6 pounds, at a recent electronics car
boot sale.
Economical watchdog
The final stages of the block diagram are the voltage monitor and
the switch that supplies power to the load. The difficulty here is that
C s must be monitored constantly to see whether it has accumulated
enough energy, but at the same time no current should be drawn
from it. We regarded a separate battery supply for the monitor as
unacceptable. Once again we found the solution in a Maxim device:
the MAX931 is an ultra low power, low cost comparator with 2%
16
01-2011 elektor
ENERGY HARVESTING
reference, and it draws almost no current as long as \/ cc is less than
2.5 V. Above that point this user-friendly 1C draws only 2.5 pA.
Furthermore, the input leakage current is only around 0.03 nA.
This means that high-value resistors can be used to set the trigger
thresholds, so the current consumption remains in the microampere
range. Figure 6 shows the schematic diagram. The selected resistor
values yield an upper trigger threshold of approximately 5 V and a
lower trigger threshold of approximately 2 V. This broad hysteresis
is necessary to ensure that the comparator output level is always
either high or low. The calculation of the resistor values is explained
in the data sheet I 5 !. The resistor and capacitor at the output are
optional; they keep the MOSFET in the on state as long as possible.
The MOSFET must have a low gate-source on voltage (Ic-son) and
the lowest possible on resistance (Ro-son)- We found the ZVN4424A
suitable for currents up to 260 mA, and the IRF3708 can be used for
higher-current tasks. Both devices are readily available (from Farnell
and other sources).
Conclusion
In this article we have examined several ideas that you can use
according to your own wishes. Germanium transistors are still
available in relatively small quantities as ‘new old stock’, but they
are no longer being made (unless someone rediscovers this market
niche). All of the circuits can easily be built on prototyping board,
so there are no PCB layouts in this article.
Of course, you are probably wondering what these circuits can
actually do in practice. The answer depends largely on the position
of the solar cell relative to the sun, the weather, and the required
voltage. With a panel costing around 1 0 pounds, we were able to
charge our 0.1 5 F capacitor to approximately 9 V and use it to power
a small 1 2 -V pump. The cycle time for this was 5 minutes in full
sun and approximately 30 minutes in rainy weather, which is not
a problem for a small pump that supplies water to a few garden
plants. We also placed a chime arrangement with a small 5-V
motor on the window sill. On very cloudy days it played a couple
of times a day, but in sunny weather we heard it every hour. Solar
energy is free, but especially in the winter it’s scarce. Bear in mind
that large organisms, such as broad-leafed trees, spend the entire
winter waiting for better times. In a certain sense, these circuits are
comparable to such organisms.
(100533)
Internet Links and References
1 . http://focus.ti.com/docs/toolsw/folders/print/
ez430-rf2500-seh.html
2. www.cymbet.com/content/products-energy-harvesting.asp
3. www.maxim-ic.com/datasheet/index.mvp/id/1 01 7
4. Louie Pylarinos et al., Charge Pumps: An Overview,
Department of Electrical and Computer Engineering, University of
Toronto (www.scribd.com/doc/21 06051 6/Charge-Pumps)
5. www.maxim-ic.com/datasheet/index.mvp/id/1 21 9
Figure 7. The circuit of
Figure 6 implemented
with an IRF3708 and
a 0.1 5-MF electrolytic
capacitor drives the small
pump at the rear.
The connector is for the
solar panel.
Figure 8. The
arrangement of Figure 7
in an experimental
waterproof setup.
Figure 9. A solar cell
supplies 0.2 to 1 V
to a Dickson charge
pump with 17 stages
constructed on a piece of
prototyping board. The
motor starts running at
approximately 5 V.
elektor 01-2011
17
PROGRAMMING
Thin FAT
Open source FAT file system libraries
for embedded applications
By Stephen Bernhoeft (UK)
The FAT file system has become the de
facto universally readable file system.
A number of architecture-neutral,
open-source implementations
exist. Before using a solution,
it behoves the developer to
understand something about how the File
Allocation Table system actually works.
Before choosing a solution, read this!
' pr r Jr am,
** 4 /*»*?*.
/fee
fs**
** p fmsr
'wof St* _ i jj, Jg"*»m*.d4 C
The core idea
A File Allocation Table (FAT) holds a collection of linked lists. There
is one list associated with each file and each successive list element
describes where to find the next part of a file and where to find the
next list element.
The lists are the simplest conceivable. Each element consists only
of a pointer to the next element — there is no explicit data in the
FAT. Given that there is no explicit data in the FAT then how can it
be useful? The answer is that the data is implicit. Each non-reserved
value in a FAT chain has two meanings: one is that of pointer to next
list element, the other is pointer to file data.
A FAT can be considered as an array (Figure 1). Given the value
of FAT[x] we can find the next item. For example, if the FAT chain
for a given file begins at FAT[3] and this holds ‘14’ (OxE), the next
item in the list is FAT[14].
Now FAT[ 1 4] may hold the
value ‘4’ so the next item
is FAT[4]. If FAT[x] holds
the reserved value ‘EOC’
(End Of Cluster) then that
is the end of that chain.
The first two FAT entries ( FAT [ 0 ] , FAT [ 1 ] ) are reserved. No FAT
entry can ever point to these first two entries. The first, FAT [ 0 ]
holds a legacy field, the ‘media byte’. The second, FAT[1 ], is used
by the operating system to record a ‘clean’ or ‘dirty’ shutdown. An
important corollary is this: when interpreted as a cluster number,
a FAT entry must first have 2 subtracted from it. If a FAT entry is 14,
then the cluster number is (14-2) = 1 2 (OxC). So in figure 1 FAT[1 4]
also points at cluster 14-2 = 12 which holds the first part of the
actual file data, and FAT[1 1 ] points at cluster 11 -2 = 9 which holds
the final part of the actual file data.
This can be considered the basis of the FAT system, however much
extra detail must be added to describe a real implementation.
FAT entry point
How is FAT navigated? The idea is that we begin at the root directory.
A directory is a single file, which holds a series of 32-byte entries
(this is true for FAT1 6 as well as FAT32). Each 32-byte entry holds
a structure describing another file or directory. The entry includes
create time, file attributes and a ‘pointer into the FAT’. The way we
initially locate the root directory differs from FAT1 6 to FAT32. With
FAT1 6 we calculate the location and size of the root directory using
the Volume Boot Record (VBR). In FAT32, the VBR gives the FAT
chain start-index of the root directory file — a FAT32 root directory
file can grow without
bound. In both cases we
can also work out where
the FAT itself begins using
information in the VBR.
The first FAT element in
a FAT chain is not found in the FAT itself, it is found in a directory
entry. The single exception to this rule is the FAT32 VBR field BPB_
RootClus, which contains the first FAT element in the FAT chain for
the root directory.
Disk space is allocated in clusters of contiguous hardware sectors.
Because the cluster size is known and clusters are composed of
contiguous sectors, FAT needs only the starting sector of a given
cluster. Sector size is usually 51 2 bytes although FAT supports sector
sizes of 51 2, 1 024, 2048 and 4096 bytes.
What is the purpose of clusters? It is to keep the number of FAT-
FAT uses little endian format
18
01-2011 elektor
PROGRAMMING
Media
nzr
\ y ————————
[ [Optional MBR]
FAT32
FAT chain
MyFile
txt
20
0003
SubO
10
modbus
c
20
Root Directory File
r
Typical
FAT chain
for
one file
FAT
A
X 0
X 1
0000 2
000E 3 .
000B 4
0000 5
0000 6
0000 7
0000 8
0000 9
0000 A
FFFF B
0000 c
0000°
, 0004 E
0000 F
0003-2 = 0001
— f
— I
l
l
l
1
1
1
1
1
j 000E-2 = 000C
1
1
! 0004-2 = 0002
i
[000B-2 = 0009
l
1
Last file
cluster
Cluster of sectors
(First sector @0009)
Cluster of sectors
(First sector @0002)
Cluster of sectors
(First sector @000C)
First file
cluster
Cluster of sectors
(First sector @0001)
100569 - 11
Figure 1 . Overview of FAT file system and media organisation. (OxFFFF is the end of the example FAT chain). Partitioned media hold a
Master Boot Record (MBR), not located in a partition, which contains the primary partition table. Each entry in this table tells us the
partition type (FAT, OS/2, Linux, etc.), starting sector and count of sectors in the partition.
addressable regions at a sensible value: with a cluster size of 1 , a
large file would have a very long FAT chain; one element for each
logical sector occupied by the file. With a cluster size of 64, we
only need a single FAT entry for every 64 logical sectors, with the
disadvantage that a file using 65 logical sectors (blocks) wastes
63 logical sectors.
Open source FAT libraries
Many FAT implementations are available on the net, commercial and
free, and sometimes they are part of a larger project. It was decided
to concentrate on open-source, platform-independent FAT libraries.
The minimum requirements for the tests were:
• Access to root directory files;
• Create/Open/Read/Write/Truncate;
• FAT32 support (for maximum media compatibility);
• ANSI C (C90 preferred).
We also have an additional preference:
• There is no obligation to publish user code.
In other words, ideally we should be free to use the code as we like.
Is this inconsistent with the spirit of open source? Not necessarily:
I may be happy to share the source to a module (such as a FAT
library), but it may be commercially suicidal to share the code to a
complete application, such as a novel piece of test gear.
To aid testing, a ‘library test suite’ was developed. This is a DOS-like
interface (Figure 2) allowing the user to interactively test the library
elektor 01-2011
19
PROGRAMMING
Formattin
As embedded programmers we typically do not require a format function. If you do need to format flash media, be aware that it is usually
a mistake to use one of the standard PC utilities. The reason is that the various file system structures (partitions, clusters, etc.) should be
aligned to so-called erase blocks. It is not possible to erase one byte. Instead, an entire erase block (perhaps 64 sectors) must be erased.
Careful positioning of FAT structures done by the SD card manufacturer assists the card’s internal logic in performing its main tasks:
• Wear levelling — ensuring long life of the card.
• Fast read and write access
If the format program is not ‘SD-Card aware’, performance and card life will suffer.
Only two of the surveyed libraries actually support a format function:
• EFSL - Maybe! The function mkfs_makevfat is undocumented by the authors, and the few references found on the web are not
encouraging. Perhaps the default volume label, ‘DISCOSMASH!’ is a warning...
• FatFs - Flash media aware.
using DOS-like commands via a terminal emulator such as Realterm.
The test suite is available on the web page for this article PI.
When customising a generic library one typically has to define:
• A media-initialise function;
• A sector write function;
• A sector read function.
There will usually be a library configuration file where the amount
of file buffering can be adjusted (more RAM means faster file I/O)
and the types of file operation required can be specified (more ROM
means greater functionality).
The example target was Microchip’s PIC18F Starter Kit 1
(DM1 80021 ), running code generated by the Cl 8 compiler, with
all optimisations enabled. Compilation was also done for the
PIC24FJ256GB1 1 0 using the C30 compiler. This compiler allows a
code size/speed trade-off: the smallest possible code size option
was chosen. No hardware was available to test the results, however.
EFSL
The ‘state of play’ with EFSL is a little hard to judge. The obvious
download at sourceforge.net/projects/efsl/ is efsl-0.3.6. The
SD cards and licensin
I SanDisk
'
Many microcontroller development boards nowadays have an SD card connector. In most of these
systems the SD card connector is simply hooked up to the SPI bus of the microcontroller, without the
use of a dedicated host controller. The SD card standard is controlled by the SD Card Association, “an
industry-wide organization setting industry standards to promote SD product acceptance in a variety
of applications”. The SD Card Association requires that all companies planning to or manufacturing
SD host products (e.g. cell phones, cameras or computers) or SD ancillary products (e.g. adapters or
SD I/O cards) join the SD Card Association and enter into a Host/Ancillary Product License Agreement
(HALA) with the SD Card Association and the SD-3C, LLC. This is regardless of how the card may be
used, in SPI mode only or not.
It will be very likely that your system will not comply with the host
controller specification and so your board can not qualify as an SD
host product. But please don’t take our word for it; this is what
we make of it. If in doubt, ask the SD Card Association. Elektor
cannot accept any responsibility for any loss or problems caused by
improper interpretation of the SD Card Association’s rules.
www.sdcard.org/developers
SDCard
So, if you design or build such a board, do you need to pay a license fee? Even if the SD Card
Association would like you to, the answer is probably No. According to the document SD Host
Controller Simplified Specification Version 2.00 February 8, 2007 an SD host product is a system
containing a host controller
that complies with this
specification. According to
the SD Card Association the
host controller is situated
between the SD host connector and the SD bus driver.
20
01-2011 elektor
PROGRAMMING
accompanying manual warns “This version is currently not really
usable”. The current stable version is 0.2.8. The source tree comes
with some example targets and good documentation.
To use EFSL first modify the example header files to suit your target.
For the PIC, the following files/modifications apply:
config-sample-avr . h
/ /#define HW_ENDP0INT_ATMEGA12 8_SD
#define HW_ENDPOINT_P IC_SD
/ /#define DEBUG
interface . h
#elif defined (HW_ENDPOINT_P IC_SD )
#include "pic_efsl.h"
types . h
Confirm euintl 6 etc are correct.
Configuration options exist to trade-off performance for RAM
usage. However, there are no configuration options available to
trade functionality off against code-size. For example, file write is
always available.
The core user contribution is to define one structure and four
functions (see examples atmegal 28. h, atmegal 28. c). Equivalent
PIC files (pic_efsl.h, sd.c) were written for this article.
In config.h, we chose “#define ioman_numbuffer l”. The
manual recommends one buffer per File-System object, two
buffers per file, an extra buffer for seek/rewrite operations, and
an extra three buffers to “smoothen” file list operations.
For our test program (one file open
with seek and list),
this is already
sect ,
1000
txt
read:
FAT test
FatFs Mir
22 TEE1.TXI
SUB0UI"!
SUBS
3 iten
FatFs>o|ren test.txt
pAtFs>P4&d 1000
Hello
<2> Goodbye
Requested: 1009. read: ;
FatFs >seek 4
Fptr = 4
FatFs >L7idte hi-lio
5 bvftRfi vritfcftn, fp: 9^
FatFs >c lose
1*0=0 FR_OK
FtiLFs>ui)i;n t oat .txt
FatFs ad 1003
<±> hi-hn
<2> Goodbye
Faquested; 1000,, read: !
FatFE>opei> new-01»tsct
FatFs 1234567
7 bytes written. fp= 7.
FatFs >u lose
rc =0 Ffl_OK
FatFs>i'eari 1000
fil*
file sise
7x512 = 3584 bytes. We
could not afford that on the example
target, and so we used just one buffer.
Licence
“...you are allowed to statically link against the library without having
to license your own code as GPL as we//.”
Conclusion
Figure 2. Screenshot of a library test session.
EFSL is quite widely used — for example NXP’s AN1 091 6 and ST’s
AN3102. It does not appear to be as widely used as FatFs however.
It is worrying that the new version, 0.3.6, seems to have been
abandoned.
On the other hand, the actual source code and documentation are
of a high standard, and the fact that major chip vendors have used
in their application notes is reassuring.
Internet
sourceforge.net/projects/efsl/files/
FatFs
FatFs has an impressive
collection of sample projects.
Along with code, there are
schematics showing
interfaces to MMC/
SD, IDE Hard Disk
and Compact Flash
media. Platforms
covered are ATMega, H8,
LPC2368, PIC24, pPD70F3706, and
Win32 (PC-based). There are extensive statistics showing code
footprints and performance benchmarks for these platforms with
various library configurations on the FatFs website. There is fair
scope for trading code size against functionality, although some
functions are grouped. Thus (f_truncate, f_stat, f_getfree, f_unlink,
f_mkdir, f_chmod, and f_rename) cannot be individually enabled.
Adapting FatFs to your needs is similar to the EFSL process. The core
user contribution is to define six functions — declared in diskio.h.
elektor 01-2011
21
PROGRAMMING
Microsoft applied for, and was granted, a series of patents for key
parts of the FAT file system in the mid-1 990s. On December 3, 2003
Microsoft announced that it would be offering licenses for use of its
FAT specification and “associated intellectual property” at the cost
of a $ 0.25 royalty per unit sold, with a $250,000 maximum royalty
per license agreement. To this end, Microsoft cited four patents on
the FAT file system as the basis of its intellectual property claims. All four pertain to long-filename extensions to FAT first seen in Windows 95.
Many technical commentators have concluded that these patents only cover FAT implementations that include support for long filenames,
and that removable solid state media and consumer devices only using short names would be unaffected, (source: Wikipedia)
Four of these functions are essentially identical to those needed
by EFSL.
When testing FatFs with the Cl 8 compiler it was necessary to
amend the code in ff.c to avoid run-time errors:
int chk_chr (const char* str, int chr)
must be re-declared as
int chk_chr (static char
rom *str, int chr)
This is a compiler-specific
issue.
Licence
No restriction on use.
Conclusion
FatFs is very widely used, and is being actively maintained. It
appears to be the most popular library, and thus should be relatively
bug-free. The range of sample targets and statistics makes this
library stand out. The source code is not easy to follow, and is very
cramped in style. Documentation is reasonable, but not as clear as it
could be. The user forum is useful
but primitive.
Internet
elm-chan.org/fsw/ff/00index_e.html
Petit FatFs
This is a minimal version
of FatFs targeted at 8-bit
microcontrollers. It offers very
limited write functionality:
1. You may only overwrite an
existing file;
2. You cannot create a file;
3. You cannot extend the file.
In short, it does not satisfy our minimum requirements.
Licence
No restriction on use.
Conclusion
Petit FatFs is useful on (sma
systems that only need read
capability like MP3 players and
digital picture frames.
Internet
elm-chan.org/fsw/ff/00index_p.html
SD-Reader
The web site gives a good impression. This library differs from
others in at least three important ways:
1. Source requires C99 compiler. Thus, for example, the Cl 8
compiler is unsuitable.
2. It is specifically targeted at SD cards.
3. The user interface is very different from the other FAT libraries.
It is not sector-based; rather it is byte-offset based, where the
byte offset is not aligned to a 51 2-byte boundary. However, the
supplied file, sd_raw.c, provides
most of the code required to use
the library.
One issue is that there seems
to be no way for user code to
access the file position, because
the ‘field pos’ is defined in a C file
rather than an H file. (There is no
ftell function either).
Another aspect is that file open
does not use the familiar ‘a+’
etc file mode parameters. In the
tests, custom code had to be
written to replicate the *a+* mode
22
01-2011 elektor
PROGRAMMING
Table 1. A comparison of several open source FAT libraries
Library
Compiler
Target
Code
Data
Comments
EFSLO.2.8
Cl 8 v3.35
PIC46J50
34292
1258
C30 v3.23
PIC24FJ256GB1 1 0
15516
1266
ARMCC
STM32F1 07xx
8338
—
FatFs R0.08
Cl 8 v3.35
PIC46J50
21572
658
Read & Write, _FS_MINIMIZE= 1.
C30 v3.23
PIC24FJ256GB1 1 0
9099
826
WinAVR
AVR
8386/
12700
~600
Read & Write, _FS_MINIMIZE = 3/0
CH38
H8
6980/
10686
C30
PIC24
7395/
11376
V850ES
CA850
4930/
7730
SHC
SH-2A
5600/
8592
WinARM
ARM7TDMI
6636/
10520
VC6
x86
4923/
7545
sd-reader
C30 v3.23
PIC24FJ256GB1 1 0
5616
204
The code footprint appears remarkably small. Flowever,
this is probably because a lot of the work is done in the
interface code which does the media-specific access.
File sd_raw.c uses 4341 bytes. For comparison, EFSL’s
interface code was 2649 bytes, and that for FatFs was
1071 bytes.
File i/o library
Cl 8 v3.35
PIC46J50
24648
2256
Large data space footprint
C30 v3.23
PIC24FJ256GB1 1 0
35958
2258
(append if file exists, else create).
Licence
GPLv2 or LGPLv2.1 .
Conclusion
An interesting project, but currently lacks the functionality of the
other examples and is sd/mmc specific, rather than media-generic.
Data/variable requirements are the smallest of all the reviewed
solutions.
Internet
www.roland-riegel.de/sd-reader/index.html
FAT File 10 Library
As happens too often with open source projects, this library has
gone missing since the article was written. We decided to publish
our findings anyway in case it pops up again. The version we used is
included in the download on the web page for this article PL
Using and configuring this library is particularly straightforward.
The only user-code demands made by this library are sector read /
write routines (it is up to you to call your own initialisation code).
In fat_opts.h, one may choose whether to support long file names, the
number of buffers, and number of simultaneously open files. It was not
possible to test the code on the sample PIC1 8 target due to lack of RAM
(PIC variable space). The library required 2256 bytes of RAM out of a
total on-chip of 3.8 KB. By ‘inventing’ extra RAM via the Cl 8 linker script
however, some Cl 8 estimated statistics were derived.
Licence
GPL. If you include GPL software in your project, you must release
the source code of that project too. If you would like a version with
a more permissive license for use in closed source commercial
applications please contact the author for details.
Conclusion
An easy-to-use library, but fairly high code space and data space
requirements.
Internet
The FAT File I/O library used to be here: www.robs-projects.com/
filelib.html
(100569)
Internet Links
[1 ] www.elektor.com/ 1 00569
elektor 01-2011
23
THERMOMETER
Nixie Tube
Thermometer
Retro temperature display
By Dieter Laues (Germany)
In this article we describe the union of a modern microcontroller with a
classic display technology to create a novel temperature indicator. In its
transparent enclosure the device will set off any mantelpiece to advantage
and what’s more, the unit even doubles up as a night light. An external
sensor allows the temperature at any desired location to be displayed.
Nixie tubes have a special charm all of their
own. The author’s Sputnik-style digital
clock using the tubes appeared in Elektor
in January 2007, and many variations on
the theme have appeared on the inter-
net. This digital thermometer, which uses
just two tubes, is a little bit different. The
temperature measurement itself is done
by a DS1820 one-wire sensor, while an
AT89C2051 microcontroller processes the
temperature information and drives the
Nixie tubes.
Hardware
Special attention was paid when designing
this circuit to make construction as straight-
forward as possible. There are only a few
components, no SMDs, and no adjustments
to be made. The circuit is shown in Figure 1
and is arranged as follows.
An external mains power supply provides
between 1 2 V and 1 5 V DC to the circuit.
From this voltage IC6 generates the 5 V
operating voltage for microcontroller IC1
and nixie drivers IC2 and IC3.
The high voltage supply required for the
tubes is generated using a step-up con-
verter based around IC5. The MC34063
device used is a tried-and-tested PWM
controller that is easy to find, inexpensive,
and available in a leaded package. External
MOSFET switching transistorTI , coil LI and
Schottky diode D6 generate and smooth
the high-voltage output. The output volt-
age of the regulator is given by
\/ 0 = y re f x R9/R10
and with the values given in the circuit dia-
gram, we have
V 0 = 1 .25 V x 820k / 5.6k = 1 83 V.
This relatively high voltage has the advan-
tage that the display will be bright. In his
prototype the author used a value of 680 k£l
for R9 in the interests of reducing power dis-
sipation: in this case the voltage across C4 is
about 1 52 V. Using values between 680 l<£2
and 820 k£l for R9 you can adjust the volt-
age and hence the display brightness to
taste.
R4 and R5 take the high voltage supply to
the anodes of the IN-16 tubes, giving an
operating voltage of around 143 V (with
1 80 V across C4), and an anode current of
about 1.72 mA. This is a suitable operat-
ing point for Nixie tubes of Russian manu-
facture, which are inexpensive and easy to
obtain. Also, the Russian Nixie driver 1C type
K1 55ID1 can be substituted for the 741 41 ,
which is now hard to obtain.
In the interests of maximising brightness, it
was decided not to multiplex the displays.
The tiny MCS-51 -compatible microcon-
troller fits all the software required to read
temperature values and convert them to
BCD format for output in its 2 KB of program
memory. The 12 MHz clock is produced
using XI , which is a resonator with built-in
load capacitors. The RC network compris-
ing R6 and Cl provides a power-on reset
function, and IC4 (a Maxim-Dallas DS1 820)
is the temperature sensor itself. The device
comes factory-calibrated and delivers tem-
perature readings serially over its one-wire
bus to pin PI. 3 on the microcontroller. If
jumper JP1 (on P3.4) is fitted, the tempera-
ture is shown in Fahrenheit.
Options
LEDs D1 to D4 and their series resistors
R2, R3 and R7 are optional and can be dis-
pensed with if desired. D1 and D2 show the
temperature trend, while D3 and D4 pro-
vide a little additional effect lighting to the
tubes.
D1 and D2 indicate whether it is getting
warmer or colder. Red LED D2 lights when
the temperature is rising, while blue LED D1
lights when the temperature is falling. If the
temperature is steady from one reading to
the next, neither LED lights.
A temperature reading is taken more than
once a second, and so it can happen that
the display alternates fairly rapidly between
two adjacent values. To make the display
less distracting it would be possible to aver-
age readings over a longer period: readers
are welcome to experiment in this direction
as there are a few bytes of program mem-
ory to spare, and commented source code
can be downloaded at PI free of charge.
LEDs D3 and D4 illuminate the Nixie tubes
from below, one LED for each tube. Holes
are provided at suitable points on the
printed circuit board to allow the light
through, with the LEDs soldered to the
underside of the board, pointing upwards.
The brightness of the LEDs can be adjusted
by changing the value of R7, and of course
24
01-2011 elektor
THERMOMETER
Features
Display range:
Temperature sensor:
Power supply:
Current consumption:
Tubes:
Microcontroller:
Firmware:
Options:
0 to 99 (Celsius or Fahrenheit)
Maxim-Dallas DS1 820, accuracy 0.5 l<
AC power adaptor, 1 2 V to 1 5 V DC
170 mA at 12 V
Russian IN-16, 13-way solder connections
Atmel AT89C2051 (available ready-programmed)
BASCOM (source and hex files available for free download)
Choice of Celsius or Fahrenheit display
Tube illumination
LED trend (warmer/colder) indicators
+180V*
_2_
vi
Nixie IN16
V2
Nixie IN16
+5V
O
TCT
R1
©
DQ
DS1820
o
CM
12
13
14
15
_9
11
(? 0 1 2 3 4 5 6 7 8 9
IC1
P1.4
AIN1/P1.1
P1.5
P1.2
P1.6
P1.3
P1.7
AT89C2051
P3.4/T0
P3.0/RXD
P3.5/T1
P3.1/TXD
P3.7
P3.2/INT0
P3.3/INT1
CNJ
0
2
X
X
O
un
XI
iDi
CM
O)
CO
CO
CO
1
CM
O
LT>
CO
CM
a>
CO
OO
CO
CM
O
1
1
H
f— 1
H
H
H
+5V
l r>
CO
O
0
CO
LT)
CO
H
O
1
OO
o>
1
H
H
H
CM
H
H
CO
CD
H
rH
H
H
H
CM
O
OOOOOOOOOO
VCC
GND
IC3-X
74141
o
<
CM
<
CO
<
12M H z
D5
1N4004
rM
CIO
lOOu
25V
IC6
7805
C9
lOOu
25V
+5V
o
C8
lOOn
8
o
SC ^ Cl
IC5
IS SE
MC34063
C7
100n
+180V*
O
C4
lOu
250 V
090784 - 11
Figure 1 . Simplicity is the watchword: only a few components, no SMDs, and no adjustments.
elektor 01-2011
25
THERMOMETER
COMPONENT LIST
Resistors
R1 =4.7ka
R2,R3 = 220£1
R4,R5 = 22kft
R 6 = 10l<^
R7 = 1 ka
R 8 = 1 50£1
R9 = 820 1<^
R10 = 5.6k£l
Capacitors
Cl = 1 0jiF 63V, radial, 0.1 in. lead pitch
C2,C3,C5,C7,C8 = lOOnF ceramic, 0.2. in.
lead pitch
C4 = 1 0juF 250V, radial, 0.2 in. lead pitch
C 6 = 470pF, 0.2 in. lead pitch
C9,C1 0 = 1 0OpF 25V, radial, 0.1 in. lead
pitch
Inductor
LI = 330pH, 1 A, axial, DxL = 1 1x32.5
mm max., e.g. Epcos B82500CA8 or
Fastron 77 A-331 M-00
Semiconductors
D1 ,D3,D4 = LED, 3mm, blue
D2 = LED, 3 mm, red
D5 = 1 N4004
Figure 2. The easy-to-populate printed circuit
board is available from the Elektor Shop.
D 6 = BYV26 (e.g. Vishay)
T1 = IRF820 (Vishay, International Rectifier
IRF820PBF)
IC1 = AT89C2051-24PU, programmed, Elek-
tor# 090784-41*
IC2,IC3 = 74141 or K1 55ID1 (Russian:
K155MA1)
IC4 = DS1 8S20 (Maxim/Dallas)
IC5 = MC34063
IC 6 = 7805 (TO220)
Miscellaneous
XI = 1 2MFIz resonator, 3-pin, e.g. AEL
Crystals type Cl 2M000000L003
JP1 = 2-pin pinheader, 0.1 in. lead pitch
(optional jumper, see text)
K1 = 2-way PCB screw terminal, lead pitch
5mm
VI ,V2 = Nixie tube type IN-1 6 (e.g.
Sovtek l/IH-16)
PCB # 090784-1 * (artwork free download
at [1])
* seewww.elektor.com/090784 or
Elektor Shop page.
you can select the size and colour of the
LEDs as you wish. In the author’s prototype
he used blue LEDs, which were particularly
effective in the dark in conjunction with the
orange glow of the tubes. Unfortunately,
the IN-1 6 tubes bought for the Elektor lab
prototype came with an opaque grey plastic
base, and so it was not possible to recreate
the LED illumination effect.
Software
The software running in the microcontroller
was written using the BASCOM 8051 com-
piler from MCS Electronics, which includes
commands to support the one-wire bus
interface.
After initialisation of all variables and of
the sensor the software runs in an infinite
loop fetching a new temperature reading
roughly every 750 ms. The value is con-
verted to Fahrenheit if required, the frac-
tional part is discarded, and the result con-
verted to tens and units digits in BCD format
to be passed to the Nixie drivers. The read-
ing is also stored and used in the next itera-
tion of the loop to drive the trend indicators
D1 and D2.
Despite the simplicity of the software
structure, it turned out to be harder than
expected to get the timing of communica-
tions with the DS1 820 right. The bus must
be reset between requests, and the chip
must not be disturbed by a request while it
is carrying out a measurement. Sometimes
a mistimed request can make the chip get
into a state where it stops responding alto-
gether and must be reset. However, none of
this need concern the constructor, who can
just use the software downloaded from I 1 ]
or a ready-programmed microcontroller
from the Elektor Shop.
If the temperature should go negative the
display will simply show ‘00’ (the minimum
reading) and temperatures above 100 °C
are displayed as ‘99’ (the maximum read-
ing). The display also flashes ‘99’ if the tem-
perature sensor is not connected or is faulty.
Construction and operation
All components apart from the Nixie tubes
are fitted to the printed circuit board (Fig-
ure 2), which is available from the Elektor
Shop. At first, just solder in sockets for IC1 ,
IC2 and IC3. Take care to check the polarity
of the electrolytic capacitors, and in particu-
lar of C4, before applying power! Now plug
in the mains adaptor, and check that a volt-
age of approximately 1 80 V appears across
C4 (if R9 is 820 k£l). Take care here with the
high voltages, and do not touch the printed
circuit board while power is applied.
Now allow C4 to discharge and fit the tubes.
On the back of each tube, exactly in the cen-
tre behind the glass there is a light stripe
that indicates pin 1 (see also the datasheet).
It can be quite fiddly to thread thirteen
wires of identical length through the holes
in the board, so it is a good idea to trim the
wires to different lengths so that each one
is a little shorter than the next, like organ
pipes. It is then easy to thread the wires one
at a time, starting with the longest. Finally
make sure the tube is vertical and solder the
connections.
Now fit the Nixie driver ICs and the pro-
grammed microcontroller in their sockets.
When power is reapplied the temperature
should appear on the displays.
Enclosure
The prototype was mounted in a clear
acrylic pipe of diameter 80 mm cut to
75 mm in length. This type of pipe is hard
26
01-2011 elektor
THERMOMETER
f "T*
^ \
H
- %
to come by in the DIY sheds, but a wide
selection of sizes and wall thicknesses is
available from online emporia. It is impor-
tant to cut the pipe exactly perpendicular to
its axis as any unevenness in the end faces
will look unsightly, although it is relatively
easy to work acrylic by hand using a file or
sandpaper. A circular saw
is the best way to cut the
pipe, but if necessary it
can be done by hand,
for example using a
hacksaw with
a fine-toothed
metal blade. A
U-shaped mitre
block of the type
intended to help with cut-
ting skirting boards makes a
good guide for a clean square cut.
The side cheeks were made from
solid wooden wheels bought from a DIY
shop with a diameter of 1 00 mm. A single
cut created a flat on the wheel on which the
unit stands. It would be possible to paint the
side cheeks, or to make them from acrylic
sheet with a thickness of around 4 mm.
Two holes were made in the pipe, one for
a jack socket for the temperature sensor
and the other for the power socket. The
side cheeks were each drilled for two M3
screws at exactly the right height for the
fixing bracket, which must be threaded on
at least one side.
Figure 3. The prototype board populated and
tested in the Elektor labs.
Of course, the thermometer can be used for
other purposes too, such as measuring the
temperature inside another device (perhaps
that tube amplifier you have alongside it?).
Internet Link
[1 ] www.elektor.com/090784 (web pages for
this project)
Next the sockets were wired to the appro-
priate points on the printed circuit board
for the sensor and power supply, and the
assembly slid into the pipe. The side cheeks
were screwed to the interior brackets from
outside using M3 screws. The board is now
suspended between the two side cheeks,
which in turn are fixed to the acrylic pipe.
With a little judicious twisting of the assem-
bly things can be arranged so that the board
is inclined upwards, making it easier to see
the Nixie tubes from slightly above.
Because of the heat generated by the tubes
and the voltage regulator it is not practical
to mount the temperature sensor on the
board or inside the enclosure. To measure
the ambient temperature, place the sensor
away from the device on the end of a cable.
Conclusion
The circuit generates high voltages inter-
nally, and so it is important to use an insu-
lating enclosure with no exposed metal
parts. Nylon screws and insulating sockets
should also be used, or alternatively the
mains adaptor and the temperature sen-
sor can be connected permanently using
well-insulated wires with suitable strain
relief and grommets for the holes in the
enclosure. The connections to the DS1 820
should also be insulated, or the whole sen-
sor assembly can be enclosed in heatshrink
tubing. The reward for all this effort is the
pleasure of seeing warm orange, occasion-
ally flickering digits lighting up your living
room!
(090784)
Design Resources
www.atmel.com/atmel/acrobat/doc0368.pdf
(AT89C2051 datasheet)
http://datasheets.maxim-ic.com/en/ds/
DS1 8S20.pdf (DS1 820 datasheet)
http://www.tube-tester.com/sites/nixie/data/
in16.htm
(information on the IN-1 6 tube)
http://gadget.mda.or.jp/pdf/K155ID1
(K1 55ID1 datasheet)
www.onsemi.com/pub_link/Collateral/
MC34063A-D.PDF (MC34063 datasheet)
www.die-wuestens.de/
(Nixie tubes and drivers)
elektor 01-2011
27
ATMi8
Flight Data Recorder
For hikes and rides too
Your Captain: Gregory Ester (France)
No need for a piggy-back board any more — the
ATM18 module takes to the air to give you
a whole heap of very useful information
recorded during your flight in a radio-
controlled plane. Are you ready? Well,
fasten your seatbelts, we’re about to
take off. Welcome aboard flight ATM18
in the company of Elektor!
So you haven’t actually got your pilot’s
licence yet, even though you know how to
fly a Cessna or a Big Lama? When a curious
passer-by shyly enquired: “What speed does
your little plane fly at?” my off-the-top-of-
my-head answer was received with a certain
degree of scepticism. In this sort of situa-
tion, the project described here may be of
interest to you.
Measuring the speed
The MPR-AIR-V3 detector consists of a Pitot-
static tube and allows us to measure the
speed of any craft moving in the air, as long
as the plane doesn’t go over 563 km/h...
Version 3 of this module also lets us display
the result directly on the PCB via a 7-seg-
ment display.
The electronics PCB weighs 4 g and the Pitot
tube 3 g, and the resolution (step size) is
1 .6 km/h (1 mph). The supply voltage must
be at least 3 V and must not exceed 1 6 V.
The whole thing is factory-calibrated and
temperature-compensated.
The two silicone tubes connect the probe to
the electronics board, as is clearly shown in
Figure 1 . The holes on the Pitot probe must
be positioned at least 13 mm clear of the
leading edge of the wing, so as to avoid any
disturbance to the measurement. Of course,
the nose of the aircraft would be the ideal
place for the probe, but as you’ll already
have realized, it’s not a jet we’re flying here,
and so we need a propeller to push the air
behind our nice plane.
Once all the elements have been positioned,
it’s a very good idea to glue or firmly fix
the silicone tubes and the probe in place
in order to immunize them against any
vibration.
Measuring the altitude
The MPR-ALT-V3 detector is an altimeter
(weighing in at just 4 g!) that uses atmos-
pheric pressure to measure the altitude.
It too is factory-calibrated and tempera-
ture-compensated. The maximum altitude
reached can be directly read on the PCB via
a 7-segment display. That’s certainly handy,
but it’s not what we’re really interested in
here.
The maximum altitude that can be meas-
ured is 1 0,000 ft... No, you’re not dream-
ing: there really are four noughts after the
‘1 ’ — equivalent to 3,048 m! So which of us
is going to fly their plane the highest in the
sky? The competition is open!
The PCB can be installed wherever you
like in the plane. The hole for detecting
the air pressure must be perpendicular to
the direction of flight. If the detector is
enclosed, a small silicone tube can be used,
brought out flush with the fuselage.
The resolution (step size) is 4 ft (1 .2 m), and
the supply voltage must be a minimum of
3 V but must not exceed 1 6 V.
Just a word about the single-digit display
when used stand-alone (i.e. without the
project described here); an example may
help. The circuit is powered up, and the
plane flies off. Our Wizz plane (Figure 4)
has reached an altitude of 328 ft (around
100 m). When it returns to the ground,
all you have to do is look at the lone digit,
which will display, for example (in feet) 3
then 2 then 8 then blank, then once again
3-2-8, and so on. The maximum value
reached and stored will be reset when the
module is powered down. In this mode, you
can select either the imperial system (feet)
or the metric system (metres) by wire-
strapping or jumpering the brown and yel-
low pins. At start-up, if the figure that blinks
is a ‘O’, the reading will be in imperial units;
28
01-2011 elektor
ATMi8
Figure 1 . The MPR-AIR-V3 module with its Pitot-static tube.
Figure 2. The flight data recorder PCB with connector references.
if it’s a ‘1’, in metric.
It’s worth pointing out that
the Eagle Tree data sheets are
extremely clearly and thor-
oughly written. This is an important >
factor, as the technical documen-
tation, closely followed by the appli-
cation notes, is the sole link between the
product and the end user! What’s more,
it’s best to go directly to the manufactur-
er’s website I 1 ] so you can download the lat-
est version.
Watch out: there’s an l 2 C about!
We’re going to be using both Eagle Tree
modules in l 2 C mode, but to do this
we need to ‘unblock’ them using
the eLogger 8.63 application
in association with the eLog-
ger V3 module. But don’t worry, ^
you won’t have to fork out for
this module, all you need do
is to state clearly in a note with your
order that you want the “l 2 C mode
unblocked detector” and Alexandre
at Studiosport, France I 2 ] will prepare your
order accordingly.
The flight data recorder board...
...is based on the use of the EM-406A GPS
receiver, the VDRIVE1 or 2 from Vinculum,
and our two Eagle Tree detectors (Fig-
ure 2). In the centre is the ATM1 8 module
without its mother board. The data recorder
circuit diagram (Figure 3) comprises above
all connectors, so you’ll need to identify
these before you can make the intercon-
nections with the peripherals:
• K1 : 5 V DC V| N . FI and D1 together pro-
tect our recorder against power-supply
reversal. The ratings for the diode and
the fast-blow fuse should be chosen
according to the power supply being
used.
• l<2: ISP connector.
• All the pins of the ATM1 8 module are
brought out to l<3, l<4, l<5, and l<6. So
this featherweight board (just 53 grams)
can also be used as a universal develop-
ment board!
• K7:VDRIVE module.
• l<8: EM-406A GPS module. Pin 6 is
brought out to l<9.
• K12: 1 (GND-Eagle), 2 (VCC-Eagle), 3
(PB1 -SDA_Eagle), 4 (PC2-SCL_Eagle).
Pins 5-1 0 are not used. All K1 2’s con-
tacts are brought out on K1 0 and K1 1 .
Jumpers JP3 and JP4 enable use of the LEDs
D2 (orange, 0) driven from PC4 and D3
(yellow, Y) driven from PC5, respectively.
These are useful for displaying informa-
tion about our system; the orange LED
indicates power-on reset (file set-up and
marker writing) and the yellow LED lights
during recording. So it’s best not to remove
the USB key while these LEDs are lit. Note
too that it’s best to plug in the key before
powering up the circuit.
Jumper JP2 offers an optional reference volt-
age for the ADC and JP1 allows the micro-
controller to be restarted (reset).
The microcontroller’s PB2 port lets us
choose the mode for the data recorder. If
the port is left floating, the circuit operates
as a flight data recorder. If PB2 is connected
to 0 V, it goes into RDR mode (see below).
For flight data recorder mode operation:
1 . Connect up the four wires from our two
Eagle detectors: ground to K1 2(1 ), 5 V to
K1 2(2), SDA to K1 2(3) and SCL to l<1 2(4)
2. Apply power
3. Program the microcontroller using the
70_WIZZ_RIDE_DATA_RECORDER soft-
ware I 5 !
elektor 01-2011
29
ATMi8
Vcc Vqc Vcc
Figure 3. The circuit diagram consists almost entirely of connectors.
Recording format
The “WDR.TXT” file created at start-up
is going to contain all the data collected
from the detectors. Below is an example
of the file contents:
WDR — >
'k'k'k-k'k'k-k-k'k'k-k-k'k'k-k-k'k'k-k-k'k'k'k
UTC : 15hl6m04 .000s
LAT : 4 6Deg2 1 ' 3 9.4' 'N
LON: 0 0 6Deg2 8 ' 45 . 5' ' E
SAT: 06 SIGNAL: 1
ALT : 495 . 5M
0 . kmh 0 . m
'k'k'k'k'k'k-k'k'k'k'k'k'k'k'k'k'k'k'k'k'k'k'k
UTC: 15hl 6m20 .000s
LAT : 4 6Deg2 1 ' 39.6' ' N
LON: 006Deg28' 45 . 4' 'E
SAT: 09 SIGNAL: 1
ALT : 476 . 5M
0 . kmh 0 . m
The first line tells us that the system
is configured in flight recorder mode
(WDR = Wizz Data Recorder), the marker
“WDR->” is written into the file each
time the system is powered up afresh.
The universal time (UTC), the latitude,
longitude, and the number of satellites
used to calculate the values are collect-
ed, along with the altitude, by means of
the EM-406A GPS receiver.
The last line corresponds to the plane’s
speed and altitude. At power-up, these
values are 0.
4. Power down
5. Plug in the USB key, then power the
whole thing up again.
The microcontroller’s PC0 port lets you
select the units. If the port is left floating,
the speed will be in km/h and the altitude in
metres, while if PC0 is connected to 0 V, the
speed will be in mph and the altitude in feet.
GPS
The GPS module incorporates GlobalSat’s
EM406-A device with built-in antenna. Of
course, there’s nothing to stop you using
another GPS receiver, or even your own
GPS/EIA-232 module using bipolar NRZ
(non return to zero) coding, interfaced
using the well-known MAX232 device or an
equivalent.
Pins 1 and 5 of our EM406-A module are
connected to ground, while pin 2 is con-
nected to the 5 V rail. Pin 4 is connected
to the input of an inverter, which is in turn
connected to another inverter and thence
to PD0. This is necessary, as the high level
output from the EM406 (2.85 V) is lower
than the minimum high threshold of the
PD0 input (V,H = 0.6 x V cc with V cc = 5 V,
i.e. 3 V minimum for the PD0 input to be
regarded as ‘High’). So without the pres-
ence of 74LS04, the UART would never
receive anything at all.
The use of six satellites for the data calcu-
lation ensures very acceptable accuracy.
Recording of this data will only begin once
this condition has been verified; the data
from the Eagle detectors, on the other
30
01-2011 elektor
ATMi8
Carry out testina before aona airborne!
In order to test the
modules before
making the final
connections to the
flight data recorder,
we’re going to use
the Minimodi 8.
Minimodi 8 is the
big sister of ATM 18,
let’s recall its
specifications:
• Ideal size, at
8o x 25 mm, and
weighing 27 g.
Do not take photos while flying!
its ATmega328P-AU
controller.
• An elephant’s memory: 32 l’.
Print #2 , "OPW WDR.txt" +
Chr (13) ;
Print #2 , "WRF " ; "8" + Chr (13);
Print #2 , "WDR — >";
Print #2 , Chr (13) ; Chr (10);
Print #2 , "CLF" + Chr (13);
To be able to control our module by send-
ing it ASCII commands, the first operation
involves modifying the file named “firm-
ware” — and I did say just “the file”. To do
this, we’re going to use the Vinculum Firm-
ware Customiser VI. 1 b software plus the
file VNC 1 L firmware V 3 . 68 ! 3 ]. In the options,
you’ll need to be careful to select IPA Mode
ASCII a nd Ext Command Set Mode and check
LEDs Flash at Power-on. After giving the file
containing the new configuration a new,
customized name, click Write then Finish to
conclude the procedure. You will be asked
for a firmware code (you can just enter
“ 123 ”, for example).
At this stage, all you now need to do is load
the file containing the new configuration,
i.e. your new firmware that you have just
customized. For this action, we’ve con-
nected the VDRIVE module directly to a USB
on the PC using FTDI’s USB/TTL- 223 R serial
converter, having first fitted the jumper
CN4 or J4 as shown in Figure 5. Once the
firmware has been loaded using the VPROG
VNC 1 L- 1 A Flash Programmer software and
the jumpers have been put back into their
original positions, the VDRIVE t 7 l module is
ready to be incorporated into our project.
Ride/ hike data recorder
By now you might be wondering about the
purpose of the RDR mode. If you like hiking,
and like the author never quite know which
way to fold your map up, the following may
be useful.
elektor 01-2011
3 i
ATMi8
Figure 4. The flight data recorder has been tailor-made for the Wizz Kl.
After each hike, you carefully note down
your impressions of the walk on a note that
you put away more or less carefully in the
right drawer with the reference of the cor-
rect large-scale map, onto which you have
Figure 5. VDRIVE2 & VDRIVE1 .
more or less approximately pencilled the
route taken. Ideally, of course. Now, the
Ride Data Recorder (RDR) is the state of the
art, paperless equivalent of it all.
A battery + a 5 V switch-mode Battery Elimi-
Figure 6. A nice little walk.
nator weighing 1 2 g + the RDR + some choc-
olate or a few muesli bars + a bottle of water
in the backpack and we’re off! Don’t forget
your walking shoes!
Given that the circuit in this configura-
tion draws an average current of around
200 mA, you’ll be able to do a quick calcu-
lation to choose a battery capacity to suit
the duration of your hike.
All you have to do to enable the RDR mode is
connect the DR_MODE pin (PB2) to ground.
For as long as the USB key is plugged into
the VDRIVE, a RDR.TXT file receives only the
RMC frames sent from the GPS module.
In order to be able to plot the route corre-
sponding to these frames, all you have to
do is unplug the USB key and convert the
RDR.TXT file into the KML format using the
NMEA2KML software I 6 !. With Google Earth
already installed, you can then run the file
in KML format. The result is then displayed
graphically (Figure 6).
Create a folder bearing the name of your
hike, for example “Mont Blanc 2010”, and
copy/paste the KML file there. All that then
remains is to use a word-processor to write
down your impressions. All stored in the
same place, in the same directory. You’re
now a thoroughly modern hiker! And it
works for railroad journeys too!
(100653)
Internet Links
[1] www.eagletreesystems.com
[2] www.studiosport.fr
(Eagle Tree modules, contact Alexandre)
[3] www.ftdichip.com/Firmware/
Precompiled.htm
[4] www.model2a.com
[5] www.elektor.com/ 1 00653
[6] thomaspfeifer.net/
g ps_ro ute_co n verter. h tm
[7] www.ebconnections.com
(supplier for VDRIVE)
32
01-2011 elektor
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ENERGY SAVING TIPS
Energy Saving Tips
(some less serious)
Wind it up
The best energy saving device 1 can think of has been on the window sill in our kitchen for many years now: the Freeplay radio. It has a large, transpar-
ent blue enclosure with a crank on the back (twenty turns of the crank gives it enough energy for a cooking session) and a solar cell. This device is
based on an original design by Trevor Baylis, which is now available in many different forms.
He intended it to be used in regions and countries where electrical power and information
are scarce. Sadly enough, the situation has not changed significantly since then.
The nicest thing about this radio is the surprises. It always stops by itself when the energy
from the winding crank is exhausted or there isn’t any sunlight, and of course it also starts
playing by itself, often when you least expect it. For many years this radio was the first her-
ald of spring; it spontaneously started playing a cheerful tune when the sun rose higher
and peeked around the corner of the window. My tip: instead of using
batteries, try using a wind-up or motion-powered
device.
/ ^ U> ^ause
^ ' /StJV,n 9 resources
The ‘LED OFF’ tip
Almost every circuit has a power-on LED. This LED is always on, even if we don’t care. The charger of my electric toothbrush for instance has such
an LED; it is always on, but I only look at it when I replace my toothbrush (three times a day of course). My router/modem and Wi-Fi access point
both have several LEDs shining brightly 24 hours a day without anyone around to look at them. Each of these LEDs consumes probably 1 0 mA, the
default current that most designers force out of habit through an LED.
There are two ways to save energy here. First of all, stop passing 10 mA through an
LED, often 2 mA or even less is more than enough. How often do you need to look at it
in bright sunlight? That’s right, hardly ever.
The second way to save energy is simply to stop using LEDs everywhere. Or, if you really
want one, put a pushbutton in series with it so that it will only light up when you press
the button. Another way would be to use LEDs to indicate fault conditions only. Indicator on demand, that’s all you need.
4
•if
1
'k
IT
Energy awareness
How about marking each switch with a sticker showing the estimated annual electricity consumption and cost? And of course, this sort of sticker
should be mandatory for all AC power adapters.
34
01-2011 elektor
ENERGY SAVING TIPS
Just do it
The laws of physics tell us that every action causes an immediate reaction. This also ap-
plies to energy costs: it’s easy to start reducing your electricity consumption.
For example, systematically de-energising (unplugging) all devices with a standby operat-
ing mode can save the average household more than 50 pounds per year.
Kill standby power consumption
Make a list of all the devices powered from
the various distribution circuits in your house.
When you leave home for an extended peri-
od, use this list to switch off the circuits that
power devices that don’t need to be left
on. Naturally, you should leave the alarm
system, the refrigerator and the freezer
on, but you can prevent ‘hidden’ energy
consumption for standby power by sim-
ply flipping the switch for the other de-
vices. This can yield significant savings,
especially with long journeys.
Convert your car to run on hydrogen
A conversion kit for cars so they can run on hydrogen generated in an environmentally
friendly manner (such as from solar energy or wind energy). If you think this is all wish-
ful thinking, you should have a look at the website listed below (using your energy-effi-
cient computer, of course), http://www.switch2hydrogen.com/
Digital photo frame with motion sensor
Digital photo frames are becoming more and more popular. Prices have dropped dra-
matically in the last while; now you can pick up a nice digital photo frame now for just
a few dozen pounds. It also looks quite attractive in your living room or bedroom. The
photo frame displays the pictures you have stored in its memory, periodically changing
to a new picture. That’s a lot nicer than an old-fashioned photo frame with an unchang-
ing paper print.
However, a digital photo frame requires a constant source of electricity - usually from
the AC power grid. A relatively large model consumes a good deal of power, mainly for
the background light. Who switches it off when nobody is in the room? Most likely no-
body; you might think to do this before going to bed. Accordingly, it wouldn’t be a bad
idea to link a motion sensor to a digital photo frame so it doesn’t go on unless someone comes near it. An ordinary motion detector, such as the
types sold by electrical shops or DIY home improvement centres, could be used for this. Plug the AC adapter of the photo frame into the motion
detector and you’re all set. You should adjust the sensor time setting so the photo frame does not constantly go on and off, and you need a photo
frame that can be configured to start showing photos right after it is switched on, instead of ending up in some menu state.
There is also a manufacturer that recently introduced a digital photo frame with a built-in motion sensor: http://www.nix-digital.com/
elektor 01-2011
35
ENERGY SAVING TIPS
Mind your maintenance
Postponed maintenance (or worse yet, no maintenance) of equipment causes lower efficiency or
degraded performance. This leads to higher electricity consumption, and therefore to higher energy
expenses. For this reason, you should defrost your freezer periodically. When you buy a new freezer,
select a model with automatic defrosting. Even coffee machines, electric kettles and washing ma-
chines need maintenance when the heating element becomes covered with lime or scale deposits.
This significantly increases how long it takes to heat the water, so the devices use much more energy.
This can easily be corrected with a simple descaling product.
The ‘Pull the plug on DECT phone’ tip
The AC power plug, that is. Most DECT phones, both base and ex-
tension, are in their charger cradle
which is wasting energy big time
through the standby current of the
wallwart adapter and the continu-
ous trickle charging of the phone’s
batteries. Both are unnecessary. In
especially bad cases, the AC power
adapter block is a traditional linear
power supply that’ll easily waste 2
watts of power all the time, just
touch it if you’re not convinced.
Make sure the phone’s battery is
fully charged, then unplug the
adapter. From time to time, in-
spect the battery symbol on the
phone, if it’s any good it will tell
you when charging is due
—
again. My own Philips
Kala DECT base phone
easily lasts four days
on a single charge and
an average of two
1 0-minute calls a day and
one short battery test by briefly ringing an extension and
watching the BATT symbol. It’s got two dead standard 650-mAh NiCd batteries fitted. Work
out your personal average for the week and allow headroom to make sure there’s always enough battery
capacity when the CEO phones late at night with good news. Apply stochastically distributed charging between
DECT stations, that way a phone will always ring and the worst that can happen really is a short climb up the stairs to answer a call. Your health as
well as that of the batteries will benefit, not forgetting the advantage of having an AC outlet free for, say, an electric kettle.
The ‘Make your cellphone charge last longer’ tip
It’s a little known fact that the transmitter in your mobile phone employs stepped RF output power to save battery energy. In essence, the stronger
the signal received from the cellphone mast, the lower the radiated energy required on the phone to set up two-way communication. A fine sys-
tem ignored by but most people who will phone away till the battery goes flat. By contrast, those with the keenest sense of energy savings and
wishing to make a call, will first sight the nearest cellphone mast (if necessary, using optics) and walk or drive to it to effectively reduce the dis-
36
01-2011 elektor
ENERGY SAVING TIPS
tance and so enable the call to be made at the lowest battery load. The savings are enormous, and
the reward is increased peace of mind on the environment. I may be overlooking something but just
can’t put my finger on it, must be I’m not using my mobile too often.
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elektor 01-2011
37
MICROCONTROLLERS
All-Soft-555
ATtiny plays 555 MMV and AMV
By Dr. Thomas Scherer (Germany)
The chip with three fives in its type code sure is among the biggest selling ICs of all times but from
today’s perspective the internal block diagram certainly looks a little dated with its multitude of analogue
signal paths. Can you imagine, we’re even expected to calculate the value of external components and
solder real resistors and capacitors to make the thing work! What’s more, it isn’t really that flexible. We
give the design a 21 st Century makeover to produce a much more versatile ‘virtual 555’ using an 8-pin
microcontroller.
While modifying the motor controller of my
electric bike I came to the conclusion that
the design would benefit from an additional
monostable multivibrator (MMV, mono-
flop). I knew I had a good supply of all the
various incarnations of the 555 timer chip
in my workshop. The monostable however
needed to be retriggerable and the 555 can
only manage that with the help of some
extra circuitry. One good feature of the 555
is how little board space it occupies.
With space at a premium the extra cir-
cuitry was making the 555 solution look
a little less appealing. Maybe a CD4098
monostable from the digital CMOS 4000
series would be an alternative but this is a
1 6-pin device making it twice as big as the
555 even before you start adding the exter-
nal components. After a fruitless search
for a CD4098 and much head scratching I
came up with this solution called the All-
Soft(ware)-555’. This would be a digital
equivalent of the generic 555 timer chip
built into an 8-pin microcontroller. All of its
operational characteristics are programmed
in software and no additional external com-
ponents are necessary.
Pick a controller
There are now any number of small pow-
erful microcontrollers on the market from
several different manufacturers. The author
found some ATtiny25 PI, ATtiny45 and
ATtiny85 AVR microcontrollers in a drawer
and thought they might just be up to the
job. In addition to having the correct num-
ber of pins (in the DIL versions) they also
contain a hardware timer and an A/D con-
verter, what more could he possibly need?
The only difference between the three con-
trollers is the 2, 4 or 8 KByte flash (and RAM /
EEPROM) capacity.
BASCOM_AVR from MCS-Elektronik is a
simple but effective BASIC compiler for
software development for these microcon-
trollers. The author experimented using
both machine code and compiled routines
to generate the time intervals and found
that there was no discernable disadvan-
tage using the compiled code. What’s more
there is a download link on the page of the
Elektor website for this article I 2 1 where the
free demo version of BASCOM-AVR can be
downloaded. The only restriction on its use
is the size of the finished code cannot be
greater than 4 KBytes. This is ample for the
project’s firmware, including any foresee-
able system expansion.
Better than the original
The conventional 555 I 3 ] can in principle be
configured as either a monostable or asta-
ble multivibrator. The pulse timing is both
stable and relatively unaffected by changes
of the supply voltage. As a monostable it
can generate pulses from a few microsec-
onds long up to hundreds of seconds. As an
astable it can go from a few hundred kilo-
hertz down to a few millihertz. Any digital
implementation of a 555 should also be able
to at least match this performance.
Despite its popularity the conventional 555
has always had a number of disadvantages:
• it requires external components.
• the monoflop isn’t retriggerable.
• the trigger input only responds to nega-
tive-going pulse edges.
• calculating the multivibrator duty cycle
is not straightforward.
It isn’t necessary of course to incorporate
all the 555’s shortcomings in our ‘micro-
38
01-2011 elektor
MICROCONTROLLERS
controller’ 555 variant. The function of the
multivibrator is now configurable under
software control. The active trigger edge
and other finer points of operation can be
changed in the firmware (see ‘Features’).
Memory capacity would be a problem if
all the multivibrator functions were incor-
porated into one program particularly for
the smallest variant microcontroller. In any
application the All-Soft-555 will be used as
either a monostable or astable multivibra-
tor so it is sensible to divide the firmware
along these lines also. The two programs
are called iMono and iMulti, accepting that
the latter name sounds good rather than
striving for technical accuracy (both pro-
grams emulate a multivibrator).
Physical pin to pin compatibility with the
original 555 is however not possible: The
ATtiny uses pin 4 as ground while the 555
uses pin 1 , and for other reasons we have
not kept to the original pinouts.
MMV program iMono
The pinouts for the monoflop shown in Fig-
ure 1 are fairly conventional. When the All-
Soft-555 is used in an application requir-
ing precise and/or narrow pulses a crystal
can be fitted between pins 2 and 3. Inher-
ent parasitic capacitance of the crystal usu-
ally means that the (1 0 pF to 1 5 pF) load-
ing capacitors at either end of the crystal
to earth can usually be omitted thereby
cutting down on the external component
count. For the majority of applications the
8 MHz and 1 28 kHz internal oscillator will
suffice. Tests by the author indicate that you
can expect the uncalibrated frequency to be
within 1 0 %. Pin 7 is the trigger input while
Pins 5 and 6 are the normal and inverted
outputs respectively.
Comments in the iMono source code
indicate exactly which values need to be
changed to tailor the behaviour of the pro-
gram to your requirements. The firmware
will not accept any invalid parameters. The
user can choose anyone of three operating
modes:
• - not retriggerable
• - retriggerable
• - extended
Features
MMV (iMono) features
• Digital, configurable monostable
multivibrator
• Three modes: non retriggerable,
retriggerable and extended pulse
• Programmable trigger edge: falling or
rising
• Non inverting and inverting outputs
• Pulse width from o.8 ps to 524 s
• Documented source code in BASIC
iMono
E
RESET VCC
3
[I
XTALl
TRIGGER
E
XTAL2
OUT-
11
E
GND
OUT+
a
ATtiny25
Figure 1 . Pin assignments of an ATtiny25
used and programmed as a monostable.
In the last mode the trigger input extends
the selected monostable pulse width.
The following characteristics can be pro-
grammed in software:
• trigger edge: rising or falling.
• ticks: 2 to 255 or 1 to 256 timer ticks
• clock prescaler: 1/2/4/8/16/32/64/256
• timer prescaler: 8/64/256/1024
• oscillator type: internal/external
The ATtiny25 has only an 8-bit timer so it
can count from 1 to 256 timer ticks. An
extra prescaler divides down the oscillator
to produce the effective clock frequency
(f ef f). The timer has a prescaler which in turn
is driven by the effective clock. The output
pulse length is therefore given by:
Pulse length = ticks x clock prescaler x timer
prescaler / clock
Using the 8 MHz oscillator and a clock
prescaler of 8 we get an f eff of 1 MHz. The
AMV (iMulti) features
• Digital, configurable astable
multivibrator
• Four modes: Fast, Fixed value, VCO and
VCDC
• Gate input defined in software either
active High or Low
• Waveform true or inverted
• Frequency adjustable by software or
control voltage
• Duty-Cycle adjustable by software or
control voltage
• Frequency range 10 MHz to 1.91 MHz
• Documented source code in BASIC
iMulti
E
RESET VCC
a
E
XTALl
cv
E
XTAL2
OUT
a
E
GND
GATE
a
ATtiny25
Figure 2. Pin assignments of an ATtiny25
used an programmed as an astable.
timer prescaler is set to 1024, counting
98 ticks to give a pulse length of:
t = 98 x 1 024 x 8 / 8 MHz = 1 00.352 ms
This produces a reasonably accurate
1 00 ms MMV pulse although the accuracy
of the internal oscillator cannot be guar-
anteed. Table 1 indicates the achievable
pulse lengths using combinations of the
four parameters. The first column in ital-
ics using a timer prescaler of 8 does not
produce precise results and because of its
limited processing power can only count a
minimum of two ticks ratherthan one as in
the other cases.
AMV program iMulti
Pinouts on the iMulti astable mode are
shown in Figure 2. They are not the same
as the monostable version and reflect the
different roles the two versions perform.
An external crystal can again be connected
to pins XTAL1 and XTAL2 when a higher
elektor 01-2011
39
MICROCONTROLLERS
Table 1 . All-Soft-555, MMV mode
Select the desired pulse width for the MMV program. The values in italics with a prescale of 8 have limited accuracy.
20 MHz external
Ticks:
2
256
1
256
1
256
1
256
Clockdiv
feff(Hz)
Delay
Prescale: 8
Prescale: 64
Prescale: 256
Presc.:
1024
1
20 M
0.5 (is
0.8 (is
102 (is
3.2 (is
81 9 (is
1 2.8 (is
3.28 ms
51 .2 (is
13.1 ms
2
1 0 M
1 (IS
1 .6 (is
205 (is
6.4 (is
1 .64 ms
25.6 (is
6.56 ms
102 (is
26.2 ms
4
5 M
2 JLLS
3.2 JLLS
410 (is
1 2.8 (is
3.28 ms
51.2 (is
13.1 ms
205 |LLS
52.4 ms
8
2.5 M
4 (is
6.4 (is
81 9 (is
25.6 (is
6.56 ms
102 (is
26.2 ms
410 (is
105 ms
16
1 .25 k
8 (is
1 2.8 (is
1 .64 ms
51.2 (as
13.1 ms
205 (is
52.4 ms
819 (is
210ms
32
625l<
16 (is
25.6 (is
3.28 ms
102 (is
26.2 ms
410 (is
105 ms
1 .64 ms
419 ms
64
312.5I<
32 (is
51.2 (is
6.56 ms
205 (is
52.4 ms
819 (is
210ms
3.28 ms
839 ms
128
156.25 k
64 (is
102 (is
13.1 ms
410 (is
105 ms
1 .64 ms
419 ms
6.56 ms
1.68 s
256
78.125l<
1 25 (is
205 (is
26.2 ms
819 (is
210ms
3.28 ms
839 ms
13.1 ms
3.36 s
8 MHz internal
Ticks:
2
256
1
256
1
256
1
256
Clockdiv
feff(Hz)
Delay
Prescale: 8
Prescale: 64
Prescale: 256
Presc.:
1024
1
8 M
1 .2 (is
2 (is
256 (is
8 (is
2.05 ms
32 ILLS
8.19 ms
128 ILLS
32.8 ms
2
4 M
2.3 jits
4 (is
51 2 (is
16 (is
4.10 ms
64 (is
1 6.4 ms
256 ills
65.6 ms
4
2 M
4.5 (is
8 JLLS
1 .02 ms
32 (is
8.19ms
128 (is
32.8 ms
512 (is
131 ms
8
1 M
9 (is
1 6 (is
2.05 ms
64 (is
1 6.4 ms
256 (is
65.6 ms
1 .02 ms
262 ms
16
500l<
1 9 (LIS
32 (is
4.10 ms
1 28 JLLS
32.8 ms
512 (is
131 ms
2.05 ms
524 ms
32
250 k
38 jus
64 (is
8.19 ms
256 (is
65.6 ms
1 .02 ms
262 ms
4.10 ms
1.05 s
64
125k
75 (Lis
128 (is
1 6.4 ms
512 (is
131 ms
2.05 ms
524 ms
8.1 9 ms
2.10s
128
62.5 k
1 50 (is
256 (is
32.8 ms
1 .02 ms
262 ms
4.10 ms
1.05 s
16.4 ms
4.19 s
256
31.25l<
300 (is
51 2 (is
65.6 ms
2.05 ms
524 ms
8.20 ms
2.10s
32.8 ms
8.39 s
128 kHz internal
Ticks:
2
256
1
256
1
256
1
256
Clockdiv
feff(Hz)
Delay
Prescale: 8
Prescale: 64
Prescale: 256
Presc.:
1024
1
128l<
80 (is
1 25 (is
1 6 ms
500 (is
128 ms
2 ms
512 ms
8 ms
2.05 s
2
64l<
160 (is
250 (is
32 ms
1 ms
256 ms
4 ms
1.02 s
16 ms
4.10 s
4
32l<
320 (is
500 (is
64 ms
2 ms
512 ms
8 ms
2.05 s
32 ms
8.19s
8
16l<
640 (is
1 ms
128 ms
4 ms
1.02 s
16 ms
4.10 s
64 ms
16.4 s
16
8I<
1 .25 ms
2 ms
256 ms
8 ms
2.05 s
32 ms
8.19s
128 ms
32.8 s
32
4I<
2.5 ms
4 ms
512 ms
16 ms
4.10 s
64 ms
16.4 s
256 ms
65.5 s
64
2I<
5 ms
8 ms
1.02 s
32 ms
8.19s
128 ms
32.8 s
51 2 ms
131 s
128
1 k
10 ms
16 ms
2.05 s
64 ms
16.4 s
256 ms
65.5 s
1.02 s
262 s
256
500
20 ms
32 ms
4.10 s
128 ms
32.8 s
51 2 ms
131 s
2.05 s
524 s
or more exact output frequency is called
for. The two internal oscillators producing
8 MHz and 1 28 kHz should be suitable for
the majority of applications.
These alone allow operation up to 4 MHz
which a conventional 555 can only dream of.
Pin 5 is a gate input, used to turn the output
signal on and off. The square wave output
signal is produced from pin 6. The CV input
on pin 7 should be a DC voltage in the range
of 0 V to Vcc. It can be used to either control
the output signal frequency by more than
one octave or vary the mark/space ratio of
the output signal in the range from 1 to 99 %
(frequency modulation and PWM).
Altogether the AMV program (iMulti) has
four operating modes:
• fast: high frequency with a 50:50 square
wave output.
• fix: Frequency and duty cycle adjustable
in software.
• VCO: Frequency via CV (1 :2.56) with the
duty cycle adjustable in software.
• PWM: Duty cycle via CV (1 to 99%) with
the frequency adjustable in software.
40
01-2011 elektor
MICROCONTROLLERS
Table 2. All-Soft-555, AMV mode
Output frequency selection of the AMV program. Ticks of less than 100 can only be used if it is running in fast mode.
20MHz
Ticks:
2
100
256
2
100
256
2
100
256
2
100
256
2
100
256
Cl.div
f eff (Hz)
Prescale: 1 (Hz)
Prescale: 8 (Hz)
Prescale: 64 (Hz)
Prescale: 256 (Hz)
Presc.:i024 (Hz)
1
20 M
1 0 M
200l<
78.1 k
1 .25 M
25l<
9.77 l<
156l<
3.13l<
1.22l<
39.1 k
781
305
9.77 l<
195
76.3
2
1 0 M
5 M
100l<
39.1 k
625l<
1 2.5 k
4.88 k
78.1 k
1.56l<
610
19.5I<
391
153
4.88 k
97.7
38.1
4
5 M
2.5 M
50l<
19.5I<
313l<
6.25 k
2.44 k
39.1 k
781
305
9.77 k
195
76.3
2.44 k
48.8
19.1
8
2.5 M
1.25 M
25l<
9.77 k
156l<
3.13l<
1 .22 k
19.5I<
391
153
4.88 k
97.7
38.1
1.22l<
24.4
9.54
16
1 .25 l<
625l<
12.5I<
4.88 k
78.1 k
1 .56 k
610
9.77 k
195
76.3
2.44l<
48.8
19.1
610
12.2
4.77
32
625l<
313l<
6.25 k
2.44l<
39.1 k
781
305
4.88 k
97.7
38.1
1 .22 k
24.4
9.54
305
6.1
2.38
64
312.5I<
156l<
3.13l<
1 .22 k
19.5I<
391
153
2.44 k
48.8
19.1
610
12.2
4.77
153
3.05
1.19
128
156.25 k
78.1 k
1.56l<
610l<
9.77 k
195
76.3
1.22l<
24.4
9.54
305
6.1
2.38
76.3
1.53
596 m
256
78.125l<
39.1 k
781
305l<
4.88 k
97.7
38.1
610
12.2
4.77
153
3.05
1.19
38.1
763 m
298 m
8MHz
Ticks:
2
100
256
2
100
256
2
100
256
2
100
256
2
100
256
Cl.div
f eff (Hz)
Prescale: 1 (Hz)
Prescale: 8 (Hz)
Prescale: 64 (Hz)
Prescale: 256 (Hz)
Presc.:i024 (Hz)
1
8 M
4 M
80 k
31.3 k
500 k
10l<
3.91 k
62.5 k
1 .25 k
488
1 5.6 k
313
122
3.91 k
78.1
30.5
2
4 M
2 M
40 k
1 5.6 k
250 k
5k
1 .95 k
31.3 k
625
244
7.81 k
156
61
1.95 k
39.1
15.3
4
2 M
1 M
20 k
7.81 k
125 k
2.5I<
977
15.6 k
313
122
3.91 k
78.1
30.5
977
19.5
7.63
8
1 M
500 k
10 k
3.91 k
62.5 k
1.25l<
488
7.81 k
156
61
1.95 k
39.1
15.3
488
9.77
2.81
16
500 k
250 k
5I<
1 .95 k
31.3 k
625
244
3.91 k
78.1
30.5
977
19.5
7.63
244
4.88
1.91
32
250 k
125 k
2.5I<
977
1 5.6 k
313
122
1.95 k
39.1
15.3
488
9.77
2.81
122
2.44
954 m
64
125 k
62.5 k
1.25 k
488
7.81 k
156
61
977
19.5
7.63
244
4.88
1.91
61
1.22
477 m
128
62.5 k
31.3I<
625
244
3.91 k
78.1
30.5
488
9.77
2.81
122
2.44
954 m
30.5
610 m
238 m
256
31.25k
1 5.6 k
313
122
1 .95 k
39.1
15.3
244
4.88
1.91
61
1.22
477 m
15.3
305 m
119m
128kHz
Ticks:
2
100
256
2
100
256
2
100
256
2
100
256
2
100
256
Cl.div
f eff (Hz)
Prescale: 1 (Hz)
Prescale: 8 (Hz)
Prescale: 64 (Hz)
Prescale: 256 (Hz)
Presc.:i024 (Hz)
1
128l<
64l<
1.28l<
500
8I<
160
62.5
1 k
20
7.81
250
5
1.95
62.5
1.25
488 m
2
64l<
32l<
640
250
4I<
80
31.3
500
10
3.91
125
2.5
977 m
31.3
625 m
244 m
4
32l<
16 k
320
125
2 k
40
15.6
250
5
1.95
62.5
1.25
488 m
15.6
313m
122m
8
16 k
8I<
160
62.5
1 k
20
7.81
125
2.5
977 m
31.3
625 m
244 m
7.81
1 56 m
61 m
16
8I<
4I<
80
31.3
500
10
3.91
62.5
1.25
488 m
15.6
313m
122 m
3.91
78.1 m
30.5 m
32
4I<
2I<
40
15.6
250
5
1.95
31.3
625 m
244 m
7.81
1 56 m
61 m
1.95
39.1 m
1 5.3 m
64
2I<
1 k
20
7.81
125
2.5
977 m
15.6
313m
122m
3.91
78.1 m
30.5 m
977 m
1 9.5 m
7.63 m
128
1 k
500
10
3.91
62.5
1.25
488 m
7.81
1 56 m
61 m
1.95
39.1 m
1 5.3 m
488 m
9.77 m
2.81 m
256
500
250
5
1.95
31.3
625 m
244 m
3.91
78.1 m
30.5 m
977 m
19.5 m
7.63 m
244 m
4.88 m
1.91 m
Also:
• gate: gates the o/p signal (High or Low)
• period length: 2 to 256 or 1 00 to 256
Timer-Ticks
• duty cycle: 1 to 99 %
• clock prescaler: 1/2/4/8/16/32/64/256
• timer prescaler: 1/8/64/256/1024
• oscillator type: internal/external
The full range of ticks from 2 to 256 is only
valid for operation in fast-Mode. Modes
producing a variable duty cycle must have
a minimum number of 1 00 ticks in a period.
The ATtiny’s 8-bit timer is used in fast-PWM
mode.
The frequency f eff is derived from the oscil-
lator and the clock prescaler from which the
timer and timer prescaler are clocked. The
output frequency is given by:
Frequency = clock / (ticks x clock-prescaler
x timer prescaler)
For example using an 8 MHz clock and a
clock prescaler of 8 we get f eff = 1 MHz.
Choosing a timer prescaler of 64 and 1 56
elektor 01-2011
4i
MICROCONTROLLERS
Figure 3. Under test using a prototyping board.
ticks therefore gives an output frequency
of:
f= 8 MHz / (8 x 64 x 1 56) = 1 00.1 602564 Hz
This generates a 100 Hz signal assuming
the internal oscillator is reasonably accu-
rate. Table 2 indicates the frequency range
of the AMV firmware based on the selection
of four variables.
Code & Chips
The source code of both the iMono (MMV)
and iMulti (AMV) firmware together with
two hex files implementing a 1 00 ms mono-
stable and a 1 00 Hz multivibrator with a
25 % duty cycle are available to download
freely from the Elektor webpage for this arti-
cle [2], The iMono firmware is 694 bytes. This
gives plenty of space even on the ATtiny25
for any additional code you may wish to add
to expand the system. The situation is dif-
ferent for the iMulti firmware which takes
up 2022 bytes leaving only 24 bytes free in
an ATtiny25 memory. The reason for this is
largely due to the additional code needed
for the A/D converter.
A close look at the iMulti source code
reveals that the procedure for configur-
ing the timerO registers including the start
and stop commands are coded ‘by hand’.
The reason is that fast PWM modes are not
directly supported in the current version
(1.12.0.0) of BASCOM. The iMono firm-
ware however uses the standard options
for TimerO which are much simpler.
Any pin not defined as an output will by
default be an input and (with the exception
of the CV input in the iMulti) with an inter-
nal pull-up resistor to guard against the pos-
sibility of undefined input levels if an input
is left floating. This is also the case for the
reset input. The definition ‘Const lnt_osc =
False’ disconnects internal pull-ups on the
crystal connector pins XTAL1 and XTAL2 so
that an external crystal can be connected.
Clock selection is made by burning the
appropriate fuses. The 8 prescaler which
is normally set by a fuse will have no effect
because the prescaler is set by the firmware.
One point to be aware of is with very low
frequency outputs or long pulses it is nec-
essary to use the internal 128 kHz oscil-
lator. The serial ISP programming inter-
face expects a minimal serial frequency of
1.2 kHz and the effective clock speed of
the processor must be a minimum of four
times the serial clock speed. The practical
limit for ISP programming is therefore with
the clock prescaler set to 1 6 which gives an
f e ff = 8 kHz. With a prescaler setting of 32
and upwards you will find on programming
the device you have made a totally differ-
ent type of ‘one shot’ i.e. it will only be pos-
sible to program the chip once over the ISP
interface.
There are tips on the Internet indicating
how a chip which has been locked in this
way can be recovered. The simplest method
is to use so-called ‘high voltage serial pro-
gramming’ (e.g. the STK500 programmer
from Atmel) which is clock independent.
General points
To get the best from the All-Soft-555 it is
worth bearing the following points in mind
when selecting a particular pulse width or
frequency from the table:
• The higher the value of timer prescaler
the more precise the timing will be i.e.
with a prescale of 256 the timer is very
accurate.
• When the iMono uses a prescale value of
8 and a low value of Ticks (<16) the tim-
ing is not particularly precise.
• Current consumption by the ATtiny is
proportional to its clock frequency.
A controller running at 5 V with an
f e ff = 8 MHz draws a supply current of
approximately 8 mA, but at 3.3 V and
1 MHz it falls to 0.7 mA. At 1 28 kHz and
2.5 V it is happy with just 0.1 mA which
is almost as low as the CMOS version of
a real 555.
We hope you find this virtual timer chip use-
ful. If this example has inspired you to try
your hand at producing a virtual version of
some other standard 1C the author and the
editors at Elektor would be interested to
hear from you.
( 100691 )
Internet Links
[1] ATtiny25 data sheet:
www.atmel.com/dyn/resources/prod
documents/doc2586.pdf
[2] Visit the web site for this article:
www.elektor.com/ 1 00691
[3] Download the BASCOM-AVR demo
version:
www.mcselec.com/index.
php?option=com_docman&task=cat
view&gid=99<emid=54
[4] Wikipedia 555 info:
http://en.wikipedia.org/
wiki/555_timer_IC
42
01-2011 elektor
Under Scrutiny: the Xmega Board
by Jens Nickel (Germany)
It’s not only here at Elektor Labs that the ATtiny and ATmega
AVR controllers top the polls for favourite processor. Many of
you in Elektor land think the same too, judging by your many
e-mails. No wonder then the community reacted with enthu-
siasm when Atmel announced in spring 2008 that it was plan-
ning to expand its 8-bit range with the ATxmega controller.
Outstanding new features PI included significantly improved
processing performance of up to 32 MIPS at 32 MHz as well as
an Event System (enabling peripheral events to trigger external
circuitry functions without involving the CPU).
Now an increasing number of manufacturers are following up
this opportunity to produce development boards and tools
designed specially for the Xmega. One of these is the Serbian
firm Mikroelektronika based in Belgrade, who sent us a sample
of their ‘Xmega Ready Board’ forevaluation in our lab.
The board is pictured here. It’s immediately obvious that the
PCB (unlike other AVR boards from the same firm) is not over-
provided with options. You’ll search in vain for any user inter-
face involving LEDs, press-buttons or even any kind of display.
The only off-board connectivity is a single USB connector and a
pair of screw terminals for the power supply. This minimal inter-
face imposes two restrictions that you’ll just have to live with.
First, power to the board cannot fed over the USB connection.
Second, you cannot install hex files through the bus (at least on
an unmodified controller), simply because the board does not
include an integrated USB programmer.
Our first investigation into the Xmega Ready Board came to
a fairly rapid conclusion, simply because we couldn’t lay our
hands on either an AVR ISP-compatible or a JTAG programmer
(evidently Mikroelektronika could not either!). When we asked
them how they managed without these, they told us they were
working on a solution. Sure enough, two weeks later they sent
us another package containing exactly the same board, only
this time the ATxmegal 28A1 they supplied was now equipped
with a bootloader. And this was not a one-off solution for us, as
you can read on their website PI. Click on the Download section
of the site and you find not only demo versions of the respected
Mikroelektronika compiler but also sample programs (for C,
BASIC and Pascal) plus a PC program for transferring hex files
over the USB connections to the bootloader.
We immediately tested out the whole package (see screen shot)
and it all worked very smoothly. A minor shortcoming is the fact
that the corresponding function is not integrated in the IDE.
Instead you must first produce a hex file with the compiler (lim-
ited to a code length of 4 KB in the free downloadable version)
and then use the auxiliary program to transfer it to the Xmega.
For our first trial we tested the ‘LED Blinking’ routine. After
flashing this successfully we were puzzled; there was no sign
of any LED blinking at us. This was pure and simply because
the board is not equipped with any LEDs (other than a green
^ mikroXMEGA and XMEGA -Ready Bootloader
i^JI
X
mikroBootloader
Select MCU
AVR XMEGA
Setup COM Port: COM22
port Baud Rate: 1 15200
Change
Settings
Tfi Conn
in
Rx
Tx
9
Connect
with MCU
Choose
HEX file
Start
bootloader
Disconnect
t .
Browse
for HEX
Begin
uploading
History Window
Msg: Waiting MCU response
Disconnected
—
Setup: Port COM2 2
Msg: Waiting MCU response
Connected
Bootloading
progress bar
Show Activity
'
No files opened,
elektor 01-2011
43
power-on indicator)! But if you can wield a soldering iron you
will not find this a major hurdle, because every pin of the Xmega
controller is taken to its own solder terminal on this board. In
addition the board contains a special prototyping area where
users can install circuitry of their own. A multimeter reassured
us that our experiment had been blessed with success and the
accessibly written source code explained that the specified port
pins should alternate between High and Low level to make an
LED flash.
The second sample program we tried out was called ‘Flash_Test’
(see screen shot) and sent a test sequence of bytes across the
USB interface to the PC. We were able to control this process
using Hyperterminal. Four other code samples are provided, for
working with timers, the internal EEPROM and other functions.
According to Mikroelektronika other sample programs are in
preparation (for ADC, PWM, UART, LCD/GLCD/TFT controllers
and more). These will include demo code that will work with
corresponding compiler-specific commands ratherthan provide
fully developed applications. This should not be taken to mean
you should not look to other sources for software. Users are
free to flash other hex files (developed with WinAVR) into the
controller using the bootloader.
A major plus-point of this board is undoubtedly the low price of
29 US dollars (the distributor Tigal is currently offering it for 24
euros I 3 !). If your development turns out successful you can even
build the board permanently into your application without leav-
ing yourself vastly out of pocket. At this stage it’s worth men-
tioning that the manufacturer also offers an even more com-
pact version of the board. This is admittedly somewhat pared-
down (as you’ll see on the right-hand side of the photo); it lacks
the screw terminals for the power supply and the prototyping
area for example). But with a price of just $24 the mikroXmega
board is even better value for money than the Xmega Ready
Board l 4 L
Shortly before we went to press the news reached us that the
guys at Mikroelektronika were working on a lavishly equipped
‘Multimedia Xmega Board’. This is planned to include a TFT dis-
play, an accelerometer, an MMC/SD-card socket, an audio inter-
face and much more on board. This PCB will also be available in
a more compact micro version.
(100716)
[1] www.atmel.com/products/AVR/default_xmega.asp
[2] www.mikroe.com/eng/products/view/579/
xmega-ready-board/
[3] www.tigal.com/product.asp?pid=2039&lang=en
[4] www.mikroe.com/eng/products/view/580/
mikroxmega-board /
Spotted at electronica 201 0
Between the 9 th and 1 2 of November this year we found ourselves at electronica 201 0 billed as the world’s leading trade fair for
electronic components, systems and applications. Held in the massive Munich trade fair centre it was packed to the rafters with so
many products and exhibitors that it’s impossible to give a fair overview so we just picked a few products here which caught our eye.
Elektor were of course also there and this year we were pleased to be sharing a booth with our US sister publication ‘Circuit Cellar’.
It was a good opportunity for Elektor editors and engineers including Ernst Krempelsauer, Antoine Authier and jens Nickel to press
the flesh and chat with readers about our projects and publications. With so many exhibitors under the same roof it was a good
opportunity for them to spot the latest products and trends. With an area this big we couldn’t help thinking that visitors would
have benefited from their very own Elektor Wheelie!
(100843)
LTl
00
The Stellaris Robotic Evaluation platform (Evalbot) from Texas
Instruments is based on a Stellaris LM3S9B92 microcontroller
supporting a small real-time kernel. It uses many of the manu-
facturer’s analogue components for motor drive, communi-
cations and power supply. The kit is available from a number
of distributors and just needs a few minutes assembly time
before its ready to go. It retails at $1 50.00 according to the
Tl website.
www.ti.com/litv/pdf/spmu166
44
01-2011 elektor
On the Glyn stand we found this powerful new development
board incorporating the FTDI Vinculum II featuring a snap-off
debugger and Flash tool. This board is supplied as part of a
one-day Vinculum II workshop costing 60 euros. A nice appli-
cation shows it interfaced to a USB Logitech webcam, display-
ing the image on a Seiko TFT display. Apart from the Vinculum
no other controller is needed.
www.glyn.de
Aaronia were showcasing their impressive range of innova-
tive hand-held spectrum analysers. These devices have excel-
lent sensitivity and are a world first in portable real-time spec-
trum analysis (real time bandwidth up to 200 MHz). Together
with a (powerful) computer they can stream received data to
a hard disk. The system can log the entire radio traffic passing
through a mobile phone mast. The basic 6 GHz version retails
at around 3000 euros and includes the antenna, LiPo battery,
mains adapter, carry case, analysis software and accessories.
www.aaronia.co.uk
Prema semiconductors produce analogue and mixed signal
ASICs. On show was a ‘Speaten Filter’ audio chip developed by
Dedekind R&D. This filter boosts bass and treble frequencies
without affecting the mid range. This produces improved live-
liness especially in the reproduction of instrumental sounds.
Tiny loudspeakers at their stand were reproducing unbeliev-
ably rich sounds, really quite impressive.
www.prema.com
www.dedekind.jp/pdf/mz01_e.pdf
These high-tech, dimmable AC powered LED lamps incorpo-
rate a small active heatsink from Nuventix to keep the LED
running cool. Power for the LED comes from a highly efficient
mains interface designed by Fairchild. The LED modules are
from Everlight (10 W) and Hueyjann (20 W).
www.fairchildsemi.com
OUT
LEir
our
RIGHT
PREF.U Gtfttleonduetar GrnbH
elektor 01-2011
45
Here comes the Bus!
By Jens Nickel
The best things in life may or may not be free (in the Elektor labs
we know a song about that), but sometimes there just isn’t time
to get round to them. Lots of good ideas come out of our edito-
rial planning meetings, but many just end up languishing in the
bottom of a drawer never to see the light of day.
‘E-Labs Inside’ to the rescue! As the chief lab correspondent,
I often find myself looking around at what my colleagues are
doing. Sometimes this can be a source of ideas, and on this
occasion I was inspired to dust off an old project that had
never come to fruition, and use it as an example to show how
a concept is developed from scribbles on the back of an enve-
lope to reality.
A few details were nailed down at the first
brainstorming session with Clemens and
Chris. We wanted to keep things as simple
as we could, and so for the lowest protocol
layer (the purely electrical specification) we
decided to use an established standard and
readily-available components. Clemens sug-
gested using Ethernet, and I proposed a bus
based on the RS-485 standard. Either would
be able to work with cable runs of tens of
metres, enough for wiring up the elegant
castle that is the Elektor nerve centre.
There are fairly cheap microcontrollers avail-
able with a built-in 1 0Base-T Ethernet trans-
ceiver, giving a data rate of up to 1 0 Mbit/s
(see for example the ‘NetWorker’ project in
the last edition I 1 !; circuit diagram snippet
in Figure 1). RS-485 buses can in principle
achieve similar data rates. With a 1 0 Mbit/s link we have plenty
of bandwidth: even enough to send high-quality sampled audio
data in real time.
It was clear, however, that not every network node would need
to be capable of top-speed performance. To make the project
interesting to as many readers as possible, we decided that the
components for a minimal node, perhaps for connecting up a
simple sensor, shouldn’t come to more than fifteen euros. That
seemed feasible, as RS-485 transceivers (such as the LTC1 535,
or the SN65HVD08P, which Clemens had used in the InterScep-
tre project i 2 i) are available for about five pounds. And, if we
make the simple bus node run at ordinary UART data rates up
to say 1 15.2 kbit/s, we can use an ordinary AVR microcontroller
for its brains.
LO
QO
After a bit of thinking I narrowed the choice down to two large-
scale project ideas, and went to consult a couple of colleagues:
Luc and Chris from the lab and Clemens from the international
editorial team, who has already seen several large projects
through to print debut.
The first idea was a general-purpose microcontroller base board,
into which a variety of processor boards could be plugged. Per-
haps we could include AVRs, PICs and 8051 -series processors?
The second idea was to develop our own bus system for inter-
connecting sensors, actuators, instruments and anything else
we could think of.
We soon came to the conclusion that ‘ElektorBus’ would be the
better choice for illustrating the development process in the
‘E-Labs Inside’ series, and so the ‘Elektor Controller Platform’
went back in the drawer until next time.
The ElektorBus should, we decided, be able to carry rapidly-
sampled sensor measurements as well as control signals, and be
suitable for use in a small home automation system. We would
be able to add new types of nodes gradually, the whole thing
would be easy to build and, of course, the software would be
open source down to its last bit.
O/LEDA/ANO
1/LEDB/AN1
/AN2/VREF-
/AN3/VREF+
RA4/T0CKL
RA5/AN4
S0/T13CKI
/ECCP2/P2A
ECCP1/P1A
SCK1/SCL1
/SDI1/SDA1
RC5/SD01
C6/TX1/CK1
C7/RX1/DT1
46
01-2011 elektor
RS-485 thus looked like the ideal option, and, as many readers
will know, is the electrical standard on which many diverse bus
systems are based. But still Ethernet, with its highly-developed
and sophisticated protocol stack and, significantly, enormous
open-source code base, seemed too attractive to discard.
Clemens had an idea: why not use both? Previously we
described a USB-to-RS-485 adaptor that uses a standard Ether-
net cable with four twisted pairs and RJ45 plugs at each end to
carry RS-485 signals (Figure 2) l 3 L RS-485 needs just two data
wires, and 1 0Base-T Ethernet uses just two of the four pairs in
the cable. Can we carry RS-485 and Ethernet in the same cable?
Could we even use the last remaining pair to supply power to
the nodes?
There is always a catch, and in this case it was the fact that mod-
ern Ethernet networks are arranged in a star topology. This
means that if we want to wire up a few sensors and actuators
in a single room, we end up with a spaghetti of cables. Many
home automation networks have a hierarchical structure where
Ethernet is used between the individual rooms of the house, but
the wiring between the nodes within each room uses a two-
wire bus.
Furthermore, as Chris pointed out, our combi-cable would be
incompatible with existing (mostly 1 0OBase-T) Ethernet equip-
ment. Often in modern devices the spare pairs in the Ethernet
cable are grounded (see for example Figure 3) t 4 ’ 5 l Clemens
started thinking about how to make best use of ready-made
cables in practice. For example, it is not possible to thread them
through a cable gland, so it is not easy to see how to make a
waterproof node for use outside or in the bathroom. This prob-
lem hadn’t even occurred to me, so it was a good thing that
there were three heads brainstorming rather than one!
We decided to leave out of our first specification any details that
we had not settled on. We would definitely use standard Ether-
net cable with four twisted pairs, with one pair for our bus and
one pair for 1 2 V and ground. (Clemens thought 1 2 V was the
best choice for most applications, as it gives some headroom
when powering 9 V or 5 V equipment.) The remaining pairs we
would reserve for future expansion, or perhaps an enterprising
reader might come up with a clever use for them. Of course
anyone making such ‘unauthorised’ modifications would have
to forfeit the right to use our neat ElektorBus logo on their
devices...
What bit rate should the RS-485 bus operate at? If we are using
just one twisted pair then it is simplest if all communications
happen at the same speed. We decided to take things gently
and first define an ‘ElektorBus low speed profile’ with a standard
bit rate of 9600 bit/s. This will allow us to use standard crystals
and probably also experimental hardware and software that we
already have. When that is working we will then venture on to
define ‘standard speed’ (1 1 5.2 kbit/s) and perhaps also ‘high
speed’ (around 5 Mbit/s) profiles.
To keep communications at different speeds separate we could
later make use of the spare pairs in the cable. Clemens was also
considering how he might arrange for different speed com-
munications to run on a single conductor pair. The transmit-
ter could transmit away, and the receiving node would have
to determine from a preamble sequence whether the mes-
sage was being sent at a speed it could read. Would the higher
bit rates have to be multiples of the slowest, he wondered? It
wasn’t long before we were deep in grisly protocol details...
What do you think? You can help inspire the design: the
ElektorBus team welcomes your ideas, improvements and
thoughts. Send them by email to editor@elektor.com.
(100817)
[1] www.elektor.com/ 1 00552
[2] www.elektor.com/ 1 001 74
[3] www.elektor.com/ 1 00372
[4] www.elektor.com/090607
[5] http://en.wikipedia.org/wiki/Ethernet_over_twisted_pair
VCCusb
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TEST MODE 0
U4 = 74LVC2G14
elektor 01-2011
47
Headphone Amp
Music to your ears
By Stefan Dellemann (Germany)
There have of course been numerous designs for headphone amplifiers before this one, either more or less
successful and simpler or more elaborate. The design presented in this article is straightforward, sounds
quite good and can be built using well-established components.
Specifications (output load: 33 £1, supply voltage: ±9 V)
• Input impedance (without Pi)
• Bandwidth
• THD + Noise (i kHz, i mW/33 £ 1 )
• THD + Noise (20 Hz - 20 kHz, 1 mW/33 £ 1 )
• Signal to noise ratio (ref. 1 mW/33 £ 1 )
• Max. voltage (into 33 £ 2 )
• Max. input voltage
• Current consumption
10 k£l
3.4 Hz - 2.4 MHz
0.005 % (B = 22 kHz)
0.01 % (B = 80 kHz)
89 dB (B = 22 kHz)
92 dBA
3.3 V (THD+N = 0.1 %)
0.57 V (with Pi set to maximum volume)
19 mA
These days it’s not that easy to find a sepa-
rate headphone amplifier in the shops. They
do exist, especially in the hi-fi world, but they
come with a matching price tag. The design
presented here comes in a bit below these
high-end circuits, but can be built using eas-
ily obtainable components and still manages
to have quite a good sound quality.
The circuit
The circuit could be described as a type of
power-amp, built with discrete components
(see Figure 1 ). At the input we find a vol-
ume control (PI , which is connected via a
header) and a coupling capacitor (Cl ), fol-
lowed by a differential amplifier (T 1 , T 2 )
with a constant current source (T 3 ) in the
emitter branch. The preset between T 1 and
T 2 (P 2 ) is used to set the symmetry, or in
other words, the output voltage is set to
0 volt DC compared to ground. For the best
sound quality we should have the same col-
lector current flowing through both transis-
tors. This can be seen from voltages at test
points F and G in the circuit diagram, which
are nearly equal. The input offset across R 1
is caused by the base current flowing into
T 1 . This causes the voltage at point A (V^)
to be slightly negative. A quick measure-
ment of the prototype showed that the base
current into T 1 was about 3 jiA. Without
the offset compensation provided by trim-
pot P 2 the output offset voltage V 0 would
exceed 0.2 V:
\^o = (1 + R 6 /R 5 ) x V (A)
V 0 = (1 + 1 0 / 1 . 5 ) x 0.028 = 0.21 5 V
The offset can therefore be removed by set-
ting the differential amplifier to operate
48
01-2011 elektor
MINI PROJECT
slightly asymmetrically. Although this isn’t the
best method as far as the sound quality is con-
cerned, it does keep the circuit much simpler.
Constant current settings
The current source in the emitter branch
(T3) is set to about 3 mA with diodes D1 ,
D2 and resistor R4, which results in T4 being
driven as linearly as possible.
The audio signal then makes its way to the
driver stage, T4, which drives the more
powerful output transistors (T6 and T7).
C4 has been added to provide a greater
internal gain. The quiescent current in the
output stage is set to about 5 mA with T5
and R9. Assuming a gain (/? FE ) of 50 in the
output transistors, this 5 mA could theo-
retically provide a linear 0.005 Ax50x32 £1
= 8 V peak into 32 £1. However, some limita-
tions are introduced by constant current
source T5 and the voltage drop across the
base-emitter junction of T7 (about 1 .5 V).
We should also take account of the voltage
divider around R1 1 and R1 2 (R1 0 and R1 2)
in the calculations. The maximum voltage
Umax across the load (R L ) then becomes
V max = R l |(R l +R^^+RU)x(9-^.5)
Wnax = 4.6 V peak
This corresponds to about 3.26 V rms , which
is what we measured, as you can see in the
specifications. This means that the circuit
can deliver (3.26 2 /32) = 330 mW into 32 £1,
which should be enough to keep most pop
and rock fans happy.
Resistor R12, which follows the output
stage, limits the output current and keeps
the circuit stable when a capacitive load is
connected, such as a long shielded cable to
the headphones. This prevents the output
transistors from overheating when there
is a short circuit. R1 0 and R1 1 keep things
symmetric. Despite the value of C2 in the
feedback circuit, the bandwidth is still much
greater than the audio bandwidth (see the
specifications). To obtain a low corner fre-
quency at the input we used 4.7 pF for Cl .
A capacitor of 2.2 pF (which is easier to
obtain) still results in an acceptable corner
frequency of 7 Hz (-0.6 dB at 20 Hz).
The measurements from one of our pro-
totypes are shown in the circuit diagram.
These should be seen as guideline values
T1,T2,T3,T5 = BC550C
T4 = BC560C
T6 = BD139
T7 = BD140
© 6..10V
A = - 28mV
B = - 33mV
C = 0.73V
D = 0.71V
E = 1.37V
F = 1.31V
G = 1.37V
H = 0.71V
I = 1.4V
J = 83.5mV
K = 80.5mV
♦
2x 1N4148
100701 - 11
© 6..10V
Figure 1 . The circuit forthe simple headphone amplifier uses easy to get components
(one channel shown).
Figure 2. The completed circuit is still compact despite the lack of SMDs.
elektor 01-2011
49
MINI PROJECT
COMPONENT LIST
Resistors
R1,R6 = 10kn
R2,R3 = 1l<£2
R4 = 270£1
R5 = 1.5kn
R7 = 4.7kn
R8,R9 = 150£1
R10,R11,R12 = 10£1
PI = 10kft
P2 = 100£2 trimpot
Capacitors
Cl = 4.7jiF, lead pitch 5mm or 7.5mm
C2 = 6.8pF, lead pitch 5mm
C3 = 1 0pF, lead pitch 5mm
C4,C5,C6 = 1 0OpF 1 6V radial
Semiconductors
D1 ,D2,D3,D4 = 1 N4148
T1 ,T2,T3,T5 = BC550C
T4 = BC560C
T6 = BD139
T7 = BD140
Miscellaneous
Connection for PI = 3-pin pinheader, lead
pitch 0.1”
Connection for PI = 3-way socket strip,
lead pitch 0.1 ”
7 pcs 1 .3mm diam. solder pin
PCB# 100701, see [1].
Figure 3. The component layout
for the no-frills headphone
amplifier.
rather than as exact requirements. The PN
junctions and the gain of the transistors can
of course vary depending on the manufac-
turer (this also applies to the current con-
sumption given in the specifications).
Experimenting
For those of you who don’t mind a little bit
more noise (although it will still be inau-
dible with most headphones), you can
increase the impedance of the feedback
loop to about 1 0 k£l. This can be achieved
by increasing R5 and R6 in the parallel cir-
Figure 4. The circuit has a distinctive appearance when it’s built into a ProjectCase.
cuit to 1 0 k£l. In this case the base currents
of T1 and T2 will compensate each other.
If you like experimenting you can replace
R5 with a resistor of 1 2 l and R6 with a
resistor of 68 k£l (perfectionists should use
1 1 .5 k£l and 76.8 k£l from the E96 series).
It is unlikely that this offers an audible
improvement, but there may be a smaller
offset this way.
Construction
A small printed circuit board has been
designed for this circuit (see Figure 2),
which can be ordered via PL From here you
can also download the board layout in PDF
format. The component layout is shown in
Figure 3. As usual, construction is easiest
if you start soldering the lowest compo-
nents (resistors, diodes) and then continue
mounting increasingly higher components
(capacitors, transistors, connection pins).
You will need two boards for a stereo ver-
sion, in which case PI has to be replaced
with a stereo potentiometer, so that the
volume can be controlled on both channels
simultaneously. If your audio source already
includes a volume control, you can leave out
PI (put a jumper on the header or solder a
wire link on the board from pin 1 and pin 2
of the header instead of the actual header).
The input impedance of our suggested cir-
cuit (which includes PI ) has a minimum of
5 l (PI set to maximum volume). This
shouldn’t be a problem for most modern
audio sources. Take note of the pin spac-
ing of decoupling capacitor Cl ; the board
accommodates 5 mm and 7.5 mm versions.
For the power supply you could use two
9V batteries. Alternatively, a 2x6 V, 5 VA
transformer with a 1.5 A bridge rectifier
and 8200 pF/1 6 V per supply rail is another
option. This could optionally be supple-
mented with a pair of voltage regulators.
The output transistors (T6 en T7) probably
don’t need heatsinks in practice, although a
small heatsink will make sure that they will
be short circuit proof.
We decided to build this circuit into an
Elektor ProjectCase I 2 ]. This is very easy to
do and it gives it a distinctive look and a
good view of the electronics (see Figure 4).
(100701)
Internet Links
[1 ] www.elektor.com/ 1 00701
[2] www.elektor.com/ 1 00500
50
01-2011 elektor
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ALTERNATIVE ENERGY
Free Energy
By Harry Baggen (Elektor Netherlands Editorial)
For centuries, savants have searched for ways to make devices move perpetually or to generate energy
from nothing. These pursuits still occupy the attention of many people, as can be seen from the massive
interest in this topic on the Web, along with innumerable projects. Is it truly possible to generate free
energy, or are we simply deceiving ourselves and others? Here we describe a selection of interesting ideas
and projects.
In the past, before the discovery of electricity, many savants spent
their time trying to develop a perpetual motion machine — a device
that would keep moving forever after it had been put in motion,
effectively drawing energy from the void. In the last two centuries
electrical energy has become increasingly important in our soci-
ety, and during this time the focus of people who invent devices
of this sort has shifted towards generating ‘free energy’, usually in
the form of electricity. However, the laws of thermodynamics say
that this is not possible. Despite the fact that these laws have been
known for more than a century, each year countless patent applica-
tions are submitted for devices of this sort. Highly ingenious lines of
thought and instructions appear in these patent applications, but
detailed examination of these devices ultimately reveals that they
do not work or that there is actually some source of energy present,
either concealed or perhaps unknown to the inventor.
History
It is known that self-powered machines were developed in ancient
India, starting as early as the seventh century. One of the best
known designs from that time is a wheel with a number of mer-
cury-filled cylinders attached to it. People in the western world also
attempted to develop similar types of self-powered devices. One
example is a device that uses falling hammers. Naturally, the free
energy devices designed by Leonardo Da Vinci are very well known,
but it is questionable whether he expected that they would actu-
ally work, since he said that according to his understanding they
could not possibly work. Many other inventors of perpetual motion
devices appeared after him. The first such device that ‘actually’
worked is ascribed to the inventor John Joseph Merlin, originally
from Belgium, who designed a self-powered clock in 1760. How-
ever, its operation was found to be based on natural changes in
ambient temperature and air pressure, which means that it cannot
be regarded as a true self-powered perpetual motion device.
Despite the progress of scientific knowledge, the dream of a perpet-
ual motion device continued to inspire many people. Especially from
the middle of the twentieth century onward, many inventors have
concentrated on the concept of ‘free energy’ (also known as zero
point energy), which involves devising a construction that delivers
more energy than what is supplied to it. Of course, there are vari-
ous ways to do this - a device that supplies electricity from sunlight
52
01-2011 elektor
ALTERNATIVE ENERGY
or water power effectively delivers energy for free without requir-
ing any sort of mysterious events. However, there are people who
go much further and try to extract energy from magnetic fields or
from an extra spatial dimension that has not yet been discovered
by anyone else.
With many of these inventions, it is very difficult to determine
whether they actually work. Although the inventors are convinced
that they work, in many cases they are unable to provide a reason-
able scientific explanation of how they work or demonstrate their
inventions.
Overviews of the history of perpetual motion devices, some with
background information and names of well-known persons may be
found at various websites including PI.
Figure 1 . Structure of a ‘Simple Magnetic Overunity Toy’ (SMOT).
(photo source: I 11 ))
Electricity from nothing
In the remainder of this article we focus on electrical free energy
devices, whose objective is to generate more electrical energy than
they consume. Here we are mainly interested in devices with the
least possible number of mechanical parts, and especially in devices
employing a lot of electronics.
Most of the devices we found on the Web utilise magnetic fields in
some way or the other, primarily with the aid of permanent mag-
nets and coils. The explanations of how these devices operate are
highly varied.
To demonstrate that it is possible to use magnets to cause an object
to move without supplying external energy, there is a very simple
experiment that can be performed using two bar magnets, a length
of aluminium U channel and a steel ball. This miniature perpetual
motion device (shown in Figure 1) is called the ‘Simple Magnetic
Overunity Toy’, or SMOT for short. The magnetic field between the
two magnets, which are positioned at a slight angle to each other,
causes the ball to roll uphill ‘by itself when it is placed at the low
end of the slightly inclined U channel. This idea dates from 1922,
and in 1 997 Greg Watson produced an updated version. A detailed
description of a practical implementation and test results are avail-
able on the website of French experimenter J.L. Naudin l 2 L It’s fun
to try this for yourself. Incidentally, a variety of explanations of how
the SMOT works can be found l 3 l.
Most energy generators use a rotating wheel fitted with several
magnets. The magnets rotate beneath coils that act alternately
as drive coils and detection coils with the aid of electronic control
circuitry. This objective of this arrangement is to generate more
energy than the drive energy supplied to the coils to keep the wheel
turning. Many systems of this sort have rather complicated mechan-
ical constructions, but there are a few very simple generator designs
that are quite suitable for experimentation by people who are not
expert machinists. For instance, at Kl there is a description of howto
convert an ordinary PC fan into an energy generator. There is also a
YouTube video t 5 ] that shows you how to make the conversion. Fig-
ure 2 shows the simple schematic diagram of the full circuit.
John Bedini has developed several projects that are very popular
with everyone interested in free energy generators. He has sev-
eral decades of experience in this area, and a large number of gen-
erators of various types are described on his website I 6 !. To show
Figure 2. A simple circuit is all you need to convert a PC fan into a
free energy generator, (source: P 2 1)
Figure 3. This free energy generator from Ron Pugh has a
reasonably simple mechanical design, (source: P 2 1)
elektor 01-2011
53
ALTERNATIVE ENERGY
Figure 4. The MEG is a generator with no moving parts. This is the
original schematic diagram from US patent 6.363.71 8 B1 . (source: l 7 l)
The MEG v3.0 build and tested by JL Naudin - Nov 22th, 2000
Motionless Electromagnetic Generator from Tom Bearden
Email: Jnaudin509@aol.com - http://go.to/jlnlabsy
Figure 5. A practical MEG transformer implementation designed by
J.L. Naudin. (source: I 7 !)
how easy it is to build your own version of a Bedini generator, he
describes a special design that he claims can be built by a ten-year-
old schoolgirl.
A design by Ron Pugh based on Bedini’s ideas (which is also
described clearly and extensively at HI) is illustrated in Figure 3.
The mechanical construction of this design is reasonably simple. It
has a homemade rotor with six pairs of magnets glued into slots in
the rotor. Three coils used to drive the rotor and generate energy
are mounted around the perimeter of the rotor. The control elec-
tronics essentially consists of a number of power transistors and a
few passive components. An experienced electronics enthusiast can
probably design a tidier version of the electronics (with a PCB), but
what ultimately matters is the overall concept.
The ‘Motionless Electromagnetic Generator’ (MEG) is an invention
of Tom Bearden etal. I 7 ] based on a special transformer with a per-
manent magnet fitted in the middle (see Figure 4). Two large wind-
ings for energy output are fitted on the outer ends of the trans-
former core, while two smaller windings for energy input are fitted
near the middle. This device is claimed to be able to extract electro-
magnetic energy from the vacuum, thereby supplying more energy
than it consumes. Here again the Frenchman J.L. Naudin has devel-
oped a very nice prototype (Figure 5) with a number of improve-
ments compared to the original design I 8 !. He has also generated a
simulation of the magnetic field for this design.
Finally, we wish to draw your attention to the ‘Tesla Switch’ I 9 ], since
it can be built using only electronic components with no need for a
special transformer. The circuit is based on Tesla’s ideas, as imple-
mented by Ronald Brand and John Bedini in the form of a circuit with
three rechargeable batteries that are repeatedly connected in series
in different configurations in which one of the batteries is charged
by the other two. The ultimate result is three fully charged batter-
ies, which means that energy has been extracted from an unknown
source in some way or the other. The circuitry of the Tesla Switch
is fairly simple. An especially interesting version of this idea can be
obtained by replacing two of the batteries with electrolytic capaci-
tors, so that only one battery is necessary (Figure 6). Unfortunately,
few detailed circuits based on this principle can be found on the Web.
As you can see, the ‘free energy’ area is a hotbed of experimen-
tal activity. The question is whether it ultimately delivers anything
useful. In this regard, we wish to conclude this article with the fre-
quently given advice ‘don’t try this at home’, accompanied by a
request to subject a number of the designs described to detailed
examination and even try to develop your own design for a sim-
ilar sort of energy generator. We are very interested in hearing
about your experience, results and conclusions, both positive and
negative.
Internet Links and References
[1] www.theorderoftime.com/ned/wetenschap/nieuweenergie/4.
html, www.hp-gramatke.net/perpetuum/index.htm
[2] http://jnaudin.free.fr/html/smotidx.htm
[3] www.mathematik.tu-darmstadt.de/~bruhn/SMOT.HTM
www.lhup.edu/~dsimanek/museum/smot.htm
[4] www.free-energy-info.co.uk/Chapt6.html
[5] www.youtube.com/watch?gl=US&feature=related&hl=uk&v=e
DS9qk-Nw4M
[6] http://johnbedini.net/
[7] http://cheniere.nii.net/megstatus.htm
[8] http://jnaudin.free.fr/meg/meg.htm
[9] www.icehouse.net/john1 /tesla. html
[10] www.lhup.edu/ ~dsimanek/museum/unwork.htm#top
[11 ] www.hcrs.at
[12] www.free-energy-info.co.uk
54
01-2011 elektor
ALTERNATIVE ENERGY
SCALAR WAVE CONTROLLER
THE SCALAR BATTERY CHARGER
Figure 6. A yield of more than 1 00% is possible with the Tesla Switch’, which alternately charges and discharges two electrolytic capacitors.
Figure 6a shows the basic concept according to Bedini, while Figure 6b shows a detailed circuit designed by Naudin. (sources: and t 9 l)
If you find the entire subject of free energy preposterous, we sug- After visiting this website, you will doubtless find yourself reinforced
gest you have a look at the ‘Museum of Unworkable Devices’ I 10 ). in your convictions.
(100672-I)
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elektor 01-2011
55
WIRELESS ECG
Wireless ECG
Monitoring cardiac signals with ZigBee
By M. Denoual, 0. Clouard, M. Sligard, B. Hu,
N. Bessot and S. Moussay (France)
The combination of electronics and biology
always yields interesting projects. The system
describe here is easy to build and enables the
wireless monitoring of cardiac signals. ZigBee
modules are used for the wireless link.
Kev features
• ECG resolution 10 bits
• ZigBee wireless data transmission
• Range 100 m (outdoors)
• Based on XBee modules
• No programming necessary
• Serial computer interface
• Identical PCBs for acquisition and
receiver boards
Many devices are available for recording
or visualising electrocardiogram (ECG) sig-
nals. Protection of the subject (patient) is
a paramount requirement with all of these
devices, which is why circuits of this sort are
typically powered by batteries. This circuit is
also battery powered, but it uses a wireless
link as an elegant solution to the problem
of galvanic isolation, completely eliminat-
ing any hazard to the subject. The wireless
link also gives the subject more freedom of
movement.
This special approach forms the basis for
this project, which was originally developed
for monitoring athletes while they are exer-
cising or performing.
Why ZigBee?
ZigBee technology is an ideal choice for this
application in terms of cost, ease of use and
low power consumption. The data transmis-
sion rate of 250 kbit/s is sufficient for appli-
cations such as transmitting ECG signals,
which have a narrow bandwidth. The range
of 1 00 m (300 ft.) outdoors or 30 m (1 00 ft.)
indoors with the selected XBee modules i 3 l
is sufficient for monitoring in a gym or sta-
dium, and the range could be extended to
1 km for monitoring outdoor sporting events
by using higher-power modules and relay
modules. Finally, ZigBee modules (in partic-
ular the XBee modules from Digi) have inte-
grated A/D converters, which simplifies over-
all circuit design and construction.
Hardware
The system consists of two parts: a data
acquisition board that senses the ECG sig-
nal and a receiver board that is connected
to a PC for displaying the ECG signal. In this
article we also describe a third module that
can be used to adjust the data acquisition
board and test the wireless data link. It is a
sort of signal generator that produces an
artificial ECG signal.
Acquisition and receiver boards
The block diagram and schematic diagram
of the acquisition board are shown in Fig-
ure 1 and Figure 2, respectively. The board
is designed to be used with three electrodes
(two sense electrodes and one reference
electrode; see the ‘ECG Measurement’
inset). It has an analogue stage that ampli-
fies and filters the input signal before it goes
to the 1 0-bit A/D converter integrated into
the XBee module. The board is designed
to allow all components to operate from a
single 3.3-V supply voltage, which matches
the operating voltage of the XBee module.
A compact 3.3-V lithium-ion button cell
would be a good choice for powering the
board. However, during development it was
more convenient to use a regular 9-V bat-
56
01-2011 elektor
WIRELESS ECG
Figure 1 . Block diagram of the acquisition circuit.
tery together with a 3.3-V regulator on the
board to power the circuit.
The 3.3-V supply voltage restricts the choice
of components for the analogue functions.
The economical AD623 instrumentation
amplifier is able to operate from a single
supply voltage, and so are the OPA237 opa-
mps used in the filter stages. The reference
level for the circuitry is provided by a 1 .2 -V
potential generated by a MAX6120. This
potential is applied to the subject’s body by
a reference electrode, and it determines the
common-mode level of the signals picked
up by the sense electrodes. A reference
potential of 1 .5 V can also be used if a suit-
able reference voltage 1C in an SMD package
is available.
The first-order high-pass filter built around
IC5 and the low-pass filter built around IC3
limit the effective frequency band of the
signal and amplify the signal. The low-pass
filter also acts as an anti-aliasing filter for
the A/D converter. A passive twin-T filter is
placed ahead of the converter input (pin 20
of the XBee module) to suppress any 50-Hz
mains hum that may be present. If desired,
it can be bypassed when the board is used
in an environment free from mains interfer-
ence. The 3.3-V supply voltage is connected
to pin 1 4 to serve as the reference voltage
for the A/D converter.
IC6
LM317/CYL
BAV99
high-pass filter
A=lf c = 0.15 Hz
3.3V
O
low-pass filter
A = 142 f c = 102 Hz
3.3V
O
double-T filter f c = 50 Hz
JE
□Lj
CO
CO
CO
CO
br
— 1
»
mnn
1
—
080805 - 17
Figure 2. Schematic diagram of the acquisition circuit.
elektor 01-2011
57
WIRELESS ECG
ECG Measurement
This circuit uses three electrodes to sense the electrical acti-
vity of the subject’s heart. Two of the electrodes are placed on
the subject’s wrists, and the third is placed on the left leg. The
electrodes on the wrists pick up the electrical signal, while the
electrode on the leg provides a reference level for the other
electrodes.
The adjoining figure shows the electrical signal generated by a
beating heart and the phases of the cardiac cycle:
• P wave: contraction of the auricles. Blood from the veins is
pumped into the ventricles.
• QRS complex: contraction of the ventricles. Blood
flows out of the heart and is pumped into the arteries.
The combination of P and QRS waves generates the
characteristic lub-dub’ sound of a heartbeat.
• T wave: repolarisation of the ventricles. The heart muscle
returns to the relaxed state.
See reference [2] for more information on ECGs.
Relationship between the electrical activity of the heart
and the phases of the heartbeat cycle. Pulse R has an amplitude
of only a few millivolts. The bandwidth of the pulses
in the ECG signal is 0.1 to 1 00 Hz.
Electrodes
In order to make good ECG measurements, it is essential to use good electrodes and to attach and connect them properly.
We recommend using shielded cables to reduce interference from external sources. In theory, shielded audio cables are quite suitable for this
purpose, but the ends of these cables are fairly fragile. We therefore recommend using small connectors in combination with heat-shrink tub-
ing to virtually eliminate the risk of breakage (see Figures a and b).
You may have already noticed the shields are connected only at the acquisition board end pf the cables and are carefully insulated at the elec-
trode ends to prevent any contact with the skin.
If you terminate the cables in 4-mm plugs, you can use commercial electrodes (Figure c), but the prices of these electrodes may put you off
(more than 1 0 pounds each, and you need three of them). However, you can also make your own electrodes from coins containing nickel to
make the electrodes (some research required to find suitable coins; “Google is your friend”). Solder a length of 4-mm metal tubing onto each
coin to receive a 4-mm plug, and you’re ready to go.
Use elastic straps (one for each electrode) to hold the electrodes securely in place on the subject’s wrists and lower calf. You can make your
own straps by cutting suspenders straps into suitable lengths and sewing or gluing Velcro table to the ends. Straps cut from a bicycle or scoot-
er inner tube are also serviceable.
58
01-2011 elektor
WIRELESS ECG
The wireless signal is received by a board
holding only an XBee module only. All
you actually need to receive the data and
transfer it to your PC is an XBee module
and a USB to TTL adapter cable (avail-
able from the Elektor Shop; item num-
ber 080213-72 for the 3.3-V version).
To power the module from the USB bus,
install wire link A on the board. Actually,
the combination of an XBbee module and
a USB-TTL cable (caution: 3.3 V version
required, Elektor order code 080213-72,)
is sufficient to receive data and convey
it to the computer You can also use this
cable for configuring the XBee modules.
For this purpose, be sure to connect the
supply voltage lead of the cable (on the
TTL connector) to the XBee module. For
data reception, the XBee module only
needs to be configured for a serial data
interface.
Configuring the XBee modules
The XBee modules can be configured using
a 3.3-V USB to TTL adapter cable and the
free program X-CTU I 4 !. The default serial
data transmission rate of the XBee mod-
ule is 9600 baud. To configure a module,
connect it to the PC via the serial interface
adapter cable, connect a power source to
the module, and launch the X-CTU program
(Figure 3).
You can use the ‘Modem Configuration’ tab
to read and modify the configuration regis-
ters of the XBee module. After selecting this
tab, click ‘Read’ to read the current register
settings. You can modify them directly by
selecting values from a drop-down menu,
or you can enter new values from the key-
board. After changing the settings, select
‘Write’ to save the new register contents.
The first time you use X-CTU, you may be
asked to download a new version of the
modem firmware for the connected XBee
module. Click ‘Download new versions...’ to
do this automatically, after which you can
use the ‘Function Set’ and ‘Version’ menus
to select the new modem versions for your
modules.
Before you configure the modules, it’s a
good idea to assign them ID codes so you
can tell them apart. After this you must give
Figure 3. User interface of the X-CTU program for configuring XBee modules.
Figure 4. Block diagram of the ECG simulator.
+5V
Figure 5. Schematic diagram of the ECG simulator.
elektor 01-2011
59
WIRELESS ECG
COMPONENT LIST
Resistors (SMD 0805 )
R1 ,R19,R20 = 10k£2
R2,R11,R14= 1MO
R3=470I<£1
R4 = 240Q
R5,R9 = 27k£l
R6,R7,R12,R13,R16 = 33I<£1
R8 = 360^
R10 = 8.2I<£2
R15,R17,R18 = 47kn
Capacitors (SMD 0805, ceramic, except
C1,C7)
Cl ,C7 = 47|iF 1 0V, SMD, Kemet
B451 96E2476K409
C2,C4,C8,C9,C1 1 ,C1 2 = 1 0OnF
C3,C6,C13 = 10nF
C5 = 3,3nF
Cl 0 = 1 jllF
Semiconductors
D1 = 1N4148SMDMinimelf
D2,D3,D4 = dual diode BAV99 (SOT23)
IC1 ,IC3,IC5 = OPA237NA/250 (SOT23-5)
IC2 = MAX61 20EUR+T (SOT-23)
IC4 = AD623ARZ (SOIC-8)
IC6 = LM31 7LM (SOIC-8)
Miscellaneous
K1 ,l<2 = 2-pin pinheader, lead pitch 0.1 ”
(2.54mm)
l<3 = 5-pin pinheader, lead pitch 0.1 ”
(2.54mm)
l<4 = 6-pin pinheader, lead pitch 0.1 ”
(2.54mm)
SI = pushbutton, make contact, PCB mount,
6mm, e.g Multicomp type MC32830
XB1 = XBee module, ZB ZigBee with chip an-
tenna, Digi type XB24-Z7CIT-004
A = no wire link
PCB #080805-1, see [1]
Receiver only
XBee-module, Digi type XB24-Z7CIT-004
USB-to-TTL cable, 3.3V version, Elektor #
080213-72
R19.R20 = 10l<£2
l<4 = 6-pin pinheader, lead pitch 0.1 ”
(2.54mm)
SI = pushbutton, make contact, PCB mount,
6mm
A = wire link
PCB #080805-1, see [1]
Component layout of the
acquisition board.
each module a unique address. Every XBee
module actually has two addresses. The first
is a long unique address (64 bits) in the form
of a serial number assigned by the manufac-
turer, which is divided into two parts: ‘Serial
Number High’ (SH) and ‘Serial Number Low’
(SL). The second is a short address (16 bits)
assigned by the user. The short address is
used in this system. Configure the short
addresses of the modules by setting the
‘Destination Address High’ (DH) register to
‘0’ and the ‘Destination Address Low’ (DL)
to a value less than ‘OxFFFE’.
Configuring the module
on the acquisition board
• ‘Networking & Security’ menu: Con-
figure the module as an end station by
setting ‘Coordinator Enable’ (CE) to ‘O’.
Then set the destination address (DL) to
‘0x1 234’ and the source address (MY) to
‘0x5678’.
• ‘I/O Settings’ menu: Set ‘DO’ to ‘2’ to
enable the A/D converter connected to
pin 20 (ADC 2). The XBee module has six
ADC inputs (ADO to AD5) on pins 11,15,
and 1 7-20. Set ‘IR’ to ‘3’ to configure
the sample rate interval to 3 ms. This
interval is sufficient for digitising the
ECG signal applied to pin 20 of the mod-
ule after amplification and filtering. IR
will subsequently be set to ‘1 ’ for trans-
mitting the sampled data sequence.
Configuring the module
on the receiver board
• ‘Networking & Security’ menu: Set ‘CE’
to ‘1 ’, since this module controls the
transmission process. Set the addresses
to DL= ‘0x567’ and MY = ‘0x1 234’.
• ‘I/O Settings’ menu: Enable the I/O
enable command (I/O Output Enable) by
setting III to ‘1 ’ (Enabled).
• ‘I/O Line Passing’ menu: Set ‘I/O Input
Address’ (IA) to ‘0x5678’, which is the
same as the address of the module on
the acquisition board. If you set ‘PWMO
Configuration’ (PO) to ‘2’ (PWM Out-
put), you can view the transmitted ECG
signal on the receiver board with an
oscilloscope after connecting a 200-Hz
passive filter to the PWMO output on
pin 6.
ECG signal simulator
We designed this circuit (see Figures 4
and 5) to allow tests and measurements
One of the first ECG diagrams taken with the system.
The three electrodes are vessels filled with saline water.
60
01-2011 elektor
WIRELESS ECG
E T ]
Figure 6. Simulated ECG signal at the output of a low-pass filter connected to the PWM
output of the receiver module (trace 1 ) and the signal from the ECG simulator after
attenuation (trace 2).
on the entire system to be made safely dur-
ing the design phase. It generates a signal
that resembles a real ECG signal in terms of
period, pulse width and amplitude. This arti-
ficial ECG signal is generated by an NE555
configured as an astable multivibrator.
The outputs are referenced to a level of
approximately 1 .2 V by R7/R8 and R9/R1 0,
so they can be connected directly to the
inputs of the acquisition card. Capacitor
C6 connected to the output of the NE555
shapes the pulse waveform. The diode
clamps the negative pulses, and the ampli-
tude of the resulting signal is reduced to a
few millivolts by voltage divider R5/R6.
Assembly
Assembling the acquisition and receiver
cards is relatively straightforward. Note
that the XBee modules have an unusual
lead pitch of 2 mm and the leads are square.
However, special matching connecters are
available. Nine leads of the module on the
acquisition card are used, while only five
leads of the module on the receiver card are
used. Individual socket posts cut from an 1C
socket can be used for the connections to
the module leads.
To allow the modules to be programmed,
reprogrammed or used later for other pur-
poses, they should not be soldered directly
to the PCB.
You can use stimulation electrodes for the
body electrodes, or you can make your own
as described in the ‘Electrodes’ inset.
Viewing the ECG signal
For safety reasons, you should never con-
nect an oscilloscope directly to the acquisi-
tion board in order to view the ECG signal.
However, you can view the signal on the
receiver card if you connect a filter to the
PWM output. An example is shown in Fig-
ure 6. Another option is to view the signal
on the PC monitor by using a program that
displays the data received from the inter-
face cable in graphic form. Figure 7 shows
an example of an ECG plotted with the aid of
an interface developed with LabVIEW. It is
available as an executable file on the Elektor
web page for this article Pi and on the pro-
ject website t 5 l. This simple program allows
the ECG signal to be visualised quickly.
(080805-I)
Internet Links
[1] www.elektor.com/080805
[2] ‘GBECG’, Elektor October 2006,
www.elektor.com/050280
[3] ‘ZigBee Transceiver’, Elektor March 2007,
www.elektor.com/060348
[4] www.digi.com/support
[5] www.enseignement.ensicaen.fr/claro-
line/course/index.php?cid=PRJECGXBEE
(in French)
VlSArtftMtti
(MdhlrftCf
^11.
fietj
: Site fcJSi \'Vt M»[ QQJI a| a=
WSjsJrtis
RSI
Kfi SS
Figure 7. An actual ECG signal on the PC monitor, visualised using a LabVIEW interface.
elektor 01-2011
61
IR CAMERA
Groping in the Dark
Webcam conversion to night-vision camera?
By Thijs Beckers (Elektor Netherlands Editorial)
Cameras with night-vision capability are not all that cheap.
Webcams are. Can you modify such a webcam so that
it becomes suitable as a night-vision camera? Several
Internet sites claim that this can be done. We will put
some these claims to the test.
There is a nearly limitless supply of these on the Internet: tutorials
for converting all kinds of (electronic) devices. This time our eyes
were drawn to converting a cheap webcam into a camera with night-
vision capability, that is, a camera which is still able to see in com-
plete darkness. The phrase ‘in complete darkness’ is however a little
deceptive in this case. To illuminate the field of view of these cam-
eras an infra-red floodlight is used, which operates at a wavelength
that is not visible to the human eye (all electromagnetic radiation
above 780 nm).
Anyhow, we were very curious whether this would be possible
with any arbitrary webcam. According to the tutorials, you have
to remove the IR filter that is in the camera, so that infra-red light
will now also register on the CCD of the camera. So, time to get
cracking.
Not too expensive
For our ‘test’ we ‘borrowed’ two webcams from our colleagues.
Preferably as cheap as possible. We had a Sweex WC002 and a Konig
Computer CMP-Webcam75 at our disposal, neither more expensive
than 30 pounds. As a consequence, the quality of the images is not
that great, but that was to be expected. The CMP-Webcam75 had
the biggest CCD and also the highest resolution: the camera can
supply up to 1 290 x 960 pixels. Displaying the image with the same
resolution on the laptop screen resulted in the ‘best’ picture. By the
way, the webcam is offered on several web sites as a ‘webcam with
night-vision’. But don’t be fooled: the four built-in white LEDs are
barely sufficient to illuminate your face when you’re directly in front
of the cam-
era, while chatting
and the like. Anything
further away than about
1 metre remains practically invisible to the unmodified camera.
Results before...
After installing the accompanying drivers for these webcams, we
decided to test the cameras before making any modifications, so
that we could clearly establish any differences brought about by
the modifications. In the basement we found a place were we could
work that was practically completely dark, which was therefore per-
fect for our test location.
First we looked at the images with the lights still on (Figure 1 ).
On the left is the picture from the CMP-Webcam75, which is set
to 640x480 and on the right the picture from the WC002, set to a
resolution of 352x288. For clarity we stretched the latter picture to
the same size as the Konig webcam. Although the Sweex claims that
640x480 is possible, this is not the case at 30 frames per second...
Both drivers are at their default settings.
To be able to see something in the dark with these cameras we used
Figure 1 . With the lights on both cameras show a
(not all that high a quality) image.
Figure 2. Without lights the image of both cameras
remains black.
62
01-2011 elektor
IR CAMERA
a few individual IR-LEDs and a — somewhat older, but nevertheless
still very well functional — IR-floodlight with 28 IR LEDs from Con-
rad Electronics.
Neither of these webcams were able to see anything in complete
darkness, despite the fact that the infra-red LEDs were turned on
(Figure 2). Some image noise and the odd lost red, blue or green
pixel were the only things visible on the laptop screen. Only when
we pointed the IR LEDs directly into the lens could we see that they
were actually turned on. It was not possible to recognise any objects
at all in the dark.
From this it appears that both cameras have a built-in IR filter. So,
open them up, because that has to come out.
...and after modification
The lenses are relatively easily removed from the cameras. The
Sweex camera is simply snapped together and with the Konig the
lens can be unscrewed easily. At certain angles it was possibly to
see a red gleam on both lenses: the IR filter. With the Sweex lens
we suspected that this could be a coating on the outside of the lens.
Attempts to remove the coating, even with a strong cleaning solu-
tion, proved to be unsuccessful (the plastic of the lens was melted
by the solvent, but unfortunately not the coating). The other lens
was different. Here it appeared that on the inside there was a real
glass filter. After some careful fiddling (it still had to look nice for the
camera) we were able to remove the glass and had the IR filter in our
hand (see Figure 3). And now the proof is in the pudding: was the
camera with the modified lens more sensitive to IR-light, and if yes,
was it actually able to see anything in complete darkness?
Figure 4 shows the picture after modification, on the left the Konig
and on the right the (unmodified) Sweex. We were quite impressed
with the difference! Even with only three IR LEDs it already became
clear what objects there were in the dark room. And not only the
outlines! It was even possible to read the text on the removal box at
a distance of about 5 meters. The result with the IR floodlight was
even better (Figure 5). Movement detection is easily possible. We
would even dare to suggest that it would be suitable for a security
camera at home.
We do however have to make a marginal note: we noticed that the
focus for the modified lens with IR illumination was different from
the focus for normal lighting. When we switched the lights on after
we had focussed the Konig lens with IR light, we obtained the pic-
ture of Figure 6 on our screen. It was hard to find the correct focus
for the Konig webcam. This ‘trick’ is therefore not all that suitable
if you want to be able to use the camera both at night and during
the day. But because the webcams are so cheap, even the purchase
of a pair — one for during the day and one for at night - is still con-
siderably cheaper than a real night-vision camera.
The conclusion is therefore that if the IR filter can be removed, then
the webcam is perfectly suitable as night-vision camera, but the IR
filter is not easily removed with all cameras.
( 100537 -I)
Figure 3. With the Konig lens the removal of the IR filter was quite
easy to do.
Figure 4. Using only 3 IR-LEDs a nice picture already begins to form
with the modified camera. The camera with IR-filter is still groping
in the dark.
Figure 5. The IR-floodlight from Conrad makes everything clearer
still. People are easily recognisable in complete darkness.
Figure 6 . Using the modified camera during both the day and night
is unfortunately not very practical: the focussing has to be redone
every evening and morning, and by hand.
elektor 01-2011
63
DESIGN TIPPS
Opamp versus Comparator
Superficially similar yet decidedly different
By Michael Holzl (Germany)
Practically every lecture course or textbook on electronics describes
how to use an operational amplifier as a comparator. Here we look
at the possibility in more detail, and see how it can often be a very
poor idea.
The idea behind the comparator configuration is simple. An opamp
has a very high open-loop DC gain which means that even a tiny
differential input voltage will drive the output to one extreme or
the other. If the voltage at the non-inverting (*+’) input is greater
than that at the inverting (*-’) input the output goes high; oth-
erwise the output goes low. In other words the two voltages are
compared and the output is a binary indication of which of the
two is the greater. So the opamp looks like the perfect device to
provide digital logic levels at their outputs while accepting sym-
metrical analogue input signals.
What do these differences mean in practice? Comparators can react
very quickly to changes in their input voltages with short propa-
gation delays and output rise- and fall-times all specified by the
manufacturer. In contrast, because opamps are not expected to be
used in this mode, manufacturers tend not to give explicit speci-
fications for propagation delay and rise- and fall-times (although
they do normally specify slew rate), and these characteristics can
be considerably poorer for opamps than for comparators. To take
an extreme example, a low-power opamp might have a propaga-
tion delay measured in milliseconds, whereas a comparator might
react in nanoseconds: a million times faster.
U1
1
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r
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1
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SPICE simulation results: an LT1 028 opamp pressed into service as a comparator versus a real comparator type LT1 720.
use as a comparator. But why then do there exist special-purpose
comparator devices?
Looked at from the outside, opamps and comparators appear indis-
tinguishable. Besides power connections, they both have *+* and
inputs and a single output. Taking a look at the internal circuit dia-
gram, again the two devices appear broadly very similar (although
a comparator device with an open-collector or open-drain output
does look more obviously different from an opamp). The big dif-
ference, which is not apparent without looking at the circuit more
closely, is that the output stages of operational amplifiers are
designed for linear operation, with the general aim of amplifying
the input signal with as little distortion as possible (assuming that
some negative feedback is provided), but in the case of a compara-
tor the output circuit is designed to operate in saturation, that is, to
switch between the upper and lower output voltage limits without
the provision of external feedback. Comparators often also offer a
ground connection in addition to the usual power connections, and
There is a further problem with opamps. Many devices exhibit sig-
nificantly increased power consumption when the output is in satu-
ration, the resulting power dissipation on occasion being enough
to destroy the device. Also, many opamps (those not advertised as
having ‘rail-to-rail outputs’) are not capable of driving their out-
puts close to the supply rails, for example having a maximum out-
put voltage of 3 V with a 5 V supply. There can also be restrictions
on the inputs. Some opamps are equipped with antiparallel diodes
across their input terminals, which prevent differential input volt-
ages of more than about 0.6 V whereas comparators’ inputs are
often allowed to vary over the whole supply range.
Of course, there are many non-critical applications where an opamp
will work perfectly acceptably as a comparator, but it is not a prac-
tice to be recommended. The sceptic should lash up a quick test
with a comparator and an opamp side-by-side, each fed with a
squarewave signal with rapid edges. Some of the potential pitfalls
64
01-2011 elektor
are shown up more easily in simulation, such as the possibility of an I
opamp being so slow that it entirely misses a narrow pulse. It is hard f
to guarantee circuit performance, current consumption, and even I
the survival of the device.
The illustrations show a SPICE simulation of a relatively nimble
opamp (an LT1 028 with a minimum slew rate of 1 1 V/ps) and a type
LT1 720 comparator. It is clear that the comparator responds sooner
and with a much shorter rise-time. Its output swings all the way to
+5 V rather than the 3 V managed by the opamp. The situation is
similar when the output swings low: the opamp is much slower and
only reaches an output voltage of -3 V rather than -5 V. The original
squarewave is hardly recognisable at the opamp’s output. Although
the LT1 028 cannot achieve its maximum specified gain with a ±5 V
supply, it is still a factor of at least 20 faster than an LM324 (with a
slew rate of 0.5 V/ps); what the latter would make of our square-
wave would not be a pretty sight. The opamp fails to cope at all
with shorter pulses, which are then effectively ‘swallowed’, while
the comparator continues to handle them without difficulty.
Worthwhile further reading on this subject is Texas Instruments
Application Note SLOA067 by Bruce Carter, entitled Op Amps and
Comparators - Don’t Confuse Them!.
(100050)
WWW.
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elektor 01-2011
65
MICROCONTROLLERS
Support Board
for Arduino Nano
By Philippe Fretaud & Francois Auger (Saint-Nazaire Institute of Technology, France)
Arduino boards exist in several formats. The standard board
(which itself also exists in several versions like the Diecimila, the
Duemilanove, the Uno, etc.) is the one that measures around 5x7cm
and to which can be added a ‘shield’ — an Arduino extension board.
The LilyPad board is a circular Arduino for
clothing applications, and the Nano is a
small Arduino module (18 x 43 mm) spe-
cially designed for use with prototyping
boards and breadboards.
As these two outputs can’t supply much
current, an additional 5 V linear regulator
has been incorporated into the support
board. The 9 V input rail is also wired to l<6
and l<7.
In place of the standard Arduino’s female
connectors, the Nano has two rows of 1 5
solder pins on a 2.54 mm (0.1 ”) pitch. So
it looks quite a bit like the boards for older
microcontrollers like the Basic Stamp 2 or
the CUBLOC CB320, with an additional USB
link that is ideal for current computers.
Unlike a standard Arduino module, the
Nano needs a support board if we want to
use it in an application. In this article, we’re
proposing a motherboard that was origi-
nally designed for a robotics application,
but which can very well be used for other
jobs too. The robotic aspect of this board
can be seen in the 6 V supply and connec-
tors l<4 and l<5, to which a servomotor can
be connected. If you’re not using servos,
you can dispense with the 6 V supply.
For the rest, the board is very simple: All
the Nano’s inputs/outputs are quite simply
brought out to two 25-pin sub-D connec-
tors (l<6 and l<7).
The boards are powered by 9 V. The Nano
has an on-board 5 V linear regulator, and
also makes available the 3.3 V rail produced
by the USB interface chip. By means of JP1 ,
one of these two voltages can be connected
to K6and l<7, by fitting a jumper to contacts
1 and 2 (5 V) or 2 and 3 (3.3 V). These rails
are also available when the Nano is powered
via its USB port.
(100396)
66
01-2011 elektor
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COMPUTERS
Three Out of Two Ain’t Bad
Add a tachometer output to 2-wire fans
By Volker Schmidt (Germany)
If you replace a broken three-
wire fan in a PC or other device
with a more readily-available
two-wire fan, the missing
tachometer (‘tacho’), signal
will cause the system to report
a fault and possibly even refuse
to function at all. The problem
is solved with the circuit shown
here, which analyses the fan
current to generate a signal
that corresponds to its rotation
speed.
Three-wire fans have an internal tachome-
ter which produces a signal on the third wire
(the other two being the supply voltage and
ground) whose frequency depends on the
rotation speed. This output can be used by
the device being cooled by the fan to check
that the fan is running.
If such a fan is replaced by one of the two-
wire variety, it is possible to simulate the
tacho signal with an astable multivibra-
tor circuit, for example using a 555 timer.
However, this has the disadvantage that
the operation of the fan can no longer be
properly monitored by the device. One way
to generate a meaningful tacho signal is to
analyse the current draw of the fan.
The simple circuit shown here uses a read-
ily-available TL074 quad op-amp and just a
handful of other ordinary components.
How it works
The circuit does not look at the absolute
level of current draw of the fan: rather, it
analyses the regular variations in current
which are synchronised with the rotation
of the fan. The oscilloscope trace in Figure 1
shows the characteristic regular interrup-
tions to the current flow from which our cir-
cuit derives the tacho signal. We use a low-
value resistor as a current sensor, coupled to
a differential amplifier to extract the signal.
The resulting signal is then cleaned up and
used to trigger a monostable circuit.
The details
The circuit of the tacho signal generator
(Figure 2) is centred around a type TL074
quad op-amp. A few passive components,
three diodes, one Zener diode and two tran-
sistors complete the circuit.
R1 is the current sensor, with a value of 1 Q.
The low value means that the voltage to
We tested the circuit in the Elektor labs
with a two-wire fan made by Canon (type
number CF80-T21 1 N1 D). We compared
the tacho signal output by the circuit
with that of a three-wire fan, a Sunon
KDE1 208PTB1 -6A, which provides its ta-
cho signal on a yellow wire.
With a 1 2 V supply the circuit worked well.
the fan will not be reduced to a significant
extent. Differential amplifier IC1 .A ampli-
fies the voltage drop across R1 by a factor
of about 21 and inverts the signal. Interrup-
tions to the fan current therefore appear as
positive-going spikes at its output. Capaci-
tor Cl couples these to the input of compar-
ator IC1 .B. If the spike peak should exceed
the threshold set by the voltage divider
comprising R6 and R7 the output of IC1 .B
will swing high, almost to the positive sup-
ply rail. The spikes are thus converted into a
rectangular wave signal (see Figure 3).
The third op-amp (IC1.C) forms a mono-
stable triggered by positive-going edges
The duty cycle is not 50 % and falls at reduced
supply voltage and fan rotation rate: the pulse
width remains the same, but the interval be-
tween pulses increases as rotation slows. Our
test fan gave a duty cycle of 50 % with a 1 2 V
supply using a value of 56 nF for C2.
Since the virtual ground generated by Zener
diode D4 and T1 is fixed relative to the system
ground, the supply becomes asymmetric at
68
01-2011 elektor
COMPUTERS
of this rectangular wave. The period of the
monostable is given by the formula
t= R9xC2xln (1 + R1 1/R10)
and with the suggested component values
the output pulses are a little over one mil-
lisecond wide. The output stage, consist-
ing of IC1 .D and T2, provides this signal as
an open-collector output. As T2 inverts the
signal, IC1.D is also wired in an inverting
buffer configuration (gain of -1 ). JP1 gives
the choice of this open-collector output or
a direct output from IC1 .C.
The circuit takes its power from the +1 2 V
supply to the fan, which is normally pro-
vided by the device being cooled. D3 and C3
smooth the supply and the circuit around
T1 provides a virtual ground at around half
the supply voltage. In effect this provides a
symmetric ±6 V supply to the op-amps in
the TL074, referenced to the virtual ground.
In practice
When building the circuit, be aware that
the ground symbol that appears at vari-
ous points in the circuit diagram is not
system ground, but the virtual ground at
around half the supply voltage. These vir-
tual ground points should be connected to
one another, but not, of course, to system
ground! System ground is connected only
to the GND pin of K1 and thence to other
points in the circuit marked in the diagram
with an inverted triangle.
The circuit can be built on a piece of proto-
typing board (Figure 4) with the following
external connections:
supply voltages of less than 1 2 V. Soon the
TL074 will be operating outside of its rated
common-mode range, and the supply voltage
will also soon be below the device’s specifica-
tion. If the speed of the fan is to be controlled
by adjusting its supply voltage it is a good
idea to improve the symmetry of the supply,
for example by replacing Zener diode D4 by
a 2 l<^ resistor (1 .8 to or 2.2 to will do). The
circuit will now operate from a supply of be-
Figure 1 . Oscilloscope trace showing
regular interruptions in the fan current,
from which the tacho signal is derived.
Figure 3. The signal at the output of the
differential amplifier (upper trace) and the
tacho signal at the output of the circuit
(lower trace).
K1
IC1 = TL074
JPl
R13 Opamp
C
/■
?
1 22k 1
Open Collector
V
c
7
)
100257 - 11
%
Figure 2. The circuit uses a resistor as a current sensor, with the signal being amplified by a
differential amplifier before being cleaned and fed to a monostable stage.
tween 6 V and 1 2 V, with the virtual ground
being at slightly above half the supply volt-
age (which does not impair performance). If
the supply voltage falls to 5.5 V or below the
circuit will start to oscillate: the TL074 is not
designed to work at such low voltages.
The suggested component values worked
well with the Canon fan. The period of the
output varied from 4.1 5 ms (at 1 2 V) to
8.4 ms (at 6 V). The ‘real’ tacho pulse gen-
erator on the three-wire Sunon fan was in
reasonably good agreement, with periods
of 5.9 ms at 1 2 V and 1 0.8 ms at 6 V.
The current consumption of the circuit it-
self was measured at 1 8.7 mA at 1 2 V and
9.4 mA at 6 V.
Ton Giesberts (Elektor Llabs)
elektor 01-2011
69
COMPUTERS
Figure 4. The Elektor lab prototype,
assembled on a piece of prototyping board.
connector in the PC or other device;
the tacho signal from the pin marked ‘sen-
sor’ on K1 , taken to the tacho pin on the fan
supply connector;
system ground to the ‘GND’ pin on l<1,
taken from the ground pin on the fan sup-
ply connector;
the two wires to the replacement fan, its
+12 V positive supply being connected to
the point marked *+’ on the circuit diagram
(at the junction of R1 and R2)and its ground
to the GND pin of K1 (system ground).
marked ‘sensor’ in the diagram is labelled
‘rotation’ by the manufacturer.
Operation of the circuit has been tested
with Mag Lev-series fans made by Sunon as
well as other types. The circuit may need to
be adapted to suit certain types of fan.
For proper operation the circuit needs a sig-
nal amplitude of around 200 mVpp across
current sense resistor R1. If this level is
not achieved, make suitable adjustments
either to R1 itself or to the gain of differen-
tial amplifier IC1 .A by changing the ratio of
R5 to R3 and of R4 to R2.
+ 12 V to the pin marked ‘+ 1 2 V’ on l<1,
taken from the +1 2 V pin on the fan supply
The pin arrangement for K1 shown in the
circuit diagram is compatible with the con-
nector for three-wire fans usually found
on PC motherboards. Sometimes the pin
For slow fans the monostable period of 1 ms
may be too short. Increase it if necessary by
increasing the value of C2 and/or R9.
(100257)
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RADIO
Notch Filters
for Intermediate Frequencies
Effective and selective
By Michael A. Shustov (Russia)
In radios designed for long distance
communication, a notch filter is used
to suppress or hopefully wipe out
noise, whistles, buzzes, static, chirps,
woodpeckers and what have you that
persistently degrade the wanted signal.
In this article we cover simple LC and
RC notch filters for use in the radio’s
intermediate frequency (IF) section.
Notch filters — sometimes called or band reject filters or just notches
— need to be extremely selective for the obvious reason that you
do not want them to start affecting the wanted signal, although
in most cases that can’t be ruled out entirely. Rephrasing for tech-
nospeak, great attention must be paid to the notch filter’s tuning,
bandwidth and steepness of the frequency response. Notch fil-
ters occur, and may be applied at, RF (antenna), IF (intermediate
frequency; typically 1 0.7 MHz, 9 MHz, 500 kHz or 455 kHz) or AF
2N3686
TO-72
Cl
2n2
R1
X
T1 T2
LI
470uH
C2
2x
©
2N3686
T R2
2n2
In
L2
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220uH
ll
C5 5p...25p C6
II
R3
X
In
C7
HI
R5 2n2
C3
l
+12V
-©
O*
090686 - 11
Figure 1 . A peaking LC filter designed for an IF of 500 kHz. Tweak
R4 to adjust the effectiveness. SI is the ‘defeat’ switch and C4 acts
as a fine tuning control.
2N3686
TO-72
ci
2n2
R1
X
R3
T1 T2
R5 R6
C2
II
2n2
C3
II
I
I
660p
C5
2x
2N3686
©
R4
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330p
SI
PI
II
330p
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R2
100R
R7
X
+12V
-©
R8
C6
II
2n2
R9
090686 - 12
Figure 2. This filter with an RC network in the positive feedback
path offers a true notch (frequency reject) response.
72
01-2011 elektor
RADIO
► f [kHz] 090686 - 14
Figure 3. Frequency response of the LC filter
(curve 1 : SI open; curve 2: SI closed).
Figure 4. Frequency response of the RC filter
(curve 1 : SI open; curve 2: S closed).
(audio; now the accepted realm of DSPs). A well trained radio opera-
tor is able to juggle his notches at RF, IF and AF (if available), ward-
ing off all types of interference that mess up the signal he wants to
hear, decode or process. Lots of skill is required, as well as a trained
ear, to continually tune notches in the fight against rapidly chang-
ing noise patterns, interfering traffic on a channel or breakthrough
from local stations.
Although technically speaking not a ‘notch’, a very steep bandpass
filter has similar effects to a notch on weak telegraphic (CW) or sin-
gle-sideband (SSB) signals — zooming in, as it were, on the wanted
signal heavily affected by noise either side, instead of suppressing
individual noise components.
L, C, R and FET to combat noise
The notch filters described here are of the LC and RC type, and
intended for application in the intermediate frequency (IF) section
of a radio receiver. Their principle of operation is identical, though
the circuit in Figure 1 is a sharp filter tuned to the signal, and the
one shown in Figure 2, a notch suppressing selected noise compo-
nents. Both have an on/off control and a ‘depth’ (or ‘peak’) control
included. They are designed for operation at 502.7 kHz (basically
500 kHz IF + 2.7 kHz sideband) in terms of the frequency-deter-
mining components.
The filters consist of a source fol lower T1 at the input and an ampli-
fier stage T2 with a degree of positive feedback. The operating fre-
quency of the filters is defined by the LC (Figure 1) or RC parts (Fig-
ure 2) in the positive feedback path.
The amount of positive feedback and with it the effectiveness of the
filters is adjusted by selection (or fine tuning) of resistor R4 in the
LC circuit (Figure 1 ), or adjustment of PI in the RC circuit (Figure 2).
The operating frequency (rejection frequency) of the LC filter can be
fine tuned by trimmer C4. Alternatively, a varicap (variable capaci-
tance diode) with a 25 pF range may be used in this position. Switch
SI is the On/Defeat control for both filters.
Performance
As shown in Figure 3, the LC filter achieves a steep ‘inverted notch’
response with a peak at 37 dB. By closing switch SI the IF signal is
passed with no filter action and minimal attenuation.
Compared to the LC filter, the RC variant allows effective and selec-
tive suppression of interfering signals within the IF passband, see
Figure 4. At a rejection frequency of 504.0 kHz, depending on filter
adjustment, the noise suppression can reach 83-90 dB with an over-
all attenuation of about 40 dB for all other signals. When switch SI is
closed, the filter is disabled you’re looking at an overall attenuation
of about 22 dB. Remembering that we are dealing with a 500 kHz
IF signal, this should be relatively easy to restore back to its original
level by adding an extra gain stage.
(090686)
elektor 01-2011
73
Electronics at all the right levels
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Fax (+44) 208 2614447 Email: hexadoku@elektor.com
F
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The competition is not open to employees of Elektor International Media, its business partners and/or associated publishing houses.
elektor 01-2011
75
RETRONICS
Tandberg Model 5 &
Stereo Record Amplifier (ca. 1959)
By Ricard Wanderlof (Sweden)
In the late 1 950’s, stereo was in its
infancy as far as Joe Bloggs was
concerned — what little equip-
ment there was being firmly
aimed at the rich & wealthy.
While mainstream stereo radio
was still a long way off, probably
due to the investment in infra-
structure that was required (i.e.
not only radio receivers but also
studios and transmitters would
have needed to be upgraded),
record players and tape players
were starting to become available
in stereo versions.
Record players and tape recorders
Meanwhile manufacturers offered mono record players and reel-
to-reel tape recorders with stereo upgrade capa-
bilities. In the case of record players, many
devices were fitted with stereo pickup
cartridges, with the channels wired
in parallel for mono use, but eas-
ily upgraded to stereo by a simple
rewiring operation.
When it came to tape record-
ers, things weren’t so simple. As
opposed to a vinyl record, where
both channels are in principle
recorded on adjacent sides of a
single groove, magnetic tape
requires two separate tracks for
stereo operation. This gives the
user the obvious option of ste-
reo recording, or mono record-
ing with twice the recording
time. With hindsight, this capa-
bility completely escaped the compact
cassette format, but resurfaced in the
Minidisc system many years later.
From mono to stereo
With not a lot of stereo material to record
and FM stereo radio broadcasts few and far
between or experimental only, many
tape recorder manufacturers offered
mono machines with some form of
stereo playback capability using
some form of external amplifier.
Some manufacturers like the
Norwegian Tandberg released
several variations on the
theme. One such machine,
the Tandberg Model 5,
launched at the end of
the 1950s (Figure 1),
was one of the first
four track tape record-
ers in the world. Basi-
cally, it allows for record-
ing four tracks on the ta pe-
as the name implies — i.e. two
in each direction of the tape.
The Model 5 is a rather unusual machine in that it has two
complete amplifiers, for complete stereo playback, but only one
of them can be put in recording mode. It also has just one internal
speaker, but that is not too unusual; even with two speakers the ste-
reo effect is rather limited in such a relatively small device, so many
manufacturers opted to have one speaker external for stereo repro-
duction. In many cases the external speaker would be contained in
the removable lid of the tape recorder, such
as in a few Philips stereo machines
from the same period.
An add-on stereo
recording amplifier
The Stereo Record Ampli-
fier pictured in Figure 2
was supplied by Tandberg
as an accessory to their
Model 5 tape recorder. This
add-on device plugs into
the rather unusual DIN con-
nector on the rear head cover
of the tape recorder (Figure 3),
supplying the lower half of the
tape head (right hand chan-
nel) with a recording signal.
The unit gets its power from
the tape recorder via a connec-
tor with a four-pin socket emanat-
ing from the AC power cable stor-
age compartment on the back of the
machine (Figure 4).
The Stereo Record Amplifier contains a
For some time in the early 1 960’s it
seemed that audio equipment manu-
facturers expected stereo to completely
take over from mono, but that was not
destined to happen for another ten years.
76
01-2011 elektor
RETRONICS
complete recording amplifier for
the right hand channel, with line
and microphone inputs, a volume
control, a ‘magic eye’ recording
level indicator, and a speed selec-
tor switch which would have to
be set to the same setting as the
one on the tape recorder to get
proper recording equalization.
The Model 5 is the only Tandberg
to employ an external amplifier
in this way, and indeed I’ve never
come across any other machine
from another manufacturer with a
similar setup.
. - .v
Why Tandberg opted for the exter-
nal amplifier like this is a bit of a
mystery to me. Indeed, as noted above, few people would have
anything to record in stereo, but given that the Model 5 already
had two amplifiers, having built-in stereo recording capabilities
would be mostly a question of a few additional connectors and a
bit of signal switching. This machine was already the top-of-the line
model at its time, so it must have been rather expensive — hence
I don’t think the additional cost
would have made much of a differ-
ence. Perhaps the stereo recording
capability was added as an after-
thought, late in the development
phase of the machine.
and after it...
A further variation came soon
(that’s right, after the Model 5)
with the Model 4, which offered another variation on the same
theme. In contrast to the Models 3 and 5, it did not have two
complete playback amplifiers, and did not support recording in
stereo at all; instead it had a preamp for the right-hand chan-
nel and required an external amplifier such as a tabletop radio
for playing back in stereo. This layout was not too uncommon
in those days, the rationale being
that if someone wanted to play
back in stereo they could provide
their own amplifier for the right
hand channel without the cost of
the machine going up as a result
of something that most people
would never use.
The rationale for that was that two-
track mono was the norm in those days (flipping over the tape at
each end to record on both ‘sides’), but stereo was around the corner,
and the natural step would be to use both channels for stereo. It was
probably assumed that few people would record in stereo, the fea-
ture being intended primarily for the playback of pre-recorded tapes.
Going further, at the beginning of
the 1 960s, Tandberg launched the
Model 7 which had a complete ste-
reo recording and playback sys-
tem including two loudspeakers.
The EM71 indicator tube had been
replaced by the smaller EAM86 so
that there was space for two indi-
cators side by side for the left and
right channels, and thus oddball
machines like the Model 5 with its add-on Stereo Record Amplifier
became history.
(100733)
Special thanks are due to Jan Didden for supplying the mint Tandberg
stereo recording amplifier pictured here.
lowed by the four-track Model 5.
With four-track capability came
the option of recording either in
stereo or getting twice the play-
ing time by recording on the left
and right tracks separately. The
Model 5 could thus record either on
the right or left tracks, or play back
either in stereo, or in mono from
either track, and of course, record
in stereo together with the external
record amplifier.
MP3 generation R U still there?
Before the Model 5...
Putting it all in perspective, the
first stereo Tandberg was the
Model 3 Stereo, introduced a cou-
ple of years before the Model 5.
The ‘3’ could play back two track
stereo (it had two complete ampli-
fiers but only one speaker like the
Model 5), but recording on one
channel only (left).
Shortly afterwards, four track recording was introduced, which
I believe was deemed to be the future, and the Model 3 was fol-
Retronics is a monthly column covering vintage electronics including legendary Elektor designs. Contributions, suggestions and
reguests are welcomed; please send an email to editor@elektor.com
elektor 01-2011
77
ELEKTOR
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elektor 01-2011
79
SHOP BOOKS, CD-ROMs, DVDs, KITS & MODULES
Going Strong
A world of electronics
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Experiments with
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An introduction to digital control electronics
Experiments with
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This book presents fundamental circuits
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A
Use only free or open source software
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Learn to interface and program hardware
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A must-have for audiophiles
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75 Audio designs for home construction
dvd The Audio
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This DVD contains more than 75 different
audio circuits from the volumes 2002-
2008 of Elektor. The articles on the DVD-
ROM cover Amplifiers, Digital Audio,
Loudspeakers, PC Audio, Test & Measure-
ment and Valves. Highlights include the
ClariTy 2x300 W Class-T amplifier, High-
End Power Amp, Digital VU Meter, Valve
Sound Converter, paX Power Amplifier,
MP3 preamp and much more. Using the
included Adobe Reader you are able to
browse the articles on your computer, as
well as print texts, circuit diagrams and
PCB layouts.
ISBN 978-90-5381 -263-1
£17.90 • US$28.90
elektor 01-2011
81
SHOP BOOKS, CD-ROMs, DVDs, KITS & MODULES
110 issues, more than 2,1 00 articles
dvd Elektor
1990 through 1999
This DVD-ROM contains the full range of
1 990-1 999 volumes (all 1 1 0 issues) of
Elektor Electronics magazine (PDF). The
more than 2,1 00 separate articles have
been classified chronologically by their
dates of publication (month/year), but are
also listed alphabetically by topic.
A comprehensive index enables you to
search the entire DVD.
ISBN 978-0-905705-76-7
£69.00 • US$100.00
(December 2010)
An Internet connection would beavalua-
ble addition to many projects, but often
designers are put off by the complexities
involved. The ‘NetWorker’, which consists
of a small printed circuit board, a free soft-
ware library and a ready-to-use microcon-
troller-based web server, solves these
problems and allows beginners to add In-
ternet connectivity to their projects. More
experienced users will benefit from featu-
res such as SPI communications, power
over Ethernet (PoE) and more.
Module , ready assembled and tested
Art.# 100552-91 • £53.00 • US$85.50
More than 75 power supply designs
cd The Power Supply
Collection 1
This CD-ROM contains more than 75 dif-
ferent power supply circuits from the
volumes 2001-2005 of Elektor. High-
lights include the Cuk Converter, Auto-
matic Battery Switchover, Battery
Voltage LED, Digital Benchtop Power
Supply, Lithium-Ion Charger, Electronic
Fuse, High Voltage Regulator, Power
Supply for USB Devices, Step-up Conver-
ter for White LEDs, Vehicle Adapter for
Notebook PCs and much more. Using the
included Adobe Reader you are able to
browse the articles on your computer,
as well as print texts, circuit diagrams
and PCB layouts.
ISBN 978-90-5381 -265-5
£17.90 • US$28.90
Digital Multi-Effects
Unit
(September 2010)
It’s a simple fact: every recording sounds
better with the right sound effects. Here
we prove that it’s possible to generate a
variety of effects digitally, including hall,
chorus and flanger effects, without having
to workyourself to the bone with DSP pro-
gramming. The circuit is built around a
highly integrated effects chip and featu-
res an intelligent user interface with an
LCD. The result is a treat for the eye and
the ear.
Kit of parts including PCBs , programmed
controllers and EEPROM
Art.# 090835-71 • £165.00 • US$266.20
The Elektor DSP radio
(July/August 2010)
Many radio amateurs in practice use two
receivers, one portable and the other a
fixed receiver with a PC control facility.
The Elektor DSP radio can operate in ei-
ther capacity, with a USB interface giving
the option of PC control. An additional
feature of the USB interface is that it can
be used as the source of power for the re-
ceiver, the audio output being connected
to the PC’s powered speakers. To allow
portable 6 V battery operation the circuit
also provides foran audio amplifierwith
one ortwo loudspeakers.
PCB, assembled and tested
Art.# 100126-91 • £149.00 • US$240.40
Reign with the Sceptre
(March 2010)
This open-source & open-hardware pro-
ject aims to be more than just a little board
with a big microcontroller and a few use-
ful peripherals — it seeks to be a fast pro-
totyping system. To justify this title, in
addition to a very useful little board, we
also need user-friendly development tools
and libraries that allow fast implementa-
tion of the board’s peripherals. Ambitio-
us? Maybe, but nothing should deter you
from becoming Master of Embedded Sys-
tems Universe with the help of the Elektor
Sceptre.
PCB, populated and tested , test software
loaded (excluding Bluetooth module)
Art.# 090559-91 • £89.00 • US$143.60
82 Prices and item descriptions subject to change. E.&O.E
01-2011 elektor
January 2011 (No. 409)
£
US$
+ + + Product Shortlist January: See www.elektor.com +
+ +
December 201 0 (No. 408)
NetWorker
100552-91 .... Module, ready assembled and tested
....53.00
..85.50
Heating System Monitor
090328-41 .... ATmega328-20AU (TQFP32-08), programmed
....11.00
..17.80
Stroboscopic PC Fan
100127-1 Printed circuit board
4.50
....7.30
1 001 27-41 .... ATtiny 231 3, programmed
....14.20
....8.75
ARM Freephone Control
080632-91 .... ECRM40 module, ready assembled and tested
....32.00
..51.70
Modular LED Message Board
1 00664-41 .... MC9S08SH32CWL, programmed
8.75
..14.20
Speed Controller for Small DC Motors
100571-41 .... ATtiny44-20PU, programmed
8.75
..14.20
November 201 0 (Nr. 407)
Micro Fuel Cell Measures Oxygen Concentration
090773-91 ..
... PCB, populated and tested
with programmed bootloader
56.00...,
....90.40
The 5532 OpAmplifier (2)
100124-1 ....
... Amplifier board (one channel)
23.00...,
....37.10
100124-2....
... Power supply board
17.95...,
....29.00
Camera Interval Timer
081184-41 ..
... PIC1 6F886-I/SP, SPDIP28, programmed
8.00...,
....12.90
October 201 0 (No. 406)
CL-3 Digital Rotary Combination Lock
100026-41 ....AtmelATTINY2313-20PU, programmed 8.00 12.90
WheelieGT
1 00479-7 1 .... Kit of parts upgrade kit controller board +
2x Hall sensor board 105.00 169.40
September 201 0 (No. 405)
Elektor Project Case
100500-71 .... Predrilled Lexan sheets with standoffs 14.90 24.10
Digital Multi-Effects Unit
090835-31 .... EEPROM 24LC32 4.00 6.50
090835-41 .... ATmega8-16PU 8.30 13.40
090835-42 .... ATtiny2313-20PU 8.30 13.40
090835-71 .... Kit of parts including PCBs, programmed controllers
and EEPROM 165.00 266.20
Dual Voltage/Current Display
100166-71 .... Kit of parts incl. PCB, item -41, LCD 62.00 100.00
Vision System for Small Microcontrollers
090334-1 PCB 19.90 32.10
090334-41 .... PIC1 6F690-I/P, programmed 8.00 1 2.90
V
July/August 201 0 (No. 403/404)
The Elektor DSP radio
1 001 26-41 .... ATmegal 68 PU 1 2.50 20.20
100126-91 .... PCB, assembled and tested 149.00 240.40
Daggerboard Position Detector
080307-41 .... PIC1 6F628A-DIL-1 8, programmed 8.00 1 2.90
PIC RJ-45 Cable Tester
090643-41 .... PIC16F72, programmed 8.00 12.90
3D LED Pyramid
090940-41 .... ATtiny2313-20SU, programmed 8.00 12.90
Digital Thumbwheel Switch
090538-41 .... ATtiny231 3 dip20, programmed 8.00 12.90
Whistler: Electronic Trainer/Coach
1 00203-41 .... PIC1 6F88 DIP1 8, programmed 8.00 1 2.90
Solar Cell Battery Charger/Monitor
090544-41 ....PIC16F877A, programmed 16.50 26.70
Bestsellers
^ A I n y- • r A
O
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GO
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O'
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>
Q
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{/)
W
1
2
3
5
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C# 201 0 Programming and PC interfacing
ISBN 978-0-905705-95-8.... £29.50 US $47.60
Experiments with Digital Electronics
ISBN 978-0-905705-97-2.... £26.50 US $42.80
Fundamental Amplifier Techniques
with Electron Tubes
ISBN 978-0-905705-93-4.... £65.00 ...US $104.90
RM Microcontroller Interfacing
ISBN 978-0-905705-91-0.... £29.50 US $47.60
Power Electronics in Motor Drives
ISBN 978-0-905705-89-7 .... £29.50 US $47.60
he Power Supply Collection 1
ISBN 978-90-5381 -265-5 .... £1 7.90 US $28.90
DVD The Audio Collection 3
ISBN 978-90-5381 -263-1 .... £1 7.90 US $28.90
B DVD Elektor 1 990 through 1 999
ISBN 978-0-905705-76-7 .... £69.00 ...US $1 00.00
Masterclass
A DVD High-End Valve Amplifiers
ISBN 978-0-905705-86-6.... £24.90 .... US $40.20
1
2
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DVD LED Toolbox
ISBN 978-90-5381 -245-7 .... £28.50 US $46.00
NetWorker
Art. # 1 00552-91 £53.00 US $85.50
Digital Multi-Effects Unit
Art. #090835-71 £1 65.00 US $266.20
Elektor DSP radio
Art. #1001 26-91 £149.00 US$240.40
Reign with the Sceptre
Art. # 090559-91 £89.00 ...US $1 43.60
Wheelie GT
Art. #100479-71
£105.00 US$169.40/
Order quickly and securely through
www.elektor.com/shop
or use the Order Form near the end
of the magazine!
Elektor
Reg us 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
elektor 01-2011
83
COMING ATTRACTIONS
NEXT MONTH IN ELEKTOR
Telephone Interface for VoIP
Next month we describe a so-called Foreign Exchange System Adapter with a USB inter-
face. This enables an ordinary analogue telephone set to be linked to a Voice over IP (VoIP)
system. For the associated Linux software we’re using the Asterisk IP PBX software that’s
well known among insiders. With this small board so you can start using your trusted land-
line phone for VoIP communication.
Automatic Morse Generator
There are still many radio amateurs who enjoy morse. Those who are proficient in it like to
use paddles enabling the dots and dashes to be generated via separate controls (paddles)
using thumb and finger. The circuit was developed specially for this type of key. It looks
after a lot of time related issues such as the pauses between dots, lines, spaces, etc., and
also provides a standard mode as well as an Ultimatic mode. A small monitor amplifier is
also accommodated on the PCB.
Light Alarm
You’ve probably seen them, alarm clocks with built-in lighting that wake you up gracefully
and gently. Such lights should not be too difficult to make yourself, with the added advan-
tage of being able to adapt the software to your preferences. This circuit contains all basic
functions of a so-called light alarm clock, but thanks to the availability of the source code
you can make changes to your heart’s content.
Article titles and magazine contents subject to change; please check the Magazine tab on www.elektor.com
Elektor UK/European February 2011 edition: on sale January 20, 2010. Elektor USA February 2011 edition: published January 73, 2070.
w.elektor.com www.elektor.com www.elektor.com www.elektor.com www.elektor.com w\
Elektor on the web
Also on the Elektor website:
• Electronics news and Elektor announcements
• Readers Forum
• PCB, software and e-magazine downloads
• Time limited offers
• FAQ, Author Guidelines and Contact
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 downloads, circuit
boards, programmed ICs and corrections and updates if applicable. Complete magazine issues may also be downloaded.
In the Elektor Shop you’ll find all other products sold by the
publishers, like CD-ROMs, DVDs, kits, modules, equipment,
tools and books. A powerful search function allows you to
search for items and references across the entire website.
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ElektorWh
84
01-2011 elektor
Description
Price each Qty. Total Order Code
CD The Power Supply Collection 1 C
\ £17.90
p
Fundamental Amplifier Techniques
with Electron Tubes C
A £65.00
ARM Microcontrollers 1 ^
A £29.50
Experiments with Digital Electronics ^
A £26.50
C# 2010 Programming
and PC interfacing
Elektor Per sonal Organizer 2011
LEDs 1 (Special Project)
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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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 guaran-
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dispatch note number. 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 1 0-days (UK); 1 4-days (Europe) or 21 -days (all other countries).
Cancelled orders All cancelled orders will be subject to a 1 0% 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 responsi-
bility or liability for failing to identify such patent or other protection. Copyright All drawings, photographs, articles, printed circuit boards,
programmed integrated circuits, diskettes and software carriers published in our books and m agazines (other than in third-party adver-
tisements) are copyright and may not be reproduced or transmitted in any form or by any means, including photocopying and recording,
in whole or in part, without the prior permission of Elektor in writing. Such written permission must also be obtained before any part of
these publications is stored in a retrieval system of any nature. Notwithstanding the above, printed-circuit boards may be produced for
private and personal use without prior permission. Limitation of liability 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 by Elektor shall be determined in all respects by the laws of England.
January 201 1
SUBSCRIPTION RATES FOR ANNUAL SUBSCRIPTION
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Cheque sent by post, made payable to Elektor Electronics. We can
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January 201 1
Create complex electronic systems
in minutes using Flowcode 4
Design - Simulate - Download
Flowcode is one of the World’s most advanced
graphical programming languages for micro-
controllers (PIC, AVR, ARM and, brandnew,
dsPIC/PIC24). The great advantage of Flowcode is
that it allows those with little experience to create
complex electronic systems in minutes. Flowcode’s
graphical development interface allows users to
construct a complete electronic system on-screen,
develop a program based on standard flow charts,
simulate the system and then produce hex code for
PIC, AVR and ARM microcontrollers.
Convince yourself.
Demo version, further
information and ordering at
www.elektor.com/flowcode
Index of Advertisers
Astrobe, Showcase www.astrobe.com
78
Atomic Programming Ltd, Showcase . . . .www.atomicprogramming.com 78
Avit Research, Showcase www.avitresearch.co.uk 78
Beta Layout, Showcase www.pcb-pool.com 37, 78
Black Robotics, Showcase www.biackrobotics.com 78
CEDA, Showcase www.ceda.in
78
Designer Systems, Showcase www.designersystems.co.uk 78
Easysync, Showcase www.easysync.co.uk
78
Elnec, Showcase www.elnec.com .
78
Embedded Adventures, Showcase www.embeddedadventures.com 78
E u ro c i rc u its www. euro circuits, com
55
EzPCB/Beijing Draco Electronics Ltd www.v-moduie.com 11
First Technology Transfer Ltd, Showcase .www.ftt.co.uk 78
FlexiPanel Ltd, Showcase www.flexipanel.com 78
Future Technology Devices, Showcase. . .www.ftdichip.com 78
Flameg, Showcase www.hameg.com.
78
FlexWax Ltd, Showcase www.hexwax.com 79
Labcenter www.labcenter.com
88
Linear Audio, Showcase www.linearaudio.net 79
Microchip www.microchip.com/mtouch 2
MikroElektronika
MQP Electronics, Showcase. .
Nurve Networks
NXP Contest
NXP Product
Pico
Quasar Electronics
Relchron
Robot Electronics, Showcase.
Robotiq, Showcase
RS Components
Showcase
Steorn SKDB Lite, Showcase .
USB Instruments, Showcase .
Virtins Technology, Showcase
. www. mikroe. com 3
.www.mgp.com 79
.www.xgamestation.com 65
. www. circuitcellar. com/nxpmbeddesignchallenge 1 3
. . . www. nxp. com /I pc 11011
71
. . .www.picotech.com/ scope2030
65
. . .www.guasarelectronics.com
51
. . .www.proto-pic.co.uk
55
. . .www.robot-electronics.co.uk
79
. . .www.robotiq.co.uk
79
. . .www.designspark.com/pcb
33
78, 79
. . .www.kdb.steorn.com/ref25
79
. . .www.usb-instruments.com
79
. . .www.virtins.com
79
Advertising space for the issue 15 February 2011 may be reserved
not later than 18 January 2011
with Huson International Media - Cambridge House - Gogmore Lane -
Chertsey, Surrey KT16 9AP - England - Telephone 01932 564 999 -
Fax 01 932 564 998 - e-mail: lauren.palmer@husonmedia.com to whom all
correspondence, copy instructions and artwork should be addressed.
elektor 01-2011
87
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PRE-PRODUCTION CHECK .
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All Connections Routed -
Power Planes Generated -
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