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magazine

October 2013 | £ 4.90

• 8x8 Two-color LED Matrix I Numitron Clock & Thermometer |

Android ElektorCardiVscope (3) I Modular RF Link using Manchester

Code (2) # DesignSpark Tips & Tricks • Negative Energy

LPC800 Getting Started #Heathkit IT-28 Capacitor Checker

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Contents

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Community

8 Elektor World

• The Iso-Pi Board

• Xpressly for Audio

• The Next Step: Arduino.next

• Circuit Cellar 'refreshed'

• Animal-Friendly Mosquito Trap

Projects

10 Xmega Web Server Board

The microcontroller board described
here is particularly well suited to
monitoring and control applications.
The plug-in TCP/IP module allows
you to implement a web server and
other network-oriented applications
and a microSD card provides mass
storage. Four LEDs, four buttons,
and a removable display provide

the user interface options. And of
course the board comes with a wide
range of external interfaces.

22 8x8 Two-color LED Matrix

This article describes an alternative
method for driving a matrix consisting
of a large number of LEDs, while using
only a few I/O lines from a microcon-
troller. As an example application for
this circuit, a small game was devel-
oped in which an LED can be directed
across the matrix using a joystick.

30 Numitron Clock & Thermometer

The idea for this project was to take
the Arduino world off of its Shields
and Breadboards and out into a
world of Elektor DIY projects while
also hopefully appealing to the die-
hard AVR hackers. These worlds are
so close but are so often treated as
separate. The project happily com-
bines today's microcontroller tech-
nology with 1950's Soviet tubes
now available 'NOS' from Ebay.

36 Android Elektor CardiVscope

Flere now is the last installment of
the article series, concentrating on
calibrating the pre-assembled board.
The job is done using a few home
built resistor networks, and dedicated
software running on the smartphone.

• DesignSpark

44 Modular RF Link

using Manchester Code (2)

Flaving concluded the hardware side
of this project, it's time to go soft-
ware. While the proper hardware
design and board layout guarantees
the correct radiation and recep-
tion of the RF signals, the software
(sometimes referred to as firm-
ware) plays a fundamental role in
the reliability of the message being
carried by the signal. We're off to
Manchester!

4 | October 2013 | www.elektor-magazine.com

Volume 39

No. 442

October 2013

52 DesignSpark Tips & Tricks,
Day #4: A Simple Project

Having learned how to set up and
use libraries in DesignSpark, we can
proceed with the schematic and cir-
cuit board editors. Today we'll make
a simple bi-color LED driver to get
the hang of it.

• Labs

56 Getting Started with the
LPC800 Mini Kit

The NXP LPC800 Mini Kit sports an
LPC810 32-bit ARM Cortex-M0+ mi-
crocontroller (MCU) in an 8-pin DIP
package, a voltage regulator, two
pushbuttons, an LED and two small
prototyping areas. Here are a few
hints to get the board up and run-
ning in no time.

60 Negative Energy

How on earth can three series con-
nected 1.5-V batteries persistently
supply ... 1.5 volts?

• Industry

62 News & New Products

A selection of news items received
from the electronics industry, labs
and organizations.

• Magazine

68 Retronics:

Heathkit IT-28 Capacitor
Checker

The story of bringing a vintage tube
checker back to life. The instrument
cane as a set of parts in a box sup-
plied by the greatest electronics
kit maker of all times: Heathkit.
Series Editor: Jan Buiting.

74 Hexadoku

Elektor's monthly puzzle with an
electronics touch.

76 Gerard's Columns: Breaking
the Laws of Physics

A column or two from our columnist
Gerard Fonte.

82 Next Month in Elektor

A sneak preview of articles on the
Elektor publication schedule.

www.elektor-magazine.com | October 2013 | 5

Community

Volume 39, No. 441
September 2013

ISSN 1947-3753 (USA / Canada distribution)

ISSN 1757-0875 (UK / ROW distribution)

www.elektor.com

Elektor Magazine is published 10 times a year including
double issues in January/February and July/August,
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E-mail: j.dijk@elektor.com

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Copyright Notice

The circuits described in this magazine are for domestic and
educational use only. All drawings, photographs, printed circuit
board layouts, programmed integrated circuits, disks, CD-ROMs,
DVDs, 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 transmitted in any form or by any means,
including photocopying, scanning and recording, in whole or in
part without prior written permission 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 Publisher disclaims any responsibility for the safe
and proper function of reader-assembled projects based upon or
from schematics, descriptions or information published in or in
relation with Elektor magazine.

© Elektor International Media b.v. 2013

Printed in the USA Printed in the Netherlands

Red Fruits, Italian Heroes,

Penguins, and Texan Bones

Ever since Steve Wozniak assembled a 6502
based microprocessor system, and Steve Jobs
literally created a market for it, we techno-
inclined folks have delighted in creating and
hearing product names with a disarming, if not
charming, ring: apple, raspberry, acorn, pen-
guin, Captain Zilog, KIM, Junior. I'm convinced
a good number of the names given to micro-
processor systems and platforms from the early
days of computing have helped significantly to
unnerdify the craft of programming and staring
at command lines for hours on a 15-inch CRT screen propped up by pizza boxes.
The Linux community in particular has set the bar in creative product naming with
every new release of "their" operating system. Where the "men in suits" simply put
the next higher number behind the product name, a letter "b", or a year, the follow-
ers of Tux the Penguin came up with names you'd expect from a Tolkien book.

The main embedded platforms with clearly defined entry levels and educational
aims are Raspberry Pi and Arduino, and both are covered extensively in Elektor.
Magazine and Elektor.POST. However, in good engineering tradition there's more
to choose from in a diversified market. Elektor's Embedded Linux board is linked
this month to a range of extension boards through its "Gnublin" connector (that'll
be a young goblin running GNU's Not Unix). The same boards, we're proud to
say, also connect seamlessly to the Raspberry Pi and— as we've just discovered—
to the BeagleBone Black. Have a look at the article on page 28 to see how our
modules for controlling relays, displays, stepper motors, I/O devices and temper-
ature sensors can be connected to the latest embedded microcontroller systems
running Linux as the abstraction layer. Keeping abstraction and fantasy apart was
never easier though as Penguin, Beagle and Gnome seem to get along very well,
at least in this edition of Elektor. Let's hope no unadapt, badly named creatures
appear on stage, like T-Roll or CE02B.

More creatures and creations in this issue!

Jan Buiting, Editor-in-Chief

The Team

Managing Editor:
International Editorial Staff:

Design staff:

Membership Manager:
Graphic Design & Prepress:
Online Manager:

Managing Director:

Jan Buiting (editor@elektor.com)

Harry Baggen, Thijs Beckers, Eduardo Corral, Wisse
Hettinga, Denis Meyer, Jens Nickel, Clemens Valens

Thijs Beckers, Ton Giesberts, Luc Lemmens,

Tim Uiterwijk, Clemens Valens, Jan Visser

Raoul Morreau

Giel Dols, Jeanine Opreij, Mart Schroijen
Danielle Mertens
Don Akkermans

6 September 2013 www.elektor-magazine.com

Our network

United Kingdom

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+31 ( 0)46 4389428

w.hettinga@elektor.com

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+49 241 88 909-17
f.tewalvaart@elektor.de

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+34 91 101 93 95
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Wisse Hettinga

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@ektor

VOICE iJl COIL

CIRCUIT CELLAR

Connects you to

Supporting Companies

Beta Layout

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Crystalfontz

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FTDI

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83

Not a supporting company yet?

Contact Peter Wostrel (peter@smmarketing.us, Phone 1 978 281 7708,
to reserve your own space in Elektor Magazine, Elektor«POST or Elektor.com

www.elektor-magazine.com September 2013 7

Community

Compiled by

Wisse Hettinga

Elektor World

Every day, every hour, every minute, at every
given moment designers and enthusiasts are
thinking up, tweaking, reverse-engineering
and developing new electronics. Chiefly for fun,
but occasionally fun turns into serious business.

Elektor World connects some of these events and activi-
ties — for fun and business.

= The Iso-Pi Board

When Circuit Cellar contributor Brian Millier received his first Raspberry Pi in late 2012, he started a project that
would inspire his two-part series "Raspberry Pi I/O Board", which appears in CC's August and September 2013
issues. Millier, a former instrumentation engineer at Dalhousie University in Halifax, Canada, outlines his own Pi
learning curve and shares the versatile I/O board he designed for the single-board computer. "In the time since I
received my Raspberry Pi, one of the board's developers has
designed an I/O board called the Gertboard," Millier says.

"I feel my board is quite distinct and has some advantages
over the Gertboard."

For example, Millier says, his board "provides complete gal-
vanic isolation between all the I/O devices on-board and the
Raspberry Pi itself (which protects the Raspberry Pi board)."

You can find out how to configure Millier's "Iso-Pi" in Circuit
Cellar's September 2013 issue.

A short ribbon connects the Raspberry Pi board (right)

to Millier's "Iso-Pi" I/O board.

CM 1NIWVA1 iUb 1 h t H*",*/:*,! I put AJUIU iw,: h 1 1 Ui,

UUMIM IM IVMillHh <U AuA-tfl FCMAHt

xpress

Xpressly for Audio

Special

135th AES Convention

New York 2013

v 5 . "

' .A- 1 "' J *\ •-Ir’* - - ■

E3 i l liii nki - Audm Ptpmiiig ■ i*L rc-tii I Iri ■ Trjmdiinri ■

Rt-cocdbvj * ^tvdh> ■ Live Sound ■ Br-ajdcjrt ■ Networked Audio •
StrpjcnJng.l^TiidufLElDi l^n. Thf Ik LtinDlY Audla ■ IliirLi^r EKlnHBfK

m

kibtion tr-amduc-an
mi

PLUS

The long History of Audio in Elektor magazine enters a new era with the re-launch of audi-
oXpress. In 2011 Elektor acquired audioXpress, Voice Coil , Loudspeaker Industry Source-
book, World Tube Directory, assorted audio books, and more. Believing that the work of
enthusiasts should serve as a model for the industry in the excellence of design and quality
of constructions, the titles were founded in the US by Edward T. Dell (1923-2013) and, for
over 35 years, served the build-it-yourself audio fan as well as those working in the indus-
try, with great articles, projects, tips and technologies.

A new editorial team reinforced by selected authors from Elektor's network is currently
working on a redesign of the publication with an expanded format. The new AudioXpress
reaches out to the global audio engineering community, not forgetting to cover the R&D
efforts in the industry in many new application areas.

"audioXpress restyled" will be launched at the forthcoming AES convention in NY (October
17 - 20, 2013) with a new graphic layout in print as well as all-digital formats, including
a regular newsletter to (currently) over 30,000 members. audioXpress is already engaging with the global audio
community though Twitter (@audioXP_editor) and Facebook (facebook.com/audioxpresscommunity).

www.audioxpress.com

th+ ■n^ev.rlivt-
FlcxIMr Aifiplrfl** 1 Sunwiii ng
lecfriMriofy (PAST} from 1J&C

DcsigriEng for U!ta~UW

THD+N in Anatog Circuits

8

October 2013

www.elektor-magazine.com

All Around the World ...

a^|F5 gag

II

The Next Step: Arduino.next

For sure, Arduino has become one of the main gateways to Technology World for many young students.
One key to its success may be the ease of creating an app in minutes. You don't need a deep knowledge
of electronics or programming. Almost everything is on the Internet— simply copy and paste some code,
reproduce a simple circuit and your application is ready to run.

But what if you want to go a little deeper? How can you change the behavior of your application? What can
you do to make it work in a different way? What circuit do you need to run a new function?... We asked our-
selves all these questions and are working to come up with proper answers, simple and easy to understand to
help you to take the next step on your favorite embedded platform. That step is called Arduino.next and will be
up & running soon— powered by Elektor.

Stay tuned to our communication channels! Follow us on Facebook, www.facebook.com/arduinonext, and on
Twitter, @ arduinonext, and check out the Arduino products already on sale at www.elektor.com.

_

Circuit Cellar 'refreshed'

With the September 2013 issue, Circuit Cellar magazine unveils a bold new layout and
fresh content for electrical engineers, academics, and serious embedded systems design-
ers everywhere. Together with the Elektor International Media staff, the CC team delivers
a modern, clean layout that makes studying photographs and analyzing schematics easier
and more exciting. Built into the layout are also handy direct links (QR codes as well) to a
variety of essential online resources, such as source code, videos, and parts lists.

As for new content, CC is delivering two informative columns: Green Computing by Ayse
Coskun (Issue 278) and Programmable Logic in Practice by Colin O'Flynn (Issue 279).
Another new feature is CC World (p. 8). Much like the Elektor World section of Elektor mag-
azine, CC now provides monthly updates on topics of interest to the community, such as
the CC Weekly Code Challenge (http://bit.ly/lbrGEIU).

The team hopes you enjoy the refreshed CC. To submit articles and projects ideas, write
to editor@circuitcellar.com.

e

circuit cellar

MCU- BASED COLOR
DATA ACQUISITION

Animal-Friendly Mosquito Trap

For a lot of you the annual 'August fight' with the mosquitos has begun. Good luck—
you will probably wake up every night, exploring the bedroom for them small little
!@#$$$%'s that are after your blood.

Or... do like Aurelien Moulin, our Elektor Labs trainee from France. Always on the
look for new projects he proposed his 'ultimate bug killer'; an LED and an old com-
puter ventilator. When the jokes had subsided we asked him if had tried this for
real— his answer was simply, 'yes' (our French trainees are invariably deadly seri-
ous). The idea is simple— the LEDs attract the mosquitoes, then the ventilator sucks
them down into a small net. Aurelien made an undemanding prototype and to our
great surprise the contraption caught around 120 mosquitoes (say, one hundred
and twenty!) on the first night!

But now the $10 6 dollar question! All mosquitos caught in the net were still alive.
Question to you— how do you think these mosquitoes defied the killing speed of
the vent blades?

www.elektor-magazine.com October 2013 9

•Projects

XMEGA Web
Server Board

Display, SD card, Ethernet,
RS-485, buttons iand LEDs

The microcontroller board
described here is particularly
well suited to monitoring and
control applications. The plug-
in TCP/IP module allows you to
implement a web server and other
network-oriented applications, and a
microSD card provides mass storage. Four
LEDs, four buttons, and a removable display provide the user interface options.
And of course the board comes with a wide range of external interfaces.

By Jens Nickel (Elektor Germany Editor)
Development: Achim Lengl and Bernd

Koppendorfer (KopLe Engineering)

10 October 2013 www.elektor-magazine.com

XMega Web Server

The popularity of the ElektorBus demonstrated
that there is significant demand among our read-
ers for monitoring and control applications. Of
course it is always possible to use a PC as a
central controller, but for many applications this
is overkill, in terms of cost, size and noise. For
some applications the Elektor Embedded Linux
board is a good choice, although not everyone will
be comfortable using its free operating system.
And in many cases all that is needed is an 8-bit
microcontroller, such as one from the AVR series.
External interfaces are essential on a board like
this, so that remote sensors and actuators can
be accessed. Here RS-485 is a good choice, and
of course an Ethernet interface is useful. An SD
card interface makes it easy to store sensor read-
ings, and a text display, along with buttons and
LEDs, allows the construction of simple menu-
based user interfaces.

Based on an XMEGA

The board described here answers to the above
shopping list. Figure 1 shows its block diagram.
KopLe Engineering [1] brought some addi-
tional ideas, and designed the circuit and
the printed circuit board. The fruit of
their work is available from Elek-
tor either as a ready-built and
tested board or as a blank
PCB [2]: see Figure 2.
With web server
applications in mind
we chose a microcon-
troller with plenty of flash
memory. We decided against the
ATmega2560 (which is used, for exam-
ple, on the larger Arduino boards) and went
instead for the ATxmega256A3. This device has
256 KB of flash memory and 16 KB of RAM, as
well as a few nice extra features such as an
advanced event system [3]. This allows us, for
example, to count level transitions on any of the
GPIO pins. The interrupt controller with configu-
rable priority levels is also useful in more sophis-
ticated applications. At first it seemed rather a
disadvantage that the register layout is not com-
patible with older members of the ATmega fam-
ily, and even programmers familiar with AVR
devices might need a few hours' study of the
new datasheet to get up to speed. A quicker
approach is to use the drivers for the UART, SPI
and other interfaces provided by the manufac-
turer, who also provides a freely-downloadable

Features

• ATxmega256A3 with 256 KB flash and 16 KB SRAM

• Four pushbuttons and four LEDs

• Plug-in display module, three lines of sixteen characters, with LED
backlight

• RS-485 driver with screw terminals for A and B signals, plus 12 V and
GND (ElektorBus compatible)

• Optional header for attaching FTDI USB-to-TTL cable

• Optional header for Elektor BOB USB-to-TTL converter module

• Additional UART pins brought out to optional mini-DIN socket

• Optional headers for connection to almost all pins of the
microcontroller

• MicroSD card slot connected to SPI interface

• Socket for WIZ820io module, available from Elektor (# 130076-91)

• Embedded extension connector with three ADC inputs, two GPIOs,

SPI and I 2 C on a 14-pin (2x7) header, range of expansion boards
available from Elektor

• Printed circuit board fits Hammond enclosure 1598REGY and RS part
number 220-995

• Programmable using low-cost AVRISP programmer and free Atmel
Studio software

• Software library in C for all peripheral modules available for free
download

ETHERNET

TCP/IP

Micro

SD-CARD

SPI

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SPI

SPI

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[

12V

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REGULATOR

12V

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MCU

XMEGA256A3

O O O O

]

EEC
(EXTENSIONS)

SPI

DISPLAY

ELEKTOR

BUS

° UART (FTDI/BOB— >USB)

° UART (MINLDIN)

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p

p

p

p

BUTTONS

LEDS

120126 - 13

Figure 1. The Elektor XMEGA board is available ready built and tested. It can be
expanded with additional modules via optional pinheaders.

www.elektor-magazine.com October 2013 11

•Projects

Figure 2. Block diagram of
the Elektor XMEGA board.

development environment called Atmel Studio 6.
At Elektor we have made things even simpler: we
provide an API (application programming inter-
face) for the microcontroller and a driver file for
the board, covering all the device's peripherals.
More on this below.

Power supply

As is de rigueur for modern electronics, the
XMEGA microcontroller requires a power supply
voltage of 3.3 V. It was therefore clear from the
outset that we would have to have supplies at
both 3.3 V and 5 V on the board, just so that we
could communicate with existing 5 V electronics.
Hence there are two power supply circuits, each
built around an energy-efficient MC34063A [4]
switching regulator: see the circuit diagram in
Fig ure 3. There is a handy tool to help with
component selection for this circuit available on
the Internet [5].

On the input side both regulators are fed with
12 V. This supply can come either from a ter-
minal block (see below) or from a jack: observe
the correct polarity! JP1 is used to select the
power source.

Connector K1 is the 6-way programming and
debugging interface, which allows in-circuit
programming of the microcontroller. The pinout
of this connector is different from the familiar
in-system programming connector for the ATmega
series, but nevertheless the low-cost AVRISP mkll
programmer [6] can still be used: it will automat-
ically work with the 3.3 V supply of the XMEGA
device. And, of course, there is a reset button.

Interfaces

The tried-and-tested UART interface is still the
most popular for board-to-board communication.
The programming required is simple thanks to
the hardware UARTs built into the microcontroller.
Furthermore, there are many converters avail-
able, for example to RS-485 and USB. Our micro-
controller contains six UART modules, of which
three are used directly on the board.

Signals PC2 and PC3 from one of the UARTs are
taken to an RS-485 driver device, with the RS-485
A and B lines brought out on a terminal block.
Ground is also available on this terminal block,
which makes it easy to connect to other RS-485 or
ElektorBus boards. For example, our RS-485-to-
USB converter [7] can be connected using three
wires, allowing remote control, possibly over a
considerable distance, using a PC; the Elektor
AndroPod module [8] allows similar control using
a tablet or smartphone. A fourth connection on
the terminal block allows the board to be powered
from the 12 V rail on the ElektorBus.

The digital signals DE and /RE control transmis-
sion and reception by the RS-485 interface chip.
JP2 enables a 120 Q. termination resistor on the
bus. The optional resistors Rll and R18 pull the
A and B lines to a defined level if no other node
on the bus is transmitting, which reduces the
board's sensitivity to interference. In any case,
in our experiments on the ElektorBus we did not
notice any problems without this biasing in place.
We have wired the pins of a second UART to a
mini-DIN socket (not fitted as standard on the
board), along with four GPIO signals. This is con-
venient for communicating with other electronics
over a suitable cable. For example, the mini-DIN
socket is compatible with the mini-DIN socket on
the Andropod module. For maximum compati-
bility JP3 selects whether the signal levels are
suitable for 3.3 V or 5 V logic.

A third UART (on pins PD2 and PD3) is designed
to be connected to a USB-to-UART converter. We
have given constructors the choice between an

12 October 2013 www.elektor-magazine.com

XMega Web Server

+3V3 JP3 +5V +3V3 JP4 +5V

Figure 3. Circuit diagram of the XMEGA board. Extensive use is made of the microcontroller's I/O facilities, including three SPI modules, three
UARTs and an I 2 C module.

www.elektor-magazine.com October 2013 13

•Projects

Figure 4. Circuit diagram
of the display module. The
four buttons allow a menu
system to be implemented.

sion boards designed for the Elektor Linux board
by the Embedded Projects team. Among those
available from Elektor are an expansion board
with a display, a port expander and a real-time
clock [9], a relay board [10], a stepper motor
driver board, a temperature sensor and more:
see earlier articles [11] and [12].

It is also possible to fit further headers or sockets
around the microcontroller for testing, debugging
and expansion: these provide access to practi-
cally all of the pins of the XMEGA. As supplied by
Elektor a socket is only soldered in the row along
the bottom edge of the chip, but this is purely
to provide additional mechanical support for the
display module described below; it does not have
any electrical function when used in this way.

User interface

It is useful to have a display connected to the
board if it is to be used at the center of a moni-
toring and control application. But not all appli-
cations will need a display, and so we have made

... Web server and other network applications the

simple way ...

FTDI USB-to-TTL adapter cable and the Elektor
'BOB' USB-to-TTL converter board, both of which
are available from Elektor Online Store [2]. Again
a level shifter is provided for compatibility with
both 3.3 V and 5 V logic levels: the desired volt-
age is configured using JP4. The constructor can
fit straight or right-angled headers, whichever is
more convenient for the application.

Expansion

Although the above interfaces will prove enough
for many applications, it is easy to imagine situ-
ations where the board's capabilities need to be
expanded by adding extra devices. Mostly these
devices will be controlled over I 2 C or SPI inter-
faces, and so we decided to bring out the corre-
sponding controller pins to a header. At this point
we hit upon the idea of using the same pinout
for the connector as Benedikt Sauter had used in
the Elektor Embedded Linux board. This means
that we can use the 14-way 'embedded extension
connector' (EEC) to connect any of the expan-

it a separate module that can be fitted to the
controller board if required. This also gives the
option of mounting the display elsewhere, for
example in a separate enclosure.

Header K8 for the display has twelve pins, of
which three are reserved for ground and the two
supply voltages. The display itself is controlled
over SPI: as well as the usual SPI signals MOSI,
SCK and CS there is a fourth signal RS which
specifies whether a given byte is to be inter-
preted by the display as a command or data.
More information on this can be found in the
datasheet [13].

When the display module is attached to the
controller board it takes pin 4 on the header
to ground. This pin is connected to port PB6 of
the microcontroller. If PB6 is configured in soft-
ware as an input and the internal pull-up resistor
is enabled, then the microcontroller can detect
whether the display is fitted by checking the level
on this input.

Four further pins are dedicated to the four push-
buttons that are also fitted on the display mod-

14 October 2013 www.elektor-magazine.com

XMega Web Server

Figure 5. A range of
expansion boards can
be connected via the
'embedded extension
connector'.

ule (see Figure 4). The buttons are arranged
directly below the display so that a menu system
can easily be implemented.

Even if an application does not make use of a
display, the pushbuttons might still be required.
For this reason the buttons are duplicated on the
main board, connected to the same port pins on
the microcontroller. Capacitors C12, C18, C19
and C23 serve to debounce the contacts.

Last but not least in this section we will men-
tion the LEDs, which are indispensable not just
as status indicators in an application, but also
for debugging code. The board sports a total of
four LEDs

SD card and network

The SD card slot accepts microSD cards, which
serve as mass storage for our board. The SD card
is driven in so-called 'SPI mode', with the four
signals MISO, MOSI, SCK and CS connected to
a hardware SPI peripheral module on port E of
the XMEGA. As with the other peripheral units
on the microcontroller we have included support
in the form of a small library. The library deals
only with raw data stored on the card: in other
words, only supporting reading from and writ-
ing to the card on the board itself. If you wish to
develop the driver further, you will find a good
introduction to the subject at [14]. The CD pin on

the SD card slot is taken to ground when a card
is inserted, and this signal is connected to port
pin PE3 on the XMEGA microcontroller.

A special feature of the board is the space pro-
vided to fit a WIZ820io network interface module.
This module, also available from Elektor Online
Store (# 130076-91) [2], is a self-contained pro-
cessor board incorporating a TCP/IP stack. This
relieves the XMEGA microcontroller of the task
of dealing with network traffic at the protocol
level. All the microcontroller has to do is tell the
module when to open a socket (specifying an IP
address and a port), when to send characters,
and so on. Data can be received over a network
socket in a similar way. Communication between
the XMEGA and the network interface module is
again over an SPI bus, in this case connected
to port C of the microcontroller. Space does not
permit a full description of the module here, but
documentation can be obtained from the Korean
manufacturer WIZnet [15]. Drivers are available
in C for a wide range of microcontrollers, provid-
ing an interface to application code (a web server,
for example) in the form of functions such as
SocketOpen ( ) . We have adapted the back end of
the driver for our board and for the XMEGA, and
have extended the front end by adding a couple
of simple extra functions. We will cover the use
of the board in a home network and connected

www.elektor-magazine.com October 2013 15

•Projects

Listing 1. Demonstration with LEDs, pushbuttons and display

int main (void)

{

Controller_Ini t ( ) ;

Board_Ini t ( ) ;

//Extension_Ini t ( ) ;

Appli cationSetup ( ) ;

whi le (1)

{

Appli cationLoop ( ) ;

}

};

void Appli cationSetup (void)

{

L EDBu tton_ Li bra ry Setup (Button Even tCallback) ;

Di splay_Li brarySetup ( ) ;

Di splay_Wri teStri ng(0 , 0, “Display©”);

//Di splay_Wri teStri ng(l , 0, “Displayl”);

}

void Appli cationLoop ( )

{

ButtonPollAll ( ) ;

}

void ButtonEventCallback(ui nt8 BlockType, uint8 BlockNumber,
uint8 ButtonPosi ti on , uint8 Event)

{

//Buzzer (Buzzer Bloc kFi rst Index , 1000 ,

BUZZER_TONEMODE_RAMP) ;

if (Event == EVENT_BUTTON_PRESSED)

{

ToggleLED(0 , 0) ;

Di splay_Wri teNumber (0 , 1, BlockNumber);

Di splay_Wri teNumber (0 , 2, ButtonPosi ti on) ;

}

}

to the Internet in a separate article to be pub-
lished in the near future.

Software

The existing ElektorBus library, a small display
library from KopLe and the WIZnet driver all had a
role in fostering the development of the 'Embed-
ded Firmware Library', which has been the sub-
ject of two previous articles in Elektor [16][17].
Since the development of this framework has
been focused on support for the XMEGA web
server board, we are now in the happy position
of being able to offer library modules for all the
peripheral blocks on the board.

The current EFL code base can be downloaded
at [2] and [18]. This includes the individual code
modules and a demonstration application for the
board. The XMEGA microcontroller API is as usual
contained in a pair of files, ControllerEFL.h and
ControllerEFL.c. In this case the two files reside in
the subdirectory Xmega256A3. Functions are pro-
vided to set and read digital outputs and inputs,
to take ADC readings, to send and receive data
using the UART blocks, and much more besides.
And all this without having to read a datasheet!
The board file contains code that calls these
microcontroller functions. Low-level functions to
talk to the peripheral blocks are provided for the
use of higher levels of the EFL. So, for example

void Di splay_SendByte (ui nt8
Di splayBlocklndex , uint8 ByteToSend, uint
DATABYTE_COMM AND BYTE)

is a function which sends a byte over the SPI
block that is connected to the display (the internal
peripheral block table contains a reference to this
unit). The function also sets the RS signal to the
correct level according to whether a command
or data byte is to be sent: to do this the function
has to look up which pin of the microcontroller
is connected to the RS line on the display. The
higher-level code now does not need to know
the wiring of the board, and the application can
use the display library in a hardware-indepen-
dent fashion. Also, as far as the application is
concerned, it does not matter whether the dis-
play is connected over an SPI interface or a (four
bit wide) parallel port when it calls the function
Di splay_SendByte ( ) .

Similar low-level functions are provided in the

16 October 2013 www.elektor-magazine.com

XMega Web Server

Figure 6. By adding eight
relays a powerful control
unit can be constructed. The
unit can also be controlled
from a PC over an RS-485
bus.

board file to drive the SD card and the network
module. The code base includes documentation
for the functions, produced using Doxygen. The
'Manuals' directory also includes an extra doc-
ument describing the internals of the EFL, in
English, French and German.

My first program

The hardware-independent display library files
(DisplayEFL.h/.c) are located in the directory
'Libraries' in the code base.

The application code initializes the library with
the call

Di splay_Li brarySetup ( ) ;

and can then talk to up to four displays, num-
bered from zero to three, located on the controller
board or on an extension board. The demonstra-
tion application 'XmegaDemo' shows this off: in
the code base click on the directory 'Applications'
and find the file 'XmegaDemo. atsln'. A double
click on this file opens the project in Atmel Stu-
dio 6. When the microcontroller has been suc-
cessfully flashed with the hex file, the first line of

the display should show 'DisplayO'. If you press
one of the buttons its number will be shown on
the display and the first LED on the board will
turn on and off.

Listing 1 shows the source code. In the applica-
tion setup function we initialize both the Display
library and the LEDbutton library. As part of the
initialization we tell the library which function
in the application is to be called when a button
is pressed.

To ensure that the buttons are polled sufficiently
frequently the main loop in the application must
include a call to ButtonPollAll() .

The function ButtonEventCallback() contains
the code that is to be executed when a button
press is recognized. The argument ButtonPosi-
ti on gives the number of the button that has
been pressed on the XMEGA web server board
(from zero to three). The variable Event can take
on the values event_button_pressed (= l) or
event_button_re leased (= 2) . The application
can therefore react differently to the press and
the release of a button.

www.elektor-magazine.com October 2013 17

•Projects

About the Development Team

Bernd Koppendorfer and Achim Lengl studied electronics and
information engineering at the Georg Simon Ohm Institute
of Technology in Nuremberg, Germany, graduating in 2009.
In 2010 they founded their own company KopLe Engineering
GbR in Oberasbach, close to the city. Since then they have
worked as consultants to various companies, undertaking
development work in the field of analog and digital circuit
design, from simple modules to complex real-time image
processing systems implemented in FPGAs.

Expansion

If you are the lucky owner of a Linux extension
board [9], you can connect it via the 'embed-
ded extension connector' using a ribbon cable:
see Figure 5. A pair of files 'ExtensionEFL.h/.c'
accompanies this board, providing the necessary

Listing 2. Control over RS-485 or UART

int main(void)

{

Controller_Ini t ( ) ;

Board_Ini t ( ) ;

Extension_Ini t ( ) ;

Appli cati onSetup ( ) ;

while (1)

{

Appli cationLoop ( ) ;

}

};

void Appli cati onSetup (void)

{

UARTInterface_Li brarySetup ( ) ;
UARTInterface_SetBaudrate (0 , 38400) ;

BlockP rotocol_ Li brarySetup (UARTInterf ace_Send , 0 ,
UARTInterface_GetRi ngbuf fer (0) ) ;

}

void Appli cationLoop ( )

{

BlockProtocol_Engi ne ( ) ;

}

low-level driver functions for its peripheral blocks.
These files are already included in the project,
and all we have to do is remove the comment
characters at the beginning of the line contain-
ing the call to Extension_init() . We then do the
same with the other commented-out lines in the
main source file.

With the program recompiled and flashed into
the XMEGA the three buttons on the extension
board will now also be polled. The function But-
tonEventCallback() can determine which group
of buttons was responsible for a callback using the
argument BlockNumber, where a value of 0 means
the buttons on the main board, and a value of 1
means the buttons on the extension board.

As you can see, it makes no difference to the
application code whether the buttons or display
are located on the main board or on the extension
board. What makes this even more noteworthy
is that the buttons on the Linux extension board
are connected to analog inputs on the microcon-
troller rather than digital inputs (see the section
on virtualization in the extra EFL documentation).

Plug and play

As described in previous articles, we can now
connect the board to a PC using its RS-485 inter-
face and the RS-485-to-USB converter [6], and
connect the relay board described in the previous
issue [10] to the expansion connector. The set-up
should appear as shown in Figure 6.

The application we will use is 'XmegaRelay.atsIn'.
The code in the main source file is remarkably
short: see Listing 2. The application set-up code
and the application loop code are described in
detail in the article on the EFL in the June 2013
edition [17]. As well as setting up the UART inter-
faces on the board (both for RS-485 and for
the FTDI cable or BOB), we initialize a library
that implements a simple control protocol called
'BlockProtocol'.

In the application loop function the line

BlockProtocol_Engi ne ( ) ;

polls to determine whether a new command has
been received by the board from the PC.

Once the hex file has been flashed into the micro-
controller we run a terminal emulator program on
the PC, select the appropriate COM port and set
the baud rate to 38400. The terminal emulator
must also be configured so that when the Enter
key is pressed the complete line of characters is

18 October 2013 www.elektor-magazine.com

XMega Web Server

sent, followed by a carriage return (ASCII 13).
On entering

R 0 0 + <ENTER>

the first relay should pull in, and on entering

R 0 0 - <ENTER>

it should drop out again. The other relays can be
controlled using commands of the form R 0 x ...,
where x ranges from one to seven.

If you do not have a USB-to-RS-485 converter,
you can use an FTDI cable or BOB to connect
the PC. The code needs to be modified to use
the second UART interface block (numbered '1')
rather than the first, which is simply a matter of
changing a single line of code from

CONTROLLER BOARD

Resistors

All SMD, 0805

R1 = 1.6kft

R2 = 100ft

R3,R21-R31= lOkft

R4,R7,R8,R10 = 1ft

R5 = 1.2kft

R6,R15 = 3.6kft

R9,R12,R16,R17,R19 = 680ft

R11,R18 = 680ft (optional)

R13 = 120ft

R14 = 2.2kft

R20 = 5.6kft

Capacitors

Cl = 220pF (0805)

C2,C4,C7,C9-C15,C17,C18,C19,C21-C29 =
lOOnF (0805)

C3,C6 = 47pF 10V tantalum (SMD-D/E)
C5,C30 = lOpF 16V tantalum (SMD-C)

C8 = 150pF (0805)

C16,C20 = 22pF (optional)

Inductors

L1,L2 =470pH (Ferrite, PIS4728)
L3 = lOpH (LQH3C)

Semiconductors

D1,D4-D8 = LED, type LG T67K (PLCC2)
D2,D3 = MBRS140
IC1,IC2 = MC34063A (S08)

IC3 = LT1785CS8 (S08)

IC4,IC6 = TXB0106 (TSSOP16)

IC5 = ATXmega256A3-AU (TQFP64)

Miscellaneous

JP1,JP2 = 2-pin pinheader, 0.1" pitch, with
jumper

JP3,JP4 = 3-pin pinheader, 0.1" pitch, with
jumper

K1 = 6-pin pinheader (2x3), 0.1" pitch
K2 = 2.5-mm-jack socket, solder mounting
K5 = 4-way PCB screw terminal block, 0.2" pitch, sol-
der mounting

K8 = 12-pin pinheader, 0.1" pitch
K9 = 8-way mini-DIN socket (optional)

K12 = 2 pcs 6-way socket, 0.1" pitch for Wiz820io
module

K15 = 14-pin pinheader, (2x7), 0.1" pitch

K16 = 6-pin pinheader, 0.1" pitch, for Elektor 'BOB'

USB/TTL converter (optional)

K17 = hinge socket for microSD card
K18 = 6-pin pinheader, 0.1" pitch, for FTDI USB/TTL
cable (optional)

Q1 = 16MHz quart crystal (optional)

S1,S2,S3,S4,S5 = SMD short-action pushbutton
PCB # 120126-1

Alternatively

Elektor # 120126-91 Controller Board,
ready assembled and tested

COMPONENTS LIST

www.elektor-magazine.com October 2013 19

•Projects

COMPONENTS LIST
Display Module

Resistors

(SMD, 0805)

R1,R2,R4 = 27ft
R3 = Oft

R5 = Oft (optional)

Capacitors

Cl = 10pF 16V tantalum (SMD-C)

C2-C5 = lOOnF (0805)

Miscellaneous

DISPLAYl = Display EA-DOG-M163X-A with LED
backlight LED55X31

20-way SIL receptacle 0.1" pitch + 2 pcs 2-way, for
mounting DISPLAYl
K1 = 12-pin pinheader, 0.1" pitch
K2 = 12-pin pinheader, 0.1" pitch (optional)

K3,K4 = 8-pin pinheader, 0.1" pitch
S1,S2,S3,S4 = short-action pushbutton

PCB, Elektor #120126-2
Alternatively

Elektor # 120126-92 Display Module,
ready assembled and tested

BlockProtocol_Li brarySetup (UARTInterf ace_
Send, 0, UARTInterf ace_GetRi ngbuffer (0) ) ;

to

BlockP rotocol_ Li brarySetup ( UARTInterf ace_
Send, 1, UARTInterface_GetRi ngbuffer (1) ) ;

Messages will now be received over the second
UART channel. Alternatively we can arrange to
receive messages over TCP/IP by changing the
line to

BlockP rotocol_Li brarySetup (I Pinter face_

Internet Links

[1] www.koeple.de (website in German)

[2] www.elektor.com/120126

[3] www.atmel.com/Images/Atmel-833 1-8-
and-16-bit-AVR-Microcontroller-XMEGA-
AU_Manual.pdf

[4] www.onsemi.com/pub_link/Collateral/
MC34063A-D.PDF

[5] www.nomad.ee/micros/mc34063a/

[6] www.atmel.com/tools/AVRISPMKII.aspx

[7] www.elektor.com/110258

[8] www.elektor.com/1 10405

[9] www.elektor.com/120596

Send, 0, IPInterface_GetRi ngbuffer (0) ) ;

We will look in more detail at the possibilities
this opens up in the next article in this series.

( 120126 )

[10] www.elektor.com/130157

[11] www.elektor.com/130212

[12] www.elektor.com/gnublin

[13] www.lcd-module.de/eng/pdf/doma/
dog-me.pdf

[14] http://elm-chan.org/docs/mmc/
mmc_e.html

[15] www.wiznet.co.kr/WIZ820IO

[16] www.elektor.com/120668

[17] www.elektor.com/130154

[18] www.elektor-labs.com/efl

20 October 2013 www.elektor-magazine.com

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•Projects

8x8 Two-color LED Matrix

With an ATmega328P

By

Ruben van Leeuwen

and

Cederique Prevoo

(Netherlands)

This article describes an alternative method for driving a matrix consisting of a
large number of LEDs, while using only a few I/O lines from a microcontroller. As
an example application for this circuit, a small game was developed in which an
LED can be directed across the matrix using a joystick.

Figure 1.

Design principle of
charlieplexing.

An LED matrix is a good starting point to gain
experience in the details of driving LEDs. Such a
matrix will quickly accumulate a large number of
LEDs and since a microcontroller will usually have
too few I/O pins to control them all individually,
it is necessary to use some type of multiplexing
method. Here we chose a less well-known multi-
plexing variant, namely charlieplexing (invented
in 1995 by Charlie Allan from Maxim). In the
more usual multiplexing, the rows of a matrix

130146 - 13

are controlled with drive signals (Low or High),
while the columns are activated one at a time in
the rhythm of the refresh frequency. With char-
lieplexing the functions of row and column sig-
nals change all the time, which allows a larger
number of LEDs to be controlled with the same
number of I/O lines. Figure 1 shows the basic
design. Instead of only one LED, there are now
two anti-parallel LEDs between each junction in
the matrix. By changing the level of the row or
column signal, you can turn on either one of the
LEDs, or turn them both off by pulling both drive
signals High or Low simultaneously.

Matrix

The LED matrix used here comprises 8x8 two-
color LEDs. This type of LED has both a red and
a green LED chip in each LED package, and is
connected as shown in Figure 2 (these two-
color LEDs have three connections: two anodes
and a common cathode— the connection for the
red chip is on the side of the package that has

22 October 2013 www.elektor-magazine.com

8x8 Two-Color LED Matrix

the flat). The schematic for the matrix, which is
accommodated on a separate circuit board, is
shown in Figure 3.

Control electronics

The control of the LEDs is provided by an
ATmega328P, an 8-bit AVR microcontroller with
32 KB programmable flash memory, 1024 bytes
of EEPROM and 2 KB of SRAM. In this application
the internal oscillator of the ATmega is used, so an
external crystal is not necessary. The controller
drives three 8-bit shift registers, type 74HC595,
one for the green LEDs, one for the red LEDs and
one for the common cathodes (IC3, IC4 and IC5
in the schematic of Figure 4). With this arrange-
ment we save a large number of port pins on the
microcontroller, which now remain available for

SV3

Green

R9

-| 12QR |-

R11

-| 120R |-

R12

— | 120R |-

R13

] 12QR |-

R14

-| 12QR |-

R15

-| 120R |-

R16

-| 120R |-

LD1

rn— m

LD9

rn— m

LD17

rn— m

LD25

rn— m

LD33

rn— m

LD41

rn— ■ m

LD49

rn— m

LD57

rn— m

LD2

rn— ■ nn

LD10

rn— m

>1

M

LD18

rn— m

Hr W

LD26

rn— m

LD34

rn— m

LD42

rn— ■ m

HrW

LD50

rn— m

H

M

LD58

rn— m

LD3

rn— ■ m

LD11

rn— m

WrM

LD19

rn— m

LD27

rn— ■ nn

LD35

rn— ■ m

WrH

LD43

rn— ■ m

LD51

rn— m

LD59

rn— ■ m

LD4

rn— m

H

H

LD12

rn— m

LD20

rn— m

LD28

rn— m

LD36

rn— nn

LD44

rn— m

LD52

rn— m

LD60

rn— m

1 2 3 4 5 6 7

Figure 3. The schematic for the matrix with the 64 two-color LEDs

mounted on their own circuit board.

LD5

rn— m

LD13

rn— m

LD21

rn— m

LD29

rn— m

LD37

rn— m

LD45

rn— m

LD53

rn— m

LD61

rn— m

sv2 1 66666666 | row

LD6

rn— m

LD14

rn— m

LD22

rn— ■ m

LD30

rn— ■ m

HrK

LD38

rn— m

LD46

rn— - m

LD54

rn— m

LD62

rn— m

MrH

LD7

rn— m

LD15

rn— m

LD23

rn— m

HrM

LD31

rn— m

LD39

rn— ■ m

LD47

rn— m

MrH

LD55

rn— ■ m

WrM

LD63

rn— m

LD8

rn— m

-| 120R |-

LD16

rn— m

-| 120R |-

LD24

rn— m

R3

120R

LD32

rn— m

LD40

rn— nn

LD48

rn— m

R6

-| 120R [-

LD56

rn— m

-| 120R |-

LD64

rn— m

R8

-| 120R |-

SV1

Red

www.elektor-magazine.com October 2013 23

•Projects

Figure 4.

The driving electronics
consists mainly of an
ATmega microcontroller and
three shift registers.

24

October 2013

www.elektor-magazine.com

8x8 Two-Color LED Matrix

Table 1. Port connection

some other applications.

The microcontroller continually sends serial 8-bit
data to the shift registers of the two colors to
prepare the information for each row. After these
eight bits are sent, a pulse is applied to the Out-
put Enable inputs of the two-color registers and
the common-cathode shift register so that a com-
plete row of LEDs can turn on.

When the common-cathode shift register drives
a row to the activate state, this row sees a Low
signal level; an inactive row has a High signal
level. This ensures that there is a voltage drop
of 0 volts across the LEDs in the inactive rows
(so these LEDs will therefore not turn on). In
the active row there will be a voltage difference
of 5 V, so the LEDs that are connected to this
row can light up.

This whole process takes place eight times per
'frame' so that all rows are driven in turn. A
'frame' in this case is a user-programmed code
which represents an entire picture of 8 x 8 red
and green LEDs.

The turning-on of the LEDs takes place at a fre-
quency that is above 60 Hz, so that to the human
eye it appears that all the LEDs are turned on
simultaneously, instead of only one row at a time.
This means that 60 frames per second are dis-
played, which is equivalent to one frame per
0.017 s.

The function of each of the port pins is listed in
Table 1. Here you can see that there is also a
joystick present, which is connected
to ports PCO and PCI.

That is because on these ports there is also an
A/D converter available, which makes it possible
to read the position of the joystick as an ana-
log value. In addition, the circuit also contains
a DC buzzer to generate sounds. This type has
the advantage that it contains a built-in oscilla-
tor, but the disadvantage is that it can produce
only one fixed frequency. In the schematic we
can also find the ISP connector for the in-circuit
programming of the ATmega. In this way changes
to the software can be programmed quickly and
then tested.

Inputs:

Microcontroller port

Black button

PC5

Red button

PC4

Joystick horizontal axis

PCO

Joystick vertical axis

PCI

Outputs:

Microcontroller port

Buzzer

PC3

First Row pulse

PD5

Serial data red

PDO

Serial data green

PD4

Serial clock

PD3

Row clock

PD2

www.elektor-magazine.com October 2013 25

•Projects

Figure 5.

The printed circuit board
for the LED matrix. Make
sure that the LEDs are fitted
in straight lines and at the
same height.

R9 p.

-czz>

R10

■O'

Rll

£12 ( M

H. > -
H I I H

R13 p.

- —nzz>-

R14

HlZZj-

R15

— CZZ3—

R16

LD1

LD9.

LD 1 .

LD2.

LD3

LD4

LD4

LD5

LD2-^ LD3^-=^ LD4^=^ LD5^-=^ LD 6^-=^ LD LD8

^y ey ry

LD10- I nil— LD12- LD13— LD14- LD1

^y ry ry r^

I ni8-~ I ma~ LDp~ LD2J

ft! ry ry ft it

I LDZg=~ LD2p=~ LD2£

19 19 ry 19

ld /^ =! ^. ld ^ =! ^ ld ^ == ^ ld /^
19 19 19 19

LD i^ =: ^ LD ^ == ^ LD i^ = ^ LD i^

19 19 19 19

i i dfll~ i lds;

fti fy fy fta

i LDp~ i n^a-- LD 6 j

® ® © fta

SU2 8

/ V V V V* V V \

A \ /\ /S /\ /S /\ /S /\ /

LD2,

LD3

LD3.

LD4

LD5

LD 6

HIZ ZIH
W*^ LD16 R1

— c I H

LD ?3==*v LD24 R2

H I H col

L03J-. LD32 R3
R4

W HO

LD -P=^ HI ~H

/ftZl LD40 R5

LD4Z = J**C IH ‘

LD48

HI ~H

LD||- LD56 R 2

' H ~H

LD ^=5s. LD64 R 8

Note: both circuit boards
shown at 80 % of actual size.

Figure 6.

The main circuit board has
been designed in such a way
that the matrix board can
be attached in the middle on
top of it.

Elektor <c> 2013

130146-1 U1.0
8x8 Dual LED matrix

Main board

J0Y1

Rl ftCK

C0N2

COMPONENT LIST

Main Board
Resistors

R1,R5 = 390ft
R2,R3,R4,R6 = lOkft
R7 = lkft

J0Y1 = 2-axis joystick 2xl0kft w. pushbutton (e.g.
Conrad Electronics # 425637-89, matiching button
# 710047-89)

Capacitors

Cl-Cll = lOOnF, 5mm pitch

Semiconductors

D1 = 1N4004

LED1 = LED, red, 5 mm

T1 = BC547

IC1 = ATmega328P-PU, programmed, Elektor #
130146-41
IC2 = 7805

IC3,IC4,IC5 = 74HC595
IC6,IC7 = 74HCT04

Miscellaneous

Buzzer = DC buzzer, 30mA / 5V
ISP = 6-pin (2x3) boxheader

51 = slide witch w. make contact

52 = pushbutton w. make contact, red cap

53 = pushbutton w. make contact, black cap
S5 = miniature pushbutton w. make contact
CONl,CON2,CON3 = 8-pin SIL connector
9-V battery w. holder

PCB # 130146-1 [1]

Display Board

R1-R16 = 120ft

LD1-LD64 = dual LED green/red, IF = 10 mA (e.g.

Conrad Electronics # 156269-89)

SV1,SV2,SV3 = 8-pin pinheader
PCB # 130146-2 [1]

26 October 2013 www.elektor-magazine.com

8x8 Two-Color LED Matrix

The power supply is taken care of by a 5-V regu-
lator of the type 7805. The current consumption
of the circuit, including the LEDs, amounts to a
maximum of 50 mA. The input voltage has to
be between 7 and 12 VDC (from a wall adapter,
for example), but for the occasional game a 9-V
battery is also sufficient (there is an option for
fitting this battery on the back of the board).

Printed circuit boards

Two separate circuit boards have been designed
for this circuit, one for the LED matrix (Figure 5)
and one for the control circuit (Figure 6). Since
only leaded components are used the construc-
tion should not present any problems. It is best
to use sockets for the digital ICs. For powering
the circuit it is possible to mount a 9-V (6LR22)
battery holder on the solder side of the circuit
board using four small nuts and bolts. Make sure
that on the matrix board you mount the LEDs in
neat rows and columns: both the rows and the
columns have to be in straight lines, and all the
LEDs have to be fitted at the same height. To
help with this you can slip a piece of cardboard
between the legs of the LEDs before you solder
them in place. Also make sure that you mount
the LEDs all the same way around; the connec-
tion for the red LED corresponds with the flat side
of the package. So this side of the LED has to
face the same way for all the LEDs on the board
(in the direction of the 'Red' screen print label).

Program

There are a few important parts to the program
which we will explain in detail here: the serial
data control for the matrix, the reading of the
analog value from the joystick and the game that
is used as the application example to demon-
strate this circuit.

Three inputs of the 74HC595 shift register are
used, namely Serial-Data, Serial-Clock and Out-
put-Enable. The Serial-Clock input is used to shift
the eight bits present in the shift register by one
bit on every clock pulse, so that the LSb is lost
and the current level of the Serial-Data input is
added as the MSb.

After eight new bits have been shifted in, and
when the Output-Enable input is activated, the
values of these bits in the shift register will be
copied to the output buffers of the IC.

For each frame, an array of 8 characters is pro-
cessed and analyzed, so that it is clear which
LEDs have to be turned on for each row. The

Listing 1.

i f (RowNmbr ! =0) //check if the current Row is not the first
{

//Set First row out to High = PD5 (DDRD ObOOlOOOOO)
PORTD&=0bll011111;

}

else i f (RowNmbr==0)

{

//Set First row out to Low = PD5 (DDRD ObOOlOOOOO)

PORTD | =0b00 100000 ;

}

//supply a row clock pulse
PORTD |=0b00000100;

PORTD&=0blllll011;

for (1=0 ; I<8 ; I++) //repeat the routine 8 times to get all the
bi ts
{

//get the right bit value by bit shifting the bit
i f ( ( (RedRowData>> (7-1) ) 962 ) ==1)

{

//set the serial Red output High = PDO (DDRD ObOOOOOOOl)
PORTD |=0b00000001;

}

else

{

//set the serial Red output Low = PDO (DDRD ObOOOOOOOl)
PORTD&=0blllllllO ;

}

//get the right bit value by bit shifting the bit
i f ( ( (GreenRowData>> (7-1) ) 962) ==1)

{

//set the serial Green output high = PD4 (DDRD ObOOOlOOOO)
PORTD |=0b00010000;

}

else

{

//set the serial Green output Low = PD4 (DDRD ObOOOlOOOO)
PORTD&=0blll01111;

}

//give a serial clock pulse = PD3 (DDRD ObOOOOlOOO)

PORTD |=0b00001000;

PORTD&=0bllll0111;

}

www.elektor-magazine.com October 2013 27

•Projects

program first checks whether it is for the first
row (in this case a pulse will be provided for the
common-cathode shift register) and subsequently
each bit in a row is tested for the active state; a
'1' indicates active and a '0' for inactive. When
it has been determined that a particular bit is
active, the Serial-Data input of the correspond-
ing color, together with the Serial-Clock input,
will be activated; if the bit is inactive only the
Serial-Clock input will be activated.

A section of the serial control software can be
seen in Listing 1.

In order to read the position of the analog joy-
stick, the existing functions in the avr/io.h library
of the AVR development software are used (AVR
Studio 5). The following global variables are
declared in the program. h header file:

• PortJoyV - The actual vertical value of the
joystick,

• PortJoyH - The actual horizontal value of the
joystick.

The code shown in Listing 2 can be found in
Programlnit.cpp.

Listing 2.

//analog reading setup

ADM UX=0 bO 1000000 ;

//

For Aref=AVcc;

ADCS RA= 0b 10000 110 ;

//

prescale div factor = 64

Listing 3.

//Reading the analog signal of the joystick Vertical-Axis

//Reads vertical joystick (port 0)

ADMUX&=ObllllllOO ;

//Start Single conversion

ADCS R A |=0bO10OO0O0; //ADSC = high

//Wait for conversion to complete
whi le ( ! (ADCSRA&0b00010000) ) ;

//Clear ADIF by writing “one” to it
ADCSRA | = (1<<ADIF) ;

ADCS RA&= Ob 10111111 ;

Port JoyV=ADC ;

The reference voltage for the A/D-converter is set
to 5 V, which is equal to the power supply voltage
for the microcontroller (AVcc). The 'prescale div
factor' furthermore ensures that the A/D-con-
versions take place at the correct speed. The
code in the file Dataln.cpp subsequently reads
the position for each axis of the joystick. In List-
ing 3 you can find an example showing how the
position of the vertical axis is read in.

The example program for this project, which is
available as a free download from [1], is a little
game in which you have to steer a green LED
across the matrix using the joystick in such a way
as to avoid the oncoming red LEDs.

After an introductory animation the game will
begin when the red button is pressed. The first
'level' that is found in the file LoadLevel.cpp is
loaded into an array of 117 characters, this there-
fore represents the values of eight bits high (the
complete height of the LED matrix and 117 bits
wide. The present position of the green LED is
also stored in a character variable and this can
be changed by moving the joystick up or down.
After each frame, the position of the green LED
is bit-wise ANDed with the next row of the level.
If these happen to be the same, the loop will end
and the game will begin again, restarting with
the same level that was being played.

There is also a test function built in. If you press
and hold the black button after playing the game
or after turning-on of the power supply voltage,
you can move a block of four LEDs across the
entire matrix using the joystick.

So enjoy the game, but also have fun program-
ming your own applications.

( 130146 )

The development of this project was the
practical project part of an electronics course
at the ROC Leeuwenborgh in Sittard, the
Netherlands.

Internet Link

[1] www.elektor.com/130146

28 October 2013 www.elektor-magazine.com

▲

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through Friday, January 10, 2014

Las Vegas, Nevada V CESweb.org • #CES201 4

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•Projects

Numitron Clock &
Thermometer

Developed on the Arduino platform

The idea for this project was to take
the Arduino world off of its Shields
and Breadboards and out into a
world of Elektor DIY projects
while also hopefully appealing to
the diehard AVR hackers. These
worlds are so close but are
so often treated as separate.
The project happily combines
today's microcontroller tech-
nology with 1950's Soviet
tubes now available 'NOS'
from Ebay.

By Paul Court (UK)

For the clock I decided against the traditional
7-segment LEDs in favor of something much more
beautiful in the form of ex-Soviet Numitron tubes.
Numitrons are cousins of the Nixie tubes featured
in several Elektor projects, but run on about 4
volts rather than >150 volts, hence are more
suited to experimentation. Just like the Nixies,
Numitrons are readily available on sites such as
eBay at very reasonable rates.

So here we have the project, a Numitron bulb,
clock & thermometer built on a single board. The
project is based on the Arduino UNO, meaning the
UNO and its IDE were used as development tools
only. In the final project there are no shields, no
modules and no plugins — just an ATMega328 with
peripheral hardware devices around it, although
that may be oversimplifying the build ahead, as
we'll see.

Features

• Four IV-9 Numitron tubes

• Date/Time/Year/Seconds/Temperature readout

• ATmega328 microcontroller

• Developed on Arduino platform

• On-board adjustable SMPSU for optimal Numitron brightness setting

• Powered from 9-12 VDC 500 mA power adapter

• No high voltage used

• All development code freely available

• Design powered by Elektor.Labs

The next 'tron': Numitron!

Dekatron, Klystron, Thyratron, Magnetron ,
Trochotron , Whatever next, Annoyatron ? the
low-voltage generation may ask, and everyone
invariably ending up at www.radiomuseum.org for
a glimpse at more baffling, -tron suffixed vacuum
tube devices from the dark pre-Internet ages.

You don't have to master classic Greek to fathom
that a /Vumitron does something with numbers.
And indeed a Numitron tube is capable of dis-
playing numbers 0 through 9 and a few letters,

30 October 2013 www.elektor-magazine.com

NumiTron Clock & Thermometer

using seven discrete segments, which are actually
little incandescent bulbs. On many Numitrons, a
sort-of-comma (decimal symbol, ds) is included
as an 'eighth segment' in the right-hand bottom
corner. The segments in a Numitron share a com-
mon positive supply line, and their other ends
are brought out to wires— not pins. Like many
Nixies, Numitrons are wire tubes.

Numitrons are the 'warm-light' variants of the sol-
id-sate 7-segment LED display. Originally devel-
oped in the Cold War period, i.e. in the tube era,
they are still available as NIB (new in box) a.k.a.
NOS (new old stock) items, particularly from Rus-
sian suppliers— mostly Ukrainian— active on the
Internet. The type IV-9 Numitrons Luc Lemmens
wanted in order to replicate the project at his
desk in the Elektor Labs were ordered through
EBay (a US company for sure) and arrived from
Russia intact despite rudimentary but amusing
packaging methods applied by the 5-Kstar rated
seller. See the photo story in Figure 1 triggered
by your Retronics Editor: LOL.

The main technical specs of the IV-9 numitron
used here are given in Table 1. As we men-
tioned in the article on the Nixie VU Meter using
the IN-9 [1], what we like to think of as "design
data" on these Sovjetisk tubes is subject to (1)
wide interpretation, (2) even wider tolerance,
and (3) stencil printing in Cyrillic.

Circuit description

Looking at the circuit diagram in Figure 2, you
might be surprised to see that no multiplexing
is applied to the display elements. Instead, each
of the four digits of the clock has its own driver
IC type SN74LS47D. You can't really multiplex
the IV-9, being a tungsten filament bulb it's just
too slow and either flickers, or is too dim. Each
channel therefore has its own driver and a set
of four BCD drive lines, except VI, the highest
clock digit, which needs only two. While using
four 74LS47's and no latch or multiplexer uses
up more Atmega pins, it is easier to understand
when it comes to coding. Each tube having its
own BCD lines, it can be directly addressed by
toggling the pins High or Low.

On supply voltages, the circuit has two inter-
nally: + 5 V from an ordinary 78L05 regulator
(IC1) and +4.00 V (adjustable on PI) from a little
switch-mode supply around the familiar MC34063

Figure 1.

Hey, the Numitrons have
arrived all the way from
Dot-ua Land. And a good
read included free! Paid for
in US$ using a credit card,
and cleared by customs, the
little tubes came all the way
from the Ukraine.

www.elektor-magazine.com October 2013 31

•Projects

Figure 2.

Schematic of the Numitron
Clock & Thermometer. Note
that each Numitron V1-V4
has individual drive, rather
than multiplexed.

Table 1. IV-9 Main Specifications (attempt @ )

Type

IV-9 (l/IB-9)

Brand

Reflector/ Sovtec

Substitute(s)

-

Displayed symbols

7 segment, ds

Symbol height (length)

10 mm (0.400 ")

Overall dimensions

11 mm (0.433 ") dia. x 35 mm (1.38 ")

Pin diameter

0.5 mm (0.020 ")

Typ. (max.?) supply voltage

4.5 V

Typ. current per segment

19.5 mA

Base

TO-lOO, pin 1 in front

Socket

Njet. Wires— no socket needed

C12

lOOn

A

B

C

O

VCC

YO

IC5

Y1

LT

Y2

BI/RBO

Y3

rbF

Y4

Y5

GND

Y6

SN74LS47D

C13

lOOn

A

B

C

□

VCC

YO

IC6

Y1

LT

Y2

BI/RBO

Y3

RBI

Y4

Yb

GND

Y6

SN74LS47D

C14

lOOn

LAI

v+

A

B

C

O

VCC

YO

IC7

Y1

LT

Y2

BI/RBO

Y3

RBI

Y4

Y5

GND

Y6

SN74LS47D

C15

lOOn

A

B

C

O

VCC

YO

IC8

Y1

LT

Y2

BI/RBO

Y3

rbF

Y4

Y5

GND

Y6

SN74LS47D

a

b

CA

c

d

e

f

0

g

dp

4

IV-9

120740 - 11

32

October 2013

www.elektor-magazine.com

NumiTron Clock & Thermometer

(IC2). The IV-9's filament voltage range is actu-
ally 3.15-4.50 volts and you want to set PI to a
level that best suits your viewing. Each filament
draws about 19.5 mA. The whole clock requires a
DC input of 7.5 V unregulated at about 500 mA.
The internal supply voltages were chosen as
5 volts and 4 volts (3.00 V-4.50 V), and not
3.3 V only, because

• the higher voltage allows the Atmega to
work at 16 MHz;

• 3.3 V is too low considering the 74LS47D
LS-TTL 'open collector' outputs powering the
filaments from the V+ do not quite pull down
all the way to 0 V when On.

The heart of the clock is an ATmega328P, which
is the chip used in the UNO and Duemilanove
series of Arduino boards. If purchasing or using
a chip with an Arduino Boot Loader pre-installed
the Duemilanove version is preferred.
Programming of the ATmega328P is via the stan-
dard 6-pin ISP header and AVR Studio, or via the
optional Elektor FT232 BOB, the BOB being used
by the Arduino IDE software (VI. 0 or greater)
with the Duemilanove Bootloader pre-pro-
grammed on the ATMega. As far as the Arduino
IDE knows it's talking to a standard 'Arduino
Duemilanove w/ ATmega328' Board.

The real-time clock (RTC) is a DS1307, and the
temperature sensor, a DS18B20— both compo-
nents are well supported in the Arduino and AVR
communities. Their 'One-Wire' data is read by
the ATMega controller on the last two available
port lines, PD2 (temperature) and PC4 (RTC).
The expected ISP (in-system programming) con-
nector is available (K2) to allow the ATmega chip
to be programmed without removing it from its
socket.

MODI, an Elektor BOB-FT232 (break out board),
is optional. It provides USB connectivity and is
useful to have if you are keen on working on the
clock software within your Arduino environment.

The software

The source and hex files for the ATmega328 are
available from the Elektor website [1]. Ready
programmed ICs are also available: Elektor Store

• 120740-41.

The code is written to loop every 500 ms (V 2
second)— this is most obvious by the indicator
bulb Lai that flashes on and off once per second,

plus this delay gives time for the RTC to recover
between reads. If you read too often you get rub-
bish back! BTW Lai is a "grain of wheat" (GOW)
style miniature light bulb as used in dollhouses
and model railways.

On each cycle the code starts by checking if the
set button (S2) has been pressed and if not then
updates the indicator bulb. At this point the RTC
is read and, using some basic Integer division
math, the hours and minutes are each split into
Tens and Units, each value is then sent to the
correct Numitron digit.

For simplicity of the code each digit has its own
routine but they all work in a similar way with the
only exception being the 'Hour Tens' that only has
two binary bits (on IC5/V1). Finally using another
useful math trick (Bitwise AND) we then convert
the decimal number into Binary ready for the
74LS47's. More info on Bitwise operations may be
found at [2]. While it looks a little long winded
it's actually very simple, and a really useful way
to convert Decimals to individual Binary digits.
We have two extra functions to add value and
interest. The first is called on the 10-second and
30-second points, reading and displaying the tem-
perature in degrees Celsius. This works as above
using Mod and Bitwise math to take the reading,
convert it to binary and display it via the 74LS47s,
the exception to this being the lowest digit that
is sent a decimal '10' which makes the 74LS47
on that digit (V4) to display a 'c' thus complet-
ing the display to show for example '22.5c'. The
74LS47 is unable to display 'f', hence a Fahren-
heit readout is not supported.

Lastly on the 50 th second the showdate() rou-
tine is called that displays the date, month and
then year.

The code is very basic and I'm sure you could
find other functions for the clock (Egg timer?),
so why not join the project at Elektor.Labs [4]
and show us your code/updates/tweaks, or just
share your ideas and suggestions.

Build it, use it

Being SMD-free the project should be easy to
build at home, at school, at TechShop San Jose
CA, or in a small lab. The circuit board shown in
Figure 3 tallies with the Component List. Fig-
ure 4 shows the benchmark you're up against as
far as tidiness, component selection and proper
soldering are concerned. Initially, set preset PI
for +4.00 volts on the V+ rail.

www.elektor-magazine.com October 2013 33

•Projects

Figure 3.

The double sided printed
circuit board designed for
the project by Elektor Labs.

COMPONENT LIST

Resistors

R1 = 0.18ft 3W
R2,R3,R7,R8,R9 = lOkft
R4,R5,R6 = 4.7kft
PI = 4.7kft preset, top adjust

Capacitors

C1,C2,C6,C7,C8,C12,C13,C14,C15,C16 = lOOnF
C3 = lOOpF 25V radial

+ in gnd

i P1 (C) Elektor

120740-1
V2.1

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R3 R5 R6 ii

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C4 = 220pF
C5 = 22pF 25V radial
C9 = lOpF 50V radial
C10,C11 = 22pF

Inductors

LI = 18uH choke, 3.4A, 0.036ft (Panasonic type
ELC10D180E)

Semiconductors

D1 = 1N5819
IC1 = 78L05
IC2 = MC34063

IC3 = ATmega328-PU, programmed, Elektor Store #
120740-41 [2]

IC4 = DS1307
IC5,IC6,IC7,IC8 = 74LS47
IC9 = DS1820

Miscellaneous

V1,V2,V3,V4 = IV- 9 Numitron tube
JP1 = 2-pin pinheader + jumper cap, 0.1” pitch
XI = 32.768kHz quartz crystal
X2 = 16MHz quartz crystal
MODI = BOB-FT232R (optional), Elektor Store #
110553-91

Btl = CR2032 battery

S1,S2 = pushbutton, SPST, chassis mount

K1 = power jack, 2.1mm, PCB mount

K2 = 6-pin (2x3) boxheader

Lai = 5V 300mW light bulb, GOW

PCB # 120740 [2]

j

Si

3

4 ii li - '

Small delays in the code de-bounce the buttons
and make everything smooth.

Once the minutes are correct, another press on
set switches to the Hours, then Day, Month and
finally, Year. On completion of this cycle the new
values are written to the RTC and the code returns
to the main Loop.

( 120740 )

Internet Links

[1] Nixie VU Meter, Elektor November 2012,
www. elektor.com/1 10744

[2] www.elektor.com/120740

[3] http://playground.arduino.cc/Code/
BitMath#bitwise and

Figure 4.

The assembled and tested
board, ready for use.

To set the clock, jumper JP1 must be removed
('Run' mode). Pressing the set button S2 will
cause the setclock() routine to be called, firstly
displaying the Minutes. Pressing the adjust but-
ton SI counts up by 1 on each press or keeps
adding 1 every Vi second if holding the button.

[4] www.elektor-projects.com/project/nu-
mitron-arduino-clock-and-thermome-
ter-120740.12460.html

34 October 2013 www.elektor-magazine.com

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•Projects

Android

eiektorcardivscope

Construction, adjustments, and
operating instructions

By Marcel Cremmel

(France)

in co-operation with

Raymond Vermeulen

(Elektor Labs)

Thanks are due to Aurelien
Moulin, 12 student at ESEO,
Angers (France), trainee at
Elektor Labs, for his active
participation in testing and
debugging the first few
assembled modules supplied
by the elektorPCBservice.

Here now is the last installment of
the article series. As far as we know
nothing comparable exists commer-
cially, neither in terms of performance
nor price.

Construction: a few comments

For constructing the elektorcardioscope (also
referred to as the ECG interface), half the work
has already been done for you, as the module is
available assembled, tested, and ready-to-use
[8]. All the components for the circuit published in
the first article [9] fit on a modestly-sized board
(100x60 mm) (Figure 19) that's been designed
to fit (without needing screws!) into a common
case with a battery compartment (see component
list). The only thing to be done for the interface
board itself is to connect up the two supply cables.
If you fancy the challenge of building the PCB
yourself instead of buying the ready-to-use mod-
ule, only attempt this if you have solid experience
in the subject. The regulator IC12 must be an
MCP1640BT (lower noise version). It is possible
to use a different Bluetooth module from the one
suggested (Figure 4c in the first article), just as
long as it uses the SPP protocol. The advantage
of this one is that it offers the possibility of reset
(S3). By not fitting or by unsoldering the ferrite
bead interference suppression inductor L3, it is
easy to test the various parts of the circuit sep-
arately. The pin header on the underside of the
PCB is optional. It allows you to reprogram the
microcontroller "in circuit" (ICSP) using a compat-
ible tool (e.g. PICkit2 or PICkit3 from Microchip).
The functions of the three buttons and two LEDs

is shown in the front panel drawing (Figure 20):
SI = Off (and microcontroller reset), S2 = On,
S3 = Bluetooth Reset, D3 = Data Transmission
to the Android Terminal (TX) and D4 = Bluetooth
Module Status (BT).

You will still need to make yourself a connector
for your electrodes, and maybe the electrodes
themselves - we'll come back to this later. First,
we're going to get our ECG interface up and run-
ning. Once power has been applied from the two
AA cells, all you have to do is briefly press S2 and
the assembled module will show signs of life by
flashing D4 (2 Hz), showing that the Bluetooth
module is able to be identified.

2 October 2013 www.elektor-magazine.com

Cardiyscope

COMPONENTS LIST

Resistors (Default: SMD 0603 shape , 1%)

R1,R13,R15,R18,R19,R20,R33,R34,R54 = lOkQ 0.25W
R2, R12 = 3.3kQ
R3 = 523kQ
R4 = 300kft
R6 = 150Q
R7-R11,R23 = lkfl

R14,R53,R55,R56,R57,R59-R62 = lOOkQ
R5,R16,R17,R35 = 1MQ
R21,R36,R37,R38 = 330kQ
R22 = 100Q
R24,R65 = 390kQ
R25,R29 = 47MQ 5%

R26,R30 = 10MQ
R27,R31 = 2.2MQ
R28,R32 = 470kQ
R39,R40,R49-R52 = 47kQ
R41,R42,R45,R46 = 28.7kQ
R43,R44 = 1.4MQ
R47,R48 = 45.3kQ
R58 = 9.1kQ
R63,R64 = 27Q

P1,P2 = 5kQ 20% adjustable (Vishay TS53YJ502MR10)

P3 = 2kft 20% adjustable (Vishay TS53YJ202MR10)

Capacitors

Default: SMD 0603

C1,C13 = 33|jF 6.3 V, tantalum (case A)

C2,C4,C7,C9,C12,C14 = 10|jF 6.3V, X5R
C3,C5,C6,C8,C10,C15,C21,C22,C23,C24,C39,C40,C41,C42,C43
,C44 = lOOnF 25V, X7R
C11,C16,C25,C26,C31-C38 = lpiF 10V, X5R
C17-C20 = InF 50 V, X7R*

C27, C29 = 470pF 50 V, 5%,NP0
C28, C30 = 47nF 25V 5%, X7R

* C18, C19, C20 are 1 nF 50V, not 100 nF 50V as shown in
the schematic.

Inductors

LI = 4.7pH 20% 0.5A (Wuerth 744032004)

L2-L9 = ferrite bead, 30Q @ 100MHz (Murata
BLM18PG330SN1D)

Semiconductor

Dl, D2 = BAV99S

D3, D4 = LED, red, (PLCC-4)

T1 = PSMN6R5-25YLC NMOSFET
IC1 = PIC24FJ32GA002-I/SS, programmed, Elektor #
120107-41

IC2 = TPS60403DBVT
IC3-IC7 = TLC2252AIDRG4
IC8 = LMC6482AIMX/NOPB
IC9 = DG4053 AEQ-T1-E3
IC10, IC11 = CD74HC4052PW
IC12 = MCP1640BT-I/CHY
IC13 = LTC1981ES5#TRMPBF

Miscellaneous

K1 = 5-pin pinheader, 0.1" pitch
K2 = 6-pin pinheader, 0.1" pitch
K3 = 2-pin pinheader, 0.1" pitch

MODI = Bluetooth module, Roving Networks/Microchip type
RN-42

S1,S2,S3 = pushbutton, Omron type SPNO B3FS-1052) with
cap, Omron type B32-2010
Case, Pactec PPL-2AA
PCB, Elektor # 120107-1 or
Assembled module, ready for use,

Elektor # 120107-91

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Figure 19. The ECG interface
fits into the palm of your
hand. Connoisseurs will
appreciate the good
separation in the routing
between the analog and
digital parts of the circuit,
vital here.

Figure 20. Front panel
design with 3 buttons and
2 LEDs.

The numbering of the figures
and links continues from the
two previous articles.

www.elektor-magazine.com October 2013 3

•Projects

Figure 21. Menu for
selecting the Bluetooth link
to be established between
the ECG interface and a
nearby Android terminal.

Figure 22. Overview of
the touch-screen interface
functions.

Selection: Standard Derivation (DI, DII and Dill), or Enhanced
Derivation (aVR, aVL and aVF)

Vertical Gain (xl, xl.2, xl.5, x2 or x3)

Timebase Selection: zoom xl (250 pixels/s), x2 (125 p/s), x4
(62.5 p/s), or x8 (31.25 p/s)

Block/Verify Data Transmission
(reduce interface power consumption)

| Current Cardiac Rhythm

Open Context Menu

Verify Calibration Signal Production

Verify Cardiac Beep

ED

Select Derivation:
set of 3, or individual

130295-29U

Android application

Installation is conventional: download the Android
application package (file ANDROECG.apk) [10],
copy it into the root of the Android terminal and
select it using the File Explorer. It will be installed
automatically (assuming you have already allowed
installation of non-Market applications in your
Android terminal's Security menu).

You can then place a shortcut wherever you like.
If the terminal's Bluetooth interface is not enabled
when the application is run, the application tells
you. Of course, you must enable it.

At this stage, the BT radio link between the ECG
interface and the Android terminal has not yet
been established. To do this, you must open the
menu and request Paired BT Devices (Figure 21).
The connection should be established straight-
away after you have chosen the ECG interface's
Bluetooth module. In this case, the graph starts
to scroll and the BT (State) LED on the interface
stays lit. At the first connection, you'll need to
enter the PIN code (here: 1234) for the BT mod-
ule. The BT peripheral is now registered in the
Android terminal and you won't be asked for the
PIN again. The interface's microcontroller is not
involved in this protocol. The MAC code printed
on the BT module and displayed on the Android
terminal may make it easier to identify the ECG
interface if the list of BT devices is long.

If no BT connection is established within 5 min-
utes, the interface will be powered down
automatically.

It won't take you long to get to grips with the
menus and functions of the elektorcardioscope
software on the Android terminal, thanks to the
intuitive "Instructions for use" in Figure 22.
There's also a demonstration video [11].

Now all that remains is to move on to adjust-
ing the interface, which involves just two simple
operations: setting the common-mode rejection
ratio (CMRR), and balancing the gains.

Setting the CMRR for each channel

The first adjustment consists in optimizing the
CMRR for each differential amplifier with the help
of a function generator. Start by constructing
the calibration accessory on the left in Figure 23
(BNC + pin header with no resistors). Plug it into
socket Kl, making sure you get it the right way
round: pin 1 is on the right when you are holding
the interface with the buttons toward you. The

4

October 2013 www.elektor-magazine.com

Cardiyscope

RA, LA, and LL inputs are connected together so
as to inject a common-mode signal via pins 1, 2,
and 3 of the calibration jig; its pin 4 is connected
to the body of the BNC socket and hence to the
ground of the LF function generator, while pin 5
(the ECG interface ground) is left floating.
Adjust the generator to obtain an AC sinewave
at 50 Hz with an amplitude of 1 V. Power up the
ECG interface and run the application ANDROECG.
Establish the Bluetooth connection and observe
the DI and DII leads at maximum amplification.
Then adjust PI and P2 to reduce the peak-to-peak
amplitudes as much as possible. They should be
barely visible at xlO amplification (Figure 24).
In the absence of an LF function generator, you
can work as follows:

• touch the interface GND with a finger on one
hand;

• with a finger on the other hand, touch the
common point of the three electrodes RA,

LA, and LL: by so doing, you are injecting
a common-mode signal picked up by your
body from the 50 Hz power line;

• observe the DI and DII signals on the
Android terminal;

• using your third hand (maybe you'll need a
guinea-pig!), adjust PI and P2 to obtain the
flattest possible curves.

Balancing the gains

The total gain of amplifiers in each channel must
be identical, as the DI and DII signals are used
for calculating the other leads (see Leads box
[9]). A signal generator is recommended for this
adjustment, with an attenuator, as the signal to
be injected must be very low: 1.4 mVpp (on right
in Figure 23, BNC + pin header + resistors). This
attenuator, formed from two 1.5 kft and 150 kft
resistors connected as shown in Figure 25, must
be inserted between the function generator and
the ECG interface in socket Kl: pin 1 is on the
right when you are holding the interface with the
buttons toward you.

Set the generator to produce a 1 Hz sinewave at
an amplitude of 140 mVpp. If not already done,
connect your Android terminal to the ECG inter-
face and observe the DI, DII, and Dill leads
using x2 amplification. You should observe 1 Hz
sinewaves on DI and DII as seen at image 1 in
Figure 26. Now adjust P3 to minimize the trace
for the Dill lead. In point of fact, the Android
terminal calculates Dill = DII - DI: Dill should

Figure 23. You'll only need
to turn on your soldering
iron to build these two
calibration jigs.

Fig 24 = The amplitude of
residual 50 Hz components
must be minimized.

OV RL LL LA RA

Figure 25. This adjustment
jig divides the injected
calibration signal by 100.

ATTENTION

Manufacturing and using medical devices are governed by national and
international laws [14]. The Elektorcardioscope has no medical approval
and hence is not intended for professional use.

In order to comply with protection class III, it must be battery powered
only, and may be used only for the purpose of personal study and
experimentation. Under no circumstances shall the author of this article
or the Publishers be able to be held liable for the consequences of using
this interface.

www.elektor-magazine.com October 2013 5

•Projects

The gain balancing
requires injecting
the highest
possible level
without driving
the amplifiers into
saturation. Before
the adjustment,
ensure that
the sine waves
displayed on the
terminal are free
from saturation
effects or distortion
(particularly DI).
Reduce the signal
level if necessary.
In principle,
saturation should
not occur as there
is a small drive
margin left when
injecting 1.4 mV.

Figure 26. These readings
will help you balance the
amps IC3 and IC4 (DI and
DII channels): the trace
for the Dill lead must be
minimized.

Figure 27. Every minute,
the interface produces a
2 Hz/1 mV CAL signal for
10 s, which can be used for
balancing the gains (see
Figure 26).

be null when DI = DII. The amplification can be
increased to obtain greater sensitivity, and dis-
play only Dill. Images 2 and 3 represent Dill
before and after adjustment.

In the absence of a signal generator, wait for the
periodic injection of the CAL calibration signal
at the ECG interface input (Figure 27, see also
Figure 9 in the second article) and adjust P3 to
obtain as little residual CAL signal as possible
on DHL Images 4 and 5 (Figure 26) show the
results before and after adjustment; note that
it isn't possible to eliminate the fine spikes seen
in image 5.

Note: impatient users force an immediate injec-
tion signal by un-ticking and again ticking the
"Cal." Button.

The elektorcardioscope is now operational and
you can use the various touch buttons on the
Android terminal screen (Figure 22) to choose the
graphs, amplify the amplitudes, change the time-
base, and move around within the trace memory.
But to be able to observe your electrocardiograms
on your Android terminal's screen, you'll need to
equip yourself with some electrodes— and find a
willing patient.

Electrodes

The electrical signals we're going to be picking
up with the help of the electrodes are infinitely
weaker than the ones we're usually familiar with.
Hence it will only be possible to obtain a good
electrocardiogram using good electrodes, properly
positioned, and correctly wired. As a reminder,
on the electrodes connector (Figure 28a), the
ground is on the left when you are holding the
ECG interface with the buttons toward you. At
the patient end, get into the habit of adhering
to the color code [9]:

• red — RA (right arm)

• yellow — LA (left arm)

• green - LL (left leg)

• black — RL (right leg)

If you don't want to go to the expense of buy-
ing four commercially-available electrodes - the
clamps, very handy with children, are not cheap -
you can easily make some yourself. Any electrode
with its connecting cable is also a great antenna,
and here you'll have four: so it's essential to
use shielded cable, to minimize the influence of

6 October 2013 www.elektor-magazine.com

Cardiyscope

unwanted signals. The shield is connected at the
interface end only; at the electrode end, it must
be insulated so as to avoid any contact with the
skin. Watch out! Although audio cable is electri-
cally suitable, it is mechanically fragile. Strain
reliefs reduce the risk of failure (Figure 28b).
The 4 mm banana plugs allow you to use com-
mercially-available accessories (Figure 29) like
banana to spring-terminal adaptors [12] or screw-
fit bananas (RS Components ref. 641-8053).

If you've still got some nickel-alloy coins around
you can also produce these accessories yourself
more cheaply. The only tricky part if to solder a
4-mm socket onto the coin (Figure 30), which will
then be held in place on the wrists and ankles by
four elastic bracelets (suspender elastic + Velcro
strip). You can also use rings cut from a motor-
bike or scooter inner tube. Fit the electrodes to
the wrists and ankles, if possible using conducting
gel, which improves the quality of the ECGs by
significantly reducing noise and contact voltages.

Saving and playing back ECGs

These operations are simple, no options are
offered : you save or playback the 10 min of sam-
ples for the DI, DII, and Dill leads. The index of
the most recent sample (the current one) within
the circular ECG memory is also saved in order
to be able to get back the same appearance of
the traces in playback (latest sample represented
on the right of the screen: see Figure 17 in the
second article).

The save and playback operations are offered
in the menu. A window offers you the choice
between an existing file and a new file, for which
you just have to enter the name (Figure 18 in
the second article [13]).

Other functions

The "CAL" checkbox gives you the choice to peri-
odically inject a calibration signal (Figure 22) in
place of the ECG signals. Cardiologists are very
familiar with this calibration signal, with an ampli-
tude of exactly 1 mV, which is used as a reference
against which to compare ECGs.

The Android application calculates the cardiac
rhythm using an algorithm based on the deriv-
ative of the DI signal. This algorithm can some-
times go wrong, together with its display on the
screen, and an audible 'beep' generated. As this
noise can become annoying, it can be turned off
using the SP button.

Figure 28. We made up this
adaptor for a commercially-
available electrode
connector (Figure 28a).

Note the cable clamps on
the robust home-made
connector (28b) produced
in 2006 for the Gameboy
version, which used one less
electrode.

Future functions

A project like this is constantly evolving. In its
current state, the only display application avail-
able is the Android version. However, Elektor
would be delighted to publish versions for iPhone,

Figure 29. Commercially-
available accessories are not
cheap, but do look the part.

Figure 30. Satisfactory
electrodes can be obtained
using nickel-silver coins, as
long as you can manage to
solder to them a 4-banana
socket.

www.elektor-magazine.com October 2013 7

•Projects

The author Marcel
Cremmel is a
qualified Electrical
Engineering
instructor,
electronics
option, on the
Higher Diploma
in Electronics
course at the Louis
Couffignal College
in Strasbourg.
Website: http://
electronique.
marcel.free.fr/
Email: marcel.
cremmel.llc@free.fr

Linux, Mac, or PC if interested readers would like
to come up with them. In the meantime, the fol-
lowing functions are under development for the
Android application:

• digital filter for 50 Hz (or 60 Hz) power line
noise rejection;

• cloud hosting for the ECG readings via
a Google API (Application Programming
Interface).

I am also working on a Windows application for
consulting ECGs saved onto an SD card and even
display them live via a Bluetooth interface.

Looking further ahead, I shall be offering some
code to copy onto your website that will let you
receive and display ECGs read via your Android
terminal and transmitted to your site. If you so

wish, your doctor or cardiolo-

0H OFF f-ESCT BT

©ektor

Internet Links

[8] www.elektor.com/120107

[9] Part 1: Elektor July & August 2013, www.
elektor.com/120107

[10] ANDROECG.apk application: www. elektor.
com/130295

[11] Demo video: in production, please check
the "elektorim" channel on Youtube.

[12] Electrodes: www.praxisdienst.fr/fr/home/

[13] Part 1: Elektor September 2013, www.
elektor. com/130227

[14] Legal guidance: http://homeusemedical-
devices.com/humd.html

Banana to Snap-On adapters:

http://goo.gl/5WWYFu or

http://www.praxisdienst.com/en/Diagno-

sis/Specialised+diagnosis/ECG+devic-

es+and+accessories/oxid+oxid/Press+-

stud+adapter+for+ECG+red.html

Limb clamps:

http://goo.gl/bZIKXf or

http://www.praxisdienst.com/en/Diagno-
sis/Specialised+diagnosis/ECG+devic-
es+and+accessories/oxid+oxid/Limbs+-
Clip+electrode+Adult+ red.html

8 October 2013 www.elektor-magazine.com

Cardiyscope

Rhytm and Rate

The normal resting heart rate is between 50 and 100 beats per minute. Below 60 (sometimes,
50) is sinus bradycardia, over 100 is sinus tachycardia.

Atrial depolarization: P wave

Normal duration is less than or equal to 0.1 s.

Its normal amplitude is less than or equal to 0.25 mV, i.e. V* of the amplitude of the CAL
calibration signal.

The P wave is generally maximum in DI, Dill, and aVF. The P wave is always positive in DI and
DII and negative in aVR.

PR or PQ interval

The normal duration of the PR interval is between 0.12 and 0.20 s. It is measured from the start
of the P wave to the start of the QRS complex. It corresponds to the time taken to conduct the
influx from the atrium to the ventricles. This may reduce when the heart rate increases with
exertion. Above 0.20 s, it indicates a problem with atrioventricular conduction.

QRS amplitude

In the front leads, the amplitude is very variable. With an amplitude lower than 0.5 mV (V 2 CAL)
in all of these leads, we speak of micro-voltage.

Duration of the QRS complex

This is on average 0.08 s; it must be below 0.12 s. Above this, it is most often an asynchronism
in the depolarization of the two ventricles, associated with a problem with intra-ventricular
conduction.

Ventricular repolarization: ST-segment - T wave - U wave

The ST-segment separates the QRS complex from the T wave. It starts at the end of the QRS.
The T wave is usually of low amplitude, asymmetrical with the rising slope lower than the falling
slope, and in the same polarity as the QRS. It is normally positive in DI, DII, Dill, and aVF. A T
wave that is biphasic or negative in Dill must be considered as physiological.

The U wave, inconsistent, follows on from the T wave. It has the same polarity, but a lower
amplitude. Its significance is debated.

The QT interval (start of QRS, end of T) varies according to the heart rate. For a rate of around
60 bpm, the duration of the QT interval is around 0.4 s.

www.elektor-magazine.com October 2013 9

Modular RF Link using
Manchester Code (2)

Part 2: Software

RF MODULE
RXM-315-LR-S
LOT RR3D01 -

h

O a

In the previous installment we elaborated on the hardware side of this project.
Now it is time to go software. While the proper hardware design and board lay-
out guarantees the correct radiation and reception of the RF signals, the software
(sometimes referred to as firmware) plays a fundamental role in the reliability of
the message being carried by the signal.

By

Marcelo Maggi (USA)

As mentioned in the first installment, the RF mod-
ules proper have no intelligence included, so if
our radio communication system is supposed to
have 'brains' it must be provided by the micro-
controllers' software. In this respect, 'intelligence'
includes the selection of the proper coding pro-
tocol, the link speed (bit rate), data organization
and error detection/recovery mechanisms.

The software has been designed in a modular
way with all the essential functions organized in
'drivers' that remain unchanged. The user has
complete freedom to implement any routine in the
main area. A call on the TX driver sends the infor-
mation. On the receiver side, the RX driver also
takes care of all the complicated tasks, returning
just the useful data to the main program.

Manchester code

The Manchester Code has proven to be a basic
but very reliable way to send data over a radio
link. With this project speeds of up to 5,000 bps
have shown good stability, being the top bit rate
of our link; a lower speed option is available for
added versatility. For transmission the data is
organized in a macro structure called frame. An
error correction byte is included. Its logic is quite
simple: every bit is represented by a transition,
instead of a logic level.

Figure 1 shows the logic behind the Manchester
Code and the two conventions to represent each
bit. We will be using the IEEE 802.3 definition:
a logic '1' will be represented by a Low-to-High
transition, while a logic '0' will be the opposite

44 October 2013 www.elektor-magazine.com

Manchester-Code RF Link

(High-to-Low). The advantages of this form of
coding are quite obvious:

• The signal clock is always present in each
transition, no matter the bit sequence, and it
is easily recovered at the receiver end.

• The average DC level of the signal is con-
stant, around 50%.

• Using an OOK (On-Off Keying) RF link, like
the one we use here, the average transmit-
ting power is reduced. This is useful not only

to save power in portable applications, but
also to stay within the power limits man-
dated by local regulations for ISM band
usage, while the peak power may be larger
to increase range.

The Linx modules are rated up to 10,000 bps.
While this speed is possible, our link will have
a maximum speed of 5,000 bps. This is due
to the coding, since each bit will have two
logic levels; with a simple binary transmission
the bit rate would double. However, given the
advantages the Manchester Code, we sacrifice
transmission speed for simplicity and reliability.
At 5,000 bps an RF link over distances in excess
of 600 ft (180 m) proved reliable.

A lower speed (2,500 bps) is provided to be
used in case of very noisy environments or to
extend the range. Linx claims that distances up
to 3,000 ft (just under 1 km) are feasible with
the proper hardware setup.

Data format

The data to be transmitted is composed of three
elements, 1-byte long each: address, data and
CRC. The address byte is intended to indicate to
which receiver the transmission is directed. Being
1-byte long, there would be 256 possibilities. In
most situations this would be a waste of bits,
so the most efficient way would be to use the
address byte to indicate receiver and function:

• Upper nibble (4 bits) used to call the
receiver (16 addresses).

• Lower nibble used to call the function within
the receiver (16 options).

This way receiver number 5 can be ordered to
run command number 9 using data, which may
be turning on a servo mechanism and position
it based on the contents of data.

In our example code, address will be used sim-
ply to indicate the receiver; it contains the num-

Features

• One transmitter, multiple receivers
possible.

• Range up to 600 ft (180 m).

• Bit rate selectable between 2,500 bps
and 5,000 bps (software).

• Error correction can easily be
implemented.

• PCB artwork files and example software
code available free of charge [2].

dock

Data

juuinnjiruinnnr

rLnn—n

1 ! 0 1 1 ! 0 i 1

Manchester

{IEEE 802.3)

Manchester

(G.E. Thomasj

IflllKI

Figure 1.

Manchester Code logic and
conventions.

ber 15, just to show how it may be used. At the
receiver side, when 15 is read from the address
byte, data will be considered valid and processed
by the code. In binary form 15 is represented
00001111, which is easily recognized on an oscil-
loscope. In Manchester code this is represented
by the sequence 1010101001010101.

The data byte carries the actual information and
can be a fixed value, such as an order to execute
a defined task, or a variable one, like the out-
put of an A/D converter. The example code will
send a different data byte based on the status of
pin B3 (RB3/CCP1, pin 9): if Low, data will contain
a fixed '1'; if High, data will alternate between
'0' and '1', using an internal timer to control the
change. On the receiver side this will be used to
turn LED D1 ON (1) and OFF (0). This is a very
simple way to test the link and demonstrate how
to use the data byte.

Despite the simplicity of the provided example
code, take note of its abilities. By properly using
the address byte it's easy to send more than one
data byte at a time. The lower nibble may be
used to indicate which byte you are sending, so
the receiver can properly reassemble and com-
plete the data. Sending more than one data byte

www.elektor-magazine.com October 2013 45

lit i till if ljtiiiii ilia

xxkkkkhhIOx xxxxxkkIOxxxxxxxx

1 0

r ,,

fir

n

synchronization

Address | Data | crc

12D1S7-12

Figure 2.

Complete frame structure.

is much more efficient than sending one byte
at a time. In this example we demonstrate the
basics of the RF link, but a few changes in the
code will allow any number of data bytes to be
sent at once.

CRC, or Cyclic Redundancy Check, contains infor-
mation useful to validate the previously received
data byte (or bytes) and may provide elements
to recover a missing bit. The various methods
and algorithms generally available for creating
a CRC byte are beyond the scope of this article,
but a proper data stream should have one, so it
is included. In the example code CRC is a copy of
data. At the receiver end, if CRC is not equal to
data , you know that something went wrong. How-
ever, there is no way to tell which one is wrong.

Composing a frame

Now to put the main three elements together in
a macro structure called frame. Since every RF
link is susceptible to noise, the receiver must
contain elements to determine whether a frame
is valid, and where it starts. Hence 'frame syn-
chronization' is added preceding each frame. This
synchronization is a non-changing sequence that
cannot be emulated by any combination of the
previously described three bytes.

We will use bit sequence 111111111111111111110.
A 'spacer' is added to the frame. This is a short
sequence, just '1' and 'O', added at the end of each
byte. A synchronization conflicting sequence (when
address and data are both 11111111 and CRC is
11110XXX) will thus be prevented: 11111111 10
11111111 10 11110XXX 10. The long sequence
of 'l's is broken by the spacer, thus guaranteeing
that no combination will emulate the synchronism
sequence. Figure 2 shows a complete frame and
its components in Manchester Code.

Bit rate

The transmission speed is selected at the trans-
mitter (TX) side. It is predefined by the firmware,
but can also be selected using input B2 (RB2/TX/
CK, pin 8) of the microcontroller, accessible via
K2 pin 11. If low, the bit rate will be 2,500 bps,
if high, it will be 5,000 bps. The receiver detects

the speed automatically. Since the detection is
based on time measurements using the local
oscillator as the reference, it is very important
to keep the 20-MHz quartz crystal unchanged.
The transmitter needs to send the frames at cer-
tain intervals for the link to work. An isolated
frame may not be received correctly, as may
frames spaced more than 10 to 15 ms apart.
The receiver must be 'awake' and have the right
gain settings dialed in to properly receive and
demodulate the signal. After 10 ms or more of
inactivity the receiver may not be ready for an
incoming frame.

The simple solution is to send the frames repeat-
edly at intervals of 10 ms or less. While this
works, it has two major drawbacks:

• A microcontroller task requiring more than
10 ms is not allowed.

• Besides transmit power, local or national
legislation in place for ISM band usage may
prohibit the time a transmitter is active at a
set frequency.

The solution is simple: set an internal timer in the
main program and transmit two or three frames
in a single burst, spaced 10 ms or less. Then, let
the transmitter idle for a few seconds.

Note: The provided example, downloadable from
[1], is only to show how the link works and to
make a functional test. The main code should not
be used in an actual device as is. Please check
your local ISM band regulations so your final
device is fully compliant. It is your responsibility.

Transmitter firmware (TX)

Both the fundamental transmitter and receiver
routines have been grouped in a separate file, like
PC hardware drivers. These routines contain the
most complex parts of the code and can remain
unchanged, no matter the application. The main
program, with only a few lines to perform the
previously described basic functions, is provided
to show how the link works. Here is where you
should write your own code.

All software has been written in C, using the CCS
C compiler. Comments are added in the code pro-

46 October 2013 www.elektor-magazine.com

Manchester-Code RF Link

RX driver

The frame is received and decoded in the
receiver driver. All the complexity of the link
resides in this driver, which incorporates
comments to explain each section. The
receive function mc_rx, called from the main
program, calls the rest of the bit-gathering
functions.

First the bit rate is detected: baud_detect
counts the duration of two halves of one bit.

All these activities are triggered by the rising
edge of an incoming signal. The first bit of
a frame is a '1'— in Manchester Code, low
to high— so when the interrupt is triggered,
the first half of this first bit is already gone.
Therefore, baud_detect counts the second half
of one bit and the first half of the next.

Isn't it enough to measure one half, since
the bits are symmetrical? Yes and no. If we
send data continuously, the receiver will
be continuously active and the internal DC
levels will be stable. Then the bits are fairly
symmetrical. However, if the frames are
spaced, let's say by 10 ms, the receiver may
not be completely ready when each new
frame arrives. As a consequence, the first
bits of the frame may not be symmetrical,
as shown in Figure 3. While the link still
works, if we do not measure a complete bit to
recover the bit rate there is a real possibility
that we have the wrong figure, thus making
any subsequent bit detection impossible. In
our example code we send the frames 1 ms
apart, so there is no major issue. However,
the baud_detect function has been designed
with those extreme cases in mind.

After the first half of the second bit timerO
will contain the bit duration... sort of. Some
simple math:

• A 20-MHz oscillator results in a 5-MHz
instruction clock.

• The period of one cycle is 1/5,000,000 =

0.2 ps.

• TimerO increases every 0.2 psxl6 = 3.2 ps.

• One bit at 5,000 bps lasts 200 ps, so after
one complete bit timerO = 200/3.2 = 62.5.

Being an 8-bit integer, timerO may either
be 62 or 63. But this is not really relevant.

By nature, radio signals will exhibit a
phenomenon called jitter, random shifting
of the edges (transitions) of the signal,
shortening or stretching the bits. So timerO
varies around 62.5. Any of these surrounding
values are interpreted as the actual bit length
as calculated. The program implements this
by accepting a range, between 55 and 70. If
timerO falls within this range, the bit duration
is 200 ps, so half a bit will be 100 ps. This
is exactly what is stored in the variable
semi, returned by the function, and named
semiperiod. For 2,500 bps semiperiod is
200 ps and the detection range for timerO is
118 to 133.

Now that the bit time is known, the detection
of the bits is easy: Read the signal status,
wait until it changes, read the next status,
compare. Every bit will have a signal status
change in the center of the bit period. Before
reading the next bit we wait an interval
semiandjitter to ensure that the next bit
is read and not the tail of the previous. If
status 1 is higher than status 2 (high to
low transition, ini and in2 in the code), the
received bit is 'O', otherwise it is '1'. Then
this bit is added to a 32-bit variable ( three_
byte_rx), which is then shifted to the left so
it is ready to accept the next bit. By carefully
eliminating the spacers, three_byte_rx will
contain address, data and CRC with the
remaining 8 bits left empty.

Provided there is no error in the process,
three_byte_rx is now called ad_da_cr_rx and
moved to frame_rx in the mc_rx function.

Its contents are then shifted 8 bits to the
left (x256) and semiperiod is added. Frame_
rx is now ready to be returned to the main
program where it will be known simply
as frame. In case of an error, the routine
forwards this to the main program by sending
an empty frame_rx.

A final note: as with the transmitter program,
to avoid conflicts please check the names of
the variables used here and do not to use
them in the main program.

www.elektor-magazine.com October 2013 47

Figure 3.

Received signal with frames
spaced 10 ms apart, as
captured on an oscilloscope.

viding additional information. Let's examine the
transmitter code, split into three files:

• Manchester_Link_TX.c— main program,

• Manchester_Link_TX.h— PIC setup,

• MAN_TX.c— transmitter driver.

The main program is quite simple. After the initial
definitions the program enters an infinite loop,
where pin B2 is read to set the bit rate, address is
fixed at 15, pin B3 is read to determine the value
of data and CRC is made equal to data. With all
four variables set, the transmission function is
called with mc_tx (baud , address, data, crc);.
Here the main program sends the variables to
the transmitter driver. No matter how simple or
complex the main program may be, this is the
only line required to transmit the information.
The last line is just a 1 ms delay before starting
all over again.

The transmitter driver is the true value of this
design. It will remain unchanged, no matter what
application the user may come up with. It needs
to be included in the main program at the very
top, after the PIC setup. The driver contains all
the elements to create a frame in Manchester
Code using just the four variables received from
the main program. The bit rate is converted into
half bit time ( semiperiod ), so the Manchester
Code is easily obtained. The frame synchroniza-
tion is constructed by calling function one twenty
times, and then one time function zero.

Each byte is analyzed bit by bit, starting at the
MSB side. Depending on the result, the proper
function is called ( one or zero), inserting the
spacer after each complete byte. And that's it!
A complete frame with all the bells and whistles
previously described is sent out via pin BO at
the speed set by the bit rate variable. There is

no need to change the driver program to send a
standard frame. If more data bytes have to be
included in the frame, only a few changes will
be required.

Additionally, an LC display is implemented in order
to display the encoded information ( address , data
and CRC).

Receiver software (RX)

Similar to its hardware counterpart, the receiver
(RX) code is just a little more complex than the
transmitter. But not to worry: the complexity
resides in the driver, which is discussed in the
text frame RX driver. The same three-file struc-
ture is maintained here:

• Manchester_Link_RX.c (main program);

• Manchester_Link_RX.h (PIC setup);

• MAN_RX.c (receiver driver).

Again, the main program is quite simple. After
the LCD procedures, the standard definitions are
stated. Note that the Interrupt Service Routine
(ISR) function is defined in void detection,
i s r ( ) ; . This is important since the received
information will enter through pin BO (RBO/INT,
pin 6) by triggering the external interrupt on the
rising edge. The program will jump to this func-
tion as soon as this edge is detected.

Another important line that must be included is
the setting of timerO inside the main function:
setup.ti mer.O ( RTCC.INTERNAL | RTCC . . .. This
defines timerO as an 8-bit timer that is incre-
mented every 16 th period of the instruction clock.
This internal timer is used to determine the bit
rate of the incoming signal (by measuring the
length of one bit).

Since we use interrupts, these must be enabled
using enable.interrupts (GLOBAL) ;. Then the
program enters an infinite loop, in which the
incoming data is monitored. User program code
can be entered here, provided none of the activ-
ities disable the interrupts. Some activities, like
showing data on an LCD, may disable interrupts,
hence these must be programmed inside the ISR,
after the information is received and validated.
Remember that the receiver is waiting for a sig-
nal to arrive.

When a rising edge is detected, the program
jumps to the ISR, where the interrupts are
disabled and the receive function is called:
f rame=mc_rx ( f rame) ;. This function is located
in the receiver driver and it returns the 32-bit
variable frame. The beauty of this is its simplic-

48 October 2013 www.elektor-magazine.com

Manchester-Code RF Link

Figure 4.

First prototypes with LCD.

ity. A signal arrives, the mc_rx function is called,
and frame contains all the information that was
received.

Being a 32-bit variable, frame contains 4 bytes:
address, data, CRC and halftime of the received
frame. The bytes are extracted from the frame
as follows. We copy the 32-bit frame to an 8-bit
variable, so only the 8 least significant bits (LSBs)
are copied: halftime=f rame; . Halftime now con-
tains the fourth byte of frame. Then we shift
the contents of frame 8 positions to the right
and repeat the copying process to extract the
next byte.

Halftime contains the duration of half a bit, so the
bit rate can be calculated from there. The rest
of the instructions show how to use the received
information in a very basic way. If there is an
error in the received frame, the function will
return a 'O', so HALFTIME will be 0. This is used
here to set the error flag.

If address is 15 (as set in the transmitter) and
there is no error, then data contents are used
to turn the LED ON and OFF. CRC is not used in
this brief example.

The LCD continuously displays received informa-
tion (address, data and CRC) after the interrupt is
enabled. If the receiver does not receive any data,
the LCD shows Error is '1' and Bit status is 'L'.

Improvements and applications

While the link is fully functional and proved to be
extremely reliable during various tests, there is
plenty of room for improvements and custom-
izations, like sending more than one data byte
at a time. Additional bytes could easily be added
to a frame, you just need to know how many to
expect to avoid missing any. Obviously a single
32-bit variable will not be able to contain all bits,

so a structure should be considered.

The applications are endless, limited only by the
user's imagination; this is just a building block
for many bigger projects.

Figure 4 shows the prototypes assembled
at Elektor Labs with an LCD display showing
address = 15, data and CRC = 1, Bit rate (B) is
high (H = 5,000 bps) and Error (E) = 0 (no error).
This simple application shows the potential of
these units and it is very useful to debug the
code when things do not turn out as expected.
This concludes the second and last part of this
project. Should you have any questions, con-
cerns or just comments regarding the hardware
or software presented, do not hesitate to join
our topic on [2] or visit the author's web page
at [3]; PCB artworks and software routines will
be available for direct download.

( 120187 )

Correction to Part 1
(Elektor September 2013)

In the previous installment, the caption with
Figure 5 mentioned that the "Transmit Output
Power can be trimmed using R3". This should be
corrected to read: ... Rl.

Internet Links

[1] www.elektor.com/120187

[2] www.elektor-projects.com/120049

[3] www.magusporta.com

www.elektor-magazine.com October 2013 49

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DESIGNSPARK PCB

h r

DesignSpark
Tips and Tricks

Day #4: a simple project

By Neil Gruending

(Canada)

Last time I talked about how to setup and use libraries in DesignSpark. Today we'll
make a simple bi-color LED driver to learn how to use the schematic and circuit
board editors. There are several ways to drive a bi-color LED and today we will use
an H bridge variation which is hardwired to turn one of the LEDs on.

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Figure 1.

Schematic of the bi-color
LED driver.

Drawing the schematic

The first thing we need to do is to create a project
file to link the schematics and PCB by using the
"File->New" command. You then add a schematic
to the project by using the "File->New" command
again, but make sure that you check the "Add To
Open Project" button. At this point you can also
choose the technology file to use for the sche-
matic like we talked about in an earlier article.
Figure 1 shows the schematic we will be using.
Designspark has a schematic entry tutorial at
[1] which covers how to add components and
edit the schematic.

Moving visible component fields like reference
designators around in a DesignSpark schematic
is different than in some other packages because
all of the fields are moved in 1 block. For example,

in the example schematic there's a part number
and reference designator visible for each tran-
sistor. Clicking on either one will highlight both
fields and they can be dragged to a new posi-
tion as a group. This can cause problems when
mirroring components, which DesignSpark calls
flipping, because the text can be incorrectly lined
up. Fortunately the text alignment can be easily
changed by right clicking the text and selecting
the "Properties" menu. There in the "Text" tab
you will find an alignment field that will let you
choose between "Left", "Center" and "Right" text
alignment.

Also, don't forget that power and ground sym-
bols are components in DesignSpark. The default
ones are in the DesignSpark schema library, but
you can also create your own library of symbols
to your liking. Note that if you connect a power
symbol to an existing net DesignSpark will warn
you that it will rename the net even though that's
what you want.

The LED component

For the transistors and resistors I used some
existing schematic symbols and PCB footprints
from the DesignSpark libraries. Flowever, for the
LED I modified an existing DesignSpark LED sym-
bol and then made a custom PCB footprint for it.
Making a custom PCB footprint is a lot easier
when you use the footprint wizard. You can access
the wizard by opening the PCB library where you
want to save the footprint with the library man-
ager and then clicking on the "Wizard..." button.
The PCB footprint wizard will then ask a series of

52 | October 2013 | www.elektor-magazine.com

Tips & Tricks

questions to make a footprint and since they are
a generic as possible it's important to pick the
closest type possible to minimize later editing.
In the case of my LED I used an axial compo-
nent with 2.54-mm (0.1") lead spacing so that
all I needed to do was to edit the silkscreen and
mark the polarity on pin 1.

DesignSpark also includes similar schematic sym-
bol and component wizards.

Getting ready for layout

Now we're ready to layout our circuit board by
creating a new PCB file using the "Tools->Trans-
late to PCB" menu which will start the New PCB
Wizard. We are going to create a 2-layer metric
design that's a 20 mm square. If you tell the
wizard to place the components outside of the
board you will get something like in Figure 2.

I like to place components on a 0.25 mm grid so
I changed the working grid to 0.25 mm before
placing the components on the circuit board to
get an arrangement like in Figure 3.

Before routing the board I want to talk about
the routing grid used when placing the copper
traces on the circuit board. DesignSpark doesn't
include an interactive autorouter which means
that you have to set the routing grid to the width
of the trace you're routing. This way when two
traces touch the spacing is 0 mm, and when
there's a gap between them the spacing is at
least the trace width. This works because the
routing grid is applied to the center of the trace
instead of the edges. Therefore, if you want to
route a 0.2 mm trace then you would set the
routing grid to 0.2 mm spacing to get 0.2 mm
trace spacing. The downside of this technique is
that all the trace widths should be multiples of the
smallest size. For example, 0.2 mm and 0.6 mm
would work but 0.2 mm and 0.35 mm would not.
Also, be sure to create a style for each trace
width that you want to use in the design tech-
nology settings (Settings->Design Technology...
and then select the "Track Styles"). That makes
the different trace widths much easier to manage
in more complicated designs because you can
change the current trace width by just changing
the style. You can change the current track style
by pressing "s" while routing and then choosing
the new style you want.

The same is also true for vias and in DesignSpark
you configure the via styles using the "Pads
Styles" tab in the "Design Technology" window.

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0.25 mm grid.

I recommend making a "SignalVia" style and any
other styles that you may need. I chose to make
the signal vias in this design with a 0.45 mm hole
and a 0.95 mm pad. You can change the current
style used for vias by right clicking while routing
and going into the "Change Via Style" menu to
choose the style you want.

DesignSpark uses the "Settings- > Defaults" menu
to set the track and via defaults, although I hav-
en't been able to get DesignSpark to recognize
the new settings even with a restart.

More information is available from the
DesignSpark website about PCB setup and place-
ment is available at [2].

www.elektor-magazine.com | October 2013 | 53

DESIGNSPARK PCB

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Figure 4. End result of the board design work.

Figure 5. Applying the Design Rule Check (DRC) tool.

Layout

Once everything is configured it's time to lay
out the circuit board. The result is pictured in

Figure 4.

I routed all of the signal traces on the top layer
and used a polygon pour to make a bottom ground
plane. When routing the board it's important to
make sure that you double click on the "rat's
nest" interconnect line when starting to route a
trace. As you run the trace you can change how
DesignSpark deals with corners by right clicking
and choosing a different segment mode.

If you look closely at the layout you can see
a "rat's nest" line between Q4 and Q5 for the
ground connection which means that DesignSpark
thinks that those two transistors aren't connected
to ground. Fortunately DesignSpark includes a
design rule check (DRC) in the tools menu that
can verify all of the board connections— see
Figure 5.

Once you click the "Check" button DesignSpark
will then verify that the layout meets all of the
selected design criteria and it will generate a
report summarizing any errors. Errors are also
marked in the layout and if you mouse over them
the error message will be displayed. All of the
clearance rules are set in the design technol-
ogy settings "Spacing" tab where there's a table
listing all of the clearances between different
object types.

For more information about routing a board with
DesignSpark, a tutorial is available at [3].

Conclusion

Today we created a simple PCB from a schematic
and then verified the design using DesignSpark's
verification tools. Next time we'll generate a BOM
and the Gerber files so that we could build the
design.

(130230)

Internet References

[1] www.designspark.com/eng/tutorial/
schematics-entry

[2] www.designspark.com/tutorial/
pcb-setup-placing-components

[3] www.designspark.com/tutorial/pcb-routing

54 | October 2013 | www.elektor-magazine.com

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•Labs

Getting Started with
the LPC800 Mini Kit

Just before the summer started Elektor offered its members the opportunity to
receive a little microcontroller board for free. The board was an LPC800 Mini
Kit sporting an LPC810 32-bit ARM Cortex-M0+ microcontroller (MCU) in an
8-pin DIP package, a voltage regulator, two pushbuttons, an LED and two small
prototyping areas. The campaign was a huge success: all boards were gone in
about 45 minutes...

By

Clemens Valens

(Elektor. Labs)

If you were among the Fast & Lucky having man-
aged to get your hands on one of these boards,
you have had all summer to experiment with
it. Now, we know how these things go: as soon
as you receive the kit, you open the box, have
a good look at the board, connect it to a PC to
see the LED blink, and then put it on your desk
for later use. And, for many of those kits, this
is where they still are. Therefore, to save these
kits from e-oblivion, here is a short tutorial to
explain you how to get started with this little kit.
To play with the Mini Kit you will need these
things:

• a Mini Kit;

• a PC with a 3.3 V logic-level compatible
serial port;

• a 5 V power supply;

• the Serial Wire Debug (SWD) pod (optional).

You can tick off the first line— to tick off the sec-
ond you either need a PC with a real serial port
connected to a level adapter like a MAX3232
powered at 3.3 V, or— much easier as it also
takes care of the third item— a 3.3 V "FTDI" cable

(available from the Elektor Store, # 080213-72).
You can also use our "BOB" USB/Serial Bridge
(Elektor Store # 110553-91), which is more flex-
ible, but needs a hot soldering iron because you
have to set its solder jumper to the 3.3 V position.
Both the FTDI cable and the BOB can provide the
5 V supply voltage needed to power the Mini Kit.
The Mini Kit has a connector compatible with
a 3.3-V FTDI cable, but I prefer to use a BOB
mounted on a small adapter board on which I
placed some jumpers that allow me to discon-
nect the serial port data lines without cutting
the power (Figure 1). That's useful for experi-
menting as some functions of the MCU share pins
with the serial port. It is also possible to select
the voltage on the VCC (0 V, 3.3 V or 5 V) pin.
If you use this adapter circuit, place a jumper
on JP1 pins 1 and 2 to select 5 V as VCC. This is
necessary to make the Mini Kit's on-board volt-
age regulator work.

The serial port is needed for programming the
MCU— real debugging is not possible. If you own
a Serial Wire Debug (SWD) pod you can use that
instead of the serial port to load your programs
into the MCU. The pod also allows debugging

56 October 2013 www.elektor-magazine.com

Elektor Dot Labs

them. Sadly I do not have an SWD pod— I will
use the serial port in the remainder of this article.
Once you have all the hardware, you need to
set up some software. All you need is free,
you only have to download it. Go get:

• LPCXpresso IDE

(big, requires registration) [1];

• Flash Magic [2];

• LPC800 Mini Kit code base [3].

Needless to say that you need the latest ver-
sions of all tools and libraries. Install the first
two tools in random order (people planning on
using an SWD pod do not need Flash Magic).
Unpack the code base somewhere on a disk— your
project folder would be a good place.

With Flash Magic installed you can check the
communication between the Mini Kit and the PC.
Connect the board to the serial port (using a BOB,
FTDI cable or your own level adapter) and make
sure that it is powered. You can also power the
board through the USB connector if you prefer
(this connector only provides power— the data
lines are not connected). The on-board power
LED should light up and if your board is brand
new the user LED will start blinking.

Press the ISP button and keep it depressed
while you press the Reset button. The blink-
ing LED should stop blinking (if it was blinking).
Launch Flash Magic, 'Select../ the correct MCU
(LPC810M021FN8) and the right 'COM Port'. The
'Baud Rate' can be 115,200 baud but I expe-
rienced problems at that speed; 38,400 baud
always worked for me. 'Interface' should be 'None
(ISP)' and the 'Oscillator' field can be left blank
(Figure 2). From the 'ISP' menu select 'Read
Device Signature...'. A window pops up and if all
is well it should get filled with some data. If you
get an autobaud error chances are that either
your cable is not working properly or that the
MCU is not in ISP mode. Try again after check-
ing your cable and maybe on a different speed.
Possibly the MCU's Reset pin has become disabled
(due to your earlier experiments). In this case
you should disconnect the power (or the serial
cable), then hold the ISP button down while you
reconnect the power (or the cable). This trick
will always put the MCU in ISP mode. If you still
can't read the device's ID, then you must have
a connection problem.

Now it is time to launch the LPCXpresso IDE.
When you are asked for a workspace, point it to

a folder

you want to use for stor-
ing your projects. Remember
the path because you will need it later. The IDE
takes a while to start, but when it is finally ready
it offers a quick access menu named 'Start here'
containing the most important functions (and

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The Elektor BOB adapter
board used to program the
LPC800 Mini Kit.

Figure 2.

Flash Magic and the settings
that work for me.

www.elektor-magazine.com October 2013 57

•Labs

Figure 3. The LPCXpresso IDE showing a successful build
of the LPC800_CodeBase project.

Figure 4. My LPC800 Mini Kit development setup with the
BOB on its adapter board (yes, I know it's upside down).
The IC on the lower part of the board is a type PCF8563
I 2 C real-time clock (RTC).

www.elektor-labs.com

some more) that you will use often, like new
project, build & debug. Here you will also find
an option to import example projects. Click the
link 'Import project(s)' to open the import dia-
log, then click the 'Browse../ button to the right
of the 'Root directory' field if you unpacked the
code base (if you kept it as an archive you can
click the other 'Browse...' button) and navigate
to the LPC800 Mini Kit Code Base folder. Once
you have found it click 'Ok' followed by 'Next'.
Make sure the LP810_CodeBase project is ticked
before clicking 'Finish'.

You will now have a project called 'LPC810_Code-
Base' in the 'Project Explorer' window. Select it
to build it from the 'Start here' menu. Observe
the messages that scroll through the 'Console'
window; there should not be any errors or warn-
ings (Figure 3). If for some reason you do have
an error or a warning, click on the 'Problems' tab
to get more information. Double clicking a line in
this window will take you to the offending code.
After a successful build, you will find a HEX file
in the 'Release' folder of your project that's been
copied into your workspace during the import.
Click the 'Browse...' button in Flash Magic to nav-
igate to your HEX file. Put your Mini Kit in ISP
mode before clicking 'Start'. If all is well the
MCU will be programmed with your new HEX file.
Press the Reset button on the board to launch
the program.

You are now ready to start developing your own
projects. The Elektor.Labs website [4] has a few
get-u-going projects using this board. If you do
something awesome, useful, interesting or what-
ever with the Mini Kit we would like to know about
it. To inform us please post your LPC800 projects
on Elektor.Labs.

( 130188 - 1 )

Internet Links & References

[1] LPCXpresso IDE: http://lpcxpresso. code-red-
tech .com/LPCXpresso

[2] Flash Magic: www.flashmagictool.com

[3] LPC810 Code Base: http://lpcware.com/
Ipc800-mini-kit

[4] Elektor.Labs: www.elektor-labs.com

58 October 2013 www.elektor-magazine.com

E

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Tips & Tricks

The LPCXpresso IDE is based on Eclipse, a popular
albeit-in my humble opinion-absolutely horrible
tool. I therefore recommend the inexperienced user
to use the example project as a starting point for
new projects. You can copy & paste a project in the
'Project Explorer' window using right mouse clicks —
that way you will be sure to get the settings right.
Projects created from scratch will not produce a
HEX file. To correct this, copy the settings from the
example project: select the sample project; on the
menu click 'Project' then 'Properties'. Expand 'C/

C++ Build', click 'Settings' and then the 'Build Steps'
tab. Copy the content of the 'Command' field of the
'Post-build steps' area and copy it into Notepad or
something similar so as not to lose it during the steps
that follow. Close the 'Properties' dialogue. Now select
the new project and repeat the steps above to return
to the post-build steps, but this time of the new
project. Replace the post-build steps command line
with the line you just copied. Click 'OK' to save the
settings. Repeat this procedure for every configuration
you may have created (release, debug, other).

Only build for Release or you will quickly run out of
program memory (the LPC810 has only 4 KB). Of
course, if you have an SWD pod you may want to
build debug versions too, but Flash Magic users have
nothing to gain here.

Adding existing source code files to a project is rather
counterintuitive (or should I say counterproductive?):
'File' — ► 'Import...' — ► select 'Filesystem', click 'Next',
browse to the file's location, check the file you want
and click 'Finish'. Since the IDE does not remember
the last path you used you may need a lot of mouse
clicks to get things done. But, you can also copy
the file directly into your projects folder using your
favorite file manager (Total Commander in my case).
After copying the files press 'F5' to refresh your
project and the new files appear.

The MCU's reset function can be disconnected from
the pin so that the latter can be used for something
else (see the MCU's switch matrix). The Reset button
on the board then becomes useless and entering
ISP mode is more difficult. In this case you should
switch off the power to the board, and hold the ISP
button down while you switch the power back on. This
trick will always put the MCU in ISP mode. This will
also re-enable the SWD interface in case you had it
disconnected.

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NEW]

Retronics

80 tales of electronics bygones

This book is a compilation of about 80 Retronics installments published in
Elektor magazine between 2004 and 2012. The stories cover vintage test
equipment, prehistoric computers, long forgotten components, and Elektor
blockbuster projects, all aiming to make engineers smile, sit up, object,
drool, or experience a whiff of nostalgia.

www.elektor-magazine.com October 2013 59

•Labs

Negative Energy

By It just so happened that on the last visit to my

Dr. Thomas Scherer in-laws their electric doorbell had just stopped
(Germany) working. It is a wireless type I installed around

two years ago at their side entrance which
never gets much use. The curious thing is that
I remember replacing the batteries just two
months ago. My father in law, as ever takes the
pragmatic approach and suggests replacement
batteries. However, he has clearly underestimated
my determination— there is an anomaly here that
needs resolution. "You don't happen to have a
multimeter in the house" I asked.

He had, I can't remember the last time I used
one of these analog moving-coil multimeters.
Engraved in the heavy plastic casing were
the words 'Battery Tester', and I figured the
instrument should do the job nicely as long as it
was still working. With both parts of the doorbell
now on a table in front of me and in the absence
of any sophisticated test equipment I confidently
assumed that the flashing LED is evidence that
the bell push and transmitting half of the unit is
functioning correctly. With the receiver half of the
doorbell now right next to the transmitter I think
we can rule out any issues of range. The finger
of suspicion looks to be pointing at the receiver
unit, showing no activity whatsoever, be it on a
LED or an attempt at plying the Big Ben chime .

As I think, a tick list of possible causes is already
starting to scroll up on that imaginary screen
inside every engineer's head. In this case it went
something like this:

1. Gramps playing a trick on me? (possible but
unlikely)

2. A bad set of batteries, (gramps scores— duh)

3. Electronic failure, (always possible)

4. Something else, (can't rule that one out)

What's your guess?

With the battery compartment opened the three
AA cells I fitted not two months ago are still in
position and before you ask... Yes, they are all
the right way round. With the battery tester
set to 4.5 V full-scale I touch the test prods
across the three series connected cells and read
a measly 1.5 V.

So hypothesis #2 seems probable. My father in
law is now starting to look a little too pleased
with himself. I take out all three cells, set the
meter to the 1.5 V range and measure each
battery individually. The first one reads 1.5 V...
curious, does that mean that the next two are
completely flat? The second one also reads 1.5 V,
now I'm confused, two batteries each reading 1.5
V but the voltage across all three is just 1.5 V! I
measure the third battery and watch the needle
swing the wrong way and try to wrap itself around
the end stop. This one seems to be outputting
a negative voltage; I switch the probes around
with the red one to the negative terminal and the
black one on the positive to get a reading of 1.5 V.

1.5 V + 1.5 V - 1.5 V = 1.5 V. No wonder!

The problem was fixed by just replacing the faulty
battery. The question remains: is it possible for
a battery to reverse its polarity? Well no, cell
chemistry defines the direction of current flow.
I took the faulty battery home to look at it a
bit more closely. Next morning it still showed a
negative voltage but my DVM was now indicating
just -35.9 mV after the cell had been resting out
of the circuit for about eight hours.

The most likely explanation is that the faulty
cell had probably suffered a manufacturing
fault leaving it with very low capacity. Once its
initial energy had been used up the current flow
produced by 3 V from the other two healthy cells
(the bell receiver is permanently on) had the
effect of reverse charging the faulty cell.

( 130108 )

60 October 2013 www.elektor-magazine.com

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•Industry

Power Factor Co

erection

Controller

Improved Power Factor Controller

Intersil Corporation's new
active power factor con-
troller type ISL6730A fea-
tures a patent-pending
breakthrough in negative
capacitance technology
which reduces EMI filter
size, improves THD and PF
and provides maximum
efficiency over a wide
input supply range and
output power (input voltages from 85 VAC to 270 VAC
and power range from 50 W to 2 kW). This technology
also minimizes zero crossing distortion, compensates
for input filter capacitance PF displacement error and
reduces the magnetic component size by up to 66 per-
cent. For example, in an 85 W power supply the EMI fil-

ter inductor can be reduced from 150 jjH to 56 pFI. The
small external components result in a lower cost design
with improved performance.

The device's excellent power factor correction capability
is compatible with the requirements for a power factor
higher than 0.9, as currently required by ENERGY STAR
Program Requirements for Computers Version 5.0. The
ISL6730A also achieves excellent light load efficiency
using integrated skip-mode, and includes an internally
clamped 12.5 V gate driver delivering 1.5 A peak cur-
rent to the external power MOSFET.

The ISL6730A enables a reliable system that is fully
protected with features such as cycle-by-cycle over-cur-
rent, power limiter, over-temperature, input brownout,
output over-voltage and under-voltage protection.

www.intersil.com (130167-VII)

Toradex Embedded Design Challenge

Flere's your chance to transform your ideas into reality. Toradex has launched the "Embedded
Design Challenge" which is open for students and other individuals at education and research
institutions. All the student innovators from all over the world are invited to participate. We wel-
come any innovative idea, there is no required theme.

To participate in the challenge all you need to do is to submit the product proposal of what you
want to build. On the selection of your proposal you will receive a free Toradex Colibri NVIDIA
Tegra™ Kit (worth $250 USD) to bring your idea to life. Along with the kit Toradex also offers tech-
nical support from our engineering team, access to support libraries and online knowledge base.
Twice a year the projects are judged and the winner will receive a prize of $20,000. Addition-
ally there will be four selected honorable mentions which will receive a prize of $5,000 each.
Toradex is currently accepting project proposals! Compete individually, or in teams! The process
to submit your proposal is very simple, entries have to be submitted online at:

www.challenge.toradex.com (130306-V)

V -- jP1_

-Toradex

Swiss. Embedded. Computing.

ange.

Transform your ideas into reality!

Apply for free NVIDIA© Tegra™ Kit

Ultra-Low Noise Dual JFETs

Linear Integrated Systems, a leading full-service
manufacturer of specialty linear semiconductors,
announces the immediate availability of its LSK489 1.8
nV at 1 kHz, low-capacitance, N-channel monolithic
dual JFET. This is part of a family of ultra-low-noise,
dual JFETs specifically designed to provide users bet-
ter-performing, wider bandwidths and cheaper solu-
tions for obtaining tighter I DSS (drain-source satura-
tion current) matching and better thermal tracking
than matching individual JFETs.

Available packaged in surface mount and ROHS compli-
ant versions, the LSK489 is an ideal improved functional
replacement for the similar JFETs that have similar
noise characteristics but greater gate-to-drain capaci-
tance. The LSK489 SOT-23 and SOIC packages are ideal
for space-limited circuits in audio and instrumentation
applications. LSK489 available packages are: TO-71;
SOT-23-6L, SOIC-8L.

The most significant aspect of the LSK489 is how it
combines a noise level nearly as low as the LSK389
while having much lower gate-to-drain capacitance, 4

62 | October 2013 | www.elektor-magazine.com

news & new products

pF versus the 25 pF, Flail said. While the LSK389 pro-
vides ultra-low noise of less than a 1 nV at 1 kHz, the
capacitance is high enough to cause designers to have
to use a cascode feature to handle higher bandwidths
without intermodulation distortion.

Like the Linear Systems LSK389, the LSK489 features a
unique Monolithic Dual design construction of interleav-
ing both JFETs on the same piece of silicon to provide
excellent matching and thermal tracking and a low-
noise profile having nearly zero popcorn noise.

Lead-Free, ROHS compliant versions are available. Lin-
ear Integrated Systems' in-house fab and domestic fac-
tory stock guarantee short lead times, ensuring no dis-
ruption in production schedules.

Summary of Features:

• Low noise (typically 1.8 nV/VHz @ 1kHz)

• Nearly zero popcorn noise

• IDSS (drain-source saturation current) matching to
10% max

• Low offset/tight matching (|\/ gsl - V gs2 \ = 20 mV
max)

• Low capacitance (C ISS =4 pF)

Efliiiei

Du* I JFET

ILIA 01 1

New LSMS9
u*l N-Ch JFET
Lower Noise

LSK 489 Series

• High input impedance

• High breakdown voltage
( BV gss = 40 V min)

• Monolithic Dual (2 JFETS
on one piece of silicon,
better matching and
thermal tracking)

• Low noise, reduced
device count alternative
for the classic dual JFET
cascode configuration

• Improved replacement
for Siliconix U401 series

• Surface mount SOIC
versions and the smaller
SOT23-6 package

• Lead-free ROHS compliant versions available
Applications include microphone amplifiers;
phono preamplifiers; audio amplifiers and preamps;
discrete low-noise operational amplifiers; battery-
operated audio preamps; audio mixer consoles; acous-
tic sensors; sonic imaging; and instrumentation ampli-
fiers; wideband differential amplifiers; high speed com-
parators; impedance converters.

www.linearsystems.com (130306-11)

1.8 nV Low Noise Dual JFET

First LIN Slave Companion IC to Support Automotive
IS026262 Requirements

ams AG announced that the AS8530 is the world's first miniature power/transceiver IC to support LIN slave
applications, which complies with the IS026262 functional safety standard.

The AS8530 is a power management and communication device that includes a LIN 2.1 transceiver, a 50mA
LDO to supply a local micro and a reset generator in an 8-pin SOIC 8 package. As a differentiator, the AS8530
offers a series of system management functions through a shared pin serial interface, all within the same
small, 8-pin SOIC8 package. The addition of enhanced diagnosis functions provides built-in support for the
requirements of IS026262. A two-wire serial port routed through shared Enable and TX pins allows the device
to read out status registers and provide diagnosis information to the system's microcontroller. It also supports
additional features such as a window watchdog function and access to back-up registers to
store data when the microcontroller shuts down.

These features are crucial in the design of IS026262-compliant systems, which must be able
to cease operation safely when in a fault condition, before the vehicle is at risk of endangering
passengers or other road users.

The AS8530 is suitable for any LIN-networked sensor and actuator slaves including those found
in door modules, sunroofs and headlight positioning units. It is ideally suited for safety-critical
systems that require an ASIL grading under the provisions of the IS026262 standard.

The on-chip LDO provides a factory-selectable 3.3V or 5V output. The chip also offers a reset
generator and an output voltage monitor and has a unique chip ID to support traceability
requirements. Power-saving, stand-by and sleep modes, as well as the normal operating mode,
can be triggered via the Enable pin.

The AS8530 LIN IC is in volume production now. It is priced at $2.21 for 1,000 pieces.

www.ams.com/Interface/LIN-Bus-System/AS8530 (130306-IV)

www.elektor-magazine.com | October 2013 | 63

•Industry

CHIP QUIK

CH1PQUIK

Chip Quik Removes SMDs Safely & Easily

The Chip Quik® SMD removal kit enables SMD parts to be removed from circuit boards
with no more than a soldering iron.

Suitable for low temperature reworking, the product removes QFP's , PLCC's, SOIC's,
chip components, and other surface mount configurations. Chip Quik removal alloy
melts at 300°F (150°C). Fast, safe, and easy to use, Chip Quik eliminates the need
for complex expensive equipment. You can learn how to remove SMD's in minutes;
there is no need to stock a large inventory of expensive tips & nozzles. No damage to
PC boards or adjacent components, no more burning of boards, lifting pads or lands,
reflowing adjacent components, damage to double sided boards, throwing PC boards
away because of unreliable removal methods.

Chip Quik is now used extensively worldwide throughout the Electronics Industry.
The product is a low temperature removal alloy with excellent wetting ability. When
melted into the existing SMD solder connections, both alloys combine, resulting in a
new lower temperature alloy. Each pin/pad connection stays molten long enough to
easily remove the SMD.

SMD 1 Kit Contains: 2.5 ft. Chip Quik Removal Alloy (removes approx. 8 SMD's); 2cc
syringe of Chip Quik No CleanTack Flux; Alcohol Pads for Clean Up; Complete Instruc-
tion for SMD Removal & Clean Up.

Chip Quik was tested at Elektor Labs with excellent results.

www.chipquik.com (130306-1)

CapSense Express Mechanical Button Replacement

Cypress Semiconductor Corp. announced a new
CapSense® Express™ capacitive touch-sensing control-
ler optimized to replace mechanical buttons in front
panels for industrial and consumer applications, porta-
ble medical devices, gaming devices and home automa-
tion systems. The new low-power CY8CMBR2110 device
supports up to 10 buttons and drives up to 10 LEDs with
fully configurable LED effects.

Cypress also introduced the EZ-Click™ customizer tool,
GUI-based software that combines device configuration,
visual feedback, and production line testing for stream-
lined register configuration of the CY8CMBR2110 con-
trollers, thereby accelerating time-to-market. Designers

can use the tool to implement customized LED effects
and buzzer output for audio feedback. Controllers in the
Mechanical Button Replacement (MBR) family leverage
Cypress's SmartSense™ auto-tuning algorithm, which
completely eliminates the requirement for manual sys-
tem tuning and is the only solution that maintains opti-
mal button performance during run-time.

The CapSense Express MBR family includes the CY8C-
MBR2016 matrix keypad solution, the CY8CMBR2010
ten-button controllers and the CY8CMBR2044 four-but-
ton hardware configurable controllers. Devices in the
family offer the industry's lowest power consumption
with supply current in run mode of 15 pA per button
and a 100 nA Deep-Sleep mode. The devices operate
over a 1.71 V to 5.5 V range, making them ideal for a
wide range of regulated and unregulated battery appli-
cations, and enabling them to operate from a single
coin cell battery. The family delivers robust sensing in
noisy environments using Cypress's patented CapSense
Sigma Delta (CSD) sensing method, ensuring supe-
rior immunity to conducted and radiated noise. These
devices also feature an integrated voltage regulator to
address power supply noise, as well as filters for any
spurious noise.

The MBR family features SmartSense auto-tuning,

64 | October 2013 | www.elektor-magazine.com

which dynamically optimizes the capacitive baseline
and detection threshold for each button. The algorithm
adjusts for the optimal capacitance sensing range at
power-up and during runtime as environmental con-
ditions change, including noise, temperature, and
humidity. Eliminating the need to tune is a significant
advantage for large and small manufacturers alike, as
it saves engineering time and yield loss that can occur
with even slight variations in manufacturing tolerances.
This savings is greatly multiplied for customers with a
global factory footprint and multi-sourced supply chain.
SmartSense auto-tuning can eliminate the need for
additional test steps required by competing solutions to
address manufacturing variations in PCBs and overlays.

Cypress offers the CY3280-MBR2 CapSense Express
with SmartSense Auto-Tuning Evaluation Kit to sup-
port the CY8CMBR2110 controller. The MBR family's
accompanying Design Toolbox is a simple, interactive
spreadsheet that provides detailed resources to ensure
optimal performance and validate CapSense systems.
The toolbox delivers advanced system debug features
and offers application specific guidelines for capacitive
buttons, allowing customers to take designs directly
to production for significantly shorter time-to-market.
The CY8CMBR2110 CapSense Express MBR controller is
currently in production in a 32-pad QFN package.

www.cypress.com/go/capsense (130306-III)

Propeller C Learning System

Parallax' new Propeller C Learning System consists of a programming
tool and a suite of tutorials featuring simple circuits and libraries with
code samples for core devices and sensors. The program simplifies learn-
ing to program in the C language for new users, but also allows for deep-
dive exploration of the libraries and background code for those that want to know
more. The program is being launched with the Propeller Activity Board (#32910),
a new hardware platform featuring the Propeller multi-core microcontroller. Each
core of this on-board chip can be dedicated to process a different task. Each process can run in paral-
lel, providing truly seamless processing for maximum efficiency and multitasking. The board features an
ideal balance of on-board peripherals to complement the program's activities without the need for stacking.
Among them an XBee socket for wireless capabilities, a microSD card socket to allow data logging or audio file

playback and breadboard to allow the easy solder-less connections to servo motors or LCD displays.

Visit the Propeller C Learning System page for all the resources or visit the Propeller Activity Board product
page for hardware specification or to order this exciting new hardware from Parallax. Visit Parallax.com search
"Activity Board." Retail: $49.99

www.parallax.com (130306-VI)

Microchip: World's First USB2 Controller Hubs

Available in three families, optimized for mainstream USB2, mobile USB2 and simultaneous USB2 and HSIC designs,
Microchip's programmable USB2 Controller Hubs (UCH2) help to overcome the challenges of extending battery life
and supporting multiple platforms and communication protocols.

The on-chip "Quad Page" OTP Flash memory eliminates the need for external configuration memory by reserv-
ing space for interoperability and enabling easy customisation using Microchip's free ProTouch
Configuration Editor software tool. The UCH2 hubs also provide direct I/O bridging to I 2 C™, SPI,

UART and general-purpose I/O, with support for vendor-specific messaging and FlexConnect for
port reversals.

Low-power modes, such as Link Power Management (LPM), and advanced BC1.2, Apple®, SE1 and
China battery-charging modes, enable UCH2 hubs to extend battery life and provide a replace-
ment to wall chargers.

Free and low-cost development tools provide fast time to market for multi-platform USB2 designs:

• Free ProTouch Configuration Editor at www.microchip.com/get/2M4E

• USB2534 Eval Board (EVB-USB2534) for USB-charging designs

www.microchip.com/get/euUCH2 (130306-IX)

www.elektor-magazine.com | October 2013 | 65

Flowcode 5 is one of the world’s most
advanced graphical programming
languages for microcontrollers (PIC,
AVR, ARM and dsPIC/PIC24). The great
advantage of Flowcode is that it allows
those with little to no programming
experience to create complex electronic
systems in minutes.

www.elektor.com/flowcode

...for electronics

E-Blocks are small circuit boards each of which contains
a block of electronics that you would typically find in an
electronic or embedded system. There are more than
40 separate circuit boards in the range; from simple LED
boards to more complex boards like device program-
mers, Bluetooth and TCP/IP. E-blocks can be snapped
together to form a wide variety of systems that can be
used for teaching/learning electronics and for the rapid
prototyping of complex electronic systems. Separate
ranges of complementary software, curriculum, sensors
and applications information are available.

MIAC (Matrix Industrial Automotive Controller) is an industrial grade control unit which
can be used to control a wide range of different electronic systems including sensing,
monitoring and automotive. Internally the MIAC is powered by a powerful 18 series
PICmicro device which connects directly to the USB port and can be programmed with
Flowcode, C or assembly. Flowcode is supplied with the unit. MIAC is supplied with an
industrial standard CAN bus interface which allows MIACs to be networked together.

•■T Pbua Art 4a 1 Hi*. “ 1 T.

u i * r - - a t .►

...for industrial control

Flowkit provides In Circuit Debugging for a range of Flowcode applications for PIC and
AVR projects:

• Start, stop, pause and step your Flowcode programs in real time

• Monitor state of variables in your program

• Alter variable values

• In circuit debug your Formula Flowcode, ECIO and MIAC projects

New features in Flowcode 5

Flowcode 5 is packed with new features that make development
easier including:

• New C code views and customization

• Simulation improvements

• Search and replace function

• New variable types and features, constants
and port variables

• Automatic project documentation

• New project explorer makes coding easier

• Implementation of code bookmarks for
program navigation

• Complete redesign of interrupts system allows
developers access to more chip features

• Compilation errors and warnings navigate
to icons

• Disable icons feature

• Improved annotations

• Improved links to support media

• Support for MIAC expansion modules and
MIACbus

. . . f or USB projects

...for robotics

■p a* -u ru

Formula Flowcode is a low cost robot vehicle which is
used to teach and learn robotics, and to provide a platform
for competing in robotics events. The specification of the
Formula Flowcode buggy is high with direct USB program-
ming, line following sensors, distance sensors, 8 onboard
LEDs, sound sensor, speaker and an E-blocks expansion
port. The buggy is suitable for a wide range of robotics
exercises from simple line following through to complete
maze solving. E-blocks expansion allows you to add displays,
connection with Bluetooth orZigbee, and GPS.

ECIO devices are powerful USB programmable microcontrollers with either 28 or 40 pin
standard DIL (0.6”) footprints. They are based on the PIC 18 series and ARM 7 series
microcontrollers. ECIO is perfect for student use at home, project work and building fully
integrated embedded systems. ECIO can be programmed with Flowcode, C or Assembly
and new USB routines in Flowcode allow ultra rapid development of USB projects inclu-
ding USB HID, USB slave, and USB serial bus (PIC only). ECIO can be incorporated into
your own circuit boards to give your projects USB reprogrammability.

More information and products at:

www.elektor.com/eblocks

•Magazine

By Dan Koellen (USA)

Heathkit IT-28

Capacitor Checker

Figure 1. The IT-28 weighs a hefty 5 lbs (2.2 kg) and needs to be plugged in, while the
battery powered Pico C-Super is a relative lightweight physically but not in measurement
capabilities. The open magic eye shown here occurs when the bridge is balanced.

Recently I had the pleasure of building the Elek-
tor Pico C-Super instrument [1]. I was impressed
with the range of capacitance that could be mea-
sured, the accuracy and precision, and the ease
of measurement; the frequency counter and
signal generator were nice additions as well.
While characterizing and using the Pico C-Super
I remembered that I had an old Heathkit capacitor
checker somewhere in my garage workshop. After
searching I found the IT-28 capacitor checker a
bit caked in dust and spider webs but looking in
pretty good condition considering it was once
a drenched victim of a fierce storm that blew
away the backyard shed that it was residing in.
The original assembly manual was in very good
shape. The IT-28 and Pico C-Super are pictured
together in Figure 1.

The glory years

In the 1960's and 70's the Heathkit Company was
a well-known source of electronic kits success-
fully covering consumer devices, amateur radio,
and test equipment. Though homebrewing was
popular back then, projects such as an amateur
radio transceiver could be difficult and costly for
a hobbyist to build on their own from a schematic
and locally sourced parts only. By contrast, kits
came with highly detailed assembly manuals and
all components and mechanical parts in a box
delivered by the mailman. And since electron-
ics were mostly hand assembled, kits could be
offered at competitive prices.

Table 1. IT-28 Measurement Ranges and Standards for Capacitance and Resistance

Note: pfd = pF; ppfd = pF; nfd = nF.

Capacitance

Resistance

Selection

Standard

Range

Selection

Standard

Range

C x .0001

200 ppfd (200 pfd) mica

10 ppfd (10 pfd) to

0.005 pfd

R x 1

200 ft 1%

5 ft to 5000 ft

C x .01

.02 pfd (20 nfd) mylar

O.OOlpfd (1 nfd) to 0.5 pfd

R x 100

20 kft 1%

500 ft to 500 kft

Cxi

2 pfd mylar

0.1 pfd to 50 pfd

r x io kn

2 Mft 1%

50 kQ to 50 MS2

C extended

2 pfd mylar + 9 kft 1%

20 pfd to 1000 pfd

External

Standard

Maximum 25:1 ratio to

external known standard

External

Standard

Maximum 25:1 ratio to

external known standard

68 | October 2013 | www.elektor-magazine.com

fRjet%amc& XXL

From IT-11 to IT-28

Heathkit introduced the IT-11 Capacitor Checker
kit in 1961. Minor changes were made in 1968 with
the model number changing to IT-28, which was
offered until 1977. The changes included a three-
wire power plug, a spring clamp on the 6AX4 rec-
tifier, upgraded capacitors, 120 V or 240 V opera-
tion, a new paint color and other cosmetic changes.
The three tube IT-28 is an AC bridge circuit
driven by an internal 60 Hz (mains) signal from
a 1:2 transformer connected to the 6.3 VAC fila-
ment supply (Figure 2). The bridge may also be
driven from a front panel sourced external signal.
The IT-28 is much more versatile than its name
implies since it is able to also measure resis-
tance, inductance and transformer turns ratio.
Capacitance and resistance are measured against
internal standard components, while inductance
and transformer turns ratio depend on exter-
nal standards. A 1-kohm precision wire-wound
potentiometer is split between the remaining two
legs of the bridge to balance the bridge. Each
measurement range is shown in Table 1; notice
that each range is quite wide covering 500x for
capacitance and lOOOx for resistance.

The balance potentiometer's position is the front
panel scale from which you obtain the value of
the test capacitor, resistor or ratio. The potential
across the bridge is AC coupled to the grid of the
triode section of the 6BN8 tube acting as an AC
amplifier. The other two sections of the 6BN8 tube
are diodes connected as a half-wave doubler of
the output of the triode AC amplifier. The resulting
DC from the half-wave doubler is connected to the
control grid of a 6E5 magic eye tube.

A magic eye tube, also called a cat's eye or tuning
eye, had been used in radio receivers to indicate
signal strength. The tube's glowing phosphor 'eye'
closes as the control grid potential gets more
negative. As a radio signal strength indicator,
the more the eye is closed the better, i.e. the
stronger the signal. But in this application bridge
balance is indicated by the widest non-glowing
section, i.e. the nulling of the bridge gives us an
'open eye'. The 6E5 'magic eye' driver circuit in
the IT-28 is shown in Figure 3. It is a prominent
element on the IT-28's front panel— see Figure 4.

Those leaky electrolytics

In addition to measuring capacitance the checker
is able to determine if a capacitor is exhibit-
ing leakage at working voltages from 3 volts to
600 volts. While checking for leakage the user

Figure 2. The bridge circuit as shown in the assembly manual. The unknown component
value is read from the position of R13 on the front panel scale. The bridge is balanced
when reactances are balanced: X unknown =X standard x (Ri 3 a /Ri 3B ).

Figure 3. The 6E5 'magic eye' circuit from the assembly manual. The 6BN8 triode section
is an AC amplifier followed by a voltage doubler using the same tube's two diode sections.
A negative potential on the 6E5 magic eye control grid closes the eye.

CAPACITANCE ■■C"

RESISTANCE H R”

CAPACITANCE "C*

RESISTANCE "R"

EXT, STANDARD

Figure 4. A close up view of the front panel scale and a closed eye.

www.elektor-magazine.com | October 2013 | 69

•Magazine

Figure 5. A view of the tube side of the chassis. The 6E5 magic eye is the horizontally
monted tube on the left of the chassis. The center tube is the 6BN8 and the lower tube
is the 6AX4 high voltage rectifier. A few of the standard capacitors and resistors can be
seen at the right of the 6BN8.

has to choose whether an electrolytic, 'min. 'lytic'
or paper/mica capacitor was being measured.
Initially I was puzzled by the term 'min. 'lytic'
which I assumed to be a small value electrolytic
capacitor. The Heathkit assembly manual some-
what cleared up the conundrum:

Figure 6. A view of the component side of the chassis. The leftmost wafer is the Bridge/
Discharge/Leakage switch. The middle wafer switch is the voltage ladder for selecting the
working voltage. The three potentiometers in the upper right adjust the leakage threshold
for each capacitor type.

"NOTE: A MIN. 'Lytic (miniature electrolytic) can be dis-
tinguished from an electrolytic by its high capacitance,
low working voltage and small size. Miniature electro-
lytics are usually encased in ceramic or plastic and are
completely sealed."

Times have changed, now with our low oper-
ating voltages 'min. 'lytic' capacitors are the
more commonly used electrolytic around. Back
when this checker was designed, tube based
equipment required power supplies delivering
hundreds of volts, so electrolytics of very high
working voltages and tens of microfarads were
commonly used.

Leakage is measured by monitoring the charging
current through the test capacitor. The charging
current flows through a resistor to ground; the
potential across the resistor is applied to the grid
of the 6BN8 triode section. During leakage testing
the 6BN8 is configured as a DC amplifier whose
output is directly connected to the control grid
of the 6E5 magic eye; the 6BN8 diode sections
are not in circuit. Initially the charging current
is high which causes the eye to close; when the
capacitor is fully charged this current drops to
zero so the eye opens back up. If the capacitor is
leaky, current through the grid resistor will con-
tinue to flow keeping the eye closed. The value
of the grid resistor is different for each type of
capacitor as selected on the front panel, provid-
ing different leakage thresholds.

Power factor can also be measured, which is basi-
cally a measurement of effective series resistance
(ESR). ESR has to be calculated using the formula
given in the assembly manual.

The IT-28 awakened

After cleaning the outside of the metal enclosure
I took a look inside; it was surprisingly clean-
see Figure 5. All the solder joints looked good
and the wiring appeared to be correct; there
were no signs of burnt or broken components
or other obvious problems. The date codes on
the components are from the third quarter of
1972 so I estimate that it was built in the late
part of that year, or in 1973.

One potential problem I found was a blown line
fuse. I checked for any obvious shorts, checked
the electrolytics for leakage using an analog
ohm meter and verified the resistance of all
the bleeder resistors. The two smaller standard

70 | October 2013 | www.elektor-magazine.com

XXL

capacitors were verified to be good with the Pico
C Super, a DMM was used to verify the stan-
dard resistors and the 2 pF capacitor standard.
After replacing the fuse I crossed my fingers and,
lacking a variac, plugged the unit directly into
the wall outlet and flipped on the power switch.
Fortunately there was no smoke, the fuse did
not blow and I saw life in the tubes. An occa-
sional arc and erratic switch action led me to
more diligent cleaning of the chassis and switch
contacts. After this second cleaning (Figure 6)
there was no more arcing and the operation was
much more consistent.

With all the tubes looking good and the 6E5
revealing a beautiful closed eye a sonnet came
to mind:

All filaments are aglow
Not one red hot plate
No tubes with a purple glow
Now this will work great!

It was entertaining to watch the magic eye open
when measuring various resistors and capacitors
from my junk box. For small capacitors the eye
opening can be easily missed. The manual sug-
gests using 1000 cps (1 kHz) external signal for
better eye opening with small capacitors, I did
not try that but will be kept in mind for future
measurements.

Enter Pico C

Now that the unit appears to work it was time
to check the functionality and calibration. For
calibration of component measurement the kit
was shipped with a 200-ohm 1% precision resis-
tor. The procedure was to simply measure this
resistor and position the pointer on the bridge
potentiometer until it is over 200 on the panel
scale and assume the calibration will hold for all
ranges and for capacitors as well. I verified the
calibration with resistors and capacitors that I
had checked with my DMM and the Pico C Super.

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www.elektor-magazine.com | October 2013 | 71

•Magazine

Table 2. Measurement results near range centers

Note: pfd = pF; ppfd = pF; nfd = nF.

Range

DMM

Elektor Pico
C-Super

Heathkit IT-28

C x.0001

-

210 pF

205 ppfd

C x .01

-

20.8 nF

.0205 pfd

Cxi

1.96 pF

2.1 pfd

R x 1

220 n

223 n

R x 100

22.6 kft

22,700 n

R x 10 k

2.32 Mft

2,350 kft

junk box would be a good leakage candidate.
I was thrilled when the magic eye would not
open showing it was leaky. After repeating the
measurement a few times I was quite surprised
to find that the capacitor was no longer leaky!
After a bit of research on the web I found that I
had reformed the capacitor. The recommended
procedure is to start at a low working voltage
and work in steps up to the full working voltage
rather than initially applying the full working volt-
age like I did. This is a handy feature of the IT-28
allowing you to reform your old capacitor stock.

In the center of the range (and scale) the agree-
ment was quite good (Table 2) but the perfor-
mance degraded as one goes to the extremes
of the range. This would be expected since the
measurement is the ratio of the resistance on
either side of the wiper of the balancing poten-
tiometer. This is not linear, and quickly goes to
zero or infinity at either scale extreme making the
scale more crowded. Measurements away from
the range center are good enough to determine
if the test component is okay but will not provide
much accuracy or precision. Another difficulty is
the multiplicity of scales on the front panel and
that the capacitance scale direction is opposite
of resistance and ratio. This and the need for
interpolation not only makes the IT-28 harder
to use than the Pico C-Super or a DMM, but one
is less confident of the resolution and precision
of the measurement. Though the specification
for minimum capacitance is 10 pF (10 ppF in
old money) I would not trust the measurement
near that extreme.

I had several unmarked inductors in my junk box
that I was able to compare to a newly bought
'standard' inductor. This would have been very
handy when I was experimenting with the
AVR SDR project where I had to determine an
inductor's value by finding the resonance with
a known capacitor that was measured with the
Pico C-Super.

Capacitor reforming

The calibration procedure for leakage was simply
adjusting the threshold of current at which the
magic eye just closes for each capacitor type. I
also verified that the charging potentials were
all within 10% of their selected value. To ver-
ify leakage operation I hoped a 1962 date code
NOS 10 pF paper encased electrolytic from my

Lightweight wins

While the IT-28 is a welcome addition to my
bench I will still be using the Pico C-Super for
most capacitance measurements. The ability of
the much smaller and lighter Pico C-Super to
measure capacitance under 1 pF while compen-
sating for leads, the superb resolution, and the
easy to read digital readout makes it the preferred
instrument for capacitors smaller than 500 nF.
The Pico C-Super is also a handy frequency and
period meter and I use the square wave genera-
tor quite often. Likewise I will continue to use my
DMM for resistance measurements and capacitors
larger than 500 nF. But I will be powering up the
IT-28 when I need to determine the inductance
of a coil, find the turns ratio of an unmarked
transformer, check capacitors for leakage, reform
an old electrolytic from my junk box, or when I
simply want to indulge in the pleasure of open-
ing and closing the magic eye.

( 130193 )

Internet Reference

[1] Pico C-Plus and Pico C-Super,

Elektor February 2012,
www. elektor.com/1 10687

IESP 20041

Retronics is a monthly section covering
vintage electronics including legendary
Elektor designs. Contributions, suggestions
and requests are welcome; please telegraph
editor@elektor.com

72 | October 2013 | www.elektor-magazine.com

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•Magazine

Hexadoku Puzzle with an electronic touch

With wintertime almost upon us it's a good idea to prepare for being outside less and devote time to the thought phase
of projects and creations. One way of slowly adapting to deep thinking again is to solve our Hexadoku puzzle. Find the

solution in the gray boxes, submit it to us online, and you automatically enter the prize draw for one of four vouchers.

The Hexadoku puzzle employs numbers in the hexadecimal
range 0 through F. In the diagram composed of 16 x 16 boxes,
enter numbers such that all hexadecimal numbers 0 through F
(that's 0-9 and A-F) occur once only in each row, once in each
column and in each of the 4x4 boxes (marked by the thicker

black lines). A number of clues are given in the puzzle and
these determine the start situation.

Correct entries received enter a prize draw. All you need to do
is send us the numbers in the gray boxes.

Solve Hexadoku and win!

Correct solutions received from the entire Elektor readership
automatically enter a prize draw for one Eurocircuits PCB voucher
worth $140.00 (£80.00) and three Elektor book vouchers worth
$60.00 (£40.00) each, which should encourage all Elektor readers to
participate.

Participate!

Before November 1, 2013,

supply your personal details and the solution (the numbers in the
gray boxes) to the web form at

www.elektor.com/hexadoku

Prize winners

The solution of the July-August 2013 Hexadoku is: 3B4CD. The Eurocircuits $140.00 (£80.00) voucher has been awarded to Jozsef Nagy (Hungary).
The Elektor $60.00(£40.00) book vouchers have been awarded to Mary Chang (USA), Olavi Parkka, and Jacqueline Deletombe (France).

Congratulations everyone!

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The competition is not open to employees of Elektor International Media, its business partners and/or associated publishing houses.

74 | October 2013 | www.elektor-magazine.com

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Gerard's Columns

Breaking the Laws of Physics

By Gerard Fonte (USA)

The crude quip for the three laws of
thermodynamics is: 1) You can't win, 2)
You can't break even and 3) You can't get out of
game. So you can imagine my surprise when I
found out that every major manufacturer of "1000 watt"
home theater systems (with speakers) specifies more output
power than it consumes. They've apparently invented an entirely
new game of thermodynamics!

The Line-up

Let's examine the JVC model TH-G31, LG model LHT-854, Panasonic
model SC-BT730, Philips model HTS3371, Samsung model HT-C5500
and the Sony model HT-SF370. All of these are 5.1 channels, rated
at 1000 watts of output power (class D) and include speakers. All of
these, except the Philips, consume between 75 watts and 130 watts.
These output power and input power values come directly from the
operator's manual that is provided by the manufacturer (and is avail-
able at the manufacturer's website). The LG-854 input power was
taken from the chassis nameplate because it is not listed (!) in the
operator's manual. The Philips consumes 180 watts.

There are those that will dismiss this as just creative marketing. And
that it's just a matter of how the power is distributed to the individual
channels. It is true that it is marketing and that it is creative. It is also
impossible. You can't get more power out than what you put in— Law
#1 above. Every model, except the Philips, claims more power out for
each and every individual channel, than it consumes. The per-chan-
nel power varies from a low of 125 watts to a high of 250 watts. The
Philips outputs 167 watts for every channel (with 180 watts input).

The Federal Trade Commission (FTC)

But aren't there regulations that are supposed to protect the US con-
sumer from fraud and misrepresentation? Yes. That's the FTC's job.
And they have defined the testing standards required for amplifiers
in CFR (Code of Federal Regulations) Title 16 Part 432 "Power Output
Claims for Amplifiers Utilized in Flome Entertainment Products" (avail-
able on-line). All "associated" channels must be driven to maximum
output power for five minutes. According to FTC Staff Attorney Mr.
Jock Chung, at least the right and left channels must be "associated"
as specified in the Federal Register Notice of June 26 (Volume 75,
page 3985). So, at least two channels must be driven at maximum
power for five minutes. This makes things twice as impossible for
all of them, except the Philips. It's only plain impossible to get 334
watts out (167 x 2) with 180 watts in, for that.

Perhaps the amplifiers consume more power during the test? Perhaps.
But that raises a safety issue. The amplifiers would be using several
times the power than was specified. This could overload branch cir-
cuits and potentially be the source of electrical fires. Product safety
is something that manufacturers generally take very seriously.

Then there's that pesky FTC Part 432.5 clause. "No performance
characteristics to which this part applies shall be represented or
disclosed if they are not obtainable when the equipment is operated
by the consumer in the usual and normal manner without the use
of extraneous aids."

The Consumer Electronics Association (CEA)

The CEA is an international association of manufacturers that sets
standards for their products. This is a voluntary agreement. These
standards are not enforceable. The apparent CEA Standard is CEA-
490-A R-2008 "Test Methods of Measurement for Audio Amplifiers".
Unfortunately, "Self-powered loudspeakers. ..as well as manufactur-
er-packaged audio and home theater systems (systems that include
loudspeakers) are specifically not covered by CEA-490-A." I talked
to Mr. David Wilson of the FTC and he agreed that any home theater
system that included speakers was exempt from CEA-490. The appar-
ent reason was because the amplifier/speaker combination provided
a fixed speaker impedance to the amplifier and made it more diffi-
cult to test. (Note that this means that computer amplifier/speaker
systems are also exempt. They have some fantastic output power
specifications as well.)

RCA RT2870

This all started when I bought an RCA RT2870 system rated at "1000
watts RMS" some time ago. The performance was beyond abysmal
and when I investigated I was shocked and awed. (Note that the
RCA name/logo was purchased by a Canadian company [Venturer
Electronics Inc.] which has since disintegrated.) The speakers that
are supposed to handle 167 watts RMS are marked as "8 ohm 60 W".
So it is clear that the there never was any possibility of 167 watts
going to any speaker.

I contacted Mr. David Flanna, Director of Consumer Affairs for RVA /
Venturer with a written letter (yes— real snail mail). I eventually got a
response from him that was illuminating. It included this sentence:
"Furthermore there are far too many inconsistent tests done on con-
sumer equipment for an engineer to put his or her faith into a con-
sumer grade product." This is a remarkable statement. The RT2370 is
clearly a consumer grade product. And what if you aren't an engineer?

FTC Again

I sent in a formal, written complaint to the FTC some months ago.
The complaint was very detailed and consisted of about 75 pages
of documentation. To date, I have not received any response at all.
The FTC rules (432. 4-c) state: "The rating and testing methods or
standards used. ..are neither intended nor likely to deceive and con-
fuse the consumer...". Do you think you are deceived and confused?
If so, join the club.

( 130310 )

76 | October 2013 | www.elektor-magazine.com

Ordering Information

ORDERING INFORMATION

To order, contact customer service for your region:

USA / CANADA

Elektor US

111 Founders Plaza, Suite 300
East Hartford, CT 06108
USA

Phone: 860.289.0800
E-mail: service@elektor.com

Customer service hours:

Monday-Friday 8:30 AM-4:30 PM EST.

UK / ROW

Elektor International Media

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London W1H 1DP

United Kingdom

Phone: (+44) (0)20 7692 8344

E-mail: service@elektor.com

Customer service hours:

Monday-Thursday 9:00 AM-5: 00 PM CET.

PLEASE NOTE: While we strive to provide the best
possible information in this issue , pricing and availability
are subject to change without notice. To find out about
current pricing and stock , please call or email customer
service for your region.

COMPONENTS

Components for projects appearing in Elektor are usually
available from certain advertisers in the magazine. If
difficulties in obtaining components are suspected, a
source will

normally be identified in the article. Please note, however,
that the source(s) given is (are) not exclusive.

TERMS OF BUSINESS

Shipping Note:

All orders will be shipped from Europe. Please allow 2-4
weeks for delivery.

Returns

Damaged or miss-shipped goods may be returned for
replacement or refund. All returns must have an RA #.

Call or email customer service to receive an RA# before
returning the merchandise and be sure to put the RA# on
the outside of the package. Please save shipping materials
for possible carrier inspection. Requests for RA# must be
received 30 days from invoice.

Patents

Patent protection may exist with respect to circuits,
devices, components, and items described in our books,
magazines, online publications and presentations. Elektor
accepts no responsibility or liability for failing to identify
such patent or other protection.

Copyright

All drawings, photographs, articles, printed circuit boards,
programmed integrated circuits, discs, and software
carriers published in our books and magazines (other
than in third-party advertisements) are copyrighted
and may not be reproduced (or stored in any sort of
retrieval system) without written permission from Elektor.
Notwithstanding, printed circuit boards may be produced
for private and educational 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 connection
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 with respect to
the goods.

MEMBERSHIPS

Membership renewals and change of address should be sent to the Elektor Membership Department for your region:

USA / CANADA

Elektor USA

P.O. Box 462228

Escondido, CA 92046

Phone: 800-269-6301

E-mail: elektor@pcspublink.com

UK / ROW

Elektor International Media

78 York Street

London W1H 1DP

United Kingdom

Phone: (+44) (0)20 7692 8344

E-mail: service@elektor.com

O Do you want to become an Elektor GREEN or GOLD Member
or does your current Membership expire soon?

Go to www.elektor.com/member.

www.elektor-magazine.com | October 2013 | 83

•Store

Concept, implementation and assessment

E Designing Tube Amplifiers

This book looks at tube amplifiers from more than
just a theoretical perspective. It focuses primarily
on the design phase, where decisions must be taken
with regard to the purpose and requirements of the
amplifier, and it addresses the following questions:
How do these aspects relate to subjective and objective
criteria? Which circuits sound the best, and why? If
you want to develop and market an amplifier, what
problems should you expect? What are the significance
and meaning of measurements? Are they still
meaningful, or have they lost their relevance? Thanks
to the enormous processing power of computers, we
can now measure more details than ever before. How
can these new methods be applied to tube amplifiers?
Menno van der Veen will give you all the answers!

188 pages • ISBN 978-1-907920-22-6
£29.50 • € 34.50 • US $47.60

Learning to fly with Eagle

I EAGLE V6 Getting
Started Guide

This book is intended for anyone who wants an
introduction to the capabilities of the CadSoft's EAGLE
PCB design software package. This book will quickly
allow you to obtain an overview of the main modules

of EAGLE: the schematic editor; layout editor and
autorouter in one single interface. You will apply your
knowledge of EAGLE commands to a small project,
learn more about some of the advanced concepts of
EAGLE and its capabilities and understand how EAGLE
relates to the stages of PCB manufacture. After reading
this book while practicing some of the examples, and
completing the projects, you should feel confident about
taking on more challenging endeavors.

208 pages • ISBN 978-1-907920-20-2
£29.50 • € 34.50 • US $47.60

The luxury of precision within everyone's reach

E3 500 ppm LCR Meter

The remarkable precision of this device and its amazing
ease of use are the result of careful design. It works
so well behind its uncluttered front panel that one
could almost forget the subtleties of the measurement
techniques employed. A dream opportunity for our
readers who are passionate about measurement to
enjoy themselves. If, like us, you wonder at the marvels
modern techniques bring within our reach, come along
and feel the tiny fraction of a volt.

Set: main board and LCD board, assembled and
tested

Art.# 110758-93

See www.elektor.com/lcrmeter

Display, buttons, real time clock and more

Elektor Linux Board
‘ Extension

This extension board was developed to further
propel our Embedded Linux series of articles and the
matching GNUblin board. It has a display, buttons,
a real time clock and 16 GPIOs. Linux devotees,
switch on your solder irons. The Linux extension
board includes everything needed to provide the user
interface for a wide variety of projects!

Module, SMD-populated and tested board, incl.
LCD1, XI, K1-K4, BZ1, BT1 for home assembly
Art.# 120596-91
£31.10 • € 34.95 • US $50.20

140 Minutes video presentation and more

. DVD Feedback in
Audio Amplifiers

In this Masterclass we address several aspects
of feedback in audio amplifiers. The focus of this
Masterclass, although not entirely math-free, is on
providing insight and understanding of the issues
involved. Presenter Jan Didden provides a clear
overview of the benefits that can be obtained by
feedback and its sibling, error correction; but also of
its limitations and disadvantages. Recommended to

78 | October 2013 | www.elektor-magazine.com

Books, CD-ROMs, DVDs, Kits & Modules

audio designers and serious audio hobbyists!

ISBN 978-907920-16-5
£24.90 • € 29.95 • US $40.20

Taming the Beast

E FPGA Development Board

FPGAs are unquestionably among the most versatile but
complex components in modern-day electronics. An
FPGA contains a maze of gates and other circuit elements
that can be used to put together your own digital circuit
on a chip. This FPGA development board (designed in
the Elektor Labs) shows how easy it is for any electronics
enthusiast, whether professional or amateur, to work
with these programmable logic devices.

Module, ready build and tested Art.# 120099-91
See www.elektor.com/fpgaboard

Sound Secrets and Technology

E Electric Guitar

What would today's rock and pop music be without
electric lead and bass guitars? These instruments
have been setting the tone for more than forty years.
Their underlying sound is determined largely by their
electrical components. But, how do they actually
work? This book answers many questions simply, in

an easily-understandable manner. For the interested
musician (and others), this book unveils, in a simple
and well-grounded way, what have, until now, been
regarded as manufacturer secrets.

The examination explores deep within the guitar,
including pickups and electrical environment, so
that guitar electronics are no longer considered
highly secret. With a few deft interventions, many
instruments can be rendered more versatile and
made to sound a lot better - in the most cost-
effective manner.

287 pages • ISBN 978-1-907920-13-4
£29.50 • € 34.50 *US $47.60

More than 75,000 components

CD Elektor's Components
Database 7

is CD-ROM gives you easy access to design data
for over 11,100 ICs, 37,000 transistors, FETs,
thyristors and triacs, 25,100 diodes and 2,000
optocouplers. The program package consists of
eight databanks covering ICs, transistors, diodes
and optocouplers. A further eleven applications
cover the calculation of, for example, zener diode
series resistors, voltage regulators, voltage dividers
and AMV's. A colour band decoder is included for

determining resistor and inductor values. All
databank applications are fully interactive, allowing
the user to add, edit and complete component data.

ISBN 978-90-5381-298-3
£24.90 • € 29.50 • US $40.20

80 tales of electronics bygones

EI Retronics

Quite unintentionally a one-page story on an old
Heathkit tube tester in the December 2004 edition of
Elektor magazine spawned dozens of 'Retronics' tales
appearing with a monthly cadence, and attracting
a steady flow of reader feedback and contributions
to the series. This book is a compilation of about 80
Retronics installments published between 2004 and
2012. The stories cover vintage test equipment,
prehistoric computers, long forgotten components,
and Elektor blockbuster projects, all aiming to make
engineers smile, sit up, object, drool, or experience
a whiff of nostalgia. Owners of this book are advised
to not exceed one Retronics tale per working day,
preferably consumed in the evening hours under lamp
light, in a comfortable chair, with a piece of vintage
electronic equipment close and powered up.

193 pages • ISBN 978-1-907920-18-9
£24.80 • € 29.95 • US $40.00

www.elektor-magazine.com | October 2013 | 79

•Store

^Microcontroller Pro™*,"

IW f

Ml FARE End (anlattieu Mi In Ajuplksttm

in 10 caplivdting Fes-son-s,

0lckfcor

Wireless and button-free

. Android

* Elektorcardioscope

Instructive, fascinating, and potentially useful to
everyone: perform your own electrocardiograms
on your Android smartphone or tablet! The project
involves skillfully combining a small PIC interface to
control an analog input stage with a great deal of
software. Our ECG interface is available in the form
of a ready-to-use module to which you just have to
add four electrodes and an Android application for
smartphone or tablet; there's no physical connection
between this terminal and the interface, as it uses
Bluetooth communication!

Ready assembled board • Art.# 120107-91
See www.elektor.com/elektorcardioscope

10 captivating lessons

. PIC Microcontroller
1 Programming

Using the lessons in this book you learn how to
program a microcontroller. You'll be using JAL, a free
but extremely powerful programming language for
PIC microcontrollers. Assuming you have absorbed
all lessons you should be confident to write PIC
microcontroller programs, as well as read and

understand programs written by other people. You
learn the function of JAL commands such as include,
pin, delay, forever loop, while loop, case, exit loop,
repeat until, if then, as well as the use of functions,
procedures and timer- and port interrupts. You
make an LED blink, build a time switch, measure a
potentiometer's wiper position, produce sounds,
suppress contact bounce, and control the brightness
of an LED. And of course you learn to debug, meaning:
how to spot and fix errors in your programs.

284 pages • ISBN 978-1-907920-17-2
£29.50 • € 34.50 • US $47.60

MIFARE and Contactless Cards in Application

IE RFID

MIFARE is the most widely used RFID technology, and
this book provides a practical and comprehensive
introduction to it. Among other things, the
initial chapters cover physical fundamentals,
relevant standards, RFID antenna design, security
considerations and cryptography. The complete
design of a reader's hardware and software is
described in detail. The reader's firmware and
the associated PC software support programming
using any .NET language. The specially developed
PC program, "Smart Card Magic.NET", is a simple

development environment that supports sending
commands to a card at the click of a mouse, as well
as the ability to create C# scripts. Alternatively, one
may follow all of the examples using Visual Studio
2010 Express Edition. Finally, the major smart card
reader API standards are introduced. The focus is on
programming contactless smartcards using standard
PC/SC readers using C/C++, Java and C#.

484 pages • ISBN 978-1-907920-14-1
£44.90 • €49.90 • US $72.50

110 issues, more than 2,100 articles

. DVD Elektor

1990 through 1999

This DVD-ROM contains the full range of 1990-1999
volumes (all 110 issues) of Elektor Electronics magazine
(PDF). The more than 2,100 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. What's more, this DVD also contains the entire
'The Elektor Datasheet Collection 1...5' CD-ROM series,
with the original full datasheets of semiconductors,
memory ICs, microcontrollers, and much more.

ISBN 978-0-905705-76-7
£69.00 • € 89.00 • US $111.30

80 | October 2013 | www.elektor-magazine.com

Books, CD-ROMs, DVDs, Kits & Modules

Ultrasensitive wideband E-smog detector

E TAPIR Sniffs it Out!

Attention boy scouts, professionals and grandfathers!
This ultrasensitive wideband E-smog detector offers
you two extra senses to track down noise that's
normally inaudible. TAPIR — short for Totally Archaic
but Practical Interceptor of Radiation — also makes a
nice project to build: the kit comprises everything you
need. Even the enclosure, ingeniously consisting of the
PCB proper! Using the TAPIR is dead easy. Connect the
headphones and an antenna and switch it on. Move it
around any electrical device and you'll hear different
noises with each device, depending on the type and
freguency of the emitted field.

Kit of parts, incl. PCB

Art.# 120354-71

£13.30 • € 14.95 • US $21.50

LabWorX 2

• Mastering Surface
Mount Technology

This book takes you on a crash course in technigues,
tips and know-how to successfully introduce surface
mount technology in your workflow. Even if you are
on a budget you too can jumpstart your designs
with advanced fine pitch parts. Besides explaining
methodology and eguipment, attention is given to

SMT parts technologies and soldering methods. Many
practical tips and tricks are disclosed that bring
surface mount technology into everyone's reach
without breaking the bank. A comprehensive kit of
parts comprising all SMT components, circuit boards
and solder stencils is available for readers wishing to
replicate three projects described in this book.

282 pages • ISBN 978-1-907920-12-7
£29.50 • € 34.50 • US $47.60

Ideal reading for students and engineers

E Practical

Digital Signal Processing
using Microcontrollers

This book on Digital Signal Processing (DSP) reflects the
growing importance of discrete time signals and their

UK /ROW

Elektor International Media
78 York Street

London - W1H 1DP United Kingdom
Phone: +44 20 7692 8344
E-mail: service@elektor.com

use in everyday microcontroller based systems. The
author presents the basic theory of DSP with minimum
mathematical treatment and teaches the reader how
to design and implement DSP algorithms using popular
PIC microcontrollers. The author's approach is practical
and the book is backed with many worked examples
and tested and working microcontroller programs.
The book should be ideal reading for students at all
levels and for the practicing engineers who may want
to design and develop intelligent DSP based systems.
Undergraduate students should find the theory and
the practical projects invaluable during their final year
projects. Similarly, postgraduate students should be
able to develop advanced DSP based projects with the
aid of the book.

428 pages • ISBN 978-1-907920-21-9
£44.90 • € 49.90 • US $72.50

USA / CANADA

Elektor US

111 Founders Plaza, Suite 300
East Hartford, CT 06108 USA
Phone: 860.289.0800
E-mail: service@elektor.com

Further Information and Ordering: WWW. elektor. COm/store

or contact customer service for your region

www.elektor-magazine.com | October 2013 | 81

•Magazine

NEXT MONTH IN ELEKTOR MAGAZINE

CAN Tester

Modern vehicles are moving networks really,
with a variety of control units all interconnect-
ed via wires and even wirelessly. Many car
manufacturers employ the CAN bus (Controller
Area Network). CAN is marked by its high de-
gree of immunity to interference. The down-
side of CAN is its complexity and the inherent
difficulty to track down and repair failures.
That's one of the reasons why the CAN Tester
got developed.

Multi-Channel
Temperature Logger

Logging multiple digital temperature sensors
type DS18B20 at the same time? No problem
with this 6-channel data logger with built-in
Real Time Clock. A keypad is used for con-
trolling the circuit, and a 4x20-character LCD
for displaying the necessary information. Data
is stored on an SD card, which makes it easy to
open for processing on the computer.

Audio Switchboard

Got a faulty input selector switch on your
amplifier? Or are you looking for just a sim-
ple but decent selector switch for your sound
system? This circuit, built from conventional
parts only (i.e. no SMD parts) lets you select
four input source. It's even possible to make
two sources active simultaneously without
shorting them out.

Article titles and magazine contents subject to change; please check the Magazine tab at www.elektor.com.
Elektor November 2013 edition is published to Members on October 15, 2013.

See what's brewing
@ Elektor Labs 24/7

Check out

www.elektor-labs.com

and join, share, participate!

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Create a Project

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82 | October 2013 | www.elektor-magazine.com

Technology

PicoScope® 6000 Series

• High-performance PC oscilloscope

• 500 MHz with 5 GS/s

# ■

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• Industry-leading 2 Gsample buffer memory!

• High-performance function /arbitrary waveform generator

• SuperSpeed USB 3.0 interface

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i " ••

PicoScope

Bandwidth, ...
Sampling Rarf^

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Price

Compatibility

6402C 6402D

250 MHz

6403C

6403D

6404C

256 MS
£1995

AWG

512 MS
£2495

USB

4

350 MHz
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FG AWG

500 MHz

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£2995

1 GS
£3495

1 GS
£3995

& 3.0, Windows XP, Windows 7 & Windows 8

ALL MODELS INCLUDE PROBES, CARRY CASE, FULL SOFTWARE AND 5 YEAR WARRANTY.
SOFTWARE INCLUDES MEASUREMENTS, SPECTRUM ANALYZER, SDK, ADVANCED
TRIGGERS, COLOR PERSISTENCE, SERIAL DECODING (CAN, LIN, RS232, l 2 C, PS, FLEXRAY,
SPI), MASKS, MATH CHANNELS, ALL AS STANDARD, WITH FREE UPDATES.

www.picotech.com/PS236

PROTEUS DESIGN SUITE VERSION O

Featuring a brand new application framework, common parts database, live netlist and 3D
visualisation, a built in debugging environment and a WYSIWYG Bill of Materials module, Proteus 8
is our most integrated and easy to use design system ever. Other features include:

■ Hardware Accelerated Performance. ■ Board Autoplacement & Gateswap Optimises

■ Unique Thru-View™ Board Transparency. ■ Direct CADCAM, ODB++, IDF & PDF Output.

. Over 35k Schematic & PCB library parts. ■ Integrated 3D Viewer with 3DS and DXF export.

■ Integrated Shape Based Auto-router. ■ Mixed Mode SPICE Simulation Engine.

■ Flexible Design Rule Management. ■ Co-Simulation of PIC, AVR, 8051 and ARM MCUs.

. Polygonal and Split Power Plane Support. - Direct Technical Support at no additional cost.

Labcenter Electronics Ltd. 21 Hardy Grange, Grassington, North Yorks. BD23 5AJ.
Registered in England 4692454 Tel: +44 (0)1756 753440, Email: info@labcenter.com

Visit our websitE or
phone 01756 753440
for more details