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£3.70

www.eleklor’eJedronits,co.uk

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Our friend the battery

As I see it, a battery is simply a device that allows people to have electrical energy available even in the most
unexpected of places just inink of the construction worker in a dark cellar using his cordless power drill and
helmet-mounted torch, or the businessman whose cellphone or PDA starts to ring while in the Gents. Invariably
we want batteries to be as light as possible and to supply lots of energy right there and then. This requires the
battery contents to be of a very special nature, cramming as much as energy as possible into lightweight, envi-
ronmental-friendly substances, while the packaging remains robust yet unobtrusive. New technologies like fuel

cells and polymeric structures promise a lot in this respect and on article on these will appear in the January
2005 issue.

A while ago I found a 100-percent natural product meeting all the above requirements: well sealed, of a design
perfected over millions of years [as opposed to less than three months on some industrial designer's PC], light-
weight and containing lots or energy — although not of the electrical type and certainly not rechargeable.

While doing an oil check on my wife s Suzuki Alto, I discovered a perfectly intact chicken egg carefully tucked
away between a long bolt and the vehicle battery. Facts: Jl) the car is always parked on the driveway; (2) our
neighbours hove two geese and about 10 chickens and (3) martens are very common where we live. One of
them, or a couple, must have been extremely adept at carrying the egg without breaking it, os the fowl-run is
Fenced by six feet high fine mesh chicken wire. My wife may well have driven around For hundreds of miles
with on extra source of natural energy under the bonnet. About three months after this hilarious sighting we
found a large bread crust in the very same hiding place. I am happy the marten leaves the car wiring wefl
alone and now like to think of it climbing up the small engine and enjoying a midnight snack in a warm and

dry place. Instant energy in an unexpected place. To us, maybe — to the nimble animal, it's just another way of
charging up.

Jan Bulling, Editor

leL'dJoir

lectrorics

Volume 30, Number 337, November 2004 ISSN 0268/45 i 9

Efektor Electronics aims at inspiring people to master elec-
tronics at any personal level by presenting construction proj-
ects and spotting developments in electronics and informa-
tion technology.

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Segment: b.v. 2004 Printed m the Netherlands

11/2004 ■ efftdor elettfenics

5

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Lithium | (

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BATTEFiY

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|ATT £RY

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1 ■ 1 1 mk "

( £ JTiT* i 1 1

The main driving Force for battery development
has been the boom in portable equipment such
as mobile phones, laptops, camcorders, and
MP3 players. The result: different customer
demands, battery types and associated charging
methods. An overview.

Defective batteries are a common problem. Since pre-
vention is naturally better than cure, here we present a
circuit that can keep your battery in shape in a simple
but effective manner. Requiring no external power
source, this little circuit was specially designed to get 6-V
and 1 2-V vehicle batteries through the winter period.

Informative Articles

Regulars

14

ABC of Rechargeable Batteries

5

Foreword & Colophon

26

Sealed Lead-Acid Batteries

8

Mailbox

30

Bring out your Dead

10

News & New Products

34

P1CXEX1 8 and PlCWinl8

79

Quizz'away

38

Goodbye '16, Welcome PIC1 8F (2)

82

Readers Services

42

Equations, equations

84

Sneak Preview

46

USB-Cyberclocks

84

Index of Advertisers

56

Thermoelements

66

Bistable Relay Driver

74

inside out: Ready, Steady, Fatty

3

Bring our your Dead

USB Cyberclocks

Fatty

What do we do with those tons of surplus,
defective or damaged electronic equipment
and components? Soon, the landfill is no
longer a viable option. In 2006 European leg-
islation on electrical and electronic waste
comes into full force. Across North America,
slates are passing laws to deal with electronics
waste. These measures reflect a hidden but
growing problem. Chris Bayliss reports.

Quartz oscillators are the way to go
when you need a precise, stoble fre-
quency source but what do you do
when an application calls for a non-
standard frequency? Custom-made
crystals are an expensive option but
now Cypress has come up with a
cheaper alternative. Excellent for low-
noise VCOs and PLLs.

Th is month's inside out pages look at
body fat meters. Sensible people look
after their health. And of course you
want to keep an eye on your condition,
for example with scales that also show
your body fat percentage.

Perhaps you already have one oF these
at home, but how do they work?

uuailbox

Message from Australia
Dear Jan — Congratulations
for a well done and well pre-
sented restyled Elektor
Electronics. I am glad you
have done this. It gives our
profession and interesting
hobby a new life!

At this doy and age of ICT
(Information and
Communication Technology),
more and more electronics
magazines have dropped out,
for example here in Australia
we used to have three publi-
cations but now we are down
to one (Silicon Chip) — when
there were Electronics
Australia and Electronics
International Today).

Similarly in the UK we used to
have Radio & Electronics
World, Hobby Electronics,
Maplin Electronics, Practical
Electronics, Everyday
Electronics (now known os
Everyday Practical Electronics],
ET1 UK whereas today we are
left with Elektor Electronics and
Electronics World.

In the USA, we used to have
Radio Electronics, Popular
Electronics [merged as
Poptronics), Electronics
Now, Audio X press and
Nuts & Volts. We are now
left with Audio Xpress and
Nuts & Volts. Audio Xpress
specialises only on audio
electronics areas.

There are now more comput-
ing magazines than electron-
ics magazines. The fact is, it
Is easier to learn computing
today than yesterday where
only professionals could work
on them as they were mainly
mainframe computers. Today
with desktop, laptops, and
portable computers and
Windows as opposed to
MVS life in ICT is easier.

On the whole, I hope Elektor
wil) draw young readers in
with your restyled look.
Restyled alone is not a winner.
Elektor has provided 're-inter-
est r in the Field of electronics.
Every issue is getting mare

exciting. Reading is much
more pleasant and topics pub-
lished are superb! Excellent
work from you and your team.
For the record I have been
subscribing to Elektor since
] 974 when you first started.

I believe l have every Issue of
Elektor.

Michael Ong

Uke you we do not fail to observe
the on-going slimming down of
ihe market for specialist maga-
zines and regret the demise and
mergers of so many renowned
magazines on electronics. How-
ever, we’re holding our own and
ore proud to have been o round
without failure these past 30
years.

Missed opportunity or
future project?

Dear Jan — A while ago 1
had a go at the U3B/RS232
converter Item you published
(April 2003, Ed.). I gave up at
the PCB layout stage, as there
were too many vla's required
under the two small SMT chips
— one mounted opposite each
other (top and bottom) on
PCB. 1 was going to have
another go at the layout,
bringing the tracks (and via s)
out from under the devices, but
have not hod the time.

I was Interested to see there-
fore, the approach of Jim
Spence in his Swiss Army
Knife (September 2004, frd.(,
where the interface (USB or
RS232) could be changed with
a different plug in module. This
Is on ideal solution to the PC
Serial Port Legacy problem.

Hos Elektor missed an oppor-
tunity here? In the original
project, the pdPs of the lay-
out were available, but the
blank PCB could not be pur-
chased. In this latest project,
the USB section is physically
part of the entire Swiss Army
Knife project.

Why not publish as a project
(or just market the pcb's) with
the USB interface on it's
o wn? Regarding the PCB, this
could be the USB section
from the Army Knife project,
duplicated 3 or 4 times, to
make the pcb production cost
worthwhile. ! am sure most
home engineers would hove
a need for more than one
interface and this pcb would
fit the bill, perfectly.

Ian King

An excellent idea which has keen
copied into our design fab. I 'm
sure you've noticed that the USB
inf erfcce ferine SAK project does
not supply 'real' R5232 levels
although that functionality is eas-
ily obtained by adding a
MAX213 chip.

By the way t regarding me ’origi-
nal' project [April 2003 j, any
PCB that's not supplied by our
Readers Services may be
obtained from our business part-
ner The FCBShop ' {EuroCircutfs}.

T J oly switch looking at the
components list for the USB
UART project (December
2001) ( noticed an unfamiliar

description 'TOO mA paly-
switch' to identify R2. I
believe a resistance value
should be expressed in ohms,
and I have no idea wha!
'polyswitch' means. Can you
enlighten me and perhaps tell
me where such a device can
be bought?

M, van Engelenburg

A poly switch is a PTC (positive
temperature coefficient) resistor, : In
this case, if the device passes a
current exceeding 100 mA it will
run hot and as a result increase its
resistance abruptly from less than
1 ohm to a value in the kilo-ohms
range . In this way the poly switch
acts as a current limiter. Once
cooled down , its resistance drops
again, allowing the current to rise.
If you are unaefe to obtain a real
poly switch, you may substitute an

ordinary resistor of 1 ohm.
Although ibis will not provide self-
restoring protection , it is better
than nothing as the resistor will
burn out in response to excessive
current flow. A 100-mA fuse will
also do although it too is a dis-
posable component!

Regarding availability, poly-
s witches are stocked by mail
order companies like R5 Compo-
nents and Farnell.

Item Tracer in trouble
When launching my E1T
(Elektor item tracer) software I

a

ekktof etecfrecuo- lt/2004

was often greeted by 'over-
flow' errors. After some
researching, the problem
could be narrowed down fo
my version of Microsoft Data
Access Components (MDAC).
Fortunately, Microsoft have a
hotfix available, see
Q3294 1 4 on microsoft.com:
support, microsoft/ com/defau
lFospx?sdd-kb;en-

us;G329414. The EiT will
run fine and no overflow
errors pop up if you use
MDAC version 2.7.

Reading AT micros

Dear Editor — triggered by
your articles I've fust started
experiments with Atmel
microcontrollers. Is it possible
to read code from these
devices? Programming is no
problem for me. I om using
the Elekfor 89S8252 Flash
Micro board. Do I have to
use a separate programmer
for each controller type?

M, Verwoard

The AT89S8252 can be read cut
only if the security bits are not
programmed. The software we
supply is however unable to read
the controller contents . To do this

■r

you need a dedicated reader, for
example , B. Kainka's
atmeiips.zip"',, which may be
found at hfip://b.kainka.beiJ-
online.de/basismi. him (scroll to
bottom o f page}. Our Multi Pro-
grammer on USB (June 2004)
handles many different microcon-
trollers including the 89S8252.

IDE disk on USB

Dear Editor — what do you
think of this suggestion: a
USB2.0 interface for a
portable hard disk! Now that
looks like the perfect project
for Efektor readers os I'm

sure many will have old IDE
hard drives lying around. As
t see it, such an interface
should not be too hard to
design and dedicated chips
□re probably available.

(a subscriber)

You may have missed that this
type of interface is now widely
available from computer shops at
prices that defeat any attempt at
horns construction . As to cost r the
interface circuit would probably
match the value of the old hard
disk and conversely if would be
just as expensive as a new exter-
nal USB hard disk. Consequently,
such interfaces are typically
bo ughf by people regretting to
part with dear old hardware.

NICd batteries —
environment vs,
quick profits

Dear Editor — today's
rechargeable batteries are
vastly superior to the old
Nickel-Cadmium units of 30-
odd years ago. They have
several times the charge den-
sity, don't surfer the memory
problems, and don't contain
highly toxic cadmium. Why,
then, do so many products
still come to market with
NiCd cells in them? What
possible advantage do they
offer to manufacturer or con-
sumer?

Second question: since
NiMH cells have the same
voltage and at least twice as
much current capacity as Ni-
Cd, is it safe to replace Ni-
Cd cell packs with NiMH
units of similar voltage and
size? Yd love to extend fhe
life of my cordless screwdriv-
er, phone, shaver, etc.
George Price, Atlanta,
Georgia

NiCd batteries still proliferate (also
in new consumer electronics) due
to commercial forces . You may

have missed that over the past few
years the NiCd production
process has matured fo the extent
that impressive capacity (exceeding
2 Ah for AA cells} can be
achieved at very low cost. The
production of NiCd batteries will
be banned scon but considering
the vast production capacity (and
stocks} of Far Eastern and Chinese
battery manufacturers we fear
NiCd technology will be around
for quite a few years to come.

You cannot charge a NiMH cell
with a NiCd charger unless if
has on adapted end- of- charge
defector See also the article
ABC of Rechargeable Batteries''
in this issue.

Radio articles resource
on fhe web
Good morning jan, it is
many years since we last
spoke and I submitted articles
to Elektor. 1 hope thot you are
well. I have recently set up
my own business. One ele-
ment of this is a website that
I have run for a number of
years* I have recently given it
a major overhaul and I am
re-launching it. Its aim is to
be a resource of free Infor-
mation, articles and data
□bout radio and electronics.
The URL is

wvw.radiQ-eledronics.com

Ian Poole

Thanks Ian , the word is being
passed on.

l-see adapters
Dear Sir — for those of us
that are older who enjoy
electronics as a hobby and
want fo use the smaller for-
mat of integrated circuit
packages.

I am sure that there many of
us who would like to obtain
adapter RGBs to convert from

ssop to dip, soic to alp, etc.,
to include the any pins used*
Would you consider making
available through your PCB
Service a selection of the dif-
ferent small packages to DIP
8 pin to 28 pin?

I have noticed in
RadioSpares these cost about
£5.00 each.

If you know a source for
these useful parts t would
appreciate their address.

E. Lea

Thanks for fhe suggestion which
has been copied info our design
department . Meanwhile, for ICs
in T5SOP or SSOP cases with up
to 20 pins have a look at fhe
adapter board sold by
AKMODULBUS,
www.ak-modul-bus.de

MailBox Terms

- Publication of reader a correspon-
ds nee s$ at the discretion of the

Editor.

- View paints exp: esse d by corres-

pondents ere not necessarily
those of Lns Editor or Fub , E , ne r -
- Correspondence may be translated
or ed:iso for length, clarity and

style.

Y.’Trsn replying to Mailbox, corre-
spondence please quote Issue

number.

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spondence to:
editor 12 e ej doiyelsclrgn cs cojik o r

Hektor E Fee Iron i cs Tns Ed tor. RO.

Eox 190,

Tunbridge Wells TN 5 7 VvY England.

1 1/2004 -dsklor tlttlrocks

9

news & new products

10 Gigabit/s Ethernet ©ver twisted

Pkil Turtle

If we look back over history, there
is an observable cycle out o?
which has grown the dominance
of Ethernet — and which causes
the ever-present desire of network
managers to future proof".

Moore s law slates that comput-
ing power doubles every 18
months. Although it does not
apply directly to active equips
merit and cabling, it is a signifi-
cant driven Active equipment fol-
lows a roughly four-year lifecycle*
Now here lies the difficulty for
netv^ork managers. Computers
are being changed out every
two to four years; actives every
four years — yet the cabling
infrastructure is expected to last
8, 1 2 perhaps even 20 years.
So it's quite evident that struc-
tured cabling capability has to
lead active equipment deploy-
ment — in practice, by between
four and six years.

Alien forces

There are two technical prob-
lems to be overcome in the move
from Gigabit to 10 Gigabit/s.
One is the much greater inser-
tion loss of twisted pair at
500 MHz, the other is crosstalk
— signals induced from adja-
cent cables that cannot readily
be cancelled electronically.
Developing o cost-effective, prac-
tical 10 Gtgabit/s system relies
heavily on the passive cabling to
counteract these two problems.

So difficult, in fact, is this task
that until November 2003 most
people in the cabling industry
believed that an unshielded
(UTP) approach was not passible
and that shielded cabling was
the only solution. Indeed, many
were proposing to exclude even
the possibility of an unshielded
(UTP) cabling solution From the
up-coming 70 Gigabit/s Ether-
net standard*

However, an innovative develop^
ment came from KRONE'S labs
who produced a new copper
cable - CopperTen After care-
ful measurement and external
validation by one of the active
electronics manufacturers,
KRONE were able to demon-
strate to the IEEE study group
that 10 Gigabit/s over UTP was
indeed a practical proposition.

Shielded or unshielded

From the late 80s there has been
disagreement in the industry and
around the world as to whether
shielded [STP] or unshielded
[UTP] cabling solutions are the
best, with many companies back-
ing one horse or the other —
and then trying to convince the
market that theirs is the only way,
KRONE has always recognised
(hot bath have their advantages
in different situations and that
whilst STP might be the solution
of choice in one market, UTP will
be preferred in another.

Whilst custom and practice in
Germany ond central European

pair capper

(

i

countries is to use shielded solu-
tions, most of the world is UTFcen-
tric. In fad in 80o of the world
ihe skill base of network designers
and installers is in unshielded tech-
nology and systems.

This is why KRONE worked
against almost impossible odds
to prove to the industry that a
UTP implementation of 10 Giga-
bit/s was possible* Otherwise,
over the coming years, the indus-
try would hove found a situation
where every installer would have
had to be re-trained ond up-
skilled to be able to undertake
the more complex, and far less
forgiving task of installing
shielded systems. This in turn
would have added three extra
cost elements into the 10 Giga-
bit/s solution - the higher cost of
screened cables, the higher
labour costs of slower installation
and the oncost of installer re-
training* KRONE does not how-
ever hold a claim that UTP is the
only solution, also developing
shielded solutions so that users
have choice.

Early adopter risk

As ever, being on early adapter
is not without risk. For example,
□ number of other cable and
connector manufacturers have
been promoting Cot 6e" prod-
ucts which hove focused on
improving the internal electrical
performance of cobles and con-
nectors. As it turns out, these
Improvements have proved to

be exactly the opposite when it
comes to crosstalk — the killer
factor for 10 Gigabit/s. Instead,
"augmented Cat 6", on which
the KRONE CopperTen solution
is based, is the clear favourite.

The bottom line

10 Gigabit/s Ethernet over
twisted pair copper is now cer-
tain to became a standard
IEE802.3an (10GBA5E-T]. A
structured cabling solution is
therefore needed* Generally the
structured cabling solution is
needed four to six years before
the relevant Ethernet ports are
installed in bulk.

Network managers need work-
able solutions as early as possi-
ble. Many cannot afford to wait
for ratified standards. KRONE"s
UTP CopperTen solution offers
users the latest technology based
on the latest information* With
a warranted 1 8 Gigabit/s Shan-
non capacity, it outperforms the
requirements of oil (he Ethernet
solutions currently being studied.
CopperTen is on augmented
form of Category 6 UTP technol-
ogy which installers and man-
agers are familiar wiih. With its
Category 6 pedigree but lOx
greater throughput, at a rela-
tively small premium, it could
soon become the solution of
choice.

Further information from
www.kjone.co.uk

:7S-5)

10

^Sekiar decfronirs - 11/2004

Mew range of component kits

Fast Components Limited, a new
component supplier is targeting
hobbyists with its brand new
range of component kits. Co-
founder Thomas Arundel says
Electronic hobbyists have had
a rough iime of late. Leaded
components are becoming more
difficult to find, and incumbent
suppliers are imposing 'small
order* or high shipping
charges '. As a result, the Fast
Components team are offering a
fresh and more economic way to
buy electronic components.

'We sell brand new component
kits'' says Tsuyosht Kihara., the

co-founder who's behind Fast
Components' supply network,

‘ As former product designers
we were frustrated with time
and effort it took to build up a
decent stock of bench-top com-
ponents. Once we started inves-
tigating a supply chain, we
realised that we could sell kits of
commonly required components
at one third of the price that
those same components would
cost separately.

Fast Components have opened
their range with kits containing,
1000 1% metal film resistors
spread over 93 values, 240
50V ceramic capacitors spread

over 24 values, 93 radial elec-
trolytic capacitors spread over
12 values, and 100 miniature
polyester capacitors spread over
9 volues. The resistor kit retails
at £9,99, and the capacitor kits
at £4.99. Customers can order
direct from the Fast Components
website, where they con pay
securely with credit cards, Pay-
Pal, or Cheque / Postal Order.
Full Adobe PDF datasheets of all
kits are available on the Fast
Components website.

"We've started with a useful col-
lection of kits to get hobbyists
(especially newcomers) started

says Thomas. ‘We're planning
to Follow up with mare passives,
surface mount kits, mechanical
hardware kits and semiconduc-
tors through the autumn."
Postage & packaging is at cost
with no minimum order charge

Fast Components Limited,

Winchester House, Winchester Road,
Wall on On Thames, Surrey,

KTI2 2RH.

Tel: +44 (0) 870 750 4468.

Fax: +44(0) 870137 6005. Email:
snles@fa5komponents.co.uk
Web : www/fos i co mpc neat s . co. u k

C+0168-

Class-2 Bluetooth IRS-232 Adapter

SMART Modular Technologies,
Inc. announced its new Bluetooth
1.1 compliant RS-232 adapter
for the industrial, medical, and
scientific markets. This RS-232
adapter features an onboard
antenna, an embedded configu-
ration utility, and an embedded
Bluetooth communications stack
complete with the Bluetooth Ser-
ial Part Profile. When used in
combination with other Blue-
tooth-enabled products (that
either have builtTn Bluetooth
capability or are also equipped
with adapters), the SMART Blue-
tooth RS-232 adapter replaces
traditional serial cables in prod-
ucts such as laptop computers,
industrial data collection sys-
tems, and medical monitoring
equipment. Offering significant
convenience and maintenance
advantages, this adapter elimi-

nates the need for cable installa-
tion and repairs.

Th e new SMART RS-232
adapter automatically delects a
power source, allowing if to use
either power (via pin 9) or an
external power source, It fea-
tures maximum data transfer
rates up to 200 kb/s and sup-
ports Class 2 (*2 dBm typical
transmit power with a maximum
range of 30 m). Power consump-
tion is specified at less than
150 mA maximum during con-
tinuous operation, with 100 to
1 20 mA typical During sleep
mode, power consumption drops
fa below ] mA.

Smart Modular Technologies,

421 1 Starboard Dr, Fremont, CA
94538-6427, USA*
wwwjmarlnuom

(O-T - -

i 1/20Q4 - defter electronics

11

y ews & new product

MPLAB® PM3 Universal Device Programmer

Microchip's new MPLAB® PM3
Universal Device Programmer
supports all of Microchip's PIC-
micfoconirollers (MCUs) and
dsPIC® digital signal controllers
[DSCsj. The PRO MATE® II uni-
versal programmer was previ-
ously raled one of the leading
programmers in CMP's 2002
Embedded Market Study, and
ihe MPLAB PM3 adds a number
of improvements. These include
faster programming, USB con-
nectivity, improved socket mod-
ule connection, $D and MMC
card storage and a builMn fn-Cir-
cuit Serial Programming inter-
face.

The new programmer can be
connected to a PC via a USB or
serial port, or can be used as a
stand-alone unit. For maximum
easeoF-use in standalone mode,
it features a larger and brighter
128-64 pixel graphic LCD
screen providing menus, pro-

gramming statistics and status
information, and an 5D/MMC
flash card slot for easy and
secure data storage and transfer.
When connected to a PC, the
MPLAB PM3 is fully Integrated
into Microchip's free MPLAB Inte-
grated Development Environ-
ment (IDE) software, or can be
used via o separate command
line interface. Other key feolures
of the MPLAB PM3 include:
Complete line of interchange-
able socket modules to support
all programmable Microchip
devices and package options
[sold separately!.

Adapter allows PRO MATE II
socket modules to be used on
MPLAB PM 3 (sold separately)
Serialized Quick Turn Program-
ming^'^ for encoding unique
serial numbers in PC hast mode
Buzzer noiification for noisy envi-
ronments.

The MPLAB PM3 Universal

Device Programmer is supplied
with a power supply, serial and
USB cables, and an ICSP cable,
and is available now For $895.

Arizona Microchip Technology Ltd.,

Microchip House, 505 Eksdafe Road

Winner sh Triangle,

Wokingham RG4I 5TU.

TeL (+44) (0)1 18 921 5858.

Fax (+44) (0)1 IS 921 5835.
www»micr<KhiF»com »

I- - - _ -S

MP3 Surround Sound Multiple-channel MP3

Hans Weber

The Fraunhofer Institute
has released an MP3-conv
patible compression
scheme for surround
sound.

The Fraunhofer Institute for Inte-
grated Circuits 3 IS in Erlangen,
Germany, developed the MP3
compressed audio Format in
1992 Since then it has become
a standard worldwide, from tiny
portable players to music on the
Internet, the MP3 format con be
tound everywhere where high
quality stereo sound is required
but the available data rate or
storage space is limited.

How con it be improved? The
opportunities for greater com-
pression and hence lower data
rates would seem to be
exhausted. However, with the
trend towards multichannel

audio and surround sound,
development has progressed in
another direction: MP3 now also
supports multiple channels. The
new product Is colled 'MP3 Sur-
round' and was developed over
the last year by the Fraunhofer
Institute In collaboration with the
American company Agere Sys-
tems. It was shown at the AES
Convention in Berlin.

Despite offering greater capabil-
ities, MP3 Surround operates at
data rates not significantly
higher than normally used In
ordinary stereo MP3 files. The
trick is very simple: the 5.1 input
signal is 'mixed down' into o
two-channel stereo signal. This
has the additional advantage of
perfect backwards compatibility.
Today's MP3 decoders can read
the new format ond produce
stereo sound as before. A 'Spa-
tial Audio Encoded is then used
to generate a relatively small
amount of ancillary data which
is added to the stereo MP3 bit-

stream. The decoder employs
Inis ancillary data to reconstruct
ihe other channels. Although the
results are not quite of the qual-
ity that can be achieved using
genuine 5.1 playback, most of
the people Involved in listening
tests, professionals ond non-pro

fesslonals alike, described the
sound as excellent. The first com-
mercial applications for MP3
Surround are expecied os early
as this summer.

.C-^2'3-!

Web poinfer:

www.iis.fraunhoferde

12

ekltlw eledrcnks -11/2004

New PC Oscilloscopes

Pico Technology, has announced
a new series of high-perform-
ance PC oscilloscopes. The
3000 series debuts with three
instruments: the PicoScope
3204, 3205 and 3206. All
three are cost-effective replace-
ments for traditional bench top
instruments. The top of the range
oscilloscope boosts a sampling
rate of 10 GS/s, an analogue
bandwidth of 200 MHz, and a
record length of 1 MB,

The combined high sampling rate
and large memory buffer of the
PicoScope 3206 enable the cap-
ture and display of fostoccurring
and complex signals. With 1 MB
of memory, the 3206 con capture
at least 30 rimes as much data,
allowing the user the ability to
zoom in on areas of interest.

All three PicoScopes in the 3000
series connect to a PC via
USB2.0: drawing their power
from the PC, so no need for a
separate power supply, In addi-
tion to being high-performance
oscilloscopes, the PicoScope
3204, 3205 and 3206 all fea-
ture o spectrum analyser mode
and (when used with PicoLog
software) can also be used for
high-speed do to acquisition.

The 3205 and 3206 also
include built-in signal generators,
cop able of sweeping up to
1 MHz. The signal output on the

oscilloscopes'
external trigger'

BNCs, can be a
sine, square or tri-
angular wave.

The PicoScope
3000 series fea-
tures more than
30 automated
measurements
such as: fre-
quency; pulse
width; rise time;

THD and SNR;
and five

enhanced display
modes including
Digital Colour
(ideal far spotting
intermittent
glitches In digital
signals] and Analogue Intensity
[useful for displaying video
waveforms and analogue modu-
lation signals).

The th ree instruments in the Pico-
Scope 3000 series have the fol-
lowing features:

PicoScope 3204 - 2.5 GS/s
sampling rate [repetitive signals),
50 M5/s single shot sampling,
50 MHz analogue bandwidth,
and record length of 256 K.
Spectrum range 0 to 25 MHz.

PicoScope 3205 - 5 GS/s
sampling rate (repetitive signals),

1 00 MS/s single shot sampling,
100 MHz analog bandwidth,
and record length of 512 K.
Spectrum range 0 to 50 MHz,

PicoScope 3206 - TO GS/s
sampling rate (repetitive signals),
200 MS/s single-shot sampling,
200 MHz analogue bandwidth,
and record length of 1 MB.
Spectrum range 0 to T 00 MHz

Using these instruments, it is easy
to share waveforms and instru-
ment settings with other users
[and waveforms can even be
exported as JPEGs for posting on

□ web site or using in reports).
The three new PicoScopes are
supplied with PicoScope and
PicoLog software — demo and
full versions of which can also
be downloaded free of charge
from www. pIcofech.com . The

3204 retails for £399 + VAT, the

3205 for £599 + VAT and the

3206 for £799 + VAT.

< 347176-1

Pko Technology Ltd., Mill House,
Cambridge Street,

St Neats PEI 9 1GB,

TeL{+44) (0)1480 396395.

Web; www.pftoteth.com

Backlighting goes bk;o

Lascar Electronics has added the
SP 400-BLUE to their popular SP
Series of digital voltmeters. The
SP 40G-8LUE is a 31 /2-digit
LCD voltmeter with bright blue
LED backlighting providing
exceptionally clear visibility
under law light conditions. Other
features include a low battery
warning, a 200-mV DC meas-
urement range with auto-zero
and autopolarity, and user-selec-
table decimal points.

The SP 4Q04JLUE features a neg-
ative rail generator which
enables the meter to measure a

signal referenced to its own
power supply GND. A one-
piece housing ensures splash
proof protection when correctly
mounted with the supplied seal.
The SP 400-BLUE Is available
immediately at o cost of £ 1 9,95
(£1 1.97 in OEM quantities of
250+) .

bscar Electronics Limited, Module
Hose, Whiteparish, Salisbury, Wilt-
shire SP5 25J* TeL (+44) (0)1794
884567, Fax (+44) (0)1794 884616,
wwwj u scorefectro rtlcs . com

{C-4~ ■ 47 c

1 1/2004 -dehor e'edronks

13

ABC of Rechm

Basics , pitfalls & recommendations

Gert Helles, Maxim Integrated Products Inc., Hadsten , Denmark

The use of batteries has never been greater. Batteries are
becoming smaller and lighter even as they package more and
more energy per unit volume. The main driving force for battery
development has been the boom in portable equipment such
as mobile phones, laptops, camcorders, and MP3 players.

The following brief overview or charging methods and
current battery technologies is intended to lend a better
understanding of the batteries used in portable
devices, h includes discussions of nickel-codmium
[NiCd], nlckehmetal-hydride (NiMH) and lithium-ion
(LI-s-) battery chemistries. The article also describes a
product for protection of single-cel! lithium-ion and
lithium-polymer batteries.

Definition of a battery

Colling a battery on energy storage system poses a defi-
nition that also includes such things as flywheels and
clock springs. In the context of modern technology, how-
ever, batteries are usually portable, self-contained chemi-
cal systems that produce electrical energy.

Disposable batteries (called non-reehargeabte or primary
cells) create electricity from a chemical reaction that per-
manently transforms the cell. Discharging a primary cell
leads to a permanent and irreversible change in the cell
chemicals. By contrast, rechargeable batteries, also
called secondary cells, can be recharged by a charger
after having been discharged by the application.

The charge or discharge current Is usually expressed [in
amperes) as o multiple of the rated capacity (called the C-
raie). For example, a C/10 discharge current for a bat-
tery rated at one ampere-hour (1 Ah) Is 1 Ah/ 10 =

1 00 mA. The rated capacity of a cell or battery (in Ah or
mAh) Is the amount of electricity that it can store (produce)
when fully charged under specified conditions. Thus, the
total energy of a battery Is its capacity multiplied by its
voltage, resulting in a measurement of watt-hours.

Defining battery performance

The chemistry and the design of a battery cell together
limit the current it can source. Barring the practical fac-
tors that limit performance, a battery could produce an
Infinite current, if only briefly. The main impediments to

Infinite current are the basic reaction rates of the chemi-
cals, the cell design, and the area over which the reac-
tion takes place. Some cells are inherently able to pro-
duce high currents. Shorting a nickel-cadmium cell, for
instance, produces currents high enough to melt metals
and start fires. Other batteries can produce only weak
currents.

The net effect of all chemical and mechanical factors in a
battery can be expressed as o single mathematical factor
called the equivalent internal resistance. Lowering the
internal resistance enables higher currents.

No battery stores energy forever. Unavoidably, the cell
chemicals react and slowly degrade, causing degrada-
tion in charge stored by the battery. The ratio of battery
capacity to weight [or size) is called the battery's storage
density. High storage density enables the storage of more
energy in a cell of given size or weight.

Table 1 lists nominal voltage and storage density
[expressed in watt-hours per kilogram of weight, or
Wh/kg) for the major chemistries used in storage batter-
ies for personal computers and cell phones: Table 2
contains quick comparison data to enable designers to
choose the best cel! type for a particular application
(note that NiCd will be banned soon).

So why not always choose secondary cells, if primary
and secondary cells fulfil the same purpose? Secondary
cells hove drawbacks:

- All practical secondary cells lose their electrical charge
relatively quickly, through self discharge.

- Secondary cells must be charged before use.

- Secondary batteries supply less energy at the same vol-
ume and weight.

Charging batteries

A new rechorgeable battery or battery pack [several bat-
teries in one package) Is not guaranteed to be Fully

14

elelslor e'ctlrcdts - 1 1/2004

(Geable Batteries

charged; in Fact, it is likely to be nearly discharged. The
First thing to do, therefore, is to charge the battery/pack
in accordance with the manufacturer's chemisfrydepend-
eni guidelines.

Every charging operation applies voltage and current in
a sequence that depends on the battery chemistry. Thus,
a look at battery-cell chemistries reveals different require-
ments to be met by the charger and the charging algo
rithm. The terms most commonly Found in battery charg-
ing are constant current (CC), used For NiCd and NiMH
cells, and constant current/constanf voltage (CC/CV),
applied to lithium-ion and lithium-polymer ce Is (Figures
1-6). Table 3 summarizes today's most frequently used
charging techniques and the associated parameters per
cell type. The methods to determine the very important
end oF charge moment are listed separately in Table 4.

Charging nickel-cadmium ceils

NiCd cells are charged by applying o constant current
in the range 0.05 C to more than 1 C. Some low-cost
chargers terminate the charge by means of absolute tem-
perature. Though simple and inexpensive, that method
of charge termination is not accurate. A better choice is
to terminate charging when the condition of Full charge
is indicated by a drop in voltage. The — AV phenomenon
is most useful For charging NiCd cells at 0.5 C or
greater. The ~AV end-ofcharge defection should be com-
bined with battery-temperature measurement as well,
because aging cells and mismatched cells can reduce
the voltage delta.

You can achieve a more precise Full-charge detection by
sensing the rate of temperature increase (dT/dfj, and that
method of charge detection is kinder to the battery than
is a fixed-temperature cut-off. Charge termination based
on a combination oF AT/dt and -AV cut-off enables a
longer life cycle by avoiding overcharge.

Fast charging improves charge efficiency. At I C, the effi-
ciency is close to 1 . 1 [91 %), and the charge time For an
empty pack will be slightly mare than one hour. When
applying a 0.1 C charge, the efficiency drops fa 1.4
(71 %] with a charge time of about 14 hours.

Because the charge acceptance of a NiCd battery is
dose fa 100%, almost all energy is absorbed during the
initial 70% of charging, and the battery remains cool,
Ultra-Fast chargers use this phenomenon to charge a bat-
tery to the 70 percent level within minutes, applying cur-
rents equal to several times the C rating without heat
build-up. Above 70% the charging continues at a lower
rate until the battery is fully charged. Eventually, you top
off the battery by applying a trickle charge in the range
0.02 C to 0.1 C.

Charging nickel-mefal-hydride cells

Though similar to NiCd chargers, an NiMH charger
employs the AT/dl method, which is by far the best

Table 1 . Storage density values.

CeEl type

Nominal

voltage

Storage density

(fyp-)

Lead Acid

2.1 volts

30 Wh/kg

Nickel Cadmium

1 .2 volts

40 to 60 Wh/kg

Nickel Metal Hydride

1 .2 volts

60 to 80 Wh/kg

Circular lithium Ion

3 .6 volts

90 to 1 00 Wh/kg

Prismatic Lithium Ion

3.6 volts

? 00 to 1 1 0 Wh/kg

Polymer Lithium Ian

3.6 volts

1 30 to 1 50 Wh/kg

Table 2 .

Quick comparison chart.

Attribute

Nickel

Cadmium

Nickel

Metal

Hydride

—

Lithium-Ion

Energy

Density

Lav/

Medium

High

Energy

Storage

Low

Medium

Medium

Cycle Life

High

High

High

Cost

Low

Medium

High

Safety

High

High

Medium

Environment

Law

Medium

Medium

Figure J.

SemFcanstanf cur-
rent charging —
chiefly l used in
applications like
shavers, cordless
phenes and toys.

Figure 2,

J imer-contro! led
charging is used
mainly m applica-
tions like notebooks
data terminals,
wireless equipment
and cellular phones

11/2304 ■ efekror tlefe'is

15

Table 3. Battery charging methods.

Chemistry

Charging

Method

Feature

# of
termi-
nals

Charge

time

Charge

Current

Trickle

Current

Charge
level at

End of
charge

Figure

Nickel
based
(NiCd &
NiMH)

Semi-constant

current

charging.

Most typical system

Simple and low cost.

2

15 Hours

0.1 C mA

—

——

[

j 1

Timer

Controlled

charging

More reliable than semi-
constant current system.

Relatively simple and low-
cost

2

6-8 hours

0.2 C mA

1/20-
1/30 C
mA

Aoprox.

1 20%

2

-AV cut-off
charging

Most popular

More complex

2

1-2 hours

0.5-1 C mA

1/20-
1/30 C
mA

Aoprox.
110-1 20%

3

DT/dr

cut-off

charging

More costly but over-
charging can be avoided
enabling longer lire cycle
than the others

3 or 4

1-2 hours

> 1 C mA

1 /20-
1/30 C
mA

Approx.
100-1 10%

4

Trickle

charging

Simple ond low cost

Applicable for continuous
charging

2

1 5 hours

0. 1 C mA

5

Lithium

based

Constant
Current -
Constant
Voltage

[CCCV]

Not recommended for the
moin charge control sys-
tem for NiCd /NiMH bat-
teries.

j

Prevailing charge method
for li-ion and U Polymer

Relatively complex charg-
er design

2

i

1-3

Hours

1C mA

Aoprox.

100%

6

method for charging NiMH cells. The end-of-charge volt-
age decrease for NiMH batteries is smaller, and far small
charge rales [below 0.5 C, depending on temperature]
there may be no voltage decrease at alb

New NiMH batteries can show false peaks early in the
charge cycle, causing the charger to terminate prema-
turely. Moreover, an end-of-charge termination by -AV

Table 4. End-of-charge detection.

Chemistry

NiCd

NIMH

II*

Charging

Constant

current

Constant

current

Constant cur-
rent / con-
stant Voltage

Full charge
detect

-AV/dt

and/or

AT/dl

AV/dt - 0
ond/or

AT/df

Charge =

eg 0.03C
and/or time

detection alone almost certainly ensures an overcharge,
which in turn limits the number of charge/discharge
cycles possible before the battery fails.

It seems there is no available -dV/dt algorithm that
works well for charging NiMH batteries under all condi-
tions: new or old, hat or cold, and fully or partly dis-
charged. For that reason, don't charge o NiMH battery
with a NiCad charger unless it utilizes the dT/dr
method for end-ohcharge termination. And because
NiMH cells do not absorb overcharge well, the trickle
charge must be tower [about 0.05 C) than that recom-
mended for NiCd cells.

Slow-charging o NiMH battery is difficult if not impos-
sible, because the voltage and temperature profiles
associated with a C-raie of 0.1 C to 0.3 C do not pro-
vide a sufficiently accurate and unambiguous indica-
tion of the full-charge state. The slow charger must
therefore rely on a timer to indicate when the charge
cycle should be terminated. Thus, to fully charge a
NiMH battery you should apply a rapid charge of
approximately 1 C (or a rate specified by the battery
manufacturer), while monitoring both voltage (AV=GJ

dAtor ekrironks - M//0D4

and temperature (dT/df) to determine when the charge
should be terminated.

Charging lithium-ion
end lithium-polymer cells

Whereas chargers far nickel-based batteries are current-
limiting devices, chargers for lifhiumTon batteries limit
both voltage and current. The first lithium-ion cells called
for a charge-voltage limit of 4,10 V/celL Higher voltage
means greater capacity, and cell voltages as high as
4/2 V have been achieved by adding chemical additives.
Modern Li-ion cells are typically charged to 4.20 V with
a tolerance of ±0.05 V/celL

Full charge is achieved after the terminal voltage has
reached the voltage threshold and the charging current
has dropped below 0.03 C, which is approximately 3%
of I charge (Figure 6], The time far most chargers to
achieve a full charge is about three hours, though some
linear chorgers claim to charge a Li+ battery in about
one hour. Such chargers usually terminate the charge
when the battery's terminal voltage reaches 4.2 V. That
kind of charge determination, however, charges the bat-
tery only to 70% of Its capacity.

A higher charging current does not shorten the charge
time by much. Higher current lets you reach the voltage
peak earlier, but then the tapping charge fakes longer.

As a rule of thumb, the topping charge will take twice as
long as the initial charge.

Protection modes

Overvoltage: If the cell voltage sensed at Vp[> exceeds
the overvoltage threshold Vqv for a period longer than
the overvoltage delay f OVD , the DS2720 shuts off the
externa! charge FET and sets the OV flag in the protec-
tion register. The discharge path remains open during
overvoltage. The charge FET is re-enabled (unless
blocked by another protection condition) when the cell
voltage falls below the charge-enable threshold Vq:, or
discharging causes V DD - > Vqq

Undervoltage, If the cell voltage sensed at V DD drops
below the undervoltage threshold Vyy for a period
longer than the undervoltage delay tyyD* the D52720
(see inset) shuts off the charge and discharge FETs, sets
the UV riag in fhe protection register, ond enters sleep
mode. After the cell voltage rises above Vyy ond a
charger is present, the 1C turns on the charge and dis-
charge FETs.

Short Circuit. If fhe cell voltage sensed at V DD drops
below the depletion threshold V S c for a period of f SCD ,
the DS2720 shuts off the charge and discharge FETs and
sets the DOC flag in the protection register. The current
path through the charge and discharge FETs Is not re-
established until the voltage on PLS rises above
Vqp-Vqc* The D52720 provides a rest current through
internal resistor Ry 5 j (from Vqq to PLS) to pull up PLS
when Vpp rises above This test current allows the
DS2720 to detect removal oFthe offending low-imped-
ance load. In addition, if enables a recovery charge pafh

F inure 3.

u

Charging is termi-
nated via -AV cut-
off in applications
like notebooks. da r
terminals, cam-
corders. wireless
equipment , and ce
luhr phones .

Figure 4.

Charging is termi-
nated. via -dT. dr
cut-off in applica-
tions like power
tools and electric
took.

Figure 5.

Trickle charging is
mainly used in
applications like
emergency lights .
guide lights and
memory backup .

Figure 6. Constant-
current constant-
voltage charging is
used in application,
like cellular phones,
wireless equipment
cad Notebook PCs.

through Rj ST from PLS to V DD ,

Overcurrent: If voltage across the protection FETs
(^DD^PLS) is greater than Vqc f° r Q period longer
than tQCD* the DS2720 shuts off the external charge
and discharge FETs and sets the DOC flog in the protec-
tion register. The current path is not re-established until

1 1/2004 - deleter e!ec1t units

17

the voltage on PLS rises above V dd -Vqc- I he DS2720
provides a test current through internal resistor R T5T
(from Vqq to PLS] to detect removal of the offending
low-impedance load.

Overtemp era ture. [f the DS2720 temperature

exceeds Tvax, the device immediately shuts off the exter-
nal charge and discharge FETs. The FETs are not turned
back on until two conditions are met: cell temperature
drops below and the host resets the OT bit.

Charging at high and low temperatures.

Efforts should be made to charge at room temperature.
Nickel-based batteries should only be fast-charaed
between 10°C to 30°C (50 s F to 86 3 F|. Below 5°C (41°F)
and above 45"C (1 13 S F], ihe charge acceptance of
nickel-based batteries is drastically reduced. Li-ion batter-
ies offer reasonably good charge performance through-

out the temperature range, but below 5" C (41 "F] the
charge rate should be less than 1 C.

Conclusion

NiMH chargers can accommodate NiCd batteries, but
not the other way around. Chargers dedicated to NiCd
batteries will overcharge a NiMH battery. The cycle life
and performance of nickel-based batteries are enhanced
by fast charging because it reduces the memory effect
due to formation of internal crystals. Nickel- and lithium-
based batteries call for different charge algorithms.

Li-r batteries need protection circuitry to monitor and pro-
tect against overcurrent, short circuits, over- and under-
voltage, and excessive temperature. Remember to
remove a battery from its charger when the battery is not
used regularly, and apply a topping-charge before use.

Lithium-ion safety — meet the DS2720

Because overcharging (or overdischarging) o Li-ion
cel! can cause It to explode and injure people, safety
is a major concern in handling this type of storage
cell. As a result, commercial Li-ion battery packs con-
tain a protection circuit such as the DS2720
(Figure A), which provides all electronic safety func-
tions required for applications involving rechargeable
Li-r batteries: protecting the battery during charge,
protecting she circuit against excess current flow, and
maximizing battery life by limiting the level of cell
depletion.

DS2720 ECs control the conduction paths for charge
and discharge currents with external switching devices
such as low-cost nchannel power MOSFETs. The IC's
internal 9-V charge pump provides high-side drive to
the external n-channel MOSFETs, yielding lower on-
resistances than do the same FETs operating in a more
common low-side protection circuit. FET on-resistance
actually decreases as the battery discharges
(Figure B),

The DS2720 lets you control the external FETs from
the data interface or from a dedicated input, thereby
eliminating the redundant power-switch controls other-
wise required in a rechargeable Li+ battery system.
Through its 1-wire interface, a DS2720 provides the
host system with read /write access to ihe status and
control registers, instrumentation registers, and gener-
al-purpose data storage. A factory-programmed 64-bit
net address allows each device to be individually
addressed by the host system.

The DS2720 provides two types of user memory for
battery-information storage, EEPROM and lockable
EEPROM. EEPROM Is a true non-volatile (NV) memory
whose contents (important battery data) remain unaf-
fected by severe battery depletion, accidental shorts,
or ESD events. When locked, a lockable EEPROM
becomes a read-only memory (ROM) that provides
additional security for unchanging battery data.

Figure A. Typical application diagram for fine D52720 lithium-cell
protection 1C ,

Fig ureB . The rest's tones af p refection FETs con fro lied b y th e
DS2720 {'high-side mods j is Sower than FETs operating in the
traditional low-side mode. FET resistance-controlled by the
DS2720 actually areas with battery voltage.

18

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11/2004 -efeklot tlafronks

Karel Wa I raven

This design is a follow-up to
the triumphant 'Battery
Revitalised project published in
the September 2001 issue of Elektor
Electronics . From numerous reader responses, it appears that
defective batteries are a common problem. Since prevention is
naturally better than cure, here we present a circuit that can keep

your battery in shape in a simple but effective manner.

20

aliktei Elctlr&Qks- 11/2354

battery

young

The quality of lead-acid storage batter-
ies has always been an awkward sub-
ject, Motorcyclists among our readers
will he the hist to agree with this. The
most common example is a motorcycle
that’s put in storage for the winter and
proves to have battery problems when
spring comes. This involves more than
just the fact that the battery has
become partially discharged; since in
many cases the battery has also
noticeably deteriorated. Tnat can be
seen from the fact that even immedi-
ately after being charged, it performs
poorly and quickly loses it charge.

This is also true for all situations in which
lead-acid batteries are not used for an
extended length of time. You might
immediately think of cars 'put away 1 for
the winter, but this problem also occur in
other situations, such as batteries in
backup power supplies (UPSs) that are
not used for a while, batteries used with
voltage inverters (in caravans), and bat-
teries in pleasure boats that simply sit
around doing nothing for most of the year
after the boating season is over. It’s thus
easy to think of situations in which lead-
add batteries age prematurely due to
lack of use. Tne inset provides additional
information about the background of the
process responsible for all of this, which
is called ‘sulphatiori.

Idleness is deadly

For the purpose of this article, it's actu-
ally not necessary to know exactly
why unused batteries deteriorate. It's
sufficient to note that a bit of exercise at
the right time can help keep them in
shape. And that's what the circuit
described here provides.

Unlike the Battery Revitalised
described in the September 2001 issue
of Elektor Electronics, this design is not
intended to resuscitate apparently
defective batteries, but instead to pre-
vent premature aging due to lack of use.
Tb avoid possible misunderstandings, it
should be noted that tills circuit cannot
cou nter act normal aging or other condi-
tions that can lead to defects.

As the whole idea is to keep the bat-

tery a little bit active, the circuit does
not require a separate power supply.
The necessary energy is simply taken
directly from the battery itself. In the
process, sulphation is prevented by
loading the battery with a hefty cur-
rent (40 A) for a short interval (50 us)
approximately every two minutes. Of
course, this will ultimately cause the
battery to discharge more quickly but
a Cully charged car or motorcycle bat-
tery will easily make it through the
winter; After all, the current consump-
tion at 12 V is only around 2 mA.

Operation

The first 555 timer (IC1 in Figure 1)
operates as an astabie multivibrator
and generates a continuous stream of
pulses. The second 555 is a monostsble
multivibrator that is triggered on each
negative edge of the pulses coming
from its companion. As a result, it gen-
erates short pulses that drive power
FET T1 fully on. The FET connects the
battery directly to a power resistor,
causing a heavy current to flow. The
size of this current is primarily deter-
mined by the value of resistor RB.

Tne FET is Intentionally driven here via
a gate stopper resistor with a relatively
high value. This causes it to switch on
and off somewhat more slowly, which
reduces the amount of interference gen-
erated. In this case, 'slow’ means a few
microseconds; a FET that’s driven hard
switches within a few nanoseconds.
Here it isn't necessary to switch quickly,
and there's no need to be concerned
about a bit of extra power dissipation
Despite the relatively slow switching,
rather large voltage spikes can occur
when the FET switches off. It is thus
essential to connect a fast Zener diode
(D5) across the FET for protection.

Construction

it's important to ensure that the ICs and
IC sockets are fitted with the correct ori-
entation. The sockets usually have a
notched or bevelled comer, and the ICs
have a dimple in the package. As seen

from above, the topmost pin to the left
of this marking is pin L It’s best to use
CMOS versions of the ICs, since this
will keep the standby current consump-
tion as low as possible. Several differ-
ent manufacturers make the CMOS ver-
sion of the 555, so type numbers such
as TLC555, ICM7555 and LMC555 (as
well as many others) all refer to the
same kind of IC. However, the NE555,
SE555 and LM555 are not CMOS types.
They can also be used, but the current
consumption will then be quite a bit
higher (more than 10 mA).

Most of the current is actually used by
the LED, so you should use a low- cur-
rent type here (also referred to as a ’2-
mA LED ). When fitting it to the circuit
board, make sure the long lead goes
next to the triangle marking.

The capacitors m the circuit (except for
the electrolytic capacitors) are ceramic
types. That’s because component
value tolerance is not terribly impor-
tant in this case, and a bit of tempera-
ture dependence also doesn’t particu-
larly matter.

New electrolytic capacitors also have
one lead that’s longer than the other
one. That’s usually the positive lead.
On the circuit board, it must be placed
next to the open rectangle. There’s
usually also a white stripe with minus
(-) signs printed on the case of the
capacitor. This marks the negative
lead, which is indicated on the circuit
board by a solid rectangle (the open
rectangle is the + terminal).

Safety

Most people don’t realise that despite
the modest voltage, working with vehi-
cle batteries can be quite hazardous.
This is because such batteries can
deliver especially high currents. That
means you have to be especially careful
with metal objects in the vicinity of a
charged battery A dangerous short
circuit can be caused not only by a
simple screwdriver or wrench, but also
by dangling jewellery and wrist-
watches, both of which are notorious
causes of avoidable suffering.

3 1/2004 - ekktsr dsdronlB

2 !

Figure 1. The general-purpose 555 once again proves its merits

BUZ100

BUZ1D

BUZ11

E°3

Prevent short circuits; make sure you use a properly insulated cord !

If something goes wrong with the cir-
cuit, there’s thus an especially good
chance that something will be
destroyed. Normally, the victim will he
the power resistor, the FET (see the
inset) or a track on the circuit board. If s
certainly possible for this to be accom-
panied by the release of beat, or even a
bang and a bit of smoke. Consequently,
you should always fit the circuit in an
enclosure and ensure that no flamma-
ble materials are in the vicinity Discon-
nect the circuit before charging the bat-
ten 7 in the usual m ann er. Use flexible
mains cable with a reasonably large
cross-section (2 x 0,75 ram 2 , for exam-
ple) for the connections to the battery.

Everything OK?

For initial testing, we recommend leav-
ing Cl off the circuit board and tem-

Figure 2. The circuit can be safely built using this printed circuit board design. Copper track layout available from our website .

COMPONENTS

LIST

Resistors:

R1 = 6Mf28
R2 = 3M.Q3
R3 = 4kQ7
R4,R5 - lOkQ
R6 - 2kU2
R7 = t OQkn

R8 = 01215. 5W or 10W
R9 = 1500

Capacitors:

C1,C6 = 1 OuF 25V radial
C2,C5 = 1 OnF

C3 - InF
C4 = 4nF7
C7 - lOOnF

Semiconductors:

Dl = LED. low current
D2 - 1N4148

D3 = zener diode, 13V 0.5W
D4 = Schottky diode, e.g., BAT43,

BATS 5

D5 - fast zener diode, e.a., BZI03 24V,
27V or 33V)

T1 = BUZ 10, BUZ1 I , BUZ 100 or 1RF54G
!C1 ,IC2 = 7555 (CMOS)

PCB, ready-made, order cede 044021 -
1 [see Readers Services page). PCB
layout available from Free Downloads
section on www.elek tor-electron ics.co.uk

22

elrktni dertrasics - 11/2 CM34

Safe Operating Ares

Fifs

We have listed several options for FET 11, but the choice here h
not critical. It's also unnecessary to make any changes la the cir-
cuit if you use it at 6 V. Still, in this case the preferred type for T ]
is the IRF540, That's because this type of FET works with a lower
gore voltage than the FETs in ihe BUZ family. For the same reason,
FETs designated os logic-level FETs' are more suitable if you want
to use the circuit at 6V, bur they aren't essential In principle, you
con thus use any desired type of n-channel power FET that can
handle at least 20 A at 50 V.

You're probably wondering how o FET rated at 20 A con handle
a current of 40 A or mare. To understand why this is possible,
have a look or the 'Safe Operating Area' chart for the BUZ TO
(Figure 3). It shows how much current can flow continuously
(20 A), and how much current can Row for a short time. As ihe
FET only conducts far a few tens of microseconds each time, the
maximum allowable current during this short interval is just under
100 A. This information can also be obtained from the 'Absolute
Maximum Ratings' in the date sheet, v/hich specify 23 A and
92 A respectively.

Figure 3. Safe Operating Area: max/mum currents
and voltage s for the BUZ W.

CAR AND DEEP CYCLE BATTERY FAQ

Car and Daep Cycle battery answers to Frequently Asked Questions (FAQs), ftps. Information,
references and hyperlinks are contained on this free consumer oriented Web site about car,
motorcycle, power sports, truck, boat, marine. RV (recreational vehicle}, and other starting and
deep cycle applications.

You can learn a lot more about lead- acid batteries and the dreaded sulphalian
process (among other things) at wwwMuhome. de/v/flliQm.darclen /,

porarily soldering a 100- nF capacitor to
the board in its place. The LED should
then flash approximately once a sec-
ond. With a 10-liF capacitor fitted in
this position, the period is a lot longer (2
to 3 minutes), and that’s not so nice for
testing, if the lamp blinks, you can con-
fidently solder the 10- uF capacitor in
place on the circuit board.

Voltages are marked at various places on
the schematic diagram, lithe circuit dees
not immediately work the way it should,
you can compare your circuit with our
tried & tested protop pe by measuring
these voltages. Here we should note that
if you make measurements on pen 2, 6 or
7 of IC1* proper operation of IC1 will tem-
porarily be disturbed, and you may have
to wait a little while for the reading to
stabilise. The stated values were meas-
ured using an electronic multimeter
(10 MO impedance).

Six voifs too

Many old-timers {vintage cars and
motorcycles) use 6- volt batteries.
Strictly speaking, this voltage is usu-
ally bit on the low side for switching a

FET fully on. As a result, in practice
the current through T1 will be a bit
smaller, but it will still be s urn c rent to
ensure obtaining the proper effect
(keeping the battery fresh), Il r s thus

not necessary to reduce the value of
R8 r since the circuit is designed to be
used with 6 -volt and 12- volt batteries
without any modifications.

Sulphation

The capacity of a leod-acid batlery gradually decreases during its service life due to normal wear and leap for a variety of reasons.
However, the aging process is considerably accelerated if an uncharged batlery is stored for longer than a week at a temperature
below 10 C or remains unused (while charged) for an extended length of time. That's because in such situations, a layer of nan-
conductive lead sulphate (FdS 04) rorms on and around the electrodes. This reduces the effective surface area of the electrodes, thus
decreasing ihe capacity of the battery. This process is difficult or impossible to reverse by normal charging and discharging.

However, it is possible to break down sulphate crystals info lead and sulphuric acid by using high (or very high) charging cur-
rents, This method con be used to restore at least part of the lost capacity [see 'Lead-acid batlery revitalised in the September
2001 issue). Still, its better to prevent ihe formation of sulphate. One way to do this is to periodically apply a load to the idle
battery. The circuit described in this article is especially suitable for this purpose.

11/2001 - dcktnr dedroris

23

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doctor t krtronki ■ 11/2004

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SLAs still going strong

Lead-acid batteries still form an essential part of the on-board
power systems in cars, motorcycles, boats and caravans. In its
new form, featuring a fixed electrolyte and a sealed
enclosure, this veteran battery technology (invented in 1 850!)
is now more versatile than ever.

Sealed batteries with a fixed electrolyte have been in pro-
duction For more than forty years. The electrolyte (dilute
sulphuric acid) is fixed either using silica gel (lead-gel, or
dryfit' battery) or using a glass Fibre mat (AGM or
absorbed glass mat' technology). This allows the oxygen
produced at the positive electrode when the battery is
overcharged to diffuse to the negative plate where it con
recombine into water. This cycle of recombination makes
the battery emit practically nothing in the way of gases,
and so it can be built into a sealed enclosure. To prevent
rupture in the event of the pressure getting too high, the
cells (as in almost every sealed battery) are equipped
with self-dosing safety valves. Tne combination of fixed
electrolyte and a sealed enclosure allows operation in
any orientation (although AGM batteries must not be
charged upsidedown]. The most important advantages

of sealed lead-acid batteries, besides their low price, are
their low self discharge, simple charging method, and
long life, especially when continuously charged.

Although the bosic principles of operation of the sealed
lead-odd battery have not changed, steady development
over the years has led to significantly better battery char-
acteristics:

- Improved behaviour when overcharged

- Relatively low sensitivity to deep discharge

- Improved life

- Higher specific capacity

- Improved cycle life

- Quicker charging

- Improved current output

26

fckktor tbdrflmES- 1 1/2004

Manufacturers such as Yuasa, Panasonic and Sannerv
scheln/ExIde offer various ranges of batteries optimised
for one (or more) different applications. So, for example,
there are batteries available optimised for long life
designed to last for 20 years and 1500 cycles,

I he most important application areas today are emer-
gency power supplies of various types [for example for
alarm systems, IT equipment, lighting, and medical
devices), electric vehicles [such as golf buggies and
wheelchairs), electric starter motors, amboard power sup-
plies in boats, caravans and gliders, and, last but not
feast, solar power systems that are independent of the
mains.

Voltage, current and capacity

The state of charge of a lead-add battery can be deter-
mined by measuring its no-load voltage. Figure 1 shows
typical values for sealed 6 V and 1 2 V batteries. The fig-
ure also indicates the accuracy that can be expected
using this measurement: the voltage varies from around
2.2 V for a fully-charged cell to 1.9 V for a discharged
cell. These values are valid at room temperature (20 D C).
If ihe battery has recently been charged or discharged,
the values are respectively higher and lower.

The usable capacity C of a sealed lead-acid battery,
measured in amp-hours (Ah), depends to a great extent
an the discharge current. The lower the discharge cur-
rent, the lower the losses during discharge, and so the
higher the usable capacity. Far this reason, the discharge
current is generally quoted in CA, giving the current as a
fraction or the nominal capacity C. For example, a
capacity C specified at C/10 (or 0.1 CA) for a 1 Ah bat-
tery means that the capacity given Is valid for a dis-
charge current of 0.1 A [100 mA). In this case the capac-
ity may also be written as Cjq (capacity for 10-hcur dis-
charge). Nominal capacities of lead-acid batteries
quoted according to the German DtN standard are given
for a 20-haur discharge (I.e. f at 0.05 CA) and with a
final discharge voltage of 1 75 V per cell.

Charging

In principle sealed leod-acid batteries can be charged at
a constant voltage. The maximum charge voltage that
can be used depends on the temperature, and it Is impor-
tant that this voltage is not exceeded during charging.
Figure 2 shows the relationship between temperature
and voltage for two different charging regimes. The
higher value is used for normal (cyclical) operation, while
the lower value is for when the battery is trickle-charged
to maintain Its condition over a long period. In standby
operation a voltage that Is even only slightly too high will
have a negative impact on the life of the battery, and so
if the operating temperature will not be constant a tem-
perature-compensated charging circuit is essential. What
can happen If the charge voltage is nor adjusted to suit
the tempera lure is dearly shown In Figure 3,

T 2 - V r e-v
tuBsnss,

Figure i.
Relationship
ter -A een m ess ure d
open-circuit voltagt
end remaining
c opacity.

Charging at constant voltage is very simple. Any regu-
lated power supply can be used as long as its output volt-
age can be set to the correct value. At room temperature
[20 c C) a value of 2.45 V (say between 2.4 V and
2.5 V) per cell Is suitable for norma! cyclical charging;
for trickle charging a suitable value is 2.275 V (say
between 2.25 V and 2.3 V) per cell. Cells should not be
charged far too long at higher voltages. One criterion
that can be used to determine when to stop charging is to
test when the charge current, which falls continuously dur-
ing the firs! few hours of charging, reaches 0,07 CA (or
less) and remains unchanged for three further hours. If
this test is not used, then time-controlled charging should
be limited to a maximum of ] 6 to 20 hours.

The initial charge current is determined by the internal
resistance [or, if available, current limiting) of the power
supply. Raising the maximum initial current does not
reduce the charge time as much as might be expected.

Figure 2, Charge
vu Hoge S per ceil) in
relation to
temperature for
cyclic charging
(above} and trickle
charging f below).

1D0

£

I

10

t 1

0.1

Figure 3. Effect of

temperature an
barery life with
continuous charging
of a constant

2.27a V per ce .

11/200-5 - elaklor c'ectfcr

27

Figure 4. Charging
behaviour cf
constant 2.275 V
per cell at tour
different current
limit seif mgs.

Figure 5. Effect of
dec J ,n of dr. 5 ch a rge
on life in cyclic
operation.

Figure 6 , Typical
fall' off in capacity
in trickle-charged
operation.

Figure 7.
This simple circuit
meets oil the monu-
fcctjrer7 main rec-
omrrerdatiors hr
charging sealed
lead-acid batteries.

Typical values

[all voltage data are per cell and at 20 ~C\

Recommended charging voltage:

2.45 V (2.4 V fo 2.5 V) far normal charging
2.275 V (2.25 V io 2.3 V) for tackle charging

Recommended current limit:

0.25 CA to 0.4 CA

o

ICO

4W eoo eoa iooo
* > no. of cycles

1100 1400

Uttzl - 15

ec-Ti^iuetf* er.i’i'-j - 24; ts 24'.
Ejnb "ibiiI Let - perztLre - 20 C - 24 C

Figure 4 shows how the charge current changes when
the charge voltage is set to 2.275 V using four different
current limit settings. The charge current (in amps) is
shown on the vertical axis as a percentage of the battery
capacity Qq. If the C]q capacity is, for example, 1 Ah,
then we are considering initial currents from 450 mA (or
45 % of C] o) down to 1 00 mA [1 0% of C]q). The figure
shows that the initial limit current only flows at the beg rn-

^VS

IW0332 - 17

Maximum charge time (normal charging):

1 6 h to 20 h

Final discharge voltage:

1 .75 V

Open circuit voltage:

2.2 V (charged)

2.1 V (half-discharged)

1 .9 V (discharged)

ning of the charge cycle. The current proceeds to Fall off
exponentially, almost to zero at the end of the charging
procedure. Manufacturers recommend initial current limit
values in the range from 0.25 CA to 0.4 CA; values
above 0.5 CA are best avoided in the interests of pre-
serving the life of the battery.

Battery life

The life of the battery depends to a great extent on the
depth of discharge, expressed os a percentage of the
nominal capacity. Figure 5 gives on idea of the effect of
cyclic operation an battery life. To maximise the number
of useful cycles it is best to choose a battery with a larger
capacity so that ihe depth of discharge is reduced.
Although discharge depth is the main Factor, temperature
also has an effect an life. Temperatures above 50 C
should be avoided, and below -15 C there is a signifi-
cant drop in capacity. Charging at too high a voltage, or
for too long, will damage the battery.

Temperature and charging voltage are the main factors
affecting life in continuously-charged operation.

Figu re 6 illustrates typical performance in ihts case,
where 60 % of the battery's capacity still remains avail-
able after 5 years' use. The 60 % level is considered to
mark the end of the useful life of ihe battery in industrial
applications.

In addition to the factors mentioned above, the construc-
tion of the battery also affects its life. For example, in
standby operation the small charge current that continu-
ously Hows results in the plates gradually becoming thin-
ner and thinner Batteries with sturdier plates last consid-
erably longer in such use. There are also batteries avail-
able that ore optimised for cycle life. Exact specifications
for the various ranges can be found on the manufactur-
ers' websites (see list).

Not recharging the battery after a deep discharge also
has o negative effect. Sealed lead-acid batteries should

28

dcfcler dedfMiG- 11/2001

Gel and AGM-lead batteries

Conventional fead^icid batteries have a few decisive disadvantages:
they are filled with highly acid and therefore hazardous liquids which
may spill into the environment not just when the battery case is cracked
but also when far from positioned upright. Also, these batteries are
marked by a high degree of self-discharging and a limited number of
charging cycles. This may be tolerable For o vehicle starter battery, but if
the battery is to power a vehicle supply system (and be subject to com-
plete charging cycles including deep discharging) then it will protest by
developing amounts of sulphate.

With the above in mind, it is not surprising to see lead-acid batteries
with fixed electrolytes used in such applications as back-up PSUs and
solar systems. These variants ore sealed, maintenance-free and wifi nor
easily spill their contents. Sulphatian can hardly occur because the free
sulphuric acids are captured' by the internal gel mass. Self-discharging
is noticeably smaller, although charging instructions must be observed
closely. Unfortunately sealed lead-acid (SLA) batteries exhibit consider-
ably lower energy densities than their liquid acid counterparts, which
mokes them generally unsuitable for use as vehicle starter batteries.

Apart from the well-known lead-gel technology there is another method to fix electrolyte in a lead-acid battery: AGM.
AGM stands for absorbent glass mat'; o separating layer pressed between ihe electrodes. The construction of an AGM
battery is shown diagrammoticolly in the illustration (source: Hawker). The capillary action of the mot causes the elec-
trolyte to be fully absorbed, preventing it from moving around freely. AGM batteries typically supply higher currents than
gel types and ore also cheaper. On the down side, they are marked by some excess electrolyte os well os worse heat dis-
sipation — at high temperatures, AGM batteries are susceptible to drying out.

not be left In a deeply-discharged state for more than a
few days, ond should be recharged as soon as possible.
The deep discharge capability or a battery indicates
whether [and how quickly) it will accept charge again
after being left discharged for a long period. Modern
AGM-type batteries accept charging relatively quickly
after a month in a deeply-discharged stale and subse-
quently return to Sheir normal charging characteristics. To
ovoid the possibility of leaving the batteries discharged
for a long time, they should be stored in ihe charged
state. Recharging is recommended when ihe open-circuit
voltage reaches 2.1 V per cell, which corresponds to a
self-discharge to about 50 % of ihe nominal capacity. A
healthy battery at room temperature will discharge so
slowly that this value will only be reached after about
1 8 months. At 30 C it wifi take around 9 months to
reach half capacity, and at 40 Z C, around 4.5 months.

At lower temperatures (down to -15 = C) charge is lost
even more slowly than ot room temperature. The low self-
discharge and associated long storage life, along with
long fife In standby operation, are the most important
advantages of sealed leod^acid batteries over other bat-
tery technologies.

In practice

Most battery manufacturers recommend charging using a
constant voltage and current limiting, with temperature
compensation. A simple charging circuit that satisfies
these recommendations is shown in Figure 7. An
LM317 is used as the voltage regulator with a current
limit of 1 .5 A. To ensure that the charge voltage is main-
tained at the level set by PI , the voltage at the input to
the LM3 1 7 must be kept at least 3 V higher than that at
the output. The input voltage can be provided from a
(plug-in) mains adaptor (unregulated is fine) or from a
1 4 V boar power supply. The latter option is only suitable
if the battery to be charged contains no more than four

celts.

The charge voltage is set using PI to the optimal value
far the number of cells, battery type (see manufacturer s
data) and type of charging (normal or trickle). The volt-
age at the output of the charger should be checked using
a digital multimeter svith the battery not connected. The
range of voltages offered by PI can be altered if neces-
sary by changing R2 to suit the number of cells in the bat-
tery.

If charging Is always to be carried out at room tempera-
ture, the temperature compensation diodes between R2
and PI (shown dotted) can be dispensed with. Otherwise
it is necessary to find our what temperature coefficient
[TC] the manufacturer recommends for compensation. A
TC value In the range from —2 fo -5 mV/ ; C can be
realised using our circuit as follows.

Inserting as many 1N4148 diodes in series between R2
and PI as there are cells in ihe battery will give a TC of
-2 mV/ = C: for a 12V battery, ihat means six diodes. If
the number of diodes is doubled to 1 2, the TC value will
be -4 mV/-C; with nine diodes, the value will be
-3 mV/‘C. As you con see, the TC can easily be
adjusted by varying the number of diodes. 3n order to
correct for the voltage drop across the diodes, the resist-
ance of R2 must be decreased by about 120 Q for each
diode added.

Web pointers;

http : / /' www. y u a sa ba tie ri es . co m

http ; / / v/ww, n e two r k p o w e r. ex i d e , com /

h ft p : / A wav, b o tie ry po w eronllne.com/
htio://v f n >w/.Dnna5onic.CQm/indu5frtol/bQriery/

http:/ /www.panasonic-com/iridustriQl/bgiiarv/oem/chem/

seol/index.himl

11/2004 ~ eleklar eifdrania

29

In 2006 European legislation on electrical and electronic
waste comes into full force. Across North America , states are
passing laws to deal with electronics waste. These measures
reflect a hidden but growing problem.

As any electronics enthusiast who has recently tried to
repair a consumer product will know, it is more likely to
be cheaper to dispose of and replace an item than to
repair it. Worse still, many items on the market are likely
to be in good working order at the end of their life. The
keen electronics consumer races a dilemma; a desire to
own the latest technology leaves perfectly good products
obsolete. At the root of this problem manufacturers are
beginning So supersede their own technologies and prod-
ucts at an unsustainable rate. The EU estimates shot 4% of
household waste consists of electrical and electronics
products and this figure is increasing at a worrying rate

of 1 c>28"a every five years.

A glance at the statistics and listening to green organiza-
tions would suggest a depressing future. There exists
however, a movement to exploit the electronics waste
problem where a posiiive attitude and creativity results in
novel solutions.

It's alt around us

A potential mountain of electronic waste surrounds us all
in our homes and offices. The gap between recognizing
the electronics waste problem and acting upon it has left

30

thkfcf electronics - 1 1/2004

Solutions to
electronic waste

us svilh products not designed to be repaired, or dis-
posed of efficiently or safety.

Substances & methods

Common substances found in electrical and electronic
v/asie include cadmium, PCB's, mercury, lead and
bromine. The sheer volume and toxicity of these materials
means landfill is no longer an option. After taking away
the small percentage of goods sold on as 'second hand'
o forge quantity of obsolete and unwanted goods
remain. If these ore to ovoid the landfill then a method of
recycling is required.

Recycling an electronics product involves reducing it to
component ports and converting these bock into usable
parts or raw materials. This con be performed by one
of two methods, manual disassembly or destructive dis-
assembly. Put simply, destructive disassembly involves
the product passing through an industrial grinder. The
granules produced are smelted and the raw materials
separated ror re-use. Considering the toxicity of some of
the materials involved destructive disassembly is a
rather crude method. A large quantity of destructive dis-
assembly is performed in the Far East where labour
costs are lav/ and environmental laws relaxed, ironi-
cally, many of these countries sell the salvaged raw
materials back to the countries that exported them. A
greener and more economically viable solution may be
provided by manual disassembly.

If it ain't broke...

Electronics from waste products has undergone a 'burn
in' period and as such, could be considered to be of a
proven quality and equal fo or more reliable than compo-
nents Fresh oh the production line. The lifespan of many
components now realistically exceeds that of the parent
product. In theory 'harvested' components can be refused
in new products. Research has suggested that whilst theo
rerlcolly possible, a psychological barrier exists at the
manufacturer and consumer level at the thought of utiliz-
ing harvested components in new products.

Electronic Data Logging (EDL)

Researchers at the power tool manufacturer Bosch have
made a suggestion that may help to overcome the
obove [quite natural) fear, the Electronic Dota Loqqinq
(EDL) device.

EDL records general information ranging from life hours
or the product to more specific component operating his-
tory. In theory, this Information could be retrieved by the
recycling agency via a 'green port' on fhe device with re-
usable parts identified, harvested and incorporated
directly inio new products. Successful implementation of

Figure 1.

Student at QDA
University of
Johannesburg . PCs
donated by
Computer Aid
International

EDL in the future may promote more recycling of parts. If
harvesting offers an opportunity for a greener electronics
future then how would this be performed?

Current harvesting operations ore either performed
manually or using robotics. Manual disassembly
involves the application of heat to remove components
from boards and is a labour-intensive operation. It has
enabled charities and other non-profit organizations to
recycle old electronics for good causes. Computer Aid
for example refurbishes PCs from corporate donors and
distributes them to worthy causes in the developing
world (Figure 1).

Many charities have also been successful In raising funds
From the sole of re-conditioned or recycled mobile phones
to Eastern Europe. Manual harvesting has one major
drawback. The cost of skilled labour required to perform
fhe task has proven a barrier to widespread commercial
parts harvesting. This mokes robotic harvesting a more
attractive option. Whilst efficient for large batches of the
same product, robots have to be programmed to disas-
semble each new product they encounter. This can make
the disassembly of small batches or single electronics
products impractical. The search for a commercially
viable method of disassembling batches of small and

V

V ■
%

°A

*3

"o

% %

|

gJ'

&

* ■

s 2™

(O

■J:

IZM-EE Toolbox

' C; i

lolboxl

Figure 2,
iZM/EE Toolbox
promotional image,
(Fraunhofer Institute.

1 1; Z0G4 - eblttBr electronics

31

Figure 3,
Blu-Ray player; 25-
G3 cartridge: front
and rear view of
disc. (Sony)

a

Biu-rsy Disc

v 1 .r ■

Beam Spot

3 W0% 2tj~z

Cover Layer

0.6mm 0.1mm

Numerical Aperture
0.60 085

Laser Wavelength

650n m I> 4 □ 0 n m

b

Figure 4.
(a) DVD vs Blu-Ray
comparison chart /
(bj structure of Blu-
Ray disc.

Lzissr light

mixed electronics waste could be considered the holy
grail of the emerging electronics waste industry.

An alternative: ADSM

Like all good problems a surprisingly simple solution
emerged, a team from Brunei University in the UK devel-
oped the self-disassembling product. The method known
as 'Active Disassembly Using Smart Materials' (ADSM)
involves the incorporation of actuators and components
made From smart metals and plastics. At a predefined
value above the ambient and operating temperature,
these materials change shape. Nov/ imagine these smart
materials integrated into an electronics product. Disassem-
bly of the product is achieved by the application of heat,
no costly labour or robotics requiring programming.

Smart material screws shrink and simply fall out of the
product, a carefully placed smart material actuator such
as a spring expands splitting open the housing. Internal
components break loose from the main assembly ready
for easy removal. The self-disassembling product offers an
exciting future for recycling. Assuming the majority of
manufacturers chose to use smart materials, recycling of
mixed batches of electronics waste becomes possible.
Self-disassembly offers a cheap solution, neatly sidestep*
ping costly robotics and harmful destructive disassembly.

Designing for minimum waste

The Fraunhofer Institute has developed a software prod-
uct to assist the electronics designer. The so ffwa re-based
1ZM/EE Toolbox (Figure 2) enables the electronics
designer to investigate a range of areas from toxicity and
recyclability of a design to more abstract areas such as
the energy required to produce the rasv materials
required, even the energy consumed by the product. In
the future the electronics designer may integrate complex
green issues at the design stage with the push of a but-
ton. Creative thinking at the design stage has the poten-
tial to both clean up the product life cycle and provide
the consumer with desirable new technologies. Sony
recently demonstrated this with their Blu-ray disc.

(Figure 3). Consisting of 5 1 % paper, the new disc pro-
vides greater data storage than existing DVD technology
(Figure 4) and offers greener mass production opportu-
nities. At the end of its working life the product can sim-
ply be shredded and recycled, offering both a green end
of life solution and enhanced data security.

Dealing with electronics waste effectively either at the
design or end of lire stage could be considered an insur-
ance policy for the electronics industry. The European
Union already predicts that 10,500 new jobs could be
created by electronics waste recycling. For the electronics
consumer and enthusiast the future not only looks greener
but we could be seeing some innovative new technolo-
gies emerge. Today's green electronics pioneers will lead
the market tomorrow.

Looking East

ADSM and EDI offer pioneering solutions using available
technology. All this technology still requires one essential

32

ekli&j daTrcflks - 11/2004

ingredient, imagination. If we want to see electronics
waste management in action then look no further than the
heartland of electronics, japan.

In 2001 Japan implemented its Electrical Home Appli-
ances recycling lav/. The recycling law covers only four
types of appliances; air conditioning units, televisions,
fridges and washing machines. These were Found to
constitute a significant proportion of Japanese con-
sumer waste.

Consumers in Japan can now return their old appliance
to the vendor of their new purchase irrespective of the
brand. The vendor posses ihe used appliance aver to a
recycling company. Each returned product is tagged and
its recycling history recorded and stored for three years.
This gives companies a unique perspective on the life
cycle of their product and provides an overall picture on
recycling. From the consumer end the returned product
can be tracked via websites. Information regarding
where the product was recycled is available. If this
sounds too good to be true then you would be right. The
Japanese consumer covers the cost or transporting and
recycling the waste.

And West again..

Absorbing the cost of recycling the product may not
prove to be a popular option with the European con-
sumer. Avoiding added cost means returning to the draw-
ing board and thinking about the design process.

All electronics products begin their life as a design. An
integral part of this is the product life cycle. Traditionally
ihe life cycle of an electronics product ended at the con-
sumer. Legislation and corporate social responsibility
now means manufacturers look at the impact of their
product from the manufacturing process through to prod-
uct disposal. To make electronics recycling work, all parts
of ihe industry need to be involved. Realistically, not all
companies have the funds or the resources available to
spend time looking at issues such os recyclability and tox-
icity of fheir products. However, over recent years com-
puter software has been developed to address this issue.
Examples include two more utilities from Fraunhofer's
IZM/EE Toolbox: the Toxic Potentials Indicator ij T PI J (Fig-
ures 5, 6, 7 ) and the Recycling Potential Indicator (Fig-
ure 8), Just before printing this article, Fraunhofer Insti-
tute kindly advised that on updated and extended version
of the IZM/EE Toolbox documentation is due for release
by the end of this year.

Substances
Dec la ratio ns
(R -phrases}

Workplace Pollution

Concentration Classification
(MAK) (WGK)

a 1

3^

Projection on
Numerical Scale
and Aggregation

TPffrnass unit

t— 100

Ecological Material Rating
(points per mass unit)

CJJB17-&S

Figure 5.

Taxk Potential
Indicator (TP!)
soWare enables
calculation of
product toxicity
during product
design stage.
(Fraunhofer Insfifuf

i i

Vj.V-'j . 1 Fra/ualfdn
an Stamf-isd Sca. : ?

Figure 6 .

A more in-depth
description of the
TPt calculation
process.

(Fraunhofer Instituh

Figure 7.

Example of TFI in
action.

(Fraunhofer Institute

a PCS - rJltfisH totdstri

Web Pointers

[1 } hffp://europa.eu.int/ scodplus/leg/en/lvb/121 2 10. him
|2J vAvw.ban.org

[3] VAvw.ca mp u te r-a id . o rg

[4] wvAv.bnjnel.ac.uk/ research/ odsm/homs.htm]

[5] vAvw.matsushlta.co. jp/ environment/ en/meEec/in dex.himl

[6] vawv. pb.Izm. Fng.de/ ee/070_services/75_foolbox/

0 1 Ojdnleitung.html

[ 7} www. b ta- rayd I s e-offid af.org/

[8] va 1 Av.6lectTOnicsrecydjng.org hftp://www,i cer.org.uk/

Figure 8 .

The Recycling
Potential Indicator
(RPlj utility from the
IZM/EE Toolbox
allows calculation o
proportion of
recyclable material
in product at an
c-arly stags.
(Fraunhofer tn stitv te

IZU-fiPL

Re'Z’jtStwj Locator

■ 72

II IfHrtled KS

n c? rw

M/2QQ4 - ebbor

33

Laurens fe Grange

This article describes the development of a multi-tasking
operating system for the PIC1 8xxx micro controller from
Microchip. The code and RAM memory requirements are
minimal and the basic idea straightforward, but it can
simplify the implementation of an application on this micro
controller considerably.

Applications are easier to specify, design, code and
debug if you start off by separating if into functional ele-
ments, or call it tasks. A software structure to handle the
tasks could then look like figure T,

Here our 'operating system' is nothing more than a cou-
ple of CALL instructions with a GOTO MAIN instruction
at the end. The CALL instruction activates the task, and
the task must cooperate by executing a RETURN instruc-
tion to pass control back to the operating system.

The above could do for some small applications, but usu-
ally the functions/tasks making up our application
require some form of control over their own execution
and that of other tasks. For example a key-scanner task
could continuously monitor a few push buttons- When
one is operated the task associated with that button
needs to be activated by the key-scanner task- Or a
sequence (task) could be executing one of its [many)

steps and then proceed to the next step (code section]
once a particular condition is met.

If is clear that we will require more than RETURN instruc-
tions for the scanner and sequence tasks above to coop-
erate in a system. The key-scanner task needs to activate
one of a few dormant (switched OFF) tasks, while the
sequence task must have the ability to modify its own
entry point so thot only a particular section of its code
[i.e. the active step and its criteria) is executed at a time.
A task's entry point is the memory location at which the
task's code will storf executing when the operating system
posses control to Shot task.

PICXEX18 functionality

In PICXEX] 8 the following functions are provided in the
form af macros that the programmer uses in his task
code.

Figure h
A basic software
structure for
implementing an
application thot is
divided into 3
functional elements .

or tasks.

XexTaskON TaskNr

With this macro the user can activate any task in the
application. It con also be used in code outside a task,
for instance an interrupt service routine can start o task,

XexTaskOFF TaskNr

With this macro the user can deactivate any task in the
application. It can also be used in any code.

XexTaskExit

A macro used in a task to pass control back to the open
ating system.

XexSetE Point TaskNr, E Point

Modify a task's entry paint. It con also be used in any
code.

XexEPNext TaskNr

Set a task s entry point to the next instruction. Only to be

34

ebkfar -11/2034

Operating System and Monitor
for PIC Microcontrollers

used in the code of the task of which ihe entry point is to
be modified.

In Figure 1 the operating systems 'task activation code'
is a single CALL TA5K_X instruction. This will hove to be
extended. Firstly we need to add a test to prevent o task
from being activated if it is switched OFF. Secondly we
must be able to change a task's entry point during run-
time, in which case a CALL instruction cannot be used as
the destination address of this instruction is fixed at
assembly time.

The ON/OFF test for a task is implemented by assigning
a bit variable to each CYCLE TASK, which if set, will indi-
cate thof the task is in the active state. The facility to mod-
ify o task's entry point is implemented by using the
PifCl 8 s ability to push an address on its return stack.

So the CYCLE TASK activation code needs to first test the
task s ON/OFF flag, if it is set then get the task's current
entry point value, push it on the Return Stack, and exe-
cute o RETURN instruction.

For each CYCLE TASK 3 RAM bytes are reserved. The
first byte holds the ON/OFF flag in its Bif<7> and the
next two bytes the task's current Entry Point value.
Application design can be further simplified by adding to
our operating system the ability to execute tasks at selec-
table time rates. This allows the programmer to concen-
trate on the task code itselF without having to be earn
cerned about how to code timing or counting mecha-
nisms io regulate execution of that code.

P3CXEX 1 8 allows for 8 TIME TASKS with the execution
rate of each task being set at assembly time in the file
xextaskLdef. As their execution depends on time these
tasks cannot be switched ON or OFF by the user, and
their entry points cannot be modified, POEX1 8 uses a
CALL instruction to activate a TIME TASK. This allows For
a simple activation mechanism — if ihe task's ON/OFF
flag is set ihen CALL the task's cade. To pass control back
to the operating system the programmer uses the Xex-
TaskExii macro inside the task code. If you look at the
actual code for this macro you will see that a RETURN
instruction will do the same [oh. Using the macro is just a
better way of indicating in your cade where the task's
exit point is.

The basics of the P1CXEX1 8 multltasker can now be
described by referring to Figure 2. Before a CYCLE
TASK is activated a rest is made to determine if there are
any TIME TASKS waiting to be executed. If there is, then
control is passed [with a CALL MAI NO! instruction) to the
code in Fig ure 3.

Here those TIME TASKS, of which ihe Task Request Bits
are set, will be executed. At the end of the TIME TASK list
is a RETURN Instruction, which will take us back into the
CYCLE TASK loop of Figure 2, so execution of CYCLE
TASKS carry on from where it left off.

Figure 2.

Main Cycle Task
bzpofPiCXEXIS

showing how the
test for TIME TASK
request is done
before o CYCLE
TASK is activated.

As shown In Figure 2 we test for requests to execute TIME
TASKS between the executions of CYCLE TASKS. It is
therefore important for CYCLE TASKS not to reioin control
of the CPU for longer than about 5 ms. A PIC running at
a modest 8 MHz can get through a lot of code in 5 msl
A scheduler subroutine in P1CXEX18 controls the activa-
tion of TIME TASKS by setting the Task Request Bits at the
required times.

For the scheduler to function your code must provide for
a timer routine to CALL the scheduler subroutine every
1 0 ms.

Figure 3. The
operating system
will execute a GALL
MAIN01 instructiof
if any TIME TASK
Request Bit is set
MAIN01 will
activate oil TIME
TASKs of which the
Request Bit is set.

ll/2fl(M -efektor dttirorits

35

Figure 4.
For the TIME TASK
scheduler of
PICXFX18 to func-
tion j he user must
arrange for a timer
routine to execute a
CAR SCHEDOO
instruction every
}0 ms.

\ Timer

Interrupt

Restart

Timer

I

I

J i

1 t

I owua-i-i

figure 4 gives the basics of a timer interrupt service rou-
tine (which is your code] containing a call to ihe subrou-
tine SCHEDOO. The following execution rotes [in ms) ore
available for Time Tasks:

}Q, 20, 40, 50, 100, 200

The time task scheduler uses a 20-entry look-up table to
save the task timing information. Every 10 ms ihe sched-
uler routine fetches the next entry in this table and OR it to
the RAM location holding the 8 TIME TASK request bits.
The entries in the look up fable are generated at assembly
time using information from the file xextaskl .def.

The source code for PICXEX1 8 is contained in the follow-
ing three files:

Xextaskl .def
Xexl Stsk.mac
Xexl Bmak.asm

77me Task t Cycle Task 1

Pulse

Pulse, 0

JUT

Pnrmfpr

Count (16)

Generator

vuuii ic i

Xextaskl. def

This is the only file that requires modification. The file is
used to define ihe following:

Number of CYCLE TASKS.

Label at the start of each TIME TASK.

Execution rate for each TIME TASK.

Bias time for each TIME TASK.

Figure 5.
Functional diagram
of the examp/e
application, a
combined
Pulse/Romp
Generator :

Time Task 2

Saw (8) Cycle Task 2

15

Xexl Stsk.mac

Source cade for task control macros.

XsxISmak.asm

This file contains the code for PICXEX1 8. When this fife is
assembled it will generate the CYCLE and TIME TASK
loops and the scheduler table.

Using PICXEX18

The archive file 040149-11 *zip you can download for
free from our website contains all the source code
required for ihe following example application to demon-
strate the use of PICXEX1 8. To generate the .HEX file sim-
ply assemble the file ELEKTOR.ASM using the MPASM
assembler (free from Microchip). The latter file contains

Figure 6.
PicV/in 8 monitor in
action. Here , the
'Fuzzy' version is
shown (still under
development).

- ] ■

Free

Downloads

Ail assembler files for
PECXEX1 8 and the
Pulse/Ramp demo
program.

PICWinS executable and
user guide.

File number: 040149-1 1.zip

www.elektor*
electronics.co.uk/dl/ dl.hlm ,

select month of publication.

36

“!=«. r :r eteriinua- 11/200'!

the directives to include the other riles required. The
application contains Iwo Cycle Tasks and two Time Tasks.
Time Task 1 is a pulse generator It will pulse the bit
Pu!se r O at a rate of one pulse every 400 ms.

Time Task 2 is o sawtooth generator It will cause the
byte Saw' to ramp up in 2550 ms to a value of 255 and
then reset to 0. On every reset the bit 'Zero,0' is set (it
will be reset by the active step of the sequence).

Cycle Task 1 is a pulse counter. Every rising edge on
the bit 'Pulse, 0' will increment the value 'Count'.
Cycle Task 2 is a sequence with three steps. The
sequence will remain in a step until the bit 'Zero,0' is set.
This bit will be cleared and the sequence advance to the
next step. When in the third step and bit 'Zero, O' is set,
then the sequence will revert back to step number 1 . The
byte StepNr' indicates the number of the current step.
Once you have assembled this application, it can be tested
by running it using the MPLAB simulator. To verify that the
two time tasks are in fact being executed at the required
rates of 20 0 and 40 ms, use a breakpoint at the tasks s start-
ing point PULSE_GEN and RAMPJ3EN) and MPLAS's Stop-
watch function to see how long it takes between executions.
The application was programmed into a PIC I 8F452
clocked ot 8 MHz.

PICWin8

When testing an application where a few things are haf>
pening at the same time it is very helpful to be able to

see how the different signals are behaving, in the ELEK-
TOR. ASM file, right after fe setting of the configuration
bits, you'll find a statement to set the assembler variable
'PicWin'. Th is is used to include the assembly code for an
interrupt service routine for the UART to handle the data
exchange with a PC utility to monitor and modify vari-
ables in the PIC. The screenshot of the PicWin monitor in
action, Figure 6, shows trend traces of the Four vari-
ables of our application, which, as you can see, is func-
tioning as required.

The PicWin monitor has the following features:

- V86 application

- Baud rate 9600 (fixed)

- Can display & trend up to 6 values simultaneously

- 4 fields supplied for commands (modify PIC RAM loca-
tions).

- Each trend buffer = 800 samples. Display = 400 sam-
ples with scroll

- Data types: bit, byte, word, Fpomt

- Adjustable scan rate

- Performance; the screenshot shows four traces scanned
at 87 ms. Each trace was shifted to get a better view of
what's happening.

A user guide and setup instructions for the PicWin moni-
tor may be found in a text file included In the zip archive
for this project. Happy Pic king!

:4:: 45-1

PicoScope 3000 Series
PC Oscilloscopes

The PicoScope 3000 series oscilloscopes are the latest
offerings from the market leader in PC oscilloscopes
combining high handwidths with large record memories*
Using the latest advances in low power electronics, the
oscilloscopes draw them power from the USB port of any
modern PC* eliminating the need for mains power.

High performance: 1 0 G S/s sampling rate

£ 200MHz bandwidth

1MB buffer memory

Advanced display £ trigger modes

Compact £ portable

Supplied with PicoScope (oscilloscope/spectrum
analyser) & PicoLog (data acquisition) software

VKl.'-ti-.

Hit.

3l‘!i f.
l*i *V J,

i D E14HI ! i Ci*** -G IlM 1

Tel: 01480 396395

www.picotech.com/scope222

let hiuthty x [.united

1 1/2004 - elefelcr cfitfrer^fs

37

Goodbye '16,

Part 2: ROM (program memory) and long lookup tables

Ron Coates

The 1 8Fxx2 series of processors have
either 1 6 k or 32 k of Flash ROM.
However, each program instruction takes
at least one word (i.e., two bytes) so in
terms of the number of lines of program
code you could write, you are looking at
a maximum of 8 k or 1 6 k.

Consequently, in terms of programming,
you can only ever address even
numbered ROM locations.

38

eleJtlor e!«ffrofixs ■ I0/M4

: COME PIC 1 8F

If you look at the program memory window for o ] 6F
series program, the program address increments by one
for each line, i.e., 0000, 0001 , 0002 etc. The same
code in an 1 8F would produce a program where each
line incremented by two; 0000, 0002, 0004 etc
Th is doesn't matter in the normal course of events, but
when we come to lookup tables, it does.

The whole of the ROM memory is completely linear and
there are no problems with CALL or GOTO instructions,
no matter what the length of the program.

Look up fables

One of the features of PIC processors which has come in
for some criticism in the past has been that lookup rabies
of any reasonable length were difficult to implement.

One of the most useful features of the '1 8 series is that
you can write lookup tables of virtually any length that
will fit in the amount of Flash ROM available.

It might be useful at this point fo look in detail at the only
way you could implement o look up table in the 16
series.

This was called a 'computed goto' by Microchip and
required the programmer to prepare the lookup table as
a subroutine storting with the command to add the value
in the W register fo the program counter. This was fol-
lowed by a list of the values that were fo be returned. To
use the table you had to ensure that the value in W was
the required table position before you called the subrou-
tine. After the subroutine, the main program would have
the looked up value in W.

The following example would return the maximum speed
a driver should do in any intermediate gear. We will call

the subroutine SPEED.

SPEED ADDWF

PCL

RBTLTC

OxFF

RETLW

OxOA

RETLW

0x20

RETLW

0x3C

RETLW

0x50

If the main program had the value of the gear [I, 2, 3 or
4) in W, then calling this subroutine would cause the pro
gram to jump to the line corresponding to the gear and
return the maximum speed as a hex number. Note that
the first line of the table corresponds io a value in W of
zero. Since in this instance we would never have a value
of zero, a dummy value (FF) is inserted.

The limitation of the above is that the value in W con
only vary between 00 and FF [or 0 to 255 in decimal).
And so you con only have 256 lines in the table. If you
need a longer table that this, you have fo split your fable
into 256 line chunks and use additional calculations to
make sure you look up the right chunk. Clearly for values
of several thousand, this is not practical.

The above method con still be used on the 18 series and
is still useful for short fables. However the situation is
even worse now, as the program counter only recognises
even numbers. This means that whether W contains 0 or
1 makes no difference and the program will jump to the
first line of the table (QxFF in the above example). Far the
program above to work properly with an 1 8F, you would
need values of 2, 4, 6 and 8 in W. This also means that
the maximum length af your table is now only 128.

If you need longer look up fables, you need to use an
alternative method. This is described in detail in section 5
of the Data Sheet but these are general principles only.
Any amount of the available Flash ROM can be used by the
programmer as a lookup table (or series of lookup tables).
So if we were using a chip with 32 k of ROM and we only
needed 4 k for the program itself (remember this would be
the equivalent of about two thousand lines of code), then
28 k would be available os look up table space.

This is a very significant step Forward and may well
mean that applications which previously used on external
EPROM to store data can now become true 'single-chip
applications with considerable savings in complexity,

PCB size and, of course, cost.

There are olso larger 18F chips available with up fo
128 k of ROM. Consult the Microchip website for the lat-
est information on these.

The ability to address ihis amount of space hinges on fable
pointers. There are three of these, TBLPTRU (Table Pointer
Upper) only 5 bits of which ore available, TBLPTRH (Table
Pointer High) and TBLPTRL (Table Pointer Low). Together
these are used to form a 21 -bit long address which can
access up to two megabytes. In practice, with the proces-
sors th of we are talking about, TBLPTRU can be left at zero
since the sixteen bits of the other pointers is more than suffi-
cient fo address the amount of ROM available.

These tobies can be read and written to during program
operation so you need to be careful with the setting of
the pointers os if is perfectly possible to overwrite yaur
program code.

So how do we get the data into these fables? This is a
point where the data sheet is strangely silent. What you
can't do is write it in with the program, in the way that
you do with the computed go io. You con go to the Pro-
gram Memory window in MPLAB and directly amend the
values, and indeed this is useful For debugging purposes.
However there is no way of saving these amendments
and as soon as you exit the editor, the information is lost.
In any cose if you have gat an eight kilobyte look up
table you hardly wont fo input all the values by bond!

We can think of two ways oF doing if, and perhaps read
ers could suggest others. As an example let's fake the val-
ues of a sound sampled musical instrument, for example,
a piano. If w'ould be normal fo use o PC to manipulate
and store data of this type, so we will assume lhat the
table you wont to get into the PIC is presently residing as
o file in your PC.

1072004 - ebkt&f Electronics

IF you can write a suitable program For the PC, then
either the parallel or serial port could be used to down-
load the file. The PICs we are discussing all incorporate a
hardware US ART (Universal Synchronous/Asynchronous
Receiver Transmitter] which can easily be set up to com-
municate with the RS232 serial port of a PC.

If your skills do not extend to programming PCs, then an
alternative method is to use an EPROM programmer to
transfer the information to an EPROM, and then write a
program in the PIC to transfer the information from the
EPROM to the PIC's memory. This is rather long winded
as it means you have to program in the code (using a
P1CSTART programmer or equivalent), then transfer the
PIC to a board which has been made up just to transfer
data from EPROM to PIC, before Finally using the PIC in
the target application.

Transferring an existing
16 F application

Page one of the 1 8FXX2 data sheet has the rather opti-
mistic statement that the 1 8F is 'source code compatible
with 1 6C .instruction sets'. This might make you think
that all you hove to do with an existing application is
amend the references to the model number of the PIC
and all will be well. In fact you will probably get a long
list of error messages but it is not difficult to sort this out.
First of all, the status register bits RPO and RP1 which
were used for bank switching in the I6F, no longer exist.
You will certainly have references to these as you could
not otherwise hove set up the I/O ports with the TRIS reg-

isters. All references to these must therefore be deleted.
Another problem will exist only if your original program
used indexed addressing. If it did, you will certainly have
made references to the FSR registers. We now have three
FSR registers labelled FSRO, FSR1 and FSR2 and each of
these has a low and high byte. So all references to FSR
will have to be changed to FSROL A similar problem will
occur with references to the 1N0F register These can be
quickly sorted out by using the search and replace facility
in the editor.

Finally, if you embed your CONFIG statements in the
source code, these will also show up as an error The
CONFIG statements for the 1 8F series are completely dif-
ferent In format to the 16F and the best way is to delete
the 16F statements and start again using the 1 8F
INCLUDE file as a guide.

Syntax errors like these can be quickly sorted out. It is just
as important that you review the program structure to
make sure you are taking advantage of all the goodies
these new chips provide.

Further outlook; DSP

Up until the beginning of this year, the 1 8F series were
the most powerful processors that Microchip produced.
That all changed o few months ago with the introduction
of the dsPIC series. These are full 16 bit processors which
also incorporate features usually found only on Digital
Signal Processors (DSPs), As always E/efcfor Electronics
will be the first to bring you details of these. Watch this
space.,,

:4x;-s-2. :

See your design in print i

Elektor Electronics (Publishing)
are looking for

Freelance Technical Authors/Designers

If you hove

HF an innovative or otherwise original design you would like to see in print
in Europe's largest magazine on practical electronics

* above average skills in designing electronic circuits

# experience in writing electronics-related software

♦ basic skills in complementing your design with an explanatory text

# a PC, emoii and internet access for efficient communication with our
in-house design staff

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

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RQ> Box 75 r NI-6190-AB Beek, The Netherlands, Pax: (+31) 46 4370161
Email: k.walraven@segmeni.nl

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1 1/2004 - e Idler elerti&ria

41

e-online

Calculate and convert

Harry Baggen

Electronics is not always plain sailing. Although a small
circuit can be built quickly without jotting down complex
formulas, a deeper or more theoretical approach soon calls
for equations and basic maths. There is no need however
to know everything from the top of your head as the Internet
is avai lable to assist.

-'--4 i r -^T.v:

t >? & rVto 6rfj<-rr.tf;iTTT-

li wby* or HS ■ - cj-.j J sd pjtdxn ttfch fa-niss, £rm. 3 tl 1 eees

ftjuia&a- Or* : V"- r -ji£ j dtiai d gn n A±tr PTj-~

1 TKT tlWwitl.tfTt I ■ jra — 3 ~ Go j ~ . I Em i

Handbook of Mathematical Functions

wilt

Formulas, Graphs, and Mathematical Tables

Edited by Mfllon AbramowiLi: and Ireae A, Stcguii

1 m Introduction

The present Handbook baa been de&gned to
ovide sdcnliiic luratbators with a compre-
GH iT# and stmunary of tha maths-

* -t . „ 1 /.u. tL _ . . i - l i

pro
t £B

tnaEtcal luncliOEi5 thaE arisa in physical end engi-
nwrbg probkraa. The welbknoFti Tables of
Functions by E. Jxhnke And F. E^da lus bast
inratiiabte to workers in tbeso ceids in ite many
editions 1 .during th« past half-centurr. The

E resent volume extendi the work of three authors
j girtE^T more 6 stens 7 i and more accurate
numerical tables, ted by giving larger co1l*cfion3

rtf nt tii!i f i- t - -t

tkmal importance, Many namEHL-d examples
art given to illustrate tbs n&e of the tables and
also tie computation of function values which lie
cucaide thdr range. At tbs sad of the text in
eath chapter there la a short bibliography giving
books dnd papm In which proofs of the mathe-
matical properties stated m the chapter mar bo
found. Abo listed in the bibliographies are the
more important nyiESricAl ‘ Comprehen-

=ire ibis of tables are given in the Index men-
tioned above, and current inf onus tioa on new

r_ t k* v..,v i o

Electronics con be down right easy...
bur also horrendously difficult. Once
you've mastered a few baste laws'
and have an idea of the operation of
a number of passive and active
parts, youll get remarkably far in
designing a circuit. However, far
more learning is In order for a theo-
retical approach or more accurate
calculations on electronic circuits.
Soon, you may feel drowned In for-
mulae and equations and the fun
wears off quickly. Those of you who
hove completed a formal education
in electronics probably don't have to
be told how complex a circuit design
can rum out to be.

In addition to a solid base in electron-
ics and mathematics there are many
bits of knowledge you da not need
every day — just think of the horrors
of a Laplace transformation or a

42

dfcktor d'edroiiiis- 11/2004

Fourier series. In those cases it is useFul to have
an overview handy or where to Find such sub-
jects, Sure, they are covered in electronics text-
books, but where exactly?

The internet contains nice compilations of cal-
culations for o multitude of electronics sub-
jects. Even if you do not have your moths
ready just there ond then, it is good to know
you can almost instantly refresh your memory.
A good base for such a calculus collection' is
found at the RF Cafe [1], Right at the top of
the homepage you'll find a table that begins
with Equations & References. Belov/ it you can
dick on two links. Electrical a nd General . Both
supply an alphabetical list of technical sub-
jects, where the first is of course the most inter-
esting to us. Although the RF Cafe is mostly
dedicated to high frequency (radio) design,
this overview does not fail to cover a much
wider range: from the size of miniature bulbs
right up to the design of PCB mrcrosfnps. Even
browsing around in this overview will soon
enable you to pick out some really useful bits
like the elementary calculations for various
passive components and all filter transfer func-
tions. Not forgetting, of course, copper wire
gauge comparison tables and resistor series.
The more RF inclined among you will certainly
appreciate the VSWR calculations and the
Smith chart.

Nearly all subjects have their own page in the
RF Cofe website. Some links head off to other
websites, unfortunately including some dead
ones. However, the amount of ready to use
information crammed info the website is such
that these errors can be excused.

On the General page you'll find general-pur-
pose information like bolt St nut sizes, the
Greek alphabet, global timezanes, sound
properties in different materials, thermocouples
and heatsink calculations just to mention a few.
Although the Calculator section contains sev-
eral links to commercial software packages, ft
does include lots of nifty calculation programs
for direct use.

The RF Cofe has lots more to offer, particularly
of course on RF design. Well hold the subject
over to another instalment of electronics
online; else we should have called this instal-
ment 'RF Cafe' straight way! There's one link
however we simply must tell you about: on the
Electrical Conversions , Formulas & References
page is a reference to the entire (scanned)
Handbook of Mathematical Functions , a more
than 1,000 pages thick standard textbook
containing just about any formula, graph and
table we could think of. The entire book (origi-
nally published in 1964) is available free of
charge from Canvertit [2].

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43

leading the way

V

Take out an 18-month
subscription to elektor
electronics and receive
a free MP3 player with
128 MB Memory*.

Please fill out the Order
Form with this Issue.

Subscription rates and
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’ Offer available to Subscribers who have not
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ihe last 12 Months, Offer Subject to Availability.

Burkhard Kainka

Quartz oscillators are the way to go when you need a
precise, stable frequency source but what do you do when an
application calls for a non-standard frequency? Custom-made
crystals are an expensive option but now Cypress has come
up with a cheaper alternative...

The buzzword is CyberClock and describes a relatively
new technology in the field of dock generators for use in
complex systems like PC motherboards. If you take o look
at an aid motherboard it is easy to spot the crystal gener-
ators dotted around the board providing all the different
clock sources. More modern systems are increasingly
employing just a single clock generator and deriving alf
the other signals from this one source.

Pll Technology

The clack generator chips contain a Phase Locked Loop
(PLL) with the fastest versions having an output frequency
range from ] 00 MHz to 400 MHz. The PLL layout is
shown in Figure 1 * It differs from a standard PLL by hav-
ing programmable dividers at the input and output and in
the feedback path. The input clock F^f (typically a crys-
tal) is connected to a programmable divider Q. This
clock signal is now compared in the Phase Detector (PD)
with the output frequency from the Voltage Controlled
Oscillator (VCO) divided by P and fed to the Charge
Pump (CP). The CP output is a function of the phase dif-
ference and controls the VCO. The VCO output is passed
through the output divider N to produce Fqup Altogether

there are three dividers (G, Pand N] all of which can be
independently programmed.

We shall take a closer look at two of the Cypress clock
chips. Firstly the CY22393 ( Three-PLL Serial Programma-
ble, flash Programmable Clack Generator') has six con-
figurable outputs (Figure 2). The device con be flash-
programmed (non volatile) from a special external pro-
grammer. The programming algorithm is not in the public
domain presumably for licence protection and to guard
against over-clocking or simitar abuse. While the oscilla-
tor is running it is possible for the contents of internal reg-
isters can be overwritten via the l-C-Bus but this storage
is volatile and they will be lost on power down.

The CY27EE16 ( One-PLL In-System Programmable Clock
Generator with individual 16K EEPROM') is particularly
interesting for lav/ volume production applications or cir-
cuit development. The internal EEPROM does not need o
special programmer; it can be programmed via the built-
in 1-C bus Interface. Register contents can also be over-
written 'on the fly' as above. A default configuration can
be programmed into the chip and this will be loaded
each time at power up. This facility brings the concept of
an individually programmable oscillator one step closer.
The internal structure of the chip (Figure 3) shows the

46

dskf&r tkrtrcnks-lI/MM

For low-noise
VCOs & PLLs

possibilities for clock generation using just one PLL The
output dividers con be internally connected to either the
VC O output or directly from the reference clock. One fre-
quency can be Freely chosen while the other outputs must
be derived from the VCO or reference frequency.

Both ICs allow direct connection of a crystal in the range
between 8 MHz and 30 MHz. The output Frequency is
selectable up to 200 MHz.

A range of evaluation boards from Cypress featuring
USB connectivity supports the family of clock generator
chips. These boards are known os 'Candy Boards' (pre-
sumably because they are simple to use). The Pepper-
mint board' has the CY22393 fitted while the 'Blueberry
board contains the CY27EE16. Each of these evaluation
boards is a versatile stand-alone universal frequency gen-
erator and can be used in many applications. Cyber-
Clocks (Figure 4) is a free program that greatly simpli-
fies the process of directly programming and controlling
the Candy Boards.

Cypress also produces free downloadable software sup-
porting the entire range of clock generators. From the
CyoerClock start menu select the sub-family then the chip
part number. The CY22393 can be found under
CyClacksRT white the CY27EE16 Is under ISR.

The program displays a window for the selected chip
with the programming options. The desired output fre-
quency and the input clock frequency can be entered
along with the pinout configuration and the software will
calculate the division factors Q f Pand N and also all the
necessary internal register values. The settings con be
saved in a JEDEC format file that is compatible with most
hardware programmers. The starter boards also feature a
USB interface.

grommed settings will be retained on the board as long
as it is powered up. Once power is disconnected the set-
tings will revert to their default example values.

The Blueberry Board

Far use in the lab the Blueberry Board (CY30703) with
the CY27EE16 is particularly interesting. The double E
in the port number gives away the fact that the chip con-
tains an EEPROM. This has space to store 2 kbits for reg-

Frz?

vco

!P

*

Figure t. The PLL
principle with
feedback divider.

Logic Bloc* SXsgrsm- 0*223*3

Figure 2.

The CY 22393 U
diagram.

The Peppermint Board

The demo board type CY30701 [Peppermint Board) is Fit-
ted with the CY22393 ond contains an on-board
10 MHz crystal together with a USB interface. The
CyberClocks program can be used to configure the chip
once the desired output frequencies are entered.

The example in Figure 5 shows the generation of three dif-
ferent frequencies in the range between 6.55 MHz and
122 MHz. A buffered output clock from the quartz oscillator
is also used as an output. With the software In Advanced
Mode it is passible to see all the configuration settings.
Details of each of the PLL and divider settings as well as all
the infernal links are shown. Another program feature that
proved useful during system development is the Bit-Viewer,
this displays the contents of all the interna! registers.

When the Peppermint board is first connected to the PC it
should be automatically detected and the appropriate
Human Interface Device (HID) driver wilt be loaded by
Windows. An on-board status LED will blink to Indicate
successful USB communication.

The board takes its power directly from the -t-5 V USB
and has an on-board 3.3 V voltage regulator. Pro-

Figure 3.
TheCY27FE16i
and divider

Figure 4.

The CyberClock.
programming fc

1 1/2004 - deklar dedtMla

47

isfer contents ond a further 16 kbits for general program
use. No special hardware is necessary to program the
device. The clock configuration parameters can be stored
either In RAM or EEPROM, Storing to RAM allows the
dock to be configured 'on the fly'. After a power
down/up cycle the dock will be reconfigured to the

parameters stored in EEPROM.

This chip has only one internal PLL but with careful pro-
gramming of the dividers many different dock frequen-
cies can be generated. To increase flexibility the output
dividers can be switched to either the PLL output or to the
oscillator frequency and an output crosspoint switch
matrix routes the docks to the user defined output pins.

Figure 5. Frequency
selection on the
peppermint board.

, Cnnrlyr Board - Collect all flavors:

C&nfy Board List
|l. CY223S3 z\

- S2/Su:p»r.-i

o r i

Shutdovm/OE
r 0 f* 1

Figure 6.
USB auto transfer.

Fesdbsck:

Figure 7.
Programming the
settings Into

EEPROM.

Figure 8.
Factors P Q and N
in the VCO
calculator.

Rctagnce

PLL

Dr-'C^r

PFV

P 9

[233

p“ JTiT

fesis

!*

p fsT

Q W

l _

RF applications

These signal generators are essentially intended as dock
sources for microprocessor systems and their peripherals
but we are all in favour of a bit of experimentation so
why shouldn't we try it out for RF applications? The main
concern is whether the generator con meet the more strin-
gent requirements of an RF environment. In particular the
increased level of phase noise in a PLL system compared
to a Direct Digital Synthesiser (DDS) could impact on a
receiver's performance. The acid test would be to use it
in place of the synthesised signal at the first Injection
oscillator input to the digital (DRM) receiver published in
March 2004 of Elektor Electronics. For example, to
receive DRM transmissions from the German station RTL
(broadcasting an 6095 kHz) we require a first oscillator
of 6550 kHz (with an IF of 455 kHz, 6095 + 455 =
6550 kHz). After substituting the PLL dock for the DDS
dock the resulting performance was surprising good: The
DRM signal was completely dean and indistinguishable
From the quality achieved with the DDS clock source.
Based on this result there seems to be no good reason
why the programmable oscillator should not be consid-
ered for use in critical RF applications also.

Anyone who has worked with PLLs will be aware of the
usual problems: A VCO is controlled by the output signal
from a phase comparator and a loop filter, this configura-
tion gives rise to relatively high levels of phase noise and
the effects of loop resonance, in critical RF applications LC
oscillators with high Q characteristics are used to reduce
these tendencies but never the less PLL based receivers
usually tend to have higher levels of phase noise than for
example, DDS controlled receivers. The performance
achieved here is therefore remarkably good.

The VCO Calculator In CyberClocks details how
6.550 MHz is derived from the 1 0 MHz clock. The G
divider is set to 4, giving a fairly high comparison fre-
quency of 2.5 MHz. The PLL (the P divider) multiplies ihe
frequency by a factor of 131 to produce 327.5 MHz.

The VCO output is divided by 50 In ihe output dividers to
give on output of: 1 0 MHz / 4 - 131 / 50 =

6.550 MHz.

ihe secret of the high qualify signal lies in the fact that
the VCO and comparison frequency are relatively high
and the VCO phase noise on the ouiput signal is effec-
tively divided down by the output divider chain (N). By
comparison a conventional PLL system with a channel
spacing of 10 kHz would typically use a comparison fre-
quency of 10 KHz with the output frequency sourced
directly from the VCO output, this set-up makes it far
more difficult to produce a clean signal
The Blueberry board can generate signals higher than
those produced by the DDS of the Elektor Electronics
DRM receiver so it is now possible to explore the short
wave region around 26 MHz. The receiver design uses o
wideband first mixer stage connected directly to the aer-
ial so It Is also possible to push ihe oscillator frequency
up a bit more and receive signals in the VHF band. It is
perfectly possible to cover transmissions In the aircraft
and 2 m amateur radio band; all we need now are some
DRM stations up there to listen to.

43

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49

n the three-part article for the ClariTy 2 x 300-W fina
the various input and output filters
were not described.

In this article we
remedy that situa-
tion. The circuits
described here can
also give excellent
results when used
with other designs.

amplifier,

For GariTy and
other final amps

Extremely high currents at relatively
high frequencies are present in ampli-
fiers such as our ClariTy design (Elec-
tor Electronics June, September, Octo-
ber 2004). In such situations it is recom-
mended to take measures to suppress
interference signals (electromagnetic
interference, or EMI for short). This can
be done by using additional filters for
all connections to the outside world.
For an amplifier, three different types of
filters are necessary. They are respec-
tively used for the loudspeaker connec-
tions, the signal inputs and the 230-V
mains connection.

For the inputs and the loudspeaker
connections, it is common practice to
filter only the interference currents
shared by the two conductors {signal
and ground), which is called common-
mode suppression’. This causes the
least possible effect on the audio spec-
trum. At the inputs to the 2 x 3QG-W
amphner, for example, it is dear that
only common- mode interference can
be present. This is because an ana-
logue gain stage is present at the input
of the TA303G amplifier IC, and there is
also no question of interference arising
directly from the signal source.
Another factor is that here the loud-
speaker outputs drive loads having
very low impedance, which means
large currents can occur. However, the
filters already present on the circuit
board of the ClariTy amplifier suppress
only the PWM signal. Such a signal is
actually a purely differential-mode
i nte rf erenc e s ig n al .

In the case of this amplifier, common-
mode interference primarily arises from
the amplifier as a whole. This interfer-
ence can thus be found on all of its
connections. That means that separate
filters for suppressing com mom mode
interference must also be used for the
loudspeakers in order to reduce EMI.
As a PWM amplifier also loads its
power source with a 'nasty 1 signal, it's
a good idea to use a combination of
common-mode and differential-mode
suppression for the mains filter. This

can be implemented relatively easily
by winding the filter coil in a special
manner.

Toroidal cores are used for all of the fil-
ters described here. This minimises
inductive coupling to the surround-
ings. Another advantage of using
toroidal cores is that they make it pos-
sible to wind inductors that only gen-
erate an inductance for common-mode
signals. By now it should thus be clear
that inductors for mains filters gener-
ally have to be would differently than
inductors for loudspeaker filters.

In filter

Let's start at the beginning: the input.
In practice, iris clear from measure-
ments made using an Audio Precision
analyser that a sturdy input filter can
provide significant benefits. Without
such a filter, the measurements made
on the ClariTy amplifier were instable
and in fact unusable.

The input filter (Figure 1) thus pro-
vides common-mode isolation between
the signal source and the amplifier. In
addition, capacitors for differential-
mode suppression are included as a
precaution. We prefer not to use
ceramic capacitors in the signal path
for audio applications, but in this case
they are present in parallel with the
output of the preamplifier for audio sig-
nals. If the preamplifier has low output
impedance, the effect on the sound
quality will be negligible. The two
channels are kept fully apart on the cir-
cuit board, so the entire signal path
between the preamplifier and the final
amplifier remains separate for the two
channels. The two grounds must be
connected together at a single point at
the analogue power supply neutral
potential. In the case of our amplifier,
this point is thus on the amplifier
board The filter also prevents ground
loops from arising.

The inductor uses a very small toroidal
core with dimensions of 10 x 4 mm. It
has two windings, each just a bit more

than a single turn, hi practice* this
proves to be more than adequate (for
our application). Two short (but suffi-
ciently long) lengths of 0.5-mm diame-
ter enamelled copper wire (ECVV) are
passed through the centre of the small
toroidal core and wound together
around the core (btffiar) in a single
loop. The other ends thus emerge on
the opposite side of the core. This
yields a self-inductance of twice 14 pH
and a leakage inductance of less than
100 nH. The leakage inductance is the
virtual inductor that contributes to the
differential-mode effect of the filter.
Incidentally, it's difficult to measure
the leakage inductance.

Ffom the value of 14 nH, it's apparent
that each winding behaves as though
it had nearly two turns. This can be
seen from the fact that according to the
data sheet,, the value of the Al factor
for this toroidal core is 3470 nH. You
can calculate this for yourself using the
formula L = N 2 x A L (where N is the
number of turns).

Just as for the filters described later
on, a printed circuit board has been
designed for this filter. The inductor
should be fitted vertically on the circuit
board* and its leads must be pulled
tight and soldered to the circuit board
under tension. This avoids the need for
any additional fastening. The compo-
nent overlay (Figure 2) and photo (Fig-
ure 1) clearly show what is intended.
Cinch sockets can also be fitted to the
circuit board. The board should be
fixed firmly in place using the five
mounting holes.

The connections marked with the 'out-
put’ arrows and ground symbols must
be connected to the amplifier inputs,
using good- quality screened audio
cable. The pin between these connec-
tions must be connected to the enclo-
sure via the shortest possible path.
This can be done by fitting air M3
washer with soldering lugs to one of
the fastening screws.

In the dimensioning of the capacitors,
the primary consideration was the

11/2001 - tlektoi cktlFMits

51

K1

K 2 12

AMP IN

Fig ure h The input filter suppresses both common-mode and differential-mode signals. Pay particular attention to how the
inductors must be wound and placed. Copper track layouts from our website.

Figure 2 . A single printed circuit board has been designed for all of the filters. The portions for the loudspeaker filters are laid out
as mirror images of each other.

Components

list

Resistors;

R i e R 2 = 470kQ

R3,R4 = Varistor 275V (Epcos SIOV-
52GK2 75 t Farnel! # 580-284]

Capacitors:

Cl f C2,C3 f C6 = 390pr
C4,C5,C7,C8 = 100pF
09,010X13,014= 1 nF 400V, lead
pitch 5mm or 7,5 mm

Cl 1 P C12X15,C16= 1 OnF 400V, bad
pitch 5mm or 7.5 mm

Cl 7X1 8 = lOnF 275 V AO Class X2,
lead pitch 1 5mm

Cl 9X20 = lOOnF 275 V AC , Class X2 r
lead pitch 15mm

Inductors;

LI ,L2 = 2 x 1 turn (bifilar) 0,5mm dia.
|SWG26] enamelled coppper wire on
Ferroxcube core TLI0/6/4-3E5 (Farneil
# 305-6960)

13 14 = 2 x 18 turns (bifiJarj 1 .5 mm dia.
(SWG1 6) enamelled coppper wire on
Ferroxcube core TX36/23/15-3E25
[Famell #305-7021)

L5 - 2 x 16 turns 1 .5mm dia. (SWG1 6)
enamelled coooper wire on core
TN36/23/1 5-3E5 (Famell # 305-7010)

Miscellaneous;

K1 r K2 = PCS mount cinch socket [T-709G
from Monacor/Monarch)

K3 - 3-way PCS terminal block, lead pitch
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8 x spade terminal (laston), PCB mount,
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52

elsktor ekcfieciics -11/2404

S2QK275

S20K275 &HJ311-14

Figure 3. The mains filter is a quite
conventional design, and like the input
filter it suppresses both common-mode
and differential-mode signals.

For safety, the two inductor windings
must he separated as far as possible .

capacitive load on the preamplifier.
With this filter, it is only 880 pF (Cl +
C3 F C5).

Mains filter

The mains inlet naturally amounts to a
second input. Here we chose a conven-
tional design (Figure 3). We used the
largest possible core here {in terms of
availability), which results in a large
load capacity as well as high induc-
tance. For mains filters, the inductance
normally decreases as the load imped-
ance increases (for the same dimen-
sions). By using a large core (36 mm
outside diameter) with 1.5- mm diame-
ter wire wound in only a singly layer
(which increases the maximum per-
missible current), we obtained a filter
that can easily handle loads as high as
1000 VA.

The inductor has two identical wind-
ings, which are well coupled but sep-
arate. The separation is important due
to the mains voltage connected
between the two windings. For supe-
rior coupling, we selected 3E5 core
materia], It has very high permeability;
the Ai factor for this core is no less
than 11,400 nH.

The two windings are wound tightly
on the core. This takes a certain
amount of strength, since they are
wound using 1.5-mm copper wire and
a gap of at least 3 mm must remain
between the opposing windings (for
Glass 1 insulation). If you can t man-
age this, just reduce each winding by
one turn. Note that the two windings

must be as nearly possible identical.
This prevents premature saturation of
the core.

With 16 turns per winding, you will
have two windings with a self- induc-
tance of somewhat more than 3 m.H
-30 % (which is also the self- induc-
tance of the inductor for common-mode
signals) and a leakage inductance of
around 15 uH.

j*

The niter also contains two robust
varistors that provide additional pro-
tection against sporadic mains distur-
bances (transients), although they
dont protect against common-mode
transients.

R1 and R2 ensure that the capacitors
are quickly discharged if no mains
voltage is present (and after it’s dis-
connected). This prevents dangerous
voltages from remaining present on
the mains connector For safety, use
plastic stand-off bushes for mounting
the circuit board in order to maintain
adequate clearance between the cir-
cuit board tracks and protruding con-
nections on the copper side and the
metal parts of the enclosure. For a
Class- 1 device, a separation of 3 mm
is in principle sufficient, but 6 mm is
recommended.

As the inductor is attached to the cir-
cuit hoard quite securely by its four
leads, additional mechanical fastening
is not required. For anyone who never-
theless considers mechanical fasten-
ing necessary, a hole is provided in the
circuit board in the middle of the
inductor. Be sure to use only plastic
parts for any such fastening, in order
to avoid affecting the inductance of the
coils. The layout of the printed circuit

board Is shown In Figure 3,
Capacitors C19 and C20 form part of
the differential-mode suppression
network, but given the low imped-
ance of the power supply and mains
network, they have less effect than
Cl 7 and C18, which provide common-
mode suppression. These two capac-
itors are configured in parallel for
common-mode signals, so they con-
stitute a 20-nF capacitor that forms
an LC filter in combination with the
self- inductance of Lb.

The impedance of the amplifier for
common-mode signals primarily
depends on the parasitic capacitance
between the primary and secondary
windings of the supply transformer
(as well as the impedance of the
wiring inside the enclosure), and it is
reasonably high. This means that the
self-inductance of the inductor is pri-
marily responsible for filtering com-
mon-mode signals.

The values of C17 and CIS cannot eas-
ily be increased, since they also gener-
ate leakage currents to ground when
the filter is connected to the mains
voltage (via one of the two capacitors,
depending on which one is connected
to the live mains lead).

The ground rail of the filter is con-
nected to the enclosure together with
the ground connection of the mains
inlet connector.

Speaker filter

In contrast to the mains filter, the
inductors for the loudspeaker filters
(Figure 4) are would bifilar (see Fig-
ure 5), Consequently you have to wind

11/Z004 - ekfelor cLeVradrs

53

(B)

L3

AMP

0

(C)

L4

Figure 4. The output filler for the loudspeaker signals is
specifically intended to provide common-mode suppression .

Figure 5. The inductors are wound bi filar

two lengths of 1.5-mm copper wire on
the core at die same time, which takes
even more strength.

Bifilar winding ensures excellent cou-
pling between the two windings and
causes the leakage inductance to be
very small. You have to bear in mind
that peak currents of around 20 A can
flow through the wires of the inductor.
If the windings are not identical, the
inductor will saturate and the niter will
be ineffective*

Naturally, using these biters slightly
increases the output impedance of the
amplifier. Flat tab connectors are used
for the connections, due to the poten-
tially high currents. This also makes it
possible to connect leads directly to
the circuit board using M3 solder lugs
(spade terminals). Tins helps avoid a
certain amount of contact resistance.
Another possibility is to solder the
leads directly to ihe copper side.

Here we selected 3E25 core material,
it has somewhat lower permeability
than 3E5 material, but it can be used
over a wider frequency range and is
less prone to saturation (although that,
isn't so important if the inductor is
wound properly). The selected core
has the same dimensions as the one
used in the mains filter
As no special insulation between the
two windings is necessary here
(although the copper wires must natu-
rally have a heavy enamel coating), it’s
easily possible to add two more turns.
The two 18 -turn windings of 1.5 -mm
enamelled copper wire yield an induc-
tor with a self-inductance of approxi-

mately 2 x 2 A rhH ±26 % and a leak-
age inductance of only 2 uH.

Be sure to leave the windings leads
long enough to allow them to be prop-
erly fitted to the circuit hoard. This will
require a bit of 'cut and try'. The induc-
tor is held reasonably firmly on the
board by its four leads, but we recom-
mend using a small sheet of plastic
and plastic screw to secure it to the
circuit board. These filters should be
placed as close as possible to the
amplifier outputs.

Next a few remarks about the capaci-
tors. C1 T C12, C15 and C16 are actually
intended to filter out RF interference
(in differential mode); they do not have
any effect on common-mode signals.
However, they are connected in paral-
lel with the output of the amplifier, so
they have intentionally been kept
rather small in order to keep their
effect as small as possible. They
increase the filter capacitance by just
less than 10 %.

There are also capacitors in the filter
that do provide common-mode sup-
pression: C9, CIO, C13 and C14. They
are effectively in senes for differential-
mode signals, so they can practically
be ignored for such signals. For com-
mon-mode signals, by contrast, they
are effectively in parallel and provide a
capacitance of 2 nF. The junction of
C9 CIO and C 13/C 14 must be con-
nected to the enclosure.

If you use our printed circuit board
design, be sure to pay attention to the
polarisation of the filters for two -chan-

nel applications, since they are oppo-
site to each other. For stereo use,
swapping the phases of the outputs
wouldn't be obvious, but if the ampli-
fier is used in bridge mode, it is es sen-
rial ensure that the phasing is correct.
For this reason, the circuit boards for
the two channels are designed as mir-
ror images of each other, so equivalent
connections are close together and on
the same side of the board.

Finally, we mustn't forget the cabling.
Generally speaking, cables make
excellent aerials, with a common- mode
impedance of approximately 150 0.
Particularly with the pulse-width mod-
ulated signals coming from our ampli-
fier, the cables can be blamed for a sig-
nificant portion of the interference radi-
ated to the surroundings.

The simplest way to counter this is to
keep the distance between the ampli-
fier and the loudspeakers as short as
possible. Another possibility is to slide
a pair of substantial ferrite cores over
tire cables (at the amplifier end), which
can increase the common-mode
impedance by a factor of as much as
several hundred. Another option is to
run the loudspeaker cables inside
metal screens connected to the ampli-
fier enclosure.

Ferrite cores of various sizes can also
be fitted to the other cables (mains
cable and input signal cables).

.I.:::- - .

Speaker e®b8®s

54

cMlardeEtrofiG - 11/2004

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Easy processing with the MAX6675

Design engineers like to use thermoelements when it comes to
probing around in really wide temperature ranges. Modern
integrated circuits are available that act as sensor interfaces to
a microcontroller.

The operation of thermoelements is based on the See-
beck effect: a temperature difference across a wire
causes movement of free electrons. The amount of charge
displacement is dependent on the electrical properties of
the wire.

As illustrated in Figure 1 , thermal energy is applied to
electrons normally moving inside a crystal grid structure.
The applied energy causes the electrons to move faster
and eventually diffuse from the hot to the cold end. There
they slow down again, releasing their energy. As elec-
trons concentrate at the cold end, a negative electrode is
formed relative to the hot end. At the same rime an elec-

a

b

OO a O°Q,
• 'I •- O c o °

- G = D : O "

- ~ - Q =» G = D

G D O ^ O ^ O 3 O
® e O o O D Oj o
G o Q * O* G ! O

Q - Q c Q & Q

; atoms

= free electron s C4GG77 - m

0=0 0=0
0*0 o

■ O G ■ O

f-o 0 = 0 o

O 6

C <5 - r£.

0 5 0 c 0 s 0
i- ; - ;

o = 0 ° o ° o

Q O s O * Q 5 *

WOO 77 - 1th

fricol field is established maintaining a dynamic balance
between the electrons.

If the voltage between the hot and the coid end is to be
measured, one thing you have to do is connect the hot
end to an electrical conductor that's also exposed to the
temperature changes. If this second conductor has the
same electrical properties as the first one, then no volt-
age can be measured between the charge density points.
However if two different conductors are used, a voltage
exists between the two "cold ends that's dependent on
the temperature difference and the electrical properties of
both conductors.

in the test arrangement shown in Figure 2, no absolute
thermovoitage can be measured, only differential fevels.

!n order to establish ihe temperature a! the measurement
point, the temperature at the connection terminal has to
be known as well as constant. Datasheet values like *iher-
movoltage at 200 J C' always relate to o comparison to
the thermovoitage at 0

If the end of the thermoelement is at an unknown temper-
ature (and far removed from the measurement electronics)
it has to be extended right into the area of known temper-
ature (comparison point), using a special compensating
conductor. A problem arises with the measurement of
thermovoitage using an instrument whose connection ter-
minals are made of a different material. These create two
additional thermoelements, which may be compensated,
though, either by keeping the comparison point at a
known temperature, or perform an appropriate correction
at the instrument terminals.

NrCr

/T\o«o o*o/TY>°o p c o*cf

0 = 0 = o°

I l*O*Q = 0;
/ /G Q>G 0

0=0 0*0
O a G a Q“-

\ \ 0*0 OcO/TY^ Q .0/0

0=0 o

I I *0-0*0
\ J J- O 0 = 0 Q

§°O s G| G j O

0*0^0
B -B e 6 1.n

JO Q O Q S Q B

©

CJ-:*j77 - lie

Figure f. ho conductor

U r

valence electrons ore
equally distributed (aj. but
diffuse to nie cold side
when the conductor h
heated at one side (bj. If
hvo conductors c f different
material are connected at
the net sides, the rree
electrons couse a voltage
di ffe r eree by cc rtcen trati r q
of the cold side.

56

ehfctDF electro 'its - 1 0/2G04

Thermoelements

The voltage caused by the thermoelectric effect is very
small ot just a few millivolts per Kelvin, depending on the
metal or alloy combination* As a result, thermoelements
are not used for measurements in ihe range -30 °C to
+50 “C because the temperature difference with the ref-
erence Is simply too small to ensure a reliable signal.
Consequently thermoelements are typically used for
measurements up to 1000 ~C.

From the multitude of metal and alloy combinations, a
few have been selected and their voltage series laid
down in DIN standard EN 60584 (types L and U are
obsolete and now replaced by J and T)* The element
types differ in respect of maximum temperature and their
characteristics as shown in Figure 3. The maximum tem-
perature is the highest value or which the tolerance is
maintained. Under 'defined up to you find the highest
temperature at which the thermovoltage complies with the
standard* With the thermocouples listed, the first material
is always the positive terminal.

As you can see From the response curves, the voltage
supplied by thermoelements is not a perfectly linear func-
tion of applied temperature* If you want really accurate
readings, then a linearisation circuit is required specifi-
cally designed for each type of element. Figure 4 shows
that for a K element the maximum deviation from the lin-
ear function Is no more than 0,5 K a 750 C C. If you con
live with such a small error in a relatively narrow meas-
urement range, then a complex linearisation circuit is not
in order.

Processing the values

In a previous publication from our archive, "Fash Precise
Thermometer (5/e.ttor Electronics January 1992), we
already proposed a thermoelement application, in that
circuit, the comparison point compensation was handled
by discrete components. Today, the semiconductor Indus-
try supplies complete, dedicated converters in a chip* An
example is the MAX6675, a 1 2-bit A/D converter with
SPI Interface (and complementary control) and a noise-
suppressing, buffered differential measurement amplifier
In front of it (not shown). The internal diagram
[Figure 4; also reveals a compensation diode that coj>
tures the temperature at the comparison point and so pro-
vides the necessary correction of the measured value.

The MAX6675 is ready for measurement point tempera-
tures from 0 "C to 1023,75 = C and is capable of com-
pensating comparison point temperatures of -20 to
+85 "C. This results in an impressive resolution of
0.25 C* By comparison, another 1C from the series, the
MAX7774 with 10-bit resolution achieves a resolution
of 1 *C.

SPI

I he cleaned measurement value Is finally digitized by the
A/D converter, serialized, and may be requested by o
microcontroller (read-only]. The extremely simple 3P1 proto-

col supplies a 1 6-bit word In response to o clock signal.
Not much needs to be said about the timing, as lots of liter-
ature on the protocol is available from Internet. Figure 5
shows the structure of the 1 6-bit word, A sequence of
zeroes at positions 3 (LSBJ through 14 (MSB) means a tem-
perature of 0 C, while twelve ones indicate 1023.75 C
which Is just another rather uncomfortable level.

Figure Z Structure
o f a them", oe . 'em e ~ ;
with a hot measure-
ment junction and ■:
cold ccmporiscn
junction. A com pec
nation wire c iows
the comparison
point to he remote
horn ihe connection
point

figure 3. Thermo -
voltages mom a

■M

number of stan-
ce rd i sed m eiu i a n 6
a Hoy co mhtn of bn s .

Figure d. internal
cl; cor am of ihe

/ AAX6675 .

1 Q/Z] 04 - ^Sakfar dectronics

57

Thomas Johann

Thomas Johonn Seebeck was
bom on April 9, 1 770, in Reval,
now Talinn, ihe capital of Estonia.
Info a wealth/ merchant family.
His father being of German ori*
gin, medical science studies at ihe
Universities of Berlin and
Gottingen were more or [ess
Imposed on young Thomas
Johann, fn 1302 he graduated as
a medical doctor and although he
aid set up practice in Gottingen,
Seebeck decided to change to
physics research, hence he is
known from his experiments in
physics rather than his achieve-
ments as a general practitioner. Mostly self* educated and a
freeman student he went to Jena, Bayreuth and Numberg
where he deepened his knowledge of physics. He met Jahann
Wolfgang von Goethe and joined him in his work an ihe [anti-
Newtonian) theory of colour and coloured light.

Seebeck investigated the heating effect of different colours in
the solar light spectrum. In 1308 he was the first to produce
potassium-amalgam and in 1810 he noticed the colour suscep-
tibility af moist silver oxide (a precursor to colour photography),
in the same year Ssebsck observed the magnetic properties of
nickel and cobalt. A few years later. In 181 B, he discovered the
optica! activity (rotation of the polarized area) of sugar solu-
tions. He then returned to the University of Berlin where he
researched electrical magnetization of Iron and sleek In 1821

Seebeck

Seebeck discovered the thermae lectriceffect and two years Eater
proposed a thermoelectric voltage series os well as published
the fruits of his research in "Magnetic Polarization of Metals
and Ores by Temperature Difference. Proceedings of the
Prussian Academy of Sciences', Seebeck continued to work at
the Berlin Academy for 1 3 years. He died in Berlin on 1 0
December 1831.

Element

Max. temperature

Defined up to

Positive

terminal

J: Fe-Cu Hi

750 : C

120D : C

black

T: Cu-Cutii

350 “C

400 =C

brown

| K: NiCr-Ni

1.200 =C

1,370 C C

green

E: NiCr-CuNi

900 -0

1,000 C C

violet

N: NiCrSi-NiSi

1.200 Z C

1.300 =C

lilac

S: PtlORh-Pt

1.600 =C

1.540=0

orange

R: Pt13Rh-Pi

1.600 = C

1.760 'C

orange

B: Pt3GRh-Pt5Rh

1 JOQ -Q

1,820 C C

—

Bit 2 has a special function. It is normally low, but will
carry a High when ihe thermocouple input is open, for
example, as the result of a cable malfunction. This will
only work, however, when the T- input is grounded (as
dose as possible to the GND connection).

Practical use

A number of requirements should be fulfilled in order to
achieve maximum accuracy.

- Self-healing of ihe MAX6675 should be avoided. Pro-
vide for sufficient ventilation and large ground planes,

- The thicker the wire used for the thermoelement and the
compensation line, the smaller the risk or measured val-
ues being corrupted by the wire resistance^) ,

- If you cannot avoid the use of a thin thermoelement,
you still need to employ a thick compensation wire,

- Mechanical stress on the cable and ihe element is to be
avoided.

-Twisted-pair cable should be used with long thermoele-
ment connections.

- Sudden temperature changes are to be avoided.

- Users should always observe the maximum temperature
specified for the thermoelement, as well as the much
lower value for the compensation line.

- The mechanical loading of the element is to be
matched to the application.

- Despite the use of a low-noise measurement amplifier
inside the MAX6675, the thermoelement, all wires and
connections should be kept for removed from of electri-
cal noise sources,

{04G077-1)

For further reading

MAX6675 datasheet

http: // pdfserv.mQxim-ic.com/ en/ds/ MAX6675 .p df

hrtp://en.wikip5dio.org/wiki/T. J. Seebeck

Figure 5. Structure
of the 1 6-bit v?ord
supplied by the

MAX6675*

BIT

DUMMY

SIGN BIT

12-BIT

TEMPERATURE READING

THERMOCOUPLE

INPUT

DEVICE

ID

STATE

Bit

15

14

13

12

11

10

9

8

7

6

f—

5

4

3

2

1

0

0

MSB

LS5

0

Three-

state

&mri - is

58

tfe ki or d&tfrerki - 10/200-1

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Uses serial port and any
standard terminal comms
program. 4 LED's display
the status. ZIF sockets
not included. Supply: 16-ii
Kit Order Code: 3123KT - £29.95
Assembled Order Code: AS3123 - £34.95

NEW! USB & Serial Port PIC Programmer
USB/Serial connection. Header
cable for ICSP. Free Windows
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Secure OnTIne Ordering Facilities Full Product Listing, Descriptions & Photos Kit Documentation & Software Downloads

3 1/2004 - ricktar elcdronics

59

Automatic Presei

for om DRM receiver

Burkhard Kainka

A PC-controlled
receiver is very con-
venient, especially for
DRM, since it makes
it easy to locate your
favourite stations.
However, this advan-
tage is lost if you
have a manual prese-
lector and must tune
the antenna by hand:
an automatic prese-
lector is what you
need!

With a PLL-controlled receiver things
are very simple. The PLL timing volt-
age can he used simultaneously to
control the first HF stage. Instead of
one varicap diode two are used. If DDS
tuning is used, then although we have
better phase purity which is a decisive
advantage in DRM applications, there
is no tuning voltage available for the

hist stage. What is needed is a circuit
to generate a suitable tuning voltage
automatically

The circuit can be seen as a kind of
passive PLL. Rather than a tracking
oscillator, here we have a tracking res-

onant circuit. The resonant frequency
of the circuit is made to track the fre-
quency of the controlling signal.

At the heart of the tracking circuit is
an NE612 mixer (1C1) which is used
here as a phase detector. The NE612
was used in a similar way by Gert
Baars in 'Alignment-nee FM Detector'

Tracking Filter

60

eWrtwr- ! 1/200-i

LECTOR

I

i

in the July /August 2001 issue of Ehk-
tor Electronics.

The controlling input signal can, for
example, be taken directly from the
VFO pin on the TUF-1 ring mixer in the
DRM receiver Tills goes directly to the
mixer input (pin 1) of the NE612 as
well as to the oscillator input (pin 6}
via a resonant circuit tuned by a vari-
cap diode (LI and D2). A DC difference
signal is available at the output of the
mixer which carries information as to
the phase lag between the direct sig-
nal and that coupled through the reso-
nant circuit. At resonance the phase
difference and hence the differential
voltage is zero.

The control loop amplifier constructed
around IC2.A controls the resonant fre-
quency in such a way that it tracks the
VFO frequency. The output voltage
thus automatically follows this fre-
quency as well. The final result is that
we have at the output of the opera-
tional amplifier a tuning voltage that
varies from about 1 V at 5.7 MHz to 7 V
at 16 MHz. These values are obtained
with a BB112 tuning diode for D2 and
a fixed 1.3 UH inductor for LL The res-
onant circuit needs to be fairly heavily
damped by a 1 Ml resistor (Rl) to pre-
vent the control loop oscillating.

Toe second varicap diode (Dl) receives
the same control voltage and thus
automatically tunes the first stage res-
onant circuit formed by L2 and CIO. As
in any superheterodyne receiver it is
not easy to achieve optimal tracking
between oscillator and input circuit.
The received frequency always lies
455 kHz below the oscillator frequency.
L2 in the input circuit is a tunable coil
and can be adjusted for maximum sen-
sitivity at the lower end of the tuning
range. A sim il ar adjustment for the
upper end of the range can be made
using trimmer capacitor CIO. This

should then also give good tracking
over the middle part of the range. Our
prototype worked without problems
from 5 MHz up to 16 MHz.

The first amplifier stage itself is a JFET
source -follower built around Tl. A
BF245 may be used instead of the
J310. The resonant circuit is only
lightly damped. The voltage gain is
determined by the transformer ratio
between the antenna input and the
resonant circuit. In our prototype we
used 15 turns of 0.3 mm enamelled
copper vrire on a ferrite coil former
with a diameter of 5 mm. The antenna
tap was on the third turn.

The BB112 has a capacitance of about
500 pF with a tuning voltage of 1 V.
Higher values can be achieved by
reducing the voltage further, down to
nearly 0 V, The disadvantage of doing
this is that the Q factor falls rapidly. In
practice tuning works without prob-
lems in the 75 m band, and so the DRM
station at 3995 kHz can be received. In
this case the tuning voltage is only
around 0.1 V.

Hints and tips

Varicap diodes for AM frequencies are
not easy to get hold of. The BB112 can
be obtained from Geisi Electronic in
Germany and from the online shop of
the German magazine Funkanmieui.
Equally suitable are the dual tuning
diode type BB313 and the similar
KV1270NT from Toko. Most of the AM
varicap diodes that are still available
appear to come from surplus stock.
However, they must still be being
made somewhere (presumably in
China) as otherwise we would have no
FLL-based medium wave, shortwave
or long wave receivers! There are prob-
ably considerably more broken radios
thrown away every year than there is

demand for varicap diodes for home-
built receivers: a few minutes with a
soldering iron can prove very worth-
while: see, for example, www.b-
kainka.de/bastel99.htm (in German).
Finally a brief note on using the auto-
matically-tuned preamplifier. In most
cases DRM will work perfectly well
without preselection. In just a few
cases is the SNR significantly
improved by preselection. The device
is of course particularly useful when
there is interference at the image fre-
quency.

However, in AM mode there is a signif-
icant improvement. Every dB of image
frequency attenuation can reduce
interference by 1 dB. For example, the
Austrian ORF transmissions on
6155 kHz (OI) often suffer interference
from strong SSB transmitters in the
40 m band. The automatic preselector
completely solves this problem. The
effect is even more marked when try-
ing to pick out very weak amateur
transmissions from among the broad-
cast programmes: in this case a tuned
preamplifier is essential.

With a little extra effort a second pres-
election stage can be added for even
greater image rejection. Either a two-
stage tuneable bandpass filter can be
used or a further tuning circuit can be
added after the preamplifier, that is,
between Oil and the output connector.

11/2004 -skliiuur

61

Room Thermometer

i

Gregor Kleine

Just add an A/D converter and a few discrete LEDs to this
temperature sensor chip and you get a simple thermometer.
Th is application builds an accurate and stable thermometer
displaying room temperature with a resolution of 1 °C.

The MAX6610 from MAXIM is a rela-
tive new comer to the field of tempera-
ture sensing IC’s. The chip has a built-
in voltage reference and an analogue
output scaled to simplify integration
with an 3 or 10-bit A/D converter (see
textbox). A simple room thermometer
dees not usually require such precision
and we run a risk or being accused of
using a sledgehammer to crack a nut
but the chip is quite versatile and this

application provides a useful introduc-
tion to some of the features of the
device. For more information on this
device see the inset.

The complete room thermometer block
diagram is shown in Figure 1. The
MAX661Q precision temperature sen-
sor outputs an anaiogue signal that's
linearly proportional to temperature.
The signal is converted into a digital
value by the 8-bit MAXI 52 analogue to

digital (A/D) converter. Only five bits
of the output byte are used by the
decoder to light a single LED to indi-
cate room temperature. Finally two
monostables (monoflops) are used to
generate all the timing signals neces-
sary to control events in the circuit.
The first produces the conversion sig-
nal to the A-D converter while the sec-
ond controls a MOSFET in the power
supply line to maintain power to the

62

dchsr ckdredo - 1 1/2084

circuit during the measurement
process. After an adjustable period it
switches tire thermometer o fT It is only
necessary to press SI briefly to acti-
vate the circuit and the temperature
will be displayed for a few seconds.

On closer inspection

Figure 2 shows the complete circuit
diagram of the room thermometer. IC1
contains the temperature sensing ele-
ment and can be used in the Tempera-
ture range from -AO : C to -f- 125 X. The
sensor contains an on-board reference
so that it does not require any calibra-
tion and is designed to interface with
an analogue to digital (A-D) converter.
It outputs a reference voltage of
2.560 V from pin 5. Pin 4 is the ana-
logue TEMP output; the voltage level
at this pin is proportional to tempera-
ture. If an 8 -bit A-D converter is used
to produce a digital value each single
bit change corresponds to exactly 1 = C
temperature change. With a VREF of
2.560 V and an 8-bit A-D converter
each bit change of the output is equal
to an Input change of 10 mV. IC I pro-
duces an output signal with a charac-
teristic of 10 mV/K with a DC offset of
0.750 V. The voltage rp is given by:

^temp = 750 mV + T x 10 mV
[with T in X)

Table 1 shows the output horn an A-D
converter represented as decimal
(dec) hexadecimal (hex) and binary
(bin) values.

The sensor will be used at room tem-
peratures so it is not necessary to dis-
play the complete temperature range.
Table 1 shows that we only need to
look at the least significant five hits at

e&mi - it

Figure J . The room thermometer block diagram.

the output of the ADC if the displayed
temperature range is limited from
+5 X (0101 0000) to -f-36 r C (0111
1111). The codes between these tem-
peratures are not repeated. Table 2
lists the digital output values for tem-
peratures within this range.

Each degree is represented by a sin-
gle LED so a total of 32 LEDs are
required if a temperature range of
32 degrees is to be displayed. A 4 to
16 way decoder is used to decode bits
D1 to D4 from the output f IC2, The
least significant bit, DQ r is used to
switch either transistor T3 or T4 r these
drive two columns of eight LEDs, T4 is

conducting when DO output is low
while T3 conducts when DO is hiqh.
This arrangement effectively produces
a 5 to 32-way decoder function. Only
one of the green LEDs will be lit at any
one time so current limiting on each
column can be performed by a single
resistor (K6 and R7).

Although the decoding is available to
display a temperature range of 32 X
this can be reduced by simply omitting
any LEDs that are not required. The
circuit diagram shows just 15 LEDs fit-
ted to display a range from - 15 G to
-i-2S X, Any other range can be chosen
providing it falls within + 5 C to 36 0.

Table 1 , Correlation between temperature, sensor output voltage
and digitised measurement value.

Temperature

V TEMP

ADC del

^^hex

ADC bin

-40 X

0.350 V

35

23

0010 0011

-20 X

0.550 V

55

37

0011 0111

-10 X

0.650 V

65

41

0100 0001

-5 °C

0.700 V

70

46

01000110

0=C

0.750 V

75

46

oioo ion

+5 D C

0.800 V

80

50

0101 0000

+1 0 x

0.850 V

85

55

0101 0101

+15°C

0.900 V

90

5A

0101 1010

+20 X

0.950 V

95

5F

0101 1111

+25 X

1 .000 V

100

64

01100100

+30 X

1 ,050 V

105

69

0110 1001

+35 °C

L10QV

no

6E

0110 1110

+40 X

1.150 V

115

73

011 1 0011

+50 X

1.250 V

125

7D

0111 1101

+80 °C

1 .550 V

155

9B

iooi ion

+100 X

1.750 V

175

AF

loioini

+1 25 X

2.000 V

200

C8

1 IG0 1000

U/200-S - 1! titer dsctrorics

63

+3V

c

n

2F

.

UU

B E

BC850

c

B E

BC860

D

G D S

BSP171P

Figure 2 The circuit diagram showing iest points and voltage levels.

Table 2. Digitised temperature values within measurement range.

Temperature

VjEMP

ADC bin

T3 / T4

IC3

+5 X

0,800 V

0101 0000

T4

Q8

46 X

0.810 V

0101 0001

T3

Q8

47 X

0.820 V 'j

0101 0010

T4

Q9

48 X

0.830 V

0101 001 1

T3

Q9

...

...

417X

0.920 V

0101 1100

14

Q14 |

+ 18 X

0,930 V

0101 1101

T3

Q14

4l9X

0,940 V

0101 1110

T4

Q15

+20 'C

0.950 V

0101 1111

T3

Q15

421 X

0.960 V

0110 0000

14

GO

+22 °C

0.970 V

011 0 0001

T3

GO

+ 23 X

0,980 V

0110 0010

T4

G1

424 X

0.990 V

01 10 001 1

T3

QT

+25 3 C

1.000 V

0110 0100

T4

G2

+26 =C

1.010V

0110 0101

13

Q2

-***

. 4 .

...

—

431 X

| 1 .060 V ;

0110 1010

T4

G5

432 X

j 1 .070 V |

0110 1011

13

Q5

433 X

1 .080 V

0110 1100

14

Q6

434 X

1 .090 V

0110 1 101

T3

G6

435 X

1.100 V

ono ino

14

G7

+36 X

1.110 V

oho mi

T3

Q7

Temperature

sampling

The Iv!AX152 (IC2) 8-bit A-D converter
operating from a +3 V supply is used
to digitise the analogue output voltage
from IC1. A logic low on the read input
(RD, pin 8) and the chip select input
(CS T pin 13) configures IC2 to stand-
alone mode so that a pulse at the WR
(pin 6) input will cause the converter
to sample the analogue input voltage
and output its digital value. The digi-
tal data is valid approximately 2 ps
after the rising edge of the WR pulse.
Figure 3 shows the timing diagrams
corresponding to the n umb ered test
points on the circuit.

Pressing SI switches power to the cir-
cuit and starts the temperature meas-
uring process. The monoflop IC4.B sup-
plies the WR pulse to the A/D con-
verter but the start of this pulse is
delayed (Ti - 500 ps) by C3 and R9 to
allow the temperature sensor (IC1) to
stabilise before its output is sampled.
The WR pulse width (T2 = 1 us) is gov-
erned by RIO and C2. Toe conversion
time (T3) of IC2 is approximately 2 ps
so the output signals to the decoder
(IC3) and transistors T3/T4 will be sta-
ble after a total time of T1+T2-S-T3

64

debar derit allies - 13, 2004

Author profile

Gregor Kfeine (41) has been a development engineer with a well-
known Munich-based test equipment manufacturer for the past
10 years. He is currently designing signal generator equipment for
the RF spectrum up to 6 GHz used mainly for digital TV testing. He
graduated from Aachen Technical University in 1989. He has con-
tributed many articles both analogue and digital for Eiektor
Electronics in the past 20 years and has also penned many inform-
ative articles on communication technology including Digital TV,
ADR, ADSL, UMTS and Bluetooth.

(503 /is). This time period is so short
that any LED that may incorrectly light
during this period should go unnoticed.
The trigger for monoftop IC4.A is also
produced by the C3/R9 network during
power-up and generates a 3-second
pulse (pin 10) to switch transistor T2
and MOSFET TL The MQSFET is con-
nected in parallel to SI so the pushbut-
ton can be released and mono flop
1C 4, A ensures that the circuit will stay
powered for about 3 seconds.

Resistor R8 discharges the supply at
the end of the timing period to ensure
that the supply voltage falls to zero rel-
atively quickly when the circuit
switches off (Figure 3). At the end of
the 3-second measurement period the
inverting output of IC4.A (pin 9) will go
high and residual charge in the supply
is discharged through R8. This ensures
that the circuit will be ready to take

(J> FWRDWN f

WR

(3> DO

G>

Pin 9 r [C4.A

V

k

5J&H 1 * T?

Figure 3. Timing waveforms of the circuit test points.

another temperature reading again rel-
atively quickly after each measure-
ment cycle is completed.

A precision temperature sensor

The MAX661Q/MAX66 1 1 is a temperature sensor with a built-in
voltage reference. The digital output is conveniently scaled so that
when it Is connected to an 8-bil A/D convener the LSB of the out-
put Is equivalent to 1 C change of temperature. Wilh a 10-bit
A/D the output LSB is equal to a temperature change of 0.25 : C.
The reference output features a proprietary temperature-coefficient,
curvature-correction circuit and laser-trimmed thin film resistors that
result in a maximum temperature coefficient of 50 ppm/ ; C and an
initial accuracy of ±0.5 %. During normal operation the maximum
current consumption is 250 pA, this is reduced to 1 pA in shut-
down mode. The supply voltage range is 4.5 V to 5.5 V for the
MAX 66 1 1 ond 3,0 V to 5.5 V far the MAX6610,

The MAX6610/MAX661 1 reference output voltage can be used by
an external A/D converter It con supply a maximum of I mA with
a maximum loading capacitance of 1 pF, The reference voltage has
been chosen so that if an 8-bit A-D converter is used each step
value of the digital output represents a 1 O mV change of the ana-
logue input voltage. A 1 0-bit A-D converter will offer greater reso-
lution with each step in output representing 2,5 mV change of the
analogue input.

The analogue temperature output voltage is o linear function of the
chips die temperature:

Vjemp = 1 2 V + [FC X 1 6 mV/°Q [MAX661 1 }

Vtbwp = 075 V + (FC X 10 mV/T) [MAX6610)

The slope of the output voltage is equal to Ve^f/ 256 per r C
(16 mV/ C for the MAX661 1 and 10 mV/"C for the MAX6610),
The MA X661Q/MAX661 1 have an active low shutdown input
(5HDN), In this mode the reference voltage is pulled to ground
via a 1 50 kQ resistor ond the TEMP output is switched Info a
high imped ance s tate. Current consumption in this mode is less
than ] pA. SHDN should be connected ta Vq^ if this feature is
not needed.

If the MAX66 1 0/MAX66 1 ] Is used to measure the temperature of
on active component far example,

dose proximity to or on that
component. There is a good
thermo! path between the
sensing element In the chip
and its external pins, this
ensures that the device wilt
accurately measure the tem-
perature of the PCS on
which it is mounted.

The MAX66 1 0/MAX66 1 1
Is a low'pawer device ond
the self-healing effect pro-
duced by its own power dis-
sipation is negligibly small.

the chip must be mounted in

MAX66 ID

TEMPERATURE VOLTAGE
vs. TEMPERATURE

1 T/2004 - eldci:r dalrc.-'n

65

Although bistable relays boast significant advantages, their use
appears limited to niche applications, probably because their
practical use requires just a tad more attention to design details than
classic relays. Those days may be over soon with the introduction of
a special driver 1C from Quasinil (what's in a name?].

It appears that mast manufacturers of bistable relays hove
now succeeded in simplifying their products to the extent
that a demagnetising circuit is no longer required, and a
single switching signal does the job. In same cases it Is
possible to realise a driver circuit based on just a few dis-
crete components. In this article we show the intricacies
of bistable relay control, analyse a Few simple circuits,
mention the pros ond cons and, Finally, introduce the ded-
icated drivers type DRT5 and DRL5,

Pros and cons of bistable relays

Advantages

The main advantage of a bistable relay is evident from its
name: os soon as the relay has switched, it remains in

that position without consuming energy. This unique char-
acteristic has quite a few consequences: no current con-
sumption means less heat production, hence smaller
heatsinks while the (rechargeable) battery sees Its load
current much reduced. In some cases, the use of a
bistable relay allows o circuit to be simplified.

Disadvantages

- In general, the drive circuit is a little more complex than
with a classic relay. Depending on the type of bistable
relay, we need to either reverse the current Flow or
drive just one of the two coils. If we ore looking at
demagnetisation circuits, then it Is also necessary to
limit the current in compliance with the manufacturer's
specifications.

rlektor tJedronics - 1 1 /20O4

o

-To be able to benefit from the bistable character of the
relay the driver needs to have a riming element in the
form of an RC network or an 1C with a few passive
components around it.

- If we're after energy reduction only, then the bistable
character can work against us. To enable the relay to
toggle when the supply voltage drops, a small amount
of energy needs to be stored for use by the relay circuit
watching the supply level

C/asses of bistable relay

Bistable relay with two coils

This is the most commonly found type. Each coil is
responsible for a certain state of the relay. Some manu-
facturers indicate that series connection of the two
coils allows the relay to be controlled as if it had just
one coil.

Bistable relay with one coil

Less frequently seen, but very interesting if you are after
significant energy reductions in your circuit. The entire
coil is used to energize the contacts, as opposed to just
half the coil length in ihe case of a 2-coil relay. With
relays requiring a demagnetisation circuit, the demagneti-
sation has to be effected by means of a special resistor,
in general, reversing the current in a coil is a bit more dif-
ficult. Further on in this article, a special circuit is shown
for that purpose.

What to take into account

- To begin with, there's the minimum drive signal length,
which should not be confused with the relay's energis-
ing time. Were looking at the time needed to make

relay change over to its new position and remain in
that state. If this lime is specified in the datasheets, it is
usually called 'min. signal width' or 'pulse length'. Lack-
ing this information we may use the 'set time' and 'reset
time' specifications and add a safety margin.

- Minimum switching voltage: 'must operate voltage',
thus is the lowest voltage at which the relay is guaran-
teed to toggle. l\ is essential to check whether the drive
voltage reaches this level during the minimum pulse
duration.

- Maximum switching voltage: just as with a classic
relay, this voltage may not be exceeded.

-With regard to isolation and contact ratings, the same
applies as with traditional relays. If a relay is used as an
isolator for ihe sake of electrical safety in a circuit, then a
lower coil resistance results in better isolation properties.

- Distance to other relays: some manufacturers specify a
smallest distance to other relays in order to minimise
mutual disturbances.

-Maximum energising time: some relays do nor with-
stand continuous driving, having been optimised for the
duration of the switching pulse only With this type of

1 1/M4 - efekfer slcdroruG

Figure I. Relay
con fro I bayed ono
elastic contact* ho Id
configuration

relay, pay special attention to an accurately defined
switching pulse.

Some really thrifty control circuits

Relay drive with hold by way of switching con-
tacts (Figure I]

Principle

When a logic High level is applied, T1 will conduct and
current will How through coil 'SET'. As soon as the relay
pulls in, T1 blocks, cutting the relay coil current. When
ihe control signal goes logic Low, the same happens with
T2 and the 'RESET' coil.

Advantages

- F . Lr ro? aiqo rpnni i a Usn tefcvs' . b -j o n iko *0 1 r/ ■ ■

in the case of a malfunction or a slowly rising supply volt-
age.

- Suitable for a 5-V suppy.

- No capacitor required.

Disadvantages

- One relay contact is sacrificed for the control method.

- Isolation sets higher demands to board layout.

- Depending on the relay type used, the relay switching
time may be shorter than the prescribed minimum switch-
ing time, hence a risk of intermittent switching is created.

- The position of the contacts when powering off depends
on the decoy time of the supply voltage.

Adaptations

- Add energy buffer for swifch-aff phase.

- Add bridge rectifier For singlecoil variant.

- Delay switching contacts to increase switching time.

Relay drive with a series capacitor
(Figure 2}

Principle

At an input voltage of 1 2 V, Cl is charged, causing a
brief current through the coil so ihe relay toggles. Next,
the current remains limited to level determined by R1 . If
the input voltage drops abruptly to 0 V, the capacitor dls-

67

Figure 2. Relay
drive using a
ca pad for.

charges via the relay coil with a reversed current caus-
ing the relay to change to the reset stare.

Advantage

- Simple structure for applications with dearly defined
switching voltages.

Disadvantages

- Short pulses at the input may charge or discharge Cl
without the relay switching (for example, while the sup’
ply is switched on or off).

- Functions badly ot switching voltages of just 5 V.

Figure 3. Switching
with the aid of a
logic signal and a
DRT5.

Adaptations

- Schmitt trigger to be added when faced with slowly ri$~
ing or dropping supply voltages.

- Modification possible for 2-coil relays.

- Possibility to add an energy-wise control input.

The DRT5 driver

The Quasinil company offers o series of driver ICs specifi-
cally designed for driving bistable relays. The ICs are
best described with the aid of a few examples. In the first
of these, the basic operation ts explained, while the sec-
ond allows us to benefit from one of the most interesting
and worth while characteristics: low-energy drive. A third
example, finally, shows an example illustrating guaran-
teed switching levels.

Switching by logic level (Figure 3)

With V cc = 5 V and = 5 V the driver switches the
relay to the ON position (10 ms pulse). When Cde
returns to 0 V, the OFF state is switched on (20 ms pulse).
Take into account that the driver will attempt to switch the
relay to the OFF state when Vcc drops below about
3.7 V. The success of this operation is wholly dependent
on Vcc.

Figure 4. A simple
dusky CO wn 5 witch.

1

sound

C6A)43jT31S

<3X357 ■ t-l

Advantages

- Uncluttered, only one part needed.

- Suitable for 5-V powering,

- No capacitor required

Disadvantages

- Slightly lags the control signal (approx. 20 ms).

- V cc not allowed to exceed 5.5 V.

- If V cc drops too quickly, the relay may not make it to the
OFF state.

Adaptations

- Also works with 2-coil relays.

- For a simple method of supply voltage detection it is suf-
ficient Eo connect Cop and Cde (although in that cose the
supply voltage has to drop very slowly).

Dusk/dawn switch (Figure 4]

Principle

Direct current furnished by solar cells charges capacitor
C exi . When the voltage across C sxt exceeds about 4.4 V,
the relay will switch to ON. When the light intensity

68

elsklw etctfroflits - 1 t/£0D4

drops, ihe voltage across C drops also, At a level of

3 .7 V, the relay switches to OFF again.

Advantage

- No battery required.

Disadvantages

- Relatively long charge and discharge times (approx. 1
minute assuming two solar cells exposed to daylight).

- Large hysteresis: much more Sight is required to switch the
relay to ON than to OFF

Adaptations

- For poor light conditions, use solar cells that supply a
higher voltage. Prated ihe circuit with a low-drop voltage
regulator (IP2950CZ-5).

- Although the configuration may also be used with a 2-
coll relay, this option is less appealing because the capac-
itor becomes larger and with it the charge time,

- This type of circuit (typ. current consumption 20 mA) rep-
resents a cheap alternative to an oplocoupler input.
Depending on ihe source and ihe length of ihe cable ii
may be necessary to protect ihe driver's Cj e input.

- Employ a power relay if larger currents are to be
switched.

Controlling the mains supply in an USB device
(Figure 5)

When the PC is switched on, capacitor C 5Xt is charged
via a current limiting resistor. Once the capacitor voltage
has risen to 4.4 V, the relay follows the state of the USB
microcontroller, switching to ON, When the PC is
switched off, the relay returns It its initial state. In this
way, the supply in a peripheral device is switched syn-
chronously with the PC,

Advantage

- OFF state guaranteed when PC is switched off.
Disadvantages

- Slightly lags the control signal (approx. 20 ms).

- Supply voltage not fo exceed 5.5 V.

- Driver is relatively expensive.

Adaptations

- The relay in the example is o power relay, hence the
value of the capacitor. Depending on the power fo be
switched and the desired degree of isolation, a small
relay moy be chosen. A single-coil relay allows a smaller
capacitor to be used.

- lr the peripheral is to receive Its supply voltage together
with the PC, ihe microcontroller is not required. Simply
connect the 5 V of the USB connector fo and fit a
1 00-kQ resistor between Cde and ground.

Choice between DRT5 and DRL5

In the three above examples we discussed a few aspecis
of these new driver ICs, The choice of the type of driver
is closely related to the application and the relay to be

Figure 5 Swj'fo/img
c SB internal supply
on end oft

controlled. Below is o short discussion of the parameters
For these drivers and some advice to choose the right
type.

DRT or DRL: The DRL5 driver is suitable for use in
equipment with a supply or control voltage greater than
4,75 V. By contrast, the DRT5 moy be used at a lower
supply level storting at 4.4 V, This difference in supply
voltage is also relevant to applications using an external
capacitor.

Maximum current of the control input: This
parameter is especially important if the driver is used
without a power supply. In that case, capacitor Cext
needs to be charged from, say, a logic gate. Depending
on the allowed or desired control current we choose the
version with current limiting at 1 mA, 10 mA, 20 mA or
50 mA.

Control pulse length: This time has to exceed the
'minimum switching rime' required by the relay. Possible
times are 5, 10, 20, 30 or 50 ms. The OFF switching
pulse is twice as long, which allows the value of the
external capacitor fo be optimised if necessary.

Really useful!

Compared with existing solutions, the DRT5/DRL5 drivers
enable relays to be controlled with very low currents
Indeed, fake the switching characteristics of the relay
fully into account and guarantee the stale of the relay
when me equipment is switched off. Unfortunately the
down side of the new drivers is fheir relatively high cost.
Of course, we hope that the price will drop with volume
production. In any case, these new devices offer the elec-
tronics designer extra options in circuits where energy
consumption is o prime consideration, such as all newly
designed equipment powered by batteries or solar cells.

More information on these components may be
obtained from QuasiniPs internet site at

blip:/ /wvAY.quosi nil.com
and in particular this address

http:/ /20qp. Qvh.net/-qua5inil/drivers eno.htm

S7-

11/2004 - ekkiDf ilectTGir.yu

69

3 ? .

4 /

kitchen table

'Ear

Experience
an auditory illusion

GGLE

Rev. Thomas Scarborough

Th is month we invite ail fans of the 'kitchen table' series to
build a classic auditory illusion that has had psychologists and
neuroscientists puzzled for decades. Although we're
presenting a mini project built from a handful of cheap parts,
it will not fail to produce stunning effects and results.

This article is of the "zero -hardware /
huge background' variety and as such
fits perfectly in our "kitchen table’
series of mini projects aimed not only
at developing electronics skills but also
at triggering experimentation. This
month, a dead simple two -tone two-
phase oscillator produces a mind-bog-
gling effect (quite literally) — guaran-
teed to cause a good deal of wonder &

excitement in the physics and electron-
ics classroom.

In a nutshell

A two-tone "siren’ or octave switcher
plays into stereo headphones. To best
create the illusion you or your guinea
pig(s) are about to experience, the two
tones are separated by one octave (a

factor of two in frequency) and alter-
nate at about 4 Hz (250 ms). The siren is
played out of phase into each head-
phone.

According to biology textbooks, each
ear would hear a two -tone siren. How-
ever what you will actually perceive is
best described as a two-tone ping-
pong effect which seems to jump from
ear to ear. So what has our mind done

¥

70

ekktor dedrimln * 1

Figure L Just anoiher synchronised dual- tone oscillator, sure , but wait until you've
actually listened to the output on headphones .

with the missing tones? Are they
being suppressed or what? To add to
the confusion, just reverse headphones
and — depending on the person's

handedness — the tones are likely to
jump back to where they were before.
However, let's not get carried away
and first look at the electronics.

The eircui f

Figure 1 shows a circuit diagram
that’s low in confusion and rich in sim-
plicity. Two oscillators, IC1B and IC1.E
are buffered by IC1.C and IC1.D
respectively to play into stereo head-
phones, The frequency of the oscilla-
tors is being modified by switching R 2
and R 5 in or out of parallel with R4 and
R3. by means of T1 and T2. These two
FETs axe in turn being switched on
alternatively ('out of phase 1 ) by means
of slow square wave oscillator I Cl. F
and inverter IC1.A. Since the oscilla-
tion frequency of IC1J3 (IC1.E) doubles
as R2 (R5) is shunted Into circuit by T1
(T2), a regular jump of one octave is
achieved.

Although almost any power MOSFET
should he suitable for T1 and T2 : weVe
opted for a small- signal FET type
BS170 which also achieves clean
switching and a sufficiently low ‘on’
resistance in the drain- source juncrion.
In this circuit, you should aim at using
matched components for the tone fre-
quency determining devices, i.e., R2,
R4, C2 : R5, B3 and 03. to make sure the
tones played into each channel match
each other — the better the match, the
better the illusionary effect.

The circuit is powered from a stable 5-
VDC source like a lab supply or an

Dichotic Effect, Octave Illusion and Handedness

Are you still tnere? The illusion comprises on octave interval played high-low in one ear, and law- high in she other ear. It is Important to lis-
ten wiih headphones so that ine signal to each ear is well separated. Where do you hear the high pitch? Right-handers typically hear the
nigh pitch in the right ear and the lav/ pitch in the left ear For left-handers the results are mixed. For some, the illusion does not work well.
Nov/ reverse the headphones. Where do you hear the high pitch now? Most people hear it In the same ear as before. So, how did the hiqh
pitch switch channels? Well, it did not — Inis is the Illusion. High-low is played to each in opposite order, however, one ear hears

high tone - silence - high tone - silence

and the other

silence — low tone - silence - low tone

The psychoocoustic details of the illusion are still not fully
understood, but Diana Deutsch was inquisitive enough to dis-
cover the effect as early os in 1 974. Deufsch reported on her
research at the Spring ) 97 A Meeting of the Acoustical Society
and in Nature, 1974, 251, 307-309. Further investigations
into ihe basics of the octave illusion appeared the Journal of
Experimental Psychology and the Journal of the Acoustical
Society of America (JA5A).

It seems the illusion is correlated wiih what is known as brain
lateralization and that certain functions are localized to one
hemisphere or the other. It has also been discovered,, first by
Paul Broca (a French neurosurgeon) in the 1 800 s that right-
handed people hove language functions in the left brain hemi-
sphere and spatial functions. In the right hemisphere. Whereas
left-handed people can have the same lateralization as right-
handers or sometimes the opposite! More recent research
using PET scans indicates that brain lateralization is not so
simple and that the brain is a highly interconnected network
with many regions active or 'firing" when complex tasks ore
performed. Hopefully that excludes reading this article!

lm&: (I'so-ficri

1 1/?0O4 - efsklor Everts

71

COMPONENTS

LIST

Resistors:

R1 = 1 OOkQ
R2-R5 - 15kQ

Capacitors:

C1,C4 t C5 = IGpF 25V, radial

C2,C3 = 1 00 nF
C6 = 1 GOpF 25V radial

Semi con d actors :

T1 J2 = BS170
1C1 =40106

Miscellaneous:

PCS no. 0401 1 8-1 , available from The
PCBShop (EuroCircuits)

Figure 2. Component mounting plan of the small PCB designed for the project The copper track layout may be found on our
website (Free Downloads).

existing supply using a 7805 regulator
1C. Current consumption wOl be no
more than a few rmlhamps,

Construction

The circuit may be built on Veroboard
or t for a touch of sophistication, on the
printed circuit board shown in Fig-
ure 2. The copper track layout of the
board may be found on our website,
look for file no. 040118-1 in the Free
Downloads section, under month of

publication. Ready-made boards may
be ordered from The PCBShop (Enro-
Circuits).

Building up the board should not
pose insurmountable problems as
long as you stick closely to the parts
list and the component overlay. Polar-
ized components like the four elec-
trolytics, the two FFTs and the 40106
IC must, of course, be fitted the right
way around, not forgetting the 5 -volt
power supply wires!

Warning, This circuit is not approved
for medical use or research. When
using headphones, every precaution
should be taken to prevent ear damage
by excessive sound levels. The experi-
ments described in tills article should
not be carried out on persons suffering
from seizures or epilepsy.

3401! B-!)

Further reading

Musical Illusions and Paradoxes ,

Diana Deutsch (1995),

Postings on www. auditory. ora

-Zczi:

Forest Electronics - PIC and AVR ANSI C Compiler Products

FED's ANSI C Compiler for PIC or AVR processors

* Fully integrated editor with syntax highlighting, multiple pages etc.

* Full project support - include and manage multiple source files, simulator,
assembler files and notes ^comments within one project

* Fully integrated simulator and waveform analyser step from C line to C line,
or examine code in assembler form. View device pins using a logic analyser
application.

* Simulator supports LCD modules, keypad, buttons, LED s, displays,
analogue inputs, serial and asynchronous data.

* Designed to ANSI C standards

* PIC - Supports I8xxx. 16xxx, 12xxx series 14 and 16 bit core processors

* AVR - Supports standard and MEGA core processors

* Generates MPLAB/AVR Studio projects and source flies and completely
standard hex output files.

Prices from £45.00 - www.fored.co.uk for full details.

W/Z-C / AVIDICY

Drag and Drop rapid application development
using ANSI C for PIC and AVR

m-— -

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a] | '

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C language (WIZ- C for the PIC, AVIDICY for the AVR)

• Drag and drop your software component selections on to your design

• Included components support timers, serial interfaces, I2C, LCD, 7 Seg
displays, keypads, switches, port controls, many bus interfaces including 1IC
and Dallas iButton, AVR/PIC Hardware, and more.

• Connect software components to MCU pins by point & click

• Parameters set from drop down list boxes, check boxes, or text entry

• Links your code automatically into library events (e,g. Button Pressed, Byte
Received etc.)

« Automatically generates your base application including full
initialisation, interrupt handling and main program loop

■ The complete C Compiler and AVR Simulator programs are
integrated into AVIDICY - total editing 1 compilation /
assembly / simulation support in one program

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• Demonstration available from our web site

Prices from £50.00 - full details from www.fored.co.uk

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LYMfNGTON. Hampshire, S041 6DU.

01 590-68! 511 (Voice/Fax)

Full details from - www.fored.co.uk

Email -

“info@fored.co.uk"

72

slikivi sljdicaio - 1 1/2555

More information on www.elektor-electronics.co.uk

CD-ROM

Order now using the Order Form in
the Reeders Services section in this issue.

Elektor Electronics (Publishing)
ROL Box 190 * Tunbridge Wells TT
ENGLAND

Telephone +44 (0) 1580 200 657 *

TN5 7WY

Fax +44 (0) 1580 200 616

FAVOURITE PRODUCTS EVERY MONTH
IN THE ELEKTOR SHOP

A large collection of data-
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tricks and Internet links to
assorted robot constructions
and general technical Infor-
mation. All aspects of modern
robotics are covered, from

sensors to motors, mechanical
parts to microcontrollers, not forgetting
matching programming tools and libraries
for signal processing. £12.05 (USS 21.25)

Robotics

302 circuits

302 Circuits

ISBN 0905705-25-4
354 pages
£10.35 (USS 21.00)

304

CIRCUITS

304 Circuits

ISBN 0-905705-34-3
366 pages
£13.45 (USS 27,00)

305 Circuits

ISBN 0-905705-36-X
369 pages
£15.55 (USS 31.00)

series now!

Complete your 30x circuits

ECD

The ECD gives you easy
access to design data for over
5,700 ICs, more than 35.000
transistors, FETs t thyristors
and iriacs, just under 25,000
diodes and 1 ,800 optocoupiers.

All databank applications are
fully interactive, allowing
the user to add, edit and
complete component data. £12.95 (USS 22,90)

Toolbox 2

The second Toolbox CD-ROM
contains a vast collection of
carefully selected software
tools for, and information
about, microcontrollers.

This CD-ROM Is a must-have
for all electronics enthusiasts.

307

CIRCUITS

TT

cd-rom Audio Collection 2

A unique CD-ROM for the true audio lover,
containing no fewer than 75 audio designs from
elektor electronics magazine year volumes
2000 through 2004. £1 2,05 (USS 21 .25)

The 30x series of Summer Circuit compilation books have been
bestsellers for many years. You can use these books not only for
building the circuits
described, but also
as a treasure trove
of ideas or circuit
adaptions for your
own experiments.

Many readers have
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that new approach,
new concept, or
new circuit they
were looking for.

307 Circuits

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342 pages
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ISBN 0-905705-66-1
367 pages
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£12.05 (USS 21.25)

Gameboy Digital Sampling
Oscilloscope

The GBDSO is a plug-in module that turns
the popular Nintendo Gameboy Classic.
Pocket, Colour or Advanced into a versatile
dual-channel oscilloscope. An optional link to
a PC even allows measured oscillograms
to be viewed or stored on the PC, The GBDSO
rocked the electronics hobby world and that's
why we continue offering ready-bulEt
GBDSO modules (including the associated
PC software and the magazine articles).

£90.00 (USS 160.00)

David Daamen

Ready , ; Steady,

iody Fat Monitor Scales

iSensible people look after their health: no smoking,
moderate drinking, regular exercise and a healthy
diet. And of course you want to keep an eye on your
condition, for example with scales that also show
your body fat percentage. Perhaps you already have
one of these at home, but how do they work?

It wasn't that Jong ago when
the body weight was the most
important quantity when we
looked to see if we were over-
weight. These days your body
fat percentage is considered to
give a better indication of your
overall health. It tells you
something about the chances
of developing certain illnesses
when you are too fat, such as
heart and circulatory diseases,
certain types of cancer and
type-2 diabetes. Too little fat
can also give rise to problems,
especially in women. It can
affect the menstruation and
there is a greater chance oi

developing osteoporo-
sis (calcium defi-
ciency in bones).

It is generally
accepted that it is
sensible to keep
your percentage body
fat within certain limits.
Table 1 gives an overview of
the ideal values.

Determining the
body fat percentage

Good electronic scales use the
so-called bioelectrical imped-
ance analysis (BIA) to calcu-
late your body fat percentage.

With this
method the elec-
trical impedance Z of
the body is measured. This is
put into a formula along with
the length, of the 'conductor 1 , J,
{in this case your body) and
the resistivity of body tissue p:

TBW=pxi/Z

The
result
gives the
total volume
of water in your
body (TBW — total
body water).

When this is used along
with your weight, which
was measured at the same
time, a good estimate can be
made of your body fat percent-
age.

This method is widely used in
the medical world and nor-
mally uses electrodes on leads.

How to obtain the best results

You should first go to a specialist for an accurate body rot measure-
ment. This result can men be used to estimate how accurate your
body tot monitor scales are. There is little point in comparing your
score with that of others. You should only use the body lot monitor
to observe any changes. The following guidelines will help keep
any possible measurement errors as small [and constant) as possi-
ble:

-Take the measurement at a fixed time of the day.

- Take the measurement at the same ambient temperature, as the
temperature of the skin affects its conductivity.

- Moke sure that your feet are clean and dry. For ihe best result
you should use alcohol,

- One hour before every measurement you should drink an identi-
cal amount of water.

- Don't take a measurement directly after exercise. The perspiration
causes a lass of body fluids, which affects the measurement.

1 8-30 years

31 -40 years

> 40 years

Men 15%

17,5%

20 io 25 %

Women 25 %

27,5%

30 to 35 %

Tobk /. Mbs . 1 body hi p^rz&nfuge for differ* *nt age crot#» and gender.

74

dakfDF electnuia ■ il/W

which are connected to the
wrist and ankle, causing the
alternating measurement cur-
rent to flow through the whole
body. On body fat monitor
scales for use in the home we
have to make do with fixed
electrodes, which are under-
neath the feet.

total quantity of lean tissue
can now he made with the
help of several standardised
formulae. The amount of fatty
tissue is then calculated by
subtracting the weight of lean
tissue from the total body
weight.

j

Operation

BIA is based on the difference
in conductivity between fatty
and lean tissue in the body, A
constant alternating current
is fed through the body via
two electrodes, with one
placed underneath each foot.
Typical values are about
800 LlA and 50 kHz. The
resulting voltage is measured
using two different elec-
trodes, also placed under-
neath the feet (Figure 1). This
then allows us to calculate
the impedance of the body

The impedance of lean tissue,
which contains the most intra-
cellular fluids and electrolytes,
is lower than that of fatty tis-
sue. The measured impedance
therefore gives an indication of
the total volume of water in
the body. An estimate of the

Better accuracy

A more accurate result can be
achieved when you take into
account that tissue consists of
a combination of resistive and
capacitive conductors (Fig-
ure 2). The fluids inside the
body provide the resistive part
of the impedance, whereas cell
membranes have a capacitive
effect. Fat cells don't have cell
membranes, so they don't con-
tribute to the capacitive part
of the impedance.

When a wide -band signal is
used to measure the imped-
ance over a larger frequency
spectrum, a better distinction
can be made between the
contribution of extracellular
fluid (low frequencies) and
the impedance of all fluids
(higher frequencies). This
method is often called 'multi-
frequency EIA f , The Tefal

Figure 1. The impedance is measured using a constant current AC
source and four electrode s.

scales that we looked at in
the lab also operates accord-
ing to this principle.

Dependability

Although the BIA method is
based on known physical phe-
nomena, a few question marks
remain about its dependabil-
ity. For example, it assumes
that the body can be repre-
sented by a uniform cylinder
filled with tissues. You don't
have to be an expert to see
that this is not the case.

In general we can assume that
a simple setup {with elec-
trodes only connected to the

feet), which is used in uncon-
trolled conditions (as far as
temperature, hydration and ori-
entation of the body are con-
cerned). is unsuitable for fak-
ing absolute measurements.

Scales with a (multi-frequency)
BIA can be used to keep track
of changes in the body fat per-
centage over the long term.
More so when several ground
rules are followed when taking
the measurements (see inset).

.■=j] i

Figure 2. Body tissue con be represented by an RC equivalent.

1 I/20Q4 -efeklor shdrcda

75

start here

Battery Charging
©n ySB

Harry Baggen

Besides being handy for connecting and
disconnecting equipment while the comput-
er is running, USB includes a built-in supply
line that can provide a certain amount of
power to connected devices. That can be
handy for quickly charging a battery when
you can't find a real charger.

+5V

VEJU5 l> D+ NO GND

2 3 4 5

V

SERIES 8

SERIES MINI'S

1 - 1

f

Figure. L I wo common// used types of connect ors tor USB ports on
peripheral devices.

Nowadays every computer has
several USB ports, which have
taken aver the task formerly han-
dled by the RS232 bus. USB
cobles have different connectors
at each end lo prevent incorrect
connections. Figure 1 shows
types of device receptacles,
which are used in peripheral
equipment.

A USB connection has only four
lines, consisting of a data line in
each direction, a ground line,
and o supply line. The supply line
can be used to power peripheral
devices. The host device (o PC or
notebook computer) can source a
maximum of 500 mA from each
USB port. In USB terms, this is
called five unit loads. A hub with
its own power supply can provide
the same amount, but a bus-pow-
ered hub can provide only one
unit load per port. However, the
host will only provide a current of
500 mA after communication
with the connected USB device.
Immediately after a connection io
a USB device has been estab-
lished, the device cannot draw
more than 1 00 mA from the bus.
The host does no! decide whether
to allow the device to draw a
maximum current of 500 mA until
the identification phase ('enumer-

ation') has been completed.
Simple devices actually da not
need this enumeration, as long as
they ensure that they don't draw
more than 1 00 mA from the bus.
This can be exploited to simply
tap off a bit of current from o USB
port without causing the computer
any problems. Some examples
are mini-lamps and small fans
with USB cables, which are cur-
rently sold for use with notebook
computers. They 'misuse 1 the USB
part in exactly this manner.

This ] 00 mA can also be used to
charge a couple of batteries
when you don't have a real
charger to hand. That's very easy
to do, as can be seen from Fig-
ure 2. A diode and o resistor
are sufficient for charging two AA
(penlEght) or AAA cells connected
in series, either NiCd or NiMH.
It takes o while, since you're lim-
ited to a current of 1 00 mA, but
in on emergency it's a perfectly
good solution.

The component values for the
circuit assume that the supply
voltage on the USB line has o
nominal value of 5 V and a min-
imum value oF4.5 V. The diode
is tar protection, to prevent dam-
age to the USB port ir the bo tier-
ies are connected backwards.

Resistor Rl is dimensioned for a
current of approximately 90 mA
through the two NiCd or NiMH
cells. They can handle this for
days on end without becoming
overcharged, but it also means
that they can't be fully charged
In just a few hours. But once
again, this is Intended os a
makeshift solution.

Profession^ products

Various semiconductor manufac-
turers have now developed spe-
cial products far charging batter-
ies using a USB port. Some of
them are intended to be used for
charging lithium-ion batteries,
but that's not particularly Interest
mg for D1Y circuits, due to the
difficulty of obtaining that type
of battery.

Maxim has developed an idea
for powering a circuit from a sin-
gle NiMH cell shot con be
recharged from the USB port.
Figure 3 shows such o design
using two Maxim ICs. The
MAX 1692 (Ul) Is a DC/DC step-
down convener with current limit-
ing. It charges the NiMH penlight
cell (B I ) from the USB supply line
at a current of 300 to 400 mA.
Although the converter is not acti>
oily a true current source, it is

good enough (even with o
shorted cell) to effectively charge
the battery. The advantage of
using a DC/DC converter Is that
the current drown from the USB
port is only 150 mA when the
NiMH cell Is being charged at
current of 400 mA. This leaves
350 mA for directly powering the
connected device, in addition to
the charging current. The second
1C, U2, is o DC/DC boost con-
verter [MAXI 722) that transforms
the voltage from the single
rechargeable battery back to
3.3 V. When the battery is being
charged, this converter is dis-
abled and the output voltage Is
4.7 V (derived from the USB volt-
age via diode Dl). The draw-
back of the charging circuit In fig-
ure 3 is the absence of over-
charge protection; the user must
manually disconnect the circuit
from the USB port when the bat-
tery is fully charged.

Protection

The USB specifications do not
make any clearly defined state-
ments regarding protection of
USB ports. Same PC manufactur-
ers provide reliable electronic cur-
rent limiting for each port, while
others only provide simple Fuses
on ihe circuit board, ft Is thus pos-

76

skfct&r dtttrfoiJG - 11/2004

Vbus O

imooi

©

2x - +
HiCtWilMH ~

G'lO

a

C+S37-<-12

Figure 2. Two NiCd or NiMH batteries connected in series con easily he
charged using a diode and a resistor.

txz .'*-- J

Figure 3. This Maxim design uie; two DC/DC converters to charge a
NiMH cell and power the connected circuit with a supply voltage of of

least 3.3 V.

+9V...+ 15V

©

see text

040154 - 11

sible la 'blow up r a USB port if
you try to draw too much current
from it. National Semiconductor
has developed a special 1C that
protects host ports against exces-
sive output currents. The black
diagram of this 1C (LM3525) is
shown in Figure 4. As scon as
the output voltage drops more
than 1 00 mV below rhe Input sup-
ply voltage, the output current is
limited to 1 A by the built-in
power FET. Even wiih simple
charging circuits such as the one
shown in Figure 1, it's o good

idea to include an 1M3525
between the USB connector and
the charging circuit, in order to
prevent damage to the PC or
notebook computer.

H4QT7^1:

#

LM3525

30-mA

LED Dimmer

Eberhard Houg

If you've ever tried dimming a
LED with a simple potentiometer,
you know that ihe approach does
not work very well. Just as with
ordinary diodes, the voltoge^ur-
reni characteristic of LEDs is far
from linear The result — depend-
ing on the potentiometer setting
the LED brightness will hardly
ch ange most or ihe time as the
poi is turned and a sudden varia-
tion ot the end.

The best method to tockle this
problem is to power the LED from
a current source with zero to
1 00"o adjustment range. The cir-
cuit shown here is an example.

A low-current LED [Dl] is used to
generate a reference voltage
that's first buffered by one half oF
an LM358. The actual current
source that powers the LED(s) is
built around the second opornp
in the chip.

The potentiometer allows the out-
put current to be adjusted, with
R2 acting as a current sense, the
resistor dropping ihe same volt-
age os the one obtained from the
pot. Using Ohm's law we find

that the maximum current through
R2 amounts to about 29 mA
- 1 .6 V / 56 O).

IF necessary, the current may be
adapted 1o suit other LED tyaes
for example, 20 mA is obtained
wiih R2 - 82 £2 and 10 mA at
R2 = 150Q.

It Is also possible to connect sev-
eral LEDs in series. The total volt-
age available for the LEDs is
determined by the voltage drop
across series resistor and the
opornp, and, of course, the sup-
ply voltage. In this way, ihe high-
est number of LEDs may be found
from LA ?=[) i c ^i — —5.1 V. In

principle, it Is possible to increase
the supply voltage to 30 V In
order to connect even more LEDs
in series. This does, however, call
For the value of series resistor R1 to
be increased to prevent overload-
ing the lowcurrent LED used In
the voltage reference.

IF you intend to experiment with
larger numbers of LEDs (soy, in
arrays) then the maximum load-
ing of the opomps becomes on
Issue. The DIP version of the
LM358 may dissipate up io
830 niW. The power, P, Is calc lf-
lated from P = -1.6 —

^±D,tafn5 ^ ^LED.mux

Figure 4, The Notional Semiconductor LM 3525 provides a simple soh w
tion for protecting USB host ports against overloads.

l!/2&D4-ddctor demerits

77

Servicing Your Complete: Prototype Needs

R 1

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lectr tes

Flash Microcontroller

Starter Kit

Elektor Hardware & Software

Contents of Starter Kit:

89S8252 Flash Microcontroller board (ready-assembled and tested
PGB), 300-mA mains adapter serial cable for COM port an a software
bundle on CD-ROM. Article compilation on CD-ROM:

* 89S8252 Flash Microcontroller Board (December 2001)

* Microcontroller Basics Course parts 1-6 (January through June 2002)

* Microcontroller Basics FAQ (September 2002)

* Port Line and ADC Extension for 89S8252 Flash Micro Board
(December 2002)

* Chess Computer using the Flash Micro Board,

Order now using the Order Form

e

issue.

Elektor Ejectfouigs (Publishing) P.O. Box 190
Tunbridge Wells TN5 7WY England
Telephone +44 (0) 1580 200 657
Fax +44 (0) 1580 200 616

See also

www.elektor-electronics.co.uk

78

dsViof ekriioriits-ll/MOt

As of She September 2004 issue Guizzaway is □ regular feature in Elektor Elec-
tronics. The problems to solve are supplied by Professor Martin Ohsmonn of
Aachen Technical University.

Assuming ideal components are being used and LI = 12 = 2 mH, inductor LI ini-
tially (t < 0) passes a current 1 1 (0) = 1 A while for L2 12(0) = 0, At instant ! = 0 switch
S is opened*

How much energy
Wp is converted
into heat by resi s-
tor R if you wait
infinitely long?

W R =±L 1 *lj(0) = lmWs

the likely solution

for ideal, lossless inductors is

not correct in this case.

Hint 2;

Make use of 'dual noiions' like

voltage <=> current
capacitor « inductor
resistance conductivity
charge retention <=* ?
electrical energy magnetic energy
series network c= parallel network
switch open = switch closed
perfect conductivity *=? perfect isolation

Solution to the
September 2004 problem

[p. 80 , resistance measured in an infinite array)

Inject c current of 1 mA into one test node; call if
node A, By symmetry the current wifi divide
equally among the 4 resistors terminating at node
A; i.e, 0.25 mA per resistor. Extract a current of
1 mA (the return current) from the test node adjo-
cent to node A; call it node B. Again by symmetry,
the current converges In equal value 5 from each
of the 4 resistors terminating at node B, i.e.
0.25 mA per resi star.

Using superposition and observing she current
directions, the injected and extracted currents
flowing in the resistor linking nodes A & B are

algebraically summed, adding up to 0.5 mA

through ft A B-

A resistance of 1 IcH x 0*5 mA gives V AS = 0.5 V.
For on injected/ extracted current of I mA,

= 500 mV/1 mA = 500 Q.

and win*

Send in the best answer to this
month's Quizz'away question
and win this

DRM Receiver Board

worth £85 (www. a k-mod uhbus.de).

All answers are processed by Marlin
Ohsmonn in cooperation with Elektor edi-
torial staff. Results are not open to discus-
sion or correspondence and a lucky winner
is drawn in cose of several correct answers.

Qwizz'away conditions

Please send your answer to this month 's
Quizz away problem by email fax or letter to:

Quizz'away, Elektor Electronics, FQ Box 190 ,
funfandge Wells JN5 7WY, England .

Fax (+44) (0)1580 200616.

Email editQr@elektor-electronics-co.uk ,
subject: * quizzaway 1 1-04

The closing date is 22 November 2004

(solution published in January 2005 issue).
The outcome of the quiz is final. The quiz is not
open fo employees of Segment by., its business
partners and/or associated publishing houses.

I1/M4 ■ defter dechorics

79

LINKS

To book your website space contact Bernard Hubbard

Tel

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Fax: 0044 (0)1 242 226626

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Full range of books, back issues on CD

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Developer and manufacturer of

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NET

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World-class site: Your magazine project
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Prompt service.

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AlLrl.S&iL

PROMOTE YOUR WEBSITE HERE

Elektor Electronics have a feature to help customers
to promote their websites. Net Links - a permanent
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■ For just £1 20 + VAT t£lU.9G per issue for eleven
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ELECTRONIC

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Onfy one magazine rests its projects and
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Contact:

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11 2084 -elakfQrelertuHifcs

31

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31 JH

No, 331 APRIL 2004

Drop -In Micro centre Iter Board

@ 020145-1 FCB

S^§

1520

@ 920*45-1 1 Kf'. ssmf& preset as

430

5.55

Pandora’s Sound s Music Box

j§ §304024 FCE

10-60

15 75

g ii 3JM02-1 * Kji sc-.rcs ^d hi* code fSss

490

8.65

EB04 02-41 Pffil 67E/1P p-i-p -m -r2

20-55

36.40

VHF'Lnw Explorer

@ D20416-1 PCS

6-S9

15.5-3

No. 330 MARCH 2004

Build Your Own DRM Receiver

.3 020755-1 PCS

9-10

15.10

® 030365-11 Dvi.i-L DF!V: t J£- p^znTi

4-93

3.65

Code Look

@ 020434-1 FCB

960

16.95

@ 020434-1 1 Disk, source A bet csde fifes

4-93

8 65

02D4344 1 Pel 6F84A4 R pro^anrr»M

14-70

26.00

Hands-on CPLDs (2J

@ 03H052-1 PCS

6^0

15.75

@ 030052-11 S^TAais

4-93

3.65

03005241 5P.W 1 2S5LCS4 1 5. proQ^T.Tigc

3340

59,10

Mullicbannel Failsafe for Radio Cantralled Models

@ 020162-1 1 Dfe.L =: cc-:^ f7e

490

3.65

02038241 418-9052-24 JL prc^s“Ted

a-70

1540

MulLifunctian Frequency Meter

© §30136-1 PCS

9-35

1655

a 0 30 i 35- 1 1 0 fe.‘_ preset sstw

4'90

8.65

D 301 3 641 AT30S23T 3-1 C?€ . pmgfsuni&d

7^95

14 05

No. 329 FEBRUARY 2004

Digital Alarm Clock

x: 03008641 DsL F : ,C aid fs< cods

4^t

B.65

03309641 F3CT6FB4-01 p. pfo^rsnsiEd

1520

26.^3

iAccess

g -7Z0 1 63- i 1 D7 '. til 5-0 JC5 d l enSnd sdIta- ej=

7*50

1330

0201 6341 ATo 558252-1 IK . pfogismma*

13-K3

24 60

Simple 12-to-23DV Power Inverter

■g 020435-1 PCs

8-50

1505

Touch-conlmEJed Switch

,§ 03021441 [fe- PiC^-teccc^

49fl

365

03021 441 FrCt 2C505A9J 3 C-3.

^15

10.93

Multi Programmer

m 027238-1 PCS

E-30

15.60

x 020336-11

P ii r™ !VcT 2 fit K-L'CS s-:4r

4- 99

865

Pocket Pong

a 030320-11

Dk>:. RCsdt/rsre

4^0

3.6.5

Rail Rnuler

.1. l:-j4D2--

PCB

10-SO

19.15

@ 03045341

2- ;>■ FiC c= PC ri-rT.Vi-c

4*90

8.65

03O40.3-; 1

P Cl 6? 577-25 ? tx-z'i -- i-d

2145

37.55

Smoclh Operator

e 03 : 109-11 ffelL Pffi 5d!*ara

4-00

5.55

0 3:>21-4 ■

Pffi16F044Of3 H'og r LTTrjj

1470

26.00

No. 332 MAY 2004
Design Your Own iC

@ 03(6854 PCB 15 65 27.70

No. 328 JANUARY 2004
64-K 80C55Z Flash Board

%■ 030042-1 PC3

9-35

16 55

x Q3-0Q42-11 D r ^L mi5C.

4-^3

6.65

039342-21 29P01D, prasramaiEd

10-09

17.70

03.0242-31 C4L 1 EVc 015CR prlfe^rr^j

310

10 59

Climate Logger

m 030076-1 pea

7-75

13.70

@ G 30S7 5-11 D,sL ViViEkr a s seta. *5

4 50

8 65

FMS Flight Simulator Encoder

% §30036-1 FCB

1020

13.05

§30066-41 flTLPCTGjFBH, pm^r^d

17i^

50.15

LED Reulefle

§ 0301 68-1 PlB

17*50

31 21

% 035! 6-3-1 ‘ EHs? S'i ins and is:*, if. s

490

5.65

t

82

dekier efadiortks- M/2G04

r

US s

£

uss

03016841 59C2C6M2FC.

805

14.25

@010202-11 Ds K V7 4 do a s se ta.

4-93

8.65

Multi-event Alarm Cluck

5152524 2 -rGi6-.6 T 4-2C ? a oc - , nsd

53-55

41.65

g C r 2&’-24-‘l Ds* C {source 1 f:E« ffes

490

E.E5

Polyphonic Oaorhell

020304-41 ATS9C2B51-12PC, fcogiannied

fi-10

10.60

3 02655441 pjp^ softwi'i

4-90

8.65

Stepper Motors Uncovered

0703544 1 PSCl FTE4A-1 0 F prc-^ST^-id

14 45

25.55

0 20 1 274 1 m 1 £-9373 -29 BP

19-10

33.80

Precision Measurement Central

No. 327 DECEMBER 2003

030060-91 Rti d,-E5i^ tC" o :f4dd brard

ValvE PreamplitiEr (1)

OTO

11250

FM Remole Control Transmitter & Receiver

g 020353-1 PC3, STnp ’“-c> DdiTd

11-55

20.40

@ 034044-1 PCS

10-20

1SJ05

5 G2 03-53- 2 PCS. pa*Er suppSy bcErd

11 40

20.20

LED Christmas Decoration

,© 0263S3-3 PCB-ltltMSTd

10-10

1760

@ 030157-1 PCS

P87LPC76X Programmer

755

13.35

No. 323 JULY /AUGUST 2003

@ 03- 03 13-11 Dv:V p ■ e el a frwsre

490

6.65

Add a Sparkle

Project Timekeeper

4 020293-11 D : HEX s>J saais Hies

4-90

8.65

© 02035-0-1 1 D4>- source & ofc^ci cod3 f.J»

4-90

5.65

02029341 F>C12C5&5A-G4-SL r progBrnr^J

7-40

13,10

0203504 1 P,C 1 tf84 - 1 G-R proprajiSEnsd

13-15

2355

AT90S2313 Programmer

Stepper Motors Uncovered (2)

@ 034636-1 PCS

94>5

16,00

@ 020127-11 Disk. . SSfcTC a fie

490

S.65

Hard Disk Selector

Universal Clock GEnerator

S 834050-1 PCO

0-45

16.75

1 6203 95-t 1 D £■-. t 4 etc ? f >

490

8,65

Mini Running Text Display

Wireless HS232 Link

,g 020385-11 CsTk StULTES COCfe

4Ki

865

@ (J302C4-1 PCS

S7Q

15.40

Mini Test Chart Generator

■@ 0-i 04 03-1 1 Ds >l RC sc.'L.r c : -3=

4-90

8,65

No. 326 NOVEMBER 2003

Programming Tout for ATtmylS

PrEcisinn Measurement Cenlral

@ 0390^1 PC 6

7-55

13.35

© 030060-4 FC3

3-70

15.40

© 030320-11 CE^- project s^twere

Quad Bridge Car Amp

4 '90

8.65

No, 326 NOVEMBER 2003

© 034030-1 PCS

3-70

15,35

Rev Counter for R C Models

Remote Light Control with Dimmer

@ G24H1-1 FC3

17-50

31.00

& 828337-1 1 Disk. HEX. et-J ezkjes ftes

4-9Q

665

024111-11 D.^k. scons ssa hex cafe

02411141 69C2Q51-12PC, piBeraranea

4- 90

5- 53

a, si

15 65

0203.37^1 ATB8C20SI-12. pw^rarened

No. 322 JUNE 2003

625

11. 05

Running Text Display

@ 020497- ’ ’ 04, sujre* sod hs* rads

4-90

3,65

AVR TV Tennis

USB Analogue Converter

@ 030028-1 v^n F€i

6-70

15.40

M 020374-1 pcs

7-65

13.50

g O3082&-2 Pj^itaitfiin PCS

6-60

1525

% 020374-1 t Oik, tes cosfe an d V.' n : ; : ? 4 u re

4-30

8.65

© 0-3 "026-1 1 L' Ev kVR SDL! ■ L 5 C&3 i

4-ffi

855

02037441 RCieC765 r pro^mmed

13 25

23.45

03602541 ATS0S515, pro^wr/red

Electronic Knotted Handkerchief

15-20

2690

No. 325 OCTOBER 2003

© 020203-11 Di- PC ssd con^t^ seJtffara

490

5.65

DDS RF Signal Generator

02030841 AT90S23T3-ltffC r

12-60

22.30

@ 02 G2G9 4? PC 5 . : 5 a p-pi

12-in

21.45

Low-Cost LCD Controller (2}

03 02594 1 AT90585T 5 8FC, p/ugnsivred

30-55

54,05

a 020114-1 PCS

e-70

15,35

Minimalist Induclicn-Ba lance Metal Detector

g 0201 t 4-1 1 IKsx. prc.;=ct soil ware

4-90

3.65

@ 02029*34 PCS

a -55

15.65

Right LlgM Central

Xilinr PROM Programmer

© 020115-11 Efi^het and source code

490

£.55

I Q1D109-"

4-SQ

8.65

020 n >4 i 4T&IB231 3-1 OK. Tri

Universal XA Oevelopmenl Board

12-85

22.75

No* 324 SEPTEMBER 2003

ATV Picture Generator

@ 020295-11 tfei, sura & ha code fes
020236-? 1 AT50S051S4FC. pragszTfnjd
0202 6 5-4 2 AT 90 S12D>1 2FC. £-:c^t2?T^

DTMF Remote Telephone Switch

@ 020294-1 P€B
1 3202244 1 t project ~ aft* ^

020294-41 PiCl6F3AV20 H pi^r^x^

LC Display wilh I2C Bus

@ D30O5O-2 F€B

4-90 3.65

15-20 26.50

13- &0 24,60

11-65 2060

490 fi.65

14- 70 25.00

7-35 13, CO

g 01 0103-1 PCS

© 01 01 03-i 1 Dis# , Gil -: ;-i r. EPF D V, te * f ?s . XftflEV
Olf 103-21 EPSOM O. 27C25&90. jMBgnanfr^

0 1 0 1 03-22 £Frt Q-J.1 K3 , 27C2 56-90, Djisrrar*d
010103-31 GAL 1EY3, pfD3rariCT£d

No. 321 MAY 20 03

Countdown Timer

g 020295-11 Bfct ehuies arid f©t code
020295-4 1 AT933 1 290 . prcoizir

1-3-20 2135

490 6.65

IQ-QO 17,70

1?H>3 17.70

430 150

4-93 3,55

13-ffl 24.60

PIGPfog 2003

@ 010 202- I =

9-05 16.00

P/oriucfs fm older projects, (if ai milablej may be found an our web site

ftttp:flwww>etektor-electroni£s, co.uk

' ' /

-

: 1 jci . . z. £i S

-

/

, i~ t,

i n

■

9n;xrsrj Orsuli ••. - -

Double Sided, 1*6 mm,
Plated Through,

Green Solder mask,

Hot Air Level,

1 White Legend*

Price including
tooling + plotting + VAT

I1/20D4 - dsklor eledronks

sneak preview

Ultrasonic Distance Meter & Liquid Level Gauge

When ii comes to measuring relatively short distances, room and
object sizes electronic instruments have a number of advantages
over traditional fools [ike (he yardstick.

The circuit we've in mind is aha suitable For liquid level measure-
ments in tanks and containers.

DECEMBER 2004 BUMPER CHRISTMAS ISSUE

Alongside 20-odd regular-size articles and columns the December 2004 issue
will contain a collection of about 40 small circuits and design tips
fa get you through the Christmas holidays.

Do not miss this extra-thick issue — place an order now with your newsagent!

Home Bus Systems
A number of processes In and aroun d the
home fend themselves to automation. However,
on infrastructure is required before you can
connect equipment and sensors to a central
PC. In this article we describe a number of
existing (professional) bus systems and reveal
options available for home automation.

Also*..

Home Compliant \ l C Bus
System, Frequency Meter,
The Road io Delphi,

XI 0 Bus System,
Telephone Amplifier,
Gpamp Tester,

R/C Mode! Finder.

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□ascription

Price each Qty. Total Order Code

cd-rom Audio Collection 2

12.05

CD-ROM Robotics

Z 12.05

2x3O0W Amplifier board
with SMDs pre-fitted

£ 34.50

Micro Web Server:

MSC 1210 board

E 69.00

Network extension

E 41.95

Combined package

E 103.50

Flash Microcontroller Starter Kit

Z 69.00

GBDSO Board

£ 90.00

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E n g Sa rid. January 2004

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FROM JANUARY 2004 ISSUE

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January 2004

POWER AMPLIFIER
19 INCH STEREO A

-ACTIVE CROSS/OVERS,

Try us for Tivoli Radio

Hyc-l: Radio 1 Just £91 ,95 C&Tiage £3 CO

M ELECTROS 1C 5

OMP MOS-FET POWER AMPLIFIERS

HIGH POWER, TWO CHANNEL 19 INCH RACK

10,000*5
SOLD
TO PRO
USERS

THE RENOWNED MXF SERIES OF POWER AMPLIFIERS

FOUR MODELS:- MXF2G0 (100W + 1QGYV) MXF4GC (200 W + 200 WJ

MXF6Q0 (300W + 300W) MXF90Q (45QW + 45QW)

Epea.<er

protector)

USED TriF WORLD OVER EN CLUBS PUBS. CK9IAS, DISCOS ETC

SLZESi-

MXF200 W19 T Dir H37T
MXF400 W19 D12‘ H57* m
MXF60QW19’ D1 3” H57^
MXF900 W19" D14* H57/

2U

3U

3U"

3U

PRICES:- MXF200 £175. 00 MXF400 £233.85
MXF600 £329.00 MXF900 £449.15
SPECIALIST CARRIER DEL £12.50 Each

ABSOLUTE HIGH END CLASS D AMPLIFIER

The OMP MFD600 can be used as a stand alone
monoblock amplifier or fitted into existing loudspeakers to
make them active

Compact design due to switch mode RS.U .
90% Efficient high switching frequency
Small size , fits in a 110mm x 92mm opening
Neutrik - Combi input balanced / unbalanced
Output fully protected
Status LEDS - Presence / Clip / Profecf
600W/2 Ohm - 500W/4 Ohm - 3Q0W/QOhm
All powers in RMS.

Volume control. Input sensitivity 775mV
Freq. Response 2Hz-20kHz

Light weight 3kg

For further information please
look at our website at
VA.vw.bkelec.com and click on
the modules and hybrids button

Special quantity pricing
and customised artwork for
OEM’s.

Stunning performance
Audiophile Quality

Price £281 .1 2 Inc Vat Each or
£499.00 Per Pair when quot-
ing this advert

Carriage UK Mainland Only £B,00

# m

efli -St" -Mi* ''-1 ’ L ‘* T
= < rtaro
-at: 3

BASS AMPLIFIER PANELS

The BSB Range of Sub Bass Antp-isrs coasisls of 5
panels with pmverDutpyts of 59W to 5Q0W to sufl mo&
of the DIY enthusiasts needs. AL parish sis airtight and
come equipped with both high ard lew te. d Inputs iVfdi
separate gain confrtrfs, frequency adjust and 0-1 HO
Deg. contfoous phase control adjustment A full
connection lead pack Lndudsd

XLS 200 Subwoofer Sytem

Save £100 T s buying factory direct

ALL POWER RATINGS ARE R.M.S. INTO 4 OHMS. WITH BOTH CHANNELS DRIVEN

FEATURES:- * Independent power supplies with two toroidal transformers
* Twin LE.D. Vu Meters 1 Level controte ' Illuminated on-off switch * Jack / XLR inputs *

[We have combined the famous Reeder XLS 10
| with our renowned BSBP20OM sub bass panel
| In a compact MDF cabinet that measures only
D390 x H295 x H295 to produce a Iroly
awesome sub woofer system suitable for both
Hi-Fi and A\ use.

- >*. a r ■ -

Features:- ’High and tow le.e inputs ^Frequsirov
adjust ’ContlncLES phase control ’2 DOW RMS
'Separate centre! of high and gv. leva! gs'n
'Automatic Speaker Protection. Comes
comp-ete v*ith mains !ead 5m stereo phono
lead. 10m High level lead and Spikes

Available in Sliver or Black, for further
Information please look on our website at
http://www.bkeEec.com

£279.00 Each plus £8,00 carnage within the UK mainland. International carriage charges
to Germany, France, Belgium. Luxebourg and Holland at only £1600 per XLS200

MXF120QD 60 OW Per Channel Class D

Price:- 469.95 Inc. V.A.T.
Carriage £8.00

file MXF12O0O fe not oniy a must for PA end Disco use. but Is stunning performance fends
feel reacSy to Stucco snd FBgh Paw AV Cnema instate, i is sfeci sulati'e for E-O-End Hj-R use.
Can be driven c roci from a CD player and has balanced XLR input, unbalanced Jack input.

The latest In higlvtedi Class D amplifiers coupled to two iixiepafidant switidvrocde power
supples. Front Panel:- Presence Led's, Clip Led's. Independent volume controls and
pov.'er On' Oft switch with coot blue Eliminated surrounds. Rear Panel:- Matos IEC input
Neutrik Sees ken outputs and Neutrik Combi inputs

Golf Ball Height

Specification:- Output power 60GW RMS into 2 Ohm, 50OW RMS
r>io - Ohm. 300','. RMS me S Ohm Freouerc 1 , response 2 Hz to

22kHz. Input sensiljviy 775m V, Input fmp.7.5k Ohms, T.H.D. 0.1

: .

'V,

S N SddS, P ower Supply 230V AC 50Hz, Switch - r: Fret -50kHz,
Weight 8.0kg, Size H44 x W482 x 1376mm

OMP MOS-FET POWER AMPLIFIER MODULES

SUPPL ED ready
bl.lt and tested

These modnSes now enjoy a wotid-vwfe r^x^on for Quafry, reSatiayarci pcribfmsiee s a reafeSc price. ftxr
nni-i 5T- £p. j si;=ziii "J3 tji= cf tjig frofef-" " 5 fd hoctpy marked M. Irdus^y. fmir r* IfE^lcneri^
and tiH efc. When compamg press. NX>TE &st ai modefe hdkide toroiM pev.e - supply, rrssrs hsa’sr-k.
gLss fore p.C.S end ousts i to pawc a compefoie W m^r. A* medsfe are open 5«J short proof

THOUSANDS OF MODULES PURCHASED BY PROFESSIONAL USERS

Model Shown:- BSSP200

MODEL

PRICE

IMP.

* Please

BSBP5G

£89.95

8 Ohm

State 4

B5BP1G0

£117.44

w 4/8 Ohm

or 8 Ohm

SSBP2G0

£149.50

Mf8 Ohm

when

BSBP300

£184.50

4 Ohm

ordering

BSBP5G0

£219.50

4 Ohm

SPECIFICATIONS:-* POWER 20DW RPAS @ 4 or 8 OHMS 'FREQ RESP, 10Hz 15KHz
-3dB * DAMPING FACTOR >200 ' DISTORTION 0.05% ' S/N A WEIGHTED >1G0dB '
SUPPLY 230V A C 'WEIGHT S.OKg * SJZE H254 X W254 X D95mm

THERE ARE 2 VERSIONS OF THE ABOVE PANEL AVAILABLE :-BSB2Q0/8
8 OH M VERSION BS B 200 ,44 OHM VERSION CHECK WEBS PE FO R PAN ELS U P TO 3^>0W

OMP/MF 100 Mos-Fet Oufout Po', l i 5 er 110 wafls
R.M.S. into 4 ohms free jency response 1Hz|-
100kHz -3dB. Damping Factor >300 r Slew Rate
4bVfuS, T.H.D. Iypicar0.002^, Input SensitivBy
500mV, S.N.R, llOdB. Size 300 x 123 x GOmrii.
Price:- £43.85 + £4,00 P&P

OMP/MF 200 Mos-Fet Output Power 200 wafe
R.M.S J. into 4 ohma.firequency response 1Hz -
lODStffe -3a B. Damping Factor >360]fBtew-Rate
50V/ uS, T.H.D. typscarD.001%. Inpift -Sensitfviy
c-_Lrr-V. S.N.R IIOdB. S : ze 3“ • 155 x iGOmm
Pnce:- £67.35 + £4.00 P&P

OMP/MF 300 Mos-Fet Output Power 309 watts
R.M.S. intp 4 ohm s T fr ecm e n cy respense 1Hz -
100kHz -3dB Damping Factor >300, Slew Rate
GOVliS. l.H.D. lypcarO.Gul^L Input Sensitivity
SfomU S.N.R. ITOdB. Size 330 x 175 x 100mm.
Price:- £84,75 + £5.00 P&P

SBBODanB

=3^3=

QMP/ME 450 Mos-Fet Output Power 450 ivatts
R.M.S. into 4 Ohma.frequency response 1Hz -
100kHz -3d&rOampfog Factor >3QD. Slew Rate
75V/uS, T.H.D. typical 0,001%; In out Sensitrvfty
SOOfriV. S.N.R.' HOdB. Fan Coo'ed, DC.
LoixJs peaks r Protect] an, 2 Second Anti Thump
Delay. Size 385 x 2 1C x TG5mm.

j Price:- £137. as + £0.00 P&P L

OSJPJHnJS^nS^EnJutpu! F^crwer IMq .vans
R.M.S. into 2r ohms. frecjusncy response 1Hz -
100kHz -3dB. Damping Factor >309, Slew Rate
75 VjuS, T.H.D. tymeaf 0.001 Input SensItL r,
50DmV S.N.R/ tIOdB r Fan Coaled, D.&
Loud s a sake r Protection,— 2- ; Second Anti Thump
Delay. Size 422 x 300 x 125mm.

Price:- £264.00 + £12.00 PSP

NOTE: h«DSFErMCCU_E= -FE - -.L-3E NT» , X)L'ET^O L S
STK'DASD - JEUT 10OTL OR FSt

(FTtEFESSCK-^ =:■. C^,W1SB - SOB

TTari'^eA'^.'/OTr- £t>:-L ORDER STANDARD OR PEC

The reoiMrned Pee-Less XLS 1 0 Dm e unit e possSity one of fee best 1 0
such sufa peeler dn , . , =i= s’yz zr-i^ today. V.a^e in Denrnz r X c, Peeftes=
m cornpaiyy ^Ynonymous \STlh quality ^nd crsftsmansJ^p. This drive unit
]s raea far IndustiHi nto srr;a endcstires cf ^.T.un-3 "7 L/ee ir"
give 3 tight controlled deep bass output- To further enhance the qu£§-
of th<5 ur t gre=te _ c-jfpyt and deeper fcsss can tse achieved tj cc j-
p: Lr-g ttie XLSl 0. with it s compenkwi passive radiator the XLS 1 OP

Peerless XLS 1 0 £89.00, Peerless XLS1 OP 32.90

Carriage £8.00

For full specification and prices goto our website at http:/A wav. bkeEec.com
and try our new shopping basket facility

VISA

DELIVERY CHARGES:- PLEASE INCLUDE AS ABOVE. A MINI- i.i-.ji
MUM CHARGE OF £8,00 TO A MAXIMUM AMOUNT OF £30,00.
OFFICIAL ORDERS FROM SCHOOLS. COLLEGES. GOVT..

PLCs ETC. PRICES INCLUSIVE OF VA.T, SALES COUNTER!

CREDIT CARD ORDERS ACCEPTED BY POST PHONE OR FAX.

B.K. ELECTRONICS

UNIT 1 COMET WAY, SOUTHEND-ON-SEA, ESSEX. SS2 6TR.

TEL.: 01702-527572 FAX.: 01702-420243
Web:- http://www.bkelec.com E-Mail sales@bkelec.com

Simulation

ii;n i mri

* 1 it i

Models

#

Supports PIC, AVR, 8051, and BASIC STAMP micro-controllers.
Co-simutate target firmware with your hardware design.

Includes interactive peripheral models for LED and LCD displays,
switches, keypads, virtual terminal and much, much more.
Compatible with popular compilers and assemblers from
Microchip, Crownhill, IAR, Keil, and others.

www. labcenter. to. uli
in fo@labt enter. to. uli

abc enter

Electronics

53-55 Main Street, Grassington. BD23 5AA

Proteus VSM - Co-simulation and debugging for popular Micro-controllers

The Co

ete Electronics Design System

■ %

VeW • «n *u nt J _ r_ j- -* * T "

Schematic f p f

i- Capture H M]

dirt

r

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Schematic &
PCB Layout

Powerful & flexible schematic capture.

Auto-component placement and rip-up/retry PCB routing
Polygonal gridless ground planes.

Libraries of over 8000 schematic and 1000 PCB parts.
Bill of materials, DRC reports and much more.

Mixed Mode SPICE Circuit Simulation

Berkeley SPICE3F5 simulator with custom extensions for
true mixed mode and interactive simulation.

6 virtual instruments and 14 graph based analysis types.
6000 models including TTL, CMOS and PLD digital parts.
Fully compatible with manufacturers’ SPICE models.

in Version 6.5

• Textual library part search.

• User defined keyboard map.

• CADCAM output to ZIP file.

• Bitmap import function.

• Truetype fonts on PCBs.

• Enhanced printer output.

Call Now for Upgrade Pricing