~~ ~~

April1992 • £1.50

SCIENCE AND TECHNOLOGY

The latest in portable electronic technology and products

Product Reviews
AEG. Olympia Notebook
Sharp 108200 organiser
Vortec 1220 Lapbool< ·
Comfax portable fax
Nintendo Game Boy
Apple PowerBook
Sony Watchman
Vortec 3340DX
Data Discman
Psion MC-400

Plus
Inside a walkman
Build an infra-red torch
30 1V that really works
Who needs electronic mail?
How semiconductors are made
I I Ill
04
Barry Fox on how to be a guinea pig
9 770032 637017 111111 1
 No. or I<its
Whether your requirement for surveillance equipment is amateur, professional or you are just fascinated by this unique area of
electronics SUMA DESIGNS has a kit to fit the bill. We have been designing electronic surveillance equipment for over 12 years
and you can be sure that all of our kits are very well tried, tested and proven and come complete with full instructions, circuit
diagrams, assembly details and all high quality components including fibreglass PCB. Unless otherwise stated all transmitters
are tuneable and can be received on an ordinary VHF FM radio.
UTX Ultra-miniature Room Transmitter URX Ultra-miniature Telephone Transmitter
Smallest room transmitter kit in the world' Incredible 10mm x 20mm including mic. 3- Smallest telephone transmitter kit available. Incredible size of 1mm x 20mm! Connects
12Voperation. 500m range.. . ... £16.45 to line (anywhere) and switches on and off with phone use. All conversation transmitted.
MTX Micro-miniature Room Transmitter Powered from line. 500m range.... .. ................ £15.9!5
Best-selling micro-miniature Room Transmitter nX7110 Micro-miniature Telephone Transmitter
Just 17mm x 17mm including mic. 3-12Voperation. 1000m range... . ...... £13.45 Best-selling telephone transmitter. Being 20mm x 20mm it is easier to assemble than
STX High-performance Room Transmitter UTLX. Connects to line (anywhere) and switches on and off with phone use All
Hi performance transmitter with a buffered output stage for greater stability and range. conversations transmitted. Powered from line. 1OOOm range .. .. ............. £13.4~i
Measures 22mm x 22mm including mic. 6-12V operation, 1500m range.. ...... £15.45 SRX High-performance Telephone Transmitter
VT500 High-power Room Transmitter High performance transmitter with buffered output stage providing excellent stability
Powerful 250mW output providing excellent range and performance. Size 20mm x and performance. Connects to line (anywhere) and switches on and off with phone us~.
40mm. 9-12V operation. 3000m range . ....... £16.45 All conversations transmitted. Powered from line. Size 22mm x 22mm.
1500m range .. . ...... £16.45
VXT Voice Activated Transmitter
Triggers only when sounds are detected. Very low standby current. Variable sensitivity TKX9110 Signalling/Tracking Transmitter
and delay with LED indicator. Size 20mm x 67mm. 9Voperation. 1000m range .. £19.45 Transmits a continous stream of audio pulses with variable tone and rate. Ideal for
signalling or tracking purposes High power output giving range up to 3000m. Size
HVX400 Mains Powered Room Transmitter 25mm x 63mm. 9V operation.. .. ............... £22.95
Connects directly to 240V AC supply for long-term monitoring. Size 30mm x 35mm.
500m range. ...... £19.45 CD400 Pocket Bug Detector/Locator
LED and piezo bleeper pulse slowly, rate of pulse and pitch of tome increase as you
SCRX Subcarrier Scrambled Room Transmitter approach signal. Gain control allows pinpointing of source. Size 45mm x 54mm·. 9V
Scrambled output from this transmitter cannot be monitored without the SCDM decoder operation .. . ................ £30.95
connected to the receiver. Size 20mm x 67mm. 9Voperation. 1000m range ........ £22.95
C116110 Professional Bug Detector/Locator
SCLX Subcarrler Telephone Transmitter Multicolour readout of signal strength with variable rate bleeper and variable sensitivity
Connects to telephone line anywhere, requires no batteries. Output scrambled so used to detect and locate hidden transmitters. Switch to AUDIO CONFORM mode to
requires SCDM connected to receiver. Size 32mm x 37mm. 1OOOm range ........... £23.95 distinguish between localised bug transmission and normal legitimate signals such as
SCDM Subcarrier Decoder Unit for SCRX pagers, cellular, taxis etc. Size 70mm x 1OOmm. 9V operation .. .. .............. £50.95
Connects to receiver earphone socket and provides decoded audio output to QTX1 80 Crystal Controlled Room transmitter
headphones. Size 32mm x 70mm. 9-12Voperation .. ........ £22.95 Narrow band FM transmitter for the ultimate in privacy. Operates on 180 MHz an:J
ATR2 Micro Size Telephone Recording Interface requires the use of a scanner receiver or our QRX180 kit (see catlogue). Size 20mm x
Connects between telephone line (anywhere) and cassette recorder. Switches tape 67mm. 9V operation 1OOOm range. ........... £40.95
automatically as phone is used. All conversations recorded. Size 16mm x 32mm. QLX180 Crystal Cointrolled Telephone Transmitter
Powered from line.. ...... £13.45 As per QTX180 but connects to telephone line to monitor both sides of conversations.
20mm x 67mm. 9V operation. 1OOOm range.. .. ............... £40.95

*** Specials ***

DLTXIIILRX Radio Control Switch
Remote control anything around your home or garden, outside lights, alarms, paging
system etc. System consists of a small VHF transmitter with digital encoder and receiver
QSX180 Line Powered Crystal Controlled Phone Transmitter
As per OLX180 but draws power requirements from line. No batteries required. Size
32mm x 37mm. Range 500m..
QRX1 80 Crystal Controlled FM Receiver
. ......... £35.95

For monitoring any of the 'Q' range transmitters. High sensitivity unit. All RF section
supplied as a pre-built and aligned module ready to connect on board so no difficulty
unit with decoder and relay output, momentary or alternate, 8-way dil switches on both setting up. Outpt to headphones. 60mm x 75mm. 9V operation .. .. .............. £60.95
boards set your own unique security code. TX size 45mm x 45mm. RX size 35mm x
90mm. Both 9V operation. Range up to 200m.
A build-up service is available on all our kits If required.
Complete System (2 kits) ......................................................................................£50.95 UK customers please send cheques, POs or registered cash. Please add
Individual Transmitter DLTX ..................................................................................£19.95 £1.50 per prder for P&P. Goods despatched ASAP allowing for cheque
Individual Receiver DLRX ......................................................................................£37.95 clearance. Overseas customers send sterling bank draft and add £5.00 per
MBX·1111-Fi MicrO Broadcaster order for shipment. Credit card orders welcomed on 0827 714476.
Not technically a surveillance device but a great idea! Connects to the headphone output
of your Hi..fi, tape or CD and transmits Hi..fi quatity to a nearby radio. Listen to your OUR LATEST CATALOGUE CONTAINING MANY MORE NEW
favourite music anywhere around the house, garden, in the bath or in the garage and
you don't have to put up with the OJ's choice and boring waffle. Size 27mm x 60mm. SURVEILLANCE KITS NOW AVAILABLE. SEND TWO FIRST
9V operation. 250m range .....................................................................................£20.95 CLASS STAMPS OR OVERSEAS SEND TwO IRCS.

4·--.·~
SUMA THE WoRI<SHoPs, UNIT
BAXTERLEY, NEAR ATHERSTONE,
PE, 95 MAIN RoAD, I •._! I
1...:.:.:.:.:.:.:.:...1

DESIGNS WARWICI<SHIRE CV9 2LE 0827 714476

VISITORS BY APPOINTMENT ONLY
 Apri l 1992 • Volume 28 No. 4

The ever decreasing size of electronic Small Is Beautiful ................................10

components has created a whole new The electronics industry likesthings small
world of portable equipment. Not just
portable computers but portable TVs, Portable Electronics ... ..................... ... ... 13
games, tax machines and electronic Setting the scene for this month'sspecial feature
books. As well as looking at the Liqutd Crystals- Through AGlass Darkly? ... 30 Get Portable - page 13
practical applications of these we also Thetechnology behind flat screen TVs and portable computers
take a close look at some of the
enabling technologies with articles on Into The Third Dimension ........ ...... ...... ...34 r-------------~

TFT liquid crystals and semiconductors. An exclusive report on the perfect three dimensional TV system
This month's PE also has an Faster Than ASpeeding Bullet ............ ..... 37
exclusive preview of a new development Why don 't we all use electronic mail?
in 3D TV technology - see page 34 - and
a report about electronic mail systems. Transistors Made From Sand .................. .40
We explain where the electronics industry gets its chips from?
Kenn Garroch, Editor Seeing In The Dark ............................... 49
Howto build aninfra red torch n-=-tr-a-re-d=-=t-or-eh
':--
1 =--
--pa
- g-e-=4-=-
9--'

~~
~ --:-.,_~_
m _ __ _ _ _,; .;, .
Sony Data Discman - handheldbook.. .. .14
SonyWatchman- handheld TV ... ........15
Nintendo Game Boy- handheld game ...•16
AEG Olympia- 386SX notebook...........1T ·
Vortec 3340DX- 386DX portable .......... 18
Apple PowerBook- Mac compatible ......19
Psion MC-400- 'indie' portable ......... .. 20
Vortec Laptec 1220 - 286 portable•.... ..21
Sharp 108200- electronicorganiser.......22
Data flex Comfax - pocket fax machine ...24

Innovations ...................................6
Fast video machine, fibre-optic link kit and Windowsspeed·up
What's New ...................................8
Launch version of Photo-GO plus some smart camcorders
New Product Developments ... ... ... .......26
Winter CES with DCC, pen powered Poqet and adigital compass
Digital Compact Cassette- page 26 How lt Works .. ... ...... ... ......... .......... 32
We take the back of a Walkman personal stereo
Wavelengths ...... ............ .. .... ..........36
Time and again: the argument for adecimal clock
Techniques ............................... .....57
High fidelity entertainment systems. Solutions to TV receptionproblems
loudspeakers, amps, decks, tuners,CD,
equalisers, DCC, Minidisc, plus: Barry Fox ...................................... 62
Build A SubWoofer Loudspeaker System Are we all just un·paid guinea pigs for theelectronics industry?
Out On 2 April
Cover i!\Jstraflon Ktn ~ Ganoch

EO• tor. Kenn Garroch Advertrsement Manager David Banner ProductiOn Manager: Richard Mllner Publisher: An96IO Zgoretec • Practical Electronics Intra House 193 Uxbridge Road London W12 9RA Tet:
081-743 8888 Fax: 081·743 3062 Telecom Gold: 87: SQQ567 • Advertisements lhe Publishers ol PE rake reasonable precautions to ensure thal advertisements published in the maga1rne are genuine. but
ca~~nor take any responsibi~ty in respect or slatements or cla•ms made by advertisers. The Publishers also cannot accept any liability in respect of goods not being deiJvOied or not working properly. • ©Intra Press t991.
Copyright Inall drawings, phot()'Jraphs andarticles published In PRACTICAL ELECTRONICS is lully protected, and reproductionor imitations inwholeor in pari are exp1essly forbidden. All rease<lableprecautions are laken
by PRACl iCAL ELECTRONICS to ensure IIJat theadvice and data g1ven to readers rs reliable. Wecannot. h011ever, guarantee it, and we cannot accept legal res~cosibillly for 11. Prices quotea are thosecurre11t as we go :o
press. All material rs accepted lor publication on ihe express undersianding that lhf contributor has the authority to parmlt us 10 do so • Practical Electronics is typeset at Intra Press on Macintosh computers
using Quark Xpress. Reproduction by Circle Rule Ltd. Printing by Andovor Press, St Ives plc. Distribution by Seymour Press •ISSN 0032·6372 •

February 1992 Practical Electronics 3

 EXPLORE THE W
The Facts, Theories,
il.iiULA=I HOW THE CLUB WORKS
All we ask in re.rum is that you buy at least one book from each
ol the fint four magazines, and that you continue to do 10 for as
long as you remain a member. If alter four magazines you wish to
)Cii:ncc What you receive
AI a member. you will receive a free club magazine approximately
ttery I0 weeks, describing and illunrating the latest books on oiler.
cancel, you may do 10 by giving one month's noti<e in writing.

BOOK CLUB With a wide range in mry magazine, and with the list constantly
The Popular Science Book Club faces the isslle$ of today - updated as new books are published, there is plenty to choose from.
and of tomorrow- bringing you an exciting range of books Indeed, tht choice is much wider than you'll find in moSt
covering a wide range of topical scientifiC and bookshops. And there are no special editions - all our books are
environmental subjects. identical in quality and content to the publishen' editions.
From the smallest particles of matter to the farthest
reaches of space, from discoveries about prehistory to Great savings
spe<ulation about the future, science is brought out of the As well as new and important wori<l on S<ientific issues, you will
laboratory and research centre and into your living room. also qualify for valuable savings. All our books are offered at
Evolutlon, genetic engineering, black holes, paraDe! substantial discount~ usually 25% off publishe11' prim (excluding
universes, global warming - we bring you the key issues poStage and packing). of~n much more.
addresstd by the top authors.

JARED "' lit ' I I_!.:

DIAMOND '!Ill \ /llli 1 !

rm: Ill"' \\ n n il.

OF TifF THIRD
CHJ\IP\ ~ZEE
 HOW TO JOIN

Choose your introductory books by completing and returning the

coupon. but send no money at this stage. Examine them without
obligation and if you don't want to join, just return the books
within I0 days and you will owe nothing. If you do decide to join,
send your payment within that time and you will automatically
become a member. r when you join the Popular Science Book Club
7Wd'Saa.
Tht Popobr lcitna 8ocl< Club belongs to lltadm Union.
p,...,nal dat> will be u~ed for dirtct marketing purposes only by ~"' Unioo and
in a!lO(iaud oompanie. AIin of rhell may be obwned f"' from lltadm u.....
lit<rdm Unron obse""' rbe c.dt ol Pooiu <f tht l.sSO<i>tion of Hail Order Publirbe•.
Dmar of tht Code may be obt>ined by sending. rell·addrns.rl r· ' ,. tnvtlopo
Save on our introductory offer today,
(rampod at tbe rau of 60 g"mmll) to Dept CP ar the addr!u btlow.
lltadm Union Umiud. Brunei House. WewtOR Abb~ O...n IQillrYW
then carry on saving with every book you buy.

Alrflly wll!aion of tua!l 'Witidl Lool!l 31 me llatiUiGll pouibiliti!s Tht uory of the dii<OY!fY and The auoni!hing ~orr ol how a
dirarss a wid! 11nge of i!!U!I and of an inmdible amy of evenn. d!'ltiopment of the nudeat winter grorrp of ~ienrilts de'ltiopod a
cooJrcwersits in M~luri)n and from being birtttl by • dog to theory, wb21 it "'"'"' and wilat ~tem to beat the las Ytgas 'rysrem'
sde.1ufK hist{lry. sucauful~ suing for lil>tl. mu:s1 bt dont eo aYOid it becoming - and then I"'' n into pr.octi<f.
roality.

HAMLYN ALL·COLDUR -----------

~
To: The Popular Science Book Club, Brunei House,
Newton Abbot, Devon TQ 12 lOW
Please enrol me as a member of the Popular Sdence Book Club and send me
the bookl indicatld, for which I will bt <harg!d the special offer prices, plus
£2.25 • tor.ll towards postage and par:kin& If I am not <ompletely satisfied I may re1um
ihem within 10 days. my membellhip will be can<flle<l aoo I will owe nDihing. As a
member I agne to buy a book fromeach magazine sent fr~ at appro~imately IO·week
int!f\'als.l undemand that the minimum length of membership is for four magazines. If
after that time I wish to cancel, I may do ~ by giving one month's notice in writing.
PLEASEIEHDHEIHTRODUCTOkY BOOK HOI
PWJC ~liT (LfMlT
DDD 31

Ml\.tiRIIIUSI.,/Ii/TI
=illliii
=~:::-:Ololi1E=-------------

ADDRESS--- - -- - - -- - - -- -
TOWN _ _ _ __ _ _ __ _ _ __ _ __

(0UNTY _ _ _ _ _ __ P()H(00Epu.. _ __ _ _ _

IIGNATURE_ _ _ _ _ _ _ _ _ _ _ _ _ -==-=-=--
''"'""''B""nold.u!"'"lmdra-w. TJPSC3A

il.iiULA~
)Cii:nCi:
BOOK CLUB
1\oadO!Ihioo lll. ~""OffiCe. s...~ H- N..... Ahbor. 0.... TQI! !OW. f'li>•nd •!Joa~od ~~ 14~ V
---------- - O"o
Innovations--------------------------------

Innovations
New this month: a video edit suite for PCs and Macs, a novel mains adaptor, a fibre-optic
link kit and a super fast SVGA card.

of ready built transmitter

and receiver modules
which are connected via
3m of optical fibre. The
system has been designed
to be used with data
transmission rates up to
20kbps - fast enough to
transfer a page of PE text
every two seconds.
Designed to allow
experimentation with
optical links, the units
and cable are supplied
complete with full
instructions and circuit
diagrams and cost £22.95.

Video Control
Until very recently,
computerised video
editing was confined to
Speedy Windows built for under $500. No £19.95, it is available from
UK price details are Maplin Electronic
either expensive high
quality studio systems or
If you think that running
available as yet but when Supplies, Tel. 0702 554161 low quality minority
Microsoft Windows on
it arrives, it should Also new from Maplin home computers such as
the average 386 is rather
provide a good cheap is fibre optic digital data the Commodore Amiga.
slow, a solution has been way to upgrade to high link module. This consists Now, Fast Electronic has
presented by Qak speed, high quality
Technologies. Its graphics Map Iin's eight way socket.
graphics. For more
chip is said to boost the information con tact , . . - - - - - - - - - - - - - - - - - - - - - - - - - - - - ,
performance of Windows Oak Technology Inc,
programs by five times.
Working in 24-bit colour
the chip removes the
bottleneck that occurs
139 Kifer Court,
Sunnyvale, CA, USA,
fax (408) 737 3838.
• •
when the main
microprocessor is writing
graphics to the screen.
The OTI-087 is basically a
Octal Power
Maplin has announced
high quality graphics chip a very unusual mains
that attaches directly to socket. The Carousel
the 32-bit local bus on the offers eight sockets
motherboard and mounted in an octagon
provides high speed with space in the centre
facilities such as bit block for the 0.6m extension
transfers (bit blitting) and cord. Each socket is
a hard wired 64x64 pixel individually shuttered
cursor. It conforms to the and a red power-on
Super VGA (SVGA) lamp shows when the
standard and is should unit is active. Priced at
allow video boards to be

6 Practical Electronics April1992

 Innovations

effects. All processing is

performed by the add-on
board so that they work
smoothly and in real time,
not taking up any of the
computers processing
power.
A number of video
standards can be used
with the Video Machine
and facilities are provided
to merge PAL and NTSC.
Both video in and out can
be S-video or composite
and a digital encoder chip
makes sure that the
output signal is of
broadcast quality. The
whole package will cost
around £2000 and is
Fibre optic link kit. available from Magnifye -
introduced a system for combined with computer to mix two live video Tel. 071 221 8024. •
IBM PC compatibles and generated graphics sources and apply effects. The World's 1st surface mount LED
Apple Macintoshes. The including Postscript (a No additional hardware is
Video Machine uses the page description needed and a number of
graphical interface on the language) fonts and effects libraries are
computer to control the layouts from other provided with the system.
video editing facilities. sources. These include slides,
The video information Unlike other systems curtain effects, wipes,
can come from a variety in the market, the Video smooth zoom and shrink,
of sources and can be Machine allows the user negative and blue box

FAST Video Machine

VHS S-Video I
composite

S-Video I composite

S-Video I
composite

Input Output

Digital effect library

Antialiased tiling
Transistions
Framegrabbing
Grafics with Alpha Channel
Player control

April1992 Practical Electronics 7

What's New- V i d e o - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

These groovy camcorders are from Fuji. At the top is the Fujix-8 F60wide
8mm which features one touch conversion from standard to wide field of view
in the camera's 6x zoom lens. Other features include six speed shutter (up to
1/4000s) and the Easy Finder viewfinder which allows the user to see both the
subject of the shot as well as the surrounding scenery.

On the left is the Fujix Hi8 which offers 41 0,000-pixel resolution for sharp
images- the horizontal resolution is more than 400 lines. In addition, it sports
stereo sound and an Bx power zoom lens. Both models have the dual-position
Multi-Action grip which, in one position, can be used as a carry handle and in
another is the stabilising handgrip with built in trigger. The handle can also be
used as a tripod with built in remote control.

This new FST (Flat Square Tube) portable

from Ferguson is one of two new models.
They both offer a 15in colour screen and the
A36F sports Fastext. The A36R costs £229.99
and the A36F £249.99.

8 Practical Electronics April1992

 What's New

The Walkstations from

=------ Triumph Adler are
powerful portable computers

L------------;,;;b~ that have special docking stations. These go on a user's desk

and by simply placing the machine into a "zero pressure" coupling, they can communicate
with a network, printers and even high resolution colour monitors.

The Kodak Photo CD model PCD870 shown below is the machine that will appear later this year, able to display home
photographs on a TV. New features will be added to later models that allow sound to be played alongside images- a
pre-recorded disc will be able to carry BOO pictures and 72 minutes of CD quality sound. In future, Kodak
hopes to offer consumers the ability to select their own sound tracks to go
with their photograph collection.

April1992 Practical Electronics 9

Technology F e a t u r e - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

From ATwitch In A
Frog's Leg...
Early experimenters detected electricity by its effect on muscles. Things have moved on a
little since then as Jane Fuller explains.

ver since the development of as powerful if not

E the transistor, the trend in

electronics has been towards
smaller and more powerful devices.
more so that many
minis and look set
to leap ahead of
The move from discrete devices - the mainframes in
transistors packaged in single the very near
containers with just three leads future.
sticking out - to integrated circuits What the
was just another step in a microprocessor is
continuing process. Nowadays, good at is taking
almost every electronic gadget in information,
relies on integrated circuits of one making decisions
kind or another and most use that on the basis of it
all-purpose device; the and then exerting
microprocessor. control signals. It
is the perfect
control device
Early Days whose capabilities
are now limited
~===~---------------------"'==--'
This electronic dictionary holds over 100,000 words.
The computers developed in the
early 1950s relied on the valve as a mainly by squeeze more and more transistors
switching device. As soon as the programming. onto a chip were also being used for
transistor came along, it was other devices. Mass storage systems
snapped up by computer designers increased in ea paci ty. Specialised
to reduce the size of their machines dedicated controllers, such as those
drastically it also increased their Other Technologies used to drive video displays acd
reliability and speed. Again, While the microprocessor was manipulate the signals from a disk
integrated circuits were a big step under development a number of drive or from a microphone were
forward with large numbers of associated technologies were also also being thought up and then
transistor switches improving. The techniques used to improved upon. The
being fabricated The finest quality music on the move. capabilities of electronic
onto one chip. The components were
move to put the increasing dramaticaLy
whole computer, or while reducing in size and
as much of it as plummeting in cost.
possible, onto a
single piece of
silicon came soon
afterwards and Electronic Gadgets
resulted in the The electronics industry
microprocessor. has now reached the stage
With greater levels where, demand has a
of miniaturisation tendency to create a
and integration, supply. The invention of
more and more the W alkman showed the
processing power world that high quali:y
became available personal stereos were
until nowadays, possible. Now the portable
microprocessors are

10 Practical Electronics April1992

----------------------------------Microelectronics

Nothing•s Impossible
Although the gadget on the left
may not actually exist, it shouldn't
be too long before it does.
Developments in LCD screens
and electronic communications
encoders should enable a
portable video-phone to be a
reality before the end of 2010.
The limitations on such a
device are less on the capabilities
of the electronics than on the
radio bandwidths available.
Transmitting video pictures
requires a huge bandwidth
compared to speech.
One solution is to compress
the video images. Removing
unnecessary information such as
parts of the image that don't
move and sections that have a
single colour.

The ability to produce a picture such as

this is a tribute to modern electronic
technology. A high resolution image
scanner digitised the two photographs
and then a high speed microcomputer
with sophisticated graphics software
was used to distort and fit them
together.

CD player and soon DCC and Sony

Minidisc players will provide
in the current recession, such is the
demand. Everybody expects the
The Near Future
The next few years will see more
facilities never before see or heard - latest technology to be smaller, and more electronic gadgets
without the creation of the cheaper and use less power. For appearing. Technologies such as
Walkman, no-one would have example, TV sets have gone from high resolution colour LCDs are
realised the demand for such being huge beasts that dominate the already with us - Sharp has an
equipment could exist. The same corner of a room and consume exhibition in London's West End
can be said of the portable considerable power, to the hand which has a number of wall
computer and its offspring the sized Watchman the large systems hanging flat screen LCD TVs and
palmtops and personal organisers. still exist but they are more compact they are working on 16in and 20in
All of these are science fiction come and offer almost amazing facilities models which should be available
true. such as picture within picture, within two years. A lot of portable
Nowadays, the consumer teletext, remote control and so on. electronics products relied on SV
electronics market is growing, even power supplies until recently. Now
manufacturers are moving to 3V
Modern electronic devices are small enough to fit a radio onto a credit card.
systems since they reduce battery
bulk and give a longer battery life.

The Next Century

It is always hard to foresee what
will happen in the future but
electronics should go on getting
smaller, cheaper and less power
hungry. We will begin to find it in
areas previously untouched and
find uses for it that are now
unimaginable - back at the
beginning of the century the science
of electricity was in its infancy and
who would have dreamed what
could happen in a mere hundred
years. Imagine what could happen
in another hundred. •

April1992 Practical Electronics 11

 PSST...
Powerful Software Saves Time!
ANNOUNCING ARES VERSION 11 AND ARES 386
Our high performance PCB design products have been enhanced with further time saving
features such as Auto Track Necking -ARES will automatically replace sections of a wide
track with narrow segments where design rules dictate. Other new features include further
support for netlist driven design modification, multiple package libraries, multi user (network)
operation, Gerber viewing, DXF export and curved tracking with full connectivity support.
ARES 386 is a full 32 bit version of ARES AUTOROUTE offering much faster operation and,
for practical purposes, unlimited design capacity.

ARES ....................................................................... £275

ARES AUTOROUTE .............................................. £475
ARES 386 ................................................................ £675

• Topological Route Editor (another Labcenter innovation)

• Unlimited user configurable pad, track and via styles.
• Full surface mount and metric support.
• 10 copper + 2 silk layers.
• 1 thou resolution.
• 30x30 inch max board size.
• Object oriented 20 drawing for silk screen graphics.
• Ful! connectivity and design rule check functions.
• Drivers for dot matrix, pen plotters, lasers, POSTSCRIPT,
Photoplot (Gerber), NC drill (Excellon).
• Graphics export in IMG, BMP, DXF or EPS formats.

ISIS - Intelligent Schematics Budget Price CAD Software

ISIS DESIGNER ...................................................... £275 ISIS SUPERSKETCH .............................. from only £69
An exceptionally easy to use schematic capture Our highly popular schematic drawing program has all
package designed for use with ARES or other EDA the editing features of ISIS DESIGNER and our
software. Provides facilities for single button Graphical User Interface makes it exceptionally easy
integration to any DOS application. to learn and use.
ISIS DESIGNER+ ................................................... £475 Diagrams produced with SUPERSKETCH can be
rendered on all common printers/plotters including
Adds advanced design management features
POSTSCRIPT and graphics export to most DTP and
including hierarchical design, fully automatic
Wordprocessing packages is also possible
annotation/packaging, Design Global Annotation and
ASCII Data Import for handling component stock An extended device library containing TTL, CMOS,
codes, prices etc. Memory, Microprocessor and Analogue ICs is
available for £30.
• Auto wire routing, dot placement and label generation.
PCB 11 ................................................................ only £69
• Powerful editing facilities.
• Object oriented 20 drawing with symbol library. An exceptionally easy to use manual PCB drafting
• Comprehensive device libraries provided. package offering most of the features of ARES
• Device editor integral to main program . (including Auto Track Necking & Curved Tracks)
• Output to dot matrix, pen plotters, lasers, POSTSCRIPT.
• Export to DTP packages in IMG, BMP, DXF or EPS formats.
but without the netlisting capabilities.
• Multi-sheet and hierarchical designs held in one file. PCB 11 shares the same user interface as ISIS
• Netlist output to most popular EDA software. SUPERSKETCH and both packages plus the
• Bill of Materials and Electrical Rules Check reports.
extended device library are available for just £149.

lobcenter
COMBINATION PRICES
ISIS DESIGNER & ARES ................ £495
IS IS DESIGNER & ARES AR ........ £675
j: ' • Call
Tel.for demo
0274 packs
542868 a:······:
· :··
ISIS DESIGNER+ & ARES .............. £675 Fax: 0274 481078 •
IS IS DESIGNER+ & ARES AR ........ £850
Electronics ISIS DESIGNER+ & ARES 386 ........ £995
14 Marriner's Drive, Bradford. BD9 4JT
Prices exclude and VAT.

12 Practical Electronics April1992

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - S p e c i a l Feature

Setting The Scene...

Portable Electronics
Kenn Garroch takes a quick run through the background of the machines in this month's
review section.

his month's special feature but in portable form. As a portable system it can be

T looks at the current state of

the art in portable
electronics. The first two items are
used either in an office as a fully fledged desktop
machine or on the move allowing full scale computing
any place, any time. Of course, if a 386SX is not fast
from Sony, the Data Discman and enough then the power of the 386DX which runs at
Watchman. Both of these are 33MHz is the next step. This is actually more powerful
.::...:...._ _, examples of equipment that will than many desktop only systems and when coupled
change the way in which we live our lives. Next comes with 4Mb of Memory and an 40Mb hard disk drive as
the Gameboy, possibly the most successful Christmas in the Vortec 3340DX-4, it is truly a machine to be
present of 1991/2, it easily outsold its rivals and is reckoned with.

O
steadily taking over as 'the' machine to be seen with. f course, not everyone
As with the Sony products it makes good use of the wants to use an IBM PC
liquid crystal display (LCD) screen, a technology compatible and its major
without which most portable electronics would be competitor, Apple, also produces
impossible. The Nintendo currently has over 100 game laptop computers. The
titles available in its slot-in cartridge - another PowerBook series are fully
technology becoming widely used in portable systems. '-----------' compatible Macintosh systems
Both the Psion MC 400 computer and the Psion IQ8200 with large memories and hard disk plus the latest
make good use of slot-in cards to distribute software, system 7 operating system that is so easy to understand
add memory and provide expansion capabilities.The and use, a 4 year old can operate it. Alternatively there
Nintendo Gameboy also uses the ubiquitous is the option to get away from standardised systems
microprocessor to control its screen, sound and run its completely. After all, they do tend to use rather power
games- many players now spend hours pitting their hungry microprocessors and their operating systems
wits against a tiny piece of silicon which, through its were not originally designed to be portable. The Psion
programmability, has so many capabilities we have MC-400 is a good example of a portable computer that
scarcely even begun to tap them. The other main use of offers all of the functions required of a laptop,
the microprocessor is in personal computers (PCs). wordprocessing, databases and so on but in a more
nce upon a time, PCs were portable form.

O large desk bound boxes

with hulking great
monitors that lurked on the side of Y
et another alternative to
portable computing is the
electronic organiser. At its
the office desk. Thanks to simplest this is an electronic
advances in integrated circuit (IC) version of the filofax with
technology, they have are now on calendars, phone books, sheduler
the move en-mass. and a calculator - all the
, - - - - - - - - - , A t the bottom end of the necessities needed to lead a thoroughly modern
range are the i286 based lifestyle. At its most sophisticated the organiser can run
systems which run the, spreadsheets, communicate with other computers, hold
now old-fashioned, Intel 80286 a dictionary, help manage new ideas and run a wide
microprocessor. The Vortec 1220 variety of specialised software. The Sharp IQ8200 with
with its 1Mb of memory and 20Mb its 128kb of memory outperforms most of the home
hard disk is typical of the type of computers of 8 years ago and is small enough to fit in
'-----------' machine. It can run most PC the average inside pocket. It can even be used with a
applications at a reasonable speed though it is rapidly portable fax system such as the Comfax to send
being superseded by more powerful systems which information around the world from a portable cellular
engender more sophisticated software. The next step telephone. The Comfax is a fully functional modem
up is the 80386SX microprocessor which, running at again, small enough to be put in a pocket. Since it is
20MHz, is at the heart of most PC systems these days. battery powered, it can be used anywhere any time-
The AEG Olympia is a good example of a 386SX system truly the mark of a portable electronic gadget. •

April1992 Practical Electronics 13

 Portable Data

Sony Ushers In The

Electronic Book
Micro-electronics has made almost everything portable, even the book. fan Burley looks at
Sony's attempt to take us ever nearer the future.

he Sony Data Discman has

T arrived in the UK at last. We

first saw this compact portable
CD ROM player two years ago and
after one face-lift it has been
launched in the UK as the DO-lEX
with a recommended price tag of
£350. Over 100,000 have already sold
in Japan with an average of two
"electronic book" CD ROM titles sold
per Data Discman.
What you get is a unit slightly
smaller in width and depth than a
portable compact disc player, though
slightly thicker. The DD-1 EX weighs
just over 700 grams. Flip up the lid
and a qwerty keypad plus a 3.5"
diagonal back-lit LCD screen are
revealed. The screen has a 256 by 200
pixel resolution and solid text is
displayed in 30 columns by 10 lines.
Underneath the keypad and
accessible by flipping it up is the courses in Europe. The Data by key word for a sort of thesaurus-
"electronic book" bay. Data Discman Discman's graphics capabilities are like search, combination searches,
"books" are 3.2in compact disks exploited by The London Guide menu searches and graphics
enclosed in a protective case or published by Nicholson, which searches. Finally there is a hyper-card
caddy - rather like a 3.5in floppy features a series of maps to text and graphics cross-referenced
disk. These disks have a 200Mb accompany texts on tourist search.
capacity. Sony likens this to 100,000 information, shopping, theatres, A lot of thought has gone into
pages of text, but you're not where to stay, and so on. Prices so far power sources for the Data Discman.
restricted to the written word - range from around £40 to £60 per Unlike some electronic devices I
theoretically up to 32,000 illustrations title. Sony is very keen to assist the could mention, you would be very
could be held on one disk. If you get corn pila tion of new ti ties and unlucky not to have access to either
bored with your book you can swap prospective EB publishers are offered AA batteries (six alkalines give 6
it for a standard 3in audio CD single a complete authoring and mastering hours operation), a mains electricity
and listen via the 3.5mm stereo service. Currently over 85 other EB source, car cigar lighter socket or a
headphone socket. titles have already been published in 2.5 hour rechargeable battery pack.
Sony says there are a dozen UK- Japan and America. Incidentally, full The Data Discman captures the
produced electronic books, or EBs, marks to Sony for not only providing imagination; it's another bit of that
available right now- three of which the DO-lEX with a TV /Video once elusive future popularised in
are bundled with the player, one of display adaptor, but including the science fiction. Whether it's a
which has been confirmed as the three main TV standards, Pal, Secam practical and genuinely useful
H u tchinson Encyclopcedic and NTSC as well- the DO-lEX is alternative to the printed book, only
Dictionary. It's expected that up to obviously aimed at jet-setters. Up to time will tell. It's a pity you can't
fifty UK EB titles will be available by twelve languages can be supported play full size 12cm audio COs and
the end of the year. Titles range from by Data Discman too. one also wonders why Sony invented
travel guides, dictionaries and even There is a barrage of search a third incompatible standard for the
the Thomson Directory, to such options to help you find the required Mini Disc audio system. Still, it's the
exotica as the Michelin Restaurant passage to view. You can search perfect gift for people who thought
Guide and a guide to the best golf simply by word or parts of a word, they had everything! •

14 Practical Electronics April1992

 Portable TV

Review...
Sony Colour Watchman
Andrew Armstrong wanted to buy a portable TV so after checking out the competition, he
decided on the Sony Watchman.

he Sony Colour Watchman

T TV is a liquid crystal
television which differs from
the market norm. It has a three-inch
screen, but is the size of a small
portable radio, and is powered by
six C cells instead of the more usual
AA cells. This is in marked contrast
to most other miniature portables
on the market.
When looking to buy a portable
colour TV, my initial thought was
that the larger-screen models might
be easier to watch. The screen size
ranged from 2.2in to 4in and I
found that the viewing angle was
very limited. In non-ideal viewing
conditions, the colour quality and
contrast were lacking and I
remained unsure that I wanted to
spend money on one of these sets.
I then came across the Colour the batteries fitted- about as much plug an external aerial into the
Watchman and was immediately as the proverbial bag of sugar - and 3.5mm jack socket if it is necessary
impressed by the brightness and has a stable and reasonably to boost reception. The set also has
clarity of the picture and by the fact ergonomic carrying handle, which an audio/video input socket, an
that it remained viewable over a earphone output and an external
doubles as a prop for desktop use.
range of angles - it also has a much power socket.
The styling is elegant in mat grey
larger loudspeaker giving a much This is where I come to my first
with a black surround to the screen
better sound. criticism. Though the power socket
The picture is better than that on and a fine, punched metal grille
over the loudspeaker. As you might is of the concentric type, commonly
other sets because the liquid crystal used for this purpose, it is of a non-
screen uses a different technology. expect from the company that
pioneered play-as-you-go audio, standard size. Though I have a
Thin film transistors (TFT), employ suitable 9V regulated power
amorphous transistors deposited on the Colour Watchman is robustly
built without being overweight. supply, I cannot use it to run the
the screen glass to drive the liquid television, because I cannot buy a
crystal elements. This means that Another nice touch is that the
plug of the right size to fit it. The
each dot can be driven all the time, on/ off and band-change switches
mains adaptor is included with the
rather than being scanned. TFT are easily thumb-controllable from set in all countries except the UK. In
technology is described in more the carrying handle. The drawback this country, the power adaptor is
detail on page 30. is that you do pay for this quality. sold separately and costs the best
When I say that the set is As well as covering the UK part of £20. The controls comprise
"larger" than many other small UHF /PAL signals, the set can the slider-type band and on/ off
portables, it isn't a monster. The receive European PAL and VHF. It switches already mentioned, rotary
overall dimensions are 208mm would not work in France, where volume, brightness and colour
wide by 116.5mm high by 72.5mm SECAM is in use, but you should be controls. The knobs are slightly
to the back of the battery able to receive German broadcasts recessed, reducing their
compartment. It weighs in Germany. The set has an integral vulnerability, have a smooth travel
approximately 1.1 kilograms with telescopic aerial and it is possible to Continued on page 58

April1992 Practical Electronics 15

 Video Game

Review...
Nintendo Game Boy
Richard Milner is hooked on computer games and reckons, although admitting to be a little
biased, that the Game boy is tops.

L
ots of people play computer
games these days and they're
not all kids or teenagers.
Quite a lot of them are
sophisticated City bankers
moonlighting on their firms' PC or
Unix networks outside trading
hours. Nintendo in America
recently stated that, to their
surprise, about 40% of Game Boys
were being used by players over 18
years old. But what happens when
you leave the office and get on the
Docklands Light Railway for the
long drag back to your studio flat?
You need a portable game machine
to get your fix of pixel action. This
is were handheld machines come
in.
In my (biased) opinion the
Nintendo Game Boy is the only
portable worth considering. It
totally fulfills the requirements and
is essentially the game computer
version of a W alkman. It is small
enough to go into a hip or breast
pocket, light enough to be held for
long bursts of action without your
arms getting tired, narrow enough Final Fantasy Adventure, a graphic and use it as an electronic address
to stop your elbows sticking out (an role-playing game that took about book.
important consideration on a 30 hours to complete, and The Game Boy is a lot cheaper
crowded tube train). It uses only Nobunaga's Ambition, a historical than its rivals at £70 including a
four AA batteries, which is what simulation of feudal Japan of the free copy of Tetris. Individual game
most rechargers will do at one go 1560s combining elements of Risk packs range from £20 to £35.
(two sets of rechargeable batteries and economic control games like The main disadvantage of the
are essential equipment), and they the venerable Yellow River Game Boy is that it has a mono
last for hours. You can play all day Kingdom. Apart from the standard screen which is not backlit. This is
on one set - a lifetime of 10-12 selection you will find at Smiths
why the batteries last so long, but it
hours for Ni-Cads is standard. and Dixons, there are plenty of
can be difficult to see the screen in
The Nintendo has a massive import games, including original
Japanese models, available from bad light. There is a lighting
selection of games - well over 100 attachment you can get to solve this
at the last count - and the game- stockists in the gadget heaven of
paks are small and sturdy, packed Tottenham Court Road. If you go problem, as well as other gadgets
in individual plastic cases. The for these you must watch out, like a screen magnifier and a
games available range from straight because the on-screen instructions carrying case, but with all these
ahead shoot-'em-ups to complex are often in Japanese alphabet. If hanging off the Game Boy it stops
adventure and strategy simulations. you need an excuse to carry a Game being a neat handful and turns into
Two recent favourites of mine are Boy get the Personal Organise pack a mutant monster. Less is more. •

16 Practical Electronics April1992

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - P o r t a b l e Computer

Review...
AEG Olympia Lapbook SX
Kenn Garroch gets to play with a mid-range PC compatible 386SX portable computer and
finds that it does the business rather well.

otebook computers are now The keyboard is

N available from a wide range

of manufacturers - it seems
that anyone who make a personal
one thing that limits
the size of any
notebook computer.
computer makes a notebook. The It has to be close
AEG Olympia is fairly typical of the enough to full size
latest crop of machines. It uses an to allow the average
Intel 80386SX microprocessor - this fingers to hit the
is a full power version as seen in keys reliably. Some
many desktop machines - an LCD short-cuts are
VGA screen, a full size keyboard, possible with half
contains a 40Mb hard disk drive, a height function keys
3.5in floppy, 1Mb of memory and and doubling or
has a rechargeable battery that even tripling the
gives approximately 3 hours of use. functions of other
Speed wise, it is fully as capable keys. In this respect,
as the average desktop machine the Olympia is
running under a microprocessor rather good. It
clock of 20MHz. This allows it to devotes full keys to
run any PC compatible software, arrows, page, home,
from Windows and Core! Draw, to end and insert
dBase and MS-Word. many manufacturers
Unfortunately, there are a few have chosen to
drawbacks, the first being that the double these up. The
controls are provided and the side
w~ol~ thing is fairly weighty. Partly obvious trade off in a portable is the
lack of a numeric keypad. An lighting system means that the
tlus IS the battery, but mainly it display is quite visible under a
seems to be the case and disk attempt is made to get around the
problem with a num-lock key that wide range of light conditions.
drives. Although it comes with a
smart carry bag, complete with converts part of the main keyboard This type of portable is useful
handle and pouches for the mains to numbers. The trouble with this is for both the commuter and the
adaptor and some disks, it is rather that qwerty keyboards have person who needs to save a little
a chore to lug around. staggered rows whereas numeric desk space. Ideally it would be
Another drawback is the use of a keypads don't. recharged every night, ready for the
full power microprocessor. This On the back of the Olympia, train journey the next morning.
tends to reduce battery life and, hidden away behind rather flimsy During the day, it could be used as
whenever possible, the unit must be shutters, are the external connectors a desktop machine being powered
plugged into the mains supply to be and ports. All of the usual facilities
are available, 2xserial and a parallel from the mains. The journey home
recharged. Another drain on the could then see more use. It is a full
battery is the hard disk, although port, as well as connectors for an
external colour VGA monitor speed, fully fledged PC compatible
this switches off if it hasn't been with the only real drawbacks being
used for a moment or two - any external keyboard, and additional
floppy disk drive. the relatively short time between
package which does a lot of disk
accessing will reduce the useful life The screen is a VGA compatible recharges and the weight.
of the machine further. A second LCD which acts just like a Pricing and availability.
problem with the disk powering monochrome VGA system. It works 1Mb +MS Works+ Mouse £1699
well for most applications although 2Mb +MS Works+Mouse £1799
do:vn is that there is quite a
noticeable delay when it has to spin because of its sluggish update 5Mb +MS Works+Mouse £1999
speed, it can blur quite a lot when Available from:
up to speed again - slightly
trying to run fast moving computer AEGOlympia
disconcerting in a wordprocessor games. Brightness and contrast
and quite irritating in a database. Tel 0753 630111 •

April1992 Practical Electronics 17

 Portable Computer

Review...
Vortec 3340DX
Nigel Gregory takes a liking to to this super powered notebook computer even though he
finds it somewhat of an effort to lug it up the stairs to his flat.

W
hen you have recently
moved house and had to
lug an old PC compatible
and monitor up two flights of stairs,
you begin to realise the attraction of
a notebook sized computer.
However, potential purchasers
should be warned that while a
notebook PC may fit into a
briefcase, it will feel like you have
placed a couple of bricks in with
your papers, not a notebook.
The Vortec 3340DX is not very
different from its competitors when
it comes to weight and size,
weighing in at 8 lbs with the battery
pack connected, and measuring
about the size of a thick A4 pad.
In terms of specifications the
review model contained: a 3.5in
1.44 Mb floppy drive, an 80Mb hard
disk, a backlit black and white LCD
VGA screen, and 1Mb of memory. the battery needs recharging. For managed to keep this to a sensible
Various combinations of memory my liking the Vortec's 2hrs does not minimum.
and hard disk size are available. really seem long enough. If a There are two benefietal
Where the Vortec differs from machine is to be truly portable, then additions included with the
several of its rivals is that it uses a having to operate from the mains package.
fully blown 386 (386DX) every two hours is a distinct Firstly, it comes with a one year
microprocessor, rather than its disadvantage. With the current warranty cover which is mobile. If
more lowly cousin the 386SX. In specification a second battery pack it develops a fault, an engineer will
practice this means that it runs would seem like a worthwhile come out to you on an eight hour
faster, working at 33Mhz compared investment. basis (the next day), providing you
to a more typical 20Mhz for an SX. When it comes to the display, are in the UK mainland. Secondly,
While this might seem like an the screen is quite adequate for it comes bundled with an up-to-
obvious plus, you should think most portable uses, but in common date operating system OR-DOS 6. It
carefully whether you need this with many LCD screens fast
is also nice to be able to report that
extra power, a 386SX machine is moving graphics tended to blur.
the manual is readable, and even
quite capable of running modern In terms of design the computer
does well. The casing is of solid contains some pictures of actual
applications like Windows. There screen messages.
may be times when the added construction, with the added bonus
of an attractively styled carrying With a Recommended Retail
speed would be useful, running
case. The keyboard has firm Price of £2,099 for the 2 Mb, 40 Mb
large spreadsheets would seem an
obvious example. response click style keys and the hard disk version, increasing to
While size and weight might layout is fairly straightforward. £3,299 for the 16Mb, 80Mb hard
seem the most obvious With all notebooks the lack of space disk version, the Vortec 3340DX
considerations, there is another entails several keys doubling up seems like a serious contender in
important factor that should be and performing more than one the market for powerful portable
looked at - the length of time before function. Vortec to their credit have business computers. •

18 Practical Electronics April1992

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Portable Computer

Review...
Apple PowerBook 140
John Dean switches on a portable computer and falls in love with a machine that tells him
bedtime stories.

nlike most other portable

U computers, the Apple

PowerBook series is not an
IBM PC compatible. It doesn't run
MS or OR DOS or MS Windows.
Instead it is a completely portable
Apple Macintosh. The 140 and 170
machines are actually as fast and
powerful as the Mac II series and
will run all the Mac software that
runs on the standard machines.
On opening up the clamshell
top, an number of unusual features
are revealed. The first is that this
portable has a built in tracker ball -
a necessity since all Mac software
requires a mouse in one form or
another which this replaces. Above
and below the ball are the mouse
button switches. Both do exactly the
same thing and there are two of
them, presumably because the
manufacturer couldn't decide
which was the best position.
Another unusual feature is the
positioning of the keyboard. The
two large blank spaces on either
side of the tracker ball serve as printer driver), others are only a minutes or so of use before another
hand rests. When using the point and click away. message pops up to say that the
machine in a mobile environment - The screen is the standard LCD machine will close down in 10
say a bus or a train, the machine type and, on the Mac, has the seconds which it duly does with a
can be held steady on the knee with disadvantage of smearing the rather brusque "Good Night".
easy access to the keyboard, tracker mouse. The top of the range Fortunately, all is not lost and
ball and mouse buttons. This is a PowerBook 170 has an active matrix plugging in the mains adaptor
very ergonomic style and, although system which should improve on
unusual to start with, soon proves revitalises the system leaving the
this. The size of the screen means application in the same state at
its worth. that it is a little larger than a
When compared to IBM PC which it was stopped. Overall
standard Mac Plus/Classic/SE
compatibles and MS DOS displays and it provides a clear operation time was about 3 hours
machines, Apple computers seem crisp bright display. twenty minutes non-stop use.
to come bundled with lots of On the power management The only real problem with the
software. Most of this is the front, the PowerBook outperforms PowerBook is the price. At £1375
operating system which is a most of its rivals. Around 35 for the model100, £2195 for the 140
complete task sharing system that minutes before the battery actually and £3150 for the top of the range
allows a number of applications to runs out a message pops up on the 170, they are expensive. On the
be loaded up at once. Although screen to say that power is running other hand, they are very easy to
only the current task actually runs low and mains power should be use and fully compatible with the
(with a few exceptions such as the used. Ignoring this gives another 25 wide range of Macintosh software. •

April1992 Practical Electronics 19

 Portable Computer

Review...
Psion MC 400
Portable computers come in all shapes, sizes and flavours. Psion's offering is definitely not
vanilla as fan Burley explains.

he PC world has laid down an example's batteries

T unwritten specification for

compact 'notebook' portable
computers. Typically this means a
haven't been replaced for
three months.
The first thing
battery life of just 2-3 hours in a 6- noticeable about the MC is
7lb device that must behave, as its first-class production
much as possible, like its desktop engineering - it looks
dinosaur ancestor and can be superb. The 400 has a
hidden in a slim line case . When 640x400 pixel resolution
you realise PC technology is retardation film LCD. It's
constrained by, what is basically, a unlit but razor-sharp. On
ten year old system architecture, its both sides of the keyboard
no surprise that portable PCs are are flip-up hinged covers
riddled by compromise. hiding four small memory
Psion bravely decided to look cartridge slots. These
from scratch at the requirements of accommodate SSDs (solid
personal computer portability; the state drives) either
PC environment was simply not battery- backed RAM (up
suitable. To run PC software you to 512K) or Intel Flash
needed an expensive, heavy, Memory (up to 1Mb)
unreliable and power-hungry hard cartridges. Underneath c _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __j

disk which was out of the question. are two expansion module communications terminal,
So late in 1989 the Psion MC bays. One is usually occupied by a clock/ calendar and diary I time
(Mobile Computer) series was born. combined parallel and serial manger. File transfer capabilities
There are three models in the communications interface. The are provided for PC and also Apple
MC line-up, the non-PC compatible second could accommodate a Mac users.
200, 400 and the PC-compatible 600. diminutive 2400bps error corrected There isn't much else software
The 200 is a cheaper version of the modem, a bar code reader interface to be had for the MC400 besides a
400 sporting a smaller and inferior or even a digital sound recorder Lotus 123 compatible spreadsheet,
screen. Its only saving grace is that which can be used to verbally
which comes on a cartridge. But
it consumes even less battery power annotate word processor
what else does a portable user
than the already outstanding 400. documents. Unfortunately the latter
doesn't appear to be actually on really need? You can write your
The 600 was supposed to be Psion's own applications using the quirky
insurance policy against market sale.
Another novel feature of the MC but powerful Psion OPL language
reluctance towards things PC Despite some frustration with a
incompatible but has proved to be 200 and 400 (but not the 600) is a
touch-pad mouse-pointer rather fragile comms/modem
an even worse compromise than
controller. It works well enough, section which I rely on a lot as a
your average notebook PC.
That leaves the MC400, a but the pointer's position on the journalist, I personally think the
portable modestly driven by a screen is relative to the exact MC400 is a brilliant piece of kit,
lOMHz PC/XT class 80C86 position of your finger (or other especially as the price is now £200
processor, running a proprietary convenient stylus like a biro cap) on cheaper at a much more realistic
multi-tasking and windowing the pad. I'd like to see the option of £495. But then my enthusiasm is
operating system called Epoc. It has a "drag and leave" operation -just unfettered by PC dogma. In reality,
no conventional disc drives - hard like a mouse. the MC range has not so far been a
or floppy, and can run for around Built in software includes a commercial success -everybody, it
fifty hours off one set of eight word processor, card-style free seems, prefers a PC-compatible,
ordinary alkaline AA batteries. My format database, calculator, compromise and all. •

20 Practical Electronics April1992

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - P o r t a b l e Computer

Review...
Vortec 1220
James Smith opens up a low price portable computer and finds a natty looking machine
that, among other things, is an excellent wordprocessor.

he V ortec La ptec 1220 is a

T 12MHz 286 based laptop that

comes with 1Mb of memory, a
20Mb hard disk drive plus built in
floppy disk. It is a lower end
machine but for the price, is pretty
good value.
It is a compact system with full
sized keyboard - apart from the
space bar which has been shortened
to make room for the insert, alt,
delete and home keys. This is not
really a handicap, especially if, like
me, you are a two fingered typist.
The main problem with the
keyboard is that in a quiet room, it
is rather noisy. While pounding
away at the keys, a light ringing
sound can be heard presumably
the key springs. Although the keys
are full sized, there is no room for
all those 102 keys you get on a
standard PC keyboard so some of
the have to be doubled up.
Fortunately, this is kept to the Whilst on the subject of using the Filelink command allows data
minimum although there are a the Laptec in a truly portable to be transferred at rates up to
number of purely system functions situation; it does have a rather natty 115,200bps -fast enough for most
placed on the keys as well. These carrying case and when packed up transfers. Alternatively, a portable
allow the size of the screen to be with its power supply I charger, the modem can be hooked in allowing
altered as well as inverted - some whole caboodle is rather heavy. connection to a main phone socket
of the normal VGA screen formats Most of this weight is the two or even a cell phone for real
don't actually fit exactly onto the battery packs which slot into the communications on the move.
LCD layout so they have to be top back of the case. They can be On the whole the Laptec is a
mapped to fit, these extra keys are a taken out and recharged separately machine to be proud of. It has the
quick way to do the job. The other so that by carrying two sets of power to run most PC software
function on the keyboard is a quick batteries around, the useful though it would be a bit slow for
shutdown key - function and then portable life of the machine can be Windows. As a portable
enter which switches the hard extended. wordprocessor it is excellent and
disk off with an audible click and Even though the portable comes for running smallish databases,
blanks the screen as well. with a 3.5in floppy disk drive, there basic spreadsheets and the odd
Everything comes back at the press are times when large pieces of game, it is ideal. At £999 the only
of a key and is just as it was when it software or data files must be real grumble I have is that the
was shut down. The system is still moved to or from its hard disk. The clamshell screen does not tilt back
consuming power but not as much 1.44Mb floppy is not really up to far enough for comfortable viewing
and gives the user time to leap off this. The answer is to use one of the while sitting in an upright chair
one bus and onto the next without two serial ports on the back. with it on my knee.
having to leave the machine Linking up to another machine Vortec can be contacted on:
completely on. running OR DOS 6 and invoking 081 569 7513 •

April1992 Practical Electronics 21

Electronic O r g a n i s e r - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Review...
SharpiQ8200
Kenn Garroch files his facts and gets organised with this high specification pocket sized
machine from Sharp.

eeping track of events, system.

K people, addresses, phone

numbers and ideas is
becoming more and more of a
The basic
hardware of the
IQ8200 is an 8
chore. Unless you are a mnemonic line by 40
expert, it is difficult to remember character LCD
more than several telephone screen, 128kB
numbers at once, let alone four or battery backed
five addresses. The electronic RAM built in, an
personal organiser was designed to 80 key keyboard
solve exactly these problems. which is set out
The Sharp IQ8200 is the latest in QWERTY
Sharp electronic organiser and, in format rather
some ways, can be considered to be than the
the state of the art. As well as all of alphabetical
the usual functions - calendar, (ABCDEF and so
memo pad, address book, calculator on) sequence
and idea outliner - it also has an used on other
organisers. Other
almost infinite expandability via
keys allow quick
plug in cards.
access to the
Positioned to the right of the
main functions,
main screen is a touch sensitive
memo, scheduler
area behind which the cards slot in
and so on. Some obvious but I managed to lose a
-only one at a time. On the front of
of the extra functions are accessed couple of memos by hurriedly
the card are small pictures that give by a special SHIFT key - set-up
meaning to the transparent touch turning the IQ off when my train
functions and communications
switches. Applications ranging arrived, only to find that everything
options and so on. Other keypress
from spreadsheets, extra memory, had gone when I turned it on again
options are available on the touch - quite an unnecessary fault.
computer programming languages, screen for use with the slot in cards.
dictionaries, legal databases and Another niggle was that the
In use, the QWERTY keyboard
even the complete King James Bible calculator had to be used from the
makes it just about possible to type
are available. Sharp has bent over number keys across the top of the
memos and idea outlines -
backwards to enable organisations keyboard, slow and inconvenient,
especially if you are a two fingered
to create bespoke software that typist. There is a help facility built especially when the enter key
works with the IQ by making all all doesn't double as the'='. ·
in which gives guidance in a
of the necessary information freely context sensitive manner. Apart from a few minor faults,
available. It is used on the road by Unfortunately, there are a number the IQ8200 is small and neat
salespersons, not only to keep track of functions not covered by the help enough to fit in the average inside
of appointments, but also to keep a and there seems to be no way of pocket. Priced at £259.99 with plug
full database of stock, orders and searching the help files for a in cards ranging from £35 to £100 it
invoicing details. particular keyword. Perhaps the is not excessively expensive. The
Built in communications most annoying aspect of the built in plug in cards make the whole
software operates through a software is that after typing system very flexible - in this sense
standard voltage RS232 link to something in, the enter key must be it is much more than just a personal
allow data to be uploaded and pressed if the information is to be organiser and is definitely moving
downloaded from the machine to a saved. This may sound rather towards to low end of the laptop
PC, Mac or any other compatible computer market. •

22 Practical Electronics April1992

 .(f
' ;')~-~~
,<;
{\-~ Antex
;:; ~ soldering kits
have been
special~ produced
to give hobbyists and
electronic enthusiasts the
• perfect tools for a w1de range
of soldering JObs. The kits
include a compact iron, handy

Newfor1992 soldering stand, a pack of

solder and a complete booklet
guide to soldering.
*New MOSFET Amplifiers There are four different kits to suit your
improved range of SMOS modules part1cular needs. Each bit contains a thermally
30VV, 30+30VV, 60VV, 120VV balanced Antex Soldering Iron (different wattage
according to kit), for which a wide range of soldering
* 20 watt Class A Amplifier bits are available. 18 and 25 watt versions include a
combined hook and finger protector. The MLXS
* Low profile PCB Transformers contains a 12 volt iron with long 31/2m lead and croc-
a range of encapsulated transformers clips for field, hobby, boat or caravan use.
4VA, 6VA, 10VA, 18VA, 24VA, 30VA
Available from leading electronic
Write or phone for data and prices ... shops and distributors.
which include details of standard range of Complete your tools with Antex
toroidal transformers and audio modules. Soldering Irons.

No price increase for 1992

Jaytee Electronic Services

143 Reculver Road, Beltinge, Herne Bay, Kent CT6 6PL Antex Electronics 2Westbridge Industrial Estate,
Telephone: (0227) 375254. Fax: (0227) 365104 Tavistock, Devon PU9 8DE Telephone: (0822) 613565
Fax: 617598

~OD
NATIONAL
COLLEGE OF
ELECTRONICS LTO
TECHNOLOGY l NEW 1992 CATALOGUE I
~-.

u §~~~
DISTANCE LEARNING COURSES
!(
The National College of Technology offer a range of packaged I I
learning short courses for study at home or in an industrial
training environment which carry national BTEC awards. Study
BOOKS BOXES & CASES CABLE & WIRE CAPACITORS
can commence at any time and at any level, enabling you to
create a study routine to fit around existing commitments.
Courses on offer include:
Analogue Electronics
Digital Electronics
Fibre/Optoelectronics KITS RESISTORS SEMICONDUCTORS
Programmable Logic Controllers
Tutor support and BTEC certification are available as options
with no travelling or college attendance required. These very
popular courses which are ideal for vocational training contain
workbooks, audio cassette lecturettes, PCBs, instruments, SPEAKERS VIDEO HEADS SWITCHES TOOLS & TEST GEAR
tools, components and leads as necessary to support the
SEND NOW FOR THE
theoretical and practical training. Whether you are a
newcomer to electronics or have some experience and simply
need an update or certifications, there is probably a distance
learning course for you. Write or telephone for details to:
COMPONENT CATALOGUE. PLEASE SEND .. . . COPIES OF CRICKLEWOOD
ELECTRONICS CATALOGUE @ £2.00 EACH. PLEASE MAKE
National College of Technology ONE OF THE BEST
RANGES AVAILABLE
CHEQUES OUT TO CRICKLEWOOD ELECTRONICS ETC.

NCT Ltd. PO Box 11, Wendover, Bucks CRICKLEWOOD ELECTRONICS LTD, 40 CRICKLEWOOD BROADWAY
Tel: (0296) 624270 LONDON NW2 3ET. TEL 081 450 0995,081452 0161 FAX 081 2081441

April1992 Practical Electronics 23

 Portable Communications - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Review...
Dataflex Comfax
Mobile communications is a major area of development for micro-electronics and, until
now, sending taxes required a tax machine - Kenn Garroch looks at an alternative.

iniature portable modems

M have been around for quite

a while whereas fax
machines have remained large desk
bound beasts. The Cornfax from
Dataflex is a very flexible modern
which not only allows standard
telephone communications up to
2400bps but can also send faxes.
The Cornfax supplied for this
review came as part of a Sharp
IQ8200 package. In practice, it
could be used with any computer
supporting RS232 communications
and having appropriate
communications software. Hooking
up the IQ to the telephone is
simple, just open the slot on the
side of the machine, plug in modern
cable, plug in to the telephone wait for it to dial. The Cornfax which is required for the lines of
socket and select the number to should connect to any fax machine the message is output- very useful
dial. The 2400bps speed is not all and had no trouble at all with the for short messages.
that fast, especially when switch box I use at home which As mentioned before, the
performing large downloads allows me to have a fax and answer Cornfax is able to operate on any
(transferring data from an online
phone on one line this is more computer with an RS232 serial port.
service to the IQ). However, for just
than can be said for some fax The manual explains the complete
sending and receiving ernail it
machines which just sit and bleat at Ha yes AT command set which the
works well.
All settings are made on the IQ's the answerphone. Cornfax supports. It is not
Once a connection is established, something for the nervous and,
phone list, name, number, speed
and comrns information. Once set a number of codes are shown which fortunately, most cornrns packages
up, the number can be dialled at the reassure the user that the system is will operate in an invisible way
touch of a button. To differentiate indeed talking to a fax. The next saving any need to 'get your hands
between normal cornms numbers, step is to upload a memo file which dirty'.
such as for bulletin boards or ernail is repeated back, again mainly as As far as specifications go, the
services, and fax numbers, the latter reassurance. Disconnection is a Cornfax is fully Hayes compatible
simply have the letter 'f' placed in matter of sending a 'control Z' and and supports the following
front of them. As with all data that's all there is to it. At the other communications protocols: V21,
communications systems, you have end, the fax machine produces a V22, V22BIS, V27TER and operates
to know the settings of the printout of the message in the same with error correction up to MNP
receiving system to be able to type face used in the IQ and, unlike level 5. It will run for up to four
communicate with it. The modern is messages sent from normal fax hours continuously on a single PP3
very flexible and allows virtually machines, no image scanning is battery and a mains adaptor is
any data format to be set up. involved so there is no loss of included as part of the package. The
Up to a point, sending a fax is as quality. The message comes out whole thing costs £399 which,
simple as hooking into any other perfectly clear and more readable considering its ea pa bili ties is a
communications system - press the that the average fax. There is also a pretty good deal if you're looking
required button for the number and saving on fax paper since only that for communications on the move. •

24 Practical Electronics April1992

 Over 11,000 Installations BRITISH
in 70 Countries Worldwide! DESIGN
eRuns on:- PC/XTIATI AWARD
2861 3861 486 with
Hercules, CGA, EGA or 1989
VGA display. _
r--~:::;::::_ _:===~=::.,
eDesign:-Single sided,
Double sided and
Multilayer (8) boards .
.,_~--1 •Provides full Surface
Mount support.
•Standard output
includes Dot Matrix I
Laser I Inkjet Printer,
Pen Plotter, ~c :~~=:u; ~ Ovtl
,,_ !Cl !Cl

Photo-plotter and N.C.

Drill. <>---!:5?r'-~;==--c
0 '...:::~~
·...
JC2 JC2

• Tech Support - free.

IJ!!!!I~:....;;::_..;:~~;;;~~LJJ •Superbly easy to use.

Options:-500 piece Surface Mount Symbol Library £48,

1000 piece Symbol Library £38, Gerber Import facility £98.
DIGITAL ANALOGUE SMITH CHART CAD
SIMULATION £195 SIMULATION £195 £195

... ~~-·-·
51
~iliil
:::
.....
.,..,
1
..... -
'"""'
""'
,.,_,
::
IIUTtG ...r-----
11\i Chocl.•

::m
:::
••- ...--~---
:._·- ....-... -. . ----1'-----:,- ~...
..... .,--..~-.--- ~=----------=--~
V.:t.,.-' ............ 1• o.--
Plol U..•n

eAt last! A full featured Digital • NEW powerful ANALYSER Ill has eZ-MATCH 11 simplifies RF
Circuit Simulator for less than full graphical output. matching and includes many
£10001 eHandles R's,L's,C's, Bipolar more features than the standard
• PULSAR allows you to test your Transistors, FET's, OP-amp's, Smith Chart.
designs without the need for Tapped and Untapped • Handles transmission line
expensive test equipment. Transformers, and Microstrip transformers, stubs, discrete
•Catch glitches down to a pico and Co-axial Transmission Lines. components, S Parameters etc.
second per week! •Plots Input I Output Impedance, •Supplied with many worked
•Includes 4000 Series CMOS Gain, Phase & Group Delay. examples.
and 74LS Libraries. 74HCIHCT eCovers 0.001 Hz to > 10GHz •Superbly easy to learn and use.
libraries only £48.00 each. eFor PC/XTIATI286I386I486 with eRuns on IBM PC/XTIATI386I486,
•Runs on PC/XTIATI286I386I486 EGA orVGA. CGA,EGA,VGA.
with EGA or VGA. • Very fast computation. •Ideal for Education and Industry.

For full information, Write, Phone or Fax:- • TECHNICAL SUPPORT FREE FOR LIFE I
ePROGRAMS NOT COPY PROTECTED.
Number One Systems Ltd. J.
REF: PE, HARDING WAY, ST.IVES, HUNTINGDON, CAMBS, ENGLAND, PE17 4WR.
Telephone: 0480 61778 (71ines) Fax: 0480 494042
International: + 44 -480-61778, Fax:+ 44-480-494042 ACCESS, AMEX, MASTERCARD, VISA Welcome.

Apri11992 Practical Electronics 25

 New Products

Wintering In
Las Vegas
fan Burley reports on the latest DCC machines, Toshiba with Video Plus, a digital compass
and widescreen HDTVs.

L
as Vegas was once again the
venue for this year's US
consumer electronics industry
showcase; CES. It was at last year's
event that Philips, with the crucial
backing of Matsushita
(Panasonic/Technics) and Tandy,
rocked the industry by
demonstrating DCC (Digital
Compact Cassette), its nomination
for the replacement of the 26 year
old analogue compact cassette. The
prize for trying the hardest at
Winter CES was probably earned
by Philips again this year as the
Dutch giant demonstrated its
involvement in a wide range of key
technology developments including
DCC, Compact Disc-Interactive
(CD-I), Multimedia PC (MPC), DCC in its most compact portable form.
digital HiFi and Kodak's Photo CD trickle of DCC units should start Tandy, Demon, Sanyo and others.
system. shipping around mid-summer, well Philips itself showed the DCC900
A year on, Philips has not yet in time for Christmas when deck at CES. This has a projected
started to ship DCC, but production price of about $700 (£390) -
prototypes were on display for the production should be in full swing. reasonably competitive with up-
first time. Philips admits they are Philips DCC models will be joined market analogue cassette decks and
behind schedule, but the initial by examples from Panasonic, right in the OAT ball-park. The
DCC for the HiFi system. DCC900 will exploit some of DCC s
advanced features like a karaoke-
style recorded text display as well
as playback-only capability for
conventional analogue cassettes.
Bitstream digital to analogue sound
shaping is standard. Another
prototype, the DCC180 walkman,
was also on show. Philips claims
the DCC180 is impervious to shock
and vibration in normal use.
Initial DCC decks are unlikely to
be as cheap as Philips was
projecting last year. The reason is
that the all-important PASC sound
coding electronics still consumes
nine chips. Mass-market affordable
DCC equipment should start to
appear once PASC integration has
reduced the chip-set count to two

26 Practical Electronics April1992

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - N e w Products

Video Plus has been taken on-board by big names such as Toshiba.
or three and ultimately one. When has been a huge success in the available, users will be able to
this has been achieved, the relative States and Toshiba's move is bound upgrade their sets conveniently to
mechanical simplicity of DCC will to be followed by others. full HDTV operation. Until then, we
see pricing dramatically below
equivalent DAT units. HDTV wide screen 16:9
------------------------------------
( Normal TV 4:3 ~
Toshiba And Video Plus
There was considerable demand
during Christmas for the newly
introduced Video Plus
programmable timer I remote for
video and satellite TV receivers and
stocks quickly ran out (see last
month's PE). At CES Toshiba
demonstrated the logical evolution
of Video Plus application by
building the device into one of its
video recorders. No longer does a
Video Plus user have to ensure
nobody moves the infra-red
transmitter inadvertently before the
desired programme has been
successfully recorded. Video Plus The difference between normal and wide screen TV at a glance.
DCC in the car.
will have to be content with
Wide-Screen TVs viewing wide-screen (standard
Wide screen (16:9 aspect ratio) resolution) home videos, a feature
TV is well established at CES now offered by an increasing
shows. JVC (absent from this number of camcorders, or banishing
year's event), RCA (owned by the letterbox effect typical of some
the French Thompson group), broadcast wide-screen movies.
Panasonic, Sharp, Goldstar, and
others have all demonstrated
either full-blown HDTV Sharp On HDTV
systems or wide-screen sets for Meanwhile, just a couple of weeks
normal 4:3 aspect ratio after CES finished, Sharp dropped a
broadcasts in the past. This year bomb-shell in Japan by announcing
both RCA and Philips exhibited a 36in HDTV set for well below
HDTV ready 16:9 'monitors' £5,000. That price is roughly a
as soon as HDTV services start quarter the cost of rival HDTV sets
and the relevant decoders are in Japan. Sharp says it has

April1992 Practical Electronics 27

 New Products

succeeded in slashing its almost two years ago, but at CES

manufacturing costs through Sanyo looked like being the first to
further decoder integration - only bring such a device to market -
six chips are now needed. The price though it's not expected to go on
is under the threshold analysts had sale until the latter end of this year.
predicted would send Japanese Sanyo's new baby has a four inch
consumers dashing for their first colour LCD screen and there are
HDTV. Cynics point out that the plans to introduce a kids version
announcement is perfectly timed with a built in graphics tablet next
for this year's Olympic games; year. Sanyo also demonstrated
Sharp could be gambling on another hi-tech device aimed at
relatively high volume sales. At kids, a portable CD+G player ideal
press-time there was considerable for karaoke which Sanyo expects to
scepticism that Sharp had avoided ship for less than £200.
cutting quality. Japan currently
enjoys 8 hours of HDTV
broadcasting daily, which is set to APen For Your Poqet
rise during the Olympics. It's Poqet Computer, best known for its
predicted that Sharp's rivals will be diminutive pocket-sized Poqet PC,
working over-time to match Sharp's has announced a pocket-sized pen-
achievement. PC, the PoqetPad. The 1.2lb device
closely resembles another compact
pocket computer unveiled by
Hand-held Video Projector Epson at the Comdex expo in the
Fuji, better known for its States last October. There is no
photographic products, showed a keyboard and most of the top
pocket-sized video projector at CES. surface of the device is occupied by Pen Driven Poqet.
The P40 device has a single colour a 7.25in diagonal 640x200 pixel
LCD projection panel. Conventional supertwist LCD screen. Dimensions flashy executive; it's a serious
cathode ray projectors have three are 9.65in by 4.59in by 1.26in. Just attempt to get into the portable data
image sources, one for each two AA batteries will provide up to acquisition market which the likes
primary colour, as do most 48 hours operating time. The of Husky, Psion and others
professional standard LCD video operating system is MS-DOS 3.30 in currently dominate. A full PC-
projectors. The P40 weighs less than 1Mb of ROM and there is 640K of based applications development
one pound and can be optionally system memory with room for two package is available. US Pricing is
powered by a camcorder NiCd PCMCIA mass storage cards. The around the $2,000 mark (£1,115).
rechargeable battery. The projected pen-centric interface has been PoqetPad may not be a consumer
image can reach 40 inches across. borrowed from Tandy and product itself but it demonstrates
provisional pricing is $800 or about handwriting recognition is that all the right ingredients are
£450. provided by NestorWriter. Textual there to produce an advanced,
input is via telescoping stylus and compact, pen-based personal
the pen-sensitive screen is good for computer - just what Apple has
Portable CD·I From Sanyo a writing resolution of 200 dots per been hinting hard that it is
currently working on.
Sony first demonstrated a inch.
prototype portable CD-I player PoqetPad is not aimed at the
Those LED Blues
When was the last time you saw a
blue LED, and I don't mean a gas
plasma or other fluorescent device?
Well, the chances are you have
never seen one. Blue LEDs do exist,
based either on silicon carbide or
gallium nitride, but they have not
been commercially popular as they
are extremely inefficient or difficult
to make. At last, however, the
standard red and green LEDs may
eventually be joined by bright new
blue LEDs, if experimental results
from various researchers around
the world are verified. The primary
colour set in LEDs would then be
complete. The significance of this is
that blue LEDs could open up a
whole new range of applications,
including large display colour TVs
and signs.

28 Practical Electronics April1992

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - N e w Products

Two research teams in Austria with sequences of motion video. Philips' CD-I.
and Japan have come up with There are obvious specialist QuickTime is a great idea, but
completely different ideas in the multimedia uses for such a facility, there are critics of its quality and
quest for the elusive blue LED. The but the beauty of QuickTime is that none more vociferous than Acorn
Austrians at the Technical it has been designed to be used, 'cut Computers which revealed its full
University of Graz have used and paste' fashion, in ordinary motion video system based, called
semiconducting organic polymers applications like word processors Replay, at the same time as Apple.
to successfully construct a blue light and even spreadsheets. For the QuickTime movies can be played
diode. It has potential because they latter, for example, you could have on any Mac, but there is a trade off
should be very easy to make a pre-recorded clip showing a in terms of frames per second rate
commercially. The only drawback is factory floor scene next to a
that they remain very inefficient. In spreadsheet graph showing its and picture size on the screen.
Japan researchers at Nagoya productivity _ complete with audio Critics say that QuickTime is too
University have produced a blue commentary. The idea is that users flickery and jerky as well as being
LED which is almost a hundred would digitise fairly short displayed too small on the
times more efficient through sequences of video, perhaps shot on commonest Apple Macs like the LC
refinement of the original gallium amateur equipment or sourced and Classic models. Acorn's Replay,
nitride process. We're still a long from high quality libraries or which runs on the firm's
way from blue LEDs being featured broadcast TV. These sequences, or Archimedes RISC workstation,
in Maplin Magazine for a few pence "movies" in Apple parlance, can plays movies on relatively large
each, but there is hope. then be pasted into an application windows and at a constant 25
of your choice. Computer generated frames per second. Acorn is big in
animation can also be incorporated. the education market in the UK, but
The Solid State Compass Watch out for a new growth area; it has little hope of dislodging
Another survivor of the mechanical CD ROM QuickTime "clip art." By QuickTime from the world PC
age has finally succumbed to the using advanced data compression market especially with the prospect
solid state age; this time it's the techniques, QuickTime movies can of MS Windows compatibility.
magnetic compass. A Plymouth- be viewed on even the least However, there may be a twist
based team at the Polytechnic of the powerful Mac Classic models and to this little story. Apple has bought
South West has come up with a Apple has revealed that a
magnetic field sensor which could Quick Time replay package into Acorn's RISC processor
be used as an electronic compass compatible with Microsoft technology, now managed by the
small enough to fit into a wrist Windows on IBM PC compatibles is spin-off ARM Ltd company. Apple
watch. The key to the technology is to be made available later in the has also confirmed it will use these
a special substance which, in year. There is also a sign that RISC processors in its as-yet secret
conjunction with an electric field, QuickTime technology could be new range of consumer products.
changes its current resistance used in a mass-market consumer One could speculate that a
according to the presence and multimedia product, perhaps to consumer version of QuickTime
magnitude of a magnetic field. Tiny rival Commodore's CDTV and will eventually be Acorn powered. •
stripes of the special ferric-nickel Multimedia on the Archimedes.
material are printed on to glass and
this enables a magnetic field
perpendicular to the stripes to be
detected. A pair of these devices can
be used to find the actual direction
of the magnetic field. Apparently
the prototypes work extremely well,
with high sensitivity and the
researchers are now working on
miniaturising the technology in
chip form. Since modern wrist
watches can monitor your heart
beat, check your blood pressure,
calculate, measure altitude, record
and play back sound and so on, a
compass function might almost
seem routine.

Picture The Action

Still life on your PC is now old hat
and that's official. This is because
Apple has launched QuickTime for
its Macintosh computers.
QuickTime lets you replace static
illustrations in desktop applications

April1992 Practical Electronics 29

 Technology

TFT Liquid Crystal

Technology
Andrew Armstrong explains how the technology behind the latest hand-held TV colour
screens works.

ost liquid crystal colour

M televisions use a passive

matrix liquid crystal
screen. This gives a picture of
Glass plates with
transparent electrodes

limited contrast and poor

sharpness. The Sony Colour
Watchman reviewed elsewhere in
this issue uses an active drive
technology with a transistor to
drive each display element in an
arrangement somewhat like a
dynamic ram. This gives clearer Fig. 1.
and brighter pictures.
To explain how it works, we
must first look at the principles on
which a liquid crystal display
operates.

Twisted Nematic
A liquid crystal is a liquid in which
the array of molecules is
crystallised. It has some of the
characteristics of both crystal and
liquid and is usually an organic
chemical made up from cigar-
shaped (nematic) arrays of
molecules. applied across the two plates, the picture streaking. These constraints
To make a display using liquid crystals line up end to end and have result in low contrast and a limited
crystals, a thin layer of the liquid no effect upon the polarisation of range of viewing angles.
crystal is sandwiched between two light. If crossed polarisers are fitted Clearly, in order to produce an
glass plates, each having a on either side of the glass plates, as analogue television image, rather
metallised layer in contact with the illustrated in Fig. 3, the application than te pixellation used on the
liquid crystal. The direction in of a voltage prevents the liquid screen of a computer, a
which the molecules lie is crystal from rotating the plane of proportional response is required.
determined by the surface finish, polarisation and hence prevents the The extent to which the picture
and, in the twisted nematic display, light passing through the entire element rotates the light, and hence
the two plates are arranged so that sandwich. the brightness of the element,
the molecules in contact with each A passive liquid crystal dot depends upon the drive voltage.
face like at right angles to those in matrix display, illustrated in Fig. 4, Most LCD televisions use a
contact with the other face, as works by addressing each picture fluorescent lamp behind the display
shown in Fig. 1. element in turn. The chemistry of to illuminate the pixels, which have
Polarised light entering from the liquid crystal must be designed red, green, and blue coloured
one side has its plane of so that it will remain in its non- filters. Thus the displays are
polarisation rotated through 90° as polarisation-rotating state in the transmissive rather than reflective,
it passes through the rotated array intervals between being addressed. but similar principles apply to
of molecules. However, as shown in It must also return to its inactivated reflective displays as used in
Fig. 2, if a suitable voltage is state rapidly enough to avoid calculators and some computers.

30 Practical Electronics Apri11992

 TFT

insignificant compared with the

Fig. 3. advantages conferred by TFT
technology.
Thin film transistors are made
by depositing amorphous silicon on
glass. Until about a decade ago, it
used to be necessary to make
transistors from high quality
crystalline silicon. Amorphous
silicon layers, though pure, had too
many unattached bonds giving rise
to energy-wells, which trapped
charge carriers. Amorphous silicon
semiconductors were made
practical by attaching hydrogen to
the spare bonds.
The technique was first applied
to amorphous solar cells, which are
used in many of the calculators now
Drive voltage on sale. The amorphous silicon
solar cells which these employ are
Fig. 4. only about half as efficient as
Passive display crystalline cells, but they are very
cheap to mass-produce.
Further developments of the
amorphous technology have made
•• it possible to produce amorphous
transistors. These do not have the

•• performance of transistors made

from crystalline silicon, but they are

••• adequate for the purpose of driving

liquid crystals, and can be

••••••••
Crosstalk to adjacent pixels is possible
economically deposited onto the
glass plates.
According to news reports about
five years ago, the means of using
thin film transistors was first
Active Drive brightness of the element.
Fig. 6 shows the pixel layout of
devised by a British engineer. He
could not get funding to develop
With active liquid crystal displays, an active TFT display. The picture this in Britain or elsewhere in the
there is one thin-film transistor elements cover most of the screen European Community, so by
(TFT), as shown in Fig.S. When the area, with a small cutout in the default the technology is now
TFT gate is energised, the capacitor bottom right corner where the thin Japanese, who have put it to good
is charged to the voltage present on film transistor is deposited. The loss use in a number of innovative
the data line. This sets the of light due to this cutout is products. •

Gate line
0,....__--1

Capacitor
holds the
data level
between
scans

Fig. 5.
!ransparent
p1xel electrode

April1992 Practical Electronics 31

 How lt Works

How lt Works ...

The Personal Stereo
Jim Haskins' mission this month is to take apart a walkman. With great care and the aid of
some miniature screwdrivers he succeeds - this is his report...

he original Sony Walkman allow the cassettes to slot in and personal stereo range now come :in

T has inspired numerous

imitations and personal
stereo's now come in a wide
provide protection for the
electronics - some models are even
splash-proof.
three main sizes, all of which take
advantage of high power
permanent magnets to produce
variety of shapes and sizes. The The other limitations on size are high quality sound. At their
idea of a pocket sized tape playing the need for a power supply that smallest, headphones are lodged
system able to play standard audio will give a reasonable playing time, inside the ears which,
compact cassettes through the motors, batteries and tape unfortunately reduces the quality
miniature headphones at HiFi playback head, all of which have of the sound - a lot of fidelity is
quality was originally developed minimum sizes. Power usually picked up by the outer portions of
by Sony in Japan. comes from two or more batteries the ear. Medium size headphones
The main components of a which must be of a commonly sit just outside the ears and
personal stereo cassette player are available variety, such as AA or produce better sound - they also
the tape transport, electronics, AAA. The more batteries there are, have the drawback of producing
headphones and the power supply. the longer the unit will operate but, high frequency noise to people who
All of this, apart from the the heavier and larger it will be. aren't listening to the music. Full
headphones, is compressed into a Most of the machinery inside size headhones have become more
case hardly larger than the cassette the casing is used to move the tape popular with personal stereos quite
itself. A standard 3.5mm from one reel to another past a recently. Since they cover most of
(sometimes 2.5mm) stereo jack plug head which picks up the magnetic the ear, they give very good sound
and socket are used to connect the fluctuations. These are amplified to reproduction. They can also have
headphones to the main unit produce the sounds heard in the muffling built in to that noise
allowing the player to be placed headphones. To maintain as
pollution is limited. •
conveniently in a pocket with just a constant a speed
cable going to the headphones. as possible a
Apart from the basic ability to pinch and
play back stereo audio cassettes, flywheel system
most modern players come with a is used. In
number of extra features. Almost addition, more
standard are such things as Dolby advanced
noise reduction circuits, balance designs use
control, fast forward, rewind and electronic
repeat play. Other features can feedback sensors
include four channel equalisation, to lock the speed
built in stereo FM radio, metal tape of the motor.
capabilities and built in This can be vital
microphone allowing the unit to in a portable
record as well as playback although system since any
this also requires an extra tape movement of the
flywheels and
erase head.
The main limitation on the size motor will tend
to cause changes
of a personal stereo is the set size of
in the tape speed
audio compact cassettes. Some of
causing the
the latest machines are actually
sound to "wow".
smaller than this and simply clip
The head-
onto the outside of the cassette
phones of a
case. More commonly, the units

32 Practical Electronics April1992

 1

1
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - HowltWorks
1

Metal tape FliP up lid is just

select switch
/
/
.......
larger than an audio 1

1
DolbY noise
reduction switch 3.5mm jack socket
tor headphones 1

Reverse play 1
capstan Protective leather
carry case
1

Rewind
1

The unit is powered 1

by two AAA batteries
1

1
Playback
head --tltf+-H--h--41-~
1

Surface mount chips 1

provide amplification,
sound and tape
transport control 1

Tape repeat
1
select
Battery
cover 1

Illustration: Derek Gooding Apri11992 Practical Electronics 33

1
 3D TV

Taking AThree
Dimensional View
The 50 year old dream of three solid television looks set to become reality with this new
idea from a British inventor. Adam Forth looks at the details.

hree dimensional television

T has been the dream of

inventors since John Logie
Baird first showed that moving
The 30 Telejector Top laser

pictures could be transmitted

electrically. Until recently, all 30
systems have attempted to fool the
eyes and brain into thinking that Where beams
the flat image it was seeing actually intersect, the
gas light up
had depth. However, a recent
invention by a British amateur
electronics enthusiast looks set to
take the world by storm.
The new system, designed by
Alan Frith, produces a solid moving Side laser
image in a tank. The viewer is able
to see the picture by looking
through one of three sides and gets
the impression of a completely solid Side laser
image.

Underground Ideas beams hit it together. Its special

atomic structure causes electrons to
unnoticeable due to the fine contrcl
over the laser beams and their
The idea for the invention,
move from orbit to orbit when focussing mechanisms.
according to the designer, came one
energised by three particular To obtain a three dimensional
day while travelling on the London image, the laser beams scan across
wavelengths. If only one or two
Tube. An advert showed two old
beams hit it then nothing happens each of the three faces of the cubic
age pensioners looking at a solid,
and the gas remains transparent. gas tank in the same way as a
three dimensional football match, Where three three beams intersect,
all in miniature with the viewers
however, the gas emits a number of
able to move around to see different Top
photons of light. video
aspects of the playing field. After
Unfortunately, the amount of
thinking about the idea for a while,
light emitted from a particular gas
Alan Frith decided to have a go at
molecule is constant so some
designing a real system to produce
method had to be devised to allow
the same effect. Ten years later, he
the light spots to vary in brightness.
has a working machine which,
The solution was to vibrate the
although it is only black and white,
scanning beams at high frequency
produces three dimensional
so that a 'cloud' of molecules are
moving images.
illuminated producing more light
similar to the dither patterns used
How ltWorks in printing. Here a patch of black
dots can be made to simulate a
The solid Video system uses three
single dot having various shades of
laser beams mounted at right
grey by changing their number and
angles around a tank of special gas.
pattern. The loss in resolution in the
The secret lies in the way in which
solid Video is completely
the gas fluoresces when the three

34 Practical Electronics Apri 11992

 3D TV

normal TV. This raster scan builds

up the light dots that make the Seeing Exited Atoms
picture from the back, bottom Atoms are made up from a core of neutrons and protons surrounded by a series
corner of the tank to the front, top. of shells of electrons. Due to the quantum nature of very small structures,
This makes sure that portions of the electrons can only sit in shells at specific levels -there are no 'in-between' states.
When the atom is exited, either by heating it up or by pumping photons into it, the
picture at the front of the cube are
outer electrons move from one shell to another to absorb the energy and then
not obscured by those at the back. move back again to release it. As an electron moves it creates an
The scanning also has the electromagnetic wave. Different atoms have different numbers of electron shells
advantage that moving images can with possible shells existing at higher energy states. The distance that the
be sourced from three standard electr~n move~ determines the wavelength of the electromagnetic radiation so,
video recorders. by u~!ng the nght type ~f atom and method of making its electrons jump, a
spec1f1c wavelength of radiation can be created.
At its simplest level, an incandescent light bulb heats the atoms in its filament
Record And Playback so that the electrons move up ~n~ down in a random manner creating white light.
In a more controlled and soph1st1cated way, a laser is energised to produce an
Because of the way in which the
exac~ _wavelength of light. The gas in Alan Frith's Solid Video reacts to three
solid image is viewed, the 3-D
spec1f1c wavelengths which combine to excite the electrons to produce light.
system works best for staged events
-at the moment the is no way to
is fed to the laser vibration burst
process all sides of a possible
image. Three standard video units and the scanning position
information derived from the G Electron
cameras are positioned at right
angles, top the left, right and above combination of the three video
synch signals. The lasers then scan
Outer shell t /\.fV\_ Light emitted
the stage area. The action is then
filmed and stored on three VCRs - across the inside of the cube and Inner shell
where they intersect they produce Nucleus
these are cross linked to provide
perfect synchronisation. This is a small bursts of light which
simple approach to the problem of eventually build up the picture.
how to film in three dimensions A critical part of the system is
and all of the interpretation and the way in which the gas is made
interpolation needed to produce the reactive to the laser light. It must be
final solid projected image is kept at a specific temperature and
performed by the electronics that pressure. This is maintained by a
controls the lasers. special pump and conditioning unit
is currently being shown to a
The basic operation of the connected to the base and both
sides of the display cube. The number of possible manufacturers
system is shown in Fig. 1. The three both in the UK, Japan and USA. The
images from the synchronised current temperature and pressure
are sensed from within the system inventor believes that with a little
VCRs are fed into the three laser development work, it could be the
drivers. These are cross linked in and feedback control is used to
keep the whole thing stable. The next big thing after HDTV.
such a way that interference
between the three images removes formula for the gas is still a secret Future improvements to the
unwanted parts of the picture. The although it is believed to based system will include full colour,
lines of each aspect (from each around C 60 Buckminsterfullerine using a mixture of three gases and
camera) are then split into pixels - and was originally been developed three excitation lasers, and the
standard analogue TV signals are in the USA as part of a particle development of the idea for use as a
not actually pixelated until they hit beam weapon research project. computer display. With Solid
the shadow mask behind the TV The working model of the Solid Video, the dream of 3DTV seems to
screen. The brightness of each pixel Video has had a patent granted and have finally materialised. •

April1992 Practical Electronics 35

 Wavelengths

The Campaign For

Real lime
Eamon Fitzpatrick wants to make time decimal but will anyone accept such a radical change
to a centuries old tradition?

read "The Naming Of Names" second? It was my ambition, attoseconds are the order of the day

I by Ashley Jones in the February

issue of PE with great interest.
The information contained in it
together with some of my
colleagues, to develop and establish
a decimal clock. Some of us were
in expressing the time taken for one
event to happen.Why not just start
all over again with a smaller base
regarding the System International convinced that if such a decimal unit?
d'Unites is extremely useful, time system were introduced, it Consider also the complex
especially for those who were would eventually replace the old divisions which must be
brought up on the 'old' Imperial system. Remember how electronically performed to provide
Units of measurement. 1 can recall apprehensive we all were when clock pulses for atomic time.
how apprehensive we all were Ireland and Britain decided to Instead of saying that Ce 13 3 has
when Ireland (and Great Britain) decimalise their currency? How 9,192,631,770 transitions per second,
decided to "go metric" in the were we going to work out the why not use this natural resonance
1970's. I was in my final years as a decimal equivalent of 13s.9d? How or that of some more convenient
student of Medical Laboratory much would it cost to buy our copy isotope and base the new time
Sciences at the time and can still of Practical Electronics in the 'new constant on a multiple of its period?
feel the anxieties as we prepared to money'? Well, whatever happened, Even if the decimal clock is not
cope with the new units. There we managed because we had to. acceptable to the world at large,
were chapters included in most Is it not reasonable to suggest could the scientific community
textbooks at the time reminding us that a decimal clock, while having nevertheless adopt it? For instance,
of the impending change and some opposition to begin with, the 'person in the street' still refers
giving tables of conversion factors would eventually be accepted and
to car speeds in miles per hour and
for converting Imperial to SI units. become commonplace. Obviously
even the car manufacturers talk of
The two systems lived side by side there would have to be some
consumption in terms of miles per
for several years before full thought given to the exact way in
transition occurred and, indeed, which the new clock would be gallon. There are many other such
many examination questions which structured. examples in common use - so much
were set using the older units We can do little about the length for decimalisation and metrication.
ended with the dreaded warning of the day. However, into how Well, whether or not
that "all answers must be expressed many units would it be divided? decimalisation of our clock ever
in SI Units!" In some cases the Would there be, for example, 10 takes place, one thing is certain:
necessary conversion tables were hours per day, giving us 2.4 'old' time will fly just as fast as it does at
supplied (if you knew how to read hours to the 'new hour'? Would present.
and apply them!) but in many each hour be divided in to 100 Eamon S Fitzpatrick
subjects you were expected to minutes and each minute into 100 Dublin
know, for example, that the gas seconds? This conversion would Ireland
constant (R), which we all knew appear to be a step in the right
was 1. 987 calories per mole per direction at least, as it would In practice, the second like the metre
degree centigrade, was now 8.3144 shorten the value of the second, a and ampere is an SI base unit. All
Jmol-1K-1 unit which appears to be getting too calculations are performed with and
There was, however, one thing big to be really useful. One reads result in multiples of seconds -
that always puzzled me about the every month in this magazine of the kiloseconds, megaseconds, ~seconds.
SI system and Ashley Jones' article advances being made in the There is really no need to convert to
came tantalisingly close to processing speed of CPU' s or the minutes, days, weeks and so on for
discussing it before it ran out of number of bits of information that scientific purposes and I don't suppose
space. It is this: why should a can be optically transmitted per anybody else really cares. On the other
metric and decimal system use such second, and more and more it hand, just think of the boost for the
an un-decimal unit of time as the appears that nano, pico, femto and clock and watch industry ... Kenn. •

36 Practical Electronics April1992

-----------------------------------Communications

Growing Pains...
The Email Dilemma
Arthur King ponders the future of electronic mail. Why hasn't it replaced the Royal Mail and
why are taxes so popular yet so un-green?

echnology has always been

T the key to better

communications. Over the last
few years the postal service has
reached new heights of efficiency.
The fax machine boom means
words and pictures can be
transmitted to the other side of the
globe in seconds. Billions of pounds
are shunted electronically between
banks every day. More and more
firms carry out their business with
the help of paperless electronic
trading. But whatever happened to
electronic mail? It's estimated that
the users of public electronic mail
networks number a mere hundred
thousand or so in the UK. Email is
still a long way from achieving
critical mass.
Over the last ten years, the most now approaching one million fax would be involved at all. It's also
advanced electronic sorting machines in the UK, another secure - only authorised eyes
machinery in Europe has endowed triumph of technology in the quest would have access to the message
the Royal Mail with productivity for convenient global store at the other end. In this age of
and efficiency improvements of communications. A fax machine is the word processor, do we need
50%. Nine out of ten first class just like a photo copier. It's so easy scraps of fax paper which
letters now reach their destination anybody can use one. In the USA a somebody might have to re-type?
the next day. But electronic mail fax machine often complements a To view an email message once it
usually gets to its destination phone in the home and it isn't has been received, all you need to
within a few minutes, seconds unknown to order 'pizzas to go' via do is load it into a word processor.
even. You don't need to find an fax. That a fax requires paper Once there you can do anything
envelope, a stamp or a post box. originals and transmissions are you like with the text.
There's no need for a postman to vulnerable to line noise glitches What about PC documents with
lug sacks of paper to a sorting seems to be tolerated by most. graphics? The pretty graphtcs
office, no need to burn vast But £axing documents is daft, generated by spreadsheets and
quantities of fossil fuels in especially if the original is CAD drawing systems, for
transporting your letter to another computer generated. Electronic example, are nothing but compact
sorting office at the other end. On mail lets you transmit a PC arithmetic codes. Pages of solid
reflection the logistics of posting a document without the strange need graphics could total megabytes of
letter conventionally are an eye- to convert it into that wasteful and data and so tie up a fax machine for
opener, but we take it for granted. relatively useless printed paper ages. The spectre of line noise
Parcels and personalised stationery form. Your average PC with a ruining it all will be ever present
will always need a postal service, typical modem could transmit a ten and the result will always be
but so much ordinary written or page word processed document via limited to 200 dots per inch
typed correspondence would be email in roughly two minutes. The resolution. Colour? -forget it unless
more suitably sent via electronic transmission would be crystal clear, you have a very large wallet. Those
mail. error free and no precious paper same graphics could be transmitted
So what about fax? There are

April1992 Practical Electronics 37

 Em ail

companies simply became newer

islands in an expanding sea which
was desperately short of ships.
Electronic bulletin board systems
devised their own inter-mail
systems, like Fidonet while Unix
system users enjoyed the Usenet
system-linker. Basically these
systems involved one location
dialling the next and exchanging
batches mail several times a day.
Public notices could end up in
Hawaii at the end of the day after
first being posted in Swindon that
morning! But these were still
proprietary solutions. It was
recognised ten years ago that all
these 'islands' needed to talk to
each other via an internationally
agreed protocol and the result was
the introduction in 1984 of X.400.
with virgin clarity, retaining colour share part of the blame. It is still However X.400 took a long time to
attributes, via email in seconds. difficult to send a message from one be widely adopted. The good news
Even bit-image data, pre-drawn network to another and without is that the implementation of the
images, can be squirted across an access to everybody else's X.400 specification is gaining pace.
email link with retained resolution mailboxes, the point of email is But even with X.400 users still have
faster than a fax by using file severely restricted. It's like having to struggle against the complexities
compression. Take the screen shots incompatible rival phone systems. of finding the right mail address for
for this article; six pictures in all The attraction of an email service is the recipient.
were sent, each 16 colour original directly related to the number of Email addresses, or IDs, are
70K long. Compression reduced people you would want to usually very compact. The Telecom
over 400K of data to just 27K, which communicate with on that system. Gold email ID for Intra Press,
took less than two minutes to send. With a few exceptions in the US, publishers of PE, is 87:SQQ567. On
PE Editor Kenn Garroch at the PE most email services turned out to be the Compulink Information
office quickly de-compressed the relatively small, exclusive Exchange (CIX) it's simply
images on his Apple Mac and communities of users. These started 'PROGNOW' the condensed title
pasted a selection directly into the off as public email services for of one of PE's sister titles, 'Program
pages you are reading now. enthusiasts, education and some Now'. X.400 returns to the original
Neither the pictures or the text forward looking businesses. Then concept of a postal address; you
you are looking at used up a single email of a form took off in the need to the recipients name, a
fibre of paper in getting from me at corporate world through PC country code, a public system name
home to Kenn at the office. The networking. Suddenly everybody and a whole host of optional
telephone time used was a mere in a company had email access to parameters. But you need only
three minutes or so, just a few each other. But networked establish the details once per
pence at off-peak rates. Compare
that with the cost of a stamp and
envelope, finding the post-box and
then the 24 hour delay before the
bits of paper arrive at the other end
-assuming you're not the one out
of ten who suffers and extra day's
delay or worse still, whose mail
gets lost. And then what rigmarole
would have to be performed at the
office to make use of posted
information ... ? Fax may be
instantaneous, cheap even, but
what comes out the other end is
hardly presentable. Imagine pasting
a faxed graph into a report; it's just
not done.
While the fax machine was
undoubtedly a major force keeping
the lid on email, the email network
providers themselves must also

38 Practical Electronics April1992

 Em ail

user interfaces have already made a

considerable impact on the user
friendliness of communications
programs. Once users had to
contend with stark online prompts
and meaningless command
syntaxes, but now there are comms
packages which can shield the user
from these horrors and to a large
degree automate the business of
logging on, fetching and delivering
mail and logging off.
So what ever became of the
paperless office ideal? More letters
are posted today than ever and
offices have never used more paper.
All this is despite the introduction
of various forms of electronic
information interchange like EDI
(Electronic Data Interchange for
recipient. compared to the relatively complex paperless trading), BACS (direct
So can we assume that by giving fax machine with all its moving wages payment) and EFTPOS
a PC users some insight into the parts, but increased demand and (Electronic Funds Transfer at the
advantages of email and providing improved modem chip technology Point Of Sale), etc.
universal inter-system will continue to drive prices down. Electronic mail is such an
compatibility, that email will In the USA, where demand is obvious solution to deficiencies in
become an overnight success? higher, the same modem typically established comm unica ticns
Possibly, but not until it's cheap costs $150. Many online services methods like letter post, fax and
and easy enough. Online services now offer 9600 and even 14.4K bps even telex. Hand delivered mail
mostly require registration and a links, useful for large document may one day become robotised, but
standing charge plus usage charges, transfers or big graphics files. Don't we will always expect packages and
just like the telephone. The beauty forget that many electronic bulletin other bits of paper delivered this
of the postal system is that it's pay boards offer downloadable public way. I can see the time when email
as you go. It's arguable that domain or shareware software, will take over from fax. Indeed, fax
electronic mail is just that, an which can involve lengthy and email are already moving
electronic version of the post, not an downloads. closer together. PC-dedicated iax
alternative to, say, the phone even if Ease of use is an area in which modems, which enable paperless
the phone network happens to be the fax machine, for all its fax transmission and reception are
used as the carrier. As email use is weaknesses, has email beat, for the already gaining popularity, as are
nowhere near critical mass, public time being at least. Fax is as easy to models which combine fax and
network providers have to rely on use as boiling a kettle while email is email capability.
premium charges. It's a vicious as difficult to use as your PC. But The chances are that if you aren't
circle typical of an emerging service PC operating systems are getting using email yet, you will be sooner
technology; charges will remain better all the time. Windows-type or later. •
high until demand driven discounts
can be triggered, yet the inherently
high cost of the facility stunts that
crucial growth. Old-fashioned 'snail
mail' and the rough and ready fax
machine are unhindered by the
kinds of growing pains experienced
by electronic mail.
The cost of hardware has also
been a problem. There is no great
outlay involved in posting a letter
and even a fax machine can be had
for less than £300 - hardly a luxury
these days, especially for
businesses. Only recently have PC
modem prices started to fall. An
error corrected (MNP standard)
modem offering 2400 bits per
second transmission speed now
typically sells for between £200 and
£300. This is still expensive

April 1992 Practical Electronics 39

Semiconductors----------------------------------

The Making 01
Semiconductors
Mike Sanders tells you all you need to know about the technology behind the
semiconductor industry.

ll materials consist of atoms fewer electrons than orbits further

A which have a nucleus

surrounded by electrons.
This nucleus is made up from
away with inner orbits being filled
before outer orbits. The orbits
correspond to the rows of the
Electron

protons (positively charged periodic table and when one is

particles) and neutrons (particles filled, a new one starts.
with no electric charge) - Fig. 1. The Elements with the same number
electrons move in various orbits or of electrons in the outermost shell
shells surrounding the atom. are placed in the same column. The
For the atom to have a neutral number of electrons in the
Proton
charge, the number of electrons outermost shell is indicated by the
must equal the number of protons. group number. For example, all the
Increasing the number of electrons elements in column one have one Fig. 1. The structure of the atom.
ionises the atom giving it a negative electron in their outermost shell.
charge. The gain or loss of electrons The Russian chemist Dimitri
Ivanovich Mendeleev observed that fill and empty the shells
usually occurs in the outermost
orbits since, being further away, chemically inert elements have respectively to form an ionic or
they have weaker electric bonds to eight electrons in the outermost electric bond.
the positively charged nucleus. shell. This goes some way to Similarly, a group six element
Fig. 2 shows the periodic table of explaining why group seven will react with a group two.
elements based on the arrangement elements will readily react with However, the electric field will not
of electrons around the nucleus. those in group one - stealing the be strong enough to steal two
Orbits close to the nucleus contain single electron to make eight and electrons so these are shared to
Group Fig. 2. The Periodic Table Of Elements.
~

lA Inert gases
~ -2
Atomic number
H He
RydPagen IIA Symbol IliA IVA VA VIA VII .....
3 4- ~ 5 6 7 8 9 10
Li Be"' 8 c N 0 F Ne

...--s
Udllum BePylllam 1111'111 Cll'llla Nlll'llll flllrlll 11111

-
11 12 13 14 15 16 17 18
Na Mg VIII AI Si p Cl Ar
IIIB IVB VB VIB VIIB .- __...._
....... IB liB .....
..
S8llilml Maaaesilln 11111:8 l'liiiiPIIII'II Clllli'lll

....
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
K ea Se Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
.,...
PDtasslum Clllclum Scandllmi ~ VIRadlum Chromium Manganese 11'1111 Collal! NICkel lllll: Galllln GIPiiiMa IPSIIIIc llrlllill

-
37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
Rb Sr
llllllltum Sll'llllllllm
V
Ylll'111m
z Nb Mo Tc Ru Rh Pd Ag Cd
lll'&1lllllm NIDiilum MD\J1III8IIllll Tetlmellum lllltlleDl11rn lllillllllm PaBRlllm SlveP ~
In
llllllln
Sn Sb Te
1111 ll1iiiPIIIII
I
1111111
Xe
X..
73 74 75 76 77 78 79 80 81 82 83 84 86
55 56 57 72
w 85

87
Cs Ba La Hf Ta
ClleSIIIm

Fr
IPam:lllll
88
llil'lllm

Ra Ac
llalllum
L8lllllaDum
89

Ac1bllum
HaiDium

58
1lm1alum

59
IYlJifm

60
Re Os
Rllllnium

61
Osmium

62
1-
lr

63
Pt Au Hg Tl
PlatJnllm

64
Golll

65
MercaPy

66
T1lllliiR

67
Pb Bi Po As Rn
1.1111

68
IIISnlldll

69
1'1111111111

70
-- 71
11111111

Lanthanides Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
CUrium I'Peseedynlum Neodynlum Prmnelhillm SamariiiD IIII'8IIIIID lladalinlum TerbiUm IIJ$III'ISillll II8IIIIIID 11'1111111 T1lllliiR Y1IINIIIIl 1111111111

--
90 91 92 93 94 95 96 97 98 99 100 101 102 103
Actinides Th Pa
liiiii'IIID I'POiecllnlam
u Np Pu Am Cm Bk Cf Es Fm
IIPaoiiiD F..-
Md Plllfmllum Amerlcum CUrium lleltellllm l:allfariiiiD liiiSIIIIIIIIII Mllilllllvllm ...... LlwPIIclln

40 Practical Electronics April1992

-----------------------------------Semiconductors

be added to produce either a This is the starting point of a

Fig. 3. Hole movement from right to leH. shortage (holes) or surplus of process that consists of three main
electrons. Silicon has four electrons steps:
in its outermost orbit and doping it First of all, sand (Si0 2 ) and
with group IliA elements like carbon (C) are brought together in
boron, aluminium or gallium an electric arc furnace to produce
•••••• produces holes. Similarly, doping
silicon with group V A elements
the following reaction:

•••••• 0 • 1+1 produces a surplus of electrons. Si02 + 2C = Si + 2CO

Elements that provide holes are
called acceptor impurities and The silicon dioxide is reduced to
••••• 0 • • 1+2 produce P-type (positively charged) 99% pure silicon (metallurgical
materials. Those that provide excess grade) and carbon monoxide gas .
• • • • 0 • • • 1+3 electrons are called donor Next, the silicon is purified
impurities and produce N-type further by converting it to
form a covalent (sharing) bond. (negatively charged) materials. trichlorosilane (SiHC1 3 ) by adding
Other groups that will combine are Commonly used group V A hydrochloric acid and heating to
three with five and four with four. elements are arsenic, phosphorous 1260C:
and antimony.
The carriers within a Si + 3HC1 SiHC1 3 + H 2
Top Of The Class semiconductor, the holes and
There are a number of ways to electrons, move by two methods, Trichlorosilane is a liquid at
classify materials, one of which is drift and diffusion, and determine room temperature and is purified
by the ability to conduct electricity. the total current flowing within the by distilling (fractionation). This
Materials grouped in this way are material. Drift is the movement of gets rid of many chlorides such as
classed as insulators, conductors or the carriers under the influence of those of copper, iron, phosphorous
semiconductors. Insulators have all an electric field. Without this the and boron as well as silicon
their electrons bound tightly to the carriers would move about tetrachloride (SiCl 4).
atoms so that none are able to move randomly instead of in a fixed The final stage is to take the
around and conduct electricity. direction. Diffusion is the purified trichlorosilane and heat it
Conductors have many free movement of carriers from a region in the presence of hydrogen to
electrons enabling them to carry of high concentration to a region of produce pure silicon and
current. Semiconductors are in- low concentration - rather like a hydrochloric acid again. The
between having just a few free squirt of dye in water. At first only reaction takes place in a chemical
electrons. the immediate area is coloured, vapour deposition reactor (Fig. 4).
In semiconductors, the absence then fingers of colour spread out The silicon is deposited on pieces of
of an electron is called a hole and until finally all the water is more or pure silicon called 'slim rods' which
has an effective positive charge (the less uniformly coloured. are heated resistively.
opposite to an electron). The hole is The resulting silicon bars are 2m
a vacancy and can move around the to 3m in length, up to 20cm in
material as electrons move into it - Purification diameter and are now ready for
the vacancy thus moves in the Silicon makes up about a quarter of growing crystals. The complete
opposite direction- Fig. 3. the earth's crust and is found purification process takes several
Starting with pure silicon, mainly as silicon dioxide (Si0 2 ) - hours.
various impurities or dopants can more commonly known as sand.

Quartz _ ___,.._,
chamber

Slim rod

Deposited. --1+-il!§'l
layer

Chamber

Inlet
~ Rod holder
Melt

Fig. 4. CVD reactor. Fig. 5. The Czochralsku process.

April1992 Practical Electronics 41

 Prototypes manufactured directly in your own Lab in only a few hours.
THE NAME IN INNOVATIVE

1\NC. COMMUNICATION PRODUCTS LPKF offers a complete solution:

Professional periphery
STOP NUISANCE CALLS for every CAD System.
PROTECT YOURSELF AGAINST UNWANTED
TELEPHONE CALLS Time spec sheet
DL20 TELEPHONE CALL of a 4 layer multi layer
milling inner layer: 45 min
FILTER-MONITOR-ANSAPHONE pressing: 120 min
* Call-Screen: Displays the number of incoming calls before drilling:
through plating:
10 min
105 min
the telephone is answered milling outer layer: 60 min
* Call-filter: No more unwanted calls operating time: 5 hrs. 40 min
* Call-Counter: Check number of calls
on return
* Call-Register: Stores 40 incoming
* call numbers and the time of call
Call-Monitor: Listen to any noise in
your home/office by a secret code
when calling

** Normal time display

Memory back-up during power
cut
£ 118 29
•
all prices are exclusive of VAT £3pp
Through Plating

* Can connect both tone or pulse telephone systems

For prototype production LPKF Mill/Drilling Request info material or call:
machines have proven its merits in thousands
* 20 phone number memories can be stored and recalled of installations all over the world. CAD data can
* OGM: To record a personalised outgoing message be downloaded from any CAD system and
prototypes are manufactured automatically
either through the mill/drilling machine or by
NORTHERN MARKETING CONCEPTS means of our latest laser technology.
.,._ 24 HOUR ORDER The CONTAC through plating system and the
~ HOTLINE MULTI PRESS completes the system
TEL (09442) 8887 Suitable for any CAD system I
Also suppliers of-
SCANNERS • TELEPHONE RECORDERS • COMPUTER-AIDED
SURVEILLANCE SOFTWARE
Please note that certain equipment may need approval before connection or use

OMNI ELECTRONICS
stock a wide range of
electronic components at
174 Dalkeith Road
"SBC-1" Edinburgh EH16 5DX
£17.50 Tel: 031 667 2611
+SOp P&P
Open Mon-Thu 9.15am-6.00pm
+VAT
Fri 9.15am-5.00pm
A computer doesn't have to look hke you'd expect a computer to look
lt doesn't have to have a keyboard and a screen and floppy dtsks and _.. Sat 9.30am-5.00pm ~
~ 1990/91 catalogue costs £1.50 ll!iili!!IJ
so on
The SBC-1 has the bare mmtmum of chtps a ZBO computer can have
and st1ll be a computer A 4 MHz Z80-CPU chip, an EPROM Chip (up contains vouchers to use against purchases
to 32K), a stat1c RAM ch1p (up to 32K) and a pa~r of 8255A 1/0 (input
output) chtps gtving 48 tndtvtdual lines to waggle up and down. There Do you have your copy yet?
are one or two addtttonal "glue" crups mcluded, but these are stmple
"74LS" or "HC" parts
A star feature IS that no spec1al or custom ch1ps (1e PALs, ULAs. ASICs
etc) are used and thus there are no secrets. The ZSOA IS the fastest
and best established of all the 8-bit microprocessors - possibly the
cheapest tool
Although no senal 1ntertace IS mcluded. 1t IS easy for a ZSOA to waggle
one b1t up or down at the appropnate rate the cost 1s a few pence
worth of code 1n the program: why buy hardware when software wtll do? MAKE YOUR INTERESTS PAYI
over the past 100 years more than 10 million students throughout the world have found
Apphcat1ons already 1dent1fled mclude: Magnetic Card reader, mtn1 it worth their while! An ICS home-study course can help you get a better job, make more
printer 1ntertace. pnnter buffer, push button keypad. LCD alphanumenc money and have more fun out of life! ICS has over 100 years experience in home-study
panel 1ntertace, 40~zone secunty 1ntertace for auto sendmg of secunty courses and is the largest correspondence school in the world. You learn at your own
alarms, code converter (eg IBM PC keyboard codes to regular ASCII), pace, when and where you want under the guidance of expert ·personal' tutors. Find out
real t1me clock (w1th plug tn module), automatiC horttcultural 1rngat1on how we can help YOU. Post or phone today for FREE INFORMATION on the course of your
controller. choice. !Tick one box only!J

--------------------·
By d1sabling the on-board ZBOA-CPU this card w1ll plug mto our lnterak
1 CP/M Plus disk-based development system, so 1f you don't fancy
hand-assembling Z80 mach1ne code you don't have to'
The 1dea IS (if you are a manufacturer) you buy 1ust one development
system and then turn out the cheap SBC-1 systems by the hundred. If
you are really lazy we can wnte the program for you and assemble the
SBC-1 cards so you can get on w1th manufactunng your product, leav1n
all your control problems to us

Greenbank - - - - - -
For more details write or phone us·
Greenbank Electronics, Dept PE03 460 New Chester Road, Rock
Ferry, Birkenhead, Merseyside. L42 2AE. Tel 051-645 3391

42 Practical Electronics April1992

----------------------------------Semiconductors

Rod holder---llll--~•1>

z z
2 2 n
'I
I I

Chamber
'
Polycrystalline rod - - - i l - - - . l l i I
''
I
I '' I

I
I
' ',1 2 1,' 2
RF c o i l - - - - - - - - - I X X
I
I
I
I
I I I
11,''
"

2 2 Fig. 7. Miller Indices.

Fig. 6. The Fz reactor. z z

Growing Crystals In practice, the pull rate runs at

different speeds varying between
by means of an optical pyrometer
which measures the temperature of
The two methods used for growing
single crystal silicon for five and 12in per hour at the the crystal. This is connected to a
semiconductors are the float zone beginning and two to four inches closed loop system that makes
and Czochralski method - usually per hour at the end. The initial corrections to the temperature,
abbreviated to Fz and Cz narrow part is called the neck and is rotation and pulling speeds.
respectively. withdrawn at a faster rate to avoid Since the level of the melt drops
Up to 90% of the crystals are crystal dislocations. The neck is as the wafer is grown, the crucible
grown by the Cz method which followed by the shoulder and body is lifted slowly to keep the melt
uses a crucible made from pure as shown in Fig. 5. level within the hot area of the
silicon dioxide (quartz) as shown in To keep the melt at a constant furnace. If impurities are required
Fig. 5. Pieces of silicon crystal, temperature, it is stirred by rotating in the wafer, they are added to the
called the charge, are placed in the the seed holder at six to eight revs melt before the crystal is grown.
crucible and heated to a per minute (rpm) while rotating the The float zone method does not
temperature of 1415C, their melting crucible in the opposite direction at use a crucible so there is no oxygen
point. The heating is carried out 12 to 14 rpm. The gas used to cloak contamination from it. The high
either thermally or by induction the crystal during the process is resistivity materials produced by
using radio frequency (RF) energy. argon - a very un-reactive element the Fz method are used in SCRs
A seed crystal with the desired which will not produce any (Silicon controlled rectifiers), power
lattice structure is dipped into the impurities. diodes and transistors.
melt and withdrawn slowly, pulling The eventual diameter of the In the Fz method a rod of crystal
out the melt which solidifies as it crystal depends on the pulling rate, silicon is placed in a chamber with a
leaves the crucible. If the pull rate is rotation speeds and the seed crystal attached to one end -
correct, a crystal of the same temperature of the melt. The Fig. 6. The chamber is filled with an
structure as the seed is grown. diameter is controlled automatically inert gas and the heating process
Silicon dioxide Anode Silicon dioxide ·1 dioxide

Fig. 8. Epitaxial deposition of a diode. Fig. 9. Transistor using an epitaxial collector.

April1992 Practical Electronics 43

 Semiconductors-----------------------------------

Fig. 10. Transistor using an epitaxial base. Fig. 11. Bipolar integrated circuit.
begins. An induction coil is used, Two common defects in crystals plane at infinity - since and
starting at the seed crystal end, are dislocations and planar slips. parallel lines are said to meet at
melting a portion of the seed and Dislocations are due to irregular infinity.
the rod. The radio frequency coil heating or cooling and slips occur Fig 7b shows a crystal that
then moves upwards giving the rod when one part of the crystal shears. intersects the x axis at 1 but doesn't
the same structure as the seed Defects can be detected by etching intersect either of the y or z axes
crystal. The crystal diameter and staining the wafer. The two and thus has a Millar index of 100.
depends on the speed of movement manufacturing techniques have
of the induction coil with the been sufficiently perfected to
diameter being limited to about prevent defects but these can arise Manufacture 01 Waters
7.5cm because of the danger of in subsequent handling. The crystal is ground into a disk
collapsing the rod. and the orientation determined.
Boron or phosphorous are used Which crystal face will be presented
as impurities in the Fz process. Cut Up on the surface is decided by the
These are introduced as a gas and The cut or a silicon wafer is defined seed crystal but the outer axes are
produce uniform resistivity by the orientation of the crystal to decided by the rotational
throughout the length. the x, y and z axes. These are called orientation of the crystal rod. The
By contrast, in the Cz method as Miler indices and are defined as: crystal has axes along which it is
the crystal solidifies, impurities easier to break it into smaller pieces.
(dopants) are injected back into the Xmdex-
-X- - - This has to be taken into account
melt, making it richer as the level int er sec tio11 before building circuits onto it. To
gets lower. This makes the tail end make a reference plane, a flat
of the crystal more heavily doped surface is ground onto the crystal
1
than the seed end. Yindcx = Y. and then etched to remove any
1J t "' St'C fiJ'" rough surfaces.
Fig. 11. Bipolar integrated circuit. The crystal orientation is
1 detected by an x-ray diffraction
,i dioxide
zindcx = z inter sec tim
process, ground with one or more
flat areas, then sawed into thin
If the crystal slices called wafers by the inner
intersects the axes at edge of a ring shaped saw.
x=1, y=1 and z=1 then Diamond powder is sprinkled onto
the orientation is 111 as the saw blade to assist cutting. At
shown in Fig 7a. If the this stage care is taken not to chip
crystal does not intersect or flake the crystal and saw marks
a particular plane then it are removed from the wafer by
is said to intersect that etching.
Unfortunately, the wafer is still
not flat enough for processing and
must be polished on both sides by a
process known as lapping. Any
damage caused by this is removed
by etching with acid which can take
between 1O!lm and 30!lm from each
side of the wafer.
A mixture of ascetic, nitric and
hydroflouric acid is used for
etching. Alternatively, hot caustic
etching using sodium or potassium
hydroxide can be used - at
Fig. 12. CMOS integrated circuit. temperatures between 70C and

44 Practical Electronics April1992

----------------------------------Semiconductors

130C. Acid is faster but more • An arrangement for ~ RF heating coil

hazardous, less friendly to the handling waste gases ••••• * •• *.
environment and gives a less The reaction chamber
uniform finish than caustic etching. itself may be made of __ ...,__Gas in
The wafers are checked for · 1ess stee 1, quartz, Gasout
stain
resistivity, flatness and thickness aluminium or even a Quartz tube
and then mounted onto a polisher cloak of nitrogen.
to give one side a mirror finish. The Epitaxial growth is a Susceptor Fig. 13. Horizontal chamber.
special case L __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __J

and is used for epitaxial layer on a more heavily

producing both doped substrate, Fig. 11 and 12.
integrated circuits as well
as discreet components
based on silicon. The Reaction Chamber
Epitaxial growth, Three types of chamber are used,
together with high horizontal, vertical and barrel. In
temperature diffusion, the first (Fig. 13), the gases enter at
are also used in one end and exit at the other. They
manufacturing light pass over the wafers which lie flat -
emitting diodes. the wafer bed slopes to compensate
Expitaxial growth for the low concentrations of gas
produces devices with towards the exit.
Fig. 14. Vertical chamber. higher speeds and In the vertical chamber, the
breakdown voltages as gases enter an exit vertically (Fig
wafers are then cleaned and well as being able to handle higher 14). The wafers still lie flat and the
examined for again for resistivity, current. In manufacturing diodes, wafer bed, called the susceptor,
flatness and contamination. the silicon substrate is heavily rotates within the chamber to
doped to provide low resistance encourage the gas to circulate and
which lowers the reverse junction hence produce a more uniform
Growing Layers breakdown voltage. To counter this deposit.
The chemical vapour deposition a lightly doped epitaxial layer is In the barrel chamber the wafers
(CVD) process decomposes a gas deposited on the substrate as shown are mounted on the vertical faces of
compound and deposits a stable in Fig. 8. a rotating susceptor, Fig. 15. The
layer on a heated substrate. Transistors can be manufactured gas enters at the top of the chamber
Growing epitaxial layers is a either by starting with an epitaxial and leaves at the bottom.
particular kind of CVD where the layer to form the collector and The susceptor is made of
structure of the deposited layer is diffusing the emitter and base (Fig. graphite coated with a thin film of
the same as the substrate. All CVD 9), or by starting with an epitaxial silicon carbide. The wafer board is
processes require: layer to form the base and then called a susceptor because it is
• A reaction chamber diffusing the emitter as in Fig. 10. susceptible to heating by RF waves.
• A means of controlling the gas Bipolar integrated circuits as The carbon atoms in the graphite
flow well as MOS and CMOS are made to vibrate by the RF
• A method of controlling the (complementary metal oxide energy producing heat and the
sequence and timing of events semiconductor) devices are silicon carbide film prevents carbon
• A means of heating the substrates manufactured using highly doped contamination of the wafers.
The horizontal and vertical
Optical reactors both employ RF heating
temperature with temperature monitoring by
Susceptor sensor Gas in optical techniques. Both the colour
and intensity are monitored against
known values and corrective action
is applied to the RF energy. For
example a white colour indicates a
higher temperature than red.
Metallic sensors cannot be used
since the RF energy will couple
with the sensor.
The barrel reactor employs
quartz lamps for heating and
therefore a thermocouple may be
used. The epitaxial process is called
a cold wall process because the
walls of the chamber are cooler than
the susceptor and the rate of
deposition is faster on the hotter
Gas out
Fig. 15. Barrel chamber. surfaces.

April1992 Practical Electronics 45

Semiconductors----------------------------------

required temperature. temperature (950C to 1050C) used

6 Considering the for processing silane means that the
number of gases that doped regions of the wafer are less
Damaging
have to flow in and out of affected by migration of impurities
HCI
4 region the chamber, flow meters than in higher temperature
% as well as timers are processes. The reactions are:
3 Polishing
reg1on required. In the early
2 days, operators used stop SiH4 =Si+2H 2
watches whereas today,
1180 1200 1220 1240 1260 1280 1300 1320 most of the processes are Silicon tetrachloride is kept in
Degrees C automatic,. The operator the liquid state in a container near
simply watches the dials OC and hydrogen passed over it to
Fig. 16. Wafer etching with HCI.
and loads and unloads pick up the vapour. The amount it
the wafers. picks up depends on the
Two of the most common temperatures of the container and
Going With The Flow methods of controlling the flow of the rate of flow of the hydrogen
Various gases are used to flush the gas are to measure the cooling effect carrier. The reaction is:
chamber, etch the wafer, coat the of the gas on a heated wire or to
wafer and carry dopants. float a sphere in the stream. The SiCL4 +2H 2 =Si +4HC1
Before heating up the reactor, air exhaust gases need to be made safe
must be flushed out with a neutral to discharge into the environment. If the concentration of SiCL 4 is
gas such as nitrogen. Similarly, The equipment that does this is too high, far from depositing an
during cooling down, after the called a scrubber and adds large epitaxial layer, etching takes place
epitaxial layer has been deposited, amounts of nitrogen to cool and and silicon is removed. The reaction
the remaining gas must be flushed dilute the gases. The gases then is:
out. pass through long curtains of water
During the etching and doping to cool and dissolve and gases Si + SiC14 = 2SiC1 2
processes, hydrogen is used as a further.
carrier gas to maintain a steady Also, at this temperature (1150C
flow and uniform conditions. to 1225C) the diffusion profile of
Nitrogen cannot be used at these The Epitaxial Process doped regions could alter as the
temperatures since it will react with The wafer is cleaned with solvent to dopants migrate.
the silicon. Helium can be used remove grease then with acids and When the epitaxial growth is
instead of hydrogen. dried. The acids used in sequence complete, the temperature is
The gases used for doping must are sulphuric, nitric and reduced and at SOOC, hydrogen is
be compatible with the gases hydrochloric. The wafer is also replaced with nitrogen for flushing
already present in the reactor. scrubbed to remove particles. and further cooling. The wafer
Compounds of hydrogen are used Once the wafers are clean they surfaces are oxidised to protect
and, since they are only carried in are not handled by the front them against contamination and
small percentages (highly diluted) surfaces. Instead suction is applied they are unloaded with care.
of the carrier (hydrogen), it is easy to the back by means of vacuum
to control the flow and hence the wands to load the wafers onto the
dopant. Diborane (B 2 H 6 ) gives P- susceptor. The susceptor heats up Non-epitaxial Processes
type material, arsine (AsH3) and and nitrogen flushes the chamber. The three types of reactor used for
phosphine (PH 3) produce N-type. When SOOC is reached, hydrogen is epitaxial processes can also be used
Before the epitaxial layer is used as the carrier gas to transport in non-epitaxial processes. In
deposited, the surface is prepared HCl acid to etch the surface. addition, the reactions can also take
by etching. Hydrochloric acid (HCl) As silane requires the lowest place in a blanket of inert gas like
gas is used at a concentration of 1% operating temperature and silicon nitrogen- Fig. 18.
to 4% in hydrogen to give a fairly tetrachloride the highest In cold wall systems, the walls
linear etching rate. About 0.25Jlm to temperature, we can examine these are only cold when compared to the
1Jlm of surface is removed. The two sources for epitaxial growth
difference between a nicely Silane is diluted with hydrogen Inert blanket

polished surface and a pitted when stored in a tank since it

surface depends both in the ignites on contact with air. The low

lrnnl
concentration of the HCI as well as
the temperature (Fig. 16).
For depositing the epitaxiallayer Required Rate of
a compound containing silicon and temperature deposition
hydrogen or silicon and chlorine or Material in C in um/min
both hydrogen and chlorine is used Silane (SiH•) 950- 1050 0.1-0.25
Dichlorosilane (S1 H2CI2) 1025- 1100 0.1 - 1.0
- Fig. 17. Silicon tetrachloride is a
Trichlorosilane (S1 HCI3) 1100-1175 0.2-2.0
liquid at room temperature but the Silicon tetrachloride (SiC I•) 1150- 1225 0.2- 1.0
others are gases. Fig. 17 shows the
rate of deposition as well as the
Fig. 17. Wafer etching with HCI. Fig. 18. Gas blanket reactor.

46 Practical Electronics April1992

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Semiconductors

Temperature in C Material deposited Film SiH4 + 4C02 = Si02 + 4CO + 2H20

Si02
Plasma enhanced CVD 100-300 Poor
SiN
At the higher temperature of
Si02
Atmospheric CVD 300-500
Phosphorous olass
Good SOOC to 1000C, hydrogen must be
Si02
used as a carrier to give:
Low temperature LPCVD 300-500 Good
Phosphorous glass
Si02
Medium temperature LPCVD 500-900 Phosphorous glass Very good
SbN4
Polysilicon In the semiconductor industry, it
can be seen from the above
Fig. 19. CVD at different pressures and temperatures. reactions that many hazardous
wafers and such systems employ through several slits along the chemicals and gases such as carbon
RP or ultraviolet heating. Systems reactor. The barrel reactor produces monoxide, arsenic and various
using thermal resistance heating are a more even gas distribution but acids are used. This demands the
hot wall systems. Cold wall systems cannot handle as many wafers. most stringent precautions as some
can.be heated and cooled rapidly Many different materials can be acids even appear as exhaust gases.
because of the small mass that deposited using the CVD process A layer of silicon dioxide doped
needs heating. This is also assisted but in processing semiconductors, with phosphorous is sometimes
by the large volume of gas flowing. the materials commonly deposited used to prevent the migration of
CVD processes must guard are: impurities. Unfortunately, if the
against contamination from leakage • Silicon nitride phosphorous content is mote than
of oxygen or water vapour and the • Silicon dioxide, dope or pure 5%, the metal layer is etched when a
key to successful processing is good • Polycrystalline silicon voltage and moisture are present.
gas flow control, a uniform Silicon nitride is deposited to To prevent this a layer of undoped
temperature and an optimum form a dielectric. If nitrogen is used silicon dioxide can be used between
position for the substrate in the as carrier, at a temperature of 600C the phosphorous doped layer and
chamber. to 700C, the reaction is: the metal.
Low temperature CVD is Silicon crystal which does not
popular for depositing silicon have a structure extending
nitride and phosphorous glass for
throughout is called polycrystalline
creating passive layers directly over Alternatively, using hydrogen
metal layers. However, the or poly. It is deposited using
as a carrier and a temperature of nitrogen as a carrier and a
disadvantage is that the layer is not 900C to 1100C the same reaction is
uniform and processes in the higher temperature of 600C to 700C or
obtained. hydrogen at a temperature of 850C
temperature range SOOC to 900C Silicon dioxide can be deposited
provide better insulation between to 1000C. At both temperatures the
doped with boron, arsenic or
layers. reaction is:
phosphorous and is usually
Low pressure CVD processes are deposited at temperatures below
becoming popular because of their 450C to prevent damage to existing
more uniform coverage and Fig. 19 metal layers. It is usually deposited
shows the materials deposited and to guard against scratches and can Polycrystalline deposition is
the film quality by suing a be deposited at temperatures of used if the deposition temperature
combination of pressure and 200C to SOOC using nitrogen as a is below that used for growing a
temperature. carrier to give the reaction: single crystal. It is also used in the
Most low pressure CVD rate of deposition is higher if the
processes use a horizontal reactor substrate lacks a crystal structure.
with the wafers placed vertically as Poly can be deposited doped or
in Fig. 20. A resistance heater covers Or at a temperature of 500C to undoped and us usually the latter.
the length of the quartz chamber SOOC and still using nitrogen as a It is doped later to provide a
which has a vacuum pump at one carrier a different reaction occurs: conducting layer. •
end and a gas flow control at the
other.
Although the horizontal Heating coil
chamber can handle a large number 00000000000000
of wafers, there is the old problem
of depleting the gas of reactive
elements. One method of Gas+--
overcoming this is to have a out
temperature gradient along the 1111111111111
reactor but this could increase the
thickness of the film at higher 00000000000000 ~
temperatures. Another method Quartz chamber
Wafers
would be to maintain a constant
temperature but inject the gas

April1992 Practical Electronics 47

 Happy Memories
Memories Motherboards
4116 150ns (Pulls) 1 00 80286 12MHz EMS on board , Up to 4Mb RAM £55
. 80286 16MHz " " £72
4164 100ns 1·45 80286 20MHz £89
41256 80ns 1.65 80386SX 20MHz Up to 20Mb RAM £155 25MHz £169
41464 80ns 2.25 80386DX 25MHz Cache Up to 32Mb RAM £275
414256 80ns 3.95 80386DX 33MHz 128K Cache " £335
411000 80ns 3.95 80486SX 20MHz £420 80486DX 33MHz 64K Cache £595
256 x 9 SIMM 80ns 11.50 Diskdrives
256 x 9 SIPP 80ns 12.00 5%" 1.2Mb Floppy £43 3.V2" 1.4Mb Floppy £36
1Meg x 9 SI MM 80ns 29.50 40Mb 25Ms IDE 3 112" £139 85Mb 19Ms IDE 3112" £215
1Meg x 9 SI PP 80ns 30.50 104Mb 19Ms IDE 3V2" £240 180Mb 19Ms IDE 3112" £375
IDE Controller for 16 bit bus. 2 x FDD & 2 x HDD £18
4Meg x 9 SIMM 80ns 110.00 Ditto with Serial, Parallel and games ports on board £29
36 bit (72 pin) SIMMs Call Video
6264 100nsLP 1.95 TIL Mono/Parallel Printer card. Hercules compatible. £12.95
62256 100nsLP 2.95 VGA card, 16 bit 256K RAM, upto 800 x 600 resolution £29.95
2764 250ns 1.85 VGA card, 16 bit 512K RAM, upto 1024 x 768 £59.50
27128 250ns 2.25 VGA card, 16 bit 1Meg RAM, 1024 x 768 in 256 colours £79.50
27256 250ns 2.45 Amber TIL 12" monitor £85.00
27C256 250ns 2 45 VGA paper white 14" inc. on-site warranty £89.50
· VGA colour monitor 1024 x 768 14" inc. on site warranty £260
27512 250ns 3 .45 1/0, plug-ins etc:
27C512 250ns 3.75
120Mb internal tape streamer (uses floppy controller) £199
102 Key Tactile Keyboards £29.50
MS compatible serial mouse, 9/25 pin adapter, software £13.95
2 serial, 1 parallel & games port 1/0 card £12.95
Desktop case with 200W power supply and all fittings £75.00
Carriage on Motherboards, Floppy drives & Keyboards £5, Mice, Video & Controller cards £3, Cases, Hard disks & Monitors
£10, IC's free if over £20 nett, else add 75p. VAT to be added to the total. List of other IC's and computer parts on request.
Send orders to: HAPPY MEMORIES, FREEPOST, KINGTON ,HEREFORDSHIRE HR5 3BR
TEL: (054 422) 618 FAX: (054 422) 628

COPPERSET(~
MQP ELECTRONICS SYSTEM 200
UNIVERSAL DEVICE PROGRAMMING SYSTEM
• Fast and reliable programming
• Low cost
• Expandable system - buy only what you need PUTS PLATED THROUGH-HOLES
• Virtually all programmable devices covered
• Easy to upgrade WHERE YOU WANT THEM
• Manufacturer approved algorithms
• Efficient and attractive software interface
• Special batch mode for production Multicore's Copperset is a remarkable new process
which instantly converts selected plain holes in PCBs to
System 200 is one of the most versatile programming systems available. At
the heart of the system is the award-winning Model 200A programmer. plated through-holes.
Designed to quickly connect to the serial or parallel port of any PC compatible, e No tooling charges, no
the Model 200A is controlled by PROMDRIVER, widely acclaimed as the best
driver software available for any programmer.
waiting

• EPROMs, EEPROMs and FLASH memories up to e lnvaluble for prototyping

4Mbit and beyond and repairs
• Microcontrollers from most manufacturers including • Dramatically reduces cost
- 8748 and Family compared with
- 8751 Family (including 87C751/2 and 87C552) alternative systems
- Z8 Family
- PIC16C5x Family • Portable kit for fast,
on-the-spot hole
• Emulators
conversion
• 8 pin Serial EEPROMs
• PAls, GAls,EPLDs etc
• Bipolar PROMS

Write or phone today for Free Information Pack:

Phone: (0666)825146 Fax:(0666)825141
IIilmm MOP Electronics Ltd., Park Road Centre Find out more by calling
Multicore's Sales Department on
'l.i.Ja..r--- Malmesbury, Wiltshire SN16 OBX UK MULTICORE SOLDERS 0442 233233 or fax 0442 69554.
European D1stnbutors· Oigitron. Norway Tet 071-17 890; Synatron, Germany Tel: 089/4602071; logtek, Sweden Te!: 08 770 1470;
Elexind, llaly Tel: 020 9210 35 54

48 Practical Electronics April1992

 Project

Looking Into The

Darker Corners
Robert Penfold describes how to build a hand held infra-red scanning device that takes over
where your eyes leave off.

his security device is basically

T much the same as a standard

passive infra-red detector, but
with the general setup reversed.
Normally the infra-red sensor
remains fixed and the person being
detected moves. If the "target"
does not move, then it is not
detected. The infra-detector unit
featured here is a hand-held device
which is used much like a torch.
You slowly scan the unit across an
area, and two LEDs "blink" if an
infra-red source is detected. The
movement is provided by the
detector, and it will detect any
"targets" within the scanned zone
whether they are moving or
stationary.
Perhaps of more importance in
security applications, anyone
detected by the unit will be
unaware of this fact. The unit is a
passive detector, which does not
require a beam of light or infra-red metres. This is achieved by adding lenses have a slight shift in their
to be shone at the "target". It a piano-convex lens in front of the effective focal length, but nothing
responds to body heat. pyro sensor. This gives an angle of more drastic than this. At about
Consequently, unless you tell them, view of only about two degrees. By 1011m (10000nm) most lenses seem
there is no way that someone gathering up the infra-red radiation to be more or less opaque! They fail
detected using the unit will know over a relatively large area and to provide any significant focusmg
that they have been discovered. concentrating it on the elements of of the infra-red energy. Therefore,
They would presumably not even the pyro sensor the lens greatly it is important to use the special
know that you were using some boosts the maximum operating lens specified in the components
form of night vision device. The range of the unit. list. The unit is unlikely to work at
unit operates at ranges of up to It must be emphasised here that all using other lenses.
about 30 metres incidentally. not just any convex lens will work On the electronic side of things
in this application. With infra-red the unit is pretty simple. The
projects that use infra-red LEDs and output swing from the pyro sensor
System Operation photo-diodes the choice of lens is
not critical. However, in a system
will often be no more than a few
millivolts peak to peak, and with
The block diagram of Fig. 1 helps to
explain the way in which this unit such as this it is much longer distant targets it could be under one
functions. The pyro sensor detects wavelengths that are involved. millivolt. Two high gain amplifiers
the heat from the "target", but it Whereas infra-red LEDs have peak are therefore used to boost t:he
has a wide angle of response and a output at about 900 to 950nm (not voltage swing to a more useful
very limited range if used unaided. far from the visible red part of the figure of a few volts peak to peak.
In an application of this type we spectrum), passive infra-red Bandpass filtering helps to avoid
require an angle of view of just a detectors operate at around 1 to spurious output signals due to
few degrees and a range of many 2011m. At around 950nm most noise and drift in the pyro sensor.

April1992 Practical Electronics 49

 IR Detector

Fig. 1. The infra-red torch block diagram.

The frequencies involved in this lower gain gave more clear results, a simple sensing device. Firstly, it
application are sub-audio at about but at the expense of much reduced actually contains two sensing
0.2Hz to 3Hz. The slow innate range. elements. Secondly, in common
response of the pyro-sensor Simply driving two LEDs with most pyro sensors, it contains
precludes a wider bandwidth at the connected to operate out-of- phase an FET pre-amplifier. The circuit of
high frequency end. The practical seems to give much better results. the sensor is shown in Fig. 2 and, as
result of this is that the "torch" As one LED gets brighter, the other will be seen from this, the two
must be scanned fairly slowly if it is grows dimmer. This helps to sensing elements are connected in
to operate at maximum sensitivity. emphasise any change in series and out-of-phase. On the face
Swishing it around all over the brightness, giving clearer of it, the two sensors cancel out
place in a sword-like fashion will indications than if a single LED was each other's output signals, always
render it largely ineffective. used. Results are easy to interpret giving zero output from the unit.
In the original design a LED because you can see whether you As far as any changes in the general
indicator was driven from the are getting a small or a large background infra-red level are
output of the amplifier via a trigger response from the unit. This makes concerned, this is true.
circuit. In practice this did not it easy to ignore any minor The main point of using twin
work very well. With the gain background responses, and to element sensors is to obtain this
ahead of the trigger set high, the concentrate on any strong immunity to changes in the ambient
unit gave good range but tended to responses. infra-red level. Although it might
give confusing results. The seem as though the sensor will not
apparently random flashing from respond to the infra-red signal from
the LED was impossible to interpret Pyro Sensor "targets", this is not so. Remember
reliably even after gaining some The pyro-sensor used in this design that the unit is not designed to pick
experience with the unit. Using is actually something more than just up static infra-red signals, but
should respond to moving signals.
This movement causes an infra-red
signal to pass across the sensor
elements. In doing so the energy
activates the first sensor, then both
sensors, then only the second
sensor. This gives a strong output
pulse of one polarity, followed
shortly afterwards by a pulse of the
opposite polarity.
A slight problem with most twin
element sensors is that they must be
orientated correctly. If they are
fitted with the wrong orientation
the infra-red radiation is swept
across them simultaneously, and no
significant output signal is
produced. In the present
application this would mean having
to hold the torch the right way up,
or it would not work efficiently.
This is undesirable, since there is no
way of telling how someone will
hold a unit of this type. There is no
problem with the specified sensor

50 Practical Electronics April1992

 IR Detector

frequency response of the circuit at its small size, it is essential that

frequencies of more than a few small resistors and capacitors
Hertz. Highpass filtering is should be used. The electrolytic
provided by using coupling capacitors are miniature radial
capacitors which provide a suitable (vertical mounting) types and the
cut-off frequency at the low other capacitors are all printed
frequency end of the response. circuit mounting polyester types
Dl and D2 are the LED having 7.5 millimetre lead spacing.
indicators, with current limiting Do not overlook the two short link
provided by RlO and Rll. These set wires (one above CS and the other
the LED current at only a few between C6 and IC3).
milliamps but, as the unit will be None of the semiconductors are
used in something approaching static sensitive types incidentally,
total darkness, this gives more than but I would still recommend the use
adequate LED brightness. The of holders for IC2 and IC3. Be
current consumption of the circuit careful not to leave finger marks on
(an SBA04) as it is a new type which is only about 6 milliamps, and a the pyro sensor's "window". If you
has special sensing elements which PP3 size battery is therefore should get finger marks on it, clean
render it omni-directional. The adequate to power the unit. them off with a soft cloth or the
elements are of the "69" variety range of the unit might be seriously
(that is, shaped like the figures "6" impaired. Fit double-sided pins to
and "9", and suitably entwined). Construction the board at the points where
This ensures that a strong output Details of the printed circuit board connections to the off-board
signal is produced regardless of are provided in Fig. 4 (component components will be made.
how the infra-red signal is swept overlay) and Figure S (copper track The printed circuit board has
across the sensing elements. pattern). Construction of the board been designed to fit a Maplin ABS
The preamplifier is a simple is fairly straightforward but, due to box type MB2. This has built-in
source follower type which requires
a discrete load resistor. The source r--
impedance of the sensors is very I
high and the FET preamplifier
ensures that a suitably extended
low frequency response is obtained.

Circuit Operation +
Fig. 3 shows the circuit diagram for
the infra-red torch. ICl is the pyro
sensor and Rl is the external source
load resistor for its FET
preamplifier. IC2 acts as the basis
of the first amplifier stage, which is
a form of non- inverting amplifier.
IC3 is used in the second amplifier,
and this is an inverting amplifier
Fig. 2. The circuit for the pyro sensor contains the components shown within the dashed
having a relatively low voltage gain lines- a separate load resistor is needed for the FET.
figure. CS and C7 roll-off the

S1 on/off

R10
1k
l-
81 I
9V :
--L-
R11
1k
IC1: SBA04
IC2: LF351N
IC3: !lA741C
01, 02: Red LED

Apri11992 Practical Electronics 51

 lA Detector

The finished circuit board.

printed circuit guide-rails, and the drilling one of about 12mm in to smear adhesive over the main
board slots into the middle set of diameter and then enlarging this part of the lens, which could greatly
rails. If a different case is used it using a reamer. The lens must be reduce its efficiency.
will almost certainly be necessary to glued in place over this cut-out. The two LEDs and on/ off switch
modify the board slightly in order The lens has an outer rim about SI are mounted at the rear of the
to mount it in the case. Life is likely 3mm wide for fixing purposes. I unit (that is, the end one opposite
to be much easier if the specified think that the lens is designed to the one on which the lens is
case is used. The board will operate with the plain surface mounted). The final wiring-up can
prevent the lid of the case from facing away from the sensor but it them be completed. The cathode
fitting properly, as it will obstruct seems to give much the same ( +) terminals of the LEDs will
the ridge around the underside of results either way round. As the probably be indicated by "flats" on
the lid. To avoid this it is merely case and the lens are both made their bodies, or by shorter leads.
necessary to file a couple of notches from softish plastics, not all There is plenty of space for the PP3
in the ridge at the appropriate adhesives will stick them together size battery in the rear section of the
points. reliably. In particular, most "super- case. A double-sided adhesive pad
A 30mm diameter hole must be glues" are not effective with or tape can be used to hold it in
made in the case directly in front of materials of this type. An epoxy place.
the pyro-sensor. I found that a adhesive seems to be a good choice The focal length of the lens is
suitable hole could be made by first for this type of thing. Be careful not 30mm which means that the pyro
sensor should be positioned 30mm
Fig. 4. Printed circuit board component layout and wiring. behind the lens in order to obtain
maximum sensitivity and the
narrowest possible angle of view.
01 D2 With the suggested layout and the
pyro sensor's leadouts left full
+ + length, the sensor will probably be
slightly too far back. This slight
Sl defocussing of the optics will
reduce the range somewhat but will
broaden out the "beam" slightly
81+ making the unit easier to use.
However, if you wish to optimise
the range, simply mount the sensor
on pins so that it is brought forward
slightly. The sensor should be
positioned centrally behind the
lens, or the "beam" will not be in
81- quite the same direction as you aim
the unit.

52 Practical Electronics April1992

 IR Detector

L-------------------------------1
Inside the box. Components
Resistors
Testing And Use function properly.
The unit is easily tested out with
R1 47k
R2, R3 3k9
At switch-on you will probably
the aid of a helper, or even using R4, R6 1M
notice that one LED switches on, passers-by as test "targets". There R5 4M7
followed by the other LED is no need to wait for darkness in R7 3k3
switching on as welL After several order to test it - the unit functions R8 220k
seconds the LEDs will "blink" and perfectly well in daylight. In fact it R9 2M2
then both switch on again. At this is better to test it in daylight as this R10,R111k
stage the unit is ready for use. This makes it easier to assess results. All 0.25W 5% carbon film or better
so-called "warm-up" period is due Bear in mind that the unit is not, Capacitors
to the extended low frequency strictly speaking, a person detector, C1 220fl1 OV radial elect
response and high gain of the C2 220n polyester
and that it will respond to anything
amplifier stages. It takes some time C3 470!11 OV radial elect
that is warm (a radiator for C4 22111 OV radial elect
for the capacitors in the circuit to example). If in use it seems to give C5 1On polyester
settle down at their normal a false alarm, it is likely that it has C6 470n polyester
operating voltages. If the "warm- detected something warm that you Cl 3n3 polyester
up" period is very long indeed, or have not noticed. For optimum Semiconductors
never ends, it would suggest that sensitivity scan with the unit quite IC1 SBA04
C4 has too high a leakage leveL slowly. Scanning rapidly massively IC2 LF351 N
This should be a high quality reduces the effective sensitivity of IC3 IJA741C
electrolytic capacitor, or even a the unit, and can give very limited D1, D2 Red panel LED
tantalum type, if the unit is to range.
• Miscellaneous
S1
81
SPST sub-miniature toggle
9 Volt (PP3 size)
Fig. 5. The PCB copper track pattern (1 :1)- mirror image. Plastic case type MB2
Lens type CE01
Two 8-pin DIL sockets
Battery clip-on connector
Wire, solder, and so on

The CE01 lens and SBA04 pyro sensor

are available from:
Chartland Electronics Ltd.
Chartland House
23 Twinoaks
Cob ham
Surrey
KT11 2QU
Tel. 0372 84 3976

April1992 Practical Electronics 53

Classifieds-------------------------------------

Practical Electronics Classified Ads

Reach thousands of serious electronic and computer enthusiasts- advertise in PE Classified pages:
Rates 20p (plus 4p VAT) per word or £8.50 (plus £1.49 VAT) per column cm. All classified
advertisements must be pre-paid. Send your copy, with remittance payable to Intra Press, (Payment by
Visa or Access accepted - ads may be phoned in) to:
Practical Electronics, Intra House, 193 Oxbridge Road, London W12 9RA.
Tel: 081-743-8888. Fax: 081-743-3062

Education Retailers

Start trainine now for Project your

the followine courses.
LJ Telecomms Tech C&G 271
retail image
LJ Radio Amateur Licence C&G
0 Microprocessor
here!
LJ Introduction to Television

Send for our brochure- without obligation or

••••••
telephone us on 06267 79398 (Ref PE4/92) Phone David Bonner
Name.................................................... . for details on
081-743-8888 Prices Include postage. Add 51111 (plus VATJ tu ordiii'S below £5.00
All Hems new llllless stated. Add 17.5% VAT tu all prices.
Send an SAE fer our latest list or fOr mlll'tllnla.
Radio & Telecommunications Oupt PE, 374 Mllllln Raad, Cllmbrldge, CB41SU
Correspondence School, Tel: 0223 424802, 0831 430498 er 0831 4311552 (Mall erder only)
12 Moor View Drivel TeiQnmouth,
Devon T01 '+ 9UN LONDON N WEST
Components
BTEC ELECTRONICS
TECHNICIAN CATALOGUE £1.00 + 25 P&P
FULL-TIME TRAINING ELECTRONICS LED1 ]mm or 5mm red/green ....... . .. .... 6p each. Yellow 11 peach.
THOSE ELIGIBLE CAN APPLY FOR E.T. GRANT SUPPORT
AN EQUAL OPPORTUNITIES PROGRAMME
O.N.C. H.N.C. O.N.D. One of the largest ranges of ..................£S.95
... ..... .£.1.95
Next Course Commences ................. £8.60
6th June 1992
components in the UK!
FULL PROSPECTUS FROM

LONDON ELECTRONICS COLLEGE 40 Cricklewood Broadway,

(DEPT. EE) 20 PENYWERN ROAD
EARLS COURT, LONDON SWS 9SU LONDON NW2 3ET
TEL 071-373 8721
Tel: 081-450 0995/452 0161

Surplus Modernising your workshop?

Sell your old equipment
TURN YOUR SURPLUS through PE Classilieds pages.
ICS transistors etc into cash, immediate
settlement. WE welcome the opportunity to
Wide range of CMOS TTL 74HC 74F Linear tran~istor~ kits
quote for complete factory clearance.
Contact:
COLES-HARDING & CO., FOR SALE JPG Electronics 276 • 278 Chatsworth Road
103 South Brink, Wisbech, Cambs.
ESTABLISHED 15 YEARS
Practical Electronics Chesterfield S40 2BH
Tel: 0945 584188- Fax: 0945 588844 in Binders volumes one
(1965) to ten (197 4) and Practical Electronics Classifieds
Recycle your old projects and generate later loose copies. Offers listthe best sources for unusual or
useful cash from spare components for lot (0905) 54318. back catalogue components

54 Practical Electronics April1992

-------------------------------------Ciassifieds

Surveillance
UNIVERSAL PROGRAMMER
Hi-Lo ALL-03 £295
Take advantage of Asian low labour cost!
Suma Designs
*Texas Instrument approved. Good quality.
* PC based, programs stored into 5 diskettes.
*Program most MPU, PLO, EPROM, EEPROM, BP ROM.
sell top quality
* Adaptors for PLCC devices are available.
* 1 year guarantee. Money back if not satisfied.
*Price includes postage but not VAT.
surveillance equipment
Write for free catalogue and price list.
Active Action Industrial Ltd
in kit form or as ready
Rm 1307, Wing Tuck Coml Ctr.
177-183 Wing Lok Street 01
"'
Miniature Polyester Capacitors 250V Wkg. Vertical Mounting
015.022 033,047 068 4p 01 5p 01522-6p
built units.
Hong Kong Mylar Capacitors 100V Wkg. Vertical Mounting E12 Series
TOOOpto 8200p 3p 001 to 068- 4p 01 015.022 6p See our full page
Classifieds can be a
Subm. Ceramic Plate 100V Wkg. E12 Series Vertical Mounting
IPS to 4?P- 3p 56P to 330P 4p 10% 390P to 4700P- 4p
Plate/disc ceramic SOV. Wkg. Vertical Mount.
E6 ser~es 1500P \o47000P- 2p 01 3p
tPO to toooP &
display ad in this issue
Polystyrene Capacitors 63V Wkg. E12 Series Axial Mounting

TIGHT SQUEEZE
10Pto820P- 4p 1000Pto 10 000 Sp 12 OOOP -6p

PROGRAM SERVICES
EPROMs programmed to customer
Give your ad room to requirement. EPROM masters £6 and
copies 50p.
breathe Sizes up to 512kB. Send used or new
in our and include listings and/or relevant
disks.
THE C.R. SUPPLY CO.

DISPLAY PAGES 127 Chesterfield Road,

For further information contact:
Sheffield SS ORN. Mr C. Thomas, 128 Crestway,
Tel: 0742 557771
Downsview, Chatham, Kent ME5
OBH. Tel: 0634 847050
Contact David Banner
on Green\Neld
Ne\Nsline SCOPES
081-743 8888 0891505121
Calls charged at 36p;min cheap rate, 48p/mm other times
Repaired and recalibrated. All makes,
all models. Nationwide collection and
delivery. Copies of handbooks and
For a weekly update on our latest spares for most popular models,
surplus bargains- call now!! Our latest including golden oldies.

73
AMATEUR list FREE from GREENWELD, 27 Park
Road, Southampton S01 3TB
Phone Mendascope Ltd
069-172 597
RADIO
TODAY SURPLUS/REDUNDANT ELECTRONICS Kits, Plans, Assembled Units,
Surveillance Microtransmitters,
Broaden your COMPONENTS WANTED Phone Recording Switches, Trackers,
ICs- Tuners- Transistors- Valves- Diodes etc- any quantity
horizons. considered -immediate payment.
Defence /Protection Circuits, Plus
Subscribe to the much more. Send 2 x 24p stamps for
ADM ELECTRONICS SUPPLIES lists, or tel. 05436 76477 24hrs.
world 1s leading Radio Everything for the budding 007.
Ham magazine. Tel 0827 873311 Fax: 0827 874835
ACE(PE). 53 Woodland Way,
European rates for Burntwood, Staffs. WS7 SUP.
surface and air mail Surveillance devices, lasers, Tesla
available on request
from: Contact
HST for all your component
coils, scramblers, ultrasonic and
many more, over 150 designs. Send
SAE to: Plancentre, Old Wharf,
73 Amateur needs. Send for your free Dynock Road, Ledbury HR8 2HS for
catalogue and details of free list.
Radio Today special offers. NEW VHF MICROTRANSMITTER KIT,
PO Box50330 HST Ltd,
tuneable 80-135 MHz, 500 metre
range, sensitive electret microphone,
Boulder Technology House, high quality PCB. SPECIAL OFFER
Prospect Road,
eo. Carlton, Nottingham
complete kit ONLY £5.95, assembled
and ready to use £9.95 post free.
80321-0330 NG4 &LA
Tel: 0602-587225
Access orders telephone 021 411 1821.
Cheques/ P.O.'s to: Quantek
USA Fax: 0602-484530 Electronics Ltd, (Dept P.E.), 3

April1992 Practical Electronics 55

Classifieds-------------------------------------

SERVICE MANUALS
Available for most equipment T.V. Video, Audio,
Missing a vital Writing Classified Advertisements
Test ,Amateur Radio, Military Surplus, Kitchen, Etc.
That Work
Any Video Recorder, Video Camera or
Oscilloscope
Manual £15.00 (subject to stock). All Others
Manuals £10.00 (subject to stock). Ovwe 100,000
Practical 0 Start by mentioning the product or
service you are selling. By doing so, you
make it easier for the reader to see what you

Electronics
manuals available for equipment from 1930's to
the present Circuit sections supplied on full size are offering.
sheets
up to A1 size (33" X 24") if applicaple. Originals f9 Always include the price of whatever it is
or photostats supplied as available. FREE Repair and you are selling. Research has shown that
Data Guide Catalogue with all orders or send SAE for back issue? 52% of people who read classified ads will
your copy today.
Don•t despair! not respond to advertisements that fail to
include the price.
Mauritron (PE),_
8 Cherry Tree Road,Chinnor, Reprints of articles and ~Keep abbreviations to a minimum. lt
Oxfordshire, OX9 4QY. software listings are available makes whatever you have to say more easily
understood.
Tei:(0844)51694 Fax:(0844) 52554 for £2 each from Intra Press,
Intra House, 193 Uxbridge o Pretend to be your prospective customer.
Houldey Road, West Heath, Ask yourself what it is you would like to
Road, London W12 9RA, or know about the product or service that you
Birmingham, B31 3HL by phone on 081 743 8888. are selling that would make you want to buy
Super VHF Microtransmitters. Long We cannot accept credit card it. For example, you could include
range, high sensitivity. Tuneable 75- information such as brand names, colours
115 MHz. Listen on any FM radio.
orders below £5 total value.
and specifications.
Assembled, ready to use. High
quality, fully encased. Full area. 0428 683733 after 6:30pm.
and others. JD Soft. Tel: 061 4305208
instructions, guaranteed. Ideal Xmas IBM PC PD/shareware, electronic
presents as baby monitors etc. £9.50 Wanted: Does anyone have a
post free. Cheques/POs; Mr B.
Hicks, 24 Brewster Road, Boston,
Lines, PE21 ODY. Tel: 0205 362003
Advertising Index
EPROM PROGRAMMING
SERVICES. All sizes all makes up to Antex ..........................................23
512kb. Data can be sent as written text BK Electronics ......................... IBC
or as data file on 3.5" or 5.25"f/ disk,
PC or AMIGA compatible. For details Bull Electrical ............................ 60
contact: W.Vincent,159 Askew Cricklewood Electronics .......... 23
Road,London,W12 9AU, Tel.081 749 GH Tracks Systems ................... 42
7304
Greenbank Electronics ............. 42
Oscilloscope 53 SA with two lA 1 Happy Memories ........................ 48
plug-ins plus spares and manuals.
Offers J.M. Wilson. Tel: 0532 505364 lntl. Corr. School ....................... 42
Amstrad 2086 PC. 30Mb hard disk, .Jaytee Electronic Services ...... 23
3.5-inch floppy, mono VGA, mouse, Labcenter Electronics ............... 12
manuals. VGC. £350 ovno. Some MQP Electronics ........................ 48
electronics books, rather old, £3 each.
Phone Richard, 0895 810680
Multicore Solders ...................... 48
(Oxbridge) ~C:1r ••••••••••••••••••••••••••••••••••••••••••••• 2ll
IBM PC Public Domain Shareware ~orthern Marketing Concepts .42
sg: EE Draw 2.2, PCB CAD; PC ~umber One Systems ................ 25
Route 2. On 3.5 inch disk, £2.50. Omni Electronics ....................... 42
What's more, ham radio, loud
speaker cross assembler. J.D. Soft. Readers Union .......................... 4-5
Tel: 061 430 5208 Silica Systems ........................ OBC
Wanted: Electronics engineer to Suma Designs ........................... IFC
make up small electrical component Swift TV Publications .•.............. 54
for a novice. Good fee paid. Surrey
Top Secret Electronics ............. 61
56 Practical Electronics April1991
 Q&A

Techniques
Having trouble with your TV picture? Andrew Armstrong suggests a few solutions.

olin McTavish of Sutton

C Coldfield writes to ask how

he can run two televisions in
widely separate locations from one
R+75Q +R=75Q
aerial. He writes: I have tried
simply joining two pieces of coax z
together and connecting them both 37.5+ 1.5R = 75
to the aerial outlet in the living =:::} 1.5R = 37.5
room, but the picture ends up
=:::} R= 25Q
blurred. Using a television Y
adaptor solved the clarity So choose 2412 though 2212
problems, but there must have been should work okay if 2412 is
too much attenuation, because the not available
pictures became rather noisy, and
teletext did not work. I imagine that
a TV aerial booster with two outlets
would solve the problem, but they
are rather expensive. Has PE Fig. 1. Aerial ''Y" connector.
recently published a design for
one? resistive Y connection suitable for design. This should provide slightly
Taking things in order: it is three cables to be joined, Clearly the more gain than is required to
never a good idea to star-connect calculations for the resistor values compensate for the loss in the Y
several coaxial cables carrying RF could be extended to more cables, connector, without having so much
or video. This sort of connection but more signal would be lost. gain as to be vulnerable to
can work at audio frequencies You are right that an aerial interference by local amateur radio
because the cable is not matched. amplifier would improve the or CB transmitters. should such
Television aerials use 75 ohm coax, situation, and now that you already interference occur, the filter shown
and if several lengths are to be have a Y connector (which almost in Fig. 3 could be added to the
joined at one point, then the certainly is connected as shown in input.
impedance looking in at any point Fig. 1) an ordinary aerial amplifier Little needs to be said about the
must be 75 ohms if reflections are would do the job. circuit. Connections to decoupling
to be avoided. The blurring of the There are two main ways of capacitors should be kept very
picture, which you noticed, was designing aerial amplifiers: one is short and the unit should be built
probably a very short interval to use a transistor to provide the on an earth plane. Ll, L2, and L3
ghosting caused by reflections from gain, the other is to use a hybrid should be made by winding six
the cable junction. Fig. 1 shows a circuit. Fig. 2 shows a transistor turns of 0.5mm to 1mm diameter

----.- +9V supply

47012

,
From
aerial
----------------i
C5
--- -;-To
__________ __________ _ TV
C2 C3
L1 1n 1n __.__OV

Fig. 2. Aerial amplifier.

April1992 Practical Electronics 57

 Techniques

wire on a pencil. A screen between

From aerial input and output may be necessary.
The power connections shown
are to power the circuit remotely
5mm
<--------,}>
from its power source, for example
> if it is mounted on the masthead. If
_Q 1 turn this is not necessary, L2, L3, and CS
can be omitted and the power
connected directly.

Fig. 3. High pass filter.

Hybrid
Fig. 4 shows the design of a hybrid
TV aerial amplifier. All the
Fig. 4. Layout of hybrid aerial amplifier. necessary circuitry is in the hybrid
IC and all that is needed to make it
Slotted screen work is a board to mount it on and
• +24V a power supply. Note, however,
•• that a screen must be fitted between
• input and output, with as narrow a
••• slot as possible to accommodate the
•• IC. If this is not done, some samples
• of the re will oscillate in the
Input 0 0 •• 0 0 0 0 0 Output
television band, due to capacitance
•• across the IC itself. This circuit
••• provides in excess of 20dB of gain
.
••
Bottom view
and is more likely to be vulnerable
to interference. The filter circuit of
Fig. 3 is still suitable for this, but in
Note that grey areas denote un-etched copper severe cases a commercially
available in-line CB filter may be
required.
The top and bottom earth planes
should be joined together, either by
a series of pin-throughs next to the
I I I I I hybrid circuit, or by thin wires
I I I I I I inserted in each earth hole and
I I I I I I
I I I I I I soldered top and bottom before the
I I I I I I hybrid is inserted. The latter
I I I I I I method is better, if practical.
V
@ 0 0 @ 0 0 1mm (7 holes)
A
The high frequency transistor for
the design in Fig. 2 is available from
Cirkit, and the OM335 hybrid is
available from Electromail. An
aerial amplifier kit using the OM335
Top view hybrid is available from Specialist
Semiconductors. •
Continued from page 15 strong enough for me to want to total four or five can be seen. The
and a useful adjustment range. I switch to low sensitivity. other defects would not be
would have preferred to have had a The display is specified as a noticeable if you were not looking
contrast control available, as well. twisted nematic liquid crystal with for them; only the worst one might
The ability to reduce the contrast TFT active matrix drive. There are catch the eye of the viewer not
very slightly on occasions would be 89,505 picture elements, and better looking for it.
an advantage. On the rear of the set than 99.99% of them are specified to The instruction sheet is clear and
is a signal sensitivity switch. work effectively.
adequate, but modelled on the lines
The people in the Sony shop tell In use, there is only one picture
me that one of the reasons why the of the type of hikers' map that can
defect (it is in the middle area of the
picture has less noise on it is screen) which is noticeable under only be refolded by an expert.
because the Sony Watchman normal viewing conditions with the Fortunately, the Watchman is easy
incorporates a switched signal slightly noisy signal available in my to operate.
booster. On the high sensitivity area. Two more defects are visible The Sony Colour Watchman
setting, this gives more gain than on some picture material, and with costs £229.95 from most dealers,
usual. In practice, I have not yet a really good signal and the sort of including the specialist Sony outlets
found anywhere where the signal is picture that shows up the faults, in which are now springing up. •

58 Practical Electronics April1992

 How to design
your own satellite
TV system and
get it right ...
requires
... with the SATMASTER program IBM PC compatible with
by D] Stephenson) you can! MS DOS 3.0 or higher

• Design your own system and test its • 20,000 word on-screen technical
performance before you install it! guide and context-sensitive help!
• Quickly find essential dish setup • Calculates full link budget
angles: elevation, azimuth, including dish size optimisation
polarisation offset for any satellite ensures the best quality picture!
from any location in the World! • Plot beamwidths and lobe patterns
• Easy-to-use pop-up menu interface and judge potential interference
makes tedious tasks simple for from neighbouring satellites!
everyone! • Results and graphs can be output
• Complete with User Manual! to screen or printer!

Take out the guesswork ... order SATMASTER today.

Swift Television Publications
17 Pittsfield, Cricklade, Swindon SN6 6AN Tel or Fax 0793 750620
-----------------
ORDER FORM
I program(s)
Please send me _ _ SATMASTER
disk)
(3S each, postage
@ £35
Name:
--------------
I FREE in UK, Europe add £2, Other add £4. Address: _ _ _ _ _ _ _ _ _ __

j l enclose cheque/PO for £ made

payable to Swift Television Publications, or
1 please debit my AccessNisa credit card,

I No. .
Expires: P'!§~~ ~ Postcode. _ _ _ _ __
L .. ~ .~ .~ ~ ~ ~. ~._....... ............. ~. ~ ............

April1992 Practical Electronics 59

 VGA PAPER WHITE MONO monitors new and cased 240v
AC. £59.00 ref 59P4R
ALARMPIRSENSORSStandard12valarmtypesens.orwillinter-~
face to most alarm panels. £16.00 rei 16P200
AMSTRAD PORTABLE PC'S FROM £149 (PPC1512SD). 25 WATT STEREO AMPLIFIERc. STK043. With the addition of ALARM PANELS2 zone cased keypad entry, entry exrt nme delay
£179 (PPC1512DD). £179 (PPC1640SD). £209 a handful of components you can bUJid a 25 watt amplifier. £4.00 rei etc. £18.00 rei 18P200
(PPC1640DD). MODEMS £30 EXTRA.NO MANUALS OR 4P69R (Circuit dia included) MODEMS FOR THREE POUNDS! I
PSU. BARGAIN NICADS AAA SIZE 200MAH 1.2V PACK OF 1 Fully cased UK modems des1gned ford1al up system (PSTN) no data
£4.00 REF 4P92R, PACK OF 100 £30.00 REF 30P16R or into but only £3.00 rei 3P145R
HIGH POWER CAR SPEAKERS. Stereopairoutput 100w each. FRESNEL MAGNIFYING LENS 83 x 52mm £1.00 rei BD827R. TELEPHONE HANDSETS
4ohm impedance and consisting of 61/2" woofer 2" mid range and ALARM TRANSMITTERS. No data avaliable but nicely made Bargain pack of 10 brand new handsets with mic and speaker only
1 "tweeter. Ideal to work with the amplif1er descnbed above. Price per complex radio transmitters 9v operation. £4.00 each ref 4P81 R. £3.00 rei 3P146R
pair £30.00 Order rei 30P7R. 12V 19A TRANSFORMER. Ex equipment but otherwise ok. Our BARGAIN STRIPPERS
2KV 500 WATT TRANSFORMERS Suitable for high voltage price £20.00 Computer keyboards. Loads of switches and components exCE>I!ent
experiments or as a spare for a m1crowave oven etc. 250v AC input. GX4000 COMPUTERS. Customer returned games machines value at £1.00 rei CD40R
Now only £4.00 rei 4P157 complete with plug in game, joysticks and power supply. Retail price DATA RECORDERS
MICROWAVE CONTROL PANEL Mains operated. with touch is almost£100. Ours is £12 00 rei B12P1 Customer returned ma1nsbatteryunitsbuiltin m1c ideal for Computer
switches. Complete with 4 d1git display, digital clock, and 2 relay or general purpose aud1o use Price 1s £4.00 ref 4P1 OOR
ULTRASONIC ALARM SYSTEM. Once again in stock these
outputs one for power and one for pulsed power (programmable). units conslst of a detector that plugs into a 13A socket in the area to
SPECTRUM JOYSTICK INTERFACE
Ideal for all sorts of precision timer applications etc. Now only £4.00 protect The receiver plugs into a 13A socket anywhere else on the Plugs mto 48K Spectrum to prov1de a standard Atari type JOystick
rei4P151. same supply. Ideal for protecting garages, sheds etc. Complete port Our pnce £4.00 ref 4P1 01 R
FIBRE OPTIC CABLE. Stranded optical fibres sheathed m black system £25.00 rei B25P1 additional detectors £11.00 rei B11 P1 ATARI JOYSTICKS
PVC F1ve metre length £7.00 rei 7P29R IBM XT KEYBOARDS. Brand new 86 key keyboards £5. oo rei Ok for use with the above tnterface, our pnce £4.00 ref 4P1 02R
12V SOLAR CELL200mA output ideal for trickle , 5P612 BENCH POWER SUPPLIES
charging etc. 300 mm square. Our price £15 00 ref ~J IBM AT KEYBOARDSBrand new 86 key keyboards£15.00 rei Superbly made fully cased (metal) givmg 12v at2Aplusa 6V supply.
15P42R ~ 15P612 Fused and short a rcUJt protected. For sale at less than the cost of the
PASSIVE INFRA-RED MOTION SENSOR. .? ,:;.. case! Our pnce IS £4.00 ref 4P103R
386 MOTHER BOARDS. Customer returned units without a cpu
Co~pletew1th daylight.sensor, adjustab!e lights )(~......~ fitted. £22.00 rei A22P1
SPEAKER WIRE
on timer (8 secs ~15 mms), S?' rang~.wtth a 90 r<"\: '·~,_·:__~\(< Brown twm core msulated cable 1 00 feet for £2.00 REF 2P79H
deg co:verage. Manual ovende fac1bty. Corn- . , \ J ; ·t.../.,' MAINS FANS
plete w1th wall brackets, bulb holders etc. Brand ·· ;.~~;\~t'1 .17 COLOUR MONITORS
Brand new 5" x 3" complete wtth mounting plate quite powerful: and
new and guaranteed. Now only £19.00 ref ""r.::;.;.!....:-.. qu1te Our price £1 00 ref CD41 R
19P29 AMSTRAD CTM644 DISC DRIVES
Pack of two PAR38 bulbs for above umt £12.00 rei 12P43R Customer returned un1ts m1xed capac1t1es (up to 1.44M) We have not
VIDEO SENDER UNIT Transmit both audio and video signals RGB INPUT sorted these so you JUSt get the next one on the shelf. Pnce is only
from either a video camera, VIdeo recorder or computer to any £7.00 rei 7P1 R (worth 1t even as a stripper)
standard TV set Within a 100' range! (tune TV to a spare channel). £75.00 REF A 75P1 HEX KEYBOARDS
12v DC op. £15.00 ref 15P39R SUitable mams adaptor £5.00 rei Brand new units approx 5" x 3" only £1.00 each ref CD42R
5P191R 286 MOTHER BOARDS. Brand new but customer returns so may PROJECT BOX
FM TRANSMITTER housed '" a standard working 13A need attention. Complete With techni~al manual £20 00 ref A20P2 51/2" x 3112" x 1"black ABS with screw on lid. £1.00 refCD43R
adapter (bug is mains dnven) £26.00 ref 26P2R .....~ )· 286 MOTHER BOARDS. Brand new and tested complete with SCART TO SCART LEADS
MINATURE RADIO TRANSCEIVERS A pa~r of ~c">l ~ technical manual. £49.00 rei A49Pt Bargain pnce leads at 2 for £3.00 ref 3P147R
walk1e talkies with a range of up to 2_kllometres. Untts \·~"'~1 \'!}\ UNIVERSAL BATTERY CHARGER.Takes AA's. c·s. D's and SCART TO D TYPE LEADS
~::~~ ~2x52x155mm.
2 ~_) ~~J
Complete With cases. £30.00 Standard Scart on one end, H1 denSity D type on the other. Pack of
PP3 nicads. Holds up to 5 batteries at once. New and cased, mains
operated. £6.00 rei 6P36R ten leads only £7 00 rei 7P2R
FM CORDLESS MICROPHONE.Small hand held un1t with a 500' IN CAR POWER SUPPLY. Plugs into cigar socket and gives OZONE FRIENDL V LATEX
range! 2 transmttpower levels reqs PP3 battery. Tuneable to any FM 250ml bottle of hqwd rubber setstn 2 hours. Ideal for mounting PCB's
3,4,5,6,7 5,9, and 12v outputs at 800mA_ Complete with un1versal
receiver. Our price £15 ref 15P42AR ~ ··~ spider plug. £5.00 rot 5P167R fiXIng w~res etc £2.00 each ref 2P379R
12 BAND COMMUNICATIONS RECEIVER.9 short~ RESISTOR PACK.10 x 50 values (500 reSistors) all 1/4 watt 2"/o QUICK SHOTS
bands, FM, AM and LW DXJiocalsWJtch, tuning 'eye' mams ~ metal film. £5.00 rei 5P170R. Standard A tan compatible hand controller (same as JOys"bcksl our
or battery. Complete wtth shoulder strap and mat ns lead price is 2 for £2.00 rei 2P380R
NOW ONLY £19.001! REF 19P14R. VIEWDATA SYSTEMS
CAR STEREO AND FM RADIO.Low cost stereo system giving Brand newumts made by TANDATA complete w1th 1200/75 built m
5 watts per channeL Stgnal to noise rat10 better than MIRACOM WS4000 MODEMS modem mfra red remote controlled qwerty keyboard BT appproved
wow and flutter less than .35%. Neg earth. £25.00 ref
25P21R.
I I 45db,
Prestel compatible, Centronics printer port RGB colour and compos-
ite output (works with ordinary televtston) complete with power
LOW COST WALIKIE TALKIES.Pa~r of battery op· D liil V21/23 supply and fully cased. Our pnce IS only £20.00 ref 20P1R
erat~d units wtth a range of about 200'. Our pnce £8.00 bl
b;_ AC STEPDOWN CONVERTOR
a pair rei 8P50R ATCOMANDSET Cased units that convert 240v to 11 Qv 3" x 2'' w1th mains input lead
and 2 pin American output socket (sUitable for resistive loads <)nly)
7 CHANNEL GRAPHIC EQUALIZEf!:>ius a 60 watt power amp!
20·21 KHZ 4-8R 12·14v DC negative earth. Cased. £25 rei 25P14R. our price £2.00 rei 2P381R
NICAD BATTERIES. Brand new top quality. 4 x AA's £4.00 rei AUTODIALIAUTOANSWER SPECTRUM +3 LIGHT GUN PACK
4P44R. 2 x C's £4.00 rei 4P73R. 4 x D's £9.00 rei 9P12R. 1 x PP3 complete wtth software and instructions £8.00 ref 8P58R
£6.00 rei 6P35R CURLY CABLE
TOWERS INTERNATIONAL TRANSISTOR SELECTOR
FULLSOFnNARECONTROL Extends from 8"to6 feet! D connector on one end, spade connectors
GUIDE. The ultimate equ,valents book. Latest ed1non £20.00 rei on the other ideal for jOyStickS ate (6 core) £1 00 each rot CD44R
COMPUTER JOYSTICK BARGAIN
20P32R. TONE AND PULSE DIALLING Pack of 2 joysticks only £2.00 rei 2P382R
CABLE TIES.142mm x 3.2mm white nylon pack of 100£3.00 rei
3P104R. Bumper pack of 1,000 ties £14.00 rei 14P6R BUGGING TAPE RECORDER
Small hand held cassette recorders that only operate when thE-re is
1992 CATALOGUE AVAILABLE NOW
£29 sound then turn off 6seconds after so you could leave it in a room all
day and JUSt record any th1ng that was said. PnceJs£20.00 ref20P3R
IF YOU DO NOT HAVE A COPY PLEASE REQUEST
ns operated new pump. Not self IEC MAINS LEADS
WHEN ORDERING OR SEND US A 6"X9" SAE FOR A Complete w1th 13A plug our price JS only £3.00 for TWO! ref 3P, 48R
prinnng £5.00 rei 5P18R.
COPY. COMPUTER SOFTWARE BARGAIN
IBM PRINTER LEAD. (025 to centron1cs plug) 2 metre parallel.
£5.00 rei 5P186R 10 cassettes with games for commodore 64, Spectrum etc. Our
GEIGER COUNTER KIT.Complete w1th tube, PCB and all compo- bargam price one pound! ref CD44R
COPPER CLAD STRIP BOARD 17" x 4" of .1" pitch "vero"board.
nents to butld a battery operated getger counter. £39 00 ref 39P1R NEW SOLAR ENERGY KIT
£4.00 a sheet ref 4P62R or 2 sheets for £7 00 rei 7P22R
FM BUG KIT.New design with PCB embedded co1l. Transmits to Contains 8 solar cells, motor, tools, fan etc plus educational booklet.
STRIP BOARD CUTTING TOOL£2.00 rot 2P352R
any FM radio. 9v battery req'd. £5.00 rei 5P158R Ideal for the budding enthusiast! Pnce IS £12.00 ref 12P2R
50 METRES OF MAINS CABLE £3.00 2 core black precut in
FM BUG Built and tested supenor9v operation £14 00 rei 14P3R POTENTIOMETER PACK NO 1
convenient 2 m lengths. !deal for repairs and projects. ref 3P91 R
COMPOSITE VIDEO KITS. These convert composite video into
4 CORE SCREENED AUDIO CABLE 24 METRES £2.00
separate H sync. V sync and video. 12v DC. £8.00 rei 8P39R.
Precut mto convement 1.2 m lengths. Ref 2P365R
SINCLAIR CS MOTORS 12v 29A (full load) 3300 rpm 6"x4"114"
TWEETERS 21/4" DIA 8 ohm mounted on a smart metal plate for
0/P shaft. New £20.00 rei 20P22R.
easy fixing £2.00 ref 2P366R
As above but wtth fttted 4 to 1 inltne reductJon box (800rpm) and
toothed nylon belt drive cog £40.00 ref 40P8R. COMPUTER MICE Ongmally made for Future PC's but can be
adapted for other machines. Swiss made £8.00 ref 8P57R. Atari ST
SINCLAIR CS WHEELS13'' or 16" dia mcluding treaded tyre and
conversion k1t £2.00 ref 2P362R
inner tube. Wheels are black, spoked one p1ece poly carbonate. 13"
6 1/2" 20 WATT SPEAKER BUitt 1n tweeter 4 ohm £5.00 rei
wheel £6.00 rei 6P20R, 16" wheel £6.00 rei 6P21 R 35MM CAMERAS Customer returned un1ts with built in flash and
5P205R
ELECTRONIC SPEED CONTROL Klllor c5 motor. PCB and all 28mm lens 2 for £8.00 rei 8P200
components to build a speed controller (0-95% of speed). Uses
ADJUSTABLE SPEAKER BRACKETS Ideal for mounting
speakers on Internal or external corners, uneven surfaces etc. 2 for
STEAM ENGINE Standard Mamod 1332
pulse width modulation. £17.00 ref 17P3R. engine complete with boiler piston etc £30
SOLAR POWERED NICAD CHARGER.Charges 4 A_ £5.00 rot 5P207R
WINDUP SOLAR POWERED RADIOI FM!AM rad1o takes re- rei 30P200 T~~~t;;~
AA meads in 8 hours. Brand new and cased £6.00 ref ~ TALKING CLOCK I
chargeable batteries complete with hand charger and solar panel
6P3R. LCD display. alarm. battery operated.
12 VOLT BRUSHLESS FAKI112" square brand new ideal tor 14P200R
240 WATT RMS AMP KIT Stereo 30-0-30 psu reqwed £40.00 rei Clock Wtll announce the "bme at
boat, car, caravan etc. £5.00 ref 5P206. push of a button and when the
40P200R
ACORN DATA RECORDER ALF503 Made for BBC computer alarm is due. The alarm ,·o o~•·t eh''n"'
300 WATT RMS MONO AMP KIT £55.00 Psu required ret
but suitable for others. Includes mains adapter, leads and book. from vo1ce to a cock crowing!£14.
£15.00 rei 15P43R 55P200
HANDHELD TONE DIALLERS
VIDEO TAPES. Three hour superior quality tapes made under Small units that are designed to hold over the mouth piece of a
licence from the famous JVC company. Pack of 5 tapes New low telephone to send MF dialhng tones. Ideal for the remote control of
price £8.00 rei 8P161 answer machines. £5.00 rot 5P209R
PHIUPS LASER. 2MW HEUUM NEON LASER TUBE. COMMODORE 64 MICRODRIVE SYSTEM
BRAND NEW FULL SPEC £40.00 REF 40P10R. MAINS Complete cased brand new dnves with cartridge and software 10
POWER SUPPLV KIT £20.00 REF 20P33R READY BUll T times faster than tape machmes works with any Commodore 64
AND TESTED LASER IN ONE CASE £75.00 REF 75P4R. setup. The orginal price for these was £49.00 but we can offer them
12 TO 220V INVERTER KITAs supplied it will handle up to about to you at only £25.00! Rei 25P1R
15wat220vbut with a larger transformer it willhandle80watts. BaSic USED SCART PLUGS
kit £12.00 rei 12P17R. Larger transformer £12.00 rei 12P41 R. Packet 10 plugs suitable for making up leads only £5.00 rei 5P209R
VERO EASI WIRE PROTOTYPING SYSTEM!deal for design- C CELL SOLAR CHARGER
ing proJects on etc. Complete with tools, wire and reusable board. Same style as our4x AAchargerbutholds2 C cells. Fully cased with
New low bargain price only £2.00 rei B2P1 flip top lid. Our price £6.00 Rei 6P79R
HIGH RESOLUTION 12" AMBER MONITORI2v 1.5A Hercu·
les compatible (TTL input) new and cased £22.00 re! 22P2R IN SUSSEX? CALL IN AND SEE US!

60 Practical Electronics Apri11992

 ~ SLASH YOUR PHONE BILLS!!! ~
e::=J 100% FREE DIALLING!!! C:::::::J
"CREDITCALL"
AFTER MONTHS OF LEGAL BATTLES
WE CAN NOW OFFER YOU THE
CREDITCALL FROM THE
INVENTORS OF THE
ORIGINAL 'BLACK BOX'!!!
Car Alarn1 This ingenious little marvel is a Plug-
in Adaptor designed to work on all the

Con~petition very latest systems.

COMPLETELY
Winners UNDETECTABLE!!!
The lucky winners the car alarm kits are:
Simply plug the remarkable 'creditcall'
B Mossadad, Edinburgh into any authorised socket, then plug
S M Cording, Broxbourne, Herts your telephone into the 'Creditcall'. This amazing little
S A Meredith, Warrington, Cheshire gizmo can save you a fortune! 'Creditcall' works by
blocking the metering pulses on the line and suppressing
M Rooney, Crosby, Liverpool the charge signals.
I Moore, Belfast
TAKE ADVANTAGE OF A LOOPHOLE IN THE
The answers were: LAW ALLOWING US TO SELL THIS UNIQUE
1: IRradiation ranges from 1012 Hz to 1014 Hz UNIT; BUT ACT NOW!
2: The max speed for cars in the UK is 70mph
'Creditcall' comes complete with a Universal Adaptor plus
3: Modern cars are negative earth full instructions of how you can start slashing your bills.
- - - - - - - - - - - - - - - - - - - - - - - - ; Before ordering, please read the warning below.
Continued from page 62
convert, without first having to transcode every file YOU COULD SAVE £££'S!!!
to ASCII. Automating transfer via ASCII is
impractical because it involves stepping through 24HR CREDIT CARD ORDER LINE
files, all with different names and creating new fifes ALL MAJOR CREDIT CARDS ACCEPTED
with matching names.
The "convert" program which comes with A. 09442 8887 ~
WordPerfect only handles a few well-known old PRIORITY TELEPHONE ORDERING SERVICE
word processing packages. The instructions which PLEASE ALLOW UP TO 7 DA VS FOR DELIVERY
purport to advise on other conversions will be
gibberish to all but a very few of the most skilled
computer !iterates. I sent Godwin a floppy disk BEWARE OF INFERIOR COPIES
containing files in Quill and asked the simple BEING SOLD IN LONDON FOR WELL
question surely it would not be difficult for WP to OVER£200!
ignore everything except carriage returns, and
double carriage returns for paragraphs, to make
conversion quick and easy. Top Secret Electronics (UK) WARNING
It took two months and many nagging phone (Callers by appointment only) The use of th1s unit on
telecommunications system
calls and faxes from me to get a completely useless 26 Woodlands Road, Rillington, Action may be taken
'Post Office' Acts or criminal
answer. "There are indeed some software programs Malton, Y017 8LD proceedings under the Theft Acts. This
Please rush me the remarkable 'Creditcall'. I unit must not be used on any
which are now obsolete and are not supported by enclose cheque/P.O. for£.. .... made payable to telecommunicai!Ons system without the
full consent of the system provider. The
WordPerfect's conversion program. Unfortunately 'Top Secret Electronics (UK)'. I have read the unauthorised obtainmg of free
warning & fully understand that the use of this telephone call(s) is a crimmal offence
this creates a problem for people in your position
unit in the UK is illegal. I sign to state that I am
who would like to switch to WordPerfect or purchasing this unit as a novelty only, further I GUARANTEE
LetterPerfect but have too much material stored in will not connect direct/indirect to any telephone If you are not entirely delighted
system without the prior consent of the system with the remarkable 'Creditcall'
another format", writes God win, simply re-stating simply return in the received
provider.
my question and confirming that would-be new condition for a full no quibble
Signed ................................................ . money·back refund.
users must go to third party software companies Top Secret Electronics (UK)
Date ................................................... .
which specialise in document conversion inevitably 26 Woodlands Road,
Name ................................................. . RIUlngton, Mallon, V017 8l0
at far too high a price for anyone with a large
Address .............................................. .
number of files.
I never got my disk back and there is no reason to
Postcode .......................................................................... .
suppose that anyone at WP UK even bothered to
All orders are in strictest confidence -tick for no mailings 0
checkit. • • Please note that the coupon must be s1gned & dated else we are unable to supply this unit in the UK. This unit
is supplied as a novelty only We w11l not be liable in the event of any illegal UK use. The slogan 'Slash your
phone bills' applies to our adv1ce w1th the supplied uM
 Barry Fox

Tried And Tested...

By Pigs
Barry plays with CD TV, MS-DOS 5. 0 and WordPerfect and realises that he is being used as
a Guinea Pig -in fact we all, unwittingly, provide free testing for new products.

ommodore is now turning automatically, as for instance

C about face on CDTV. The

interactive CD system,
launched last April, was targeted
routinely offered by Quarterdeck's
Optimise program that comes
with QEMM/Desqview. Manual
optimisation is a tricky, time-
at the consumer "brown goods"
market with the emphasis on consuming job which- as the DOS
worthy "entertainment" software, S manual neatly proves - defies
developed especially for CDTV. simple description.
Consumer sales of CDTV Microsoft have already made
players have been pitifully slow what it tactfully calls a "silent
and Commodore now admits it upgrade". DOS SA should lack
made a hash of the launch. CDTV some of the bugs which those who
has already been renamed Amiga bought DOS S have found. But
CDTV and reduced in price, but there is still no automated
that hasn't worked. So this spring memory optimisation. Presumably
the 2.7 million owners of Amiga we shall have the chance to buy
SOO computers in Europe will be this with DOS 6.
offered a £300 CD-ROM add-on his company Microsoft were in the For my money, the best feature
drive which plays CDTV discs. The right place at the right time. Gates of DOSS is the "uninstall" program
software emphasis will shift from was recently named America's which returns the PC to its original
encyclopa?dias to games, ported richest man, worth $6.4 billion at state, in my case running DOS 3.3.
from Amiga floppies to CDTV the age of thirty-six. This, like the old Morris Minor, has
optical discs. Thanks to Gates PC users must now been tested on enough paying
I finally got to try a CDTV struggle to identify files with a pigs to have become a working tool.
player, nine months later than maximum of eight letters and buy Many offices now use
promised. Access times were bolt-on software like N orton' s WordPerfect word processing
terribly slow, without advice signs Utilities to undo the damage DOS software with their DOS PCs. I do
on screen. There was horribly can do with commands like Delete, not particularly like WP, but am all
distorted sound on the demo disc. Format and Recover - which have for a quiet life and was quite happy
Poorly thought-out software kept all the subtlety of thermonuclear to switch from my now obsolete
locking and crashing the system. devices. word processing software (Psion' s
Only a computer company When Microsoft released DOS Xchange I Quill) for the sake of
could make the mistake of trying to version S.O, there was the usual consistency. This is quite a
foist this on the public as a glossy demonstration for the press commitment because the
consumer product. History will who were able to see the system commands of any wordprocessing
judge it a miracle that the computer working cleanly on rows of package become second nature and
industry has, so far, managed to computers set up for the occasion. must be unlearned. More to the
grow fat on using its customers as As usual, I refused to write a point, I have literally hundreds of
paying guinea pigs. review on the strength of any such disks and thousands of files stored
We are now up to Version S of pre-packaged glitz and tried a copy in the old format.
the MS-DOS operating system, the for myself. Exactly as I feared, DOS- So, when I saw an article written
de facto standard for non-Mac S is a lot less neat and tidy than by Da vid God win, Director of
computers. DOS became the Microsoft would have you believe. Marketing at WordPerfect UK,
standard only because IBM chose it Ver S soaks up hard disk space about "document compatibility" I
ten years ago. The decision was by duplicating N orton' s rescue wrote to him suggesting that if he
taken in a hurry by IBMers who tools. It claims better memory wants to win over people with old
knew nothing about the consumer management but lacks any facility software, WP must make it easy to
computer business. Bill Gates and to optimise memory settings Barry continues on page 61

62 Practical Electronics April1992

 These modules now enjoy a world-wide reputation lor quality, reliability and per1ormance at a realistic price.
models are available to suit the needs of the professional and hobby market i.e. Industry, Leisure, Instrumental and Hi-Fi
etc. When comparing prices, NOTE that all models include toroidal power supply, integral heat sink, glass fibre P.C.B. and
drive circuits to power a compatible Vu meter. All models are open and short circuit proof.
THOUSANDS OF MODULES PURCHASED BY PROFESSIONAL USERS
OMP/MF 100 Mos-Fet Output power 110
R.M.S. into 4 ohms, frequency response 1Hz- 1
-3dB, Damping Factor > 300, Slew Rate 45V/uS,
T.H.D. typical 0.002%, Input Sensitivity SOOmV, S.N.R.
-110 dB. Size 300 x 123 x 60mm.
PRICE £40.85 + £3.50 P&P

OMP/MF 200 Mos-Fet Output power 200 waHs

R.M.S. into 4 ohms, frequency response 1Hz -100KHz
THE RENOWNED MXF SERIES OF POWER AMPLIFIERS -3dB, Damping Factor > 300, Slew Rate SOV/uS,
FOUR MODELS:- MXF200 (100W + 100W) MXF400 (200W + 200W) T.H.D. typical 0.001%, Input Sensitivity SOOmV, S.N.R.
MXF600 (300W + 300W) MXF900 (450W + 450W) -110 dB. Size 300 x 155 x 100mm.
ALL POWER RATINGS R.M.S. INTO 4 OHMS, BOTH CHANNELS DRIVEN PRICE £64.35 + £4.00 P&P
FEATURES: *Independent power supplies with two toroidal transformers * Twin l.E.O. Vu meters*
* * * *
Level controls Illuminated on/oH switch XLR connectors Standard 775mV inputs Open and short circuit OMP/MF 300 Mos-Fet Output power
proof * *
latest Mos~Fets for stress free power delivery into virtually any load *
High slew rate Very low R.M.S. into 4 ohms, frequency response 1Hz-
*
distortion *Aluminium cases MXF600 & MXF900 fan cooled with D.C. and thermal -3dB, Damping Factor > 300, Slew Rate 60V/uS,
USED THE WORLD OVER IN CLUBS, PUBS, CINEMAS, DISCOS ETC. T.H.D. typical 0.001%, Input Sensitivity SOOmV, S.N.R.
-110 dB. Size 330 x 175 x 100mm.
SIZES:- MXF200 W19"xH3''•" (2U)xD11"
MXF400 W19"xHS 1;4' (3U)xD12" PRICE £81.7 5 + £5.00 P&P
MXF600 W19"xH5 11•" (3U)xD13"
MXF900 W19"xH5 1'4' (3U)xD143t•" OMP/MF 450 Mos-Fet Output power 450 waHs
PRICES:-MXF200 £175.00 MXF400 £233.85 R.M.S. into 4 ohms, frequency response 1Hz -100KHz
MXF600 £329.00 MXF900 £449.15 -3dB, Damping Factor > 300, Slew Rate 75V/uS,
EACH .H. D. typical 0.001%, Input Sensitivity SOOmV, S.N.R.
-110 dB, Fan Cooled, D.C. Loudspeaker Protection, 2
[t] VI :1'7·1 ;J ti :J §t 3.,,., ;1; i ,., ;J' J'i; t·f~i tl Second Anti-Thump Delay. Size 385 x 210 x 105mm.
.,~ * Manual arm * Steel chassis * Electronic speed PRICE £132.85 + £5.00 P&P
NOTE: MOS..FET MODULES ARE AVAILABLE IN TWO VERSIONS:
control 33 & 45 R.P.M. * Vari pitch control * High STANDARD -INPUT SENS 500mV, BAND WIDTH 100KHz.
torque servo driven DC motor * Transit screws * PEC (PROFESSIONAL EQUIPMENT COMPATIBLE) - INPUT SENS
, 12" die cast plaHer * Neon strobe * Calibrated 775mV, BAND WIDTH 50KHz. ORDER STANDARD OR PEC.
' balance weight * Removable head shell * ,,,,
cartridge fixings * Cue lever* 220/240V 50/60Hz
* 390x305mm * Supplied with mounting cut-out
template.
PRICf£ £61.30 + £3.70 P&P
GOLDRING G950

ti 13 ;13•'·' tii•'V' •:13 ;•·r'171·I·; AVAILABLE, INCLUDING CABINET FITTINGS, ,.,....,.,..,.,n.

GRILLES, CROSS-OVERS AND HIGH POWER, HIGH
STEREO DISCO MIXER with 2 x 7 band FREQUENCY BULLETS AND HORNS, LARGE (A4) S.A.E.
L & R graphic equalisers with bar graph
(SOp STAMPED) FOR COMPLETE LIST.
LED Vu meters. MANY OUTSTANDING
FEATURES:· including Echo with repeat & ~~From McKenzie Professional Series
speed control, DJ Mic with tone control lSJ- From McKenzie Studio Series
& talk-over switch, 7 Channels with McKENZIE:-INSTRUMENTS, P.A., DISCO, ETC
individual faders plus cross fade, Cue
Headphone Monitor. Useful combination of
following inputs:- 3 turntables (mag), 3
5 Line for CD, Tape, Video etc.

11

THE VERY BEST IN QUALITY AND VALUE

Made espec1ally to su1t today's need for compactness w1th h1gh output
sound levels, fm1shed 1n hard weanng black vymde w1th protective
corners, grille and carry1ng handle. Each un1t Incorporates a 12" driver
plus high frequency horn for a full frequency range of 45Hz-20KHz.
Bolh models are 8 Ohm impedance. Size: H20" x W15" x 012".
CHOICE OF TWO MODELS
POWER RATINGS QUOTED IN WATTS RMS FOR EACH CABINET

OMP 12-100WATTS(100dB) PRICE 1:163.50 PER PAIR

OMP 12·200WATTS (200dB) PRICE 1:214.55 PER PAIR

CAR
150 WATTS (75
Bridged Mono
250 WATTS (125 +
Bridged Mono
400 WATTS (200 +
Bridged Mono
ALL POWERS INTO 4 OHMS
Features:
* Stereo: bridgable mono * Choice of
high & low level inputs * l & R level
controls* Remote on-off* Speaker &
 CITIZEN I

ALWAYS A GOOD IDEA 9 PIN PRINTER

Silica presents some great FREE DELIVERY
Ne-xt Day • Anywhere m the UK mafnlana
80 COWMN
offers on the award winning • Citizen 1200+ - ~ pifl - 80 column
• t44cps Draft, 30cp$ NLD
range of high quality matrix
printers from Citizen. Each
FREE STARTER KIT
\'IOOh t29.3S • Yhth every CitizeApinrer f'Om Si!ie:a
• 4K Printer Bufter + 2 Fonts
• Parallel Interface as Standard
Citizen printer is built in the • GraPhics Resolutfon: 240x240dpl
U K to exacting standards, 2 YEAR WARRANTY
S11ica o11ec a 2 ~ear warranty (lnctudmo tne
• Epson aQd !BM Em(!l!lfion
• Pull tractor & bottom feed
ensuring superb reliability pm!er head) v.ith every Cffirefl prlm:r from SiliCa • FREE Silica Printer Starter Kit
and output. Our confidence
in Citizen's quality is such WINDOWS 3.0
f(ee Windows 3.0 dnYef.
S£AIAL UITEAMCf OPtiON
The J200 s;rirr.er G Nililble wit!l
a s.crial tnt~rface for t139 -+\91,l,
that we are pleased to in- llltlud'ed With the smea S1a!Ut ~<tt RIJf: PRI21$ • ttS333 ~ w.
clude a 2 year guarantee
with every printer. Plus, if FREE COLOUR KIT

£1Z9
V/. 1n ewry Swih 9 and S•••ift 2LC printer
you buy a Citize n printer
from us, we will give you FREE HELPLINE
N!l~ine
li!dlnJCal suppc:tl dunAQ ol!ice hours.
the Silica Systems Printer opt!f'l

Starter Kit (worth £29.38),

FREE OF CHARGE! MADE IN THE UK
Citizer ptners sreManutacturelt to high staMards. ·. +VAT=£151.58 rei: PRI 2120

9 PIN PRINTERS 24 PIN PRINTERS

• Citizen StMft 9x 9 pin - 136 CCIUfllt'J

p

! ~f~htcer·-"' .;.,,.. • 192cps OrBit. 4/lef>S NLO

• BK Printer 8ufler .,_ 3 Fonts
• Paraflellnterlace • Parallel tnterface
• Gr.fphlcs Rcsoluffon: 240x240dpi • GraphicSJltJ$1J/UYon: 240X2400P!
• £pson and IBM EmulatiDfl • Epson and IBM Emulatlen
• FJj££ C0/11Ur Kit • A3 /a.tJdSCape priming

..,,
COUIUIIIU'L --
e FREE SiliCa Ptlmer Srafler X1t

$UIIT111 •n . ·-:~
l3i

I'OML Ml'f 13ft

• FAEE Sl'lica Ptlnter Staner Kit
Rat: ...... 1319
SIAIITt• l iT .....:J!!

5.4/,\\'&~
~lftltr1 'im

ACCESSORIES STARTER KIT

SH~ET FEEDERS

•
•
Citizen 1240 - 24 pin - 80 col
144cps Draft, 48cps LQ
PM 1200 UIO , , , , tn..at
PRA 12ts- 124111224 IW9i'24124t •. [18.71
PRA. 1228 124111224 Sw9.'24124t . t4t.ot
SERIAL INTERFACES
FREE!Worth: £25 +'IAT=£19.38
PRA 1189 t210+ .............. ....... £51.45 To 081-)'0U t.;1 cr~d nmiQJ !f>ith)(l(lr new
• BK Printer Buffer + 2 Fonts WIA -no9 12401224 Sw*n I £32..2$ ~ntef from Silica;
PRA t709 t wltt 24124• ........ ... £.21.31 e 31+...-Disk • AmiJI & ST OltVets
• Parallel Interface 32K MEMORY EXPN • ., .... Ditlt · OriwnfltrWiftftws3
• Graphics Res: 360x360dpi PRA 1753 1240/t2:4 hifl 2'124e t13.1t • 2 M1tre Pltl-//~1 Prilfter C#ble
• Epson and IBM Emulation PRINTER STAND • 211 Sbuh ol CDRtllfut~ut Plptr
• Citizen PN48 Notebook Pri mer· Pf!A t242 1240/1U s.tl2412.,_ .. £U.03
e Non•iQlP8Ct PritU!ng On Plain Papsr • 1110 ColttiltiiDII$ Add"" UH!i
• LASER QUALITY - 64cps • Citizen Swift 24_x - 24 pin - 136' column
• FREE Silica Print8r Starter Kit Pf!A 1274 &wilt M4t .. . .. . . . E3U6 • s c,IIRUHS Et1N~ops
ORIGINAL RIBBONS
• 4K Prlfllef Buffer + 2 Fcnts • 192cps Draft. 64cps L.O ;:....;;.:....:..:..=;....__----., RRP: .. ........ ...... £249 Rill 3$20 12101SWII'I 9 Black. .. . tU1
If '100 alreat1y own aprimer. a:.d WOtiiCI
m. to buy a ijt. you m;y O<®ror» (rei:
• Rea-r and BoNom Pa,wr LOAding • 8K Printer Buffer + 4 Fonts STARTER KIT.. ...... £2~ Rl8 3949 Swift t.c Bttck ........ ...... 27.15
• Parallel Interface • Parallel Jnterf3ce RIB 3924 12<11122< Sollil.. lloct tUV KIT 5500) for £24.ll5 · £5 oN RRPl
• Gt:Jphics Resofutjon: 360x360dp; • Graphics Resolution: 360x360dpl 70TAL RRP:rzi4 RIB 39G5 lwll 112'12.. C~OO! 11U3
• F.pson, I(JM, NEC P6 & Citizen Em~Jatjons • Eoson. IBM and NEC P6 Emulation SAVING:~ RIB 3~48 - Slog• !1rib .. .... US1
• · A3 1andscape printing . FREE Colour Kit RIB 3348 fiWI Mllltl $1rilt , . U-61
• Pt!wer Mains. 83ffSJY or C8r Adaptor
• !'REI! Silica Primer Starter Kff • FREE Silica Printer Starter Kit COLOUR KITS
PAA t23& Swill tlt4Jto&c U$.2:6
RAP: .... £325 ARP! .......... C4ft PiU. 1243 s.ut t .ntt . .. tss.2S
ST•RTEA IUT .. ;,£!:
mAt. RR,: aso
SAVING: !!Q!
SILICA '-"'Cl: _!.!!
£249 STARTER KIT .
~L
Ja!
RAP: l$1.41
!WING:~
SIUCA PRICE: £.:W9
£149 PN48 ACCESSORIES
PAA 1148 . . . llne!y .
m uss ""' c.1e Ena
PM 11&2 tiMI e.r • •
. t!U G
£ tac
... . . r 1BC
All pric. . l ncfludit VAT • I'ICI Fr. . 4otliv•ry .

MAIL ORDER: 1-4 The Mews. Hatherley Rd, Sidcup, Kent. OA14 40X Tal: 081·309 1111
I SILICA SYSTEMS OFFER YOU I Ofd6r L inO$ Open: MOI'I•S8t 9.(l()am·6.00pm
LONDON SHOP:
Op~nifl.g Hours: Mon·Sat 9.30am-6.00pm
N~ Lal9 N!ah\ Op4oning
52 Tottenham Court Road, London. WIP OBA
No t.atq Night Qp41!ni ttg
Fax No~ OEil;.::;oe oeoB
Tal: 071·588 4000
Fax No:, O'Tt·S23 4'r.11
• FREE OVERNIGHT DELIVERY: On all hardware orders shipped in the UK mainland. LONDON SHOP: Selfrldges (1St floor), Oxford Street, London, WlA lAB Te.l: 071-629 1234
• TECHNICAL SUPPORT H ELPLINE: Team of technical experts at your service. Openin-g Hours: Mon·Set ~~.OOpm Lltle. Night: ll'ltusday until 8pm Extafl6ion: 3914

--------------
• PRICE MATCH: We normally match competitors on a " Same product - Same price" basis. SIDCUP SHOP: 1-4 The Mews, Hathertey Rd, Sidcup, Kent, DA14 ~OX Tel: 081-302 8811
Opgni ng Hours: lA01'1•5al 9003m-.5.30pm Late Ntgh1· Frklay until 7pm F2ll: No: 081-309 0017
• ES TABLISHED 12 YEARS: Proven track record in professional computer sales.
• BUSINESS + EDUCATION + GOVERNMENT: V()lume diSCOUntS available for large orders.
• SHOWROOMS: Demonstration and training facilities at oor London & Sidcup branches_ I 10: Silica Systems, Oept PRNOW-1291-55, 1-4 The Mews, Hathertey Rd. Sidcup, Kent, OA14 4DX1
• FH E FULL STOCK RANGE: All of your requirements from one supphe< ..........
•
•
FREE CATALOGUES: Will be mailed to you with offers and software/peripheral detaJis.
PAYMENT: By cash, cheque and all major Cledit cards. 11PLEASE SEND A CITIZEN COLOUR CATALOGUE l1
Before you decode when to buy your new printer, we suggest you thi n~ very caretufly about WHERE
you buy~. Cooslder what If wJII be like a few months after you have made your purchase, when you
I Mr/MrSJMs: Initials: ..... ...... .. .. Surname: ..... ................................................ 1
may require addftjonal peripherals or software, or help and advice. And. wm th e company you buy from Address:
contact you w1th deta,lfS ol neoN products? At. Silica Systems, we ensure 1hat you will nave nothing to
worry abOut, we have been established for over 12 years an d. wUh Ol)r unrivalled experience and ex~
pen lse. we can now claim to meet our c ustomers requtrements with an unoerslanding w hich is second II I
to none. But don't just take our word for it. complete and return the coui).On n ow tor ou r latest Free
literat:Jre and begin to experience. tne " Silica Systems Servtce... · Postcode: . ...................................... I
I Tef (Home)· • . ..... .................... .... . . .. .. Tef (Work)·
~ MAIL ORDER HOT LI N E
SILICA I
6 081· 309 1111 SYSTEMS I
Company Name (rf apphcabfe). .... ...... ....
Which computer(s). If any, do you own? .... .
.. .................................
....................... . 55C I

~----- - -------;;;,
i J OO • A(IYtn••e<l pr.eH .:.nd tpoci<hcauon~ m"y oh.aft90 . Ploas.e r~rn en~ ooo.~po~ tol lh(> ~!Oiit tntom>;ation.