Jan - American Radio History

Jan - American Radio History
DIY protection
Van Gogh on
a VCR
Simplified circuit design
Electronic repairs from Weka
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January 1992 • Volume 28 No. 1
In last month's issue I mentioned
that I would rather like a laptop
Macintosh computer. At the time, the
machine was just a rumour and
phoning Apple had produced a
resounding ·no comment·. Days after
the magazine was sent to be printed, a
press release arrived on my desk from
Apple announcing the launch of three
new laptop computers- just in time to
miss the deadline. Fortunately, Apple
were kind enough to let me play with
the new PowerBook 140 for a few days
- the full review can be seen on page
10.
Also in last month 's issue we
featured the Joint European Torus. As
everyone will know now, they
achieved a fusion reaction that
produced 2MW of power on 9th Nov
1991 and are looking forward to
continuing their research up until
1996.
Here at PE we try to keep you in
touch with all of the latest technology.
Kenn Garroch, Editor
What A Year lt Was .................... 14
fan Burley Looks at what was new in 91.
The Multimedia Myth ................. 20
A riot of buzzwords looking for a technology
All That's New At Comdex Fall ... 25
/an Burley takes a trip to the USA
Future Technologies ................. .45
Atom sized switches and superconducting logic
Look After Your Plants .............. .48
Build a greenhouse monitor
Reviews
The New Laptop Mac .................. 10
PE gets hold of one of the first machines
Protect Your Car ..........................35
The Electronize car alarm system under scrutiny
Analogue Circuit Analysis ............ 36
The latest CAD software
Painting Pictures On A TV ........... 38
Next month ...
Laura Esterman looks at the Vtech Video Painter
The Ideal Book For Mr. Fixit.. ....... 39
The WEKA Electronics Repair Manual
Hunting The Snark ......................43
We send Ffona Gammie to the theatre
SCIENCE AHD TI:CHNDLOOY
Video Recorders
Regulars
Wavelengths .........................5
Innovations ........................... 6
Price cuts from Toshiba & MT
What's New ........................... 9
Computers from Amstrad, Fujitsu & Apple
Silicon Valley .... ................... 13
Introducing an 8-Bit Rise Microcontrol/er
How lt Works ......................32
Telephone answering machine
Practical Technology .......... .40
PE looks at the best of the VCRs, CAD,
3D sound, games machines, how a
camera flash works plus all of the
regulars.
Out On 5 December
PC display cards for high quality graphics
Techniques ..........................57
Barry Fox ............................62
ChannelS, who will start the bidding?
Editor Keno GatrO<:II Ea1toua1 Asslmnl; Laura Eslerman Advertisement Manager !Y.ovod Bonner Proouctioo Mana9er: Richard Mllner Prod~•on Ass slant 0<110 0 gloacch no Publosher: .Mgelo Zgorcloc
• Practical Electronict Intra House 193 U•brldge Road London W12 9RA To I: 081·7-IJ 8888 Fax: 081·7-IJ 3062 Tolotorn Gold: 87: S00567 • Allfllftlsemonts The Publishels or PE lake reasonal)le precautoonsto
ensure that adverlistrnenls pu!JIIsloel!ln the maga.~loe are gen•lne. bOt CMOOI takll any responsibilirt in resjle(( ol statements or claoms mads ~Y arll'enlsers The PUCIIshers also cannot accept any liabil~y in respoct of goods not beillg
delivered or not worki<9 properly • Cl lnua Press 1992 CopyriQht in all d13'1olngs. photoglaJ)hs and articles published in PRACIICAl ELECTRONICS is fully protected. and repmduC11on or 1111italions in whole or in part are expressly
forbrdden All reasonable precautions are la~en by PRACTICAl ELECTRQ\IICS 10ensure that the advice 300 data giV~~n :o reade~s is reliable. We cannot. ho•'!ller. guarantee il. ana Wll cannot accepllegalresnonsibility for il. Prices QUOted aro
Ihose current as we go 10 press All rn:Jicrlal is accepted lor pJblication on the expmss underslandlng lhallhe contrrbutor nos the authority to pi)Jmol us to ao so • Practical Electronics is typeset at Intra Press on Macintosh
computers using Quark Xpress. Reproducbon by Clrtle Rule Ltd. Printing by Andover Press, St Ives plc. Distribution by Seyrnour Press • ISSII 003Z-tS72 •
January 1992 Practical Electronics 3
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-----------------------------------letters
Wavelengths
If you have any comments, suggestions, subjects you think should be aired, write to PE
Subjective Speakers
Your review of the Canon S-50
speakers in December's PE proved
to be a little confusing. The two
diagrams at the top of page 39
purporting to show how the
speakers work was rather unfair.
Normal speakers spread their
sound far more than is shown and
it is difficult to see how the S-50s
offer any advantage. It would have
been nice to have seen a more indepth analysis of their operation
showing their physical and audio
characteristics. As it was, the article
was subjective from beginning to
end.
W M Partridge
Hemel Hempstead
Herts
It would have been nice to do an indepth test but, unfortunately, we don't
have the facilities. In defence of the
review, sound reproduction from a
HiFi system is rather a subjective
matter so examining them in that way
is fair - I have actually heard the S-50s
myself and I must admit that they do
sound different- Ed.
Flat Presentation
I read with interest the letters
about Sharp's' monstrously framed
flat screen TVs, and I would like to
add my comments.
Any new technology needs to be
presented in a way that makes it
appeal to the general public. After
seeing the frames in question (last
month's PE page 5), I can't help
thinking that Sharp have gone
about it the wrong way. A wall
hanging TV screen is something of
a mistake in any case as most TVs
sit noisily in the corner on their
own stand. Any technology that
wants to replace them will have to
look like them, at least to begin
with. To hang a TV on the wall
would require it to be placed at
about waist height or lower, just
where it could get knocked or
smashed. Any higher and we
would have cricked necks trying to
watch it. As they stand, the wall
hanging TVs a la Sharp, are only
good for displaying art- perhaps
computer art.
The upshot of all this is that new
technologies have to be designed
and presented in a way that makes
them immediately recognisable as
to their function. If this is not done
they will never take off.
MMathews
Bolton
Lanes
Scanning Data
Last month you featured an
article about image scanners
"Putting you in the picture". In the
main it was quite interesting but I
would be grateful if you could
answer a couple of questions.
Firstly, the picture you used as
an example was obviously an
etching and so was quite grainy. Is
the reproduction as good on normal
photographs?
Second, on page 36 you gave a
sequence of images showing the
difference in quality at different
resolutions which were to be
viewed clockwise. Even looking
closely, the only one that stands out
is that which was scanned with 16
grey levels. Which of the others is
which, or are they all the same?
Thirdly, you don't really specify
which scanner you used and where
you can get it from.
Aside from the above, it looks as
though you may have succeeded in
proving that scanners can replace
traditional
methods
of
reproduction, for black and white at
least. Will you be looking into
colour scanners at any point?
Andy Marshall
Hampstead
London
In answer to your first question, the
pictures on pages 5 (Wavelengths) and
44 were scanned from black and white
photographs the first also appeared in
PE September 91 on page 28.
The pictures on page 36 start at the
top left and move across the top row
with the 600dpi image being at the
start of the second row - it is virtually
impossible to distinguish between the
150, 300 and 600dpi images.
The scanner used was the
Panasonic FX-RS307 and should be
available through Panasonic dealers or
though Panasonic at Panasonic House,
Willoughby Road, Bracknell, Berks,
RG12 4FP.
Hopefully, quality colour scanners
will become relatively cheap in the near
future in which case, we will get one in
a put it through its paces.
JET Mistake
Thank you for an interesting
article about fusion reactors and
JET in your December issue. One
small point is that your artists
seems to think that there are two
protons in Tritium and not two
neutrons.
P J Cherry
Littlehampton
Sussex
You're quite correct. My thanks to
everyone else who pointed it out.
•
Errata
A number of errors crept into last
months issue of the magazine,
especially on pages 30 and 31,
Electronics Goes Under The
Hammer.
William Crookes was bestowed
with the Order of Merit in 1910,
not the Mint as stated.
On page 48, the circuit diagram
for the head phone amplifier had
01 inverted laterally , the emitter
should be connected to R1 and
not the collector. In addition, the
cathode of the valve should have
been connected to the HT supply.
January 1992 Practical Electronics 5
Innovations--------------------------------
Innovations
This month, JET produces 2MW of power, Toshiba and Mannesman Tally cut their prices
Price Slash
Signalling the rapid
decline of the 24pin dotmatrix printer market,
Mannesman Tally has
announced that it will be
cutting the price of its
bottom of the range 4
page per minute MT904
laser printer. Originally
priced at £999 when it
was launched in April,
this has been dropped to
£825 to allow MT to take a
larger share of the laser
printer market.
Toshiba Down
Also in the price cutting
competition is Toshiba. It
is knocking up to 30% of
its range of portable PCs,
printers and accessories.
Hoping to start a
Christmas rush on its
products, Toshiba will
drop its prices on Nov 4
bringing, for example, the
T1000LE
portable
(reviewed in PE August
91) down from £1495 to
£999 and the T2000SX/20
from £2650 to £1499. The
bottom of the range, the
TlOOOSE now costs a mere
£525. It looks as though
6 Practical Electronics January 1992
laptop computers are
finally reaching prices
where they are affordable.
JET Generates
At 7.44pm on Saturday 9
November 1991, JET, the
European experimental
fusion reactor based at
Culham near Oxford,
announced that it had
produced a significant
amount of energy from a
fusion reaction. Between
1,500,000 and 2,000,000
Watts of power were
generated
using
deuterium and tritium
fuels held in a magnetic
containment vessel.
This is the first time
these two particular fuels
have been used. Previous
experiments have used
only the non-radioactive
deuterium (an isotope of
hydrogen with two
neutrons instead of one).
Starting
with
low
concentrations of tritium
(another isotope of
hydrogen with three
neutrons), JET is aiming
to move up to a full
power system using a
50/50 (0/T) fuel mix by
1996.
The next step for the
project
is
to
get
--------------------------------Innovations
equipment is required at
the reproduction stage.
An ideal application
would be in stereo TV
where the separation
between the speakers is
limited.
For more information
contact Sound BASE Ltd,
Court,
W a tford
Throgmorton St, London
EC2N 2AT, Tel 071 256
8716
Battery Mains
confirmation of funding
from the EC to keep the
experiment open until
1996. With the successful
demonstration of a fusion
reaction, there is now a
good chance that the
project will get the
requiredjunding.
When the project
finishes in 1996, an
experimental reactor ITER
capable of generating
1000 mega Watts of
power
will
be
constructed.
If
experiments with this
work
well
then
commercial reactors could
be a reality within 30
years.
More
information
about the Joint European
Torus can be found in the
December
issue
of
Practical Electronics.
to allow the brain of a
listener to receive more of
the source information in
a way that enhances the
sound.
BASE is normally used
at the mixing or recording
stage and once the sound
has been encoded, it can
be transferred to CD,
OAT, cassette LP and so
on, without loosing the
added effect. The main
result of this effect is to
add an "out of speaker"
and "height" dimension
to the sound.
As well as being used
on Kiss FM, BASE was
used in the films Star Trek
V and The Hunt For Red
October. The advantage
of the system over other
techniques is that no extra
The Handy Mains unit is
a power inverter that
allows up to 200W
continuous power at 220V
to be drawn from a car
battery. This could
provide power for a TV,
fax, electric drill and so
on, even a vacuum
cleaner. The basic model
is priced at £59.95 with a
Super model providing
more start up power,
more continuous power,
thermal
overload
protection and an audible
warning when the battery
is running low, costing
£89.95. For details contact
Switched Mode Ltd, Unit
2, The Markham Centre,
Station Road, Theale,
Berks, RG7 4P
R. Tel. 0734 302113
•
250WATT
Kiss FM Goes 3D
Regular listeners to Kiss
FM, a London based
independent
radio
station, will have heard
the new 30 sound system
recently introduced. The
effect of BASE (Bedini
Audio
Spacial
Environment)
sound
processing technology is
January 1992 Practical Electronics 7
New P r o d u c t s - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
A roundup of the latest in computers, video and
electronic technology.
Just when you thought they were obsolete,
Amstrad has improved and revamped its range of
PCW computers. The 9512+ comes with a built in
3.5in 720k floppy disk drive, 512k RAM, paper
white monitor, daisywheel printer, and Locoscript
2 wordprocessing software, all running under
CP/M Plus. Another option is to swap the
daisywheel for the, more up to date and faster,
Canon BJ010e bubble jet printer.
All this costs £449 (£527 .58 inc VAT) with the daisy
and £549 (£645 inc VAT) with the bubbles.
Another new computer range from Amstrad is the
Series 5. This features two basic machines, the
PC50S6 and the PC5286. The first is based around
an 8086 microprocessor running at 8MHz with
640kb of memory plus a single 720kb 3.5in floppy
disk drive and a VGA monitor - in other words a
basic PCXT. Additions to this include an extra
floppy drive and a 40Mb hard drive.
The PC5286 is based around an 80286
microprocessor with 1Mb or RAM, VGA, mouse and a
single floppy disk drive making it a cut down PCAT. An
optional 40Mb hard disk is available for those who
need the extra space.
Prices range from £399 (£469 inc VAT) for the PC5086
and ££999 (£1174 inc VAT) for the top of the range
PC5286. A special version of the PC5286 is available at
£899 (£1 056) that adds a games pack including two
external speakers, a sound card and analogue joystick
plus three computer games, Links, F15 Strike Eagle and
Prince Of Persia.
8 Practical Electronics January 1992
What's New
Also from Amstrad is the new SRD600 satellite receiver.
This offers automatic switching between PAL and
D2MAC, two separate dish inputs, a decoder for Sky
Movie channel, an integrated decoder for Eurocrypt
signals, 99 channel capacity, HiFi digital stereo
sound, infra-red remote control and parental lock.
This system should allow you to receive all
current and future European satellite channels
well into the next century.
Only recently announced, the Apple PowerBook
100 offers all of the power of an Apple Macintosh
is a laptop/notebook computer. The built in tracker
ball replaces the mouse and with 2 or 4Mb of
memory. a built in 20 or 40Mb hard disk and triple
Supertwist LCD display, it looks set to take the
world of portable computing by storm. For a full
review of this and the other models in the range see
page 10 of this issue.
Set to make portable computer even
smaller, this 2.5in hard disk drive from
Fujitsu offers storage capacities of 45 to
goMb in a low high package.
For even smaller drives, see the Comdex
show report on page 25.
January 1992 Practical Electronics 9
The Latest Portable - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Apple•s New Babies
Kenn Garroch gets to play with the new Apple PowerBook and likes what he sees.
n the December issue of PE one
of my Christmas wishes was to
have a portable Macintosh
computer. About three days after
the magazine was finished, Apple
announced three new notebook
portable machines and, on phoning
and asking, agreed to lend me one
for evaluation purposes.
At the bottom of the range is the
PowerBook 100 which measures
8.5x11xl.8in and weighs l.Slb, the
smallest and lightest in the range. It
comes with either 2Mb or 4Mb of
memory and a 20Mb internal hard
disk drive. On the software side a
full implementation of the n~w
system 7 is included running on a
16MHz 68000 microprocessor. This
allows all existing Apple Mac
software to be run at about the
same speed as on a Mac plus or
perhaps SE. Built in interfaces allow
the machine to be hooked up to an
external disk drive, a Mac Localtalk
network or other computers via a
serial link (RS232 compatible).
The PowerBook 140 is the midrange system that offers all of the
functions of the 100 but adds an
internal 3.5in floppy "Superdrive"
able to read IBM PC disks as well as
Mac formats
useful for
transferring data between the Mac
and a PC. The processor is
upgraded to a 16Mhz 68030
off~ring
processing
power
eqmvalent to a Mac Hex. It weighs
6.8lb and measures 9.3x11.25x2.25in
and can have a 40Mb hard disk
instead of the usual 20Mb version.
The top of the range is the 170.
The microprocessor speed is
increased to 25Mz and a 68882
maths eo-processor is added.
Instead of the backlit supertwist
LCDs used in the 100 and 140 an
active matrix LCD provides fa,ster
screen updates and better visibility
under more varied light conditions.
4Mb of RAM is standard as is a
40Mb hard_ disk. The processing
power of this machine is better than
many of the high end Macs
currently in use for electronic
publishing (DTP).
I
10 Practical Electronics January 1992
What's In The Box
A brief look at the portable
computer market will help to put
the new PowerBooks into some sort
of context. Laptop or notebook
computers running of the IBM-PC
type have been available for a few
years now and recently, virtually
every manufacturer of desktop PCs
also has been adding a laptop to its
range of machines. The latest of
these
sport
Intel
386
microprocessors and colour LCD
displays offering all of the
fun~tionality of a top of the range
busmess machine in a package
roughly the size of an A4 sheet of
paper and about 1.5in thick. The
only company not to offer such a
machine has, up until now, been
Apple. With the launch of the
PowerBook series, all of this has
~hanged and it looks like Apple has
Jumped to the top of the market in
terms of laptop capabilities, speed,
functionality and style.
Tracker Balls
The first noticeable thing about the
PowerBook computers is their
keyboard layout. Instead of taking
up the whole of the top of the
computer, it is confined to the top
half with the tracker ball
dominating the lower. A big
problem with portable computers
has always been, what to do with
the mouse? A number of solutions
have been tried but the integral
tracker ball is the best so far. The
two empty areas on either side of
the ball serve as rests of the hands very useful when travelling on a
bumpy train as they also allow the
comp~ter to be held stationary.
Usmg the ball is not as easy as a
normal mouse and takes a bit of
getting used to. Positioning is not as
accurate as a mouse because there
is no stable surface to push against
and when clicking the buttons
(above and below the ball), the ball
tends to move putting the cursor in
the wrong place.
~he keybo~rd is a little squishy
~mt IS very qmet - a big advantage
m a laptop as _clicking and clacking
away m meetmgs can be very offputting for the speakers and
embarrassing for the users.
When not in use on a knee, the
powerbook has two sturdy click out
legs to give the keyboard a better
angle for typing.
PowerBook Review
Battery Mains
As a test of the batteries and mains
power of the PowerBook 140, it was
connected to the mains adaptor and
put to sleep overnight. The battery
level indicator then showed a full
charge. Leaving the machine running
just on batteries gave 2.75 hours of
operation before an alert message
popped up advising me that the
machine was running on reserve
power and that it should be
connected to the mains as soon as
possible. Ignoring this and continuing
work produced another message
25mins later to the effect that the
machine should be plugged into the
mains
adaptor
immediately!
Operation of the disk at this point
produced a slightly flickering screen
but another 1Omins of operation were
possible before the final message
came up saying that the machine
would be shutting down in i Osecs,
"Good Night" and off it went Leaving
it a while longer and then plugging in
the mains adaptor and pressing a key
brought the PowerBook back to life
just where it left off with no data loss.
This came to around 3 hours and 20
minutes, pretty good tor a portable
with a hard disk drive.
On Screen
On the whole, the screen display of
the 140 is very good. It is just that
bit larger than a standard Mac
Plus/Classic/SE type screen and
allows a document plus a couple of
desk accessories (calculator, battery
power, clock and so on) to be
displayed at once. Unfortunately,
because standard triple supertwist
LCDs are used, the update time is
rather slow and anything that
moves around the screen at speed,
such as the mouse, tends to smear.
The drawback with this is that small
pointers tend to "get lost" - the
normal method of finding the
pointer or cursor on a Mac is to
whizz the mouse around and the
movement on the screen catches the
eye. With an LCD, this doesn't
work too well and the eye has to
hunt around to locate it.
The viewing angle of the LCDs
is reasonable although the screen
can really only be seen by one
person at a time. The backlighting
works well but when turned off, the
screen cannot be seen at all. It
would have been nice to have had a
rear reflector so that the light could
be turned off to save battery power.
Presumably the 170 with its
active matrix LCD reacts much
more quickly and, although it
consumes more power, will give a
superior display.
System 7
All PowerBooks come with the
latest version of the Mac operating
system, System 7. This is a full
graphical user interface (GUI) and
provides all of the functions
expected of a Mac. It is easy to use,
easy to learn and generally intuitive
(unlike most of its look-a-likes). The
4Mb of memory allows two or
possibly three applications to be
run at once (though not usually
multi-tasking) and a virtual
memory system allows applications
of virtually any size - depending
upon the amount of disk space
available. A RAM disk is also
possible allowing the use of the
hard disk and its motor to be cut to
a minimum.
One good feature of the machine
is its protectiveness. Unlike
standard Macs, which can lose a lot
of work if the power is removed at
an inopportune moment, the
PowerBook with its battery keeps
everything current even when the
power is off. The machine can be
shut down and restarted in the
normal way. However, as the
hidden restart button on the back
proves, this is not the way to run a
portable. Instead, the sleep function
is activated when the machine is not
being used. Switching back on
again is simply a matter of pressing
a key on the keyboard. Operations
continue where they left off
although there is a lull of two or
three seconds after the machine
comes on and before anything
happens.
Power Supplies
One of the most important aspects
of a portable computer is the
battery power system. On the
Powerbooks, two systems are used.
The 100 uses a sealed lead -acid
battery that gives from two to four
hours use and the 140 and 170 have
NiCd batteries that provide two to
three hours.
To help conserve the batteries
there are a number of power saving
levels, the first of which is that
sections of the hardware are put to
sleep when they are not being used.
At the next level, the hard disk
drive shuts itself down after a
preset time, coming back on only
when it is needed. At the top level,
the whole computer switches off
after a user defined delay. Pressing
a key on the keyboard brings it back
to life at the position where it left
off. Of all of these, the most
annoying is the hard disk drive
switching off. The way in which the
Mac's operating system runs is that
sections program code are brought
in from the disk when they are
needed - especially for rarely used
alerts and sampled sounds. This
means that there is a delay of about
three seconds which the disk runs
up to speed before any transfer can
take place. It would have been nice
to have had a small indicator
somewhere on the screen to say that
this was happening. The disk drive
is so quiet that there is no way of
telling why the machine has
suddenly stopped.
Otherwise, the battery operation
and mains supplies are faultless,
especially the warnings about
power shortages - see box.
With the PowerBook range of
laptop portable computers, Apple
has entered the notebook market in
a serious fashion. In the main, the
operation of the machines is on par
with their equivalent desktop
counterparts. A little thought could
have been given to the casings
which, although sturdy enough,
were a little clumsy to carry. This is
made more of a problem by the fact
that they cost a minimum of £1375
for the 100 model and over £3000
for the 170- not something to drop.
Indeed, this is the main problem
with the machines, although they
offer a fantastic amount of
computing power for such small
portable systems, they are quite
highly priced and, more than ever,
•
I'd like one for Christmas.
Specifications
PowerBook 1002Mb RAM, 20Mb hard
disk drive £1375 (bottom of the range)
PowerBook 1404Mb RAM, 40Mb hard
disk drive £2195 (mid range)
PowerBook 1704Mb RAM, 40Mb hard
disk drive £3150 (top of the range)
There are a number of alternatives within
this with various other configurations of
memory and disk systems. Also available
are internal modems, extra rechargeable
batteries and an external disk drive for the
model 100.
For more information dial 100 and ask for
Freephone Apple.
January 1992 Practical Electronics 11
£3995
COMPACT
DMM
Autoranging/Manual. Easy to read
LCD display, diode and continuity
checker. Measures to 1000V DC, 750
VAC, 10A AC/DC. Resistance to 2
megohms. Requires 2 "AA"
batteries.
22-184 .......... ···················· ········· £39.95
£5995
30-RANGE
DMM
With Capacitance And Transistor
Gain Functions. Continuity sounder.
Measures to 1000 VDC, 750 VAC, 10
amps AC/DC current, 20 megohms
resistance, 20uF capacitance, NPN/
PNP hFE. Requires 9v battery.
22-194 ....................................... £59.95
ALL THE ACTION AS IT HAPPENS!
lnterTAN U.K. Ltd., Tandy Centre,
Leamore Lane, Walsall, West Midlands WS2 7PS
Tel: 0922 710000
12 Practical Electronics January 1992
VOICE
METER
Talking Meter. Press a button on the
probe and meter calls out reading in
clear English while displaying it. Full
autoranging. Measures 1000 VDC,
750 VAC, 300 mA AC/DC, 30
megohms resistance. Requires four
"AA" batteries. 22-164 ............. £79.95
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Micro-controllers
Silicon Valley...
AFaster Microchip
The latest micro-controller from Microchip is an 8-bit RISC running at 16MHz. Kenn
Garroch takes a quick look at its innards.
icrochip
has
just
announced the release of
its latest 8-bit RISC microcontroller, designed specifically for
complex real-time embeddedcontrol applications. Its processing
power and throughput is several
times faster than most other 8-bit
micro-controllers, the main
competition being from the Hitachi
H-8 series which is currently more
expensive at around £10-£20 each,
in volume, compared to less than £5
for the PIC17C42.
Aimed at the automotive,
industrial, office automation and
telecom markets, the PIC17C42
uses a 16-bit single word, single
cycle, 8-bit data-word reduced
instruction set (RISC) architecture.
It includes a built-in 2k x 16-bit
EPROM program memory, 232 x 8
M
general purpose and 48 special
function registers in static RAM
(SRAM).
There
are
11
external/ internal interrupts, 33 user
configurable I/0 pins, three 16-bit
counter I timers and two high-speed
pulse width modulation (PWM)
outputs (15.6kHz conversions at 10bit resolution) a full featured
universal asynchronous receiver
transmitter
(US ART)
serial
communications system running at
260kHz with a chip clock speed of
16MHz. Future devices are planned
to have a clock speeds of 25MHz
and 33MHz.
The use of a RISC system allows
the controller to run at high speed
since each of the 55 instructions
occupies a single 16-bit word that
executes in a single cycle. The use
of a pipeline to read instructions in
and process them simultaneously
also contributes to a speed-up of
performance. The only two-cycle
instructions are used in branches
and table look-up - the branches,
GOTO, CALL and so on, require an
extra fetch for the branch addresses.
To help the development
process with the new controller,
Microchip has also introduced the
PICMaster-17. This is a PC-based
MSDOS development system that
runs under Windows 3 and
provides assembler software, an incircuit-emulator and EPROM
programmer. Real-time trace data
can be captured and displayed
without halting the emulation. The
PICMaster can be used with all
current and future Microchip 8-bit
controllers simply by changing a
device personality card and an
emulator control pod.
•
Read/Write
decode for
registers
mapped in
data space
Shifler
Data bus 18
Data RAM
232X8
literf;lf
l l
ROF
WRF
January 1992 Practical Electronics 13
Looking Back
1991 AYear In
Consumer Electronics
/an Burley looks back over the old year to see what was new, what was good, what
succeeded and if any of it has a future.
s ever it has been a very
interesting year in the world
of new electronics products.
It's not easy to pick out all the
highlights but for me, several new
product
developments,
announcements and arrivals spring
readily to mind; Digital Compact
Cassette, Mini Disc, CDTV, CD-I,
HDTV, fuzzy logic, Dolby S, and
more ...
The year started off with a bang;
Philips started to turn the screw on
Sony' s long beleaguered DA T
(digital audio tape) standard by
stealing the show at the big
Consumer Electronics Show (CES)
in Las V egas with an ingenious
alternative. For the first time the
general public was getting wind of
an Philips' new digital audio
cassette standard which was
cheaper than OAT and could even
play Jhe billions of original
analogue compact music cassettes
already owned the world over. This
was Digital Compact Cassette, or
A
14 Practical Electronics January 1992
DCC. Sound processing directly
modelled on the characteristics of
human hearing enabled Philips to
promise the prospect of 90-120
minutes of near-CD quality
listening on a new ruggedised
cassette tape which borrowed
design points from both video
cassettes and PC floppy discs.
Crucial backing from Matsushita,
the giant Japanese electronics gro1.1p
whose brand names include
Panasonic and Technics, and Tandy
in the US provided the foundation
for Philips' eventual triumph in
establishing DCC as the new digital
heir to the music cassette throne.
Despite
initial
flustered
protestations that OAT would not
be threatened by DCC, Sony later
licensed Philips' DCC technology
and OAT was suddenly a has-been
in the consumer market.
Sony wasn't going to admit total
defeat, however, and the second
digital audio technology bombshell of the year arrived with the
announcement of Mini Disc (MD). I
have personally been waiting
extraordinarily patiently for a
random
access
CD-quality
recording medium - a recordable
compact disc in other words. Sony' s
MD system is just that. At the
summer CES event in Chicago,
Sony showed that it too could
Looking Back
match Philips' ingenuity. Using a
tiny 2.5in disc and hybrid magneto
optical (MO) read/write heads
combined with a space-efficient
digital encoding technique not a
million miles from the one Philips
uses for DCC. Sony showed a CD
player you could slip into a shirt
pocket and go jogging for 74
minutes without any interruption
to listening. It seemed apparent that
Sony had been forced to show its
hand. The prototypes we saw in
Chicago
were
very
early
developments and recording
demonstrations were not possible.
However, like DCC, I was
impressed by the sound quality of
pre-recorded material auditioned.
Hifi perfectionists might be able to
claim detected imperfections in the
music, but for myself and I suspect
millions of others, the audio quality
and stability of DCC and MD
players will be perceived as a
quantum leap from existing
analogue audio cassettes. The Sony
versus Philips struggle ended
amicably, too, with Philips
following Sony' s example and
licensing its rival's technology. Back
on the analogue front, Dolby's SIeve! noise reduction system
entered production a little over a
year after it had been announced,
but it's not likely it will become a
household term like Dolby B;
digital systems have seen to that.
1990 was supposed to have been
the year of Multimedia. The idea of
combining audio, visual and textual
information in a structured form on
ordinary compact discs to provide
interactive multimedia databases is
certainly here to stay. A lot of
things happened in the multimedia
world this year, but the industry is
still far from mature. Commodore
January 1992 Practical Electronics 15
Looking Back
invented the MPC (multimedia PC)
standard based around an extended
version Microsoft's Windows
graphical user interface, CD ROM
and an add-in stereo sound
extension.
The battle for supremacy in high
definition TV (HDTV) generated
much discussion this year. In the
US, moves to establish an HDTV
standard were accelerated, with
final test trials of the half dozen or
so proposals scheduled for early in
1992. The impressive looking, but
rather elderly Japanese HDTV
system went live this year, but in
Japan only and for just a few hours
a day. Most still can't afford the
exorbitant costs of a HDTV set. In
Europe there has been an almighty
admitted
its
schedule
of
introducing CDTV (Commodore
Dynamic Total Vision) by
Christmas 1990 was hopelessly
optimistic. A year after CDTV was
first announced in a blaze of selfindulgent glory, it was re-launched
and the first production machines
were shipped during the summer.
Personally, I think Commodore is
trying to do too much with CDTV
on a hardware platform (a stripped
down Amiga personal computer)
which was never designed for the
job. CDTV's main rival is CD-I, or
Compact Disc Interactive, invented
by Philips back in 1986 and once
again being eo-developed by
Matsushita, Sony and Tandy
among others. CD-I was nearly
written off a while back as deadline
after deadline was missed. CD-I
was what the inventors of the term
vapour-ware had in mind! At last in
1991 the first consumer CD-I
machines hit the shops in the US,
albeit without long-promised fullscreen motion video. We're told
that machines will accept chipupgrades next year when the
motion video chip-sets go into
production. European is expected
to get full-spec machines with
motion video sometime before the
summer of '92. Kodak also
announced that CD-I machines
would be capable of displaying still
images from its Photo CD discs.
CDTV has had the advantage of
beating CD-I to the market place,
but sales are not exactly boiling
over. CD-I is undoubtedly superior
on the technical side and has the
backing of major consumer
electronics manufacturers. 1992 will
be make or break for both systems.
Meanwhile the PC industry got
its multimedia act together and
Panasonic's Program Director.
scrap between the European
Commission, TV manufacturers
and the broadcasters. The EC wants
to impose on the industry HDMAC, the satellite broadcast high
definition
system
which
manufacturers like Philips and
Thomson have invested heavily in.
Broadcasters are very worried that
established standard resolution
wide screen format TV, D2-MAC,
will be damaged by the EC
proposals. Then there's PAl Plus,
which aims to use extremely
sophisticated signal processing at
the broadcasting end to preserve
compatibility with existing
television sets but offer a widescreen option. Perhaps 1992 will see
16 Practical Electronics January 1992
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•
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1
The National College of Technology offer a range of packaged
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can commence at any time and at any level, enabling you to
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January 1992 Practical Electronics 17
or
Whether your requirement for surveillance equipment is amateur, professional or you are just fascinated by this unique area
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
Smallest room transmitter kit in the world! Incredible 10mm x 20mm including mic. 312V operation. 500m range........ ...........................
.. ....................... £16.45
MTX Micro-miniature Room Transmitter
Best-selling micro-miniature Room Transmitter
Just17mm x 17mm including mic. 3-12V operation. 1OOOm range
......... £13.45
STX High-performance Room Transmitter
Hi performance transmitter with a buffered output stage for greater stability and range.
Measures 22mm x 22mm including mic. 6-12V operation, 1500m range ............. £15.45
VT500 High-power Room Transmitter
Powerful 250mW output providing excellent range and performance. Size 20mm x
40mm. 9-12Voperation. 3000m range
........................ £16.45
VXT Voice Activated Transmitter
Triggers only when sounds are detected. Very low standby current. Variable sensitivity
and delay with LED indicator. Size 20mm x 67mm. 9Voperation. 1000m range ... £19.45
HVX400 Mains Powered Room Transmitter
Connects directly to 240V AC supply for long-term monitoring. Size 30mm x 35mm.
500m range..............................................................................
.. ................. £19.45
SCRX Subcarriar Scrambled Room Transmitter
Scrambled output from this transmitter cannot be monitored without the SCDM decoder
connected to the receiver. Size 20mm x 67mm. 9V operation. 1000m ranga ........ £22.95
SCLX Subcarrier Telephone Transmitter
Connects to telephone line anywhere, requires no batteries. Output scrambled so
requires SCDM connected to receiver. Size 32mm x 37mm. 1OOOm range ........... £23.95
SCDM Subcarrier Decoder Unit for SCRX
Connects to receiver earphone socket and provides decoded audio output to
headphones Size 32mm x 70mm. 9-12V operation..
. .................. £22.95
ATR2 Micro Size Telephone Recording Interface
Connects between telephone line (anywhere) and cassette recorder. Switches tape
automatically as phone is used. All conversations recorded. Size 16mm x 32mm.
Powered from line..
. ................................ £13.45
*** Specials ***
DLTXJDLRX 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
unit with decoder and relay output, momentary or alternate, S-way dil switches on both
boards set your own unique security code. TX size 45mm x 45mm. RX size 35mm x
90mm. Both 9V operation. Range up to 200m.
Complete System (2 kits) ......................................................................................£50.95
Individual Transmitter DLTX ..................................................................................£19.95
Individual Receiver DLRX ......................................................................................£37.95
MBX-1 HI·FI Micro Broadcaster
Not technically a surveillance device but a great idea! Connects to the head phone output
of your Hi-Fi, tape or CD and transmits Hi-Fi quality to a nearby radio. Listen to your
favourite music anywhere around the house, garden, in the bath or in the garage and
you don't have to put up with the DJ's choice and boring waffle. Size 27mm x 60mm.
9V operation. 250m range .................................................................:...................£20.95
18 Practical Electronics January 1992
UTLX Ultra-miniature Telephone Transmitter
Smallest telephone transmitter kit available. Incredible size of 1mm x 20mm! Connects
to line (anywhere) and switches on and off with phone use. All conversation transmitted.
Powered from line. 500m range ............................................................................£15.95
TLX700 Micro-miniature Telephone Transmitter
Best-selling telephone transmitter. Being 20mm x 20mm it is easier to assemble than
UTLX. Connects to line (anywhere) and switches on and off with phone use. All
conversations transmitted. Powered from line. 1OOOm range....
.. ... £13.45
STLX High-performance Telephone Transmitter
High performance transmitter with buffered output stage providing excellent stability
and performance. Connects to line (anywhere) and switches on and off with phone use.
All conversations transmitted. Powered from line. Size 22mm x 22mm.
1500m range..............
.. ............ £16.45
TKX!IOO Signalling/Tracking Transmitter
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
25mm x 63mm. 9V operation
................. £22.95
CD400 Pocket Bug Detector/Locator
LED and piezo bleeper pulse slowly, rate of pulse and pitch of tome increase as you
approach signal. Gain control allows pinpointing of source. Size 45mm x 54mm·. 9V
operation .... .....................
... ......................... ........
.. ........ £30.95
CD&OO Professional Bug Detector/Locator
Multicolour read out of signal strength with variable rate bleeper and variable sensitivity
used to detect and locate hidden transmitters. Switch to AUDIO CONFORM mode to
distinguish between localised bug transmission and normal legitimate signals such as
pagers, cellular, taxis etc. Size ?Omm x 1OOmm. 9V operation ............................. £50.95
QTX180 Crystal Controlled Room Transmitter
Narrow band FM transmitter for the ultimate in privacy. Operates on 180 MHz and
requires the use of a scanner receiver or our QRX180 kit (see catlogue). Size 20mm x
67mm. 9Voperation. 1000m range.....
.. .................................... .£40.95
QLX180 Crystal Cointrolled Telephone Transmitter
As per QTX180 but connects to telephone line to monitor both sides of conversations.
20mm x 67mm. 9V operation. 1OOOm range.
.. ........ £40.95
QSX180 Line Powered Crystal Controlled Phone Transmitter
As per QLX180 but draws power requirements from line. No batteries required. Size
32mm x 37mm. Range 500m ............................... .. ......................................... £35.95
QRX180 Crystal Controlled FM Receiver
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
setting up. Outpt to headphones. 60mm x 75mm. 9V operation ........................... £60.95
A build-up service is available on all our kits if required.
UK customers please send cheques, POs or registered cash. Please add
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Looking Back
modore's CDTV.
all these arguments resolved.
I'll not forget in a hurry the
advances in LCD colour screen
technology this year. Elsewhere in
this issue we look at the latest
notebook PCs which now sport
colour LCD screens. We're getting
ever closer to the goal of dumping
the veteran cathode ray tube and
replacing it with flat panel LCD
screens. Toshiba has exhibited a
very attractive 10" portable colour
TV which is a mere three inches or
so thick. Sharp is also working hard
to perfect acti ve-ma tric colour
screen technology for domestic TV s.
In October we looked at what
appears to be a big trend in Japan;
fuzzy logic. If a household
appliance has practically any form
of user-adjustment, you can bet
some Japanese engineer is trying
graft fuzzy logic onto it. Washing
machines, elevators, vacuum
cleaners, camcorders, microwave
ovens, industrial robots, even pen
plotters computer CAD systems
now use fuzzy logic technology to
enhance their operation. The
Japanese government has just
announced it is to pour hundreds of
millions of dollars into a long-term
project to develop super-fast neural
computing mainframes featuring
fuzzy logic operating systems.
Experts are convinced the products
of this research will make today's
so-called
fifth-generation
supercomputers look pretty feeble.
It's also expected that these "sixthgeneration" computers will have a
relatively
high
degree
of
intelligence hard-wired into them,
making operations like object
recognition and abstract problem
solving far easier than via
traditional digital computing
methods.
After fuzzy logic vacuum
cleaners, what about neuro-fuzzy
robots to do the vacuuming for
you? That's not quite a reality yet,
but Samsung in South Korea has at
last produced an affordable
(almost) domestic robot which does
more than just prance around
emitting horrid digitised noises.
Launched at the Summer CES show
in
Chicago,
the Samsung
ScoutAbout works as a robot
intruder and fire alarm system with
the ability to alert fire or police
services.
Other developments in 1991
which come to mind include
Canon's surreal-looking widestereo image S-50 speakers. They
work but Canon's engineers are not
quite sure why. Back to Sony and
SIRCS II - the promise of HiFi and
AV equipment intelligently linked
up in a simple network. Switch on
your CD player and the amp
springs to life as well. Then switch
on your VCR and if you're not
playing a CD the amp switlihes to
the VCR input and the CD powers
down. Apparently Sony envisaged
SIRCS II as a way of alleviating
pressure on A V /HiFi sales people
from customers querying exactly
how to use their newly purchased
electronic marvels. Panasonic gets
my vote for a device which solves
one of the biggest problems in
contemporary consumer electronics
- how to work the VCR remote
control
timer
recording
programmer. Panasonic's Program
Director does away with buttons
and introduces stunningly simple
to use thumb-wheels.
There isn't actually enough
room to list even a decent fraction
of the positive happenings in
consumer electronics technology
this year. But to bring the optimists
down to earth with a bump, here's
a quick reminder of how things can
go sadly wrong. Two technologies
I've had high hopes for have been
practically laid to rest this year.
Keyline, the artificial-intelligence
portable teleshopping terminal
which was to have pioneered the
use of electronic money stored in
smart cards, went deadly quiet in
1991. This was also the year that
three out of the four DTI licensed
Telepoint digital cordless phone
service operators folded. The fourth
(Hutchison Rabbit) still breathes
but has yet start its service.
At least the good news far outweighed the disappointments. Let's
hope it stays that way in 1992.
•
January 1992 Practical Electronics 19
Cover Feature
Multimedia- What•s
All The Fuss?
If you believe all the hype and the buzzwords, multimedia is the technology of the
nineties.Julie Saunders checks it out.
ultimedia
has
been
receiving a great deal of
hype over the past six
months or so. It has its own
magazine, there was a recent show
at Earls Court devoted to the latest
happenings in the area and it has
been heralded as a technology set to
revolutionise the world of
publishing.
Trying to attach a short
definition to multimedia is not all
that easy. At one end of the
spectrum it is an interactive
television system and at the other a
way of creating new worlds.
Possibly the best simple
description is that multimedia is a
combination of sound, vision and
computers. The fact that there are a
number of ways in which these can
be integrated gives some idea of the
variety of which multimedia is
capable.
M
The Hardware
The roots of multimedia probably
lie with the invention of the laser
20 Practical Electronics January 1992
disc and the personal computer.
Using one to control the other
meant that images could be selected
at random from the disc and text
overlaid from the from the
computer to create captions and
menus. One of the first systems to
use this technology was Domesday
Project, which linked a BBC Micro to
a Laser Disc player, holding
information about the UK in map,
text and video form. To get at the
information, a tracker ball was used
to position a pointer on a map of
Britain. Clicking a button zoomed
into the map showing finer and
finer detail until the town, city or
village level was reached. At this
point still photos and selected
information from the area were
available. Like its 900 year old
predecessor, the whole thing was a
snapshot of the country though, in
a more easily accessible format.
At the base of modern
multimedia are CD-ROMs compact disc read only memories.
COs use laser beams to scan small
pits on the spinning disc which
hold digital information this can be
music, text, images or instructions
to a computer. Because laser beams
can be made to track very fine
points, a large amount of data,
around 650Mbytes or 150,000 pages
of text, can be stored and with the
disc being relatively small, access
Multimedia
times are relatively quick. COROMs are now widely used as a
publishing
medium
with
dictionaries, newspapers, workshop
manuals and the Complete Works
Of Shakespeare, to name but a few,
all available in this electronic form.
The next step up from simple
text publishing is to supply
pictures. COs are able to cope with
stills but the old adage that a
'picture says a thousand words' is
rather wide of the mark for moving
images. The amount of data
required for 25 seconds worth
would completely fill the average
CD. A way around this problem is
to compress the data, usually by
examining which portions of each
image actually change from frame
to frame and only recording the
changes. The drawback with this is
that it either slows the whole
system or requires a vast amount of
computer processing power.
Two commercial systems that
use COs are Compact Disc
Interactive, or CD-I, from Philips
and Commodore Dynamic Total
Vision,
or
CDTV,
from
Commodore. Both of these use
standard COs containing a mixture
of text, graphics and compressed
still video in conjunction with a
computer system that allows the
user to interact with the data. As yet
moving images can only be
provided by the controlling
computers graphics animation
capabilities - in the case of the
CDTV, the Commodore Amiga at
its heart is able to provide high
revolution moving graphics images
as well as high quality digitised
sound.
Among titles already available
for COTV are Time Table Of
History which covers the American
past and Music Maker, the ultimate
in electronic jukeboxes. Other titles
are becoming available as the
market grows.
Another aspect of multimedia,
first announced by Kodak and more
recently by Philips, is a facility to
allow 35mm photographs to be
transferred to CD for later viewing
on TV or personal computer. The
Kodak Photo CD system takes
colour transparencies and digitally
January 1992 Practical Electronics 21
Multimedia
Multimedia What does it all mean?
Multimedia was the latest
computer buzzword a year ago.
For six months you couldn't open a
copy of MacUser without reading a
product announcement or an
article. Now it's got into the general
vocabulary.
So
what
is
multimedia?
Multimedia means digitising
information from many sources text, pictures, video, music - and
recording it on a computer system
where it can be manipulated and
recombined. The computer press
spent six months telling us this
would change our lives, then gave
up; MacUser admitted a huge
proportion of their readers just
weren't interested. What went
wrong?
Don't believe the hype!
There are two basic problems with
multimedia. First; you need a lot of
expensive high-power computer
equipment to make it work.
Digitising video and sound and
replaying it in real time is beyond
current PCs because of the huge
resources required in processor
speed, display capability and
memory storage. A single scanned
image can use up over 1OMb of
scans them at 3000x2000 resolution
for storage on a CD. All the user
needs is a Kodak Photo CD player
and a TV or a CD ROM XA and a
personal computer.
22 Practical Electronics January 1992
hard disk. Can you imagine how
much space you need for a 20
minute video? Second; what would
we do with all that capability, if we
had it? Things like animated
dancing memos and on-screen
World Cup while you enter data
sound great. But who's got time to
assemble those memos, when a
simple written note will do, and
what will your boss think about
your typing speed and accuracy?
Today the world, tomorrow the
solar system ... Multimedia for the
rest of us ...
Of course multimedia isn't
totally useless. In fact it's been
around for longer than you might
imagine. Video games using laser
disks are one example, karaoke is
another. lt's also driven progress in
the technologies of image
compression and data handling,
and this is already spinning off
benefits in the computer world. But
until the Spare-alike is the standard
pocket computer, with a simple
graphic interface and easy-to-learn
software, multimedia will remain
the tool of professionals with a real
need for it and the ability to commit
the necessary resources.
Richard Milner
Production Manager of PE
In Training
One of the main uses of multimedia
is in interactive training. The user
can be put into certain situations or
supplied with information in visual
form that teaches them how to
react. Language learning is popular,
as is management training - there
are even programs that teach you
how to cope with stress. At the
moment, many of these systems
rely on moving images and are not
really compatible with current CD
technology - they run from the
larger laser discs. However, as
capacity increases, they will move
to the smaller CD and will probably .
become a standard method of
tuition.
New Worlds
The aspect of multimedia which has
generate most comment is virtual
reality, also known as cyberspace.
This uses the modelling capabilities
of the computer to create a digital
world which can be seen and
touched. Viewing is by means of a
small pair of LCD screens mounted
in front of the user's eyes. The
images supplied by the computer to
each of these give rise to a three
dimensional view. Adding a pair of
headphones supplies 3D sound and
special feedback gloves allow
physical interaction. Early versions
of these gloves simply used strain
gauges to sense the movement of
the fingers. The latest versions use
ultrasonic or radio signalling to
sense the position of the glove in
space and, as well as tracking the
movement of the fingers, supply
feedback via hydraulic 'fingers' cyberspace is now solid.
Building a virtual reality world
involves a great deal of hard work.
Objects are built up from points
grouped together to form polygons,
which can be filled to give the
appearance of solidity. By
determining the angle of the
lighting on a scene, the colours of
the polygons can be altered to make
them look real. Since each of the
points has to be defined
individually in space, a lot of work
is involved. Increasing the amount
of information increases the quality
of the image. For example, a
virtually real room could have
chairs, tables, a telephone, pens,
pencils and so on. Increasing the
detail would put numbers on the
telephone buttons and a make on
the pencil. In theory, the ultimate
virtual reality would be a model of
the whole world with detail down
to the litter on the streets. The main
Multimedia
drawback would be keeping it up to
date as things move around. On the
other hand, exploring it would be
enormous fun.
Advanced virtual reality systems
have actually been around for years
in the form of flight simulators.
Allowing pilots to make mistakes
on a mock-up of an aircraft rather
than the real thing not only saves
lives and money, it also trains them
in the correct reactions to
emergency situations. All that is
required is a cabin mounted on
hydraulic rams which allow it to be
moved around, giving the pilot the
feeling of a bumpy ride. The
graphics and animated runways
plus other air-traffic all add to the
reality. The main problem with
scaling down such environments is
the processing power needed to
create the images and the cost of a
system that allows the user to feel
the effects of what is happening.
Visitors to amusement arcades will
now be quite aware that a
simulation of driving in a grand
prix or flying a jet fighter into battle
are now experiences available to
everyone. Although the graphics
are generated by computer, this is
nonetheless a variation on the
cyberspace concept and multi
media.
•
Buzz Words
Apart from a new technology, multimedia has spawned a large amount of jargon.
The following table gives a taste for the subject:
Audio Video Interleave- Microsoft multimedia. Microsoft were the
AVI
original authors of the operating used on IBM PC type computers
BIMA
British Interactive Media Association
Compact Disc- a plastic disc upon which large amounts of digital
CD
information can be stored
CD-I
Compact Disc Interactive- Philips' multimedia machine
CD-ROM
Compact Disc Read Only Memory- uses a CD to store digital
information in a form which cannot be read
CD-ROM XA CD-ROM with extended architecture- a PC based system that
interleaves sound and vision as a parallel stream allowing sound
always to be linked to motion
Commodore Dynamic Total Vision- Commodore's multimedia
CDTV
machines which has an Amiga 500 at its heart
Digital Vision Interactive lntel's multimedia system. EMC
DVI
European Multimedia Centre
Monochrome graphics adaptor for IBM PC compatibles
Hercules
an interactive database system that connects information via
Hypertext
graphics and uses a mouse pointer to select data.
Interactive technology Development Group
ITDG
Joint Photographics Experts Group- an International Standards
JPEG
Organisation (ISO) committee working on compression standards
for still video
Moving Picture Experts Group- an International Standards
MPEG
Organisation (ISO) committee working on compression standards
for moving video
a system to store 35mm photographs on COs
PhotoCD
Point Of Information- a multimedia system used to give
POI
information to customers
Quicktime
Apple's multimedia
Video Graphics Array- computer display system for IBM PC
VGA
compatible machines offering high resolution and multi colour
Super VGA- the next step up from VGA
SVGA
January 1992 Practical Electronics 23
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24 Practical Electronics January 1992
•
Show Report
Cramming 21Mb Into A
3.5in Floppy Disk
This month /an Burley visits Comdex Fall in the USA and discovers a computer world about
to be invaded by colour LCD computers, pen computers and floptical disks.
omdex is a massive tradeonly show and convention
for the personal computing
industry held twice-yearly, and
Comdex Fall 91 had no less than
1900 firms from all over the world,
exhibiting on 3,000 stands. Most of
the big names attend and there are
usually lots of new technology
developments to see. Here are a few
which caught my eye:
C
Floptical
For the first time the new hybrid
magnetic and optical floppy disc
standard, Floptical, exhibited in
force at a Comdex. Key members of
the Floptical lobby are magnetic
media giants 3M and Maxell. What
they're pushing is an affordable
floppy disk with a data capacity of
at least 21Mb - thirty times greater
than a 720K floppy for example!
Hybrid technology is used,
combining high density magnetic
data
storage
and
optical
registration. Importantly, the
Floptical standard, which is 3.5in, is
downwards compatible with 720K
and 1.44Mb PC floppy disks.
Floptical is not magneto-optical
Comdex features all the big names.
(MO) like IBM's new high capacity
read I write optical disc, for
example. There's more on those
later. Instead, the optical aspect of
Floptical is for accurately
registering the high-density
magnetic read/write head over
extremely narrow tracks. Standard
Maxell re-writable Magneto Optical Disk
3.5in disks usually work at 135
tracks per inch density. Floptical
crams 1250 tracks per inch of media
width. Optical registration of the
head is accomplished by an LED
sensor which lines up with tiny
pitted grooves , rather like a vinyl
record, adjacent to each track although unlike a record the tracks
are not spiral. The optical grooves
are indelible and so unaffected by
magnetically encoded data changes.
The drive mechanism has a pair of
read/write heads, one for
conventional standard capacity
double or quad density disks plus
one for the super-high density
Floptical disks. Standard 3.5in drive
mechanisms are now available to
the trade for as little as $30. A
Floptical drive will cost ten times
that, but it is still an attractive
alternative. Maxell and 3M say that
when the disks start shipping later
in 1992 they will be attractively
priced, with Mb/$ costs well below
January 1992 Practical Electronics 25
ShowReport------------------------------------------------------------------
The World's first 1.8in hard disk drive.
standard floppies. There is also talk
of enhancing the technology further
and eventually releasing an 80Mb
floppy.
Floptical is undoubtedly
attractive, but there is one
ingredient for success still to be
found - IBM' s endorsement.
Currently, IBM is backing the
relatively puny 2.88Mb 3.5in floppy
standard established earlier in 1991.
At the other end of the removable
disk storage media scale there is
IBM's 128Mb MO standard.
Logically Floptical fills a gap, but
the future for Floptical won't be
rosy unless IBM decides the gap
needs filling.
Pen Power
If you are unlucky enough to be
booked by a policeman in San Jose,
California, there's a reasonable
chance the officer won't jot your
details into a ticket pad but instead
scribble directly onto the LCD
screen of a GRiDP AD keyboardless
portable PC. The San Jose police
force is the largest in Silicon Valley
- where else would you find hightech constables?
Comdex was a veritable
keyboardless computing showcase.
While Go Corporation with its
PenPoint operating system and
Microsoft (Pen Windows) prepare
to battle it out on the software side,
there were plenty of hardware
developers showing their pencompatible wares.
Samsung, NCR (now owned by
US telecomms giant AT&T), IBM,
Momenta, Microslate, Epson,
Trigem and GRiD among others ·
exhibited working PCs without
keyboards. Actually, that's not
strictly true as several have
connectors for conventional
keyboards should the user so desire
and the Momenta makes a virtue of
its compact optional keyboard.
Most of these next-generation
computers rely on a pen or stylus
being used directly on a sensitive
LCD screen for inputting numbers
or text and selecting menu
liny Hard Disks
Just a few years ago the 3.5in hard
disk was an amazing feat of
miniaturisation. It made the original
10Mb 5.25in 'compact' hard disk
supplied with the first IBM PCs ten
years ago look elephantine. In 1991
we were just getting used to 2.5in
hard disks with area dimensions
not much bigger than a credit card and disk capacities of up to 80Mb as
well. Comdex saw the introduction
of the 1.8in hard disk from Integral
Peripherals in Boulder, Colorado.
The firm hopes its microscopic new
devices will be a hit in the fast
growing notebook market as they
exhibit
very
low
power
consumption as well as being petite.
The 20Mb 'Mustang' version with
its controller PCB relocated off the
drive case is just 1Omm thick. The
other dimensions are just 3x2in. A
twin platter and slightly thicker
40Mb 'Stingray' will be introduced
soon.
26 Practical Electronics January 1992
Epson's EHT-20 features a touchscreen LCD.
-----------------------------------------------------------------ShowReport
Momenta, yet another pen based system.
functions. The primary advantage
over the current trend in
miniaturised computing, notebook
PCs, is that unlike a notebook with
its keyboard, you can hold a pen PC
and 'write' onto it conveniently on
the go - walking around a
warehouse or at the scene of an
accident for example.
Some pen-input computers are
finger compatible as well. Philips
didn't show a machine, but it
announced a pen or finger
compatible LCD display system
which is also sensitive to how much
pressure is being applied. The
system is called PAID or Philips
Advanced Interactive Display.
Visualise a drawing program which
make lines thicker the harder you
press, for example.
The huge Korean industrial
conglomerate, Hyundai, was due to
exhibit a pen computer but it failed
to materialise due to technical
problems. This highlights how early
in the development phase pen
computing is. GRiD and Microslate
have been shipping their hardware
for a while now, but pen computing
in general isn't set to take off in
earnest until about the time of the
next Comdex Fall. By then some
useful operating systems will be
available and the hardware will be
more stable. Advanced handwriting
deciphering algorithms will also
benefit from even more powerful
CPU chips later in 1992. IBM even
showed a colour LCD pen
computer currently being evaluated
for use on the New York Stock
Exchange.
For many, the pen is far more
intuitive than either a keyboard or
mouse. Quite soon I expect to see
peripherals
for
deskbound
computers to provide pen/ finger
input instead of the traditional
mouse. Personally I'd rather speak
to my PC rather than poke it
around with a finger, but useful
voice recognition is a year or two
away yet.
If you prefer a pen or stylus,
Wacom Technology's cordless pen
input device could be the answer.
The device uses no batteries and
relies
on
electromagnetic
'resonance' technology developed
by the firm. Basically the pen's
position is determined by the screen
radio signals being resonated by a
coil in the pen. I can't see tethered
pens having a long shelf life so
Wacom has a good head start in
what will undoubtedly be a very
busy niche of the emerging pen
computing industry.
Most of the pen computers·
shown were full size devices
designed to show a whole page of
A4 text. Indeed, some were
positively bulky. Epson was an
exception; it's EHT-20 hand-held
could be just the first of a flood of
similar pocketable touch -screen
personal computers, or palm-tops.
The Epson, a 10MHz 8088 DOScompatible also accepts finger
input. JEIDA (PC Card) credit-card
sized
non-volatile
memory
cartridges are used for storage.
Epson sees its palmtop as a hardworking pocket computer in the
same mould as Psion' s Organiser II,
of which half a million are now
used in industrial and retail
applications.
In 1992 we can expect a major
advance in palm-top computing
with the much rumoured Apple
machine which will almost certainly
use British ARM RISC processor
technology originally developed by
Acorn Computers in Cambridge. A
lot of people are going to be
forgetting about keyboards in 1992!
Low Power CPUs
There is a big battle raging in the
PC chip world. Intel' s dominance of
the PC with its 386 chip range is
under serious threat from both
Advanced Micro Devices (AMD)
and Chips & Technologies, both of
whom have developed cheaper and
faster 386 clones. AMD has also
produced a special version of the
386SX which not only runs 25%
faster at 25MHz than Intel' s version
but requires just 3.3V to operate
instead of SV - very attractive for
battery-hungry notebook PC
makers. Intel' s answer is a special
version of the 386SX chip, the SL
with special power saving functions
built in - basically the chip stops
January 1992 Practical Electronics 27
Show R e p o r t - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - when it is not needed to save
precious milliamps. Over at C&T,
better known for its PC support
chips, not only has the firm joined
AMD in producing a range of 386
clones, but at the other end of the
scale it has produced a single-chip
PC; just a single square package IC
containing an 8088 processor
(PC/XT compatible), memory
management, interfacing and 1/0
support. All you need to do is add
memory.
Colour Screens
The history books will note Comdex
Fall 1991 for the arrival of colour
LCD notebook PCs. This has
provided a second chance for the
passive-matrix colour LCD which
was rapidly losing out in favour of
the sharper, faster, brighter but
much more expensive and power
hungry thin film transistor (TFT)
active-matrix
colour
LCD
technology.
Only two firms, Sharp and
Epson were spotted showing activematrix colour screen notebook PCs.
Sharp's display was up to the usual
incredible standards offered by
active-matrix technology, but
nobody on the Sharp stand would
admit how long, or not so long as
the case might be, the colour
notebook's battery life compared
with a conventional mono
notebook.
Epson was much more candid as
their active matrix screen,
developed by subsidiary Seiko
Epson, actually had some new
features. Active matrix it is, says
Epson, but TFT it is not. Instead
Epson calls its new colour screen
technology metal-insulator-metal,
or MIM. Advantages over TFT
technology
include
higher
production yields due to less
assembly stages, so it's cheaper to
make and lower in power
consumption. The screen, to my eye
at least, wasn't quite as brilliant as
the Sharp TFT example, but
certainly miles better than any of
the passive matrix screens around.
We should be hearing more about
MIM screen technology.
Infra-red LAN system in a stylish box.
Nickel-Hydride doesn't suffer from
recharge capacity reduction or
'memory' problems and has a
higher charge density. Most 386
notebook computers claim about 3
hours of continuous use in typical
conditions with NiCd batteries.
Epson, by combining the new low
power Intel 386SL CPU with Nickel
Hydride
batteries,
claims
continuous use of up to 8 hours or a
week in 'sleep' mode between
recharges.
Also catching the attention at
Comdex was a new infra-red local
area networking system from a firm
called Infralink - just imagine - no
messy cables! The transceiver units
are very neatly styled as well. As
mentioned earlier, MO technology
is gaining ground, especially after
IBM introduced a 128Mb removable
3.5in cartridge earlier in 1991.
Maxell and Epson both introduced
128Mb 3.5in MO devices at Comdex
and JVC even showed a dinky 2.5in
40Mb MO disc. Finally there's just
time to mention a new drafting
plotter made by the Japanese firm
Mutoh. Yes, that versatile of
tecnhologies, fuzzy logic (PE
October 91), has made its way into
computer peripherals. Fuzzy
processing is used to choose the
best vectors to be drawn first in
order to speed up the drawing
process.
•
Battery Developments
Like Toshiba and a couple of other
notebook PC makers, Epson now
offers Nickel-Hydride rechargeable
batteries instead of the traditional
Nickel-Cadmium type. Over NiCd,
28 Practical Electronics January 1992
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Seetrax CAE • Hinton Daubnay House
Broadway Lane • Lovedean • Hants • POS OSG
Tel: 0705 591037 • Fax: 0705 599036
~-Interak
Pay by Visa or Access
1-
SINGLE BOARD COMPUTER
"SBC-1"
£17.50
+ 50p P&P
+VAT
A computer doesn't have to look like you'd expect a computer to look.
1t doesn't have to have a keyboard and a screen and floppy disks and
so on.
The SBC-1 has the bare minimum of chips a Z80 computer can have
and strll be a computer: A 4 MHz Z80-CPU chip, an EPROM chip (up
to 32K), a static RAM chrp (up to 32K) and a pali of 8255A 1/0 (input
output) chrps g1ving 48 1ndrv1dual lrnes to waggle up and down. There
are one or two additional "glue" crllps included, but these are s1mple
"74LS" or "HC" parts.
A star feature IS that no special or custom chips (1e PALs, ULAs, ASICs
etc) are used- and thus there are no secrets. The Z80A 1s the fastest
and best established of all the 8-bit microprocessors - possibly the
cheapest too!
Although no senal 1ntertace is Included, 1t IS easy for a Z80A to waggle
one bit up or down at the appropnate rate - the cost is a few pence
worth of code 1n the program: why buy hardware when sottware will do?
Applications already identified include: Magnetic Card reader, m1n1
pr<nter intertace, printer buffer. push button keypad, LCD alphanumenc
panel Interface, 40-zone security Interface for auto sending of security
alarms. code converter (eg IBM PC keyboard codes to regular ASCII),
real time clock (w1th plug 1n module), automatrc hortrcultural rrngatron
controller.
By disabling the on-board Z80A-CPU th1s card will plug rnto our lnterak
1 CP/M Plus disk-based development system, so if you don't fancy
hand-assemblrng Z80 machine code you don't have to 1
The idea is (if you are a manufacturer) you buy JUSt one development
system and then turn out the cheap SBC-1 systems by the hundred. If
you are really lazy we can write the program tor you and assemble the
SBC-1 cards so you can get on with manufactunng your product, leav1n
all your controi problems to us.
Greenbank - - - - - - For more details write or phone us:
Greenbank Electronics, Dept PED1 460 New Chester Road, Rock
Ferry, Birkenhead, Merseyside. L42 2AE.
Tel: 051-645 3391.
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January 1992 Practical Electronics 29
Product R e v i e w - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Combating The
Deathriders
Car burglar alarms are sadly becoming a necessity for most car owners. Kart Hastings takes
a look at a system available in kit form.
ith car thefts on the rise
and Death-riders on the
rage, the need for some
sort of car protection is becoming
vital.
A number of systems are
available, some simple, other
sophisticated. Most of those that
have to be fitted professionally are
expensive, leaving a lot of scope for
the DIY enthusiast.
One supplier of car alarm kits is
Electronize Design, which markets
a range of systems that can be
connected up in a variety of ways to
form a customised alarm system
suitable for both a particular car
and a particular cost.
W
Aspects Of Acar Alarm
The main function of a car alarm is
to stop anyone tampering with the
vehicle. At the first sign of trouble,
it sets off an alarm, either the horn,
a special siren, or some other sort of
deterrent. Hopefully, this will
attract attention to the car and make
a thief think twice before going any
further. Unfortunately, some
systems can quite easily be set off
accidentally. Sometimes this can
just be a gust of wind rocking the
car or it may be someone letting off
a firework nearby - another likely
situation is somebody with a
shopping trolley accidentally
knocking the car. Usually, alarms
set off in this way are faulty or they
are too sensitive and need adjusting
Intruder Sensors
When it comes to sensing an
intruder, a number of methods are
available. A simple method is to
hook into the cars electrical system
and detect any voltage changes.
30 Practical Electronics January 1992
The micro-pressure sensor.
These will occur when a door is
opened and the courtesy light
comes on - since the system is
battery powered the small dip in
voltage cause by the light activating
is easily detected. This type of
system is known as a "volt drop
detector".
An alternative, yet still relatively
simple, system uses a pressure
sensor. Most modern cars are fairly
air-tight and when a door is
opened, there will be a sharp, short,
drop in the internal air pressure.
Alternatively, if someone tries to
break a window, the pressure
sensor will react to the small
pressure change. The micropressure sensor is the system used
in the Electronize alarm covered in
this review; its main drawback is
when using it with older cars. These
tend not to be very airtight.
The more sophisticated alarm
systems use infra-red movement
sensors.
These
ignore
all
happenings outside the vehicle but
as soon as someone starts moving
around inside, the alarm is set off.
Which alarm is ideal for the car
depends on the type of car
available. The best thing is to
analyse how the sensing system
works and make sure that this will
work in your particular car. For
example, a micro-pressure alarm
will not be all that good in an open
top sports car, neither will the infrared detector. On the other hand,
cars that don't have courtesy lights
won't work with volt-drop systems.
In Control
Having fitted an alarm, there have
to be ways of activating and deactivating it. Again, a simple way is
possible. This connects into the
ignition circuit. When the key is off,
there is usually no power in the
car's system and the alarm is active.
Turning the key, turns on the
power and deactivates the alarm.
The problem with this system is
Car Alarm
that there must be a delay between
the alarm being set off and the siren
sounding to let the owner open the
door, put the keys in the ignition
and turn it on. This would give
plenty time for a thief to remove
something from the car and be
running away the owner then
returns to the car to find the alarm
sounding and goods gone.
The solution is to be able to
activate and deactivate the alarm
from outside the car. A small infrared transmitter which sends a
coded pulse to a receiver on the
dash of the car which, in turn,
signals to the alarm sensor unit to
turn off is the normal approach.
The components.
AReal System
The Electronize system looked at
here consists of a micro-pressure
sensor plus infra-red transmitter
and receiver. All three units came in
kit form, though they are available
ready made, and in this case the
only need is to be fitted.
The kits comprise almost
everything required to build the
items: components, circuit boards,
cases
and
even
solder.
Unfortunately, one of them had a
component missing - it is best to
check everything before starting
any construction. To complete the
construction, all that is needed are a
soldering iron, some small wire
clippers and a small cross head
screwdriver.
The Instructions
The instruction leaflets are adequate
for the construction but a little thin
on installation advice. All of the
components are listed along with
details on how to recognise them including the resistor colour codes
so beginners should have no
trouble. There are step by step
instructions on how to solder and
the order in which the board should
be put together. Altogether, the
construction
was
very
straightforward, all component
positions are on the board and a
picture of the assembled board is
supplied to show where everything
should go.
Fitting
Building the three items takes about
four hours in total, with time off for
cups of tea and diagram scrutiny.
The next step is to fit them to the
car. In the case of the micropressure sensor, the instructions try
to cover every eventuality and all
possible car wiring systems. It helps
to have some sort of meter or
voltage trace - a 12V bulb attached
to a crocodile clip at one and and a
sharp probe at the other perhaps.
Most cars hide their ignition switch
systems well out of harm's way and
dissecting parts of the steering
column or dashboard can take a bit
of thought - it is not always easy to
see how they were put together in
the first place. Tracing out the
correct wires is easy if a workshop
manual is handy, otherwise it is a
matter or tracing incoming and outgoing voltages to the switch. The
instructions don't really cover this
in a lot of detail but most amateur
electronic engineers should have
little trouble.
Once wired in and tested, the
sensor can be attached firmly to the
car and the infra-red remote control
set up. The in-car unit attaches to
the top of the dashboard in plain
view of the outside world. The
transmitter attaches to a key ring
and, although not extremely small,
is rounded in shape so it shouldn't
wear out too many pocket linings.
Before completely assembling
the remote control, the code
number must be set up. This is the
same in both the transmitter and
receiver. All that is required is to
make or leave open a set of links on
the printed circuit board. There are
59,046 possible combinations so the
chances of anyone else having the
same code are fairly remote. An
advantage
of
Electronize' s
marketing system is that extra key-
fob transmitters can be purchased
and set to the same code if more
than one person needs to use the
car.
In Use
Most of the time, the alarm seemed
to work - the car hasn't been
broken into recently - although a
little adjustment was needed to get
it to react well to the door opening.
The system was used to activate
the horn which was loud enough to
deter anybody. For those who want
to personalise things a little, or who
have quiet horns, a siren might be a
useful alternative. These can be a
little more distinctive making it
easier to distinguish at a distance
which car has had its alarm
triggered.
In the end, whether to go for a
ready made system or do-ityourself comes down to the
difference in price and whether you
want to get your hands dirty. In
either case, it has to be fitted to the
car so some sort of electronic
fiddling will be necessary.
•
Specifications
IR transmitter
Kit
£13.95
Assembled
£17.95
IR receiver
£21.35
£26.55
Micro-pressure trigger £10.95
£11.95
Available from Electronize Design
2 Hillside Road, Four Oaks,
Sutton Goldfield, 874 4DQ
Tel. 021 308 5877
January 1992 Practical Electronics 31
The Answerphone - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
How lt Works ...
The Answerphone
The number of telephone answering machines in use is growing daily Richard Topping
describes the basic operation of this ubiquitous device.
ne of the biggest areas of
growth
in
the
telecommunications market
after the privatisation of British
Telecom has probably been in the
area of answerphones.
The capabilities of telephone
answering machines varies quite a
lot. Usually, the more expensive
machines have better facilities and
"you pays yer money and takes yer
choice". The machine shown in the
drawing opposite offers functions
found on most machines and is a
good general example.
O
Operation
When the phone rings, the
answering machine allows three or
four rings to pass by before picking
up the line. This allows the user to
answer the phone if they are
nearby. If no-one picks up the
receiver then the machine plays its
outgoing message. In cases, this is
recorded by the user and resides at
the beginning of the incoming
message tape. An alternative it to
use a voice synthesiser to generate a
message - in the example machine,
this can be one of four messages
that can include the telephone
number of the answering machine
is on and a divert telephone
number.
After the message has gone out
to the caller, a number of beeps are
transmitted that tell the caller when
to start speaking. After the message
has been recorded, the answer
machines increments its incoming
call counter and displays the
number on a readout. Most systems
limit the length of a message so that
the tape does not become full too
quickly. In more sophisticated
machines, this can be set to a
32 Practical Electronics January 1992
predetermined period, in a basic
model, messages can be of any
length up to the end of the tape great for people who like to talk to
answerphones.
After a number of calls have
been recorded, playing them back is
simply a matter of pressing one
button. In some machines, the
synthesised voice is used in
conjunction with a built in clock to
record the time each message
arrived. Other machines just play
the messages to the end of the tape
and beep a couple of times. At this
point the user presses the replay
button again and the tape is
rewound and the message counter
set to zero.
A remote control facility allows
the user to play back any recorded
messages from a remote location.
By ringing up the answerphone and
using a touch-tone handset to play
a code number to the machine, a
number of commands can be
executed. These range from simply
playing back the calls to selecting
individual calls and recording new
outgoing messages.
The Future
Telephone answering machines are
becoming more and more
sophisticated and the latest are
completely solid state. A digital
sampling system records the
outgoing and incoming messages
into a RAM (RAndom Access
Memory) or to a computer disk.
Callers who have touch-tome
phones can ask for diversion
numbers or pass messages along.
As soon as computers are able to
understand general speech reliably,
answering machines should
become intelligent enough to
answer questions an take specific
messages for particular people. •
Battery stack
Sounder
Pushbutton
The remote control
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - H o w lt Works
Read write
cassette head
Connection to
telephone line
Power supply in from
mains transformer
Cassette drive motor
Cassette for incoming
message storage
8749 microcontroller
Speech
processor
chip
Loudspeaker tor listening to
incoming calls and messages
Volume control and
tamper proof switch
LED readout and replay
message button.
Artwork by Derek Gooding
January 1992 Practical Electronics 33
electronize
SUBSCRIBE TO
CAR ALARM KITS
MICRO-PRESSURE CAR ALARM
This new type of alarm is triggered by a unique pressure sensing system. As
any vehicle door is opened air is drawn out, causing a minute drop in air
pressure. A sensor detects this sudden pressure change and sets off the
alarm. An electronic filter, tuned to only 3Hz., and adjustable sensitivity avoid
false alarms whilst an arrangement of timers provide automatic operation.
-t. Operates on all doors and tallgate - no switches needed.
-:. Automatically armed 40 seconds after leaving vehicle.
-:. t 0 second entry delay with audible warning. ( 0.5 second available.)
1< Sounds horn or siren Intermittently for 30 seconds - then re-arms.
-:. Easy fitting - only 3 wires to connect • no holes to drill.
-:. Controlled by Ignition switch, hidden switch or coded remote control.
(The optional siren and coded remote control are supplied separately.)
MICRQ-PRESSURE ALARM
Parts kit £15.95 Assembled £22.35
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NEW
COOED IR REMOTE CONTROL
Our latest addition allows control of our alarms from outside the vehicle. Both
transmitter and receiver use a chip designed specially for car security systems
with 59,046 code combinations. You can even set your own code, with several
vehicles on the same code or several transmitters for one vehicle if required.
-:.High security, customer selected, 24 bit code.
-t. Key-ring transmitter with long life mlnature alkaline battery.
1< High power Infra-red emitter with range up to 5 metres.
-:.Low profile dash top receiver/decoder.
-:. Flashing high Intensity red L.E.D. warns off Intruders.
-t. Green L.E.D. shows alarm Is oft.
Use the coded transmitter and receiver with our Micro-Pressure or Volt Drop
alarm to form a coded remote controlled system.
CODE TRANSMITTER
Parts kit £13.95 Assembled £17.95
CODE RECEIVER
Parts kit £21.35 Assembled £26.55
Also available :VOLT DROP CAR ALARM
Parts kit £14.90 Assembled £20.95
120dB PIEZO SIREN
Assembled £11.95
MICRQ-PRESSURE TRIGGER Parts kit £10.95 Assembled £14.95
EXTENDED COl IGNITION
Parts kit £22.75 Assembled £28.45
All the above Include cable, connectors and clear easy to follow instructions.
All kits Include case, PCB, everything down to the last washer, even solder.
All prices now include post, packing and VAT on U.K. orders. Same prices
apply to all European countries. For delivery outside Europe please add £3.
Telephone orders accepted with VISA or ACCESS payment.
Order direct (please quote ref. PE1) or send for more details from :-
ELECTRON/ZE DESIGN
Tet. 021 308 5877
2 Hillside Road. Four Oaks. Sutton Coldfield. 874 400
COMPONENTS
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WE CAN SUPPLY A VAST RANGE OF SPARES !or many
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Return this coupon with your payment to PN Subs, Intra
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VfC6500.... . .
.. ............. £2.49
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34 Practical Electronics January 1992
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Above models....
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VC~8113B6r.l88r.l!l0 ............£5.67
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3VOOI06116122123124 .............£5.17
SERVICE MANUALS
BINATONE 0119771 ................................. £6.99
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22DC570/670-00 ... .......... £3.25
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FERGUSON 3V23129!30/32 Reel Idler ........ £3.55
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ZX8~02 (OL)...
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FM Omnidirectional Aerial ........................£18.24
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75154PC 4 x line driver ........... £1.85
64Kx 1 DRAM (120ns) .............£1.99
64K x 1 DRAM (150ns) ............£1.69
64Kx 4 DRAM (lOOns) ............ £2.99
SPECIAL OFFERS
SONY High Speed CPU (8MHz)- Same
as NEC V30 Direct replacement for
8086 CPU (Approx 25% faster) £9.99
While stocks last.
SED9420CAC ....
.. ......... £14.93
74LSOIJ TTLIC ................ 18p ea. (1+)
... 15pea.(5+)
TEXAS DRAM (TMS4532-15NL4)- For
Spectrum48K
...................... £1.72ea.(1+)
...................................£1.22ea. (5+)
MAIL ORDER ONLY. Please add 95p (UK) P&P but not VAT. All items
subject to availal:lility - Prices can change without notice.
Marapet (PEA)
1 Hornbeam Mews
Gloucester GL2 OUE
Competition
Competition
Win A Car Burglar Alarm
The Electronize keyring transmitter and dashtop receiver when used in conjunction with a
micro-pressure sensitive alarm offer high
security for your car. With a range of 59,046
possible codes, the system is unusual in
that the user can set the code used. This
had obvious advantages where two or
more people want to use the same car but
don't always want to swap keyrings.
The transmitter uses high power multiple
pulse infra-red system to give a range of
up to five metres. The low profile
receiver is designed to sit in full view
on top of the dash board. To warn off
intruders, a high intensity red LED
flashes continuously when the system
is armed and a green LED flashes
once the correct code switches off
the alarm.
To win a Micro-pressure alarm plus infra-red transmitter and dash-top receiver simply
answer the following questions:
The frequency of infra-red radiation ranaes from aporoximately:
a
10 12 F-izto 10 14 Hz
b
JOG'Hzto 10108Hz c
10 20 Hzto 1024 Hz
2
The maximum speed for cars not on the motorway in the UK is:
a
50mph
b
60mph
c
70mph
3
Most modern cars connect which side of the battery to earth:
a
positive
b
negative
c
neutral
~·························································································································································································································································
Please tick the appropriate boxes:
1
a
0
2
a
0
3
b
0
c
0
c
0
c
0
a
c
c
0
0
0
Fill in your name and address
Name ......................................................................... .
Md~s ....................................................................... .
Town .......................................................................... .
Coun~·········· ..
....................................... .
Post Code ................................................................... .
I subscribe to PEO
Send your entry to:
PE Alarm Competition, Intra Press, Intra House, 193 Uxbridge Road, London W12 9RA
The competition ends on 1 Feb 1992. The first five entries pulled out of the hat will receive prizes. The judge's
decision is final and no correspondence will be entered into.
January 1992 Practical Electronics 35
Software R e v i e w - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Looking At
11 Linearly
A/an Smith loads up Number One Systems' new linear circuit analysis program and finds a
new way of designing circuits.
N
umber
One Systems,
famous for its PCB and
digital circuit CAD systems
has extended its range to include a
sophisticated analogue circuit
simulator, Analyser 3, an upgrade
of its existing Analyser 1 and 2
systems.
All electronic circuits can be
treated as black boxes with input
and output connections. Some form
of signal is fed into the system
which performs an operation
producing an output signal. For
digital circuits, this is more or less
all there is to it. However, analogue
circuits have other characteristics
such as input and output
impedance and phase change as
well as the change in gain with
amplitude.
Supplied on a 3.5in or 5.25in
disk, installing Analyser 3 could
have been made easier. Although it
is acceptable to assume some
knowledge of the operation of a PC
from someone who is going to
gain/phase plot of an amplifier network.
analyse a circuit, it isn't difficult to
write an install program or batch
file. As it stands, the user has to
create a directory on the hard disk
and copy all of the necessary files
across before getting started.
Gain/phase plot of a lowpass filter.
36 Practical Electronics January 1992
On starting the system up, the
user is presented with a blank
graph and a selection of menus. The
system runs under a Graphical User
Interface (GUI) - windows and
mouse pointer - but could do with
a little tweaking to make it a bit
more intuitive. As it stands, the
manual is needed to figure out
what menu does what and what to
do next.
All circuits are held in a network
list format which defines the
components as modules. Each has
an input and an output and can be
linked up with other components to
form circuits. Setting this up is
rather an involved affair and the
circuit must be drawn up and
labelled before it can be entered.
The user interface is purely text
based and it would have been nice
to be able to design circuits with a
graphical CAD system. However,
the netlist file format is given so it
should be possible to interface it to
CAD systems such as Easy PC.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - S o f t w a r e Review
Built in primitives
Resistance with parasitic capacitance
Pure resistor
Capacitor
lnductor
Bipolar transistor
Field effect transistor
Operational amplifier
Transformer
Tapped transformer
Transmission line
Strip line (Micro Strip)
Device library
ZTX239,ZTX313,ZTX450, BF240,
2N918. 2N5179 bipolar transistors
BF245A, BF256A FETs
LF351, LF356, LF357, LM202,
LM741, LM748, TL080 op-amps
Gain/phase plot of notch filter.
Once deigned, components and
modules can be added to libraries
and combined to make more
complex modules.
There are four basic plots that
can be made for a circuit, gain,
input and output impedences and
group delay. All of these are plotted
against the frequency of the input
signal which can range from 0.001
to 999GHz. An analysis consists of
testing the circuit at a range of
frequencies in a specified number of
steps. It can be viewed in graphical
form or as a table of results, either
of which can be printed out. Some
example displays are shown in the
Figs. On the machine used for the
test, an admittedly fast 386 PC
running at 33MHz, the analyses ran
very quickly. On a 286 they might
take a little longer
The manual takes the user
through the operation of the system
in the form of a "Grand Tour",
introducing each new section in
turn. The drawback with this
method is that new users can't play
around with the system and look
up the relevant bits in the manual
when necessary. More of a
reference would have been nice.
Analyser 3 provides a relatively
easy to use way of analysing
circuits before committing solder to
copper. It could be used by
beginners to understand how to
analogue circuits work although
extra tuition in the form of a circuit
analysis book would also be
necessary.
At £195 plus VAT, it is probably
a good buy for anyone interested in
designing or analysing complex
analogue circuitry.
•
Input impedance for notch filter.
Gain/phase table for notch filter.
January 1992 Practical Electronics 37
Hardware Review
Van Gogh Meets The
Video Recorder
Easy computer graphics for the masses? Laura Esterman connects up the Vtech Video
Painter to her VCR and finds out.
esigned for the creative
couch potato, this product
consists of a graphics tablet
which hooks up to a video tape
player and allows the user to draw
pictures onto his or her television
screen. With Video Painter you can
draw lines and shapes, colour them
in, paste ready-made graphics and
do limited animation.
D
Main Features
There are twelve colours to work
with and you can draw over one of
the pre-set backdrops or create your
own. Using a pen-shaped stylus,
you select one of the drawing tools,
which are divided into eight
different options: drawing, fills,
erasing, expand I magnify, copy,
move, pre-drawn graphics and
animation. Many of these options
are subdivided to include choice of
line thickness, fill pattern, lettering
text and a zoom feature. Most of the
commands reacted in the same way
as those on a computer graphics
package, however I was frustrated
by the undo feature; this erased not
only the last command, but every
one in the option last selected. The
animation, too, is restricted to
simple pre-set movements of the
graphics provided.
Hooking Up
Connecting the unit to my video
recorder was slightly difficult. It
isn't that it's complicated -you
merely have to plug the lead into
your VCR's "video in" socket- it's
just that with the variety of
connectors made by different video
manufacturers, you may need to
obtain an adaptor to fit your
particular model.
38 Practical Electronics January 1992
Vtech's Video Painter, computer graphics for all.
Video Artistry
The system reacts best to
m ani pula tions of the pre-set
designs, as drawing freehand is
often compromised by the poor
resolution on the drawing tablet.
Unfortunately, there is no way to
import images into the system;
imagine the possibilities of being
able to personalise a video tape on
your screen ..The system also comes
equipped with a game, but this is so
simple I quickly moved onto the
main object of creating pictures. It is
possible to save your creations by
recording them on your VCR,
however there is no way, obviously,
to print them out. I also found some
of the colours showed up better on
the screen than others did, and the
cursor seemed to jump a bit when I
had finished drawing a line or took
the stylus off the drawing pad. The
entire picture jumped and went
erratic when the colour white was
selected - I'm not sure if this was
my VCR or the Video Painter, but if
the fault was on my system, it
reacted skittishly with it. Still,
despite the drawbacks, it was fun to
let loose my artistic tendencies and
interact with the television screen
rather than just stare at it.
•
Specs Box
Vtech Video Painter
Price £79.99
Available from all good toy
shops around the UK.
Vtech stockists can place
orders directly with the
company.
Contact Vtech on
0235 555545
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - M a n u a l Review
How To Repair
Electronic Equipment
Bruce Godstone opens the pages of the Electronics Repair Manual to find a huge amount of
information on a wide range of subjects.
M
ost pieces o.f electronic
equipment have labels on
the bottom that say "no
user serviceable parts inside". In
reality, this is rarely true and most
things can be repaired with a little
knowledge and the right approach.
The W eka Electronics Repair
Manual attempts to provide the
information and experience for the
would-be repair technician
enabling them to tackle just about
anything. Some knowledge of
electronics is assumed so beginners
will need to learn some of the basics
before they can get started.
The manual itself is a huge tome
that consists of 13 chapters covering
a variety of topics all printed in a
large friendly type face. It is aimed
mainly at the amateur, although a
number of comments from the
authors do give the impression that
a professional repair workshop
could be set up using the manual as
a basis. Unfortunately, life is rarely
this simple and a good grounding
in electronics is essential as well.
After the contents and index, the
first part of the book consists of a
sort of "all you wanted to know
about electronics and never dared
ask".
Following
a
short
introduction and a brief section on
safety and first aid for electric
shock, a wide selection of
abbreviations, symbols and
quantities are covered. The next
section looks at electronic
components, in detail. Because
these are the main cause of trouble
in electronic equipment, this section
has been made quite exhaustive. A
large amount of information is
given
on
manufacturers
specifications and codings - useful
for identifying a replacement of a
broken part.
After looking at what tools will
Electronics
Repair Manua,J
be needed, the manual gets onto the
nitty-gritty of fault finding
techniques. Oddly this is a
relatively short chapter - this could
be because there really isn't all that
much to say on the subject. Finding
a fault is a matter of the correct
approach. The first thing is to
understand what the equipment
should do, then find out what it
doesn't do anymore and what
happened to make it faulty. The
next step is a matter of tracking the
fault down.
The final eight chapters examine
specific items of equipment and
cover them in varying amounts of
detail. There is a lot of stuff about
HiFi amps, radio receivers and
home computers, but rather less on
video recorders, compact disc
players and camcorders. What
makes this section of the manual
interesting is not that it helps much
with repairing equipment directly,
but that it gives a good description
of how the equipment and its
subsystems operate (or would if
they didn't need repairing).
One of the main selling points of
the manual is that regular updates
on equipment and technology are
supplied. This should mean that the
rather thin sections on the more
modern equipment will fill up as
more data and experience becomes
available. In the end, this is what
should make the manual a valuable
•
reference tool.
Electronics Repair Manual
WEKA Publishing
Freepost
The Forum
74/80 Campden Street
London NW1 1YW
Tel. 071 388 8400
Price £44.95+£5.50 p&p
January 1992 Practical Electronics 39
Graphics C a r d s - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Practical Technology...
PC Graphics Cards
High quality graphics are a must for the latest IBM PC compatible computers. Eric Dunstan
examines the current standard, VGA and its successor, SVGA.
ne of the oddities about
modern
computers,
especially
IBM
PC
compatibles, is that they are sold
without monitors. Some dealers
may offer one type of display,
others may offer something else
entirely. The main point of all this is
that a basic PC, whether XT or AT
or even 386, is an expandable
system and the monitor is an addon.
O
Slotting In
In the back of the PC are a number
of expansion slots - usually six.
One of these is set aside for the
printer port, another for the serial
port and one perhaps for a hard
disk. One of the spare ones must
also be set aside for the monitor or
display card. These come in a wide
variety of types and capabilities
from the simple MDA or
monochrome display adaptor, to
the SVGA, or super video graphics
array.
Many machines come with
Hercules boards fitted, as this is a
cheap system that allows
monochrome text and graphics to
be displayed on a relatively low
cost and low quality monitor.
Unfortunately, most of the latest
software uses high resolution
graphics and colour that requires at
least a VGA card. This means that
most cheap PCs bought over the
past few years will have to be
upgraded with a new card and
monitor - with some software, the
old card and monitor can be used at
the same time as the new one; some
CAD packages allow text to be
displayed on the older display
adaptor.
Upgrading is not all that
40 Practical Electronics January 1992
difficult as IBM style systems are
made to have cards added. It is
simply matter of opening the
machine, slotting in the card,
closing up and switching on. The
operating system and software take
care of any details and the change
in quality is dramatic.
What is VGA
The basic VGA card supports
medium resolution graphics at
resolutions up to 800x600 pixels.
Unfortunately, it can only display
16 colours at once in this mode and
to get 256, a lower resolution of
320x200 pixels must be used. The
hardware that achieves this is not
particularly complicated and most
modern designs have virtually all
of their functions integrated onto a
single chip. The main external
component is the memory required
to hold the graphics data. Unlike
the display systems used on
machines like the Commodore
Amiga, Atari ST and Acorn
Archimedes, the video memory is
not strictly part of the main
computer memory. Instead it is
supplied separately on the video
card.
Three types of video monitors
can be driven from VGA, analogue,
digital and monochrome. The first
allows virtually any colour to be
displayed by placing the correct
mix of voltages on its red, green
and blue input lines. Since the
voltages on the lines can be
continuously various between 0
and 1 V and infinite number of
colours can be displayed. In
practice, this is limited by the
graphics card resolution. The video
data held in the graphics card
memory is pushed through a DAC
(Digital to Analogue Convertor) to
drive the colour lines. The number
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - P r a c t i c a l Technology
a horizontal pulse that tells the
monitor when to start a new line of
the image, and the vertical pulse,
which starts a new scan - the image
is a raster scan composed of
horizontal lines scanned from left to
right and stacked vertically. The
frequency of the synchronisation
signals has two main effects. The
higher this is, the better the
resolution of the image since more
dots or pixels can be shown. Also,
increasing the refresh rate of the
screen reduces the amount of flicker
seen by the eye, making it much
easier to work with.
All of the above comments apply
mainly to VGA. However, a new
standard that has more or less taken
over in the past year or so is super
VGA (SVGA) or enhanced VGA
(EVGA). This increases the
maximum screen resolution to
1023x768 and the number of colours
displayed at the same time to 256 the difference in quality can be seen
in Fig. 1. A number of
configurations are possible with
different amounts of on-card
memory. At 256k the system
performs in much the same way as
a standard VGA. Moving up to
512k increases the screen resolution
to 1024x768 but only 16 colours. At
1M the full 1024x768 pixel
resolution with 256 colours is
possible.
The Next Step
Fig. 1. The top image is from an SVGA 1024x768 256 colour screen. The bottom is the
320x200 by 256 colours of VGA.
of possible colours displayed is
determined by the number of bits
the DAC can convert - 4-bits gives
16 colours and 8-bits 256 colours.
A digital monitor also has red,
green and blue inputs but each has
only two states, on or off. Used on
their own this would allow only
eight colours to be displayed.
However, associated with each is an
intensity control so the number of
colours is squared to 64. The
limitation on colours is imposed by
the monitor and not the display
card.
Monochrome systems are
usually digital in form and have
two input pins, one for the video
information and one for intensity.
The first defines whether a
particular should be on or off and
the second, the brightness of the
pixel. This sort of system greatly
limits the output of a VGA card and
would not normally be used. An
alternative form of monochrome is
the grey scales possible with a
single colour analogue monitor. In
this situation, the red, green and
blue outputs of the card are
combined to form a single intensity
signal which allows a number of
shades of grey to be viewed.
The final point to be made about
the monitor is the synchronisation.
This normally comes in the form of
There are a number of systems that
are better than SVGA. Some
workstations offer 2034x1024 pixels
and even 1280x1024. However,
these are quite a bit more expensive
and require fast memory and
sophisticated monitors. They are
mainly used for computer aided
design where good screen
resolution is a requirement.
•
Specs Box
The video cards used in this feature
were supplied by Southern
Peripherals.
For more information contact
Southern Peripherals
17 c London Street
Basingstoke
Hampshire
RG21 1NT
Tel. 0256 819221
January 1992 Practical Electronics 41
VERO EASI WIRE PROTOTYPING SYSTEM Ideal for design·
mg proJects on etc. Complete with tools, w1re and reusable board
experiments or as a spare for a microwave oven etc 250v AC 1nput
Our pnce £6 00 ref 6P33R
MICROWAVE TURNTABLE MOTORS. Ideal for wondow displays etc £5 DO ref 5P165R
STC SWITCHED MODE POWER SUPPLY220v or 11 Ov rnput
g1ving Sv at 2A, +24v at 0.25A, +12v at 0.15A and +90v at 0.4A £6 00
ref6P59R
HIGH RESOLUTION 12'" AMBER MONITOA12v 1.5A Hercu·
les compatrble (TTL input) new and cased £22.00 ref 22P2R
VGA PAPER WHITE MONO monitors new and cased 240v
AC. £59.00 ref 59P4R
25 WATT STEREO AMPLIFIERc STK043. W1th the add1t1on of
£10.00 ref 1OP93R
MICROWAVE CONTROL PANEL.Ma~ns operated, w•th touch
a handful of components you can build a 25 watt amplifier . .C4 00 ref
4P69R (Circuit d1a included)
switches. Complete with 4 digit display, digital clock, and 2 relay
outputs one for power and one for pulsed power (programmable)
!deal for all sorts of precision timer applications etc. £6 00 ref 6P1 BR
LINEAR POWER SUPPLY Brand new 220v ~nput +5 at 3A, +12
al1A, -12 all A Short corcuit protected £12 00 ref 12P21R
MINI RADIO MODULE Only 2" square wrth ferrite aenal and tuner
Superhel Req's PP3 batlery. £1 00 ref BD716R
BARGAIN NICADS AAA SIZE 200MAH 1.2V PACK OF 10
£4.00 REF 4P92R, PACK OF 100 £30.00 REF 30P16R
FRESNEL MAGNIFYING LENS 83 x 52mm £1 oo ref BD827R
ALARM TRANSMITTERS. No data avalrable but nrcely made
complex transmrtters 9v operation £4.00 each ref 4P81 R
UNIVERSAL BATTERY CHARGER. Takes AA's, C's. D's and
AMSTRAD PORTABLE PC'S FROM £149 (PPC1512SD).
£179
(PPC1512DD).
£179
(PPC1640SD).
£209
(PPC1640DD). MODEMS £30 EXTRA.NO MANUALS OR
PSU.
HIGH POWER CAR SPEAKERS. Stereo pa~r output 1oow each
4ohm Impedance and cons1sti ng of 6 1/2" woofer 2" mid range and
1"tweeter. Ideal to work w1ththe amphf1er descnbed above Pnce per
pa1r £30 00 Order ref 30P7R
2KV 500 WATT TRANSFORMERS Suitable for hrgh voltage
FIBRE OPTIC CABLE. Stranded optical frbres sheathed in black
PVC. Five metre length £7.00 re! 7P29R
12V SOLAR CELL.200mA oulpulrdeal for tnckle ~")
chargtng etc. 300 mm square. Our pnce £15 00 ref - - --
15P42R
PASSIVE INFRA-RED MOTION SENSOR.
Complete with dayhght sensor, adjustable lights
on timer (8 secs -15 mins), 50' range wtth a 90
deg coverage. Manual overide facility Complete with wall brackets. bulb holdersetc Brand
PP3 meads Holds up to 5 battenes at once New and cased, mams
operated £6.00 ref 6P36R
ASTEC SWITCHED MODE POWER SUPPL YSOmm x 165mm
(PCB size) grves +5 at 3.75A, +12 al1.5A, -12 at 0 4A Brand new
£12.00 ref 12P39R
VENTILATED CASE FOR ABOVE PSLW•th IEC frltered socket
new and guaranteed £25 00 ref 25P24R
Pack of two PAR38 bulbs for above unrt £12.00
ref 12P43R
VIDEO SENDER UNIT Transmit both audro and video signals
and power switch. £5.00 ref 5P190R
IN CAR POWER SUPPLY. Plugs mto c1gar socket and gtves
3,4,5,6,7 5,9, and 12v outputs at SOOmA. Complete with un1versal
vtd~o camera, video recorder or computer to any
standard TV set WJthm a 100' range! (tune TV to a spare channel).
12v DC op. £15.00 ref 15P39R SUitable mams adaptor £5.00 ref
from either a
spider plug. £5 00 ref 5P167R
RESISTOR PACK. 10 x 50 values (500 resistors) all1 14 watt 2%
metal film £500 ref 5P170R
CAPACITOR PACK 1.100 assorted non electrolytic capacitors
£2 00 ref 2P286R.
CAPACITOR PACK 2. 40 assorted electrolytic capacitors £2 00
ref 2P287R.
QUICK CUPPA? 12v immersion healer wrth lead and c•gar lighter
plug £3 OD re! 3P92R.
LED PACK .50 red leds, 50 green lads and 50 yellow leds all Smm
£8.00 re! 8P52R
FERRARI TESTAROSSA.A true 2 channel radro controlled car
with forward, reverse, 2 gears plus turbo. Workmg headlights.
5P191R
FM TRANSMITTER housed in a standard w~rking 13A adapter
(bug IS mains dnven) £26.00 ref 26P2R
MINATURE RADIO TRANSCEIVERS A pair of
walkie talkies with a range of up to 2 kilometres. Units
measure 22x52x155mm. Complete with cases. £30 00
ref 30P12R
FM CORDLESS MICROPHONE.Small hand held unrt
with a 500' range! 2 transmit power levels reqs PP3 battery Tun-
eable to any FM receiver Our price £15 ref 15P42AR
12 BAND COMMUNICATIONS RECEIVER.g short ,
bands, FM, AM and LW DXIIocal switch, tuning 'eye' mains EJ~
or battery. Complete w1th shoulder strap and matns lead
NOW ONLY £19.001! REF 19P14R.
WHISPER 2000 LISTENING AID.Enables you to hear sounds
that would otherw1se be maudible! Complete Wtth headphones
E!!:tt]
£22.00 ref 22P6R
WASHING MACHINE PUMP.Ma1ns operated new pump. Not self
priming £5.00 rei 5P18R
IBM PRINTER li;AD. {025 to centronics plug) 2 metre parallel
Cased. £5.00 ref 5P179R
CAR STEREO AND FM RADIOJ...ow cost stereo system g1vmg
5 watts per channel Signal to noise rat1o better than 45db, wow and
flutter less than 35%, Neg earth £25.00 ref 25P2~ R
LOW COST WALIKIE TALKIES.Pair of battery oper-
I I
ated units with a range of about 200' Our price £8 00 a ~ ~--_
pair ref 8P50R
1 CHANNEL GRAPHIC EOUAUZEF\>Ius a so watt ~:
::,.1
power amp I 20-21KHZ 4-SR 12-14v DC negative earth Cased £25
ref 25P14R
NICAD BATTERIES. Brand new lop quality 4 x AA's £4.00 ref
4P44R 2 x C's £4.00 re! 4P73R, 4 x D's £9.00 ref 9P12R, 1 x PP3
£6 00 ref GP 35R
TOWERS INTERNATIONAL TRANSISTOR SELECTOR
GUIDE. The ultimate equivalents book. Latest edifion £20.00 ref
20P32R.
CABLE TIES.142mm x 3.2mm white nylon pack of 100£3 00 ref
3P1 04R. Bumper pack of 1 ,000 t1es £14.00 ref 14P6R
GEIGER COUNTER KIT.Complete with tube, PCB and all components to build a battery operated geiger counter. £39.00 ref 39P1R
FM BUG KIT.New destgn with PCB embedd&d coil Transmits to
any FM radio 9v battery req'd £5 00 ref SP158R
ELECTRONIC SPEED CONTROL Klllor cs motor. PCB and all
SOLAR POWERED NICAD CHARGER.Charges 4
AA nicads in 8 hours Brand new and cased £6.00 ref
6P3R
·N·
,..;.·,'
SV 1 OAH LEAD ACIDsealed battery by yuasha ex equipment but
in &xcellent condition now only 2 for £10.00 ref ~OP95R
Superbly made fully cased (metal) g1vmg 12v at2Aplus a 6V supply
Fused and short ci rcUJtprotected For sale at less than the cost of the
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SPEAKER WIRE
Brown twm core insulated cable 100 feet for £2 00 REF 2P79R
MAINS FANS
Brand new 5" x 3" complete With mounting plate qu1te powerfu11 and
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DISC DRIVES
Customer returned units mixed capac1t1es (up to 1 44M} We have not
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HEX KEYBOARDS
Brand new units approx 5" x 3" only £1.00 each ref CD42R
PROJECT BOX
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SCART TO SCART LEADS
Bargarn pnce leads al2 for £3 00 ref 3P147R
SCART TO D TYPE LEADS
Standard Scart on one end H1 denSity D type on the other. Pack of
ten leads only £7.00 ref 7P2R
OZONE FRIENDLY LATEX
250mlbottle of liqu1d rubber sets1n 2 hours. !deal for mount1ng PCB's
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Standard Atari compatible hand controller (same as joysticks} our
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VIEWDATA SYSTEMS
Brand new units made by TANOATA complete> w1th i 200175 built m
modem infra red remote controlled qwerty keyboard BT appproved
Preste! compatible. Centron1cspnnter port RGB colour and compos~
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31NCH DISCS
Ideal for Amstrad PCW and Spectrum +3 machines pack of 10 dtscs
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and 2 pin American output socket (suitable for resistive loads only)
our pnce £2 00 ref 2P381 R
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ments etc £2 00 ref 2P383R
£5 00 ref 5P207R
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PIR LIGHT SWITCH Replaces a standard
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NEW SOLAR ENERGY KIT
max Not suitable forflourescenls. £14 00 ref 14P10R
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WINDUP SOLAR POWERED RADIO! FM/AM radio takes re-
Contains 8 solar cells. motor, tools, fan
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ADJUSTABLE SPEAKER BRACKETS Ideal for mountong
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Small hand held cassette recorders that only operate when there JS
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day and just record anyth1ngthatwassaid Priceis£20 00 ref20P3R
value at £1 00 ref C040R
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ACORN DATA RECORDER ALF503 Made for BBC computer
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port Our price £4 00 ref 4P1 01 R
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ALARM PIR SENSORS Standard 12v alarm type sensor will inter-
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COMPOSITE VIDEO KITS. These convert composrle vrdeo into
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SINCLAIR CS MOTORS 12v 29A (full load) 3300 IPm 6"x4" 114"
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As above bul with fitted 4 to 1 i nli ne reduction box (BOO!pm) and
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COPPER CLAD STRIP BOARD17"x 4"of .1" prtch "vero"board
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50 METRES OF MAINS CABLE £3.00 2 core black precut rn
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1992 CATALOGUE AVAILABLE NOW
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COPY.
input plug drsc drive and mother board fly leads Our price is £5
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286 AT PC
286 MOTHER BOARD WITH 640K RAM FULL SIZE METAL
CASE, TECHNICAL MANUAL, KEYBOARD AND POWER SUP·
LY £139 REF 139P1 (no ilo cards or drrves included)
35MM CAMERAS Customer returned unrts wrth built on flash and
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STEAM ENGINE Standard Mamod 1332
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~.._.._,._
TALKING CLOCK
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Clock wil! announce the t1me at
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HANDHELD TONE DIALLERS
Small units that are designed to hold over the mouth piece of a
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COMMODORE 64 MICRODRIVE SYSTEM
Complete cased brand new dnves with d1sc and software 10 t1mes
faster than tape machines works with any Commodore 64 setup
The orginal pnce for these was £49 00 but we can offer them to you
at only C25 DO' Ref 25P1R
USED SCART PLUGS
12 TO 220V INVERTER KIT As supplied it will handle up to about
Packof 10 plugs suitable for making up leads only £5 00 ref 5P209R
15wat 220v but 'Nith a largertransformerit will handle 80 watts. Baste
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Same style as our4 x AA charger but holds2C cells Fully cased with
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Review
PE Goes To
The Theatre
The Hunting Of The Snark is a multimedia extravaganza. To see if all that technology spells
good entertainment we sent Fiona Gammie to see it.
t is not every day you are invited
to the "ultimate high-tech multimedia fantasy adventure" and I
thought I had better go along and
find out what it was all about. The
Hunting of the Snark is the
brainchild of Mike "Remember
you're a Womble" Batt and is no
ordinary West End musical.
A vast array of 144 projectors
(no I didn't count) create wonderful
moving images from seagulls and
waves to flowers that grow so
incredibly high. They are controlled
by six computers and this means
quite complex animation sequences
can be run from the roof to the
stalls throughout the performance.
As the credits rolled, I was not
sure if I had gone into the Odeon
down the road but then the front
row of the orchestra started
dancing and I guessed I was in the
right place.
The story line is a touch
tenuous. A motley crew take to the
high seas in search of a snark, a
weird creature that found fame in
Lewis Carroll' s nonsense poems.
I
The action takes place on various
moving levels against a backdrop
created by the high tech animation.
When it comes down to it, you
can use technology to create the
slickest production in town, but
does it make a good show? Perhaps
a psychedelic experience would be
more apt. Nevertheless I was
sufficiently inspired to dust off my
lacrosse stick this weekend and go
snark hunting ...
Fiona Gammie
The Hunting Of The Snark is on at the
Prince Edward Theatre, Old Compton
Street, London Wl. Call 071 836 3464
for booking details.
no further. Starting off with diode
circuits, there are more of these
than you might think, it moves on
to cover the basic principles of
transistors, amplifiers, waveform
generators and FETs.
Apart from the more everyday
circuits, this collection includes
some quite obscure ones such as
current mirrors and lie detectors.
The FET section of the book
looks more at the construction and
characteristics of the various types
available than actual circuits. There
are a few of these, lamp controllers
and touch switches. However,
many others are simply versions of
the transistor circuits shown
previously.
The book is aimed at people
who know something about
electronics and are able to build a
project from the circuit diagram,
beginners should start with
something simpler first.
•
Kenn Garroch
Back To The Books
Diode, Transistor and FET circuits
Manual
RMMarston
Price £12.95
Publisher Newnes
ISBN 0-7506-0228-7
If you want to know anything
about circuits that involve diodes,
transistors or FETs, you need look
January 1992 Practical Electronics 43
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~~~.?~~ar EB~~Pa:deg~;~~~ ~~~Je; c~u~1~d ~t~
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·· ••
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~~~~~~~~)~~~~r ~a~~C.B3~1!~~~ t~~os;t~n~~~:.
Designed for boiler 1Qn1t1on. Dozens of uses m
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26 65
~~~gE~~~2CD;EPd&~ &m~A~ .
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THIS IS JUST A SAMPLE- MANY OTHERS AVAILABLE
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Thurtby PSU PL320MD 30V 2A Quad Mod Digital ...... £200
Thom Bench PSU 0-40V G-30V Metered ....................... £300
Famell PSU H30!100G-30V G-100A ...
................. £750
Gould K40 LogiC Analyser 32 Channel. .
. ........£500
Telequipment CT71 CuNe TRacer
£250
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Philips PM6622 UniVersal Timer/Counter. Sot-AHz 9 Dgrt:
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Feedback FG600 Fun Gen. Sine/Sq!Tri 0.01 Hz-100KHz£55
Avo Valve Charcteristic Meter MKIV
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£450
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leader LMV186a Two Ch MV Meter 5Hz-500KHz.
1mV-300V ...
...................... £100
Kikusui AVM23 AC Voltmeter Dual Ch 1OHz-500KHz
3Q!41V-100V ...
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Sdartron 7045 Mu~meter 4.5 D1grt 30 Ranges. AutoJMan£95
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Gould OS300 20MHz Dual Trace 2mV/cm Small. lightweight
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Far better than some of the New Rubbish available!
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Crouzet 1
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pnce of a made-up unit k1t of pans less case mcludes me VAT & p&p £18.86.
12m 8 watt 2537 Angst Tube BaUast umt. pa1r of b1-pm
RHEOSTAT
leads. neon md1cator. on/off SWitch. safety microswitch and SOW 2 ohm 5 amp ceramic power rheostat pnce me
c1rcU1t £14.00+ £2.00 p&p
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Approx 16 JOules AdJUStable speed £4B.OO+ £2 00 p&p
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Teklron1x 2215 Dual Trace 60MHz Delay Sweep
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Tektromx 475 Dual Trace 200MHz Delay Sweep...
.. ....... £550
Tektrontx 465 Dual Trace 100MHz Delay Sweep.....
. .... £450
Schlumberger-Enertec 5218 Three Trace 200MHz Delay
Sweep
£550
Schlumberger-Enertec 5220 Dual Trace 1OOMHz Delay
Racai/Dana W1deband Level Meter 5002
Raca!A)ana Synthesized Sig Gen 10KHz-1 04MHz
Racai/Dana (AIM) LCR Oatabndge 9341
Wayne Kerr LCR Meter 4210
Wayne Kerr Automabc Component Bndge 8605..
Wayne Kerr Umversal RF Bridge 8602 ... :...
Wayne KerrComponent Tester 8424....
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neon or argon tubes etc Pnce less case
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Tektronix2445 Four Trace 150MHz Dual TB .........................£1200
Tektromx 485 Dual Trace 350MHz ...
.. .£1 000
Tektrom 2225 Dual Trace 50MHz Delay Sweep ................£600
Sweep
£400
Phrlips PM3217 Dual Trace 50MHz Delay Sweep ................ £400
Hrtachi V650F Dual Trace liOMKz Delay Sweep.
. £450
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Bruel & Kjaer Sound Level Meter
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44 Practical Electronics January 1992
D.V.M. Module Brand new full spec 3 1/2 Dig1t Voltmeter Module Large 0 56 LED D1splay, FSR +/- 200mV
Supply requ1red from 8 to 18V Si?e Scm x 5 5cm Circuit SUP!=Iied for mult1meter
£18 75
MEGAPROM Programs 2764/128/256/5120/010/020 (1 Meg/2 Meg 28/32 p1n) HMOS. CMOS, NMOS type
EPROMs Attractively cased and supplied w1th power unit Powerful operat1ng software Includes full screen
Ed1tor, extens1ve f1le handling (lntel Hex, Binary, ASCII
Byte/block or complete ROM
program/VerifiCatiOn/editing. Fast algorithm 1K x 8 81! per
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Auto Tracks V6 PCB Designer Produce
PC/XT/AT or Amstrad 1640. Single/Double
Various line/pad s1zes L1brary & User defined
Text Too many fea:ures to l1st here. SAE for
graph1cs, Epson pnnler, Mouse opt1onal
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Telephone: 0532 537 507
New Technologies
The Future 01
Semiconductors
Atom sized switches, superconducting logic and ultra-fast logic all feature in tan Poole 's
analysis of the latest developments in semiconductors.
uper-conducting integrated
circuits are set to revolutionise
the electronics industry in the
next few years. This has been
indicated by the fact that Hypress
Inc in Elmsford New York have just
fabricated a 4-bit shift register
which has been tested up to 9.6
GHz and only dissipated 40f1Watts.
In fact the upper frequency limit
was not that of the chip, but the test
system, and it is expected that it
will operate at frequencies
significantly higher than this.
Furthermore, computer simulations
have
indicated
that
these
techniques should be capable of
operation up to 25 GHz or more.
The superconducting logic is
based on the Josephson Junction. It
uses a relatively wide geometry of
around 3.0flm in contrast to
Gallium Arsenide (GaAs) devices
for the same frequency which
require O.Sflm. The structure is
fabricated using a ten layer thin
film deposition process. A
Josoephson tunnel junction uses a
lOA barrier in a vertically stacked
structure.
The fabrication process uses a
very low temperature of 150°C.
This means that it will work with
almost any flat substrate. In turn
this allows for it to be combined
with standard Silicon (Si) and GaAs
technologies for interfacing to other
circuits.
In view of the difficulties and
cost of maintaining the superconducting temperatures, it is not
intended that these ICs would be
used as stand alone chips. Instead
the idea is that these first chips are
used only as proving grounds for
much larger systems. Eventually it
is hoped that super-conducting
logic systems will be combined
S
· The Josephson Effect was
forecast by Brian Josephson at
Cambridge University in 1962
and verified in 1963 at Belf
Labs.
When
two
-....::.~~~-.;:__~.;:__..:.----.--__;_----superconductors are separated
Superconductor
by a very thin layer of insulating
material - 10A or so in
thickness (top-left) - a current
flows from one to the other
when the voltage between them
is zero. This is shown by the
- - - - - - - - - - P ' - - - - - - - - - g r a p h (bottom-left). Below or
10Athininsulating layer
above the critical current,
normal
single
electron
tunnelling ensures the currents
either side of the zero point.
The jump from positive to
negative and vice versa as the
voltage hits zero is due to pairs
of electrons tunnelling through
the insulator. The tunnelling is
possible because quantum
Critical current
mechanics defines the position
of an electron as a probability
and for thin insulating layers,
this can straddle the layer
allowing the electron to be
either side. The change in
conduction at the critical
current allows the Josephson
effect to be used as a high
speed switch and hence in logic
gates.
with a suitable interface so that they
can communicate with standard
circuitry.
Initially it is hoped that it will be
possible to fabricate a number of
items including correlators running
at 10 GHz for military radar
systems. Other ideas include logic
which can be included into very
high speed processors and ADCs
(Analogue to Digital Convertors).
These items would find uses in
digital signal processors for radio
communication, detection and
radar systems. With faster chips it
will be possible to achieve far more
than is currently possible.
Another aim which is further
into the future is to build a
complete processor. With current
estimates a multi-IC unit using 16
superconducting chips would have
1000 times the processing power of
a V AXll /780, a sizable minicomputer, and yet the active
circuitry would consume less than a
watt.
Even though this seems a long
way off some high density
fabrication has already taken place.
Shift registers up to 700 bits long
have been fabricated to prove that
January 1992 Practical Electronics 45
Future T e c h n o l o g i e s - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
N Channel HFET
P Channel H FET
The complicated C-HFET structure.
the necessary processes can be
achieved. However, as yet the chips
have not been tested at high speed.
When this happens the way will be
opened for dramatic improvements
in data processing techniques.
High Speed ICs
A breakthrough in low power GaAs
ICs has recently been achieved at
the Honeywell Research Centre at
Minneapolis. This is particularly
important because GaAs offers a
much higher frequency capability
than Silicon. Up until now the
problem with this technology has
been its high power consumption.
In turn this has limited the level of
integration which has been possible
because of the problem of removing
excess heat from the chip. With the
introduction of the new low
powered ICs the level of integration
for gallium arsenide is set to rise,
and with it the frequency limits for
large scale integration (LSI) chips.
It has long been accepted that
complementary circuits like those in
CMOS chips are the key to low
power consumption. This has
spurred the development of a
CMOS like structure for gallium
arsenide devices. However this is
not easy and has led to the use of a
new
structure
called
a
complementary HFET (C-HFET).
Essentially it is based upon a
46 Practical Electronics January 1992
heterojunction field effect transistor
which is configured to give the
complementary feature required by
IC designers.
The first departure from normal
is that the chips do not consist of
bulk GaAs. Instead they achieve
much better performance by using
an aluminium GaAs I indium (In)
GaAs structure. Like CMOS, this
new structure only draws current as
the circuit changes state. This
means that power consumption is
vastly reduced and integration
levels can rise.
In addition to achieving its
primary aim there have been a
number of other advantages. One is
that it can be run over a very wide
range of temperatures. At one
extreme it can operate in liquid
nitrogen which makes it ideal for
interfacing with superconducting
logic. At the other extreme it has
been shown to tolerate 200oc which
means that it is ideal for using in
extremely harsh environments.
To achieve this new structure it
has been necessary to use a process
known as molecular beam epitaxial
deposition (MBE). This enables the
creation of very precise areas for the
heterostructure on top of a buffer
region of bulk gallium arsenide.
This introduces very stringent
alignment problems in the
lithographic stages and to overcome
this, a self aligned 1J.Lm metal
silicide gate structure is used.
Although the development of
this process is still in its early stages
of development a 4k bit static RAM
has been fabricated. This was
shown to have an access time of 4
nS and only dissipated 100 mW- a
fifth of that used by a standard
GaAs memory of the same size.
Future developments of this
structure include reducing the size
of the gate to about 0.3J.lm. This
would permit the frequency of
operation to be raised even further,
as well as the level of integration.
However, despite these early hopes
a spokesman said that there is still a
considerable amount of work to be
done before these chips are
commercially viable.
Atom Sized Switches
A considerable amount of work is
being undertaken around the world
to pack more into an IC. To do this
chips are being made larger to
accommodate more circuitry and in
parallel with this work individual
components on the chips are being
made smaller. Currently, transistor
dimensions of around 0.5/-lm are the
smallest which can be made, but it
is expected that this will be reduced
by about half at the turn of the
century, with final reductions to
about 0.1/-lm.
In order to reduce dimensions
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - F u t u r e Technologies
Glossary
4 bit shift register
A logic device that holds bits of
information is parallel but can
move them sideways under
external control.
Josephson Junction
See page 45
GaAs devices
As an alternative to the usual
Silicon semiconductor, GaAs or
Gallium Arsenide can be used to
make integrated circuits that
operate at higher speeds. They are
also more expensive.
Substrate
The base layer of an integrated
circuit (IC) upon which other
layers can be placed.
Flat nickle crystal
ADCs
Analogue to Digital Convertors are
integrated circuits that convert
voltage levels into digital numbers.
Atom sized switch structure.
Bulk gallium arsenide
' - - - - - - - - - - - - - - - - - - - - - - - - - - - - , A large number of ICs can be
made on one disc shaped piece of
further than this, radically new
The switch was operated by
semiconductor, either Si or GaAs.
approaches are needed. One of applying a short voltage pulse
these may have actually began with across the electrodes. This caused
This is then broken up to form the
some work which has been started
individual chips. Each disc is cut
the Xenon atom to jump across the
at IBM's Research Centre in gap from one electrode to the other
from a long bar of the material
California. Here some experiments causing the tunnelling current to
which is made in bulk.
have shown how the movement of a
single atom can produce a switch.
In these experiments a single
atom of Xenon was successfully
moved between two electrodes
spaced apart by a few atom
diameters.
The effect was
monitored by looking at the change
in tunnelling current flowing
between the two electrodes as the
position of the atom changed. As
two distinct states were noted this
could be equated to the two levels
of a digital switch.
Obtaining the effect was not
easy. It required a temperature of
269°C and a very specialised
tunnelling scanning microscope.
One electrode was the tungsten tip
of the microscope whilst the other
was made from a nickel crystal. In
fact the shape of the tungsten tip
compared with the flat nickel
crystal was critical for the operation
of the device.
change. This could just be detected.
To return the switch back to its
original state the voltage pulse was
reversed. Both the Xenon atom and
the current returned to their
original state.
In view of its revolutionary
nature the switch is only in its very
early stages of development and it
is not clear if it can be made on a
commercial basis. One reason for
this is that no process currently
exists for making the device outside
a laboratory experimental set up.
Even so, it is expected that this
research will have a major impact
on
future
generations
of
miniaturised devices in the not too
distant future. Looking further
ahead it may be possible that
atomic switches could be made
viable enough to become as
common as today's logic families. •
Aluminium gallium arsenide I
indium gallium arsenide
structure
By combining different elements
with basic semiconductor
materials, they can be made to act
in different ways. lndium and AI
are added as impurities in a
technique known as doping.
Super-conducting logic
By reducing the temperature of the
logic ICs, quantum effects such as
tunnelling can be used to perform
logic functions. The loss of
resistance in a superconductor
also helps decrease the power
required as superconductors have
no resistance.
1A (angstrom) is equal to 10·10 m
January 1992 Practical Electronics 47
Project
Automatic Greenhouse
Watering System
Owen Bishop's digitally controlled watering system checks the temperature, time of day
and soil moisture to make sure your plants are kept in the best possible condition.
lants consist of about 90%
water, so it follows that
providing a regular supply is
a vital to keep them alive.
Unfortunately, the rush of a
modern lifestyle means that making
sure the plants get the water they
deserve is not always possible. The
solution is an automatic, electronic
watering system which can also
provide an extra dose of water if
the plants begin to dry out
unexpectedly. For those who do not
wish to install an elaborate
irrigation system, the moisture
sensing section of the circuit can be
built separately to be used as a
simple battery powered indicator
for testing the soil in individual
pots.
Different people have different
ideas about when and how they
should water their plants. Different
plants have different ideas on when
and how they should be watered.
This project attempts to cater for all.
The system is completely automatic
P
48 Practical Electronics January 1992
and allows the water to be
controlled in a number of ways
including overhead sprinklers and
mats. It takes its water supply
either from tanks or from the
mains.
The electronics is designed to
operate on small electric water
pumps or valves with the
mechanics of actually distributing
the water being left to the reader's
preferences.
Fig. 1. shows the main elements
of the system. The monitor relies on
three sensors feeding information
into a logic unit which decides
when to supply water. The logic
will never disturb the neighbours
by turning on the water at night
and it will never risk damage to the
pump or valves by trying to turn on
the water in frosty conditions.
The light sensor determines
whether it is night or day, or rather,
when there is a change from one to
the other. This provides the
information the logic needs if the
system has been switched to
operate under one of its first three
modes:
Mode A: water at dusk.
Mode B: water at dawn.
Mode C: water at dusk and dawn.
Although these will suit most
situations, the system also provides
two rather more plant orientated
modes:
Mode D: water during the day
whenever the soil is dry.
Mode E: water during the day
whenever the soil is dry, provided that
the greenhouse is not too hot.
These modes rely on the soil
moisture sensor, the light sensor
and the temperature sensor. The
sixth mode is intended for plants
that require continuously humid
conditions and is best for spray
nozzles:
Mode F: spray for short periods
intermittently throughout the day.
The system as published allows
only one mode of operation at any
one time but there should be no
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - G r e e n h o u s e Monitor
difficulty in expanding it to allow
for quite different modes to be used
in different parts of the greenhouse.
In a multiple system, the basic
sensors and logic circuit control two
or more sets of delay, timer and
relay circuits.
Construction
The circuit is assembled on a single
PCB (printed circuit board) as in
Figs. 7 and 8. The off-board
components are mounted on the lid
or panel of the enclosure (Fig. 9).
Begin with the sensor systems,
testing each one as it is completed.
The light-sensing circuit may be
tested with Rl,VR1 and the yellow
LED (D1) temporarily connected.
The LED goes on when R1 is
shielded from the light and off
when it is exposed. Remember the
low frequency filtering and allow
about 10 seconds for the circuit to
respond to changes in intensity.
The moisture sensing circuit is
tested by attaching a pair of test
leads to the soil probe terminal on
the board and to the OV line.
Temporarily connect D3 and VR2 to
this circuit. The voltage at IC3 pin 3
is approximately 1.1 V when the
probe leads are not connected to
each other. The output of IC3 is low
(0-2V) and the LED is on.
Connecting the probe leads, either
by touching them together or
pushing them into moist soil causes
the voltage at pin 3 to rise by an
amount varying with the resistance
between the probe leads. If the
voltage rises above that set by VR2,
the output of the IC rises almost to
+ 12V and D3 goes out.
In the temperature sensing
circuit, check that the voltage at
pins 3 and 5 of IC5a are correct:
V=(Temp+273) /100
Adjust VR3 so that the voltage at its
wiper is about 2.87 V. If the room
temperature is greater than se the
output at pin 1 is high. Set the
voltage at the wiper of VR4 to
correspond with a temperature of
about 2C above room temperature.
The output at pin 7 of IC5 is low,
but goes high if IC4 is placed
between a finger and thumb to
warm it up.
Install IC10 and check its
operation. Adjust VR5 until the
voltage at pin 5 rises and falls once
every 21 seconds. This gives the
required timings at pins 1 to 3.
Check the delay timer IC11 by
connecting the buzzer. Temporarily
connect pin 6 to +12V using a flying
Circuit Details
The light sensor is a light-dependent
resistor (R1 shown in Fig. 2). Under
dark conditions its resistance rises,
raising the voltage at the junction
between R1 and VR1. The rising or
falling voltage is sent to a low-pass
filter, consisting of R2, R3, C1 and
C2. Their high resistance and
which is the inverse of its input, is
high by day and low by night. The
Schmitt trigger has a sharp response
so the
change
is
almost
instantaneous. VR1 can be varied to
set the exact light level at which the
change occurs. The output of IC1 a,
inverted by IC1 b, is used to drive an
Fig. 2. light-sensing circuit.
Connects to pin 14 at IC1
VR1
10k
r
----------+Signal to the
main logic
01
Connects to pin 7 at IC1
ovo-~~----~----~--------~------------------~
capacitance result in a very low cutoff frequency, at about 0.08Hz. The
effect of this is that only very slow
changes of voltage pass through the
filter. As day becomes night or night
becomes day, the voltage received
by IC 1a falls or rises steadily. By
contrast, rapid changes of light, such
as those caused by people
wandering around, are filtered out
and ignored.
The NAND gate of IC1 a has
Schmitt trigger inputs. Because of
these, the output of this changes
state only for major swings of input
voltage. Smaller changes, such as
might be caused by the transitory
cloud obscuring the sun, are
ignored. Thus the output of this gate,
LED (light emitting diode). This
comes on in the dark and is off
during the daylight.
A special water sensing IC
(integrated circuit) is used to monitor
the dampness of the soil (Fig. 3).
This generates a signal of about 6Hz
which passes through C4 to pin 10.
However, if there is a conductive
pathway between pin 10 and OV, the
signal strength falls appreciably. Pin
10 is connected to one metal rod of
the probe inserted in the pot of soil
or compost. The other rod is
connected to the OV rail. The
conductivity of the soil depends
mainly on its moisture content. The
damper the soil, the weaker the
signal picked up by pin 10. In dry
Fig. 3. Moisture sensing circuit.
03
Soil probe connects here
Connect to pin 4 of ICS
OVo----------+--------*--+-----------------~
January 1992 Practical Electronics 49
Greenhouse Monitor - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Connect to pln 8 of IC5
TEMPi
>----,-.,.--o 0~J~~(oi0
logic
+
TEMP2
IC4 LM 33;5Z
>-----o o~~~~~io
-
logic
VR4
10k
R11
180k
Connect to pin 2 oiiC5
OVo---._----~~--------~----------------~
Fig. 4. Temperature sensing circuit.
soil, the signal is received at full
strength. A detector in the IC
produces an alternating voltage at
pin 12, the average level of which is
proportional to the level of the signal
reaching pin 10. 01 rectifies this
signal. The amount of current drawn
from CS during the negative swings
of the signal depends upon the
signal amplitude. If the soil is damp,
signal amplitude is low and the
current passing through R7 is able to
maintain a reasonable charge on
CS. If the soil is dry, signal amplitude
is high and a greater current is
drawn from C5. The voltage across
C5 is low.
The varying voltage level across
C5 is converted to a logical low or
high by IC3, wired as a comparator.
Output is high when soil is damp and
low when it is dry. VR2 sets the
moisture level at which the output
changes. 03 indicates the current
state, being off when the soil is damp
and on when it is dry.
The fact that the signal to the
probe is alternating is important
because direct current (DC) would
cause the metal probes to corrode
by electrolysis - this still occurs but
the effect is reversed when the
voltage is reversed.
The temperature sensor (IC4 in
Fig. 4.) is a band-gap device with a
voltage output which is proportional
to the absolute temperature. The
output voltage, at the junction
between R8 and IC4 is 0.01V per
Kelvin. Thus the output is 2. 73V at
273K, equivalent to oo on the Celsius
scale. To find its output at other
temperatures simply add 273 to the
temperature in Celsius and divide by
100 to find the output in volts. There
are two comparators in the
temperature sensing circuits. IC5a
detects low temperatures and its
output (TEMP1) goes low when the
temperature is near to freezing. This
is done by setting VR3 so that the
voltage at its wiper is a little above
2. 73V, say 2.80V. IC5b detects
excessively high temperatures. For
example, it could be set to detect
temperatures in excess of 30°C by
setting VR4 to supply 3.03V to pin 6.
The comparator outputs are high for
temperatures above the set levels.
TEMP1 can be set in the range -5°C
to 5°C; TEMP2 can be set in the
range 5°C to 40°C.
Fig. 5. shows how the logic uses
the information supplied by the
sensors:
Mode A: IC6a and IC6b generate
a high-going pulse when the output
of the light sensor falls from high to
low.
Mode 8: IC6b and IC6d generate
a high-going pulse when the output
of the light sensor rises from low to
high.
Mode C: IC7a and IC?b perform
the OR operation on the pulses of
modes A and B thus reproducing a
high pulse at dawn and dusk.
lead, then briefly connect it to OV
and back to +12V again. The siren
sounds for about 10 seconds. Now
add VR6 to this circuit. Repeat the
test and note that the relay operates
at the instant the siren ceases to
sound. The relay may operate when
the power is first applied. If this
happens, turn VR6 to give
minimum time, then wait until the
relay is released before testing.
Finally, insert the logic ICs (IC6IC9) in their sockets. Use a test lead
to temporarily connect one of the
terminals S2A to S2F to the terminal
S2. Run through the various
combinations of the inputs for each
mode of operation. Check that the
circuit is triggered by the required
combination of events for each
mode, but is not triggered when it
should not be. To avoid undue
noise at this stage it is a good idea
to disconnect the buzzer and rely on
measuring the voltage output at pin
5 of ICll to confirm that the logic is
working correctly. When testing
modes 0 and E, turn S2 to the 0.75h
position (IClO, pin 21) then turn it
to the INSTANT position to trigger
the pulse generator. This makes it
unnecessary to wait each time for
the clock output to go high.
The PCB has provision for a
number of terminal pins on the OV
and 12V rails to provide return
paths for various off-board
connections. However, it simplifies
the wiring if these returns are made
in the off-board ·wiring instead as in
Fig. 9.
There are various ways of
constructing the soil moisture
probe. The simplest is to use a twopin plug. A better result is obtained
with a probe made from two brass
or stainless steel rods about 50mm
long, 3mm in diameter, mounted
parallel to each other and spaced
about 20mm apart. They can be
held in two holes bored in a block
VR2
Power + 12lJ
rcq
1
~0
~o~o~o
VR4
c:\
't!:J. ~
~Cl!:
R
S1ren
~ VR 1
\)
'~e•c
~
Re!
=
R22Q
TR1
TR2
a~
Cl!
+"'
'..../
_.l Do4 Ocls
Rl7
Om
~~~ ~n
S2C
--.J
-=
=
R!B
~on
OSlB
"'=
Cl6
~~~
connection
Fig. 7. PCB component layout
50 Practical Electronics January 1992
RB
6
D
L--RL_A_l_
03K
03R
~- ~ OR~R<
"'0
£ Cl0
8+ _g_ VR
VRl "'
Rl Rl
~a~ a~ ~0 UR81 'iC8'
S2F
~
S20
!
+
Ltl per-
0
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Greenhouse Monitor
IC~
lC6
IC7
4093
4001
4001
IC9
4011
Fig~ 5. Repeat clock
and logic circuits with
power switch.
108 4001
The following IC pins connect to +12V
IC1,1Q6, IC7, IC8,1C9 pin 14
IC10 pin 16
The following IC pins connect to OV
IC1, IC6, IC7, IC8, IC9 pin 1
lC 10 pins 8 and 12
I. ~~J
IC1d
To delay
+12V
C81!1
0
IC10
4060
s
B8
121--------o
I
instant
+12V battery
0
13~o-'---o
d-o
~connections
14f-'----o
Toaii+12V
S1b
OOff
~
OV
L:1J
TEMP1o------------------------------------------------~
of plastic. The block must not be too
large as this might prevent the
water from reaching the soil
immediately below the block.
Installing the system
The unit is mounted where it is not
likely to have water sprayed or
dripped on it. It should be sheltered
from direct sunlight so as to avoid
overheating of the temperature
sensor. The light sensor Rl is
mounted where it receives full
daylight and is not unduly subject
to shading from trees or other fixed
objects. A lead from Rl runs to
sockets SKT1-SKT2 on the front
panel of the unit.
The soil probe is connected by a
lead to sockets SKT3 and SKT4 on
Mode 0: this depends on the
action of the repeat clock IC1 0. The
oscillator of IC1 0 runs at 1.5Hz and
this frequency is divided by 212 , 213
and 2 14 to give square waves
repeating by 0.75h, 1.5h and 3h
intervals. One of these signals is
selected by S3b. The pulse
generator produces a high pulse
every time the output from IC1 0
rises. The action of IC8c, IC9c and
IC9d is to produce a high pulse
whenever the repeat clock pulse
arrives, provided that it is daytime
(LIGHT is high) and that the soil is
dry (SOIL is low).
Mode C: the output from IC9c (a
low pulse coincident with the repeat
clock, provided it is daytime and the
soil is dry) is NORed with the TEMP2
output to prevent watering if the
greenhouse
temperature
is
excessive. A high pulse is produced
by IC9a if the temperature is
suitable.
Mode F: IC9a and IC9b produce
a high pulse every time the repeat
clock pulses, provided it is daytime.
The repetition rate of the clock is
selected by the setting of S3, which
also acts as a power ON/OFF
switch. S3 also has a fifth position.
INSTANT. This triggers the system
to water the plants immediately,
irrespective of the clock state.
Watering lasts for a single period of
1 to 30mins, according to the setting
of the timer.
The high-going pulse produced
as above is selected by S2 and
passed to a NAND gate IC1d.
Provided that TEMP1 is high (no risk
January 1992 Practical Electronics 51
Greenhouse M o n i t o r - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
R13
R19
1M8
logico----1---------+----~
lCfd
pin 11
100k
0"Prom
IC11
76555
13
12
TR2
ZTX300
C10
10)l
OV
+
o---~---------_.
C11
470!-l
___________.___~C~1~2~1~0~n_____~~--~
Fig. 6. Delay, timer and relay circuit.
' of freezing) this pulse appears as a
low at the output of the gate and
go~s to the delay circuit.
The delay circuit consists of one
of the timers in the 7556 dual timer
package. This is wired as a
monostable (Fig. 6.). When it is
triggered by the low pulse from the
logic circuit, its output (Pin 5) goes
high for about 20s. The high output
turns TR1 on and causes the solidstate siren (buzzer) to sound. This
warns that a deluge is imminent. The
output of the first timer (pin 3) is
connected to the trigger input (pin 8)
of the second timer by way of
capacitor C 12. Normally the trigger
input is held high by R23 but when,
at the end of the 20s delay, the
output of the first timer goes low, a
low pulse is transmitted to the trigger
input of the second timer. This is
also wired as a monostabfe but with
a period which can be varied from
one minute to about 20 minutes by
setting VR6. The high output from
the second timer turns off TR2 and
the coil of the relay is activated.
The relay is used to turn on one
or more electrically-powered water
pumps or valves. Small pumps are
available that operate on a 12VDC
supply so these can be powered
from the same supply as the monitor
circuit. However, they require a
considerable current (usually about
2A) and will quickly drain a normal
battery system. lt is better for the
power for the circuitry and pump to
be provided either from a lead-acid
battery or a mains powered 12VDC
unit. This must be rated to supply 2A
or more, but the supply need not be
the front panel. The probe is
inserted in a pot of soil or compost.
Whether or not the pot also contains
a plant is optional. The pot is
located in what is regarded as a
typical part of the greenhouse. It
should receive average sunlight,
average ventilation and an average
amount of water when the system
switches on. Probably several trials
will be needed to find the most
suitable location.
Obviously a single watering
regime cannot possible suit all the
plants in the greenhouse. Much can
be done by placing the plants so
that those which need most water
receive the most when the system is
running, while those which need
the least are at the extreme of the
watered area.
•
Fig. 8. PCB tracks from copper side.
52 Practical Electronics January 1992
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Greenhouse Monitor
ateg: 111e length of time a
. ,,' ill ra'sf defsen~s rriainly on
·tn~time a pump will be running. Fot
~v~~mple, using a 2A pump and
IH~tering for 15 minutes once per
Clay requires 0.5AH - half an amp
each hour. A lead-acid battery such
~s ..used in the average car has
15AH and will last for one month
Without recharging. On~demand
watering (Modes D and E) requires
niore or less than this depending oh
SI,!Ch factors as the season, the type
of plants ana whether or not the
greenhouse has summer shading.
. Electronically controllea water
valves are available for use with a
+12V DC supply and their
requirements are similar to those for
water pumps. If mains-powered
valves are to be used, appropriate
precautions must be taken when
wiring up and installing the circuit,
particularly to avoid water entering
the enclosure - this is really a job
for a qualified electrician.
The circuit itself requires just
over 1OOmA at 12V DC. In order to
avoid possible interference caused
by the switching on of the pump or
solenoiCl in a valve, it is
recommended that the circuit has its
own power supply. If a mains supply
is available in the greenhouse, the
best source of power is a 12VDC
mains adaptor; this should have a
regulated output and a type rated at
300mA is very suitable. If the mains
is not available, a lead-acid battery
of 1.9AH capacity will power the
system continuously for 19 days. As
a separate unit, intermittently
used,the moisture sensing circuit
can be run on a 9V PP3 battery.
,
03
Components
R~,~istors,an
carbon or metal film,
0.25W, 5%, except where stated.
R1 ORF'12 light dependent resistor
R2, R3
1M
R4
180
R5
39k
R6
1k
R7
4k7
R8
390
R9
9k1
R10
620k
R11
180k
R12
200k
R13
62k
R14,R15,R16,R22 1Ok
R17
270k
R18
3M3
R19
1M8
R20,R23
100k
R21
22k
VR1, VR2, VR4 1Ok carbon pot
VR3
10k horizontal preset
VR5
1OOk horizontal preset
VR6
2M2 carbon pot
Capacitors
C1, C2
211 polyester
C3
1n polystyrene
C4
47n polystyrene
C5
1011 tantalum
C6, C7, C9 1On polyester
CB
1!l polyester
C1 0 1011 electrolytic 16V radial leads
C11 470)1 electrolytic 16V radial leads
C12, C13, C14, C15 1OOn polyester
Semiconductors
01 light emitting diode, 5mm yellow
02, D4 1N4148 signal diode
03 light emitting diode 5mm green
TR1, TR2 ZTX300 NPN transistor
Integrated circui.ts
IC1
4093 CMOS quad 2 input NAND
with Schmitt inputs
IC2 LM1830F fluid level detector
IC3 LF351 single JFET op-amp
IC4 LM335Z precision temperature
sensor
IC5 LF353 dual JFET op-amp
IC6, IC7, IC8
4001 CMOS quad
two input NOR gate
IC9 4011 CMOS quad two input
NAND gate
IC1 0 4060 CMOS 14-stage binary
ripple counter with internal
oscillator
IC11 7556 CMOS dual timer
Miscellaneous
RLA 1 12VDC miniature relay with
change-over contacts rated to
withstand a minimum of 2A DC or
mains voltage.
S1, S2 rotary switch, 2 pole, 6-way
knobs for S1, S2 and the
potentiometers
12V solid state audible warning device
(siren, electronic buzzer)
Plastic enclosure approximately
220mmx150mmx60mm or larger
OIL IC sockets, 8-pin (2 off), 14-pin (7
off), 16-pin (1 off)
panel mounting sockets with plugs (4
off)
printed circuit board
1mm terminal pins
plastic self-adhesive PCB mounting
strip about 1OOmm long (2 off)
Lead-acid cells or other power supplysee text
connecting wire, solder, materials for
making probe.
Fig. 9.
Panel
wiring from
rear.
Di
IC3
pin 6
IC7 pins 12
and 13
IC2 pin 10 SKT3
PCB+12V
~
A
0
Prob
ov
PCB i 2 V - - ) . J
TRi
SKT2
January 1992 Practical Electronics 53
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56 Practical Electronics January 1991
O&A
Techniques
Andrew explains how to fix a cassette recorder with a Swiss army knife and some vodka.
his Techniques column, like
last month's, has a seasonal
bias. B.Robertson of Swindon
writes to say that he is intending to
take his Walkman on a ski trip with
him this winter. "The chalets
normally provide some sort of
radio/ cassette player for our
entertainment," he continues, "but
the cassette mechanism has often
not been cleaned for so long that it
chews up tapes and cannot be put
right. How can I use my cassette
player to play tapes through the
radio set?"
I know just what you mean - I
have ended up mending the
cassette player in a chalet with a
Swiss army knife myself. Trying to
clean the pinchwheel with vodka
(and trying to avoid making it
sticky) after removing the chewed
pieces of tape is the worst part.
T
Coupling
There are two obvious approaches
to this question. First of all, you can
buy a coupling unit which looks
like a cassette with a lead issuing
forth from it and which is designed
to feed a signal into the stereo tape
head of a cassette player. The
normal use for these coupling units
is to play a CD Walkman through a
car stereo, but it should play an
ordinary Walkman through a radio
cassette player unless the head itself
has been damaged.
If you don't want to spend the
money on one of these units,
and I or if you fancy a novel
approach to the problem, you could
use the signal from the W alkman to
modulate an oscillator somewhere
in the FM frequency band and tune
the radio to pick up this signal. The
circuit shown in Fig. 1 is the
simplest I have seen which will do
this job.
From an RF point of view, both
of the power supply rails are at
ground potential, and the base of
Ql is decoupled to ground via Cl.
The RF part of the circuit then
reduces to a transistor with a
parallel tuned circuit as its collector
load, and feedback from collector to
emitter, roughly impedance
matched by C3 and C4.
The base of the transistor is not
decoupled from the point of view of
audio frequencies, and the stereo
audio signal from the W alkman is
converted to mono by Rl and R2
and used to modulate the base
voltage. This varies the operating
point of the transistor enough to
cause the frequency to wobble in
time with the sound, producing a
frequency-modulated signal. There
is also a small amount of amplitude
modulation, but this does not
usually have any significant effect.
Linearity
Different transistors work in
different ways in this circuit.
BC182s produce a fair amount of
amplitude modulation, with very
Fig. 1.
L1 (4T)
*See text
R1 4k7
C3
10p
C6
100n
•. PP3
.
CS
R4
10k
C4
10p
2-1 Op
January 1992 Practical Electronics 57
Techniques
Grounded screen
B1100k
C1
~
R4
10k
C3
10p
C8
C4
15p
C5
2-10p
:
2-10p l C6
l100n
OV
fig. 2.
little frequency variation, which
makes the signal rather distorted.
BC108s always seem to work
reasonably in this circuit, with some
samples giving virtually no
amplitude
modulation
and
seeming-ly
linear frequency
variations. Some samples of 2N2369
work well, but not all work well
enough. To get a good quality
signal, some experiment is
necessary.
If this oscillator is placed near
the FM radio, it will be able to be
picked up at a good strength.
Strictly, this would possibly
constitute an illegal transmission,
though if a BC108 is used the range
is very short indeed. If a 2N2369 is
used, the range could be 10 yards or
more, depending on the physical
dimensions of Ll, which influence
how effective an aerial the coil
forms.
If one wished to avoid any
possibility
of
an
illegal
transmission, the obvious answer
would be to reduce the power still
further and connect the output
straight to the radio. Unfortunately,
it is very difficult to make this work
in practice, because if the power is
reduced too far, the oscillator tends
to stop. In addition, connecting the
output of the oscillator to anything
alters its frequency. To get around
these problems, the circuit of Fig.2
58 Practical Electronics January 1992
may be used. If this is built in a
screened box, then the only signal
coming out is from the low-power
buffer stage. This output can be
directly connected to other things,
for example, to the aerial of an FM
radio, without affecting the
frequency of the oscillator.
The oscillator stage itself is like
that of Fig. 1, but the modulation is
done in a more conventional
manner, using a varicap diode. This
gives good quality sound regardless
of what type of transistor is used.
A small amount of signal is
coupled to the next stage via a 1
turn secondary winding on L1. The
output of the second stage is
adjusted by varying its bias with
RV1. In order to provide just the
output level needed to feed to an fm
tuner, the poten tiometer will
probably need to be advanced only
a fraction of a turn above the OV
end. Indeed, if it were turned up far
the power output (and battery
consumption) of the stage would
increase and it would become a
transmitter with quite a respectable
range if an aerial were connected.
To tune the output stage, RV1
should be adjusted to produce a
current of about 1 to 2 milliamps in
Q2 - which may be verified by
measuring 100 to 200 millivolts
across R8. A few centimetres of wire
should be connected as a temporary
aerial, and a radio should be tuned
to the radiated frequency. The aerial
of the radio should be retracted,
and it should be placed at a range of
several feet. RV1 should then be
turned down until reception
becomes noisy, and CS should be
adjusted for maximum signal.
The power should now be
reduced to the minimum level
required, in order to prolong
battery life.
If a very small circuit is required,
because of luggage restrictions, the
circuits could probably be made to
run on a single 3V lithium cell (or at
most two in series) if the transistors
were re-biassed. For example, in
Fig. 1 R3 would be reduced to 8k2,
and R5 would be reduced to 680n
lnductors
Some experiment may be required
to find the best design for the
inductor. An experimental circuit
used 4 turns of 0.2mm wire
solenoid wound on a piece of Smm
diameter Pyrex rod, superglued
into place. This resulted in a stable
oscillator which has been used
successfully to play my walkman
through
my
car
radio,
demonstrating its stability against
temperature
changes
and
mechanical shock.
•
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Continued from page 62
until now been regarded as spare. But of course they
are not really spare. They are used to connect VCRs,
satellite tuners and computer video games to TV sets.
Inevitably, powerful Channel 5 transmissions will cause
interference where frequencies clash.
A clause in the Broadcasting Act 1990 requires the
Ch. 5 franchise winner to pay for whatever re-tuning,
modification or replacement of equipment is necessary.
Obviously this would kill Ch. 5. So another clause,
which the Home Office slipped in quietly, says that
people who erect the modified aerials (different
frequency range and different polarisation) which will
be necessary to receive Ch 5 will forfeit their free cure
for interference.
The ITC has now published a technical report (cost
£500 + VAT) by National Transcommuniations Ltd
(formerly the IBA Labs at Winchester) on the likely
extent of re-tuning. The press has been shown a
synopsis. NTL estimates that by 1994, when Ch. 5 starts
broadcasting, there will be anything between 4 and 8
million VCRs which need re-tuning. But it assumes that
half of their owners will have forfeited their rights.
The report largely ignores satellite receivers and
video games. The ITC plays the omission down. But
there is now a resurgence of interest in video games.
Witness Nintendo fever. There are already 1.5 million
satellite dishes in the UK with sales at around 70,000 a
month.
The report also ducks the issue of how much
technical assistance will cost.
Of course not all equipment will be at risk, but by
1994 there could easily be 10 million pieces of
equipment suffering interference. Common sense tells
that once the word gets around, people will claim any
free help they need - or think they need - before
erecting a new aerial and starting to watch Ch. 5. This
will bankrupt the franchise. 5.
Beware those who blandly say that retuning is easy.
Anyone who has juggled a daisy chain of tuned RF
connections knows otherwise. By 1994, when Ch. 5
switches on and triggers nationwide interference, no
engineer will make a house call for less than £50. No
broadcaster will be able to afford the bill, and no service
facility will be able to make all the calls immediately.
Personally I do not care if someone is daft enough to
bid for the Ch. 5 franchise and goes bust. But I do care
about the electronic mess they will have caused.
•
N
C1
+ C6
Last month's headphone amplifier circuit diagram had a sligh
mistake in it. Thanks to those readers who pointed it out.
The Valve HT supply was not shown conqected.
60 Practical Electronics January 1992
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Advertising Index
73 Amateur Radio Today ...... 55
Active Action Electricl .......... 55
ADM Electronics Supplies ... 55
AGS Electronics ...................55
Alphavite ............................... .4
AstroFest 92 ......................... 61
BK Electronics .................... IBC
Bull Electrica1. ..................... .42
Cadsoft ................................ 60
JPG Electronics ...................55
Limrose ............................... .44
London Electronics College .54
Maplin .............................. OBC
Marapet. .............................. .34
Mauritron .............................56
Morrison ..............................44
MOP ......................................4
NCT ..................................... 17
Cambridge Computer Sci .... 54
Cirkit. ................................... 17
Coles-Harding &Co ............54
Computer Instruments .......... .4
CR Supply Company ........... 55
Cricklewood ......................... 29
Electronize Design ............... 34
Greenbank ............................ 29
Henry's Audio ...................... 17
International Corr Schl. ........ 60
Number One Systems .......... 24
Omni ....................................44
Program Now .......................34
Radio &Telecom Corr Schl..54
Seetrax .................................29
Service Trading ................... .44
Stewart of Reading .............. .44
Suma Designs ..................... 18
Tandy ...................................12
Tsien ................................... IFC
Barry Fox
Not The Best Way To
Make Money From TV
Barry examines the current trend of selling franchises in the TV industry. With ITV already
gone, will ChannelS and Teletext face the same problems?
t would be hard to find anyone
who thinks the new procedure
for granting commercial TV
franchises is fair, sensible and of
advantage to anybody, except the
Treasury. Bidders for what was
ITV, and will now be known as
Channel 3, had to say how much
they will pay the government for a
franchise. Unless there are
"exceptional circumstances", the
highest bidder won.
I
Taking AChance
The blindingly obvious risk is
that the highest bidder will run out
of money and either go bankrupt or
inflict viewers with cut-price
programmes, bought in from
abroad. The lower bidders with
more money to spend on better
programmes will never get the
chance to prove their promises. The
bidding process has had an
I
!rsonally I
do not care
. if
someone 1s
daft enough
to bid for the
ChannelS
franchise and
goes bust.
62 Practical Electronics January 1992
unsettling effect on the existing ITV
stations who do not know whether
they will still be broadcasting after
the end of 1992. Witness how
pitifully little the ITV companies
have done to exploit Nicam stereo.
All we can do now is watch the
Channel 3 system fail painfully and
publicly like the poll tax - and
wait for the government to find a
way of changing the system
without too much loss of face.
In the meanwhile there are two
more franchise pantomimes to go
through.
Teletext Trouble
In November the Independent
Television Commission will start
selling off the commercial TV
teletext services to the highest
bidder. The current licenses for
Oracle's services on ITV and
Channel4, expire at the end of 1992.
The new licences will be granted by
April 1992. As with the Channel 3
licences the Broadcasting Act 1990
lets the ITC accept a lower tender
only
under
"exceptional
circumstances".
On 9 September the ITC
published its draft licence for
teletext, asking for comments by 7
October. Obviously this made it
impossible for monthly specialist
magazines to advise readers in time
- these are the magazines most
likely to read the small print and
spot the technical restriction which
will adversely affect all viewers in
the 7 million homes which now
have a teletext TV set.
Current teletext services use up
to 12 picture lines in the vertical
blanking interval (which make up
the black borders at top and bottom
of the TV picture) to carry the
digital data for around 250 pages of
information. The ITC plans to
licence only 7.5 lines. The
remainder will be sold off for other
uses, such as closed user group data
services where encrypted data is
available
only
to
paying
subscribers.
Oracle currently uses 11 lines for
ITV and 12 for Channel 4. It
estimates that a reduction to 7-line
working would mean a loss of 100
pages of text. If the same number of
pages are transmitted, it will take
longer for them to appear on
screen. Either way viewers will
then only get part of the service
they have grown to expect.
Who Wants Channel 5?
In January the ITC will advertise
the franchise for Channel 5,
Britain's fifth TV channel. The
winning bidder will broadcast to
over 70% of the UK, using
frequencies (mainly UHF channel
numbers 35 and 37) which have
Continued on page 60
i
now enjoy a world·wide rep~tatlon for quality, reliability and performance at a realistic price.
available to suit the needs of the professional and hobby market i.e. Industry, Leisure, Instrumental and
comparing prices, NOTE that all modt:tls Include toroldal power supply, integral heat sink, glass fibre P.C.B.
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 watts
R.M.S. into 4 ohms, frequency response 1Hz -3dB, Damping Factor > 300, Slew Rate
T.H.D. typical 0.002%, Input Sensitivity 500mV, S.N.R
-110 dB. Size 300 x 123 x 60mm.
PRICE £40.85 + £3.50 P&P
THE RENOWNED MXF SERIES OF POWER AMPLIFIERS
FOUR MODELS:- MXF200 (100W + 100W) MXF400 (200W + 200W)
MXF600 (300W + 300W) MXF900 (450W + 450W)
ALL POWER RATINGS R.M.S.INTO 4 OHMS, BOTH CHANNELS DRIVEN
FEATURES: *Independent power supplies with two toroidal transformers * Twin L.E.D. Vu meters *
*
*
*
Level controls Illuminated on/oH switch
XLR connectors
Standard 775mV inputs* Open and short circuit
Latest Mos-Fets for stress free power delivery into virtually any load
High slew rate
Very low
proof
*
*
dislortion * Aluminium cases* MXF600 & MXF900 fan cooled wilh D.C. loudspeaker and lhermal
USED THE WORLD OVER IN CLUBS, PUBS, CINEMAS, DISCOS ETC.
*
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MXF400 W19"xH5 1t4'' (3U)xD12"
MXF600 W19"xHS';.'' (3U)xD13"
MXF900 W19"xH5''•" (3U)xD14~•"
PRICES:·MXF200 £175.00 MXF400 £233.85
MXF600 £329.00 MXF900 £449.15
SPECIALIST CARRIER DEL. £12.50 EACH
* Manual arm * Steel chassis * Electronic speed
control 33 & 45 R.P.M. * Vari pitch control * High
servo driven DC motor * Transit screws *
die. casl plaller * Neon slrobe * Calibrated
balance weight * Removll'ble head shell * ,,,,
cartridge fixings * Cue lever* 220/240V 50/60Hz
* 390x305mm * Supplied with mounting cut-out
lemplale.
PRICE £61.30
+
£3.70 P&P
COLDRINC C950
THE VERY BEST IN QUALITY AND VALUE
Made especially to sutt today's need for compactness wtth h1gh output
sound levels, fmished in hard wearing black vynide with protective
corners, grille and carrying handle. Each unit incorporates a 12" driver
plus high frequency horn for a full frequency range of 45Hz-20KHz.
Both models are 8 Ohm impedance. Size: H20" x W15" x 012".
CHOICE OF TWO MODELS
POWI:R RATINGS QUOTED IN WATTS RMS FOR EACH CABINET
OMP 12-1 OOWATTS ( 1 OOdB) PRICE 1:163.SO PER PAIR
OMP 12-200WATTS (200dB) PRICE 1:214.55 PER PAIR
CAR STEREO BOOSTER
150 WATTS (75
Bridged Mono
250 WATTS (125
Bridged Mono
400 WATTS (200
AO.t'ILIFIEIRS
T
Bridged Mono
ALL POWERS INTO 4 OHMS
Features:
* Stereo, bridgable mono
*
* Choice of
R level
* Speaker &
*L&
high & low level inputs
controls
Remote on-off
ORCERS FROM SCHOOLS, COLLEGES, GOVT. BOCIES, PLCa ETC.
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ACCESS ACCEPTED ElY POST, PHONE OR FAX.
OMP/MF 200 Mos-Fet Output power 200 watts
R.M.S. into 4 ohms, frequency response 1Hz ·100KHz
-3dB, Damping Factor > 300, Slew Rate 50V/uS,
T.H.D. typical 0.001%, Input Sensitivity 500mV, S.N.R.
-110 dB. Size 300 x 155 x 100mm.
PRICE £64.35 + £4.00 P&P
OMP/MF 300 Mos-Fet Output power 300 watts
R.M.S. into 4 ohms, frequency response 1Hz • 1OOKHz
-3dB, Damping Factor > 300, Slew Rate 60V/uS,
T.H.D. typical 0.001%, Input Sensitivity 500mV, S.N.R.
-110 dB. Size 330 x 175 x 100mm.
PRICE £81.7 5 + £5.00 P&P
OMP/MF 450 Mos-Fet Output power 450 watts
R.M.S. into 4 ohms, frequency response 1Hz -100KHz
Damping Factor > 300, Slew Rate 75V/uS,
typical 0.001%, Input Sensitivity 500mV, S.N.R.
·110 dB, Fan Cooled, D.C. Loudspeaker Protection, 2
Second Anti-Thump Delay. Size385 x 210 x 105mm.
PRICE £132.85 + £5.00 P&P
NOTE: MOS-FET MODULES ARE AVAILABLE IN TWO VERSIONS:
STANDARD- INPUT SENS 500mV, BAND WIDTH 1OOKHz.
PEC (PROFESSIONAL EQUIPMENT COMPATIBLE) - INPUT SENS
775mV, BAND WIDTH 50KHz. ORDER STANDARD OR PEC.
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