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HIFI REVIEW
Tandy's new CD
with remote control
player
Fluke. First Family of DMMs.
When accuracy, performance and value
are important, professionals the world over
look to Fluke - the first family of DMMs.
Reliable Fluke-quality 3½- or 4½-digit
DMMs fit every need - from design engineering to industrial troubleshooting.
There's the low-cost 70 Series - the
most DMM you can get for the money. The
tough 20 Series - totally sealed and built
to survive the dirtiest, grimiest, roughest
jobs. The reliable 80208 Series - made
to withstand the rigors of the field service
environment. The precise 8060A Series the most powerful and complete test and
measurement system available in~ handheld package. And, of course, the versatile
Bench/Portables that carry on the Fluke
tradition for precision and durability in
lab-quality bench instruments.
Fluke comes in first again with the
world's largest selection of quality accessories to help extend the capabilities of
your DMM even further.
There's no need to look anywhere else.
Uncompromising Fluke design and leading edge technology are the reasons why
attempts at imitation will never fool the
millions of professionals that accept nothing less than a Fluke.
FROM THE WORLD LEADER
IN DIGITAL MULTIMETERS.
IFLU KEI
®
E L MEASCO
Instru m e nts P t 11. Ltd.
Dealer enquiries welcome
f aik to your local Elmeasco distributor about Fluke
• A&.L.. John Pope Electrical (062) 80 6576 • J Blackwood & Sons (062) 80 5235 • George Brown (062) 80 4355
• ll.SJ:1!. Ames Agency 699 4524 • J Blackwood & Sons • George Brown 519 5855 Newcastle 69 6399 • Auto-Catt Industries 526 2222
• D.G.E. Systems (049) 69 1625 • W.F.Di xon (049) 69 5177 • Ebson 707 2 111 • Macelec (042) 29 1455
• Novacastrian Electronic Supply (049) 62 1358 • Obiat Ply Ltd 698 4776 • Petro•Ject 569 9655 • David Reid 267 1385 • Selectroparts 708 3244
• Geoff Wood 427 1676
• N.TERRITQRY J Blackwood & Son (089) 84 4255, 52 1788 • Thew & McCann (089) 84 4999
• O~NS~N£ 55Auslec (07) 854 1661 • G.Brown Group (07) 252 3876 • Petro-Ject (075) 91 4199 • St Lucia Electronics 52 7466 • Cliff
t:le ronics 1
• Nortek (Townsville) (077)79 8600 • l. E.Boughen 3691277 • Fred Hoe & Sons 277 4311 • The Electronics Shop (075) 32 3632
• Thompson Instruments (Cairns) (070)51 2404
• S AUSTRALIA Protronics 212 3111 • Trio Electrix 212 6235 • Industrial Pyrometers 352 3688 • J Blackwood & Sons 46 0391
• Petro -Ject 363 1353
• TASMAWA George Harvey (003) 31 6533 (002) 34 2233
• VICTORIA Radio Parts 329 7888 • George Brown Electronics Group 878 81 11 • G.B. Telespares 328 4301 • A.W.M. Electrical Wholesalers
• Petro-Ject 419 9377 • J Blackwood & Sons 542 4321 • Factory Controls (052) 78 8222 • Mektronics Co 690 4593
• Truscott Electronics 723 3094
• WAUSTRALIA Atkins Carlyle 481 1233 • Dobbie Instruments 276 8888 • Protronics 362 1044
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MARCH 1988
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TANDY'S NEW CD-1500 is a
mid- priced CD player that comes
with remote control as
standard. We tell you how it
performs in our review starting
page 16.
FEATURES
6 New Life for Radio-Cassette Players by Homer Davidson
12
16
65
76
81
Simple service tips to bring back the good sound
Vintage Radio: How it Began by John Hill
From spark transmitters to the Audion
Tandy's CD-1500 CD Player by Leo Simpson
Mid-priced unit has remote control
High, Low, Sink and Source by Leo Simpson
What the jargon means
The Evolution of Electric Railways by Bryan Maher
Pt.5 - Electrics in Australia
Digital Fundamentals, Pt.5 by Louis Frenzel
Counters & shift registers
DON'T PUT UP with
interruptions from extension
phones. When you pick up one
telephone, this simple device
automatically cuts the
extension phones dead.
Details page 18.
PROJECTS TO BUILD
18 Line Grabber for Telephones by Greg Swain
Pick up one phone & it cuts the others dead
26 Remote Switch For Car Burglar Alarms by John Clarke
The transmitter attaches to your keyring
40 Endless Loop Tape Player by Greg Swain
Use it as a novel doorbell
43 Technilab 301 Function Generator by David Whitby
Useful test instrument doubles as a signal tracer
56 Old-Time Crystal Radio by John Hill
Its performance will surprise you
60 Build Your Own Light Box by Leo Simpson
Low cost & easy on the eyes
PRESS THE BUTTON on a
small keyring transmitter and
this project will automatically
turn your car's burglar alarm
on and off. Construction
begins on page 26
SPECIAL COLUMNS
50 Serviceman's Log by the original TV serviceman
A baffling exercise
68 Amateur Radio by Garry Cratt
Antennas for the VHF & UHF bands
72 The Way I See It by Neville Williams
The quest for the ultimate in hifi sound is half the fun!
DEPARTMENTS
2 Publisher's Letter
3 Mailbag
4 News & Views
15 Bookshelf
38 Circuit Notebook
88 Product Showcase
94 Ask Silicon Chip
96 Market Centre
FANCY A BARKING doorbell?
This endless loop tape player
is the answer. It can also serve
as a novel pre-recorded
message system. See page 40.
MARCH 1988
1
SILICON CHIP
PUBLISHER'S LE't·t'ER
Publisher & Editor-In-Chief
Leo Simpson, B.Bus.
Editor
Greg Swain, B.Sc.(Hons.)
Technical Staff
John Clarke, B.E.(Elec.)
Ro.bert Flynn
Regular Contributors
Neville Williams, FIREE, VK2XV
Bryan Maher, M.E. B.Sc.
Jim Yalden, VK2YGY
Garry Cratt, VK2YBX
Jim Lawler, MTETIA
Photography
Bob Donaldson
Editorial Advisory Panel
Philip Watson, MIREE, VK2ZPW
Norman Marks
Steve Payor, B.Sc. , B.E.
SILICON CHIP is published 1 2 times
a year by Silicon Chip Publications Pty Ltd. All material
copyright (c) . No part of the contents of this publication. may be
reproduced without prior written
consent of the publisher. Kitset
suppliers may not photostat articles without written permission
of the publisher.
Typesetting/makeup: Magazine
Printers Pty Ltd, Waterloo, NSW
2017 .
Printing: Macquarie Publications
Pty Ltd, Dubbo, NSW 2830.
Distribution: Network Distribution
Company.
Subscription rates are currently
$42 per year (12 issues) . Out-.
side Australia the cost is $62 per
year surface mail or $1 20 per
year air mail.
Liability: Devices or circuits
described in SILICON CHIP may be
covered by patents. SILICON CHIP
disclaims any liability for the infringement of such patents by the
manufacturing or selling of any
such equipment.
Address all mail to: Silicon Chip
Publications Pty Ltd, PO Box
139, Collaroy Beach , NSW
2097. Phone (02) 982 3935.
ISSN 1030-2662
* Recommended and maximum
Australian price only .
2
SILICON CHIP
Tell us what you like
and what you don't like
Welcome to the March issue of SILICON CHIP which is the fifth since
we started. Already, this magazine is gaining a considerable following
as more people come to know about it. That is very gratifying but we'd
like you to tell us how to improve SILICON CHIP. Too few people are telling us what they think.
Quite a few readers have taken out a subscription and have pencilled a note on the coupon saying "top magazine" or some similar comment. Now this gives us a warm inner glow but it does not tell us which
parts of the magazine you really like. Maybe there were some parts
you didn't think much of. Or maybe there was an article that you
disagreed with. Perhaps you thought that an article could have been
improved or it omitted some useful information.
Please give us this sort of feedback. We want your constructive
criticism so that we can give you the highest editorial standard. So if
you think that something in SILICON CHIP is good or could be improved
or whatever, please jot down those thoughts in a letter and send it to
us, straight away.
Don't worry about whether your writing is neat or whether you use
correct sentence structure. Just write to us. We'll get the message.
This month's Mailbag carries a number of letters which give a good
example of what we're talking about. These letters mention an article
which appeared then proceed to tell us how it might have been improv- .
ed or what it omitted. Good. We might not agree with everything that is
written but we're not afraid to publish criticism if it is constructive.
If you feel that we should cover a particular topic or describe a pet
project of yours, please put in your request. We might not be able to do
it but there's a much higher chance of us doing so if you write to us.
And if you wish to see a controversial subject discussed in some
detail, say in Neville Williams' column "The Way I See It", don't
hesitate to write - there is a good chance that Neville will get stuck
into it.
There are several other ways you can contribute to SILICON CHIP. If
you're really keen you might submit an ar\icle for publication. You
might send in an idea for the Circuit Notebook pages. Or you might ask
a question to be discussed in the " Ask Silicon Chip" pages. It's over to
you. We'd love to hear from you.
Leo Simpson
SILICON CHIP,
PO Box 139,
Collaroy Beach 2097.
MAILBAG
Converter needs crowbar
I only discovered SILICON CHIP by
accident when looking over the book
stand in the local newsagent. At first
I didn't take much notice of it - just
another electronics magazine, I
thought - but when I noticed the two
names up top, things suddenly clicked. Judging by the comments in
"Mailbag" for January, your
magazine looks like a winner.
Also I would like to comment on
your 24 to 12V converter in the
December 1987 issue. I feel that the
12 volt output from the unit should
have some sort of overvoltage protection. If Q3 goes short-circuit for any
reason, the full 24 volts would be fed
straight to any 12 volt equipment connected to it, so causing damage to the
equipment. The fuses would no doubt
blow but not before the equipment
was damaged.
A "crowbar" protector of some
sort may be the best approach.
P.W.Bell
Glenorchy, Tas
A crowbar could be simply incorporated into the circuit by connecting
a 15V or 16V 20W zener diode across
the 12V output. If an overvoltage condition did occur the zener might short
circuit but it would also take out the
5-amp fuse and thus prevent damage
to the equipment.
A thousand issues
My compliments on your new
magazine. It's nice to see the familiar
pens back at work again. All power to
you and may this be the beginning of
a thousand issues.
Jim Lawler
Hobart, Tas
CD hyperbole
I am becoming rather annoyed at
the ridiculous amount of advertising
garbage that is being associated with
compact disc players. For example,
an ad from one manufacturer boasts
of a chassis built from materials such
as Cosmal-Z alloy, lead, ferrite and
alloy materials. Many companies are
dishing out these "space-age
breakthroughs". A few years back I
read an audio magazine that claimed
that a "remarkably audible improvement" could be obtained from CD
players by using an aftermarket
"disc stabiliser" to stop the disc from
resonating.
Now maybe I'm missing something
but these sort of claims seem to be
nothing short of pure hyperbole. If
the CD itself is a circular spiral of
pits representing 1 's or O's, the resultant bits for the data stream can only
be either 1 or O and in any case, a
Schmitt trigger would soon remove
any discrepancies. If the radial and
focussing servos are working properly, the data stream should be able to
be decoded without any problems.
Then there are the claims that
three-spot lasers offer vast improvements over single spot systems.
This had me intrigued since back in
1969 Philips were working on
Videodisc players which used a
three-spot system. Yet Philips, who
pioneered the laser disc revolution,
both video and audio, now use a
single spot laser in all their CD
players.
The list goes on and on. I feel sorry
for the poor innocent customer who
has these claims rammed down his
throat.
Stephen McBride
Townsville, Qld
Vintage radio circuits
Congratulations on your successful
start with SILICON CHIP. You certainly
have my support.
For those people interested in
restoring old radios, I have copies of
the Australian Service Manuals
covering Australian-made radio
receivers from 1937 to 1946. I would
be happy to supply copies of receiver
circuits in return for two 3 7 cent
stamps to cover copying and postage.
In addition to the make and model,
it would be helpful to know the year
of manufacture, number and types of
valves, and the wave bands
available.
J. Emery
BulJ Creek, WA
Wants beginner articles
Congratulations on your new
magazine. I'm enjoying the train
series, as well as the rest. In fact, I
haven't enjoyed reading an electronics magazine as much for years ,
and I started in 1958.
I hope you will be able to write a
significant number of your articles
and projects aimed at the beginner. I
think it is of great importance to encourage our young people as much as
possible. I guess I'm particularly
thinking of my son, who at eleven, is
ready to tackle almost anything with
the nearest screwdriver but who
needs some encouragement to
discover "how it works".
W. Adams
St. Lucia, Qld
Further hazards of the
MEN system
I have a comment on the article
"Your House Wiring Could Kill You",
as published in the November 1987
issue. Where you suggest removal of
the earth connection to clean it, you
have not considered the neutral connection from the meters and frequency injection relay/time clock. In the
event of high neutral circuit
resistance between the house switchboard and the substation, the earth
current from the clocks etc will flow
back to the transformer via the earth
connection (as you have accurately
described). However, the meters cannot be isolated by the main switches.
The only way to isolate this equipment and remove the neutral/earth
current is to remove the county council's service fuses which, of course, is
against the law.
Another potential danger is where
an installation remote from the
substation has a high resistance main
neutral connection. The current will
then flow via the earth connection (as
described in your article). For houses
close to the substation, this earth current can then flow "back up" through
their earth connections and into the
main neutral conductor to reach the
substation.
The possibility then exists for an
earth current to be measured when
the main switches are off and the
council service fuses are removed!
Naturally a voltage will appear under
these circumstances if the earth connection is removed for cleaning.
I suggest that earth connection
cleaning should only be performed by
a licensed electrician because of the
above possibilities.
Footnote: I too have had trouble
convincing a council that their
neutral connections were not good.
When finally investigated they found
that the substation neutral connection had been burnt off completely!
John Lean
South Tamworth, NSW
MARCH 1988
3
NEWS&VIEWS
Australian TV manufacture ceases
In January of this year, the
Sanyo TV plant in Albury closed
its doors and all the equipment
was disposed off. This follows
the closure of the Philips TV
plant in Clayton in October last
year. The closures are partly as
a result of progressive tariff
reductions on TV imports.
We have very mixed feelings
about the closures. While the
tariff reductions will, in theory,
lead to cheaper TV sets, it may
BBC goes cold
on stereo TV
Five years ago, when Australia
adopted the German developed
method of stereo TV transmissions
there was criticism in some circles.
Some prominent engineers were
disappointed that Australia had not
selected the technically more
elegant BBC digital stereo system.
This has been a moot point over the
intervening period as stereo TV has
slowly grown in popularity. For
those people with stereo TV
receivers the sound quality is every
bit as good as that from TV/FM
stereo simulcasts. The only question is, when is the ABC going to
adopt stereo TV?
Late last year, it became clear
that Australia had made the right
be more expensive in the long
term as parts for repairs become
more difficult to obtain.
The other factor to be considered is that TV sets will no
longer be designed to suit the
special requirements of the
Australian market. In the future
we will just be supplied with
variants of "world" sets. It remains to be seen whether such
sets perform as well as those
designed for our market.
decision. While it may have
developed the more elegant system,
the BBC has more or less abandoned its stereo TV system, leaving a
number of TV and IC manufacturers in the lurch. Britain still may
have stereo TV if the IBA and Britain's TV manufacturers have their
way.
In view of the BBC's decision, will
the ABC now decide to adopt stereo
TV broadcasts? It's about time they
did.
Black hole defeats
heat seeking missiles
Everyone has heard of heatseeking missiles which home in op
the jet exhaust of fighter planes, no
matter how much they dodge about.
Now McDonnell Douglas engineers
have come up with the Black Hole
Infrared Suppression System which
is currently in use on the US
Apache helicopter.
Engine exhuast is mixed with outside air and routed through a series
of pipes before being expelled
through finned nozzles. The result
is that the exhaust is so cool that it
is ignored by heat-seeking missiles.
It is a pity they couldn't come up
with a system to reduce the noise of
helicopters as well. Currently,
helicopters are the greatest source
of aircraft noise nuisance above
our cities.
Radio service for
Japanese tourists
The projected start of Japanese
language transmissions in major
tourist locations throughout
Australia have been slightly
delayed. Originally scheduled to
begin in February (see SILICON
CHIP, January 1988 issue, page 11),
they should be under way in
Sydney by the time you read this
issue.
The transmssions are in narrowband FM on 151MHz. We are
gratified to report that the
transmitters being installed in locations around Australia are all
designed and manufactured in this
country. The receivers also have
been designed in Australia but will
be manufactured off-shore.
Magnetic fields may be hazardous
According to a recent report
in IEEE Spectrum there is growing concern in the United States
about low level magnetic fields.
For some time there has been
concern around the world about
the health effects of high intensity electric fields, as radiated by
high voltage power lines.
Although no state has regulations on magnetic fields, six
states have regulations regarding exposure to electric fields
from high voltage power lines.
Now attention is shifting to the
4
SILICON CHIP
possible effects of low level
magnetic fields and the National
Cancer Institute is likely to start
a large scale study of childhood
leukemia and the possible part
played by magnetic fields.
At present no domestic electric appliance has been fingered
as a source of magnetic field exposure although at least one US
researcher is inclined to
discourage the use of electric
blankets by young children.
Some researchers are cautioning
that prolonged exposure to
magnetic fields 'may' cause
cancer.
In Australia, most authorities
warn against children using electric blankets anyhow but not for
any risk of leukemia. Young
children do not have well a
developed ability to regulate
their body temperature. If they
are placed on electric blankets
there is a strong risk that their
body temperature will rise to
dangerous limits. If not caught
quickly, this can lead to convulsions and ultimately, death.
The Singing Detective
now available on LP
Many readers will have no doubt
watched the six part series of "The
Singing Detective" which was
televised by the ABC during
December and January. The series
was notable for its clever dialogue
and the way in which old songs
were reworked as the hallucinations of Philip Marlow; Marlow is a
psychological case suffering from a
horrible skin disease.
In a touch of marketing brilliance, the ABC had the record
of the music on sale before
Christmas and many must have
been sold, to thousands of keen
viewers. Alas the music sounded
better over the television than it
does on a hifi system. No doubt the
music has much more impact when
backed up by the brilliant choreography of the show but the sound
quality is marred, as the sleeve
notes admit.
· How much better might it have
been if it had been re-mastered by
Australia's noted specialist on old
recordings, Robert Parker? And
wouldn't it have been better still if
it had been available on compact
disc?
Shonky fast
nicad charger
One of the shonkiest products
we've seen to date came on the
market late last year. It's a fast
charger for nickel-cadmium batteries and specifically intended for
recharging AA cells for radiocontrolled model cars and toys.
Now the whole subject of fast
charging nick.el cadmium batteries
is a controversial one. Mostly the
manufacturers and distributors of
nicad cells don't want to know
about it. They know that lots of cells
are being fast-charged but they
warn that cell life will be reduced.
Our enquiries lead us to believe
that fast charging is OK provided it
is done carefully. The charger must
have a timer or some means of sensing the cell voltage or cell
temperature. If the cells are left on
a high charge rate after they are
fully charged they are certain to be
ACS services project a big market
This is the ACS adaptor module described in SILICON CHIP in January
1988. It can be fitted to just about any FM tuner.
Since reporting in our January
issue about the authorisation of
ACS subcarrier transmissions
for FM stations, thfh'e have been
a number of interesting developments. Besides the ABC in
Sydney, a number of other
metropolitan stations have taken
out or are in the process of applying for licences. In Sydney,
2MBS-FM is broadcasting stock
exchange information (using a
digitally encoded transmission)
while 2SER-FM also has an ACS
encoder installed and is in a position to start broadcasting. Stations in Brisbane and Perth also
have encoders installed.
The biggest market for ACS
transmissions looks like being for
racing information. We would
assume that it will be a corndamaged. But with these provisos,
fast charging is safe and practical.
Well it is one thing to have a fast
charger which controls the rate of
charge and then disconnects the
cells after a certain time or after a
certain voltage has been reached.
This latest product is something
else. It just uses a 12V 120mA DC
plugpack feeding an 8-cell holder.
There is no current limiting other
than the natural limit of the
plugpack itself, no timer and no
voltage cut out. In a word, it's
crude.
plementary service to that
already available on Teletext.
Early market projections give a
potential demand as high as
100,000 receivers.
And here is an interesting
wrinkle. The Department of
Transport and Communications
will be charging the provider of
ACS services a licence fee for
each receiver in use. And you
thought licence fees were a thing
of the past. The catch is that ACS
(Ancilliary Communications Service, known in the USA as SCA,
Subsidiary Communications
Authorisation) is a special service not intended for normal
public service.
Note: SILICON CHIP published
an ACS decoder for FM tuners in
the Januai:y issue.
Now maybe the internal impedance of the AC plugpack will
limit the current through the cells
to a safe value but maybe it won't.
The blister pack instructions tell
you to charge the cells for three to
four hours and they warn against
over-charging. But what happens if
you put them on charge in the afternoon and then forget them until the
next day? We hate to think.
We would be very wary about
any charger that does not have a
timer or some other cut-out system
to stop charging.
M ARCH 1988
5
By HOMER L. DAVIDSON
NEW LIFE FOR
RADIO-CASSE'I*I'E
PLAYERS
Ghetto-blas.ters and portable cassette players can
sound awful after a few years. Here's how to
bring back the good sound.
Everything with moving parts runs down with age.
When it comes to electronic equipment, the sound gets
fuzzy and distorted, power drops off and so on. After a
while you might be considering dropping the whole lot
in the bin and then lashing out on a new one. But it
doesn't have to be. You can resurrect most portable
audio gear without being a servicing genius.
Of all the gear that suffers the ravages of time and
use, the portable "ghetto-blaster" suffers the most
because it's always in harm's way. If it's not getting
bounced, dropped, or fried in the boot of a car, it's getting beach sand in the tape drive and rain in the
speakers.
A few simple adjustments and repairs are often all
6
SILICON CHIP
it takes to make sluggish portables come back to life.
And keep in mind that a few simple repairs early
enough can prevent an expensive repair later on.
With the cost of servicing the way it is nowadays, it is
better to do preventative maintenance now rather
than having to discard it later on because a repair job
is too expensive to be worthwhile.
Here are a few easy-to-make repairs that can be
done by just about anyone who can tell one end of a
soldering iron from the other.
Dead -
Nothing
Perhaps the most common fault in a portable player
is that it will appear to be dead when you turn it on.
Inspect the dial drum (4) and the plastic pulleys (1, 2 3)
if tuning problems are encountered. If necessary, '
restring the dial-cord assembly. Make sure that the dial
pointer moves in the correct direction as you rotate the
tuning knob.
Check the power supply's silicon diodes when there's
no sound, or no tape movement. When tested with an
ohmmeter, a leaky or shorted diode will indicate a low
resistance measurement in both directions.
This is often after a period of weeks or days when it
hasn't been used. This is where your powers as a
detective come into play.
To determine if a portable stereo cassette player is
dead only when connected to the mains power, try
switching over to battery operation. Suspect a defective mains cord or plug if the unit operates on batteries but not from the mains power. Try another cord,
if handy. Sometimes the power cord of your electric
shaver will fit the two-pin mains socket on the player.
Don't force it though as you may damage the socket.
Check the continuity of the mains cord by testing it
with the ohmmeter function of your analog or digital
multimeter. If the cord tests OK, check the mains onoff switch. Often these are slide switches of dubious
quality and their contacts become sloppy after a few
years.
If the switch is OK check the silicon diodes used in
the power supply. Look for breaks or burn marks. You
may find two or four diodes wired as a full-wave or
bridge rectifier circuit. On a normal diode a low
resistance should be found in only one direction. If 'the
diode also shows a reading in the other direction (ie,
with the test leads reversed), remove one end from the
printed circuit board and repeat the test. If it still
shows a reading in the reverse direction, the diode is
leaky and should be replaced.
the battery compartment and terminals, and from the
printed circuit board. It is important to remove every
trace of electrolyte because it really can cause serious
corrosion damage. If this corrosion is allowed to go too
far, the player will have to be tossed out.
Clean up each battery contact with emery paper until they are sparkling clean.
Before installing new batteries, polish their end
caps to make sure they are thoroughly clean. Make
sure that the polarity of each battery is correct, as you
insert it. If the player doesn't operate with a new set
of batteries, check the total voltage at the battery terminals with your DMM when the batteries are under
load - ie, when the radio or tape player is turned on.
If the batteries are new and the voltage is seriously
down on what you'd expect, you may have a more
serious fault in the player.
If the player works but doesn't sound brilliant,
Dead When Battery-Powered
Make sure that the radio plays when mainspowered before checking for poor batteries. One dead
or several weak batteries can prevent proper operation; the sound may distort or the tape may run at a
lower-than-normal speed. Inspect the battery terminals for dirty or corroded contact areas.
Sometimes, when the batteries are left in the player
for a long time they will leak and seriously corrode the
battery terminals. If the batteries have leaked,
thoroughly clean all traces of battery electrolyte from
A dirty play/record or function switch can cause
motorboating and erratic or intermittent operation.
Spray contact-cleaning fluid inside the switch area and
work the switch back and forth a few times to clean the
contacts.
MARCH 1988
7
around the pulleys and back to the drum (using masking tape to hold the dial cord on the pulleys until finished). Attach the free end of the cord to the small spring
sticking out of the drum. Then pull on the cord to
slightly stretch the spring before securing the cord
with a knot.
Place a dab of glue on each end of the dial cord to
prevent it from unraveling after you're certain that
the drum is rotating in the right direction.
Erratic Operation
A loud popping noise, motorboating, or intermittent
or erratic operation may be caused by a dirty function
switch. A loud squealing noise may be heard when in
the record or play mode of a cassette recorder if the
function switch is dirty. To clean the switch, spray
contact-cleaning fluid on the switch's contacts, then
move the switch back and forth a few times to clean
the contacts. Do the same with other dirty switch contacts, or a dirty (noisy) volume control.
Slow speeds can be caused by a dry or worn rubber
pressure roller (3), gummed spindles or drive motor (4,
5, 6), very dirty heads (1, 2), or a dry or gummed
counter (7).
maybe the batteries are due for replacement. Most
portables will perform reasonably well provided the
battery voltage is at least 75% of the nominal value.
For example, if your portable has four 1.5V cells giving 6V, you can expect it to give reasonable sound
down to about 4.5 volts. Below that it probably will
still work but it will sound yuck. Replace the batteries.
While on the subject of batteries, it is a good idea to
use alkaline cells instead of carbon zinc batteries.
Alkaline cells give longer life and their generally
lower internal impedance can help the portable's
amplifiers to deliver better sound quality.
Keep The Dial Cord On Track
Check for a broken dial cord, or a dial cord that's
slipped off a pulley, when stations can't be tuned in or
the dial pointer won't move. Remove the back or front
cover to get at the dial-cord assembly. Most of the
larger portable players can be inspected internally by
removing several Phillips-head screws located in the
back cover.
Inspect the dial cord for a break or slippage.
Sometimes the plastic dial-cord pulleys break loose
from their plastic bearings and allow the dial cord to
lie loose. Repair the pulley's plastic bearing by
substituting a metal screw (use a small screw that fits
inside the pulley area).
To do that, first make a sketch of the dial-cord
stringing, then remove the dial cord. While holding the
damaged pulley in the correct position, apply heat
from a soldering iron. When the plastic softens, press
the screw into the plastic and let the assembly cool.
Then restring the dial cord.
To restring a broken dial cord, draw a rough sketch
showing where the cord passes around each pulley
and the drum that's attached to the tuning capacitor.
Select a piece of dial cord 30cm longer than necessary
and tie one end to the drum. Then route the cord
8
SILICON CHIP
Slow Speeds
Incorrect tape speed, or no tape movement at all,
can be caused by tape that's wrapped itself around
the , capstan drive shaft, or an old, dry capstan
pressure roller, or a defective motor. Inspect for tape
wrappage around the pressure roller or its bearing.
Also inspect the capstan by rotating it with your
fingers. Notice if the capstan/flywheel seems to drag,
indicating dry or gummed bearings. Suspect a defective motor if the capstan appears to be free.
Rotate the motor pulley with the cassette player
turned on. Sometimes, a dead motor starts if this is
done, indicating that its operation is intermittent.
Measure the voltage at the motor's power supply terminals if the motor appears to be dead. No voltage indicates poor wire connections or a dirty off-on switch.
If the motor proves defective, replace it with a unit
having the exact same part number.
A Good Cleaning
A dirty tape head may produce weak volume, or a
A dirty tape head can cause weak sound, distortion, or
a noise in one or both channels. Check the erase head
for excess oxide that may prevent full erasure of a
previous recording.
dead or noisy channel. Use a cotton bud saturated in
alcohol to clean the record/replay head, erase head,
capstan, and pressure roller. Deposited tape oxide appears brown or shiny-black in colour, so remove
anything that resembles those colours from the
pressure roller and tape-head surfaces. (Those parts
usually can be cleaned through the front loading
area).
Clean off the oxide each week if the portable is
operated continuously. A cleaning cassette can also
be used to help keep the tape path clean. When the
plastic cover is removed to make other repairs, clean
up all oxide from the chassis and mechanical areas
with a cleaning stick soaked in alcohol.
A Loud Rushing Noise
Suspect a broken tape-head lead, its connection, or
an open tape head when a loud rushing noise is heard
on either channel of the cassette player. Often, the
tape-head wires will break off right at the connections. After you make the repair, make sure the tapehead cable is flexible and moves freely with the tape
head.
Check the tape-head windings for continuity by
switching your DMM to the 2k-ohm range. Compare the
measurements with the resistance readings of a tape
head known to he in good condition.
Usually, a stereo tape head will have four connections
for two separate windings.
Compare both stereo windings. They should be quite
close in resistance. An infinite resistance reading indicates an open winding. A very low or zero resistance
measurement may indicate leaky or shorted turns.
Check the resistance between the head's high terminal and the chassis ground because it's possible to
find leakage between the metal shell and a tape-head
winding. Push or pull the tape-head terminals with the
DMM leads attached. Sometimes an intermittent connection will show up when you do this. The continuity
of the erase head may be tested in the same manner.
Tape Spillout
A loud, rough noise may be produced by an open-circuit
tape head (1, 2) winding or because the wires have
broken loose from the tape head terminals. Turn the
volume up to determine if the noise is in one or both
speakers. Often the dead or defective channel is
indicated by the VU meters (if so equipped).
Recordings that sound jumbled can be caused by a
defective or dirty erase head. First, remove (clean) the
oxide from the erase head and then try making
another recording. Suspect an open erase head or circuit if the previous recording isn't erased. Make sure
that you check the wiring connections at the rear of
the erase head.
Checking The Record/Play Head
The record/play tape head can be checked with a
DMM. First, inspect the tape head's connections, then
make a low-ohm continuity test of the tape head.
Tape drag or spillout can be caused by a dirty or
worn pressure roller, an erratic or slow take-up reel,
or a defective cassette. Most tape spillout problems
are caused by erratic operation or non-rotation of the
take-up reel. While drag causes wow and flutter - or
gurgles [as if the tape were playing under water) spillage allows the tape to come out of the cassette and
foul any of the rotating mechanisms. Whatever it gets
into, the tape outside the cassette gets damaged permanently.
Often, erratic operation is caused by dirt that has
become sticky over a period of time. Clean up both reel
spindles with alcohol and a cotton bud. Also, check the
hub for gummed or dry bearings. To inspect the bearing area, remove the "C" washer at the top and pull
the hub off. A single drop of oil on the bearing might
help. Also, notice whether the take-up reel rotates
smoothly.
Other checks
In some models, a spider ring inside the plastic turntable is rotated to a higher speed to apply more
pressure to the take-up reel. Rotate the spider ring for
greater pressure and check the take-up adjustment.
Don't forget to check the rubber pressure roller for
wear, or for any sticky substance that can cause tape
MARCH 1988
9
spillout. A binding tape-counter assembly can cause
tape drag (slower speed). Most important, don't
assume that the cassette's shell is good because it
looks good. A slight warp, unnoticed by a quick glance,
can cause tape drag, spillout, or total lock-up.
Intermittent AM or FM
Go directly to the AM-FM selector switch when
either band is erratic or intermittent. Often, a dirty
AM-FM selector switch prevents FM stations from being tuned. Locate the switch and spray contactcleaner fluid inside the contact area. Spray into the
end area of a slide-type band switch. Move the switch
back and forth to work the cleaner into the contacts.
Also, inspect the switch's terminal wires for broken or
poorly-soldered connections.
Intermittent Sound
Intermittent sound can be caused by a defective
speaker, earphone jack, or amplifier section. First,
check for the intermittent sound on both radio and
tape operation. If the sound is intermittent on both,
suspect a defective speaker or amplifier. Connect an
external speaker to determine if the radio's own
speaker is intermittent.
Suspect a defective earphone or jack cable when
the sound is intermittent only for earphone operation.
Flex the earphone cable to test for loose or broken
wires. Inspect the male plug to check for possible poor
contacts or broken internal connections. Check the
female jack for poor wire connections. A bent, dirty,
or shorting earphone jack can prevent speaker
operation.
Distorted Sound
Weak and distorted sound may result from a faulty
Tape pulling or spillout may be caused by a jammed or
slow take-up reel or turntable. You should also suspect
a broken belt or a drive pulley that isn't engaging the
take-up reel.
10
SILICON CHIP
If the sound is noisy or distorted, check for foreign
objects poked into the speaker's cone (1 and 2). Also,
check the speaker's terminals for poorly soldered
connections. Always replace a defective speaker with
one that's the same size and impedance.
audio power amplifier integrated circuit or the
speaker. Determine if distortion is only from one
speaker channel. Inspect the body of the integrated
circuit for indications of overheating.
Keep in mind that a problem in the audio power
amplifier can disable the entire audio section because
the preamplifier, booster and output stage might be
part of a single integrated circuit.
Comparison voltage measurements can isolate a
leaky or open power amplifier IC. If the radio or tape
player uses two of the same kind of integrated circuit,
measure the voltage on the same terminals of similar
devices for comparative voltage measurements. If the
voltages vary by a few volts or more, suspect a faulty
IC.
A channel may appear dead, weak, noisy or
distorted if its speaker is defective. Exchange the
wires of the suspected speaker with those of the other
channel.
You can even connect another speaker across the
suspected one with test leads to determine if the
speaker, earphone jack contacts, and the amplifier
are working. In fact, a speaker with leads can be used
to signal trace the sound from the audio power
amplifier's output capacitor to the dead speaker.
A distorted or noisy speaker may have foreign objects poked into, or adjacent to, the speaker's cone. Inspect the speaker's terminals for poorly soldered connections. Replace the defective unit with one that's the
same size and has the same impedance.
Before you replace the cover, check the dial-cord
movement, clean the tape heads and switches, and
possibly replace the batteries. Make certain the each
lever or pushbutton of the cassette player is working.
Clean up the whole cabinet with a common
household window spray after replacing the covers.
Replace all the knobs. If you have the equipment pressurised air in cans or from a compressor - spray
a jet of air into the corners and brush out the dirt with
a small paint brush.
·! c
Adapted by arrangement from an original article which appeared in HANDS ON ELECTRONICS. Copyright (c) Gemsback Publications, USA.
VOOD FOR CHIPS ..• WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR C
TRIMPOT COVERS
CARD EDGE
CONNECTOR
SPECIALS
.~-~
Wouldn't it be handy if you could mount a
rectangular multi-turn trimpot on a front
panej? Well you can with a trimpot cover.
Only $2.00 and you'll need a trimpot tool
to adjust it with . This handy little gadget is
just like a pen and has a blade at each end.
One end is specially designed so it can't slip.
Well worth $2.00 .
IBM PRINTER
CABLES
Available in two lengths - 1.8m and 4m. Both
have quality connectors each end. You
couldn't make one for the price!
1.
.95 4m 3
SHORTING LINKS
Take your pick of these three 0.1" pitch
Card Edge Connectors Genuine 3M brand IDC 50 way
or Belgian made Franelco Wire Wrap in 62 or
86way
An unrepeatable bargain at only $13.95
ear::h.
ONLY
$1.00
KEYBOARD
SWITCHES
Ideal for programming and test linking on
circuit boards , these links have a standard
0.1" spacing . Contact is partially exposed for
touching a probe on. Packet of ten $2.95.
23 PIN 'D'
CONNECTORS
j
Building your own keyboard? Then here's the
ideal switch . Single momentary make
contact. Complete with ivory key cap.
What a bargain at Only $1 .00
No it's not a misprint - there are now 23pin Dconnectors on some of the newer PC's. So if
you're finding it hard to get plugs and
sockets to match, Geoff of course has 'em.
Male, Female and Backshell all the same
price $3.50.
TRIMMER
CAPACITORS
Miniature circular type only 6mm diameter
and 5mm high. 8 types to choose from 2 to 16pF, 3 to 11pF, 3 to 225pF, 4.2 to
20pF, 5.2 to 30pF, 6.8 to 45pF, 10 to 120pF,
60 to 160pF. All $1.50.
DIP SWITCHES
Geoff carries a wide range of DIP switches
including a rotary type . Ch ec k yo ur
requirements :
Conventional - 2way 60c, 4 way $1 .75,
6 way $2.30, 7 way $2.40, 8 way $2 ,50.
Right Angle 8 way $4.00
Rotary 8 way $5.50
NATIONAL 32000
DESIGNER'S KIT
Geoff has had to order two consignments of
these kits in since we advertised them . They
are only suitable for advanced computer
hobbyists and professionals.
Two versions - one with 32016, the other with
a 32032. Both have a 32082 Memory
Management Unit, a 32201 Timing Control
Unit, a 32081 Floating Point Unit, 1 32202
Interrupt Control Unit and two "Tiny
Development Systems" (TDS) PROMs.
That's seven chips altogether.
There's a massive pack of literature
including a databook 40mm thick, a 20mm
thick instruction set reference manual, a
TDS user guide, a programming reference
guide, application notes on UNIX , 32 bit
architecture and even a PASCAL li sting to
aid development of 32000 code using a PC.
To top it all off there's an article reprint from
the US on a UNIX co-processor for under
$US400II
These are definitely not for beginners but
wha! a great buy - 32016 kit is just $132.
The 32032 costs $180. (P&P $6.00 local or
$ 15.00 airmail - it"s a big packl)
Contact
Geoff
for
all
your
semiconductor
and
IC
requirements.
Our
range
ts
constantly expanding.
Always
remember
to
call
"Wood
for
Chips!"
MULTI-TURN DIALS
If you use multi-turn potentiometers you
need these beaut Dials
10 turn Digital Multi-Dial has three digit
readout. One turn of the knob gives a count
of 100. Resolution to one fifth of a digit
graduations! Measures approx 45x25x25mm
(inc knob). Incorporates lever action locking
mechanism. $36.50.
Circular Multi-Dials have 50 graduations with
turns counter which goes up to fifteen turns .
Available in two sizes 23mm and 46mm
diameter. The smaller one 1s ideal for
cramped panel layouts.
23mm $24.00 and 46mm $36.50.
THUMBWHEEL
SWITCHES
~
~
Cl:
0
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Cl
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~
These are genuine C&K high quality.
Avai lable in decimal or BCD format. PCB
edge .connector or solde r leads on directly.
Both types are $6.85 each . End plates are
$3.80 a pa ir and screws are $1 .40 a pa ir.
They com e in sizes dependi ng on num ber of
wafers 1- 3 or 3 to 7. Please specify when
ordering.
~
8.30 to 5 Monday to Fnday 8.30 to 12 Sat.
Mail Orders add $5.UO to cover postal charges.
GEOFF WOOD ELECTRONICS P/L
Q::
All prices INCLUDE sales tax.
(02) 427 1676
D
0
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Cl
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Tax exemption c ertificates accepted ,1 llne value
exceeds $10.00.
BANKCARD, MASTERCARD. VISA, CHEQUES
OR CASH CHEERFULLY ACCEPTED
==--fl.::::::oc::=====
i
•o
! ~.~.:"'
INC IN NSW
229 Burns Bay Road (Corner Beatrice SI)
Lane Cove West N.S.W.
P.O.Box 671 , Lane Cove N.S.W.2066
Fax: (02) 428 5198
specialising in electronic components for the professional and hobbyist.
The early days of radio were
exciting times. Inventors
leapfrogged each other with
new developments and the art
progressed to a science in a
very short time.
By JOHN HILL
Some time ago I wrote a couple of articles on the
subject of vintage radio. Both stories delved into the
joys and tribulations of collecting and restoring old.
valve radio sets.
These articles were very well received by readers
and it was pleasing to know that there were others doing what I'm doing. It doesn't matter how obscure
one's hobbies may be, there are always others interested in the same things.
So once again I pick up the pen to write about my
restorations. This time my stories will be more detailed, and each article will deal with a specific aspect of
collecting and restoring vintage radios.
However, before commencing on this series of
useful articles, I thought it appropriate to discuss
briefly some of the more interesting developments that
lead up to the science of radio a§! we know it. today.
Many of the things that we now take for granted in
this modern world of ours began life in such a crude
way that it is quite amazing that they were ever considered useful. Radio had such a beginning. In the early days, spark transmitters and coherers were used
solely for Morse code transmission and reception the equipment was incapable of transmitting or
receiving speech or music.
Early experiments
Heinrich Hertz was the originator of the spark
transmitter and, in 1888, discovered that signals could
be transmitted to a receiver without the use of connecting wires. The equipment that Hertz used was extremely simple and very short ranged; in fact, the
12
SILICON CHIP
transmission range was within the space of a single
room! How often great discoveries have such humble
beginnings. Although Hertz didn't know it at the time,
he had discovered radio waves. These invisible waves
were soon to be referred to as "Hertzian waves".
Hertz' transmitter was simply a large Leyden jar
(an early type of capacitor) connected in series with a
coil of wire and a spark gap. When the charged
capacitor discharged across the gap, radio waves
were produced by the coil which acted as a transmission aerial.
The receiver consisted of a similar coil connected to
a considerably smaller gap. When the crude transmitter sparked, a corresponding spark was reproduced at
the receiver gap.
Now those early pioneers of radio were no fools.
Hertz soon calculated the speed of his Hertzian waves
and determined that they travelled at exactly the
same speed as light which had already been determined with reasonable accuracy by 1849.
The limiting factor of Hertz' equipment was that it
would only work over very short distances of a few
metres. If these Hertzian waves he had discovered
were to be useful at all, it would require considerable
improvement to both transmitter and receiver.
The first receiver refinement was the development
of the "coherer" in 1892. A number of inventors can
lay claim to several versions of the device but the
Frenchman Edouard Branly developed the type of
coherer that Marconi successfully used in his early
radio experiments.
Compared to modern radio receivers, the coherer is
incoming signal would automatically activate the
decoherer and the recorder.
Marconi
Collecting and restoring vintage radio sets is a
fascinating hobby. This old American Silvertone is
missing most of its veneer but still has its original dial
(complete with tuning eye) and all its original knobs.
the ultimate in crudeness. It consisted basically of a
small glass tube containing two metallic plugs (usually
silver) that almost met in the middle, leaving about a
one millimetre gap. In this small area was placed a
mixture of zinc and silver filings (although Marconi used nickel and silver because it was more sensitive).
When the coherer came under the influence of Hertzian waves, the filings in the gap would cohere (stick
together, just as iron filings do when under the influence of a magnetic field). Unfortunately, the filings
would stay that way after the signal ceased and the
device had to be tapped with a pencil or like instrument to settle the filings ready for the next signal.
The big coherer breakthrough came about when a
Russian by the name of Popoff invented a device for
"decohering" the coherer. Popoff's invention
employed an electric bell-like mechanism that kept
tapping the coherer.
The coherer had the unique ability of being a conductor when cohered and a non-conductor when
decohered. When properly set up with a battery and
relays, it would operate telegraphic recorders such as
a Morse sounder or a Morse inkE;ir. The latter instrument put the dots and dashes on a strip of paper. An
This early two-valve receiver is the Marconiphone V2A,
made around 1923. (Photo courtesy Orpheus Radio
Museum, Ballarat).
Guglielmo Marconi, an Italian, was the next person
of importance on the radio scene and he is often given
the credit for inventing radio communications. In actual fact, Marconi invented very little but had the happy knack of improving and adapting other people's inventions for his own benefit.
In 1895, Marconi broke new ground with a successful transmission over two kilometres using
Branly's coherer and Popoff's decoder. For this he
was granted the first English patent for Wireless
Telegraphy.
Marconi soon improved his equipment and set a
new record when messages were transmitted and
received between two British warships that were
some 20km apart.
At the tender age of only 23 years Marconi formed,
with the backing of some wealthy English
businessmen, The Wireless Telegraph and Signal
Company.
A vintage Martin radio. The compartment below the
control panel housed the receiver's batteries. (Photo
courtesy Orpheus Radio Museum).
In 1899, Marconi (again using someone else's ideas,
in this case, Sir Oliver Lodge) incorporated tuned circuits in .his wireless equipment and patented the idea
in 1900. This was a significant step forward as it
helped reduce interstation interference.
By this stage, the range of Marconi's radio was
around 120 kilometres and wireless equipment was
mainly used for ship to shore contact. An amateur
radio enthusiast during those days could spend the
night staring at the coherer of his homemade receiver, hoping to pick up a signal from a passing ship. Imagine the excitement he would experience
if the filings in his coherer suddenly stood to attention
as a signal was received. If he knew Morse code, he
could even decipher the message.
American contributions
The Americans also contributed well to early radio,
although they were a bit slow off the mark. Two of the
MARCH 1988
13
Vintage Radio
more prominent names on the other side of the Atlantic were Reginald Fessenden and Lee De Forest.
Fessendon thought more along the lines of radio
telephony as opposed to Marconi's radio telegraphy.
To this end he dabbled with high frequency alternators in order to experiment with continuous wave
transmissions. He also developed an electrolytic
detector which actually rectified the incoming constant wave signals.
De Forest also developed an electrolytic detector
which caused much conflict between he and
Fessendon.
The electrolytic detector consisted of a small cup of
dilute acid into which a silver wire was dipped. It was
similar to the crystal and cat's whisker detector which
was yet to be discovered. The electrolytic detector
was far more sensitive than the coherer and had the
ability to rectify incoming radio-frequency signals.
Meanwhile, back across the Atlantic again,
Englishman Ambrose Fleming had been experimenting
with his two-element valve. He found that its diode
characteristic could be used to rectify or detect radio
signals.
It is interesting to note that Edison had observed the
one way characteristic of the diode (the Edison effect)
some years previously, but it was Fleming who found a
use for it.
This Polle Royale is an American 5-tube battery set
from the mid-1920s. It employed three tuning controls
and a staggered valve arrangement.
While De Forest, Fleming and Edison were of the
same era and all experimented ,,vith crude diodes,
they should not be thought of as inventors of the
device. Observation of the Edison effect goes back a
long way.
In 1725, Duffay discovered that if one or two closely
spaced insulated metal spheres was heated, a current
carrying path was formed between them. So the thermionic diode goes back two and a half centuries.
Edison's experiments centred around removing the
dark coating that attached itself to the inside of his incandescent lamps. He figured that a plate inside the
glass envelope could prevent that from happening.
Strange that a hundred years later the same problem
still exists in incandescent bulbs.
The Audion
The inclined basket coils in this glass covered custommade receiver indicates that it employs a Neutrodyne
circuit. (Photo courtesy Orpheus Radio Museum).
Fleming's diode was a glass envelope containing a
filament (cathode) and a plate (anode). Those· unfamiliar with vacuum tube operation may appreciate
an explanation of its function. The glowing filament
emits electrons which form an electron cloud that
hangs around the general proximity of the filament.
However, if a positive charge is connected to the plate
by means of a siza]Jle "B" battery, the plate draws the
negatively charged electrons to it, hence the one way
flow. The negative of the filament ("A") battery and
the negative of the plate ("B") battery must be connected for this effect to take place.
14
SILICON CHIP
Unfortunately, Fleming's moment of glory was
somewhat short lived and insignificant compared to
what Lee De Forest was developing at the time. De
Forest's "Audion" valve was perhaps the greatest
single development in the history of radio.
De Forest's brilliant idea was to put a control grid (a
spiral of fine wire) between the filament and the plate,
thus making a 3-element valve. Varying the 9tate of the
charge on the grid controls the electron flow from
cathode to anode. When the grid is negatively charged
it repells the electrons back towards the filament and,
when positively charged, allows most of the electrons
to pass through to the plate.
.
Therefore, slight signal variations on the grid of De
Forest's three-element valve produced larger but proportional variations in the plate current. The Audion
not only rectified radio frequency signals but it
amplified them as well. It was later found that the new
valve could also be used in oscillator circuits.
De Forest's revolutionary discovery was a great
step forward in the development of radio and a whole
new era was about to start.
This short history of radio will continue next month
and will include the period that lead up to commercial
broadcasting in the early 1920s. After that, we'll start
collecting and restoring vintage radios.
BOOKSHELF
Servicing compact
disc players
Compact Disc Player Maintenance
and Repair, by Gordon McComb
and John Cook. Published 1987 by
TAB Books Inc, Blue Ridge Summit,
PA 17214. Soft covers, 235 x
188mm, 245 pages. ISBN
0-8306-2790-1.
This is a general book which
describes basically how a compact
disc player works, how discs are
made and simple maintenance. The
complex detail required for fullscale repair of all types of compact
disc machines cannot be included
in a single book.
The philosophy behind the information provided in the book is that
most CD player faults are due to
dirty switch contacts, broken connections, a dirty lens or disc problem. Major faults are best tackled
by a repair centre. Even if you cannot repair the fault yourself, you
will be far better placed to describe
the fault to the repair organisation.
There are ten chapters plus five
appendices. Chapter 1 discusses
the compact disc, its standards, encoding, manufacture and the types
of players~ Chapter 2 describes how
CD players work. This details the
IBM PC & XT
Reference Manual
IBM PC & PC XT User's Reference
Manual, by Gilbert Held. 2nd edition published 1987 by Hayden
Books, Indianapolis, Indiana. Soft
covers, 235 x 180mm, 479 pages.
ISBN O 672 46427 6.
Unlike most computer books,
which concentrate on software,
this manual also covers the hardware aspects of the IBM PC and XT.
Chapter 1 kicks off with a detailed
hardware overview of the two computers. The various customising options are also covered, along with
mechanical and electronic basics
such as focusing, digital-to-analog
conversion and the controls.
Chapter 3 covers CD specifications, including frequency
response, signal-to-noise ratio,
channel separation, phase, distortion, dynamic range and error
correction.
The next chapter discusses setting up the CD player for best performance. Chapter 5 is on tools and
other equipment necessary for CD
player maintenance. It discusses
multimeters, logic probes and laser
detectors. Cleaners and test discs
are also covered and the text even
tells you how to make your own error correction test disc. This section is an interesting concept but
descriptions of several cards that
can be plugged into the system expansion slots.
The next chapter gives a detailed
description of the system setup. It
covers on-board memory expansion, shows how disc drives and
adapter cards are installed and
describes how the assembled
system can be checked out. Chapter
3 concentrates of floppy dies and
covers such topics as data storage,
drive incompatibility and storage
capacity.
The remaining chapters deal
with the software aspects of the
IBM PCs, with detailed descriptions
of DOS {Disc Operating System) and
we won't give the game away in this
review.
The next chapter is on preventative maintenance and chapters 8
and 9 on troubleshooting. The
troubleshooting chapter contains
many flow charts to assist in
locating the fault. A lot of it is the
sort of commonsense servicing procedure that would be used for
repairing any piece of audio equipment but it is nonetheless valid for
all that.
Finally, chapter 10 gives details
on many popular CD players
although some have not been sold in
this country. There are a number of
appendices too with Appendix E being the most interesting. It lists the
specifications of a large number of
CD players which are or have been
available in the USA. Quite a few
have not been sold in this country
and, as might be expected, a great
many current models are not listed
because the book was compiled
before they were released.
Considering that there have been
such large number of CD players
sold, there is very little available on
servicing these complex products.
This book is very welcome for that
reason. Our copy came from Dick
Smith Electronics. (J.C.)
the BASIC programming language.
The chapter headings are as
follows: The Disc Operating
System, Fixed Disc Organisation,
BASIC Overview, Basic BASIC,
BASIC Commands, Advanced BASIC,
Data File Operations, Text and
Graphics Display Control, Batch
Process-ing and Fixed Disc Operations, Audio and Data Communications, and Introduction to TopView.
Finally, the book concludes with
four appendices: ASCII Code
Representation, Extended Character Codes, BASIC Error Messages,
Programming Tips and Techniques.
Our sample copy came direct
from the publisher. {G.S.)
MARCH 1988
15
HIFIREVIEW
Tandy's CD-1500 remote
controlled CD player
Compact disc players continue to become cheaper,
smaller and lighter. Typical of this trend is Tandy's
latest CD player, the remote-controlled Realistic
CD-1500.
Reviewed by LEO SIMPSON
Even though compact disc
players have been with us now for
five years we are still amazed at
their inherent complexity. Yet each
new model brings more refinements, whether in user facilities,
simplification in manufacturing, or
both.
This latest CD player from Tandy
is one of the smallest units on the
market, apart from those specifically intended for portable or car use.
It measures 370mm wide, 270mm
from front to back and 73mm high
and weighs just 2.9kg.
Inevitably, it has an all-black
finish; plastic front panel and a
painted steel chassis and cover.
The digital display is a very fine
white vacuum fluorescent unit, not
the rather coarse liquid crystal
display depicted in the current Tandy catalog. The display indicates
track, elapsed time and playing
mode. It also has provision on the
display for index information.
Controls
Playing controls are relatively
simple although there are eleven
pushbuttons in all. On the left is the
power button and adjacent to the
disc drawer is the open/close button. Underneath the display are
buttons for Auto Space, Repeat
Memory, and further to the right,
Track/ ASMS, index forward and
reverse. To the right of the display
is the play/pause button and below
that, the stop/clear button.
On the back, the chassis is bare
expect for a pair of RCA sockets
The remote control is supplied as standard with the
CD-1500 and duplicates most of the front panel
controls.
16
SILICON CHIP
and power cord entry. No headphone socket is fitted which is a pity really since we believe that many
people these days wish to listen to
their CDs direct on headphones,
without the need of a separate
amplifier.
Inside the chassis, the CD-1500 is
revealed as one of the simplest
players we have seen. It has the
smallest CD player mechanism,
made largely from plastic and with
a flexible multiway printed conductor strip coupling the digital signals
to the large printed board. This accommodates four LSI (large scale
integration) chips with one being a
surface mount type.
Other printed boards are provided for mains termination and the
mains switch (near the power
transformer) and the front panel
display and pushbuttons.
All told, it is hard to see how a CD
player could be made simpler
although future models will be just
that; such is the march of progress.
Playing it
Pushing the open/close button on
the CD-1500 extends the drawer
ready to accept a disc. The drawer
is different from most CD players in
that it pushes a door flap down as it
The interior of the Realistic CD1500 is neat and uncluttered and uses just four
LSI chips. The player mechanism is made mainly from plastic.
emerges, a difference which is not
important but a difference nonetheless. Pushing the open/close button causes the disc drawer to go
back into the player whereupon the
number of tracks and total playing
time are shown on the display.
Alternatively, after placing the
disc on the extended drawer, you
can push the Play button to initiate
playing immediately.
You can push the disc drawer in
by hand and it will withdraw by
itself although the instruction
manual warns against this. We
deliberately did it a number of
times to see if the mechanism would
jam but it didn't. We think this is
important because users will abuse
players in this way in spite of any
warning to the contrary.
An interesting feature is the
Auto-Space button. If this is pushed, a four-second interval is inserted at the end of each track. This
can be handy if you are dubbing
CDs to cassettes and wish to use the
automatic music search facility
now on a lot of cassette decks.
The Memory button allows the
playing order of the disc tracks to
be programmed before playing
starts. Up to 24 tracks can be programmed in this way. Pushing the
Stop/Clear button clears the
memory.
The next facility, Track/ASMS,
functions differently to that on
other CD players. Pushing the lefthand button during play puts the
Specifications
Audio
Frequency response
Dynamic range
Signal-to-noise ratio
Harmonic distortion
Separation
Line output at 0dB
5Hz-20kHz, ± 1 dB
90dB
90dB
.006% (at 1 kHz)
90dB
2V RMS
Signal format
Sampling frequency
Quantisation
Transmission
44.1 kHz
1 6 bit linear
4 .3218 Mb/s
laser pickup back to the start of the
track being played whereupon playing recommences. Further pushes
put the pickup back to subsequent
tracks. Pushing the righthand button moves the pickup to the start of
the next track so that play starts
there. So where does the ASMS
(Automatic Search Music System)
feature come in?
The owner's manual does not explain it except to give the explanation just described. It certainly does
not function in the way of
Automatic Music Selection on a
number of CD players we have seen
whereby they will play the first ten
seconds of each track until you stop
it. From the foregoing, we think the
ASMS designation is a misnomer.
The Index buttons were similarly
confusing. They function as skip
forward or skip back buttons but at
no time were we able to locate indexed points on discs using these
buttons. Nor were index numbers
ever displayed. The owner's
manual makes no mention of the Index facility so we are inclined to
the view that this feature was planned but left out in production
models.
One very worthwhile geature of
the CD-1500 is the remote control
handpiece. This duplicates the
front panel controls with the exception of the power, open/close and
auto space buttons. It has a range
of about five metres and uses two
penlight AA cells.
Performance
As the accompanying spec panel
shows, the CD-1500 is pretty standard. It uses a single D-A converter
and samples at the 44. lkHz rate.
Our tests confirmed the specifications pretty closely. For example,,
we measured harmonic distortion
at lkHz and 0dB at 0.007% versus
the specified figure of 0.006%. The
small discrepancy is due to the
residual 44. lkHz in the output
which is about 83dB down.
The frequency response is ruler
flat over much of the range but has
the usual small irregularities at the
extreme top which is the result of
the steep filtering used to remove
the 44 . lkHz sampling artefacts. It
also has the (inaudible) 24.lkHz
beat which is present when you atcontinued on page 89
MARCH 1988
17
LINE G
BER
FOR TELEPHONES
Don't put up with interruptions from
extension phones. When you pick up the
telephone, this simple circuit cuts the
extension phone(s) dead.
H ZHO~
©3VAO£Z
O!tl"
By JOHN CLARKE & GREG SWAIN
We all know what it's like to be in
the middle of a phone call and have
someone pick up an extension
phone and start dialling. Or do you
have young children in the
household who like to mischievously listen in? Or maybe you operate a
modem in parallel with your existing phone. Any interruption from
an extension phone during
transmission will result in garbled
data, which is annoying to say the
least.
This simple circuit solves those
problems. We've called it a "Line
Grabber" because that's exactly
what it does. When you pick up the
phone it "grabs" the line and cuts
the extension phones out. It makes
it impossible for someone else to interrupt from an extension phone.
18
SILICON CHIP
Any extension phone picked up
while you have your phone off-hook
will be completely dead and will remain so until your call is finished.
If another phone is then picked
up, that phone will then "grab" the
line and all the other phones will be
dead.
As far as incoming phone calls
are concerned, the same thing applies. The phones ring normally and
if you pick up the phone first, you've
got the call. The outside caller does
not perceive any difference in the
way the phone works though and
nor will you, apart from the complete freedom from interruptions.
The benefits are obvious: no
more eavesdropping, no more unwanted dial tones or clicks on top of
your conversation, and no more in-
The single version is designed for
installation inside the telephone, hut
can also be built into a plastic case
fitted with a telephone plug and
socket.
terruptions to data transmissions.
With the Line Grabber, the phone
line is exclusively yours until you
hang up.
Of course, if you want to transfer
an incoming call to another extension that can still be done. Just hang
up the phone you first took the call
on and then pick up the extension
- the incoming call will be there.
A separate Line Grabber circuit
must be built for each extension
phone. That sounds messy but the
circuit only uses a few cheap parts
so the overall cost will not be high.
We've produced two different versions so that you can choose the one
that best suits your particular
application.
The first version consists of a
single circuit built onto a small PCB.
This version could be installed inside the telephone itself (one for
each phone) and is used where the
phones are plugged into different
sockets. Alternatively, you could
build this single Line Grabber into a
zippy box, combined with a phone
plug and socket. Either way, you
will need two Line Grabber circuits
for two telephones, three for three
telephones, and so on.
The second version has two Line
Grabber circuits on a single PCB.
This is housed in a small plastic
case which is fitted with a
telephone plug and two sockets. It is
the logical choice where a
telephone and a modem are
operated in parallel from the same
socket. Additional single Line Grabber circuits can then be installed inside other extension phones as
required.
Circuit details
Fig.1 shows the circuit details for
a two-telephone system. Each sec-
The dual version has two Line Grabber circuits on a single printed circuit
hoard. This is the version to go for where two telephones (or a telephone and
a modem) are operated in parallel from the same socket.
tion uses a bridge rectifier and an
associated SCR (silicon controlled
rectifier) to provide a DC and an AC
path for the phone.
Diodes Dl to D4 form the bridge
rectifier for phone 1 while D6 to D9
form the rectifier for phone 2. Normally, when the phones are onhook, there is no DC path through
either phone and therefore the two
bridges and their associated SCRs
are effectively out of circuit.
Now let's take phone 1 off-hook.
When this happens, a DC path is
created through the phone. Current
then flows via the bridge rectifier
and SCRl and through the phone.
This allows you to either answer an
incoming call or dial for an outgoing
call.
Let's just look at that sequence in
a little more detail. Normally, when
a phone is on-hook, the voltage
across the phone lines will be about
50V DC. When the phone is taken
off-hook, DC voltage is applied via
the bridge rectifier and LED 1 to the
anode of SCRl.
At the same time, current flows
via the 100kQ resistor and zener
diode D5 into the gate of SCRl. This
gate current immediately causes
SCRl to conduct and allows current
to flow through the phone. So as far
A
4x1N43R4
2
A/BN
WHT
2
2
WHT
WHT
LINE
IN
0.1
8250VACI
PHONE 2
PHONE 1
GOBLUE
mrn
K AG
PHONE LINE GRABBER
KA G
SC12·1·488
Fig.1: each section of the circuit uses a bridge rectifier and an SCR to provide a DC and an AC path for the phone.
This diagram shows the details for a two-telephone system.
MARCH 1988
19
-.~<.:..-~;,;-\,)
PHONE
') , , C,
'~ , ·,.co c ·;
Fig. 2: parts layout for the single
version of the Line Grabber.
You will have to build one of
these for each extension phone.
The O.lµF capacitor is fitted to
the first board only and is omitted
from the rest.
· 20
SILICON CHIP
··.•.,(.',\(.
)
;·,0:1 " ' '
c :.> 250VAC , · c,
PHONE 2
Fig.3: follow this wiring diagram if
you wish to build the dual version.
It has two identical sections on the
one PCB.
The PCB for the dual version clips into the integral supports inside the case.
The leads from the sockets and plug terminate on the back of the PCB.
as phone 1 and the phone lines are
concerned, everything is normal.
There is an extra voltage drop
across the bridge rectifier, LED 1
and SCRl of about 3.5V but that
does not affect the operation of the
phone.
Now consider what happens
when phone 2 is lifted? Normally,
without the Line Grabber, someone
would be able to listen in to your
conversation on phone 1. However,
with phone 1 off the hook, the
voltage across the line is only about
10 to 12V. This means that no gate
current can flow via 18V zener
diode DlO to the gate of SCRZ and
so there is no DC path to phone 2.
C'
As far as phone 2 is concerned,
the line is dead. Phone 2 cannot be
used until phone 1 is hung up.
Similarly, if phone 2 is used first, it
kills the line to phone 1.
The LED associated with each
SCR is illuminated when the
associated phone grabs the line
(because of current flow via the
SCR).
That sums up the operation of the
Line Grabber as far as conventional telephones are concerned but
there are still a few wrinkles to consider. What about electronic
phones which always consume
several microamps of DC when they
are on-hook? The Line Grabber
Fig.4: the Line Grabber circuit can
also be built on Veroboard. Use an
oversize drill to make the cuts in
the copper tracks.
caters for this situation by providing a DC path through the bridge
rectifer, the l00kQ resistor, the
zener diode and the 2.2kQ gate
resistor of the SCR. This current is
not sufficient to trigger the SCR but
is does allow the circuitry in
pushbutton phones to · function
normally.
The only remaining component to
be explained is the 0.lµF 250VAC
capacitor across the incoming line.
This is intended to suppress transient voltages which could falsely
trigger the SCRs. For example, if
phone 1 is in use, a spike on the line
could falsely trigger SCR2 if phone
2 happened to be off-hook. This
would then place both phones on
the line, which would defeat the
purpose of the Line Grabber.
While it won't be obvious from
our circuit description above, an attractive feature of the Line Grabber
is that it causes no loading of the
phone lines when the phones are
on-hook. This is good because it
means you can build as many Line
Grabbers as you want, without worrying about line loading.
Building it
First, you must decide which version you are going to build. If you
build the dual version you will need
the large printed circuit board
which measures 60 x 46mm. The
smaller version measures 38 x
46mm.
Whichever board you use though,
you will need the same case. We used a plastic jiffy box from Altronics
r-
PARTS LIST
1 PCB, code SC12-1 -488-1,
60 x 46mm (double version)
1 PCB, code SC12-1 -488-2,
38 x 46mm (single version)
1 plastic case, 83 x 54 x
28mm (Altronics Cat No
H-0105)
1 telephone line plug
1 telephone line socket
Semiconductors
Fig.5: above are actual-size etching patterns for the two PCBs.
=.-I~.{1{1 j.'
Capacitors and Resistors
f,/:J·
PHONE LINE GRABBER
PHONE 1
e
e PHONE 2
Fig.6: full-size front panel artwork for the dual version.
measuring 83 x 54 x 28mm (Cat No
H-0105}. You can mount the phone
sockets on the base of this box
while the phone plug is wired to a
flying lead. The PCB is wedged into
the integral supports inside the
case, as shown in the photo.
The SCR is laid on its side as
shown in the photos. The LED pokes
out through a hole in the side of the
case.
You can also make the Line Grabber on Veroboard. We have shown
a wiring layout for a single version,
to fit in the same case. If you want
the double version just build two on
a wider section of Veroboard.
Assembling the boards should
present no problem at all. Just make
sure that you observe correct
1 C106D silicon controlled
rectifier
1 red light emitting diode
1 18V 400mW zener diode
4 1 N4004 silicon diodes
1 0.1 µ,F 250VAC metallised
polycarbonate capacitor
1 1 OOkO 0.25W resistor
1 2.2k0 0.25W resistor
1 1000 0.25W resis tor
Note: the above parts list is . for
the single version only, unless
noted.
Grabbers you build you only need
one 0.1µ,F 250VAC capacitor.
When you're finished the board
or boards, they need to be wired to
the sockets and phone plug. The
wiring is shown in the circuit
diagram (Fig.1}.
Checking it
This is what the Veroboard version
looks like. Take care - it's easy to
make a mistake with Veroboard.
polarity for the diodes, SCRs and
LEDs. You can leave the LED[s) out
if you wish. Just install a link in
place of the 1000 resistor(s).
Regardless of how many Line
What About the Off-Hook Indicator?
You may be wondering about the pros and cons of the Line Grabber as
compared to the Off-Hook Indicator circuit published in the N~vemb~r
1987 issue of SILICON CHIP . The Line Grabber has advantages 1n that 1t
is a simpler circuit and does not cause any loading of the phone lines . It
also stops eavesdropping and you can build as many as you like.
By comparison, the Off-Hook Indicator allows you to have more than
one extension in use at a time, when you want to have a 3-way con~ers~tion . It also tells you when any extension is off the hook which 1s
important.
It is possible to check the circuit
before you connect it to your
phones. You'll need an adjustable
DC power supply with an output of
20 volts or more. Connect the Line
Grabber to the power supply in
series with a limiting resistor of
several hundred ohms. Polarity is
not important because of the bridge
rectifier. Initially, no current
should flow.
Now short the connections between pin 2 and pin 6 on the Line
Grabber phone socket (for phone 1,
if you've built a dual version). Wind
up the supply voltage and observe
that the LED is illuminated once the
supply voltage rises above 18 volts.
If the LED illuminates at quite low
supply voltages it is possible that
you have reversed the polarity of
D5 (or DlO}, so that it is not working
correctly as a zener diode.
If current is flowing (you can
continued on page 93
M A RCH 1988
21
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1 a150
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K 6755
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Country Clients Please Allow Additional 48-72 Hours
~-------------------------------~
Dual Trace 20MHz Oscilloscope
This all new CRO must be the beat valued quallty Oscilloscope
In Australlal
This new model is a 20MHz dual-trace Oscilloscope using a high
brightness CRT with an illuminated scale. The vertical amplifiers have
high sensitivity 1mV-5V/Div. The unit has LED's to indicate when the
controls are in the 'uncal' postion, and to indicate if the trace has been
triggered . The brilliant triggering circuit will trigger on just about any
waveform applied. The highest triggering sweep is 0.2uSec/Div. The
Q 0120 also features a 'Hold Off' control for seeing the front end of the
input wave form.
Features: Large6" rectangularCRTwith internal graticule.• High
sensitivity: 1mV/ Div. • High accuracy: +or-3% • Stable, low-drift design
• 8 divisions of displayed dynamic range and accurate distortion-free
waveform measurements• This instrument has a special TV sync
separation circuit for quick measurements of video signals
• AconvenientX-Y operation mode allows phase difference
measurements between two waveforms.
Full 12 Months Warranty
CR O Probe Sets
High quality LABTECH
Oscilloscope probes. Ideal for use
with the Q0120 Oscilloscope. Suits
all other brands: 1:1 or 10:1
Attenuation.
Audio Frequency
Generator
Often in testing audio circuitry it is
necessary to have an accurate and
adjustable audio signal source
available. This little generator even
allows you to test 455KHz IF stages
Specifications: Freq.Range 10Hz 1MHz Accuracy +/-3% +2Hz
Output Waveform• Sine/ Square
Output Level Sine : 8V RMS
Square: 10V P-P Output
Attenuator -20db, -40db and fine
adjust.
RF Slgnal Generator
An RF signal generator is an
absolute necessity when it comes
to radio servicing. With provision
for both internal and external
modulation, this generator is a
winner.
Specifications: Freq.Range 1OOKz 150MHz in 6 Ranges RF Output
Level 100mV RMS Accuracy +/ -3%
Modulation:- Internal (30% depth)
1KHz • External - 50Hz - 20KHz
• Crystal Locked Oscillator
o1540 s249.oo
Q 0175
s49.es
..-~
Nifty Little Chassis
Maker & Pan Brak
Bender
Save Over 30%
ead Acid Batteries
igh performance batteries are
r systems where uninterrupted
quired i.e . Security Systems,
lar Power Systems etc .
T 2400 $
NOW
s8 0
/ ~leaee Note: This product is a
..,,:,: /
1
.,•,••••,·,•·•,·•,· 1
/
(
)
)
genuinePan Brake Bender
~~c~~:~
fs~ts:!~mi~;t~:~\~~7is
and is not to be confused with
inferior Non Pan Brake simple
benders currently sold by our
competitors.
Make Your Own
Chassis Boxes,
brackets,etc. Unique
slotted upper clamping bar
allows complex r,orner bends
Portable Multimeter With
Bench Stand
Normally
S 5065
12V/ 1 .2AH
S 5067
12 V/ 2.7AH
S 5069
12V/ 4.5AH
$22.95
$34.50
$45.00
Clock Movement
Fit your own custom clock face.
Great for novel applications such
as fitting to pictures etc. Very
accurate, runsforapprox.1 year on
tu:: : :
./ W.{
I:
t :C:fi
one AA battery.
Includes Continuity Buzzer
20,000 Ohms/Volt DC• 8 ,000 Ohms/Volts AC,
s18 ■50
X 1010
,,,,,_,,,:
]I ]
l:il
~;~obgai~~~~tc~~~;eo~~\~i: !:~~e~~eic11!0
doubles as a bench stand.
Includes Battery Tester
Free C a r ry C aae This Month Normally
: :i i:!
Q 1080
)I •!
New Model lf3D Has
Fantastic Range
$4.95
s3 9 .95
~~{~f~f.ft£l;~rn;1t~~:-~~7;
Economy Pocket Tester
1
~~.. ~:-.,.re_e_c_~_:_r:_m~__~_;_e$-~-~-~_'s_M•o•n•t•h-•$■-•1__9__
111 1
Infra Red
MD~~:~~~t
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<._:..• .•f.:.:,'.
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,hl·,1·ww®.·,,;:_e_._t_,.."· .·.•.·: '.·
.::.·.'..:,1.'.X·
:;.,mww ·""··
;
174 Roe St Perth WA 6000
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Perth Metro & After Hours (09) 328 1599
ALL MAIL ORDERS
P.O. Box 8350 Perth Mail Exchange WA6000
i•
1
~~Ea~~1\~:~i~i~n~~;:w~~fi
0
1~Vii~~!1lvji{~{~{~ii~%{fa:;~ff~e~~~
$10.00 HEAVY HEAVY SERVICE - All orders of 10Kgs or more must travel Express
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please request " Insurance".
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ALTRONICS RESELLERS
Chances are there is an Altronics Reseller right near yo u - check this list or phone us for
details of the nearest dealer. Pleaoe Note: Resellers have to pay the cost of freight and
insurance and therefore t he prices charged by individual Dealers may vary slightly
from this Catalogue - in many cases, however, Dealer prices will still represent a
significant cost saving from prices charged by Altronics Competitors.
Don't forget our Expre■ a Mall and Phone Order Service - for the coat of a local call,
Bankcard, VIH or Maatercard holdera can phone order for aame day deapatch.
More Altronlcs Dealers Wanted
If you have a Retail Shop, you could increase your income
significantly by becoming an Altronics Dealer,
Phone Fred Bloffwitch (09) 328 2199 for Details .
WA
COUNTRY ALBANY BP Electronics ■ 412681 ESPERANCE Esperance Communications 713344 GER ALD T ON K.B .Electronics &
Marine 212176 KALGOORLIE Todays Electronics ■ 212777 KARRATH A Daves Os ci tronics 854836 MA NDU R AH Lan c e Rock
Retravision 351246 NEWMAN Watronics 751734 WYALKATCHEM D & J Pease 811132
NT ALICE SPRINGS Ascom Electro nics 521713 Farmer
Electronics 522967
ACT CANBERRA Bennett Commercial Electronics 805359 Scie~tionics 548334 VICTORIA CITY Active Wholesale ■ 6023499
All Electronic Components 6623506 SUBURBAN ASPENDALE Giltronics 5809839 CHELTENHAM Talking Electronics 5502386 C ROYDE N Truscott
Electronics ■ 7233860 PRESTON Preston Electronics 484()191
COUN TRY BEND I G O KC Johnson ■ 411411 M O RW E L L Morwell
Electronics 346133 SWAN HILL Cornish Radio Services 321427 QUEENSLAND
CITY Delsound P/ L 8396155 SUBURBAN FO RTITUDE
VALLEY Economic Electronics 2523762 SALISBURY Fred Hoe & Sons Electronics 2774311 WOODRIDGE David Hall Electro.nics 8082777 COUNTRY
CAIRNS Electronic World ■ 518555 BUND A BERG Bob Elkins Electronics 721785 GL A D ST O NE Supertronics 72 4 32 1 MA C KA Y Philtronics
■ 578855
NAMBOUR Nambour Electroni c s 411604 PALM BEACH The Electroni c Centre 3412 48 ROCKHAMPT ON Access Electronics (East
St.) 221058 Electron
World 278988 Purely Electronics (Shopping Fair) 280100 Xanthos El ectronics 278952 T OO W OO MBA Hunts Electronics
■ 329677 TOWNSVILLE Solex ■ 722015 SA
CITY Electronic Comp & Equip. 2125999 Force Electronic ■ 2125505 SUBURBAN BRIGHTON Force
Electronics ■ 2963531 CHRISTIES BEAC H Force Electronics ■ 3823366 ENFIELD Force Electronics ■ 3496340 FIND O N Force Electronics
■ 3471188 PROSPECT Jensen Electronics ■ 2694744 COUNTRY
MT ,GA M BIER South East Electronics 25003 4 WHYALLA Eyre El ectronics
■ 454764 TASMANIA
HOBART Georg e Harvey ■ 342233 LAUNCESTON Advanc9d Electronics 315688 Geo rge Harvey ■ 316533 Nichols Radio
TV 316171
NSW CITY David Reid Electronics ■ 2671385 SUBURBAN BLAC KTO WN Wavefront Elect ronics 8311908 CAR IN GHAH Hicom
Unitronics 5247878 LEWISHAM PrePak
Electronics 5699770 SMITHFIELD Chantronics 609721 8 COUNTRY ALB UR Y Webb's
Electronics
■ 254066 COFFS H A RBOUR
Coifs Habour Electronics 525684 GOSFORD Tomorro w s Electronics ■ 247246 NE LS ON BA Y Nelson Bay
Electronics 813685 NEWCASTLE Novocastrian Elect.Supplies ■ 621358 NOWR A Ewing Electronics ■ 218412 RAYM O ND T E RRA C E Alback
Electronics 873419 TENTERFIELD Nathan Ross Electronics 362204 WINDSOR M & E Electronics ■ Communications 775935 WOLLON GON G Newtek
Electronics ■ 271620 Vimcom Electronics 284400
These Dealers generally carry a comprehensive range of Altronic products and kits or w ill order any required item fo r you.
I
Build this circuit and you can turn your
car's burglar alarm on and off by
pressing the button on a small keyring
transmitter.
By JOHN CLARKE
The main purpose of this project
is to add a remote control facility to
the Protector Car Alarm described
in February. Basically, it lets you
switch your car's burglar alarm on
and off from outside the vehicle,
simply by pushing the button on a
small keyring transmitter.
Apart from the obvious added
convenience, remote control offers
improved security (no need for hidden switches) and allows the
elimination of entry and exit delays.
All sensors can now be wired to the
instant trip input to give instantaneous alarm response to any attempted break in.
With this unit, you can customise
your burglar alarm to suit your own
needs, making it quite complex (as
presented) or quite a lot simpler.
For example, it gives you a choice of
piezo alarm or siren to tell you
when the alarm is turned on or off
and it will also flash the car's traffic indicators briefly when the
alarm is armed or disabled.
The circuitry presented here
could also be used as the basis for
any single channel remote control
application. It is simple to set up
and very reliable. The accompanying panel lists the main features. As
you can see, it's a very versatile circuit although the basic concept is
fairly simple.
ICl is a Motorola MC145026
trinary encoder. This uses a 9-bit
trinary code. Trinary code is like
binary code except is uses three
logic states instead of two. The
three trinary states used by this IC
are high, low or open-circuit. Only
one transmitter code word (one
9-bit word) is possible, as selected
by the connections to the IC's nine
address inputs, Al to A9.
In keeping with the trinary states
just mentioned, each of the nine address inputs can be connected to
the + 12V rail, to ground or left unconnected. In our application,
because of the particular decoder
used in the receiver, the A9 input
must be either connected to the
+ 12V rail or ground.
The 9-bit code word is sent as a
series of pulses from pin 15 of ICl.
The frequency of the pulses is set
by the two resistors and the
capacitor connected to pins 11, 12
and 13. For our circuit, the frequency is about 2kHz.
Transmitter
Main Features
The transmitter comprises a
digital encoder integrated circuit
(ICl) and a UHF oscillator operating
at 304MHz. Fig.1 shows the details.
•
•
•
•
•
11
•
•
•
•
•
SILICON CHIP
UHF transmitter and receiver
on 304MHz
Two versions of the handheld
transmitter.
Transmitter uses a single IC
and one transistor.
Single button to activate and
disable alarm.
40-metre transmitter range.
Trinary digital coding wiMl
13,122 codes for security.
Multi-optioned receiver (build it
as you want it).
Relay switch-on and off for any
burglar alarm.
Momentary traffic indicator
flashing for alarm set.
Piezo alarm or siren for audible
indication of alarm set.
Pushing the Transmit button (S1)
causes the IC to deliver the coded
word from pin 15. This is used to
key the UHF oscillator Ql on and
off at a rate of 2kHz. When pin 15 is
high ( + 12V), Ql oscillates.
Ql is a BFR91A, a surface mounting transistor intended for use in
UHF and microwave amplifiers. Inductor L1 and the
2-6pF capacitor
The Remote Switch can be teamed with the Protector
Alarm, or with any commercial alarm. The small
keyring transmitter is in the foreground.
form a tuned circuit load for the
collector of Ql. Its base is grounded
(to AC signals) by a 4 70pF
capacitor. Stray capacitance between the emitter and collector of
Ql provides positive feedback
which causes it to oscillate, at
304MHz.
To increase the oscillator's output, the emitter degeneration
resistor is bypassed with a 1.5pF
capacitor, which is critical in value.
The size of this capacitor cannot be
too large since it would reduce the
positive feedback and thereby stop
oscillation.
The transmitter is powered from
a 12V lighter battery (VR22, EL12,
GP23 or equivalent). Actually, the
circuit could be made to work at
voltages down to 4.5V but the
selected battery is the one best
suited for the job since it is so compact. The battery is bypassed by a
0. lµF capacitor located near IC1
and by a 0.047µF capacitor near
the tuned circuit for Ql.
When S1 is closed the current
drawn by the circuit is a few
milliamps, the exact figure depending on the code word selected at
Al to A9. The current through LED
1 is about 7mA. When S1 is open,
the current drain is less than 200
nanoamps (0.2 microamps).
The transmitter can be built into
one of two cases which are small
enough to be attached to a key ring.
T
m:
16
..I..
1
LOW
14
IC1
MC145026
47k
15
10k
470pFl
.,.
13
12
TE 11
.,.
t
ENCODING
OPTIONS
100k
.0022
220k
+
E
TYPE
MARKING
.,.
L1 : 32mm OF 0.71mm TINNED COPPER WIRE FOR SMALL VERSION.
LARGER VERSION USES PCB TRACKS.
toN LARGE VERSION ONLY
UHF REMOTE ALARM SWITCH TRANSMITTER
SCD3·1·28B
Fig.1: the transmitter uses an MC145026 trinary encoder IC to key UHF
oscillator Qt on and off. A1-A9 are connected to give the address code (see
text).
We'll talk about these later in the
section on construction.
Receiver
The receiver circuit is shown in
Fig.2. It consists of four sections: an
RF input amplifier and detector (Ql
and Q2), a tuned 2kHz amplifier
(IC1), decoder IC2, and optional
relay driver circuitry.
The transmitted signal is picked
up by the antenna which is loaded
MARCH 1988
27
This view shows the UHF switch receiver installed in the same case as the Protector Car Burglar Alarm described in
February. Connections between the two PCBs are via PCB-mounting terminal blocks (see Fig. 12).
by inductor L1. The signal is then
coupled via a .001µF capacitor to
the base of Qt , which is an RF
amplifier with a tuned collector
load.
Signal from the collector of Qt is
fed from a voltage divider consisting of a 2.7pF and a 22pF
capacitor to self-oscillating detector stage QZ. This operates on the
principle that whenever signal is
received the circuit oscillates at
304MHz, but when the signal is not
received, the circuit is quiescent.
The detected signal from QZ is
extracted from the 0.001µF
capacitor connected to its base.
This capacitor bypasses the
304MHz signal but not the ZkHz
pulse modulation which is superimposed on the signal fed to the
antenna.
This ZkHz pulse signal is ACcoupled via a 2.2µF capacitor to
ICta, an inverting op amp with a
gain of about 470.
ICtb is a Schmitt trigger. It
squares up the amplified signal
from ICla before feeding it to ICZ,
the trinary decoder.
ICZ is a MC:::145028 decoder
which is compatible with the
MC145026 used in the transmitter
28
SILICON CHIP
circuit. It is set up to respond only
to the unique code word sent by the
transmitter. This is done by connecting the address inputs Al to A9 in
exactly the same way as for IC1 in
the transmitter.
When IC2 detects a correct code
from the transmitter, the output at
pin 11 goes high and charges the
2.2µF capacitor at the input of IC3a
via the 2.2k0 resistor and diode Dl.
It takes about 5ms before the output
of Schmitt trigger IC3a goes low.
When transmission ceases, the output of ICZ goes low and the 2.2µF
capacitor discharges via the 470k0
resistor. This takes about one second after which the output of IC3a
goes high again. This delay is to
prevent false triggering.
Just how the circuit operates
from this point on depends on how
you build it. For example, you could
decide to use it to momentarily
close relay RLY1 every time the
transmitter button was pushed. To
accomplish this, connect link LK1
(following IC3a), leave out link LK2
and omit IC4, IC5, Q4 and all the
associated components. If you do
this, pins 8 and 9 of IC3 should be
connected to pin 7.
Every time the transmitter button
is pressed, the resulting momentary
low output from IC3a causes IC3d
to go momentarily high and turn on
transistor Q3. This closes relay
RLY1 for one second.
Alternatively, you can go for a
more complex circuit function by
omitting link LK1 and installing link
LKZ instead.
Now, with ICZ detecting the valid
code and the resultant pulse
delayed and squared up by IC3a, a
further pulse inversion takes place
in IC3b, before the signal is fed to
the clock input of IC4a, a D-type
flipflop. This is connected to change
states when it receives a clock
pulse.
The Q-bar output of IC4a connects to the input of IC3d via link
LKZ. IC3d drives transistor Q3
when its output is high and this in
turn operates RL Yt. Thus, relay
RLY1 closes at the first push of the
transmitter button and opens with
the second push on the button.
This function could be used to
turn any commercial burglar alarm
on and off.
Audible options
IC5 is a CMOS 555 timer connected as a monostable (ie, con-
4.m
. . - - - - -....- - - + - - -....-'JW,-----------..------~>------..----
ANTENNA
+8V
.01J
4.7M
10k
F16
L2
22pF
L1
+4
3.3pF
10
10k.,.
.,.
+
16VWJ
.,.
.001!
.,.
L1 : 190mm OF 0.63mm ENAMELLED COPPER WIRE. 15T ON 3.2mm FORMER
L2 : 65mm OF 0.71mm TINNED COPPER WIRE. 1.5T ON 5mm FORMER.
F16 FERRITE SCREW CORE.
8V
+
100
16VWJ
.,.
9
INPUT
..----1--+12v
I
05
1N4002
LK1 : MOMENTARY RELAY 1
LK2 : ON/OFF RELAY 1
2x1~ioo2
RELAY 1
...+-M-+-011 RIGHT
D1
1N4148
2.2k
OUTPUT
LK1
06-11>-----..,.09
LK2
.---+----+12v
_ _ _..__ _ _ ___,_ _ _ _ _ +8V
02
1N4148
100k
PIEZO
SIREN
VR1
1M
12
47k
.022I
.001
.,.
IC5
TLC555
10
+12V
180k
.,.
.,.
0.1+
.,.
PIEZO
TRANSDUCER
13
10
+12V
COMMON
470k
11
+
2.2
16VW+
DECODING
OPTIONS
INDICATORS
214
100k
Z01
33V
1W
100
16VW
+
1_
00k
_
IC3b
CHASsIsn.:1- - - . . __ _ _...._ _ _ _ _- 1 . - - . -
.0471
1/E!
PLASTIC
f1
lmUT
1
s-··.6:
i'"'"'
m
+ 8V
r - - - - - - - - 0 7 DISABLE
TYPE
Q1
50
BELOW
GNO
3
CK
s
4013
IC4a
2.2k
ii2
R
7 4
8V
11
16VW
470k
SC03·H88
+
.011
10
16VW
"-4.._._._,......,_.-tiF-Q& OFF
Q 12
11 CK
.,. .,.
UHF REMOTE ALARM SWITCH RECEIVER
D4
1N4148
14
IC4b
13
9D
R
10
s
8
.,.
03
1N4148
'----li-tll--+---Q 8 ON
Fig.2: the receiver circuit can be built
so that relay 1 provides momentary
or on/off switching.
MARCH 1988
29
.
•'
TRANSMITTER
~TINPLATE
15mm x 5mm
SCOJ-1-288-3
TINPLATE
/15mm x 5mm
~
'-------4.---'
~ 4 x 1mm x 6mm
WIRE STAKES
Fig.3: battery clip detail for
the small transmitter.
Fig.5: parts layout for the
small transmitter PCB. The S1
switch contacts are made from
tinned copper wire.
nected to deliver one pulse when it
is triggered). When the output of
IC3a goes low (when a transmission
occurs), pin 2 of IC5 is pulled low
and the output at pin 3 goes high,
for about 120 milliseconds. The timing is mainly determined by the
0.22µF capacitor at pins 6 and 7
and the lMO trimpot and lOOkO
resistor connected to the + 8V line.
The timing is modified by the 100k0
resistor connected to pin 5 from the
Q output of IC4a.
Pin 5 controls the threshold
voltage of the comparators within
the IC. When the Q output of IC4a is
high, pin 5 is pulled higher than its
nominal setting (2/3 Vee) and the
PLASTIC SUTTON
~-;::::::::>=====b
TINPLATE
16mm x 5mm
SCREW ANO NUT
1.5mm OIA. x 3mm
Fig.4: the switch for the small
transmitter is made from ·a
piece of tinplate and a small
plastic button.
Fig.6: to code the transmitter
each A1-A8 input is connected
to the high rail, the low rail, or
left open circuit. A9 must be
connected high or low.
timing period becomes longer.
When Q of IC4a is low, pin 5 is pulled lower and the timing period
becomes shorter.
Pin 3 of IC5 drives transistor Q4
to turn on the piezo siren. Because
the voltage on pin 5 of IC5 is controlled by the Q output of IC4a, the
siren emits a short burst of sound
when IC4a is clocked to the off state
and a longer burst when IC4a is
clocked to the on state.
Pin 3 of IC5 is also connected to
pin 9 of IC3c. When pin 3 of IC5 is
high, IC3c oscillates and drives the
piezo transducer. This is a lower
cost alternative to the piezo siren
driven by Q4.
Traffic indicator option
Relay RLY2 is also driven by Q4
via diode D6. It has a 2200µF
capacitor connected across it and
this is charged via D6, Q4 and the
120 resistor. The resistor limits the
initial surge current while the
2200µF capacitor is used to keep
the relay energised for about a second after Q4 turns off.
The contacts of relay RL Y2 are
arranged so that they can switch on
the vehicle indicators for a short
time to provide visual indication of
a received signal. Diodes D7 and D8
isolate the left and right indicators.
IC4b is clocked by the pin 3 output of IC5 while its D input, pin 9, is
connected to the Q-bar output of
IC4a via a delay network consisting
of the 2.2k0 resistor and O.OlµF
capacitor. The delay ensures that
IC4b is clocked with data from Qbar of IC4a before it changes state.
The Q outputs of IC4b follow the
Q outputs of IC4a and are used to
provide on and off signalling for the
Protector Alarm described in the
February 1988 issue.
The Q output connects via diode
D3 to the on input of the Protector
alarm, while the Q-bar output is
capacitively coupled to the off input. This provides a short pulse
which is sufficient to switch off the
alarm circuit.
A further output from the. Q-bar
output is used to provide the
Disable control. This can be used to
disable an ultrasonic movement
detector which we hope to describe
in a future issue.
Power for the circuit comes mainly from a 7808 3-terminal regulator.
This isolates the sensitive circuitry
from the 12V automotive electrical
system. A 33V zener diode protects
the input of the regulator from any
voltage spikes on the 12V line.
Construction
Fitting the parts in the Jaycar case is bit of a challenge but it can be done if
the parts are 'squashed' down on the PCB. The pen points to the two switch
contacts which are made from looped tinned copper wire.
30
SILICON CHIP
As noted above, the handheld
transmitter may be built in one of
two cases, one from Dick Smith
Electronics and one from Jaycar
Electronics. We have designed two
transmitter boards to suit the two
cases.
The larger of the two cases is
from Dick Smith Electronics. It
measures 31 x 58 x 17mm (DSE Cat
No H-2497). The printed board to
I
12V
J
+
Fig.7: alternative transmitter
PCB for the DSE case. The
.0022uF capacitor lies flat
across the IC (see photo).
Fig.8: Al-A9 address pins for
the alternative transmitter.
Make sure the transmitter
code matches the receiver.
The larger of the two transmitters is
still compact enough to fit your
keyring.
The two transmitters look different but their circuits are the same. Coil L1 is
part of the PCB pattern for the larger version, while the smaller version uses
a wire loop. Power comes from a 12V lighter battery.
suit it measures 46 x 33m (SC code
3-1-288-2). The case from Jaycar is
smaller, measuring 34 x 43 x 13mm
(Jaycar Cat No HB-6072). The board
to suit measures 30 x 30mm (SC
code 3-1-288-3).
While the Jaycar case is notably
smaller, it has the disadvantage
that a switch and battery clips are
not available and will have to be
made. Nor can the LED indicator be
fitted into it. The Dick Smith case is
supplied with battery clips and a
commercial switch can be used.
Construction of the transmitter in
the Dick Smith case should be
straightforward. The smaller
transmitter is more difficult to construct due to the necessity to make
the switch and battery clips.
We made the battery clips for
ours from pieces of tinplate 15mm
long by 5mm wide. They are each
soldered to two wire stakes on the
PCB. This is shown in Fig.3.
The switch is also made using
tinplate. It is secured to the lid of
the case using a screw and nut. A
small plastic button is glued to the
tinplate as shown in Fig.4. Contacts
for the switch are mounted on the
PCB using tinned copper wire loops.
These are raised about 4mm above
the PCB surface but some adjustment in height may be necessary to
provide a satisfactory switch
action.
The component layout for the
smaller transmitter board is shown
in Fig.5.
The smaller transmitter PCB requires a 5.5mm hole to clear the
screw pillar in the lid and a 5mm
hole for the transistor. Before
assembling components on the PCB,
check that the PCB will fit within
the case. You may need to file off
the corners of the PCB so that it will
follow the internal corner radius of
the case.
Install the IC with pin 1 towards
the battery clip side of the PCB. The
transistor is mounted on the underside of the PCB. Tin the PCB tracks
with solder before soldering the
transistor leads in place.
The remaining components are
not so easily installed. None of the
parts can sit more than 6mm above
the PCB surface to avoid fouling the
lid of the case. To achieve this low
profile, the resistors are mounted
end on and bent over so that they lie
close to the PCB. The smaller
capacitors can be mounted upright,
however the larger ceramic
capacitors should be bent over. The
0.0022µF greencap should be
mounted side on.
The trimmer capacitor can be
mounted in the normal fashion. The
11 inductor is made using 32mm of
0.71mm diameter wire looped and
laid flat on the PCB as shown in
Fig.5.
The larger transmitter version in
the Dick Smith case uses the
SC03-1-288-2 PCB. Components for
this PCB can be installed as shown
in Fig.7.
The battery clips are pre-shaped
and are simply inserted into the
PCB and soldered on the underside.
Now install the IC and link. Some
MARCH 1988
31
Receiver
ANTENNA
INPUT
Fig.9: parts layout for the receiver PCB. For momentary relay switching, install
LK1 and omit LK2, IC4, IC5, Q4 and associated parts. Also, connect pins 8 and
9 of IC3 to pin 7. For latched contacts, omit LK1 and install LK2 and all parts.
L2 FORMATION
DIMENSIONS IN MILLIMETRES
Fig.10: L2 is
wound using
0.71mm
tinned copper
wire.
resistors are mounted flat on the
PCB while others are mounted end
on as shown on the overlay. All the
capacitors are mounted flush
against the PCB except the .0022µF
greencap which is bent to lie flat
over the top of the IC.
The switch is mounted so that the
flat side of the switch body is
towards the battery terminal end of
the PCB.
The LED is mounted 11mm above
the PCB surface. The transistor is
mounted on the underside of the
PCB. Tin the PCB tracks with solder
before finally soldering the transistor pins in place.
Fig.11: connect the A1-A9 receiver inputs to exactly match the transmitter
code. A1-A8 can be high, low or open circuit; A9 must be tied high or low.
32
SILICON CHIP
The UHF receiver is built on a
PCB coded 03-1-288-1 and measuring 132 x 87mm. It can be installed
in a plastic utility case measuring
159 x 96 x 51mm or, if you have
made the Protector Burglar Alarm,
you can build it into the same case.
Begin construction of the
receiver by installing all the low
profile components such as the
resistors, links, diodes, and ICs.
When installing the links, decide
whether relay RLYl is to be wired
with momentary or on/off operation
and install either link 1 or link 2
accordingly.
Fig.9 shows the receiver board
with all parts installed. We assume
that many readers will build versions with some of the options omitted. If this is the case, examine the
layout diagram carefully to determine what parts can be left out.
The BFR91 transistors are
mounted on the underside of the
PCB. Before mounting and soldering
each of these transistors, tin the
tracks with solder. This makes it
easier to solder each transistor into
place.
L1 is made using a 190mm length
of 0.63mm enamelled copper wire
wound around a 3.2mm (1/8-inch)
drill bit. Wind on 15 turns and strip
the insulation from the ends with a
sharp knife before soldering it to
the PCB.
12 is wound on a 5mm plastic
former which is fitted into the PCB
so that it is a tight fit. The winding
details are shown in Fig.10. Don't
forget to screw in the F16 ferrite
core.
Continue construction by installing the capacitors, relays, remaining transistors, the 3-terminal
regulator and the insulated terminal block. Take care with the
orientation of the electrolytic
capacitors and transistors.
The antenna is simply a 300mm
length of hookup wire soldered to
the antenna input pad on the board
(see Fig.9).
The receiver can be mounted in
its own case using PCB standoffs. A
Scotchcal label measuring 90 x
153mm is secured to the front
panel. The artwork is shown in
Fig.13.
Alternatively, the PCB can be
PROTECTOR ALARM
: 1,2 + 12V TO VEHICLE BATTERY
e 3 TO BATTERY BACKUP VIA 3A FUSE--
-
-
- --
- --
- -•40N
- - - 5 OFF
6 POWER GROUND
....-
IGNITION COIL
e
e 7 VEHICLE BATTERY
e 8 IGNITION
e 9 INSTANT
e 10 DELAY
a,
GND
5A ALARM CONTACTS 4,
DASHBOARD FLASHER
PIEZO SIREN 1
,----------------+-12-V14-......,.._----, - ~
-~•m,s
PIEZO TRANSDUCER 13 - - : - - PIEZO SIREN 12 ~ INDICATORS
R~~~~ : ~ ~ -1------::
COM MON 9
ON 8
DISABLE 7 . . . . _
OFF 6
NORMALLY CLOSED 5
NORMALLY OPEN 4
COMMON 3
UHF REMOTE ALARM SWITCH
+ 12V 2
GROUND 1
ALTERNATIVE
CONNECTION
e-!- -..., --- TO "DISABLE" ON
e
ULTRASONIC DETECTOR
e
I
e
: ::::"---Jf----f:2:'.Jr--;::n±-_--=.IJ:::;--.......
1
CHASSIS
Fig.12: here's how to wire the UHF remote switch to the Protector car alarm. The piezo transducer
can be omitted if you have fitted the piezo siren.
mounted in the Protector alarm
case as shown in one of the
photographs. It is mounted on
15mm standoffs at the terminal end
of the PCB and supported using Ushaped brackets at the opposite
end.
Fig.12 shows how the UHF
remote switch is wired to the Protector car alarm. The remaining
connections to the Protector alarm
are as shown in the February issue.
Testing and alignment
Both the transmitter and receiver
must be coded before they can be
tested. Figs.6, 8 and 11 show the Al
to A9 code inputs on the copper
side of the PCB for two transmitters
and the receiver respectively. Note
that the receiver code must exactly
match the transmitter code, otherwise the unit won't work.
Initially, to allow testing, we
recommend that only the A9 input
of the transmitter and receiver be
coded. This input must be bridged
to either the high or low rails (it
must not be left open circuit).
The transmitter frequency must
This fully-optioned receiver board features on/off switching for relay 1. The
second relay (top right) provides the traffic indicator option.
be set to 304MHz by using a frequency meter. Temporarily connect
pin 15 of ICl to the positive rail.
This will set the oscillator in operation. Now hold the transmitter near
the input of the frequency meter
and adjust the trimmer capacitor
for a reading of 304MHz. In some
cases it may be necessary to connect a coil of wire between the inM ARCH 1988
33
r:
:-J
C
L:
PIEZO TRANSDUCER
PIEZO SIREN
RIGHT
INDICATORS [
LEFT
COMMON
ON
DISABLE
OFF
NORMALLY CLOSED
NORMALLY OPEN
COMMON
+12V
GROUND
UHF REMOTE ALARM SWITCH
Fig.13: actual size reproduction of the front panel artwork.
I
SC03-1·288·2
Flg.14: etching pattern for
the larger transmitter PCB.
Fig.15: etching pattern for
the small transmitter PCB.
Fig.16 (right): etching
pattern for the receiver
34
SILICON CHIP
r
14
13
12
11
10
9
8
7
6
~
2
1
PARTS LIST
Transmitter
1 transmitter case (Jaycar Cat.
HB6072, 34 x 43 x 13mm;
or DSE Cat. H-2497, 31 x
58 x 17mm)
1 PCB, code SC03-1-288-3,
30 x 30mm (for Jaycar
case); or SC03-1-288-2, 46
x 33mm (for DSE case)
1 PC-mounting pushbutton
switch, DSE Cat. S-1 200 (for
DSE case)
1 3mm LED (for DSE case)
1 50mm x 5mm tinplate (for
Jaycar case)
1 5mm x 4mm plastic button
(for Jaycar case)
1 1.5mm dia x 3mm screw
plus nut (for Jaycar case)
1 12V lighter battery (VR22,
EL 12, GP23 or equivalent)
32mm 0.71mm tinned copper
wire (for L 1, Jaycar case)
Semiconductors
1 BFR91 NPN lJHF transistor
1 MC145026 trinary encoder
Capacitors
1 0.1 µ.F miniature polyester
1 .04 7 µ.F ceramic
1 2200pF metallised polyester
(greencap)
1 4 70pF ceramic
1 1.5pF ceramic
1 2-6pF ceramic trimmer
Resistors (0.25W, 5%)
1 X 220k0, 1 X 100k0, 1 X
put and ground of the frequency
meter to obtain a satisfactory
reading.
Once the frequency has been set,
remove the temporary connection
to pin 15.
Now connect the receiver to a
12V power supply. Apply power
and check that the output of the
regulator is at + 8V.
Next, connect a multimeter set to
read DC volts between test point
TPl and ground. Apply power and
wait 10 seconds for the 2.2µ.F
capacitor at the base of Q2 to
charge. Adjust the slug in L2 for
maximum signal when the transmitter switch is pressed (ie, for maximum reading on the DMM). You
may need to progressively move the
transmitter away from the receiver
47k0, 1 x 1 OkO, 1 x 1.5k0 (if
LED is required), 1 x 1 kO
Receiver
1 plastic utility case, 159 x 96
X 51 *
1 Scotchcal front panel, 1 53 x
90mm*
1 printed circuit board, code
SC3-1-288-1, 133 x 87
1 1 0-way PC-mounting
insulated screw terminal
block
1 4-way PC-mounting insulated
screw terminal block
2 1 2V SPOT relays*
1 piezo transducer*
1 piezo siren*
Semiconductors
1 MC145028 trinary decoder
1 TL062 low power dual op
amp
1 4013 dual D flipflop*
1 4093 quad NANO gate
1 7808 3-terminal 8V regulator
1 TLC555 CMOS timer*
2 BFR91 NPN UHF transistors
1 BC337 NPN transistor*
1 B0681 NPN Darlington
transistor*
3 1 N4002 1 A diodes*
4 1 N4148, 1 N914 diodes
1 33V 1W zener diode
Capacitors
1 2200µ.F 16VW PC
electrolytic*
2 100µ,F 16VW PC electrolytic
and repeat the adjustment for L2 to
obtain the setting for maximum
sensitivity.
Once adjusted, the receiver
should be respond to a transmission
by activating relays RLYl and
RL Y2 (if fitted).
Relay RL Y2 should close on
receipt of a transmission and remain closed for about one second.
Connecting a piezo transducer between terminals 13 and 14 or a piezo
siren between terminals 12 and 14
will then provide the audible indicator for the receiver.
A short burst of sound will be
heard during the off transmission
and a longer burst of sound during
the on transmission. Trimpot VRl
adjusts the lengths of these tone
bursts.
3 1 Oµ.F 16VW PC electrolytic
2 2.2µ.F 16VW PC electrolytic
1 1µ.F 1 6VW PC electrolytic
1 0.22µ.F PC electrolytic
2 0.1 µ.F metallised polyester
1 O. 04 7 µ.F metallised polyester
1 0.022µ.F metallised polyester
1 0.01 µ.F metallised polyester
1 0 .01 µ.F ceramic
1 0 .001 µ.F metallised polyester
4 0 .001 µ.F ceramic
1 22pF ceramic
1 3.3pF ceramic
1 2. 7pF ceramic
1 2.2pF ceramic
Inductors and wires
L 1 190mm 0 .62mm enamelled
copper wire
L2 65mm 0 .71mm tinned
copper wire, 5mm former
DSE cat L-1010, F16
ferrite screw core
L3 3 .3µ.H
300mm 1 mm solid core
insulated wire (for the
antenna)
Resistors (0.25W, 5%)
2 x 4.7MO, 3 x 470k0, 1 x
180k0, 1 x 150k0, 6 x 1 OOkO, 2
x 47k0, 1 X 39k0, 1 X 22k0, 1 X
18kQ, 6 x 1 OkQ, 2 x 2.2k0, 1 x
1 kQ, 1 X 4 70Q, 1 X 270Q, 1 X
12n, 1 x 4.7n, 1 x 1Mn
miniature vertical trimpot
*
optional
text).
components
(see
Coding
The receiver and transmitter can
now be coded using selected high,
low or open circuit connections to
Al to A8. Each Al to AB input can
be bridged to the high rail, the low
rail or left open circuit. For example, you could bridge Al to the high
rail, A2 to the low rail, leave A3
open circuit, bridge A4 high and so
on.
It's a good idea to write your
selected code down on a piece of
paper before actually making the
necessary connections. Make sure
that the receiver and transmitter
coding are identical.
Finally, drip some molten candle
wax into the screw core of L2 to
prevent it from moving and thus
detuning the receiver.
It
M ARCH 1988
35
Easy Serial Links
RS232 Breakout Box
Parallel Switch Box
Male/Male Gender Bender. Adapts female
serial cables without resoldering or reconnecting. All 25 pins wired pin to pin.
Simply plug in twin male D825 sockets.
Cat X-3565
Just what you need for modems or any
serial applications. D825 male to female.
Pin 1 is permanently wired, all others are
open with wire links supplied . Perfect for
making up special serial cables. Cat X-3568
No more cable changing! The parallel
switch box can save you heaps of time.
Lets you run one printer and two
computers or even two printers and one
computer. Just plug it in and it does the
s27so
80286 ·Mother Board
Your own 'Baby AT'! Use it with our do-ityourself kit or your own custom computer.
Provision for 256K, 512K, 640K or 1024K
RAM, selectable 6,8, 10 & 12MHz speeds,
8 inpuVoutput slots, IBM PC/AT
compatibility, Award BIOS and much
more! Cat X-1000
s499
Serial Switch Box
RS232 Permanent
Jumper Box
Female/Female
Gender Bender
The same as above but with twin female
sockets permanently wired. Makes cable
connections quick and hassle free!
Cat X-3566
Lighbling Fast or NLQ.
Super fast 135cps dot matrix printer for
home or office use. Just what you need for
letters, graphics ... all your printing
requirements. The DSE 135 Printer, great
value and exceptionaj quality.
Correspondence, invoicing, reports,
designs, graphs ... anything. Cat X-3225
s
This one's similar to the breakout box but
the connections are made internally and
soldered for permanent applications. All
25 pins are open with wire links supplied.
Cat X-3569
s995
;g;' ,.
•
What a pain in the .... , they never give you
more than one serial port! What's more,
there's so many serial applications. Well,
we've solved the problem. The serial
switch box lets you connect two devices
to your serial port. A modem and a mouse,
two modems, a printer and a .... whatever
you like. Cat X-3573
s59es
80 Column Printer
Stand
Takes the foul-ups out of printing. Keeps
your printer and paper working NEATLY
together and gives you the time to go
about your work while the printing's being
done. Saves space and time. Cat X-3811
s39es
CPU Floor Stand
Lets you store your CPU 011 it's side out of
harms way. Great when space is at a
premium! With more space on your desk
you'll most likely end up with less mess
- now that seems sensible. Cat X-3810
132 Column Printer
Stand
When you need to use the larger format
paper then this is the printer stand for
you. Just like the 80 column stand. Helps
eliminate paper jams by storing and
taking-up paper during printing. Cat X-3812
s49es
~
The ultimate modem at just the right price! The Bit Blitzer 12E with
selectable full duplex 1200/1200 or 300/300 baud, auto answer, auto dial,
auto disconnect, Hayes AT command set compatibility and more. Fully
keyboard controllable, so it's easy to operate. Cat X-3306
JUST
Now with Viatel
With the Bit Blitzer 123E you get all the advanced features of the 12E
PLUS the advantage of 1200ll5 baud Viatel operation. At this great low
~ Q , l / ~'"' ~ ,_,,.,
Order by phone: 24 hour
.despatch through DSXpress.
Call TOLL FREE (008)22 6610
(Sydney Area, call 888 2105)
s399
..
s499
DICl<<at>.sMITH
ELECTRONICS
PTY LTD
I
~
Make your own PCB'S with... DATAK
Pos/Neg Film
Refills
Tinit - Tin Plate
Powder
Circuit-Fix It
Assorted Marks
Pack contains enough dry
developer, fi xer and wash to
process up to 15 5" X 6" film
Great for control panels, meters,
dial plates, etc. 6 sheets of
transfers including letters in
black, gold and white. Cat N-5750
s1195
$9995
----------!! !l!lilil l l'! '_ ..
60 MHz CRO Probes
You'd expect to pay $$$ more for a CRO
Probe with this versatility. With x 1/x 10
switch, coax CRO connector, IC adaptor,
spring clip, wandering earth, BNC adaptor
and more! Cat 0-1247
The ER-17 filter is just what you
need for any pos/neg work. Keep
it clean and dust free and you'll
have it for years cat N-571 1
Just about everything you'll need
for pcb work .. Hundreds of
transfers. 5 sizes of d_oughnuts,
square p_
ads, 16-12 pm DIP, T092trans1storsandm.ore!
1095 ·
0
Cat N-5766
5
1995 t··
Burnisher
~
_.,,.,
t
~
.
Negative Resist
Developer
Yellow Pos/Neg
Filter ·
Assorted PCB
Transfers
$
11 ., >>.
-
t l ..····.·
,., ;;·
·,:,"·J···
' ·~
The Complete PCB Kit
All the chemicals you need to create your own professional pcb's!
Use the kit to make your own artwork or use magazine art, use the
patented Pos-Neg process to make photo ne~ative, sensitize and
expose blank copper, develop and etch - its all made easy! Save
time and money wi)h Datak PCB Kit ER-4. cat N-5700
sheets cat N
~ 59.09
5
A solvent that will develop
negative acting photo resist. In
handy 483ml container. Cat N-5905
'<1 s1195
.'\\'\~ j \
~\ ·
.. .,.
~1
ER-71 Neg_ative
Photo Resist
Assorted Targets
A liquid cinnimate resist in bottle
with pump sprayer for easy
application. Covers 4000 sq mm.
;;Sas , ,
S0995 pair
Safe~ Yellow
3.5 Digit
Multimeter
300ohm Plug
This is one of our be.st selling
3.5 digit Multimeters - it's
no wonder when you see the
features! Includes Tr, diode,
continuity PLUS battery
checker. Checks current to
10A and resistance to 200
megs. Cat 0-1445
2 x 40 fluoro starters. Keep a
pack handy and you won't be left
in the dark. Cat P-5625
s1 !!O
3.5 Digit with
Capacitance
Checker
Similar to our safety yellow
Q-1445 only this has a
capacitance checker and
goes to 20 megohms
resistance. Resolution is
great and it has a fast 300ms
cycle time and fuse protected
meter. Cat 0-1465
~ESS
DICK SMI TH ELECTRON/CS EXPRESS ORDER SER VIC E
Plug to suit ribbon cable for TV
antenna. Cat P-2082
s120
Fluoro Starter Pack
24 Hour Timer
3.5 Digit with
Temperature
An LCD that's ready for work.
With many more ranges than
you'd expect at the price
including full AC/DC current
up to 10A. It also checks
diodes and continuity and
has overload protection on all
ranges. Cat 0-1511
Sl 15
Order by phone: 24 hour
despatch through DSXpress.
Calf TOLL FREE (008)22 6610
(Sydney Area, call 888 2105)
Mounts on wall or skirting. With
75 ohm connector for coax.
Cat P-2044
s495
~
Great security device! Lets you
time lights, appliances, etc to
switch on and off automatically.
cat P-5701
300ohm
Wall connector
Plug and socket for wall mounted
300 ohm ribbon cable connection.
s39 95
Power Point
Safety Tester
s·
Cat P-2080 ~
d
t
J
1
imp 1e an easy O use. uSt P ug
it into the power point and the
light pattern indicates any faults.
52as
cat P-5390
~
s7ss
----~,- -----------
DICK0 SMITH
ELECT
PT Y LTD
Interesting circuit ideas which we have checked but not built and tested. Contributions from
readers are welcome and will be paid for at standard rates.
Adjustable Load for
Power Supplies
When designing power supplies,
a variable load is needed to determine the current capacity. You
could use a large power rheostat (a
variable wirewound resistor) but
these are now very expensive and
hard to obtain. And a rheostat's
capacity to dissipate power
depends on what proportion of the
element you use. If you use half a
rheostat's resistance element, it
will only be able to dissipate half its
rated power.
So if you use a rheostat right at
the bottom of its resistance range,
the small portion of the element in
use will tend to seriously overheat.
The solution to this problem is to
use a power transistor mounted on
a large heatsink. By connecting the
collector and emitter of the power
Handy Hints
Hint #1: Do you make your own
printed circuit boards? The first
step is to thoroughly clean and
dry the copper surface prior to
coating it with photo-resist. To
obtain a dust-free surface, do not
use paper towels as they often
shed lint. Instead, dry the surface with a hair-dryer. This gives
an absolutely clean, dust-free
surface.
Hint #2: In many circuits, fuses
are desirable but they can take
up quite a lot of space on small
circuit boards. In quite a few applications though, a small
resistor will do the same job and
take up a lot less space. Values
below 10 ohms and with a rating
of 0.25W are the ones to go for.
They will provide current
limiting and fusing for currents
of several hundred milliamps. As
a bonus, resistors are much
cheaper than fuses and are more
readily available.
38
SILICON CHIP
+12vo------Q1
8D681
+
OVU---41---------tt-----41""-0
transistor to the DC power source
to be measured, the amount of load
current can be easily adjusted by
varying the base current drive to
the transistor.
Our circuit uses the readily
available 2N3055 (Q2) as the power
transistor and a BD681 Darlington
(Ql) as the source of base current.
VR1 varies the base current to Ql
and hence varies the current
drawn from the supply.
The amount of power able to be
dissipated by the 2N3055 depends
on the size and effectiveness of its
heatsink. With a reasonably large
heatsink, it should be possible to
dissipate about 40 watts. The maximum current drawn from the
power supply can be found by
dividing the dissipation (say 40
watts) by the voltage between collector and emitter. For 20 volts between collector and emitter, the load
can draw 2 amps.
Note: the circuit is suitable as a
DC load only. It will not work on AC
without being modified.
Updated Synchroscope
for Frequency Comparison
This is the frequency comparator to beat all frequency
comparators. While some
designs use four LEDs in a circle
(see page 63, November 1987) to
produce a rotating display, this
circuit drives 16 LEDs to produce
a far more visually satisfying
effect.
Two 74121 monostables (IC1
and IC2) are used to generate
short (30 nanosecond) pulses to
be fed to a 74193 up/down 4-bit
counter. The output of this
counter is fed to a 74154 binary
1-of-16 decoder which drives the
16 LEDs.
Ordinary 74-series TTL integrated circuits have been
specified here as this is essentially a "junk-box " project but
74LS types may be used instead.
The circuit may also be adapted
to use a 7442 1-of-10 decoder
and a 74192 up-down counter.
Further, a 74123 dual monostable could be used but it does
not have a Schmitt trigger "B"
input like the 74121.
The 74121's "B" input has
typical switching thresholds of
+ 1.35V and + 1.55V. An input
sensitivity of 200mV peak-peak
could be obtained by simply biasing the input to + 1.45V with a
pull-down resistor. However, the
resulting input impedance would
be quite low.
To overcome that, the accompanying JFET input stage has
been included which should be
satisfactory for most applications. In some cases the 1k0
drain load resistor may need to
be increased if the FET has a low
Idss.
$30 to Steve Payor,
Kogarah Bay, NSW.
Precision Reset
for Microprocessors
CRO Probe Modification
If you are using an oscilloscope probe
in a sensitive circuit such as a high gain
audio preamplifier or power amplifier,
off a resistor
it can cause problems.
The probe's capacitance
and attach
it to the probe
can be sufficient to cause a
tip as shown in
power amplifier to exhibit low
the accompanying illevel instability.
lustration. The resistor
The way to
effectively isolates the probe
avoid this
capacitance from the
problem is to
clip the leads
--1ok RESISTOR
sensitive circuit being
measured. Usually a value of
between 1k0 and 10k0 will
suffice. The technique can also
be useful when measuring RF or
high speed logic circuits.
,----------+VDD
MICROPROCESSOR
- - - - - - - ~ - - -VSS
Most designers of dedicated
microprocessor equipment use a
simple RC network for resetting
when the supply voltage is low.
This usually works without trouble
but it can lead to problems in some
cases. A more precise method involves using the Seiko S-8054HN
voltage detector.
This 3-terminal device in a T0-92
package uses a window comparator
which delivers a logic low (OV) at its
open drain output whenever the
supply voltage is in the precise
range from 3.8 to 4.2 volts DC.
Other applications include level
discrimination, power failure indicator and charging monitor.
The Seiko S-8054HN is available
directly from VSI Electronics (Aust)
Pty Ltd. Phone (02) 439 8622.
Help! Save Us From Circuit Burnout!
We know we're brilliant. You've said so yourselves. But we know that
there are lots of ingenious circuits lanquishing out there in readers' brain
cells. So bung 'em into us and we'll publish them in their full glory. You'll
not only make some money but you'll also save us from the dreadful "circuit burnout s~~drom~ which happens to anyone who has to generate
too many c1rcu1t ideas in too short a time .
We'll pay up to $50 for a really good circuit. So transfer your circuit to
paper and send it SILICON CHIP, PO Box 139, Collaroy Beach NSW
2097 .
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MARCH 1988
39
Endless loop tape
Fancy a barking doorbell? Or how about
a novel pre-recorded message system for
a shop display, or for the home? This
endless loop tape recorder is the answer.
By GREG SWAIN
Initially, we didn't quite know
what to do with this intriguing little
gadget. After all, what possible use
is a tape recorder that can only
play for 20 seconds before
repeating itself?
Then we began to think of all
sorts of applications. In addition to
those already mentioned, it could
be used for pre-recorded announcements over a PA system, as
an appointments reminder, or as a
convenient message system for
family members. It could even be
used to store telephone numbers, or
just as a source of amusement.
If you want a really novel
doorbell, this unit will do the job.
You could record a message telling
your guests that the barbeque is
around the back, or you could
record the spine-chilling sound of a
slobbering, salivating dog. Mind
you, the effect would be lost when
the caller took his finger off the
button.
(One of our staff members, who
shall mercifully remain nameless,
decided to do an imitation of a
furious canine and performed with
great gusto while holding down the
record button. It was very effective
too although the effect was not
quite what he intended. We all
broke up whenever it was played
back).
A pre-assembled tape recorder
module from Jaycar Electronics
forms the basis of the unit. Instead
of the familiar cassette mechanism,
it uses a continuous tape loop with
only one spool. The tape is wound in
a couple of layers on the outside of
the spool and is withdrawn from
+v---•.il.\!!!.---------------.
S1
R-P
RECORO/
PLAYBACK
an
SPEAKER
.,.
MICROPHONE
ELECTRET
.,.
22D
+
1DVWJ
47Dll
+
sotw :
MOTOR
ERASE
.,.
ENDLESS LOOP TAPE PLAYER
SC1-1-488
Fig.1: the circuit for the endless loop tape player. IC1 provides signal amplification while IC2 is for motor speed control.
40
SILICON CHIP
player
PARTS LIST
1 ED-1 000R endless loop tape
unit (available from Jaycar)
1 plastic case, 159 x 96 x
54mm (Altronics Cat No
H-0201 or equivalent)
1 Scotchcal front-panel label,
154 x 90mm (optional)
1 50mm diameter 811
loudspeaker
1 4-way AA battery holder
4 AA batteries (preferably
alkaline)
1 battery clip to suit holder
1 momentary pushbutton
switch
1 pushbutton cap (to suit
changeover switch)
1 electret microphone
We built the tape module into a plastic zippy case, along with a battery power
supply. The speaker, microphone and run switch were fitted to the front
panel.
Miscellaneous
Screened cable, hookup wire,
scrap aluminium for battery
clamp, self-tapping screws
the bottom layer. Apart from that,
the rest of the transport mechanism
is fairly standard with a capstan,
pinch roller and belt-drive from the
motor.
A spring-loaded multipole pushbutton switch on the side of the
module provides the changeover
from playback to the record mode.
Whenever power is applied the unit
is automatically in the playback
mode. Putting the module into
playback is a good way of finding
out what "endless" means; it goes
on and on and on.
All that is need to make it work is
an electret microphone insert, a
small 811 loudspeaker and a source
of DC which may be anywhere between 4.5 and 6 volts. This power
can be derived from batteries or a
4.5V DC mains plugpack.
How it works
Fig.1 shows the circuit of the
ED-1000 endless loop tape
recorder. Most of the work is done
by ICl which provides all the
necessary signal amplification.
This view shows the parts layout inside the case. The tape module is secured
to one end of the case by two self-tapping screws.
In the playback mode , ICl
amplifies the signal from the
record/playback head and drives
the loudspeaker via a 100µ,F
capacitor. In the record mode, it
amplifies the signal from the electret microphone and drives the
record/playback head via a parallel
33k11 resistor and .022µ,F capacitor.
This network provides a modest
degree of treble boost for the
recorded signal.
A 5-pole 2-position slide switch,
referred to above, is used to switch
the circuit between record and
replay. In the record position, DC
MARCH 1988
41
Above: follow this labelled photograph when hooking up
the external connections to the tape player PCB. Note
that the electret microphone should be wired using
shielded cable. At right is a close-up of the player module
showing the endless tape-loop mechanism and the record
and replay heads.
bias is supplied to the erase head
via a 4700 resistor and to the
record/playback head via a 22k0
resistor.
IC2 (KA2402) and its associated
components are used for motor
speed control.
Construction
The above circuit details have
been induded so that you'll know
r.
where to hook the external
components.
We mounted the tape mechanism
in a plastic case measuring 159 x
96 x 54mm. The loudspeaker, electret microphone and switch are all
mounted on the lid of the case,
while the tape unit is secured to the
base using self-tapping screws.
Start construction by drilling two
holes in the base that align with the
•
ENDLESS LOOP TAPE PLAYER
L:
42
•
plastic posts on the bottom of the
tape unit. Clean up the holes with
an oversize drill bit, then drill and
ream a 16mm hole in the end of the
case to allow finger access to the
record switch.
The lid of the case should have
holes drilled for the speaker grille,
the microphone and the power
switch. Attach the Scotchcal art-
•
• • •
•••••
•
• • •
RUN
Fig.2: here is an actual-size reproduction of the front panel artwork.
SILICON CHIP
.:J
Jiu.ii.a·this versatile test instrument
Techni]ab 301
function generator
This versatile test instrument packs a 10Hz-110kHz
function generator, a power supply, and an audio amplifier
and loudspeaker into one compact package.
By DAVID WHITBY
If your funds don't extend to a
workshop full of exotic test gear,
this multi-function test instrument
is for you. It features a function
generator, power supply and audio
amplifier all in one package, and is
ideal for testing prototype circuits
and for service work. We think that
it will more than earn its keep in
many small workshops and labs.
The idea behind the Technila b
301 was to provide a versatile test
instrument at an affordable price.
This has been achieved with a very
clever circuit that uses just three
low-cost ICs and a couple of
3-terminal regulators. As well as
keeping the cost low, this also
makes the unit extremely easy to
build.
There are many potential applications for the instrument. Here
are just a few:
(1) Audio servicing: you can use the
unit as a signal tracer for servicing
audio circuits. A signal injected
from the function generator can be
traced by the built-in amplifier and
loudspeaker.
(2) Loudspeaker testing: by connecting the generator output to the
amplifier, you can ·use the unit for
frequency response testing of
loudspeakers or amplifiers.
(3) Variable frequency code practice oscillator: a Morse key connected between the generator output and the amplifier input is all
The Technilah 301 is housed in a grey plastic case with red front-panel
lettering. It can generate sine, triangle and square waves from 10Hz to
110kHz.
that's required to make a Morse
code practice oscillator.
(4) Power supply: the unit provides
both ± 6V regulated and ± 15V
filtered supply rails for powering
prototype circuits. Other voltages
can be derived from these rails by
means of external voltage regulation circuits (eg, zener diodes or
3-terminal regulators). The instrument can provide up to 200mA
which is sufficient for most small
projects using op amps or logic ICs.
Perhaps the most important
feature of the Technilab 301 is the
built-in function generator. A function generator is useful for checking out audio and logic circuits.
Despite the very simple circuit
employed, the Technilab is capable
of providing sine, triangle and
square waveforms with frequency
continuously variable from lOHz to
1 lOkHz over four ranges.
MARCH 1988
43
FREQUENCY
VR1
1M LIN.
100k
+6V
82pF
VR5
10k
H~
.~.
.OOl X100
~
.01
33k
+6V
x10
Sla
0.1
K
Slb
1k
RANGE
l
':'
1-4)
AXED
OUTPllT
.I1IL
4069
IC1a
1
LE01
15pF
39k
0
2
.It.
100k
\I\
10
S2a
S2b
220k
40
400
mV/DIV
S3b
1M
+6V
D1
1N4002
OFF
SINE
• SYMMETRY
VR7
10k
+15V
HOM
ON
0
I
-~
+6V
02
1N4002
_;~
~;_,
OV
03
1N4002
S3a
12VAC
INPUT
OUTPUT
OUTPUT
VR8
1k UN
REG
AMPLIFIER IN
iov ~1
.1
7806
':'
":'
+15V
•
LUME
100pFI
-6V
REG
,.
i:k
LOG
.
.
GND
7906
-15V
NOM
06
1N4002
IN
TECHNILAB 301
Fig.1: the function generator circuit is based on CMOS hex inverters IC1 and IC2, while IC3 is the audio amplifier
stage. D1, D2 and the two 3-terminal regulators provide the ± 15V and the ± 6V power supply rails.
The output level is also continuously variable (from 0-4V over
three ranges). And, as a bonus,
there is a separate 6V p-p square
wave output which is completely independent of the level set. This
feature allows reliable external
oscilloscope triggering and/or frequency measurements, regardless
of the level being fed into the test
circuit.
The output from the generator is
made available on small binding
post terminals on the front panel. It
can then be fed directly to the circuit under test or to the in-built
44
SILICON CHIP.
audio amplifier. The amplifier can
deliver 1W into an 80 load and connecting an external lead via the
3.5mm OUT socket automatically
disconnects the internal loudspeaker.
How it works
Take a look now at the circuit
details in Fig.1. This can be split into three sections: a function
generator based on CMOS hex inverters ICl and IC2; a power supply
stage built around two 3-terminal
regulators; and an audio amplifier
stage based on IC3. We'll consider
the function generator circuitry
first.
ICla is connected as an integrator with four switched
capacitors from input to output.
These capacitors ar e selected by
Sla and provide the four decades of
frequency range.
IClb and IClc together form a
Schmitt trigger. This is fed from the
output of ICla via one of the trimpots VR2-VR5 , as selected by Slb.
The output of IClc is then fed back
to the input of ICla via a lkD
resistor and the main frequency
control (VRl) to form a surprisingly
*MOUNTED ON UNDERSIDE OF BOARD
12VAC
INPUT
Fig.2: install the parts on the PCB as shown in this diagram. Note that the
3-terminal regulators, the 4700µF filter capacitors and the loudspeaker are .
mounted on the back of the board. Take care with component polarity.
simple but stable 4-decade
oscillator with both triangle (pin 1)
and square wave (pin 6) outputs.
The four trimpots (VR2-VR5)
11llow adjustment of each frequency
decade to match the dial calibration. Inverter stage ICld buffers the
output of IClc to provide the fixed
6V p-p square wave output. Additionally, the square wave output of
IClc is fed direct to switch S2a and
to S2a via a 39k0 attenuator.
The triangle wave is derived
from pin 2 of ICla and applied to
buffer/amplifier stage ICle which
is wired in linear mode. After that,
the signal is fed to a shaping network (33pF // 18kn) and then fed to
S2a. Similarly, the sinewave output
is produced by driving the triangle
wave into soft limiting stage IClf
which is also wired in linear mode.
VR6 and VR7 provide adjustment
for level and symmetry to produce a
rough approximation of a sinewave.
Switch S2a selects the appropriate waveform and feeds it to
an output stage consisting of six
4069 inverters (IC2a-IC2f) wired in
parallel. This stage is used in linear
mode in the first three switch positions for sine, triangle and square
waves and provides a 4V p-p signal
to the output attenuator. In the
fourth switch position, the 27kn
feedback resistor is switched out
and IC2 inverts the output of IClc to
provide a 6V p-p square wave to the
attenuator network.
The 6V p-p variable output is
useful for driving digital circuits
operating from 6V supply rails and
Specifications
Waveform functions
Frequency range
Output level
Output impedance
Amplifier power output
Power supply rails
Maximum supply current
Sine, triangle and square wave
1 OHz-11 OkHz
0-4V p-p continuously variable on sine,
triangle and square wave, 0-6V p-p
continuously variable on square wave, 6V
p-p fixed square wave output
600 ohms
1W into 8 ohms
± 15V unregulated, ± 6V regulated
200mA
also has faster switching times,
especially on the highest frequency
range. Note: this output is independent of the 6V p-p fixed square
wave output from ICld.
The signal from the 4069 output
stage is AC-coupled via a 470µF
capacitor to the attenuator network. This network consists of a
lkn pot, fixed 9.lkO and lOOkO
resistors, and switch S3b. Depending on the setting of the pot, the
output impedance will be no more
than about 6000.
The audio amplifier circuitry is
about as simple as you can get and
is based on an LM380 audio IC.
This has a power output of 1W into
80, a gain of about 10 and a frequency response from 30Hz to
30kHz (-3dB).
Starting at the input, a O. lµF
ceramic capacitor couples the incoming signal to 500kn pot VR9
which functions as a volume control. From there, the signal is coupled via another O. lµF capacitor to
the pin 2 input and also to the pin 6
input via a 220k0 resistor and
parallel 33pF capacitor. The 220k0
limits the gain, while the 33pF
capacitor determines the upper frequency rolloff.
The amplified output signal appears at pin 8 and is fed to the
loudspeaker via a 470µF capacitor
and series 4. 70 resistor which provides short-circuit protection. The
series 4.70 resistor and O. lµF
capacitor across the output form a
Zobel network which ensures
stability of the amplifier.
Power for the circuit is derived
from a 12V AC plugpack
transformer. Dl and Cl half-wave
rectify the incoming AC to provide a
nominal + 15V rail, while DZ and
C2 provide a nominal - 15V rail.
Note: these rails will be closer to
+ 18V and - 18V under no-load
conditions.
Finally, regulated ± 6V rails are
derived using 7806 and 7906
3-terminal regulators. Diodes
D3-D6 protect the supply against
reverse polarity connection to external voltages (eg, charged
capacitors).
Construction
A complete kit of parts for this
project is available from Technikit
Electronics (see panel). To make
MARCH 1988
45
PARTS LIST
1 plastic case with silkscreened front panel (predrilled)
1 carrying handle
3 knobs
1 PCB, code Technilab 301,
146 x 86mm
1 8 n loudspeaker with
attached pedastal
1 0 threaded brass spacers
3 2-pole 4-position slide
switches
1 3.5mm DC power socket
1 3 .5mm switched line socket
Semiconductors
Above shows the completed PCB, ready for installation in the case. Note the
threaded spacers and screws which form the 10 binding post terminals.
2 4069 hex inverter ICs
1 LM380N audio amplifier IC
1 7806 +6V 3-terminal
regulator
1 7906 -6V 3-terminal
regulator
6 1 N4002 or 1 N4004 diodes
Capacitors
A small pedastal is used to support the loudspeaker on the back of the board.
Note that the PC pattern has been modified to eliminate the wire link.
construction really easy, the case
comes pre-drilled with the speaker
grille already fitted to the rear
panel. The front panel features red
screen printing on a dark grey
background for a professional
finish.
All the components, except for
the power input jack, are mounted
on a printed circuit board [PCB)
measuring 146 x 86mm. The three
pots, along with the 3-terminal
regulators, 4700µ,F filter capacitors
and the loudspeaker, are mounted
on the back of the board, with all
other parts mounted on the front.
Begin assembly by installing all
the parts on the front of the PCB as
46
SILICON CHIP
shown in Fig.2. You can install the
parts in any order you wish but
make sure that the ICs, diodes and
electrolytic capacitors are correctly oriented.
The three electrolytics used (2 x
470µ,F and 1 x 10µ,F) are all RB
types and should be installed with
their bodies flat against the PCB
[see Fig.2). To do this, bend the
leads of each capacitor at right
angles before mounting it on the
PCB. The power indicator J;..ED
should be stood off the board by
about 8mm [the long lead is the
anode).
Ten terminals must also be
mounted on the board for the
2 4700µ,F 25VW axial
electrolytics
2 4 70µ,F 16VW PC electrolytic
1 1 Oµ,F 16VW PC electrolytic
5 0 .1µ,F ceramic
1 0.1 µ,F greencap
1 .01 µ,F green cap
1 .001 µ,F greencap
1 1OOpF ceramic
1 82pF NPO ceramic
2 33pF ceramic
1 1 5pF ceramic
Resistors (0.25W, 5%)
1 x 1 MO, 3 x 220k0, 3 x 1 OOkO,
1 X 39k0, 1 X 33k0, 3 X 27k0, 1
x 22k0, 1 x 18k0, 1 X 9.1 kO, 2 x
1k0, 1 x470, 2 x4.70, 1 x 1MO
trimpot, 1 x 500k0 log potentiometer, 6 x 1 OkO trimpots, 1 x
1 kO linear potentiometer
various inputs and outputs. These
consist initially of 25mm nickelplated screws which are fastened
to the PCB by means of 12mm tapped brass spacers. The ends of the
screws are later passed through
the front panel and fitted with
washers, nuts and plated knurled
knobs to finish the terminals.
Check that the three 4-position
slide switches are pushed down
firmly onto the PCB before soldering. The loudspeaker socket is installed with its earth terminal
towards the bottom of the PCB.
You can now install the parts on
the frequency control on the x1,
x10 and xlO0 ranges. The x1k
range begins at l0kHz, so how
much of this range you hear will depend on your hearing.
Finally, use your multimeter to
check the supply voltages. The
± 6V rails should be very close to
their nominal values for loads up to
200mA (within 5%). The ±15V rails
should vary from around ± 18V at
no load down to a minimum of
± 14V with a l00mA load.
Calibration
The loudspeaker, 3-terminal regulators, and 4700µF capacitors are mounted on
the back of the PCB. The regulators are kept cool by finned heatsinks.
the rear of the PCB. The pots go in
first. Bend their leads at right
angles so that they mate with their
respective pads on the board.
Secure the pots from the front of
the board with the washers and
nuts provided before soldering the
terminals. Note that the pots are all
different values so be sure to use
the correct pot at each location.
Next, solder 35mm lengths of
hookup wire to each of the speaker
output pads on the back of the PCB.
The two 4700µF capacitors can
now be mounted, followed by the 6V
regulators. Bolt small TO-220 style
heatsinks to the 6V regulators as
shown in the photograph. Make
sure that these don't short with the
leads from the 4700µF electrolytics.
The loudspeaker supplied with
the kit comes with a "pedestal" attached to its magnet (see photo).
This pedestal consists of a fibre
disc, a 12mm threaded spacer and
a screw. The whole assembly is
simply mounted on the back of the
PCB and secured from the front using a nut.
You can now complete the wiring
by attaching the speaker leads and
by connecting leads from the PCB
AC-input pads to the 3.5mm socket
on the rear of the case.
Testing
A final check of component orientation and placement is advisable
before switching on. When you are
satisfied that everything is correct,
apply power and check that the
LED comes on. Now turn the gain
full on and touch the amplifier input
terminal - you should hear a
healthy "blurt" from the speaker.
If everything is OK so far, set the
output level to 40 x 5, select the
square waveform, and connect a
wire link between the generator
output and amplifier input terminals. You should now hear tones
from the loudspeaker as you vary
Where to buy the kit
A kit of parts for this project is available from Technikit Electronics. The
kit includes all parts and comes with a pre-drilled case and a silkscreened front panel. Price: $69 .50 plus $6 .50 p&p ($8 .50 to NZ) . Add
$1 0. 00 for the 1 2V AC plugpack transformer.
Payment may be made by cheque or Bankcard/Mastercard number with
mail order, or by Bankcard/Mastercard number for telephone order.
Send your order to: Technikit Electronics, 654 Calder Hwy, Keilor, Vic.
3036. Phone (03) 336 7840. The Technilab 301 is also available in fully built-up form. Contact Technikit Electronics for further details .
Calibration involves adjusting the
six preset pots (VR2-VR7) along one
edge of the PCB. For non-critical applications, these can all be set to
mid-travel. The dial calibrations
will then be accurate to ± 10% and
you will get quite a reasonable
sinewave.
To accurately calibrate the instrument, you will need a digital
frequency meter (eg, the 1GHz DFM
described in SILICON CHIP from
Nov.87 to Jan.88). The procedure is
as follows:
(1). connect the DFM to the
generator output terminals;
(2). set the output to maximum on
square wave and set the main frequency dial to 110;
(3). set the frequency range to xl
and adjust trimpot VR2 so that the
DFM reads 110Hz;
(4). adjust VR3 on the xlO range for
a reading of 1 lO0Hz, VR4 on the
xlO0 range for a reading of 11kHz,
and VR5 on the xlk range for a
reading of 1 lOkHz.
An oscilloscope is required to accurately set the sinewave shape.
Set the output frequency to lkHz,
then adjust VR7 (symmetry) so that
the positive and negative peaks are
as close as possible to the same
shape. After that, it's simply a matter of adjusting VR6 (sine level) for
smooth rounding of the sinewave
peaks. Don't go too far or you will
flatten the peaks too much.
Once calibration has been completed, the PCB can be fitted to the
front panel and secured by fitting
nuts and washers to the terminals.
Complete the terminals by fitting
the round knurled nuts, then screw
the handle to the rear panel.
Finally, fit the front panel
assembly to the case and secure it
using the four corner screws.
~
MARCH 1988
47
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....
YCAR
r LOW COST UTILITY TIMER
rLOW DISTORTION AUDIO OSCILLATOR
YCAR
Ref: EA Feb 1988
YCAR
Ref: EA Dec 1986
Whether you wish your egg soft but not too soft, or whether
YCAR
At last it's available, the metered version of our auudio oscillator. Compares wtth the very
YCAR
you want to add the time factor to a game ofTrtvtal Pursuit,
best laboratory standard sine wave equipment available.
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this utility timer Is Ideal.
Cat KA-1677
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Complete ktt
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"Cat.
KA-1697
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SUPER SIMPLE MODEM
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rTRANSISTOR, FET AND
Ref: AEM Sept 1986
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Due to customer demand, we have decided to Introduce this Into our range. It's very cheap
ZENER TESTER
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and It works well. Kit Is suppl1ed with RS232 female connector and all other parts except
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power
pack. which Is extra $13.95 (Cat MP-3020)
Ref:
EA
Feb
1988
YCAR
Revamped version of an oldie. Checks transistors, fets and
\.. Cat KM -3046
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zencrs as well as checking transistor breakdown voltages.
YCAR
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Great for the workbench, and also for showing how
'!'CAR
semiconductor devices operate. Complete kit Includes box,
r LOW OHMS ADAPTOR FOR DMM's
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meter, transformer and all parts.
'l'CAR
Ref: Silicon Chip Feb 1988
-...cat. KA· 1698
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Another handy kit from SC which utlllses your digital multlmeter.
YCAR
....
Cat. KC-5023
'!'CAR
~ ELEPHONEINTERCOM
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"I
Ref: ETI Feb 1988
'!'CAR
rMODEM END OF FILE INDICATOR
'!'CAR
Use 2 old telephones to make an intercom. Kit includes
'l'CAR
power supply, filter capacitors, box and all parts.
Ref: Silicon Chip Feb 1988
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PC board and all parts supplied Including switch.
•
CaL KE-4731
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Cat
KC-5024
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"YCAR
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rDOOR MINDER
ULTIMATE CAR BURGLAR ALARM
'l'CAR
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Ref: Silicon Chip Feb '88
Ref: Sllcon Chip Feb '88
'l'CAR
9V
power
supply
New gcnerat1on door opener alarm.
Includes flashing light switch, back-up battery and lgn1tlon ldller.
'!'CAR
Cat MP-3010 $18.50
Cat KC-5020
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•
A baffling exercise
It was the Count of Monte Cristo who, prompted by
his creator Alexander Dumas, made the profound
observation that, "Only he who has known the
greatest sorrow can know the greatest joy." After
battling with a particularly stubborn video
recorder recently, I felt the same way.
Fortunately, my first story did not
cause all that much frustration. It
concerns a Toshiba colour TV set; a
model C-1416, 33cm set of some five
years vintage. The job started out
as a fairly routine assignment but
caused some head scratching at
one stage.
It started off with a phone call
from a new customer who, after
describing the make and model of
the set, complained simply that it
had stopped. I tried a few discreet
questions to get some idea of what I
might be up against, but quickly
realised that this wasn't getting
anywhere; the set had stopped and
that, as far as the customer was
concerned, was all there was to it.
All I could do was suggest that he
bring it into the shop.
So it was that he turned up at the
shop a couple of days later and sat
the Toshiba on the counter. I plugged it in while he was there and confirmed that, at least as far as he
was concerned, the set was totally
dead; no picture, no raster, no
sound. But it wasn't totally dead to
my ears, because I could hear the
power supply hiccuping away merrily, suggesting an overload which
it didn't like.
I am not very familiar with this
particular set but there were a couple of points in my favour; I had a
service manual and, when I came to
work on it, I found it a lot easier to
get at than many designs I could
mention. The circuit was well laid
out and easy to follow, and appeared to be a fairly conventional
arrangement. As I said, it all looked
fairly straightforward.
Likely suspects
With symptoms like this the two
areas I first suspect are the power
supply and the horizontal output
stage. The power supply was fairly
typical; a switchmode arrangement
running from a bridge rectifier connected directly to the mains. Much
the same applied to the horizontal
output stage; a horizontal driver
transistor, Q402 (2SC2482), driving
__
PIN 1,
LOT T461
.JLf\_
......,.
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890VP-P
C464
560pf
C463
.0022
2kV
Fig.1: horizontal output stage of the Toshiba model C-1416 TV set. Note
the protective resistor and diode built into the 2SD896 transistor.
50
SILICON CHIP
the horizontal output stage (Q404)
via a transformer (T401). The
horizontal output stage was a
2SD869, a transistor with built-in
protection (ie, a resistor from the
emitter to base and a diode from
collector to base).
The main HT rail was shown as
114V, which was applied to pin 3 of
the horizontal output transformer,
then from pin 1 to the collector of
the aforementioned 2SO869. That
much digested I decided to measure
the HT rail, which can often provide a clue as to the likely culprit. It
turned out to be well down, around
50V, and I mentally filed this figure
for future reference.
At this stage it was a toss-up
whether to move to the right of the
circuit, towards the horizontal
stage, or to the left towards the
power supply. Fully aware that
Murphy would be lurking around
the corner, to make sure that which
ever way I went would be the
wrong way, I took a punt on the output stage.
Well it seemed that Murphy must
have slipped out for a cup of Irish
coffee, because that was the right
decision.
In greater detail I simply disconnected the output transistor. These
transistors are not the easiest to
test, since they tend to show a low
resistance from collector to base,
regardless of polarity, due to the
protective diode. Similarly they
show a low value resistance, ranging from about 400 to 900 according to type, between base and
emitter. Granted, one can allow for
these characteristics but it is usually easier to simply fit a new
transistor.
But, before fitting a new one, I
switched the set on with the
original one removed. I wasn't quite
sure what kind of a HT reading I
would get, but I hoped it would
come up to something near normal,
if the transistor had been faulty. On
the other hand, there was a risk
that it might go high and trigger any
over-voltage protective circuitry.
Once again, it seemed that I had
done the right thing because the HT
rail came up almost spot on the circuit value. It seemed that it was my
lucky day; I should have the job
knocked over in short order. All I
had to do was fit a new transistor
and we should be up and running.
It must have been around this
time that Murphy finished his coffee and came back on duty. I switched the set on, full of confidence,
only to find that it was in exactly
the same condition as before;
power supply hiccuping and low HT
rail. Somewhat taken aback, I
reached for the CRO leads and
made a quick check of the signal
from the driver stage, through the
driver transformer, and to the base
of the output stage. As nearly as I
could tell, allowing for the reduced
rail voltage, this section appeared
to be functioning.
At that point the only logical
thing I could think to do was to take
the new transistor out, check the
HT rail and power supply
behaviour again, and try to decide
what to do next. And that operation
produced surprise number two the rail voltage had risen, but not
all the way; it was now sitting at
around 75V. What the heck was going on?
Smoke signals
I double checked the connections
to the transistor, confirmed that
they were correct, and began looking for any other silly mistake I
might have made. I found nothing,
but had left the set running during
those few minutes. Suddenly my
nose told me that something was
getting hot somewhere and a few
seconds later I pinpointed the
source.
A thin curl of smoke was rising
from a capacitor which forms part
of the output stage assembly; C464,
a 560pF, 2kV unit connected between the collector and the emitter
of the output transistor. It was a
blue plastic encapsulated unit
which had suddenly developed a
brown spot that grew larger as I
watched it.
Well, that was the breakthrough.
I pulled the capacitor out and then,
before refitting the output transistor, turned the set on and checked the HT rail again. And this time
it came up just above the nominated
value, exactly as it had done the
first time. Which I reckoned proved
the point.
At a more practical level I needed a replacement capacitor. My
stocks didn't run to an exact
replacement, but I did find a 560pF
unit with a 3kV rating. This was fitted, the original output transistor
wired back in, and the set given
another try. And this time
everything worked; the set gave
forth sound, the HT rail came up
spot on, and a first class picture appeared as the set warmed up.
So that was that and the set was
duly returned to a happy customer.
But it is worth speculating on what
caused the sequence of events just
related. Fairly obviously, the
capacitor was faulty all along, being unable to withstand the peak
level of nearly 900V generated by
the output stage, and pulled the HT
rail down accordingly.
But with the output stage removed no such voltage was generated,
and all it had to withstand was the
114V from the HT rail. Initially, at
least, it was able to do this but it
must have been on the point of
breaking down completely. My test
run with the replacement transistor
must have been the last straw; by
the time I tested the set without the
output stage for the second time, it
was breaking down at 114V and
went up in smoke.
Which is all very satisfying from
a technical point of view, but most
of my diagnosis was wasted; a few
more minutes running on the bench
would have produced the curl of
MARCH 1988
51
SERVICEMAN'S LOG
smoke and revealed the fault with
no effort on my part.
That's the luck of the game and it
had a happy ending anyway.
A failure to erase
My next story involves a much
more frustrating experience. It concerns a Sanyo beta video recorder,
type VTC 5005, that belonged to a
regular customer. The first intimation of the trouble came via a phone
call from the lady of the house. The
fault was rather unusual in that the
machine would record the video
signal satisfactorily but, on odd occasions, would fail to record the
sound or erase any previous sound
track.
She went on to enquire whether
this was a common fault, whether I
knew what would cause it, and, of
course, was it going to be expensive
to fix. I had to reply that it was a
fault I had not encountered before,
that I could only assess the likely
cause in broad terms, and that it
was almost impossible to estimate
the cost. However, I did promise not
to let costs get out of hand without
consulting her. In the meantime I suggested that she
bring the set in.
So the lady turned up at the shop
a couple of days later with the
machine and, commendably, she
had thought to bring a faulty tape
with it. In the event it didn't help a
great deal, except to confirm the
symptoms she had described, but
even that was useful and I wish all
my customers could be so
thoughtful. I tried the machine
while she was there, but I need
hardly add that it behaved perfectly. This surprised neither of us.
I have not had much experience
with this machine, but I do have a
manual and I fished this out immediately. In particular I concentrated on the section designated
"VD-1 Audio Circuit"; the section
which handles the audio signal taking it from the record/replay
head, or feeding it to it, as required
- and which also incorporates the
bias and erase oscillator.
It was this latter which interested me most because it was
this function that was failing
somewhere along the line. But exactly where was the real question.
It could be in the oscillator itself, it
could be the erase head, or it could
be the flexible lead and plug and
socket which connects the head to
the board.
The record/replay head seemed
an unlikely suspect, in that there
had been no replay problems as
such. And if the bias line to this
head had failed somewhere on
the board I would have expected that the system would
still erase, but fail to record
anything but a weak and
distorted signal. So the
odds were strongly in
favour of a failure within
the erase circuit, or
failure of the oscillator
itself.
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52
SILICON CHIP
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But I needed to be sure. And
when you think about it, this isn't
an easy function to monitor. Simply
letting the machine run in the
record mode is of little value, since
any failure will not be apparent until the tape is replayed, by which
time the fault will most probably
have vanished. But, in any case, the
time involved in such an approach
would be quite unacceptable.
As depicted on the accompanying
circuit the erase/bias oscillator
(near the bottom) consists of transistor Q2007, transformer T2001,
and a few minor components. The
secondary of T2001 feeds the erase
head directly from pin 5, and supplies the bias for the record head
from pin 6, via C2027 and tab pot
VR2003. The erase head is connected via plug and socket S2002
and the record/replay head via
S2001.
Fortunately, the circuitry involved is fairly easy to reach. In fact the
audio circuit, as shown separately
in the manual, is really a part of the
complete video/audio board, and
the print side of this is directly accessible when the main covers are
removed. After that, removal of a
few screws permits the board to be
swung up, giving access to the component side.
For a start I set the machine up in
the record mode and connected the
CRO to the active terminal of the
erase head, this being about the
most convenient access point. This
confirmed that the oscillator was
functioning, at least for the present,
so I decided to leave it running in
this way, while I went on with other
jobs, simply glancing at the CRO
from time to time to check what was
happening.
Initially, this approach paid off.
After it had been running for some
time I checked the CRO and realised that the erase signal had vanished. Unfortunately, before I could
make any further tests the system
came good. I wasn't too worried at
this stage; I blissfully imagined
that, since the fault was obviously
in a mood to happen spontaneously,
a little prodding, freezing, or
heating would encourage its reappearance.
I should have known better. I
tried every trick in the book; I froze
every component likely to be involv-
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------------------------------------
Fig.2: relevant section of the audio circuit of the Sanyo VTC 5005 VCR. Note the erase head plug at bottom left.
ed and blasted the whole area with
a hair dryer. I tugged the leads,
wriggled the plugs and sockets, and
prodded every component with
everything short of a sledgehammer. Nothing produced the
slightest hint of a fault. Had I not
known better, I would have been
prepared to swear that there was
absolutely nothing wrong.
All I could do now was to continue the tests as before. And this I
did, for several hours each day for
the next couple of weeks. But not
once did the CRO pattern so much
as flicker, even though I repeated
some of the previous brute force
tactics from time to time. It was a
stalemate.
I would have been happy to leave
things set up for as long as was
necessary, but this would hardly
suit the customer. In fact they had
already made a couple of polite enquiries and I sensed that they were
becoming impatient. Among other
things, I realised that they used the
machine more for playing prerecorded tapes from the video shop
than for recording off-air programs.
The upshot was that I explained
to them what I had discovered so
far [which wasn't really very much)
and that, until the machine elected
to fail again - which it appeared to
be stubbornly refusing to do at this
stage - there was very little
chance that I could make any progress. So it was agreed that they
take the machine away and make
such use of it as they could, until
such time as the fault worsened.
Weeks went by, then several
months, before I saw them again.
Then the lady contacted me with a
completely different problem and I
took the opportunity to enquire
about the recorder. "Oh, it's going
fine", she replied, "whatever you
did seems to have fixed it."
I know the feeling: after that
length of time I could almost kid
myself that I had done something to
fix it; almost, but not quite. Deep
down I knew it was only a matter of
time before the gremlin would
strike again.
But more months went by and a
couple of discreet checks on my
part produced the same answer,
"It's going fine. " Then came the
day when the lady was on the
phone with a tale of woe. "The
recorder is really playing up now. It
is almost impossible to record
anything." This was the best news I
had heard about the machine so far
and my enthusiasm probably showed when I suggested she bring it in
immediately. She lost no time in
responding.
Before disturbing anything I loaded a tape into the machine and
made a brief test recording. Sure
enough, the fault was there. So,
very gently, I removed the covers
and connected one of the CRO probes to the active lead at the audio
erase head. This confirmed that the
fault was still present and I reached for the second CRO probe with
the idea of checking progressively
along the board.
At which point the system suddenly came good and there was no
more I could do until it decided to
play up again. Fortunately I didn't
have to wait very long. When it failed this time I very gently removed
the necessary screws and lifted the
MARCH 1988
53
SERVICEMAN'S LOG
board so as to provide access to the
component side. This didn't disturb
anything and the fault remained.
I reached for the second CRO
probe and approached the print
side of the board in the vicinity of
the two pins which mate with
socket S2002, and which carries
the leads to the erase head. By just
touching the board, and before I
could make an electrical connection, I cleared the fault.
Suspect plug and socket
I immediately suspected the plug
and socket assembly, and this seemed to be confirmed when I wriggled
the lead and the plug and found
that, by stressing the assembly in a
certain way, I could make the fault
come and go. At last it looked as
though I was getting somewhere.
In this setup the plug on the lead
is actually the female connection,
the male contacts being two pins
soldered into the board. I was
specially suspicious of the female
contacts, particularly where they
made contact with the cable. This is
a crimped connection and it is not
54
SILICON CHIP
unusual to find the crimping does
not penetrate the insulation properly, resulting in an intermittent
connection.
Removing contacts from plugs of
this type is a little tricky. They are
held in by a small tongue or barb
punched into the contact, and
which is depressed when the contact is inserted into the plug. It springs up when the contact is fully inserted and effectively locks it in
place.
To remove these I use a long,
thin, pointed probe with which to
TETIA CORNER
Thorn 9904 (Q Chassis)
Symptom: No luminance . Sound
and colour OK. A normal picture
appears briefly if the set is switched on again quickly after switching
off. 12V rail reads high at 15.5V.
Cure: D231 (EQA01-12S) 12V
zener diode open circu it. This
diode sets the 1 2V rail and the
higher voltage when it fails blanks
the video output from IC201 .
depress the tongue and thus allow
the contact to be withdrawn from
the back of the plug. With both contacts out I examined them carefully.
As far as I could see they were
quite OK, but I also checked them
with an ohmmeter. Again they
seemed faultless, even when the
wires were vigorously tugged and
wriggled.
Nevertheless, I put them through
my own "extra crimping" process.
This involves applying pressure to
the stem of the contact, in the valley
where it is supposed to punch
through the cable insulation. To do
this, I use a pair of cutters, with one
blade lying the length of the valley. I
know it sounds drastic, and it certainly looks risky, but it is merely a
matter of applying a judicious
amount of pressure. And it does
work.
But it didn't help much in this
case. I re-assembled the plug, fitted
it back on the board and gave the
whole setup another wriggle test. It
behaved exactly as before;
pressure on the plug or tension on
the cable could make the fault come
or go. And, since I felt that I had
cleared the plug, the next likely
suspect was the pair of pins on the
board.
Conned
I examined the joints where these
pins were soldered to the board,
even though I had already been
over them once before, but could
see nothing suspicious. Nevertheless I resoldered them, just to
make sure. But this achieved
nothing either and I was forced to
the conclusion that there was probably nothing wrong with the plug,
socket, and cable assembly; that I
had been conned by their sensitivity
to pressure.
And I had been conned in more
ways than one. It had seemed so obvious that this was where the fault
lay that I hadn't even bothered to
make the other obvious check
which I had set out to make at the
beginning; whether the oscillator
itself continued to function when
the waveform vanished from the
erase head.
I quickly made amends, connecting the second CRO probe directly
to the oscillator circuit. Then I
wriggled the plug and socket
assembly again, created the fault,
and established that it was the
oscillator that was failing, not the
circuit to the head, in spite of the
symptoms.
That much established, the next
likely possibility seemed to be a
faulty component in the oscillator
circuit and, by now, I would have
been quite happy to replace every
component in this part of the circuit
if it produced a quick cure. After
all, there was only one transistor
and a handful of resistors and
capacitors. The transformer,
T2001, was about the only special
item.
But before taking that drastic
step I decided on another freeze,
heat, and bash routine. After all,
the thing was much more touchy
now than it had been when I tried
this before, and it might just work.
And so I set to, with the machine in
the record mode, both CRO probes
connected, and the fault condition
evident, this having been achieved
by much wriggling of the aforementioned erase head plug.
I drew a blank with the freezer,
and similarly with the heating, so I
reached for the sledge-hammer actually the butt end of an insulated
alignment tool - and began prodding. Nothing happened until I
came to C2029, a 100µ,F 16V electrolytic, when the lightest touch
caused the oscillator to come good.
Which was very encouraging, except that no amount of additional
prodding, freezing, or heating of
this component could reverse the
procedure. So what did it mean?
Was the capacitor faulty, or was
this another furphy like the erase
head plug where, apparently,
vibration and pressure was being
transmitted to the fault somewhere
nearby on the board?
In any event, it seemed logical to
remove the capacitor, check it as
thoroughly as possible and, if any
suspicion remained, replace it. But
it didn't come to that because, as I
unsoldered one of the lugs, the
solder came away much too readily
and I was convinced that I had uncovered a dry joint, one that had
defied my visual inspection.
Closer inspection of the lug confirmed my suspicion. It had been
tinned during manufacture but I
was convinced that the solder on
...
the board had never really "wet" it.
Most likely it was a "cold" joint;
one where the temperature of the
lug had never reached the melting
point of the solder.
I measured the capacitor as a
matter of course, and it was well
within tolerance. I cleaned the lug,
tinned it again, put it back on the
board, and made sure it was well
and truly soldered to the pattern.
Then I checked the whole system
again.
I wasn't really surprised when it
came good immediately, because it
had done that many times. But I
was gratified to find that wriggling
the erase plug no longer had any effect. Considering how touchy it had
been before, I felt it was very
significant.
But there was more to it than
that. The capacitor's position on the
board was slap alongside the two
pins which mated with the erase
plug. So wriggling the plug could
easily have aggravated a dry joint
at the capacitor lug.
I ran the machine for several
hours a day for a week or so after
that, and it never missed a beat. Of
course it had done that before too,
so I couldn't be one hundred percent sure that I had fixed it. The only thing I felt sure about was that I
had found a dry joint, even if the only evidence I had was my own
observation when I unsoldered it.
And so the machine was returned to the customer, with a strong
emphasis on the need to contact me
immediately should the fault show
again. Thafwas several months ago
and a couple of check calls have
confirmed that there has been absolutely no sign of the fault.
Only time will tell though. I'm
keeping my fingers crossed.
~
RCS Radio Pty Ltd is the only company which
manufactures and sells every PCB & front panel
published in SILICON CHIP, ETI and EA.
651 Forest Road, Bexley, NSW 2207
Phone (02) 587 3491 for instant prices
4-HOUR TURNAROUND SERVICE
MARCH 1988
55
OLD-'I'I M f.
CRYSTAL
DXing with a crystal set can be a lot of
fun. This old-time crystal radio comes as
a kit and delivers a performance that
will surprise you.
By JOHN HILL
The story of this old-time crystal
radio begins in the Victorian city of
Ballarat. Like many towns these
days, Ballarat is chasing its share
of the tourist dollar and offers
many first-class attractions for the
tourist to see.
The latest addition to Ballarat's
sights is something that should be of
interest to SILICON CHIP readers,
especially those old enough to
remember the early days of radio.
Ballarat now boasts the Orpheus
Radio Museum which is full of
56
SILICON CHIP
fascinating electronic relics from
the past.
However, the premises are not
used solely as a museum. In a
separate factory area at the rear,
museum owner Richard Wilson has
a workforce of approximately 20
employees producing computer
equipment and other hi-tech electronic gear under sub-contract, as
well as their own products
marketed under the "Atron"
tradename.
An unusual aspect of the
10
business is the production of vintage radio kits which are sold
through the museum and by mail
order. These kits include a 1-valve
receiver, a 2-valve receiver and a
"Super Crystal Set". Both of the
valve radios are battery-operated
"reaction" types.
The crystal set
The Super Crystal Set is of particular interest and is based on an
early Navy circuit which is most efficient. I have built this set and its
performance is so good I had difficulty in believing the station call
signs I heard.
Any crystal set that can separate
about 15 stations and pull in interstate transmissions at listenable
volume is a mighty fine design. I
might add that this remarkable performance was possible even with a
local 5kW station only 6km away.
Without that local station, the
t::o------c
,11 I
~
E
.__---~·
#
START
)
S1
CJ
HIGH Z
PHONES
I
T EARTH
SUPER CRYSTAl SET
Fig.1: unlike other crystal sets, this design has two separate tuning circuits with
variable inductive coupling (via L2). Result - greatly improved station selectivity.
◄ The Super Crystal Set control panel
is well laid out. Black bakelite , brass
fittings and gold lettering give the
receiver an authentic vintage radio
appearance.
Super Crytal Set would perform
even better.
Personally, I relate rather well to
crystal sets, for it wa s these simple
receivers that fostered my interest
in radio some 40 years ago. I built
them in all shapes and sizes, including some in matchbo xes.
However, I was always restricted
to one station listening. As I lived in
Bendigo at the time, 3BO was all I
ever heard on any of my crystal
sets.
My crystal sets were set up in my
bedroom and I would often go to
bed early and lay in the dark with
the headphones on and listen for
hours. I did a lot of listening to
crystal sets simply because they
were all I could afford at the time.
Yes, I have very fond memories of
my home made crystal receivers.
Getting back to the Super Crystal
Set again: it is available in kit fo rm
and is very well presented. The kit
is complete and comes with a bra ss
stud switch, a headphone jack, and
every nut, bolt and washer - in
short, the lot! The front panel and
baseboard are pre-drilled so tha t
the set goes together with a
minimum of fuss.
This end of the set tunes the radio frequencies before the signal is fed to the
detector. The small tuning capacitor at right is the author's modification
Spiderweb coils
Construction of the Super Crystal
Set is quite intricate and it takes a
good many hours to build. It requires the winding of thr ee
The detector end of the set is fairly conventional. The small white spider web
coil is the "swinging" coupler that varies the coupling between the two
sections of the receiver.
M ARCH 1988
5:7
Crystal sets require high impedance headphones hut you can also use low
impedance phones provided you use a matching transformer. Shown is an old
STC headset. This has an impedance of 2000 ohms and is guaranteed to put
callouses on your ears within one hour.
"spiderweb" coils, two of which
are tapped. One coil is of the "swinging'' variety and is used to vary
the coupling between the two
stages of the receiver. These two
separate stages in the receiver require further explanation.
Most crystal sets have a single
tapped coil and a tuning capacitor
to select the stations. Such a set-up
usually gives very broad tuning and
if there are a number of strong
local stations, as is the case in
capital cities, then the set may not
be selective enough to separate
each signal without interference.
The Super Crystal Set is not like
this. It has two separate tuning circuits that are connected by a
variable inductive coupling which
also helps to make the receiver very
selective. In other words, the set
has a tuned radio frequency (RF)
stage before the detector, with the
two stages inductively coupled by a
high-frequency transformer (the
swinging spiderweb coil). Such a
circuit design has a dramatic effect
on selectivity, with very little loss in
volume.
Tuning the Super Crystal Set is a
two-handed job since each circuit
must be tuned separately (no fancy
ganged capacitors back in the good
ol' days)! The RF circuit is tuned
with a brass stud switch, while the
detector circuit is tuned with a
variable capacitor.
The brass stud switch is connected to the aerial coil which is
tapped every eight turns. This eight
turn tapping set-up proved to be interesting in the set that I built.
Some stations were received at
equal volume on two adjoining
studs, indicating that the true
resonance point of the coil was midway between the studs. I reasoned
that a bit of fine tuning could
perhaps make this excellent
receiver even better.
To eliminate this slight error, a
small variable capacitor was added
to the radio frequency circuit in
order to smooth out the courseness
of the 8-turn tappings. The addition
of this capacitor was so successful
it almost doubled the number of stations received.
Note: this small capacitor is not
included in the kit and w_a s strictly
my own experimental modification.
If you wish, you can do exactly the
same. The variable capacitor is
shown by the broken line on the circuit diagram (Fig .1).
The general appearance of the
Super Crystal Set is most pleasing
to the eye. The kit has been designed in keeping with the early radio
scene and all fittings are made of
brass and black Bakelite. The
assembled components are
mounted on a stained and polished
baseboard. Gold lettering on the
front panel adds the finishing touch
to a well-presented product. Lacquering of the baseboard is the or.ly
preparation required by the constructor before assembly.
No cat's whisker
Anyone familiar with crystal sets
will recall how tedious it was to
This back view shows the complexity
of this particular crystal set. Quite a few
hours are required to assemble the kit.
58
SILICON CHIP
find a "good spot" on the crystal
and how easy it was to bump the
cat's whisker off that good spot
once it was found. The Super
Crystal Set solves that problem by
using a fixed detector which takes
the form of a good-quality ger-
manium diode. Mounting the diode
inside a fibre tube makes it look a
little more authentic.
Actually, the gold-bonded diode
is the secret to the set's success. If
a real crystal detector were used, it
would reduce the receiver's
sensitivity.
One novel aspect of a crystal set
is the fact that it costs absolutely
nothing to run, as it utilises the
radio frequency energy that's picked up by aerial. Of course, the
aerial must be long enough to collect sufficient energy to operate the
set. A suitable aerial should be in
the vicinity of 30 metres long and as
high as it can be conveniently
strung. An earth connection is also
a must for good crystal set
reception.
My aerial is a single strand wire
that is approximately 25 metres
long and six metres high. Such an
aerial is only average in crystal set
terms, but the reception I obtain is
the best I've ever experienced.
On a good night I can pick up two
Adelaide stations (5AN and 5CL),
two Melbourne stations (310 and
3AR), one Sydney station (2BL), and
one Queensland station (4QD). The
latter is about 1,500km, as the crow
flies, from my home in Maryborough, Central Victoria.
If anyone had told me that a
crystal set could do that prior to my
building the Super Crystal Set, I
wouldn't have believed them. The
Super Crystal Set is well named it really does give super results!
Headphones
The sound reproduction from the
set is also surprisingly good and the
tonal quality quite acceptable
through either my Brown or STC
headphones. Although phones such
as these are designed for maximum
sensitivity rather than hifi reproduction, they aren't too bad to listen
to . Crystal set headphones need to
be of high impedance - around
2000 ohms.
If high-impedance phones are not
available, low impedance phones
can be matched up to a crystal set
by using an old speaker
transformer. These gives the advantage of more comfortable listen-
ing with better tone, but a slight
drop in volume is apparent.
A small speaker transformer,
complete with box, plug and socket
is available as an optional extra if
required. Those who wish to build
the Super Crystal Set can do so
regardless of what type of headphones they have.
In these days of computerised hitech everything, it makes a pleasant
change to build a good oldfashioned crystal set. There's
something about going back to
basics that's hard to explain.
The cost of this particular piece
of nostalgia is $89.50 for the kit and
$5.00 for packaging and postage.
Yes, I know you could buy quite a
good transistor radio for that
amount, but I doubt if you would
have as much fun with it. Believe
me, DXing with a good crystal set is
pretty exciting stuff!
Footnote: the Super Crystal Set
is available from Ballarat Electronic Supplies, 5 Ripen St,
Ballarat, Vic 3350. Phone (053)
31 1947 .
Build This Old-T1Dle Crystal Set
Suppliers of * R A D · I O ~
vintage wireless kits
and wireless parts. RSD B98 Ballarat, 3352.
Ph. (053) 34 2513 Send for a free catalogue today!
WHEN NEXT IN BALLARAT DON'T MISS THE
ORPHEUS RADIO MUSEUM
CNR. RING RD. & WESTERN HWY. BALLARAT OPEN 7 DAYS A WEEK 10am - 5pm
MARCH 1988
59
How-
Do you design your own printed circuit
layouts? That being the case, you need a
good light box. This one is cheap, easy
on the eyes and easy to build.
By LEO SIMPSON
At SILICON CHIP we needed a
good light box. We design our
printed circuit boards using Bishop
tapes so we needed a light box for
that. And we needed a light box for
checking our wiring and overlay
diagrams and for marking up all the
photographs for page layouts.
When we came to look at commercially available light boxes though,
there were few that met our
requirements.
There were plenty of large commercial units, intended for use in
photocomposing rooms and so on
60
SILICON CHIP
and some intended for doctors' and
dentists' surgeries, but few that
were reasonably compact and cool
and comfortable to work on. None
were cheap.
Most, if not all, used frosted float
glass as the working surface. We
did not want these. Glass light
boxes often break and therefore
can be a real hazard to anyone
working with them. Frosted glass is
expensive and inconvenient to
replace too, so that was another
reason not to use it.
Hence, we decided to design and
build our own. We are presenting
the details here for anyone who
needs a similar unit and who is able
to handle a saw and screwdriver.
The total cost is less than $70, if
you buy all new materials.
Essentially, all that is required is
a suitably shaped box, painted
white inside and fitted with an 18
or 20 watt fluorescent light batten.
On top is mounted a sheet of white
translucent Perspex. And that is all
there is to it.
·
We even saved ourselves the
trouble of painting it by using white
Melamine-coated particle board,
16mm thick. This was cut to size,
screwed together and the job was
half done. We spent more time
shopping for the materials than actually putting it together.
To make it easy to work on, particularly if you are taping up a
printed board design, we made the
box with a sloping top, angled at
15° to the horizontal. At the front ,
to build a light box
the box tapers down to 38mm, so it
is quite comfortable to work on.
Tools required
You can get by with the very
minimum of tools for this project. In
fact you could manage the whole
job using hand tools. To make it
easier though, you will need an
electric drill and a circular saw,
preferably with a tungsten-carbide
tipped blade.
The assembly process consists of
cutting the Melamine-surfaced particle board to size, drilling the holes
for the screws, power cord entry
and ventilators and then simply
screwing it together. Glueing the
box together is not practical, since
the Melamine surfaces won't take
glue.
The first task is cut the various
pieces to size.
We dimensioned the box to suit a
standard 18 or 20 watt fluorescent
batten (batten is the term used to
describe the whole fitting, including
the tube) with a few millimetres
clearance at each end. Just to be
sure though, measure your batten
before you mark up the sheet for
cutting it would be most
frustrating to find you had made
the box too small.
The top edges of the front and
back pieces of the box should be
chamfered to match the 15° slope
of the sides. This is easily achieved
by setting the baseplate of the circular saw to the correct 15°
setting.
With care in your saw work, all
the pieces should fit together
squarely with little need for work
with a plane or rasp.
To ensure you achieve straight
cuts, use a straight edge as a guide
for your circular saw. The idea is to
clamp a thin straight-edged length
of timber to the particle board and
use it as a guide for the saw.
Don't forget to drill the various
holes for the power cord and ventilation. We used kitchen cupboard
vents which fit in a 28mm (actually
1-1/8 inch) hole. You will need a
hole saw or a Speedibore (an auger
18W FLUORESCENT LIGHT BATTEN BOLTED TO REAR »F
- - - - BOX WITH TWO 5mm DIA. x 35mm SCREWS AND NUTS.
SPACE BATTEN FROM REAR OF BOX BY ONE NUT THICKNESS.
HOLES A: 28mm DIA. TO ACCEPT CUPBOARD VENTILATORS
8: 10mm DIA. MAINS CORD ENTRY
C: 6mm DIA.
REAR 130x613
A
i
/
--1
BASE 312x613
i
130
J
CHAMFER TOP EDGES OF FRONT AND
REAR TO SAME ANGLE AS SIDES (15').
ASSEMBLE BOX WITH 40mm COUNTERSUNK
PARTICLE BOARD SCREWS. COVER SCREW HEADS
WITH DRESS CAPS.
MATERIAL: 16mm PARTICLE BOARD COATED WITH WHITE
MELAMIME ON BOTH SIDES. COVER EXPOSED EDGES WITH IRON-ON
EDGE STRIP.
COVER TOP OF BOX WITH 360x645 PIECE OF WHITE TRANSLUCENT
5mm ACRYLIC SHEET.
DIMENSIONS IN MILLIMETRES
LIGHT BOX
4
rv
38
Fig.1: we made our light box from 16mm-thick Melamime-coated particle board. The dimensions shown suit a standard
20W fluorescent batten but we suggest that you check the length of your batten before marking the sheet for cutting.
MARCH 1988
61
The fluorescent batten is fitted to the rear of the case to give an even spread
of light. Kitchen cupboard vents are used to cover the ventilation holes.
bit made for electric drills) to drill
these holes. When drilling these
holes, drill through until the bit just
breaks through the surface and
then finish the hole by drilling
through from the other side. This
stops you making a mess of the hole
and possibly tearing the Melamine
surface.
Finish off the sawn surfaces with
a rasp or sanding block before going to the next step, which is to
make the rightangle butt joints to
assemble the box.
The various sections are then
screwed together. We used Chipboard screws (Bg x 40mm, countersunk, made by W.A. Deutscher)
which have a coarse thread for
good holding power. Underneath
each screw head we placed the
countersunk plastic washer for a
white Snap Cap (decorative screw
caps made by Furnco ).
Alternatively, you can use Furnco Directors, which are particle
board screws which are supplied
with their own decorative caps.
Either way, there is no need to
coutertsink the screw heads into
the particle board.
We used fourteen screws (and
decorative caps) to assemble the
box.
To finish off all the exposed
edges of the particle board, use an
iron-on Melamine edging tape
(Armaflex-GL) and then trim to fit
using a sharp utility knife.
Now fit four rubber feet to the
underside of the box so that it does
not scratch or move around on the
table.
The next step is to fit the Perspex
top. Assuming that you have made
the box to the same size as our
drawing, the Perspex sheet should
be 360 x 645mm. We used some
3mm thick sheet we had on hand
but we suggest 4.5mm material as a
better choice as it will be more
rigid. You can get Perspex cut to
size from glass suppliers or you can
go to a specialist outlet such as
Cadillac Plastics in Sydney.
We attached the Perspex to be
top of the box using four countersunk head self tappers, 20mm long.
Drill and countersink the screw
holes before you remove the protective paper coating from both sides
of the Perspex.
Having fitted the Perspex,
remove it again so the fluorescent
light fitting can be installed.
Remove the tube and the top cover
from the batten and place it in the
box as shown. Mark the positions of
the mounting holes at both ends and
drill the box for 5mm diameter
Close-up view of the batten wiring. The mains cord should be anchored with a
clamp and its leads connected to the 3-way terminal block.
62
SILICON CHIP
screws. Before securing the batten,
fit the cord entry hole with a junction box grommet.
Secure the fluorescent batten
with two 5mm screws and nuts,
with one nut used on each screw to
space the batten away from the
rear surface of the box.
You may think that a more even
spread of illumination could be obtained by moving the batten more
towards the centre-line of the box
but we found that it gives a hot
bright strip across the middle
which is unsatisfactory.
Now connect a 3-core mains
power cord fitted with a 3-pin plug.
These battens are fitted internally
with a 3-way insulated terminal
block for this purpose. The centre
terminal is connected to the earth
wire. The cord should also be anchored with a clamp.
Now the cover and tube can be
fitted to the batten and power applied to test it. We didn't bother to
fit a mains switch on the box, by the
way, as it seemed superfluous.
Now fit the snap vents. Of course
you don't really have to fit these but
the vent holes look a bit grotty
without them. You could also fit a
handle to each end, to make it
easier to lift.
And that completes the light box.
Let there be light.
~
LIST OF MATERIALS
1 sheet of 1 6mm Melamine
surfaced particle board
1 18-watt fluorescent batten,
including tube
1 3-core power flex and 3-pin
plug
1 4 40mm x 8 gauge Chipboard
screws (or Furnco Directors)
1 4 Furnco white Snap Caps
size 8/8 (not necessary if
Furnco Directors are used)
4 20mm x 1 0 gauge
countersunk head selftapping screws
·
4 rubber feet
2 5mm 20mm long screws,
with nuts and washers
5 kitchen cupboard vents
1 sheet of white 4.5mm or
6mm Perspex, 360 x
645mm
Miscellaneous
Iron-on Melamine edging tape
(Armaflex G-L)
THE ELECTRON/CS MAGAZINE FOR THE ENTHUSIAST
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We believe that electronics is a fascinating pursuit, and the most useful hobby that anyone can
have, particularly for a young person in school.
Anyone with a good grounding in electronics is
better prepared to meet the challenge of today's
and tomorrow's technology.
Because we believed that many more people
should come to know about and enjoy electronics,
we decided to start a new magazine expressly for
electronics enthusiasts, whether they be nervous
beginners or seasoned veterans. We called it
SILICON CHIP, a name which focuses on the very
basis of today's electronics technology.
We started SILICON CHIP as an independent
magazine completely free from the influence of
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wanted to establish the highest possible standards for accuracy and attention to detail. Our
team is very small: founders Leo Simpson and
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SILICON CHIP has now been on sale for five
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Australia. Considering the hard work in getting
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But we want to make SILICON CHIP even better.
To do this, we need the resources to employ more
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people. This is the only way that we can be sure of
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We know this is what you want. Your letters
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Regular Features
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Constructional Projects For
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HiFi Review
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adopting this policy but we
believe that your privacy is
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►
1988
63
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64
SILICON CHIP
~
/
::X
-/ ,
LIMITED NUMBERS OF
BACK ISSUES ARE
AVAILABLE SO DON'T
DELAY
Electronic jargon explained
ffigh, low, sink and source:
What do they mean?
We use the terms high, low, sink and
source frequently in the circuit
descriptions for Silicon Chip projects.
Let's take a closer look at these terms.
To the electronics novice and
perhaps even to the more experienced, these terms can cause
considerable confusion. High and
low are terms frequently employed
when describing logic and switching circuitry but they can also be
used when describing analog circuitry, particularly comparators.
Consider Fig.1 which is the
triangular symbol used for an
operational amplifier. It is usually
drawn with two inputs (inverting
and non-inverting) and one output.
If the op amp is biased for normal
linear operation, its output pin will
usually "sit" at about half the
voltage between the positive and
negative supply pins.
In the case of op amps with
± 15V supplies, this means that the
output will "sit" at close to 0V
when no signal is present.
When the op amp is fed with a
large DC input signal the chances
are that its output will go "high" or
"low" depending on the polarity of
the input signal and the configuration of the circuit. By high or low,
we mean that the op amp output is
driven as high or low as it can go. In
most op amps running with ± 15V
rails, the output will go to about
+ 13V when driven high and about
- 13V when driven low.
In a comparator, which is an op
amp specially designed for sensing
whether a signal is above or below
set thresholds, the output can go
higher, typically almost to the
positive and negative supply rails,
provided it is lightly loaded.
In CMOS logic circuits which are
specially designed for switching
and normally run from a single DC
rail, the outputs will always sit at
virtually the positive rail or at 0V,
except during the time that they are
changing "state". There is a proviso though; they must be lightly
loaded.
If an electronic device is more
heavily loaded, its output voltage
will not go as high or as low as it
can when it is lightly loaded. The
reason is that typical op amps and
logic circuits do not behave like
ideal voltage sources. They are
Fig. 1
OPAMP
-V
- V
Fig. 2
COMPARATOR
+v
+L
J)
Vrel.
-V
When the output of an op amp is
high, it will deliver current to its external load, as in Fig.3.
This
depicts current lo flowing out of the
op amp and through the load to the
0V line. The op amp is therefore
said to "source" current.
On the other hand, when the op
amp output is low, current will flow
through the load from the 0V line
and back into the op amp, as
depicted in Fig.4. Here, the op amp
is said to "sink" current.
By the way, we're talking about
conventional current flow here,
from positive to negative.
Most op amps can source just as
much current as they can sink but
some can sink a lot more than they
can source. Take for example the
LM324 op amp. This device can
operate from a single supply and it
has a number of special features
which make it a very handy in a lot
of applications. However, it cannot
source as much current as it can
sink.
Similarly, consider the LM3900
which is a quad Norton op amp.
(The term Norton means that its inputs are current controlled rather
than voltage controlled). Each op
amp in the LM3900 package can
continued on page 93
lo
+
IN
"sink".
+V
+v
+
strictly limited in the amount of current they can deliver. And that brings us to the terms "source" and
f ig. 3
CURRENT SOURCE
-1
+
.,.
-v
Fig. 4
"!"
~URRENT SINK
MARCH 1988
65
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1
AMATEUR RADIO
By GARRY CRATT, VK2YBX
Antennas for the
VHF & UHF bands
One of the most difficult decisions the amateur is
faced with today is the choice of antenna to use.
This article sets out to explain the advantages and
disadvantages of the various types of antennas
available.
One of the most commonly held
beliefs is that antennas should be
judged on gain alone, and that an
antenna with high gain is better
than one with low gain. But that's
not all there is to it. Antenna gain is
closely related to antenna directivity, which in turn is closely related
to the radiation pattern.
A high gain antenna may be unsuitable in some cases if, for example, it radiates energy in the wrong
direction. In fact, it is the ability of
an antenna to radiate most of the
energy fed to it in a particular
direction (and minimum radiation
in other directions) that provides
power gain. The general direction
of maximum radiation when the
radiation pattern is plotted is called
the major lobe. The areas of lower
radiation levels (as no antenna is
perfectly directional) are called
minor lobes.
The term front to back ratio is
also commonly used in discussions
on antennas. This is simply the ratio
of the power radiated in the preferred direction to the power radiated
in the opposite direction - see
Fig.1.
The power gain is the ratio of the
maximum radiation signal in a
given direction to the maximum
radiation signal produced by a
theoretical reference antenna with
the same power input. This
theoretical reference antenna is
.
w
-'
z
<
w
d
ffi
>
RELATIVE POWER (uW)
Fig. 2: graph showing how the angle of radiation decreases as the antenna
approaches one wavelength. A lower angle of radiation gives greater gain.
68
SILICON CHIP
MAJOR
LOBE
~NORf
LOBES
Fig.I: the general direction of
maximum radiation is called the
major.lobe, while the areas of lower
radiation are the minor lobes.
Fig.3: dimensions for a discone
antenna to cover 140-450MHz. The
disc can be solid aluminium while the
cone can be wire mesh.
known as an isotropic radiator,
which is a hypothetical, lossless omnidirectional antenna.
In practice, antenna gain measurements are normally made in
comparison to a single half-wave
dipole. Because the radiation pattern of a half-wave dipole is
somewhat imperfect, its power gain
compared with the theoretical
isotropic radiator has been
mathematically calculated at
2.15dB. This means that the gain oI
a practical antenna can be referred
to an isotropic radiator by adding
~
COAX
\::!f__c_oA_x_~
Fig.4: a vertical collinear antenna can be made by joining pieces of coaxial
cable (see text). The antenna can be centre-fed or end-fed.
2.15dB to the measured gain
against a half-wave dipole.
All this is easy to visualise when
applied to a directional antenna
such as a yagi, quad etc, but takes a
little more explanation when applied to omnidirectional vertical
antennas.
Beca u s e it is used as th e
reference, it follows that a halfwave dipole has a unity gain. If we
take a vertical half-wave dipole and
replace its lower half with a
groundplane, the image of the vertical quarter-wave radiator is
reflected in the groundplane. As a
result, the groundplane antenna
produces similar results to a halfwave dipole.
There are many other factors,
too detailed to explain here, that
also come into play. Suffice to say,
the qua rter wave radiator is
groundplane dependent, and incapable of substantial gain.
In order to obtain usable gain
from a vertical antenna, we need to
compress the major lobes so that
they have a low angle of radiation
compared to the horizontal plane see Fig.2 . In fact useful gain in this
type of antenna is closely related to
a low angle of radiation. VHF vertical gain antennas, for example,
may comprise two half wave
dipoles fed in phase etc, and use
compression of the major lobes to
obtain a low angle of radiation.
Such an antenna is called a
collinear.
that of a quarter wavelength
radiator.
Fig.3 shows the dimensions for
both disc and cone to cover the frequency band from 140-450MHz.
Discones are sold commercially by
Emtronics, Vicom, Dick Smith Electronics, etc.
Vertical collinears
Vertical collinear antennas can
be easily fabricated by using coaxial cable.of either 75-ohm or 50-ohm
impedance. This type of antenna is
made from a series of lengths of
coa xial cabl e , each a halfwavelength long and fed in phase.
The elements are joined together
with the outer braid and centre
conductors transposed at each connection. Fig.4 shows the details.
COAXIAL CA■L■ SP■Cll'ICATIONS
Cable
No
The discohe, so called because it
comprises a metal or mesh cone, is
a broadband vertically polarised
antenna which acts as a wideband
impedance matching transformer,
coupling the 50-ohm input to the
higher impedance of free space.
The radiation pattern is similar to
Nomi1111I
Imp
Zo(j)
"-L
Cable
Outoide
Diam 1MHz
A - (d■ /1-)
Velocity
Factor
10MHz
100MHz
c-ltanc:e
RG-5/U
RG-5 ■ /U
RG-IA/U
RG-IA/U
RG-9/U
RG-9■ /U
RG-10A/U
RG•11A/U
RG-12A/U
RG-13A/U
RG•14A/U
R(l-11/U
RG•17A/U
RG-11A/U
RG,19A/U
RG 20A/U
RG,21 A/U
RG-29/U
RG-34A/U
0
RG-34 ■ /U
RG-35A/U
RG 54A/U
RG-55/U
RG,SSA/U
RG-51/U
RG-51C/U
RG,59A/U
RG-59■ /U
RG,82A/U
RG-74A/U
RG-13/U
RG-171/U
RG-213/U
RG-211/U
RG, 220/U
52.5
50.0
75.0
50.0
51 .0
50.0
50.0
75.0
75.0
75.0
50.0
52.0
50.0
50.0
50.0
50.0
50.0
53.5
75 0
75.0
75.0
58.0
53.5
50.0
53.5
50.0
75.0
75.0
93.0
50.0
35.0
50.0
50.0
50.0
50.0
8.45
8.45
8.45
10.3
10.66
10.8
12.06
10.3
12.06
10.8
13.85
18
22.1
24
28.4
30.35
4.7
4.6
16
18
24
6.35
5.2
5.4
4.95
4.95
6.15
6.15
6.15
15.6
10.3
2.0
10.3
22.1
28.4
Maximum
Operating
(pF/10011) Voltage
1 - H • 3000MHz
(mm)
0
The discone antenna
Thus the sections are assembled
by soldering the centre conductor
of the first section to the braid of
the second section and vice versa.
The gain, bandwidth and radiation
pattern are all governed by the
number of elements used. Bandwidth can be roughly calculated as:
BW = 2f/(3n + 1)
where f is the operating frequency
and n is the number of elements.
For example, a 16 element array
operating at 438MHz will have a
bandwidth of 438MHz x 2 -:- 49 =
17.9MHz bandwidth.
The entire array can be secured
inside a piece of PVC conduit. Alternatively, the junctions of the
elements can be sealed with
weatherproof insulation tape or
heatshrink tubing.
Using PVC conduit will cause the
centre frequency to be pulled low,
so it is best to start construction by
cutting a length of coaxial ea ble to
an electrical half-wavelength (using
the formula 150/f(MHz) = half
wavelength (metres). Once this has
been done, strip back the PVC
sheath 15mm at both en d s ,
separate the outer braid, then twist
the braid conductors together and
tin them with solder.
(rms )
0.21
0.16
0.21
0.16
0.16
0.175
0.16
0.18
0.18
0.18
0. 12
0.1
0.066
0.066
0.04
0.04
1.4
0.33
0.065
0.07
0.18
0.36
0.36
0.33
0.42
0.34
0.25
0.10
0.23
2.6
0.16
0.066
0.04
0.77
0.66
0.78
0.55
0.57
0.81
0.55
0.7
0.66
0.66
0.41
0.4
0.225
0.225
0.17
0.17
4.4
1.2
0.29
0.3
0.235
0.74
1.3
1.3
1.25
1.4
1.10
1.10
0.85
0.38
0.8
5.8
0.6
0.2
0.2
2.9
2.4
2.9
2.0
2.0
2.1
2.0
2.3
2.3
2.3
1.4
1.2
0.8
0.8
0.68
0.68
13.0
4.4
1.3
1.4
0.85
3.1
4.8
4.8
4.65
4.9
3.40
3.40
2.70
1.5
2.8
13.8
1.9
1.0
0.7
11.5
8.8
11.2
8.0
7.3
9.0
8.0
7.8
8.0
8.0
.5
8.7
3.4
3.4
3
3.5
43.0
16.0
3.0
5.8
3.5
11 .5
17.0
17.0
17.5
24.0
12.0
12.0
8.6
6.0
9.6
46
8.0
4.4
3.6
22.0
16.7
21.0
16.5
15.5
18.0
16.5
16.5
16.5
16.5
12.0
16.0
8.5
8.5
7.7
7.7
85.0
30.0
12.5
8:6
21.5
32.0
32.0
37.5
45.0
26.0
18
.11 .5
24.0
76
0.659
0.659
0.659
0.659
0.659
0.659
0.659
0.66
0.659
0.659
0.659
0.67
0.659
0.659
0.659
0.659
0.659
0.659
0.659
0.66
0.659
0.659
0.659
0.659
0.659
0.659
0.659
0.66
0.84
0.659
0.66
0.665
0.66
0.66
0.66
28.5
29.5
20.0
30.5
30.0
30.5
30.5
20.5
20.5
20.5
30.0
29.5
30.0
30.5
30.5
30.5
30.0
28.5
20.5
21 .5
20.5
26.5
28.5
29.5
28.5
30.0
20.5
21.0
13.5
30.0
44.0
27.9
29.5
29.5
29.5
3000
3000
2700
4000
4000
4000
4000
5000
4000
4000
5500
6000
11000
11 000
14000
14000
2700
1900
5200
6500
10000
3000
1900
1900
1900
1900
2300
2300
750
5500
2000
5000
11000
14000
Table 1: coaxial cable specifications. Use low-loss cable for long runs and
check that the impedance is correct. (Courtesy Dick Smith Electr onics).
MA RCH 1988
69
MAST
s
(a) STACKING IN THE SAME PLANE
(b) STACKING IN PARALLEL PLANES
Fig. 5: additional antenna system gain can be achieved by stacking in either
the same plane or parallel planes. Our diagram shows two vertically-polarised
antennas, but horizontally-polarised antennas may also be stacked.
Next, strip 5mm of dielectric
from the centre conductor and tin
the centre conductor. You can now
check the resonant frequency of
this length of cable with a grid dip
oscillator (GDO). This is done by
shorting the braid and centre conductor at one end of the element,
and coupling the GDO to the other
end.
Because the formula used to
calculate the half-wave section
does not take into account the
velocity factor of the cable, it is normal for the cable to be too long at
first. It can be made to resonate at
the correct frequency by progressively reducing its length by
trial and error.
An advantage of the coaxial collinear is that it is an easily
reproduced design. Because of this,
it is used by many commercial
antenna manufacturers.
Cables and connectors
Having selected a suitable antenna, care must be taken to maximise
the available antenna system
performance by selecting a suitable
feedline.
As can be seen from Table 1, the
main factor with which we are concerned is attenuation. The difference in attenuation between,
say, RG-58C/U and RG-213 over a
length of 30 metres at a frequency
of 100MHz is 3dB. Clearly, for long
coaxial runs, we need to select a
cable with low loss. For mobile installations, where the length of
70
SILICON CHIP
coaxial cable used is less than
three or four metres, the loss incurred by using a smaller diameter
cable is a worthwhile tradeoff compared to the ease of installation.
Of course, the selection of cable
is also determined by price. Lowloss cable can be expensive, particularly for UHF work.
Connectors also form an important part of any antenna system,
particularly at VHF and UHF. Of
prime importance is the impedance
of the connector, which is largely
determined by the physical construction and design. The materials
used in manufacture are also important, particularly the dielectric
insulation.
An inferior connector will create
an impedance mismatch, causing a
high SWR (standing wave ratio). It
may also have a high insertion loss,
thereby further reducing antenna
system performance. Connectors
should be chosen carefully, as there
are many inferior types available
which are quite unsuitable for RF
work and which should really be
limited to video use. Many connectors are also available in both
50-ohm and 75-ohm variations, so it
is important to choose the correct
type.
or vertically polarised antennas. By
stacking yagi antennas (or any
derivative of a yagi), between 5/8
wavelength and 1-1/4 wavelengths
apart, an additional 2.5 to 3dB of
gain can be realised. Stacked
antennas must be fed in phase, and
because a typical VHF or UHF yagi
is a 50-ohm device, a matching
transformer must be used.
To feed the two antennas in
phase they must be fed in parallel.
This means that to obtain a
reasonable match to 50-ohm
feedline, we must transform the impedance of each antenna to 100
ohms, so that the two antennas in
parallel have an impedance of 50
ohms. This is easily achieved by using a coaxial line transformer, made
from 75-ohm coaxial cable.
The formula used to calculate
this is as follows:
Zs = Zq x Zq/Zl
where Zq is the impedance of the
matching transformer, Zl is the
feed impedance, and Zs is the required antenna impedance for
parallel operation. If we substitute
figures from the above example, we
get:
100 = Zq x Zq/50
Thus, Zq x Zq = 5000, so Zq =
70.7 ohms. In practice 75-ohm cable
presents a minimal mismatch.
Because each antenna must be
fed with one of these coaxial
transformers, the physical construction should look like Fig.6.
Note also that each impedance
transformer must be a single
quarter wavelength in length, or an
odd multiple of a quarter wavelength.
With that background, you
LINES
PARALLELED
'
----50r! TAIL
Stacking antennas
Additional antenna gain can be
achieved by stacking two identical,
directional antennas, in either the
same plane or in parallel planes.
This applies equally to horizontally
TO MAIN
FEEDLINE
Fig.6: phasing harness for stacked
antennas. Each section must be an
odd multiple of a quarter wavelength.
should now find it easier to select
an antenna for a particular application. Let's take a look at a few
examples.
Base station operation
For maximum directivity, either
horizontally or vertically, a yagi
antenna is a good choice. A rotator
will then enable 360° operation.
For omnidirectional operation, a
five-eighths wavelength antenna
could be used provided a good
groundplane is available. If no
suitable ground plane is available,
a vertical collinear antenna could
be used instead. Note that a
suitable location is required for
good omnidirectional operation (eg,
the top of a hill).
The discone anternia is suitable
for omnidirectional operation on a
variety of VHF & UHF frequencies,
provided that 3dBd gain (dBd
means gain referred to a dipole) is
acceptable. For directional operation on a variety of VHF & UHF frequencies, a log periodic antenna
can be used with a rotator.
Mobile operation
The size of the antenna and the
mounting method on your vehicle
are the two main considerations
here. As virtually all mobile applications require vertical polarisation and omnidirectional operation,
the choice of antennas can be
reduced to the following:
(1). Quarter-wave whip - generally requires drilling a hole in the
middle of the car's roof for best
results. Advantages: (a) physically
short; (b) relatively high angle of
radiation which gives better results
in city or hilly locations, particularly at UHF. Has marginal gain of
ldBi.
(2). Five-eighths vertical - requires
a ground plane as above, but has a
low angle of radiation, providing
better gain than a quarter wave
whip (almost 3dBi). Offers good performance on flat terrain (but probably worse in hilly terrain).
(3). Half-wave radiator - ground
independent and so can be easily
gutter mounted. Has ldB of gain
over a quarter-wave whip.
(4). Two half-wave radiators end
fed - ground independent, improved gain (almost 5.2dBi), but
SAFETY WATCH
Lt
Safety Watch will be an occasional feature in SILICON
CHIP drawing attention to issues of electrical s afety
in the workshop and home.
VCRs and water
don't mix
Vases of flowers should never
be placed on top of TV set or
near a video cassette recorder. If
the vase is knocked over, the
water could do a lot of damage to
the internal circuitry of the TV
or VCR and may even cause the
picture tube to crack.
Worse, if splashed water
comes into contact with mains
wiring inside the VCR, it could
create a path between the mains
and chassis. Because most VCRs
are double-insulated (ie, they only have a two-core power flex),
any leakage between the mains
and chassis could mean that the
VCR exterior is live and lethal.
Moral: keep all vases, drinks and
other containers of liquid away
from your VCR and TV set. Keep
it well away from your stereo
equipment too.
sign of deterioration. They're not
cheap but then neither is a fire in
the kitchen.
Safety with
the iron
Hazardous
power cords
We recently came across a
power cord fitted to a vertical
grille which had shorted at the
point where the cord entered the
grille base. When the sheath was
removed from the cord, the insulation surrounding each of the
three leads was found to be badly perished. The short occurred
between Active and Neutral.
When more closely examined,
the outer rubber sheath of the
cord was noted to be shiny from
continued exposure to grease
and had tell-tale signs of cracking and perishing where the cord
entered the moulded 3-pin plug.
Moral: carefully examine power
cords used for frypans and vertical grilles. Such cords are prone to perishing because of their
exposure to grease and cooking
oil. Replace the cord at the first
Avoid placing appliances on stove
tops. This is what can happen.
Some people put their electric
iron on the stove to cool off
before it is put away in a cupboard. This photo shows what
happened when the iron was
dislodged slightly, onto an adjacent hotplate which had been inadvertently left on. As you can
see, a great deal of damage was
done to the iron in only a few
seconds. The iron had to be
replaced.
Moral: if you put your iron on the
stove to cool down, place it well
away from the hotplates. Better
still, leave it on the ironing board
to cool down and then put it way.
continued on page 93
M ARCH 1988
71
THE WAY I SEE IT
By NEVILLE WILLIAMS
The quest for the ultimate
in hifi sound is half the fun!
As I hung up the phone recently, after a lengthy
conversation with an old-time hifi enthusiast, I was
more than ever convinced by the obvious: that, for
such a person, hifi would be nowhere near as
interesting, fascinating, or challenging if there
wasn't the possibility of improving the sound even
slightly!
Back in the 78rpm era, there was
virtually unlimited scope for improvement. The discs themselves
carried a substantial content of
distortion and noise, such that a
prime objective was to suppress
both in some way, without unacceptably compromising the wanted
signal.
With the appearance of microgroove recordings in the fifties,
the search was on for styli,
cartridges and pickup arms that
combined suitably low mass with
user-ruggedness. It was a combination that didn't come easily - any
more than did affordable wow-free,
rumble-free playback turntables.
As the signal source gradually
improved, attention was diverted to
amplifiers and loudspeaker
systems, leading to a boom in the
British hifi industry, with famous
brand names like Acos, BAKER,
Goodmans, Leak, QUAD, Rogers,
Wharfedale, &c. I doubt that there
ever could be another batch of enthusiasts more varied, more interesting or more dedicated than
the founders of that particular
group of companies.
By the sixties, tape emerged as a
rival for disc and stereo had ap72
SILICON CHIP
peared, so the entire evolutionary
process had to be updated and
repeated: groove geometry, styli,
pickups, turntables, amplifiers,
loudspeakers and even the layout of
the listening room itself.
To use the old cliche, there never
was a dull moment; never a period
when enthusiasts could relax,
secure in the knowledge that they
could settle back and enjoy the
ultimate. There was always some
other aspect to explore, some new
challenge appearing on the horizon.
Running out of challenge?
It's certainly been that way for
as long as I can remember, but
what of the future? Surely, as hifi
sound equipment gets better and
better, there must come a time
when technology has overtaken our
needs and, more specifically, our
own physical limitations. Will the
fascination of hifi sound diminish
by half when equipment can be installed, used and largely forgotten,
except when it malfunctions; like
power, water, refrigeration and
plumbing systems?
The now-retired enthusiast, who
triggered off this whole line of
thought with his phone call, has
been collecting cherished recordings for as long as I can remember
and fussing over them like a mother
hen. From constant listening, he
knows their every last quiver and
quaver.
A few years back, unsettled by
the prospect of the compact disc
revolution, he sought my assurance
that it made sense for him to stay
with his present collection and
equipment, rather than trade it for
a fraction of its original worth and
re-invest in CDs. Knowing his age
and background, I agreed with his
proposition.
This time around, after the opening pleasantries, he hit me with the
question: "How good is the top-ofthe line Shure cartridge?" The purchase price mentioned was around
$600.
I answered in a general way, based on my recollection of a very
favourable review of the V-15 type
V-MR which had been published
some time ago. It seemed to me that
anyone who had acquired and
carefully set up a Shure cartridge
at that price level should have little
to worry about, bearing in mind the
performance parameters applicable to phono players.
But there was more to come:
"How good are the Australian Garrott replacement styli? The makers
claim a much better contour and
polish than the standard commercial equivalent".
My answer was along the lines
that the Garrott brothers had been
working with styli for many years
and, by now, they ought to be pretty
good at it! But whether a new Gar-
rott stylus would actually sound
better or last longer than a new
Shure stylus in a Shure cartridge, I
was not in a position to say.
His next question was a doublebarrelled effort: "Having in mind
the cost of a new stylus, what do
you think of the idea of putting the
money towards the purchase of a
new Garrott cartridge? And, if the
Garrott was really as good as the
makers claimed, would the difference justify the hassle of having
to set up the arm to suit it?" I could
offer no definitive answer because I
had never been through the particular exercise.
"Well, who can I ask?", he said.
"It's not sufficient simply to talk to
the companies concerned, because
they have a vested interest. Hifi
dealers have their own pet lines.
Magazines review cartridges from
time to time but they rarely do a
comparative anlysis. Who would
know the answer to my questions?"
It was about then that I realised
that I hadn't been witness to an
argument about phono cartridges
for quite a long time. Vinyl disc
enthusiasts still have their preferences and strongly held opinions
but they make the headlines much
less frequently than once they
did; and they certainly feature less
in conversation where audio
engineers gather.
Even in the strongholds of conservatism, compact disc is now plainly
winning acceptance as the best
way to store and reproduce sound,
with the vinyl disc system being
relegated to a lesser role - by its
very nature technically inferior, no
matter how good the particular
stylus and cartridge.
What about a listening test?
When I talked along these lines,
my enthusiast friend suddenly had
another bright idea. What if he
bought a new Garrott cartridge
complete and, if it could be arranged, have me over to share in a comparative listening test to decide
which offered the best sound?
I declined, on the basis that at my
age, I did not consider myself able
to offer a definitive subjective opinion on ultimate sound quality.
Yes, I was well able to appreciate the difference between
good and not-so-good sound, and I
had been active in the game long
enough to know whether other people's statements and opinions made
good technical sense. But, in this
situation, I would not be comparing
good and not-so-good sound but trying to pick possible subtle differences between two very good
cartridges, involving the portion of
the spectrum which I could no
longer hear to advantage, if at all.
"But I'm the same age as you and
I reckon my hearing's still pretty
good", he said. To which I could only reply: "For your sake, I hope it is,
but it would make you very much an
exception to the rule".
"On the other hand, if your hearing is merely average for your age,
you may well be worrying about
subtleties to no good purpose, and
at considerable cost". And that's
about where we left it - in
practical terms, a rather futile
conversation.
A few days later, he rang to say
that he had checked his hearing
with a frequency disc in his collection and could still hear lOkHz.
"Good", I said, "but did you leave
the volume control set for the complete run?" No he hadn't, he'd
"cheated a fair bit!" With a normal
level response, he would probably
be lucky to hear anything above
about BkHz.
He went on to say that another
retired friend had insisted that a
trained listener could hear more
than the average person, despite
what a frequency check might show
- an idea that I, for one, would be
delighted to see proven. But my own
experience and observation would
suggest that, while such a person
may indeed be very perceptive with
what faculty he has, he would still
be missing out on the top end of the
audio spectrum.
He would be in much the same
position as a short-sighted projectionist, trying to adjust to critical
focus - without his spectacles!
Back to the introduction
Having equipped himself with a
wow-free, hum-free, vibration-free
turntable, a good arm and either
one of two top-line cartridges, my
enthusiast friend may well have
reached the stage where there is no
real point in doing anything beyond
maintaining what he already has.
Problems?
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MARCH 1988
73
An apparent lack of intestinal fortitude!
Dear Mr Williams,
I read with interest your comments regarding the repair of electronic equipment, the delays and
the lack of service and spares
encountered.
I wonder, however, why you
bother to write about it when you
are obviously supporting this
policy.
Yes, you . You claim to be fair by
not naming the companies who are
not prepared to supply service or
spares, thus denying consumers
answers to the questions they ask
before buying equipment.
Certainly you do not know all the
companies that are not supplying
service but you certainly know at
least some of them and should
have the intestinal fortitude to
, name those against whom you
have evidence, rather than making
sweeping generalisations against
all.
Having been in the industry, you
know that no managing director
will provide adequate fund alloca, tions to the service department
unless he perceives that lack of
service is costing his company
sales.
Ask any salesperson about service and you will be assured that
service is perfect, regardless of
the actual situation, so to whom
can the customer turn for unbiased
information?
If you want to see what effect
exposure of company shortcomings has, I suggest you subscribe
to the ACA magazine, " Choice".
There you will find (to the best of
their ability) a reasonable report on
many consumer items. It is
noticeable that appliances that
don't perform well are named, and
often disappear from the retailers'
shelves.
The same concept, of course,
applies to service and spares.
The other thought that occurs to
me is that the companies you have
not named could be advertisers or
possible suppliers to the magazine
for, after all, how fair is it to name
Tandy or Hills as being good
organisations, whilst refusing to
name the bad ones?
D.T., (Traralgon, Vic).
Keep the records spotless (as he
does), check the arm and turntable
regularly, check and replace the
stylus as necessary and that's
about the end of it.
If he did decide to change over to
compact disc, he could just about
forget about maintenance, as well!
Again, assuming that his amplifier is to full modern specifications, it is difficult to see
why he would need another one,
advertising claims notwithstanding.
That leaves his loudspeakers as
the one area where he might find
reason to invest in something different, because loudspeakers do
vary a lot in the their subjective impact. Imagine it: one more step to
take and most of the fascination,
speculation and challenge of hifi
would have vanished. Or would it?
• With compact disc, we had a
storage and playback medium with
a vanishingly small amount of noise
and distortion.
• With digital audio tape in immediate view, we would be able to
record and play back a nearperfect signal.
• We had practical, affordable
amplifiers to match.
• We had drift-free, lowdistortion FM-stereo tuners, some
with AM-stereo as a bonus.
• We'd never had a wider or better choice of loudspeakers.
Maybe, I said, as people realised
that they had access to nearperfect equipment, some of the
fascination, speculation and
challenge that had characterised
hifi for 60 years (since the term was
first used) would begin to taper off.
As you might expect, Leo did not
agree at all. He stated that while
compact disc players were pretty
good they were still being refined
and improved by the manufacturers. And there were presently
1
"
The search continues
Talking over this theme with Leo
Simpson, I suggested as a try-on
that, for all practical purposes, hifi
" perfection" may well be in sight.
74
SILICON CHIP
very few amplifiers which truly
matched the standards offered by
CD players.
Nor were speakers anywhere
close to the standards offered by
even mediocre amplifiers of twenty
years ago. When loudspeakers commonly offered a frequency response
flat to within ± 2dB, we might be
getting somewhere.
Nor were most tuners all that
marvellous. With a few exceptions
most FM tuners would be hard put
to deliver a stereo signal-to-noise
ratio of much better than 70dB.
Most would be hard put to
reproduce a stereo signal with less
than 0.5% harmonic distortion. And
even if they could do these things,
the FM transmitters couldn't!
And that was without mentioning
the enormous differences between
the acoustics of the concert hall
and those of the average listening
room. Really, we've only just
started on this problem.
In fact, Leo disagreed totally with
my proposition. He says that hifi
may be good but anyone who thinks
that "things have gone just about as
far as they can go" is no longer
really interested in hifi. Pretty
strong words indeed!
When pressed, I'd have to agree.
Now matter how good the specifications of present equipment, or by
how much they appear to surpass
our aural capability, there'll still be
plenty of room for improvements.
That's what hifi is all about!
Back to electronic servicing
On reading the letter in the accompanying panel from D.T. in
Traralgon, Vic, my immediate impression was that he would make
an excellent mob orator, his
message replete with sweeping
statements, and uninterrupted by
pauses for reflection.
How my criticism of present-day
servicing attitudes and standards,
with its emphasis on unacceptable
delays, can be construed as "supporting the policy" escapes me.
I "bothered" to raise the subject
in the November issue for reasons
quite specifically stated at the
beginning of the article and, in so
doing, I just happened to be telling
the truth!
Faced with a number of unsatisfactory servicing situations, as
detailed, I made a number of inquiries (also detailed) in an effort to
establish whether my disturbing experience was unusual or typical.
Unfortunately, the indicators
pointed strongly to the latter, with
the problem being industry wide,
rather than confined to a few offending manufacturers.
Sorry D.T. but, on that basis, I
stand by my statement in the
December issue that it would have
been unfair to single out for
criticism typical companies which
had come to my attention, either
directly, or in casual conversation.
There is a considerable difference
between disturbing observations
and the sort of evidence necessary
to justify black-listing in a magazine.
In that same November article,
the editor inserted a panel (p.17)
suggesting that "there must be
another side" to this "rather uncomplimentary" picture and inviting contrary opinion from companies and readers. To date, no-one
has complained of injustice, the
overwhelming response being support for the original article, as
presented.
D.T. makes an issue of a
managerial link between back-up
service, customer goodwill, and
Did you
sales. He seems not to have noticed
that, under the heading "Spare
parts problem" (Nov. p.16), I
assume the existence of such a link
and go on to suggest important
economic reasons why the traditional relationship has been
distorted to the disadvantage of
back-up service. Since making that
observation, the Australian dollar
has slipped yet further from 100 to
around 90 yen.
Perhaps D.T. should also re-read
the last couple of columns on page
17 of the same issue. Far from
abandoning readers to · the glib
assurance of "any salesperson"
about "perfect service", the article
seeks to alert them to that very
possibility. I quote:
"Don't assume that your friendly
emporium will take over your service worries, because they have been
so nice to you in other ways. Check
out the warranty, read the fine print,
and discover exactly what's involved. What is the warranty period and
what does it cover ... "
D.T. then suggests that I/we
should investigate and report on
products and services in the manner of Choice magazine.
He has completely missed the
point that Choice is a special kind of
•
miss
I.so Simpson and Greg 5waln Pffl!S!IIII•••
magazine, supplied only to people
who, by virtue of their subscription,
become members of the Australian
Consumers Association. In effect,
they constitute a private group funding research reports, which they
alone receive in the form of a monthly journal. It exists purely for that
purpose and relies on membership
fees to cover the cost of administration, research and publication.
In short, Choice operates on a
completely different legal basis to
publications like SILICON CHIP,
which is available to anyone who
cares to buy a copy from the
newsagent. For all such magazines
and newspapers, comment on products and services is an optional
small segment of the editorial content, commanding an equally small
segment of the budget and subject
to the normal legal constraints
relating to "publication".
The "logic " of D.T's final
paragraph intrigues me: If you have
reason to commend someone, it is
only fair to balance it with a condemnation of somebody else. If you
fail to do so, you probably have an
ulterior motive - like needing their
support as an advertiser.
Thanks for the vote of confidence!
~
these issues?
Issue Highlights
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in V our Home; 1 GHz
Frequency Meter; Capacitance
· Adaptor for DMMs; Off-hook
Indicator for Phones.
December 1 98 7: 1 00W PmNer
Amplifier Module; Passive
lnfrared Sensor for Burglar
Alarms; Universal Speed
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Price: $5.00 each (incl. p&p).
Fill out the coupon at left (or a
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MARCH 1988
75
Introduced in 1927, this
wooden electric
passenger car was one
of many which ran on
the Sydney metropolitan
system up until the late
1960s. (Bryan Maher
photo).
'l'H E EVOLUTION OF
ELECTRIC RAILWAYS
As in other countries, Australia had
some experience with electric traction
before the turn of the century. However,
it was not till much later that extensive
electrification took place.
By BRYAN MAHER
suburbs. Expanding gradually, the
Railways Department built and
operated a large system of high
voltage feeders from their power
stations to many country towns and
cities. They used 33kV lines from
Newcastle to the Hunter River
Valley and up the north coast
towards Grafton; 66kV lines fr om
Sydney to the Blue Mountains; and
also Australia's first intercity
power line interconnector, the
66kV line built in 1942 to join
Newcastle and Sydney.
One of the spans of that
Newcastle-Sydney interconnector
was a record 960 metres long,
across the Hawkesbury River. This
particular span was believed to be
the longest power line span on
wooden poles in the wo r ld .
Originally built using 19-strand 10
gauge cadmium-copper conductors,
that span with a 61-metre sag in the
middle had each phase supported
by a pyramid structure made of
three 18 metre wooden poles sunk
4.3 metres into the rocky hilltop.
The whole 66kV line fro m
Hamilton substation in Newcastle
to St. Leonards substation in
Sydney was designed to carry 200
amperes, and at full current 6000
The absolute first electric traction of any type in Australia was an
electric tramway using a direct current overhead trolley wire system
in Sydney, from Waverley to Bondi
Junction. This came into operation
on 9th November, 1890. Direct current supply was generated by the
New South Wales Railways at an
installation a small distance away
in the direction of Randwick.
That little DC generator near
Randwick marked the first entry into t h e electr icity generating
business by the New South
Railways, starting an enterprise
which continued to grow for the
following seventy years.
The Railways Department during
that time not only generated all
power used by electric trams,
trains, stations, yard lighting,
workshops and signals in the
Newcastle, Sydney and Blue Mountains districts, but also supplied,
owned and operated at Newcastle
the largest electric and hydraulic
coal loading wharf system on the
Pacific Ocean.
Furthermore, in that period, the
New South W ales Ra il ways
operated 50Hz and 25Hz coal burning power stations at Ultimo and
White Bay in Sydney and at Zara
Street in Newcastle, and for a long
time owned some of the largest synchronous motors in Australia 10MW in Newcastle and 30MW in
Sydney.
During that time, the Zara Street
plant also supplied 90 percent of all
power used in Newcastle and its
- -_
ELECTRICS IN AUSTRALIA
76
PART 5 S ILICON CHIP
volts was lost over the length by
resistive losses. This was the first
time in Australia that two large
cities had their power systems synchronised and joined.
Victorian Electrics
Melbourne became the first
Australian city to boast electric
suburban trains, in 1918. Some
wooden carriages, previously
steam-hauled, were converted to
electric traction by the fitting of
pantographs, control gear and new
bogies containing electric motors.
Overhead wiring construction
was proceeding on a number of
suburban lines and the first electric
train, from Sandringham to Essendon, ran in 1919. Construction of
AC-DC substations and overhead
conductors above the tracks continued and Melbourne's 1500 volt
DC electric suburban railway
system eventually grew very large.
Australia's early use of electric
locomotives was confined to the
coalfields in the eastern corner of
Victoria where the very considerable brown coal deposits are
mined by the open cut method. The
first electrically hauled coal train
ran in 1923.
The Melbourne Electric Tramway system has, since quite early
days, been working with the
railways in shifting millions of commuters. Nowadays, this system is
the only extensive electric tramway
system remaining in Australia. A
shining example to the rest of
Australia, Melbourne has extended
the tracks and purchased many
new tramcars. The up-to-date "Z"
class, of which 215 new cars have
been put into service over a ten
year period, are now being
augmented by the latest order of 52
modern "A" class trams.
In 1985, a $100-million contract
was let by Melbourne's Metropolitan Transport Authority for the
supply of 130 Articulated Light Rail
Vehicles for use on long tram routes
and later on two converted railway
routes. These advanced vehicles
consist of two cars sharing three
bogies. Propulsion is by two 600
volt DC 195kW AEG traction
motors. These can speed the 32.5
tonne vehicle with its 182
passengers along at a brisk 72km/h.
The modern control system uses
Grand old Locomotive No 1, the first steam loco in NSW. This beautifully
restored loco is on permanent display in the Sydney Powerhouse Museum.
(SRA photo).
AEG thyristor DC-to-DC chopper
circuits.
Melbourne showed the world
that construction of 1500 volt DC
underground railways was still
alive and well by opening their City
Loop Line in 1981. Circling the City
from Spencer Street Station via
Flagstaff, Museum and Parliament
Stations to Flinders Street or outer
suburbs, this new line takes
passengers within walking distance
of their city workplace, easing
street traffic congestion.
Adelaide's longest surviving electric tramway, the famous fast
Glenelg Tram has always been an
example to Australia of the
quickest way to move people. And
the people of Brisbane were for
many years served well by an electric tramway installation which
reached the peak of its importance
about 1930. Sadly, Brisbane eventually followed the lead of many
other cities and scrapped all electric trams in favour of diesel buses.
Newcastle and Sydney
To appreciate the early story in
Newcastle and Sydney we have to
keep in mind the intimate relationship in New South Wales between
the railways, tramways, power stations and coal loading wharves.
These were all administered by the
Department of Railways. Electric
tramway systems had been expanding since their beginning in 1890,
long before electric trains appeared.
Newcastle was originally founded because a certain British Army
lieutenant saw coal protruding out
of the ground between Cooks Hill
and Merewether while he was out
chasing escaped convicts. With a
working railway from Newcastle tci
East Maitland from 1857, the
discovery of large deposits of
Australia's best gas-coal over an
area from Walls end to Cessnock
opened the possibility of an export
market as a permanent boost to the
colony's finances.
Seizing the opportunity, the New
South Wales Railways built the
largest coal loading wharves in the
country on an unused expanse of
low-lying land known as Bullock
Island on the north side of Newcastle harbour. Initially, five hydraulic
coal loading cranes were installed,
later extended to thirteen. Before
the turn of the century, and for
many decades after, Newcastle
was the greatest coal loading port
on the Pacific Ocean.
So many sailing ships called at
the port that while awaiting loading
they were tied up three deep over
miles of wharves.
MARCH 1988
77
This was one of the 500 horsepower 6.6kV motors which drove the centrifugal
pumps for the hydraulic cranes. These were used for coal loading at
Newcastle. (Bryan Maher photo).
To handle all the coal trains, the
New South Wales Railways built
the largest railway yard in the
Southern Hemisphere. Complete
with four weighbridges the whole
installation, including storage and
loading yards, was seven kilometres long. Running through five
suburbs, the storage section reached sixty tracks wide, capable of taking 200 fully-loaded trains.
Coal loading
The hydraulic cranes installed
for coal loading used water as the
working fluid at a pressure 700 psi.
The original steam-driven pumps
were augmented in 1914 by two
electric motor driven 3-cylinder
piston pumps. The 600 volt DC 200
kilowatt compound motors were
designed to start and stop
automatically to keep up the supply
of high pressure water as required
by the cranes.
Much later, in 1943, a fourteenstage centrifugal water pump
driven by a double-ended 500hp
(373kW) three phase 6600 volt induction motor was added to augment the hydraulic system.
About 1914, the coal loading
facility received a boost with the
addition of seven huge electric
cranes each weighing 240 tonnes
and capable of lifting 15 tonnes.
These were equipped with twin
75kW hoist motors and 56 kilowatts
each for the travel and slew motors,
on 600 volts DC.
The Bullock Island 600 volts DC
system grew in useage and was inter c onne cte d to the growing
Newcastle suburban electric tramway system. To provide the required 600 volt direct current for
all these loads, a 600 volt 3000 amp
DC rotary converter was installed
in the substation. Also provided
were 300 lead-acid cells, each big
enough to have a bath in. These
constituted a 600 volt battery
capable of providing 1000 amps of
load current for hours (sometimes
all night) if and when the AC supply
or the substation were shut down.
A rotary converter resembles a
large DC generator with commutator and brushes but with the
addition of tappings from some armature coils. These taps are connected to slip rings and are fed with
AC, usually 6-phase, supplied from
a 3-phase transformer. The converter runs at a synchronous speed
determined by the AC frequency
and the number of armature poles
while DC output is delivered from
the commutator and brushes. It is
an efficient and compact machine,
superior to an AC motor driving a
separate DC generator.
Because rotary converters work
better with low frequency AC, all
NSW Railways power stations
generated 25Hz 6600 volt AC for
traction supply, and separately
generated 50Hz 11,000 volt AC for
lighting and other loads.
A very strange machine
A 33-class loco shunts long lines of coal wagons at the Newcastle loading
docks in the 1940s. The hydraulic cranes can be seen in the background.
(Bryan Maher photo).
78
SILICON CHIP
Other Newcastle tramway
substations, each containing two
25Hz AC to 600V DC rotary converters, were built at Hunter Street
and Hamilton. This latter substation supplied 600 volts DC to
Newcastle's southern and western
suburbs, the most distant being
Wallsend, 13km from the city. Con-
"to shoot through like a Bondi
Tram."
Electric trolley buses were introduced on a limited scale in
Sydney near Town Hall and in the
suburbs of Kogarah, Rockdale and
Brighton-Le-Sands. These clever
machines used two trolley poles
contacting both a positive 600 volt
and a zero potential overhead contact wire. Capable of being steered
on any part of the road, these
rubber-tyred vehicles called at the
kerb for passengers and their quiet
operation and fast acceleration
distinguished them from diesel
buses. At crossovers and junctions
the construction of the oppositepotential parallel trolley wires was
quite a headache.
The Balmain beautie
An earlier motor used to drive hydraulic accumulators at the Newcastle
dockyards. Installed in 1914, it ran on 600V drawing 386 amps. (Bryan Maher
photo).
diderable voltage drop occurred
along the long 600 volt feeder
cables. To compensate for this
voltage drop a rather strange
machine called a Direct Current
Series Generator was added at the
Hamilton substation. This generator was driven at constant speed
by a 3-phase AC motor.
Now a series DC generator (ie, a
DC generator with its field coils in
series with its own armature) has a
very strange and somewhat unstable voltage/current characteristic.
When driven at constant speed
such a generator's output voltage is
more or less proportional to its own
load current. If we draw no current
from it, this generator will generate
almost no voltage at all. If we draw
a small current from it the machine
will generate a small voltage and if
we draw a large current, this same
machine will generate a large
voltage.
Now that series generator was
itself placed in series with the 600
volt feeder supplying trams which
were out at the end of the W allsend
line. With the rotary converters
generating a constant 600 volts, the
series generator added extra volts
proportional to tram current, extra
volts intended to be just equal to the
voltage drop along the cable, so
that the correct 600 volts always
appeared at the other end.
In peak hours, when trams at the
end of the line could take as much
as 500 amps, up to 300 volts was
added to the system 600 volts, making 900 volts in all at the substation
end. If we now subtract the 300-volt
drop along the long cable due to its
resistance, we get 600 volts out in
the distant suburb, so the tram and
passengers were all happy.
Do you believe it? Yes, it really
did exist.
Theoretically minded readers
will see it as a case of a positive
resistance (the feeder cable) being
cancelled by an equal negative
resistance [the series generator) of
- 0.6 ohms. Wow!
Sydney electric tramway
Meantime, back in Sydney, the
electric tramway system was growing too. It also ran on 600 volts DC
and a similar system of rotary converters in DC substations was built
at strategic points of the suburban
system. But whereas Newcastle
trams were propelled by two
motors, one in each bogie, many
Sydney tramcars were equipped
with four motors, to cope with the
hilly terrain. These gave good acceleration on level streets and led
to the world-famous Australianism
Many
Sydney
harbourside
streets feature a "steep-drop-tothe-water" but do readers recall
the remarkable installation once used to allow trams to safely-descend
the hill to Balmain Wharf arid then
make the very steep ascent back up
again?
The tram's traction power and
rail adhesion were insufficient for
this short steep climb. Therefore,
below the road, right under the
tram tracks, was constructed a tunnel on the same slope as the road.
In the tunnel was laid a standard
gauge rail track upon which ran a
heavy four wheel truck weighing
about 12 tonnes. Up above, on the
tram track, was mounted a strong
but light four wheel truck. These
two trucks were tied together by a
long heavy steel cable, the steel
cable passing over a pulley
mounted just below the road surface at the top of the hill.
You can work out what happened, can't you? Left to themselves,
the two trucks rested with the
heavy truck in the tunnel at the bottom of the hill, and the light truck
sitting all alone on the tram track in
the middle of the street at the top of
the hill, held by the steel cable. So
any attempt to push the light truck
downwards on the tram track
meant pulling the heavy truck up
the track in the tunnel below.
Of course the tunnel and the
heavy truck in it were completely
hidden from view. All that was visible was that silly looking light truck
MARCH 1988
79
To provide a 600V DC supply for the Newcastle dockyards, a 3000 amp rotary
converter was installed, in conjunction with a 600V battery capable of
supplying 1000 amps. The small motor on the shaft was used for starting.
in the middle of the road.
Just imagine it. Along comes a
d·ouble tram wanting to go down the
hill to the wharf. It stops at the top
of the hill and slowly nudges forward till it meets the light truck sitting on the track in front of it. The
tram then drives forward, pushing
the light truck down the hill and in
so doing pulls the heavy truck in the
tunnel to the top of the hill.
Meanwhile, at the wharf, a
Sydney ferry arrives and disgorges
hundreds of weary city workers.
All climb aboard the double tram
which then starts up the hill, traction motors working hard and with
the light truck now pushing from
behind because of the weight of the
heavy truck in the tunnel. The combined effort of tram's motors and
the truck push is sufficient to haul
the tram and its 200 tired
passengers to top of hill. Success.
Sadly, Sydney decided (followed
by Newcastle) to scrap all 600 volt
DC electric trams, to be replaced by
80
SILICON CHIP
diesel buses. All tram tracks,
overhead wiring and substations
had to be demolished. The destruction, begun in the mid 1940s, pleased some and disturbed others who
saw electric trams as the quickest
way to move large crowds at important public events.
Two clever machines
The Railways also used the 600
volt DC system to supply cranes in
the large railway workshops at
Everleigh and Chullora in Sydney.
A similiar system supplied cranes
in the Newcastle area at Cardiff
Locomotive Workshops, Honeysuckle Point Rail Shops, and the
Bullock Island coal loading depot.
So at least some 600 volt DC rotary
converters survived for a few more
years.
Because Cardiff Workshops
were built out of Newcastle, too far
out to be supplied at 6600 volts AC
25Hz, use was made of the 33kV
50Hz AC ring main from Hamilton-
Cardiff-Maitland. This presented a
design difficulty for the Cardiff 600
volt DC substation as rotary converters suffer bad commutation
and brush arcing if run on 50Hz
supply. To solve this problem, a
pair of very clever machines called
Motor Converters were installed,
each rated to deliver 600 volts at
500 amps DC.
These machines had an AC stator
winding supplied with 2200 volts
5GHz 3-phase AC. This induced currents in the rotor by ordinary induction motor action except that the
rotor ran at exactly half synchronous speed. This resulted in
rotor currents being half frequency, ie 25Hz.
The stator was extended to carry
a set of DC compound field coils and
the long rotor had a commutator
connected to all rotor windings at
that end. DC output was collected
from the commutator by brushes in
the same manner as rotary converters. With only 25Hz currents in
the rotor, commutation was perfect
in these machines.
It can be shown that half the output energy was derived by motor
generator action and half by rotary
converter action, and that the efficiency was higher than a straight
motor generator but lower than a
simple rotary converter.
Advances in coal loading
The State Rail Authority in 1961
moved out of the coal loading
business at Newcastle, that industry being taken over by the Port
of Newcastle (part of the Maritime
Services Board). Two of the electric
coal loading cranes, Nos.12 and 13,
with their 29-metre high jibs were
retained for loading of general
cargo, while all other cranes were
removed.
All coal loading is now performed
by fast belt convevors, capable of
delivering up to 10,000 tonnes per
hour. The new wharves are
suitable for ships up to 229,000 tonnes and 15.5 metres draught.
Of the once-remarkable hydraulic crane system, all has passed into history except the handsome
solid stone Hydraulic Power House
building, listed by the National
Trust.
Next month we will have a close
look at some DC electric railways.
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LESSON
5: COUNTERS & SHIFT REGISTERS
,,·
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By Louis E. Frenzel, Jr. ·
· ··--~~nt·
®
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The two basic types of logic circuits are combinational circuits and sequential circuits. Combinational
circuits are made up of logic gates connected in a
special way. The outputs are a function of the inputs
and how the gates are interconnected. Sequential circuits are made up of both gates and flipflops. The
flipflops are the primary components as they are used
to store binary states. Those states can be changed by
input signals to form new states.
Sequential logic circuits are designed to perform a
variety of storage and timing operations. A sequential
logic circuit can retain a binary word or manipulate it
in various ways. Sequential circuits can also perform
many different kinds of timing and sequencing operations. The two most commonly used sequential logic
circuits are counters and shift registers. Virtually
every digital circuit contains a counter or a shift
register of some type.
Binary Counters
A binary counter is a series of JK flipflops which
counts the number of input pulses that appear at the
PARALLEL COUNTER
OUTPUT
A(LSB)
COUNT
8
J
--~·r
IN
K
T
c
K
ii
RESET OR
CLEAR
Fig. 1: a 4-bit binary counter. All J and K flipflops are
connected to binary 1 (high). Each flipflop toggles on the
trailing edge of a clock waveform applied to input T.
'
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t
input to the first flipflop. The counter stores the sum of
input pulses as a binary number. To determine the
number of input pulses applied to the counter, you
simply look at the flipflop outputs and read the binary
number stored there. Many digital circuits require
that you keep track of the number of pulses that occur
at a given point in the circuit. A counter is used for
this purpose.
Fig.1 shows a logic diagram of a simple 4-bit binary
counter with the JK flipflop outputs designated as A,
B, C and D. Each flipflop output is connected to the
clock or toggle (T) input of the next flipflop in the
series. This is referred to as cascading. The pulses to
be counted are applied to the toggle input of flipflop A.
All J and K inputs are assumed to be at binary 1 (high).
Another important connection shown in Fig.1 is that
all the clear (C) or reset inputs to the JK flipflops are
connected together to form a common reset line. A
binary O applied to the reset line will clear the
flipflops so that the binary number stored in the
counter is zero (0000).
We can read off the binary number stored in the
counter by looking at the logic states of the normal
flipflop outputs. These are read from right to left, or
DCBA. The A bit is the LSB (least significant bit) and
the D bit is the MSB (most significant bit).
Now let's see how the counter operates. Assume
that we are using JK flipflops that change state when
the clock input switches from 1 to 0. We call this the
trailing edge or the negative-going transition of the input pulse. Now assume that an input pulse occurs that
switches from high to low. This causes flipflop A to
toggle from the binary Oto the binary 1 state. Looking
at the flipflop outputs and reading them in the DCBA
order, we see that the binary number stored in the
MARCH 1988
81
NUMBER OF
INPUT PULSES
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0
C
B
A
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
1
1
0
1
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Fig.2: truth table for a 4-bit binary counter.
counter is 0001. This is the binary reading for the
decimal number 1. So one input pulse has occurred.
When the second input pulse occurs, flipflop A is
toggled again. This time it switches from the 1 to 0
state. As its state changes, the A output switches from
high to low. That in turn causes flipflop B to toggle and
set, its normal output going from O to 1. The transition
appears at the clock input to the C flipflop, but the
flipflop ignores low to high transitions. If we now look
at the counter outputs, we see that the number stored
there is 0010 or the binary equivalent of decimal 2.
Two input pulses have now occurred.
If you continue to apply input pulses to the counter,
one flipflop will simply toggle the next in sequence and
the binary number stored in the counter will increase
by one for each input pulse that occurs. When this
happens, we say that the counter is being incremented. The counter counts up from O to the maximum value that the counter is capable of holding.
Fig.2 shows the truth table of the 4-bit binary
counter. Note that the decimal number of input pulses
applied to the counter corresponds to the binary value
displayed by the outputs. This is true only if the
counter has been reset prior to counting.
An important point to note is that when fifteen input
pulses have occurred, the binary number stored is
1111. When the 16th input pulse occurs, flipflop A toggles to 0. This in turn toggles B to 0, which in turn toggles C to 0, which toggles D to 0. The binary number
PULSES TO BE COUNTED
1I
2I
3I
4
I
5I
6
I
7I
8
II
9
10I
11l
12I
13l 14I
15I
A
I
1
C
0
0
0
I I I---
1
1
1
1
1
1
I
o
0
0
1
...o_"-o_...o_o=----=-o__,o..._..::.o__,o'-'! 1
1
1
Fig.3: input and output waveforms for
a 4-bit binary counter.
82
SILICON CHIP
0
1
~
I
I
0
1
1
1
1
1
·now indicated in the counter is 0000. This is
equivalent to the initial reset state described earlier.
In other words, the number 16 is too large for the
counter to store. So once a 4-bit counter counts to 15,
the next input pulse simply returns it to zero and it
starts again.
Fig.3 shows the input and output waveforms for the
4-bit binary counter as 16 input pulses are applied.
Those timing waveforms illustrate all possible states
of the counter. You may want to trace through the
logic diagram of the counter and correlate each of the
pulses shown in the timing diagram with each flipflop.
This will ensure that you understand how each flipflop
changes state on the high-to-low transition of each input pulse.
Counting to Higher Values
To count to larger numbers, all you do is add more
flipflops to the counting chain. Each additional flipflop
lengthens the binary word of the counter by one bit,
thereby doubling its maximum count capability. The
total number of states that a counter can assume is 2N
where N is the number of flipflops. With four flipflops,
the total number of states is 24 = 2 x 2 x 2 x 2 = 16.
Those states are O (0000) through 15 (1111).
You can determine the maximum count capability of
the counter with the simple formula shown below:
M = 2N - 1
where M = maximum count number and N = number
of flipflops. With four flipflops, the maximum count
capability is:
M = 24 - 1 = 15
A 5-bit counter has a maximum count capability of
31. A 6-bit counter can count to 63, a 7-bit counter to
127, an 8-bit counter to 255, a 12-bit counter to 4095
and so on.
'
A binary counter can also be used as a frequency
divider. Take a look at the waveforms shown in Fig.3.
Recall that a JK flipflop acts as a divide-by-2 circuit.
As you can see in Fig.3, the output of the first flipflop
has a period that is twice the period of the input pulses
being counted. This means that the output of flipflop A
is half that of the input frequency.
Now look at the output of flipflop B. Again, you can
see that its frequency is half that of flipflop A's output.
A similar relationship exists in the remaining
waveforms. The output frequency of flipflop B is onefourth that of the input to flipflop A. The outputs of
flipflops C and D are one-eighth and one-sixteenth of
the input frequency respectively.
The frequency division factor of a binary counter is
simply 2. With four flipflops, the frequency division
factor is 16. A binary counter with eight flipflops will
divide an input frequency by:
28 = 2 X 2 X 2 X 2 X 2 X 2 X 2 X 2 = 256
Thus, if a 6.4MHz input signal is applied to the 4-bit
binary counter, the output of flipflop D will be 6.4
16 = 0.4MHz or 400kHz.
Preset Counters
The term preset means to put a flipflop into one
state or the other prior to another operation taking
Fig.6: count sequence of
a 4-bit down counter.
INPUT PULSE
1
1
1
1
1
1
1
1
0
0
0
0
0
0
1
2
3
COUNT
.4
IN
K
C
5
6
7
8
ii
9
10
11
12
13
14
15
Fig.4: flipflop preset circuitry.
place. Presetting a counter simply 1!1eans load~ng a
binary number into the counter pnor to the mput
pulses being applied. In many applicat~ons, the preset
can simply be a clear or reset operation. If this was
not done, the binary numbers stored in the co~nter
would have no meaning unless you knew the bmary
number stored in the counter beforehand.
It's not too hard to see that it's a lot simpler to clear
the counter first so that the binary number stored in
the counter exactly represents the number of input
pulses that occurred.
On the other hand, there are applications where it
is desirable to begin counting at some predetermined
number. This is done with preset circuitry that takes
advantage of the asynchronous set (S) and clear (C) inputs of the JK flipflops. A typical circuit for one
flipflop is shown in Fig.4.
If you would like to preset the flipflop to binary 1,
you apply a binary 1 to the preset input _at gate fi-:-·
Then you apply a binary 1 to the LOAD mput. This
forces the output of gate A low and the output of gate
B high, The result is that the asynchronous set input of
the flipflop causes it to store a binary 1. Applying a
binary O to the preset input and then switching LOAD
from low to high will cause the flipflop to be reset or
store a binary 0.
.
When all flipflops in the counter have the preset circuitry shown, then a parallel binary number can be
applied to the counter and loaded into it prior to beginning the count operation.
To show how that presetting works, assume that the
4-bit binary counter described previously has preset
circuitry. Suppose that we apply the binary number
1010 to the preset inputs and load it into the counter.
The counter outputs DCBA will read 1010 (decimal
10). Then assume that input pulses occur. If four input
pulses occur, the counter is incremented to 1110 (ie, to
decimal 14).
Down Counters
The binary counter described previously is an up
counter as each input pulse increments the binary
IN
Fig.5: a 4-bit binary down counter.
OUTPUTS
C
B
0
1
1
1
1
0
1
1
1
1
0
0
0
0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
1
0
0
0
0
0
0
0
A
1
1
0
1
1
0
0
0
1
1
1
0
1
0
0
0
INPUT
PULSES
A
B 1
C 1
1
Io
0
0
o
I
Io
1
I
0
0
I
I
0
1
1
1
Io
01
0
0
0
0
0
0
01
Fig.7: input and output waveforms for a 4-bit down
counter.
number stored in the flipflop. That is, as each input
pulse occurs, one is added to the count.
It is also possible to construct a down counter so
that the binary number in the counter is decremented
by one as each input pulse occurs. As a result, down
counters count backwards. For example, if a 4-bit
binary down counter were preset to 1111, sequential
input pulses would decrement it to 1110, 1101, 1100,
etc. Some digital applications require this capability.
Fig.5 shows how to connect four JK flipflops to form
a down counter. Again the flipflops are cascaded by
connecting the output of one flipflop to the clock (T) input of the next in series. The main difference here is
that we connect the complement output of each
flipflop to the clock input of the next.
However, we still monitor the normal flipflop outputs to determine the count stored there. With this arrangement, the count sequence shown in Fig.6 is obtained. The table shows the counter starting with the
maximum count stored in the flip flops (1111 ). When
the count is decremented to zero, the next input pulse
simply flips the counter back to its maximum count
value of 1111. The cycle then repeats.
Down counting is illustrated in the timing
waveforms of Fig.7. Those output waveforms are the
ones that occur at the normal flipflop outputs. Since
the complement flipflop outputs are not shown, it is
more difficult to trace the operation of that counter.
If you'd like to see how each input pulse causes the
toggling and triggering of each flipflop in sequence,
simply draw the complement signals to each of the
MARCH 1988
83
A
IN
T
COUNT
CONTROL
Fig.8: a 4-bit binary up/down counter. When the count control signal is high (binary 1), the circuit is an up
counter. When the count control signal is low, the circuit is a down counter.
waveforms in Fig.7 before doing a pulse-by-pulse
analysis. Keep in mind that a down counter can also
include preset circuitry so that it may begin decrementing from some particular value.
By adding some logic circuitry to the counter you
can make it count up or down. This is illustrated in
Fig.8. An up/down COUNT CONTROL line is added to
determine the direction of counting. If a binary 1 is applied to that input, the counter will count up. This
binary 1 enables all of the A gates and it causes the
normal flipflop outputs to pass through the gates to the
clock (T) inputs of the next flipflop in sequence.
If the up/down control line is made binary 0, the B
gates are enabled by the inverter and the A gates are
inhibited. This causes the complement outputs to be
passed through to the clock inputs. The counter then
counts down.
While binary counters can easily be made up of in' 192, ' L192,'LS192
( 13)
BO RR OW
! 12J
CAR RY
O UTPUT
OUTPUT
dividual flipflops and gates, that is rarely done
anymore. The integrated-circuit manufacturers have
already constructed binary counters in a variety of
configurations, usually in multiples of four or eight
bits. TTL, CMOS and ECL ICs are available, including
those with presetting, down counting, etc.
A Typical IC Counter
One of the most-used IC counters is the 4-bit MSI
device shown in Fig.9. The device is a 4-bit binary
up/down counter with presetting. In other words, it incorporates all the features we discussed previously.
The counter has four outputs and four parallel data
lines are used for applying a preset input. The loadinput line causes the parallel binary word applied to
the data inputs to be loaded into the flipflops. The
counter also has a clear line for resetting it to zero.
Instead of having a single count input like the
up/down counter discussed previously, this device has
two inputs. To decrement the counter, you apply input
pulses to the down-count input. To increment the
counter, you apply pulses to the up-count input.
Carry and Borrow
c~~~~ .o:<•:c._
1 - - - I > <>-+ttt-1-t-t---+t---,
UP !SJ
COUNT
DA TA 19)
INPUT D
The carry and borrow outputs have not been
discussed previously. These are used when counters
are cascaded. The carry output is produced by an AND
gate that looks at the normal flipflop outputs. It
detects when the counter content is 1111 which is the
maximum value. The next input pulse will cause it to
return to zero. When this happens, the carry output
generates a pulse which is applied to the next counter
in series, so that the overflow will be recorded.
The borrow output is used for cascading counters in
a down count application. The borrow output signal is
generated by an AND gate that monitors the complement outputs of the flipflops. When the counter is
decremented to 0000, the borrow output signal is
generated and applied to the down count input of the
next counter in series. With those signals, multiple
counters can be cascaded to form binary counters
with lengths of 8, 12, 16, 20 or any other multiples of 4
bits.
BCD Counters
Fig.9: schematic diagram for the Texas Instruments
74192 4-bit binary up/down counter.
84
SILICON CHIP
While such counters are useful, there are many
situations where it is desirable to use a decimal-like
representation. To cope with this problem, some
special binary codes have been developed. The most
popular of those is binary coded decimal (BCD). BCD is
BCD
DECIMAL
D
C
0
0
0
0
0
0
0
1
2
3
4
5
6
7
8
9
0
0
0
0
1
1
B
A
0
0
0
0
1
1
1
1
0
1
1
0
0
1
1
1
0
1
0
1
0
0
0
0
0
1
Fig.10: decimal to
binary-codeddecimal (BCD)
equivalents.
0
still a binary code in that decimal values are
represented with binary numbers but only the decimal
numbers 0 to 9 are used. The BCD code is shown in
Fig.10. Decimal numbers are represented by 4-bit BCD
numbers, one for each digit. For example, the number
729 in BCD is 0111 0010 1001.
By using flipflops and gates it is possible to construct a BCD counter - that is, one that counts by
tens. It has 10 states, 0 to 9. Such a counter is called a
BCD counter, decimal or decade counter; you see one
in Fig.11. Notice that the first three flipflops are
cascaded in a standard 4-bit binary counter with the
normal output connected to the clock input of the next
flipflop in the chain. The last flipflop, on the other
hand, has its clock (T) input connected to the normal
output of the A flipflop.
Note that the signal controlling the J input on the D
flipflop is dervived from an AND gate that monitors
flipflops Band C. Note also that the complement output of the D flipflop is fed back to the J input of the B
flipflop. The result of all these unusual interconnections is that the counter has only ten states instead of
the usual 16 for a 4-bit counter. The counter counts in
the BCD sequence previously described in Fig.10.
The waveforms generated by the BCD counter are
shown in Fig.12. The counter counts from 0 (0000) to 9
(1001) in the normal sequence. When the tenth input
pulse is received [trailing edge), the counter returns to
0 and the sequence repeats.
While it's possible to construct a BCD counter from
individual gates and flipflops, there's no need to
bother since such devices are available as single integrated circuits. Most of these feature a master clear
or reset line and many feature both presetting and
up/down counting capabilities.
To count values higher than 9, BCD counters may be
cascaded as shown in Fig.13. The first BCD counter
then counts in units of Oto 9. After 10 input pulses occur, the MSB output of the first counter (ie, the D output) triggers the next counter in sequence. The second
IN
.I.
1
A
o o oI
...............
_
co
OO
0
0
1
1
1 ...~o~o_l_o
0
0
0
0~
I
Fig.12: input and output waveforms
for a BCD counter.
counter represents the tens decade and is incremented every 10 input pulses. The tens counter in
turn drives the hundreds counter. Additional counters
can be added for thousands, tens of thousands, hundreds of thousands and so on.
To read the content of the counter, you observe the
BCD codes at the counter outputs. For example, the
number stored in the counter shown is 853. Note that
in reading the output of a BCD counter, the 4-bit
groups are separated from each other. The output is
three 4-bit BCD numbers (1000 0101 0011).
Just as you can use binary counters for frequency
division so can you use BCD counters for that application. The circuit shown in Fig.13 will produce frequency division by some multiple of 10. The first BCD
counter will divide the input frequency by 10 (ie, its D
output will be one-tenth the frequency of the input).
The second counter will produce division by 100 while
the third will produce division by 1000.
Both binary and BCD counters can be used in counting and frequency dividing applications at very high
frequencies. Standard TTL MSI counters can achieve
speeds upward of 50MHz while Schottky TTL
counters can achieve speeds up to 125MHz. CMOS
counters have a much lower limit of approximately
25MHz, but progress is being made in extending this.
ECL counters are available for frequencies up to
2GHz.
Shi£t Registers
Another sequential circuit made up of flipflops is
the shift register. Like a counter, multiple flipflops are
used to store a binary word. However, the flipflops are
interconnected in such a way that incrementing and
LEAST
1100
SIGNIFCANT A B C D
DIGIT (LSD)
COUNT
IN
Fig.11: schematic diagram for a BCD counter. All
unused J and K inputs are connected to binary 1 (high).
0
II
1
1
0
1
0
A
B
C
D
BCD COUNTER
BCD COUNTER
UNITS
TENS
MOST
SIGNIFICANT
DIGIT (MSD)
HUNDREDS
Fig.13: cascaded BCD counters
MARCH 1988
85
IN
SHIFT
(CLOCK)
Fig.14: logic diagram for a 4-bit shift register.
decrementing counting operations are not achieved.
Instead, the connections are such that the binary word
stored in the counter is shifted either to the right or to
the left. In other words, as each clock pulse occurs,
the bit stored in one flipflop is shifted into the flipflop
next to it. A common 4-bit shift register is illustrated in
Fig.14.
All the clock (T) inputs are connected together to a
single line. The normal and complement outputs of one
flipflop are connected to the J and K inputs respectively of the next flipflop in sequence. A single input line is
used for entering data into the shift register a bit at a
time.
Shift registers are used to deal with serial data
words. A serial pulse train, that occurs in synchronism with the shift clock pulses, applied to the input will be entered into the shift register a bit at a
time. This is illustrated in simplified form in Fig.15.
The individual blocks represent each of the flipflops in
the shift register. All the flipflops are initially reset.
When the first clock pulse occurs, the first bit in the
serial pulse train at the input will be shifted into the
first flipflop. A binary O is shifted out of the D flipflop.
As each shift clock pulse occurs, the next bit is shifted
into the register. The first bit moves over to flipflop B
to accommodate the new input bit. After four clock
pulses have occurred, the entire serial word is then
contained in the shift register, as shown.
Holding the input line at zero and applying four additional shift pulses will cause the binary number
stored in the shift register to be shifted out a bit at a
time, thereby generating a serial output word. The
process is illustrated in Fig.16. As you can see, the
shift register can be used to accept, store and
generate serial binary data words.
One of the most common applications for a shift
1101
register is serial-to-parallel data conversion. A serial
data word can be shifted into the shift register. If the
outputs of the individual flipflops are available, then
that word will appear as a parallel data word as
shown in Fig.17 A.
If the flipflops in the shift register have presetting
circuitry similar to that described earlier for binary
counters, then the register can be loaded with a
parallel binary number. Once the shift register is
preset with the parallel number, shift pulses will shift
the word out a bit at a time. This creates a serial version of the parallel input word. Thus, the shift register
accomplishes parallel-to-serial data conversion as
shown in Fig .17B.
Like counters, shift registers are available as
prepackaged circuits in a variety of forms. MSI
devices with four and eight bits are common. Those
feature preset, clear, shift right, or shift right and left.
Larger shift registers can be created by simply
cascading 4 - and 8-bit devices. For example, a 32-bit
shift register can be created by cascading four 8-bit
devices.
Very large LSI shift registers are also available for
special applications. For example, a 256-bit MOS shift
register is available for memory applications. Such a
register is not used to store a single 256-bit word. Instead, it is used to store many smaller words. For example, a 256-bit shift register can store 256 -;- 8 = 32
bytes. Those bytes are retained in the shift register
flipflops end to end as illustrated in Fig.18. The data is
entered serially and read out serially. Because there
are so many flipflops, parallel output is not feasible.
Fig.19 shows a circuit for using the 256-bit shift
register as a memory. The gates at the input of the
shift register are used for entering serial data when it
is desired to store a byte and for data recirculation.
When clock pulses are applied to a shift register, data
that is shifted out is generally lost. However, it doesn't
have to be.
By taking the serial output of the shift register and
feeding it back into the shift register input, the serial
word will be restored at the input as it is read out.
This is accomplished with gates A and Cat the input to
the shift register. The CONTROL line is used to select
whether new serial data is to be stored or whether
recirculation is to be accomplished.
When the CONTROL input is high, the shift register
lolololol
ORIGINAL STATE
Fig.15: how serial data is
entered into a shift register.
o-1 oI oI111 1o,
11lol1lololoo
2ND
2ND
o-1 oI oI o1, 1, o,
1l1lol1lolooo
3RD
3RD
1,1,101110000
4TH
86
. SILICON CHIP
Fig.16: how serial data is
removed from a shift register.
o-!o I olo lo 11011
4TH
1
A
0
1
0
RECIRCULATE
mJ
101ololojojoj
ORIGINAL STATE
AFTER 4 SHIFT PULSES
256•BIT
SHIFT REGISTER
Bffl
ORIGINAL STATE
0
1
1
SERIAL
OUT
~
AFTER PRESET
Wr90~0110
0
0
1
1
0
CLOCK
Fig.17: shift register applications for (A) serial-toparallel conversion and (B) parallel-to-serial conversion.
IN
---i
BYTE
BYTE
BYTE
31
30
29
I
1
BYTE ADDRESS
o=D---ouT
BYTE
BYTE
BYTE
2
1
0
Fig.18: a 256-bit shift register used as a serial memory
to store 32 bits of data.
will recirculate. Serial data output is fed to gate A
which is enabled by the control line. This passes
through OR gate C to the shift register input. During
this time, any new serial data is ignored by gate B
which is inhibited by the inverter operated by the CONTROL line.
To enter new data, the CONTROL line is set to binary
0. This enables gate B and inhibits gate A. No recirculation will take place. However, as the shift pulses
are applied, the new serial byte to be stored will be
shifted in a bit at a time.
To keep track of where the different bytes are
stored in the shift register memory, the circuit in
Fig.19: a 256 bit shift register used as a memory bank.
Fig.19 uses a 3-bit binary counter and a 5-bit binary
counter. The 5-bit binary counter is a word counter
and its output is a 5-bit binary word we call the
address.
Remember we said that it is possible to store 32
bytes in a 256-bit shift register. We label those bytes
byte O to byte 31. The 5-bit counter has a maximum
count capability of 31, therefore, the address appearing at the output of the counter designates which byte
appears to the far right of the shift register, ready to
be shifted out.
The 3-bit binary counter is used to count clock
pulses. This 8-state counter counts to eight for each
byte stored or read out.
Reproduced from Hands-On Electronics by arrangement.
Gernsback Publications, USA.
~
©
SHORT QUIZ ON DIGITAL FUNDAMENTALS 1 . A 4-bit binary up counter is preset to 001 0.
Seven input pulses occur. The decimal value of the
counter content is:
c. 9
a. 2
d. 11
b. 7
2 . The maximum number of states that a 6-bit
counter can represent is _ _ _ _ _ __ _ __
3. The maximum number count capability of a 7-bit
counter is ___________ _ _ __
4. A 3-bit binary counter is cascaded with a BCD
counter. An input frequency of 400kHz is applied
to the circuit. The output frequency is _ _ _ kHz.
5. How many BCD counters does it take to
represent the number 1 9, 900?
a. 2
c. 4
b. 3
d. 5
6. A 4-bit binary down counter is preset to 0011 .
Six input pulses occur. The binary value of the
counter content is:
a. 0011
c. 1010
b. 0110
d. 1101
7. Clearing a counter or shift register means the
same as presetting it to _____ _ _ _ __
LESSON 5
8 . The maximum count of a 4-bit BCD counter is:
a. 1000
c. 101 O
b. 1001
d. 1111
9. Counters and shift registers are a type of _ _
logic circuit.
10. List four ways that data can be entered,
stored and read out of a shift register .
a.
c.
b.
d.
ANSWERS
ino repas 'U! 1a1reJed ·p
ino 1a11eJed 'U! 1epas ·o
lno 1a11eJed 'U! 1a11eJed ·q
ino 1epas 'u! 1epas ·e ·o L
1e11uanbas ·6
(6 1ewpap) LOO L ·q ·g
OJaZ 'L
.( LO L L '0 L L L ' L L L L '0000
' LOOO 'O LOO Oj S8W!l X!S pa1uawaJoap S! L LOO) . LOLL ·p
·(1!6!P lpea JOJ Ja\unoo 0:)8 auo) g ·p
'ZH)j9 = 08 ~ ZH)jQQv ·o L Aq
Ja\unoo 088 a41 pue g /4q sap!A!P Ja\unoo 11q•£ a41 'ZH)f9
LG L = L - (G X G X G X G X G X G X G) = L - LG
v9 = G x G x G x G x G x G = gG
6 = L + G = L + 0 LOO JO '. 6 ·o
MARCH 1988
·g
·g
·v
'8
·G
.L
87
Bearcat BCB00XLT
Scanning Receiver from Uniden
Designed for the US market, the Bearcat BCB00XLT
scanning receiver should be of considerable
interest to communications enthusiasts. Here we
review its main features.
While most scanner enthusiasts
recognise the name Uniden, few
realise that this is also the
manufacturer behind the wellknown Bearcat brand of scanning
receivers. The BCB00XLT is top-ofthe-line in the Bearcat range, mainly because if its ability to receive
the new cellular telephone
frequencies.
But the BCB00XLT has other attributes that make it special in
Australia. The only version
available here is the US model
which means that it covers important communications bands not normally covered by scanners made
specifically for the Australian
market (see Table 1).
As such, the Bearcat BCB00XLT
88
SILICON CHIP
should be of interest to amateur
radio operators, pilots, mariners,
commercial users, satellite enthusiasts, UHF CBers and scanner
enthusiasts alike. It covers four
amateur radio bands, commercial
VHF and UHF bands, the aviation
band, and both PAMTS and cellular
telephone frequencies.
As with other scanners now on
the market, the unit includes
microprocessor control. It has 40
memories which can be linked or
programmed separately, allowing
two banks of dedicated service frequencies to be scanned. This means
that you can scan all 40 channels or
elect to scan channels 1-20 or
21-40.
The keyboard is easy to use and
is laid out in two sections to allow
programming and operation. The
program section allows the direct
selection of any of 40 stored frequencies, while the operations section provides for channel lockout,
direct channel access, automatic
search, scanning, priority override
and delay functions. The frequency
and operating mode are displayed
on a 9-digit green fluorescent
display.
Perhaps one of the more interesting features is the priority
override. This allows the user to
monitor transmissions on one channel while actually listening to
another. What happens is that the
priority feature samples the frequency on channel 1 every three
seconds. If a signal is detected on
this channel when sampled, the
receiver then remains tuned in to it
until the transmission ceases. The
scanner then reverts to the
previous mode of operation.
Band (MHz)
Sensitivity
(12dB SINAD)
Channel
Steps
29-30
30-50
50-54
118-135.975
136-144
144-148
148-174
0.3µV
0 .3µV
0.3µV
0.8µV
0.3µV
0.3µV
0 .3µV
5kHz
5kHz
5kHz
5kHz
5kHz
5kHz
5kHz
406-420
0 .5µV
12.5kHz
420-450
450-470
0.5µV
0.5µV
12.5kHz
12.5kHz
470-512
0 .5µV
12.5kHz
806-912
0 .7µV
12.5kHz
Supplied with the 800XLT are
two antennas, one for the VHF/UHF
bands (telescopic) and the other for
the 800-900MHz band. These attach to sockets on the top and rear
panels. Alternatively, an external
antenna can be used for better
reception of weak or noisy signals.
Because the 800XLT scanner is a
US version, it does have a couple of
minor drawbacks. First, the
squelch controls operates in
reverse; ie, you rotate it anticlockwise to mute the receiver. Second, the scanner has a key marked
Service
continued from page 17
10-metre amateur
Cordless phones
6-metre amateur
AM aircraft
Polar orbiting satellites
2-metre amateur
VHF commercial; VHF
marine
UHF low band
commercial
7 0cm amateur
Ul-iF commercial; police
rescue helicopter
UHF CB; PAMTS mobile
phones
Cellular telephones
"WX" which is designed to scan
local weather stations in the US
(162.4MHz-162 .55MHz). Unfortunately, this feature is of no use in
Australia.
But, apart from these quibbles
and the fact that the unit is only
available for 12V DC operation, the
BC800XLT is well worth consideration by those with an interest in
VHF and UHF communications. It is
priced at $749 and is available
from Santronic Corporation, 345
Princess Highway, Rockdale 2216.
Phone 599 3355. (Garry Cratt).
Spot light for
video film-making
Most recent model domestic
video cameras are usable in
quite low values of light, down to
only 5 or 6 lux in some cases. But
to really give the best results,
with bright colours, they need
lots of light. This video accessory
light from Arista gives plenty of
that.
It consists of a lightweight
holder with a quartz halogen
lamp which can be attached to
most video cameras via a
bracket. Four "barn doors" on
the lamp housing allow the beam
to be controlled.
The unit is powered from a
12V gel battery which is held in a
shoulder pack and weighs
Hifi Review
2.75kg. The unit comes with a
charger.
For further information, contact Arista Electronics Pty Ltd,
57 Vore Street, Silverwater,
NSW 2141. Phone (02) 648 3488.
tempt to measure distortion at
20kHz. In other words, the performance is well up to standard for a
medium-priced CD player.
The CD-1500 also went through
our usual tests for tracking and error correction and showed up well.
Nor is it fazed by physical shock to
the case and it is better in this
respect than a number of more expensive players.
In summary, the Realistic
CD-1500 is a good machine which
performs well and has most of the
facilities which most people want.
The only drawback is that, considering it is basically a no-frills
player with remote control, it is a
touch dear. To be fair though, it is
backed up by the largest electronic
retail network in the country with a
service record second to none.
That being the case, it is worth
paying a premium for the CD-1500.
It is priced at $529.00. You can
hear it at any Tandy store.
~
Tape Player
continued from page 42
work first so that it can be used as a
drilling template (optional). A small
clamp made from scrap aluminium
was used to hold the batteries in
position and is secured to one end
of the case using a screw and nut.
It's now simply a matter of mounting the parts and completing the
wiring as shown in the coded
photograph. The electret microphone should be wired using shielded cable, while the remaining wiring can be light-duty hookup wire.
Be sure to connect the battery leads
the right way around.
To test the unit, first press the
run button and check that the tape
motor runs. If it does, you can now
record a message by pressing the
run and record buttons at the same
time while speaking into the
microphone. Check that the
message plays back and repeats if
the run button is held down.
Finally, you can add a volume
control by connecting a 5000 potentiometer in series with the speaker.
Connect the amplifier output to one
side of the pot and connect the
loudspeaker to the pot ·wiper.
.~
MARCH 1988
89
NEWPRODUCTS-CTD
National Series
32000 Designer Kit
For those in the computing business, all the
interest has moved into the 32-bit arena, with
microprocessors such as the National 32000 series.
To help the development process, a Designer Kit
has been made available at a very reasonable
price.
The NS32000 32-bit family series
of ICs are designed for high performance applications such as in CAD
workstations, multi-tasking, multiuser systems, robotics and artificial
intelligence. The power of this
series of microcomputers brings
super mini and mainframe power to
a desktop or personal computer.
The design is optimised to use high
level languages (HLL) such as C,
Pascal and FORTRAN 77 while
operating with UNIX.
National's designer kit is a very
economical way to obtain the major
integrated circuits plus documentation and software for a complete
32-bit microcomputer.
ICs supplied with the designer kit
are the NS32032 central processing
unit (CPU), an NS32081 floating
point unit (FPU), an NS32082
'?'A National
D semlconduct.nr
Series 32000
Desi•
. . gtlerKit
Fir,stin ~~Bit Microprocessors
90
SILICON CHIP
memory management unit (MMU),
an NS32201 timing control unit
(TCU) and NS32202 interrupt control unit (ICU). In addition, a set of
four PROMs programmed with the
Tiny Development System (IDS)
and a PAL (programmable array
logic) address decoding IC are
supplied.
These components can be built
onto a printed circuit board with
the addition of extra memory, logic
and peripheral components, to complete the 32-bit microcomputer. A
full circuit diagram is given for the
computer and copious information
is provided to enable construction
of the PCB. A suitable PCB can be
obtained by sending US $129.95 to
Computer Talk in the USA, using
the order form included with the
kit.
Once complete, the computer
PCB can be connected to an IBM
PC/AT COMt port. The PC terminal
and keyboard are then used for the
transfer of files between the
designer kit and PC/AT using the
IDSCOM software utility supplied
on disc with the kit.
A Tiny Development System
(IDS) enables generation of 32000
executable code. The TDS features
include writing, editing assembly,
debugging and execution of source
code programs.
Architecture
Architecture for the Series
32000 products is very clean, even
though the floating point arithmetic
and memory management could not
be incorporated onto the same chip
as the CPU. The CPU has an optimum number, size and scope of
registers. There are eight 32-bit
general purpose registers and eight
32-bit floating point data registers.
The memory management unit is intended for implementing demand
paged virtual memory. At any point
in time a program sees an addressing space of up to 16 megabytes.
The design reduces bus interference between direct memory
access, multiple CPUs and graphics
by reducing memory bus traffic. It
does this by maximising information in each transfer and eliminates
transfers by keeping information
where it is needed.
Overall, the powerful instruction
set, 32-bit bus and complete family
of chip sets available plus the ability to operate HLL and UNIX make
up a very advanced machine. Undoubtably, the National Series
32000 microprocessor chip sets will
be widely used in the future.
The Series 32000 Designer Kit is
available for just $180 including
tax from Geoff Wood Electronics
Pty Ltd, 220 Burns Bay Road, Lane
Cove West, NSW 2066. Phone (02)
427 1676 . .
Velleman kits from
Eagle Electronics
Made in Belgium, the Velleman
range of electronic kits is very comprehensive and encompasses projects such as a microprocessor
universal timer, electronic ignition,
electronic thermometer, a motor
speed control, a light computer and
a Centronics interface. Each kit is
well presented and packaged.
We had a look at a sample kit, the
Stereo VU LED meter, K-1798
which is based on two Siemens
UAA170 ICs together with two 741
op amps. The kit is packaged in a
see-through plastic box and uses a
well finished screen-printed, tinned
and solder-masked printed board.
The LEDs are mounted behind a
screen-printed panel which could
be part of the front panel of a mixer
or similar piece of audio equipment.
For further information on the
Velleman range, contact Eagle Electronics Pty Ltd, 54 Unley Road,
Unley, South Australia. Phone (08)
271 2885 .
The LogicBridge. A new concept in
handheld logic analysers.
The LogicBridge 136 is a dedicated logic instrument for
those involved in the design, repair or maintenance of
digital electronic circuits and equipment. It is handheld
and battery powered .
While it performs like an intelligent 3 channel logic
probe. it is also able to store waveiorms like a logic
analyser. Waveforms can be viewed and measured on
a custom LED display. Stored waveforms can later be
serially transferred to a personal computer for further
analysis.
Being a dedicated logic instrument, the LogicBridge
has a range of speci al digital debugging and
indentification faci lities. As well , an audio output may be
used for triggering and waveform identification .
With over 10,000 units sold in the U.S. alone. it is the
ideal unit for the workshop or the field technici an alike.
SHOWROOM SALES
86 Parramatta Road
Camperdown 2050
VIC
OLD
WA
Radio Parts Group. Melbourne. Phone 329 7888
Bailee Systems. Brisbane. Phone 369 5900
Nortek. Townsv1lle Phone 79 8600
H1nco Engineering . Perth. Phone 381 4477
ACT
SA
TAS
Phone· (0215193933
Fax 10215501378
Electronic Components. Fyshw1ck Phone 47 3688
!nt"I Commurncat1ons Systems. Por1 Adelaide Phone 47 3688
George Harvey Electronics. Hobart Phone 34 2233
MARCH 1988
91
NEWPRODUCTS-CTD
20MHz oscilloscope
from GW Instruments
One of the lowest cost
oscilloscopes presently available is
the GOS-522 20MHz dual trace
model from GW Instruments. It has
a 15-cm rectangular tube with internal graticule. Accelerating
potential is approximately 2.2kV.
Additional features offered by
the GOS-522 include vertical mode
triggering, auto trigger level lock
and variable hold-off. The auto trigger facility is handy for triggering
from waveforms where the DC offset level is varying while the
variable hold-off feature is useful
when monitoring digital and video
waveforms with irregular or
uneven duty cycle. Signal shot
Sideways printing
and all that
As versatile as the the average
BO-column dot matrix printer is,
there are many things it just won't
do or won't do without a hell of a lot
of programming. For example, say
you're printing out a big spreadsheet or a family tree (something
we know you do every week or so).
The only way to print it out is to do
it sideways.
Now there is a software package
which allows your IBM PC and dot
matrix printer to do it. It also
allows a wide variety of fonts, as
well as the full IBM character set.
Note: as well as the standard
80-odd ASCII characters on the
keyboard, the IBM also has provision for the Greek alphabet, maths
symbols and graphics characters.
The new program also allows
printing enhancements to programs
such as W ordstar which do not normally allow you to use all the fonts
available on your printer (without
customising Wordstar, that is).
Called Printworks, the new software is also available in a version
to suit laser printers. Contact PC
Extras, GO3 The Watertower,
Redfern Hill. Phone (02) 319 2155.
Effective new
strippers
from Arista
Small oven for
printed circuit boards
An oven for curing the resist on
PC prototypes is the latest in a line
of equipment from Sesame Electronics for making PCBs in small
quantities.
The unit has an electric heating
element, a dial thermostat, and a
timer. The PCB, which can be any
size up to 250 x 200mm, rests on a
wire tray inside the oven.
For further information contact
Sesame Electronics Pty Ltd, PO Box
452, Prahan, Vic 3181. Telephone
(03) 527 8807.
92
SILICON CHIP
Arista have two new wire strippers in their range of tools for the
technician and enthusiast. One
model, the CS 500, is for stripping
coax cables, (cable types RG58 and
RG59) while the other, a brutallooking but effective beast, the CS
100, is for stripping single and
multi-strand wires.
For further information, contact
your Arista stockist or Arista Elec-
Line Grabber for Phones
sweep mode is also available.
The GOS-522 has a genuine
20MHz bandwidth and has a 20
nanosecond/division sweep range
to make timing measurements at
high frequencies much easier.
For further information on the
GOS-522 contact your GW Instruments stockist or the Australian distributor, Emona Instruments, 86 Parramatta Road,
Camperdown, NSW 2000. Phone
(02) 519 3933.
check this by measuring the voltage
across the limiting resistor) but the
LED is not illuminated, it is likely
that the LED is installed the wrong
way around.
If you can't get the LED to illuminate for supply voltages above
20 volts, try shorting out the SCR.
This will indicate whether the SCR
and its associated components are
faulty or not.
Repeat these tests for your other
Line Grabbers. You should be sure
that they are working correctly
before you connect them to the
phone lines.
A further wrinlcle
There is another variation of the
Line Grabber you could use if you
Amateur Radio tronics Pty Ltd, 5 7 Vore Street,
Silverwater, NSW 2141. Phone (02)
648 3488.
continued from page 21
wanted to be clever. Say you had a
phone which you use a lot and you
don't want to fit the Line Grabber to
it. That's OK. All you do is fit Line
Grabbers to all the other extensions
but not to your phone.
This will allow your phone to
grab the line at any time but if
another extension is picked up
before yours, you can still listen in.
That could be useful in situations
when another extension answers a
call intended for you.
~
Acknowledgement: we thank Arista
Electronics Pty Ltd for giving us the
idea for this project. They will have
a commercial version available
shortly.
Antennas
physically long. Suitable only for
UHF due to physical instability.
Next month, we'll describe a few
practical antennas that you can
build yourself.
Corrections
In Table 1 on p.77, January 1988,
the location of the VK4RAT
transmitter should have been listed
as Townsville (not Brisbane). Also,
the vision input signal should read
426.25MHz (not 444.25MHz).
Would readers also please note
that the address of the Sydney ATV
continued from page 71
Group is now 24 Larra St,
Guildford, 2161, NSW. The
repeater operates from 6.30-9pm
on Mondays, Tuesdays and
Thursdays, and from 12-5pm on
Saturdays and Sundays. We thank
the two readers who contacted us
with the above information.
Finally, the author would like
to acknowledge the following
amateurs who provided information on amateur TV for the January
issue: VK2BTV, VK2ZZO, VK2AAK,
VK3PC, VK3BFG, VK5AWA and
VK5KG
~
High, Low, Sink & Source
Strobe warning light
This self-contained Xenon strobe
light can be used as a warning
beacon on boats or cars, as an
attention-getter for shop displays,
as a Christmas or party decoration,
or as an external indicator for a
domestic burglar alarm. It runs
from 12V DC, battery or mains
plugpack, and draws about 150mA.
Flash rate is about two per second.
The screw-on lens cap is available
in red, orange or blue. The unit is
weatherproof and has a screw
mounting base. It retails for $35
from Arista outlets.
source up to about 18 milliamps but
depending on the output voltage it
can sink only about one milliamp.
Some logic circuits can sink a lot
more current than they can source.
The prime examples of this aTe TTL
(transistor-transistor logic) devices
which can typically sink about
25mA, or a lot more in the case of
Schottky devices, when their outputs are low (ie, close to 0V) but can
source virtually no current when
their outputs are high (5V).
These examples of devices which
have unequal source and sink current capability invariably have output stages which are essentially
non-symmetrical. In some cases,
they may have open-collector out-
continued from page 65
puts which means that they can
sink quite a lot of current but can
source no current at all unless they
have an external "pull-up" resistor
to pull their outputs high.
Finally, before we leave this
discussion, there is another definition of high and low which is relevant to comparators and logic circuitry. A signal is said to be high if
it is high enough to cause a comparator or logic gate to change
state. In this definition, high means
above the positive threshold of the
device's input. For example, in a
logic circuit running at 15V, high
may be any voltage above + 7.5V.
Similarly, low many be any voltage
below + 7.5V.
~
MARCH 1988
93
ASK SIUCON CHIP
Got a technical problem? Can't understand a piece of jargon or some electronic principle? Drop us a line
and we'll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097.
Capacitance Adapter
for DMMs
I am writing regarding the
Capacitance Adapter for DMMs
described in the November issue of
SILICON CHIP. I purchased the kit
from Altronics in Perth and after
building it, tested the unit on the
"pF " range with a lOOOpF
capacitor. I found it did not read accurately and only reached 857pF. I
was not able to correct this situation with the LOW adjust trimpot
VR1.
I found the only way to get a correct reading was to remove the
120kQ resistor in series with VR1
and replace it with a link. It now
reads accurately on all ranges.
Could you please tell me why I had
to remove this resistor? (K.A., Kambalda West, WA).
• The immediate explanation for
the need to remove the 120kQ
resistor is that the upper and lower
input signal thresholds of the
74HC132 NAND Schmitt trigger are
outside the tolerances catered for
by our circuit. In fact , on the face of
it, the thresholds are much further
apart than we catered for.
When we looked at various
manufacturers' data again, prompted by your letter, we note that
the range of hysteresis values (difference between upper and lower
threshold voltages) is more than
four to one for a supply voltage of 5
volts.
For example, at one extreme
of manufacturing tolerance, a
74HC132 could have an upper
threshold of about 3.5 volts and a
lower threshold of 1 volt, giving a
hysteresis of 2.5 volts (ie, the difference). At the other extreme, a
74HC132 could have an upper
threshold of 2.5 volts and a lower
threshold of 1. 9 volts, giving a
hysteresis value of 0.6 volts. If you
divide 2.5 by 0.6 you get a value of a
little over 4, as we quoted above.
When such a NAND Schmitt trig94
SILICON CHIP
ger is used in the oscillator circuit
of the Capacitance Adapter (see
ICla), the likely range of the frequency it will produce, without adjustment, is about 4.5 to one. This is
because the charging and discharging of the .047 µF capacitor is an exponential function.
Without going into the maths of
the oscillator function, it's looks as
though we goofed rather badly
doesn't it? After all, the combination of 100kn trimpot and 120kn fixed resistor only gives a range of
1.83:1 (220kn divided by 120k0)
does it not? We can see all our
readers nodding in agreement.
...------+sv
74HC132
VRl
100k
This is the oscillator circuit of the
Capacitance Adapter featured in the
November 1987 issue. Wide tolerance
limits on hysteresis for the gate
inputs mean that the frequency can
vary by more than 4.5:1 before
adjustment.
But before we get out the
sackcloth and ashes, one other factor should be considered. All the
upper and lower threshold levels in
the four gates of a particular
74C132 should be roughly equal,
should they not? Therefore, even
though the oscillator frequency of
IC la can be expected to vary over a
wide range, before adjustment,
oscillator IClc can be expected to
more or less "track" ICla. Similarly, the switching levels of IClb can
be expected to vary as much as the
other two gates.
Therefore, the range of adjust-
ment we have provided for the
oscillator of ICla should have been
enough to cater for variations between the gates of particular
74C132 devices. Unfortunately
though, manufacturers do not give
any clues as to the expected variation between gates of individual
devices. We are in the dark on that
topic.
So the bottom line is, we are not
sure why you had to replace the
120kn resistor with a link. It should
not have been necessary to remove
it completely. In fact, if a lOOOpF
capacitor was giving a maximum
reading of 85 7pF as you claim, then
it should have been possible to get
sufficient range of adjustment by
replacing the 120kQ resistor with a
value of 82kQ.
Clearly though, your experience
suggests that a greater range of adjustment is necessary. We will
therefore play it safe and suggest to
the suppliers for this kit that they
change the 100kQ trimpot VR1 to
200kQ and the 120kQ resistor to
47kQ. This will give an overall frequency adjustment range of 5.25:1.
Infrared sensor for
driveway monitor
I wish to construct an infrared
sensor to mount under the eaves at
the front of my house, to detect people approaching up the driveway
and to turn on an outside light.
Would the passive infrared sensor for burglar alarms as described
in your December 1987 issue be
adaptable to this function? Also
could it be disabled during
daylight? (W.D., Mt Waverley, Vic).
• Yep. The PIR sensor described
in December should be just what
the doctor ordered. You could
disable it during daylight hours by
using a light dependant resistor
(ORP12 or similar) connected between pin 2 of IC4 and the + 12V
line.
Note that if you intend to use a
How to dim
fluorescent lights
I built the Speedi-Watt dimmer
descibed in the December 1987
issue of SILICON CHIP and I have
tried it out as a dimmer for a 20
watt fluorescent lamp fitting. Unfortunately, it will only dim over a
very limited range below which it
flickers badly. Also, the lamp will
not start if the dimmer is wound
down before power is applied.
What do I have to do to make the
circuit dim reliably? (B.L., Curl
Curl, NSW).
• Fluorescent lamps do not like
being dimmed, as you have found. It
is possible but the circuit gets complicated by the need for a
transformer.
When a fluorescent lamp is
operated at full mains voltage the
filament electrodes at each end of
the tube run quite warm and so provide plenty of electrons to maintain
the discharge. If you use a dimmer,
the normal discharge current is
reduced and so the filaments
become cooler.
The way around this is to maintain the filaments at a constant
temperature by running them from
a transformer with two separate
low voltage windings, one for each
end of the tube.
The transformer should have two
6V windings and should be connected to the mains so that its
primary voltage is independent of
the setting of the dimmer. The cirmains spotlight, the relay should
have contacts rated for 240V AC.
Transistor
replacement
for amplifier
I am interested in your 100W
module as published in the
December 1987 issue. It would
seem an ideal replacement for a
Millbank Electronics amplifier I
have under repair for a friend. This
particular amplifier failed and in
the process one BDY7 4 power transistor failed on each side. I have
repaired the main board but have
been unable to source any BDY74
power transistors.
C4
.01
25DVAC
This circuit shows how the Speedi-Watt Dimmer published in the
December 1987 issue can be adapted to dim fluorescent lamps.
cuit is shown in the accompanying
panel. Note that it uses the SpeediW att dimmer featured in the
December 1987 issue of SILICON
CHIP.
This will allow the tube to be dimmed over a much greater range but
even so it is best to start it with full
voltage applied and then to dim
down.
Companies that make fluorescent
ballasts generally make these dimmer filament transformers. To buy
them you will have to contact a
lighting supplier.
Note that there is one other trap
to the circuit. It needs a rapid start
tube and rapid start ballast; ie, the
conventional starter and ballast is
dispensed with. In effect, this
means that the lamp fitting has to
be completely re-wired. The only
bits you get to re-use are the
metalwork and the "tombstones".
Furthermore, rapid start tubes
are becoming harder to get, as are
most of the older tubes with a
diameter of 3 7mm. On the other
hand, you may find that a 20W or
18W tube will start fairly easily,
despite the fact that it is not a rapid
start type.
The truth is that dimming fluorescent lamps is a pain which is why it
is not done on a commercial basis
very frequently. It can be done with
a high frequency "electronic"
ballast, but that is another story.
Your 100W module does seem an
ideal repalcement, however the
transformer in the Millbank
amplifier delivers ± 55 volts DC
under quiescent conditions, with
full power consumption being
220VA.
Could I use your 100W module to
slot straight in or would I have to
reduce the voltage output of the
supply? The output of the Millbank
amplifier can either be taken direct
from the output stages into an an
load or via an output transformer.
The output transformer is wired in
parallel with the direct output and
can be configured for two separate
50V supplies or a single 100V
supply.
I would presume the primary of
the output transformer to be an impedance. So again, could I use your
100W module? (J.B., Broadmeadows, Vic).
• According to our references,
the BDY7 4 is a 115 W silicon power
transistor with a collector voltage
rating of 150V and a current rating
of 15 amps. It was originally sourced by Philips and Mullard. With
those ratings, it should be easy to
obtain a suitable replacement. We
suggest the 2N3773, sourced by
RCA and Motorola, or the Motorola
MJ15003. Both these have higher
power ratings than the BDY74 and
the latter transistor is available
continued on page 96
MARCH 1988
95
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Altronics .. .. ... ....... .. ... ....... 22-25
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Elmeasco .... ........ .. .. ... .. .. .... . IFC
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PC Boards
21 ($9.40)
22 ($9.80)
23 ($10.20)
24 ($10.60)
25 ($11.00)
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Ask Silicon Chip
continued from page 95
from stores such as Jaycar, Dick
Smith Electronics and Altronics.
The above really answers your
question in full but your letter does
raise a few points of interest. First,
as noted in these pages last month,
the 100W module described in
December 1987 will not run safely
with supply voltages much above its
nominal ± 40V DC.
Second, it is not really intended
for driving an output transformer.
To do so, it would require flyback
diodes (such as 1N5404) across
each output transistor (ie, each
diode reverse biased). The diodes
safely damp any spikes which
would otherwise be generated by
the transformer's inductance when
the amplifier is driven into clipping
(or if the protection circuits
operate). The amplifier should also
incorporate a trimpot adjustment to
minimise any residual DC output
96
SILICON CHIP
voltage which would cause direct
current to flow in the transformer.
By the way, we suspect that the
output transformers in your
Millbank amplifier are autotransformers which can be configured
for 50V or 100V lines. This means
that your amplifier is mainly intended for public address applications.
The 100V (or 50V) output is intended for driving lots of small speakers
in parallel with its own step down
transformer.
The idea is to keep on adding
speakers, of say 5-watt rating, until
the amplifier is fully loaded. Thus, a
200W amplifier with 100V lines
could drive 40 5 watt speakers.
If readers are interested in a
100W public address amplifier
with suitable microphone and mixing facilities, we would like to know
about it. If there is enough interest,
we'll do it.
~
Printed circuit boards for SILICON
CHIP projects are made by:
• RCS Radio Pty Ltd, 651
Forest Rd, Bexley, NSW 2207 .
Phone (02) 587 3491 .
• Jemal Products, 5 Forge St,
Kewdale, WA 6105. Phone (09)
451 8726 .
Notes & Corrections
Capacitance Adapter for DMMs,
Nov. 1987: to give more range of
calibration adjustment, trimpot
VRl should be changed to 200k0
and the associated 120k0 resistor
reduced to 47k0.
24V to 12V Converter, Dec. 1987:
the wiring diagram on page 31
shows the lOOJLF capacitor
(associated with D9) incorrectly
polarised. The circuit diagram on
page 30 is correct.
To provide crowbar overvoltage
protection in the event of a circuit
mishap, connect a 15V 5W or 20W
zener diode across the 13.6V output. The zener's anode should connect to the positive output terminal.
If the output voltage exceeds 15V
the zener will conduct heavily and
blow the fuse. The zener may also
fuse and become short-circuit.
Note: Jaycar Electronics can supply a 15V 5W zener diode, type
1N5352B, which would be suitable
for this application.
~~JI
PARTS CLEARANCE SALE
Computer Connections
Archer Enclosures
4000/TTL Digital ICs
3
-
1. Subminiature Connector Hood. 276-1529
Reg4.99 .•.... ... .. ...... Sale! 1.29
2. Experimenter's PC Board. 276-170
Reg5.95 .• • ••..•.....••.. Sale!2.49
3. Plug in Board with RS-232 Port. 276-187
Reg 3.99 ................. Sale! 1.99
DualType.276-2413 Reg2.99 .. Sale!49<
Decade Counter/Divider. 276-2417
Reg 3.99 ...... .. ...•.• • • Sale! 79<
Quad Bilateral Switch. 276-2466
Reg 2.99 •••..•.••.•• •• .. Sale! 49•
Quad NANO Gate. 216- 1801
Reg 1.89 ........... .... . Sale! 29<
4. Utility Box. With cooling vents.
270-9520 Reg 11.95 ......... Sale! 7 .95
5. Economy Case. 210-222
Reg5.95 ... . .. . ........ Sale!3.95
6. Box & PC Combos. 5.4x8.4x 3.5cm.
210-ZBJ Reg6.95 .... . ...... Sale! 4.95
7. lx6x3.2cm. 270-284 Reg 7 .95 Sale! 5.95
High Quality Relays
Compacitor/Film/ Circuits
Tantalums & Trimmers
"'~
7. Micro-Mini SPOT. With 12V DC coil.
275.241 Reg3.49 .. .. . ........ Sale! 2.49
8. SPST Reed. 5V DC coil. 275.m
Reg 2.99 ................. Sale! 1.99
12VDCcoil.m-m Reg2.99 ... Sale! 1.99
9. Mini SPOT. With leads. 215-004
Reg4.29 .........••••.... Sale! 2.99
16
□
18
19
-
<at>
~
a -a
20
21
27
~
10 4.7
10 3300
II
220
II
470
II
1000
II
4.7
12 .01
13 .01
16. Trim Gasket. 270-036
Reg 1.99 .......... Sale!5'
17. IC Test Probe Adapter.
270-335 Reg 1.99 .... Sale! 49'
18. Switch Panel. 275-705
Reg 1.49 ......... Sale! 99'
19. On/Off Switch. Label
plates. 275-320
Reg99' ... .. .. . . . Sale! 10'
20. Replacement Lamp .
Flange. 272-1125
Reg 1.09 ......... Sale! 29'
21. Bayonet. 272-1155
Reg 99' ..... ... .. Sale!29'
22. Neon. 272-1102
Reg 1.29 ......... Sale! 49'
23. 6 Volt Bulbs. 272-341
Reg 2.49 . ........ Sale!99'
=·.
I,-. •
28
35
35
16
16
16
35
Cat.No.
Reg
Sale
272- 1012
272- 102 1
272-956
272-957
272-958
272-1024
272-1065
272-1051
.99
1.49
.99
1.09
1.19
.79
1.29
.99
.29
1.99
.29
.29
.29
.29
.49
.29
uf
WVDC
Car. :So.
Reg
Sale
H
0. 1
.47
1.0
2.2
10
272-1432
272-1 -1 ll
272-1 -1 34
272- 1415
272- 1-116
272- 1-117
.99
.99
.99
1.09
1.29
.49
.49
.49
.59
.69
22
35
15
15
15
16
16
Fi~
Va lu e-
WVDC
Cat. No.
Reg
Sal('
15
3 t o l OpF
I
500
I 10
272-1 Jl8
1.-19
.99
"
H
H
14
1-1
to
60 rF
272-11 4 0
1.-19
2.49
.i9
.99
Fuse Holder
240V 5 Amp
Thermal Circuit
Breaker. 210-96,,1
Reg7.95 Sale! 1.99
24. 3PDT Centre-Off. rn-661
Reg6.95 .............. Sale!4.95
25. Submini Toggles. 275-326
Reg4.29 .............. Sale! 2.29
SPOT Centre-Off. 275.325
Reg4.99 ...... ........ Sale!2.99
26. Heavy Duty Slide Switch. 275-275
Reg 2.49 .............. Sale! 1.49
29
Er
-r.andy
It
Fig
14
24
Reg5 .95 .. . . .................. Sale!95•
28. Connector. Type CF-56. 278-223
Reg 2.29 ...................... Sale! 49•
29. Connector. PAL chassis socket. 278-9604
Reg 2.99 ................. ..... Sale! 59'
PAL chassis plug.278-960, Reg 2.99 ... Sale! 59•
30. Bushing. For RG59, RG58, RG62 cable.
218-1643 Reg79• ...•••••••......... Sale!9•
ELEeTR8NleS
WVDC
Switches
27. Adapter. Female 'F' to BNC male. 21a-z5 1
'
uf
Extras
~
17
Fig
20K Turn Trim Pot. 271-1-1,,
Reg 2. 79 . . . . .... Sale! 79 '
Hook Up Wire Packs
Colnur Gq
m
Ydlow
Bllll·
l l)O
10
10
Ca i. Ntl.
R,:i.:: Sall·
278-9633 7,9; 2.9i
\()() 278-963 -t 7.9; 2.95
AC Circuit Breaker
Rated 2 amps, 120V
AC. With 120
seconds at 1. 7 5
amps, 60 seconds at
2 amps. ZiL'-9ll L'
Reg 3.29 . . Sale! 1.99
f}'~~.,,
31. 8-Pin Mike Plug. 21H25 Reg4.99. Sale! 3.99
32. Accepts Phono Plug. ZH-lL'6
Reg4.49 ..................... Sale! 3.99
33. Chass Sock, 4' Pins. 21-1-%1-1
Reg 2.29 ........ . .... ........ Sale! l .49
34. Dual Phono Jacks. 21-1-112
Reg 1.99 ........ .. ........... Sale! 1.49
35. lnline Plugs, 5 Pins. 27-1-%Zi
Reg 2.49 ........ .. ....... . ... Sale! 1.49
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