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Vol.9, No.1; January 1996
Contents
FEATURES
4 Living With Engine-Managed Cars
We take a look at some of the do’s and don’ts when it comes to maintaining a
modern engine-managed car. Also, is it worthwhile changing the chip or are
there better ways of increasing engine performance? – by Julian Edgar
10 Recharging Nicad Batteries For Long Life
Nickel cadmium and nickel metal hydride batteries often don’t last very long
before requiring replacement. One solution is to use “burp charging” which is
claimed to greatly extend battery life – by Horst Reuter
53 Satellite Watch
THE DO’S AND DON’TS OF LIVING WITH
ENGINE-MANAGED CARS – PAGE 4
A new column that gives you satellite reception reports for Australia and New
Zealand – by Garry Cratt
PROJECTS TO BUILD
22 Surround Sound Mixer & Decoder
Build this unit and add depth and realism to your home videos. It provides realistic
surround sound mixing and even includes a simple decoder – by John Clarke
40 Build A Magnetic Card Reader & Display
Check out what’s written on the magnetic stripe on your credit card. This unit could
also be used as the basis for an electronic door lock, restricting access to those with
“authorised” cards – by Mike Zenere
54 The Rain Brain Automatic Sprinkler Controller
BUILD A MAGNETIC CARD READER
& DISPLAY – PAGE 40
Comes as a kit and controls up to eight solenoids plus a master solenoid. You
program it yourself to selectively water any area of your garden as little or as
often as you like – by Graham Blowes
70 IR Remote Control For The Railpower Mk.2
Provides complete freedom of operation and has pushbutton control for
everything. An optional speed meter is also included – by Rick Walters
SPECIAL COLUMNS
32 Computer Bits
Upgrading your PC; is it worthwhile? – by Geoff Cohen
80 Serviceman’s Log
The complaint seemed simple enough – by the TV Serviceman
8-STATION SPRINKLER
CONTROLLER – PAGE 54
86 Vintage Radio
Converting from anode bend to diode detection – by John Hill
DEPARTMENTS
2 Publisher’s Letter
3 Mailbag
16 Circuit Notebook
63 Product Showcase
69 Order Form
92 Ask Silicon Chip
94 Notes & Errata
95 Market Centre
96 Advertising Index
IR REMOTE CONTROL FOR THE RAILPOWER MK.2 – PAGE 70
January 1996 1
Publisher & Editor-in-Chief
Leo Simpson, B.Bus.
Editor
Greg Swain, B.Sc.(Hons.)
Technical Staff
John Clarke, B.E.(Elec.)
Robert Flynn
Rick Walters
Reader Services
Ann Jenkinson
Advertising Enquiries
Leo Simpson
Phone (02) 9979 5644
Regular Contributors
Brendan Akhurst
Garry Cratt, VK2YBX
Marque Crozman, VK2ZLZ
Julian Edgar, Dip.T.(Sec.), B.Ed
John Hill
Jim Lawler, MTETIA
Philip Watson, MIREE, VK2ZPW
Jim Yalden, VK2YGY
Bob Young
Photography
Stuart Bryce
SILICON CHIP is published 12 times
a year by Silicon Chip Publications
Pty Ltd. A.C.N. 003 205 490. All
material copyright ©. No part of
this publication may be reproduced
without the written consent of the
publisher.
Printing: Macquarie Print, Dubbo,
NSW.
Distribution: Network Distribution
Company.
Subscription rates: $49 per year
in Australia. For overseas rates, see
the subscription page in this issue.
Editorial & advertising offices:
Unit 34, 1-3 Jubilee Avenue, Warrie
wood, NSW 2102. Postal address:
PO Box 139, Collaroy Beach, NSW
2097. Phone (02) 9979 5644. Fax
(02) 9979 6503.
PUBLISHER'S LETTER
Crystal balling
the telephone
With the advent of the new year and the
new century being not far away, it is timely
to think about products that could appear in
the near future. After all, with people being
so conscious of computers, cellular phones,
video and pay TV, the Internet and so on, it is
common topic of conversation: “what will be
next big consumer product?” No-one really
predicted that cellular phones would be as
popular as they have become and it is my opinion that another telephone
derived product will be the next big seller.
An obvious derivative, to my mind, is a small computer combined with
a fax machine. Perhaps it would be called a “fax terminal” or something
similar. This would have a typewriter keyboard and LCD screen and probably not much storage but you could type a message on the screen and then
send it to another person’s fax machine. It could also receive fax messages
but would not normally print them out, unless you wanted it to. Perhaps
it would send a short voice message as well. You could also use it to pay
bills and do all the things that a fax machine can do now. Such a machine
is feasible now. It could be in many homes within five years.
Another more expensive product would be a home telephone exchange
and burglar alarm system. Most small businesses have a phone system now,
with three or four incoming lines and up to eight extensions. They can
transfer calls, allow conferencing and operate as an intercom. Currently
priced at around $2000 to $4000, such systems are becoming cheaper all
the time. Five years ago, equivalent systems were priced at around $8000 or
more and are now just starting to be installed in larger homes where their
convenience is really appreciated – no more shouting to call people to the
phone, no more running to answer the phone and so on.
Such a system could be extended to provide a full home security system,
with computer interfacing as well. You could be able to connect a computer
modem to any handset so that any member of the household could connect
to the outside world. How long before we see such a product marketed I
wonder?
Further into the future, with the advent of highly compressed video and
optical fibres, it seems likely that video phones are just a matter of time. It
is not hard to envisage several or most rooms of a household having a video
terminal which will do everything: provide entertainment, phone and com
puter services, the whole bit.
There are more variants on this theme but essentially they are all derivatives of the humble telephone. Who would have thought we want or need
more telephones?
Leo Simpson
ISSN 1030-2662
WARNING!
SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should
be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the
instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with
mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages,
you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed
or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. 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. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government
regulations and by-laws.
Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act
1974 or as subsequently amended and to any governmental regulations which are applicable.
2 Silicon Chip
MAILBAG
Old house wiring is
often dangerous
I would like to comment on your
Publisher’s Letter, November 1995,
on the subject of house wiring safety. Congratulations for raising this
subject. You state the house was
built before 1950. This is significant.
You express surprise that the study
power point was not earthed. At the
time the house was wired, unless
the room was considered an earthed
situation, the wiring regulations did
not require earthing of the power
point. This would also apply to most
bedrooms.
It was not until the 1960 wiring
rules that earthing was mandatory.
I was employed as a Supply Authority Inspector from 1966 until
retirement. While working in a
country power station in the 1950s,
we received pages of interpretations
on the wiring rules, including three
pages explaining where earthing
was required or not.
I could never understand the
type of thinking that permitted and
perpetuated non-earthing of power
points. It is virtually a booby trap
for someone. The installation of a
circuit breaker switchboard with old
wiring would have been a good first
move towards a complete rewire.
R. Brownjohn,
Charlton, Vic.
Pinking vs pinging:
which is correct?
I notice that in his article on
“Knock Sensing” (SILICON CHIP,
December 1995), Julian Edgar
refers to the term “pinging” as “a
light, barely observable knock”.
Although this term is widely used,
it is not correct.
In a package put out by the ABC
a few years ago, called “Know Your
Car”, the speaker refers to this phenomenon as “pinking”. I thought
that this was a language problem
at the time, so I checked and
found that he was correct. I double
checked today in the Macquarie
Dictionary and see that it seems to
be still right. This may not be real-
ly important but I feel that Julian
would appreciate the point. I would
also like to thank him for his many
interesting and informative articles.
L. Cook,
Numurkah, Vic.
Comment: the Macquarie Dictionary
gives both terms as descriptive of
knocking. We prefer “pinging” as
it seems to be the most widely used
in the trade. “Pinging” is also more
precise in terms of onomatopoeia – it
imitates the actual sound.
SATELLITE
SUPPLIES
Aussat systems
from under $850
SATELLITE RECEIVERS FROM .$280
LNB’s Ku FROM ..............................$229
LNB’s C FROM .................................$330
FEEDHORNS Ku BAND FROM ......$45
FEEDHORNS C.BAND FROM .........$95
DISHES 60m to 3.7m FROM ...........$130
Oxygen sensor is the hard way
Your fuel injector article in November was interesting but, given
the simple way the mixture or
“burn” of the typical aircraft piston
engine is sensed, controlling it by
exhaust oxygen seems to be the hard
way. Especially with lower-powered, carbur
etted mills, exhaust
gas temperature (EGT), metered
with a simple thermocouple, is
often used to gauge the burn. The
latter is leaned out until EGT peaks,
indicating maximum combustion
heat and least fuel flow at the extant
throttle setting.
If cylinder head temperature,
sensed by a couple on the hottest
jug, is too high, the burn is richened
to cool it down. (On larger mills, the
mixture control is usually set to auto
lean). Jug temperature alone can
be used but either ploy optimises
shaft horsepower for the fuel used.
Although such a mill may run with
near-constant parameters for some
hours (easing the problem), why
wouldn’t EGT controllers work as
well for autos?
G. Lindley,
Redfern, NSW.
Comment: your remarks about the
ease of monitoring exhaust tem
perature are no doubt correct but
the reason for monitoring exhaust
oxygen content is to obtain the best
compromise between carbon mon
oxide on the one hand and nitrogen
oxides (NOx) on the other. Simply
maximising exhaust temperature
will lead to excessive nitrogen oxide
production.
LOTS OF OTHER ITEMS
FROM COAXIAL CABLE,
DECODERS, ANGLE
METERS, IN-LINE COAX
AMPS, PAY-TV DECODER
FOR JAPANESE, NTSC TO
PAL TRANSCODERS, E-PAL
DECODERS, PLUS MANY
MORE
For a free catalogue, fill in & mail
or fax this coupon.
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on your satellite systems.
Name:____________________________
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Suburb:_________________________
P/code________Phone_____________
L&M Satellite Supplies
33-35 Wickham Rd, Moorabin 3189
Ph (03) 9553 1763; Fax (03) 9532 2957
January 1996 3
The do’s & don’ts of
Living with
engine-managed
While over the last few years we’ve covered
in detail the technical make-up of current
cars’ electronic engine control systems, a more
general treatment of what the average owner
should and should not do with their car has
been lacking. Here’s the remedy!
By JULIAN EDGAR
In general, the engineers employed
by the car manufacturers really do
know best – they’re the people who
have worked with the investment
of millions of dollars in developing
the technology. This means that the
maintenance schedule laid out in the
owners’ manual should be followed
to the letter. It doesn’t, however, necessarily mean that the official dealer
needs to do the servicing of the car.
Many dealer mechanics in my experience are quite ignorant about the
cars for which they’re supposed to be
experts and do quite illogical things
in response to perceived problems.
Injector blockage can be avoided by regularly replacing the fuel filter. In
addition, injector removal and back-flushing every 50,000km or so can be a
worthwhile service precaution.
4 Silicon Chip
An example of this is where, during a
routine service, a dealer-trained mechanic instigated an ECU self-check
investigation because he thought that
the exhaust note of my car ‘sounded
funny’.
Given that the car runs a modified
75cm diameter exhaust with free-flow
mufflers, it wasn’t surprising that the
exhaust note was non-standard! But
checking this by using the self-diagnosis function of the ECU...?
Having said this, there are some
mechanics who really do take their
marque to heart and have an incredibly
detailed knowledge about their cars. If
you find such a mechanic stick with
him (or her) but unfortunately they are
few and far between.
General maintenance
The frequently advertised invitations to use oil additives or “upper
cylinder lubricant” can generally
be ignored – unless specified in the
official maintenance schedule. However, the occasional use of an in-tank
injector cleaning additive can be a
worthwhile addition to the manufacturer’s recommendations. Also, about
every 50,000km or so, the injectors can
be removed and back-flushed to clean
their inbuilt filters.
However, note that injector problems are much more likely to occur if
the fuel filter is not changed at the recommended service intervals. I’ve not
bothered having the injectors removed
for cleaning in any of my six EFI cars
(some with more than 170,000km on
the clock) but note that I have regularly
changed the fuel filter.
Most engine-managed cars use high
combustion pressures to achieve efficiency (and so fuel economy) gains.
d cars
Firing the spark with high cylinder
pressures requires a high-energy ignition system and these do not respond
happily to high tension leads which
are losing their insulation integrity.
The best replacements for worn leads
are usually the original equipment
products – unless they are terribly
expensive. But surely a set drawn
from the plethora of aftermarket leads
would give better results? An example
tells an interesting story.
I once covered the building of a
very powerful Nissan FJ20 turbo four
cylinder engine. Having a standard
power of 200bhp, this particular race
unit used a new turbo, was run on
methanol using fully-programmable
Many current cars require a spark plug change only
every 50,000 or 100,000 kilometres. Reducing the quality
of the replacement plug will result in poor performance.
Changing the ECU’s main memory
chip is unlikely to give any noticeable
improvement in power, with
independent tests showing that losses
are as likely as gains.
engine management and ended up
producing just over 400bhp! Some
very high-tech spark plug leads were
initially tried but were soon discarded
High energy ignition systems place great demands on the
ignition leads. Experience has shown that the original
equipment leads are often the best.
January 1996 5
A modified exhaust system using free-flow mufflers will result in power gains in
electronically managed cars, with the average peak-power benefit being about 10%.
when the dyno-mounted engine put on
a full display of pyrotechnics when it
came on boost!
The replacements were the old
original Nissan leads which went on
to perform faultlessly.
Likewise, be careful when replacing spark-plugs. Some manufacturers
specify platinum-tipped plugs, with a
service interval of 50,000 or 100,000
kilometres. When they come due for
replacement they will be expensive
but they will also go on to perform for
the next 50,000 or 100,000 kilometres
without problems!
Electrical system
Because engine-managed cars place
a larger-than-convention
al demand
on the electrical system, make sure
that the alternator and battery remain
in good condition. Corrosion on the
battery terminals can result in more
than just poor headlight performance
and it can be illuminating to feel the
temperature of the battery terminals af-
One reason that frequent tune-ups are no longer required in modern cars is
the presence of an exhaust gas oxygen sensor. This constantly indicates the air/
fuel mixture strength to the ECU. The changes made to injector pulse widths as
the result of this information allows the system to take into account changing
parameters such as engine wear.
6 Silicon Chip
ter the car has been running for
some time. When it comes time
for the battery to be replaced,
it’s advantageous to replace it
with a similar-sized package
which has a larger capacity –
especially if you live in a cold
environment where starting
loads will be high.
If your car does not have
an on-dash indication that
the ECU has logged a problem
(that is, if there is no “Check
Engine” or equivalent warning light), make sure that you
perform an ECU self-diagnosis
each time the oil is changed.
In the situation where it has a
problem, this prevents the car
from being con
stantly driven
in limp-home mode – which
may be undetectable unless you
regularly check fuel economy or
performance figures.
Engine mods
Everyone likes getting a little additional oomph under the bonnet – or
its corollary, better fuel consumption
at smaller throttle openings. However, this area is fraught with traps for
naive players.
Basically, modification of electronically engine managed cars can be
divided into four different categories:
(1) chip changes in otherwise standard
engines; (2) inlet and exhaust changes;
(3) turbocharger boost pressure changes (obviously, only in turbo engines);
and (4) major mechanical modifications (porting, cams, compression ratio
and so on).
The last item on the list can result
in substantial gains in engine power
but its detailed examination is beyond
the scope of this magazine.
Chip changes (which give different
ignition and fuel maps to that which
exist as standard) may look attractive
but in general give little or no real
benefit. In fact, in some cases the performance can actually be worsened!
Chassis dynamometer testing of a
variety of ECU chips installed in a VR
V6 Commodore gives a good guide to
the changes made by installing a new
chip alone. In this case, the power
gains or losses at each 500 RPM step
in the engine’s rev range were recorded and then averaged. The results are
shown in Table 1, the comparison being against the standard Holden chip.
As can be seen, there was a greater
Table 1: Chip Substitution Results
Chip
Average Gain Or Loss
Across New Range
A
1.6% loss
B
1.7% loss
C
1.0% gain
D
1.9% loss
E
0.6% gain
Standard Chip +
PULP
1.9% gain
overall power gain (1.9%) made by
simply filling the tank with premium
unleaded petrol (PULP) while retaining the standard chip! And a gain of
just 1.9% is quite trivial. In short, making just a chip change (in a car which
doesn’t use forced induction) is likely
to make no discernible difference to
its performance. This is not the case
when mechanical modifications have
been made, where the fuel and ignition
requirements may well have changed
from standard.
Intake and exhaust changes can
improve power and economy. Fitting
extractors and a larger exhaust system
will improve peak power output by approximately 10% in most late-model
cars. Fuel economy will also be improved, with a gain of 10-20% realisable in country running. Incidentally,
the noise output of the exhaust will
also increase but this may not be discernible from within the cabin.
Changing the air filter in the standard box – as is advocated in numerous
magazine advertisements – will gain
very little power and in some cases
will actually reduce power. Chassis
dyno tests undertaken on both a
late-model Falcon and a late-model
Commodore showed, if anything,
power reductions with a top aftermarket filter installed in the box. And
that was in comparison with a dirty
standard filter!
Ducting cold outside air to the
filter’s air box will improve power in
many EFI cars. Using plastic storm
water pipe and fittings (painted black)
is an efficient and cost-effective way
of doing this. If a new air pick-up
point is used, more frequent changing of the air filter element may be
needed, as a greater quantity of dust
is ingested. However, power gains of
5% are easily achieved in this way
for under $50.
Lifting turbo boost pressure by 20-
Ducting cold air into the standard air filter box can result in power gains of 5%
for less than $50. The trade-off is the requirement for more frequent air filter
changes as more dust is usually ingested.
A cold air intake duct can be made from plastic stormwater pipe and fittings,
painted black with a spray-can. The hole saw was used to cut a path through
the inner guard.
30% in turbo cars will invariably result
in an increase in engine power, with
no negatives to speak of. If you undertake this course of action, fuel with an
appropriate octane rating (for example,
premium unleaded) will usually need
to be used but there will be no other
costs while an agreeable increase in
power will be realised.
Note that there is usually no need
for ECU software changes – sufficient
latitude has been built into the fuel
system to cope with this type of increase in power.
Conclusion
The electronic side of current cars
is usually much more reliable than
the old-tech equivalent systems. This
generalisation isn’t always the case,
of course but most engine-managed
cars will run reliably for 150,000km+
without even the need for a traditional
tune-up.
Incidentally, if paying large amounts
for a tune, ask what is actually being
done. In most current cars there’s no
need for plug changes, points re-gapping, mixture adjustment and so on
and so a “full tune” can sometimes
involve just an oil and filter change,
together with a quick visual once-over.
In terms of gaining more power
easily, in non-turbo cars the fitting of
a good exhaust and extractors will give
the best cost/benefit. In turbo cars, fit
the modified exhaust and also lift turbo
SC
boost a little.
January 1996 7
NICS
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2223
LEC
7910
y, NSW
EY E
OATLBox 89, Oa8t5leFax (02) 5s7a0 C a rd
MANY OF THE PRICES LISTED APPLY DURING
APRIL AND MAY ONLY
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choice for a special price. Choose motors from
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M17 / M18 / M35. $44.
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You can also purchase this kit with the
B a n k x accepte most mix 0. Orders
stepper motor pack described above: $65.
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Kit without motors is also available: $32.
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order 4-$10; NZ world.net
FLUORESCENT TAPE
$
<at>
High quality Mitsubishi brand all weather
Aust. IL: oatley
50mm wide red reflective tape with self
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by EM
adhesive backing: 3 metres for $5.
MISCELLANEOUS ITEMS
LED BRAKE LIGHT INDICATOR: make a 600mm long high
intensity line display, includes 60 high intensity LEDs
plus two PCBs plus 10 resistors: $20 (K14). AC MOTOR:
1RPM geared 24V-5W synchronous motor plus a 0.1 to
1RPM driver kit to vary speed; works from 12V DC: $12
(K38 + M30). TOMINON SYMMETRICAL LENS: 230mm
focal length - f1:4.5, approximately 100mm diameter an
100mm long: $25 (O14). SPRING REVERB: 30cm long
with three springs: $30 (A10). MICROSONIC MICRO
RECORD PLAYER: includes amplifier: $4 (A11). MOTOR
DRIVEN POTENTIOMETER: dual 20k with PCB: $9. ANGLED
TELEPHONE STANDS: Angled, smoky perspex: 4 for $10
(G47). LARGE METER MOVEMENTS: moving iron, 150 x
150mm square face, with mounting hardware: $10. New
ARLEC brand 24VDC-500mA approved plugpacks: $9. One
FARAD 5.5V capacitors: $3.
SPECIALS – POLLING FAX LINE
Poll our 579 3955 fax number for new items and some very
limited quantity specials.
ALCOHOL TESTER KIT
Based on a high quality Japanese thick film alcohol sensor.
The kit includes a PCB, all on board components and a
meter movement: $30. The circuitry includes a latching
alarm output that can be used to drive a buzzer, siren etc.
We should also have other gas sensors available for this kit.
WIND POWER GENERATOR KIT
In late April we will have available a low cost kit that employs
a low cost electric motor, as used in car radiator cooling
systems, to serve as a wind powered electricity generator.
Construction drawings for an 800mm 2 blade propeller are
supplied. The combination puts out up to 30W of power in
high winds. Electronic kit price should be approximately
$30. Price of a used suitable motor (available from car
wreckers) should be under $40. We will have a limited
quantity available for $35.
LED FLASHER KIT
3V operated 3 pin IC that can flash 1 or two 2 high intensity
LEDs. Very bright and efficient. IC plus 2 high intensity LEDs
plus small PCB: $1.30.
SIMPLE MUSIC KIT
3V operated 3-pin ICs that play a single tune. Two ICs that
play different tunes plus a speaker plus a small PCB: $2.50.
CD MECHANISMS AND CD HEADS
Used CD mechanisms that have a small motor with geared
worm drive assy. Popular with model railway enthusiasts:
$5. Also new CD heads that include a laser diode, lenses
etc: $3.
STEPPER MOTOR PACK
Buy a pack of 7 of our stepper motors and save 50%!!
Includes 2XM17, 2XM18, 2XM35 and 1 used motor. Six new
motors and one used motor for a total of: $36.
COMPUTER CONTROLLED STEPPER MOTOR DRIVER
KIT
This kit will drive two 4, 5, 6 or 8-wire stepper motors
from an IBM computer parallel port. The motors require a
separate power supply (not included). A detailed manual on
the computer control of motors plus circuit diagrams and
descriptions are provided. Software is also supplied, on a
3.5" disk. NEW SOFTWARE WILL DRIVE UP TO 4 MOTORS
(2 kits required), with LINEAR INTERPOLATION ACROSS
FOUR AXES. PCB: 153 x 45mm. Great low cost educational
kit. We provide the PCB and all on-board components kit,
manual, disk with software, plus two stepper motors of your
8 Silicon Chip
UHF REMOTE VOLUME CONTROL SPECIAL
As published in EA Dec 95-Jan 96. We supply two UHF
transmitters, plus a complete receiver kit, including the
case and the motorised volume control potentiometer: $60.
PC CONTROLLED PROGRAMMABLE POWER SWITCH
MODULE
This module is a four channel programmable on/off timer
switch for high power relays. The timer software application
is included with the module. Using this software the operator
can program the on/off status of four independent devices
in a period of a week within a resolution of 10 minutes. The
module can be controlled through the Centronics or RS232
port. The computer is opto isolated from the unit. Although
the high power relays included are designed for 240V
operation, they have not been approved by the electrical
authorities for attachment to the mains. Main module: 146
x 53 x 40mm. Display panel: 146 x 15mm. We supply: two
fully assembled and tested PCBs (main plus control panel),
four relays (each with 3 x 10A / 240V AC relay contacts),
and software on 3.5" disk. We do not supply a casing or
front panels: $92. (Cat G20)
STOP THAT DOG BARK
Troubles with barking dogs?? Muffle the mongrels and
restore your sanity with the WOOFER STOPPER MK2,
as published in the Feb 96 edition of Silicon Chip. A high
power ultrasonic sweep generator which can be triggered
by a barking dog. We supply a kit which includes a PCB and
all the on-board components: all the resistors, capacitors,
semiconductors, trimpotentiometers, heatsinks, and the
transformer. We will also include the electret microphone.
Note that our kit is supplied with a solder masked and silk
screened PCB, and a pre-wound transformer!: $39.
Single Motorola piezo horn speakers to suit (one is good,
but up to four can be used): $14. Approved 12VDC-1A
plugpack to suit: $14.
UHF REMOTE CONTROL FOR THE DE-BARKER OF
ANNOYING DOGS
Operate your Woofer Stopper remotely from anywhere in
your house, even your bedside. Allows you to remotely
trigger your Woofer Stopper at any time. Nothing beats
a randomly timed “human touch”. We supply one single
channel UHF transmitter, one suitable UHF receiver and
very simple interfacing instructions: $28.
Based on the single channel transmitter and a slightly
modified version of the 2 channel receiver, as published
in the Feb 96 edition of Silicon Chip. Note that the article
features 3 low cost remote controls: 1 ch UHF with central
locking, 1-2 ch UHF, and an 8 ch IR remote.
MOTOR DRIVEN VOLUME CONTROL/POT
New high quality motor driven potentiometer, intended for
use in commercial stereo sound systems. Includes clutch,
so can also be manually adjusted. Standard 1/4" shaft,
stereo (dual 20k pots) with 5V/20mA motor: $12 (Cat A13).
MINI HIGH VOLTAGE POWER SUPPLY
Miniature potted EHT power supply (17 x 27 x 56mm)
that was originally designed to power small He-Ne Laser
tubes. Produces a potent 10mm spark when powered from
8-12V / 500mA DC source. Great for experimentation, small
portable Jacobs Ladder displays, and cattle prods. Use on
humans is dangerous and illegal. A unit constructed for
this purpose would be would be considered an offensive
weapon. Inverter only: $25.
CCD CAMERA SPECIAL
Very small PCB CCD camera including auto iris lens: 0.1
Lux, 320K pixels, IR responsive; overall dimensions:
38 x 38 x 25mm. We will include a free VHF modulator
kit with every camera purchase. Enables the viewing of
the picture on any standard TV on a VHF Channel. Each
camera is supplied with instructions and a 6 IR LED
illuminator kit. $170.
CCD CAMERA - TIME LAPSE VCR RECORDING SYSTEM
This kit plus ready made PIR detector module and “learning
remote control” combination can trigger any domestic IR
remote controlled VCR to RECORD human activity within
a 6M range and with an 180 deg angle of view! Starts
VCR recording at first movement and ceases recording
a few minutes after the last movement has stopped: just
like commercial CCD/TIME LAPSE RECORDING systems
costing thousands of dollars!! CCD camera not supplied.
No connection is required to your existing domestic VCR as
the system employs an “IR learning remote control”: $90
for an PIR detector module, plus control kit, plus a suitable
“lR learning remote” control and instructions: $65 when
purchased in conjunction with our CCD camera. Previous
CCD camera purchasers may claim the reduced price with
proof of purchase.
SOUND FOR CCD CAMERAS/UNIVERSAL AMPLIFIER
(To be published, EA). Uses an LM386 audio amplifier IC
and a BC548 pre-amp. Signals picked up from an electret
microphone are amplified and drives a speaker. Intended for
use for listening to sound in the location of a CCD camera
installation, but this kit could be used as a simple utility
amplifier. Very high audio gain (adjustable) makes this unit
suitable for use with directional parabolic reflectors etc.
PCB: 63 x 37mm: $10. (K64)
LOW COST IR ILLUMINATOR
Illuminates night viewers or CCD cameras using 42 of our
880nm/30mW/12 degrees IR LEDs. Power output (and
power consumption) is variable, using a trimpotentiometer.
Operates from 10 to 15V and consumes from 5mA up to
0.6A (at maximum power). The LEDs are arranged into
6 strings of 7 series LEDs with each string controlled by
an adjustable constant current source. PCB: 83 x 52mm:
$40 (K36).
MASTHEAD AMPLIFIER SPECIAL
High performance low noise masthead amplifier covers
VHF - FM UHF and is based on a MAR-6 IC. Includes two
PCBs, all on-board components. For a limited time we will
also include a suitable plugpack to power the amplifier from
mains for a total price of: $25.
VISIBLE LASER DIODE KIT
A 5mW/660nM visible laser diode plus a collimating
lens, plus a housing, plus an APC driver kit (Sept 94 EA).
UNBELIEVABLE PRICE: $40. Suitable case and battery
holder to make pointer as in EA Nov 95 $5 extra.
SOLID STATE “PELTIER EFFECT” DEVICES
We have reduced the price of our peltiers! These can be
used to make a solid state thermoelectric cooler/heater.
Basic information supplied. 12V-4.4A PELTIER: $25. We
can also provide two thermal cut-out switches and a 12V
DC fan to suit the above, for an additional price of $10.
PLASMA EFFECTS SPECIAL
Ref: EA Jan. 1994. This kit will produce a fascinating
colourful changing high voltage discharge in a standard
domestic light bulb. Light up any old fluorescent tube or
any other gas filled bulb. Fascinating! The EHT circuit is
powered from a 12V to 15V supply and draws a low 0.7A.
Output is about 10kV AC peak. PCB: 130 x 32mm. PCB
and all the on-board components (flyback transformer
included) and the instructions: $28 (K16). Note: we do not
supply any bulbs or casing. Hint: connect the AC output to
one of the pins on a fluorescent tube or a non-functional but
gassed laser tube for fascinating results! The SPECIAL???:
We will supply a non-functional laser tube for an additional
$5 but only when purchased with the above plasma kit:
TOTAL PRICE: $33.
400 x 128 LCD DISPLAY MODULE - HITACHI
These are silver grey Hitachi LM215 dot matrix displays. They
are installed in an attractive housing. Housing dimensions:
340 x 125 x 30mm. Weight: 1.3kg. Effective display size is
65 x 235mm. Basic data for the display is provided. Driver
ICs are fitted but require an external controller. New, unused
units. $25 ea. (Cat D02) 3 for $60.
VISIBLE LASER DIODE MODULE SPECIAL
Industrial quality 5mW/670nM laser diode modules.
Consists of a visible laser diode, diode housing, driver circuit,
and collimation lens all factory assembled in one small
module. APC control circuit assures. Features an automatic
power control circuit (APC) driver, so brightness varies little
with changes in supply voltage or temperature. Requires 3
to 5V to operate. Overall dimensions: 12mm diameter by
43mm long. Assembled into an anodised aluminium casing.
This module has a superior collimating optic. Divergence
angle is less than 1 milliradian. Spot size is typically 20mm
in diameter at 30 metres: $65 (Cat L10).
This unit may also be available with a 635nm laser diode
fitted.
dimensions: 25 x 43mm. Construction is easy and no coil
winding is necessary as the coil is pre-assembled in a
shielded metal can. The solder masked and screened PCB
also makes for easy construction. The kit includes a PCB
and all the on-board components, an electret microphone,
and a 9V battery clip: $12 ea. or 3 for $33 (K11).
CYCLE/VEHICLE COMPUTERS
BRAND NEW SOLAR POWERED MODEL! Intended for
bicycles, but with some ingenuity these could be adapted
to any moving vehicle that has a rotating wheel. Could
also be used with an old bicycle wheel to make a distance
measuring wheel. Top of the range model. Weather and
shock resistant. Functions: speedometer, average speed,
maximum speed, tripmeter, odometer, auto trip timer,
scan, freeze frame memory, clock. Programmable to allow
operation with almost any wheel diameter. Uses a small
spoke-mounted magnet, with a Hall effect switch fixed to
the forks which detects each time the magnet passes. The
Hall effect switch is linked to the small main unit mounted
on the handlebars via a cable. Readout at main unit is
via an LCD display. Main unit can be unclipped from the
handlebar mounting to prevent it being stolen, and weighs
only 30g. Maximum speed reading: 160km/h. Maximum
odometer reading: 9999km. Maximum tripmeter reading:
999.9km. Dimensions of main unit: 64 x 50 x 19mm:
$32 (Cat G16).
FM TX MK 3
This kit has the most range of our kits (to around 200m).
Uses a pre-wound RF coil. The design limits the deviation,
so the volume control on the receiver will have to be set
higher than normal. 6V operation only, at approx 20mA.
PCB: 46 x 33mm: $18 (K33).
PASSIVE TUBE - SUPPLY SPECIAL
Russian passive tube plus supply combination at an
unbelievable SPECIAL REDUCED PRICE: $70 for the pair!
Ring or fax for more information.
27MHZ RECEIVERS
Brand new military grade 27MHz single channel telemetry
receivers. Enclosed in waterproof die cast metal boxes,
telescopic antenna supplied. 270 x 145 x 65mm 2.8KG.
Two separate PCBs: receiver PCB has audio output; signal
filter/squelch PCB is used to detect various tones. Circuit
provided: $20.
BATTERY CHARGER WITH MECHANICAL TIMER
A simple kit which is based on a commercial twelve-hour
mechanical timer switch which sets the battery charging
period from 0 to 12 hours. Employs a power transistor and
five additional components. It can easily be “hard wired”.
Information that shows how to select the charging current
is included. We supply the information, a circuit and the
wiring diagram, a hobby box with an aluminium cover
that doubles up as a heatsink, a timer switch with knob,
a power transistor and a few other small components to
give you a wide selection of charge current. You will also
need a DC supply with an output voltage which is greater
by about 2V than the highest battery voltage you intend
to charge. As an example, a cheap standard car battery
charger could be used as the power source to charge any
chargeable battery with a voltage range of 0 to 15V. Or you
could use it in your car. No current is drawn at the end of
the charging period: $15.
SIREN USING SPEAKER
Uses the same siren driver circuit as in the “Protect
anything alarm kit”. 4" cone / 8 ohm speaker is included.
Generates a very loud and irritating sound that is useful
to far greater distances than expensive piezo screamers.
Has penetrating high and low frequency components
and the sound is similar to a Police siren. Output has
frequency components between 500Hz and 4KHz. Current
consumption is about 0.5A at 12V. PCB: 46 x 40mm. As a
bonus, we include all the extra PCBs as used in the “Protect
anything alarm kit”: $12.
FM TRANSMITTER KIT - MKII
Ref: SC Oct 93. This low cost FM transmitter features preemphasis, high audio sensitivity (easily picks up normal
conversation in a large room), a range of around 100
metres, and excellent frequency stability. Specifications:
tuning range: 88-108MHz; supply voltage 6-12V; current
consumption <at> 9V: 3.5mA; pre-emphasis: 75uS; frequency
response: 40Hz to greater than 15KHz; S/N ratio: greater
than 60dB; sensitivity for full deviation: 20mV; frequency
stability with extreme antenna movements: 0.03%; PCB
MOTOR SPEED CONTROLLER PCB
Simple circuit controls small DC powered motors which take
up to around 2 amps. Uses variable duty cycle oscillator
controlled by trimpot. Duty cycle is adjustable from almost
0 - 100%. Oscillator switches P222 MOSFET. PCB: 46 x
28mm. $11 (K67). For larger power motors use a BUZ11A
MOSFET: $3.
ELECTROCARDIOGRAM PCB + DISK
The software disk and a silk screened and solder masked
PCB (PCB size: 105 x 53mm) for the ECG kit published in
EA July 95. No further components supplied: $10 (K47).
DC MOTORS
We have good stocks of the following high quality DC motors.
These should suit many industrial, hobby, robotics and
other applications. Types: Type M9: 12V. I no load = 0.52A
<at> 15800 RPM at 12V. Weight: 150g. Main body is 36mm
diameter. 67mm long: $7 (Cat M9). Type M14: made for slot
cars. 4 to 8V. I no load = 0.84A at 6V. At max. efficiency I
= 5.7A <at> 7500 RPM. Weight: 220g. Main body diameter is
30mm. 57mm long: $7 (Cat M14).
MAGNETS: HIGH POWER RARE EARTH MAGNETS
Very strong. You will not be able to separate two of these by
pulling them apart directly away from each other. Zinc coated.
CYLINDRICAL 7 x 3 mm: $2 (Cat G37)
CYLINDRICAL 10 x 3 mm: $4 (Cat G38)
TOROIDAL 50mm outer, 35mm inner, 5mm thick: $9.50
(Cat G39)
CRYSTAL OSCILLATOR MODULES
Small hermetically sealed, crystal oscillator modules. Used
in computers. Operate from 5V and draw about 30mA. TTL
logic level clock output. Available in 4MHz, 4.032MHz,
5.0688MHz, 20MHz, 20.2752MHz, 24.74MHz, 40MHz, and
50MHz.: $7 ea. (Cat G45) 5 for $25.
XENON FLASH BOARDS
Flash units with small (2cm long) xenon tube, as used
in disposable cameras. Power from one AA 1.5V battery.
Approx 7 joules energy: $3 (Cat G48).
INDUCTIVE PICKUP KIT
Ref: EA Oct 95. Kit includes coil pre-wound. Use receiver in
conjunction with a transmit loop of wire which is plugged
in in place of where a speaker is normally used. This wire
loop is run around the perimeter of the room / house you
wish to use the induction loop in. We do not supply the
transmit loop wire. Also excellent for tracing AC magnetic
fields. PCB: 61 x 32mm. Kit contains PCB and all on board
components: $10 (K55).
SLAVE FLASH TRIGGER
Very simple, but very effective design using only a few
components. Based on an ETI design. This kit activates a
second flash unit when the master, or camera mounted,
flash unit is activated. This is useful to fill in shadows and
improve the evenness of the lighting. It works by picking
up the bright flash with a phototransistor and triggering an
SCR. The SCR is used as a switch across the flash contacts.
This circuit does not false trigger even in strongly lit rooms,
but is sensitive enough to operate almost anywhere within
even a quite large room. Of course, by making more of
these and fitting them to more slave flash units even better
lighting and more shadow reduction is obtained. PCB: 21
x 21mm: $7 (K60).
SOUND ACTIVATED FLASH TRIGGER
Based on ETI project 514. Triggers a flash gun using an
SCR, when sound level received by an electret microphone
exceeds a certain level. This sound level is adjustable. The
delay between the sound being received and operation of
the flash is adjustable between 5 and 200 milliseconds. A
red LED lights up every time the sound is loud enough to
trigger the flash. This is handy when setting the unit up to
suit the scene, without waiting for the flash unit to recharge
or flatten its batteries in the process. This kit allows you take
interesting pictures such as a light bulb breaking. PCB: 62
x 40mm: $14 (K61).
OPTO
PHOTO INTERRUPTER (SLOTTED): an IR LED and an
phototransistor in a slotted PCB mounting assembly.
The phototransistor responds to visible and IR light. The
discrete components are easy to separate from the clip
together assembly. Great for IR experiments: $2 ea. or
10 for $15.
IR PHOTODIODE: similar to BPW50. Used in IR remote
control receivers. Peak response is at 940nm. Use with
940nm LEDs:
$1.50 ea. or 10 for $10.
VISIBLE PHOTODIODE: this is the same diode element as
used in our IR photodiode but with clear encapsulation, so
it responds better to visible and IR spectrum: $1.50 ea.
or 10 for $10.
LDRs: large, 12mm diameter, <20ohm very bright
conditions, >20Mohm very dark conditions: $1.
LEDs
BRIGHTNESS RATING: Normal, Bright, Superbright,
Ultrabright.
BLUE: 5mm, 20mA max, 3.0V typical forward voltage
drop. $2.50
RED SUPERBRIGHT: 5mm, 0.6 to 1.0 Cd, 30mA max,
forward voltage 1.7V, 12 degrees view angle, clear
encapsulation:
10 for $4 or 100 for $30.
BRIGHT: 5mm. Colours available: red, green, orange, yellow.
Encapsulation colour is the same as the emitted colour.
30mA max.: 10 for $2 or 100 for $14.
BRIGHT NARROW ANGLE: 5mm, clear encapsulation, 30mA.
Colours available: yellow, green: 10 for $2.50 or 100 for $20.
TWO COLOUR: 5mm, milky encapsulation, 3 pins, red plus
green, yellow by switching both on: $0.60.
ULTRABRIGHT YELLOW: Make a LED torch!: $2.50.
PACK OF 2mm LEDs: 10 each of the following colours:
red, green, amber. We include 30 1.0K ohm resistors for
use as current limiting. Great for model train layouts using
HO gauge rails: $10.
IR LEDs: 800nm. Motorola type SFOE1025. Output 1mW
<at> 48mA. Forward voltage 1.7V. Suitable for use with a
focussing lens. At verge of IR and visible, so has some
visible output. Illuminates Russian and second generation
viewers: $2.
HIGH POWER IR LEDs: 880nm/30mW output <at> 100mA.
Forward voltage: 1.5V. The best 880nm LEDs available.
Excellent for IR illumination of most night viewers and
CCD cameras. We use these LEDs in our IR illuminator
kit K36. Emits only a negligible visible output. Both wide
angle (60 degrees) and narrow angle (12 degrees) versions
of these LEDs are available. Specify type required: 10 for
$9 or 100 for $80.
IR LEDs: 940nm. Commonly used in IR remote control
transmitters. Good for IR viewers with a deeper IR response.
No visible output. 16mW output. 100mA max. Forward
voltage is 1.5V: 10 for $5.
18V AC <at> 0.83A PLUGPACKS
Also include a diecast box (100 x 50 x 25mm): Ferguson
brand. Australian made and approved plugpacks. Output
lead goes to diecast box with a few components inside.
Holes drilled in box where LED and 2 RF connectors are
secured: $8 (Cat P05).
CASED TRANSFORMERS
230Vac to 11.7Vac <at> 300mA. New Italian transformers in
small plastic case with separate input and output leads, each
is over 2m long. European mains plug fitted; just cut it off
and fit the local plug. This would be called a plugpack if it
sat on the powerpoint: $6 (Cat P06).
FREE CATALOGUE WITH YOUR ORDER
Ask us to send you a copy of our FREE
catalogue with your next order. Different
items and kits with illustrations and
ordering information. And don’t forget our
website at:
http://www.hk.super.net/~diykit
January 1996 9
New from Smart Fastchargers, this nicad and NiMH charger
caters for a wide range of battery voltages and capacities and
uses the patented Reflex charging method. It has eight buttons
to set the rate of charge, a rotary switch to select the battery
voltage and a LED bargraph to indicate the cell voltage. An
audible beep, at one second intervals, gives an indication that
the main charge is still in progress.
Recharging nicad
batteries for long life
Nickel cadmium and nickel metal hydride
batteries are widely used in all sorts of portable
equipment but they often don’t last long before
they must be replaced. One solution is to use
“burp charging” which is claimed to provide
many thousands of charge/discharge cycles.
By HORST REUTER*
Battery powered equipment is undeniably practical – lightweight, portable and small, with no cables to drag
around. But there is a price to pay for
that convenience. Rechargeable bat
teries are costly to buy and often don’t
last long. The problem can usually be
traced back to the type of charger used.
Unfortunately, most of the nicad
chargers supplied with appliances at
10 Silicon Chip
present require manual termination;
ie, the user has to switch off the charger
and disconnect the battery. This makes
it practically impossible to avoid
overcharging the batteries, thereby
reducing their life expectancy. The key
to long life lies in the charging method.
In this article, a battery is defined as
consisting of one cell or several cells
connected in series. Internal cell im
pedance is defined as the sum of the
resistance of the internal connections
and plates (both constant) and the
degree of difficulty the ions encounter
passing through the separators and
electrolyte (variable).
Nicad or NiMH?
From an environmental point of
view it would be an advan
tage to
change to NiMH batteries. Nickel Metal Hydride (NiMH) batteries are made
without cadmium and are therefore
less damaging to biological systems. At
present, they have about 20% higher
energy density than nicad cells (AA)
and produce no memory effect (more
about memory effect later).
However, typical NiMH cells have
a higher internal im
pedance than
nicad cells; 50mΩ instead of 10mΩ
for 1200mAh cells. As a consequence,
NiMH batteries have lower maximum
discharge currents. This means they
are only suitable for low current ap
pliances like handheld radios. The
maximum discharge current is 3C for
NiMH AA cells and 2C for NiMH button cells, whereupon the cell voltage
drops to approximately 1.1V. “C” is
defined as the current that equals the
rated battery capacity. For example,
charging a 1.2Ah battery with a 4.8A
current is a 4C charge. The same 4.8A
current applied to a 4.8Ah battery is
a 1C charge.
In practice, the useful discharge currents for NiMH batteries are limited to
less than 1C (the cell voltage remains
above 1.2V). For currents above 1C,
nicad batteries are superior. Fig.1 is a
comparison of the load characteristics
of one 1200mAh AA size NiMH cell,
one 600mAh AA size nicad and one
1200mAh sub-C size nicad cell. The
load was only applied for 5 milliseconds.
The tests showed that a fully charg
ed 12V 1200mAh nicad battery as used
in power drills delivers a maximum
of 11.9V with a 10A load. Even a
12V 600mAh nicad battery delivers a
maximum of 10.9V with a 10A load.
However, a 1200mAh NiMH battery
with the same load delivers only 7.65V.
NiMH batteries also differ from
nicad cells in that the chemical reaction during charge is exothermic; ie,
the charging process produces heat.
The chemical reaction in nicad cells
is endothermic; the reaction absorbs
heat. However both battery types
produce some heat during the main
charge cycle because of internal impedance and both produce heat when
overcharged. Over
charging creates
heat and gas but does not produce
any further energy storage in the cells.
The heat produced during the
main charge in nicad cells due to cell
impedance is absorbed in the endo
thermic reaction. In NiMH cells, the
cell heating due to internal impedance
is added to the heat of the exothermic
reaction. When NiMH batteries reach
the overcharge region, they are therefore hotter than nicads.
All available NiMH cells I have
tested vented at around 43-45°C case
temperature – much lower than for
nicads. This means that charge termination at high charge rates is critical
and cannot safely be achieved with
delta V termination chargers. The case
temperature should not exceed 40°C
Fig.1: a comparison of the load characteristics of a 1200mAh AA
size NiMH cell, a 600mAh AA size nicad and a 1200mAh sub-C size
nicad cell. The load was only applied for 5 milliseconds. This clearly
demonstrates that the higher internal impedance of NiMH batteries
limits their usefulness in delivering high currents.
for NiMH cells and 45°C for nicads.
Delta V termination utilises the
voltage drop at the beginning of the
overcharge region of the cell voltage
curve (see Fig.2). The magnitude of
this voltage drop is generally not as
well defined in NiMH cells as it is in
nicad cells. It depends on factors like
charge current, ambient temperature,
cell impedance, cell capacity, etc.
The situation can be worse in battery packs. Several unmatched cells
may cause the battery voltage to reach
only a very shallow peak if some cells
reach their individual peaks while
others are still charging. Even if the
Fig.2: delta V termination utilises the voltage drop at the beginning of the
overcharge region of the cell voltage curve. The magnitude of this voltage drop
is generally not as well defined in NiMH cells as it is in nicad cells. It depends
on factors like charge current, ambient temperature, cell impedance, cell
capacity, and so on.
January 1996 11
the nickel hydroxide to
nickel oxyhydroxide.
This process is reversed
during discharge.
If each cell in the battery pack is discharged
completely and then
charged, the individual
crystal sizes on the cell
plates remain unaltered.
However, if the cadmium is not completely
converted back into cadmium hydroxide during
partial discharge, on
the following charge
the cadmium hydroxide crystals will clump
together, forming larger
crystal structures.
Although it is not yet
fully understood how
Fig.3: the patented Reflex or “burp” charge
this happens, scanning
method consists of a positive charge pulse
followed by a high current, short duration
electron micrographs
discharge pulse. This is quite different from
of batteries with and
other chargers which have an essentially
without memory effect
pulsed output but no discharge pulses.
clearly show the difference in crystal sizes.
The net result is that we
charger circuit is able to detect a very
are left with a smaller, less reactive
small voltage drop (<10mV) at the very surface area and therefore reduced
start of the overcharge region, the fact capacity.
remains that we are already operating
The clumping of crystals is mostly
in the overcharge region.
a slow process but is cumulative.
Overcharging is not acceptable if we However, as we will see later, it is
want to achieve maximum battery life reversible.
for nicad cells. For NiMH cells it can
End point voltage
be dangerous if used in combination
with high charge currents. It can lead
The usual strategy to prevent memto venting and consequent loss of ory effect is to discharge each cell to
capacity and in extreme cases to cell
1.1V or 1.0V, a level where very little
explosion, due to a build up of gas useful energy is left. This is only partly
pressure.
effective with single cells and with
If NiMH cells are charged with new and well matched cells in battery
delta V termination char
gers, then
this has to be done at the rate the
manufacturer recommends, typically
C/10 (120mA) for 1200mAh cells. At
this rate, any heat produced during
charging and overcharging will be
safely dissipated.
packs. Not all cells in a battery pack
will age equally or charge and discharge equally at different operating
temperatures. In the end, some cells
will only be partly discharged when
others are deep discharged.
At the final stage of the battery discharge, a sudden substantial voltage
drop occurs. This can lead to reverse
charging of the weakest cell in a battery pack of more than 12 cells and
will still cause a clumping of crystals
in all cells (except the weakest cell)
during the next charge. The magnitude
of memory effect in each cell depends
on the depth of discharge.
Unlike some other types of cells,
nicads can be totally discharged and
then even shorted to avoid the memory
effect but not without reducing life
expectancy. The life expectancy of all
types of batteries, including nicads,
is partly dependent on the depth of
discharge.
Hence, a total discharge will reduce
life expectancy (up to a factor of 10
in cases of frequent total discharge).
Totally discharging a battery to 0V –
unlike discharging a single cell – is a
sure recipe for extremely short battery
life due to cell voltage reversal.
Shallow discharge, less than 25% of
total capacity, makes for long battery
life but creates the conditions for memory effect. A 1.1V or 1.0V discharge
voltage is only a compromise, not a
magic value.
Freezing cells
Another strategy to combat memory
effect, the practice of freezing batteries to break up the clumping of the
crystals, creates mechanical stresses
in the cells. This can also lead to
Memory effect
Let’s look at the major problem
of nicad cells: memory effect. This
is caused by charging a partially
discharged battery and enhanced by
slow charging and high operating
temperatures. During charging, the
negative plate loses oxygen and converts cadmium hydroxide to metallic
cadmium, while the positive plate goes
to a higher state of oxidation, changing
12 Silicon Chip
Fig.4: the essential characteristic of the Reflex charging method is a
high current charge pulse, followed by a short rest period and then
an even higher discharge pulse for 5ms. The battery voltage is then
measured before the next charge pulse.
This is the view inside
the prototype from
Smart Fastchargers. It
uses a total of three PC
boards and can charge
batteries at a rate of up
to 9A.
reduced life expectancy since a high
degree of mechanical precision goes
into the production of today’s high
capacity cells. It is also a time consuming method, since all cells in the
battery have to be slowly warmed to
above 10°C after freezing for efficient
fast charging.
All these are makeshift solutions.
The problem should be tackled at the
roots, by using a charge method that
will reduce crystal size in batteries
where crystal clumping has occurred
and avoids crystal clumping during
the charging of partially discharged
batteries.
Another area that needs improvement is the small number of recharge
cycles suggested for most nicad batteries. In the case of some hand-held
radios, the batteries are supposed to
have only 300 recharge cycles. Batteries for other appliances are rated for
500 and 1000 cycles.
Theoretically, 5000 charge/discharge cycles are possible over a
minimum life span of 10 years. One
power hand tool manu
facturer advertises 3000 cycles and 10 minutes
charging time. This is achieved by
using advanced charger technology
and fast charge batteries. 3000 cycles
represent approximately 6.5 cents per
cycle as compared to 55 cents per cycle
for the hand-held radio batteries (at
presently quoted prices).
Another problem is the excessive
time required to charge nicad and
NiMH batteries with delta V termination chargers: generally between one
hour for fast charge nicad batteries and
15 hours for standard nicad batteries
and NiMH batteries. Only in exceptional cases, as with some chargers for
battery powered tools, is it possible to
achieve charge rates of less than one
hour for nicad batteries.
Burp charging
One overseas company has designed
a fast charger that achieves an amount
of recharge cycles close to the theoretical limit. This patented charger,
well proven in industrial and military
applications, is used to charge aircraft
batteries, emergency standby batteries
for hospitals, etc and operates fully
automatically. It automatically detects
the type of battery (nicad, NiMH,
lead-acid, etc), battery capacity and
voltage and adjusts itself accordingly.
These complex chargers use the
patented Reflex or BURP charge method. This consists of a positive charge
pulse followed by a high current,
short duration discharge pulse. This
should not be confused with pulse or
switchmode chargers which switch
the charge current on and off but do
not apply a discharge current – see
Fig.3.
By using a charger circuit with the
patented Reflex method incorporated
in a licensed integrated circuit, it is
possible to obtain a dramatic increase
in the charge/discharge cycles of nicad
batteries, to at least 3000 cycles if
reasonable care is exercised. There is
no need to run appliances until the
batteries are flat to avoid the memory
effect. It is now possible to recharge
the batteries after each use. Partial dis
charge, as opposed to full discharge,
will significantly increase the life of
the batteries.
A microprocessor calculates and accurately terminates the applied charge
by evaluating the inflection points on
the charge voltage curve. The termination point varies according to the
charging characteristic of the battery;
it occurs just prior to the transition
into overcharge (see Fig.2).
The circuit provides a fast charge,
preceded by a series of soft start charge
pulses. Then, if the battery is left in
January 1996 13
Fig.5: the timing for soft start, fast, topping and maintenance charges. The
charge/discharge pulse combination for the topping and maintenance modes
remain the same as for the fast charge cycle; only the rest time is changed.
the charger, the fast charge will be
followed by a topping charge and a
non-destructive indefinite maintenance charge.
All of the above can be done by
one charger with an adjustable output
current sufficient for batteries of
7000mAh capacity at the 1C (1 hour)
charge rate or for 1900mAh capacity
batteries at the 4C (15 minute) charge
rate, taking the charge efficiency into
account. To fully charge a battery,
approximately 20% more charge than
has been withdrawn has to be put back
into the battery if charged at or above
C/10 at 20°C.
The charge efficiency of batteries
depends on charge current and ambient temperature. High or very low
ambient temper
atures and/or low
charge currents decrease the charge
efficiency; in extreme cases to a point
where the battery cannot be fully
charged.
Soft start
Batteries can exhibit a high impedance during the initial stages of
charging. The resulting voltage peak
can be interpreted by the processor as
a fully charged battery.
However, with the soft start cycle, at
first only short duration current pulses
are applied to the battery. Starting at
200ms, the pulse width is gradually increased to approximately one second
in duration. This gradual increase in
pulse width takes place over a period
of two minutes to avoid voltage peaks.
Fast charge
During the main charge cycle, each
positive current pulse is followed by
a discharge pulse, as shown in Fig.4.
The discharge pulse is 2.5 times the
amplitude of the charge pulse. After
the main charge, if the battery is left
on the charger, it will be fed a topping
14 Silicon Chip
charge. This charge is at a current low
enough to prevent cell heating but high
enough to convert all active material
in the cells to the charged state.
Due to higher temperatures and
gas bubbles (see explanation further
on), 100% charge cannot be achieved
with fast chargers. Standard constant
current chargers create heat and gas
bubbles on the cell plates during
charging. This results in less than 90%
efficiency.
This version of the Reflex charger
is approximately 95% efficient, since
the termination method largely avoids
cell heating and the charge/discharge
pulse sequence removes most of the
gas bubbles from the cell plates. The
2-hour C/10 charge tops up the battery
if the time is available or 100% capacity is required.
Maintenance charge
After the full charge and topping
charge, the C/40 charge compensates
for the internal self-discharge of the
battery, at the same time preventing
dendrite formation and maintaining
the crystal structure. The battery can
remain on the charger until used –
there is no time limit. This charge
cycle can be useful in standby applications, as in security installations.
Fig.5 shows the timing for soft start,
fast, topping and maintenance charges.
The charge/discharge pulse combination for the topping and maintenance
modes remain the same as for the
fast charge cycle; only the rest time
is changed.
The removal of gas bubbles from
the cell plates during charge keeps the
cell impedance low, reduces operating
temperature and allows higher charge
currents for nicad and NiMH batteries.
The following charge times can be
achieved: fast-charge nicad batteries
in less than 15 minutes at the 4C rate,
standard nicad and NiMH batteries in
less than one hour.
As well, memory effect in batteries
can be eliminated. This works even
when the battery no longer holds any
charge. It requires a minimum of three
complete charge/discharge cycles. A
typical case in practice involved a
4.8V 600mAh cellular phone battery
pack. This had only 20% of its stated
capacity, after it had been used over a
period of six months with the supplied
charger. After five charge/discharge cycles, it had recovered to approximately
95% of capacity.
The possibility to rejuvenate shorted nicad batteries is also a feature.
Whenever a nicad battery has been
stored charged and has then slowly
self-discharged over a very long period
of time at an elevated temperature, or
has been charged at a low current over
a long period, as in constant current
trickle charging in standby applications, crystals on the cell plates can
form crystalline fingers, or dendrites,
which can propagate through the plate
separators and across the cell plates.
In extreme cases, these crystalline
dendrites can partially or completely
short-circuit a cell. Such cells can be
rejuvenated by this charger.
Charger circuit
Fig.6 shows the block diagram of
a charger using the patented Reflex
charging method. The charger covers
a battery voltage range from 1.2V to
13.2V at charge currents from 0.1A
to 9.0A. The central part of the battery charger is basically a reduced
instruction set microprocessor (RISC)
to handle the complex calculations for
the charge termination point.
The microprocessor uses an
analog-to-digital converter (ADC)
with 300µV resolution to convert the
battery voltage, normalised to one
cell by the input attenuator VR1. The
ADC is followed by a filter to limit
the effects caused by battery voltage
jumps and ADC noise and to eliminate
Fig.6: the block diagram of a charger using a RISC microprocessor programmed
with the patented Reflex charging method. The charger covers a battery voltage
range from 1.2V to 13.2V at charge currents from 0.1A to 9.0A.
any large aberrations in the battery
voltage curve.
The microprocessor controls the
charge, topping and main
tenance
modes. One input of the microprocessor controls the charge rates (1C
or 4C) and is linked to the bank of
push- buttons for selection of charge
current.
One input resets the microprocessor
to repeat a charge cycle or to charge
shorted cells. In this case, the reset
button has to be activated until the
LED “cell voltage” display indicates
acceptance of the charge current.
A battery voltage guard circuit
avoids automatic charging of shorted
batteries. This is necessary since the
current required to kick start a shorted
battery varies from case to case and
should be controlled manually.
Another detect circuit avoids the
automatic charging of batteries with
a voltage or more than 2V per cell.
This condition is due to high internal
impedance, as found in new batteries
that have not been cycled and in some
batteries which have been stored for
several months. Charging these batteries would cause excessive heating.
The DC input to the charger can
range from 11.5V to 28V, depending
on the number of cells in the battery
to be charged. Essentially, this is a
minimum of 2V per cell plus an additional 2V. Hence a 6V battery (5 cells)
requires a minimum of 12VDC to the
charger while a 12V battery (10 cells)
requires a minimum of 22VDC.
Safety cut-off
In case the voltage sensing for end of
charge does not work there is a timeout circuit which is set for 72 minutes
at the 1C rate and 18 minutes for the
4C rate. In addition, there is a heatsink
temperature sensor to interrupt the
charge as a safety measure in extreme
hot weather conditions.
The microprocessor controls three
output circuits and two LED indicators. The charge circuit is a switch
mode current source, adjustable
from 0.1A to 9A with VR2 (a bank of
pushbutton switches). The discharge
circuit is a pulsed constant current
sink adjusted to between 0.25A and
22.5A (2.5 times the charge current).
During the main charge cycle, a
small piezo speaker emits a brief tone
once a second, synchronised to the
discharge pulses. This is a convenient
audio cue to tell the user the battery is
still in the main charge sequence. The
tone control on the front panel actually
adjusts the volume, so that the tone is
not obtrusive.
Other details of the operation can
be gleaned from the block diagram.
By this time this issue goes on sale,
the charger will have been released
for sale. For information concerning
availability and price, contact Smart
Fastchargers, R.S.D. 540, Devonport,
Tas 7310. Phone/fax (004) 921 368.
*Horst Reuter is Technical Manager
of Smart Fastchargers.
January 1996 15
CIRCUIT NOTEBOOK
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.
Automatic level control
for line signals
This circuit adapts the Plessey
Sl6270 gain control chip to line
levels. Intended for automatic level
control of balanced microphones, the
SL6270 was featured in the August
1995 issue. In this circuit, it will accept up to 1V RMS of signal before
clipping and will provide a constant
output level for input signals between
14mV and 1V.
The 1.5kΩ and 1kΩ resistors at the
input provide the necessary attenuation of the signal to prevent clipping
within IC2. IC1 is simply used to buffer
the signal and drive the 150Ω input
impedance at pin 4. The 470Ω resistor
in IC1’s feedback path increases the
impedance seen by the op amp to 600Ω
to prevent distortion.
The signal output at pin 2 of IC2 is
AC-coupled to buffer amplifier IC3a.
By virtue of feedback action, pin 2 of
IC3a applies signal to the pin 7 input
of IC2 where it is rectified and filtered
to determine the gain. VR1 sets the
output level.
SILICON CHIP.
to turn on transistor Q1 which drives
the relay. After two minutes or so, as
determined by the 470kΩ resistor and
220µF capacitor at pin 6, the output
at pin 3 will go low and Q1 will turn
off. The relay must have adequate
ratings to handle the current drawn
by the pump.
If you need a longer pumping time,
increase the value of the 470kΩ resistor
and vice versa.
SILICON CHIP.
Bilge pump timer uses a
mercury switch
This circuit was designed to enable a mercury switch to replace the
contacts in a float switch for a bilge
pump. The mercury switch can be expected to last indefinitely compared
with the limited life of mechanical
contacts in a float switch. However,
the mercury switch cannot be used to
control the pump directly. Therefore
it is used to initiate a 2-minute timer
based on a 7555.
The mercury switch is mounted on
the float switch lever in such a way
that it closes when the water reaches a preset level. This momentarily
pulls the trigger input (pin 2) low to
start the timer. This takes pin 3 high
16 Silicon Chip
PWM speed
controller
This circuit can be
used to provide a wide
range of speed control
for a 6V DC motor, with
very little power dissipation in the controlling
transistor.
Op amp IC1a forms
a Schmitt trigger oscillator with a 45% duty
cycle, as set by the
voltage divider resistors
at pin 3. The frequency
is varied between 47Hz
and 500Hz by VR1. The
wave
form at pin 6 of
IC1b is a sawtooth and
this is compared with
the DC threshold voltage
set by VR2 at pin 5. With
VR2 set for a low voltage, IC1b delivers
short pulses; for a high setting, long
pulses are delivered.
IC1b drives a Darlington transistor
(Q1) to switch the motor. Diode D1
clips the back EMF, while the .047µF
capacitor helps suppress EMI from the
motor’s brushes.
The circuit can also be used with
higher supply voltages whereupon the
bipolar transistor can be substituted
with a Mosfet such as an MTP-3055E
or BUZ71.
M. Schmidt,
Edgewater, WA. ($30)
DC amplifier for a
centre-zero meter
Moisture monitor for
pot plants
This circuit will sound a piezo
beeper when your plants need a
drink.
IC1a is a free-running Schmitt
trigger oscillator which produces
a brief positive pulse once every
three minutes. This is fed to pin 8
of IC1b and to pins 5 & 6 of IC1d via
a 470kΩ resistor and the potplant
pot. IC1d is connected to invert the
pulses fed to pin 9 of IC1b. This
gate’s output remains high and
inhibits an oscillator comprising
IC1c, as long as the soil is moist
and conducts.
When the soil is dry, IC1d’s output goes high so that IC1b enables
IC1c and the beeper sounds. VR1
acts as a sensitivity control.
B. Avi,
Rose Bay, NSW. ($30)
This circuit will allow a 5mA FSD
centre-zero meter to be used where a
50µA meter movement would otherwise be required.
The circuit is based on an LF411 op
amp which has been specified for its
low drift. It operates as a current amplifier. VR1 is used to zero the meter
when the input signal is zero, while
VR2 adjusts the full scale deflection.
SILICON CHIP.
Circuit Ideas Wanted
Do you have a good circuit idea? If so,
sketch it out, write a brief description &
send it to us. Provided your idea is original, we’ll publish it & you’ll make some
money. Send your idea to: Silicon Chip
Publications, PO Box 139, Collaroy, 2097.
January 1996 17
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
dicksmith.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
dicksmith.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
dicksmith.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
dicksmith.com.au
Surround Sound
MIXER & DECODER
PART 1 – By JOHN CLARKE
Build this unit and add depth, realism and effects
to your home videos. It provides realistic surround
sound mixing, while an inbuilt decoder provides the
rear channel signal during playback if a surround
sound processor is unavailable.
22 Silicon Chip
W
HILE HOME VIDEOS usu-
ally provide fairly bland
viewing for all but a few
doting grandparents and close relatives, this does not have to be so.
Surround sound can capture the
audience so that they become part
of the action.
Adding surround sound will add a
new dimension to your video recordings. It may even stir you into creating
bigger and better movie productions,
as you experiment with surround
mixing.
As well as surround mixing, this
Surround Sound Mixer & Decoder
can also be used to mix normal stereo
signals; ie, by using just the Left and
Right channels. You can also mix in
signals from two other sources via the
A and B channels.
By adding the Centre and Surround
channels, you will have surround
processing. Signals from the A and
B inputs can be mixed into any of
the Left, Centre, Right and Surround
channels using the L-R and the C-S
pan controls. The resulting surround
sound signal is encoded into the Left
and Right channels and is subsequently decoded on replay.
To simplify the task of mixing, signal level meters are fitted to all four
Main Features
•
•
•
Surround sound encoding and decoding.
•
•
Compatible with normal stereo and mono outputs.
•
•
•
•
•
•
A-channel panning between L-R and C-S.
Encoding similar to 4-channel Dolby® surround format.
Encoded signals can be decoded by Dolby Pro Logic® and passive surround sound units, or by using the internal decoder in the mixer.
Separate Left, Centre, Right and Surround inputs, plus A and B channel
inputs.
B-channel panning between L-R and C-S.
Separate level controls for all inputs.
Balanced or unbalanced microphone and line input options.
Single output level control.
LED level meters for the L, C, R & S channels (-24dB to +3dB).
output (L, C, R & S) channels. They
comprise 10-LED displays with a
-24dB to +3dB range in 3dB steps. In
operation, they monitor the encoded
Left and Right channel signals and the
Centre and Surround channels.
Surround sound playback
The encoded signals can be played
back in stereo or mono but in order
to obtain surround sound, they must
be re
played through a stereo VCR
and decoder. While the mixer does
incorporate a simple decoder, its main
purpose is to provide the meter signals.
Ideally, for best sound effects, the
L & R outputs from the VCR should
be fed through a Dolby Pro Logic surround sound decod
er. This
could be a commercial unit
or you could use either of the
two units described in SILICON CHIP (see Dec.94-Jan.95
and Nov.95-Dec.95). Fig.1(a)
shows the basic scheme.
If you don’t have a Dolby
Pro Logic decoder, the basic
decoder built into the Surround Sound Mixer & Decoder
can be used instead. In this
case, the L & R outputs from
the VCR connect to the Left
Fig.1: the encoded signals on
the video tape can either be
decoded using a Dolby Pro
Logic unit as shown at (a),
or fed through an internal
decoder in the mixer itself as
shown at (b). In the case of
(b), the Centre (C) channel is
not normally used, while the
Surround (S) channel should
ideally pass through a 20ms
delay before being fed to its
power amplifier.
January 1996 23
Fig.2: block diagram of the Surround Sound Mixer and Decoder. The various
inputs are mixed in summing amplifier stages before being fed to the Left and
Right outputs via level controls VR11a and VR11b. On playback, IC9a sums
the Left and Right channels to provide the Centre output, while IC9b produces a
difference output which is then filtered to provide the Surround output.
and Right channel inputs of the unit
in the line mode – see Fig.1(b). The
overall volume can then be controlled
by the Output Level control, while
the balance is adjustable using the
individual Left and Right level pots.
Note that, ideally, the Surround
channel output from the mixer unit
should be passed through a 20ms delay (a suitable 20ms delay unit will be
described in the February 1996 issue
of SILICON CHIP). The Centre output
is best left disconnected here, since
it will have poor separation from the
Left and Right channels.
Note also that the decoded sound
will be nowhere near as realistic as
from a Dolby Pro Logic unit. The
decoder built into the mixer is very
much a “poor man’s” approach to
surround sound, although it can still
give good effects.
In either case, separate amplifiers
are required for the Left, Right, Surround and Centre channels in order
to drive the loudspeakers. The Left
24 Silicon Chip
and Right channels are normally fed
to an existing stereo amplifier, while
a second stereo amplifier can be used
for the Surround and Centre channels.
Alternatively, some Dolby Pro Logic
decoders have several audio amplifiers
built in.
Inputs & outputs
As shown on the main circuit diagram (Fig.3), each input has a stereo
jack socket which can accept either a
microphone or a line level signal, as
selected by a toggle switch.
Either a balanced or an unbalanced
source can be used for the microphone
input, while line level inputs must be
unbalanced. If necessary, unbalancing
can be achieved by using either a mono
plug or a stereo plug wired with the
ring connection to ground.
At the other end, the outputs are
run to RCA sockets to provide the
Left, Centre, Right and Surround (L,
C, R & S) signals. For recording purposes, the Left and Right channels
only connect to the tape recorder
(or VCR).
Although making a stereo recording
is fairly straightfor
ward, 4-channel
recordings will require a fair degree
of prac
tice. Fairly obviously, you
will need four microphones – one
for each channel. For a concert, the
Left, Centre and Right microphones
should be spread across the stage. The
rear channel microphone can either
be placed behind the stage or within
the audience, depending on the effect
you want.
The A and B inputs can be used
to add background sounds or music
to one or more channels. And, if
desired, you can produce the effect
of movement between one channel
and another by pan
ning. There are
four panning controls in all (two for
the A input and two for the B input)
and these provide panning between
the Left and Right channels (Pan L-R)
and between the Centre and Surround
channels (Pan C-S).
Block diagram
Fig.2 shows the block diagram of the
unit. Starting at the left, there are six
amplifiers for the Left, Centre, Right,
Surround, A and B inputs. The output
Output level control
The SUM3 and SUM4 outputs are
now fed to output level controls VR11a
and VR11b, respectively. These are
sections of a dual-ganged pot and are
used to adjust the encoded Left and
Right channel output levels. From
there, the encoded signals are fed to
the Left and Right channel output
sockets. They are also used to drive the
Left and Right signal strength meters.
In addition, the encoded Left and
Right channel outputs drive summing
circuit SUM6 and difference circuit
DIFFERENCE 1. The SUM 6 output
provides the Centre channel and is
inverted (IC10a) before being fed to the
output socket and to the Centre meter.
PARTS LIST
1 sloping front console cabinet,
170 x 213 x 31 x 82mm
1 PC board, code 02302961,
144 x 194mm
1 PC board, code 02302962, 76
x 105mm
1 PC board, code 02302963, 72
x 82mm
1 self-adhesive front panel label,
166 x 215mm
1 self-adhesive rear panel label,
165 x 78mm
6 10kΩ log pots (VR1-VR6)
4 10kΩ linear pots (VR7-VR10)
1 10kΩ dual ganged pot (VR11)
1 1kΩ horizontal trimpot (VR12)
7 SPDT toggle switches (S1-S7)
6 6.35mm stereo PC board
mount switched sockets
1 2 x 2-way PC-mount RCA
panel socket (Altronics P0211)
1 DC panel socket (to suit
plugpack)
1 12VAC 300mA plugpack
4 knobs with blue insets
2 knobs with red insets
2 knobs with purple insets
3 knobs with black insets
15 cable ties
1 15m length of single shielded
cable
1 1.5m length of yellow hook-up
wire
1 500mm length of red hook-up
wire
1 500mm length of green hookup wire
1 800mm length of blue hook-up
wire
4 9mm tapped spacers
4 6mm untapped spacers
4 3mm dia. x 12mm screws
5 3mm dia. x 6mm screws
The DIFFERENCE1 output provides
the Surround signal. This is rolled off
above 7kHz by low pass filter stage
IC10b before being applied to the
output socket and metering circuitry.
Circuit
Refer now to Fig.3 for the complete
circuit details. Although it may appear
quite complicated at first glance, there
is in fact a considerable amount of
duplication for the various inputs.
Let’s begin by taking a look at the
1 3mm nut
74 PC stakes
4 11-way pin headers (13mm
long pins)
Semiconductors
10 LM833 dual op amps (IC1IC10)
1 TL071, LF351 single op amp
(IC11)
4 LM3915 log. display drivers
(IC12-IC15)
1 7812T 3-terminal regulator
(REG1)
1 B104 1A bridge rectifier (BR1)
4 BC328 PNP transistors (Q1Q4)
4 1N914 signal diodes (D1-D4)
40 3mm red LEDs (LED1-40)
Capacitors
1 2200µF 25VW PC electrolytic
1 100µF 16VW PC electrolytic
12 47µF 16VW PC electrolytic
6 10µF 16VW PC electrolytic
20 2.2µF 16VW PC electrolytic
19 0.1µF MKT polyester
2 .0027µF MKT polyester
2 680pF ceramic
6 220pF ceramic
1 180pF ceramic
1 100pF ceramic
Resistors (0.25W, 1%)
4 1MΩ
8 4.7kΩ
4 100kΩ
12 2.2kΩ
19 22kΩ
4 1.2kΩ
4 16kΩ
8 1kΩ
2 20kΩ
4 680Ω
4 13kΩ
6 220Ω
1 12kΩ
4 150Ω
30 10kΩ
5 100Ω
2 8.2kΩ
input circuitry for the Left signal. This
circuit is based on op amp IC1a which
is wired in the balanced configuration.
Fig.3 (following pages): the input
and summing circuitry is based on
LM833 dual op amps (IC1-8), and
these are also used in the decoding
circuitry (IC9-10). IC11 is used to
derive the split supply, while the
four signal level meters are based
on LM3915 display driver ICs.
January 1996 25
▼
levels from these stages are set by
potentiometers VR1-VR6 respectively.
The Left amplifier output connects
to summing junction SUM1 which
comprises IC4a. This mixes in the
Centre amplifier output after it has
been attenuated by 3dB. Similarly,
the Right amplifier output connects
to summing junction SUM2 (formed
by IC5a) and this also mixes in a -3dB
Centre signal.
The A and B amplifier outputs are
each amplified by two, using IC7a
and IC7b respectively. This is done to
compensate for losses in the following
L-R pan circuit stages. The resulting
L-R pan signals are then mixed into
the SUM1 and SUM2 junctions.
Similarly, the Surround amplifier
output is summed at SUM5 with the
C-S (Centre to Surround) pan control
outputs. The summed output is then
filtered using low-pass filter stage IC6a,
so that only signals below about 7kHz
are fed to the following stages.
Following IC6a, the Surround signal
is fed in two different directions. In
one direction, it is first phase shifted
by 180° (ie, inverted), then attenuated by 3dB and mixed at SUM3 with
the signal from SUM1. In the other
direction, it is fed straight to a 3dB
attenuator (ie, no phase shifting) and
then mixed at SUM4 with the signal
from SUM2.
The process so far is similar to
the encoding process used for Dolby
Surround Sound recording, except
that no noise reduction is used in the
Surround signal path. This lack of
noise reduction encoding circuitry
is not important in this application,
particularly as we wanted to keep
costs down.
26 Silicon Chip
January 1996 27
Assuming that S1 is closed (LINE),
the input signal is attenuated by the
220Ω resistor and the overall stage
gain is +1. The output from IC1a
appears at pin 1 and is fed to level
control VR1.
IC1b, IC2a, IC2b, IC3a & IC3b are
the input amplifiers for the Centre,
Right, Surround, A and B channel
inputs respectively. These stages are
all identical to IC1a and their outputs
feed level controls VR2-VR6.
Following VR1, the Left signal is fed
to summing amplifier IC4a via a 10kΩ
resistor. Similarly, the Right signal is
fed via a 10kΩ resistor to summing
amplifier IC5a. The Centre channel
output at the wiper of VR2 is buffered
using IC4b before being applied to each
of these summing junctions via a 14kΩ
resistance (made up of 13kΩ and 1kΩ
resistors in series).
This arrangement effectively attenuates the Centre channel signal by
3dB with respect to the Left and Right
signals. That’s because IC4a & IC5a
operate with a gain of -1 for the Left
and Right signals, and a gain of -0.714
for the Centre signal.
Moving now to the Surround channel, the signal on the wiper of VR4 is
coupled to pin 6 of IC5b, where it is
summed with the Centre-Surround (CS) pan signals (more on these shortly).
The output of IC5b then drives IC6a.
This op amp is wired as a 2-pole lowpass filter stage and rolls off frequencies above 7kHz.
Performance of Prototype
Signal-To-Noise Ratio
Better than 84dB with respect to 1V output
Frequency Response:
L, C, & R Channels: -1dB at 10Hz & 40kHz
A & B Channels: -3dB at 40Hz & -1dB at 40kHz
S Channel: -3dB at 7kHz
Total Harmonic Distortion
0.01% at 1kHz and 300mV input
Decoder Separation
Surround to Centre Channels: 42dB minimum at 1kHz
Left to Right Channels: 76dB at 1kHz
Left & Right to Centre Channel: 12dB
Left & Right to Surround Channel: 15dB
Signal Handling
2V RMS maximum for line input
Sensitivity:
Mic Input: 30mV for 300mV out. Line Input: 300mV for 300mV out.
Assuming that S1 is in the MIC position, it has a gain of -10 for signals
fed to its inverting input and +11 for
signals fed to its non-inverting input
(as set by the 22kΩ feedback resistor
and the 2.2kΩ input resistors).
However, signals applied to the
non-inverting input are first attenuated by 0.909 using a resistive divider
(2.2kΩ & 22kΩ) before being amplified.
As a result, the overall stage gain for
signals applied to the non-inverting
input is +10, which matches the gain
for the inverting input. This gives good
common mode rejection for balanced
signals (eg, from a microphone).
For unbalanced signals, the inverting socket connection must be ground
ed externally by a mono plug (or by
earthing the ring terminal of a stereo
plug). This means that only signals at
the socket tip will be amplified, with
IC1a now operating as a non-inverting
amplifier.
TABLE 1: RESISTOR COLOUR CODES
❏
No.
❏ 4
❏ 4
❏
19
❏ 4
❏ 2
❏ 4
❏ 1
❏
30
❏ 2
❏ 8
❏
12
❏ 4
❏ 8
❏ 4
❏ 6
❏ 4
❏ 5
28 Silicon Chip
Value
1MΩ
100kΩ
22kΩ
16kΩ
20kΩ
13kΩ
12kΩ
10kΩ
8.2kΩ
4.7kΩ
2.2kΩ
1.2kΩ
1kΩ
680Ω
220Ω
150Ω
100Ω
4-Band Code (1%)
brown black green brown
brown black yellow brown
red red orange brown
brown blue orange brown
red black orange brown
brown orange orange brown
brown red orange brown
brown black orange brown
grey red red brown
yellow violet red brown
red red red brown
brown red red brown
brown black red brown
blue grey brown brown
red red brown brown
brown green brown brown
brown black brown brown
5-Band Code (1%)
brown black black yellow brown
brown black black orange brown
red red black red brown
brown blue black red brown
red black black red brown
brown orange black red brown
brown red black red brown
brown black black red brown
grey red black brown brown
yellow violet black brown brown
red red black brown brown
brown red black brown brown
brown black black brown brown
blue grey black black brown
red red black black brown
brown green black black brown
brown black black black brown
Fig.4: install the parts on the main PC board as shown here. Note particularly that IC11 is a TL071.
The filtered output from IC6a is
summed in IC8b with the signal from
IC5a. It is also inverted by IC6b (ie,
phase shifted by 180°) and summed
in IC8a with the signal from IC4a.
Note that, in both cases, the filtered
Surround signal is attenuated by 3dB
in the summing amplifiers due to the
14kΩ input resistances (again made up
of 13kΩ and 1kΩ resistors).
Following these two summing amplifiers, the signals are fed to output
January 1996 29
The Surround Sound Mixer and Decoder is built into a compact console case
with a sloping front panel. Note that there is a fair amount of internal wiring to
be run, most of it between the main board and the front panel controls.
level controls VR11a and VR11b. The
encoded Left and Right signals are
then coupled to their respective output
sockets via 2.2µF capacitors.
Panning
Now let’s take a look at how the pan
signals are derived.
In the case of the A input, the signal
at the wiper of VR5 is first buffered and
amplified by IC7a. This stage functions
as a non-inverting amplifier with a gain
of two. The output from IC7a is then
applied to pan control VR8 via a 4.7kΩ
resistor and to pan control VR7 via a
second 4.7kΩ resistor and two 10kΩ
isolating resistors.
VR7 is used to pan the “A” signals
between the Left and Right channel
summing amplifiers (IC4a and IC5a),
while VR9 does the same for the “B”
signals. Similarly, VR8 and VR10
(Pan C-S) pan the “A” and “B” signals
between the Pan L-R controls and the
input to IC5b.
In theory, VR7 and VR9 pan between
the Left and Right channels, while VR8
and VR10 pan between the Centre and
Surround channels. In practice, however, there is some interaction between
these controls.
Surround sound decoding
The internal decoding circuitry is
30 Silicon Chip
based on IC9a, IC9b, IC10a & IC10b and
is normally only used on playback –
see Fig.1(b). IC9a and IC10a are used
to derive the Centre channel. This is
achieved by first adding the Left and
Right channel outputs together in
summing amplifier IC9a. The output
of IC9a is then buffered by unity gain
inverter IC10a and coupled to the
Centre output socket.
A different technique is used to derive the Surround output. In this case,
the encoded Left and Right channel
outputs are fed to IC9b which is configured as a difference amplifier. This
configuration is arrived at by feeding
the Left channel to the inverting (pin
6) input and the Right channel to the
non-inverting (pin 5) input.
The output from IC9b is simply
the difference between the two input
TABLE 2: CAPACITOR CODES
❏
❏
❏
❏
❏
❏
❏
Value
IEC Code EIA Code
0.1µF 100n 104
.0027µF 2n7 272
680pF 680p 681
220pF 220p 221
180pF 180p 181
100pF 100p 101
signals. This signal is filtered and
inverted by low-pass filter stage IC10b
and fed to the Surround output socket.
Signal meters
As mentioned previously, the circuit contains four signal level meters
which monitor the Left, Right, Centre
and Surround outputs. These four
meters are all identical, so we’ll just
look at the meter that monitors the
Left output.
The circuit is based on IC12 which
is a 10-LED display driver wired in
dot mode. In operation, the incoming signal is first buffered by emitter
follower stage Q1. It is then rectified
by D1, filtered and applied to pin 5
of IC12.
The filter components on pin 5
consist of a 0.1µF capacitor and a 1MΩ
resistor, connected in parallel. These
give the meter a fast attack time and
a slow decay response, so the meter
effectively displays the peak average
value.
As well as acting as a buffer, Q1
also compensates for the voltage
drop across D1, since its emitter is
always approximately 0.6V above its
base. While this compensates fairly
well, the balance is not perfect since
there is more current through Q1’s
base-emitter junction than through D1.
This slight imbalance is taken care of
by using VR12 to set an offset voltage
on pin 3 (RLO) of IC12. This jacks the
pin 3 voltage up so that it equals the
voltage at pin 5 when the input signal
is tied to ground.
The full scale deflection value for
the meter depends on the voltage on
pin 7 and is set by the 4.7kΩ and 680Ω
resistors. In this case, the voltage on
pin 7 is set to 1.64V, which corre
sponds to a peak value of 3dB above
774mV RMS (ie, LEDs 1-10 lit). As
a result, the meter is calibrated for
0dBm, which corre
sponds to 1mW
into 600Ω.
Power supply
Power for the circuit is derived
from a 12VAC plugpack. This is fullwave rectified using BR1, filtered by a
2200µF capacitor and applied to REG1
to derive a regulated +12V output.
IC11 is used to provide the circuit
ground, so that the op amps are effectively fed from split supply rails.
It does this by buffering the 5.45V
output from a voltage divider (12kΩ
& 10kΩ) wired across the regulator
output. The 100Ω resistor at IC11’s
output isolates the op amp from the
following 100µF capacitive load and
prevents oscillation.
As a result, the +12V rail is 6.55V
above ground, while the 0V rail is
5.45V below ground; ie we effectively
have split supply rails of +6.55V and
-5.45V.
Construction
Despite the circuit complexity,
building this unit is quite straightforward. Most of the circuitry is
contained on three PC boards: (1) a
main board coded 02302961 (144 x
194mm); (2) a display driver board
coded 02302962 (76 x 105mm); and (3)
a LED display board coded 02302963
(72 x 82mm).
Begin the construction by checking
the PC boards. In particular, check
for any breaks in the tracks and for
shorts between adjacent tracks. The
board mounting holes should all be
drilled to 3mm, while a 3mm hole is
also required on the main board for
the regulator (REG1) mounting screw.
Fig.4 shows the parts layout on the
main PC board. Start by installing PC
stakes at all external wiring points,
then install the wire links (using
tinned copper wire).
The next step is to install the ICs.
Note that these must all be oriented
in the same direction. Note too that
IC11 is a TL071 while the rest are all
Make sure that all polarised parts are correctly oriented when building the
main PC board. The 2200µF capacitor (bottom, right) is installed on its side and
is secured to the board using silicone sealant to prevent lead breakage.
LM833s, so don’t get them mixed up.
The bridge rectifier (BR1) can also now
be installed (orient it as shown), followed by 3-terminal regulator REG1.
Secure REG1’s metal tab to the PC
board using a screw and nut.
The resistors and capacitors can
now be mounted. Table 1 lists the resistor colour codes but it is also a good
idea to check them with a multimeter,
as some colours can be difficult to
decipher. Table 2 lists the capacitor
codes. Make sure that the electrolytic
capacitors are all correctly oriented
and note that the 2200µF capacitor is
mounted on its side.
Use silicone sealant to secure the
body of the 2200µF capacitor to the
board, to prevent its leads from flexing
and eventually breaking.
As shown on Fig.4, three of the
6.35mm stereo sockets are mounted
directly on the main board. Install
these now, along with the 2 x 2 RCA
socket package. The mounting clips
on the underside of RCA socket package will have to be removed using
side cutters before it is installed on
the board.
That's all we have space for this
month. Next month, we will resume
with the parts layout diagrams for
the display driver and display boards
and give the complete wiring and
testing details. We will also publish
the full-size PC board patterns and the
front-panel layout.
Note: “Dolby”, “Pro Logic” and the
Double-D symbol are trademarks of Dolby Laboratories Licensing Corporation,
San Francisco, CA 94103-4813 USA.
January 1996 31
COMPUTER BITS
BY GEOFF COHEN
gcohen<at>pcug.org.au
Upgrading your old PC – is
it worthwhile?
Is it worthwhile upgrading your old PC or
should you put the money towards a new
one? The answer depends on the state of your
old PC and the applications you wish to run.
There are a swags of old 286, 386
and even 486SX PCs floating around
now and a question I often get asked
is “is it worthwhile upgrading my old
PC to run Windows, or should I buy
a new one?”. The answer depends, of
course, on what sort of PC you have
and how much you want to increase
the performance – and thus how
much you are prepared to spend on
the upgrade.
The options are: (1) do a minimal
upgrade and recycle the old PC so
the kids can run Windows (word processing and games); or (2) go for a full
upgrade by replacing the motherboard,
CPU and hard disc.
Is it worth it?
First, you have to decide if it is
worthwhile upgrading your PC. If you
have a PC with a mono screen, a hard
disc smaller than 80Mb and less than
4Mb of RAM, upgrading the PC to run
Windows (especially Windows 95) is
not really an economic proposition.
In addition, if you have a major
brandname PC (IBM, Compaq, etc),
you will need to check if the beast
uses a standard size motherboard,
with normal plug in cards. Many
brand- name computers use specialised components and cannot accommodate some of the standard parts
used in clone PCs.
However, if you your PC has a
minimum of a VGA card, a colour
monitor and at least 4Mb of RAM, it
may be worthwhile upgrading it. At
the time of writing (November 1995),
Fig.1: the SimmVerter from Cameleon Technology accepts four 30-pin memory
modules (either 4 x 1Mb or 4 x 4Mb) and effectively converts them to a single
4Mb or 16Mb 72-pin memory module that plugs into the latest motherboards.
32 Silicon Chip
the cost of upgrading to a 486DX2-66
motherboard (including the CPU) is
around $300.00, while a 545Mb hard
disc drive and controller can be had
for just $280.00.
The cost of RAM is not too bad
either, with the price of a 4Mb 72-pin
RAM module currently around $230.
What should I upgrade to?
The answer to this question depends
on what you want to do. Here are a
couple of alternatives to consider:
(1) Windows/games PC. If you only
want to run Windows 3.1 at a reasonable speed – eg, so that the kids can
run Word and a few games – I would
recommend upgrading to:
(i) a 486DX2-66 CPU (these are so
cheap it’s not worthwhile using a
slower CPU);
(ii) 4Mb RAM; and
(iii) an 80Mb or preferably bigger
hard disc.
(2) Microsoft Office/Windows 95
PC. These programs require a bit more
firepower than the system listed above.
To run Microsoft Office the minimum
system would be:
(i) a 486DX2-66 or 486DX4-100/120
CPU, a Pentium being even better;
(ii) 8Mb RAM for Windows 3.1 or
16Mb for Windows 95;
(iii) a 540Mb, 850Mb or even a 1Gb
hard disc.
In addition, a CD ROM drive is
handy for installing pro
grams like
Office and Windows 95 , as it saves
having to install from multiple flopp
ies.
I have noticed that there are still
suppliers advertising Windows 95
systems with only 8Mb of RAM. I have
tried this and it is very slow with Office
95. In fact, you need at least 16Mb for
better performance and allow more
programs to be opened. 16Mb is a
good size for Windows 3.1 and 32Mb
for Windows 95.
Parity or non-parity RAM
Most new motherboards have a
CMOS option to enable or dis
able
parity RAM, the default option being
non parity in the motherboards I have
tried. Unless the PC is going to be
used as a network server, non parity
RAM should be adequate, as a RAM
test is performed every time the PC
is switched on. In any case, I cannot
remember the last time I had a faulty
RAM chip – it was, at least, several
years ago.
Disc controllers
Some motherboards have two sets of 72-pin RAM sockets and four sets of
30-pin sockets. This photo shows a SimmVerter module, itself carrying four 30pin SIMMs, plugged into one of the 72-pin sockets at the rear.
a Windows 95 system if it is to operate
at a reasonable speed.
Using your old memory
A major problem used to be that
while older motherboards used 30-pin
SIMM RAM, the latest 486 and Pentium motherboards only have sockets
for the new 72-pin SIMM RAM. This
meant that upgrading to a new motherboard with 72-pin sockets necessitated
throwing out (or selling cheaply) any
existing 30-pin RAM, which was a tad
annoying.
Fortunately, a new device in now
available which overcomes this problem. It’s called a “SimmVerter” and it
effectively allows four 30-pin SIMMs
(1Mb or 4Mb) to be converted to one
4Mb or 16Mb 72-pin SIMM module.
All you have to do is plug four 30-pin
SIMMs into the sockets on the SimmVerter. The SimmVerter itself then
plugs into a 72-pin RAM socket on
the motherboard.
SimmVerters cost around $30 each,
which is far less than the cost of having to replace 4Mb of RAM. They are
available in four different shapes so
that you can easily accommodate four
SimmVerter modules adjacent to each
other, if necessary – see Fig.2.
Another approach is to see if there
is any secondhand RAM available,
either on the Net (eg, aus.ads.forsale.
computers) or in the Saturday paper.
An important difference with the Pen-
tium is the need to fit 72-pin SIMMs
in groups of two. I won’t mention
who fell for that trap the first time he
installed a Pentium motherboard and
used a single 8Mb SIMM, instead of
two 4Mb SIMMs, and then complained
that the !<at>#$%^&* thing wouldn’t
work.
If you want to improve Windows
performance, the cheapest option
is to increase your RAM. Upgrading
from 4Mb to 8Mb makes the biggest
difference and Word 6, for example,
loads many times faster with this
simple upgrade. Increasing the memory even further will provide even
MODEL B
MODEL A
MODEL C
MODEL D
Fig.2: SimmVerters come in four
models (A, B, C and D) so that they
can be fitted to adjacent memory
sockets.
An upgraded disc controller card
may be necessary if you are upgrading
the hard disc. Assuming that you are
going to stick with an IDE disc, you
can purchase a multi-I/O card for
around $25.
As well as running your floppy
drives and two IDE hard discs, this will
also generally provide two serial ports,
a parallel printer port and a games
port. If you have (or are upgrading to)
a VESA motherboard, then you should
buy a VESA multi-I/O card, as they are
much faster than a standard ISA card.
Note, however, that most new Pentium PCI motherboards will already
have the floppy, hard disc and I/O
controllers on board. In that case, you
don’t have to worry about a separate
I/O card.
Hard discs
Depending on your requirements,
you could stay with an existing 80200Mb hard disc and buy a used 100200Mb drive. However, a new 500Mb
hard disc is only around $200 and a
minimum of 150Mb is needed to run
the full Windows 3.1 and Microsoft
Office suite of software.
If you are fitting a hard disc of
500Mb or above and have thousands
of files, you need to consider how to
partition it. For drives under 512Mb,
a one byte file will take 8192 bytes.
This increases to 16,384 bytes for 5121024Mb drives, and so on.
In other words, the larger the logical
drive, the larger the space that a one
byte file effectively takes up and this
wastes space. For example, if you
have an 850Mb disc with 10,000 files,
this will waste (on average) 10,000 x
January 1996 33
The ZIP Drive – 100Mb On A $33 Disc
speed at which Windows updates the
screen may not be all that fast if an
old ISA video card is fitted. Starting
at around $120, a VESA or PCI video
card will speed things up considerably. Typical examples, using ATPERF
for relative performance details, are:
Old ISA 2
VESA
12
PCI
20
Another item to consider, if you
want to use high resolution (ie, 1024
x 768 or larger), is the amount of video
RAM. A new video card should have
a minimum 1Mb of RAM (preferably
with sockets to accept more), or you
can just bite the bullet and get a video
card with 2Mb of RAM for even better
performance.
Installation
Most computer users don’t consider backing up the large hard discs
that are now being sold. There’s an
old saying that there are only two
types of computer users: those who
have lost data and those who will
lose data. The truth is that backing
up onto floppy discs is often too cumbersome, while tape drives have the
capacity but are quite slow when it
comes to retrieving files (unless you
have a DAT tape drive).
External drive
An external drive is the answer to
backup problems. One interesting
new device is the Zip drive which has
recently been released by Iomega.
This is a (relatively) cheap 100Mb
removable disk drive which retails for
around $370, with the 100Mb discs
selling for around $99 for a pack of
three. When installed, it is assigned
a drive letter and is treated just like
any other disc drive.
I have been using the parallel
port version for several weeks now.
It really is quite nifty – you just plug
it into a parallel port, run GUEST.
16,384/2 bytes, or around 80Mb.
However, if this disk was configured
into two 425Mb partitions, you would
save over 40Mb of space. So consider
carefully how you should partition the
34 Silicon Chip
EXE and copy to/from the ZIP disc.
A SCSI version is also available for
the same price and is reported to be
three times faster than the parallel
version. On the downside, the SCSI
version isn’t as portable and you
have to buy a SCSI controller for it.
Testing
I did some testing and found that
large database files copied to the
Zip drive at about 4.5Mb per minute. Alternatively, by using Norton
Backup and saving to a logical disc
drive, I was able to copy at an effective 8-10Mb per minute and fit over
250Mb (before compression) on one
100Mb disc. So, at just $33 per disc,
the Zip drive is good for archiving
applications.
Assuming that it stands up to prolonged use, the Zip drive is a good
product. I tested mine by copying
files to and from it for over 20 hours
without any problems. Zip drives are
imported by Polaroid Australia (1800
066 021) and are available from
computer dealers and from Harvey
Norman retail stores.
disc (using FDISK), before you actually
start using it.
Video cards
Even with a Pentium processor, the
For timid souls, there are many
computer shops and technicians who
will upgrade your PC for a reasonable
labour cost. If you are more adventurous, replacing a motherboard is a
relatively straightforward job.
First, remove all cables from the
PC (including the power cord) and
remove the cover (this is usually done
by removing a number of self-tapping
screws). Once inside the PC, remove
all the plug-in cards from the mother
board.
Depending on the age of the PC, the
motherboard itself will probably be
secured by two or more screws that
will need to be removed. Once this
has been done, the motherboard will
then either lift or slide out.
The next step is to swap the nylon clips from the old to the new
mother
board, after which the new
motherboard can be installed in the
case and the plug-in cards reinstalled.
An important point to note here is
that if you have two connectors that
go to the power connector on the
motherboard, the black wires should
be next to each other when they are
plugged in.
Another option that you may want
to consider is a new case, especially
if the old one is looking a bit tacky.
A complete mini-tower case and
power supply can be purchased for
less than $100 and would certainly
improve the value of the PC if you
wanted to sell it.
Finally, if you have any problems
locating a SimmVerter, I purchased
mine from The Logical Approach in
Canberra – phone (06) 251 6511. SC
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Rod Irving Electronics Pty Ltd
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
Rod Irving Electronics Pty Ltd
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Rod Irving Electronics Pty Ltd
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
Rod Irving Electronics Pty Ltd
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Rod Irving Electronics Pty Ltd
By MIKE ZENERE
Build a magnetic card
reader & display
Have you ever wanted to find out what’s written
on your credit card or other magnetic stripe
cards? Now you can do it. This unit will enable
you to read and display the contents of track
two on any magnetic card and could be used as
the basis for an electronic door lock.
Magnetic cards have been around
for many years and have found their
way into many fields such as banking,
security and vending machines. Most
cards follow defined guidelines as to
their construction and layout and are
therefore very flexible to the designer.
40 Silicon Chip
Each card has three tracks but the most
commonly used is track two.
Recalling data from the card has
become relatively simple in the last
few years with modern card readers.
These generally have a single on-board
chip to decipher the raw data from the
read head. This looks much like the
record/play head in a cassette deck.
The on-board chip generally contains conditioning circuitry to pick up
the signal, reject noise and provide a
digital output. Most card readers interface via three wires which are Clock,
Data and Card Valid.
Assuming that a microprocessor is
hooked up to the card reader, a typical card read takes place as follows.
When a card is swiped through the
card reader, the Card Valid line goes
low after eight or nine flux reversals,
indicating that a valid card is present.
The microprocessor monitors the
clock line and waits until the Clock
Magnetic Card Standards
Most magnetic cards
adhere to defined standards
that describe the physical
as well as electrical layout.
The standards outline card
size, magnetic stripe and
track positioning, and format
information.
The information is recorded onto the card using
a technique known as
Two Frequency Coherent
Phase Recording or F/2F.
This allows for serial recording of self-clocking data on
each track. The data consists of data and clocking
bits together. When a flux
transition occurs between
Fig.1: the track layout on a magnetic card. Track 1 can record alphanumeric data,
clock cycles, a “one” is
while tracks 2 and 3 provide only numeric data.
obtained and when there is
an absence of flux between
encoded using 4-bit BCD with odd
start of the actual data to be read,
cycles a “zero” is obtained.
parity.
followed by the data, the end sentiStandard magnetic cards have
nel, LRC and finally, trailing zeros to
All tracks are recorded with the
three data tracks and each has its
the end of the card. The term LRC
least significant bit first and the parity
own subtle differences. Track 1 has
stands for “longitudinal redundancy
bit last. The higher density track three
a bit density of 210 bits per inch,
check” and is used for horizontal
holds up to 107 numerics while track
giving it the ability to hold a total of
error detection.
two holds only 40. The necessity for
79 characters over the entire length
start and end sentinels and other
By far the most commonly used
of the card. Each character on this
separating characters reduces the
track is track two. Although holding
track is made up of six data bits and
above storage capabilities to a cerless information than the others, this
one parity bit, providing 64 differtain extent.
track has all the data required to do
ent alphanumeric combinations to
a banking transaction. If there is a
choose from. The card and track
Reading or writing of data to the
need for the customer’s name to be
layout is shown in Fig.1.
card generally follows the same
present, then track one is used as it is
path for all three tracks. First, leadThe remaining tracks, two and
the only one that holds alphabetical
ing zeros are encoded to indicate
three, provide only numeric data
characters. The third track is special
the presence of data and to provide
and have a bit recording density of
in that data may be written or read
synchro
n isation. Next, the start
75 bpi and 210 bpi respectively. The
during a transaction.
sentinel is encoded to indicate the
character set for these two tracks is
line goes low, indicating that data is
present on the data line. The data bit is
collected and temporarily stored until
a succession of bits is gathered to make
a 5-bit word, with four data bits and
one parity bit. When the 5-bit word is
obtained and stored, the cycle repeats
itself until all the 5-bit characters have
been read into memory. The processor
can now go back over the data and
analyse it for parity.
Date rate & swipe direction
The data rate even for the high
density tracks is quite low, allowing
almost any microprocessor to sample
and collect the data. Let’s assume that
the card is passed through the reader
at around one metre per second.
This translates to around 9983 bps
or 1426 7-bit characters per second,
meaning that a new data bit is presented about every 100µs. Most card
readers are capable of reading two of
the three tracks in one swipe. Even
allowing for this extra load, most
microprocessors running at 1MHz or
more will handle this with ease.
Although data is written onto the
card in a particular format, there being
a start and end sentinel, this does not
limit the programmer to write software
to read a card when swiped forwards
or backwards.
In a “backward read”, the card data
is simply read as usual and stored in
memory but this time the last character
is first and the first character is last.
The program simply detects this by
looking for the start and end sentinels
and then corrects itself.
Card reader
The card reader and display unit to
be presented here is self-contained on
January 1996 41
42 Silicon Chip
Fig.2: the circuit is based on a magnetic card reader module with its own on-board decoding. The data from
this module is fed via three lines to the microprocessor (IC1) and this in turn drives a multiplexed 4-digit
display. The track 2 contents of four cards can be stored in the EEPROM (IC2) and this data can be used
as the basis of an electronic door lock. IC3 and its associated parts form a watchdog timer circuit and this
automatically resets the microprocessor if signal activity from pin 11 ceases, indicating that the processor
has “crashed”.
a PC board measuring 128 x 101mm.
As well as the card reader module
with its integral PC board, there is
a 4-digit display, a 28-pin 68705P3
microprocessor (IC1), a piezo buzzer
and three pushbuttons. The circuit is
shown in Fig.2.
The card reader and its integral PC
board has all the circuitry necessary
to decode and convert the raw data
coming from the card being read. The
data is transformed into logic levels
and is then sent out via three serial
lines to the processor. The card reader
is connected to the logic board via a
5-way cable, with three of the lines
for data and the other two for power.
The recording function of the circuit
is performed by a small serial EEPROM,
IC2. Once the unit is placed in the
record mode and a card is swiped
through, the data will be saved in the
EEPROM.
Because timing is not critical in this
project, a crystal for the microprocessor is not necessary. Instead, by placing
an 18kΩ resistor from pin 5 to the +5V
rail, an inbuilt oscillator is enabled,
causing the processor to run at near
full speed.
Beeper & relay driver
A DC self-oscillating beeper is
connected to port B, pin 12, on the
processor. Port B can sink up to 10mA
which is sufficient for this application
and is pulled low to turn on the beeper.
The relay is driven by transistor Q1
which is controlled by the line from
pin 24. This line is normally low and
the relay is off. When a valid card is
swiped through the reader, the proces
sor port pin 24 goes high for a period of
time and turns on Q1 which operates
the relay.
The display consists of four 7-segment common anode displays multi
plexed together. The cathodes are
driven directly by port lines from the
processor, while each display anode
is driven by its respective PNP driver
transistor (Q2-Q5).
The processor receives an interrupt
every 5ms from an internal timer. Each
time an interrupt is received, the processor switches off the current display
digit that it is driving and turns on
the next. In this manner, each digit is
only on for 5ms before the next digit is
updated. This gives each digit a total
on-time of around 250ms per second;
ie, a duty cycle of 25%.
The SHIFT LEFT and SHIFT RIGHT
buttons are used to move the display
laterally to enable the user to view the
entire number.
Construction
Begin assembly of the PC board
by mounting the four standoffs, one
at each corner. This done, install the
diodes, resistors, links and capacitors.
Note the polarity of the electrolytic
capacitors and the diodes. Install the
7805 regulator and fit it with a small
heatsink.
Next, install the transistors, the
two small ICs and the socket for IC1
but do not install the processor until
after the unit has been powered up
and a voltage check performed. When
installing the four 7-segment displays,
their decimal points should be close
to the edge of the PC board.
The remainder of the components
can now be mounted, noting the orientation of the pushbutton switches.
The card reader module is attached to
the PC board with screws fitted from
the underside. The back of the read
head should face the outside edge of
the board.
When all the assembly work is complete, apply 12V DC to the board and
check that +5V is present at pins 3 &
6 of the socket for IC1, at pin 8 of IC2,
pins 4 & 8 of IC3 and at the emitters
of Q2-Q5.
If this checks out, remove the power,
plug in the processor and connect the
card reader module. Reapply power
– the buzzer should beep four times
and the display should read “OPEr”.
The unit is now ready for a test drive.
Before you start, here are a few tips.
The mode button is used to cycle
through the various available modes.
Each time you press this button, the
next option appears on the display.
The modes are OPEr (operate), rEC
(record), d EL (delete), p LAY and
rEAd. When in the operate mode,
the display blanks out after about 30
seconds to conserve power. If any
button is pressed after this time the
display will light and programming
may continue.
Initial set up
If this is the first power-up you
will need to reset the memory of the
EEPROM and this is done by holding
down SHIFT LEFT and SHIFT RIGHT
and applying power. The EEPROM will
be cleared and the relay on-time will
be set to three seconds.
PARTS LIST
1 PC board, 128 x 101mm
1 magnetic card reader module
1 piezo buzzer
1 12V miniature SPDT relay
3 momentary contact pushbutton
switches
1 5-way connector
1 2-way connector
2 3-way PC-mount insulated
terminal blocks
4 PC standoffs
Semiconductors
1 MC68705P3 programmed
microprocessor (IC1)
1 93C46 EEPROM (IC2)
1 555 timer (IC3)
1 7805 5V 3-terminal regulator
(REG1)
4 HD11310 7-segment red LED
displays (DISP1-4)
3 1N4004 silicon diodes (D1-D3)
2 PN100 NPN transistors
(Q1,Q6)
4 PN200 PNP transistors
(Q2-Q5)
Capacitors
2 100µF 16VW electrolytic
1 1µF 16VW electrolytic
4 0.1µF monolithic
Resistors (0.25W, 5%)
1 1MΩ
1 1kΩ
1 33kΩ
7 330Ω
1 18kΩ
1 22Ω 0.5W
11 10kΩ
Miscellaneous
Screws, nuts, shakeproof
washers, solder.
Where to buy the parts
A complete kit of parts for the
magnetic card reader is available
from the author. This includes all
electronic components except for
the 12VDC power supply and a
case. The price is $75.00 plus
$7.50 for postage and packing.
Completely assembled and tested
units are also available at an extra
cost of $20.00. The documented
source code is a further $8.00 for
the print out.
Please make postal money orders
payable to Mike Zenere, 83 Head
ingley Road, Mt. Waverley, Vic
3149. Phone (03) 9803 3535.
Note: copyright© of the PC board
is retained by the author.
January 1996 43
Fig.3: install the parts on
the PC board as shown here,
taking care to ensure that
the displays, switches and
other polarised parts are
correctly oriented. The card
reader module is connected
to the main PC board via a
5-way cable.
The unit can be used in two modes
which enable the user to: (1) read and
display cards; and (2) operate the relay.
Let’s initially talk about the first option. After power-up, the unit should
be showing “OPEr” indicating that it
is in the door access mode. To change
this, push the mode button until the
display shows “rEAd”, indicating that
if a card is swiped, its track 2 contents
will be displayed.
Swipe any card through and you
should see some digits or letters on
the display. These will correspond to
the digits stored on the magnetic card
with the start sentinel (b) being the first
character. The display can only show
four numerics at a time so to view the
rest, push the SHIFT LEFT button once
to view the next character to the right.
Keep doing this until the display
shows the end sentinel (F) or until the
display shifts no further . While doing
this, look at the front of the card and its
embossed number. You should see this
number appear in the display as you
move along. If you wish, you can move
the display to the right by pushing the
SHIFT RIGHT button.
To view another card, simply swipe
it through the slot.
Door lock applications
The following functions relate to
the operate mode which is when the
44 Silicon Chip
unit is used as a door lock. After going
through the functions listed below,
place the unit in the operate mode by
hitting the mode button until “OPEr”
is displayed.
After a short time, the display will
blank out and the unit will now be
ready to compare swiped cards with its
memory contents. If a match is found,
the door release relay will operate for
a set time and a single beep will be
heard. If no match is found, two beeps
will be heard.
Recording a card
The unit can store up to four cards
in the serially fed EEPROM. The MODE
button is hit until the “rEC” message is
displayed. If the memory is full, there
being four cards stored already, the
display will alternate between “FULL”
and “rEC” and you will not be able to
store any more cards until you have
used the delete function. Each time a
card is entered, the unit jumps back
to the operate mode until the function
key is once again hit.
Deleting a card
You can delete a previously entered
card by first hitting the mode button
until “dEL” is displayed. Swipe the
card to be deleted through the slot
and if the card is found and deleted
from memory, a single beep is heard.
If the card is not found the unit will
beep twice.
Relay operation
When a card has been successfully
recognised by the unit, it will operate
the relay for a set time which will be
between one and nine seconds. To set
this time, hit the MODE button until
the “rLAY” message is shown. Hit
either of the SHIFT buttons to display
the current setting.
Using the SHIFT LEFT and SHIFT
RIGHT buttons, set the relay on-time
in the display to the desired number;
eg, the display may show something
like 0002, indicating that the relay will
operate for about two seconds.
Hit the mode button again to save
the new number in memory.
If using the unit as a door lock, you
can remove the magnetic card reader
module from the PC board and extend
its con
necting cables to enable the
two sections to be housed separately.
The two separated units can then be
mounted on either side of the wall to
provide greater security.
Battery back-up
Provision has been made for battery
back-up in case of a power failure. The
battery GND is commoned to the power
supply ground and the battery +12V
SC
is connected via D2.
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SATELLITE
WATCH
Welcome to the first Satellite Watch
column, where we will keep you
updated with satellite signal reception
reports for Australia and NZ.
• INTELSAT – 70-66° E longitude, C
band: This satellite is visible only from
the west coast of Australia and carries
Worldnet programming from the USA,
CFI from Paris and various other itinerant
signals.
• GORIZONT – 19 - 96.5° E longitude, C
band: This satellite carries the Russian
“Network 1” programming on 1475MHz,
with audio at 7.02MHz. An additional
radio service is also carried at 7.5MHz.
CCTV 4 Chinese television can be seen at
1325MHz and now carries a new English
News service. Az Tv from Azerbaijan
can be seen on an irregular basis at
around 1800AEST and can be found at
IF 1425MHz.
• ASIASAT II – 100.5° E longitude, C
band: Scheduled for launch last November, this will provide new programming
for satellite enthusiasts. After months of
delay caused by previous failures aboard
the Long March launcher, this is the
launch that will make or break Great Wall.
Mooted to carry similar programming to
ASIASAT I, this satellite will be visible
over Australia and New Zealand with a
small (2m) dish. At least five channels
will be free to air, according to prelaunch
press releases.
• GORIZONT 25 – 103° E longitude, C
band: Another Russian satellite carrying
Network 1 programming, for a different
time zone to Gorizont 19.
• ASIASAT 1 – 105.5° E longitude, C
band: Visible in the northern and north
western parts of Australia, this satellite
has a potential northern hemisphere audience of over a billion viewers and covers
from India to the Middle East. Reports as
far south as Albury (NSW) and the Barossa Valley area indicate sidelobe signals are
visible in some parts of southern Australia. Programming carried includes Prime
Sports, Star Movies, Zee TV and other pay
*Garry Cratt is Managing Director of
Av-Comm Pty Ltd, suppliers of satellite
TV reception systems.
services. Transponder frequencies can be
obtained by dialling the Hong Kong Info
service number: 0011 852 172 777 01. Call
charges are at normal IDD rates.
• PALAPA B2P – 113° E longitude, C
band: Presently visible only in the Northern part of Australia, this satellite was
placed in an inclined orbit in November,
to conserve station keeping fuel, whilst
waiting the launch and subsequent
replacement by PALAPA C1, a higher
powered satellite covering all of Australia
and New Zealand. Palapa C1 will now be
launched by Lockheed Martin of the USA.
Prior to this announcement in October,
the launch was scheduled with Arianne
space but the launch company was unable
to keep to the original schedule.
It is expected that all current users will
transfer to the new satellite, now scheduled for launch in January 1996. Amongst
signals on the B2P satellite is Australia’s
ATVI, the international arm of the ABC.
Weekly program data can be obtained by
polling fax # 055 29900.
• JCSAT 3: First observed early in October, this satellite has the capability to
cover Australia and New Zealand with
strong signals. Reports from the east coast
of Australia, Japan, Hawaii and Noumea
indicate the testing phase of this satellite
is almost complete. It is expected that
some programming could become available early in 1996.
• RIMSAT G1 – 130° E longitude, C band:
The orbit of this Russian Gorizont class
satellite is only slightly inclined, making
24-hour small dish reception of RAJ TV, a
Tamill language broadcast, a reality. RAJ
TV operates at 1475MHz.
• RIMSAT G2 – 142.5° E longitude, C
band: Until September 12, this satellite
carried the ATN network from India. Due
to unresolved difficulties involving the
satellite operator RIMSAT, the Russian
government space agency and ATN, this
transponder ceased operations temporarily during September but now appears to
be operating on a permanent basis. The
other full time transponder, oper
ating
Compiled by
GARRY CRATT*
at 1265MHz, carries EM TV from Papua
New Guinea. This transponder operates
LHCP (left hand circular polarisation) and
carries a mix of Nine network (Australia)
and local programming.
During late November, ATN changed
format to two adjacent half transponders.
Whilst continuing with the regular ATN
broadcasts on IF 1465MHz, ATN PRIME
will commence early December using an
IF of 1480MHz.
• OPTUS B1 - 160° E longitude, K band:
This satellite carries outback TV in
BMAC, as well as up to five interchange
services in PAL. Interchange IF frequencies are: 1219, 1155, 1425 (all vertically
polarised) and 1249MHz horizontal.
• OPTUS B3 – 156° E longitude, K band:
The latest Optus satellite came into operation last August. Presently, it carries several closed user group BMAC services, as
well as the OTEN network (Victorian and
NSW education departments) and several
interchange services. IF frequencies are
1233, 1361 and 1094MHz. The Optus
A3 satellite, until recently co-located at
156° E, is most likely part way through a
planned drift back to 164°, where it could
be used to replace the ageing A2 satellite,
now in an inclined orbit.
• PANAMSAT PAS-2 – 169° E longitude,
C band: Although many services on this
bird use either secure BMAC or MPEG 2,
there are still some analog services that
can be viewed by enthusiasts. CNN, NHK
and CNBC Asia operate on 1153, 1113
and 1035MHz IFs. Recent itinerant users
include the American ABC network and a
number of news feeds from Osaka, Japan,
during the recent ASEAN conference.
• INTELSAT 511 – 180° E longitude, C
band: This ageing satellite, now in an inclined orbit but due to be replaced during
1996, carries Deutsche Welle programming
from Germany, RFO from Tahiti and
Worldnet from the USA. In the last few
months several servic
es have migrated
from Intelsat to other satellites, whilst
some previous analog services (CNN, NBC)
SC
have gone to digital format.
January 1996 53
n
i
a
R
n
i
a
Br
By GRAHAM BLOWES
This automatic sprinkler controller allows
you to selectively water any area of a garden
or nursery as little or as often as you like.
It can control up to eight solenoids plus an
optional master solenoid.
T
HE FIRST VERSION of this de-
sign was published in the July
1992 edition of SILICON CHIP.
It was a popular project and I still get
enquires from the original article.
About a year ago, I decided that an
update was due. The most obvious
thing that needed replacing was the
microcontroller, as the NMOS 68705P3
microcontroller was to be discontinued. The controller now uses a PLCC
version of the popular 68HC705C8.
There was also some changes made
54 Silicon Chip
to the power supply, which now uses
a switching IC.
While I was at it, I also decided to
make a couple of changes to the front
panel layout. First, I deleted the row
of green LEDs that were used to indicate which solenoids were on. This
function is now taken care of by the
row of red LEDs – when a solenoid
turns on, the appropriate LED flashes at a fast rate to provide the “on”
indication.
I also added an extra button to the
front panel to make it easier to get back
to the default mode. Apart from that,
the layout of the front panel worked
pretty well, so I kept it that way.
The PC board is also now a lot easier
to put together than before. And finally, I’ve added three inputs –designated
Rain 1, Rain 2 and Frost 1 – that enable
almost complete automation of your
garden!
Two of the inputs are for optional
rain switches that enable the controller to turn off selected cycles if it
is raining. This facility is especially
important in a country like Australia,
where many parts of the country suffer from low rainfall. Wasting water
costs money, especially these days
with the in-vogue user-pays principle,
so turning off the sprinklers when it
rains makes economical (and ecological) sense.
The third input is for a temperature
sensor (again optional). This enables
the controller to switch in extra cycles
on a hot day. It even works in reverse;
an extra cycle can be switched in if the
temperature falls below a set trip point.
The controller even stores the MIN and
MAX temperatures (time stamped) for
today and yesterday.
Each rain switch and temperature
trip point can be set on a cycle by
cycle basis. The default mode can
display the time and date, or the time
and current temperature. This facility
n
Main Features
(1). Uses a 16 x 1 liquid crystal display
(LCD) to show time, date and sprinkler
settings, plus all the various system
menus.
(2). Controls up to eight solenoids plus
a master solenoid.
(3). Each station can have up to four
cycles on Program A and Program B,
or eight cycles on Program C (Program
C = Program A + B). Each cycle can
operate with either the three-week
built-in calendar or on a continuous
schedule for up to 99 days
(4). Each station (and cycle) is completely autonomous, providing a possible 64 programmable start times per
day (Program C).
(5). LED indication of station status.
Continuously lit = auto mode on; fast
flash = solenoid on; 1Hz flash = Rain
Off mode.
(6). Manual on/off control for each
solenoid. The run time of cycle 4
can be used to provide an automatic
cutoff feature. This lets you manually
is pro
grammable via the “CONFIG”
menu. More about that later.
Main features
The original version allowed sprinklers to turn on every day, every second day, every third day, etc. While
this system worked OK, it was a bit
difficult to nail down exactly which
days the sprinklers would turn on. To
rectify this, the Rain Brain now has a
3-week cycle as well as the original
method – the original method being
useful for plants that require watering
at a set interval, regardless of whether
it is a weekend or not.
The “3-week cycle” method is
based on a built-in calendar. It lets
you choose exactly which days the
sprinklers will turn on up to three
weeks in advance! For example, you
could program the unit so that solenoid 1 turned for two 1-hour cycles on
Monday of the first week, Wednesday
of the second week and Thursday of
the third week.
All the facilities mentioned above
are available to every single cycle, and
are programmable via the “AUXILIARY
FUNCTIONS” menu.
To cater for the extra facilities, the
Rain Brain has twice the EEPROM
capacity of the previous version. Each
switch on a sprinkler and forget it.
The sprinkler will then automatically
turn off after the run time of cycle 4
has expired.
(7). Run time (per cycle): 1-99 minutes.
The cycles can be joined so the maximum run-time (per solenoid) is: 8 x 99
minutes = 13 hrs, 10 mins.
(8). An EEPROM stores all settings,
so settings are not lost if the backup
battery fails. Battery backup is provided
by a 3V lithium battery.
(9). A “Rain Mode” deactivates all automatic cycles while saving program
settings.
(10). Two fully programmable Rain
Switches (optional) allow any/all of
the 64 cycles to be controlled by
the immediate weather conditions
automatically.
(11). An optional Temperature Sensor
enables any/all of the 32 cycles of Program A (or B ) to switch to another cycle
if the programmed trip temperature is
exceeded. This allows extra cycles to
of the eight stations can switch on as
often as eight times a day (ie, there are
up to eight daily cycles), or as little as
once every 99 days! As before, each
cycle can be programmed for an “on
time” of 1-99 minutes.
A new feature allows you to choose
from three standard programs, designated A, B and C. Programs A and B
allow each station to programmed for
four cycles per day, while program C
combines programs A and B to provide up to eight cycles per station per
day. If this isn’t enough, you can add
optional extra memory plus a switch
to select an alternative group of A, B
and C programs.
The row of eight LEDs beneath the
LCD indicates the status of the solenoids at a glance. If a LED is flashing
quickly, this indicates that the solenoid is turned on. If a LED is steady,
the station is active, meaning that it
will switch on automatically once its
“turn on” conditions are satisfied. And
if all enabled LEDs are flashing slowly
(1s on, 1s off), a rain switch has been
activated.
A flash rate of 0.5s on, 0.5s off indicates the “RAIN OFF” mode. This
means that all automatic cycles have
been globally disabled (see later). This
mode has precedence over the rain
be automatically added; eg, so that
plants get extra water on a hot day!
The sensor is accurate to ±0.1°C and
has a range from -20°C +60°C.
(12). The controller stores the maximum and minimum temperatures
sensed that day and the time at which
these extremes occurred is also recorded. This information is accessed
by pressing the “Cursor” button while
in the Default Mode. The previous
day’s temperature extremes can also
be displayed, as well as the current
temperature!
(13). Uses the well proven MC68HC
705C8 microcontroller. A watch dog
circuit ensures a proper reset is issued
to the microcontroller if it “crashes” due
to a mains glitch.
(14). All appropriate solenoids are enabled and the various cycles completed
after a reset, or when power is restored
after a power failure.
(15). Runs from a 10-24VAC or a 1035V DC 1A plugpack supply.
switch inputs and the fast flash rate
has precedence over them all.
Although these different flash rates
may seem initially confusing, it all
makes perfect sense when you start
using the unit.
Power requirements
The unit is powered by the usual
24V AC plugpacks associat
ed with
watering systems, or from voltages as
low as 10V DC. As with the first version, flat batteries are not a problem, as
all settings are stored securely inside
an EEPROM. The controller reads the
EEPROM when it is first turned on, so
it knows exactly which mode it should
be in (RAIN OFF or DEFAULT) and
which sprinklers are active.
Other uses
By this stage, you are probably already thinking of other uses for this
versatile controller, apart from its
primary use as a sprinkler solenoid
controller. For example, those of you
who have an interest in satellites can
set the controller to switch on a tape
recorder at the time it is due to pass
overhead, even though you may be on
holidays for a few weeks.
Alternatively, the unit could be
used as a security light controller or
January 1996 55
56 Silicon Chip
Fig.1 (left): the circuit is based on IC4,
a 68HC705C8 microcontroller. IC3 is
a real-time clock (RTC), while IC1 is
an EEPROM and is used to store the
programmed settings.
as a general-purpose timer. In these
applications, the on-board relays can
act as slaves to appropriately rated offboard relays, so that other equipment
can be controlled.
How it works
The circuit is fairly straightforward
(Fig.1), with all the heavy work being
done by the software in the micro
controller (IC4).
Starting with the power supply,
diodes D1-D4 rectify the 24V AC
input, which results in about 35V DC
across C1. IC8 (LM2574-5) is from the
“simple switcher” series from National
Semiconductor and provides a very
efficient method of providing a 5V rail
to power the circuitry.
The resultant 5V across C2 is further
decoupled by L1 and L2. These inductors attenuate any spikes generated by
the solenoids as they switch on and off.
Note that the relay driver (ULN2804,
IC5) is supplied from the “noisier” 5V
across C2.
C16, C17 and C18 are spread around
the PC board to decouple the power
supply. The circuit draws the following currents from a 24V AC plugpack
under the following conditions: (1)
all LEDs off = 26mA; (2) all LEDs on
= 32mA; and (3) all LEDs and relays
on = 88mA.
The microcontroller (IC4) uses a
standard 3.58MHz crystal (Xtal2) as
a timebase. A feature of this micro
controller is an internal watchdog
function, called the Computer Operating Properly (or COP). I tried to
get this to work but the maximum
timeout period with this crystal is a
bit over one second. This is a bit short
and I eventually opted for a tried and
tested alternative built around timer
stage IC2.
The time function is supplied by
real time clock stage IC3 (PCF8573),
hereafter referred to as the RTC. This
RTC chip inter
rupts the micro
con
troller every minute. Each time it
receives an interrupt, the microcon
troller reads the RTC and stores the
time in an internal RAM buffer.
After this, it reads 12 bytes of
January 1996 57
set if any of these inputs are activated. The temperature
input (PD4) is read every minute, for one second exactly.
During this time, writes to the LCD and LED flashing
routines are disallowed, so as to prevent incorrect temperature measurements.
Button switches
The button switches are connected directly to the
microcontroller (PD0-PD4 & TCAP). An RC network attached to each pin provides a small amount of debounce,
while the software does the rest.
Buttons S1-S4 (Menu, Cursor, Up, Down) are polled
during the main loop, whereas button S5 (Exit) is connected to the TCAP input. The TCAP pin is an interrupt
pin associated with the internal timer function. In this
application, it is simply used to notify the microcontroller
that the button was pressed in a manner similar to how
a normal interrupt would be used.
Watchdog timer
This circuit comprises a CMOS 7555 IC (IC2), configured as an astable multivibrator but normally prevented
from oscillating. If IC4 is functioning correctly, PA7 (pin
5) is set to a logic 1 within the timer interrupt routine
and cleared in the mainloop. The resulting waveform
continually charges and discharges C14. This means that
Q1 is continually turned on and off, which prevents C4
from charging up and thus disables IC2.
However, if the pulses from PA7 stop due to a spike
causing the program to stop and/or crash, IC2 will begin
to oscillate. After about 10 seconds, its pin 3 output will
pull IC4’s reset pin (pin 1) low via D16, thereby resetting
the microcontroller. Note that the time-out period is set
to 10 seconds to allow for the “dead time” during the
EEPROM read cycle every minute. The timer interrupt
interval is set to 5ms.
Fig.2: install the parts on the PC board as shown here.
Note that IC1, IC3, IC4 & IC11, the relays and the LCD
should not be mounted until after an initial “smoke” test
has been carried out (see text).
EEPROM (IC1 or IC11) associated with cycle 1 of solenoid
8 and compares the stored start times with the current
time and date. It then repeats the process 31 more times
for the other cycles and solenoids (this process takes twice
as long when program C is selected).
The LCD and the two 8-bit latches IC6 & IC7 (74HC573)
share port B as a common data bus. When the micro
controller needs to send data to either latch, pin 11 of
the required latch is pulsed high (by either PA5 or PA6).
At reset, all port pins are initialised as inputs (high Z),
therefore the OE pin (pin 1) of IC7 is held high by R18
until the latch is cleared and PA2 is made an output. This
stops inadvertent operation of any relays until initialisation is complete.
The LCD data is validated by the E pin (pin 6, LCD
connector). As the microcontroller is not required to read
the internal RAM of the LCD display, the R\W pin can be
tied low, which is write mode. VR1 is used to adjust the
contrast of the display.
The two Rain Switch inputs (PD7 & PD5) are tested
during the timer interrupt routine. Appropriate flags are
58 Silicon Chip
The EEPROM
The EEPROM is an 8Kb device, internally organised
as 1024 x 8 bits. Each cycle of each solenoid is allocated
12 bytes of the EEPROM (11 of these are used, with one
spare). Another part of the EEPROM is set aside for storing
“global” variables like the current year, the LED status,
and whether “Rain Mode” is active or not.
Pin 3 (A2) of IC1 and IC11 is an address pin, which
allows two of these chips to be connected onto the same
I2C bus. The A2 pins are connected to either side of S6,
which allows either of the EEPROMs to be switched into
circuit.
The selected EEPROM is read at power up, to determine
which mode it should be in (ie, “RAIN OFF” mode or just
the Default mode) and which LEDs are active. At the next
interrupt from the RTC (IC3), any cycle that satisfies the
“On Time” conditions will be switched on. No settings
will ever be lost!
Real time clock
The RTC chip (IC3) interrupts the microcontroller
every minute, causing it to read the time. IC3 requires a
32.768kHz crystal (commonly called a “watch” crystal)
for its internal dividers. The oscillator can be trimmed
using C12 to provide very accurate time keeping. Note
that the FSET pin (frequency SET) is brought out to a
The switches, the eight station indicator LEDs and the
LCD are all installed on the reverse side of the board.
PC board pin to facilitate easy tuning
using a frequency meter.
When power is lost from the main
circuit, a 3V lithium battery (B1) cuts
in and keeps IC3’s oscillator going.
The battery is held off via D14 and
D13 when normal power is applied to
the circuit. IC3 draws about 7µA when
the power is off.
Note that if the HOURS or MINUTES
setting is altered when setting the time,
the seconds counter in the RTC will be
reset. The DAY and MONTH settings do
not cause the seconds counter to reset
but the HOUR and MINUTE settings are
written to. The YEAR and (P)rogram
settings have no effect on the RTC.
Rain/temperature inputs
The three input circuits are identical and are based on LM393 comparator ICs. VR2-VR4 are used to adjust
the trip voltages, which can vary from
about 0.9V to about 2V. Resistors R3,
R15 & R16 (1MΩ) provide hysteresis
to prevent the outputs from oscillating.
R8, R9 and R10 provide the current
The programmed data in the EEPROM is backed up by a
3V lithium cell. Take care with the orientation of IC4.
feed to the rain switches and temperature sensor circuit. The output circuits
of the rain switch and temperature sensor act as constant current sinks. If the
probes are wet, then the Rain Switch
draws an extra 13mA compared to
when the probes are dry. The current
flows to ground via 68Ω resistors R4,
R14 & R17.
The extra current flowing when
the probes are wet causes the voltage
across these resistors to increase,
which in turn causes the comparator
to trip. Normally, the open collector outputs of the comparators are
held high by 10kΩ pullup resistors.
When they trip, the outputs turn on,
thereby presenting a logic 0 to the
microcontroller port pins (PD7, PD5
& PD4).
The temperature input requires a
frequency that is directly proportional
to the temperature at a resolution of
50Hz/°C. 1000Hz corresponds to 0°C,
2000Hz corresponds to 20°C and so on.
When the temperature sensor is not
connected, the temperature display
will be -19.9°C.
Relay drivers & relays
IC7 drives IC5, a ULN2804 relay
driver IC. This device has open collector outputs and can therefore be
used to drive relays with an operating
voltage different to that specified. To
do this, the component side track
marked “*” (above the battery holder)
must be cut. A wire running off to a
separate power supply is then soldered
into the via on the solder side, about
10mm below the “*”.
The controller can operate all of
the specified relays at once if need
be. Each relay draws about 41mA at
5V. This does not mean that all solenoids should be operated at once,
however. This very much depends on
the transformer that is used to power
your sprinkler system. Most solenoids
draw around 300mA when supplied
by 24V AC.
Diodes D5-D12 form an 8-input
diode AND gate. If any of the relays
(RLY1-RLY8) is (are) switched on,
then the associated diode(s) will also
be forward biased, thereby switching
on RLY9 (the master relay). This relay
January 1996 59
The PC board is mounted on the front panel using 12mm spacers and machine
screws and nuts. Similarly, the lower edge of the LCD module (near the LEDs) is
secured to the PC board using 5mm spacers and machine screws and nuts.
can be used to switch on the master
solenoid in a sprinkler system, or to
start a pump in a rural situation.
Manual operation
In addition to automatic operation,
the solenoids can also be switched on
manually.
To do this, you simply select the
solenoid with the Menu button, then
press the Down button; the selected
solenoid will immediately turn on,
as indicated by the fast flashing LED.
It will subsequently automatically
switch off after the “Run Time” of
cycle 4 (cycle 8 if program C) for that
solenoid has expired.
If the “Run Time” is set to “00”, then
the solenoid will switch off at the next
interrupt from the RTC. Note that this
facility works whether the “RAIN OFF”
mode is active or not.
Construction
Construction of the Rain Brain is
straightforward, since it is supplied
as a complete kit. All the parts
mount on a double-sided PC board
with plated-through holes and a
screened layout overlay, so that you
can see at a glance where the parts
go. As always, eyeball the PC board
for any obvious faults before starting
assembly.
Begin by fitting all the ICs and sockets (except the PLCC socket for IC4).
The RTC IC (IC3) and the EEPROM(s)
(IC1 & IC11) are the only ICs that
require sockets. Do not use sockets
for the other ICs. In particular, IC8
(LM2574-5) absolutely must be sol
dered to the PC board
This done, fit the PLCC socket. This
socket has one corner chamfered and
this must match up with the screened
60 Silicon Chip
The five pushbutton switches are
all mounted in modified 6-pin DIP
sockets on the track side of the board.
Note that two pins of each socket are
removed – see text.
overlay on the PC board. Also pin 1
on the PC board is square, and you
will see a little ridge on the side of the
socket that denotes pin 1. Do not plug
the microcontroller in yet!
The three SIL resistor networks
(R1, R2 and R7) should be installed
next, noting that the pin with the dot
goes into the square hole. Note that
two of these resistor networks are
10kΩ types, while the other is a 1kΩ
type so don’t get them confused. All
three can be either 9-pin or 10-pin
types.
The following parts are mounted on
the solder side of the board: LEDs 1-8
(discussed later), the five 6-pin DIP
sockets, and the 14-pin SIL connector
for the liquid crystal display.
Pins 2 & 5 of the 6-pin DIP sockets
(used to mount the push buttons)
have to be cut out so that they won’t
interfere with the PC board (pushing
the pins out with the hot soldering
iron results a neater job).
Solder in all five sockets, then turn
the board over and fit the battery holder (don’t fit the battery yet). This done,
solder in the 14-pin LCD connector,
remembering that it goes onto the
solder side of the board (along with
the five switch sockets).
Next, fit the four trimpots (VR1VR4) and the trimmer capacitor (C12).
Set VR2, VR3 and VR4 to midway,
then install power supply components IC8, C1, C2, D15 and L3. Note
that the cathode of D15 goes into the
square hole.
The resistors can now all be installed. In particular, install R15 (1MΩ
near pin 1 of IC10) so that its long lead
goes into the top hole. The same goes
for R16 (1MΩ below IC10), while R3
(1MΩ near pin 1 of IC9) should have its
long lead to the left. The reason for this
is that these long leads are used as test
points when adjusting the comparator
trip points.
The capacitors, diodes, the transistor and the two crystals can be fitted
now. You will notice that all the diode
cathode pads have square holes, as do
all the positive pads of the electrolytic
capacitors.
L1 and L2 have small lengths (23mm) of spaghetti sleeving fitted over
their mounting leads so that they
stand proud of the board. If only one
EEPROM is to be installed, solder a
link between the bottom two holes
of S6 (marked SW1 on the screened
overlay). This links the A2 pin of IC1
to ground.
Installing the LEDs
As mentioned earlier, the LEDs are
mounted on the solder side of the
board, so that they match up with
clearance holes in the front panel.
Insert each LED into its position,
remembering that the cathode (short
lead) goes into the square hole but do
not solder any yet.
This done, carefully fix the front
panel to the PC board using 12mm
spacers and machine screws and nuts
– just install two spacers diagonally
opposite each other, as this is only a
temporary operation. Once the panel is
on, manipulate the LEDs so that they fit
into the appropriate holes, then solder
These two photos show typical displays for the Auxiliary Functions menu. At
left, rain sensor 1 has been enabled (1R), the temperature trip point is 10°C, the
three-week cycle mode (W) has been selected, week 1 has been selected (—),
and the sprinkler will turn on every day of this week. In the photo at right, the
continuous schedule (D) mode has been selected and the sprinkler will turn on
every day (01).
them in from the component side and
remove the front panel.
Now fit the fuse clips and the connector blocks to the PC board. Don’t fit
the LCD or the relays yet, as a smoke
test needs to be done first!
Smoke test
Before applying power, ensure
that IC3, IC4, IC1, IC11 (if supplied)
and the LCD have not been fitted.
This done, connect a suitable power
supply to the designated connectors
and switch on.
Now check that 5V is present across
the power supply pins of IC6 (or IC7);
ie, between pins 20 & 10. If so, touch
the top of each IC for a few seconds,
particularly IC8.
All the ICs should be cool to the
touch. If all is well, switch off and plug
in the rest of the ICs. Make sure that
you install the microcontroller around
the right way. The chamfered corner
of the IC must match the chamfered
corner of the socket.
the connector on the main board and
force it down slightly so that it firmly
grips the pins.
Now turn the power on, while
making sure that nothing on the LCD
board can short against the main
board. You should be greeted with
a message telling you to check the
battery, a software version message
for a second or two, and then the time
and date display.
Assuming that all is well, the LCD
can be permanently mounted. The
lower edge of the LCD (near the LEDs)
is secured to the main board using
5mm spacers and machine screws and
nuts. Once these are fitted, judge the
gap at the connector edge and solder
tack a pin. This done, check that the
LCD board is parallel to the controller board, adjust it as necessary, then
solder the rest of the pins.
By the way, all the LCDs are tested
before they are packed into the kits, as
are the microcontrollers. However, it is
still nice to know that it works before
soldering it in as it is an unpleasant
job trying to unsolder them.
The five pushbutton switches can
now be installed by fitting them to
the previously installed DIP sockets
(there’s no need to solder them). Once
they’re in, the plastic switch caps can
be clipped into position.
If you have purchased the additional
memory kit, solder the wires to the
toggle switch, then mount the switch
in a convenient location on the side
of the case. Make sure that this switch
can not foul other parts on the main
board when it is installed in the case.
Now the front panel can be refitted
using the four 12mm spacers provided.
This done, clip the lithium battery into
its holder (positive side up), connect
a power supply and switch on. The
LCD should go through the same routine as above. Once the time has been
programmed into the RTC, the battery
flat message should not show at power
up unless the battery is flat.
Note that, at this stage, the time
display will have miscellaneous characters in the time and date fields.
Memory initialisation
The next step is to put the memory
Where To Buy The Parts
Parts for the Rain Brain Sprinkler Controller are available as follows:
ITEM
Rain Brain Kit (excludes relays)
Relays – FBR211D005M (Price ea.; specify number required)
PRICE
P&P
$175.00
$10.00
$4.50
Installing the LCD
Built & tested (relays extra)
$225.00
$10.00
Before installing the LCD, the six
tabs that secure the metal frame to
the LCD board should be bent over
slightly. This is to prevent possible
contact with any of the leads protruding through the main PC board. Also
check that none of the tabs is shorting
to any of the fine tracks around the
edges of the tab holes.
Next, turn VR1 clockwise until it
stops, so that it is in the full contrast
position. This done, fit the LCD to
Rain switch kit (Price ea.; specify number required)
$25.00
$2.00
Temperature probe kit
$33.00
$2.00
Optional memory kit
$12.00
$2.00
Optional super twist LCD with LED backlight upgrade
$8.00
Note 1: p&p is $10.00 for Rain Brain kit plus any combination of other kits. Individual parts
are also available (POA).
Note 2: Payments by cheque or money order to Mantis Micro Products. Send order to
Graham Blowers, 38 Garnet St, Niddrie, 3402 Vic. Phone/fax (03) 9337 1917.
For COD orders, you pay $4.75 COD charge plus postage at the destination post office. The
Post Office will notify you when the parcel arrives.
January 1996 61
PARTS LIST
1 double-sided PC board, code
SPV6
1 plastic case with screened front
panel
1 P1601 liquid crystal display (H1)
1 BH800 battery holder (BH1)
1 3V lithium battery (B1)
9 5V SPDT relays,
FBR211CD005M (RLY1-9)
2 M205 fuse clips (FH1,FH2)
11A M205 fuse (F1)
2 ferrite (6-hole) inductors (L1,L2)
1 470µH inductor (L3)
1 50kΩ miniature horizontal
trimpot (VR1)
3 10kΩ miniature horizontal
trimpots (VR2-VR4)
1 44-pin PLCC IC socket
1 8-pin DIP socket
1 16-pin IC socket
5 momentary contact pushbutton
switches plus plastic caps (S1S5)
5 6-pin DIP sockets (for switches)
4 15mm x 3mm dia. machine
screws plus nuts
4 12mm x 3mm dia. spacers
2 5mm x 3mm dia. spacers
1 14-way connector (X1, for LCD)
1 6-way terminal block (X2)
4 3-way terminal blocks (X3-X6)
2 PC pins (X7,X8)
Semiconductors
1 CAT24C08P EEPROM (IC1)
1 LM7555 CMOS timer (IC2)
1 PCF8573P real time clock (IC3)
1 MC68HC705C8FN
microcontroller (IC4)
into a known state. To do this, turn off
the power, hold down the Menu and
Cursor (⇒) buttons, and turn the power
back on. This time, the LCD will tell
you to press the Menu button. Once
this is done, the “Config” menu will
be displayed. This consists of three
options:
(1). “M” is memory initialisation.
Press the Down (⇓) button to ini
tialise the memory. As each block of
16 bytes is initialised, a LED lights.
The LEDs chase each other from left
to right, eight times. This routine also
acts as a fault locater. If more than
one LED lights at the same time, then
there is a short circuit on the port B
62 Silicon Chip
1 ULN2804 8-channel driver (IC5)
2 74HC573 latches (IC6,IC7)
1 LM2574-5 5V switching
regulator (IC8)
2 LM393 dual op amps (IC9,IC10)
1 BC548 transistor (Q1)
4 1N4004 silicon diodes (D1-D4)
11 1N4148 silicon diodes (D5D14,D16)
1 MUR120RL fast recovery diode
(D15)
8 3mm red LEDs (LED1-8)
1 32.768kHz crystal (Xtal1)
1 3.579545MHz crystal (Xtal2)
Capacitors
1 1000µF 16VW electrolytic (C2)
1 220µF 63VW electrolytic (C1)
4 10µF 10VW electrolytic
(C3,C4,C10,C11)
1 1µF 10VW electrolytic (C13)
10 0.1µF monolithic (C5-8,C1418,C20)
2 27pF monolithic (C9,C19)
1 3-40pF trimmer capacitor (C12)
Resistors (0.25W, 1%)
1 10MΩ
5 2.2kΩ
4 1MΩ
1 1kΩ
1 33kΩ
3 470Ω 1W
5 10kΩ
3 68Ω
1 4.7kΩ
2 10kΩ SIL resistor networks
1 1kΩ SIL resistor network
Optional memory kit
1 CAT24C08P EEPROM (IC11)
1 8-pin DIP IC socket
1 SPDT switch (S6)
data bus.
Each cycle is set to 00:00:00 which is
actually a start time of midnight, with
a run time of 00 minutes. All cycles
and both rain switches are enabled.
The temperature trip point is off. The
3-week cycle is active, with all days
set to on (uppercase).
(2). Press the Cursor (⇒) button to
move to the next option (A) which is
the VR4 adjusting mode. This mode
continually reads the temperature and
displays the result. If VR4 is adjusted
correctly, the display will show a
steady temperature. How to do this
is included as part of the temperature
sensor kit.
(3). D is the default display setting.
A “D” indicates that the date will be
displayed in the default display. A
“T” means that the temperature will
be displayed instead of the date. Press
the Down (⇓) button to toggle from
“D” to “T”.
Adjustments
The contrast pot (VR1) should already be set up. The range isn’t very
broad, so maximum is probably the
best to start with (fully clockwise). The
other pots (VR2-VR4) were originally
set during construction.
Assuming that you are using the optional Mantis Rain Switches (available
from the author), VR2 and VR3 can be
further adjusted to set the trip voltages to 1.5V. This can be monitored by
connecting the positive lead of your
meter to the top lead of R15 for Rain
Switch 1 (VR2), or to the top lead of
R16 for Rain Switch 2 (VR3).
To adjust IC3’s oscillator, connect
a frequency meter to the pin marked
“128Hz” (X7) and the ground lead to
the GND pin (X8) nearby. Now tune
C12 until a display of “128.0000 Hz”
is obtained. Note that the frequency
counters built into some multimeters
will probably prove unsuitable, as
they do not have the resolution required.
If a frequency meter is unavailable,
check the time against a known good
source and tweak the trimmer until
the unit keeps good time.
Installation
The case is not waterproof, so
mount it on a wall in the garage or in
some other sheltered location. If you
must have it outside, the controller
will have to be installed in a waterproof case.
You will have to drill two rows of
five holes (5mm dia.) in the bottom
of the case to provide access for the
external wiring. Position one row close
to the back of the case and the other
row about 5mm away.
Programming
At first sight, programming this controller may seem a little daunting but
it only takes about 20 minutes to get
the hang of things. If you can program
a VCR, you can program this device.
We don’t have space to include
the programming instructions here
but full instructions will be supplied
SC
with the kit.
PRODUCT SHOWCASE
Tektronix P5200 high-voltage
differential probe
The measurement of high voltage or AC
mains voltage signals presents problems
that are not easily overcome with standard
dual channel oscilloscopes. One solution
is to use a Tektronix P5200 high voltage
differential probe.
The attenuators of most general
purpose oscilloscopes pro
v ide a
maximum input sensitivity of 5V/
division. With the screen displaying
eight vertical divisions this means
that the maximum input signal can
only be 40V peak-to-peak with a direct
probe or 400V peak-to-peak using a
10:1 divider probe. Larger signals
can be displayed using the variable
input control but then the amplitude
measurement facility is lost.
If the signal to be measured is a
mains AC waveform or other higher
voltage which is not ground referenced then it can be displayed using
a dual trace oscilloscope in the Add
mode. Once again the maximum calibrated display voltage will be 400V
peak to peak. As an alternative, some
organisations adopt the practice of
using an oscilloscope with its mains
earth disconnected to display floating
and mains voltages. This is a highly
dangerous procedure with nothing to
recommend it.
Displaying the mains voltage waveform using a regular probe with the
tip connected to the active lead and
the earth clip connected to the neutral is also a dangerous procedure.
Transposition of the live and neutral
connections to the probe is always
a possibility and if this mistake is
made then the best that can happen
is a blown fuse and the worst is electrocution.
What is really required is an instrument with a differential input, some
level of signal attenuation and
a single ended output signal to
apply to the following measuring equipment. To cater for
signals with fast rising wave
fronts – eg; SCR circuits,
switchmode supplies, etc – it
should also have a wide bandwidth and fast rise time.
The Tektronix P5200 high
voltage differential probe
meets all these requirements
and allows the aforementioned measurements to be
made easily and safely. It is
supplied with two sets of
connectors and a 9VDC 1A
plugpack power supply. One
Table 1: Specifications
Maximum applied voltage between either input and ground............ 1kV (DC + peak AC)
Maximum applied voltage between inputs.................................... 1.3kV (DC + peak AC)
Rise time .........................................................................................<14ns in 1/50 range
DC CMRR .........................................................................................>5000:1 at 500VDC
AC CMRR................................................ 60Hz >10000:1; 100kHz >300:1; 1MHz >300:1
Bandwidth ..................................................................DC to 25MHz (-3dB) in 1/50 range
Maximum operating input voltage.................... 1/500 differential 1.3kV (DC + AC peak);
1/500 common mode, 1kV (DC + AC peak); 1/50 differential, 130V (DC +
AC peak); 1/50 common mode, 1kV (DC + AC peak)
Range accuracy................................... ±3% between 20-30°C after 20 minute warmup.
Input impedance........... 8MΩ + 3.5pF between inputs; 4MΩ +7pF each input to ground
DC output drift............................................................................................... ±0.5mV/°C
Propagation delay.................................................................................................... 20ns
Operating temperature range ............................................................................... 0-40°C
January 1996 63
pair of connectors are long reach
plunger probes and the other pair
are heavy duty, double insulated
crocodile clips.
Its dimensions are 185mm (L) x
66mm (W) x 32mm (H). Two 500mm
long input connectors are at one end
of the case and these are terminated
with shrouded plugs to fit the probe
connectors. At the other end of the
case is a 1500mm long output lead
termi
n ated with a moulded plug
that carries an input socket for the
plugpack and a 300mm long coaxial
lead terminated with a BNC male plug
to supply output to the measuring
instrument which will usually be an
oscilloscope.
The face of the probe case features
a pushbutton switch which provides
1/500 or 1/50 attenuation to the input
signal. There are also LEDs for Power
and Over Range and a table showing
the effective volts/division of the
combined probe plus oscilloscope for
different settings of the oscilloscope’s
input attenuator. Output level from the
probe is a maximum of 2.6V.
The specifications for the P5200 are
shown in Table 1.
We used a sample P5200 in our
laboratory and found that it does all
that is claimed for it. It enables safe
and accurate measurements when the
source is not referenced to ground,
par
t icularly where mains voltage
signals are concerned. In addition, it
offers a much higher common mode
rejection ratio than any typical dual
channel oscilloscope when used
in the “Add” mode – an important
advantage.
The Tektronix P5200 is priced at
$658 plus sales tax where applicable.
For further information, contact Tek
tronix Australia Pty Ltd, 80 Waterloo
Rd, North Ryde, NSW 2113. Phone (02)
888 7066 or fax (02) 888 0125.
Fast-charger IC for
lead-acid batteries
Reptechnic has introduced the
Benchmarq bq2031 lead acid fast
charge IC. This incorporates current
and voltage regulation with fast charge
control to produce a highly cost effective fast charge system.
Available in a 16-pin narrow DIP or
SOIC package, the bq2031 is designed
for controlling constant voltage and
constant current charging of lead acid
batteries in emergency lighting, backup power, industrial equipment and
consumer electronics applications. It
can be configured for linear or gated
current regulation applications.
The bq2031 meets the battery manufacturers’ charge recommendations
for both cyclic and float/maintenance
charge. It includes a flexible pulse
width modulation regulator which
is suitable for high efficiency switch
mode designs. Direct LED control outputs are featured for displaying charge
status and fault conditions.
Pre-charge qualification tests have
been per
formed on the device for
shorted, open or damaged cells, allow
ing it to condition the battery for fast
charge. Charging is also qualified by
selectable temperature and voltage
KITS-R-US
PO Box 314 Blackwood SA 5051 Ph 018 806794
TRANSMITTER KITS
$49: a simple to build 2.5 watt free running CD level input, FM band runs from 12-24VDC.
•• FMTX1
FMTX2B $49: the best transmitter on the market, FM-Band XTAL locked on 100MHz. CD level input 3
stage design, very stable up to 30mW RF output.
$49: a universal digital stereo encoder for use on either of our transmitters. XTAL locked.
•• FMTX2A
FMTX5 $99: both FMTX2A & FMTX2B on one PCB.
FMTX10 $599: a complete FMTX5 built and tested, enclosed in a quality case with plugpack, DIN input
•connector
for audio and a 1/2mtr internal antenna, also available in 1U rack mount with balanced cannon
input sockets, dual VU meter and BNC RF $1299. Ideal for cable FM or broadcast transmission over
distances of up to 300 mtrs, i.e. drive-in theatres, sports arenas, football grounds up to 50mW RF out.
FMTX10B $2599: same as rack mount version but also includes dual SCA coder with 67 & 92KHz
subcarriers.
•
AUDIO
Audio Power Amp: this has been the most popular kit of all time with some 24,000 PCBs being
•soldDIGI-125
since 1987. Easy to build, small in size, high power, clever design, uses KISS principle. Manufacturing
rights available with full technical support and PCB CAD artwork available to companies for a small royalty.
200 Watt Kit $29, PCB only $4.95.
AEM 35 Watt Single Chip Audio Power Amp $19.95: this is an ideal amp for the beginner to construct;
uses an LM1875 chip and a few parts on a 1 inch square PCB.
Low Distortion Balanced Line Audio Oscillator Kit $69: designed to pump out line up tone around studio
complexes at 400Hz or any other audio frequency you wish to us. Maximum output +21dBm.
MONO Audio DA Amp Kit, 15 splits: $69.
Universal BALUN Balanced Line Converter Kit $69: converts what you have to what you want, unbalanced
to balanced or vice versa. Adjustable gain. Stereo.
•
•
••
COMPUTERS
I/O Card for PCs Kit $169: originally published in Silicon Chip, this is a real low cost way to interface
•to Max
the outside world from your PC, 7 relays, 8 TTL inputs, ADC & DAC, stepper motor drive/open collector
1 amp outputs. Sample software in basic supplied on disk.
PC 8255 24 Line I/O Card Kit $69, PCB $39: described in ETI, this board is easy to construct with
•onlyIBM3 chips
and a double sided plated through hole PCB. Any of the 24 lines can be used as an input or
output. Good value.
19" Rack Mount PC Case: $999.
•• Professional
All-In-One 486SLC-33 CPU Board $799: includes dual serial, games, printer floppy & IDE hard disk drive
interface, up to 4mb RAM 1/2 size card.
PC104 486SLC CPU Board with 2Mb RAM included: 2 serial, printer, floppy & IDE hard disk $999; VGA
•PC104
card $399.
KIT WARRANTY – CHECK THIS OUT!!!
If your kit does not work, provided good workmanship has been applied in assembly and all original parts
have been correctly assembled, we will repair your kit FREE if returned within 14 days of purchase. Your
only cost is postage both ways. Now, that’s a WARRANTY!
KITS-R-US sell the entire range of designs by Graham Dicker. The designer has not extended his agreement
with the previous distributor, PC Computers, in Adelaide. All products can be purchased with Visa/Bankcard
by phone and shipped overnight via Australia EXPRESS POST for $6.80 per order. You can speak to the
designer Mon-Fri direct from 6-7pm or place orders 24 hours a day on: PH 018 80 6794; FAX 08 270 3175.
64 Silicon Chip
AV-COMM PTY LTD
www.avcomm.com.au
PCB POWER
TRANSFORMERS
1VA to 25VA
allow designers to experiment with
the bq2031. For further information,
contact Reptechnic, 3/36 Bydown St,
Neutral Bay, NSW 2089. Phone (02)
9953 9844.
Jaycar kits now made
under AS9002
Manufactured in Australia
Harbuch Electronics Pty Ltd
9/40 Leighton Pl. HORNSBY 2077
Ph (02) 476-5854 Fx (02) 476-3231
limits. Key specifications include
temperature, float voltage reference,
pin selectable charge and maintenance
modes, and pin selectable charge
termination by maximum threshold
voltage, minimum current and maximum time.
A switchmode development system, the DV2031S1, is available to
Pocket-sized fax
machine & organiser
Now available at Dick Smith Electronics, the Handifax 1000 is a 256K
electronic personal organiser and fax
machine in one. In a lightweight, compact 72 x 198mm unit, Handifax 1000
gives you the capability of faxing your
colleagues and clients anywhere, any
time, by simply using it in conjunction
with a standard touch tone telephone
or analog mobile phone.
Simply type the message you want
to fax, place the handset of the tele
phone or mobile phone on the acoustic
The head office, warehouse and kit
department of Jaycar Electronics has
successfully passed all requirements
and has been accredited to AS/NZ ISO
9002:1994.
“We realised that sooner or later
we would have to seek this level of
quality of management, documentation and quality control,” commented
Managing Director, Gary Johnston. “As
it turned out, our existing organisation was close to the high standards
required anyway, so achieving the
AS9002 level of quality was not particularly difficult. Our kits have always
been very high quality. Now we have
independent proof that they are.”
According to Mr Johnston, the
quality accreditation is part of an
ongoing commitment by Jaycar to
provide a high standard of service in
the industry.
YOU CAN
AFFORD
AN INTERNATIONAL
SATELLITE TV
SYSTEM
SATELLITE ENTHUSIASTS
STARTER KIT
YOUR OWN INTERNATIONAL
SYSTEM FROM ONLY:
FREE RECEPTION FROM
Asiasat II, Gorizont, Palapa,
Panamsat, Intelsat
coupler speaker and microphone, dial
the fax machine you are calling and
press SEND.
Handifax 1000 can communicate
with any standard fax machine at
speeds of up to 9600 bps. Quick and
simple to use, it will hold up to 120
faxable pages and its auto dialling
facility ensures that there is no need
to manually dial numbers or access
codes. The unit has built-in fax cover
pages and the ability to customise fax
headers, standard orders, invoices, etc.
With a 256K memory, Handifax
1000 also doubles as a personal organiser, capable of storing more than
3500 entries. A 7-digit
password can be used to
protect all data. An optional PC interface allows
users to back up and store
information on any standard IBM compatible PC.
The Handifax comes
complete with an operation manual, an instruction video and is
available at all Dick Smith
Electronics stores for just
SC
$699.
HERE'S WHAT YOU GET:
●
●
●
●
●
●
400 channel dual input receiver
preprogrammed for all viewable satellites
1.8m solid ground mount dish
20°K LNBF
25m coaxial cable
easy set up instructions
regular customer newsletters
BEWARE OF IMITATORS
Direct Importer: AV-COMM PTY. LTD.
PO BOX 225, Balgowlah NSW 2093
Tel: (02) 9949 7417 / 9948 2667
Fax: (02) 9949 7095
VISIT OUR INTERNET SITE http://www.avcomm.com.au
YES GARRY, please send me more
information on international band
satellite systems.
Name: __________________________________
Address: ________________________________
____________________P'code:
__________
Phone: (_______) ________________________
ACN 002 174 478
January 1996 65
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.altronics.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.altronics.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.altronics.com.au
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January 1996 69
IR remote control for
the Railpower Mk.2
This remote control gives you complete
freedom of operation for the Railpower
Mk.2 train controller. It has pushbutton
control for everything & pulls negligible
current when not in use.
By RICK WALTERS
As presented in the September &
October 1995 issues, the Railpower
Mk.2 is a walkaround throttle. It
allows you to follow your trains as
they go around the layout. As such, it
performs very well. But perhaps you
don’t like being tethered by a remote
control cable. If so, you will want this
infrared remote control. It operates just
like any other remote and is based on
70 Silicon Chip
the same microprocessor used in the
Railpower Mk.2.
The remote control handpiece has
six pushbuttons but does not have
the meter which was included in the
walkaround hand control. Instead,
we have designed a small PC board
which has an array of 10 LEDs, to give
an indication of train speed. This is
mounted inside the main unit, along
with a small PC board for the infrared
receiver.
The remote control uses the same
plastic case as for the walkaround
hand control. It contains a small PC
board (coded 09101961) and a battery.
The board contains six pushbuttons,
three transistors, one IC, one crystal
and a few other components.
As you can see from the circuit of
Fig.1, the battery is connected all the
time, as is standard practice in all
infrared remote controls. But instead
of a dedicated IC as found in most remote controls, we have used a Z86E08
microprocessor.
To conserve the battery, we have
used a feature which was not previously exploited. The Z86E08 is a
CMOS device and normally does not
draw much current but for battery
operation, it can be put into a “sleep”
mode, whereby the current it draws
Fig.1: the transmitter circuit. This uses a Z86E08 microprocessor to produce
coded IR pulses when the buttons are being pressed. When the buttons are not
being pressed, the microprocessor goes into sleep mode to conserve the battery.
is only 10µA. This greatly increases
the battery life.
When IC1 is put to sleep. it takes
pins 16, 17 & 18 high (ie, to the battery
positive line, +4.5V). Later, when any
button is pressed, R0 or R1 (ie, row
zero or row one of the pushbutton
matrix) will go high, turning on transistor Q1 via diode D1 or D2. Q1 pulls
pin 4 of IC1 low, to “wake it up”, after
which it takes pins 16, 17 & 18 low
and scans the buttons to see which
one was pressed.
C3 (column 3), the input to the
INERTIA button, is high and if this
is pressed, pin 9 of IC1 will go high.
If this button is not pressed the processor then takes pin 16 (C2) high.
As you can see from the circuit, the
STOP or FASTER button, if pressed,
will take pin 8 or pin 9 of IC1 high
and the code for this button will be
sent. Pins 17 and 18 are taken high in
sequence and if any of the remaining
buttons are pressed, their code will
be transmitted.
The pulse code appears on pin 3
of IC1 and turns Q2 and thus Q3 on
and off. Q3 pulses two infrared LEDs
(LED1 and LED2).
Remember, only one button is press
ed at a time and the code for this button
will be sent many times before you can
release it. With the jumpers set on 1,1
a burst of code takes 20 milliseconds
to be sent.
Each time the processor finishes a
scan, it takes all column outputs high
(C0-C3) and looks at the collector of
Q1. If it is low, indicating a button is
pressed, it will scan the buttons again;
if high, it will go into sleep mode to
conserve the batteries.
The RATE links A and B must be
the same in the transmitter and the
Below: this photo shows the
completed IR receiver board being
installed in the Railpower case.
Note the mounting details for the
Acknowledge LED and the LT536
infrared diode (PD1).
January 1996 71
Fig.2: the IR receiver circuit. This uses two cascode transistor stages (Q1, Q2
and Q4, Q5) with AGC to provide the necessary large gain for the photodiode
signal. The signal decoding is done by IC4, a Z86E08 microcontroller
programmed for this purpose.
receiver. These links could allow you
to have one hand control with a 3-position selector switch and this could
control three Railpower IR receivers,
each with a different rate setting.
Infrared receiver
The infrared receiver consists of
photodiode PD1, cur
rent-to-voltage
converter IC1, two cascode transistor amplifiers (Q1, Q2 and Q4, Q5)
with AGC (automatic gain control), a
comparator and AGC detector (IC2),
a pulse stretcher (IC3) and a data
decoder, IC4. These are all mounted
on a PC board (coded 09101962)
which is housed in the case of the
72 Silicon Chip
Railpower controller. The circuit is
shown in Fig.2.
Photodiode PD1 sees the IR pulses
emitted by the remote control and
varies its current accordingly. This
variation in current is converted to
voltage pulses by op amp IC1 which
drives the base of Q1 via a .015µF
capacitor.
The pulses from IC1 can vary from
around 0.2V peak-peak when the remote control is close to PD1 to being
lost in the noise when it is some distance away. For this reason, we need
a lot of gain for weak signals but not
very much for the stronger ones. We
obtain lots of gain by using cascode
circuits and then we use automatic
gain control (AGC) on both to cope
with large signals.
Gain control
The two cascode circuits are similar, the first using PNP transistors
Q1 & Q2, the second using NPN
transistors Q4 & Q5. AGC is applied
to the first pair by FET Q3, while
FET Q6 applies AGC to the second
cascode pair.
The gain of the first cascode stage,
with Q3 turned off, is around 3.3 while
the gain of the second stage, with Q6
turned off, is 2.2 giving an overall gain
of 7.3 (3.3 x 2.2). With Q3 & Q6 turned
on fully, the gain of each cascode
stage can be in excess of 200, giving
an overall gain of 40,000 or more for
very small input signals.
PARTS LIST
Remote Control Transmitter
1 PC board, code 09101961, 85
x 50mm
1 plastic case (Jaycar HB-6032
or equivalent)
1 4MHz crystal (HC18, HC49)
2 yellow PC mount momentary
switches (Jaycar SP-0722 or
equivalent)
1 red PC mount momentary
switch (Jaycar SP-0720 or
equivalent)
1 black PC mount momentary
switch (Jaycar SP-0721 or
equivalent)
1 white PC mount momentary
switch (Jaycar SP-0723 or
equivalent)
1 green PC mount momentary
switch (Jaycar SP-0722 or
equivalent)
1 single AA cell holder (see text)
3 L1154 alkaline batteries
1 18 pin IC socket (optional)
4 #8 x 10mm self-tapping screws
4 5mm untapped spacers
1 100mm-length red wire
1 100mm-length black wire
1 50mm-length 1mm sleeving
Semiconductors
1 Z86E08 programmed TXA (IC1)
2 1N914 signal diodes (D1,D2)
2 BC338 NPN transistors (Q1,Q2)
1 BC640 PNP transistor (Q3)
2 CQY89A LED (or equivalent)
Capacitors
1 100µF 16VW electrolytic
2 0.1µF 50VW monolithic
2 22pF ceramic
In practice, the output signal from
the collector of Q5 is monitored by
IC2b which is connected as a peak
rectifier. With no input signal present,
pin 2 of IC2b is pulled high by the
47kΩ resistor connected to the +5V
rail. Negative-going pulse signals at
the collector of Q5 cause IC2b and
its associated diode D1 to pull pin 2
towards 0V and hence discharge the
100µF capacitor. Thus, the gates of Q3
& Q6 tend to be taken high for small
signals, to increase the gain. Conversely, large signals tend to result in the
gates of Q3 & Q6 going toward 0V, to
Resistors (0.25W, 1%)
4 100kΩ
1 470Ω
1 22kΩ
1 100Ω
1 10kΩ
2 1Ω
1 1kΩ
IR Receiver Board
1 PC board, code 0911X951, 120
x 50mm
1 4MHz crystal (HC18,HC49)
1 18-pin IC socket (optional)
2 3mm x 15mm threaded spacer
2 3mm x 10mm screw
2 3mm x 6mm screw
1 200mm-length black hook-up
wire
1 200mm-length red hook-up wire
1 200mm-length orange hook-up
wire
1 200mm-length yellow hook-up
wire
1 200mm-length green hook-up
wire
Semiconductors
1 TL071 op amp (IC1)
1 TL072 dual op amp (IC2)
1 74HC132 quad 2-input NAND
gate (IC3)
1 Z86E08 programmed RXB (IC4)
2 2N2907 PNP transistors
(Q1,Q2)
2 BC549 NPN transistors (Q4,Q5)
2 BS170 FET (Q3,Q6)
1 LT536 photodiode (PD1)
1 1N914 signal diode (D1)
1 5mm red LED (LED1)
Capacitors
1 100µF 16VW electrolytic
3 10µF 50VW electrolytic
turn them off and reduce the gain.
In practice, the circuit continuously
varies its gain so that the signal amplitude at the collector of Q5 is more
or less constant.
Q3 & Q6 are connected to the emitters of their respective cascode stages
via 0.1µF capacitors. This means that
the gain of the cascodes increases at
high frequencies but not at 50Hz or
100Hz, to reduce any interference from
incandescent or fluorescent lights.
IC2a is connected as a comparator
and compares the signal from the
collector of Q5 with the DC voltage at
6 0.1µF 50VW monolithic
1 .015µF 100VW MKT polyester
1 .01µF 100VW MKT polyester
1 .001µF 100VW MKT polyester
1 820pF disc ceramic
1 680pF disc ceramic
2 22pF capacitors
Resistors (0.25W, 1%)
1 220kΩ
1 18kΩ
3 100kΩ
3 10kΩ
1 68kΩ
1 3.3kΩ
2 56kΩ
1 2.2kΩ
2 47kΩ
2 1kΩ
3 33kΩ
1 470Ω
3 22kΩ
Speed Display Board
1 PC board, code 09101963, 65
x 50mm
1 5kΩ horizontal trimpot (VR1)
1 1kΩ horizontal trimpot (VR2)
Semiconductors
1 LM3914 bargraph driver (IC1)
1 10-LED display (Jaycar ZD1700)
Capacitors
1 10µF 50VW electrolytic
1 1µF 16VW electrolytic
1 0.1µF monolithic
Resistors (0.25W, 1%)
1 100kΩ
1 4.7kΩ
1 15kΩ
1 820Ω
1 15kΩ 9-resistor array (10-pin
SIP)
Miscellaneous
Hookup wire, PC stakes.
its pin 5. It effectively squares up the
signal pulses and removes any residual
noise. IC2a drives IC3, a CMOS quad
NAND gate which is used as a pulse
stretcher. This allows us to supply a
consistent pulse width to IC4, regardless of the output of IC2a.
Data decoder
IC4 is another Z86E08 microprocessor which has been programmed
to accept the IR data transmitted by
the hand control and convert it to the
correct code on pins 15, 16 & 17 to
operate the Railpower functions. The
January 1996 73
This topside view of the remote control transmitter board shows how the crystal
is laid flat. Make sure that the two IR LEDs are correctly oriented.
Fig.3: the component layout for the
transmitter PC board. Note the three
capacitors mounted on the underside
of the board. These are shown dotted
within the outline for IC1.
microprocessor stores two consecutive codes from the transmitter and
compares them. If they are identical,
it will send the information to the
Railpower; if they differ, it will ignore
them and compare the next two codes
received. As mentioned previously,
the rate links on the receiver must be
the same as those on the transmitter.
The three output lines from IC4 are
This view inside the completed transmitter shows the mounting details for the
three capacitors on the copper side of the board. Note the modified AA cell
holder for the three button cells.
Fig.4: the component
overlay for the IR
receiver board. Note that
the rate links on this
board must match the
rate link settings on the
transmitter PC board.
74 Silicon Chip
This view shows how the IR receiver board is mounted vertically along one side of the Railpower Mk.2
case, while the speed board is mounted upside down, with the LEDs protruding through the front panel.
RESISTOR COLOUR CODES
❏
No.
❏ 1
❏ 8
❏ 1
❏ 2
❏ 2
❏ 3
❏ 4
❏ 1
❏ 1
❏ 4
❏ 1
❏ 1
❏ 1
❏ 3
❏ 1
❏ 2
❏ 1
❏ 2
Value
220kΩ
100kΩ
68kΩ
56kΩ
47kΩ
33kΩ
22kΩ
18kΩ
15kΩ
10kΩ
4.7kΩ
3.3kΩ
2.2kΩ
1kΩ
820Ω
470Ω
100Ω
1Ω
4-Band Code (1%)
red red yellow brown
brown black yellow brown
blue grey orange brown
green blue orange brown
yellow violet orange brown
orange orange orange brown
red red orange brown
brown grey orange brown
brown green orange brown
brown black orange brown
yellow violet red brown
orange orange red brown
red red red brown
brown black red brown
grey red brown brown
yellow violet brown brown
brown black brown brown
brown black gold gold
5-Band Code (1%)
red red black orange brown
brown black black orange brown
blue grey black red brown
green blue black red brown
yellow violet black red brown
orange orange black red brown
red red black red brown
brown grey black red brown
brown green black red brown
brown black black red brown
yellow violet black brown brown
orange orange black brown brown
red red black brown brown
brown black black brown brown
grey red black black brown
yellow violet black black brown
brown black black black brown
brown black black silver brown
January 1996 75
Adding A Speed Meter To The Railpower Mk.2
Fig.5: the speed meter is a conventional LM3914 LED bargraph circuit. It takes the place
of the analog meter in the original walkaround control for the Railpower Mk.2.
If you wish to add a speed meter to the Railpower Mk.2, then
use the LED bargraph display we
have designed. It sits above the
LED indicators on the front panel
of the main unit and consists of a
bar of 10 red LEDs. It is a standard
circuit employing an LM3914 LED
bargraph display driver. The two
preset potentiometers on this board
are adjusted in a similar manner to
the meter setup in the hand control.
The circuit is shown in Fig.5 while
the component overlay for the PC
board (coded 09101963) is shown
in Fig.6.
Fit the IC, SIP and resistors, then
the capacitors and potentiometers.
If you wish, you can solder the
potentiometers on the copper side
of the board, as we have done, to
make them easy to adjust.
Connect a red wire to the +17V,
orange to the +5V, black to the
ground and yellow to the input
terminal, as shown on the layout.
The other end of the red wire connects to +17V on the main board
(REG1 input), the orange to +5V
(REG1 output) and the black wire
to ground. The other end of the
yellow wire should be soldered to
pin 4 of IC1 (top of VR5).
connected to IC1 in the Railpower
unit.
handpiece and the IR receiver board.
As mentioned previously, we have
also designed an optional LED bar
graph speed indicator which takes the
place of the speed meter in the original
walkaround hand control.
Let’s start with the remote control
transmitter PC board. Its component
layout is shown in Fig.3. Check the
board for open circuit tracks or shorts,
especially the track that passes between pins 7 and 8 of IC1. While you’re
at it, check the other two boards for
any etching problems and make any
fixes as required.
The first step is to mount the blank
board in the plastic case. It goes in the
half with the brass inserts (the front),
with the copper side of the PC board
facing up.
A small hole has been drilled at the
centre of each group of four pushbutton pads to allow you to drill pilot
holes through into the case front for
the six pushbuttons. When you have
drilled them, remove the board from
the case. (By the way, these pilot holes
are not present in the photo of our
prototype).
Fit the two long and two short links
Construction
In discussing the construction, we
will assume that you have already
built the Railpower Mk.2, as described
in the Sep
tember & October 1995
issues. We will also assume that you
have built up the original wired hand
control and have made everything
function as described in the setup
procedure.
To add the infrared remote control,
you need to build the remote control
76 Silicon Chip
Calibration
Once the maximum and minimum speeds have been set satisfac
torily on the main Railpower PC
board, FORWARD should be se-
This assembled speed meter shows nine discrete
resistors instead of the specified SIP resistor array.
lected and the minimum pot (VR2)
on this board set so that the first
LED lights. The controller should
then be taken to full speed and the
maximum pot (VR1) adjusted so
that LED number 10 is lit. There is
a small amount of interaction and
the adjustments may have to be
made several times to get it right.
As an alternative to the speed
bargraph, there is no reason why
you could not mount the original
walkaround control meter in the
front panel, fitting a meter zero
adjust control the same as in the
handpiece and taking the positive
meter wire to pin 2 on the DIN
socket.
at the LED end of the board and the
two rate links. We suggest you initially
code it 1,1 as shown on the overlay,
as this gives the fastest transmission
rate. Next, fit and solder the diodes and
resistors, followed by the transistors,
capacitors and crystal. Push the transistors well down so that they are only
about 2mm off the board. Bend the
crystal’s leads at right angles and lie
it down flat. The electrolytic capacitor
should also lie flat on the board.
Lastly, fit the pushbuttons, noting
that all the flats face in the same direction (towards the rate links). Do not
The two adjustment pots are mounted on the underside
of the speed meter board for easy access.
Fig.6 (right): install the
parts on the speed meter
PC board as shown in this
wiring diagram. Check that
all the LEDs are correctly
oriented and note the
mounting details for VR1
and VR2 (see photo above
right).
fit the LEDs as this will be done later.
If you elected not to use an IC socket,
fit and solder the IC marked TXA (this
Z86E08 has been programmed as the
transmitter); otherwise, solder in the
IC socket. In either case, be sure to
check the orientation of pin 1.
As the PC board is rather small, we
elected to mount three capacitors on
the copper side. These can be fitted
now. The 0.1µF monolithic type is
soldered from pin 5 to pin 14, then
laid flat against the board towards the
pin 1 end. The two 22pF capacitors
are soldered from pin 6 to pin 13 and
from pin 7 to the pad on the copper
track between pin 13 and pin 10. Both
are laid flat, facing towards the other
end of the socket. These details can be
checked in the relevant photo.
Battery holder
The battery consists of three 1.5V
button cells in series. These are held
in a half-sized holder made out of a
single AA cell holder. Cut the battery
holder in half with a saw or sharp knife
about 28mm from the spring end. Our
holder had a moulded ridge at this
point. Carefully cut the non-spring
January 1996 77
plastic end out of the holder and locate it in the piece with the spring to
make a half-size unit. The easiest way
to retain the end is to melt the plastic
with your soldering iron. If you do
this inside and out, the end will be
held firmly in place. Alternatively, you
can do a neater job if you have access
to ACC adhesive as used in plastic
model making). Solder a red wire to
the spring end and a black wire to the
other end, then connect the red to the
positive supply terminal on the PC
board and the black wire to the nega
tive terminal.
Now drill one of the case end pieces
to take the IR LEDs. Drill two 5mm
holes on the horizontal centreline
and 7.5mm either side of the vertical
centreline. Slip 10mm of 1mm-dia.
sleeving over each long LED lead, sit
the PC board and LEDs in the case
and bend the leads so that 2-3mm of
each LED protrudes through the end
piece. The longer sleeved lead should
be on the right when viewed from the
component side.
Once you are satisfied, solder in the
LEDs, insert the IC if you used a socket
and fit the board in the case using the
self-tapping screws and spacers. The
battery holder can be kept in place
with a dab of BLU-TACK® adhesive.
Receiver board
The component layout for the receiver board is shown in Fig.4. Start
by fitting the one link and the resistors.
Next, fit the ICs, using a socket for IC4
if you prefer. Make sure that all the
ICs are correctly oriented. This done,
solder in the MKT capaci
tors, the
transistors, electrolytic capacitors and
finally the crystal. Don’t mount PD1 or
the acknowledge LED yet.
RAILPOWER
SLOWER
FASTER
REVERSE
FORWARD
leads so that it protrudes satisfactorily
through the front panel. Locate the sensor centrally behind the rectangular
cutout. Both anodes (longer lead) are
towards the top of the PC board. When
you are satisfied with their positions,
solder them both in place.
Solder the black wire to the centre
pin of REG1 (ground) and the red wire
to the output pin of REG1 (+5V). The
orange wire should be soldered to pin
1 of IC1, the yellow to pin 2 and the
green to pin 3.
Reassemble the unit and after applying power, check that the walkaround
control still operates. If it doesn’t, the
most likely cause is a short between
pins 1, 2 or 3 on IC1.
Testing
INERTIA
STOP
Fig.7: the full-size artwork for the
remote control front panel.
Fit 200mm lengths of hook-up wire
to the board, in the wire colours as
shown in Fig.4, for the signal output
and supply connections. This done,
mount the PC board in the righthand
side of the Railpower case, using two
tapped metal spacers.
Drill two 5mm holes in the front
panel for the photodiode and acknowledge LED. File the hole for the photodiode to a 5 x 7.5mm rectangle, then
replace the panel and bend the LED
Clip the three cells into the holder on
the IR remote control unit, observing
their polarity. They are back-to-front
compared to standard cells, the small
cap being the negative connection.
Point the remote control at the receiver
and press a button. If all is well, the
acknowledge LED on the Railpower
should light and the corresponding
function should be indicated by the
Railpower LED.
If it doesn’t work, the problem is
knowing which unit is not operating correctly, the transmitter or the
receiver.
First, check that the battery voltage
is around 4.5V on the transmitter.
If you have an oscilloscope, hold a
button down and check pin 7 of IC1
to see that the crystal is oscillating at
4MHz. Now check at the anode of one
of the transmitter LEDs.
There should be a pulse train output
whenever a button is pressed. If the
pulses are being sent continuously,
RAILPOWER
Fig.8: this is the full-size front panel artwork for the remote control version of the Railpower Mk.2.
78 Silicon Chip
AC
K
ER
PO
W
ST
OP
FO
RW
AR
D
RE
VE
IN
RS
ER
E
TI
A
OF
F
OV
E
RL
OA
D
CUTOUT
Fig.9: here are the full
size etching patters for
the IR receiver board
(right), transmitter PC
board (bottom right) and
the speed meter PC board
(below). Check the etched
boards carefully before
installing any of the parts.
then one of the pushbuttons has been
inserted incorrectly.
If an oscilloscope is not available,
remove the batteries and connect a
DC power supply set to 4.5V. When a
button is pressed, the current should
be around 9mA. As soon as the button
is released, the current should drop
to about 5mA and after one second
drop to 100µA. If this occurs, you can
assume that the transmitter is working
satisfactorily. If not check the capacitors on the crystal pins.
IR receiver board
On the receiver, check that pin 14
of IC3 is at +5V with respect to pin 7.
If you have an oscilloscope, check pin
7 of the processor to confirm that the
crystal is oscillating at 4MHz. Hold the
transmitter close to the receiver with
a button pressed.
The output at pin 6 of IC1 should
be a negative-going pulse of several
hundred millivolts. It should be positive-going at Q2’s collector and 3-4V
negative-going at Q5’s collector.
The output of IC2a (pin 7) should be
positive-going, while the signal into
pin 9 of IC4 should be a negative-going
5V pulse 33µs wide.
This close-up view shows how the leads of the infrared photodiode (PD1) on the
receiver are bent over, so that the active surface of the device faces the hole in
the front panel.
If you don’t have an oscilloscope,
the best approach is to compare the
DC voltages measured in your receiver
with those shown on the circuit. They
should be within 10% of each other.
If there is a discrepancy, check the
component values around the relevant
stage and also your soldering.
Check also that the A and B rate
links on the transmitter and receiver
match each other. If they don’t, the
SC
remote control won’t work.
January 1996 79
SERVICEMAN'S LOG
The complaint seemed simple enough
Yes, it did sound simple. And, relatively
speaking, it was. The trouble was, it didn’t stop
there – it had brought all its gremlin mates along
with it. By the time I’d knocked them all over, it
was a major exercise.
This story concerns a Sanyo colour
TV set, model 6627 (79P chassis),
which lead me a merry dance with a
succession of faults – these in addition
to the original complaint.
The set belongs to a pensioner, one
of several among my regular customers, and whom I regard as being in
something of a special category. In
general, their equipment tends to be
older than average, for the very simple
reason that, for many, the cost of new
equipment is almost prohibitive. So
they keep their old units and call on
me to keep them going for as long as
possible.
Of course, I do my best to help
them, even though at times it taxes
one’s ingenuity and patience. (After
all, I’ll be old myself someday – and
no editorial comment, please). Anyway, this case was a classic example
of this sort of job and, as is typical,
involved a set that was over 10 years
old.
But the owner’s complaint seemed
simple enough – distorted sound. And
a quick check while he was there confirmed the complaint; the distortion
was quite bad. Even so, I reckoned
it should be a snack; that I would be
able to knock the job over in no time.
And that, as the reader has doubtless
guessed, was where I came a gutser.
Sound circuitry
The sound section in this set is quite
straightforward – see Fig.1. It consists
of a sound IF amplifier and demodulator IC (IC151), the latter feeding two
output transistors, Q151 and Q152.
These are both specified as 2SC2568
or 2SC2456.
80 Silicon Chip
My first step was to check the 220V
main HT rail, which came up spot
on, as did several secondary rails derived from it. OK, so where to in the
sound section? My first inclination
was to suspect one of the two output
transistors and, with more haste than
wisdom, I whipped them out and
tested them.
They both tested OK, which
served me right for rushing in. I
then did what I should have done
first – checked the voltages around
these transistors. And, yes there was
something wrong. The base voltage
of Q151 is shown on the circuit as
“80V-106V”, which seemed an unusually large spread. But that was
largely academic anyhow, because
the actual voltage was way down on
even the lower figure.
And this was where I encountered the first of several discrepancies between the set on the
bench and the circuit. And I
don’t meant bodgie repairs;
I’m referring to original components. The bias resistor
for Q151 (R151) is shown
as 39kΩ but the one in the
set was 27kΩ. Or, more correctly, it was coded 27kΩ.
In fact, it measured over
100kΩ.
Well that seemed like the
answer and I promptly fitted a
new 27kΩ resistor. That brought
the voltages back to within tolerance of those on the circuit and
wiped out most of the distortion.
And I say “most” because there
remained a niggling level. It was
nothing like the original but it
was enough to indicate that there was
still something wrong.
And that’s just about the nastiest
kind of fault I can imagine. It was at
such a level that, at times, on certain
pro
g ram material, one could kid
oneself that it wasn’t there. Then the
program would change and it was all
too obvious. There was nothing for it;
it had to be found.
So, with all the stage’s operating
voltages restored to normal, where
should I go from here? The IC seemed
the next most likely culprit. I had one
on hand and changing it was not a
particularly difficult job. But, alas, I
drew another blank.
Down to basics
It was time to really get down to
basics. I went right over the output
stage and, by one means or another,
checked each component in turn. And
in the process, I encountered another
circuit discrepancy; a diode, D153,
which was in the set but not on the
circuit. It has been drawn in on the
circuit shown here.
I paid particular attention to electrolytic capacitors C151 (1µF) and
C157 (2.2µF on the circuit, 4.7µF in
the set). Low value electrolytics are
always suspect. But these and all the
other components, except one, were
cleared.
That one component was C153, a
5600pF capacitor connecting to pin
13 of the IC. And I had left it until last
because, initially, I couldn’t identify it.
I had been looking for a small ceramic
capacitor or something similar but
without success. In the end, I had to
trace the copper pattern and, when I
found it, it was quite a surprise.
It wasn’t a ceramic capacitor and it
wasn’t 5600pF. It was an electrolytic
and it was 0.47µF; the biggest change
from the original circuit I had found
so far. More to the point, being an
electrolytic – and of very low value
to boot – it was a prime suspect and I
lost no time in reefing it out and fitting
a new one.
And that was the answer, with the
set now producing clean sound. And
to confirm it, the suspect electrolytic
showed sub
stantial leakage when
tested. So that looked like the end of
the exercise. I gave the set the usual
once over for general performance and
minor adjustments, then set it up on
the end of the bench and let it run.
The set carks it
Initially, it ran for several hours and
then, suddenly, I was aware that it
was completely dead, with no picture
and no sound. Well, I took another
punt: the horizontal output transistor
(2SD838 on the circuit, 2SD621L in
the set). And I picked it in one; it was
short circuit.
This failure, in itself, did not present any real problem, except that the
2SD838 was cheaper – at around $30
– than the 2SD621L ($42) but was no
longer available. It was something of
a slug for a pensioner but that’s life.
More importantly, I was concerned
as to why the transistor had failed. It
has a pretty hard life in this set. The
waveform shown on the collector is
1900V p-p which is high by any stan
dards. That means that the stage is
vulnerable to any spikes or rubbish
on the driving waveform. And from
experience, the most likely cause is
a failure in C483, a 1µF electrolytic,
which decouples the 220V rail to the
horizontal drive transistor, Q481.
Again, experience has shown that
this capacitor dries out, allowing all
kinds of rubbish to reach the driver.
So I pulled it and replaced it. And,
as an attempt at insurance, I upped
the value to 10µF. I can’t guarantee
how much it will help but it won’t
do any harm.
When I switched the set on again,
there was sound but no picture. So
what on earth could be wrong now?
My first reaction was to suspect the
operating voltages on the picture tube.
I fished out the probe and checked
the EHT. There were plenty of volts
there, something over 25kV, and so
I checked the screen voltage, focus
voltage and the RGB drive transistors.
All seemed OK.
I have experienced trouble in the
past around transistor Q191. This
forms part of the ACL (Automatic Contrast Limiter) circuit and the problem
concerns resistor R197 (220kΩ) which
goes high. And while the trouble
had never been anything like this, I
checked it, found it somewhat high
January 1996 81
Fig.1: the audio output stage in the Sanyo 6627. Note the additional diode
(D153) which has been drawn in between the base and emitter of Q151.
As well, R151 is now 27kΩ, C157 is now 4.7µF and C153 (top left) is now
a 0.47µF electrolytic.
and replaced it. But I wasn’t surprised
when it had no effect.
Next I did a waveform check, right
through the video chain, but could find
nothing wrong. I stopped and had a
think and a caffeine fix and went over
the checks I had made.
And suddenly I became suspicious.
I realised that all the voltages I had
measured – EHT, screen, focus, RGB,
etc – had all been marginally high. I
hadn’t taken as much notice of this as
I should have, the complete picture
failure suggesting a total loss of voltage
somewhere.
Now I went back to taws – the main
HT rail. And there was the answer, or
part of it. Instead of the previous spoton 220V, it was now 275V. It was only
a symptom but it was a start. I went
straight to the power supply and, after
a few preliminary checks, attacked
Q901, the power regulator. And that
was it; it was short circuit.
I fitted a new one and switched on.
And everything came up roses; 220V
on the HT rail and a picture on the
screen.
And that was the end of the drama. But why did the excessive HT
rail voltage create the effect it did?
Frankly, I don’t know. I considered a
number of likely reasons – including
the possible action of an over-voltage
protection circuit somewhere in the
system – but I’m afraid I was too fed
82 Silicon Chip
up with the set to want to spend any
more time trying to find out. I let it run
for another day or so, then called the
customer to come and collect it. And
I was glad to see the back of it.
Granted, I was lucky in one way. At
least those secondary faults occurred
while the set was still on the bench. If I
had returned the set immediately after
fixing the first fault – as I might have
done had the customer been in hurry –
then I would have had it bounce. And
that can generate bad will on the part
of the customer.
So let’s be thankful for small mercies.
The crook Telefunken
My next story is about a Telefunken
colour set. It used an ICC4 chassis and
while it had its problems, it wasn’t
quite the headache of the previous
story.
The set came from a colleague. He
passed it over to me for a couple of
reasons. First, he is not particularly
keen on servicing European sets and,
second, he was rather snowed under at
the time and didn’t want to be caught
with something that might take up a
lot of time. And I gathered that it had
been through several other organisations before it came to him.
The complaint was quite straightforward; it was completely dead. Fortunately, my colleague had a circuit,
although it was a trifle grotty in places.
And so I let myself be saddled with
the monster.
It was quite an elaborate set, with
most of the modern features: a very
impressive remote control system,
Teletext, and so on. As with any dead
set, the first thing to check is the rail
voltages and, by implication, the
power supply. So I went straight to
the power supply. And, yes, it was
completely dead.
The supply itself is a fairly standard
switchmode arrange
ment, the main
difference being that, in order to accommodate the remote control on-off
function, the supply runs continuously while ever the power point is on.
The set itself is turned on or off via its
12V rail and this comes from IP61, an
LM317T adjustable 3-terminal regulator. This regulator is in turn controlled
by a signal from pin 7 of IR25.
In addition to the aforementioned
12V rail, there is also a 13V rail, a 22V
rail and a 90V rail, the latter being the
main supply rail. And, at first glance,
there also appears to be a 17V rail emanating from the chopper transformer
(UP40).
In fact, this is something of a furphy;
the 17V rail is actually generated at pin
10 of the horizontal output transformer
and this apparently takes over from the
13V rail (which feeds the regulator)
once the horizontal stage fires up.
(Note the arrow configuration on the
17V block).
No voltage
More to the point, there was no
voltage on any of these rails. I moved
over to the primary side of the chopper transform
er (UP40). There was
voltage out of the bridge rectifier
and, in fact, this was applying some
350V across the main filter capacitor
(CP11 – 100µF). I traced this through
the primary winding, pins 9 & 1, of
the transformer to the collector of the
chopper transistor, TP32.
I subsequently spent some time
checking likely components around
this stage but could find nothing
wrong. But I did make one useful observation. With the CRO connected to
the waveform points indicated on the
circuit, I found that, at the moment of
switching on, there was a very brief
indication of activity but the waveforms vanished almost immediately.
The stage was trying to oscillate but
couldn’t continue.
Fig.2: part of
the switchmode
power supply in
the Telefunken
ICC4. IP61 is an
LM317 adjustable
3-terminal
regulator which
produces a +12V
rail. This +12V
rail is switched
off (to turn the
set off) when the
main control IC
pulls pin 2 of the
regulator low (via
a transistor).
This started a different train of
thought. Perhaps there was a short
circuit or overload on one of the rails
which was placing an unacceptable
load on the power supply?
First, I checked each rail with the
ohmmeter but found nothing suspicious. This was not conclusive of
course – there could still be a breakdown or leakage at the operating voltage, which would not show up with
an ohmmeter check. I also checked
the diodes supplying each of the rails.
Again I drew a blank.
Next, I checked the horizontal output transistor, TL37 (BU508A), which
connects to pin 2 of the horizontal
output transformer (UL65) and thence
to the 90V rail via pin 6. This checked
out OK.
On the basis of all these tests, and
assuming that the overload theory
was still a valid suspicion, the next
obvious step was to disconnect each
of the rails in turn. I started with the
90V rail by disconnecting the 0.22Ω
safety resistor, RP51, at pin 2 of UP40.
As it turned out, this was the wrong
way to do the right thing. It was right
because the power supply now show
ed signs of life. Each of the other rails
now came up, partially and briefly,
and then died away. (On reflection, I
suspect that the aforementioned weird
17V rail configuration had something
to do with this strange behaviour).
Unfortunately, disconnecting the
rail at that point was the wrong way
to do it, because it was directly on the
transformer pin and did not allow me
to check the 90V rail itself.
I restored the 0.22Ω resistor and
went back to the horizontal stage. This
is a very complex arrangement and
difficult to follow, both in the set and
on the circuit. But the 90V rail goes to
a choke (LL54), through diode DL56,
and thence to pin 6 of the horizontal
output transformer via LL57. And
LL54 provided a convenient place to
break the 90V rail and check it.
In fact, it did come good, in a similar manner to the way the other rails
had responded. The trail was getting
Fig.3: part of the horizontal output stage in the Telefunken ICC4. The 90V rail connects (via LL54, DL57 & LL57) to pin
6 of the horizontal output transformer, while pin 2 connects to the horizontal output transistor (TL37 – not shown).
January 1996 83
SERVICEMAN’S LOG – CTD
warmer now. I restored the connection
at LL54, then disconnected the rail at
pin 6 of the transformer – same result.
So the fault was either somewhere
on the other side of this transformer
winding, in a circuit connected to one
of the other windings,
or in the winding
itself. I restored the
pin 6 connection and
lifted the pin 2 connection. And it was
a different story this
time. I was now back
to the original fault,
with no voltage on
any of the rails.
By now, I was becoming more and
more suspicious of
the transformer itself
– so much so that I
went for broke and
pulled it out. My idea
was to check it for
shorted turns, which
I felt was the most
likely explanation.
But first I made a
routine check of each
winding with an ohmmeter. Well, they were
all intact individually
but when I happened to check between
winding 2-6 and winding 1-5, I struck
oil; there was a dead short between
them.
Naturally, there was only one answer to a fault like that; I needed a new
transformer. But that had me worried
initially because I knew of no current
Australian agency for Tele
funken.
Fortunately, a few enquiries revealed
that Hitachi use the same transformer,
a type 243445. In fact, as I understand
it, they actually make it and Telefunken buys it from them. Anyway, they
are readily available, and one was
obtained and fitted.
End of story? Not quite. Oh, the
switchmode supply leapt into life
alright at switch-on but there was one
little snag – the set was still dead.
A quick check with the voltmeter
provided the first clue; all the rails
were up and spot on, at least out of
the power supply. But there was no
12V rail out of pin 3 of regulator IP61.
The reason wasn’t hard to track down.
As mentioned earlier, IP61 is controlled by pin 7 of the remote control
IC, IR25. This control signal is fed
to pin 2 of IP61 via transistor TR74
(BC547B). And TR74 was shot – it was
as simple as that.
A replacement BC547B was fitted
and I finally had everything running
at full bore. And a very nice result it
was too. I gave the set the usual routine
adjustment check, let it run for a day
or so, and then passed it back to my
colleague to return to his customer.
It wasn’t going to be cheap, of
course, taking into account the new
transformer. But that’s the way it goes
SC
and I hope he was happy.
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Newnes Guide
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336 pages, in paperback at $49.95.
Installation, Reception & Repair.
By Derek J. Stephenson. First
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This is a practical guide on the
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Computers are prone to failure
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This is a practical handbook from
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Optoelectronics:
An Introduction
By J. C. A. Chaimowicz. First
published 1989, reprinted 1992.
This particular field is about to
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Prepared by Sony’s technical
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Power Electronics
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Components, Circuits & Applica
tions, by F. F. Mazda. Published
1990.
Previously a neglected field, power
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particularly in the areas of traction
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Surface Mount Technology
By Rudolph Strauss. First pub
lish-ed 1994.
This book will provide informative
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Electronics Engineer’s
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Edited by F. F. Mazda. First pub
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January 1996 85
VINTAGE RADIO
By JOHN HILL
Anode bend to diode detection
During the early to mid-1930s era, the low
priced 5-valve superhet console radio was very
popular. Many employed anode bend detection
but they can be easily converted to diode
detection for improved audio performance.
The early ’30s were the tough times
of the Great Depression years, when
about 25% of the workforce was out
of work. And, of course, they were
without the back-up support that the
unemployed have today. This meant
that any radio manufacturer who wanted to stay in business had to produce a
range of receivers that were affordable.
The formula, in most cases, was to
keep things fairly basic.
The usual format for these cheaper
radios was the autodyne superhet – a
5-valve receiver with an autodyne mixer, IF stage, anode bend detector and
a single output stage. Some designs
used a 175kHz IF and this necessitated a pre-selector stage, using a 3-gang
Fig.1: the circuit of a typical anode bend detector. The
valve type shown is a 24A tetrode or similar sharp
cutoff tetrode. Later circuits used a type 57 pentode,
although the basic arrangement remained the same.
Fig.2: this is what the circuit looked like after conversion to diode
detection. The original type 24A tetrode was replaced by a type 27
triode valve.
86 Silicon Chip
tuning capacitor, in order to control
the double spot problem created by
of such a low value.
Other makers chose a 455kHz IF,
which was rapidly gaining popularity, and which solved the double spot
problem automatically. This allowed
the use of a cheaper 2-gang capacitor.
Either way, this broad design concept was a compromise between price
and quality and while these sets work
ed reasonably well, they had several
disadvantages.
Design drawbacks
One problem was the lack of automatic gain control. This circuit innovation came into existence in the early
1930s but was only found on the more
up-market receivers.
Another difficulty with the auto
dyne setup was that, while it worked
OK on broadcast band frequencies,
its performance on short
wave was
not so good.
And finally, the anode bend detector
used in these sets created a level of
audio distortion that left something
to be desired. While this distortion
may have been acceptable in the 1930s,
by today’s standards it is not very good
and can be quite distracting. It may
have been fairly distracting in the
1930s too, because by the middle of
that decade most manufacturers had
changed to diode detection.
Some of those old receivers with
anode bend detection sound better
than others and in many instances
the loudspeaker must play a part. The
moving coil loudspeaker had been in
existence for only a few years at that
stage of radio development and there
were still things to learn and manufacturing techniques to master. While
an early ’30s moving coil loudspeaker
was a remarkable improvement on
a ’20s horn speaker, there was still
quite a lot of developmental work
ahead of it.
Basic circuit
Fig.1 shows the circuit of a typical
anode bend detector. The valve type
shown is a 24A or similar sharp cutoff
tetrode. When the type 57 valve (a pentode) was developed, it replaced the
radio frequency tetrode, although the
circuit arrangements for anode bend
detection were still the same.
The main aspect of the anode bend
detection method is the very high
cathode bias resistor, which operates
the valve at close to cutoff. The term
“cutoff” simply means that the anode
or plate current will be at or near zero
when no signal is being received.
When a modulated radio frequency
(RF) signal is applied to the control
grid, there will be pulses of anode
current during the positive half cycles and little or no anode current
during the negative half cycles.
Therefore, the anode current is a rectified version of the signal waveform
at the grid.
Filtering of the RF component after
detection is achieved by a small plate
bypass capacitor (typically around
250pF) to chassis and an RF choke in
series with the plate load.
Anode bend detection has some
odd characteristics and the distortion it produces can be minimised
by varying the value of the cathode
bias resistor.
However, if the cathode bias is
selected to give good low distortion
sound with a strong signal at the
control grid, then the performance is
not as good on a weak signal and vice
versa. So, after much experimenting,
the cathode circuit is often returned
to its original form, as the manufacturer’s setup was probably a reasonable
compromise.
Detector conversion
I have quite a number of old auto
dyne/anode bend console radios and
I find some of them quite irritating
due to their high levels of distortion.
There are times I like to listen to my
radios for hours on end and if they
sound crook, there is no listening
pleasure at all.
The last of these receivers to come
off the restoration assembly line was
an old 1932 Darelle (see June 1995).
While the Darelle was no more annoying to listen to than any of the
Shown here is the Darelle 5-valve superhet cabinet. It is affectionately known
as the “tea chest on legs”. The Darelle’s chassis was converted from anode bend
detection to diode detection and this simple modification gave a significant
improvement in sound quality.
others, it was the one I selected to see
if the sound reproduction could be improved by converting the set to diode
detection. The experiment produced a
surprisingly good result, so allow me
to fill you in on the details.
There are several choices when it
comes to converting a set to diode
detection. One can use either a valve
with diodes in it, a triode connected
as a diode, or do the unforgivable and
use a germanium signal diode.
As the old Darelle used tetrode
valves, there was no applicable diode
type valve apart from the 55 duo-diode
triode. The use of this valve would
require a valve socket change from
5-pin to 6-pin.
Using a triode connected as a diode
was not an option either because there
was insufficient room to accommodate
it. So that left the unthinkable – a germanium signal diode.
Not being a modern electronics man,
I was not really sure how to incorporate a solid state diode into a valve
circuit. I mentioned what I planned to
do to young David (a collector friend)
and he drew up a circuit of what he
thought I needed to make a solid state
diode detector work in a valve receiver
– see Fig.2. I might add that David’s
January 1996 87
24A audio amplifier. It was tried as a
tetrode, a triode, with high and low
plate voltages, and with a variety of
cathode bias setups. None proved to be
really satisfactory, although the triode
connection wasn’t too bad except for
a drop in overall volume. It had to
be considered unsatisfactory for that
reason alone.
Valve replacement
The original anode bend detector valve was a 24A, as shown at left. This was
replaced with a 27 triode (right) and this worked well as an audio amplifier,
something that the 24A could not do.
circuit was a little more involved than
what I had in mind.
Another aspect of my conversion
was to retain the existing 24A anode
bend detector valve and use it as an
audio amplifier – if that was at all
possible. David was not confident that
this could be done but as I wanted
to keep the original valve line-up, I
would try to do it anyway. Whether
or not it would be successful was in
doubt at that stage.
Many radio frequency valves (the 57
and the 6J7 for example) can be used
as audio valves when connected as
either pentodes or triodes. Hopefully,
the 24A would perform likewise, although there is no mention of audio
frequency application in the valve
manual. (Editorial comment: the 24A,
being a tetrode – as distinct from the
above mentioned pentodes – is less
suitable for use as a resistance/capacitor coupled audio amplifier. When
it was used as an audio amplifier, it
was usually in the choke/capacitor
coupling mode. This permits a much
greater plate voltage signal swing
without distortion).
The detector circuit was made up
on a small piece of tagstrip to form a
compact detector module (see photo). This module was then bolted to
a convenient part of the chassis and
wired to the second IF transformer
and the control grid of what was the
anode bend detector. But while the set
worked, one could not say that it was
working well.
Actually, the sound quality was
really good at moderate volume levels, but distorted badly as the volume
increased.
Various alterations were made to the
The diode detector
module was built from
miscellaneous compon
ents mounted on a
tagstrip. The small size
of the module allows it
to be mounted in some
out-of-sight location if
so desired.
88 Silicon Chip
It was time to do what should have
been done in the first place and that
is fit a valve that was more suitable
for audio frequency work than a 24A.
A 27 was a logical choice as its 5-pin
base was compatible with the existing
valve socket. Rewiring the socket to
suit the triode valve required a couple
of alterations, as the 27 has no top-cap
grid connection.
After fitting the 27, all the previous
problems associated with the diode
detection modification suddenly
disappeared. Triode audio amplifiers
were all the go in the early 1930s
and a triode also proved to be most
successful with this particular circuit
arrangement.
Once everything was working OK,
it was time to experiment a little. The
detection module was disconnected
and another signal diode substituted.
This setup used no grid leak, no coupling capacitor or anything else – just
the diode between the IF transformer
and the grid of the valve. It made little
difference apart from an ever so slight
increase in volume.
So it would appear as though there
are many ways to incorporate a signal
diode into a valve circuit – and they
will all probably work. However, if
one decides to do this modification,
remember that the second IF transformer will require realignment. That
would be about the only inconvenience incurred.
After this little experiment, the original detector module was reconnected
into the circuit.
Practicality vs originality
No doubt some readers will have
difficulty in understanding why I
would want to modify an existing
circuit and ruin the set’s originality!
Well, in this case, I want to listen to
the radio and not be annoyed by it. It
is as simple as that! What’s more, if a
receiver can be significantly improved
by implementing such a simple modification, then why not do it? In this
RESURRECTION
RADIO
VALVE EQUIPMENT SPECIALISTS
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involved some socket rewiring and the removal of the top-cap connector. It was
worth the effort, as it solved the problem of trying to use the 24A in a role for
which it was never intended.
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The missing top-cap and connector may look a bit odd but so be it! Removing
the anode bend detector and replacing it with diode detection was an
experiment that paid off with a cleaner audio output.
instance, the improvement was well
worth the effort.
Should a future owner wish to
convert the receiver back to original,
it can easily be returned to its anode
bend state. Why someone would want
to do this I don’t know, but if they
did, they may not be happy with the
distortion that this detection method
produces.
The diode detector described
here can be a completely invisible
modification if so desired. Although
I chose to mount the diode and accompanying components on a small
tag strip underneath the chassis, there
is no reason why it cannot be housed
inside the second IF transformer
shield can or positioned in some
other out-of-the-way place where it
is out of sight.
As far as I’m concerned, if everything
looks OK then that’s all that matters.
A few devious modifications here
and there don’t upset me in the least,
especially if they improve the set’s
performance. The fact that the old
Darelle sounds a bit better than most
radios from that era must be worth
SC
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January 1996 89
Silicon Chip
October 1990: Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator;
DC Offset For DMMs; Using The NE602 In Home-Brew
Converter Circuits.
BACK ISSUES
November 1990: How To Connect Two TV Sets To One VCR;
A Really Snazzy Egg Timer; Low-Cost Model Train Controller;
Battery Powered Laser Pointer; 1.5V To 9V DC Converter;
Introduction To Digital Electronics; Simple 6-Metre Amateur
Transmitter.
September 1988: Hands-Free Speakerphone; Electronic Fish
Bite Detector; High Performance AC Millivoltmeter, Pt.2;
Build The Vader Voice.
Tips For Your VCR; Speeding Up Your PC; Phone Patch For
Radio Amateurs; Active Antenna Kit; Speed Controller For
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April 1989: Auxiliary Brake Light Flasher; What You Need
to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2;
LED Message Board, Pt.2.
February 1990: 16-Channel Mixing Desk; High Quality
Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random
Wire Antenna Tuner For 6 Metres; Phone Patch For Radio
Amateurs, Pt.2.
May 1989: Build A Synthesised Tom-Tom; Biofeedback
Monitor For Your PC; Simple Stub Filter For Suppressing
TV Interference; LED Message Board, Pt.3.
July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor);
Extension For The Touch-Lamp Dimmer; Experimental Mains
Hum Sniffers; Compact Ultrasonic Car Alarm.
September 1989: 2-Chip Portable AM Stereo Radio (Uses
MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Studio Series 20-Band Stereo Equaliser, Pt.2; Auto-Zero
Module for Audio Amplifiers (Uses LMC669).
October 1989: FM Radio Intercom For Motorbikes Pt.1;
GaAsFet Preamplifier For Amateur TV; 1Mb Printer Buffer;
2-Chip Portable AM Stereo Radio, Pt.2; Installing A Hard
Disc In The PC.
November 1989: Radfax Decoder For Your PC (Displays Fax,
RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2;
2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive
Formats & Options; The Pilbara Iron Ore Railways.
December 1989: Digital Voice Board; UHF Remote Switch;
Balanced Input & Output Stages; Data For The LM831 Low
Voltage Amplifier IC; Index to Volume 2.
January 1990: High Quality Sine/Square Oscillator; Service
March 1990: 6/12V Charger For Sealed Lead-Acid Batteries;
Delay Unit For Automatic Antennas; Workout Timer For
Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The
UC3906 SLA Battery Charger IC.
April 1990: Dual Tracking ±50V Power Supply; Voice-Operated Switch (VOX) With Delayed Audio; 16-Channel Mixing
Desk, Pt.3; Active CW Filter For Weak Signal Reception; How
To Find Vintage Receivers From The 1920s.
June 1990: Multi-Sector Home Burglar Alarm; Low-Noise
Universal Stereo Preamplifier; Load Protection Switch For
Power Supplies; A Speed Alarm For Your Car; Fitting A Fax
Card To A Computer.
July 1990: Digital Sine/Square Generator, Pt.1 (Covers
0-500kHz); Burglar Alarm Keypad & Combination Lock;
Simple Electronic Die; Low-Cost Dual Power Supply; Inside
A Coal Burning Power Station.
August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace
The Electronic Cricket; Digital Sine/Square Generator, Pt.2.
September 1990: Remote Control Extender For VCRs;
Power Supply For Burglar Alarms; Low-Cost 3-Digit Counter
Module; Simple Shortwave Converter For The 2-Metre Band.
December 1990: DC-DC Converter For Car Amplifiers; The Big
Escape – A Game Of Skill; Wiper Pulser For Rear Windows;
A 4-Digit Combination Lock; 5W Power Amplifier For The
6-Metre Amateur Transmitter; Index To Volume 3.
January 1991: Fast Charger For Nicad Batteries, Pt.1; Have
Fun With The Fruit Machine; Two-Tone Alarm Module; LCD
Readout For The Capacitance Meter; How Quartz Crystals
Work; The Dangers When Servicing Microwave Ovens.
February 1991: Synthesised Stereo AM Tuner, Pt.1; Three
Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design
Amplifier Output Stages
March 1991: Remote Controller For Garage Doors, Pt.1;
Transistor Beta Tester Mk.2; A Synthesised AM Stereo Tuner,
Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal
Wideband RF Preamplifier For Amateur Radio & TV.
April 1991: Steam Sound Simulator For Model Railroads;
Remote Controller For Garage Doors, Pt.2; Simple 12/24V
Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical
Approach To Amplifier Design, Pt.2.
May 1991: 13.5V 25A Power Supply For Transceivers; Stereo
Audio Expander; Fluorescent Light Simulator For Model
Railways; How To Install Multiple TV Outlets, Pt.1.
June 1991: A Corner Reflector Antenna For UHF TV;
4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply
For Transceivers; Active Filter For CW Reception; Tuning In
To Satellite TV, Pt.1.
July 1991: Battery Discharge Pacer For Electric Vehicles;
Loudspeaker Protector For Stereo Amplifiers; 4-Channel
Lighting Desk, Pt.2; How To Install Multiple TV Outlets, Pt.2;
Tuning In To Satellite TV, Pt.2.
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August 1991: Build A Digital Tachometer; Masthead Amplifier
For TV & FM; PC Voice Recorder; Tuning In To Satellite TV,
Pt.3; Step-By-Step Vintage Radio Repairs.
June 1993: Build An AM Radio Trainer, Pt.1; Remote Control
For The Woofer Stopper; Digital Voltmeter For Cars; Remote
Volume Control For Hifi Systems, Pt.2.
September 1991: Studio 3-55L 3-Way Loudspeaker System;
Digital Altimeter For Gliders & Ultralights, Pt.1; The Basics
Of A/D & D/A Conversion; Windows 3 Swapfiles, Program
Groups & Icons.
July 1993: Single Chip Message Recorder; Light Beam Relay
Extender; AM Radio Trainer, Pt.2; Quiz Game Adjudicator;
Programming The Motorola 68HC705C8 – Lesson 1; Antenna
Tuners – Why They Are Useful.
October 1991: Build A Talking Voltmeter For Your PC, Pt.1;
SteamSound Simulator For Model Railways Mk.II; Magnetic Field Strength Meter; Digital Altimeter For Gliders &
Ultralights, Pt.2; Getting To Know The Windows PIF Editor.
August 1993: Low-Cost Colour Video Fader; 60-LED Brake
Light Array; A Microprocessor-Based Sidereal Clock; The
Southern Cross Z80-Based Computer; A Look At Satellites
& Their Orbits.
November 1991: Colour TV Pattern Generator, Pt.1; Battery
Charger For Solar Panels; Flashing Alarm Light For Cars;
Digital Altimeter For Gliders & Ultralights, Pt.3; Build A
Talking Voltmeter For Your PC, Pt.2.
September 1993: Automatic Nicad Battery Charger/Discharger; Stereo Preamplifier With IR Remote Control, Pt.1;
In-Circuit Transistor Tester; A +5V to ±15V DC Converter;
Remote-Controlled Cockroach.
December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Solid-State Laser Pointer;
Colour TV Pattern Generator, Pt.2; Index To Volume 4.
October 1993: Courtesy Light Switch-Off Timer For Cars;
Wireless Microphone For Musicians; Stereo Preamplifier
With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1; Programming The Motorola 68HC705C8
– Lesson 2.
January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A
Power Supply, Pt.1; Baby Room Monitor/FM Transmitter;
Experiments For Your Games Card.
March 1992: TV Transmitter For VHF VCRs; Studio Twin Fifty
Stereo Amplifier, Pt.1; Thermostatic Switch For Car Radiator
Fans; Telephone Call Timer; Coping With Damaged Computer
Directories; Valve Substitution In Vintage Radios.
April 1992: IR Remote Control For Model Railroads; Differential Input Buffer For CROs; Studio Twin Fifty Stereo
Amplifier, Pt.2; Understanding Computer Memory; Aligning
Vintage Radio Receivers, Pt.1.
May 1992: Build A Telephone Intercom; Low-Cost Electronic
Doorbell; Battery Eliminator For Personal Players; Infrared
Remote Control For Model Railroads, Pt.2; Aligning Vintage
Radio Receivers, Pt.2.
June 1992: Multi-Station Headset Intercom, Pt.1; Video
Switcher For Camcorders & VCRs; Infrared Remote Control
For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look
At Hard Disc Drives.
July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger;
Multi-Station Headset Intercom, Pt.2.
August 1992: Build An Automatic SLA Battery Charger;
Miniature 1.5V To 9V DC Converter; Dummy Load Box For
Large Audio Amplifiers; Troubleshooting Vintage Radio
Receivers.
September 1992: Multi-Sector Home Burglar Alarm;
Heavy-Duty 5A Drill speed Controller (see errata Nov. 1992);
General-Purpose 3½-Digit LCD Panel Meter; Track Tester
For Model Railroads; Build A Relative Field Strength Meter.
October 1992: 2kW 24VDC To 240VAC Sinewave Inverter;
Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For
Personal Stereos; Build A Regulated Lead-Acid Battery
Charger.
January 1993: Peerless PSK60/2 2-Way Hifi Loudspeakers;
Flea-Power AM Radio Transmitter; High Intensity LED Flasher
For Bicycles; 2kW 24VDC To 240VAC Sinewave Inverter, Pt.4;
Speed Controller For Electric Models, Pt.3.
February 1993: Three Projects For Model Railroads; Low Fuel
Indicator For Cars; Audio Level/VU Meter (LED Readout); An
Electronic Cockroach; MAL-4 Microcontroller Board, Pt.3;
2kW 24VDC To 240VAC Sinewave Inverter, Pt.5.
March 1993: Build A Solar Charger For 12V Batteries;
Alarm-Triggered Security Camera; Low-Cost Audio Mixer
for Camcorders;A 24-Hour Sidereal Clock For Astronomers.
April 1993: Solar-Powered Electric Fence; Build An Audio
Power Meter; Three-Function Home Weather Station; 12VDC
To 70VDC Step-Up Voltage Converter; Digital Clock With
Battery Back-Up.
May 1993: Nicad Cell Discharger; Build The Woofer Stopper;
Remote Volume Control For Hifi Systems, Pt.1; Alphanumeric LCD Demonstration Board; The Microsoft Windows
Sound System.
November 1993: Jumbo Digital Clock; High Efficiency
Inverter For Fluorescent Tubes; Stereo Preamplifier With
IR Remote Control, Pt.3; Siren Sound Generator; Electronic
Engine Management, Pt.2; Experiments For Games Cards.
December 1993: Remote Controller For Garage Doors;
Low-Voltage LED Stroboscope; Low-Cost 25W Amplifier
Module; Build A 1-Chip Melody Generator; Electronic Engine
Management, Pt.3; Index To Volume 6.
November 1994: Dry Cell Battery Rejuvenator; A Novel
Alphanumeric Clock; 80-Metre DSB Amateur Transmitter;
Twin-Cell Nicad Discharger (See May 1993); Anti-Lock
Braking Systems; How To Plot Patterns Direct To PC Boards.
December 1994: Dolby Pro-Logic Surround Sound Decoder,
Pt.1; Easy-To-Build Car Burglar Alarm; Three-Spot Low
Distortion Sinewave Oscillator; Clifford – A Pesky Electronic
Cricket; Cruise Control – How It Works; Remote Control
System for Models, Pt.1; Index to Vol.7.
January 1995: Sun Tracker For Solar Panels; Battery Saver
For Torches; Dolby Pro-Logic Surround Sound Decoder,
Pt.2; Dual Channel UHF Remote Control; Stereo Microphone
Preamplifier; The Latest Trends In Car Sound; Pt.1.
February 1995: 50-Watt/Channel Stereo Amplifier Module;
Digital Effects Unit For Musicians; 6-Channel Thermometer
With LCD Readout; Wide Range Electrostatic Loudspeakers,
Pt.1; Oil Change Timer For Cars; The Latest Trends In Car
Sound; Pt.2; Remote Control System For Models, Pt.2.
March 1995: 50W/Channel Stereo Amplifier, Pt.1; Subcarrier
Decoder For FM Receivers; Wide Range Electrostatic Loudspeakers, Pt.2; IR Illuminator For CCD Cameras; Remote
Control System For Models, Pt.3; Simple CW Filter.
April 1995: Build An FM Radio Trainer, Pt.1; Photographic
Timer For Darkrooms; Balanced Microphone Preamplifier &
Line Filter; 50W/Channel Stereo Amplifier, Pt.2; Wide Range
Electrostatic Loudspeakers, Pt.3; 8-Channel Decoder For
Radio Remote Control.
January 1994: 3A 40V Adjustable Power Supply; Switching
Regulator For Solar Panels; Printer Status Indicator; Mini
Drill Speed Controller; Stepper Motor Controller; Active Filter
Design; Electronic Engine Management, Pt.4.
May 1995: Introduction To Satellite TV; CMOS Memory
Settings – What To Do When the Battery On Your Mother
board Goes Flat; Mains Music Transmitter & Receiver; Guitar
Headphone Amplifier For Practice Sessions; Build An FM
Radio Trainer, Pt.2; Low Cost Transistor & Mosfet Tester
For DMMs; 16-Channel Decoder For Radio Remote Control.
February 1994: 90-Second Message Recorder; Compact &
Efficient 12-240VAC 200W Inverter; Single Chip 0.5W Audio
Amplifier; 3A 40V Adjustable Power Supply; Electronic Engine
Management, Pt.5; Airbags – How They Work.
June 1995: Build A Satellite TV Receiver; Train Detector For
Model Railways; A 1W Audio Amplifier Trainer; Low-Cost
Video Security System; A Multi-Channel Radio Control
Transmitter For Models, Pt.1; Build A $30 Digital Multimeter.
March 1994: Intelligent IR Remote Controller; Build A 50W
Audio Amplifier Module; Level Crossing Detector For Model
Railways; Voice Activated Switch For FM Microphones;
Simple LED Chaser; Electronic Engine Management, Pt.6.
July 1995: Low-Power Electric Fence Controller; How To Run
Two Trains On A Single Track (Plus Level Crossing Lights
& Sound Effects); Setting Up A Satellite TV Ground Station;
Build A Door Minder; Adding RAM To A Computer.
April 1994: Remote Control Extender For VCRs; Sound &
Lights For Model Railway Level Crossings; Discrete Dual
Supply Voltage Regulator; Low-Noise Universal Stereo
Preamplifier; Build A Digital Water Tank Gauge; Electronic
Engine Management, Pt.7.
August 1995: Vifa JV-60 2-Way Bass Reflex Loudspeaker
System; A Fuel Injector Monitor For Cars; Gain Controlled
Microphone Preamp; The Audio Lab PC Controlled Test
Instrument, Pt.1; The Mighty-Mite Powered Loudspeaker;
An Easy Way To Identify IDE Hard Disc Drive Parameters.
May 1994: Fast Charger For Nicad Batteries; Induction
Balance Metal Locator; Multi-Channel Infrared Remote
Control; Dual Electronic Dice; Two Simple Servo Driver
Circuits; Electronic Engine Management, Pt.8; Passive
Rebroadcasting For TV Signals.
September 1995: A Keypad Combination Lock; The Incredible Vader Voice; Railpower Mk.2 Walk-Around Throttle For
Model Railways, Pt.1; Build A Jacob’s Ladder Display; The
Audio Lab PC Controlled Test Instrument, Pt.2; Automotive
Ignition Timing, Pt.1.
June 1994: 200W/350W Mosfet Amplifier Module; A Coolant
Level Alarm For Your Car; An 80-Metre AM/CW Transmitter
For Amateurs; Converting Phono Inputs To Line Inputs;
A PC-Based Nicad Battery Monitor; Electronic Engine
Management, Pt.9
October 1995: Build A Compact Geiger Counter; 3-Way Bass
Reflex Loudspeaker System; Railpower Mk.2 Walk-Around
Throttle For Model Railways, Pt.2; Fast Charger For Nicad
Batteries; Digital Speedometer & Fuel Gauge For Cars, Pt.1;
Automotive Ignition Timing, Pt.2.
July 1994: Build A 4-Bay Bow-Tie UHF Antenna; PreChamp
2-Transistor Preamplifier; Steam Train Whistle & Diesel
Horn Simulator; Portable 6V SLA Battery Charger; Electronic
Engine Management, Pt.10.
November 1995: LANsmart – A LAN For Home Or A Small
Office; Mixture Display For Fuel Injected Cars; CB Transverter
For The 80M Amateur Band, Pt.1; Low Cost PIR Movement
Detector; Dolby Pro Logic Surround Sound Decoder Mk.2,
Pt.1; Digital Speedometer & Fuel Gauge For Cars, Pt.2.
August 1994: High-Power Dimmer For Incandescent Lights;
Microprocessor-Controlled Morse Keyer; Dual Diversity Tuner
For FM Microphones, Pt.1; Build a Nicad Zapper; Simple
Crystal Checker; Electronic Engine Management, Pt.11.
September 1994: Automatic Discharger For Nicad Battery
Packs; MiniVox Voice Operated Relay; Image Intensified
Night Viewer; AM Radio For Aircraft Weather Beacons; Dual
Diversity Tuner For FM Microphones, Pt.2; Electronic Engine
Management, Pt.12.
October 1994: Dolby Surround Sound – How It Works;
Dual Rail Variable Power Supply (±1.25V to ±15V); Talking
Headlight Reminder; Electronic Ballast For Fluorescent
Lights; Temperature Controlled Soldering Station; Electronic
Engine Management, Pt.13.
December 1995: Engine Immobiliser For Cars; Five Band
Equaliser For Musicians; CB Transverter For The 80M Amateur
Band, Pt.2; Build A Subwoofer Controller; Dolby Pro Logic
Surround Sound Decoder Mk.2, Pt.2; Knock Sensing In Cars;
RAM Doubler Reviewed; Index To Volume 8.
PLEASE NOTE: November 1987 to August 1988, October
1988 to March 1989, June 1989, August 1989, May 1990,
February 1992, November 1992 and December 1992 are
now sold out. All other issues are presently in stock. For
readers wanting articles from sold-out issues, we can
supply photostat copies (or tearsheets) at $7.00 per article
(includes. p&p). When supplying photostat articles or back
copies, we automatically supply any relevant notes & errata
at no extra charge.
January 1996 91
ASK SILICON CHIP
Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line
and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097.
Sins of omission
in a preamplifier
I recently constructed the Low Noise
Universal Preamplifier as described
in April 1994, for use with a pair of
unbalanced binaural microphones.
During construction, I decided to omit
all components between the input
pins and the op amp, as these seemed
to relate largely to the phono preamp
version. Any comments? It seems to
work perfectly well. Would the omitted part of the circuit have made any
difference or improvement?
As part of the same project, I intend
to build balanced outputs. The December 1989 issue of SILICON CHIP gives a
design utilising a pair of LM833s per
channel to provide balanced ins and
outs. Is the PC board for this available
anywhere? I also came across a design
in “ETI” in the December 1982 issue
for a Balanced Input Differential
Preamp. This used a pair of 5534 op
amps, one for each of the balanced
line conductors, feeding a TL071. Any
comments on the pros and cons of the
two different approaches to producing balanced inputs? (D. M., Canton
Beach, NSW).
• Omitting all the components between the input pins and the op amp
Speed controller
for a 2hp router
Have you produced a speed control for a 2hp router. I am using it
with some large diameter bits and
the recommendation is to reduce
the speed for safety. I know you
produced a 5A speed controller
but I obviously need something
bigger.
By the way, the current rating
for the router is 10A. Could I
upgrade your 5A design by just
using a bigger Triac? (N. M., Sey
mour, Vic).
• The 5A speed controller is the
92 Silicon Chip
is not good practice, even though,
as you have observed, the circuit
will still work. The RF suppression
components, consisting of the inductor L1, 150Ω resistor and the 100pF
capacitors, are desirable in order to
prevent pickup of interference, particularly AM radio stations. Second,
the 100kΩ resistor on the op amp
side of the 47µF capacitor should be
retained so that, if the microphone is
unplugged, the op amp continues to be
correctly biased; otherwise there will
be a loud ‘pop’ whenever the microphone is plugged in or out.
The 47µF capacitor is desirable to
prevent the bias current of the LM833,
typically around 0.5µA, from flowing
through the microphone. This could
lead to non-linearity or possibly de
mag
netisation, over a long period.
Finally, the second 100kΩ resistor is
required to make sure that the 47µF
capacitor is always charged and does
not charge via the microphone when it
is plugged in; if this happened, a loud
‘pop’ would result.
The PC board for the balanced output circuit is available from RCS Radio
Pty Ltd, 651 Forest Road, Bexley, NSW
2207. Phone (02) 587 3491.
The ETI circuit for balanced inputs
would certainly work but a superior
highest rating we have produced
and it already uses a 40A Triac.
As it stands, you could use the 5A
design for your 2hp router provided you change the 10A fuse to a
“slow-blow” type and you arrange
for better heatsinking for the Triac.
This would most easily be done
by using a reasonable size diecast
aluminium box.
Note that at the full speed setting
with any half-wave speed control,
the maximum speed of the router
will be reduced by about 20%. So
a 20,000 RPM router would immediately be reduced to a maximum
of 16,000 RPM.
circuit using the special purpose
SSM2017 was published in the April
1995 issue of SILICON CHIP. A kit for
this project is available from Altronics,
in Perth.
Altering timer for
burglar alarm
I have just completed wiring up
your Multi-Sector Home Burglar
Alarm from the June 1990 edition and
thankfully (for me) it worked straight
away. My question is what do I alter to
get a five minute alarm instead of the
10-minute period? And just as a query,
why did you put the sector switches
with the off position down? Thanking
you for a really good magazine for
novices as well as the brighter boys!
(H. M., Ballina, NSW).
• The 10-minute timer comprises IC4,
IC6 & IC7. Halving the 10-minute period is simply a matter of using the Q5
output (pin 5) of IC6 to drive IC7. So
disconnect pin 6 of IC6 and connect
pin 5 instead.
We’re not sure what you mean by
your question about the sector switches being down in the Off position. The
design was presented in the form of
PC boards so the way in which it was
built was up to the constructor.
Combination AM/FM
radio trainer wanted
Could the AM Radio Trainer (June/
July 1993) and the FM Radio Trainer
(April/May 1995) be combined to
make an AM/FM Radio Trainer? Over
the years I have built AM valve radio
sets and AM transistor sets. I did not
make the FM Radio Trainer because it
only had the one section.
Completely designing a radio trainer
would be desirable so that a person
could obtain experience aligning the
AM/FM coils using a cheap oscilloscope, sweep generator or FM-AM
generator. It would be a good idea if a
sweep generator kit was developed for
alignment of the FM section.
By this method, one would learn
Coolant alarm for
plastic radiators
I refer to the very successful
coolant alarm project from the June
1994 issue. I have just purchased
a new Mitsubishi Magna sedan
and to my surprise, I find that the
radiator appears to be of composite
manufacture, with plastic head and
bottom tanks moulded on to a metal
heat exchanger.
The metal heat exchanger is
earthed to the car body, according
to my ohmmeter, and as the plastic header tank is an insulator, it
would appear that a suitable sensor probe could be made by just
drilling and tapping a 1/8-inch
brass metal thread into the header
tank. However, I would like your
comments please. (B. P., Port Macquarie, NSW).
more alignment procedures experimentally. If possible, rather than IC1IC4 of the FM side being integrated
circuits they should be completely
transistorised. Then one could learn
the internal structure of each circuit
on the FM side. (L. F., North Bondi,
NSW).
• Although FM/AM radios and tuners
are standard commercial products,
frequently using only one or two ICs,
there is no easy way of combining
our radio trainer circuits onto one PC
board. These discrete circuits are quite
difficult to produce on a freestanding
PC board and our final versions were
only arrived at after quite a few prototypes had been built.
Car burglar alarm
malfunction
I’m hoping you can help with a
number of problems I’m having with
the Car Burglar Alarm featured in December 1994. I’ve obviously botched
something somewhere and anything
you can suggest to get the alarm working properly would be appreciated.
After assembling the kit carefully
and doing a neat solder
ing job, I
installed it in the car and no matter
what I do to the trimpots it doesn’t
seem to work properly at all. The car
it is fitted in is a Volkswagen Beetle,
•
A large number of modern cars
now use radiators with plastic
header tanks. While a bolt attachment to the top tank would be a
simple addition, we’re not keen
on the idea of drilling and tapping the tank to fit a brass screw.
A screw might work its way out
after a time and then you really
would have a loss of coolant. Nor
are we keen on the idea of fitting a
brass screw in close proximity to
the aluminium radiator core. That
seems like asking for corrosion
problems.
We think it would be preferable
to fit a stainless steel bolt and nut
to this type of radiator, together
with flat washers and a lockwasher. Naturally, this would need to
be installed close to the radiator
cap, in order to attach the nut and
washers to the bolt.
not a very complicated car in terms of
wiring, so installation was easy, even
for an amateur like me. About the only
extra items fitted to the kit are two pin
switches under the bonnet and boot
which are connected to the “Immediate Sense” circuit of the alarm and
a key switch as opposed to the toggle
switch included in the kit.
When I arm the alarm with the key
switch the LED doesn’t “continuously
light” as described in the assembly
instructions. But after the set exit delay period, the LED starts flashing to
indicate the alarm is set. When I then
open a door or the bonnet or boot to
set off the alarm/horn siren, the LED
continues to flash instead of turning
itself off to indicate it is going to sound
the horn siren. However, the horn siren
fails to go off at all. The LED continues
to flash and switching the keyswitch
to “disarm”, fails to have any effect on
the LED (and obviously the alarm as
well) and the only way to turn it off is
to push in the door pin switch of the
open door. So it appears I can arm the
alarm (sort of) but not disarm it. (J. C.,
Melbourne, Vic).
• As far as we can tell from your description, IC2 and the LED are operating normally. The LED does not start
to flash until after the exit period. We
suggest that you carefully check the
voltages around the circuit and also
If you are seeing a blank
page here, it is
more than likely that it
contained advertising
which is now out of date
and the advertiser
has requested that the
page be removed to
prevent
misunderstandings.
Please feel free to visit the
advertiser’s website:
www.avico.com.au
January 1996 93
Door minder
is insensitive
I have recently assembled the
“Door Minder” kit as published in
the July 1995 issue of SILICON CHIP.
I find that it is not very sensitive
and it only works in a small room
with the windows shut and if I give
the door a hefty pull.
I would be most grateful if you
could tell me how to make it more
sensitive; the preset pot is adjusted to the most sensitive it will go.
The article says it works with open
windows in an adjoining room.
Also, where can I purchase the
Philips ETD49/25/16 transformer
components and the TEA100
nicad monitor IC for the Fast Nicad
Charger, as published in the September 1995 issue?
I refer to the letter on page 7 of
the April 1995 issue, on making
PC boards by photocopying the
original back to front and rubbing
with thinners mixture on the back. I
have had limited success and find it
is best if the photocopy is removed
whilst still moist.
I say moist and not wet, as too
much thinners gets underneath
and smudges the pattern. When
dry, doing it a second time darkens
the picture but use a fresh, new
photocopy.
monitor the output of IC1 to see that
it delivers the correct signal from its
output in response to the arm/disarm
switch.
How to reduce
preamp gain
I recently put together the preamp
section of your 50W amplifier design
and find it very satisfactory. My amplifier and speakers are of very high
sensitivity so I need much less gain
than is provided. Would you please
advise the correct way of changing the
feedback components around IC1 to
achieve closer to unity gain? I prefer
to do this rather than use attenuators.
(K. A., Moss Vale, NSW).
• The gain of IC1 can be reduced by
increasing the 4.7kΩ resistor at pins
6 & 2. To halve the gain, increase the
94 Silicon Chip
However, the result produces a
porous copper surface which has
to be heavily layered with solder.
An improvement can be made by
going over the whole pattern with
a fine felt tip pen which is water
resistant. (D. S., Caloundra, Qld).
• We are surprised that your Door
Minder is so insensitive. You
should check that the 0.1µF and
1µF capacitors on IC1a’s input
are the correct values and that the
1µF capacitor is inserted with the
correct polarity. Also confirm that
the two resistors around IC1a are
47kΩ and 3.9MΩ – a wrong value
may have been fitted. Also, did
you ground the case of the electret
insert?
Check that the regulated DC is
about 8V and the voltage on pin 1
of IC1a is 3.3V. As the circuit has
a gain of 80 it only needs 10mV
from the microphone to trigger the
chimes. It should not be necessary
to increase the gain of the circuit,
as it is quite adequate. Perhaps the
microphone insert is faulty.
You can get some extra gain by
decreasing the 47kΩ input resistor
to 39kΩ but any more variation
could alter the passband of the
filter.
Regarding the parts for the Fast
Nicad Charger, these can be purchased from Jaycar Electronics.
4.7kΩ resistor to 10kΩ. To obtain unity
gain, omit the 4.7kΩ resistor.
Frigid remote control
won’t respond
I have just built the UHF remote
switch from the December 1989 issue
of SILICON CHIP. It is operating perfectly from a distance of 10 metres but only
when the temperature is over 20°C.
Can you advise how to overcome this
problem as the temperature in Victoria
is generally under 20°C. (P. L., Spring
vale North, Vic).
• Ever thought of moving to warmer
climes? It appears as though one or
more of the transistors or possibly one
of the ICs is temperature sensitive.
As a first step, we suggest you check
all voltages in the circuit. Second,
check all soldering on the PC boards.
Cold solder joints can be temperature
sensitive. Third, with a can of freezer
spray, freeze each semiconductor
component to see if it causes the
problem. Alterna
tively, replace the
transistors one by one to see if you
can effect a cure.
Extended leads for a
digital thermometer
Recently, I bought a digital thermometer with indoor/outdoor display
from Jaycar (Cat QM-7210). I intended
to extend the outdoor twin lead by a
further 12 metres to enable the probe
to be sited in the foliage of a bushy tree
for a genuine outdoor reading.
Doing this increased the leads’
total resistance by about 0.3Ω which,
in turn, increased the readout figure
by 7°C. I tried counteracting this by
adding 0.3Ω in parallel with the probe
but then the readout for this probe
disappears.
I cannot see any internal adjustment to compensate for extra lead
length. Have any readers had similar
experience along these lines? (M. B.,
Taree, NSW).
• We doubt whether the additional
resistance in the probe leads has
caused the increase in temperature
reading. We are more inclined to think
that the long leads may be picking up
hash which is adding to the reading.
Try connecting a 0.1µF greencap or
MKT capacitor across the probe leads
where they enter the case.
Note & Errata
Dolby Pro Logic Surround Sound Decoder, Pt.1, November 1995: the anode
of diode D12 is shown incorrectly
joined to the junction of the cathode
of D14 and an associated 10kΩ resistor.
Instead, D14 and the 10kΩ resistor
should connect directly to pushbutton
switch S7.
Dolby Pro Logic Surround Sound
Decoder, Pt.2, December 1995: the
resistor connected to pin 21 of IC2 is
marked “30O” on the layout diagram
(Fig.4, p71). The correct value of this
resistor is 30Ω.
Five-Band Equaliser, December 1995:
the supply pins for IC2 on the circuit
diagram (Fig.5, p24) are shown reversed. Pin 4 should go to the +15V
rail, while pin 11 should go to -15V.
The parts layout diagram (Fig.6, p25)
SC
is correct.
MARKET CENTRE
Cash in your surplus gear. Advertise it here in Silicon Chip.
FOR SALE
BUSINESS FOR SALE: electronic
service and repair business for sale
in the fastest growing inland city in
NSW. Plenty of fresh air, sunshine and
country hospitality. At present servicing mainly audio gear, specialising in
car audio. Service agent for leading
car audio brands. Regular, wide customer base. Plenty of room to expand
CLASSIFIED ADVERTISING RATES
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To run your classified ad, print it clearly in the space below or on a separate
sheet of paper, fill out the form & send it with your cheque or credit card details
to: Silicon Chip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details
to (02) 979 6503.
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in premises and business, including
into retail. Good lease available. This
business is offered for genuine urgent
sale due to the owner’s ill health. Price
$45,000 WIWO. Enquiries phone (068)
84 1158.
MicroZed are supplying BS2 upgrade
kits free with purchase of BS2 and carrier, regardless of where you bought
your legit BS1. Proof of purchase
required.
NEW SPRINKLER CONTROLLER
KITS: RAIN BRAIN version uses ‘C8
and switch mode supply. Features galore!! Contact Mantis Micro Products,
38 Garnet St, Niddrie 3042. Phone/fax
(03) 337 1917.
EDUCATIONAL ELECTRONIC KITS:
Easy to build. Guaranteed to work.
Good quality. Latest technology. Cheap.
Good selection. LESSON PLANS
FOR TEACHERS. Send $2 stamp for
catalogue and price list. Log onto our
bulletin board for full details. DIY Elect
ron
ics, 22 McGregor St, Numurkah
3636. Ph/Fax (058) 62 1915. E-Mail:
laurie.c<at>cnl.com.au BBS (058) 62
3303.
SATELLITE DISHES: international reception of Intelsat, Panamsat, Gorizont,
Rimsat. Warehouse Sale – 4.6m Dish
& Pole $1499; LNB $50; Feed $75. All
accessories available. Videosat, 2/28
Salisbury Rd, Hornsby. Phone (02) 482
3100 8.30-5.00 M-F.
❏ Bankcard ❏ Visa Card ❏ Master Card
✂
Enclosed is my cheque/money order for $__________ or please debit my
RCS RADIO PTY LTD
Card No.
Signature__________________________ Card expiry date______/______
Name ______________________________________________________
Street ______________________________________________________
Suburb/town ___________________________ Postcode______________
RCS Radio Pty Ltd is the only company that manufactures and sells every
PC board and front panel published
in SILICON CHIP, ETI and EA.
RCS Radio Pty Ltd,
651 Forest Rd, Bexley 2207.
Phone (02) 587 3491
January 1996 95
MicroZed Computers
Specialist in controllers with on-chip interpreters
Boards, Software, Chipsets, Books.
Easy to learn. Fast prototyping
Low cost. Chipsets available for volume production
Easy to use – get going in hours, not months
Raw PIC chips available too, JW & OTP
Send 2 x 45c postage stamps for information package.
PO Box 634 (296 Cook’s Rd), ARMIDALE 2350.
Ph (067) 722 777 Fax (067) 728 987
Mobile (014) 036 775
Advertising Index
BASIC Stamp I 8 I/O; and BSII 16 I/O
Altronics ................................ 66-68
Scott Edwards Electronics
Av-Comm................................64,65
Accessories for Stamp and second source for Stamp I
Avico Electronics.........................93
Versa Tech
Car Projects Book....................OBC
TICkit – a 21 I/O PIC based controller
NEW Micro
68HC11 F1 boards with resident FORTH. Other languages
supplied, ASM. Small C & BASIC
Dick Smith Electronics........... 18-21
Harbuch Electronics....................65
Instant PCBs................................96
Jaycar ................................... 45-52
MEMORY * DRIVES * MODEMS
SPECIAL! (Incl Tax)
1Mbx9 – 70ns Simm $60
1Mbx9 – 80ns Simm $45
SIMMS
(Parity/No Parity)
4MB 30 PIN-70 $179 $185
4MB 72 PIN-70 $177 $148
8MB 72 PIN-70 $353 $303
16MB 72 PIN-70 $695 $605
32MB 72 PIN-70 $1389 $1210
EDO SIMMS
4MB (1Mbx32)-70ns $198
8MB (2Mbx32)-70ns $370
MAC
8MB P’BOOK $437
VIDEO MEMORY
256KX16 70ns (SOJ) $24
256KX16 70ns (ZIP) $58
Kits-R-US.....................................64
L & M Satellite Supplies.................3
LASER PRINTER MEMORY
HP 2MB UPGRADE
$156
CO-PROCESSORS
80387SX/DX to 40MHz $90
COMPAQ
8MB CONTURA AERO $445
TOSHIBA PORTEGE/SATELLITE
8MB / 16MB
$650 / $1218
DRIVES SEAGATE
850MB EIDE 11ms 3yr $325
1080MB EIDE 10.5ms 3yr $360
2150MB SCSI 9ms 5yr $1033
MODEMS (Includes Sales Tax)
14,400 BANKSIA 5yr W $283
14,400 SPIRIT 2yr W $203
28,800 BANKSIA V.FC $321
28,800 SPIRIT V.34/V.FC $410
Phone for other products not listed
EX TAX PRICING AS AT JANUARY ‘96
MicroZed Computers...................96
Oatley Electronics...................... 8-9
Pelham........................................96
Railway Projects Book...............IFC
RCS Radio ..................................95
Resurrection Radio......................89
Rod Irving Electronics .......... 35-39
Scan Audio Pty Ltd
Silicon Chip Bookshop.................85
PELHAM
Ph: (02) 9980 6988
Fax: (02) 9980 6991
Suite 6, 2 Hillcrest Rd, Pennant Hills, 2120.
ETI PIC Basic Interpreter: BASIC57/
XT/P $45, BASIC84/04/P $45. 2K EEPROM $8, 8K EEPROM $16. PC serial
port driven. 18 and 28-pin PCB $20,
4MHz Xtl $5. Windows Software free.
InfoFax: Voice then Fax, (03) 9338 2935
Password ‘# 1111’. Don McKenzie, 29
Ellesmere Crescent, Tullamarine 3043.
Phone (03) 9338 6286.
MICROCRAFT PRESENTS: Dunfield
(DDS) products are now available exstock at a new low price; please ask for
our catalogue. Micro C, the affordable
“C” compiler for embedded applications.
Versions for 8051/52, 8086, 8096,
68HC08, 6809, 68HC11 or 68HC16
$139.95 each + $3 p&h • Now on special is the SDK, a package of ALL the
DDS “C” compilers for $399 + $6 p&h •
EMILY52 is a PC based 8051/52 high
speed simulator $69.95 + $3 p&h • DDS
demo disks $7 + $3 p&h • VHS VIDEO
from the USA (PAL) “CNC X-Y-Z using
car alternators” (uses car alternators as
cheap power stepper motors!) $49.95
+ $6 p&h (includes diagrams) • Device
programming EPROMs/PALs etc from
96 Silicon Chip
Scan Audio..................................96
Silicon Chip Back Issues.............90
Sales Tax 22%, O/Night Delivery $8. Ring For Latest Prices.
Credit Cards Welcome. We Also Buy And Trade-In Memory.
Silicon Chip Walchart.................IBC
_________________________________
PC Boards
Printed circuit boards for SILICON
CHIP projects are made by:
$1.50 • Fixed price electronic design and
PCB layout • Credit cards accepted • All
goods sent certified mail • Call Bob for
more details. MICROCRAFT, PO Box
514, Concord NSW 2137. Phone (02)
744 5440 or fax (02) 744 9280.
COMPLETE WORKSHOP PROGRAM:
suit IBM compatible 386 or better computer. Handles: Stock Control, Sales,
Service Records, Debits, Credits, Faults,
Service Manuals and Phone Directory.
Full price $399.00. For demo disk, phone
or fax your details to (045) 71 1640.
Jack Albers Electronics & Software
Development.
C COMPILERS: Dunfield compilers are
now even better value. Everything you
need to develop C and ASM software
for 68HC08, 6809, 68HC11, 68HC16,
8051/52, 8080/85, 8086 or 8096:
$140.00 each. Macro Cross Assemblers
for these CPUs + 6800/01/03/05 and
6502: $140 for the set. Debug monitors:
• RCS Radio Pty Ltd, 651 Forest
Rd, Bexley, NSW 2207. Phone (02)
587 3491.
• Marday Services, PO Box 19-189,
Avondale, Auckland, NZ. Phone (09)
828 5730.
$70 for 6 CPUs. All compilers, XASMs
and monitors: $400. 8051/52 or 80C320
simulator (fast): $70. Demo disk: FREE.
All prices + $5 p&p. GRANTRONICS
PTY LTD, PO Box 275, Wentworthville
2145. Ph/Fax (02) 631 1236 or Internet:
lgrant<at>mpx.com.au.
HC11s AND ICs - http://worf.albanyis.
com.au/bobhome.html.
SOUND TECHNOLOGY 3100A/3200A
programmable transmission/audio test
system, operating manual, $9500. (03)
9499 1524.
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