This is only a preview of the April 1994 issue of Silicon Chip. You can view 28 of the 96 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Articles in this series:
Items relevant to "Remote Control Extender For VCRs":
Items relevant to "Sound & Lights For Level Crossings":
Items relevant to "Discrete Dual Supply Voltage Regulator":
Items relevant to "Low-Noise Universal Stereo Preamplifier":
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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which is now out of date and the advertiser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
Vol.7, No.4; April 1994
FEATURES
4 Electronic Engine Management, Pt.7 by Julian Edgar
Other input sensors
THE THROTTLE position sensor
plays an important role in your
car’s engine management system.
Find out how this & other sensors
work by turning to page 4.
36 Microcontrollers With Speed by Darren Yates
The new PIC series from Microchip
56 PC Product Review: The Video Blaster by Darren Yates
Imports PAL or NTSC video signals into your PC
70 Spectrum Analysis With The Icom R7000 by J. Lloyd & J. Storey
It operates under computer control
80 G-Code: The Easy Way To Program Your VCR by Leo Simpson
Just enter the numbers in your TV guide & that’s it!
PROJECTS TO BUILD
16 Remote Control Extender For VCRs by John Clarke
EVER WANTED to operate
your VCR from another room
while watching the picture on a
second set? This Remote Control
Extender relays signals from the
handpiece to an IR LED located
near the VCR – see page 16.
Lets you operate your VCR from any room in the house
22 Sound & Lights For Level Crossings by John Clarke
Companion unit to the Level Crossing Detector
29 Discrete Dual Supply Voltage Regulator by Darren Yates
Provides regulated supply rails from ±5V to ±12V
32 Low-Noise Universal Stereo Preamplifier by Darren Yates
Use it with a magnetic cartridge, cassette deck or microphone
60 Build A Digital Water Tank Gauge by Jeff Monegal
Displays water level & can automatically activate a pump
SPECIAL COLUMNS
40 Serviceman’s Log by the TV Serviceman
ADD REALISM TO your model
railroad layout with this Sound &
Lights module. It mates with the
Level Crossing Detector & flashes
lights & produces a realistic bell
sound when a train approaches.
Construction starts on page 22.
A couple or real stinkers
54 Computer Bits by Darren Yates
Experiments with your games card, Pt.5
86 Vintage Radio by John Hill
Bandspread tune-up for an Astor multi-band receiver
DEPARTMENTS
2
3
10
53
84
Publisher’s Letter
Mailbag
Circuit Notebook
Order Form
Back Issues
80
90
93
94
96
Product Showcase
Ask Silicon Chip
Notes & Errata
Market Centre
Advertising Index
THIS DIGITAL GAUGE will keep
tabs on the water level inside a
tank & can turn on a pump when
the water falls below a preset
level – turn to page 60.
Cover design: Marque Crozman
April 1994 1
Publisher & Editor-in-Chief
Leo Simpson, B.Bus.
Editor
Greg Swain, B.Sc.(Hons.)
Technical Staff
John Clarke, B.E.(Elec.)
Robert Flynn
Darren Yates, B.Sc.
Reader Services
Ann Jenkinson
Sharon Macdonald
Marketing Manager
Sharon Lightner
Phone (02) 979 5644
Mobile phone (018) 28 5532
Regular Contributors
Brendan Akhurst
Garry Cratt, VK2YBX
Marque Crozman, VK2ZLZ
John Hill
Jim Lawler, MTETIA
Bryan Maher, M.E., B.Sc.
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) 979 5644. Fax
(02) 979 6503.
PUBLISHER'S LETTER
Should we reduce our
mains voltage to 230V?
Recently, there have been moves afoot to
standardise much of the Western world’s
electricity supplies, transformers, machines
and appliances. If Australia goes along with
it, our domestic mains voltage would be reduced from a nominal 240 to 230 volts AC.
This suggestion came originally from the
International Electrotechnical Commission
(IEC) in 1983.
As far as Europe is concerned, the move to
standardise on 230 volts, or any other figure for that matter, is probably a good
one. Presently, Europe has a range of mains voltages – 220, 230 and 240 volts –
and it makes sense to standardise on the one voltage in the long term. Britain,
which now uses 240 volts, is going along with the idea but the USA, as is their
usual conservative stance in these matters, will stick with its 110 volts at 60Hz.
However, any suggestion that Australia should automatically follow Europe
should be treated with cynicism. Dr David Sweeting, chairman of the Australian Institute of Engineering’s 230-volt working group, is quoted in the Sydney
Morning Herald (March 5th, 1994) as saying “It is going to improve the opportunities for the electrical equipment we produce, opening up the world to our
industry”. Oh really!
Let’s face it, any Australian manufacturer who wants to export is already
meeting the standards of world markets or they should be. If they want to sell a
product in an overseas market, it has to meet the standards of that market and
it will not make one whit of difference whether Australia has the same electrical standard or not. On the other hand, it might make it easier and cheaper for
importers of electrical equipment and, heaven knows, Australian manufacturers don’t need any more competition from imports. In virtually every field of
endeavour, Australian manufacturers have heavy competition from aggressive
importers. Do we really want to make it easier for the importers and thereby put
our balance of payments in even more jeopardy?
Remember also that if we change to 230 volts AC for domestic use that automatically means a change to the 3-phase distribution standard of 415 volts AC
to 397 volts. So all the equipment designed to run at 415 volts will be slightly
less efficient, as will 230 volt equipment. The 230-volt working group referred
to above estimates the reduction would add about 0.5% to the cost of electricity.
I would question that figure too.
If the voltage is reduced by a nominal 5% from 240 to 230VAC, the I2R losses
in the distribution system will be more like 10%. And when you consider that
a great deal of the domestic distribution network actually runs at 250 volts AC
or more, the distribution losses would be more like 15% if the change was fair
dinkum. That is a huge cost to Australia, for the doubtful benefit of being in line
with a European standard.
I could go on poking holes in the argument but I think I’ve made the point.
Should we reduce our mains voltage to 230 volts AC? We’d like to hear from you.
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
Information on
guitar amplifiers
With reference to the “IF Generator
Is Nifty” letter from L.T. of Eaglehawk,
(Ask SC, December 1993), he(?) asked
for a course on antique musical instruments, specifically guitar amplifiers. In
1989, I purchased a paperback book
from McGill’s bookshop in Melbourne,
called “The Tube Amplifier Book II”
by R. Aspen Pittman. As far as I can
tell, it is published by Groove Tubes,
13994 Simshaw Avenue, Sylmar, California 91342, USA (my edition was
published in 1988).
There are 400 pages to this book and
it has 32 pages of photos of various
guitar amplifiers and a few other items.
There is a considerable rundown on
the history and technical details of
many amplifiers, including 10 pages
listing valve types used in various
makes and models. There is a small
cross reference list of US/industrial/
European type equivalents, a list of
Groove Tube companies and instrument manufacturers (worldwide list)
and, most importantly, 277 pages of
circuits of all the big name guitar amplifiers. If this book is still available, it
should be just what is needed.
As a regular reader, let me compliment you on your excellent magazine. I
am a collector of early radio equipment
and a technician by trade, so I read the
Vintage Radio and Serviceman’s Log
columns first, followed by the rest of
the magazine articles.
I am a member of the Historical
Radio Society of Australia and a local
vintage radio club (The North East
Vintage Radio Club). About 17 of our
members went across to see John Hill’s
museum in Maryborough a few weeks
ago. How I wish I had as many of my
radios restored and somewhere to
display them like that!
E. Irvine,
Benalla, Vic.
Environmental
concern
I am writing to you because of
concern I have about the Engine
Management feature in the January
1994 issue of SILICON CHIP, in which
Julian Edgar explains how to “Change
The System”. My concern is that with
the environment now being such an
important issue, is it really the proper
thing to do to explain to people how
to increase the performance of their
car which can lead to increased fuel
consumption and an increase in exhaust pollutants?
Also something which Julian omitted from his article and which I think
is important is that, on some cars, the
radiator cooling fan is controlled by
the ECM. By changing the information
the ECM receives from the coolant temperature sensor, the ECM “thinks” the
motor is running cooler than it really
is. This could lead to the engine overheating because the radiator cooling
fan is not turned on.
F. Loprete,
Cabramatta, NSW.
Comment: We accept your concern
about increased performance leading to more pollution but we also
think that is more useful to make
this information available than to
suppress it. We have also spoken to
Julian Edgar on your concern about
the ECM thinking that the engine is
cooler than it really is, leading to a
danger of overheating. He agrees that
your concern is valid.
SILICON CHIP,
PO Box 139,
Collaroy, NSW 2097.
the “high” or the “low” coding line on
the PC board. The switch should just
protrude through the case lid when the
two halves are fitted together.
The receivers then need to be coded in such a way that pressing the
original button operates one receiver
and pressing both operates the other.
An example of this coding would be
1-low, 3-high, 4-low and, through the
extra switch, 5-high. This would mean
that the original button would operate
a receiver coded to 1-low, 3-high and
4-low, while pressing both would
operate a receiver coded 1-low, 3-high,
4-low and 5-high (all other lines open).
If the extra coding line is to be taken
high, it may also be possible to switch
the transmitter as well so that only one
button is pushed for each receiver – I
have not tried this, however.
W. Sutton,
Adelaide, SA.
EFI cars have
more poke
I can’t let G. J. Hunt’s letter in
the March 1994 Mailbag pages pass
without comment. He reckons that
his wife’s Daihatsu Charade is easily
beaten by an 18-year old Mini. Just for
interest, I’ve tabulated their comparative performance figures.
Converting a UHF remote
control to dual operation
I recently built the UHF Remote
Switch and the Garage Door Controller
designed by Oatley Electronics, as described in the December 1993 issue of
SILICON CHIP. I have found both units
to be reliable and excellent value.
Because I use the UHF switch to
operate the central locking on my car,
I need to have a remote controller for
both the garage door and the locking
system. Rather than carry two remotes,
I cut a small (about 4mm) hole in the
top of the transmitter case directly
over the encoder IC. I then fixed (using
several layers of double sided tape) a
switch to this. In order to allow the
switch to sit correctly, the legs needed
to be bent outwards.
The normally open contact of the
switch was then connected to either
1993 Daihatsu
Charade
1976 Leyland
Mini
0-60km/h
4.4 seconds
7.5 seconds
0-100km/h
11.4 seconds
23 seconds
Top speed
172km/h
125km/h
The Charade test figures are from
the September 1993 issue of “Motor”
magazine while the Mini figures are
from the April 1976 issue of “Wheels”
magazine. E’nuff said?
Julian Edgar,
Para hills, SA.
Comment: we are in no doubt that
modern cars with engine management
systems are far superior to 20-year old
vehicles and your figures bear this
out. It seems likely that the Charade
referred to by G. J. Hunt might be the
3-cylinder version which is a little
underpowered.
April 1994 3
Electronic
Engine
Management
Pt.7: Other Input Sensors – by Julian Edgar
In addition to the airflow and exhaust oxygen sensors previously discussed, engine management systems
run other input sensors to allow the
system to monitor changing engine
and environmental parameters. For
example, the temperature of various
parts of the engine is another factor
that influences fuel and ignition
requirements. This is especially so
at engine start-up, as a cold engine
requires substantially more fuel to
run satisfactorily.
Temperature sensors
The engine coolant temperature
plays a major role in deter
mining
the amount of fuel enrichment. The
lower the engine tem
perature, the
greater the fuel correction applied to
the base injector opening time. Sometimes this correction factor, which is
A potentiometer type throttle position sensor. It measures the precise amount of
throttle opening and feeds this data to the ECM (electronic control module) to
control fuel enrichment.
4 Silicon Chip
also tied to idle speed, is applied in
a series of discrete steps. As a result,
the engine idle speed reduces in a
corresponding series of abrupt steps
as the water temperature rises.
The coolant temperature sensor
also plays a major role, even when the
engine is up to operating temperature.
In one system, for example, when
the coolant temperature is over 95°C
and the throttle position switch idle
contacts are open (ie, the throttle is
applied), fuel injection is increased
by 10% over the base quantity. This
enriches the mixture to counteract
possible detonation. If the same high
engine temperature exists at start-up,
the fuel pressure is increased to avoid
possible vapour-lock problems.
The ignition timing control is also
affected by the engine coolant temperature. For example, in one engine
management sys
t em, the ignition
timing is advanced by about 7° when
the coolant temperature is below 0°C.
This allows greater time after ignition
for maximum combustion pressures
to occur.
Pollution control mechanisms
may also be influenced by coolant
temperature. In one car, for example,
the evaporated fuel from the fuel
tank is purged from its absorption
canister by being vented to the intake
manifold –but only when the engine
is sufficiently warmed-up to burn it
without further emissions release.
Inside a switch-type throttle position sensor – note the
contacts for idle & full-throttle positions. The movable arm
(centre) follows the track in the guide cam (see also Fig.9).
Fig.1: cross-section of Holden VL Commodore
optical crankshaft position sensor. It uses two
LEDs and two matching photodiodes to sense
slots cut into a rotating disc mounted in the
base of the distributor.
Other temperature sensing which may be carried out
includes the intake air temperature (especially with
engines running vane-type airflow meters), cylinder
head temperature and – in some programmable injection
systems – engine and gearbox oil temperature.
Invariably, temperature sensing is carried out by a
thermistor mounted within a heat-conductive body.
Road speed sensor
A vehicle road speed sensor is also generally used to
feed data to the ECM. This data may be used in several
ways.
First, many vehicles feature over-run fuel injector
cut-off. This means that when the throttle is lifted, fuel
injector operation ceases, resuming only when the engine rpm approaches idle speed. This reduces exhaust
emissions and improves fuel economy.
An example of fuel shut-off occurs in the Nissan
6-cylinder engine used in the VL Commodore. In this
case, the fuel injectors are shut off if the throttle position
switch contacts are closed (ie, if your foot is taken off
the accelerator) at any engine speed above 2000 rpm.
The proviso here is that the engine coolant must have
reached normal operating temperature.
Fuel injection resumes when the engine speed falls
below 2000 rpm. In some cars, however, the injector-resume speed is as low as 1500 rpm and a slight jerk can
often be felt by the sensitive driver when the injection
starts again. The road speed sensor input is relevant here
because injector cut-off operation occurs only above a
certain speed – 8km/h in the VL Commodore.
A second use for road speed data occurs in those cars
which run a speed limiter as part of the engine man
agement system. Its job is to cut off the fuel or ignition
when a certain road speed is reached. This is often well
above the speeds reached in normal conditions – even
in the Northern Territory! However, domestic Japanese
cars run either a 145 or 180km/h speed limiter.
The road speed sensor is usually built into the back
Fig.2: the rotating disc in the VL Commodore’s
distributor has 360 1° slots around its periphery
to provide a signal that’s proportional to engine
speed. Also on the disc are six slots at 60°
intervals to indicate the crankshaft position.
The large slot at the top indicates the position of
the number one piston.
Fig.3: this diagram shows
how the rotating disc &
the optical sensor are
mounted in the base of
the distributor.
April 1994 5
The crankshaft position sensor is often built into the base of the distributor, as
in this Holden 4-cylinder engine. This distributor-based system uses an optical
pick-up but an inductive pick-up system using a coil & a magnet to sense
protrusions on a crankshaft sprocket can also be employed.
of the speedometer and so uses
the speedo cable to drive it. Other
systems mount the sensor on the
gearbox.
Crankshaft position sensor
One very important sensor is the
crankshaft (or camshaft) position sensor. This provides vital inputs to the
ECM so that it can provide the correct
injection and ignition timing.
Fig.1 shows a cross-section of the
optical sensor used in the Holden VL
Commodore engine. It uses two LEDs,
two photodiodes and a rotating disc.
The rotating disc is built into the
base of the distributor and has 360 tiny
slots near its outside edge (see Fig.2).
These slots rotate between one LED
and its corresponding photodiode and
provide a signal to the ECM that’s proportional to engine speed. In addition,
there are a further six slots in the disc
but further towards the disc’s centre.
Five of these are of the same size but
the sixth is much larger.
Fig.4: the Subaru Liberty uses an inductive pick-up
sensor to determine the crankshaft position. This
sensor consists of a magnet & coil assembly & is
mounted close to a toothed crankshaft sprocket.
6 Silicon Chip
These six slots are placed 60° apart
and are used to signal the crankshaft
angle (or piston position) to the ECM.
The large cutout is used to show the
position of number one piston. Fig.3
shows the whole assembly.
Other manufacturers use an inductive system, whereby a crankshaft
sprocket with specifically located
protrusions rotates past a moulded
pick-up containing a magnet and coil.
Fig.4 shows the cross-section of the
inductive sensor used by Subaru in
the Liberty.
Fig.5 shows the layout of the system.
Note that the pick-up is separated from
the toothed sprocket by only a small air
gap. In operation, the magnet briefly
magnetises the sprocket protrusion as
it passes the sensor and a voltage is
then induced in the coil as the air gap
changes. An AC waveform (Fig.6) is
emitted by the pick-up, with the pulses
occurring at different crankshaft positions. Camshaft position sensors often
work in the same way.
Knock sensor
Knock (or detonation) occurs when
fuel in the combustion chamber ignites before the progressively-moving
flame front actually reaches it. When
this happens, a sudden increase in
combustion pressure occurs and this
blow to the piston is the “tinking”
sound heard inside the car. The fact
that this sound is produced by a detonation hitting the crown of the piston
Fig.5: as each protrusion on the crankshaft
sprocket passes the sensor, a voltage is induced
in the pick-up coil. This voltage is then fed to
the ECM to indicate the crankshaft position.
This late 1980s Holden 4-cylinder engine is fitted with six major input sensors for the ECM
plus three minor sensors.
Fig.6: the shape of the output waveform from an
inductive pick-up sensor.
Fig.7: cross-section of a typical knock sensor.
It uses a piezoelectric transducer as the sensing
element.
April 1994 7
Fig.8: the knock sensor control process, as
developed by Bosch. A filtering & evaluation
system is needed to differentiate detonation
noise from ambient engine noises.
deep inside the engine indicates the
violence of this phenomenon!
Detonation can occur because the
ignition timing is too advanced, the
fuel octane rating is too low, or the
tur
bocharger boost pressure is too
high – or due to a combination of these
factors. However, maximum efficiency
is often gained by running engines very
near to the onset of detonation and so
knock sensors are now being used in
some engine management systems to
prevent engine damage.
Knock sensors employ piezoelectric
elements, with elaborate filtering and
Fig.9: the layout of switch-type throttle position sensor.
The movable contact is controlled by a guide cam & closes
with the power contact when the throttle is opened.
comparison circuits to differ
entiate
knock from normal engine noise. Fig.7
shows a typical knock sensor, while
Fig.8 shows the control process carried
out by the ECM.
The sensor itself is usually screwed
into the block near to the head (some
systems use separate knock sensors for
each cylinder but most road-going engines make do with one). When knock
is sensed, the ECM usually retards
ignition timing and then, when the
problem has gone, slowly advances
the timing back to its original figure.
Knock sensors are notoriously
A typical intake air-temperature sensor. It is bolted into one of the intake
runners. Temperature sensors invariably use a thermistor mounted inside a
heat-conductive body.
8 Silicon Chip
prone to false-alarming. In one car, the
fault-code indicating a problem with
the knock sensor is almost sure to be
registering – with no apparent fault
present! Shielding of the input cable is
generally used to prevent interference
but problems have continued to plague
this device in production cars.
Throttle position sensors
Throttle position sensors (TPS) do
just that – they indicate to the ECM
the opening of the throttle valve. In
the past, these sensors were invariably
simple switches, with contacts for
idle and full load. Current cars can
run switches of this sort or can use a
combination of an idle-position switch
and a potentiometer to indicate the
precise throttle opening. Other cars
use just a potentiometer. Fig.9 shows
a switch-type throttle position sensor.
Input data from the throttle position
sensor is used to indicate when full
load and/or acceleration injection
enrichment is needed, and to signal
injector cut-off on the over-run. This
sensor also sometimes causes the
air-conditioner clutch to be switched
off under full throttle, thereby allowing maximum road performance.
Those cars using a potentiometer
TPS also often use an ECM that’s
programmed to take note of the speed
of the throttle opening, as well as its
angle. Rapidly flooring your right
foot will then give different ignition
advance and fuel rates compared to
gentle acceleration to full throttle. SC
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M36 $55
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$45
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100MHz Oscilloscope
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VCD-150
DI-10
DI-1
TDI-0.8
CM-25
CM-50
150mm/6" Electronic Digital Vernier in box $120
200mm/8" Electronic Digital Vernier in box $180
150mm x 0.02 Dial Vernier Caliper $75
10 x 0.01mm Dial Indicator $45
1" x 0.001" Dial Indicator $45
0-0.8 x 0.01mm Test Dial Indicator $95
0-25mm x 0.01mm Outside Micrometer $45
25-50mm x 0.01mm Outside Micrometer $55
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CM-75
50-75mm x 0.01mm Outside Micrometer $65
CM-01
0-1" x0.001" Outside Micrometer $45
MB-6
CZ-6C Magnetic Base Stand $55
VC-150 Dual Scale Vernier Caliper 150 x 0.02mm/6" x 0.001" $35
VC-200* Dual Scale Vernier Caloper 200 x 0.02mm/8" x 0.001" $45
VC-600* Dual Scale Vernier Caliper 600 x 0.02mm/24" x 0.001" $250
HI-600 600mm/24" x 0.02mm Height Gauge
$550
*WITH FINE ADJUSTMENT
Affordable Laboratory Instruments
SSI-2360 60MHz
Dual Trace Dual Timebase
Oscilloscope
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Bandwidth DC to 100MHz; Rise time
<=3.5ns; Deflection factor 5mV/div to 5V/
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display mode; Horizontal deflection - main &
delayed timebases; A - 0.5s/div to 0.05µs/div
in 22 steps; B - 50ms/div to 0.05µs/div in 19
steps; Trigger - main/delay sweep; Coupling
AC, DC, LF Rejection, HF Rejection
TOP VALUE $1150
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Vertical sensitivity 1mV/div.
Maximum sweep rate 5ns/div.
Built-in component tester
With delay sweep, single sweep
Two high quality probes
$1050 + Tax
PS303D Dual Output Supply
• 0 to 30V and 0 to 3 amps
• Four output meters
• Independent or Tracking modes
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PS303 Single Output Supply
PS305D Dual Output Supply
PS305 Single Output Supply
• 0 to 30V and 0 to 5 amps
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**Illustrations are representative only
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.
Battery-life indicator
for radio microphones
This idea came about because one
of our local churches plans to increase
the number of radio microphones
in its sound system from two to six.
The problem is that the transmitter
batteries must be replaced at about
nine hours as a compromise between
reliable life expectancy and the possibility of a sermon or music item fading
out if the batteries are left in too long.
The present method of manually
logging the transmission times of
two channels is impractical for the
impending array of six channels.
What follows is a solution that combines non-vola
tile memory of total
elapsed transmission time for each
Block signalling
for model trains
This project provides a realistic
signalling effect for model trains.
It sets a CLEAR signal to DANGER
as a train enters a section and then
resets it to CLEAR again as the train
leaves the section. No modification
of rolling stock is required.
The project provides two independent block circuits which detect occupancy. They can be used
anywhere on your layout to operate
signals or simply to indicate on your
control panel that a train is in a section. This makes it ideal for use on
hidden sidings.
Phototransistors are positioned
under the rails, one at each end
of a block section. One block uses
phototransistors Q1 and Q2, while
the other uses Q3 and Q4.
When the signal is green, the
shadow of a passing train interrupts
light falling on the phototransistor as
it enters the section. This causes the
circuit to switch the red signal on in
place of the green. As long as the train
remains in the section, the red will
stay on. As it leaves the section, the
10 Silicon Chip
microphone with excellent accuracy,
simplicity and low cost.
The design takes advantage of the
fact that a 6V line from each VHF
receiver becomes active during reception from its corresponding transmitter. A combination of a resistor and a
LED drops the 6V to a working voltage
of 1.5V to operate a common quartz
clockwork mechanism as sold by some
electronics outlets. The minute and
second hands can be discarded and the
hour hand cut short so that the clocks
only take up a small amount of room
in the sound desk console.
Escutcheons need to be made up for
the clocks with numbers from 1 to 12
hours and access to the mechanisms
must be provided to enable manual
resetting of each clock to zero when
its transmitter battery is replaced.
The LEDs can double as activity
indicators.
Glen Host,
Doubleview, WA. $15
train’s shadow causes the circuit to
switch back to green.
IC1a and IC1b are arranged as an
RS flipflop. When no train is present,
light falling on Q1 and Q2 causes
them to conduct and so pins 1 and
5 of IC1a and IC1b are low. When a
train subsequently passes over Q1 or
Q2, it turns off and the corresponding input to the flipflop goes high,
causing it to change state.
A green LED is connected to one
output of the flipflop, while a red
LED is connected to the other. This
output (pin 4) is also used to control
transistor Q5. When pin 4 is high, the
relay is on (as is LED 1, since pin 3 of
IC1a is low). Conversely, when pin 4
is low, the relay and green LED are
off and the red LED is on.
The basic circuit will operate
colour light signals which use LEDs
but not small grain-of-wheat lamps.
To drive these, the relay is required.
The second section of the circuit,
consisting of Q3, Q4, IC1c, IC1d, Q6
and RLY2, operates in exactly the
same manner and is used to control
the second section of track.
If your signals use lamps, you will
need to build the complete circuit
and use the relay contacts to switch
the lamps. On the other hand, if you
only intend driving LEDs, you can
leave out Q5, Q6, R7, R10, D2, D3
and the relays.
The MEL12 phototransistors are
connected to the board with long
leads. Note that the base connections
are not used in this circuit.
In most cases, the signal for a block
will be near the first MEL12 so you
will only need to run one wire for
LED common, one each for the two
LEDs, one for the MEL12 collector
and one for the MEL12 emitter. If
you get the wrong indication (ie, red
instead of green), just swap the LEDs
(the relay will now be activated when
the red signal shows).
You can use the LEDs as indicators
on your control panel or you can use
them for both signalling and indication by connecting an additional LED
in series with the first.
Don’t make the wires to the
MEL12s and the LEDs any longer
than absolutely necessary – some
are over two metres long on my
layout but if you make them too
long, you are inviting interference
problems. It’s a good idea to twist
VHF1
RECEIVER
+6V
VHF1
RECEIVER
0V
+6V
0V
LED1
LED6
CLOCK1
CLOCK6
Simple 4-step voltage comparator
IN
+8-15V
This circuit provides visual indication of DC input voltages
over four steps. It can be easily adjusted to suit a range of input
voltages simply by changing a few resistors.
IC1 is an LM324 quad op amp IC which is wired to form
a line of comparators (IC1a-IC1d). The inverting inputs are
connected up to a resistor string which taps off a 5V reference
from a 7805 regulator. This regulator also supplies the power
to the circuit. The voltages at the tap-off points are shown
on the circuit and, for the resistor values shown, range from
3.4V to 4.6V.
The incoming voltage is divided by a 10kΩ trimpot (VR1)
and two 10kΩ resistors and the resulting voltage applied to all
the non-inverting inputs. When the voltage on a non-inverting
input rises above the voltage on the inverting input, the LED
for that comparator turns on. Thus, as the input voltage rises,
the LEDs turn on in sequence. Conversely, as the input voltage
goes down, the LEDs turn off.
VR1 is adjusted to give the correct change-over points during
the setting-up procedure. With the resistor values, shown the
circuit can be easily adjusted to operate in 1V steps over the
range 8-11V to serve as a low battery indicator in a car.
Power to the circuit can be anywhere between 8 and 15V.
The current consumption depends mostly on the number of
LEDs that are lit but should be no more than about 25mA..
Darren Yates,
SILICON CHIP.
10
16VW
7805
GND
OUT
0.1
+5V
5.6k
3
+4.6V
2
4
IC1a
LM324
1 560
LED1
5.6k
5
+4.2V
6
IC1b
7
560
LED2
5.6k
10
+3.8V
Vin
VR1
10k
9
IC1c
8 560
LED3
5.6k
10k
10k
13
+3.4V
12
IC1d
14 560
11
LED4
47k
The circuit for the 4-step voltage comparator is based
on an LM324 quad op amp.
D1
1N4004
R1
10k
R2
10k
R3
10k
LED1
GRN
R4
10k
R5
680
14
1
3
IC1a
2
4001
Q1
MEL12
6
12V
C1
100
16VW
Q2
MEL12
IC1b
4
LED2
RED
LED3
GRN
D2
1N4002
R6
680
R7
4.7k
RLY1
Q5
BC547
9
Q3
MEL12
IC1c
LED4
RED
R8
680
D3
1N4002
RLY2
R9
680
5
10
8
13
Q4
MEL4
12
IC1d
11
R10
4.7k
Q6
BC547
7
each pair of wires together to help
in this regard.
The MEL12s must be placed in
natural or artificial light so that the
shadow of a passing train switches
the circuit. If they are in a tunnel, a
source of light will be required (eg, a
small lamp or an infrared LED placed
high enough above the rails to clear
the trains).
As an option, you can use the relay
contacts to control the supply to a
short section of track immediately
before the block. When a train enters
the block, the supply is removed immediately behind it and is restored
only after the train has left. This
prevents another train from entering
an occupied section.
S. Oppermann,
George Town, Tasmania. ($40)
April 1994 11
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
Remote control
extender for VCRs
This simple device will allow you to operate
your VCR via its IR remote control from
another room in the house. It works by
receiving the IR signal from the handpiece
& then retransmitting it to an IR LED near the
VCR via a 2-wire cable.
By JOHN CLARKE
Many families now have two colour
TV sets, one usually located in the
living room with a VCR and a second
set in the kitchen, rumpus room or
one of the bedrooms. But although it’s
quite easy to link both TV sets to the
VCR (via a 2-way splitter), operating
the VCR from the same room as the
second set is usually impossible.
This Infrared Remote Extender
solves that problem. It sits in the same
room as the second set and picks up
infrared signals from the VCR’s remote
16 Silicon Chip
control. This signal is then converted
to an electrical signal and sent down a
2-wire cable to an infrared LED located
near the VCR in the living room – see
Fig.1.
Because the signal from the infrared
LED mimics the signal picked up by
the receiver, the VCR will now respond
to any com
mands from the remote
control in the other room. Of course,
the extender is not only limited to
VCRs – it can be used to re-transmit
virtually any IR signal (eg, for CD
players or burglar alarms).
As shown in the photos, the circuit
for the Infrared Remote Extender is
housed in a small metal case. An
ACKnowledge LED on the front panel
lights whenever a signal is received
from the remote control, to let you
know that the unit is working correct
ly. There is just one control – an on/
off switch.
The rear panel of the device carries
two sockets, one for power (12V DC)
and the other to allow the cable for the
remote infrared LED to be plugged in.
Before moving on to the circuit description, we should briefly mention
the Infrared Remote Control Extender
published in the September 1990 issue. This proved to be an extremely
popular project but was not without
problems. Based on numerous enquiries from people who had constructed
the project, it was clear that the circuit
required some component adjustments (mainly around the AGC section) so that it would operate reliably
with a variety of infrared controllers.
This completely new circuit solves
the problems associated with the previous design.
How it works
Fig.2 shows the circuit schematic.
It uses an infrared photodiode (IRD1)
to receive the signals and a Plessey
SL486 infrared remote control preamplifier (IC1) to amplify these signals.
An elaborate AGC circuit based on
IC2a provides gain control for the am
plifier stage inside IC1, while inverter
stages IC3a-IC3e drive the infrared
and ACKnowledge LEDs (IRLED1
and ACK).
In greater detail, signals from
the remote control trans
mitter are
picked up by IR photodiode IRD1
and converted to electrical pulses.
These pulses are then filtered by a
twin-T filter with a notch frequency
of 100Hz to eliminate interference
from mains-powered lights and then
applied to the differential inputs of
IC1 at pins 1 and 16.
Normally, the twin-T filter is not
required since IC1 provides sufficient
attenuation at 100Hz when using its
recommended capacitor values to produce a roll-off below 2kHz. However,
we have altered the gain of IC1 at low
frequencies so that the roll-off begins
INFRARED
EXTENDER
INFRARED
LED
VCR
SECOND RECEIVER
MAIN RECEIVER
VCR
REMOTE
CONTROL
ROOM 1
ROOM 2
Fig.1: the basic concept. The IR extender picks up infrared light from the VCR’s
remote control & converts it to an electrical signal. This signal is then sent down
a 2-wire cable & drives an IR LED located in the same room as the VCR.
at 666Hz. This is to allow the circuit
to amplify signals from those transmitters with outputs centred on 1kHz.
The 22µF and 220µF capacitors
at pins 2 and 3 respectively of IC1
set the pi functions of two internal
gyrator circuits. In low ambient light
conditions, the gyrator circuit using
the 22µF capacitor is switched into
circuit, while in high light conditions,
the gyrator using the 220µF capacitor
takes effect.
The remaining capacitors at pins 5,
6 and 15 provide roll-off at frequencies
below 666Hz. This low frequency
roll-off works in conjunction with
Most of the parts are mounted on a small PC board & this must be fitted inside a metal case. Power
comes from a 12V DC plugpack supply.
April 1994 17
47
10
22
220
2
0.1
3
5
K
6
IC1
SL486
A
6.8k
6.8k
OUTPUT
16
REG IN
0.47
15
0.22
TP2
+6V
7
1
IRD1
BPW50
22
10k
4
14
12
AGC
13
680
.015
IC3a
74C14
IC3b
12
13
9
8
IRLED1
CQY89A
D2
1N4148
IC3d
100Hz NOTCH
3
100k
13
5
Q2
BC328
B
47
+6V
AGC
ADJUST
VR1
10k
FILTER
BUFFER
3
5
10
0.1
9
IC2d
8
100k
6
4
IC2b
7
2
2.7k
1
IC2c
INFRARED REMOTE EXTENDER
Automatic gain control
The automatic gain control (AGC)
output at pin 8 is normally connected
to a 0.15µF capacitor. This filters the
amplified signal and controls the gain
of IC1 to prevent signal overload.
Unfortunately, this AGC system
is only suitable for remote controls
which produce very narrow pulses of
infrared light. In most cases, however, the transmission code consists of
bursts of signal which can be anywhere
between 1kHz and 100kHz in frequen
cy. This type of coding produces too
much AGC for IC1, thereby rendering
the amplifier ineffective.
For this reason, we have completely
revamped the AGC circuit so that the
18 Silicon Chip
C
12VDC
INPUT
BUFFER
S1
1M
1000
16VW
D3
B
A
K
A
K
AMPLIFIER
Fig.2: each time an IR light pulse is received, pin 9 of IC1 switches high & drives
IRLED1 via IC3a & IC3b. A sample of the output pulse from pin 9 is also fed to
IC2a which works with IC2b, IC2c & IC2d to provide automatic gain control.
the 100Hz twin-T filter to provide a
high degree of attenuation for 100Hz
signals. If this were not done, noise
signals from mains-powered lighting
could degrade the receiver’s sensitivity
and reduce its effective range.
+6V
Q1
BC338
B
E
22
BP
DC OFFSET
-6V
TP1
+6V
E
C
3.3k
100k
11
0.1
14
IC2a
LM324
K
ACK
LED2
6 680 A
D1
1N4148
12
220k
IC3e
4
A
K
A
8
3.6k
POWER
LED3
680
IC3c
22
-6V
47k
10
7
9
.047
0.22
14
11
receiver will work with a wide range
of remote control transmitters without
the hassle of fiddly adjustments.
The modified AGC circuit works
as follows. First, the amplified output at pin 9 of IC1 is attenuated by
about 20% using a voltage divider
(47kΩ and 220kΩ) and applied to
the non-inverting input of op amp
IC2a. This op amp is connected as a
unity gain buffer and simply provides
current drive for an AGC filter consisting of D1 a 100kΩ resistor and a
47µF capacitor.
In operation, IC2a and the AGC filter
act as a peak detector for the output
signal that appears at pin 9 of IC1.
Each time a signal is received, the
47µF capacitor charges via D1 and is
then discharged by the 100kΩ resistor
so that the filter output decays after a
few seconds.
This filtered signal is applied to op
amp IC2b which operates with a gain
of 11, as set by the 1MΩ and 100kΩ
E
C
VIEWED FROM
BELOW
1N4004
ALL VOLTAGES MEASURED
WITH RESPECT TO GROUND
feedback resistors. The 22µF capacitor
across the feedback path filters the
output to provide the required AGC
response time.
Bias for the inverting input of IC2b
comes from the AGC adjust pot (VR1)
and is applied via unity gain buffer
stage IC2d.
IC2c and transistor Q1 together form
a high-current buffer stage for the output of IC2b. A 10kΩ pullup resistor
provides the collector load for Q1,
while feedback is provided from Q1’s
collector to the non-inverting input of
IC2c at pin 3. The buffer is made stable
by the 22µF capacitor at pin 8 of IC1,
the capacitor effectively slowing down
the open loop gain of the stage.
Because IC2c and Q1 operate with
unity gain, Q1’s collector voltage
follows the voltage fed to IC2c. Thus,
under no-signal conditions, pin 2 of
IC2c is at ground and so pin 1 goes
high and turns on Q1 (ie, Q1’s collector goes low). Conversely, when a
signal is received, the voltage on pin
2 rises and Q1 progressively turns
off. As a result, Q1’s collector voltage
12VDC
A
47uF
IC1
SL486
IC2
LM324
680
1
220uF
1
680
3.3k
22uF BP
680
Q1
LED2
K
1000uF
0.1
22uF
0.1
22uF
D3
D2
IC3
74C14
.015
3.6k
0.22
0.22
1
K
A
Q2
TP2
100k
A
K
IRD1
1M
LED3
2.7k
K
TP
GND
K
22uF
100k
10uF
VR1
0.1
47k
.047
6.8k
0.47
6.8k
220k
S1
100k
D1
K
K
LED3 LED2
A
A
10k
47
TP1
K
A
IRLED1
Fig.3: here’s how to wire up the IR Remote Extender. Take care with component
orientation & note that IRD1 is mounted with its leads untrimmed so that it can
be adjusted to line up with its viewing hole in the front panel. The board must
be fitted inside a metal case which is connected to the circuit via the solder lug
(at the top of the diagram).
rises so that it remains equal to the
voltage on pin 2.
The output from this buffer stage is
fed to the AGC pin (pin 8) of IC1. This
pin has a low input impedance but Q1
provides sufficient drive to overcome
the internal AGC level.
The AGC action works like this:
when the output signal from IC1 at
pin 9 exceeds the voltage preset by
VR1, the AGC voltage increases on
pin 8. This reduces the gain of IC1
and so the signal level is reduced.
Conversely, when the output from IC1
falls below the preset AGC voltage,
the AGC voltage at pin 8 falls and the
gain increases.
Signal drive
The resulting signal from pin 9 of
IC1 is squared up by Schmitt trigger
IC3a and inverted by IC3b. This then
drives the infrared LED (IRLED1)
via a 680Ω resistor. Thus, each time
a pulse of infrared light is received,
IC3b’s output switches high and
pulses IRLED1.
LED 2 (ACKnowledge) and its associated circuit provide visible indication that a signal has been received.
However, LED 2 cannot be driven by
IC3b because the pulses from this stage
are so short.
To overcome this problem, IC3a’s
output is inverted by IC3c and this
drives a pulse extender circuit consisting of diode D2, a 0.1µF capacitor
and 100kΩ resistor. Each time IC3c’s
output goes high, the 0.1µF capacitor
charges via D2 and buffer stages IC3d
and IC3e drive the ACKnowledge LED
via a 680Ω resistor.
Conversely, when IC3c’s output goes
low (ie, when no signal is being received), the 0.1µF capacitor discharges
via the 100kΩ resistor and the ACK
nowledge LED goes out. Thus, depending on the code from the transmitter,
LED 2 will flicker on and off but at a
much slower rate than IRLED1 due to
the time constant formed by the 100kΩ
resistor and the 0.1µF capacitor in the
pulse extender network.
Power supply
Power for the circuit is derived
from a 12V DC plugpack supply.
This is applied via reverse polarity
protection diode D3 and decoupled
by a 1000µF capacitor. Note that the
resulting supply lines have been
labelled +6V and -6V, rather than
+12V and 0V. This has been done to
simplify the supply labelling for the
rest of the circuit, particularly around
the op amps.
IC1 has an internal regulator which
RESISTOR COLOUR CODES
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
No.
1
1
3
1
1
2
1
1
1
3
1
Value
1MΩ
220kΩ
100kΩ
47kΩ
10kΩ
6.8kΩ
3.6kΩ
3.3kΩ
2.7kΩ
680Ω
47Ω
4-Band Code (1%)
brown black green brown
red red yellow brown
brown black yellow brown
yellow violet orange brown
brown black orange brown
blue grey red brown
orange blue red brown
orange orange red brown
red violet red brown
blue grey brown brown
yellow violet black brown
5-Band Code (1%)
brown black black yellow brown
red red black orange brown
brown black black orange brown
yellow violet black red brown
brown black black red brown
blue grey black brown brown
orange blue black brown brown
orange orange black brown brown
red violet black brown brown
blue grey black black brown
yellow violet black gold brown
April 1994 19
gives about 6V between the positive
rail and ground. This 6V supply provides power for the rest of the circuit,
with the exception of the LEDs.
Transistor Q2 acts as a buffer stage
for the regulator ground supply. Its
emitter is effectively at ground (actually 0.7V), which means that the LED
currents flow through Q2 to the -6V
rail. This prevents the regulator inside
IC1 from being overloaded by the LED
currents (since these currents do not
flow to ground).
Finally, a 22µF capacitor is used to
decouple the 6V supply, while a 47Ω
resistor and a 10µF capacitor provide
additional supply line decoupling for
IC1 to prevent noise from affecting the
sensitive amplifier stages.
PARTS LIST
1 K&W metal case, 127 x 68 x
39mm
1 PC board, code 15303941, 59 x
115mm
1 self-adhesive label, 63 x 33mm
1 self-adhesive label, 63 x 11mm
1 12VDC 300mA plugpack
1 2.5mm panel mount DC socket
1 2-pin panel mount DIN socket
1 2-pin DIN line plug
1 SPDT toggle switch (S1)
2 5mm LED bezels
1 10kΩ horizontal trimpot (VR1)
4 9mm tapped standoffs
1 solder lug
4 3mm dia. x 15mm long screws
5 3mm dia. x 9mm long screws
9 3mm nuts
1 10-metre length 2 x 14/0.19 twin
cable
1 350mm-length twin rainbow
cable
1 120mm-length twin hookup wire
1 100mm green hookup wire (for
earth lead)
1 50mm-length 0.8mm tinned
copper wire
12 PC stakes
4 small rubber feet
Semiconductors
1 SL486 infrared preamplifier
(IC1)
1 LM324 quad op amp (IC2)
1 74C14, 40106 hex Schmitt
trigger (IC3)
1 BC338 NPN transistor (Q1)
1 BC328 PNP transistor (Q2)
2 1N4148, 1N914 signal diodes
(D1,D2)
1 1N4004 1A diode (D3)
1 BPW50 infrared photodiode
(IRD1)
1 CQY89A, LD271 infrared LED
(IRLED 1)
1 5mm green LED (LED 2)
1 5mm red LED (LED 3)
Capacitors
1 1000µF 16VW PC electrolytic
1 220µF 16VW PC electrolytic
1 47µF 16VW PC electrolytic
3 22µF 16VW PC electrolytic
1 22µF 50VW bipolar
1 10µF 16VW PC electrolytic
1 0.47µF MKT polyester
2 0.22µF MKT polyester
3 0.1µF MKT polyester
1 .047µF MKT polyester
1 .015µF MKT polyester
Construction
Most of the parts are mounted on a
PC board coded 15303941 and measuring 59 x 115mm. Fig.3 shows the
assembly details.
Begin the assembly by fitting PC
stakes to all the external wiring points
and to the three test points (TP1, TP2
& TP-GND). This done, install the wire
links, resistors and diodes. Be sure to
use the correct diode at each location
and make sure that it is correctly
oriented.
Now install the ICs, transistors and
capacitors. Note that the ICs are all
oriented in the same direction. The
22µF bipolar capacitor can be installed
either way around but take care with
the orientation of the remaining electrolytic capacitors.
Check the transistor type numbers
carefully when installing these parts
Resistors (1%, 0.25W)
1 1MΩ
1 3.6kΩ
1 220kΩ
1 3.3kΩ
3 100kΩ
1 2.7kΩ
1 47kΩ
3 680Ω
1 10kΩ
1 47Ω
2 6.8kΩ
Miscellaneous
Heatshrink tubing, solder,
insulation tape, etc.
+
+
+
ON
ACK
POWER
+
INFRARED LED SOCKET
(CENTRE ANODE)
INFRARED
REMOTE
EXTENDER
12VDC POWER INPUT (CENTRE +)
▲
Fig.4: here are the full-size artworks for
the front & rear panels.
20 Silicon Chip
Left: bend the leads of the infrared
photodiode (IRD1) so that its face lines
up with the matching front-panel cutout
but make sure that its leads don’t short
against the metalwork.
The infrared LED (IRLED1) is mounted at the end of the 2-wire cable. It can be
installed in a small case or taped in some inconspicuous location near the VCR.
Note that the anode lead of the LED goes to the centre pin of the DIN plug.
on the PC board. Q1 is an NPN type
while Q2 is a PNP type, so don’t get
them mixed up. Push the transistors
down as far as they will comfortably
go before soldering their leads.
The board assembly can now be
completed by installing the infrared
photodiode (IRD1). This device should
be mounted with its leads untrimmed
so that it can later be bent into position
to align with the hole in the front of the
case. Fig.1 shows the pin connection
details for photodiode.
Final assembly
A standard K&W metal case measuring 127 x 68 x 39mm is used to
house the PC board. Attach the front
and rear panel labels to the case (see
photos), then drill out the mounting
holes for the power switch (S1) and
for the Power and ACK LEDs.
The square cutout for IRD1 is made
by first drilling a small pilot hole and
then filing this to shape with a small
three-cornered file. This done, attach
a short piece of insulating tape to the
inside of the case beneath the hole to
prevent IRD1’s leads from shorting to
the metalwork – see photo.
Moving now to the rear panel, the
two sockets must be mounted high up
to provide sufficient clearance to the
PC board. Again, use small pilot holes
to begin with, then enlarge these to size
using a tapered reamer. A three-cornered file will be required to provide
the final shape for the DC socket. Once
the sockets fit their respective holes,
mark and drill the four holes for the
mounting screws.
The PC board is mounted in the case
on four 9mm-long standoffs. Use the
board as a template for marking out its
mounting holes, then drill these holes
to 3mm. You will also have to drill a
mounting hole for the earth solder
lug – see Fig.3.
Fig.5: check your etched PC board against this full-size artwork before installing
any of the parts.
Before installing the PC board in
the case, you will need to wire up
and install the power LED (LED 3).
Use twin rainbow cable for the LED
wiring and insulate the leads with
heatshrink tubing to prevent shorts to
the underside of the PC board. This
done, secure the earth solder lug to
the case and solder a short length of
hookup wire to it.
The PC board can now be installed
in the case and the wiring completed
using light-duty hookup wire. Check
your work carefully against Fig.3 to
prevent any mistakes.
The remote IR LED (IRLED1) is connected to the receiver via a long length
of light-duty speaker cable. This LED
can be either mounted in a separate
small case or taped to an inconspicuous location near the VCR. Be sure to
connect the anode lead of the IR LED
to the centre pin of the DIN plug.
Testing
To test the circuit, apply power from
a plugpack and check that the power
LED lights. Assuming all is well, check
the voltage between TP2 and the GND
terminal – the meter should read between 5.9V and 6.5V DC.
Next, activate the remote control
transmitter and check that the ACK
nowledge LED flickers when a button
is pressed. If it does, connect your
multimeter between TP1 and GND,
activate the remote control, and adjust
VR1 for a reading of 2V. This adjustment sets the AGC level.
The maximum range for the receiver can now be checked. This will
vary according to the remote control
transmitter but you should be able to
achieve at least five metres.
Finally, plug in the lead to the infrared LED and check that it correctly
activates your VCR in the other room
each time a transmitter button is
pressed. Note that the infrared LED
should be placed within one metre of
the VCR’s sensor for best results.
For some remote controls, you may
need to tweak the AGC level (using
VR1) to obtain the maximum range.
This should be done on a trial and
error basis, although the final setting
should not be too far from the setting
arrived at earlier.
In some cases, it may also be necessary to move the receiver away from the
TV set to prevent interference from the
line flyback pulses which can desensiSC
tise the front-end circuitry.
April 1994 21
Sound & lights for
level crossings
This Sound & Lights module is intended to
be controlled by the Level Crossing Detector
published last month. It drives LEDs or
miniature incandescent lamps for the level
crossing signs & produces a most convincing bell
sound as an accompaniment.
By JOHN CLARKE
Apart from the lifelike effect of
flashing lights, the particular attraction
of this project is the uncanny sound
of the bell. Anyone who has stopped
at a level crossing on a rainy or foggy
night will recall the eerie sound of the
bells as their rate of ringing wavers up
and down. This circuit reproduces
this effect and thereby greatly adds to
the realism.
The Sound & Lights module comprises an on/off control, a lamp flasher and circuitry to generate the bell
sound, as depicted in Fig.1. The on/
22 Silicon Chip
off control (IC2) prevents the circuit
from operating unless its input is low.
The lamp flasher alternately flashes
the two lamps at a rate of about twice a
second which is close to the rate used
on typical level crossing lights. The
bell sound circuitry is more complex
and comprises a ringing oscillator
which provides the bell tone, a bell
rate oscillator which determines the
rate at which the bell is struck, and a
warble oscillator to vary the rate of the
bell rate oscillator.
The ringing oscillator produces
a pure sinewave whenever the bell
rate oscillator pulses its input. The
sinewave starts with a high amplitude which dies away in volume
until the next pulse from the bell
rate oscillator.
The amplifier stage (IC3d) boosts
the signal to a suitable level for the
loudspeaker. It produces only a small
amount of drive, just sufficient to
make the bell sounds audible when
you are close to the speaker which
will be concealed under the layout
close to the level crossing. The sound
level must not be too loud, otherwise
it will be “out of scale” with the rest of
the layout and would quickly become
annoying.
Now have a look at the complete
circuit of the Sound & Lights module,
as shown in Fig.2. We’ll discuss the
flasher section first. It employs IC1, a
4093 quad 2-input Schmitt NAND gate
package. IC1a is used as a conventional Schmitt trigger oscillator and its
frequency is determined by the 47µF
capacitor at pins 1 & 2, together with
the series 2.2kΩ resistor and 50kΩ
trimpot VR1.
IC1c inverts the output of IC1a so
that the two Schmitt triggers constitute a two-phase square wave oscillator with the outputs fed to gates
IC1b and IC1d. These two gates are
enabled or disabled by IC2a which can
be thought of as the master switch; it
is part of the on/off control referred
to earlier.
When pins 9 & 12 of IC1 are pulled
low by IC2a, their outputs at pins 10
& 11 are high and the circuit is effectively disabled. When pins 9 and 12
are high, the alternating square wave
signals from pins 3 & 4 are fed through
to transistors Q1 and Q2 to drive the
level crossing lights.
Note that there are four lights in
total, two for each side of the crossing,
and they must be cross-connected so
AMPLIFIER
IC3d
BELL RATE
OSCILLATOR
IC3a
ON/OFF
IC2b,c
RINGING
OSCILLATOR
IC3c
WARBLE
OSCILLATOR
IC3b
ON/OFF
CONTROL
INPUT
SPEAKER
IC2a
LIGHTS
LAMP
FLASHER
Fig 1
Fig.1: the Sound & Lights module uses three oscillators to produce the bell
sound and another for the lamp flasher.
Fig.2 (below): just three ICs are used in the circuit for the Sound & Lights
module. One of the op amps in the LM324 package drives the loudspeaker
directly via a 68Ω resistor and 1µF capacitor.
+10V
0.1
10
10
OSCILLATOR
ADJ
VR 3 500W
100k
100k
100k
10k
100k
6
5
IC3b
LM324
10
100k
100k
10
IC2c
11
RATE
VR2 50k
11
2
8
27k
+10V
10
IC2b
8
.0047
100k
10k
14
9
6
+11.5V
D1
1N4004
2.7k
12V
INPUT
IC2a
4066
1
68
1
IC3d
12
1M
BELL STRIKER
RATE OSCILLATOR
10k
3
14
.0047
47k
+10V
13
10
33k
IC3c
D2
1N418
100
WARBLE OSCILLATOR
8
IC3a
9
100k
10k
4
12
3.3M
7
10k
68
+10V
ZD1
10V
1W
1000
16VW
2
13
7
INPUT
+10V
1
1
IC1a
4093
IC1b
13
3
2
FLASHER
RATE
VR1 50k
12
5
2.2k
IC1c
4
8
6
B
47
A
K
9
C
VIEWED FROM
BELOW
14
IC1d
+11.5V
2.2k
11 22k
10 22k
B
Q1
BC557
7
2.2k
E
B
Q2
BC557
C
1
LAMP
1A
LAMP
1B
LEVEL CROSSING LIGHTS AND BELL
E
C
2
LAMP
2A
LAMP
2B
1
LED
1A
LED
1B
A
A
K
2
LED
2A
LED
2B
A
A
K
OPTIONAL LED LIGHTS
K
K
1k
1k
April 1994 23
Fig.4: the wiring diagram. Note
that IC3 is oriented differently to
the other two integrated circuits.
D1
1uF
22k
2.2k
GND
100k
2.7k
PARTS LIST
1 PC board code, 15203932,
150 x 97mm
1 10-way PC mount screw
terminal block
1 4-way PC mount screw
terminal block
1 small 8-ohm loudspeaker
2 50kΩ horizontal trimpots (VR1,
VR2)
1 500Ω horizontal trimpot (VR3)
Semiconductors
1 4093 quad NAND Schmitt
trigger (IC1)
1 4066 quad analog switch (IC2)
1 LM324 quad op amp (IC3)
2 BC557 PNP transistors
(Q1,Q2)
1 1N4004 1A diode (D1)
1 1N4148 diode (D2)
1 10V 1W zener diode (ZD1)
4 2mm red LEDs (see text)
Capacitors
1 1000µF 16VW electrolytic
1 47µF 16VW electrolytic
4 10µF 16VW electrolytic
1 1µF 16VW electrolytic
1 0.1µF MKT polyester
2 .0047µF MKT polyester
Resistors (1%, 0.25W)
1 3.3MΩ
5 10kΩ
1 1MΩ
1 2.7kΩ
8 100kΩ
3 2.2kΩ
1 47kΩ
2 1kΩ
1 33kΩ
1 100Ω
1 27kΩ
2 68Ω
2 22kΩ
24 Silicon Chip
2.2k
D2
22k
10k
10k
TO LAMPS 1
and is connected to the
threshold voltage input
2x.0047
(pin 10) of IC3a via a 3.3MΩ
TO LED CATHODES
VR1
VR3
Q2
resistor. This slightly varies
the threshold voltage of the
bell striker oscillator (IC3a)
100k
1k
2.2k
to provide a small variation
1k
in the pulse rate.
The resulting pulses from
IC3a drive the centre leg of
that each pair of lights on the level a T-section filter connected across the
crossing signals flash alternately.
1MΩ feedback resistor of op amp IC3c.
The circuit can be made to drive This op amp is adjusted using trimpot
red LEDs rather than miniature incan- VR3 so that it is just on the verge on
descent lamps. We have shown the oscillation. As a result, each time it
alternative connection for LEDs with receives a pulse from IC3a, it briefly
a 1kΩ current limiting resistor for each bursts into oscillation.
cross-connected pair.
This effect can be seen in the oscilloscope photograph of Fig.3. The top
Bell oscillators
trace of this photograph shows the
The bell circuit comprises op amps very brief pulses which trigger IC3a
IC3a-IC3d. IC3 is an LM324 quad into operation, while the lower trace
op amp and IC3a is connected as a shows the bursts of oscillation which
Schmitt trigger oscillator to provide come at varying intervals.
the bell strike rate. It operates as fol
Amplifier stage
lows.
Initially, the 10µF capacitor at pin
Op amp IC3d functions as an am9 is discharged and the output of plifier to drive the loudspeaker. As
IC3a is high. Pin 10 of IC3a is held at explained previously, only a modest
about +6.6V by the 100kΩ resistors power output is needed and so an op
to ground, to the +10V supply and amp is quite adequate.
to the op amp’s output (pin 8). When
IC3d is biased at half supply via the
power is applied, the capacitor begins two 10kΩ voltage divider resistors at
to charge via diode D2 and the 100Ω pin 3, with bypassing provided by
resistor. When its voltage reaches the
6.6V threshold, the output at pin 8 goes
low and pin 10 now drops to about
+3.3V (due to the loading effect of the
100kΩ resistor to pin 8).
The 10µF capacitor now discharges
via the 47kΩ resistor and trimpot VR2
until it reaches the 3.3V threshold, at
which point the op amp output again
goes high. Thus, we have an oscillator
which produces very short pulses at a
rate of about twice a second (depending on the setting of trimpot VR2).
Fig.3: the top trace of this photograph
IC3b is also set up as a Schmitt shows the very brief pulses which
trigger oscillator and this charges and trigger IC3a into operation while
discharges the 10µF capacitor at pin the lower trace shows the bursts of
6 via a 100kΩ resistor. The oscillator oscillation which come at varying
output in this case is a square wave intervals.
47uF
33k
VR2
ZD1
IC1
4093
2x10uF
1
1M
1
10k
IC3
LM324
10uF
100k
0.1
47k
IC2
4066
100
+
+12V
TO SPEAKER
3.3M
+
GND
Q1
1
100k
SPARE
INPUT
10k
GND
100k
INPUT
100k
10uF
68
27k
68
10k
100k
100k
100uF
TO LAMPS 2
Fig.5: actual
size artwork for
the PC board.
Check your
board carefully
against this
pattern before
mounting any
of the parts.
the associated 10µF capacitor. IC3c is
also biased from this voltage divider,
via trimpot VR3. The bell signal from
IC3c is fed to IC3d via analog switch
IC2b which is closed while its pin 6 is
high. Since pin 6 of IC2b is controlled
by the same signal line which enables
the flasher circuitry, it ensures that the
two circuits switch on and off at the
same time.
One analog switch has not been
mentioned so far and that is IC2c
which is connected between the inverting and non-inverting inputs of
IC3d. IC2c is closed (ie, conducting)
whenever IC2b is open. Thus, when
the bell signal is not being fed to IC3d,
switch IC2c ensures that the amplifier
stage is fully muted.
IC3d drives the loudspeaker via a
68Ω resistor which limits the current,
while the 1µF capacitor prevents any
DC from flowing through the loudspeaker’s voice coil.
Construction
All the components for the Sound
& Lights module are assembled onto a
PC board measuring 150 x 97mm and
coded 15203932. Before you begin any
soldering, check the board thoroughly
for any shorts or breaks in the copper
tracks and repair any faults that you
do find.
This done, install the resistors, link,
PC stakes (if used) and ICs. Note that
IC3 is oriented differently to the other
ICs. Now install the transistors, zener
diode and diodes, making sure that
they are all oriented correctly.
The trimpots and capacitors can be
mounted now, taking care with the
orientation of the electrolytic capacitors. Finally, if you are using terminal
blocks, mount these as well.
Once the PC board has been assembled, it is ready for testing. Note that
the power for the PC board should
be obtained from a 12V DC supply.
If you built the Walkaround Throttle
described in the April & May 1988 issues of SILICON CHIP, or the IR Remote
Controlled Throttle described in the
April, May & June 1992 issues, you
won’t need a separate supply as this
facility is already provided.
Make sure that you have your
multimeter handy, so that you can
measure the DC voltages on the PC
board. Connect an 8Ω loudspeaker
and two lamps (or LEDs) to the board
in their designated positions. Now
apply power and check that the voltage
across ZD1 is close +10V. If not, switch
off and find the fault before applying
power again. Even though the voltages
are all correct, the circuit should not be
operating unless the you have a jumper
wire in the input terminal block, to
connect the input to GND.
With the input connected to GND,
the lamps should be flashing alter-
nately and you should be able to adjust the rate of flashing with trimpot
VR1. The correct rate is about twice
a second.
You will probably also find that the
loudspeaker is howling and this can be
stopped by rotating trimpot VR3 clockwise, after which it should sound like
“dink dink dink dink ..”. By carefully
rotating VR3 anticlockwise, you will
reach a point where the loudspeaker
sounds just like a bell. You can also
adjust the rate at which the bell is
struck by rotating trimpot VR2 but after
doing that, you may need to tweak VR3
again for the best effect.
With the board complete and running, you can install it underneath
your layout and operate it with a
switch when required or have it controlled by the Level Crossing Detector
board described last month.
Finally, we should comment about
the size of the LEDs used for level
crossing signs. Ideally, these should
be as small as possible. If you have
an HO-scale layout (1:87), even 3mm
LEDs are too large as they will “scale
out” to a diameter of 261mm. Ideally,
you should use 2mm LEDs as made by
Hewlett Packard (they make them in
red, orange, yellow and green).
You can purchase these miniature
LEDs from HT Electronics, PO Box
491, Noarlunga Centre, South AustralSC
ia 5168. Phone (08) 326 5590.
April 1994 25
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
Need a dual
supply regulator in
a hurry but don’t
have any LM317 or
7805
3-terminal
regulators handy?
This simple circuit
can provide
regulated supply
rails from ±5V to
±12VDC at up to
800mA.
I
F YOU’RE NOT in the component
buying business, then you’ll probably be unaware that there has
been a severe world-wide shortage of
parts during the last 12 months – particularly 3-terminal regulators. Now
since these devices get a guernsey in
just about every project designed, we
recently decided to see if we could
come up with some sort of replacement based on readily available components.
Since doing this work, the supply
situation has vastly improved but
we still feel that the design may be
suitable for many applications. The
fact that it uses only junkbox parts is
a major plus.
All the parts for the regulator are
built onto a small PC board. This contains everything necessary to convert
the AC voltage from a centre-tapped
mains transformer to regulated plus
and minus DC supply rails, including
a bridge rectifier and filter capacitors.
It will provide an output voltage of
between ±5V and ±12V DC at currents
up to 800mA.
Circuit diagram
Fig.1 shows the circuit diagram for
the Dual Regulated Power Supply. It
uses four power diodes, an LM358
dual op amp, a zener diode, a couple
of transistors and sundry resistors and
capacitors.
Power is derived from a 12-24V
centre-tapped mains transformer. Its
output is fed to a bridge rectifier consisting of diodes D1-D4 to produce
positive and negative rails which are
then filtered using two 470µF electrolytic capacitors. These rails are then
fed to the collectors of transistors Q1
and Q2 respectively and are also used
to power the dual op amp (IC1).
Discrete dual supply
voltage regulator
By DARREN YATES
The assembled PC board can form the basis
of a simple variable power supply or can be
used to provide fixed regulated supply rails
from ±5V to ±12V DC.
April 1994 29
R2
10k
6
4x1N4004
A
240VAC
N
D4
R1
10k
D1
5
F1
2A
6-12V
Q1
BD139
8
7 100
IC1a
LM358
B
E
D4
.047
1N4148
1k
C
+VOUT
0V
6-12V
D3
470
25VW
D2
10
16VW
ZD1
4.7V
400mW
470
25VW
Fig.1: the regulated
positive supply rail is
derived by using ZD1 to
set a reference voltage
on pin 5 of inverting
amplifier stage IC1a.
This in turn drives
current amplifier stage
Q1. Inverting amplifier
stage IC1b & current
amplifier Q2 are used to
derive the negative rail.
GND
PLASTIC
SIDE
100k
470
25VW
E
C
470
25VW
100k
-VOUT
.047
2
B
1
IC1b
3
100
4
F2
2A
B
Q2
BD140
E
C
DUAL REGULATED POWER SUPPLY
IC1a and its associated zener diode
(ZD1) form the heart of the regulation
circuit. This op amp is connected as
a bootstrapped-diode reference source
and drives current amplifier stage Q1.
IC1b, on the other hand, simply functions as a unity gain inverter stage; it
drives current amplifier Q2
Zener diode ZD1 functions as the
reference element and is part of a positive feedback path around IC1a. This
feedback path may not be all that clear
at first glance – it starts at the output
of IC1a (pin 7) and goes via the 100Ω
resistor, the base-emitter junction of
Q1, diode D4 and the 1kΩ resistor,
before ending at the non-inverting
input (pin 5). This loop ensures that
the output voltage remains constant.
The 10µF capacitor across ZD1 filters
out any noise on the line and improves
the regulation.
Note that it is necessary to include
the transistor (Q1) in the feedback loop
so that the op amp can compensate for
the voltage drop across the base-emitter junction to give the required output
voltage.
Setting the output voltage for the
positive rail is now just a case of selecting the negative feedback network
to set the gain of IC1a. This feedback
network consists of two resistors (R1
and R2) connected in the usual way;
ie, one from the output to the inverting
input (pin 6) and the other from the
inverting input to ground.
30 Silicon Chip
The formula for the output voltage
is: Vout = 5.3V x (R2 + R1)/R1
where the 5.3V reference is equal to
the voltage across ZD1 plus the voltage
across D4 (ie, 4.7 + 0.6 = 5.3V). With
the current values, IC1a’s gain is set
to two and so the output voltage is set
to 10.6V. However, this can be easily
PARTS LIST
1 PC board, 04103941, 107 x
53mm
6 PC stakes
2 M205 (2AG) fuse clips
2 M205 2A fuses
2 Micro-U heatsinks
1 centre-tapped mains
transformer to suit (see Table 1)
Semiconductors
1 LM358N dual op amp IC
1 BD139 NPN transistor
1 BD140 PNP transistor
1 4.7V 400mW zener diode (ZD1)
4 1N4004 rectifier diodes
1 1N914 signal diode
Capacitors
4 470µF 25VW electrolytic
1 10µF 16VW electrolytic
2 0.047µF 63VW MKT polyester
Resistors (0.25W, 1%)
2 100kΩ
1 1kΩ
2 10kΩ
2 100Ω
altered by changing the value of R1,
R2 or ZD1.
The negative rail is much simpler
to produce because all we need do is
invert the output of the positive rail.
This is done by feeding the voltage
on the emitter of Q1 to the inverting
input (pin 2) of IC1b via a 100kΩ
resistor.
As previously mentioned, IC1b
functions as a unity gain inverting amplifier. Its output at pin 1 drives PNP
power transistor Q2 via a 100Ω current
limiting resistor. As before, the output
transistor is included in the feedback
loop to ensure that its base-emitter
voltage is compensated for. In this way,
the negative rail mirrors the voltage on
the positive rail.
The two .047µF capacitors connected across the base-emitter junctions of
Q1 and Q2 reduce the sensitivity of the
circuit to noise or glitches and improve
the regulation. The final outputs are
taken from the emitters of Q1 and Q2
and filtered by two 470µF capacitors.
A maximum of 800mA can be supplied
by both sections.
Construction
All of the components for the Discrete Power Supply, including the two
2A fuses, are installed on a PC board
coded 04103941 and measuring 107
x 53mm.
Before you begin construction, it’s
a good idea to check the PC board
TABLE 1
1k
R2 10k
F1
D1-D2
470uF
0V
IC1
LM358
D3-D4
470uF
AC2
D5
470uF
ZD1
R1 10k
AC1
.047
100W
Q1
10uF
100k
+VOUT
0V
100k
470uF
-VOUT
Q2
Fig.2: install the parts on the PC board as shown here & note that small finned
heatsinks should be fitted to Q1 & Q2. Resistors R1 & R2 are selected to set the
required output voltage – see text.
Fig.3: this is the full-size etching pattern for the PC board.
for any shorts or breaks in the tracks.
You can do this by carefully checking
your etched board against the full-size
pattern. Generally, there won’t be any
problems here but it’s always a good
idea to make sure.
Begin the board assembly by installing the two wire links, followed by
the resistors, diodes and capacitors.
Be sure not to confuse the zener diode
with the rectifier and signal diodes.
After that, install the IC and power
transistors. Be particularly careful
with these components – check the
orientation of the IC carefully and note
that the transistors are installed with
their plastic faces towards the adjacent
.047µF capacitors.
Transformer
5V
12V CT
6V
15V CT
8V
18V CT
12V
24V CT
.047
100
F2
DC Output (V)
Note also that Q1 is an NPN transistor while Q2 is a PNP type, so be
sure to use the correct transistor at
each location.
Finally, solder in six PC stakes at
the external wiring points, install the
fuse clips and bolt two small finned
heatsinks to the power transistors.
There’s no need to isolate the transistors from the heatsinks but don’t let
them short against any of the other
parts on the board.
To test the circuit, you need a
centre-tapped mains transformer (or
you can use an AC plugpack supply
with a centre tap). Table 1 shows the
transformer input voltage you need
for a given DC output voltage. Wire up
the secondary windings of the transformer to the PC board as shown on
the overlay diagram and the primary
to a mains terminal block.
Warning: use extreme caution when
installing the mains wiring – 240VAC
can kill! The transformer and the PC
board should be mounted inside a
metal case and this must be securely
earthed. Cover all mains connections
with heatshrink tubing to avoid the
possibility of electric shock.
Before applying power, check your
wiring carefully for any wrong connections. Once you’re sure that everything
is OK, switch on and check the output voltage with your multimeter. If
you have used the values shown on
the circuit, you should get a reading
of about 10.6V on both rails with
respect to ground (this will depend
on the exact voltage across the zener
diode). If need be, you can substitute
a trimpot for resistor R2 and trim the
output voltage until it is exactly what
you require.
A variable supply
By replacing R2 with a 20kΩ linear
potentiometer, you can make a simple
dual-tracking variable power supply
capable of covering the range from ±5V
to about ±12VDC. The circuit could
thus form the basis of a very useful
benchtop power supply for powering
experimental lash-ups.
For lower output voltages, you could
replace ZD1 with a number of signal
diodes. If only one diode is used, the
output voltage will be about ±2.4V.
Remember, the formula for the output
voltage is: Vout = (VZD1 + VD4) x (R2
SC
+ R1)/R1.
RESISTOR COLOUR CODES
❏
❏
❏
❏
❏
No.
2
2
1
2
Value
100kΩ
10kΩ
1kΩ
100Ω
4-Band Code (1%)
brown black yellow brown
brown black orange brown
brown black red brown
brown black brown brown
5-Band Code (1%)
brown black black orange brown
brown black black red brown
brown black black brown brown
brown black black black brown
April 1994 31
This universal preamplifier
can be easily constructed for
use with a magnetic cartridge,
cassette deck or a dynamic
microphone. It uses a single
dual op amp IC & has very
low distortion.
By DARREN YATES
Low-noise universal
stereo preamplifier
T
HIS PROJECT WAS borne out of
the recent news that National
Semiconductor has discontinued its LM380 series of stereo pream
plifier ICs. These have been around
since the early 1970s and have been
popular with enthusiasts for all sorts
of projects. In fact, these devices were
not all that good by today’s standards
which is another reason to produce an
up-to-date design.
Our little universal preamp uses
the industry standard LM833 dual
op amp IC which has very low noise
and distortion. Perhaps the prime use
will be for those people who have
an integrated stereo amplifier which
they are quite keen on but which has
a phono or tape preamp which could
be improved. And that applies to
the phono preamps in a great many
amplifiers. They weren’t designed to
32 Silicon Chip
give the minimum noise, minimum
distortion and the greatest overload
margin. In fact, about the best thing
you can say about the preamplifier
stages in many older amplifiers is that
they are still working.
By comparison, the performance of
the design presented here is far better
than most preamplifiers in most stereo
amplifiers – that’s a pretty ambitious
statement but it is true nonetheless.
How do you decide whether it would
be worthwhile to upgrade your amplifier’s preamplifier. That is fairly easy
to determine, providing you still listen
to vinyl records.
Just set your amplifier’s controls to
their normal settings and listen for
hiss with no record playing. Can you
hear hiss from the loudspeaker (or
headphones) at your normal listening
position? If so, does this hiss greatly
reduce or disappear when you rotate
the volume control to its minimum setting? If the answer to both questions is
yes, then it is likely that your existing
preamplifier produces more than its
fair share of noise. This new design
is extremely quiet so you are sure to
hear a reduction in hiss.
Even if you don’t need to upgrade
your existing amplifier’s preamplifier, you may still have an application
for the design presented here. For
example, you may want to run two
turntables. If your amplifier only has
one pair of phono inputs, you could
use this external preamplifier for the
additional turntable and then feed its
outputs to one pair of the line inputs
of the stereo amplifier.
Alternatively, you may have an
audio mixer which does not have a
phono preamplifier or you may wish
LEFT
INPUT
+15V
L1
150
100k
47
BP
3(5)
100pF
100k
2(6)
8
1(7)
IC1a
LM833
0.33
1M
4
L1 : 4T, ENCU WIRE
ON PHILIPS 4330 030 3218
FERRITE BEAD
100
LEFT
OUTPUT
-15V
IC PIN NUMBERS IN BRACKETS
ARE FOR RIGHT CHANNEL
R1
16k
R2
200k
C1
.0047
C2
.015
R4
390
47
BP
R1
0W
+15V
+15V
R3
3.6k
C3
.015
R1
0W
R2
200k
R4
200
47
BP
0.1
GND
0V
0.1
-15V
R2
200k
-15V
R4
390
C2
22pF
47
BP
UNIVERSAL PREAMPLIFIER
Fig.1: the circuit is shown with three different feedback networks: one for a
magnetic cartridge (top); one for tape or cassette decks (centre); & a third for
microphones (bottom). The inductor, series resistor & 100pF shunt capacitor at
the input form a filter circuit to remove RF interference signals.
to incorporate it into a public address
system.
We have also shown how this
preamp could be used with a tape deck
which does not have its own playback
electronics or where the existing tape
preamp is unduly noisy.
Finally, this design can function as a
high-quality microphone preamplifier
for use with cassette decks (which normally don’t have microphone inputs)
or in a public address system.
We’re presenting this universal
preamp as a PC board only, leaving
you with the opportunity to install it
anywhere you have space for it. The
major rule is to keep it away from any
mains wiring or transformers. This
will reduce any hum pickup.
The circuit
The circuit shown in Fig.1 looks a
little odd but we’ve presented it this
way to avoid having to show three
completely separate versions. So
we have shown just one channel of
the preamplifier with three different
feedback networks: one for magnetic
cartridge, another for tape or cassette
decks and a third for microphone.
For the magnetic cartridge function,
IC1a not only has to amplify the signal
but must also apply RIAA equalisation. It takes the low level signal from
the moving magnet cartridge (typically, a few millivolts) and applies a
gain of 56, at the median frequency
of 1kHz. Higher frequencies get less
gain while lower frequencies get
considerably more, as shown in the
accompanying equalisation curve of
Fig.2.
To be specific, a 100Hz signal has a
boost of 13.11dB while a 10kHz signal
has a cut of 13.75dB.
The phono signal is fed directly
April 1994 33
from the input socket via inductor L1,
a 150Ω resistor and a 47µF bipolar capacitor to the non-inverting input (pin
3) of IC1a. The inductor, series resis
tor and shunt 100pF capacitor form a
filter circuit to remove RF interference
signals which might be picked up by
the phono leads.
The 100pF capacitor is also important in capacitive loading of the mag-
PARTS LIST
(Magnetic cartridge version)
1 PC board, 01106941, 80 x
78mm
8 PC stakes
2 Philips ferrite beads 4330 030
3218
Semiconductors
1 LM833 dual op amp (IC1)
Capacitors
4 47µF 50VW bipolar electrolytic
2 0.33µF 63VW MKT polyester
2 .015µF 63VW MKT polyester
2 .0047µF 63VW MKT polyester
2 100pF ceramic
Resistors (0.25W, 1%)
2 1MΩ
2 390Ω
2 200kΩ
2 150Ω
4 100kΩ
2 100Ω
2 16kΩ
Miscellaneous
Shielded cable, screws, nuts,
tinned copper wire.
+20
20Hz (7950uS)
netic cartridge. Most moving magnet
(MM) cartridges operate best with
about 200 to 400pF of shunt capacitance. The 100pF capacitance in the
preamp input circuit plus the usual
200pF or so of cable capacitance for
the pickup leads will therefore provide
about the right shunt capacitance.
For its part, the 47µF bipolar capacitor is far larger than it needs to be
as far as bass signal coupling is concerned. If we were merely concerned
with maximising the bass signal from
the cartridge, then an input coupling
capacitor of 0.47µF would be quite
adequate. At 20Hz, a capacitor of this
value would have an impedance of
around 15kΩ which is considerably
less than the nominal 50kΩ input
impedance of the preamp.
But having a large capacitor means
that the op amp “sees” a very low impedance source (ie, the DC resistance
of the cartridge) at low frequencies
and this helps keep low frequency
noise, generated by the input loading
resistors, to a minimum.
RIAA/IEC equalisation
The RIAA equalisation is provided
by the feedback components, R1, C1,
R2 and C2, between pins 1 and 2 of
IC1a (or pins 6 and 7 of IC1b, in the
other channel, which is not shown).
These equalisation components provide the standard time constants of
3180µs (50Hz), 318µs (500Hz) and
75µs (2122Hz). The phono pream
plifier also adds in the IEC recom-
mendation for a rolloff below 20Hz
(7950us). This is provided by the
0.33µF output coupling capacitor in
conjunction with the load represented
by the following amplifier’s volume
control and input circuitry (which is
likely to be around 50kΩ).
There is also a further low frequency rolloff, at around 9Hz, caused by
the 47µF capacitor in series with the
390Ω resistor. The 390Ω resistor sets
the maximum AC gain at very low
frequencies while the 47µF capacitor
ensures the gain for DC is unity. This
means that any input offset voltages
are not amplified, which would inevitably cause trouble with asymmetrical
clipping and premature overload in
the preamplifier.
Actually, the magnetic cartridge
version of the circuit just described is
identical to the phono preamplifier of
the Studio 200 Control Unit, published
in the June and July 1988 issues.
Incidentally, the mention of RIAA/
IEC equalisation above refers to two
different disc recording standards.
The RIAA standard was originally set
by the Record Industry Association
of America in 1953. The later IEC
variation was recommended by the
International Electrotechnical Commission in the 1970s.
Tape equalisation
In the tape equalisation version, the
value of R2 is identical to that of the
phono preamplifier but R4 is changed
to 200Ω and R1 is replaced by a wire
50Hz (3180uS)
DECIBELS
+10
2.12kHz (75uS)
0
500Hz (318uS)
-10
-20
2
10
20
100
HERTZ
1k
10k
Fig.2: this graph shows the RIAA/IEC equalisation characteristics provided by the feedback components
for the magnetic cartridge preamplifier version.
34 Silicon Chip
20k
0.33
47uF
1M
R2
R1
47uF
47uF
0.1
IC1
LM833
1
C1
L1
100k
LEFT OUTPUT
100pF
1M
R2
R4
GND
100
100k
0.33
0V
-15V
R1
150
GND
+15V
C1
0.1
L1
R3
150
RIGHT INPUT
C2
R4
100pF
100k
GND
100
GND
LEFT INPUT
C3
100k
R3
RIGHT OUTPUT
C2
C3
47uF
Fig.3: refer to the main circuit diagram for the values of
R1-R4 & C1-C4 & install these parts to suit your application.
link. C1 and C2 are omitted and replaced by R3 and C3.
Microphone version
In the microphone version, R2
and R4 are the same as in the phono
preamp while R1 is a short circuit
and C1 is omitted altogether. The microphone preamp has a gain of 513,
making it suitable for low impedance
microphones. If less gain is required,
it is simply a matter of changing the
ratio of R2 to R4. For example, if you
want a gain of 100 times, make R4
470Ω and R2 47kΩ.
Power supply
The required power supply is a
regulated source of ±15V DC at around
10mA. This could come from 7815 and
7915 3-terminal regulators or derived
from supply rails in your existing
equipment. If you want a PC board for
this job, refer to the “Universal Power
Fig.4: check your PC board before installing the parts
by comparing it with this full-size etching pattern.
Supply Board for Op Amp Circuits”
published in the August 1988 issue of
SILICON CHIP. (This issue is now out
of print but we can supply photostat
copies of the article for $6. Alternatively, you could use the discrete
regulator design published elsewhere
in this issue.
Construction
All the input circuitry for the universal preamp goes onto a small PC
board measuring 80 x 78mm and coded
01106941. Before you begin construction, check the PC board carefully
for any shorts or breaks in the tracks.
If you find any, correct the problem
before installing any parts.
When you’re happy that the board
is OK, you must decide which version
you are going to construct. In each
case, make sure you know which resistors and capacitors numbers must be
included and which must be left out or
replaced with wire links. In any case,
use the component wiring diagram of
Fig.3 to carefully check the position
of all components.
Begin by installing the wire links,
followed by the resistors and the MKT
capacitors. This done, solder in the IC
and then continue with the electrolytic
capacitors.
Once the board is fully assembled,
check it for correct installation of all
the components. You can now connect
the ±15V supplies and check the DC
voltages with respect to one of the PC
stakes which is connected to 0V to
GND. You should have +15V at pin 8
and -15V at pin 4 of the IC.
You can also check the offset voltages at the outputs of IC1, pins 1 & 7. The
voltage at these pins should be within
±100mV of 0V but will most likely be
a lot less than this. If that is the case,
the PC board is ready to be installed
SC
into your equipment.
RESISTOR COLOUR CODES
❏
No.
Value
4-Band Code (1%)
5-Band Code (1%)
❏
2
1MΩ
brown black green brown
brown black black yellow brown
❏
2
200kΩ
red black yellow brown
red black black orange brown
❏
4
100kΩ
brown black yellow brown
brown black black orange brown
❏
2
16kΩ
brown blue orange brown
brown blue black red brown
❏
2
390Ω
orange white brown brown
orange white black black brown
❏
2
150Ω
brown green brown brown
brown green black black brown
❏
2
100Ω
brown black brown brown
brown black black black brown
April 1994 35
Review: PICSTART Development System
Microcontrollers with
speed: the new PIC series
The new PIC-series microcontrollers from
Microchip Corporation use new RISC
architecture which contain as little as 33
instructions. We review these microcontrollers &
the new PICSTART development system.
By DARREN YATES
Microcontrollers have taken off in
the last few years or so, yet the internal
structure of most of them is based on
the 8-bit microprocessor system that
dates back to the days of the Z-80.
At the moment, there would hardly
be a semiconductor house that doesn’t
manufacture at least one micro
controller. And most have at least a
dozen or more in their range. Looking
through the databooks, many are simply variations on the same theme with
maybe just extra I/O ports.
The PIC series from Microchip are
radically different from the rest of the
pack because of the RISC (reduced
instruction set) architecture.
There are only 33 instructions in
the most basic unit but because each
instruction is 12 bits wide, it gives
each instruction a much greater degree of flexibility. What’s more, all
instructions are single- or two-clock
cycle, with most being one clock cycle.
This makes time-related programming
much simpler than most of the standard 8-bit controllers.
The RISC architecture also enables
PICs to run very fast. In fact, they can
operate at up to 20MHz yet they are
still low power devices. At 4MHz,
the current consumption is less than
2mA at 5V and only a tiny 15µA at
3V for 32kHz operation, making them
This is the initial screen displayed by the MPSTART system. This menu-driven
package is used to program most of the PIC series microcontrollers.
36 Silicon Chip
ideal for extended battery operation.
Further, there are extra features to
improve power consumption performance, including sleep modes and
low-power clock oscillators. They are
also guaranteed to operate down to
2.5V supply.
Each device has on-board EPROM
memory varying from 512 bytes to 2Kb
for program storage, as well as between
25 and 72 8-bit registers for general
use. There is also a code protection
fuse which can be blown once final
code has been programmed in. One of
the most useful programming features
is the inclusion of an 8-bit real time
clock\counter with a programmable
prescaler. This makes it easy to program the device to work as some clock
type function.
There are two main families of PICs
– the PIC16CXX and PIC17CXX series
which are tailored for different applications but all with the high-speed
RISC system.
PIC16C5X series
The basic PIC series is the
PIC16C54/5/6/7. The PIC16C54 is
the simplest and smallest, and comes
housed in an 18-pin DIP package, either ceramic or plastic. You can also
get it in surface mount. It has 512 bytes
of 12-bit EPROM, 32 bytes x 8 bit RAM
and 12 I/O lines.
The PIC16C55 is the same as the
above 16C54 but with 20 I/O lines.
It comes in a 28-pin package. The
PIC16C56 is also based on the ’54 but
with 1Kb of EPROM. The top of the
range PIC15C57 has 2Kb of EPROM,
80 bytes of RAM and 20 I/O lines. For
most applications, this makes the PIC
the ideal single-chip computer since
there is no external memory or driver
hardware required.
In all PICs, the RAM is individu-
The PICSTART Development System comes with two manuals: the complete
Microchip Databook & the Embedded Controller Handbook.
ally addressable when programming
whereas the EPROM is addressable
in 512-byte pages. The I/O lines are
banked in groups of eight so that they
can be read as either single inputs or
as a byte from say an 8-bit analog to
digital converter (ADC).
For mass production, the 16CXX series is available in erasable-UV form as
well as OTP (one time programmable)
for code protection once the device is
in the marketplace.
Second generation PICs
The PIC16C71 is the start of the second generation of PIC microcontrollers
which include 14-bit wide instruction
sets and only 35 instructions. What
sets this apart is the on-board 8-bit
ADC.
This ADC has four multiplexed
analog inputs, sample and hold, 20µs/
channel conversion time and an external reference input. Accuracy is
quoted at ±1 LSB.
The PIC16C71 also has 1Kb x 14-bit
EPROM, 16MHz clock speed, 13 I/O
lines (each with individual direction
control) and an external interrupt pin.
All this is in a package that only has
18 pins. The has been achieved by
multiplexing most of the pins to perform two functions. Depending upon
the instruction, the pins are set to act
as either inputs or outputs.
The I/O pins are capable of sinking
and sourcing up to 20mA, which
reduces the need for external drivers
and helps to reduce the design cost.
Power consumption for the ’71 is
basically the same as the PIC16CXX
series with slightly more current
consumed with the ADC in operation.
Other 16CXX series features such as
power saving sleep mode, 8-bit real
time clock/counter, power-on reset
and watchdog timer are also included.
The watchdog timer is basically a
free-running RC oscillator which has
a nominal timeout period of 18ms but
can be prescaled with a division ratio
of up to 1:128 to produce a period of
2.5 seconds. Once the timer has timed
out, it generates a RESET condition
which can be used in programming
to either reset the device or branch to
another section of code.
PIC16C84
All of the devices so far have used
an EPROM which is UV-erasable. The
16C84 differs in that it contains a 1Kb
x 14-bit electrically erasable PROM for
program and a 64 byte EEPROM data
memory. This could be used for entering external data which changes from
device to device while the program
code remains unchanged.
It operates down to 2V and has a
standby current consumption of less
than 1µA. The package is an 18-pin
outline with 13 I/O lines, capable of
25mA sinking and 20mA sourcing current. Maximum speed is 10MHz with
a 400ns instruction cycle. Program
interrupts are available from one of
four sources – the external INT pin,
real time clock overflow, toggling of
one of the I/O lines and filling of the
data EEPROM.
The PIC17CXX series
The PIC17C42 represents the latest
step in RISC microcontroller design
with 16-bit wide instruction at up to
25MHz clock speed. What makes this
device different is that it has four modes
of operation: standard microcontroller
mode, secure microcontroller mode,
extended microcontroller mode with
both internal and external program
access, and microprocessor mode with
external program access only.
The 17C42 has 2Kb of 16-bit EPROM
for internal stored programs or it can
address a maximum of 64Kb x 16
memory space outside.
In standard microcontroller mode,
the 17C42 allows only internal program execution so that only the onboard 2Kb EPROM memory can be
April 1994 37
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38 Silicon Chip
used. Secure mode incorporates code
and write protection so that your
program code cannot be overwritten
or copied.
Extended mode allows the inclusion of external memory above 2Kb
(between 2Kb and 64Kb) and the use
of the internal EPROM below 2Kb. In
microprocessor mode, the entire 64Kb
memory is mapped externally and the
internal EPROM cannot be used.
Other features of the 17C42 include
two high-speed pulse-width-modulation outputs with 10-bit resolution and
15.6kHz speed. These could easily be
used with say an H-pack output drive
circuit in part of a switching power
supply, for example. There are 232 x
8-bit general SRAM registers and up
to 33 I/O lines.
As with the other PICs available, it
also has a watchdog timer with its own
internal RC oscillator as well as three
16-bit timer/counters. For those who
require external control, there are 11
external/internal interrupts available
as well.
One of the more unusual features
is the fully featured serial port (USART) which includes a baud rate
generator. This can be configured
for either full-duplex asynchronous
or half-duplex clocked synchronous
mode. An 8-bit dedicated baud rate
generator which can be programmed
is also included.
Development system
To help the PIC push into the marketplace, Microchip have come up
with the PICSTART – a microcontroller
development system which mates
with any IBM AT. It contains a small PC
board which has a connector for your
serial port and a zero-force-insertion
(ZIF) socket. As part of the system,
the software package includes a PIC
device programmer called MPSTART;
the MPALC Microchip PIC Assembly
Language Compiler; and MPSIM, a PIC
simulator.
All software supports the PIC16C54
to 84 devices and can be run on any
PC with the following requirements:
(1) 1.44Mb drive; (2) hard disc drive;
(3) serial port; (4) 640Kb RAM; and (5)
DOS 3.3 or higher.
A text editor, VGA screen and mouse
are highly recommended but not mandatory. The PC board requires a 9VDC
250mA power supply which can quite
easily come from a 9VDC plug pack.
The board is quite small at just 117
x 76mm and you also get two sample
PICs to play with.
All programs run under DOS and
do not require Windows which is
a great idea. The programmer, MP
START, is activated simply by typing
MPSTART<enter>. It’s a menu-driven
package which automatically sets up
the link between the PC board and the
computer and warns you when the
connection isn’t made, for example,
if the power supply is not connected.
It has context-sensitive on-line help
in case you get into trouble at any
stage, as well as normal file handling
facilities. The program is completely
menu-driven so you don’t have to
remember any fancy command calls.
MPALC
The assembler, MPALC, is a command line driven program which requires your source code to be already
in an ASCII format file. To assemble
code, you simply add in the source
code file
name and the destination
filename of the compiled code plus a
number of option directives.
For example, the /P option allows
you to compile code for a specific device. Thus, “/P 16C54” would compile
code specifically for the PIC16C54
controller.
MPSIM
The MPSIM simulator, which also
runs from DOS, allows you to test
program files by loading them into
the simulator and checking the various registers and ports to check the
program’s correctness.
Programs can be tested by either
single command stepping or execution
up to a certain command or address
in EPROM. Register values are maintained on-screen at all times.
Overall, the PIC-series of micro
controllers represent a big step forward
in microcontroller design. They feature high speed and low cost in terms
of both code development time and
production. Watch out for the PICs to
make big waves in the microcontroller
industry.
The PICSTART system also includes
two manuals: the complete Microchip
Databook and the Embedded Controller Handbook. The PICSTART is
available from NSD Australia for the
bargain price of just $250, which is
peanuts compared to many other development systems. You can contact
SC
them on Sydney (02) 898 0133.
SERVICEMAN'S LOG
Nothing unusual happened this month
I don’t have any stories from my own bench
this month, since nothing sufficiently unusual
has happened. So I have had to call on a
couple of colleagues, who have come to the
party with some really tricky ones.
The first story comes from my colleague on the NSW south coast and
it concerns a problem peculiar to his
area.
In fact, for readers not familiar
with this area, it is necessary to set
the scene in terms of the local TV
channels. In the early days of TV,
residents of Wollongong, about 80km
south of Sydney, managed as best they
could with signals from the Sydney
channels.
It was a chancey business. As well
as the distance, they had to contend
with less-than-favourable topography.
Tall masts, high gain antennas and
masthead amplifiers were the order
of the day. Some managed reasonably
well; others took what was there on
a day-to-day basis and were grateful
for it. Further south, around Nowra,
Bateman’s Bay and their surrounds,
it was virtually hopeless.
First relief for the area came with
the establishment of a couple of VHF
transmitters at Knight’s Hill, south of
Wollongong. Today, the area is served
entirely by five program sources in the
UHF band, using five main transmitters and five translators.
In order to appreciate my colleague’s
story, it is necessary to set out these
channels. The five main transmitters,
at Knight’s Hill, use channels between 53 (701-708MHz) and 65 (785792MHz), while the translators use
channels between 30 (540-547MHz)
and 48 (666-673MHz).
So, against that background, here’s
my colleague’s story, more or less as
he related it to me.
The fussy Rank
The set was a Rank-NEC model
C-1413. It was brought in many months
ago by one of my lady customers with
the complaint that “the picture goes
funny on some of the channels only”.
Well, I’ve had worse descriptions
although, as it turned out, it was
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40 Silicon Chip
accurate enough; it just wasn’t very
helpful. In cases like this, one of the
points I have to watch in this area is
the need to determine, right from the
start, which transmitters a customer
uses; the main transmitters, the translators, or even combinations of both
in odd cases.
This fine distinction is usually lost
on most people; they think in terms of
names – ABC, SBS, Prime, etc – with
little appreciation of how the program
comes to them. But some careful questioning in this case finally pinpointed
the main transmitters on Knight’s Hill
as the signal source.
So that was where we started. The
model C-1413 is one of a series of
sets which use essentially the same
circuit and appear under several brand
names. As a Rank, it also appears as
the C-1414 and C-2020 (among others)
but it also appears under the GE label
as GE482 and under the General label
as GC205.
I have most of these circuits, including the C-1413 and the C-2020.
As luck would have it, the 2020 came
out of the file along with the 1413 and
I left it out.
As far as the symptoms were
concerned, the lady was right and
the pictures from Knight’s Hill were
“funny”. And that wasn’t such a silly
term either. The effect isn’t easy to
describe; my best attempt would be
random pulling and rolling, with the
suggestion that this might have been
hum related. The lady was also right
in that there was no sign of the trouble
on the translator channels. In fact, I
explored this aspect very thoroughly
to make quite sure.
OK, so we had a frequency related
problem. That meant trouble somewhere in the front end; probably in
the UHF tuner itself. This set uses
two mechanical tuners; the UHF tuner
which down-converts to VHF, and a
VHF tuner which then down-converts
these signals to the IF. Of course, it
can process off-air VHF signals as
one carrying the supply rail, the AGC,
AFT and chassis connections, one for
the IF lead, and one for an auxiliary
network for the UHF tuner RF bias
control. With the two sets close together, there was enough lead length
to allow the suspect tuner assembly
to be replaced with the known good
one, without any need for mechanical
demounting.
I was fully confident that this would
confirm that there was a tuner fault. If
so, it would make things easy because
I had a couple of spare tuners from
junked sets and a replacement would
be a cheap and easy solution.
But no – the set behaved exactly
the same with the replacement tuner
assembly. This was a really revolting
development; any complacency I
had allowed myself up to this point
was completely dispelled. I had a
real stinker on my hands, defying all
the rules. If the fault was in the main
circuit, which was carrying nothing
higher in frequency than the IF, then
how did it know when the set was
tuned to something above 700MHz?
And if use of the word “know”
sounds a bit way out, it was no more
so than the fault itself.
Caffeine fix
well. It’s all quite conventional really
and I imagined that the job would be
fairly routine.
The first thing I tried was feeding in
a signal from the colour bar generator.
This happened to be set to channel
36 (575-582MHz) in the translator
group and, as expected, it produced a
perfectly steady picture.
I then reset the generator to channel
67 (799-806MHz) in the transmitter
group, fully expecting that I would
be able to observe the fault under controlled conditions. But not a bit of it.
The colour bar signal was just as steady
on this channel as it had been on the
lower one. It was a nasty setback.
OK, so it was back to the real world.
I switched to one of the Knight’s Hill
transmitters and confirmed that the
fault was still very much alive. So
what next?
Well, luck was with me; I had another identical set in the workshop at
this time. There wasn’t much wrong
with it and I could use it for a spot
of swapping. In particular, I had in
mind to swap the tuner assemblies,
thus either confirming or rejecting this
section as being at fault.
It was a simple exercise. The tuner
assembly is connected via three plugs,
After I’d had a caffeine fix and
calmed down a little, I had another
thought. Could it be a power supply
fault? A long shot surely – how could
the power supply be involved? It was
just about as far removed from the frequency selection process as anything
could be.
Yet I’ve had some very funny faults
traced to power sup
plies. We tend
to forget that there are signal paths
through or around all power supplies,
usually involving capacitors other
than the filter capacitors, and that
failure of these can create faults a long
way from the source.
More to the point from a practical
point of view, it took only a few minutes to patch the power supply from
the other set into this one and settle the
point once and for all. And it did – it
made no difference.
The next most likely possibility was
distortion of the sync pulses. I could
think of no way that such a fault could
be frequency conscious but the idea
could not be ignored.
The IF signal from the tuner goes
through an amplifier stage (TR201), a
SAW filter (FL201), and thence to pins
April 1994 41
Fig.1: the IF circuitry in the Rank C-1413 colour TV set. The IF input is at extreme left & feeds TR201, while C208 is
below IC201, between pins 11 & 14. Note capacitors C221 and C222 from pin 11 to chassis.
1 & 16 of IC201 – see Fig.1. It emerges
on pin 12 and a clear staircase waveform pattern is given for this point. So
the CRO was hitched to pin 12 and the
colour bar generator used to provide a
staircase signal.
But, again, there was no cry of “Eureka” – or a triumphant dash down
the main street. As far as I could see
the waveform was perfect; exactly
according to the circuit, with no hint
of dis
tortion or compression, from
either a channel 36 or channel 67
signal. Nor did the signal level appear
to matter. The generator can deliver
a solid signal – stronger than most
off-air signals in practice – and so I
took this right down until the pattern
dropped out of colour. The sync pulse
remained perfect.
Nor did varying the AGC adjustment have any effect. But what about
off-air signals? I checked some of the
translator signals and the sync pulses
appeared much the same as from the
generator. The pulses from the Knight’s
Hill transmitters didn’t look too bad
either, although that “too bad” implies
a qualification.
Yes, the shape was still OK but
one difference did catch my eye, although I still don’t know whether it
was relevant. As I said, the shape was
correct but there appeared to be some
rubbish, or noise, inside the pulse
rectangle. It was nothing that could
be resolved and is still a mystery.
42 Silicon Chip
All I know is that it was only on the
troublesome signals.
Hard slog
So now it was down to hard slogging
and a lot of hope. I changed transistor
TR201, the SAW filter, and even IC201.
I changed the capacitors on the AGC
line (pin 4), including C210 (4.7µF),
C212 (0.01µF) and C209 (4.7µF), plus
sundry resistors. None of these had
any effect.
By this stage, I had reached the
point where I had to stand back and
take a long hard look at the whole
situation, not only technically but
financially. I had spent a lot of time
on it; somewhat more that could
reasonably be justified for something
which was now looking as though it
might be a write-off.
I contacted the customer and
brought her up to date on the situation. She was quite co-operative,
in that she was in no hurry to get
the set back. To be truthful, I gained
the impres
sion that she was quite
prepared to write it off. But she was
prepared to spend up to $100 to get
it working. So, at least the pressure
was off. I had more pressing jobs to
attend to and so the set was put aside
in one corner of the bench.
I had fully intended to get back to
it reasonably soon but, as often happens, other jobs kept piling up and
I kept putting it off. And so several
months went by. But its mere presence provided a nagging factor; every
time I looked at it, I felt guilty – and
apprehensive. I had no idea how I was
going to tackle it.
Eventually, when things slackened
off over the Christmas/New Year break,
I knew that the moment of truth had
come. I fished it out again, determined
to settle the situation one way or the
other.
Fortunately, I had scribbled a few
notes and kept the components which
had been changed, so I was soon back
in the picture. But I didn’t really have
any fresh ideas. The best I could do
was to continue replacing likely – or
even unlikely – components and hope
for a breakthrough.
And that’s what happened. After a
couple of false tries, which included
capacitors C222 (47µF) and C221
(0.01µF) in parallel with it, I came
to capacitor C208 – a 2.2µF tantalum
electrolytic connected between pins
11 & 14 of IC201. I hadn’t tried it earlier
because it was hidden on the copper
side of the board. Only its presence
on the circuit diagram as part of the
AGC circuit sent me looking for it. Its
location may be significant, considering what followed.
I pulled the capacitor out and
checked it. It measured spot on but
I replaced it anyway. Well, sort of – I
didn’t have a 2.2µF capacitor handy, so
I settled for 1µF. The result was quite
dramatic; not a total cure but such an
improvement that I could have almost
let it go. There was just an occasional
tendency to pull.
My natural reaction, initially, was
that if I fitted the correct value, it
would complete the cure. It might have
too, but a number of things happened
to change my approach.
To explain this, I have to make it
clear that I had abso
lutely no idea
as to the function of this capacitor.
I didn’t even know the function of
pin 11; whoever drew the circuit had
omitted to identify it. In hindsight,
I could have easily worked it out by
tracing the circuit but didn’t I realise
this. But I was curious about C208.
It was then that the C-2020 circuit
stuck its nose in – see Fig.2. It had
been updated, with pin 11 marked
as VCC (the supply rail pin). On the
C1414, it connects to the 12V rail via
a 22Ω decoupling resistor (R223), bypassed by the previously noted C221
and C222.
Suddenly, C208’s role became clear.
It is a bypass capacitor for pin 14. Pin
14 is part of the internal AGC circuitry
and, while I have no idea of its exact
role, it is clear that it is held at around
7V by a 560kΩ resistor (R209) to chassis. And C208’s job is to peg this point,
at RF, to chassis.
Only it doesn’t go direct to chassis –
it goes to pin 11. And pin 11 is pegged
to chassis at all but DC by C221 and
C222. It’s a rather roundabout route
but a perfectly valid one – at least in
theory.
In the process of working all that
out, I became aware that the pin 14
bypass circuit was quite different in
the C-2020 circuit. In this case, the
bypass capacitor, now designated
C223 and reduced to 1µF, goes directly to chassis. In practical terms,
this seemed to me to be a much more
elegant approach and since someone
a lot smarter than I had preferred it,
why not try it?
The rest is history, as our political
commentators like to say; I made the
changes and it was a perfect cure. I
ran it for a couple of weeks before
calling the lady and it remained rock
steady.
So we had a happy ending. But I
realise that the story poses as many
questions as it answers. While it is
clear that the pin 14 bypass arrangement is critical – and that someone at
engineering level must have discov-
Fig.2: this is the IF circuit from the Rank C-2020. Note the changes on pin
11 & 14 compared with the C-1413.
ered this – I still can’t explain why the
fault was frequency conscious.
But then I’m not an engineer; I’m
only the poor bloke who has to try to
make sense of these weird situations
in the field. All I can do is learn from
the experience and, by passing it on,
perhaps help some other poor blighter from going round the bend – as I
nearly did.
Well, that’s my colleague’s story,
and a good one it is too – as a story.
But I can only sympathise with him
over the anguish and frustration it
must have caused. Nor can I answer
any of the questions it poses. Any
suggestions?
A thorny problem
And so to colleague number two;
old faithful, J. L. from the island way
down the bottom. Here’s his contribution.
By all that’s reasonable, the old
Thorn model 3504 should have been
junked 10 years ago. It was released by
AWA in early 1975 as the company’s
first ever colour TV set.
By 1984-85, the model was beginning to show its age and by 1990 most
examples had succumbed to the years
and were only to be found on the
municipal tip. However, a few have
survived and one of these came to my
attention last week.
I’ve been caring for this set for close
to 15 years. I don’t know to what extent
its longevity is related to my atten
tions but I do know this – when I last
worked on it about two years ago, it
still produced a good picture.
So when he called me last week and
said that the picture had gone “...all
purple” I wasn’t particularly worried. I
was confident that it wasn’t the picture
tube and fairly sure that it was going
to be a simple electronic problem. I
was even more convinced it was the
latter when he said that thumping the
cabinet sometimes restored the picture
to normal.
A purple picture results from the
loss of green content, so this problem
had something to do with the green
video output or the green gun. I firstguessed the former because, in the
3504, the video output load resistors
are etched onto a ceramic substrate
and I have found a number of these
breaking down recently.
In greater detail, the connecting
pins break away from the ceramic
where they are attached to the etched
pattern. I’ve had no luck resoldering
this connection; it is more practical
to replace the printed resistors with
discrete 10W units.
Nowadays, I don’t have to resort to
such subterfuge since I have a large
collection of good boards taken from
sets that have paid the supreme sacrifice. And so I decided it would be
easier to do the job in the customer’s
home, by simply replacing the suspect
board with a known good one from
this collection.
And this did appear to be the answer; at least for a few moments after
I had made the swap. But soon the
green part of the picture disappeared
April 1994 43
again and I had to admit that it was
really a different fault. So where to
start looking?
I seem to have a habit of making
the same mistake over and over again.
The mistake this time was to forget to
use my multimeter. Circuit voltages
are one of the best indicators of circuit performance, yet I always seem
to make this my last test instead of
the first!
If I had made a quick check of the
tube base board, I would have found
that the fault lay with the screen (first
anode) voltage, not with the cathode
or grid voltages. So having done at last
what I should have done at first, I set
about trying to adjust the voltage on
the green screen (pin 5).
The result was uncertain – the green
could be restored but it was erratic.
It was hard to say exactly how it was
varying, although the instability was
seemingly related to the position of the
screen potentiometer, R793.
All of this made me think that we
had a dirty screen pot. I’ve had these
before and they usually respond to a
44 Silicon Chip
squirt of contact cleaner. So, two or
three squirts later, the picture came
good and no amount of mechanical
abuse would alter it.
I let the set run for half an hour or
so while I had a very welcome cuppa’
with the owner. The picture never
varied and so, by mutual consent, we
declared the job done.
Pride commeth ...
What is it that they say about pride
coming before a fall? That night the
owner rang to say that everything was
back as it had been – no green, purple
picture, and all!
When I left the workshop next time,
I made sure I had packed a complete
convergence board. This panel carries
not only the many convergence controls but also the three screen pots and
their associated beam switches.
My plan was to change over the
whole board to make a quick and simple repair. What I had forgotten was
that the “new” board had been set up
for a different picture tube and would
have to be completely readjusted.
When I fitted it to the set, the picture
came up with plenty of green but the
convergence was grotesquely out of
ad
justment. I could see that it was
going to be a long operation to do a
complete convergence setup and I’d
already spent as much time on the job
as I could afford.
So I decided to refit the original
board and just change the doubtful pot
for one of the good ones from the new
board. And it was then that I found the
true cause of the trouble. As I prepared
to remove one of the screen pots from
the new board, I noticed that the three
beam switches were of two different
types. Then I remembered!
On a few occasions in the past, I
have found that these beam switches develop internal shorts. It seems
not to be a mechanical problem but
an electrical one within the switch
material itself. No amount of cleaning
compound will cure the trouble – the
only answer is to change the switch,
something that I had obviously done
on the new board at some time in the
past.
So instead of changing the screen
pot, I changed the beam switch, S752.
After a gray scale adjustment, we had
as good a picture as any I’ve seen on a
set this age. In fact, the colour, contrast
and brightness were all excellent, as
was the convergence.
When I commented about the excellent picture on a set of such advanced
age, the customer’s wife commented
that they only used the set for a couple of hours at night. News and the
early-evening soaps were all they ever
watched and it was never on during
the day.
I made a quick calculation. Two
hours a day, 365 days a year, for 18
years, makes over 13,000 hours! I seem
to recall something about 10,000 hours
being a reasonable life for a picture
tube. So this one is not only well past
its presumed lifetime but looks capable of going on for many hours yet!
The only problem is that the set has
only a VHF rotary tuner. However, the
owner professes to have no interest
in channels other than the ABC, so
perhaps he really doesn’t miss the
UHF facility.
Thanks, J. L. – I hope you can keep
the old clunker going for a few more
years. As for the UHF channels, why
not add a junked video recorder to the
set to tune these stations; one in which
the front end is still functioning? SC
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April 1994 53
COMPUTER BITS
BY DARREN YATES
Experiments with your games card, Pt.5
This month, we give some general information
on the various games cards available & look at
what you can and can’t do with them. We also
present details on a simple games card breakout
board.
Most if not all PCs these days have
the games/joystick port built into an
“all-in-one” card which handles your
hard drive, if it is an IDE (Intelligent
Drive Electronics) type, as well as the
serial ports and printer port.
While this is a good idea and frees
up a number of what would otherwise
be used expansion sockets on your
motherboard, the games port is not
the “full quid”. What they in fact do
is leave out the second joystick input,
so you’ll find that while you can still
plug your joystick in and shoot down
the Red Baron, you won’t be able to
run dual joysticks.
What this means is that with a card
of this type, you’ll only have two
analog inputs and two digital inputs,
rather than four analog and four digital
inputs with a full games card.
The easiest way to tell what type
of games card you have is to open
the lid of your computer and locate
the card that con
tains the joystick
(DB15) socket. Next, unscrew the
Phillips-head screw and remove
the card. Make sure that you keep a
record of which cables and plugs fit
into which sockets, otherwise you’ll
find yourself in a real spot.
When you’ve removed the card,
examine the ICs on the board. Somewhere near the joystick socket, you
should find either a 556 or a 558 chip.
The prefix will depend on the manufacturer of the device. It could be “LM”
for National Semiconductor or “NE”
for Signetics/Philips.
Whatever the case, if you have a
556 chip, then you only have the
single joystick input. If you have a
558, then you have all available input
functions.
For the 556 version, pins 9-14 of
the joystick connector are left disconnected and pins 1-8 function as
normal. All of the experiments we
have done so far require only the
analog input of pin 3 or the digital
(fire button) input of pin 2, so even if
you only have the ‘half-joystick’ card,
you can try out the programs we have
developed so far.
Full games cards are available from a
number of retailers including one from
Rod Irving Electronics which sells for
only $29. For more details, contact
Rod Irving Electronics in Sydney or
Melbourne.
Installing the games card
The DB15 socket on the games breakout board allows you to use an existing
DB15 extension cable to connect between the board & computer.
54 Silicon Chip
If you’ve purchased a separate
games card, it’s not just a case of plugging in the card into a spare slot and
away you go. You first have to disable
the games port on your IDE card before
the separate card will function.
The major problem you will find
here is that there are a number of IDE
cards available from different manufacturers and all have a different
method of disabling the games section
of the port. All IDE cards have a row
of two or three-pin jumpers which are
used to enable serial ports, hard disc
drives, etc.
Depending upon your card, there
will be a jumper that will need to be
either swapped to another pin or lifted
or run your circuits off the games
card 5V supply. Never mix the two
or else you’re asking for trouble. Also
don’t attempt to pull more than about
100mA from the card. It will probably
handle more but we would caution
against it as the sockets and tracks on
the board are not designed to handle
much current.
One thing that should be considered as a rule is never let the end-user
have the option of connecting into the
computer’s 5V supply through your
project. The possibilities for trouble
are endless.
Games breakout board
The PC board has a patchboard area which will hold a number of ICs for simple
projects & allow you to prototype designs as you go.
off. Unless you have the manual for
your IDE card, you’ll need to contact
the company you purchased your
computer from.
This is where you can run into
trouble if you purchased your machine
from one of the discount stores rather
than a specialised electronics dealer.
Companies such as Rod Irving Elec
tron
ics and Dick Smith Elec
tronics
are able to supply lots of information
on the computers they sell but don’t
expect the same sort of backup from
a discount store.
5V supply
One thing which we haven’t mentioned so far is the 5V supply. Unlike
the parallel printer port, the games
card has a 5V supply rail located on
pins 1 and 9. This connects through the
expansion socket to your computer’s
5V supply rail.
This supply rail must be treated
with respect and caution for a number
of reasons. Firstly, it is the main supply
for the majority of your computer’s
ICs. So if you somehow damage that
supply rail, you risk damage to your
motherboard – in fact, you risk just
about all of the devices that are in
your computer.
Secondly, if you take of the lid off
your computer, you’ll see that the
power supply carries a number of
specifications regarding output voltage and current. Your computer uses
four supply rails and they are +5V,
-5V, +12V and -12V. The +5V rail sup
plies most of the equipment in your
machine and is usually cap
able of
supplying around 15 to 20 amps, so
be very careful.
As a general rule, when you are
interfacing with the games port, either
use a separate supply for everything
Fig.1: this
is the fullsize etching
pattern for
the PC board.
Be that as it may, we don’t want to
frighten you all off – just make you
aware of the possible problems. So to
make things easier, we’re presenting
a simple breakout board, which in
many cases will be all that you need
for some projects.
The board has connections to all
connected pins of the joystick port,
including the 5V supply, with all
pins marked on the copper side of the
board. There is also a patchboard area
which will hold a number of ICs for
simple projects and prototype your
designs. The main benefit is that the
DB15 socket on the board allows you
to use an existing DB15 extension cable to connect between the board and
computer rather than having to make
up a separate cable.
DB15 male to male extension cables
are available from Rod Irving Electronics (Cat. P-19016) for $30.95.
You can make the board yourself
by using the pattern published here.
We will be using the board in the near
future for a Nicad Battery Monitor for
PCs. There are many circuits and pro
jects which could use the joystick port
as an input so if you come up with any
using the breakout board, please write
to us here at SILICON CHIP and let us
know what you’ve done.
Ok, that’s enough for this month.
Over the last few months, we’ve given
you enough information for you to get
started with some experiments of your
own. You can easily modify the STICK.
BAS and BUTTON.BAS programs to
suit your own application. Remember to optimise the execution speed
and make sure you include the line
“DEFINT A-Z” early in the program.
This increases the speed, whether
you using a QuickBASIC compiler or
SC
MS-DOS QBasic.
April 1994 55
PC Product Review
The Video Blaster is
one of the lowest cost
ways of entering the
world of PC video.
Import your PAL
or NTSC composite
video signal from
a camera or VCR,
then frame grab and
create all sorts of
visual effects.
VIDEO BLASTER
By DARREN YATES
W
HEN THE ORIGINAL Sound
Blaster hit the streets a few
years ago, few would have
predicted its rise to prominence as
the standard for PC audio. The 16-bit
ASP model released a year or two
later upped the stakes by bringing
CD-quality audio to your PC – playing
CDs through your PC via a CD-ROM
became a reality.
Now there’s a system that does for
video what the Sound Blaster did for
PC audio and, by no surprise, it comes
from the same people at Creative Labs
in the US.
Features
Here are some of the features:
Supports NTSC and PAL systems;
Software selectable video and audio
input sources;
• 16-bit card;
•
•
56 Silicon Chip
•
Supports PCX, TIFF, BMP, GIF and
TARGA file formats in 640 x 480 res-
olution;
• Supports up to 2 million colours;
• Live and still image zooming and
scaling;
• Freeze, save and load images;
• Crop and resize images;
• Windows® software (Video for Windows from Microsoft).
The VB pack also includes manuals
for all software packages, as well as
instructions on installing both the
card and software. For those who are
running other equipment such as CDROMs, the I/O addresses, frame buffer
base address and software interrupts
are all selectable and a test program
checks whether your choices are valid.
Bundled software
As much as the Video Blaster can
do, it is remarkably easy to drive with
a host of Windows-based software
packages to allow you to make the
most of its capabilities.
Along with Microsoft’s Video for
Windows, Tempra Special Edition
allows you to edit video images with
shapes and paint and supports all the
usual file formats. Tempra SHOW is
a multi-media presentation package
that integrates audio, video, animation
and still graphics into high-impact
interactive presentations.
ACTION from Macromind lets you
import graphics from spreadsheet,
paint and graphics programs and
comes with over 100 templates for
your own designs.
System requirements
•
The basic system requirements are:
IBM PC-AT or higher system;
•
•
•
Full length 16-bit slot;
DOS version 3.1 or higher;
VGA or multisync monitor running 50-70Hz with a
scan rate of about 31.5kHz;
• VGA card with a features connector;
• Not more than 15Mb of system RAM.
This last point may seem a little strange with the
latest trends aiming for more and more system RAM
but there is a very good reason for this. The VB card
has 1Mb of RAM on board which it needs to overlay
on to the system. This RAM is used to store the image
and to display it as fast as possible to produce real-time
video displays.
The IBM PC-AT (or 286) has a 24-bit address bus which
limits the maximum address RAM to 16Mb. Even on 386
machines, which are capable of addressing 4 gigabytes,
the ISA bus limits the effective RAM to 16Mb.
It turns out that the most efficient way to display the
video image is to map this RAM into the system at the
15-16Mb boundary. However, this causes conflicts with
any memory which exists so in order for the system to
work correctly, no system RAM can use the 15Mb-16Mb
addressing area – hence the 15Mb system restriction. This
base address can be lowered for systems which have less
than 15Mb of system RAM.
Setting the system up
This is a little more involved than you might think. To
start with, you need a VGA card that has a feature connector on the top of the board. This is an edge connector
similar to that found on 5.25-inch floppy drives.
An internal-to-the-system cable connects from the VB
card to the feature connector on your VGA card. A separate external cable then links the VGA output from your
VGA card to the VB card. Your VGA cable then connects
to the DB15 output socket on the VB card.
What actually happens with the system is that it doesn’t
really use the VGA card to produce the on-screen display.
It uses a method called chroma-keying and is similar to
the effect you often see on the evening news where the
weather forecaster is seen standing in front of various
meteorological photos and maps.
The VGA card produces a blank colour screen which
The Video Blaster allows either a PAL or NTSC composite
video signal on any one of three inputs to be displayed on
a VGA screen. This dialog box allows the user to select the
video standard & the polarities of the sync signals.
April 1994 57
the VB card uses to key in the video
image. You can see this if you try to
paste the screen image to the Windows
Clipboard. When you go into the Clipboard, all you will see is a pink screen
below the top menu.
Installing the software
Installation of the software is a
much simpler affair. The Video Blaster
driver software is loaded first under
Windows and it automatically loads
all the relevant files. You can change
the destination drive and directory if
you wish.
Once the software is installed, you
then have to run one of two setup
programs to start the software drivers
– there’s one for Windows and one for
DOS. The Windows version is easier to
drive and still allows you maximum
flexibility. It automatically selects
the correct I/O address and software
interrupts.
Real time video display
After running the Windows setup
program, you can then connect up your
video source (either VCR or camcorder) to one of the video inputs, select
it with the software selector and then
click on the VIDEO KIT icon.
After maximising the window, you
should see the Windows menu routine at the top and whatever signal
you have from the video source being
displayed on the VGA screen.
Tempra Show comes bundled with the Video Blaster software & is designed
to incorporate sound & animation into the captured video images. This is the
opening screen that appears when the program is loaded.
The Video Blaster allows either a
PAL or NTSC composite video signal on any one of three inputs to be
displayed real time on a VGA screen.
This is quite a breakthrough compared
to some of the systems we have seen
previously which have relied on
small screen windows showing just a
few frames a second. VB uses the full
screen size for a much greater impact.
What makes this all possible is a
16-bit nearly full-length card which
not only contains stereo input mixing
from a CD player or tape and output
amplifiers to drive loads down to 4Ω
but all the necessary circuitry to convert both NTSC and PAL signals with
either negative or positive syncs.
At any time while video is being
displayed, you can select the freeze
option in the main menu in VIDEO
KIT, and grab a frame. The grabbed
image is then frozen on the screen. To
save the image, you just select one of
the file formats, whether it be TIFF,
BMP, PCX, GIF or TARGA and save it
to disc. You can now import that image into either Windows Paintbrush
or just about any desktop publishing
program.
Video for Windows
The “slider bars” on this dialog box
allow the picture colour to be quickly
adjusted, either in continuous mode
or in freeze frame mode.
58 Silicon Chip
This package from Microsoft is fast
becoming the basic standard for PC
video and is a great addition to the
Video Blaster package. It requires
Windows 3.1 and it is capable of some
pretty fancy effects.
Among its features is the ability
to capture real time video and audio
using VidCap, however your machine
needs to be quite good. The system
requirements are:
• 33MHz 80386 or better
• 4Mb of 32-bit RAM minimum
• 100Mb hard drive to hold reasonable
amount of video – also must have a
write capability of at least 320Kb per
second.
Video for Windows will handle
S-video, RGB and digital video as
well if you happen to have another
video board capable of capturing these
standards. It also comes with a CDROM full of captured video examples
which you can look at and edit to your
heart’s content.
Even if you don’t have a CD-ROM,
there’s quite a good little sample file
on the distribution discs – at 1Mb, it
gives you an idea of just how much
space you need to capture a decent
length of video!
Conclusion
Overall, the Video Blaster package
is very impressive. The only thing
which we feel they could have added
is the ability to produce composite
video of the edited capture. That
would have made it the complete PC
video system.
Be that as it may, the package represents good value for money at $899.
It is available from all Dick Smith
SC
Electronics stores.
Do you have a water tank on your
property? This digital gauge will
let you keep tabs on the water level
without having to look in the tank
itself. It has the option of two digital
displays & is controlled by
a microprocessor.
By JEFF MONEGAL
Build this digital
water tank gauge
W
HILE MOST people on farms
have large water tanks, they
are now also becoming more
common in the cities for people who
want rain water to drink or for use on
their gardens. On a farm (and now in
the cities), water conservation is paramount and keeping a constant eye on
water usage is mandatory.
The problem arises when users need
to take a reading of the present tank
level. This usually involves trudging out to the tank with a calibrated
measuring stick, manoeuvring a heavy
manhole cover out of the way, then
dipping the stick into the tank to read
off the contents.
It would be much easier to glance
at a digital display in the kitchen;
especially if your tank is 200 metres
60 Silicon Chip
from the house and it is a freezing day.
Freeze no more, this digital tank gauge
will do the job. It has a 2-digit display
which indicates the tank contents from
zero to 99%. If you have access to a
secondary water supply such as a bore,
the project will also control a pump to
maintain the level of water in the tank
at a preset percentage.
The digital tank display consists of
two parts: the main unit which sits
out on the tank and the remote display which is situated in the house;
it can be up to 800 metres from the
main unit. The main unit contains
most of the electronics, including the
microprocessor.
The remote display will normally
be situated in the kitchen but a second
display can be built in the unit at the
tank. This is how the prototype was
built and how it is shown in the dia
grams and photos in this article.
Like many projects, this one was
borne out of necessity. The author lives
on a property which uses a concrete
water storage tank and so this project
was produced, the result of many
months of research and development.
Four prototype installations were
used and originally the project used
many ICs (13 just for the main unit)
to achieve the desired result. As time
and the project evolved, 10 of the ICs
were replaced with a microprocessor
and more functions were added.
Principle of operation
Essentially, the circuit works by
transmitting a pulse of ultrasonic en-
Circuit description
Fig.2 shows the main circuit of the
Digital Tank Gauge while Fig.3 shows
TRANSDUCER
HEAD ASSEMBLY
TANK LID
OVER-FLOW
OUTLET
WATER INLET PIPE
FROM HOUSE
GUTTERING
MAXIMUM WATER LEVEL
90mm PVC TUBE
FITTED THROUGH
HOLE CUT IN
STRAINER BASKET
CONCRETE
OR STEEL
TANK
CABLE TO
MAIN PCB
400mm
ergy down a tube to the surface of the
water. The pulse is reflected off the
water surface back to an ultrasonic
receiver. The microprocessor then
com
putes the time period bet
ween
the initial pulse and the received
pulse and then calculates the level of
water in the tank as a percentage. Fig.1
shows the general installation with the
transducer assembly mounted at the
top of a tube which fits into the tank.
You may wonder why the tube is
necessary. There are two reasons. The
transmitter only pulses the ultrasonic
transducer very briefly but being a
mechanical device, the transducer
will continue to “ring” for some time
after each pulse. Because of this, the
system has a minimum range below
which it will not function. Therefore,
the transducer must be positioned so
that the a minimum distance above
the highest water level is 400mm. This
means that the transducers must sit
above the top of the tank. The tube
acts as a support for the transducers,
suspending them 400mm above maximum water level.
The second reason for the tube is
that it acts as a baffle. The surface of
the water can be quite rough at times,
especially when the tank is being filled
from a tanker or during heavy rain.
This rough water surface can result
in readings which jump up and down
by as much as 10%. By using the tube,
the surface of the water inside is very
smooth.
One of the problems with the test
units was a jittery display. Software
was then written to allow the microprocessor to store the last five readings
and then only to update the display
if they are all equal. This results in
a much more stable display. Once
conversion has been done, the microprocessor displays this value on
its digital display and then transmits
the reading to the remote display. The
microprocessor then compares the
present reading against presettable
upper and lower limits to see if a pump
should be turned on or off.
As well, diagnostic routines are
written into the software. The reading
is updated every few seconds and an
alarm in the remote display will sound
every half hour for a few seconds if the
level in the tank drops below 20%.
EXISTING
PLASTIC
STRAINER
BASKET
WATER LEVEL
Fig.1: this diagram shows the general scheme for mounting the ultrasonic
transducers in a tube above the surface of the water. The transducers must be
mounted 400mm above the maximum water level in the tank.
the circuit for the remote display. The
entire circuit is under the control of a
68705P3 microprocessor which has
internal RAM and ROM. The latter
memory stores the program which
controls the transmitter and receiver
circuits and drives the digital displays.
Let’s start the circuit description
with the ultrasonic transmitter which
is shown at the top right-hand corner
of Fig.2. Actually, the microprocessor
(IC4) is the source of the transmitter
signal. Its pin 16 delivers a 3-cycle
burst at 40kHz which is fed to transistors Q2 and Q3 to drive the ultrasonic
transducer X2. Q2 and Q3 are fed by
an adjustable DC supply comprising transis
tor Q1, trimpot VR3 and
This is the transducer assembly for the Digital Tank Gauge. It consists of the two
ultrasonic transducers (transmitter & receiver) plus a small light bulb which
automatically switches on at night & serves as an anti-condensation heater.
April 1994 61
62 Silicon Chip
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▲
Fig.2: the circuit of the Digital
Tank Gauge is based on a 68705P3
microprocessor (IC4) which is
programmed with software to
provide quite a few functions. The
microprocessor pulses ultraso
nic transmitter X2 via Q2 & Q3 &
counts the time until a return pulse
is received at transducer X1. It then
converts the count to a percentage
reading for the 2-digit display.
associated components. After sending the transmitter pulse, IC4 takes
pin 6 of IC2b briefly low to allow for
the ringing period of the transmitter.
Then it goes high again, to enable the
receiver circuitry.
The reflected pulse is picked up by
the ultrasonic receiver transducer X1
(see top lefthand corner of Fig.2). This
is AC-coupled to trimpot VR1 and then
fed to op amps IC1a & IC1b, which
have a combined gain of about 3700
at 40kHz. Pin 7 of IC1b drives diode
D1 which charges the .01µF capacitor
at pin 5 of IC2b.
When a pulse is amplified by IC1
and detected by D1, the voltage at pin
5 of NAND gate IC2b will go high. The
other input of IC2b is high, as determined by the microprocessor. Hence,
IC2b’s output goes low and pulls the
interrupt pin (4) of the microprocessor
low which is the cue for a number of
events.
First, it takes pin 6 of IC2b low. This
effectively closes the gate. During the
time between the transmitter pulse
and the received pulse, the microprocessor counts pulses from IC3, a
555 timer connected in astable mode.
The count is converted to percentage
terms and sent to the local and remote
displays. A couple of internal counters
are now reset and the microprocessor
waits for a few seconds and then does
it all again.
This photograph shows the main PC board in the local unit. The microprocessor
is clearly visible at centre right & is mounted in a socket (sockets for the other
ICs are optional). Note the heatsink fitted to Q5.
A piezo buzzer connected to pin 15
of the microprocessor is used to communicate with anybody who wants to
listen. Each time a reading is taken the
buzzer will beep once. If the processor
talks to the remote display, it will beep
the buzzer again.
If the setup link (pin 12, IC4) is
in the setup position, then the microprocessor does not check the last
five readings. It simply sends the last
reading to the displays and gives a
beep. If the link is in normal mode
then the microprocessor will compare
the last reading with the previous four
readings and if they are all equal it will
talk to the remote display as well as
the local display.
When it does talk to the displays, it
will give another beep. What all this
means is that if the buzzer beeps once
then an echo was received after the
last transmission. If the buzzer beeps
twice, then an echo was received
and the processor sent the reading to
both displays. There is a third buzzer
indication and that is six short beeps.
This means that a burst of energy was
sent but no echo was received within
the time allowed for the pulse to go
Local display
The local display is driven by 4511
7-segment decoder/drivers, IC7 & IC8.
Also on the local display PC board
is Q8. If the upper and lower trigger
points have been set, the microprocessor uses Q8 to drive relay RLY1.
The relay supplied is rated at 10 amps
and 240VAC. The local PC board is
connected to the expansion plug on
the main PC board via a standard 10way ribbon cable and IDC (insulation
displacement connectors) connectors.
The display board in the local unit is connected back to the main PC board via
a 10-way cable fitted with IDC connectors.
April 1994 63
The PC boards for the remote display unit fit inside a small plastic instrument
case with a red filter at one end for the displays to shine through. The buzzer
can be considered optional & can be left out of circuit.
down to the bottom and return. This
may mean that the calibration is not
set correctly.
Want to leave that buzzer out? Why
not? Once you have the unit up and
running, this buzzer is largely superfluous.
Remote display data
As noted above, you can have a
remote display which can be up to
800 metres away. The 8-bit serial data
is sent via standard 6-way telephone
cable by IC5, a Motorola MC3487 RS422 line driver. The microprocessor
sends data to pin 1, clock signals to
pin 7 and any alarm information to
pin 9. IC5 converts these single line
digital signals to two-line antiphase
signals and these are sent along the
telephone cable to the MC3486 quad
RS-422 line receiver chip (IC1, Fig.3)
which converts them back into single
line digital signals.
Monostable IC3a & IC3d is triggered
on the positive edge of the first clock
pulse from IC1. Pin 3 of IC3 goes high
while the BCD data is clocked into
8-bit shift register IC2. This takes about
4ms. About 5ms later, pin 3 of IC3 will
go low and this signal is AC-coupled
to the latch enable pins of the display
driver chips, IC4 & IC5. The data sent
by the microprocessor is then shown
on the 7-segment displays.
When pin 3 of the monostable goes
64 Silicon Chip
low at the end of its time period, pin
11 of IC3d goes high and triggers a
second monostable comprising IC3c
& IC3b. Pin 10 of IC3c goes low and
at the end of the timing period will go
high again and reset the shift register
ready for another 8-bit word from the
microprocessor. The whole process
then repeats itself.
Alarm
A third line into the remote display
is for the alarm. If the contents of the
tank drop below 20%, the microprocessor takes its pin 14 high. This high
appears at pin 13 of IC1 on the remote
display board; it enables oscillator
IC6a and, via IC6b, removes the reset
condition on counter IC7. IC7a’s output drives the blanking inputs of IC4
and IC5, causing the display to flash.
Counter IC7 now starts to count the
pulses from the Schmitt oscillator,
IC6a. 2048 pulses later, its pin 1 goes
high and triggers monostable IC6c &
IC6d and at the same time resets itself
via D3. Pin 11 of IC6d now turns on
Q2 which drives the buzzer. Therefore,
approximately every 30 minutes the
buzzer will beep on and off for about
6 seconds. If the alarm condition is
removed by filling the tank up above
20%, the buzzer will stop and the
display will cease flashing.
(Editor’s note: if you decide that
having the display flashing is enough
warning of a low tank, you could
dispense with the buzzer and the
components associated with Q1 & Q2).
Transducer heater
The circuit built around transistors
Q6 and Q7 (Fig.2) turns on a light bulb
which is situated on the same board
as the two transducers. During daylight hours, the LDR (light dependent
resistor) has a low resistance which
holds Q6 and therefore Q7 off. The
result is that the lamp is out. When
night falls the resistance of the LDR
rises. At a point around dusk, Q6
will turn on. This will supply base
current to Q7 and the lamp will light.
The lamp supplies a little warmth to
the transducers to keep condensation
from forming on them.
Finally, we come to the power supply. This uses op amp IC6 to control a
Darlington transistor pair (Q4 & Q5). A
10V zener, ZD1, regulates the supply
to IC6 and trimpot VR4 is used to set
the output voltage, Vcc, to +5V.
Not much more can be said about
the circuitry itself except that if the
remote display is less than 100 metres
from the main unit, then power can be
supplied down the main data cable
by using 8-core cable. If the distance
is further than that, a separate power
source will be required.
Assembly
The alarm board in the remote
display unit sits upside down on top
of the main board, as shown in this
photograph.
When building this project you must
decide whether or not to include the
local display PC board. If you only
want to have a display in the house of
DISP1
MSD
LC5611
VCC
16
16
9
7
CLK
D
Q0
5
7
4
1
Q1
IC2b
4015 Q2 3
10
Q3
RST
6
3
LT
A
f
B
2
C
6
5
e
IC4
4511
D
d
c
LE
4
b
BI
a
1
ALARM
14
CLOCK
7
6
10
15
9
9
1
10
2
11
4
12
6
13
7
a
f
e
c
d
DISP2
LSD
LC5611
VCC
IC1
MC3486
15
3
5
1
RST
13
D
IC2a
CLK
13
7
12
1
11
2
2
6
VCC
3
LT
A
g
f
B
C
e
IC5
4511
D
5
8
d
c
LE
4
b
BI
a
7x 470
10
14
15
9
9
1
10
2
11
4
12
6
13
7
a
f
g
e
5.6k
1
11
c
0.1
3
IC3a
2
VCC
0.1
0.1
8
IC3c
9
27k
3,8
D1
1N914
27k
1
b
d
8
4001
14
13
IC3d
12
b
3,8
16
14
8
g
27k
D2
1N914
2
15
14
8
16 12 4
DATA
g
7x 470
10
VCC
5.6k
1
4.7k
5
IC3b
4
Q1
BC558
C
6
7
E
B
VCC
BUZZER
VCC
IN
GND
5
OUT
6
14
270k
IC6b
4093
4
D3
1N914
10k
IC6a
IC6c
10
VCC
3
2
RST
IC7
4040
16
10
Q12
12
IC6d
11
4.7k
C
B
E
D5
1N914
Q2
BC548
1
47k
BR1
W04
CLK
8
220k
22
13
9
11
1
8
7
B
E
C
VIEWED FROM
BELOW
D4
1N914
IN
12-16V
AC OR DC
1000
4.7
7805
GND
OUT
10
VCC
.0033
DIGITAL TANK GAUGE REMOTE DISPLAY
Fig.3: the remote display has data sent to it via an RS-422 link which is
converted back to normal data by IC1. The data is fed into shift register IC2 &
then decoded by IC4 & IC5.
present tank contents and not a display
on the main unit then you do not need
the extra PC board. Alternatively, you
may opt not to have a display in the
house, thereby saving the problems of
running the data cable. In this case,
all you need to do is install the unit
as described and supply power at
the tank. Normally the main pump is
situated near the tank and from here
you can get power.
Depending on what type of installation you want, there can be up to five
circuit boards to build. We will start
with the main PC board. Go over the PC
board with a magnifying glass to spot
any track faults and fix any that you
find. This done, insert the resistors,
capacitors and trimpots. Next, insert
all diodes and transistors, making sure
that they are correctly oriented, then
insert all remaining components but
at this stage do not install the microprocessor.
Check all your work to ensure that
all components are in the correct positions and properly soldered. Now
connect a DC or AC supply of 10 to
18V. LED1 should light. Using your
multi
meter measure the voltage at
the emitter of Q5. Adjust trimpot VR4
until the meter reads +5V. Measure
the voltage at the supply pins of all
chips and ensure that +5V is present.
Measure the voltage at the emitter of
Q1. It should be somewhere between
April 1994 65
SQ-40R
X1
Fig.4: the component wiring
diagram for the main unit with
local display. Note that the local
display is optional.
SQ-40T
X2
12V
LAMP
0.47
2.7k
D2
Q1
LAMP
IC9
4011
0.47
Q8
0.47
D
1
D3
4.7k
1
TO RLY1
TO EXPANSION
SOCKET ON
MAIN BOARD
1
+8V and +15V. Adjust trimpot VR3
and make sure that the voltage reading
varies. Reset the voltage to +8V for the
time being.
Before you can go any further a
display must be built. Either the
local or remote display will do. Our
description will start with the local
display. Insert all components into
the PC board and solder them in. Ensure that the displays are inserted the
correct way.
Having completed the local display
the system can be tested. Using the
66 Silicon Chip
100k
TX
F
E
BUZZER
1
2
100k
5
1uF
SET UP
ALARM TX
RX
EXPANSION
CLOCK TX
1
DATA TX
VR1
.01
27k
B
27pF
.01
1
A
C
IC4 68705P3S
10uF
1
LK2
X3
2.2M
27k
27k
IC8 4511
6
47uF
2.2pF
10k
1
1
IC5
MC3487
.01
IC1
LM358
LK1
10k
10k
10k
10k
10k
10k
1M
10k
IC7
4511
68
47k
.01
TP1
Q7
LDR
TP1 CRO
TRIG
10
D1
470
TP2
10k
1
Q5
1
3
IC2
4093
Q6
Q2
0.47
1
4
VR2
1k
100uF
470
470
470
470
470
470
470
VR3
7.5k
Q3
470
470
470
470
470
470
470
1k
.01
1k
10k
100uF
100k
10uF
VR4
22uF
1.5k
IC3
555
DISP2
Q4
K
10k
1
LED1
A
2200uF
DISP1
1
1k
47k
.0047
820
10uF
IC6
LM741
4.7k
2200uF
100
220
BR1
ZD1
12-16V AC OR DC
assembled cable supplied, connect
the local display to the main PC board
expansion pins, insert the microprocessor and switch on.
After a few seconds the buzzer
should give six short beeps. There
may or may not be anything on the
display. Place the setup link in the
setup position, furthest away from the
microprocessor. This shorts pin 12 of
IC4 to pin 7. The buzzer should beep
six times, pause about a second, then
beep six times again. This will contin
ue as long as the transducers are not
connected. Place the setup link in the
normal position. The six beeps will
now be followed by a 6-second gap. If
everything is happening as described
then your system will function correctly when the transducer assembly
is connected.
Transducer assembly
The transducer assembly can be
built now. Solder the two transducers
into the PC board as well as the lamp
holder. Next connect the cable. The
cable used has to be 3-core shielded.
D5
22uF
D4
IC6
4093
IC7
4040
10k
1
220k
D3
4.7uF
10uF
1
Q1
BUZZER
1
1
Q2
4.7k
47k
270k
4.7k
Fig.5: the component wiring
diagram for the remote
display. This has three
boards, the one at the top
providing a tank level alarm.
1
7x 470
27k
0.1
.0033
1
7805
6
A
BR1
1
D2
0.1
27k
5.6k
100uF
7x 470
1
27k
IC3
4001
0.1
1uF
IC4 4511
5
DISP2
1
1uF
1
4
IC2
4015
B
DISP1
3
IC5
4511
IC1
MC3486
2
5.6k
TO MAIN PCB MATCHING NUMBERS
Solder two leads to the active
sides of the transducers and the
third lead to the positive side of
the lamp. The earth braid goes to
the earth track on the PC board.
Be sure to remember which cable went to which point as the
transmitting and receiving transducers will not work properly if
they are swapped over.
Next, connect the transducer
assembly cable to the corre
sponding terminals on the main
PC board. Place the setup link
into the setup position, then place
the transducer assembly over the
90mm tube in the tank and again
supply power. This time after a
few seconds the buzzer should
beep twice then after a second
or two beep twice again. This
should then continue as long as
power is connected. The display
should show some number. Adjust the calibration trimpot VR2
and the reading should vary.
If all is well, then measure
the actual depth of water at the
moment. Convert this to a percentage of the maximum level of water,
then adjust the calibration trimpot VR2
until the reading on the display corresponds with the calculated reading. Do
not worry if the reading jumps a digit
or two either side of the value you want
as this is quite normal.
Now place the link in the normal
D1
12-16V
AC OR DC
position and listen to the buzzer. This
time the buzzer will beep once every
six seconds. If it beeps a second time
then the display is updated. The software remembers the last four readings
and compares the last reading with
these. If they all the same then the
displays are updated and the buzzer is
The light dependent resistor (LDR) is mounted on the
top of the case & is connected back to its terminals on
the main PC board via flying leads. It can be secured in
position using epoxy resin.
beeped a second time to indicate that
the reading is correct and the display
was updated. When in the setup mode
this software checking of the last four
readings is bypassed.
The last thing to be done at the main
PC board is to test the anti-condensation heater. Connect the LDR to the
The display board in the remote display unit is soldered
at right angles to the main board. Lightly solder tack the
two outside connections first, then make any necessary
adjustments before soldering the remaining connections.
April 1994 67
PARTS LIST
1 PC board, code CE/93/DTG,
128 x 84mm,
1 PC board, 100 x 52mm (local
display)
1 PC board, 70 x 32mm
(transducer head assembly)
1 plastic utility case, 159 x 95 x
54mm (Altronics Cat H-0151)
1 3.579MHz crystal (X2)
1 SQ-40R 40kHz ultrasonic
receiver (X1)
1 SQ-40T 40kHz ultrasonic
transmitter (X2)
1 PC-mount piezo buzzer
1 MES lamp and holder
1 12V DC 500mA plugpack
1 U-shaped heatsink to suit Q5
(Altronics H-0502)
2 10-pin DIL header sockets
1 10-way cable for local display
1 50kΩ 10-turn trimpot (VR1)
1 10kΩ horizontal trimpot (VR2)
2 1kΩ horizontal trimpots (VR3,
VR4)
1 1µF 16VW electrolytic
4 0.47µF monolithic
3 .01µF monolithic
1 .0047µF metallised polyester
1 27pF ceramic
1 2.2pF ceramic
Semiconductors
1 TL072 dual op amp (IC1)
1 4093 quad NAND Schmitt
trigger (IC2)
1 555 timer (IC3)
1 68705P3 programmed
microprocessor (IC4)
1 MC3487 RS-422 line driver
1 741 op amp (IC6)
2 4511 7-segment decoder/drivers
(IC7,IC8)
1 4011 quad NAND gate (IC9)
5 BC548 NPN transistors
(Q1,Q2,Q4,Q6,Q8)
1 BC559 PNP transistor (Q3)
1 TIP31 NPN transistor (Q5)
1 BD139 PNP transistor (Q7)
2 1N914, 1N4148 signal diodes
(D1,D2)
1 1N4004 silicon diode (D3)
1 3mm red LED (LED1)
2 LC5611-11 7-segment LED
displays
1 W04 bridge rectifier (BR1)
1 10V 1W zener diode (ZD1)
Semiconductors
1 MC3486 RS-422 receiver (IC1)
1 4015 dual 4-bit shift register (IC2)
1 4001 quad NOR gate (IC3)
2 4511 7-segment decoder/drivers
(IC4,IC5)
1 4093 quad NAND Schmitt trigger
(IC6)
1 4040 12-stage counter (IC7)
1 7805 3-terminal 5V regulator
1 BC558 PNP transistor (Q1)
1 BC548 NPN transistor (Q2)
1 W04 bridge rectifier (BR1)
5 1N914 signal diodes (D1-D5)
Capacitors
2 2200µF 16VW electrolytic
1 1000µF 16VW electrolytic
2 100µF 16VW electrolytic
1 47µF 16VW electrolytic
1 22µF 16VW electrolytic
3 10µF 16VW electrolytic
68 Silicon Chip
Resistors (0.25W, 5%)
1 2.2MΩ
1 1.5kΩ
1 1MΩ
5 1kΩ
3 100kΩ
1 820Ω
2 47kΩ
14 470Ω
3 27kΩ
1 220Ω
10 10kΩ
1 100Ω
1 7.5kΩ
1 68Ω
2 4.7kΩ
1 10Ω
1 2.7kΩ
Remote display
1 PC board, 85 x 50mm (main)
1 PC board, 50 x 25mm (display)
1 PC board, 60 x 50mm (alarm)
1 plastic case, 120 x 60 x 30mm
1 buzzer (with internal electronics)
Resistors (0.25W, 5%)
1 270kΩ
1 10kΩ
1 220kΩ
2 5.6kΩ
1 47kΩ
2 4.7kΩ
3 27kΩ
14 470Ω
Capacitors
1 1000µF 16VW electrolytic
1 22µF 16VW electrolytic
1 10µF 16VW electrolytic
1 4.7µF 16VW electrolytic
1 1µF 16VW electrolytic
3 0.1µF monolithic
1 3300pF ceramic
Miscellaneous
Red perspex filter, screws, nuts,
lock washers, hookup wire.
appropriate terminals on the PC board
and insert the lamp into the holder
in the transducer assembly. Cover
the LDR with a dark cloth. The lamp
should light and then go out when the
LDR is uncovered.
The next thing to do is to waterproof
the transducer head assembly. We simply poured Selleys “Kwik Grip®” into
the assembly. Use enough to cover the
PC board by about 3mm. Do not allow
any glue to enter the transducers or
lamp holder.
Installation
Installation involves laying a
standard 8-core telephone cable from
the remote display to the main unit
at the tank. As well as this, a 90mm
hole must be cut in the top of the tank.
Normally this would be done in the
plastic strainer.
If you do not require the remote
display inside the house, then installation involves only cutting the 90mm
hole and supplying power to the unit.
Calibration is done by adjusting trimpot VR2.
Included in the software are a few
diagnostic routines. These are activated using a clip lead with one end
connected to Vcc while the other end is
touched on pins soldered to the circuit
board. Bridging pin B to Vcc will put
the unit in diagnostics mode. Pins C,
D, E and F are now used to select the
diagnostic routines.
Pin C will cause the transmitter to
give a burst of energy then wait just
long enough for the returning echo
before transmitting again.
This routine makes it easy to test
the transmitter and receiver sections
as the whole Tx/Rx trace can be more
easily viewed on an oscilloscope.
Under normal operating conditions
the Tx/Rx trace occurs for about 12ms
every five seconds. This makes it
difficult to check the operation of the
receiver but if we use this diagnostic
routine, the Tx/Rx waveform is easy
to inspect.
Pin D will cause the displays, both
remote and local, to be clocked from
0 to 99 and then through to 0, then
upwards to 99 again. This test routine
is useful in testing the data transmit
ter and remote display, as well as the
cable.
Pin E will turn the relay on if it is
fitted and pin F will turn it off again.
It should be noted that before the next
routine can be executed the unit must
Kit availability
This project will be available in kit form from CTOAN Electronics, PO Box
211, Jimboomba, Qld 4280. Phone (07) 297 5421.
Kit 1 contains the PC boards for the main unit and the transducer head
assembly, plus all on-board components including the transducers, lamp
holder, heatsink and a programmed microprocessor (note: does not include
the local display board or components). Price: $90.00 + p&p.
Kit 2 is a complete local display kit containing displays, PC board and all
other components, including a strip of red perspex and a pre-assembled
connecting ribbon cable. Price: $26.00 + p&p.
Kit 3 is a complete remote display including case, PC board and all components. The plugpack is not included. Price: $32.00 + p&p.
Postage and handling on each kit is $5.00.
CTOAN Electronics will also be offering the following back-up service on this
project: (1) Fix any fault not including microprocessor replacement – $30.00;
(2) Microprocessor replacement – $25.00; (3) Reprogram microprocessor
with updated software – no charge.
Note: copyright of the PC boards for this kit remains the property of CTOAN
Electronics.
be taken out of diagnostic mode by
bridging pin A to Vcc. Now re-enter
diagnostic mode and select a different
routine.
When in normal mode (the default
mode at power-up), bridging pin C
will display the presently set upper
limit. Note that the power-up default
for the upper limit is 99, while the
lower default is zero. This effectively
means that the relay is disabled when
the unit is first turned on.
Bridging pin E will advance the tens
digit and pin F will advance the units
digit. Once the required upper limit is
on the display, bridge pin A. This will
store the new upper limit and put the
system back into normal mode.
The lower limit is set in a similar
fashion by bridging pin D which will
display the presently set lower limit.
Pins E and F will again advance the
tens and units digits as before and pin
A will store the new value and put the
system back into normal mode.
Be aware that the software does
not check to see if the upper limit is
higher than the lower limit and visa
versa. You must ensure that this does
not happen when you set the upper
and lower limits.
Once the limits have been changed
from the default values, the pump
will effectively be enabled. The pump
relay will be energised when the level
in the tank falls below the set lower
limit and will remain energised until
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the level of water rises above the set
upper limit.
Remote display assembly
There is nothing special about the
construction of the remote display –
just follow Fig.5 and make sure that
your soldering is of a high standard.
Once you have completed the remote
display, connect it to the system
via suitable cable. We used 8-way
ordinary telephone cable. Power for
the main PC board at the tank was
supplied along two of the wires in
the 8-way core telephone cable. The
whole system was then powered by
a 500mA plugpack.
Power up the system and check
the operation of the remote display.
It should read the same as the local
display. To test the operation of the
alarm, raise the tube in the tank until
the reading drops below 20%. This is
best done with the setup link in the
setup mode. The display should start
flashing when the level reads 19% and
30 minutes later the buzzer should
sound for about six seconds.
One last point to consider is that the
box that you use for the main PC board
out near the tank must be made waterproof. Any water that gets in during
rain will surely damage the unit. Also
remember that the microprocessor is
only rated to 60°C so do not leave the
unit in direct sunlight. It should be in
SC
permanent shade.
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April 1994 69
Using the Icom R7000
as a spectrum analyser
The Icom-R7000 & similar receivers can be
readily interfaced to a personal computer to
form a simple, inexpensive spectrum analyser.
The resulting analyser has 100dB of dynamic
range & is capable of examining almost any
section of the spectrum between 25MHz & 2GHz.
Several different resolutions can be selected,
from 2.8kHz to 150kHz.
By JAMES LLOYD & JOHN STOREY*
What makes this possible is that the
Icom, like many modern receivers,
incorporates a CPU-controlled PLL
synthesiser. This same CPU controls
the other functions of the receiver
and can itself be controlled from the
RS-232 port of a personal computer.
The only modification required to
the receiver is to tap into the AGC
(automatic gain control) line to meas*School of Physics, UNSW, Kensington.
70 Silicon Chip
ure the signal strength. Once this is
done, all that is required is software
to scan the receiver through the range
of frequencies of interest, to record the
signal strength at each frequency step,
and to display the result.
Receiver interface
The interface between the PC and
receiver is the “Icom Communication
Interface V” (CI-V). The first thing
needed is a small piece of hardware to
convert the CI-V voltages to and from
RS-232 levels. This little box is avail-
able from Icom but in fact, it contains
little more than a MAX-232 integrated
circuit and would be easy to build.
The Icom CI-V is a serial, half-duplex bus which has the advantage of
being able to control several receivers.
This actually presents a few difficulties in interfacing to a PC. Firstly, the
RS-232 standard is full-duplex (having a separate transmit and receive
line) and has hardware handshaking
facilities. This hardware handshaking
allows the transmitter and receiver
to agree when they are both ready to
exchange data. The CI-V bus, however,
consists of just a single data wire plus
ground.
The problem of bus arbitration (or
agreeing who can talk and when) is
tackled with the CSMA/CD (Carrier
Sense Multiple Access with Collision Detection) protocol. This simply
means that any device may try to use
the bus at any time. Any collisions
(more than one party attempting to
transmit simultaneously) are detected
and resolved by one of them waiting
for the other to complete. This allows
multiple devices on the one bus and
is generally an efficient protocol if the
bus is not over-committed. However,
it does present some difficulties in
implementation on a PC, since there
is no readily available “carrier-sense”
signal.
We solved this problem by allowing all the communications between
the receiver and the computer to be
handled by a shareware communications library. This tests for “line busy”
by monitoring the traffic in and out
of the data buffers, thus emulating
the “carrier sense” signal, equating
carrier to transmission or reception
of data.
When the receiver detects a collision, it transmits a series of jammer
codes which cause the software to
stop sending. At the end of a command string the receiver transmits
“acknowl
edge” signals which are
monitored to ensure reliable operation.
The general command structure is
a stream of bytes, consisting of two
preamble bytes (to signify the start of
the command, each being the value
FE hex), a destination or “to” address
(08 hex is the default for the R7000),
a sender or “from” address (default
E0 hex for the controller), one or two
bytes specifying the command number
and an optional subcommand number,
a variable number of data bytes and
an-end-of-command byte (FD hex).
The frequency data is sent as five
BCD (Binary Coded Decimal) bytes,
in least significant to most significant order. Binary coded decimal is
a scheme whereby each decimal digit
is encoded as a 4-bit nibble and thus
a 2-digit number can be encoded in
one byte. For example, the frequency
123.456789MHz would be sent as the
bytes 89 67 45 23 01 (BCD). Since the
tuning step is 100Hz, the first byte
(1’s and 10’s of Hz) is ignored. The
GHz digit is also ignored, since the
1-2GHz range of the receiver is set
by manually pressing a button on the
control panel.
To “set frequency” the command
number is 05, with no subcommand.
To tune the receiver to the frequency
123.4567MHz, the command string
would be FE FE 08 E0 05 00 67 45
23 01 FD. The receiver then sends a
response, addressed to the controller,
with a value in the command number
field indicating the success (FB) or
failure (FA) of the command. Thus,
a successful command would return
Fig.1: this buffer circuit was used to
isolate the AGC line from the receiver
and thereby avoid any loading effects
from the PC.
the string FE FE E0 08 FB FD. The
complete process of stepping to a new
frequency thus requires a total of 17
bytes. At 1200 baud, this takes approximately 120ms, plus the response time
of the receiver CPU.
The minimum step size of the synthesiser is 100Hz. Actually, the digital
synthesis is done in 1kHz increments.
The 100Hz steps are generated within
the Icom with a D/A converter driving
a VFO. However, for our present purposes this is of no consequence. The
maximum step size can be anything
you like and in fact the receiver could
be hopped about in frequency in a
completely random manner, though
it’s hard to imagine why anyone would
want to do so.
Normally, one would choose a step
Fig.2: this spectrum is the electromagnetic interference from a 33MHz 386 PC
taken over the range from 50 to 100MHz. Radiation below 50MHz was found to
be negligible. The 99MHz peak is most likely the third harmonic of the 33MHz
internal CPU clock & the others are probably harmonics of the bus clock.
April 1994 71
the same way as for the frequency
commands.
Extracting the AGC voltage
To extract the AGC voltage, it is
necessary to open the receiver, identify
the relevant circuit connection and
bring it out to a suitable socket. We
chose to add a buffer amplifier to avoid
any possibility of disturbing normal
operation of the receiver.
As shown in Fig.1, the buffer circuit uses an OP90 op amp as it has
low power consumption, low offset
voltage and operates from a single
supply. The circuit has a gain of 2,
to bring AGC voltage swing up to the
full input range of the analog/digital
converter.
Icom are even kind enough to supply the R7000 receiver with a spare
RCA jack on the rear panel, so no
chassis work is required.
Measuring the AGC voltage
Fig.3: this is the radiated spectrum of ABC channel 2 as received at Kensington,
on the UNSW campus. This plot shows the structure of a television signal in the
vicinity of the vision carrier (& should convince any doubters, if they still exist,
of the reality of sidebands). The video signal is amplitude modulated onto the
carrier & the dominant frequency component of this modulation is at the linescan frequency of 15.625kHz. The sidebands are thus located 15.625 kHz apart
and extend symmetrically either side of the carrier. (Close in to the carrier the
sidebands are expected to be equal. If the scan covered a wider frequency range
the vestigial sideband character of the modulation would become apparent).
The scan was performed with the “SSB” filter (FWHM of 2.8kHz), in 1.4kHz
steps.
size equal to half the filter bandwidth.
This “Nyquist sampling” ensures the
maximum amount of information is
extracted from the spectrum.
The settling time of the receiver
tuning circuit is very fast. However,
the AGC amplifier incorporates a time
constant which is different for each of
the receiver modes. In a moment we
will show how we use the different
modes to give the different filter resolutions. For the AM filter, the AGC
time constant has been measured and
found to be approximately 200ms. The
AGC settling occurs concurrently with
the transmission of the “acknowledge”
signal, so it is not all “dead” time.
Including all overheads and settling
time, reliable tuning of the receiver
(to a signal stable within 0.5%) is
72 Silicon Chip
achieved in approximately 500ms.
Slight speed improvements could be
made by increasing the transmission
speed, or sacrificing stability in the
signal.
The resolution of the scan can be
selected by choosing the R7000 receive mode which then selects the
IF filter bandwidth. The filters have
bandwidths of 2.8kHz (SSB), 6kHz
(AM/FM narrow), 15kHz (AM/FM),
150kHz (FM wide). The receive mode
(and hence filter bandwidth) is selected with command number 06 prior
to beginning a scan, in a similar way
to the frequency stepping mode. For
example, selection of the AM filter
(data field 02) would be done by the
command string FE FE 08 E0 06 02
FD. The receiver responds in exactly
In order for the computer to be able
to read the AGC voltage, an analogto-digital (A/D) converter is of course
required. Almost any A/D would be
suitable here, as the application is
quite undemanding. We used a 12bit PC ADDA-12 card from ESIS in
Sydney. This inexpensive unit works
particularly well and has a conversion
time of only 60 microseconds but
care must be taken when using a fast
computer.
The card uses a monolithic successive-approximation converter which
is clocked by strobing a register on
the card. If this happens too quickly,
the converter becomes confused and
the accuracy drops dramatically. On
the 386-33 PC that we used, we had
to add delays in the code to prevent
this from happening.
The AGC voltage output of the receiver is highly non-linear with signal
strength, as one might expect. Conversion of the raw AGC voltage to signal
strength is achieved in the computer
using a simple look-up table with
linear interpolation between points.
Creating the look-up table requires
the use of either a calibrated signal
generator or a signal generator plus
calibrated attenuator.
The Icom R7000 receiver conveniently includes a 20dB switchable
attenuator in the front end which
could be used to get the calibration
procedure off to a good start. Separate tables are needed for each of the
SOLID STATE “PELTIER EFFECT”
COOLER - HEATER
Further to our advertisment somewhere
else in this issue, we can offer a set
of major parts needed to make a solid
state thermoelectric cooler - heater. We
can provide a large 12V-4.5A Peltier
effect semiconductor, two thermal cutout switches, and a 12V DC fan for a
total price of:
$45
We include a basic diagram/circuit showing how to make a small refrigerator/ heater. The major additional items required will
be an insulated container such as an old
“Esky”, two heatsinks, and a small block
of aluminium.
CAR ALARM
We have purchased a good but limited
quantity of this well known brand Australian made car alarm. It has been made
obsolete because it doesn’t feature UHF
remote control. But look at the features:
voltage drop detection (wired directly or
internal), pin switch detection for bonnet/
boot, piezoelectric movement sensor,
optional passive arming via ignition
switch, ignition disable via master switch if
passive arming is not used, may be wired
to existing door pin switches to act as a
switch - sensing last door arming alarm,
30-second entry delay, 7-second entry
delay, flashing LED - intrusion indicator
provided, flashes vehicle indicators when
alarm is sounding, extra negative output
to power second siren or pager, colour
coded wiring siren provided, powerful
40 watt 125dB siren which employs a
dynamic speaker: a sound that makes
most car alarm sirens sound like toys!!
$48
With the car alarm package we will also
include a circuit and notes on how to
modify the entry and exit times, and how
to make it UHF remote controlled: our
single channel UHF remote control is
available: $17 for the transmitter, $34 for
the receiver.
C.O.B. SOUND GENERATOR
MODULES
Stamp sized PCBs with an LSI sound
generator IC that is surface mounted on
them. Work from approximately 3V and
have negligible standby current. Require
a few external components to become
complete sound generators: typically two
resistors, one capacitor, one transistor
and a speaker.
FOUR TRAIN NOISES (excellent for
model railways): $4
AMBULANCE, FIRE + POLICE SIREN,
PLUS MACHINE GUN: $2.50
16 DOOR-CHIME TUNES: $4
CLASSIC DING-DONG DOOR CHIME:
$3
IR “TANK SET”
*** SUPER SPECIAL ***
ON SPECIAL is a set of components that
can be used to make a a very responsive
infrared night viewer. The matching lens
tube and eyepiece sets were removed
from working military quality tank viewers. We also supply a very small EHT
power supply kit that enables the tube
to be operated from a small 9V battery.
The tube emloyed is probably the most
sensitive IR responsive tube we ever
supplied. The resultant viewer requires
low level IR illumination. Basic instructions provided. The price is
$120
for the tube, lens, eyepiece and the
power supply kit. When ordering, specify
preference for a wide angle or a telescopic
objective lens.
IR FILTERS
A high quality military grade, deep infra
red IR filter. Used to filter the IR spectrum
from medium-high powered spotlights. Its
glass construction makes it capable of
withstanding high temperatures. Approx.
130mm diameter and 6mm thick. For use
with IR viewers and IR responsive CCD
cameras. Limited stock:
$40 Ea.
ARGON HEADS
These low voltage air cooled Argon Ion
Laser Heads are priced according to their
hours of operation. They produce a bright
BLUE BEAM (488nm) and a power output
in the 30-100mW range: depends on the
tube current.
The head includes power meter circuitry,
and starting circuitry. We provide a simple
circuit for the supply. Limited supplies at a
fraction of their their real cost:
$500 - $650
FIBRE OPTIC TUBES
In early May we will have some used
single stage, first generation, “passive”
image intensifier tubes in stock. These are
US made, in excellent condition, and have
25/40mm diameter, fibre-optically coupled
input and output windows. Both the tubes
are basically cylindrical. The 25mm tube
has an overall diameter of 57mm and is
60mm long, whilst the 40mm tube has an
overall diameter of 80mm and is 92mm
long. The gain of these is such that they
would produce a good image in aproximately less than 1/4 moon illumination
when used with suitable “fast” (low light
lenses), but they can also be IR assisted
with low level IR sources to see in total
darkness. The superior resolution of these
tubes would make them suitable for low
light video preamplifiers, high quality wild
life observation, and astronomical use.
Each of the tubes is suplied with a 9V/
EHT power supply kit and they are priced
at an incredible:
$125 .... for the 25mm intensifier tube/
supply.
$190 .... for the 40mm intensifier tube/
supply.
very interesting pattern displays from a
laser beam. Includes two motors, two potentiometers, two Darlington transistors,
two front surfaced aluminium mirrors,
instructions and small hardware: most
items that are needed to make a two
motor laser deflection kit.
$15
X-Y LASER SCANNER - KIT
You could spend thousands of dollars
buying commercial X-Y scanners for
laser beam deflection. This X-Y scanner
compromises by employing two suitable
DC motors to achieve good results. With
normal levels the motors don’t actually
spin but simply vibrate around the set
position.
The PCB and components kit include
rectification and filtering (power supply),
audio preamplifiers, audio filtering, and
two separate power amplifiers to drive
the two deflection motors. The scanner is
powered from a 16VAC-900mA plugpack.
In one of the modes of operation the
scanner can produce a totally random
2-dimensional display which is dependant on the actual music picked up by the
electret microphone. A second mode of
operation enables the power amplifiers to
be driven from external oscillators and/or
pre-taped signals recorded on a stereo
cassette recorder.
A short form kit of parts is available for the
X-Y scanner. It includes a screened and
solder masked PCB and all the on-board
components, an electret microphone, two
motors, and two lightweight mirrors.
LASER POINTER
Improve and enhance all your presentations. Not a kit, but a complete commercial 5mW/670nm pen sized pointer at a
SPECIAL PRICE of:
$120
DIVERGING LENS
A high quality laser beam diverging
(beam expander) glass lens, mounted
on an aluminium plate, with mounting
screws provided. Dimensions: 25 x 25
x 6mm. Two of these cascaded provide
sufficient expansion for use in HOLOGRAPHY. In conjunction with additional
lenses these can also be used to diverge
a laser beam. Great for experimenting
with laser beams.
$5
CRYSTAL OSCILLATOR MODULES
These small TTL Quartz Crystal Oscillators are hermetically sealed. Similar
to units used in computers. Operate
from 5V and draw approximately 30mA.
TTL logic level clock output. Available in
4MHz, 4.032MHz, 5.0688MHz, 20MHz,
20.2752MHz, 24.74MHz, 40MHz, and
50MHz.
$7Ea. or 5 for $25
LED DISPLAYS
National Semiconductor 7-segment common cathode 12-digit multiplexed LED
displays with 12 decimal points. Overall
size is 60 x 18mm, and pinout diagram
is provided.
2.50 Ea. or 5 for $10
FM MICROPHONE
Features a stainless steel case and a
UNIDIRECTIONAL microphone insert,
powered by two “AA” batteries. High
quality at:
$28
DYNAMIC MICROPHONE
Stage quality unidirectional (cardioid)
600-ohm dynamic microphone in a black
metal housing. Has on/off switch and
Cannon connector. Prewired lead and
clip provided.
$39
FANS
Brand new German made PAPST brand
115V-12W fans with metal blades. Overall
dimensions 80 x 80 x 38mm. Use two
in series to run off mains? LIMITED
STOCKS.
$14
PROFESSIONAL MICROPHONE
CABLE
High quality twin core flexible shielded microphone cable. Heavy duty construction,
red in colour, overall diameter is 6mm, has
a tightly woven shield and two 24-strand
centre conductors (red and black). Uses
lots of copper: the resistance of one of
the centre wires is 2.4 ohms per 100
meters, which is lower than the resistance
of one of the conductors in a typical 10A
mains extension lead! The resistance of
the shield is 1.4 ohms per 100 metres.
Excellent for professional use in rugged
environments and stage use. Also suitable
for low voltage shielded power cables.
Priced at a small fraction of its real value:
$1.50 PER METRE
SPEAKER GIVEAWAY
One 3" tweeter, one 4" woofer, a non
polarized crossover capacitor, plus a
diagram:
$10 for the set
2 sets (STEREO) for $18!!
MEDIUM BRIGHTNESS LEDs
With a luminous output of approximately
7mCds <at> 20mA, these 5mm LEDs are
more than 10 times brighter than ordinary
LEDs. Available in GREEN, YELLOW
and AMBER, and priced below ordinary
LED prices:
20c Ea. 10 for $1.80 or 100 for $15
For any mix of colours.
OATLEY ELECTRONICS
MOTOR DEFLECTION KIT
This inexpensive kit can produce some
PLEASE ALSO SEE OUR ADVERT ON PAGE 39
PO Box 89, Oatley, NSW 2223
Phone (02) 579 4985. Fax (02) 570 7910
Major cards accepted with phone & fax orders. P & P for
most mixed orders: Aust. $6; NZ (airmail) $10.
April 1994 73
monotonicly decreasing part of the
curve, where there is only one signal
value for a given AGC voltage. At
zero and 10dB on the FM wide filter
curve, there are two signal strength
values for the one AGC value). Thus
the system currently has a (software
limited) sensitivity of 3 microvolts in
the most sensitive bands.
Software
Fig.4: this is a spectrum taken of the FM band from 88 to 108MHz, taken with
the FM WIDE filter (150kHz) in 75kHz steps. The antenna was just a length of
wire. The large peak at 107.3MHz is 2SER which is located on the University
of Technology building in Ultimo and has a line of sight view to the Physics
building at UNSW. The peak at 102.5MHz is 2MBS, with a transmitter located
on the AMP building in Sydney, again very close and line of site to Kensington.
Although the stations with powerful transmitters (2DAY 104.1, 2MMM 104.9,
2JJJ 105.7 and ABC 92.9) appear very weak, it should be noted that the vertical
scale is linear and these stations are only a few dB below the most powerful.
receiver filters and (at least in principle) for each of the four “front-ends”
which the receiv
e r automatically
switches between as it changes bands.
However, this variation of calibration
with frequency is probably only a
small effect and in many applications
the system is only required to operate
over a narrow frequency band.
The data gathered by the calibration
procedure is used to convert AGC
voltage to signal strength, using a
look-up table with linear interpolation. The discontinuities in the graph
are an artefact of the signal generator used and occur at points where
it switches circuits to alter range.
Note the very wide dynamic range
achievable, 100dB in the case of the
AM filter. The software used only the
The Icom R7100 Communications Receiver
The Icom communications receiver pictured here is the R7100 model. This
supersedes the R7000 model referred to in this article but it can be used for
spectrum analysis in exactly the same way. Among its many features, the R7100
continuously covers the frequency spectrum from 25MHz to 2000MHz, has
all-mode capability, 900 memory channels, and either direct keyboard entry or
manual frequency selection.
For further information, contact Emtronics, 92-94 Wentworth Ave, Sydney.
Phone 211 0988.
74 Silicon Chip
Depending on capabilities of the
PC and on what your favourite programming language is, the software
can range from simple to complex.
We wrote our program in C, with the
following modules: (1) R7000LIB to
handle the communications to the
receiver, covering commands to set
and read the frequency and receiving
mode and interpret the responses for
the receiver; (2) ADDALIB to perform
the A/D conversions; and (3) AGCTOSIG to convert AGC voltages to signal
strength using the data files generated
from known signal strengths.
Using these libraries, we built programs to perform auto
mated scans,
interactively scan, draw graphs and
so on.
The system can be used as a spectral
analyser for virtually any application
within the tuning range of the receiver (25-999MHz and 1025-1999MHz
in the case of the Icom R7000). The
main limitation is one of speed.
Because of the time taken to scan
across the spectrum, the result will
only be meaningful if the spectrum
is effectively unchanging during this
time. The accompa
nying spectrum
plots demonstrate the capabilities of
the system.
Conclusion
Computer interfacing to the Icom
R-7000 receiver is straightforward and
gives satisfying results. In fact, under
computer control the extraordinarily
good performance of these receivers in
terms of versatility, stability, sensitivity and low spurious response levels
becomes apparent.
The spectrum analyser described
here is just one example of what can be
done once a PC is given control of the
receiver and is able to monitor signal
strength. Another interesting application for the avid SWL or DX’er would
be to log the signal from various HF
stations from around the globe. Why
not become your own ionospheric
SC
prediction service?
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.
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.
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
PRODUCT SHOWCASE
Kenwood K series
midi sound systems
Kenwood’s new K series midi lineup comprises the K-99M, K-88M,
K-77M and K-66. Aside from their
stylish lines, the new line-up has
such features as Environmental Sound
Enhancement, DSP, Omni-Directional
speakers (optional), Graphic Equaliser/Spectrum Analyser, Dolby Pro-Logic Surround Sound, Dolby 3-stereo
and Karaoke (K-99M). All systems
are designed to be used as dedicated
audio systems or to be integrated into
the home video system.
The DSP and presence circuits
create the ambience of a number of
“live” venues in the user’s own living room. Kenwood’s DSP (K-99M
& K-88M) offer the choice of seven
modes including Jazz Club, Church,
Arena and Stadium, while the K-77M
and K-66 offer similar effects through
Kenwood’s ASP (Acoustic Sound
Processor) circuitry.
The AI (Acoustic Intelligence) features (eg, Auto Edit) allow the user to
trim or rearrange songs so that a longer
CD will fit on a shorter cassette. Addi-
Crystal oscillator
without an oven
The trouble with traditional
designs of crystal oscillator is that
they require an oven to maintain
high temperatures for stable output. This means that they are bulky,
require a high current of typically
500mA and take as much as 20
minutes to warm up to temperature
when switched on.
GEC Plessey Semiconductors
(GPS) has solved these problems
with a new design of crystal oscillator, which uses digital tem
perature compensation to achieve
an ultra-stable output without the
need for an oven. The OD9301 has
no warm-up delay and the typical
current consumption is less than
15mA. Also, as an oven is not required, the OD9301 is supplied in
80 Silicon Chip
tionally, AI automatically checks the
CD being played and creates the ideal
equalisation curve to match it. These
curves can also be stored in memory
for later use (K-99M).
The K Series midis can also be configured with several options including:
turntable (all models), omnidirectional speakers, surround speakers
and centre speaker (K-99M only),
surround speakers and subwoofer
a small package measuring only 36
x 26 x 12mm.
The OD9301 allows for external
frequency trimming and may be
specified anywhere within the
frequency range of 4-25MHz. The
device uses a proprietary algorithm
that enables it to give superb phase
noise and short term stability performance whilst also meeting very
tight frequency versus temperature
specifications. The excellent frequency stability of ±0.3 parts per
million (-10°C to +70°C) or ±0.5
parts per million (-40°C to +85°C)
makes it ideal for use as a reference
source in base stations for GSM,
DECT and PCN or for military
communications systems.
For further details, contact GEC
Electronics, Unit 1, 38 South St,
Rydalmere 2116. Phone (02) 638
1888.
(K-99M, K-88M), subwoofer (K-77M).
Pricing is as follows: K-99M $3859;
K-88M $3099; K-77M $2699; and the
K-66 $2199. All models are covered
by a 3-year parts and labour warranty
with 12 months on the laser pick-up.
If you would like further information on the K Series, contact Kenwood
Electronics Australia Pty Ltd on (02)
746 1888 for your nearest Kenwood
dealer.
Dali 5A Mk2
loudspeaker
Dali 5A Mk 2 is the largest in the
range of Australian assembled Dali
models. The Dali 5A Mk 2 features
dual 18cm bass drivers with rubber
suspension surrounds, textile dust
caps and thick polypropylene cones.
The powerful magnetic circuit features
an aluminium short-circuiting ring in
the pole piece which reduces second
harmonic distortion. The use of two
relatively small bass drivers within
the one cabinet gives high sensitivity
(93dB for one watt at one metre) with
high power handling; amplifiers up
to 120 watts per channel are recommended.
The tweeter chosen for the speaker
is a special design using a soft textile
dome with a ferrofluid coiled voice
coil. This is particularly well damped
and has excellent transient response.
The front baffle of the Dali 5A Mk 2 is
Digital handheld clamp meter
Meter International has released the MIC 2080W
handheld, clamp-on, autoranging power meter. It is
designed to measure various electrical parameters
without the need to break the circuit.
The meter features AC/DC current measurement to
1000A and true RMS voltage to 650VAC or 1000VDC.
The MIC 2080W can measure true power to 200kW
and frequency to 2kHz. The meter uses Hall Effect
technology to measure true RMS current accurately,
almost regardless of the waveform, to a crest factor
of three.
The measured value is displayed on a 3.5-digit liquid crystal display
with an analog output provided for monitoring the current waveform
with an oscilloscope.
The MIC 2080W is available from Computronics International, 31 Ken
sington Street, East Perth, WA 6004. Phone (09) 221 2121.
covered in “Acousti-Flock” absorbent
material, in order to reduce edge diffraction and improve stereo imaging.
Dali 5A Mk 2 is supplied with
rigid steel spikes, which are claimed
to couple the speaker securely to the
floor and improve bass response and
stereo imaging.
Dali 5A Mk 2 is supplied in mirror-imaged pairs and sells for $1598
per pair. For further information,
contact Scan Audio Pty Ltd, 52 Crown
Street, Richmond, Vic 3121. Phone
(03) 429 2199.
Ultrasonic cleaner for
small components
Until you have used one of these ultrasonic baths for cleaning small components you don’t know how handy
and effective they can be. They’re great
for cleaning drawing pens, jewellery,
small mechanisms, connectors, PC
boards, camera bits and even (perish
the thought) your dentures.
Essentially it consists of a small
stainless steel bath which has a piezoelectric transducer epoxied to its
underside. The piezo transducer is
driven ultrasonically and it agitates
the cleaning fluid so completely that
dirt, grease and grime just stream out
of the components.
This new model from Jaycar has
four timer intervals of 4, 8, 12 & 16
minutes and its tank capacity is 570
millilitres. It runs from 240VAC, is
priced at $169 and is available from
all Jaycar Electronics stores and
dealers.
Model railway
sound module
Oatley Electronics has sourced a
sound generator module that will
directly appeal to model railway enthusiasts. Essentially it is an LSI chip
bonded directly to a very small PC
board measuring 29 x 16mm. This has
14 circuit connections brought to one
edge and requires two external resistors, one capacitor and a battery pack,
a loudspeaker and a 4-way switch to
select one of the four available sound
effects: whistle blowing, train chugging along, level crossing bell and train
crossing a bridge.
The module can be powered from a
battery pack ranging from 2.4V to 6V
although the sound effects are voltage
dependent and to be honest, some effects are much more convincing than
others. We have not had a chance to
try modifications but it is possible to
change the external components to
modify the sound effects.
Current consumption is very low:
less than 1µA on standby and 0.2mA
when operating. The cost is very cheap
at just $4.00.
Also available are three other modules: four sound effects (ambulance,
fire, police siren and machine gun) for
$2.50, a 16-tune door chime for $4.00
and a ding-dong door chime for $3.00.
They are available from Oatley
Electronics, PO Box 89, Oatley, NSW
2223. Phone (02) 579 4985.
CALLING ALL HOBBYISTS
We provide the challenge and money for you to design and build as many
simple, useful, economical and original kit sets as possible.
We will only consider kits using lots of ICs and transistors.
If you need assistance in getting samples and technical specifications while
building your kits, let us know.
YUGA ENTERPRISE
705 SIMS DRIVE #03-09
SHUN LI INDUSTRIAL COMPLEX
SINGAPORE 1438
TEL: 65 741 0300 Fax: 65 749 1048
April 1994 81
Product Review
G-Code: the easy way
to program your VCR
Are you one of the millions of Australians
who can’t or can’t be bothered programming
your VCR to record? If you are, this new
product, called G-Code, could make it a
whole lot easier.
By LEO SIMPSON
G-Code is a small plastic box which
you program with numbers from “TV
Week”. The G-Code Instant Video
Programmer then controls your VCR
via its infrared LEDs and you no longer
have to worry about the intricacies of
programming.
The G-Code Instant Video Programmer is claimed to work with any of
82 Silicon Chip
90 brands of VCR. The only proviso is
that it must have an infrared remote
control. G-Code controls the VCR by
emulating the remote control functions of record, channel selection
and stop.
The G-Code Programmer looks like
a small version of a portable CD player
and measures 99mm wide, 120mm
deep and 32mm thick. Like a portable CD player, it has a liquid crystal
display and a lift-up lid but instead
of a CD compartment it has an array
of pushbuttons, as can be seen in the
photo below. There is an array of numerical buttons plus buttons marked
Cancel, Review, Weekly, Once, Daily
(M-F) and Add Time.
Not shown in the photo is a row of
seven smaller buttons which are used
in the initial setting up of the unit.
These are labelled Video, Cable/Sat,
Channel, Clock, Alter, Save & Enter.
When (and if) you buy the G-Code
unit, you first have to tell it what brand
of VCR you have. You do this by sitting
the unit near your VCR which should
be switched into the standby mode.
You then enter the two digit code
which is peculiar to your brand of
VCR and press the ENTER button. For
example, the code for JVC models is
21. That done, the VCR should turn on
as it is addressed by the G-Code unit.
You then press the SAVE button and
continue to set G-Code unit’s clock
with the date and time.
Having set the date and time, you
then have to tell it which TV stations
are received on your VCR and what
channel numbers are allocated to
them. Again, this is a straightforward
procedure, set out in the brief and
well-written manual.
Finally, you can run a test to make
sure that everything is set up correctly.
You place a blank tape in your VCR
and turn it off, then key in the highest
channel number your VCR is able to
receive.
For example, if your VCR can receive 15 channels, you key in 0015
and then hit the “Once” button. The
G-Code Programmer flashes an orange
LED to indicate that it is transmitting
and it turns on your VCR, selects channel 15, makes a brief recording and
then turns the VCR off again.
From then on, the unit is ready to go
and you can program it to make your
VCR record at any time. Initially, the
G-codes will be featured in “TV Week”
magazine but it is expected that all
major TV guides will quickly adopt
the codes.
The procedure is quite simple. Say
you want to record a program such as
“The Bill” on ABC TV. Look up “TV
Week” and note the digital code – this
can range from three to eight digits and
appears to be quite random.
Enter the code and the liquid crystal
display will indicate the stored channel, time and date, and the length of
tape required to record the program.
At the appointed time, the G-Code unit
will operate your VCR, and provided
it has a blank tape cassette inside,
it will record the program and then
switch the VCR back into standby
mode. Magic, eh?
The G-Code Programmer can store
up to 12 shows to be recorded at various times and you can review these
times by pushing the Review button.
You can program up to 27 days in
advance. The unit will flag any clash
between programs to be recorded and
you then have the option of cancelling
a particular program. You can also arrange to add extra time, in increments
of 15 minutes, to cater for a program
running over time.
The G-Code Programmer runs from
four AAA alkaline cells and battery
life is estimated to one year under
normal usage. When the battery is
due to be replaced, a “LO BATT”
message will be indicated on the
LCD panel.
We had a sample G-Code Programmer for this review and I set it up with
my 7-year old Sharp VCR. The setting
up procedure took about five minutes
and it all went exactly according to the
book. Indeed it is quite uncanny to see
your VCR silently turn itself on and go
into record mode when you know you
have not touched the machine or its
remote control and it is has not been
programmed itself.
Programming the G-Code Programmer is much easier than fiddling with
the itty-bitty buttons on your VCR,
even to one familiar with the procedure. Instead of kneeling down and
peering at poorly lit buttons on the
VCR, you can sit at a table in good light,
and simply punch in the numbers for
each program to be recorded.
So why have we had to wait so long
for this product? It has been available
overseas for some time under various
names. In the USA for example, it is
known as VCR-Plus. It was developed
by Gemstar in the USA and is now
being distributed exclusively in Australia by Philips Consumer Products.
Initially, the G-Code numbers will be
used in “TV Week” magazine and are
expected to be eventually licensed to
most major TV program guides.
The G-Code Programmer comes
with a cradle which can be positioned on top of your VCR, with the
unit slightly overhanging the front.
However, you can position the unit
virtually anywhere in an average
sized room since it has infrared LEDs
aiming from its back corners as well
as the front – this unit really does
seem to have been well thought out.
And if you get into any strife while
setting it up or using it, Philips has
a toll free number (131 124) to help
you sort it out.
The G-Code Programmer is priced
at $129 and will be available Australia-wide from department and electrical stores. It comes with a 6-month
SC
warranty.
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April 1994 83
Silicon Chip
Designing UHF Transmitter Stages.
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;
PC Program Calculates Great Circle Bearings.
BACK ISSUES
September 1988: Hands-Free Speakerphone;
Electronic Fish Bite Detector; High Performance
AC Millivoltmeter, Pt.2; Build The Vader Voice;
Motorola MC34018 Speakerphone IC Data; What
Is Negative Feedback, Pt.4.
November 1988: 120W PA Amplifier Module
(Uses Mosfets); Poor Man’s Plasma Display;
Automotive Night Safety Light; Adding A Headset
To The Speakerphone; How To Quieten The Fan
In Your Computer.
December 1988: 120W PA Amplifier (With Balanced Inputs), Pt.1; Diesel Sound Generator;
Car Antenna/Demister Adaptor; SSB Adaptor For
Shortwave Receivers; Why Diesel Electrics Killed
Off Steam; Index to Volume 1.
April 1989: Auxiliary Brake Light Flasher; Electronics For Everyone: What You Need to Know
About Capacitors; Telephone Bell Monitor/ Transmitter; 32-Band Graphic Equaliser, Pt.2; LED
Message Board, Pt.2.
May 1989: Electronic Pools/Lotto Selector; Build
A Synthesised Tom-Tom; Biofeedback Monitor For
Your PC; Simple Stub Filter For Suppressing TV
Interference; LED Message Board, Pt.3; All About
Electrolytic Capacitors.
June 1989: Touch-Lamp Dimmer (uses Siemens
SLB0586); Passive Loop Antenna For AM Radios;
Universal Temperature Controller; Understanding
CRO Probes; LED Message Board, Pt.4.
July 1989: Exhaust Gas Monitor (Uses TGS812
Gas Sensor); Extension For The Touch-Lamp
Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; NSW 86 Class Electric
Locomotives.
September 1989: 2-Chip Portable AM Stereo
Radio (Uses MC13024 and TX7376P) Pt.1;
Alarm-Triggered Telephone Dialler; High Or Low
Fluid Level Detector; Simple DTMF Encoder;
Studio Series 20-Band Stereo Equaliser, Pt.2;
Auto-Zero Module for Audio Amplifiers (Uses
LMC669).
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;
VOX With Delayed Audio; Relative Field Strength
Meter; 16-Channel Mixing Desk, Pt.3; Active CW
Filter For Weak Signal Reception; How To Find
Vintage Radio 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; Design Factors For Model
Aircraft; Fitting A Fax Card To A Computer.
October 1989: Introducing Remote Control; 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.
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; Weather Fax Frequencies.
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.
August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket;
Digital Sine/Square Wave Generator, Pt.2.
December 1989: Digital Voice Board (Records
Up To Four Separate Messages); UHF Remote
Switch; Balanced Input & Output Stages; Data For
The LM831 Low Voltage Amplifier IC; Installing A
Clock Card In Your Computer; Index to Volume 2.
January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Speeding Up
Your PC; Phone Patch For Radio Amateurs; Active
Antenna Kit; Speed Controller For Ceiling Fans;
September 1990: Music On Hold For Your Tele
phone; Remote Control Extender For VCRs; Power
Supply For Burglar Alarms; Low-Cost 3-Digit
Counter Module; Simple Shortwave Converter For
The 2-Metre Band.
October 1990: Low-Cost Siren For Burglar
Alarms; Dimming Controls For The Discolight;
Surfsound Simulator; DC Offset For DMMs; The
Dangers of Polychlorinated Biphenyls; Using The
NE602 In Home-Brew Converter Circuits.
Please send me a back issue for:
❏ April 1989
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❏ March 1991
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❏ August 1991
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Card No.
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.
December 1990: DC-DC Converter For Car
Amplifiers; The Big Escape – A Game Of Skill;
Wiper Pulser For Rear Windows; Versatile 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; Laser Power Supply; 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; LowCost Sinewave Oscillator; Fast Charger For Nicad
Batteries, Pt.2; How To Design Amplifier Output
Stages; Tasmania's Hydroelectric Power System.
March 1991: Remote Controller For Garage
Doors, Pt.1; Transistor Beta Tester Mk.2; Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O
Board For PC-Compatibles; Universal Wideband
RF Preamplifier For Amateurs & 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; Setting Screen Colours
On Your PC.
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; Electric Vehicle Transmission
Options; 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; PEP Monitor For Amateur Transceivers.
August 1991: Build A Digital Tachometer;
Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; Installing
Windows On Your PC; Step-By-Step Vintage
Radio Repairs.
September 1991: Studio 3-55L 3-Way Loudspeaker System; Digital Altimeter For Gliders
& Ultralights, Pt.1; Build A Fax/Modem For
Your Computer; The Basics Of A/D & D/A
Conversion; Windows 3 Swapfiles, Program
Groups & Icons.
October 1991: Build A Talking Voltmeter For Your
PC, Pt.1; SteamSound Simulator Mk.II; Magnetic
Field Strength Meter; Digital Altimeter For Gliders
& Ultralights, Pt.2; Getting To Know The Windows
PIF Editor.
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; Modifying The Windows INI Files.
December 1991: TV Transmitter For VCRs With
UHF Modulators; Infrared Light Beam Relay;
Solid-State Laser Pointer; Colour TV Pattern
Generator, Pt.2; Windows 3 & The Dreaded Un
recoverable Application Error; Index To Volume 4.
January 1992: 4-Channel Guitar Mixer; Adjustable
0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Automatic Controller For Car
Headlights; Experiments For Your Games Card;
Restoring An AWA Radiolette Receiver.
February 1992: Compact Digital Voice Recorder;
50-Watt/Channel Stereo Power Amplifier; 12VDC/240VAC 40-Watt Inverter; Adjustable 0-45V 8A
Power Supply, Pt.2; Designing A Speed Controller
For Electric Models.
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 Direct
ories; Valve Substitution In Vintage Radios.
April 1992: Infrared 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; LowCost 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; What’s New In Oscilloscopes?;
A Look At Hard Disc Drives.
July 1992: Build A Nicad Battery Discharger;
8-Station Automatic Sprinkler Timer; Portable
12V SLA Battery Charger; Off-Hook Timer For
Telephones; 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;
Internal Combustion Engines For Model Aircraft;
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; Electronically
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 Simple Projects For Model
Railroads; A Low Fuel Indicator For Cars; Audio
Level/VU Meter With LED Readout; Build An Electronic Cockroach; MAL-4 Microcontroller Board,
Pt.3; 2kW 24VDC To 240VAC Sinewave Inverter,
Pt.5; Making File Backups With LHA & PKZIP.
March 1993: Build A Solar Charger For 12V
Batteries; An Alarm-Triggered Security Camera;
Low-Cost Audio Mixer for Camcorders; Test Yourself On The Reaction Trainer; 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;
A Look At The Digital Compact Cassette.
May 1993: Nicad Cell Discharger; Build The
Woofer Stopper; Remote Volume Control For Hifi
Systems, Pt.1; Alphanumeric LCD Demonstration
Board; Low-Cost Mini Gas Laser; The Microsoft
Windows Sound System.
June 1993: Windows-Based Digital Logic
Analyser, Pt.1; Build An AM Radio Trainer, Pt.1;
Remote Control For The Woofer Stopper; A Digital
Voltmeter For Your Car; Remote Volume Control
For Hifi Systems, Pt.2; Double Your Disc Space
With DOS 6.
July 1993: Build a Single Chip Message Recorder; Light Beam Relay Extender; Build An AM
Radio Trainer, Pt.2; Windows Based Digital Logic
Analyser; Pt.2; Low-Cost Quiz Game Adjudicator;
Programming The Motorola 68HC705C8 Micro
controller – Lesson 1; Antenna Tuners – Why
They Are Useful.
August 1993: Low-Cost Colour Video Fader; 60LED Brake Light Array; A Microprocessor-Based
Sidereal Clock; The Southern Cross Z80-based
Computer; A Look At Satellites & Their Orbits;
Unmanned Aircraft – Israel Leads The Way; Ghost
Busting For TV Sets.
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 Electronic
Cockroach; Restoring An Old Valve Tester; Servicing An R/C Transmitter, Pt.1.
October 1993: Courtesy Light Switch-Off Timer
For Cars; FM Wireless Microphone For Musicians;
Stereo Preamplifier With IR Remote Control, Pt.2;
Electronic Engine Management, Pt.1; Mini Disc
Is Here; Programming The Motorola 68HC705C8
Micro
controller – Lesson 2; Servicing An R/C
Transmitter, Pt.2.
November 1993: Jumbo Digital Clock; High
Efficiency Inverter For Fluorescent Tubes; Stereo
Preamplifier, Pt.3; Build A Siren Sound Generator;
Electronic Engine Management, Pt.2; More Experiments For Your Games Card; Preventing Damage
To R/C Transmitters & Receivers.
December 1993: Remote Controller For Garage
Doors; Low-Voltage LED Stroboscope; Low-Cost
25W Amplifier Module; Peripherals For The
Southern Cross Computer; Build A 1-Chip Melody
Generator; Electronic Engine Management, Pt.3;
Index To Volume 6.
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 For
Beginners; Electronic Engine Management, Pt.4;
Even More Experiments For Your Games Card.
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: More Than Just Bags Of Wind;
Building A Simple 1-Valve Radio Receiver.
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; Switching
Regulators Made Simple (Software Offer)
PLEASE NOTE: all issues from November 1987
to August 1988, plus October 1988, January,
February, March & August 1989, May 1990, and
November and December 1992 are now sold out.
All other issues are presently in stock, although
stocks are low for some older issues. For readers
wanting articles from sold-out issues, we can
supply photostat copies (or tearsheets) at $7.00
per article (incl. p&p). When supplying photostat
articles or back copies, we automatically supply
any relevant notes & errata at no extra charge.
April 1994 85
VINTAGE RADIO
By JOHN HILL
Bandspread tune-up for an old
Astor multiband receiver
As readers could well imagine, I have met a
lot of fellow radio collectors over the years,
particularly since I began writing Vintage
Radio. My monthly column has brought about
many meetings and, in some instances, long and
lasting friendships.
However, being a so-called “authority” on vintage radio does have
its disadvantages, including the occasional knock on my door by complete
strangers seeking advice on a particular receiver.
In fact, it was a knock on the door
that started this month’s story although, in this case, the owner of the
receiver is well known to me. Gener-
ally, he is quite capable of servicing
his own radios and can usually track
down an elusive fault and fix it.
In this particular case, the receiver – a 1950 5-valve dual-wave Astor
table model – had been repaired but
the remaining problem was alignment.
Not only was there an annoying double
peak response when tuning but there
was also the matter of three band-
spread shortwave bands that were
badly out of alignment. It seemed as
though someone had tightened up
all the adjustment slugs so that they
wouldn’t fall out.
In a past series of three articles,
I covered receiver alignment fairly
thoroughly but shied away from
multiband shortwave tune-ups. After
three consecutive months devoted to
align
ment, it seemed about time to
change the subject.
However, a multiband receiver
such as this Astor offers different
tune-up problems which should be
discussed. Both the five and 6-valve
versions of these Astors were popular
radios back in the early 1950s and
there are still a lot of them around.
No doubt, a good many of them could
do with a tune-up.
In my opinion, a realignment of this
type cannot be satisfactorily carried
out without a radio frequency generator and an output meter. It was the
owner’s lack of these items that led
him to seek my assistance.
IF transformers
This particular style of Astor receiver was popular in the early 1950s. It was
available in four, five & 6-valve versions, some of which had three bandspread
shortwave bands.
86 Silicon Chip
The first step was to align the
intermediate frequency (IF) transformers, particularly as a double-peak
problem is usually the result of these
devices being out of alignment. Un
fortunately, the IF alignment was not
a straightforward job, as one of the
adjustment slugs was stuck solid. To
make matters worse, the adjustment
slot in the soft iron core had been
gouged out by a screwdriver blade.
Nothing is ever as simple as first
thought!
Tuning the RF generator slowly
across the IF showed up the double
peak, with one peak being stronger
to performance. It is definitely a better
alternative to a double peak.
Broadcast band alignment
The wave change switch in the old Astor is surrounded by a bewildering array
of components & wiring. However, a close examination of the switch will reveal
which coil is in circuit for each switch position. There are eight coils to adjust
plus a trimmer.
The shortwave coils are arranged in two clusters of three. Shown here are
the coils that are switched (one at a time) into the oscillator circuit. The wave
change switch controls a large number of components.
than the other. The strong peak was
at 455kHz while the lesser one was
at 463kHz.
When correcting a problem of this
nature there are a number of options
available: (1) replace the faulty IF
transformer if a replacement is available; (2) add correcting trimmer capacitors to the base connections; or (3)
compensate for the immovable slug by
shifting the ones that will move to the
frequency of the one that has stuck. I
tried the latter option, as it seemed the
easiest solution.
After setting the RF generator to
455kHz, the IF transform
ers were
readjusted to that frequency but there
was no noticeable improvement. Readjusting the transformers to 463kHz
produced a much sharper peak and,
what’s more, without any hint of the
previous double peak. Try doing that
without an RF generator and an output
meter!
Not having a circuit diagram for
the old Astor, I could only guess at
what the IF was supposed to be but
it would be unlikely to be anything
other than 455kHz. While pulling
the transformers off frequency a little
is perhaps undesirable in theory, in
practice it makes little or no difference
The next step was the alignment
of the broadcast band. The Astor is
fitted with a nonadjustable aerial coil,
an iron-dust cored oscillator coil and
a trimmer on each of the tuning capacitor’s two sections. As there were
pointer marks at each end of the dial,
the pointer was adjusted to coincide
with these marks. There were also
marks at 600kHz and 1400kHz for
alignment purposes.
Starting at the low-frequency end of
the band, a 600kHz generator signal
was fed into the aerial and earth terminals and the oscillator coil adjusted
for maximum output as shown on the
output meter. As there was no adjustment provided in the aerial coil, it was
necessary to rock the tuning capacitor
while adjusting the oscillator coil slug
so as to locate the aerial coil peak.
This adjustment did not quite bring
the dial pointer to the 600kHz mark
and so the pointer was slid along the
dial cord a couple of millimetres until
it coincided.
After injecting a signal of 1400kHz
and transferring operations to the other
end of the dial, the pointer was found
to be spot on its designated mark. If
it had not been, the pointer position
could have been moved by adjusting
the oscillator trimmer.
All that remained was to adjust the
aerial trimmer for maximum output
at the 1400kHz position. It too was
almost spot on and the screw required
only a few degrees of rotation to peak
the output meter. This completed the
broadcast band alignment.
Shortwave bands
To the uninitiated, the 3-band,
bandspread shortwave section with
its array of six coils and adjustment
slugs can be rather intimidating.
However, taking one band at a time
removes a lot of the mystery and two
thirds of the coils.
If one looks closely at the wavechange switch, it is not difficult to
work out which pair of coils (three
pairs altogeth
er) are brought into
circuit at each of the three shortwave
positions. It helps if the coils are then
marked: a simple 1, 2 and 3 to correspond to the switch positions is all that
is needed. This is fairly important for
there is nothing more annoying than
April 1994 87
This photo shows the broadcast band coil (the large coil at bottom left) plus the
three smaller shortwave coils that are switched into the aerial circuit.
The three shortwave bands (19, 25 and 31 metres) are marked at the bottom
of the dial. Note the clear frequency markings in MHz for each of these three
shortwave bands.
to move a previously aligned coil slug
by mistake.
These pairs of shortwave coils are
adjusted in much the same way as
those for the broadcast band. During
the alignment procedure, one coil from
a group of three is switched alternately
into the oscillator circuit and its slug
adjusted to give the correct frequency
on the dial. The other three coils are
switched into the aerial circuit and
are adjusted for maximum output.
There are no trimmers with this type
of set up.
In a bandspread receiver, such as
the Astor, three of the more common
shortwave bands were usually cho88 Silicon Chip
sen. They are the 19, 25 and 31-metre
bands. (Note: in a bandspread receiver
of this type, a large fixed capacitor is
connected in series with the tuning
capacitor to restrict its tuning range.
This is designed to make it easier to
select stations without requiring a
large step-down ratio in the tuning
capacitor drive).
19-metre band
Alignment of the 19-metre band
was first. As the dial is also marked
in MHz, a frequency of 15.4MHz was
chosen because it is towards the high
frequency end of the dial. The RF
generator was set to this frequency
and its output injected into the aerial
and earth terminals.
Selecting a frequency of exactly
15.4MHz on an RF generator is a difficult task without some assistance. The
assistance in this instance was provided by a modern multiband receiver
with digital tuning. All one has to do
is tune to the required frequency on the
synthesised receiver and place it near
the RF generator. The RF generator is
then adjusted until a squeal is heard
in the receiver.
By using this technique, almost any
obscure frequency can be dialled up
on the synthesised receiver and the
RF generator adjusted to suit. Receiver alignment on the shortwave bands
can be a hit and miss (mostly miss)
affair unless the generator frequency
is accurately set.
All three shortwave bands required
similar treatment; ie, adjustment of the
oscillator coil slug to bring the frequency in line with the dial graduation,
followed by aerial coil adjustment for
maximum output.
Everything went fairly smoothly
in the shortwave depart
ment, with
no tight slugs to give trouble. The
slug positions were held in place by
re-melting the wax that was originally applied to them for that purpose.
Just re-melting the wax with a warm
soldering iron was enough to shift the
frequency a little and some readjustment was required on one band. It
doesn’t take much to alter the settings
on shortwave adjustments!
If the receiver had been a 6-valve
model with a stage of RF amplification, then there would have been
additional coils requiring adjustment
in the RF section. These would need
to be adjusted for maximum output
after the oscillator and aerial coils had
been reset.
Testing
Testing the receiver was a bit of an
anticlimax. It was midday in January
and there was almost nothing to be
heard on any of the three shortwave
bands. It gave the impression that the
shortwave bands had been completely
detuned.
Fortunately, after-dark reception
was a completely different story and
all three bands responded well to all
corners of the globe. The Astor’s owner
was very pleased.
All things considered, the realignment of the old Astor was a relatively
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An RF generator is indispensable when aligning a shortwave receiver like the
old Astor. The other essential item (not shown here) is an output meter.
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Radio and Electrical Books
Almost any desired frequency can be set accurately on the RF generator with
the aid of this Sangean ATS-803A synthesised receiver. The receiver dial reads
15.4MHz – a convenient alignment point on the 19-metre band. It would be
impossible to accurately set the RF generator to this frequency without the assis
tance of the digital receiver.
straightforward process. On the other
hand, to attempt such a task without
the aid of the RF generator and output
meter would result in far from optimum results.
Alignment fiddles
Many of the valve receivers that we
collect today are getting quite long in
the tooth, this particular Astor being
well over 40 years old. It is unreasonable to expect that someone at some
time in the past hasn’t had a fiddle
with the alignment adjustments. If
they used the right equipment and
knew what they were doing, OK. But
that may not have been the case.
I know from my own early alignment attempts that I’m guilty of mis
aligning many a good receiver. I’m sure
I’m not the only one to do so.
Correct receiver alignment is an absolute necessity if the full potential of
any radio is to be attained. A restoration
is incomplete without a comprehensive
SC
tune-up to finish it off.
1914 Catalog Electro Importing Co ............$18
1936 Radio Data Book ...............................$15
Hammarlund Short Wave Manual (1937)....$11
Henley’s 222 Radio Circuit Designs ......$26.50
Neon Signs (1935) ................................$28.50
How to Become a Radio Amateur (1930) .....$7
How to Build & Operate Short Wave
Receivers ...................................................$18
How to Build a Solar Cell ...........................$11
High Frequency Apparatus (1916) .............$29
Radio for Beginners ................................$6.50
Radio for the Millions .................................$20
Short Wave Radio Manual (1934) ..............$30
Television (1938) .........................................$7
Tesla Coil ....................................................$11
Tesla Coil Secrets .......................................$16
Tesla Said ...................................................$79
Construction of Large Induction Coils ........$23
The Wimshurst Machine How to Make .$19.50
The Wireless Man ......................................$27
Wireless Experimenter’s Manual 1920 .......$31
Electrical Goods & Radio Apparatus ..........$14
Electroplating (1911) ............................$17.75
Experimental Television How to Make ........$34
Meissner “How to Build” Instructions ........$22
How & Why of Radio Apparatus ...........$20.50
All prices include postage. Payment can be
made by cheque or money order made out
to Plough Book Sales, PO Box 14, Belmont,
Vic. 3216. Phone (052) 66 1262.
April 1994 89
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.
Time signal
generator wanted
My brother-in-law is the president of
a community radio station in country
NSW and has asked me to design a
time signal generator. The station often
runs out of volunteer announcers and
they just leave a multi-disc CD player
running. With the pips going to air the
listeners would at least have an idea
of the time.
Building something is no problem
for me but designing it is. I understand
time signals in days gone by were
synced to a PMG pulse generator and
they had to be accurate for ships at sea
and aircraft navigation. I don’t think
aircraft or ships would be interested
in any of the programs broadcast
from this low-power community FM
station.
The only ideas I can come up with
are three 555 timers, one counting
down 59 minutes, then triggering
another to count down 55 seconds
and the third to count down the five
seconds with six half second audio
tone bursts, or pips. But how? Please
help. (R. P., Toowong, Qld).
• Your idea of using 555 timers
Measuring soil
conductivity
Being an electronics enthusiast
who has recently taken up hydroponic gardening, I was interested
to read in my gardening literature
that the nutrient strength (ie, the
amount of dissolved salts in the
water base) is measured by a unit
called the “Conductivity Factor”.
To quote my source: 1 CF unit =
0.1 EC units; or 0.1 millimhos; or
0.1 millisiemens.
This represents approximately
65 ppm.
How do these figures relate to
Ohms? Is it possible to measure
CF with an ordinary ohmmeter?
Could you please comment on this
90 Silicon Chip
would not be very accurate and they
would tend to drift as time went on.
You really need to sync the generator
with a source of accurate time signals
such as from Radio VNG. The resulting circuit is not likely to be simple,
however.
Perhaps one of our readers has faced
the same problem and has produced
an easy solution. If so, we’ll pass the
details on to you.
UHF antenna for
Tasmanian aggregation
I have constructed UHF antennas
from past issues of SILICON CHIP. Just
recently, I’ve learnt that aggregation
will occur in Tasmania in April and
May of this year. A lot of translators
will beam programs on UHF while
some such as the Southern Cross net
work will still be transmitting on VHF.
Where we live at Sheffield, we
will still receive Southern Cross on
VHF and the ABC on UHF, as well
as Tas-TV and SBS. This means that
a combined VHF/UHF antenna will
be required.
As a future project, you may be
keen to include an article on how to
and consider the possibility of publishing a CF meter circuit if such
an instrument would be economic?
Thank you for a fine magazine.
When will you be publishing the
second part of your video fader
unit? (C. G., Eden Hills, SA).
• We are not aware of what an E.C.
unit is although we assume that
it refers to “electrical conductivity”. The “Siemen” is the unit of
conductivity and supersedes the
“mho” which is the reciprocal of
the unit of resistance, the “ohm”.
One millisiemen is equivalent to
1000 ohms or 1kΩ. By the same
token, 0.1 millisiemens (0.1mS) is
equivalent to 10kΩ. Yes, you can
use your ohmmeter or multimeter
to measure these quantities.
build a good long-range combined
VHF/UHF antenna. I’m sure a lot
of keen readers would welcome the
challenge to build one as the prices
they’re asking are very high. (R. P.,
Sheffield, Tas).
• We’re not keen on the idea of building a combined VHF/UHF antenna as
the time we would need to spend on
design and evaluation could be prohibitive. We also wonder if it is really
necessary. Presumably, you already
have a VHF antenna which is quite
serviceable. Why can’t you keep on
using that together with a suitable UHF
antenna and a VHF/UHF combiner
which you probably also have?
We also have doubts whether a
combined VHF/UHF design would
perform as well as separate antennas.
We will be having another look at
a UHF design soon though, so stay
tuned.
Queries on fluorescent
lamp inverter
I am writing about the high efficiency inverter featured in the November
1993 issue of SILICON CHIP.
Being new to electronics and not
having precision fault finding equipment, or the knowledge yet to operate
them, I have to try to find other means
to have a basic idea on what’s happen
ing in a circuit.
Looking at the circuit diagram, I
wondered about the resistors in series
and realised that this was to distribute
heat loss more evenly. Then, after reading some of the text, I came across the
two 150kΩ load resistors coming from
the 680pF capacitor and it occurred to
me that if a faulty connection or tube
was pres
ent, these resistors would
take the load.
If so, could an indication lamp be
combined with them or incorporated
with similar resistances to allow you
to monitor when the load has altered?
And could an adjustment within safe
limits be added to compensate for any
tolerances that exceed the requirements?
This would allow one to monitor on
what side of the circuit a fault might
occur, if one was able to do the same
within safe limits on the feedback
side. Is the feedback affected by low
battery voltage and could this cause
excessive switching in IC1? If so and
if this could be damaging, is there a
way to indicate when this happens or
to protect the circuit? (J. C., Cooma,
NSW).
• The two 150kΩ resistors connected
in-series are to allow equal heat dissipation in each. This is in preference to
a higher wattage 330kΩ single resistor
which is bulkier and more expensive.
If there is a faulty connection to the
tube, the circuit will revert to the
starting pulse configuration whereby
Q4 is driven with pulses from the Diac.
There is no easy way to add indication
that this is happening since a neon
lamp connected between the 340V
rail and the drain of Q4 via a suitable
resistor will glow with similar brightness whether the fluorescent tube is
lit or not.
The circuit does not specifically
shut down for low battery voltages.
However, the ultimate fall in the
+340V supply rail as the battery voltage drops below a critical level, whereby the feedback is no longer effective,
reduces the tube current and consequently reduces the current drawn
from the battery. Eventually, the tube
will extinguish due to loss of sufficient
voltage to fire it and the circuit will
revert to supplying starting pulses. In
this condition, the circuit cannot be
damaged by excess dissipation.
Preamps & speakers
for musicians
I am writing in response to the
letter by K. S. of Sellicks Beach in
the March 1994 issue, regarding
the guitar preamplifier and speaker.
By way of introduction, I am a professional musician, audio engineer
and electronics hobbyist, and I have
spent the last five years specifically
studying musical instrument amplifi
ers (both solid state and valve), so I
believe I am in a position to make a
few suggestions.
There are two problems with the
mixer/preamp from the point of view
of the average electric guitar. The
first is that the input impedance of
the circuit is too low at 10kΩ. This is
fine with active pickups, as the article
Artificial dawn
for exotic fish
Your November 1993 article
on a high efficiency inverter for
fluorescent tubes seems to be a
good starting point for a type of
lighting system needed by many
people interested in keeping or
breeding many kinds of animals
and particularly fish. Apparently,
fish dart around when the light is
switched on and a zoologist friend
of mine said he thought that this
sudden brightness frightened them
and possibly also shortened their
life cycle.
What is required is the ability
to create a dawn and possibly a
twilight cycle. This needs a flickerfree start at a low output; even 30%
would be sufficient in an aquarium
using two lamps as this is only 15%
of the total.
I believe that a commercial unit
with a 10-volt stepless control is
available (it goes from 1V to 10V
for 20% output to full output) but
it is expensive. If you could design the ballast, there would be a
whole range of control systems. A
simple multiple relay system using
two tubes would probably be the
cheapest way to go while the ideal
approach would be to use a D/A
converter in conjunction with your
Z80 computer in the August 1993
edition. (A. S., Moonah, Tasmania).
• Our inverter circuit for fluorescent tubes cannot be easily adapted
for dimming. The circuit as de-
states, but for passive instruments, or
failed actives (batteries do run down
at the most inconvenient moments,
usually half-way through a song), this
low impedance combined with the
induction of the pickup coil forms a
low-pass filter, which removes all of
the nice harmonics of the instrument.
The second problem is the tone
control stage. This is a fairly standard
3-way Baxandall type, more at home
with hifi and the processed sound of
keyboards than guitars. This type of
tone control works in frequency bands,
with areas of maximum control and
areas of minimum control.
It just so happens that the area of
scribed applies a filament preheat
current before the tube starts and
this is removed once the tube has
fired. To enable reliable dimming
of the fluorescent lamp, preheat
current must be maintained after
the tube has fired.
In fact, it would be much easier
to start the tube at full brightness
and then dim down. Starting the
tube reliably at a low brightness
and then increasing the illumination would be impossible with the
present circuit.
Should you wish to pursue the
idea, dimming ballasts are available from lighting suppliers which,
in conjunction with a conventional
light dimmer, can be made to dim
the tubes over a limited range. The
circuitry for this is supplied with
the dimming ballast.
As an alternative, you could
use a conventional incandescent
lamp which is designed to produce a daylight spectrum. These
are available from lighting stores
as Philips Daylight lamps. They
have blue glass to filter out red light
and a special filament which emits
light toward the blue end of the
spectrum. The incandescent lamp
can be dimmed using a standard
dimmer. A fluorescent tube could
then be lit later once the lamp is
fully alight to provide the normal
illumination.
Be careful if you want to control
the dimming using a D/A converter.
This circuitry must be fully isolated from the 240VAC mains.
minimum control between the mid
and high bands corresponds to the part
of the guitar’s frequency spectrum that
provides all of the “bite” (not a techni
cal term, but evocative enough). Since
the sound with keyboards is already
satisfactory and fiddling with components would change this, the simplest
solution would be to add a switchable
paramet
ric equaliser module, such
as the one available from Jaycar (Cat.
KE-4724).
As far as 4-way speakers (or quad
boxes as they’re known in the trade)
are concerned, the editors of SILICON
CHIP may not recommend them but
manufacturers like Marshall, Fender,
April 1994 91
Query on Twin 50
stereo amplifier
I am writing in reference to the
“Studio Twin 50 Stereo Amplifier”.
After carefully considering the
circuit, I wrote to one of the Australian kit retailers asking whether
individual parts would be available
for the unit. They responded with a
catalog and a recommendation that
purchasing the entire unit would
be cheaper.
Preferring to construct, in “doit-yourself” fashion, at least the
preamplifier portion of that design, I cannot fathom what kind
of taper the balance control (VR5)
is. The article specifies an “M/N”
taper. Neither local retailers nor
technicians at Clarostat Controls
(a manufacturer or potentiometers)
could help me.
Can you help me identify what
kind of control is intended for
the balance section? Is it a custom-made unit available only with
the kit, or is there a retailer, either
in Australia or (better) the USA
who carries a dual-gang 10kΩ M/N
control? Another part that I cannot
locate, and that even the Philips
USA parts centre cannot identify
Laney, Wasp, Trace Elliot, Hi-Watt and
Peavey (to name but seven) certainly
do. There would be damping problems as mentioned if the boxes were
designed for full range operation, but
they are designed in such a way as to
present a high mechanical impedance
to frequencies below 84Hz (bottom “E”
on a guitar; since this is the lowest
note, why cater for anything lower?).
Thus, most quad boxes are sealed
and have a lower volume than you
would expect for the same speakers in
a hifi box. It is worth noting that the
Marshall model 1969 quad, using 16Ω
speakers, is switchable between series/
parallel (16Ω) or pure parallel (4Ω).
There is no reason for not using the
10-inch speakers from Jaycar, although
the maximum power handling would
be only 130 watts at 8Ω single input, or
130 watts at 4Ω dual input. Dual input
is possible for quad boxes and is an option on the aforementioned Marshall
1969. I hope that my observations will
92 Silicon Chip
by the given part number, is L2
(an inductor at the phono input).
In the parts list, it is identified as a
“ferrite wideband choke”, Philips
Ω4312-020-36760. Help? (M .F.,
Staten Island, NY, USA).
• The M/N taper dual gang pot is a
standard type used in balance controls in many Japanese amplifiers.
As depicted on the circuit, each
resistance element is short-circuit over half the wiper travel so
that the gain in one channel does
not increase once the wiper has
reached the mid-point, while the
other channel is reduced in gain
as the wiper moves past mid-point.
While it may not be of much
help, Japanese manufacturers
such as Alps make this pot as a
standard item. Alternatively, you
may be able to buy the M/N as a
replacement item for an amplifier
brand such as Sony, Panasonic, etc.
Failing that, you could substitute a
standard log/antilog dual gang pot.
The Philips inductor is a standard part number taken from their
Soft Ferrites catalog. However, it
is not a critical part and you could
substitute a small ferrite bead with
a few turns of enamelled copper
wire wound through it.
be of some help to K. S. and to anyone
else experiencing similar troubles. (T.
N., Balmain, NSW).
Building a TV signal
strength meter
By utilising a secondhand tuner
from a VCR, could not an acceptable
signal strength meter for siting TV
aerials (in bad signal areas) be made?
Commercial units are expensive. (B.
P., Port Macquarie, NSW).
• It would be possible to use a defunct
VCR’s tuner as the basis of a signal
strength meter but TV antenna installers who do not have a signal strength
meter have a far more practical ap
proach – they use a small portable TV
set. This gives a good idea of signal
strength and also gives an indication
of ghosts.
That said, we will have a look at the
possibility of doing a signal strength
meter as a project.
Pointless ignition
wanted
I am interested in building and experimenting with a pointless ignition
system for my lawn mower. Has your
magazine the circuitry of these modules and if so, in what issue? (A. C.,
Benowa, Qld).
• Unfortunately, we have no circuits
for ignition systems for mowers. We
understand that they are capacitor
discharge systems with the capacitor
charged by magneto. Similar systems
are used on motorbikes and modules
can be quite expensive to replace. Does
any reader have more information?
Debouncing needed
for counter input
I am a year 11 student at Benedict
Senior College at Auburn and am
studying a 1-unit electronics course.
As a final project, I decided to build
a 3-digit counter module, which is
featured in your June 1990 magazine.
However, when the button is pressed
it advances three, four or even 10
numbers at a time.
I understand that the problem is
called debounce. I tried placing a
0.1µF greencap capacitor across the
terminals of the pushbutton switch but
there was no change; nor did larger capacitor values help. I also tried building a debounce circuit from a book.
However, after much experimentation
with all of these ideas, I have made
no headway. Please help me. All I am
after is a simple circuit diagram or any
type of information that will solve this
problem. (G. F., Auburn, NSW).
• You will need to buy a 74C14 hex
Schmitt trigger IC and build the circuit
below – see Fig.1. The original project
was designed to go with existing circuitry, not a pushbutton arrangement,
+VCC
100k
13
0.1
74C14
14
12
7
TO
COUNTER
Fig.1: this simple debounce
circuit will advance the count
of the 3-Digit Counter Module
by one each time the button is
pressed.
but this circuit will do the job. Make
sure you connect pins 14 and 7 of the
74C14 to the supply lines of the 3-digit
counter project.
Speed control for
a golf buggy
Notes & errata
Stereo Preamplifier with IR Remote
Control; September, October and
November 1993: on some units, the
bass control is liable to become noisy
and produce a scratchy sound from
the loudspeakers when it is rotated.
This problem is caused by a small DC
voltage which appears across the bass
control pot. This voltage is developed
by the input bias current to pin 2 of
IC6 and IC106.
To prevent this problem, we recommend replacing IC6 and IC106 with
OP27GP or LM627 op amps. These
have signifi
cantly lower input bias
currents than the NE5534 op amps
specified originally.
Note that the 10pF capacitors between pins 5 and 8 for both IC6 and
IC106 should be removed from the PC
board since the replacement op amps
are internally compensated.
Finally, some early kits from Jaycar
may have problems with the remote
control not operating. The problem is
due to a short between ceramic resonator X2 (on the main PC board) and
ground, which prevents the oscillator
inside IC23 from functioning.
To cure the problem, go to the 4.7kΩ
resistor side of the X2 pad and cut the
copper between this pad and the adjacent ground track with a sharp utility
knife. The problem has been corrected
SC
on later kits.
SILICON CHIP FLOPPY INDEX
WITH FILE VIEWER
Now available: the complete index
to all SILICON CHIP articles since the
first issue in November 1987. Now
you can search through all the articles
ever published for the one you want.
Whether it is a feature article, a project,
a circuit notebook item, or a major
product review, it doesn’t matter; they
are all there for you to browse through.
The index comes as an ASCII file on a
3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers and you
can use a word processor or our special file viewer to search for keywords.
Now with handy file viewer: the Silicon Chip Floppy Index now comes with
a file viewer which makes searching for that article or project so much easier.
You can look at the index line by line or page by page for quick browsing,
or you can make use of the search function.
Simply enter in a keyword(s) and the index will quickly find all the relevant
entries. All commands are listed on the screen, so you’ll always know what
to do next. Note: requires CGA, EGA or VGA graphics card, IBM-compatible
PC, MSDOS 3.3 and above.
Disc size: ❏ 3.5-inch disc ❏ 5.25-inch disc
❏
❏
❏
❏
❏
❏
❏
Floppy Index (incl. file viewer): $A7 + p&p
Notes & Errata (incl. file viewer): $A7 + p&p
Bytefree.bas /obj / exe (Computer Bits, May 1994): $A7 + p&p
Alphanumeric LCD Demo Board Software (May 1993): $A7 + p&p
Stepper Motor Controller Software (January 1994): $A7 + p&p
Printer Status Indicator Software (January 1994): $A7 + p&p
Switchers Made Simple – Design Software (March 1994): $A12 + p&p
Note: Aust, NZ & PNG please add $A3 (elsewhere $A5) for p&p with your order
Enclosed is my cheque/money order for $__________ or please debit my
❏ Bankcard ❏ Visa Card ❏ Master Card
Card No.
Signature_________________________ Card expiry date______/______
Name _____________________________________________________
PLEASE PRINT
Street _____________________________________________________
Suburb/town __________________________ Postcode______________
Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or
fax your order to (02) 979 6503; or ring (02) 979 5644 and quote your credit
card number (Bankcard, Visacard or Mastercard).
✂
I have a golf buggy which is driven
by two 12V electric DC motors marked
SWN 402-400V 12V/23, with one motor on each wheel. What I require is a
circuit to control these motors. (G. R.,
Tura Beach, NSW).
• The most practical approach would
probably be to use the DC speed control published in our November &
December 1992 issues. Unfortunately,
we do not have any back copies of
these issues but we can send you a
photostat copy of the articles for $6
each including postage. You can also
purchase a kit for the controller from
Silvertone Electronics – phone (02)
533 3517.
April 1994 93
MARKET CENTRE
Cash in your surplus gear. Advertise it here in Silicon Chip.
ANTIQUE RADIO
CLASSIFIED ADVERTISING RATES
Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50
cents for each additional word. Display ads (casual rate): $20 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale.
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.
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
ANTIQUE RADIO RESTORATIONS:
specialist restoration service provided for
vintage radios, test equipment & sales.
Service includes chassis rewiring, recon
densering, valve testing & mechanical
refurbishment. Rejuvenation of wooden,
bakelite & metal cabinets. Plenty of parts
– require details for mail order. About
1200 radios within 16,000 square feet.
Two-year warranty on full restoration.
Open on Saturday 10am-4.30pm; Sunday
12.30-4.30pm. 109 Cann St, Bass Hill,
NSW 2197. Phone (02) 645 3173 BH or
(02) 726 1613 AH.
FOR SALE
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
THE HOMEBUILT DYNAMO: (plans)
brushless, 1000 DC watt at 740 revs. $A85
postpaid airmail from Al Forbes, PO Box
3919 - SC, Auckland, NZ. Phone Auckland
(09) 818 8967 any time. Rotor magnets
(3700 gauss) kit now available.
WEATHER FAX programs for IBM XT/ATs
*** “RADFAX2” $35 is a high resolution,
shortwave weather fax, Morse & RTTY
receiving program. Suitable for CGA,
EGA, VGA and Hercules cards (state
which). Needs SSB HF radio & Radfax
decoder. *** “SATFAX” $45 is a NOAA,
Meteor & GMS weather satellite picture
receiving program. Needs EGA or VGA
plus “WEATHER FAX” PC card. *** “MAXISAT” $75 is similar to SATFAX but needs
2Mb expanded memory (EMS 3.6 or 4.0)
Enclosed is my cheque/money order for $__________ or please debit my
❏ Bankcard ❏ Visa Card ❏ Master Card
✂
Card No.
RCS RADIO PTY LTD
Signature__________________________ Card expiry date______/______
Name ______________________________________________________
Street ______________________________________________________
Suburb/town ___________________________ Postcode______________
94 Silicon Chip
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
and 1024 x 768 SVGA card. All programs
are on 5.25-inch or 3.5-inch disks (state
which) & include documentation. Add
$3 postage. Only from M. Delahunty, 42
Villiers St, New Farm, Qld 4005. Phone
(07) 358 2785.
MJ802 $6.00, B/rect CM3504 35A400V
$3.00, WO4 $0.50, 1N5404 $0.12,
SCR/C106DI (equiv.) $0.75, LM324CN
$0.55, CD4001 $0.45, CD4071 $0.35,
BC547/548 $0.07, BC547C/558C
$0.08, BC327/337 $0.10, 5mm LEDs
RED/GRN/YEL $0.15. Capacitors:
1000µF 35V RB $0.60, 1000µF 25V
RB $0.50, 0.1µF 250V AC $0.35. 2-way
PCB-mounting screw term blocks
$0.40. Payment cheque, money order,
Bankcard. Minimum order $10.00. Add
$4.00 for postage. Fax: (049) 42 2984.
LE Agencies, PO Box 770, Charlestown,
NSW 2290.
ROMLoader EPROM EMULATOR (EA
Jan/Feb 92) - upgrade to handle 27128,
27256 EPROMs. Includes memory edit
facility. 8051 Proto-Boards (EA Feb 93)
also available. Send SAE for details.
Tantau Australia, PO Box 1232, Lane
Cove 2066. AH (02) 878 4715.
PRINTED CIRCUIT BOARDS for the
hobbyist. For service & enquiries contact:
T. A. Mowles (08) 326 5590.
SUBSTITUTE FOR A HANDFUL OF
ICs: Parallax “BASIC STAMP”. A general
purpose small circuit module, it is really
a 25 x 50mm board with a computer chip
(4MHz PIC 16C56), EEPROM, 8 I/O pins,
board space includes prototyping area.
Program it on a PC (only 33 instructions)
with development kit which includes one
“BASIC STAMP” ($249 plus S/T & post),
extra modules ($66 plus S/T & post).
Send 45c stamp for more information.
Parallax distributor and technical support
in Australia: MicroZed Computers, PO
Box 634, Armidale, NSW 2350. Facsimile
(067) 72 8987.
MICASOFT Electronics and Computing
tutor program, written in UK, ideal for
TAFE, schools, or individual use. Now
available in Australia. Send $1.80 in
stamps for demo disk (tell us what size).
MicroZed Computers, PO Box 634, Armidale 2350.
UNUSUAL BOOKS: Electronic Devices,
Fireworks, Locksmithing, Radar Invisibility,
Surveillance, Self-Protection, Unusual
Chemistry and more. For a complete cat-
Silicon Supply and Manufacturing
4002B
4010B
4011B
4012B
4013B
4014B
40150
4017B
4019B
4023B
4025B
4027B
4040B
4048B
4050B
4053B
4060B
4069B
4070B
4071B
4075B
4082B
4094B
.86
.70
.86
.77
.82
1.53
1.55
1.88
.82
.67
.67
.67
2.13
1.15
.77
1.39
1.71
.69
.69
.69
.69
.69
1.31
74LS11
74LS12
74LS13
74LS14
74LS20
74LS21
74LS27
74LS30
74LS33
74LS49
74LS73
74LS74
74LS83
74LS85
74LS90
74LS92
74LS109
74LS126
74LS138
74LS139
74LS147
74LS148
74LS151
.60
.60
1.00
.65
.65
.50
.50
.50
.60
2.85
1.35
.55
.90
.75
1.10
1.45
1.10
.60
.75
.75
2.85
1.25
.60
74LS155
74LS158
74LS160
74LS164
74LS175
74LS191
74LS193
74LS196
74LS240
74LS241
74LS245
74LS257
74LS273
74LS366
74LS368
74LS373
74LS374
74LS393
74HC11
74HC27
74HC30
74HC76
74HC86
.60
.85
.90
.90
1.00
1.00
1.00
1.65
1.10
1.15
1.00
.75
1.00
.65
.75
1.00
1.05
1.05
.55
.50
.50
.65
.55
All prices include sales tax.
Phone (02) 554 3114; Fax (02) 554 9374. After
hours only bulletin board on (02) 554 3114
(Ringback). Let the modem ring twice, hangup, redial the BBS number, modem answers on
second call.
PO Box 92, Bexley North, NSW 2207.
TRANSFORMER REWINDS
ALL TYPES OF TRANSFORMER REWINDS
TRANSFORMER REWINDS
Reply Paid No.2, PO Box 438,
Singleton, NSW 2330.
Ph: (065) 76 1291. Fax: (065) 76 1003.
SECONTRONICS
COMPONENTS, COMPUTERS, ELECTRON TUBES
S/H TEST EQUIPMENT, COMPUTER REPAIRS
PC COMPATIBLE KEYBOARDS 101 AT:$39
I/O + IDE/FDD
$35
RECYCLED EPROMS
AT I/O CARDS
$22
2716
$1.50
2SD1169
$2.00
2732
$1.50
2N3440
$0.80
2764
$2.00
2N3439
$0.80
27128
$3.00
2SC3157
$4.00
27256
$3.50
27C41
$0.80
27512
$3.50
7406
$0.20
27C101
$4.00
8250 $5 8251 $2
8259 $2 6809 $8
MC8050 $2
MCT275 $1.20
MOC3032 $2
VALVES:
QQV07/50 $25
3D21 $8
12AU7 $6
6SG7 $8
6U8A $8
1S2 $3
1T4 $6
CV553 $3
2C39A $30
2C40A
$40
3A4 $8
5651 $6
5651A $6
6AK5 $6
6J6WA $7
6AM6 $5
6BA6 $4
SPECIAL: SURFACE MOUNT COMPONENT PACK – 180 RESISTORS, 40 ZENERS, 30 TRANSISTORS AND 2 ICs. $6.50 INC.
PACK & POST
PHONE OR MAIL ORDERS, CREDIT CARDS ACCEPTED FOR
ORDERS $20 & OVER, DISCOUNTS FOR QUANTITY ORDERS.
NOW AT SHOP 5, 79 RICKSTON ST, MANLEY WEST, QLD. 4179.
OPEN TUES - FRID 9.30AM - 5PM, SAT. 9AM - 2PM.
MAIL ORDERS TO PO BOX 34 CANNON HILL QLD. 4170.
PHONE (07) 396 1859, FAX (07) 855 1014.
MEMORY & DRIVES
PRICES AT MARCH 7TH, 1994
SIMM
1Mb x 3
1Mb x 9
4Mb x 9
4Mb (72-pin)
8Mb (72-pin)
16Mb (72-pin)
70ns
70ns
70ns
70ns
70ns
70ns
DRAM DIP
1 x 1Mb
256 x 4
70ns $8.50
70ns $8.50
IBM PS.2
50/55/70
70/35
90/95
2Mb
4Mb
4Mb
$150
$265
$265
MAC
4Mb 4Mb x 80 80ns
6Mb P’Book
$125
$420
$63
$72
$265
$265
$545
$985
CO-PROCESSORS
387SX to 25
387DX to 33
$105
$105
LASER PRINTER HP
with 4Mb
$260
TOSHIBA
T3200SX
T44/6400
T5200
4Mb
4Mb
2Mb
$360
$305
$160
SUN
SPARC 10/20 16Mb $1140
1Mb V2 BAT SRAM
$230
2Mb V2 BAT SRAM
$380
2Mb V2 FLSH SRAM $380
Sales tax 21%. Overnight delivery.
Credit cards welcome. 5-Year Warranty
Ring for Latest Prices
1st Floor, 100 Yarrara Rd, PO Box 382, Pennant Hills, 2120.
Tel: (02) 980 6988
Fax: (02) 980 6991
alog, send 95 cents in stamps to Vector
Press, Dept S, PO Box 434, Brighton,
SA 5048.
A WORD IS only worth a micro-picture. Need the full picture? Send $2 in
stamps, cash, or food parcels for Don’s
3.5-inch MS-DOS DEMO/PROMO disk.
Covers all of my hardware kit projects.
Don McKenzie, 29 Ellesmere Crescent,
Tullamarine 3043. Phone (03) 338 6286.
VALVE AMPLIFIERS: Australian made.
Mono, stereo, guitar using 2A3, 211, 6L6
or 807 valves. Williamson reproductions.
Parts available for DIY constructors.
Circuit diagrams and construction details for many types of valve amplifiers.
Valve equipment repairs. Lancroft Pty
PELHAM
Ltd, PO Box 439, Bexley 2207. Phone
(02) 567 5390.
SOSUTHERN CROSS SBC, accessories & EPROM emulator. See SC
8/93 & 12/93. Ideal for TAFE, schools
& individual use. Alpine Technologies,
tel/fax (03) 751 1989.
NETWORK YOUR PCs with “Little
Big LAN”. Share disk drives and files
(multi-user record locking), CD-ROMs
and printers (with spooling). Connect
PCs via serial or parallel ports, Arcnet
and/or Ethernet cards. Supports up to
250 computers per network for only
$95 ($100 for 3.5") for a whole network.
Add $3 for postage in Australia. Works
with MS-DOS, DR-DOS and Windows.
April 1994 95
Software & Parts
PC Voice Recorder V1.3 (SC 8/91)
PC Talking Voltmeter V1.2 (10/91)
Serious Guide to Building Kits V2.2
Transistor Specification Index V1.3
Op Amp Specification Index V1.3
$12
$17
$12
$15
$15
5.25 or 3.5" disc/PC CGA-VGA required
LM3876T 50W amplifier IC
$14
10 or more - 10% off
Send Cheque/Money order to:
Darren Yates, PO Box 134,
French's Forest, NSW 2086.
For more information, write to GRAN
TRONICS, PO Box 275, Wentworthville
2145. Phone A/H (02) 631 1236.
68705 DEVELOPMENT SYSTEM:
in-circuit simulator/emulator and pro
grammer board for $250. Supports
68HC705C8/C4/J2/K1, 68705P3/U3/
R3 micro controllers and more. Contact Robert Priestley, PO 38/4 Illawong
Village, Fowler Road, Illawong 2234.
Phone/Fax (02) 541 0734.
BINARY CLOCK - OCTOBER 1993:
complete documentation supplied,
includes introduction to binary, how it
works, PLD source listings, conversion
tables. Kit with PCB and all components
$75 + $5 p&p. Optional Z frame stand
(includes spacers and chassis DC connector) $25 + $5 p&p. Prototype Electronics, 1/29 Stewart St, Parramatta,
NSW 2124. Phone (02) 683 3510; Fax
(02) 630 3148. Pay by cheque, money
order, credit card.
FLUORESCENT INVERTER KIT (SC
Feb 91) 12V or 24V/5W-21W.48V
ver
sion on request. Secondary wind,
board plus components $30.00 plus
ICL 286 Board
Kits
All in one board with two serial,
printer, IBM keyboard, high
density floppy & IDE mono
video interface. Up to 4Mb
RAM, 80286-16cpu, MS-DOS
compatible, 130 page manual,
small size 170mm x 255mm.
Max I/O kit for PCs, 7 relays,
ADC, DAC, stepper driver, TTL
inputs, with software
$169
PC I/O card with 8255 chip 24
I/O lines programmable as inputs
or outputs
$69
1.5 watt AM broadcast transmitter XTAL locked
$49
2.5 watt FM broadcast transmitter 88-108MHz.
$49
Digi-125 audio power amp
(over 19,000 sold since 1987)
50 watt/8 $14 125 watt/4 $19
New 200 watt/2 version $29
Infrared relay kit
$9
Remote control tester
$4
$299
Ampo little PC
All in one NEC V40 CPU board,
MS-DOS compatible, high density floppy. SCSI hard disk, 2
serial, printer, solid state hard
disk, IBM keyboard interface,
(4W), CMOS single +5V rail,
up to 768Kb RAM, 384Kb
ROM, 145mm x 250mm, 98page manual.
$299
P.C. Computers
36 Regent St, Kensington,
SA. Phone (08) 332 6513.
Altronics ................................ 26-28
Antique Radio Restorations.........94
A-One Electronics........................59
Av-Comm.....................................33
Ctoan Electronics........................96
David Reid Electronics ..............57
Dick Smith Electronics........... 12-15
Electronic Fault Info.....................83
Harbuch Electronics....................57
Instant PCBs................................95
CTOAN ELECTRONICS
Low voltage lighting systems designed
for your garden. Lights that dim up as the
sun goes down create a great showpiece.
Call us for your controlled garden lighting
system. PO Box 211, Jimboomba 4280.
Phone (07) 297 5421.
Jaycar ................................... 45-52
JV Tuners.....................................41
L & M Video.................................69
Macservice....................................9
Nilsen Instruments.....................IFC
P&P $4.00. Fluorescent inverter kit (SC
Nov 93) 12V/24V/48V, 18W and 38W
P.O.A. Solar battery charging regulator
short form kit 12V or 24V (series) (SC
Jan 94) employs Mosfet to switch solar
array max current 10A $54.00 plus
p&p $4.00. Additional Mosfet $8.00
and Schottky diode $5.00 to make 20A
regulator. Cheques and postal money
orders accepted with mail orders. Send
orders to Otakar Priboj, PO Box 362,
Villawood, NSW 2163, Australia. Phone
(02) 724 3801.
KIT REPAIRS
KIT REPAIRS and assembly. All work
guaranteed. Phone (047) 51 5620.
SILICON CHIP FLOPPY INDEX
WITH FILE VIEWER
Now available: the complete index to all SILICON CHIP articles
since the first issue in November 1987. Now you can search
through all the articles ever published for the one you want. The index comes
as an ASCII file on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible
computers and you can use any word processor or our special file viewer to
search for keywords.
Now with handy file viewer: the file viewer makes searching for that article or
project so much easier. You can look at the index line by line or page by page
for quick browsing, or you can make use of the search function.Simply enter in a
keyword(s) and the index will quickly find all the relevant entries. All commands
are listed on the screen, so you’ll always know what to do next. Note: requires
CGA, EGA or VGA graphics card, IBM-compatible PC, MSDOS 3.3 and above.
Price $7.00 + $3 p&p. Silicon Chip Publications, PO Box 139, Collaroy 2097.
96 Silicon Chip
Advertising Index
Oatley Electronics...................39,73
PC Computers.............................96
Pelham........................................95
Plough Book Sales......................89
RCS Radio ..................................94
Resurrection Radio......................89
Rod Irving Electronics .......... 75-79
Secontronics................................95
Silicon Chip Back Issues....... 84-85
Silicon Chip Binders..................IBC
Silicon Chip Software..................93
Silicon Supply & Manufact...........95
Transformer Rewinds...................95
Yuga Enterprise...........................81
_________________________________
PC Boards
Printed circuit boards for SILICON
CHIP projects are made by:
• 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.
• H. T. Electronics, 35 Valley View
Crescent, Hackham West, SA 5163.
Phone (08) 326 5590.
Especially For
Model Railway
Enthusiasts
Order Direct
From
SILICON CHIP
Order today by phoning (02) 9979 5644 & quoting your credit card number;
or fill in the form below & fax it to (02) 9979 6503; or mail the form to
Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097.
This book has 14 model railway
projects for you to build, including
pulse power throttle controllers,
a level crossing detector with
matching lights & sound effects,
& diesel sound & steam sound
simulators. If you are a model
railway enthusiast, then this
collection of projects from SILICON
CHIP is a must.
Price: $7.95
plus $3 p&p
Yes! Please send me _______ copies of 14 Model Railway Projects
Enclosed is my cheque/money order for $_________ or please debit my
Bankcard Visa Card Master Card
Card No.
Signature_________________________ Card expiry date_____/_____
Name _________________________Phone No (____)_____________
PLEASE PRINT
Street ___________________________________________________
Suburb/town __________________________ Postcode____________
|