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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which is now out of date and the advertiser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.8; August 1994
FEATURES
FEATURES
NEED A DIMMER for a large
domestic or stage application?
This unit can dim incandescent
or halogen lamp loads of up to
2400W or can be used for fan
speed control. Details page 24.
4 Review: Philips Widescreen Colour TV Set by Leo Simpson
Advanced set has picture-in-picture & Dolby sound
14 Electronic Engine Management, Pt.11 by Julian Edgar
Fuel & air systems
80 Review: Philips P65 UHF CB Set by Marque Crozman
Has user programmable scanning & up to 5W power output
PROJECTS
PROJECTS TO
TO BUILD
BUILD
24 High-Power Dimmer For Incandescent Lights by Marque Crozman
Can dim lamp loads of up to 2400 watts
37 A Microprocessor Controlled Morse Keyer by Alexandre Zatsepin
Lets you store & playback Morse messages
THIS MICROPROCESSOR
controlled Morse Keyer will
really polish up your sending. It
even has a memory that lets you
record & replay a Morse message
up to 64 characters long. Turn to
page 37.
40 Dual Diversity Tuner For FM Microphones by John Clarke
It automatically selects the best signal from two antennas
52 A Simple Go/No-Go Crystal Checker by Darren Yates
Build it for just a few dollars
68 Build A Nicad Zapper by Darren Yates
Zap the dendrites & give your cells a new lease of life
SPECIAL
SPECIAL COLUMNS
COLUMNS
56 Serviceman’s Log by the TV Serviceman
OLD NICAD BATTERIES can
often be given a new lease of
life by blasting away internal
dendritic growths. And for that,
you need this Nicad Zapper – see
page 68.
Time to talk about timers
65 Remote Control by Bob Young
Modellers with dedication
84 Vintage Radio by John Hill
Watch out for incorrect valve substitutions
DEPARTMENTS
DEPARTMENTS
2
23
50
79
80
Publisher’s Letter
Mailbag
Circuit Notebook
Order Form
Product Showcase
88
90
93
94
96
Back Issues
Ask Silicon Chip
Bookshop
Market Centre
Advertising Index
THIS DUAL DIVERSITY TUNER
automatically selects the best
signal from two antennas to
ensure a noise-free reception
from FM wireless microphones.
Deatails page 40.
Cover concept: Marque Crozman
August 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
Advertising Enquiries
Leo Simpson
Phone (02) 979 5644
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
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Printing: Macquarie Print, Dubbo,
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in Australia. For overseas rates, see
the subscription page in this issue.
Editorial & advertising offices:
Unit 34, 1-3 Jubilee Avenue, Warrie
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PO Box 139, Collaroy Beach, NSW
2097. Phone (02) 979 5644. Fax
(02) 979 6503.
PUBLISHER'S LETTER
Trivialising science
& technology will not
help to promote it
These days, the products of science and
technology surround us and we enjoy the
benefits to the full. Paradoxically though,
science and technology appear to be becoming less popular in schools and universities. Students appear to be taking the
softer options of humanities-based courses
rather than the more rigorous courses required for science and engineering.
This is a serious problem and one which is occurring in most western
economies. The lack of interest in science and technology can be attributed
to a number of factors. For a start, there is a disenchantment with science
and technology since it is now recognised that it does not have the cures
and solutions for all the world’s problems. Second, with the loss of much
traditional manufacturing to the oriental and developing countries, it is
perceived that there are less job opportunities for engineers and technicians.
That second point is arguable but it is a perception nonetheless.
While this problem is serious, it does not have an easy solution. Certainly,
it will not be helped by the efforts of some organisations to popularise science
and technology. I am thinking particularly of museums and the makers of
science programs for television. When you visit museums these days, the
emphasis seems to be on “hands-on” or interactive displays. Hence, museums have a tendency to become vast video games parlours where all sorts
of science is supposed to be illustrated but not much is learnt. Now I agree
that museums with working exhibits are more interesting than those where
all displays are static but this all out effort to make everything interactive
is counterproductive.
But if museums are on the wrong tack, some science program makers are
completely off course as they have a strong tendency to trivialise their material. Prime examples of this are “Beyond 2000”, which has degenerated into
little more than a showcase of fairly boring products from overseas, and the
current ABC program “Hot Chips”. I suppose the name says it all – it is the
“fast food” approach to science and technology. The ABC program “Quan
tum” is far better and its presenter Karina Kelly at least gives the impression
that she is interested and committed to the featured topics.
Let’s face it, there is no easy way to promote science and technology. The
sooner museums and other would-be promoters realise that, the better. Most
people are interested and eager to take advantage of the latest developments
in science and technology. It is sad to see that interest dissipated by halfbaked efforts to capitalise upon it.
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
Consumer Product Review
By LEO SIMPSON
Philips’ revolutionary
wide-screen TV receiver
Recently, Philips
released their
newest wide format
TV receiver onto
the Australian
market. Called
the Matchline
76cm, it has every
conceivable feature
that could be
crammed into a TV
receiver, including
Dolby Surround
Sound, Picture-inPicture, Teletext and
100Hz digital flicker
reduction. We
borrowed a sample
unit & watched it
long & hard to bring
you this report.
4 Silicon Chip
T
HIS IS NOT THE FIRST WIDE-SCREEN TV receiver from Philips,
as they released their first model in Australia about two years
ago. However, this 76cm Matchline is a completely new model
with many more features and a lower price. So why would you want a
TV set in the new 16:9 format? Given that there is not much program
material at present, Philips has worked hard to make the new set as
enticing as possible.
If you have a laser disc player with movies recorded in the wide screen
16:9 format you will immediately appreciate the benefits of the new
Philips receiver. The wide screen has a more dramatic presentation so
that when you come to view a conventional TV set with its 4:3 screen
it seems to lose a great deal of visual impact.
Before we go much further, we should explain these formats of 4:3 and
16:9 for the benefit of readers not familiar with these terms. Conventional
TV sets have a screen which is four units wide and three units high. For
a 63cm set (diagonal measurement), the screen will be nominally 50cm
wide and 38cm high. Movies on the other hand, and the new HDTV
standard, call for a 16:9 screen format and so the screen is 1.77 times as
wide as it is high – much wider than a normal TV.
When movies are broadcast by TV stations they have several options.
They can aim a conventional camera at the movie screen and thereby
clip off the edges of the screen; they can pan the camera to take in the
action on the screen or they can broadcast in “letter box” format which
results in a black strip at the top and bottom of the screen. This latter
option is used quite often these days on SBS television and also by
commercial TV networks when they are rolling the credits at the start
of movies. Whichever way they do it though, the result is hardly what
the movie producer intended.
In producing this widescreen set, Philips give the viewer the option
of watching normal programs in wide-screen format – the “superwide”
mode. This means that you do not have to watch 4:3 programs with a
black band down each side of the screen – you can expand the picture to
fill the screen and in doing so, you lose very little at the top and bottom.
Contrary to what you might expect, this does not lead to grossly
distorted pictures with balloon faced people, extra long cars and so on.
Philips has been much more clever than that. But before we explain
what they have done, let’s talk about the general details of the new set.
The new set is big and heavy but not overly so. It is 836mm wide,
591mm high, 593mm deep and weighs close to 55kg. The main component of the weight and the reason for the considerable depth of the set is
the tube. Glass is heavy and the tube needs to be quite deep to provide
for such a wide deflection.
All of the cabinet is plastic with a dark matt finish, very much in the
style of today’s TV sets which are quite subdued in appearance. Also
as with most of today’s sets, the new Philips Matchline is designed to
be controlled exclusively by the infrared remote handpiece; very few
Philips’ new 76cm Matchline TV receiver has a 16:9 format picture tube &
this gives a much more dramatic presentation than a conventional TV set.
Particular features are the 100Hz flicker reduction circuitry & the scan velocity
modulation system to enhance picture highlights.
functions can be controlled from the
set itself. Those that can are in an array
of buttons down the lefthand side of
the set and are as follows: Power On
(standby), Video (select), Install, Volume (up/down) and Channel (select).
These are grouped with RCA sockets
for video and stereo audio inputs and
an S-video socket. In practice, apart
from the Install button which would
only be used at the time of installation,
these buttons would never be used
unless the remote control handpiece
was temporarily out of order due to
flat batteries.
In fact, the only control on the set
which is likely to be used on a regular
basis is the main power switch which
is on the lefthand side of the cabinet.
Philips recommend that it be used to
turn the set off at night, thus avoiding
any standby power drain, and also
because when the set is turned back
on again, the picture tube will auto-
matically be degaussed, to maintain
good picture quality.
As you might expect, the remote
control handpiece has a myriad of
buttons and these can be quite confusing and hard to follow for those
who are not technically inclined.
With that in mind, some genius at
Philips has come up with the idea
of providing a second remote control
which provides just the basic func
tions. This is doubly handy when the
main remote control gets wedged in
behind the lounge cushions and one
is desperate to mute the sound, for
example.
Many features
Even in a very long and detailed
review it would not be possible to
cover all the technical and user features of the Philips set. After all, it
comes with two owner’s manuals, a
brief one and the comprehensive one.
Two infrared remote controls are
supplied with the receiver, one with
all the bells & whistles & the other
with just the basic functions. Both
have a very good operating range.
August 1994 5
This photo shows one of the many on-screen menus which are brought into
operation with the remote control. This one is for picture features & shows CTI
highlighted. CTI stands for colour transient improvement & this feature mainly
enhances the red details in the picture.
The comprehensive one has 78 pages
and it is only in English, not multiple
languages! Therefore we’ll just discuss the main features in broad detail.
Apart from the wide screen, the
Philips Matchline has a brace of features which are all linked together
technically: 100Hz flicker reduction,
picture in picture, digital noise reduc
tion, colour transient improvement
(CTI), multiple system compatibility
and still (freeze frame).
A big problem with television viewing in Australia (and other countries
which use 50Hz AC mains supply) is
picture flick
er. This becomes much
more noticeable in large screen sets
and even more noticeable in wide
screen sets because the peripheral
vision of the eye is so sensitive to flicker. Clearly, a wide screen set without
some sort of flicker reduction would
be unpleasant to watch.
This set and others on the market
combat the problem by scanning the
picture at 100Hz instead of 50Hz. That
one change requires an enormous
increase in set com
plexity because
it immediately means that a digital
field store is required. Just a few years
ago, digital field stores were only to
be found in TV studios and they cost
immense amounts of money.
In essence, the luminance and
chrominance signals are digitised by
an analog-to-digital converter (ADC).
Conversion takes place at a sampling
frequency of 16MHz which, by the
Nyquist criterion, limits the video
bandwidth to 8MHz. This is wider
than the 7MHz bandwidth required
in Australia but this is a world set,
capable of receiving TV broadcasts in
any of 27 different formats, covering
all the variations of PAL, NTSC and
SECAM. After sampling, the digitised
This series of on-screen photographs shows the images
produced from a crosshatch pattern. Above left is the
6 Silicon Chip
picture information is written to a
bank of video memory. It is then read
out twice, with a clock frequency two
times that used to store it.
The detail of this system is a great
deal more complex but suffice to say
that scanning the fields at 100Hz
instead of 50Hz is not the complete
solution. While it solves broad area
flicker (which is noticeable even on
VGA screens scanned at 70Hz), it
does not solve alternate line flicker.
This is often very noticeable when TV
stations put pictures in small boxes on
the screen.
Philips has solved the line flicker
problem by not just doubling the vertical scan frequency to 100Hz but by
also doubling the scan frequency as
well, to 31.5kHz. Note that this is not
exactly twice the PAL scan frequency
of 15.625kHz but it is twice the NTSC
scan frequency of 15.75kHz and ties in
with the world nature of this set. Not
only that, but the set uses a complex
algorithm whereby alternate lines
may be scanned in ‘ABAB’ mode for
stable parts of the picture where flicker
would be noticeable and in ‘AABB’
mode where the picture is moving and
so flicker is not perceptible (where A
and B stand for alternate lines in an
interlaced picture).
The result is a picture on the screen
which is so stable and flicker-free that
it is uncanny. If the picture is stationary as well, it is absolutely still, just
as if it came from a slide projector – it
is that good.
Digital noise reduction
Digital noise reduction (DNR) is a
feature which is only made possible
because of the fact that there is actually
enough video RAM to store two complete fields. The set uses an algorithm
pattern produced in 4:3 mode, together with a PIP display.
Superwide mode (above) expands the image horizontally
to compare the video signals, line
by line, with the previous field and
thereby distinguish between random
noise (snow) and legitimate variations
in the video signal. DNR can be introduced in two stages with the remote
control and it can make a worthwhile
improvement in signals which have
a modest noise content. However, it
also results in a minor loss of detail
on less noisy signals and so it is often
difficult to decide whether to switch
it in or out.
Colour transient improvement (CTI)
is another byproduct of the digital
video processing and gives sharper
transitions for colour picture information. The remote control gives you
the option of turning CTI on or off but
unless you know what to look for, it is
hard to tell the difference with it on
or off. Its main effect is to sharpen up
red signals which can otherwise be
quite blurry. Once you have noted the
effect, you will leave the CTI switched
on because it is beneficial.
Picture in picture
Picture in picture (PIP) might be
regarded by some as a gimmick but
in practice it is a very useful feature
which allows you watch one channel
while keeping an eye for the start of a
program on another channel. Not only
does it require a digital field store so
that the two pictures can be synchronised together but it also needs two
complete video processing chains: two
TV tuners (UHF & VHF), two IF strips
and so on. Hence, you can watch any
video channel on the main picture and
any channel on the PIP. You can even
display a Teletext picture on the full
screen while continuing to watch (and
listen to) the PIP.
Finally, as a byproduct of the field
The chassis of the new Philips set is essentially a large motherboard with quite
a few smaller boards plugged into it. Not shown is the superwoofer enclosure
which is attached to the rear cover.
store, it is possible to independently
freeze the main picture using the
STILL button on the remote and the
PIP using the FREEZE button. This is
not a particularly useful feature but
it can be amusing to freeze some TV
personalities while they are talking.
Other picture enhancements
The new Philips set has two other
picture enhancements, one of which is
extremely worthwhile and one which
is arguable. The first is the SCAVEM
circuit while the other is “black level
stretch”. SCAVEM stands for SCAn VElocity Modulation and is used to delay
the scan voltage to compensate for the
delay in large video signal transitions
which are caused by the capacitance of
the picture tube. Normally, this capaci-
by about 25%. Wide Screen is used for showing 16:9
program material, while Movie Expand (right) is used
tance causes blurring of black-to-white
and white-to-black transitions and this
is quite noticeable on captions, weath
er maps and so on. This feature really
does work and makes the picture so
much sharper than on conventional
sets. In fact, in my opinion, apart from
the flicker reduction of this set, the
SCAVEM circuit is the feature which
makes the biggest contribution to the
outstanding picture quality of this set.
We are not so sure about the “black
level stretch” feature. As with other
sets on the market, the new Philips set
has a picture tube with a black face
which gives a much higher picture
contrast and makes the picture much
easier to see in brightly lit and sunny rooms. So compared with sets of
seven or eight years ago, the pictures
to fill the screen while showing movies which have been
broadcast in letterbox format.
August 1994 7
are watching movies that the sound
system really comes into its own (all
the bass included). The set is supplied
with satellite speakers for the rear
surround channels and also has audio
outputs to drive external amplifiers.
Nor is their any need to connect a
centre channel speaker because the
Philips set simulates a centre speaker
with its “phantom” speaker setting, via
the front speakers. Even if the movie
you are watching does not have Dolby sound, you can have a very good
surround effect by selecting “matrix”
which includes acoustic delay for the
rear speakers.
Chassis design
This photograph shows how Teletext pictures can be displayed in 4:3 format
while you watch (& listen to) a large PIP image. Note that the barrel distortion of
the picture is mainly due to the photographic technique & is not evident on the
set.
already have better blacks and better
contrast range (ie, over the full range
from white to black, with all the greys
in between).
What the “black level stretch” is
supposed to do is to increase the picture contrast of the dark parts of the
picture. As I understand it, it pushes
the black level down towards the
blanking level so that the blacks are
“blacker than black”.
In my opinion though, it merely
makes the picture too dark. I was able
to make a direct comparison between
this set and another Philips set which
is 9 years old. The older set revealed
more detail in the greys of the picture,
simply because they weren’t so black.
In effect, the black level extension
seems to compress the bottom of the
grey scale so that dark greys become
black.
Picture preferences
Being something of a “video hifi
enthusiast” I believe there is only
one setting of contrast, brightness and
colour temperature (picture white)
which gives the best overall picture.
However, Philips has provided for a
number of picture preferences which
are entitled Rich, Soft, Natural and
Personal. In my opinion, the Rich picture is much to dark, the Soft picture is
blurred and the Natural picture is not
too far away from being right although
it still loses detail in the dark greys.
Thankfully, you can set up your own
personal preference and when that it
done, it is excellent.
8 Silicon Chip
Similarly, you can chose your colour temperature for the white areas
of the picture and these are given as
Normal, Warm and Cool. Warm makes
the whites look pink while Cool makes
them look blue. Normal is correct.
Sound preferences
In line with the concept of viewer
democracy, Philips give the viewer
a whole bunch of sound preferences
which are listed as Voice, Music, Theatre and Personal. For most programs,
the Philips set just gives too much bass.
In fact, it has a superwoofer enclosure
intended to boost the bass and it does
that very efficiently. Consequently, in
order to make the sound as intelligible
as possible, it is necessary to cut the
bass right back and this became my
“personal” setting.
All of these adjustments are done
via on-screen menus which appear
superimposed on the picture every
time your press a relevant button on
the remote control. Even setting the
volume is done to the accompaniment
of a bargraph on the screen. And that
brings me to another minor criticism.
The available increments in the volume setting are too big, so much so
that with the volume setting at half
way, the sound is at bellowing level.
This could be easily fixed with some
running changes to the software in the
microprocessor’s ROM.
Dolby surround sound
Philips has full Dolby Pro-Logic
decoding in this set and it is when you
We’ve included a photo which
shows the general setup of the chassis.
Actually, there is no chassis as such
but there is a large motherboard with
quite a few vertical boards plugged
into it.
Interestingly, the set has its own
error message system via an array of
seven LEDs on the main board and
these are driven by the microprocessor. These will no doubt help in fault
diagnosis should service be necessary.
Picture evaluation
To come back to the main feature
of this set, throughout our evaluation
we were intrigued by the various
wide picture modes, their effects and
how they were achieved. According
to one explanation we had from the
Philips technical people in Australia,
when you switch to the “Superwide”
mode, the major area of the picture is
undistorted although it is magnified
slightly, by about 10%; it is only the
two vertical edges of the picture which
are stretched to fill the screen.
The method used to stretch the
picture is quite simple in theory; just
vary the S-compensation applied to
the picture tube yoke drive. Having
been given the above explanation,
we found it hard to understand. After
all, it takes 52µs to scan one line on a
normal picture and clearly the scanning voltages do have to be varied to
provide the varying degrees of picture
stretch.
Note that the picture is also stretch
ed vertically (although not as much as
horizontally) in the Superwide mode.
This can cause a problem with pictures
that have captions at the bottom of the
screen or where the image is cropped
at the top. To solve this problem, the
When in Super-Wide mode, the 10% vertical expansion means that some of the
top & bottom of the image will be lost & this can cause a problem with captions.
The top image is in Super Wide mode, while the bottom image is in Movie
Expand mode. We found Super Wide quite satisfying for 4:3 programs.
remote control has two buttons to
nudge the picture up or down by a
small amount. This picture shift is
brought into play by an additional
deflection coil on the tube yoke. Thus,
you can nudge the picture up to fully
view the captions or nudge it down if
someone’s head is being scalped at the
top of the screen.
Other deflection trickery by the
Philips set means that movies shown
in “letter box” format can be expanded
to fill the screen (which means that you
lose the edges of the picture.
To more precisely judge the effects of the various stretched picture
modes, we took a series of off-screen
photos displaying a crosshatch pattern
provided by a TV pattern generator.
Each mode is identified with an on-
screen label such as NORMAL 4:3,
SUPERWIDE and so on. Note that
the 4:3 screen photo has black strips
on each side of the screen. We were
also able to make direct comparisons
between the Philips widescreen set
and a 9-year old Philips 63cm set (the
KR683 chassis, one of the last Philips
sets to be designed and manufactured
in Australia).
When these direct comparisons
were made we noted the horizontal
and vertical picture overscan present in the older set. This amounted
to about 7% or 8% which does not
sound like a lot but it is quite significant when you see a picture which is
not overscanned. When you consider
this factor, the amount of picture
stretching in the SUPERWIDE mode
is not as much as you might think. If
you look at the 4:3 crosshatch picture
you will see that it has 10 horizontal
lines and 13 vertical lines while the
SUPERWIDE picture has 9 horizontals
and 12 verticals.
Note that the squares are stretched
horizontally more than vertically.
In fact, we judged that in SUPER
WIDE mode, the horizontal stretch
is about +25% while the vertical
stretch is about 12%. Furthermore, the
amount of horizontal stretch is pretty
even across the screen.
Having demonstrated the various
picture modes, it occurred to us that
if PIP was on the screen it would be
stretched too. So we tried it. Guess
what? The PIP stays virtually the same
size and in the same position, regardless of which picture stretch mode is
selected. This is very clever because it
means that the synchronising and sizing of the PIP image which is inserted
into the main picture has to be digitally
varied to suit the stretch mode!
Having tried all the variations, we
have to say that watching normal programs in the Superwide format quickly
become the norm. Even though there is
some slight overall horizontal stretching of the image, it is hardly noticeable,
particularly if you have been used to
watching a conventional TV which
is normally overscanned more in the
horizontal than vertical direction. The
bigger image is simply more satisfying.
And when applied to movies broadcast
in “letter box” format, it also increases
the satisfaction.
All told, we were very impressed
by this new wide format TV set from
Philips. It contains a host of technological innovations which really do
add to the viewing satisfaction. We
certainly did not want to send the
review set back!
Such technology does not come
cheaply although you have to admit
that compared with any other consumer product, this set does have a lot
to offer. It has a recommended retail
price of $6299. An optional matching
stand is also available.
Finally, as an extra service, Philips
will install, connect and tune the set
in the new owner’s home and demonstrate most of the features. This home
installation service will be available
seven days a week and after hours,
throughout Australia. Not only that,
Philips will also remove all the packSC
ing materials for recycling.
August 1994 9
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
Electronic
Engine
Management
Pt.11: Fuel & Air Systems – by Julian Edgar
Electronic engine managed cars run
fuel and air induction systems that are
completely different from those in cars
with carburettors.
In an engine managed car, fuel is
pumped in a circuit from the tank to
the fuel injector supply rail and then
back to the tank again. This continuous flow of fuel around the system
keeps it cool to avoid vaporisation
and means that a supply of high-pressure fuel is available whenever it’s
needed.
Fuel supply components
The fuel supply system can be di-
vided up into a number of sections,
starting with the fuel pump:
(1). Fuel Pump: fuel pumps in EFI
systems are of the high pressure, roller-cell type. Because this type of pump
works poorly without a head of fuel, it
is located either below the fuel level
or is primed by a second, low-pressure
pump located in the tank.
The pump’s electric motor is cooled
by the fuel flowing through it and the
pump is protected against outlet line
blockage by a pressure release valve.
Another valve, which is a non-return
type, is located on the outlet side of
the pump.
Fuel injectors come in a variety of shapes & forms but are all basically electric
solenoid valves.
14 Silicon Chip
The fuel pressure in Bosch systems
is usually held at 250kPa (36psi), although the pump is capable of up to
500kPa (72psi).
(2). Fuel Damper: following the
fuel pump in some cars is a small inline damper, comprising an internal
chamber and a coil-spring diaphragm.
As the pump operates, it generates
a pulsing effect in the fuel pressure.
High volume pulses will deflect the
diaphragm in the fuel damper, temporarily increasing the size of the internal
chamber and so absorbing the pressure
spike. Conversely, momentary drops
in pressure cause the diaphragm
to move into the chamber, thereby
maintaining the output pressure at
a constant value. As well as reducing minor pressure fluctuations, the
damper can also lower pump noise.
(3). Fuel Filter: a large, metal-encased fuel filter follows the fuel damper. This filter may be located close to
the fuel tank or can be situated in the
engine bay. Particles down to a size of
10 microns (.0001mm) are trapped by
the filter to ensure that the fuel injector
nozzles aren’t blocked.
(4). Fuel Rail and Injectors: fuel
flows from the filter to the fuel rail,
where the individual injectors take
their feed. The fuel rail is of a larger
internal diameter than the fuel line
from the tank. This is to ensure that
as each injector operates, there is still
sufficient fuel in reserve to prevent
fuel pressure regulator controls the return flow to the tank and so maintains
the fuel-rail pressure. As Fig.4 shows,
this device is divided by a diaphragm
into fuel and air chambers, and has a
vacuum line to the manifold plenum
chamber. Rather than maintain the
fuel at a constant pressure above atmospheric pressure, the fuel is kept at
a constant pressure above that found
in the manifold.
The injectors are located so that they squirt fuel immediately behind the inlet
valves. Note the large volume square cross-section fuel rail above them.
pressure variations occurring from
injector to injector. The injectors can
either be held in place by collars and
bolts, or by the fuel rail itself.
The role of the fuel injectors is critical – they have to be able to respond
very quickly (1-1.5ms typical opening
time), produce a well-atomised spray,
and be durable in the extremes of
temperature and vibration under the
bonnet.
A fuel injector is basically an electrical solenoid valve. It consists of a
gauze filter on the inlet, a solenoid
winding around the armature, a
needle valve and the electrical connec
tion. The coil resistance varies with
different designs, with four ohms resistance being typical. In general, the
lower the coil resistance, the faster the
response-time of the injector.
(5). Cold-Start Injector: some cars,
especially those with relatively early
EFI systems, have an additional injector mounted on the plenum chamber.
This injector is activated by the electronic control module during cold
starts and enriches the mixture. More
recent EFI systems simply run longer
injector pulse widths to provide the
extra fuel needed.
(6). Fuel Pressure Regulator: the
Because fuel injectors only have a
very small opening lift, they can
easily become blocked. To prevent this
from happening, the fuel filter blocks
particles down to .0001mm diameter.
Fig.1: a typical multi-point fuel injection system.
August 1994 15
A single cold start injector (see above) is used on some
systems to ensure satisfactory running when the engine is
cold. It fires into the plenum chamber to enrich the starting
mixture. The fuel pressure regulator (right) maintains the fuel
at a constant pressure relative to the manifold pressure. The
actual fuel pressure constantly varies, however.
This means that when an injector
opens for a certain length of time, the
same amount of fuel will flow irrespective of whether the manifold pressure
is high or low. If this weren’t the case,
then manifold pressure variations
would cause unwanted changes in the
fuel injection quantity.
Air induction systems
Because fuel is added to the airstream just before the engine inlet
Fig.2: this diagram shows the in-tank fuel pump
& fuel level sender unit used in the Subaru
Liberty.
16 Silicon Chip
valves in the majority of EFI cars, the
air induction system can be designed
almost solely for greatest airflow. In
carburettor designs, the inlet manifold
has to be kept short and sometimes
heated to prevent fuel droplets from
Fig.3: the fuel injectors are positioned so that
they spray fuel into the intake port immediately
behind the intake valves.
This photo shows a modified Subaru Liberty Turbo air intake system. At the
bottom left is a new fabricated intake duct to the air-filter box. The airflow
meter is located just behind this box & the airflow then passes through a rightangled duct to the shiny section of pipe, which was made to replace a silencing
resonator volume. The right-angled rubber bend then takes the induction air to
the turbo inlet. These modifications reduced the pre-turbo intake pressure drop
by 40%, with a commensurate increase in performance.
forming on its walls. In addition, the
throat size needs to be restricted so
that intake gas velocities remain high
Fig.4: a fuel pressure regulator
consists of a fuel chamber & an air
chamber with a vacuum line to
the intake manifold. The manifold
pressure controls a diaphragm that
separates the two chambers (Holden
VL Commodore).
in all driving conditions. In EFI cars by
contrast, resonant tuning of long intake
runners is employed and the ducts can
be sized to provide the lowest pressure
drop at full load.
(1). Intake Silencers: the combustion air is generally drawn from
outside the engine bay to avoid the
induction of hot air. In some cars, it
then passes into a silencing volume,
often comprising a plastic box located
under the mudguard. A duct then carries the air to the air-filter box.
(2). Air Filter: the air filters used in
modern cars are generally flat corrugated paper element types. They are
located in plastic boxes positioned to
one side of the engine bay. The volume
of the air-filter box is sometimes part
of the intake resonant tuning which
is employed to gain better cylinder
filling. In addition, the air-filter box
also generally acts as an additional
intake silencer.
This intake air silencer volume is
from a Subaru Liberty & is located
inside the mudguard.
(3). Airflow Meter: in cars not
employing a MAP sensor, the airflow
meter follows the air filter. The airflow
meter can be of the vane, vortex or
hot-wire type.
August 1994 17
Right: This view shows a
typical 4-cylinder intake
manifold. The plenum
chamber is at the top,
while below it are the
individual cylinder
runners.
The throttle body is a simple butterfly valve
which controls the airflow into the engine.
Fig.5: the fuel pressure is typically regulated so that it is 250kPa greater
than the manifold pressure. This ensures that the fuel injectors deliver a
constant amount of fuel for a given pulse length, regardless of manifold
pressure variations.
This photo of a modified Mazda rotary engine clearly shows the throttle body,
with the plenum chamber located behind it & the intake port runners in the
foreground. Note that this racing engine does not use an air bypass valve & so
the throttle blade is set so that it is slightly ajar at idle.
18 Silicon Chip
(4). Throttle Body: the throttle body
is the main butterfly controlling the
airflow into the engine. The vast majority of throttle butterflies are controlled
by a cable linkage to the accelerator
pedal, although some exotic cars now
run ‘drive-by-wire’ arrangements.
A bypass passage is often built into
the throttle body, with an adjustment
screw to vary idle speed.
(5). Auxiliary Air Valve: when the
engine is cold it needs more fuel and
air to idle satisfactorily than it does
when warm. The extra fuel is supplied
by either a wider injector pulse width
or by a cold-start injector. The extra air
is provided by the auxiliary air control
valve (sometimes called the bypass air
control valve). Its function is to allow
intake air to bypass the throttle body
butterfly. These valves can be either
controlled mechani
cally by engine
coolant temperature or can be electrically pulsed or otherwise controlled
by the ECM.
This valve can also be used – in
conjunction with ignition timing
control – to give a constant idle speed,
irrespective of engine loads like the
air-conditioner. In some cars, additional air-bypass valves perform the
idle-speed control function, with the
auxiliary air valve used only during
warm-up.
(6). Plenum Chamber and Inlet
Runners: following the throttle body,
the air enters a plenum (or surge)
chamber, before flowing to the inlet
valves through long runners. The res-
The powerful Nissan Skyline GT-R twin turbo sports car uses a huge log-type
intake manifold & six throttle butterflies.
Fig.6: a typical air intake system for a fuel injected car.
Fig.7: typical air intake flow diagram for a fuel-injected, turbocharged
& intercooled engine (Subaru Liberty).
onant intake tuning is related to the
length and diameter of the individual
cylinder runners and the volume of
the plenum chamber. Tests have indicated that an increase in maximum
engine torque of as much as 25% can
be gained by appropriate tuning of
this system.
Some engines, notably those with
four valves per cylinder, use two intake
runners for each cylinder. The two sets
of intake ducts are of different lengths
and are activated by ECM-controlled
butterfly valves located within the
induction system. Sophisticated twin
Helmholtz resonance intake systems
SC
are used on some cars.
August 1994 19
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
MAILBAG
Alternative probe
for coolant alarm
In relation to the Coolant Level
Alarm project featured in the June
1994 issue of SILICON CHIP, our company is able to offer an expanding
rubber probe as an alternative to the
probes shown in the article. Installation of the rubber expansion probe
requires only the drilling of a 3/8-inch
hole in the radiator top tank, enabling
fitting without removal of the radiator
from the vehicle. These probes are
constructed of high density rubber
and stainless steel with a brass spade
electrical tab connector and can be
supplied for $16.85 each, including
postage.
We are also able to supply a screw-in
plastic probe complete with a threaded
brass bushing, that is soldered to the
radiator tank, for $26.00, including
postage. Contact Rob Sym
mans at
Monteck Electronics Pty Ltd, Phone
(09) 330 6817 (BH) or (09) 457 0301
(AH); or write to 11 Portulaca St, Willetton, WA 6155.
Coolant alarm
too sensitive
It’s been over three years now since
the publication of my automotive coolant level alarm in the Circuit Notebook
section, so it was fabulous to see the
idea developed into a kit at long last.
It should not only start to save a lot of
Australians a lot of money, but it will
help push the automo
tive industry
into providing such an alarm as a long
overdue standard fitting.
However, after reading the article
through, I think the kit in its present
form is doomed to be unreliable. The
coolant sensor input is far too sensitive. In a new car it will work fine
for a few months perhaps, but with
dirty or old coolant and ageing cars
and trucks, the scum in the coolant
will coat a conductive layer over the
sensor’s insulator which will conduct
enough current to the stainless steel
pin to give a false reading to the circuit. There will be no alarm when it
is needed!
In placing the sensor into the top
radiator hose, you have possibly
forgotten that the hose is fed by a
reasonably strong water pump. Your
circuit resets itself very quickly when
coolant covers the sensor (assuming
that the hose fitting is also immersed
internally), so you could lose most of
the coolant out of the system and have
no coolant flow and yet the pump can
splash and surge enough water onto
the sensor to keep the alarm from
sounding off. This is not as damaging
as losing all water because the excess
heat will dissipate by turning the water
to steam but that will not encourage a
lot of faith in the circuit.
My notes on the test of the Ford
Fairlane in 1990 are as follows. Its
alarm would come on (visual only) if
a resistor of 18kΩ or more ohms was
fitted between the sensor lead and
earth for more than 10 seconds. But
at 15kΩ or less the alarm lamp would
extinguish immediately.
I do not have a record of the open
circuit sensor voltage, but perhaps 5V
as you have chosen is quite logical. For
the Ford circuit to take 10 seconds to
operate and yet clear immediately with
a slight change in the sensor’s current
indicates to me that their alarm timing
section of the circuit is buffered from
the sensor by a comparator.
The Ford timing arrangement would
also be useless with a sensor in the
radiator hose but with the standard
radiator nut fitting it is fine. Three of
the cars at our house now have the
correct radiator nut supplied from a
radiator repair business.
My suggestions are that the sensor
input capacitor be increased to 1000µF
and the 100kΩ resistor vertically above
it in the schematic be replaced with a
10kΩ resistor. This is for the radiator
nut version but the radiator hose will
likely have higher normal resistance
readings than that.
Glen Host,
Doubleview, WA.
Comment: we did fairly extensive tests
when we designed the coolant alarm
and found that the value of 100kΩ
used was about right. We also recommend that the radiator be regularly
flushed & the correct inhibitor used
to prevent false triggering.
SILICON CHIP,
PO Box 139,
Collaroy, NSW 2097.
Further comments on
12V battery charging
The letter commenting on the solar
regulator in the May 1994 edition suggested charging lead acid batteries at
14.2V and then reducing this to 13.8V.
In my experience, 13.8V is a little low
and you won’t get maximum use from
your batteries, something that is important with a solar power system. On
the other hand, 14.2V is a little high
and will cause gassing and electrolyte
loss. It’s a pain to have to keep topping
up your batteries.
I settled on a charging voltage of
14V. This will give a good charge with
very little gassing. I have not had to
top up my battery in almost two years
and the battery is used daily with
faultless performance so far. These
figures could change slightly for different types and brands of batteries
but the manufacturer told me 13.8V
to 14.2V is the recommended range
for my battery and that 14.4V is the
maximum (anything above this and
damage was likely).
I recommend that people not sure
of the best voltage should contact the
head office of the manufacturer of their
particular brand of battery and ask
their advice. This way, maximum life
is assured from your batteries.
Now on to another matter: the
Publisher’s Letter in the same edition, May 1994. It was said that with
lower mains voltage, 230VAC instead
of 240V, the picture on an old style
tele
vision would shrink. Not true
– with lower voltage on the final
anode of a picture tube, the picture
actually blooms or gets bigger. I know
it doesn’t sound logical but it’s true.
Any TV serviceman will agree, and
a detailed explanation would take
many pages. Sorry to pick at an otherwise great magazine.
D. Haddock,
Kamerunga, Qld.
Comment: our writer for the Serviceman pages has noted that with
virtually all solid state TV sets, the
reduction in mains voltage will make
no difference. On old valve sets, a reduction in mains voltage will certainly
cause the picture to bloom.
August 1994 23
A high-power
dimmer for
incandescent lamps
Need a dimmer for a large domestic or
stage application? This unit will dim
an incandescent or halogen lamp load
of up to 2400 watts. It can also dim 12V
transformer-driven halogen lamps or
be used for fan speed control.
Design by MARQUE CROZMAN
24 Silicon Chip
Low power dimmers for loads up to
500 watts or so are readily available
and quite cheap at around $20. But
if you want to dim much larger loads
than this the cost of a commercial
dimmer becomes quite expensive
and can range up to several hundred
dollars. Why pay that much when
you can save money by building this
version and incorporate extra features
as well?
For example, this circuit can be
remotely controlled by a 0-10V DC
signal. This means that the dimmer
itself can be installed out of the way
while three wires at low voltage can
run to the dimmer potentiometer. This
can then be placed in a convenient
location. Alternatively, you could
incorporate a local/remote switch
so that the dimmer could be directly
controlled by the knob on its case or
via the remote potentiometer. Furthermore, these options can always
be incorporated later if you don’t need
them right now.
The dimmer is housed in a rugged
diecast aluminium case measuring
170 x 121 x 55mm. The case provides heatsinking for the Triac as
well as external protection for the
circuit. As already noted, it can
dim up to 2400 watts of lamps
which may be made up in any
combination. Minimum recommended lamp load is 40 watts.
Let’s now have a look at the
circuit diagram which is shown
in Fig.1. This looks fairly complicated but is essentially a phase
controlled Triac, similar to that in
any commercial light dimmer. The
major difference between this circuit
and most 300-500W commercial
10
25VW
A2
D3
24V
CASE
PIN2
IC1b
E
4.7k
2
3
1
1
1k
IC1b
2
2
3
4
5
6
D2
1N914
7 100
B
8 1k
+15V
ZD1
10V
400mW
PIN14
IC2
+15V
100k
SET MIN
BRIGHTNESS
VR2
10k
10k
E
0.1
C
220
100k
100k
+15V
5.6k
IC2d
5
1
SET MAX
BRIGHTNESS
VR3 50k
A
N
240VAC
F1
10A
820k
IC2c
12
7 13
IC2b
6
10k
8
IC2a
10 LM324
11
4
9
D4
2x
1N4004
BR1
DB104
100
50VW
IN
GND
REG1
7815
OUT
CASE
A1
I GO
C
E
7
13
14
11
IC1f
IC1e
12
10
6
IC1d
5
VIEWED FROM
BELOW
B
2
4
IC3
MOC3021
A
K
.033
250VAC
6
1
4
14
3
10k
10k
2.4kW LAMP DIMMER
G
0.1
L1 : 19T, 1mm DIA ENCU ON A PHILIPS
4330 030 60271 TOROID
+15V
A
E
CASE
N
GPO
2.4kW MAX
0.1
250VAC
L1
G
TR1
BTA41A
A2
A1
0.1
250VAC
22
1W
240VAC
470
390
A
LED1
K
2.2k
0.5W
+4.6V
DIMMMER
VR1
50k LIN
D1
1N914
Fig.1 (right): the full circuit of the
dimmer. Most of the circuitry runs
at low voltage & is isolated from the
240VAC mains via the transformer &
the optocoupler IC3.
4.7k
9
IC1a
40106
As with any dimmer circuit, the
power to the lamps is varied by
Q1
BC547
Circuit principle
100k
dimmers is that most of the circuit is
isolated from the 240VAC mains supply by virtue of an optocoupler and a
transformer.
The heart of the circuit is the Triac,
TR1. This is a BTA41A Triac, a 600
volt, 40 amp device which has been
selected to cope with the high surge
currents when switching on an incand
escent lamp load totalling 2400 watts.
Typically, the surge current at switchon can be 10 to 15 times the normal
load cur
rent; ie, the surge current
could be 100-150 amps and last for
several milliseconds.
The Triac must also be able to cope
with the high fault currents that flow
when high power lamps blow their
filaments. To explain, when a lamp
blows its filament the now loose
sections can flay around and come in
contact with the stem supports. When
that happens a high fault current can
flow which is not extinguished until
the stem fuse blows. Clearly, the Triac
must be rugged to cope with this.
680
•
•
•
•
•
IC1c
•
Features
2400W maximum lamp load
40W minimum lamp load
Industry standard 0-10V dimming
control
Dims transformer-driven halogen
lamps
10A mains supply fuse
Adjustable maximum brightness
Adjustable minimum brightness
RF interference suppression
7.5kV optocoupler isolation
between control circuitry and
240VAC mains for safety.
+15V
•
•
•
August 1994 25
This view shows how the completed PC board is mounted in the case, along
with the GPO & the mains terminal block. The front panel controls are
connected to the board via a 7-way pin header.
switching on the Triac early or late in
each mains half-cycle. For high power
operation, the Triac is triggered on
late in each mains half-cycle so that
the effective voltage fed to the lamp
load is low. Similarly, for high power
operation or full on, the Triac is triggered early in each mains half cycle so
that virtually the full mains voltage is
applied to the lamp load.
This method of power control is
referred to as “phase control” because
we vary the phase of the Triac trigger
pulses with respect to the mains
waveform. Most small dimmer circuits use a Diac or similar capacitor
discharge device to trigger on the
Triac but this circuit is more complex,
mainly to provide isolation between
the control circuitry and the 240VAC
mains supply.
Circuit description
Before we dive into a full description of the circuit shown in Fig.1,
let’s identify some of the key sections.
First, at the top righthand corner is
the Triac itself which feeds the lamp
26 Silicon Chip
load via a standard 3-pin mains socket.
In the lower righthand corner is the
low voltage supply which uses a 24V
transformer feeding a bridge rectifier
and 3-terminal regulator. In the top
lefthand corner is the ramp generator
(IC1a & IC2a) while below that, in the
bottom lefthand corner, is the 0-10V
DC control circuitry.
Now that you are oriented, let’s start
with the low voltage supply involving
the 24V transformer. As already noted,
this feeds a bridge rectifier (BR1) and a
100µF capacitor to drive a 3-terminal
regulator REG1, which produces a 15V
WARNING!
While most of the circuitry operates
at low voltage, this is a mains operated circuit and must be regarded
as potentially lethal when power
is applied to it. This project is not
one for beginners and should only
be attempted by constructors who
have previous experience with
mains powered circuits.
DC supply. The reason for using the
relatively high transformer voltage of
24VAC has to do with the ramp synchronisation. Two diodes, D3 and D4,
feed the rectified but unfiltered DC to
a network at the input of IC1a which
consists of a 4.7kΩ resistor, diode D1
and a 2.2kΩ resistor.
As a result of this network, the
voltage at the input of Schmitt trigger
IC1a will be at +15V for most of the
time but will drop to +4.6V at the beginning of each mains half-cycle. This
waveform is inverted and squared up
by IC1a to produce a series of narrow
positive pulses synchronised to the
50Hz mains supply.
This pulse train drives the base
of transistor Q1 which discharges
the capacitor at its collector every
10ms. In between each discharge the
capacitor is charged via the 100kΩ
resistor connected to the +15V rail.
The resulting sawtooth waveform is
buffered by op amp IC2a and inverted
by op amp IC2b and then fed to pin
13 of op amp IC2c which is connected
as a comparator.
Op amp IC2d is fed by the 50kΩ
dimmer potentiometer VR1 which
is fed with +10V from zener diode
7
D3
3
K
2
LED1
1
D1
Fig.2: this diagram shows the additional circuitry
required for the remote dimming facility. It is
connected to the main circuit via a 7-way header
plug and socket on the PC board.
ZD1
1
IC3
1k
ZD1. Thus the input from VR1 can
range anywhere from zero to 10V
DC, depending on the desired lamp
brightness. The DC voltage from VR1
is buffered by op amp IC2d which has
an adjustable gain of less than unity
(ie, it is an attenuator). The voltage
from IC2d is fed to pin 12 of comparator IC2c which compares it with the
100Hz sawtooth voltage at pin 13. The
result is a variable width pulse train
corresponding to the dimmer setting;
ie, wide pulses for a high brightness so
that the Triac is triggered early in each
1k
100k
VR3
100k
1
HEADER
22 1W
0.1
250VAC
.033 250VAC
0.1
250VAC
MOC3021
Fig.3 (right): the part layout diagram for the PC board. This
should be used in conjunction with the wiring diagrams of
Figs.4 & 5. Note the wire link between ZD1 and the adjacent
220Ω resistor. Note also that the two pads immediately above
the 7-pin header are vacant.
D2
1
4.7k
680
A
10uF
4.7k
2.2k
10k
5.6k
10k
1
100k
VR2
D4
POWER
TRANSFORMER
IC2
LM324
820k
Q1
10k
100
OPTIONAL
REMOTE CONTROL
100uF
BR1
4
10k
0.1
5
IC1
40106
1
S1
VR1
50k
LIN
100k
24V
220W
XLR
1 PLUG
6
390
3
470
2
REG1
(MOUNTED ON CASE)
PRIMARY
50k
LIN
XLR
2 PANEL
SOCKET
3
7
L1
F1
TRIAC1
ACTIVE NEUTRAL
mains half-cycle and narrow pulses for
a dim setting.
The pulses from IC2c are then
buffered by four paralleled inverters
(IC1c,d,e & f) which drive the opto
coupler IC3. In turn, the optocoupler
triggers the Triac which drives the
lamp.
At this stage you have most of the
picture of the circuit operation but
there are some details yet to be discussed. For example, the remaining
inverter in the 40106 hex Schmitt
trigger package, IC1b, is connected to
G
A2
A1
LOAD
the output of IC2c and is used to drive
indicator LED1 via a 1kΩ resistor. This
LED then provides a rough indication
of the brightness setting of the dimmer
since it is driven from the same pulses
as are used to trigger the Triac.
A 7-pin header socket on the board
provides for local or remote operation. On the dimmer panel, a 50kΩ
slider pot (VR1) provides the dimming
control. Alternatively, switch S1, an
additional 50kΩ linear potentiometer
and a 3-pin XLR socket can provide for
remote dimming, as shown in Fig.2.
RESISTOR COLOUR CODES
❏
No.
❏ 1
❏ 4
❏ 4
❏ 1
❏ 2
❏ 1
❏ 2
❏ 1
❏ 1
❏ 1
❏ 1
❏ 1
❏ 1
Value
820kΩ
100kΩ
10kΩ
5.6kΩ
4.7kΩ
2.2kΩ
1kΩ
680Ω
470Ω
390Ω
220Ω
100Ω
22Ω
4-Band Code (1%)
grey red yellow brown
brown black yellow brown
brown black orange brown
green blue red brown
yellow violet red brown
red red red brown
brown black red brown
blue grey brown brown
yellow violet brown brown
orange white brown brown
red red brown brown
brown black brown brown
red red black brown
5-Band Code (1%)
grey red black orange brown
brown black black orange brown
brown black black red brown
green blue black brown brown
yellow violet black brown brown
red red black brown brown
brown black black brown brown
blue grey black black brown
yellow violet black black brown
orange white black black brown
red red black black brown
brown black black black brown
red red black gold brown
August 1994 27
CORD
GRIP
GROMMET
Fig.4: this diagram shows all the
off-board wiring & the primary
& secondary connections for the
power transformer. Note that the
earth leads from the power cord
& power socket must be soldered
to an earth lug which is securely
bolted to chassis.
MAINS
CORD
REG1
(MOUNTED ON CASE)
100k
10k
820k
VR3
100k
100
IC1
40106
470
1
390
100k
1
1k
ZD1
IC3
D2
4.7k
220
SECONDARY
PRIMARY
POWER
TRANSFORMER
5.6k
10k
1
100k
VR2
10uF
1k
100uF
Q1
10k
IC2
LM324
0.1
24V
1
HEADER
7
22 1W
0.1
250VAC
.033 250VAC
0.1
250VAC
MOC3021
L1
F1
A
N
G
A2
A1
5
O/P
4
3
1
TRIAC1
2
A
VR1
EARTH
(GREEN/
YELLOW)
K
LED1
EARTH
LUG
NEUTRAL
(BLUE)
ACTIVE
(BROWN)
N
E
PANEL MOUNT
POWER SOCKET
A
Note that the potentiometer must be
a linear type otherwise the dimming
characteristic will not be smooth and
progressive.
Brightness adjustments
Adjustments are provided in the
circuit for maximum and minimum
28 Silicon Chip
brightness settings. First, VR2 provides the minimum brightness setting,
when the main potentiometer VR1 is
at is zero setting.
VR3 sets the gain of op amp IC2d and
thereby sets the maximum brilliance
setting. It is set by taking VR1 to its
maximum setting and then noting the
lamp brilliance. VR3 is then rotated
clockwise to note if there is any increase in brilliance and then backed
off slightly. The idea is to set it so that
the maximum setting of VR1 does in
fact give the maximum brilliance. The
settings of VR2 and VR3 will interact
so it will be necessary to adjust each
XLR PANEL
SOCKET
ON/OFF
SWITCH
A (OUTPUT)
A
2
7
3
240VAC
50k
LIN
LAMP
DIMMER
LOAD
1
N
N
E
5
Fig.6: this diagram shows how the dimmer could be
wired up in a permanent installation. The dimmer
itself could be installed in the ceiling, while the low
voltage potentiometer connections & 10A switch
could be on a standard architrave plate. Note that
this installation can legally only be performed by a
licensed electrician.
6
S1
4
3
1
2
A
VR1
Fig.7: this diagram
shows the mounting
details for the
insulated tab Triac. No
mica washer or plastic
bush is required.
K
LED1
Fig.5: this diagram shows the wiring of the remote control
version with all connections made via a 150mm length of
rainbow cable & a 7-way header plug.
in turn several times to finalise the
settings.
High voltage circuitry
So far, virtually all of the circuit
description has ap
plied to the low
voltage portion but the components associated with the Triac need explanation. First, the 22Ω resistor and 0.1µF
capacitor comprise a “snubber” circuit
which allows the Triac to commutate
correctly (ie, switch off reliably) at the
end of each mains half-cycle when the
load is inductive. This would be the
case when dimming 12V transformer
driven halogen lamps.
The optocoupler is also provided
with snubber protection and this takes
the form of the 390Ω and 470Ω current
feed resistors which are tapped off by
the .033µF 250VAC capacitor.
One of the drawbacks of this type
of dimmer circuit is the very fast
switching of the Triac. This produces switching transients which range
up to 30MHz or more, resulting in
a buzz
ing sound when received by
radios. To eliminate this problem, RF
suppression is provided by inductor
L1 which is in series with the load
socket, together with the 0.1µF capacitor across the load. L1 and the 0.1µF
capacitor comprise a low pass filter
which is a very effective at reducing
the amount of radiated interference.
Note that a critical aspect of L1 is
that it is wound onto an iron powder
toroid. This gives an inductor with a
relatively low Q-factor, ensuring that
oscillations caused by the fast switching of the Triac are well damped.
Construction
The specified Triac is an insulated tab device which is mounted directly to
the case for good heatsinking. Note the plastic cable tie which secures the
interference suppression toroid (L1) to the PC board.
The new dimmer is housed in a
diecast aluminium case meas
uring
171 x 120 x 55mm, as noted above.
Most of the circuitry is mounted on a
PC board measuring 96 x 79mm and
coded 10107941. This also has the
transformer mounted on it, as can be
seen in the component overlay diagram of Fig.3. Note that this is slightly
August 1994 29
This inside photo shows all the wiring, including the wired remote control
facility. Note that there are slight differences between the board in this photo
and the diagram of Fig.3.
different from the PC board shown in
the photos.
Before you begin any soldering,
check the board thoroughly for any
shorts or breaks in the copper tracks.
These should be repaired with a small
artwork knife or a touch of the soldering iron where appropriate.
Mount the diodes, resistors and
wire links first. Note that one row
of resistors is installed “end on” to
save board space. You can use the
clipped off resistor leads for the wire
links. Now mount the 3AG fuse clips,
the capacitors and the two trimpots.
Note that VR2 is 10kΩ while VR3 is
50kΩ; don’t inadvertently swap them
around. This done mount the transistor and the integrated circuits and
make sure you install them with the
correct orientation which is shown by
the notch at the pin 1 end.
Fig.8: this is the full size etching pattern for the PC board.
30 Silicon Chip
The transformer is bolted to the
board using screws, nuts and lock
washers and then its primary and
secondary leads are soldered in.
Note that the secondary wires are
not depicted on the overlay diagram
of Fig.3 but they are shown on the
wiring diagram of Fig.4. This was
done for clarity.
The iron powder toroid (Philips
4330 030 60271) is wound with 19
turns of 1mm diameter enamelled
copper wire. Strip the wire ends for
soldering and space the turns evenly
around the core. When soldered to the
board, secure the toroid with a Nylon
cable tie – see photos.
Finally, you can mount the 3-terminal regulator and the Triac. The regulator is mounted on top of the board in
the conventional way while the Triac
leads are soldered to the underside of
the board so that its metal tab can be
bolted to the floor of the diecast case.
Case assembly
At the time of writing this article
we do not know whether kits will be
offered with pre-punched metalwork.
If not, there will be quite a lot of drilling and filing to be done to prepare
the case. You will need to drill and
cut the holes for mounting the board,
3-terminal regulator and Triac, the
Earth solder lug, the 2-way insulated
terminal block for the mains cable,
the hole for the cordgrip grommet,
the flush-mount mains socket and the
dimmer potentiometer.
Note that all screw holes in the underside of the case and the lid should
be countersunk. Four adhesive rubber
feet should be fitted to the bottom
of the case to avoid scratching table
surfaces.
The slider requires a slot 2mm wide
and 50mm long. As well, if you require
the optional remote facility, you will
also need to drill or punch holes for
the XLR socket and switch. The front
panel artwork shown in Fig.9 shows
how the front panel components are
laid out. Use a photocopy of the artwork as a drilling template.
The PC board is mounted on four
6mm pillars on the base of the case.
Before installing it, you should attach
the 250VAC 10A rated hook-up wires
which will connect to the AC socket
and to the insulated terminal block.
Use brown for the Active lead and
Blue for Neutral.
Having mounted the board, the
The 3-terminal regulator (REG1) is heatsinked by bolting it directly to one end
of the case. Do not use an insulating washer here, as the tab of the regulator
actually grounds the low voltage side of the circuit to the case.
3-terminal regulator and Triac can be
bolted to the case. Note that the metal
surface must be smooth and free of
metal swarf. Use a light smear of heatsink compound under the metal tab to
improve heat transfer. Note that mica
washers are not required for either of
these semiconductor devices. In fact,
the tab of the 3-terminal regulator
actually grounds the low voltage side
of the circuit to the case. The specified
Triac, on the other hand, is an insulated tab device, so no mica insulation
kit required.
The mains cable should be secured
in the case with a cordgrip grommet
and its yellow/green wire should be
attached to the earth solder lug. An
earth wire from the mains socket runs
to the same solder lug.
All the wires to the lid of the case
are run as a multi-strand (rainbow)
cable to the 7-pin header socket on the
PC board. If you require the optional
remote facility, you will need to wire
the front panel as shown in the diagram of Fig.5.
The header plug comes un-assem
bled as the plastic shroud together
with a strip of pins. Carefully strip
back and tin seven strands of a 150mm
length of rainbow cable. With the pins
still attached as a strip, crimp each pin
onto the tinned wires before soldering.
The pins can then be separated from
the strip and pushed into the plastic
shroud. Push until the locking spring
on each pin becomes seated in the
header. Once assembled, the rainbow
cable can be wired to the front panel
components.
When all the wiring is complete,
check your work carefully against
the circuit of Fig.1 and the wiring
diagrams of Figs.3 & 4. Now you
are ready to apply power but do not
local
remote input
remote
Max. load 2400W Fuse rating 10A (inside case)
DANGER 240 VOLTS AC INSIDE
lighting dimmer
Fig.9: full size artwork for the front panel.
August 1994 31
PARTS LIST
1 PC board, code 10107941, 96
x 79mm
1 sealed diecast aluminium case,
171 x 121 x 55mm
1 Philips toroid, Part No. 4330 030
60271
1 M2854 24V CT transformer
1 Clipsal 10A flush mount GPO
socket
1 7-way single-in-line PCB header
& socket (0.1-inch spacing)
1 female 3-pin XLR socket
1 SPDT round rocker switch
1 black slider pot knob
1 LED mounting bezel
1 self-adhesive front panel
1 earth lug
1 terminal block
4 adhesive rubber feet
1 1-metre length 1mm diameter
enamelled copper wire
1 150mm-length 7-way rainbow
cable
1 cordgrip grommet for mains
cable
1 10A 240V AC 3-core mains
cable & moulded plug
2 PCB mount 3AG fuse clips
1 10A 3AG fuse
9 3mm dia. x 10mm countersunk
machine screws
3 3mm dia. x 25mm countersunk
machine screws
12 3mm hex nuts & washers
4 6mm standoffs
1 50kΩ linear slider pot (60mm
travel) (VR1)
1 10kΩ horizontal trimpot (VR2)
connect a load at this stage. Fit the 10amp fuse, put the lid on the case and
apply power. Move the slider up and
down and observe the LED. It should
brighten and dim in accordance with
the control setting. If that happens,
you are practically finished apart from
setting the minimum and maximum
brightness settings. To do this, you
must connect a lamp load of 40 watts
or more and take the lid off the case
to do the adjustments.
Warning: this circuit is potentially
lethal due to the presence of 240VAC
on the Triac and associated components.
With the power on, set the dimmer
pot to the minimum setting and adjust
trimpot VR2 so that the lamp filament
32 Silicon Chip
1 50kΩ horizontal trimpot (VR3)
Semiconductors
1 40106 hex Schmitt inverter (IC1)
1 LM324 quad op amp (IC2)
1 MOC3021 (IC3)
1 BTA41A Triac (TR1)
1 BC547 NPN transistor (Q1)
2 1N914 diodes (D1,D2)
2 1N4004 diodes (D3,D4)
1 10V 400mW or 1W zener diode
(ZD1)
1 7815 15V regulator (REG1)
1 DB104 bridge rectifier (BR1)
1 5mm red LED (LED1)
Capacitors
1 100µF 50VW electrolytic
1 10µF 25VW electrolytic
2 0.1µF MKT polyester
2 0.1µF 250VAC metallised
polycarbonate (0.4-inch lead
spacing)
1 .033µF 250VAC metallised
polycarbonate (0.4-inch lead
spacing)
Resistors (0.25W,1%)
1 820kΩ
1 680Ω
4 100kΩ
1 470Ω
4 10kΩ
1 390Ω
1 5.6kΩ
1 220Ω
2 4.7kΩ
1 100Ω
1 2.2kΩ
1 22Ω 1W
2 1kΩ
Scope photo 1 – ramp generator
waveforms: top, waveform at pin
8 of IC1a; bottom, waveform at the
collector of Q1.
Scope photo 2 – comparator wave
forms: top, waveform at pin 8 of IC2a;
bottom, waveform from pin 14 of
IC2c.
Miscellaneous
Heatsink compound, cable ties
is at red heat. Now set the dimmer
control to its maximum setting and
adjust VR3 so that the lamp just gets
to maximum brightness when VR1 is
brought to its maximum. The settings
of VR2 and VR3 will then have to be
repeated because they do interact.
Finally, attach the lid to the case and
you are finished.
What if it doesn’t work? The first
point to check is the DC voltage as
marked on parts of the circuit of Fig.1.
You can use the case as the negative
connection point for your multimeter.
Note that the DC output of IC2d should
vary in response to the setting of the
potentiometer VR1. If you have an
oscilloscope, you can check for the
presence of the waveforms shown in
Scope photo 3 – Triac waveforms: top,
waveform at A2 of the Triac; bottom,
waveform at pin 2 of IC3. Note that
the mains waveform is flattened due
to external causes.
the accompanying scope photographs
If not, you can still check for the
presence of trigger pulses at the outputs of IC2c, IC2d and the paralleled
outputs of IC1. This can be done because your multimeter can measure
the average DC level of the pulses. At
maximum setting, the pulsed DC output will measure close to +15V while
at minimum it should be close to 0V.
Failing that, check your soldering very
carefully. The main cause of failure in
SC
projects is bad soldering.
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
A microprocessor
controlled Morse keyer
Here is a state-of-the-art Morse keyer which
you can use to polish up your sending. It has
a relay to control the keying of the transmitter
& a loudspeaker so that you can listen to your
sending. It also has a memory so that you can
store a Morse message up to 64 characters long.
Design by ALAEXANDRE ZATSEPIN
It may seem like a contradiction
in terms to have a “state-of-the-art”
microprocessor controlled Morse
keyer. After all, Morse code is the
oldest method of sending messages
over the air or along wires (telegraph)
and many people probably think it is
obsolete. However, without joining
that debate and whether Morse should
be used by amateur radio operators,
this microprocessor controlled keyer
is an elegant device to send your code.
In fact, our photo shows it combined
with an equally elegant Morse paddle;
a highly desirable item to those who
delight in CW (continuous wave)
transmissions.
Perhaps we should briefly mention
that Morse code actually preceded radio transmissions by almost 50 years.
Samual Morse patented his telegraph
system in 1840 and it was not until
1898 that Guglielmo Marconi sent the
first paid radiogram from the Isle of
Wight. Even today, Morse code is used
for radio messages and it is a method
which can succeed in very difficult
transmission conditions where other
more up-to-date methods fail.
The Morse keyer is mounted on a
small PC board which carries a Z8
microprocessor, a non-volatile mem
ory chip, a miniature relay and not
much else. The paddle is connected
to a 4-way connector while the loudspeaker and relay output connections
are made via 2-pin headers. A 2.1mm
DC socket provides the power connection which can be to a 9V battery or to
a 9V DC plugpack adaptor.
Three buttons on the board control
recording, speed and tone, while a
August 1994 37
9x3.3k RESISTOR
ARRAY
P1
DOT
2
1
PADDLE
+5V
1
430
3
4
5
6
7
2
8
9 15
16
3
DASH
TONE
S1
17
18
5
8
VCC
P00
P22
P23
P02
5
D
VIEWED FROM BELOW
12
100
Q1
VN0106
D
G
S
13
2
P25
3
P26
4
P27
QIN
Q
OUT P31 P32 P33 GND
7 X1
6
8
9
10 14
4MHz
G
O
P01
IC1
Z86E08
11
K
4
D0
IC2 D1 3
93C46N SK 2
1
CS
GND
I
LED1
STATUS
P21
+5V
PLAY
S3
8
A
VCC
P20
1 P24
SPEED
S2
G
P3
S
A
K
100pF
9VDC
INPUT
P4
100pF
RLY1
1
Q2
VN0106
D
G
S
D1
1N4002
REG1
LM293-5
IN
100
16VW
P2
2
GND
OUT
+5V
100
16VW
MORSE KEYER
Fig.1: the circuit is based on pre-programmed microcontroller IC1 (Z86E08) &
non-volatile memory IC2. The non-volatile memory stores the message, tone,
speed & cyclic redundancy code (CRC).
setting is stored in the memory buffer
upon release of the key.
LED indicates one of three possible
states of the keyer. If power is applied
and the LED is off, this indicates that
the speed and tone settings are from
the last operation and that there are
no messages stored in the non-volatile memory. In this state, the keyer
is in operating mode as described
below.
If the LED is on after power up,
the speed and tone settings are from
the last operation and there is a valid
message in the memory.
If the LED flashes after power up, the
information in memory is invalid and
is random. This condition may occur
the first time the unit is powered up
or if the non-volatile memory has been
changed. To enter the operating mode,
simply push the paddle key to the left
or right; dot to the right and dash to
the left, for example. The LED will stop
flashing as soon as the key is operated
and upon releasing the key, the circuit
will enter the operating mode with
a default speed of 70 characters per
minute and a 1kHz tone (delivered via
the loudspeaker).
The relay operates in tandem with
the loudspeaker.
Record mode
Sending speed
To alter the sending speed, you press
and hold down the SPEED button. To
increase the speed, push the paddle
38 Silicon Chip
key to the DOT position; to decrease
the speed, push the paddle key to the
DASH position. The Speed setting is
stored in the non-volatile memory
upon release of the key.
To vary the tone from the loudspeaker, you press and hold down the TONE
button and then push the paddle key
to the DOT position to raise the frequency and to the DASH position to
lower the frequency. Again, the Tone
SPEAKER
P3
Q1
BATTERY
P3
100uF
100
100uF
1
D1
KEY
P2
DOT
2x100pF
Q2
PLAY
S3
K
Playback mode
430
X1
RELAY 1
REG1
IC1
Z86E08
1
GND
SPEED
S2
3.3k
RES
ARRAY
1
DASH
IC2
936C46N
TONE
S1
The record mode allows you to store
up to 64 characters in the memory.
To enter the RECORD mode, press the
SPEED and TONE buttons together.
This will erase the existing message
and the new message characters are
loaded into the memory buffer. Pauses
between characters are automatically set to one dash. Upon re
ceiving
64 characters, the RECORD mode is
terminated and after approximately
0.1 second, the keyer reverts to the
normal operating mode. To terminate
the RECORD mode without entering
all 64 characters, you press the PLAY
button. After 0.1 second, the speaker
will beep and the unit will revert to
the normal operating mode.
After a message is stored, the LED
will be on.
A
LED1
P1
Fig.2: install the parts on the PC board
as shown here. Note particularly the
orientation of the three switches.
This is simple; just press the PLAY
button. Any message in the buffer will
start to play at the current speed and
tone until the message is complete. To
stop the message playback, you push
the paddle key to either side.
Circuit description
The main element of the keyer is a
Z86E08 microcontroller (IC1). This device incorporates a one-time programmable read-only memory (OTP ROM)
PARTS LIST
1 PC board, 70 x 45mm
1 4MHz crystal (X1)
1 DIL relay (RLY1)
1 miniature 8-ohm loudspeaker
3 momentary contact PC-mount
pushbutton switches
1 4-way PC mount male socket
(P1)
2 2-pin headers and matching
plugs (P2,P3)
1 2.1mm DC socket (P4)
Semiconductors
1 Z86E08 programmed microcontroller (IC1)
1 93C46N non-volatile memory
(IC2)
1 LM293-5 5V regulator (REG1)
2 VN0106 FETs (Q1, Q2)
1 green LED (LED1)
1 1N4002 rectifier diode (D1)
which is loaded with the software. The
Z86E08 has 14 input/output lines. Five
are programmed as inputs (P20-P24),
five are programmed as outputs (P26,
P27, P00, P01 & P02) and one (P25) is
programmed as bidirectional. Three
of the input lines (P31, P32 & P33)
are grounded.
The internal oscillator of the micro
controller runs at 4MHz, as set by the
crystal connected to pins 6 & 7. A
Capacitors
2 100µF 16VW electrolytic
2 100pF ceramic
Resistors
1 9 x 3.3kΩ resistor array
1 430Ω 0.25W resistor
1 100Ω 0.25W resistor
Kit availability
A complete kit for the Morse Keyer
is available from FLC Microdesign
Pty Ltd, 28 Haughton Rd, Oakleigh,
Vic 3166. Phone (03)563 3096; Fax
(03) 563 3017. Payment may be
made by cheque or postal money
order. Pricing is as follows:
Complete kit (does not include
DC plugpack) .....................$45.00
Optional DC plugpack ........$10.00
Postage & packing .............$10.00
9-way resistor network pulls all the
inputs to +5V and when any of the
buttons is pushed, the respective input
is pulled to 0V. Of the three outputs,
P00 drives the LED directly, P01 drives
the loudspeaker via FET Q1, and P02
drives RLY1 via FET Q2.
The non-volatile memory (IC2)
(93C46N) has 1024 bits organised as
64 x 16. It stores the message, tone,
speed and cyclic redundancy code
(CRC) in the absence of power. CRC
is used for error detection, to prevent
wrong messages, speeds or tones being
accepted.
Power is supplied via the DC input
socket and then through the protective
diode D1 to voltage regulator REG1
to provide the +5V supply rail. The
total current consumption is less than
25mA with the optional relay.
Assembly
Construction of the Morse keyer is
very straightforward since it is such
a small board with few components.
The PC board measures 70 x 45mm.
Mount all the small components
first, such as the diode, the voltage
regulator, resistors, the two FETs and
the capacitors. Make sure that these
components are correctly polarised
or oriented. This done, mount the
two header sockets, the DC socket, the
4-way socket for the paddle keyer and
the three button switches. Finally, you
can mount the microcontroller (IC1),
the memory chip (IC2) and the relay.
After you have checked all your
work carefully, you can apply power
and check voltages on the board. The
output of the 3-terminal regulator
should be at +5V and this voltage
should also be present at pin 5 of IC1
and pin 8 of IC2, as well as pin 1 of
the resistor array.
This being the case, connect a loudspeaker and a paddle and you can send
SC
Morse code.
August 1994 39
Dual diversity tuner for
FM microphones; Pt.1
Plagued by signal dropouts from FM wireless
microphones? This Dual Diversity Tuner
automatically selects the best signal from two
antennas to ensure a drop-out free reception.
By JOHN CLARKE
FM wireless microphones are now
commonly used for stage and public
address work. They have the obvious
benefit of allowing the performers (or
speaker) to roam about the stage without being tied to a microphone cord.
In its most basic form, an FM wireless microphone setup consists of
a small FM transmitter (to transmit
the signal from the microphone), a
receiving antenna and a companion
FM receiver. The receiver picks up
the signals from the transmitter and
feeds the demodulated signal to the
stage amplifier or PA system.
At least, that’s the way it’s supposed
to work in theory. Unfortunately, this
type of system is often plagued by
bursts of noise due to signal drop-outs
40 Silicon Chip
as the performer moves about on stage.
That’s because the received signal
strength can vary quite markedly as
the wireless microphone moves from
one position to another.
These signal strength variations are
caused both by ob
structions in the
signal path between the transmitter
and the receiving antenna and by
nulls due to signal reflections from
various objects in the room. The most
obvious sources of obstruction are the
performers’ bodies and other on-stage
objects, with metallic objects causing
the greatest problems (depending on
size). Careful siting of the receiving
antenna can help to mini
mise this
problem but the results are often far
from satisfactory.
The best way to dramatically improve reception is to use two receiving antennas which are separated by
several wavelengths. In this situation,
the signal is usually good in at least
one antenna and, by using a receiver
which can automatically choose the
best signal, good reception can be
maintained for virtually 100% of the
time. This type of tuner is called a
“diversity tuner”.
While commercial diversity tuners
are available, they are generally quite
expensive. As a result, this design
should appeal to those capable of
building their own equipment. It
will cost considerably less than a
commercial unit but provides similar
performance.
The design is also easy to build
and requires no special equipment
for alignment, so you shouldn’t have
any problems on that score. It can
be used with any standard wireless
microphone which operates in the
commercial FM band (88-108MHz);
eg, the microphone FM transmitter
published in SILICON CHIP in October
1993. Alternatively, you can use one of
the readily-available commercial FM
wireless microphones.
As can be seen in the photographs,
the circuitry is housed in a slimline
rack mounting case. On the front panel
are a 10-LED signal strength bargraph,
two LED indicators to show the active
antenna (either A or B), a test switch
to enable manual selection of either
antenna, an audio level output control,
and a power switch. The rear panel
carries two 75Ω PAL sockets for the
antennas, an RCA output socket (audio
out) and a fuseholder. The audio output connects to your mixer or power
amplifier.
Performance
Fig.1 and the accompanying specifications panel show that the FM
tuner is an excellent performer. As
shown, the sensitivity is very good,
with -3dB limiting occurring with an
input RF level of just 1.3µV, while
the signal-to-noise ratio reaches 60dB
at just 7µV input and is an excellent
75dB at 100µV. These figures ensure
a good-quality, low-noise signal for a
wide range of RF signal inputs.
Note that the signal meter levels are
useful for showing the relative noise
level from the FM tuner. At level 5, the
tuner has reached ultimate quieting
(75dB), while at signal level 2, the
signal to noise ratio is 60dB. At level
10, the AGC is coming into effect to
prevent overload.
While this tuner performs equally
as well as a commercial hifi tuner, it
differs in that it requires two antennas
and has fixed tuning. And, of course,
it only provides for mono reception.
The two antennas connect to the
tuner via shielded RF cables and
should be mounted several wavelengths apart. If the signal from the
wireless microphone deteriorates in
the active receiving antenna, the tuner
automatically switches to the other
antenna in an effort to maintain signal
quality. It does this according to one
of three modes of operation.
• The first mode occurs when a
good signal is always available from
at least one antenna. In this mode, the
tuner only switches between the two
antennas when the signal level in the
active antenna drops below a preset
threshold. Provided that the signal
level in the active antenna is above this
threshold, then this antenna remains
selected regardless of their relative
signal strengths.
If, however, the signal strength in
the active antenna drops below the
threshold, the second antenna is
selected. This antenna now remains
selected until its signal drops below
the threshold, at which point the first
antenna is selected again, and so the
process continues.
The preset threshold, by the way,
is the signal strength at which the
signal-to-noise ratio has reached its
maximum. Fairly obviously, it is unnecessary to switch antennas in this
situation.
• The second mode of operation
occurs when both antennas provide
signal strengths below the threshold.
In this situation, the tuner selects the
antenna that provides the best signal
strength but that’s not all it does. At
intervals of about one second, it also
briefly switches to the other antenna
to check its signal strength. If it’s lower
than the active antenna, it quickly
switches back again but if it’s higher,
it stays there and briefly monitors the
previous antenna at regular intervals.
This constant switching between
antennas does cause a slight distur-
Main Features
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•
•
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•
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•
•
Dual antenna inputs
Fixed tuning – can be set anywhere in FM broadcast band (88-108MHz)
Low distortion
Excellent signal-to-noise ratio
High sensitivity
Typical open air range of 60 metres with dipole antennas
10-LED bargraph display for signal strength indication
Active antenna indicator LEDs
Test switch to manually select alternative antenna (useful for setting up)
Adjustable audio level output
AGC to prevent overloading of tuner input
Three modes of antenna switching to minimise antenna switching
disturbances
Automatic muting if poor signals received from both antennas to
minimise noise
50µs de-emphasis (can be easily altered to 75µs)
August 1994 41
10
+10
AUDIO
9
-10
8
-20
7
-30
6
-40
5
MUTE
THRESHOLD
-50
4
-60
3
-70
2
-80
-90
AGC SET POINT
1
'S' METER
AUDIO OUTPUT (dB)
0
10
100
RF LEVEL AT 98MHz (uV)
1k
1
0
10k
Fig.1: this graph shows the performance of the FM tuner front end. The sensitivity is very good, with -3dB
limiting occurring at an RF input level of just 1.3µV, while the signal-to-noise ratio reaches 60dB at just 7µV
input & is an excellent 75dB at 100µV.
ANTENNA
'A'
FM TUNER
ANTENNA
'B'
IF OUTPUT 'A'
SIGNAL STRENGTH
DECISION
CIRCUIT
SIGNAL STRENGTH
FM TUNER
CONTROL
COMBINER
IF
DEMODULATOR
AUDIO
OUTPUT
IF OUTPUT 'B'
TRADITIONAL DUAL DIVERSITY TUNER
Fig.2: most dual diversity tuners use two FM tuner front ends to receive signals
from separate antennas. The signal strength in each tuner is monitored by a
decision circuit & this controls a combiner circuit so that the best signal from
the FM tuner outputs is fed through to the demodulator. This scheme works well
but the need for two FM tuner stages adds to the cost.
ANTENNA
'A'
FM TUNER
ANTENNA
'B'
IF
DEMODULATOR
AUDIO
OUTPUT
SIGNAL
STRENGTH
ANTENNA
SWITCH
CONTROL
DECISION
CIRCUIT
SILICON CHIP DUAL DIVERSITY TUNER
Fig.3: the SILICON CHIP Dual Diversity Tuner differs from the
traditional approach by using a single FM tuner stage & an antenna
switch to select between the two antennas. In this case, the decision
circuit monitors the signal strength in the FM tuner & controls the
antenna switch to ensure that the best signal is selected.
42 Silicon Chip
bance in the audio signal but this is
barely noticeable, particularly as the
signal is already down in the noise.
Of course, if the signal strength in one
antenna rises above the threshold,
then the tuner will maintain selection of that antenna until the signal
drops again.
• The third mode of operation occurs when the signal strength is very
poor from both antennas. In this case,
the audio is muted to prevent noise.
The tuner then continuously assesses
the signal strength in each antenna
and, when one rises above the preset
minimum, it immediately locks onto
that antenna and releases the muting.
Normally, the first mode is the
one that operates since, with correct
antenna arrangement, the signal can
be expected to be good in at least one
antenna virtually all of the time. Under
these circumstances, the switching
action will be inaudible. If due care is
taken with antenna siting, the second
and third modes should operate rarely
(if at all).
Basic arrangement
Fig.2 shows the traditional arrangement of a dual diversity tuner. It uses
two receiving antennas, with each
antenna feeding a separate FM tuner.
The signal strength from each tuner is
monitored by a decision circuit which
then controls a combiner stage.
ANTENNA
'A'
SIGNAL
LEVEL
AGC
CONTROL
IC1
ANTENNA
'B'
AUDIO
ANTENNA
SWITCHER
D1-D4
IF FILTER
T2, X1
MIXER
IC1
Q1
RF
AMPLIFIER
IF FILTER
X2
IC1
IF AMPLIFIER
AND LIMITER
10.7MHz
IF AMPLIFIER
LOCAL
OSCILLATOR
IC1, T1, D5
IC1
DEMODULATOR
IC2, L10
AUDIO
OUT
MUTE
IC7
AMPLIFIER
IC6, VR3
AFC CONTROL
MUTE COMPARATOR
IC5a, VR2
'A'
'B'
SIGNAL
LEVEL
INDICATORS
LED11, LED12,
IC8e,IC8f
BUFFER
IC4a
LED1
LED10
VREF
CONTROL
MINIMUM
SIGNAL
COMPARATOR
IC5b, VR3
ANTENNA
R SWITCHING
OSCILLATOR
IC9
CE
D-A CK
CONVERTER
IC11
R
SIGNAL LEVEL INDICATOR
IC3
ANTENNA
SWITCHING
LATCH
IC10a
MANUAL
IC10b, S2
'0' OUT
R
TIMER
IC12
Fig.4: this is the complete block diagram of the SILICON CHIP Dual Diversity
Tuner. The signal level generated by the IF amplifier stage in the FM tuner (top
of diagram) is monitored by comparators IC5a & IC5b & these then control the
antenna switching logic (IC9-IC12).
There are various ways of combining
the IF signals from the two tuners.
One way is to simply select the largest
signal, while another method involves
adding the two outputs together. A
third method involves adding the
outputs according to a weighting determined by the signal-to-noise ratio
of each IF signal. The first method is
the easiest and is the one most commonly used.
Following the combiner stage, the
resulting IF signal is demodulated to
produce an audio output.
The main drawback of this approach
is that it requires two tuners and this
adds to the cost. It also presents problems as far as the design is concerned,
since each tuner must be able to lock
onto the signal without being affected
by the other’s local oscillator. This
problem is usually cured by shielding
each tuner in a separate metal case or
by using a common local oscillator.
By contrast, the SILICON CHIP Dual
Diversity Tuner uses an entirely different approach that makes do with
just one FM tuner stage – see Fig.3.
In this design, the signals from the
two antennas are fed to the tuner via
an antenna switch. Only one antenna
is selected at a time and a decision
circuit, which monitors the signal
strength from the FM tuner, selects
the antenna which will provide the
best results.
The main advantage of this approach is that it eliminates the second
tuner, thereby reducing the cost and
simplifying construction. Only a few
extra parts are needed for the antenna
switch, although the decision circuit
is slightly more complicated than in
the previous case.
Block diagram
Refer now to Fig.4 – this shows
the full block diagram for the Dual
Diversity Tuner. The antenna switch,
FM tuner and demodulator make up
the top half of the diagram, while the
decision circuit occupies the bottom
half.
The antenna switcher uses low capacitance VHF diodes D1-D4 to switch
the antennas and the selected antenna
signal is amplified by tuned RF amplifier stage Q1. This amplifier has AGC
(automatic gain control) applied to it,
the AGC level being set by the signal
level from IF amplifier stage IC1 and
by the signal level from the output of
the RF amplifier itself.
Nominally, the AGC only comes into
effect when the RF signal is greater
than 10mV. Its job is to prevent overload by reducing the gain of the RF
amplifier at high signal levels.
Following the RF amplifier, the signal is fed to balanced mixer stage IC1
where it is mixed with the local oscillator signal. This local oscillator stage
(IC1, T1 & D5) operates at a frequency
that’s nominally 10.7MHz below the
RF signal. As a result, the mixer stage
converts the incoming RF signal to a
10.7MHz FM signal (plus other sum
and difference signals).
This 10.7MHz signal is now filtered
(T2, X1), amplified and filtered again
August 1994 43
44 Silicon Chip
.01
.01
D1
BA482
.01
.033
220k
3.3k
10
2.2k
2.2k
.01
+12V
2.7k
K
A
7
14
6
5
6
8
K
4
7
4
4.7k
10
2.2k
L4
L5
X2
10.7MHz
.01
2.7k
0.1
IF AMPLIFIER AND
DEMODULATOR
0.1
2.2k
D4
BA482
.01
.01
ANTENNA B
D3
BA482
IC8f
.01
A
IC4a
LM358
2.7k
3
+12V
.01
L3
.01
ANTENNA
A
LED11
RED
TP1
IC8e
74C14
5
.01
ANTENNA
B
LED12
GREEN
L1
L2
D2 .01
BA482
ANTENNA A
2
3
L6
10
8
IC5b
LM393
0.1
0.1
300W
0.1
.01
1
47
16VW
16
17
15
2
1
390
10k
0.1
L10
IC2
TDA1576
4
560pF
1
6
750
L8
27pF
6
13
IC8a
5
7
ANTENNA
SWITCHING
TIMER
12
0.1
4
33pF
10
5V
11 SIG
12 14
METER
ZERO
VR1 10k
33pF
3
.01
S
.001
.001
G1
D
L7
Q1
BF981
.001
G2
+12V
.001
10
.001
10
0.1
1.2M
220k
VC1
8.550pF
RF PREAMPLIFIER
+12V
8
13
10
1
IC9
7555
18
2
22k
.018
6
3
.001
10
IC8b
3.9k
0.33
3
2
11
10
11
10
5
5 4V
REF
9
LO
OUT
6
13
14
16
0.1
T1
6
15pF
MIXER AND IF FILTER
2
3
4
4
47
3
390pF
X1 10.7MHz
3.9pF
390pF
5
1
T2
D5
BB119
33pF
2
.01
.01
100k
10
1
8
16
D7
1N4148
1.5k
1.5k
17
18
7
10k
6
14
13
2
12
4
11
3
5
ANTENNA
SWITCHING
OUTPUT
1
D IC10aQ
4013 2
CK
Q
S
R
6
4
10
SIGNAL STRENGTH METER
IC3
LM3914
15
3
9
0.1
LED LED LED LED LED LED LED LED LED LED 82
1
2
3
4
5
6
7
8
9 10 5W
11 10 12
D6
1N4148
4
17
7
LO
AGC 8
IN
IC1
TDA1574
15
18 AGC
OUT
1.8pF
6.8pF
6.8pF
100k
220k
220k
.01
10
+12V
.01
VC2
530pF
.0068
8
9
33pF
L9
33pF
+12V
+12V
+12V
I GO
ANTENNA UPDATE TIMER
2
3
1
0
1
22k
D-A CONVERTER
4.7k
IN
0V
47
16VW
4
S1
CASE
E
N
240VAC
F1
250mA
A
10
10k
10k
10k
10k
+12V
6.3V
T1
M2852
10k
7
5
6
IC6b
8
7
220k
1
0.1
220k
4
IC7
4066
12
14
10
11
6.3V
2
47k
D9-D12
4x1N4004
OUTPUT
LEVEL
VR4
100k
47pF
IC6a
LF353
3
6
IC5a
7
10k
4700
25VW
10
1
MUTE
THRESHOLD
VR2
10k
+12V
5
330k
+12V
GND
REG1
7812
AUDIO
OUTPUT
MINIMUM
SIGNAL
LEVEL
VR3
10k
1
OUT
10k
+12V
4
27k
33k
2
2
3
7
39k
2
IC4b
3
47k
56k
10
1
4
5
IC8c
8
IC11
4017
13
CE
4
1
IC12
R 7555
8
+12V
15
R
16
CK
14
10k
10k
2
10
100k
10k
6
3
+12V
0.1
D8
1N4148
D8
1N4048
9
DUAL DIVERSITY FM TUNER
IC8d
0.1
8
S2
ANTENNA
TEST
10k
10k
D
A
K
G2
VIEWED ON
LABEL SIDE
S
D CK
11
9
R
Q
IC10b
S
10
8
G1
7
12
0.1
14
(X2), after which it is applied to a
limiter stage. The limiter restricts the
signal level applied to the following
demodulator stage (IC2, L10) and also
improves the signal-to-noise ratio.
The demodulator converts the FM
IF signal into an audio signal and
provides an automatic frequency control (AFC) line to the local oscillator.
This line is used to control the local
oscillator so that it always oscillates
at a frequency that’s exactly 10.7MHz
less than the tuned RF signal.
Let’s return now to the IF amplifier/
limiter stage. As well as driving the
demodulator, this stage also provides a
signal level output and this is applied
to the signal level indicator (IC3) and
to buffer stage IC4a. As previously
mentioned, the signal level indicator
drives a 10-LED bargraph.
Buffer stage IC4a drives the following mute comparator and minimum
signal comparator stages (IC5a and
IC5b, respectively). In operation, the
mute comparator compares the signal
level with a reference voltage and
controls the mute circuit (IC7) at the
output of the demodulator. When the
signal level is very low (which would
result in considerable noise in the
audio output), the mute comparator
activates the muting circuit so that
no signal is fed to amplifier stage IC6.
The minimum signal comparator
(IC5b) compares the signal level
from IC4a with a voltage set by a D-A
converter (IC11). When a high signal
level is applied to IC5b, the antenna
switching oscillator (IC9) is off and
the output of the D-A converter is at
a maximum.
However, if the signal level drops
below the output from the D-A converter, IC5b’s output toggles and releases the reset on the antenna switching
oscillator. This oscillator now starts
Fig.5 (left): the final circuit uses low
capacitance VHF diodes D1-D4 to
switch the antenna outputs to RF
amplifier stage Q1. IC1 & IC2 form
the heart of the FM tuner, while IC3
& LEDs 1-10 form the signal strength
meter. Depending on the signal
strength, comparator IC5b controls
the antenna switching latch (IC10) via
IC9 to select the appropriate antenna.
IC5b & IC7 mute the audio output if
the signals from both antennas fall
below a preset threshold.
August 1994 45
Specifications
Preset frequency range ������������������������������������� 88-108MHz
Audio output at 75kHz deviation ������������������������ 620mV RMS to 1.7V RMS
(adjustable)
Frequency response into 4.7k٠load ���������������� -0.4dB at 20Hz and 15kHz
Signal-to-noise ratio at 75kHz deviation ������������ 75dB for >100µV RF input
Total harmonic distortion at 50kHz deviation ����� Better than 0.15% at 1kHz
De-emphasis ����������������������������������������������������� 50µs (75µs optional)
RF input at -3dB before limiting (98MHz) ���������� 1.3µV RMS
AM rejection ������������������������������������������������������ Typically 54dB (1kHz, 30%
AM modulation)
Isolation between antennas ������������������������������ 27dB
Antenna switching response time ���������������������� <100µs
and clocks the antenna switching
latch (IC10a) to select the alternative
antenna. If the signal from this antenna is sufficiently high (ie, above the
level from the D-A converter), IC5b
immediately resets the switching oscillator so that the antenna selection
is maintained.
However, if the signal from both
antennas is low, the antenna switching oscillator remains on and the two
antennas (A & B) are alternatively
switched in and out by IC10a at a rapid
rate. During this time, the switching
oscillator also clocks the D-A converter, which reduces its output voltage on
each clock cycle. When this voltage
eventually drops below the signal
level, IC5b stops the antenna switching oscillator and IC10a latches the
currently selected antenna.
At this point, timer IC12 is activated and, after about 1s, resets the D-A
converter so that its output is again at
maximum. As previously described,
the minimum signal comparator (IC5b)
now compares the D-A output with the
signal voltage and so the above process
is repeated indefinitely.
Finally, a manual switching circuit
(IC10b and S2) enables either antenna
to be selected at the press of a switch.
Each time S2 is pressed, the alternative
antenna is selected and this selection
can be maintained by holding the
switch in. This is a useful feature for
testing and setting-up purposes, since
it enables the antennas to be sited for
best signal strength.
Circuit details
Fig.5 shows the final circuit of the
Dual Diversity Tuner. It uses 12 ICs,
46 Silicon Chip
a dual gate Mosfet (Q1), several coils
and numerous minor components to
perform all the functions described
above.
Despite the apparent complexity of
the FM tuner from the block diagram,
it really is quite straightforward. It’s
based on a Philips chip set consisting
of two ICs (IC1 and IC2) and these only
require the addition of suitable coils,
a varicap tuning diode and sundry
minor parts to give a basic high-quality
monophonic FM tuner.
IC1, a TDA1574 Integrated FM
Tuner IC, forms the front end of the
tuner. It contains a balanced mixer,
local oscillator, linear IF amplifier and
AGC circuitry. Its companion, IC2 (a
TDA1576 FM IF Limiter), provides
a limiting IF amplifier, a quadrature
demodulator, AFC output and field
strength indicator output.
An RF amplifier based on dual-gate
Mosfet Q1 increases the sensitivity
by about 28dB. The signal for the RF
amplifier is supplied from either antenna A or antenna B via the antenna
switcher. Let’s take a closer look at
how this switcher works.
Diodes D1-D4, along with coils
L1-L4, form the basis of the antenna
switcher. D1-D4 are actually Philips
Silicon Planar Diodes. These have a
very low capacitance of 0.65pF at a
reverse voltage of 12V, and a forward
resistance of about 0.6Ω at a forward
current of 5mA. These specifications
are for 100-200MHz operation, which
makes them ideal for switching FM
broadcast band antennas.
The DC control lines for the antenna switcher are driven by the Q and
Q-bar outputs of flipflop IC10a via 10Ω
resistors. For example, when Q is at
+12V, Q-bar is at ground. D2 is thus
forward biased via its 2.2kΩ anode
resistor and L2, while D4 is forward
biased via L4 and its 2.2kΩ cathode
resistor. At the same time, D1 and D3
are reverse biased at +12V and are
therefore non-conducting.
In this situation, the signal from
antenna A can pass via D2 and the
associated .01µF capacitors to the
input of the RF amplifier at L5. The
signal from antenna B, however, is
blocked by diode D3 and is instead
shunted to ground via D4 to ensure
maximum isolation from the RF amplifier input.
Conversely, when Q-bar of IC10a
switches to +12V and Q goes to
ground, the situation is reversed.
D1 and D3 are now forward biased,
while D2 and D4 are reverse biased.
The signal from antenna B is now
coupled to the RF amplifier input (via
D3), while the signal from antenna
A is blocked by D2 and shunted to
ground via D1.
Note that all the diodes are AC-coupled using .01µF capacitors. This is
done to isolate the DC voltages which
switch the diodes from the antenna.
Inductors L1-L4 complete the DC paths
through the diodes; they act as short
circuits at DC but provide a high impedance at 100MHz to avoid loading
the antenna signals.
The signal from the antenna switcher is amplified by the RF preamplifier
stage, as described previously. This
stage consists of dual-gate VHF Mosfet
Q1 and inductors L5-L7. L5 inductively couples the signal to L6 which forms
a tuned circuit with trimmer capacitor
VC1. VC1 is adjusted to tune the circuit
to the wireless microphone frequency,
so that out-of-band fre
quencies are
rejected.
The signal at the bottom of L6 is
AC-coupled to ground via a .01µF
capacitor, while the top end of L6
connects to gate G1 of Q1. This gate is
DC biased to 4V from pin 5 of IC1 via
a 220kΩ resistor which also serves to
dampen the very high Q of the L6-VC1
resonant circuit. Note that this line is
decoupled using a .001µF feedthrough
capacitor, two .01µF capacitors and a
10Ω resistor, to shunt any RF signal
to ground.
Gate G2 of Q1 is used as the AGC
input and the control voltage is derived from the AGC output (pin 18)
of IC1 via a 10Ω resistor. The .001µF
Most of the parts for the Dual Diversity Tuner are installed on two PC boards: a
main board & a much smaller board which holds the RF amplifier components.
The full assembly details will be published in Pt.2.
feedthrough capacitor and .001µF
capacitor on either side of the resistor
ensure that RF signal is not fed back
to the AGC pin of IC1.
Normally, the voltage on G2 is
about 10V and this biases Q1 so that
it provides full gain. However, at very
high signal levels, the AGC voltage
goes down. When it drops below 8V,
the gain of Q1 is reduced by about
6dB/volt.
Q1 is connected in a common
source configuration with the amplified signal appearing at its drain.
The quiescent current through Q1 is
set by a 390Ω source resistor and this
is bypassed by a .001µF capacitor to
ensure maximum AC gain. The supply to Q1 (via L7) is filtered using a
10Ω resistor and .001µF feedthrough
capacitor.
The amplified RF signal is fed to
L8 via a 27pF capacitor. L8 then inductively couples this signal into a
tuned circuit consisting of L9, two
33pF capacitors and trimmer VC2. A
220kΩ resistor is connected in parallel
with VC2 to damp out the high Q of
the LC resonance, to make the circuit
easier to align.
Balanced mixer
Following this tuned circuit, the
signal is AC-coupled to the balanced
mixer inputs of IC1 (pins 1 & 2). In
addition, some of the signal is coupled
via a 1.8pF capacitor to pin 3, which
is the wideband input for the AGC
circuit.
The local oscillator inputs are at
pins 7 and 8 of IC1, while the output
appears at pin 6. Its frequency is set
by the tuned circuit formed by the
primary winding of local oscillator
coil T1 (pins 4 & 6), the associated
15pF and 33pF capacitors, and varicap diode D5. The capacitance of D5
is set by a control voltage from the
AFC (automatic frequency control)
output of IC2.
Feedback for the local oscillator is
developed via the secondary winding
between pins 2 and 3 of T1. Note that
the dots on pins 2 and 4 indicate the
winding phase required to obtain
oscillation.
Pins 16 and 17 of IC1 are the balanced mixer outputs and these are
fed to the primary winding of IF
transformer T2. This winding and the
two associated 390pF capacitors form
a 10.7MHz tuned circuit, while the
centre tap of the winding connects to
the +12V supply to provide a load for
the open collector outputs of the mixer.
The secondary of T2, at pins 4 and 5,
drives 10.7MHz ceramic filter (X1) via
a 47Ω resistor. This resistor, together
with the impedance of T2’s secondary,
provides the correct 300Ω load for the
ceramic filter.
Following X1, the signal is fed to
the IF amplifier input at pin 14 of
IC1. The output from this stage then
appears at pin 10 and is further filtered
by 10.7MHz ceramic filter X2 before
being coupled to pin 15 of IC2.
Limiting & demodulation
IC2 includes a 4-stage limiter amplifier which amplifies the signal from X2
and limits the signal once it reaches
about 30µV at the pin 15 input. The
limiter amplifier also provides a signal
strength output voltage at pin 13 and
this voltage is fed to the to the AGC
input (pin 12) of IC1. IC1 monitors
both this narrowband signal level and
the wideband signal level at pin 3
and initiates AGC at its pin 18 output
whenever the signal level exceeds a
predetermined level.
Following the limiter amplifier, the
signal is converted to an audio signal
using a quadrature demodulator. Inductor L10 across pins 4 and 6 forms
the quadrature coil and this is driven
from pins 3 and 7 via 33pF capacitors.
The 560pF capacitor across the quad
rature coil provides tuning, while the
parallel 750Ω resistor damps the Q
to ensure minimum distortion in the
recovered audio signal.
The resulting audio outputs appear
at pins 8 and 9 of IC2 and are identical
except that they are 180 degrees out of
phase. Note that a .0068µF capacitor
is wired between pin 8 and 9 to provide the required 50µs de-emphasis,
to compensate for the pre-emphasis
in the wireless microphone. If the
wireless microphone has a 75µs
pre-emphasis, this capacitor should
be changed to .01µF.
August 1994 47
Both audio outputs have a DC offset
of 5.5-9.8V, the exact value depending
on the frequency of the local oscillator. As previously mentioned, the DC
output at pin 9 is used to provide AFC
for the local oscillator by applying the
offset voltage to varicap diode D5. This
voltage is applied to D5 via two series
100kΩ resistors, while the associated
0.33µF and .01µF capacitors filter out
unwanted RF and audio signals from
this line.
As well as driving the AGC input
of IC1, the signal strength voltage at
pin 13 of IC2 is also fed to pin 5 of
IC3, an LM3914 linear dot/bar LED
driver. This device, in company with
a 10-LED bargraph display, forms the
signal strength meter.
Inside IC3 is a string of 10 comparators and a voltage reference. As
the signal level rises, these internal
comparators progressively switch
their outputs low to light the corresponding LEDs. The two 1.5kΩ
resistors set the LED brightness and
the display range.
Note that the supply to IC3 is decoupled using a 0.1µF capacitor, while
the supply to the LEDs is decoupled
using a 10µF capacitor and an 82Ω 5W
resistor. This resistor ensures that most
of the power dissipation takes place
outside the IC so that its ratings are
not exceeded.
Audio muting
The signal strength voltage at pin
13 of IC2 is also filtered using a 3.3kΩ
resistor and a .033µF capacitor and
applied to unity gain op amp IC4a.
The output from this buffer stage then
drives pin 5 of mute threshold comparator IC5a and pin 3 of minimum
signal level comparator IC5b.
IC5a compares the signal level on
its pin 5 input with a preset voltage
from VR2. In practice, VR2 is set so
that the output from IC5b is normally
high. This high output closes CMOS
analog switch IC7 so that the audio
signal from pin 8 of IC2 is fed to IC6a.
However, if the signal level falls below
the threshold set by VR2, pin 7 of IC5a
goes low and IC7 opens to mute the
audio signal.
IC6a is the output audio amplifier.
It is wired in non-inverting mode and
its gain can be varied from 5.7 to 15.7
using VR4. The 47pF capacitor in the
feedback path reduces high frequency
noise in the audio output.
Pin 2 of IC6a is biased at half supply
48 Silicon Chip
using buffer stage IC6b. This stage is
itself biased at half supply using two
10kΩ resistors, while the 10µF capacitor at the non-inverting input provides
decoupling.
Antenna switching
IC5b (the minimum signal level
comparator) has two control functions.
First, it controls the clock enable (CE)
input of D-A converter IC11. Second, it
controls antenna switching oscillator
IC9 via inverter IC8a.
If the signal level on pin 3 of IC5b is
greater than the level set by VR3 on pin
2, pin 1 of the comparator will be high.
IC9’s reset input will thus be low and
so this oscillator (a 7555 timer) will
be off. At the same time, the high on
CE of IC11 will also prevent clocking
of this counter. In practice, this means
that the currently selected antenna
will be maintained.
However, if the signal level drops
below the threshold set by VR3, IC5b’s
output switches low and releases the
reset on IC9. When this happens, pin
3 of IC9 immediately goes high and
clocks IC10a, a 4013 D-type flipflop,
which toggles its Q and Q-bar outputs.
These outputs, in turn, control the antenna switcher (D1-D4) in the manner
described previously. They also drive
inverter stages IC8e and IC8f which
activate the antenna LED indicators
(LEDs 11 & 12) to show which antenna
has been selected.
If the signal level from the new
antenna is now higher than the reference voltage set by VR3, IC5b’s output
immediately goes high again and IC9
is held reset to maintain the selection.
However, if the signal level is lower
than the threshold, IC9 will continue
clocking IC10a and so the antennas
will be alternately switched at about
2.8kHz (ie, once about every 360µs).
Each time an antenna is selected,
IC9 clocks decade counter IC11 via
inverter IC8b (ie, IC11 is clocked at
2.8kHz). As shown on Fig.5, IC11’s
“0” to “5” outputs are connected to
resistors which range in value from
22kΩ up to 56kΩ.
IC11 and its associated resistors
form the D-A converter. Initially,
output “0” of IC11 is high and the
maximum voltage is applied to pin 3
of IC4b. As the counter now counts
up, this voltage steps down as each
output goes high in turn, finally reducing to 0V when output “6” (not
shown) goes high (since outputs “0”
to “5” are now all low). This voltage
remains at 0V when outputs “7”, “8”
and “9” go high.
IC4b amplifies the applied voltage
by about three times and provides a
buffered output for VR3. As the voltage falls, it is continually compared
by IC5b against the incoming signal
level (selected from each antenna in
turn), until it falls below the signal
level. At this point, IC5b’s output goes
high again, IC9 is held reset and the
current antenna is held. IC11 also stops
counting due to the high on its CE
input (pin 13). In this way, the circuit
selects the antenna with the highest
signal strength.
Counter reset
IC12, together with inverters IC8c
and Ic8d, is used to reset the counter
(IC11). As soon as the “0” output of
IC11 goes low (ie, on the first clock
cycle from IC9), pin 2 of IC8c goes
high and releases the reset on oscillator
stage IC12. Pin 3 of IC12 now goes high
for about 1s and then switches low
again. This low is inverted by IC8d
and applied to the reset input (pin 15)
of IC11 via a 0.1µF capacitor.
IC11’s “0” output now immediately
switches high again and so IC12 is once
again held reset via IC8c (ie, pin 3 of
IC12 remains low). Diode D8 protects
the reset input of IC11 by clamping
this input to ground when the output
of IC8d goes low.
At this point (ie, following reset), the
output from the D-A converter is at its
maximum and so the threshold voltage
set by VR3 is also at maximum. IC5b
now compares the signal strength from
the selected antenna against this new
threshold and so the selection process
begins again.
Manual antenna switching
IC10b is the other half of the 4013
dual-D flipflop. It basically operates
as a debouncing circuit for the antenna test switch (S2). Each time S2
is pressed (ie, pin 10 is pulled high),
Q-bar toggles high and clocks IC10a
via isolating diode D7 to select the
alternative antenna.
This antenna selection is maintained while ever the switch is held
down. When the switch is released,
Q-bar of IC10 goes low again and the
circuit returns to normal mode.
Power for the circuit is derived from
the mains via a 12.6V transformer.
This secondary AC voltage is rectified
PARTS LIST
1 1-unit high black anodised rackmounting case with screen
printed front & rear panels
1 PC board, code 06307941, 207
x 161mm
1 PC board, code 06307942, 28
x 49mm
2 pieces of blank single-sided PC
board, 53 x 15mm
2 pieces of blank single-sided PC
board, 38mm x 15mm
1 piece of blank single-sided PC
board, 38 x 12mm
1 Altronics M-2852 12.6V 3.78VA
mains transformer
1 DPST illuminated rocker switch
with red Neon indicator (S1),
Altronics Cat. S-3217 or
equivalent
1 M205 safety fuse holder (F1)
1 M205 250mA fuse
1 TO-220 mini U heatsink, 26 x
30 x 12mm
1 100kΩ log pot (VR4)
1 16mm OD black anodised knob
1 SPDT momentary pushbutton
switch (S2)
2 insulated panel mount PAL
sockets
1 insulated RCA panel socket
4 rubber feet
6 cable ties
17 PC stakes
1 solder lug
4 5mm standoffs
6 2mm screws & nuts for panel
sockets
4 3mm screws & nuts for
standoffs
3 4mm screws & nuts to secure
mains transformer & earth
solder lug
1 3mm star washer for earth
solder lug
3 10kΩ horizontal trimpots (VR1VR3)
1 700mm length of 0.8mm tinned
copper wire
1 400mm length of 0.6mm
enamelled copper wire (ECW)
1 250mm length of 0.5mm ECW
1 200mm length of 0.25mm ECW
1 piece of large diameter
heatshrink tubing (to insulate
contacts of S1 and F1)
Coils and filters
4 balun formers, Philips 4313 020
4003 1 (L1-L4)
3 Neosid type ‘A’ adjustable
inductance assemblies, type #
99-007-96 (base, former, can &
F29 screw core) (T1,T2 & L10)
2 matched Murata SFE10.7ML
10.7MHz ceramic filters
(X1,X2)
Wire & cable
1 7.5A mains cord & plug
1 300mm length of 3-way rainbow
cable
1 400mm length of single core
shielded audio cable
Semiconductors
1 10-segment LED bargraph
(LEDs1-10)
1 3mm red LED (LED11)
1 3mm green LED (LED12)
1 TDA1574 Integrated FM Tuner
(IC1)
1 TDA1576 FM/IF Amplifier (IC2)
1 LM3914 linear LED dot/
bargraph driver (IC3)
1 LM358 dual op amp (IC4)
1 LM393 dual comparator (IC5)
1 LF351 dual op amp (IC6)
1 4066 quad CMOS analog
switch (IC7)
1 74C14, 40106 hex Schmitt
trigger (IC8)
2 7555, LMC555CN CMOS
timers (IC9,IC12)
1 4013 dual D-flipflop (IC10)
1 4017 decade counter decoder
(IC11)
1 7812 1A 12V 3-terminal
regulator (REG1)
1 BF981 dual gate Mosfet (Q1)
4 BA482 low capacitance VHF
silicon planar diodes (D1-D4)
1 BB119 VHF varicap diode (D5)
3 1N4148, 1N914 switching
diodes (D6-D8)
4 1N4004 1A rectifier diodes (D9D12)
using diodes D9-D12 and filtered with
a 4700µF capacitor to derive an 18V
(approx.) DC rail. A 3-terminal regulator (REG1) then provides a stable +12V
supply for the circuitry.
The 47µF capacitor at the output
of the regulator is included to ensure
regulator stability.
Capacitors
1 4700µF 25VW PC electrolytic
2 47µF 16VW PC electrolytic
4 10µF 16VW PC electrolytic
1 1µF 16VW PC electrolytic
1 0.33µF MKT polyester
5 0.1µF ceramic
9 0.1µF MKT polyester
1 .033µF MKT polyester
1 .018µF MKT polyester
19 .01µF ceramic
1 .0068µF MKT polyester for
50µs de-emphasis (use .01µF
for 75µs)
2 .001µF ceramic
4 .001µF feedthrough ceramic
1 560pF ceramic
2 390pF ceramic
1 47pF ceramic
5 33pF NPO ceramic
1 27pF NPO ceramic
1 15pF NPO ceramic
2 6.8pF NPO ceramic
1 3.9pF NPO ceramic
1 1.8pF NPO ceramic
1 8.5-50pF miniature trimmer
capacitor (VC1), Altronics Cat.
R-4009 Green
1 5-30pF miniature trimmer
capacitor (VC2), Altronics Cat.
R-4007 Yellow
Resistors (0.25W, 1%)
1 1.2MΩ
1 3.9kΩ
1 330kΩ
1 3.3kΩ
6 220kΩ
3 2.7kΩ
3 100kΩ
4 2.2kΩ
1 56kΩ
2 1.5kΩ
2 47kΩ
1 750Ω
1 39kΩ
1 390Ω
1 33kΩ
1 300Ω
1 27kΩ
1 47Ω
2 22kΩ
9 10Ω
10 10kΩ
1 82Ω 5W
2 4.7kΩ
Miscellaneous
1 plastic alignment tool (to adjust
slugs & trimmer capacitors)
1 plastic tuning wand with a brass
screw on one end and an F29
ferrite slug on the other (joined
by plastic tubing – see Pt.2).
That completes the circuit description. Next month, we will continue
with the complete construction and
SC
alignment details.
August 1994 49
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.
Theft protection
for automatic cars
N/C
Preventing engine cranking rather than killing the
COM
KEYPAD
D1
COMBINATION LOCK
1N4004
ignition or fuel injection as
SILICON CHIP
a means of theft protection
JULY 1990
has the advantage that the
device is only operative
while the vehicle is stationary.
This simple device prevents cranking by making use of the lock is wired to operate a relay (RLY1)
switch circuit on the drive selector which has heavy duty contacts to carry
of an automatic transmission. This
the starter solenoid current.
prevents engine cranking unless the
Note that the relay contacts are in
transmission is in Neutral or Park. It series with the switch on the transmismakes use of the combination lock sion drive selector. The lock circuit is
keypad featured in the July 1990 issue wired for monostable operation which
of SILICON CHIP. This is available as a means that the cranking circuit is enkit from Dick Smith Electronics (Cat abled for 20 seconds after the correct
K-8403). The relay in the combination code is entered to the keypad. To use
A sensitive lightmeter
for the darkroom
Photographic printing papers have
increased in sensitivity and some require light of the order of 0.1 Lux for
exposures of 10 seconds. A lightmeter
for the darkroom must therefore be
capable of measuring reliably to better
than .01 Lux and have a small sensitive
area to permit spot measurements.
It should have no hysteresis effect
so that it is ready for measurements
immediately after the room light is
switched off.
A desirable feature would be to
have direct reading of time required
for correct exposure in a range of 5-20
seconds and a direct reading of relative
paper sensitivity so that when paper
from the same batch is used
at a later date, the controls
can be set immediately and
printing started.
This meter circuit meets
all the above criteria and is
PD1
easy to use. It uses an eye reBPW21
sponse photodiode from RS
Components, part num
ber
303-719, with an active area
50 Silicon Chip
L2 TO SWITCH ON DRIVE SELECTOR
L1 FROM "CRANK" CONNECTION ON
IGNITION SWITCH. (REMOVED FROM
SWITCH ON DRIVE SELECTOR)
N/O
less than 3mm squared. The photocell
is sealed, has no hysteresis and covers
a light range from less than .01 Lux to
greater than 100,000 Lux. It is used in
the open circuit voltage mode which
gives a logarithmic response and covers the whole range with an output
ranging from 40-550mV. Doubling the
incident light increases the output by
about 20mV and this is pretty consistent across the range.
The photocell anode is connected
directly to the gate of the FET rather
than via a PC board to maximise the
input resistance. VR1 is adjusted so
that increasing the light by one stop on
the enlarger lens increases the reading
by 10mV. The reading on the meter can
be balanced to zero by setting VR3 and
VR4 in the gate of the balancing FET,
470
16VW
Q1
2N5486
G
S1
D
S
VR1
10k
10T
DVM
200mV
25
16VW
25
16VW
RLY1
TO IGNITION CONNECTION ON IGN. SW.
TO CHASSIS
the system, the ignition is turned on,
the code is entered and the engine can
be started.
There is no need for a secret switch
although the device should be disabled
when the vehicle is being serviced, to
avoid the need to divulge the keypad
code.
Ron Searle,
Bundaberg, Qld. ($20)
Q2. VR4 is adjusted for the exposure
time of 5-20 seconds.
Calibration is performed by the
following steps: (1) Use switch S2
to short out the gate of FET Q2; (2)
Adjust VR1 for a change of reading of
10mV for each one-stop change in the
enlarger lens setting; (3) Use switch S1
to short the photocell and adjust VR2
to obtain a zero reading on the digital
voltmeter (DVM); (4) By trial and error,
produce a good print with the usual
adjustment of enlarger aperture and
printing exposure time; (5) set trimpot
VR4 to the corresponding exposure
time; (6) Open switches S1 & S2;. (7)
Select the spot to be measured (or
use a diffuser in front of the enlarger
lens to measure average) and adjust
VR3 (paper sensitivity) to read 0mV
Q2
2N5486
D
G
S
VR2
10k
10T
S2
PAPER
SENSITIVITY
VR3
10k
EXPOSURE
TIME
VR4
1k
1k
100k
470
10VW
ZD1
5.6V
1W
9V
Low-cost
LED level display
There are many audio LED level
circuits and kits on the market for
use in preamplifiers and amplifiers, or as standalone units, and
these work well. However, most
are built on a large PC board and
are generally quite expensive. This
circuit uses only eight components
and one IC to perform the same
operation and can be built for
about $15.
The circuit is designed to connect to the line out of a CD player
or tape deck but, by changing the
input resistor to a higher value,
it could also be connected to the
speaker output of any amplifier or
hifi system.
An LM3914 LED bar/dot driver
IC forms the basis of the circuit.
This IC contains a series of 10 op
amp comparators which compare
the incoming signal with a divided
reference signal (about 1.2V). Each
op amp then drives a LED (LEDs
1-10) and this produces a moving
display which fluctuates according
the level of the audio signal.
In operation, the incoming audio signal is fed through a 470Ω
limiting resistor and into a 100kΩ
on the DVM; (8) Short the photocell
with switch S1 and adjust time to 10
seconds and note the reading on the
DVM. This becomes the relative paper
sensitivity and any time you want to
use this batch of paper short the cell,
set VR4 to 10 seconds and adjust VR3
to give this reading on the DVM; (9)
Open switch S1 and proceed with your
measurement of any negative at any
magnification by adjusting enlarger
aperture and time dial to achieve 0mV.
This gives you the correct conditions
for printing.
The cell output has a temperature
coefficient of -2mV/°C; this becomes
about -1mV/°C on the meter. Therefore
note the temperature at the time of
measurement of the paper sensitivity
and correct this value by the difference in ambient temperature during
printing; ie, reduce paper sensitivity
by 1mV for every 1°C increase.
Victor Erdstein,
Highett, Vic. ($45)
+5V
INPUT
GND
470
VR1
100k
3
D1
1N914
9
LED1-10
1
1
Q1
BC558
18
5
17
2.2
1k
15
6
14
7
13
680
11
3
4
5
6
7
12
2
2
16
IC1
LM3914
1
8
9
10
10
4
trimpot (VR1) which acts as a level control. From there, the signal
passes through a 1µF electrolytic
capacitor which acts as a high
pass filter.
Because Q1 (BC558) is a PNP
transistor, positive going excursions of the audio signal are
ignored and are clamped by D1
(1N914) to the positive rail. Negative going signals, however, cause
Q1 to conduct and the output is
8
taken from the collector and fed
into pin 5 of IC1.
The 680Ω resistor on pins 6 & 7
sets the internal reference voltage
and the LED brightness, while the
2.2µF capacitor sets the LED “fallback” time. Pin 9 may be connected
to the positive rail to produce a
bar display, or left open circuit to
produce a dot display.
L. Trengove,
Sawtell, NSW. ($25)
27
4.7k
6
270
2
IC1
ZD1901
4
8
IC2
555
Q1
MJE340
3 270
+12V
OUTPUT
100
16VW
ZD1
9.1V
1
0V
Optoelectronic pickup
for ignition systems
This circuit has been designed
as an optoelectronic trigger for
the High Energy Ignition System
featured in the May 1988 issue
of SILICON CHIP. It uses a readily
available photo-interrupter, IC1,
from Jaycar Electronics (Cat. ZD-
1901). This is used to drive IC2, a
555 timer which is used simply as
a Schmitt trigger.
IC2 in turn drives switching
transistor Q1 which connects to
the points input on the ignition
circuit, as shown on page 34 of the
May 1998 issue.
Des Logan,
Ingle Farm, SA. ($20)
August 1994 51
This photo shows the completed
Crystal Checker. If the crystal is
working, the LED will light.
A Simple Go/No-Go
Crystal Checker
This simple circuit will help you sort through
that pile of crystals lying on your workbench. If
the crystal works, the LED lights. Best of all, it
can use parts which you probably already have
in your junkbox.
By DARREN YATES
If you’ve had a go at building any
RF projects in the past you’ll probably
have a couple or maybe quite a few
crystals lying around. Crystals are
quite fragile components because of
their construction. Unlike a resistor
or capacitor, if you drop one on the
ground from a decent height, it’s a
50-50 bet whether it will work again.
Testing them is not a breeze either.
You just can’t take out your trusty
multimeter and plug the crystal in. In
fact, the only real way is to try it in an
oscillator circuit. And that’s exactly
what this little Crystal Checker does.
The crystal is placed in the feedback
network of a transistor oscillator. If
it oscillates, meaning that the crystal
works, a LED lights up. If the crystal
52 Silicon Chip
doesn’t work, the LED stays off. You
can’t get much simpler than that.
Note that if you have overtone
crystals, the circuit will not tell you
whether or not the crystal is operating at the designated frequency, just
whether or not it will oscillate at its
fundamental frequency.
Circuit description
Let’s take a look at the circuit in
Fig.1. As you can see, there are only
two transistors, a couple of diodes, a
LED and a few other components. Q1
is a BF199 RF transistor and with its
associated components forms an untuned Colpitts oscillator. The crystal
forms the main element of the circuit.
Positive feedback comes from the
emitter through the .001µF capacitor
back to the crystal and base.
If the crystal works, the circuit will
begin oscillating immediately and a
waveform will appear at the emitter
of Q1. If you look at this on your oscilloscope, you could expect to see a
rough sinewave with and an amplitude
of about 2V peak-to-peak, depending
on the frequency.
Diodes D1 and D2 rectify the signal from the emitter of Q1 and the
resulting DC voltage is fed to the base
of transistor Q2. Once this voltage exceeds 0.6V, transistor Q2 turns on and
lights LED 1. As soon as the crystal is
removed, the circuit stops oscillating
and the LED goes out.
As a point of interest, if the crystals
you have are less than 10MHz, then
you could probably get away with
a BC548 for Q1. The BC548-series
transistors have a high FT (gain-bandwidth product) of about 100MHz or
so but they don’t tend to work well
in oscillator circuits above about
10MHz. FM microphones often get
away with a BC548 but the output at
the required 100MHz or so is quite
Q1
BF199
47k
B
CRYSTAL
UNDER
TEST
10
16VW
2x1N914
.001
100pF
B1
9V
A
C
E
.001
1k
2.2k
LED1
Q2
K
BC548
C
B
D1
D2
10k
BF199
E
B
E
0.1
BC548
B
C E
VIEWED FROM BELOW
C
A
Fig.1: the circuit
of the Crystal
Checker is
shown with a
BF199 for Q1
but a BC548 will
work with many
crystals under
10MHz.
K
Construction
Construction of the Crystal Checker
is a snap and shouldn’t take you any
Resistors (0.25W, 1%)
1 47kΩ
1 2.2kΩ
1 10kΩ
1 1kΩ
Fig.2: this sample waveform was
taken from the emitter of Q1 with
the scope probe set to 10:1 division.
The crystal was an American TV
intercarrier type with a frequency
marking of 3.579545MHz. The onscreen measurement shows the
frequency as 3.5MHz, well within the
accuracy of most oscilloscopes. As
you can see, the signal amplitude is
about 2.4V peak-peak.
more than an hour or so. All of the
components except the 9V battery fit
on a small PC board, coded 04106941,
and measuring only 52 x 40mm.
Before you begin any soldering,
check the board thoroughly for any
10uF
1k
47k
Q2
.001
0.1
10k
LED1
Q1
.001
B1
K
2.2k
CRYSTAL
UNDER
TEST
A
Semiconductors
1 BF199 RF NPN transistor (Q1)
1 BC548 NPN transistor (Q2)
2 1N914 signal diodes (D1,D2)
1 5mm green LED (LED1)
Capacitors
1 10µF 16VW electrolytic
1 0.1µF 63VW MKT polyester
2 .001µF 63VW MKT polyester
1 100pF ceramic
SIMPLE GO/NO-GO CRYSTAL CHECKER
low – in the order of millivolts which
is too low for our application. Below
10MHz, they work quite well with a
good output voltage. Why not try one
out and see what you get. You can’t
damage the crystal and it’s always fun
to experiment!
Power is supplied by a 9V battery
which is bypassed by a 10µF electrolytic capacitor. We haven’t specified
a power switch mainly for the reason
that it would double the cost of the
parts! Besides, once you’ve checked
all your crystals, you can unclip the
battery and use it on something else.
You could also experiment with
different supply rails. The circuit
should work well with any voltage
between 6V and 15V although if you
are using a BC548 for Q1 and a supply
voltage of less than 9V, it may not like
the higher crystal frequencies. Again,
experiment and see for yourself! The
quiescent current should be around
3mA, pushing up to 6-8mA with the
LED on.
PARTS LIST
1 PC board, code 04106941, 52
x 40mm
4 PC stakes
1 9V battery
1 battery clip
D2 D1
100pF
Fig.3: the component layout diagram for
the PC board. We suggest connecting a
pair of leads with crocodile clips to make
connections to the crystal.
shorts or breaks in the copper tracks.
These should be repaired with a small
artwork knife or a touch of the soldering iron where appropriate.
When you’re satisfied that the board
is OK, start by installing the resistors
and diodes, followed by the capacitors
and transistors. Be sure to follow the
overlay diagram (Fig.3) carefully, as
some of these components are polarised and won’t work if you install them
the wrong way around.
Finally, solder in the LED and the PC
stakes for the battery and the crystal.
You might like to make up a pair of
short alligator clip leads to connect
the crystal – see photo.
Testimg
Testing the circuit is pretty much
the same as normal use. Find a crystal that you know works,
preferably something
between 32kHz to 4MHz,
pop it in and connect the
9V battery. If the circuit
works, you should see the
LED light.
If it doesn’t, check that
the components are in
their correct locations
and check the orientation
of components such as
the LED, transistors and
Fig.4: this is the full size artwork
diodes. In addition, check
for the PC board. Check your board
the solder con
nections
carefully against this pattern before
for dry joints or shorts
mounting any of the parts.
between tracks.
SC
August 1994 53
SPECIALS BY FAX
If your fax has a polling function, dial (02) 579
3955 and press your POLLING button to get our latest
specials, plus our item and kit listing. Updated
at the start of each month.
HF ELECTRONIC BALLASTS
Brand new “slim line” cased electronic
ballasts. They provide instant flicker free
starting, extend tube life, reduce power
consumption, eliminate flicker during operation (high frequency operation), and are
“noise free” in operation. The design of these
appears to be similar to the one published in
the Oct. 94 SILICON CHIP magazine. One of
the models even includes a DIMMING OPTION!! Needs external 100K potentiometer
or a 0-10V DC source. We have a good but
limited stock of these and are offering them at
fraction of the cost of the parts used in them!
Type A: Designed to power two 32W - 4’
tubes, will power two 40W - 4’ tubes with
no noticeable change in light output, has
provision for dimming: $26
Type B: Designed to power two 16W - 18"
tubes, will power two 18W - 18" tubes with
no noticeable change in light output: $18
MISCELLANEOUS
FLAT NOSE PLIERS: $4 per pair. BATTERY
CHARGER: S2 accessory set for Telecom
Walkabout “Phones”. Includes cigarette
lighter cable, fast rate charger, and desktop
stand. Actually charges 6 series connected
AA Nicad batteries: $27. BATTERY PACKS:
Contain 6 AA Nicad batteries wired in
series, can easily be pulled apart, used
units, satisfaction guaranteed: $2 per pack.
LITHIUM BATTERIES: Button shaped with
pins, 20mm diameter, 3mm thick. A red led
connected across one of these will produce
light output for over 72 hours (3 days): 4 for $2.
CIGARETTE LIGHTER LEADS: Cigarette
lighter plug with 3 metres of heavy duty fig. 8
flex connected. Should suit load currents up
to 20A: 5 for $5. SUPERCAPS: 0.047F/5.5V
capacitors: 5 for $2. HOUR METER: Non
resettable, mains powered (50HZ), WARBURTON FRANKI, 100,000 Hours maximum,
0.01Hr resolution: $15. PCB MOUNTED
SWITCHES 90 deg. 3A-250V, SPDT: 4 for $2.
AC POWER SUPPLY: Mains in, two separate
8.5V/3A outputs, in plastic case with mains
power lead/plug and output leads/plugs: $15
Ea. MONITOR PCB’s: Complete PCB and
yoke assembly for high resolution monochrome TV monitors (no tube). Operate from
12V DC, circuit and information provided:
$15. MODEMS: Complete mains powered
non standard 1200 baud Telecom approved
modems. We should have brief information
available. Limited stock at below the price of
the high quality case that these are housed
in: $30 for 2 modems.
MEDICAL LASER
One only water cooled medical laser with
selectable outputs: Argon (7W multiline) or
Dye laser (1W red). Large water cooled unit
with a separate control box and accessories
(350kg):
$15,000
LEVEL RECORDER
One only, Bruel & Kjaer level recorder type
2305, in good condition:
$300
54 Silicon Chip
DIE CAST BOXES
These large (187 x 120 x 56mm) aluminium
die cast boxes have several holes drilled in
them and have a C&K toggle switch and a
6.25mm phono socket fitted. New units from
an unfinished production project:
$4 Ea.
WELLER SOLDERING IRON TIPS
New soldering iron for low voltage Weller soldering stations and mains operated Weller
irons. Mixed popular sizes and temperatures.
Specify mains or soldering station type:
5 for $10.
NICAD BATTERY PACKS
Brand new Toshiba 7.2V-2.2AHr Nicad
Battery packs in a plastic assembly:
$20 Ea.
If you purchase three packs we will supply
a matching fast charger (90min.) that can
charge up to three of these batteries (one at
a time). Modern unit that employs “delta V”
voltage detection to terminate charge, needs
an external 12V-2.2A unregulated supply:
$60 for three battery packs and a
three way charger.
PLUGS/SOCKETS
3 pin chassis mounting socket and a matching covered three pin plug. Good quality
components that will handle a few amperes
at low voltage:
$5 for 4 pairs.
DYNAMIC MICROPHONES
Low impedance dynamic microphones
with separate switch wiring, 3.5mm mic.
plug, 2.5mm switch plug, as used on most
cassette recorders:
$4 Ea.
40mW IR LASER DIODES
New famous brand 40mW-830nM IR laser
diodes, suit medical and other applications:
$90 Ea. Constant current driver kit to
suit: $10.
HIGH POWER LED IR ILLUMINATOR
This kit includes two PCBs, all on-board
components plus casing: Switched mode
power supply plus 60 high intensity 880nm
IR (invisible) LEDs. Variable output power,
6-20VDC input, suitable for illuminating IR
responsive CCD cameras, IR night viewers
etc. Professional performance at a fraction
of the price of the commercial product.
COMPLETE KIT PRICE:
$60
LOW COST 1-2 CHANNEL UHF
REMOTE CONTROL
Late in October we will have available a
single channel 304MHz UHF remote control
with over 1/2 million code combinations
which also makes provision for a second
channel expansion. The low cost design
includes a complete compact keyring
transmitter kit, which includes a case and
battery, and a PCB and components kit
for the receiver that has 2A relay contact
output! Tx kit $10, Rx kit $20. Additional
components to convert the receiver to 2
channel operation (extra decoder IC and
relay) $6. INCREDIBLE PRICES:
COMPLETE 1 CHANNEL TX-RX KIT:
$30
COMPLETE 2 CHANNEL TX-RX KIT:
$36
ADDITIONAL TRANSMITTERS: $10
FIBRE OPTIC TUBES
These US made tubes are from used equipment but in excellent condition. Have 25/40
mm diameter, fibre-optically coupled input
and output windows. The 25mm tube has an
overall diameter of 57mm and is 60mm long,
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 approximately 1/2 moon illumination, when
used with suitable “fast” lens, but they can
also be IR assisted to see in total darkness.
Our HIGH POWER LED IR ILLUMINATOR
kit, and the IR filter are both suitable for use
with these tubes. The superior resolution
of these tubes would make them suitable
for low light video preamplifiers, wild life
observation, and astronomical use. Each of
the tubes is supplied with an 9V-EHT power
supply kit. INCREDIBLE PRICES:
$120 for the 25mm intensifier tube
and supply kit.
$180 for the 40mm intensifier tube
and supply kit.
We also have a good supply of the same
tubes that may have a small blemish which
is not in the central viewing area!:
$65 for a blemished 25mm intensifier
tube and supply kit.
$95 for the blemished 40mm intensifier tube and supply kit.
SIEMENS VARISTORS
420VAC 20 joule varistors that are suitable
for spike protection in Australian 3 phase
systems:
10 for $5.
TAA611C ICs
TAA611C Audio power amplifier ICs, no more
information: 5 for $5.
INTENSIFIED NIGHT VIEWER KIT
SC Sept. 94. See in the dark! Make your own
night scope that will produce good vision in
sub-starlight illumination! Has superior gain
and resolution to all Russian viewers priced
at under $1500. We supply a three stage
fibre-optically coupled image intensifier
tube, EHT power supply kit, and sufficient
plastics to make a monocular scope. The
three tubes are supplied already wired and
bonded together.
$290 for the 25mm version
$390 for the 40mm version
We can also supply the lens (100mm f2:
$75) and the eyepiece ($18) which would
be everything that is necessary to make an
incredible viewer!
MAINS POWERED GAS LASER
Includes a professional potted mains power
supply and a new 3mW red tube to suit. One
catch, this supply requires a 4-6V (TTL) enable input which is optically isolated, to make
the unit switch ON. Very low consumption
from a 4.5V battery.
$100 for a new 3mW tube plus a TTL
mains power supply to suit.
SUPER DIODE POINTERS - HEADS
These pointers probably represent the
best value when you compare them on
a “brightness per dollar” basis. They are
about 5 times brighter than 5mW/670nm
pointers! They have an output of 2.5mW at
650nm, which is about equal in brightness
to a 0.8mW HE-NE tube!! SPECIAL INTRODUCTORY PRICE:
$150
We will also have available some of the
3V diode modules used in these pointers
at approximately $125, and also some
2.5mW/635nm laser diode modules with
special optics at approximately $280.
VIDEO TRANSMITTERS
Low power PAL standard UHF TV transmitters. Have audio and video inputs with
adjustable levels, a power switch, and a
power input socket: 10-14V DC/10mA operation. Enclosed in a small metal box with an
attached telescopic antenna. Range is up to
10m with the telescopic antenna supplied,
but can be increased to approximately
30m by the use of a small directional UHF
antenna. INCREDIBLE PRICING:
$25
TDA ICs/TRANSFORMERS
We have a limited stock of some 20 Watt
TDA1520 HI-FI quality monolithic power
amplifier ICs, less than 0.01% THD and
TIM distortion, at 10W RMS output! With
the transformer we supply we guarantee an
output of greater than 20W RMS per channel
into an 8ohm load, with both channels driven.
We supply a far overrated 240V-28V/80W
transformer, two TDA1520 ICs, and two
suitable PCBs which also include an optional
preamplifier section (only one additional IC),
and a circuit and layout diagram. The combination can be used as a high quality HI-FI
Stereo/Guitar/P.A., amplifier. Only a handful
of additional components are required to
complete this excellent stereo/twin amplifier!
Incredible pricing:
$25
for one 240V-28V (80W!) transformer, two
TDA1520 monolithic HI-FI amplifier ICs, two
PCBs to suit, circuit diagram/layout. Some
additional components and a heatsink are
required.
LIGHT MOTION DETECTORS
Small PCB assembly based on a ULN2232
IC. This device has a built in light detector,
filters, timer, narrow angle lens, and even a
siren driver circuit that can drive an external
speaker. Will detect humans crossing a
narrow corridor at distances up to 3 metres.
Much higher ranges are possible if the
detector is illuminated by a remote visible
or IR light source. Can be used at very low
light levels, and even in total darkness: with
IR LED. Full information provided. The IC
only, is worth $16! OUR SPECIAL PRICE
FOR THE ASSEMBLY IS:
$5 Ea. or 5 for $20
GAS LASER SPECIAL
We have a good supply of some He-Ne laser
heads that were removed from new or near
new equipment, and have a power output
of 2.5-5mW: very bright! With each head
we will supply a 12V universal laser power
supply kit for a ridiculous TOTAL PRICE of:
$89
AA NICADS
Brand new AA size Saft brand (made in
France) 500mA Hr. batteries, also have
solder connections (can be removed):
$2 Ea. or 10 for $ 16.
TWO STEPPER MOTORS PLUS A
DRIVER KIT
This kit will drive two stepper motors: 4, 5, 6
or 8 eight wire stepper motors from an IBM
computer parallel port. Motors require separate power supply. A detailed manual on the
COMPUTER CONTROL OF MOTORS plus
circuit diagrams/descriptions are provided.
We also provide the necessary software on
a 5.25" disc. Great “low cost” educational kit.
We provide the kit, manual, disc, plus TWO
5V/6 WIRE/7.5 Deg. STEPPER MOTORS
FOR A SPECIAL PRICE OF:
$42
CAMERA FLASH UNITS
Electronic flash units out of disposable
cameras. Include PCB/components and
Xenon tube/reflector assembly. Requires
a 1.5V battery.
$2.50
IR LASER DIODE KIT
auto iris lens. It can work with illumination
of as little as 0.1Lux and it is IR responsive.
Can be used in total darkness with Infra Red
illumination. Overall dimensions of camera
are 24 x 46 x 70mm and it weighs less
than 40 grams! Can be connected to any
standard monitor, or the video input on a
Video cassette recorder. NEW LOW PRICE:
$199
IR “TANK SET”
A set of components that can be used to
make a very responsive Infra Red 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 employed is probably the most sensitive IR responsive tube we ever supplied.
The resultant viewer requires low level IR
illumination. Basic instructions provided.
$140
BRAND NEW 780nm LASER DIODES
(barely visible), mounted in a professional
adjustable collimator-heatsink assembly.
Each of these assemblies is supplied with
a CONSTANT CURRENT DRIVER kit and a
suitable PIN DIODE that can serve as a detector, plus some INSTRUCTIONS. Suitable
for medical use, perimeter protection, data
transmission, IR illumination, etc.
For the tube, lens, eyepiece and the power
supply kit.
5mW VISIBLE LASER DIODE KIT
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.
$40
Includes a Hitachi 6711G 5mW-670nm
visible laser diode, an APC driver kit, a
collimating lens - heatsink assembly, a
case and battery holder. That’s a complete
3mW collimated laser diode kit for a TOTAL
PRICE OF:
$75
BIGGER LASER
We have a good, but LIMITED QUANTITY
of some “as new” red 6mW+ laser heads
that were removed from new equipment.
Head dimensions: 45mm diameter by
380mm long. With each of the heads we
will include our 12V Universal Laser power
supply. BARGAIN AT:
$170 6mW+ head/supply. ITEM No.
0225B
We can also supply a 240V-12V/4A-5V/4A
switched mode power supply to suit for $30.
12V-2.5 WATT SOLAR PANEL
SPECIAL
These US made amorphous glass solar
panels only need terminating and weather
proofing. We provide terminating clips and a
slightly larger sheet of glass. The terminated
panel is glued to the backing glass, around
the edges only. To make the final weatherproof panel look very attractive some inexpensive plastic “L” angle could also be glued
to the edges with some silicone. Very easy
to make. Dimensions: 305 x 228mm, Vo-c:
18-20V, Is-c: 250mA. SPECIAL REDUCED
PRICE until the end of 94!:
$20 Ea. or 4 for $60
Each panel is provided with a sheet of
backing glass, terminating clips, an isolating
diode, and the instructions. A very efficient
switching regulator kit is available: Suits
12-24V batteries, 0.1-16A panels, $27. Also
available is a simple and efficient shunt
regulator kit, $5.
CCD CAMERA
Monochrome CCD camera which is totally
assembled on a small PCB and includes an
SOLID STATE “PELTIER EFFECT”
COOLER-HEATER
These are the 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. ITEM No. 0231
RUSSIAN NIGHT VIEWER
We have a limited quantity of some passive
monocular Russian made night viewers
that employ a 1st generation image intensifier tube, and are prefocussed to infinity.
CLEARANCE:
$180
INFRA RED FILTER
A very high quality IR filter and a RUBBER
lens cover that would fit over most torches
including MAGLITEs, and convert them to
a good source of IR. The filter material withstands high temperatures and produces an
output which would not be visible from a few
metres away and in total darkness. Suitable
for use with passive and active viewers. The
filter and a rubber lens cover is priced at:
$11
DOME TWEETERS
Small (70mm diam., 15mm deep) dynamic
8ohm tweeters, as used in very compact
high quality speaker systems: $5 Ea. We
also have some 4" woofers: $5 Ea.
VIDEO ZOOM LENSES
Wire antenna - attached, Microphone: Electret condenser, Battery: One 1.5V silver oxide
LR44/G13, Battery life: 60 hours, Weight:
15g, Dimensions: 1.3" x 0.9" x 0.4".
$25
REEL TO REEL TAPES
New studio quality 13cm-5" “Agfa” (German) 1/4" reel to reel tapes in original box,
180m-600ft: $8 Ea.
MORE KITS-ITEMS
Single Channel UHF Remote Control, SC
Dec. 92 1 x Tx plus 1 x Rx $45, extra Tx $15.
4 Channel UHF Remote Control Kit: two
transmitters and one receiver, $96.
Garage/Door/Gate Remote Control Kit:
Tx $18, Rx $79.
1.5-9V Converter Kit: $6 Ea. or 3 for $15.
Laser Beam Communicator Kit: Tx, Rx,
plus IR Laser, $60. Magnetic Card Reader:
professional assembled and cased unit that
will read information from plastic cards,
needs low current 12VDC supply-plugpack, $70.
Switched Mode Power Supplies: mains in
(240V), new assembled units with 12V-4A
and 5V-4ADC outputs, $32.
Electric Fence Kit: PCB and components,
includes prewound transformer, $28
High Power IR LEDs: 880nm/30mW/12deg.
<at> 100mA, 10 for $9 Plasma Ball Kit: PCB
and components kit, needs any bulb, $25.
Masthead Amplifier Kit: two PCBs plus
all on board components: low noise (uses
MAR-6 IC), covers VHF-UHF, $18.
Inductive Proximity Switches: detect
ferrous and non-ferrous metals at close
proximity, AC or DC powered types, three
wire connection for connecting into circuitry:
two for the supply, and one for switching the
load. These also make excellent sensors for
rotating shafts etc. $22 Ea. or 6 for $100.
Brake Light Indicator Kit: 60 LEDs, two
PCBs and ten Rs, makes for a very bright
600mm long high intensity Red display, $30.
IEC Leads: heavy duty 3 core (10A) 3M
LEADS with IEC plug on one end and an
European plug at the other, $1.50 Ea. or
10 for $10.
IEC Extension Leads: 2M long, IEC plug
at one end, IEC socket at other end, $5.
Motor Special: these motors can also
double up as generators. Type M9: 12V, I
No load = 0.52A-15,800 RPM at 12V, 36mm
Diam.-67mm long, $5. Type M14: made for
slot cars, 4-8V, I No load = 0.84A at 6V, at
max efficiency I = 5.7A-7500 RPM, 30mm
Diam-57mm long, $5.
EPROMS: 27C512, 512K (64K x 8), 150ns
access CMOS EPROMS. Removed from
new equipment, need to be erased, guaranteed, $4.
Green Laser Tubes: Back in stock! The
luminous output of these 1-1.5mW GREEN
laser diode heads compares with a 5mW red
tube!: $490 for a 1-1.5mW green head and
a 12V operated universal laser inverter kit.
40 x 2 LCD Display: brand new 40 character by 2 line LCD displays with built in
driver circuitry that uses Hitachi ICs, easy
to drive “standard” displays, brief information
provided, $30 Ea. or 4 for $100.
RS232 Interface PCB: brand new PCB
assembly, amongst many parts contains
two INTERSIL ICL232 ICs: RS232 Tx - Rx
ICs, $8.
Modular Telephone Cables: 4-way modular
curled cable with plugs fitted at each end,
also a 4m long 8-way modular flat cable with
plugs fitted at each end, one of each for $2.
12V Fans: brand new 80mm 12V-1.6W
DC fans. These are IC controlled and have
four different approval stamps, $10 Ea. or
5 for $40.
Lenses: a pair of lens assemblies that were
removed from brand new laser printers. They
contain a total of 4 lenses which by different
combinations - placement in a laser beam
can diverge, collimate, make a small line,
make an ellipse etc., $ 8.
Polygon Scanners: precision motor with
8 sided mirror, plus a matching PCB driver
assembly. Will deflect a laser beam and
generate a line. Needs a clock pulse and DC
supply to operate, information supplied, $25.
PCB With AD7581LN IC: PCB assembly
that amongst many other components
contains a MAXIM AD7581LN IC: 8 bit, 8
channel memory buffered data acquisition
system designed to interface with microprocessors, $29.
EHT Power Supply: out of new laser printers, deliver -600V, -7.5KV and +7kV when
powered from a 24V-800mA DC supply,
enclosed in a plastic case, $16.
Mains Contactor Relay: has a 24V-250ohm
relay coil, and four separate SPST switch
outputs, 2 x 10A and 2 x 20A, new Omron
brand, mounting bracket and spade connectors provided, $8.
FM Transmitter Kit - Mk.II: high quality high stability, suit radio microphones and
instruments, 9V operation, the kit includes
a PCB and all the on-board components,
an electret microphone, and a 9V battery
clip, $11.
FM Transmitter Kit - Mk.I: this complete
transmitter kit (miniature microphone included) is the size of a “AA” battery, and it
is powered by a single “AA” battery. We use
a two “AA” battery holder (provided) for the
case, and a battery clip (shorted) for the
switch. Estimated battery life is over 500
hours!!: $11.
High Power Argons: the real thing! Draw
pictures on clouds, big buildings etc., with
a multiline water-cooled Argon laser with a
few watts of output. “Ring” for more details.
Argon-Ion Heads: used Argon-Ion heads
with 30-100mW output in the blue-green
spectrum, will be back in stock soon, priced
at around $400 for the “head” only, power
supply circuit and information supplied.
Two only 10:1 video zoom lenses, f=15150mm, 1:1.8, have provision for remote
focus aperture and zoom control: three
motors, one has a “C” mount adaptor, 150mm
diam. by 180mm long:
OATLEY ELECTRONICS
MINIATURE FM TRANSMITTER
Phone (02) 579 4985. Fax (02) 570 7910
$390 Ea.
Not a kit, but a very small ready made self
contained FM transmitter enclosed in a small
black metal case. It is powered by a single
small 1.5V silver oxide battery, and has an
inbuilt electret microphone. SPECIFICATIONS: Tuning range: 88-108MHz, Antenna:
PO Box 89, Oatley, NSW 2223
Bankcard, Master Card, Visa Card & Amex accepted with
phone & fax orders. P & P for most mixed orders: Aust. $6; NZ
(airmail) $10.
August 1994 55
SERVICEMAN'S LOG
Time to talk about timers
Why is there such an unbridgeable gap between
one of the video recorder’s main features & the
way the public reacts to it. I refer to the program
timer, which allows the VCR to record programs
in our absence. They can cope with almost any
timing requirement, yet hardly anyone uses
them.
The story is really about the mechanics of a tricky VCR timer problem
which, I suspect, may be more widespread than is realised. It may, just
possibly, also be age dependent. But
it set me thinking about the public’s
response to timers.
The particular case involved a
National NV-370 machine; a very
popular model which first appeared
some 10 or 12 years ago. And it says
something for the quality of these
machines that most of them are still
giving excellent service. Serious
faults have been minimal, with most
service work being simply routine;
eg, cleaning, replacing worn belts and
the occasional head replacement for
well-used units.
In this case, the owner was an
elderly lady and her complaint was
that the timer function was giving
trouble, but “only sometimes”. I didn’t
like the sound of it because of all the
intermittent faults one can think of, a
timer function intermittent is about
the worst imaginable.
And had it been anyone else, I
would have immediately suspected
finger trouble; the inability of the user
to set up the timer function correctly.
For the truth is that the majority of
VCR owners are incapable of using
this facility – and readily admit it.
Some have never even tried. Others
have tried a couple of times, fouled it
up and given the idea away. And that’s
a pity, because it is one of the most
valuable features of a VCR, allowing
users to capture programs they would
not otherwise enjoy.
I’m not sure why this is such a
problem. Customers often complain
that these devices are, to use a glib
“in” phrase, not “user-friendly”. In
response, the makers have responded
by producing new models which are
claimed to be “more user-friendly”.
Yet, in reality, the more they try, the
more complicated they seem to make
them and the more the public shies
away.
Conversely, many early machines
like the NV-370 were relatively simple to set up and most had a good
instruction book. Even so, few of my
customers seemed to have mastered
the simple procedures involved.
There are probably many factors
involved but I do suspect one: the
24-hour clock which most makers
now use but which is foreign to
most users.
Not that I blame the makers for
using it. It is far more logical than the
clumsy AM/PM arrangement which is
CLOCK
ON
OFF
CLOCK
NORMAL
PROGRAMME
ON
OFF
DAY
HOUR
MIN
TIMER REC
Fig.1: the clock and timer controls for the National NV-370 VCR. The 24-hour
clock used in most VCRs confuses many users.
56 Silicon Chip
itself wide open to confusion. Unfortunately, program guides are invariably
set out in 12-hour times. Perhaps it
would help if they could include both
time systems with the 24-hour figures
in brackets.
Well, it’s just an idea.
Back to the VCR
But I digress – back to the lady’s NV370. I suppose it goes without saying
that when I put it up on the bench and
checked the timer function, it worked
perfectly. But I know the lady well
enough to rule out finger trouble. She’s
been using this timer function for years
and, in a sense, is more familiar with
it than I am.
So I proceeded on the assumption
that there really was a fault. And in
order that those not familiar with this
machine can follow the story, it will
help if I set out the various controls
involved and how they are used.
The clock and timer controls occupy
the right-hand half of the front panel
and are normally concealed by a small
fold-down flap. And, from the left, they
are: Timer Selector, On, Off, Day, Hour,
Min-, Min+ and Timer Rec (the latter
coloured orange).
The Timer Selector is a 3-position
slide switch, the three positions being
designated (from left) Clock, Normal
and Programme. The other controls
are pushbuttons; toggle, hold down
or lock, as appropriate.
Setting the Timer Selector to the
Clock position (left) allows the clock
to be set to the correct day and time,
simply by holding down the Day,
Hour and Min buttons in turn, until
the appropriate reading is obtained
for each. In practice, the clock is set so
that it is slightly ahead of the real time
and this reading is held until the real
time coincides with it. Then, when the
Timer Selector is switched to Normal,
the clock will start and keep time.
Normally, of course, the clock
doesn’t need resetting unless the power has been turned off at the mains.
When the Timer selector is set to the
Programme position (right), the timer
function can be set up. Pressing the
On button brings up the clock display,
which is then programmed by holding
down the Day, Hour and Min buttons,
until the required starting time is displayed. The Off button is then pressed,
so that the required finishing time can
be similarly set up.
Finally, the Timer Rec (orange)
button is pressed and locks into the
On position. At the same time a small
clock symbol appears to confirm that
the timer function is set. The Timer
Select button is then reset to Normal.
It’s not a particularly complex procedure really but mistakes can still all
too easily occur. Common mistakes include setting the wrong 24-hour time,
the wrong day or the wrong channel,
neglecting to press the orange button,
and forgetting to rewind the cassette,
to name just a few.
Anyway, those were the steps I went
through to test the timer, normally
setting the starting time a minute or
so ahead and the finish time a minute
after that. Even so, it takes time, and I
tried to fit the tests in during natural
breaks.
Initially, I couldn’t fault it but persistence eventually paid off. I had set
the Timer Selector button to Program,
then pressed the On button. But the
normal On function did not respond.
I fiddled with the On button and, after
several tries, it came good and I was
able to set an On time. I then went to
the Off button, only to find that it was
reluctant also.
At this point, more or less by chance,
I happened to touch the Timer Select
button, whereupon the clock display
flashed off and on again. I wiped that
setting and went through the procedure again. And again the On button
did not respond but this time I fiddled
the Timer Select slide switch button
and was rewarded with a most erratic
flashing clock display.
So, a faulty slide switch? Dirty
contacts? Worn contacts? Well, it was
something like that.
Access requires removal of the top
and bottom covers, which then allows
the front panel to be unclipped.
By then undoing one screw,
the timer board can be lifted out for examination.
And a point to note here
is that the Timer Select
slide switch is soldered
directly to the underside of
this board but is not supported
in any other way.
The first thing I did was
squirt some CRC into the
switch and flick it back and
forth a couple of times. I
then went through the timer
sequence again but there appeared to be no improvement
and so I turned the machine
over to check the under
side
of the board. In particular, I
wanted to take a closer look at
the soldered joints that secured the
switch. At first glance they appeared
to be OK but the jeweller’s loupe told
a different story. Two of the joints were
cracked – not dry joints, but definite
fractures.
I was puzzled as to what might have
caused this but, for the moment, I
was more interested in having found
a fault (hope
fully, the fault). Some
careful attention with a good hot iron
and solder effectively remedied the
cracks and proved to be a complete
cure. Prolonged testing on the bench
and follow up checks with the owner
have proved the point; it hasn’t missed
a beat since.
More to come
Well, that was the end of that particular episode but there was more
to come. It was the first time I had
encountered or heard of such a fault
and thus alerted, I decided to make
some routine checks as any NV-370s
came through the workshop.
I have handled several since then,
mainly for routine checks and cleaning, and have found one more with
the same fault. Which brings me back
to the question as to why it happens,
remembering that we are talking about
fractures and not dry joints.
The best theory that I can advance
is that the soldered joints are not quite
adequate, the solder layer being quite
thin. While they are undoubtedly
adequate electrically, they are simply
not strong enough mechanically to
withstand the stresses as the switch
is actuated during regular use.
And that conclusion leads to a
August 1994 57
SERVICEMAN’S LOG – CTD
somewhat contradictory thought.
For those people who don’t use the
timer facility – which, as I have already implied, is the majority – such
a weakness is not a problem. So the
facility will not cause problems, as
long as you don’t use it. (There must
be something wrong with that line of
reasoning somewhere)!
More realistically, it probably explains why this problem has not surfaced to any extent before this; it has
probably taken this long, with regular
use, to find the weakness.
Colour TV set
The “worn-out” VCR
And there is one more incident
worth relating. One of my customers is
a local electrician and, while on a job
one day, his customer asked him if he
had any use for an old video recorder,
adding that it was destined for the tip
because, as far as he was concerned,
it was “worn out”.
The electrician already had a VCR
but it so happened that he did have
a use for another one – “worn out”
or not. His need was for a UHF/VHF
down-converter, for use with an old,
but still good, VHF-only TV set. And
he knew enough to know that the
down-converter function should still
work, even if the rest of the machine
really was “worn out”. So he grabbed
it with both hands.
I first learned about this when his
wife brought their main VCR in for a
minor service. After relating the story,
she asked whether I thought it would
be worthwhile checking it out and
possibly restoring it to full operation
(they had not even tried it in this role).
I suggested she bring it in so I could
make some preliminary checks.
The machine turned out to be an
NV-600, an up-market version of the
NV-370. A preliminary check proved
quite promising. I found only one
serious mechanical fault – failure of
a back tension brake, due to loss of
its felt pad.
I replaced that, then put the machine through its paces, checking out
both the record and replay functions.
Would you believe it? – it turned in a
first class performance. And it was on
its way to the tip!
That left only one more test – and
I’ll bet you’re way ahead of me. That’s
58 Silicon Chip
then the original owner of the NV-600
may not have been far wrong when he
used the term, “worn out”, much as
I dislike the expression. Personally,
I’ve always regarded it as a convenient
don’t-know, couldn’t-care-less, copout phrase, but in this case, wear may
have been a significant factor.
Fig.2: this diagram from the
Hitachi Fujian 1425B colour
TV set shows the tuner (vertical
block at top right) & the V164
zener diode (bottom, centre) that’s
connected to the collector of
transistor V105.
right, the timer function. And you’ve
prob
ably also guessed that it was
faulty. Right again but more to the
point, the symptoms were virtually
identical with those on the original
NV-370.
So it was into the works for a look
at the same board. The only snag was
that, in this machine, it is a proper
swine to get at. But when I did reach
the board the jeweller’s loupe told the
same story; two fractured joints.
Once these had been remade, the
timer worked perfectly. So the electrician had scored an up-market recorder,
in excellent condition, for no cost
other than my routine service charge.
It was smiles all round.
But one final thought. If my theory as
to the cause of these failures is correct,
My next story is on quite a different
theme. It concerns a Hitachi Fujian
colour TV set, model HFC-1425B,
which is in many ways similar to the
HFC-1421B dealt with in my June
1994 notes.
Initially, the exercise seemed like
a fairly routine one; so much so that
I was not sure whether the story was
worth the telling. I finally decided
that it was, mainly because the exact
nature of the fault was new to me and
I thought that it was worth passing
on for someone else’s benefit. In the
event, it turned out to have an unusual twist.
But first I will detail the service
exercise just as it happened. The
set came in with the complaint that
“there’s no picture and no sound”. I
interpreted this as meaning a completely dead set, which could mean
anything from a blown fuse to an obscure fault in the switchmode power
supply.
Well, the description was literally
true. There was no picture and no
sound but the set was still very much
alive. It was scanning normally and
displaying a beautiful off-channel
snowstorm, indicating that the fault
was somewhere in the front end.
Of course, this kind of fault would
normally produce plenty of noise in
the speaker but I had momentarily
forgotten that this chassis features a
muting circuit which kills the sound
if there is no signal.
This set employs a search and program system for channel selection and
this was the first thing I tried. I began
by checking for any channels that may
have already been programmed into it
and then, when this revealed nothing,
I initiated the search function.
But this didn’t work either and,
more to the point, there was no change
of any kind to the screen image during
these checks. Normally, there is some
variation as the system searches and
encounters odd patches of interference
but, in this case, there was just a steady
snowstorm.
Fortunately, the set is fairly easy to
work on, for which I give due credit
to the manufacturer. I went first to the
tuner, which is shown on the right- had
side of the accompanying circuit as a
small vertical block with nine terminals – see Fig.2.
The IF output terminal is at the
bottom, with the +12V supply terminal above it. This was the first one
to check and this was OK. The next
ones to check were the three marked,
respectively, BL, BH and BU. These
are +12V supply rail terminals for the
low (BL) portion of the VHF band, the
high (BH) portion of the VHF band,
and the UHF (BU) band. These are
energised individually, according to
the selected channel.
So, as the set is put through its
programming procedure, each of
these terminals should, in turn, go to
+12V. Which, in fact, is exactly what
happened. So that cleared that part of
the system.
That didn’t leave much, except
terminal VT. This carries the tuning
voltage – a variable voltage developed
at the collector of transistor V105 in
response to the signal fed to its base
from pin 1 of IC101.
So I should have been able to detect
a voltage on this pin, ranging from
about 0V to (typically) about 30V during a search function. Alternatively, it
should show a fixed voltage if a particular channel is selected. However,
there was no voltage of any kind on
this pin, regardless of which tuning
function was initiated.
Well that seemed fairly straightforward. Pin VT connects to the collector
of transistor V105 via three resistors:
R167, R168, and R169. These were
easily checked and cleared. From the
collec
tor of V105, the circuit goes
(down) to a voltage regulator circuit;
the kind of setup commonly found in
tuner supply systems and designed to
minimise any drift in tuning voltage.
It consist
ed of R182 (15kΩ), C175
(270pF) and zener diode V164 which,
I assumed from its type number, operated at around 33V. This circuit is
fed, in turn, from the main 113V rail.
And the solution was simple; resistor R182 was open circuit. Well, that
was a new one in a Hitachi Fujian,
although I have had trouble with a
similar resistor in a Samsung and also
in a Philips. In the latter two sets, the
resistor went high resistance, which
restricted the tuning range to the low
end of each band.
Anyway I fitted a new resistor and
the set came back to life. Nevertheless,
it was necessary to check that the full
tuning voltage range was available
and that all three bands could be programmed correctly. In fact, everything
checked out 100% and, after a routine
check of overall performance and a
few minor adjustments, the job was
finished.
Never-ending story
End of story? Not quite. And I wonder if any reader has spotted what
appears to be a contradiction in the
circuit as I described it above.
Well, take heart if you didn’t because I didn’t either; at least, not
initially. The truth is that, in practical
servicing, one cannot afford the luxury
of analysing every part of a circuit as
one works on it, particularly when it
is a simple operation like looking for
a lost voltage.
So, initially, I simply took the circuit at face value. But then I decided
to write this story; and I began making
notes and mentally organising how I
should present it. And, of course, it
August 1994 59
SERVICEMAN’S LOG – CTD
was obvious that, in order to put the
reader in the picture, I would have
to describe the circuit, just as I have
done.
Then suddenly it struck me. How
can we have a variable voltage developed at the collector of V105, when
that collector is fed directly from a
zener diode voltage regulator circuit?
And the simple answer is, we can’t.
So how does the system work? I
pondered over this at some length
and was still pondering over it in the
workshop when a colleague walked
in. Glad of an opportunity to pick
someone else’s brains, I immediately
buttonholed him.
When I filled him in, he readily
agreed that it didn’t seem to make
sense. His suggestion was that there
was an error in the circuit; that there
should be a collector load resistor between the regulator circuit and V105’s
collector. In fact, he felt sure he had
seen such an arrangement in another
circuit for a differ
ent model of the
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60 Silicon Chip
same make of set, only he wasn’t sure
which one.
At that point, he left me to ponder
some more. But I was through pondering. If his theory was correct, it
was easy enough to prove. The set
was still in the workshop, the owner
having left it with me before going
on holidays.
At the first opportunity, I pulled
the back off and traced out the circuit.
But there was no sign of any extra
resistor; the set was exactly the same
as the circuit.
So what’s the explanation? I made
some more careful measurements of
the voltages appearing on terminal VT
and, while they can range up into the
20V plus range, they went nowhere
near the 30V or so of the zener rating.
So, in fact, the zener wasn’t functioning. So why is it there?
The best explanation I can offer
is that the 15kΩ resistor, R182, is
the collector load resistor and the
113V rail, from which it operates, is
regarded as being sufficiently well
regu
l ated as not to need further
regulation.
But that still doesn’t explain the
role of the dormant zener, V164. My
guess is that it is purely a protective
device, designed to protect the tuner
in the event of a failure of, say, V105.
It this went open circuit, or ceased
to draw current for any other reason,
then close to the full 113V of the main
HT rail would be applied to the VT
terminal – and I imagine the tuner may
not like that.
Well, that’s my theory, and it looks
like I’m stuck with it. That is, unless
someone out there is on better terms
with Hitachi Fujian sets and can come
SC
up with another explanation.
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REMOTE CONTROL
BY BOB YOUNG
Modellers with dedication
In this & the following column, we will be
looking at the work of two modellers who
richly deserve the above description. For those
who have complained about such things in the
past, here you will find no flying sandshoes,
high speed model aircraft or radio controlled
machinery – just good solid R/C modelling of the
most excellent kind.
The first of the two is Keith Mealey,
one of my oldest and most loyal customers. He specialises in R/C boats
and, in particular, Murray River paddle steamers. Keith’s fleet of paddle
steamers include the P.S. Adelaide,
the P.S. Canberra and, for good measure, two models of the P.S. Pevensey,
one in 1:16 scale and the other in a
smaller scale.
Just for a change I will allow Keith
to tell his own story in his own matter-of-fact way. By the way, all the
dimensions are Imperial, for which
Keith makes no apology.
The P.S. Pevensey
“The first of these models is the
P.S. Pevensey which is a 1:16 scale
replica of this notable paddle steam-
er and measures about 84 inches
(2.1 metres) in length and 27 inches
(686mm) across the paddleboxes. It
has been scratch built using plans
available from the Port of Echuca
and additional measurements taken
from the actual vessel. Construction
commenced in 1991 and only a few
details are required to complete the
model.
The materials used in construction were 3/8" x 7-ply timber for the
hull frames and 3/32" x 3-ply for the
hull sides and bottom, overlaid with
1/16" thick Obechi planks below the
water-line. Obechi is also used for
the superstructure. The internal keelsons are made of 3/4" x 1-1/2" square
section aluminium with a 1/8" wall
thickness.
The engine is a twin cylinder type
(built from castings — the cylinders
being machined by the late Reg Wood)
of 3/4" bore and 1-1/2" stroke and fitted
with Stephenson reversing gear. Steam
is provided by a 6" diameter 10" long
copper Scotch Return boiler with
Inglis modification (certificated to
100 psi). The boiler is fired by bottled
propane gas.
Radio control
This photo shows the 1:16 scale model of the P.S. Pevensey paddle steamer. A
6-channel FM transmitter & receiver control the following functions: throttle,
rudder, reversing gear, whistle, steam-operated cylinder drain-cocks & an onboard automotive cassette player.
The model is controlled by a custom-built Silvertone FM 6-channel
transmitter and receiver. The functions
controlled are throttle, rudder, reversing gear, whistle, steam-operated
cylinder drain-cocks and an on-board
automotive cassette player. Power to
the electronics system is provided
through a Silvertone custom-built 12V
to 6V voltage regulator, connected to
the same 12V, 6A.hr gel-cell battery as
the cassette player. The regulator has
a high current capacity to power the
high-torque servos used.”
One of the reasons I have chosen
to present this series of articles apart
August 1994 65
from the obvious very interesting
content of these articles, is that each
of these modellers approached me
for custom built transmitters and
receivers.
Models such as those built by Keith
require a special type of transmitter.
This is in order to gain full operational advantage of the very spectacular
models they turn out. This past development work has made it possible
to present a design for a transmitter
and receiver in SILICON CHIP. The
receiver will be presented first, in a
few months’ time.
Now you may well ask, “Why present an R/C kit when there is so much
cheap, high quality gear available on
the market?” The answer is that apart
from the obvious pleasure and knowledge obtained from building your own
R/C system, one of the advantages of
the system to be presented is the builtin flexibility.
Our system will be capable of expansion from 2 to 32 channels, will
use AM or FM, and will have many
features not commonly found on commercial systems. Most importantly, it
will be done with readily obtainable
components, thus making servicing
easy.
However I digress. Let us allow
Keith to continue his story with an
account of his second paddle steamer,
the P.S. Adelaide.
The P.S. Adelaide is a 1:16 scale replica of the original & measures about
five feet in length. The radio control system is a JR FM 4-channel unit which
operates the throttle, rudder, forward/reverse & whistle.
The P.S. Adelaide
“This model is a 1:16 scale replica of
the P.S. Adelaide and measures about
five feet in length. It has been scratch
built from measurements taken from
the actual vessel and has taken over
1000 hours to complete (excluding the
machining of the engines). Construction commenced in 1987.
The materials used in the construction of the model were; 3/8" x 7-ply
timber for the hull frames, 1/8" x 3/8"
Spruce planks for the hull and 1/16"
Obechi planks for the superstructure.
The internal keelsons are of 1" x 1"
square box section aluminium.
This model is driven by two Stuart
10H 3/4" bore and stroke engines
coupled and mounted above the boiler. They are fitted with Stephenson
reversing gear. Steam is provide by
a gas-fired Stuart centre-flue marine
boiler (commercially built) which is
certificated to 50 psi.
The radio control system is a JR
FM 4-channel unit which operates
66 Silicon Chip
The P.S. Canberra radio control system is a commercial JR FM 5 channel radio
control unit which operates the rudder, throttle, forward/reverse & a cassette
player. Motor control is via a fully proportional electronic speed controller
which incorporates a 12V to 6V voltage regulator (to power the radio receiver).
the throttle, rudder, forward/reverse
and whistle.
The P.S. Canberra
Finally, there is P.S. Canberra. “This
is a 1:16 scale replica of the P.S. Canberra and measures about five feet in
length. It has been scratch built from
measurements taken from the actual
vessel.
Materials used in the construction
of the model were 1/4" x 5-ply timber
for the hull frames, 1/16" x 3/8" Obechi
for planking the hull (laid over 1/16"
plywood) and 1/16" Obechi planks
for the superstructure. The internal
keelsons are of 1" x 1" square section
aluminium.
This model is driven by a 12V Marx
decaperm motor with reduction gearbox, the final drive to the paddleshaft
being by toothed belt. Motor control
is via a Frank Brown (Maritime Model
Club of NSW Inc) fully proportional
electronic speed con
troller which
incorporates a 12V to 6V voltage regulator (to power the radio receiver),
forward/reverse control, neutral point
adjustment and maximum speed adjustment.
back to the interesting conversations,
the endless quest for perfection and,
most of all, the enthusiasm which
permeated every aspect of their lives
and compare those days with the money-centred conversations of today, I am
sad to the extreme.
Custom radio
This close-up view shows the 6-inch diameter x 10-inch long boiler in the P.S.
Pevensey. Also visible in the foreground is the propane gas bottle that’s used to
fire the boiler. The engine is a twin cylinder type of 3/4-inch bore & 11/2-inch
stroke & is fitted with Stephenson reversing gear.
The R/C system is a commercial
JR FM 5-channel control unit which
operates the rudder, throttle, forward/
reverse and cassette player.”
The above is a bare bones description which does little justice to the
exquisite workmanship that has gone
into these models. From the joggling
of the deck planking to the attention
paid to the steam plumbing, Keith
has spared no effort in his quest for
excellence.
Many people have great difficulty
in coming to terms with this type
of modelling and typical comments
when viewing this superb workmanship range from “I could not spend that
amount of time on a project that does
not earn any money” to “I just simply
would not have the patience!” What
these comments reveal is a complete
lack of understanding of the personality of the dedicated modeller.
The true, dedicated modeller is on
his own Quest of the Holy Grail and
in the case of modellers like Keith the
Grail becomes the perfect model. Every
joint in the framework or the tiniest
of details become mini adventures in
their own right, to be carried through
in a spirit of excellence. In the end,
the fact that onlookers may gasp at
the finished product is only icing on
the cake. The true satisfaction comes
from the inside but sadly this is a spirit
which is dying in our increasingly
materialistic society.
When I was young, there were thousands of these people and they were
my heroes. They built models of all
kinds of things but most of all they
glowed with an internal fire fuelled by
an increasingly rare commodity these
days; they were content! They were
great people to keep company with and
I mourn their passing. When I think
The transmitter for the P.S. Pevensey
is a built around standard Silvertone
RF (FM) & encoder modules. The
unusual steering wheel was hand
made & is fitted to a standard Futaba
2-channel wheel type steering unit
But enough of the philosophising.
Let us return to Keith’s radio. The
transmitter is a built around standard
Silvertone RF (FM) and encoder modules. There is nothing fancy about the
RF section but the encoder features
some interesting techniques. It is
basically a multiplexed output type
with a single tuning control to set the
1.5ms neutral. This is sent to each
control pot in turn, with the extremes
being the usual 1-2ms. Symmetrical
balanced reference voltages are used
which allow servo reversing.
The servo reversing is achieved by
bringing the three wires from the control pot to a 3-pin header socket (positive, signal, negative). Each channel
output has its own 3-pin header plug.
This allows some interesting features:
(1) Servo reversing is simply a matter of turning the plug through 180°.
(2) Channel shuffling can be achiev
ed by rearranging the order of the
control pots on the header pins. Thus,
different receivers can be used with
the correct servo outputs.
(3) Servo reversing is locked away
inside the Tx case and is not easily
switched into reverse by accident or
by fiddlers.
(4) The encoder PC board becomes
a true module and may be replaced
easily and quickly for servicing.
The photo of Keith’s Tx shows that
it is fitted with an unusual steering
wheel. This was hand made by Keith
and is fitted to a standard Futaba
2-channel wheel type steering unit.
The lever to the left of the case (throttle) is a standard single axis Silvertone
stick unit, fitted with a mechanical
trim lever. There are two slide controls
one above the steering wheel and one
on the left hand side of the case. Two
toggle switches and a momen
tary
switch complete the control complement. There is one spare, unused
channel built into the transmitter in
case of future expansion.
The receiver is a standard Silvertone
FM 8-channel unit. Next month, I will
describe some models by another dedSC
icated enthusiast.
August 1994 67
Bring your old nicad batteries back
to life. Blast them with this:
r
e
p
p
a
Z
d
a
c
Ni
Do you have a few suspect nicad batteries
lying around in your kitchen drawer? Why
not try bringing them back to life with this
Nicad Zapper? It zaps the cell with a highvoltage, high-current burst to blast away any
internal shorts caused by dendrites.
By DARREN YATES
Nicad batteries are one of the few
items in electronics that everyone
has an opinion on – you either love
‘em or hate ‘em! They can make life a
lot easier but they can also be a right
royal pain if you don’t treat them with
“kid gloves”.
The reason for most of the hate
mail they receive is the well-known
“memory effect”. This effect occurs if
the cell is not completely discharged
before being recharged. After numerous cycles, it “remembers” the
68 Silicon Chip
partially charged state to which it is
repeatedly discharged and thereafter
only discharges as far as this point.
The battery then behaves as though it
has gone “flat”.
When that happens, many people
assume that the cell has “had it” and
a new cell is substituted. It doesn’t
have to end this way though. Nicad
cells that suffer from memory effects
can often be restored to full health by
subjecting them to several complete
discharge/recharge cycles.
The better approach, of course, is
to avoid the memory effect in the first
place. This can be done by completely
discharging the cell to its end-point
voltage (usually 1.1V) before placing
it in the charger. An automatic nicad
battery discharger was described in
the November 1992 issue of SILICON
CHIP, while a complete charger with
automatic inbuilt discharging circuitry was featured in the September
1993 issue.
Another frequent cause of nicad
failure is dendritic growth within the
cell as it ages. Because they have a
fairly low impedance, these tiny dendritic growths create shorts across the
internal cell structure and so the cell
can no longer deliver its rated power.
Once again, the approach for most
people is to replace the cell with a
new one. However, it’s amazing how
often we keep these crook cells rather
than discarding them. Often, they are
thrown into a drawer or placed on
a shelf in the garage, perhaps in the
D1
1N4004
+9-20V
4.7k
68k
.01
Q1
BC548
C
B
68k
D2
1N4004
Q3
BC558 E
B
4.7k
.001
18k
C
B
E
E
B
5.6k
ZD1
33V
400mW
C
1M
100
35VW
ZAP
S1
Q7
MTP3055
D
1k G
S
100k
A
Q6 READY
BC557 LED1
C
K
10k
10k
B
C
L1 : 2 LAYERS OF 0.4mm DIA. ENCU
ON NEOSID L-5110 TOROIDAL CORE
Q8
BC548
E
1000
35VW
1000
35VW
NICAD
CELL
1k
1k
0V
390
+V
Q5
BC557
E
D3
FR104
E
1k
C
E
B
2.7k
Q4
BD139
C470 B
Q2
BC548
0.1
L1
100
35VW
PLASTIC
SIDE
B
E
C
A
VIEWED FROM
BELOW
K
E
C
B
GD S
NICAD ZAPPER
Fig.1: the circuit uses multivibrator stage Q1 & Q2 to switch transistors Q3 &
Q4 on & off. Q4, L1 & D3 form a step-up converter circuit; it charges the 100µF
reservoir capacitor at its output to 33V & so the two 1000µF output capacitors
also charge to 33V. The output capacitors are then discharged through the nicad
cell via MOSFET Q7 which is turned on by pressing S1. Q5 & ZD1 provide output
voltage regulation, while Q6 & Q8 drive the ready indicator LED.
forlorn hope that they’ll somehow,
magically, “get better”.
The cure
If you’ve got any crook nicads in
your home, its quite possible that
many of them can be resurrected using
this Nicad Zapper. Just as fuse wire
“blows” when you push too much
current through it, it’s also possible
to “fuse” (or blast away) the dendritic
growths by zapping the cell with a
brief high-voltage, high-current pulse.
Because the pulse is kept very brief,
no damage is done the cell itself.
However, the dendrites disinte
grate
and the cell can now be recharged to
full capacity, thus effectively bringing
it back to life.
As a result, the Nicad Zapper can
save you lots of dollars. Nicad batteries aren’t exactly cheap; at least, not
when you have to keep constantly
replacing them.
Well, that’s how it works in theory,
anyway. And while we can’t guarantee
that the idea will work for every nicad
cell (or battery pack), it should work
for at least some.
In operation, the Nicad Zapper
provides a 5ms burst of charge at
33V from two 1000µF capacitors. It
operates from a 9-20V DC plugpack
(or battery) supply and is easy to use.
You simply connect it to the battery
and push a single switch to deliver
the required “zap”. One zap should
generally be enough, but you can deliver several zaps to the battery if you
want to be really sure of getting rid of
all the nasties.
The circuit
Let’s now have a look at the circuit
for the Nicad Zapper – see Fig.1. As
you can see, discrete transistors do all
the work, from waveform generation
to charging and zapping.
Transistors Q1 and Q2 form a standard multivibrator circuit. It works as
follows.
When power is initially applied,
both transistors are forward biased and
are in a race situation. If Q1 turns on
first (for example), its collector pulls
the base of Q2 low via a .01µF capacitor and so Q2 will be biased off. The
.01µF capacitor now charges via its
associated 68kΩ resistor and, when it
reaches 0.65V, Q2 turns on and turns
off Q1 via the .001µF capacitor, and
so the process continues indefinitely.
The ratio of the two cross-coupled
capacitors sets the duty cycle of the
output waveform to 1:10, while the
frequency of operation is set by the two
capacitors and their associated 68kΩ
resistors to about 3kHz. As a result,
the circuit generates a train of brief
negative going pulses at Q2’s collector
and these pulses are fed to Q3 via an
18kΩ resistor.
Transistor Q3 functions as a driver
stage for NPN power transistor Q4.
Thus, each time a negative-going pulse
appears at Q2’s collector, Q3 and Q4
turn on.
Transistor Q4, inductor L1 and diode D3 together form a simple step-up
switching converter. It works like this:
each time Q4 switches on, current
flows through L1 and so energy is
stored in this inductor. During this
time, D3 is reverse biased since its
anode is effectively connected (via
Q4) to ground.
When Q4 subsequently switches off,
the collapsing magnetic field around
the inductor tries to maintain the
current through it and so the voltage
across the inductor rises. D3 is now
forward biased and so the inductor
dumps its stored energy into a 100µF
reservoir capacitor. The output from
this stage in turn charges two parallel
1000µF capacitors via a 390Ω current
limiting resistor.
Regulating circuitry
Left to its own devices, the output
voltage (ie, the voltage across the two
1000µF capacitors) could rise to over
70V, which is far too high. To prevent
August 1994 69
switch charges via the 100kΩ resistor
to ground and the 1kΩ gate resistor.
When it reaches full charge (after about
10ms), Q7’s gate is at 0V and so it no
longer conducts. This prevents the
user from holding the circuit on (by
keeping S1 pressed) and allows the
main reservoir capacitors to recharge
again.
This arrangement ensures that the
circuit can deliver only a one brief
zap to the nicad cell each time S1 is
pressed.
When S1 is released, the associated
1MΩ resistor discharges the 0.1µF
capacitor and so the switch circuit is
effectively re-armed.
LED1
A
S1
D1
0.1
L1
18k
68k
4.7k
.01
68k
Q3
100uF
+9-20V
Q8
Q6
0V
Q7
B
1k
100uF
Q4
2.7k
10k
D3
100k
Q5
1k
5.6k
10k
1k
Q2
470
Q1
390
1k
.001
4.7k
D2
1M
K
E
1000uF
TO NICAD
CELL
Ready LED
1000uF
Because we want the output capacitors to charge to the maximum
voltage (ie, 33V) in order blast away
any internal shorts in the cell, we need
some sort of indicator to tell us when
the circuit is ready. This is because
it takes a few seconds for the output
capacitors to fully recharge each time
S1 is pressed.
The ready indicator circuit is based
on LED 1, Q6 and Q8. If the output
voltage is less than 33V, then ZD1 is
non-conducting and Q6 is off. However, as soon as the output reaches
33V, ZD1 conducts and Q6 turns on.
This then turns on Q8 which lights
LED 1.
Power for the Nicad Zapper can
come from any 9-20VDC source capable of supplying around 200mA;
eg, a plugpack supply or the cigarette
lighter socket in your car. Diode D1
provides reverse polarity protection,
while the 100µF capacitor provides
C
ZD1
Fig.2: several different transistor types are used on the board, so check
their type numbers carefully against the circuit diagram (or parts list)
before mounting them in position.
this from happening, a voltage regulator circuit based on transistor Q5
and zener diode ZD1 is employed. It
monitors the voltage on D3’s cathode
and controls Q3 accordingly.
While ever the voltage on D3’s
cathode is below 33V, ZD1 is non-conducting and Q5 is off since its emitter
and base voltages are equal. However,
when the output voltage rises above
33V, ZD1 conducts and Q5 turns on
and pulls Q3’s base voltage above
its emitter voltage. Q3 now turns off
and so Q4 also turns off, effectively
shutting down the step-up converter
circuit.
The output voltage now falls again
and when it drops below 33V, Q5 turns
off and the step-up converter starts
again. As a result, the output voltage
is maintained at about 33V.
Q7, an N-channel MOSFET, is used
to discharge the output capacitors into
the cell. This transistor is controlled
by momen
tary pushbutton switch
S1. When S1 is pressed, Q7 turns on
(since its gate if pulled high) and so the
charge in the two 1000µF capacitors is
dumped into the nicad cell to provide
the required “zap”.
What happens now is that the 0.1µF
capacitor connected to one end of the
TABLE 1: RESISTOR COLOUR CODES
❏
No.
❏ 1
❏ 1
❏ 2
❏ 1
❏ 2
❏ 1
❏ 2
❏ 1
❏ 4
❏ 1
❏ 1
❏ 1
70 Silicon Chip
Value
1MΩ
100kΩ
68kΩ
18kΩ
10kΩ
5.6kΩ
4.7kΩ
2.7kΩ
1kΩ
470Ω
390Ω
2.2Ω
4-Band Code (1%)
brown black green brown
brown black yellow brown
blue grey orange brown
brown grey orange brown
brown black orange brown
green blue red brown
yellow violet red brown
red violet red brown
brown black red brown
yellow violet brown brown
orange white brown brown
red red gold brown
5-Band Code (1%)
brown black black yellow brown
brown black black orange brown
blue grey black red brown
brown grey black red brown
brown black black red brown
green blue black brown brown
yellow violet black brown brown
red violet black brown brown
brown black black brown brown
yellow violet black black brown
orange white black black brown
red red black silver brown
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**Illustrations are representative only
The completed PC board is mounted on the base of the case using machine
screws & nuts, while a dab of epoxy resin can be used to secure the inductor (L1)
in position on the board. Note that although a small heatsink was fitted to Q4 in
the prototype, this is not really necessary & may be safely deleted.
supply decoupling. The current
consumption is about 120mA while
the output capacitors are charging,
reducing to about 15mA once they are
fully charged and the ready LED is lit.
Construction
All of the components for the Nicad
Zapper, except for the switch and LED,
are installed on a PC board coded
11106941 and measuring 102 x 57mm.
Fig.3 shows the wiring details.
Before you begin the construction,
check the board careful
ly for any
shorts or breaks in the copper tracks
by comparing it with Fig.4. Fix any
faults that you do find (such faults
will be rare), then begin the assembly
by installing PC stakes at the external
wiring points, followed by the resistors
and capacitors.
Table 1 shows the resistor colour
codes but it’s also a good idea to check
each unit with your multimeter to be
doubly sure of its value.
The zener diode (ZD1), diodes (D1-
D3) and transistors (Q1-Q8) can now
be installed, taking care to ensure that
each part is mounted in the correct
location and with the correct polarity.
Note particularly that diode D3 is an
FR104 fast recovery type, so don’t
confuse it with D1 or D2.
Note also that some of the transistors
are NPN types while others are PNP
types, so refer to the circuit (or to the
parts list) for their type numbers when
mounting them on the board.
The MOSFET (Q7) must be installed
with its metal tab towards the adjacent
1kΩ resistor – see Fig.1 for the pinout
details.
Inductor L1 is made by winding two
layers of 0.4mm enam
elled copper
wire on a toroidal core. The simplest
way to wind it is to first take a 2-metre
length of wire and feed it half-way
through the core so that you have two
equal lengths. Now take one end and
wind on one complete layer, keeping
the turns tight and close together. The
other half of the wire is then used to
wind the second layer over the top of
the first.
When the windings have been completed, strip and tin the wire ends and
solder the inductor into place on the
board. The board assembly can now
be completed by connecting LED 1
and switch S1 via flying leads. Make
sure that the LED polarity is correct,
otherwise it won’t light when the circuit is ready.
Testing
Before applying power, it’s a good
idea to carefully check the board
against the wiring diagram (Fig.3) for
possible errors.
You will need a power supply capable of delivering between 9V and 20V DC (a 12V
DC plugpack supply is ideal).
This should be connected to
the board via your multimeter
12VDC
which should be set to the
+
400mA (or 1A) range.
Check that the supply polarWhen LED is on,
+
ity is correct before switching
press button to
on. After an initial surge current
zap battery
of about 100-150mA, (depending on the supply voltage),
ZAP
READY
the current should drop back
to around 15-20mA and, after
about four seconds, the LED
should light.
If the current doesn’t drop and
Fig.3: this full-size artwork can be used as a drilling template for the front panel, or
the LED doesn’t light, check the
you can vary the front panel layout to suit your own requirements since the layout
circuitry around zener diode
is not critical.
NICAD
ZAPPER
72 Silicon Chip
PARTS LIST
Fig.4: check your board carefully against this full-size etching pattern
before mounting any of the parts.
ZD1 and transistors Q5 and Q6. In
particular, make sure that these parts
have been installed correctly and that
there are no solder splashes on the
underside of the board.
If the current does drop but the
LED refuses to light, check the voltage across the 100µF capacitor. If this
voltage is 1.2V less than the supply
voltage, check the pulse generator
circuit (Q1 & Q2) and the step-up converter circuit (Q3 & Q4). If the voltage
is correct (ie, about 33V), check Q6
and Q8 in the LED indicator circuit
and check the LED polarity.
Finally, connect a 0.22Ω 1W resistor across the output terminals to the
nicad cell and use your multimeter to
monitor the voltage across the 1000µF
capacitors. This should normally be
about 33V but should drop to almost
0V when S1 is pressed. If it doesn’t,
check the Q7 has been installed correctly.
Assuming that the board works
correctly, it can now be installed in
its plastic case. First, attach the label
to the lid of the case and drill out the
mounting holes for the switch and the
indicator LED. It’s best to drill a small
pilot hole for the switch to begin with
and then enlarge this to the correct size
using a tapered reamer.
The hole for the LED should be
made just large enough to ensure a
tight fit. If you make the hole too
big, then you will either have to use
a LED bezel or epoxy resin to secure
the LED.
The DC socket is mounted on one
end of the case and an additional hole
is drilled adjacent to this to provide
access for the leads to the nicad cell.
In addition, you will have to drill four
mounting holes in the base of the case
to mount the PC board. You can use
the board itself as a template when
marking out these holes.
The various items of hardware can
now be mounted in position and the
PC board secured using 3mm screws
and nuts, with an additional nut under
each corner to serve as a spacer. This
done, the wiring can be completed as
shown in Fig.3. The output leads can
be fitted with crocodile clips (red for
positive and black for negative), or
fitted with some other connector to
suit your nicads.
Battery packs
While this circuit was really designed to work with single nicad cells,
it is quite possible that it will also work
with some nicad battery packs, such as
camcorder and racing packs. However,
it will generally be less effective with
these because of the higher impedance
of a battery pack and because of the
lower voltage that would appear across
each cell.
In addition, because of the experimental nature of this project, we can’t
guarantee that it will work with every
dud nicad cell you have lying around.
Nicad cells do fail eventually and no
amount of zapping will bring them
back to life. However, it should work
with at least some cells and if you use
lots of nicads, it will save you money
in the long run.
Upgrading the MOSFET
Finally, be warned that the output
circuitry of the Nicad Zapper is not
short-circuit proof. MOSFET Q7 can
1 PC board, code 11106941,
102 x 57mm.
1 2.1mm DC panel mount socket
1 momentary pushbutton switch
(S1)
1 plastic zippy case, 130 x 68 x
41mm
1 front panel label, 126 x 62mm
1 14.8mm OD toroidal core
(Altronics Cat. L-5110, Jaycar
Cat. LF-1240, or equivalent)
2 metres of 0.4mm dia.
enamelled copper wire
1 black medium alligator clip
1 red medium alligator clip
4 self-adhesive rubber feet
Semiconductors
3 BC548 NPN transistors
(Q1,Q2,Q8)
1 BC558 PNP transistor (Q3)
1 BD139 NPN transistor (Q4)
2 BC557 PNP transistors
(Q5,Q6)
1 MTP3055A/E MOSFET (Q7)
2 1N4004 power diodes (D1,D2)
1 FR104 1A fast-recovery diode
(D3)
1 33V 400mW zener diode
(ZD1)
1 red 5mm LED (LED1)
Capacitors
2 1000µF 35VW electrolytics
2 100µF 35VW electrolytics
1 0.1µF 63VW MKT polyester
1 .01µF 63VW MKT polyester
1 .001µF 63VW MKT polyester
Resistors (0.25W, 1%)
1 1MΩ
2 4.7kΩ
1 100kΩ
1 2.7kΩ
2 68kΩ
4 1kΩ
1 18kΩ
1 470Ω
2 10kΩ
1 390Ω
1 5.6kΩ
1 2.2Ω 1W
Miscellaneous
Machine screws, nuts & washers;
light duty hook-up wire.
fail if S1 is pressed repeatedly while
the output leads are shorted together,
but it should be adequate for normal
cell “zapping”. If you do want to make
the output short-circuit proof, then
a higher rated MOSFET, such as an
IRF540, should be used but note that
this device costs about $5 more than
SC
an MTP3055.
August 1994 73
SILICON
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SILICON
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SILICON
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If you are seeing a blank page here, it is
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SILICON
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If you are seeing a blank page here, it is
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August 1994 79
PRODUCT SHOWCASE
Review: Philips P65 UHF CB radio
Radios of all kinds continue to get smaller & CB
radios are too, as is shown by this latest offering
from Philips. Small enough to fit in your pocket,
it has plenty of power & more features than most
people will ever use.
The first thing that strikes you
about the new Philips P65 UHF CB
transceiver is its size. At only 300
grams, it is tiny and very comfortable
to hold but has features you would
expect from larger radios. Styled in
black with a stubby "rubber ducky"
antenna, it has two scanning modes,
a facility for repeater operation and
a back-lit LCD.
It has two knobs on the top, on/off
volume and channel selection. The
squelch control is also on the top but
does not protrude, to avoid accidental
adjustment. The digital display shows
the current channel number and
function settings, while a 14-segment
bargraph serves as both a transmit and
receive signal strength indicator.
The push-to-talk switch is on the
lefthand side of the case, making it
easy for right or left-handed operation.
The FUNC switch immediately above
the push-to-talk switch accesses the
control settings. The triangular buttons
to the left of the display are pressed in
conjunction with FUNC to adjust the
output power, the scanning options
and the backlight for the LCD.
The radio covers all 40 channels of
the UHF CB band from 476.425MHz
to 477.400MHz in 25kHz steps. There
are a further eight channels (41-48)
that operate with offsets for repeater
use. Scanning modes can either toggle
between all 48 channels or a group
of user programmed channels. While
scanning, the unit can also be instructed to stop at busy channels until the
carrier disappears or to pause for five
seconds before resuming. Scan
ning
modes are indicated on the LCD by a
80 Silicon Chip
flashing hyphen between the
CH and the channel number.
Four different battery packs
are available for the P65. The
battery packs slide into the
bottom of the case and lock into
place. A 7.2V 700mAh nicad
pack is standard while a 12V
600mAh nicad pack, for higher
power, is optional. There are
also two other optional packs
that accept indi
vidual cells;
a dry cell pack (six AA cells)
and a pack that takes six AA
nicad cells. The last pack has
a charging socket to charge the
individual cells in situ.
The radio comes with a
trickle charger plug pack for the
7.2V pack. This will fully recharge the battery in 14 hours,
with the battery still connected
to the radio or separately, via
a small socket in the bottom of
the pack. The optional 12V nicad pack
has a separate matching trickle charger
that will also recharge it in 14 hours.
A desktop fast charger is also
available that will recharge nicad
battery packs in one hour and shut
off automatically. It has dual slots to
allow charging of two batteries simultaneously.
Another worthwhile accessory is a
speaker-microphone that plugs into a
socket adjacent to the antenna. This
allows you to leave the radio in your
pocket or clipped onto your belt while
it is in use.
Nominal output power with a 12V
pack is 5 watts for the high power
setting and 1 watt for the low. This
reduces to 2.5 watts (high) and 1 watt
(low) using the 7.2V pack. When you
power up, the output power is always
initially set to low, to conserve the
battery.
The P65's size (60 x 32 x 142mm)
and smoothly sculpted edges make it
very comfortable to hold and operate.
The LCD is large enough to read at a
glance and in low light conditions, the
greenish backlight is very effective.
To save power, the backlight turns
off after five seconds, giving you just
enough time to find out what channel you're on and the power setting
you're using.
If you want to use the various scanning modes and functions, you must
read the manual first, as they certainly are not self-evident.
The need to press the FUNC button to access each feature
is a double-edged sword. It does mean that you can't accidentally change any of the settings whilst handling but
means you have to go through a complicated set of steps
to modify any function.
This aside, the P65 performs well and from signal
reports, has good audio quality. It a comes with a vinyl
case that has a clear window for the display. With its neat
styling, transmitter capable of 5 watts output, a receiver
that is surprisingly sensitive and a price tag of $599, it is
an attractive package. (M.C.)
PC-mount toroidal transformers
now available
PC-mount transformers have been widely used in
industry for many years but up till now, toroidal transformers have not been available in PC-mounting form.
Now they are.
This new range of toroidal transformers is fully encapsulated and each has a threaded 4mm insert for securing
it to the PC board. They are available in seven power
ratings – 1.6, 3.2, 5, 7, 10, 15 and 25VA – and all have
class A insulation (105°C). There is a choice of secondary
voltages – 2 x 7V, 2 x 9V, 2 x 12V, 2 x 15V, 2 x 18V and 2 x
22V – and the two secondary windings may be connected
in series or parallel.
For further information, contact the Australian distributors, Tortech Pty Ltd, 24/31 Wentworth Street,
Greenacre, NSW 2190. Phone (OZ) 642 6003 or Fax (OZ)
642 6127.
Universal drill has
collet chuck
Pictured is one of two
drills available for a range
of hobby work. The Model
O400 has coilets to take drills ranging from 0.3 to 3.2mm.
The unit can be powered from a model train controller or
battery charger with an output of 12-18V DC and a current
capacity of at least one amp. Depending on the input
voltage, the no-load chuck speed ranges from 12,000 to
20,000 RPM. It is priced at $56.00.
Also available is the larger model 0600 which has a
quick change chuck and thrust ball bearing for long life.
PC COMPUTERS (08) 364 0902 (08) 332 6513
36 Regent St, Kensington, South Australia
High Power 2.5 Watt Transmitter Kit FMTX1
$69
This kit uses a single transistor to provide up to 2.5 watts into a 50-ohm load. It can be
set on the FM band from 88-108MHz. Audio is 500mV P-P with Australian pre-emphasis.
Power supply from 12-24 volts DC. Range up to 100 miles. Leaky coax distribution can
be used with any of our transmitters, terminate up to 2km of coax with a 50-ohm resistor
and no radiation occurs. Use a 150-ohm WW pot and you can set the level of radiation up
to 300 metres from the coax. You can use this method to comply with DOTC schedule 3.
XTAL Locked 30mW Transmitter (The best quality kit transmitter
in Australia) FMTX2B
$49
This transmitter is XTAL-locked on 100MHz (XTAL supplied) and is the most stable kit
transmitter on the market. It features a 3-stage design with only two tuned circuits and
a clean output. This design can be used as the basis of a station exciter.
Digital Stereo Coder (All Digital Design With Australian
Pre-emphasis) FMTX2A
$49
This is a universal stereo coder able to be used with all of our transmitter designs and
many others. Its performance is superior to domestic encoder single chip designs.
Dozens have been sold to FM stations as a standby stereo coder or with the FMTX2B
as an exciter.
Both FMTX2A and FMTX2B on 1 PCB as a complete stereo transmitter FMTX5
$99
MAX I/O Board for PCs (Talk To The Outside World)
$169
This kit features 7 relays, ADC, DAC, stepper motor driver with sample software in
Basic and connects to a PC’s parallel port. Now also available I/O bits software for
MS Windows so you can program functions without being a programmer. Call relays
by a name like stop relay, assign its own icon - uses a simple VISUAL interface to
make your own PLC. Full developer’s version has DOS runtime so you do not require
Windows and optional support for LCD displays. Data logging ADC and DAC boards
and more. MAX version $169.
FM Band Linear Amplifier Kits (All Imported Kits)
New 30mW to 1 watt linear coming in September 1994 (advance orders taken)
500mW to 5 or 10 watts
$199
250mW to 25 watts
15 watts to 110 watts
$599
40 watts to 300 watts
Power supplies and heatsinks not included in short form kit price.
$99
$249
$999
Other kits available. Call for a list or see Silicon Chip April-June 1994 or the
Silicon Chip Model Railway Book.
August 1994 81
SATELLITE
SUPPLIES
Aussat systems
from under $850
SATELLITE RECEIVERS FROM .$280
LNB’s Ku FROM ..............................$229
LNB’s C FROM .................................$330
FEEDHORNS Ku BAND FROM ......$45
FEEDHORNS C.BAND FROM .........$95
DISHES 60m to 3.7m FROM ...........$130
Baby stereo mixer
from Jaycar
This little mixer is designed to
mix up to four stereo sources and
a microphone input. The stereo
inputs all accept line levels with
two switchable to accept phono
signals from turntables. A crossfader permits fading between these
two channels.
A talkover switch adjacent to the
microphone input drops the music
level to allow announcements to
be made. With the aid of a set of
headphones, individual channels
may be cued, prior to being added
to the output mix. Headphone
LOTS OF OTHER ITEMS
FROM COAXIAL CABLE,
DECODERS, ANGLE
METERS, IN-LINE COAX
AMPS, PAY-TV DECODER
FOR JAPANESE, NTSC TO
PAL TRANSCODERS, E-PAL
DECODERS, PLUS MANY
MORE
For a free catalogue, fill in & mail
or fax this coupon.
✍
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on your satellite systems.
Name:____________________________
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Suburb:_________________________
P/code________Phone_____________
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Ph (03) 553 1763; Fax (03) 532 2957
82 Silicon Chip
levels are adjustable too.
Two 5-segment LED VU meters
above the input sliders display the
output levels of the mixer. RCA
sockets are used for all inputs and
outputs except for the microphone
input and record output which use
6.5mm jack sockets.
The case is steel finished in black
crinkle enamel and with moulded
plastic side panels. Power to the
unit is via a 3.5mm jack socket on
the rear panel and a 12V AC plugpack is supplied.
Priced at $159, themixer is available from all Jaycar Electronics
stores and dealers. (Cat AM-4212).
The chuck will take drills from 0.4 to
3.5mm and has a no-load speed the
same as above. It is priced at $77.00.
Both drills are available in carrying cases with 11 tool bits. For
further information, contact Anton's
Trains, Cnr Prince & Mary Sts, North
Parramatta, NSW 2151. Phone (02)
683 3858.
Micron soldering
station from Altronics
This temperature controlled soldering station has a 40 watt ceramic
heater element and a stainless steel
barrel.
The iron-clad tip is chrome plated
and has a large thermal inertia to
improve temperature stability. The
temperature dial on the front panel
selects tip temperatures from 250430°C while a LED indicates when the
heating element is on.
Instead of the usual step-down
transformer, this soldering station
uses zero voltage switching circuitry
to cycle the element on and off. At the
same time, the insulation between the
heating element and the grounded tip
is quoted at greater than 100MW, so tip
voltages are very low.
The soldering station is priced at
$129 and is available from Altronics,
174 Roe St, Perth, WA 6000. Phone
1800 999 007 (toll free).
Tiny B/W CCD camera
on a PC board
Now available: the complete index to
all SILICON CHIP articles since the first issue in November 1987. The Floppy Index
comes with a handy file viewer that lets
you look at the index line by line or page
by page for quick browsing, or you can
use the search function. All commands
are listed on the screen, so you’ll always
know what to do next.
Notes & Errata also now available:
this file lets you quickly check out the
Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index
but a complete copy of all Notes & Errata text (diagrams not included). The file
viewer is included in the price, so that you can quickly locate the item of interest.
The Floppy Index and Notes & Errata files are supplied in ASCII format on a
3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File
Viewer requires MSDOS 3.3 or above.
ORDER FORM
PRICE
❏
Floppy Index (incl. file viewer): $A7
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Notes & Errata (incl. file viewer): $A7
❏
Alphanumeric LCD Demo Board Software (May 1993): $A7
❏
Stepper Motor Controller Software (January 1994): $A7
❏
Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7
❏
Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7
❏
Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7
❏
Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7
❏
I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7
POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5
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✂
It's amazing what you can find
on a PC board these days. This tiny
PC board, which measures just 70 x
46mm, is actually a complete black
and white (B&W) CCIR video camera.
It has only three connections: +12VDC,
video out and ground. The video
output is CCIR 50Hz standard, which
means that it's compatible with any
PAL VCR. All you do is hook up the
power supply and connect the video
output from the camera to the video
input of th,e VCR, and you are ready
to record.
The charge-coupled device (CCD)
image sensor has 320,000 pixels (picture elements) and 400 TV lines and
the picture is excellent for something
so small. It also has auto-iris control
so that you don't need to set the light
level. The automatic shutter can vary
between 1/50th to 1/32,000th second
speed.
The wide-angle lens has a lens cover
and a grub screw to lock the current
focus into place. This can be loosened
and the lens focused either on infinity
or as close as 4mm! Minimum required
luminance is quoted as 0.1 Lux. Six
infrared LEDs provide extra light for
low-light applications. The output
signal is composite video with 1V p-p
amplitude and 750 impedance.
Power requirements are 11V to
15VDC but it will run down to around
9VDC. The supply current requirement is quoted at less than 200mA (the
supply current for the sample pictured
above measured 130mA).
The price of this camera is just
$239 and it is available from Oatley
Electronics, PO Box 89, Oatley, NSW
2223. Phone (02) 579 4985 or fax (02)
570 7910. (D.Y.)
SILICON CHIP SOFTWARE
August 1994 83
VINTAGE RADIO
By JOHN HILL
Watch out for incorrect valve
substitutions in old receivers
There are many traps to watch out for when
repairing old valve radios. Often, valve radios
are obtained with an incorrect valve fitted or
with the valves in the wrong sockets.
I was repairing a radio recently and
ran into a distortion problem that took
quite a while to solve. As is often the
case, once the fault had been found and
rectified, it was all fairly obvious and
I should have solved it much sooner
than I did. Sometimes, what should
be obvious isn’t very obvious at all.
The receiver in question was a
mid-1950s 5-valve Philips mantel, a
relatively small, budget-priced radio
which is quite straightforward in
design and normally a simple one to
repair.
This particular receiver had been
well worked over long before it found
itself on my workbench. Someone had
already replaced the paper capacitors
with polyester types and several of
the mica capacitors had been replaced
with an assortment of styros and ceramic disc types.
Someone had also installed a few
resistors and these stood out like neon
signs because they were the old, large,
one watt types and not the smaller
units that were originally used in the
receiver.
The electrolytics, however, had not
been replaced and looked in very poor
condition. These were removed and
new 450-volt capacitors installed in
their place.
All things considered, the underside
of the chassis looked far from original,
as there had been many replacements
and alterations, some of which were
not very neat.
The valve complement consisted
of: 6AN7, 6N8, 8BD7, 6M5 and a 6V4
rectifier. The valves were checked in a
valve tester and all tested good.
The reason for the receiver not
working was soon found to be an
open primary winding in the output
transformer, which is a fairly common
fault. A new transformer was installed
and the set worked once again.
Distortion problems
Although the receiver in the text was referred to as a 5-valve Philips, it is in fact
the Fleetwood version of that radio. The set had been worked on extensively in
the past & came fitted with a substitute valve that was not working correctly.
84 Silicon Chip
However, it did not work very well,
the most obvious symptom being
noticeable distortion in the sound.
What’s more, after the set had warmed
up and was starting to work, there was
a background squeal accompanying
the sound for about a 10-second period
before it faded away.
Squeals and distortion can sometimes be due to a faulty valve and,
although all of the valves tested OK,
valve testers cannot diagnose a valve
with a built-in squeal.
After replacing the valves, one at a
time, the same faults remained. Both
the squeal and the distortion were still
there, which quickly disproved the
theory that it might be a crook valve
that was causing the problem.
It was a very hot day and my patience was wearing thin. It was time
to put the job aside and do something
else.
That night, I lay awake thinking
about my distortion problem and went
through all the likely possibilities. It
was well after midnight when it suddenly dawned on me. The 6N8 was the
wrong valve for that particular line up.
Almost never does one find two valves
with twin diodes in the one receiver.
Why use a 6N8 with diodes and a
6BD7 also with diodes in the same
set? Surely the 6N8 had been used as
a substitute for a 6BH5.
The next morning, I withdrew the
6N8 from its socket and slipped in
a 6BH5 to take its place. The result
was as expected – no squeal and no
distortion. Someone at some time
had installed an incorrect valve and
I wasn’t observant enough to pick it
up. In fact, all I had to do was check
off the valves in the receiver against
those listed on the sticker attached to
the rear dust cover. There it was in full
view for anyone who cared to look –
a 6BH5 was used as the IF amplifier,
not a 6N8.
These are the two valves mentioned in the text: the 6BH5 & the 6N8. While
both valves can be used as intermediate frequency (IF) amplifiers, they require
slightly different socket connections. In the case of the Philips set, someone’s
failure to make the necessary modifications resulted in a distorted output.
Pin connections
If one checks the base pin connections of these two valves, everything
works out reasonably well until pins
7, 8 and 9. Pin 9 on a 6N8 connects to
the suppressor grid and, in this case, it
wasn’t earthed. There is no connection
at pin 9 on a 6BH5.
In a 6BH5 valve, the suppressor grid
is earthed internally via the cathode,
whereas in the 6N8, the suppressor
connects to pin 9 and must be earthed
externally from the socket connection
if the valve is to function properly.
Therefore, using a 6N8 as a substitute for a 6BH5 was simply asking
for trouble because it was operating
without the suppressor grid.
In a pentode valve, the electrons
from the cathode strike the plate with
such velocity that some bounce back
and would be attracted to the positively charged screen grid except that
the suppressor repels them back to the
plate. Without the suppressor grid,
noticeable distortion results.
If pin 9 had been earthed, then the
6N8 would probably have worked
quite satisfactorily and the two valves
could then be interchanged. Table 1
shows the base pin details of the 6N8
and 6BH5 valves.
Many valves use only some of their base connections. For example, the 5Y3 (left)
has just 5 pins, while the 6V6 (right) has 6 or 7 pins. Receiver manufacturers
often used vacant socket terminals as convenient mounting points for other
components & so a substitute valve may require considerable socket rewiring.
Table 1: Pin Connections For The 6BH5 & 6N8 Valves
Pin No.
1
2
3
4
5
6
7
8
9
6BH5
G2
G1
K,G3,IS
H
H
A
IC
IC
NC
6N8
G2
G1
K,IS
H
H
A
D1
D2
G3
Obscure faults
What I have just described is one of
the seemingly endless problems that
regularly confront the vintage radio
repair man. Due to many obscure
reasons, quite a number of old valve
radios have “built in” faults that can
be difficult to locate. The new chum
to valve radio repairs can encounter
many a headache. Wheth
er he can
solve them or not depends on his
ability and perseverance.
Those magnificent old radio servicemen from yesteryear, who have
August 1994 85
Like all radiOs, the HMV Little Nipper will only work with the right valves
in the right sockets. None of its valves are interchangeable. It is always an
advantage to know what valve types go where because sometimes old radios are
obtained with incorrect valves or with the valves installed in the wrong sockets.
spent all or most of their working life
in the trade, have a sixth sense when
it comes to troubleshooting. They
have encountered every conceivable
problem so many times that they
almost instinctively know what it is
going to be.
On the other hand, vintage radio
repairers are often hobby
ists, like
myself, and each repair is a new and
baffling experience. When this is the
case, it takes a long time to become
reasonably proficient and even then
there are plenty of faults that can really
fatigue the grey matter.
A wrong valve, as in the previously mentioned Philips receiver, was
something that I should have picked
up immediately but my brain was out
of gear and free-wheeling at the time.
I will try to save face by blaming my
lapse on the extremely hot weather at
the time.
Radios having an incorrect valve or
two are a common occurrence when
buying non-working receivers from
secondhand dealers.
Some dealers even have a big box
of miscellaneous valves which they
use to fill up the empty valve sockets
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
86 Silicon Chip
of any receivers that may need them.
I have encountered this on many
occasions – radios with two or three
rectifiers, a radio frequency valve in
the output socket, and so on. In fact,
the variations are almost unlimited –
just fit a couple of TV valves here and
a frequency converter there; anything
to fill the empty sockets and make a
receiver look complete.
Then again, a receiver may have all
the right valves but some may not be
in their correct sockets. It is therefore
important to learn the functions of
various valve types and know how
they work in relation to a superhet
receiver.
Of course, there is a decided advantage in buying a radio that actually
works but then one always pays more
for goers than non-goers.
What’s more, as the radio described
earlier clearly demonstrates, just
because a set is working, it doesn’t
necessarily mean that it has the right
valves in it – working and working
properly are two different things.
The difference in the case of the little Philips receiver was just one valve
with a slightly incompatible base pin
configuration.
Substitute valves
There are not many substitute
valves in the true sense of the term.
If another type of valve is used as
Valve data manuals are invaluable when it comes to substituting valves. These
manuals contain details of various valve types & show their socket connections.
rate components may be conveniently
joined at a blank valve socket pin.
This situation can cause problems
when substituting another valve if
what was once a non-connection
becomes a valve pin connection.
Naturally, any components soldered
to that particular socket terminal must
be removed and mounted somewhere
else.
Obviously, any radio repair involving valve substitutions is quite difficult
if one does not have a comprehensive
valve characteristics manual. A valve
manual provides all the necessary base
pin information and is a much needed
guide when it comes to substituting
valve types.
Now for a quick change of subject. I
recently came home from a fortnight’s
holiday with a gramophone and four
radios, including a 1936 console.
Amazingly, there was still room for
my wife and all our holiday luggage
in our little Ford Laser.
I might add that packing the car was
a fairly delicate operation. And, with
spare wheel located underneath all the
junk, I was thankful that no roadside
wheel changes were necessary on the
SC
way home.
TRANSFORMERS
• TOROIDAL
• CONVENTIONAL
• POWER • OUTPUT
• CURRENT • INVERTER
• PLUGPACKS
• CHOKES
Equivalent manuals are also handy guides when looking for substitute
valves. An equivalent valve is one that will fit into the socket & work without
modifications to the circuit. A substitute valve, on the other hand, may require
extensive socket rewiring or even the fitting of another type of socket.
a replacement, it may need socket
alterations (as was the case with the
6N8), and/or other changes such as
different plate, screen and cathode
resistors, so that the replacement
valve can work as intended. There
is nothing quite like using the right
valve for the job. Regrettably, the
right valve is not always available or
affordable and a compromise is the
only way out.
While we’re on this subject, there is
another aspect to be wary of regarding
the use of substitute valves.
Many valves do not use all of their
base pins and, in the case of some
octal based valves, not all of the pins
are fitted. For example, 6V6 valves
often have 6 or 7 pins while 5Y3s
have only 5 pins. The missing pins are
not fitted for the simple reason there
are no connections to them anyway
and it makes economical sense not
to have them.
However, it is frequently the case
that the socket connec
tions corresponding to the missing pins have
components soldered to them.
Radio manufacturers often used
these socket terminals as connection
points to join other components and,
in some instances, three or four sepa-
STOCK RANGE TOROIDALS
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August 1994 87
Silicon Chip
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.
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.
Fluid Level Detector; Simple DTMF Encoder;
Studio Series 20-Band Stereo Equaliser, Pt.2;
Auto-Zero Module for Audio Amplifiers (Uses
LMC669).
October 1989: FM Radio Intercom For Motorbikes
Pt.1; GaAsFet Preamplifier For Amateur TV; 1Mb
Printer Buffer; 2-Chip Portable AM Stereo Radio,
Pt.2; Installing A Hard Disc In The PC.
April 1989: Auxiliary Brake Light Flasher; What
You Need to Know About Capacitors; Telephone
Bell Monitor/ Transmitter; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2.
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.
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.
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.
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.
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;
Designing UHF Transmitter Stages.
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
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.
March 1990: 6/12V Charger For Sealed Lead-Acid
Batteries; Delay Unit For Automatic Antennas;
Workout Timer For Aerobics Classes; 16-Channel
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.
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.
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.
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.
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.
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Card No.
January 1991: Fast Charger For Nicad Batteries,
Pt.1; Have Fun With The Fruit Machine; Two-Tone
Alarm Module; LCD Readout For The Capacitance
Meter; How Quartz Crystals Work; The Dangers
When Servicing Microwave Ovens.
February 1991: Synthesised Stereo AM Tuner,
Pt.1; Three Inverters For Fluorescent Lights; 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.
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.
August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder;
Tuning In To Satellite TV, Pt.3; Step-By-Step Vintage Radio Repairs.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
July 1993: Build a Single Chip Message Recorder;
Light Beam Relay Extender; AM Radio Trainer,
Pt.2; Windows Based Digital Logic Analyser;
Pt.2; Quiz Game Adjudicator; Programming The
Motorola 68HC705C8 Microcontroller – Lesson 1;
Antenna Tuners – Why They Are Useful.
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
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).
April 1994: Remote Control Extender For VCRs;
Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator;
Low-Noise Universal Stereo Preamplifier; Build
A Digital Water Tank Gauge; Electronic Engine
Management, Pt.7.
May 1994: Fast Charger For Nicad Batteries;
Induction Balance Metal Locator; Muilti-Channel
Infrared Remote Control; Dual Electronic Dice; Two
Simple Servo Driver Circuits; Electrronic Engine
Management, Pt.8; Passive Rebroadcasting For
TV Signals.
June 1994: 200W/350W Mosfet Amplifier Module;
A Coolant Level Alarm For Your Car; An 80-Metre
AM/CW Transmitter For Amateurs; Converting
Phono Inputs To Line Inputs; A PC-Based Nicad
Battery Monitor; Electrronic Engine Management,
Pt.9
July 1994: SmallTalk – a Tiny Voice Digitiser For
The PC; Build A 4-Bay Bow-Tie UHF Antenna;
PreChamp 2-Transistor Preamplifier; Steam Train
Whistle & Diesel Horn Simulator; Portable 6V SLA
Battery Charger; Electronic Engine Management,
Pt.10.
PLEASE NOTE: all issues from November 1987
to August 1988, plus October 1988, December
1988, January, February, March & August 1989,
May 1990, and November and December 1992
are now sold out. All other issues are presently
in stock. For readers wanting articles from soldout 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.
August 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.
Drum kit
amplification
I have a drum kit at home and
would like to amplify it. I realise I
need microphones, a mixer, a preamp,
an amplifier and, of course, speakers.
When it comes to building electronic
kits there is no problem at all.
However, I don’t understand all
the technical jargon that comes with
these kits. I’m not sure on the type of
mic I should use so maybe you could
tell me the type (unidirectional vs.
omnidirectional) and what impedance I need if I want to use two mics
overhanging my cymbal clusters and
a mic on each drum.
I was very keen on the Digitor series
with the XLR plugs on page 24 of the
Dick Smith Electronics catalog (93/94).
These mics are quite affordable and
I would like to use them if they are
suitable. If not, could you recommend
something similar?
I have read about the 4-Input Guitar
Mixer in the January 1992 issue of
SILICON CHIP. That is similar to what
I need but I would like a mixer with
more channels, preferably 8-12, reverb, and some kind of echo or effects
that could be used in each or some of
the channels.
Is there a kit or kits that can do most
of this and still accept microphone
outputs and possibly contain a 9-band
equaliser or similar? Could you match
a preamp to this and specify a power
supply for this preamp.
Where does the Effects Loop go in
relation to the amplifier or preamp?
Also, where does the mixer go exactly;
after the mics but before the preamp,
I thought?
In the amplifier, I would like 100W
or preferably more. This allows me
to expand in other areas and not be
restricted by my gear. I noticed a 100W
module in the Dick Smith Electronics
catalog, page 145. This was good as
Tape equalisation
for preamp
Thanks for the universal
preamp project in the April
1994 issue. It is a most useful
project and I will be building
a few for applications that I
have. However, I would like
to ask for feedback network
details to allow the module
to be used with open reel tape
decks. I want to provide NAB
equalisation at 1.875ips (possibly the same as cassette),
3.75ips, 7.5ips and 15ips. (R.
C, Pakenham, Vic).
• While it is possible to
modify the circuit to provide
equalisation for the different
tape speeds, we must emphasise
that the results may be far from
optimum. This is because the
preamplifier really needs to be
designed to suit the impedance
90 Silicon Chip
and the record/playback response
of the particular heads.
The accompanying sketch shows
suggested equalisation but we
should also point out that this is
a starting point only and we have
not tried it out.
there was a power supply designed
for it.
There was also a 200W module in
an advertisement for Altronics. It says
that it comes with no power supply.
Perhaps you could suggest one and
the transformer that corresponds with
it. Also, what type of heatsink would
be suitable for each amplifier? Would
these amplifiers go with your suggestions about the mixer and preamp?
Finally, the speakers: if I were to
use the above combo or similar, what
power rating would the speakers need
(as I don’t understand the relationship
between RMS and maximum power).
Also, what line/brand would you
recommend if I would like a woofer
and a horn and I don’t want to spend
over $250 for one enclosure. What
design for enclosure would be suitable
to your recommendation of speakers.
Also would I need a cross
over or
anything?
Could I build all of the above, except mics and speakers, into a cabinet
(so it becomes a power mixer) without any inter
ference, humming, or
extra distortion, etc? (S. R., Cronulla,
NSW).
• We are not able to give detailed answers to your questions since your application is so specialised. For a start,
since the sound pressures associated
with drum amplification are so high,
you need microphones which have a
very high dynamic range, otherwise
they will distort.
As we understand it, the best microphones for drum work are condenser types and these are generally
“phantom powered” at 48V DC via
the balanced microphone lines. They
need to be matched to the following
preamplifier or mixer.
We have published a 16-channel
mixer with equalisation and an effects
loop (in the Feb-May 1990 issues) but
it did not have phantom power for
condenser microphones.
In any case, since it was such a large
and complex device, it was quite expensive to build (around $2000) and
it is no longer available in kit form.
You could still build it though, as all
parts except the front panel are readily
available.
A mixer normally has a preamplifier for each channel and the
preamplifier signals are then mixed
in an “adder” stage. The effects loop
in a mixer can be thought of as the
tape monitor loop in a normal stereo
system. It allows devices such as
reverberation systems to be readily
inserted in the signal path.
If you build a power amplifier you
will also need to build a power supply
to suit and normally a suitable circuit
would be included in the design,
even if it is not included in the kit.
Suitable heatsinks are also suggested
in the article. You should also be prepared to pay a lot more for the power
supply than for the amplifier module
and then a suitable case will also be
required.
We cannot suggest any designs for
the loudspeakers which will need
to be large and very rugged for your
application. Jaycar Electronics can
provide cabinet designs for some of
their PA loudspeakers which might
be suitable.
Really, if you are going to do the job
properly you will need to spend quite
a few thousand dollars. We suggest you
consult someone who has been in the
music business for a number of years
before you start spending.
Keep those
projects coming
I have been buying your magazine
since it began in 1987 and I congratulate you for keeping the quality so
high. I would like to suggest some
ideas you may like to use for articles
and/or projects.
First, how do voice scramblers
work? Are they simple to build?
I have seen on some of the more
expensive micro recording cassette
players that they have variable speed
and variable pitch, so that you can play
at a higher speed but be able to hear
the voice playing faster but without
the “Chipmunk” sounds (Tandy sells
such a device). The variable speed is
easy to make but what about the gadget
that varies the pitch?
During summer, it gets quite hot
here at nights (yes, Armidale can get
hot). We have a 3-speed desk fan.
However, it’s not much help at night
as it is too strong (even on the lowest
Substitute for
magnetic detectors
I have just purchased your excellent production “14 Model Railway
Projects” as I am still a novice in
the world of electronics and I am
trying to learn more about the possibilities of adapting electronics to
my own model railway.
Of particular interest to me is
the article titled “Level Crossing
Detection for Model Railways”.
However, I have a small problem
in that my stock is fitted with delayed action uncouplers for which
I have placed permanent magnets
between the rails at strategic locations.
Having previously tested the
principle used in the article of
placing magnets under the rolling
stock, albeit with a locomo
tive
fitted with magnets for magnetic
track adhesion (no longer used), I
have found that the magnets tend
to retard the loco movement when
passing over the track mounted
magnetic uncouplers.
While this particular loco would
work fine on the system in your
article, I am reluctant to use this
method of detection on other items
of stock as I have a considerable
number of uncouplers already in
place around the layout.
While reading through the book
I noticed that the “Diesel Sound
Gen
erator” (on page 30) uses a
photo-interrupter to detect the
train. Would it be possible to adapt
the photo-interrupter to the Level
settings) and it makes too much noise
to allow you to sleep. Would it be OK
to install a dimmer switch to the fan?
It has a rating of 50W.
I was very interested in the Security Camera project which was in
the March 1993 edition. However, it
seemed to me to be a bit inefficient
firing the shutter. I would have thought
that the shutter on many of these cameras was electrically controlled. If so,
then some of the trickiest parts of the
circuit could be bypassed (the electric
motor and gears). Perhaps you could
publish the modifications.
I was interested to read a letter published in the January 1994 edition by
Crossing Detector circuit? If so
would you please supply me with
the revised circuitry. (G. K., Valley
Heights, NSW).
• Magnetic uncouplers may pre
sent a problem with retarding the
train. However, your tests were
carried out with magnets for track
adhesion and these would probably
be considerably more powerful
than the magnets specified for
the Level Crossing Detector. We
recom
mend testing the train by
using the magnets specified in the
article. If the train is not slowed
down significantly, use the magnets
and Hall effect detector circuitry as
described.
The optical method used for the
Diesel Sound Generator can be
used but this does have the problem of multiple triggering as the
carriage wheels pass between the
optical sensor pickup and the light
source. The LED from the optical
sensor can be powered from the
+12V supply via a 470Ω resistor
and the emitter load for the detector can be a 180kΩ resistor as per
the diesel sound generator circuit.
Simply connect the emitter output
to the input of the Level Crossing
Detector at position 3.
Note that you will need to have a
common earth connection between
the position 2 input and the ground
supply for the optical sensor. The
sensitivity from the optical pickup
is far greater than that from the
Hall Effect sensor and so the 1MΩ
feedback resistors on IC1a & IC1b
should be reduced to 100kΩ.
C. P. regarding the muting of wireless
microphones. I agree with what he
says about the problems with noise
when the mike is switched off. I see
in the March 1994 issue a “voice activated audio switch for FM wireless
microphones” pro
ject. This would
obviously be good in many situations.
It would be more use to me if the FM
receiver had a squelch. Is it a simple
matter to add one to the “Simple FM
Receiver”?
Many projects become costly when
they require a meter or an LCD display
and as I am only an experimenter I
rarely build any that are expensive. I
am always pleased when projects are
August 1994 91
Long distance
communication via CB
In 1991, my wife and I purchased
two Midland 70-530D UHF CB sets.
Since 1991 we have not been able
to use these sets between our farm
and our house in Brisbane. There
is 125km in a straight line between
our farm and our house.
So-called Australian radio experts (university doctor, professor,
specialised firm) have all told me
it was impossible to communicate
beyond a mountain with UHF
(300-3000MHz). In October 1993,
a very comprehensive article on
long distance UHF propagation appeared in “The Australian National
Geographic”. Mention was made
of UHF CB bouncing from planes,
large struc
tures, Moon bouncing,
etc. I wrote seven letters to each
one of the people mentioned in
the article. Every letter came back
saying that what was described
in the article was only theory and
imagination.
That is why I really welcome
your very positive article in the May
1994 issue on passive TV re-broadcasting. Last year, ARRL (USA) told
me very positively we should be
able to communicate over 125km
on UHF CB, even with a mountain
between; especially if we use Yagis
and some power. This obviously
conflicts with information from the
Australian experts.
This is a serious matter. We have
been quoted $10,000 to put in 2km
described that connect to the multi
meter. There are a couple of things
that I would like to make that may be
able to use the multimeter (perhaps
using the frequency range). The first
is a pulse rate monitor and the second
is an anemometer. If it isn’t a simple
matter using a multimeter, what about
using a computer?
There haven’t been too many articles
around lately about biofeedback. How
about something about measuring
brainwave activity? Simple monitors
costing about $100 were selling in the
USA. How do they work? What about
a project?
I hope you don’t think I am demanding these projects or articles. That is
92 Silicon Chip
of Telecom land line on our farm.
All the ground below 600mm feet
is granite and every pole has to be
blasted by high explosive. Austel
doesn’t allow people to use trees
to hang telephone line.
By arrangement with Mobile Net
management, on the 2nd to 4th
April 1994, I was able to use an extremely sensitive and well aligned
portable telephone on 820MHz. I
was able to receive signals 80 metres below the line of sight, 10km
from the edge of the mountain,
with the transceiver 50km from the
Telecom repeat
er. The so-called
experts when confronted with
my practical field results could
not give any explanation. (G. C.,
Corinda, Qld).
• UHF communication over the
125km path you refer to is certainly possible but it would not
be consistent and would depend
very much on the vagaries of the
weather. Even if you are using high
power plus Yagis, you would be
depending on tro
pospheric scatter for communication over the
mountain and this would only be
possible at certain times. Bounce
communication via aeroplanes or
the Moon is also possible but you
could not depend on having the
Moon or a plane handy to bounce
the signals off every time you wanted to make a call.
It seems that if you want consistent and reliable long distance
communications 24 hours a day, the
only way is to install a telephone.
not my intention. I am merely suggesting ideas that you may or may not
want to use. Keep up the good work. I
look forward to all your issues. (G. E.,
Armidale, NSW).
• Thanks for your letter and enquiries
about various circuits. We will answer
them in order. First, scramblers work
in a variety of ways which may involve
analog or digital circuit techniques.
Perhaps the simplest is a frequency
shifting system whereby the signal is
shifted by about 1kHz or so which is
enough to make it unintelligible. We
have not published any circuits along
these lines.
Speed and pitch normally have a
direct relationship in a tape recorder
– if you increase the tape speed, the
pitch goes up in exact proportion.
Those tape players which increase the
speed of playback without changing
the apparent pitch mainly do so by
chopping out the pauses in speech.
You cannot use a dimmer circuit to
control a fan motor without modifications. The modification mainly involves an RC circuit called a “snubber”
across the Triac. This enables the Triac
to commutate (ie, switch off) properly
at the end of each 50Hz half-cycle.
We published suitable circuits for fan
speed control in the December 1987
and January 1990 issues.
While some low-cost cameras
are available with motorised film
winding, there are very few available with electronic or motorised
shutters. Hence, the motorised firing
scheme in the Security Camera was
necessary.
Most FM tuners used in home hifi
systems have muting. Squelch is effectively the same thing except that
the threshold is adjustable. Muting
(or squelch) stops an FM receiver
from producing spurious noise when
the RF signal is insufficient to “quiet”
the receiver (ie, to produce noise-free
audio). The VOX circuit was published with the specific requirement
that it mute the microphone while
the transmitter circuit remained
active. A squelch circuit would not
achieve the same thing and it normally produces a “squelch” sound as it
operates, which can be undesirable
in some cases.
Thanks for your other circuit suggestions. We’ll put them on the list of
things to do.
Mixer has
loss of bass
I am using an op amp (circuit enclosed) as a mixer between several
cassette decks and the main amplifier.
When the signal (about 400mV) is run
through the op amp circuit, there is a
considerable loss of bass but with a
direct connection between any tape
deck and the amplifier there is no
bass problem. Are you able to give
me some information on overcoming the bass loss? (R. M., Cambridge
Park, NSW).
• The essential problem would appear to be that your input coupling
capacitor is not big enough. Try using
SC
1µF or larger.
SILICON CHIP
BOOK SHOP
Newnes Guide
to Satellite TV
336 pages, in paperback at $49.95.
Installation, Reception & Repair.
By Derek J. Stephenson. First
published 1991, reprinted 1994
(3rd edition).
This is a practical guide on the
installation and servicing of
satellite television equipment. The
coverage of the subject is extensive, without excessive theory or
mathematics. 371 pages, in hard
cover at $55.95.
Servicing Personal
Computers
By Michael Tooley. First pub
lished 1985. 4th edition 1994.
Computers are prone to failure
from a number of common causes
& some that are not so common.
This book sets out the principles
& practice of computer servicing
(including disc drives, printers &
monitors), describes some of the
latest software diagnostic routines
& includes program listings. 387
pages in hard cover at $59.95.
The Art of Linear
Electronics
By John Linsley Hood. Published
1993.
This is a practical handbook from
one of the world’s most prolific
audio designers, with many of his
designs having been published in
English technical magazines over
the years. A great many practical
circuits are featured – a must for
anyone interested in audio design.
Optoelectronics:
An Introduction
By J. C. A. Chaimowicz. First
published 1989, reprinted 1992.
This particular field is about to
explode and it is most important
for engineers and technicians to
bring themselves up to date. The
subject is comprehensively covered, starting with optics and then
moving into all aspects of fibre
optic communications. 361 pages,
in paperback at $55.95.
Digital Audio & Compact
Disc Technology
Produced by the Sony Service
Centre (Europe). 3rd edition,
published 1995.
Prepared by Sony’s technical
staff, this is the best book on
compact disc technology that we
have ever come across. It covers
digital audio in depth, including
PCM adapters, the Video8 PCM
format and R-DAT. If you want to
understand digital audio, you need
this reference book. 305 pages, in
paperback at $55.95.
Power Electronics
Handbook
Components, Circuits & Applica
tions, by F. F. Mazda. Published
1990.
Previously a neglected field, power
electronics has come into its own,
particularly in the areas of traction
and electric vehicles. F. F. Mazda
is an acknowledged authority on
the subject and he writes mainly
on the many uses of thyristors &
Triacs in single and three phase
circuits. 417 pages, in soft cover
at $59.95.
Surface Mount Technology
By Rudolph Strauss. First pub
lish-ed 1994.
This book will provide informative
reading for anyone considering
the assembly of PC boards with
surface mounted devices. Includes
chapters on wave soldering, reflow
soldering, component placement,
cleaning & quality control. 361
pages, in hard cover at $99.00.
Electronics Engineer’s
Reference Book
Edited by F. F. Mazda. First pub
lished 1989. 6th edition 1994.
This just has to be the best reference book available for electronics
engineers. Provides expert coverage of all aspects of electronics
in five parts: techniques, physical
phenomena, material & components, electronic design, and
applications. The sixth edition has
been expanded to include chapters
on surface mount technology,
hardware & software design,
Your Name__________________________________________________
PLEASE PRINT
Address____________________________________________________
_____________________________________Postcode_____________
Daytime Phone No.______________________Total Price $A _________
❏ Cheque/Money Order
❏ Bankcard ❏ Visa Card ❏ MasterCard
Card No.
Signature_________________________ Card expiry date_____/______
Return to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097.
Or call (02) 9979 5644 & quote your credit card details; or fax to (02) 9979 6503.
semicustom electronics & data
communications. 63 chapters, in
paperback at $140.00.
Radio Frequency
Transistors
Principles & Practical Appli
cations. By Norm Dye & Helge
Granberg. Published 1993.
This timely book strips away the
mysteries of RF circuit design.
Written by two Motorola engineers, it looks at RF transistor
fundamentals before moving on
to specific design examples; eg,
amplifiers, oscillators and pulsed
power systems. Also included are
chapters on filtering techniques,
impedance matching & CAD. 235
pages, in hard cover at $85.00.
Newnes Guide to TV &
Video Technology
By Eugene Trundle. First pub
lish-ed 1988, reprinted 1990,
1992.
Eugene Trundle has written for
many years in Television magazine
and his latest book is right up date
on TV and video technology. 432
pages, in paperback, at $39.95.
Title
Price
Newnes Guide to Satellite TV
Servicing Personal Computers
The Art Of Linear Electronics
Optoelectronics: An Introduction
Digital Audio & Compact Disc Technology
Power Electronics Handbook
Surface Mount Technology
Electronic Engineer’s Reference Book
Radio Frequency Transistors
Newnes Guide to TV & Video Technology
$55.95
$59.95
$49.95
$55.95
$55.95
$59.95
$99.00
$140.00
$85.00
$39.95
Postage: add $5.00 per book. Orders over $100 are post
free within Australia. NZ & PNG add $10.00 per book,
elsewhere add $15 per book.
TOTAL $A
August 1994 93
MARKET CENTRE
Cash in your surplus gear. Advertise it here in Silicon Chip.
CLASSIFIED ADVERTISING RATES
VINTAGE RADIO
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): $25 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.
VINTAGE RADIO SWAP meet/fair.
Inc. military, amateur radio and antique
sound. Sunday 23rd October, 1994
10am to 5pm. Glenroy Technical School
Hall, Melbourne. Bookings: R. Howarth,
PO Box 9, Junortoun 3551. Phone (054)
49 3207.
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
_____________ _____________ _____________ _____________ _____________
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.
SATELLITE TV DX SUPER RX receiver.
Threshold 2.5dB. Also digital picture,
sound, synchron, resolution processors.
Mobile DX receivers, pay TV decoders.
TV, radio, picture, sound modulators.
Digital, analog signal meters. Send $5
for info and catalog/refundable to John
Papp, PO Box 472, Sanderson, NT
0812. Fax/Ph:(089) 27 4985.
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
Enclosed is my cheque/money order for $__________ or please debit my
RCS RADIO PTY LTD
Card No.
✂
❏ Bankcard ❏ Visa Card ❏ Master Card
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
Zelcon Technic Pty Ltd
•
•
•
•
PCB Supplier
Photoplotting Services
SMT/Through-Hole Assembly
CAD facilitites
PO Box 149, Glenorchy, Tas 7010
Ph: (002) 71 8120, Fax: (002) 71 8182
BBS: (002) 73 0799
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.
MEMORY PRICES
Building Your Speakers?
Need Help?
PRICES AT JUNE 8TH, 1994
SIMM
1Mb x 3
1Mb x 9
4Mb x 9
4Mb (72-pin)
8Mb (72-pin)
16Mb (72-pin)
DRAM DIP
1 x 1Mb
256 x 4
IBM PS.2
55/65SXVP
L40/N33
90/95 PS1
70ns
70ns
70ns
70ns
70ns
70ns
70ns
70ns
$61
$63
$225
$238
$476
$952
$7.50
$8.00
4Mb
4Mb
4Mb
$238
$238
$280
MAC
4Mb x 80
80ns
6Mb P’BOOK
$210
$380
CO-PROCESSORS
387S/DX to 40
$90
LASER PRINTER HP
2Mb L’jet 4L
$135
COMPAQ
PROLINEA
8Mb
$476
TOSHIBA
2000SX
46/1900 3.3
8Mb
4Mb
$541
$300
SUN
SPARC 10
16Mb
$975
PCMCIA
1Mb V2 BAT SRAM
2Mb V2 BAT SRAM
2Mb FLASH RAM
20Mb SUN FLASH RAM
1st Floor, 100 Yarrara Rd, PO Box 382, Pennant Hills, 2120.
PELHAM
CAMCORDER BATTERIES: factory
sealed rechargeable packs to suit
SONY, SANYO, PANASONIC, JVC,
SHARP, CANON. Best possible prices
- eg, SONY 1800mAh - ONLY $54.90!
Ring after 6pm (02) 818 4968. D. R.
BATTERIES, 17 Bay Street, Birchgrove,
2041.
SANYO NICADS - BEST PRICES:
Sanyo nicads from 50mAh to 4400mAh.
Separate cells or packs made to order.
Best prices, eg N1300SC - $5.50;
KR4400D - $14.00, N600AA - $3.50.
Ring after 6pm (02) 818 4968. D. R.
BATTERIES, 17 Bay Street, Birchgrove,
2041.
EPROM & SRAM EMULATOR: 2K x
8 (or 16) to 64K x 8 (or 16). Download
and verify via standard PC printer port.
Supports Binary, Intel and Motorola
hex formats. Including Binary Editor.
For more information, contact Northern
Eastern Digital, PO Box 1252, Collingwood, Vic 3066. Fax (03) 484 5133/432
1063; Phone (03) 432 1699.
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.
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)
and 1024 x 768 SVGA card. All programs
are on 5.25-inch or 3.5-inch disks (state
Australian Audio Consultants
Box 1031, Aldinga Beach, SA 5173.
Phone or fax on (085) 56 6370
CTOAN ELECTRONICS
Got a great idea for a new device?
Don’t leave it as just an idea. Call
us; we can help make is work.
You describe it – we’ll design it.
PO Box 211, Jimboomba 4280.
Phone (07) 297 5421.
•
TRANSFORMER REWINDS
ALL TYPES OF TRANSFORMER REWINDS
TRANSFORMER REWINDS
Reply Paid No.7, PO Box 1058,
St Marys, NSW 2760.
Ph: (02) 833 1146. Fax: (02) 623 5559.
which) & include documentation. Add
$3 postage. Only from M. Delahunty, 42
Villiers St, New Farm, Qld 4005. Phone
(07) 358 2785.
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 Ltd, PO Box 439, Bexley
2207. Phone (02) 567 5390.
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, Parra
matta,
NSW 2124. Phone (02) 683 3510; Fax
Speaker parameters measured
Boxes designed & manufactured
Crossovers designed
Systems for lounge, car or PA
For more details contact:
$205
$330
$345
$1500
Sales tax 21%. Overnight delivery. Credit cards welcome.
5-Year warranty. Ring for latest prices.
Tel: (02) 980 6988
Fax: (02) 980 6991
•
•
•
•
•
•
•
350 Watt Power MOSFET
Amplifier Module
As published in the June 1994 issue
of Silicon Chip. Kit price $159.00.
Postage and handling $8.00.
Payment by M/C, B/C, Visa, Cheque
or Money Order.
3kg O/N Air Bag $10.00
Computer & Electronic Services Pty
Ltd 27 Osborne Avenue, Trevallyn
Launceston, Tasmania 7250
Phone 003-34 4218; Fax 003-31 4328
(02) 630 3148. Pay by cheque, money
order, credit card.
THE 8051 MICRO-COMTROLLER
book includes a simulator disk ($40).
ROMLoader EPROM Emulator (EA Jan/
Feb 92, EA June 94) (PCB $30). 8051
Proto-Boards (EA Feb 93) (PCB $30).
Tantau Australia, PO Box 1232, Lane
Cove 2066. Phone AH (02) 878 4715.
CONTROL RELAYS, Robots, Radios
or Railways from LPT1: of your XT
to 486 PC. 64 bits. Fully expandable.
Demo programs, flow charts, circuits,
drivers in M.L. & Basic. Bare PCB and
software $38, or demo/promo disk $2.
Don McKenzie, 29 Ellesmere Crescent,
Tullamarine, Vic 3043. Phone (03) 338
6286.
PIC16Cxx PROTO-PCB for 18, 28-pin
PICs. Includes Basic Stamp cct, XTL/
RC, up to 20MHz, MAX-232, MAD Bus,
Relay Bus, 3 LEDs, and lots more. Don’s
August 1994 95
ELECTROSTATIC
LOUDSPEAKERS
Microprocessor For
Stereo Preamplifier
3-PANEL FULL RANGE DESIGN,
AVAILABLE IN KIT FORM OR FULLY
ASSEMBLED.
LOCALLY DESIGNED & MANUFACTURED.
FOR INFORMATION BROCHURE,
PHONE/FAX (09) 397 6212 OR WRITE TO:
E. R. AUDIO,
119 BROOKTON HWY, ROLEYSTONE,
WESTERN AUSTRALIA 6111.
Now back in stock: the 68HC705-C8P
pre-programmed microp roc essor
for the Infrared Remote Controlled
Stereo Preamplifier (SILICON CHIP,
Sept.-Oct. 1993). Also suits the
Remote Volume Control (May &
June, 1993).
Price: $45 + $6 p+p
Payment by cheque, money order or
credit card to: Silicon Chip Publications,
PO Box 139, Collaroy, NSW 2097.
Phone (02) 9795644; Fax (02) 979
6503.
RS-232 driven O/S available soon for
18 I/O bits. PCB and data $20. Promo
disk $2. Don McKenzie, 29 Ellesmere
Crescent, Tullamarine 3043. Phone (03)
338 6286.
INTELLIGENT INFRARED RECEIVER
(ref SILICON CHIP, March 94). Now
with 8 outputs. Use your TV or VCR
infrared remote control transmitter to
control your TV or hifi appliances with
an intelligent infrared receiver kit. Also
available infrared transmitters, preprogrammed and learning models. For details call BENETRON P/L (018) 20 0108.
NEW CHINESE ANTENNA: made from
recycled jam tins. Cost $79.50; sell $20
ono. Phone 971 9539.
UNUSUAL BOOKS: Electronic Devices, Fireworks, Locksmithing, Radar
Invisibility, Surveillance, Self-Protection,
Unusual Chem
istry and more. For a
complete catalog, send 95 cents in
stamps to Vector Press, Dept S, PO Box
434, Brighton, SA 5048.
VALVES SPECIALIST: buy, sell, modify
and service. Thousands valves in stock.
Altronics ..........................IFC,20-22
Aust. Audio Consultants...............95
Av-Comm.......................................3
Computer & Elect. Services.........95
Ctoan Electronics........................95
David Reid Electronics ..............59
Dick Smith Electronics........... 10-13
E. R. Audio...................................96
Harbuch Electronics....................59
Instant PCBs................................95
EL34 $20, KT88 $38, 655OWA $34,
6922 $12, 12AX7WA $8, 300B $140,
845 $100. MIT, WONDER, SOLEN, OIL
capacitors, etc. Wanted to buy valves
and equipment. Mobile (0414) 22 3245.
Fax (02) 816 4515.
Jaycar ......................... 33-36,61-64
L & M Video.................................82
Macservice..................................71
McLean Automation.....................81
Oatley Electronics.................. 50-51
PRINTED CIRCUIT BOARDS for the
hobbyist. For service & enquiries contact: T. A. Mowles (08) 326 5590.
PC Computers.............................81
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.
RCS Radio ..................................94
REAL TIME ICE!!! The only way to go.
MOTOROLA 6805 EMULATOR and
programmers. Prices and data from Graham Blowes, Mantis Micro Products,
38 Garnet Street, Niddrie 3042. Phone
(03) 337 1917 (a/h), (03) 575 3349 (b/h).
Fax (03) 575 3369.
Silicon Chip Projects Book......OBC
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. Simply enter in the 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.
Price $7.00 + $3 p&p. Send your order to: Silicon Chip Publications, PO Box 139,
Collaroy 2097; or phone (02) 979 5644 & quote your credit card number; or fax the
details to (02) 979 6503. Please specify 3.5-inch or 5.25-inch disc.
96 Silicon Chip
Advertising Index
Pelham........................................95
Philips.........................Centre Insert
Rod Irving Electronics .......... 74-78
Silicon Chip Back Issues....... 88-89
Silicon Chip Binders..................IBC
Silicon Chip Bookshop.................93
Silicon Chip Software..................83
Tortech.........................................87
Transformer Rewinds...................95
Yuga Enterprise...........................86
Zelcon Technic.............................95
_________________________________
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.
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