This is only a preview of the October 1996 issue of Silicon Chip. You can view 24 of the 96 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Items relevant to "Send Video Signals Over Twister Pair Cable":
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October 1996 1
R
AUSTRALIA’S BEST AUTO TECH MAGAZINE
It’s a great mag...
but could you be
disappointed?
If you’re looking for a magazine just filled with lots of beautiful cars,
you could be disappointed. Sure, ZOOM has plenty of outstanding
pictorials of superb cars, but it’s much more than that.
If you’re looking for a magazine just filled with “how to” features,
you could be disappointed. Sure, ZOOM has probably more “how to”
features than any other car magazine, but it’s much more than that.
If you’re looking for a magazine just filled with technical descriptions
in layman’s language, you could be disappointed. Sure, ZOOM tells it
in language you can understand . . . but it’s much more than that.
If you’re looking for a magazine just filled with no-punches-pulled
product comparisons, you could be disappointed . Sure, ZOOM has
Australia’s best car-related comparisons . . . but it’s much more than
that
If you’re looking for a magazine just filled with car sound that you
can afford, you could be disappointed. Sure, ZOOM has car hifi that
will make your hair stand on end for low $$$$ . . . but it’s much more
than that.
If you’re looking for a magazine just filled with great products, ideas
and sources for bits and pieces you’d only dreamed about, you could be
disappointed. Sure, ZOOM has all these . . . but it’s much more than
that.
But if you’re looking for one magazine that has all this and much, much more crammed
between the covers every issue, there is no way you’re going to be disappointed with
ZOOM. Look for the June/July 1998 issue in your newsagent
From the publishers of “SILICON CHIP”
Vol.9, No.10; October 1996
Contents
FEATURES
4 An Introduction To Smart Cards
A revolutionary new plastic card could soon find its way into your pocket. Here’s
a look at how the new “smart” cards work – by Sammy Isreb
25 Snappy: Just Click The Mouse Button For High-Res Video
Images
WIRED VIDEO TRANSMITTER
& RECEIVER – PAGE 12
This new frame grabber plugs into your computer’s parallel port and captures
good quality images from any video source – by Greg Swain
PROJECTS TO BUILD
12 Send Video Signals Over Twisted Pair Cable
Wire your home or business with remote video for entertainment or CCTV
security systems – by John Clarke
22 Power Control With A Light Dimmer
Use it to dim a table lamp or for low temperature soldering – by Leo Simpson
32 600W DC-DC Converter For Car Hifi Systems
Provides high-voltage split supply rails to drive high-power car amplifiers (up
to 180W RMS per stereo channel, or 360W RMS total) – by John Clarke
POWER CONTROL WITH A LIGHT
DIMMER – PAGE 22
53 Infrared Stereo Headphone Link; Pt.2
We complete this project by describing the receiver – by Rick Walters
66 Build A Multimedia Sound System; Pt.1
Get big sound from your computer with this project. It plugs into the motherboard
and boosts the output from your soundcard (via special speakers)– by Rick Walters
SPECIAL COLUMNS
40 Serviceman’s Log
To tip or not to tip: a few tips – by the TV Serviceman
600W DC-DC CONVERTER FOR
CAR HIFI SYSTEMS – PAGE 32
75 Satellite Watch
What’s available on satellite TV – by Garry Cratt
82 Radio Control
Multi-channel radio control transmitter; Pt.8 – by Bob Young
88 Vintage Radio
A new life for an old Hotpoint – by John Hill
DEPARTMENTS
2 Publisher’s Letter
3 Mailbag
8 Circuit Notebook
65 Order Form
79 Product Showcase
93 Ask Silicon Chip
95 Market Centre
96 Advertising Index
MULTIMEDIA AMPLIFIER FOR ENHANCED
COMPUTER SOUND – PAGE 66
October 1996 1
Publisher & Editor-in-Chief
Leo Simpson, B.Bus., FAICD
Editor
Greg Swain, B.Sc.(Hons.)
Technical Staff
John Clarke, B.E.(Elec.)
Robert Flynn
Rick Walters
Reader Services
Ann Jenkinson
Advertising Manager
Christopher Wilson
Phone (02) 9979 5644
Mobile 0419 23 9375
Regular Contributors
Brendan Akhurst
Garry Cratt, VK2YBX
Julian Edgar, Dip.T.(Sec.), B.Ed
John Hill
Mike Sheriff, B.Sc, VK2YFK
Philip Watson, MIREE, VK2ZPW
Bob Young
SILICON CHIP is published 12 times
a year by Silicon Chip Publications
Pty Ltd. A.C.N. 003 205 490. All
material copyright ©. No part of
this publication may be reproduced
without the written consent of the
publisher.
Printing: Macquarie Print, Dubbo,
NSW.
Distribution: Network Distribution
Company.
Subscription rates: $54 per year
in Australia. For overseas rates, see
the subscription page in this issue.
Editorial & advertising offices:
Unit 34, 1-3 Jubilee Avenue, Warrie
wood, NSW 2102. Postal address:
PO Box 139, Collaroy Beach, NSW
2097. Phone (02) 9979 5644. Fax
(02) 9979 6503.
PUBLISHER'S LETTER
Getting onto the Internet
can cost big money
One of the common enquiries we get from
readers is “Are you on the Internet yet? So
far, the answer has been “No, not yet.” Naturally, the enquirer is usually disappointed
at this reply but when questioned further, as
to why they want to know, people generally
state that they just like to browse. They don’t
really want anything specific via the Internet
but they like to have a good look around.
For many businesses, the Internet is a huge conundrum. On the one hand,
large numbers of business are eagerly jumping onto the bandwagon so that
they can grab the kudos of being seen to be innovative and forward-looking.
On the other hand, other more cautious firms, ours included, are wondering
whether all the effort will produce any worthwhile financial return.
I would go further and say that, for some firms, there is risk of a considerable loss via the Internet. I am thinking particularly of copyright. Just
recently, the Australian Performing Rights Association has decided to target
information service providers and charge them for songs being downloaded
on the net. That is likely to result in a protracted legal battle. Once a firm’s
intellectual assets are available via the Internet, particularly software, then
the chances of any return are virtually nil. The same comment applies to
unauthorised material on bulletin boards.
Unless a business can point to a real return from the very substantial
investment required to produce and properly maintain a web site, then the
Internet can be guaranteed to be a financial loss. Sure, proponents of the
Internet will point to savings on international phone calls and faxes and
may even be able to identify some business generated by the Internet but
as far as I can determine, very few businesses make any real money from
it. They would be better off devoting their scarce resources to the business
activity they know best.
In fact, I predict that quite a few businesses will see the light and close
down their web sites. The same will apply to businesses which have bulletin
boards – they will add up all the costs and figure that it is not worthwhile.
The obvious exceptions to this are firms involved in software distribution
and service.
This is not to say that the Internet will not provide substantial business
opportunities in the future. I am sure it will. But at the moment, the Internet
is the 1990s equivalent of the CB boom – everybody is talking about it but
most of the information on it is pretty trivial.
Leo Simpson
ISSN 1030-2662
WARNING!
SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should
be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the
instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with
mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages,
you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed
or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON
CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of
any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government
regulations and by-laws.
Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act
1974 or as subsequently amended and to any governmental regulations which are applicable.
2 Silicon Chip
MAILBAG
Electronic construction
alive & well
I was in Australia on business
late in March and during a week
of vacation that followed I was introduced to your magazine by the
people at Altronics in Brisbane. I
bought the April 1996 issue – very
well done. The USA used to have
several magazines like this in wide
circulation.
In the USA we have become a
nation of buy it, plug it in, and
use it for a while, then toss it out.
Repair is expensive so why not just
buy a new one. Construction is for
the dedicated amateurs who read
“Audio Constructor” or “QST”.
It’s nice to see that electronic construction is still alive and well in
Australia.
D. Gaynor,
Woodridge, Illinois, USA.
Computer Bits easy to follow
Thank you for publishing articles over the last few months about
getting better performance from
computers (“Computer Bits”).
We have found your articles a
lot easier to follow than some of
the “user’s guides” supplied with
our computer and the hints and
suggestions regarding upgrades,
etc, a lot more down-to-earth and
practical than some similar things
published elsewhere. We’re looking forward to many more similar
articles!
D. Terrey,
Chatswood, NSW.
ESD causes
semiconductor failures
I have been purchasing SILICON
CHIP since the first issue and have
always found the content to be of
a high standard and thoroughly
enjoyable to read. Of particular
note would be the Serviceman’s
Log section, along with those brilliant drawings. I hope you find the
following to be constructive rather
than just critical.
Your Publisher’s Letter in the
August 1996 issue talks of new
technology and states that “plastic
rules supreme”, all of which is true.
I should like to suggest that in light
of this “new technology” that you
could be paying more attention to
handling and mounting issues associated with these devices. I refer
to the projects contained within the
same issue of the magazine where
there is no mention of correct
handling procedures for any of the
semiconductor devices used nor
any reference to the existence of a
requirement for special handling
procedures.
I concede that many home constructors will probably ignore such
procedures and few would have the
required equipment anyway. This
does not alter the fact that these
things should always be included
in the text of a technical journal.
Firstly, I raise the issue of anti-static handling procedures. This
is an issue that is largely ignored in
many sectors of the electronics industry, yet experience would show
that ESD (electrostatic discharge)
is responsible for at least 90%
of all field failures in electronic
products.
The statement that ESD control
is largely ignored can be verified at
almost any TV/video service centre
and also at many computer outlets
where ESD control procedures are
non-existent. Please don’t you follow the same path and ignore this
issue like so many others.
I conducted a survey of all
product failures for Stanilite Communications whilst a production
engineer in that company which
is where the figure of 90% comes
from. The other 10%, by the way,
is made up of things such as faulty
wave soldering, etc.
The extent of ESD damage was
enough for Stanilite to authorise a
$50,000 plus budget for equipment
specifically for ESD control and
this at the Perth facility only. Many
people assume that only CMOS devices are at risk from static damage
when in fact all semiconductors are
at risk. Even chip resistors and capacitors can be (and are) damaged
in this way.
Most static damage does not
result in instant catastrophic failure but more insidiously causes
degradation of performance ultimately leading to premature failure
of a product in the field. Murphy
ensures that this happens at the
worst possible moment, when
the product is least accessible for
service and when the end user will
have the worse possible view of the
suppliers’ quality control.
The other 10% of failures mentioned above consist of a significant amount of failures caused
by incorrect mounting of power
devices, in particular tab-mount
plastic devices. It would seem that
the single biggest no-no with these
devices is that the leads should not
be bent at all unless really necessary and bending at or near the lead
to plastic (case) junction is strictly
not allowed.
Fig.10 in the 350W amplifier
article (August 1996) clearly shows
the leads deliberately bent right at
the case. Whilst the bending of the
leads like this will generally only
produce a small percentage of premature failures, some failures will
definitely occur and you should
not be (perhaps unwittingly) advocating such poor engineering
practices.
One other item to mention is that
Fig.7 in the same 350W amplifier
article shows a suggested power
supply. While the actual figures
for peak current (derived from
transformer impedance, secondary
volts, effective diode resistance and
capacitor ESR, etc) would seem to
make it OK, experience with the
common variety of 25A bridge
would suggest that some sort of
surge limiting would be a distinct
advantage.
The surge rating of a typical
25A bridge is usually quoted to
be around 320A and while most
applications do not exceed this
rating I have seen too many bridge
failures to have a lot of confidence
in the quoted 320A figure.
D. Woodbridge,
SC
Kelmscott, WA.
October 1996 3
This “Tellcard” is an early European smart card, built by
Bull CP8.
A 1985 prototype for a electronic travellers cheque card,
also developed by Bull CP8.
An introduction
to smart cards
For decades, magnetic stripe cards have been
used in a variety of applications involving small
amounts of identification data. These magnetic
cards have become the norm in applications
such as credit and key cards, to name just two.
However, they have many drawbacks and will
eventually be replaced by a new technology.
By SAMMY ISREB
The system that will most likely
replace magnetic stripe cards is the
newer smart card technology. A smart
card is similar in appearance to a
conventional magnetic card but that
is where the similarities end. Unlike
a conventional card, a standard smart
card contains a CPU (central processing unit) and associat
ed memory.
Because this setup offers read/write
capabilities, new information can
be added, removed, or processed as
needed.
An average smart card on the market today contains an 8-bit 5MHz
microprocessor, 8K bytes of ROM, 288
bytes of RAM and up to 16K bytes of
EEPROM, all fabricated using CMOS
technology.
4 Silicon Chip
Physically, smart cards have the
same dimensions as stan
dard magnetic stripe cards but have from six to
eight gold I/O contacts along the top
lefthand corner.
These I/O contacts are used in
conjunction with a compatible smart
card reader to transfer data. Hidden
under the gold contacts is a single IC,
containing the entire CPU and memory
contents of the smart card.
Possibly the greatest feature of smart
cards, apart from their high data storage capabilities, is the fact that they
are very secure against unauthorised
data reading/writing. On the simplest
level, they are much more secure than
magnetic stripe cards, as the data is
stored inside the card on board an
IC and not on the surface where it
can easily be read as is the case with
magnetic stripe cards.
On a more sophisticated level, the
fact that a CPU is onboard allows en
cryption methods to be employed in
order to protect sensitive data. And
because both the memory and the CPU
are on a single IC, it is not possible
to “spy” on the data lines that would
otherwise be used to connect two or
more chips. All these features, along
with the fact that most smart cards
will destruct when their plastic casing
is removed, makes them very secure
indeed.
The main drawback of smart cards
(one that will not be solved in the immediate future) is their relatively high
price. A magnetic stripe card can be
manufactured for around $1, whereas
an average smart card can cost from
$15-25. Top-of-the-range cards can
cost many times more, however. Until
this cost barrier is overcome, magnetic
cards will continue to dominate the
market.
Memory cards
For some applications that do not
require the complexity of a CPU,
memory cards are available. These are
composed solely of a memory chip,
An electronic travellers cheque card from Thomas Cook
Financial Services.
usually a form of EEPROM or non-volatile RAM. These cards do not have the
security of a fully-fledged smart card
but are quite adequate for all forms of
prepaid value cards, such as telephone
or stored value cash cards.
Contact or contactless?
As already mentioned, most smart
cards have a number of power and I/O
contacts on their surface that allow
interaction with a card reader. The
number and arrangement of these
contacts varies, depending on the
type of card. This setup does have one
drawback, however – the card must
be inserted into the card reader each
time it is used.
To solve this problem, contactless
smart cards have been developed that
can communicate with the card reader
by radio. The cards receive power
from a 125kHz incident magnetic field
A stored value telephone smart card, which began
operation in France in 1983.
generated by the card reader (along
with timing information), which also
is used for data transfer at rates up to
19.2Kb/s.
Typical contactless smart cards
contain an IC which consists of a
CPU, ROM, EEPROM and either 128
bytes or 512 bytes of non-volatile
ferro
e lectric RAM. A single coil,
located inside the card, is used for
data transmission, reception and
inductive power pickup.
Contactless smart cards have a range
of about 10cm to 1m, depending on
the card and the type of reader being
used. Most systems also have the ability to simultaneously accept multiple
cards in the reading area without data
interference between the units.
A less sophisticated version of the
contactless smart card does away
with the need to obtain its power
inductively from the card reader’s
Fig.1: block diagram of Hitachi’s H8/3102 Smart Card.
magnetic field. Instead, it uses a wafer-thin battery inside the card. This
has two disadvantages in that the card
is slightly thicker than normal and
the card must be replaced every few
years because the battery eventually
goes flat. The advantage is extended
range – up to 10 metres in some cases.
Full or mini-size?
Although most smart cards are the
same size as standard “credit cards”,
mini smart cards have gained popularity in applications where size is
critical. These cards are identical in
operation to the standard smart cards
but are much smaller. They are designed for applications where the card
is to be left in a device for long periods
of time and where size is crucial, such
as in lightweight GSM phones.
Uses of smart cards
Because of their incredible versatility, smart cards already have a wide
(and growing) range of applications. In
Australia at the current time, probably
their largest public use is in the SIM
cards for the GSM digital phones.
These cards are supplied by the
network provider, such as Telstra
or Optus, and contain the owner’s
account information. By using the
card in any digital phone with the
same sized slot, the owner can retain
his/her phone number and account
details, regardless of the phone is
being used.
In some countries, banks are replacing their magnetic stripe cards with
smart cards. However, because of the
relatively high cost of smart cards, the
transition period will be quite lengthy.
In Australia, the infrastructure for such
a move is not yet in place.
October 1996 5
could get rid of the wad of plastic now
found in most people’s wallets.
Choosing a system
A screen capture from the Smart Card Cyber Show world wide web page.
This web site, http://cardshow.com/index.html, is great for those interested in
implementing smart cards in their business.
However, during the next decade or
so, it is quite possible that the switch
to smart cards will occur.
In some parts of Australia, companies are already trailing various
types of stored value smart cards.
When these cards are bought, they
contain a fixed cash value, which is
diminished when purchases are made.
When the card is exhausted, it can be
“recharged” at a bank. This type of
system may even do away with the
need for cash in the future.
One of the most exciting possibilities is the development of smart cards
that combine a number of applications.
Because of their high storage capabilities, it’s possible to make a smart card
that’s a bank card, a SIM GSM mobile
phone card and a stored value cash
card all in one, with a good many other
applications thrown in as well. This
For those keen business people out
there who currently employ magnetic
cards for their customers, a switch to
a smart card system may not only be
feasible but may end up being more
profitable in the long run.
The first step is to identify which
of the advantages of smart cards will
make their use worthwhile. It could
be their extra security features, their
increased memory capacity, or their
inbuilt CPU.
If smart cards are a likely option, a
combination of a smart card system
and suitable reader must be found.
Searching “smart cards” on the Inter
net will reveal a list of manufacturers
and suppliers who can be contacted to
arrange a system that best suits your
needs. Alternatively, a Smart Card
Cyber Show world wide web page
has been set up at web site http://
cardshow.com/index.html.
Conclusion
Smart cards will be one of the most
exciting technologies to watch in the
next decade. When fully implemented, they have the chance to make our
lives simpler, more efficient and more
secure. However, there is still some
way to go before smart cards replace
magnetic stripe cards. Until then,
watch as your magnetic cards start
SC
disappearing, one by one.
TIMELINE OF EARLY SMART CARD DEVELOPMENT
1974: the world’s first memory card
developed. This consisted of a chip
housed in an epoxy board and was
developed by CII-Honeywell Bull.
1980: first Philips smart card developed. Contained two separate
ICs: one microcontroller IC and one
memory IC.
1975: the first memory card in a
“credit card” format, with the chip
and its contacts on one side. This
card was designed by CII-Honeywell Bull.
1981: first true smart card using a
single IC for the microcontroller and
memory, developed by Bull CP8. First
smart card cash payment system
trials in a small European town.
1977: world leader in smart card
technology, Bull CP8, formed from
CII-Honeywell Bull.
1983: first smart card payphone
system established in France.
1989: Thomas Cook experiments
with the use of a smart card as an
electronic travellers cheque. ISO
standard 7816-3 concerning the
electrical characteristics and exchange protocols relating to smart
cards set up.
1987: several International Banks
consider introducing smart cards.
ISO Standard 7816-1 concerning
the physical characteristics of smart
cards set up.
1990 onwards: proliferation of smart
card technology begins. However,
it is slow to take off in Australia,
except for the GSM digital mobile
phone area.
1979: first microprocessor card (twochip) designed by Bull CP8. This card
used a Motorola 3870 microcontroller
and a 2716 EPROM.
6 Silicon Chip
1988: Midland bank introduces smart
cards to its customers. ISO Standard
7816-2, concerning the role and position of smart card electrical contacts,
is set up.
VISIT OUR WEB SITE
OUR COMPLETE CATALOGUE IS ON OUR SITE.
A “STOP PRESS” SECTION LISTS NEW AND LIMITED
PRODUCTS AND SPECIALS. VISIT:
https://www.oatleyelectronics.com/
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HP switched mode, power in plastic case, 100-240V
AC input, 10.6V/1.32A DC output, slightly soiled: $14
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bright enough for a disco laser light show, good
results with the Automatic Laser Light Show: $75
...AUTOMATIC LASER LIGHT SHOW KIT: 3 motors,
mirrors plus PCB and comp. kit, has laser diode reg.
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(With keychain) is very bright, with 650nM/5mW
diode: $65 ... LEDS SUPER PRICES, INCLUDING A
SUPER BRIGHT BLUE!: All the following LEDS are
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DIODES: 1.52-1.66V <at> 10uA: 10 for $7 ...MASTHEAD AMPLIFIER PLUS PLUGPACK SPECIAL: Our
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suitable plupack to power it: $20, Waterproof box:
$2.50, bottom box:$2.50 ...17mm MAGNIFIERS:
Made in JAPAN by Micro Design these eyepiece style
metal enclosed magnifiers will see the grain of most
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Single tube 36W Dimmable high frequency ballasts:
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design with LED status indicator: $8.80 ...LASER
POINTER KIT: A special purchase of some
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the price of our Laser Pointer kit, includes everything
except the batteries: $29 ...SPECIAL BATTERY AND
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total price for both is: $33 ...USED BRUSHLESS DC
FANS: 4"/12V/0.25A: $8, 24V/6"/17W: $12
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MECHANICAL TIMERS: 55X48X40mm, 5mm shaft
(Knob not supplied), two hours timing per 45deg.
rotation, two 25V/16A SPST switches which close at
the end of the timing period: $5 ...USED IEC LEADS:
Used Australian IEC leads: $2.50 ...STANDARD
PIEZO TWEETERS: Square, 85X85mm, 4-40KHz, 35V
RMS: $8, Wide dispersion, 67X143mm, 3-30KHz,
35V RMS: $9 ...COMPUTER POWER SUPPLY:
Standard large supply as used in large computer
towers, +5V/22A, +12V/8.5A, -5V/0.5A, -12V/0.5A,
used but in excellent condition, guaranteed: $30
...MAGNIFIERS: Small eyepiece: $3, 30mm Loupe:
$8, 75mm Loupe: $12, 110mm Loupe: $15, a set of
one of each of these magnifiers (4): $30 ... NEW
NICAD BATTERY BARGAIN: 6 PACK (7.2V) OF 1.2V
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easy to seperate: $4 per pack or 5 packs for $16,
FLAT RECTANGULAR 1.2V, 400mAh NI-CAD BATTERIES with thermal switch, easy to seperate, (Each
batt: 48x17x6 mm): $4 per pack or 5 packs for $16
...UV MONEY DETECTOR: Small complete unit with
cold cathode UV tube, works from 2 X AA batteries
( Not supplied), Inverter used can dimly light a 4W
white fluoro tube: $5Ea. or 5 for $19 ...MISCELLANEOUS USED LENS ASSEMBLIES: Unusual lens
assemblies out of industrial equipment: 3 for $22
...USED PIR MOVEMENT DETECTORS: Commercial
quality 10-15M range, used but tested and guaranteed, have O/C transistor (BD139) output and a
tamper switch, 12V operation, circuit provided: $10
Ea. or 4 for $32 ...CCD CAMERA WITH BONUS: Tiny
(32X32X27mm) CCD camera, 0.1lux, IR responsive
(Works in total dark with IR illumination), connects
to any standard video input (Eg VCR) or via a modulator to aerial input: $125, BONUS: With each
camera you can buy the following at reduced prices:
COMMERCIAL UHF TRANSMITTER for $15 (Normally $25), IR ILLUMINATOR KIT with 42 X 880nM LED’s
for $25 (Normally $35), REGULATED 10.4V PLUGPACK for $10 (Normally $25) ...PIR CASE FOR CCD
CAMERA: Used PIR cases of normal appearance, use
to hide the CCD camera, plenty of room inside: $2.50
Ea. or 4 for $8 ...CAMERA-TIME LAPSE VCR RECORDING SYSTEM: Includes PIR movement detector and interface control kit, plus a learning remote
control, combination can trigger any VCR to start
recording with movement and stop recording a few
minutes after the last movement has stops: $90
...GEIGER COUNTER KIT: Based on a Russian tube,
has traditional “click” to indicate each count. Kit includes PCB, all on-board components, a speaker and
Yes, the geiger counter tube is included: $30 ...RARE
EARTH MAGNETS: Very strong! 7X3mm $2, 10X3mm
$4, Torroidal 50mm outer, 35mm inner, 5mm thick:
$10 ...IR TESTER: Kit includes a blemished IR
converter tube as used in night vision and an EHT
power supply kit, excellent for seeing IR sources,
price depends on blemishes: $30 / $40 ...ARGON-ION
HEADS: Used Argon-Ion heads with 30-100mW
output in the blue-green spectrum, power supply
circuit provided, size: 350X160X160mm, weight 6Kg,
needs 1KW transformer available elsewhere for about
$170, head only for: $350 ...DIGITAL RECORDING
MODULES: Small digital voice recording modules as
used in greeting cards, microphone and a speaker
included, 6 sec. recording time: $9 ...WIRED IR
REPEATER KIT: Extend the range of existing IR remote
controls by up to 15M and/or control equipment in
other rooms: $18 ...12V-2.5W SOLAR PANEL KIT:
US amorphous glass solar panels, 305X228mm, Vo-c
18-20V, Is/c 200mA: $22 Ea. or 4 for $70 ...MIDI
KEYBOARDS: Quality midi keyboard with 49 keys, 2
digit LED display, MIDI out jack, Size: 655115X35mm,
computer software included, see review in Feb. 97
EA: $80, 9V DC plugpack: $10, also available is a
larger model which has mor features and has touch
sensitive response keys: $200 ...STEREO FM TRANSMITTER KIT: 88-108MHz, 6-12V DC supply, 8mA <at>
9V, 25X65mm PCB size, PCB plus all on-board
comp’s, plus battery connector and 2 electret mic’s:
$25, plastic case to suit: $4 ...WOOFER STOPPER
KIT: Stop that dog bark, also works on most animals,
refer SC Feb. 96, Kit includes PCB and all on board
comp’s, wound transformer, electret mic., and a horn
piezo tweeter: $39, extra horn piezo tweeters (drives
up to 4) $6 Ea. ...ALCOHOL BREATH TESTER KIT:
Based on a thick film alcohol sensor. The kit includes
a PCB, all on board comp’s and a meter : $30 ...CENTRAL LOCKING KIT (NEW): A complete central
locking kit for a vehicle. The kit is of good quality and
actuators are well made, the kit includes 4 actuators,
electronic control box, wiring harness, screws, nuts,
and other mechanical parts: $60, The actuators only:
$9 Ea. ...CODE HOPPING UHF CENTRAL LOCKING
KIT PLUS A ONE CHANNEL UHF REMOTE CONTROL:
Similar to above but this one is wireless, includes
code hoping Tx’s with two buttons (Lock-unlock), an
extra relay in the receiver can be used to immobilise
the engine, etc., kit includes 4 actuators, control box,
two Tx’s, wiring harness, screws, nuts, and other
mechanical parts: $109 ...ELECTROCARDIOGRAM
PCB + DISK: The software disk and a silk screened
and solder masked PCB (PCB size: 105 x 53mm) for
the ECG kit published in EA July 95. No further
components supplied: $10 ...SECURE IR SWITCH:
IR remote controlled switch, both Rx and Tx have
Dip switches for coding, kit includes commercial 1
Tx, Rx PCB and parts to operate a relay (not supplied):
$22 8A/4KV relay $3 ...FLUORESCENT TAPE: High
quality Mitsubishi brand all weather 50mm wide Red
reflective tape with self adhesive backing: 3 meters
for $5 ...LOW COST IR ILLUMINATOR: Illuminates
night viewers or CCD cameras using 42 of our 880nm
/ 30mW / 12 degrees IR LEDs. Power output is
varied using a trimpot., operates from 10 to 15V,
current is 5-600mA ...IR LASER DIODE KIT: Barely
visible 780nM/5mW (Sharp LT026) laser diode plus
constant current driver kit plus collimator lens plus
housing plus a suitable detector Pin diode, for medical use, perimeter protection, data transmission,
experimentation: $32 ...WIRELESS IR EXTENDER:
Converts the output from any IR remote control into
a UHF transmission, Tx is self contained and attaches with Velcro strap under the IR transmitter, receiver has 2 IR Led’s and is place near the appliance
being controlled, kit includes two PCB’s all components, two plastic boxes, Velcro strap, 9V transmitter
battery is not supplied: $35, suitable plugpack for
the receiver: $10 ...NEW - LOW COST 2 CHANNEL
UHF REMOTE CONTROL: Two channel encoded UHF
remote control has a small keyring style assembled
transmitter, kit receiver has 5A relay contact output,
can be arranged for toggle or momentary operation:
$35 for one Tx and one Rx, additional Tx’s $12 Ea.
OATLEY ELECTRONICS
PO Box 89
Oatley NSW 2223
Phone (02) 9584 3563
Fax (02) 9584 3561
orders by e-mail:
branko<at>oatleyelectronics.com
major cards with phone and fax orders,
P&P typically $6.
October 1996 7
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.
Muting the
LM3886 module
This circuit can be used with the
LM3886 50 watt/channel stereo module described in February 1995 and
the LM3876 mono amplifier module
described in March 1994. It will allow
the modules to be briefly muted at
switch-on to avoid turn-on thumps.
Because both of these modules are DC
coupled throughout, they normally
should have no turn-on thumps but
this can happen if they are preceded
by some AC-coupled preamplifiers.
One solution is to use a relay circuit
to disconnect the loudspeakers briefly
at switch-on. This can be done by the
Loudspeaker Protector featured in July
1991. Alternatively, it is possible to
use the inbuilt muting feature of the
LM3876 and LM3886 chips. Pin 8 is
the mute pin and it needs to have a
current of at least 0.5mA drawn from
it to keep the circuit unmuted. In the
amplifier modules referred to above
this is achieved with a suitable resistor
connected to the negative supply rail
via a link on the PC board.
This add-on circuit will briefly mute
Printer port zero
voltage detector
This circuit will detect the
zero voltage crossing times for
the 240VAC 50Hz mains supply
8 Silicon Chip
the circuit at switch-on. It works as
follows: at switch-on the BC560 PNP
transistor has no bias applied and
therefore it cannot conduct. After
about three seconds, the 100µF capacitor is charged sufficiently via the
82kΩ resistor to bias the transistor on
and unmute the LM3886. At switch-
and generate an appropriate 50Hz
signal to be fed into the parallel
printer port of an IBM-compatible
computer.
The circuit works as follows:
the 240VAC mains voltage is
off, the 1N4004 diode across the 82kΩ
resistor rapidly discharges the 100µF
capacitor to mute the chip again and
minimise turn-off thump. Note that if
signal is passing through the amplifier
while it is being muted or unmuted, it
will briefly cause distortion.
SILICON CHIP
fed via the 0.47µF capacitor and
470Ω resistor to a bridge rectifier
consisting of diodes D1-D4. The
rectified 50Hz is then filtered by a
100µF capacitor and regulated to
16V DC by zener diode ZD1. This
DC supply powers the input side
of IC1, a 4N28 optocoupler. The
240VAC is also fed via two series
47kΩ resistors to zener diode ZD2
and the 16V clipped signal drives
the base of Q1.
Transistor Q1 drives the internal LED of IC1 and hence the
internal phototransistor between
its pins 4 & 5. The result is a 50Hz
signal at pins 10 and 25 of the
printer port which is on for every
positive half-cycle of the mains
waveform.
SILICON CHIP
6V motor speed/
direction controller
This circuit was designed
for use in a hard-wired, remote-control toy car. It has
forward, reverse, two pre
settable
speeds and can be controlled by either +6V logic or switches to the +6V
rail. It uses pulse-width modulation
for efficient speed control and relay
switching for minimum series voltage
drops.
In the toy car application, two
speed/direction controllers are used,
one operating a 6VDC motor and reduction box on each rear wheel. The
front wheel is a trailing, castor-type
wheel mounted under the chassis.
I used a 6VDC, 4Ah, SLA battery
in the car, to cope with the heavy
current demand during takeoff and
manoeuvring.
The circuit could also be useful in
antenna rotator, reversible fan, model
railway and similar applications, with
IC1 and IC2 replaced by VR3 and the
associated 1kΩ series resistor, if only
speed control is required.
For speed control, IC3a is an oscillator running at 100Hz. Its output is
pulse-width modulated by IC3b. The
length of these pulses is determined by
whichever speed preset potentiometer
is currently switched to pin 13. This
switching is achieved by IC1, half of
a 4013 dual D-type flipflop wired as
an RS flipflop and IC2a/IC2b, half of a
4016 quad analog switch.
The PWM output of IC3b is buffered
by Q1, a 2N3055 which is mounted on
a heatsink. The direction is controlled
by Q2 & Q3, two BC547 transistors,
driving two 6V relays. To ensure that
the motor only switches on if one but
not both the FWD or REV inputs are
brought high, a 4070 XOR gate, IC4a,
is used.
To operate the circuit, bring FAST
or SLOW momentarily high to select
the required speed preset, then hold
FWD or REV high to run the motor. The
motor will slow or stop (depending
on load) if “FAST” and “SLOW” are
brought high simultaneously.
S. Carroll,
Timmsvale, NSW. ($35)
THE “HIGH” THAT LASTS IS MADE IN THE U.S.A.
Model KSN 1141
The new Powerline series of Motorola’s
2kHz Horn speakers incorporate protection
circuitry which allows them to be used safely
with amplifiers rated as high as 400 watts.
This results in a product that is practically
blowout proof. Based upon extensive testing,
Motorola is offering a 36 month money back
guarantee on this product should it
burn out.
Frequency Response: 1.8kHz - 30kHz
Av. Sens: 92dB <at> 1m/2.83v (1 watt <at> 8Ω)
Max. Power Handling Capacity: 400W
Max. Temperature: 80°C
Typ. Imp: appears as a 0.3µF capacitor
Typical Frequency Response
MOTOROLA PIEZO TWEETERS
AVAILABLE FROM:
DICK SMITH, JAYCAR, ALTRONICS AND
OTHER GOOD AUDIO OUTLETS.
IMPORTING DISTRIBUTOR:
Freedman Electronics Pty Ltd, PO Box 3, Rydalmere NSW 2116. Phone: (02) 9638 6666.
October 1996 9
Silicon Chip
Back Issues
Converter; Introduction To Digital Electronics; Simple 6-Metre
Amateur Transmitter.
December 1990: The CD Green Pen Controversy; 100W
DC-DC Converter For Car Amplifiers; Wiper Pulser For Rear
Windows; 4-Digit Combination Lock; 5W Power Amplifier
For The 6-Metre Amateur Transmitter; Index To Volume 3.
January 1991: Fast Charger For Nicad Batteries, Pt.1; Have
Fun With The Fruit Machine; Two-Tone Alarm Module; LCD
Readout For The Capacitance Meter; How Quartz Crystals
Work; The Dangers of Servicing Microwave Ovens.
September 1988: Hands-Free Speakerphone; Electronic Fish
Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build
The Vader Voice.
Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random
Wire Antenna Tuner For 6 Metres; Phone Patch For Radio
Amateurs, Pt.2.
April 1989: Auxiliary Brake Light Flasher; What You Need to
Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; The
Story Of Amtrak Passenger Services.
March 1990: Delay Unit For Automatic Antennas; Workout
Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2;
Using The UC3906 SLA Battery Charger IC; The Australian
VFT Project.
May 1989: Build A Synthesised Tom-Tom; Biofeedback
Monitor For Your PC; Simple Stub Filter For Suppressing TV
Interference; The Burlington Northern Railroad.
July 1989: Exhaust Gas Monitor; Experimental Mains Hum
Sniffers; Compact Ultrasonic Car Alarm; The NSW 86 Class
Electrics.
September 1989: 2-Chip Portable AM Stereo Radio (Uses
MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Studio Series 20-Band Stereo Equaliser, Pt.2.
October 1989: FM Radio Intercom For Motorbikes Pt.1;
GaAsFet Preamplifier For Amateur TV; 2-Chip Portable AM
Stereo Radio, Pt.2; A Look At Australian Monorails.
November 1989: Radfax Decoder For Your PC (Displays Fax,
RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2;
2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive
Formats & Options; The Pilbara Iron Ore Railways.
December 1989: Digital Voice Board; UHF Remote Switch;
Balanced Input & Output Stages; Operating an R/C transmitter;
Index to Volume 2.
January 1990: High Quality Sine/Square Oscillator; Service
Tips For Your VCR; Phone Patch For Radio Amateurs; Active
Antenna Kit; Designing UHF Transmitter Stages; A Look At
Very Fast Trains.
February 1990: 16-Channel Mixing Desk; High Quality
April 1990: Dual Tracking +/-50V Power Supply; Voice-Operated Switch (VOX) With Delayed Audio; 16-Channel
Mixing Desk, Pt.3; Active CW Filter; Servicing your
Microwave Oven.
June 1990: Multi-Sector Home Burglar Alarm; Low-Noise
Universal Stereo Preamplifier; Load Protector For Power
Supplies; Speed Alarm For Your Car; Fitting A Fax Card To
A Computer.
February 1991: Synthesised Stereo AM Tuner, Pt.1; Three
Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design
Amplifier Output Stages.
March 1991: Remote Controller For Garage Doors, Pt.1;
Transistor Beta Tester Mk.2; A Synthesised AM Stereo Tuner,
Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal
Wideband RF Preamplifier For Amateur Radio & TV.
April 1991: Steam Sound Simulator For Model Railroads;
Remote Controller For Garage Doors, Pt.2; Simple 12/24V
Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical
Approach To Amplifier Design, Pt.2.
May 1991: 13.5V 25A Power Supply For Transceivers; Stereo
Audio Expander; Fluorescent Light Simulator For Model
Railways; How To Install Multiple TV Outlets, Pt.1.
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.
June 1991: A Corner Reflector Antenna For UHF TV;
4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For
Transceivers, Pt.2; Active Filter For CW Reception; Tuning
In To Satellite TV.
August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace
The Electronic Cricket; Digital Sine/Square Generator, Pt.2.
July 1991: 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; The Snowy
Mountains Hydro Scheme.
September 1990: Low-Cost 3-Digit Counter Module; Simple
Shortwave Converter For The 2-Metre Band; the Bose Lifestyle
Music system.
October 1990: The Dangers of PCBs; Low-Cost Siren For
Burglar Alarms; Dimming Controls For The Discolight;
Surfsound Simulator; DC Offset For DMMs; NE602 Converter Circuits.
November 1990: How To Connect Two TV Sets To One VCR;
Egg Timer; Low-Cost Model Train Controller; 1.5V To 9V DC
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.
September 1991: Digital Altimeter For Gliders & Ultralights,
Ultrasonic switch for mains appliances; The Basics Of A/D
& D/A Conversion; Plotting the course of Thunderstorms.
October 1991: A Talking Voltmeter For Your PC, Pt.1;
SteamSound Simulator Mk.II; Magnetic Field Strength Meter;
ORDER FORM
Please send me a back issue for:
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❏ January 1995
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Enclosed is my cheque/money order for $______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card
Signature ____________________________ Card expiry date_____ /______
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10 Silicon Chip
Note: all prices include post & packing
Australia (by return mail) ............................. $A7
NZ & PNG (airmail) ...................................... $A7
Overseas (airmail) ...................................... $A10
Detach and mail to:
Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097.
Or call (02) 9979 5644 & quote your credit card
details or fax the details to (02) 9979 6503.
✂
Card No.
Digital Altimeter For Gliders, Pt.2; Military Applications Of
R/C Aircraft.
With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1.
November 1991: Build A Colour TV Pattern Generator, Pt.1;
Junkbox 2-valve receiver; Flashing Alarm Light For Cars;
Digital Altimeter For Gliders, Pt.3; A Talking Voltmeter For
Your PC, Pt.2.
November 1993: Jumbo Digital Clock; High Efficiency Inverter
For Fluorescent Tubes; Stereo Preamplifier With IR Remote
Control, Pt.3; Siren Sound Generator; Engine Management,
Pt.2; Experiments For Games Cards.
December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Colour TV Pattern Generator,
Pt.2; Index To Volume 4.
December 1993: Remote Controller For Garage Doors;
LED Stroboscope; 25W Amplifier Module; 1-Chip Melody
Generator; Engine Management, Pt.3; Index To Volume 6.
January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A
Power Supply, Pt.1; Baby Room Monitor/FM Transmitter;
Experiments For Your Games Card.
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; Engine Management, Pt.4.
March 1992: TV Transmitter For VHF VCRs; Thermostatic
Switch For Car Radiator Fans; Telephone Call Timer; Coping
With Damaged Computer Directories; Valve Substitution In
Vintage Radios.
April 1992: IR Remote Control For Model Railroads; Differential Input Buffer For CROs; Understanding Computer Memory;
Aligning Vintage Radio Receivers, Pt.1.
May 1992: Build A Telephone Intercom; Electronic Doorbell;
Battery Eliminator For Personal Players; Infrared Remote
Control For Model Railroads, Pt.2; Aligning Vintage Radio
Receivers, Pt.2.
June 1992: Multi-Station Headset Intercom, Pt.1; Video
Switcher For Camcorders & VCRs; Infrared Remote Control
For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look
At Hard Disc Drives.
July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger;
Multi-Station Headset Intercom, Pt.2.
August 1992: An Automatic SLA Battery Charger; Miniature
1.5V To 9V DC Converter; 1kW Dummy Load Box For Audio
Amplifiers; Troubleshooting Vintage Radio Receivers; MIDI
Explained.
September 1992: Multi-Sector Home Burglar Alarm;
Heavy-Duty 5A Drill speed Controller (see errata Nov. 1992);
General-Purpose 3-1/2-Digit LCD Panel Meter; Track Tester
For Model Railroads; Build A Relative Field Strength Meter.
October 1992: 2kW 24VDC - 240VAC Sinewave Inverter;
Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For
Personal Stereos; A Regulated Lead-Acid Battery Charger.
January 1993: Flea-Power AM Radio Transmitter; High
Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC
Sinewave Inverter, Pt.4; Speed Controller For Electric
Models, Pt.3.
February 1993: Three Projects For Model Railroads; Low
Fuel Indicator For Cars; Audio Level/VU Meter (LED Readout);
An Electronic Cockroach; 2kW 24VDC To 240VAC Sinewave
Inverter, Pt.5.
March 1993: Solar Charger For 12V Batteries; Alarm-Triggered
Security Camera; Reaction Trainer; Audio Mixer for Camcorders; A 24-Hour Sidereal Clock For Astronomers.
April 1993: Solar-Powered Electric Fence; Audio Power Meter;
Three-Function Home Weather Station; 12VDC To 70VDC
Converter; Digital Clock With Battery Back-Up.
May 1993: Nicad Cell Discharger; Build The Woofer Stopper;
Alphanumeric LCD Demonstration Board; The Microsoft
Windows Sound System; The Story of Aluminium.
June 1993: AM Radio Trainer, Pt.1; Remote Control For The
Woofer Stopper; Digital Voltmeter For Cars; Windows-based
Logic Analyser.
February 1994: 90-Second Message Recorder; 12-240VAC
200W Inverter; 0.5W Audio Amplifier; 3A 40V Adjustable
Power Supply; Engine Management, Pt.5; Airbags - How
They Work.
March 1994: Intelligent IR Remote Controller; 50W (LM3876)
Audio Amplifier Module; Level Crossing Detector For Model
Railways; Voice Activated Switch For FM Microphones; Simple
LED Chaser; Engine Management, Pt.6.
April 1994: Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; Universal
Stereo Preamplifier; Digital Water Tank Gauge; Engine
Management, Pt.7.
May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control;
Dual Electronic Dice; Simple Servo Driver Circuits; Engine
Management, Pt.8; Passive Rebroadcasting For TV Signals.
June 1994: 200W/350W Mosfet Amplifier Module; A Coolant
Level Alarm For Your Car; 80-Metre AM/CW Transmitter For
Amateurs; Converting Phono Inputs To Line Inputs; PC-Based
Nicad Battery Monitor; Engine Management, Pt.9.
July 1994: Build A 4-Bay Bow-Tie UHF Antenna; PreChamp
2-Transistor Preamplifier; Steam Train Whistle & Diesel Horn
Simulator; Portable 6V SLA Battery Charger; Electronic Engine
Management, Pt.10.
August 1994: High-Power Dimmer For Incandescent Lights;
Microprocessor-Controlled Morse Keyer; Dual Diversity Tuner
For FM Microphones, Pt.1; Build a Nicad Zapper; Engine
Management, Pt.11.
June 1995: Build A Satellite TV Receiver; Train Detector For
Model Railways; 1W Audio Amplifier Trainer; Low-Cost Video
Security System; Multi-Channel Radio Control Transmitter For
Models, Pt.1; Build A $30 Digital Multimeter.
July 1995: Electric Fence Controller; How To Run Two Trains
On A Single Track (Plus Level Crossing Lights & Sound Effects); Setting Up A Satellite TV Ground Station; Door Minder;
Adding RAM To A Computer.
August 1995: Fuel Injector Monitor For Cars; Gain Controlled Microphone Preamp; Audio Lab PC Controlled Test
Instrument, Pt.1; Mighty-Mite Powered Loudspeaker; How
To Identify IDE Hard Disc Drive Parameters.
September 1995: Keypad Combination Lock; The Incredible
Vader Voice; Railpower Mk.2 Walkaround Throttle For Model
Railways, Pt.1; Jacob’s Ladder Display; The Audio Lab PC
Controlled Test Instrument, Pt.2.
October 1995: Geiger Counter; 3-Way Bass Reflex Loudspeaker System; Railpower Mk.2 Walkaround Throttle For
Model Railways, Pt.2; Fast Charger For Nicad Batteries; Digital
Speedometer & Fuel Gauge For Cars, Pt.1.
November 1995: Mixture Display For Fuel Injected Cars; CB
Transverter For The 80M Amateur Band, Pt.1; PIR Movement
Detector; Dolby Pro Logic Surround Sound Decoder Mk.2,
Pt.1; Digital Speedometer & Fuel Gauge For Cars, Pt.2.
December 1995: Engine Immobiliser; 5-Band Equaliser; CB
Transverter For The 80M Amateur Band, Pt.2; Subwoofer
Controller; Dolby Pro Logic Surround Sound Decoder Mk.2,
Pt.2; Knock Sensing In Cars; RAM Doubler Reviewed; Index
To Volume 8.
January 1996: Surround Sound Mixer & Decoder, Pt.1;
Magnetic Card Reader; Automatic Sprinkler Controller; IR
Remote Control For The Railpower Mk.2; Recharging Nicad
Batteries For Long Life.
February 1996: Three Remote Controls To Build; Woofer
Stopper Mk.2; 10-Minute Kill Switch For Smoke Detectors;
Basic Logic Trainer; Surround Sound Mixer & Decoder, Pt.2;
Use your PC as a Reaction Timer.
September 1994: Automatic Discharger For Nicad Battery
Packs; MiniVox Voice Operated Relay; Image Intensified
Night Viewer; AM Radio For Weather Beacons; Dual Diversity
Tuner For FM Microphones, Pt.2; Engine Management, Pt.12.
March 1996: Programmable Electronic Ignition System For
Cars; Zener Tester For DMMs; Automatic Level Control For
PA Systems; 20ms Delay For Surround Sound Decoders;
Multi-Channel Radio Control Transmitter; Pt.2; Cathode Ray
Oscilloscopes, Pt.1.
October 1994: Dolby Surround Sound - How It Works; Dual
Rail Variable Power Supply; Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Temperature Controlled
Soldering Station; Engine Management, Pt.13.
April 1996: Cheap Battery Refills For Mobile Telephones;
125W Power Amplifier Module; Knock Indicator For Leaded
Petrol Engines; Multi-Channel Radio Control Transmitter; Pt.3;
Cathode Ray Oscilloscopes, Pt.2.
November 1994: Dry Cell Battery Rejuvenator; Novel Alphanumeric Clock; 80-Metre DSB Amateur Transmitter; Twin-Cell
Nicad Discharger (See May 1993); Anti-Lock Braking Systems;
How To Plot Patterns Direct To PC Boards.
May 1996: Upgrading The CPU In Your PC; High Voltage
Insulation Tester; Knightrider Bi-Directional LED Chaser;
Duplex Intercom Using Fibre Optic Cable; Cathode Ray
Oscilloscopes, Pt.3.
December 1994: Dolby Pro-Logic Surround Sound Decoder,
Pt.1; Easy-To-Build Car Burglar Alarm; Three-Spot Low Distortion Sinewave Oscillator; Clifford - A Pesky Electronic Cricket;
Cruise Control - How It Works; Remote Control System for
Models, Pt.1; Index to Vol.7.
June 1996: BassBox CAD Loudspeaker Software Reviewed;
Stereo Simulator (uses delay chip); Rope Light Chaser; Low
Ohms Tester For Your DMM; Automatic 10A Battery Charger.
January 1995: Sun Tracker For Solar Panels; Battery Saver
For Torches; Dolby Pro-Logic Surround Sound Decoder,
Pt.2; Dual Channel UHF Remote Control; Stereo Microphone
Preamplifier;The Latest Trends In Car Sound; Pt.1.
July 1993: Single Chip Message Recorder; Light Beam Relay
Extender; AM Radio Trainer, Pt.2; Quiz Game Adjudicator;
Windows-based Logic Analyser, Pt.2: Antenna Tuners – Why
They Are Useful.
February 1995: 50-Watt/Channel Stereo Amplifier Module;
Digital Effects Unit For Musicians; 6-Channel Thermometer
With LCD Readout; Wide Range Electrostatic Loudspeakers,
Pt.1; Oil Change Timer For Cars; The Latest Trends In Car
Sound; Pt.2; Remote Control System For Models, Pt.2.
August 1993: Low-Cost Colour Video Fader; 60-LED Brake
Light Array; Microprocessor-Based Sidereal Clock; Southern
Cross Z80-Based Computer; A Look At Satellites & Their
Orbits.
March 1995: 50W/Channel Stereo Amplifier, Pt.1; Subcarrier
Decoder For FM Receivers; Wide Range Electrostatic Loudspeakers, Pt.2; IR Illuminator For CCD Cameras; Remote
Control System For Models, Pt.3; Simple CW Filter.
September 1993: Automatic Nicad Battery Charger/Discharger; Stereo Preamplifier With IR Remote Control, Pt.1;
In-Circuit Transistor Tester; A +5V to ±15V DC Converter;
Remote-Controlled Cockroach.
April 1995: Build An FM Radio Trainer, Pt.1; Photographic
Timer For Darkrooms; Balanced Microphone Preamplifier &
Line Filter; 50W/Channel Stereo Amplifier, Pt.2; Wide Range
Electrostatic Loudspeakers, Pt.3; 8-Channel Decoder For
Radio Remote Control.
October 1993: Courtesy Light Switch-Off Timer For Cars;
Wireless Microphone For Musicians; Stereo Preamplifier
board Goes Flat; Guitar Headphone Amplifier; FM Radio
Trainer, Pt.2; Transistor/Mosfet Tester For DMMs; 16-Channel Decoder For Radio Remote Control; Introduction to
Satellite TV.
May 1995: What To Do When the Battery On Your Mother
July 1996: Installing a Dual Boot Windows System On Your
PC; Build A VGA Digital Oscilloscope, Pt.1; Remote Control
Extender For VCRs; 2A SLA Battery Charger; 3-Band Parametric Equaliser; Single Channel 8-bit Data Logger.
August 1996: Electronics on the Internet; Customising the
Windows Desktop; Introduction to IGBTs; Electronic Starter
For Fluorescent Lamps; VGA Oscilloscope, Pt.2; 350W Amplifier Module; Masthead Amplifier For TV & FM;
September 1996: Making Prototypes By Laser; VGA Oscilloscope, Pt.3; Infrared Stereo Headphone Link, Pt.1; High
Quality PA Loudspeaker; 3-Band HF Amateur Radio Receiver;
Feedback On Programmable Ignition (see March 1996).
PLEASE NOTE: November 1987 to August 1988, October
1988 to March 1989, June 1989, August 1989, May 1990,
February 1992, November 1992 and December 1992 are
now sold out. All other issues are presently in stock. For
readers wanting articles from sold-out issues, we can supply
photostat copies (or tear sheets) at $7.00 per article (includes
p&p). When supplying photostat articles or back copies, we
automatically supply any relevant notes & errata at no extra
charge. A complete index to all articles published to date is
available on floppy disc at $10 including packing & postage.
October 1996 11
Send video signals
over twisted pair cable
Use this Video Transmitter and Video
Receiver to wire your home or business
with remote video for entertainment or
for CCTV security systems.
By JOHN CLARKE
What’s a twisted pair cable? For all
intents and purposes, it is equivalent
to a pair of telephone wires and you
can’t send video over telephone wires,
can you? Well, with this new chipset
you could, although that is not why
we are presenting this article.
With the recent introduction of
12 Silicon Chip
low-cost monochrome video cameras,
(less than $200 retail) and this project,
you can now easily monitor your front
door, your swimming pool or any other
part of your home that needs watching
from a central location.
Video signals are normally sent
through 75Ω coax cable and for short
runs over several tens of metres there
is very little loss in signal level. But
over long distances the losses in the
cable reduce the signal to an unacceptably low level for the receiving
equipment.
One way of overcoming the signal
loss is to modulate it onto a carrier in
the UHF or VHF range. Any signal loss
in the cable can then be made good
by wideband distribution amplifiers.
However, at the receiving end, the
signal must be demodulated before it
can be displayed on a monitor.
This approach is well-proven but
coax cable and distribution amplifiers
are expensive. Wouldn’t it be nice to be
able to send video over ordinary twist
ed wires? Using the video transmitter
Fig.1: the general arrangement of the MAX435 & MAX436 ICs. The MAX435 has a differential
output while the MAX436 only has a single ended output. These are transconductance amplifiers
so the outputs produce a current that’s proportional to the applied differential input voltage.
Features
•
•
1.5km range (expected)
Video transmitted over low cost
twisted pair
•
Audio transmitted in stereo over
50m using op amp transmitter
•
Up to 1.5km range for mono
audio using video transmitter
and receiver described here, video can
be sent over distances up to 1.5km.
Transconductance amplifiers
The heart of this project is a pair of
ICs made by Maxim Integrated Products, the MAX435 and MAX436. These
two ICs are classified as high speed,
wideband transconductance amplifiers (WTAs) with true differential,
high impedance inputs. The unique
architecture of these amplifiers provides accurate gain without negative
feedback. Without the feedback, the
possibility of spurious oscillation is
virtually eliminated.
Fig.1 shows the general arrangement of the ICs. The MAX435 has a
differential output while the MAX436
only has a single ended output. The
outputs produce a current that’s proportional to the applied differential
input voltage, providing inherent
short circuit protection for the outputs. The circuit gain is set by the
ratio of the output impedance “RL”,
the user connected transconductance
network “ZT” and an internally set
current gain factor, K. In the case of
the MAX435, the current gain is nomi
nally 4 (±2.5) and for the MAX436 this
figure is 8 (±2.5).
Inside the video transmitter. The top view shows the audio board “hinged” back
to reveal the video board, which sits on the bottom of the case. The view above
shows the audio board in place.
The MAX435 has a 275MHz bandwidth and 800V/µs slew rate, while
the MAX436 has a 200MHz bandwidth
and 850V/µs slew rate. The common
mode rejection ratio for both is -53dB
at 10MHz and -90dB at DC.
While MAX ICs could also be used
to transmit audio signals, we have
taken a cheaper approach and used
dual op amps to produce a balanced
October 1996 13
Fig.2: the transmitter circuit takes composite video and provides a balanced
output to the twisted pair. The unbalanced audio signals are converted to
balanced outputs by the LM833 op amps.
audio transmitter and receiver. These
produce high quality stereo results
over short runs of less than 50m. This
will allow you to pipe composite video
and stereo audio signals around your
house. For many applications though,
we envisage that the video transmitter
and receiver boards will be all that are
required.
Transmitter circuit
Fig.2 shows the transmitter circuit.
Unbalanced video signal is applied
to the IN+ input of the MAX435. The
inverting input IN- is connected to
ground. The transconductance element impedance between pins 3 and
14 Silicon Chip
5 is set at 220Ω, while the output impedance is a nominal 50Ω. The 4.7kΩ
resistor sets the supply current for the
IC. Supply decoupling for the ±5V
rails, provided by the 0.1µF capacitors,
is necessary for best performance at the
high frequencies involved.
Power is derived from a 12VAC
plugpack. This is rectified with halfwave rectifier diodes D1 and D2 to
supply the ± rails before regulation.
The 470µF capacitors filter the raw DC
to produce a relatively smooth voltage.
REG1 and REG2 regulate the supplies
down to ±5V for IC1.
Audio input is applied to a single
ended to balanced output amplifier
comprising IC2a and IC2b for the
left channel and IC3a and IC3b for
the right. IC2a is a unity gain buffer
which is non-inverting. The output at
pin 1 is therefore the + output which
drives the positive twisted pair line
via a 680Ω resistor. IC2b is connected as an inverting amplifier and the
resulting output at pin 7 drives the
negative twisted pair line via its 680Ω
resistor. The 22pF capacitor across the
feedback resistor of IC2b prevents high
frequency oscillation.
The right channel audio amplifier
operates similarly to the left channel
circuit.
Receiver circuit
Fig.3 shows the receiver circuit.
IC4 is a MAX436 which accepts the
Fig.3: the receiver circuit uses a MAX436 to convert the balanced input from the twisted
pair to an unbalanced video output. Similarly, the balanced audio signals are converted
to single-ended signals by op amps IC5 and IC6.
balanced input from the twisted pair
and produces an unbalanced output.
The 51Ω resistors at the IN+ and INinputs at pins 2 and 6 provide the
correct loading for the twisted pair
line. A 100Ω resistor in series with
trimpot VR1 is connected between
pins 3 and 2.
VR1 sets the gain of IC4, to compensate for losses in the twisted pair
line. A second 100Ω resistor from pin
3 is connected in series with a 56pF
capacitor and VC1. The capacitance
corrects for the loss of high frequency
signal through the line. In practice the
capacitance is adjusted until the colour burst signal is at its correct level.
The 4.7kΩ resistor at pin 11 sets the
current for IC4.
The power supply circuit is iden-
Specifications
Video transmitter/receiver pair
Frequency response ����������������� typically -3dB at 200MHz
Common mode rejection ����������� typically -53dB at 10MHz; -90dB at DC
Audio transmitter/receiver pair
Signal to noise ratio ������������������ -102dB unweighted (20Hz to 20kHz) with
respect to 1V RMS
Common mode rejection ����������� -62dB at 50Hz and 1kHz
Harmonic distortion ������������������� less than .016% from 20Hz to 20kHz
Frequency response ������������������ -0.25dB at 20Hz and 20kHz
Clipping level ���������������������������� 1.7V RMS at input
Crosstalk ����������������������������������� -80dB (20Hz to 20kHz) with 20m twisted
pair alongside video pair
October 1996 15
Fig.4: the component
overlays and wiring details
for the transmitter boards.
tical to that used in the transmitter.
The audio signal is converted from
the balanced twisted pair signal to an
unbalanced output using op amps IC5a
& IC5b for the left channel and IC6a &
IC6b for the right channel.
The balanced signal is applied to
the non-inverting inputs of IC5a and
IC5b. The 330Ω resistors tie the inputs
to ground and provide a load for the
twisted pair line. A .001µF capacitor
is included across the input terminals
to remove high frequency noise from
16 Silicon Chip
the line. Both IC5a and IC5b are set for
a gain of two due to the 1kΩ feedback
resistors.
Signals which are common to each
input are rejected at the output and
this is due to the feedback for IC5a
being connected to the output of IC5b.
Difference signals are amplified at the
pin 1 output of IC5a. The 100Ω output
resistor prevents oscillation in IC5a
due to capacitive loading.
The right channel audio amplifier
operates in exactly the same manner
as the left channel audio amplifier.
Construction
The Video Transmitter and Video
Receiver are housed in separate plastic
cases measuring 130 x 68 x 42mm. The
video transmitter (using the MAX435)
is built onto a PC board measuring
60 x 102mm (coded 02306961). The
audio transmitter PC board (coded
023069623) is piggy-backed onto the
video transmitter.
The two receiver PC boards (coded
PARTS LIST
Video transmitter board
1 PC board, code 02306961, 60
x 102mm
1 plastic utility case, 130 x 68 x
42mm
1 self-adhesive front-panel label,
62 x 126mm
1 12VAC 500mA plugpack
1 SPDT toggle switch (S1)
2 3mm screws and nuts
1 DC socket
2 panel-mount RCA sockets
8 PC stakes
1 40mm length of 0.8mm tinned
copper wire
Semiconductors
1 MAX435CPD high-speed
transconductance amplifier
(IC1)
1 7805 3-terminal regulator
(REG1)
1 7905 3-terminal regulator
(REG2)
2 1N4004 1A silicon diodes
(D1,D2)
Video Receiver board
1 PC board, code 02306962, 60
x 102mm
1 plastic case, 130 x 68 x 42mm
1 front panel label, 62 x 126mm
1 12VAC 500mA plugpack
1 SPDT toggle switch (S2)
2 3mm screws and nuts
1 DC socket
2 panel-mount RCA sockets
8 PC stakes
1 40mm length of 0.8mm tinned
copper wire
1 500Ω horizontal trimpot (VR1)
Semiconductors
1 MAX436CPD high-speed
transconductance amplifier
(IC4)
1 7805 3-terminal regulator
(REG3)
1 7905 3-terminal regulator
(REG4)
2 1N4004 1A diodes (D3,D4)
Capacitors
2 470µF 16VW PC electrolytic
2 10µF 16VW PC electrolytic
3 0.1µF ceramic
Capacitors
2 470µF 16VW PC electrolytic
2 10µF 16VW PC electrolytic
3 0.1µF ceramic
1 56pF ceramic
1 3-60pF trimmer (optional)
Resistors (0.25W 1%)
1 4.7kΩ
1 75Ω
1 220Ω
2 51Ω
Resistors (0.25W, 1%)
1 4.7kΩ
1 75Ω
2 100Ω
2 51Ω
Audio transmitter board
Audio receiver board
1 PC board, code 02306964, 60
x 102mm
4 12mm spacers
4 6mm spacers
4 20mm x 3mm screws
4 3mm nuts
11 PC stakes
1 20mm length of 0.8mm tinned
copper wire
1 PC board, code 02306963, 60 x
102mm
4 12mm spacers
4 6mm spacers
4 20mm x 3mm screws
4 3mm nuts
11 PC stakes
1 20mm length of 0.8mm tinned
copper wire
Semiconductors
2 LM833 op amps (IC2,IC3)
Semiconductors
2 TL072 op amps (IC5,IC6)
Capacitors
4 10µF 16VW PC electrolytic
2 22pF ceramic
Capacitors
4 10µF 16VW PC electrolytic
1 .001mF MKT polyester
Resistors (0.25W, 1%)
6 x 10kΩ
2 330Ω
4 680Ω
Resistors (0.25W, 1%)
8 x 10kΩ
2 100Ω
4 330Ω
YOU CAN
AFFORD
AN INTERNATIONAL
SATELLITE TV
SYSTEM
SATELLITE ENTHUSIASTS
STARTER KIT
YOUR OWN INTERNATIONAL
SYSTEM FROM ONLY:
FREE RECEPTION FROM
Asiasat II, Gorizont, Palapa,
Panamsat, Intelsat
HERE'S WHAT YOU GET:
●
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400 channel dual input receiver
preprogrammed for all viewable satellites
1.8m solid ground mount dish
20°K LNBF
25m coaxial cable
easy set up instructions
regular customer newsletters
BEWARE OF IMITATORS
Direct Importer: AV-COMM PTY. LTD.
PO BOX 225, Balgowlah NSW 2093
Tel: (02) 9949 7417 / 9948 2667
Fax: (02) 9949 7095
VISIT OUR INTERNET SITE http://www.avcomm.com.au
YES GARRY, please send me more
information on international band
satellite systems.
Name: __________________________________
Address: ________________________________
____________________P'code:
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Phone: (_______) ________________________
ACN 002 174 478
October 1996 17
Fig.5: the component
overlays and wiring details
for the receiver boards.
TABLE 1: RESISTOR COLOUR CODES
❏
No.
❏ 6
❏ 2
❏ 8
❏ 4
❏ 6
❏ 2
❏ 2
❏ 4
18 Silicon Chip
Value
10kΩ
4.7kΩ
1kΩ
680Ω
330Ω
100Ω
75Ω
51Ω
4-Band Code (1%)
brown black orange brown
yellow violet red brown
brown black red brown
blue grey brown brown
orange orange brown brown
brown black brown brown
violet green black brown
green brown black brown
5-Band Code (1%)
brown black black red brown
yellow violet black brown brown
brown black black brown brown
blue grey black black brown
orange orange black black brown
brown black black black brown
violet green black gold brown
green brown black gold brown
02306962 and 02306964) are mounted
in a similar fashion to the transmitter.
On both cases, RCA sockets for video
input and output are mounted at the
sides of the box while the audio sockets are at one end of the box. The DC
socket is mounted at the opposite end
while the power switch is attached
to the lid.
Fig.4 shows the component overlay
and wiring details for the transmitter
boards while Fig.5 shows the wiring
details for the receiver boards.
Begin construction by checking
each PC board for breaks or shorts in
the copper pattern or any undrilled
holes. Fix any defects before proceeding further, then insert all the PC
stakes. These are located at the signal
input and output wiring points and
for power supply.
Next, solder in all the links and
resistors. Table 1 shows the resistor
colour codes and it is a good idea to
check each resistor value with your
multimeter before soldering it into the
board. The capacitors can be mounted
next, noting that the electrolytic types
must be oriented with the correct
polarity as shown. Finally, insert the
ICs, making sure that each one has the
correct orientation.
If you do not intend to use stereo
audio channels, IC3 on the audio transmitter board and IC6 on the receiver
board can be omitted.
The voltage regulators are each
mounted horizontally on the PC board
and secured with a screw and nut.
Bend the leads for each component
before insertion into the PC board
holes. Take care to orient the diodes
correctly.
Drill holes in the plastic cases for the
RCA and DC sockets using the front
panel as a guide to their location. A
hole is also required in the lid for the
power switch on each box.
Wire up the PC boards as shown in
Fig.4 and Fig.5. In each case, the audio
board is stacked on top of the video
board and the two are separated by
metal spacers. The integral side pillars
in each box will need to be removed
so that the PC board assembly can fit
comfortably within the case. Affix the
label to each lid and attach the power
switches.
Testing
The completed units are now ready
for testing. Apply power to the transmitter PC boards and check voltages.
These two photographs show the completed boards inside the receiver case. The
top view shows the video receiver board, while above is the audio board.
Fig.6: the top trace of the oscilloscope display shows a PAL colour bar as
the video source signal. Note the colour burst at the far lefthand side of the
trace. The lower trace shows the received signal after transmission over
20m of twisted pair. The gain has been compensated for signal loss and for
video colour burst level. Note the faithful reproduction of the signal.
October 1996 19
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They are made from a distinctive
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Price: $A11.95 plus $3 p&p each
(NZ $8 p&p). Send your order to:
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PO Box 139
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Or fax (02) 9979 6503; or ring (02)
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20 Silicon Chip
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TRANSMITTER
L
R
AUDIO IN
BALANCED
VIDEO OUT
Silicon Chip Binders
L
R
BALANCED AUDIO OUT
24/31 Wentworth St, Greenacre 2190
Phone (02) 642 6003 Fax (02) 642 6127
VIDEO IN
Fig.7: actual size front panel & PC board artworks for the transmitter. Check
your PC boards carefully before installing any of the parts.
Connect the negative multimeter lead
to GND and touch the positive lead
on pins 1, 12 & 14 of IC1 where +5V
should be present in each case. Similarly, there should be -5V on pins 7, 8
& 10 of IC1. IC2 and IC3 should have
+5V on pin 8 and -5V on pin 4.
For the receiver PC boards, there
should be +5V on pins 1, 12 & 14 of
IC4 and -5V on pins 7, 8 & 10. IC5 and
IC6 should have +5V on pin 8 and -5V
on pin 4.
To transmit video you will require
one twisted pair while each audio
channel will require a separate twisted
pair. Use 75Ω coax cable from your
video source to the transmitter and
from the receiver to the video input of
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R
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VIDEO OUT
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R
AUDIO OUT
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Fig.8: actual size front panel & PC board artworks for the receiver. All PC
boards measure 60 x 102mm.
your monitor or VCR. Audio connec
tions should be made using standard
shielded audio cable.
VR1 on the receiver is adjusted to
obtain best black and white levels as
seen on the monitor. The 56pF capacitor on IC4 should be satisfactory for
twisted pair up to 50m. A larger capacitor value can be used if the colour
burst signal is marginal. This can be
adjusted until the monitor provides a
solid colour picture.
Lack of picture sync (rolling) means
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away from mains power wiring or
use shielded pair earthed to the GND
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October 1996 21
Power control with
a light dimmer
By LEO SIMPSON
In this article we show you how to wire a
standard light dimmer in a plastic case to
do low temperature soldering, control an
electric blanket or to dim a table lamp. No
electronics assembly is required, just some
drilling of the plastic case and a little wiring.
This article was prompted by a reader who wanted to do some low temperature soldering of white metal model
railway kits. White metal is an alloy
of tin and lead, with small amounts
of antimony and copper (typically
19% antimony, 1% copper, 75% lead
22 Silicon Chip
and 5% tin). While white metals have
long been used in the manufacture of
bearings, they are also used in small
castings for model railway locomotives, rolling stock and structures. The
reason that white metal is used is that
it has a low melting point, typically
around 200-250°C. That low melting
point means that normal tin-lead solders cannot be used; the casting melts
before the solder!
There are a variety of low temperature solders available but the one
normally used for soldering white
metal castings is based on cadmium
(tin-lead-cadmium). The most popular
is made by Carr’s Modelling Products,
a UK company. Carr’s 70 is a solder
that melts at 70°C.
This cannot be safely handled or
worked with using an ordinary soldering iron or even one that is temperature-controlled, for that matter.
Why not? Most temperature controlled irons are not designed to op-
Fig.1: here's how to wire the dimmer unit to the mains cord
and the 3-pin socket.
erate reliably with a tip temperature
below 200°C. So there is a need to run a
soldering iron at much reduced power;
sufficient to melt and work the solder
but not hot enough to cause heavy
metal gases to be evolved or damage
the white metal casting. In fact, it is
absolutely imperative that solders con
taining cadmium (or bismuth and antimony) should not be overheated by the
tip of the soldering iron – otherwise
you will end up breathing poisonous
metal fumes.
One way to reduce the power to a
standard soldering iron to a low level
is to use the 5A heavy duty drill speed
controller published in the September
& November 1992 issues of SILICON
CHIP. That will certainly work but it
is rather like using a sledge hammer
to crack a walnut. It is also more expensive than the dimmer approach
described in this article.
Our suggestion is to purchase a
low power soldering iron rated at
between 15 and 30 watts and use it
in conjunction with the dimmer as
described here. Use the dimmer at a
setting just hot enough to make the
solder workable and mark that setting
on the dimmer plate so you can repeat
it in the future. Second, use the iron
only for low temperature work. Do not
October 1996 23
55 x 85mm but there are a number of
alternatives available.
Whichever plastic case you use,
it needs to be big enough to accommodate the dimmer panel on its top
surface and a surface-mount 3-pin
socket at one end. As well as this
socket, you will need a 3-core mains
flex with moulded 3-pin plug and a
cordgrip grommet.
You will need to drill holes in
one end of the case for the surface
mount socket – two 3mm holes for
the mounting screws and three 5mm
holes for the lead entry. At the other
end of the case, you will need to drill
and file an elongated hole to take the
cordgrip grommet.
Finally, you will need to drill two
3mm holes and cut a rectangular hole
in the lid so that the dimmer can be
mounted.
Wiring
This view shows the wiring inside the case. Make sure that the mains cord is
securely clamped and note that plastic cable ties are used to secure the internal
wiring. The Neutral and Earth leads from the mains cord go direct to the socket.
use it for normal soldering because if
you do, when the iron is hot enough
to melt normal solder it will boil off
any cadmium residue and you could
end up breathing it!
Assembly work
First, purchase your dimmer. Shop
around for it as you will find a wide
range of prices. At the time of writing
we found dimmer prices to range from
$12 at Woolworths to more than $28
at some electrical wholesalers. The
one we used is made by HPM (Cat
500A/500VA) and was purchased for
$16.60. Other brands of dimmer, made
by GAF and Arlec, are cheaper.
Second, you will need a suitable
plastic box. The one we used came
from Altronics and measures 125 x
The yellow/green Earth lead from
the mains cord is terminated directly to the earth terminal of the 3-pin
socket. The blue Neutral wire from the
mains cord also terminates directly to
the Neutral terminal of the 3-pin socket. The brown Active wire from the
mains cord goes to one of the switch
terminals. The other switch wires goes
to the dimmer module.
Finally, the second wire from the
dimmer module goes to the Active
terminal on the 3-pin socket. Fig.1
shows the details.
When you have completed the wiring, check it against Fig.1 and then
test the dimmer on a table or desk
lamp. Don’t forget to screw the lid
on the case before you do the test. If
everything works as it should, push
the plastic screw covers into the
dimmer mounting screw holes and
SC
you are finished.
Using A Standard Light Dimmer
What they can do: most standard
wall-mounting light dimmers are rated
at between 300 and 500 watts but
there are conditions applied to this
rating. Apart from dimming lights,
most standard dimmers can be used
to control fans and low powered
heating appliances such as soldering
irons and electric blankets.
What they can’t do: because they
24 Silicon Chip
have such a modest rating, light
dimmers cannot be used to control
the speed of a typical power tool or
food mixer. If you do attempt to use
a light dimmer, it will fail immediately.
Most light dimmer manufacturers
also warn against dimming lights
where the individual lamps have
a rating in excess of 150 watts or
where the lamp is upright rather
than hanging down from the fitting. In
both cases, when the lamp fails the
broken filament is likely to flail around
and come into contact with one of
the stem supports. This will cause a
brief but very large fault current which
often blows the Triac in the dimmer.
The good news is that such dimmers
can generally be fixed by replacing
the Triac with an SC141D.
Snappy
Just click the
mouse button
for high-res
video images
By GREG SWAIN
This new technique just has to be the lowest
cost way to capture high-quality video images
on a PC. It’s called “Snappy” and teamed
up with a standard camcorder, it produces
images that can rival those from expensive
digital cameras costing $6000 or more.
A
CTUALLY, SNAPPY should be
classified as a frame-grabber
because that’s what it does – it grabs
video frames from a camcorder (or
some other video source). But unlike
a conventional frame-grabber which
plugs into your PC’s mother
board,
Snappy is a compact external device
that plugs into the parallel port.
This makes for a much more convenient arrangement. You don’t have
to pull the cover off your PC and you
don’t have any of the installation
hassles that can occur with plug-in
cards (IRQ settings and the like). It also
means that you can easily move the
device from one computer to another,
should the need arise.
In use, Snappy can be teamed with
any video source, such as a camcorder,
VCR or TV tuner. It’s then simply a
matter of clicking the mouse button
to preview a video frame via the
proprietary software that comes with
the device. This frame can then be
captured and saved in a number of
standard file formats, including bmp,
pcx, tif, tga and jpg.
Image quality
The big difference between Snappy
and conventional frame grabbers lies
in the image quality. Conventional
frame grabbers are strictly low-resolution devices and the image quality is
limited. By contrast, this new device
us claimed to provide video stills
at resolutions up to 1500 x 1125
(1,687,500) pixels and in 16.8 million
(32-bit) colours.
That’s more than twice the resolution from a conventional frame grabber
but there are a few other enhancements
to the image along the way. In fact, this
is claimed to be the world’s highest
resolution video grabber.
A clever IC
The clever part of Snappy is a custom chip hidden inside the hardware.
This chip, the HD-1500, was developed by Play Incorporated (USA) and
digitally enhances the captured image
before it is fed to the PC. Among other
things, it provides 8-times oversampling, sets the black level and features
adaptive comb filtering and timebase
correction.
Provided the source material is up
to scratch, the resulting image is sharp
and has good colour and contrast.
You can get some idea of the quality
from the accompanying photographs.
These photographs were supplied as
jpeg compressed files on a demonstration disc and have not been enhanced
in any way. All that we have done is
open them in Photoshop, convert the
resolution from 72 dpi to 266 dpi,
resize them and convert them from
RGB to CMYK format.
From what we’ve seen, Snappy is
perfect as a quick and painless way of
capturing good-quality video images.
You don’t have to muck about getting
film processed and then scanning the
resulting images, all of which costs
October 1996 25
time and money. Of course, the results
aren’t as good as those from a drum
scanner or dedi
cated transparency
scanner but then we’re talking horses
for courses.
The software
Fig.1: this is the interface that you get when you boot the Snappy video capture
program. Clicking the Preview button brings up a frame grab on the screen.
Fig.2: the Snappy software lets you make all sorts of adjustments to the
previewed image, including colour, brightness, contrast, picture (gamma) and
sharpness. You can also adjust the colour balance.
This video grab, from the Snappy demonstration disc, was obtained at a
resolution of 1500 x 1125 pixels.
26 Silicon Chip
The Snappy software is easy to use,
with an intuitive interface – you just
click on the action buttons or turn the
control knobs. You don’t need fancy
hardware to run it either. The specifications are a PC-compatible with a 386
processor or better, 4Mb or RAM, 4Mb
of hard disc space and a VGA (640 x
480 or better) video card. The software
runs under Windows 3.1, Windows
3.11 and Windows 95 but no mention
is made of Windows NT.
Fig.1 shows the interface that’s presented when you boot the software. To
preview the image, you just click the
Preview button. Clicking the Adjust
button then brings up the window
shown in Fig.2. From there, you can
make adjustments (if necessary) to various aspects of the image (eg, colour,
brightness, contrast picture (gamma)
and sharpness).
It’s then simply a matter of clicking
the Snap button to save the image
to the disc in one of the standard
formats.
One very useful feature of the software is that you can “invert” the image from a negative to a positive. This
can be useful if you have a negative
colour transparency, for example. The
trick is to place the transparency on
a lightbox, aim the camera at it and
then use the software to produce a
positive image.
Despite what might seem a rather
clumsy technique, the result is still
surprisingly good. Of course, you can
use the same technique to capture
images from a positive transparency
but without “inverting” the image.
As well as the standard capture software, Snappy also comes with Adobe
Photo Deluxe, an easy-to-use image
editing program. This will let you
add special effects to your images and
even add titles. An image distorting
program (called Goo) and a morphing
program (Griffon Morph) complete the
software suite that’s sup
plied with
Snappy. Once again, these are easy
to use and you can amuse yourself
morphing grandma between her true
self and the visage of a bassett hound,
if your taste runs to such pastimes!
The saved image can also be opened
Above & left: provided some care is
taken with lighting, Snappy is capable
of producing excellent results, as
these two photos demonstrate (again
from the Snappy demo disc). Snappy
is the easiest, most cost-effective way
of obtaining video grabs that we've
seen.
in high-end imaging editing software
such as Photoshop or imported into
desktop publishing programs. In addition, Snappy boasts a Twain interface
which means that an image can be
directly acquired through Photoshop
or any other program that supports the
Twain standard.
Who will use it?
Snappy At A Glance
•
•
•
Captures images from camcorders, VCRs, laser disc players, etc.
•
•
•
•
•
Preview mode displays image on-screen prior to capturing.
•
•
•
Three capture modes: field, frame or multi-frame.
Easy to install; plugs into the PC’s parallel port.
Custom chip enhances image and provides video resolution up to 1500
x 1125 pixels in 16.8 million colours.
User adjustable image processing controls.
Twain interface; emulates scanners.
Negative mode for grabs of photographic negatives.
Saves in one of three resolutions: 1500 x 1125 (5Mb bmp), 640 x 480
(1Mb bmp) and 320 x 240 pixels (250Kb bmp).
Dimensions: 64 x 124 x 22mm
Comes with Snappy (video capture), Adobe Photo Deluxe, Griffon
Morph and Goo (image distorting) software.
Just about everyone who needs to
capture good-quality images with
minimum hassle will want Snappy.
To quote a well-worn cliche, the list
of applications is endless. This device
is perfect for producing catalogs, ad
vertisements, real estate magazines,
school reports, ID cards, newsletters
and Internet images, to name just a
few.
Provided that you have a video
camera (or some other suitable video
source), Snappy is the fastest, easiest
way to get good quality video grabs
into your PC that we’ve seen.
The cost won’t break the bank either – the recommended retail price
is $449. This price includes the hardware, all the software (Snappy, Adobe
Photo Deluxe, Goo and Morph), a video cable, a 9V battery and a manual.
For further information, contact the
Australian distributor Star Micronics,
Unit A, 107 Asquith St, Silverwater,
NSW 2128. Phone (02) 9748 4300. SC
October 1996 27
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
600W DC-DC converter
for car hifi systems
Thinking of fitting high-power audio
amplifiers to your car’s stereo system?
This 600W DC-DC Converter steps
up the battery voltage to provide the
high-voltage split supply rails required
by the amplifiers.
PART 1: By JOHN CLARKE
If you like lots of bass and high
sound levels in your car then you
will want to build this 600W DC-DC
Converter. It is used in conjunction
with one or more amplifier modules so
that up to 360W RMS total (or 180W
per stereo channel) can be delivered
to the loudspeakers.
With that sort of power, and provided your loudspeakers are up to the
task, you will have the makings of a
really first-class car hifi system. Not
32 Silicon Chip
that we are advocating that you use
this type of system to blow your brains
out or to annoy other motorists. That’s
not what a high-power car hifi system
is used for at all. Instead, it’s used to
provide good clean sound with plenty
of bass and with plenty in reserve for
those high-power transients.
What sort of amplifiers can be used
with this converter? One that immediately springs to mind is the “Plastic
Power” amplifier module described in
Features
• Output voltag
e adjustable
• High power ca
pability
• Fuse protected
• Under voltage
cutout
• Overcurrent p
rotection
• Fan cooled
• Over-temperat
ure cutout
• Power indicat
ors
the April 1996 issue of Silicon Chip.
This module requires a ±57V supply
and is capable of delivering 175W
into a 4Ω load or 125W into 8Ω. Two
of these modules (for stereo) would
provide an excellent hifi amplifier
system for your car.
That said, the choice of amplifier
module is not restricted to any specific
type, as we have catered for a wide
range of supply options. However, the
two modules in a stereo pair must be
Fig.1: block diagram of the DC-DC Converter. It uses a switchmode driver stage
to produce pulse width modulated (PWM) signals and these are used to drive
complementary Mosfet switching stages. These stages in turn drive step-up
transformer T1. Its secondary output is then fed to a bridge rectifier and filter
capacitor stages to develop the plus and minus DC output rails.
capable of operating from a common
supply voltage. The amplifiers can be
rated for any power, provided that the
total power drawn from the DC-DC
Converter is less than 600W.
This final restriction does not mean
that a single 600W amplifier or two
300W amplifiers can be powered by
the converter. We must take amplifier
efficiency into account and all amplifiers draw more power than they can
deliver into a load.
In theory, the maximum efficiency
of a class B amplifier stage is 78.5%
but this does not include the power
dissipated by the quiescent current. In
practice, the average power amplifier
module will be about 60% efficient at
full power. This means that only 60%
of the power drawn from the converter
will be supplied to the load.
This in turn sets the maximum amplifier power rating to about 60% of
600W, or 360W total. If two amplifiers
are used, then each one should be rated
at no more than 180W.
Physical arrangement
As can be seen from the photos,
the 600W DC-DC Converter is quite
large. It is built into a two-unit high
rack-mounting case and would normally be installed in the boot or, if
space permits, under a seat.
The unit is fan cooled to keep the
components within their heat ratings
and this will have some bearing on
the final mounting arrangement, as
the air vents must be kept free of any
restrictions.
The only external inputs are from
the battery and the ignition switch,
while the unit provides +V, -V and
GND connections to the power amplifiers. Heavy duty cables are used for the
battery supply connections and these
are a necessity since the unit can draw
up to 63A. Heavy duty wiring is also
used for the power supply outputs to
the amplifier modules.
Three front-panel LEDs (Power,
Output + and Output -) are used to
indicate the status of the converter.
The power LED simply indicates when
the converter is switched on, either via
the ignition or a separate switch. The
two remaining LEDs indicate that the
plus and minus amplifier supply rails
are present.
Basic principle
The basic principle of the DC-DC
converter is really very simple. It
works by alternately switching the 12V
battery supply to each half of a centre-tapped transformer primary. The
resulting AC waveform is then stepped
up by the transformer secondary and
then rectified and filtered to provide
the plus and minus supply rails.
To achieve high efficiency and reduce the number of bulky components,
the circuit operates at a switching
frequency of about 22kHz. This high
frequency allows us to use a ferrite
transformer rather than a bulky ironcored type. The circuit also uses highspeed power Mosfets to switch the
transformer and fast recovery diodes
for the rectifiers.
Power Mosfets were used because
they are very fast and have low switching losses. In addition, power Mosfets
have a positive temperature coefficient
which means that they automatically
“throttle” back if the output stage starts
to overheat.
In addition, the circuit incorporates
comprehensive protec
tion facilities.
These include low-voltage cutout,
current over
l oad protection and
over-temperature cutout.
The low-voltage cutout is a particularly useful feature. In effect, the
converter circuit monitors the battery
voltage and if it drops below a certain
level, the converter switches itself
off. This not only saves you from the
inconvenience of a flat battery but is
also necessary to protect the Mosfets.
To explain, a Mosfet is turned on
by applying a voltage to its gate. If
this voltage is too low, the Mosfet will
not fully conduct and this can lead
to excessive power dissipation and
device failure.
The current overload protection
circuitry operates at two levels. First,
there is a 63A fuse in the supply line
which will blow if there is a drastic
fault in the converter itself. Second,
the circuitry features inbuilt current
limiting to provide protection against
output short circuits.
The accompanying specifications
panel shows the performance of the
converter. Note that its efficiency is
better than 80% at full rated output.
Block diagram
Fig.1 shows the block diagram of
the DC-DC Converter. As mentioned
above, it uses a centre-tapped step-up
transformer which is driven by Mosfet
transistors. The secondary winding is
also centre-tapped and is fed to bridge
October 1996 33
WHY A CONVERTER IS NEEDED FOR HIGH POWER
OK, so why do we need a converter to boost the supply rails for
the power amplifier in the first place?
Why not simply power the amplifier
directly from the 12V battery?
To understand this, we need to
consider some basic theory. First, we
know that the power delivered into
a load is the output voltage squared
divided by the load resistance (ie,
P = V2/R).
Now let’s assume that we have
a 12V battery which is charged to
14.4V. An amplifier powered from
this battery can typically deliver a
maximum output of 11V peak-topeak or about 3.9V RMS – see Fig.2.
Thus, the maximum power which
can be delivered into a 4Ω load
from a single-ended configuration
is about 3.8W (3.9 x 3.9/4). This can
be increased by wiring two power
amplifiers in a bridge configuration.
If that is done, the output voltage
supplied to the load is doubled and
so the power output will be four times
greater at about 15W (which is still
quite modest).
All this assumes that the battery
is actually delivering 14.4V. In practice, this only happens if the motor
in your car is running and has had
time to fully charge the battery. So
in practice, the power outputs from
single-ended or bridge connected
amplifiers will be even less than the
above figures.
As a result, if we want high power,
we need to either reduce the load
resistance or increase the supply
rails for the amplifier. However, a very
low load resistance is impractical
because the current in the amplifier
output stages becomes excessive.
This in turn causes high losses in
both the amplifier and loudspeaker
wiring.
The efficient way to increase the
power is to increase the voltage,
rather than reduce the load impedance. This is because the power is
proportional to the square of the
voltage and only proportional to the
inverse of the load impedance.
This “square law” effect means
that if we double the voltage, we
quadruple the power. By contrast, if
we halve the load impedance we only
double the power. At the same time
as halving the load resistance, we
double the current which quadruples
the losses.
The only practical option is to
increase the supply rails and that’s
exactly what this DC-DC converter
is designed to do. It can deliver supply rail voltages up to ±70V DC, so
that you can run really high power
amplifier systems (up to 180W per
stereo channel).
Fig.2: an amplifier powered from a 14.4V rail can typically deliver a
maximum output of about 11V p-p or about 3.9V RMS (note: the scope
shows a slightly low RMS figure). This means that the maximum power
which can be delivered into a 4Ω load from a single-ended configuration
is about 3.8W or about 15W from a bridged configuration.
34 Silicon Chip
rectifier and filter capacitor stages to
develop the plus and minus DC output rails.
Mosfets Q3-Q5 drive the top half of
the step-up transformer, while Q8-Q10
drive the bottom half. These in turn
are driven by a switchmode circuit
which has feedback applied from the
DC output. This feedback circuit acts
to reduce the width of the pulses applied to the Mosfets if the DC voltage
rises above a preset value. Conversely,
the pulse width from the driver circuit
increases if the output voltage falls
below the preset value.
Note that the two Mosfet driver
circuits are switched in antiphase,
so that when one half of the winding
is conducting, the other is off. The
resulting primary drive is stepped-up
in the secondary windings.
Apart from the voltage feedback
which maintains a constant output
voltage regardless of load, the switch
mode driver circuit also detects overcurrent conditions via resistor Rsc. If
overcurrent occurs, the pulse width
drive to the Mosfet gates is reduced.
Note that the voltage across Rsc is amplified by over-current amplifier IC3.
Circuit details
Fig.3 shows the final circuit for the
600W DC-DC Converter. It’s based on
a dedicated switchmode IC, the TL494
(IC1). This device contains all the
necessary circuitry to generate complementary square wave outputs at
pins 9 and 10 and these drive the gates
of the Mosfets via buffer stages. The
device also contains control circuitry
to provide output voltage regulation
and low voltage dropout.
Fig.4 shows the internal circuitry of
the TL494. It is a fixed frequency pulse
width modulation (PWM) controller
containing a sawtooth oscillator, two
error amplifiers and a PWM com
parator. It also includes a deadtime
control comparator, a 5V reference and
output control options for push-pull
or single ended operation.
Fig.3 (left): the final circuit is based
on a TL494 dedicated switchmode
IC (IC1). It generates complementary
PWM signals at pins 9 & 10 and these
drive the parallel Mosfet switching
devices via buffer stages. IC3 monitors
the voltage across RSC to provide
current overload protection.
October 1996 35
Fig.4: this block diagram shows the internal circuitry of the TL494 PWM
controller. It includes a sawtooth oscillator, a PWM comparator, a dead-time
control comparator, two error amplifiers and a 5V reference. Emitter followers
Q1 & Q2 provide the complementary PWM output signals at pins 9 & 10.
The PWM comparator generates
the variable width output pulses by
comparing the sawtooth oscillator
waveforms with the outputs of the two
error amplifiers. By virtue of the diode
gating system, the error amplifier with
the highest output vol
tage sets the
pulse width.
Dead-time comparator
The dead-time comparator ensures
that there is a brief delay before one
output goes high after the other has
gone low. This means that the outputs
at pins 9 and 10 are both low for a short
time at the transition points.
This so-called “dead-time” is essential since without it the Mosfets driving one half of the step-up transformer
would still be switching off while the
Mosfets driving the other half were
switching on. As a result, the Mosfets
would be destroyed as they would
effectively create a short circuit across
the 12V supply.
Fig.5 shows the pin 9 and pin 10
output signals at the maximum duty
cycle. Note that each output is high
for only 44.7% of the time, indicating
that there is 5.3% dead-time.
One of the error amplifiers in IC1
is used to provide the under-voltage
cutout feature.
This is achieved by connecting its
pin 2 (inverting) input to the +12V
rail via a voltage divider consisting
of two 10kΩ resistors. The non-inverting input at pin 1 connects to
SPECIFICATIONS
Supply voltage ......................................................................... 10-14.8VDC
Maximum output power .............................................................600W RMS
Maximum input current ....................................................... 63A continuous
Standby current ................................................300mA (mainly fan current)
Output voltage ....................................................................±70V maximum
Efficiency at full load ..........................................................................>80%
Overcurrent cutout .......................................................... 80A peak approx.
Over-temperature cutout .....................................................................80°C
Under-voltage cutout ............................................................................ 10V
36 Silicon Chip
IC1’s internal reference at pin 14 via
a 4.7kΩ resistor.
When the voltage at pin 2 drops
below 5V (ie, when the battery voltage drops below 10V), the output of
the error amplifier goes high and the
PWM outputs at pins 9 & 10 go low,
thus shutting the circuit down.
The over-temperature cutout operates in a similar manner. The sensing
device is thermal cutout device TH1
and this is mounted on the main
heatsink along with the Mosfet output
transistors. As shown on Fig.3, it is
connected in series between the voltage divider on pin 2 and the positive
supply rail.
If the heatsink temperature reaches
80°C, TH1 opens and so the circuit
shuts down by switching the PWM
outputs low as before.
Note the 1MΩ resistor between the
non-inverting input at pin 1 and the
error amplifier output a pin 3. This
provides a small amount of hysteresis
so that this particular error amplifier
operates as a comparator.
The second error amplifier in IC1
is used to control the output voltage
of the converter and provide current
limit protection. This amplifier has its
inputs at pins 15 and 16.
Let’s consider the voltage regulation
role first. In this case, the feedback
voltage is derived from the positive
side of the bridge rectifier and is attenuated using a voltage divider consisting of VR1, a 47kΩ resistor and a
10kΩ resistor to ground. The resulting
voltage is then fed via D7 to pin 16 of
IC1 and compared to the internal 5V
reference which is applied to pin 15
via a 4.7kΩ resistor.
Normally, the attenuated feedback
voltage should be close to 5V. If this
voltage rises (due to an increase in the
output voltage), the output of the error
amplifier also rises and this reduces
the output pulse width. Conversely,
if the output falls, the error amplifier
output also falls and the pulse width
increases.
The gain of the error amplifier at
low frequencies is set by the 1MΩ
feedback resistor between pins 3 &
15 and by the 4.7kΩ resistor to pin
14 (VREF). These set the gain to about
213. At higher frequencies, the gain is
set to about 9.5 by virtue of the 47kΩ
resistor and 0.1µF capacitor in series
across the 1MΩ resistor.
This reduction in gain at the higher
frequencies prevents the amplifier responding to hash on the supply rails.
The 27kΩ resistor and .001µF capacitor at pins 6 and 5 respectively set the
internal oscillator to about 44kHz. This
is divided using an internal flipflop
to give the resulting complementary
output signals at pins 9 & 10, which
means that the resultant switching
speed of the Mosfets is 22kHz.
Pin 4 of IC1 is the dead-time control
input. When this input is at the same
level as VREF, the output transistors are
off. As pin 4 drops to 0V, the dead-time
decreases to a minimum.
At switch on, the 10µF capacitor
between VREF (pin 14) and pin 4 is
discharged. This prevents the output
transistors in IC1 from switching
on. The 10µF capacitor then charges via the 47kΩ resistor and so the
duty cycle of the output transistors
slowly increases until full control is
gained by the error amplifier. This
effectively provides a “soft start” for
the converter.
Resistor R1 has been included to
provide more dead-time if necessary. It
prevents the 10µF capacitor from fully
charging to 5V and this increases the
minimum dead-time. R1 (1MΩ) is only
necessary in those rare circumstances
when current limiting occurs at full
load. This is indicated by a buzzing
sound from the transformer.
Current limiting
The current limiting circuit is based
on op amp IC3. This is wired as a
non-inverting amplifier with a gain of
101 and is used to monitor the voltage
Fig.5: these waveforms show the complementary pulse signals from the TL494
PWM controller at the maximum duty cycle. Note that one output always
switches low before the other switches high and that each output is high for only
44.7% of the time, indicating a 5.3% dead-time.
Fig.6: these waveforms show the converter performance when there are
transient load changes from no-load to almost full load. The converter is
supplying the power rails to an amplifier which is driving a 4-ohm load at
317W when the signal is on (this corresponds to more than a 500W load on the
converter when efficiency is taken into account). The middle trace shows the
100Hz tone burst input signal, the top trace is the positive supply rail for the
amplifier (20V/div) and the lower trace is the negative supply rail (20V/div).
Note the small voltage droop and minimal overshoot when the load is removed.
developed across resistor RSC. The
output of IC3 in turn drives the pin
16 input of the second error amplifier
in IC1 via diode D8.
RSC is actually a short length of wire
with a value of about 0.7mΩ. It is connected between the commoned Mosfet
sources and ground, which means that
all the transformer primary current
flows through it.
October 1996 37
Despite the heavy-duty nature of the circuit, the 600W DC-DC Converter is easy
to build since virtually all the parts are installed on a single large PC board. A
large heatsink and a fan at one end help keep things cool.
As long as the current through RSC
remains below 79A, the output of IC3
will have no affect on the operation
of the error amplifier. However, if the
current attempts to rise above 79A,
the output of IC3 will rise above 5.6V
and so the voltage applied to pin 16
of IC1 will rise above 5V. As a result,
the output of the error amplifier rises
and this reduces the output voltage
and thus the current.
Complementary outputs
The complementary PWM outputs
at pins 9 & 10 of IC1 come from internal emitter follower transistors.
These each drive external 10kΩ load
resistors. They also each drive three
paralleled CMOS non-inverting buffer
stages (IC2a-c and IC2d-f). These in
turn drive transistors Q1 and Q2 on
one side of the circuit and Q6 and Q7
on the other side.
Thus, when pin 10 goes high, Q1
turns on and drives the paralleled
gates of Mosfets Q3-Q5 via a 4.7Ω
resistor. Note that each Mosfet gate is
connected via a 10Ω “stopper” resistor
to minimise any parasitic oscillations
which may otherwise occur while the
paralleled Mosfets are switching on
38 Silicon Chip
and off.
When pin 10 subsequently goes low,
Q2 switches on and quickly discharges
the gate capacitance of Mosfets Q3Q5, thus switching them off. Pin 9
then switches high at the end of the
dead-time period and Q6 switches on
Q8-Q10 to drive the other half of the
transformer primary.
Q1, Q2, Q6 & Q7 have been included
to ensure that the Mosfets are switched
on and off as quickly as possible. This
minimises the time that they spend in
the linear region where they dissipate
high power.
Zener diodes ZD2 and ZD3 ensure
that the Mosfets are protected against
switching spikes generated by the
transformer. If the voltage between
the drain and gate of any Mosfet rises
beyond the zener breakdown voltage
plus the gate threshold voltage, that
Mosfet switches on to suppress the
voltage. Diodes D1 and D2 prevent
the gate signals from shorting to the
drains via the zener diodes.
Note the 1Ω resistors connected
between the cathodes of ZD2 & ZD3
and the drains of the Mosfets. These
prevent large currents from flowing in
the PC board tracks. The high-current
paths between the drains of the Mosfets and the transformer primary are
run using heavy-duty wiring.
Note also the six 10µF capacitors between the centre-tap of the transformer
primary and the commoned Mosfet
sources. These capacitors are there to
cancel out the inductance of the leads
which carry the heavy currents to the
transformer.
The transformer, T1, is a relatively
small ferrite-cored unit designed to
be driven at high frequencies. The
primary winding is made up of flat
copper sheet with two turns on each
side of the centre-tap. The secondary
uses conventional enamelled copper
wire with the number of turns set to
provide the required output voltage.
In summary, the power Mosfets in
each phase of the circuit alternately
switch each side of the transformer
primary to ground, so that the transformer is driven in push-pull mode.
When Q3-Q5 are on, the 12V supply
is across the top half of the primary
winding, and when Q8-Q10 are on
the supply is across the bottom half.
This alternating voltage is stepped
up by the transformer secondary and
applied to bridge rectifier D3-D6. This
produces positive and negative supply
rails with respect to the secondary
centre tap. These rails are then filtered
using four 2200µF capacitors.
PARTS LIST
1 PC board, code 05308961, 310
x 214mm
1 2-unit rack case (without rack
front panel)
1 front panel label
1 fan heatsink, 214mm long x
69mm wide with fins on one
side cut off
1 12V DC fan, 80 x 80 x 24mm
2 Clipsal BP165C18 brass link
bars
1 63A (A3 type) cartridge fuse (F1)
1 Neosid 17-745-22 iron
powdered ring core (L1)
1 Philips ETD49 transformer
assembly with 3F3 cores (T1)
(2 cores 4312 020 38041,
former 4322 021 33882, 2 clips
4322 021 33922)
3 5mm LED bezels
1 5mm red LED (LED1)
2 5mm green LEDs (LED2, LED3)
6 PC stakes
2 2AG fuse clips
1 1A 2AG fuse (F2)
4 TOP3 insulating washers
4 TO-220 insulating washers
10 insulating bushes
2 6-10mm cable glands
1 80°C cutout switch (TH1)
1 100kΩ horizontal trimpot
1 2-metre length of red 4GA
cable (length dependent on
installation)
1 2-metre length of black 4GA
cable (length dependent on
installation)
1 6-metre length of 3.5 sq. mm
multi-strand wire (length
dependent on installation)
1 55mm length of 3.5 sq. mm
multi-strand wire (Rsc)
Inductors L1a and L1b limit the
peak transient currents in the diodes.
Note that L1a and L1b are wound as
a compensated choke on a common
ferrite core, so that the flux generated
by L1a’s winding is cancelled by the
flux generated by L1b. This prevents
the core from saturating.
LEDs 2 and 3 connect across the
positive and negative output rails respectively, to indicate that these rails
are present. The 6.8kΩ resistors limit
the LED current.
Voltage regulation is achieved by
sampling the positive supply rail and
1 1.5-metre length of 3.3 sq. mm
black multi-strand wire (for T1)
1 400mm length of 3.3 sq. mm red
multi-strand wire (for T1)
1 1-metre length of 1.78mm dia.
solid core insulated wire
1 1.2-metre length of blue hookup
wire
1 400mm length of red hookup
wire
1 400mm length of green hookup
wire
1 2-metre length of red hookup
wire for ignition connection
(length dependent on installation.
1 1.2-metre length of 1.5mm dia.
ENCU (for L1)
1 6-metre length of 1.25mm dia.
ENCU (for T1 secondary)
1 150mm length of 0.8mm tinned
copper wire
4 large eyelets for 8mm dia. wire
with 12mm hole
6 eyelets for 3mm dia. cable and
3mm screws
3 eyelets for 4mm dia. cable and
4mm screws
4 1/8th inch x 9mm long
cheesehead screws
10 3mm x 15mm screws
24 3mm x 6mm screws
3 3mm x 9mm screws
13 3mm nuts
6 3mm star washers
4 9mm tapped standoffs
7 15mm tapped standoffs
3 4mm dia. x 15mm screws plus
nuts & star washers
2 8mm dia. x 15mm bolts, nuts &
washers
1 12mm dia. x 15mm bolt & nut
1 copper strip, 75 x 18 x 0.6mm
feeding this back to pin 16 of IC1 via
a voltage divider network.
The internal error amplifier on this
pin then controls the PWM comparator to provide voltage regulation, as
described previously. Trimpot VR1
allows the output voltage to be set to
the desired value.
Power supply
The 12V supply from the car battery
connects via heavy duty cable and fuse
F1 to the centre tap of T1. Because of
the high currents involved, there is no
on/off switch.
1 copper strip, 295 x 41 x
0.315mm
10 small cable ties
Semiconductors
1 TL494 switchmode controller
(IC1)
1 4050 CMOS buffer (IC2)
1 LM358 dual op amp (IC3)
2 BC338 NPN transistors (Q1,Q6)
2 BC328 PNP transistors (Q2,Q7)
6 BUK436-100A Mosfets (Q3-Q5,
Q8-Q10)
4 1N914, 1N4148 signal diodes
(D1,D2,D7,D8)
4 MUR1560 15A 600V fast
recovery diodes (D3-D6)
1 16V 1W zener diode (ZD1)
2 47V 400mW zener diode
(ZD2,ZD3)
Capacitors
4 2200µF 100VW electrolytic
(Philips 2222 050 19222)
1 100µF 16VW PC electrolytic
2 10µF 16VW PC electrolytic
6 10µF 100VW MKT polyester
(Philips 2222 373 21106)
2 0.47µF MKT polyester
4 0.1µF MKT polyester
1 .0056µF MKT polyester
1 .001µF MKT polyester
Resistors (0.25W 1%)
2 1MΩ
3 4.7kΩ
1 470kΩ
1 2.2kΩ
2 47kΩ
7 10Ω
1 27kΩ
2 4.7Ω
6 10kΩ
6 1Ω
4 6.8kΩ 0.5W
Miscellaneous
Solder, insulating tape, heatshrink
tubing, battery terminals
Power for the rest of the circuit is
supplied via the ignition switch (or a
separate switch could be used). LED1
indicates the presence of the 12V rail
and is supplied via a 2.2kΩ resistor.
In addition, a 12V fan is wired directly across the supply and this runs
continuously whenever power is applied. Finally, a 10Ω resistor and 16V
zener diode (ZD1) provide protection
against transient voltages for the low
current circuitry.
That’s all we have space for this
month. Next month, we shall give the
SC
full construction details.
October 1996 39
SERVICEMAN'S LOG
To tip or not to tip – a few tips
Ever wondered what happens to equipment
which is written off as not worth repairing?
Typically, it would be stripped for any
worthwhile spares and what was left would go
to the tip. But not always.
Yes, sometimes there is the temptation to try to salvage an item, even
if obviously uneconomical at a commercial level and there is a risk that
the attempt may not be successful.
One may spend many hours searching
for an elusive – possibly intermittent
– fault and not find it. Or, if a fault is
found, it may turn out to be a component which, for one reason or another,
cannot be replaced. But that’s the risk
one has to take.
I encountered two such exercises
recently which illustrate this situation very clearly. One is from my
own bench and one is a colleague’s
experience.
My own story involves what the
makers (Grundig) simply call a receiv-
er – Receiver 3000 (GB) – although it
would be better described as a tuner/
amplifier combination. It consists of an
elaborate stereo amplifier plus an AM/
FM stereo tuner, the latter featuring
press-button tuning, as well as continuous tuning and a “Digital Frequency
Indication Module”.
There are several input sockets to
take external signals of various kinds
and an appropriate switching system
to go with it. It also features both automatic and manual muting systems, and
these operate when switching between
stations or other signal sources.
All-in-all, it is a most attractive unit
and this example was in good physical
condition. So what was the story behind it? It belonged to a colleague and
apparently had had a rather chequered
service history, having previously
belonged to someone else.
But now, as my colleague summed it
up, it didn’t go and he had earmarked
it for the tip. When I expressed regret
that such a nice unit was to meet
such a fate, my colleague responded
instantly: “take it if you want it – you
can send it to the tip as easily as I can”
(he is not given to undue optimism).
And so I took it. I wasn’t sure what I
was going to do with it, assuming I
could fix it. For the moment, it was
mainly a challenge.
A nasty mess
At the first opportunity I put it up
on the bench but it was dead. I pulled
the covers off and this revealed a rather
nasty mess. There were three fuses,
one of which was obviously the mains
fuse while the other two were on the
secondary side of the power transformer. All three were blown. In addition,
there was a swag components which
had been unsoldered. Someone had
really gone to town on it.
Fig.1: the power supply circuitry in the Grundig 3000. Mains fuse Si.I is at extreme right, while fuses Si.1 and Si.2
are to the left of the transformer. T2 and IC1 are at the extreme left.
40 Silicon Chip
I decided the only logical approach
was to put everything back and start
from taws. I re-soldered all the components, then looked at the fuse situation.
The mains fuse, designated as Si.I was
marked 2A and the other two were
designated as Si.1 and Si.2. Si.1 was
marked as 250mA and Si.2 as 1.25A.
(No, there weren’t two Si.1s; the mains
fuse designation used a capital “I”.
Talk about planned confusion!)
I replaced the mains fuse and Si.2
and switched on. Splat! Si.2 blew immediately. I realised then that it would
be fruitless to go on without a service
manual or, at least, a circuit.
I rang Southern Cross Electronics,
the local agents for Grundig, and
asked about a manual. There was some
mucking about here. I had to fax a
request and they replied a week later
quoting $25 for a circuit photostat. I
placed an order and it arrived after
another week.
There were 10 A3 sheets in all.
Six were circuit diagrams taken from
what were originally two large foldout
sheets. The rest were parts lists, etc.
After dispensing lots of sticky tape and
patience, I eventually reconstructed
the foldout sheets, each of which
turned out to be 1.2 metres long!
After all that, I started over
again. I tackled the Si.2
fuse circuit first. Si.2 is
between a 12V secondary
winding and a full-wave
bridge rectifier (GL2)
which generates a 15V rail.
This is then applied to a
voltage regulator (IC1) to
provide a 5V rail.
I suspected IC1 and
I was right but in more
ways than I expected.
First, it was short circuit,
which didn’t surprise
me. What did surprise me
was that it turned out to be
a bodgie component. It was
not a 5V regulator at all but, in
fact, a 12V unit.
Just why this had been changed
and by whom remains a mystery.
It had probably failed because it
was the wrong type, particularly as
it was working directly into a 5V
zener diode (although the zener’s
role is something of a mystery in
itself).
Anyway, I replaced the regulator
with the correct type, fitted another
fuse and switched on. This time
the fuse held and we had a 15V
rail and a regulated 5V rail, with
no signs of distress.
So far, so good. Now to fuse
Si.1. This is part of another supply
rail which is derived from a 63V
transformer winding. This drives
bridge rectifier GL1 which in turn
drives another voltage regulator
based on T2. T2 is not a regulator
within itself, however. It is a Darlington pair, housed in a TO-220
flat pack encapsulation, and takes
its reference from external zener
diode D4. This arrangement provides a 55V rail.
When I switched on there was
an immediate response – R8, a 47Ω
1W resistor in the collector line to T2,
began to overheat. T2 was the obvious
suspect but an ohmmeter check failed
to reveal anything wrong.
Nevertheless, I unsoldered it and
pulled it out. And there was the fault
in full view – the insulating washer
between the heatsink (collector) and
chassis had punctured. And it was
obviously a voltage sensitive breakdown, immune to the low voltage of
the ohmmeter.
I fitted a new washer and tried
again. This time Si.1 held and I had
October 1996 41
Serviceman’s Log – continued
tran
sistors form part of the muting
circuit. When an appropriate voltage
is applied to their bases, they turn on
and mute the tuner signals into the
amplifier. I confirmed this operation
by the simple expedient of shorting
the base of each transistor to chassis in
turn, whereupon I had normal output
from the amplifiers.
So, the problem was really quite
simple – the “muting” voltage (or
possibly some other voltage) was
being applied to the bases of these
transistors and turning them on, even
though the muting switch was off.
All I had to do was find out what was
causing this.
Complicated circuits
a 55V regulated rail. I had rather
hoped that the thing would burst
into life now but it didn’t. Granted,
some of the LED displays and other
lights were now on but the frequency
display was dead.
A healthy buzz
I wasn’t sure of the significance of
this but decided to ignore it for the
moment and concentrate on getting the
sound path working. I pushed a scrap
of bare wire into the various amplifier
input DIN sockets and, eventually, was
rewarded with a healthy buzz from
each of the speakers.
So, the amplifiers were working –
we were making progress. But there
was no sign of life from the tuners.
Initially, I suspected that the frequency
display failure could be a symptom of
a major failure in the tuner section,
which was rather a nasty thought.
But then I noticed something else.
If I turned the volume control fully
up, I could detect faint sound when I
pressed some of the channel selector
buttons. So, was the tuner working
but unable to pass its signals to the
amplifier? After poring over the FM
tuner circuit on the other foldout
sheet, I pinpointed the stereo outputs
as being, initially, at transistors T5 and
T6. From there, the signals went to T8
42 Silicon Chip
and T9 and from there – on the other
sheet – to the switching circuits ahead
of the power amplifiers.
One of the most useful pieces of test
gear I have is a small audio amplifier
which is equipped with a probe. I use
it to trace audio signals and track down
losses and distortion. And this quickly
confirmed my suspicions; there were
strong healthy signals at both T5 and
T6 and also at T8 and T9.
OK, over to the switching circuits.
The tuner stereo signals come into the
switch bank on terminals 12A1 and
12A3 and emerge on terminals 4A1
and 4A3. From there, they go to the
amplifiers via switch position A3/B3
and plug socket SA10.
Only they didn’t. The signals were
present at the outputs of transistors T8
and T9 but not at the 12A1 and 12A3
switch input terminals. This drew
my attention to another part of this
circuit. Although the tuner signals
are routed through the switches to
the amplifiers they also go directly
to another pair of transistors, also
designated as T8 and T9, just to make
it harder.
These two transistors are connected
between the audio lines and chassis in
such a way that, if they are conducting, they pull the audio lines down
to chassis. In greater detail, these
But what had gone before was
merely routine compared with what
lay ahead. It was a real round-theworld-for-sixpence job. These circuits
are drawn using what I call draughtsmen’s cables; long thick black lines
into which individual lines disappear,
identified only by a number. One has
to follow the line until the number is
found, usually on another sheet.
And as likely as not, after a small
digression into a piece of circuitry,
it will go back into the cable on its
way back to the first sheet. Believe
me, it’s easy to go bonkers trying to
trace a circuit like this. Thankfully, I
didn’t go bonkers or at least I don’t
think I did.
I won’t bore readers with all the details of my circuit tracing. In any case,
without the circuit, which is much
too large to reproduce here, any such
description would be meaningless. I
actually lost count of the time I spent
on it and as readers will appreciate,
there is no way one could ever charge
a customer for this work.
In summary, I first tracked down
the manual mute switch (i1/i2) and
backtracked from there to an 8-pole
switch which is used to select the
FM preset channels. Only seven poles
of this switch are used for the actual
channel selection – the eighth pole is
in the muting circuit I had been tracing. And its function is to momentarily
activate the muting function whenever
any of the channel selection buttons
is pressed, thus masking any clicks,
bangs, or crackles, generated in the
process.
It was here that I struck oil – the
switch was faulty. Not only were the
muting contacts jammed closed but
the whole mechan
ism was giving
trouble. In a sense, I had already been
made aware of this. I had noticed
that, when a button was pressed, it
often took several attempts to get it
to lock into position. However, I had
previously put this fault to one side,
as something to be attended to when
the electrical problems were solved.
In fact, it was causing one of those
problems.
As a practical short term solution I
removed pin 1 from the plug assembly connecting to this switch, which
permanently disa
b led the muting
contacts. I could still mute the system
via the aforementioned manual mute
switch and the auto-muting, on weak
stations and between stations, still
functioned correctly.
The digital readout
Putting the switch problem on hold
for the moment, I turned my attention
to the only other remaining problem:
the Digital Frequency Indication
Module.
This is in a small metal box and, on
removing the covers, I was rewarded
with the sight of numerous dry joints
– more than I could be bothered to
count, in fact. How many more less
obvious ones there were I had no
idea. To solve the problem, I finished
up resoldering every joint but it was
worth it. The thing came to life and
worked perfectly.
And that’s how things now stand. I
consider it a pretty good effort, especially as I had done what, apparently,
those before me could not.
So, what about the switch? Should
I repair it? No way; it is made up of
numerous tiny pieces, many of them
under spring tension. Tackle that lot
and there would be bits flying every
where.
What about fitting a new switch?
That’s the logical answer but it’s no
longer available off the shelf and finding one may be difficult. It was most
likely specially designed for this set,
which is probably now about 10 years
old. The agents are currently checking
to see if one can be obtained from the
manufacturer.
And that’s about the best I can hope
for.
Scrounged video recorder
My second story, from a colleague, is
about a device he scored from another
colleague – a National NV-180 portable
video recorder. Because its fault had
proved elusive and so was potentially
expensive, the customer had written it
off and so it had been sitting in a corner
of colleague No.2’s shop for about a
year. But it left him in a quandary. He
wasn’t keen to spend more time on it,
yet felt guilty about sending it to the
tip. So, when my colleague showed an
interest, a deal was struck.
My colleague’s interest was understandable. He has a personal interest in
video cameras and associated portable
recorders. The NV-180 was originally
supplied with the models A1, A2
and similar video cameras. Although
bulky by modern standards, it was
regarded as a major breakthrough in
its day, weighing only 2.3kg without
the battery.
Apart from its portable role, it is an
attractive unit in its own right, featuring a large multi-function digital display, slow motion and variable speed
stop motion. Its accessories include
an AC adaptor, a tuner and a remote
control unit.
Unfortunately, after a year, the original fault details were rather vague. All
that my colleague could find out was
that it was something to do with tape
speed and a possible faulty capstan
motor. As a result, he had to start from
scratch. However, before presenting
his story, a brief review of the transport
control system may help the reader to
follow it more readily.
In considering the playback mode,
it is obvious that the speed of the
drum and the capstan – and therefore
the tape – must be held constant, at
a speed very close to the recording
speed. During recording, the speed
is controlled by the incoming signal
but there is no such reference during
replay; the system is on its own.
In this mode, it is controlled by an
internal reference; eg, a crystal. The
capstan motor itself is equipped with
a pulse generating device, typically a
sensing head (inductive or capacitive)
mounted close to a rotating wheel or
magnet.
The resulting pulses are fed to a
servo system which compares them
with the reference (crystal) frequency. This system then generates error
correction voltages which hold the
speed of the motor constant. A similar
system is used to control the drum
motor speed.
But that is only part of the story. As
well as running at the correct speed,
the system must also be in correct
phase. The drum must be positioned
so that a head, when it meets the tape,
exactly engages the beginning of a
track. And not just any track. If we are
talking about head No.1, then it must
engage a track recorded by head No.1.
It’s a similar story for head No.2.
The way in which this is done is
quite straightforward. When a tape
is being recorded, square-wave reference pulses, derived from the vertical
sync pulses, are recorded every 40ms
(alternate field) on a control track on
the lower edge of the tape. These are
used to provide the aforementioned
phase control and also the switching
between heads.
OK, here’s my colleagues story, as
he tells it.
Donald Duck sound
My mate had been right about there
being something wrong with the
capstan speed; it was fast, much too
fast. As a result, the sound had gone
“Don
ald Duckish” and there were
noise bars running up the screen. But I
didn’t buy the idea of a capstan motor
fault; capstan motors normally either
work or they don’t. Perhaps they might
run slow but I’ve never ever seen one
run fast.
The first thing I did was to give the
machine a good once over mechanically. This involved a routine clean,
belt tension and pinch roller checks,
and a check of the pause and search
functions. I found nothing wrong. I
then checked the main supply rails.
There was 5V at pin 13 of IC2505 and
9V at pin 14 of plug FJ24 – exactly as
marked.
My next step was to check the electrolytic capacitors around the capstan
motor drive, mainly C2532, C2533,
C2534, C2535. These were checked
by simply bridging them with another
unit of the same value but this had
no effect.
It was time to put the CRO to work
and check pulses. Unfortunately, the
compact nature of the device means
that servicing it can be difficult. For
example, I needed to check the Servo/
Power PC board which mounts hard
behind the front panel.
In order to gain access to both sides,
it is necessary to remove the front
panel and then mount the board in
a special jig – Service Connector Jig
(VFK0275) – which sits it at an angle
of 45 degrees, while maintaining all
October 1996 43
Serviceman’s Log – continued
connections. Fortunately, I have such
a jig.
I started by checking for the reference (FG) pulses generated by the
capstan motor and the CRO confirmed
that these were correct. The FG pulse
(FG1) appears at terminal 4 of the
capstan motor block and, via an allover-the-place path, finishes up on
pin 25 of IC2001 (AN3615K), which
is also test point TP2015. I traced the
pulses right through to this test point.
Next, I checked the internal reference (clock) frequency to which the
drum and capstan are locked. This is
a 4.43MHz crystal oscillator which
applies a 1.2Vp-p signal to pin 26 of
IC2001. And as a matter of routine, I
also checked the control pulses from
the Audio Control Erase (ACE) head,
although these are basi
cally phase
rather than speed control pulses.
These were present and checked
through to pin 9 of IC2001.
So, we had FG1 pulses from the
capstan, clock frequency pulses from
the crystal and control pulses from the
control head, all being fed to IC2001.
But for some reason, the capstan motor
was out of control and running free.
What followed was a laborious
check of various voltages and waveforms on the Servo/Power PC board.
This was at times quite difficult but
it eventually lead to pin 4 of IC2001
(test point TP2004) where there should
have been a 4.43MHz 50mV p-p waveform. However, this waveform was
missing; nor was there any voltage on
this pin, shown on the circuit as 3.2V.
The upshot of all this was that I
concluded that the IC was faulty and
ordered a new one on spec. And that
was a big mistake. When it arrived I
found I’d been billed for $93 – yes $93,
for one IC. Move over Mr Kelly.
There was worse to come. It was a
small IC, with closely spaced pins,
and mounting it on the double-sided
PC board was not easy. The job took a
long time – and achieved absolutely
nothing. The fault was there exactly
as before. Words failed me – well, in
print anyway.
The real fault
I had to find the real fault now.
Taking a closer look at the circuit
around the IC, I noted that pin 4
44 Silicon Chip
was internally connected to
two functions: (1) a playback
control amplifier (P.B. CTL
AMP); and (2) a tracking
mono multivibrator (TRACKING MMV), the latter connecting to pin 13. Pin 13 then goes
to the tracking control. It was
supposed to be at 0.6V – or higher
– but was in fact at 0V.
I hadn’t checked this voltage before, due to the difficult
access. Nor had I previously
checked the tracking control.
I checked it now; it wasn’t
working.
I traced the circuit
through to the tracking control (R6562,
100kΩ). This pot is
panel-mount
ed and is
connected via a short
length of 3-conductor
ribbon to connector P205.
And the one which ultimately connects to pin 13
was broken where it joined
the connector. It wasn’t immediately obvious, however, as it
is normally obscured and the
other two conductors held
the ribbon in place.
Of course that was it,
although how it happened is a puz
z le. I
can’t imagine any kind
of user abuse which
would cause it. More
likely, I suspect, the unit
had originally suffered
from a quite different
fault. The serviceman
had fixed this but had
broken the lead in the process. And
the resulting symptoms had proved
too tricky and confusing for the fault
to be traced.
In fact, it is not immediately obvious
just how the tracking control circuit
upset the speed. But, as far as I can
see, the loss of a connection to pin
13 was sufficient to upset the whole
capstan servo function within the IC.
If only I had checked the tracking
control first off.
And that’s my colleague’s story. My
first reaction is to quote another of my
colleagues who, in such situations,
was wont to remark, “that’s a decent
sort of an oops”. Which it was and I’m
glad I didn’t make it. But that’s not to
say that I might not have in similar
circumstances.
The bright side
On the bright side, my colleague
scored a very nice machine for the
price of the IC, plus his labour. Not
bad, really and he does have a spare
IC in his drawer.
But I feel the moral of both stories
is obvious; think very carefully before
you tackle an undertaking like this.
And be prepared for a lot of work – and
SC
the risk of failure.
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Last month, we introduced our new Infrared Stereo
Headphone Link, which allows you to settle back and
enjoy your favourite music, the TV or other audio source
without being tied down by a cord. This month, we
complete the project with the receiver section.
Infrared
stereo
headphone
link
PART 2 – THE RECEIVER
Fig.1 (page 55) shows the circuit of
the infrared stereo receiver. As with
the transmitter, it follows some of the
circuit techniques used in stereo FM
transmission and reception.
A photodiode, PD1, detects the IR
pulse stream from the transmitter and
produces DC current pulses which
are fed directly to op amp IC1a, a
current-to-voltage converter. IC1a is
AC-coupled to op amp IC1b which
has a gain of 6.8.
The amplified signal is fed to IC2,
an LM311 comparator. Its output is an
88kHz 6V peak-to-peak square wave
when there is no audio modulation
from the transmitter and an 88kHz
PWM stream when audio modulation
By RICK WALTERS
October 1996 53
TL062 for IC1 and a TL064 for IC6
because of their low current consumption, an important factor in a battery
operated circuit.
The more common TL072 and
TL074 types can be used instead but
the current consumption is appreciably higher.
Left channel identification
There are two PC boards in the infrared receiver but only one is visible in this
photo. The IR receiver LED is underneath the top board, at the focal point of the
lens assembly on the lefthand side.
is transmitted. This waveform contains all the audio information that
was encoded by the transmitter; all we
have to do is decode it. This is done
in two steps.
First, we recover the signal in mono.
To produce the mono signal, all we
need to do is to connect a low pass
filter at the output of comparator IC2.
To produce the stereo left and
right channels though, we need to de
multiplex the audio by switching it to
the left and right channels in sequence,
using a square wave with the same frequency and phase as the multiplexing
frequency in the transmitter.
Phase locked loop
This is where the phase locked loop,
IC4, comes into the picture.
IC4 can be considered to be a square
wave oscillator which is “locked” to
an incoming reference frequency. Its
output frequency will be the same
as the transmitter’s but 90° out of
phase and the filter components are
selected so that it will not follow the
modulation.
To ensure an exact symmetrical
square wave we run IC4 at double the
received frequency; ie, at 176kHz. This
is divided by two, using flipflop IC3a,
to give an 88kHz square wave. This is
divided by two again, by flipflop IC3b.
In this case, the 18kΩ resistor
and 100pF capacitor delay the clock
signal to IC3b by 90° to ensure that
54 Silicon Chip
its outputs are in phase with the incoming signal.
The 44kHz outputs of IC3b, at pins
12 and 13, are used to switch the signal
from IC2 to the right and left channels
alternately using IC5, an HC4066
CMOS switch.
This switching process is called
“demultiplexing” and is the reverse
of the multi
plexing process in the
transmitter.
The left and right channel signals
appear at pins 1 and 11 of IC5, respectively. As there is a large amount
of high frequency noise on the recovered audio signals, heavy filtering is
required. To this end, we use a 4-pole
filter which gives an attenuation rate
of 24dB per octave, above 10kHz.
For the right channel the first filter
consists of the two 10kΩ resistors
and .0012µF and .0018µF capacitors
around op amp IC6a. The second filter
involves the .0015µF capacitors in a
similar configuration around IC7a,
Q1 & Q2.
There is identical filtering for the
left channel, involving op amps IC6b,
IC7b, Q3 & Q4.
To compensate for the high frequency pre-emphasis which was applied
in the transmitter we use the 1kΩ series resistor and the .022µF capacitor
across each volume control to attenuate the upper frequency response. This
is de-emphasis.
By the way, we have specified a
To establish which is the left channel we take the signal from the output
of the left channel filter, IC6b pin
7, and feed it to two cascaded 10Hz
bandpass filters, comprising op amps
IC6d and IC6c.
The 10Hz signal, if it is present in
the left channel, will be amplified,
clamped to ground by D1 and then
will charge the 0.1µF capacitor at the
gate of FET Q5, via D2. This will hold
Q5 turned on and its drain will be
almost at 0V.
If the left channel signal has been
switched to the right amplifier there
will be no 10Hz signal present in
IC6b’s output, thus the 10MΩ resistor
will discharge the 0.1µF capacitor on
Q5’s gate and the FET will turn off.
This will allow the drain of Q5 to
rise to the battery voltage (+6V) via the
47kΩ resistor.
Because the set input of flipflop
IC3b is connected to this point, the
flipflop will be held set. This holds
pin 13 of IC3b high, switching the
input signal permanently to the left
amplifier, thus allowing the 10Hz
signal to be fed to the bandpass filters.
The FET will turn on as described
previously and the flipflop will begin
to toggle again to give correct de
multiplex operation.
Due to the low frequency of the synchronising signal (10Hz) and consequently, the long time constants in the
FET gate circuit, it may switch several
times before it gets the phase right.
Loss of infrared signal
Since the audio signal is sent via an
infrared beam, what happens when the
beam is interrupted? When the PLL,
IC4, is locked to the incoming frequency, the signal at pin 1 is normally high
with a brief negative transition every
Fig.1 (right): the circuit of the infrared
stereo receiver uses seven ICs,
four transistors and two FETs. Its
operation is explained in the text.
October 1996 55
PARTS LIST – RECEIVER
1 PC board, code 01109962,
120 x 60mm
1 PC board, code 01109963,
45 x 42mm
1 plastic box, 130 x 68 x 41mm,
Jaycar HB6013 or equivalent
1 lens assembly, Oatley
Electronics OLP1 or equiv.
1 pushbutton switch, Jaycar
SP0710 or equivalent (S1)
2 AA battery holders, Jaycar
PH9202 or equivalent
2 216 snap-on battery connectors
1 3.5mm stereo socket, Jaycar
PS0132 or equivalent
1 red knob, Altronics H6001 or
equivalent
1 green knob, Altronics H6005 or
equivalent
11 PC stakes
2 6PK x 6mm self tapping screws
2 10kΩ 16mm diameter PC mount
log pots, Jaycar RP3610 or
equiv. (VR1,VR2)
Semiconductors
1 TL062 dual op amp (IC1)
1 LM311 comparator (IC2)
cycle; when it is not locked this output is low. The resistor and capacitor
at pin 1 filter the negative spikes,
feeding a steady voltage to pins 12
and 13 of IC5.
If this voltage is high, the audio is
switched through to IC6a and IC6b
but if it is low, the switches are open.
Therefore, if the transmitted light
source is obstructed for any reason
the audio signal to the headphones
will be “killed” and there will be no
extraneous noises produced.
56 Silicon Chip
1 4013 dual D flipflop (IC3)
1 74HC4046 phase lock loop (IC4)
1 74HC4066 quad CMOS switch
(IC5)
1 TL064 quad op amp (IC6)
1 LM833 audio amplifier (IC7)
2 BC337 NPN transistors (Q1,Q3)
2 BC327 PNP transistors (Q2,Q4)
2 BS170 FETs (Q5,Q6)
1 LT536 or equiv. photodiode
(PD1)
2 1N914 silicon diodes (D1,2)
MKT polyester or ceramic
3 .0012µF 63VW
MKT polyester or ceramic
1 .001µF 63VW
MKT polyester or ceramic
2 120pF 63VW
MKT polyester or ceramic
1 100pF 63VW
MKT polyester or ceramic
Note: if ceramic capacitors are
used, they should be within ±10%
tolerance.
Capacitors
2 470µF 16VW electrolytic
(for 8Ω headphones)
1 330µF 16VW electrolytic
4 100µF 16VW electrolytic
2 4.7µF 16VW electrolytic
2 0.47µF 16VW electrolytic
4 0.15µF 63VW MKT polyester
1 0.1µF 50VW monolithic
6 0.1µF 63VW MKT polyester
2 .022µF 63VW MKT polyester
1 .01µF 63VW MKT polyester
2 .0018µF 63VW
MKT polyester or ceramic
4 .0015µF 63VW
Resistors (0.25W, 1%)
2 10MΩ
1 18kΩ
2 2.7MΩ
2 12kΩ
3 1.2MΩ
17 10kΩ
1 680kΩ
4 8.2kΩ
1 470kΩ
1 6.8kΩ
1 120kΩ
4 1kΩ
1 100kΩ
1 820Ω
2 68kΩ
1 220Ω
1 47kΩ
2 47Ω
1 39kΩ
You will notice in the photos that
the end of the receiver case has a tube
mounted on it. This is a lens assembly
and its job is to focus the received IR
radiation onto the photodiode. It gives
a significant increase in the distance
that the transmitter and receiver can
be separated.
Miscellaneous
Hookup wire, machine screws and
nuts, solder.
Accordingly, IC7a drives a pair of
complementary emitter followers Q1
and Q2, which are connected within
the negative feedback loop to keep
distortion low.
The inputs of the LM833 have to be
Below: opening out the top PC board
reveals the method of construction,
We have used an LM833 dual op with the batteries and lower board
amp but this does not have sufficient clearly shown. Use no more wire
output to drive all headphones. between the boards than is necessary
to allow them to come apart.
Headphone drive
Fig.2: the parts overlay for the two receiver PC boards. It should be followed
closely during assembly. In particular, check that all polarised components
(semiconductors, diodes and capacitors) are inserted the correct way around.
biased to half the supply voltage to
ensure a symmetrical output swing. To
do this and also to simplify things, the
“earthy” ends of the volume pots are
taken to this potential; ie, +3V.
Automatic switch-off
As the receiver is battery operated
there will be a tendency to take the
headphones off and walk away “for
a minute or two” leaving the unit
running. When you come back, in a
week’s time for example, the batteries
could be very flat.
To avoid this embarrassment, we
have an automatic off switch comprising Mosfet Q6 and a few other
components. Hence, there is an ON
button but no OFF switch.
When the ON button is pressed, the
330µF capacitor connected from gate
to source of Q6 is charged to +6V via
the 220Ω resistor. This turns Q6 on,
applying power to the receiver. The
330µF capacitor will then gradually
discharge via the 10MΩ resistor until
the voltage is insufficient to keep the
FET switched on.
At this stage, a few squawks will
come through the headphones to alert
you to the imminent switch-off. Pushing the ON button again will let you
listen for another half hour or so, the
idea being to press it at the beginning
of each program.
modating IC7, Q1, Q2, Q3 & Q4. The
larger board, coded 01109962, holds
the remainder of the circuitry.
Note that neither PC board has holes
for mounting screws or pillars. Instead,
the headphone drive board is secured
in place by soldering two PC stakes at
the corners to the metal cases of the
volume controls which mount on one
end of the plastic case.
The main board has the corners cut
out to clear the integral pillars of the
case. It is neat fit into the case and is
sandwiched between the lid and a
piece of foam rubber. We’ll cover more
of the details as we go.
Fig.2 shows the component overlays
Case assembly
Receiver assembly
Now let’s start constructing the
receiver. This has the two boards
shoe-horned into a plastic case. The
smaller board, coded 01109963, is
the headphone driver board, accom-
for the two receiver PC boards. Let’s
start with the audio amplifier board.
First, fit the nine PC stakes, the resistors and the IC into the board and
solder them. This done, insert and
solder the four MKT capacitors, the
four transistors and lastly, the four
electrolytics.
If you are going to use 32Ω headphones (as supplied with Walkman-type cassette players) all the time,
then we suggest fitting 100µF output
coupling capacitors to the board. However, if you expect to use conventional
8Ω headphones, you will need to use
470µF output coupling capacitors,
otherwise the bass response will be
deficient.
The larger board has six links which
should be fitted first, followed by resistors and diodes, IC sockets (if you use
them) and then the capacitors.
We don’t recommend using PC
stakes in this board except as test
points for the left and right audio outputs, as it is more convenient to bring
the wires from the copper side of the
board to the volume controls and the
audio amplifier.
The ICs, being CMOS devices,
should be plugged into the sockets or
soldered in last.
The photodiode is mounted on the
copper side of the PC board with full
lead length. Make sure that the chamfer is on the left side when viewed
from the front.
The infrared beam is focused on the
photodiode by this lens assembly to
significantly increase the range.
As already noted, the headphone
drive board is secured by soldering
two corner PC stakes to the cases
of the two volume controls. These
volume controls must be the 16mm
diameter type otherwise they will not
fit together in the confines of the case.
October 1996 57
Fig.3: this wiring diagram shows how the wiring is
run from the underside of the larger board to the top
of the smaller board. Note that the photodiode, PD1,
is soldered to the underside of the larger board. Make
sure that this device is oriented correctly.
points on the main board. Fig.3 shows
the full details of the wiring between
the main PC board and the headphone
drive board.
Follow the wiring diagram of Fig.3
carefully. It is probably easier to solder
the wires onto the volume control lugs
before you mount them in the case,
as you will have easier access to the
terminals.
Testing
As well as drilling holes in one end
of the case for the pots, you will need
holes in the side for the pushbutton
ON switch and the 3.5mm stereo
headphone socket.
Finally, you will need to drill
holes in the other end of the case to
take the lens assembly which was
58 Silicon Chip
mentioned above. It is supplied by
Oatley Electronics (OLP1). Note that
the lens assembly should not be fitted
until the transmitter and receiver have
been tested.
Two double-AA cell holders provide
the 6V battery supply. These are wired
in series and then to the +6V and 0V
If you are very careful with your
assembly and check everything closely
there is no reason why it won’t work
first up. If it doesn’t, you will have to
decide which of the units is not functioning properly. If you have access to
an oscilloscope this is easily checked
out. If no scope is available, testing is
a little harder.
Starting with the transmitter, normally the first things to measure after
you apply power are the rail voltages.
In this project, if these check out at
+15V and -15V and the regulator tabs
don’t burn your finger, it’s a good start.
If you have a multimeter with a frequency response to above 100kHz, you
will be able to check for the presence
of signal at pin 3 of IC1 (176kHz), pins
1, 2, 12 & 13 of IC2 (88kHz, 44kHz),
pin 7 of IC5 and IC6, and the collector
of Q1 (set the meter to AC volts). If
all these points have signals you can
feel reasonably sure that there are no
problems with the transmitter.
RESISTOR COLOUR CODES
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
No.
2
2
3
1
1
1
1
2
1
1
1
2
17
4
1
4
1
1
2
Value
10MΩ
2.7MΩ
1.2MΩ
680kΩ
470kΩ
120kΩ
100kΩ
68kΩ
47kΩ
39kΩ
18kΩ
12kΩ
10kΩ
8.2kΩ
6.8kΩ
1kΩ
820Ω
220Ω
47Ω
The audio can be followed through
from the inputs to pin 2 of IC5 or IC6
with high impedance headphones or a
signal tracer. If a signal is missing you
must check around that area until you
find the cause of the trouble.
To work on the receiver you must
have the transmitter turned on and
pointing in the direction of the receiver. Press the ON button on the receiver
and measure the battery current. It
should be around 17mA.
To test for the presence of an 88kHz
carrier, set your multimeter to AC volts
and check pin 7 of IC2, pin 3 & pin 4
of IC4 and pin 1, pin 12 & pin 13 of
IC3. If the sound only comes through
the left channel it means that the FET
Q5 is turned off. Check the soldering
4-Band Code (1%)
brown black blue brown
red violet green brown
brown red green brown
blue grey yellow brown
yellow violet yellow brown
brown red yellow brown
brown black yellow brown
blue grey orange brown
yellow violet orange brown
orange white orange brown
brown grey orange brown
brown red orange brown
brown black orange brown
grey red red brown
blue grey red brown
brown black red brown
grey red brown brown
red red brown brown
yellow violet black brown
RESISTOR COLOUR CODES
No.
❏
❏
❏
❏
❏
❏
❏
❏
❏
Value
IEC Code EIA Code
0.15uF 150n 154
0.1uF 100n 104
.022uF 22n 223
.0018uF 18n 183
.0015uF 15n 153
.0012uF 12n 123
.001uF 10n 103
120pF 120p 121
100pF 100p 101
around the bandpass filter and also
ensure that diodes D1 and D2 are
inserted correctly.
If you want to install an on/off
5-Band Code (1%)
brown black black green brown
red violet black yellow brown
brown red black yellow brown
blue grey black orange brown
yellow violet black orange brown
brown red black orange brown
brown black black orange brown
blue grey black red brown
yellow violet black red brown
orange white black red brown
brown grey black red brown
brown red black red brown
brown black black red brown
grey red black brown brown
blue grey black brown brown
brown black black brown brown
grey red black black brown
red red black black brown
yellow violet black gold brown
switch to replace the FET switch, omit
Q6, the 330µF capacitor and the 10MΩ
and 220Ω resistors. Connect one end
of the switch to the battery minus (Q6
source) and the other side of the switch
to 0V (Q6 drain).
Finally, after testing is complete, the
main board can be assembled into the
receiver case. Before this is done, the
photodiode must have its leads bent
so that its face is square in the hole in
the end of the case; its face should be
flush with the outside surface of the
case, as this is the focal point of the
lens assembly.
The lens assembly can then be secured in position with two self-tapping
screws. Finally, fit the lid of the case
SC
and the job is done.
Fig.4: check your PC board against this full-size etching pattern before installing any parts.
October 1996 59
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Silicon Chip Publications
PO Box 139, Collaroy 2097
No postage stamp required in Australia
October 1996 65
Get big sound from your
computer with this . . .
Multimedia
Sound System
Most computer sound systems are wimpy
little boxes with poor quality sound. This
system is compact, has plenty of power
and produces high quality wide range
sound with oodles of bass.
Design by RICK WALTERS
66 Silicon Chip
Let’s face it, while today’s computers may be superfast, with millions
of colours on their monitors and
connected to the whole world via the
Internet, their sound quality is strictly yesterday’s fodder. Not only are
the amplifiers on sound cards puny
by comparison to any home music
system, most Multimedia speakers
are just a joke – you could get better
quality out of an old 6 x 9-inch car
radio speaker!
So what do you want from your
Left: the neat speakers flanking this monitor are only part of
our new Multimedia Sound System. The other part is the power
amplifier and electronic crossover board (above) which plugs into a
spare slot in your computer. It puts out better sound than you have
ever heard from a computer.
Multimedia sound system? For a start,
if you are into games, you want the
sound effects to be at least halfway
realistic. If you’ve just blown up the
robber kingdom with a 5-megaton
bomb, the sound effect should be a
little more notable than a sneeze from a
guinea pig. And if you’ve just crashed
out of the Monte Carlo rally, you expect
to hear a little more than a few coins
rattling inside a drink can. Well, don’t
you? We certainly do.
And if you are listening to CDs or
sound tracks via your CD-ROM player,
you have every right to expect clean
wide-range sound, every bit as good
as from a home music system with a
CD player.
Our new Multimedia Sound System will deliver the goods. It has
decent power output, high quality
low distortion amplifiers and decent
loudspeakers which cover the full
audio spectrum from 50Hz to 20kHz.
They will blow existing commercial
computer sound systems and speakers
into the weeds!
Total power output of the audio amplifier system is in excess of 20 watts,
distortion is less than 0.2% and signal
to noise ratio is better than 65dB with
respect to full power.
And as the photos show, you don’t
need a massive amount of electronics
to get this power. It all fits on a standard half-size card which slips into
any vacant slot in your PC. There is
no power supply required because
the card makes use of the 12V supply
inside the computer.
Apart from slotting the amplifier PC
board into your computer, there is no
other modification required to your
machine. You will need to connect
cables from your computer’s sound
card to the amplifier PC board and
there are also the connecting cables to
the two speakers. But once you have
the amplifier and speakers connected,
your computer will function exactly
Performance
Output power �������������������������������1.5 watts per channel into 8٠(tweeter);
9 watts per channel into 4Ω (woofer)
Frequency response ��������������������-4dB at 20Hz and -0.2dB at 50kHz (see
Fig.3 & Fig.4)
Input sensitivity ����������������������������32mV for tweeter amplifier; 40mV for
woofer amplifier
Harmonic distortion ���������������������0.2% (see text)
Signal-to-noise ratio ��������������������65dB with respect to 1.5 watts (tweeter);
59dB with respect to 8 watts (woofer)
October 1996 67
AUDIO PRECISION SCTHD-W THD+N(%) vs measured
10
LEVEL(W)
20 AUG 96 15:22:48
1
0.1
0.1
1
3
Fig.1: power output of the tweeter drive amplifier. Maximum power is about 1.5
watts before clipping. Note that the true harmonic distortion is less than 0.2%.
AUDIO PRECISION SCFREQRE AMPL(dBr) vs FREQ(Hz)
15.000
20 AUG 96 14:11:44
10.000
5.0000
0.0
-5.000
-10.00
-15.00
3k
10k
50k
Fig.2: this graph shows the frequency response of the tweeter amplifier, over the
range from 3-50kHz.
as it did before, except that you will
have big sound to match.
Nor is there any need for massive
loudspeaker boxes that would dwarf
your computer system. While they are
bigger than typical Multimedia speakers, they are still quite compact – the
volume of each enclosure is a mere five
litres. So they will sit quite comfortably on either side of your computer
68 Silicon Chip
monitor. Naturally, the woofers and
tweeters in the enclosures have full
magnetic shielding so there will be
no adverse effects on your monitor.
Power amplifier features
As already noted, the power amplifiers for this new Multimedia system
are all on one PC board which is the
size of the standard half-size card for a
PC-compatible computer. On board are
three Philips TDA1519A stereo amplifier ICs which are specifi cally designed
for use in car radios. Why three ICs?
We’ll tell you about that later.
Only four connections are made via
the PC board edge connector to the
computer’s motherboard: two for the
earth or 0V connection and two for the
+12V and -12V supply rails.
There are two 9-pin female D sockets
on the metal mounting bracket, together with a 3.5mm stereo jack socket and
two screwdriver-adjustable multi-turn
volume controls. These are set when
you first connect the system up but
after that they are not touched – you
will normally set the volume by using
your mouse and on-screen controls.
The 9-pin D sockets are used for
making the loudspeaker connections.
The two enclosures each have a
5-inch woofer and a 1-inch tweeter.
The enclosures are ported, to give an
extended bass response down to 50Hz.
Each loudspeaker is connected to the
amplifier PC board via a 4-way cable;
two wires for the woofer and two for
the tweeter. There are no crossover
networks inside the loudspeaker enclosures since the tweeters and woofers are separately powered.
Now let’s have a look at the electronics on the amplifier card.
Fig.5 shows the circuit of the whole
Multimedia Sound System. Both
channels are shown. If you look at
the righthand side of the diagram you
will see that each tweeter is driven
by its own power amplifier while
each woofer is driven by two power
amplifiers in “bridge” mode. In effect,
this doubles the power delivered to
the woofer and makes best use of the
power available from the 12V supply
in the computer.
There are several reasons for this
unusual amplifier setup. First, the
specified tweeter is an 8Ω type and
has an efficiency of 94dB at 1 watt
and 1 metre (usually expressed as
94dB/1W/1m).
By contrast, the woofer is a 4Ω type
and has an efficiency of only 86dB.
In other words, the tweeter is twice
as efficient. Therefore, we need to deliver four times as much power to the
woofer as to the tweeter. This is why
the woofer is driven in bridge mode.
Using a 12V supply rail, the TDA
1519 can typically deliver a maximum
of 1.5 watts into an 8Ω load before
clipping, from each channel. This is
AUDIO PRECISION SCFREQRE AMPL(dBr) vs FREQ(Hz)
15.000
20 AUG 96 14:05:54
10.000
5.0000
0.0
is loafing along, using the regulated
12V supply in the computer.
That is just as well, because we
have mounted the three TDA1519As
on quite small heatsinks, bearing in
mind that most of the time they will
be delivering little or no power at all.
And just in case the chips do get too
hot, they are thermally protected and
will shut down safely if the going
gets too tough. By the way, they are
also protected against short-circuited
outputs.
Performance graphs
-5.000
-10.00
-15.00
20
100
1k
5k
Fig.3: frequency response of the woofer amplifier from 20Hz to 5kHz. Note the
3dB boost in the region of 35Hz.
AUDIO PRECISION SCTHD-W THD+N(%) vs measured
10
LEVEL(W)
20 AUG 96 13:27:36
1
0.1
0.2
1
10
20
Fig.4: power output of the woofer amplifier. Maximum power from the bridged
amplifiers is about 9 watts before clipping.
what the tweeters get. In bridge mode,
the two amplifiers in the TDA1519A
are driven out of phase so that their
output voltages add across the speaker.
Under this condition, the TDA1519A
can deliver 9 watts.
In practice, this gives a safety margin
– we don’t need to drive the woofers
at a power level six times that of the
tweeter but it is good to have a little
in hand.
By the way, if you come across the
specs for the TDA1519A you will see
that it is rated for a maximum power
output of 22 watts in bridge mode into
a 4Ω load. However, this is for a supply
of 14.4V and a harmonic distortion
level of 10% – hardly what you would
regard as hifi specs. By comparison,
under our design conditions the chip
The performance of the Multimedia
Sound System is summarised in the
accompanying panel and we have
included a number of graphs which
need a little explanation. Fig.1 shows
the power output of the tweeter drive
amplifier and as you can see, it delivers about 1.5 watts before clipping, at
which point the harmonic distortion
suddenly rises.
The minimum distortion on this
graph is 0.4%, which is double what
we claimed above for this parameter.
What the graph doesn’t show is that
the distortion measured is mostly due
to the 54kHz hash superimposed on
the computer’s power supply. This
is completely inaudible and does not
affect the sound quality; as stated
above, the true harmonic distortion
is less than 0.2%.
Fig.2 shows the frequency response
of the tweeter amplifier, over the range
from 3kHz to 50kHz. Similarly, Fig.3
shows the frequency response of the
woofer amplifier from 20Hz to 5kHz.
Note the 3dB boost in the region of
35Hz.
Fig.4 shows the power output of
the woofer amplifier and the above
remarks about power supply hash also
apply here. The power supply hash
also affects the signal-to-noise ratio,
so while we have quoted a figure of
-65dB for the tweeter amplifier and
-59dB for the woofer amplifier, the true
figures are considerably better.
In any case, there is little point in
having signal-to-noise ratio figures
much in excess of -60dB in a Multimedia sound system since the computer
itself generates so much noise from its
fan and disc drives.
Now let’s have a closer look at the
circuit details shown in Fig.5. At the
lefthand side of the circuit are the
stereo inputs, at the jack socket SK1.
These are fed via 2.2µF non-polarised
October 1996 69
70 Silicon Chip
Fig.5: the two tweeters are driven from single power amplifiers (IC5), while each woofer is driven in bridge mode by a pair of
power amplifiers. IC1 and IC2 provide slight bass boost and the electronic crossover at 3.5kHz.
The amplifier board is the same size as a typical half-size PC card and plugs
directly into a slot on the motherboard. The edge connector makes contact with
the ±12V rails of the computer and the 0V line.
(NP) capacitors to the 10kΩ multiturn
trimpots, VR1 & VR2.
Now let’s talk about the left channel
only, since both channels are identical.
VR1 feeds an op amp buffer, IC1d, and
then the signal is split into two paths.
The first is via a bass boost stage involving op amp IC1a.
This is really a high pass filter which
gives a 3dB boost to frequencies in the
region from 35Hz to 50Hz.
Following the bass boost stage,
the signal is fed to a low pass filter
employing op amp IC2d. This is a
Linkwitz-Riley filter which rolls off
signals above 3.5kHz and drives a voltage divider comprising resistors R1 &
R2. These are used to adjust the drive
signal to the amplifier stage so that the
woofer signal level can match that of
the tweeter. The equivalent resistors
in the right channel are R3 & R4. The
Linkwitz-Riley filter configuration is
used here because it gives the flattest
response from the two speakers in the
crossover region.
Woofer drive
The signal is then coupled via
a 2.2µF capacitor to the inputs of
bridged amplifiers IC3a & IC3b, the
TDA1519A. Note that the signal drives
the non-inverting input of IC3a (pin 1)
and the inverting input of IC3b (pin 9).
Note also that pin 3 is the inverting
input of IC3a and the non-inverting
input of IC3b (internally connected).
This automatically gives the condition whereby the outputs of the two
amplifiers are out of phase; ie, when
the output at pin 4 is swinging positive, the output at pin 6 is swinging
negative. This means that the total
voltage across the speaker is the sum
of the two amplifier outputs. Hence
This shot shows how the audio cables
from a sound card are plugged into
the power amplifier PC board. The
two female D sockets for the four-way
cables to the speaker boxes.
the output power delivered to the
speaker is about four times what it
would be if a single amplifier was
employed.
As both inputs of IC3 are biased to
the same DC potential (half the 12V
supply), there is negligible DC voltage across the 4Ω woofer and so no
large coupling capacitor is required.
However, Zobel networks, consisting
of a 4.7Ω resistor and 0.1µF, are used at
the output of each amplifier to ensure
stability at high frequencies.
Tweeter drive
Going back the buffer stage IC1d, it
also feeds a Linkwitz-Riley high-pass
filter based on op amp IC2a. This
rolls off frequencies below 3.5kHz.
The output of IC2a feeds one power
amplifier, IC5a. As the output voltage
at pin 4 of IC5a is close to +6V the
tweeter must be AC-coupled and a
100µF electrolytic capacitor is used
to do this. A Zobel network is also
connected at the output.
Due to phase inversion in the filter
(IC2a) at the crossover frequency, the
tweeter polarity must be the reverse
of the woofer. This is why the positive
terminal of the tweeter is grounded.
On the right channel tweeter, you
will notice that the tweeter connection
is different. In this case, the positive
terminal is driven by the output of
October 1996 71
Fig.6: this is the component layout for the PC board. Note the two long jumpers underneath the board.
Fig.7 (right): this diagram
shows the dimensions of the
two heatsink brackets.
IC5b and the negative terminal is
grounded. The reason for this is that
because of the internal connection of
the amplifier inputs at pin 3, IC5a must
be driven via its inverting input at pin
9. Therefore it inverts the signal and
the tweeter connections must therefore
be reversed.
This reversing of tweeter connections is automatically taken care of by
the PC board and so each speaker box
is wired identically via its respective
cable and 9-pin D connector.
Note that IC1 and IC2, the two TL074
quad op amps, are powered from the
±12V rails of the computer whereas
the power amplifiers, IC3, IC4 and
72 Silicon Chip
IC5, are powered only from the +12V
rail. The -12V rail in the computer
cannot deliver lots of current but IC1
and IC2 will typically draw a total of
less than 20mA.
PC board assembly
Fig.8: this diagram shows the
details of the heatsink mounting
for the TDA1519As. Be very
careful when bending the legs
of the IC at right angles that you
do not stress the leads where
they come out of the IC body.
Enough of how it works, lets get
into making it work. The PC board assembly is reasonably straightforward.
Before mounting any components,
check the board carefully for any defects such as shorted or broken copper
tracks or undrilled holes. You can
check the pattern against the artwork
shown in Fig.10.
Fig.6 shows the component layout
PARTS LIST
Amplifier PC board
1 PC board, code 01110961,
145 x 108mm
1 PC-mounting bracket (see
Fig.9)
2 9-pin “D” females PC mounting
socket
2 9-pin “D” male plugs
2 9-pin “D” backshells
1 3.5mm miniature PC mount
stereo socket
1 3.5mm miniature stereo plug
2 14-pin IC sockets (optional)
1 PC mounting bracket (with
holes for D-sockets, etc)
2 10kΩ multiturn potentiometers
Bourns 3006P (or equivalent)
Semiconductors
2 TL074 quad op amps (IC1,IC2)
3 TDA1519A dual power
amplifiers (IC3,IC4,IC5)
Capacitors
4 470µF 16VW electrolytic
9 100µF 16VW electrolytic
2 2.2µF 50VW non polarised
(NP) electrolytic
2 2.2µF 50VW electrolytic
12 0.1µF 63VW MKT polyester
7 0.1µF 50VW monolithic
ceramic
8 .01µF 63VW MKT polyester
Resistors (0.25W, 1%)
2 150kΩ
2 1.5kΩ
2 22kΩ
4 100Ω
2 10kΩ
6 4.7Ω
8 4.7kΩ
Fig.9: details of the PC board mounting bracket.
for the PC board. Fit and solder the
wire links first and don’t forget the
two long jumpers, made from insulated hookup wire, which install on
the copper side of the PC board. These
connect the outputs of IC5 to the
respective D sockets. Leave the link
marked “Power” off the board for the
moment. This is connected during the
testing procedure.
The next step is to fit the resistors,
small capacitors, trimpots and 3.5mm
jack socket. Note that the 0.1µF monolithic ceramic capacitors are used for
supply filtering, so they are the ones
adjacent to the 100µF electrolytics.
The 0.1µF MKTs are specified in the
signal parts of the circuit.
The small electrolytic capacitors are
next, followed by the larger ones and
then the female D sockets. The two
TL074s can be soldered in or if you
prefer, plugged into sockets.
The heatsinks for the power amplifiers are made from 3mm thick aluminium angle, 20 x 12mm. The heatsink
for IC5 is 30mm long and the one for
IC4 & IC5 together is 55mm long. Fig.7
shows the drilling details.
The nine leads of each TDA1591A
need to be bent at right angles before
soldering into the board. With each
TDA1519A facing you and the type
number visible, bend the leads down
at right angles, 8mm from each IC
body. Note: do not put any stress on
Miscellaneous
1 55mm length 20 x 12 x 3
aluminium angle
1 30mm length 20 x 12 x 3
aluminium angle
22 3mm x 20mm bolt
22 3mm nut
30 3mm flat washer
6 2.5mm x 12mm screws
6 2.5mm nuts
6 2.5mm spring washer
6 2.5mm flat washer
3 TO3 mica washers
the leads where they come out of the
IC body.
To avoid stressing the leads, hold
them with long-nose pliers when
bending each one. This done, apply
a smear of heatsink compound to
October 1996 73
Fig.10: check your
PC board against
this full size etching
pattern before
installing any of the
parts.
the metal mounting surface of each
IC and mount it on its heatsink – see
Fig.8.
Testing
To test the amplifier board, you
will need a power supply capable of
delivering ±12V at several amps. We
strongly suggest that you do not just
build the amplifier board and plug it
into your computer. If there is a fault
on the board you could damage your
computer’s power supply.
Three PC stakes are provided on
the PC board for supply connections.
They can be seen near the edge connector, on Fig.6. Connect the power
supply to the PC stakes and then use
The enclosures have an internal volume of only five litres but that, combined
with a spot of low down bass boost, is enough for them to put out good bass
down to below 50Hz. We’ll describe their construction next month.
74 Silicon Chip
your multimeter to measure voltages
around the circuit.
The principal voltages should be
as follows:
• IC1 & IC2 – pins 1, 2, 3, 5, 6, 7, 8,
9, 10, 12, 13 & 14, 0V; pin 4 +12V; pin
11 -12V.
• IC3, IC4 & IC5 – pins 2 & 5, 0V; pins
1, 3, 4, 6 & 9, +6V; pin 8, floating; pin
7, +12V.
For some of the pins of IC1 and IC2,
designated as 0V, your multimeter
may actually measure a few tens of
millivolts above or below 0V. That is
normal. The current drain at this stage
should be between 15 and 20mA, or
thereabouts. This is the current drawn
by IC1 and IC2. The current drain of
the power amplifiers is negligible at
this stage since we have not connected
pin 8, the MUTE pin, to +12V.
If all the voltage checks so far are
correct, you can now install the link
marked “Power” on the board. This
enables the power amplifiers. When
power is applied the total current drain
should be around 140-160mA, with no
signal applied.
Well, that is as far as we can take
it this month. Next month, we will
describe how to build the speakers
and give the parameters of the BassSC
Box design.
SATELLITE
WATCH
Compiled by GARRY CRATT*
PALAPA C1 to C2M CHANGEOVER: The change over from Palapa
C1 to the Palapa C2M satellite at the
end of June has done little to solve the
reception problems being experienced
by enthusiasts in Australia and New
Zealand. There has been virtually no
change in the receive level of transponders of either polarity on the
new C2 satellite, meaning that those
wishing to receive this satellite in the
eastern states of Australia will need a
3.7m dish for good results.
GORIZONT 19/27 - 96.5°E longitude: Early indications (at August 31st)
show that this satellite was replaced
on August 20 by Gorizont 27. This new
satellite runs a lower power level over
Australia, requiring users to upgrade to
a larger dish, perhaps up to 3.7m. The
degree of inclination of this satellite is
much less compared to Gorizont 19.
OPT 1 continues to be the sole source
of programming available, on IF
1475MHz.
ASIASAT 2 - 100.5°E longitude: The
two new Chinese stations reported in
the August issue of Satellite Watch
have now been identified as Henan TV
(IF 1430MHz) and Guangdong Satellite
TV (IF 1310MHz). In addition, MTB
from Mongolia appears at IF 1470MHz
each night around 7pm AEST. TVSN,
otherwise known as “The Value Channel”, appeared on this satellite during
August, on IF 1485MHz, supplementing their service on Panamsat PAS-2.
Meanwhile, a trickle of MPEG
decoders continues to arrive in this
country from South Africa. Available
for around $1600 and originally supplied for the “Multichoice” pay TV
service in South Africa, these decoders
work well on the European Bouquet of
channels broadcast on AS2.
GORIZONT 42 - 142.5°E longitude:
Global TV’s adult channel “21 Plus”
has not yet commenced operations despite a July 1st start being advertised.
Industry reports indicate that Global’s
contract was not in place at deadline
and startup has hence been delayed.
Meanwhile, Filipino channel RPN
(primarily English language programming) has a 90-day contract to operate
using the same transponder from
2200-1600UTC daily. Broadcasts are
currently in NTSC. Its IF is 1375MHz.
The screen grab
is from TVSN
(The Value
Channel), which
appeared on
Asiasat2 during
August on IF
1485MHz.
Other broadcasters on this satellite
continue normal operations: EM TV
at 1265MHz and Asia Music/Zee Education at 1470MHz.
APSTAR 1A - 131°E longitude:
Launched successfully on July 3rd
aboard a Long March launch vehicle
from China, this bird may be parked
permanently at 131°E longitude, despite having no authorisation from the
ITU to do so. This is a similar situation
to the one occurring after the launch
of Apstar 1 several years ago.
In that instance, Apstar 1 was parked
initially at 131°E degrees, much to the
horror of operators of satellites at both
132°E and 130°E. Finally, they negotiated the orbital “slot” of 138°E with
Rimsat. It seems this time, the Chinese
owners of the satellite plan another
“brute force” orbital intrusion.
OPTUS B3 - 156°E longitude: This
satellite carries the Galaxy pay TV
service on transponders 10 and 11
in MPEG2. New to market, Panasat
MPEG IRDs can be used to receive
Galaxy MPEG transmis
s ions sent
without conditional access, such as
“The Value Channel” and the Galaxy
“Preview” channel.
PANAMSAT PAS2 - 169°E longitude: Normally inactive on K band
other than for special events, this satellite carried the Network 7 feed from
the Olympic games at Atlanta during
July. C band activity continues as follows: 1115MHz NHK Japan, 1183MHz
CNNI, 1405MHz The Value Channel,
1057MHz NBC digital service. The
NBC digital service requires an MPEG
IRD and whilst operating at present
with no conditional access, this situation may change in the future. SC
*Garry Cratt is Managing Director of
Av-Comm Pty Ltd, suppliers of satellite TV
reception systems.
October 1996 75
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
PRODUCT SHOWCASE
Dick Smith Electronics opens
new Powerhouse retail store
Dick Smith Electronics has opened a vast
new electronics retail store in Bankstown,
Sydney. It is six to eight times larger than
the average DSE store, with a floor space of
2000 square metres.
Since it represents a new concept
for Dick Smith Electronics, it has been
named the "PowerHouse". It has been
designed to focus on the convergence
of electronics technology.
Not only does the new store devote
a much larger area to conventional
electronics parts and semiconductors, the PowerHouse new store has
a much wider range of products than
ever before.
As well as a large area devoted to
computers and software, printers,
multimedia sound systems and other
peripherals, it has a large display of
TV sets, a car radio and amplifier
display and a range of camcorders,
each working with a standard monitor.
This camcorder display alone is better
than virtually any electronics retailer
in Australia.
There is also an amateur radio
shack, a hifi sound lounge, a theatre
surround sound lounge, and a Telstra
kiosk selling mobile phones and other
services such as Easycall and Foxtel.
You can have mobile hands-free kits
and car radios fitted at the store as
well.
For those curious about the Internet
and the World Wide Web, there is an
Internet bar with several machines
permanently connected. And if you
are upgrading your computer with
memory, drives or new cards, there
is an on-site technical service centre
where this can be done while you
wait.
The PowerHouse will also have regular clinics for electronics enthusiasts
and this will demonstrate the building
of current kits and also trouble-shoot
kits which have been built by customers. This could be a great service to
constructors.
A really impressive aspect of the
PowerHouse is the large number of
working product displays. For example, they have a large selection of multimedia sound systems, all of which
can be demonstrated and selected by
a touch screen.
Anything else? Well, they have a
large range of audio CDs in stock, a big
BassBox
®
Design low frequency loudspeaker enclosures
fast and accurately with BassBox® software.
Uses both Thiele-Small and Electro-Mechanical
parameters with equal ease. Includes X. Over
2.03 passive crossover design program.
$299.00
Plus $6.00 postage.
Pay by cheque, Bankcard, Mastercard, Visacard.
EARTHQUAKE AUDIO
PH: (02) 9948 3771 FAX: (02) 9948 8040
PO BOX 226 BALGOWLAH NSW 2093
October 1996 79
STEPDOWN
TRANSFORMERS
60VA to 3KVA encased toroids
Harbuch Electronics Pty Ltd
9/40 Leighton Pl. HORNSBY 2077
Ph (02) 9476-5854 Fx (02) 9476-3231
range of printer consumables such as
paper and ribbons.
We visited the PowerHouse just after
it had opened and it was difficult to
comprehend the range and scale of
products on display. It is certain to establish a benchmark for all electronics
retailing in Australia.
Dick Smith Electronics' PowerHouse is located at the Christies Home
KITS-R-US
RF Products
FMTX1 Kit $49
Single transistor 2.5 Watt Tx free
running 12v-24V DC. FM band
88-108MHz. 500mV RMS audio
sensitivity.
FMTX2A Kit $49
A digital stereo coder using
discrete components. XTAL
locked subcarrier. Compatible
with all our transmitters.
FMTX2B Kit $49
3 stage XTAL locked 100MHz
FM band 30mW output. Aust
pre-emphasis. Quality specs.
Optional 50mW upgrade $5.
FMTX5 Kit $98
Both a FMTX2A & FMTX2B on 1
PCB. Pwt & audio routed.
FME500 Kit $499
Broadcast specs. PLL 0.5 to 1
watt output narrowcast TX kit.
Frequency set with Dip Switch.
220 Linear Amp Kit $499
2-15 watt output linear amp
for FM band 50mW input.
Simple design uses hybrid.
SG1 Kit $399
Broadcast quality FM stereo
coder. Uses op amps with
selectable pre-emphasis.
Other linear amps and kits
available for broadcasters.
80 Silicon Chip
Centre, Cnr Chapel Street & Canterbury
Road, Bankstown, NSW 2200. It is
open seven days a week.
Meters for light &
colour measurements
800V Mosfets have
low on-resistance
Emona Instruments have available
the Tektronix LumaColor photometers. Two photometers and their
eight interchangeable heads form the
TekLumaColor family.
Each head transforms the handheld
into a different precision photometer,
radiometer or colourimeter. Each combination automatically displays the
appropriate units on a large, backlit
LCD screen.
Designed for on site as well as production use, the TekLumaColors are
manufactured with a rugged exterior
to protect from shock and vibration.
They can operate for 30 hours on a 9V
battery or connect to an optional AC
power supply. An RS-232 port allows
the user to automate testing and data
recording.
The J18 TekLumaColor II is designed primarily for testing, calibrating and adjusting colour displays.
With Its J1810 chromaticity head,
the TekLumaColor II updates colour
and comparison readings twice each
second.
The unit stores ten reference settings
IXYS Corporation have expanded
their line of power Mosfets with the
introduction of five new high voltage
devices. They have a minimum blocking voltage (BVdss) of 800V and are
fabricated using the company's HiPerFET process. This process guarantees
a high avalanche energy rating and
a faster switching intrinsic rectifier,
providing higher reliability while
reducing component cost in power
switching circuits.
The new devices range in current
from 8A to 27A and offer some of
the industry's lowest on-resistance
(Rds(on)) and highest current ratings
in their respective packages. For example, the 15A IXFH15N80 offers the
industry's lowest Rds(on) in a TO-247
package at 0.6#.
For further information, contact
GEC Electronics Division, Unit 1, 38
South Street, Rydalmere NSW 2116.
Phone (02) 9638 1888; fax (02) 9638
1798.
PO Box 314 Blackwood SA 5051
Ph 0414 323099 Fax 088 270 3175
AWA FM721 FM-Tx board $19
Modify them as a 1 watt op
Narrowcast Tx. Lots of good RF
bits on PCB.
AWA FM721 FM-Rx board $10
The complementary receiver
for the above Tx. Full circuits
provided for Rx or Tx. Xtals
have been disabled.
MAX Kit for PCs $169
Talk to the real world from a
PC. 7 relays, ADC, DAC 8 TTL
inputs & stepper driver with
sample basic programs.
ETI 1623 kit for PCs $69
24 lines as inputs or outputs
DS-PTH-PCB and all parts. Easy
to build, low cost.
ETI DIGI-200 Watt Amp Kit $39
200W/2 125W/4 70W/8 from
±33 volt supply. 27,000 built
since 1987. Easy to build.
ROLA Digital Audio Software
Call for full information about
our range of digital cart players & multitrack recorders.
ALL POSTAGE $6.80 Per Order
FREE Steam Boat
For every order over $100 receive
FREE a PUTT-PUTT steam boat kit.
Available separately for $19.95,
this is one of the greatest educational toys ever sold.
Portable data acquisition system
National Instruments
has announced a high-resolution, portable data
acquisition box that communicates through the
parallel port with PC
compatible computers.
The DAQPad-MIO16XE-50 features a 16-bit
ADC with a 20ks/s sampling rate, 16 single-ended or eight differential
inputs and enhanced timing and triggering capabilities,
programmable gain up to 100, two 12-bit DACs with voltage outputs, one constant current source for powering
resistance temperature detectors (RTDs), eight lines of
TTL-compatible I/O and two 24-bit up/down counter/
timers for timing I/O.
It is compatible with the Enhanced Parallel Port (EPP)
standard defined by IEEE 1284 as well as the original
Centronics or standard parallel ports (SPP). As well, it
has a second parallel port connector for a pass-through
connection to a printer.
It can be powered from an AC plugpack, an optional
BP-1 rechargeable battery pack or any 9-42VDC source.
For more information, contact National Instruments
Australia, PO Box 466, Ringwood Vic 3134. Phone (03)
9879 5166; fax (03) 9879 6277.
and is calibrated at D6500 for accurate
white light readings. It offers RS-232
control, analog output capabilities and
RGB bar graphs for easy calibration.
For applications where real-time
colour isn't critical, the J17 TekLumaColor is a unit that shares many of
the family's features, including auto-range, auto-zero, hold, colour coordinate conversions and US to Metric
conversions.
The family of eight heads provides
measurements for luminance, illuminance, chromaticity, irradiance,
luminous intensity and radiant intensity. Measurement applications range
through CRT displays, flat panel and
projection displays, photographic
equipment, infrared LEDs and lasers
and coloured LEDs.
For more information, contact Emona Instruments on (02) 9519 3933 or
fax on (02) 9550 1378.
PC board
touch-up pen
Now available is a range of marker
pens intended for touching up PCBs
before they are etched. Available in
blue or red, the ink resists etchants
such as ferric chloride and ammoniated alkali (eg, ammonium persulphate).
Ink marks can be erased with a cloth
or Q-tip moistened with napthas or
chlorinated solvents.
For further information, contact
Australian Warehouse Solutions Pty
Ltd, PO Box 146, Roseville 2069.
Phone (02) 9417 7550; fax (02) 9417
7953.
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.emona.com.au/
Stop and direction
arrow kits for cars
Oatley Electronics has two simple
kits for cars. One is a Stop sign while
the other is a direction arrow, both
made using an array of high intensity LEDs on a PC board. These are
connected in parallel with the brake
and direction indicator lamps of your
car and would normally be mounted
inside the rear window, on the parcel
shelf.
The complete Stop sign kit is $30
while the direction arrow kits are $15
each. For further information, contact
Oatley Electronics, PO Box 89, Oatley,
NSW 2223. Phone (02) 9579 4985; fax
(02) 9570 7910.
October 1996 81
RADIO CONTROL
BY BOB YOUNG
Multi-channel radio control
transmitter; Pt.8
This month we will deal with the more
complex programming functions which
can be provided in this very advanced
R/C transmitter.
But first, let’s get this month’s grizzles, whinges and additions out of
the way. In Pt.6 (July, 1996), which
dealt with the construction of the
transmitter case, Fig.2 showed
the wiring arrangements for the
various control elements. In this
drawing set, mention is made of
the connecting cable for these
functions being a blue/white/
blue 3-core ribbon cable.
As these leads are intended
for reversing, the blue/white/
blue was to indicate that polarity
was not important on these connectors. The b/w/b also matched the
transmitter interior which is all in
blue and white and it added to the
internal appearance. The cable was
ordered weeks before that article was
written and the order clearly stated
blue/white/blue.
Months passed and still no cable.
The July issue came out, still no cable. Finally, the big day arrived. The
delivery docket stated b/w/b, the
invoice stated b/w/b but it
appears the production
people decided that
red/white/blue
would look
much better.
As I was
desperate
for cable by
this time I
had no alternative but
to use the r/w/b ribbon and to my
amazement, the production people
were absolutely correct. The finished
transmitter did look much better,
especially since I had increased the
cable length after looking at the July
issue photos. The leads now run neatly
around the sides of the case.
From now on, all leads will be
red/white/blue as dictated by the
cable manufacturers. This has one
advantage in that it removes the
need to paint a dot on one side of
the connector (recommended in the
July issue), as it is now very easy to
determine visually if the lead is normal or reversed.
All jokes aside, this business of
quality control is driving me nearly
insane. Almost without exception,
every major component has been
returned due to lack of quality or
correctness. My heart is in my mouth
every time I open a new batch of
components. From powder coating
to pots, I have sent back more components than I have accepted. Under
these conditions, delivery promises
mean nothing, and even now I am still
struggling to get the project running
smoothly with regards to deliveries.
However, I digress.
The wiring in those July photos
looked totally disorganised. By increasing the lead length, it is now possible to run the leads right around
the outside of the case (see photo).
This was mentioned in the July issue but not highlighted. The lengths
shown in Fig.2 of the July issue were
the corrected, longer values.
The addition of the frequency interlock key, as
described in the text, eliminates the possibility of
two transmitters operating on the same channel.
82 Silicon Chip
Fig.1: the frequency interlock key, developed by the Author, cuts off the
power to the transmitter while it is plugged into the charging socket.
When the transmitter is in use, the key is removed and hangs on a key
board in the club.
Another nice touch added to the
kits is the inclusion of self-adhesive
cable clamps which stick to the case
sides and secure all the cables neatly.
These are made out of the large
headed split-pin type paper clips,
available at any stationers. The legs
are clipped in length and covered in
heatshrink and the heads stuck to the
case side with double-sided foam tape.
They sit flat against the wall, can hold
a large number of cables and are dead
easy to open and close, in order to add
and remove cables; in other words, the
ideal cable clamp.
Also, since the July issue, I have
found a source of components for
crimp connectors which allows me to
crimp my own leads. These feature a
housing similar in size to the Futaba
servo connector housing but less the
polarising flange. These are fitted with
high contact pressure, gold-plated
pins. All kits will henceforth use these
connectors which will be pre-crimped.
These connectors are of a higher
quality and are less fiddly to assemble
than the original solder connectors.
They also have one large flat face
which is ideal for a self-adhesive
numbering label.
A sheet of self-adhesive numbers is
now included in all kits as an aid in
identifying the leads. The following
list gives the lead numbers in production transmitters:
The view inside the case from the rear. The operating channel is set by the
plug-in crystal near the centre top of the photo. The interconnecting wiring is
now laid around the perimeter of the case for a much neater appearance.
1. Throttle pot
2. Aileron pot
3. Elevator pot
4. Rudder pot
5. Switch 1 (outside left)
6. Aux 1 pot (left)
7. Switch 2 (inside left)
8. Switch 3 (inside right)
9. Aux 2. Pot (right)
10. Switch 4 (outside right)
Please note that these numbers are
not meant to correspond with those
given in the channel allocation table
in the August issue.
As I have no idea which switch you
will use for what application, I cannot
possibly match these numbers to the
channels. They are only a guide to
identifying the leads.
Frequency interlock
There is one correction for the August article. It stated that the charge
plug must be a 2.5mm non-shorting jack. This should read “3.5mm
non-shorting”. In the kit will be found
two 3.5mm jack plugs. One is for the
charger while the other should be fitted
to the frequency key as shown in Fig.1.
This plug/key combination forms the
basis of the Silvertone Frequency Interlock system.
Under the rules of operation for the
Silvertone Keyboard frequency control
system, each transmitter has its own
individual key which is inserted into
the Keyboard to reserve the frequency and bandwidth required for the
transmitter.
The only person allowed to insert
or remove a key in order to reserve
a frequency is the operator of the
transmitter on that frequency. Thus,
the logical position for the key at all
other times is for it to be plugged into
the transmitter, thereby rendering it
inoperative.
The plug/key combination performs
this function. When it is inserted into
With the back of the case on, the
channel-setting crystal is instantly
obvious. Only one transmitter may
use this channel, for obvious reasons.
October 1996 83
Fig.2 (left): detail of
the mixing inputs and
outputs. Any channel
may be mixed with
any other and multiple
mixes are possible.
Fig.3: this diagram shows how the various micro-shunts (shorting
links) must be placed across TB10 if the configuration module is
not used.
the charge socket located on the bottom right of the transmitter control
panel, the +9.6V line is open circuited,
thereby rendering the transmitter inoperable even if the switch is left on.
When the operator wishes to switch
on, he takes his transmitter to the
Keyboard and checks to see if his
frequency is clear. If it is, he then
removes his key from the charge socket and inserts it into the Keyboard.
Thus, we now have a true frequency
interlock system. If the key is in the
Keyboard, the transmitter is cleared
for transmission. At all other times,
the key is in the charge/interlock
socket on the transmitter so that the
latter is inoperative.
Bingo, no more inadvertent shoot
downs by transmitters accidentally left
on in the transmitter pound!
There is an interesting sidelight to
this story. When Silvertone invented
and patented this system in 1969, the
importers went berserk for the simple
reason they would have had to pay
a royalty on every transmitter sold
in this country, had the system been
officially adopted in Australia.
They kept the system out of official
use with a particularly vindictive campaign until about two years after the
patent had expired. Then the very people who so vehemently campaigned
against the system were the very first
to start manufacturing and selling it
when the coast was clear.
Today the system is known as the
Australian National Frequency Con84 Silicon Chip
trol System and is approved for use
by the MAAA at all national contests,
although the frequency interlock aspect of the system is never mentioned.
However, every Silvertone transmitter produced since 1969 has featured
frequency interlock.
Simple mixing programming
This explanation will concentrate
on the basic principles involved rather
than covering every possible combination of mixing. Once the principles
have been mastered, the rest falls into
place quite easily.
Four simple mixers are built into
the standard Mk.22 encoder module.
Two are inverting and two are non-inverting. These are located at the top
righthand corner of the module and
consist of a quad op-amp IC (LM324),
four mix volume pots, and a double
row 8-pin header plug. Fig.2 shows
these controls in detail.
In radio control parlance, a mixer
is essentially a variable gain buffer
amplifier, necessary to prevent reverse
mixing when the channel inputs and
outputs are connected together.
Thus, a mixing amplifier is necessary for each mixing function. The
input of the mixer is connected to the
output of the control channel and the
output of the mixer is connected to
the input of the mixed channel. If you
are confused by this explanation, you
may like to refer back to the article on
mixing in the December 1995 issue.
Mixers 1 & 2 are inverting while
mixers 3 & 4 are non-inverting. A
non-inverting mixer will give the
same direction of rotation in the mixed
channel as the primary control channel. An inverting mixer will give the
opposite (reverse) direction of rotation
in the mixed channel to the primary.
Any channel may be mixed with
any other channel and multiple channel mixing is possible. Referring to
Fig.3 (repeated from page 73 of the
August 1996 issue), the pins numbered 1-8 carry all control input data
to multiplexer IC5, including dual
rate switching. The pins identified
by letters are the outputs from the
control stick potentiometers via the
gain control pot wipers (see the circuit
diagram in March 1996) and are used
in certain complex mixing functions.
When discussing mixing, the primary
control channel from which the mix
data is to be derived is considered to
be the output channel.
The mixer inputs and outputs may
be found on the Mix Input/Output
connectors TB27 and TB28, located
at the extreme top right corner of the
encoder module. Fig.2 shows these
inputs and outputs in detail.
Note that there are four pins for
each mixer: an input, an output and
two for the mix IN/OUT switch. Fig.4
shows the details of the mixing patch
cord used to connect the mixer inputs/
outputs to the pins on TB10.
One patch cord is required for each
Fig 4: the mixing patch cord used to connect the mixer inputs/outputs to
the pins on TB10. One patch cord is required for each mixing function.
mixing function. The 2-wire, 2-pin
socket connects to the appropriate
mixer input/output pair with blue
to mix/in and white to mix/out. The
split leads go to TB10. The blue 2-pin
connector is connected to the primary
control (channel output) and the white
2-pin connector to the mixed channel
(channel input).
Two pins of the 3-pin socket on any
toggle switch are connected to the
switch pin pair. This provides front
panel switching for mix in/out. The
sense of the toggle switch (UP/OFF)
is determined by which two pins
are used (centre/left, centre/right). If
remote switching of the mixer is not
required, then the toggle switch may be
replaced with a micro-shunt across the
two pins. One switch or micro-shunt
is required for each mixing function.
Servo throw
That completes the description of
the basic components in the mixing
circuits. Before proceeding any further, there is a very important point to
bear in mind when setting up mixing
functions. Each mixer input has an
additive effect on servo throw and
this must be taken into account when
setting mix ratios. Failure to observe
this may result in the servo being
driven into its internal end stops with
attendant gear damage.
The Mk.22 has automatic compensation built in but it is still possible to
drive the servo into over-travel if the
mix ratios are set too high. Therefore,
be sure to check the final servo travel
with the full extremes of mixing applied, as servo travel varies with the
brand of servo used.
To illustrate the point being made
in the above warning, let us examine
the mixing process for a delta aircraft
featuring elevons (Delta mix). Such an
aircraft uses two control surfaces, one
on each wing, and each control surface
performs two functions: aileron and
elevator control – hence the name
“elevon”. Fig.5 shows the control
sequence in detail.
To bank such an aircraft, one control
surface goes up and the other goes
down, thereby imparting a rolling
motion to the aircraft. To raise or lower
the nose (pitch control), both control
surfaces go up or down, respectively.
Complications arise when one
wants to bank and climb at the same
time. If full throw on the aileron servo gives the desired rate of roll, what
Fig. 5: the control sequence for each of a variety of movements in an
aircraft fitted with elevons. Elevon controls are very complex to set up
correctly. Step-by-step instructions are included in the text.
happens when we then apply full up
elevator to impart a climbing motion
to the aircraft?
If we are turning left, then some
“up” mixed into the right elevon
(which is down in a left roll) is easily
accommodated. However, there is no
more travel available in the left servo
which is already full up.
To apply an additional pulse width
variation will only drive the servo hard
into the end stops and possibly strip
the gears. Therefore, the controls must
be mechanically arranged so that 50%
differential servo travel (one up, one
down) gives the maximum rate of roll
and 50% common servo travel (both
up or both down) gives the maximum
pitch angle.
If this is done, then we may apply
full pitch and roll commands simultaneously. Oddly enough, at this point
only one servo actually moves and it
goes to full travel.
The two commands on the opposing
servo cancel each other out and the servo remains in neutral. Elevon controls
are very complex to set up correctly,
especially when you start to consider
the reflex and unequal differential angles which must be taken into account
for the correct aerodynamic conditions
October 1996 85
Fig. 6: this revised diagram shows the configuration module socket (TB10) in the centre of the encoder PC
board. This socket was inadvertently left off the diagram published on page 73 of the August 1996 issue.
required by “tail-less” aircraft.
So let us move towards this complex
programming task cautiously and one
step at a time.
Simple 2-channel mixing
Such applications as Coupled Aileron/Rudder, Flap with elevator compensation and Main Rotor/Tail Rotor
mixing all come under the heading of
simple mixing applications and may
be accomplished with the use of the
simple programming patch cord and
the on-board mixers. Dedicated, complex mixing utilises the configuration
module and these mixing functions
will form the basis of later articles.
Coupled aileron/rudder
with dual rate mixing
In this program mode, the Aileron
and Rudder controls will be coupled
with an adjustable ratio of mix which
will change proportionally to the dual
rate ratio.
To program for coupled Aileron/
Rudder, we are going to take some output from the Aileron channel and feed
it into the input of the Rudder channel
via one of the on-board mixers and the
mix select connectors TB27 and TB28.
Both the output and input programming pins are located on TB10, the
configuration port connector (Fig.3).
At this point, it is necessary to
establish whether an inverting or
non-inverting mixer is required for
your application. Such details as the
direction of rotation of the servos and
the placement of the control linkages
will all play a part here.
If the complexity of working it out
in your head proves too much, just
whack the 2-pin connector onto a
non-inverting mixer and if the rudder
moves the wrong way, plonk it onto an
inverting mixer; very scientific! The
procedure is as follows:
(1). Replace the micro-shunt from pin
2 of TB10 with the Blue socket. Next
remove the micro-shunt from the rudder input on TB10 (pin 4) and replace
it with the White socket.
(2). Connect the 2-pin socket of the
patch cord to the appropriate MIX
INPUT/OUTPUT connectors on TB27
and TB28, with the Blue lead to “IN”
and the White to “OUT”.
A close-up view of the frequency interlock key. It plugs into the charging socket
on the transmitter when the latter is not being used.
86 Silicon Chip
(3). If remote switching of MIX IN/
OUT is required, connect two pins
of the appropriate toggle switch to
the “Switch” pin pair, checking the
sense of operation as you go. If permanent mixing is required then place
a micro-shunt across the “switch”
pin pair.
(4). Adjust the dual rate ratio using
the Aileron channel ATV potentiometer in the usual manner and set the
ratio of mix using the mix control pot
associated with the mixer you have
chosen.
You are now programmed for Coupled Aileron/Rudder with dual rate
mixing.
Coupled aileron/rudder without dual rate mixing
In some cases, it may be desirable to
change the dual rate without changing
the mix ratio. In this case, replace
Steps 2 and 5 in the above with the
following:
(2). Connect one pin of the Blue
socket to pin A on TB10, leaving the
other to float free. Next, replace the
micro-shunt on pin 4 with the White
socket.
(5). Set the ratio of mix using the appropriate mixer potentiometer.
Having mastered the basics of simple mixing, and it really is simple
once you get the hang of it, the same
principles apply to all 24 channels in
the Mk.22 transmitter. Any channel
can be mixed with any other channel
and even multiple channel mixing is
possible using the same principles.
Let us now look at the more complex
task of programming for elevons. In
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this application we begin to confront
the concept of channel allocation
which really is at the heart of complex
mixing.
Referring back to our earlier discussion on elevons and comparing it now
with the channel allocation table, we
find that there are no Aileron or Elevator channels, at least in the sense that
we normally understand them.
Instead, we are confronted with a
left elevon servo and a right elevon
servo, both of which respond to Aileron and Elevator commands.
Where do we go from here? We still
have an Aileron stick on the transmitter as well as an Elevator stick. If we
allocate one to left Elevon and the other to right Elevon, I hate to think what
would happen. I do not think humans
would be too good at manually mixing
these controls.
The answer is quite simple really.
We will use cross-coupled simple
mixing in which we will mix channel
2 into channel 3 and channel 3 into
channel 2. We will also allocate the
Aileron control stick to Channel 2 and
the Elevator Control stick to channel
3. Thus, the Aileron stick reverts to
its normal action, as does the Elevator
stick.
So the programming sequence
for servos of the same rotation is as
follows:
(1). Set both the channel 2 and channel 3 vary/normal headers to the vary
position.
(2). Take two patch cords and connect
one to an inverting mixer and the other
to a non-inverting mixer on TB27 and
TB28.
(3). Connect the Blue lead from the
non-inverting mixer to pin E on TB10
and the Blue lead from the inverting
mixer to pin A on TB10.
(4). Remove the micro-shunts from
TB10 pins 2 & 3 and replace them
with the White socket from the
non-inverting mixer to pin 2 and the
White socket from the inverting mixer
to pin 3.
(5). Fit micro-shunts to the appropriate
“switch” positions on TB27 and TB28.
(6). Use both channel 2 and 3 ATV
pots and both mixer volume pots to
achieve perfect balance between the
movement on both servos.
Remember here that Aileron will
send the servos in opposite directions
(differential), while Elevator will
send the servos in the same direction
SC
(common).
October 1996 87
VINTAGE RADIO
By JOHN HILL
A new life for an old Hotpoint
My first commercial radio was a 1940s
4-valve AWA Radiola. Recently, I had the
chance to restore an almost identical model
and that’s what this month’s story is about.
So how did an old Hotpoint get into the act?
I have mentioned before my early
interest in radio and how my spare
time as a lad was spent building crystal
sets and simple regenerative receivers.
This was an exciting time of my life
and I have fond memories of those
distant days. But although this period
spanned many years, it came to a very
abrupt end.
My tinkering with home-made radios finished the day my father bought
me a new receiver for my bedroom.
Actually, I think my mother was the
main instigator behind this move because she had tired of the perpetual
mess that graced the top of a chest of
drawers. For years, this area had been
strewn with a variety of radios, mountains of batteries, including a smelly
rechargeable lead-acid B battery, and
other miscellaneous accessories such
as headphones, with their long dangling cords.
From my mother’s viewpoint, that
was untidiness of the worst kind and
it had to go!
However, in order to remove the
junk without fuss or ill feeling, there
had to be a satisfactory replacement.
Enter one new radio in the form of
a late 1940s 4-valve AWA Radiola
mantel model with a brown Bakelite
cabinet.
It must have been Mum’s idea because it wasn’t even Christmas or my
birthday – it just happened!
The little Radiola was in regular
use for about 10 years up until the
time I left home for the big smoke.
Sometime after that it strangely disappeared. Presumably it developed
some terminal complaint and was
gently laid to rest. At the time I never
bothered to ask what happened to it.
Now that I would like to know, no-one
can remember.
Different styles
The Hotpoint receiver after restoration. This particular model with the ovalshaped Bakelite dial escutcheon (part of the cabinet moulding) survives better
than the model with the separate moulded plastic escutcheon.
88 Silicon Chip
My old Radiola had a cabinet style
that was not as common as a similar
and slightly larger model of that era.
As a result, I had, for quite a while,
been looking for one to add to my
collection – not that postwar 4-valve
Radiolas are highly sought after collectables. I just wanted one the same
as the one I had back in the 1950s for
sentimental reasons.
Just why there were two distinct
cabinet styles is something of a mystery. However, the smaller one had an
oval shaped dial while the other had a
rectangular dial. Otherwise they were
much the same inside and the dial
shape was about the only noticeable
difference between models.
It was the oval version that I was
seeking. This cabinet style is far more
durable than the rectangular model.
The reason for this difference is that
the oval dial has a Bakelite escutcheon
whereas the other is white plastic. The
latter warps and cracks with age and,
after 40 years or so, is inclined to fall
to pieces.
Many other Radiolas of similar
vintage have the same lousy plastic
in their speaker grilles and these too
can look terrible due to the distortion
that takes place over the years. When
it comes to plastics, some are far more
stable than others.
Bakelite vs. plastic
Before going further, let’s briefly
digress and examine the differences
between Bakelite and plastic, just to
clarify that last paragraph.
Although they are both plastics,
Bakelite is a thermosetting plastic
which is very stable and holds its form
extremely well, even over time spans
exceeding 60 years.
Thermoplastics, on the other hand,
have quite different characteristics and
many early thermoplastics virtually
self-destruct after 40 years or so. However, thermoplastics can be re-melted
and recycled, whereas thermosetting
plastics cannot!
From a collector’s point of view,
I’m not particularly interested in restoring any receiver that has a badly
deteriorated cabinet due to the use of
poor quality plastics. A restoration
job should result in a receiver that
both looks and performs as new (or
close to it).
If the cabinet or cabinet fittings have
cracked or warped out of shape, then
the set is not worth restoring. Well,
that’s how I see the situation!
A Radiola with the rectangular dial escutcheon. This 4-valve model is unusual
in that it is a dual-wave receiver. Very few 4-valve sets have a shortwave band.
The Hotpoint substitute
Anyway, the little 4-valve Radiola
I was seeking finally came my way in
the form of a Hotpoint! This was, in
fact, exactly the same as a Radiola but
marketed under another name. Both
sets were made by AWA and there were
sometimes minor cabinet differences
to distinguish the two but not in this
instance.
Unfortunately, the Hotpoint had a
white cabinet with numerous cracks
which showed up as black lines. Although the set was working, it was in
terrible condition with an intermittent contact in the on/off switch and
crackles in both the volume and tone
controls.
But for the miserable sum of $10, it
was worth buying, even if it wasn’t a
Radiola in a Bakelite cabinet.
The old Hotpoint receiver used a couple of unusual valve types: an N78 (6BJ5)
and a 6AR7 GT. Note the shield on the 6AR7, a peculiar characteristic of this
Australian-designed and manufactured valve.
What I didn’t realise at the time was
that there was a suitable Bakelite cabinet stowed away in the shed, which
I had completely forgotten about. I
have no recollection as to where it
came from or how it was acquired.
The Radiola cabinet was discovered
quite by accident while I was looking
for a valve tester which, I might add,
could not be found. No doubt it will
be unearthed while I am looking for
something else some other time.
So it was only a matter of combining
the Hotpoint chassis with the Radiola
cabinet and I would have a working
model of my original little 4-valve
radio.
Cleaning up
The Bakelite cabinet had seen better
October 1996 89
A rear view of Hotpoint chassis. This chassis uses a 5-inch (125mm) permag
speaker whereas many radios of this era still used electrodynamic speakers.
The chassis cleaned up quite well.
days. The dirty front half looked so
different to the reasonably clean back
half that I initially assumed they may
not have been a matched pair.
To explain, each batch of Bakelite
has its own colour char
acteristics
and an unmatched pair of cabinet
halves can stand out like a neon sign.
Fortunately, this was not the case because when the cabinet was washed
and polished, the two pieces blended
together perfectly.
The Radiola dial had been cracked
in two places and this meant that the
Hotpoint dial had to be used. Because
there appears to be no difference between the Radiola and the Hotpoint
radios, I guess I can tolerate a name
change.
Valve types
This 7-pin miniature valve socket is fitted to a chassis that has obviously been
designed for octal valves. The other 4-valve chassis uses an octal 6V6GT in this
position.
90 Silicon Chip
Repairs to the receiver were relatively straightforward and started off
well when all four valves tested OK.
The valves used were: 6BE6 frequency
converter, 6AR7 IF amplifier and detector, N78 (6BJ5) audio output, and
a 5Y3 rectifier.
The valve complement in the Rad
iola 4 varies quite a bit. The other
receiver shown in one of the accompanying photographs uses a 6A8, 6AR7,
6V6 and 6X5. There receivers were
made at a time when manufacturers
often had to use whatever components
were available, not necessarily what
they wanted to use.
Getting back to the Hotpoint valve
line up, the 6AR7 is an odd type in
that it is an Australian-designed and
made valve used only in locally made
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Front view of Hotpoint chassis. The loudspeaker sits directly behind the dial.
Note that the dial setup uses approximately two metres of dial cord.
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The UV People
ETCH TANKS
● Bubble Etch ● Circulating
Shown here are the volume control (left) and the combined tone control and on/
off switch (right). Both potentiometers were repaired by cleaning the resistance
track and repositioning the wiper arm. The switch responded to a flush-out with
a non-lubricating cleaning fluid.
equipment. It usually tests poorly for
some reason or other but this one was
OK. An EBF35 will work in its place
if a 6AR7 is unobtainable.
The N78 is also an unusual output
valve as far as domestic radio receivers are concerned. The only receivers
I have encountered that use this valve
have been these early postwar Radi
olas. Should a substitute valve be required, a 6AQ5 with a rewired socket
and grid bias modification should do
the trick.
Grid bias
Speaking of grid bias, it is worth
noting that many 4-valve receivers
are under biased. In fact, the output
valve’s bias voltage is often at about
half the recommended value, even
taking into account the lower plate
voltages at which some of these small
receivers work.
If the bias is changed in order to
produce the correct voltage, there is
a noticeable drop in output volume.
Presumably, the output valve is
deliberately under biased to raise the
output level of the receiver. One must
remember that a 4-valve receiver is really only a 3-valve receiver (plus rectifier)
and needs every bit of encouragement
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October 1996 91
In the case of the little Hotpoint, a
hollow had been worn through the
resistance track on the tone control.
This control was combined with an
on/off switch and had turned the set
on and off many thousands of times
during its 45-year life span. This problem was eliminated by simply bending
the wiper arm away from the damaged
area and onto an unused portion of
the track.
New capacitors
When the text refers to poor quality thermoplastics, it really means poor quality.
Shown here is a Radiola plastic escutcheon that has badly distorted with age. A
Bakelite escutcheon, on the other hand, would have held its shape, even over a
long period of time.
in the performance department it can
get. Under-biasing the output valve
helps to give a bit more gain on those
weaker signals –even at the expense
of valve life and sound fidelity, which
apparently doesn’t amount to much
anyway.
Problem areas
The worst problem areas of the
receiver were the volume control and
the combined tone control and on/off
switch. These components were very
worn and highly suspect, especially
the on/off switch which was making
such poor contact the dial lights were
flickering in unison. None of these
controls was replaced. Instead, they
were all repaired and they came up
quite OK.
Many volume and tone control potentiometers can be restored to good
working order simply by cleaning the
resistance track. However, this can be
a fairly temporary repair if the track
is worn.
A better repair results if the wiper
arm is bent away from its original
contact path and is placed on a
previously unused part of the track.
Such a simple modification can give
a worn potentiometer a completely
new lease of life.
Faulty on/off switches also respond
well to a cleanup and a flush-out with
a non-lubricating contact solvent is
a good starting point. An ohmmeter
set to the 1-ohm range will quickly
indicate the condition of the switch
contacts. Any measurable resistance
in a switch must eventually cause
trouble.
It is also a good idea to turn old receivers on and off at the power point,
as a 40-50 year old switch deserves a
rest. On cannot expect them to keep
working forever. Any potentiometer
combined with an on/off switch will
also benefit from switching at the
power point, as this will reduce the
wear on the track that would otherwise
occur each time the switch was used.
These replacement control knobs were so tight that the
flats on the control shafts had to be filed down so that
they could be fitted.
92 Silicon Chip
Replacing all of the paper capacitors
with more modern varieties raised
the high tension voltage by 20V. The
electrolyt
ics were the originals and
seemed OK but they were replaced
anyway.
After applying some Silastic® silicone rubber compound to the thin
outer rim of the loudspeaker, it was
time to find three control knobs.
Finding them was not a problem but
getting them to fit the control shafts
was another matter. They were so
tight that breaking them was a distinct
possibility.
This problem was solved by filing
the flats on the control shafts. They can
now be fitted and removed without
risk of breaking.
So there it is: a quick and relative-ly
easy restoration of a humble 4-valve receiver, with a few repair hints thrown
in for good measure.
From my point of view, it was a satisfying project because I could relate
to that particular model receiver. Of
course, it would have been better if
the set had been 100% Radiola. But I
guess a mix of Radiola and Hotpoint
isn’t a bad compromise, especially
when they were both made in the
SC
same factory.
This view shows the replacement loudspeaker cloth
around the dial escutcheon. Even the dial light windows
were removed and cleaned during the restoration process.
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.
Drill speed controller
has limitations
I recently purchased a 5A Heavy
Duty Drill Speed Controller kit, as described in the September & November
1992 issues of SILICON CHIP. Although
called a Drill Speed Controller, your
article does indicate that it is suitable
on all “brush type” motors.
It also indicates that the incorporation of the Silicon Bilateral Switch
has improved the previous circuit
which had the problem of “not being
particularly good at very low speed
settings”.
I purchased the kit for a specific
purpose usage – I have a 5-inch Makita
angle grinder (9800 RPM) and I wanted
to reduce its speed to about 1000-2000
RPM for use as a buffing machine for
polishing cars.
The problem with the controller
seems to be twofold. At low speeds
it seems to make the motor of the
machine click on and off, causing an
unacceptable jarring of the motor (I am
sure it couldn’t be doing the machine
any good!) and, at low speeds, the
power of the machine is so reduced
that it is not practical to use.
To overcome these problems I have
Stopping stray cats
at night
This is a cry for help! I built
your May 1993 Woofer Stop
per
with great success, not for dogs,
but for cats. It was a pleasure to
watch them go like greyhounds
when the Woofer Stopper was
aimed at them.
Now that they have the message
they don’t come near our garden
during the day. Instead, they’ve got
crafty and come during the night
and there’s nothing I can do to stop
them, and this is where the cry
for help comes in. I would like to
build your Woofer Stopper Mk.II
but before I do I would like your
to increase the speed of the motor so
that it spins smoothly to a speed that
unfortunately causes burning of the
paintwork (the reason a normal angle
grin
der cannot be used for buffing
paint).
The technician at the shop where I
bought the kit checked my completed
speed controller and he felt that I had
successfully constructed the kit – he
felt that the problems I have outlined
above are inherent in the device.
I would appreciate your comments
on whether these are typical problems
or whether they can be fixed. If they
cannot then perhaps you should state
on the advertising literature that it is
unsuitable for use on angle grinders.
(R. K., Lismore, NSW).
• It is true that the circuit will work
with most universal “brush type”
motors but we would not go so far as
to say that it will work with “all”. In
general, these motors should not be
used at such a low speed that their inbuilt fan becomes ineffective because
no cooling is then available. It is not
possible to say how long a particular
motor can be used at low speeds but
if the case becomes noticeably warm,
it would be prudent to stop work to
allow it to cool down again.
We should also note that all universal motors, when run with this type of
speed control and at very low speeds,
will have very little useful power
output. Your Makita angle grinder is
designed to run at a very high speed at
which it develops considerable power but it is to be expected that if you
want to run it at below 2000 RPM, its
power output will be feeble. Running
a polishing disc actually requires quite
a lot of power and even the average
3/8-inch electric drill is really not
up to the task – they tend to quickly
overheat.
Your symptom of jarring at very
low speeds is also normal. When a
universal motor is running at a very
low speed it develops very little
back-EMF and so these types of speed
control are subject to “cogging”. Just
how bad this cogging is will depend
on the amount of iron in the field and
armature cores.
Normally, the higher the operating
speed of the motor, the smaller will be
the amount of iron and correspondingly, the cogging will be worse. The only
cure is to run the motor at not such a
low speed setting.
advice on how to bypass the nine
minute timer so that I can switch
it on with the toggle switch for
a whole night. (J. G., Maylands,
WA).
• Disabling the 9-minute timer in
the original Woofer Stopper can be
done by removing Mosfet Q8 and
connecting a shorting link between
its Drain and Source connections
on the board. Alterna
tively, just
remove Q3 and Q8 will be turned
on permanently.
In the Woofer Stopper Mk.II, the
timer is presettable for time intervals of five seconds to 160 seconds.
If you wish to build it without the
timer, omit IC3 and IC4 and connect pin 4 of IC5 permanently high.
I am writing in regard to the Engine
Immobiliser kit that appeared in the
December 1995 issue of SILICON CHIP.
I constructed the circuit and the test
voltages were all close to what they
should be. I then installed the immobiliser into a 1993 model Mitsubishi
Magna and it worked as it should.
However, one day I accidentally left
the ignition on while the Immobiliser was switched on and, after about
five minutes, I could smell someth
ing burning and quickly switched
everything off.
After inspection of the Immobiliser,
I found that the high voltage transistor had overheated to an extent that
the plastic case had partially melted.
Surprisingly, it still worked.
Even though this was an accident,
Car engine immobiliser
melt-down
October 1996 93
Low Voltage Rails for Plastic Power Amplifier
I am about to start the “Plastic
Power Amplifier” featured in the
April 1996 issue of SILICON CHIP
and would be obliged if you would
let me know the following:
(1) Would it be OK to use trannies
I have, which are 300VA toroidals,
giving a 40 volt rail, without compromising the circuit?
(2) If OK, I guess the setting of the
quiescent would remain the same?
(3) Approximately what output
would I have – 100 watts?
(4) Do you use only off-the-shelf
devices and parts; eg, matched
pairs, o/p devices?
Many thanks for your previous
articles. I hope the Plastic Power
amplifier is as good as my SILICON
the same thing would happen if a car
thief was to leave the wires connected
after trying unsuccessfully to steal my
car. I would then return to the carpark
and find nothing but a pile of molten
metal! I am confident that the circuit
was constructed and installed correctly. It operates fine over any period of
time when the key is in accessory position. However, when the ignition is on,
+12V is present at the coil connection
and the circuit overheats.
Could this be a design fault? If so,
how could it be rectified? (T. V., North
Adelaide, SA).
• We think that your unit may be
malfunctioning. When transistor Q1 is
turned on, the current through the coil
should be no more than about four or
five amps, as determined by the coil
resistance and its associated ballast,
if it has one. Hence, the transistor
should only be dissipating about 6 or
7W, when it is turned on.
However, the transistor is only
turned on for about 0.7 seconds in 2.9
seconds (0.7s on, 2.2s off) or 24% of
the time. Therefore, even if the circuit
is powered up continuously, the power
transistor should only dissipate less
than 2W. This will make it hot but
is not likely to be enough to melt the
plastic case or your car!
It should be possible to check for
correct operation of the Immobiliser
with it out of the car. Connect a 1kΩ
resistor between the collector of Q1
and the +12V supply and then apply
94 Silicon Chip
CHIP amplifier using boards SC111287 (December 1987) which more
than compares with a Tandberg
amplifier I had (to me anyway). (H.
M., Balga, WA).
• You can run the amplifier with
40V rails; the quiescent current
setting would be the same. However, the power output would be
markedly reduced, to around 50W
into an 8Ω load or 100W into 4Ω
loads.
We have not bothered to use
matched output devices in our
circuits because they are generally
not readily available. However, the
use of matched pairs can produce
a slight reduction in the harmonic
distortion of an amplifier.
power. Use your multimeter to measure the voltage between collector and
emitter of Q1. It should be +12V (or
close to it) for 2.2 seconds, then close
to 1V for 0.7 seconds, and so on. If it
does not follow this sequence, check
the operation of Q2 and the 555.
Zener diode tester has
incorrect transformer
I purchased a zener diode test kit
from Dick Smith Electronics and have
noted a couple of changes to the original circuit as published in the March
1996 of your magazine:
(1) T1 has prewound secondary winding with 136 turns and not 40 as per
circuit. The primary winding was 18
turns and not 20 as per circuit and this
was for the constructor to wind. The
transformer in your article was stated
to be a 2:1 step up transformer, thus the
windings on the supplied transformer
made it, by my calculations, to be a
7.5:1 step-up transformer.
(2) ZD1 was a 75V 5W diode not 56V
3W as in the March 1996 circuit.
I decided to construct the circuit as
supplied and on completion the output voltage measured 470V instead of
112V. I checked and double checked
with no change to my test results, so
I decided to rewind the transformer
with 36 turns to the secondary and 18
turns to the primary, as I felt this would
make it a 2:1 step up, and also be more
in line with the original circuit. The
output voltage now read 141V. As ZD1
is higher than original specs, the higher voltage output of 141V is probably
acceptable. On testing known value
zener diodes, the circuit appears to
be measuring correctly.
Could you please advise me of the
implications of changing the ratio of
turns on windings as I have done with
my circuit. (G. M., Seven Hills, NSW).
• We are aware that Dick Smith Electronics has been supplying a different
transformer. However, the zener diode
should still be 56V as specified, in
order to be certain that the various
versions of MTP3055 which may be
used will not break down.
The turns ratio for the transformer
does not need to be precisely 2:1 since
the circuit has current feedback from
the Source of Q1 and this controls the
overall level of power delivered to the
zener diode under test. However, the
turns ratio should still be in the region
of 2:1 for correct operation, given that
zener diode ZD1 is 56V. Accordingly,
with the 136 turn secondary, the primary winding should be somewhere
between 60 and 70 turns. Alternatively, as you have found, the transformer
can be wound with lesser turns on
the primary and secondary and with
a ratio of 2:1.
We have advised Dick Smith Electronics to this effect.
Making Clifford work
in daylight
I built your Mini Electronic Cricket
(Clifford) as described in the December
1994 issue of SILICON CHIP. I would
like to know how to reverse the LDR
so it comes on in the light. (I. B.,
Strathpine, SA).
• It should be possible to make the
circuit operate in ambient light by
swapping the positions of the LDR and
the associated 47kΩ resistor.
Notes & Errata
Fluorescent Lamp Starter, August
1996: the circuit diagram on page 16
shows D1-D4 as 1N4004 diodes. They
should be 1N4007 1000V types, as
specified in the parts list.
2-Amp SLA Battery Charger, July
1996: the wiring diagram on page
57 has reversed polarity signs on the
output cable crocodile clips. The cable
coming from the lefthand side of the
SC
PC board should be positive.
MARKET CENTRE
Cash in your surplus gear. Advertise it here in Silicon Chip.
FOR SALE
LARGE VALVE AMPLIFIER: Make an
offer. Greg Wolfe, Warne Street, Bombala. Phone (064) 58 3663.
CUSTOM CIRCUIT BOARDS: For all
your single and double-sided prototypes.
Prompt service, competitive rates.
Phone (03) 6228 2600.
KITS KITS KITS: EPROM Emulator
CLASSIFIED ADVERTISING RATES
Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50
cents for each additional word. Display ads (casual rate): $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 below & 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) 9979 6503.
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$103.70. PIC 16C84 programmer
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Disassemblers for 12 CPUs only $75.
Demo disk: FREE. All prices + $5 p&p.
GRANTRONICS PTY LTD, PO Box 275,
Wentworthville 2145. Ph/Fax (02) 9631
1236 or Internet:
http://www.mpx.com.au/~lgrant
EASY PIC’n Beginners Book to using
MicroChip PIC chips $50, Basic Compiler to clone Basic Stamps into cheap
❏ Bankcard ❏ Visa Card ❏ Master Card
Card No.
✂
Enclosed is my cheque/money order for $__________ or please debit my
RCS RADIO PTY LTD
Signature__________________________ Card expiry date______/______
Name ______________________________________________________
Street ______________________________________________________
Suburb/town ___________________________ Postcode______________
RCS Radio Pty Ltd is the only company that manufactures and sells every
PC board and front panel published
in SILICON CHIP, ETI and EA.
RCS Radio Pty Ltd,
651 Forest Rd, Bexley 2207.
Phone (02) 587 3491
October 1996 95
Your next project will be easy, fast and satisfying with a development kit from
MicroZed Computers
Scott Edwards Electronics
Microchip
OPTO 22 NEW Micro
Micro Engineering Labs (PICBASIC)
MICROMINT
PicStic
DOMINO
BLACKJACK
PO Box 634, ARMIDALE 2350 (296 Cook’s Rd)
Advertising Index
Altronics................................. 76-78
Ph (067) 722 777 – may time out to Mobile 014 036 775
Fax (067) 728 987 (Credit Cards OK)
Av-Comm.....................................17
http://www.microzed.com.au
B & M Electronics........................91
Specialising in easy-to-get-going hard/software
kits.
Send 2 x 45c stamps for information package
Stamp kits now have a compiler for 16C58
Dick Smith Electronics........... 28-31
Earthquake Audio........................79
EDA Solutions.............................21
MEMORY * MEMORY * MEMORY
SPECIAL! (Ex Tax)
1Mbx9 – 70ns
$18
30-pin Simms
PIC16C84’s $135, CCS C Compiler
$145, heaps of other PIC stuff, Programmers from $20, Real Time Clock,
A-D. Ring or fax for FREE promo disk.
WEB search on Dontronics, PO Box
595, Tullamarine 3043. Phone 03 9338
6286. Fax 03 9338 2935.
SIMMS
(Parity/No Parity)
4Mb 30 PIN-70
$47
$63
4Mb 72 PIN-70
$50
$42
8Mb 72 PIN-70
$90
$67
16Mb 72 PIN-70 $167 $143
32Mb 72 PIN-70 $355 $284
EDO SIMMS
8Mb (1Mbx32) – 60ns $76
16Mb (2Mbx32) – 60ns $144
32Mb (4Mbx32) – 60ns $290
MAC MEMORY
8Mb P’BOOK 190 $147
8Mb DOCK DUO $249
16Mb P’BOOK $257
MicroZed Web page always under construction. http://www.microzed.com.au
KIT CONSTRUCTION: Electronic and
speaker kits assembled at reasonable
prices. Money back guarantee. Phone
(014) 93 1227.
96 Silicon Chip
Emona.........................................81
Freedman Electronics....................9
Harbuch Electronics....................79
Instant PCBs................................96
Jaycar ................................... 45-52
Kalex............................................91
Ex Tax Pricing – Delivery $8. Pricing as at 28/8/96. Phone for latest.
Sales Tax 22%.
Credit Cards Welcome. We Also Buy And Trade-In Memory.
PELHAM
Memory Pty Ltd
MICROCRAFT PRESENTS: Dunfield
(DDS) products are now available
ex-stock at a new low price; please
ask for our catalogue. Micro C, the
affordable “C” compiler for embedded
applications. Versions for 8051/52,
8086, 8096, 68HC08, 6809, 68HC11
or 68HC16 $139.95 each + $3 p&h •
Now on special is the SDK, a package
of ALL the DDS “C” compilers for $399
+ $6 p&h • EMILY52 is a PC based
8051/52 high speed simulator $69.95 +
$3 p&h • DDS demo disks $7 + $3 p&h •
VHS VIDEO from the USA (PAL) “CNC
X-Y-Z using car alternators” (uses car
alternators as cheap power stepper
motors!) $49.95 + $6 p&h (includes
diagrams) • Device programming
EPROMs/PALs etc from $1.50 • Fixed
price electronic design and PCB layout
• Credit cards accepted • All goods
sent certified mail • Call Bob for more
details. MICROCRAFT, PO Box 514,
Concord NSW 2137. Phone (02) 744
5440 or fax (02) 744 9280.
LASER PRINTER MEMORY
2Mb UPGRADE
$150
COMPAQ
8Mb CONTURA AERO
$147
All other models available $Call
TOSHIBA
8Mb Portege/ Sat EDO
$135
16Mb Portege/ Sat EDO
$235
16Mb Tecra 500/610 Sat $298
All other models available $Call
CACHE
256K PIPELINE BURST
$25
256K 7200/8500
$100
VIDEO MEMORY
256K x 16 70ns (SOJ)
$17
1Mb 7200/7500/9500
$83
SO DIMMS
8Mb/16Mb
$108/227
Suite 6, 2 Hillcrest Rd,
Ph: (02) 9980 6988
Pennant Hills, 2120.
Fax: (02) 9980 6991
Email: pelham1<at>ozemail.com.au
Kits-R-US.....................................80
MicroZed Computers...................96
Oatley Electronics..........................7
RAIN BRAIN 8-STATION SPRINKLER
KIT: Z8 smart temp sensor, LED display,
RS232 to PC. Uses 1 to 8 DALLAS
DS1820. Call Mantis Micro Products,
38 Garnet Street, Niddrie, 3042. P/F/A
(03) 9337 1917.
mantismp<at>c031.aone.net.au
Pelham........................................96
RCS Radio ..................................95
Rod Irving Electronics .......... 60-64
Silicon Chip Bookshop...............IBC
MicroZed has MICROCHIP NEW
PICSTART kits also Programmers from
Parallax and Micro. Eng. Lab.
Silicon Chip Software..................87
68HC705 Development System:
Oztechnics, PO Box 38, Illawong NSW
2234. Phone (02) 9541 0310. Fax (02)
9541 0734.
http://www.oztechnics.com.au/
Silicon Chip Wallchart..............OBC
WANTED
WANTED: Circuit of Silver SS171. Box
535 Geraldton, WA 6531. Tel (099) 21
2176.
SWAP MEET
VINTAGE RADIO SWAP MEET: Sunday October 20th 1996. Glenroy Tech
School Hall, Melbourne, Victoria. Mel
way Ref Map 16.K.2. Admis
sion $3.
Inquiries (054) 49 3207.
Silicon Chip Back Issues.............10
Tortech.........................................20
Zoom Magazine.........................IFC
_________________________________
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.
electronic design, and applications.
The sixth edition has been expanded
to include chapters on surface mount
technology, hardware & software
design, semicustom electronics &
data communications. 63 chapters,
in hard cover at $120.00.
Silicon Chip Bookshop
Radio Frequency
Transistors
Newnes Guide
to Satellite TV
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.
Guide to TV & Video
Technology
By Eugene Trundle. First publish-
ed 1988. Second edition 1996.
Eugene Trundle has written for
many years in Television magazine
and his latest book is right up date
on TV and video technology. 382
pages, in paperback, at $39.95.
Servicing Personal
Computers
By Michael Tooley. First published 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.
format and R-DAT. If you want to
understand digital audio, you need
this reference book. 305 pages, in
paperback at $55.95.
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.
336 pages, in paperback at $49.95.
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.
Digital Audio & Compact
Disc Technology
Electronics Engineer’s
Reference Book
Hard cove
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
Power Electronics
Handbook
Your Name__________________________________________________
PLEASE PRINT
Address____________________________________________________
_____________________________________Postcode_____________
Daytime Phone No.______________________Total Price $A _________
❏ Cheque/Money Order
r
Edited by F. F. Mazda. version now
available
First published 1989.
6th edition.
This just has to be the best refer
ence book available for electronics
engineers. Provides expert coverage
of all aspects of electronics in five
parts: techniques, physical phenomena, material & components,
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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.
Principles & Practical Applications. By Norm Dye & Helge
Granberg. Published 1993.
This 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, impedance matching
& CAD. 235 pages, in hard cover
at $85.00.
Surface Mount Technology
By Rudolph Strauss. First pub
lished 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.
Audio Electronics
By John Linsley Hood. Published
1995.
This book is for anyone involved
in designing, adapting and using
analog and digital audio equipment. Covers tape recording,
tuners & radio receivers, preamplifiers, voltage amplifiers, power
amplifiers, the compact disc &
digital audio, test & measurement,
loudspeaker crossover systems
and power supplies. 351 pages, in
soft cover at $52.95.
Title
Newnes Guide to Satellite TV
Guide to TV & Video Technology
Servicing Personal Computers
The Art Of Linear Electronics
Digital Audio & Compact Disc Technology
Power Electronics Handbook
Electronic Engineer's Reference Book
Radio Frequency Transistors
Surface Mount Technology
Audio Electronics
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
Price
$55.95
$39.95
$59.95
$49.95
$55.95
$59.95
$120.00
$85.00
$99.00
$52.95
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