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SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
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Please feel free to visit the advertiser’s website:
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Contents
Vol.10, No.2; February 1997
FEATURES
4 Computer Problems: Sorting Out What’s At Fault
It pays not to jump to conclusions when your computer plays up. We take a
look at a couple of typical problems – by Greg Swain
66 Cathode Ray Oscilloscopes; Pt.6
Digital oscilloscopes can give misleading results if not used correctly. Here’s
how to interpret the on-screen display – by Bryan Maher
PROJECTS TO BUILD
10 PC-Controlled Moving Message Display
This easy-to-build moving message display plugs into your PC’s parallel port.
You just type the message in on the keyboard – by John Western
COMPUTER PROBLEMS: SORTING
OUT WHAT’S AT FAULT – PAGE 4
16 Computer Controlled Dual Power Supply; Pt.2
This month, we describe the interface board that lets you control the supply
from your computer – by Rick Walters
24 The Alert-A-Phone Loud Sounding Alarm
This very loud ringer plugs in parallel with your existing telephone and is
Austel approved – by Derek Diggles
40 Build A Low-Cost Analog Multimeter
You can learn about multimeters and kit assembly by building this simple unit.
And you’ll wind up with a useful test instrument – by Leo Simpson
BUILD A PC-CONTROLLED MOVING
MESSAGE DISPLAY – PAGE 10
56 Control Panel For Multiple Smoke Alarms, Pt.2
The full construction and installation details are in this month’s issue. Build it
and control up to 10 smoke detectors – by John Clarke
SPECIAL COLUMNS
30 Serviceman’s Log
Don’t monkey with a VCR – by the TV Serviceman
53 Satellite Watch
The latest news on satellite TV – by Garry Cratt
74 Radio Control
THE ALERT-A-PHONE LOUD
RINGER – PAGE 24
How models can be lost through interference – by Bob Young
86 Vintage Radio
The combined A-B battery eliminator – by John Hill
DEPARTMENTS
2
38
54
82
90
Publisher’s Letter
Mailbag
Circuit Notebook
Product Showcase
Back Issues
92
93
94
95
96
Ask Silicon Chip
Notes & Errata
Order Form
Market Centre
Advertising Index
CONTROL PANEL FOR MULTIPLE
SMOKE ALARMS – PAGE 56
February 1997 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
Brendon Sheridan
Phone (03) 9720 9198
Mobile 0416 009 217
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
Photography
Glenn A. Keep
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
Tariff reductions on cars
may not be wise
As this issue goes on sale, we can expect that
the Government will be placed under intense
pressure to speed up tariff reduction in the car
industry. Just before Christmas, the Produc
tivity Commission brought down a majority
report that urged tariff reduction from 15%
in 2000 to just 5% in 2004. Presently, tariffs
on imported cars are at a level of 25% and to
reduce them to 5% in less than 10 years is a
huge reduction in anyone’s language.
Many economists would argue that Australia should proceed down the path of
tariff reduction for all economic activities and in terms of hard financial figures,
they are undoubtedly right. When tariffs are removed or reduced, the products
affected invariably are reduced in price and consumers are better off. But will
we be better off overall?
We have already seen this happen with electronics consumer products and
there is no doubt that they are much cheaper now than they would have been
if tariffs had been maintained. The problem is that while all those goods are
undoubtedly cheaper, we have also lost a great number of skills that went with
the manufacturing and servicing of those electronic products. Not only the
skills but most of the jobs have been lost and in many cases the people directly
affected have never got equivalent satisfying employment again, if they have
managed to get jobs at all.
The same thing will happen as tariffs are reduced on cars. New cars and sec
ondhand cars will become cheaper. But then we will lose many thousands of
jobs in manufacturing, not only in the car industry itself but in all of the support
industries, and that includes some electronics manufacturing, surprising though
it might seem. But it will go much further than that. If new cars are cheaper,
then it will become uneconomic to repair cars. So we will inevitably lose huge
numbers of jobs in repair shops – not only mechanical repairs but in smash
repair shops as well. Many more cars will simply be written off and sent to the
crushers after even quite minor accidents.
It is fairly safe to say that most of the people working now in the car manufac
turing and repair industries would never get equivalent jobs again. And youth
unemployment which is unacceptably high now, will go even higher.
No, while we would all like to buy cheaper cars and enjoy the safety and
driving pleasure that a new car entails, we will be paying a huge social price if
we go down that road too rapidly. Sure, we are paying a high price to effectively
subsidise a lot of jobs in the car industry. But people and the general community
are always better off if they are gainfully employed instead of being on the dole.
Let us hope that the history of the Australian electronics consumer industry
is not repeated in the car industry.
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
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
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Macservice Pty Ltd
*!#$*&<at>*
COMPUTERS
Sorting out what’s really to blame
If there’s one thing I’ve learnt about computers
over the years, it’s not to jump to conclusions
when something doesn’t work properly. When
things go wrong, it’s all too easy to blame the
obvious, without getting to grips with what’s
really at fault.
By GREG SWAIN
How often have you heard that a par
ticular operating system is unstable?
Or that it doesn’t work on such and
such a computer? Or that a particular
item of hardware has a “bug” and
should be avoided? Or that something
just doesn’t work when your own ex
perience indicates otherwise?
When it comes to computers, there
are enough real problems to sort out
without having to also sift through a
mine of misinformation, straight-out
even been told that PCs are no good
in this role because “they just don’t
work” and because “they have font
problems”.
Well, you could have fooled me.
There we’ve been all those years, suc
cessfully producing a magazine using
PCs that don’t really work – at least
according to the hearsay of several
self-appointed experts.
What rubbish! We’ve used PCs in
the desktop publishing role for over
“A computer is really a box full of
gremlins, just waiting to wreak all
sorts of havoc at the user’s expense”.
bad mouthing and old wives’ tales.
I’d like a dollar for every time that
someone has rolled their eyes to the
ceiling when told that SILICON CHIP
is produced using PCs, for example.
I mean, everyone knows that Macs
are the all the go when it comes to
desktop publishing, don’t they? I’ve
4 Silicon Chip
six years now with very few problems
but try telling that to some people.
Not that it’s ever really worth the
bother – a few pointed questions in
variably reveal that such people know
very little about PCs, and are simply
basing their opinions on “common
knowledge”.
It’s all the stuff of myths and legends
but if it’s “common knowledge”, then
it must be true. I’m not seeking to belit
tle Macs here, by the way. I’m simply
making the point that the PC is a valid
alternative for desktop publishing, de
spite what many ill-informed people
will try to tell you.
The most common misconceptions
by far arise out of hardware and soft
ware upgrades. The reasons are not
too hard to find. Hardware upgrades,
in particular, are often not straight
forward for a variety of reasons. After
several recent experiences of my own,
I’m convinced that a computer is
really a box full of gremlins just wait
ing to wreak all sorts of havoc at the
poor user’s expense.
OK, so I’m exaggerating somewhat
but if you’ve ever attempted to add
hardware to a PC, you’ll know what
I mean. Even Windows 95’s much
vaunted Plug and Play (PnP) system
has problems in some circumstances.
Let me give you a couple of examples
of what can happen when even rela
tively simple upgrades are attempted.
The not-so-crook RAM
Recently, we decided to upgrade
the RAM in a couple of our office
machines from 32Mb to 64Mb. These
two machines used identical mother
boards and in each case, the existing
RAM consisted of two 16Mb SIMMs.
As a result, we decided to purchase
two new 32Mb SIMMs for the first
machine and transfer its existing 16Mb
SIMMs to the second machine.
Installing the new 32Mb SIMMs was
straightforward enough but when we
We solved the problem by leaving
the new SIMMs in the third machine
and sharing its original four 16Mb
70ns SIMMs between the first two
machines. So all three machines ended
up with 64Mb of RAM – it’s just that
the two new 32Mb SIMMs ended up
in an unexpected location.
But it’s easy to see how misun
derstandings can arise in this sort of
situation. We could have easily been
fooled into returning perfectly good
RAM to the supplier, demanding that
it be replaced. And of course, the re
placement RAM would have caused
exactly the same problems.
upgrades. Win95 cannot automati
cally assign interrupts (IRQs) to nonPnP expansion cards (now referred
to as “legacy” cards) and can easily
get itself into a knot if left to its own
devices.
To explain, a standard PC has 16
interrupts (0-15) available but most of
these are taken by the system, leaving
about six free for expansion cards (de
pending on the configuration). Each
expansion card must be assigned a
unique IRQ; if two cards have the same
IRQ, there will be a conflict and the
system won’t work properly.
The “minimalist” approach usually
works well when install
ing Win95,
particularly if you have a mixture of
legacy and PnP cards. This involves
removing all non-essential cards, such
as sound cards and network cards,
before installing the software. Once
the system is up and running properly,
you can add the expansion cards back
in, one at a time.
By the way, it’s best to add the legacy
cards first, as the PnP cards are auto
matically assigned the leftover IRQs.
In addition, the system assigns IRQs
to PnP cards in ISA slots before those
in PCI slots.
Note also that you should reserve
the appropriate IRQs for the legacy
cards in the system BIOS, where this
facility exists (ie, if the motherboard
has a PnP BIOS). This will usually be
found under a “Plug and Play Config
uration” (or similar) menu. For exam
ple, if you have a legacy card that’s set
to IRQ10, then you must assign IRQ10
for use by an ISA card.
The above step is quite important. If
you don’t do it, Win95 may automat
ically assign an IRQ that’s already in
use to a PnP card.
Operating system myths
The suspect motherboard
There are also plenty of myths
floating around regarding operating
systems. One that I’ve heard from a
couple of people is that Windows 95
needs a Pentium processor and won’t
run on a 486. Wrong! What they really
mean is that they couldn’t get it to
work on their particular 486 for some
reason or other.
To prove the point, we recently
installed the Win95 upgrade pack on
an old 50MHz 486 machine. It ran
without a hitch and I’ve even heard
of people running Win95 on a 386.
Hardware conflicts are often the
root cause of aborted operating system
It’s not just hardware conflicts that
can be a problem. Hardware bugs can
also cause problems and lead to unfair
criticism of an operating system or
even individual programs.
Consider my own experiences with
Windows 95 which is installed on my
main office machine. This is one of
the machines described above that
didn’t like the 60ns 32Mb SIMMs and
the problem I am about to describe
is directly related to the memory
upgrade.
As mentioned earlier, this machine
was originally configured with 32Mb
of RAM (2 x 16Mb SIMMs). It is set up
This new motherboard cured an unstable Windows 95 installation. The bus
speed of the motherboard in the original machine had apparently been pushed
beyond its design limitations – or, at least, that’s one theory.
switched on, the machine refused to
boot. Sometimes it would just hang
after completing the BIOS checks. At
other times, it would start to boot the
operating system and then halt, with a
screen full of obscure error messages.
Our first thought was that we must
have dislodged a cable when installing
the new RAM but a quick check re
vealed that all was as it should be. Our
next snap diagnosis was crook RAM
and this was seemingly confirmed
when it also failed to work in the sec
ond machine. Yet when we substituted
the old RAM, both machines booted
without problems.
That was it, of course – one of those
new 32Mb SIMMs just had to be faulty!
But was it? Perhaps the problem was
in the two machines which, after all,
were virtually identical. The only way
to find out was to try the new SIMMs
in a third machine with a completely
different motherboard. When we did,
it booted straight up and performed
flawlessly.
So much for our snap diagnosis of
faulty RAM! Instead, it appears that the
motherboards in the first two machines
weren’t happy with the 60ns RAM
on the new SIMMs (the older SIMMs
used 70ns RAM). And there were no
settings in the system BIOS that could
compensate for this.
February 1997 5
You can easily check for
hardware conflicts in
Win95 by double-clicking
the “System” icon in
“Control Panel”, then
selecting the “Device
Manager” tab. Doubleclicking on a specific
device then gives you
the “Resources” tab,
which lets you view the
resources allocated.
as a dual-boot Windows 3.11/Win95
system but I was never entirely happy
with the system under Windows 95
as it occasionally crashed when the
going got heavy.
My first inclination was to blame
which ever program I happened to
have running at the time but eventu
ally I began to suspect Windows 95
itself. However, the pattern was too
intermittent to really get to grips with
the problem.
The breakthrough came when
6 Silicon Chip
the extra 32Mb of RAM was added.
Windows 3.11 continued to work
normally but not so Windows 95. It
now frequently crashed, generat
ing
“Unexpected Exception” errors in the
process. And when it crashed, it would
often refuse to boot again unless the
additional RAM was removed.
This meant that the problem was
probably hardware related. Initially,
I simply tried replacing the original
RAM with the second two 16Mb
SIMMs but this made no difference.
I also tried swapping memory banks
and substituting the memory from the
machine’s twin without result.
By now, the finger of suspicion was
pointing fairly and squarely at the
motherboard. After all, it had previ
ously failed to work with the 32Mb
SIMMs, so it was definitely suspect
when it came to handling memory.
And there was another thing. The
machine ran a 133MHz Pentium
processor but the manual that came
with the motherboard only mentioned
75MHz and 90MHz processors. An
8-way DIP switch is used to set the
bus and processor clock speeds but the
manual gave no details of the settings.
Fortunately, the settings were
screen-printed on the moth
erboard
in a vacant area adjacent to the micro
processor. But what was interesting
was that the machine’s twin, which
was purchased four months later,
also showed an additional setting for
a 100MHz processor. And both ma
chines were set to this configuration.
That aside, the motherboard was
obviously originally designed to op
erate at a bus speed of either 60MHz
when used with a 90MHz processor, or
50MHz when used with a 75MHz (or
100MHz) processor. That’s because the
processor always runs at some ratio of
the bus frequency, the available ratios
in this case being 1.5x and 2x (ie, 1.5
x 50MHz = 75MHz, 1.5 x 60 = 90MHz,
and 2 x 50MHz = 100MHz).
So what was going on? A 133MHz
processor requires a 66MHz bus so
the board must have been tweaked to
run at this higher speed – probably by
the simple expedient of substituting
a different crystal in the clock circuit
during manufacture. Fairly obviously,
this was an existing design that had
been hastily adapted to cater for the
faster processor but it appeared that
it wasn’t up to the task – at least not
with Windows 95.
There was nothing for it but to
change the board.
It ain’t that easy
Now if you thought that changing
the motherboard in a Win95 system
was a straightforward task, think again.
The mechanical installation is easy
enough but getting everything up and
running again is a different matter.
Windows 3.11 was OK (it’s too dumb
to recognise the swap) but Windows
95 is too clever by halves, tying itself
in all sorts of knots when it discovered
SILICON CHIP SOFTWARE
Now available: the complete index to all
SILICON CHIP articles since the first issue
in November 1987. The Floppy Index
comes with a handy file viewer that lets
you look at the index line by line or page
by page for quick browsing, or you can
use the search function. All commands
are listed on the screen, so you’ll always
know what to do next.
Notes & Errata also now available:
this file lets you quickly check out the
Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index
but a complete copy of all Notes & Errata text (diagrams not included). The file
viewer is included in the price, so that you can quickly locate the item of interest.
The Floppy Index and Notes & Errata files are supplied in ASCII format on a
3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File
Viewer requires MSDOS 3.3 or above.
ORDER FORM
PRICE
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Floppy Index (incl. file viewer): $A7
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❏
Alphanumeric LCD Demo Board Software (May 1993): $A7
❏
Stepper Motor Controller Software (January 1994): $A7
❏
Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7
❏
Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7
❏
Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7
❏
Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7
❏
I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7
POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5
Disc size required: ❏ 3.5-inch disc
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order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number
(Bankcard, Visa Card or MasterCard).
✂
the new motherboard.
This problem apparently stems from
the fact that the parameters of the new
motherboard and its BIOS don’t match
the existing registry settings. In the
end, the only way around the problem
was to clean off the existing installa
tion and its associated applications
and reinstall all software.
If you’re ever in this situation, by
the way, don’t be tempted to simply
reinstall the operating system over
the top of the existing installation. It’s
best to clean everything off and go for
a fresh installation.
The Win95 reinstallation was not
without a small glitch, however. I’d
removed the sound card but left in
a SCSI card and a PnP network card.
Everything went fine until the first
boot. Windows 95 made it past the
logon dialogs but then announced that
it was searching for new hardware.
There followed a brief period of hard
disc activity, after which it just “hung”.
I tried switching the machine on
and off several times but always with
the same result. Eventually, I pulled
the network card and tried again. And
that was it – the system now booted
correctly and I was able to reintroduce
the sound and network cards.
Windows 95 now recognised the
network card, installed the correct
driver for it and automatically as
signed an available IRQ. Now why
didn’t it do that in the first place?
Did the new motherboard do the
trick? Well, based on my limited obser
vations so far, the answer is yes. I now
have a stable Windows 95 installation
but just think how easy it would have
been to jump to conclusions and badmouth the operating system.
Strangely enough, the other ma
chine with the identical motherboard
operates perfectly with its 64Mb of
RAM but then it’s running Windows
NT. So is Windows 95 fussier than NT
about the hardware company it keeps?
Or was it just a matter of manufac
turing tolerances between the two
boards? Or was the problem caused by
some subtle hardware conflict which is
now resolved and nothing to do with
the motherboard at all?
Finally, could I have cured the prob
lem by changing the DIP switches so
that the motherboard ran at a slower
bus speed (yes, this would have throt
tled back the processor)?
We’ll probably never know the an
SC
swers to those questions.
February 1997 7
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
PC-controlled moving
message display
Have you got an old PC sitting around
gathering dust? You can use it to control this
moving LED message display which plugs
into the PC’s printer port. All you have to do
is type the message in on the keyboard.
Design by JOHN WESTERN
Moving LED message displays are
common in shops and clubs and are
very effective as advertising signs.
Now you can have your own by build
ing this unit. All you need to drive it
is an old XT (or better) computer and
you can easily set the unit up to repeat
a message or a number of messages.
While LED message displays use a
variety of formats, this one employs
characters which are seven LEDs high
by five LEDs across and these move
along the LED array at a fixed rate.
As presented here, the display con
sists of a 48 x 7 LED matrix arranged
10 Silicon Chip
on a single large PC board. This board
basically consists of three 16 x 7 LED
modules: a master module which also
contains the necessary parallel port
interface circuitry, and two extension
modules. Each module has enough
LEDs to display three characters,
which means that the basic unit can
display up to nine characters at any
given time.
If you wish, you can increase the
display width by adding another one
or two extension modules. This will
allow either 12 or 15 characters to
be displayed at any one time. The
additional extension modules are sim
ply cut from a second PC board and
connected to the lefthand end of the
message display using 12 wire links.
Conversely, you can reduce the
display width by cutting off one of
the extension modules, to give a 32 x
7 (6-character) LED display.
Of course, the length of the message
is not limited by the number of char
acters that can be displayed at any
one time. Basically, you can make the
message as long as you like. In opera
tion, the leading characters appear on
the righthand side of the display and
scroll across to the lefthand side before
disappearing off the “edge”. The mes
sage continues scrolling until all the
characters have been displayed and
can easily be set up so that it repeats.
Our prototype was built to the stand
ard 9-character configuration; ie, a sin
gle PC board with three modules. This
is housed in a folded smoked-Perspex
case to produce an attractive display.
It is powered by a 12V AC plugpack
and is connected to the parallel port
of the PC via a DB25 socket mounted
on one end of the board.
How it works
Each character to be displayed is
produced by turning on all the appro
priate LEDs in a row for a short period
of time. This is repeated for each of the
seven rows, to make up the character
in a multiplexed fashion. Because
this happens at a very high rate, all
the LEDs appear to be turned on at
the same time.
Fig.2 shows the circuit diagram of
the Moving LED Display. Each row of
LEDs is driven by a Darlington tran
sistor pair consisting of a BC549 and a
BC639; ie, Q1 & Q2 for row 1, Q3 & Q4
for row 2, etc. These seven Darlington
transistor pairs are in turn driven by
the printer port data lines.
Note that each line from the printer
port is filtered by an RC network con
sisting of a 47Ω resistor and a 220pF
capacitor. These filters prevent noise
pulses from disturbing normal opera
tion of the display.
The LED columns are controlled by
separate BC549 transistors (Q15, Q16,
etc), in turn driven by 74LS164 shift
registers (one for each group of eight
columns). These shift registers accept
the serial data applied to their A & B
data inputs and convert it to parallel
format at their Q0-Q7 outputs. So each
shift register controls eight transistors
Fig.1: this diagram gives a breakdown of the basic operation just to
light one LED. In this case, we want to light the LED at row 4 column
3 (ie, R4,C3). This involves clocking a logic 1 into the shift register
and then moving it until the third output goes high, represented here
by the closed switch between the shift register and C3. Switch SW3 is
then closed to light the row
and thus eight LED columns.
Note that, for the sake of clarity,
our circuit only shows the first eight
LED columns, their corresponding
transistors (Q15-Q22) and one shift
register (IC1). The circuitry for each
successive eight columns is identical,
with pin 13 of IC1 clocking the data
inputs of the next shift register, and so
on down the chain.
IC1 is driven by one of the parallel
printer port data lines, while two
other data lines drive the clock and
reset pins (pins 9 & 8). Basically, data
is shuffled into IC1 in serial fashion
and its appropriate Q outputs go high,
thereby turning on the corresponding
column transistors. One of the row
data lines is then briefly taken high
to light the required LEDs.
In greater detail, the character to
be displayed is broken down into
the required pattern of dots for each
row. Initially, the shift registers are all
cleared by applying a pulse to the MR
line. This sets all outputs to a logical
low condition, turning all columns off.
The required data is then applied to
the A & B data inputs and the CLK line
pulsed to move the data into the first
shift register. Successive data is sub
sequently applied in a similar fashion
until the required pattern of dots for
a particular row is set up in the shift
registers. Once the data is ready, the
row is turned on for a short period of
time after which the shift register is
cleared (reset) and the process starts
again for the next row.
Fig.1 gives a breakdown of the basic
operation just to light one LED. In this
case, we want to light the LED at row
4 column 3 (ie, R4,C3). This involves
clocking a logic 1 into the shift regis
ter and then moving it until the third
output goes high, represented here by
the closed switch between the shift
register and C3. Switch SW3 is then
closed to light the row, in this case the
single LED at R4,C3.
February 1997 11
Where To Buy The Parts
The parts for this design are available from Oatley Electronics, PO Box 89,
Oatley, NSW 2223. Phone (02) 9584 3563; fax (02) 9584 3561. The options
are as follows:
Complete Kits (does not include case)
(1) PC board, all on-board parts, software on 3.5-inch disc, a surplus plugpack
& bright red, green or amber LEDs (you specify): $165
(2) Above kit with super bright LEDs (narrow viewing angle): $200
Shortform Kits & Accessories
(3) PC board only plus software on 3.5-inch disc: $75
(4) 336 bright LEDs (red, green or amber – please specify): $45
(5) 336 super bright LEDs: $90
(6) Suitable small 10.6V 1.4A surplus switchmode power supply in case: $12
Note 1: none of the above options includes a case or the Perspex channel
shown in the photos. Please add $6.00 p&p to any combination.
Note 2: the PC board associated with this design is copyright Oatley Electronics. In addition, the software supplied is copyright John Western and must
not be altered in any way or used for other purposes without permission.
Note, however, that the basic circuit
of Fig.1 works in the opposite sense to
the circuit of Fig.2. In reality, the shift
registers drive transistors and these
provide logic lows, while the printer
port data lines and their associated
Darlington transistors pull the rows
high.
To sum up, the printer port data
lines pull each row high in succes
sion to light the appropriate LEDs.
And in between times, the shift reg
isters are reset and new data appro
priate for the next row is clocked in.
Add to this the fact that the display
moves from left to right and you can
see that the timing process is quite
complicated.
Fortunately, that’s all taken care
of by a machine language program
which is called LEDs.COM. This
program manipulates all the control
lines from the printer port to control
the LED display.
Power supply
The display is powered from a 9-12V
DC plugpack rated at 1A. The DC rail
from the plugpack is applied to REG1,
which delivers a regulated 5V rail to
power the LED arrays and the shift
registers.
The 10µF and 1µF capacitors at
the input and output of REG1 are
there to ensure regulator stability. In
addition, the supply pins of all the
12 Silicon Chip
shift registers are filtered using 0.1µF
capacitors
Construction
This design is available as a com
plete kit of parts from Oatley Electron
ics, who own the copyright on the PC
board (see pricing panel).
The board is double-sided with
plated-through holes which means
that there are no links to install. It
is also solder-masked and carries a
screen printed overlay to make the
job of assembly as straightforward as
possible.
As mentioned earlier, the basic con
figuration is a 3-section board with a 48
x 7 LED array. Each section (or module)
contains 16 LED columns plus a pair
of matching shift registers. In addition,
the master module carries the DB25
socket plus the Darlington transistors
and power supply components.
Fig.3 shows the parts layout on the
PC board. Note that this only shows
the master module plus part of the
first extension module. The pattern
of LEDs, shift register ICs and other
parts simply repeats towards the left.
Begin the assembly by installing
the resistors and capacitors, then add
the transistors and the ICs. The use
of IC sockets is recommended here,
since a dud IC (rare) is very difficult
to remove if it is soldered directly to
a double-sided board. Take care with
the polarity of the ICs – they are all
installed with the notched end to
wards the right.
Similarly, take care to ensure that
the transistors are all correctly ori
ented and note that Q2, Q4, Q6, Q8,
Q10, Q12 & Q14 (ie, the transistors
immediately adjacent to the LED rows)
are all BC639s.
Now for the LEDs. There are 336
LEDs in all, so installing them will
take some time. The main thing to
watch out for here is to ensure that
they are all correctly oriented. You can
identify LED polarity in two ways: (1)
the anode lead is the longer of the two;
and (2) the cathode lead is adjacent to
a small flat section on the bottom lip.
Push the LEDs down onto the board
as far as they will go before soldering
their leads.
Once all the LEDs are in, you
can install the DB25 socket and the
7805 regulator (REG 1). The latter is
installed with its leads bent at right
angles and its metal tab bolted to the
PC board along with a small finned
heatsink.
The prototype board was installed
in a smoked Perspex channel (470mm
long x 150mm high) and secured using
machine screws and nuts at the back.
This Perspex channel was bent up by
a local plastics supplier. Alternatively,
you can make up a suitable wooden
or metal case with a Perspex viewing
window for the LED arrays.
Software & testing
The software for the Moving LED
Display comes on a 3.5-inch floppy
disc and consists of six main files plus
a brief readme file. The files leds3.com,
leds4.com and leds5.com are for dis
plays with from three to five modules
(including the master module), while
the ledset.com file configures the basic
setup.
First, copy the correct leds_.com
file to the hard disc (or to another
floppy), along with the ledset.com file.
Next, rename the copied leds_.com
file to leds.com, then run ledset.com
Fig.2 (right): the Moving LED Display
is controlled via the PC’s parallel port.
The rows are driven by Darlington
transistor pairs, while the data in the
shift registers (IC1, etc) controls the
column switching transistors (Q15,
Q16, etc).
February 1997 13
Silicon Chip
BINDERS
These beautifully-made binders
will protect your copies of SILICON
CHIP. They feature heavy-board
covers & are made from a dis
tinctive 2-tone green vinyl. They
hold up to 14 issues & will look
great on your bookshelf.
★ High quality
★ Hold up to 14 issues
★ 80mm internal width
★ SILICON CHIP logo printed in
gold-coloured lettering on spine
& cover
Price: $A14.95 (includes postage
in Australia). NZ & PNG orders
please add $A5 each for postage.
Not available elsewhere.
Silicon Chip Publications
PO Box 139
Collaroy Beach 2097
Or fax (02) 9979 6503; or ring (02)
9979 5644 & quote your credit
card number.
Use this handy form
Enclosed is my cheque/money order for
$________ or please debit my
Bankcard Visa
Mastercard
Card No:
_______________________________
Card Expiry Date ____/____
Signature ________________________
Name ___________________________
Address__________________________
__________________ P/code_______
14 Silicon Chip
Fig.3: follow this diagram when installing the parts on the PC board. Note that
only the master module and part of the first extension module are shown here.
The pattern of LEDs, shift register ICs and other parts simply repeats. Note that
a heatsink should be fitted to REG1 (see photo).
The basic PC board includes a master module (at right) plus two extension
modules to make up a 48 x 7 LED array. Up to two extension modules, each
with a 16 x 7 LED array, can be added to the lefthand end of the board. Note
the heatsink fitted to the 7805 regulator (REG1).
Fig.4: the ledset.com program lets you
configure the ledsx.com program to
suit your computer. The values shown
are good starting points for a 133MHz
Pentium machine (see text).
to configure the display driver to the
required parameters.
Fig.4 shows the setup that appears
when ledset.com is run. There are
three parameters that can be varied: (1)
the printer Port address; (2) the Delay;
and (3) the Duty cycle. The latter sets
the speed at which the message move
across the screen, while the Delay sets
the period between messages. The
up and down arrow keys select the
parameter to be altered.
In most cases, the default printer
port address of 0378H will be cor
rect. If not, the address can either be
gleaned from the system BIOS or by
running the Microsoft Diagnostics
program (type msd at the command
prompt).
Often, too, the address will be dis
played at some stage during the com
puter’s boot sequence. If you are using
Windows 95, double click the System
icon in Control Panel, then click the
Resources tab, select the printer port
and click Properties and Resources to
view the address.
The numbers for Delay and Duty
will depend on the speed of the PC
used. A Delay of 00500 and a Duty of
001 are good starting points for an XT
but these numbers should be increased
for higher speed PCs. We found that
a Delay of 02500 and a Duty of 250
produced good results on a 133MHz
Pentium machine. Note that you have
to type in each digit in an entry, start
ing from the leftmost digit, until the
number is correct.
The display can now be plugged
into the PC and the leds.com program
run from the DOS prompt. The mes
sage to be displayed must be included
on the command line; eg, to display
the message DOES YOUR DISPLAY
WORK?, you type leds does your display work? at the command prompt.
Note that all characters are displayed
in upper case, regardless as to how
they are typed.
The above command will display
the message once before returning con
trol to DOS. If you want the message
to be displayed repeatedly, you simply
use a full stop as the first character of
the message.
For example, the command leds
.silicon chip will repeatedly cycle the
message SILICON CHIP across the
display. The display can be stopped
at any time by pressing Ctrl C on the
computer keyboard.
Assuming that the unit works cor
rectly, you can now experiment with
the Delay and Duty values in the
ledset.com program. If a row of LEDs
fails to light, check the associated
Darlington transistor pair. Similarly, if
a column of LEDs fails to light, check
PARTS LIST
1 double-side PC board with
plated-through holes, 414 x
107mm (incl. three modules)
1 smoked Perspex channel case
with Perspex window or (see
text)
1 mini U-shaped heatsink to suit
TO220 regulator, 19 x 19 x
11mm
1 PC-mount DB25 male socket
1 DB25 cable, male-to-female
1 9-12V DC 1A plugpack supply
6 14-pin IC sockets
Semiconductors
6 74LS164 shift registers
7 BC639 PNP transistors
55 BC549 PNP transistors
1 7805 5V 3-terminal regulator
336 LEDs
Capacitors
1 10µF 25VW electrolytic
7 0.1µF monolithic ceramic
10 220pF ceramic
Resistors (0.25W, 5%)
10 10kΩ
48 68Ω
48 4.7kΩ
10 47Ω
the associated column switching
transistor.
Finally, a batch file can be used to
allow a sequence of messages are to be
displayed continuously. An example
of this is as follows:
:start
leds message 1
leds message 2
leds message 3
goto start
These lines must be created in an
ASCII text editor and the file saved
with a bat extension; eg, message.bat.
February 1997 15
Pt.2: adding the parallel interface board
BY RICK WALTERS
Computer controlled
dual power supply
Last month, we presented the standalone
version of this power supply. By building &
fitting the interface board described here, you
will be able to control it from your computer.
The power supply interface board
connects via a 25-way cable to the
parallel port of your computer. The
interface allows your computer to
perform two functions.
The first is to set the required posi
tive and negative output voltages and
current limit which will be delivered
by the power supply. The second is to
display the actual voltage and current
from the power supply on the comput
er’s video monitor.
16 Silicon Chip
Normally the voltages set by the
computer will be the same as those
displayed but if the power supply
goes into current limit, the associated
output voltage will be reduced.
One good feature of the computer
control is the ability to use the settings
which were in use the last time the
supply was turned off. These settings
are stored in a file which is read each
time the software is run. This gives you
the option of using the same supply
values and printer port as previously
or selecting new values or a different
printer port.
Now let’s have a look at the circuit
of Fig.1 and even the most dyed-in-thewool computer hardware enthusiast
would have to admit that it’s not too
inspiring. However, before you turn
the page and give up, let’s note a few
key points.
First, if you refer to the circuit
presented last month, you will note
that there are four outputs labelled
IN1, IN2, IN3 & IN4 and three inputs
labelled D/A1, D/A2 & D/A3.
The outputs from the power supply
board become the four inputs for the
A/D converter on the interface board.
They are fed to IC7, a 74HC4051 1-of8 multiplexer. Depending on the BCD
data at its ABC inputs, it feeds the
selected IN value through to IC8, the
ADC0804 analog-to-digital converter.
The four IN values relate to the fol
Fig.1: the circuit allows data from the computer’s printer port to set the sup
ply’s voltage and current outputs. It also allows the voltage and current to be
monitored on the computer screen. Octal latches IC1, IC2 and IC3 are used as
D/A converters and are controlled by IC4, a 74HC137 latched one-of-eight
decoder.
February 1997 17
Fig.2: follow this parts layout diagram to assemble the interface board. The
assembly is straightforward but take care to ensure that the ICs are all correctly
oriented and that the correct IC is used at each location.
lowing four power supply parameters:
IN1 Positive output voltage (V+)
IN2 Output current (I+)
IN3 Negative output voltage (V-)
IN4 12V supply
All these IN values will be in the
range of 0-5V and will be converted
by the ADC0804 chip, IC8, to an 8-bit
word (a number between 0 and 255)
which is fed to the computer’s paral
lel port, on pins 10-17. Note that the
parallel port is bidirectional so it can
accept data on these pins, as well as
outputting data.
Three of the IN values, IN1, IN2 and
IN3, are displayed on the computer’s
screen.
As we just remarked, the parallel
port also outputs data and in this case
it delivers 8-bit data to control the volt
age and current settings on the power
supply. This 8-bit data is delivered on
pins 2-9 (D0-D7) of the 25-pin socket.
From there it is connected to the D0-D7
inputs of IC1, IC2 and IC3. These are
used as three D/A (digital to analog)
converters.
Digital to analog converters
IC1, IC2 and IC3 are octal (8-bit)
latches under the con
trol of IC4, a
74HC137 latched one-of-eight decod
18 Silicon Chip
er. Depending on the data fed to its
pins 1, 2 & 3, IC4 enables IC1, IC3 or
IC3 (via their latch enable pin 11 and
inverters IC5b, IC5e & IC5c) so that the
data on their input pins 2-9 is latched
onto their Q outputs, pins 19-12 (Q0
to Q7).
Each 74HC573 has a ladder network
consisting of 10kΩ and 20kΩ resistors
connected to the eight outputs. These
networks convert the 8-bit data at
the output to a voltage with a value
between zero and 5V. These analog
voltages are D/A1, D/A2 & D/A3,
corresponding to the positive volt
age setting Vo+, current limit setting
Io, and the negative voltage setting
Vo-.
We have just described the two main
functions of the interface board: first,
monitor the four IN values from the
power supply board and provide the
three control values for positive and
negative voltage and the current limit
setting. Apart from that, there is little
point in going further with the circuit
description since the interface board is
entirely under software control.
PC board assembly
The interface board measures 178
x 100mm (code 04101972) and has a
25-pin D socket mounted at one end.
Fig.2 shows the component layout on
the board.
The board assembly is reasonably
straightforward. In essence, you have
a few rows of equal value resistors
and eight ICs to install, and not
much else.
As usual, before starting assembly,
check the copper pat
tern for open
circuit or shorted tracks or undrilled
holes. Make any repairs required and
then fit and solder the 21 links and
10 PC stakes.
Next, fit the resistors and diodes,
followed by the IC sockets, capacitors
and finally, the D connector. Check
your soldering when you are finished
to make certain that no IC pads are
bridged.
Interconnecting wiring
Most of the interconnecting wires
should have been taped up when you
built the power supply. If you followed
the colour code that we suggested last
month, the brown wire will go to D/
A1, the red to D/A2 the orange to D/
A3 and the black to ground.
There should be four other loose
wires: the blue goes to IN1, grey to IN2,
brown to IN3 and white to IN4. Two
leads need to be run from the anode
of D3 to TP14 and from the remaining
PC stake to TP4 on the power supply
board.
Fig.3: the parallel port interface board is mounted at one end of the chassis,
with the DB25 connector protruding through the rear panel. Use this chassis
wiring diagram and the wiring table from last month’s issue to make the offboard connections. Because only low currents are involved, you can run the
connections to the interface board using rainbow cable
February 1997 19
to the positive output voltage.
If you set the front panel voltmeter
to read the positive supply voltage and
short the positive output, the current
reading on the computer should read
.05 and the digit colour should change
to red. Also the positive voltage should
read 0 or .1 and again should be red,
indicating that it is not the selected
value.
The current limit changes colour
as the limit setting is reached to let
you know that the power supply is in
current limit mode.
Voltage calibration
The interface board mounts vertically on one side of the case and is attached to
the rear panel via the rightangle 25-pin D connector.
Mount the PC board to the back pan
el using the hex head bolts to secure it,
with the components facing the power
transformer. We stuck a mounting foot
on the metal chassis to keep the board
parallel to the case, and another on the
plastic cover to keep the board firmly
in place.
Testing
You will need a 25-way D female to
25-way D male cable to connect the
computer to the power supply. This
done, load GW Basic and SCREG.BAS
and follow the on-screen instructions
(see Fig.5).
As there are no previous values
saved, you should enter 10V for the
positive voltage, 15V for the negative
voltage, .05 for the current limit, and
1 or 2 for whichever printer port you
plan to use. It is probably wise at
this stage to use LPT1, the parallel
port you have been using to drive
your printer, as you know that this
port works.
When you switch the power supply
to remote, the voltages you have set (or
values very close) should be displayed
as in Fig.5.
Pressing the plus key should in
crease the positive voltage and the
minus key should reduce it. If you
press the “T” key the negative volt
age should reduce to the same value
as the positive and follow it. This is
the “tracking” condition whereby the
negative output voltage is always equal
Software Features
Positive and negative voltage setting in 100mV steps from 0-25.5V
Individual output voltages or negative supply tracking positive supply
Current limit setting in 10mA steps from 0-2.55A for both supplies
simultaneously
Computer screen readout of positive and negative output voltages
Voltage reading changes from yellow to red for out of tolerance voltage
Computer screen readout of positive supply current
Current reading changes from yellow to red at current limit
Selection of printer port 1 or 2
All settings are saved and can be restored at program start
20 Silicon Chip
In spite of the fact that the power
supply will have already been cal
ibrated for standalone operation, it
needs to be recalibrated for computer
control.
The procedure is similar to that
outlined last month.
Set both supply rails for 24.5V out
put and with your DMM across the
negative output and ground, adjust
VR4 until the voltage reads exactly
-24.5V. Now set VR6 so that the posi
tive output voltage is identical.
If you can measure current with
your DMM, find a 10Ω 5W or 10W
resistor and connect it in series with
your ammeter across the positive sup
ply. Set the voltage to 22V and set the
current limit for 1.95A.
Disconnect your DMM, switch it
back to volts and with just the 10Ω
resistor for the load and using the
front panel meter to check that the
current is around 1.95A, adjust VR5
so that the voltage on TP8 is 3.82V
(1.96 x 1.95).
If your meter can’t measure current,
wire the 10Ω resistor across the pos
itive terminal and earth, then set the
positive voltage to 22V and the current
limit to 1.9A.
Measure the voltage across the 0.1Ω
resistor in the emitter of Q2, multiply
it by 1.96 and adjust VR5 until you
can measure this voltage at TP8. Be
careful as the resistor will get very
hot. This will not be quite as accurate
as the previous method as it assumes
that the resistor value is exactly 0.1Ω.
The linearity of the power supply
output voltage versus the computer
setting is excellent, with the DMM
reading precisely tracking the reading
on the computer screen.
The voltage fed back to the computer
is not quite as linear. There are slight
errors in the converted voltages due
Fig.4: actual size artwork for the PC board. Check your etched board carefully
against this artwork before installing any of the parts.
to A/D linearity around half scale,
resistor tolerances, etc.
We have made provision in the soft
ware to apply five correction factors to
these readings.
The first is for values between 0 and
5.5V, the next between 5.6V and 11V,
the third between 11.1V and 16.5V,
the fourth between 16.6V and 22V and
the last between 22.1V and 25.5V. This
will be explained later in the software
description.
Parallel port
Before we start discussing the soft
ware we should give a quick rundown
on the parallel printer port and its
peculiarities.
It was originally designed to drive
an 8-bit parallel printer, with suffi
cient additional lines to provide data
transfer in both directions, such as a
BUSY line to prevent the computer
feeding data to the printer faster than
it can process it and a PAPER OUT line
to allow an intelligent message to be
shown on the computer’s screen if this
should occur.
Because the original interface was
for a Centronics printer, some bits are
true high, others are true low.
These signal lines are split over
three addresses on the IBM interface.
For LPT1 which is the normal (and
often only) printer port supplied, the
addresses are 378H (hexadecimal, 888
in decimal) for the eight data lines,
379H for the next five lines and 380H
for the remaining four lines. These are
often called ports A, B and C.
The data lines of port A are unidi
rectional, capable only of sending data
to the printer. The other nine lines can
be used as inputs and those of port C
can be used as outputs. This gives us
the capability of sending and receiving
8-bit data from an external device to
the computer.
Port B has the highest bit inverted
and port C only has one of its four bits
true high. A subroutine in the software
(at line 3000) untwists the input value
Parts List
1 PC board, code 04101972, 178
x 105mm
1 rightangle 25 pin D male connector (COON1)
4 20-pin IC sockets
3 16-pin IC sockets
1 14-pin IC socket
10 PC stakes
2 3mm x 15mm machine screws
4 3mm x 10mm machine screws
6 3mm nuts
8 3mm flat washers
6 3mm spring washers
tinned copper wire
hookup wire
Semiconductors
3 74HC573 octal latch (IC1-3)
1 74HC137 latched 1-of-8 decoder (IC4)
1 74HC14 hex Schmitt trigger
(IC5)
1 74HC147 decimal-to-BCD encoder (IC6)
1 74HC4051 analog multiplexer
(IC7)
1 ADC0804 analog-to-digital converter (IC8)
4 1N914 diodes (D1-D4)
Capacitors
1 100µF 16VW electrolytic
4 0.1µF MKT polyester
1 .022µF MKT polyester
1 .001µF MKT polyester
1 150pF ceramic
Resistors (0.25W, 1%)
4 1MΩ
27 20kΩ
2 47kΩ
23 10kΩ
February 1997 21
Only a few connections need to be made from the interface board to the power
supply board. The wiring diagram (Fig.2) has the details.
which is the sum of port B and port
C and gives a true value (TIN) for any
data placed on these lines.
Software
The control program has been
written in GW Basic, using screen
9, the highest resolution (640 x 350
pixel) colour screen. Contrary to the
statement in last month’s issue, the
software will work with EGA and VGA
monitors, not just VGA types.
The software code is quite conven
tional and will run in QuickBasic if
lines 1-14 are removed. You will also
have to create a separate program
containing just lines 5100-5199 and
run it to create the file before you run
the main program.
Space does not allows us to present
the full software listing in this article
but we have included the main section
from lines 20-999.
Lines 20-70, as you can see from the
comments, define the functions to be
22 Silicon Chip
used, paint the introductory screen,
read the previous settings from the
hard disc and give you the option of
reusing them or entering new values.
Should you wish to retain an exist
ing value, just press ENTER. The value
will be accepted and the program will
step to the next item. This is useful
should you just wish to change the
printer port for example, but retain
the previous voltage settings.
The values you selected are now
written to the screen (line 60) then
sent to the power supply in line 70.
By structuring your program in this
way you can write and debug each
subroutine individually. Then if you
decide to include an additional fea
ture, it is only a matter of writing the
routine, debugging it, then adding a
gosub in the appropriate place.
Main program
The main program, after the initial
isation and preliminary housekeeping
(lines 20-70), consists of lines 80-160
which, while there is no keyboard key
pressed, will run lines 100 and 110
continuously. That is, read the data
from the power supply and write these
values to the computer screen.
As the standard 8x14 text numerals
look quite insignificant on the screen,
we produced some larger, chunkier
numerals using a rectangular block
(CHR$219), defined on line 1260 and
drawn by subroutine 4000.
Keyboard input
When a key is pressed the program
branches to line 10000 which is the
keyboard service subroutine. If a key
which it recognises is pressed it will
carry out the command and send a
new value to the power supply. If a
non-programmed key is pressed, it
will be ignored and the program will
return to running lines 100 and 110.
If you read the comments at lines
10021 to 10028 you will understand
which keys do what. We used both E
and V for the positive voltage and A
and I for current, accepting both upper
and lower case characters, just so you
don’t have to try to remember which
keys to use. When you are typing the
program there is no need to include
the comments but if you come back to
study it at a later date, they will help
your understanding.
As described previously we have
two functions, read from and write
(send) to the power supply. We
read the power supply voltages and
current and write values to the D/A
converters.
Writing to D/A converters
The write function is carried out
by first placing the value we wish to
write to a particular D/A converter
on PORTA, then writing its address to
PORTC. These addresses are listed in
lines 1330-1400. The address for the
first D/A converter ODA1 is 9. We can’t
call it DA1, as we have defined D as a
string in line 1030.
You will notice that all the addresses
are odd numbers, which indicates that
the strobe line will be low (as we have
explained previously, the logic for this
line is inverted).
When the address is written to
PORTC, pin 4 of IC4 (latch enable) will
be pulled low but after a short delay
will go high as the .001µF capacitor
charges through the 10kΩ resistor.
The strobe is then taken high again
to prevent the A/D converter being
enabled (see “reading power supply
values”) and placing data on the POR
TA bus. ODA1 is now deselected, as
any changes to PORTA data would be
transferred to IC1’s output.
Now the data which was present on
PORTA has been latched by IC1 and
is available as an analog voltage at D/
A1 output. The other converters are
loaded in a similar manner.
When we write to the D/As we al
ways update the three of them and this
is done in subroutine 8000.
Listing 1
20 GOSUB 1000 ‘Initialise
30 GOSUB 2000 ‘Write screen heading
40 GOSUB 5000 ‘Get previous saved values from file
50 GOSUB 6000 ‘Write old settings to screen with option to change
60 GOSUB 7000 ‘Write selected data to screen
70 GOSUB 8000 ‘Output data to power supply
75 ‘MAIN PROGRAM loop 80 - 160 starts here. Monitor power supply & keyboard
80 K$ = INKEY$
90 WHILE K$ = “”: K$ = INKEY$ ‘While no key is pressed
100 GOSUB 9000 ‘Read data from PSU
110 GOSUB 7000 ‘Write data to screen
120 WEND ‘A key has been pressed
130 GOSUB 10000 ‘Service keyboard
140 GOSUB 6360 ‘Update preset values
150 GOSUB 8000 ‘Write new values to power supply
160 GOTO 80 ‘Loop again
900 GOSUB 5100 ‘Save power supply settings
999 CLS: SYSTEM
Fig.5: the positive and negative output voltages are displayed on screen, along
with the output current. Also shown are the instructions for varying the output
voltages and for setting the current limit and tracking.
Reading power supply values
To read a value from the power
supply we latch its address into IC4.
This time we don’t take the strobe line
high as we did previously, as we want
to turn on the A/D converter, IC8.
After the delay introduced by the
resistor and capacitor between the
output of IC5a and the input of IC5f,
this will be the case as its chip select
(CS) will go low. This connects its
tri-stated output to the PORTB and
PORTC bus.
For the PORTB and PORTC lines to
be used as inputs they must all be set
high. Then they will either stay high
or be pulled low by the A/D. This
procedure is carried out by subrou
tine 9000.
The last area to cover is the line
arisation of the readings returned by
the power supply. Lines 1420-1440
list the correction factors we found
satisfactory for our supply. These are
implemented in subroutine 9000 on
lines 9140, 9210 and 9280. These have
been REMmed out and values of 1.0
substituted in lines 1411-1413.
The procedure is to make a table of
the output voltage at the terminals ver
sus the voltage shown on the screen.
You then cal
culate the adjustment
factor to give the correct reading for
each range. Once you have the values,
delete lines 1411-1413, remove the
REMs from lines 1420-1440 and enter
SC
your values.
February 1997 23
The Alert-A-Phone consists of a plastic
box containing the electronics, a 12V DC
plugpack and a weatherproof metal horn
loudspeaker (not plastic as shown here).
Essentially, it is a high-powered telephone ringer for noisy environments.
The
Alert-A-Phone
. . . a very loud ringer for your telephone
Do you work in a very noisy environment and
you can’t hear the phone when it rings? Or are
you hard of hearing? If so, this project is for
you. It is the Alert-A-Phone Loud Sounding
Alarm. It connects in parallel with your existing
phone and it is Austel-approved.
DESIGN By DEREK DIGGLES*
24 Silicon Chip
The Alert-A-Phone Loud Sounding
Alarm has nothing to do with burglar
alarms – a point we want to clarify
right at the start. It is intended for use
in noisy environments where normal
phones are just about impossible to
hear.
The Alert-A-Phone can be turned up
to a level which is really loud; deaf
ening, in fact. That is its main feature.
The others are listed in a separate
panel in this article.
As well as a weatherproof horn
loudspeaker, the Alert-A-Phone com
Fig.1: two integrated circuits are used. IC1 is for AC ring signal detection and
ringer tone generation while IC2 is a 20W bridged audio power amplifier which
drives the horn loudspeaker.
prises a small plastic case to house
the electronics, a 12V DC plugpack
and a standard phone plug with a
3-metre cord.
While the phone and the Alert-APhone will normally be within three
metres of each other, the horn loud
speaker can be up to 20 metres away
and can be mounted outdoors since it
is weatherproof.
Other features of note are anti-tinkle
circuitry and it will work with the
new distinctive ring patterns used
by Telstra and Optus as well as the
normal ring cadence. The ring tone
is adjustable in pitch, so that more
than one Alert-A-Phone can be used
if required with different phone lines.
The Alert-A-Phone is housed in
a plastic case measuring 128 x 42 x
65mm and this has a label on both
sides. On the topside is the volume
knob which is removable, to stop
unwanted fiddling with the control.
The label on the underside has the
supplier’s name, address and phone
numbers: Telephone Technical Ser
vices, PO Box 357, Cleveland, Qld
4163. Phone (07) 3821 1222; fax (07)
3821 2161.
Now let us discuss the circuit which
is shown in Fig.1.
connected directly to the incoming
telephone line and is powered from it.
Fig.2 shows a block diagram of the
circuitry within the LS1241 chip. The
chip is powered from the telephone
line by virtue of the bridge rectifier
connected between pins 1 & 8 and
the DC filtering is provided by a 22µF
capacitor connected to pin 7. The AC
ring voltage is detected (ie, when the
phone rings) by the internal thresh
old circuit and this enables the tone
generator. The tone generator then pro
vides a ring tone in the same cadence
as the incoming AC ring voltage. The
ring tone is adjustable in pitch by the
10kΩ potentiometer VR1.
WARNING
Operation of this device may
infringe Environmental Noise
Pollution Regulations and could
DAMAGE HEARING if exposure is
prolonged. It is the user’s responsibility to control the volume and to
switch off the device if necessary
to conform to local environmental
guide lines.
The output stage connected to pin
5 normally drives a pie
zoelectric
transducer but in this case, as shown
in Fig.1, it drives a 2.2µF capacitor in
series with an isolation transformer
(T1) which couples the tone ringer
signal to the volume control VR2 and
Circuit description
Two integrated circuits are used, one
for AC ring signal detection and ringer
tone generation and the other an audio
power amplifier which drives the horn
loudspeaker.
IC1 is an LS1241 electronic two-tone
ringer made by SGS Thomson Micro
electronics. It is designed to replace
the bell in telephone handsets. It is
Fig.2: block diagram for the LS1241 electronic two-tone
ringer. It is powered from the phone line by dint of the bridge
rectifier between pins 1 & 8.
February 1997 25
Fig.3: the waveforms that can be expected in the circuit. The top trace
(channel 1) is the incoming AC ring voltage with an amplitude of just
over 200 volts peak-to-peak. The bottom trace shows the signal generated
by the tone ringer measured at the output of the transformer T1 and the
amplitude is around 12 volts peak-to-peak. Note: the waveforms are taken
from the screen of a Tektronix TDS 360 digital scope and because of the
very low timebase speed of 0.5s/div there are symptoms of aliasing in both
waveforms.
the input of the power amplifier IC2.
IC2 is a TDA7240 20W bridged pow
er amplifier normally intended for use
in car radios. It is a 7-pin package with
a heatsink tab. Its normal operating DC
voltage is up to 18V. Its power output is
quoted at up to 20W at 10% harmonic
distortion. Contrary to what you might
expect, it will deliver fairly close to this
power even though the DC plugpack is
only rated at 1A continuous; ie, 12W.
The reason it can deliver such high
power is that the ring signal is inter
mittent, giving the supply plenty of
time to recover between each ring.
Another factor in the high power de
livery is that harmonic distortion is not
an important factor – what is wanted
is lots of loudness!
Since the TD7240 is a bridged pow
er amplifier, the horn loudspeaker is
directly connected to pins 7 & 5; no
coupling capacitor is necessary.
Zobel networks consisting of a 2.2Ω
resistor and 0.22µF capacitor are con
nected to both outputs at pins 5 & 7 to
ensure amplifier stability, especially
as long output lines are being used.
Fig.3 shows the waveforms that
can be expected in the circuit. The
top trace (channel 1) is the incoming
AC ring voltage with an amplitude
of just over 200 volts peak-to-peak.
The bottom trace shows the signal
generated by the tone ringer measured
at the output of the transformer T1
and the amplitude is around 12 volts
peak-to-peak.
Note: the waveforms are taken
from the screen of a Tektronix TDS
360 digital scope and because of the
very low timebase speed of 0.5s/div
there are symptoms of aliasing in both
waveforms.
The bottom waveform is modulated
in both frequency and amplitude to
give the typical warbling tone of a
modern telephone.
Putting it together
Since this is an Austel approved
device, there is only one way you
can build it. You must purchase
the complete kit and no component
substitutions or modifications are
allowable. It must also be powered
from the supplied approved 12V DC
plugpack. If these conditions are not
followed, the Austel approval will be
null and void.
All the electronic componentry is
mounted on a PC board measuring 123
x 58mm. This board mounts upside
down in the plastic case and it has
large corner holes which fit over the
integral corner plastic pillars in the
case. This method avoids any screw
Fig.4: the component overlay for the PC board. This board mounts upside down in the plastic case.
26 Silicon Chip
The small transformer in the centre of the board provides 3kV AC isolation
between the telephone ringer IC and the bridged audio power amplifier.
heads protruding from the case which
would probably not meet Austel
standards.
For the same reason, the removable
volume control knob and shaft is of
plastic construction. Fig.4 shows the
component layout on the board.
The PC board has a screen-printed
component overlay on the topside and
the copper pattern side has a green
solder mask.
The first step is to install the resis
tors and the capacitors, ensuring that
the four electrolytic capacitors are
correctly oriented. This done, install
the diodes, potent
iometers and the
4-way insulated terminal block. IC1 is
soldered direct to the PC board while
IC2 is soldered in and fitted with a
small finned heatsink which is also
soldered at two points on the board.
Two spade lugs are soldered at one
end of the board at points A & B for
the telephone line connection. The
last component to be installed is the
isolating transformer. This is soldered
in and secured to the board with a
Nylon cable tie.
The kit will include a 3-metre phone
cable with a standard phone plug at
one end and two spade connectors on
the other end. These are pushed onto
the spade lugs on the board, after the
cable has been passed through the
adjacent hole.
At the other end of the board, you
will need to connect the two wires
from the horn loudspeaker and the two
wires from the DC plugpack. Make sure
that you connect the DC plugpack cor
rectly; the positive wire must go to the
positive terminal on the board, marked
with a + sign on the copper pattern
and on the screen-printed overlay. If
you do manage to inadvertently swap
the supply leads though, there will be
no damage, by virtue of the protection
diode D1.
Initial test
When all the assembly is complete,
apart from putting the lid on the box,
Features
Very loud alarm; up to 120dB at 1 metre
Volume control on front panel plus internal pitch control
Can be turned off at the power point (no need to disconnect from phone
line)
Weatherproof horn speaker can be up to 20 metres away from the AlertA-Phone
Reverse polarity protection for DC supply input
Power amplifier has overload protection
Do-it-yourself installation
Austel approved: Permit A9601B/0017
Ringer equivalence number REN = 1
February 1997 27
Electronic
Projects
For Cars
5
$8.9
PLUS P
&
$3 P
The PC board mounts upside down in the case and the large corner holes of the
PC board fit over the integral pillars of the case.
Available only
from
Silicon Chip
Price: $8.95 (plus $3 for postage). Order by phoning (02)
9979 5644 & quoting your credit
card number; or fax the details
to (02) 9979 6503; or mail your
order with cheque or credit card
details to Silicon Chip Publications, PO Box 139, Collaroy,
NSW 2097.
Final testing
For the final test you will need to
connect the unit to the phone line, in
parallel with a standard telephone.
Rotate the volume control almost fully
anticlockwise (minimum setting) and
have someone phone in on that line (or
use a cellular phone to call the line).
The horn loudspeaker should ring in
unison with the phone. From here,
you make an adjustment to the pitch
control VR1 is desired.
Finally, the unit can be permanently
installed. If the horn loudspeaker is
mounted outdoors, it should point
downwards so that it does not catch
the rain. The volume control should be
adjusted for an adequate level. There
is no point in having it too loud as it
will only cause annoyance to people
SC
near and far.
*Derek Diggles is the principal of Tele
phone Technical Services.
Use this handy form
initial testing can be performed, before
any connection to the phone lines.
Plug in the plugpack and check that
you have about 14V across ZD1. Wind
the volume control clockwise and
put your finger on the junction of the
volume control VR2 and the 300kΩ
resistor. You should immediately hear
a loud blurt from the speaker. If this
does not occur, check all the compo
nents around IC2.
Enclosed is my cheque/money order for
Where To Buy The Kit
$________ or please debit my
The design of the Alert-A-Phone is copyright. Kit pricing is as follows:
Bankcard Visa Mastercard
(1). Complete kit, including 15W metal horn loudspeaker, 12V DC plugpack,
drilled and labelled case, fitted telephone cord and 5m speaker flex and
telephone double adaptor plug, $131.50 plus $7.00 for air freight anywhere
within Australia.
Card No:
______________________________
Card Expiry Date ____/____
Signature ________________________
Name ___________________________
Address__________________________
__________________ P/code_______
28 Silicon Chip
(2). Kit service fee: $30 including return delivery, provided workmanship is
normal.
(3). Fully built and tested Alert-A-Phone, $193.50 plus $7.00 for air freight
anywhere within Australia.
Payment may be made by cheque, money order, Bankcard, Visa or Master
card to Telephone Technical Services, PO Box 357, Cleveland, Qld 4163.
Phone (07) 3821 1222; fax (07) 3821 2161.
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/
SWITCHED MODE POWER SUPPLY:Compact
(50X360X380mm), enclosed in a perforated metal
case, 240V AC in, 12V DC/2A and 5VDC/5A out: $17
...HP POWER SUPPLIES: Compact (120X70X30mm)
HP switched mode, power in plastic case, 100-240V
AC input, 10.6V/1.32A DC output, slightly soiled: $14
...LASER MODULE: Very bright (650nM/5mW) focusable module, suit many industrial applications,
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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...LASER POINTER: Our new metal laser pointer
(With keychain) is very bright, with 650nM/5mW
diode: $65 ... LEDS SUPER PRICES, INCLUDING A
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in a 5mm housing ...By far THE BRIGHTEST BLUE
EVER OFFERED, superbright at 400mCd: $1.50Ea.
or 10 for $10 ... 1C red: 10 for $4 ...300mC green:
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MIXING THE OUTPUT OF THE PREVIOUS 3 LEDS?
..3Cd Red: $1.10Ea. or 10 for $7 ... 3Cd yellow (Small
torch!) also available in 3mm: 10 for $9 ... Superbright
flashing LEDS: $1.50 Ea. or 10 for $10 ... PHOTOTRANSISTORS: Enclosed in clear 5mm housing
similar to the 5mm LEDS, 30V/3uS/<100nA dark
current: $1.30 or 10 for $9 ...CONSTANT VOLTAGE
DIODES: 1.52-1.66V <at> 10uA: 10 for $7 ...MASTHEAD AMPLIFIER PLUS PLUGPACK SPECIAL: Our
famous MAR-6 based masthead amplifier plus a
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
papers, used, limited qty.: $4 Ea. ...HF BALLASTS:
Single tube 36W Dimmable high frequency ballasts:
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CHARGERS, 13.8V / 650mA, proper “switching”
design with LED status indicator: $8.80 ...LASER
POINTER KIT: A special purchase of some
660nM/5mW laser diode means that we can reduce
the price of our Laser Pointer kit, includes everything
except the batteries: $29 ...SPECIAL BATTERY AND
CHARGER OFFER: When our 7AHr/12V SLA battery
($30) is bought with the SLA battery charger the
total price for both is: $33 ...USED BRUSHLESS DC
FANS: 4"/12V/0.25A: $8, 24V/6"/17W: $12
...100,000uF ELECTROLYTIC CAPACITORS:
30V/40Vsurge, used but in exc. cond.:$10 ...12Hr.
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
/ 800 mAHr. AA NICAD BATT’s plus 1 X thermal switch,
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
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current is 5-600mA ...IR LASER DIODE KIT: Barely
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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.
SERVICEMAN'S LOG
A tale of two Sharp VCRs
VCRs can fail for all sorts of reasons but I
recently had one that really takes the cake.
Fortunately, not all jobs are like that one,
with most being quite routine.
Just when I’d thought I’d seen every
thing in the servicing game, along
comes something to really set me back
on my heels. Spilt drinks or other
liquids are common reasons for TV
and VCR failures but monkey urine?
–you’ve got to be kidding!
Of course, out of the thousands of
servicemen in Australia, it had to be
yours truly that got saddled with the
job.
The story started out innocently
enough. Some months ago, the local
vet brought in a mid-drive Sharp VCR
with the complaint that it stopped
working after about two seconds on
“play”.
The set was a 1992 VCA34X which
looked to be in good condition – at
least from the outside. Unfortunate
ly, it didn’t smell quite so good and
had a quite distinct “pong” of stale
urine about it. However, seeing that
it had come from the animal surgery,
I assumed that this “pong’ had been
picked up from something in the air.
The fault description turned out to
be quite accurate and when I removed
the top cover, I could see that fast
forward and rewind were OK. The
play mode was a different matter,
however – the arms loaded the tape
properly, the drum motor started and
the capstan motor started but it only
did a revolution or two before stopping
and unloading the tape. It all looked
OK, so why didn’t it work?
Unfortunately, I don’t have the
service manual for this model but the
deck was a very common type; only the
electronics were different. So the first
question was “is this a mechanical or
an electronic problem?” I decided to
inspect the whole machine carefully
30 Silicon Chip
and turned it upside-down to remove
the lower cover plate. Immediately, it
was obvious from the severe corrosion
where the smell was coming from. It
was also obvious that this was where
the problem lay.
Fairly obviously, the machine had
been sitting in a pool of urine, perhaps
up to 12mm deep. And although this
had long been cleaned off by someone
else, the corrosion was abundant to
see up to the high level mark. I was
about to phone the vet and tell him
that all was lost and that he should
get a new VCR but then I had a little
think to myself.
To fix or not to fix
Perhaps this wasn’t a hopeless case
after all. First, all the major motors
were actually turning and secondly,
someone else had already done a pret
ty good job of cleaning up the mess
inside. Added to that, all the bottom
printed circuit boards looked OK and
so I concluded that the job was worth
investigating further to see if the ma
chine could be salvaged.
At this stage, my main suspect was
the drum motor as it seemed hesitant
to start and its speed appeared to be
intermittent when it was strobed under
a neon mains light. I also discovered
that, occasionally, when the video was
switched from EE mode (ie, Tuner) to
the Play mode, a picture could almost
be seen although not always in sync.
My next step was to fire up the CRO
and check the output of the PG (pulse
generator) head. This revealed a pulse
generator signal but it was fluctuating.
Also there was 12V on pin 3 of the plug
to the drum motor.
From this evidence, it seemed likely
that the drum stator board or its com
ponents had corroded and so I decided
to remove it to see if anything could
be done.
The connection to this motor is via
a special 6-lead flat printed circuit
ribbon cable harness whose end is
just pushed into a receptacle. When I
removed this, I found it to be badly cor
roded. I cut about 12mm off, scraped
away the white varnish covering the
tinned strands, cleaned the socket and
reinserted the harness.
When I powered up and pressed
“Play”, the motor spun up quickly
and continued to play correctly. I then
checked the other sockets in this area
but they were all OK. In hindsight, I
should have suspected a cable connec
tion but everything looked fine until
the cable was actually removed.
I returned the video to the vet with
a warning that despite cleaning it, he
would probably have further problems
in the long term as it is very hard to
prevent a chemical reaction of this
type from continuing.
He apologised for the state of the
VCR – apparently a monkey (would
you believe it) had had an “accident”
in that corner of the room and even
though he had got a friend to check
the VCR out, he must have missed that
particular socket.
Just how long the machine will last
is anybody’s guess and I didn’t press
the vet for any further details on the
monkey or what it was doing there.
Let’s just say that it doesn’t pay to
have a monkey monkeying around
near a VCR.
Another Sharp VCR
I thought no more about this repair
until a few months later when another
similar Sharp VCR came in. This time
it was a slightly older model, a VCA105X, and the complaint was that
it wouldn’t play. The unit looked in
good condition throughout and this
time there were no unpleasant odours!
As with the previous unit, this too
would load up, the drum motor would
spin and the capstan motor would
spin a few revolutions before it would
unload and stop. This time, I did have
the service manual and it also had a
troubleshooting guide for the exact
symptoms being experienced.
The first step is to check the head
switching pulse applied to pin 3 of
IC801 (IXO491) and the PG (pulse gen
erator) signal applied to pin 4 of servo
control IC701 (IX04313GE). Well,
the PG pulse was there but there was
definitely no head switching pulse
(HSWP) . In fact, all the voltages and
inputs seemed correct going into IC701
but nothing was coming out of pin
28 and there appeared to be no short
circuit on that line.
In view of these symptoms, I felt that
the problem had to be electronic and,
at this stage, considered IC701 and/
or the system control microprocessor
IC801 as the main suspects. Before
replacing these devices however, I first
checked out all the B+ lines and the
various clock signals but could find
nothing wrong. The HSWP also went
to the Y/C module and onto the head
preamp board. I tried disconnecting
these boards in turn but there was still
no sign of a pulse.
With reluctance, I ordered IC701
first as I knew these ICs would be ex
pensive. It arrived a few days later and
I wasted no time in fitting it. Unfortu
nately, it made no difference, so that
was expensive mistake number one.
I was now faced with the prospect of
having to replace the main micropro
cessor (IC801), which was even more
expensive. Before ordering it however,
I tried replacing the mode select switch
in case it wasn’t engaging quite correct
ly – to no avail. Finally, I went ahead
and ordered IC801. It too arrived after
a couple of days and I went about the
laborious task of removing the old 64pin IC and soldering in the new one.
And that was expensive mistake
number two because it also made ab
solutely no difference – there was still
no head switching pulse. Murphy was
really working overtime on this job!
A new approach
I was discussing my expensive folly
with several colleagues when one said
that he had recently obtained the same
model as a trade-in.
What’s more, he offered to lend it
to me so that I could pinpoint the
location of the faulty parts without
spending any more megabucks on use
less guesses. He was also of the strong
opinion that it was an intermittent
capstan motor that was causing the
problem as this occasionally occurs
February 1997 31
Serviceman’s Log – continued
on this series of decks and gives many
similar symptoms.
Well, this was indeed a stroke of
luck and I started by swapping over
the capstan motor but that too made
no difference. By now, I felt that my
original diagnosis – that the fault
was electronic – must be correct.
As a result, I began swapping all the
electronic circuitry between the two
machines, board by board, but again
this made no difference.
After changing the last board, I was
forced to conclude that I was looking
at a mechanical/motor problem. In
fact, it had to be the drum motor, even
though all the pulses and voltages
from it were correct and it looked as
though it was reaching the correct
speed when viewed under the strobe
light. I couldn’t be certain of this, how
ever, as it was unloading as soon as it
apparently reached the correct speed.
In fact, the machine did not even have
time to switch from EE mode to Play
mode, so no picture was available.
Anyway, I proceeded to replace the
drum motor and try again. Unbelieva
bly, it worked this time but I couldn’t
understand why.
Out of curiosity, I measured the
output from the new motor and it
matched the old one exactly. How
could this be? To solve this mystery,
I replaced the old motor and in the
process noticed that the ribbon con
nector cable had come away from its
32 Silicon Chip
hardened plastic support and that
the tracks were somewhat loose and
frayed. I didn’t pay much attention to
this until I retried the old motor which,
to my amazement, was now working.
So what was the answer? As it is not
possible to prove, I can only speculate
that the ribbon connector cable was
either shorting or not making a proper
connection with the socket. I guess I
should have remembered the symp
toms of the earlier repair and examined
this connection more carefully first.
Bread & butter
The next morning, I faced up to
two TV sets that were awaiting my
attention. The first was a 34cm Toshiba
144R8A made by Samsung (a P54S)
and it was quite dead. Often, a set
of this size is not really worthwhile
repairing as they are so cheap to buy.
It all depends on how difficult the
fault is to fix and sometimes it can be
quite difficult to decide whether to go
ahead or not.
On the plus side, the faults in this
chassis are fairly well known which
does reduce the amount of time spent
in diagnosis.
In the 34cm model, most of the
problems are in the power supply, due
to the electrolytic capacitors drying
out. This causes the chopper power
transistor Q801 (2SC3552/BU508A)
in the switchmode power supply to
blow, which also takes out the fuse
and/or R801 (5.6W 7W).
In this case, the transistor had tak
en out the resistor and so I replaced
these parts and four electros (C808,
C813, C812 & C811) all at once. When
I switched it on again, the set was ob
viously struggling to fire up and was
making funny noises in the power
supply. I immediately switched it off
again to prevent another failure of the
chopper transistor and then started to
check for shorts on the B+ rails.
The line transistor Q404 and capaci
tor C413, a common culprit, were both
OK. In fact there were no shorts and
no, or extremely small, output from
the chopper transformer.
Checking the voltage across C807
confirmed there was 340V out of the
bridge rectifier and I checked and
cleared resistors R806 and R807. The
oscilloscope confirmed that the circuit
was oscillating though the waveforms
were incorrect and Q801 was getting
hot. I changed IC801 which is the main
IC in the power supply but that made
no difference.
And that really only left the trans
former (T801). Removing it, I tested it
with a shorted turns oscillator/tester
which indicated that pins 1 and 3 were
shorted. This test is not always conclu
sive as I don’t know what frequency
the circuit is designed to resonate at.
However, I decided to take a punt – a
new chopper transformer was ordered
and it subsequently proved that my
diagnosis was correct. The repair cost
really made it quite a marginal exer
cise, however.
Sony KV2064
The second set was a Sony KV2064
and the customer thought that it had
to be the on/off switch because it was
intermittently dead. Of course, power
switches can sometimes be faulty but
it never ceases to amaze me that many
people think that a TV set consists of
a tube, a valve, a switch and a fuse.
That’s it – it has to be one these items
which is faulty if the set doesn’t go!
As it turned out, the owner of the set
was a very heavy smoker and there was
a film of nicotine over every surface
and component inside the set. The
switchmode power supply had 240V
AC coming into it, which cleared the
on/off switch, and there were no fuses
blown. This of course left only the tube
and the valve!
A close examination of the power
supply circuitry revealed that the start
up resistors were the likely culprits.
There was over 300V on the collector
the chopper transistor (Q602) and
the four high-value 0.5W resistors
were all discoloured, although only
one (R602, 330kW) was open circuit.
I changed them all for high voltage
types, reworked the solder just in case
and switched on. It was all an anti
climax – everything worked perfectly
and the set now started every time it
was switched on.
All I have to do now is explain to
the customer that it wasn’t the on/off
switch.
The reluctant NEC
Later that morning, a lady dropped
in her NEC video with the symptoms
that it wouldn’t fast forward or rewind
and turned itself off.
When I eventually got the chance
to look at it, I found that there was
virtually little or no take up torque,
which suggested a reel idler problem.
Being an N9083A, this machine was
a later (1991) version of the N9000
series, with the reel drive being a
sub-assembly which is fairly easy to
remove from underneath.
The main problem is due to two
tyres within this assembly which
are supplied in the VBK83 tyre and
belt kit. However, one of the tyres is
an integral part of an idler assembly
and the replacement will not stay on
satisfactorily without gluing.
You can either purchase the entire
sub-chassis assembly for around
$55.00 trade (part no. 016192683 – this
not shown in the service manual) or
forego replacing that one tyre. It’s a
real nuisance that it is not available
as a complete pulley idler on its own.
It is also worth noting that earlier
models also require a modification to
the white CR slider – this part is now
black (part no. 016457582) and costs
around $2.00.
One can only hope that the customer
clearly understood that the cutdown
repair would not last as long as the
original. Still, I spelt it out as clearly
as I could.
This afternoon saw a dead IBM
monitor arrive. It was PS/1, manufac
tured in June 1993, series 028-004. I
have seen quite a few of these units
with blown mains fuses (F601 2.5AT),
usually without any apparent cause.
In one case, however, it turned out to
be the chopper IC itself that intermit
tently blew the mains fuse.
This particular unit also had a dud
mains fuse. I replaced it, checked the
rest of the supply for any obvious
faults and then, just to be on the safe
side, switched the set on with a 200W
globe in series with it. Initially, the
globe went bright, then dimmed and
came on again at half about luminance.
The first current surge was obvi
ously due to the degaussing circuit
kicking in and there was obviously
still quite a lot of current being drawn
at the end of the degaussing cycle – at
least 0.75A. However, the compliance
plate said the full current drawn was
1.4A, so I tried it without the globe
and the fuse held and the screen gave
a good picture.
For the rest of the day, I cyclically
switched the monitor off and on for
periods of 15 minutes, without further
problems. In the end, I could only ad
vise the customer that the cause was
probably either due to a mains surge
or fatigue in the old fuse.
All we can do now is keep our fin
SC
gers crossed.
February 1997 33
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
MAILBAG
Doubts On
Auto-Transformer Safety
This is a quick note to express
some strong concerns with the article
entitled “Stop Blowing Incandescent
Lights” in the January 1997 issue of
SILICON CHIP.
First up, I have to admit that I have
not thought through all the electrical,
insulation or failure implications of
running mains through a secondary
winding but initially I had the con
cerns with this that I did some years
ago with an amplifier project in ETI
which did a similar thing.
My concern is that we are running
240VAC mains through part of the
transformer that has a much lower
breakdown voltage than the 240V
primary winding – figures of 500VAC
as opposed to 4000VAC come to mind.
This seems to be an enormous risk
and if it caused a fire then the insur
ance company would be in the right
(if they knew) to oppose payment in
view of the fact that a non-approved
non-standard use was made of an
electrical component (insurance com
panies do this with motor car parts if
it suits them).
On a more pragmatic note the heat
levels at which the transformers op
erate are high and you are indicating
that they are dependent on “free
air flow unimpeded by any ceiling
insulation material” etc. This is very
tenuous. Let’s think about possible
scenarios. In my area the average
length of ownership of houses is about
five years.
So let’s suppose the original owner
puts in this arrangement for his lamps
and then five years later he sells. The
new owner decides, in sunny Queens
land, that he will insulate the roof.
Will the previous owner have passed
on a “House Circuit Manual” or “List
of Precautions”? Not likely!
Who will tell the contractor put
ting in the insulation not to cover the
transform
ers? Will the new owner
even know they are there? Not likely?
Do you know with certainty how your
house is done (if purchased from an
other party)? What if this is installed
38 Silicon Chip
by someone in a more northern area
– hotter still?
All in all, I was not impressed with
the article although there was some
excellent data in there about lamp life
and the effects of UV etc which I am
raising with our occupational health
and safety staff. We have many halogen
lamps in reception areas – this could
be a simmering compensation issue
for some time in the future!
R. Grant,
Chapel Hill, Qld.
Comment: we can address your concerns as follows. First, as we understand it, the bobbin construction of the
specified transformer means that the
secondary winding automatically has
a high breakdown voltage. Second, the
metalwork of the transformer is completely shrouded by the outer plastic
housing so that even if the transformer
winding did break down, there would
be no hazard.
We have warned about not surrounding the transformer with insulation because it is good practice and
it is required by wiring standards in
any case. Household wiring should
not be covered by insulation and all
electricians and insulation contractors
should be aware of this.
In any case, the specified transformer does have an integral thermal
overload cutout and so if the transformer did overheat, it would cut out.
If used as described in the article, the
transformer will be running within its
ratings and therefore should never be
an issue in the event of an insurance
claim. Indeed, we think there is a
higher chance of fire from halogen
light fittings themselves; they get extremely hot and again, should never
be covered by ceiling insulation; nor
should any flush-mount ceiling light
fitting.
As a final note, we consulted with
the manufacturers of the transformer,
Atco Controls Pty Ltd, to ensure that
there were no problems with this mode
of operation.
Your comment about Occupational
Health & Safety is interesting. We think
that the UV output of the mercury dis-
charge lamps used in many sporting
complexes is particularly dangerous. It
can cause “sunburn” after a few hours
and could be a compensation issue at
some time in the future. In our opinion,
such lamp fittings should have a UV
filter as a standard feature.
Marconi School of
Wireless Reunion
I am writing for your assistance in
organising a reunion of ex-Marconi
School of Wireless students to be held
in Sydney some time next year.
The school closed in 1981 and with
it into retirement went Ces Bardwell
who joined the school as an instruc
tor in 1939. Ces became principal/
manager, I believe in 1949, and held
that position until the school closed
in 1981.
Ces will be 80 next year and he will
be guest of honour at this reunion. My
task is to find out where all the “ex”
Marconi students and instructors are
today and ask them to express an in
terest in attending this function.
Information required from those
interested in attending this function
should include the year/years of
attendance and whether full-time or
part-time. I can be contacted as fol
lows: fax (make attention to “David
Hawksworth”) 044 210032 or email
techfm<at>peg.apc.org
David Hawksworth,
84 Duncan St,
Vincentia, NSW 2540.
Further Advice On
Networking Computers
Early in 1996 I networked a Pent
ium 166 and an old 486 almost iden
tically to the method you described
in the January 1997 edition of SILICON
CHIP. My experience, at least initially,
was not quite as straightforward as
laid out in your article. When I set
up my network system, I was not
aware that both systems require the
same “protocol” to communicate with
each other.
Win 3.11 defaults to NetBEUI while
Win95 defaults to TCP/IP. Initially,
NetBEUI was not installed in the Con
trol Panel/Network/Configuration of
my Win95 system. After some weeks of
trial and error (mostly error) I installed
(added) the NetBEUI protocol to my
Win95 setup. The network was then
up and running within 15 minutes.
The above may be of some help
to your readers if they have similar
problems. The article itself was very
well done and is a very useful and
practical demonstration of what can
be achieved with surplus equipment.
Peter Lynch,
Bayshore Park, Singapore.
Windows Dual-Boot Success
I had refused to have anything to
do with Windows 95, as I dreaded
having to learn another new system,
until I read the “dual boot” article in
the July 1996 issue of SILICON CHIP. I
thought that was just what I wanted.
It would allow me to continue work
ing with my current programs under
Windows 3.1 but to have a peek at
Windows 95 every now and then to
see what it has to offer and to learn
how to use it.
So I bought a “95” upgrade and a
1.2Gb hard drive and installed it ac
cording to the article. As time went
on my peeks at “95” became longer
until I am now transferring most of my
programs over to it. What I would like
to know now is, how can I make my
“95” D: drive a self-booting C: drive?
Is it just a matter of transferring the
Autoexec.xxx and Config.xxx files
across?
For many years now I have been
trading in my car on a new one about
every four years. I did this so as to
reduce the chance of being held up
in the “sticks” by a major breakdown.
But I had always been dubious about
electronic fuel injection and shied
away from cars fitted with it. As
electronics is my trade I know how
delicate electronic equipment can be
and I was always concerned about it
breaking down in an EFI car while out
in the bush somewhere.
Then I read your excellent series on
Electronic Engine Management and
learnt that EFI is fairly reliable after
all and that if it did break down, it
wouldn’t disable the car completely
and leave you stuck in the wilderness.
So my last new car was one fitted with
EFI. It seemed to perform quite well.
The thing I liked about it was how it
started the same, hot or cold.
But my new car did break down!
With a broken timing belt! At 7000km!
Luckily, I was able to call for assis
tance with my CB radio and catch a
bus home.
Three days later I was on the road
again and haven’t had any more prob
lems. The warranty has just expired.
So it just goes to show, you don’t know
what’s going to happen. A timing belt
can go at any time in any vehicle and
here I was concerned all the time with
the EFI.
Keep up the good work with your
magazine.
T. Vieritz,
Emerald, Qld.
Comment: unfortunately, there is no
easy way to make your Windows 95 D:
drive into a self-booting C: drive. The
only foolproof way is to reformat the
drive, reconfigure your hardware setup
as necessary, and then load everything
back on in the way you want it. We
suggest you wait until you are sure
that you can do without Windows 3.1
and then make a complete change to
Windows 95.
Your comments about vehicle electronics are interesting. Apparently, by
far the most common cause of modern
car breakdowns is a flat battery.
Power Supply Weakness For
Smoke Alarm Control Panel
I have just read the article on the
Control Panel for Multiple Smoke
Alarms in the January 1997 issue of
SILICON CHIP. I feel this is a most dan
gerous project, due to the fact that the
loss of the 9V supply, due to a short
anywhere in the field, complete
ly
shuts down the whole system. That
is the reason that the 240VAC units
require a 9V battery backup for mains
loss, so detectors can still work.
L. Hirning,
Dee Why, NSW.
Comment: while we agree that the
loss of the 9V supply would disable
the whole system, there is a visible
indicator in every smoke alarm to
tell you that it is being monitored. If
you can’t see it flashing, you know it
is dead. The same criticism could be
applied to every burglar alarm – if the
main supply is lost, the alarm is dead
but again, there is visible monitoring.
Our approach to the Smoke Alarm
Control Panel is essentially the same
as in large building installations where
the individual alarms usually are all
connected to an RS232 line and have
their own unique addresses and no
backup batteries. Again, each detector
has a visible LED indicator to show
that it is being monitored.
Flashing Lights Foil
Hunting Cats
In your response to a letter from
K.F., of Albion Park Rail, on page 93
of your August 1996 edition, headed
“Cat deterrent not humane”, you invite
comment.
It was an interesting and perceptive
observation that you made in reply to
the reader’s suggestion that emitted
sonics would not deter birds in pref
erence to bells attached to cats’ collars.
We are given to believe by the avian
experts that sonics do not indeed have
any deterrent effect on birds.
Your thoughts that cats should not
be let out at night are not without prec
edence. In Victoria, there is a curfew
placed upon them in cities and shires
that have elected to enforce, what is
now state law, and bird and reptile
population is now on the increase in
those areas.
Because cats hunt, by preference
during the hours of sunset to sunrise,
so we have researched and developed
a tiny battery driven unit which emits
high intensity flashing light from a
position behind the cat’s neck. It can
thus be used by responsible cat own
ers as a “Skare” for birds and other
creatures.
The cat is unaware of this and the
“Skare” acts as a far more effective
deterrent than tinkling bells but has
added safety benefits for the cat in
that it is illuminated if crossing roads
in unlit areas.
This device will shortly be market
ed through our existing “K-9 Collar”
outlets whose primary purpose is the
humane and safe containment of dogs,
by proven methods using sonics and
avoidance therapy.
John Foley,
Canine Invisible Enclosures (Qld)
Pty Ltd, Tugun, Qld.
February 1997 39
Build this low cost
ANALOG MULTIM
Are you in the market for a low cost
analog multimeter? They do have
their uses in spite of the fact that digital multimeters have taken over. So
why not put this kit meter together?
You’ll learn about multimeters in the
process of assembling it.
By LEO SIMPSON
You wouldn’t build this little multimeter to save
money although it is pretty cheap. No, the reason for
building it would be to gain a little experience in kit
construction and to learn about analog multimeters.
We foresee that large numbers of these meters will be
built as part of school and TAFE college courses. That
is what happened with the last analog multimeter we
described, in the November 1989 issue of SILICON CHIP.
And even though we’re quite sure that virtually every
reader of this magazine has a digital multimeter, there
are times when an analog meter is more suitable than a
digital type. This is especially the case when the reading
you are taking is fluctuating. When this happens it is
not easy to make any sense of rapidly changing readings
on a DMM (digital multimeter) but the movement of the
pointer on the analog meter will give you a clear picture
of what is happening.
Two examples of measurements where the reading
can fluctuate will demonstrate the point. The first is
when you are carrying out an alignment procedure on
a radio – the analog meter allows you to easily tweak
the coil slugs for a peak reading.
The second is when you are using the “Ohms” range
of a multimeter to judge the leakage of a capacitor,
particularly an electrolytic type. Judging by the speed
with which the pointer moves up the scale, you can tell
whether the capacitor is good or bad, especially if you
have a known good capacitor to make a comparison.
One other really good point about an analog meter is
that its battery does not go flat at the most inconvenient
time – when you want to use it, of course. How often
40 Silicon Chip
have you dragged out your digital
meter only to find that it has gone off
duty because its battery is flat.
This happens quite often with the
cheaper DMMs because they are a bit
hungry on batteries. By contrast, while
all analog multimeters have a 1.5V cell
and possibly a 9V battery to run the
Ohms ranges, it very seldom goes flat
and anyhow, you can still make voltage
and current measurements even if the
battery is completely dead.
No off switch
As part of this battery eating con
cern, you never have to worry about
turning an analog meter off. Just leave
it as you last used it and it will sit there
contentedly, not using any battery
power at all. Unless your DMM has
an “auto-off” function, you can’t say
that about a digital meter.
So while analog meters have been
superseded by digital multimeters
for most work, they are still handy
to have.
Multimeter features
The meter in question is quite a good
size and measures 148 x 99 x 34mm
thick. This means that the scales are
reasonably large and easy to read – an
important point with an analog meter.
This one has no less than eight scales
on the meter face.
The meter movement has the stand
ard DC sensitivity of 20,000 ohms/volt
on DC ranges. What this means is that
it will draw 50 microamps from the
circuit being measured, for a full scale
deflection (FSD) of the pointer. When
measuring voltages in high imped
ance circuits it is most important to
take this loading effect into account,
otherwise the readings will be very
misleading.
Most of the relevant multimeter
functions are listed in the accompany
Fig.1: the circuit of this analog meter is passive; ie, there are no active devices to amplify signals. The four diodes are the only
semiconductors. D1 & D2 enable the meter to read AC voltages and currents. D3 & D4 are there to prevent damage to the meter
movement in the case of a severe overload. All the switch contacts and tracks are integrated into the pattern of the PC board.
METER
February 1997 41
SPECIFICATIONS
DC VOLTAGE
Ranges ...........................................0.1V, 0.5V, 2.5V, 10V, 50V, 250V, 1000V
Sensitivity ........................................20,000Ω/V
Accuracy .........................................±4% at FSD
AC VOLTAGE
Ranges ...........................................10V, 50V, 250V, 1000V
Decibels ..........................................-10dB to +22dB on the 10V range (add
+14dB, +28dB for the 50V and 250V ranges; 0dB = 1mW into 600Ω)
Sensitivity ........................................9,000Ω/V
Accuracy .........................................±5% at FSD
OUTPUT TERMINAL
Capacitor coupled to the (+) terminal for blocking DC voltage when making AC
measurements
Coupling capacitance .....................0.047µF
Maximum DC voltage ......................100V
DC CURRENT
Ranges ...........................................50µA, 2.5mA, 25mA, 0.25A
Voltage burden (drop)......................100mV (50µA range), 250mV (other ranges)
Accuracy .........................................±3% at FSD
RESISTANCE
Scale ...............................................0 to infinity, 20Ω midscale
Ranges ...........................................x1, x10, x100, x1k, x10k
Maximum current ............................150mA, 15mA, 1.5mA, 150µA, 60µA respectively
TRANSISTOR (ICEO) & DIODE (IR) LEAKAGE
Ranges ...........................................150mA, 15mA, 1.5mA, 150µA
Maximum voltage ............................3V
TRANSISTOR CURRENT GAIN (hFE) (using hFE adapter)
Range .............................................0-1000 (calibrated for silicon transistors)
Base current ...................................100µA maximum
Collector current .............................11mA maximum
ing specifications panel. The circuit is
shown in Fig.1 and is fairly conven
tional as analog multimeters go. The
multi-position range switch controls
all functions, switching multipli
er
resistors in and out for the various
ranges.
Note the diode protection of the
meter movement, with D3 and D4.
These prevents the meter movement
from being mechanically damaged or
burnt out if it is connected to an exces
sive voltage while switched to a low
voltage or low current range. However,
if an overload does occur the meter’s
pointer will still slam hard against the
stops and the relevant range multiplier
resistor may be burnt out. Oh, and the
fuse may blow as well.
Output terminal
Some readers may be unfamiliar
with the function of the OUTPUT termi
nal which is connected to the positive
input connec
tion via C1, a .047µF
100V capacitor. This has nothing to
do with an output from the meter
but is a traditional feature on analog
multimeters, harking back to the days
of valve amplifiers. It enables you to
measure AC voltages at the plates of
valve stages. The capacitor is there to
block DC voltage while allowing the
AC voltage to be measured.
While the traditional feature is fine,
it could be a trap for young players
on this meter, if they do attempt to
measure AC signal voltages in a valve
amplifier. For a start, the voltage rating
The assembly work mainly consists of soldering
the components onto the PC board and putting
the selector switch together. The only components
to be assembled on the copper side of the board
(see above) are the zero adjust trimpot (R25), the
buzzer and the banana jack socket sleeves.
42 Silicon Chip
of the capacitor is much too low for
such measurements. We would prefer
to see the capacitor rated for at least
600V DC. The only problem is that
such a capacitor would not fit in the
available space.
Analog meter construction
When you open the kit, you will
find a number of small plastic bags as
well as the meter case with the meter
movement already installed.
Fig.2 shows the component over
lay for the PC board and the wiring
inside the case. This diagram shows
the component values while the PC
board is screen printed with compo
nent numbers; eg, R1, R2 etc. When
you install each component make sure
that its value on the circuit is matched
with the component number on the
PC board.
There are quite a few steps in the
assembly, as follows:
(1). Solder all resistors to the main
board. Check the colour codes against
the list or check the values with a
digital multimeter. Note: place a
link across one of the two positions
marked R8, if only one resistor for R8
(ie, 15MΩ) is supplied or you may be
supplied with one 10MΩ and one 5MΩ
for the two R8 positions.
(2). Solder all diodes into place.
(3). Solder C1 & C2 in place.
(4). Solder all precut wire links into
place. Follow the dotted lines on the
overlay diagram for their positioning.
(5). Solder trimpot R1 into place.
The circuit shows 1kΩ but the sup
plied value is likely to be 680Ω.
(6). Solder the buzzer onto the cop
per side of the PC board. Space the
buzzer 3mm above the PC board so
that its leads can be soldered. Space
the leads so that the body of the buzzer
is flush with the edge of the PC board.
(7). Solder the “zero adjust” poten
tiometer R25 in place on the copper
side of the board.
(8). Solder the fuse clips to the board
and then fit the 500mA fuse.
(9). Insert the ‘B1’ battery terminals
into the PC board and solder. Note;
they are inserted from the copper side
of PC board.
(10). Insert the three banana socket
sleeves into the copper side of the PC
board and solder evenly around each
one. Each sleeve will sit flush with the
top of the PC board.
(11). Now we are ready to assemble
the rotary switch. First, take the rotary
Fig.2: most of the components are wired on top of the PC board.
The exceptions are the zero adjust trimpot (R25), the buzzer and
the banana jack socket sleeves.
RESISTOR COLOUR CODES
Resistor
R3
R4
R5
R6
R7
R8
R8
R8
R9
R10
R11
R12
R13
R14
R15
R16
R17
R18
R19
R20
R21
R22
R23
R24
R26
Value
5kΩ
40kΩ
150kΩ
800kΩ
4MΩ
15MΩ
10MΩ
5MΩ
3kΩ
102Ω
10Ω
0.99Ω
83.3kΩ
360kΩ
1.8MΩ
6.75MΩ
20kΩ
2kΩ
44.2kΩ
18.5Ω
200Ω
34kΩ
190kΩ
10kΩ
2.1kΩ
5-Band Code (1% tolerance)
green black black brown brown
yellow black black brown
brown green black orange brown
grey black black orange brown
yellow black black yellow brown
brown green black green brown
brown black black green brown
green black black yellow brown
orange black black brown brown
brown black red black brown
brown black black gold brown
black white white silver brown
grey orange orange red brown
orange blue black orange brown
brown grey black yellow brown
blue violet green yellow brown
red black black red brown
red black black brown brown
yellow yellow red red brown
brown grey green gold
red black black black brown
orange yellow black red brown
brown white black orange brown
brown black black red brown
red brown black brown
February 1997 43
Where To Buy The Kit
The kit for this multimeter is available from all Dick Smith Electronics
stores for $29.50. (Cat K-1050).
The finished PC board clips into the back of the meter case. As can be seen, most
of the components are multiplier resistors for the various ranges.
knob and make sure it fits onto the
selector plate. Make sure that, when
pushing the knob onto the selector
shaft, the keyway on the shaft lines
up with the knob.
•
•
•
•
•
•
Next, insert a small spring into the
hole located on the side of the selector
plate. Smear a little petroleum jelly
(Vaseline) around the selector housing
where the ball bearing will run and
MULTIMETER SAFETY WARNING
This meter must not be connected to high energy sources which have transient
voltages greater than 1000V. This includes the 240VAC mains.
Do not connect the meter to a circuit which is greater than 1000V peak above
ground.
Do not use the meter if it is damaged.
Inspect the test leads for damaged insulation or exposed metal. Check test
lead continuity. Damaged leads should be replaced.
Select the proper function and range for your measurement.
Do not change ranges while the meter is connected to live circuits.
44 Silicon Chip
place a dab into the end of the spring.
This done, place the selector plate into
the case housing and push the spring
with its accompanying ball bearing
into position.
Now turn the meter over, at the same
time applying pressure to the selector
plate so that it doesn’t pop out. Line
up the selector knob keyway and from
the front of the meter, push the knob
into place.
(12). Position the rotary wiper on
the selector plate, with the integral
plastic pillar locating the metal tab.
Use a hot soldering iron to melt the top
of the plastic pillar so that the wiper
is permanently fixed in place.
(13). Solder the meter wires to the
PC board (note polarity).
(14). Solder the 9V battery terminal
wires to the PC board (points B2+ and
B2-; note the polarity).
(15). Before clipping the PC board
into position, clean and polish the
circular tracks of the selector switch.
Methylated spirits will help dissolve
any flux residues from soldering.
(16). Insert the batteries into their
respective holders. Fit the back of the
meter case and its retaining screw; do
not overtighten it. Finally, fit the knob
for the zero adjust trimpot (R25).
Congratulations, you have finished
the assembly. There’s one more step
before you can make measurements.
Zeroing the meter
Before doing any measurements,
always check that the meter pointer
is on zero at the left end of the scale:
(1). Put the meter in the position that
it will be in when measurements are
made; ie, normally horizontal.
(2). Remove the leads from the meter
and check that the pointer is not being
deflected by stray electromagnetic
fields.
(3). If the pointer is not on zero then
rotate the slotted plastic ‘screw’ near
the pivot axis of the pointer.
(5). Give the meter a light tap on
the side to ensure that the pointer has
settled properly.
Now you are ready to make meas
SC
urements.
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.jaycar.com.au
SATELLITE
WATCH
Compiled by GARRY CRATT*
Apstar 1A, 134°E longitude:
The location of Apstar 1A has angered
Indonesian satellite operator Pacifik
Satelit Nusantara, who claim to have
registered the orbital location in 1993 for
their Palapa Pacific 1 satellite. The com
pany intends to make a formal complaint
to the ITU. As has been demonstrated
in the past, orbital location conflicts
are becoming more common with the
squeeze for spots over Asia. Indonesia
has been testing a new ground station,
causing interference to the Apstar signal.
Asiasat 2, 100.5°E longitude:
The Egyptian Telecommunications
Union has signed a multiple year lease
for one 36MHz transponder on this satel
lite for the provision of Arabic language
(and others) throughout the Pacific. The
transponder should be operational by the
time this column goes to press.
Elsewhere on AS-2, the final partic
ipant in the European bouquet, Italian
broadcaster Rai International com
menced operation in early November.
The 5-channel digital TV service is now
fully loaded and carries German, French,
Italian, Spanish and the European music
channel MCM, as well as 10 European
radio stations.
A further addition to this package is
the projected feature of a 1-way Internet
browser, to the Deutsche Welle service.
By tuning a digital satellite receiver to
the signal and through the addition of
a simple decoder box between receiver
and computer, selected Internet sites
can be downloaded at up to 255kbp/s,
a significantly better rate than through
a telephone line.
The service is due to commence on
Asiasat 2 in March, following successful
trials on some of the Deutsche Welle
analog satellite channels in Europe and
the USA. A 2.3m satellite dish is required
for the reception of this digital package,
in both Australia and New Zealand.
Panamsat 2, 169° E longitude:
Chinese Television Corporation (CTN)
has announced it will use this satellite to
transmit news feeds from within Taiwan,
Northwest Asia and the Western USA to
studios in Taipei.
Use of the transponder should com
mence early in February. Few analog
transponders remain on this satellite
(CNN, NHK, TVSN), as Panamsat has
elected to adopt the Scientific Atlanta
MPEG PowerVu compression system
exclusively, when a digital platform is
required. The proprietary S/A PowerVu
system is not immediately capable of re
ceiving DVB compliant MPEG-2 signals.
Gorizont 30, 142.5°E longitude:
Papua New Guinea broadcaster EM
TV has now adopted Video
crypt full
time, based on observations made dur
ing December last year. The motive for
scrambling all programs (even four hours
of test pattern every morning) remains
unclear as the broadcaster had advised
they would be scrambling selected
programs only, to prevent unauthorised
re-broadcasting.
Tamil broadcaster “Raj TV” has now
disappeared from this satellite. Many
operators have shown concern at the
increasing degree of orbital inclination
of this class of Gorizont satellite.
Equipped with only north/south atti
tude correction, geostationary operation
can only be guaranteed for two years or
so, before inclined orbit operation is
necessary. The effect of this is to force
all ground stations to adopt dish tracking
which is often not practical. No doubt
EM TV will be faced with the decision
to “ytrack” or change satellites during
1997.
Gorizont 29, 130°E longitude:
Although reported as being sold to
a consortium in the Philippines and to
be used for coverage of the Asia Pacific
Economic Forum held in Manilla in No
Italian broadcaster Rai International
commenced operation on Asiasat 2 in
early November.
vember last year, the satellite remained
on station at 130°E instead of being
moved to 153°E as previously advised.
All television broadcasts on this
satellite have ceased and the fate of the
satellite, which still has several more
years of active life (in an inclined orbit)
remains unclear.
Optus B1, 160°E longitude:
Sky network New Zealand will com
mence their long awaited satellite pay
TV service in April. Initially, it will be
operated in analog using Videocrypt
scrambling (the same system used on the
Sky network terrestrial pay TV system
in New Zealand).
As deregulation of the pay TV industry
will occur on July 1 this year, the service
could be available in Australia almost
immediately after commencement.
Measat 2, 148°E longitude:
First signal reports of testing on this sat
ellite were received in December last year.
By the time this column goes to press, C
band signals should be observable along
SC
the east coast of Australia.
* Garry Cratt is Managing Director of AvComm Pty Ltd, suppliers of satellite TV
reception systems. Phone (02) 9949 7417.
http://www.avcomm.com.au
February 1997 53
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.
AC power supply for
photographic flashgun
This circuit has been used to power
a professional flashgun of about 200
joules. It has capacitors of 1500µF
rated at 500V with a maximum surge
voltage of 530V.
The power supply delivers a regulat
ed 480V to the high voltage capacitors
and allows for mains variation of ±9%.
An Arlec transformer which had two
secondary windings of 12.6V <at> 3.5A
on a segmented bobbin was rewound
to provide a secondary voltage of
395V AC.
A full-wave rectifier gives positive
half sinewaves of 560V peak and these
are truncated at 480V, using four 120V
zener diodes in series. This zener-reg
ulated voltage is applied via diode D5
to the gate of SCR1.
The SCR fires every time its gate
is higher than the cathode by about
0.6V. The resultant pulses charge the
capacitors until they reach 480V and
then the SCR stops conducting and
then fires intermittently to maintain
54 Silicon Chip
the voltage. The fluctuation appears
to be around ±1V.
A neon lamp was used as a flashing
“ready” indicator. It fires at around
85V and drops to 62V while con
ducting. This range is increased by
the divider action and was deemed
unsatisfactory. A 0.1µF capacitor
was connected in parallel with the
neon, transforming it into a relaxation
oscillator. Every time the capacitor
reaches the firing voltage of the neon,
it fires and discharges the capacitor.
The cycle is repeated while ever the
supply is above 450V. This is adjusted
by the 100kΩ resistor (in parallel with
the neon).
The 470Ω 20W resistor limits the
current charging the capacitors when
they are fully discharged and natu
rally affects the time taken to reach
full voltage. The system takes about
six seconds to recharge the capacitors
after each flash firing. When the flash
extinguishes the capacitors still have
about 100V when starting to recharge.
The SCR is protected by diode D6
when the AC is switched off and the
capacitors are still charged.
Many modern flashguns of this ca
pacity operate at 350V and the supply
should be modified accordingly.
Warning: this high voltage supply is
potentially lethal. Only experienced
persons should attempt to build it.
V. Erdstein,
Highett, Vic. ($40)
Precision analog
multiplier
The National Semiconductor LM
13600 and LM13700 ICs, known
as “dual output transconductance
amplifiers” differ from ordinary IC
amplifiers in two main respects. First,
they produce output currents instead
of output voltages and second, their
gains (gm) are variable as functions
of input (control) currents.
These properties make these ICs
useful in applications such as voltage
controlled amplifiers and filters, auto
matic gain control (AGC) amplifiers
and voltage multipliers. Examples of
the latter include RMS voltmeters,
power meters and watt-hour meters.
One problem with these ICs is that
the relationship between gain and in
put control current is not perfectly lin
ear over their entire operating ranges.
In some applications this may not be a
serious problem but if these ICs are to
be used in precision applications then
it could be significant. That turned out
to be the case with a project which
was intended to measure the energy
in high voltage pulses.
The design concept involved us
ing one of the two amplifiers in an
LM13600 to generate an output voltage
proportional to the square of an input
pulse voltage. This voltage could then
be integrated using an ordinary op amp
to obtain the pulse energy. The circuit
used was a “four quadrant multiplier”
and was an adaptation of a circuit
in the National Semiconductor data
sheets for this device.
The problem showed up as an
asymmetry in the output waveform
for the positive and negative halves
of a sinusoidal input. The degree of
asymmetry in the waveform began
to be significant for output voltages
outside the range of 0-200mV peakto-peak. This effectively limited the
basic operation within this range
since gain symmetry was a critical
requirement.
The non-linearity problem was
solved by a cancellation method: two
identical circuits were set up but with
the signal into one reversed in phase
with respect to the other and the out
puts of the circuits were combined, as
shown in the accompanying circuit.
In this mode of operation, the out
put waveform was symmetrical over
the range of 0-3V peak-to-peak (a 15:1
improvement over the basic circuit).
Also, the output distortion at frequen
cies above 10kHz was significantly re
duced at all signal levels. The circuit is
usable for input signals up to 200kHz.
Herman Nacinovich,
Gulgong, NSW. ($50)
February 1997 55
Control
Multipl
Last month, we featured the circuit details of
this Smoke Alarm Monitor. It will control up to
10 smoke detectors with the ability to disarm
and automatically rearm two detectors so
you can cater for childrens’ parties, candlelit
dinners and open fires in the winter. This month
we give the construction and installation details.
Based on cheap and readily avail
able ionisation smoke detectors, this
Smoke Alarm Control Panel solves
the problems of maintaining contin
uous monitoring of up to 10 smoke
detectors. Why 10? As outlined in last
month’s article, if you have only one or
two monitors in the typical Australian
home, you are not safe against fire. Fire
56 Silicon Chip
could start in a room with a closed
door and even if a smoke detector is
ultimately triggered it may be too late
to save your home or your life.
As noted last month, you need a
smoke detector for every bedroom
which has any electrical equipment
plus a detector for every other room
with electrical gear, apart from the
kitchen and garage. For more informa
tion along these lines and the circuit
description, you will need to refer to
last month’s issue.
In setting out the construction
details, we will first discuss the as
sembly of the Control Panel and then
continue with the modification of
standard smoke detectors which are
available from any hardware store or
supermarket. Finally, we will discuss
the installation of a typical home
system.
Control panel assembly
The SILICON CHIP Smoke Alarm
Control Panel is housed in a plastic
case measuring 180 x 260 x 65mm.
This would normally be mounted on
a wall and so the top cover of the case
becomes the control panel. We fitted
PART 2:
By JOHN CLARKE
l Panel For
le Smoke Alarms
Left: the finished Smoke Alarm
Control Panel has 10 LEDs which
cycle through as each smoke detector
is polled. The smoke detectors are
modified battery operated units which
are much cheaper to buy than mainspowered detectors.
our prototype with a Dynamark label
measuring 127 x 144mm.
Inside the case, the circuit compo
nents are mounted on two separate PC
boards. The main board measures 149
x 251mm and is coded 03312961. It is
installed in the base of the case and
has a number of multi-way terminal
connectors for all the connections
from the smoke detectors. Two large
holes at the top of the main board are
for cable entry for the smoke detector
wiring, although these may not be used
if the cables are brought in via one of
the side panels.
The second board measures 112
x 151mm. It is coded 03312962 and
it carries all the LED indicators and
pushbutton switches for the smoke
detectors.
Before you begin assembly of the
The finished front panel board with all the LEDs in place. Note that they must
be test-fitted in the front panel before they are soldered.
PC boards, check each one for shorts
between tracks or breaks in the cop
per pattern. You may need to drill
out some holes for mounting the PC
boards, the transformer, REG1 and
for cable ties to hold down the SLA
battery. The component overlay for the
main board is shown in Fig.1 while the
second board is in Fig.2.
Install all the links first and note
February 1997 57
Fig.1: this is the
parts layout for the
main PC board.
Take care to ensure
that all polarised
parts are correctly
oriented and note
that a heatsink
must be fitted to
REG1. The 12V SLA
battery is secured to
the board using two
plastic cable ties.
58 Silicon Chip
Fig.2: the component overlay for the front panel board. This board mounts
face down into the front panel.
that you must choose the appropriate
link for the preset disarm period you
require. Fig.2 shows the link for a
15-minute disarm period although we
suggest that most people will want a
longer delay – the choice is yours.
Next, install the resistors, using the
resistor colour code table as a guide to
the values. Alternatively, use a digital
multimeter to check each resistor be
fore it is installed. This done, insert
the diodes, taking care with their
orientation. Note that diodes D1-D20
(see Fig.1) are installed with their
cathode bands facing IC2. Similarly, on
the second board, diodes D22-D29 are
all oriented the same way, with their
cathode bands away from the switches.
Note that there are two types of
diode used on the main PC board: 1A
1N4004s which have a black body
and the smaller 1N914s which usually
have an orange glass body. The 13V
zener diode ZD1 is similar in size to
the larger diodes so be careful to install
it in its correct place.
Five PC stakes are installed on the
main PC board. Four of these are for
the transformer secondary and the
SLA battery terminals. The fifth is
mounted at the end of the SLA battery
position to stop it from moving along
the board and encroaching on adjacent
capacitors.
Next, insert and solder in the ICs.
Take care with the orientation of each
and check that the correct type has
been installed before soldering. The
3-terminal regulator REG1 is mounted
horizontally on a small heatsink using
a 3mm screw and nut. Bend its leads
so that they insert into the holes pro
vided. There are three transistors to
be mounted on the main board; make
sure they are oriented correctly.
Take care with the polarity of the
electrolytic capacitors when they are
installed. Note that the electrolytics
on the front panel board are mount
ed horizontally to allow clearance
between the board and front panel.
Switches S1-S13 are oriented with
the flat side towards the top edge of
the board. We used grey switches for
S1-S11 and S13. Green switches were
used for S12 and S14.
When installing the terminal strips
RESISTOR COLOUR CODES – CONTROL PANEL
No.
2
10
3
25
3
3
1
1
1
Value
470kΩ
100kΩ
33kΩ
10kΩ
2.2kΩ
1kΩ
680Ω
120Ω
100Ω
4-Band Code (1%)
yellow violet yellow brown
brown black yellow brown
orange orange orange brown
brown black orange brown
red red red brown
brown black red brown
blue grey brown brown
brown red brown brown
brown black brown brown
5-Band Code (1%)
yellow violet black orange brown
brown black black orange brown
orange orange black red brown
brown black black red brown
red red black brown brown
brown black black brown brown
blue grey black black brown
brown red black black brown
brown black black black brown
February 1997 59
Fig.3: the wiring details
inside the case. Apart
from the mains wiring,
the interconnections are
made using rainbow
cables terminated to
headers.
on the main board, orient them with
the wire entry side as shown on Fig.1.
Also mount the 180Ω 5W resistor and
the pin headers for the A, B, C and D
connectors. If you use 8-way headers
in the 7-way C and D positions, the end
pin of each should be cut off.
Transformer T1 is mounted on the
main board using 3mm screws and
nuts. The earth solder lug is secured
on the transformer mounting screw
with a star washer and nut. The SLA
battery is mounted on its side with the
terminals facing the 180Ω 5W resistor.
60 Silicon Chip
Secure the battery to the PC board
using cable ties as shown.
Drilling the case
Because it is assumed that the Con
trol Panel will be mounted on a wall,
we have used the case unconvention
ally. The main board is mounted in
the case lid (recognised by the brass
inserts in the four corner posts), while
the front panel is mounted in the base
of the case. This has been done so
that after installation, the lid can be
removed by undoing the four screws.
You will need to drill a hole for the
cord grip grommet adjacent to where
the transformer will be positioned. The
main PC board can be attached to the
lid of the case using 3mm screws at
the mounting standoffs.
The front panel section of the case
will need to be drilled for the switch
es, LEDs and fuseholder. S15 and the
fuseholder should be located 17mm in
from the lefthand edge of the case to
provide clearance for the transformer
body. Position the fuse and S15 at
25mm and 55mm respectively up from
the bottom edge of the case.
The disarm LED11 for alarm 1 is
located 22mm in from the righthand
edge and 22mm from the top edge of
the case. Attach the Dynamark label
with LED11 in the above position and
drill out holes for the switches and
LEDs and insert the 3mm LED bezels.
Place the front panel PC board in
position under the front panel and
secure with 3mm screws and 6mm
spacers into the integral standoffs in
the case. (The spacers can be held in
place over the screw using “Blu-Tack”
as an aid in assembly).
Push the LEDs into the bezels and
solder in place on the board. Then re
move the front panel PC board which
is now ready for wiring.
Fig.4: one of these
PC boards needs to
be fitted inside each
smoke detector. The
board is designed to
fit inside the battery
compartment.
This is a
finished smoke
detector PC
board, about
to be installed
in the battery
compartment
of a Kambrook
smoke detector.
Wiring
All of the wiring details not shown
on Fig.1 & Fig.2 are shown in the di
agram of Fig.3.
This should be closely followed, in
conjunction with the circuit diagrams
published last month.
Cut a 220mm length of 6-way and
a 160mm length of 6-way rainbow
cable. You also need a 400mm length
of 7-way and a 250mm length of 7-way
rainbow cable. Strip one end of each
cable and insert the 220mm 6-way
length into the A bus of the front panel
PC board. The 160mm length of 6-way
cable is inserted into the B bus.
The 400mm length of 7-way cable
is for the C bus and finally the 250mm
length of 7-way is for the D bus. Strip
the other ends of each cable of insu
lation and attach the header pins to
each lead. Now slide the pins into the
header shell and plug it into the main
PC board.
Use 250VAC rated hook-up wire
for the mains wiring. Alternatively,
strip some wire out of the mains cord.
The mains cord should be secured
with the cordgrip grommet so that it
cannot be pulled out of the case. The
green/yellow striped wire should be
soldered to the solder lug located on
the transformer mounting foot.
Use heatshrink tubing over the fuse
and mains switch wiring to prevent
accidental contact with the live ter
minals.
Similarly, the terminals to the trans
former primary must be sheathed in
heatshrink tubing after wiring. Con
nect the short lengths of hookup wire
from the transformer secondary to the
PC stakes on the main PC board.
The battery terminal wiring consists
of short lengths of hookup wire with
spade terminal clips attached to one
end. Solder the free end to the PC stake
on the board, taking care with the po
larity when connecting to the battery.
Apply power to the circuit and
check that there is about 9V between
GND and the + terminal on the ter
minals strips. Initially, LED1 should
light and then LEDs 2-10 should light
in sequence, taking 7 seconds to cycle
through. Press the disarm switches and
check that the associated LED11 or
LED12 lights. They should extinguish
when the associated rearm switch is
pressed.
If you find that the circuit does not
operate as described, check that the
rainbow connectors are terminated
in the correct positions and with the
right polarity. Also check the supply
to all ICs. There should be 9V between
pins 1 & 8 of IC1, IC4, IC5 & IC6; 9V
between pins 16 & 8 of IC2 & IC7; 9V
between pins 4 & 8 of IC3; and 9V
between pins 14 & 8 of IC8.
Smoke detector PC board
The small PC boards for the smoke
detectors can now be constructed.
These measure 46 x 23mm and are
RESISTOR COLOUR CODES – DETECTOR PC BOARD
No.
1
1
1
1
1
Value
1MΩ
100kΩ
33kΩ
10kΩ
1kΩ
4-Band Code (1%)
brown black green brown
brown black yellow brown
orange orange orange brown
brown black orange brown
brown black red brown
5-Band Code (1%)
brown black black yellow brown
brown black black orange brown
orange orange black red brown
brown black black red brown
brown black black brown brown
February 1997 61
This folded-out view of the Control Panel shows the wiring to the two PC
boards. Take care to ensure that the mains cord is correctly anchored.
coded 03312963. You will need one of
these boards for each smoke detector.
Install the five resistors and single
diode and then the transistors; take
care to use the correct type in each
place. Insert and solder the four PC
stakes on one end of the PC board
and the 4-way terminal strip at the
other end.
The capacitors are mounted as close
as possible to the PC board with the
polarity as shown. The LED mounts
with its leads bent at right angles so
that it protrudes above the edge of
the board. We used Kambrook SD28
smoke detectors as our prototypes
and the PC board is mounted with a
self-tapping screw through the battery
holder side panel as shown in the
photograph.
It should be possible to mount the
PC board in the battery compartment
of the smoke detector but the LED may
need to be connected to the lid with
The front panel board is secured to the lid on 10mm standoffs. It is linked to the
main board using rainbow cables terminated in header plugs.
62 Silicon Chip
flying leads in some cases.
Cut off the battery clip for the smoke
detector and solder the supply wires
to the + and GND terminals on the
PC board. To make a connection to
the ionisation chamber, we used an
alligator clip soldered to a length of
hookup wire. You can’t solder to the
ionisation chamber because it is stain
less steel and you can’t undo one of the
screws because they are tamper proof.
To make a secure connection, bend out
one of the metal slots and attach the
alligator clip to this.
On other smoke detectors it is pos
sible to make a connection to a wire
which is attached to the ionisation
chamber.
Finally, attach a length of hookup
wire to the piezo terminal which has
a red wire from the smoke detector
circuit already connected.
We drilled a hole in the side of the
smoke detector case to allow access to
the lower screw terminals on the addon PC board. You may have to make a
different arrangement for other models
of smoke detector. We have produced
a label to designate the external con
nections and a copy of this should be
affixed to the terminal block in each
detector.
Drill a hole in the alarm lid for the
LED bezel, taking care to mark the
correct place before drilling.
Since the smoke detector has now
been modified to be powered from an
external source, there is no need to
access it once it has been installed.
We have produced a label which states
that the are “No user serviceable parts
inside”. Copy as many as you need and
affix them to each detector. This is to
comply with Australian Standards
AS3786-1993.
Testing
When you have finished modifying
all the smoke detectors, they can be
temporarily connected to the Control
Panel. Make sure that the connections
are correct before switching on power.
Note that the “in” and “out” terminals
on the smoke detectors connect to the
“test” and “in” terminals on the con
trol panel. To avoid confusion, they
have also been labelled A and D. The
A terminal (in) on the smoke detector
should attach to the A terminal (test)
on the control panel. Similarly connect
the B to B, C to C and D to D.
Apply power and check that the
LED in each smoke detector flashes
about once every three seconds. Press
the disarm switches to check that the
The modified Kambrook smoke detector. The LED on the PC board protrudes
through the lid and flashes every three seconds as an indication that it is
powered.
Fig.5: this is the
full-size etching
pattern for the
front panel PC
board. Once
again, check the
board carefully
before installing
any parts.
February 1997 63
Fig.6 (left): this is
the artwork for
the main board,
reduced to 70%
actual size. It can
be reproduced
full size on a
photocopier set to
1.41x.
Fig.7 (above):
full size artwork
for the smoke
detector board.
Up to 10 of these
boards will be
required, one
for each smoke
detector.
64 Silicon Chip
No user serviceable
parts inside
Fig.8: copy this label on a photostat
machine and attach it to the outside
of each smoke detector.
A B C D
Fig.9: attach this label
In + Gnd Out to the terminal block in
each smoke detector.
LEDs for smoke detectors 1 and 2 stop
flashing. Press the rearm switches to
reapply power. Before proceeding fur
ther, use some “Blu-Tack” in the top
of each smoke detector piezo siren to
reduce the sound level.
Now press the test switch on the
Control Panel for one of the connect
ed smoke detectors. Its siren should
sound after a few seconds and when
the LED on the Control Panel lights,
it should remain lit for about four
seconds. The alarm will then stop
and the next LED will light. During
this 4-second time interval some of
the other sirens may sound. Make this
test on all connected smoke detectors.
If the test switch on one of the smoke
detectors is pressed, then when the
associated LED on the Control Panel
lights (ie, when the detector is polled,
all the other smoke detector alarms
will sound.
Next, disconnect the mains power
and check that the SLA battery con
tinues to power the circuitry. Do not
forget to remove the “Blu-Tack” from
the piezo sirens after all the checks
have been completed.
Installation
As noted previously, the Smoke
Alarm Control Panel is designed to
mount on a wall and preferably in
side a closet or cupboard. The smoke
detectors should be mounted in ac
cordance with the brochure supplied
with each unit.
Each detector should be linked
back to the Control Panel via its own
length of 4-way telephone cable and
these cables should all be in the ceiling
space. After all, it would be no good if
a fire started and burnt out the cables
before the alarm went off!
Finally, note that the parts list pub
lished last month should show four
1kΩ resistors (not three), while a 47kΩ
resistor should be added to the circuit
between pin 11 of IC5f and the +9V
supply. In addition, one of the 100µF
bypass capacitors should be 10µF. SC
We made the connection to the stainless steel ionisation chamber via an
alligator clip. Other smoke detectors are easier, as they have a wire connection
to the chamber.
ALARM
TEST
REARM DISARM
1
+
+
+
+
+
2
+
+
+
+
+
3
+
+
4
+
+
5
+
+
6
+
+
7
+
+
8
+
+
9
+
+
10
+
+
SMOKE
ALARM
CONTROL
PANEL
Fig.10: this is the full-size front panel artwork for the control panel.
February 1997 65
Part 6: Interpreting Digital Oscilloscope Displays
We must learn to interpret what we see
on the digital oscilloscope screen. The
display is only a reconstructed image of the
waveform which is sampled during a very
small fraction of the total signal time. And
incorrect operation can introduce alias
“ghosts” – signals which don’t exist at all.
By BRYAN MAHER
While digital oscilloscopes are
powerful instruments, they take some
getting used to, particularly for peo
ple who have used analog scopes for
many years.
In reality, there are significant
differences between displays of the
same signal seen on a digital or analog
oscilloscope. And both displays are
likely to be different from the real
live signal.
Each scope shows a different
image, neither of which is a true
representation of the actual electri
cal waveform. For anyone who has
used an analog scope for many years,
there must first be the realisation that
the screen display is not reality and
that both analog and digital scopes
66 Silicon Chip
give different “filtered” views of real
signals.
All of which is an admission that
the signal seen on a digital scope can
look quite different to the same signal
on an analog instrument. Moreover,
on a digital scope, it will probably
look much noisier. Is that noise really
there? Well, yes, in many cases it is
and it is just not seen on the analog
instrument.
These noisy traces are in sharp con
trast to the smooth traces of an analog
scope. Together with the complexities
of screen menus, they make some longtime analog scope users reluctant to
invest in a digital storage scope. This
aversion is unfortunate, for it denies
those people access to the great signal
processing advantages of the digital
instrument.
Why the trace wriggles
The wriggly nature of the trace hits
you in the eye, even on large amplitude
signals, such as that shown in Fig.1.
By contrast, the same signal displayed
on an analog scope is likely to be as
clean as whistle.
What happens when we photo
graphically enlarge a portion of the
baseline trace seen in Fig.1? The result
of an 8-times magnification is shown
in Fig.2. The wriggles are a form of
noise. But their large amplitude, even
on signals as big as 8V, indicates some
source other than random noise at the
scope input. And because of the dig
itising process the digital scope trace
tends to have a characteristic “jaggy”
appearance.
This is very different from the nat
ural random noise generated in high
gain preamplifiers which we see on
analog scopes. But some noise im
pulses are too fast to generate enough
light in the phosphor and so are not
visible unless we turn up the bright
ness. This means we are never sure of
the true amount of noise when using
an analog scope.
The jaggies on all digital scope
displays operating in simple mode
Fig.1: a digital scope can find an elusive glitch but the trace is wriggly,
even on 8V signals.
Fig. 2: photographically enlarging the trace of Fig.1 shows an artificial
jaggy waveform, characteristic of digital scopes used in simple mode. This
jaggy waveform is independent of signal amplitude.
stem from four sources. The first and
predominant cause is inherent noise
within the analog to digital (A/D)
converters.
Digitising rates
Designers face great problems when
digitising rates from 100MS/s up to
8GS/s are required. At this rate, even
flash A/D converters are inadequate,
because their speed is ultimately
limited by the slew rate of the analog
comparators used. A new technology
is needed.
In many Tektronix digital scopes an
extra component is added. At a very
fast sampling rate, one complete re
cord (collection) of samples is passed
into a proprietary line of special sem
iconductor analog storage elements.
Then the sampler pauses, while this
temporarily stored analog record is
shifted out at a slower rate to an A/D
converter. The digital data so produced
is concurrently recorded in the mem
ory. This double shuffle achieves the
complete digitisation at an apparent
rate extending up to 5GS/s.
Other manufacturers combine many
digitising paths to achieve high speed.
The Hewlett Packard HP54720/10
model contains 16 500MS/s 8-bit
flash A/D converter channels. All the
data outputs can be interleaved to
produce an equivalent 8GS/s rate of
A/D conversion, with an extremely
short effective sampling period of one
picosecond.
Such speeds are way beyond the
capabilities of any direct single stage
A/D converter technology currently
in existence. Digitisation in multiple
stages, though necessary to achieve
the required speed, unfortunately does
generate noise. This is the dominant
cause of the wriggly baseline and trace
observed when any digital storage
scope is used in simple mode.
Digital oscilloscope manufacturers
admit that the displayed baseline and
trace always contains wriggles of two
to three pixels in amplitude. One pixel
is the smallest possible increment in
vertical amplitude of the display and
is equal to 1/256 or 0.4% of the screen
height.
Because the digitising section comes
after the preamplifier and attenuator
stages, this noise introduced by A/D
conversion is the same at all signal
levels. In stark contrast, analog scopes
only show baseline noise on tiny
signals, of much less than a millivolt.
Averaging mode
One way to reduce the apparent
noise on a digital scope waveform
is to operate in averaging or High
Resolution mode. Averaging means
the digital data from a number of suc
cessive recurrent sweeps is averaged
before being displayed. HighRes is an
ingenious method wherein averaging
can be done even on a oneshot. Be
cause random noise averages out to
Fig.3: to
demonstrate
quantisation noise,
the lower trace
sinewave signal
was sampled,
digitised and
immediately
reconverted back
to analog, then
displayed in the
upper trace. Any
imperfections not
noticed in the lower
trace are enlarged
in the upper trace
by the digitisation.
February 1997 67
zero, the trace then seen on the screen is much smoother.
We will investigate averaging and high resolution modes
in the next chapter.
Quantisation noise
A second cause of the wriggly trace in digital scopes is
the quantisation noise described in the previous chapter.
Readers will recall that the A/D converter breaks down
the continuous analog signal into 256 or more discrete
decision levels. The A/D converter output data is a digital
code representing the nearest decision level below the
voltage of the analog sample.
Quantisation noise arises from the difference between
the actual voltage of each sample and the smaller voltage
values represented by the corresponding digital words.
A steadily rising analog voltage into an A/D converter
produces a digital output rising in a staircase of discrete
steps. The same applies for falling slopes. So the trace
displayed on any digital scope is fundamentally a series
of small increments, rather than a smooth continuous
line.
Quantisation also results in a secondary source of
noise. If an analog signal is just below some particular
decision level, any tiny fluctuation or noise spike can
push the signal momentarily above that decision level.
Thus the next higher digital data is generated by the A/D
converter, lifting the display up one whole pixel each
time this occurs.
It is possible to demonstrate quantisation noise. In
the analog scope photo of Fig.3, the lower trace shows
a sinewave which was also fed into a sampler and A/D
converter.
The resulting digital data was immediately converted
back to analog form by a digital/analog (D/A) converter
and the result shown as the upper trace.
Small irregularities are present in the lower sinewave
but are too fast or too small to be noticed. And some
noise exists in the reference voltage of the A/D convert
er. Each fast noise impulse momentarily lifts the analog
amplitude up into the next decision level, so producing
a higher digital word. Thus lots of small step errors are
produced.
Pulse stretching
This sequence of scope waveforms shows a
sinewave signal at 10kHz displayed on a digital
and an analog scope. The top waveform is from a
Tektronix TDS 360 digital scope in sample mode at
2 megasamples/second while the middle waveform
is at the same sample rate but in average mode
(128 waveforms averaged). Finally, the bottom
waveform is from an analog scope. Note the very
smooth trace.
68 Silicon Chip
A third effect which makes quantisation noise worse
could be called “interference pulse stretching”. Many
noise pulses are too fast to be seen on an analog scope
but when captured by a digital scope’s sampler, it
holds the signal voltage steady until the next sample
is taken. Hence the sampler stretches fast noise pulses
out to equal the sampling period, so they can be more
clearly seen.
A fourth very important contribution to the wobbly
trace displayed on any digital scope is directly related
to the waveform capture rate and screen update rate.
This points up the vital difference between the dis
play on any scope and the real live signal we wish to
investigate.
Using an analog scope, in many circumstances you
will never see noise impulses, for two reasons, as illus
trated in Fig.4.
Firstly, they are usually not in synchronism with the
scope’s horizontal sweep and so occur on a different part
Fig.4: an analog scope may update
its display every five microseconds,
with about 500 sweeps superimposed.
Individual asynchronous noise pulses
do not overlay, so they are usually not
seen.
of the trace each sweep.
Secondly, and this is of the utmost
importance, very often the display on
an analog scope is an overlay of hun
dreds or thousands of superimposed
sweeps.
Suppose for example that you are
looking at the 3MHz signal shown
in Fig.4(a), with the sweep speed set
to 0.1µs/div. The forward trace takes
1µs and the retrace and holdoff might
occupy 2µs each, as illustrated in
Fig.4(b). That is 5µs for each complete
display cycle. Therefore, your scope
trace will sweep across the screen
200,000 times each second.
This is your update rate, the num
ber of times your display is renewed
each second. All these traces are being
drawn on your screen, each one on top
of the last.
You are capturing and displaying
only one out of every five microsec
onds of the live signal. You could say
your waveform capture rate is 200,000
waveforms/second, which in this case
is 20% of the live signal.
If you have turned up the brightness
(intensity) such that the effective per
sistence time of the screen phosphor is
2.5 milliseconds, then the display you
see is the overlay of about 500 traces
superimposed, each showing the same
signal pattern.
The display is really the average of
500 views of the input signal, with
the noise averaging towards zero.
Therefore you will never notice the
noise that is present and the trace and
baseline will be the smooth clean lines
which analog scope users have come
to expect.
But this means that analog scope us
ers are blissfully ignorant of noise and
interference which could be playing
Fig.5: a conventional digital scope may sample the real live signal for only one microsecond, then display
that segment for perhaps 33,000us. You see only 0.003% of the live signal.
February 1997 69
Fig.6: a 2kHz
sinewave was
sampled at 2200S/sec.
This too-slow rate
generated a 200Hz
alias frequency which
modulated the input
sinewave, producing
the false waveform
displayed.
havoc with the circuit or equipment
they are measuring.
When those same signals and inter
ferences are fed to a digital scope as
illustrated in Fig.5, the display will be
quite different. Because of the effects
listed above, noise pulses are recorded
along with the wanted signal.
Even though these interference
pulses may be only nanoseconds in
duration, they are liable to be dis
played. That might be regarded as a
disadvantage of the digital scope. But
many digital scopes also have a big
advantage – they can be programmed
to find glitches.
The scope waveform of Fig.1 is such
a case. The scope was programmed to
search for and trigger the scope display
on any pulse which had a duration
between 0.5 and 4.5µs.
The instrument found one interfer
ence pulse having a duration of 2.01µs
within a collection of thousands upon
thousands of clean signals. With the
scope triggered on this glitch you can
see and analyse it.
Some digital scopes can be set up
to be triggered on runt pulses or on
specified glitches as short as 2 nano
seconds. This is just not possible with
analog scopes.
sinewave you will see about two cycles
of that signal, indicating a frequency of
only 50Hz! But if you raise the sweep
speed to 20ns, the scope will sample
at 2GS/s. Then a little more than two
cycles of the same input signal will
be displayed, indicating the true fre
quency, 13MHz.
We should always use the scope
to achieve the fastest sample rate
possible, otherwise the display may
show the wrong frequency reading.
Or in other cases we may observe
distortion on fast edges in a complex
waveform, with the low harmonics re
produced larger and out of proportion
to the high harmonics. In other cases
a signal may seem to drift across the
screen untriggered, like some weird
apparition.
Alternatively the screen may
display a signal component at a fre
quency which does not exist at the
scope’s input terminals, as illustrated
in Fig.6.
Here the input signal is a 2kHz
sinewave and the digital scope is in
correctly operated with an effective
sampling rate of 2200 samples/second.
The display of the 2kHz signal ap
pears to be modulated with a slower
component, which has a period of
5ms, representing a frequency of
200Hz. Yet no 200Hz signal was ap
plied to the scope. Where is it coming
from?
We say the 2kHz real signal is also
masquerading under an “alias” (a false
name) at a lower frequency, 200Hz.
You can see an apparent modulation
pattern which has a 5ms period. It is
important to understand what causes
these strange phenomena and how to
prevent them.
Picturing voltage signals
Normally, when we draw a signal
waveform, we get something like
Fig.7(a) which depicts a 1kHz sine
wave signal. We say that this is drawn
in the frequency domain because the
horizontal axis of the diagram is time
which can be seconds, milliseconds,
microseconds or whatever.
But there is another way of depict
ing the same 1kHz sinewave signal
and that is the frequency domain, as
shown in Fig.7(b).
In this case, the horizontal axis of
the diagram is frequency and since we
only have one frequency it is depicted
as a vertical line at the 1kHz spot on
the axis. The height of the vertical line
is measure of the amplitude, just as it
is in the time domain.
When you connect a 1kHz signal
to a digital scope it will be sampled
at some rate, which we will call the
effective sampling frequency, fs.
Any sampling process generates
harmonics and so the sampler output
will contain the 1kHz input frequen
Aliasing
A completely different type of error
is sometimes seen on a digital scope
when incorrectly used. The effective
sample rate achieved is approximately
proportional to the sweep speed you
select.
For example, a scope which is ad
vertised to sample at 2GS/s will only
achieve that rate when you select the
fastest sweep speed.
But the same scope, when switched
to a sweep speed of 5ms/div has an
effective sampling rate of only 10kS/s!
That difference is crucial.
At that setting, if you apply a 13MHz
70 Silicon Chip
Fig.7: a 1kHz sinewave (a) can be represented in the frequency domain
(b) as a vertical line on the horizontal frequency axis. Its height shows its
amplitude. Sampling (c) at rate fs produces extra frequencies at fs ±1kHz.
Fig.8: complex waveforms (a) can be depicted in the frequency domain (b) by a sequence of vertical lines representing
the fundamental and all significant harmonics. The sampler (c) generates extra copies of all harmonics at the sum
and difference of the sample rate fs and each harmonic frequency.
cy, the sampler frequency fs, plus the
sum frequency (fs + 1kHz) and the
difference frequency (fs - 1kHz). These
frequencies are shown graphically in
Fig.7(c).
If the sampling frequency is 1MHz,
then the diagram of Fig.7(c) will show
the input at 1kHz, sampling frequency
at 1MHz, and the sum and difference
frequencies:
(1MHz + 1kHz) = 1,001kHz; and
(1MHz - 1kHz) = 999kHz
This description is a simplification,
for the sampling process also generates
an almost infinite number of other
multiples at still higher frequencies,
which we choose to ignore.
But most real life waveforms, espe
cially digital signals, are more com
plex and might be like the example
depicted in Fig.8(a). Squarish wave
forms like this can be represented as
the sum of a fundamental frequency
sinewave plus many harmonics.
And each harmonic is a sinewave
with an appropriate amplitude and
a frequency which a multiple of the
fundamental.
So the waveform shown in the time
domain diagram of Fig.8(a) might be
described in the frequency domain of
Fig.8(b) as a fundamental frequency of
1kHz plus many harmonic multiples at
frequencies 2kHz, 3kHz, 5kHz, 7kHz .
. . 21kHz, etc.
We have stopped at the 21st harmon
ic on the assumption that harmonics
beyond 21kHz will be insignificant.
We say that the input signal occu
pies a frequency spectrum extending
from zero to the highest significant
harmonic.
In this case the bandwidth B ex
tends up to 21kHz. We refer to 21kHz
as fB, the highest frequency in the
input signal. We imagine an envelope
shown as a dotted line in Fig.8(b) as
the boundary of this spectrum B.
When the complex waveform
shown in Figs.8(a & b) is sampled, the
sampler output looks something like
Fig.8(c). Here we arbitrarily chose the
sampling rate fs = 1MHz, so that fs is
much larger than fB.
The sum components generated by
the sampler include the frequency fs
added to the fundamental and to each
harmonic of the input. These extend
from fs up to the frequency (fs + fB).
The difference components extended
from fs down to the frequency (fs - fB).
That is, the spectrum of the sampling
products extends from (fs - fB) up to
(fs + fB).
Low pass filter
The A/D converter must only see the
spectrum of the input signal up to fB
but none of the products of sampling;
ie, above 21kHz in this case.
To achieve this rejection, digital
scopes include a programmable dig
ital low pass filter (LPF) between the
sampler and the A/D converter. The
lower part of Fig.8(c) shows this filter
and its passband, drawn here just a
smidgen wider than fB.
This filter passes the input signal
spectrum on to the A/D converter but
blocks all other frequencies above fB.
That desirable result depends on the
sampling rate fs being much higher
than the highest significant harmonic
(fB) in the input signal. That point is
vital!
Just how much higher is enough?
And what happens if fs is not high
February 1997 71
Fig.9: if the sampling rate is too low (a) the spectrum (fs - fB) overlaps the filter passband, so alias frequencies are
displayed. But (b) if fs > 2fB, all terms generated by the sampler are rejected by the filter LPF, so preventing aliasing.
enough? Fig.9(a) illustrates a case
where the input signals extend 21kHz
but the sampling rate is only 22.5kHz;
much too low.
This could occur if you operate the
digital scope at too slow a sweep rate.
This figure shows just the outline of
Fig.10: this diagram
explains the alias
frequency component
seen mixed with the
2kHz signal in Fig.5.
The alias frequency
is: (fs - f(in)) = (2.2kHz 2kHz) = 200Hz.
72 Silicon Chip
each spectrum instead of depicting
each and every harmonic.
The vital point
Now here is the vital point. Because
fs is so low, the sampler products in
trude into the spectrum of the input
signal. More importantly, many of
those sample frequencies will pass
through the low pass filter (LPF). So
they pass to the A/D converter and are
displayed on the screen!
Frequencies generated by the sam
pler which overlap the LPF passband
include (fs - fB) = (22.5kHz - 21kHz)
= 1.5kHz; then (22.5kHz - 19kHz) =
3.5kHz; then 5.5kHz, etc in steps up
to 20.5kHz. These “false” signals will
appear on the screen, mixed in with
the real signal.
With all those false frequency com
ponents mixed into the input signal,
the waveform displayed on the screen
will be nothing like the true shape.
Aliasing can make a signal look like
something it is not!
Nyquist criterion
So what is the minimum sampling
frequency needed to avoid aliasing?
Fig.9(b) shows the situation where
aliasing is just avoided.
Here the lowest frequency produced
by the sampler, (fs - fB), is just a smid
gen higher than fB. The frequency
clearance between fB and (fs - fB) pre
vents any overlap of the two spectra.
So under this condition aliasing is
avoided.
To put that into figures, we need:
(fs - fB) > fB; meaning that fs > (fB + fB)
or ultimately, fs > 2fB.
In plain English, that means that
the sampling frequency must be more
than twice the highest frequency com
ponent in the input signal.
This requirement is called the
Nyquist Criterion, which is invoked to
prevent aliasing errors in any system
which uses sampling.
The foregoing discussion supposes
that the response of the filter drops like
a rock to zero at the end of its nominal
passband; ie, a “brick-wall” filter.
But the response of real low pass
filters is never as steep as that and
some harmonic components beyond
the nominal passband will always
pass through.
Hence, to prevent aliasing distor
tions, we prefer the sampling frequen
cy to be at least five or even 10 times
the input signal bandwidth.
Weird modulation explained
We can now explain the weird mod
ulation of the waveform seen in Fig.6.
As Fig.10 shows, the input in Fig.6 was
a single frequency sinewave at 2kHz
but the sampling rate was too low at
2.2kHz. Sampling generates the extra
frequencies: (fs - fB) = (2.2kHz - 2kHz)
= 200Hz and also: (fS + fB) = (2.2kHz
+ 2kHz) = 4.2kHz.
200Hz is the alias frequency which
intrudes into the passband of the
low pass filter and mixes with the
2kHz input signal. This produces
the amplitude modulated waveform
seen in Fig.6 even though no 200Hz
component was present in the input
signal.
At very slow sweep speeds, you
might only see the 200Hz signal, noth
ing else; a real trap for young players!
To avoid alias problems when using
a digital scope, keep the sampling rate
high by using either the auto setup
facility or the highest possible sweep
speed. To determine if a signal seen is
an alias, raise the sweep speed or use
the Peak Detect mode.
Lastly, we observe that analog
scopes, because of their linear vertical
deflection systems, cannot produce
SC
aliasing errors.
Acknowledgements
Thanks to Tektronix Australia, Philips
Scientific & Industrial and Hewlett Packard for data and illustrations.
February 1997 73
RADIO CONTROL
BY BOB YOUNG
How radio-controlled models
can be lost through interference
This month, we will continue with the comparison between AM and FM and examine some of
the ramifications of the two systems. One surprising result is the ease with which a model
can be lost through interference.
In the last November 1996 article
I mentioned that we received many
letters and phone calls about the Mk.22
R/C system and that the most common
query was why 29MHz AM? As a result
we went into an in-depth analysis of
the relative merits of AM and FM and
concluded that both systems were
incorrectly named and that “FM” was
greatly oversold against “AM”.
In the end we demonstrated that
the difference between the two sys
tems was much less than commonly
believed. The 29MHz discussion we
left in abeyance and we will have to
deal with that another time.
We also dealt briefly with capture
effect in FM models which in my
Fig.1: the scope trace at the detector of an FM receiver running off a 6-channel
transmitter and with a 7-channel transmitter interfering on the same frequency
at a signal level of approximately 1:2.
74 Silicon Chip
mind is a very serious issue, especially
when we come to single conversion
receivers operating on 36MHz. Let
me explain.
In our discussion on capture effect
in FM receivers we noted that capture
is a phenomenon that occurs when
an interfering signal on the same fre
quency exceeds the wanted signal by
a small margin. The actual point at
which capture occurs depends on the
capture ratio of the receiver and may
vary from 1dB (1.12:1) to a maximum
of 3dB (1.41:1), whereas capture in AM
receivers occurs with signal levels of
100:1 or more.
Figs.1, 2 & 3 show the sequence of
events leading to capture of a radio
control receiver by an interfering trans
mitter. Fig.1 shows the scope trace at
the detector of an FM receiver running
off a 6-channel transmitter and with
a 7-channel transmitter interfering on
the same frequency at a signal level of
approximately 1:2. Fig.2 shows the
same Rx with the two transmitters at
approximately equal level. Note the
severe disruption of the signal.
Fig.3 shows that the signal from
the 6-channel transmitter has gone
bye-bye and it’s hello to the 7-channel
transmitter signal. Control has now
passed over completely to the inter
fering transmitter, which has exceeded
the 1:1 signal level ratio.
At this point, the interfering trans
mitter now has complete control
and the model could easily be flown
away. Indeed, when FM first made
its appearance in England, the press
there reported on a spate of incidents
where models were flown away by
pirate transmitters.
“So what?”, I can hear the “experts”
Fig.2: the same Rx as in Fig.1, with the two transmitters at approximately equal
level. Note the severe disruption of the signal.
saying. Nobody is going to be silly
enough to fly two models on the same
frequency and in years of flying FM
in Australia, there has never been a
recorded incident of a model being
pirated away.
Well let me tell you there is still a
very definite risk of running into strong
interference every time you fly on a
field using both ends of the 36MHz
frequency allocation. There may be no
intention of deliberate interference or
pirating but you could still lose your
model.
When you see how this interference
and capture can easily take place you
will see that there is still a strong ar
gument for operation on the 29MHz
band.
Interference on 36MHz
For some time now, there have been
rumblings amongst the technically
inclined R/C modellers about the pos
sibility of transmitters spaced 455kHz
apart causing interference with each
other.
The significance of 455kHz is that
it is the intermediate frequency (IF)
used in all R/C receivers. This has been
reinforced by the number of glitches
experienced on some flying fields.
There have also been rumblings about
AM receivers not being satisfactory on
36MHz and this has been put down to
interference from harmonics arising
from broadcast FM stations.
The problem arises on the 36MHz
band due to the fact that it consists
of 59 spots spaced 10kHz apart in a
600kHz block.
The 27MHz, 29MHz and 40MHz
bands are only 300kHz wide or less
and therefore there can be no trans
mitters spaced 455kHz apart in these
bands. Hence we are looking at some
thing relatively recent from an R/C
point of view. Thus at each end of the
36MHz band there are a number of
frequencies which are spaced either
450 or 460kHz apart.
All of this has lead to a deal of con
fusion on exactly how to handle the
situation. It particularly affects me
because as the designer and supplier
of the Silvertone Keyboard system of
frequency control, I am responsible
for arranging the keyboards for safe
operation on 36MHz.
Up till now I have always recom
mended that where single conversion
receivers are used, they should be
on frequencies in the middle of the
36MHz band, while dual-conversion
receivers could be used with frequen
cies at each end of the band. In other
words, use dual-conversion receivers
on channels 601-614 (36.010MHz to
36.140MHz) and channels 646-659
(36.460MHz to 36.590MHz) and sin
gle conversion receivers on channels
615-645.
The rationale behind this is that by
using single conversion receivers in
a band only 300kHz wide, a 455kHz
difference signal would not arise in
the mixer and therefore no interfer
ence would occur. For the double
conversion receivers, the first IF is
10.7MHz and therefore the possibility
of the 455kHz difference would not be
a problem. That’s as I saw it, anyway.
How wrong I was! All of this as
sumes that the only two channels
being affected were the overlapping
pair of transmitters.
The situation is complicated some
what by the fact that 455kHz falls
midway between two frequencies. As
long as we use only 20kHz keys (2inch), the key width protects us from
this complication.
What has forced me to rethink this
problem has been a host of discussion
about the existing keyboard and its
shortcomings in dealing with the
new MAAA 10kHz frequency alloca
tions. When I sat down to write the
instructions for the new keyboard I
thought that the 455kHz difference
was not really a problem. But when
I thought about it in detail I realised
that maybe I was coming at it from
the wrong angle.
I needed to get the facts, so I warmed
up the old spectrum analyser, signal
generator and CRO and went to it. All
of this of course was one day before
the magazine deadline (as usual, I can
hear Leo muttering). One hour later I
finished my refresher course on mixer
theory and realised we had all been
thinking inside the square. What I
rediscovered is this:
Any pair of transmitters separated
by 450kHz or 460kHz will generate a
very high level of signal in the mixers
of single conversion receivers, AM or
FM! This will happen in every receiv
er operating on that flying field, regardless of frequency! In other words
one overlapping pair of transmitters
will interfere with all 59 receivers
operating on the 36MHz band.
Now this is pretty startling stuff and
needs some explanation but it is really
quite simple. First of all, the receivers
operating in the 36MHz band (or any
other band for that matter) are wide
open to all frequencies in that band.
That means that a single conversion
receiver which may have a crystal in
the centre of the band still receives all
the transmitted frequencies across that
band – nothing too radical here, so far.
What happens is that normally all
of the difference frequencies between
February 1997 75
Fig.3: here, the signal from the 6-channel transmitter has gone bye-bye and
it’s hello to the 7-channel transmitter signal. Control has now passed over
completely to the interfering 7-channel transmitter, which has exceeded the 1:1
signal level ratio
the incoming frequencies and the local
oscillator (crystal) frequency appear at
the output of the mixer.
However, the IF amplifier is a very
narrow filter which will only pass a
455kHz difference signal to the receiv
er detector. That is why we change
both the transmitter and receiver
crystals when we change frequencies,
so that the difference between the two
is 455kHz.
But if we also have two other trans
mitter frequencies on the band which
differ by 455kHz, they will be picked
up by the front end of the receiver,
will be fed through to the mixer and
the same difference frequency will
automatically appear at the output.
So now we have an apparently
legitimate signal at the output of the
mixer which is very much an inter
fering signal.
Whether this becomes a problem or
not depends on its strength in com
parison to the wanted control signal.
And this is where capture effect comes
into its own.
Capture effect usually works in
our favour and tends to lock out the
455kHz interference in all but the
worst cases. Thus, it is very difficult
to simulate the problem in a simple
three transmitter field test. The danger
arises mainly in situations where the
transmitter radiation patterns sudden
ly favour the interfering pair.
Now the effects on the flying field of
all of this have yet to be verified and
extensive testing needs to be put in
train immediately. In practice, the lev
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76 Silicon Chip
el of interference will vary depending
on a whole host of factors including
capture effect, mixer compression, re
ceiver bandwidth, oscillator injection
levels, relative signal level ratios and
PC board leakage.
The most probable effect is random
interference showing up in the form of
brief glitches as models move in and
out of transmitter radiation patterns.
Add to this the random nature of the
pairing on any one flying field on any
one day. Some days the club would
have some overlapping transmitters,
some days none, some days a large
number.
The more overlapping transmitters
that are transmitting at any one time,
the higher the level of 455kHz gener
ated in the mixers of all receivers on
that field. The effect is cumulative and
impossible to predict.
Now you can see why capture is
so important. Nobody would be silly
enough to fly on the same frequency
but we are accidentally generating the
same frequency every day on flying
fields all over Australia, wherever
overlapping pairs of transmitters are
allowed to operate.
The testing I have carried out to date
is brief and incomplete. I simulated
the 3-transmitter scenario by removing
the crystal from a single conversion
receiver. I could then work the servos
from my modulated signal generator
using a second unmodu
lated trans
mitter 455kHz away to supply the
mixing signal.
In this mode, I could achieve the
equivalent of normal receiver sensitiv
ity, depending on the relative strengths
of the incoming signals.
With a crystal in the receiver (any
frequency) and no carrier from the
wanted transmitter, this effect was still
pres
ent but diminished somewhat,
probably due to mixer compression.
I did not test with a carrier because
capture would confuse the issue and
it is here that extensive testing needs
to be done.
To reiterate, wherever single conver
sion receivers are in use, transmitters
overlapping by 450kHz or 460kHz
must not be used.
The foregoing is yet another reason
for me to continue to push for 29MHz
AM. It is simple, cheap and reliable.
It is free of the complications and
expense of 36MHz FM and is by far
the most cost-effective system for
SC
sports fliers.
SILICON
CHIP
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more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Rod Irving Electronics Pty Ltd
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
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SILICON
CHIP
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more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Rod Irving Electronics Pty Ltd
SILICON
CHIP
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more than likely that it contained advertising
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has requested that the page be removed to
prevent misunderstandings.
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SILICON
CHIP
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has requested that the page be removed to
prevent misunderstandings.
Rod Irving Electronics Pty Ltd
PRODUCT SHOWCASE
WeatherVox – an automatic weather
station with telephone access
Sphere Communications has launched an
innovative weather station system called
WeatherVox. It has all the main features of a
normal weather station except that you can
phone it from anywhere and get a voice report
of the weather over the last 24 hours.
Most of us rely on the Australian
Bureau of Meteorology for the nightly
weather report but more individuals
and organisa
tions, the Bureau’s re
ports are insufficient or not localised
enough.
For example, a rural fire brigade
may be responsible for a large region
of rugged mountainous country which
is heavily forested. Access may be vary
difficult and the weather may easily
vary between extremes on the one day
and from one small area to another.
The only way to know the weather
in each location is to have a weather
82 Silicon Chip
station in each area. That may be well
and good but how do you access the
weather information which is being
recorded?
This was the question that exercised
the minds of the people at Sphere
Communications. They could see
many applications for this device,
among rural fire brigades, boating
organisations, golf clubs, life savers,
fishermen, farmers, foresters or anyone
with a need for specialised weather
information.
Even people with holiday homes or
boats on remote moorings could have
an application for this device.
What Sphere Communications did
was to design a computer to interface
to an Ultimeter 2000 commercial
weather station made by Peet Bros
Company, Inc, a company based in
New Jersey, USA.
The computer interface reads all the
weather data from the weather station
and stores it in RAM. Then, when ac
cessed by phone, it will give a voice
report on all the weather information
that it has been programmed to give.
The voice used to deliver the
weather information is that of wellknown Sydney radio & TV announcer
Grant Goldman. His voice, or rather,
many words and phrases, are stored
in two ISD 2590P 90-second voice
recorder ICs (this device was featured
in the February 1994 issue of SILICON
CHIP).
The WeatherVox is a actually a sin
gle board computer with an RS-232
input for the weather station connec
tion and a telephone interface, using
American RJ-11 and RJ-12 telephone
sock
ets, respectively. A number of
functions within the WeatherVox can
be addressed or changed by pushing
buttons of a standard DTMF tone
phone.
Three levels of voice report are
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Intermediate and Detailed. The Brief
report includes time of day, current
outdoor temperature, overnight low
tempera
ture and time at which it
occurred, wind speed and direction,
peak gust today and time of occur
rence, average wind speed over the
last ten minutes, average wind speed
over the last minute, barometric pres
sure, relative humidity and this week’s
rainfall.
The Intermediate report includes
all of the Brief report’s details and
adds this week’s rainfall, this month’s
rainfall, this year year’s rainfall, wind
chill and dew point.
The detailed report includes all of
the Brief and Intermediate reports and
adds highest and lowest temperature
today and times of occurrence, highest
and lowest temperature this month
and times of occurrence plus the high
est and lowest temperature this year
and the times of occurrence.
The parameters can be measured
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can be recorded in Fahrenheit or
Celsius; Wind speed can be metres/
second, knots, km/h or mph; Rainfall
can be in centime
tres, millimetres
or inches; Barometric pressure can
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hectopascals or millibars and finally,
wind direction can be in degrees or
Cardinal points.
All of this information is obtained in
raw data form from the Ultimeter 2000.
It is a compact self-contained unit with
a large LCD screen and 16 pushbuttons
to display the various readings on the
screen. It has inbuilt sensors for tem
perature and barometric pressure and
has external sensors for wind speed
and direction, rain gauge, temperature
and humidity.
The WeatherVox unit itself is a
grey plastic box about the size of a
VCR tape housing. It measures 110 x
200 x 30mm. It contains a multi-layer
PC board that accommodates all the
circuitry. It has been wholly designed
and manufactured in Australia. It car
ries an Austel permit: A95/12/0464.
For more information, contact
Sphere Communications, 161 Bunner
ong Road, Kingsford, NSW 2032.
Phone (02) 9344 9111; fax (02) 9349
5774.
New loudspeakers
from Jamo
Jamo has just released a new range
of loudspeakers called the “8-Series”.
This consists of three bookshelf
and two freestanding models plus
matching centre and surround sound
speakers. All have similar styling with
a moulded front baffle and they are
available in black or mahogany finish.
All have a nominal impedance of 6#.
The details of Jamo 8-Series are as
follows. The Jamo 28 is a compact
bookshelf with a 130mm woofer and
a dome tweeter. Its power rating is
55 watts and it is priced at $399 a
pair. The Jamo 38 is a slightly larger
bookshelf, again with a 130mm woofer
and a dome tweeter. It is rated at 60
watts and retails for $499 a pair. The
model 68 is the largest bookshelf with
a 165mm woofer and a dome tweeter.
Its rating is 80 watts and retails for
$699 a pair.
The model 98 is a 2-way floor-stand
ing speaker with two 165mm woofers
and a dome tweeter. Its rating is 90
watts and it retails for $999 a pair.
AUDIO MODULES
broadcast quality
Manufactured in Australia
Harbuch Electronics Pty Ltd
9/40 Leighton Pl. HORNSBY 2077
Ph (02) 9476-5854 Fx (02) 9476-3231
BassBox®
Design low frequency loudspeaker enclosures
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Uses both Thiele-Small and Electro-Mechanical
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$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
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.
February 1997 83
Finally, the 128 is a large 3-way tower
design with two 200mm woofers. It is
rated at 140 watts and retails for $1499
a pair. Both floor-standing models have
magnetic shielding of the drivers.
All Jamo loudspeakers come with a
5-year warranty and are available from
selected hifi dealers around Australia.
For more information contact Scan
Audio Pty Ltd by phoning 1 800 700
708; fax 03 9429 9309.
Monolithic wireless IC
converts both ways
a range of phase-shift (PSK) half-du
plex wireless digital communications
transceivers. These includes wireless
local area networks, time-division
duplex quadrature modulated commu
nications systems and time-division
multiplex access packet protocol
radios.
Due to its power management mode,
the HFA3724 is suitable for use on
PCMIA cards and other portable ap
plications such as wireless handsets.
It comes in an 80-lead TQFP package.
For further information, contact the
Australian distributor for Harris Sem
iconductor, BBS Electronics Australia
Pty Ltd, Unit 24, 5-7 Anella Ave, Castle
Hill, NSW 2154. Phone (02) 9894 5244;
fax (02) 9894 5266.
1kV miniature
ceramic capacitors
The Harris HFA3724 is the world’s
first monolithic IF/quadrature mod
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Broadcast quality FM stereo
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Other linear amps and kits
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84 Silicon Chip
Philips has recently extended its
range of miniature ceramic capacitors
with the release of a 1kV DC series.
These are available in values from
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±0.25pF or ±5% for SL types and ±10%
or ±20% for class II types.
The operating temperature range is
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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
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Guide to TV & Video
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By Eugene Trundle. First publish-
ed 1988. Second edition 1996.
Eugene Trundle has written for
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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
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latest software diagnostic routines
& includes program listings. 387
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format and R-DAT. If you want to
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this reference book. 305 pages, in
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The Art of Linear
Electronics
By John Linsley Hood. Published
1993.
This is a practical handbook from
one of the world’s most prolific
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English technical magazines over
the years. A great many practical
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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
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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
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digital audio in depth, including
PCM adapters, the Video8 PCM
Power Electronics
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Granberg. Published 1993.
This book strips away the mysteries of RF circuit design. Written
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& CAD. 235 pages, in hard cover
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Surface Mount Technology
By Rudolph Strauss. First pub
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This book will provide informative
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cleaning & quality control. 361
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Audio Electronics
By John Linsley Hood. Published
1995.
This book is for anyone involved
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amplifiers, the compact disc &
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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
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February 1997 85
VINTAGE RADIO
By JOHN HILL
The combined A-B battery eliminator
The year 1927 was notable in radio history
because it marked a real change in the type
of receiver being offered for sale. For the
first time, radios that plugged into household
power became practical and a number of
makes and models were made available.
While there were mains-operated
receivers around before 1927, they
were few and far between and not
many could be de
scribed as being
really successful. But valves such as
the 26, 27, 71A and 80 changed all
that and made workable mains-pow
ered radios possible. From that time
onward, radio receivers became better
and better.
Prior to 1927, almost every radio
was battery-powered and the cost of
replacing those batteries was a major
problem. To help counter this prob
lem, special devices such as “B” bat
tery eliminators and “A” battery trickle
chargers were developed. Of course,
these money saving accessories were
only of use in electrified areas but that
included most of the cities and big
towns, even back then.
For the benefit of younger readers,
it may useful to clarify the terms “A”,
“B” & “C”, as applied to batteries or
associated circuits. The term “A” bat
tery was used for the filament battery
The old Van Ruyten battery eliminator is shown here stripped, ready for
repairs. Like most vintage radio equipment it was in a fairly sorry state.
86 Silicon Chip
and, by usage, the filament circuit as
a whole. The term “B” battery was
used for the high tension battery and
its associated circuitry, while the “C”
battery was for grid bias circuits.
Of course, battery-powered valve
receivers continued in use for a long
time after 1927, in some cases until the
late 1950s and early 1960s. It took that
long for the electricity grid to reach
some of the more remote regions of
the country.
The battery eliminator
Electrification was a mixed blessing
for some country folk in that, although
their homes had electric power, its
arrival meant the obsolescence of
some existing household appliances,
including the battery radio. In many
instances, however, these radios were
kept in use by the same device that
powered many early battery receivers
– the battery eliminator.
The more modern versions were
actually combined “A” and “B” elim
inators. This type was never on offer
in the 1920s because a satisfactory
A battery eliminator was beyond the
technology of the day. Such a device
required large capacitors and a rec
tifier capable of passing an amp or
more of current. Although such things
were available at the time, their large
size and high price excluded them
from being used in domestic radio
applications.
As a result, the rechargeable “A”
battery continued in use in combina
tion with a trickle charger. This was
the best that could be done at the time.
The combined “A-B” battery elim
inator of the post-war years solved
this problem by using a copper oxide
rectifier and large value electrolytic
capacitors.
Battery receivers made during this
period used low consumption 1.4V
These old electrolytic capacitors were next to useless. Three had virtually no
capacitance while the fourth had an internal short.
this month’s Vintage Radio will delve
into its construction, operation and
restoration.
This particular eliminator uses a
5Y3GT valve rectifier for the high
tension or “B” voltage supply and a
copper oxide rectifier for the filament
or “A” voltage supply. Both voltages
are well filtered using chokes and
electrolytic capacitors. There is also
a rheostat to adjust the output voltage
of the “A” circuit.
The copper oxide rectifier was an
early solid state device and the one
in the Van Ruyten is quite small. It
provides full wave rectification in con
junction with a centre tapped trans
former winding. It was an interesting
exercise to check it and compare its
performance with a pair of 1A silicon
diodes.
In this particular setup, both recti
fiers performed similarly, producing
exactly the same voltage under load.
And although the silicon diodes,
which are quite small, ran warm
under test, the copper oxide rectifier
remained quite cool.
Because it worked so well, the old
rectifier was put back into service
so as to keep the unit working with
as many of the original components
as possible. At least the comparison
proved that a couple of silicon power
diodes could be used to replace the
copper oxide rectifier in this circuit if
the need ever arose, without altering
the output voltage of the unit.
Output adjustment
This view shows the copper oxide low tension rectifier in the foreground, with
the replacement electrolytics to the left. The new electros were mounted on
a piece of thick cardboard as they were too small to be held by the original
clamps.
valves and had considerably reduced
low tension requirements compared
to receivers from the 1920s and 1930s.
A 4-valve set using 1.4V valves con
sumes only 250mA of filament current.
By comparison, a single old 201A
valve pulled 250mA at 5V.
An “A” battery eliminator circuit
using a transformer (which it shares
with the “B” eliminator), a copper
oxide rectifier, a choke and a pair of
500µF electrolytics could supply the
filament requirements of a late-model
battery radio quite easily. Combined
“A-B” eliminators kept many battery
receivers working without the need
to trade-in or modify the receiver for
AC operation.
Restoring an eliminator
Battery eliminators are not that com
mon these days but that doesn’t mean
that they are not worth finding. Any
working “A-B” eliminator is a very
convenient way to operate a vintage
battery radio receiver.
Recently, I was lucky enough to
find such a unit, a Van Ruyten, and
Now this old battery eliminator, like
most other power supplies of that era,
is unregulated in both the “A” and
“B” circuits. To counter this problem
a 6-ohm rheostat is incorporated into
the “A” circuit to help compensate
for various loads that may be applied.
This allows the correct voltage to be
delivered to suit a particular current
demand and there is enough adjust
ment to allow use at 1.4V and 2.0V,
although the latter situation is very
marginal.
The adjustment procedure for set
ting the “A” supply is as follows: (1)
with the eliminator hooked up to the
receiver, connect a voltmeter to the
“A” battery terminals of the set; (2)
back off the rheostat as far as it will
go before switching on; and (3) slowly
advance the rheostat until the desired
voltage is shown on the voltmeter.
And that’s it!
February 1997 87
to fit the new switch to vary the “B”
voltage.
Performance
This view shows the power transformer, the 5Y3GT HT rectifier and the two
Trimax brand filter chokes (beneath the chassis).
The original “B” supply had no ad
justment for altering the output voltage
but this facility was added during the
restoration procedure.
There were a number of other items
that needed attention and the old Van
Ruyten was completely stripped so as
to make the necessary repairs. These
repairs included: replacement of the
filter capacitors and the 5Y3GT rectifi
er valve, a new power cord, repainting
of the steel cabinet and, as mentioned
above, alterations to the high tension
circuit to permit the “B” voltage to
be varied.
The modification to the “B” cir
cuit involved adding a multi-pole
3-position switch so that two pairs
of resistors could be switched into
the plate circuits of the high tension
rectifier. The resistors used here were
10kΩ and 27kΩ and they reduced the
“B” voltage to approximately 60V at
4mA and 45V at 2mA. The unloaded
voltage without the resistors is 150V.
This simple modification was nec
essary so that the eliminator could be
used on 1- and 2-valve regenerative
receivers, which have much lower
“B” voltage and current requirements.
Another reason for incorporating
the variable “B” voltage switch was to
fill a hole in the control panel. Origi
nally the power cord exited through
this hole but a previous repairer has
cut a new power cord hole (and a fairly
ragged one at that) in a far better posi
tion on the side of the cabinet.
As a result, the leftover hole in the
control panel was the logical place
A close-up view of the two filter
chokes prior to installation. The
larger one at the rear is for the low
tension supply.
Because the low tension supply is
unregulated, the supply voltage
varies with the load. This wirewound
rheostat is used to adjust the “A”
voltage to suit the receiver.
88 Silicon Chip
With the restoration completed, a
couple of wirewound potentiometers
were set up in conjunction with volt
and amp meters to monitor the Van
Ruyten’s output capabilities.
The results only proved just how
good modern regulated power sup
plies really are compared to something
from the Van Ruyten’s era. The “B”
voltages can vary by as much as 50V,
depending on the load, while “A”
voltages varied by up to 2.5V.
No wonder there is a rheostat in the
“A” circuit so that the voltage could
be adjusted to suit the load – see Table
1 for details.
Table 1 shows that the “A” supply
is capable of delivering no more than
340mA at 2.0V. Any additional cur
rent is obtained at the cost of reduced
voltage.
These figures seemed to indicate
that an average 1930s battery receiver
with 2V valves would not work sat
isfactorily since it would draw more
filament current than the eliminator
could supply. It was time to find out
whether or not this was to be the case.
The only 2V battery receiver availa
ble for test was a 1937 4-valve Radiola
with a valve complement of 1C6, 1D5,
1K6 and 1D4. All up, these valves
draw about 540mA so it was fairly
unlikely that the Van Ruyten would
be able to fully power this particular
receiver.
And so it proved to be. Even with
the rheostat fully advanced, the “A”
voltage was a meagre 1.6V and while
the set worked, it certainly lacked
performance. In fact, it sounded a bit
sick! Fairly obviously, the old Van
Ruyten power pack was designed for
receivers with 1.4V valves.
Replacing the “A” battery eliminator
with a modern 1A regulated power
supply showed that the 2V valves
would work down to 1.75V. Below
that, the performance starts drops off,
with the receiver virtually ceasing to
function at 1.5V.
Not being the type that gives up
easily, I checked all my spare battery
valves to see if any were more suitable
to the task. Valve filaments are made
to tolerances so some must consume
less current than others.
Eventually, I selected another set of
valves that consumed slightly less cur
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The finished battery eliminator, or “Portapac” as it was called, includes a rotary
switch on the front panel. This switch serves to fill the hole originally used
for the power cord and allows the “B” voltage to be varied in three steps. The
rubber grommet near the output terminals allows screwdriver adjustment of the
“A” voltage rheostat.
rent than the originals. This squeezed
the operating voltage up to just over
1.7V and the old receiver fired up
much better than before.
This was mainly due to a particu
lar 1D4 output valve which had a
much more economical filament con
sumption than the others. That extra
tenth of a volt made a considerable
difference to the set’s performance and
another tenth would bring the set up
to its full potential.
(Editorial note: it has been suggested
in the past that running valve filaments
at less than their rated voltage, but
with normal anode voltage applied,
may shorten the life of the valves.)
Incidently, the “B” voltage drops to
around 125V when the old Radiola is
working properly. The maximum “B”
battery voltage rating for the receiver
is 135V.
Eliminator hazards
Unfortunately, using an unregulated
“A” supply can have serious repercus
sions if one of the valve filaments fails.
That’s because the voltage to the other
valves immediately increases because
of the reduced load.
In the case of the 1D4 (with its 0.25A
filament) failing, approximately 3V
would be applied to the other valve
filaments. While a minute or so of that
sort of treatment probably wouldn’t
do much harm, it mightn’t do 60-year
Table 1
“A” Voltage
1.5V
2.0V
4.0V
“B Voltage”
150V
120V
110V
100V
Max. Current
400mA
340mA
60mA
Current
unloaded
10mA
15mA
20mA
old battery valves much good either.
So if you are contemplating rebuilding
an old battery eliminator, a regulated
supply is the way to go.
Who knows or cares what’s inside
when the lid is screwed on? However,
such an approach is a marked depar
ture from the original circuit and is an
unacceptable restoration as far as some
collectors are concerned.
Trying out the old Van Ruyten
eliminator on a 2-valve bat
tery re
ceiver also proved a disappointment,
although the results were expected.
What may be an acceptable level of
hum in a loudspeaker is not acceptable
through headphones. It mattered not
whether the “A” or the “B” supply,
or both, were used – the hum levels
were distracting. Small regenerative
receivers using headphones perform
SC
best on batteries.
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40 Wallis Ave E. Ivanhoe 3079
Ph (03) 9497 3422
FAX (03) 9499 2381
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Phone (02) 642 6003 Fax (02) 642 6127
February 1997 89
Silicon Chip
Back Issues
September 1988: Hands-Free Speakerphone; Electronic Fish
Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build
The Vader Voice.
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.
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: A 16-Channel Mixing Desk; Build A High Quality
Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random
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.
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.
Wire Antenna Tuner For 6 Metres; Phone Patch For Radio
Amateurs, Pt.2.
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.
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.
July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz);
Burglar Alarm Keypad & Combination Lock; Simple Electronic
Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power
Station.
August 1990: High Stability UHF Remote Transmitter; Universal
Safety Timer For Mains Appliances (9 Minutes); Horace The
Electronic Cricket; Digital Sine/Square Generator, Pt.2.
September 1990: Low-Cost 3-Digit Counter Module; Simple
Shortwave Converter For The 2-Metre Band; the Bose Lifestyle
Music System; The Care & Feeding Of Battery Packs; How To
Make Dynamark Labels.
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; Build
An Egg Timer; Low-Cost Model Train Controller; 1.5V To 9V DC
Converter; Introduction To Digital Electronics; Build A Simple
6-Metre Amateur Band Transmitter.
December 1990: The CD Green Pen Controversy; 100W DC-DC
Converter For Car Amplifiers; Wiper Pulser For Rear Windows;
March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; A Synthesised AM Stereo Tuner, Pt.2;
Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband
RF Preamplifier For Amateur Radio & TV.
April 1991: Steam Sound Simulator For Model Railroads; Remote
Controller For Garage Doors, Pt.2; Simple 12/24V Light Chaser;
Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To
Amplifier Design, Pt.2.
May 1991: 13.5V 25A Power Supply For Transceivers; Stereo
Audio Expander; Fluorescent Light Simulator For Model Railways;
How To Install Multiple TV Outlets, Pt.1.
June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel
Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers,
Pt.2; Active Filter For CW Reception; Tuning In To Satellite TV.
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.
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: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator Mk.II; Magnetic Field Strength Meter; Digital
Altimeter For Gliders, Pt.2; Military Applications Of R/C Aircraft.
November 1991: Build A Colour TV Pattern Generator, Pt.1;
A Junkbox 2-Valve Receiver; Flashing Alarm Light For Cars;
Digital Altimeter For Gliders, Pt.3; Build A Talking Voltmeter
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90 Silicon Chip
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Card No.
For Your PC, Pt.2.
December 1991: TV Transmitter For VCRs With UHF Modulators;
Infrared Light Beam Relay; Colour TV Pattern Generator, Pt.2;
Index To Volume 4.
January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A
Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Experiments For Your Games Card.
March 1992: TV Transmitter For VHF VCRs; Thermostatic
Switch For Car Radiator Fans; Telephone Call Timer; Coping With
Damaged Computer Directories; A Guide To 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; IR 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.
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.
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.
August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light
Array; Microprocessor-Based Sidereal Clock; Southern Cross Z80Based Computer; A Look At Satellites & Their Orbits.
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.
October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless
Microphone For Musicians; Stereo Preamplifier With IR Remote
Control, Pt.2; Electronic Engine Management, Pt.1.
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 1993: Remote Controller For Garage Doors; LED
Stroboscope; 25W Amplifier Module; 1-Chip Melody Generator;
Engine Management, Pt.3; Index To Volume 6.
January 1994: 3A 40V Adjustable Power Supply; Switching
Regulator For Solar Panels; Printer Status Indicator; Mini Drill
Speed Controller; Stepper Motor Controller; Active Filter Design;
Engine Management, Pt.4.
February 1994: Build A 90-Second Message Recorder; 12240VAC 200W Inverter; 0.5W Audio Amplifier; 3A 40V Adjustable
Power Supply; Engine Management, Pt.5; Airbags - How They
Work.
Pt.1; Jacob’s Ladder Display; The Audio Lab PC Controlled Test
Instrument, Pt.2.
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.
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.
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.
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.
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.
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.
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.
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.
December 1994: Dolby Pro-Logic Surround Sound Decoder,
Pt.1; Easy-To-Build Car Burglar Alarm; Three-Spot Low Distortion
Sinewave Oscillator; Clifford - A Pesky Electronic Cricket; Cruise
Control - How It Works; Remote Control System for Models,
Pt.1; Index to Vol.7.
January 1995: Sun Tracker For Solar Panels; Battery Saver For
Torches; Dolby Pro-Logic Surround Sound Decoder, Pt.2; Dual
Channel UHF Remote Control; Stereo Microphone Preamplifier;The Latest Trends In Car Sound; Pt.1.
February 1995: 50-Watt/Channel Stereo Amplifier Module; Digital
Effects Unit For Musicians; 6-Channel Thermometer With LCD
Readout; Wide Range Electrostatic Loudspeakers, Pt.1; Oil Change
Timer For Cars; The Latest Trends In Car Sound; Pt.2; Remote
Control System For Models, Pt.2.
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; Index To Volume 8.
January 1996: Surround Sound Mixer & Decoder, Pt.1; Magnetic
Card Reader; Build An 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.
March 1996: Programmable Electronic Ignition System; 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.
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.
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.
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.
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; Cathode Ray Oscilloscopes, Pt.4.
September 1996: Making Prototype Parts 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); Cathode
Ray Oscilloscopes, Pt.5.
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.
October 1996: Send Video Signals Over Twisted Pair Cable; Power
Control With A Light Dimmer; 600W DC-DC Converter For Car
Hifi Systems, Pt.1; Infrared Stereo Headphone Link, Pt.2; Build
A Multi-Media Sound System, Pt.1; Multi-Channel Radio Control
Transmitter, Pt.8.
April 1995: Build An FM Radio Trainer, Pt.1; A Photographic
Timer For Darkrooms; Balanced Microphone Preamplifier & Line
Filter; 50-Watt Per Channel Stereo Amplifier, Pt.2; Wide Range
Electrostatic Loudspeakers, Pt.3; 8-Channel Decoder For Radio
Remote Control.
November 1996: Adding An Extra Parallel Port To Your Computer; 8-Channel Stereo Mixer, Pt.1; Low-Cost Fluorescent
Light Inverter; How To Repair Domestic Light Dimmers; Build
A Multi-Media Sound System, Pt.2; 600W DC-DC Converter For
Car Hifi Systems, Pt.2.
May 1995: What To Do When the Battery On Your PC’s Mother
board Goes Flat; Build A Guitar Headphone Amplifier; FM Radio
Trainer, Pt.2; Transistor/Mosfet Tester For DMMs; 16-Channel
Decoder For Radio Remote Control; Introduction to Satellite TV.
December 1996: CD Recorders – The Next Add-On For Your PC;
Active Filter Cleans Up CW Reception; Fast Clock For Railway
Modellers; Laser Pistol & Electronic Target; Build A Sound Level
Meter; 8-Channel Stereo Mixer, Pt.2; Index To Volume 9.
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.
January 1997: How To Network Your PC; Using An Autotransformer To Save Light Bulbs; Control Panel For Multiple Smoke
Alarms, Pt.1; Build A Pink Noise Source (for Sound Level Meter
calibration); Computer Controlled Dual Power Supply, Pt.1;
Digi-Temp Monitors Eight Temperatures.
July 1995: Electric Fence Controller; How To Run Two Trains
On A Single Track (Incl. Lights & Sound); 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,
PLEASE NOTE: November 1987 to August 1988, October 1988
to March 1989, June 1989, August 1989, May 1990, February
1992, September 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.
February 1997 91
ASK SILICON CHIP
Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line
and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097.
12V to 6V
conversion
It is common practice, when work
ing on old cars, to upgrade the elec
trical system from 6V to 12V. This is
mainly for convenience because 12V
batteries and light bulbs are far more
readily available than 6V equipment
and if your old car is running on 12V
you can always use the battery from
your modern car to start it.
The bulbs and ignition system can
be replaced with 12V types and a 12V
dynamo or alternator can be fitted. The
car’s starter motor can stand the extra
voltage under normal use and there’s a
bonus in that it spins the engine faster,
making starting easier.
Where the 6V to 12V conversion
starts to get a bit tricky is when you
have to deal with items such as fuel
gauge senders, fan motors, wiper
motors, original radios, solenoids,
etc that can’t be replaced with 12V
equivalents.
One method sometimes adopted
is to create a separate 6V source and
wire it separately to the equipment that
needs it. This can be messy, especially
if you need both 12V and 6V feeds
through the ignition switch.
My purpose in writing is to ask if
SILICON CHIP can design a small cheap
12V to 6V device that can be fitted to
the supply wire of each 6V item that
Mono output from
stereo amplifier
I have a 30W stereo amplifier
and wish to run a mono extension
loudspeaker. I joined the left and
right stereo active signal outputs
but this just causes the amplifier
to overload and cut out. How can
I add a mono speaker to play both
channels?
Thanks for your magazine. I have
every copy which I cherish. (K. A.,
Castle Hill, NSW).
• As you have found, you cannot
92 Silicon Chip
has to stay that way. This seems to
me to be a fairly neat solution to the
problem. If you can come up with
such a device, it would be of great
help to the old car movement. (R. W.,
Yeronga, Qld).
• We have published two circuits
which could form the basis of a 12V
to 6V converter for use in cars. The
first is the PCB Drill Speed Controller
published in January 1994. This would
be good for about one amp or so and
is available as a kit from Dick Smith
Electronics.
Second, another drill speed con
troller was published in August
1992 in the Circuit Notebook pages.
Provided the output transistor had a
suitable heatsink, it could supply sev
eral amps. In either case, you would
adjust the circuit to deliver about
6.8V, for good performance from 6V
accessories.
Solenoid-operated
door strike
I have built the magnetic card reader
described in the January 1996 issue of
SILICON CHIP and I am going to use it
as a door lock. I need to know where
to obtain a solenoid lock and the cost.
And could you please tell me how to
wire it up. (D. H., Como West, NSW).
• It should be possible to purchase
a solenoid-operated door strike from
join the active left and right stereo
outputs to drive a mono loud
speaker. In effect, this connection
would place a short across the two
amplifier channels for the differ
ence signal. Your existing left and
right speakers would not work in
stereo either.
The only way to drive a mono
speaker is to mix the left and right
channel signals via isolating resis
tors (say 22kΩ) and then feed the
mixed signal to a separate power
amplifier which will then drive
your mono speaker.
most locksmiths. Most are powered
from 12V (for just short time) and
could be operated by the relay on the
Magnetic Card Reader. Make sure you
purchase a solenoid strike to suit your
particular door lock.
Remote control for
outdoor use
I am trying to design and build a
remote controller for outside use with
a minimum of 10 buttons, all of which
must be configurable as toggles or mo
mentary action. I know I could adapt
the IR remote train controller circuit
of the Railpower design produced by
yourselves but my first question is
would the IR system be prone to erratic
operation if used outside in any kind of
weather ranging from hot sunlit days
to rainy nights?
I ask this because I realise that the
Railpower unit and most IR control
lers as used for TV etc are designed
for inside use, not outdoors. My next
question is that if no problems would
arise from using this system in those
conditions, then where could I source
the ICs. (S. B., Sydney, NSW).
• No infrared system can be expect
ed to work outdoors in daylight. The
only effective outdoor remote control
will be RF-based, probably UHF, to
obtain a small size. You could adapt
the Railpower system to UHF, using
one the UHF circuits featured in our
February 1996 issue. Better still, why
not adapt the 8-channel design fea
tured in February 1996 to UHF. It is a
relatively simple matter to swap the
IR transmitter output stage to a UHF
output.
Protecting fragile
loudspeakers
My wife has a Mitsubishi hifi unit
and up till now, keeps blowing up the
speakers. Although a bit of a pain, I
have been able to overcome this prob
lem through the local electronic shops
being able to supply same or similar.
This time she has also put paid to
one of the output power transistors,
an NEC D587.
Unfortunately, this has stumped
the locals, who don’t require a lot of
stumping, if I may say so. If you can
help me in sourcing a supplier I would
be most grateful. The only reason the
speakers go is because my other half
is getting hard of hearing. A hearing
aid would be cheaper but this is a
no-go area. Hope you can help. (H. F.,
Perth, WA).
• We suggest that you consider in
stalling PTC polyswitch thermistors
in series with the speakers. These
go temporarily open circuit if their
current rating is exceeded. We suggest
you try installing a type RXE090 or
RXE110 PTC thermistor. These are
available from Jaycar Electronics in
Perth. Phone (09) 328 8252.
As far as the output transistors are
concerned, why not contact your local
Mitsubishi service agent? They are at
329 Collyer Road, Bassandean WA
6054. Phone (09) 377 3400.
Troubleshooting the
Insulation Tester
The Insulation Tester described in
the May 1996 issue of SILICON CHIP
is a very useful piece of equipment
but I have found that the voltages
produced are somewhat lower than
expected. The 100V, 250V and 500V
ranges all produce about 150V. The
600V and 1000V ranges both produce
about 450V.
This is an improvement upon the
19V, 148V, 465V, 540V and 290V being
produced from the respective (lowest
to highest) voltage ranges after first
completing the project but still not
optimal. I effected this improvement
by replacing the CMOS oscillator
chip as I had noticed that the CRO
traces from the oscillator when the
100V range was selected were almost
nonexistent. Could the replacement IC
be faulty as well or is there a problem
with the error amplifier?
Keep those great projects coming.
(N. P., Seven Hills, NSW).
• Your problem is possibly due to
incorrect transformer windings. Check
that the secondary is wound in the
same direction as the primary wind
ing as shown in the diagram of Fig.4
(page 35, May 1996). Try winding the
secondary in the opposite direction to
the way it was.
In addition, check that the range
Dud micro in
Dolby decoder
I have recently purchased the
Dolby Pro-Logic Surround De
coder, Mk 2, as described in the
November & December 1995 issues.
My problem is that, upon powering
up the unit, the display does not
flash “—” at all and the relays do
not change state. In addition, the
noise LED does not light when the
noise sequencer button is pressed.
I have measured the voltages on
the power supply module and all
are ±5%. I have also measured the
voltages on ICs 1-9 as indicated on
page 78 of your magazine article
(bearing in mind the errata previ
ously advertised).
I have identified that when the
unit is powered up, the measured
voltage at PC0 is 0V and remains
at 0V; ie, it does not go high. Hence
Q1 does not switch on to energise
the relays. I have removed IC6 and
applied 5V to each of the 7-segment
LEDs and ascertained that the
7-segment displays are not burnt
out but are in good working order.
resistors on switch S2b are arranged
on your PC board in the correct order.
Flatpack transistor
washers
I am looking to use the new flatpack
MJL21194/21193 tran
sistors as fea
tured in the April 1996 issue but am
having trouble finding the isolating
mica/silicon washers. The magazine
article shows a washer bigger all round
than the transistor. Where did you get
yours? (R. G., Chapel Hill, Qld).
• You can obtain these washers from
Altronics in Perth. They have two
types: silicone/fibreglass Cat. H-7220
x 4 or mica type Cat. H-7120 x 4. You
can phone Altronics on 1 800 999 007.
Trigger happy laser
pistol user
I am writing in regards to the laser
pistol and electronic target described
in the December 1996 issue of SILI
CON CHIP. Could you please suggest
a way to alter the circuit so that the
Each of the switches S5, S6 and
S7 produce 5V at pins 17, 18 and
19 of IC6 respectively when not
pressed and 0V at the same pins
when the respective switches are
pressed. Pin 2 of IC6 remains at 5V
all the time.
I have noted that the voltage sig
nals for “B, A, E, R, S, D” are 5.4V,
1.0V, 2V, 2V, 2V respectively and
that they do not change under any
condition. I have noticed, though,
that IC6 was supplied as an MC
68HC705C8ACP, not an MC68HC
705C8P. I assume that this is just
another variation of the MC68HC
705C8P microprocessor chip and
is a valid substitute. Could you
please help me identify what is
the problem with this kit? (C. C.,
Leeming, WA).
• It appears that the microproces
sor (IC6) is either not programmed
or faulty. If it is programmed it
will be marked accordingly. Either
way, the microprocessor should
be replaced. The ACP version is
slightly different to the P version
but we have programmed them to
accommodate this difference.
laser will remain on constantly when
ever the trigger is pressed down? It
occurred to me to short the 1.5kΩ
resistor but I figured this would still
create a pulse because of the 100µF
capacitor. Your help in this matter
would be much appreciated. (J. N.,
Greenacre, NSW).
• As you suggest, shorting the 1.5kΩ
resistor will allow the laser to stay on
while ever the trigger is pulled. The
100µF capacitor can then be omitted.
Notes & Errata
MultiMedia Loudspeakers, November
1996: the perspective diagram on page
61 shows the wrong enclosure depth;
it should be 224mm.
Control Panel For Multiple Smoke
Alarms, December 1996: a 47kΩ re
sistor should be added to the circuit
between pin 11 of IC5f and the +9V
rail, while one of the 100µF bypass
capacitors on the +9V rail should
be 10µF. Note also that the parts list
should show four 1kΩ resistors (not
SC
three).
February 1997 93
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94 Silicon Chip
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Silicon Chip Publications
PO Box 139, Collaroy 2097
No postage stamp required in Australia
MARKET CENTRE
Cash in your surplus gear. Advertise it here in Silicon Chip.
FOR SALE
A POWER AMPLIFIER: 500W 4/8/16,
50/70/100V 5 R.U. $250. 8-channel microphone mixers 600 in/out 1 R.U. $180.
All excellent order, ex airport service.
Several available, ship anywhere. Fax
(070) 55 0371.
AUSTRALIA’S BIGGEST FIELD DAY
for Radio and Electronics enthusiasts.
Come to the Central Coast Field Day,
Wyong Racecourse, 8.30 a.m. to 3.30
p.m. Sunday 23rd February for truck
loads of new and used Radio and Electronic gear at bargain prices. Displays,
lectures, radio fox hunts and equipment
demonstrations throughout the day.
Enquiries phone (043) 40 2500.
C COMPILERS: Ever ything you
need to develop C and ASM software for 68HC08, 6809, 68HC11,
68HC12, 68HC16, 8051/52, 8080/85,
8086 or 8096: $140.00 each. Macro
Cross Assemblers for these CPUs
+ 6800/01/03/05 and 6502: $140.00
for the set. Debug monitors: $70 for 6
CPUs. All compilers inc ‘HC12, XASMs
and monitors: $480. 8051/52 or 80C320
Simulator (fast): $70.
Disassemblers for 12 CPUs only $75.
Try the new C-FLEA Virtual Machine
for small CPUs, build a “C-Stamp”.
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.
WEATHER FAX DECODERS: for HF,
VHF/UHF use with JVFAX, MAXISAT
and SATFAX. Details D. G. Hopkins, 4
Handsworth Street, CAPALABA 4147.
(07) 3390 3328.
COMPLETE C BAND SATELLITE
SYSTEM: 4.6m segmented mesh dish
with pole and self install instructions,
dual input receiver with low threshold
and inbuilt dual axis positioner, 2 actu-
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 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.
❏ Bankcard ❏ Visa Card ❏ Master Card
Card No.
✂
Enclosed is my cheque/money order for $__________ or please debit my
Signature__________________________ Card expiry date______/______
Name ______________________________________________________
Street ______________________________________________________
Suburb/town ___________________________ Postcode______________
ators, multi-polarity feedhorn, 20 degree
LNB plus all cables. Never used. Private
sale. $3,800. (086) 32 1035.
SATELLITE DISHES: international
reception of Intelsat, Panamsat, Gori
zont,Rimsat. Warehouse Sale – 4.6m
dish & pole $1499; LNB $50; Feed $75.
All accessories available. Videosat, 2/28
Salisbury Rd, Hornsby. Phone (02) 9482
3100 8.30-5.00 M-F.
MICROCRAFT PRESENTS: Dunfield
(DDS) products are now available exstock at a new low price; please ask for
our catalogue. Micro C, the affordable
“C” compiler for embedded applications.
Versions for 8051/52, 8086, 8096,
68HC08, 6809, 68HC11 or 68HC16
$139.95 each + $3 p&h • Now on special is the SDK, a package of ALL the
DDS “C” compilers for $399 + $6 p&h •
EMILY52 is a PC based 8051/52 high
speed simulator $69.95 + $3 p&h • DDS
demo disks $7 + $3 p&h • VHS VIDEO
from the USA (PAL) “CNC X-Y-Z using
car alternators” (uses car alternators as
cheap power stepper motors!) $49.95
+ $6 p&h (includes diagrams) • Device
programming EPROMs/PALs etc from
$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)
9744 5440 or fax (02) 9744 9280.
EASY PIC’n Beginners Book to using
MicroChip PIC chips $50, Basic Compiler to clone Basic Stamps into cheap
PIC16C84’s $135, CCS C Compiler
$145, heaps of other PIC stuff, Programmers from $30, 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.
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
February 1997 95
BASIC STAMPS
& PIC Tools
Enhancements from
Microchip
Opto Isolators from
Scott Edwards Electronics
PIC Chips
MICROMINT
DOMINO
PO Box 634, ARMIDALE 2350 (296 Cook’s Rd)
Ph (067) 722 777 – may time out to Mobile 014 036 775
Fax (067) 728 987 (Credit Cards OK)
http://www.microzed.com.au
OPTO 22
Micro Engineering Labs
MicroZed Computers
PICBASIC Compir
and proto boards
PicStic
BLACKJACK
Specialising in easy-to-get-going hard/software kits.
Stamp kits now have a compiler for 16C58
Send 2 x 45c stamps for information package
(most credit cards OK)
Advertising Index
Av-Comm.....................................33
Dick Smith Electronics..... 8,9,34-37
Earthquake Audio........................83
Emona.........................................73
Freedman Electronics..................83
Harbuch Electronics....................83
MEMORY * MEMORY * MEMORY
SPECIAL! (Ex Tax)
1Mbx9 – 70ns
$15
30-pin Simms
651 Forest Rd, Bexley 2207
makes all the project PCBs
published in SILICON CHIP
and other Australian magazines
Tel +61 2 9587 3491 Fax 9587 5385
E-mail rcsradio<at>cia.com.au
SIMMS
(Parity/No Parity)
4Mb 30 PIN-70
$50
$42
4Mb 72 PIN-70
$44
$29
8Mb 72 PIN-70
$80
$50
16Mb 72 PIN-70 $144 $114
32Mb 72 PIN-70 $288 $216
EDO SIMMS
8Mb (1Mbx32) – 60ns $47
16Mb (2Mbx32) – 60ns $108
32Mb (4Mbx32) – 60ns $219
MAC MEMORY
8/16Mb DIMMS $63/113
32/64Mb DIMMS $252/488
16Mb P’BOOK 520/540 $258
LIFETIME WARRANTY!!
Ex Tax Pricing – Delivery $8. Pricing as at 07/01/96. Phone for latest.
Sales Tax 22%.
Credit Cards Welcome. We Also Buy And Trade-In Memory.
PELHAM
Memory Pty Ltd
C COMPILERS: Dunfield compilers
are now even better value. Everything
you need to develop C and ASM
software for 68HC08, 6809, 68HC11,
68HC12, 68HC16, 8051/52, 8080/85,
8086 or 8096: $140.00 each. Macro
Cross Assemblers for these CPUs +
6800/01/03/05 and 6502: $140 for the
set. Debug monitors: $70 for 6 CPUs. All
compilers, XASMs and monitors: $400.
8051/52 or 80C320 simulator (fast): $70.
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
MicroZed has16C84 at $8, 16C58A at
$5, 1C71 at $7. JW versions too. Discounts start at 10 pieces. Add $5 post
on IC orders. Available now: new Stamp
book Ver. 1.7, $35 post $8.00.
PCBs MADE, ONE OR MANY. Low
prices. Hobbyists welcome. Sesame
Electronics (02) 9554 9760.
HOMEMADE GENERATORS: how to
instructions. Eight pages free text and
colour photos on the Internet at http://
www.onekw.co.nz/onekw
96 Silicon Chip
LASER PRINTER MEMORY
4Mb HP 4&5
$53
COMPAQ
8Mb ARMADA 1100
$139
All other models available $Call
TOSHIBA
8Mb Portege/ Sat EDO
$134
16Mb Portege/ Sat EDO
$229
16Mb Tecra 500/610 Sat $229
All other models available $Call
CACHE
256Kb PIPELINE BURST
$21
256Kb 7200/8500
$92
VIDEO MEMORY
256K x 16 70ns (SOJ)
$12
1Mb 7200/7500/9500
$83
SO DIMMS
8Mb/16Mb
$82/138
Suite 6, 2 Hillcrest Rd,
Ph: (02) 9980 6988
Pennant Hills, 2120.
Fax: (02) 9980 6991
Email: pelham1<at>ozemail.com.au
B/W CCD CAMERA. Chinon CX103
miniature PCB-board 46 x 44mm, 25mm
high. Automatic electronic shutter. 7V to
16V. 2 lux. $95.
PELTIER MODULE 12V, 4.4A, $18.
LCD 16 x 2, no b/l, $9. All prices
include air postage & data sheet.
DIY Electronics, Hong Kong. Fax:
852 2725 0610. Email diykit<at>hk.
super.net. See web site for direct component buying www.hk.super.net/~
diykit
MICROS: 68HC705C8ACFN PLCC
$11.50. 68HC705C8ACFS DIL $11.00.
Erased Chips 68705P3 $5.00. DISPLAYS: LCD 2 x 20 $15; LED HPDL2416
$13; VFD 2 x 40 $50. Min qty 4 of $7.50
p+p. Michael (03) 9803 3535.
CAR/RALLY COMPUTER KIT: including fuel sensor & speed sensor.
68HC05 & HC11 Development Systems: Oztechnics, PO Box 38, Illawong
NSW 2234. Phone (02) 9541 0310. Fax
(02) 9541 0734.
http://www.oztechnics.com.au/
WANTED
VALVES: new and used. All types required. Phone: 047 51 5620.
Instant PCBs................................96
Jaycar ............................IFC, 45-52
Kalex............................................89
Kits-R-US.....................................84
Macservice....................................3
MicroZed Computers...................96
Oatley Electronics........................29
Pelham........................................96
Rod Irving Electronics .......... 77-81
Silicon Chip Back Issues....... 90-91
Silicon Chip Bookshop.................85
Silicon Chip Binders....................76
Silicon Chip Model Railway
Projects Book..........................OBC
Silicon Chip Software....................7
Tortech.........................................89
Zoom Magazine.........................IBC
_________________________________
PC Boards
Printed circuit boards for SILICON
CHIP projects are made by:
• RCS Radio Pty Ltd, 651 Forest
Rd, Bexley, NSW 2207. Phone (02)
9587 3491.
• Marday Services, PO Box 19-189,
Avondale, Auckland, NZ. Phone (09)
828 5730.
R
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