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November 1999 1
2 Silicon Chip
Contents
Vol.12, No.11; November 1999
FEATURES
4 USB: Hassle-Free Connections To Your PC
USB makes it easy to add peripherals to your PC but what hardware and
software do you need? – by Peter Smith
39 Electric Lighting; Pt.15
How neon signs are made – by Julian Edgar
56 Setting Up An Email Server
USB: Hassle-Free Connections
To Your PC – Page 4.
Want to set up your own email server and cut telephone costs? We show
you how – by Peter Smith
PROJECTS TO BUILD
16 A Speed Alarm For Cars; Pt.1
Is your licence looking a bit dodgey? This compact speed alarm will help
you stick to the speed limits – by John Clarke
31 Multi-Colour LED Christmas Tree
A low-cost microcontroller chip produces multiple colours and multiple
patterns – by Les Grant
Build A Speed Alarm For Your
Car – Page 16.
62 Build An Intercom Station Expander
It’s called the “Addacom” and it lets you add four extra stations to any existing
2-way intercom – by Paul Hoad
72 Foldback Loudspeaker System For Musicians
It uses readily available drivers and can be built using basic hand and
power tools – by John Clarke
80 Railpower Model Train Controller; Pt.2
Final article describes the IR remote control circuit and gives the full construction details – by John Clarke
SPECIAL COLUMNS
Multi-Colour LED Christmas Tree
– Page 31.
26 Serviceman’s Log
Price isn’t everything – by the TV Serviceman
68 Vintage Radio
The case of the disappearing TV sets – by Rodney Champness
DEPARTMENTS
2
22
44
53
55
Publisher’s Letter
Circuit Notebook
Mailbag
Product Showcase
Electronics Showcase
89
90
93
94
96
Subscriptions Form
Ask Silicon Chip
Notes & Errata
Market Centre
Advertising Index
Foldback Loudspeaker System
For Musicians– Page 72.
November 1999 1
PUBLISHER’S LETTER
www.siliconchip.com.au
Publisher & Editor-in-Chief
Leo Simpson, B.Bus., FAICD
Production Manager
Greg Swain, B.Sc.(Hons.)
Technical Staff
John Clarke, B.E.(Elec.)
Peter Smith
Ross Tester
Rick Walters
Reader Services
Ann Jenkinson
Advertising Enquiries
Rick Winkler
Phone (02) 9979 5644
Fax (02) 9979 6503
Mobile: 0414 34 6669
Regular Contributors
Brendan Akhurst
Rodney Champness
Garry Cratt, VK2YBX
Julian Edgar, Dip.T.(Sec.), B.Ed
Mike Sheriff, B.Sc, VK2YFK
Philip Watson, MIREE, VK2ZPW
Bob Young
SILICON CHIP is published 12 times
a year by Silicon Chip Publications
Pty Ltd. A.C.N. 003 205 490. All
material copyright ©. No part of
this publication may be reproduced
without the written consent of the
publisher.
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NSW.
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Company.
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rates, see the subscription page in
this issue.
Editorial & advertising offices:
Unit 8, 101 Darley St, Mona Vale,
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Phone (02) 9979 5644.
Fax (02) 9979 6503.
E-mail: silchip<at>siliconchip.com.au
ISSN 1030-2662
* Recommended and maximum price only.
2 Silicon Chip
DC power in the home;
it could be made to work
Last month’s Publisher’s Letter about the
possibility of DC power in the home triggered
off quite a response from readers. Some raised
the obvious safety issues of the difficulty of
safely switching high voltage DC and the possibility that a DC shock can be more dangerous
than AC. These drawbacks must be admitted.
Others though, saw the potential in the idea
and went on to expand the concept.
My feeling is that most people have such a
reliable 240V AC supply that they would never
contemplate ever having any other system; it
works, why fix it? For those that do have an unreliable mains supply, and
I include myself in that category, the occasional inconvenience might be
extremely irritating but it would not justify the investment and time necessary to eliminate it. And whether a DC power system would be the way to
go would probably be a moot point.
However, for those who are in remote locations far away from any mains
power supply, a combination high and low voltage DC system based on
solar arrays could be made to work. As one of our readers points out in the
Mailbag pages this month, quite a few appliances could be made to work
on DC. But would it be safe?
Now that the problem of high voltage DC switching has been highlighted,
could be it be overcome? The answer is yes. But it would not be necessary
to have large mechanical power switches to turn the appliances, lights or
whatever, on and off. The logical approach would be to have electronic
switching which could cope with high voltage DC and AC. This would be
pretty straightforward, when you think about it.
After all, many appliances these days do not rely on mechanical on/off
switches; they use electronic switching. Virtually any appliance which comes
with a remote control uses electronic switching. The same point applies to
microwave ovens, many washing machines and dishwashers. An electronic
switch based on a power Mosfet or IGBT (insulated gate bipolar transistor)
could be made to handle the switching job for AC and DC. So a compact,
reliable and rugged power switch is not an insurmountable problem.
Nor is the problem of automatic degaussing for TVs and computer monitors
running from DC insoluble - there has to be an electronic solution.
So as I remarked last month, there is no reason why most appliances
could not be made to run on 250V DC. Will it ever happen? Probably not.
To be realistic, if you were faced with providing power in a remote location, the most practical approach would probably be to power as many
appliances as possible at 12V DC and for those that cannot be run from
low voltage DC, use a 12V DC to 240VAC inverter which would only run
when an appliance was switched on. Many of the bigger inverters already
have an auto-sensing feature and it is very worthwhile because it stops the
inefficiency of running inverters continuously.
Leo Simpson
*Full details at www.tol.com.au
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Come and visit our online catalogue & shop at www.mgram.com.au
Phone: (02) 4389 8444
Dealer Enquiries
Welcome
sales<at>mgram.com.au
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We welcome Bankcard Mastercard VISA Amex
Unit 1, 14 Bon Mace Close, Berkeley Vale NSW 2261
Vamtest Pty Ltd trading as MicroGram Computers ACN 003 062 100
Fax: (02) 4389 8388
Web site:
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FreeFax 1 800 625 777
November 1999 3
Connecting a new device to your PC can be
a real hassle. But imagine being able to add
peripherals without opening the case, adding
interface cards or even having to switch the
PC off or reboot it. Those are just some of the
advantages offered by USB.
By PETER SMITH
M
OST OF US at one time or
another have struggled with
the software or hardware
configuration when installing new
peripherals on personal computers.
The Plug and Play (PnP) standard
introduced with Windows 95 helped
PC
HOST
CONTROLLER
& ROOT HUB
USB
PORTS
to ease the pain a little but what do
you do when that scanner, printer and
Zip drive just won’t work together on
the same parallel port? The answer
is USB!
USB is an acronym for Universal Serial Bus. Developed over the last few
years by a group of industry leaders
including Intel, Microsoft, Compaq
and NEC, USB has finally opened
the way for stress-free peripheral
connection. The key goal for the USB
designers was to create an expansion
bus that would make adding peripherals as easy as plugging a connector
into a socket.
A multitude of USB-ready devices
are already available, including scanners, cameras, Zip drives, modems,
keyboards, mice, ethernet (network)
adapters and joysticks. So let’s have a
MONITOR
& 2-PORT HUB
KEYBOARD
& 2-PORT HUB
UPSTREAM
PORT
4-PORT HUB
SPEAKERS
MOUSE
JOYSTICK
DOWNSTREAM
PORTS
The USB ports on this computer are
located on the rear panel, just below
the two PS/2 ports.
4 Silicon Chip
Fig.1: most modern PCs come with two USB ports and many USB
peripherals include inbuilt hubs so that other devices can easily be
added to the bus. Alternatively, you can use a dedicated hub to add
extra ports.
CLIENT SOFTWARE
USB DRIVER
SOFTWARE
HOST CONTROLLER DRIVER
SCOPE OF
OHCI/UHCI
SPECIFICATION
HOST CONTROLLER
HARDWARE
USB DEVICE
Fig.2: the OHCI and UHCI standards affect the
host controller hardware and its software driver.
Motherboards that use Intel chipsets are UHCI
compliant while many add-on controllers are
OHCI compliant – see text.
look at some of the advantages of this
new system and how it all fits together.
USB basics
Adding a new device to your PC in
the past usually meant opening up
the case, installing an interface card
and worrying about such things as
IRQs and I/O addresses, etc. That no
longer applies with USB – you just
plug the device into a USB connector
and it works.
Up to 127 devices can be connected
to the USB bus – more than most of
us will ever need. Connections to the
bus can be made without switching
off the power (known as “hot-plugging”), making it possible to add
peripherals and to move them between machines with a minimum
of fuss.
USB has two bus speeds to optimise
efficiency: (1) a “low-speed” mode
that operates at 1.5 megabits per second (1.5Mb/s); and (2) a “full-speed”
mode that operates at 12 megabits
per second (12Mb/s). The low-speed
mode is intended for interactive peripherals such as game pads and mice,
whereas the full-speed mode provides
lots of throughput for printers, scanners and video cameras, etc.
High-speed devices like fast disk
drives and fast (100Mb/s) networking
controllers are not suitable for use
with USB. Table 1 compares the fullspeed USB transfer rate with the rates
of other interfaces. As can be seen, it’s
a lot faster than a standard serial or
parallel port.
The majority of IBM-compatible
PCs designed from 1998 onwards have
The USB standard has two connectors: (1) an upstream Series
“A” connector as shown at right and (2) a downstream Series
“B” connector as shown at left. The different connector styles
make it impossible (at least, in theory) to connect two downstream ports or two upstream ports together.
USB ports as standard equipment.
But that doesn’t mean that you can’t
have USB if your PC is older than this.
Many older machines can easily be
upgraded to support USB but more
on that later.
Adding ports
Most PCs provide only two USB
ports but expansion is a simple matter
of adding a low-cost hub. USB hubs
provide one port for connection to the
PC side of the bus (called the upstream
port) and typically between four and
seven output ports for connecting peripherals or even another hub (these
are called downstream ports) – see
Fig.1. Some peripherals also come
with hubs built in, allowing devices
to be daisy-chained.
Both the signal and power connections are provided by a single
USB cable, eliminating the need for
separate power sources for low power
peripherals. Devices that draw power directly from the bus are said to
be “bus-powered”, whereas devices
that have their own power source are
called “self-powered”.
Self-powered hubs (and this includes the “root” hub that is part of
the USB host controller in the PC)
can supply a maximum current of
500mA per port. On the other hand,
bus-powered hubs can supply only
100mA per port, so this is something
to look out for when selecting a hub or
a peripheral with an embedded hub.
As a matter of interest, power distribution on the bus is under software
control and this ensures that the bus
is not inadvertently overloaded.
USB connectors
Because simplicity is an important
part of the design, only two types of
connectors exist in USB: (1) Series “A”
and (2) Series “B”. The Series “A”
type is used for all upstream connections (ie, towards the host PC), while
the Series “B” connectors are used for
the downstream connections (towards
peripherals and hubs).
Small devices usually have a captive (moulded in) cable with a Series
“A” plug on the end. Larger devices,
such as monitors, printers and hubs,
usually have removable cables, with
a Series “A” plug on one end and a
Series “B” plug on the other. These are
commonly referred to as “A-B” cables.
November 1999 5
USB Peripherals From Namlea Data Systems
A self-powered 4-port USB hub: an upstream port (not visible) connects to
the PC while the four downstream ports are for the peripherals. (Namlea
Data Systems, phone (02) 9429 0800; www.ndsonline.com.au).
The idea behind the different connector types is to prevent accidental
“bus loop-back”, by making it impossible to connect two downstream or
two upstream ports together (eg, on
two different hubs).
We should mention here that although it is physically possible to
connect two computers together using
a non-standard USB cable (ie, with a
Series “A” connector on both ends),
the results could be catastrophic! To
perform this function, go shopping
for a USB bridge – it performs the
necessary magic and protects your
motherboard from possible damage.
Typically, cables are available in
2, 3 and 5-metre lengths, with five
metres being the maximum allowable
length. It is possible to extend this
distance by cascading hubs (up to
five levels deep) but USB was never
intended for long hauls. If you need
to cover long distances but still want
to use USB, consider using USB-to-Ethernet adaptors.
Dual standards
This bus-powered USB-Ethernet adapter with LED indicators lets you
connect a PC fitted with a USB port to a network. (Namlea Data Systems).
USB to IEEE1284 parallel converter
cable. (Namlea Data Systems).
6 Silicon Chip
While the Universal Serial Bus itself
is now a well-defined standard, two
different standards were drafted for
the PC interface side of the USB host
controller and the software components that communicate with it. In
particular, Intel developed the Universal Host Controller Interface (UHCI)
standard, while other USB developers, including Microsoft, Compaq
and NEC, developed the Open Host
Controller Interface (OHCI).
Naturally, all motherboards with
Table 2: Win 95/98 Releases
Version Number
Windows Release
4.00.950
Windows 95 retail
4.00.950A
4.00.950C
Windows 95 OSR 1
Windows 95 OSR 2.0
or 2.1
Windows 95 OSR 2.5
4.10.1998
Windows 98
4.10.2222A
Windows 98 SE
4.00.950B
Intel chipsets are UHCI-compliant, as
are motherboards with Via Technologies chipsets. However, many add-on
USB cards use hardware from other
chip manufacturers (such as OPTi, Ali,
CMD, National Semiconductor and
RealTech) and are OHCI-compliant.
A few problems have surfaced recently with a number of peripherals
when connected to OHCI-compliant
controllers. Windows 98 Second
Edition fixes some but apparently
not all of these problems. Check the
list of supported USB controllers
and peripherals in the Windows 98
SE hardware.txt file if you are having intermittent problems or plan to
upgrade.
Further information on USB support in Windows 98 can be found
on the Microsoft web site at http://
support.microsoft.com
Operating system support
If you want to use USB peripherals
on a PC, Windows 98 is the way to
go. It includes full support for USB,
with its Plug and Play (PnP) system
A bus-powered USB
to RS232 serial port
converter. This could
be used for connecting
a modem, for example.
(Namlea Data Systems).
If you don't already have USB ports on your computer,
a USB adapter card is the answer. This unit plugs into a
spare PCI slot on your motherboard and gives you two USB
output ports on the backplane connector. ($49 from
Microgram Computers. Phone (02) 4389 8444; web site
www.mgram.com.au).
perfectly suited to the task.
If you plug in a simple device like a
mouse or keyboard, it is usually (but
not always) immediately recognised
and a generic driver automatically
installed. Other more complex peripherals may also be recognised but
their functions will often be limited
until the manufacturer’s USB driver
software (supplied with the hardware)
is installed. Of course, this only needs
to be done once.
Unfortunately, Windows 95 provides only partial support and as far
as we know, no future updates will be
made available to extend this support.
Some USB peripheral manufacturers have even dropped support for
Windows 95 altogether, so if you’re
running Windows 95 and don’t want
to upgrade just yet, check out the
operating system requirements before
you buy USB peripherals.
What about Windows NT4? Unfortunately, NT doesn’t have true Plug
and Play support and so is unsuitable for USB. On the other hand, IBM
provides limited support for USB in
their OS/2 Warp 4 operating system.
However, you will need to obtain the
OS/2 USB Basic driver from IBM’s
web site (see Table 3).
For Mac users, Apple provides
USB support with their Power Mac
G4, iBook and iMac systems, with
many peripheral drivers pre-loaded.
If you have a Mac, check to ensure
that the operating system offers full
USB support.
Finally, USB stacks are now appearing for various flavours of Linux
and FreeBSD.
Adding USB to your PC
By now, some readers will be wondering whether their PC has USB
support or not. Alternatively, they
may just wish to check that the USB
function is working correctly before
adding their first USB peripheral.
So what are the basic hardware and
software requirements for USB? We’ll
discuss the requirements below and
describe some of the potential pitfalls
as they relate to IBM-PC compatible
systems running Windows 95/98.
Motherboard manufacturers began
integrating USB controllers into their
first generation Pentium designs.
Unfortunately, not all early Pentium
motherboards have USB controllers
built-in but if you have a free PCI
slot, you can purchase an add-on USB
controller card that will do the job.
These are now widely available and
retail for around $40.
In addition, PC assemblers do not
always install the necessary USB
port connectors. If you think that
your motherboard has an inbuilt USB
controller but there are no external
connectors, check the system docuNovember 1999 7
Fig.3: this entry in System Properties
(Device Manager tab) is for an Intel
UHCI-compliant USB controller.
Fig.4: this dialog box is similar to
Fig.3 but shows the entry for an
OHCI-compliant USB controller.
Fig.5: this dialog box lets you
check the hardware version of
your PCI-to-USB host controller.
mentation for details or give the supplier a call. Suitable brackets with port
connectors and cables that plug into
the motherboard are available but note
that the motherboard connector styles
can vary between manufacturers.
Many first generation Pentium
motherboards utilise the Intel 82371
SB PCI-to-USB host controller. However, the first revision of this controller
may not work reliably in some applications, as standards development
was still under way when this chipset
was designed.
To check if your machine is affected,
right-click on the My Computer icon
on the desktop and select Properties.
Click on the Device Manager tab and
expand the Universal Serial Bus controller device – see Fig.3.
If an 82371SB PCI-to-USB host
controller is listed, double-click on
that line to display its properties – see
Fig.5. On the General tab, look for
the “Hardware version” line. If the
version is “000”, then you may have
difficulties. Later versions are OK.
Motherboards that incorporate
Via Technologies VT82C586B or
VT82C596 PCI-to-USB host controllers need a software patch installed to
correct a number of problems. Check
out the Via Technologies website (see
Table 3) for details.
Many Pentium II and III machines
will already have all the right hardware installed but the USB controller
may not be enabled in the BIOS setup.
The procedure to check this varies
considerably between machines (depending on the BIOS), so refer to your
motherboard’s manual.
In rare cases, you may also need a
flash BIOS update. If you are an experienced user, you can download the
latest BIOS for your motherboard from
the manufacturer’s website and install
it yourself. Be careful here though – if
you mess things up, you will be left
with a machine that won’t boot until
you get the BIOS chip replaced. Depending on the age of the machine,
your supplier may also be able to help
with BIOS updates.
Finally, if all else fails, it’s possible
to disable the on-board USB controller
in the BIOS setup and install an addon controller card – assuming that you
have a free PCI slot.
USB TV Tuner: it turns your PC into a TV set
and lets you convert live video into AVI files
Called the “LifeView”, this
external TV tuner simply
plugs into a USB port on
your PC (no need to turn
the power off), making it
easy to “hot-swap” from one
machine to the next.
It supports all TV standards including PAL, NTSC
and SECAM in their various
formats and features external video inputs (both composite and S-video) so that
you can connect a VCR. The
video window can be scaled
from 80 x 60 up to 640 x 480
pixels using the supplied software.
In addition, live video can be
captured and saved as AVI files and
you can also capture and save still
images. A digital camera suitable for
8 Silicon Chip
Windows 98
video conferencing or video email is
included with the unit, which is also
TWAIN-compliant.
The unit is available from Vision
Beyond 2020. Phone (03) 9558 0333.
As mentioned before, Windows 98
automatically detects and installs the
correct drivers for most built-in USB
controllers. If you’re installing an
add-on USB controller card though,
you’ll probably need to load the
manufacturer’s driver. The appropriate instructions and software will be
supplied with the card.
A simple utility from Intel called
USB Ready gives an indication of
USB hardware and software status and
is available for free download from
http://www.usb.org/data/usbready.
November 1999 9
Table 3: Useful USB Websites
Fig.6: the USB View utility (supplied
with Windows 98) allows you to
quickly check the status of the USB
hardware connected to your PC.
exe Yet another utility called USB
View is supplied on the Windows 98
CD – look for it in the \tools\reskit\
diagnose folder. Fig.6 shows a typical
output from USB View. In this case,
we have a 4-port hub connected to
USB Port 2 of the PC. A USB-Ethernet
Adapter and a USB Com Port have
then been plugged into Ports 1 & 3
of the hub.
It’s also worth checking that both
the USB host controller and root hub
appear in System Properties. This
can be found by right-clicking the
My Computer icon on the desktop,
selecting Properties and then clicking
the Device Manager tab – see Figs.3 &
4. A red cross through either the controller or root hub obviously indicates
a problem.
Sometimes this can be cured by
deleting the devices and restarting the
machine – Windows 98 will detect the
devices again and reinstall the drivers.
The first release of Windows 98
apparently has a number of USBrelated problems, many of which are
addressed in Service Pack 1. This
pack can be downloaded from http://
windowsupdate.microsoft.com or
contact Microsoft to get a copy on CD.
Windows 95
We said earlier that Windows 95
does not provide full USB support.
If you’d like to give it a shot anyway,
you will need to have Windows 95
OSR 2.0, 2.1 or 2.5 installed – earlier
versions won’t work.
You also need a UHCI-compliant
USB controller, as OHCI-compliant
controllers are not supported. Note
that motherboards with built-in USB
controllers using Intel and Via chipsets are UHCI-compliant, while addon USB controller cards are generally
OHCI-compliant.
You can check which version of
Windows 95 you have by right-click10 Silicon Chip
USB Impl ementer's
Forum
http://www.usb.org
Intel USB techni cal
http://www.intel.com/design/usb
Intel USB support
http://support.intel.com/support/technologi es/usb
Intel chipset support
http://support.intel.com/support/chipsets
Microsoft Windows 98 http://www.mi crosoft.com/hwdev/busbios/usbwin98.htm
Appl e
http://www.appl e.com/usb
Appl e Macintosh
http://www.macintouch.com/imacusb.html
Appl e USB Peripheral s http://guide.appl e.com/uscategories/usb.html
IBM OS/2 Warp
http://servi ce.software.ibm.com/os2ddpak/html /uni versa
Vi a Technologi es
http://www.viatech.com/dri vers
CMD
http://www.cmd.com/semiconductor/support/docs/670/usbpatch.cfm
FreeBSD
http://www.etl a.net/~n_hibma/usb/usb.pl
Linux
http://www.linux-usb.org
Aten Technology
http://www.aten-usa.com/
USB Stuff
http://www.usbstuff.com
USB Workshop
http://www.usbworkshop.com
A l l U SB
http://www.allusb.com
ing the My Computer icon on the
desktop, then select Properties. The
version number will be shown on the
General tab.
If USB support is already installed,
it will be listed in Add/Remove
Programs in Control Panel as “USB
Supplement to OSR2”. Note that if
the supplement has been uninstalled,
the Windows version number will
change from 4.00.950C to 4.00.950B!
Table 2 shows the various Windows
95/98 releases.
If you have Windows 95 OSR 2.5,
the USB supplement files can be
found on the Windows CD in the
\other\updates\usb folder. Look for
a file called usb.txt, which describes
the installation procedure.
Windows 95 OSR 2.0 and 2.1 users
can download the USB supplement
from the web in a single file called
usbsup.exe. We couldn’t find this file
on the Microsoft website but you can
get it from a number of other sites – try
the USB Workshop (see Table 3). You
simply run usbsup.exe to perform the
installation and reboot you machine
when it is complete.
Note that a minor problem can occur
when installing the USB supplement.
Windows may pause after it detects
the host controller and prompt you
for the location of the file uhcd.sys.
All you need to do is change the path
to c:\windows\system and hit OK.
A further complication arises with
Windows 95 and hardware support.
Motherboards designed after Windows 95 was released incorporate new
features that are not detected by the
operating system and this includes
the USB controller. A disk (or CD)
may have been provided with your
PC that includes the necessary drivers
for Windows 95 and this should have
been pre-loaded by your supplier.
However, if Windows 95 has since
been reinstalled from scratch using
the original Microsoft CD, the drivers
will also need to be reinstalled.
If you don’t have these drivers and
you know which chipset is used on
your motherboard, you can download
them from the manufacturer’s website
(see Table 3).
Windows 95 users can also run
the USB Ready utility to verify the
USB hardware and software status
on their PC.
What, USB 2.0 already?
Readers who are already familiar
with USB 1.1 may have heard about
the new USB 2.0 specification. At
time of writing, USB 2.0 was still in
the drafting stages but we can tell you
that the main difference between 1.1
and 2.0 is the speed. USB 2.0 will run
at 360 megabits per second (360Mb/s)
or more, while still maintaining
backward compatibility with USB
1.1 peripherals. And no, that’s not a
SC
misprint!
R
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November 1999 11
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.dse.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.dse.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.dse.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.dse.com.au
Speed Alar
Is your driver’s
licence looking a bit
dodgy? This easy-tobuild speed alarm
can help prevent a
fine and save you
from losing any more
demerit points. As
a bonus, it can also
function as a digital
speedometer while
still maintaining the
speed alert function.
Pt.1: By JOHN CLARKE
A
NYONE WHO DRIVES a car
inevitably exceeds the posted
speed limit on occasions, either
deliberately or due to lack of atten
tion. But these days, it’s really not a
good idea to speed. Apart from the
obvious safety considerations, there
are lots of speed cameras about and
it’s all too easy to cop a heavy fine and
maybe even lose your licence.
You don’t have to be a speed demon
either. On a long trip, your speed can
gradually creep up as you become
used to the road conditions. It’s also
16 Silicon Chip
quite difficult to stick to the speed
limit in a 60km/h zone after you have
been driving at high speed on the
open road – 60km/h seems agonisingly slow after driving at 100km/h.
In this situation, a speed alarm can
keep you on your toes and ensure that
you stick within the posted limit.
Another situation where it’s easy
to inadvertently exceed the speed
limit is if you using a cruise control.
Now while cruise controls are a great
help when it comes to maintaining
a set speed, they do have one inher-
ent limitation – the speed of the car
can increase beyond the set limit on
downhill stretches. Once again, a
speed alarm can instantly warn you
when you’ve overstepped the mark.
Main features
Our new Speed Alarm is quite compact and fits neatly into the smallest
available jiffy/zippy box. By contrast,
our previous Speed Alarm (described
in the December 1997 issue) used
a case this size just for the display
circuitry. The rest of the circuit was
rm
All the parts fit on two small PC boards which are housed in a compact
plastic case. Note the black cardboard sleeve around the 7-segment displays
in the photo at left. This prevents light leakage from the LEDs adjacent to the
pushbutton switches from spoiling the appearance of the readout.
housed in a separate instrument case
and while it was OK for large vehicles,
it wasn’t all that easy to squeeze into
the average family sedan.
So how have we managed to shrink
the circuitry so dramati
cally? The
answer is that we have replaced all
the discrete control circuitry with
a low-cost PIC microprocessor and
come up with the necessary software
to control the internal “smarts” of this
device. The resulting circuitry all fits
on two small PC boards which are
stacked inside the case.
It’s also just as easy to drive as before. As shown, the front panel carries
a 3-digit LED display, a LED indicator and three pushbutton switches.
Two of these pushbuttons let you set
the alarm speed in 5km increments
between 0km/h and 155km/h (one
switch increases the speed; the other
reduces it). As soon as you exceed
the preset speed, the indicator LED
lights and an internal piezo alarm
briefly sounds at 10-second intervals
to provide a warning.
The third switch selects between
three display modes: (1) the alarm
speed value; (2) the actual vehicle
speed (ie, the unit functions as a digital speedometer); and (3) the alarm
off mode. Each press of the switch
cycles the unit to the next operating
mode – it really is that easy to operate.
The alarm off mode is indicated by
three dashes (---) on the display. In
this mode, the alarm is off and there
is no overspeed indication (either
audible or visual).
The speedometer mode displays
the vehicle speed with a resolution of 1km/h over the range from
0-159km/h. If you exceed 159km/h,
the display shows 888 to indicate
overrange so the circuit is not suitable
for use on a racetrack.
By the way, the speed alert function
continues to operate when the digital
speedometer mode is selected. You
can even adjust the alarm speed while
the unit is in the speedometer mode
by pressing the up and down buttons.
Each time one of these buttons is
pressed, the piezo alarm and the LED
both give brief “blips” to let you know
that the alarm speed has increased or
decreased by 5km/h.
If power to the Speed Alarm is interrupted (ie, if the ignition is turned
off), the unit “remembers” its current
speed alarm and operating mode
settings. These settings are then au
tomatically restored the next time the
engine is started.
Options
OK, so that’s the basic operation of
the unit and most drivers will be content with just those features. However,
this design uses a microprocessor and
that means we can easily include lots
of options just by programming them
into the software.
And that’s just what we’ve done, to
make this unit as versatile as possible.
These options are as follows:
(1) Disable repeat alarm: this is done
by pressing the Up button at the same
time as the ignition is turned on. The
righthand display will show a dash
(-) until the button is released. The
Speed Alarm then resumes normal
operation but with the repeat alarm
feature disabled (ie, the audible alarm
now sounds only once when you exNovember 1999 17
Main Features
•
•
•
•
•
•
Overspeed indication range of 0-155km/h in 5km/h steps.
•
•
•
•
•
•
•
•
•
Speedometer indication from 0-159km/h.
Audible and visual alarm indication.
Visual alarm stays on during overspeed.
Repeat audible alarm sounds every 10 seconds during overspeed.
3-digit LED display.
Unit can be switched to display alarm speed or vehicle speed (ie,
speedometer mode), or switched off.
Overspeed alarm works for both alarm speed and speedometer modes.
Audible and visual acknowledgement when a switch is pressed.
Repeat alarm and speedometer mode functions can be switched off.
Two selectable alarm speed threshold points.
Display brightness automatically adjusts to suit ambient light conditions.
Illuminated switches for night-time operation.
Automatic calibration.
All selected settings restored when power switched on by ignition.
ceed the preset speed limit).
The repeat alarm feature now remains disabled even if the ignition is
turned off and on again. It is re-enabled by again holding down the Up
button as the ignition is turned on. In
this case, the display will show an “r”
to indicate that the repeat alarm has
been reactivated.
(2) Disable speedometer mode: this is
done by pressing the Mode switch as
the ignition is turned on). A dash (-)
is indicated on the lefthand display
until the button is re
leased, after
which the speedometer mode can no
longer be selected. The Mode switch
now simply toggles the unit between
off and the speed alarm mode.
The speedometer mode is reactivated by again pressing the Mode switch
at power up. This time, the lefthand
display shows an “S” to indicate that
the speedometer option has been
enabled.
(3). High or low alarm threshold: if
the “low” threshold is selected, the
alarm sounds as soon as the set speed
is reached and stays on until the speed
drops by 1.25km/h. Alternatively,
if the “high” threshold is selected,
the alarm sounds when the speed
is 1.25km/h above the set limit and
stays on until the speed drops back
to this limit.
The upper threshold mode is useful
if you normally use the speedo-meter
setting. It will allow you to travel at
the set alarm speed without the alarm
sounding.
The high or low threshold is selected by pressing the Down button
during power up. If the centre display
Specifications
•
•
•
Overspeed detection accuracy better than 1% above 65km/h.
•
•
•
•
Hysteresis (alarm on to alarm off speed) 1.25km/h.
Speedometer linearity and repeatability to within 1km/h.
Speedometer and overspeed detection update time typically 0.5-3
seconds (depends on calibration).
Operating current typically less than 300mA.
Calibration accuracy typically .002% (depends on oscillator drift).
Memory storage endurance typically 10 million times.
18 Silicon Chip
shows an “L”, the low threshold is
selected. Conversely, if the display
shows an “H”, the high threshold is
selected.
Saving the settings
All settings made using the Up,
Down and Mode switches are stored
in an EEPROM (Electrically Erasable
and Programmable Read Only Mem
ory), so that they are saved when the
power is switched off via the ignition.
This type of memory can tolerate
about 10 million write operations per
bit, which means that it will never
wear out (at least not in this design).
Note that during normal program
operation, the Speed Alarm utilises
standard RAM which does not suffer
from a limited lifetime. Both the EEPROM and RAM are included in the
PIC microcontroller, so we don’t have
to use separate ICs for this memory.
When it is first built, the Speed
Alarm contains a set of default values
as follows: alarm speed = 60km/h;
repeat alarm on; speedometer mode
enabled; low threshold selected; and
calibration = 100Hz per 100km/h. The
display will be in the alarm speed
mode and so it will show 60km/h.
Circuit details
Refer now to Fig.1 for the complete circuit details of the Speed
Alarm circuit. It’s dominated by IC1,
a PIC16F84 microcon
troller which
forms the basis of the circuit. This
device takes its inputs from a speed
sensor and from the various switches
and drives the LED displays and the
piezo alarm element.
Let’s start with the speed sensor. It
consists of a coil which mounts on
the chassis, plus two magnets which
mount on a drive shaft (or tail shaft).
As the magnets spin past, they induce a voltage into the coil and this
is detected by comparator stage IC2a.
The top of the coil connects to a
2.5V supply, derived from a voltage
divider consisting of two 2.2kΩ resistors between the +5V rail and ground.
This 2.5V rail is decoupled using a
47µF capacitor and biases pin 3 (the
non-inverting input) of IC2a via a
22kΩ resistor. It also biases the pin 2
inverting input of IC2a via the coil and
a series 1kΩ resistor. Diodes D3 & D4
clamp the input signal from the coil
to ±0.6V, while the 0.1µF capacitor
filters the pickup signal.
IC2a functions as an inverting com-
parator. The output signal from the
coil is a 250mV peak-to-peak pulse
waveform as shown by the top trace
in Fig.2. This is fed to the inverting
input (pin 2) of IC2a and each time
the input swings negative, the output
of IC2a (pin 1) goes high (ie, to about
10V).
Note, however, that the output from
IC2a is fed to pin 6 (RB0) of IC1 via a
2.2kΩ limiting resistor. This is done
to convert the 10V pulse train on pin
1 of IC2a to a +5V pulse train at the
RB0 input of IC1.
So how does it do this? The answer
November 1999 19
ZD1
16V
1W
10 1W
47F
16VW
S
1k
D3
LED4
LED3
LED2
+5V
D4
47F
16VW
+5V
22k
0.1
3
2
4
8
+5V
15pF
1M
IC2a
LM358
47F
16VW
OUT
+12V
7805
REG1
GND
IN
2.2k
+5V
0.1
4
14
15
16
6
LED1
10k
5
RB7
RB4
RB3
RB2
RB1
RB6
RB5
13
10
a
g
f
d
e
c
b
a
B
IC2b
7
E
c
b
a
B
B
B
C
+5V
A
K
Q1
BC328
3,8
C
E
E
C
DISPLAY 1
HDSP5301
Q4
BC338
2
d
1
e
9
f
10
g
4
6
7
680
Q2
BC328
3,8
C
E
DIMMER
6
5
LDR1
DISPLAY 2
HDSP5301
OUT
10
9
2
1
4
6
7
GND
IN
7805
b
DISPLAY 3
HDSP5301
c
Q3
BC328
680
560
VR1
100k
3,8
C
E
f g
2
d
1
e
e
9
d
f
10
g
9
c
b
a
8
6
7
B
CAL
4
680
1k
DOWN MODE
7 x 150
1k
UP
7
12
11
RA2 1
RA1 18
RA0 17
RA3 RA4 3
2
IC1
PIC16F84
RB0
PIEZO
ALARM
ELEMENT
D1 D2
SPEED ALARM
15pF
3.58MHz
XTAL1
1
0.1
0.1
2 x 1N914
Fig.1: the circuit is based on IC1, a PIC16F84P microprocessor. This processes the pulses from the speed sensor on its RB0 (pin 6) input
and drives three 7-segment LED displays in multiplex fashion. LDR1, IC2b and Q4 automatically dim the LED displays so that they are
not too bright at night.
SWITCH LIGHT INDICATORS
680
680
2.2k
2.2k
2x
1N914
680
SPEED SENSOR
AND COMPARATOR
N
L1
L1:
500T 0.18mm
ENAMELLED COPPER WIRE
ON 8mm DIA FORMER
+12V
VIA
IGNITION
SWITCH
Fig.2: the output signal from the sensor coil is a 250mV
peak-to-peak pulse waveform, as shown by the top trace
in this scope shot. The bottom trace shows the processed
speed sensor waveform that’s fed to pin 6 of IC1.
is that the RB0 input includes internal
diodes which clamp the voltage on
pin 6 to a maximum of 5.8V.
The resulting processed speed
sensor waveform into pin 6 of IC1 is
shown as the bottom trace in Fig.2.
Note how the waveform has been
squared up and limited to 5.8V.
The 1MΩ positive feedback resistor sets the hysteresis of the Schmitt
trigger and prevents false triggering
due to noise.
Switch inputs
The pushbutton switches are all
monitored at the RA4 input. The other sides of the Up, Down and Mode
switches also connect to the RA0, RA1
& RA2 outputs respectively, while the
Cal switch connects to ground.
Normally, the RA4 input is pulled
high (ie, to +5V) via a 10kΩ resistor.
However, when a switch is closed,
it initially pulls the RA4 input low.
The microcontroller then tests which
switch is closed by first taking the
RA0, RA1 & RA2 outputs all high. If
RA4 is still low, then it must be the
Cal switch that is closed.
If the Cal switch hasn’t been
pressed, the RA0-RA3 outputs are
taken low in turn until RA4 also goes
low. In this way, the microcontroller
quickly determines which switch has
been pressed. For example, if RA4
goes low when RA0 is low, then it’s
the Mode switch that’s been pressed.
The 1kΩ resistors in series with
the Mode and Up switches are there
to ensure that the RA0, RA1 & RA2
outputs can not be shorted if more
20 Silicon Chip
Fig.3: the top trace on this shot shows the RA0 output
(2V/div) from the microcontroller, while the lower traces
(on 5V/div scales) are for the RA1 and RA2 outputs
respectively. These outputs drive transistors Q1-Q3.
than one switch is pressed at the
same time. While this is not a major
problem for the microcontroller outputs for a short time, it can produce
strange display results.
We haven’t included 1kΩ resistors
in series with the Down and Calibrate
(Cal) switches, since these are unnecessary. Note that the Calibrate switch
is only accessible with a small probe
and it is unlikely that this switch will
be pressed at the same time as any of
the other switches.
Pressing the Cal switch places the
unit in calibration mode. This switch
is accessed through a small hole in
the Speed Alarm front panel using a
pen or a similar probe.
Basically, the unit counts the pulses
from the speed sensor over a fixed
time period to calculate the road
speed. During calibration, this time
period is automatically extended
until the number of pulses counted
equals 8 per 5km/h. This time period becomes the calibration number
and is permanently stored in the
EEPROM.
In practice, this means that if you
are travelling at 100km/h, the counter
period is long enough to receive 160
pulses from the speed sensor. And
because of the way the software oper
ates, the unit is virtually self-calibrating, as we shall see later on.
LED displays
The three 7-segment LED displays
are driven by IC1 in multiplex fashion. As shown, the individual segments are driven directly from the
RB1-RB7 outputs via 150Ω current
limiting resistors, while the RA0-RA2
outputs drive the individual displays
via switching transistors Q1-Q3.
To drive one of the displays the
microcontroller must bring the corresponding RA0, RA1 or RA2 line low.
When RA0 is brought low, for example, Q1 turns on and applies power
to the common anode connection of
display 1. Any low outputs on RB1RB7 will thus light the corresponding
segment(s) of that display.
After this display is lit for a short
time, the RA0 output is taken high
and display 1 turns off. The RA1 line
is then brought low to drive Q2 and
display 2. The new 7-segment data on
the RB1-RB7 outputs is then presented to this new display, after which
RA2 is taken low to drive display 3.
Because the displays are switched
on and off at 944Hz, they appear to
be continuously lit. Fig.3 shows the
RA0 output on the top trace (2V/
div), while the lower traces (on 5V/
div scales) show the RA1 and RA2
outputs respectively.
Alarm output
The alarm output from IC1 appears
at RA3 (pin 2) and performs two functions. First, it drives the alarm LED to
produce a visual alarm output. Second, it provides a modulated 1.4kHz
tone to drive the piezo element with
a characteristic “beep, beep” sound.
In practice, the RA3 output goes
high and low at a 1.4kHz rate for about
80ms, then the output stays high for
80ms. The 1.4kHz tone is then pro-
duced for another 80ms, after which
the output goes low for 10 seconds
and the cycle repeats (assuming that
the repeat alarm feature is enabled).
As well as the piezo alarm, the
RA3 output also drives the alarm
LED (LED1). This means that when
the alarm speed is exceeded, LED1
flashes twice (because it is driven by
the two 1.4kHz 80ms pulses). The
LED then stays lit until the vehicle’s
speed drops below the alarm speed.
The two parallel diodes in series
with the piezo element prevent any
low volume tone from being produced
due to modulation of the RA3 output
as the display is multiplexed. By
including the diodes, the modulation must exceed 600mV p-p before
any sound is heard from the piezo
element.
Display brightness
IC2b is used to control the display
brightness. This op amp is wired as a
voltage follower and drives a transistor buffer stage (Q4) which is inside
the negative feedback loop. Light
dependent resistor LDR1 controls the
voltage on the pin 5 input of IC2b according to the ambient light level. The
op amp, in turn, controls Q4 and thus
the voltage applied to the emitters of
the display drivers (Q1-Q4).
During daylight hours, the voltage
on pin 5 is close to +5V because the
LDR has a low resistance in strong
light. IC2b controls Q4 so that the
voltage on pin 6 is equal to the voltage
on pin 5, so Q4’s emitter will also be
close to +5V. This voltage is applied
to the emitters of Q1-Q3 and to the
560Ω resistor in series with LED1.
This lights the displays at full brilliance, so that they can be seen during
daylight hours.
Conversely, as the light level falls,
the resistance of the LDR increases
and the voltage on pin 5 of IC2b decreases. In fact, when it’s completely
dark, the voltage on pin 5 is deter
mined by the setting of trimpot VR1.
As before, this voltage appears at Q4’s
emitter and so the displays are all
driven at reduced brightness.
In practice, VR1 is adjusted to give
the requisite display brightness at
night.
LEDs2-4 are the switch indicator
lights. They shine light through
translucent rings fitted to the holes
surrounding the switches, so that
their positions can be seen at night.
Parts List For Speed Alarm
1 display PC board, code
05310991, 78 x 50mm
1 processor PC board, code
15310992, 78 x 50mm
1 plastic utility case, 83 x 54 x
30mm
1 front panel label, 80 x 51mm
1 dark red transparent Perspex or
Acrylic window, 50 x 20 x 2.5
1 piezo transducer, 13.5mm OD
x 3.5mm (Kingstate KPE-165);
use KPE-827 (30mm dia.) or
equivalent if a louder external
alarm is required
1 3.579545MHz parallel resonant
crystal (X1)
1 LDR (Jaycar RD-3480 or
equivalent)
3 9.5 x 11.5 x 2mm translucent
rings (optional – see text)
4 or 6 button magnets
1 coil former, 15mm OD x 8mm ID
x 7mm
1 20m length of 0.18mm
enamelled copper wire
1 6mm x 25mm steel bolt, washer
and nut
6 PC stakes
1 8-way pin header launcher
2 7-way pin header launchers
1 DIP-16 IC socket with wiper
contacts (cut for 1 x 8-way
single in-line socket)
1 DIP-14 IC socket with wiper
contacts (cut for 2 x 7-way
single in-line sockets)
1 small rubber grommet
3 PC-mount click action push-on
switches (black) (S1-S3)
1 tactile switch (S4) (Jaycar SP0730 or equiv.)
1 500kΩ horizontal trimpot (VR1)
3 6mm tapped spacers
2 M3 x 6mm countersunk screws
1 M3 x 15mm Nylon screw
1 M3 x 15mm brass screw
Clock signals for IC1 are provided by an internal oscillator circuit
which operates in conjunction with
crystal XTAL1 (3.58MHz) and two
15pF capacitors. The two capacitors
are included to provide the correct
loading for the crystal and to ensure
reliable starting.
The crystal frequency is divided
down internally to produce separate
clock signals for the microcontroller
2 M3 nuts
2 M3 plastic washers 1mm thick
(insulating bush and washer
with bushing cut off) or 1 x M3
plastic washer 2mm thick
1 400mm length of 0.8mm tinned
copper wire
1 2m length of single core shielded
cable
1 2m length of red automotive wire
1 2m length of black or green
automotive wire (ground wire)
Semiconductors
1 PIC16F84P microprocessor
programmed with SPEED.HEX
program (IC1)
1 LM358 dual op amp (IC2)
1 7805, LM340T5 5V 1A
3-terminal regulator (REG1)
3 BC328 PNP transistors (Q1-Q3)
1 BC338 NPN transistor (Q4)
3 HDSP5301, LTS542A common
anode 7-segment LED displays
1 5mm high-intensity red LED
(LED1)
3 3mm red LEDs (LED2-4)
4 1N914, 1N4148 diodes (D1-D4)
1 16V 1W zener diode (ZD1)
Capacitors
3 47µF 16VW PC electrolytic
4 0.1µF MKT polyester
2 15pF ceramic
Resistors (0.25W, 1%)
1 1MΩ
3 1kΩ
1 22kΩ
6 680Ω
1 10kΩ
1 560Ω
3 2.2kΩ
1 10Ω 1W
Miscellaneous
Automotive connectors, aluminium
bracket for sensor, heatshrink tubing,
long cable ties, Silicone sealant,
super glue, thin black cardboard.
operation and for the alarm tone and
display multiplexing. The crystal frequency is also used to give a precise
time period over which to count the
incoming speed signals at RB0. The
number of pulses within a set period
indicates the speed.
That’s all we have space for this
month. Next month, we will describe
the power supply circuit and give the
SC
full construction details.
November 1999 21
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.
Refinements to the
PC Monitor Checker
The PC Monitor Checker published
in the August 1999 issue can be modified to provide more appropriate scan
frequencies for the various monitor
types than the original circuit published in the May 1999 issue of Popular Electronics. Another modification
produces the preferred sync polarity
for VGA & EGA monitors.
Table 1 shows the common horizontal and vertical scan rates and sync polarities for the various monitor types.
Obtaining the horizontal frequencies
from the 1MHz clock signal requires
the division ratios from IC2 as shown
in Table 2.
The circuit of Fig.1 shows the suggested modifications which involve
using a 2-pole 5-position switch (eg,
DSE Cat P-7508). Note that IC5c is now
unused and should have its pin 5 tied
high (+5V) or low (0V). These modifications would enable the testing of
monitors such as the Philips/Commodore 1084 which use 15,625kHz and
50Hz line and frame rates respectively,
and can accept RGB and composite
video inputs.
To produce a 50Hz vertical scan
frequency, the spare gate in IC9 (4012)
can be employed. Counter IC6 is
Table 1: Scan Frequencies
Vertical Horizontal Sync
Monitor Frequency Frequency Polarity
MDA
50Hz 18.432kHz +H -V
CG A
60H z
15.75kHz
+H -V
EG A
60H z
21.8kHz
n/a
VG A
60H z
31.5kHz
-H -V
Table 2: Division Ratios
Frequency
Divisor
IC2 Outputs
15,625Hz
64
Q7
15,750Hz
64
Q7
18,432Hz
54
Q6,Q5,Q3,Q2
21,800Hz
46
Q6,Q4,Q3,Q2
31,500Hz
32
Q6
22 Silicon Chip
Fig.1: suggested
circuit modification
for producing the
required horizontal
scan frequencies.
3
9
Q1
7
Q4
13
Q8
3
Q14
IC6
Q11 15
14
Q10
12
Q9
R
5
4
3
2
12
11
10
9
EGA
CGA
VGA
1 60Hz
+VE SYNC
13
IC11
IC5f
8
9
IC9a
12
J2/14 - VGA
J5/9 - EGA
IC5d
13
IC9b
J1/9 - MDA/CGA
50Hz
MDA
COMMODORE
12
13
11
Fig.2: suggested circuit for obtaining a
50Hz vertical scan rate.
presently wired to divide its 500kHz
input clock signal by a factor of 8329,
resulting in an output of 60.03Hz. By
connecting the Q9, Q10, Q11 & Q14
outputs of IC6 to IC9b, the resultant
output frequency is 500,000/9984 =
50.08Hz. This modification is shown
in Fig.2.
The circuit of Fig.3 corrects an
error in the labelling of +VSYNC and
-VSYNC on the original circuit. Furthermore, the original circuit (and PC
board) produced +V and -H sync for
both EGA and VGA monitors. These
are best driven by -H and -V pulses
since this appears to be a standard
mode for 640 x 480 resolution at 60Hz
and 31.5kHz. -H +V is associated with
640 x 400 resolution at 70Hz and 31.5
kHz.
Finally, Fig.4 is a minor wiring
addition to allow CGA monitors to
be driven from the MDA socket (J1).
11
IC3d
Fig.3: this circuit produces -H and -V
sync pulses for EGA & VGA monitors.
J4/3 - CGA
J5/3 - EGA
1
J1/4 - CGA
J5/4 - EGA
IC8
2
J1/5 - CGA
J5/5 - EGA
3
Fig.4: this circuit allows CGA monitors
to be driven from the MDA socket (J1).
Note: the MGA output should have
been labelled “MDA” (monochrome
display adaptor).
The CGA (colour graphics adapter)
frequencies correspond to those produced by the original circuit (60Hz
and 15,750Hz) but those for MDA
are significantly different (ie, 50Hz &
18,432Hz). There was also an MCGA
variant which was integrated into
some PS/2 motherboards but this used
60Hz or 70Hz (vertical) and 31.5kHz
(horizontal) scan rates (similar to
VGA).
Franc Zabkar,
Barrack Heights, NSW. ($100)
Daytime Lights for Cars: negative line
headlight switching
+12V
Simple Christmas
light tester
FUSE
87
Q1
47
D
86
G
S
RLY1
HIGH
LOW
85
100k
GLOBE
SOCKET
TO PARKING LIGHTS,
30 INSTRUMENT LIGHTS,
ETC.
87a
DIP SWITCH
470
D8
9V
BATTERY
LIGHTS
L1
RELAY CIRCUIT FOR
OTHER LIGHTS
LED
MODIFIED DAYTIME LIGHTS
FOR CARS CIRCUIT
As Christmas lights consist of
moulded lamp sockets all connected
in series, it is quite difficult to find a
faulty bulb if one goes open circuit.
In effect you have to painstakingly
remove each bulb from its socket and
then check if for continuity with a
multimeter.
This tester does not avoid the need
to remove each bulb from its socket
but does make the continuity test a
breeze. If the LED comes on, the bulb
is OK.
G. Moore,
Seven Hills, NSW. ($15)
EXISTING HEADLIGHT CIRCUIT
This circuit shows the modifications necessary for vehicles that have
negative line switching for their headlights. Note that inductor L1 is now
connected directly to ground.
Simple lights-on
warning
HEADLIGHT
FUSE
BUZZER
DSE CAT.
L-7009
IGNITION
SUPPLY
K
A
This is perhaps the simplest possible headlights-on warning circuit. The
red wire of a buzzer is connected to
the fuseholder for the lighting circuit.
The black wire is connected via
the diode to any other fuse which is
de-energised when the ignition key is
switched to the accessories position.
When the lights are on and the ignition is switched off, there will be a
12V potential difference between the
fuses and the buzzer will sound.
W. Movigliatti,
Warabrook, NSW. ($15)
The wiring modifications are quite minor, as this diagram shows. Note that
a 0.1µF capacitor may need to be connected between the fused side of the
positive supply to the lights and chassis, to prevent RF interference
The Daytime Lights for Cars circuit published in the August 1999
issue of SILICON CHIP was designed
to provide positive line switching
to the headlights. However, some
cars have their switching in the
negative line to the chassis rather
than in the positive line from the
battery.
This modified circuit and wiring
allows for negative line switching.
Note that the 0.1µF 250VAC capacitor is removed from the PC board
and L1 now connects to chassis
via the terminal on the side of the
case. The drain connection to Q1
now connects to the dip switch
as shown. The relay provides the
supply for the remaining lights.
A 0.1µF capacitor or an automotive suppression capacitor may
need to be connected between the
fused side of the positive supply to
the lights and chassis. This should
remove any interference evident in
your car radio when the Daytime
Lights for Cars circuit is driving the
lights at the 80% level.
John Clarke,
SILICON CHIP.
November 1999 23
TECHNICAL
LOOK: TEN NEW
NEW!
TCP/IP
EXPLAINED
By Philip Miller. Published 1997.
$
90
This concise and practical book offers readers
an in-depth understanding of the Internet
Protocol suite. It assumes no prior knowledge
of TCP/IP, only a basic understanding of LAN
access protocols, explaining all the elements
and alternatives. It leads the reader through
the Internet protocols, combining study
questions with reference material. Examples
of network designs and implementations are
given. 518 pages, in paperback, at $90.00.
LOCAL AREA NETWORKS:
An Introduction to the Technology
NEW!
SETTING UP A WEB SERVER
A complete reference for anyone setting up a
web server. Covers all major platforms, software, links and web techniques. It details each
step required to choose, install and configure
the hardware and software elements, create
an effective site and promote it successfully.
The book covers the main web server
software applications, how they differ, and
which work best in each environment. 273
pages, in paperback, at $65.00.
NEW!
65
By Tim Williams. First published 1991
(reprinted 1997).
By PK McBride & Nat McBride.
Published 1999.
$
O
R
D
E
R
H
E
R
E
29
95
If you want to create web pages for your
business or your own home site, but don't
know where to start . . . or if you have some
experience of Web page design and now
need to master all aspects of HTML form
then “HTML4.0 Made Simple” is for you.
it uses a combination of tutorial approach,
carefully focussed examples and quick
reference guides. 198 pages, in paperback,
at $29.95.
TCP/IP EXPLAINED.............................................$90.00
LOCAL AREA NETWORKS..................................$65.00
HTML 4.0 MADE SIMPLE...................................$29.95
SETTING UP A WEB SERVER.............................$65.00
THE CIRCUIT DESIGNER’S COMPANION...........$59.95
ELECTRIC MOTORS AND DRIVES......................$59.95
UNDERSTANDING TELEPHONE ELECTRONICS....$55.00
AUDIO ELECTRONICS........................................$79.00
GUIDE TO TV & VIDEO TECHNOLOGY...............$55.00
EMC FOR PRODUCT DESIGNERS.......................$95.00
THE ART OF LINEAR ELECTRONICS..................$80.00
INTERNET HOME PAGES MADE SIMPLE...........$24.95
DIGITAL ELECTRONICS .....................................$59.95
ESSENTIAL LINUX..............................................$85.00
ORDER TOTAL: $.............
24 Silicon Chip
Includes grounding, printed circuit design
and layout, the characteristics of practical
active and passive components, cables, linear
ICs, logic circuits and their interfaces, power
supplies, electromagnetic compatibility,
safety and thermal management. Aimed at
the practising designer who needs straightforward, easy-to-follow advice. 302 pages, in
paperback, at $59.95.
$
HTML 4.0 MADE SIMPLE
$
65
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THE CIRCUIT DESIGNER’S COMPANION
NEW!
By John E. McNamara. 2nd edition 1996.
Intended for those who want to become more
familiar with local area networks (LANs) without
facing the challenge of a 400-page text. The
goals of the book are to give prospective
LAN users or purchasers familiarity with the
concepts involved and to provide a head start
for reading more detailed texts. 191 pages, in
paperback, at $65.00.
NEW!
By Simon Collin. Published 1997.
59
95
ELECTRIC MOTORS AND DRIVES
NEW!
By Austin Hughes. Second edition
published 1993 (reprinted 1997).
This book is for non-specialist users of electric
motors and drives. The author explores most
of the widely-used modern types of motor and
drive, including conventional and brushless
DC, induction motors (mains and inverter-fed),
stepping motors, synchronous motors (mains
and converter-fed) and reluctance motors. 339
pages, in paperback, at $59.95.
59 95
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A very useful text for anyone wanting to
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technology. The 10 chapters explore telephone
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cover at $55.00.
AUDIO ELECTRONICS
GUIDE TO TV & VIDEO
TECHNOLOGY
$
By John Linsley Hood. First published
1993. NEW SECOND EDITION 1998.
80
All you need to get started. Create and design
your own Internet home pages that include
both text and graphics, using this practical,
easy to follow, jargon free guide. This edition
has been enhanced and updated and now
covers HTML 4.0. 182 pages, in paperback,
at $24.95.
79
$
Eugene Trundle has written for many years in
Television magazine and his latest book is right
up to date on TV and video technology. The book
includes both theory and practical servicing
information and is ideal for both students and
technicians. 382 pages, in paperback, at $55.00.
55
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DESIGNERS
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24 95
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DIGITAL ELECTRONICS –
A PRACTICAL APPROACH
By Richard Monk. Published 1998.
$
59
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With this book you can learn the principles and
practice of digital electronics without leaving your
desk, through the popular simulation applications,
EASY-PC Pro XM and Pulsar. Alternatively, if you
want to discover the applications through a
thoroughly practical exploration of digital
electronics, this is the book for you. A free floppy
disk is included, featuring limited function
versions of EASY-PC Professional XM and
Pulsar. 249 pages, in paperback, at $59.95.
ESSENTIAL LINUX
By Steve Heath. Published 1997.
By Tim Williams. First
published 1992. Second edition 1996.
Widely regarded as the standard text on EMC,
this book provides all the information necessary
to meet the requirements of the EMC Directive.
It includes chapters on standards, measurement
techniques and design principles, including
layout and grounding, digital and analog circuit
design, filtering and shielding and interference
sources. The four appendices give a design
checklist and include useful tables, data and
formulae. 299 pages, in soft cover at $95.00.
NEW!
By Lilian Hobbs. First published 1996.
Second edition 1999.
By Eugene Trundle. First published 1988.
Second edition 1996.
$
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world’s most prolific audio designers has
been updated and amended to make it the
leading practical source of information for
those interested in linear electronics and
its applications, particularly in the world of
audio design. 348 pages, in paperback, at
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DESIGNING INTERNET HOME PAGES
MADE SIMPLE
By John Linsley Hood. First published
1995. Second edition 1999.
This book is for anyone involved in designing,
adapting and using analog and digital audio
equipment. It covers tape recording, tuners and
radio receivers, preamplifiers, voltage amplifiers,
audio power amplifiers, compact disc
technology and digital audio, test and
measurement, loudspeaker crossover systems,
power supplies and noise reduction systems.
375 pages in soft cover at $79.00.
THE ART OF LINEAR ELECTRONICS
NEW!
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Provides all the information and software that
is necessary for a PC user to install and use the
freeware Linux operating system. It details,
setp-by-step, how to obtain and configure the
operating system and utilities. It also explains
all of the key commands. The text is generously
illustrated with screen shots and examples
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including all the interim updates, basic utilities
and compilers with their associated documentation. 257 pages, in paperback, at $85.00.
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N
Dovember
ecember 1999 25
SERVICEMAN'S LOG
Price isn’t everything
This month’s lead story concerns a rather
expensive, top-of-the-market European TV
set. Unfortunately though, its upmarket
status didn’t prevent it from being a right
proper stinker on the service bench.
Did you know that Loewe is a very
popular brand of TV set in Canberra?
This is because our Lords and Masters have them installed throughout
Parliament House which means that
they must be pretty good performers.
In fact, Loewe colour TVs have been
available in Australia since 1974 and
are highly-respected, German-made
sets with many advanced features.
However, this information really has
nothing to do with the Loewe Studio
70 (110C91 chassis) which Mr Canaris (not his real name) reluctantly
allowed me to take back to the workshop. He initially complained of the
sound dropping in and out, as well
as half vertical deflection, but when
I switched it on, it was dead.
“Oh yes, that too”, he replied –
offhandedly dismissing this all too
obvious fault when I phoned him back
to ask why it hadn’t been mentioned.
Fortunately, I was able to obtain a
service manual for the set (they are
available from a firm called Interdyne
in Melbourne and cost around $40).
That at least was a good starting point
and when it arrived, I wasted no time
in opening up the set for a preliminary
investigation.
The reason the set was dead was
that the power supply had blown, due
mostly to the electrolytic capacitors
(this set was now about 10 years old).
Getting it going again involved replac
ing IC611 (TDA4601), the switchmode
transistor, four electrolytic capacitors,
R613 and the start-up PTC resistor
(R622) – see Fig.1.
This done, the set came on perfectly. I adjusted variable resistor P633
Fig.1: the power supply circuit in the Loewe Studio 70-110C91.
26 Silicon Chip
(4.7kΩ) and set it for 155V at point
UB, as shown on the circuit. (Note:
some European manufacturers use
the designation “UB” to indicate the
main HT rail, while some German
manufacturers may sometimes just
use “U”).
Unfortunately, there was some initial confusion regarding this HT rail
value. The circuit involved is simple
enough, though. Diode D651 rectifies
the output from the switchmode transformer secondary at pin 18 and the
resulting DC is then filtered by R651
and C651 (47µF) to chassis. The HT is
then further filtered by coil L651 and
a second 47µF capacitor to chassis to
give the 155V HT rail (UB).
Although this value is clearly
marked on the circuit diagram, the
parts layout diagram indicated 145V
at what appeared to be the same point.
However, closer analysis of the layout
diagram clarified this; the 145V reading was the voltage at C651, whereas
the reading on the circuit indicated
the voltage at C652.
But this only created further confusion. Why was the reading across
the first filter capacitor less than that
across the second capacitor?
The logical explanation is that the
waveform across C651 still contains
sufficient ripple to upset the reading.
It needs L651 and C652 to produce
pure DC. Anyway, the set was working
for the moment and I put it aside for a
soak test, hoping that the sound and
vertical height faults would eventually show up.
Impatient customer
Unfortunately, I hadn’t counted on
the impatience of Mr Canaris who
was on the phone the very next day.
I explained that I had fixed the total
failure but hadn’t been able to observe
the other faults he had mentioned and
that obviously they were intermittent.
I would need time for them to show
up so that I could find and fix them.
He was very disappointed and although he didn’t actually say so, I got
the impression that he thought I was
incompetent. Apparently, I was supposed to wave some sort of magical
wand and all the unseen faults in his
set would disappear. Anyway, I told
him that he would have to wait a few
more days and that I would phone him
when I had fixed all the faults.
Unfortunately, the message didn’t
sink in because his wife phoned the
next day. Once again, I explained the
situation and said that I would ring
when the job had been completed.
The next day, I switched it on and
it came on with only half a scanned
picture. I heated it and I froze it and
suddenly it worked OK, before I had
time to work out which component
was responsible. Then Mr Canaris was
back on the phone wanting to know
when he could pick up the set; his
wife had said it would be ready today.
Feeling somewhat frustrated with
him by now, I told him that she had
misunderstood me and that the set
was still not ready. The next day
the fault was back, so I changed the
vertical output IC (I561, TDA8175).
The fault didn’t show again until
three days later but Mr Canaris was
still phoning every day. This was a
man who had trouble understanding
plain English.
Finally, I decided to replace all the
electrolytics in the vertical timebase.
After that, the set worked well and
there were no sound problems but I
Items Covered This Month
•
•
•
•
Loewe Studio 70 (110C91
chassis
Sharp VC-A200X VCR
Pye radio/cassette/CD player
Teac CT-M144 34cm TV set
was not convinced that I had solved
all the intermittent problems. The
manufacturers and agents are generally more familiar with difficult problems, particularly intermittents, than
individual servicemen, so I phoned
Loewe in Melbourne for advice.
As it turned out, they were very
helpful. In particular, they suggested
I replace IC I441 (APU2471) and fit a
special kit to the horizontal output
transformer to connect the ferrite core
to chassis, which might be flashing
over. I had already reworked the entire
chassis for dry joints.
I acquired and fitted IC I441 plus
the special kit as suggested, but then
just when things were looking good,
the next disaster hit – the set went
dead again. In the meantime, the
Canaris were still phoning every day
and getting very shirty, which didn’t
help matters.
This time, both the horizontal
output transistor T534 (S200AF) and
diode D536 BY228 had gone short
circuit. Replacing these restored the
picture but the horizontal system was
overscanning and there was no east/
west (E/W) pincushion correction.
By going into the service mode with
the remote control, I found that I could
adjust the picture but not enough to
correct the problem. I also noticed that
the E/W output transistor’s heatsink
November 1999 27
was getting very hot. By now, Mr Canaris was no longer phoning me but
complaining long and hard to Loewe
in Melbourne, who then did their best
to help me.
The voltages seemed correct everywhere and so did the waveform on
pin 24 of IC I511, except for some
horizontal pulses superimposed on
the lower part of the parabola. I removed and checked all the transistors
and replaced a number of electrolytic
capacitors (including C558, C546,
C583, C581, C512 and C542) but it
was all to no avail. I then replaced
C594, C536, C537, C538, C541 and
C531 but still no joy. It wasn’t until I
noticed some of the old brown goo on
L538 (incorrectly marked as R538 on
the circuit) that I realised I had a clue.
This large coil (1.6mH but marked
14323) measured shorted turns when
checked on my shorted turns tester,
so I acquired a replacement from
Melbourne and fitted it. Success at
last – the picture was good and the
only thing left was transistor T594
(BD537B) in the E/W correction circuit, which (I felt) was running far too
hot. I replaced it and its other half of
the Darlington pair, transistor T593
(BC546B) and rechecked the voltages.
There was 15V on the collector and
0.65V on the base. In addition, the
waveform on T594’s collector was
100% correct.
I rechecked all the transistors in
the E/W correction as well as all the
resistors and everything was correct.
28 Silicon Chip
In the end, I felt I had taken all possible steps to solve this problem and
the only lame idea I had left was to
add more aluminium to the heatsink
to get rid of the heat (it was literally
too hot to touch). This was done and
after soak testing for another 24 hours,
I finally agreed to let the set go home.
Mr Canaris complained long and
hard about the service, the cost,
the delay and how I didn’t know
what I was doing. For my part, I was
thoroughly fed up with him and did
little to hide my annoyance. In fact, I
doubt very much that I will hear any
more about this set. There’s so much
bad blood between us that even if
it does fail, I’m sure he will take it
somewhere else.
That’s a pity really, as I would like
to know if any more faults subsequently showed up. Some customers
really are their own worst enemies.
Perverse inanimate objects
I’m in a whinging mood at the
moment. I don’t usually whinge, at
least not in print. But fair dinkum, I’m
getting fed up with components that
keep giving different measurements.
During the last few months, I have
been beset by several such frustrating
experiences. Perhaps they are due to
what an acquaintance calls “the perversity of inanimate objects”. His philosophy was that some objects have
mind of their own and that if you want
them to behave in a certain way, they
will do all they can to frustrate you.
A questionable philosophy? Well,
maybe it is. But have you ever tried
to fit a nut to a screw, in an awkward
corner of a chassis? Or have you tried
to fit a pigtail through a hole in a PC
board from the hidden side?
Of course, these are relatively simple mechanical situations. It’s when
these inanimate objects are part of an
electronic circuit that the fun really
begins.
This month, I had a Sharp VCA200X VCR with no display. I didn’t
have a circuit but I felt it shouldn’t
matter as the circuit is so simple.
Apart from disassembling it, it wasn’t
difficult to establish that there was
-28V on the segment legs of the fluorescent display panel but no filament
volts on the ends.
Moving along to the switchmode
power supply, I measured the voltages
on each diode. There were appropriate positive or negative voltages on all
diodes with respect to chassis, except
for diode D921. As I quickly discovered, this diode rectifies an output
from the switchmode transformer and
feeds the fluorescent display.
The output from D921 is filtered by
a 100µF 6.3V capacitor, C921. There
was no voltage across this capacitor,
the capacitor wasn’t short circuit and
it made no difference when I connected another capacitor across it.
Diode D921 (FR103) couldn’t really
be measured in circuit because of
the low impedances everywhere, so
I unsoldered one end and found that
its forward resistance was too high for
my liking. This looked like the culprit
but when I removed it completely and
measured it out of circuit it measured
perfectly.
Still, I really didn’t have any other clues so I fitted another diode, a
BYV96E, in its place. This immediately restored the 3.5V rail needed to
drive the 3V filament and the display
with the word “SHARP” came up at
full brilliance.
So that solved that problem. But it
really cheeses me off, having to keep
remeasuring components because of
the uncertainty that the first reading
was correct.
So that’s my whinge for the month.
I know it’s nobody’s fault and there is
nothing I can do about it. And having
had my whinge, I feel better already.
And now here is a story from a colleague, P. K. I’ll let him tell the story
in his own words.
The Ghettoblaster
This story concerns what is often
referred to as a ghettoblaster; in this
case, a Pye radio/cassette/CD player
with two tape cassettes. The unit had
originally come in for service about
two weeks previously and I diagnosed
the problem as being in the CD player,
which required cleaning and testing.
This time it was a cassette problem.
I replaced a fuse which had blown,
after which there were some signs of
life. The radio worked, as did the CD
player and the “A” cassette. But when
I pressed the play button for the “B”
cassette, everything went dead.
Closer inspection revealed that a
switch associated with the play button
had failed. It was a leaf switch and
one of the two leaves had broken off
at the base and was hanging loose.
And in order to understand the implications of this, a brief description of
the switch’s associated mechanisms
should help.
The play button for each cassette –
the “B” button in this case – activates
the mechanical loading functions,
moving the tape against the head,
closing the pinch roller against the
capstan, etc. At the same time a lever –
at chassis potential – activates the leaf
switch, which is suitably insulated,
closing its two contacts. The intact
leaf carries the 12V supply, while
the broken one connects to the load;
the motors, the audio, oscillator and
other circuits.
Fig.2: this simple circuit was
used as an electronic switch to
replace the broken mechanical
unit in a Pye cassette player.
But now, when the button was
pressed, the lever contacted the remaining, live 12V leaf, taking it to
chassis. The result was inevitable; a
blown fuse.
It was a simple enough diagnosis
but what could be done about it? I
contacted Philips but I was advised
that a replacement was not available.
But even if one had been available, it
would have been a major job to pull
the unit apart to fit it.
My next idea was to simply bridge
the two leads. This would mean that
the “B” cassette drive would function
continuously, while ever the set was
switched on. This was not as a wild
an idea as it sounds; a number of
other model cassette players use this
arrangement.
Well, it was worth a try. And at
first I thought that it had worked. In
fact it had, to the extent that the “B”
tape worked perfectly. But now the
“A” tape would not play – the wheels
worked but there was no sound. When
i disconnected the two switch leads
which I had bridged, the “A” tape
came good but, of course, the “B” tape
was dead again.
So I could make one or other cassette work, but not both at the same
time. Why? – I don’t know; it would
have been too time-consuming to
figure it all out. All I knew was that
while the 12V rail to the “B” cassette
was activated, the “A” cassette would
not work.
Doubtless, given the time and
enough technical backup, one could
analyse the device in sufficient detail to work out how it functioned
and perhaps find a solution. But, at
a practical level, this approach was
out of the question. Considering the
age of the unit, I was beginning to fear
that the customer might be forced to
cut his losses and settle for only one
cassette player. After all, he could
only use one at a time!
Then I had another thought. Was
it possible to substitute an electronic
switch for the faulty mechanical one?
In fact, this looked to be relatively
simple.
I selected a BC327 PNP transistor as
the switch, connecting the emitter to
the 12V supply rail and the collector
to the load. The base was connected to
the emitter via a 1kΩ resistor, which
would ensure that the transistor
was switched off unless other
wise
instructed.
Obviously, an “instruction” would
be needed to turn the transistor
on when the “B” play button was
pressed. And this could have been
tricky. Fortunately, the remaining
switch leaf came into its own. It was
no longer connected to anything but
still made electrical contact with
the lever when the play button was
pressed. So the leaf was connected to
the base via a 3.3kΩ resistor, applying
forward bias to the base and turning
the transistor on.
Did it work? Yes it did – just like a
bought one! And I had another happy
customer.
Spring crisis
When it is a glorious day in spring,
one arrives at work feeling euphoric,
convinced that nothing could possibly spoil your day.
So it was last Tuesday – the birds
were singing, the tem
perature and
humidity were just right and I was full
of bonhomie when I booked in Mrs
Townsend’s Teac CT-M144 34cm TV
set. All that was wrong was a broken
RF socket on her tuner and she still
had the broken parts. It promised to
be a simple fix for a simple lad on a
sunny day – if only life could always
be this sweet.
On removing the covers, I felt I
might be able to resolder the coax
socket onto the tuner in situ. Unfortunately, I soon discovered that I
would have to remove the tuner and
its covers to resolder the centre pin
to the PC board.
I pulled the chassis out and placed
it upside down, happily whistling
a little ditty while I prepared the
solderwick to desolder. Mrs Serviceman wasn’t quite so happy – I don’t
know whether it was because she
didn’t like my ditty, because it was
out of tune and rather repetitive. Or
November 1999 29
perhaps it was because I was happy
and she wasn’t.
Anyway, all this was about to
change because, unbeknown to me,
the set had been switched on in the
last 12 hours or so and when I placed
the solderwick braid across the PC
board pattern, there was a bright flash,
a spark and a crack. Whoops! Well,
there was nothing I could do until I
had replaced the tuner.
It didn’t take long to do this but
a degree of anxiety was creeping
into me and my whistling ditty had
stopped. Where had the spark come
from and more importantly, what had
it struck? I was praying it was just a
direct short across an electrolytic capacitor but unfortunately this wasn’t
the case. When I switched on there
was no sound or picture.
There was EHT and voltage on the
CRT filament heaters but not much
other activity. Fortunately, I had a
schematic diagram and I soon established that all the obvious voltage rails
were intact (115V, 24V, 15V, 12V, 5V,
etc). And the source of the spark was
eventually traced to a residual voltage
across C260, a 2.2µF capacitor associated with the video output transistors
(Q601, Q602 & Q603). But it was one
30 Silicon Chip
thing to know where the discharge
originated and quite another to know
what it had struck.
By turning up the screen control, I
established that the raster was scanning correctly and touching the pins
of the audio IC (IC205) produced noise
in the speaker. At this point, I wished
I had insisted on having the remote
control. Because the fault had seemed
so simple, I hadn’t seen the need for
it when the set was brought in. Now I
hesitated to ask the lady for it, in case
she suspected the worst.
The front controls were having no
effect and there was no effect when
external signals were applied to the
SCART socket on the rear; neither
was there any on-screen display. By
now, I was beginning to suspect that
the microprocessor IC201 (TMP47
C434N-R214) and/or the EEPROM
had been damaged.
I checked that Vcc of IC204 (vertical output) and Vdd of the microprocessor were both getting 5V, and
that crystal XT201 was oscillating
correctly at 4.19MHz. I changed IC202
(TC89101P) first as it was cheaper and
simpler but even replacing IC201 as
well made no difference. The CRO
confirmed that the video was getting
to the TA8717 jungle IC (IC206) from
the SCART socket but no further.
By switching the IC to the TV mode,
I could also put the set into the preset
tuning mode and tune stations, using
the CRO to monitor the video input to
the jungle IC on pin 16. But, as before,
the signals were going no further. I
checked the voltages to IC206 and
then used the CRO to check crystals
XT202 and XT204. Unfortunately,
this provided no clues and it was
now obvious that I had overlooked
something, but what and where?
I went back to microprocessor
IC201 and decided to check each pin.
I discovered that even though nothing
could be seen or heard, most functions
were working and responding to the
front controls, and these could be
measured on the appropriate
pins.
I finally checked pin 26,
marked HD, and found nothing
on it. I did not know what HD - or
indeed VD next to it - stood for but
they suggested horizontal and vertical pulses. I followed the horizontal
circuit back to the collector of Q218
and then checked the base circuit.
This was fed from horizontal output
transformer T201 (pin 10) and so I
expected to see horizontal pulses - but
there weren’t any!
Following the circuit further, I
found a branch feeding diode D233
(MTZ208) and resistor R330 (10kΩ) to
pin 17 of the jungle IC (IC206) which
wasn’t getting any pulses either. It
took some time to follow the PC track
to find where D233 was situated on
the mother board but I finally found
it nestled right next to connector
CN203. And guess what was on pin
1 of this connector?
Yes, the 200V rail to the video
output transistors (Q601-Q603). This
rail is derived from pin 3 of T201 via
diode D229 and my old friend capacitor C260. Obviously, the desoldering
braid connection had shorted this rail
directly to D233, the residual voltage
in C260 instantly destroying it and
turning it into a short circuit.
The next step was to identify D233
and I worked out that it was a 20V zener diode. Fitting a new one restored
all the set’s functions.
Mrs Townsend was spared my
anguish and so remains blissfully
unaware of the trials and tribulations
involved in fixing her wretched anSC
tenna socket.
Looking for something different this Christmas?
Try our multi-coloured, multi-pattern LED Christmas Tree.
It will look great at the top of your Christmas tree
or in the front window.
By Les Grant*
November 1999 31
I
N NOVEMBER 1998, we published the Christmas Star as a novelty project and it proved extremely popular.
This year, our “just for fun” festive
season project is in the shape of a
Christmas Tree but the display is a lot
more diverse and interesting because
it uses bi-coloured LEDs. Not only
can each LED produce 16 different
colours, the LED Christmas Tree has
a fascinating range of ever-changing
patterns.
In fact, considering that the LEDs
are red/green types, you will wonder
how they can produce such a range of
colours; some of them are quite odd.
As with last year’s Christmas Star
project, this circuit uses just one
IC (OK, one-and-a-bit!) and yet the
patterns it produces are seemingly
endless.
How does it do it? Yes, you guessed
it. The Tree is controlled by a microcontroller but this one is different.
While it can be programmed by most
“high-end” (expensive) chip programmers, it can also be programmed (and
re-programmed) by a PC parallel port
with minimal hardware.
This makes it ideal for hobbyists.
If you have been avoiding microcon-trollers because of the cost of the
programming hardware, now there is
no excuse!
And most of the development soft-
ware can be downloaded free from the
Internet – that avoids another excuse!
Circuit description
Fig.1 shows the circuit. The key to
understanding any circuit is “divide
and conquer” – break it down into
functional blocks.
There are three main blocks in
the Tree circuit. The first, the power
supply, is straightforward. 9V DC is
applied from a plugpack to socket
SK1. Reverse polarity protection is
provided by diode D1. The 3-terminal
7805 regulator (REG1) then provides
a 5V rail for the LEDs and the logic.
Bypass capacitors C4 and C5 ensure
that the 7805 remains stable.
Next is the microcontroller IC1.
In the Christmas Star and Heart of
LEDs (May 1999) projects, we used
the Atmel AT89C2051. However, its
I/O port structure is not quite suitable
for this application so we have used
the similar Atmel AT90S2313. See
the section entitled “What’s in the
AT-90S2313” for a description of the
microcontroller.
IC2 is a 24C16 serial EEPROM
where the pattern data is stored.
While IC1 has some EEPROM on chip
(128 bytes), this was not enough for
the number of patterns we wanted to
provide.
The final circuit is the LED matrix.
At first glance, the PC board looks like
it contains 32 LEDs. In reality, there
are 64 LEDs as each is a bi-colour LED
capable of glowing red or green. 2-pin
bi-colour LEDs were chosen to reduce
the number of PC board tracks and
microcontroller output pins required.
3-pin LEDs would have been easier to
drive but would have required more
output pins from IC1.
To enable IC1 to control so many
LEDs with relatively few output pins
the LEDs are multiplexed. Multi-plexing is a switching technique whereby
each column of LEDs is activated for a
short time during which the appropriate rows are driven. This means that
individual LEDs are only turned on
for a short time. Provided the rate at
which the LEDs are turned on is fast
enough, our eyes don’t see any flicker.
So for multiplexing in this circuit,
we connect the LEDs in a matrix of
four columns and eight rows to give a
total of 32 LED packages. That enables
us to drive the whole matrix with just
12 output pins from IC1.
Note that while there are only four
columns of LEDs, we have to drive
each column twice in each multiplex
cycle so that we can activate the red
and green LEDs.
Consequently, each LED’s timeslot
is just 12.5% of the total. This is a
practical minimum duty-cycle for
adequate brightness from the LEDs.
The 100Ω resistors R6-R13 set the
What’s in the AT90S2313?
The AT90S2313 is a member of the Atmel AVR family of microcontrollers which range from tiny 8-pin packages to a
64-pin feature-packed “monster”. Here is a short summary of the features of the ’2313:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
118 instructions, most single-clock cycle execution
32 8-bit general purpose working registers
Up to 10 MIPS throughput at 10MHz
2k bytes (1k words) of In-System-Programmable Flash for program storage (endurance 1,000 erase/write cycles)
128 bytes of SRAM
128 bytes EEPROM (endurance 100,000 erase/write cycles)
May be locked for program and EEPROM data security
1 8-bit timer/counter with separate prescaler
1 16-bit timer/counter with separate prescaler, compare and capture modes and 8, 9 or 10-bit PWM
On-chip analog comparator (rail-to-rail inputs)
Programmable watchdog timer with separate on-chip oscillator
SPI serial interface (for in-system programming only)
Full duplex UART
Low power idle and power down modes
External and internal interrupt sources
15 programmable I/O lines in a 20-pin package
2.7 - 6.0V (4MHz parts) or 4.0 - 6.0V (10MHz parts)
32 Silicon Chip
Fig.1: the micro
drives the 32
bi-colour LEDs in
a 4 x 8 matrix with
4 columns and 8
rows. Each row and
column is driven
by complementary
emitter-follower
pairs which can
sink or source
current. This is
necessary because
the bi-colour LEDs
need to be driven in
both directions.
November 1999 33
peak LED current to about 14mA.
Because there can only be eight LEDs
on at any time, the maximum current
drawn by the Tree is about 150mA.
Any 9V DC plugpack rated at 250mA
or more should be suitable. Do not use
a 12V plugpack otherwise you will
cook the 5V regulator.
Unfortunately, the microcontroller
can’t drive the LEDs directly because
its maximum current ratings would be
exceeded. So each output pin is buffered by a transistor connected as an
emitter-follower. Because each LED
package has two LEDs connected in
inverse parallel, the emitter-followers
have to be “bi-polar” so they can both
source and sink current. So two transistors are used for each output and
they are connected as complementary
emitter-followers so that they can
source or sink current.
Software
The software for the Tree was written in C and compiled by the Dunfield
Micro/C compiler which is available
from Grantronics.
As each byte of pattern data is
read in, it is processed by a simple
interpreter. Each byte is an instruction such as “set colour to red” or
“set LED 22 to the current colour” or
“pause for 500ms”. All the complex
light patterns are built up from these
and similar simple instructions. If
you want to know more about the
instruction codes, you can download
the software from www.grantronics.
com.au
Down on the assembly line
With all the technical stuff out of
the way, let’s get the soldering iron
going and start building. Your solder-
Fig.2: the component overlay for the Christmas Tree. Make sure that you insert
each LED to match the overlay otherwise the colour patterns will not be correct.
In every case, the flat on the LED faces the closest outside edge of the PC board.
ing iron should be temperature-controlled (about 600°F or 320°C) with
a fine tip.
First, check the PC board for shorts
Parts List
1 PC board with Christmas Tree
shape
1 4MHz crystal (X1)
1 20-pin IC socket
1 8-pin IC socket
1 9V 250mA DC plugpack
1 2.1mm PC mounting DC socket (or to suit plugpack)
8 100Ω 0.25W resistors
1 1µF 16VW electrolytic
capacitor
3 0.1µF monolithic capacitors
2 27pF ceramic capacitors
34 Silicon Chip
Semiconductors
1 AT90S2313 programmed
microcontroller (IC1)
1 24C16 programmed EEPROM
(IC2)
1 7805 regulator (REG1)
12 BC547 NPN transistors (Q1,3,5,7,
9,11,13,15,17,19,21,23)
12 BC557 PNP transistors (Q2,4,6,8,
10,12,14,16,18,20,22,24)
32 red/green (bicolour) LEDs
1 1N4002 silicon diode (D1)
1 1N914, 1N4148 signal diode (D2)
between tracks and broken tracks. As
usual, start with the small items such
as wire links and resistors. Next, fit
the IC sockets, crystal, small capacitors, regulator and the diodes. The
regulator should be bolted to the PC
board.
The transistors should be fitted
next. All the BC547s face one way
and all the BC557s face the other way.
Now you can fit the LEDs. Be careful
to insert them the right way and don’t
apply too much heat as the leads are
very short when the LED is pushed
down against the board.
By the way, make sure each LED is
installed the right way around. While
no damage will result if you do put
a LED in the wrong way around, the
resulting colour pattern won’t be
right. You will notice that each LED
position on the PC board has a circular
* Les Grant is the Engineering Director at Grantronics Pty Ltd.
They can supply the programmed microcontrollers and EEPROMs for $15 plus $5 for packing and postage. Send cheque or
postal order to Grantronics Pty Ltd, PO Box 275, Wentworthville,
NSW 2145. Phone (02) 9896 7150.
Complete kits for the Christmas Tree will also be available from
all Jaycar Electronics stores.
workmanship, connect a 9V DC plugpack. No LEDs should light. Measure
between pins 10 & 20 (+) of IC1. You
should have +4.8V to +5.2V.
If all is well, remove power and
plug in IC1 and IC2. Make sure they
are correctly oriented and be careful
not to bend any of their pins as you
plug them into the sockets.
Turn your Tree on and the display
sequence should start within a few
seconds.
If it doesn’t work...
Use this same-size photograph in conjunction with the PC board overlay at
left when assembling the Christmas Tree and you should have no problems.
Be careful that the two types of transistors aren’t mixed up!
outline with a flat on one side – put
each LED in so that it matches the
outline. Finally, C3 and the DC power
connector should be fitted.
Testing
Carefully check your soldering –
use a magnifying glass and a good
light. Mistakes found now are less
embarrassing than damaged components later! Don’t plug in the two
DIL ICs yet.
Do a quick continuity check using
your multimeter’s diode check range
between pin 10 and every other pin
of IC1. There should be no shorts or
diode junctions.
Reverse the probes and you should
see diodes (base-collector junctions)
on the 12 pins that connect to the
LED matrix. A similar test should be
performed with pin 20 as the common
pin. This may seem like a lot of work
but a solder blob shorting an I/O pin
to 0V or +5V may damage IC1 and
spoil your Christmas!
When you are satisfied with your
Modern electronic components
are very reliable and faulty new
components are very rare. All microcon-trollers and EEPROMs programmed by Grantronics are individually tested so problems with these
parts are unlikely.
The reality is that the most common
causes of problems are soldering, a
wrong component or wrong component orientation. So the first step in
sorting out any problems is to thoroughly check your workmanship.
After that, we need to get more logical. If a few LEDs don’t work, are they
all in a single column or row? Maybe
they only glow red and not green?
The column drivers go high and
the rows go low for red and vice versa
for green.
To help with fault finding, the first
few patterns are simple “all one colour” displays. The patterns get more
SC
interesting after that.
AVR Resources on the Internet
Manufacturer’s data sheets, application notes, free development software
and sample source code are available at: http://www.atmel.com
Sample startup code written by Dave Van Horn for the Atmel STK200 Started
Kit: http://www.dontronics.com/8515.html
More sample code and an FAQ http://www.avr-forum.com/
Email list with an active group of AVR enthusiasts
Send an email to atmel-request<at>pic.co.za with the word JOIN in the body
of the email.
November 1999 35
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.altronics.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.altronics.com.au
SILICON
CHIP
If you are seeing a blank page here, it is
more than likely that it contained advertising
which is now out of date and the advertiser
has requested that the page be removed to
prevent misunderstandings.
Please feel free to visit the advertiser’s website:
www.altronics.com.au
Neon signs use a
straightforward high
intensity discharge
approach to creating
light. But how on
earth do they make
those signs?
Electric
By JULIAN EDGAR
Lighting
Pt.15: Making A Neon Sign
The different coloured neon tubes that are commonly available. The
colours can be created in one of three ways – different fill gases, different
fluorescent coatings, or different coloured glass. The most common
technique for generating the different colours is to use tubes with different
coloured fluorescent coatings with a fill gas of argon and mercury vapour.
November 1999 39
When the different colours are
created by the colour of the
fluorescent coating, the unexcited
tubes all look white – irrespective
of the colour they later glow! This
can lead to problems when some
of the tubes within a pack are mislabelled. Neon tube is available in
9, 15 and 18mm diameters, and
made from soda or lead glass. The
soda glass lengths are five feet
long, while the lead glass tubes
are four feet long.
The layout of the sign is
provided as a sketch on paper,
which is then transferred to a
fibreglass mat. The mat provides
a template against which to
compare the glass tube bends.
The next step is to select a piece
of tube and soften it over a
heater that uses a flame fed with
natural gas and compressed air.
The width of the flame can be
adjusted to suit the length of tube
to be heated and the temperature
of the flame can also be changed.
Take note of the single, four-foot
length of tube that you see here –
it ends up a very different shape!
The hot tube is bent to the shape
shown by the marked template.
The need for a fibreglass mat (as
opposed to a paper plan) can be
seen here – the tube is hot enough
to cause a paper plan to burst
into flames! Every bend that you
see in a neon sign is formed
individually, being compared with
the template at each step. It is a
time-consuming task that requires
patience and skill.
ING NEON SIGNS MAKING NEON
Because the letters of the sign are
made from the continuous length
of tube, often the tube needs to
wrap back on itself. Using the
least amount of tube and the
smallest number of bends means
that the sign maker needs to have
a complete mental picture of
where the tube is to go.
Sometimes, this requires that the
bending starts from one end; at
other times the bending begins in
the middle of the length of tube.
40 Silicon Chip
After each couple of bends are
formed, the bent tube is heated
with a ‘cool’ flame. This removes
any built-up stresses within the
tube. If this is not done, the tube
can crack as it cools. The tube is
quite fragile – it can be broken by
as little force as being placed
firmly on a bench. When mounted
in the signs, the tube is supported
on sprung fittings so that undue
stress isn’t placed on it.
Here’s what that straight section
of tube that we saw a few pictures
ago now looks like! Remember,
each bend that you can see here
was formed individually. The
cork in the end of the tube closest
to the camera is so that the sign
maker can blow air into the tube
to expand the glass at the bends.
Note how closely the tube follows
the template.
As the tube is bent, it tends to
close up. So that the original tube
diameter is re-formed, the bender
(having corked the other end of
the tube!) blows into it. The hot,
softened part of the tube then
returns to its original diameter.
Too much air pressure would
balloon the tube out at the bend,
so this, too, is an operation
requiring a deft touch.
Where a bend is needed near to
the end of the tube, another
section of tube is joined to provide
a convenient handhold. This tube
will later be removed, so cheaper
clear glass can be used. The ends
of both pieces of tube are heated
with a natural gas and oxygen
flame until just molten and then
the tubes are pushed together. It’s
quite amazing watching how well
they join – much easier than
welding steel tube!
Here the new clear section of
tube is being used as a handhold
while the tube is again heated in
preparation for making another
bend. Since the beginning of this
sequence, about 30 minutes has
passed – it’s a slow and careful
process. The fluorescent coating
on the inside of the tube stays
attached, despite the heat that is
applied.
N SIGNS MAKING NEON SIGNS
This particular assembly (the last
three letters of a ‘Pokies’ sign) is
formed from two four foot long
lengths. The tubes therefore need
to be joined, with the join placed
so that it falls behind part of
another letter. It will be later
blacked out by paint, so the
change in illumination caused by
the disruption to the fluorescent
coating won’t be visible.
The ends of the assembly where
the electrodes will be located
need to be cut to size. The tube
is heated with a direct flame and
then stretched to narrow the wall
thickness of the tube. After that, a
nick from a normal metal-cutting
file creates a weak spot, with the
tube breaking cleanly at that spot
when struck. It was obvious that
extreme care was now being taken
– it’s apparently easy to destroy
the 2 hours of concentrated work!
The electrode comes as a
preformed assembly. The tube
diameter closest to the camera
matches the diameter of the neon
tube being used, while the smaller
diameter tube is used to evacuate
the tube and fill it with gas. Two
conductors are connected to the
electrode and these are wired to
the test transformer in parallel.
November 1999 41
The electrode is attached to the
tube in the same way as the clear
glass extension piece was
previously attached. The flexible
plastic tube (visible at the top left)
connects the upper glass extension
of the electrode assembly to the
sign maker’s mouth, allowing him
or her to suck on the neon tube.
With a cork located in the other
end, the maker can sense when
the electrode join is airtight.
The neon tube is then ready to be
filled with gas. Those tubes using
just neon require no addition of
mercury but those using
fluorescent coatings (such as the
sign we have watched being made)
use a fill gas of argon, with
mercury then added. A syringe is
used to place the mercury in the
glass bulb assembly in the
foreground.
At left is the electrode of the neon
tube, with the mercury bulb tee’d
off from the evacuation/gas fill
tube, which leads off at the right
to the machine that is used.
During both the evacuation and
gas filling procedures, the
mercury remains in the bulb.
However, after these operations
are completed, the glass is sealed
to the right of the bulb, allowing
the mercury to be then added to
the neon tube.
GNS MAKING NEON SIGNS MAK
When the tube is being evacuated,
sheets of mica are placed between
adjoining parts of the tube. This is
done in case the tube should get so
hot that it distorts, allowing
adjoining parts to touch and so
cause cracking. The charred
paper test strip can be seen on the
right.
42 Silicon Chip
Once the tube has been evacuated,
filled with argon and then
disconnected from the machine,
the mercury remaining in the bulb
is added to the tube. This is done
by simply tilting the sign so that it
flows out of the bulb and into the
main body of the tube.
The tube is then connected to a
high voltage source and energised
on the bench. The sections of the
tube where mercury has mixed
with the argon are glowing
brightly; the sections it is yet to
reach are dull. As the tube heats
up, the mercury vaporises and
fills all sections of the tube evenly.
The neon tube is evacuated by the
machine in the background.
During this process, 20kV is
applied at currents of up to an
amp, causing the electrodes to
glow red hot. The tube also gets
hot; a strip of paper is placed
across the tube and when it starts
to char, the tube is hot enough!
Even though it is not filled with a
gas, the tube still glows brightly
during this process.
As indicated earlier, either neon
or argon can be added, depending
on the sign’s application. Argon
is much more popular, being used
with the fluorescent-coated tubes.
Neon is used most often in clear
glass tubes, lighting up red when
switched on but being clear (and
so not very visible) when switched
off. This characteristic makes
neon signs suitable for use in
‘open’ and ‘no’ (as in ‘no vacancy’)
signs.
The vacuum pump can be seen
in the foreground and the 20kV,
1-amp transformer can be seen
behind it. The machine has been
built expressly for the purpose
of making neon signs. During
evacuation, a pressure as low as
0.001mm Hg can be developed.
The pressure within the sign after
gas filling is in the range 3-20mm
Hg.
Thanks to
Australian Trade Neon
08 8351 7811
KING NEON SIGNS MAKING NEO
As can be seen here, the whole
length of tube is now glowing
brightly with the mercury mixed
evenly. When the sign is switched
off, the well-distributed mercury
vapour will condense onto the
adjacent walls. This means that
all sections of the tube will glow
with the same brightness when it
is again switched on.
The effect of the fluorescent
coating can be clearly seen here.
The blue discharge that occurs in
the mercury/argon mixture is
visible between the electrode and
the beginning of the fluorescentcoated tube, which can be seen to
be glowing very brightly. Note the
truncated evacuation tube on the
left of the electrode.
All signs are ‘run in’ on the bench.
This neon-filled tube shows the
characteristic red neon colour and
would of course be clear when
switched off. The black-painted
sections of tube are simply the
connecting links between the
SC
letters.
November 1999 43
MAILBAG
250V DC would
be dangerous
Leo Simpson’s idea of powering
DC-compatible household appliances
from 250VDC sparks a memory of an
article I saw some years back. I am
not sure if it was in SILICON CHIP or
in Electronics Australia. The subject
was the change-over from DC to AC in
a particular Sydney suburb.
The writer told a story of the days
of DC. It seems that he turned on a
light and it blew. Normally that would
be the end of things but because the
supply was DC, the arc struck by the
breaking filament did not extinguish.
Instead, it travelled up the light
globe and was half-way up the flex
to the ceiling before the author had
enough presence of mind to turn off
the switch.
The point of the story was that DC
can maintain a spark under extreme
conditions. This is obviously quite
dangerous. Another problem is that
an electric shock from DC is far more
dangerous than a shock from the same
voltage using AC. This is because AC
tends to throw the person away, while
DC tends to paralyse the muscles,
making it difficult for the victim to
escape the shock.
The higher the voltage, the greater
is the paralysing effect and hence the
greater the danger. In short, I think the
idea needs a rethink.
Jonathon Waller (via email).
DC has drawbacks
for TVs and monitors
I read the Publisher’s Letter about
DC mains in the October 1999 issue
with great interest. However, may I
bring up a few points about existing
appliances and DC mains? The first is
that you can’t use most switches on
240V DC as the distance between the
contacts is insufficient to extinguish
the arc formed when the switch is
opened. Appliances and house wiring
for DC mains generally use heavy duty
tumbler switches.
Second, colour monitors and TVs
are unsuitable for DC as the degaussing
coils would actually cause magnetisation of the CRT’s metalwork on
44 Silicon Chip
power up; quite the opposite of what
you want! You would have to feed the
degaussing coils off the switchmode
transformer & take into account the
higher frequency and asymmetrical
waveform that would have a DC
component.
Third, switchmode power supplies
and compact fluorescent lamps have
a DC supply of typically 320V. When
you specify a 250V DC source supplying these things, it would be equivalent to a 180VAC supply. This would
be at the limit of regulation for a lot of
power supplies. Compact fluorescent
lamps don’t get enough drive to their
switching transistors which overheat
and die with this lower supply (I’ve
experimented with this). This is why
you shouldn’t use a 240V peak-peak
square wave inverter for the electronic
kind of CFL.
Normal fluorescent tubes can be
used with a resistor or incandescent
lamp instead of a choke but this reduces the efficiency.
It is interesting to note that the
widespread DC mains in the UK were
subsequently killed off by the National
Grid in the 1960s. Likewise in Australia, DC mains were used in some
country towns, the overnight power
being supplied by batteries charged
during the day.
Sydney’s CBD lost its DC mains in
the mid 1980s but by this time it was
only being used for lift motors. I hope
these points are of some interest.
John Hunter (via email).
AC switches not
suitable for DC
The idea of supplying 240V DC to
certain domestic loads was floated
in your latest editorial. It might look
attractive at first but carries some risk.
There is no problem with the logic
concerning the equivalence of AC &
DC for heaters, incandescent lights
and switchmode power supplies used
in consumer goods.
However, the ratings on appliance
ON/OFF switches and domestic light
and power point switches are all
qualified by the words AC ONLY for
very good reason. Some arcing always
occurs between switch contacts when
any load current is interrupted. Inductive loads create a severe “back emf”
and are particularly hard on switch
contacts but arcing still occurs even
with purely resistive loads.
With DC, the only passive way to
extinguish such an arc is to provide
generous contact clearance – maybe
several centimetres. (We are not likely to install automatic compressed
air blast arc suppression on every
household and appliance switch!) The
switch contacts must also be robust
enough to tolerate repeated arc attack.
Since AC voltage passes through
zero 100 times/second, an AC supply
offers an inherently reliable way of
extinguishing contact arcing with
small contact clearance – typically a
minimum of around 1mm. This allows
switch designs to be compact, safe
and cheap.
I recall an anecdote related several
years ago by the late Neville Williams
in Electronics Australia. He vividly
described what happened when a
pendant light globe, supplied with DC
power at the time, failed spectacularly
in a factory where he worked in the
’30s. The globe went “pop” and an arc
occurred between the two filament
supply leads. This arc burnt into the
lamp base, up through the socket and
then just kept going up the twisted pair
rubber and fabric cable into the ceiling
rose. Fortunately, the power was cut in
time to prevent a major building fire.
Noel Erbs, Trafalgar, Vic.
DC makes sense
in remote areas
Yes, DC power in the home DOES
make sense. Your editorial in the
October 1999 issue, in my opinion, is
very sensible. I live about 400km west
of Rockhampton. For many years we
generated our own 240VAC, then solar
panels became available, not quite as
cheap as now but affordable. We went
into the cost structure very thoroughly.
Batteries were the biggest cost but we
were lucky in obtaining a couple of
sets of ex-Telecom 500A.h 2V cells.
These are harder to find now but a
350A.h unit is on the market.
So our power unit was trickle
continued on page 93
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
PRODUCT SHOWCASE
Digital Sound Level Meter
from Jaycar
Jaycar Electronics new
QM-1590 Digital Sound Level
Meter has a lot of features for
its $169 price tag.
Applications range from
industrial and workplace
sound measurement to determine safety levels, through
to the measurement and
performance-checking of hifi
speakers.
Until now, most low-cost
sound level meters have been
analog devices but this instrument has both digital and
analog output. In fact, it features dual digital/quasi analog
display and has auto and manual ranging, sound level
“hold” function and both dB “A” and dB “C” weighting.
It also offers fast and slow time weighting and maximum/
minimum level recording.
Accuracy is ±2dB under reference conditions and the
measurement frequency range is 300Hz to 18kHz. A detailed instruction manual is included, as is a 9V alkaline
battery which will give 30 hours operation.
The instrument can be examined at any Jaycar Electronics store throughout Australia or can be ordered direct
from Jaycar at 8-10 Leeds St, Rhodes NSW 2138. Phone
(02) 9743 5222, fax (02) 9743 2066, email techstore<at>
jaycar.com.au You can also view details on Jaycar’s
website, www.jaycar.com.au
D-day is coming – new
TV standards announced
One of the main standards required for digital television broadcasting in Australia has just been published
by Standards Australia.
With D-TV scheduled to commence on January 1
2001, the new standard, AS4599-1999, Digital Television – Terrestrial broadcasting – Characteristics of
digital terrestrial television transmissions, defines the
specifications for the Australian digital TV system.
It will complement the standard currently being
developed for digital TV receivers and forms the
foundations of the “next generation” of television in
this country.
The standards are based on the European DVB-T
standards with necessary modifications for Australia.
Meanwhile, Philips aren’t happy...
Philips Australia has called on the Federal Government to carefully consider which definition format it
adopts for the introduction of digital TV.
Philips believes that the proposal by Australian freeto-air TV stations to adopt high definition TV is premature and will be too expensive for average consumers.
Harry Van Dyk, General Manager, Philips Sound
and Vision, claims that the current proposal means
Australians would be forced to pay up to $15,000 for a
high definition TV receiver, display and sound system.
Philips is proposing that broadcasters should broadcast standard definition television (SDTV) to give all
Australians access to digital TV.
Another Safety Recall for Fluke T2 Testers
Fluke Australia has found a potential product malfunction in the
Fluke T2 Electrical Tester. This notice includes all units manufactured
before September 1999, with serial
numbers lower than 74165430.
The safety notice includes instruments involved in a previous safety
notice dated November 1998.
The T2’s positive battery contact
can corrode over time due to exposure to vibration. In certain situations, the instrument can operate
intermittently; sometimes it will
turn on and sometimes not.
When the malfunction occurs,
the tester may not indicate that
voltage is present, placing the user
in a potentially hazardous situation.
T2 owners are directed to stop
using their T2 Electrical Testers as
soon as possible, even if they have
not experienced this problem.
Owners of units that have serial
numbers between 70521601 and
74165430 have two options: (1)
they can request a free Field Repair
Kit, containing a new battery contact coil spring, two new AA-size
zinc-oxide batteries and installation
directions; or (2) they can return
their T2 Tester to Fluke Australia
for repair.
Customers are urged to email
david.mayhew<at>fluke.com.au or
fax their request for a Field Repair
Kit to (02) 8850 3300 as soon as
possible. If required, telephone (02)
8850 3333.
To return a T2 Electrical Tester,
send it with a Safety Notice Return
Form (available by faxing Fluke
Australia) to Fluke Australia, 26/7
Anella Avenue, Castle Hill, NSW
2154.
If the T2 owner’s unit was affected by the November 1998 safety
notice, has a serial number lower
than 70521601 and it does not have
an “R” stamped after the serial number, the T2 was not repaired in the
November 1998 recall.
This unit now MUST be returned
to Fluke for repair.
November 1999 53
CTRONICSHOWCASELECT
3990
FULL RANGE
$
ELECTROSTATIC
Now you can afford the legendary clarity,
transparency, depth and precision of an
electrostatic speaker.
The new Vass ELS-5 is a full range electrostatic speaker, able to faithfully reproduce
frequencies from 40Hz-20kHz.
• 5 Year Warranty
• Wide range of custom finishes.
• Individually hand built & tested.
MicroZed Computers
GENUINE STAMP PRODUCTS
FROM
Scott Edwards Electronics
microEngineering Labs & others
Easy to learn, easy to use, sophisticated
CPU based controllers & peripherals.
PO Box 634, ARMIDALE 2350
(296 Cook’s Rd)
Ph (02) 6772 2777 – may time out to
Mobile 0409 036 775 Fax (02) 6772 8987
1/42-44 Garden Bvde, Dingley 3172
Pyramid subwoofer Ph 03 9558 0970 Fax 03 9558 0082
separately available
email: vass<at>hotkey.net.au
http://www.microzed.com.au
Most Credit Cards OK
PRODUCT SHOWCASE – continued
SoundMan X1: quality stereo
sound for your PC
With high-quality stereo being increasingly available on the Internet,
Logitech has released a new generation
of speakers specifically intended for
this growing market.
The SoundMan X1 speakers are
housed in attractive, contemporary
cases yet require minimal space on
the desktop. The system comprises a
high- performance subwoofer and a
pair of two satellite speakers, rated at
25W RMS.
With a recommended retail price
of $149, the system is said to bring
theatre-quality sound to MP3, DVD,
CD music, gaming and other popular
multimedia applications. Bundled with
the speakers is the MP3 Music Centre
CD with more than 100 MP3 songs and
internet music software.
The SoundMan X1 system will be
increasingly available from computer
specialist and department stores.
Hobby/radio control show for Melbourne
A show of special interest to hobbyist readers is being held this month in
Melbourne.
Featuring virtually every facet of
technical hobbies, including electron-
s
entitlet
r
e
h
c
n
ou
This vo 50% discou
e
t
h
t
u
o
y
try to
for en y show.
b
Hob
54 Silicon Chip
ics and amateur radio, radio control
cars, boats, planes, model railways,
astronomy and many more, the Hobby,
Engineering and Radio Control Modelling show is being staged by St Kilda
Community Projects at 8 Chapel Street,
St Kilda from 10am to 5pm on Saturday
6th and Sunday 7th November.
Along with plenty of demonstrations,
workshops and seminars there are great
bargains promised.
And while entry is priced at a very
reasonable $2 per person, SILICON CHIP
readers can get 50% off by presenting
the coupon at left (or even a photocopy)
on admission.
For more information, contact 0411
837 187 or (03) 9523 1037; email isentz
<at>labyrinth.net.au
NDS Moves Up
Namlea Data Systems (NDS) has
relocated to a modern new distribution
centre in Lane Cove.
Located at Unit 4, 11 Orion Road,
the new premises offer vastly improved office and warehouse space
for the rapidly-expanding company,
now one of Australia’s leading data
and networking equipment suppliers.
Postal address is now Locked Bag 7,
Lane Cove NSW 1595, while the phone
and fax numbers have changed to (02)
9429 0800 and 9429 0899 respectively.
The NDS National Call Number for
general customer sales and support
remains unchanged on 1300 30 30 69.
Intelligent microphone
mixing in a half-rack
Shure has release a four-channel
automatic microphone mixer which
puts the performance of its eight-channel (SCM810) system into a half-rack
space.
The SCM410 mixer is intended for
both installed and touring applications
and increases the clarity and intelligibility of speech while dramatically
reducing feedback, reverberation and
the need for comb filtering.
The mixer incorporates Shure’s patented “Intellimix” technology which
automatically gates microphones on
and off to optimise sound quality. It
can be used on its own or linked to
other mixers.
Shure products are distributed by
Jands Electronics who can be reached
on (02) 9582 0909.
TRONICSHOWCASELECTRO
•
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SWITCHMODE POWER SUPPLIES
R.T.N
Basic Stamps, SX chips and tools.
OZ-made boards and development tools
Best pricing on temp, a/d, rtc kits
New Xilinx PLCC44 development system
New OZ made serial LCD module 2*16
Stepper and R/C servo motor chips
New super catalog on CD Rom with 40 meg of
Stamp related data. Now available via SAE and
our cost $4.50, or free with orders over $125
Phone/Fax 03-9338-3306
http://people.enternet.com.au/~nollet
Email: nollet<at>mail.enternet.com.au
NEW FROM
QUESTRONIX
DVS5 Video & Audio
Distribution Amplifier
25W500W
Extensive
Range
6 Sarich Court, Technology Park, Bentley WA 6102
Ph: 08 9470 1177 Fax 08 9470 2844
web: www.computronics.com
DVS5
Video & Audio
Distribution
Amplifier
VGS2
Graphics
Splitter
Five identical Video and Stereo
outputs plus h/phone & monitor
out. S-Video & Composite versions
available. Professional quality.
VGS2 Graphics Splitter
High resolution 1in/2out VGA
splitter. Comes with 1.5m
HQ cable and 12V supply.
Custom-length HQ VGA
cables also available.
Check our NEW website for latest prices and
MONTHLY SPECIALS
www.questronix.com.au
Email - questav<at>questronix.com.au
Video Processors, Colour Correctors, Stabilisers, TBC's, Converters, etc.
QUESTRONIX
All mail: PO Box 548, Wahroonga NSW 2076
Ph (02) 9477 3596 Fax (02) 9477 3681
Visitors by appointment only
UNIVERSAL
WIRELESS
DEVELOPMENT SYSTEM
EMC Technologies' internationally
recognised Electromagnetic
Compatibility (EMC) test facilities are fully
accredited for emissions, immunity and
safety standards.
EMC Technologies
Melbourne: (03) 9335 3333
Sydney: (02) 9899 4599
Linx RF modules from Clarke & Severn
Electronics offer a simple, efficient and
cost-effective method of making a product
wireless. Want to know more? Contact
CLARKE & SEVERN ELECTRONICS
PO Box 1, Hornsby NSW 1630
Ph (02) 9482 1944 Fx 9482 1309
email: sales<at>clarke.com.au www.clarke.com.au
USB Devices
BUSINESS FOR SALE:
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Escape to the sun in beautiful Coffs Harbour!
Stable electronic retail business
Easily run by husband and wife team.
Agent for GSM carrier
Access to large electronics suppliers (niche market).
Very strong customer base inc Government depts
and schools etc.
Five year rental option on current highway premises.
Full figures available.
Current owners (12 years) are moving to a new
business.
Price only $55,000 + SAV.
Enquiries: phone (02) 6652 5684 or fax (02) 6651 3731
Do you want
YOUR product
or service
showcased to
Australasia's
most important
electronics
marketplace?
CALL ME: RICK WINKLER
on (02) 9979 5644
and let me explain how cost effective
the SILICON CHIP ELECTRONICS
SHOWCASE can be for YOU!
Just PLUG them in!
Looking for ways to protect your peripheral investment, while moving to
USB-based systems? You can even network two computers via their USB
ports & save on the cost of network cards. You're ready to take full advantage of USB, but your desktop system does not have USB support? Not a
problem, our USB card can add 2 USB ports to any PC with a spare PCI slot.
If your motherboard already has USB port pin connectors then you can
add 2 USB ports to the backplane. USB type A & B cables also available.
Vamtest Pty Ltd trading as Microgram Computers A.C.N. 003 062 100
Web site:
Email:
www.mgram.com.au
info<at>mgram.com.au
Hubs, Adapters &
Converters, Cables,
Scanners, Bar Code
Readers, Video
Capture & more
Check out
our web
site or
Unit 1, 14 Bon Mace Close
give us a
Berkeley Vale
NSW 2261
November
1999 55
Phone: (02) 4389 8444
call
Fax: (02) 4389 8388
Setting Up
An Email
Server
If you want to streamline the email service in
your office, setting up an on-site email server is
the answer. It lets users send local email with
ease, without initiating separate dial-up
sessions. A popular solution for the Windows
platform is the MDaemon mail server package.
By PETER SMITH
The standard dial-up account offered by most ISPs (Internet Service
Providers) is often the starting point
for many small businesses when email
access becomes a requirement. A
modem, telephone line, email application software and dial-up account
are all that’s required to get online.
Standard dial-up accounts generally include one email address with
a username of choice. The domain
name part of the address (everything
after the ‘<at>’ symbol) is common to
all dial-in users of the particular
provider for this type of account. For
example, a Big Pond dial-in customer
would have an address of username<at>
bigpond.com
Of course, most businesses will
want the company name or some
derivative of it as part of the domain
name. In addition, they also usually
want multiple email accounts, including a general company account plus
individual user accounts.
That’s where the ISP comes into the
picture. An ISP can host a suitable
domain name on a company’s behalf
Fig.1: a minimum system requires the
MDaemon Server and the MDaemon
Documentation and Help components.
Fig.2: during setup, you have to enter
the IP address of your DNS server.
This address is provided by your ISP.
56 Silicon Chip
and can also offer multiple email
accounts, each account existing as a
separate mailbox on the ISPs’ server.
Individual users can then access their
email via separate modems but this
quickly becomes unwieldy if there are
more than three accounts involved.
For this reason, most businesses
use some kind of sharing technique,
so that users can access their respective mailboxes through a common
Internet connection point on the local
area network. Often, this connection
is made via a single 56K modem,
which is shared using proxy server
software such as WinGate, WinProxy
or SyGate, etc. Hardware-based proxy
servers are also available. We looked
at WinGate in detail last month and
we’ll be looking at a couple of hardware solutions in a future article.
Adding an email server
Although this type of email setup
works well in many small businesses,
there are several disadvantages.
Fig.3: select the option shown here so
that MDaemon automatically starts
and runs as a system service.
Fig.4: first-time users should run the
configuration wizard, as this greatly
simplifies the setup. All settings can
be changed later if necessary.
Fig.5: enter your domain name in
this dialog box and ignore the default
company.mail entry recommended by
the wizard.
Fig.6: the ISP’s mail server address
(POP host) and the logon name and
password are entered here (for option
A in Table 1 only).
Fig.7: leave this dialog box blank if
you entered your real domain name
in the dialog box shown in Fig.5.
Fig.8: select the option shown here if
you want MDaemon to automatically
connect to your ISP.
Fig.9: this is where you assign a name
to your dial-up profile and enter your
logon name and password.
First, adding, removing or otherwise modifying user accounts often
requires a call to the ISP and there
can be delays while the changes are
implemented at their end (a few of
the more progressive ISPs do provide
web-based account management,
however). Second, depending on
the ISP, there may be costs involved
each time account changes are made.
And third, because the email server
actually resides at the ISPs end, email
between local users must go via the
Internet connection. This not only
adds to the call costs but can also
cause significant delays and inconvenience for companies that depend
on fast message delivery.
The solution is to install an email
server on the company network, effectively relocating the user mailboxes
from the ISP’s server to the local LAN.
No changes need be made to the type
of Internet connection and all existing
email client software is retained. The
ISP still provides the domain name
hosting but rather than manage multiple email accounts, all email for the
company is either placed in a single
mailbox or forwarded directly to the
email server whenever it is connected.
One big advantage of this scheme
is that account administration is now
performed locally, so users can be
added or deleted at will. More importantly, local email never leaves the
company – instead, it is transferred
directly to the recipient’s mailbox on
the email server and can be collected
immediately. Other important administrative tasks like redirecting important email when employees are out of
the office also become much easier.
manent Internet connection, which
can be a costly proposition for small
businesses. By contrast, one of MDaemon’s key features is its ability to
operate effectively over a standard
dial-up modem connection. By using
a feature called DomainPOP mail collection, MDaemon is able to collect all
email from a single POP3 mailbox at
the ISP and distribute it to local user
accounts, which is just the shot for a
small business.
With this scheme, individual users
retrieve all their email from the local
server which means that they don’t
have to make separate phone calls.
Similarly, when individual users
want to send email, it too goes to the
local server. MDaemon then subsequently sends and retrieves email to
and from the ISP at designated intervals (eg, two or three times a day, or
even once every hour).
MDaemon
Most ISPs and some large corporations run their email servers on UNIX
operating systems or derivatives but
a small businesses will want something that runs on a more familiar
platform – either Windows 95/98 or
Windows NT.
One popular solution is an email
server program called MDaemon. This
runs on the Windows platform and
provides many advanced capabilities,
including web-based email access,
auto-forwarding, mailing lists, remote
administration, auto responders,
multiple domains and many other
features.
Many email servers require a per-
System requirements
MDaemon is available for both
Windows 95/98 and Windows NT 4.
It requires a PC with a 486 processor
or higher, 8MB of memory minimum
(we recommend 16MB) and approximately 30MB of free hard disk space
November 1999 57
Fig.10: this
dialog box is
normal. Just
click OK so that
you can proceed
with the setup.
this type of service. The two other
commonly available services can be
roughly categorised by their connection type, as shown in Table 1. MDaemon supports all of these options.
By the way, the services offered and
the prices vary significantly between
ISPs, so its worthwhile finding out
what your ISP has on offer.
Installing MDaemon
Fig.11: you only have to enter your
ISP’s mail server address here. The
installation wizard automatically
completes the other entries for you.
Fig.12: MDaemon automatically
formats new user accounts that you
create later on using the information
entered here.
(plus space for any mail that will be
stored).
The TCP/IP protocol must be installed on the network and, of course,
an Internet connection is required. In
addition, Dial-up Networking (DUN)
must be installed for Windows 95/98
and Remote Access Services (RAS) for
Windows NT 4.
All popular email client software
will work with MDaemon, the only
requirement being that they support
both the POP3 and SMTP protocols.
Compatible email applications include Outlook, Outlook Express,
Internet Mail, Netscape Mail and
Eudora, etc.
MDaemon will work with most
types of Internet connection methods
(modem dial-up, ISDN, cable modem,
etc) but consideration needs to be
given to the type of email service
provided by the ISP.
As mentioned above, MDaemon
can be configured to collect all email
from a single POP3 account. This is
the most cost-effective method, as all
the ISP need do is redirect (or alias) all
email for the particular domain into
one mailbox. Internet connection time
is reduced to a minimum too, because
the company’s email server need only
be online for long enough to retrieve
all email from the POP3 account and
send any email queued for delivery.
However, not all ISPs provide
Table 1: Common Email Service Options
Option Service & Connection Type
A
B
C
Description
Single POP3 email account The server connects to the Internet at assigned
and standard dial -up
intervals, collects all emai yrom a singl e POP3
modem connection.
account and sends any waiting email.
The server connects to the Internet at assigned
interval s to send and recei ve email. At the ISP's end,
SMTP email servi ce with
emai l recei ved for the company whil e the connection
non-permanent modem
i s off-line i s held in a queue unti l the next connection
connection.
i s made. This method i s si mil ar to option A but there
are more overheads at the ISP's end.
The server i s permanentl y connected to the Internet.
SMTP email servi ce with
The advantage of thi s system i s that there i s no del ay
permanent modem
in sending and recei ving email but it i s more costl y
connection.
than options A and B.
58 Silicon Chip
Because of its wide range of features
and options, installing and configuring this product could be a rather
daunting task for some. Certainly, we
don’t recommend that you attempt it
unless you have a basic understanding
of Internet and networking concepts.
On the positive side, MDaemon
includes a configuration wizard to
help get it up and running with a minimum of knowledge. Comprehensive
documentation is also available and
can be downloaded separately in a
variety of formats (Microsoft Word,
Adobe Acrobat, etc) from http://www.
mdaemon.janteknology.com.au
Because product improvements
occur frequently, you should verify
that you have the latest version of
MDaemon (2.8.5.0 at time of writing).
The software is available for download from the above listed website
and can be evaluated free of charge
for 30 days.
Before installing MDaemon, it is a
good idea to configure and test the Internet connection. Make sure that the
system is capable of dialling up and
logging in automatically (ie, without
the user having to manually enter a
username and password each time).
When you start the installation,
you will be prompted to enter some
basic information to get things started. Note that unless you have a permanent connection to the Internet,
you will probably not require all of
the components listed in the “Select
Components To Install” dialog box
(see Fig.1). A minimum system requires the MDaemon Server and the
MDaemon Documentation and Help
components.
After all files have been installed,
you will be asked for the IP address
of your DNS server (see Fig.2). Enter
the DNS address provided by your
ISP here.
Note that MDaemon has the ability
to run as a system service. This is the
preferred option because MDaemon
starts and runs automatically, regard-
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Fig.13: double-clicking the envelope icon in the System Tray brings up the
Message Router window. This lets you add and delete user accounts, gives a
running update of all email activity on the network (in the righthand pane) and
lets you change any of the settings.
less as to whether anyone is logged in
to the server or not (see Fig.3).
At the completion of the installation, you have the option of running
the configuration wizard (see Fig.4).
This is a good idea for first-time MDaemon users, since it greatly simplifies
the setup.
Wizardry
The following examples show the
settings we used in the wizard’s various configuration windows. Note that
we selected option A in Table 1 as our
service type of choice.
As shown in Fig.5, the wizard recommends using the default domain
company.mail. However, we recommend that you enter your real domain
name here. If necessary, the domain
name can later be changed in the Setup, Primary domain menu accessed
from the main MDaemon window (ie,
the Message Router window).
If MDaemon will be using Domain
POP mail collection (option A in Table
1), enter the ISP’s mail server address
(POP host) and the logon name and
password for the POP3 account (see
Fig.6). If not, you can leave all these
fields blank.
Next, if you used the default company.mail domain name, enter your
real domain name in the dialog box
shown in Fig.7. Conversely, if you
previously entered in your real domain name (as recommended), leave
this field blank.
The next two windows deal with
dial-up connection settings – see
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How MDaemon Manages Multiple Email Accounts
Using A Single Mailbox At The ISP
Let’s say, for example, that an organisation has a domain name stooges.
com and an accompanying mailbox three<at>stooges.com hosted at their
ISP. The organisation arranges for their ISP to alias, or forward, all email
messages sent to the stooges.com domain (regardless of the username)
to the three<at>stooges.com POP3 account.
This means that all email messages with the stooges.com domain name
received by the ISP – eg, larry<at>stooges.com, curly<at>stooges.com and
moe<at>stooges.com - are deposited in the three<at>stooges.com POP3 account. MDaemon can then log into this single POP3 email box, retrieve all
email messages, sort them out by user name (ie, larry, curly and moe), and
send them to the matching POP3 mailboxes that you’ve defined in MDaemon.
Larry, Curly, and Moe can then log into their individual MDaemon POP3
accounts on the local server and send/receive their email as usual – from
the MDaemon web site.
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Fig.14: you just enter the user’s real
name in the Account Editor and the
other fields are automatically
completed for you. You can then
manually change the entries if you
wish.
Fig.15: the Account Alias Editor lets
you nominate (or alias) an account
as the postmaster. The postmaster
receives “undeliverable” email and is
notified of any problems.
Fig.8 & Fig.9. Most users will want
MDaemon to automatically connect
to their ISP. Note that the connection
times can be chosen by the administrator and we look at this in the final
step of the installation.
At this point, the MDaemon engine
automatically starts if you are running
NT, while Windows 95/98 users have
to reboot to achieve the same result.
As soon as the engine starts a small
envelope icon appears in the system
tray.
Our installation reported “missing
or damaged” settings when it was
first launched (see Fig.10). However,
based on the author’s previous experience, this appears to be normal for
a new installation, so just click OK.
MDaemon now presents three additional screens to allow inspection of
the default settings.
In the Domain Configuration dialog box, under the Message Delivery
section, enter your ISP’s mail server
address (see Fig.11). The installation
60 Silicon Chip
wizard automatically completes the
other settings, so you don’t have to
worry about these.
The next dialog box is the “New Account Defaults”, as shown in Fig.12.
This lists a number of templates and
MDaemon formats new user accounts
according to the information entered
here. Careful setup of the templates
greatly speeds up the creation of new
accounts later on, as MDaemon will
do most of the work for you (as we
shall see later)!
We only needed to change two settings for our installation. The default
Mailbox setting generates mailbox
names from the first initial and last
name of each user; ie, the Mailbox
entry is $USERFIRSTINITIAL$$USERLASTNAME$.
This means that if we later create
a new user called Peter Smith, this
would produce PSmith as the mailbox
name and the email address would be
PSmith<at>siliconchip.com.au.
However, we wanted our addresses to use full names, with a dot as a
separating character. To do this, we
simply changed the Mailbox entry
to: $USERFIRSTNAME$.$USERLASTNAME$ (note
the full stop between the two dollar
signs in the middle). Therefore, when
we later create our email account, we
get Peter.Smith<at>siliconchip.com.au
Note that you should never use
spaces in email addresses; use an
underscore (_) or dot (.) character
instead.
The default POP password setting is
defined so that it generates passwords
from the first initial and last name of
each user. For testing purposes, we
changed this setting to use the string
“pass” for all passwords. Note that
POP passwords are case sensitive;
user names are not. This dialog box is
also accessible from the main MDaemon window (ie, the Message Router)
via Accounts, New account defaults.
The next dialog box shows the
Miscellaneous Options settings. No
changes are required here for a basic
installation, so just click OK to close
this window.
Putting it work
We now need to add at least one
user, define who the “postmaster”
will be and tell MDaemon when to
connect to the Internet to send and
receive email.
You do this by first double-clicking
the envelope icon in the System tray
to open the main MDaemon window.
This is called the Message Router
window and is shown in Fig.13.
Next, select Accounts, New Account from the menu bar to display
the Account Editor (see Fig.14). When
you enter a user’s real name, you will
notice that MDaemon automatically
completes the other fields according
to the account templates we defined
earlier. Generally, you will not need
to alter items on other tabs in the
Account Editor, so click on the OK
button to create the account.
Internet email systems also require
a “postmaster”. This user receives
notification of “exceptions” that occur
within the system, such as undeliv
erable email. Note that MDaemon
does not require a separate account
for the postmaster. Instead, you can
“alias” this user to any other defined
user.
Select Accounts, Account Aliases
from the menu bar to display the
Account Alias Editor (see Fig.15). In
the Alias field, enter “postmaster”,
then from the Mailbox drop-down
list, select the appropriate user and
click on the Add button.
Finally, you need to tell MDaemon
when to connect to the Internet.
Open the Send/Receive Scheduler
window by selecting Setup, Send/
receive scheduler from the menu bar
(see Fig.16). If you are using either
options A or B in Table 1, select which
days and times you wish email to be
transferred. In our example, we have
chosen to connect at 8am, 12pm and
Fig.16: this is where
you set up a schedule
so that MDaemon
automatically
connects to your ISP
to send and receive
email (options A or B
in Table 1 only).
Glossary Of Common Terms
Looking for an old valve?
DNS: the Domain Name Service is an Internet service that translates domain names into IP addresses. Names are obviously easier to remember
than long strings of digits and names can be cleverly chosen to represent
the owner’s interests.
or a new valve?
Domain Name: a name that represents one or more IP addresses. Domain
names form part of all resources, including email addresses, on the Internet.
For example in the address http://www.mdaemon.com, the domain name
is mdaemon.com. In email addresses, everything after the “<at>” symbol is
the domain name.
IP Address: a string of digits that identifies a computer or device on a
TCP/IP network. The format of an IP address is a 32-bit numeric string
written as four numbers separated by periods (full stops). Each number is
in the range 0-255. For example, 203.2.191.122 could be an IP address.
Regulatory bodies assign all IP addresses used on the Internet, primarily
to avoid duplicates.
ISP: Internet Service Provider.
POP3: Post Office Protocol (version 3) is a protocol used by most recent
email applications (also called email clients) to retrieve email from a server.
Proxy Server: a server that acts as an intermediary between a client application, such as a Web browser, and the Internet. Proxy servers often provide
security, administrative control and local caching of web pages.
SMTP: the Simple Mail Transfer Protocol is a protocol for sending email
messages between servers. It is also usually used to send messages
between email clients and servers. Most email systems connected to the
Internet use the SMTP protocol.
TCP/IP: an Abbreviation for Transmission Control Protocol/Internet Protocol,
TCP/IP is the defacto standard for communication on the Internet.
6pm from Monday to Friday.
In the same window, click on the
RAS Setup button. If you are using
option A in Table 1, you do not need
to change any settings (see Fig.17).
If you are using option B , leave the
“Keep Sessions Alive For At Least”
option selected and enter the number
of minutes that your server needs to be
connected each time it dials in. Your
ISP will be able to tell you what the
minimum time is but from our experience it is usually around 10 minutes.
Finally, if you are using option C,
select the “Once Established, MDaem
on Will Not Close the RAS Session”
option.
By the way, you can force MDaemon
to connect immediately and send/
receive email. You might want to do
this for urgent email or for testing
purposes, for example. To do this,
either hit the F9 key or select Queues,
Process local and remote queue and
MDaemon will connect immediately.
Well, that’s about it for a basic
setup. If you’re running WinGate or
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Fig.17: the entries in this dialog box
depend on which option you are using
from Table 1. They determine how a
dial-up session terminates.
other software that shares the Internet connection, additional changes
can be made to optimise connection
usage. Check out the MDaemon user’s
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au for tips.
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November 1999 61
Build the
addacom
and add extra stations to
any existing 2-way intercom
Do you have a 2-way intercom in your home? Would you
like to add extra stations at very little cost?
The solution is to build the Addacom. It contains a modest
amount of switching and circuitry to add the extra stations.
The Addacom is a little black box
with four pushbuttons which sits
next to the master station of a 2-way
intercom. If an extension calls in, a
light emitting diode (LED) lights up
on the Addacom and then you press
the corresponding button to talk to
that extension.
In reality, the Addacom consists
of the bank of four pushbuttons and
a little circuitry to indicate which
extension is calling the master station.
Before we describe how the Addacom works, we need to have a look
at the circuit function of a typical
2-station intercom. There is really
very little to them.
Most push-to-talk types consist of a
master and one or more slave stations.
The active master station unit con-
Design by Paul Hoad*
62 Silicon Chip
tains an amplifier, a small loudspeaker, a battery and a switch. The slave
station is much simpler, consisting of
another small loudspeaker, a switch,
capacitor, a diode and a light emitting
diode (LED)
The small loudspeakers do double duty, acting as microphone or
loudspeaker, depending on whether
the stations are talking or listening.
The basic intercom circuit is shown
in Fig.1.
We have one pair of wires and one
amplifier (IC1) so only one end can
speak to the other at any given time.
Switch S1 at the master station swaps
the connections to the two speakers
to allow for two-way communication.
The telecommunication term for
this is “half-duplex” – one station
can listen while the other talks and
then the first station can talk while
the other listens.
Telephones are actually “full
duplex” devices since both parties
can simultaneously talk and listen.
The other type of communication is
“simplex” and is one-way only, eg,
broadcast TV, radio etc. You cannot
talk back (swearing at the TV when
the ad break comes on is not counted!)
Signaling
Let’s look at the manner in which
a remote station signals the master
station. Much of the terminology is
“borrowed” from telecommunica-
Fig.1: this is the circuit of a typical 2-way intercom. The push-to-talk switch (S1)
swaps the remote and local speakers so that they can talk or listen.
tions so we’ll start by looking at what
happens in a telephone circuit.
When a telephone is in the idle state
it has a high DC resistance (although
modern phones draw a tiny current
to maintain their memory for stored
numbers). The exchange or PABX
supplies 48V DC.
When you lift a phone handset off
its cradle, the hook switches complete a circuit and current flows back
to the exchange. The exchange senses
this current and sends you a dial tone.
This is called loop signaling.
In our typical 2-way intercom, 9V
is sent from the master to the remote
Addacom opened out,
viewed from the component
side of the PC board. It is
powered from a plugpack
supply with battery backup.
November 1999 63
Fig.2: the Addacom is really just a 4-way switch-bank and the rest of the circuit just shows
which extension has called in so the right button on the switch-bank can be pressed.
station. When the button is pressed at
the remote station, switch S2 creates
the loop condition by shorting out the
capacitor in series with the speaker.
The master station responds to the
loop by producing a tone which is
heard at the master end.
On hearing the tone, the user at the
master end would turn on the intercom via double-pole switch S3 and
press the momentary contact switch
S1 (press to talk). The amplifier is now
powered on via D1, and S1 reverses
the line polarity and both LEDs are
turned on.
What happens now is that the
loudspeaker in the master station is
connected by switch S1 to the amplifier’s input to act as a microphone
while the speaker at the remote end
becomes the loudspeaker load for
the amplifier. The user at the master
end is now able to talk to the remote
station: “Yeah, mate?”
On releasing the press-to-talk
switch, the loudspeaker in the remote
64 Silicon Chip
station becomes the microphone
while the speaker in the master station becomes the loudspeaker load.
The remote user is then able to speak:
“About time, mate! Is it beer o’clock
yet?”
By pressing S1 the user at the master end can speak again. Note that
when the user at the extension speaks,
he does not have to press the button;
he can talk “hands-free”. We won’t
carry on the scintillating conversation
but you get the picture.
For the purpose of this exercise, our
typical remote station only has those
five components shown in Fig.1: loudspeaker, LED, diode, a 100µF bipolar
capacitor and a pushbutton switch.
If we want to add extensions, each
one will need those five components.
You probably won’t need to go out and
buy them because they will already
be in your parts collection.
Switching & transmission
A telephone exchange will analyse
your sent digits, then switch you to
the appropriate destination. These
days this is achieved using digital
techniques.
The switching used in this project
is via a switch bank. You decide
which extension needs to be switched
by seeing which LED is lit. There is
also an audible indication.
The voice signals are restricted to a
frequency range between 300Hz and
3.4kHz and sent down a single pair
of wires to your phone. In some of
the very large cables you may have
another 3000 pairs in the same cable
travelling side by side for several
kilometres.
Each pair of wires is colour coded
so that they can be identified. Because
all the cable pairs are so close together, won’t the lines be noisy? Well, no.
By twisting the pairs, interference
tends to be cancelled.
Twisting the pairs results in the
noise signals having the same polarity
and magnitude on each leg. Without
a potential signal difference between
the two legs, no noise current flows.
With our intercom we should also
try to twist the cable pairs joining
each station. Our main enemy here
is hum from your home’s electrical
wiring which is amplified along with
the weak signal from the microphone
(speaker).
Circuit description
Fig.2 shows the circuit of the
Addacom. Each extension is wired
to the screw terminal block and then
to switches S1, S2, S3 or S4 which
are interlocked as a switch-bank. The
interlocked switch-bank connects
only one extension to the master unit
at a time.
Let’s assume that extension 1 is
selected and the others are not. In this
condition, extension 1 is switched
straight through to the master; terminals 1 & 2 on the terminal strip
are switched via S1a & S1b through
to terminals 9 & 10, the connections
to the master station.
For the other three extensions
which are not selected by the switch
bank, switches S2a, S3a and S4a,
connect the positive supply line to
one side of their respective remote
switches.
Now, if extension 2 calls by having
its remote button pressed, the resulting line (loop) current via S2b will
turn on transistor Q2 via diode D3 to
light LED2 and sound the buzzer via
diode D4.
The pulsating current in the buzzer
also causes a tone to be heard in the
speaker for extension 2.
OK. So now the person at the master
station sees that LED2 is alight and
presses switch S2 to select that extension. So extension 2 is connected
to the master station and extension
1 is automatically disconnected
(desel-ected); that is the nature of a
switch-bank.
The master station and Extension
2 can now talk to each other, as described above, ie, the master station
has to be turned on as before and its
press-to-talk switch pushed to allow
the master to speak and so on.
The same process would occur if
extension 3 called in. In this case, the
loop current via S3b would turn on
Q3 via diode D5, lighting LED3 and
powering the buzzer via D6.
The user at the master station sees
LED3 lit, presses S3 and then exten-
Addacom viewed from the copper side of the PC board. The terminal block in
the foreground is used to connect to the master station and up to four add-on
stations. 6-pair telephone cable connects the PC board to the terminal block.
sion 3 can talk.
the unit will be powered at all times,
regardless of blackouts.
Each of the four transistors has a
47µF capacitor following its respecA couple of points need to be extive diode and before its 100kΩ bias plained about the extension stations
resistor. The capacitor allows the re- and for clarity we have repeated the
spective transistor
circuit in Fig.3.
to remain on for
First, the 100µF
about 15 seconds
coupling capaciafter the extension
tor for the speakhas called in.
er needs to be a
This gives the
non-polarised (NP
user at the masor BP) type.
ter station enough
This is because
time to identify
the switching of
the extension and
the master station
Fig.3: this is the circuit of each
select it.
reverses the supply
extension. The 100µF capacitor
Power for the
to the extension.
must be a non-polarised (NP or
Addacom comes
For the same reaBP) type because the Addacom
from a 9V DC plugson,
the LED in the
switching causes the supply
pack via diode
extension station
polarity to be reversed.
D10 and resistor
must be connected
R5 or from a 9V
in series with a
battery via diode
diode because in
D9. Zener diode ZD1 in conjunction
the idle condition, the LED will be
with R5 provides crude regulation of
reverse-biased by the positive supply
the supply to 10V.
line from the Addacom.
This supply is then available at
Construction
terminals 11 & 12 to power the master
station if this is desired. If you have
The Addacom was built in a standboth battery and plugpack supply, ard plastic utility box measuring 130 x
November 1999 65
68 x 45mm. We’ll assume that you’re
building the Addacom from a kit so all
holes will be punched in the plastic
lid for the switches and LEDs.
The interlocked switch-bank is
mounted on the PC board which
makes the wiring relatively simple
but it does take up a lot of the board
space.
For this reason, some of the components must be mounted on the copper
side, as we shall see.
Do not mount the switch-bank first;
it is left till last otherwise it is just
too difficult to mount and solder the
components. You can start with the
four transistors; these are mounted
on the copper side of the board, as
shown in Fig.5.
Take each transistor and push its
leads through the holes on the copper side. Then bend the transistor
back so that the curved part of the
transistor body touches the board.
Just solder the emitters at this stage
to hold them in.
Mount and solder all other components, as shown on Fig.5 & Fig.6
except for the LEDs, diode D9 and
the switch-bank. Make sure that you
clip off the excess leads from the
copper-side-mounted components.
It is important that the capacitors be
perpendicular (straight up) from the
board otherwise the switch actuators
will hit them.
Before you install the switch-bank,
terminate and solder the four extension pairs, the master pair and the
positive battery wire to the tagstrip
side of the switch.
Is it an intercom station? It is now but
it started life as a flip-top computer
disk box (from Jaycar). The photo at
right shows how the components were
mounted inside. Even better, a cheap
computer speaker (far right) could be
modified to suit.
66 Silicon Chip
Fig.4: these are the wiring details for the cable pairs from the switch-bank to the
12-way terminal strip.
To avoid shorts it is best to hook
the wire across the top rather than
wrap it around the tags. Twist each
pair as you solder them and follow
the colour code. Attach the M3 screws
and 12mm standoffs to the switch
and solder its terminals to the board.
Bend the leads of the four LEDs
around the shaft of a small screwdriver to achieve the 90° bend as shown
in one of the photos. Put the LEDs in
but don’t solder them in at this stage.
Attach the switch-bank to the front
panel and align the LEDs with their
holes, then solder them to the PC
board. The buzzer is held in place
with two 3mm self-tapping screws.
Next, solder the battery snap connector, buzzer and negative supply
wire to the PC board. The positive
terminal of the DC power connector is
wired via diode D10 to the PC board.
Parts List
Fig5: these components are mounted on the copper side of the PC board.
Fig.6: these components
are mounted on the top
of the board and must be
inserted and
soldered
before the
switch-bank
is soldered
in.
Put a kink in one of D10’s leads to
allow for some flexing.
Next, attach the 12-way terminal
block to the plastic case. All the wires
pass through a 1/4-inch hole to the terminal block. Terminate all the wires
according to the diagram of Fig.4.
You can attach the battery to the
inside of the case with a piece of
double-sided adhesive tape.
Making the extensions
There are several possible approaches to building the extension
stations – we show just two. One
shows the speaker and the circuit
components of Fig.3 wired into a
standard 3.5-inch disk box – cheap
and cheerful.
A more elegant approach is to purchase a pair of cheap computer speakers (we got ours from Woolworths at
just $6.99 pair!) and wire in the same
components.
Alternatively, you can use just
about any small plastic case that
comes to hand and install the components into it.
Perhaps the biggest job is running
all the cable pairs from the extensions
back to the Addacom which will
probably be mounted quite close to
the master station intercom.
We’ll leave you to figure out the
1 PC board, 100 x 35mm
1 plastic utility case, 130 x 68 x
45mm, with punched lid
1 4-way interlocking switch-bank
(S1-S4)
1 9V or 12V DC plugpack
1 DC connector socket to suit
plugpack
1 9V battery and snap connector
1 electronic buzzer
1 12-way insulated terminal block
2 12mm tapped spacers
4 M3 6mm screws
2 6mm self-tapping screws
4 47µF 16VW PC electrolytic
capacitors
Semiconductors
4 BC549 NPN transistors
(Q1,Q2,Q3,Q4)
8 1N914, 1N4148 small signal
diodes (D1-D8)
2 1N4004 diodes (D9,D10)
1 10V 400mW zener diode (ZD1)
4 5mm red LEDs (LED1-LED4)
most suitable installation.
Testing
Place a short across the cable pair
for each extension on the terminal
strip and make sure the buzzer and
the relevant LED lights up.
If the buzzer sounds when you connect an extension, reverse the cable
pair. If the buzzer sounds without any
extension calling, then you have a
short somewhere in your cabling. To
find it, remove one wire of each cable
pair and then replace it; repeat until
you find the shorted pair.
Next, plug the Addacom into the
extension of your existing intercom.
Turn the intercom off. Select each
extension with the switch-bank. If the
intercom buzzes then you may need
to reverse the wires.
If you intend using one of the extensions as a baby monitor then you
won’t need any switching for that
station – just wire in a speaker and
its 100µF coupling capacitor.
If you only need a couple of extensions then you can use the spare
switch positions for other devices.
For example, you might connect a
microswitch on a roller door, to tell
when it is open.
This is handy because it stops the
SC
door being left open at night.
Resistors (0.25W, 1% or 5%)
4 100kΩ
1 15kΩ
1 220Ω
2 47Ω
Extensions
4 speaker cabinets (see text)
4 8Ω miniature speakers to suit
cabinets
4 100µF bipolar electrolytic
capacitors
4 red LEDs
4 1N4001 diodes
4 momentary contact pushbutton
switches
Miscellaneous
Telephone cable for extension
wiring, double sided tape,
solder.
Where to buy the kit
* The copyright for this project is
owned by Hoad Electronics.
They can supply a complete kit
which includes a punched and
screened front panel for the
plastic box. The price is $34
including postage and packing
anywhere within Australia.
Contact Hoad Electronics at
19/314A Pennant Hills Rd,
Carlingford, NSW 2118.
Phone/fax (02) 9871 3686. email:
hoadelectronics<at>one.net.au
http://web.one.net.au/
~hoadelectronics
November 1999 67
VINTAGE RADIO
By RODNEY CHAMPNESS, VK3UG
The case of the disappearing TV sets
Vintage black and white TV receivers from 1956
onwards are now almost impossible to find. If
we don’t start saving the remaining examples
now, these sets may well go the way of the
Tasmanian Tiger and the Moa.
Valved black and white TV sets
are now quite rare animals. Is black
and white valved television a part of
our electronics heritage? You bet it
is and the time to start collecting is
now, otherwise the sets will be gone
for good.
Back in the March issue of “Silicon
Chip”, in the Publisher’s Letter, Leo
Simpson suggested that it was time
to save those old black and white TV
sets. Leo and I have discussed this
subject on a number of occasions and
this article will be followed by others
later on. I would like to dedicate this
68 Silicon Chip
particular article to the late Rex Wales
of the Historical Radio Society of Australia (HRSA) who was encouraging
members to get into vintage television
restoration. Sadly, he died before
much work could be done to find and
restore these old sets.
Why write about vintage television!
And what has television got to do
with vintage radio anyway? Directly,
probably very little. However some
members of the Historical Radio Society of Australia (HRSA) and the New
Zealand Vintage Radio Society (NZVRS) have started to show an interest
in preserving another aspect of our
electronic entertainment medium.
Therefore, an article on vintage tele
vision sets is very appropriate at this
time.
Unfortunately, most black and
white valve TV sets have been consigned to the rubbish heap. In the
process, quite a few were scavenged
for parts, power transformers, valves
and other odd bits and pieces. If
you don’t have a 6BX6 or a 6BL8 in
your radio junk box, you have never
wrecked a B & W TV set.
Have you considered how rare early
black and white television sets really
are? Could you lay your hands on one
of the original 17-inch Astor, Philips
or AWA TV sets, for example? Very
Below: these four sets are all AWA P1s
and have yet to be restored. Often, it’s
necessary to strip parts from one set
to get the others going.
few of us could. Fortunately, some
sets been stored in garages (or even
under the house), so there are still a
few sets around.
Most vintage radio collectors have
probably shunned col
lecting black
and white TV sets for several reasons:
(1) the sets are usually bulky (there
aren’t any mantle set size B & W TVs!);
(2) they haven’t considered B & W
TVs as being “vintage” sets. We didn’t
think of old radios as vintage until
about 15 years ago and we are now
waking up (almost too late) that B &
W TV sets are vintage as well.
(3) B & W TV sets are perceived as
being complex – which they are
compared to an AM radio receivers.
However, this and the following articles may help to dispel some of the
mystery.
(4) Replacement parts such as picture
tubes, line output transformers and
deflection yokes can be difficult to
obtain.
However, even if specialised parts
are hard to get, it doesn’t mean that
sets shouldn’t be collected – after all,
static displays of our early TV heritage
are much better than no displays at
all. For this reason, I hope that this
article and later ones will help readers
to get into this exciting “new” aspect
of vintage radio/television collecting
and restoration.
This photo shows an AWA P1 with the cabinet removed. This set is compact, has
an 11-inch picture tube and uses 13 valves.
A concise history
Television in its various forms has
been around for quite a long time.
However, like wireless (radio), it has
taken quite a few decades to evolve
into the sophisticated communications medium that it is today.
When the question is asked as to
who invented television, the usual
answer is John Logie Baird in the
1920s. But although he was at the forefront in developing the mechanical
television system, there were many
others who had also experimented
with mechanical systems, including
here in Australia.
Baird pushed for his system to be
accepted by the relevant authorities
but it was never going to be suitable
for domestic use for many reasons
– the prime one being that it was a
mechanical nightmare. But although
the mechanical system was unsuitable for use by the general public, it
did show that moving pictures could
be sent by radio waves. This opened
the way for a fully electronic method
The AWA P1 set is quite easy to service, as the PC board swings out to give
access to all the parts. The picture tube can be replaced in around 15 minutes.
to take over a decade later.
As a matter of interest, the mechanical scanning type of TV system only
had 30-60 lines to convey the picture.
By contrast, a modern PAL TV system
has 625 lines and between 150 and
600 times the definition of the mechanical systems. The early pictures
were sent on the AM broadcast band
and on nearby frequencies and only
required 10-40kHz of bandwidth, depending on the number of lines used
in the particular system.
Television became practical only
when a fully electronic system was
developed in the mid 1930s. In fact,
Britain had a working electronic tele
vision system by 1936, using a 405
November 1999 69
The AWA 242 was an up-market 21-inch set that was made during the mid
1960s. It had 21 valves and was fitted with a rotary VHF tuner.
line system. Of course, a number of
quite complex problems had to be
overcome before this became a reality,
including the development of the first
practical cathode ray tube (picture
tube) by V. K. Zworykin in 1929.
Note that, in those early days, the
pictures were rather small, being only
a few inches across.
Australian & NZ television
Television for the masses came
to Australia in 1956, in time for the
Melbourne Olympic Games. So,
we’ve had TV in Australia for over
40 years! Who’d have thought that it
was as long ago as that? Before that,
there were some early experiments
following the 1920s with mechanical
low-definition systems which were
transmitted mostly on the broadcast
band.
New Zealand had experimental TV
transmissions in Auckland from 1957
onwards and television for the masses
by 1960. Much earlier experiments
probably took place there as well but
I have no information on that subject.
It’s interesting to note that “Radio
70 Silicon Chip
& Hobbies” ran a television course in
instalments during the early 1950s.
This would have helped many servicemen later in the decade, when it
came to servicing the new technology.
Before the introduction of TV, servicemen were used to the 4/5-valve
mantle AM receiver and the occasional 8 or 9-valve multiband receiver
which had a few extra bells and whistles on it. What a shock TV was! Sets
typically had up to 25 valves (eg, the
STC 730-SU1), with several of these
valves having at least two functioning
sections (eg, the 6BL8). Some later
sets used as few as nine valves but
many of these were multifunction
“compactrons”.
In short, the circuitry and its functions were a whole new ballgame for
many servicemen of the era. Some
older servicemen hastily decided to
retire but many others went back to
school and learnt all about the new
marvel.
Early TV sets
In most cases, the black and white
valve TV sets were consoles, as were
the more elaborate radio sets of the
late 1920s through to the late 1940s.
The average wage in the early 1960s
was around 20 pounds a week and I
remember large console sets costing
up to 300 pounds at that time, or about
12 weeks pay. Today a colour TV
set can be purchased for one week’s
average pay.
In this first article, I have no intention of describing the restoration
of any particular set. Instead, the
accompanying photos are intended
to show readers what some of the sets
looked like from the outside and to
give a few glimpses of the internal
circuitry. Note that the sets shown
here have yet to be restored.
The AWA 242 console in the
photographs was one of the more
up-market sets during the mid 1960s.
It had 21 valves and the picture tube
was nominally a 21-inch unit. It was
fitted with a VHF tuner as only VHF
stations were available in Australia
until the advent of colour TV.
The AWA P1 is my favourite valve
black and white portable TV set. It
is compact, has an 11-inch picture
tube and has a total of 13 valves. The
set is quite easily serviced, as the PC
board swings out as shown in the
photographs.
In fact, it is so easy to service that
a picture tube can be replaced in
around 15 minutes.
I have a total of five P1 sets, which
means that I will be able to get at least
one operational using one or more of
the others for spare parts. I suspect
that this is the approach most vintage
TV restorers will have to adopt when
it comes to restoring sets to working
condition.
Another very interesting set shown
in the photos is the Healing. This is a
solid state receiver made towards the
end of the black and white era.
Technical details
TV receivers are very different from
AM radio receivers, although there
are a few similarities between them.
For example, TV sets are superhets as
are most vintage radios from around
1935 onwards. TV sets use much higher operating frequencies, however.
During the black and white era in
both Australia and New Zealand,
the frequency range tuned by the
sets was in the very high frequency
(VHF) band, from around 44MHz to
225MHz. This is considerably higher
than the highest frequency tuned on
most dual-wave AM receivers, which
usually don’t go past 18MHz.
As in AM broadcast receivers,
the local oscillator operates higher
than the frequency to which the set
is tuned by a fixed amount. This is
known as the intermediate frequency,
or IF. The IF for the picture carrier
was 36MHz, and the sound carrier
IF is 30.5MHz. These frequencies are
slightly different today.
In some early TV sets, two separate
IF amplifier stages were used for these
two separate parts of the TV signal.
However, apart from some rare exceptions, all the sets made in Australia
(and, I imagine, New Zealand) used
only one IF channel for both sound
and vision.
In a normal AM broadcast receiver, the IF bandwidth re
quired for
high-quality music reproduction is
around 20kHz. However, a vision
signal requires a very much wider IF
bandwidth for quality pictures to be
reproduced – around 7MHz in fact,
for both the sound and picture.
We’ll explain why this much bandwidth is required in a later article.
The signals are usually detected by
a germanium diode, after which the
audio and picture signals are separately processed. The audio is fed to
an IF amplifier stage on 5.5MHz and
thence to an FM detector and audio
amplifier. At the same time, the video
(picture) information is amplified by
a video amplifier which usually has
a response from DC to about 5.5MHz.
A number of other important components also appear at the detector.
These include the vertical and horizontal synchronising (or sync) pulses. These pulses are processed and
ensure that the picture is “locked”
vertically and horizontally into position on the screen. The horizontal
sync pulse peak level is also used to
provide automatic gain control.
As an aside, most people will have
seen pictures that roll vertically or
tear horizontally. This is usually
caused by a fault in the vertical or
horizontal sync circuitry.
The other two important components are the vertical and horizontal
blanking pulses. These pulses are
necessary to blank the screen at set
intervals, so that retrace lines aren’t
visible when the electron beam jumps
to the start of a new line or to the top
of the screen.
This view shows the chassis layout of the AWA 242 TV receiver. The set is fairly
easy to work on, with good access to most of the major parts.
This portable b&w TV set carries the Healing brand name. It was made towards
the end of the B&W era and uses solid state (transistorised) circuitry.
As can be appreciated from this,
quite a bit of circuitry is required to
process a “composite” video signal
to achieve the quality of picture and
sound that we have become accustomed to.
In later articles, simplified descriptions of how the sets work will be
presented, to assist restorers in the
task of restoring their black and white
TV receivers. As Leo pointed out in
his Publisher’s Letter, these sets are
worth restoring and are part of our
history, so start collecting even if a
complete restoration is beyond you
at this stage.
Finally, a few words of caution – be
very careful how you treat the picture
tube. A leather apron and protective
glasses should always be worn when
working with a picture tube, to give
protection if the tube implodes. SC
November 1999 71
Foldback speakers are
essential to any live
performance in a large
venue when high power
amplification is employed.
They enable each musician
to hear his or her own
playing, over and above the
general sound level. Build
these and save a bundle
of dollars compared with
commercial units.
By JOHN CLARKE
FOLDBACK
LOUDSPEAKER
BUILD A
T
HIS VERSATILE FOLDBACK
loudspeaker is suitable for stage
musicians, vocalists, entertainers and performers. It uses readi
ly
available loudspeaker drivers and can
be built using quite basic hand and
power tools.
Foldback loudspeakers, commonly called “wedges” because of their
shape, are used by musicians so that
they can hear themselves over and
above the general noise level in a performance venue. Often there are several foldback loudspeakers on stage, for
example, one for the keyboard player,
one for the vocalists and one or two
for guitarists (bass and lead).
Without foldback loudspeakers, the
performers would have to rely on the
sound projected to the audience via
72 Silicon Chip
conventional “front of house” loudspeakers. However, they may find it
difficult to hear from their location
behind the speakers and there can
also be a considerable delay before the
sound reaches them. This delay will
cause the performance to become slow
and very deliberate as the performers
attempt to sing or play and then wait
to listen. With foldback speakers, the
performance can be kept tight and
lively.
Foldback loudspeakers are designed with quite different criteria
compared to conventional types and
as a consequence they look and sound
different. While conventional loudspeakers project the sound away from
the performers and toward the audience, a foldback loudspeaker does
the opposite and projects the sound
toward the performers themselves;
this provides the perfect recipe for
acoustic feedback.
To avoid this problem, foldback
loud
speakers are designed with a
sloping front baffle to project the
sound directly toward the performers’
ears. This means that they beam the
sound to the rear of the microphones
which are usually designed to have a
minimum pickup from the rear, so as
to minimise feedback.
The design described here enables
the loudspeaker baffle to be set to 35°
or 55° to the horizontal, depending
on how the box is placed on the floor.
This will suit either close-up use (35°)
or more distant listening (55°).
Sloping the baffle is done for two
Two 200mm “Redback” woofers (one shown) and a single
Motorola KSN-1141A piezoelectric horn are used in the
Foldback Speaker. The woofers are protected by steel mesh
grilles.
other reasons. First, the sound is
beamed at the listener so that they
receive the brighter “on-axis” sound.
Second, it reduces floor reflections
back up to the microphones where
their rejection of sound is far less than
directly from the rear.
Angling the baffle does not solve all
acoustic feedback problems though.
Feedback can still occur when the microphones are spaced out on the stage,
producing the potential for a micro
phone to receive off-axis sound from
an adjacent foldback loud
speaker.
However, this new foldback design
has lobes and nulls in its off-axis
response and by placing adjacent
microphones in the “nulls” of the
foldback speaker, acoustic feedback
can be further reduced.
The SILICON CHIP foldback loudspeaker is 546mm wide, 335mm
high and 408mm deep. The box
is made of 18mm MDF (medium
density fibreboard) and covered in
loudspeaker carpet. The loudspeakers
are protected with steel mesh grilles
and moulded plastic corners provide
protection for the enclosure against
rough handling.
Two 200mm woofers and a single
piezo ceramic speaker with a 50mm
x 150mm wide dispersion horn are
used. The woofers are placed either
side of the vertically mounted horn.
This arrangement produces a symmetrical on-axis frequency response ideal
for foldback.
If the loudspeaker box is mounted
on end, the woofers will be arranged
vertically and the horn horizontal.
This allows the speaker to be used
conventionally for projecting sound
toward an audience.
The specified woofers (Altronics
Cat. C-3060) have a power rating of
60W and a nominal impedance of 8Ω.
Their Thiele-Small parameters are Vas
Specifications
Frequency range: 45Hz to
20kHz <at>-6dB
Nominal Impedance: 16Ω
Power rating: 200W into 16Ω
(equivalent to 400W into 8Ω)
Mass: 18kg
Dimensions: 546mm (W) x
408mm (H) x 335mm (D)
Baffle slope: 35° or 55°
Fig.1: only two components are
used in the crossover network
for the Foldback Speaker. The
1.8mH coil (L1) prevents high
frequencies from being fed to
the woofers, while the 0.33µF
capacitor (C1) reduces the
output of the tweeter by about
6.4dB.
November 1999 73
Fig.2: these graphs of Fig.2 show the CALSOD response predictions for the
woofer and tweeter combination. The solid line on the upper graph is the
on-axis frequency response while the dotted line is the impedance plot. The
solid line on the lower graph is the phase response.
Fig.3: this graph shows the predicted horizontal off-axis response at 30°.
The notch in the response at around 1.2kHz occurs at different frequencies
depending on the off-axis angle.
54l, Qts 0.323, Qes 0.398 and Qms of
1.72. Their resonant frequency (Fs) is
34.7Hz and sensitivity is around 89dB
at 1W and 1m. The two woofers are
connected in series to provide a nominal 16Ω impedance. This means that
we can parallel up several foldback
loudspeaker units together without
overloading the driving power ampli74 Silicon Chip
fier. Two foldback units will produce
an 8Ω load, three units a 5.3Ω load
and four units in parallel a 4Ω load.
The tweeter is a Motorola KSN
1141A piezoelectric horn which
incorporates protection circuitry to
allow its use with amplifiers rated at
up to 400W. The protection comprises
an incandescent lamp and a positive
temperature coefficient (PTC) resistor
in series. These components increase
their resistance at high power levels
to protect the tweeter element.
A common design approach when
using a piezo tweeter is to simply
connect the speakers without a cross
over. The natural rolloff of the woofer
at higher frequencies and the tweeter
at lower frequencies are supposed to
compensate each other and produce
a smooth response. This rarely works
well and inevitably the response is
markedly louder in the 1kHz to 5kHz
region as the sound level is summed
from both woofer and tweeter. Usually
the tweeter is also quite a bit more
sensitive than the woofer and so
such systems are often excruciatingly
bright at the higher frequencies.
For our design, we used a series
1.8mH inductor to roll off high frequencies to the woofers. While this
will produce a theoretical rolloff of
6dB/octave above 1.4kHz, in practice
the rolloff will be somewhat less than
this due to the woofers’ own voice coil
inductance.
In addition, to compensate for the
sensitivity mismatch between the
tweeter and woofers, the tweeter is fed
via a series 0.33µF capacitor. Since the
piezo tweeter itself has a capacitance
of 0.3µF, there is a capacitive voltage
divider effect which reduces the signal level by a factor of 0.48 or 6.4dB.
The speaker circuit diagram is shown
in Fig.1.
Note that the tweeter is connected
out-of-phase with the woofers, to
ensure a flat response. An in-phase
connection pro
duces a null in the
response at the crossover frequency.
The phase was predicted using a
computer simulation and took into
account the distance between drivers,
the offset behind the baffle and the
phase response of the drivers and
crossover.
Some readers may be puzzled by
the two jack sockets shown on the
circuit. One allows the cable from the
amplifier to be connected while the
second allows another foldback loudspeaker to be connected in parallel. In
practice, you could “daisy chain” four
of these foldback speakers together,
to provide a nominal 4Ω load to the
driving amplifier.
Design software
The crossover and low frequency
ported response was modelled using
Fig.4: the overall
dimensions for the
Foldback Loudspeaker.
Use a jig saw to cut out
the holes and rebate the
woofer holes using a
router.
an Australian developed loudspeaker
design program called CALSOD 1.40
(Computer Aided Loudspeaker Sys-
tem Optimisation and Design). This
allowed the response to be adjusted
for optimum smoothness and match-
ing between drivers. The program
allows off-axis predictions to be made
using multiple drivers.
November 1999 75
Fig.5: cut the two sheets of MDF as shown in this diagram, to make the sides, base, back, top
and baffle. The material can be cut using either a jig saw or a circular saw.
You can model and optimise cross
overs, produce phase and response
curves and also position the drivers
on the baffle. Copies of this DOS
based program can be obtained from
Audio
soft, 13 Beatty St, Ivanhoe,
Victoria 3079. Fax (03) 9497 4441.
Email audiosoft<at>netwide.com.au. The
price for the budget version CALSOD
1.40 with on-disk users manual is
$119 including postage and handling.
Professional versions which allow
importing measured data (CALSOD
3.10) are available from $369.
The graphs of Fig.2 show the CALSOD response predictions for the
woofer and tweeter combination. The
solid line on the upper graph is the
on-axis frequency response while the
76 Silicon Chip
dotted line is the impedance plot. This
shows the expected double hump at
low frequencies for the ported design
while the value rises rapidly above
5kHz due to the parallel tuned circuit
formed by the woofers’ inductance and
the capacitance of the piezo tweeter.
Note that the impedance does fall
back to lower values for frequencies
above 16kHz, as can be seen at the top
righthand corner of the graph.
The solid line on the lower graph
is the phase response. The abrupt
changes from -180° to 180° at 40Hz
and 7kHz does not mean that there is
a sudden phase change; it is simply
drawn that way so the phase plot fits
on the graph.
Fig.3 shows the predicted horizon-
tal off-axis response at 30°. The rolloff
above about 3kHz is an estimate for
the attenuation in sound level at this
angle. The notch in the response at
around 1.2kHz occurs at different
frequencies depending on the off-axis
angle.
Construction
The overall dimensions of the fold
back loudspeaker are shown in Fig.4.
It is made from one 600 x 900mm sheet
and one 450 x 1200mm sheet of MDF.
This is cut as shown in Fig.5, to make
the two sides, the base, back, top and
front pieces. We used a jig saw and
a straight edge guide to make all the
cuts although you could also use a
circular saw.
The baffle is made from the material
remaining after the base and front
pieces have been cut from the 450
x 900mm sheet. Adjust the jig saw
or circular saw so that it is set for a
35° cut. This will enable the baffle
to mate flush with the inside of the
front piece. Cut the baffle edge at
35° using a straight edge as a guide.
Measure 300mm from the inside of
this bevelled edge and draw a line
across the 510mm length. Now cut
this edge at 55°.
Assemble the base, back, sides and
front pieces together using 8g x 30mm
countersunk wood screws. Do not glue
the pieces at this stage. Fit the front
baffle and top piece in place and check
for fit. The bevelled edges may require
some adjustment using a plane to
produce a good fit. Now secure them
with screws. Check that all right angle
edges are square and that the straight
edges provide a close fit. Mark out the
pieces, indicating their orientation
and positioning to adjacent pieces.
This will make it easier to reassemble
later on. Now disassemble the pieces.
Cutting the speaker holes
Mark out and cut the baffle as shown
in Fig.4. Use a router to rebate the
woofer hole and a jig saw to cut out
the holes. The cutout for the tweeter
horn was made deliberately small to
allow a greater amount of wood between the woofer and tweeter hole.
The 63mm diameter cutout is to allow the piezo element of the horn to
fit through the baffle. Check that the
speakers and port tubes fit into their
respective holes.
Now assemble the box using PVA
glue on all mating surfaces. Assemble
one side, the base, back, top and front
first, followed by the baffle, using the
screws to secure the pieces in place.
Now glue the second side in place.
This assembly method will ensure
that the baffle can be glued on its
side. Wipe any excess glue off with
a damp rag.
We fitted braces made from 31 x
13mm timber to the inside of the base
and back. A 500mm length was used
along the base spanning from side to
side and a 290mm length along the
back spanning from base to top. These
were located offset from centre.
For extra strength in the enclosure,
we also recommend using 12 x 12mm
cleats on all right angle joints and
along the baffle to side joints. These
Fig.6: this diagram shows how the main pieces are fitted together to form
the box. The inside of the box is also fitted with braces and cleats, for added
strength – see text.
should be secured with PVA glue and
screws.
Smooth the box edges with a rasp
or plane to produce a small 2-3mm
chamfer and round off the corners
neatly. This will allow the plastic
corner protectors to fit correctly.
Test these for fit before finishing this
process.
It is probably unnecessary to sand
the box since the carpet covering
will mask any imperfections in the
surface. However, remove any large
protrusions from the box surface such
as glue runs, screw heads, etc.
You will need to drill a 25mm hole
in each side of the box for the 6.35mm
socket adaptors. The same sized holes
are also required if Neutrik panel
sockets are used. Standard 6.35mm
sockets, while relatively inexpensive,
are really not rated for driving high
powered speakers. Also they are not
airtight and may introduce extraneous
noises as the air passes through them.
While you can seal them using a
cover and silicone sealant, Neutrik
locking chassis jack sockets are
preferable because they are sealed
and attach more solidly to the case.
Standard 6.35mm sockets also have
a tendency to fall inside the speaker
box if the securing nut becomes loose
and falls off.
Alternatively, you could use Neutrik “speakon line” sock
ets. These
leaded sockets feature a 30A rating,
locking plug, rugged line plugs and
solid wire clamping on the plug.
Covering it with carpet
We covered the whole speaker box
in carpet and attached it with contact
adhesive. The carpet covers the box
in four sections. It is cut out using a
cutting mat, metal straight edge and a
sharp utility knife (eg, Stanley knife).
Start by cutting a 510 x 300mm
piece and coat the baffle with contact
adhesive. Place the carpet over the
baffle and then immediately lift it
off again. This will reveal the baffle
cutout areas on the carpet which do
not require coating with adhesive.
Coat the required areas on the carpet
and recoat the baffle where the contact
adhesive has lifted off.
Wait for the adhesive to dry, then
place the carpet in position over the
baffle, making sure that it is oriented
correctly. Now press the carpet down
firmly until it is fully attached. The
carpet will then need to be trimmed
to reveal the cutouts on the baffle.
For the woofer cutouts, trim the
carpet to the outer diameter of the
rebate using a sharp knife. The port
cutouts will need to be recut to the
November 1999 77
Parts List
2 200mm woofers (Altronics
C-3060)
1 Motorola KSN1141A piezo
ceramic speaker and horn
2 50mm adjustable speaker
ports
2 200mm speaker grilles
1 strap handle
7 box corners
2 6.35mm jack sockets (Altronics
P-0071) plus mounting cup
(Jaycar HS-8025) or 2 x
Neutrik locking chassis mount
jack sockets (Jaycar PS-0196)
or 2 x Neutrik “Speakon”
sockets (Altronics P-0790,
Jaycar PS-1094)
1 1.8mH air-cored inductor
1 0.33µF 200V polyester
capacitor
1 5-way 30A mains terminal strip
1 piece of 1m x 1.8m x 3mm
speaker carpet
1 1m x 500mm piece of speaker
wadding
1 1200 x 450mm sheet of 18mm
Medium Density Fibreboard
(MDF)
1 600 x 900mm sheet of 18mm
MDF
1 790mm length of 31 x 13mm
dressed timber (pine or
meranti)
1 250ml tin of contact adhesive
1 100ml container of PVA
adhesive
1 2m length of speaker sealant
or adhesive backed draught
excluder
46 8g x 25mm countersunk
bronzed wood screws (for
corner protectors speakers
and ports)
2 10g x 25mm cheese head
bronzed wood screws (for
handle)
50 8g x 30mm countersunk
wood screws (for securing box
panels)
3 6g x 20mm cheese head wood
screws (for terminal strip and
inductor)
4 6g x 20mm countersunk
bronzed wood screws (for
6.35mm sockets)
1 1.5m length of red 15A hookup
wire
1 1.5m length of black 15A
hookup wire
78 Silicon Chip
Fig.6: this wiring diagram shows how the 5-way terminal block is used to
terminate the leads from the jack sockets, the woofers, the tweeter and the
crossover components.
outer diameter of the port mounting
flange. This can be done by placing the
port in position and then cutting the
carpet to the flange diameter. Similarly, the tweeter horn can be fitted and
the carpet cut around its perimeter.
The second and third pieces of
carpet required are for the sides and
are initially cut to 335 x 408mm. Glue
these to the sides and then trim the
carpet along the sloping edge so that
the carpet will fold over to meet the
baffle.
Cut holes in the carpet at each side
for the 6.35mm jack socket or adaptor.
Insert the socket (or adaptor if this is
used) and trim the carpet around its
perimeter.
The final piece of carpet needs to be
550 wide by 1100mm and fits over the
top, back, base and front of the box,
starting at the top of the baffle and
going around to the base of the baffle.
Trim the carpet at one end so that it
meets the carpet already applied to
the baffle and sides. Apply contact
adhesive along those edges where
the carpet joins will be and on the
carpet itself. Fit the carpet in place
when the glue has dried. Now coat
the bulk areas of the box on the top,
back, base and front and the carpet
and fit it in place.
The corner protectors can now be
fitted with countersunk screws. These
mount on each right angle corner. We
cut another corner protector to provide two separate flat pieces and these
were fitted along the sloping edge on
each side of the box to allow it to be
stood on side for normal loudspeaker
use or for stacking during storage.
Attach the handle onto the front of
the box close to the baffle and central
to the width of the box. This should
provide the best balance point for
carrying the box.
Wiring
Use 15A hookup wire and solder
a 300mm length of red wire to the
positive terminal of each speaker and
a 300mm length of black wire to the
negative terminals. Then connect a
300mm length of red wire to each tip
connection of the jack sockets and a
black wire 300mm in length to the
ring terminals.
The crossover components are
mounted using a 5-way terminal block
Above: both the terminal block and
the inductor are secured to the bottom
of the box using wood screws. Note
that the inside of the box is lined with
wadding which is stapled in place but
this must be clear of the port holes.
which is secured to the inside of the
box with two wood screws. Mount
the inductor using a wood screw also.
Wire up the components by passing
the wires through the holes allocated
for each component as shown in the
diagram of Fig.6.
Apply a layer of speaker wadding
around the edges inside the box and
secure it in place with staples. Make
sure the wadding is clear of the port
holes.
Fit the jack sockets to the side of
the case with screws and secure the
speakers with sealant between the
baffle and speaker mating surfaces.
Cut the two 50mm ports to a length
of 125mm and secure them in place.
Fit the protective mesh grilles over
the woofers using the supplied clamps
and wood screws. Then vacuum the
outside of the box to remove wood
shavings and sawdust. Any contact
adhesive on the outside of the carpet
can be removed with mineral turps
and an old toothbrush, before it sets
hard. Then you are ready to have a
SC
listening test. Enjoy.
A 2-metre length of speaker sealant (or adhesive-backed draught excluder) is
used to seal the loudspeakers and the port tubes, to prevent air leaks.
November 1999 79
A remote controlled throttle for
model railways
PART 2: By JOHN CLARKE & LEO SIMPSON
BUILD THE
RAILPOWER
Last month, we presented the circuit
details of our new Railpower model
railway speed control. This month, we
describe the circuit of the IR remote
control and give the construction details.
L
AST MONTH, we completed
the circuit description of the
Railpower except for the infrared remote transmitter and this is
shown in Fig.5. It comprises a single
IC, two transistors, an infrared LED
and a few passive components. The
80 Silicon Chip
IC’s internal oscillator is set to 455kHz
by ceramic resonator, X1, connected
between pins 12 & 13. The 455kHz oscillator frequency is divided down by
12 to give a 37.9kHz carrier frequency
for the infrared LED (IRLED1). Current
drive for the LED is provided by the
Darlington-connected transistors, Q1
& Q2.
When any pushbutton is pressed, it
pulls the corresponding input of IC1
low and this causes the output at pin
15 to deliver a uniquely coded stream
of pulses (at 37.9kHz). The pulse
codes can be changed using different
combinations of links LK1 and LK2 so
that you have the option of using up
to four separate Railpower controllers
which operate independently on the
same layout.
This can be a boon to realistic
operation on large layouts with cab
(block) switching. Naturally the receiver coding on the main PC board
must match the respective remote
control transmitter in order to operate.
However, if you only intend to use one
Railpower controller on your layout,
you can omit the two links on both the
transmitter and the main circuit board.
The transmitter circuit is powered
by two AAA cells connected in series
to provide a 3V supply. The IC draws
only about 1µA on standby, when
the switches are not pressed, so the
batteries should last for virtually their
shelf life.
Construction
The Railpower may have a relatively complicated circuit but it is
very straightforward to build. All the
circuitry in the case is installed on a
PC board measuring 216 x 170mm and
coded 09310991.
Before you begin assembling components on to the PC board, check
that it fits properly into the base of the
instrument case. Enlarge the corner
mounting holes in the PC board to
3mm or 1/8" if these have not been
drilled to size. Check that the holes
line up with the integral pillars in
the case.
Then check the PC board for shorts
between tracks or for any breaks. Make
any repairs now, if required. Check
the holes for the 0.1Ω resistor and the
power diodes (D15-D18) as these may
need to be enlarged to accommodate
their thicker pigtails.
The component overlay for the PC
board is shown in Fig.6.
Start by installing all the links on
the PC board using 0.8mm tinned copper wire. Most of the links are 12.5mm
long so you could bend these over a
suitable former about 12mm wide, to
create a uniform appearance. There is
a longer link near IC5 and more links
adjacent to the power transistors Q16,
Q17, Q20 & Q21.
Install the PC stakes in position and
then insert and solder the resistors.
Use the accompanying colour code
table as a guide to selecting the resistor values. Better still, use a digital
multimeter to check each value before
it is inserted.
The 0.1Ω 5W wirewound resistor
should be raised above the PC board
by about 2mm before soldering the
leads.
Next, install the diodes. Several
types are used although most are the
small switching diodes (glass encapsulated). 1A types (black resin body
with silver stripe) used for D7, D8 &
D14 while the 1N5404 power diodes
Fig.5: the transmitter encoder IC has an internal oscillator set to
455kHz by the ceramic resonator, X1, connected between pins 12 &
13. The 455kHz is divided down by a factor of 12 to give a 37.9kHz
carrier frequency for the infrared LED (IRLED1). When any
pushbutton is pressed, it pulls the corresponding input of IC1 low
and this causes the output at pin 15 to deliver a uniquely coded
stream of pulses at 37.9kHz.
used for D15-D18 are larger again.
Note that you only need to install
diodes D15 & D16 if the transformer
is a centre-tapped 24V unit.
The capacitors can be installed
next, taking care to orient the electrolytic types with the polarity shown
on Fig.6. Note that you should only
Improving The Speed “Hold” Time
Following last month’s article we have had a chance to do some serious
testing of the new Railpower on a large HO layout and it came through with
flying colours, except for one aspect: the speed “hold” time.
When you set the speed with the remote control, you expect it to stay set
indefinitely. In practice, that is not possible with the “hold” circuit involving
IC4b but the circuit did need improving so that the speed setting did not
drop noticeably after a few minutes.
Therefore, we are recommending a change to the value of C1. Instead of
using a 2.2µF tantalum or low leakage electrolytic capacitor, C1 should now
be a 22µF tantalum type. At the same time, the 10MΩ resistor associated
with IC5a should now be 1MΩ while the 4.7MΩ associated with Q3 should
now be 470kΩ. In other words, C1 is now ten times larger and the associated charging discharging resistors are one-tenth of their original values.
These changes have been incorporated into the component overlay diagram of Fig.6. With the new values, a given speed setting can be expected
to drop by 36% after 15 minutes or thereabouts. This should be more than
adequate, even for the largest layouts where protracted running at a given
speed is required.
November 1999 81
Fig.6: the component overlay for the PC board. Install C3 or C4 (not both) depending on whether you want the circuit to
power up in the forward or reverse mode. For forward mode, install C3; for reverse mode, install C4.
install C3 or C4, not both. Install C3 if
you want the circuit to power up with
the controller in the forward mode.
82 Silicon Chip
To power up in reverse mode, omit
C3 and install C4.
Now insert and solder the ICs, tak-
ing care to orient them correctly. Be
sure that each is in its correct place
before soldering the pins.
Secure the mains wiring using cable ties and be sure to sleeve all exposed
terminals with heatshrink tubing as detailed in the text.
Install the transistors and regulators next, taking care to insert the
correct one in each position. REG2
and transistors Q16, Q17, Q20 & Q21
are mounted at full height with about
1mm of their leads extending below
the copper side of the PC board.
Six trimpots need to be installed,
Capacitor Codes
Value
IEC Code
EIA Code
0.1µF 100n 104
.01µF 10n 103
.001 1n
(1000p
or 102)
Resistor Colour Codes
No.
1
1
1
1
1
8
1
1
3
35
1
2
3
7
6
Value
10MΩ
4.7MΩ
560kΩ
220kΩ
120kΩ
100kΩ
47kΩ
39kΩ
22kΩ
10kΩ
4.7kΩ
3.3kΩ
2.2kΩ
1.2kΩ
1kΩ
4-Band Code (1%,5%)
brown black blue brown
yellow violet green brown
green blue yellow brown
red red yellow brown
brown red yellow brown
brown black yellow brown
yellow violet orange brown
orange white orange brown
red red orange brown
brown black orange brown
yellow violet red brown
orange orange red brown
red red red brown
brown red red brown
brown black red brown
5-Band Code (1%)
brown black black green brown
yellow violet black yellow brown
green blue black orange brown
red red black orange brown
brown red black orange brown
brown black black orange brown
yellow violet black red brown
orange white black red brown
red red black red brown
brown black black red brown
yellow violet black brown brown
orange orange black brown brown
red red black brown brown
brown red black brown brown
brown black black brown brown
November 1999 83
Fig.7: wiring details inside the case. The 240VAC mains wiring should be run in
250VAC-rated wire, with green/yellow striped wire for the Earth. The buzzer is
fixed to the board with double-sided tape.
and again, make sure that the correct
value is installed in each position.
Finally, the nine LEDs can be installed. These are all oriented with
the Anode (longer lead) to the right
and are mounted so that the cathode
lead is about 1mm below the copper
side of the PC board. This will allow
the leads to be soldered and have the
maximum height above the PC board.
The LEDs will eventually need to be
bent over at right angles so that they
84 Silicon Chip
can be inserted into the front panel
holes.
Front and rear panels
Mark out and drill the front panel to
provide an access hole for the infrared
detector, the LEDs, the power switch
S1 and the analog meter. The meter is
supplied with a cardboard template to
assist in marking out its cutout hole.
The front panel artwork should be
used as a guide for the hole positions.
The rear panel is aluminium and
it needs to be drilled for the four
transistors, REG2, the access hole for
auxiliary circuits and the IEC power
socket. Before the rear panel can be
drilled, you will need to mark the
positions of the four power transistors
and REG2.
To do this, you need to sit the assembled PC board in position on the base
of the case. You will need to shorten
some of the integral pillars with a
large drill bit so that the PC board can
sit correctly on the corner mounting
pillars. Now slide the aluminium
The H-bridge transistors (Q16, Q17, Q20 & Q21) and the 3-terminal regulator are mounted on the rear panel,
which provides the necessary heatsinking – see also Fig.8.
rear panel into place and mark the
mounting hole positions for the power
transistors and regulator.
At the same time, mark out the
hole positions for the terminals and
the auxiliary output lead hole which
will need to be fitted with a grommet.
The IEC mains socket should be
mounted as far to the side as possible to allow clearance for the leads
around the transformer. Mark out the
holes required for this and also for the
adjacent earth screw terminal.
Place the transformer on the PC
board and determine its optimum
mounting position. The mounting
hole positions for this should not
encroach onto the track area on the
board.
Drill and file out the holes on the
rear panel and do the same for the
transformer mounting holes on the PC
board. We mounted the transformer
with rubber grommets inserted into
the holes in its mounting feet. The
holes may need to be reamed to a
larger size for this.
The transformer is secured to the
PC board with a screw, a flat washer
and a nut for each foot. The nuts are
tightened down sufficiently to anchor
the transformer but not so tight as to
prevent free movement.
Secure the PC board in the case with
self-tapping screws.
Attach the IEC socket to the rear
panel using 3mm screws and nuts and
Fig.8: mounting details
for the power
transistors and
3-terminal regulator.
Use mica or silicone
washers and
insulating bushes to
isolate the metal tabs
from the metal panel.
This close-up view shows how the PIC12043 IR receiver (IC1) is aligned with
a hole in the front panel, so that it can pick up the IR pulses from the remote
control unit.
November 1999 85
The remote control transmitter board has just a handful of parts and should
only take a few minutes to assemble. Note that this board is supplied by Oatley
Electronics and is substituted for the existing board inside the transmitter case.
fit the binding post terminals. You can
also attach the meter and switch S1 to
the front panel.
Fig.7 shows all the wiring details
inside the case. The 240VAC mains
wiring should be run in 250VAC-rated
wire, with green/yellow striped wire
for the Earth. Use a plastic insulating
boot for the IEC socket terminals and
a length of insulating tubing for the
terminals of switch S1. Some of the
wires will need to be passed through
this insulation boot before soldering
them in place.
The earth connection to the transformer is made by scraping away the
coating on the transformer mounting
foot and soldering the wire in place.
Be sure it is soldered properly, with a
hot iron, and check that the solder has
flowed onto the exposed steel.
The earth terminations to the rear
metal panel are made using crimp lug
eyelets or solder lugs, each secured in
place with a 3mm screw, star washer
and nut.
Fig.8 shows the details of how the
power transistors and regulator are
mounted to the rear panel. Use mica
or silicone washers and insulating
bushes to isolate the metal tabs from
the metal panel. Use heatsink compound between mating surfaces if
mica washers are used but this is not
necessary for the silicone types. Check
that the transistor tabs and regulator
are indeed isolated from the case by
testing on the ohms range with your
multimeter. The reading should show
open circuit.
The binding post terminals are
wired with short lengths of heavy
duty hookup wire as shown. Wire up
the front panel meter with hookup
86 Silicon Chip
wire and connect the buzzer wires in
place. We secured the buzzer to the
PC board with a piece of double-sided
tape. Alternatively, it can be glued in
place with silicone sealant, contact
adhesive or similar.
The transformer secondary is wired
as shown in Fig.7, using the three
connections on the PC board for the
24V centre-tapped transformer type
or without the centre tap terminal on
the PC board (CT) for the transformer
with two 12V windings.
Transmitter construction
The transmitter is assembled into a
small case which contains an existing
PC board. This unit is supplied by
Oatley Electronics. You first need to
prise open the case and remove the
board. You then have to remove the
battery clips and 455kHz ceram
ic
resonator from this board and install
them on a new PC board that comes
with the transmitter. Fig.9 shows the
component layout for this new board.
Insert the supplied components
as shown, taking care to install the
correct transistor in each position.
Do not forget the wire links and the
insulated wire link from the positive
supply up to the 4.7Ω resistor. Be sure
to orient the IRLED correctly, with
the longer lead being the Anode (A).
It is placed so that its body sits comfortably over the integral moulding
in the case.
When completed, you can attach
the front panel label and cut the holes
out with a sharp utility knife. Insert
the PC board into the case and clip
the case together. You will need two
AAA cells to power the transmitter.
Testing
Fig.9: this is the parts layout for the
remote control transmitter PC board.
Check all your work thoroughly
before applying power. When power
is applied, the neon in the power
switch (S1) should light and some of
the LEDs should light. In particular,
the forward or reverse LED should be
on as well as the Stop LED.
Check the supply rails on the
circuit. Connect the negative lead of
your multimeter to the 0V binding
post terminal and test the voltage
on the positive terminal. It should
be +12V. Now check at pin 14 of IC2
for a reading of +5V. If either voltage
is low, you should suspect a short on
the PC board somewhere. Find it and
fix it before going any further.
There should be 12V between pins
Fig.10: use this actual size artwork to check for etching defects on your controller PC board.
4 & 11 of IC3 & IC8; between pins 4
& 8 of IC4; between pins 8 & 16 of
IC5 and between pins 7 & 14 of IC6,
IC7 & IC9.
Now check the operation of the
remote control. Pressing the control
buttons should operate the front
panel LEDs. The Aux1 & Aux2 LEDs
should light when the relevant remote buttons are pressed, with Aux1
staying on or off, after each button
press. The Inertia and Stop functions
November 1999 87
RAILPOWER
SPEED SETTING
SC
D
OVERLO
A
FORWA
RD
E
REVERS
UT
LOCKO
STOP
INERTIA
OFF
AUX2
AUX1
POWER
Fig.11: this full-size front panel artwork can be used as a drilling template for the front panel of the main control unit.
RAILPOWER
TRACK
SILICON
CHIP
40
60
AUX1
INERTIA
AUX2
STOP
REV
FOR
80
10
0
SPEED
88 Silicon Chip
20
0
SPEED
Fig.12: here are the actual size
artworks for the remote control
handpiece and the meter scale.
also should go on and off with alternate pressings of the
pushbuttons. The speed (+) and speed (-) buttons should
alter the meter reading but with this yet to be calibrated
you may not obtain good results. The lockout LED should
also switch on as the speed setting is increased.
The track LED should gradually light up as the speed
is increased and show a different colour depending on
whether the forward or reverse mode is selected. It may
come up very slowly in brightness because of the inertia
setting. You can switch the inertia out for a faster response
to the Speed buttons. Note also that the forward or reverse
mode can only be selected when the lockout LED is off.
Now connect your multimeter to the track terminals.
Adjust the speed up fully by holding the speed (+) button
down for about 10 seconds, then adjust VR1, the maximum
speed trimpot, for a reading of 12V. If you are running an
N-scale layout in which the model locomotives normally
run at a maximum of 9V, then use this as the maximum
speed setting instead.
Adjust trimpot VR2 fully anticlockwise. Use the speed
(-) button to reduce the track voltage to its minimum setting
and then connect the controller to the track on your layout.
Place a locomotive on the track, select inertia out (LED
lit) and rotate VR2 until the loco just begins to move. Then
rotate VR2 slightly anticlockwise from this setting. Now
use the speed buttons to start the loco and bring it to a
halt again. If the loco still tends to creep at the minimum
speed setting, adjust VR2 even further anticlockwise and
then check the settings again.
Next, adjust trimpot VR6 so that the meter shows full
scale at the maximum speed setting. You may want to
remove the loco when doing this.
Trimpots VR4 and VR5 are adjusted for the required
amount of inertia for starting and stopping. The Inertia
function will need to be selected (Inertia LED out) to adjust VR4.
Trimpot VR3 is adjusted so that the forward/reverse lockout LED lights at the train speed below which you consider
it safe to suddenly reverse the track voltage.
Next month, we will give the details of how to wire the
Railpower without remote control. This will give you the
ability to plug a handheld controller into any place on your
SC
layout to control trains.
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November 1999 89
ASK SILICON CHIP
Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line
and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097.
Loudspeaker
design software
I am looking for articles on subwoofer and speaker enclosures. There
was an article in the June 1996 issue
on BassBox loudspeaker software.
I would like to know if you subsequently published a design using the
compound speaker concept featured
in this article, as I would like to build
a subwoofer enclosure using two 10inch subwoofers for my car. If not, are
there any plans to feature something
along those lines in the future? (C. E.,
via email).
• We have featured only two sub
woofers designed using the BassBox
software. They were the Bass Barrel
in the August 1997 issue and the Bass
Cube in the April 1999 issue.
Flickering flame
doesn’t flicker
I recently built the Flickering Flame
as described in the October 1997 issue
of SILICON CHIP and have a problem
trying to run it off mains power using
a 240VAC AC transformer rectified to
Setting up the
capacitance meter
The Digital Capacitance Meter
described in the February 1999
issue looked very useful to me,
especially with its pF range. Unfortunately, having built the unit,
I cannot null the output of IC2a
and this ruins the low range readings. For testing, I have numerous
2% capacitors ranging from 47pF
to 0.9µF, a borrowed capacitance
meter, a DVM, oscilloscope and
frequency counter. I have noted the
Errata in May and June 1999 issues
and have checked the unit carefully. The voltages seem correct as do
the scope waveforms.
It can be made to work tolerably
well on the nF and µF ranges but
90 Silicon Chip
12V DC. The problem is the light does
not flicker; it just stays on. But when
I connect it to a car battery it works
correctly.
Could you please help me with this
problem? (G. W., via email).
• Our guess is that you have insufficient filtering on your rectified DC
supply. You would need a capacitor
of at least 4700µF at 25VW.
Temperature controller
can’t heat & cool
I gather from the article on the
Switching Temperature Controller in
the August 1999 issue that can only
run one Peltier Effect device at once.
Is this so? So in order to keep the inside of an Esky used as a brooder for
raising baby birds, two circuits would
be needed – one for cooling and one
for heating?
I assume that a Peltier device
mounted on a CPU cooling fan heat
sink would blow cool air? (T. A., via
email).
• You are right in that the circuit can
only be used for heating or cooling. If
you try to do both, both the heating
is not acceptable on the pF range.
The voltage at pin 11 of IC2a does
not dip (to 5-10mV) and rise again
but ranges from 66-89mV when
varying trimpot VR1. Changing IC1
alters this slightly but does not fix
the problem. The frequency at pin 8
of IC1 with the first 74HC132 measures 12,124Hz and 12,400Hz and
with the replacement 11,109Hz
and 10,900Hz, approximately.
The text refers to 16,160Hz and
16,000Hz. Is this significant? (R.
B., Flaxton, Qld).
• We will answer to your queries
in order:
(1) The frequency is not critical
but if it is too low then the readings
on the µF range may be erratic.
Once you get the unit working,
reduce the value of the .01µF ca-
and cooling sides of the circuit will
be powered all the time which is
highly inefficient. If you wanted to
do heating and cooling, to maintain a
constant temperature for a wide range
in ambient, the circuit would have to
be extended with extra comparators
to switch in the heating or cooling
function.
A Peltier device mounted on a
heatsink could be used to blow cool
air but it would only be slightly cooler
than ambient.
Problem with remote
central locking
In order to add remote central locking to my car, I purchased the UHF
remote control kit, as published in the
January 1993 issue of SILICON CHIP. I
also purchased a Jaycar LR-8835 Power Lock Relay and an LR-8833 Slave
Door actuator.
The problem I have is that when
the transmitter is 30cm or more away
from the receiver, the channel that is
being operated starts bouncing on and
off erratically. This in turn, via the
Power Lock Relay, pulses the actuator
pacitor at pin 2 of IC1a until the
frequency is closer to the nominal
value of 16kHz.
(2) The varying stray capacitance
of different PC boards, especially
if they have a screened overlays
and solder resist can mean that
VR1 may not have sufficient range.
The cure is to increase the 12pF
capacitor on pin 13 of IC1d to 22pF
or 33pF until VR1 can be set close
to centre.
(3) As you have an oscilloscope,
simply clip the probe on pin 11
of IC2a and carry out the set zero
adjustment. The pulse width at pin
11 will get narrower and narrower
until it disappears, then if you keep
adjusting VR1 it will reappear and
get wider. The correct adjustment
is when it just disappears.
in the same direction. With the trans
mitter within 30cm of the receiver, the
actuator operates normally.
When the actuator is removed from
the circuit, the receiver and Power
Lock Relay operate fine, even when
the transmitter is a good distance
away. This happens on the test bench
and when fitted to the car.
I have one channel doing unlock
and the other doing lock. The receiver
is set up for momentary operation. I
have earth coming from the two NO
contacts in the receiver and going
to the Power Lock Relay brown and
white inputs. Some things I’ve already
tried are: filtering the receiver’s 12V
input, supplying power for the receiver from a different source, a new
transmitter battery and even wrapping
the actuator in aluminium tape.
The car already has central locking but the driver’s door only has a
microswitch that operates the other
doors, no actuator. The new actuator
operates the lock mechanism which in
turn operates the microswitch.
I have actually gotten the system to
work using the NC receiver outputs.
Now the Power Lock Relay inputs are
normally at earth but when a button
is pushed, the Rx operates and removes the appropriate earth from the
Power Lock Relay. When the button
is released and the receiver switches
off, the earth is then reapplied to the
Power Lock Relay which drives the
actuator. But I want to get it to work
the way it’s supposed to so I hope
that you will be able to help me. (S.
B., Amberley, Qld).
• Your problem appears to be with
the remote control receiver resetting
as the heavy current drawn by the
door actuators reduc
es the supply
voltage. This can be cured by several means. First, you need to use a
separate supply lead for the actuator
positive supply. The receiver will then
have minimum voltage drop when the
actuators are powered.
Second, the receiver circuit can be
improved to reduce the incidence of
resetting. This involves reducing the
6.8V zener diode dropping resistor
from 1.8kΩ (R4) to 390Ω. This will
maintain the zener voltage even if the
12V supply drops to 9V. You can also
replace the 10µF capacitor C4 with a
100µF 16VW electrolytic to improve
supply rejection.
You may also need to connect a
large value capacitor across the door
Converting a standard
PC power supply
There has been some discussion
this year on using old computer
power supplies as general purpose
bench units but there are many
variables; one that I have hit is that
one power supply would not start
without a decent (15-20W) load on
the 5V line.
One comment that I saw was that
one reader rebuilt the 5V section
using the 12V components to get a
220W power supply at 13.8V (after
adjustment of the output voltage).
That is one hell of a good bench
supply for anyone involved in car
radio, amateur radio, CB or similar
activities.
It would be a good supply for 12V
garden lighting without the risk of
the voltage going up as lights blow.
I have a 100W transformer driving a
string of 8W lights and if more than
actuator solenoid to damp down
transients. Also a reverse connected
diode (1N5404) across the actuator
coil may help.
Loud direction indicators wanted
I need a simple circuit for people
who are hearing impaired, to amplify
a vehicle’s blinker noise, as the “click
click click “ of a normal can under
the dash is too soft to be heard. (J. C.,
via email).
• Why not just wire a buzzer so that
it is powered from both sides of the
traffic indicator switch can via a pair
of diodes? That should do the trick.
DC-DC converter
for military gear
Have you ever designed a 12V to
24V converter? I wish to use some
military equipment in a “civilian” car
for demonstration purposes. Trouble
is, all our communications gear is
designed to run off 24V DC nominal
(28V with the vehicle running). Any
ideas? (I. B., via email).
• One possibility may be to modify
the 2A SLA battery charger (published in the July 1996 issue) so that
it delivers 24V instead of 13.8V. You
three blow then the rest will blow
within 15 minutes!
PC power supplies are available
here in Canberra for $5 each with
one proviso; you have to take the
whole computer! Can you devise
a circuit board and parts list that a
mid-range experimenter could work
from to build such a beast. Tracing
out a switchmode power supply is
beyond me; I know because I have
tried. (B. W., via email).
• We have had a look at the idea of
a circuit to convert a standard PC
supply to something more useful
but the problem is that all these
supplies are different inside, even
though they all tend to use one or
another standard switchmode IC.
The only way we could do it is to
specify a particular switchmode
PC supply and then go from there
although that tends to defeat the
purpose of letting people use any
surplus supply.
would do this by changing the 22kΩ
and 2.2kΩ feedback resistors to 39kΩ
and 1.8kΩ, respectively. You would
also need to add a 4700µF 35VW
capacitor to the output. We estimate
that it should be good for about 1A at
24V. (Note: we have not tried this).
Programmable ignition
for a Landrover
I was reading the June 1999 edition
and I came across the programmable
ignition article. The Lumenition
control module on my Landrover has
just failed and I wondered if it would
be possible to replace it with a PIT
module and adapt the optical pickup
that is already fitted to the vehicle. (N.
W., via email).
• Yes, it is possible. We published a
brief note about using the Lumenition
module in the May 1994 issue.
DC-DC inverter
for car amplifier
I wish to build an amplifier to put in
my car. It needs supply rails of ±37.5V
or ±40V. Do you have a circuit design
for a DC-to-DC converter to give the
required supply rail from a 12V car
battery? (M. N., via email).
• We published a 100W DC-DC ConNovember 1999 91
Display problems
on signal generator
I built the Low Distortion Audio
Signal Generator described in the
February & March 1999 issues of
SILICON CHIP but it has a problem
I can’t explain. When I went to
set up the generator, the oscillator
worked well but the display didn’t.
I eventually found that the 0.18µF
capacitor associated with S2 and
IC1b was earthed and suspected that
it wasn’t meant to be, according to
the circuit diagram.
I cut the track and then the
display worked well, except on
the 10Hz to 100Hz range where it
dropped to 0000 at about 3/4 setting. This range could be made to
work by adjusting VR3 fully counter-clockwise. But in doing this, the
other ranges had a point midway
in their range that dropped back to
0000. I did notice that if I touched
verter for cars in the December 1990
issue and a 600W design in the October & November 1996 issues.
Command control
decoder
I am building the February 1999
version of the Command Control Decoder For Model Railways but I am
having difficulty finding the required
BD433 and BD434 transistors. Any
suggestions? (K. R., via email).
• You can substitute transistors such
as BD675/677/679/681 or BD263
for the BD433 and BD678/680/682
or BD262 for the BD434. These are
readily available from kitset suppliers.
Waiting for turbo timer
defeats purpose
I have just built the turbo timer as
published in the November 1998 issue
and tested it on the bench. It works
fine. I then did a temporary hook-up
to my car. Guess what? You cannot
take the key out of the ignition while
the engine is running, so one has to
sit while the timer runs out.
I am certainly not going to leave
the key in the car while I do my
shopping. Anyone else having the
same problem? Oh, the car is a 1992
92 Silicon Chip
the back of 0.18µF capacitor associated with IC1a, the display worked
perfectly on all ranges.
I have since put a 10MΩ resistor
across this capacitor and it works
fine. I am very happy with the end
result but cannot for the life of me
work out what I have done to cause
the problems mentioned. I checked
all the components at least twice
with the multimeter. Maybe you can
shed some light on this problem?
(A. B., via email).
• With regard to the 0.18µF capacitor being earthed on your PC
board, apparently one of the PC
board manufacturers decided that
a shield track (earthed) should
have been connected to an adjacent
pad on the PC board and so they
changed our original pattern. This
meant that some kits did have a
faulty front panel board. This was
corrected on kits as soon as the error
was discovered.
Nissan Bluebird AWD Turbo. (G. W.,
via email).
• If your turbo timer needs the ignition switch on to run, you have
taken the +12V from a point switched
by the ignition. You need to pick up
+12V from a fuse not switched by the
ignition key.
Jumbo LED clock
problems
I am having many problems with
the Jumbo LED Clock described in
the March 1997 issue. I obtained the
displays from Jaycar and I had to
drill new holes in the board as they
did not line up correctly. The project
did not work and I eventually found
out that the displays had different
connections. I rewired the displays
using separate wires between the two
boards.
I could not find a supplier for the
watch crystal, so I obtained six from
old watches that I had to hand. Checking with my DFM, one crystal oscillated at 16kHz, one didn’t work and
the other four worked at 31.25kHz.
The clock worked but it ran slow,
losing three seconds each minute.
With the oscillator running too low,
I would have thought it would have
run too fast.
Unfortunately though, the published pattern for the front panel
(page 64, March 1999 issue) does
show a thin line, making the connection from the ground track to
the 0.18µF capacitor pad. This is
due to a glitch which sometimes
occurred when the Protel file for
the artwork was imported into our
drafting package, Generic CAD.
The component overlay diagram on
the same page does not exhibit the
glitch. The original artwork sent to
board manufacturers also did not
have the shielded track connected.
The lack of output at the low
frequency end would mean that the
LDR was not receiving sufficient
light to maintain control. This was
probably due to the IR LEDs not providing full light coverage over the
LDR surface. If you are happy with
the result with the 10MΩ resistor
across the 0.18µF capacitor, then
leave the oscillator as is.
Pressing the hour button clocked up
the hours OK and the AM-PM indicator worked. Also the 1-second decimal
points worked. But on first switch
on, it indicated -004, the righthand
number being any value on switch on.
When pressing the minute button,
the number clocked up while the
button was pressed but on release the
numbers all changed to an arbitrary
figure. Adjusting the oscillator trimmer from minimum to maximum only
varied the frequency from 31.35kHz to
31.25kHz and the oscillator stopped
with the trimmer set at exact minimum. I used machined IC sockets for
all the ICs so I can change them easily.
I have an oscilloscope and a DFM. I
used an earth on the PC and a wrist
strap as I thought the ICs might be
static sensitive. (S. F., Yangebup, WA).
• We suspect that the 4526 prescaler
ICs, IC2 & IC3, may be causing the
problems of strange results from the
minute pushbutton and incorrect
timekeeping.
Check that the DP1-DP4 inputs for
IC2 and IC3 are correctly tied to the
ground or positive supply. Erratic behaviour may occur if they are floating.
Also check for shorts between tracks
around these two ICs. You should
compare your PC board pattern with
the published pattern (page 49, March
1997) to check that you have not soldered two pads together.
We are not aware that the pinouts
for the large 7-segment displays are
any different to the ones we used in
the prototype. These pinouts follow
an industry standard.
The exact frequency of operation
for a crystal oscillator cannot reliably
be tested with a probe and frequency
meter. This is because the probe’s
capacitance can load the crystal and
slow down its frequency. Normally,
if you want to reliably measure the
frequency of a crystal oscillator, you
must do it via a buffer stage.
A suitable crystal can be obtained
from Farnell Electronics, phone 1300
361 005. Their catalog number for the
crystal is 569-914.
Sync output for TV
pattern generator
I would like to know if the Colour
TV Pattern Generator described in
June & July 1997 has or can have a
separate sync output as well as the
composite video. I have an application
that requires this. (D. P., -via email).
• The composite sync signal is available at pin 16 of IC10. Since its amplitude is 5V peak-to-peak, you may
need to attenuate it to the required
level for your application.
Notes & Errata
Daytime Running Lights for Cars,
August 1999: a modification to allow
the circuit to be used with cars having
headlight switching in the negative
line is published in Circuit Notebook
this month.
PC Monitor Checker, August 1999:
circuit modifications to give more
ideal scan frequencies are published
in Circuit Notebook this month.
Mailbag: continued
from page 44
charged at about 5A by two 42W Solarex panels. These are now nearing
30 years old but the batteries have
been replaced.
All lights in the home are fluoresents modified to run from 12VDC.
My amateur station (VK4KAL) is
operated from batteries, direct where
possible or by DC/DC converters. A
1500W inverter is on standby, although rarely used. The 486 DX2/66
computer I am using is also running
from 12V DC.
We are now connected to the
grid but only for the deep freezer
and washing machine (not an automatic – these are water wasters in
our dry area). The welder has to be
AC-operated although the frame of
our home was welded using battery
power – 36VDC (we live in white
ant country!).
We use gas for cooking and our hot
water is solar-heated. Where possible, every gadget we use is 12VDC
operated. We don’t have blackouts,
although recently the system in our
area was out for three days due to
3km of mains being blown down in
a freak storm; but our lights were on.
For what it is worth, invest in a
smallish Solarex panel and a 12V
deep cycle battery. I run as a “emergency” an 18W panel charging a deep
cycle marine battery to “fire up” an
FT 747GX which draws 20A on transmit. This also lights my “shack” if
ever needs be. A couple of amateurs
living in Brisbane have similar small
setups running 12V fluoros because
of blackouts.
Don’t use inverters unless absolutely necessary. They waste power
while idling. I throw DC plugpacks
in the rubbish bin. Why shouldn’t I,
with 3kW of DC power at my disposal? We have the best of both worlds.
A. Loveday, Rubyvale, Qld.
DC concept
is worthwhile
I have just read your “Publisher’s
Letter” for October 1999. I must say
that you have touched on a point that
I have been trying to make for quite
some time, much to the amusement
of my friends and colleagues. I believe that there is little to be gained
by having domestic dwellings on the
240VAC mains. Apart from heating,
all appliances could be powered by
low voltage DC, be it 12, 24 or 32
volts. Heating, and by this I mean
cooking, space heating and hot water
systems, can be more efficiently be
handled by gas.
There are quite a few domestic
appliances (eg, TVs, videos, etc) that
are dual voltage and cooling is not a
problem with 12VDC fans, made for
large trucks, on the market. Refrigeration could also be run from 12VDC
because of the relatively new 12V
compressors available and of course,
the large 12V absorption refrigerators have been around for a while.
Air conditioning can again be via
12V compressor or evaporative, as
can all manner of power tools. Even
audio amplifiers can be low voltage
powered; those massive “thumper”
systems in cars are testimony to that.
You did mention some of these in
your article and my knee-jerk reaction was “now someone will listen
to me!” I could go on and on about
this subject but I had better stop now
and say thank you for a timely article.
The amusement mentioned above?
I am a qualified electrician! Maybe a
traitor to my trade?
J. Smith, Middleton, SA.
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.
November 1999 93
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Balgowlah, NSW 2093.
Tel: 02 9949 7417 or 9948 2667.
Fax: 9949 7095; www.avcomm.com.au
Silvertone’s RC Receiver
Still the best little performer available!
$78 for 6 CPUs. All compilers, XASMs
and monitors: $480. 8051/52 Simulator (fast, now incl. 80C320): $78. Try
the C-FLEA Virtual Machine for small
CPUs, build a “C-Stamp”. Demo desk:
FREE. All prices + $5 p&p.
Atmel Flash CPU Programmer:
Handles the 89Cx051, the 89C5x
and 89Sxx series, and the new AVRs
in both DIP and PLCC44. Also does
most 8-pin EEPROMs. Includes socket
for serial ISP cable. $199, $37 tax,
$10 p&p. SOIC adaptors: 20-pin $90,
14-pin $85, 8-pin $80. Credit cards
accepted. GRANTRONICS PTY LTD,
PO Box 275, Wentworthville 2145. Ph
(02) 9896 7150; Fax (02) 9631 1236;
or Internet:
http://www.grantronics.com.au
SOLAR PANELS: 120 watt $995.00,
80 watt $650.00, 60 watt $510.00, 40
watt $395.00 (all with 25 year guarantee). UNBREAKABLE PANELS:
64 watt $550.00, 42 watt $420.00,
32 watt $340.00, 11 watt $190.00, 5
watt $120.00, 1.25 watt $80.00. WIND
Still only $129.50 AM or $149.50 FM.
May be used with most ppm transmitters.
This and many other radio control
products available from:
Silvertone Electronics, PO Box 580,
Riverwood 2210.
Phone/Fax (02) 9533 3517.
www.silvertone.com.au
GENERATORS: 400 watt $950.00.
INVERTERS: sinewave inverters, inverter/chargers, mod. Sinewave inverters,
call with requirements. AUSTRALIA
WIDE DELIVERY (Free on orders over
$500.00). TASMAN ENERGY: (03)
6362 3050 Fax (03) 6362 3054.
SATELLITE TV DIGITAL RX NTSC to
PAL MPEG-2 FTA EPG Encryption CAM
from $399.
www.allthings.com.au
November 1999 95
Silicon Chip Binders
Keep your copies safe, secure and
always available with SILICON CHIP
binders: they’re cheap insurance!
Altronics................................. 36-38
REAL
VALUE
AT
Av-Comm Pty Ltd.........................95
PLUS P
&P
Coffs Harbour Electronics............55
$12.95
Heavy board covers with
2-tone green vinyl covering
Advertising Index
Clarke & Severne........................55
Computronics Corporation..........55
Each binder holds up to 14
issues so that you can include
catalogs
Dick Smith Electronics........... 12-15
SILICON CHIP logo printed
in gold-coloured lettering on
spine & cover
Harbuch Electronics....................54
EMC Technologies.......................55
Instant PCBs................................95
Janteknology Distribution..........IFC
Price: $12.95 plus $5 p&p each
(available Aust. only)
Jaycar .............................. 45-52,95
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.
Kits-R-Us.....................................95
Microgram Computers..............3,55
MicroZed Computers...................55
Premier Batteries.........................11
Printed Electronics...................... 95
HAMMOND ORGAN NOT WORKING:
contact Eric Warren 02 4787 6836 email
elwarren<at>ozemail.com.au to inspect
and make offer.
toria, for sale $70,000 WIWO. Suits
technician. Good return, low rent. Call
BH (03) 9743 7505 PH/FAX. 0411
149897 MOBILE.
Questronix...................................55
PCBS MADE, ONE OR MANY. Low
prices, hobbyists welcome. Sesame
Electronics (02) 9554 9760
sesame<at>internetezy.com.au http://
members.tripod.com/~sesame_elec
WANTED
RobotOz......................................95
KIT ASSEMBLY
ANY KITS assembled/repaired: professional, speedy service. Phone Neville
Walker (07) 3857 2752.
BUSINESS FOR SALE
ELECTRONICS RETAIL/REPAIR
BUSINESS in western suburbs, Vic-
VINTAGE AND CLASSIC hifi/audio,
Leak, Quad, Beam Echo, Rogers,
Marantz, Fisher, Dynaco, Heathkit,
McIntosh, Radford, Pye, Lowther,
Altec, Klipsch, SME, Garrard, Loftin-White amps, etc in any condition.
Radio and audio valves. (02) 6255
2333.
WE PAY UP TO $60 for contributions
to Circuit Notebook. Send your circuit
with a brief description to Silicon Chip
Publications, PO Box 139, Collaroy,
NSW 2097.
HELP SAVE THE NIGHT SKY!
We are losing our heritage of starry night skies. Poor, inefficient
outdoor lighting is causing glare and “light pollution”. This wastes
energy and increases greenhouse gas emissions.
You can help by joining SYDNEY OUTDOOR LIGHTING IMPROVEMENT SOCIETY (SOLIS). SOLIS aims to educate and inform about
quality outdoor lighting and its benefits. We also lobby councils, government and other bodies to promote good lighting practice. SOLIS meetings
are held third Monday night of each month at Sydney Observatory.
Individual membership is $20 pa. Donations are also welcome. Cheques payable
to “SOLIS c/- NSAS”, PO Box 214, West Ryde 2114.
Email: tpeters<at>pip.elm.mq.edu.au
96 Silicon Chip
Resurrection Radio......................61
Robotic Education Products........55
R.T.N............................................55
SC Binders..................................11
SC Computer Omnibus...........OBC
SC EFI Tech Special..................IBC
Silicon Chip Bookshop........... 24-25
Silicon Chip Subscriptions...........89
Silvertone Electronics..................95
Smart Fastchargers.....................59
Solar Flair/Ecowatch....................94
Telelink Communications.............55
Truscott’s Electronic World...........59
Vision Beyond 2020.......................9
Zoom EFI Special........................11
_____________________________
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.
Own an EFI car?
Want to get the
best from it?
Youll find all you
need to know in
this publication
November 1999 97
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