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Notes & Errata
Burglar alarm extensions, June
1999: on the circuit on page 83,
IC5a adjacent to IC4a should be labelled IC5c. IC6b’s output should
be pin 8. The “ZONE 3” label on
the line to pin 5 of IC8 should
actually be on the line to pin 7 of
IC8. In addition, the output of IC8
driving the Zone 1 relay should
be pin 12.
The second last paragraph of
page 84 should read “Pins 4, 10
and 12 of IC3 are connected to the
roller door switches”.
Audio-Video Transmitter, July
1999: on the overlay diagram on
page 38, the .001µF capacitor
shown connecting pin 3 of IC1
quite a lot of standards conversion
required in that the horizontal and
vertical sweep rates for PAL are quite
a lot slower than typical VGA. To do
the standards conversion, the circuit
would require a line or frame store.
If you need one, the best approach
would be to buy it. Two of our advertisers, Microgram Computers and
Namlea Data Systems, should be able
to help you.
Faulty sensor
on speed alarm
Back in your December 1997 issue
you published a project for a car speed
alarm. I am having trouble with this
kit. I cannot get the sender to register
any speed. It will show a speed when I
switch it on and it will show different
speeds when the buttons are pushed
but it will not show any difference
in speeds when the sensor is put into
operation. Also, is there any way that
I can make the alarm sound louder
to ground should be .01µF. The
circuit diagram is correct.
Daytime Lights for Cars, August
1999: on the overlay diagram on
page 33, the 470Ω and 1kΩ resistors shown below diode D3 should
be 4.7kΩ and 470Ω respectively.
The circuit is correct.
Line Dancer Robot, May 1999: in
the circuit diagram on page 18,
the 4.7kΩ collector resistor for Q1
should be labelled R5 instead of
R3, while the 1.5MΩ base resistor
for Q1 should be labelled R6 not
R5. On the PC overlay diagram on
page 19, the 470Ω resistor below
R14 (270Ω) can be replaced with a
link (it is in series with R5).
as I am a bit hard of hearing? (K. M.,
North Booval, Qld).
• We are not sure that you do have a
problem with your speed alarm. The
display section of the project is operating correctly since it does display
the alarm speed and can be changed
using the buttons. It will not and is
not supposed to show the difference
in speed between the set and actual
speeds as the car is driven.
However, if you are saying that
the alarm does not sound when the
preset speed is exceeded, then you
may have a problem with the sensor
circuit. Check that the magnets and
sender are located close together
when they pass each other. You may
find that the sensor operates correctly
if the magnet is flipped over so the
opposite pole is facing out. Check all
wiring from the Hall Effect board to
the main PC board.
The output level of the speed alarm
can be varied by adjusting VR2. This
alters the frequency driving the piezo
transducer and if adjusted carefully
you will find a position where the
sound is loudest. This is the resonance point for the transducer.
An alternative method of increasing the sound level is to use a powered
piezo transducer which will operate
at 5V. This can be driven between
the collector of transistor Q3 and 0V.
Note that for this connection you will
always have the siren sounding above
the alarm speed setting. A suitable
siren could be the Dick Smith Cat
L-7024 or Jaycar Cat AB-3462.
Transistor brands for
class-A amplifier
How important to the final performance of the Class-A amplifier July &
August 1998) is it to use the specified
Philips/Motorola BC547s, 557s, 327s
and 337s? I look forward to building
it. (S. H., via email).
• In a high performance amplifier
such as this, it really is important to
go for the “brand-name” transistors.
Other transistors will certainly work
but there is no guarantee that the
finished amplifier will have really
low distortion.
SLA charging
information wanted
In an issue of SILICON CHIP I read an
article on an SLA charger. That article
had quite a bit of information on SLA
batteries. I am chasing after information on charging techniques and more
importantly discharge curves for SLA
batteries. Can you pinpoint the issue
please? (A. H., via email).
• It seems likely that the article you
are referring to was one featuring the
UC3906 SLA battery charger IC, published in the March 1990 issue. We
can supply this issue for $7 including
SC
postage.
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.
September 1999 93
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