This is only a preview of the April 2003 issue of Silicon Chip. You can view 29 of the 96 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Items relevant to "Video-Audio Booster For Home Theatre Systems":
Items relevant to "A Highly-Flexible Keypad Alarm":
Items relevant to "Telephone Dialler For Burglar Alarms":
Articles in this series:
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10A Speed
Controller
I constructed the 240VAC 10A
Speed Controller from the November 1997 issue and it works well. I
initially tested it by dimming a light
and later with an angle grinder.
Everything is fine apart from the
fact that there is around 39- 40V
AC between the speed controller’s
diecast case and the alloy blade
cover of the angle grinder. I got the
same result with a router. Is this
normal?
The angle grinder is double-insulated and does not have an earth
connection. The case for the speed
controller is fully earthed correctly,
as described in the instructions.
I haven’t been game enough to
touch it – I am not sure whether or
make sure the gap between the LEDs
and infrared diodes is at a minimum.
Kill switch for
rev limiter
I have built a rev limiter from the
April 1999 issue but I also need to
have a switch which will kill the
engine completely. The car is used
for motor sport where a kill switch is
required by the regulations. It seems
that this can be incorporated in the
ignition switcher circuit in the following two ways.
(1) Installing a second capacitor at
C1 which can be switched in to kill a
very high number of sparks, causing
the engine to stall; or
(2) Install a switch between terminals 8 and 3 of IC1. When the switch is
closed, transistor Q3 will be turned on
to kill all sparks. Solution 2 would be
not the multimeter is misreading
something?
Secondly, are the motors in vertical press (Ryobi) drills brush type?
(A. P., via email).
• The reading you are measuring
will be due to the fact that the power
tools are not earthed and that there
is some capacitance between the
metal parts and the internal wiring.
The meter will read a voltage due to
its high input impedance.
Try connecting a 10kΩ resistor
between the multimeter terminals
and do the measurement again.
You should get a very low reading.
Your speed controller is probably
working completely normally.
Drill presses usually have in
duction motors, which are not
suit
able for use with this speed
controller.
easier to install. What do you recom
mend? (D. M., via email).
• Solution 2 would be best as it completely shuts down the ignition.
Low-cost
oscilloscope probe
I am interested in building a sound
card adapter kit from Electronics
Australia, on sale at one of the kitset
suppliers for $30. However, I reckon I
need oscilloscope probes so that I can
use the adapter, right?
When I checked prices of probes at
Jaycar or Dick Smith Electronics, they
were around $44 each, much more
than the price of the kit. That is too
much for a student budget. Can we
make one probe on our own? (D. B.,
via email).
• We featured a low-cost, low-capacitance scope probe in the August 1989
edition of SILICON CHIP. It utilises a
short length of coax cable, a resistor,
trimmer capacitor and a few other bits
& pieces you’d probably find in your
junk box.
Door alarm uses electret microphone
I have searched all the indexes,
including those on your website (excellent site, by the way) and I cannot
find what I seek. It is an alarm using
a microphone as a sensor. It does not
operate on sound but on changing
air pressure as a door or window is
opened. I am certain it was in SILICON
CHIP and I have every copy from issue
number one but I just can’t find it. Can
you help? (R. C., via email).
• The article appeared in the July
1995 issue. It used an electret microphone as a pressure sensor. We can
supply the issue for $8.80 including
postage.
Notes & Errata
AVR ISP Serial Programmer, October
2002: there is an error on the circuit
on page 75. Pins 1 & 4 have been
swapped on CON3. The PC board is
correct.
12V SLA Battery Float Charger, March
2003: when this charger is used with
the PortaPAL (February and March
2003), the 10µF capacitor connecting
to the adjust terminal of REG1 should
be omitted.
Simple VHF FM/AM Receiver, December 2002: a short track is missing
from the PC board, as shown on pages
88 & 90. The track should connect the
junction of the two 3.3kΩ resistors
and L1 with the adjacent end of the
22kΩ resistor. The corrected PC board
pattern can be downloaded from our
SC
website.
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.
92 Silicon Chip
www.siliconchip.com.au
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