This is only a preview of the July 1994 issue of Silicon Chip. You can view 30 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. Articles in this series:
Items relevant to "Build A 4-Bay Bow-Tie UHF Antenna":
Items relevant to "The PreChamp 2-Transistor Preamplifier":
Items relevant to "Steam Train Whistle & Diesel Horn Simulator":
Items relevant to "Build A Portable 6V SLA Battery Charger":
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Woofer Stopper
has stopped
I have assembled the Woofer
Stopper kit and it worked fine for
one day but it was accidentally left
on overnight and hasn’t worked
since. I have replaced every component except the ICs and I was
hoping you could shed some light
on what is wrong with it. I am
getting 12V out of the tweeter terminal but it still doesn’t work. (D.
F., Bradbury, NSW).
• If you don’t have test equipment
to verify that each stage is working
then you will need to test the unit
audibly. To do that, you must connect pin 1 of IC2 to pin 7 of IC1
(instead of pin 9) as described on
page 29 of the article in the May
1993 issue. This makes the circuit
capacitors to the Active and Neutral
as filters plus tried different relays. Is
my answer an opto-coupler plus Triac
combination? I usually have no problems in assembly or troubleshooting
kits but have no idea about inductive
loads or RF noise on mains or DC. (D.
D., Morley, WA).
• The problem about switching any
sort of incandescent lamp is that there
are very large surge currents involved.
These currents can be as much as 15
times the normal rated currents of the
lamps and must be completely isolated
from the relay board and the circuitry
of the Southern Cross computer.
It is also likely that the surge currents are causing momentary dips in
the supply voltage to your computer
and causing it to crash. The cure is
to use a much better regulated power
supply which will not be af
fected
by momentary drops in the mains
voltage.
We would not recommend connecting capacitors of the size you mention
to the Active and Neutral lines.
The Champ
goes mobile
I have built the “CHAMP” amplifier
(SILICON CHIP, February 1994) and
find it works exceptionally well with
my mobile phone, driving a small 8Ω
extension speaker. This set up has
only been used as a bench test and I
92 Silicon Chip
work at a frequency of 2kHz.
You should not have 12V DC
across the tweeter terminals.
There should be 0V DC and about
10VAC (at 2kHz) present across the
tweeter. You should also be able
to measure about 6V DC between
both sides of the tweeter and the
0V line.
If the circuit fails these tests,
check that +5V is present at the
output of the 78L05 regulator and
at pins 14 or 16 of the ICs. The
output of each respective IC in
the frequency divider should sit at
somewhere between 0 and 5V DC.
For example, pin 2 of IC5a should
be at about +2.5V.
Naturally, you should also
carefully check the back of the
PC board for bad or broken solder
connections.
would like your comments regarding
the suitability of this idea for an in-car
installation and hence a way of providing a clean regulated 12V supply.
I also have a question for the Serviceman. I have been trying to locate a
number of ICs for a Commander 48cm
colour TV, model CHT-9102, for quite
some time without success. I hope you
can help.
Without a circuit diagram I cannot
be sure what these ICs do, however
they are both located on the circuit
board for channel programming and
frequency lock control. Any help
would be appreciated. (B. G., Deception Bay, Qld).
• There is no need to run your CHAMP
from a regulated 12V supply as it will
quite happily run up to +16V with an
8Ω load – see Fig.3 on page 47 of the
February 1994 article. However, it
would be a good idea to protect it from
spikes and transients by connecting a
16V 1W zener diode across the supply
rail, fed by a 10Ω 0.5W resistor from
the 12V battery.
We are unable to help you with circuit information for your TV set. You
will need to approach the distributor
direct.
Using the voice
recorder in loop mode
I wish to use the ISD2590P voice
recorder in continuous loop mode.
Your data article in the February 1994
issue adequately describes how this
may be done. Is it possible to connect
a higher quality microphone to the
device? What additional circui
try
would be required if the device were
to be connected to the line out level
connection of, say, a CD or tape deck?
I assume that the ISD2545 with its
higher sampling rate would produce
better output sound quality. Who
supplies this range of devices in
Australia?
Your assistance in these matters
would be much appreciated. Congratulations on a magazine of consistently high quality. (A. C., Woodford,
NSW).
• Since this device produces voice
quality only, it is not really worth
using a better microphone and this
comment would still apply to the
ISD2545. If you did want to use a
dynamic microphone, you would
omit the 2.2kΩ and 10kΩ resistors
and the 10µF capacitor associated
with the electret bias network. The
microphone signal would then be
fed in via the existing 0.22µF input
capacitor to pin 17.
If you want to connect a CD player
or other line out source, you will need
an attenuator to bring the signal down
to a few millivolts. We suggest a 50:1
attenuator consisting of 47kΩ and 1kΩ
resistors.
The ISD range is distributed by R&D
Electronics. Their phone number is
(02) 638 0077.
Notes & Errata
12-240VAC 200W Inverter; February
1994: Transistor Q16 on the circuit
diagram (Fig.4) is incorrectly labelled
as a BC338; it should be a BC328. In addition, the transistor marked Q12 near
Q13 (Fig.4) should be designated Q14.
On the overlay diagram (Fig.5), transistors Q13 and Q14 are transposed,
while the .047µF capacitor near T2
should be a .0047µF capacitor to agree
with the circuit. The parts list should
also show a .0047µF MKT capacitor
instead of a .047µF capacitor.
Fast Charger for Nicad Batteries; May
1994: The circuit (Fig.2) shows a 680Ω
current limiting resistor for LED 1.
This should be changed to 470Ω to
agree with the parts layout diagram
(Fig.3). The parts list should also be
SC
altered.
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