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90 NUTS & VOLTS November 2005
I have a small problem trying to figure out how to make an A & B switch that
can be connected to two computers.
I want my 5 & 1 speakers to be
shared by both computers without having
to disconnect them. For instance, when I
want to hear audio from computer A, simply switch to A, etc.
Can someone provide a schematic
that I could build from?
#11051 ■F. R. Lazzu, via Internet
I have a Proview Technology color-monitor model 986 N. It is so well made, I
hate to throw it away. To repair it I need
two ICs — TDA 9536 video amplifier and
TDA 9210 video pre-amp. NTE does not
show substitutes. I have found two
places that have these chips, but they
have $100 minimum orders. Does anyone
know where I could get these chips at a
#11052 ■ Harold Eddy, Dixon, IL
an LF356. Drive a small audio transformer
with the op-amp output to provide some-
thing like an eight ohm output to feed a
twisted pair feedline. At the clock, use
another transformer and connect it to an
added winding on the original clock
antenna rod. This would allow placing the
antenna in correct orientation, as well as
allow selection of a better antenna loca-
tion. With the carrier at 60 kHz, it would
seem that audio components could be
used. I've checked the transformer — a
RadioShack 273-1380 (1K ohm to 8 ohm)
— and it seems useful at 60 kHz. My
question is, will something like this work,
or is there something better? Thanks for
any help or ideas.
#11053 ■ Don Pomeroy, via Internet
Does anyone have a simple circuit to
test capacitors in circuit?
#11054 ■ Harold Eddy, Dixon, IL
I'm trying to improve WWVB reception here in Southern New Hampshire.
The problem seems to be that the internal
antenna (tuned ferrite rod) in the clock
can't be oriented properly where I want
the clock located. I'm thinking along the
lines of a larger, 0.5 X 7. 5 inches, tuned
ferrite rod feeding a FET op-amp, maybe
I’m looking for a way to temporarily
turn off an aquarium water pump during
the feeding of my fish. I do this manually
now by pulling the plug, but usually forget
to plug the pump back in after feeding.
I need a circuit where the AC water
pump (rated at 120VAC@40W) can turn off
for about 10 minutes, then turn back on
again automatically. Ideally, I’d like a
momentary switch that when pushed,
would turn the pump off for about 10 minutes. Accuracy is not critical. I was think-