Cockpit Audio wiring (hyjacked from "gear warning")

Eric Greenwell wrote in
:

wrote:
If cutting the vario when the mic is keyed is the objective, could
the PTT be wired to cause a relay to open the vario speaker circuit?
Then the technique could be used with any radio?

Sure! I'd suggest using a small DPDT ("double pole, double throw")
relay (check Radio Shack) behind the panel. One set of contacts would
key the radio; the other set of contacts would open the lead to the
vario speaker.

The coil would be driven by the PTT switch. A 12 volt coil would work
as long as it closes with 10 volts or less, because you don't want the
radio to stop working just because you can't key it. If you are
concerned about this, you could mount a PTT switch on the panel that
is in parallel with the contacts to the radio, for use if the relay
fails. You might have to use a relay with a lower voltage coil and use
a resistor in series with it, or carefully adjust the metal tab
holding the contact spring.

A small diode should be placed across the coil to protect the PTT
contacts. Connect the diode so current does not flow through it when
the PTT is keyed; i.e., the band on the diode body should connect to
the positive side of the coil.

Undoubtedly, your club has a member that can assist you, if needed.


You could also use a DPDT PTT switch on the stick to control both
functions. A SPST PTT switch with both NO and NC contacts would probably
do the job, too. This would eliminate the relay and diode and the extra
complication and current draw, reducing potential failure points at the
expense of routing more wires to the PTT. KISS. :-)
-Bob Korves