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PTT Switch Box
 After finishing the BM-800
PC microphone project, I thought it would be useful to share its output with my portable ham radio transceiver without having to
swap
any plugs over. To achieve this, an interface is required that incorporates a PTT switch. As the mic has
quite a high output level, the easiest way to divide the signal is to
use a couple of 4K7 resistors as a passive splitter. There will be some
attenuation but nothing that can't be compensated for in the sound
settings.
The resistors are part of a separate cable assembly
and plastic enclosure which houses a 3.5mm jack socket for the mic
input and feeds out to the PC and radio via two 3.5mm jack cables. An
extruded
aluminium enclosure was used for the main PTT switch box.
 The switch box consists of a 3.5mm mono jack socket for the mic
input, a 5 pin DIN socket to connect to the radio and of course a PTT
switch. Actually,
there are two PTT switches, one momentary (for quick overs) and one
latching (for those long rag chews!), coloured green and red
respectively.
 The schematic above shows the cable used for feeding microphone audio to both PC and
radio using a simple resistive splitter.
A 10uF capacitor was added in line with the feed to the radio to block
any DC present on its microphone input (normally used to power electret
mic capsules).
 The schematic above shows the cable used for connecting a Baofeng or similar type radio. The
tip of the 2.5mm section is removed to stop it from
activating the switch contacts that cut off the internal speaker of the
radio.
PLEASE NOTE: THIS IS AN EVOLVING PROJECT AND IS LIABLE TO BE UPDATED WITHOUT PRIOR NOTICE
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