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PTT Switch Box
 This PTT switch box was built as an add on accessory for the BM-800 PC Microphone
project so it can be paired with a ham radio transceiver. As it's basically just a connection hub incorporating a 'Push To Talk'
switch, the information shown here mainly relates to the cables used and their pinouts.
 PTT switch box schematic (looking at rear of DIN sockets).
The switch box
houses three 5 pin DIN sockets. The two labelled MIC and PC (input from the microphone and output to the PC) are
interchangable and the one labelled RIG feeds off to a radio transceiver. A 10uF
capacitor was added to block any DC voltage on the mic input of
the radio (there to power electret mic capsules) and is not used for
the PC output. The sockets are wired so that no damage will occur if
the plugs are inserted in the wrong order. The two resistors form a
potential divider to reduce
the audio level to the rig and also act as a kind of isolator so
that
the radio's low impedance mic input doesn't drag down the audio feed
to the PC. This simple arrangement works well as the radio
requires less signal than the
PC.
 Pinouts for PTT switch box to microphone.
 Pinouts for PTT switch box to PC line input / USB 5V
  Pinouts for PTT switch box to AnyTone AT-778UV radio
 PC interface for easy access to line input and USB 5V
 Rear view of the PTT switch box.
To avoid any strange
hums and noises caused by stray pickup of transmitted RF getting into
the audio circuits, it's best to use good quality screened cable and
connectors. I recommend Van Damme Tour Grade Classic XKE microphone cable and Rean NYS322 5 pin DIN plugs.
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