"You can always add it to the TR5."
Except I claimed that spare pin for a dedicated PTT ground return! Both
ground pins (audio shield + PTT) bond immediately to the chassis at the mic
connector. Instead, I added my resistor in front of the TR5's preamp
transistor.
Next up, and hopefully the last TR5 mod after several, I'm adding fan
control. The same custom microcontroller that sequences QSK and develops a
raised-cosine voltage into the Tx mixer will do double-duty since I have a
couple spare I/O pins.
In a nutshell, any time the +10T voltage is active the fan starts. When
+10T drops to zero for 10 seconds after the last activation, the fan stops.
This prevents undue fan cycling in the T/R sequence. The time delay is
adjustable in the controller code.
Paul, W9AC
Paul Christensen