A quick update for anyone reading this in future.
Bob swapped the black FTDI lead ‘ground’ wire from Trig pin 6 (where he had originally put it) to pin 4 while I went flying, but on my return he reported that he was still getting no position data on the Trig. He suspected the GPS, but I pointed out that the PilotAware was transmitting, which it wouldn’t do if it didn’t have a solid GPS fix.
Checking for a ‘flashing red’ on the chip in the FTDI lead USB plug (which was in USB Port 2), we could only see a solid red light between the FTDI and the GPS board in Port 1, which I suspected was the GPS power LED. To confirm this, I temporarily removed the Rosetta GPS and replaced it with a remote GPS mouse in Port 3 (which left the FTDI chip exposed). After a few seconds, the mouse GPS got a fix and the red LED in the FTDI chip started flashing, but still no position showing on the Trig.
Next step, check the settings on both units, which showed up the problem - PilotAware USB Port 2 correctly configured to Transponder Trig and 4800 Baud, whereas the TT21 was configured to 9600 Baud. Reconfigured the Transponder to 4800 Baud - problem solved
(Alternatively I could have reconfigured the PilotAware Port to 9600 Baud - either will work as long as both are set to the same value).
A quick check showed position data now on the transponder, so swapped back to the original GPS and Bob took it for a test flight. I got a screengrab from my own PAW showing everything now OK, which Bob will need for his ADSB Out MOD. Result !!!
Regards
Peter