John,
Thank you very much for the very thorough reply.? Mostly (!) very encouraging, as I think this will save me a lot of thinking and worrying about ground loops in my RX audio and transformers and high-impedance buffers and the list goes on... I will try just putting the Teensy/Audio Board combo into the receive audio path, and call it good (my thought is, that I should already have sufficient DC blocking in the form of the Audio Board's built-in blocking capacitors on the Line-In/Out lines, from what I can see on the schematic).? Not sure if I need any other resistors for impedance matching or what not... I may just hook it up between the preamp and volume control, and cross my fingers...
I do have a decently beefy heatsink on my Raduino 5v regulator (had to bend the regulator IC "outboard", and then also bend a couple of the heatsink fins, to deconflict from the coils on the uBITX board).? But, I will try to implement a separate 5V supply for the Teensy, and add some additional filtering.?
I'll have to think about the D0/D1 thing with the TTL logic... so the way I read your description, D0/D1 and the USB are really not "interchangeable", rather they just happen to be linked to each other?? Is that the case?? I know that on Teensy, Serial and USB Serial are separate, but I thought that on Nano they are the same. Are you suggesting a pulldown resistor on D1?
Thanks,
Rob
