OK, made an improvement. I was hell-bent on using the GPIO pins, but I had the cart in front of the horse, as they can only handle 3.3v, so they cannot do a Mega or other 5v interfaces... I decided to use the CH340 plugged into the Pi ZeroW (using the special adapter cable for the Pi ZeroW from adafruit) this brings it down to two commands:
sudo apt install screen
sudo screen /dev/ttyUSB0 115200
Now, just a jumper change and should work on a Mega.... and it does, using TX0(1),RX0(0), Gnd
To think I wasted over 8 hours learning about the Pi UART quirks... time for a beer
*note - I tried using the blue wire that was connected to the SonOff 5V to power the Pi ZeroW, and it did, but do not think it was reliable enough for logging...
next up, making it log to a file and start on boot, possibly have it put the interface into debug mode?
sudo apt install screen
sudo screen /dev/ttyUSB0 115200
Now, just a jumper change and should work on a Mega.... and it does, using TX0(1),RX0(0), Gnd
To think I wasted over 8 hours learning about the Pi UART quirks... time for a beer
*note - I tried using the blue wire that was connected to the SonOff 5V to power the Pi ZeroW, and it did, but do not think it was reliable enough for logging...
next up, making it log to a file and start on boot, possibly have it put the interface into debug mode?