Is it possible to use the 6-pin USB port (aka HMI port) to export telemetry? My TELEM 1, TELEM 2, GPS 1 and GPS 2 ports are all being used by other devices, so the 6-pin USB port is the only other option.
The TELEM pin functions are listed below
and here are the USB pin functions
ardupilot does send telemetry over USB (SR0) but your problem will be to convert that USB back into something you can use. If you can convert that USB back to serial (and it’s USB target, not USB host), you’ll be ok.
Maybe a microcontroller to act as a USB host, read the USB serial data and output it back as regular serial?