Kind of ridiculous to put an relay in my device just to swap the TX/RX wires from the DUE to an external USB-TTL/FTDI Adapter, but I guess this is exactly whats going to happen
Could I tristate the Serial Pins on the DUE to disconnect and have the TX/RX from the FTDI connected constantly ? I guess this won't work as long as the FTDI Chip is powered or it might not work at all and block the lines constantly
Thanks for your answer. So there is no need for galvanic isolation?
The TX/RX logic on the Nextion is 3.3V though and this is still within limits for 5V logic so it doesn't matter.
The project is not "done" when it gets deployed also I think its much faster to upload directly via USB-TTL and I don't like the SD card/card readers hassle.