DRA-Pi-Zero Headers and Jumpers:


RX  - Position this jumper to select the RX Baud Rate - 1200 or 9600
1200 is Default.

NOTE - The RX jumper must be in the "1200" position for the TRRS jack to provide receive audio
to the soundcard chip.

TX  - Position this jumper to select the TX Audio Channel - - Left or Right
Right is Default

R12 (the larger pot) adjusts the receive audio level.
R14 (the smaller pot) adjusts the transmit audio level.
Rotation is logical - CCW is lower - CW is higher.