4. Power, radio, RS-485 connector
DB-9 male connector is used for supply voltage input, audio in, audio out, PTT,
and RS-485 bus for telemetry.
DB9 connector pins description:
•
Pin 1 – PTT output, open collector, if the external PTT output is selected in
device configuration, this pin is shorted to ground while broadcasting,
•
Pin 2 – GND,
•
Pin 3 – GND,
•
Pin 4 – APRS audio input from radio to PLXDigi,
•
Pin 5 – GND,
•
Pin 6 – RS-485 A+ positive differential input/output,
•
Pin 7 – RS-485 B- negative differential input/output,
•
Pin 8 – APRS audio output from the device to the microphone input of the radio.
This output also acts as a PTT by shorting pin to ground through a 2k2 resistor - an
option for portable radios that do not have a separate PTT input (selectable in
configuration software, 2k2 resistor is built-in),
•
Pin 9 – supply voltage input.
For handheld radios which use 2k2 resistor on microphone input line you don't need to
use any external resistor or external PTT (pin 6) output. Connect pins: 2 (audio output),
4 (audio input), 5 (ground) and set “PTT:” to “2k2 resistor” in device configuration. 2k2
resistor is located inside of the device.
If you are going to use both WXTelemetry and WXBits external telemetry modules, you
should connect them in a chained style: A+ and B- pair go from PLXDigi to first telemetry
module, and then from first telemetry module to the second one. From a schematic
point of view, both modules must be connected in parallel (A+ from PLXDigi goes to A+ of
the first module, and then to A+ of the second, similarly with B-). Never connect A+ to
B-.
7
