wiki/ RecoveryNode2mInterface

PC to 2m Transceiver Interface Hardware

Here, in all of it's glory, is a serial (COM) port to 2m packet radio interface which injects DTMF tones into the 1200 bps packet port.

Serial Link

9600 bps, 8bits, no parity, 1 stop bit ("8N1"). You can tell if your serial port is sending characters since the amber 'COM_LED' will be blinking if the interface is receiving characters. The board is wired up correctly for a DTE so it requires only a standard DB9 serial cable and does NOT require a null modem or anything fancy.


ASCII Character Behavior
0,1,2,3,4,5,6,7,8,9,a,b,c,d,*,# DTMF generator plays appropriate DTMF tone and character is echoed back
o Turns off the tone output of the DTMF generator and character is echoed back
h Keys up the transmitter (for 'high') (red LED turns on) and character is echoed back
l keys down the transmitter (for 'low') (red LED turns off) and character is echoed back
Any other key Unknown command: 'x' is echoed back over the serial line

So to send an old LV`b command, like '#*0', you'd send 'h#o*o0ol': this translates as "key up the radio, play a #, turn off the tone, play a *, turn off the tone, play a 0, turn off the tone, key down the transmitter".

Note that there's NO timing done in the interface AT ALL; that's the responsibility of the PC. So the reality is there'd be a sleep (or some time delay to be chosen later) after both playing a tone and after turning it off. I envision three different kinds of sleep, which should be customizable:

  1. sleep time after key up (time necessary for the radio to key up. Best guess: 750ms)
  2. sleep time after a tone on command (time the tone is played. Best guess: 250ms)
  3. sleep time after tone off command (time between tones. Best guess: 100ms)


There are thre LEDs on the board:

LED Name Color Description
Power Green Duh.
COM_LED Amber Flashes when a character is received on the serial line
TX_ON_LED Red On when radio is keyed up

Schematics and Firmware

... are attached below.