As part of our geocaching activity we have established several geocaches. Since beginning I thought to create a cache that can present some aspects of HAM hobby to other geocachers.

This project is the result. Idea is simple - to use the PMR radio to get the coordinates of the box. Of course the coordinates are sent by morse code. So the challenge is to manage the radio and to be able to decode CW message. Design is quite simple - I used an old PMR transceiver in the beacon, the reset is done in software of Atmel AtTiny13 MCU.
The software does following:
  • Monitor the squelch signal to identify presence of carrier signal on frequency
  • Detect a pattern indicating activation signal (two 1sec carriers separated by 1 sec)
  • After activation it activates PTT and sends a CW message
  • After message there is a 30sec dead time, during that no repeated activaton is possible (not to allow channel congestion)
  • I suppose pictures are better than other explanation. Or - check for GC8Q6Q2 on geocaching.com.

    Block diagram


    Source code

    Transceiver circuit diagram

    Controller circuit diagram

    73 OK1DX