The most boring part of fox hunts (transmitter hunts) is always having to transmit at pre-determined intervals.  This little project keys a radio at a pre-defined interval and plays a recorded message.  This helps meet the requirement of required audio transmissions during a fox hunt.  You can still use another radio on the fox frequency to give hints, blabble, sing songs, etc.

Click on the picture for a larger view.

GBPPR AutoFox Schematic  (55k PNG)  All parts, except the 74LS74, are available from Radio Shack.

  Outside view.  It is built into an old MMDS downconverter case.

  Internal view.  The large IC is an ISD1000A, the IC above that is the 74LS74 and the little 8-pin IC is the 555 timer.

  Closer view.  The top output is the relay for PTT key, below that is line audio input and finally the microphone input.