Build an Auto-Keyer for HAM Radio "Fox Hunting"
"Fox Hunting" is a popular activity for amateur radio (HAM radio) enthusiasts - which involves hiding a transmitter somewhere out-of-the-way, and then several "hunters" working to find the transmitter using their own direction-finding equipment.
In order to create a simple radio "fox", Nelson Farrier has used an Arduino board and simple circuitry to control an inexpensive 2M handheld radio. The Arduino connects to the radio's TRRS socket and not only opens and closes the transmit circuit, but also creates a tone to transmit.
Then it's a simple matter of programming the Arduino to transmit a beep, Morse code or other signal for the hunters to recognise. A quick demonstration is shown in the video below:
Kudos to Nelson for an interesting project and also spreading the news about how interesting amateur radio can be. You can learn more from the project page.