To run a Ham Rig remotely, the FCC requires the ability to shutdown a “runaway” transmitter after no more than 3 minutes of activity. There are several ways to do this. My plan is to use a small Arduino computer board to handle the timeout control function. Here is a basic diagram of the timeout circuit:

The Arduino will maintain a “watchdog timer” which will be started any time a transmission begins. The watchdog counts down until it either expires (at the three minute duration point), or it is reset because the transmission ends. If it expires, an automotive relay is deactivated, removing the 12 VDC power from the rig. After some timeout period, an attempt will be made to reset the power.

An LED is used to provide a warning to a local operator when it is getting close to time to disconnect the power. This is mainly for test purposes. An optional buzzer output is also provided for the same reason.