How can I make a transmitter time-out timer?

 I am a ham, and would like to make a circuit that will alert me when my transmission has gone for about 2 minutes and 45 seconds, so that I can reset before the repeater's timeout does. I should be able to get the button press from my headset easily. How can I build a circuit like this that will start when I press the ptt and reset when I release?

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jeff-o7 years ago
A cheap microcontroller should do the job well, with a minimal parts count and more than adequate accuracy.  An attiny13 (8-pin DIP) should be all you need.
For just a few bucks, you can buy a cheap egg timer or stopwatch that could be used for this purpose. It should be easy enough to replace the onboard switches with remote buttons if you need to.
Jayefuu7 years ago
Add to Kelseymh's google search the terms "555 monostable circuit" and you should find plenty of results.
A 555 timer for very long delays is VERY hard to make stable.

kelseymh7 years ago
You have the answer in your keywords.  Try typing "timer circuit" into Google, and choose the completion "timer circuit schematic".  That should give you dozens of solutions, ranging from simple to overly complex :-/