Timer activated by squelch on AM receiver...

Thread Starter


Joined Nov 29, 2005
Cannot read chinese for the linked receiver LEDs. Can anyone ?

Am after energizing a circuit for 5 minutes triggered by signal activity/presence at a particular channel on ~119MHz. Simple AM receiver, simple relay or mosfet to deliver power.
A timer IC can take care of the duration; using an existing receiver would work by tapping its LEDs when squelch opens, like :

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Joined Mar 30, 2018
Here is a circuit from my ‘555 timer-cookbook’ that may work. The timer is triggered by the input going low – you may need to invert the voltage signal from the LED to cause it to trigger.
It might be possible to trigger the timer based on the received audio signal if of sufficient volume.

You will need to select the values of Rt and Ct to give the required time period.

Timer circuit.jpg
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