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Sound Relay Circuit

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Suraj143

Active Member
Hi all I need a simple circuit to latch a relay when there is only sound available.
& when there's no sound the relay will off.

I'm taking sound signal from a PA amplifier speaker output.

Thanks
 
How many watts is this PA amplifier? What is the speaker impedance? You have to determine a volume level to trigger the relay. Above zero is not an option due to noise/hum/etc.
 
Hi I'm going to use this circuit is it ok?The monstable time delay cct will keep the relay latch longer time.
 

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  • Sound RL.JPG
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The 100VAC output from the amplifier might destroy the emitter-base diode of the transistor when the peak of the signal goes 140V negative.

The transistor will be turned on only for the loudest signals from the amplifier.
 
The 100VAC output from the amplifier might destroy the emitter-base diode of the transistor when the peak of the signal goes 140V negative.

The transistor will be turned on only for the loudest signals from the amplifier.

Hi audioguru thanks for your input so what do I have to do?
 
Hi audioguru thanks for your input so what do I have to do?
Place a diode from emitter to base. Cathode to base, Anode to emitter, This will protect the transistor.

For more consistent operation, place a 10K resistor in parallel with this diode.

The transistor will be turned on only for the loudest signals from the amplifier.
The circuit I see will trigger on sounds greater than about 1/10 watt. If it is too sensitive, use a 10K potentiometer from emitter to base (instead of a fixed 10K.)
 
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Hi mneary thats what I really needed.

So here is my final circuit.

Thanks for your guidance.That's really really nice :D
 

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