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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
 

kchriste

New Member
Forum Supporter
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.
 

Suraj143

Active Member
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
    Sound RL.JPG
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audioguru

Well-Known Member
Most Helpful Member
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.
 

Suraj143

Active Member
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?
 

mneary

New Member
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.)
 
Last edited:

Suraj143

Active Member
Hi mneary thats what I really needed.

So here is my final circuit.

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

Attachments

  • Sound Trigger.PNG
    Sound Trigger.PNG
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