Hello,

I'm trying to make a circuit that will take in line level audio and is able to switch something on/off when sound is coming through (e.g. the sound from a headphone jack). I'm a newbie to circuits and any direction would be appreciated. Thanks.

Vinoj

 

It's possible, but it will need it's own power, unless you have a handy source of, say, 12 volts DC.

 

I've been reading - I think I may need a voltage comparator. I do have power - 5V from the USB port on a computer. I'd just hook up the two power lines and ignore the data pins.

 

What about a comparator hooked to a relay? Then if the voltage exceeds a certain point, the output voltage could trigger the relay (switch) - could that work?

 

First you need a high impedance op amp to monitor and amplify the audio out. Then rectify it and apply it to the comparator, which can pull in a relay.

 

You might want to check the audio detection circuit at:
http://www.scary-terry.com/audioservo/audioservo.htm
The U1A/B circuit out to the top of C2 will give you an integrated output based on a audio signal exceeding a set point.
A couple more at:
http://www.alanovington.com/audio_detection_circuit.htm
http://sound.westhost.com/project38.htm

Ken

 

Thanks! That Scary Terry circuit looks like it'll do what I need it to. As I was looking around I came across a Schmitt-trigger. Would that work for this also? To provide more detail, the equipment I'm switching is a microphone - basically when the speaker is on, I want to mute the microphone. I heard something about a Schmitt trigger with an open collector. Is there an IC that anyone knows of that does the same as the Scary Terry or the Schmitt-trigger?