Gentlemen I need a circuit to activate a small relay with a microphone, however only when it hears noise louder than 75-80db.
I have seen circuits like the clap-on clap-off but I need one that it not specific to the type of sound but will activate only when any noise that is over a certain level. Having an adjustable pot to dial in what decibel level it activates at would be nice.

 

Question is would you like the relay only to be energized while the audio is above a certain level or latch above a certain level and then require a reset?

One possible approach would be to build a small microphone pre amplifier, using a simple old chip like a TL071, TL084 or similar. Come off your pre amp with a diode like a 1N914. Then run your signal into a basic comparator Use a pot to set an adjustable Vreference on your comparator. Use a comparator chip like the LM339. You want to add some hysteresis so that around your set level the relay doesn't start chattering.

Actually rather than build the microphone amp you can get a breadboard SparkFun OpAmp Breakout - LMV358 from SparkFun as seen in the link for about $5 USD. Depending on the type microphone that should work. Again, depending on the microphone type. Anyway place a diode at the output cathode side away from amp out. Then put your comparator circuit out there to drive the relay or a transistor driven relay. Use the comparator to set your level.

Ron

 

Something like this, board is $ 4.

SAR + some code detects peaks, over samples audio to capture peak.
One chip design except for a couple of resistors.




http://www.cypress.com/documentation/development-kitsboards/psoc-4-cy8ckit-049-4xxx-prototyping-kits



Regards, Dana.

 

A much more capable design where digital filter can be used, or FFT,
to eliminate "one off, bogus" sounds from measurement.

http://www.ece.drexel.edu/courses/ECE-C490SBC/Notes/singleToneDetection/AlarmDetect.pdf

Regards, Dana.

 

I was tested a sound control relay with toggle ON/OFF many years ago, you may use a op amp or comparator with a potentiometer to replace the bjt circuit.

 

Or feed your amplifier into a Lm3914 comparator, and use any output as the relay trigger.