Introduction: Sound Responsive Circuit

An easy way to make any circuit sound responsive.  

You can easily make any circuit you're working on sound responsive. I will be showing how to do this with an electret microphone.  Some people choose to use a 1/8" input (headphone jack) but I prefer a microphone so the entire system is stand alone and doesn't require running wires too it.  You can adjust for your needs.

The schematic is fairly simple.  The electret microphone inside is essentially a variable capacitor and a FET.  We use a circuit to DC bias the FET.  Then, as acoustic waves are sent into the microphone, they vibrate the "Sheets" of capacitive material.  This creates the "variable" part of the capacitor.  The output from the microphone will then be essentially an AC voltage varying over time. 

You can see in the second image from wikipedia how the microphone appears to a circuit, and the standard circuit for biasing the FET.

The output from the microphone is very small in terms of our circuit power, so we send the output from the microphone through an operational amplifier to boost the signal to a peak to peak voltage we can use.  We also use that op-amp circuit as a filter to block the DC offset from the biasing circuit.

We will then send that output to a comparator.  Sometimes I'll attach a potentiometer to the other terminal of the comparator so that i can adjust the "sensitivity" of the sound reaction.

You then have the output of the comparator.  Usually my application calls for attaching an LED to this out, which can just be sent through a 1k Ohm resistor.  But from here you can send the output to anything your heart desires.

So as the microphone picks up audio, it is sent through the amplifier/filter stage and then to our comparator.  The potentiometer will allow us to adjust whether we want the audio to be loud before it starts flashing the LED, or if we want it to respond on even quieter noises.

This can be applied to a number of different circuits and enhanced to become more accurate and more useful, but here is the basic start to making any circuit audio responsive.

I'm constantly adjusting these circuits, and your results are definitely going to be different, so you will need to adjust some of the values and play around with it until your get it working perfect.

Comments

author
tortiz-potter (author)2015-09-01

What's the input and output voltages for this circuit? I would like to attach an LED strip to the output and install this circuit in my car

author
BooRan (author)tortiz-potter2015-09-09

The input and output would really be dependent on the voltage supplied to the op amps (labeled VCC) and the ability of the op amps. you could certainly find some that are 12v tolerant and set it up to work for you. You may need to adjust some of the other components based on your needs.

BR

author
amitra3 (author)2014-02-22

can anyone tell me if this circuit will work for an audio controlled led chaser? are all the components correct?

audio led chaser.jpg
author
Basquer (author)2013-06-28

Hello "DrNicker":
Can you tell me what software did you use for designing?
Thank you in advance.

author
BooRan (author)Basquer2013-06-28

I've been using Eagle CadSoft a lot lately.
It allows you to create schematics and export to PCB design.
It seems to have a lot of support through sparkfun and Newark (a lot of part libraries) and it is fairly easy to use and understand (compared to some other tools)

One down side is it doesn't have any simulation tools built in, so it only tells you if connections are missed or traces are incorrect, etc...

They have a free download version on their website
http://www.cadsoftusa.com/download-eagle/?language=en

author
Basquer (author)BooRan2013-06-28

I am very grateful to you for all the generous support provided.
I am going to try it!
Thank you very much!!

author
Megawashu (author)2013-04-25

Yes, which resistor is the one to switch with a POT?

author
BooRan (author)Megawashu2013-04-25

You just need to route the signal through a potentiometer to ground and then have the sweeper arm continue through the rest of the circuit. There are multiple places you could do this. For example R6. Then the signal can be adjusted between 0% (ground) when the pot is turned all the way one way or 100% (full signal) when it is turned all the way the other direction.

author
oliverkellow (author)2013-04-03

R7, 680Ohm would be replaced with a Pot? or another?

I am trying to use 3mV from an inductor at 60Hz as the input, I gather this is similar to an electrets voltage output.. Thanks for this well explained building block!

author
Arguser (author)2012-10-29

Is there an alternative to LF412D? I'm not able to get it on my city.

author
BooRan (author)Arguser2012-10-29

you can certainly use any opamp that has the right specs for your circuit. The LF412 seems to be the most popular but there are tons out there.

author
Arguser (author)BooRan2012-10-30

Thanks for answering! Would you say a TL 082 would work?

Thanks again!

author
Arguser (author)2012-10-02

Nice work!

Would be awesome if you could filter bass and treble to trigger different LEDs (or whatever).

I'd like to try this circuit with Electro-Luminiscent Tape, I'm not sure how yet. If someone have an idea please advice!

author
BooRan (author)Arguser2012-10-02

I have a circuit that uses frequency response to light LED's. I'm pretty busy right now, but next time I get around to it I can upload a simple demo on how to make one.

author
amandaghassaei (author)2012-08-19

cool project, what are you using this for?

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Bio: Electrical Engineer, control systems, automation, small electronics, home automation, microcontrollers etc.
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