January 04, 2009

Tips for interfacing a electret mic with an arduino

  1. The arduino ADC is 10bit, which means the range is 0-1023 and this is mapped to 0-5V most of the time, unless you do funky things to AREF.

  2. Most amplifier circuits on the net (using op-amps or LM386s) will have a DC bias of 2.5V, this is to allow the output to swing both ways. So on the arduino side even with complete silence you will read a value ~512 or so.

  3. The resistor connecting the electret mic and power also adjust the sensitivity of the microphone in addition to providing power to the mic (which includes an internal pre-amp, by the way). This resistor is very important - if you find your microphone isn't responsive enough, then adjust this resistor first before debugging your amplifier circuit. For me this "fixed" my microphone's responsiveness. It is best of this was a variable resistor which makes adjustment trivial.

  4. I was making a simple volume meter, and I did the following: clamp upper values to about 600, then using map map this to a range between 0-7 (since I had 8 LEDs). This was because I found the value never went above 600 very often, so the upper few LEDs were essentially going to waste sitting around. YMMV.