3-pin Electret - How to use it ?

Hi Everybody!

I recently bought two Electret microphones that I wanted to use with my Arduino for basic sound detection project.

I did not pay attention when buying them, but it seems that they have 3 pins, whereas most of the Electret mics that I found on the web have 2.

Moreover, there is nothing written on them, so I cannot find the datasheet.

There are 2 normal pins + a 3rd flat pin which seems to be the ground (because connected to the metal case).
However, I don't know which is the + pin and the ground pin. I tried several circuits, found on the web, but none of them work:

http://www.flickr.com/photos/8123185@N02/505756880/lightbox/

Pictures:

I also tried to leave the flat pin unplugged and use the two others like a normal electret; but no luck.

I never get a signal that is changing depending on the noise ... It is always a flat line ...

Maybe one of you knows how those 3-pin electret work ?

Thanks

Try connecting the big flat pin to ground, one of the others to +5V, and use the other as the output. You will probably need to amplify it to get a large enough signal for the Arduino.

Connect the tab to ground and one of the two pins to power via a 1k - 10k resistor. Shout at the microphone and see if you can see output on the other pin. I suspect that one of the pins is for power (with built-in resistor) and another is for output.

Hey,

Thanks for the reply, however, it seems that I am not lucky:

If I do the following:

Flat pin ---- GND
pin 1 ----- /\/\/\ (10KOhm) ---- 5v
pin 2 ----- Signal

No matter if I swap pin 1 and 2, the result is the same : I got 1023 on the Arduino Analog pin, I guess that does not mean much...

Put on a scope and see what you get.

geforce11:
Hey,

Thanks for the reply, however, it seems that I am not lucky:

If I do the following:

Flat pin ---- GND

pin 1 ----- ///\ (10KOhm) ---- 5v
pin 2 ----- Signal




No matter if I swap pin 1 and 2, the result is the same : I got 1023 on the Arduino Analog pin, I guess that does not mean much...

Maybe the big metal tab is a red herring. Maybe it's just there to ground the case or something.

In that case you're left with a normal two-pin electret mike and you just have to figure out the polarity.

Use the circuit here: Electret microphone - Wikipedia