Working with a Microphone

I recently took apart a cellphone that had been run over. I certainly didn't expect to find much of use, but the only three components I can use are the microphone and the two speakers. I don't know what kind of microphone it is, or how to get input from it. I'm looking for hardware and software tips to get it working.

The microphone itself looks like a round disk, exactly 10mm in diameter and 3mm thick, with a small hole in the center. I have op amps and basic NPN and PNP transistors available. I am working with an arduino clone.

I would also like to know whether the sample rate would be sufficient for audio. I don't have a specific project in mind. If I can't get this to work, it's perfectly all right. Thanks for everything, folks.

Given the relatively large diameter and small thickness of the microphone, I'm wondering if it's a dynamic, or moving-coil, part.

Do you have a digital multimeter? If so, can you measure the resistance between the terminals, and post the result?

I do not have a multimeter (still need to get one that works properly). I measured it with an older ohm meter, but all I could tell with that is that it is on the order of 50 ohms. That probably won't tell you enough. I'll probably just go out and buy a multimeter; I'm going to need one eventually, right? If I do, I'll post a better measurement.

On a tangent, has anyone seen a project to use an arduino as a multimeter, or at least an ohm meter? Normally I try to search for stuff myself instead of asking, but what project thread isn't going to mention a multimeter?

OK, that measurement is good enough! A condenser or capacitor microphone element will measure close to an infinite resistance. Looks like you have a dynamic microphone. Which means, you won't need a polarising voltage and a FET follower, as you would with a capacitor microphone.

But you will need an amplifier to boost the few millivolts that you'll get from the dynamic microphone up to the few volts that the Arduino analog input pins need. Now, what sort of amplifier do you prefer: integrated circuit op-amp or discrete transistor? And what do you want to measure: average sound level or actual digitised audio?

For an average sound level measurement, you'll need to amplify the microphone by a factor of around a hundred, then rectify (diode) and smooth (capacitor) the signal.

Yes, if you are going to be playing around with a Arduion you NEED to get a digital multimeter. They don't cost much these days and I can't see how anyone could get along without on, even you software types :wink:

Example: http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=37772

Lefty

Honestly, I have no preference between op amp and discrete because I don't know the pros and cons of each. (I'm kinda new). I think I have the parts for either way. If it's simple enough, I have a pile of perfectly good transistors that I have never been able to use. Plus, my supply of op amps is fairly limited.

I was thinking I would actually capture sound, but I have no idea what I would do with it from there. I don't know if the arduino is fast enough to do any sort of signal processing. It'll probably just be something I tinker with for a while, then shelve until I can find a real use for it.

Is there a guide out there that would explain how to do all this?

I don't know if the arduino is fast enough to do any sort of signal processing.

Yes See:-

http://interface.khm.de/index.php/labor/experimente/arduino-realtime-audio-processing/

Mike: AWESOME! Just what I was looking for, but I didn't even realize it! I'm totally ditching the mic for a couple 1/4" jacks.