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mbeals

microphone input

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I'm attempting to use a microphone on a comparitor channel to trigger an event (bang detector), but I'm having issues adjusting the line level to where I need it to be. Before hooking it up to the actual micro, I've been trying it out on an o-scope but haven't been able to get anything close to measurable signal.

 

I've found a few guides online that show the mic hooked up to a 3 to 5V DC carrier, with the Vcc line coupled to the signal line through a cap (which is then fed into an opamp). I figured even without the opamp, I should be able to at least get variable noise to show on the O-scope, however I get absolutely squat even with the scope cranked as fine as it will go.....so I know I'm doing something horribly, horribly wrong.

 

I've attached a schematic of how I had it hooked up. The free ends are where I was hooking into the scope.

post-45239-135135570242_thumb.png

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i would expect to see a few mv of output even without an opamp or transistor preamp/buffer but can't see anything wrong with your schematic either. all i can suggest is that you double check your wiring. do you have another mic to try? test the mic in an amp or pc input maybe. i've used them with just a resistor and cap with phantom power from an xlr input without problems in the past. here's some basic electret info: http://www.epanorama.net/circuits/microphone_powering.html

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possibly. what are you using? r1 is to bias the fet in the mic and c1 is dc blocking - the smaller its value the less bass is allowed through, you want at least 1uf for a bang detector probably closer to 10uf.

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1k should be fine - you just bias for the least distortion/noise but should still get signal. if your cap was too small then not a lot of signal beyond the mics frequency response would get through, if any - the bigger the better for boom.

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I finally have success. r1 of 1k and a 20 uF cap give a few hundred mV of signal. I also connected the signal to ground through a 100k resistor to bring the DC offset to zero.

 

do I need to rectify the signal or is negative voltage okay for the comapator?

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thanks for that link...very interesting. If this makes it to 'version 2' status, I'm going to have to add something like that.

 

I meant to try the mic with the board today, but between playing with my new servos and making my daughter's Halloween costume it just didn't happen. I'll keep you updated on my progress though.

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