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Author Topic: Recommendation for an accelerometer used as a contact microphone?  (Read 2106 times)
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Does anyone have a suggestion for an accelerometer to be used as a contact microphone?

Something with an analog output and the ability to sense vibrations up to 4kHz, altho higher would be better. The signal would be captured by an ADC such as an MCP3208.

I assume an op-amp would be required to bump it up to ADC level, but am not sure about that.

Thanks.
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Most accelerometers will not work at these sorts of update rates. To sense vibrations up to 4kHz you need to sample at least twice that rate. Typically accelerometers sample at 2KHz or less.
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That seems about right from my searching.

I'll probably need to use the piezo element directly & amplify the voltage.
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It looks like I could use something like I attached.

* ACH_01.pdf (175.97 KB - downloaded 29 times.)
* IB_ACH_01_AmplifierBox.pdf (88.53 KB - downloaded 68 times.)
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Well you have not said what the application is so it is hard to tell if that is suitable.
« Last Edit: July 04, 2011, 12:12:38 pm by Grumpy_Mike » Logged

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There's lots of applications that I think this would be useful for.

But, for the moment, I wanted to put it on the back of a diaphragm of a stethoscope to listen to chest sounds.
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Wouldn't that accelerometer keep the diapragm from moving?
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Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
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Yes, it might, but I don't think the diaphragm is even necessary for a vibration sensor.
I think it might be helpful in not allowing vibrations in certain frequency ranges.
But, yes, it technically would not be working in the same way as a normal stethoscope.

If you put your ear up to someone's chest you can hear chest sounds. I don't see why those vibrations won't vibrate a sensor placed on the chest. If there is too much mass on the sensor, then it could be a problem like you say.
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I think I'd try something like this instead
http://www.radioshack.com/product/index.jsp?productId=2062215
I used to put these in a small box with 9V battery to use a microphone.
Then do any amplification and filtering you want on the acquired sound.
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Yeah I thought of using a condensor mic too, but I want to keep it flat. And I was hoping I wouldn't have to keep a compartment of air behind the diaphragm, but maybe I will need too like I think you are implying.
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No compartment, I just had these little boxes that held the mic sticking out of a hole on one end, the battery, and a switching jack to connect ground on the othe when cable was plugged in. The mics are not very tall, one of them next a stack of coin cell CR2032 for power and a connector would make a nice little package.
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Looking for a battery to see if this one still works!
Will see if if can pick up heartrate and play thru a little guitar amp.
Little cap for blocking DC in there too, looks like 3.3uF
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Yeah, I think I'll go ahead and pick one of those up today.

Thx.
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Success! Had to put a new battery clip in, that 25 year old one was totally corroded.
And the jacks arent making the best of contact, so it has to be held really still to avoid cable scrathy noise.

But, with a 20' guitar cable, Roland Microcube turned all the way up, and the mic pressed to my chest, could hear a little boomp,  boomp, boomp, boomp.
No talking tho, it picked that up too.
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Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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