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I am interested in making a small circuit that could sense the vibrational frequency of the object that it is attached to. The resonant frequencies would be in the audible range (likely 5kHz to 10kHz) Imagine a small circuit attached to a tuning fork, I would like to 'ping' the tuning fork and have the circuit be able to output what frequency at which it is resonating.

I have read that Piezo devices would be capable of this but I haven't been able to find anything suitable. Does anyone have any suggestions of what I could use?

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You could use a piezoelectric tuner for an acoustic guitar. These clip onto the guitar, amplify the vibrations and measure the frequency.

eg. http://guitar.lovetoknow.com/Classical_Guitar_Tuners

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    \$\begingroup\$ A piezoelectric tuner is basically a contact microphone coupled to a normal tuner. \$\endgroup\$ – Connor Wolf Feb 1 '11 at 3:46
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I would use a piezoelectric disk and attach it to your object, connect a small amplifier circuit , and use the output to go to a speaker or a an ADC pin of a uC of your choice.

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  • \$\begingroup\$ the piezo measures pressure or bending, so it would need to be between the object and something else. otherwise you're modifying the resonant frequency with the weight of the piezo \$\endgroup\$ – endolith Feb 11 '11 at 15:35
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If you attach something to the tuning fork the added mass of the device will affect the frequency, so you might be better off using a microphone and MCU to measure the sound frequency directly.

You could simply use a PC and sound card with a microphone and sound analysis software, if you don't want to build anything.

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The thing you are looking for is called a Contact Microphone. There are lots of good DIY links on google.

Alternatively, you should just be able to use any common audio microphone, since the vibrations are in the audible range.

All microphones pick up vibrations in the microphone body, in addition to vibrations in the air. Therefore, just touching a microphone to the tuning fork should pick up a pretty strong signal.

Basically, Since the microphone diaphragm has mass, moving the body will cause it to move around the diaphragm, producing a signal.

If you want to reduce ambient pickup, you could use something like a little electret capsule, plug the opening, and mechanically coupling the microphone body to your tuning fork (or what ever you want to sense vibrations in).

It's worth noting that most microphones will be much more sensitive to motion in one axis than the others. Basically, since the diaphragm is sprung so it's only free to move along one axis, movement in the other axises will not have much effect.

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In their Analog Dialogue vol.43 no.1 Analog Devices published an article titled

"Sonic Nirvana - Using MEMS Accelerometers as Acoustic Pickups in Musical Instruments"


Further reading:

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