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I have this piezo vibration sensor module from Grove: http://www.seeedstudio.com/wiki/Grove_-_Piezo_Vibration_Sensor sensor

Using this sensor and an arduino device I want to measure two things:

  • amplitude (negative and positive)
  • vibration frequency

Is it possible to measure the negative amplitude with this board? The analog input of an arduino board use a 10bit ADC. So we have 1024 values available. Is it possible to use the value 0-511 for negative measurement and 512-1023 for positive? Normally I would use a voltage devider to set an offset to the negative sensor values. But in this case I don't know how the board is handling negativ sensor values.

Here is the board circuit:

enter image description here

For frequency measurement I want use the amplitude values and do a FFT.

is there any chance to get the negative values?

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With this circuit you even can't get the positive values, only a digital signal that tells whether the input signal goes above some fixed threshold level. The threshold can be adjusted by R6.

The LM293 is a comparator that checks whether the negative input (pin 2) is higher than the positive input (pin 3). So the output is purely digital (i.e. 1 or 0).

You could, however, pick up an analog signal at the output of the OpAmp U1B (pin 7).

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  • \$\begingroup\$ Oh Ok, thanks! So with the output of that module I can just see if there is a vibration or not. Nothing more. Ok, then I need to read just the vibration sensor. \$\endgroup\$ – CPA Feb 9 '16 at 9:25

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