PVDF impact sensor

Discussion in 'The Projects Forum' started by chrispedersen, Aug 23, 2013.

  1. chrispedersen

    Thread Starter New Member

    Aug 23, 2013
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    0
    Sooo.. I am a complete novice, in way over my head.

    I got pretty excited by the ability of PVDF to generate a piezo electric effect.
    Details here:

    www.media.mit.edu/resenv/classes/MAS836/Readings/MSI-techman.pdf‎

    I was looking to use the pvdf film as a simple switch. However, it seems that that the output of this switch may be unreliable due to low pass filter effect. At least, so I was warned.

    Can someone help me understand this: It is suggesting the need for a huge Giga Ohm impedance on the input.

    However, here: www.media.mit.edu/resenv/classes/MAS836/Readings/MSI-techman.pdf

    Page 43, ff: it suggest that the pvdf films are suitable for piano keys which is my intended project.

    This
    www.media.mit.edu/resenv/classes/MAS836/Readings/MSI-techman.pdf‎
    again suggests problems with detecting strikes, or low frequency events.

    So. I'm all confused. Are 3mm x 12 mm film segments suitable for detecting a keystrike/deflection?

    What should I do about the impedance, if I wished to incorporate this into an arduino project?

    Thanks a ton in advance.
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,118
    3,042
    You may need a ultra high impedance op-amp as shown in some of the circuit examples. Last time I went looking for a high impedance op-amp, I found the LMC6035 or LMC660. I never actually used either of them.
     
  3. chrispedersen

    Thread Starter New Member

    Aug 23, 2013
    12
    0
    Is there a way to determine easily if so? The papers suggest that oscillators may not work well.

    I'm looking at the op amps..

    Can you perhaps suggest a circuit? Will an ultrahigh impedance affect the input side of the arduino?
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,118
    3,042
    No, the idea is that the op-amp will sit between the sensor and anything else, allowing you to eliminate the problem with the sensor's very high impedance. When I read that even an oscilloscope probe might be enough load to distort the sensor output, that's what tells me that you probably need a high-impedance op-amp.

    Do you already have these things? You could spend some time experimenting with the circuits offered in that write-up. The stuff starting on p.39 is helpful.
     
    Last edited: Aug 23, 2013
  5. chrispedersen

    Thread Starter New Member

    Aug 23, 2013
    12
    0
    Yeah, I 'm a big proponent of dive right in.

    However, these bimetalized sheets are almost $200. I'm trying to get samples first, and solicit input before I drop the cash.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,118
    3,042
    Well, they definitely ought to work. I noticed in the final pages they list a number of application such as keypads. For that kind of pricing, the company can likely help you a bit, maybe even provide sample application circuits for that type of application.
     
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