PVDF impact sensor

Thread Starter

chrispedersen

Joined Aug 23, 2013
12
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.
 

wayneh

Joined Sep 9, 2010
17,153
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.
 

Thread Starter

chrispedersen

Joined Aug 23, 2013
12
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?
 

wayneh

Joined Sep 9, 2010
17,153
Will an ultrahigh impedance affect the input side of the arduino?
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.
 
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Thread Starter

chrispedersen

Joined Aug 23, 2013
12
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.
 

wayneh

Joined Sep 9, 2010
17,153
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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