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Thread: piezo cable

  1. #1
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    piezo cable

    I'm trying to use this piezo cable to detect a knock but I'm getting some weird results. Basically it responds very poorly to impacts, I have to whack it really hard for it to detect a spike. I'm an electronics total noob and I'm sure I'm using it wrong. I've wired it like a regular piezo with a circuit I found online. The copper on the piezo is connected to ground and the other wire to an analog pin. A 1MOhm resistor and a 3,3v zener diode is in parrallel between ground and A0.

    Here is a datasheet for the piezo. Any electronics expert who can help me? https://www.mouser.se/datasheet/2/41...A1-1134575.pdf

    Maybe this is not suited to pick up low level vibrations like a regular piezo?

    I'm just using the serial plotter to see if I can get it to respond to taps. I know these types of cables are used as guitar pickups so should work.
    Last edited by frankzappa; 01-25-2020 at 09:37 AM.

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    Ok, found out what the problem is. This type of piezo produces less voltage than a piezo disc. Any advice on a circuit that can amplify this signal? Basically it responds between 0-480 instead of the 0-1023.

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    Senior Member+ Frank B's Avatar
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    Quote Originally Posted by frankzappa View Post
    Ok, found out what the problem is. This type of piezo produces less voltage than a piezo disc. Any advice on a circuit that can amplify this signal? Basically it responds between 0-480 instead of the 0-1023.
    Why is the reduced range a problem? That's a factor of 2 only
    You could just multiply it with 2 (that's an amplification, too ).. without having trouble with additional parts...

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    It's more that I want it to be more sensitive. I want to detect small vibration. Right now if I whack it with the thick end of a screwdriver I get a nice signal spike up to 450 or so out of 1023 but I'd like it to react if I hit it very lighly. It seems it's not that sensitive. I know these are sometimes used as underground sensors that can detect footsteps far away but I don't know how that would work since it seems very unsensitive. Either I have the wrong type of sensor or it requires some kind of different interface circuit. Problem is I haven't found much info on that.

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    Senior Member+ Frank B's Avatar
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    So you want much more than a factor 2?
    If yes, you're right you'll need a circuit.. in this case, I can't help. Maybe one of the others .. I know, some have experience with piezos.

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    Yeah I need it to be way more sensitive. It should be possible to detect faint acoustic stimuli.

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    Senior Member vjmuzik's Avatar
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    Would a non-inverting op amp circuit not be suitable for something like this? I’ve never used piezos before, but if all you need to do is adjust the voltage that seems like the simplest way to do it.

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    Quote Originally Posted by vjmuzik View Post
    Would a non-inverting op amp circuit not be suitable for something like this? Iíve never used piezos before, but if all you need to do is adjust the voltage that seems like the simplest way to do it.
    All piezos generate only little voltage. You need always a very good pre-amplifier (very low noise and very high input impedance). In past design was special FET followed by bipolar opamp.
    The special FETs (sub-nanoV noise) are not produced anymore, so best is to use very low noise FET or CMOS opamp. e,g. LTC6240 with voltage noise less than 10nV/sqrt(Hz) at 1 kHz

    This is similar to Electret Mics that for the same reason have FET already integrated.

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    Quote Originally Posted by vjmuzik View Post
    Would a non-inverting op amp circuit not be suitable for something like this? I’ve never used piezos before, but if all you need to do is adjust the voltage that seems like the simplest way to do it.
    Total electronics noob here. I've come to the same conclusion, I'm reading up on op amps. I've found some circuits for different applications of this cable (page three in the link).: http://www.ehag.ch/PDF-Files/MSI/pvdf_piezo_cable.pdf

    One example is for 100m cable, heavy impacts (trucks and such) and low frequency events.

    The other is 1km of cable, small vibration signals and a wide frequency range.

    Third is 1m of cable, foot steps detection on a mat, low frequency events.

    I'd need a circuit for 1m of cable, detect small to medium signals and a high frequency range.

    Can someone help me understand the difference in these circuits? I'm guessing I can use the 1km cable example but change the gain.

    How would I make a signal that the teensy likes?

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