Cheap and easy piezoel. pickup for vibrations

Discussion in 'General Electronics Chat' started by buffer9, May 22, 2016.

  1. buffer9

    Thread Starter New Member

    Apr 25, 2016
    6
    0
    Greetings everyone!
    I am looking for a certain piezo sensor, actually an accelerometer, vibration sensor, shock sensor or however they call them these days. This accelerometer should pick up vibrations+shocks on a table at frequencies well within 5 Hz to 20.000Hz. Possibly even less top end freuqency down to 10kHz because I can hardly imagine any high frequ. going on in my application... The measurement range of acceleration (often given in g as the gravitational acc. constant) has to be in the area of +/- 150 g or even more... I don't want them to distort.

    Are there other cheap piezos that have integrated electronics for impedance bridging, like the IEPE pieces, but only need a constant voltage supply? My observation is that the IEPE sensors are more on the expensive side and never availible under 50 $. Basically I want an easy solution to hook up the sensors to an analog-to-digital-converter without the need for much soldering.
    A problem is also that the cheap sensors often do not have all the information in the datasheet... for example the amplitude range.
    thank you so much
     
  2. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    Strip an electret mic capsule for its special JFET - that will work well with almost any piezo unit.

    Some years ago I had a TL431 based booster amp for this very purpose published in Elektor magazine.

    Last time it was mentioned; someone on this forum posted a link for an online resource of the article.

    My project with the electret mic front end was so sensitive, it could produce an output from the microphonic properties of various types of capacitor.
     
  3. Externet

    AAC Fanatic!

    Nov 29, 2005
    758
    57
    Just made one today! for another application.
    Use a piezo disc from discarded smoke alarm, telephone ringer...

    One lead of the piezo to a 2N7000 or similar gate. Drain connects to a 3.3K to +, 1uF to output and 1M to gate.
    The other piezo lead to gnd with source.
     
  4. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
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    Some of the high output sounders are 3-terminal for an additional feedback contact.

    With careful design; it can be designed into an amplifier with just enough positive feedback to increase sensitivity - but short of oscillating.

    The downside is; it sharpens the piezo disk resonant frequency.
     
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  5. buffer9

    Thread Starter New Member

    Apr 25, 2016
    6
    0
    thank you guys.
    A JFET or CMOS buffer seems to be the way to go when using a bare disk element.
    But do you know any pieces that are already in a nice housing + internal buffer?
     
  6. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
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    Already in a nice housing is; the basic electret capsule.

    you can superglue a bit of insulation from wire stripping to the electret material through the hole in the front.

    Its extremely fragile and difficult to position the bit of sleeve through the small hole and keep it steady till the glue sets.

    But it does work - the mass of the capsule itself is sufficient counter weight to register vibration.

    The piezo slug from the igniter unit in a cigarette lighter gives a large output if you construct into some form of assembly and add a counter weight. Its ideal for the JFET salvaged from an electret mic capsule.
     
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