Connect Piezo transducer to IC from USB Computer keyboard for sample trigger

Discussion in 'The Projects Forum' started by SteveSmith001, Oct 5, 2015.

  1. SteveSmith001

    Thread Starter New Member

    Oct 5, 2015
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    Hi. I hope someone can help me with a suggestion for this.

    I need to connect a Piezo transducer to the IC from a USB computer keyboard, so that I can use it as an external trigger which can be hit with a drumstick.

    I have built a similar system using momentary switches, operated by hand, which works well

    However, when I connect the Piezo to the IC and connect this via USB to the computer, then the Piezo is triggered as a buzzer.

    I am guessing that this is because the USB buss has a voltage to drive external disk drives and similar appliances

    Can anyone therefore suggest what I can do to make the peizo function only as a trigger?

    All help gratefully received...
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,791
    1,103
    Welcome to AAC!
    My crystal ball has gone cloudy ;). Can you post a schematic of your piezo input arrangement, and a link to the mystery IC?
     
  3. SteveSmith001

    Thread Starter New Member

    Oct 5, 2015
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    Thank you very much for your response - Crystal Ball polish attached ;)

    I have attached two photos - one showing the USB IC (extracted from a computer keyboard) and one showing the piezo and the IC , not connected

    I have done this before by simply connecting the two poles of a switch to two connections on the IC

    When connected by USB to a laptop, this will generate the equivalent of a keypress on a keyboard. For example - if I connect pins 1 and 6 on the IC, the computer registers the letter 'a'

    As background - in case there are other thoughts on how to do this - I would like to be able to place the Piezo underneath a mouse mat, and when the mousemat is hit, it generates a letter...

    Please do let me know if any further information would help IMGP3523.JPG IMGP3522.JPG
     
  4. Yangui

    New Member

    Oct 3, 2015
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    SteveSmith001 likes this.
  5. SteveSmith001

    Thread Starter New Member

    Oct 5, 2015
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    Thanks very much for that link, and for taking the time to answer. I have done something similar when using piezos as trigger pads attached to an acoustic drum.

    My query here is whether it is possible to prevent the Piezo being triggered as a buzzer by the voltage from the USB buss, so that it just functions as a switch.

    Alternately - is anyone familiar with a better switching system for this application? What I need to do is make a set of pads, which can be hit with a stick, which each contain a switch which will connect the two poles of the Keyboard IC

    Something along these lines:-

    http://www.plugandwear.com/default.asp?mod=cpages&page_id=22

    ??

    Or this kind of thing:-

     
  6. SteveSmith001

    Thread Starter New Member

    Oct 5, 2015
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    ... actually, to half answer my question - this sort of thing...

    https://www.adafruit.com/products/1361

    -may well be a better solution - the transducer requires not only to be amplified, but also converted to a pulsed switch signal...
     
  7. Yangui

    New Member

    Oct 3, 2015
    8
    2
    To stop it buzzing you could put diode in series , but may not solve your problem of switching by itself , you will need an amplifier stage .
    An alternative to Velostat is conductive foam used in packing IC's as an EMI shield , I have used this foam in a project as a variable resistance pressure mat.
    [​IMG]
     
    SteveSmith001 likes this.
  8. SteveSmith001

    Thread Starter New Member

    Oct 5, 2015
    5
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    The conductive foam is a good thought - time to buy some samples and get testing.

    Thank you for the suggestions
     
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