Want to build a momentary switch out of a Piezoelectric disk extracted from a buzzer

Discussion in 'The Projects Forum' started by handakes, May 24, 2015.

  1. handakes

    Thread Starter New Member

    May 24, 2015
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    Hey there,
    First and foremost, I do these kind of circuits for pure fun, and I have no formal education in electrical engineering what so ever (I am actually a senior medical student) so please, bear with me, and try to keep it simple..

    Recently, I have built a guitar controller from parts that were lying around in my house, and an xbox 360 controller's main board.. and it works great, so I was thinking I could also build a custom Drum controller as well..

    The main problem is that I need a sensor that senses vibrations and acts as a pushbutton that I can hook to my controller's board.. when I hit the drums, it should close the switch momentarily.. here's what I've learned so far:

    - a piezoelectric disk (such as the one in a buzzer) can be used as a sensor for vibration as it generates high potential, low current when deformed.
    -you need a microcontroller (like most of the readily available drum kits and midi devices) to let the board know which voltage is on and which is off.
    -you need a pull down resistor to negate the "floating" state.

    I can't use a microcontroller (strictly out of financial reasons, that and the fact that I can't code for nill) so I was wondering if there is a way to make this work without it, here's what I've tried :

    -soldered 2 wires to the "signal" and "gnd" leads of one of the buttons on the xbox 360 controller pad
    - extracted the disk from the buzzer, and connected the disk to the wires from the pad (directly) like so:
    On board Signal lead ---------> Piezoelectric Ground lead
    On board Ground lead --------> piezoelectric Voltage lead

    -tried the board to see if a tap is registered as a button press, and found that every 10-15 taps registers as only 1 button press!

    I think I need a capacitor to make sure that every single tap registers as a button press, but I am currently a bit lost, and need to know if the idea is even sound and applicable (without the use of microcontrollers that is)..

    Thanks, and sorry for the extra long question..
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    The piezo will probably work better connected one way round rather than the other, but may not be generating enough voltage when lightly tapped. Obviously, whacking it hard would up the volts, but is not the answer :). That leaves you with having to build a small amplifier ( probably not much more than a transistor and a few resistors). Ok with that?
     
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  3. handakes

    Thread Starter New Member

    May 24, 2015
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    well, I am sure up for it, with adequate instructions that is :D
    the thing is, I want to build 4 or 5 separate drums, will I need to build each one a separate amp? I don't think a single one will serve all 5 of them without the signal getting cross read by another button by mistake, or will it?
    maybe with the use of some diodes I can route the current in the right direction? I used a similar method to separate inputs when I was building a custom arcade stick once, I wouldn't know how to apply it here though..

    EDIT: oh and about that note "the piezo will probably work better one way than the other"
    when I connect it the other way around, it read the button as "always ON" for some reason! so only one way works for me..or did you mean "flexed" one way than the other ?
     
    Last edited: May 24, 2015
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    If you want the 5 different drums to be controlled individually I don't see how you can avoid having 5 piezos and 5 amplifiers.
    As for the 'always on' effect, if the piezo is feeding a very high input impedance circuit then it may be holding charge for a prolonged period.
     
  5. handakes

    Thread Starter New Member

    May 24, 2015
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    well, either way..I just tried connecting it to a a very small (1 nano farad) capacitor, and it seems to be responding better (like a button press every 5/6 taps) but it's still far from what I need.
    can you please give me an idea about how I can build the amplifier? if it's simple enough (like a transistor and a few resistors) I don't mind building 5 of them..
    and thanks a million for your continuous input :D
     
  6. ScottWang

    Moderator

    Aug 23, 2012
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  7. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Here is a Piezo trigger I just built for my project-

    1) I find that you generally want an adjustment feature, so you can dial-in the sensitivity, it's never right otherwise.
    2) Depending on where and how you hit the trigger surface material, the vibrational modes can have different phase .
    If response latency is critical, (as with my application) you want to respond to both positive and negative pulses, this circuit uses a window comparator to detect both.
    3) This circuit generates lots of pulses on every trigger, filter as necessary.

    The MCP6024 is a fast and expensive rail-to-rail opamp, works great, but cheaper parts can be substituted.
     
  8. handakes

    Thread Starter New Member

    May 24, 2015
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    Woha,guys...this is too much for my extremely basic knowledge of circuits and electronics...I'm missing out on most of what you guys are saying, I guess I hvae a LOT more reading to do..
    but this seems rather complicated, and you guys started talking about micro controllers again, I just want to make sure of one thing..is this even feasible without a microcontroller? cause if it's not then I will just drop the whole thing.
    and of course, thanks for your input.
     
  9. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Well... everything in life is a trade-off.
    All devices have some non-ideal behavior, fixing the flaws requires fancy tricks.

    Analog or digital, choose your poison, you still need to wrangle the thing down to what you want it to do.
    Micro-controllers do offer advantages, you can fix allot of things in software.
     
  10. ScottWang

    Moderator

    Aug 23, 2012
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    The circuits just provided a trigger signal as low to high _-_ when you hit the piezo, what you do is decide by yourself.
     
  11. Dodgydave

    Distinguished Member

    Jun 22, 2012
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