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I've been trying to develop an electric guitar tuner using a piezo disk to detect vibration.

I have this design but at the moment the design fluctuates randomly from 0 to 5.09V when it should remain at zero until the piezo is pressed.

The voltage source is a regulated 9V battery which is connected to the rails on my breadboard.

schematic

simulate this circuit – Schematic created using CircuitLab

Can anyone explain why this is happening?

Cheers

DonnellyOverflow
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    See this question. Seriously. http://electronics.stackexchange.com/questions/28251/rules-and-guidelines-for-drawing-good-schematics – Matt Young Oct 22 '15 at 20:32
  • Corrected my schematic. – DonnellyOverflow Oct 22 '15 at 21:03
  • Better, but now what does V1 do? Nothing useful that I can tell. – AaronD Oct 22 '15 at 21:25
  • V1 is the power source from the regulated battery. That's the symbol isn't it? – DonnellyOverflow Oct 22 '15 at 21:28
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    A normal battery symbol is a short horizontal line for the negative terminal and a longer line for the positive, possibly with additional pairs of short/long lines. The negative side of your "regulated battery" (What does that mean, anyway?) is connected to one side of two capacitors, and to nothing else, so that battery has no effect on the circuit. – Peter Bennett Oct 22 '15 at 22:56
  • A battery attached to a regulator, generating 5.09V from 9v, sorry for the confusion. The battery also connects to the op amp I removed it by accident trying to simplify the schematic. – DonnellyOverflow Oct 22 '15 at 22:59
  • Check you're interpreting data bits correctly. Interpreting the LSBs as MSBs, or misunderstanding the sign bit, can result in the behaviour you are reporting... –  Oct 22 '15 at 23:13
  • Did you check whether the op-amp is working correctly for you? Did you set up the single rail supply correctly for it? Did you split the power rails to make a virtual ground for it? The piezo ground and R4 should be connected to that. – jilski Oct 23 '15 at 18:21
  • All grounds lead back to the battery which has its own power rail. The piezo and R4 are connected to the common ground. The op-amp should work correctly due to brand new part and a simple configuration from the datasheet. – DonnellyOverflow Oct 23 '15 at 19:37

1 Answers1

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If you have wired it up the way it is pictured, you are missing a ground connectionenter image description here

David Drysdale
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