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Author Topic: Bad vibes!  (Read 389 times)
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Been working on the secret knock detector from Instructables, but when my hand approaches the piezo buzzer that is used as a microphone input, it generates enough of a signal to register as a knock even though everything is quiet and my hand is about 4" from the wires and piezo.  Seems like my hand is interacting with the sensor or the wires in a strange way.  Any ideas how I could prevent this?  It works fine if I just rework the project with a pushbutton instead of the piezo, so it is definitely coming from that.
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It sounds like a capacitive effect,

can you post your 'secret' schematic and code?
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Rob Tillaart

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Here is the link for the project:
http://grathio.com/2009/11/secret_knock_detecting_door_lock/

I followed it exactly like it is shown and even tried reversing the piezo to see if that helped but it didn't.
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Check that the 1M resistor is across your sensor. That should prevent that sort of thing from happening. Are you sure it is making contact?
If it is connected correctly then try a lower value like 470K, or 220K.
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