I'm trying to build a knock sensor, something like this:
Everything is generally working, but sometimes my threshhold (the knock) is randomly triggered, and it appears to be caused by some sort of electrical interference. I posted a video of the problem here:
The LED should only be lighting when a knock is detected.
As far as the circuit, I'm connecting the piezo's negative to ground, and the positive to analog pin 1, and I have a 1 megohm resistor between ground and analog pin 1. This is the piezo I'm using: http://www.radioshack.com/product/index.jsp?productId=2062397
And to describe the problem a bit more, usually everything works well, but seemingly randomly it stops working and the threshhold (the knock) is detected. It usually remains like this until I touch the ground wire, or even put my hand near the ground wire.
Eventually I'd like to have 6 different piezos detecting different "knocks", if possible.
Any tips on how to get rid of the bad readings?