I'm using the piezo as in "12 knock lock" project to read claps instead of knocks.
When I plug Arduino to the computer everything is fine.
If no sound I get values near to 0 form the piezo. I I clap I get higher ones.
However, if I use a "mobile charger" battery to charge Arduino my piezo sends values between 0~30 when no sound exists, and there is no way to detect claps.
Which can be the cause of this different behavoiur?