Hello I am so frustrated ,I am hitting ONE piezo (a15 the others are not connected) and you can see in the jpeg what readings I am getting , is this normal? please some advice
this bleeding (electronic crosstalk between pins )makes my project not functional! :'( you can read more here
I'm not sure I understand the problem but if you want all those other pins to read a constant value, wire them to something. I suggest maybe ground or to VCC through a 10k resistor.
I'm not sure about the Mega (that is the board you are using, right?) but the majority of multichannel analog to digital converters I have worked with have only one A/D. They get multiple channels by putting a 1 of n selector in front of the A/D. So if the a pin is floating then the A/D may be biased by the previous reading.