I am working on a project that uses a capacitive sensor to detect skin contact between two humans. (It's not as perverted as it sounds :P) I have created a program that calibrates the sensor to ignore the capacitance of the human wearing the device. First, the person would attach the metal lead of the sensor to any part of their skin, and then turn it on. The program subtracts the value each time it gets a new reading, so that when somebody else is touching their skin, it can detect a change in the capacitance. I would post the code, but there is a lot of unnecessary information in it.
Anyway, the program works perfectly when connected to a computer, but when instead connected to one 9V battery, it only works about 10% of the time. My only two guesses about why it worked connected to the computer and not the battery would be that either the battery does not supply a high enough current to do capacitive sensing, or it has something to do with the computer being grounded.
I don't know to much about theoretical electronics, so I thought it would be a good idea to ask the community. Thanks