Capacitive Sensing Part 2

Based on reading more about how capacitive sensing is done in touch screens, I changed to a new approach. Instead of trying to measure the time to charge or discharge the circuit, I'm relying on the fact that an RC circuit acts as a low-pass filter. Here's the circuit I'm using, essentially the same as when I was trying to time the discharge rate.

A square wave using the tone() function is applied to the input and a pin change interrupt is used to count CHANGE transitions on the output. If the tone is near the cutoff frequency, a small increase in capacitance will move the cutoff frequency lower, causing fewer output transitions.

Capacitive Sensing on Battery Power

I'm helping out with a project for the 2015 Alameda County Fair in Pleasanton, CA. The project is not finalized but includes touch sensors. The project lead has chosen MaKeyMaKey as an input device.

MaKeyMaKey works by sensing current flow through an object, such as a banana, through your body, toward ground.

But it requires the user to touch a ground wire or contact as well as the object you want to sense.

I was interested in getting rid of the ground wire so I looked into capacitive sensing.