[Viacheslav] built a pad that uses human capacitance to detect presses. Unlike normal s which close a physical connection, his project detects touch through the PCB substrate. He uses the ADC capabilities of an AVR ATmega8 to measure a change in capacitor charges for each sensor in the pad.
He’s posted the schematic, Eagle files, and source code with his writeup. He also points to a document on the theory behind this: QMatrix Technology White Paper (PDF). We’re impressed at how simple the circuit is: a microcontroller, capacitors, resistors, and a homemade PCB.
