This project is an experiment of capacitive touch sensor. The detector electrode (touch area) is a 10mm square copper plate put on the PCB and covered with an insulation overlay (Kapton tape). An ATtiny2313 with 1M ohms pull-up resister is used for the detector circuit.
The capacitive touch sensor detects changes of capacitance at the electrode occurred by closing a conductive object such as a finger. There are several sensing methods for the capacitance. For this project, integration method that used in capacitance meter is applied.
The integration time at normal state is determined by value of pull-up register and stray capacitance on the port and electrode. When touch the electrode with a finger, the integration time increases and can be detected the touch. The actual integration time becomes several µs to several ten µs.