Capacitive sense buttons and pads are awesome, but many of the available systems are either propitiatory or require a dedicated IC. Toumas decided to code his own based on a closed source Atmel example where a single ADC pin is used for capacitive sensing. He reverse engineered it, and documented his results:
I’ve been thinking of a project that needs a little bit more elegant user interface than your usual push buttons. Partly inspired by a video blog on Dave Jones’ EEVblog, I decided to look into capacitive touch buttons. The big issue unfortunately for me was that you usually need a separate chip for capacitive touch sensing. With some tricks, you can however use a normal microcontroller to do the job. Even using only a single pin and resistor.
A lot of these techniques are riddled with patents, so watch out if you plan to sell your hardware.
Via the forum.
“The big issue unfortunately for me was that you usually need a separate chip for capacitive touch sensing.”
What?!? I can’t think of a major MCU manufacturer that doesn’t support cap-sensing with many of the products they’ve come out with in the last few years.
I wouldn’t obsess over the legal issues until the Patent Office issues the patent for the RC time constant, frequency counting, and little swatches of copper or aluminum foil.