Capacitive slider test

I found this sort of design in a Microchip appnote. If it works well enough, I might consider it for future projects. It should be good for otherwise unused pins and doesn't cost anything extra.

I think I will have to get a cap-meter. Jyetech has a pretty cheap kit that can measure from 1pF to 500µF. The pF-range should be useable for the sensor pads. That way I can do without guesswork when selecting the size of the storage capacitor.

I'm planning to use a timer-based repetitive charge-transfer-method to measure pad capacitance, not the more simple RC-timed method.