Included on this page are various small circuits I have created over time. Some are trivial, some are a bit more complex, but hopefully all are useful in a variety of projects. Most include both the schematics as well as the source (KiCad) files.
Digital Capacitance Touch Sensor
This is a touch sensor with adjustable sensitivity, which will output a digital signal specfying whether or not it is being touched. I originally created it as a cymbal mute sensor for my electronic drum hardware, although it could be used for any sort of touch sensitive switch.
You would connect the metal touch plate to P1; the digital output is on P2. The exact value of the variable resistor will differ based on conditions, size of capacitance touch plate, etc; 200k seems to work for me, but you may need to adjust this a bit.