Capacitive sensing is used in tons of stuff like buttons, sliders, touch panels and proximity sensors. We like it because you only need to design the various buttons/sliders directly on the PCB and it works even under a face plate.
It works by measuring the changing capacitance between a pad and a users finger as it enters the pad’s electrical field. The change is measured by using that capacitance in a RC network to generate a pulsed signal. By comparing the changed frequency with a default value it is possible to detect the presence of the finger. More info in this app note.
This is all implemented in hardware in a PIC microcontroller using the capacitive sensing module. We wanted to learn more, so here’s a small round up of capacitance sensing app notes from Microchip that can get you started.
First up is an app note explaining how the Capacitive Sensing Module is implemented in PIC16f72x series. It shows how to initialize the module, do frequency measurement, and use interrupts.
Second we found a practical implementation using 6 capacitive buttons and a slider. The design consist of a 4×4 dot matrix controlled via various capacitive sensors. It is implemented on the PIC16F726, and a Allegro A6276 for driving the LEDs.
Last up is an note giving you 48 ways to implement CSM. From ordinary like self-cleaning litter boxes to our favorites:
47. Solving World Hunger
48. Bring About World Peace