I'm planning on replacing lights with smart bulbs (e.g. Yeelight RGBW) and replacing light switches with capacitive panels connected to Arduinos which will send data to RPi, which will then control the lights.
I want to make the panels by myself, like here. They will contain some round slider for RGB color and sliders for RGB brightness and White brightness, as well as bulb selection and power button.
My question is, can I use single sheet of copper (or tape), with multiple connection points, to make a single panel, where Arduino will calculate the coordinates from the multiple points? It's in case I want to change the layout, the only thing I would need to do is replace one sheet of paper and some layout file for the Pi (it will decide what to send according to the layout).
I've seen some Instructables for single-dimensional sliders, where they connect each end of the slider to a pin, so I think it will be possible.
How many points would be ideal? Could I just triangulate it from 3 values? Or would one for each corner be better? Or even 5 like one in the middle?
Also is the capacitance linear with distance? Is there any formula?
And another question: I have lots of copper tape left from guitar shielding, but it corrodes over time. Will the capacitance change with it corrosion, rendering it useless?
Thank you for all your answers.