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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.

enter image description here

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.

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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?

No. Due to the high conductivity of copper it will not be possible to differentiate between different points on the surface.

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).

To do this you would need to create a matrix of pads with sufficient "pixels" for your most demanding application.

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.

I haven't and you haven't provided a link.

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?

How do you imagine such a scheme would work?

Also is the capacitance linear with distance? Is there any formula?

If you mean with distance along the strip from the connection point then no.

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?

The copper oxide layer should be quite thin and should not affect the conductivity of the tape significantly. You can spray it with a protective coating to prevent this. A PCB conformal coating may be suitable as it is designed to protect copper.

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  • \$\begingroup\$ Thanks for all the answers, here's the link for the strip (he used alluminium foil), I was just wondering if I could possibly do it with 2 axes. \$\endgroup\$ – Rikpat Feb 27 '18 at 20:33
  • \$\begingroup\$ And I presumed that I can calculate the coordinates by measuring the ratio between the distance to the connections, much like triangulating position (there arent two points with same distance to all the connections, be it 3 or more) \$\endgroup\$ – Rikpat Feb 27 '18 at 20:39
  • \$\begingroup\$ Okay my bad, after rewatching the video with the slider, I see that it's cut diagonally and each part is connected to different pin \$\endgroup\$ – Rikpat Feb 27 '18 at 20:44

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