reading some of the capacitive sensing IC datasheets around, they always recommend an isolation overlay over the sensor pad.
Like this:
I'm wondering, why not use the actual PCB as overlay?
like this (sorry for the bad photoshop):
Please note that I'm not just going to determine the "touched/untouched" state, but the actual amount of touched area (by measuring the actual capacitance).
I've done some experiment with MPR121 sensor and some copper tape on a blank PCB material, and it works pretty good, but I'd like to hear some opinions before I'm going to make some actual PCBs.
Would that be as good as using a proper overlay?
Update: I've read that FR4 (the PCB material) should provide almost the same isolation as acrylic and other plastics, so I think it could work
Best Answer
I've done this before, it's a pain to use it in a product. Do it once and never appear again on another product.
To answer your question, yes it can be done. Just that we don't show customers our PCB directly.
http://www.ti.com/lit/an/slaa576a/slaa576a.pdf