Mutual capacitance between touch pins

copercini
Posts: 13
Joined: Wed Dec 21, 2016 4:44 pm

Mutual capacitance between touch pins

Postby copercini » Wed Oct 04, 2017 6:49 pm

Hi!

I'm building a project which needs a 12 keys keypad, like the telephone one.

As ESP32 has 9 usable touch pins (GPIO 0 cause boot issues) one possible solution is make a matrix keypad, and the best way I found to do this is using mutual capacitances, based in the section 4.2 of this document

but as I understand ESP32 implementation is quite different (please correct me if I'm wrong), it charge and discharge the pads periodically, using a self-capacitance technique, and when human body disturb this capacitance it generate a variation like the picture bellow:
Image

The way that I found to implement using seft-capacitance is putting the pads of rows and columns very near in the top plane, making a touch trigger a row and a column at same time, like this picture: https://image.prntscr.com/image/AVtjj9A ... P8IiDQ.png

The only problem is the very weak sensibility, like 5% of variation when a 2mm acrylic cover is placed over it, and the less area causes less sensitivity

There is some better way to design a layout of matrix keypad using ESP32 self-capacitance or how hard is make it works using mutual capacitance?


Obs: most images was suppressed due too much visual pollution

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