From: Harold Hallikainen <harold@mai.hallikainen.org>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Sat, 1 Feb 2020 15:07:31 -0800
Subject: Re: [EE] Capacitive touch on glass ...
Thread-Topic: [EE] Capacitive touch on glass ...
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I did not see the start of this discussion, but thought I'd throw
something in.

In the 1970s or 1980s, I got a sample of a chip to do glass push buttons.
I thought the technique was very clever. On the user side of the glass was
the conductive "button." On the other side of the glass were two
conductive areas covering the button, but split in half. This formed two
capacitors in series (inside pad to outside pad, then outside pad to the
other inside pad). One of the inside pads was driven with a square wave,
and the square wave was detected on the other inside pad. If you touched
the outside pad, the square wave would be shunted to ground and not
detected on the second inside pad.

There was a special chip for this, but I think it would be easy enough to
do with a PIC.

Harold


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