From: Alan Pearce <kiwiantipodean@googlemail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Sun, 2 Feb 2020 04:39:41 -0800
Subject: Re: [EE] Capacitive touch on glass ...
Thread-Topic: [EE] Capacitive touch on glass ...
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> 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 wa=
s
> 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.

This is effectively how the PIC chips with CTMU work.

On Sat, 1 Feb 2020 at 23:47, Harold Hallikainen
<harold@mai.hallikainen.org> wrote:
>
> 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 wa=
s
> 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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