[sdiy] capacitive sensors - AD7147

[Scott Nordlund]

>> Ensoniq did something very similar in the late 80's to early 90's.
>> There's a small metal plate under each key, and a coiled circuit
>> board trace underneath that, with a squishy foam rubber pad
>> separating them (hall effect sensors? I'm not sure).
>
> hm ... coiled circuit board like zig-zag traces? Was the rubber
> conductive?
> Hall Effect needs some magnets, if I'm not mistaken. But I may be
> wrong ...
>
> Michael. :-)

It's coiled like a spiral, not zig-zag.  It's a planar inductor,
at least as far as I can remember.  The rubber is not conductive,
but only serves as a squishy pad for the aftertouch.

It probably has nothing to do with the Hall effect, but that's
apparently the most common "folklore".

I'd guess the proximity of the metal plate changes the inductance.

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