General Instruments Capacitive Keyboard Encoder

Paul Birkel pbirkel at
Tue May 4 09:18:29 CDT 2021

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at] On Behalf Of Al Kossow via cctalk
> Sent: Tuesday, May 04, 2021 9:48 AM
> To: cctalk at
> Subject: Re: General Instruments Capacitive Keyboard Encoder
> On 5/4/21 2:33 AM, Paul Birkel via cctalk wrote:
> > I'm currently reverse-engineering an AMPEX keyboard that uses capacitive key
> > switches. 
> did all of the square foil and foam pads disintegrate in it?

It uses individual sprung metal leaves, with the exception of the caps-lock key which has a central LED and around that an annular square foil/pad that is in fine shape.  It's all nicely constructed; the case even includes a spray-on metallized surface that is connected via a sprung contact to the cable shield and the switch-body retaining plate.


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