Anyone familiar with these vintage touchscreens?
paulkoning at comcast.net
Mon Oct 21 11:49:26 CDT 2019
> On Oct 21, 2019, at 12:19 PM, John Foust via cctalk <cctalk at classiccmp.org> wrote:
> And what sort of technology was that screen using? I expected to see
> the grid array of outer infrared LEDs and detectors that I vaguely remember
> from that era, but I don't see that here. Someone was making a tube
> that was coarsely touch-sensitive?
Theinfrared array you're thinking of was invented at PLATO, for flat panel (plasma) displays. They don't work for CRTs because of the convex screen.
When CDC built a CRT-based version of the PLATO terminal (the "IST"), they had to come up with a touch panel for that. The scheme used involved two layers of plastic, thick enough to be just a little springy, with conductors on the facing side. I don't remember the type used, it may have been very thin wires or it may have been a mostly-transparent conductive coating (some indium alloy or compound comes to mind). Touching the screen would create a contact between an X and a Y conductor, so you'd get your coordinates via a scan process just like in the IR touch panel, or for that matter like in keyboards (of that time and later).
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