Anyone familiar with these vintage touchscreens?

Paul Koning paulkoning at
Mon Oct 21 11:49:26 CDT 2019

> On Oct 21, 2019, at 12:19 PM, John Foust via cctalk <cctalk at> 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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