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