21 Oct
2019
21 Oct
'19
9:49 a.m.
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).
paul