From 1985 - HP 150 TouchScreen goes for >$400 !

[Paul Koning]

>>>>> "Tony" == Tony Duell <ard at p850ug1.demon.co.uk> writes:

 >> I think I have the touchscreen frame from one of those, 4 circuit
 >> boards linked together in a box, with a lots of LEDs and
 >> phototransistors.  Always been curious what it came out of.

 Tony> Quite possibly, that's how the touchscreen worked on the 150.

Don't know about the 150, but that approach (rows and columns of light
beams) is how the touch panels on PLATO terminals -- starting early in
the 1970s -- worked.  Of course it's easier when the screen is flat,
as it always has been for plasma displays.

   paul