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

[Tony Duell]

> 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.

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

FWIW, I have the HP150 Technical manual, with the HP150-II update. It 
includes a schematic for the original touchscreen, but not, for some odd 
reason, the one used in the -II machine with the HP-HIL interface.

-tony