3775560 is referenced by 105 patents and cites 4 patents.

A crossed light beam position encoder including x and y coordinate arrays of paired infrared light sources and detectors for covering a display device surface with x and y crossed light beams, scanning means coupled to the sources and detectors for electronically sequentially scanning the x and y arrays so that only one source is emitting light and its associated detector is detecting light at any particular time. Means are included for noting the digital address of the beams during sequential scanning and for stopping the scan when the beams are interrupted, the digital address and therefor the position of the broken beams are transferred back to a computer.

Infrared light beam x-y position encoder for display devices
Application Number
Publication Number
Application Date
February 28, 1972
Publication Date
November 27, 1973
Goldhor Richard S
Johnson Roger L
Ebeling Frederick A
University of Illinois Foundation
G08c 21/00
G06F 03/33
View Original Source