3764813 is referenced by 111 patents and cites 7 patents.

In a coordinate detection system, the interruption of pulsed invisible light beams is used to determine the spatial coordinates of a passive stylus, such as a finger or a pencil, relative to an associated display. The system comprises a rectangular frame which houses two mutually perpendicular linear arrays of infrared light-emitting diodes and two perpendicular linear arrays of associated silicon detector diodes. Driving circuitry sequentially pulses the light emitters in repeating cycles. Associated detecting circuitry responds to the detectors and determines during each cycle the spatial coordinates of the interfering stylus. This spatial information is then coded and transmitted, if necessary. Sequential pulsing eliminates the need for beam collimating structures and lenses and allows for the application of high instantaneous power driving levels to the emitters.

Coordinate detection system
Application Number
Publication Number
Application Date
April 12, 1972
Publication Date
October 9, 1973
Richardson Barton Leigh
Clement Frank John
Bell Telephone Laboratories Incorporated
H01j 39/12
G06F 03/33
G01D 05/26
G01D 05/34
G01B 11/00
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