Abstract: A crossed light beam position indicator includes orthogonal arrays of paired light emitters and detectors for covering a display surface with crossed light beams and scanning means coupled to the emitters and detectors for electronically scanning the orthogonal arrays such that a single emitter at any one time is emitting light. Improved initialization means detect the first occurrence of an interrupted light beam and in response to the first detection, reset the scanning means to the initial reset position to thus avoid transmitting an address that might represent only the edge of an object placed in proximity to the display screen and caught by the scan only after the scan had passed the position occupied by the main body of the object.

Abstract: A crossed light beam position indicator includes orthogonal arrays of paired light emitters and detectors for covering a display surface with crossed light beams, scanning means coupled to the emitters and detectors for electronically scanning the orthogonal arrays such that a single emitter at any one time is emitting light. Improved scanning means include means for scanning the detector associated with a particular emitter and in addition scanning one or more adjacent detectors during the time that a single emitter is activated to provide plural light paths from a single emitter and thus more precisely define the position of an object placed in proximity to the display surface.

Abstract: Apparatus for detecting the position of a passive object includes a generally rectangular frame having an open interior, a source on the frame for emitting light through the frame interior from three sides thereof, a pair of linear image detectors, such as charge-coupled devices, being respectively mounted on the frame at two corners thereof being located at opposite ends of a fourth side thereof and adjacent respective opposite ends of the light source, a pair of aperture-defining devices located at the two frame corners between the detectors and the interior of the frame for configuring coincident fields of light from the frame interior for the detectors to view, and control circuitry connected to the detectors. Each of the detectors is capable of receiving its respective field of light from the frame interior and sensing interruption of light at any location within the field.