Radiant beam coordinate detector system

Abstract

A crossed light beam coordinate detection and encoding system having a plurality of emitter/detector pairs along each axis of the display space is disclosed. The emitters are modulated in amplitude and the detectors are biased with a low load resistance to provide a wide dynamic range. The wide dynamic range and amplitude modulation detection provides immunity to unwanted interference. After band pass filtering, the carrier is amplified by high gain amplifier with auto bias control. The output of the amplifier generates a true/false output corresponding to the presence/absence of a beam. A single chip microprocessor controller checks the screen for interrupted beams and when not clear generates coordinates of the interrupted beams. The coordinates can be calculated as a weighted average of the interrupted beams for each axis or as the min and max coordinates along each axis. Reporting is done repeatedly at preselected time intervals. Error information is generated each time the coordinates are generated to report errors such as too large or too small an object or a discontinuous object. Repeated reportings beyond the initial reporting of a coordinate of the interrupted beams can be locked out in response to the position of the interrupted beams in the display space. Diagnostics of the system can be performed at 100% and 90% output levels of the emitters. This allows diagnostics to detect marginal operation of the screen.