HIGH RESOLUTION OPTICAL POSITION CODE DETECTOR FOR INFORMATION RECORDED ON RECORD CARRIER PARTIALLY IN HUMANLY INTELLIGIBLE FORM

摘要

Abstract of the DisclosureAn optical position code detector which senses infor-mation that is recorded on a record carrier The record carrierpreferably has scan marks for synchronizing operation of thedetector and at least one track with positionally encoded datamarks which include one or more imprinted alphanumeric charactersThe detector includes photodetector which sense light that isreflected from the record carrier. The intensity of the reflectedlight varies in dependence on whether or not data marks arepresent and also varies due to the presence of spurious markson the record carrier. When a scan mark appears, a comparisoncircuit is activated which compares the voltage from each photo-detector with a reference voltage which is cycled from a lowmagnitude to a relatively high magnitude The comparison circuitdistinguishes data marks from spurious marks with a high resolu-tion. A logic circuit is connected to the comparison circuit toindicate whether or not a position code is present on the recordcarrier. If a code validity detector which is connected to thelogic circuit ascertains that a predetermined number of successiveindications have been made by the logic circuit that the sameposition code is present, the position code is decoded to providemachine-useable information, such as to update payroll files inan attendance recorder system.