High resolution optical position code detector for information recorded on record carrier partially in humanly intelligible form

摘要

An optical position code detector which senses information that is recorded on a record carrier. The record carrier preferably has scan marks for synchronizing operation of the detector and at least one track with positionally encoded data marks which include one or more imprinted alphanumeric characters. The detector includes photodetectors which sense light that is reflected from the record carrier. The intensity of the reflected light varies in dependence on whether or not data marks are present and also varies due to the presence of spurious marks on the record carrier. When a scan mark appears, a comparison circuit is activated which compares the voltage from each photodetector with a reference voltage which is cycled from a low magnitude to a relatively high magnitude. The comparison circuit distinguishes data marks from spurious marks with a high resolution. A logic circuit is connected to the comparison circuit to indicate whether or not a position code is present on the record carrier. If a code validity detector which is connected to the logic circuit ascertains that a predetermined number of successive indications have been made by the logic circuit that the same position code is present, the position code is decoded to provide machine- useable information, such as to update payroll files in an attendance recorder system.