Photo-optical detection of markings - using pair of photodiodes coupled to optical scanning system with Schmitt trigger switching stage

摘要

An optical detector system is used to identify markings without being subjected to the effects of temp., ambient light or variations in the reflectivity factor. A moving information carrying track (1) has marks (2) that are to be optically detected. A lamp (3) output is focussed (4) onto a partially reflecting mirror. Light is reflected over a lens (6) onto the mark (2). The generated signal is transmitted and focussed (7) onto two photo detectors (8, 9). The photo detectors can be two photodiodes connected between a supply with the anode of one coupled to the cathode of the other. The anode-cathode coupling is connected to a Schmitt trigger stage with a connection to earth over a resistor. Other variations utilise photodiodes connected to operational amplifier stages.