Frame detection circuitry for microfilm reader apparatus

摘要

Frame detection circuitry for sensing frame sensing marks on a microfilm uses first and second photoelectric convertors respectively responsive to the light transmitted from the frame sensing mark and from light transmitted by a light emitter to generate respective first and second output signals, whereby the light emission received by the second photoelectric convertor is unaffected by movement of the microfilm such that the second output signal is a reference level signal. The first and second output signals are compared to generate a control signal representing the sensing of a frame when the first output signal exceeds the second output signal. A circuit may be used to filter the noise detected by the second photoelectric convertor.