Light-sensitive circuits
The previous four chapters have dealt with the theory and applications of light-generating and light-reflecting devices such as LEDs and LCDs. The present chapter concentrates on the operating principles and applications of light-sensitive devices such as LDRs and photodiodes, etc.
LDR basics
Electronic optosensors are devices that alter their electrical characteristics in the presence of visible or invisible light. The best known devices of these types are the LDR (light dependent resistor), the photodiode, the phototransistor, and the PIR (passive infra-red) detector.
LDR operation relies on the fact that the conductive resistance of a film of cadmium sulphide (CdS) varies with the intensity of light falling on ...
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