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Infrared Switches for Presence Detection

Excelitas' optoswitches are ideal for non-contact sensing applications. They consist in an emitter and a detector integrated in a plastic housing. The emitter is an IR LED while the detector is either a phototransistor or a photodarlington. These optoswitches are available either in transmissive or reflective configuration.

In its most basic form, a reflective optical switch (retro) consists of a housing which holds both a light source and a detector. Light from the lamp of LED radiates outward and is reflected back should an object be placed in front of the switch. The reflected light is sensed by the photodetector whose output signal changes accordingly.

When the object to be sensed has a polished surface, such as aluminum foil or Mylar tape, often the best type of reflective switch to use is one which is designed to take advantage of the large amount of directly reflected light. This is done by mounting the emitter and detector such that their optical centers lie along the legs of an isosceles triangle such that the angle of the incidence of the emitter is equal to the angle of reflection.

When trying to sense matte objects (which do not have a highly polished surface, such as white paper), it is often possible to use a type of reflective switch optimized for sensing diffuse reflected light. Such devices have the emitter and detector mounted parallel to each other within the switch housing.