The ISTS200_ series of transmissive photointerrupters are single channel switches consisting of a Gallium Arsenide infrared emitting diode coupled to a high speed integrated circuit detector. The output incorporates a Schmitt trigger which provides hysteresis for noise immunity and pulse shaping. The gap in the plastic housing provides a means of interrupting the signal with an opaque material, switching the output from an 'OFF' into an 'ON' state.