Optical barrier drive system - has LEDs and phototransistors sequentially powered and monitored to reduce power requirements

摘要

The optical detector drive system comprises a click generator (1) and counter (3) whose capacity corresponds to the number of pulsed diode emitters (6). Each diode is activated in turn as the counter steps on. The receiver section consists of a number of parallel-connected photo-transistors controlled from a constant-current source (9). The output is connected to a threshold detector or Schmitt trigger (13). This in turn drives edge-triggered bistable circuits (14). The two outputs of the bistables are activated according to whether the transistor is activated or not. Further bistables (20, 21) monitor the photo-transistors and in the event of a fault, a light diode (22) is activated. The system lends itself to integrated circuit type of construction. Power supply demands are low.