Photoelectric output control circuit

Optoelectronic devices are generally composed of light-emitting diodes and photosensitive transistors,
which are also called photoelectric couplers. The figure shows the
output control circuit using a photodetector , which is the most basic circuit composed of photoelectric
devices. Threshold levels can be set for the voltage dividing points of Ri and M.
The distance between the light-emitting diode and the photosensitive transistor of this circuit can be in the range of 0 to 5 degrees, and it can detect direct
light or reflected light. Change the state of light and no light (or light blocking) into an electrical signal
output, and add it to the load ItL.