The diode of the optical sensor is a light emitting diode, whose output is photo triode, of which C is collector and E is emitter.

When the triode is used as a switch, the collector is usually used as the output end.

General connection method: the diode is used as the input end, of which E is connected to the ground, and C is connected to the load, where the other end of the load needs to be connected to the positive power. This connection method is widely used.

Special connection method: the diode is used as the input end, of which C is connected to VCC, and E is connected to load, where the other end of the load needs to be connected to the ground. This connection method is only suitable for the load with a very small equivalent resistance (within a few tens of ohm). If the load equivalent resistance is large, it may cause the operating point of switching transistor abnormal, making the switching operation not reliable.