Circuit T as principle: In this circuit, a laser diode LED, as a light hair emitter, in addition to other properties may also be used similar light emitter laser diode substitu
tion pipe. Resistor R. And diode VD, as the laser diode current protection circuit, multi- loop trimming potentiometer RP, for adjusting the sensitivity of the laser. Under normal circumstances, when a laser beam is irradiated to a phototransistor VT. When on, VTz conduction, VT3 base potential is zero (VL zero bias), VT3 deadline, its emitter potential is zero. The zero potential applied to the IC. (CD4001) first gate N, the input of the results of N. The output is high. But also through the high resistance of the transistor VT4 added to the base so that VT4 conduction, so that the green LED, lights up. In this case the circuit is in a standby state waiting.