Laser beam fully automatic door and window control circuit

Operating principle of circuit T: In this circuit, laser diode LED is used as the light emitter
. In addition, other light emitters with similar performance can also be used to replace the laser diode
. Resistor R. and diode VD, as the overcurrent protection circuit of the laser diode, and multi-
turn trimmer potentiometer RP, used to adjust the sensitivity of the laser. Under normal circumstances, when the laser
beam irradiates the phototransistor VT. When on, VTz is turned on, making the base potential of VT3 zero
(VL ​​zero bias), VT3 is turned off, and its emitter potential is zero. This zero potential is added to IC.
(CD4001) The input terminal of the first gate N, the result N. The output is high level.
This high level is added to the base of transistor VT4 through the resistor, causing VT4 to conduct and
the green LED to light up. At this time, the circuit is in a waiting standby state.