Digital circuit production 01-Monostable sound and light control circuit

This circuit can simulate the sound and light control switch in the corridor. When the corridor is relatively dark (the photoresistor is in a dark state), there is a sound ( the MIC collects the sound), and the LED lights up; after returning to quiet, the light turns off after a period of delay. . When the sound started again, the lights continued to come on.

When the environment is in a dark state, the photoresistor shows a high resistance state, that is, a large resistance; in the simulation diagram, a 2Meg ohm resistor is directly used to simulate the dark environment. When the sound collection sensor MIC collects sound, it converts the sound signal into an electrical signal and generates a negative pulse, which lowers the potential of the C2 capacitor in the simulation diagram and makes the base of the Q2 triode extremely low (simulated by direct grounding in the simulation diagram). Q2 is cut off, that is, the collector is at high level, and when there is no light ( R8 photoresistor is in a high resistance state) Q1 transistor is turned on, and its collector is at low level, which is equivalent to providing a negative pulse signal to the subsequent 555 monostable circuit. . The two-stage transistor switching circuit realizes that the sound signal in front can be recognized only under dark conditions, so that the LED lights up.

The collector of Q1 is connected to a monostable circuit composed of a 555 chip, which is composed of R1 , C3 and C4 . When pins 2 and 6 of 555 receive the negative pulse of Q1 . Pin 3 inputs a high level, which lights up LED1 and LED2 through the current limiting resistor R7 . When there is no sound from the front MIC , Q1 is cut off, and the power supply charges C3 through the R1 resistor . When the sizes of R1 and C3 are larger, the LED lights up longer after there is no sound (you can try changing the resistance value yourself).