Curriculum design of electric light in corridor festival? (working principle and picture) and protection circuit part

Figure 1 is the electrical schematic diagram. MIC electret microphone converts the picked-up acoustic signal into an electrical signal, and its negative signal turns off the transistor V, which is usually positively biased. During the day, the light resistance of the photoresistor is small, and the ① pin of CD40llB is low, so F 1 is prohibited. At night, pin ① is at high level, and pin ② is at high level after V is turned off, so pin ③ outputs low level, D2 outputs high level, F3 outputs low level and P4 outputs high level. Turn on the AC switch composed of SCR and D 1-D4, and light the bulb DX. At the same time, F2 outputs a high level to charge C3. When the sound passes, C3 slowly discharges to R6. After a delay of 3-4 minutes, f 3 outputs a high level, F4 outputs a low level, the thyristor turns off when the AC voltage crosses zero, and DX goes out. ?

The DC voltage of this circuit is rectified by D 1~D4 bridge, divided by R7 and R5, and provided after C2 filtering. ?

Fig. 2 is a printed circuit board diagram of the circuit. MIC and RG are directly welded on the board. The whole printed board is installed in the switch box, and there are small holes on the panel of the switch box, which is convenient for MIC pickup and Rc light transmission.