The circuit schematic diagram of acousto-optic control delay switch is shown in figure 1. The main component of the circuit is the digital integrated circuit cd40 1 1, which contains four independent NAND gates VD 1 ~ VD4, which makes the circuit simple in structure and high in working reliability. As the name implies, the acousto-optic controlled delay switch is "turned on" by sound control switch, and "automatically turned off" after a few minutes. So the function of the whole circuit is to turn the sound signal into the opening action of the electronic switch after processing. After the signal flow direction of the circuit is determined, the circuit can be divided into several units according to the main components, from which the block diagram shown in Figure 2 can be drawn. Analyze 438+0 of Figure 65 in combination with Figure 2. Sound signals (footsteps, applause, etc.). ) is received by electret microphone bm and converted into an electrical signal, which is coupled to the base of vt through c 1 for voltage amplification, and the amplified signal is sent to two pins of NAND gate (vd 1), r4 and r7 are vt bias resistors, and c2 is power supply filter capacitor. ?

In order to turn off the acousto-optic switch in the daytime, that is, the light control circuit is composed of photoresistor rg and other components, and the series-connected voltage dividing circuit is composed of r5 and rg. When there is no light at night, the resistance of the photosensitive resistor is very large, and the voltage at both ends of rg is high, that is, t=2πr8c3 between high levels. Changing the value of r8 or c3 can change the delay time and meet different purposes. Vd3 and vd4 form a two-stage shaping circuit to shape the square wave signal. When c3 is charged to a certain level, the signal passes through NAND gates vd3 and vd4 and is output as a high level, so that the unidirectional thyristor is turned on and the electronic switch is closed. After c3 is fully charged, only r8 is discharged. When it reaches a certain level, the output of NAND gates vd3 and vd4 is low level, so that the unidirectional thyristor is turned off and the electronic switch is turned off, completing a complete process from opening to closing of the electronic switch. ?

Diode VD 1 ~ VD4 rectifies the AC 220v bridge into pulsating DC, which is then stepped down by r 1 and filtered by C 2, which is the DC power supply of the circuit and supplies power to bm, vt, ic, etc.