Principle and production of sound and light controlled delay switch

Principle and production of sound and light controlled delay switch

Use the sound and light controlled delay switch to replace the switch on the corridor of the residential area. Only after dark, when someone walks through the staircase and makes footsteps or other sounds, the corridor lights will automatically light up to provide lighting. When people enter the house or walk out of the apartment, the corridor lights will automatically go out after a delay of a few minutes. During the day, even if there is a sound, the corridor lights will not light up, which can achieve the purpose of energy saving. The sound and light controlled delay switch is not only suitable for the corridors of residential areas, but also for public places such as factories, office buildings, and teaching buildings. It has the advantages of small size, beautiful appearance, easy production, and reliable operation, and is suitable for the majority of electronic enthusiasts to make it themselves.

    1. Working Principle of the Circuit
     The circuit schematic diagram of the sound and light controlled delay switch is shown in Figure 1. The main components in the circuit are the digital integrated circuit CD4011, which contains 4 independent NAND gates VD1~VD4, making the circuit structure simple and the working reliability high.

As the name implies, the sound and light controlled delay switch uses sound to control the "opening" of the switch, and the delay switch "automatically closes" after several minutes. Therefore, the function of the entire circuit is to process the sound signal and convert it into the opening action of the electronic switch. After clarifying the signal flow direction of the circuit, the circuit can be divided into several units according to the main components, and thus the block diagram shown in Figure 2 can be drawn.
    Analyze Figure 1 in conjunction with Figure 2. The sound signal (footsteps, applause, etc.) is received by the electret microphone BM and converted into an electrical signal, which is coupled to the base of VT through C1 for voltage amplification. The amplified signal is sent to the 2nd foot of the NAND gate (VD1), R4 and R7 are VT bias resistors, and C2 is the power supply filter capacitor.
    In order to make the sound and light controlled switch disconnect during the day, that is, the light is not on, a light control circuit is composed of components such as photoresistor RG, R5 and RG form a series voltage divider circuit. When there is no light at night, the resistance of the photoresistor is very large, and the voltage across RG is high, that is, the high level t=2πR8C3. Changing the value of R8 or C3 can change the delay time to 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 is output as a high level after passing through the NAND gates VD3 and VD4, so that the unidirectional thyristor is turned on and the electronic switch is closed; after C3 is fully charged, it only discharges to R8. When it is discharged to a certain level, it is output as a low level through the NAND gates VD3 and VD4, so that the unidirectional thyristor is turned off and the electronic switch is disconnected, completing a complete process of the electronic switch from on to off.
    Diodes VD1~VD4 perform bridge rectification on the 220V AC to convert it into pulsating DC, which is then stepped down by R1 and filtered by C2 to become the DC power supply of the circuit, supplying power to BM, VT, IC, etc.

    2. Selection of components
    IC uses CMOS digital integrated circuit CD4011, which contains four independent NAND gate circuits. The internal structure is shown in Figure 3. VSS is the negative pole of the power supply, and VDD is the positive pole of the power supply. The thyristor T uses the imported 1A/400V unidirectional thyristor 100-6 type. If the load current is large, unidirectional thyristors of specifications such as 3A, 6A, and 10A can be selected. The appearance of the unidirectional thyristor is shown in Figure 4. Its measurement method is: use the R×1 gear, connect the red test pen to the negative pole of the thyristor, and the black test pen to the positive pole (as shown in the printed circuit board diagram). At this time, the needle has no reading, and then touch the control electrode K with the black test pen. At this time, the needle has a reading. The black test pen immediately leaves the control electrode K. At this time, the needle still has a reading (note that the positive and negative test pens are always connected when touching the control electrode, indicating that the thyristor is intact. The electret uses a small microphone used in general recorders. It The measurement method is: use the r×100 gear to connect the red test lead to the shell S and the black test lead to D. At this time, blow air to the electret with your mouth. If the needle swings, it means that the electret is intact. The greater the swing, the higher the sensitivity. The photoresistor is 625a type. When there is light, the resistance is less than 20k, and when there is no light, the resistance value is greater than 100mq, indicating that the component is intact. The diode uses ordinary rectifier diodes 1n4001~1n4007. In short, the selection of components can be flexibly mastered, and the parameters can be selected within a certain range. Other components can be marked as shown in Figure 1.

 3. Installation and production
    After preparing the full set of components, use a multimeter to roughly measure the quality of each component (because it has been measured before leaving the factory) to know the quality.      When welding, pay attention to welding non-polarized resistors and capacitors first. Resistors should be installed horizontally and capacitors should be installed vertically, close to the circuit board. When welding polarized components such as electrolytic capacitors, microphones, rectifier diodes, triodes, unidirectional thyristors, etc., do not install them in reverse. Pay attention to the correct polarity, otherwise the circuit will not work properly or even burn the components. The printed circuit diagram is shown in Figure 5.