Traditional Chinese Infrared anti-myopia automatic dimming table lamp (Workshop Practice) — Circuit, Wiring & Debug Guide

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Infrared anti-myopia automatic dimming desk lampMost of the dimming desk lamps sold on the market are manual, that is, according to the needs of the user, the dimming knob is turned by hand to change the brightness of the desk lamp. Although it has the effect of saving electricity, it does not have the function of preventing myopia. At present, many primary and secondary school students suffer from myopia. The main cause of myopia is that they are too close to the light source when studying or doing homework under the lamp. Over time, their vision deteriorates and contributes to myopia.In order to prevent primary and secondary school students from getting too close to the lamp when reading or doing homework under the lamp. If the distance exceeds the specified (i.e. set) distance, the light will automatically dim or even go out. If they leave the specified distance, the light will automatically brighten. We designed an infrared anti-myopia automatic dimming desk lamp. It can not only prevent myopia caused by studying under the lamp, but also has the effect of automatically dimming, saving electricity and extending the service life of the bulb.The principle of infrared anti-myopia automatic dimming desk lamp is introduced as follows.1. Circuit working principleThe circuit principle of the infrared anti-myopia automatic dimming desk lamp is shown in Figure 23-1. It is composed of a regulated power supply circuit, an infrared transmitting circuit, an infrared receiving circuit and an automatic dimming circuit.In the figure, after the 220V AC is bridge-rectified, one channel passes through the resistor R1 and is clamped by the voltage regulator DW1 to obtain a DC voltage of 9V, which is supplied to the infrared transmitter circuit and the infrared receiver circuit. The other channel is added to both ends of the bulb ZD and the one-way thyristor SCR. Changing the conduction angle of the SCR can change the brightness of the bulb ZD. Since the bulb ZD passes through pulsating DC current, there is no impact current from the AC current, which can extend the service life of the bulb.Figure 23-1Transistors BG1, BG2, resistors R3, R4, capacitors C2 and C3 and infrared emitting diode LED form an infrared emitting circuit. It is a self-excited multivibrator. Its oscillation frequency is determined by resistors R3 and R4 and capacitors C2 and C3. Generally, its frequency is adjusted between 2 and 2.5 kHz. The infrared emission tube is connected to the collector of the BG2 tube and is the collector load.Infrared receiving tube DU, transistors BG3, BG4, BG5 and integrated decoder C, etc., form an infrared receiving circuit. The infrared transmitter LED and the infrared receiver are assembled together to form an "integrated" sensor device. It has high sensitivity, good anti-interference performance, and can work normally under strong light.When someone blocks the front of the transmitter, part of the high-frequency infrared signal emitted by the transmitter will be reflected back by the human body. After the infrared receiver receives this part of the signal, it amplifies the infrared signal through the amplification circuit composed of BG3, BG4, BG5 and the resistor-capacitor components C4, R6 and C5, and sends it to the ③ pin of the audio decoder IC, which is recognized and decoded by the IC, and then in I C's ⑧ outputs a low level, causing the transistor BG6 to cut off, and the power supply charges the capacitor C10 through the resistor R15 and the diode D5, which reduces the resistance between the D and S electrodes of the N-channel VMOS tube, causing the base potential of the BG7 tube to increase, and the charging speed of the capacitor C11 to slow down, causing the trigger pulse phase to shift backward, the unidirectional silicon controlled SCR conduction angle to decrease, and the brightness of the light to dim. When the person in front of the transmitter moves away, the infrared receiving circuit undergoes the opposite process, that is, it returns to its initial state and the light returns to its original brightness. The closer the human body is to the transmitter, the smaller the conduction angle of the thyristor SCR and the dimmer the light. In this way, the distance between primary and secondary school students reading under the desk lamp is limited, which plays a certain role in protecting eyesight.BG7, R20, R21, etc. form an error amplifier. The essence of the BG7 tube is to act as a variable resistor. BG8, C11, etc. form a relaxation oscillator, which is used as the trigger circuit of the one-way silicon controlled thyristor SCR. Under normal circumstances, the conduction angle of the SCR (i.e. the brightness of the bulb ZD) is determined by the voltage division of resistors R17, R18 and R19 (i.e. the base potential of the BG7 tube) and is not affected by the infrared transmitting and receiving circuits.The N-channel VMOS tube is shown in Figure 23-2. One of the characteristics of the N-channel VMOS transistor is that the resistance between the D and S electrodes changes linearly with the increase or decrease of the voltage between the GS electrodes. That is, when the capacitor C between the GS is charged, the resistance between the D and S electrodes becomes smaller. When C is discharged, the resistance between the D and S electrodes becomes larger. The second characteristic is that the resistance between the G and S electrodes is extremely high. With these two characteristics, the VMOS tube can be regarded as a variable resistor, and its control source is the voltage between the G and S electrodes. It is this characteristic of the VMOS tube that is used to change the resistance of resistor R18 in Figure 23-1, thereby realizing automatic dimming of the desk lamp.2. Component selection and installationIn the figure, the IC is an audio decoding integrated circuit, and the LM567 audio decoder is used.Figure 23-2T is an N-channel VMOS tube, and the BS107 type VMOS tube can be used. Its pin function is shown in (b) in Figure 23-2.BG1 and BG2 are NPN transistors, β>100, and 3DK4 is selected.BG2~BG6 are NPN transistors, β>150, 3DG6 or 9014 can be selected.BG7 is a PNP transistor, β>100, 3AX31 or 9012 can be selected.BG8 is a single-junction transistor, and BT33B is selected. The inter-electrode resistance should be as small as possible to reduce the total current of the control circuit.SCR is a unidirectional thyristor, using any type of 1A, 400V unidirectional thyristor. …

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