Traditional Chinese Practical Light meter: Circuit Design, Parts List & Workshop Prototype Guide

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Vision protection light meterAt present, the phenomenon of vision loss among teenagers is quite serious. One of the main reasons is that the ambient light is too weak when teenagers read and write. According to the relevant regulations of the National Education Commission and the Ministry of Health, when reading and writing, the ambient light illumination should not be less than 100lx. Here is a small production of photometric electronics. When the light illumination meets the requirements, the green LED will light up; when the light is lower than the standard illumination, the red LED will emit bursts of flashes. as a warning.Circuit principle:The photometer circuit is shown in Figure 21-1. RG is a photoresistor, which forms a voltage divider with the potentiometer RP, and the voltage dividing point is connected to the base of VT1. When the ambient light is strong, the RG resistance becomes smaller, and the potential of the base of VT1, the voltage dividing point, rises. VT1 is therefore turned on, and the green light-emitting diode LED1 is energized and emits light. At this time, the collector of VT1 is at low potential and VT2 is turned off. The flash integrated circuit IC does not work if it does not receive power, and the red light-emitting tube LED2 does not light up.Figure 21-1If the ambient light is dark, the RG resistance becomes larger, the base potential of VT1 decreases, and VT1 changes from conduction to cutoff. LED1 stops emitting light. At this time, the collector of VT1 outputs a high potential, and VT2 obtains a forward bias current from R1 and is turned on. The IC is connected to the positive power supply, and the flash integrated block starts to work. The red light-emitting diode LED2 will emit eye-catching bursts of flash to remind you that the light is too dark to continue studying.By adjusting the potentiometer RP, you can change the voltage dividing ratio so that the turning point of the photometer can be adjusted to the standard illumination of 100lx.Component selection:IC is a dedicated flash integrated circuit, model KD-01X. It uses black paste soft packaging, and the silicon chip is packaged with black paste on a small printed circuit board with a diameter of Φ22mm, as shown in Figure 21-2. There are 4 small round holes on the printing board. Holes 3 and 4 are used to plug in and solder resistor R3. Holes 5 and 6 are used to plug and solder LED2. Pads 1 and 2 are the positive and negative terminals of the power supply respectively. There are two flash frequencies of this chip: 1, 2Hz and 2, 4Hz. Each frequency is determined by the oscillation resistance of the circuit inside the chip and cannot be adjusted by the outside world. …

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