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555 electronic eyesight protector circuit

2016-09-27 12:16  
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555 electronic eyesight protector circuit
As the figure 16-5 shows, the protector is composed of the reading time limit reminder and the reading environment metering device, and it can be used to protect the students' eyesight. The multivibrator is composed of the IC1(555) and the R1, R2, C1, the oscillation period T=tcharging+tdischarging, when you are using it, press the AN1, the 555 sets, at the same time, C1 is charged by R1 and R2, the time of charging is about 50 minutes, tcharging=0.693(R1+R2)C1. When pin-6's electrical level is 2/3VDD, the 555 reverses and resets, the pin-3 has the low electrical level, the music IC sends out the voice to remind you to have a rest. The reading environment metering device is composed of the IC2, R5,R6,C2, R4 and the photoresistor RG, when the reading light intensity is lower than 100 lux, the value of RG becomes higher.