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555 writing table lamp timing control circuit

2016-08-02 09:19  
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555 writing table lamp timing control circuit
As the figure 17-23 shows, the control circuit is composed of the capacitor step-down rectifier circuit, the low-frequency oscillator circuit and the control circuit. This circuit can automaticly control the light toturn on for 50 minutes and turn off for 10 minutes, then turns on again, so it can protect your eyesight and health. The astable multivibrator is composed of the 555 and the R2,R3,C3, the oscillation frequency f=1.44/(R2+2R3)C3, the capacitor C3's charging time t=1.1(R2+R3)C3, the discharging time t=1.1R3C3. The pin-5 of control port connects to the VDD to improve pin-6's threshold level.