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555 darkroom timer circuit 1

2015-02-05 13:12  
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555 darkroom timer circuit 1
As shown in Figure 17-14, the timer includes buck rectifier circuit and 555 single stable control circuit and relay control. Buck rectifier provides +10 V voltage source for 555 timer. 555 and R1, R2, C1 form a single stable timing circuit, clicking the AN1, the timer starts, 555 sets, J pulls in, CZ2 is lit; CZ1 has no electricity, lights is off. Regular time td = 1.1 (R1 + R2) C1. After timing, J releases, CZ2 loses power, enlarger lamp gets power, the red lamp is lit, CZ1 gets electric, the red light will be like a paper developing and fixing. The resistance of R1 is 140K ~ 530kΩ; the resistance of R2 is 15k ~ 125kΩ.