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Automatic Lighting Doorbell Circuit

2014-11-11 14:46  
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Automatic Lighting Doorbell Circuit
Automatic Lighting Doorbell Circuit
When in the night and the veranda also has not light, the doorbell's button is hard to find, especially for the new visitors. They could only knock the door. If adding a LED on the doorbell button switch, and the LED would automatically flash in the night. And it would automatically shut down in the day. This would provide the convenience for the visitors.The picture 1 shows the automatic lighting doorbell circuit.When the power switch K1 is closed, the phototransistor BG1's resistance would be reduced as it is under the light in the day. And the BG2 tube's base polar's voltage would also be reduced to make the BG2, BG3 be not conducted. Then the circuit would stop workng and the LED would not flash.