Automatically Illuminating Doorbell Circuit

Published:2011/5/17 5:53:00 Author:Robert | Keyword: Automatically Illuminating, Doorbell | From:SeekIC

It's difficult to find the doorbell button when at night and the veranda has no light, especially for the visitors who come firstly and they could only knock the door. If the doorbell button switch has been installed a LED which could automatically illuminating at night and automatically closed during the day, it would be convenient for visitors. When the power switch K1 is connected, the phototransistor triode BG1's resistance would be low because of the light during the day, and BG2 base voltage would be low to make BG2, BG3 close. So the circuit would stop working and the LED would not illuminate.



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