NE555 light-controlled doorbell

The old residential area built many years ago has no public lighting on each floor. There is no doorbell either, so I had to install one each. Convenience also brings troubles. There are many rental houses in the community and many people working night shifts. In the dark, it is difficult to figure out which button is the light switch and which is the doorbell. The doorbell often rings in the middle of the night, making everyone restless. For this reason, the author used existing electronic components to make a doorbell (powered by mains electricity) that automatically opens during the day and closes at night. The doorbell has the characteristics of loud ringing, power saving, high reliability, and no false alarms.

The doorbell circuit (see attached figure) consists of a power supply circuit, a switch circuit, a light control circuit, a music doorbell circuit and a power amplifier circuit. The power supply circuit consists of a transformer T1, D1-D4, C1, etc. After power is turned on, a 12V DC voltage can be obtained at both ends of capacitor C1 to supply the time base circuit IC1 (555). One path of the 12V voltage is stabilized into 3V DC through R7, DW, and C6 to supply the soft package music doorbell IC2. Another path is used as a power switch V3 and a three-terminal regulator lC4 (7806) to provide a stable 6V voltage for the power amplifier integrated circuit IC3 (4100).

The light control circuit is composed of the time base circuit IC1, v1, V2, RG, RP, R1-R5, c2, and C3. During the day, RG is low-resistance under light, v1 is turned on, the time base circuit Ic1 ②, ⑥ pins are low level, ③ pin is high level, v2, v3 are turned on, the power amplifier IC3 has working voltage, and the bell is effective. On the contrary, at night, the bell is ineffective.

After testing, the working current of this circuit is about 20mA during the day, less than 10mA at night, and 150mA when the alarm sounds. The time base circuit, soft package doorbell chip, three-terminal voltage regulator, and power amplifier integrated circuit in the circuit are all commonly used and easy-to-buy components.