Light Sensitive Visitor Welcome Doorbell

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Here’s a very fascinating project about a doorbell circuit that welcomes light-sensitive guests. For a fixed period of time, the circuit will trigger the UM66 melody when any visitor comes close to your door or moves past the door. The circuit is broken down into three stages. The first stage is a very sensitive dark detection circuit, which is constructed using two 2N4401 transistors. Any related NPN transistors, for example, 2N3904, BC547, etc. will also operate here.

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Hardware Components

The following components are required to make Light Sensitive Doorbell Circuit

S.no	Component	Value	Qty
1.	Resistors	1K, 1M, 470 ohms	3, 1, 2
2.	LDR	–	1
3.	Electrolytic Capacitor	47uF, 0.1uF	1, 1
4.	Transistors	2N4401, BC548	2, 1
5.	IC	NE555 Timer	1, 1
6.	LED	–	1
7.	Speaker	8 ohms	1
8.	IC	UM66	1
9.	Ceramic Capacitor	0.1uF	2
10.	Battery	4.5V	1
11.	Potentiometer	1K	1

NE555 IC Pinout

For a detailed description of pinout, dimension features, and specifications download the datasheet of 555 Timer

UM66 Pinout

For a detailed description of pinout, dimension features, and specifications download the datasheet of UM66

Light Sensitive Doorbell Circuit

Working Explanation

The second stage is constructed around a timer IC 555. This stage is used to trigger the melody of UM66 for a given period of time. If the transistor Q2 receives output on IC’s control pin 2. The melody’s disabled time can be increased by increasing the value of the 47uF capacitor which is labeled in the schematic as Cx. The third stage is a circuit of the melody UM66. UM66 is a CMOS IC used in the transistor kit TO-92. It comes with a number of different melodies. A growing melody has a different code engraved on the IC. It is best to test the datasheet before buying one to buy your desired melody. A BC548 transistor is used to improve UM66 IC performance to drive an 8-ohms motor.