Morning Light Alarm Circuit

Introduction:

                        This project is named "Morning Alarm or Light Activated Alarm Circuit" and utilizes a BC-548 Transistor. The functionality of this project relies on sunlight, and a Light Dependent Resistor (LDR) is employed to sense light. When light falls on the LDR, its resistance value is low, and in the absence of light (darkness), the resistance value becomes high. This is the basic principle of the LDR. Now, let's explore how to create a "Morning Light Alarm."

Circuit Connection:

                                      

1. Start by securely fitting and soldering the Transistor in the center of the DOT Board.
   
2. Solder the LDR on the left corner at the top of the DOT Board and connect a 1KΩ resistor serially to the LDR.
3. Connect the 1st pin of the LDR to the positive terminal of the power supply and connect the 2nd pin of the 1KΩ resistor to the negative terminal of the power supply.
4. Connect the 3rd Emitter pin of the Transistor to the negative terminal of the power supply.
5. For the output side, connect a buzzer or any other output device. Connect the negative terminal of the buzzer to the 1st pin (Collector) of the Transistor and connect the positive terminal of the buzzer to the positive terminal of the power supply.
6. Connect the 2nd pin (Base) of the Transistor between the LDR and the 1KΩ resistor.
7. Provide the input supply between the positive terminal of the buzzer and the Emitter pin of the Transistor.

Circuit Diagram:

Working:

This circuit closely resembles the Automatic Night-Light Circuit. However, while the night-light circuit activates the transistor in darkness, this circuit activates the transistor in the presence of light. The Photoresistor and the Resistor together form a voltage divider. To comprehend this, it's essential to understand how the transistor operates. In darkness, the Photoresistor exhibits high resistance, much higher than R2. Consequently, the voltage divider produces a low voltage at the Transistor's Base, keeping it turned off. When the Transistor is off, the buzzer remains deactivated.

        Conversely, in the presence of ample light directly on the Photoresistor, its resistance decreases. This results in a higher voltage at the base of the transistor, causing it to turn on. Consequently, the buzzer is activated and starts producing sound.

 

Pinout Diagram of BC-548 Transistor:

Part List:

1)   BC-548 Transistor =1

2)   1KΩ ¼ Watt Resistor =1

3)   Buzzer or LED =1

4)   LDR (5mm) =1

5)   Some Wires

Uses of this Circuit:

                        If we Use this Circuit on our Top of the Outer House, We Know When the Sun was Rises.

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By,

G.Guruvel Sarveshwar,

EEE Dept.