Simple Automatic Night Light using LDR and BC547 Transistor

This circuit is a great way to save energy on your electricity bill and provide a low-light illumination source at night. It is relatively inexpensive to build and uses common electronic components.

Components Required

• LDR (light-dependent resistor)
• BC547 transistor
• 4.7kΩ resistor
• LED
• USB Male connector
• Breadboard
• Jumper wires

How it Works

The LDR is a resistor that changes resistance based on the amount of light it is exposed to. In brighter light, the resistance of the LDR decreases. When it is dark, the resistance increases.

The BC547 transistor acts as a switch that is controlled by the LDR. When there is light, the LDR allows current to flow through the base of the transistor, turning it on and allowing current to flow to the LED, which lights up. When it is dark, the LDR blocks current to the base of the transistor, which turns it off and the LED does not light.

        Schematic Diagram

Building the Circuit

1. Connect the positive lead of the LED to a resistor. Connect the other side of the resistor to the collector pin (pin 1) of the BC547 transistor.
2. Connect the base pin (pin 2) of the BC547 transistor to one leg of the LDR. Connect the other leg of the LDR to ground (negative side of the power supply).
3. Connect a 4.7kΩ resistor to the positive side of the power supply and connect the other side of the resistor to the base pin (pin 2) of the BC547 transistor.
4. Connect the positive side of the power supply to the USB male connector and the negative side of the power supply to ground.

Here are some additional tips for building this circuit:

• Make sure that the LED is connected correctly with the positive side of the LED connected to the resistor.
• You can experiment with different value resistors to change the sensitivity of the night light. A lower value resistor will make the night light more sensitive to light.
• You can enclose the circuit in a small box and mount the LDR so that it is exposed to light.

Advantages of a Simple LDR Night Light:

• Energy Saving: This night light only turns on when it's dark, reducing electricity consumption.
• Low Cost: The components are common and inexpensive.
• Automatic Operation: No need to constantly switch it on or off - it takes care of itself!
• Customizable: You can adjust the light sensitivity and enclosure to fit your needs.
• Safe and Low Heat: LEDs emit minimal heat, making them ideal for night lights in children's rooms or near fabrics.

Uses for a Simple LDR Night Light:

• Night Light: Provides a gentle glow in hallways, bathrooms, or children's rooms for safe navigation at night.
• Accent Lighting: Creates a soft ambiance in living spaces or on shelves.
• Pathway Marker: Lights up walkways or driveways for nighttime safety.
• Automatic Plant Light: Can be adapted with a stronger light source to give plants a small amount of light during dark periods.

 

This is a simple circuit that can be used to create a night light that automatically turns on and off based on the amount of light in the environment. With a little creativity, you can customize this circuit to create your own unique night light.