# Automatic Street Light Using Ldr

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## Introduction: Automatic Street Light Using Ldr

Save electricity by this simple project.

It glows during night and switches off automatically as the sun rises.

I have tried a lot of circuits but i made one and this works perfectly.

It is a project depicting the proverb "TRY AND TRY TILL YOU SUCCEED".

### Teacher Notes

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## Step 1: Components

• A LDR(Light Dependent Resistor)
• A NPN Transistor (Here I used BC547)
• 470R Resistor (R1)
• 470 k Resistor (R2)
• An LED (Desired Color)
• 9V Battery
• Wires for connection

## Step 2: Principle of LDR and Transistor Used

The working principle of LDR is that it gives less resistance in high light intensity and high resistance in low light intensity (ie) it gives high resistance in dark or night and low resistance in day or light.

Here we use transistor as a two way switch. If the voltage through base is greater than 5V it send through the emitter. If the voltage through base is less than 5V the it sends through collector.

During night the LDR gives a high resistance as a result the voltage passing through the base will become less than 5V so the LED glows.

During day time LDR gives a low resistance as a result the voltage through base is greater than 5V which switches the current to the emitter. This turns LED off.

## Step 3: Circuit and Connections

Place the transistor on the breadboard.

Connect the Emitter to the negative of the battery.

Base to one terminal of LDR

Connect the resistor(R2) to base and positive terminal of battery

Collector to the anode of LED(Small leg)

From cathode of LED(Long leg) to resistor (R1)

Another end of resistor (R1) to positive terminal of battery

Another terminal of LDR to negative terminal of battery

(The circuit and the reference for E B C of transistor have been attached)

## Step 4: Large-Scale Idea

If this is done in large-scale the a lot of electricity can be saved. No need to search of other forms of electricity.
Let's first time spend money on useful ideas of the YOUNG SHINERS

LETS BE HAPPY WITH WHAT WE HAVE!!!!!!! :-) :-) :-)

Participated in the
Make it Glow Contest 2016

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## 14 Discussions

is that really a 470R resistor???

470 kili ohm

PLEASE ELABORATE THE WORKING PRINCIPLE OF THIS CIRCUIT. I WILL BE HIGHLY OBLIGED FOR YOUR KIND HELP.

Do not forget to specify that there are two types of LDR: positive and negative. One decreases resistence with light, the other increases resistence with light (perhaps it is the opposite).

SIR, I NEED A HELP FROM YOU. WILL YOU PLEASE ELABORATE HOW DOES THIS CIRCUIT WORKS??? ACTUALLY I AM A STUDENT AND I HAVE TO ELABORATE IT TO MY TEACHER.
IF YOU HELP ME I WILL BE HIGHLY OBLIGED.

It is very easy to understand by every one and I really happy for this

May I know how the current flow through the whole circuit? Because you mention when the ldr give high resistance to the base the current flow through the collector but I think the current is flow from positive to negative side right, so how ldr give high resistance to the base?

Sir is the circuit common base or common emitter or common collector

Common Base Configuration

if you said 470 ohm it would be easier to understand..people might get confused

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