This Electronic Project is about Automatic Street Light Controller Circuit Using Relays and LDR. We all may have seen streetlights on different streets. These lights provide light at night while they are off during the daytime. This is because they turn on and off automatically with the help of an Automatic Street Light Controller Circuit. This circuit basically consists of relays and LDR.
Relays are basically open or closed switches that switch on or off when a current passes through its coil.
LDR stands for Light Dependent resistor. It is an electronic component that changes its resistance with the change in light intensity that falls upon it.
Hardware Components
The following components are required to make Street Light Circuit
| S.No | Component | Value | Qty |
|---|---|---|---|
| 1. | Breadboard | – | 1 |
| 2. | Battery | 12v | 1 |
| 3. | Lamp | 220v | 1 |
| 4. | NPN Transistor | BC547 | 2 |
| 5. | LDR | – | 1 |
| 6. | Potentiometer | 100k | 1 |
| 7. | Resistor | 1k | 1 |
| 8. | Diode | 1N4007 | 1 |
| 9. | Relay | 12v | 1 |
BC547 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of BC547
Street Light Circuit
Working Explanation
This Automatic Street Light Controller Circuit uses an LDR (Light Dependent Resistor) which is responsible for detecting light and darkness. LDR increases its resistance in darkness and reduces it in the presence of light. Here, Two BC547 NPN transistors are used to operate the relay.
At any time, when light falls over LDR its resistance decreases, transistor Q1 turns ON and the collector of this transistor goes LOW. Due to this, the second transistor turns OFF because of a LOW signal at its base. Hence, the relay remains OFF due to the second transistor.
Now, whenever LDR senses Darkness (absence of light), Q1 is turned ON due to the increase in resistance of LDR. Now due to a LOW signal at the Q1 base, Q2 gets a HIGH signal and turns ON the relay. The relay turns ON the AC load that is connected to the relay, i.e. the street lights
So, because of this circuit, Street Lights turn on at night and turn off during the day automatically.
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