Street light circuits or street lamps play an important part in maintaining safety regulations in transportation networks. In this project, we are going to build a simple street light circuit using an LDR & a 5V relay.
The circuit uses a Light Dependent Resistor (LDR) to sense light. The circuit is quite sensitive & versatile. It can be used to activate any 220-volt AC device at night and turn it off during the daytime. The circuit diagram present here is that of a street light that automatically switches ON when the night falls and turns OFF when the sun rises. In fact, you can use this circuit for implementing any type of automatic night light.
Hardware Components
You will need the following parts to build this Circuit.
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Breadboard | – | 1 |
| 2. | Connecting Wires | – | 1 |
| 3. | Battery | 9v | 1 |
| 4. | SPDT Relay Module | 9V/5V | 1 |
| 5. | AC Supply | 220V | 1 |
| 6. | Suitable Load (AC Bulb) | – | 1 |
| 7. | NPN Transistor | 2N3904 | 2 |
| 8. | Diode | 1N4004 | 1 |
| 9. | POT | 50KΩ | 1 |
| 10. | Resistor | 1KΩ, 33Ω | 1 |
2N3094 Pinout
Circuit Diagram
Working Explanation
The operation of this circuit is very similar to that of a darkness detecting circuit or a dark/ light sensor. In this circuit transistors, Q1 & Q2 behave as switches. During the daytime, the resistance of LDR decreases, subsequently increasing voltage at the base of transistor Q1. The collector of Q1 joins to the base of Q2. So, Q2 will remain off & the relay will not energize, due to which the street light will remain off.
When the night starts to fall, the resistance of LDR increases as the light intensity decreases. This triggers the transistor Q1 to switch off, due to which the voltage at the base of Q2 increases & switches on. This subsequently energizes the coil of the 9V/5V relay module & the street light turns on. In case you’re using a 9V Battery to energize the 5V relay coil, connect a 33Ω resistor in series with the coil, or else you run the risk of frying up the coil. You can also connect a 220V plug socket with the load point to connect different electronic devices but make sure the relay points are able to handle the provided load.
Applications
- Automatic street lights are usually used to control the street lights. They also serve as a remarkable battery management system for common electronic projects.
- It can be used to activate outdoor lights at night time like garden lamps, night lights, etc.
