Hardware Required
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | LDR | 5mm | 1 |
| 2. | NPN Transistor | BC547 | 2 |
| 3. | Relay | 9V | 1 |
| 4. | Diode | 1N4007 | 1 |
| 5. | Potentiometer | 100KΩ | 1 |
| 6. | Electric Bulb | 230V | 1 |
| 7. | Resistor | 1KΩ | 1 |
| 8. | Battery | 9V | 2 |
Circuit Diagram
Working Explanation
In this circuit of Automatic Street Light Controller using LDR, when the light falls on LDR it becomes an element that is less resistive and therefore allows bias to appear at transistor Q1 base. It turns ON the transistor Q1. Since there is no bias at the base of transistor Q2, therefore it remains OFF. In this condition, the Relay coil is not getting the supply, hence remaining OFF. When no light falls on LDR, now it becomes a highly resistive element and there. In this case, no bias appears at the base of the Q1 transistor, so Q1 turns OFF, and bias arrives at the base of the transistor and turns ON the transistor Q2. Now the Relay coil gets power and therefore becomes energized and makes the contact. As a result output bulb starts to glow.