A night lamp circuit is an automation system for lighting in rooms. The circuit is using an LDR to detect the darkness in the room. Additionally, diodes and transistors play a main part in circuit operation.
Hardware Components
The following components are required to make an Automatic Night Lamp Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Transistor | 2N3904 | 1 |
| 2. | LDR | – | 1 |
| 3. | Zener Diode | 12V | 1 |
| 4. | Diode | 1N4148, 1N4007 | 2, 4 |
| 5. | Capacitor | 1µF | 1 |
| 6. | LED | – | 6 |
| 7. | AC power supply | 220v | 1 |
| 8. | Variable resistor | 100KΩ | 1 |
| 9. | Resistor | 1KΩ, 470KΩ | 1,1 |
| 10. | Electrolytic capacitor | 220µF / 25V | 1 |
2N3904 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 2N3904
Automatic Night Lamp Circuit
Working Explanation
The AC power supply, first, reaches the capacitor of 1µF / 400V that converts the AC high voltage to much lower voltages. This is, then, rectified by the full wave rectifier made out of the combination of four 1N4007 Diodes. Thus, AC voltage converts to DC voltage. To filter the ripples of the signal, a 220µF capacitor does the job. Furthermore, the filtered DC signal steps down to 12V using a 12V/1W Zener Diode in the circuit.
An LDR is connected to the circuit to detect the darkness nearby. The sensitivity is set using the 100KΩ variable resistor in the circuit. In the case when the room is dark, the LDR inputs signal to the transistor 2N3904. Hence, the transistor becomes activated providing the stepped-down voltage of 12V to light the six LEDs in the circuit.
Since the circuit is connected directly to the main AC supply system, therefore, extra care must be taken while the circuit is in operation.
Application
Automation system of a house, office, or building.
