Dark dark-activated LED circuit using SCR is a simple and interesting project, it will turn on the LED when there’s darkness around the LDR, and SCR is used here for switching purposes.
SCR (Silicon Controlled Rectifiers) or thyristors are physically the same as transistors and are also used for switching in circuits but their built-in circuit and working are entirely different than transistors. SCR has three junctions, Anode, Cathode, and Gate, and operates in three states i.e., ON state, OFF state, and Reverse Blocking. It has four layers of semiconductors NPNP or PNPN. It can handle high AC voltages whereas transistors are used for low DC voltages.
Hardware Components
The following components are required to make a dark-activated LED Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Breadboard | – | 1 |
| 2. | LED | – | 1 |
| 3. | Battery | 6V | 1 |
| 4. | LDR | – | 1 |
| 5. | SCR | 2P4M | 1 |
| 6. | Resistors | 330 ohm, 1K | 1 |
| 7. | Variable Resistor | 50K | 1 |
| 8. | Wires | – |
2P4M Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 2P4M
Dark Activated LED Circuit
Working Explanation
This circuit can be operated by a 6-volt battery. The working of this circuit depends on two main components one is LDR. LDR is a Light Dependent Resistor and it works according to the intensity of the light sensed by it. When the light intensity is maximum its resistance is lowest and vice versa.
The other main component is SCR, which is working as a switch for this circuit. When there is no light in the room where this circuit is present the LDR’s resistance will be maximized and it will stop the voltage from going to the ground, SCR will get its desired voltage to switch on which will activate the LED.
The variable resistor is used to adjust the amount of the dark on which you want your LED to turn ON. The other two resistors are used to work as current limiters for LDR and LED.
Application and Uses
Since we are using an SCR instead of a transistor this circuit can be used where High AC voltages are involved. You can use this circuit as a bedside lamp with a few modifications or in different electronic projects, toys or emergency lights.
