procedure for basic circuit with LDR and relay

This is Basic Circuit with LDR and Relay, when the LDR is exposed to light its resistance falls, thus the base current increases and consequently the collector current. The LED will be illuminated and the relay will energise. RV2 will adjust the level of light needed to turn the LED on.

Procedure

1. Identify all the components you will use.
2. Place and solder the resistors R1, R2 and D1.
3. Now place and solder VR2, LDR1 and the LED.
4. Place and solder the battery clip and TR1: making sure the base connection goes to the centre hole of TR2, not to its normal position.
5. Place and solder the relay RL1.
6. Check the circuit works by connecting a battery to the clip. Set VR2 to its mid position, cover the LDR with your hand, the LED should be off and the relay de-energised. Now remove you hand from the LDR and provided there is enough light in the room the LED should come on and the relay energised. Remember VR2 acts as a light sensitivity control.

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