• Light dependent resistance LDR
• Take two transistors. (NPN Transistor - BC547 or BC147 or BC548)
• Resistance: 1K, 330Ohm, 470 ohms
• Light emitting diode (LED) - Any color
• Connection wires: Use a 0.6 mm diameter single core plastic coated wire (the standard size). You can use the wire that is used for computer networks.
• Power supply-6V or 9V
Process
• Insert the first transistor Q1-BC547 (NPN) into the motherboard (or general PCB) as shown in circuit diagram 1.
• Connect another transistor Q2-BC547 (NPN) to the test board as in step 1.
• Connect the cables through the transmitter pin of both transistors and the -ve terminal of the battery (lower / lower row of the test board).
• Connect a wire through the collector pin of transistor Q1 and the base pin of transistor Q2.
• Connect a 1K resistor through the positive battery terminal (top row of the test board) and the pin of transistor Q1.
• Connect the light dependent resistor (LDR) through the positive battery terminal (top row of the processing board) and the base terminal of transistor Q1.
• Insert a 330 Ohm resistor into the base pin of transistor Q1 and the negative terminal of the battery (the lowest bottom row of the test board).
• Connect a resistor 330R through the positive battery terminal (upper row of the processing plate) and the LED anode terminal (light emitting diode) and Connect the cathode terminal of the LED to the collector pin of transistor Q2 .
The simple circuit is ready for testing now. Connect the 6V battery terminals to the circuit as shown in the figure and see the output. When the light that falls on the light dependent resistor (LDR) is blocked, the LED lights up.
THE LED INCREASES IN LESS DARK. Use the torch light or lighter if the LED glows in less darkness. In addition, you can try to adjust the sensitivity of this circuit using a variable resistor instead of R1-300Ohm. Try this circuit with other resistors too (eg 1KΩ, 10KΩ and 100KΩ, etc.)