Fritzing

Components: --------------------   * npn Transistor 2N3904 * Resistance 100 kOhm * 5V DC Supply * LDR * Resistance 220 Ohm

• 
• 
• 
• 

Idea:

---------

 

Control the LED ON/OFF using the npn Transistor.

 

Case (1): when there's light, the transistor will be in cutoff region,

and the LED will be OFF.

 

Case (2): when there's dark, the transistor will be in active region,

and the LED will be ON.

 

And the LDR will control the operation region of the transistor.