Turn On LED On Dark Without Arduino Program

In our previous guide to Create an Arduino LDR Module With Transistor, at the end of the guide we discussed about lighting up LED without microcontroller with minimum modification of that circuit. Not all the readers are enough advanced to modify circuit own self to make the current thing. We Can Use NPN Transistor, Resistors to Turn On LED On Dark Without Need of Arduino Program. That is Great For Lighting Up Indicator LED on DIY LDR Module.

 

Circuit To Turn On LED On Dark Without Arduino Program

 

For this project, we need :

1. One 10K Ohm resistor
2. Two 1K Ohm resistors
3. One LDR
4. Few Jumper Wires
5. One LED
6. Breadboard
7. 3V to 5V power supply to breadboaard

 

We have drawn the circuit diagram using Fritzing in easy to understand way for the beginners, compare diagram of previous tutorial, Arduino board is absent in this case :

In the circuit, we are supplying 3V to 5V to two 1 K Ohm resistors. One of those 1K Ohm resistor, one is connecting to collector pin of transistor. This is a current limiting resistor which will help the transistor to switch between ON and OFF states. The same pin of transistor is also connected to one leg of LED. Another 1K Ohm resistor is connected to one leg of LDR. It is a pull down resistor. Another leg of LDR is connected to base pin of transistor and 10K Ohm resistor. End of the 10K Ohm resistor is going to emitter of transistor, (-)ve of battery and LED’s another leg. Current flowing through collector to emitter is directly proportional to the current applied at the base of the transistor.

This is quite useful easy project, specially entertaining and safe for the children as two AA batteries can be used. The circuit actually for 5V supply. You may need to adjust the resistors for lower than 3.3V or use LED with needs lesser power to light up.

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