Two-in-one Project

                              (Based on LDR)

Hi friends, Today I am going to show to “TWO IN ONE PROJECT” based on LDR...the two projects are, one is lights ON at night time and lights OFF at day time(street lights), second one is Laser security system to your home(night)

So first to know about LDR and their working…

About LDR :-

LDR means ‘LIGHT DEPENDENT RESISTOR’ and is also called ‘PHOTO RESISTOR’. It is available in two terminal device with different sizes in market.

Basically LDR is works like a SENSOR, when lights ON or OFF the resistor value is decrease or increase respectively. It changes resistor values depend on light, so LDR is also called Light dependent SENSOR. You can see below image for your understanding

Measure LDR Resistance

If we can do any project based on light we must and should use LDR for better result.

 Let’s show you the circuit diagram below

Circuit diagram :-

Two in one project circuit diagram 

List of the components :-

* Transistors BC 548 - 2 No's

* LDR - 1 No's

* Resistors 330E - 3 No's     (E - Ohms)

* 6-9V DC supply

* Indicator - LED or SPEAKER

As you seen in the circuit diagram LDR and two transistors are connected with resistors and LED. In this circuit we can use two NPN transistors (BC 548). Whenever light falls on LDR with high intensity then the resistor value is decreasing then total current is passed through LDR and resistor R1 so no current is passed through LED, then it is in OFF state. Similarly when lights intensity decreases on LDR then increases in resistor value. If resistor value increase, no current passes through LDR, then no current flows through the base terminal of the Q1 transistor, so Q1 is in OFF state. At that time Q2 is in ON state the reason is the total current is flows through R2 and base terminal of Q2 transistor. That time LED is ON the reason behind is whenever Q2 is ON, the LED is connected to ground terminal via Q2. So this working process the LED is on only night time.

(If you can use 10K variable resistor instead of 330E(R1) then we can change the sensitivity of LDR) 

WE CAN DO LASER SECURITY SYSTEM 

Use this circuit we can do laser security system at home with simple technique and very easily. First you have one laser light, on night time LED is ON continuously so whenever Laser beam in inserted on LDR the LED is OFF. If a laser beam is cut off then LED is ON. We can also connected speaker parallel to LED it becomes easily to listen sound when person is coming inside...

Advantages:-

* It is very simple and easy circuit 

* Useful project with low cost

                   https://www.youtube.com/watch?v=-gKgT8H3gL4&feature=em-upload_owner