How to make automatic street light using LDR circuit

 

How to make automatic street light using LDR circuit

Friends, today we will design the automatic street light circuit, which is made with the help of LDR, BC 547 transistor and relay. With the help of this circuit, we can get the main (220V) led bulb automatic ON and OFF. Some components are required to make this circuit. Those components are something like this.

1.   LDR ----------------------------1pc

2.   BC547 -------------------------1pc

3.   Resistance 10KΩ -----------1pc

4.   Led bulb 220V ---------------1pc

5.   Battery 9VDC ----------------1pc

6.   Relay 9VDC ------------------1pc

7.  General PCB------------------1pc

8.   Connecting wires

 Before making this circuit, it is very important to know some important components. Because the circuit we make, we must first know about the components inside it, what are they doing in our circuit.

1) LDR

As its name suggests, it is a kind of resistor, which depends on the light. As the light decreases or increases, its resistance decreases and increases. Its resistance increases very much when it is dark light. Due to which current flow is not possible. Its resistance decreases when it is bright light. Due to which current flows easily.

 2) BC547(Bipolar Junction Transistor)

As its name itself suggests, it has 2 junction (N junction and P junction). This transistor consists of 3 terminals (Base, Collector, Emitter). It is an NPN transistor. When positive supply provide to the base of the transistor, due to which the transistor works in ON condition. The direction of current of NPN transistor is emitter from collector. Transistor is current control device.  

3) Resistance 

Resistance is a property of conductor that prevents the current flowing in the circuit. The unit of the resistance is OHM (Ω). 

Now we make the automatic street light circuit.

Working

Diagram construction

As shown in Fig 1, the positive terminal of the battery is connected to a terminal of resistance R1 and cathode terminal of diode D1 and relay coil terminal 1 and the negative terminal of the battery is directly connected to the ground.

 The second terminal of Resistance R1 is connected to the base terminal of transistor BC547 (Q2) and terminal 1 of LDR1. Terminal 2 of the LDR1 is directly connected to the ground. The anode terminal of diode D1 is connected to the collector terminal of transistor BC547 (Q2) and relay coil terminal 2. The emitter terminal of the Transistor BC547 (Q2) is directly connected to the ground.

Working

As you can see in Fig 1, If it's night time there is no light on the LDR. This means that the resistance of LDR is high and there is no current flowing in the LDR. 

Fig 1

The transistor BC547 (Q2) will turn ON due to the positive resistance of the battery coming from the positive terminal to voltage resistance R1and the transistor BC547 (Q2) getting a positive supply from resistance R1. Due to turn ON the transistor BC547 (Q2) collector and emitter terminal short and ground terminal will connect to the relay coil terminal 2.

 As soon as the relay coil terminal 2 gets ground, the relay will become ON. As soon as the relay is ON, the common point of the relay will connect with the normally open(NO) and the main supply will be ON which will cause our lamp to burn. Now our lamp will keep burning at night.

 As you can see in Fig 2, as soon as morning comes the light comes on the LDR, the resistance of the LDR will decrease and current flow will start from it. Due to the low resistance in the LDR, the base terminal of the transistor BC547 (Q2) will get ground supply and the transistor BC547 (Q2) will be OFF. 

Fig 2

So that contact between collector and emitter terminal of transistor BC547 (Q2) will be lost. Now due to lack of ground of relay coil terminal 2, the relay will be OFF. As soon as the relay is OFF, the common point of the relay will  connect with the normally close(NC) and the main supply will be OFF so that our lamp will be OFF. Now our lamp will remain OFF during the day. Then in the evening the lamp will go automatic ON and in the morning the lamp will go off automatically. We can take a preset of 100KΩ instead of 10K in resistance R1 to get the lamp turned ON-OFF quickly.

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Ishan Kumar