Question

Automatic street light controller working principle

Answer 1

You have seen street light which automatically gets turned on in the night and gets turned off in the morning or day time, there are sensors who senses the light and control the light accordingly. These Street lights are an important project in smart cities.

 

So here in this project, we are going to make aSimple Automatic Street Light Controller Using Relay and LDR. This circuit is very simple circuit and can be built with Transistors and LDR, you don’t need any op-amp or 555 IC to trigger the AC load. Here we have used an AC bulb as street light. Some applications of this circuit are street light controlling, home/office light controlling, day and night indicators, etc.

 

Components Required:

Transistor BC547 -2LDR (Light Dependent Resistor)RelayResistor 1k100k PotentiometerPower Supply 12v -1Connecting wiresJumper wiresScrew terminal Block 2 pin or 3 pinBread Board or Perf Board1n4007 DiodeAC supplyAC Load or Bulb

 

What is LDR?

LDRs are made from semiconductor materials to enable them to have their light sensitive properties. There are many types but one material is popular and it is cadmium sulphide (CdS). These LDRs or PHOTO REISTORS works on the principle of “Photo Conductivity”. Now what this principle says is, whenever light falls on the surface of the LDR (in this case) the conductance of the element increases or in other words the resistance of the LDR falls when the light falls on the surface of the LDR. This property of the decrease in resistance for the LDR is achieved because it is a property of semiconductor material used on the surface.

 

 

Circuit Diagram and Explanation:

Below is the circuit diagram of this Light sensing Street Light:

 

In this project, we have used an LDR (Light Dependent Resistor) which is responsible for detecting light and darkness. The resistance of LDR increases in darkness and reduces in presence of light. This circuit is same as a Dark Detector or Light Detector Circuit, only here we have replaced simple LED with a AC load, using a Relay. Two BC547 NPN transistors are used to drive the relay.