Automatic Night Light using LDR and IC 555

Hello friends! Welcome back to ElectroDuino. This blog is based on how to make Automatic Night Light using LDR and 555 Timer IC. Here we will discuss the Introduction to the Automatic Night Light, Project Concept, Block Diagram, Components Required, Circuit Diagram, and Working Principle.

Introduction

We all install outdoor lights and garden lights at home, offices, schools, and shops, which gives light at night time. Most of the outdoor lights and garden lights are operated manually, it means we need to turn on the light in the evening and turn off it in the morning. But, we always face a problem with this manually controlled night light, that is sometimes we forget to turn on the light in the evening or switch it off in the morning. Which loss electricity and increase our electricity bill. And turning on and off the light on a regular basis is a boring job.

To overcome this problem we are going to learn in this project tutorial how to make an Automatic Night Light Circuit using LDR and 555 Timer IC. Basically, this circuit detects the presence of sunlight and turns the lights on and off automatically. It means, at the evening time when sunlight intensity is low (nearly dark) then the circuit detects dark and turns on the light automatically. On the other side in the early morning when the sunlight is coming then the circuit detects the presence of light and turns off the light automatically.

Project Concept of Automatic Night Light using LDR and IC 555

The Automatic Night Light Circuit is a fully automatic light-switching device, which detects surrounding Light and controls the light bulb automatically. The Project Concept of the Automatic Night Light Circuit is very simple and easy to understand. In the evening time when the LDR of the circuit will detect the sunlight intensity decreasing (detects Dark), then the circuit turns ON the light bulb. Vice versa in the morning time when the LDR of the circuit will detect the sunlight then the circuit turns OFF the light bulb.

This circuit is divided into two parts one is the power supply unit and another one is the control unit. Here we will use a transformerless power supply which makes this circuit low-cost and compact. The Power supply unit of the Automatic Night Light Circuit is built of a few resistors, capacitors, and rectifier diode. The Capacitors are used to drop the AC voltage and the resistors are used as the current limit to protect our circuit. Here we use 4 rectifier diodes to build a full wave bridge rectifier circuit that converts the AC voltage into DC voltage. This DC voltage is given to the whole circuit.
The key components of the control unit of this circuit are LDR (Light Dependent Resistor), 555 Timer IC, BC547 Transistor, and Relay. The LDR (Light Dependent Resistor) is a light-sensitive resistor whose resistance changes as the amount of light falling on it changes. Here the LDR is used as a light-detecting sensor, its output is given to the 555 Timer IC. The famous 555 Timer IC is the main controller chip of the control unit circuit, it controls the whole operation of the circuit. This timer IC takes the output data from LDR and generates output voltage from its Output Pin. The BC547 Transistor is work as a switching device, it is operated by the output voltage of the timer IC and it controls the relay operations. The Relay is used to handle the AC voltage, it controls the AC voltage light Bulb operation (ON/OFF).

Block Diagram of Automatic Night Light using LDR and IC 555

Components Required

Tools Required

Circuit Diagram/ Schematics of Automatic Night Light Circuit using LDR and 555 Timer IC

Working Principle of Automatic Night Light Circuit using LDR and 555 Timer IC

In this Automatic Night Light circuit we have used a transformer-less power supply to generate low-volt DC, which makes this circuit low-cost and compact. Here we used some resistors, capacitors, and diodes to design this power supply unit. At the beginning of the circuit, we used two capacitors (C1a and C2) and Resistors (R1 and R2). Where the two 1 µF, 400V capacitors C1, and C2 are used to drop the mains voltage up to the desired level, and another side two 220 Ω, 1W resistors R1 and R2 are used as current limiters which drop the current to protect the circuit from instant high current. Two 470K-ohm Resistors R3 and R4 are connected parallel to capacitors C1 and C2 respectively, these two resistors are used to discharge these two capacitors (C1 & C2) when power is off. These resistors prevent shock due to energy stored in these capacitors.
The low voltage output of capacitors C1 and C2 is not a DC voltage, it is AC voltage that contains some ripple. So we need to change it to DC voltage. For changing AC to DC voltage we used a bridge rectifier circuit which build of four 1N4007 general-purpose rectifier diodes. The output of the rectifier circuit is DC voltage, but still, some ripple is present, that’s why a 470uf Capacitor (C3) is connected to the output to filter it and make ripple-free DC output. LED1 is indicated the working status of the power supply unit and resistor R5 is a current limiter resistor that protects the LED from burning out.
The control unit of the Automatic Night Light Circuit is designed using the famous 555 timers IC and LDR (Light Dependent Resistor). The 555 timer IC is the main controller of this circuit, this IC can be configured in different modes. In this project, the 555 timer IC is configured in bi-stable mode. In this mode, the Timer IC gives High output (from pin 3) when its threshold pin becomes low, which means the output goes high when the threshold pin is connected to the ground. In this circuit, the trigger pin (pin 2) and threshold pin (pin 6) of the timer IC are connected together and these pins are further connected between LDR and 470ohm Resistor (R6) where the output of LDR appears.

At night time when no lights fall on the LDR surface, then it offers High resistance. In this condition the threshold pin of the 555 timer IC gets low voltage (ground), as a result, the internal flipflop is set and the output pin (pin 3) of the 555 Timer IC becomes High. This time the base terminal of the BC547 transistor gets High voltage, which activated the transistor and now it acts as a closed switch. For this reason, the relay is connected to the ground through the transistor, which activates the relay. As a result, the bulb gets a power supply through the relay and the bulb is turs ON.

In the daytime when sunlight falls on the LDR surface, then it offers low resistance. In this condition the threshold pin of the 555 timer IC gets high voltage, as a result, the internal flipflop is reset and the output pin (pin 3) of the 555 Timer IC becomes low. This time the base terminal of the BC547 transistor gets Low voltage, that’s why the transistor goes into the cut-off region and it acts as an open switch. For this reason, the relay is disconnected from the ground, which deactivates the relay. As a result, the bulb is disconnected from the power supply and it gets switched off.