Design And Construction Of Light Sensitive Alarm

DESIGN AND CONSTRUCTION OF LIGHT SENSITIVE ALARM

Light Sensitive Alarm

ABSTRACT

This project work is on the construction of light sensitive alarm. Which aim at activating an alarm at sunset and deactivate it at sunrise. This light sensitive alarm can triggers an alarm at Sunset indicating that there is daylight . The lamp remains on till dark hour and then turns off.
The circuit utilizes the light sensing property of LDR to activate the circuit. The LDR (Light Dependent Resistor) has very high resistance as high as 10 Meg ohms in dark which reduces to a few Ohms in bright light.

CHAPTER ONE
1.0                                                        INTRODUCTION
The controlling of street lights is usually maintained by an electrical department’s technician on several occasions. This is not only precarious but also sometimes results in wastage of power because of the negligence or unusual circumstances on part of the technician in operating the lights on and off. Not only in case of street lights, even for controlling the home appliances like garden or outdoor lights, we can utilize the light activated switch for automatic switching of the lights based on daylight’s intensity by using a light sensor.
Light Activated Switch is a  electrical project circuit by which we can switch on and off the electrical load appliances like lights, fans, coolers, air conditioners, street lights, etc., automatically based on the day-light intensity instead of manually operating the switches.
By using this method, manpower can be reduced to a great extent. In case of the street lights/lamp erected on highways it is not an easy task to manually control them, but, if uncontrolled, the chances of power wastage would increase. To get rid of this situation, the implementation of automatic light switch by using a light sensor that switches lights automatically on and off is the best option.

1.1OBJECTIVE OF THE PROJECT                                        
The objective of this work is to design a device that will trigger an alarm when light falls on the sensor                            1.2    SCOPE OF THE PROJECT
A light activated switch is an electronic  consisting of LDR, transistor and Relay as connected in the main circuit, as shown below.
The circuit shown below requires a DC voltage, which can be supplied from a battery or by using a bridge rectifier instead of the battery. The bridge rectifier uses a step-down transformer to step-down the 230v into 12v.
This circuit is to switch ON the light when the LDR is illuminated. The light dependent resistor will have high resistance in darkness and low resistance in the light. The comparator used here has LDR connected to its inverting terminal and potentiometer connected to its non-inverting pin.
When the light falls on the Light Dependent Resistor, the comparator compares the voltages at the reference pin that is with the non-inverting pin and the inverting pin of the op-amp. If the voltage at the non-inverting pin is greater than the voltage at the inverting pin the transistor cannot be switched. If the voltage at non-inverting pin is less than the voltage at the inverting pin, the output of the comparator can switch the transistor.
Thus the relay switches and light are switched on when LDR is illuminated as transistor switches.

1.3     SIGNIFICANCE OF THE PROJECT
This device is very useful in that it distinguishes daylight and dark hours. This device eliminates the need of switching the Porch lamp or Backyard lamp daily and also helps to switch ON or OFF the premises of the house when the occupants are out of station.

1.4   LIMITATION OF THE PROJECT
One of the problems of this device is that any opaque material can trigger the device, such as human shadow, movement of animals or ants across the sensor can trigger the system

1.5   APPLICATIONS OF THE PROJECT

• Useful for automatic outdoor lighting or garden lighting at home.
• Useful for automatic switching of street lights.
• Useful for switching the hoardings on and off automatically.
• Useful for self-switching operation of displaying title hoardings of companies.
• Useful as a light detector circuit.
• Useful as a dark activated switch.

 

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