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Summary

i have designed light sensing system...

Description

Automatic Light Fence Circuit with Alarm Introduction: The presence of human or any object in a specific area can be detected by using the light fence circuits. Light fence circuit is used to detect an object from 1.5 to 3 meters. Here I design the light fence circuit with the help of LDR and Op-amp. The circuit can work properly by applying 9V power supply and the presence of human, vehicle or any other object can be detected by using the buzzer. We can also use other sensors instead of LDR in such type of security system. For Example  

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Components used: In order to design an automatic light fence circuit with alarm both on breadboard and on Proteus I have used the following components: Components

Quantity

Battery - 9V

1

LM741 Op-amp IC

1

LDR

1

BC557 – PNP Transistor

1

10kΩ Resistor

1

210Ω Resistor

1

1kΩ Resistor

1

5.7kΩ Resistor

1

100kΩ Resistor

2

1MΩ Resistor

1

10µf and 0.1µ Capacitor

1

Buzzer

1

LED

1

Breadboard

1

LDR LDRs are made up of semiconductor materials which enable them to have their light sensitive properties. They are light dependent resistor. There are many types of LDR but cadmium sulphide (CdS) is mostly used. The working principle of LDR are based on Photo Conductivity. According to this principle the conductance of element increases as soon as the light start falling on LDR surface.

Figure 1 shows LDR

555 Timer IC For triggering purpose we mostly use 555 timer IC in electronic. In order to create a beep sound with buzzer I have used the 555 timer IC in astable mode. Let us discuss the behaviour of each pin of 555 Timer IC when working in astable mood.

Figure 2 shows Pin configuration of 555 Timer IC Pin 1 Ground: This pin is use for ground purpose. Pin 2 Trigger: This pin is use for trigging purpose. From negative input of comparator the trigger pin is drag. The set pin of flip flop is attach to lower comparator output. The output goes high when a negative pulse of...