Laser Security System Science Kit

Laser Security System
Abstract:
LASER BASED SECURITY ALARM's design provides inexpensive yet effective form of protection against intruders as well as it can be easily used to secure the building e.g. House, banks, and shopping malls. As it is highly sensitive due to the light activated alarm circuit. LASER-Ray goes through long distance without scattering effect and the Ray is almost invisible. Only the radiation point and incident point is visible. So by this security project we can make an invisible boundary of a sensitive area. There is two part of the system. One is transmitter and other is receiver. Transmitter can be any light or Laser light (best due to less scattering).The receiver side, there is a focusing LDR (Light depending Resistor) sensor to sense the LASER continuously. One is filtered the signal of discontinuity ray and others is alarm circuit. When anybody crossover the invisible ray the main circuit sense the discontinuity by sensor and turn on the alarm circuit. We call it as Laser Based Security alarm as it is a Light Activated Alarm circuit.
Introduction:
Security is a most important factor today. Technology develops day by day in the world. The crime gang also improves their technology to perform their operation. So technology of security should be modern with time to protect the crime works. We decide to make a security project as our project. In this project we have used laser light to cover a large area. We know laser light goes through long distance without scattering effect. It’s also visible only at source and incident point, otherwise invisible. These two properties help us to build up a modern security system, which may name as “laser security”. When any person or object crossover the laser line the security alarm will ringing and also the focus light will “on” to focus the entrance of unauthorized person. We can make a security boundary of single laser light by using mirror at every corner for reflection.
Components:  Transistor Q1 BC557 (PNP)  Transistor Q3 BC547 (NPN)  Laser light  LDR Light Dependent Resistor  220 Ohm  4.7K (4)  100K (2)  1K (2)  Reset Button  0.1 uf (1)  Vero board  9 Volt Battery and Connector  9 Volt DC Buzzer
Circuit Diagram and Explanation:
: Circuit Diagram of latching circuit is simple and can be easily built. Resistor R1 and R2 work as a current limiting resistor for Transistor Q1 and resistors R3 and R4 work as current limiting resistor for Transistor Q2. Current Limiting resistors must be used at the bases of BJT transistors, otherwise they might burn. Purposes of other components have been explained in ‘Working section’ below. Latch basically means “to become fixed in a particular state”. In Electronics, Latch Circuit is a circuit which locks its output, when a momentarily input trigger signal is applied, and retains that state, even after the input signal is removed. This state will remain indefinitely until the power is reset or some external signal is applied. Latch circuit is very useful in alarm circuits, where a small trigger signal will turn on the alarm for indefinite period, until reset manually. Before going into the explanation, we should note that transistor Q2 BC557 is a PNP transistor, which conducts or Turns On, when a small negative voltage is applied to its base and Transistor Q2 BC547 is NPN transistor which Conducts or Turns On, when a positive voltage (or ground) is applied to its base. The circuit uses two transistors. First is a PNP transistor named as Q1 and other one is a NPN transistor named as Q2. Initially, both the transistors Q1, Q2 are in OFF state, and Buzzer is deactivated. NPN Transistor Q2 BC547 base is connected to negative voltage with current limiting resistor R2, so that it won’t conducts accidently. Capacitor C1 has been used precautionary, to prevent the accidental and false triggering of circuit. Now when a small trigger voltage is applied to the base of Transistor Q1 BC557, it turns ON the transistor and Base of the transistor Q2 BC547 gets connected to the Ground. This Trigger voltage is coming from Flame Sensor Module which is describing above. Resistor R2 and R4 prevents the short circuit in this condition. Now when base of transistor BC547 gets grounded, it starts conducting and energies the buzzer. This is normal behaviour until now, but what makes it a ‘Latch’ circuit. If we notice, collector of Transistor Q2 BC547 is connected to base of Transistor Q1 BC557, through a current limiting resistor R3 and when the Transistor Q2 BC547 turns ON, current flow in two directions, first to the buzzer and second to the base of transistor Q2. So this Feedback voltage to the base of Transistor Q1 BC557, keeps the transistor Q2 BC547 ON for indefinite period. This in turns keeps the second transistor ON indefinitely and a Latch or Lock is formed instantly, it starts conducting and energises the buzzer.