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LASERBASED

INTRUDERALARM

Concept of Laser Based Intruder Alarm During the olden days a watchman would be

hired to take care of property and offer needed security in the home. Some homes also had fierce dogs that would be let out only at night. The two were supposed to provide security to our belongings even in the absence of the owner. However, hiring a watchman was not an effective method since most of them would be killed in the line of duty. Sometimes dogs would attack even visitors while some watchmen looted property.

During the olden days where there were no security systems houses were being raided by the thieves

A alarm is a type of security equipment that can be used to safeguard homes and property. If we love our home then buying burglar alarm should be our first priority when moving to a new home. Burglar crimes are continually rising with each passing day. Many have lost their homes and families through violent burglaries in many countries today. Some have lost what they considered precious and valuable to them. Things such as jewelry, vehicles, and clothes are huge investments to many. This led to the development of the alarm equipment.

About the circuit

The circuit is divided into two parts i.e. the transmitter and the receiver.

The transmitter circuit is nothing but a laser diode driven by a battery connected to the diode

In order to ensure that the current remains constant in the diode a 5V or 7.5V is applied to the diode.

The laser diode here can be the one typically used in laser pointers emitting in red. This would be more economical than buying one.

An infrared diode can also be used for invisible laser beam.

The pointer has in-built suitable series resistance and an ON/OFF switch and a battery.

The drive current in this would be 3500/47mA. The receiver part consists of a current to

voltage converter section which converts the photocurrent produced by the photodiode as a result of laser light falling.

When the laser light falls on the photodiode, the opamp output is same as Dc voltage

Block diagram

Laser diode pointer: The laser diode is a laser where the active medium is a semiconductor similar to that found in a light-emitting diode. The most common type of laser diode is formed from a p-n junction and powered by injected electric current. In this we are using 593 nm – Yellow-Orange laser pointers.

Photo transistor: A photodiode is a type of photo detector capable of converting light into either current or voltage, depending upon the mode of operation. The common, traditional solar cell used to generate electric solar power is a large area photodiode.

Op-Amp LM 356: The LM356 is a power amplifier designed for use in low voltage consumer applications. The gain is internally set to 20 to keep external part count low, but the addition of an external resistor and a capacitor between 1 and 8 will increase the gain to any value up tp 200. The inputs are grounded referenced while the output is automatically biased to one half the supply voltage. The quiescent power drain is only 24mW when operating from a 6V supply, making the LM356 ideal for battery operation.

555 Timer: The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation and oscillator applications. It includes over 20 transistors, 2 diodes and 15 resistors on a silicon chip installed in an 8-pin mini dual-in-line package. In the monostable mode, the 555 timer acts as a “one-shot” pulse generator. The pulse begins when the 555 timer receives a signal at the trigger input that falls below a third of the voltage supply. The width of the output pulse is determined by the time constant of an RC network, which consists of a capacitor (C) and a resistor (R).

Piezo buzzer: The piezo buzzer produces sound based on reverse of the piezoelectric effect. The generation of pressure variation or strain by the application of electric potential across a piezoelectric material is the underlying principle. These buzzers can be used alert a user of an event corresponding to a switching action, counter signal or sensor input. They are also used in alarm circuits.

Capacitor: A capacitor is a passive electronic component consisting of a pair of conductors separated by a dielectric (insulator). When there is a potential difference (voltage) across the conductors, a static electric field develops across the dielectric causing positive charge to collect on

one plate and negative charge on the other plate

Resistor: A linear resistor is a two-terminal, linear, passive electronic component that implements electrical resistance as a circuit element.

Diode: A p–n junction is formed by joining P-type and N-type semiconductors together in very close contact.

Switch: It’s an electrical component that break an electrical circuit.

Battery: It is used to convert chemical energy to electrical energy.

Relay: It is as an electrically operated switch. It uses an electromagnetic to operate a switching mechanism mechanically

It is used to control a circuit by a low power signal

Relays are used extensively in telephone exchange and early computers to perform logical operations.

Circuit diagram and operation

The transmitter circuit is nothing but a laser diode (LD1) driven by a 9V PP3 battery. The output of IC1 is regulated 5V as long as its input remains equal to or more than 7.5V, thus ensuring a constant drive current for the laser diode. The battery (Batt1) is connected to the circuit through switch S1. The laser diode (LD1) can be replaced with a laser pointer (torch) emitting red laser beam. The laser pointer itself can be used as a transmitter. The pointer has in-built series resistance, on/off switch and battery. The receiver circuit is basically a current-to-voltage converter built around IC LM356 (IC3). The output of IC3 is fed to the monostable built around 555 timer (IC4). The high output of the monostable drives

the piezobuzzer to sound an audio alarm. The receiver section operates off 5V DC generated from another 9V battery and voltage regulator IC 7805 (IC2). The battery (Batt.2) is connected to the circuit through switch S2. When the laser light transmitted through LD1 falls on phototransistor T1, the output of the op-amp (IC3) at its pin 6 remains high. In this condition, the output of IC4 remains low and the buzzer does not sound. When the laser beam falling on phototransistor T1 is interrupted by someone, the output of op-amp IC3 goes low and IC3 produces a pulse. This pulse triggers monostable IC4 and its output goes high to sound the alarm for a time period of about

R8xc8. Assemble the transmitter and receiver circuits on separate generalpurpose PCBs and enclose in suitable cabinets. Mount the transmitter and receiver units on opposite pillars of the entrance, aligning the two such that the laser beam from the transmitter directly falls on the phototransistor. Block the laser beam with your hand and measure the op-amp output. It should not be low. At pin 3 of IC4, we should get a positive-going pulse of one-second duration beginning with high-to-low edge of the trigger pulse appearing at pin 2 of IC4 or collector of transistor T2.

Testing Switch on the transistor circuit. Align the

transmitter and receiver circuit so that the laser beam falls on the photodiode. We can use a small transmitter receiver distance, even a few feet, for the purpose.

If necessary, change the value of one or more resistors(R5,R6,R7) to get a signal peak magnitude of 2 to 3 V at opamp output.

Block the laser radiation with our hand and again measure the opampoutput. It should be near zero.

Block the laser radiation with our hand and again measure the opamp output. It should be near zero volt.

If we have the services of an oscilloscope, observe the pulse waveforms appearning at pin-8 of IC-1 and pin-6 of IC-3. At pin-8 of IC-4, we would see a HIGH-to-LOW transition every time we block the laser beam.

We can observe change in the pitch of the audio beep by changing the frequency of the signal on the transmitter card.

Advantages

Simplicity of installation. The effective ability to be used indoors

and outdoors.  It could be used as an effective alarm for

the house/company boundaries.  It uses the normal power outlets and

telephone jacks in case it used indoors. 

 

DisadvantagesThe disadvantage of laser beam system is that it may get activated by a cat walking on the wall or a large bird sitting on the wall.

They are more expensive compared to simple security alarm systems.

Applications: Can be used as home security system

Can be used in Museums, Banks, Offices for safe guard many valuable things

Conclusion

The Laser Based Intruder Alarm was built to our satisfaction. This project is about how to prevent theft in homes, offices, banks, museums etc, This project can be implemented by both wired and wireless technologies. Another application of this instrument is as an "ANTI-THEFT SYSTEM", that means to protect vehicles from kidnapping. In short I am sure that this device is highly useful to mankind especially present scenario.