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CONTENTS


1. INTRODUCTION.
2. CIRCUIT DESCRIPITION.
a) Power supply
b) IR Transmitter
c) IR Receiver (photo diode).
d) Comparator
e) Buzzer driver.
f) Bistable
3. FUTURE EXPANSION.
4. CONCLUSION.



INTRODUCTION
In the industries and social premises security system is one of the important parts. The growth and economy all depends on this. The traditional security system is not at all full proof and also very much expensive. To safe guard the premises; the most important aspect to be considered is the trace passing. In this project the care is taken to design an security system, in which a one zone is protected.
An intruder alarm system based on the detection of an intrusion caused by the interruption of an infra-red (which is invisible to human being) light beam being emitted by an infra-red LED and falling on a matched photodiode. Both the transmitter and the receiver portions separately operate from 9v batteries. The transmitter and the receiver’s gadgets can be mounted in an aligned position on the two sides of a door to check intrusion or even on the two facing walls of inside of a locker to give you an alarm whenever an unauthorized person attempts a mischief. The gadget has a provision of both audio as well as visible indications. The audio indicator and the visible indication can be remotely located away from the location of gadget also. The IR based system is very much advanced and works very much accurately. This type of devices are designed and marketed by the different multinational companies.

CIRCUIT DESCRIPTION
a) POWER SUPPLY :-( +ve)
Circuit connection: -
In this we are using Transformer (0 -12Vac), 500mA, IC 7805 & 7812, diodes IN4007, LED & resistors.
Here 230V, 50 Hz ac signal is given as input to the primary of the transformer and the secondary of the transformer is given to the bridge rectification diode. The o/p of the diode is given as i/p to the IC regulator (7805 &7812) through capacitor (1000mf/35v). The o/p of the IC regulator is given to the LED through resistors.
Circuit Explanations: -
When ac signal is given to the primary of the transformer, due to the magnetic effect of the coil magnetic flux is induced in the coil (primary) and transfer to the secondary coil of the transformer due to the transformer action.” Transformer is an electromechanical static device which transformer electrical energy from one coil to another without changing its frequency”. Here the diodes are connected in a bridge fashion. The secondary coil of the transformer is given to the bridge circuit for rectification purposes.
During the +ve cycle of the ac signal the diodes D2 & D4 conduct due to the forward bias of the diodes and diodes D1 & D3 does not conduct due to the reversed bias of the diodes. Similarly during the –ve cycle of the ac signal the diodes D1 & D3 conduct due to the forward bias of the diodes and the diodes D2 & D4 does not conduct due to reversed bias of the diodes. The output of the bridge rectifier is not a power dc along with rippled ac is also present. To overcome this effect, a capacitor is connected to the o/p of the diodes (D2 & D3). Which removes the unwanted ac signal and thus a pure dc is obtained. Here we need a fixed voltage, that’s for we are using IC regulators (7805 & 7812).”Voltage regulation is a circuit that supplies a constant voltage regardless of changes in load current.” This IC’s are designed as fixed voltage regulators and with adequate heat sinking can deliver output current in excess of 1A. The o/p of the bridge rectifier is given as input to the IC regulator through capacitor with respect to GND and thus a fixed o/p is obtained. The o/p of the IC regulator (7805 & 7812) is given to the LED for indication purpose through resistor. Due to the forward bias of the LED, the LED glows ON state, and the o/p are obtained from the pin no-3.
b) IR TRANSMITTER
The IR LED is also light emitting diode but the junction is made out of such material that the transition of electron between the bands emits quanta of energy (E=h) having a particular frequency, which is having a particular characteristic. When a diode emits a particular characteristic signal having frequency in the range of infrared then, that diode is called a infrared emitting diode. The IR data transmitter is a high intensity IR signal transmitter. There are two diodes connected in parallel to increase the intensity to avoid data corruption.

In this section our aim is to protect the zone/door/almirah etc. from the unauthorized entry or interruption, for that we need some element that should not be visible to the unauthorized person. For that we have taken elements as IR LED as a source and photo diode as a destination. Generally, we have taken IR because IR is invisible to the eye, where as in case of LASER, which is easily visible to the human eye by which will, alert the unauthorized person. That is why we have taken IR as a transmitter which will transmit a continuously IR signal. At the receiver end the photodiode will receive the IR signal. if somebody tries to interrupt the IR signal at the transmitter end, the receiver will decide the absence of the IR signal at the receiver end.
Operation:
Whenever the base voltage (12v) is high which is connected through a base resistance Rb (1k-10k), the transistor (BC547/BC548) comes to saturation condition (ON state) thus emitter current starts flowing towards the collector junction which is connected through a collector resistance Rc (150E/2w) and connected to Vcc. Which makes an IR LED as a forward biased thus transmit a continuous IR signal.
c) IR RECEIVER.(PHOTO DIODE).
A PHOTO DIODE is light sensitive device the junction of the photo diode is such that it generates carriers when the light falls on it. There are different type of diodes, which generates carriers in different magnitudes at different frequency this depends on the nature and doping of the junction. The liberation of carriers are very small in magnitude which is very much dependant on the frequency and intensity of the light signal falling on the junction. In the forward biased condition the majority carrier current is so high that the current generated due to fall of light signal is very negligible. The photon bombardment cause the avalanche break down of the junction and generate current which is in the order of 100s micro ampere to few 10s of mA, due to the above mentioned causes the photo diodes to connected in the reverse biased condition. In the reverse biased condition the normal current is always in the order of few microamperes, the current generated due to fall of light signal on the junction is also in the order of microampere so the net current through the diode is appreciably increased. The same current pass through the resistance connected in series and drop across the resistance is increased.
If the diode junction is exposed with visible light or invisible light like Infrared / Laser in the circuit shown in fig.2, the diode current will rise, possibly to as high as 1mA,producing a significant output across R. In use, the photodiode is reversed biased and the output voltage is taken from across a series-connected load resistor.

Operation:
In this project in the data/signal receiving section, the photodiode is used as sensor/ detector purpose to detect the IR signal from the IR transmitter LED section. Whenever the signal is transmitted from the IR transmitter LED, the signal is received at the photodiode receiving section. The receiving signal is very weak in strength, for that we used an amplifier. The output of the photodiode is given as input to the amplifier (Op-amp LM393) through a current limiting resistor (15k), which is configured as a comparator, and the reference voltage is set at non-inverting terminal of the operational amplifier/comparator. There is a 10K variable resistor which is connected between +9 Volt and Ground and the variable terminal is connected to the non –inverting terminal of the comparator for providing the threshold value. The output of the LM393 swings in between +Vsat and –Vsat, even for a small variation of signal across the threshold value.
That output is given to the led indicator for indication purpose means availability of the signal. and that signal is also is given to the AND gate.

d) COMPARATOR
This section is configured with a dual comparator LM393 (is a dual comparator integrated circuit. All the comparators are receiving a common input signal from the signal conditioning section. The comparator is designed with hystersis, to avoid fluctuation at the equal set values. All the two comparators are set with different reference value; each corresponds to a particular current value. Whenever the input to this comparator from the signal section, gives beyond the set value, then the comparator toggles. As the input is given at the non–inverting terminal as the output of the comparator goes to positive saturation voltage. As the reference voltage are set in an increasing order, when the comparator set for highest value is driven into positive saturation. All the comparator must be driven into saturation. So LED s connected to the each comparator section indicate the level of current.
e) BUZZER DRIVER.
The buzzer driver consists of a buzzer & its driving ckt. It works on the principle of transistor action (Transistor acts as a switch). When the base voltage is high, the transistor comes to saturation i.e. in ON condition, which drives the buzzer because a small emitter current will flow. Similarly, when the base voltage is low, the transistor does not come to saturation i.e. OFF condition, which does not drives the buzzer.
f) BISTABLE:
The latch is the electronics device which stores the state even if the input is with drawn. So this ca be started as a single memory unit. The latch can be designed in many ways by using a discreet component or flip-flop or a IC known as 555 timer, The Latch designed using 555 timer IC is quite stable.
Operation:
The 555 timer IC conation two comparators at its input, one end of the comparator is connected to the 1/3 Vcc and 2/3 Vcc respectively. The other two terminal of both the comparator are named as trigger and threshold. The output of these two comparators are connected to a S-R flip –flop in which output toggles when the inputs are dissimilar i.e 1,0 or 0,1. The Bistable design gas two inputs, one as trigger input to change the state and the other is to reset the output. The input signal is connected to the trigger pin and the threshold is grounded. It means the output of the comparator to which 2/3 Vcc is connected and threshold (ground) is kept at fixed output. When the trigger pin is issued with an input which is less than 1/3 Vcc then automatically the comparators output toggles and hence the flip flop output toggles and the output of the 555 timer IC is set. The outputs remain in the state until unless the reset input is pulled down to ground.
Ckt Connection:
The threshold voltage pin-6 of IC555 is connected to ground and the trigger pin-2 a pull-up resistor 10k is connected to VCC normally.
Whenever the threshold voltage is low, the output of the comparation-1 infernally, the output of the flip-flop goes low. And the input of the comparator – 2 internally high than 1/3 Vcc, the output will remain in ‘LOW’ sate.
Whenever a negative edge trigger voltage will appear at the trigger pin-2, internally the output of the comparator – 2 goes high, the flip-flop will remain in high state and it will latch that output. Until we have to reset that IC through reset pin-4 to ground.

FUTURE EXPANSION
This project is developed with single objective but multiple sensors can be interfaced with microcontroller / pc to make a single system for security and safety.

CONCLUSION.
This project is tested in the laboratory and the operation found is safety.

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