20-11-2012, 02:17 PM
Home Security System project
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ABSTRACT
The main aim of this Home Security System project is intended to develop a security system to protect our home and offices from the thieves. This simple circuit rings an alarm when an unauthorized persons or thieves entering into home. Taking in consideration the need of security, it has become very essential to design security systems which should be reliable effective and economical. The home security system is act for same purpose to guide and economical and a convenient security. This project involves a laser torch which is easily available and it is used for operation of these device. The project has a combination of plane mirrors which are arranged around the house to form a net. The laser beam is directed on mirrors firstly. After proper reflection on mirrors it finally fall on LDR. The laser beam should be continuously aimed on LDR.
Any interruption of the laser beam will result into energization of the alarm and give the signal of security disturbance. This is the ideal and short working of the house security system. This simple arrangement indicates in a security disturbance in the laser net.
INTRODUCTION
In designing some precious things security is of prime importance. Security is becoming essential day-to-day due to increasing theft. Security should not be expensive then the think to be secured. This project guides us with a low cost security. To protect our house or any precious things from thieves or trespassers for designing any thing new security should be viewed first.
This project gives us a security system, which insures safety and security very conveniently. It is simple as it wcrks on a simple laser beam and a proper mirror arrangement around the thing to be secured. By networking the laser beams through reflections of mirror and by blowing the alarm if any one crosses the beam and indicating “security in danger”.
The system convenience comfort of the user it uses the most advance technology. Innovation quality assurance and reliability are silent features of system. This working is based on LASER and LDR. Microcontrollers, keil tool, embedded c programming used to design this mini ECE project.
Burglar Alarm using Photo conducting cell :-
Here is simple circuit, which uses photoconductive cell LDR (light dependant resistor). The LDR is made up of cadmium selenide or cadmium sulphide. Its resistance is very high when it is dark and its resistance falls considerably when it is illuminated. This light dependent properly of LDR is used in construction of Burglar alarm system.
When LDR is illuminated by light from the resistance of LDR drops to few ohms and transistor emmiter base junction in forward biased. This make the transistor to go in saturation and sufficient current flow through the relay coil this current is sufficient to actuate the relay.
Burglar Alarm Using Photo emissive Cell:
We shall consider here the automatic burglar alarm. The photo electric or photo emmisive cell forms part of grid circuit of triode, in plate circuit of which there is relay which works burglar alarm. As long as light in incident on cell the electrons keep the grid of triode more negative and hence, the relay is not operated. Hence bell B does not ring. But as soon as some intruder or burglar breaks into house and on entering comes in way of invisible beam, the grid becomes less negative. The plate current increases and sets the relay. The bell starts ringing and will continue ringing till the relay is reset.
LDR
A photo resistor or light dependent resistor is a resistor whose resistance decreases with increasing incident light intensity; in other words, it exhibits photoconductivity.
A photo resistor is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance.
A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, e.g. silicon. In intrinsic devices the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire band gap . Extrinsic devices have impurities, also called dopants added whose ground state energy is closer to the conduction band; since the electrons do not have as far to jump, lower energy photons (i.e., longer wavelengths and lower frequencies) are sufficient to trigger the device. If a sample of silicon has some of its atoms replaced by phosphorus atoms (impurities), there will be extra electrons available for conduction. This is an example of an extrinsic semiconductor. Photo resistors are basically photocells.
Specification and model:
There are many types of photo resistor, with different specifications and models. Photo resistors can be coated with or packaged in different materials that vary the resistance, depending on the use for each LDR.
Applications:
Photo resistors come in many different types. Inexpensive cadmium sulphide cells can be found in many consumer items such as camera light meters, street lights, clock radios, alarm devices, outdoor clocks, solar street lamps and solar road studs etc.
They are also used in some dynamic compressors together with a small incandescent lamp or light emitting diode to control gain reduction and are also used in bed lamps etc.
Lead sulphide (PbS) and indium antimonide (InSb) LDRs (light dependent resistor) are used for the mid infrared spectral region. Ge:Cu photoconductors are among the best far-infrared detectors available, and are used for infrared astronomy and infrared spectroscopy.
RELAYS:
A relay is an electrical switch that opens and closes under the control of another electrical circuit. In the original form, the switch is operated by electromagnet to open or close one or many sets of contact, because of the relay is able to control an output circuit higher power than the input circuit. It can be considered to be, in a broad sense, a form of an electrical amplifier. An electrical current through conductor will produce a magnetic field at right angles to the direction of electron flow. If that conductor is wrapped into a coil shape, the magnetic field produced will be oriented along the length of the coil. The greater the current , greater the strength of the magnetic field, all other factor being equal. Relays are extremely useful when we have a need to control a large amount of current and/or voltage with small electrical signal. The relay coil which produces the magnetic field may only consume fractions watt of power, while the contacts closed or opened by that magnetic field may be able to conduct hundreds of times that amount of power to a load. In effect, a relay acts as a binary (on or off) amplifier. Just as with transistors, the relays ability to control one electrical signal with another misapplication in the construction of logic functions. For now, the relay’s “amplifying” ability will be explored.
WORKING PRINCIPLE:
In the above schematic, the relays coil is energized by the low-voltage (12v) dc source, while the single-throw (SPST) contact interrupts the high voltage (480v) ac circuit. it is quite likely that the current required to energizes the relay coil will be hundreds of times less then current rating of the contact. Typical relay coil currents are well below 1amp, while typical contact ratings for industrial relays are at least 10amp. One relays coil/armature assembly may be used to actuate more then one set of contacts. Those contacts may be normally-open, normally-close, or any combination of the two. As with switches, the “normal” state of relays contacts is that state when the coil is de-energized, just as you wounded the relay sitting on a self, not connected to any circuit. Relay contacts may be open-air pads of metal alloy, mercury tubes, or even magnetic reeds, just as the other type of switches. The choice of contacts in a relays depends on the same factors which dictate contact choice in other types of switches. Open-air contacts are the best for high current application
Operation:
When current flows through the coil, a magnetic field are created around the coil i.e., the coil is energized. This causes the armature to be attracted to the coil. The armature’s contact acts like a switch and closes or opens the circuit. When the coil is not energized, a spring pulls the armature to its normal state of open or closed. There are all types of relays for all kinds of applications.
Transistors and ICs must be protected from the brief high voltage 'spike' produced when the relay coil is switched off. The above diagram shows how a signal diode (eg 1N4148) is connected across the relay coil to provide this protection. The diode is connected 'backwards' so that it will normally not conduct. Conduction occurs only when the relay coil is switched off, at this moment the current tries to flow continuously through the coil and it is safely diverted through the diode. Without the diode no current could flow and the coil would produce a damaging high voltage 'spike' in its attempt to keep the current flowing.
TRANSISTOR DRIVER CIRCUIT:
An SPDT relay consists of five pins, two for the magnetic coil, one as the common terminal and the last pins as normally connected pin and normally closed pin. When the current flows through this coil, the coil gets energized. Initially when the coil is not energized, there will be a connection between the common terminal and normally closed pin. But when the coil is energized, this connection breaks and a new connection between the common terminal and normally open pin will be established. Thus when there is an input from the microcontroller to the relay, the relay will be switched on. Thus when the relay is on, it can drive the loads connected between the common terminals and normally open pin. Therefore, the relay takes 5V from the microcontroller and drives the loads which consume high currents. Thus the relay acts as an isolation device.
Digital systems and microcontroller pins lack sufficient current to drive the circuits like relays and buzzer which consume high powers. While the relay’s coil needs around 10milli amps to be energized, the microcontroller’s pin can provide a maximum of 1-2milli amps current. For this reason, a driver such as a power transistor is placed in between the microcontroller and the relay.
TRANSISTOR
A Transistor is a device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.
The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems. Following its development in the early 1950s the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things.
Importance:
The transistor is the key active component in practically all modern electronics. Many consider it to be one of the greatest inventions of the 20th century. Its importance in today's society rests on its ability to be mass produced using a highly automated process (semiconductor device fabrication) that achieves astonishingly low per-transistor costs. The invention of the first transistor at Bell Labs was named an IEEE Milestone in 2009.
Although several companies each produce over a billion individually packaged (known as discrete) transistors every year, the vast majority of transistors now are produced in integrated circuits(often shortened to IC, microchips or simply chips), along with diodes, resistors, capacitors and other electronic components, to produce complete electronic circuits. A logic gate consists of up to about twenty transistors whereas an advanced microprocessor, as of 2011, can use as many as 3 billion transistors (MOSFETs). "About 60 million transistors were built in 2002 ... for [each] man, woman, and child on Earth."
BC548 transistor:
The BC548 is a general purpose epitaxial silicon NPN bipolar junction transistor found commonly in European electronic equipment. The part number is assigned by Pro Electron, which allows many manufacturers to offer electrically and physically interchangeable parts under one identification. The BC548 is commonly available in European Union countries. It is often the first type of bipolar transistor young hobbyists encounter, and is often featured in circuit diagrams and designs published in hobby electronics magazines.
If the plastic TO-92 package is held in front of one's face with the flat side facing toward you and the leads downward, (see picture) the order of the leads, from left to right is collector, base, emitter.
JEDEC and EIAJ standards:
The JEDEC numbered NPN 2N3904 and PNP 2N3906 possess very similar electrical characteristics to the BC548 and BC558 respectively but the pin outs are reversed. If the TO-92 package for these devices is held in front of one's face with the flat side facing toward you and the leads downward, (see picture) the order of the leads, from left to right is emitter, base, collector.
The Electronic Industries Association of Japan (EIAJ) assigns the 2SC prefix to NPN transistors for high frequency use. The NPN 2SC1815 and PNP 2SA1015 are usually the most the common general purpose devices which are encountered and also possess characteristics which are similar to the BC548 and BC558. If the TO-92 package for these devices is held in front of one's face with the flat side facing toward you and the leads downward, (see picture) the order of the leads, from left to right is emitter, collector and base.
SENSORS
A sensor (also called detector) is a converter that measures a physical quantity and converts it into a signal which can be read by an observer or by an (today mostly electronic) instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass tube. A thermocouple converts temperature to an output voltage which can be read by a voltmeter. For accuracy, most sensors are calibrated against known standards.
Sensors are used in everyday objects such as touch-sensitive elevator buttons (tactile sensor) and lamps which dim or brighten by touching the base. There are also innumerable applications for sensors of which most people are never aware. Applications include cars, machines, aerospace, medicine, manufacturing and robotics.
A sensor is a device which receives and responds to a signal. A sensor's sensitivity indicates how much the sensor's output changes when the measured quantity changes. For instance, if the mercury in a thermometer moves 1 cm when the temperature changes by 1 °C, the sensitivity is 1 cm/°C (it is basically the slope Dy/Dx assuming a linear characteristic). Sensors that measure very small changes must have very high sensitivities. Sensors also have an impact on what they measure; for instance, a room temperature thermometer inserted into a hot cup of liquid cools the liquid while the liquid heats the thermometer. Sensors need to be designed to have a small effect on what is measured; making the sensor smaller often improves this and may introduce other advantages.
Infrared Sensor:
A good sensor obeys the following rules:
• Is sensitive to the measured property only
• Is insensitive to any other property likely to be encountered in its application
• Does not influence the measured property
Ideal sensors are designed to be linear or linear to some simple mathematical function of the measurement, typically logarithmic. The output signal of such a sensor is linearly proportional to the value or simple function of the measured property. The sensitivity is then defined as the ratio between output signal and measured property. For example, if a sensor measures temperature and has a voltage output, the sensitivity is a constant with the unit [V/K]; this sensor is linear because the ratio is constant at all points of measurement.