1

A REPORT ON MINOR PROJECT

POWER SUPPLY &

HOME SECURITY ALARM

SUBMITTED IN PARTIAL FULFILLMENT FOR AWARD OF DEGREE OF

BACHELOR OF TECHNOLOGY

IN

E LECTRONICS AND COMMUNICATION ENGINEERING

BY

DHRUV GUPTA (2012ECA1721)

UNDER THE GUIDANCE OF

PROF.SASHI B RANA

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

GURU NANAK DEV UNIVERSITY, REGIONAL CAMPUS,

GURDASPUR

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ABSTRACT

Project - I

A power supply unit (PSU) converts mains AC to low-voltage regulated DC power for the internal components of a computer. Modern personal computers universally use a switched-mode power supply. Some power supplies have a manual selector for input voltage, while others automatically adapt to the supply voltage.

Project - II

In this project we design low cost high performance programmable home security system. This system uses a few LDR's as input sensors. When above sensor(s) get triggered system may dial the user specified phone number (using build-in DTMF generator) and activate the high power audio alarm and lights. All the parameters of DTMF generator, audio alarm and light interface are programmed through the RS232 serial interface. Current firmware of this system presents interactive control system through the RS232 interface. This control system consist with the menu driven configuration options, self-tests, system report generators, etc. This system also contain 5W (with 4Ω speaker) audio alarm with three selectable tone configurations, which include Police siren, Fire engine siren and Ambulance siren.

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ACKNOWLEDGEMENT

No volume of words is enough to express my gratitude towards my guide Prof.Sashi B Rana, who has been very concerned and has aided for all the materials essential for the preparation of this thesis report.He has helped me to explore this vast topic in an organized manner and provided me with all the ideas on how to work towards a research-oriented venture.

I am thankful to my mentor Dr.Anusheetal, Head of Department (HOD), for the motivation and inspiration that triggered me for the thesis work.

I would also like to thank the staff members and my colleagues who were always there at the need of the hour and provided with all the help and facilities, which I required for the completion of my thesis work.

I am very much grateful to Dr.Sandeep Sood,Dean GNDU for his valuable support at the Institution Level for giving me the opportunity for pursuing this B.Tech course and help in conceptualising the project/research work and to all those outstanding individuals with whom I have worked in this Institution, who helped me understanding the concept.

Most importantly, I would like to thank my parents and the almighty for showing me the right direction out of the blue, to help me stay calm in the oddest of the times and keep moving even at times when there was no hope

Dhruv Gupta

ECE

2012ECA1721

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Contents Page No.

List of Figures 5

Project – I

1.1 Introduction 6

1.2 Project Description 7

1.3 Circuit Design 8

1.4 Schematic Design 9

1.5 Working 10

1.6 Hardware Description 12

Project – II

2.1 Introduction 19

2.2 Project Description 19

2.3 Circuit Design 20

2.4 Schematic Design 21

2.5 Working 22

2.6 Hardware Description 24

References 28

Appendices 29

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LIST OF FIGURES

FIGURES PAGE NO:

CHAPTER –I

1.1 Power Supply 07

1.2 Circuit Diagram 08

1.3 Schematic Diagram of project 09

1.4 Input AC Voltage 10

1.5 DC Output Voltage 10

1.6 Filtered Voltage 11

1.7 Output Voltage 11

1.8 Transformer 13

1.9 Diodes 14

1.10 Capacitor 15

1.11 Voltage Regulator 17

CHAPTER-II

2.1 Security Alarm 20

2.2 Circuit Diagram 20

2.3 Schematic Diagram of project 21

2.4 Low Voltage Drop 22

2.5 High Voltage Drop 23

2.6 Alarm Path 23

2.7 Battery 25

2.8 Resistor 26

2.9 LDR 27

2.10 Transistor 27

2.11 Buzzer 28

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CHAPTER-I

1.1 INTRODUCTION

Introduction

Also called a power supply unit or PSU, the component that supplies power to a computer. Most personal computers can be plugged into standard electrical outlets. The power supply then pulls the required amount of electricity and converts the AC current to DC current. It also regulates the voltage to eliminate spikes and surges common in most electrical systems. Not all power supplies, however, do an adequate voltage-regulation job, so a computer is always susceptible to large voltage fluctuations.

Power supplies are rated in terms of the number of watts they generate. The more powerful the computer, the more watts it can provide to components.

A power supply is a device that supplies electric power to an electrical load. The term is most commonly applied to electric power converters that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy (mechanical, chemical, solar) to electrical energy. A regulated power supply is one that controls the output voltage or current to a specific value; the controlled value is held nearly constant despite variations in either load current or the voltage supplied by the power supply's energy source.

Every power supply must obtain the energy it supplies to its load, as well as any energy it consumes while performing that task, from an energy source. Depending on its design, a power supply may obtain energy from:

Electrical energy transmission systems. Common examples of this include power supplies that convert AC line voltage to DC voltage.

Energy storage devices such as batteries and fuel cells. Electromechanical systems such as generators and alternators. Solar power.

A power supply may be implemented as a discrete, stand-alone device or as an integral device that is hardwired to its load. Examples of the latter case include the low voltage DC power supplies that are part of desktop computers and consumer electronics devices.

Commonly specified power supply attributes include:

The amount of voltage and current it can supply to its load. How stable its output voltage or current is under varying line and load conditions. How long it can supply energy without refuelling or recharging (applies to power

supplies that employ portable energy sources).

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1.2 PROJECT DESCRIPTION

INTRODUCTION

A regulated power supply is an embedded circuit; it converts unregulated AC into a constant DC. With the help of a rectifier it converts AC supply into DC. Its function is to supply a stable voltage (or less often current), to a circuit or device that must be operated within certain power supply limits. The output from the regulated power supply may be alternating or unidirectional, but is nearly always DC (Direct Current).

The type of stabilization used may be restricted to ensuring that the output remains within certain limits under various load conditions, or it may also include compensation for variations in its own supply source. The latter is much more common today.

Applications

D.C. variable bench supply (a bench power supply usually refers to a power supply capable of supplying a variety of output voltages useful for bench testing electronic circuits, possibly with continuous variation of the output voltage, or just some pre-set voltages; a laboratory (lab) power supply normally implies an accurate bench power supply, while a balanced or tracking power supply refers to twin supplies for use when a circuit requires both positive and negative supply rails).

Mobile Phone power adaptors Regulated power supplies in appliances Various amplifiers and oscillators

Fig 1.1 Power Supply

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1.3 CIRCUIT DESIGN

Fig 1.2 – Circuit Design of Power Supply System

Circuit consists of 4 parts: Step down transformer, 4 diodes, resistor, capacitor filter & voltage regulator IC.

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1.4 SCHEMATIC DESIGN

Fig 1.3 Schematic View of Power Supply

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1.5 WORKING

Circuit consists of 4 parts: Step down transformer, bridge rectifier, capacitor filter and voltage regulator IC.

The transformer step downs the high voltage AC to a low voltage AC.

Fig 1.4 Input Voltage

During the positive half cycle of secondary voltage, diodes D2 and D3 are forward biased and diodes D1 and D4 are reverse biased, now the current flows through D2–>Load–>D3

During the negative half cycle of the secondary voltage, diodes D1 and D4 are forward biased and diodes D2 and D3 are reverse biased Now the current flows through D4–>Load–>D1

In both the cycles load current flows in same direction, hence we get a pulsating DC voltage across the points B-B’.

Fig 1.5 DC Output Voltage

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The pulsating content are called ripples and a filter capacitor is used to remove the ripples from pulsating DC.

When the instantaneous values of pulsating DC voltage increases, the capacitor gets charged up to peak value of the input.

When the instantaneous values of pulsating DC voltage decreases, the stored voltage in the capacitor reverse biases the diodes D2 and D4. Hence it will not conduct, now capacitor discharges through the load. Then voltage across the capacitor decreases.

During the next cycle, when the peak voltage exceeds the capacitor voltage, diode D2 or D4 forward biases accordingly, as a result capacitor again charges to the peak value. This process continues. Hence we get almost smooth DC voltage as shown.

Fig 1.6 Brown color indicates pulsating DC and Red color is the filtered DC voltage.

Then the filtered voltage is applied to the input of 7805 voltage regulator IC, it in turn regulates the voltage for line and load fluctuations.

Fig 1.7 Output Voltage

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1.6 HARDWARE DESCRIPTION

1.6.1 COMPONENTS REQUIRED

1. Step down transformer (IC 606). 2. Diodes x 4 (1N4001 for low power 1N4007 for moderate power) 3. Capacitor (1000µF) 4. Voltage regulator

1.6.2 DISCRIPTION OF EACH COMPONENT

Transformer

Fig 1.8 Transformer

A transformer is an electrical device that transfers energy between two circuits through electromagnetic induction. A transformer may be used as a safe and efficient voltage converter to change the AC voltage at its input to a higher or lower voltage at its output. Other uses include current conversion, isolation with or without changing voltage and impedance conversion.

A transformer most commonly consists of two windings of wire that are wound around a common core to provide tight electromagnetic coupling between the windings. The core material is often a laminated iron core. The coil that receives the electrical input energy is referred to as the primary winding, while the output coil is called the secondary winding.

An alternating electric current flowing through the primary winding (coil) of a transformer generates a varying electromagnetic field in its surroundings which causes a varying magnetic flux in the core of the transformer. The varying electromagnetic field in the vicinity of the secondary winding induces an electromotive force in the secondary winding, which appears a voltage across the output terminals. If a load impedance is connected

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across the secondary winding, a current flows through the secondary winding drawing power from the primary winding and its power source.

A transformer cannot operate with direct current; although, when it is connected to a DC source, a transformer typically produces a short output pulse as the current rises.

Transformers perform voltage conversion; isolation protection; and impedance matching. In terms of voltage conversion, transformers can step-up voltage/step-down current from generators to high-voltage transmission lines, and step-down voltage/step-up current to local distribution circuits or industrial customers. The step-up transformer is used to increase the secondary voltage relative to the primary voltage, whereas the step-down transformer is used to decrease the secondary voltage relative to the primary voltage. Transformers range in size from thumbnail-sized used in microphones to units weighing hundreds of tons interconnecting the power grid. A broad range of transformer designs are used in electronic and electric power applications, including miniature, audio, isolation, high-frequency, power conversion transformers, etc.

Basic principles

The functioning of a transformer is based on two principles of the laws of electromagnetic induction: An electric current through a conductor, such as a wire, produces a magnetic field surrounding the wire, and a changing magnetic field in the vicinity of a wire induces a voltage across the ends of that wire.

The magnetic field excited in the primary coil gives rise to self-induction as well as mutual induction between coils. This self-induction counters the excited field to such a degree that the resulting current through the primary winding is very small when no load draws power from the secondary winding.

The physical principles of the inductive behaviour of the transformer are most readily understood and formalized when making some assumptions to construct a simple model which is called the ideal transformer. This model differs from real transformers by assuming that the transformer is perfectly constructed and by neglecting that electrical or magnetic losses occur in the materials used to construct the device.

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DIODES

Fig 1.9 Diode

Structure of a vacuum tube diode. The filament may be bare, or more commonly (as shown here), embedded within and insulated from an enclosing cathode.

In electronics, a diode is a two-terminal electronic component with asymmetric conductance; it has low (ideally zero) resistance to current in one direction, and high (ideally infinite) resistance in the other. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals.[5] A vacuum tube diode has two electrodes, a plate (anode) and a heated cathode. Semiconductor diodes were the first semiconductor electronic devices. The discovery of crystals' rectifying abilities was made by German physicist Ferdinand Braun in 1874. The first semiconductor diodes, called cat's whisker diodes, developed around 1906, were made of mineral crystals such as galena. Today, most diodes are made of silicon, but other semiconductors such as selenium or germanium are sometimes used.

The most common function of a diode is to allow an electric current to pass in one direction (called the diode's forward direction), while blocking current in the opposite direction (the reverse direction). Thus, the diode can be viewed as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, including extraction of modulation from radio signals in radio receivers—these diodes are forms of rectifiers.

However, diodes can have more complicated behavior than this simple on–off action, due to their nonlinear current-voltage characteristics. Semiconductor diodes begin conducting electricity only if a certain threshold voltage or cut-in voltage is present in the forward direction (a state in which the diode is said to be forward-biased). The voltage drop across

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a forward-biased diode varies only a little with the current, and is a function of temperature; this effect can be used as a temperature sensor or voltage reference.

Semiconductor diodes' current–voltage characteristic can be tailored by varying the semiconductor materials and doping, introducing impurities into the materials. These are exploited in special-purpose diodes that perform many different functions. For example, diodes are used to regulate voltage (Zener diodes), to protect circuits from high voltage surges (avalanche diodes), to electronically tune radio and TV receivers (varactor diodes), to generate radio frequency oscillations (tunnel diodes, Gunn diodes, IMPATT diodes), and to produce light (light emitting diodes). Tunnel diodes exhibit negative resistance, which makes them useful in some types of circuits.

Capacitor

Fig 1.10 Capacitor

A capacitor (originally known as a condenser) is a passive two-terminal electrical component used to store energy electrostatically in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors (plates) separated by a dielectric (i.e., insulator). The conductors can be thin films of metal, aluminium foil or disks, etc. The 'non-conducting' dielectric acts to increase the capacitor's charge capacity. A dielectric can be glass, ceramic, plastic film, air, paper, mica, etc. Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, a capacitor does not dissipate energy. Instead, a capacitor stores energy in the form of an electrostatic field between its plates.

When there is a potential difference across the conductors (e.g., when a capacitor is attached across a battery), an electric field develops across the dielectric, causing positive charge (+Q) to collect on one plate and negative charge (-Q) to collect on the other plate. If a battery has been attached to a capacitor for a sufficient amount of time, no current can flow through the capacitor. However, if an accelerating or alternating voltage is applied across the leads of the capacitor, a displacement current can flow.

An ideal capacitor is characterized by a single constant value for its capacitance. Capacitance is expressed as the ratio of the electric charge (Q) on each conductor to the potential difference (V) between them. The SI unit of capacitance is the farad (F), which is equal to one coulomb per volt (1 C/V). Typical capacitance values range from about 1 pF (10−12 F) to about 1 mF (10−3 F).

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The capacitance is greater when there is a narrower separation between conductors and when the conductors have a larger surface area. In practice, the dielectric between the plates passes a small amount of leakage current and also has an electric field strength limit, known as the breakdown voltage. The conductors and leads introduce an undesired inductance and resistance.

Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass. In analog filter networks, they smooth the output of power supplies. In resonant circuits they tune radios to particular frequencies. In electric power transmission systems they stabilize voltage and power flow.[1]

A capacitor consists of two conductors separated by a non-conductive region.[10] The non-conductive region is called the dielectric. In simpler terms, the dielectric is just an electrical insulator. Examples of dielectric media are glass, air, paper, vacuum, and even a semiconductor depletion region chemically identical to the conductors. A capacitor is assumed to be self-contained and isolated, with no net electric charge and no influence from any external electric field. The conductors thus hold equal and opposite charges on their facing surfaces,[11] and the dielectric develops an electric field. In SI units, a capacitance of one farad means that one coulomb of charge on each conductor causes a voltage of one volt across the device.[12]

An ideal capacitor is wholly characterized by a constant capacitance C, defined as the ratio of charge ±Q on each conductor to the voltage V between them:[10]

Because the conductors (or plates) are close together, the opposite charges on the conductors attract one another due to their electric fields, allowing the capacitor to store more charge for a given voltage than if the conductors were separated, giving the capacitor a large capacitance.

Sometimes charge build-up affects the capacitor mechanically, causing its capacitance to vary. In this case, capacitance is defined in terms of incremental changes:

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VOLTAGE REGULATOR

Fig 1.11 Voltage Regulator

A voltage regulator is designed to automatically maintain a constant voltage level. A voltage regulator may be a simple "feed-forward" design or may include negative feedback control loops. It may use an electromechanical mechanism, or electronic components. Depending on the design, it may be used to regulate one or more AC or DC voltages.

Electronic voltage regulators are found in devices such as computer power supplies where they stabilize the DC voltages used by the processor and other elements. In automobile alternators and central power station generator plants, voltage regulators control the output of the plant. In an electric power distribution system, voltage regulators may be installed at a substation or along distribution lines so that all customers receive steady voltage independent of how much power is drawn from the line.

The output voltage can only be held roughly constant; the regulation is specified by two measurements:

Load regulation is the change in output voltage for a given change in load current (for example: "typically 15 mV, maximum 100 mV for load currents between 5 mA and 1.4 A, at some specified temperature and input voltage").

line regulation or input regulation is the degree to which output voltage changes with input (supply) voltage changes - as a ratio of output to input change (for example "typically 13 mV/V"), or the output voltage change over the entire specified input voltage range (for example "plus or minus 2% for input voltages between 90 V and 260 V, 50-60 Hz").

Other important parameters are:

Temperature coefficient of the output voltage is the change with temperature (perhaps averaged over a given temperature range).

Initial accuracy of a voltage regulator (or simply "the voltage accuracy") reflects the error in output voltage for a fixed regulator without taking into account temperature or aging effects on output accuracy.

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Dropout voltage is the minimum difference between input voltage and output voltage for which the regulator can still supply the specified current. A low drop-out (LDO) regulator is designed to work well even with an input supply only a volt or so above the output voltage. The input-output differential at which the voltage regulator will no longer maintain regulation is the dropout voltage. Further reduction in input voltage will result in reduced output voltage. This value is dependent on load current and junction temperature.

Absolute maximum ratings are defined for regulator components, specifying the continuous and peak output currents that may be used (sometimes internally limited), the maximum input voltage, maximum power dissipation at a given temperature, etc.

Output noise (thermal white noise) and output dynamic impedance may be specified as graphs versus frequency, while output ripple noise (mains "hum" or switch-mode "hash" noise) may be given as peak-to-peak or RMS voltages, or in terms of their spectra.

Quiescent current in a regulator circuit is the current drawn internally, not available to the load, normally measured as the input current while no load is connected (and hence a source of inefficiency; some linear regulators are, surprisingly, more efficient at very low current loads than switch-mode designs because of this).

Transient response is the reaction of a regulator when a (sudden) change of the load current (called the load transient) or input voltage (called the line transient) occurs. Some regulators will tend to oscillate or have a slow response time which in some cases might lead to undesired results. This value is different from the regulation parameters, as that is the stable situation definition. The transient response shows the behaviour of the regulator on a change. This data is usually provided in the technical documentation of a regulator and is also dependent on output capacitance.

Mirror-image insertion protection means that a regulator is designed for use when a voltage, usually not higher than the maximum input voltage of the regulator, is applied to its output pin while its input terminal is at a low voltage, volt-free or grounded. Some regulators can continuously withstand this situation; others might only manage it for a limited time such as 60 seconds, as usually specified in the datasheet. This situation can occur when a three terminal regulator is incorrectly mounted for example on a PCB, with the output terminal connected to the unregulated DC input and the input connected to the load. Mirror-image insertion protection is also important when a regulator circuit is used in battery charging circuits, when external power fails or is not turned on and the output terminal remains at battery voltage.

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CHAPTER II – SECURITY ALARM

PROJECT DESCRIPTION

2.1 INTRODUCTION:

A security alarm is a system designed to detect intrusion – unauthorized entry – into a building or area. Security alarms are used in residential, commercial, industrial, and military properties for protection against burglary (theft) or property damage, as well as personal protection against intruders. Car alarms likewise protect vehicles and their contents. Prisons also use security systems for control of inmates.

Some alarm systems serve a single purpose of burglary protection; combination systems provide both fire and intrusion protection. Intrusion alarm systems may also be combined with closed-circuit television surveillance systems to automatically record the activities of intruders, and may interface to access control systems for electrically locked doors.

Have you ever thought about implementing your own home security alarm systems? It's one of the simplest and interesting circuits for electronic beginners. Our new home security equipment uses a LDR (Light Depended Resistor) to detect security problems. Theft attempt and other security threats can be controlled by using this simple circuit to improve your security systems. To implement this alarm system for home, you have to provide an optical path (with LASER beams) around your home. The LASER path is made possible with one LASER torch and 3 mirror arrangements which encloses the whole area.

Fig 2.1 Security Alarm

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2.2 CIRCUIT DIAGRAM:

Fig 2.2 Circuit Diagram

The circuit consists of 4 parts: LDR, NPN Transistor, Buzzer and a Resistor

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2.3 SCHMATIC DIAGRAM

Fig 2.3 Schematic View of Security Alarm

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2.4 WORKING:

This circuit is based on LDR (Light Depended Resistor), a variable resistor in which

the resistance varies according to the light intensity falling on it.

The LDR and resistor R1 forms a potential divider network, which is the main part

of our security alarm circuit.

We have already discussed about how transistor acts as a switch, the same principle

is used here.

The voltage drop across the LDR is used to drive the transistor switch. When the

voltage drop is above cut in voltage (0.6V), the transistor is turned ON.

LDR has low resistance (mΩ range) in the presence of light and high resistance

(MΩ range) in the absence of light.

In our security alarm, a LASER light is allowed to fall on the LDR continuously

.Light from other sources should not be allowed to fall on the LDR, so place the

LDR in a box with a single hole to pass LASER.

In this situation, the resistance offered by LDR is too low, since the LASER light is

continuously allowed to fall on the LDR surface.

Fig 2.4

Thus the voltage drop across the LDR is also low [V=IR (Ohm’s law)] which is

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insufficient to turn ON the transistor, so the transistor remains in OFF state.

When a person (eg: thief) makes a block to the continuous flow of LASER beam,

then the light falling on the LDR gets blocked. Thus its resistance increases to a

high value in the order of MΩ range (According to Ohm’s law V=IR).

Fig 2.5

While resistance increases the voltage drop also increases, when this voltage drop

exceeds the cut in voltage of the silicon NPN transistor (0.6V; BC547), it will turn

ON.

Then current from Vcc starts flowing to ground via the buzzer and transistor, which

makes the beep sound.

The beep sound from the security alarm gives the indication of some security

failures

The project arrangement is given bellow:

Figure 2.6 The arrangement of Alarm path is shown in the above image.

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2.5 HARDWARE DESCRIPTION

2.5.1 LIST OF COMPONENTS

Battery 6V

Resistors ¼ watt (150kΩ)

LDR (Light Depended Resistor)

Transistor BC547

6V Buzzer

2.5.2 DESCRIPTION OF COMPNENTS:

1.) Battery:

An electric battery is a device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy. Each cell contains a positive terminal, or cathode, and a negative terminal, or anode. Electrolytes allow ions to move between the electrodes and terminals, which allows current to flow out of the battery to perform work.

Primary (single-use or "disposable") batteries are used once and discarded; the electrode materials are irreversibly changed during discharge. Common examples are the alkaline battery used for flashlights and a multitude of portable devices. Secondary (rechargeable batteries) can be discharged and recharged multiple times; the original composition of the electrodes can be restored by reverse current. Examples include the lead-acid batteries used in vehicles and lithium ion batteries used for portable electronics. Batteries come in many shapes and sizes, from miniature cells used to power hearing aids and wristwatches to battery banks the size of rooms that provide standby power for telephone exchanges and computer data centers

Fig 2.7 Battery

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2.) Resistor:

A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. The current through a resistor is in direct proportion to the voltage across the resistor's terminals. This relationship is represented by Ohm's law:

Where I is the current through the conductor in units of amperes, V is the potential

difference measured across the conductor in units of volts, and R is the resistance of the

conductor in units of ohms. The ratio of the voltage applied across a resistor's terminals to

the intensity of current in the circuit is called its resistance, and this can be assumed to be

a constant (independent of the voltage) for ordinary resistors working within their ratings.

Resistors are common elements of electrical networks and electronic circuits and are

ubiquitous in electronic equipment. Practical resistors can be made of various compounds

and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel-

chrome). Resistors are also implemented within integrated circuits, particularly analogue

devices, and can also be integrated into hybrid and printed circuits.

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Fig 2.8 Resistor

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3.) LDR:

An LDR (Light dependent resistor), as its name suggests, offers resistance in response to the ambient light. The resistance decreases as the intensity of incident light increases, and vice versa. In the absence of light, LDR exhibits a resistance of the order of mega-ohms which decreases too few hundred ohms in the presence of light. It can act as a sensor, since a varying voltage drop can be obtained in accordance with the varying light. It is made up of cadmium sulphide (CdS).

Fig 2.9 LDR

4.) Transistor:

A transistor is a semiconductor device used to amplify and switch electronic signals

and electrical power. It is composed of 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 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.

Figure 2.10 NPN v/s PNP Transistor

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5.) Buzzer:

Here buzzer indicates the alarm condition. Its voice or sound indicates the defect in home

security .With respective to circuit it is just a load .but with respective to alarm it form the

important part of system. Alerting devices serve the dual purposes of warning occupants of

intrusion, and potentially scaring off burglars. These devices may also be used to warn

occupants of a fire or smoke

Basically, it is an electrical device that makes a buzzing noise and is used for signalling.

An audible warning device indicating it is time to do something. Buzzer or beeper is a signalling

Device, usually electronic, typically used in automobiles, household appliances such as a microwave

Oven, or game shows. It most commonly consists of a number of switches or sensors connected to a control unit that determines if and which button was pushed or a pre-set time has lapsed, and usually illuminates a light on the appropriate button or control panel, and sounds a warning in the form of a continuous or intermittent buzzing or beeping sound

Fig 2.11 Buzzer

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REFRENCES

www.circuitsgallery.com

Google

www.en.wikipedia.org

www.engineersgarage.com

www.electroskan.wordpress.com

www.datasheetarchive.com

www.youtube.com

Various other books and magazines

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APPENDICES

DIELECTRIC: A capacitor consists of two conductors separated by non-

conductive regions. The non-conductive region is called dielectric

RECTIFIER: It is combination of diodes used to rectify an AC signal into a DC

one.

TRANSFORMER: This device is used to vary the amplitude of a signal used in

almost all the home appliances.

SEMICONDUCTOR: A solid substance that has a conductivity between that of an

insulator and that of most metals, either due to the addition of an impurity or because of

temperature effects.

FILTER: A filter circuit is an electronic circuit made using capacitors and

inductors.