Diamond security system in museum with 60Db siren

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DIAMOND SECURITY SYSTEM IN MUSEUM WITH 60DB

SIREN

Mini Project Report

Submitted in partial fulfillment of the requirement for the award of the Degree of

Bachelor of Technology

in

Electronics and Communication Engineering

By

A.Mahesh 12621A0461

D.Madhu 12621A0475

Under the guidance of

Mr. C. Pramod Kumar

Associate professor

Department of Electronics and Communication Engineering

Aurora's Engineering College Bhuvanagiri, Nalgonda District – 508 116

(Affiliated to JNTUH and Accredited by NBA, New Delhi)

(2015-16)

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Aurora's Engineering College Bhuvanagiri, Nalgonda District – 508 116

(Affiliated to JNTUH and Accredited by NBA, New Delhi)

CERTIFICATE

This is to certify that the Mini Project report entitled Diamond Security System in

Museum with 60Db siren has been submitted by Mr. A.Mahesh and D.Madhu bearing Roll

No 1262A0461 and 12621A0475 under my guidance in partial fulfillment of the degree of

Bachelor of Technology in Electronics and Communication Engineering to the Jawaharlal Nehru

Technological University Hyderabad during the academic year 2015-16.

Date:

Mr. C. Pramod Kumar Mr. I.V.S Rama Sastry

Internal Guide Mini Project Coordinator

Mrs. Latha Sahuka Mr. K. Chandrasekhar Head of Department Principal

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Acknowledgment

It gives me immense pleasure to express my deep sense of gratitude to my

supervisor Mr. C.Pramod kumar for his invaluable guidance, motivation, constant inspiration

and above all her ever co-operating attitude enabled me in bringing up this thesis in present

elegant form.

We are extremely thankful to Mrs. Latha Sahuka, Head, Department of

Electronics & Communication Engineering and the faculty members of Electronics &

Communication Engineering Department for providing all kinds of possible help and advice

during the course of this project.

We are greatly thankful to all the staff members of the department and all my

well-wishers, class mates and friends for their inspiration and help. It is a great pleasure for me

to acknowledge and express my gratitude to my parent for their understanding, unstinted support

and endless encouragement during my study.

A.Mahesh (12621A0461)

D.Madhu (12621A0475)

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Abstract

Security is primary concern for everyone. This project describes a design of effective

security alarm system that can monitor the diamond in a museum using ldr sensors. A led is

connected to this system for visual indication of the safety of the diamond. This led shows

whether the sensor has been activated and whether the wiring to the sensor is in order.

The burglar alarm is built with ldr sensor. A glowing led is placed near the diamond and a

highly sensitive ldr is placed under the diamond. Whenever somebody picks the diamond, the

light of led falls on the ldr and it triggers the scr through a switching transistor. A loud 60db siren is

connected to this scr. This siren is activated in triggered conditions.

The system is provided with a unique lock type switch. Only the authorized person will be

having the key, and he only can deactivate / activate the system.

This project uses regulated 5v, 750ma power supply. 7805 three terminal voltage regulator is

used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac output of

secondary of 230/12v step down transformer.

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CONTENTS

TITLE PAGE NO.

1. INTRODUCTION 1

1.1 Certain concepts different field security 2

2. HARDWARE EXPLANATION 4

2.1 Resistor 4

2.2 Capacitor 5

2.2.1Circuit Symbol 5

2.3 Diode 5

2.3.1 Diode Symbol 6

2.4 Light Emitted Diode 6

2.5 Switches and pushbuttons 8

2.6 Block diagram of power supply 9

3. DESCRIPTION 10

3.1 Transformers 10

3.2 Bias Principal 11

3.3 Transformer working 12

3.4 Transformer advantages 13

3.5 Classification of Transformers 13

3.5.1 Step-down-transformer 13

3.5.2 Step-up-transformer 15

3.5.3 Applications 16

3.6 Types of Transformers 16

3.6.1 Main transformer 16

3.6.2 Audio transformer 18

3.6.3 Radio transformer 18

3.7 Diodes 19

3.8 Rectifiers 19

3.8.1 The half wave rectifier 20

3.8.2 The full wave rectifier 21

3.9 Capacitor filter 22

3.10 Voltage regulator 24

3.11 LED 25

3.12 Switches and pushbuttons 26

4. LIGHT DEPENDENT RESISTOR 28

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4.1 LDR 28

4.2 Identification 30

4.3 Function 30

4.4 Consideration 30

4.5 Expert Insight 31

4.6 Benefits 31

5. TRANSISTOR SWITCH WITH SENSOR 32

5.1 Variable sensor 33

5.2 Transistor switching Circuit 33

5.3 Transistor as a switch 34

6. SILICON CONTROLLED RECTIFIER BT169 35

6.1 Mode of Operation 35

6.2 Reverse Bias 36

6.3 Thyistor turn on method 37

6.4 Theory of operation 37

6.5 Forward bias operation 38

6.6 Reverse bias operation 38

6.7 SCR protection 38

6.8 Testing the SCR 39

7. BUZZER 40

7.1 What does it do? 40

7.2 How does it operate? 41

7.3 Applications 42

7.4 Making 42

7.5 Testing 42

8. DECADE COUNTER 43

9. 60Db SIREN 45

9.1 Applications of SCR 46

10. ADVANTAGES AND APPLICATIONS 47

10.1 Advantages 47

10.2 Applications 47

10.3 References 47

11. CONCLUSION 48

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LIST OF FIGURES

FIGURE NAME PAGE NO

2.1 a) Resistor 4

b) Color Code 4

2.2 Circuit Symbol 5

2.2.1 Circuit Symbol 5

2.3.1 a) Diode symbol 6

b) Example of diode 6

2.4 a) LED 6

b) Led 7

c) Types of leds 8

2.5 witches and pushbuttons 9

2.6 Power supply 10

3.1 a) Transformer Symbol 10

b) Transformer 11

3.2 Basic Principal 12

3.3 Basic transformer 14

3.5.1 Step-down-transformer 15

3.5.2 Step-up-transformer 16

3.6.1 Mani transformer 17

3.6.2 Audio transformer 18

3.6.3 Radio transformer 18

3.7 Diode symbol 19

3.8.1 a) Half wave rectifier 20

b) AC input wave form of half wave rectifier 21

3.8.2 a) Full wave rectifier 21

b) AC input wave form of full wave rectifier 22

3.9 a) Capacitor filter 23

b) Centred tapped full wave rectifier with capacitor filter 23

3.10 Regulator 24

4.1 a) LDR 29

b) LDR circuit 29

5.1 Led lights when LDR is dark and bright 32

5.2 Transistor switching circuit 33

6.1 Silicon controlled rectifier 35

6.4 Volt-Ampere Characteristics 37

7.0 Circuit diagram of buzzer 40

8.0 Decade counter 43

9.0 Siren 45

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1. INTRODUCTION

Security is the degree of protection against danger, damage, loss, and crime. Security as

a form of protection is structures and processes that provide or improve security as a condition.

The Institute for Security and Open Methodologies (ISECOM) in the OSSTMM 3 defines

security as "a form of protection where a separation is created between the assets and the threat".

This includes but is not limited to the elimination of either the asset or the threat. Security as a

national condition was defined in a United Nations study (1986, so that countries can develop

and progress safely.

Security has to be compared to related concepts: safety, continuity, reliability. The key difference

between security and reliability is that security must take into account the actions of people

attempting to cause destruction.

Different scenarios also give rise to the context in which security is maintained:

• With respect to classified matter, the condition that prevents unauthorized persons from

having access to official information that is safeguarded in the interests of national

security.

• Measures taken by a military unit, an activity or installation to protect itself against all

acts designed to, or which may, impair its effectiveness.

Diamond Security Systems is a Dublin based company, specialising in wireless security

systems, access control and CCTV installations for commercial and residential properties.

• Electronic locks

• Access Control Systems

• Intercom and P.A Systems

• Gate/Door Automation

• CCTV Systems

• Electric fencing

• Emergency Lighting

• Alarm Systems

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1.1 Certain concepts recur throughout different fields of security:

• Assurance - assurance is the level of guarantee that a security system will behave as

expected

• Countermeasure - a countermeasure is a way to stop a threat from triggering a risk event

• Defense in depth - never rely on one single security measure alone

• Exploit - a vulnerability that has been triggered by a threat - a risk of 1.0 (100%)

• Risk - a risk is a possible event which could cause a loss

• Threat - a threat is a method of triggering a risk event that is dangerous

• Vulnerability - a weakness in a target that can potentially be exploited by a threat security

In the corporate world, various aspects of security were historically addressed separately -

notably by distinct and often non communicating departments for IT security, physical security,

and fraud prevention. Today there is a greater recognition of the interconnected nature of

security requirements, an approach variously known as holistic security, "all hazards"

management, and other terms.

Inciting factors in the convergence of security disciplines include the development of digital

video surveillance technologies (see Professional video over IP) and the digitization and

networking of physical control systems (see SCADA). Greater interdisciplinary cooperation is

further evidenced by the February 2005 creation of the Alliance for Enterprise Security Risk

Management, a joint venture including leading associations in security (ASIS), information

security (ISSA, the Information Systems Security Association), and IT audit (ISACA, the

Information Systems Audit and Control Association).

In 2007 the International Organization for Standardization (ISO) released ISO 28000 -

Security Management Systems for the supply chain. Although the title supply chain is included,

this Standard specifies the requirements for a security management system, including those

aspects critical to security assurance for any organisation or enterprise wishing to management

the security of the organisation and its activities. ISO 28000 is the foremost risk based security

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system and is suitable for managing both public and private regulatory security, customs and

industry based security schemes and requirements.

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2. HARDWARE EXPLANATION

2.1 RESISTOR:

Resistors "Resist" the flow of electrical current. The higher the value of resistance (measured

in ohms) the lower the current will be. Resistance is the property of a component which restricts

the flow of electric current. Energy is used up as the voltage across the component drives the

current through it and this energy appears as heat in the component.

2.1 (a). Resistor

Color Code:

2.1 (b).Color Code

2.2 CAPACITOR:

Capacitors store electric charge. They are used with resistors in

takes time for a capacitor to fill with charge. They are used to

acting as a reservoir of charge. They are also used in filter circuits because capacitors easily pass

AC (changing) signals but they block DC (constant) signals.

2.2.1 Circuit symbol:

Electrolytic capacitors are polarized and

least one of their leads will be marked

2.3 DIODES:

Diodes allow electricity to flow in only one direction. The arrow of the circuit sy

the direction in which the current can flow. Diodes are the electrical version of a valve and early

diodes were actually called valves.

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ric charge. They are used with resistors in timing circuits

takes time for a capacitor to fill with charge. They are used to smooth varying DC supplies by


AC (changing) signals but they block DC (constant) signals.

2.2 (a). Circuit symbol

ytic capacitors are polarized and they must be connected the correct way

least one of their leads will be marked + or -.

2.2.1 Circuit symbols

Diodes allow electricity to flow in only one direction. The arrow of the circuit sy



circuits because it

varying DC supplies by


they must be connected the correct way round, at

Diodes allow electricity to flow in only one direction. The arrow of the circuit symbol shows


2.3.1 Diode symbol:

Diodes must be connected the correct way round, the diag

and k or – for cathode (yes, it really is k, not c, for cathode!). The cathode is marked by a line

painted on the body. Diodes are labeled with their code in small print; you may need a

magnifying glass to read this on

2.4 LIGHT-EMITTING DIODE (LED):

The longer lead is the anode (+) and the shorter lead is the cathode (&minus). In the

schematic symbol for an LED (bottom), the anode is on the left and the cathode is

Lighemitting diodes are elements for light signalization in electronics.

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2.3.1 (a) Diode symbol

Diodes must be connected the correct way round, the diagram may be labeled

for cathode (yes, it really is k, not c, for cathode!). The cathode is marked by a line


magnifying glass to read this on small signal diodes.

2.3.1 (b) Examples of Diodes

EMITTING DIODE (LED):


schematic symbol for an LED (bottom), the anode is on the left and the cathode is

Lighemitting diodes are elements for light signalization in electronics.

2.4 Light Emitted Diode (LED)

ram may be labeled a or + for anode

for cathode (yes, it really is k, not c, for cathode!). The cathode is marked by a line



schematic symbol for an LED (bottom), the anode is on the left and the cathode is on the right.

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(b). LED

They are manufactured in different shapes, colors and sizes. For their low price, low

consumption and simple use, they have almost completely pushed aside other light sources-

bulbs at first place.

(c). Types of LEDS

It is important to know that each diode will be immediately destroyed unless its current is

limited. This means that a conductor must be connected in parallel to a diode. In order to

correctly determine value of this conductor, it is necessary to know diode’s voltage drop in

forward direction, which depends on what material a diode is made of and what colors it is.

Values typical for the most frequently used diodes are shown in table below: As seen, there are

three main types of LEDs. Standard ones get full brightness at current of 20mA. Low Current

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diodes get full brightness at ten time’s lower current while Super Bright diodes produce more

intensive light than Standard ones.

Since the 8051 microcontrollers can provide only low input current and since their pins

are configured as outputs when voltage level on them is equal to 0, direct confectioning to LEDs

is carried out as it is shown on figure (Low current LED, cathode is connected to output pin).

2.5 Switches and Pushbuttons:

A push button switch is used to either close or open an electrical circuit depending on the

application. Push button switches are used in various applications such as

industrial equipment control handles, outdoor controls, mobile communication terminals, and

medical equipment, and etc. Push button switches generally include a push button disposed

within a housing. The push button may be depressed to cause movement of the push button

relative to the housing for directly or indirectly changing the state of an electrical contact to open

or close the contact. Also included in a pushbutton switch may be an actuator, driver, or plunger

of some type that is situated within a switch housing having at least two contacts in

communication with an electrical circuit within which the switch is incorporated.

2.5 Switches and Pushbuttons

Typical actuators used for contact switches include spring loaded force cap actuators that

reciprocate within a sleeve disposed within the canister. The actuator is typically coupled to the

movement of the cap assembly, such that the actuator translates in a direction that is parallel with

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the cap. A push button switch for a data input unit for a mobile communication device such as a

cellular phone, a key board for a personal computer or the like is generally constructed by

mounting a cover member directly on a circuit board. Printed circuit board (PCB) mounted

pushbutton switches are an inexpensive means of providing an operator interface on industrial

control products. In such push button switches, a substrate which includes a plurality of movable

sections is formed of a rubber elastomeric. The key top is formed on a top surface thereof with a

figure, a character or the like by printing, to thereby provide a cover member. Push button

switches incorporating lighted displays have been used in a variety of applications. Such

switches are typically comprised of a pushbutton, an opaque legend plate, and a back light to

illuminate the legend plate.

2.6 Block Diagram For Power Supply

Figure: Power Supply

3.1 Transformer

A transformer is a device that transfers

inductively coupled conductors—

winding creates a varying magnetic flux

field through the secondary

electromotive force (EMF) or "voltage

induction.

Figure:

Transformer is a device that converts the one form energy to another form of energy like a

transducer.

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3. DESCRIPTION

is a device that transfers electrical energy from one circuit to another throu

—the transformer's coils. A varying current in the fir

magnetic flux in the transformer's core, and thus a varying

winding. This varying magnetic field induces

voltage" in the secondary winding. This effect is called

Figure: (a). Transformer Symbol


Figure: (b). Transformer

to another through

in the first or primary

in the transformer's core, and thus a varying magnetic

induces a varying

" in the secondary winding. This effect is called mutual


3.2 Basic Principle

A transformer makes use of Faraday's law

efficiently raise or lower AC voltages. It of course cannot increase

raised, the current is proportionally lowered and vice versa.

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Faraday's law and the ferromagnetic properties of an

efficiently raise or lower AC voltages. It of course cannot increase power so that if t

raised, the current is proportionally lowered and vice versa.

3.2. Figure: Basic Principle

properties of an iron core to

so that if the voltage is

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3.3 Transformer Working

A transformer consists of two coils (often called 'windings') linked by an iron core, as shown in

figure below. There is no electrical connection between the coils; instead they are linked by a

magnetic field created in the core.

3.3 Figure: Basic Transformer

Transformers are used to convert electricity from one voltage to another with minimal loss of

power. They only work with AC (alternating current) because they require a changing magnetic

field to be created in their core. Transformers can increase voltage (step-up) as well as reduce

voltage (step-down).

Alternating current flowing in the primary (input) coil creates a continually changing magnetic

field in the iron core. This field also passes through the secondary (output) coil and the changing

strength of the magnetic field induces an alternating voltage in the secondary coil. If the

secondary coil is connected to a load the induced voltage will make an induced current flow. The

correct term for the induced voltage is 'induced electromotive force' which is usually abbreviated

to induced e.m.f.

The iron core is laminated to prevent 'eddy currents' flowing in the core. These are currents

produced by the alternating magnetic field inducing a small voltage in the core, just like that

induced in the secondary coil. Eddy currents waste power by needlessly heating up the core but

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they are reduced to a negligible amount by laminating the iron because this increases the

electrical resistance of the core without affecting its magnetic properties.

3.4 Transformers have two great advantages over other methods of changing voltage:

1. They provide total electrical isolation between the input and output, so they can be safely

used to reduce the high voltage of the mains supply.

2. Almost no power is wasted in a transformer. They have a high efficiency (power out /

power in) of 95% or more.

3.5 Classification of Transformer

Step-Up Transformer

Step-Down Transformer

3.5.1 Step-Down Transformer

Step down transformers are designed to reduce electrical voltage. Their primary voltage

is greater than their secondary voltage. This kind of transformer "steps down" the voltage applied

to it. For instance, a step down transformer is needed to use a 110v product in a country with a

220v supply.

Step down transformers convert electrical voltage from one level or phase configuration

usually down to a lower level. They can include features for electrical isolation, power

distribution, and control and instrumentation applications. Step down transformers typically rely

on the principle of magnetic induction between coils to convert voltage and/or current levels.

Step down transformers are made from two or more coils of insulated wire wound around

a core made of iron. When voltage is applied to one coil (frequently called the primary or input)

it magnetizes the iron core, which induces a voltage in the other coil, (frequently called the

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secondary or output). The turn’s ratio of the two sets of windings determines the amount of

voltage transformation.

3.5.1 Figure: Step-Down Transformer

An example of this would be: 100 turns on the primary and 50 turns on the secondary, a ratio of

2 to 1.

Step down transformers can be considered nothing more than a voltage ratio device.

With step down transformers the voltage ratio between primary and secondary will mirror the

"turn’s ratio" (except for single phase smaller than 1 kva which have compensated secondary). A

practical application of this 2 to 1 turn’s ratio would be a 480 to 240 voltage step down. Note that

if the input were 440 volts then the output would be 220 volts. The ratio between input and

output voltage will stay constant. Transformers should not be operated at voltages higher than

the nameplate rating, but may be operated at lower voltages than rated. Because of this it is

possible to do some non-standard applications using standard transformers.

Single phase step down transformers 1 kva and larger may also be reverse connected to step-

down or step-up voltages. (Note: single phase step up or step down transformers sized less than 1

KVA should not be reverse connected because the secondary windings have additional turns to

overcome a voltage drop when the load is applied. If reverse connected, the output voltage will

be less than desired.)

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3.5.2 Step-Up Transformer

A step up transformer has more turns of wire on the secondary coil, which makes a larger

induced voltage in the secondary coil. It is called a step up transformer because the voltage

output is larger than the voltage input.

Step-up transformer 110v 220v design is one whose secondary voltage is greater than its primary

voltage. This kind of transformer "steps up" the voltage applied to it. For instance, a step up

transformer is needed to use a 220v product in a country with a 110v supply.

A step up transformer 110v 220v converts alternating current (AC) from one voltage to another

voltage. It has no moving parts and works on a magnetic induction principle; it can be designed

to "step-up" or "step-down" voltage. So a step up transformer increases the voltage and a step

down transformer decreases the voltage.

The primary components for voltage transformation are the step up transformer core and coil.

The insulation is placed between the turns of wire to prevent shorting to one another or to

ground. This is typically comprised of Mylar, nomex, Kraft paper, varnish, or other materials. As

a transformer has no moving parts, it will typically have a life expectancy between 20 and 25

years.

3.5.2 Figure: Step-Up Transformer

3.5.3 Applications

Generally these Step-Up Transformers

3.6 Types of Transformer

3.6.1 Mains Transformers

Mains transformers are the most common type.

supply voltage (230-240V in the UK or 115

The standard mains supply voltages are officially 115V and 230V, but 120V and 240V are the

values usually quoted and the difference is of no significance in most cases

3.6.1

To allow for the two supply voltages mains transformers

(windings) labeled 0-120V and 0

2a) and in parallel for 120V (figure 2b). They must be wired the correct way round as shown in

the diagrams because the coils must be connected in the correct sense (direction):

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Up Transformers are used in industries applications only.

Mains transformers are the most common type. They are designed to reduce the AC mains

240V in the UK or 115-120V in some countries) to a safer low voltage.

e standard mains supply voltages are officially 115V and 230V, but 120V and 240V are the

values usually quoted and the difference is of no significance in most cases.

3.6.1 Figure: Main Transformer

To allow for the two supply voltages mains transformers usually have two separate primary coils

120V and 0-120V. The two coils are connected in series for 240V (figure


ls must be connected in the correct sense (direction):

ications only.

They are designed to reduce the AC mains

120V in some countries) to a safer low voltage.

e standard mains supply voltages are officially 115V and 230V, but 120V and 240V are the

usually have two separate primary coils

120V. The two coils are connected in series for 240V (figure


ls must be connected in the correct sense (direction):

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Most mains transformers have two separate secondary coils (e.g. labeled 0-9V, 0-9V) which may

be used separately to give two independent supplies, or connected in series to create a centre-

tapped coil (see below) or one coil with double the voltage.

Some mains transformers have a centre-tap halfway through the secondary coil and they are

labeled 9-0-9V for example. They can be used to produce full-wave rectified DC with just two

diodes, unlike a standard secondary coil which requires four diodes to produce full-wave

rectified DC.

A mains transformer is specified by:

1. Its secondary (output) voltages Vs.

2. Its maximum power, Pmax, which the transformer can pass, quoted in VA (volt-amp). This

determines the maximum output (secondary) current, Imax...

...where Vs is the secondary voltage. If there are two secondary coils the maximum

power should be halved to give the maximum for each coil.

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3. Its construction - it may be PCB-mounting, chassis mounting (with solder tag

connections) or toroidal (a high quality design).

3.6.2 Audio Transformers

Audio transformers are used to convert the moderate voltage, low current output of an audio

amplifier to the low voltage, high current required by a loudspeaker. This use is called

'impedance matching' because it is matching the high impedance output of the amplifier to the

low impedance of the loudspeaker.

3.6.2 Figure: Audio transformer

3.6.3 Radio Transformers

Radio transformers are used in tuning circuits. They are smaller than mains and audio

transformers and they have adjustable ferrite cores made of iron dust. The ferrite cores can be

adjusted with a non-magnetic plastic tool like a small screwdriver. The whole transformer is

enclosed in an aluminum can which acts as a shield, preventing the transformer radiating too

much electrical noise to other parts of the circuit.

3.6.3 Figure: Radio Transformer

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Turns Ratio and Voltage

The ratio of the number of turns on the primary and secondary coils determines the ratio of the

voltages...

...where Vp is the primary (input) voltage, Vs is the secondary (output) voltage, Np is the number

of turns on the primary coil, and Ns is the number of turns on the secondary coil.

3.7 Diodes

Diodes allow electricity to flow in only one direction. The arrow of the circuit symbol shows the

direction in which the current can flow. Diodes are the electrical version of a valve and early


3.7 Figure: Diode Symbol

A diode is a device which only allows current to flow through it in one direction. In this

direction, the diode is said to be 'forward-biased' and the only effect on the signal is that there

will be a voltage loss of around 0.7V. In the opposite direction, the diode is said to be 'reverse-

biased' and no current will flow through it.

3.8 Rectifier

The purpose of a rectifier is to convert an AC waveform into a DC waveform (OR) Rectifier

converts AC current or voltages into DC current or voltage. There are two different rectification

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circuits, known as 'half-wave' and 'full-wave' rectifiers. Both use components called diodes to

convert AC into DC.

3.8.1 The Half-wave Rectifier

The half-wave rectifier is the simplest type of rectifier since it only uses one diode, as shown in

figure.

3.8.1 a).Figure: Half Wave Rectifier

Figure 2 shows the AC input waveform to this circuit and the resulting output. As you can see,

when the AC input is positive, the diode is forward-biased and lets the current through. When

the AC input is negative, the diode is reverse-biased and the diode does not let any current

through, meaning the output is 0V. Because there is a 0.7V voltage loss across the diode, the

peak output voltage will be 0.7V less than Vs.

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3.8.1. b).Figure: Half-Wave Rectification

While the output of the half-wave rectifier is DC (it is all positive), it would not be suitable as a

power supply for a circuit. Firstly, the output voltage continually varies between 0V and Vs-

0.7V, and secondly, for half the time there is no output at all.

3.8.2 The Full-wave Rectifier

The circuit in figure 3 addresses the second of these problems since at no time is the

output voltage 0V. This time four diodes are arranged so that both the positive and

negative parts of the AC waveform are converted to DC. The resulting waveform is shown

3.8.2. a). Figure: Full-Wave Rectifier

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b). Figure: Full-Wave Rectification

When the AC input is positive, diodes A and B are forward-biased, while diodes C and D are

reverse-biased. When the AC input is negative, the opposite is true - diodes C and D are

forward-biased, while diodes A and B are reverse-biased.

While the full-wave rectifier is an improvement on the half-wave rectifier, its output still isn't

suitable as a power supply for most circuits since the output voltage still varies between 0V and

Vs-1.4V. So, if you put 12V AC in, you will 10.6V DC out.

3.9 Capacitor Filter

The capacitor-input filter, also called "Pi" filter due to its shape that looks like the Greek letter

pi, is a type of electronic filter. Filter circuits are used to remove unwanted or undesired

frequencies from a signal.

A typical capacitor input filter consists of a filter

output, an inductor L, in series and another filter capacitor connected across the load.

1. The capacitor C1 offers low

it offers infinite reactance to the DC component. As a result the capacitor

appreciable amount of the AC component while the DC component continues its journey

to the inductor L

2. The inductor L offers high react

reactance to the DC component. As a result the DC component flows through the

inductor while the AC component is blocked.

3. The capacitor C2 bypasses the AC component which the inductor had failed to block. As

a result only the DC component appears across the load RL.

3.9 Figure: Centered Tapped Full

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3.9 Figure: Capacitor Filter

A typical capacitor input filter consists of a filter capacitor C1, connected across the r

L, in series and another filter capacitor connected across the load.

low reactance to the AC component of the rectifier output while

it offers infinite reactance to the DC component. As a result the capacitor


L offers high reactance to the AC component but it offers almost zero


inductor while the AC component is blocked.

2 bypasses the AC component which the inductor had failed to block. As

a result only the DC component appears across the load RL.

Figure: Centered Tapped Full-Wave Rectifier with a Capacitor Filter

C1, connected across the rectifier

L, in series and another filter capacitor connected across the load.

to the AC component of the rectifier output while

it offers infinite reactance to the DC component. As a result the capacitor shunts an


ance to the AC component but it offers almost zero


2 bypasses the AC component which the inductor had failed to block. As

Wave Rectifier with a Capacitor Filter

24

3.10 Voltage Regulator

A voltage regulator is an electrical regulator designed to automatically maintain a constant

voltage level. It may use an electromechanical mechanism, or passive or active electronic

components. Depending on the design, it may be used to regulate one or more AC or DC

voltages. There are two types of regulator are they.

Positive Voltage Series (78xx) and

Negative Voltage Series (79xx)

78xx:

’78’ indicate the positive series and ‘xx’indicates the voltage rating. Suppose 7805 produces

the maximum 5V.’05’indicates the regulator output is 5V.

79xx:

’78’ indicate the negative series and ‘xx’indicates the voltage rating. Suppose 7905

produces the maximum -5V.’05’indicates the regulator output is -5V.

These regulators consists the three pins there are

Pin1: It is used for input pin.

Pin2: This is ground pin for regulator

Pin3: It is used for output pin. Through this pin we get the output.

3.10 Figure: Regulator

25

3.11 Light-emitting diode (LED):

Light-emitting diodes are elements for light signalization in electronics. They are manufactured

in different shapes, colors and sizes. For their low price, low consumption and simple use, they

have almost completely pushed aside other light sources- bulbs at first place. They perform

similar to common diodes with the difference that they emit light when current flows through

them.

It is important to know that each diode will be

immediately destroyed unless its current is limited. This means that a conductor must be

connected in parallel to a diode. In order to correctly determine value of this conductor, it is

necessary to know diode’s voltage drop in forward direction, which depends on what material a

diode is made of and what color it is. Values typical for the most frequently used diodes are

shown in table below: As seen, there are three main types of LEDs. Standard ones get full

brightness at current of 20mA. Low Current diodes get full brightness at ten time’s lower current

while Super Bright diodes produce more intensive light than Standard ones.

Since the 8051 microcontrollers can provide only low input current and since their pins are

configured as outputs when voltage level on them is equal to 0, direct connecting to LEDs is

carried out as it is shown on figure (Low current LED, cathode is connected to output pin).

26

3.12 Switches and Pushbuttons

There is nothing simpler than this! This is the simplest way of controlling appearance of some

voltage on microcontroller’s input pin. There is also no need for additional explanation of how

these components operate.

Nevertheless, it is not so simple in practice... This is about something commonly unnoticeable

when using these components in everyday life. It is about contact bounce- a common problem

with m e c h a n i c a l switches. If contact switching does not happen so quickly, several

consecutive bounces can be noticed prior to maintain stable state. The reasons for this are:

vibrations, slight rough spots and dirt. Anyway, whole this process does not last long (a few

micro- or milliseconds), but long enough to be registered by the microcontroller. Concerning

pulse counter, error occurs in almost 100% of cases!

27

The simplest solution is to connect simple RC circuit which will “suppress” each quick voltage

change. Since the bouncing time is not defined, the values of elements are not strictly

determined. In the most cases, the values shown on figure are sufficient.

If complete safety is needed, radical measures should be taken! The circuit, shown on the figure

(RS flip-flop), changes logic state on its output with the first pulse triggered by contact bounce.

Even though this is more expensive solution (SPDT switch), the problem is definitely resolved!

Besides, since the condensator is not used, very short pulses can be also registered in this way. In

addition to these hardware solutions, a simple software solution is commonly applied too: when

a program tests the state of some input pin and finds changes, the check should be done one more

time after certain time delay. If the change is confirmed it means that switch (or pushbutton) has

changed its position. The advantages of such solution are obvious: it is free of charge, effects of

disturbances are eliminated too and it can be adjusted to the worst-quality contacts.

28

4. LIGHT DEPENDENT RESISTOR

4.1 LIGHT DEPENDENT RESISTOR:

LDRs or Light Dependent Resistors are very useful especially in light/dark sensor

circuits. Normally the resistance of an LDR is very high, sometimes as high as 1,000,000 ohms,

but when they are illuminated with light, the resistance drops dramatically.

Thus in this project, LDR plays an important role in controlling the electrical appliances

based on the intensity of light i.e., if the intensity of light is more (during daytime) the loads will

be in off condition. And if the intensity of light is less (during nights), the loads will be switched

ON.

LDR:

LDRs or Light Dependent Resistors are very useful especially in light/dark sensor

circuits. Normally the resistance of an LDR is very high, sometimes as high as 1000 000 ohms,

but when they are illuminated with light resistance drops dramatically.

29

4.1 a. LDR

When the light level is low the resistance of the LDR is high. This prevents current from

flowing to the base of the transistors. Consequently the LED does not light.

However, when light shines onto the LDR its resistance falls and current flows into the base of

the first transistor and then the second transistor. The LED lights.

b.) LDR

Here in our project to avoid the light from led to fall on to LDR we place a box in which

we will keep our jewelry. If any one removes the box the light from led falls directly on to the

LDR and then the transistor will be on which is monitored by the microcontroller.

A light dependent resistor is a small, round semiconductor. Light dependent resistors are used to

re-charge a light during different changes in the light, or they are made to turn a light on during

30

certain changes in lights. One of the most common uses for light dependent resistors is in traffic

lights. The light dependent resistor controls a built in heater inside the traffic light, and causes it

to recharge over night so that the light never dies. Other common places to find light dependent

resistors are in: infrared detectors, clocks and security alarms.

4.2 Identification

o A light dependent resistor is shaped like a quarter. They are small, and can be

nearly any size. Other names for light dependent resistors are: photoconductors,

photo resistor, or a CdS cell. There are black lines on one side of the light

dependent resistor. The overall color of a light dependent resistor is gold. Usually

other electrical components are attached to the light dependent resistor by metal

tubes soldered to the sides of the light dependent resistor.

4.3 Function

o The main purpose of a light dependent resistor is to change the brightness of a

light in different weather conditions. This can easily be explained with the use of

a watch. Some watches start to glow in the dark so that it is possible to see the

time without having to press any buttons. It is the light dependent resistor that

allows the watch to know when it has gotten dark, and change the emissions level

of the light at that time. Traffic lights use this principle as well but their lights

have to be brighter in the day time.

4.4 Considerations

o Light dependent resistors have become very useful to the world. Without them

lights would have to be on all the time, or they would have to be manually

adjusted. A light dependent resistor saves money and time for any creation that

31

needs a change in light. Another feature of the light dependent resistor is that it

can be programmed to turn on with changes in movements. This is an extremely

useful feature that many security systems employ. Security would be harder

without light dependent resistors.

4.5 Expert Insight

o It is possible to build a light dependent resistor into an existing light circuit. There

are many electrical plans that outline how to install one. Usually the sign for a

light dependent resistor on these plans is marked by a rectangle with two arrows

pointing down to it. This shows the placement of the light dependent resistor in

the circuit so that it will work properly. Usually only an electrician can build new

circuits, however.

4.6 Benefits

o There are many great benefits to light dependent resistors. They allow less power

to be used in many different kinds of lights. They help lights last much longer.

They can be trigged by several different kinds of triggers, which is very useful for

motion lights and security systems. They are also very useful in watches and cars

so that the lights can turn on automatically when it becomes dark. There are a lot

of things that light dependent resistors can do.

32

5. TRANSISTOR SWITCH WITH SENSORS

The top circuit diagram shows an LDR (light sensor) connected so that the LED lights

when the LDR is in darkness. The variable resistor adjusts the brightness at which the transistor

switches on and off. Any general purpose low power transistor can be used in this circuit.

The 10kΩ fixed resistor protects the transistor from excessive base current (which will destroy it)

when the variable resistor is reduced to zero. To make this circuit switch at a suitable brightness

you may need to experiment with different values for the fixed resistor, but it must not be less

than 1kΩ.

If the transistor is switching a load with a coil, such as a motor or relay, remember to add a

protection diode across the load.

Led lights when the LDR is Dark Led lights when the LDR is Bright

The switching action can be inverted, so the LED lights when the LDR is brightly lit, by

swapping the LDR and variable resistor. In this case the fixed resistor can be omitted because the

LDR resistance cannot be reduced to zero.

Note that the switching action of this circuit is not particularly good because there will be an

intermediate brightness when the transistor will be partly on (not saturated). In this state the

transistor is in danger of overheating

with the small LED current, but the larger current for a lamp, motor or relay is likely to cause

overheating.

Other sensors, such as a thermistor

variable resistor. You can calculate an approximate value for the variable resistor (Rv) by using a

multimeter to find the minimum and maximum values of the sensor's resistance (Rmin and

Rmax):

5.1 Variable resistor, Rv = square root of (Rmin × Rmax)

For example an LDR: Rmin = 100

You can make a much better switching circuit with sensors connected to a suitable IC (chip). The

switching action will be much sharper with no partly on state.

5.2 Transistor Switching Circuit

The circuit resembles that of the

The difference this time is that to operate the transistor as a switch the transistor needs to be

33

transistor is in danger of overheating unless it is switching a small current. There is no problem


thermistor, can be used with this circuit, but they may require a different


to find the minimum and maximum values of the sensor's resistance (Rmin and

Variable resistor, Rv = square root of (Rmin × Rmax)

For example an LDR: Rmin = 100Ω, Rmax = 1MΩ, so Rv = square root of (100

can make a much better switching circuit with sensors connected to a suitable IC (chip). The

switching action will be much sharper with no partly on state.

Transistor Switching Circuit

5.2 Transistor switching Circuit

the Common Emitter circuit we looked at in the previous tutorials.


unless it is switching a small current. There is no problem


, can be used with this circuit, but they may require a different


to find the minimum and maximum values of the sensor's resistance (Rmin and

(100 × 1M) = 10kΩ.

can make a much better switching circuit with sensors connected to a suitable IC (chip). The

circuit we looked at in the previous tutorials.


34

turned either fully "OFF" (Cut-off) or fully "ON" (Saturated). An ideal transistor switch would

have an infinite resistance when turned "OFF" resulting in zero current flow and zero resistance

when turned "ON", resulting in maximum current flow. In practice when turned "OFF", small

leakage currents flow through the transistor and when fully "ON" the device has a low resistance

value causing a small saturation voltage (Vce) across it. In both the Cut-off and Saturation

regions the power dissipated by the transistor is at its minimum.

To make the Base current flow, the Base input terminal must be made more positive than the

Emitter by increasing it above the 0.7 volts needed for a silicon device. By varying the Base-

Emitter voltage Vbe, the Base current is altered and which in turn controls the amount of

Collector current flowing through the transistor as previously discussed. When maximum

Collector current flows the transistor is said to beSaturated. The value of the Base resistor

determines how much input voltage is required and corresponding Base current to switch the

transistor fully "ON".

5.3 Then to summarize when using a Transistor as a Switch.

• Transistor switches can be used to switch and control lamps, relays or even motors.

• When using bipolar transistors as switches they must be fully "OFF" or fully "ON".

• Transistors that are fully "ON" are said to be in their Saturation region.

• Transistors that are fully "OFF" are said to be in their Cut-off region.

• In a transistor switch a small Base current controls a much larger Collector current.

• When using transistors to switch inductive relay loads a "Flywheel Diode" is required.

• When large currents or voltages need to be controlled, Darlington Transistors are

used.

6. SILICON CONTROLLED RECTIFIER BT169

A silicon-controlled rectifier

solid state device that controls current

Electric's trade name for a type of

engineers led by Gordon Hall and commercialized by Frank W. "Bill" Gutzwiller in 1957.

The Silicon Controlled Rectifier (SCR) is a semiconductor d

control devices known as Thyristors. The SCR has become the workhorse of the industrial

control industry. Its evolution over the years has yielded a device that is less expensive, more

reliable, and smaller in size than

generator field regulation, Variable Frequency Drive (VFD) DC Bus voltage control, Solid State

Relays and lighting system control. The SCR is a three

(as with a standard diode) plus a third control lead or

which can be controlled - or more correctly

applying a small positive voltage (VTM ) to the gate lead. Once g

be removed and the SCR will remain conducting as long as current flows through the device.

The load to be controlled by the SCR is normally placed in the anode circuit.

6.1 MODES OF OPERATION:

This device is generally used i

device restricts current to the leakage current. When the gate

certain threshold, the device turns "on" and conducts current. The device will remain in the "on"

35

SILICON CONTROLLED RECTIFIER BT169

controlled rectifier (or semiconductor-controlled rectifier

current. The name "silicon controlled rectifier" or

's trade name for a type of thyristor. The SCR was developed by a team of

led by Gordon Hall and commercialized by Frank W. "Bill" Gutzwiller in 1957.

6.1 Silicon Controlled Rectifier

The Silicon Controlled Rectifier (SCR) is a semiconductor device that is a memberof a family of



reliable, and smaller in size than ever before. Typical applications include : DC motor control,


Relays and lighting system control. The SCR is a three-lead device with an anode and a cathode

with a standard diode) plus a third control lead or gate. As the name implies, it is a rectifier

or more correctly - one that can be triggered to the “ON” state by

applying a small positive voltage (VTM ) to the gate lead. Once gated ON, the trigger signal may


The load to be controlled by the SCR is normally placed in the anode circuit.

MODES OF OPERATION:

his device is generally used in switching applications. In the normal "off" state, the

device restricts current to the leakage current. When the gate-to-cathode voltage exceeds a


SILICON CONTROLLED RECTIFIER BT169

controlled rectifier) is a four-layer

. The name "silicon controlled rectifier" or SCR is General

. The SCR was developed by a team of power

led by Gordon Hall and commercialized by Frank W. "Bill" Gutzwiller in 1957.

evice that is a memberof a family of



ever before. Typical applications include : DC motor control,


lead device with an anode and a cathode

. As the name implies, it is a rectifier

one that can be triggered to the “ON” state by

ated ON, the trigger signal may


n switching applications. In the normal "off" state, the

cathode voltage exceeds a


36

state even after gate current is removed so long as current through the device remains above the

holding current. Once current falls below the holding current for an appropriate period of time,

the device will switch "off". If the gate is pulsed and the current through the device is below the

holding current, the device will remain in the "off" state.

If the applied voltage increases rapidly enough, capacitive coupling may induce enough

charge into the gate to trigger the device into the "on" state; this is referred to as "dv/dt

triggering." This is usually prevented by limiting the rate of voltage rise across the device,

perhaps by using a snubber. "dv/dt triggering" may not switch the SCR into full conduction

rapidly, and the partially triggered SCR may dissipate more power than is usual, possibly

harming the device.

SCRs can also be triggered by increasing the forward voltage beyond their rated

breakdown voltage (also called as break over voltage), but again, this does not rapidly switch the

entire device into conduction and so may be harmful so this mode of operation is also usually

avoided. Also, the actual breakdown voltage may be substantially higher than the rated

breakdown voltage, so the exact trigger point will vary from device to device.

6.2 REVERSE BIAS:

SCR are available with or without reverse blocking capability. Reverse blocking capability adds

to the forward voltage drop because of the need to have a long, low doped P1 region. Usually,

the reverse blocking voltage rating and forward blocking voltage rating are the same. The typical

application for reverse blocking SCR is in current source inverters.

SCR incapable of blocking reverse voltage are known as asymmetrical SCR, abbreviated

ASCR. They typically have a reverse breakdown rating in the 10's of volts. ASCR are used

where either a reverse conducting diode is applied in parallel (for example, in voltage source

inverters) or where reverse voltage would never occur (for example, in switching power supplies

or DC traction choppers).

37

Asymmetrical SCR can be fabricated with a reverse conducting diode in the same package.

These are known as RCT, for reverse conducting thyristor.

6.3 Thyristor turn on methods

1. forward voltage triggering

2. gate triggering

3. dv/dt triggering

4. temperature triggering

5. light triggering

Forward voltage triggering occurs when the anode-cathode forward voltage is increased with the

gate circuit opened. This is known as avalanche breakdown, during which junction j2 will

breakdown. At sufficient voltages, the thyristor changes to its on state with low voltage drop and

large forward current. In this case, J1 and J3 are already forward biased.

6.4 Theory of Operation

6.4 Volt-Ampere Characteristics

38

Figure 1 below illustrates the volt-ampere characteristics curve of an SCR. The vertical axis + I

represent the device current, and the horizontal axis +V is the voltage applied across the device

anode to cathode. The parameter IF defines the RMS forward current that the SCR can carry in

the ON state, while VR defines the amount of voltage the unit can block in the OFF state.

Biasing

The application of an external voltage to a semiconductor is referred to as a bias.

6.5 Forward Bias Operation

A forward bias, shown below as +V, will result when a positive potential is applied to the

anode and negative to the cathode.

Even after the application of a forward bias, the device remains non-conducting until the

positive gate trigger voltage is applied.

After the device is triggered ON it reverts to a low impedance state and current flows

through the unit. The unit will remain conducting after the gate voltage has been

removed. In the ON state (represented by +I), the current must be limited by the load, or

damage to the SCR will result.

6.6 Reverse Bias Operation

The reverse bias condition is represented by -V. A reverse bias exists when the potential

applied across the SCR results in the cathode being more positive than the anode.

In this condition the SCR is non-conducting and the application of a trigger voltage will

have no effect on the device. In the reverse bias mode, the knee of the curve is known as

the Peak Inverse Voltage PIV (or Peak Reverse

Voltage - PRV) and this value cannot be exceeded or the device will break-down and be

destroyed. A good Rule-of -Thumb is to select a device with a PIV of at least three times

the RMS value of the applied voltage.

6.7 SCR Protection

The SCR, like a conventional diode, has a very high one-cycle surge rating. Typically,

the device will carry from eight to ten times its continuous current rating for a period of one

electrical cycle. It is extremely important that the proper high-speed, current-limiting, rectifier

fuses recommended by the manufacturer be employed - never substitute with another type fuse.

39

Current limiting fuses are designed to sense a fault in a quarter-cycle and clear the fault in one-

half of a cycle, thereby protecting the SCR from damage due to short circuits. Switching spikes

and transients, which may exceed the device PIV rating, are also an enemy of any

semiconductor. Surge suppressors, such as the GE Metal-Oxide-Varistor (MOV), are extremely

effective in absorbing these short term transients. High voltage capacitors are also often

employed as a means of absorbing these destructive spikes and provide a degree of electrical

noise suppression as well.

6.8 Testing the SCR

Shorted SCRs can usually be detected with an ohmmeter check (SCRs usually fail shorted rather

than open). Measure the anode-to-cathode resistance in both the forward and reverse direction; a

good SCR should measure near infinity in both directions. Small and medium-size SCRs can

also be gated ON with an ohmmeter (on a digital meter use the Diode Check Function). Forward

bias the SCR with the ohmmeter by connecting the red (+) lead to the anode and the black (- )

lead to the cathode. Momentarily touch the gate lead to the anode; this will provide a small

positive turn-on voltage to the gate and the cathode-to-anode resistance reading will drop to a

low value. Even after removing the gate voltage, the SCR will stay conducting. Disconnecting

the meter leads from the anode or cathode will cause the SCR to revert to its non-conducting

state.

When conducting the above test, the meter impedance acts as the SCR load. On larger SCRs, the

unit may not latch ON because the test current is not above the SCR holding current. Special

testers are required for larger SCRs in order to provide an adequate value of gate voltage and

load the SCR sufficiently to latch ON. Hockey puck SCRs must be compressed in a heat sink (to

make-up the internal connections to the semiconductor) before they can be tested or operated.

Some equipment manufacturers provide tabulated ohmmeter check-data for testing SCR

assemblies.

40

7. BUZZER

A buzzer or beeper is an audio signaling device, which may be mechanical,

electromechanical, or electronic. Typical uses of buzzers and beepers include alarms, timers and

confirmation of user input such as a mouse click or keystroke. Early devices were based on an

electromechanical system identical to an electric bell without the metal gong. Similarly, a relay

may be connected to interrupt its own actuating current, causing the contacts to buzz. Often these

units were anchored to a wall or ceiling to use it as a sounding board. The word "buzzer" comes

from the rasping noise that electromechanical buzzers made.

7.Circuit diagram of buzzer

7.1 What does it do?

The buzzer subsystem produces an audible tone

when powered.

7.2 How does it operate?

Buzzer circuit

.

Buzzers come in a variety of voltages and currents. The power

supply for the buzzer (which can be separate from the supply for

the rest of the electronics) m

buzzer.

Piezo sounders are a type of buzzer. They should not be confused

with Piezo transducers

drive them.

Some process units provide enough current to drive buzzers.

Typical

If

(

The circuit on the left shows the circuit needed with a driver.

Buzzer curcuit for use with

higher current process units

.

PICs

currents and can drive some buzzers directly.

Check the data for the buzzer and the process unit to make sure

that the process unit can provide more current than is needed by

the buzzer.

If this is possible, the buzzer is connec

left) rather than to +Vs.

Buzzers can either be PCB

with flying leads. Usually it is neater to mount them on the PCB.

41



the rest of the electronics) must provide the voltage needed by the

buzzer.


with Piezo transducers – which require an a.c. input voltage to

drive them.


Typical buzzers require currents in the range 10

If CMOS ICs or a higher current buzzer are used then a driver

(transistor, Darlington or MOFET) is needed to boost the current.


PICs, 555 Timer ICs and the LM324 op-amp

currents and can drive some buzzers directly.



the buzzer.

If this is possible, the buzzer is connected to the 0V rail (as on the

left) rather than to +Vs.

Buzzers can either be PCB-mounted or connected to the circuit




ust provide the voltage needed by the


which require an a.c. input voltage to


buzzers require currents in the range 10 – 35mA.

or a higher current buzzer are used then a driver

) is needed to boost the current.


can provide higher



ted to the 0V rail (as on the

mounted or connected to the circuit


42

7.3 Applications

• Making a warning sound

• Signalling that something has happened

7.4 Making

Buzzers have a positive and a negative terminal, marked on their case. The

positive terminal should be connected to the positive voltage supply. The

negative terminal should be connected to the signal from the driver.

The graphic on the left shows how part of the PCB might look for a PCB-

mounted buzzer connected to a driver.

How part of the PCB might look

If a buzzer with flying leads is used then a terminal block is mounted on the PCB and wires from

this are connected to the buzzer.

Build and test the unit that will provide the driving input signal before adding the buzzer.

7.5 Testing

Make sure that the buzzer switches on and off as power is applied from the driver unit.

43

8. DECADE COUNTER

Decade Counter

A decade counter is a binary counter that is designed to count to 1010, or 10102. An

ordinary four-stage counter can be easily modified to a decade counter by adding a NAND gate

as shown in figure 3-25. Notice that FF2 and FF4 provide the inputs to the NAND gate. The

NAND gate outputs are connected to the CLR input of each of the FFs.

Figure 8.. - Decade counter.

The counter operates as a normal counter until it reaches a count of 10102, or 1010. At that

time, both inputs to the NAND gate are HIGH, and the output goes LOW. This LOW applied to

the CLR input of the FFs causes them to reset to 0. Remember from the discussion of J-K FFs

that CLR and PS or PR override any existing condition of the FF. Once the FFs are reset, the

count may begin again. The following table shows the binary count and the inputs and outputs of

the

44

NAND gate for each count of the decade counter:

BINARY

COUNT

NAND GATE

INPUTS

NAND GATE

OUTPUT

******* A B *******

0000 0 0 1

0001 0 0 1

0010 1 0 1

0011 1 0 1

0100 0 0 1

0101 0 0 1

0110 1 0 1

0111 1 0 1

1000 0 1 1

1001 0 1 1

Changing the inputs to the NAND gate can cause the maximum count to be changed. For

instance, if FF4 and FF3 were wired to the NAND gate, the counter would count to 11002 (1210),

and then reset.

45

9. 60DB SIREN

A siren is a loud noise maker. Most modern ones are civil defense or air- raid sirens, tornado

sirens, or the sirens on emergency service vehicles such as ambulances, police cars and fire

trucks. There are two general types, pneumatic and electronic.

Many fire sirens serve double duty as tornado or civil defense sirens, alerting an entire

community of impending danger. Most fire sirens are either mounted on the roof of a fire station,

or on a pole next to the fire station. Fire sirens can also be mounted near government buildings,

on top of tall structures such as water towers, as well as in systems, where several sirens are

distributed around a town for better sound coverage. Most fire sirens are single tone and

mechanically driven by electric motors with a rotor attached to the shaft.

Some newer sirens are electronically driven by speakers, though these are not as

common. Fire sirens are often called "fire whistles", "fire alarms", "fire horns." Although there is

no standard signaling of fire sirens, some utilize codes to inform firefighters to the location of the

fire. Civil defense sirens pulling double duty as a fire siren often can produce an alternating "hi-

lo" signal (similar to a British police car) as the fire signal, or a slow wail (typically 3x) as to not

confuse the public with the standard civil defense signals of alert (steady tone) and attack (fast

wavering tone).

9. Siren

46

Electronic sirens incorporate circuits such as oscillators, modulators, and amplifiers to

synthesize a selected siren tone (wail, yelp, pierce/priority/phaser, hi-lo, scan, airhorn, manual,

and a few more) which is played through external speakers. It is not unusual, especially in the

case of modern fire engines, to see an emergency vehicle equipped with both types of sirens.

Often, police sirens also use the interval of a tritone to help draw attention.

9.1 APPLICATIONS OF SCR

SCRs are mainly used in devices where the control of high power, possibly coupled with

high voltage, is demanded. Their operation makes them suitable for use in medium to high-

voltage AC power control applications, such as lamp dimming, regulators and motor control.

SCRs and similar devices are used for rectification of high power AC in high-voltage direct

current power transmission. They are also used in the control of welding machines, mainly

MTAW and GTAW processes.

47

10. ADVANTAGES AND APPLICATIONS

10.1 Advantages:

1. Easy to operate.

2. Efficient.

3. Closed loop circuitry.

4. Durability

5. Low maintenance

6. Fit and Forget system

7. Highly sensitive

8. Low cost

9. Simple and Reliable circuit

10. Safety

10.2 Application:

Vehicles

Automatic lighting control

Burglar alarm systems

10.3 References:

• Industrial and Power Electronics by G.K Mithal

• Power Electronics by K B Khanchandani

48

11. CONCLUSION

The project Diamond security in museums is designed and implemented through

LDR, decade counter to catch the person through alerting a 60dB siren.