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 throughaswitching transistor. A loud 60db siren is
connected tothisscr. 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.

Diamond security system in museum with 60Db siren

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