Lecture 01 Introduction and applications of Electronics & SemiConductors.pdf
Babatunde undergraduate project
1. 1
DESIGN AND CONSTRUCTION OF A METAL DETECTOR
BY
AJAGBONNA BABATUNDE EMMANUEL
U07EE1051
DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING,
AHMADU BELLO UNIVERSITY,
ZARIA.
A PROJECT REPORT SUBMITTED TO THE DEPARTMENT OF ELECTRICAL
AND COMPUTER ENGINEERING, AHMADU BELLO UNIVERSITY, ZARIA-
NIGERIA IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE
AWARD OF THE DEGREE OF BACHELOR OF ENGINEERING (B.Eng.) IN
ELECTRICAL AND COMPUTER ENGINEERING.
SEPTEMBER, 2012
2. 2
DECLARATION
I hereby declare that this report is an original work undertaken by me and to the best of
my knowledge none has been presented anywhere for any purpose whatsoever. All
sources of information have been duly acknowledged by means of references and I accept
sole responsibility for any errors contained in this report.
………………………………. ……………………
Ajagbonna Babatunde Emmanuel Date
UO7EE1051
3. 3
CERTIFICATION
This is to certify that this project was done entirely by AJAGBONNA Babatunde .E under
my supervision. I certify that this work meets the requirement governing the award of the
degree of Bachelor of Engineering in Electrical and Computer Engineering and is
approved for its contribution to knowledge and literary representation.
………………….. …………………….
Engr. Dikko M.A Date
(Supervisor)
………………….. …………………...
Engr. A.M. Sani Date
(Project Coordinator)
……………………. ……………………
Dr. M. B. Muazu Date
Head of Department
4. 4
DEDICATION
I affectionately dedicate this project to Almighty God, my late father Engr. E.M
Ajagbonna and to all those who will be opportuned to read it.
5. 5
ACKNOLEDGEMENT
My profound gratitude goes to God Almighty, for seeing me through the under gratuate
program and making it a reality in my life.
Also worthy of acknowledgement is my supervisor, Engr. Dikko M.A for his advice and
patience in reading through the work and making valuable corrections despite his tight
schedule. May God bless him and continue to broaden his frontiers of knowledge.
My special thanks go to my mother Mrs. J.S Ajagbonna for her prayers, moral and
financial support, I sincerely appreciate her.
I sincerely thank my siblings, Mrs. Opeyemi Balogun, sister Eyiwumi and master Tomiwa
for their encouragement and support. Thanks go to all my buddies for their constructive
criticism and suggestions, God bless you all.
6. 6
TABLE OF CONTENTS
PAGE
Title page i
Declaration ii
Certification iii
Dedication iv
Acknowledgement v
Table of contents vi
List of tables ix
List of figures x
List of Abbreviations xi
Abstract xii
CHAPTER ONE: INTRODUCTION
1.1 PREAMBLE 1
1.2 PROJECT MOTIVATION 3
1.3 PROJECT DEFINITION 3
1.4 METHODOLOGY 3
1.5 LITERATURE REVIEW 4
1.6 SCOPE OF WORK 5
1.7 PROJECT OUTLINE 5
CHAPTER TWO: THEORETICAL BACKGROUND
7. 7
2.1 INTRODUCTION 6
2.2 RESISTOR 6
2.2.1 SERIES AND PARALLEL ARRANGEMENTS OF RESISTORS 6
2.3 VARIABLE RESISTOR 7
2.4 TRANSISTOR 8
2.4.1 BIPOLAR JUNCTION TRANSISTOR BJT 9
2.4.1.1 TYPES OF BIPOLAR TRANSISTOR 9
2.4.1.2 PRINCIPLE OF OPERATION OF BJT 10
2.5 SEMICONDUCTOR DIODES 12
2.6 LIGHT EMITTING DIODE (LED) 13
2.6.1 PRINCIPLE OF OPERATION OF LED 14
2.7 CAPACITOR 15
2.8 L7805 VOLTAGE REGULATOR 17
2.9 HARTEY OSCILLATOR 17
2.10 JRC4558IC 19
2.10.1 FEATURES OF JRC4558IC 19
2.10.2 JRC4558 IC MAXIMUM RATING 21
2.11 PIEZO BUZZER 22
CHAPTER THREE: SYSTEM DESIGN
3.1 INTRODUCTION 23
3.2 THE POWER SUPPLY UNIT (PSU) 23
8. 8
3.3 THE DISPLAY UNIT 24
3.4 THE SWITCHING UNIT 25
3.5 CHOICE OF TRANSISTOR 25
3.6 GAIN OF AMPLIFIER (COMPARATOR) 26
3.7 PRINCIPLE OF OPERATION 29
CHAPTER FOUR: CONSTRUCTION AND TESTING
4.1 INTRODUCTION 31
4.2 HARDWARE CONSTRUCTION 31
4.2.1 BREAD BOARDING 31
4.2.2 VERO BOARD 32
4.2.3 CASING AND ASSEMBILING 32
4.3 TESTING AND RESULT 35
CHAPTER FIVE: CONCLUSION AND RECOMMENDATION
5.1 CONCLUSION 37
5.2 LIMITATION OF THE STUDY 37
5.3 RECOMMENDATION 39
REFERENCE 39
9. 9
LIST OF TABLES
Table 2.1 JRC4558 IC maximum ratings 21
Table 4.1 Cost implementation of components 35
Table 4.2 Test result 36
10. 10
LIST OF FIGURES
Fig. 2.1 Parallel arrangement of resistors 6
Fig. 2.2 Series arrangement of resistors 7
Fig 2.3 Variable resistor symbol 7
Fig 2.4 Types of transistors 9
Fig 2.5 NPN BJT with forward biased E-B junction and reverse-biased B-C
Junction 11
Fig 2.6 Semi conductor diode and its symbol 13
Fig 2.7 LED schematic symbol 14
Fig 2.8 Light Emitting diode 14
Fig 2.9 Structure of L7805 regulator 17
Fig 2.10 Hartley oscillator circuit 18
Fig 2.11 Block diagram of JRC4558 IC 20
Fig 2.12 Pin configuration of JRC4558 IC 20
Fig 2.13 Equivalent circuit of JRC4558 IC 21
Fig 2.14 Buzzer diagram 23
Fig 3.1 Metal detector block diagram 24
Fig 3.2 9 Volt DC battery 25
Fig 3.3 complete circuit diagram of metal detector 29
Fig 4.1 Assembling of the metal detector using plastic trunk 34
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LIST OF SYMBOLS AND ABBREVATIONS
R = Resistor
D = Diode
CTR = Transistor
C = Capacitor
ZD = Zener diode
P1 & P2 = potentiometer
PC = Printed circuit
L1 & L2 = Mutual coils
DC = Direct current
AC = Alternating current
mF = Microfarad
pF = Pico farad
nF = Nanofarad
KΩ = kilo ohm’s
LIN = Linear
V = Voltage
LED = Light emitting diode
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ABSTRACT
This project represents the design and construction of a metal detector. The metal detector
presented in this work is built around Hartley oscillator and has a useful range of 20-
30mm depending on the size and composition of the metal it is made to detect. The circuit
operation is based on mutual inductance of an oscillator. The coils L1 and L2 when ON
generates a magnetic field which when a metal is brought into the field distort the field
condition and this create an input signal for the oscillation circuit to give an output signal
for the input stage of the amplifier which is then transferred to the displaying unit. The
frequency of the oscillator is between (150 to 200) KHz. The power supply unit is a
battery, which supply voltage (9V) to the whole circuit. The detector circuit incorporates a
light emitting diode and a buzzer which comes on when a metal is detected. The detector
circuit was constructed and tested, and it worked well.
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CHAPTER ONE
INTRODUCTION
1.1 PREAMBLE
Electronic Engineering is an aspect of electrical engineering which is concerned with the
design and analysis of electronics circuit using discrete electronic components and
integrated circuits (IC). With the advancement in Modern technology in the field of solid
state electronics, there comes the uses of electronic discrete components to create smart
electronic devices that are faster and more accurate than human beings which are used in
many applications most especially in security systems such as burglar alarms, metal
detectors etc.
A metal detector is a device which responds when a metal is brought close to it.
Detection of metal date back toward the end of the 19th century, scientists and engineers
used their knowledge of electrical theory to device a machine which would pinpoint
metal; this device gave miners a huge advantage in ore-bearing rocks[10]. German
physicist Heirich Wilhelm Dove invented the induction balance system which was
incorporated into metal detectors a hundred years later[2]. Alexander Graham Bell
attempted to use crude metal detector to locate a bullet lodged in the chest of American
president James Garfield in 1881, the attempt was unsuccessful because the metal coil
spring bed Garfield was lying on confused the detector[17]. By 1920s Gerhard Fisher
developed a system of radio direction findings, but there were anomalies in areas where
the terrain contained ore-bearing rocks. Also Shirl Herr, from Crawford’s Ville Indiana
was the first to apply for a patent for a hand – held hidden metal detector
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(1924)[1],Herr’s detector assisted Italian leader Benito Mussolini in recovering items
remaining from the Emperor Caligula’s galleys at the bottom of lake Nemi, Italy. A
polish Lieutenant Josef Stanislaw kosacki, refined Herr’s detector to a practical polish
mine detector[10]. Oregon began in the 1950s to build Oremaster Geiger Counter.
Charles Garrett pioneered the BFO (Beat Frequency Oscillator). By the advent of
transistors in 1950s and 1960s manufacturers and designers of metal detectors made
smaller lighter detectors with improved circuitry, running on small battery packs.[2]
Industrial fabrication of metal detector started in the 1960s, these detectors were and are
used in the detection of weapons such as knives and guns in airports, banks and recently
in places of worship. Also detectors are used to detect metal contaminants in food,
pharmaceuticals, beverages, textiles, garments, plastics, chemicals etc. Metal detectors
are used in detecting land mines, also in the construction industry to detect steel
reinforcing bars in concrete and pipes and wires buried in walls and floors.[10]
A non-complex metal detector consists of an oscillator producing an alternating
current that passes through a coil to produce an alternating magnetic field. When a piece
of electrically conductive metal is close to the coil, eddy currents will be induced in the
metal, and this produces and alternating magnetic field of its own. If another coil is used
to measure the magnetic field (acting as magnetometer), the change in the magnetic field
due to the metallic object can be detected. [15]
1.2 PROJECT MOTIVATION
The motivation for this project is derived from the desire to construct a metal detector
that can be used in detecting metal arms from criminals in organizations, places of
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worship, banks etc. This handy garget would also be used in detecting metallic objects
like pipes in conduit wiring.
1.3 PROBLEM DEFINITION
The problems associated with most of the metal detector built over the years vary from
total cost of construction to sensitivity of the device. This project tackles these problems.
1.4 METHODOLOGY
The methodology adopted is as follows:
a. Design a coil for the Harley oscillator
b. Design the oscillator circuit
c. Designing driver for light emitting diode and buzzer
d. Assembling and casing
1.5 LITERATURE REVIEW
16. 16
In other to achieve success in this project, a research work was painstakingly undertaken
to ensure a quality work, these works were considered in the process of this project work:
EZEH ANTHONY department of electrical engineering, ABU (2008) designed a remote
metal sensing security system, built around a TDA0161 proximity detector IC which has
a sub-unit of oscillator, peak modulator a level detector and an internal reference. An LC
circuit was also used to send electromagnetic signals to a target as well as receiver
counter induction electromagnetic signals for comparison against an internal reference
determined by the IC.
The major difference between his work and the one presented in this project is that while
he designed his system using TDA0161 proximity detector IC, the one presented in this
project is designed using Hartley oscillator.[2] The major limitation of Anthony’s
detector is that the sensitivity of the search coil he used is calibrated on the LC side by a
resistor network, while the sensitivity of the detector presented in this project is varied by
a variable resistor.
SUNDAY OKPE (2004) of Benue State polytechnic built a metal detector that gives a
respectable range for beat frequency operation (bfo) up to 90mm of a bottle. His work
was considered too straight forward and simple because the components he used for his
design were only a capacitor, two comparators and a DC battery [17]. The major
limitation of Sunday’s detector is that with the frequency of oscillation being raised to
more than a 100 KHz, accuracy becomes a significant problem. But the frequency of the
work presented in this project has being improved to about (150-200) KHz.
17. 17
AGBO JOHN (2008) of department of electrical engineering Bida Poly built a metal
detector based on ICCS209A. A 100uH coil was used to sense the presence of metal. The
inductance due to the change in the presence of metal and the resultant change in
oscillation is demodulated to create an alarm. [1]. His work was a single chip metal
detector. Hartley oscillator detector presented in this project is built from a pair of coil of
mutual inductance of 325mH as compared with the 100uH of John’s detector, thereby
improving sensitivity.
1.6 SCOPE OF WORK
This work entails the construction of a metal detector built around a Hartley oscillator.
1.7 PROJECT OUTLINE
This project is structured into five (5) chapters. Chapter one introduces the project while
chapter two gives the insight into the theoretical background on which the design is
based. Chapter three deals with general system design. Chapter four entails construction
and testing while chapter five gives the conclusion and recommendation for further work.
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CHAPTER TWO
THEORETICAL BACKGROUND
2.1 INTRODUCTION
This chapter covers all the electronic components used in the construction of the metal
detector.
2.2 RESISTORS
A resistor R is a two-terminal electronic component designed to oppose an electric
current flow I by producing a voltage drop V between its terminals in proportion to the
current. That is, in accordance with Ohm’s law, V = IR. Thus, resistance R is equals to
the voltage drop V across the resistor divided by the current I through the resistor. The
resistor can either be Fixed or variable. Resistors can be in series or in parallel.(12)
2.2.1 SERIES AND PARALLEL ARRANGEMENTS OF RESISTORS
For resistors (R1, R2 . . . Rn) in parallel configuration, the same potential difference
(Voltage) exists across each resistor. Their total equivalent resistance 𝑅 𝑒𝑞 is shown in
equation 2.1
Fig. 2.1: Parallel arrangements of resistor
19. 19
(2.1)
For two of such resistor, 𝑅 𝑒𝑞 is ;
(2.2)
The current through resistors in series stays the same, but the voltage across each resistor
is different. The sum of the potential difference (voltage) is equal to the total voltage[12].
Their total resistance is R
Fig. 2.2: Series arrangement of resistors
(2.3)
2.3 VARIABLE RESISTOR
Fig2.3: variable resistor symbol
A variable resistor often referred to as either as a potentiometer or a rheostat can have a
maximum value as high as 5MΩ.
The resistance between two terminals for equal angular rotation of the spindle of the
potentiometer may increase linearly or logarithmically. The most common one is the
20. 20
linear type, whose resistance increases, in direct proportion to the angular position of the
marker on the spindle [11]
2.4 TRANSISTOR
The transistor is the most important example of an “active” component, a device that can
amplify, producing an output signal with more power in it than the input signal. The
additional power comes from an external power source (the power supply to be
exact).[17]
The transistor is the essential ingredient of every electronic circuit, from the
simplest amplifier or oscillator to the most elaborate digital computer. Integrated circuit
(ICs) which have largely replaced circuits constructed from discrete transistors are
themselves merely arrays of transistors and other components built from a single chip of
semi-conductor material. There are frequent situations the right IC just doesn’t exist and
one has to rely on discrete transistor circuit to do the job.
There are two basics types of transistors: the bipolar junction transistor (BJT) and the
field effect transistors (FET), we would be discussing the BJT for purpose of this project.
2.4.1 BIPOLAR (JUNCTION) TRANSISTOR BJT
21. 21
A bipolar (junction) transistor (BJT) is a type of transistor. It is a three-terminal device
constructed of doped semiconductor material and may be used in amplifying or switching
applications. Bipolar transistors are so named because their operation involves both
electrons and holes
2.4.1.1 TYPES OF BIPOLAR TRANSISTORS
The two types of transistors are the NPN and PNP shown in Fig. 2.5
(i) Standard NPN transistor symbol
(ii) Standard PNP transistor symbol
Fig. 2.4: Types of Transistors
NPN is one of the two types of bipolar transistors, in which the letters "N" and "P"
refer to the majority charge carriers inside the different regions of the transistor. Most
bipolar transistors used today are NPN, because electron mobility is higher than hole
mobility in semiconductors, allowing greater currents and faster operation.
22. 22
NPN transistors consist of a layer of P-doped semiconductor (the "base") between two N-
doped layers. A small current entering the base in common-emitter mode is amplified in
the collector output. In other terms, an NPN transistor is "on" when its base is pulled high
relative to the emitter.
PNP transistors consist of a layer of N-doped semiconductor between two layers of
P-doped material. A small current leaving the base in common-emitter mode is amplified
in the collector output. In other terms, a PNP transistor is "on" when its base is pulled low
relative to the emitter.
The arrow on the NPN or PNP transistor symbol in Fig. 2.4 is on the emitter leg
and points in the direction of the conventional current flow when the device is in forward
active mode.[14]
2.4.1.2 PRINCIPLE OF OPERATION OF A BIPOLAR TRANSISTOR
The three portions of a transistor (Fig. 2.5) comprise emitter, base and collector which are
discussed below:
a. Emitter E:
The emitter is heavily doped and is responsible for emitting electrons into the base of the
transistor.
b. Base B:
23. 23
The base is lightly doped and very thin; it passes most of the emitter injected electrons
into the collector.
c. Collector C:
The collector collects electrons from the base. It is the largest of the three regions. Since
it must dissipate more heat than the emitter or base. Its doping is higher than that of the
base but lower than that of the emitter.[13]
Fig. 2.5: NPN BJT with forward-biased E–B junction and reverse-biased B–C junction
An NPN transistor can be considered as two diodes with a shared anode region as shown
in Fig. 2.5. In typical operation, the emitter–base junction is forward biased and the base–
collector junction is reverse biased. In an NPN transistor, for example, when a positive
voltage is applied to the base–emitter junction, the equilibrium between thermally
generated carriers and the repelling electric field of the depletion region becomes
unbalanced, allowing thermally excited electrons to inject into the base region. These
electrons diffuse through the base from the region of high concentration near the emitter
towards the region of low concentration near the collector. The electrons in the base are
called minority carriers because the base is doped p-type which would make holes the
majority carrier in the base.
24. 24
The collector–base junction is reverse-biased, so little electron injection occurs from the
collector to the base, but electrons that diffuse through the base towards the collector are
swept into the collector by the electric field in the depletion region of the collector–base
junction.
A peculiar property of the transistor is that the current gain, which is the ratio of collector
current to base current, is constant.[8]
2.5 SEMICONDUCTOR DIODES
It is a two terminal device which is sensitive to the direction in which current flows
through it. Diodes allow electrons to flow easily in one way through it but oppose flow in
the opposite direction.
When the diode is connected so that the current is flowing (positive to the p-type anode,
negative to cathode), it is said to be forward biased. When the connection is reversed, the
diode does not conduct, it is said to be reverse biased.
Most modern diodes are based on semiconductor p-n junctions. In a p-n diode,
conventional current can flow from the p-type side (the anode) to the n-type side (the
cathode), but cannot flow in the opposite direction.[18]
A semiconductor diode and its symbol are shown in Fig. 2.7
25. 25
(i) Semiconductor diode
(ii) Symbol of a diode
Fig. 2.6: semiconductor diode and its symbol
2.6 LIGHT EMITTING DIODE (LED)
A light-emitting-diode (LED) is a semiconductor diode that emits light when an electric
current is applied in the forward direction of the device, as in the simple LED circuit. The
effect is a form of electroluminescence where incoherent and narrow-spectrum light is
emitted from the p-n junction in a solid state material.[9]
The symbol of a LED is shown in Fig. 2.7.
Fig. 2.7: LED schematic symbol
A picture of a LED is shown in Fig. 2.8
26. 26
Fig. 2.8: Light Emitting Diode
2.6.1 PRINCIPLE OF OPERATION OF LED
Like a normal diode, the LED consists of a chip of semiconducting material impregnated,
or doped, with impurities to create p-n junction. As in other diodes, current flows easily
from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction.
Charge-carriers—electrons and holes flow into the junction from electrodes with different
voltages. When an electron meets a hole, it falls into a lower energy level, and releases
energy in the form of a photon.
The wavelength of the light emitted, and therefore its color, depends on the band gap
energy of the materials forming the p-n junction.
The semiconductor materials used in LEDs are gallium arsenide, gallium arsenide
phosphide or gallium phosphide. Silicon and germanium are not used because they are
essentially heat producing materials and are poor at producing light. LEDS present many
advantages over traditional light source, including lower energy consumption, longer life,
27. 27
improved robustness, smaller size and faster switching. However, they are relatively
expensive and require more precise current and heat management than traditional lights
sources.
Applications of LEDS are diverse. They are used as low energy indicators but also for
replacement for traditional light sources in general lighting and automotive lighting. The
compact sizes of LEDS have allowed now text and video displays and sensors to be
developed, while the switching rates are useful in communication technology.[9]
2.7 CAPACITORS
A capacitor or condenser is a passive electronic component consisting of a pair of
conductors separated by a dielectric. When a voltage potential difference exists between
the conductors, an electric field is present in the dielectric. This field stores energy and
produces a mechanical force between the plates. The effect is greatest between wide, flat,
parallel, narrowly separated conductors.
An ideal capacitor is characterized by a single constant value, capacitance, which is
measured in Farads. This is the ratio of the electric charge on each conductor to the
potential difference between them. In practice, the dielectric between the plates passes a
small amount of leakage current. The conductors and leads introduce an equivalent series
resistance and the dielectric has an electric field strength limit resulting in a breakdown
voltage.
28. 28
Capacitors are widely used in electronic circuits to block the flow of direct current
allowing alternating current to pass, to filter out interference, to smooth the output of
power supplies, and for many other purposes. They are used in resonant circuits in radio
frequency equipment to select particular frequencies from a signal with many
frequencies.
Capacitors in a parallel configuration each have the same applied voltage. Their
capacitance adds up. Charge is a apportioned among them by size. Using the schematic
diagram to visualize parallel plates, it is apparent that each capacitor contributes to the
total surface area.
Schematic diagram reveals that the separation distance, not the plate area, adds up. The
capacitors each store instantaneous charge build-up equal to that of every other capacitor
in series. The total voltage different from end to end is approx. to each capacitor
according to the inverse of its capacitance. The entire series acts as a capacitor smaller
than any of its component
Capacitors are combined in series to achieve a higher working voltage. For example,
switching a high voltage power supply. The voltage ratings, which are based on plate
separation, add up. In such an application, several series connections may in turn be than
that of the emitter [18]
29. 29
2.8 L7805 VOLTAGE REGULATOR
Voltage regulators are fabricated in form of an integrated circuit that can provide a
required fixed output voltage for a particular circuit operation. The 78xx and 79xx
regulators are fabricated in form of an IC with three terminals. The terminals are Input,
Output and Ground (common). The 78xx series are used for positive voltages. The value
“xx” represent the value of the regulated output; hence the usage of the L7805, since the
output voltage required is 5V. The structure of 78xx is shown in fig. 2.9 [17]
Fig. 2.9: structure of L7805 Regulator
2.9 HARTLEY OSCILLATOR
Fig 2.10: Hartley oscillator circuit
30. 30
The Hartley oscillator is an LC electronic oscillator that derives its feedback from a
tapped coil in parallel with a capacitor (the tank circuit). Although there is no
requirement for there to be mutual coupling between the two coil segments, the circuit is
usually implemented as such. A Hartley oscillator is essentially any configuration that
uses a pair of series-connected coils and a single capacitor.
The Hartley oscillator was invented by Ralph V.L. Hartley while he was working for the
Research Laboratory of the Western Electric Company. Hartley invented and patented the
design in 1915 while overseeing Bell System’s transatlantic radiotelephone tests.
A Hartley oscillator is made up of the following:
Two inductors in series, which need not be mutual
One tuning capacitor [5]
Advantages of the Hartley oscillator include:
The frequency may be varied using a variable capacitor
The output amplitude remains constant over the frequency range
Either a tapped coil or two fixed inductors are needed.
Disadvantages include:
Harmonic –rich content if taken from the amplifier and not directly from the LC
circuit.
31. 31
Note that, if the inductance of the two partial coils L1 and L2 is given (e.g. in a
simulator), the total effective inductance that determines the frequency of the oscillation
is (coupling factors K):
𝐿 𝑒𝑞 = 𝐿1 + 𝐿2 + 𝑘 × √ 𝐿1 × 𝐿2 (2.4)
2.10 JRC4558 IC
The JRC4558 is a high performance monolithic dual operational
amplifier.
2.10.1 FEATURES OF JRC4558 IC
I. No frequency compensation required
II. No latch – up
III. Large common mode and differential voltage range
IV. Parameter tracking over temperature range
V. Gain and phase match between amplifiers
VI. Internally frequency compensated
VII. Low noise input transistors
VIII. Pin to pin compatible with MC1458/LM358 [4,16]
32. 32
Fig. 2.11: Block diagram of JRC4558 IC
Fig. 2.12: pin configuration of JRC4558 IC
1-Output 1 5-Non-inverting input 2
2-Inverting input 1 6-Inverting input 2
3-Non-inverting input1 7-Output 2
4-Vcc 8-Vcc +
33. 33
Fig.2.13: equivalent circuit of JRC4558 IC
2.10.2 JRC4558 IC MAXIMUM RATINGS
Table 2.1 JRC4558IC maximum ratings
PARAMETER SYMBOL VALUE UNIT
Symbol voltage Vcc ±22 𝑉
Differential input voltage VI(DIFF) ±18 𝑉
Input voltage VI ±15 𝑉
Operating temperature TOPD −20~+85 ℃
Power dissipation (P-DIP 8) PD 600 𝑚𝑊
Storage temperature range TSTG −65~150 ℃
34. 34
2.11 PIEZO BUZZER
A piezo buzzer is a simple electronic noisemaking component. When given a
voltage or alternating current, it creates a buzzing sound. Many electronic beeps that we
hear in daily life are generated by piezo buzzers. This circuit shows the simplest way to
drive a piezo buzzer.
The piezo buzzer produces sound based on reverse of the piezoelectric effect. The
generation of pressure variation or strain by the application of electric potential across a
piezoelectric material is the underlying principle. These buzzers can be used alert a user
of an event corresponding to a switching action, counter signal or sensor input. They are
also used in alarm circuits.
The buzzer produces a same noisy sound irrespective of the voltage variation applied to
it. It consists of piezo crystals between two conductors. When a potential is applied
across these crystals, they push on one conductor and pull on the other. This, push and
pull action, results in a sound wave. Most buzzers produce sound in the range of 2 to 4
kHz.
The red lead is connected to the input and the black lead is connected to the
ground. [1]
35. 35
Fig. 2.14: Buzzer diagram
CHAPTER THREE
SYSTEM DESIGN
3.1 INTRODUCTION
This chapter describes the general analysis of the system and also explains how the
values of each components are been arrived at. The block diagram of the system is shown
in fig 3.1
Fig 3.1: Metal detector block diagram
3.2 THE POWER SUPPLY UNIT (PSU)
The power supply unit is designed in a way that it will be able to carry the circuit. Since
the supply-voltage range from (5V – 20V) a voltage of 9V is chosen which will be able to
carry the transistor without any breakdown, and it will make it compatible or handy as it
is to be an instrument to be carried about by the User or Technician.
The metal detector circuit is made active from a 9V PP3 battery. The current drain is
approximately 10mA when the circuit is ON and 17mA when it is detecting a metal.
From the design of the metal Detector used, it is clear that the device will have an
optimum performance compared with any other type of detector.
Voltage
supplyunit
Voltage
regulator
unit
Oscillator
unit
Amplifier
unit
Display
unit
36. 36
Fig. 3.2: 9 Volt DC batteries.
3.3 THE DISPLAY UNIT
A Red (LED) is connected at the emitter of the Q1 to indicate a glow, which signifies the
detection of metal and since the circuit in regulated to operate a 5V, then LED current for
the design is set at 0.02mA.
The value of the resistor𝑅2 is
𝑅2=V/I (3.1)
Where V = 5V and i = 0.02mA
𝑅2 = 5V/ 0.02mA
𝑅2 = 250Ω
3.4 SWITCHING UNIT
37. 37
With the aid of an inductance meter we were able to measure the value of 𝐿1 and 𝐿2 to be
1600mH and 1000mH.
Using the formula: 𝐿 𝑡 =𝐿1 +𝐿2 +2𝑀. We can obtain Lt taking measurement of two coils
when joint together and thus we have; 3250mH
𝐿 𝑡 =𝐿1 +𝐿2+ 2𝑀; if 𝐿1 +𝐿2 = 𝐿 𝑠 (3.2)
𝐿 𝑡 =𝐿 𝑠 + 2𝑀
So 𝑀 = ( 𝐿 𝑡 − 𝐿 𝑠)/2
= (3250 - 2600)/2
=325mH
𝑀 = 325mH
3.5 CHOICE OF TRANSISTOR
The factors considered in the choice of transistor are the 𝑖 𝑐𝑒 and 𝑖 𝑏 at saturation. The
𝑉𝐶𝐶 at cut off should be able to withstand the supply voltage which is 5V. In this case the
Ice of the transistor must be greater than 70mA. And the Ib must not exceed 10mA since
that’s the maximum the processor can source.
Considering the above, the BC557AP Transistor was chosen with the following
properties 𝑉𝑐𝑒𝑜= 12V
Max 𝑖 𝑐 at saturation = 170mA
38. 38
𝑉𝑐𝑒 at saturation = 0.2 V
𝑉𝑏𝑒 at saturation = 0.7V
𝐻𝑓𝑒 = 16
Base Resistors 𝑅 𝑏:
We can calculate the value of 𝑅 𝑏 required to drive the transistor to saturation at an Ice of
70mA
𝐻𝑓𝑒=𝑖 𝑐𝑒/𝑖 𝑏 (3.3)
Therefore: 𝑖 𝑏 = Ice /𝐻𝑓𝑒 , Ice = 70mA, 𝐻𝑓𝑒 =16
Therefore 𝑖 𝑏 = 70/16 = 4.37mA
But 𝑅 𝑏= (𝑉𝐶𝐶 -𝑉𝑏𝑒 )/ 𝑖 𝑏
𝑅 𝑏 = (5-0.7)/4.37m
𝑅 𝑏=4.3/4.37m
𝑅 𝑏= 983.98Ω
But this design value of 𝑅 𝑏is not realizable, because 983.98Ω is not obtainable. So
therefore𝑅 𝑏 is assumed to be 1KΩ.
3.6 GAIN OF AMPLIFIER (COMPARATOR IC2)
The gain of the amplifier is calculated as follows:
39. 39
Gain = feedback resistance/ input resistance (3.4)
Feedback resistance = 100KΩ
Input resistance =4.7KΩ
So, Gain = 100/4.7
= 21.3
41. 41
3.7 PRINCIPLE OF OPERATION
Whenever a metal is brought close to the sensor (coil) of the detector, the Q of the coil
decreases thereby decreasing the amplitude of the oscillation.
When power is switched on, the biasing resistor at the base of the NPN transistor turn it
on and this causes a current to flow through the collector to the larger winding of the coil.
A current is produced as a result through magnetic induction to flow through the smaller
coil which is fed back to the base of the transistor through the capacitor.
The output of the oscillator is taken from the collector of the transistor to be demodulated
by the combination of the IN4148 diode, the PNP transistor and the parallel resistor and
capacitor network.
The diode rectifies the RF oscillation voltage, this signal is amplified by the PNP
transistor. The output from the emitter from the transistor is filtered by the RC network
removing the remaining ripple voltage.
To make the signal more useful, it is amplified by comparator 2. The gain of the
amplifier is given by the feedback resistor divided by the input resistor which is both
connected to the inverting input of the comparator. The output of the amplifier is a much
larger variable voltage proportional to the amplitude of oscillation.
Comparator 1 does the actual triggering of the buzzer when a metal is detected. A
reference voltage is applied to the non inverting input which is set by the position of the
variable resistor at that time, while the output of comparator 2 goes to the inverting input.
42. 42
Triggering occurs when the voltage at the inverting input becomes higher than the said
voltage at non inverting input, at which the output of comparator becomes negative,
thereby driving the PNP driver transistor to turn on and provide negative current through
the emitter to turn on the buzzer and at the same time, turn on LED. Therefore,
depending on the setting of the variable resistor, the sensitivity of the metal detection can
be varied.
43. 43
CHAPTER FOUR
CONSTRUCTION AND TESTING
4.1 INTRODUCTION
This chapter describes the construction and testing of the system. In the design of circuits
from conception to construction, certain steps have to be followed. These include:
selection of components, simulation, construction and testing.
4.2 HARDWARE CONSTRUCTION
Having chosen our component and their values, the next stage is how to put them
together according to the circuit diagram which had been designed and see how the
performance will look like. In order to accomplish our task, The construction and
assembly stage is divided into sections.
4.2.1 BREAD BOARDING
It is a good design practice to always bread board our circuit first and test its output
before soldering on Vero board. Each of the various blocks in the block diagram were
separately built and tested on a bread board before transferring them to Vero board.
A breadboard has internal connections which makes it easy for use. It does not need any
soldering on the board.[5]
4.2.2 VERO BOARD
44. 44
Vero board is the panel on which all the component used are mounted. There are various
sizes of Vero board. The size used depends on how complex the circuit is. The board
consists of holes which are arranged in matrix format. The small size consists of 25 rows
and 55 columns, while the big size consists of 35 rows and 65 columns. The holes are
meant for mounting the components on the panel. The row are connected across the
column i.e. row one is connected to all the column and row two is connected to the entire
column also but separated from row one.
The row is connected together by a metallic sheath which makes it possible for easy
soldering of components on the Vero board. With proper design knowledge, this layout
of Vero board makes assembling easy and it reduces the use of jumper wires and it also
makes the work to look neat. As with the bread board, each block is soldered at a time,
tested and certified before the next stage is soldered.[5]
4.2.3 CASING AND ASSEMBLING
This is an important aspect of the design work, this is the appearance given to the final
work. After soldering on the Vero board, we do not leave it like that it has to be cased in
such a way that it looks attractive to the eye.
Plastic trunk was used in packaging the work so as to make it portable. The dimensions
of the casing were arrived at after considering various factors such as the width and
length of the Vero board, Battery and also the circuit models.
47. 47
4.3 TESTING AND RESULTS
After the construction of the circuit on bread board testing was carried out to determine if
the result obtained met the designed parameter used.
This test is done with the aid of a comparator circuit and a reference voltage is used to
determine the area of coverage of the metal detector system. It detects a metal between
01mm to 40mm depending on the size of metal and its composition. The LED indicator
comes on as you get closer to the metal as from 30mm the closer you get to the metal the
more luminance it becomes. The table below shows the voltages recorded via the
reference voltage. The beeper represent the first stage of detecting the metal and it also
beep louder as you get closer to the metal.
48. 48
Table 4.2 TEST RESULT: EFFECT OF VARYING VARIABLE VOLTAGE AT
DIFFERENT METAL DISTANCE
REFERENCE
VOLTAGE(VOLT
DC)
CHANGE IN
VOLTAGE ON
COMPARATOR
(VOLT)
DISTANCE
FROM
METAL(mm)
RESULT
2.701 2.89 40 Beeper start to beep
silently
2.610 2.97 38 Beeper increase in
Volume
2.530 3.08 36 Beeper increase in
volume
2.308 3.19 34 Beeper increase in
volume
2.010 3.67 32 Beeper increase more
volume
2.000 3.72 30 Beeper increases
more in volume
1.899 3.82 28 Beeper increases
more in volume
1.710 3.92 26 Beeper increases
more in volume
1.700 4.63 24 Beeper increases
more in volume
1.712 4.991 22 Beeper increases
more in volume
1.700 5.64 20 Beeper increases
more in volume
1.701 5.798 18 Beeper increases
louder in volume
1.711 5.80 16 Beeper increases
loader in volume
1.710 5.80 14 Beeper increases
louder in volume
1.712 5.80 12 Beeper increases
louder in volume
1.600 5.81 10 Beeper increases
louder in volume
49. 49
CHAPTER FIVE
CONCLUSION AND RECOMMENDATION
5.1 CONCLUSION
One of the primary objectives of an engineer is to endeavor to deliver the best product or
the most efficient services at the lowest cost to the end user. This particular system is
very cost effective when compared with the one designed and sold in the market, and it
provides a flexible system where additional features can be added in the future. This
feature of the system makes it very effective in the long run.
The aim of this work was to design and construct a metal detector that can be remotely
used, and the system has thus accomplished that. The system has being tested and was
found to meet the expected results.
5.2 LIMITATION OF THE STUDY
The research was limited by constraints such as time, finance and unavailability of
reference materials such as textbooks, similar projects and access to the internet. The
cost of useful components was beyond expectation not to mention their availability and
accessibility.
5.3 RECOMMENDATIONS
The metal detector presented here was designed based on Hartley Oscillator. Instead of
just designing the metal detector based on Hartley oscillator, this system can be improved
on, by using integrated circuit technology to allow the user to set sensitivity,
50. 50
discrimination, track speed, threshold volume, notch filters, etc., and hold these
parameters in memory for future use.
Also further research could be done to further improve the sensitivity of the device so as
to increase the distance range of metal detection. Seize could be worked on, to be as
compact as possible.
52. 52
17. SUNDAY OKPE, “Design and Construction of Simple Metal Detector”, Department of
Electrical Engineering, Federal Polytechnic Kaduna, 2008.
18. Theraja B.L., Theraja A.K., “A text book of electrical technology”, Ed. 21st , publication
of division of Nirja construction and Development co.,Ltd. Ram Nagar., 1994.
