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

1

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

2

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

3

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.

4

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.

5

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

6

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

7

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

8

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

9

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

11

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 (1924)

13

[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

14

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

15

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.

16

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.

17

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 Req is shown in

equation 2.1

Fig. 2.1: Parallel arrangements of resistor

18

(2.1)

For two of such resistor, Reqis ;

(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

19

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

20

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.

21

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:

22

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.

23

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

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(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

25

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,

26

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.

27

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]

28

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

29

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.

30

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):

Leq=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]

31

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 +

32

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

33

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]

34

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.

35

Voltage supply unit

Voltage regulator unit

Oscillator unit

Amplifier unit

Display unit

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

36

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: Lt =L1 +L2 +2M . We can obtain Lt taking measurement of two coils

when joint together and thus we have; 3250mH

Lt =L1 +L2+ 2M ; if L1 +L2 = Ls (3.2)

Lt =Ls + 2M

SoM = (Lt−Ls )/2

= (3250 - 2600)/2

=325mH

M = 325mH

3.5 CHOICE OF TRANSISTOR

The factors considered in the choice of transistor are the ice and ib at saturation. The V CCat

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 V ceo= 12V

Max icat saturation = 170mA

37

V ce at saturation = 0.2 V

V beat saturation = 0.7V

H fe = 16

Base ResistorsRb:

We can calculate the value of Rb required to drive the transistor to saturation at an Ice of

70mA

H fe=ice/ib (3.3)

Therefore: ib = Ice /H fe , Ice = 70mA,H fe =16

Thereforeib = 70/16 = 4.37mA

But Rb=¿ ¿ (V CC -V be )/ib

Rb = (5-0.7)/4.37m

Rb=4.3/4.37m

Rb= 983.98Ω

But this design value of Rbis not realizable, because 983.98Ω is not obtainable. So

thereforeRb is assumed to be 1KΩ.

3.6 GAIN OF AMPLIFIER (COMPARATOR IC2)

The gain of the amplifier is calculated as follows:

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Gain = feedback resistance/ input resistance (3.4)

Feedback resistance = 100KΩ

Input resistance =4.7KΩ

So, Gain = 100/4.7

= 21.3

39

Fig. 3.2 Complete circuit diagram of the metal detector

40

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.

41

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.

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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

43

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.

44

Fig 4.1: Assembling of the metal detector using plastic trunk

45

Table 4.1 COST IMPLEMENTATION OF COMPONENTS

S/

N

COMPONENTS QUANTITY UNIT

PRICE(#)

TOTAL

PRICE(#)

1 Oscillator circuit 1 800 800

2 Diode 1 30 30

3 LED 2 50 100

4 Variable resistor 1 70 70

5 L7805 regulator 1 120 120

6 Resistor 12 20 240

7 Capacitor 3 70 210

8 BC557AP transistor 3 150 450

9 Case/packaging 1 2000 2000

10 Ac wire 1 150 150

12 JRC4558 IC 1 2000 2000

13 Buzzer 1 150 150

14 9V DC battery 1 120 120

15 Vero board 1 150 150

16 Miscellaneous 1000

Total #7590

4.3 TESTING AND RESULTS

46

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.

47

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 inVolume

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

48

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,

49

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.

50

REFERNCES

1. AGBO JOHN, “Design and Construction of Simple Metal Detector”, Department of

Electrical Engineering, Federal Polytechnic Bida, 2008.

2. Anthony Ezeh, “Design and Construction of Remote Metal Sensing Security. System”,

Department of Electrical Engineering, Ahmadu Bello University, Zaria,2008.

3. Dave G.(1993); Best of Maplin Projects. Birmingham Sutton New Road London

4. Datasheet Search System [Internet]; ©2003 – 2008 digchip.com, Available at:

http//www.digchip.com/.

5. Electronic Workbench Multisim professional version (V.8)

6. Giillessen K. (1994): Light Emitting Diodes, University Press Cambridge, London

7. Howstuffworks [Internet]; © 1998-2006 How stuff Works, Available

at:http://www.howstuffworks.com/

8. (http://en.wikipedia.org/wiki/bipolar-junction-transistor)

9. (http://en.wikipedia.org/wiki/LED)

10. (http://en.wikipedia.org/wiki/metaldetectorhistory)

11. (http://en.wikipedia.org/wiki/variable-resistor)

12. (http://en.wikipedia.org/wiki/resistors)

13. Kybett H. (1979) Electronics: A self teaching guide; Macmillian company, New York

14. Paul H. (1989); Art of Electronics, University Press Cambridge London 2nd Edition

PP.65-72.

15. Robert W.F. (1987); Live Line Detector, WWW. TestechElect.Com.

16. Ronald J.T. (1996); Digital System, Continental Press, Sixth Edition PP 443.

51

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.

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