METAL DETECTORSubmitted By Vineesh A. V. Vimiya Varkey Viji M. C.

Guided BY M^. K. Gnanasheela Ms^Sumol N. C. Ms. Seena George

ABSTRACT

In security aspects, metal detector isan essential equipment. But, the metal detector, which is available in the market today, is very costly. Hence this stands as a problem for hobbyists and for small applications. Hence we have taken an endeavor to bring out a metal detector of minimum cost.

CONTENTS

INTRODUCTION BLOCK DIAGRAM CIRCUIT DIAGRAM CIRCUI DESCRIPTION AND WORKING PCB LAYOUT COMPONENT LAYOUT COST ESTIMATION CONCLUSION REFERENCES DATASHEETS

1. INTRODUCTION

In securit y aspects, metal detector isan essential equip ment. But, the metal detector, which is available in the market toda y, is ver y costl y. Hence this stands as a proble m for hobb yists and for small applications. Hence we have taken an endeavor to : bring out a metal detector of mini mu m cost.

The salient features of our project is that the equip ment is i , ' compact, simple in design and can be used practicall y an ywhere needs. The

metal detector produces an audible alar m signal when a metallic particle comes near to the sensor. A visible blinking LED is also there to indicate the presence of metal.

SENSINGCURRENTASTABEE.TRANSFORMERBOOSTERMUL TIVIBRATOR IAivlri,..ir- Ii: iv

C OMP AR ATOR, ----[>.

-----

- M ONO S i . ABLE M U LT IV IB R A TO R

BU ZZER

U

5V

detection transformer

irBD139 2 . 1K

LM555 0K o o

>0

' D/S

JK

THR

o

>

0.1 MF

A S T AB L E

3LM324 2K2 100K 100K

70M

OTR

L

>LM5550

D/S THR Q

I22MF

N O N I N V. AM P L IF I E R

COMPARATOR

M O N O S T AB L E

POWER SUPPLY

4. CIRCUIT DESCRIPTION AND WORKING

The circuit of metal detector is shown in Fig. 1. An astable multivibrator is wired around 1C 555. The free running frequenc y is selected as 1.2 KHz.

__________________________________

i

!

o' ' ,,/ _ 3

a:THfi

7 _______ 1K 2 0 IMFt

_J _______

*-

1X1

i

In astable operation, the trigger terminal and the threshold ter minal are connected so that a self-trigger is formed, operating as a multi vibrator. When the ti mer output is high, its internal discharging Tr. turns off and the VC1 increases b y exponential function with the time constant (RA+RB)*C.

When the VC1. or the threshold voltage, reaches 2Vce/3. the comparator output on the trigger terminal beco mes high, resetting the F/F and causing the timer output to become low. This in turn turns on the discharging Tr. and the C1 discharges through the discharging channel for med b y RB and the discharging 'TV. When the VCI falls below Vcc/3. the co mparator

output on the trigger terminal becomes high and the ti mer output becomes high asain. The discharging Tr. turns off and the VC 1 rises aaain.

RESET

~1iH.'.i: H ' P. KT HP E :.

TPM:.

'> =k

-----V -OUT GUI' - 1PL

''-'1

O.'-NT

5

_ 1 ' L'

ASTABLE OPERATION

This frequenc y is given to the primar y of the detecting transfor mer through a transistor. So due to the pulsating current How. a var ying magnetic field will formed in me transformer. A voltage will nor mall y induce in the secondar y coil due to the mutual induction. But the transfor mer has no core (air core) and so the ma gnitude of this induced emf is ver y low.detecting trans formerTO AMPLIFIER K\-\ ( *.C

J

i

BD139

I

21K

When a ferrite substance conies near to the winding of the transformer, an effect of core is produced and the induced emf will be much grater than former. This voltage is amplified with the help of a non inverting amplifier build with opamp L.M324.

v,....

NON INVERT ING AMPLIFIER

The amplified signal is given to the input of a voltage comparator. The reference voltage is set to a value below the magnitude of induced e mf without an y core. So. when the ferrite bod y is near to the transformer, the input of co mparator is more then thai of reference pin. Then the output of the co mparator goes low.

>1 OK

COMPARATOR

This

low

pulse

is

given

to

the

triggering

input

of

monostable multi-vibrator build around 555. The ti me is selected to 2.5 seconds and so the output will high for 2.5 seconds. The transistor BC547 starts conducting and the buzzer beeps to indicate the presence of metal. Also the LED turned off for this time.

r

ROiVT COMPARATOR '

'>N[>PI

-

[17

1-

Tt> /y- e, (rnV)

DC SUMMING AMPLIFIERe - 100k ' . :LM124eo oe2 100k iI o f ^ i- LIe3 100k of | r^r100ke4 100k o i re0 = e, +e2 -e, -e4 Where (e, te?) > (e3 *e4) to keep e0 > Ov

LOW DRIFT DETECTORHIGH INPUT Z ADJUSTABLE GAIN DC INSTRUMENTATION AMPLIFIERRl 100k t? J R2 2k

PEAK

As shown e0 = 101 (e2-.en).R3 100 k R6 100 k R4 100k 1/4 .LM124 R7 100k !!

iLM124 I T o R5 100k 1/4 :|_M124

1/4

nlyt? Ehyleritt

8/13

MOTOROLASEMICONDUCTOR TECHNICAL DATA

Order this document by BC546/D

Amplifier Transistors NPN Silicon

BC546, B BC547, A, B, C BC548, A, B, C

BAS

MAXIMUM RATINGS

EMITTER

CASE 29-04, STYLE 17 TO-92 (TO-226AA)

RatingSymbolBC 546BC 547BC 548UnitCollector-Emitter VoltagevCEO654530VdcCollector- Base VoltagevCBO805030VdcEmitter-Base VoltagevEBO6.0VdcCollector Current Continuousic100mAdcTotal Device Dissipation @ T/\ = 25=C Derate above 25Cpd625 5.0mW mW/XTotal Device Dissipation @ Jq = 25~C Derate above 25CPd1.5 12Watt mW/cCOperating and Storage Junction Temperature RangeTj. Tstg55 to +150XTHERMAL CHARACTERISTICSCharacteristicSymbolMaxU nitThermal Resistance, Junction to AmbientRHJA200c/wThermal Resistance, Junction to CaseR0JC83.3cc/w

ELECTRICAL CHARACTERISTICS (TA = 25C unless otherwise noted) CharacteristicSymbolMinTypMaxUnitOFF CHARACTERISTICSCollector-Emitter Breakdown VoltageBC546v(BR)CEO65V(IC = 1.0 mA, Ib = 0)BC54745BC54830 Collector-Base Breakdown VoltageBC546v(BR)CBO80V(IC = lOOuAdc)BC54750 BC54830Emitter-Base Breakdown VoltageBC546v(BR)EBO6.0V(lE = 10 uA, IC = 0)BC5476.0BC5486.0Collector Cutoff Current'CES(VCE = 70V,VBE = 0)BC5460.215nA(VCE = 50V. VBE = 0)BC5470.215(VCE = 35 V, VBE = 0)BC548 0.215(VCE = 30 V, TA = 125C)BC546/547/5484.0uA

REV 1

------------------------------------------ Motorola. Inc. 1996

(M)

MOTOROLA

F=/\IROHIL-D

SEMICONDUCTOR

TU

BD1 35/137/139Medium Power Linear Switching Applications Complement respectively to BD136, BD138 and

andBD140

1

TO-126

1. Emitter 2.Collector 3.Base

NPN Epitaxial Silicon TransistorAbsolute Maximum RatingsSymbolV

TC=25C unless otherwise noted Parameter Value : BD135 BD137 BD139 45 60 80 45 60 80 5 1.5 3.0 0.5 12.5 1.25 150 - 55 - 150 Units V V V V V V V A A A W w c =c

CBO

Collector-Base Voltage

VfJEO

Collector-Emitter Voltage

BD135 BD137 BD139

V

EBO

lc 'CP lB Pc Pc TjT

STG

Emitter-Base Voltage Collector Current (DC) Collector Current (Pulse) Base Current Collector Dissipation (TC=25C) Collector Dissipation (Ta=25C) Junction Temperature Storage TemperatureTc=25C

Electrical CharacteristicsSymbol VCE0(sus)'CBO 'EBOh

unless otherwise noted Test Condition lc = 30mA, lB = 0 VCB = 30V, lE = 0 VEB = 5V. Ic = 0 VCE = 2V, lc = 5mA VCE = 2V, lc = 0.5A VCE = 2V, lc = 150mA lc = 500mA, lB = 50mA VCE = 2V, lc = 0.5A 25 25 40 40 Min. Typ. 45 60 80 Max. Units VVV 0.1 10 250 160 0.5 1 V V uA pA

Parameter Collector-Emitter Sustaining Voltage : BD135 : BD137 : BD139 Collector Cut-off Current Emitter Cut-off Current

FE1 FE2 FE3

n

h

VCE(sat) VBE(on)

DC Current Gain : ALL DEVICE : ALL DEVICE : BD135 : BD137, BD139 Collector-Emitter Saturation Voltage Base-Emitter ON Voltage

Classification'61016nFE340 - 10063 - 160100 - 250 t-2000 Fawchild Semiconductor InternationalhFE Classification

Rev. A, Feb'uaiy 2000

(/-VI

t-t l_

Ml 11_ L/w w w . f ai r c h i l d s e mi . c o m

SEMICONDUCTOR*

KA78XX/KA78XXA3 -Terminal 1 A Positive Voltage Regulator

FeaturesOutput Current up to IA Output Voltages of 5. 6. 8. 9. 10. 12. 15. 18. 24 V Thermal Overload Protection Short Circuit Protection Output Transistor Sale Operating Area Protection

Description

The KA78XX/KA78XXA series of tin 'ce-tcrminul positive regulator are available in the TO-220/D-PAK package and with several fixed output voltages, making them useful in a wide range of applications. Each type employs internal current limiting, thermal shut down and safe operating area protection, making it essentially indestructible. If adequate heal sinking is provided. the\ can deliver over IA output cunenl. Although designed primarily as fixed voltage regulators, these devices can be used with external components lo obtain adjustable \oltages and currents. TO-220

D-PAK

1 1. Input Output 2. GND 3.

Internal Block Digram

INPUT

SEHlbS PASSE l.EMKNT

GND

2001 Fairchild Corporation

Semiconductor

Rev. 1.0.0