1.0 Background Introduction

This project involve designing a device which will give out an alarm when a metal object is
detected. This device will be used as a security scanner help in searching sharp objects e.g
knives or screw drivers hidden under clothes or hand bags.
Placeslike in conference hall, courtroom or night clubsthey are not allowed to enter with sharp
objects like knives or screw drivers for safety purposes in case a fight happen. Bad people hide
those items under their clothes or hand bags. Most of the time security guard they fail to find
them when they search manually by hand, and due to moral obligation a man will not search a
woman effectively.
There are different kind of industrial metal scanners help to perform searching sharp objects
but are very expensive and they are not available in local market.

1.1 Problem Statement

Since many events of injuries due to improper use of sharp objects have been reported to occur
in night clubs or during conferences regardless the presence of warning signs which prohibit
to enter with sharp objects and manual search by hand. Therefore must be a system which help
in searching.

1.2 Objectives of the Project

The objective of this project is divided into main and specific objective.

1.2.1 Main Objective
To reduce problems occurred in night clubs or during conferences due to improper uses of sharp

1.2.2 Specific Objectives
 Designing and implementing a circuit which detect presence of metal
 Designing a search oscillator
 Designing a stable crystal based reference oscillator
 Designing coupling circuit to isolate two oscillator from the mixer
 Designing a mixer or frequency comparator and simple switch amplifier
 Building the prototype

1.3 Significance of The Project
• It is easy to implement the circuit
• Components used in this project are inexpensive and are locally available

1.4 Existing System
There are different types of metal detector available on the market today, most of those
metal detector use VERY LOW FREQUENCY technology, also known as VLF or induction
balance which is currently advanced technology used. VLF uses two coils that
create an electromagnetic field. When thisfield encounter an object that conduct electricity
such as metal the object own magnetic field is detected, thus course the detector to emit an
alarm e.g audible sound, vibration or LED blinking that a metal object has been detected.
Those metal detectors available on the market are very sensitive because they employ high
technology to manufacture them therefore are relatively expensive to buy due to invention
of high technology on them. Hand scanner metal detector they cost relatively from $20 to
several hundreds dollars. Example of popular existing hand metalscanner which is extremely

• Detect items of all type of metal; ferrous and non-ferrous
• Choice of audio alarm or silent vibrate alarm
• Easy to use, 3 position switch for power, audio and vibrate
• Sensitivity setting at optimum level – no tuning required (auto tuning)
• Balanced and lightweight
• Low battery indicator
• No tool required to exchange battery

1.5 Proposed System

Proposed system uses the technique of BFO, this employ the use of two radio frequency
oscillator, the first oscillator is called search oscillator and the other is called reference oscillator.
The output of two oscillators are fed into mixer and produce the resultant signal of difference
between two input frequencies

The search oscillator is a tuned tunk oscillator, uses its inductor as search coil, when metallic
object disturbs the magnetic field of the search coil, the frequency of search oscillator shifts
slightly and the detector will produce a signal in the audio frequency range.

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