The Smart Metal Detector
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Published: Mon, 01 May 2017
This project is the combination of hardware and software product. With the aid of the micro-controller, this metal detector can have more useful function. This system consists of 3 main parts of hardware:
The construction of smart metal detector required the gathering of information/ knowledge/ concepts of obstacle sensor, LCD Display, H-Bridge DC motor driver, PIC micro-controller, metal detector technology and so on. Besides that, some knowledge in software part: PIC Assembly language and other useful software: – MPLAB, Protel XP, and multisim are also needed.
Nowadays, Metal detectors have become a very common staple in today’s society and widely used in human live in a range of usage from leisure to work and also safety purpose. For Safety purpose, Metal detector that used in airport to ensure that there is no dangerous weapon such as knives, guns or any metal objects that could be used as weapons has been brought along by terrorist into the airplane. In technical area, people used metal detector to search for the underground pipe or cable before digging in walls and floors. Besides that, many people enjoy in discovering hidden treasure or valuable metal like gold and silver by using metal detector.
Metal detector products are available in market. It has many types of metal detectors are sold which used in different area. However, many of them have the following disadvantages:
The prices of metal detectors are very expensive. Although the more expensive metal detector has higher performance and functionality, usually we don’t need so much of the function. The extra function that we don’t need will be wasted. So the prices of metal detector products that sold in market wouldn’t be afford by everyone.
Manually controlled metal detector
Many of the metal detectors are manually controlled by human where users are required to handle it and walk around to detect the underground metal. This is very exhausted and tired work.
Based on these two disadvantages, users need a low cost and have basic function of mobility metal detector. The smart metal detector is a device that used to detect metallic material such as coins, gold and other metal items. It can move and change the direction of movement in certain situation to scan the underground metal. It will take a ‘U’ turn when it reached the desired distance which already set inside the microcontroller and continue move in another track. It will avoid the obstacle with the help of sensor. When it detects a metal, it will beep on alarm to indicate user.
2.0 Statement of Aims
Below are the aims that targeted to achieve in the Smart metal detector project:
In this section, the concept of relationship between H-Bridge driver and DC motors are applied into the project. The H-Bridge driver is a circuit that used to control the direction of DC motors with the help of micro-controller.
When the device has detected an obstacle blocking in front of the metal detector, it will avoid the obstacle automatically by changing its movement direction to prevent collision happened.
A micro-controller is used to become the main brain of the mobile metal detector. The main purpose of the micro-controller is used to give instruction to control all the function of the metal detection.
Alarm beep when detect metal:
When the metal detector has been detected underground metal, the buzzer will beep on to inform users that some metal elements have been detected.
LCD display indication:
All the status and message from the metal detector are indicating in the LCD display. For example, the message of ‘Metal Found’ will be shown in LCD when the metal detector has been detected metal element.
The main objective of this project is to develop a “Smart Metal Detector” into more automation area. With the automation of metal detector, this concept will be contributed to the real life application.
The sub-objectives of this project will be elaborate below:
To apply the electric and electronic knowledge that I have learned into the real application field.
To provide a low cost metal detector for general metal detection purpose.
To learn the skill of writing software in PIC Assembly language.
To learn the skill of debugging the software problems or bugs.
To learn how to work followed the planned schedule, as well as the Gantt Chart.
4.0 Literature Review
The first person that invented the first crude metal detector in 1881 was Alexander Graham Bell. After that, the metal detector concept has been kept on improving to become more advance and applicable in various areas.
Basically, there are three technologies used in metal detectors. These three technologies are: I. Very Low Frequency (VLF) Technology
II. Pulse Induction (PI) Technology
III. Beat-Frequency Oscillation (BFO) Technology
VLF is known as induction balance and it is also the most popular metal detector technology used nowadays. There are two distinct coils that used in a VLF metal detector, transmitter coil and receiver coil. The transmitter coil is the outer coil loop which is coiled with wire. Electricity is being sent along the wire and creates the electromagnetic field. The receiver coil is the inner coil loop which is also coiled with another wire. The receiver coil acts as an antenna to pick up and amplify the frequencies which come from the target metallic objects in the ground.
The metal detector has the ability to determine approximately the deeper of the targeted buried object. This can be done by determine the strength of the magnetic field that the object generates. The concept is very simple: The stronger magnetic field will be detected if the metal detector is closer to the surface of the targeted object. Alternately, the further the object away from the metal detector, the weaker the magnetic field will be detected.
The metal detector also can differential the types of metals. It is relied on a phenomenon called as phase shifting. The differences in timing between the frequencies of transmitter coil and the targeted object is called phase shift. For example, an object with high inductance will have a larger phase shift because it takes longer time to alter its magnetic field. However, an object with high resistance will have a small phase shift. The phase shift concept provided VLF based metal detector has the capability called discrimination. The metal detector used a pair of electronic circuits called phase demodulators to compare the phase shift of target object with the average of a particular type of metal to examine the metal class of the target object. The detector will then notifies user with audible tone or visual indicator of what class of the metal is most likely to be. The phase shift concept also allowed user to filter out (discriminate) the unwanted object above a certain phase-shift level.
Pulse Induction (PI) technology is a less common form of the metal detector. PI metal detector uses only single coil as both transmitter and receiver, or using 2 or 3 coils work together. The metal detector sends powerful, short pulses of current through a coil of wire. This cause each pulse generates a brief magnetic field. The magnetic field will reverse polarity and collapses very suddenly after the pulse ends and causing a sharp electrical spike. After the spikes, a current called reflected pulse will run through another coil and this process will keep on repeating in very short time. The PI based metal detector works like echoes: If the metal detector is over a metallic object, an opposite magnetic field will create by the pulse in the object. After the collapsing of the pulse’s magnetic field, the reflected pulse will be generated, and thus the magnetic field of the object cause it take longer time for the reflected pulse to disappear absolutely.
A sampling circuit is set to monitor the length of the reflected pulse. The circuit can determine if another magnetic field has caused the reflected pulse decay in longer time (usually a few microseconds) than normal, it will suspected that some metallic object is being interfering with it. Usually the sampling circuit is connected to a device called integrator. This integrator can read the received signal from sampling circuit amplifies and converts the signal to direct current (DC). This DC’s voltage is connected to an audio circuit which used to indicate the user that targeted object has been detected. This function is almost similar to the VLF based metal detector.
PI based metal detector is not as good as VLF based metal detector in discrimination due to the limitation of reflected pulse length of various metals are difficult to separated. However, PI detector is very useful to detect object in areas that have highly conductive material such as salt-water exploration. In addition, PI detector has the advantage that can detect metal much deeper in the ground than other systems.
Beat-frequency oscillator (BFO) technology is the most basic way that used to detect metal. There are 2 coils of wire in BFO detector. A large coil is in the serarch head and the smaller coil is located inside the control box. Both coils are connected to an oscillator that generates thousands of pulses of current per second. The frequency of the pulses is slightly offset between two coils. When the search head passes over a metal object, the object’s magnetic field will interferes with the frequency of the radio waves which generated by the search head coil. After that, the frequency will deviates from the frequency of the coil in the control box and cause the audible beats change in duration and tone. The BFO detector is sold in low cost compare to other technologies detector, however, the accuracy and the level of control are not provided.
Although there are 3 different of technologies used in metal detector, the basic concept of metal detector can be simplify as using the coil of wire to detect the magnetic field of the underground metal. Hence send a feedback signal to main circuit or micro-controller to process it.
Those metal detectors have various types of function and advance performance however; most of them are manually controlled by human. This project is basically applied the technology of metal detector into a more automation field instead of using human control, but not improving of the performance of any market products.
5.0 Design Methodology
In order to complete the project in time, I have separated the whole project progress into several parts. The project development progress is shown in the flowchart form:
Literature Review in background knowledge of metal detector.
Information of hardware/components gathering
Hardware constructing (Prototyping)
Writing software (Programming)
6.0 Research and Competitive Analysis
The hardware part of smart metal detector consists of inputs and outputs. The input parts included: obstacle sensor and metal detector circuit. The output parts included: H-bridge driver, DC motors and buzzer. A micro-controller is used to interconnect and control the operations among the hardware components. It receives input signals from different inputs and gives the instruction to the outputs based on the situation. The micro-controller will only execute the program that stored inside the memory.
“Micro-controller” works as the brain of the Smart Metal detector. It gets the feedback signal from the sensors/detectors then sending signal to control the condition of the H-Bridge driver and turn on the buzzer once metal is detected.
“Obstacle Sensor” to detect obstacle that blocking in front of the mobile detector to avoid collision happened.
“Metal detector” used to detect the underground metal/mine. The metal detector circuit is uses the coil/inductor to detect the magnetic field of the underground metal. When the coil/inductor ‘cuts’ the magnetic field of the targeted metal, it will send a feedback signal to the micro-controller.
“LCD Display” can have a better looks and more powerful in showing message instead of using LEDs or Seven-Segments display. It displays the message in the form of alphabet or numbers. So, user will have a better understanding in reading the alphabet message compared to just light on some LEDs.
“Buzzer/Alarm” acts an alarm to warn/inform user that something has happened to the metal detector such as mine has been detected.
“H-Bridge driver and DC motors” used to control the direction of DC motors for different condition such as move forward, stop moving and turning. The DC motors are used to rotate the wheels of the mobile metal detector.
8.0 Software Flow Chart
The programming code is written to interconnect the input hardware and the output hardware. The received signal form inputs will be process in the microcontroller and thus send out the react instruction to the output parts. The PIC assembly language is used in this project.
The programs of the basically project can be separated into 3 main parts:
Main routine of moving.
The estimated cost of this project is to prepare a fund which enables us to control the project expenses. For this project, a sum of RM 615 will be allocated to fund the entire project including the hardware and software parts.
The cost of the project can be reduced to a certain amount by doing market research and comparing the cost among the vendors. In addition, compare different type of metal detector and obstacle sensor also needed to reduce the project cost. Another alternative is to get second-hand or used goods in order to minimize the expenditure.
Besides this, daily wages must also take into consideration. Considering 400 hours will be utilized to accomplish this project and RM 5 per hour will be paid. Yet another RM 150 is allocated to fund the resources fee such as the electricity and petrol usage. Hence, the overhead cost for this entire project will be charged at RM 2765.
11.0 Risk Assessment and Management
To complete this project, a few risks that might affect the progress of the project have been drawn out as prevention is better than cure. If there is no other alternative plan has been made or planned now, then it will definitely leave a bad impact to us if this risk does happen. Firstly, in order to make this project a success, intensive learning of assembly language through reference book and Subject EN0318 – Embedded Systems & Advanced Digital System Design is crucial because I am lack in PIC knowledge and it is new to me and it posts a risk to me.
12.0 Conclusion and Recommendation
Now just a beginning stage of the project, I have provided a clear view of the objectives and aims of metal detector project and i will complete the entire task stated step by step by following the project planning time. My project planning has stated clearly through the Gantt chart as well as the critical path analysis.
The entire research and development job has been done throughout this semester but it still in the early stage the final project. Hence, more information from supervisor, reference book and internet needed. I can increase my knowledge level by workout with the research activity and this may help me to boost up my project to quality completion.
In addition, found that many interested features and ideas can be added on to the project. But the insufficient time, knowledge and financial problems have restricted me to achieve those extra features. However, if possible I will try my best to achieve it.
The extra features are:
Measuring of the deeper of the underground metal
Password is required to activate the metal detector
Robot arm added to the mobile metal detector
As a conclusion, this project smart metal detector may give me experience as an equipment and product engineer with excellent technical and management skills with moral values and bring future benefits to me as an engineer.
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