RF communication technology

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 This project is designed using the user interface program to control the metal detector robotic vehicle through RF communication technology. The movement of robotic vehicle can be controlled up to particular destination through the RF control circuitry. Wireless data transmission unit that attached on computer communicate with user interface program through parallel communication port. This wireless data transmission unit having an encoder for converting command key data into RF signal communication data. The RF signal communication data is then send to RF signals receiver circuitry through RF signal transmitter module. A reception unit which is attached on the vehicle having a RF signal receiver, a decoder for decoding RF signal communication data and the H-bridge circuit which is then using to control the motor movement of the robotic vehicle when received the signal.  Besides that, a metal detector unit is built on the robotic vehicle to detect the metallic object present along the moving way of the robotic vehicle and a RF signal will be generate and sending back to the computer to notify the user when the metal is found. A wireless camera is mounted on the top of the robotic vehicle and act as a monitoring system which provides feedback image so that the movement of the robotic vehicle can be monitored by the user through the computer.


 Robot is one of the greatest achievements in the field of engineering technology. Many robots have been designed and built for sophisticated uses. They are ready to replacing human being working in the area of surveillance or defense, working in the deep ocean, and even to perform dangerous or unhealthy mission such as military operations and navigation in hazardous environment.  "Metal detector used the principle of electromagnetic induction to detect metallic object" [1]. In normal application, the metal detector is carrying by human being to perform the metal tracking jobs. But, in order to put the metal detecting operation in the dangerously or polluted environments such as chemical spills and radioactive, a robotic vehicle that built with the metal detector is designed. Guided remotely using video cameras is needed so that the robot movements can be monitored from the computer through a graphical user interface and the operation can be done with more precisely.  Today, RF (radio frequency) are widely used in communications and remote control due to the ability to communicate from far distance compare with the Bluetooth and also infrared wireless technology which have limited range in wireless signal. By applying the RF wireless communication technology, the metal detector robotic vehicle can be controlled from behind so that the robot is able to carry out the dangerous task or the jobs that is too difficult for humans.



The project aims is to study and develop a robotic vehicle which have a metal detector function and can be dedicate in various applications purpose such as navigation in hazardous environments and security operations purpose. The research will focus on monitoring and control system by using graphical user interface for the remote control metal detector robotic vehicle. The main considerations involved in developing the system including apply the RF technology and microcontroller in controlling the robotic vehicle movement, displaying the result when the robot successful detect the metallic object and to ensure that the integration between the hardware and software were successful.



 This project mainly consists of two sections, which are the controller part and RC (remote control) vehicle part as shown in figure1.0 below.  The user can control the movement of the robotic vehicle by keyboard or mouse through software interface. The signal will send to the encoder IC through parallel port. The encoder IC receives the coded and transforms them into the serial data before send to first RF transmitter module. The transmitter will generate a corresponding RF signal based on the user input. The first RF Receiver module at the robotic vehicle platform received the data signal in serial manner. The data is then converted back to parallel output by decoder IC. The output data signal is then used to active the H- Bridge circuit which will control the 2 DC motors turning direction to drive the vehicle movement. A metal detector is mounted on the robotic vehicle platform to detect the metals present along the way. When the metallic object is detected, a data signal will be send to PIC16F84A microcontroller via port A. The microcontroller would response by sending a signal to second encoder IC and at the same time trigger the buzzer which will act as notify alarm. These functions are programmed using the PIC assembly language. The program code can be troubleshooting by using PIC simulator program before burn into the microcontroller. The second encoder IC is then transforms the coded data into serial data and send to the second RF transmitter module. The second RF receiver module received the serial data and converted back to parallel output by the second decoder IC. This output data signal will then send to user interface program to notify user through parallel port. The computer will receives video signal from the camera that mounted on the robotic vehicle via the USB port to provide the live view function.





 The project is designed with two separate platforms. One is controller platform and the other one is robotic platform.


5.1: Controller platform

 The controller platform is simply a rectangular box that will be used to keep the remote controller circuitry on it. The box built with connector which is used to connect with computer.


5.2: Robotic platform

 The robotic vehicle is designed with 4 wheels. The two front wheels are used to turn direction either left or right while the 2 back wheels are used to move the vehicle forward or backward. The vehicle is designed with a single flat surface static platform which is dedicated to hold the controller board. The flat designed gave more space so that the controller board and also the wireless camera can be mounted on it. The platform has an extended part in front of the robotic vehicle which is used to hold the metal detector sensor so the metal detector can detect the metallic object present a long the vehicle moving way.



 H-Bridge circuit:

In this project, two 6V DC motors are required to drive the vehicle movement. The DC motor is selected because it is cheap in price compare to servo motor. One motor is used to control the direction of vehicle either left o right, while the other motor is used to drive the vehicle forward and backward. In order for DC motor able to turn in difference direction, the h-bridge circuit is required in the circuitry design. A solid state switching device such as transistor is needed to form an h-bridge circuit. Figure 1.1 above is a basic circuitry design of H- bridge circuit which contain of 2 NPN transistors and 2 PNP transistors. This circuit design enables a voltage to be flow across the motor in either direction. When the transistor Q1 and Q4 are switching ON, a positive voltage will applied to motor and cause the motor to turn in one direction. When the transistors Q2 and Q3 are switching ON and the Q1 and Q4 are switching OFF, a revered operation of motor is occurring due to reverse voltage flow across the motor. The following table summarizes the H-bridge operation. Logic 1 represents "HIGH" or turn ON while logic 0 represent "LOW" or turn OFF. Diodes D1 to D4 are used to prevent the back voltage EMF (electromotive force) that is generate by the motor coil when the motor coil is turning on and off.



 The metal detector sensor is used in this project to detect metallic object. Metal detector is basically design with one or more coil inductor that will be used to interact with the metallic object. "When a metal is present near the coil, some of the magnetic flux produce by coil will pass into the metal object and create eddy current. This phenomenon causing some of the magnetic flux disappears and thus the coil with less flux are then producing the low power output' [9].  Figure 1.2 below is the schematic for metal detector that will apply in this project. Q1 and Q2 are connected to produce a frequency of around 150 KHz fed to L1 and C1. When the LC circuit is oscillates it will induce power to L2 which causes Q2 to switch the collector at the frequency of the collector at Q1. When the metal is near to L1, it will interact with it and reduce the inductance at L2, Q2 therefore is slowly turned off and there will be more power at the collector of Q2. This will allow Q3 and Q4 to power on the LED. At the same time Q5, Q6 and Q7 will be active. Q5 and Q6 generate the frequency which is fed to Q7 to drive the buzzer. VR1 (variable resistor) is used to adjust the circuit's sensitivity level to the metal.



 The main behavior of the metal detector robotic vehicle is to search for the metallic object using its metal detector sensor. Once the metallic object is found, a corresponding signal will be sent out. This process is ongoing until there is not metallic object near to the sensor. The routine is control by the PIC16F84A microcontroller and the code is written in PIC assembly language which is then convert to HEX file before load the code to microcontroller.


 The design methodology is needed in a project design in order to complete the project successfully



 Several experiments have been performing before come to final circuit design.

The project circuit design used a lot of NPN and PNP transistor as a switching device.


10.1: Transistor circuit


To determine the approximate base resistor value for the transistor to "switch on", the following formula is apply.

"RB = (VC Ã- hFE ) ÷ (5 Ã- IC )"  [10]

Choose the nearest standard value for the RB.

Example, if RB = 97KΩ, the 10KΩ resistor is selected.


10.2: RF communication

 Testing the transmitter and receiver module to ensure that the RF is able to communicate and decoded back to 4 bits signal. Figure 1.3 and 1.4 shows the wiring diagram of RF module.  During the circuit testing, pin TE of  HT600 is connected to logic "high" which means that the encoder is in transmit enable mode. When switch 1 is closed, LED (D1) at decoder HT604L will turn on and at the same time, LED (D0) that is connected at pin VT (valid transmit) will also turn on to indicate that the signal is received. The same methode is apply to test other bits of data signal. Table below show the test results for the RF module.




In the past few months, most of the theoretical and the practical information have been research and carry out to ensure that the project progress is up to date as per planning. In the following time, more research will be focus on develop the graphical user interface controller program before proceed to final circuit assembly of the project. Hopefully with the guide and monitoring by the project supervisor and also well time planning for the project management, the project goal can be archive.