FREE SPACE OPTICAL LASER BASED DATA TRANSMISSION SYSTEM

11/16/2015

Chittagong University of Engineering and Technology

FREE SPACE OPTICAL LASER BASED DATA TRANSMISSION SYSTEM

Department of Electrical and Electronic Engineering

Chittagong University of Engineering and Technology

FREE SPACE OPTICAL LASER BASED DATA TRANSMISSION SYSTEM

Md. JOSEF AHSAN ID:0902072

OCTOBER, 2015

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A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF BACHELOR OF SCIENCE IN ELECTRICAL AND ELECTRONIC ENGINEERING

SUPERVISED BY:

Prof. Dr. Muhammad Quamruzzaman Head Department of Electrical & Electronic Engineering Chittagong University of Engineering & Technology (CUET) Chittagong-4349 ,Bangladesh

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Declaration This project is a presentation of my original research work. Whenever contributions of others are involved, every effort has been made to indicate this clearly, with due reference to the literature, and acknowledgement of collaborative research and discussions. This work was done under the guidance of Professor Dr. Muhammad Quamruzzaman, at Chittagong University of Engineering and Technology, Chittagong.

Md. Josef Ahsan ID: 0902072

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ABSTRACT Increased data transfer demands, limited RF spectral allocations, and emphasis on smaller spacecraft platforms to keep launch costs down are forcing space mission planners to consider free-space optical communications for their space-ground and intersatellite communications links. Optical communications can provide a theoretical performance advantage over conventional RF communications by as much as 60-80 dB. This advantage can be used to decrease the size of the communications terminals located at the ends of the link, and still provide significant increase in data rate capabilities (several orders-of-magnitude). Furthermore, as nearEarth missions begin flying more data-intensive instruments like synthetic aperture radars or hyperspectral imagers, communications systems that circumvent the lack of available spectral allocations will be required. Optical communications offers both the ability to achieve very high data rates with decreased-size assets on the spacecraft, while at the same time there are currently no spectral allocation limitations to the use of the spectrum. This talk will cover the basics of free-space laser communications and will apply those basics to some specific applications. First, the motivations for using laser communications will be given. Next, the technology required for a spacecraft optical communications terminal will be described, followed by the companion description of the technologies and systems at the ground end. Next, a description of several previously completed, and some planned future, space demonstrations will be discussed. Next,it is described as my project called image transmission via LASER.The applications areas for this emerging technology will be presented. While most of this tutorial will concentrate on NASA applications examples, extensions to future DoD and commercial applications will also be included.

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ACKNOWLEDGEMENT I must first thank ALLAH for giving me strength and courage to achieve my goal of obtaining this degree. I would like to express my gratitude to my honourable supervisor Prof. Dr. Muhammad Quamruzzaman for accepting me into his research group and also express my heartfelt thanks to him for his guidance, encouragement and continuous support during my project. His enthusiasm for teaching and research offered challenging opportunities to expand our scientific knowledge and our growing interest in the world of Communication System. I would also like to thank Associate Prof. Dr. Muhammad Ahsan Ullah, for his help and advice during my research. I am also grateful to lab assistants of Electronic Lab and Machine Lab for all the help they provided me with this project. This work was supported by the Electrical and Electronic Engineering Department of CUET.

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TABLE OF CONTENTS DECLARATION

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ABSTRACT

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ACKNOWLEDGEMENT

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TABLE OF CONTENTS

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LIST OF FIGURES

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LIST OF TABLES

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SYMBOLS AND ABBREVIATIONS

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CHAPTER 01: INTRODUCTION 1.1 Introduction 1.2 Background 1.3 Objectives CHAPTER 02: LITERATURE REVIEW 2.1 Introduction 2.2 Wireless Energy Transmission

1 1 1 2 3 3 3

2.3 Energy Transmission Technologies 2.4 LASER Based Experiments 2.5 Recent Ongoing Reasearch CHAPTER 03: THEORETICAL OVERVIEW 3.1 General Principal of LASER 3.2 Necessary Requirements For Lasing Effect 3.3 Properties of LASER light 3.4 Optical Detection Principal 3.5 Pulse Width Modulation

4 5 6 9 9 10 10 11 11

3.6Amplitude Modulation

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3.7 Serial Communication

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3.8 Asynchronous Data Communication

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3.9 Baud Rate

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CHAPTER 04: PROJECT COMPONENT AND ASSEMBLY

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4.1 USB-TTL 4.2 Arduino Mega 2560

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4.3 LASER

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4.4 Phototransistor

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4.5 LED

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CHAPTER 05: TRANSMISSION & RECEPTION PROCESS

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5.1 Transmission arrangement 5.1.1 Transmitter Working Principal 5.1.2 Transmitter Program

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5.2 Receiver Arrangement

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5.2.1 Reception Working Principal 5.2.2 Receiver Program 5.3 Total Performance CHAPTER 06: RESULT AND DISCUSSION

23 24 26 28

6.1 Data Rate

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6.2 Error Rate

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6.2.1 Error Rate For 1m distance

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6.2.2 Error Rate For 10m distance

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CHAPTER 07: CONCLUSION 7.1 Conclusion 7.2 Future Work REFERENCE APPENDIX-A APPENDIX-B

32 32 32 33 35 39

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LIST OF FIGURES Fig 2.3.1

Transmission and absorption in Earth atmosphere.

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Fig.2.4.1

EADS developed, fully laser powered autonomous

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rover. Fig.2.5.1

JAXA L-SPS 100x200 m reference unit delivering 10 MW via

Fig.2.5.2

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direct solar pumped lasers

JAXA L-SPS fully deployed reference system

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delivering 1 GW via direct solar pumped lasers Fig.3.1.1

Stimulated emission

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Fig 3.1.2

pumping process

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Fig.3.7.1

Asynchronous Data Format

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Fig 4.1.1

USB-TTL RS232

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Fig 4.2.1

Arduino Mega 2560 R3

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Fig 4.3.1

Typical LASER

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Fig 4.4.1

Phototransistor

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Fig 4.5.1

LED

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Fig. 5.1.1

Transmitter Circuit diagram

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Fig. 5.1.2

Transmitter Arrangement

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Fig. 5.2.1

Receiver Circuit Diagram

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Fig. 5.2.2

Receiver Arrangement

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Fig. 5.3.1

Performance of project

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Fig. 6.1.1

output matrix of image

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Fig. 6.2.1

output matrix

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Fig. 6.2.2

output matrix for 10m distance

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Chapter 01 Introduction 1.1 Introduction While the science of light and vision has always fascinated and influenced humans, the beginning of modern optics might be traced back to the famous "Book of Optics" by Ibn al-Haytham , which for the first time describes the theory of vision and light as a ray theory, unifying geometrical optics with philosophical physics. His book already described experiments with lenses, mirrors, refraction, and reflection. Modern scientific optics, with the invention of the telescope in the 17th century by Dutch and Italian astronomers and mathematicians revolutionised our way of viewing the universe and the place of Earth and thus ultimately our own place within it. Optics is already one of the most cross disciplinary disciplines, spanning from physics, chemistry, mathematics, electrical engineering up to architecture, psychology and medicine. This paper intends to describe the application of optics and light in an area where it is traditionally only marginally present: energy transmission.

1.2 Background My final year project is based on the concept of laser (Light Amplification by Stimulated Emission of Radiation) for transmitting analog as well as digital signals. I will use phototransistor to receive the signal at receiver. For voice transmission amplitude modulation of laser pulse I will use to transmit the voice signal. Condenser microphone converts the voice into electric pulse which will then amplified and transmitted through laser. Photo detector at receiver detects the laser light and voice will be output through loud speaker.

2 Data transmission is based on pulse width modulation by the use of microcontroller. Different width of laser pulse will be used for different number and character. The second microcontroller will be used to decode the different characters and the received data was displayed in LCD.

1.3 Objective 1. To provide simple and cheap wireless communication for larger data rate with less distortion. 2. To reduce the complexity for communication in the places where optical fiber or any wired communication is very difficult and expensive.

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Chapter 02 Literature review 2.1 Introduction Laser based project has been attempted before but data were inputted through computer. We have tried to simplify it by using 4x3 keypad which provides the complete set of alphabetical letters. We have also tried to enhance it by implementing voice communication as well. Laser communication is a modern technology in the world of communication where bandwidth allocation, power requirement, and dispersion parameter are becoming major hurdle due to rapid increase in number of user. So considering these facts we put our interest in this project. There were various methods for implementing this project but due to scarcity of resources, components, we decided to use simple modulation and demodulation techniques.

2.2 WIRELESS ENERGY TRANSMISSIN The first attempts to transmit energy wirelessly with the purpose of doing so are attributed to N. Tesla at his laboratory in Long Island, New York just 30 years after J. Maxwell had predicted in1873 the transport of energy trough vacuum via electromagnetic waves, validated in principle 15 years later by H. Hertz [1]. Following the invention of the magnetron and the klystron in the 1920 and 1930, the developments during the second world war made microwave beams available to a wider scientific community. The first successful engineering approach to use microwaves for effective energy transmission was done by W. Brown in the 1960s, by powering among other devices a tethered helicopter [2].

4 The first power stations in Earth orbit, taking ad-vantage of the absence of day-night cycles to harvest the energy of the sun were described by the early space pioneers K. Tsiokovski and H. Oberth. Peter Glaser is recognised as the first to combine the visions of these early space pioneers with the practical advances in transmitting energy without wires by W. Brown in his 1968 publication in Science, which contained the first engineering description of a solar power satellite (SPS).It established a vision of a sustainable, practically non depletable and abundant source of energy to meet world energy demands and triggered the imagination of researchers around the globe.

2.3 Wireless Energy Transmission Technologies In general, effective wireless energy transmission concepts need to comply with a range of fundamental constraints: 

possibility to transfer the energy though an atmosphere; transparency of the atmosphere to the used wavelength;

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possibility for directional emission;

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possibility to convert the energy from the form of its source (solar, electric, heat) to a transmittable form (e.g. microwave, laser, accuistic);

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possibility to convert the transmittable energy form back into a useful form of energy (e.g. electricity, hydrogen).

The key difference, the wavelengths used, implies the major other differences between the laser and microwave-based concepts: While most wireless power transmission rely on microwave frequencies of either 2.45 or 5.8 GHz (0.12-0.05 m; both in the industrial, scientific and medical (ISM) frequency band), laser energy transmission takes advantage of the atmospheric transparency window in the visible or near infrared frequency spectrum. (Fig. 2.3.1)

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Fig 2.3.1: Transmission and absorption in Earth atmosphere. (source: NASA)

2.4 LASER Based Experiments In 2002 and 2003, Steinsiek and Schafer• demonstrated ground to ground wireless power transmission via laser to a small, otherwise fully independent rover vehicle equipped with photovoltaic cells as a first step towards the use of this technology for powering airships and further in the future lunar surface rovers. The experiment was based on a green, frequency-doubled Nd:YAG laser at only a few Watts. It included the initiation and supply of the rover including a micro-camera as payload as well as the pointing and tracking of the moving rover over a distance up to 280 m by applying active control loops. (Fig. 2.4.1).

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Fig. 2.4.1: EADS developed, fully laser powered autonomous rover. Recently, similar experiments, however focussing less on the beam control and beam steering aspects but rather on the total transmitted power levels have been carried out in the frame of a context related to space elevators, organised and co-funded by NASA. Ground-based lasers have been used to power small PV-covered \climbers" attached to a tether with the objective to achieve maximum climbing speeds [3] [4]. One of the advantages of microwave power trans-mission over the use of laser has been the possibility to avoid moving parts in space by using an electronic beam steering system based on the control of the phase of a matrix of emitters. Recently, Schafer• and Kaya have however demonstrated that a similar system is in principle also possible for laser based systems by presenting a new concept for a retrodirective tracking system.

2.5 Recent Ongoing Research The use of laser based wireless power transmission was revisited in the early 1990s by Landis. Since several years, the Japanese space agency JAXA is pursuing a solid and targeted R&D programme to-wards the development of space based solar power stations, including as the two main technical options the microwave and laser based

7 concepts. New designs and laser system options have been proposed.[5] [6] The JAXA proposed laser based system is based on direct solar pumped lasers using a Nd:YAG crystal. A reference system has been designed, delivering in its full congruation 1 GW. The entire system would be built in a highly modular way, with individual modules of 100 m 200 m primary mirrors and an equally large radiator system as base unit delivering 10 MW each and stacked to a total length of 10 km in orbit. (Fig. 2.5.1 and Fig. 2.5.2)

Fig. 2.5.1: JAXA L-SPS 100x200 m reference unit delivering 10 MW via direct solar pumped lasers

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Fig. 2.5.2: JAXA L-SPS fully deployed reference system delivering 1 GW via direct solar pumped lasers

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Chapter 03 Theoretical Overview 3.1 The General Principal of LASER Every atom has a certain energy levels, which may be high or low. Once excited by heating, it goes to high energy level. After certain time in high energy level, it return back to original energy level, consequently emitting energy in the form of light having energy E=hf. Incident photon with energy to E2-E1 interacts with an atom in conduction band, causing it to return to low energy level with the emission of second photon. This photon has same phase, frequency and polarization as first. This whole phenomenon is known as stimulated emission, which gives the laser its spectral properties such as narrow spectral width, highly directed beam and intense light.

Fig. 3.1.1: Stimulated emission Einstein demonstrated that for stimulated emission to dominate it was necessary that the photon radiation density and population density (N2) of the upper energy level

10 must be increased relative to lower energy lever (N1). Thus when density of atom in higher energy level is greater than lower energy level (i.e. N2>N1), this phenomenon is known as population inversion and is fundamental condition for stimulated emission. To achieve population inversion it is necessary to excite atoms in upper energy level E2.This process is called pumping.

Fig 3.1.2: pumping process

3.2 Necessary Requirement for Lasing Effects  An active medium with in which a beam of electromagnetic wave is launched. It can be solid, liquid or gas. 

A resounding cavity, which contains the active media. If active media is liquid or gas, this resounding cavity is limited by two spherical mirrors, one of this slightly transparent in order to let that a beam of light escapes. Supposing the active media will be crystal, two faces of crystal are polished so that they work as a mirror.

3.3 Properties of LASER light 

It is narrow beam of coherent light i.e. all the waves are in same phase.



It is highly directed beam/intense light.

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It has shorter spectral line width.

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It has low lost coupling to fiber.

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It is power efficient.

3.4 Optical Detection Principal When device is reverse biased then the electric field developed across the p-n junction sweeps mobile carriers (holes and electron) to their respective majority sides (p and n type material). The depletion layer is therefore created on either side of the junction. This barrier has the effect of stopping the majority carriers crossing the junction in the opposite direction to the field. However, the field accelerates minority carriers from both sides to the opposite side of the junction forming the reverse leakage current of the diode. Thus intrinsic conditions are created in the depletion region. A photon incident in or near the depletion region of this device which has an energy greater than or the equal to the band gap energy Eg (i.e. hf ≥ g)E will excite an electron from the valence band to the conduction band. This process leaves an empty hole in the valence band and is known as the photo generation of an electron-hole (carrier) pair. Carrier pairs so generated near the junction are separated and swept under the influence of electric field to produce displacement by current in the external circuit in excess of any reverse leakage current. The depletion layer must be sufficiently thick to allow a large fraction of the incident light to be absorbed in order to achieve maximum carrier-pair generation.

3.5 Pulse Width Modulation In pulse width modulation the average value of voltage (and current) is controlled by turning the switch between supply and load on and off at a fast pace. The longer the switch is on compared to the periods, the higher the power supplied to the load will be. Duty cycle is expressed in percent, 100% being fully on. The advantage of using the PWM is that power loss, the product of voltage and current, of the switching device is close to zero. When it is in switch off condition then there is practically no current and when it is on there will be almost no voltage drop across the switch. Because of their duty cycle, on/off nature, they can use in digital controls too.

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3.6 Amplitude Modulation Amplitude modulation (AM) is defined as a process in which the amplitude of the carrier wave is varied linearly with the message signal. It is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. The envelope of the amplitude modulated signal embeds the information bearing signal. The total power of the transmitted signal varies with the modulating signal whereas the carrier power remains constant. The main defect of this modulation is that in an AM wave the signal is in the amplitude variations of the carrier, practically all the natural and man noises consists of electrical amplitude disturbances. As a receiver cannot distinguish between amplitude that represents noise and that contain the desired signal so reception is generally noisy.

3.7 Serial Communication Serial communication uses a single data line instead of the 8-bit data line of parallel communication. This helps to minimize the problem of transmission of data faced in 8-bit data communication. 8-bit data transmission works only if the cable is not too long, since long cable diminishes and distorts the signal. Also an 8-bit data path is expensive. Serial data communication uses either synchronous or asynchronous method for the transmission of the data.

3.8 Asynchronous Data Communication In this communication, transmitter and receiver are not synchronized. Each data character has a bit which identifies its start and 1 or 2 bits, which identify its end (framing). Since each character is individually identified, characters can be sent at any time (asynchronously). When no data is being sent, the signal line is in a constant high or masking state. Following the data bit is a parity bit, which is used to check for errors in received data. Some system does not insert parity bit. There are special IC chips for serial data communication, which are commonly known as the UART (universal asynchronous receiver-transmitter) and USART (universal synchronous-asynchronous receiver-transmitter). UART is

13 basically the chips, a piece of hardware that translates data between parallel and serial forms. UART is the communication protocol to define the data formats need to be maintained to transmit the data. The UART usually does not directly generate or receive the external signals of various connected equipment. Separate interface devices are used to convert the logic level signals, such as RS-232 and RS-485. Some signalling schemes use modulation of carrier signal (with or without wires like Bluetooth, Infrared, optical fiber etc.).

Fig. 3.7.1: Asynchronous Data Format

3.9 Baud Rate The baud rate of a data communications system is the number of symbol per second transferred. A symbol may have more than two states, so it may represent more than one binary bit (a binary bit always represents exactly two states). Therefore the baud rate may not equal the bit rate, especially in the case of recent modems, which can have (for example) up to nine bits per symbol. Microcontroller transfer and receive data serially at many different baud rates. Table3.8: Baud Rate

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Chapter 04 Project Component and Assembly 4.1 USB-TTL RS232 is a definition for serial communication on a 1:1 base. RS232 defines the interface layer, but not the application layer. To use RS232 in a specific situation, application specific software must be written on devices on both ends of the connecting RS232 cable. The developer is free to define the protocol used to communicate. RS232 ports can be either accessed directly by an application, or via a device driver in the operating system. USB on the other hand is a bus system which allows more than one peripheral to be connected to a host computer via one USB port. Hubs can be used in the USB chain to extend the cable length and allow for even more devices to connect to the same USB port. The standard not only describes the physical properties of the interface, but also the protocols to be used. Because of the complex USB protocol requirements, communication with USB ports on a computer is always performed via a device driver. It is easy to see where the problems arise. Developers have lots of freedom where it comes to defining RS232 communications and ports are often directly, or almost directly accessed in the application program. Settings like baud rate, data bits, hardware software flow control can often be changed within the application. The USB interface does not give this flexibility. When however an RS232 port is used via an USB to RS232 converter, this flexibility should be present in some way. Therefore to use an RS23 port via an USB port, a second device driver is necessary which emulates a RS232 UART, but communicates via USB. Many applications expect a certain timing with RS232 communications. With ports directly fitted in a computer this is most of the time no problem. The application communicates directly, or via a thin device driver layer with the UART, and

15 everything happens within a well defined time frame. The USB bus is however shared by several devices. Communication congestion may be the result of this, and the timeframe in which specific RS232 actions are performed might not be so well defined as in the direct port approach. Also, the double device driver layer with an RS232 driver working on top of the complex USB driver might add extra overhead to the communications, resulting in delays.(Fig. 4.1.1)

Fig 4.1.1: USB-TTL RS232

4.2 Arduino Mega 2560 The Arduino/Genuino Mega 2560 is a microcontroller board based on the ATmega2560. It has 54 digital input/output pins (of which 15 can be used as PWM outputs), 16 analog inputs, 4 UARTs (hardware serial ports), a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started. The Mega 2560 board is compatible with most shields designed for Arduino/Genuino Uno and the former boards Duemilanove or Diecimila. The Arduino/Genuino Mega 2560 is an update to the Arduino Mega, which it replaces shown in fig 4.2.1.

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Fig 4.2.1: Arduino Mega 2560 R3

4.3 LASER A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term "laser" originated as an acronym for "light amplification by stimulated emission of radiation".[1][2] The first laser was built in 1960 by Theodore H. Maiman at Hughes Laboratories, based on theoretical work by Charles Hard Townes and Arthur Leonard Schawlow. A laser differs from other sources of light in that it emits light coherently. Spatial coherence allows a laser to be focused to a tight spot, enabling applications such as laser cutting and lithography. Spatial coherence also allows a laser beam to stay narrow over great distances (collimation), enabling applications such as laser pointers. Lasers can also have high temporal coherence, which allows them to emit light with a very narrow spectrum, i.e., they can emit a single color of light. Temporal coherence can be used to produce pulses of light as short as a femtosecond.(Fig 4.3.1)

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Fig 4.3.1: Typical LASER Among their many applications, lasers are used in optical disk drives, laser printers, and barcode scanners; fiber-optic and free-space optical communication; laser surgery and skin treatments; cutting and welding materials; military and law enforcement devices for marking targets and measuring range and speed; and laser lighting displays in entertainment. 4.4 Phototransistor A phototransistor is a device that converts light energy into electric energy. Phototransistors are similar to photoresistors but produce both current and voltage, while photoresistors only produce current. This is because a phototransistor is made of a bipolar semiconductor and focuses the energy that is passed through it. Photons (light particles) activate phototransistors and are used in virtually all electronic devices that depend on light in some way.(Fig 4.4.1) A phototransistor is a bipolar device that is completely made of silicon or another semi-conductive material and is dependent on light energy. Phototransistors are generally encased in an opaque or clear container in order to enhance light as it travels through it and allow the light to reach the phototransistor’s sensitive parts. A phototransistor generally has an exposed base that amplifies the light that it comes in contact with. This causes a relatively high current to pass through the phototransistor.

18 As the current spreads from the base to the emitter, the current is concentrated and converted into voltage.

Fig 4.4.1: Phototransistor

4.5 LED A light-emitting diode (LED) is a two-lead semiconductor light source. It is a p–n junction diode, which emits light when activated.[4] When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor.In this project LED is used as a indicator of focusing of LASER i transmitter to receiver.(fig 4.5.1)

Fig 4.5.1: LED

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Chapter 05 Transmission & Reception Process 5.1 Transmission arrangement Transmitter consists of a computer, a USB to TTL converter , a Arduino Mega 2560 R3 and a LASER device. The Circuit arrangement is shown below in Fig. 5.1.1.

Fig. 5.1.1: Transmitter Circuit diagram

5.1.1 Transmitter Working Principal USB- TTL receives digitalized data of a image(pixel to pixel) from a computer. This digitalized data is fed to a Arduino Mega 2560 that transmit data through a circuit arrangement with a carriage return. Now this digital data was transmitted via LASER

20 to receiver. When Arduino passes a 1 logic LASER will be on and for a 0 logic LASER will be off to a phototransistor. Image is processed by a MATLAB program.(Fig. 5.1.2)

Fig. 5.1.2: Transmitter Arrangement

5.1.2 Transmitter Program %remember to change COM port clc; clear all; close all;

21 A = imread('e.JPG'); I = rgb2gray(A); [m, n]=size(I); %imshow(I); disp('ready'); s = serial('COM12'); set(s,'BaudRate',9600,'terminator','CR'); d=0; fopen(s); disp('sending....'); %m %n %fprintf(s,I); %fwrite(s,0); %fwrite(s,'#'); for i=1:3 for r=1:m for c=1:n b=A(r,c,i); fwrite(s,b); pause(.001); fwrite(s,255); % pause(.001);

22 a(r,c)=b; end fwrite(s,254); end fwrite(s,252); disp('sending'); end fwrite(s,253); fclose(s); delete(s); disp('finish'); subplot(2,1,1); imshow(A); title('sending image') subplot(2,1,2); imshow(a); title('received image')

5.2 Receiver Arrangement Receiver consists of a phototransistor, a LED and a USB-TTL. The circuit diagram of the receiver is shown in fig. 5.2.1.

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Fig. 5.2.1: Receiver Circuit Diagram

5.2.1 Reception Working Principal The digitalized data from transmitter is received by the phototransistor by continuous blipping of LASER from Transmitter. Then the received data was processed by MATLAB program and showed in another computer. The LED was used to understand the focusing of LASER to phototransistor. The arrangement is shown in fig. 5.2.2.

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Fig. 5.2.2: Recever Arrangement

5.2.2 Receiver Program clc; arduino=serial('COM5','BaudRate',9600); set(arduino,'timeOut',100); set(arduino,'terminator','CR'); disp('go'); fopen(arduino); r = zeros(3,3); g = zeros(3,3); b = zeros(3,3);

25 f=1; n=1; m=1; disp('started'); a=0; while(a~=253) set(arduino,'ReadAsyncMode','continuous'); a=fscanf(arduino,'%d'); a if(a==255)

%column

n=n+1; elseif(a==254) m=m+1; n=1; elseif(a==252) f=f+1; n=1; m=1; disp('working'); else if(f==1) r(m,n)=a; end

%row

26 if(f==2) g(m,n)=a; end if(f==3) b(m,n)=a; end end i=i+1; end fclose(arduino); delete(arduino); %[m,n]=size(aa); rgb=cat(3,uint8(r),uint8(g),uint8(b)); disp('showing result'); imshow(rgb);

5.3 Total Performance Main performance was done in academic building of dept. of EEE in CUET. It is examined for a distance from transmitter to receiver of 1 meter, 10 meter and 50 meter. The whole experiment is shown in fig. 5.3.1.

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Fig. 5.3.1: Performance of project

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Chapter 06 Result and Discussion 6.1 Data Rate From the experiment and characteristics from image and TTL clock we can measure the data rate.(Fig. 6.1.1)

Fig. 6.1.1: output matrix of image

Data rate= 9600 bps(bit per second)

29 6.2 Error Rate From the calculation of input image pixel matrix and output image pixel matrix i can show the error rate. Here i have shown the original image pixel rate Input image size= 121 * 95 pixel 6.2.1 Error Rate For 1m distance When the distance between transmitting LASER to receiving phototransistor is kept 1m, the error rate can be measuredfrom the output image pixel matrix. From the fig. 6.2.1 we can see the output matrix.

Fig. 6.2.1: output matrix Output image matrix= 122 * 95 Here, extra row have come from the ending stop bits. So error rate= output / input =0%

30 6.2.2 Error Rate For 10m distance

Fig. 6.2.2: output matrix for 10m distance

Error rate = 0 %

6.3 Discussion At present there are various techniques which are being successfully used for transmission of data. The data transmission techniques employ RF, FM signals for transmission of data. Here we have look into data transmission by using laser. By using laser for transmission; higher data rates are available with lower error rate which is advantageous over RF signal. The data is transmitted in the form of infrared rays. The photo transistor in the receiver unit converts the received data into electrical data and displayed on the screen. Since it is LOS, due to environment changes the disturbances can occurs in the message signal by which the quality of

31 the output decreases. The main problem with lasers is the beam dispersion can occurs due to external factors. In order to overcome these problems most advanced powerful lasers are to be employed.

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Chapter 07 Conclusion 7.1 Conclusion The final year project LASER based image transmission was done completely. The project completely based on wireless communication system. Although, wireless communication predominantly means the use of radio frequency for communication, we explored the use of light based carriers for transfer of information. The emphasis of the project was to study various wireless technologies that are used for data communication between two microcontroller controlled devices. Besides this we have gained practical knowledge of microcontroller interfacing and the project software development. Although the optical data communication technology is prevailing from last decade as optical fiber communication devices available in the market, the project was carried out to get all ideas that are behind such wireless system. And by now, we think we are successful in the respect. Also we hope our effort will be worthwhile if the project work will be hopeful for those who seek to carry out any project related to optical data communication using laser technology.

7.2 Future Work 

Multiple voice, data, picture, video can be multiplied simultaneously to perform communication using Multiplexer.



Half duplex or even full duplex communication can be achieved by software implementation



A more power laser can be used to increase the range of communication.



Laser can be replaced by IR laser that can be visible by bare eyes.

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REFERENCES [1] Nicola Tesla. The transmission of electrical energy without wires. Electrical World

and

Engineer,March1905.http://www.tfcbooks.com/tesla/1904-03-05.htm

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35

APPENDIX A A.1 Arduino Mega 2560 R3 Pin Diagram

Fig. A.1.1: Arduino pin diagram

A.2 pin Diagram Table

36 Table A.2.1: Arduino pin

37 Table A.2.2: Arduino pin

38 Table A.2.3: Arduino pin

39

APPENDIX B B.1 USB-TTL RS232 RS-232 (Recommended Standard – 232) is a standard interface approved by the Electronic Industries Association (EIA) for connecting serial devices. In other words, RS-232 is a long established standard that describes the physical interface and protocol for relatively low-speed serial data communication between computers and related devices. RS-232 is the interface that your computer uses to “talk” to and exchange data with your modem and other serial devices. The serial ports on most computers use a subset of the RS-232C standard. RS-232 protocol is mostly used over the DB9 port (commonly known as serial port), however earlier it was used over the DB25 port (also known as parallel port). We will have a look at both of them here.

Fig. B.1.1: USB-TTL RS232

B.2 Serial TTL Signal Description

40 Table B.1.1: Serial TTL signal