BULE HORA UNIVERSITY DEPARTEMENT OF ELECTRICAL AND COMPUTER ENGINEERING
“Laser light based audio transmission and alarm system”
A project submitted in partial fulfilment of the requirement for the first degree of Bachelor of Science in Electrical and Computer Engineering
By AMEHA GETACHEW ARARE ABERA ADISU WAKWEYA ABEBA KBREY MARUF USMAEL
Advisor: Mr. Liule Negash 6-16-2017
FE/R/1071/12 FE/R/0550/12 FE/R/0950/12 FE/R/0545/12 FE/R/0918/12
BULE HORA UNIVERSITY DEPARTEMENT OF ELECTRICAL AND COMPUTER ENGINEERING
““Laser light based audio transmission and alarm system”
By AMEHA GETACHEW ARARE ABERA ADISU WAKWEYA ABEBA KBREY MARUF USMAEL
FE/R/1071/12 FE/R/0550/12 FE/R/0950/12 FE/R/0545/12 FE/R/0918/12
Electrical and Computer Engineering Department Approval by Board Examiners
DECLARATION WE, the undersigned declare that this final PROJECT is our group original work, and has not been presented for a degree in this or any other university, and all sources of materials used for the project have been fully acknowledged.
Name
Signature
AMEHA GETACHEW ……………………………………………………………………… ARARE ABERA ……………………………………………………………………………. ADISU WAKWEYA ………………………………………………………………………… ABEBA KBREY……………………………………………………………………………… MARUF USMAEL ……………………………………………………………………………
Date of submission. June,16,2017
Place BULE HORA ETHIOPIAN
This project has been submitted with our approval as a university advisor and electrical and computer hade office.
Advisor Name Mr. Liule Negash Signature Department head Mr. Derara Senay
Signature
ACKNOWLEDGEMENT First of all, we would like to thank to father almighty, may you continue to give us strength and vision that I may follow your path to external salivation. We also want to express a sincere acknowledgement to our advisor, Mr. Liule Negash for giving us the opportunity to research under his guidance and supervision. Beside our advisor, we also want to thank to Mr. Surafel Getachew, Mr.Behaylu Shefera and Mr.Tewodros Tadele Electrical and electronics lab Assistance for their endless support.
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Contents
Page
ACKNOWLEDGEMENT ............................................................................................................................. i LIST OF FIGURES ..................................................................................................................................... iv LIST OF TABLE .......................................................................................................................................... v LIST OF SYMBOL ..................................................................................................................................... vi ABSTRACT................................................................................................................................................ vii CHAPTER ONE ........................................................................................................................................... 1 INTRODUCTION .................................................................................................................................... 1 1.1 BRIEF HISTORY ............................................................................................................................... 1 1.2 MOTIVATION ................................................................................................................................... 3 1.3 ORGANIZATION OF THE PROJECT ............................................................................................. 3 1.4 OBJECTIVE ....................................................................................................................................... 3 1.4.1 General objective ......................................................................................................................... 3 1.4.2 Specific objective ......................................................................................................................... 3 1.5 SCOPE OF THE PROJECT ............................................................................................................... 4 1.6 PROBLEMS OF STATEMENT......................................................................................................... 4 1.7 SYSTEM ANALYSIS ........................................................................................................................ 4 1.5 BLOCK DIAGRAM EXPLANATION .............................................................................................. 5 1.5.1 CONDENSER MICROPHONE .................................................................................................. 5 1.5.2 TRANSMITTING SECTION ...................................................................................................... 5 1.5.3 LASER TORCH .......................................................................................................................... 5 1.5.4 RECEIVING SECTION .............................................................................................................. 5 1.5.5 LOUD SPEAKERS ......................................................................................................................... 6 CHAPTER TWO .......................................................................................................................................... 7 LITERATURE REVIEW ......................................................................................................................... 7 2.1 OPTICAL AND MICROWAVE COMMUNICATIONS SYSTEMM CONCEPTUAL DESIGN FOR A REALISTIC INTERSTELLAR EXPLORER.......................................................................... 7 2.2 OPTICAL COMMUNICATION SYSTEM FOR SMART DUST .................................................... 8 2.3 TOWARD A WIRELESS OPTICAL COMMUNICATION LINK BETWEEN TWO SMALL UNMANNED AERIAL VEHICLES ....................................................................................................... 8 2.4 FREE SPACE OPTICAL LASER COMMUNICATION LINK ........................................................ 8 ii
2.5 LASER BASED INTRUDER ALARM ............................................................................................. 8 2.6 LASER BASED COMMUNICATION LINK ................................................................................... 9 CHAPTER THREE .................................................................................................................................... 11 METHODOLOGY ................................................................................................................................. 11 3.1 SYSTEM DISCRIPTION ............................................................................................................. 11 3.2 THE TRANSMITTER CIRCUIT ................................................................................................. 11 3.3 THE RECEIVER CIRCUIT ......................................................................................................... 12 CHAPTER FOUR....................................................................................................................................... 17 COMPONENTS ..................................................................................................................................... 17 4.1 LASER .......................................................................................................................................... 17 4.2 555 TIMER ................................................................................................................................... 18 4.3 LDR (LIGHT DEPENDENT RESISTOR) ................................................................................... 20 4.4 LOW VOLTAGE AUDIO AMPLIFIER IC LM386 .................................................................... 21 4.5 RESISTORS ................................................................................................................................. 22 4. 6 VARIABLE RESISTORS ........................................................................................................... 30 4.7 CAPACITOR ................................................................................................................................ 31 4.8 TRANSISTOR .............................................................................................................................. 36 4.9 BREADBOARD ........................................................................................................................... 42 CHAPTER FIVE ........................................................................................................................................ 43 RESULT AND IMPLEMENTATION ................................................................................................... 43 CHAPTER SIX ........................................................................................................................................... 45 CONCLUSION & RECOMMENDATION ........................................................................................... 45 5.1 CONCLUSION ............................................................................................................................. 45 5.2 RECOMMENDATION ................................................................................................................ 45 REFERENCES ............................................................................................................................................... APPENDIX A ................................................................................................................................................. APPENDIX B .................................................................................................................................................
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LIST OF FIGURES Fig 1. system analysis diagram………………………………………………………………….4 Fig 2. system description block diagram……………………………………………………….11 Fig 3. Transmitter circuit……………………………………………………………………….11 Fig 4. Alarm system circuit…………………………………………………………..................12 Fig 5. Receiver circuit 1………………………………………………………………………...14 Fig 6. Receiver circuit 2………………………………………………………………………...15 Fig 7. Receiver circuit 3 last circuit………………………………………………….................16 Fig 8. Laser……………………………………………………………………………………...17 Fig 9. Emission of a laser…………………………………………………………….................18 Fig 10. 555 TIMER…………………………………………………………………..................19 Fig 11. LDR…………………………………………………………………………………….20 Fig 12. LM386 IC……………………………………………………………………………….21 Fig 13. Resister color coding and band………………………………………………………....28 Fig 14. variable resister………………………………………………………………………....30 Fig 15. Capacitor………………………………………………………………………………..31 Fig 16. Energy storage in capacitor……………………………………………………………..32 Fig 17 A simple resistor-capacitor circuit demonstrates charging of a capacitor………………34 Fig 18. Schematic symbols for PNP- and NPN-type BJTs……………………………………..36 Fig 19. Simplified cross section of a planar NPN bipolar junction transistor…………………..39 Fig 20. the symbol of an NPN bipolar junction transistor………………………………………40 Fig 21. The symbol of a PNP Bipolar Junction transistor………………………………………40 Fig 22. BC548 silicon NPN BJT Transistor…………………………………………………….41 Fig 23. Breadboard……………………………………………………………………………....42 Fig 24. Internal structure of breadboard…………………………………………………………42 Fig 25. Final result of alarm system……………………………………………………………..44 Fig 26. Audio transmitter final result……………………………………………………………45 Fig 27. Audio receiver final result..……………………………………………………………..45
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LIST OF TABLE 1. PIN SPECIFICATION OF 555 TIMER…………………………….……………………….19 2. PIN SPECIFICATION OF LM 3869 IC…………………………………………………….22
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LIST OF SYMBOL 1. LDR …………………………………………..…………………………………..………….20 2. Low voltage audio amplifier ………………………..…………………………….…………21 3. Schematic symbol for PNP and NPN type BJTs…………….…………………..…………..40 4. The symbol of an NPN Bipolar junction transistor ……………….………………….……..41
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ABSTRACT Laser audio transmitter is one type of optic transmission method using simple electrical circuit we can transmit and receive any kinds of audio message by using laser beam. and also by using laser beam we can protect our home, office and shop. In our project by using laser beam or laser torch and some chip electrical component like resister, capacitor, op amp, 555 timer and breadboard we will construct a laser audio transmitter and receiver circuit and also construct alarm system circuit.so on the transmitter side we have resisters, transistors, capacitors,3.5mm audio jack, 5v dc source and laser. these components are only used to transmission section on the receiving section. we have two circuits the first one is audio amplification circuit and the second one is security alarm circuit. both circuit are connected to the LDR parallel so on this section the common component for both circuit is LDR and laud speaker. by using 9V DC source for both circuit we can received audio from the transmitter side of the circuit and also, we can protect our home from unauthorized person the general objective of our project is by using laser beam how can transmit audio signal and how to secure our home. Toward achieving the general objective mentioned the following specific objective will be accomplished in this final project.
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CHAPTER ONE INTRODUCTION 1.1 BRIEF HISTORY Laser as a communication medium can provide a good substitute for the present-day communication systems as the problem of interference faced in case of electromagnetic waves is not there and high deal of secrecy is available. Use of laser in communication systems is the future because of the advantages of the full channel speeds, no communication licenses required at present, compatibility with copper or fiber interfaces and no bridge or router requirements. Besides this there are no recurring line costs, portability, transparency to networks or protocols, although range is limited to a few hundred meters. Also, the laser transmission is very secure because it has a narrow beam (any potential eves dropping will result in an interruption which will alert the personnel. Also, it cannot be detected with use of spectrum analyzers and RF meters and hence can be used for diverse applications including financial, medical and military. Lasers can also transmit through glass; however, the physical properties of the glass have to be considered. Laser transmitter and receiver units ensure easy, straightforward systems alignment and long-term stable, service free operation, especially in inaccessible environments, optical wireless systems offer ideal, economical alternative to expensive leased lines for buildings. The laser can also be commissioned in satellites for communication, as laser radar requires small aperture as compared to microwave radar. Also, there is high secrecy and no interference like in EM waves. Further, potential bandwidth of radar using lasers can translate to very precision range measurement. For these reasons, they can be used as an alternative to present modes of communication. laser communication, which is both wide-band and high-speed. Security is a most important factor today. Technology develops day by day in the world. The crime gang also improves their technology to perform their operation. So, technology of security should be modern with time to protect the crime works. We decide to make a security project as our project. In this project, we have used laser light to cover a large area. We know laser light goes through long distance without scattering effect. 1
It’s also visible only at source and incident point, otherwise invisible. These two properties help us to build up a modern security system, which may name as “laser security”. When any person or object crossover the laser line the security, alarm will be ringing and also the focus light will “on” to focus the entrance of unauthorized person. We can make a security boundary of single laser light by using mirror at every corner for reflection. Siren is a device that produces loud noise. They are the means communication. Sirens can be seen in emergency vehicles such as police cars, ambulances and fire engines. Generally, sirens are used as indication or warning. There are different circuits to produce different sirens. Here in this project a screaming siren lights circuit is presented. Screaming siren lights are those which produces siren depending on the light intensity falling on the circuit. We can also call it as Laser Based Security alarm as it is a Light Activated Alarm circuit. The circuit illustrated here is a burglar alarm. LDR is place at such a place that when the thief enters our house then a connection of beam of light and LDR is disrupted by the intruder and the buzzer goes off. When a ray of light is interrupted by anything, the LDR used in the circuit changes its resistance and causes the buzzer to go off, producing a large siren, scaring the intruders away. Circuit can be easily modified to make the police siren instead of a simple alarming sound. The power consumption of the system is very low. It is of interest, in regard to future laser communication links, to discuss the question of whether the information transmitted along a narrow line-of-sight path to a receiver is proof against interception. The automatic assumption that a beam of light whose beam diameter is of the order of magnitude of the collector mirrors is “secure” in principle is strictly true only for propagation in empty space. In transmission through the atmosphere, scattering phenomena due to water droplets in fog, cloud or rain, ice crystals, snowflakes, dust particles, and Rayleigh scattering from the air molecules themselves produce diffusion of the light from the direct path of the beam. This diffused light can be detected and utilized. In our project by combining laser light based audio transmitter, receiver and alarm system circuit to active. And both alarm system and audio receiver circuit simultaneously work. and also in our project, the modification area is in the receiver side both alarm system and audio receiver parallelly to be functional or to work correctly. This project is about how to prevent theft in homes, offices, banks, museums and
also parallelly transmit and receive a good quality audio sound of without any license. 2
1.2 MOTIVATION Our motivation to select this project title is to design and implementation of Laser based audio transmission and laser based alarm system. and also, to solve the problems of information accuses in our campus and Parallelly we will understand the role of communication concept. Secondly, we think that our project will be done by chip and easy components that are found in our compass in workshops, laboratories and stores.
1.3 ORGANIZATION OF THE PROJECT This section describes the introduction part of our project. It introduces basic concepts laser audio transmission and laser alarm system which translates information using higher rate with a higher performance using a minimum amount of transmitted power and bandwidth. The second chapter explains the literature review. It includes back ground history of laser audio transmitter and laser alarm system and the documents used to guide during our project. The third chapter discusses the design and analysis / methodology which describe the body of our project. It explains block diagrams, calculation parts, schematic diagrams and results/out puts. Finally, the project also includes summary, conclusion, recommendation, references and appendix.
1.4 OBJECTIVE 1.4.1 General objective Using laser beam how can transmit audio signal and how to secure our home. 1.4.2 Specific objective Toward achieving the general objective mentioned the following specific objective will be accomplished in this final project. ➢ To transmit Audio using laser beam. ➢ To install a security system based on laser light conveniently at the entrance of home, bank and other similar locations to protect the same from unauthorized access ➢ To create low cost and simple circuit to avoid unauthorized entry of people.
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1.5 SCOPE OF THE PROJECT This system can be used to protect the perimeter of a building by using a cascade arrangement of multiple alarms and transmit audio simultaneously. And also It can be used in bank or treasury to protect from thieves by audio alarming to the security persons.
1.6 PROBLEMS OF STATEMENT The main problem statement of our project is to fix the problem of home, office and shop security and to fix the free space transmission problem by using laser beam.
1.7 SYSTEM ANALYSIS Basically, this is a low cost “laser based audio transmitter, receiver and alarm” system used to protect the selected locations to strengthen the security system and transmit audio using laser beam it is consisted of two electronic circuits. •
Transmitter section
•
Receiver section
Audio input
Fig 1. system analysis diagram
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1.5 BLOCK DIAGRAM EXPLANATION 1.5.1 CONDENSER MICROPHONE It is also called a capacitor or electrostatic microphone. Condenser means capacitor, which stores energy in the form of an electric field. Condenser microphones require power from a battery or external source. Condenser also tends to be more sensitive and responsive than dynamic, making them well suited to capturing subtle nuances in a sound. The diaphragm vibrates when struck by sound waves, changing the distance between the two plates and therefore changing the capacitance. Specifically, when the plates are closer together capacitance increases and a charge current occurs and this current will be used to trigger the transmitting section.
1.5.2 TRANSMITTING SECTION The transmitter section comprises condenser microphone or 3.5mm audio input jack. In transmitter. The condenser mic used in the transmitter section is used to convert the acoustic signals to the electrical signals which are modulated and send through a laser beam used in the transmitter section.
1.5.3 LASER TORCH Here we use the light rays coming from laser torch as the medium for transmission. Laser had potential for the transfer of data at extremely high rates, specific advancements were needed in component performance and systems engineering, Particularly for space-qualified hardware. Free space laser communications systems are wireless connections through the atmosphere. They work similar to fiber optic cable systems except the beam is transmitted through open space. The laser systems operate in the near infrared region of the spectrum. The laser light across the link is at a wavelength of between 780 - 920 nm. Two parallel beams are used, one for transmission and one for reception.
1.5.4 RECEIVING SECTION The receiver circuit uses an NPN phototransistor as the light sensor that is followed by a twostage transistor preamplifier and LM386-based audio power amplifier. The receiver doesn't need any complicated alignment. Just keep the phototransistor oriented towards the remote transmitter's laser point and adjust the volume control for a clear sound.
Parallelly from the phototransistor or (LDR) of two sides are connected to the alarm circuit. The 5
alarm system is 555 IC integrated circuit (chip) based. After some observation, the circuit should seem very similar to the ASTABLE MULTIVIBRATOR, that is because the circuit is a ASTABLE MULTIVIBRATOR with only one modification. This modification is done at RESET pin (PIN4). In a normal ASTABLE vibrator this pin is connected to +5V, but since in this case we are supposed to generate pulse on the condition of absence of light it is not connected directly to +5v. The resistor network provided at the RESET pin provides a virtual ground so to keep resetting the IC and so the square wave output is stopped in the presence of light. So, by combining two electrical circuit we got two perfect output that means on the receiving section there is a loud speaker, the loud speaker is connected to the alarm system and parallel to audio amplifier circuit.
1.5.5 LOUD SPEAKERS A loudspeaker (or "speaker") is an electro acoustic transducer that converts an electrical signal into sound. The speaker moves in accordance with the variations of an electrical signal and causes sound waves to propagate through a medium such as air or water.
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CHAPTER TWO LITERATURE REVIEW 2.1 OPTICAL AND MICROWAVE COMMUNICATIONS SYSTEMM CONCEPTUAL DESIGN FOR A REALISTIC INTERSTELLAR EXPLORER The concept of a realistic interstellar explorer has been addressed by the Johns Hopkins University Applied Physics Laboratory (JHU/APL) with support from the NASA Institute for Advanced Concepts (NIAC). This paper discusses the requirements, conceptual design and technology issues associated with the optical and RF communications systems envisioned for this mission, in which the spacecraft has a projected range of 1000 AU. Well before a range of 100 AU interactive control of the spacecraft becomes nearly impossible, necessitating a highly autonomous craft and one-way communications to Earth. An approach is taken in which the role of the optical downlink is emphasized for data transfer and that of the microwave uplink emphasized for commands. The communication system is strongly influenced by the large distances involved, the high velocities (20 AU/year or ~ 95 km/s) as well as the requirements for low-mass (~ 10 kg), low prime power (~ 15 W), reliability, and spacecraft autonomy. An optical terminal concept is described that has low mass and prime power in a highly integrated and novel architecture, but new technologies are needed to meet the range, mass, and power requirements. These include high-power, ³wall-plug´ efficient
diode-pumped
fiber
lasers;
compact,
lightweight,
and
low-power
micro-
electromechanical (MEM) beam steering elements; and lightweight diffractive quasi-membrane optics. In addition, a very accurate star tracking mechanism must be fully integrated with the laser downlink to achieve unprecedented pointing accuracy (~ 400 nrad RMS). The essential optical, structural, mechanical, and electronic subsystems are described that meet the mission requirements, and the key features of advanced technologies that need to be developed are discussed. The conclusion from this preliminary effort is that an optical communication downlink out to 1000 astronomical units (AU) is within the realm of technical feasibility in the next 5-10 years if the identified technical risks for the new technologies can be retired [1].
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2.2 OPTICAL COMMUNICATION SYSTEM FOR SMART DUST In this thesis, the optical communication systems for millimeter-scale sensing and communication devises known as ³Smart Dust´ are described and analyzed. A smart dust element is a self -contained sensing and communication system that can be combined into roughly a cubicmillimeter mote to perform integrated, massively distributed sensor networks. The suitable passive optical and fiber-optic communication systems will be selected for the further performance design and analysis based on the requirements for implementing these systems. Based on the communication link designs of the free-space passive optical and fiber-optic communication systems, the simulations for link performance will be performed [2].
2.3 TOWARD A WIRELESS OPTICAL COMMUNICATION LINK BETWEEN TWO SMALL UNMANNED AERIAL VEHICLES A communication system between two autonomous micro air vehicles is proposed. Laser communication offers advantages in range, power, and bandwidth when line of sight is available. Beam steering is accomplished using gyro-stabilized MEMS micro mirrors. A custom CMOS smart-pixel imager implements a 1Mbps receiver, including analog front-end and variable-gain amplifier at each pixel. Algorithms are presented for initial link establishment and maintenance [3].
2.4 FREE SPACE OPTICAL LASER COMMUNICATION LINK A Free Space Optical (FSO) LASER Communication Link is presented. This project deals with the development of a full-duplex FSO analogue / digital transceiver. In this information age, the demand for high speed, high bandwidth communications channel, is ever increasing. FSO is presented as a solution to these demands in that it is free to implement, easy to install and of very high bandwidth. The reader is introduced to the FSO system of communication and the development of a small-scale communicator using laser as the carrier signal for information transfer. Experimental results explain the performance of the completed system and offer methods of maximizing efficiency of such FSO-based communication systems [4].
2.5 LASER BASED INTRUDER ALARM “LASER BASED INTRUDER ALARM” is security system prototype which alarms and awakes people when an unauthorized intruder enters their room. This circuit is low cost and easy to install. 8
Though laser diode is used to operate the system failing of which leads to alarm the buzzer symbolized that someone has accessed the room without the knowledge of user. A simple and effective circuit prototype is developed to work efficiently in the purpose of security [5].
2.6 LASER BASED COMMUNICATION LINK Laser as a communication medium can provide a good substitute for t e present day communication systems as t e problem of interference faced in case of electromagnetic waves is not t ere and high deal of secrecy is available. Laser communications offers a viable alternative to R communications for inter satellite links and other applications where high-performance links are a necessity. High data rate, small antenna size, narrow beam divergence, and a narrow field of view are characteristics of laser communications that offer a number of potential advantages for system design. The purpose of the project is to determine the feasibility of replacing microwave communications with laser communications to remote locations. This link is unreliable and can be disrupted in fog or rain. The current system has a slow data rate of 1.54 Mbps, equivalent to using a dial up modem on any individual computer. When this link goes down, all communications to and from the stationary lost, leaving the station unable to carry out its missions. The system proposed to solve this problem utilizes a long cavity laser operating at 1550 nm. The system will also use redundancies as well as spatial diversity of seven lasers to achieve reliability and high data rates averaging 2.4 Gbps. The transmitter and receiver will be set up on gimbals connected to a control system that ensures alignment based off a pulse train on the receiver plate. This pulse train also ensures that the signal is penetrating the atmosphere over the 8-mile distance. A comparison between the microwave and laser communications was completed and future work includes implementing a proposed three phase test plan. A basic communication system is made up of three main parts being the transmitter, the medium over which the message is being sent, and the receiver. A good example of this is two people communicating from one side of a room to the other. If the person wants to communicate with the other person, he/she speaks words towards the direction of the other individual who receives the voice information and determines the message. This example is much like how any general communication system works. First, the message is determined that needs to be sent to the receiving end. The message is then sent to the transmitter. The transmitter, much like the person’s 9
mouth, is sending the signal containing the message from one person to the other. This can be compared to using an antenna to send out a signal. The signal then must travel through some type of medium to reach the receiver. For the two-people talking, this medium would be air. But, sometimes this medium is some type of cable or wire. The signal is then collected by the receiver, which is comparable to the person on the receiving end hearing the sound of the person’s voice. Sometimes the signal can be immediately understood, but other times the signal must first be decoded in order to understand the message [6].
In our project by using laser beam or laser torch and some chip electrical component like resister, capacitor, op amp, 555 timer and breadboard try to construct a laser audio transmitter and receiver circuit and also construct alarm system circuit.so on the transmitter side we have resisters, transistors, capacitors,3.5mm audio jack, 5v dc source and laser. these components are only used to transmission section on the receiving section. we have two circuits the first one is audio amplification circuit and the second one is security alarm circuit. both circuit are connected to the LDR parallel so on this section the common component for both circuit is LDR and laud speaker So, by using 9V DC source for both circuit we can received audio from the transmitter and also, we can protect our home from unauthorized person.
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CHAPTER THREE METHODOLOGY 3.1 SYSTEM DISCRIPTION Audio input Transmitter
Audio
And laser
amplifier and alarm
beam
Fig 2. system description block diagram Fig shows the block diagram of laser based system for audio transmitter, receiver and alarm system. It comprises transmitter receiver and alarm system section. The alarm system section at one end of the link provides a beep sound on the receiver circuit. For one way communication, you need to use an identical system with the positions of the receiver and the transmitter reversed with this system. In the transmitter, the intensity of the laser beam is modulated by the output of an always on code oscillator (operating at 10-15 kHz). The receiver receives the intensity modulated light signals through a light sensor and outputs an audio signal.
3.2 THE TRANSMITTER CIRCUIT
Fig 3. Transmitter circuit
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The transmitter circuit consists of capacitor, resisters, transistor, Audio input and a Laser. The Audio input positive side of wire is connected to the capacitor and also the negative side of audio input wire is connected to the R1 and Q1 and the 5V dc source, then the Capacitor C1 negative side is connected to the R1 resister and Q1 transistor of the middle pin B (bass), the transistor emitter pin is connected to the positive terminal of the laser light and collector pin is connected to the parallel resister and dc power source, finally the laser is connected to the source and the transistor .Now our circuit is completely connected each other on the bread board.
➢ Laser The laser diodes can be constructed using a variety of different materials to produce distinctive wavelengths. Semiconductor laser diodes produce a much higher output power and highly directional beams compared to the LEDs. The laser must be operated with a large drive current to get a high density of ready to combine electrons at the pn junction. The transmitter circuit shows the output power vs. forward current characteristics of a laser diode. We can divide it into spontaneous emission A and laser oscillation region B. The current required for starting oscillations is called threshold current (I th) while the forward (excitation) current necessary for maintaining the diodes specified optical output is called its operating current (I op) For the 5mW laser shown in the transmitter circuit the typical values of threshold and operating currents are 30mA and 45 mA, respectively. Keychain laser pointers available in the market have a power output of 5mW with forward current limited to 20 to 5mA.Thus a laser diode module of keychain type visible laser pointer may be used for this transmitter circuit. [5]
3.3 THE RECEIVER CIRCUIT ➢ Alarm system
Fig 4. Alarm system circuit
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Above figure shows the circuit diagram of dark detector alarm. After some observation, the circuit should seem very similar to the ASTABLE MULTIVIBRATOR, that is because the circuit is a ASTABLE MULTIVIBRATOR with only one modification. This modification is done at RESET pin (PIN4). In a normal ASTABLE vibrator this pin is connected to +5V, but since in this case we are supposed to generate pulse on the condition of absence of light it is not connected directly to +5v. The resistor network provided at the RESET pin provides a virtual ground so to keep resetting the IC and so the square wave output is stopped in the presence of light. The transistor here drives the speaker because the speaker driven by IC is not a good idea. The speaker here can be replaced with LEDs to create an output response of lighting. So once the LEDs are placed and the darkness falls we will have an emergency backup light. The transistor here need not be a PNP compulsory but one can replace it with a NPN and the pin connections should be connected accordingly [5].
➢ Working Before going to explanation, the circuit should be assumed ON and is not buzzing in the presence of light. This condition of non-buzzing in the presence of light can be achieved by adjusting the 1MΩ trim pot. Now in the circuit one can observe a voltage divider with 1M, 100K on one side and LDR on the other, the reset pin is connected in the middle. The trimmer pot is said to be adjusted because to create enough resistance on the top branch of voltage divider to drop almost all the potential (+5v) in the top branch itself. This leaves a virtual ground at the middle of divider (reset pin). Since the RESET pin of 555 is a LOW LEVEL triggered, the timer IC will be reset mode continuously and so there will be no square wave output as it should be. From this we can conclude that in the presence of light the 555 IC will be in complete reset and provides no output. Now when the darkness or the laser beam on the LDR, the resistance of the LDR increases drastically as explained in introduction, this increase of resistance in the second branch (one with LDR) of voltage divider will be enough to change the ratio of voltage sharing between the two branches of voltage divider section. Once this happen, the potential at the junction of voltage divider circuit rises from 0V to 2V (approximately). And similarly, the voltage at the RESET pin rises. This rise of voltage will be enough to lift the 555IC from reset mode. Once this reset
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mode is lifted, the timer generates square wave output. So it is concluded that once the darkness falls on the LDR the square wave output is generated by the timer. The square wave generated by the timer is fed to the PNP transistor to drive the speaker. So the speaker outputs sound in response to the square wave.
➢ Audio receiver The circuit below shows the basic format of wiring up the IC as an amplifier. Here, as discussed in the previous section, the gain of the circuit is restricted to 20 by keeping the pins 1 and 8 open. The internal connection of a 1.35K resistor across these pin-outs shunts the IC to the above gain. The output is connected to a loudspeaker via a filter capacitor, which is normally witnessed in all linear IC amplifier circuits. The pot VR1 at the input functions as the volume control for enabling the output to be adjusted to the desired levels.
.
Fig 5. Receiver circuit 1 The second circuit shows how the gain of the above fundamental design may be boosted to almost 200 by adding a capacitor across pin 1 and 8 of the IC. The value of the capacitor should not be increased above 10 µF though.
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Fig 6. Receiver circuit 2 The gain can be made adjustable from 20 to 200 by including a variable resistor of 4K7 in series with the above capacitor. Excess offset conditions may be reduced by engaging the unused input to a resistor from the ground. However, all offset issues are cancelled-OFF if the active input is coupled through a capacitor. With the circuit set at a gain of 200, it becomes essential to bypass the unused pin #7 via a 0.1µ capacitor to ground for keeping the circuit stable and avoiding unnecessary oscillations or clipping. A simple but interesting bass boost arrangement can be inserted by introducing a resistor/capacitor network across pin 1 and 5+.
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Fig 7. Receiver circuit 3 last circuit. Other than audio amplifiers many different small circuits can also be built using this versatile chip; the following datasheet will provide you with more added information. In our project by combining two different types of circuit laser audio receiver and LDR laser based alarm receiver circuit became one perfect output. And how both circuits are active simultaneously [6].
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CHAPTER FOUR COMPONENTS 4.1 LASER LASER is also known as Light Amplification by Stimulated Emission of Radiation. A laser is a device that emits light (electromagnetic radiation) through a process of optical amplification based on the stimulated emission of photons. Light emitters are a key element in any fiber optic system. This component converts the electrical signal into a corresponding light signal that can be injected into the fiber. The light emitter is an important element because it is often the most costly element in the system, and its characteristics often strongly influence the final performance limits of a given link. Laser Diodes are complex semiconductors that convert an electrical current into light. The conversion process is fairly efficient in that it generates little heat compared to incandescent lights. Five inherent properties make lasers attractive for use in fiber optics.
Fig 8. Laser [1].
➢ Type •
Gas lasers
•
Chemical lasers
•
Excimer lasers
•
Solid-state lasers
•
Fiber lasers
•
Photonic crystal lasers
•
Semiconductor lasers
•
Dye lasers
•
Free electron lasers
•
Exotic laser
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➢ WORKING OF A LASER A LASER works on the principle of spontaneous emission. Spontaneous emission is the process by which a light source such as an atom, molecule, nanocrystal or nucleus in an excited state undergoes a transition to a state with a lower energy, e.g., the ground state and emits a photon. Spontaneous emission of light or luminescence is a fundamental process that plays an essential role in many phenomena in nature and forms the basis of many applications, such as fluorescent tubes, older television screens (cathode ray tubes), plasma display panels, lasers (for startup - normal continuous operation works by stimulated emission instead) and light emitting diodes emission of photon in a laser [3]
Fig 9. Emission of a laser [1].
4.2 555 TIMER The 555 Timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation and oscillator applications. Depending on the manufacturer, the standard 555 package includes over 20 transistors, 2 diodes and 15 resistors on a silicon chip installed in an 8-pin mini dual-in-line package. The 555 has three operating modes.
•
Monostable mode: in this mode, the 555 functions as a "one-shot" pulse generator.
Applications include timers, missing pulse detection, bounce free switches, touch 18
switches, frequency divider, capacitance measurement, pulse-width modulation (PWM) and so on. •
Astable - free running mode: the 555 can operate as an oscillator. Uses include LED
and lamp flashers, pulse generation, logic clocks, tone generation, security alarms, pulse position modulation and so on. •
Bistable mode or Schmitt trigger: the 555 can operate as a flip-flop, if the DIS pin is
not connected and no capacitor is used. Uses include bounce free latched switches [1].
Fig 10. 555 TIMER [5]. Table 1. Pin specification of 555 timer Pin No.
Signal name
1
GND
2
Trigger
3
Output
4
Reset
5
Control voltage
6
Threshold
7
Discharge
8
Vcc
19
4.3 LDR (LIGHT DEPENDENT RESISTOR) A photo resistor or light dependent resistor (LDR) is a resistor whose resistance decreases with increasing incident light intensity. It can also be referred to as a photoconductor. A photoresistor is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance. A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, e.g. silicon. In intrinsic devices, the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire bandgap. Extrinsic devices have impurities, also called dopants, added whose ground state energy is closer to the conduction band; since the electrons do not have as far to jump, lower energy photons (i.e., longer wavelengths and lower frequencies) are sufficient to trigger the device. If a sample of silicon has some of its atoms replaced by phosphorus atoms (impurities), there will be extra electrons available for conduction. This is an example of an extrinsic semiconductor. [2]
Fig 11. LDR [5].
20
4.4 LOW VOLTAGE AUDIO AMPLIFIER IC LM386 The LM386 is an integrated circuit consisting of a low voltage audio power amplifier. It is suitable for battery-powered devices such as radios, guitar amplifiers, and hobbyist projects. The IC consists of an 8-pin dual in-line package (DIP-8) and can output 0.5 watts power using a 9-volt power supply.
Fig 12. LM386 IC[4].
21
Table 2. Pin specification of LM 386 IC Pin No
Signal
1
Gain
2
-Input
3
+Input
4
GND
5
Vout
6
Vs
7
Bypass
8
Gain
4.5 RESISTORS A resistor is a two-terminal passive electronic component which implements electrical resistance as a circuit element. When a voltage V is applied across the terminals of a resistor, a current I will flow through the resistor in direct proportion to that voltage. The reciprocal of the constant of proportionality is known as the resistance R, since, with a given voltage V, a larger value of R further "resists" the flow of current I as given by Ohm's law:
𝑉
𝐼=𝑅
………………………….(Eq.5.1)
Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in most electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel-chrome). Resistors are also implemented within integrated circuits, particularly analog devices, and can also be integrated into hybrid and printed circuits. The electrical functionality of a resistor is specified by its resistance: common commercial resistors are manufactured over a range of more than 9 orders of magnitude. When specifying that resistance in an electronic design, the required precision of the resistance may require attention to the manufacturing tolerance of the chosen resistor, according to its specific application. The 22
temperature coefficient of the resistance may also be of concern in some precision applications. Practical resistors are also specified as having a maximum power rating which must exceed the anticipated power dissipation of that resistor in a particular circuit: this is mainly of concern in power electronics applications. Resistors with higher power ratings are physically larger and may require heat sinking. In a high voltage circuit, attention must sometimes be paid to the rated maximum working voltage of the resistor. The series inductance of a practical resistor causes its behavior to depart from ohms law; this specification can be important in some high-frequency applications for smaller values of resistance. In a low-noise amplifier or pre-amp the noise characteristics of a resistor may be an issue. The unwanted inductance, excess noise, and temperature coefficient are mainly dependent on the technology used in manufacturing the resistor. They are not normally specified individually for a particular family of resistors manufactured using a particular technology. A family of discrete resistors is also characterized according to its form factor, that is, the size of the device and position of its leads (or terminals) which is relevant in the practical manufacturing of circuits using them.
➢ UNITS The ohm (symbol: Ω) is the SI unit of electrical resistance, named after Georg Simon Ohm. An ohm is equivalent to a volt per ampere. Since resistors are specified and manufactured over a very large range of values, the derived units of milliohm (1 m Ω =10-3Ω), kilo Ohm (1 k Ω = 103 Ω) and mega Ohm (1M Ω =106 Ω) are also in common usage. The reciprocal of resistance R is called conductance G = 1/R and is measured in Siemens (SI unit), sometimes referred to as a mho. Thus, a Siemens is the reciprocal of an ohm: S = Ω -1. Although the concept of conductance is often used in circuit analysis, practical resistors are always specified in terms of their resistance (ohms) rather than conductance [2].
➢ THEORY OF OPREATION Ohm's law The behavior of an ideal resistor is dictated by the relationship specified in Ohm's law:
𝑉 = 𝐼. 𝑅
……………………...…………………….(Eq.5.2)
Ohm's law states that the voltage (V) across a resistor is proportional to the current (I) passing through it, where the constant of proportionality is the resistance (R). Equivalently, Ohm's law can be stated: 23
𝐼=
𝑉 𝑅
………………………………………………...(Eq.5.3)
This formulation of Ohm's law states that, when a voltage (V) is present across a resistance (R), a current (I) will flow through the resistance. This is directly used in practical computations. For example, if a 300-ohm resistor is attached across the terminals of a 12-volt battery, then a current of 12 / 300 = 0.04 amperes (or 40 mill amperes) will flow through that resistor. Series and parallel resistors In a series configuration, the current through all of the resistors is the same, but the voltage across each resistor will be in proportion to its resistance. The potential difference (voltage) seen across the network is the sum of those voltages, thus the total resistance can be found as the sum of those resistances:
………………...(Eq.5.4)
As a special case, the resistance of N resistors connected in series, each of the same resistance R is given by NR. Resistors in a parallel configuration are each subject to the same potential difference (voltage), however the currents through them add. The conductance of the resistors then adds to determine the conductance of the network. Thus, the equivalent resistance (Req) of the network can be computed:
………………….(Eq.5.5)
The parallel equivalent resistance can be represented in equations by two vertical lines "||" (as in geometry) as a simplified notation. For the case of two resistors in parallel, this can be calculated using: 24
𝑅𝑒𝑞 = 𝑅1‖𝑅2 =
𝑅1.𝑅2
…………………….(Eq.5.6)
𝑅1+𝑅2
As a special case, the resistance of N resistors connected in parallel, each of the same resistance R, is given by R/N. A resistor network that is a combination of parallel and series connections can be broken up into smaller parts that are either one or the other. For instance,
……………………….(Eq.5.7)
However, some complex networks of resistors cannot be resolved in this manner, requiring more sophisticated circuit analysis. For instance, consider a cube, each edge of which has been replaced by a resistor. What then is the resistance that would be measured between two opposite vertices? In the case of 12 equivalent resistors, it can be shown that the corner-to- corner resistance is 5»6 of the individual resistance. One practical application of these relationships is that a non-standard value of resistance can generally, be synthesized by connecting a number of standard values in series and/or parallel. This can also be used to obtain a resistance with a higher power rating than that of the individual resistors used. In the special case of N identical resistors all connected in series or all connected in parallel, the power rating of the individual resistors is thereby multiplied by N.
25
➢ Power Dissipation The power P dissipated by a resistor (or the equivalent resistance of a resistor network) is calculated as:
𝑃 = 𝐼2 𝑅 = 𝐼𝑉 =
𝑉2 𝑅
…….…..…………………………………….(Eq.5.8)
The first form is a restatement of Joule's first law. Using Ohm's law, the two other forms can be derived. The total amount of heat energy released over a period of time can be determined from the integral of the power over that period of time: 𝑡2
𝑊 = ∫𝑡1 𝑣(𝑡)𝑖 (𝑡)𝑑𝑡…………………………………….…….(Eq.5.9) Practical resistors are rated according to their maximum power dissipation. The vast majority of resistors used in electronic circuits absorbs much less than a watt of electrical power and require no attention to their power rating. Such resistors in their discrete form, including most of the packages detailed below, are typically rated as 1/10, 1/8, or 1/4 watt. Resistors required to dissipate substantial amounts of power, particularly used in power supplies, power conversion circuits, and power amplifiers, are generally referred to as power resistors; this designation is loosely applied to resistors with power ratings of 1 watt or greater. Power resistors are physically larger and tend not to use the preferred values, color codes, and external packages described below. If the average power dissipated by a resistor is more than its power rating, damage to the resistor may occur, permanently altering its resistance; this is distinct from the reversible change in resistance due to its temperature coefficient when it warms. Excessive power dissipation may raise the temperature of the resistor to a point where it can burn the circuit board or adjacent components, or even cause a fire. There are flameproof resistors that fail (open circuit) before they overheat dangerously. Note that the nominal power rating of a resistor is not the same as the power that it can safely dissipate in practical use. Air circulation and proximity to a circuit board, ambient temperature, and other factors can reduce acceptable dissipation significantly. Rated power dissipation may be given for an ambient temperature of 25 °C in free air. Inside an equipment case at 60 °C, rated dissipation will be significantly less; a resistor dissipating a bit less than the maximum figure given by the manufacturer may still be outside the safe operating area and may prematurely fail. 26
➢ Resistor Marking Most axial resistors use a pattern of colored stripes to indicate resistance. Surface-mount resistors are marked numerically, if they are big enough to permit marking; more-recent small sizes are impractical to mark. Cases are usually tan, brown, blue, or green, though other colors are occasionally found such as dark red or dark gray. Early 20th century resistors, essentially uninsulated, were dipped in paint to cover their entire body for color coding. A second color of paint was applied to one end of the element, and a color dot (or band) in the middle provided the third digit. The rule was "body, tip, dot", providing two significant digits for value and the decimal multiplier, in that sequence. Default tolerance was ±20%. Closer-tolerance resistors had silver (±10%) or gold-colored (±5%) paint on the other end. ➢ Four-band resistors Four-band identification is the most commonly used color-coding scheme on resistors. It consists of four colored bands that are painted around the body of the resistor. The first two bands encode the first two significant digits of the resistance value, the third is a power-of-ten multiplier or number-of-zeroes, and the fourth is the tolerance accuracy, or acceptable error, of the value. The first three bands are equally spaced along the resistor; the spacing to the fourth band is wider. Sometimes a fifth band identifies the thermal coefficient, but this must be distinguished from the true 5-color system, with 3 significant digits. For example, green-blue-yellow-red is 56×104Ω= 560 kΩ ± 2%. An easier description can be as followed: the first band, green, has a value of 5 and the second band, blue, has a value of 6, and is counted as 56. The third band, yellow, has a value of 104, which adds four 0's to the end, creating 560,000 Ω at ±2% tolerance accuracy. 560,000changes to 560 k Ω±2%
as a kilo- is 10
27
Fig 13. Resister color coding and band [2].
28
➢ Electrical and thermal noise In amplifying faint signals, it is often necessary to minimize electronic noise, particularly in the first stage of amplification. As dissipative elements, even an ideal resistor will naturally produce a randomly fluctuating voltage or "noise" across its terminals. This Johnson Nyquist noise is a fundamental noise source which depends only upon the temperature and resistance of the resistor, and is predicted by the fluctuation dissipation theorem. Using a larger resistor produces a larger voltage noise, whereas with a smaller value of resistance there will be more current noise, assuming a given temperature. The thermal noise of a practical resistor may also be somewhat larger than the theoretical prediction and that increase is typically frequency-dependent.
However, the "excess noise" of a practical resistor is an additional source of noise observed only when a current flow through it. This is specified in unit of µV/V/decade - µV of noise per volt applied across the resistor per decade of frequency. The µV/V/decade value is frequently given in dB so that a resistor with a noise index of 0 dB will exhibit 1 µV (rms) of excess noise for each volt across the resistor in each frequency decade. Excess noise is thus an example of 1/f noise.
Thick-film and carbon composition resistors generate more excess noise than other types at low frequencies; wire-wound and thin-film resistors, though much more expensive, are often utilized for their better noise characteristics. Carbon composition resistors can exhibit a noise index of 0 dB while bulk metal foil resistors may have a noise index of -40 dB, usually making the excess noise of metal foil resistors insignificant. Thin film surface mount resistors typically have lower noise and better thermal stability than thick film surface mount resistors. However, the design engineer must read the data sheets for the family of devices to weigh the various device tradeoffs. While not an example of "noise" per se, a resistor may act as a thermocouple, producing a small DC voltage differential across it due to the thermoelectric effect if its ends are at somewhat different temperatures. This induced DC voltage can degrade the precision of instrumentation amplifiers in particular. Such voltages appear in the junctions of the resistor leads with the circuit board and with the resistor body. Common metal film resistors shown such an effect at a magnitude of about 20µV/°C. Some carbon composition resistors can exhibit thermoelectric offsets as high as 400 µV/°C, whereas specially constructed resistors can reduce this number to 0.05µV/°C [2].
29
4. 6 VARIABLE RESISTORS Variable Resistors consist of a resistance track with connections at both ends and a wiper which moves along the track as you turn the spindle. The track may be made from carbon, cermet (ceramic and metal mixture) or a coil of wire (for low resistances). The track is usually rotary but straight track versions, usually called sliders, are also available. Variable resistors may be used as a rheostat with two connections (the wiper and just one end of the track) or as a potentiometer with all three connections in use. Miniature versions called presets are made for setting up circuits which will not require further adjustment. Variable resistors are often called potentiometers in books and catalogues. They are specified by their maximum resistance, linear or logarithmic track, and their physical size. The standard spindle diameter is 6mm The resistance and type of track are marked on the body: 4K7 LIN means 4.7 kΩ linear track.
1M LOG means 1MΩ logarithmic track
Some variable resistors are designed to be mounted directly on the circuit board, but most are for mounting through a hole drilled in the case containing the circuit with stranded wire connecting their terminals to the circuit board.[2]
Fig 14. variable resister [6].
30
4.7 CAPACITOR A capacitor (formerly known as condenser) is a device for storing electric charge. The forms of practical capacitors vary widely, but all contain at least two conductors separated by a nonconductor. Capacitors used as parts of electrical systems, for example, consist of metal foils separated by a layer of insulating film. A capacitor is a passive electronic component consisting of a pair of conductors separated by a dielectric (insulator). When there is a potential difference (voltage) across the conductors, a static electric field develops across the dielectric, causing positive charge to collect on one plate and negative charge on the other plate. Energy is stored in the electrostatic field. An ideal capacitor is characterized by a single constant value, capacitance, measured in far ds. This is the ratio of the electric charge on each conductor to the potential difference between them. Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass, in filter networks, for smoothing the output of power supplies, in the resonant circuits that tune radios to particular frequencies and for many other purposes. The capacitance is greatest when there is a narrow separation between large areas of conductor; hence capacitor conductors are often called "plates", referring to an early means of construction. In practice the dielectric between the plates passes a small amount of leakage current and also has an electric field strength limit, resulting in a breakdown voltage, while the conductors and leads introduce an undesired inductance and resistance [2].
Fig 15. Capacitor [6].
31
➢ THEORY OF OPREATION: A capacitor consists of two conductors separated by a non-conductive region. The non- conductive region is called the dielectric or sometimes the dielectric medium. In simpler terms, the dielectric is just an electrical insulator. Examples of dielectric mediums are glass, air, paper, vacuum, and even a semiconductor depletion region chemically identical to the conductors. A capacitor is assumed to be self-contained and isolated, with no net electric charge and no influence from any external electric field. The conductors thus hold equal and opposite charges on their facing surfaces, and the dielectric develops an electric field. InSI units, a capacitance of one farad means that one coulomb of charge on each conductor causes a voltage of one volt across the device The capacitor is a reasonably general model for electric fields within electric circuits. An ideal capacitor is wholly characterized by a constant capacitance C, defined as the ratio of charge ±Q on each conductor to the voltage V between them:
C=Q/V ……… ………………………….(Eq.7.1) Sometimes charge build-up affects the capacitor mechanically, causing its capacitance to vary. In this case, capacitance is defined in terms of incremental changes:
𝐶=
d𝑞 d𝑣
.………………………………….(Eq.7.2)
Fig 16. Energy storage in capacitor [6].
32
➢ Energy storage Work must be done by an external influence to "move" charge between the conductors in a capacitor. When the external influence is removed the charge, separation persists in the electric field and energy is stored to be released when the charge is allowed to ret run to its equilibrium position. The work done in establishing the electric field, and hence the amount of energy stored, is given by:
𝑄
𝑄
𝑞
1𝑄 2
𝐶
2𝐶
𝑊 = ∫𝑄=0 𝑉𝑑𝑞 = ∫𝑄=0 𝑑𝑞 =
1
1
2
2
= 𝑢𝑣2 = 𝑉𝑄 …………….(Eq.7.3)
➢ Current-voltage relation The current i (t) through any component in an electric circuit is defined as the rate of flow of a charge q (t) passing through it, but actual charges, electrons, cannot pass through the dielectric layer of a capacitor, rather an electron accumulates on the negative plate for each one that leaves the positive plate, resulting in an electron depletion and consequent positive charge on one electrode that is equal and opposite to the accumulated negative charge on the other. Thus the charge on the electrodes is equal to the integral of the current as well as proportional to the voltage as discussed above. As with any anti derivative, a constant of integration is added to represent the initial voltage v (t0). This is the integral form of the capacitor equation,
𝑣(𝑡) =
𝑞 (𝑡 ) 𝐶
1
𝑒
= 𝑐 ∫𝑡0 𝑖(𝜏) 𝑑𝜏 + 𝑣(𝑡0)…...………………. (Eq.7.4)
Taking the derivative of this, and multiplying by C, yields the derivative form,
𝑖 (𝑡 ) =
𝑥𝑑𝑞(𝑡) 𝑑𝑡
=𝐶
𝑑𝑣 𝑑𝑡
…………………………..……………. (Eq.7.5)
The dual of the capacitor is the inductor, which stores energy in the magnetic field rather than the electric field. Its current-voltage relation is obtained by exchanging current and voltage in the capacitor equations and replacing C with the inductance L 33
➢ DC Circuits
Fig 17 A simple resistor-capacitor circuit demonstrates charging of a capacitor.
➢ Capacitor markings Most capacitors have numbers printed on their bodies to indicate their electrical characteristics. Larger capacitors like electrolytic usually display the actual capacitance together with the unit (for example, 220 µF). Smaller capacitors like ceramics, however, use a shorthand consisting of three numbers and a letter, where the numbers show the capacitance in pF (calculated as XY x 10Z for the numbers XYZ) and the letter indicates the tolerance (J, K or M for ±5%, ±10% and ±20% respectively).
Additionally, the capacitor may show its working voltage, temperature and other relevant characteristics.
Example A capacitor with the text 473K 330V on its body has a capacitance of 47 x 1000 pF = 47 nF (±10%) with a working voltage of 330 V.
➢ Applications Capacitors have many uses in electronic and electrical systems. They are so common that it is a rare electrical product that does not include at least one for some purpose.
➢ Energy storage A capacitor can store electric energy when disconnected from its charging circuit, so it can be used like a temporary battery. Capacitors are commonly used in electronic devices to maintain power supply while batteries are being changed. (This prevents loss of information in volatile memory.) 34
Conventional capacitors provide less than 360 joules per kilogram of energy density, while capacitors using developing technologies could provide more than 2.52 kilojoules per kilogram
In car audio systems, large capacitors store energy for the amplifier to use on demand. Also for a flash tube a capacitor is used to hold the high voltage.
➢ Pulsed power and weapons Groups of large, specially constructed, low-inductance high-voltage capacitors (capacitor banks) are used to supply huge pulses of current for many pulsed power applications. These include electromagnetic forming, Marx generators, pulsed lasers (especially TEA lasers), pulse forming networks, radar, fusion research, and particle accelerators. Large capacitor banks (reservoir) are used as energy sources for the exploding-bridge wire detonators or slapper detonators in nuclear weapons and other specialty weapons. Experimental work is under way using banks of capacitors as power sources for electromagnetic armour and electromagnetic railguns and coil guns.
➢ Power conditioning A 10,000-microfarad capacitor in a TRM-800 amplifier Reservoir capacitors are used in power supplies where they smooth the output of a full or half wave rectifier. They can also be used in charge pump circuits as the energy storage element in the generation of higher voltages than the input voltage. Capacitors are connected in parallel with the power circuits of most electronic devices and larger systems (such as factories) to shunt away and conceal current fluctuations from the primary power source to provide a "clean" power supply for signal or control circuits. Audio equipment, for example, uses several capacitors in this way, to shunt away power line hum before it gets into the signal circuitry. The capacitors act as a local reserve for the DC power source, and bypass AC currents from the power supply. This is used in car audio applications, when a stiffening capacitor compensates for the inductance and resistance of the leads to the lead-acid car battery.
35
➢ Power factor correction In electric power distribution, capacitors are used for power factor correction. Such capacitors often come as three capacitors connected as a three-phase load. Usually, the values of these capacitors are given not in farads but rather as a reactive power in volt-amperes reactive (VAr). The purpose is to counteract inductive loading from devices like electric motors and transmission lines to make the load appear to be mostly resistive. Individual motor or lamp loads may have capacitors for power factor correction, or larger sets of capacitors (usually with automatic switching devices) may be installed at a load center within a building or in a large utility substation.
➢ Suppression and coupling Signal coupling Because capacitors pass AC but block DC signals (when charged up to the applied dc voltage), they are often used to separate the AC and DC components of a signal. This method is known as AC coupling or "capacitive coupling". Here, a large value of capacitance, whose value need not be accurately controlled, but whose reactance is small at the signal frequency, is employed.
4.8 TRANSISTOR A bipolar (junction) transistor (BJT) is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications. Bipolar transistors are so named because their operation involves both electrons and holes. Charge flow in a BJT is due to bidirectional diffusion of charge carriers across a junction between two regions of different charge concentrations. This mode of operation is contrasted with unipolar transistors, such as field-effect transistors, in which only one carrier type is involved in charge flow due to drift. By design, most of the BJT collector current is due to the flow of charges injected from a high-concentration emitter into the base where they are minority carriers that diffuse toward the collector, and so BJTs are classified as minority carrier devices.
Fig 18. Schematic symbols for PNP- and NPN-type BJTs.
36
NPN BJT with forward-biased E B junction and reverse-biased B C junction. An NPN transistor can be considered as two diodes with a shared anode. In typical operation, the base-emitter junction is forward biased and the base collector junction is reverse biased. In an NPN transistor, for example, when a positive voltage is applied to the base emitter junction, the equilibrium between thermally generated carriers and the repelling electric field of the depletion region becomes unbalanced, allowing thermally excited electrons to inject into the base region. These electrons wander (or "diffuse") through the base from the region of high concentration near the emitter towards the region of low concentration near the collector. The electrons in the base are called minority carriers because the base is doped p-type which would make holes the majority carrier in the base. To minimize the percentage of carriers that recombine before reaching the collector base junction, the transistor's base region must be thin enough that carriers can diffuse across it in much less time than the semiconductor's minority carrier lifetime. In particular, the thickness of the base must be much less than the diffusion length of the electrons. The collector base junction is reverse-biased, and so little electron injection occurs from the collector to the base, but electrons that diffuse through the base towards the collector are swept into the collector by the electric field in the depletion region of the collector base junction. The thin shared base and asymmetric collector emitter doping is what differentiates a bipolar transistor from two separate and oppositely biased diodes connected in series.
➢ Voltage, current, and charge control The collector emitter current can be viewed as being controlled by the base emitter current (current control), or by the base emitter voltage (voltage control). These views are related by the current voltage relation of the base emitter junction, which is just the usual exponential current voltage curve of a p-n junction (diode). The physical explanation for collector current is the amount of minority-carrier charge in the base region. Detailed models of transistor action, such as the Gummel-Poon model, account for the distribution of this charge explicitly to explain transistor behavior more exactly. The charge-control view easily handles phototransistors, where minority carriers in the base region are created by the absorption of photons, and handles the dynamics of turn-off, or recovery time, which depends on charge in the base region recombining. However, because base charge is not a signal that is visible at the terminals, the current- and voltage-control views are generally used in circuit design and analysis. 37
In analog circuit design, the current-control view is sometimes used because it is approximately linear. That is, the collector current is approximately F times the base current. Some basic circuits can be designed by assuming that the emitter base voltage is approximately constant, and that collector current is beta times the base current. However, to accurately and reliably design production BJT circuits, the voltage-control (for example, Ebers Moll) model is required. The voltage-control model requires an exponential function to be taken into account, but when it is linearized such that the transistor can be modeled as a transconductance, as in the Ebers Moll model, design for circuits such as differential amplifiers again becomes a mostly linear problem, so the voltage-control view is often preferred. For trans linear circuits, in which the exponential I-V curve is key to the operation, the transistors are usually modeled as voltage controlled with transconductance proportional to collector current. In general, transistor level circuit design is performed using SPICE or a comparable analogue circuit simulator, so model complexity is usually not of much concern to the designer.
➢ Turn-on, turn-off, and storage delay The Bipolar transistor exhibits a few delay characteristics when turning on and off. Most transistors, and especially power transistors, exhibit long base storage time that limits maximum frequency of operation in switching applications. One method for reducing this storage time is by using a Baker clamp.
➢ Transistor 'alpha' and ‘beta’ The proportion of electrons able to cross the base and reach the collector is a measure of the BJT efficiency. The heavy doping of the emitter region and light doping of the base region cause many more electrons to be injected from the emitter into the base than holes to be injected from the base into the emitter. The common-emitter current gain is represented by βf OR hfe; it is approximately the ratio of the DC collector current to the DC base current in forward-active region. It is typically greater than 100 for small-signal transistors but can be smaller in transistors designed for highpower applications. Another important parameter is the common-base current gain, αF. The common-base current gain is approximately the gain of current from emitter to collector in the forward-active region. This ratio usually has a value close to unity; between 0.98 and 0.998. Alpha and beta are more precisely related by the following identities (NPN transistor):
38
➢ Structure
Fig 19. Simplified cross section of a planar NPN bipolar junction transistor [4].
Die of a KSY34 high-frequency NPN transistor, base and emitter connected via bonded wires A BJT consists of three differently doped semiconductor regions, the emitter region, the base region and the collector region. These regions are, respectively, p type, n type and p type in a PNP, and n type, p type and n type in a NPN transistor. Each semiconductor region is connected to a terminal, appropriately labeled: emitter (E), base (B) and collector (C). The base is physically located between the emitter and the collector and is made from lightly doped, high resistivity material. The collector surrounds the emitter region, making it almost impossible for the electrons injected into the base region to escape being collected, thus making the resulting value of very close to unity, and so, giving the transistor a large β. A cross section view of a BJT indicates that the collector base junction has a much larger area than the emitter base junction. The bipolar junction transistor, unlike other transistors, is usually not a symmetrical device. This means that interchanging the collector and the emitter makes the transistor leave the forward active mode and start to operate in reverse mode. Because the transistor's internal structure is usually optimized for forward-mode operation, interchanging the collector and the emitter makes the values of α and β in reverse operation much smaller than those in forward operation; often the α of the reverse mode is lower than 0.5. The lack of symmetry is primarily due to the doping ratios of the emitter and the collector. The emitter is heavily doped, while the collector is lightly doped, allowing a large reverse bias voltage to be applied before the collector base junction breaks down. The collector base junction is reverse biased in normal operation. The reason the emitter is heavily doped is to increase the emitter injection efficiency: the ratio of carriers injected by the emitter to those injected by the base. For high current gain, most of the carriers injected into the emitter base 39
junction must come from the emitter. The low-performance "lateral" bipolar transistors sometimes used in CMOS processes are sometimes designed symmetrically, that is, with no difference between forward and backward operation. Small changes in the voltage applied across the base emitter terminals causes the current that flows between the emitter and the collector to change significantly. This effect can be used to amplify the input voltage or current. BJTs can be thought of as voltage-controlled current sources, but are more simply characterized as current-controlled current sources, or current amplifiers, due to the low impedance at the base. Early transistors were made from germanium but most modern BJTs are made from silicon. A significant minority are also now made from gallium arsenide, especially for very highspeed applications
Fig 20. the symbol of an NPN bipolar junction transistor
NPN is one of the two types of bipolar transistors, consisting of a layer of P-doped semiconductor (the "base") between two N-doped layers. A small current entering the base is amplified to produce a large collector and emitter current. That is, an NPN transistor is "on" when its base is pulled high relative to the emitter. Most of the NPN current is carried by electrons, moving from emitter to collector as minority carriers in the P-type base region. Most bipolar transistors used today are NPN, because electron mobility is higher than Hole mobility in semiconductors, allowing greater currents and faster operation.
Fig 21. The symbol of a PNP Bipolar Junction transistor
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The other type of BJT is the PNP, consisting of a layer of N-doped semiconductor between two layers of P-doped material. A small current leaving the base is amplified in the collector output. That is, a PNP transistor is "on" when its base is pulled low relative to the emitter. The arrows in the NPN and PNP transistor symbols are on the emitter legs and point in the direction of the conventional current flow when the device is in forward active mode. A mnemonic device for the NPN / PNP distinction, based on the arrows in their symbols and the letters in their names, is not pointing in for NPN and pointing in for PNP.
➢ The BC548 is a general-purpose silicon NPN BJT transistor found commonly in European electronic equipment. If the TO-92 package is held in front of one's face with the flat side facing toward you and the leads downward, (see picture) the order of the leads, from left to right is collector, base, emitter.
Fig 22. BC548 silicon NPN BJT Transistor [4].
➢ Specifications The exact specs of a given device depend on the manufacturer. It is important to check the datasheet for the exact device and brand you are dealing with. Philips and Telefunken are two manufacturers of the BC548. Vcbo = 30 V , Ic = 100 mA ,Ptotal = 50 mW ,ft = 300 MHz The BC548 is a member of a larger group of similarly numbered transistors. Other part numbers have different characteristics and ratings. Its complement is the BC558. A family of older "BC" transistors predates the TO-92 BC54x series, the BC107, BC108 and BC109, (with complements BC177, BC178 and BC179). These are generally housed in the TO-18 metal package, the same as what the North American 2N2222 uses. These older transistors have similar characteristics as the TO-92 BC5xx devices and are electrically interchangeable. There are many other devices based on the BC54x family, such as the surface-mount versions of the BC547, 548 and 549; the BC847, BC848 and BC8. [2] 41
4.9 BREADBOARD A breadboard is used to build and test circuits quickly before finalizing any circuit design. The breadboard has many holes into which circuit components like ICs and resistors can be inserted. A typical breadboard is shown below:
Fig 23. Breadboard [3]. The bread board has strips of metal which run underneath the board and connect the holes on the top of the board. The metal strips are laid out as shown below. Note that the top and bottom rows of holes are connected horizontally while the remaining holes are connected vertically.
Fig 24. Internal structure of breadboard [3].
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CHAPTER FIVE RESULT AND IMPLEMENTATION This chapter of the project is connected with the implementation result of the laser based audio transmission and alarm system. The final result of our project is shown below
Figure.25 Final result of alarm system.
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Figure. 26 Audio transmitter final result.
Figure .27 audio receiver final result. 44
CHAPTER SIX CONCLUSION & RECOMMENDATION 5.1 CONCLUSION The Laser Based Alarm System and audio communication project was built to our satisfaction. This project is about how to prevent theft in homes, offices, banks, museums etc, and how to transfer any audio information though laser light. this project can be implemented by both wired and wireless technologies. Another application of this instrument is as an "ANTI-THEFT SYSTEM", that means to protect vehicles from kidnapping. In short, we are sure that this device is highly useful to mankind especially present scenario. After the successful working of our project, it can be concluded that this project is suitable for communication. There can be further up gradations in the project which could lead to a much better system for communication. Some of the possible ways are as follows: •
Instead of the short-range laser, high range lasers can be used which range a few hundred kilometers
5.2 RECOMMENDATION WE recommend to other laser based audio transmitter and alarm system project
•
In future, it can be commissioned in satellites for communication.
•
Lasers can also transmit through glass; however, the physical properties of the glass have to be considered and hence can be used for a very large distance communication.
•
It can be used in inaccessible areas.
•
In the future, we try to upgraded in GSM based laser alarm system and audio transmitter
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REFERENCES [1] B.G. Boone, R.S. Bokulic , G.B. Andrews, R.L. McNutt, Jr and N. Dagalakisb Optical and microwave communications system conceptual design for a realistic interstellar explorer [2] Yunbin Song Optical Communication Systems for Smart Dust. [3] M. Last, B.S. Leibowitz, B. Cagdaser, A. Jog, L. Zhou, B. Boser, K.S.J. Pister Toward a Wireless Optical Communication Link between Two Small Unmanned Aerial Vehicles [4] Andrew W. Rebeiro and Rodney Tan Free Space Optical Laser Communication Link. [5] Sanjiba Kumar sahu Laser based intruder alarm [6] SAURABH KOLHE, VATSAL TRIPATHI, VIPIN PATEL, VIRENDRA PATEL, VIVEK BHARDWAJ Laser based communication link
APPENDIX A
APPENDIX B
