CHAPTER 1
INTRODUCTION
[1]
1. INTRODUCTION OF PROJECT
1.1 PROJECT DEFINITION
Laser as a communication medium can provide a good substitute for the pr...
1.2 PROJECT OVERVIEW
Using this circuit we can communicate with your own neighbours wirelessly. Instead of RF
signals, lig...
CHAPTER 2
BLOCK DIAGRAM AND ITS
DESCRIPTION
[4]
2.1 BASIC BLOCK DIAGRAM
Fig.2.1.Basic Block Diagram
[5]
CONDERSER MIC TRANSMITTING
SECTION
LASER TORCH
RECEIVING
SECTION
L...
2.2 BLOCK DIAGRAM DESCRIPTION
2.2.1 CONDENSER MICROPHONE
It is also called a capacitor or electrostatic microphone. Conden...
body of the torch connected to the emitter of BD139 and the spring loaded lead protruding from
inside the torch to circuit...
CHAPTER 3
SCHEMATIC DIAGRAM
[8]
CIRCUIT DESCRIPTION
There are two main part of the circuit.
3.1 Transmitter Circuit.
3.2 Receiver Circuit.
3.3 Microphone....
Fig.3.1. Transmitter Circuit
A laser diode needs a certain value of current, called the threshold current, before it emits...
diode and the lens also acts as a heat sink. The laser diode should not be powered without the metal
housing in place. The...
Fig.3.2. Receiver Circuit
The transmitted signal is picked up by the photo detector diode in the receiver (shown in
Fig.3....
Sound is an amazing thing. All of the different sounds that we hear are caused by minute
pressure differences in the air a...
CHAPTER 4
HARDWARE DESIGN AND DESCRIPTION
[14]
[15]
4.1 WORKING
In all of the laser communicators on this page, the laser light is amplitude modulated. This
simply means that...
4.2 LIST OF COMPONENTS
a. Operational Amplifier.
b. VR (potentiometer/resistance Variac/Trimmer).
c. Capacitor.
d. Digital...
CHAPTER 5
DESCRIPTION OF COMPONENT
[18]
5.1 OPERATIONAL AMPLIFIER
An op-amp is a high-gain, direct-coupled differential linear amplifier whose response
characteri...
the complexity of the internal circuitry of an op amp, the op amp symbol is used exclusively in
circuit diagrams.
5.1.1 IC...
The above figure
shows the basic circuit,
including the negative
feedback loop of an op
amp. The output is fed
back to the...
Block diagram illustrating negative feedback. yo is the output, yi is called the reference or set
point that the output, y...
Variable resistors consist of a resistance track with connections at both ends and a wiper which
moves along the track as ...
5.3 CAPACITOR
The capacitor plays a crucial role in electronics -- it stores electrons for when they are needed
most. Capa...
In practice, capacitances range from 1 pF to about 150 000 µF: they depend on the area A of
the plates (large A gives larg...
5.3.1.2 MICA
Mica is naturally occurring mineral, which splits into very thin sheets of uniform thickness.
Plates are form...
Tantalum electrolytic capacitors can be used instead of aluminum in low voltage circuits where
values do not exceed about ...
5.4 DIGITAL VOLTMETER
A multimeter or a multitester, also known
as a volt/ohm meter or VOM, is an electronic
measuring ins...
Modern digital multimeters may have an embedded computer, which provides a wealth of
convenience features. Measurement enh...
5.5 BATTERY (9VOLT)
An electrical battery is one or more electrochemical
cells that convert stored chemical energy into el...
5.6 LASER TORCH
For this project we have removed the laser
assembly from a small laser pointer. The power
supply circuit i...
microphone wants to take varying pressure waves in the air and convert them into varying electrical
signals. There are fiv...
A voltage is required across the capacitor for this to work. This voltage is supplied either by
a battery in the mic or by...
Further investigation will show that the diode
current (and thus the output voltage) is directly
proportional to light int...
A photodiode is a semiconductor diode that functions as a photo detector. Photodiodes are
packaged with either a window or...
Because of their greater band gap, silicon-based photodiodes generate less noise than
germanium-based photodiodes, but ger...
Phototransistors are solid-state light detectors
with internal gain that are used to provide analog or
digital signals. Th...
nanometers (nm). Rise time, the time that elapses when a pulse waveform increases from 10% to
90% of its maximum value, is...
Fig.5.11.2 Working Of LED
1. ACTION
An LED consists of a junction diode made from the semiconducting compound gallium
arse...
2. EXTERNAL RESISTOR
An LED must have a resistor connected in series to limit the current through the LED;
otherwise it wi...
displays are usually designed to work on a 5 V supply. Each segment needs a separate current-
limiting resistor and all th...
k. Focus: The solid package of the LED can be designed to focus its light. Incandescent and
fluorescent sources often requ...
The segments of a 7-segment display are referred to by the letters A to G, as shown to the
right, where the optional DP de...
CHAPTER 6
PCB DESIGN AND FABRICATION
[44]
6.1 PCB DESIGN
Designing of PCB is a major step in the production of PCB is a major. It forms a distinct factor
in electro...
6.2 PCB FABRICATION
PCB fabrication involves the following steps
a. First the layout of the PCB is generated using the sof...
6.3 PRINTED CIRCUIT BOARD (PCB) LAYOUT
6.3.1 TRANSMITTER PRINTED CIRCUIT BOARD
Fig.6.3.1 PCB Of Transmitter Circuit
[47]
6.3.2 RECEIVER PRINTED CIRCUIT BOARD
Fig.6.3.2 PCB of Receiver Circuit
[48]
CHAPTER 7
LIST OF REQUIRED TOOLS AND
INSTRUMENT
[49]
7.1 Following tools and instruments are used for preparing the project
a. Soldering iron.
b. Desoldering pump.
c. Drill Ma...
CHAPTER 8
COMPONENT REQUIRED
[51]
8.1 COMPONET REQUIRED FOR TRANSMITTER
Table.8.1
Sl. No. Name of the component Quantity
1. Resistance (8.2 KΩ) 2
2. Resista...
2. Resistor (4.7MΩ) 1
3. Resistor (2.2 KΩ) 2
4. Resistor (1 KΩ) 1
5. Resistor (10 KΩ) 1
6. Variable resistor (50 KΩ) 1
7. ...
CHAPTER 9
CONSTRUCTION AND TESTING
9.1 CONSTRUCTION
As the photos show, both the transmitter and the receiver are built on...
The diode can be mounted on the board, or connected with leads to it. Connect a clip lead to the
inside of the laser point...
you are not getting an output, check the circuit. You won't see the laser beam intensity change with
the modulating signal...
CHAPTER 10
SETTING UPLINK AND PRECAUTION
10.1 SETTING UPLINK
Once you've tested the link, you'll probably be keen to put i...
But the longer the distance between the transmitter and the receiver, the more critical the
adjustments. For example, for ...
at the beam. We should be very careful with higher power lasers and lasers on that power
range that emit invisible radiati...
CHAPTER 11
ADVANTAGES AND DISADVANTAGES
11.1 ADVANTAGES
a. Less costly.
b. Circuit can be easily constructed.
c. High data...
h. Lasers can also transmit through glass, however the physical properties of the glass have to
be considered.
i. Narrow b...
CHAPTER 12
PROBLEM FACED
12.1 PROBLEM FACED
Although this project was successfully completed, however a few hurdles that c...
[63]
CHAPTER 13
APPLICATIONS
13 APPLICATIONS
a. Using this circuit we can communicate with our neighbors wirelessly.
b. It can ...
CONCLUSION
After the successful working of the project, it can be concluded that this project is suitable
for easily commu...
REFERENCES
a. Choudhary, D.Roy; Jain, Shalin. B; Linear Integrated Circuits; New Age Internationl
Publishers, Third Editio...
f. Rai A.; Vallave Electronics Device & Circuits- 2007.
g. Wilson, J. & Hawkes; J.F.B. (1987). Lasers: Principles and Appl...
[68]
[69]
[70]
UA741
GENERAL PURPOSE OF SINGLE OP-AMP
[71]
[72]
[73]
[74]
[75]
[76]
L 14F1 L 14F2
[77]
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electrical_project_chandresh_report on laser Transmitter and Receiver_ final report matter

  1. 1. CHAPTER 1 INTRODUCTION [1]
  2. 2. 1. INTRODUCTION OF PROJECT 1.1 PROJECT DEFINITION 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. Laser communications offers a viable alternative to RF 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 present paper involves the study of wireless, open channel communication system using laser a carrier for voice signals. [2]
  3. 3. 1.2 PROJECT OVERVIEW Using this circuit we can communicate with your own neighbours wirelessly. Instead of RF signals, light from a laser torch is used as the carrier in the circuit. The laser torch can transmit light up to a distance of about 500 meters. The phototransistor of the receiver must be accurately oriented towards the laser beam from the torch. If there is any obstruction in the path of laser beam, no sounds will be heard from the receiver. The transmitter circuit comprises condenser microphone transistor amplifier BC548 (T1) followed by an pomp stage built around μA741 (IC1). The gain of the op-amp can be controlled with the help of 1MΩ potentiometer VR1.The AF output from IC1 is coupled to the base of transistor BD139 (T2), which, in turn, modulates the laser beam. The transmitter uses 9V power supply. However, the 3-volt laser torch (after removal of its battery) can be directly connected to the circuit—with the body of the torch connected to the emitter of BD139 and the spring-loaded lead protruding from inside the torch to circuit ground. The receiver circuit (Fig. 2) uses an NPN phototransistor as the light sensor that is followed by a two-stage transistor preamplifier and LM386-based audio Power amplifier. The receiver does not 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. To avoid 50Hz humming noise in the speaker, keep the phototransistor away from AC light sources such as bulbs. The reflected sunlight, however, does not cause any problem. But the sensor should not directly face the sun. [3]
  4. 4. CHAPTER 2 BLOCK DIAGRAM AND ITS DESCRIPTION [4]
  5. 5. 2.1 BASIC BLOCK DIAGRAM Fig.2.1.Basic Block Diagram [5] CONDERSER MIC TRANSMITTING SECTION LASER TORCH RECEIVING SECTION LOUD SPEAKER
  6. 6. 2.2 BLOCK DIAGRAM DESCRIPTION 2.2.1 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. 2.2.2 TRANSMITTING SECTION The transmitter section comprises condenser microphone, transistor amplifier BC548 followed by an op-amp stage build around IC1. The gain of the op-amp can be controlled with the help of 1MΩ potentiometer VR1. The AF output from IC1 is coupled to the base of transistor BD139, which is turn, modulates the laser beam. The transmitter uses 9V power supply. However, the 3V laser torch(after the removal of its battery) can be directly connected to the circuit with the [6]
  7. 7. body of the torch connected to the emitter of BD139 and the spring loaded lead protruding from inside the torch to circuit ground. 2.2.3 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 fibre 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. 2.2.4 RECEIVING SECTION The receiver circuit uses an NPN phototransistor as the light sensor that is followed by a two stage 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. 2.2.5 LOUD SPEAKER 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. [7]
  8. 8. CHAPTER 3 SCHEMATIC DIAGRAM [8]
  9. 9. CIRCUIT DESCRIPTION There are two main part of the circuit. 3.1 Transmitter Circuit. 3.2 Receiver Circuit. 3.3 Microphone. 3.1 TRANSMITTER CIRCUIT [9]
  10. 10. Fig.3.1. Transmitter Circuit A laser diode needs a certain value of current, called the threshold current, before it emits laser light. A further increase in this current produces a greater light output. The relationship between output power and current in a laser diode is very linear, once the current is above the threshold, giving a low distortion when the beam is amplitude modulated. For example, the 650 nm 5mW laser diode used in this project has a typical threshold current of 30 mA and produces its full output when the current is raised by approximately 10 mA above the threshold to 40 mA. Further increasing the current will greatly reduce the life of the laser diode, and exceeding the absolute maximum of 80 mA will destroy it instantly. Laser diodes are very fragile and will not survive electrostatic discharges and momentary surges. However, if used within specifications, the typical life of one of these lasers is around 20,000 hours. In the transmitter circuit (Fig.3.1) the laser diode is supplied via an adjustable constant-current source. Note that the metal housing for the laser [10]
  11. 11. diode and the lens also acts as a heat sink. The laser diode should not be powered without the metal housing in place. The increasing the voltage at VR1 reduces the laser current. The setting of VR1 determines the quiescent brightness of the laser beam, and therefore the overall sensitivity of the system. The electric microphone is powered through R1 and is coupled to the non inverting input of 1C1 via capacitor. This input is held at a fixed DC voltage to give a DC output to bias. 3.2 RECEIVER CIRCUIT [11]
  12. 12. Fig.3.2. Receiver Circuit The transmitted signal is picked up by the photo detector diode in the receiver (shown in Fig.3.2). The output voltage of this diode is amplified by the common emitter amplifier around T4. This amplifier has a gain of 20 or so, and connects via VR2 to IC2, an LM386 basic power amplifier IC with a gain internally set to 20.This IC can drive a speaker with a resistance as low as four ohms, and 35OmW when the circuit is powered from a 9V supply. Increasing the supply voltage will increase the output power marginally. Incidentally, the photodiode used for this project has a special clear package, so it responds to visible light, and not just infrared. 3.3 MICROPHONE [12]
  13. 13. Sound is an amazing thing. All of the different sounds that we hear are caused by minute pressure differences in the air around us. What's amazing about it is that the air transmits those pressure changes so well, and so accurately, over relatively long distances. It was a metal diaphragm attached to a needle, and this needle scratched a pattern onto a piece of metal foil. The pressure differences in the air that occurred when you spoke toward the diaphragm moved the diaphragm, which moved the needle, which was recorded on the foil. When you later ran the needle back over the foil, the vibrations scratched on the foil would then move the diaphragm and recreate the sound. The fact that this purely mechanical system works shows how much energy the vibrations in the air can have! All modern microphones are trying to accomplish the same thing as the original, but do it electronically rather than mechanically. A microphone wants to take varying pressure waves in the air and convert them into varying electrical signals. There are five different technologies commonly used to accomplish this conversion. We use condenser microphone in our project. 3.3.1 CONDENSER MICROPHONE A condenser microphone is essentially a capacitor, with one plate of the capacitor moving in response to sound waves. The movement changes the capacitance of the capacitor, and these changes are amplified to create a measurable signal. Condenser microphones usually need a small battery to provide a voltage across the capacitor. [13]
  14. 14. CHAPTER 4 HARDWARE DESIGN AND DESCRIPTION [14]
  15. 15. [15]
  16. 16. 4.1 WORKING In all of the laser communicators on this page, the laser light is amplitude modulated. This simply means that the amount of light the laser emits varies over time. To understand what is going on, it helps to consider how a loudspeaker makes sound. A loudspeaker is a paper cone attached to a coil of wire that sits in a magnetic field from a strong permanent magnet. When an electric current flows in the loudspeaker coil, the coil becomes an electromagnet, and it moves toward or away from the permanent magnet. As it moves, the paper cone pushes on the air around it, compressing the air in front of it, and expanding the air behind it. Waves of compressed and expanded air travel to your ear, and cause your eardrum to move in time to the movements of the paper cone. The laser communicator adds two components to the loudspeaker concept. We take the electrical signal that goes to the loudspeaker, and connect it instead to the laser, so the laser gets brighter and dimmer as the electric current varies. The second component is the receiver, which converts the light back into an electric current. This current varies in time with the first current, because the amount of light that it receives is varying in time. This second electric current is used to move the paper cone of a loudspeaker, just as before. However, now the loudspeaker can be quite a distance away from the original electric current, without any wires connecting the two. [16]
  17. 17. 4.2 LIST OF COMPONENTS a. Operational Amplifier. b. VR (potentiometer/resistance Variac/Trimmer). c. Capacitor. d. Digital Multimeter. e. Battery (9V). f. Laser Torch. g. Microphone. h. Integrated Circuit. i. Photodiodes. j. Phototransistor. k. Light Emitting Diode (LED). [17]
  18. 18. CHAPTER 5 DESCRIPTION OF COMPONENT [18]
  19. 19. 5.1 OPERATIONAL AMPLIFIER An op-amp is a high-gain, direct-coupled differential linear amplifier whose response characteristics are externally controlled by negative feedback from the output to the input. OP-amps, widely used in computers, can perform mathematical operations such as summing, integration, and differentiation. OP-amps are also used as video and audio amplifiers, oscillators, etc. in the communication electronics. Fig.5.1 Symbol of Op-Amp Because of their versatility op-amps are widely used in all branches of electronics both in digital and linear circuits. OP-amps lend themselves readily to IC manufacturing techniques. Improved IC manufacturing techniques, the op-amp's adaptability, and extensive use in the design of new equipment have brought the price of IC ops amps from very high to very reasonable levels. These facts ensure a very substantial role for the IC op-amp in electronics. Fig. (5.1) shows the symbol for an op-amp. Note that the operational amplifier has two inputs marked (-) and (+). The minus input is the inverting input. A signal applied to the minus terminal will be shifted in phase 180° at the output. The plus input is the non-inverting input. A signal applied to the plus terminal will appear in the same phase at the output as at the input. Because of [19]
  20. 20. the complexity of the internal circuitry of an op amp, the op amp symbol is used exclusively in circuit diagrams. 5.1.1 IC-741 An operational amplifier often referred to as op Amp, is a very high gain high performance amplifier designed to amplify ac and dc signal voltages. Modern integrated circuit technology and large-scale production techniques have brought down the prices of such amplifiers within reach of all amateurs, experimenters and hobbyists. The Op Amp is now used as a basic gain element, like an elegant transistor, in electronic circuits. Fig.5.1.1 (a) IC-741 The availability of two input terminals simplifies feedback circuitry and makes the operational amplifier a highly versatile device. If a feedback is applied from the output to the inverting input terminal, the result is a negative feedback, which gives a stable amplifier with precisely controlled gain characteristics. On the other hand, if the feedback is applied to the non- inverting input, the result is positive feedback, which gives oscillators and multivibrator. Special effects are obtained by combination of both types of feedback. Fig.5.1.1 (b) 5.1.2 NEGATIVE FEEDBACK CONTROL [20]
  21. 21. The above figure shows the basic circuit, including the negative feedback loop of an op amp. The output is fed back to the inverting input terminal in order to provide negative feedback for the amplifier. The input signal is applied to the inverting input. As a result, the output will be inverted. It is possible to operate the op amp as a non- inverting amplifier by applying the signal to the plus input. In this circuit the feedback network is still connected to the inverting input. In more recent times negative feedback has been used extensively in the electronics industry to confer, among other things, electrical stability to electronic devices. In fact without negative feedback considerable swathes of modern technology would not be able to function. Given the ubiquity of negative feedback in man-made devices Fig.5.1.2 Negative feedback control It should therefore come as no surprise to discover that living systems employ feedback at many levels, ranging from gene regulatory network, signaling, network, metabolic networks to neural networks and hormonal control systems. It is possible to do a simple analysis which illustrates some of the essential properties conferred by negative feedback. We can represent a negative feedback system using the following block diagram: [21]
  22. 22. Block diagram illustrating negative feedback. yo is the output, yi is called the reference or set point that the output, yo, must match. ‘d’ is a disturbance acting on the controller A. ‘k’ represents the fraction of output yo returned to yi as feedback. The block diagram shown above can be expressed in algebraic form: yo = (A + d)(yi � kyo) where it is assumed that the disturbance d adds to the controller. By rearrangement we obtain: yo = yi(A + d) kd + kA If we assume that the gain in the controller, A, and the feedback, k are strong, that is Ak _ 0, then the expression is simplified to: yo = yi k This equation highlights a number of effects, the first is that the controller A, and any disturbances d are eliminated from the equation and that the output yo is a linear function of the set point yi. The performance of the feedback is therefore dependent on the quality of the feedback mechanism, k and is independent of either the controller or any disturbances. In relation to actual devices, such as a stream engine, this is a desirable property. It means that the performance of the steam engine is independent of the load and any component variation in the construction of the engine, the only requirement is that the feedback mechanism is reliable. Classical control theory has an extensive framework for analyzing feedback systems, however the terminology and sometimes the methodology does not always translate easily to biological systems. In this section we will examine the use of control coefficients and elasticities to understand the properties of negative feedback. 5.2 VARIABLE RESISTANCE [22]
  23. 23. 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 k linear track. 1M LOG means 1 M logarithmic track. Some variable resistors are designed to be mounted directly on the circuit board. F ig.5.2 Variable resistance 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. The potentiometer is a resistor of variable resistance. It has three terminals; a fixed resistance is found between two of the terminals and the third terminal slides along the fixed resistor. Often, it is used to control the volume in an audio amplifier. [23]
  24. 24. 5.3 CAPACITOR The capacitor plays a crucial role in electronics -- it stores electrons for when they are needed most. Capacitors consist of two conducting plates placed near each other. Inside the capacitor, the terminals connect to two metal plates separated by a dielectric. The dielectric can be air, paper, plastic or anything else that does not conduct electricity and keeps the plates from touching each other. A capacitor stores electric charge. It does not allow direct current to flow through it and it behaves as if alternating current does flow through. In its simplest form it consists of two parallel metal plates separated by an insulator called the dielectric. The symbols for fixed and variable capacitors are given in fig. Polarized types must be connected so that conventional current enters their positive terminal. Non-polarized types can be connected either way round. Fig.5.3 Capacitor The capacitance (C) of a capacitor measures its ability to store charge and is stated in farads (f). The farad is sub-divided into smaller, more convenient units. 1 microfarad (1µF) = 1 millionth of a farad = 10 -6 F 1 nanofarad (1 nF) = 1 thousand- millionth of a farad = 10 -9 F 1 picofarad (1pF ) = 1 million-millionth of a farad = 10 -12 F [24]
  25. 25. In practice, capacitances range from 1 pF to about 150 000 µF: they depend on the area A of the plates (large A gives large C), the separation d of the plates (small d gives large C) and the material of the dielectric (e.g. certain plastics give large C). When selecting a particular job, the factors to be considered are the value (again this is not critical in many electronic circuits), the tolerance and the stability. There are two additional factors. a. THE WORKING VOLTAGE The largest voltage (d.c.or lead a.c.) which can be applied across the capacitor and is often marked on it, e.g. 30V wkg. It is exceeded, the dielectric breaks down and permanent damage may result. b. THE LEAKAGE CURRENT No dielectric is a perfect insulator but the loss of charge through it as leakage current’ should be small. 5.3.1 FIXED CAPACITORS Fixed capacitors can be classified according to the dielectric used; their properties depend on this. The types described below in (i), (ii) and (iii) are non-polarized, those in (iv) are polarized. 5.3.1.1 POLYESTER Two strips of polyester film (the plastic dielectric) are wound between two strips of aluminum foil (the plates). Two connections, one to each strip of foil, form the capacitor leads. In the metallized version, films of metal are deposited on the plastic and act as the plates. Their good all-round properties and small size make them suitable for many applications in electronics. Values range from 0.01µF to 10µF or so and are usually marked (in pF) using the resistor colour code. Polycarbonate capacitors are similar to the polyester type; they have smaller leakage currents and better stability but cost more. [25]
  26. 26. 5.3.1.2 MICA Mica is naturally occurring mineral, which splits into very thin sheets of uniform thickness. Plates are formed by depositing a silver film on the mica or by using interleaving sheets of aluminum foil. Their tolerance is low ( + 1% ), stability and working voltage high, leakage current low but they are used in radio frequency tuned circuits where low loss is important and are pictured in figs. Polystyrene capacitors have similar though not quite so good properties as mica types but are cheaper. 5.3.1.3 CERAMIC There are several types depending on the ceramic used. One type has similar properties to mica and is used in radio frequency circuits. In another type, high capacitance values are obtained with small size, but stability and tolerance are poor; they are useful where exact values are not too important. They may be disc, rod- or plate-shaped. A disc-shaped capacitor is shown in fig. Values range from 10pF to 1µF. 5.3.1.4 ELECTROLYTE In the aluminum type the dielectric is an extremely thin layer of aluminum oxide which is formed electrolytically. Their advantages are high values (up to 150 000µF) in a small volume and cheapness. Their disadvantages are wide tolerance (-20 to + 100% of the value printed on them), high leakage current and poor stability but they are used where these factors do not matter and high values are required, e.g. in power supplies. Examples are shown in Fig. Electrolytes are polarized. Usually their positive terminal is marked with a +VE or by a groove; often the aluminum can is the negative terminal. The d.c. leakage current maintains the oxide layer, otherwise reversed polarity (or disuse) will cause the layer to deteriorate. [26]
  27. 27. Tantalum electrolytic capacitors can be used instead of aluminum in low voltage circuits where values do not exceed about 100 uF. They have lower leakage currents. Fig.5.3 Capacitors [27]
  28. 28. 5.4 DIGITAL VOLTMETER A multimeter or a multitester, also known as a volt/ohm meter or VOM, is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter may include features such as the ability to measure voltage, current and resistance. Multimeters may use analog or digital circuits—analog multimeters and digital multimeters (often abbreviated DMM or DVOM.) Analog instruments are usually based on a microammeter whose pointer moves over a scale calibration for all the different measurements that can be made; digital instruments usually display digits, but may display a bar of a length proportional to the quantity measured. Fig.5.4 Digital voltmeter A multimeter can be a hand-held device useful for basic fault finding and field service work or a bench instrument which can measure to a very high degree of accuracy. They can be used to troubleshoot electrical problems in a wide array of industrial and household devices such as electronic equipment, motor controls, domestic appliances, power supplies, and wiring systems. Modern multimeters are often digital due to their accuracy, durability and extra features. In a digital multimeter the signal under test is converted to a voltage and an amplifier with electronically controlled gain preconditions the signal. A digital multimeter displays the quantity measured as a number, which eliminates parallax errors. [28]
  29. 29. Modern digital multimeters may have an embedded computer, which provides a wealth of convenience features. Measurement enhancements available include: a. Auto-ranging, which selects the correct range for the quantity under test so that the most significant digits are shown. For example, a four-digit multimeter would automatically select an appropriate range to display 1.234 instead of 0.012, or overloading. Auto-ranging meters usually include a facility to 'freeze' the meter to a particular range, because a measurement that causes frequent range changes is distracting to the user. Other factors being equal, an auto-ranging meter will have more circuitry than an equivalent, non-auto- ranging meter, and so will be more costly, but will be more convenient to use. b. Sample and hold, which will latch the most recent reading for examination after the instrument is removed from the circuit under test. c. Current-limited tests for voltage drop across semiconductor junctions. While not a replacement for a transistor tester, this facilitates testing diodes and a variety of transistor types. d. A graphic representation of the quantity under test, as a bar graph. This makes go/no-go testing easy, and also allows spotting of fast-moving trends. e. A low-bandwidth oscilloscope. f. Automotive circuit testers, including tests for automotive timing and dwell signals. g. Simple data acquisition features to record maximum and minimum readings over a given period, or to take a number of samples at fixed intervals. h. Integration with tweezers for surface-mount technology. i. A combined LCR meter for small-size SMD and through-hole components. [29]
  30. 30. 5.5 BATTERY (9VOLT) An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery (or "voltaic pile") in 1800 by Alessandro Volta, batteries have become a common power source for many household and industrial applications. Electrons collect on the negative terminal of the battery. If you connect a wire between the negative and positive terminals, the electrons will flow from the negative to the positive terminal as fast as they can (and wear out the battery very quickly -- this also tends to be dangerous, especially with large batteries, so it is not something you want to be doing). Normally, you connect some type of load to the battery using the wire. Fig.5.5 Battery (9volt) Inside the battery itself, a chemical reaction produces the electrons. The speed of electron production by this chemical reaction (the battery's internal resistance) controls how many electrons can flow between the terminals. Electrons flow from the battery into a wire, and must travel from the negative to the positive terminal for the chemical reaction to take place. That is why a battery can sit on a shelf for a year and still have plenty of power unless electrons are flowing from the negative to the positive terminal, the chemical reaction does not take place. Once you connect a wire, the reaction starts. If you look at any battery, you'll notice that it has two terminals. One terminal is marked positive (+VE), while the other is marked negative (-VE). In normal flashlight batteries, the ends of the battery are the terminals. In a large car battery, there are two heavy lead posts that act as the terminals. [30]
  31. 31. 5.6 LASER TORCH For this project we have removed the laser assembly from a small laser pointer. The power supply circuit is the green board attached to the brass laser head. We carry similar laser pointers in our catalog that are easily disassembled for this project. The power supply circuit came conveniently marked with a plus and a minus next to two holes in the board. We solder the black negative lead from the battery clip to the hole marked minus. We solder one of the coil leads to the hole marked plus. We solder the red positive lead of the battery clip to the other lead from the coil. Fig.5.6 Laser torch 5.7 MICROPHONE Sound is an amazing thing. All of the different sounds that wehear are caused by minute pressure differences in the air around us. What's amazing about it is that the air transmits those pressure changes so well, and so accurately, over relatively long distances. It was a metal diaphragm attached to a needle, and this needle scratched a pattern onto a piece of metal foil. The pressure differences in the air that occurred when you spoke toward the diaphragm moved the diaphragm, which moved the needle, which was recorded on the foil. When you later ran the needle back over the foil, the vibrations scratched on the foil would then move the diaphragm and recreate the sound. The fact that this purely mechanical system works shows how much energy the vibrations in the air can have! All modern microphones are trying to accomplish the same thing as the original, but do it electronically rather than mechanically. A [31]
  32. 32. microphone wants to take varying pressure waves in the air and convert them into varying electrical signals. There are five different technologies commonly used to accomplish this conversion. We use condenser microphone in our project. 5.7.1 CONDENSER MICROPHONE A condenser microphone is essentially a capacitor, with one plate of the capacitor moving in response to sound waves. Condenser means capacitor, an electronic component which stores energy in the form of an electrostatic field. The term condenser is actually obsolete but has stuck as the name for this type of microphone, which uses a capacitor to convert acoustical energy into electrical energy. Condenser microphones require power from a battery or external source. The resulting audio signal is stronger signal than that from a dynamic. Condensers also tend to be more sensitive and responsive than dynamics, making them well- suited to capturing subtle nuances in a sound. They are not ideal for high-volume work, as their sensitivity. Fig.5.7.1 Condenser Microphone A capacitor has two plates with a voltage between them. In the condenser mic, one of these plates is made of very light material and acts as the diaphragm. 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. When the plates are further apart, capacitance decreases and a discharge current occurs. [32]
  33. 33. A voltage is required across the capacitor for this to work. This voltage is supplied either by a battery in the mic or by external phantom power. The electrets condenser mic uses a special type of capacitor which has a permanent voltage built in during manufacture. This is somewhat like a permanent magnet, in that it doesn't require any external power for operation. However good electrets condenser mics usually include a pre- amplifier which does still require power. Other than this difference, you can think of an electret condenser microphone as being the same as a normal condenser. 5.8 INTEGRATED CIRCUIT An integrated circuit is a pre-made circuit shrunk down to small size and put on a chip. IC’s save circuit makers time by serving common purposes like amplifying a signal which would otherwise have to be done by a new circuit built from scratch every time. Fig.5.8 Integrated circuit 5.9 PHOTODIODES If a conventional silicon diode is connected in the reverse-biased circuit, negligible current will flow through the diode and zero voltage will develop across R1. If the diode casing is now carefully removed so that the diode's semiconductor junction is revealed, and the junction is then exposed to visible light in the same circuit, the diode current will rise, possibly to as high as 1 mA, producing a significant output across R1. [33]
  34. 34. Further investigation will show that the diode current (and thus the output voltage) is directly proportional to light intensity, and that the diode is therefore photosensitive. In practice, all silicon junctions are photosensitive, and a photodiode can be regarded as a conventional diode housed in a case that lets external light reach its photosensitive semiconductor junction. In use, the photodiode is reverse biased and the output voltage is taken from across a series- connected load resistor. This resistor may be connected between the diode and ground, or between the diode and the positive supply line. The human eye is sensitive to a range of light radiation, It has a peak spectral response to the color green, which has a wave length of about 550 nm, but has a relatively low sensitivity to the color violet (400 nm) at one end of the spectrum and to dark red (700 nm) at the other. Photodiodes also have spectral response characteristics, and these are determined by the chemistry used in the semiconductor junction material. Fig.5.9 Photodiode Circuit Photodiodes have a far lower light-sensitivity than cadmium-sulphide LDRs, but give a far quicker response to changes in light level. Generally, LDRs are ideal for use in slow- acting direct- coupled light-level sensing applications, while photodiodes are ideal for use in fast-acting AC- coupled signaling applications. Typical photodiode applications include IR remote-control circuits. [34]
  35. 35. A photodiode is a semiconductor diode that functions as a photo detector. Photodiodes are packaged with either a window or optical fibre connection, in order to let in the light to the sensitive part of the device. They may also be used without a window to detect vacuum UV or X-rays. A phototransistor is in essence nothing more than a bipolar transistor that is encased in a transparent case so that light can reach the base-collector junction. The phototransistor works like a photodiode, but with a much higher sensitivity for light, because the electrons that are generated by photons in base-collector junction are injected into the base, this current is then amplified by the transistor operation. A phototransistor has a slower response time than a photodiode however. 5.9.1 PRINCIPLE OF OPERATION A photodiode is a p-n junction or p-i-n structure. When light with sufficient photon energy strikes a semiconductor, photons can be absorbed, resulting in generation of a mobile electron and electron hole. If the absorption occurs in the junction's depletion region, these carriers are swept from the junction by the built-in field of the depletion region, producing a photocurrent. Photodiodes can be used in either zero bias or reverse bias. In zero bias, light falling on the diode causes a voltage to develop across the device, leading to a current in the forward bias direction. This is called the photovoltaic effect, and is the basis for solar cells — in fact; a solar cell is just a large number of big, cheap photodiodes. Diodes usually have extremely high resistance when reverse biased. This resistance is reduced when light of an appropriate frequency shines on the junction. Hence, a reverse biased diode can be used as a detector by monitoring the current running through it. Circuits based on this effect are more sensitive to light than ones based on the photovoltaic effect. Avalanche photodiodes have a similar structure; however they are operated with much higher reverse bias. This allows each photo-generated carrier to be multiplied by avalanche breakdown, resulting in internal gain within the photodiode, which increases the effective response of the device. [35]
  36. 36. Because of their greater band gap, silicon-based photodiodes generate less noise than germanium-based photodiodes, but germanium photodiodes must be used for wavelengths longer than approximately 1 µm. 5.9.2 APPLICATIONS a. P-N photodiodes are used in similar applications to other photodetectors, such as photoconductors, charge-coupled devices, and photomultiplier tubes. b. Photodiodes are used in consumer electronics devices such as compact disc players smoke detectors, and the receivers for remote controls in VCRs and televisions. c. In other consumer items such as camera light meters, clock radios (the ones that dim the display when its dark) and street lights, photoconductors are often used rather than photodiodes, although in principle either could be used. d. Photodiodes are often used for accurate measurement of light intensity in science and industry. They generally have a better, more linear response than photoconductors. 5.10 PHOTOTRANSISTORS The standard symbol of a phototransistor, which can be regarded as a conventional transistor housed in a case that enables its semiconductor junctions to be exposed to external light. The device is normally used with its base open circuit, in either of the configurations and functions as follows. In practice, the collector and emitter current of the transistor are virtually identical and, since the base is open circuit, the device is not subjected to significant negative feedback. Consequently, the alternative circuit, in which R1 is connected to Q1 emitter, gives a virtually identical performance to that of fig. The sensitivity of a phototransistor is typically one hundred times greater than that of a photodiode, but is useful maximum operating frequency (a few hundred kilohertz) is proportionally lower than that of a photodiode by using only its base and collector terminals and ignoring the emitter. [36]
  37. 37. Phototransistors are solid-state light detectors with internal gain that are used to provide analog or digital signals. They detect visible, ultraviolet and near-infrared light from a variety of sources and are more sensitive than photodiodes, semiconductor devices that require a pre-amplifier. Phototransistors feed a photocurrent output into the base of a small signal transistor. For each illumination level, the area of the exposed collector- base junction and the DC current gain of the transistor define the output than that of a photodiode by using only its base and collector terminals and ignoring the emitter. Fig.5.10.1 Phototransistor Circuit The base current from the incident photons is amplified by the gain of the transistor, resulting in current gains that range from hundreds to several thousands. Response time is a function of the capacitance of the collector-base junction and the value of the load resistance. Photodarlingtons, a common type of phototransistor, have two stages of gain and can provide net gains greater than 100,000. Because of their ease of use, low cost and compatibility with transistor-transistor logic (TTL), phototransistors are often used in applications where more than several hundred nanowatts (nW) of optical power are available. Selecting phototransistors requires an analysis of performance specifications. Collector current is the total amount of current that flows into the collector terminal. Collector dark current is the amount of collector current for which there is no optical input. Typically, both collector current and collector dark current are measured in milliamps (mA). Peak wavelength, the wavelength at which phototransistors are most responsive, is measured in [37]
  38. 38. nanometers (nm). Rise time, the time that elapses when a pulse waveform increases from 10% to 90% of its maximum value, is expressed in nanoseconds (ns). Collector-emitter breakdown voltage is the voltage at which phototransistors conduct a specified (nondestructive) current when biased in the normal direction without optical or electrical inputs to the base. Power dissipation, a measure of total power consumption, is measured in milliwatts (mW). 5.11 LED (LIGHT EMITTING DIODE) Light emitting diode (LED ) is basically a P-N junction semiconductor diode particularly designed to emit visible light. There are infra-red emitting LEDs which emit invisible light. The LEDs are now available in many colour red, green and yellow. A normal LED emit at 2.4V and consumes MA of current. The LEDs are made in the form of flat tiny P-N junction enclosed in a semi-spherical dome made up of clear coloured epoxy resin. The dome of a LED acts as a lens and diffuser of light. The diameter of the base is less than a quarter of an inch. The actual diameter varies somewhat with different makes. It is similar to the conventional rectifier diode symbol with two arrows pointing out. LEDs often have leads of dissimilar length and the shorter one is the cathode. This is not strictly adhered to by all manufacturers. Sometimes the cathode side has a flat base. If there is doubt, the polarity of the diode should be identified. A simple bench method is to use the ohmmeter incorporating 3-volt cells for ohmmeter function. When connected with the ohmmeter: one way there will be no deflection and when connected the other way round there will be a large deflection of a pointer. When this occurs the anode lead is connected to the negative of test lead and cathode to the positive test lead of the ohmmeter. [38]
  39. 39. Fig.5.11.2 Working Of LED 1. ACTION An LED consists of a junction diode made from the semiconducting compound gallium arsenide phosphide. It emits light when forward biased, the colour depending on the composition and impurity content of the compound. At present red, yellow and green LEDs are available. When a p-n junction diode is forward biased, electrons move across the junction from the n-type side to the p-type side where they recombine with holes near the junction. The same occurs with holes going across the junction from the p-type side. Every recombination results in the release of a certain amount of energy, causing, in most semiconductors, a temperature rise. In gallium arsenide phosphide some of the energy is emitted as light which gets out of the LED because the junction is formed very close to the surface of the material. An LED does not light when reverse biased and if the bias is 5 V or more it may be damaged. [39]
  40. 40. 2. EXTERNAL RESISTOR An LED must have a resistor connected in series to limit the current through the LED; otherwise it will burn out almost instantly. The resistor value, R is given by: R = (VS - VL) / I VS = supply voltage VL = LED voltage (usually 2V, but 4V for blue and white LEDs) I = LED current (e.g. 10mA = 0.01A, or 20mA = 0.02A) Make sure the LED current you choose is less than the maximum permitted and convert the current to amps (A) so the calculation will give the resistor value in ohms ( ). To convert mA to A divide the current in mA by 1000 because 1mA = 0.001A. If the calculated value is not available choose the nearest standard resistor value which is greater, so that the current will be a little less than you chose. In fact you may wish to choose a greater resistor value to reduce the current (to increase battery life for example) but this will make the LED less bright. For example If the supply voltage VS = 9V, and you have a red LED (VL = 2V), requiring a current I = 20mA = 0.020A. R = (9V - 2V) / 0.02A = 350 , so choose 390 (the nearest standard value which is greater). 3. DECIMAL DISPLAY Many electronic calculators, clocks, cash registers and measuring instruments have seven- segment red or green LED displays as numerical indicators. Each segment is an LED and depending on which segments are energized, the display lights up the numbers 0 to 9. Such [40]
  41. 41. displays are usually designed to work on a 5 V supply. Each segment needs a separate current- limiting resistor and all the cathodes (or anodes) are joined together to form a common connection. 5.11.1 ADVANTAGES a. Efficiency; LEDs emit more light per watt than incandescent light bulbs. Their efficiency is not affected by shape and size, unlike fluorescent light bulbs or tubes. b. Color; LEDs can emit light of an intended color without using any color filters as traditional lighting methods need. This is more efficient and can lower initial costs. c. Size: LEDs can be very small (smaller than 2 mm2 ) and are easily populated onto printed circuit boards. d. On/Off time: LEDs light up very quickly. A typical red indicator LED will achieve full brightness in under a microsecond. LEDs used in communications devices can have even faster response times. e. Cycling: LEDs are ideal for uses subject to frequent on-off cycling, unlike fluorescent lamps that fail faster when cycled often, or HID lamps that require a long time before restarting. f. Dimming: LEDs can very easily be dimmed either by pulse-width modulation or lowering the forward current. g. Cool light: In contrast to most light sources, LEDs radiate very little heat in the form of IR that can cause damage to sensitive objects or fabrics. Wasted energy is dispersed as heat through the base of the LED. h. Slow failure: LEDs mostly fail by dimming over time, rather than the abrupt failure of incandescent bulbs. i. Lifetime: LEDs can have a relatively long useful life. One report estimates 35,000 to 50,000 hours of useful life, though time to complete failure may be longer. Fluorescent tubes typically are rated at about 10,000 to 15,000 hours, depending partly on the conditions of use, and incandescent light bulbs at 1,000–2,000 hours. j. Shock resistance: LEDs, being solid state components, are difficult to damage with external shock, unlike fluorescent and incandescent bulbs which are fragile. [41]
  42. 42. k. Focus: The solid package of the LED can be designed to focus its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a usable manner. 5.11.2 SEVEN SEGMENT DISPLAY A seven-segment display, or seven-segment indicator, is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot-matrix displays. Seven-segment displays are widely used in digital clocks, electronic meters, and other electronic devices for displaying numerical information. A seven segment display, as its name indicates, is composed of seven elements. Individually on or off, they can be combined to produce simplified representations of the Arabic numerals. Often the seven segments are arranged in an oblique (slanted) arrangement, which aids readability. In most applications, the seven segments are of nearly uniform shape and size (usually elongated hexagons, though trapezoids and rectangles can also be used), though in the case of adding machines, the vertical segments are longer and more oddly shaped at the ends in an effort to further enhance readability. Each of the numbers 0, 6, 7 and 9 may be represented by two or more different glyphs on seven-segment displays. The seven segments are arranged as a rectangle of two vertical segments on each side with one horizontal segment on the top, middle, and bottom. Additionally, the seventh segment bisects the rectangle horizontally. There are also fourteen-segment displays and sixteen-segment displays (for full alphanumerics); however, these have mostly been replaced by dot-matrix displays. [42]
  43. 43. The segments of a 7-segment display are referred to by the letters A to G, as shown to the right, where the optional DP decimal point (an "eighth segment") is used for the display of non- integer numbers. The animation to the left cycles through the common glyphs of the ten decimal numerals and the six hexadecimal "letter digits" (A–F). It is an image sequence of a "LED" display, which is described technology-wise in the following section. Notice the variation between uppercase and lowercase letters for A–F; this is done to obtain a unique, unambiguous shape for each letter (otherwise, a capital D would look identical to a 0 (or less likely O) and a capital B would look identical to an 8). Fig.5.11.2 (b) Seven Segment Display Showing 16 Hex Digits [43]
  44. 44. CHAPTER 6 PCB DESIGN AND FABRICATION [44]
  45. 45. 6.1 PCB DESIGN Designing of PCB is a major step in the production of PCB is a major. It forms a distinct factor in electronic performance and reliability. The productivity of a PCB, its assembly and service ability also depends on the design. The designing of a PCB consists of designing of the layout followed by the preparation of the artwork. The layout should include all the relevant aspects in details of the PCB design while the art work preparation brings it to the form required for the production process. The layout can be designed with the help of any one of the standard layout edition softwares such as Eagle, Orcad or Edwin XP. Hence a concept, clearly defining all the details of the circuits and partly of the equipment, is a prerequisite and the actual layout can start. Depending on the accuracy required, the artwork might be produced a 1:1 or 2:1 even 4:1 scale. It is best prepared on a 1:1 scale. [45]
  46. 46. 6.2 PCB FABRICATION PCB fabrication involves the following steps a. First the layout of the PCB is generated using the software ORCAD. First step involves drawing the circuit CIS which is a section of ORCAD. b. Then the layout is obtained using layout plus. This layout is printed on a paper. c. This printed layout is transferred to a Mylar sheet and touched with black ink. d. The solder side of the Myler sheet is placed on the shining side of the copper board and is placed in a frame. It is than exposed to sunlight, with the Mylar sheet facing the sunlight. e. The exposed copper board is put in hydrogen peroxide solution. It is then put in hot water; shook till unexposed region becomes transparent. f. This is put in cold water and then the rough side is struck in to the skill screen. This is then pressed and dried well. g. The plastic sheet of the five - star is removed leaving the pattern on the screen. h. A copper clad sheet is cut to the size and cleaned. This is then placed under the screen. i. Acid resist ink is spread on the screen, So that the pattern of the tracks and pad is obtained on the copper clad sheet. It is dried. j. The dried sheet is then etched using ferric chloride solution till all the unwanted copper is etched away. k. The unwanted resist ink is removed using sodium hydroxide solution , holes are then drilled. The components are soldered neatly on the board without dry soldering. [46]
  47. 47. 6.3 PRINTED CIRCUIT BOARD (PCB) LAYOUT 6.3.1 TRANSMITTER PRINTED CIRCUIT BOARD Fig.6.3.1 PCB Of Transmitter Circuit [47]
  48. 48. 6.3.2 RECEIVER PRINTED CIRCUIT BOARD Fig.6.3.2 PCB of Receiver Circuit [48]
  49. 49. CHAPTER 7 LIST OF REQUIRED TOOLS AND INSTRUMENT [49]
  50. 50. 7.1 Following tools and instruments are used for preparing the project a. Soldering iron. b. Desoldering pump. c. Drill Machine. d. Multimeter. e. Filer. f. Tweezers. g. Screw driver. h. Dual power supply. i. Flux. j. Desoldering wick. k. Petrol. l. Brush. m. Soldering Wire. [50]
  51. 51. CHAPTER 8 COMPONENT REQUIRED [51]
  52. 52. 8.1 COMPONET REQUIRED FOR TRANSMITTER Table.8.1 Sl. No. Name of the component Quantity 1. Resistance (8.2 KΩ) 2 2. Resistance (1.8 MΩ) 1 3. Resistance (10 KΩ) 1 4. Resistance (15 KΩ 2 5. Resistance (82 Ω) 1 6. Variable Resistance (1 MΩ) 1 7. Capacitor (1 mf) 1 8. Capacitor (0.1 mf) 1 9. Capacitor (470 mf) 1 10. Capacitor (1000 mf) 1 11. Semiconductor T1 BC548 1 12. Semiconductor T2 BD139 1 13. Condenser MIC 1 14. IC UA741 1 15. PCB 1 8.2 COMPONENT REQUIRED FOR RECEIVER Table.8.2 Sl. No. Name of the component Quantity 1. Resistor (6.8, 470 KΩ) 1 [52]
  53. 53. 2. Resistor (4.7MΩ) 1 3. Resistor (2.2 KΩ) 2 4. Resistor (1 KΩ) 1 5. Resistor (10 KΩ) 1 6. Variable resistor (50 KΩ) 1 7. Capacitor (0.01 mf) 1 8. Capacitor(47 pf) 1 9. Capacitor (0.1 mf) 2 10. Capacitor (1 mf) 1 11. Capacitor (100 mf) 2 12. Capacitor(10mf) 1 13. Capacitor(470 mf) 1 14. Semiconductor 2N5777 1 15. Semiconductor BC549 2 16. P.C.B 1 [53]
  54. 54. CHAPTER 9 CONSTRUCTION AND TESTING 9.1 CONSTRUCTION As the photos show, both the transmitter and the receiver are built on silk- screened PCBS. As usual fit the resistors, pots and capacitors first, taking care with the polarity of the electrolytic. IC sockets are not essential, although servicing is obviously made easier if they are used. In which case, fit these next, followed by the transistors and photo transistors The photo diode/ transistors, is mounted directly on the receiver PCB. When first mounted, the active side of the diode (Black Square inside the package) will face towards the centre of the board. You then bend the diode over by almost 180' so the active surface now faces outwards. The polarized microphone element solders directly to the transmitter PCB. The negative lead is marked with a minus sign and is the lead that connects to the metal case. The laser diode is also polarized, and has three leads. Of these, only two are used, shown on the circuit. Take care when soldering the laser in place, as too much heat can destroy it. [54]
  55. 55. The diode can be mounted on the board, or connected with leads to it. Connect a clip lead to the inside of the laser pointer where the battery touched. Usually there is a small spring to which you can attach the clip lead. The other end of the battery usually connects to the case of the laser. Since there are many different styles of laser pointer, you may have to experiment with clip lead placement to get the laser to work with the new external battery pack. You may also have to hold down the laser's push button switch by wrapping a rubber band or some wire around it. Finally, connect the speaker and 9V battery clips, then check over the boards for any soldering errors or incorrectly installed components. 9.2 TESTING First of all, it's most important that you don't look directly into the laser beam. If you do, it could cause permanent eye damage. Also, you are responsible for the safety of others near the laser, which means you must stop others from also looking into the beam, and take all necessary safety steps. This is covered by legislation. Both the receiver and the transmitter can be powered by separate 9V batteries or suitable DC supplies. Before applying power to the transmitter PCB, set VRI to its halfway position, to make sure the laser current is not excessive. To be totally sure, you could set VRI fully anticlockwise, as this setting will reduce the laser current to zero. Then apply power to the board. If the laser doesn't produce light, slowly adjust VRI clockwise. The laser diode should emit a beam with an intensity adjustable with VRI. At this stage, keep the beam intensity low, but high enough to clearly see. If [55]
  56. 56. you are not getting an output, check the circuit. You won't see the laser beam intensity change with the modulating signal. To check that the system is working, place the two PCBs on the workbench, spaced a meter or go apart. You might need to put a sheet of paper about 2Omm in front of the photodiode to reduce the intensity of light from the laser beam. Set the volume control of the speaker to about halfway. If the volume control setting is too high you'll get acoustic feedback. Move the laser diode assembly so the beam points at the receiver's photodiode. It's useful to adjust the beam so it's out of focus at the photodiode, to make alignment even easier. You should now be able to hear the speaker reproducing any audio signal picked up by the microphone. [56]
  57. 57. CHAPTER 10 SETTING UPLINK AND PRECAUTION 10.1 SETTING UPLINK Once you've tested the link, you'll probably be keen to put it to use. For a short link of say 100 meters, all you need do is position the receiver so the laser beam falls on the photodiode. Once the link is established, adjust VRI higher the laser current, the shorter will be its life. If you have an ammeter, connect it to measure the current taken by the transmitter board. Most of the current is taken by the laser, so adjust VRI to give a total current consumption of no more than 45Ma. Also, focus the laser so all of the beam is striking the photodiode. At close range, there's probably no need to focus the beam. In fact, because of the high output power (5mW) of the laser diode, excellent results will be obtained over reasonably short distances (20 meters or so) with rough focusing and quiescent current adjustments. [57]
  58. 58. But the longer the distance between the transmitter and the receiver, the more critical the adjustments. For example, for distances over 20 meters, you might have to put a piece of tube over the front of the photodiode to limit the ambient light falling on it. This diode is responsive to visible light, so a high ambient light could cause it to saturate. For very long distances, say half a kilometer, you'll probably need a parabolic reflector for the laser beam, to focus it directly onto the photodiode. For short ranges (a meter or so), or for educational or testing purposes, you can use a conventional red LED. Adjust the quiescent current with VR1. LED is not focused, and simply spreads everywhere, so a reflector might help the sensitivity. Warnings The laser diode in this project is a class 3B laser and you should attach a warning label to the transmitter, Remember that, as for any hazardous device, the owner of a laser is responsible for its proper use. 10.2 PRECAUTION a. Safety instructions for lasers: Laser beams may damage the eyes severely or may cause blindness if they radiate into the eyes directly or indirectly. Therefore the laser electronics must be installed in such a manner that radiation into the eyes will be impossible neither directly nor indirectly via marrows in the room. When using lasers with an output power higher than 1 mW, you should check about the legal regulations for prevention of accidents and be very careful. b. Normal laser pointers sold in shops have typically output power of 1.5 mW (power depends on laser pointer model and what country regulations say on maximum power). This power level is normally not very hazardous, but can cause permanent dotages your eye if you stare [58]
  59. 59. at the beam. We should be very careful with higher power lasers and lasers on that power range that emit invisible radiation, because they can cause immediate eye damage (and very high power lasers can cause skin burns or fire). c. With any high power laser make sure that you have safe operating environment, necessary regulations/permissions and somebody that takes care that these legal regulations are observed. Lasers use coherent light which has very different properties to a standard lighting effect. This is what makes lasers one of the most beautiful forms of light, but also one of the most dangerous light sources if not used with proper cautions. d. In the transmitter schematic, no ballast resistor is shown because most small LASER power supplies already have one built in. Yours may differ, and a resistor may be needed. [59]
  60. 60. CHAPTER 11 ADVANTAGES AND DISADVANTAGES 11.1 ADVANTAGES a. Less costly. b. Circuit can be easily constructed. c. High data rate. d. No communication licenses required. e. The laser transmission is very secure because it has a narrow beam. f. There are no recurring line costs. g. Compatibility with copper or fiber interfaces and no bridge or router requirements. [60]
  61. 61. h. Lasers can also transmit through glass, however the physical properties of the glass have to be considered. i. Narrow beam divergence. 11.2 DISADVANTAGES To avoid 50Hz hum (humming) noise in the speaker, keep the phototransistor away from AC light sources such as bulbs. The reflected sunlight, however, does not cause any problem. But the sensor should not directly face the sun. [61]
  62. 62. CHAPTER 12 PROBLEM FACED 12.1 PROBLEM FACED Although this project was successfully completed, however a few hurdles that came during the construction of the circuit were the breaking of the thin electrical wires after it had been soldered and the breaking of the photodiode receiver’s leg leading to an error in reception of data. Moreover the connections with the OP-AMP chip have to be dealt with very carefully because one wrong connection may damage the whole chip. If the supply to laser is greater than it will not glow. All these things are to be taken care of, for the efficient working of the project. [62]
  63. 63. [63]
  64. 64. CHAPTER 13 APPLICATIONS 13 APPLICATIONS a. Using this circuit we can communicate with our neighbors wirelessly. b. It can be used in inaccessible areas. c. In future it can be commissioned in satellites for communication. d. It can be used in conference halls. [64]
  65. 65. CONCLUSION After the successful working of the project, it can be concluded that this project is suitable for easily 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 meters. Provisions have to be made for cases when there is no heavy traffic. [65]
  66. 66. REFERENCES a. Choudhary, D.Roy; Jain, Shalin. B; Linear Integrated Circuits; New Age Internationl Publishers, Third Edition 2009. b. Gupta, J.B; Electronics Device & Circuits; S.K. Kataria & Sons, First Edition Dec 2000. - Vol. 1. c. Kumar, N. Suresh; Electronics Device & Circuits. d. Mehta, V.K; Principles Of Electronics. e. Navas, K.A; Electronics Lab Manual; Rajath Publishers, 2008. - Vol. 1&2. [66]
  67. 67. f. Rai A.; Vallave Electronics Device & Circuits- 2007. g. Wilson, J. & Hawkes; J.F.B. (1987). Lasers: Principles and Applications, Prentice Hall International Series in Optoelectronics. h. Siegmen, Anthony E.; Lasers, University Science Books U.S. APPENDIX BC 546/547/548/549/550 [67]
  68. 68. [68]
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  71. 71. UA741 GENERAL PURPOSE OF SINGLE OP-AMP [71]
  72. 72. [72]
  73. 73. [73]
  74. 74. [74]
  75. 75. [75]
  76. 76. [76]
  77. 77. L 14F1 L 14F2 [77]

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