Light ferdelity report Li-Fi

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A
Project Report of
Light Fidelity (Li-Fi)
Submitted
In partial fulfilment
For the award of the Degree of
Bachelor of Technology
In Department of Electronics & Communication Engineering
Submitted To: Submitted By:
Name: Prof. Alok Jha Name of Candidate:
Designation (Dept.): Vimal Kumar (11ECIEC037)
Head of Department Girish Kumar Chandan (11ECIEC017)
Department of Electronics & Communication Engineering
CompuCom Institute of Information Technology & Management
Rajasthan Technical University
May 2015

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Abstract of Li-Fi Technology:-
Whether you’re using wireless internet in a coffee shop, stealing it from the guy next
door, or competing for bandwidth at a conference, you’ve probably gotten frustrated at the slow
speeds you face when more than one device is tapped into the network. As more and more
people and their many devices access wireless internet, clogged airwaves are going to make it
increasingly difficult to latch onto a reliable signal. But radio waves are just one part of the
spectrum that can carry our data. What if we could use other waves to surf the internet? One
German physicist DR. Harald Haas, has come up with a solution he calls “Data Through
Illumination”—taking the fiber out of fiber optics by sending data through an LED light bulb
that varies in intensity faster than the human eye can follow. It’s the same idea behind infrared
remote controls, but far more powerful. Haas says his invention, which he calls D-Light, can
produce data rates faster than 10 megabits per second, which is speedier than your average
broadband connection. He envisions a future where data for laptops, smartphones, and tablets is
transmitted through the light in a room. And security would be a snap—if you can’t see the light,
you can’t access the data.
Li-Fi is a VLC, visible light communication, technology developed by a team of
scientists including Dr Gordon Povey, Prof. Harald Haas and Dr Mostafa Afgani at the
University of Edinburgh. The term Li-Fi was coined by Prof. Haas when he amazed people by
streaming high-definition video from a standard LED lamp, at TED Global in July 2011. Li-Fi is
now part of the Visible Light Communications (VLC) PAN IEEE 802.15.7 standard. “Li-Fi is
typically implemented using white LED light bulbs. These devices are normally used for
illumination by applying a constant current through the LED. However, by fast and subtle
variations of the current, the optical output can be made to vary at extremely high speeds.
Unseen by the human eye, this variation is used to carry high-speed data,” says Dr Povey,
Product Manager of the University of Edinburgh's Li-Fi Program ‘D-Light Project’.
Introduction of Li-Fi Technology:-
In simple terms, Li-Fi can be thought of as a light-based Wi-Fi. That is, it uses light
instead of radio waves to transmit information. And instead of Wi-Fi modems, Li-Fi would use
transceiver-fitted LED lamps that can light a room as well as transmit and receive information.
Since simple light bulbs are used, there can technically be any number of access points.
This technology uses a part of the electromagnetic spectrum that is still not greatly
utilized- The Visible Spectrum. Light is in fact very much part of our lives for millions and

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millions of years and does not have any major ill effect. Moreover there is 10,000 times more
space available in this spectrum and just counting on the bulbs in use, it also multiplies to 10,000
times more availability as an infrastructure, globally.
It is possible to encode data in the light by varying the rate at which the LEDs flicker on
and off to give different strings of 1s and 0s. The LED intensity is modulated so rapidly that
human eyes cannot notice, so the output appears constant.
More sophisticated techniques could dramatically increase VLC data rates. Teams at the
University of Oxford and the University of Edinburgh are focusing on parallel data transmission
using arrays of LEDs, where each LED transmits a different data stream. Other groups are using
mixtures of red, green and blue LEDs to alter the light's frequency, with each frequency
encoding a different data channel.
Li-Fi, as it has been dubbed, has already achieved blisteringly high speeds in the lab.
Researchers at the Heinrich Hertz Institute in Berlin, Germany, have reached data rates of over
500 megabytes per second using a standard white-light LED. Haas has set up a spin-off firm to
sell a consumer VLC transmitter that is due for launch next year. It is capable of transmitting
data at 100 MB/s - faster than most UK broadband connections.
Genesis ofLI-FI:
Harald Haas, a professor at the University of Edinburgh who began his research in the
field in 2004, gave a debut demonstration of what he called a Li-Fi prototype at the TED Global
conference in Edinburgh on 12th July 2011. He used a table lamp with an LED bulb to transmit a
video of blooming flowers that was then projected onto a screen behind him. During the event he
periodically blocked the light from lamp to prove that the lamp was indeed the source of
incoming data. At TED Global, Haas demonstrated a data rate of transmission of around 10Mbps
-- comparable to a fairly good UK broadband connection. Two months later he achieved
123Mbps.

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Fig 1.0
Back in 2011 German scientists succeeded in creating an800Mbps (Megabits per second)
capable wireless network by using nothing more than normal red, blue, green and
white LED light bulbs (here), thus the idea has been around for a while and various other global
teams are also exploring the possibilities.
Fig 1.1
How Li-Fi Works?
Li-Fi is typically implemented using white LED light bulbs at the downlink transmitter.
These devices are normally used for illumination only by applying a constant current. However,
by fast and subtle variations of the current, the optical output can be made to vary at extremely
high speeds. This very property of optical current is used in Li-Fi setup. The operational

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procedure is very simple-, if the LED is on, you transmit a digital 1, if it’s off you transmit a 0.
The LEDs can be switched on and off very quickly, which gives nice opportunities for
transmitting data. Hence all that is required is some LEDs and a controller that code data into
those LEDs. All one has to do is to vary the rate at which the LED’s flicker depending upon the
data we want to encode. Further enhancements can be made in this method, like using an array of
LEDs for parallel data transmission, or using mixtures of red, green and blue LEDs to alter the
light’s frequency with each frequency encoding a different data channel. Such advancements
promise a theoretical speed of 10 Gbps – meaning one can download a full high-definition film
in just 30 seconds.
Fig 1.2
To further get a grasp of Li-Fi consider an IR remote. (Fig 3.3). It sends a single data
stream of bits at the rate of 10,000-20,000 bps. Now replace the IR LED with a Light Box
containing a large LED array. This system, fig 3.4, is capable of sending thousands of such
streams at very fast rate.

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Fig 1.3
Light is inherently safe and can be used in places where radio frequency communication
is often deemed problematic, such as in aircraft cabins or hospitals. So visible light
communication not only has the potential to solve the problem of lack of spectrum space, but can
also enable novel application. The visible light spectrum is unused, it's not regulated, and can be
used for communication at very high speeds.

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TechnologyBrief:-
How LI-FI Light Sources Work:-
 Introduction:-
LI-FI is a new class of high intensity light source of solid state design
bringing clean lighting solutions to general and specialty lighting. With energy
efficiency, long useful lifetime, full spectrum and dimming, LI-FI lighting
applications work better compared to conventional approaches. This technology
brief describes the general construction of LI-FI lighting systems and the basic
technology building blocks behind their function.
 LI-FI CONSTRUCTION:-
The LIFI™ product consists of 4 primary sub-assemblies:
• Bulb
• RF poweramplifier circuit (PA)
• Printed circuit board (PCB)
• Enclosure
The PCB controls the electrical inputs and outputs of the lamp and houses
the microcontroller used to manage different lamp functions.
An RF (radio-frequency) signal is generated by the solid-state PA and is
guided into an electric field about the bulb.
The high concentration of energy in the electric field vaporizes the
contents of the bulb to a plasma state at the bulb’s center; this controlled plasma
generates an intense source of light.
All of these subassemblies are contained in an aluminum enclosure
 FUNCTION OF THE BULB:-
At the heart of LIFI™ is the bulb sub-assembly where a sealed bulb is
embedded in a dielectric material. This design is more reliable than conventional
light sources that insert degradable electrodes into the bulb. The dielectric

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material serves two purposes; first as a waveguide for the RF energy transmitted
by the PA and second as an electric field concentrator that focuses energy in the
bulb. The energy from the electric field rapidly heats the material in the bulb to a
plasma state that emits light of high intensity and full spectrum.
 SUMMARY:
-
The design and construction of the LIFI™ light source enable efficiency, long
stable life, and full spectrum intensity that is digitally controlled and easy to use.

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Application area of li-fi technology
Airways:-
Fig 2.2
Whenever we travel through airways we face the problem in communication media,
because the whole airways communication are performed on the basis of radio
waves to overcome this drawback on radio ways, li-fi is introduce.
Greeninformation technology:-
Green information technology means that unlike radio waves and other
communication waves effects on the birds, human body’s etc. Li-Fi never gives such
side effects on any living thing.

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 Free From Frequency Bandwidth Problem:-
Li-fi is a communication media in the form of light, so no matter about the
frequency bandwidth problem. It does not require the any bandwidth spectrum i.e.
we don’t need to pay any amount for communication and license.
 Increase CommunicationSafety:-
Due to visual light communication, the node or any terminal attach to our
network is visible to the host of network.
 Multi User Communication:-
Li-Fi supports the broadcasting of network, it helps to share multiple thing
at a single instance called broadcasting.
 Lightings Points Used as Hotspot:-
Any lightings device is performed as a hotspot it means that the light
device like car lights, ceiling lights, street lamps etc. area able to spread internet
connectivity using visual light communication. Which helps us to low cost
architecture for hotspot.
Hotspot is a limited region in which some amount of device can access the
internet connectivity.
 Smarter PowerPlants:-
Wi-Fi and many other radiation types are bad for sensitive areas. Like
those surrounding power plants. But power plants need fast, inter-connected data
systems to monitor things like demand, grid integrity and (in nuclear plants) core
temperature. The savings from proper monitoring at a single power plant can add
up to hundreds of thousands of dollars. Li-Fi could offer safe, abundant
connectivity for all areas of these sensitive locations. Not only would this save
money related to currently implemented solutions, but the draw on a power
plant’s own reserves could be lessened if they haven’t yet converted to LED
lighting.

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Undersea Awesomeness:-
Underwater ROVs, those favourite toys of treasure seekers and James
Cameron, operate from large cables that supply their power and allow them to
receive signals from their pilots above.
ROVs work great, except when the tether isn’t long enough to explore an
area, or when it gets stuck on something. If their wires were cut and replaced with
light say from a submerged, high-powered lamp then they would be much
free to explore. They could also use their headlamps to communicate with each
other, processing data autonomously and referring findings periodically back to the
surface, all the while obtainingtheirnextbatchof orders.

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Components Required:
Component Value Quantity in Pieces
Resistor 10k/15k/82ohm 1p/1p/2p
Capacitor 1000uf/470uF/0.1uF 1p/1p/1p
BC 548 - 1p
LM 741 - 1p
Solar Panel - 1p
Laser Light - 1p
Speaker - 1p
PCB - -

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Resistor:
Fig 3.1
A resistor is a passive two-terminal electrical component that implements electrical resistance as
a circuit element. Resistors act to reduce current flow, and, at the same time, act to lower voltage
levels within circuits. In electronic circuits resistors are used to limit current flow, to adjust
signal levels, bias active elements, terminate transmission lines among other uses. High-power
resistors that can dissipate many watts of electrical power as heat may be used as part of motor
controls, in power distribution systems, or as test loads for generators. Fixed resistors have
resistances that only change slightly with temperature, time or operating voltage. Variable
resistors can be used to adjust circuit elements (such as a volume control or a lamp dimmer), or
as sensing devices for heat, light, humidity, force, or chemical activity.
Resistors are common elements of electrical networks and electronic circuits and are ubiquitous
in electronic equipment. Practical resistors as discrete components can be composed of various
compounds and forms. Resistors are also implemented within integrated circuits.
Measurement/Value of Resistance in use:
2 pieces of Resistor = 82 ohm
1 pieces of Resistor = 10k ohm
1 pieces of Resistor= 15k ohm
Color Coding In Resistor:

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Fig 3.2
Capacitor:
Fig 3.3 Fig 3.4
A capacitor (originally known as a condenser) is a passive two-terminal electrical
component used to store energy electrostatically in an electric field. The forms of practical
capacitors vary widely, but all contain at least two electrical conductors (plates) separated by
a dielectric (i.e. insulator). The conductors can be thin films, foils or sintered beads of metal or
conductive electrolyte, etc. The no conducting dielectric acts to increase the capacitor's charge
capacity. A dielectric can be glass, ceramic, plastic film, air, vacuum, paper, mica, oxide layer
etc. Capacitors are widely used as parts of electrical circuits in many common electrical devices.

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Unlike a resistor, an ideal capacitor does not dissipate energy. Instead, a capacitor
stores energy in the form of an electrostatic field between its plates.
When there is a potential difference across the conductors (e.g., when a capacitor is attached
across a battery), an field develops across the dielectric, causing positive charge +Q to collect on
one plate and negative charge −Q to collect on the other plate. If a battery has been attached to a
capacitor for a sufficient amount of time, no current can flow through the capacitor. However, if
a time-varying voltage is applied across the leads of the capacitor, a displacement current can
flow
TransistorCurrent Components:-
Fig 4.1
The BC548 is a general purpose NPN bipolar junction transistor found commonly in European
electronic equipment and present-day designs in Australian and British electronics magazines
where a commonly-available low-cost NPN transistor is required. It is a part of a family of NPN
and PNP epitaxial silicon transistors that include higher-quality variants, originating in 1966
when Philips introduced the metal-cased BC108 family of transistors which became the most
used transistors in Australia[1] and taken up by many European manufacturers. The BC548 is the
modern plastic packaged BC108, and can be used in any circuit designed for the BC108 or
BC148, which includes many Muller and Philips published designs.
The BC548 is low cost and is available in most European Union and many other countries. It is
often the first type of bipolar transistor hobbyist’s encounter, and is often featured in designs in
hobby electronics magazines where a general-purpose transistor is required. The part number is
assigned by Pro Electron, which allows many manufacturers to offer electrically and physically
interchangeable parts under one identification. As viewed in the image to the right, and going
from left to right, lead 1 (left in diagram) is the collector, lead 2 is the base, and lead 3 is the
emitter.

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LM 741 IC (OperationalAmplifier):
Fig 5.1
An operational amplifier ("op-amp") is a DC-coupled high-gain electronic
voltage amplifier with a differential input and, usually, a single-ended output. In this
configuration, an op-amp produces an output potential (relative to circuit ground) that is typically
hundreds of thousands of times larger than the potential difference between its input terminals.
Operational amplifiers had their origins in analog computers, where they were used to do
mathematical operations in many linear, non-linear and frequency-dependent circuits. The
popularity of the op-amp as a building block in analog circuits is due to its versatility. Due
to negative feedback, the characteristics of an op-amp circuit, its gain, input and output
impedance, bandwidth etc. are determined by external components and have little dependence on
temperature coefficients or manufacturing variations in the op-amp itself.
Op-amps are among the most widely used electronic devices today, being used in a vast array of
consumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents in
moderate production volume; however some integrated or hybrid operational amplifiers with
special performance specifications may cost over $100 US in small quantities.[3] Op-amps may
be packaged as components, or used as elements of more complex integrated circuits.
The op-amp is one type of differential amplifier. Other types of differential amplifier include
the fully differential amplifier (similar to the op-amp, but with two outputs), the instrumentation
amplifier (usually built from three op-amps), the isolation amplifier (similar to the

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instrumentation amplifier, but with tolerance to common-mode voltages that would destroy an
ordinary op-amp), and negative feedback amplifier (usually built from one or more op-amps and
a resistive feedback network).
The amplifier's differential inputs consist of a non-inverting input (+) with voltage V+ and an
inverting input (–) with voltage V−; ideally the op-amp amplifies only the difference in voltage
between the two, which is called the differential input voltage. The output voltage of the op-
amp Vought is given by the equation:
Where AOL is the open loop gain of the amplifier (the term "open-loop" refers to the absence
of a feedback loop from the output to the input).
Open loop amplifier:
The magnitude of AOL is typically very large—100,000 or more for integrated circuit op-
amps—and therefore even a quite small difference between V+ and V− drives the amplifier
output nearly to the supply voltage. Situations in which the output voltage is equal to or
greater than the supply voltage are referred to as saturation of the amplifier. The magnitude
of AOL is not well controlled by the manufacturing process, and so it is impractical to use an
operational amplifier as a stand-alone differential amplifier.
Without negative feedback, and perhaps with positive feedback for regeneration, an op-amp
acts as a comparator. If the inverting input is held at ground (0 V) directly or by a resistor
Rag, and the input voltage VIN applied to the non-inverting input is positive, the output will
be maximum positive; if VIN is negative, the output will be maximum negative. Since there is
no feedback from the output to either input, this is an open loop circuit acting as
a comparator.
Closedloop:
Fig 5.1

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If predictable operation is desired, negative feedback is used, by applying a portion of the
output voltage to the inverting input. The closed loop feedback greatly reduces the gain of
the circuit. When negative feedback is used, the circuit's overall gain and response becomes
determined mostly by the feedback network, rather than by the op-amp characteristics. If the
feedback network is made of components with values small relative to the op amp's input
impedance, the value of the op-amp's open loop response AOL does not seriously affect the
circuit's performance. The response of the op-amp circuit with its input, output, and feedback
circuits to an input is characterized mathematically by a transfer function; designing an op-
amp circuit to have a desired transfer function is in the realm of electrical engineering. The
transfer functions are important in most applications of op-amps, such as in analog
computers. High input impedance at the input terminals and low output impedance at the
output terminal(s) are particularly useful features of an op-amp.
In the non-inverting amplifier on the right, the presence of negative feedback via the voltage
divider Rf, Rg determines the closed-loop gain ACL = Vout / Vin. Equilibrium will be
established when Vout is just sufficient to "reach around and pull" the inverting input to the
same voltage as Vin. The voltage gain of the entire circuit is thus 1 + Rf/Rg. As a simple
example, if Vin = 1 V and Rf = Rg, Vout will be 2 V, exactly the amount required to keep V− at
1 V. Because of the feedback provided by the Rf, Rg network, this is a closed loop circuit.
Another way to analyze this circuit proceeds by making the following (usually valid)
assumptions:[4]
 When an op-amp operates in linear (i.e., not saturated) mode, the difference in voltage
between the non-inverting (+) pin and the inverting (−) pin is negligibly small.
 The input impedance between (+) and (−) pins is much larger than other resistances in the
circuit.
The input signal Vin appears at both (+) and (−) pins, resulting in a current I through Rg equal
to Vin/Rg.
Since Kirchhoff's current law states that the same current must leave a node as enter it,
and since the impedance into the (−) pin is near infinity, we can assume practically all of
the same current I flows through Rf, creating an output voltage
By combining terms, we determine the closed-loop gain ACL:

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Pin Descriptionof LM 741:
Fig 6.1

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SolarPanel:
Fig 7.1
A solar cell is an electronic device that produces electricity when light falls on it. The light is
absorbed and the cell produces dc voltage and current. The device has a positive and a negative
contact between which the voltage is generated and through which the current can flow. You
connect these contacts to whatever it is you want to power. Solar cells have no moving parts.
Effectively they take light energy and convert it into electrical energy in an electrical circuit,
exploiting a physical process known as the photovoltaic effect.
The discovery of the photovoltaic effect is credited to the French physicist, Edmond Becquerel,
in 1839. He found that by concentrating the sun's light on one side of a battery the output current
of the battery could be increased. This revolutionary discovery triggered the idea that one could
produce energy from light by an artificial process. In 1883 an American inventor produced a
solar cell from a material called selenium, but it was very inefficient. Selenium became used in
light-exposure meters for cameras, but not for power production.
It was not until the 1950s that practical solar cells were developed. In 1948 the transistor was
invented, at Bell Laboratories in the United States, and it was found that the same high quality
silicon wafers used for making transistors could be used to make solar cells. This work was
published in 1954. From 1958 onwards the cells were employed in the space race. Solar cells
are still the only sensible source of electrical power for space satellites, because they are in effect
batteries that never run out.
Initially solar cells were too expensive to be used in non-space (i.e. terrestrial) applications,
though Bell Telephone did demonstrate them for rural telephone systems. They are a good idea
for country areas that have no electricity supply network, of which there are many in the
Developing World, and for maritime applications (e.g. to power flashing lights on buoys). If
cells can be made cheap enough (and great efforts are being made to achieve this) they could
even replace our normal methods of making electricity, which are either polluting and/or non-
renewable (burning fossil fuels) or waste poses a long term environmental hazard (radioactive

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waste from nuclear power plants). Solar cells produce no emissions and do not contribute to the
greenhouse effect, and the amount of energy available from the world's sunlight is far more than
we should ever need.
Individual solar cells are small and therefore not very powerful (though they can run calculators
and watches). More powerful supplies can be made by connecting many cells together in a solar
module. Modules are connected together to form solar panels, and in turn panels are connected
together to form solar arrays.
Efficiency
The efficiency of a solar cell is a measure of the proportion of the light hitting it that is actually
converted into electricity. If the cell were 100% efficient then it would turn all the incident light
into energy, but sadly this is impossible: the maximum allowed within the laws of physics is
between 30% and 40%. Practical solar cells made from silicon wafers (monocrystalline silicon)
can have an efficiency of 16% or so. Thin-film solar cells (e.g. amorphous silicon solar cells)
have lower efficiencies than this, at least for commercial cells, but are much cheaper to produce.
Around mid-day on a clear summer's day the sunlight falling on the earth has a power density of
about 1 kW (1000 watts) for every square meter of surface; (this is typically the power given off
by a one-bar electric fire). A solar module measuring 0.30 m × 0.45 m has an area of 0.135 m²,
and therefore when you point it at the sun the light falling on it has a power of 0.135 × 1000
watts = 135 watts. If the module is 10% efficient, the power available from it is 10% of this, i.e.
13.5 watts. The module is stated to have an output of 13.5 watts peak, i.e. at the peak sunlight of
1000 watts per square meter. The output will be less at other times of the day, in cloudy
conditions, or if the module is in the shade or not pointing directly at the sun.
In space the output is higher because the solar radiation there is stronger, not being affected by
the earth’s atmosphere. It has a power density of 1365 watts per square meter.
How does the light intensity effectthe solar cell?
As the intensity of light falls, because of clouds or time of day, solar cell output also falls. The
cell's current is more sensitive to the light intensity than the voltage is. Roughly speaking if you
halve the light intensity you halve the current; but the voltage falls only slightly.
The light intensity can also be reduced just by twisting the cell. The output of a solar cell is at its
maximum when it is perpendicular to the incident light beam, i.e. when it is pointed at the sun.
If you now change the angle, the cell intercepts less of the light beam; however, this smaller
amount of light is still spread out over the same area of cell, so the light intensity on the cell is
reduced.

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INSIDE A SOLAR PANEL - HOW DOES IT WORK?
Photons
Photons are what make up the light we see. Light is an electromagnetic wave that is transmitted
in tiny pulses of energy. These tiny pulses of energy are referred to as photons.
Semiconductors
All substances can be arranged in order of their ability to conduct electrical charges. Those at the
top of the list are called conductors, and those at the bottom are called insulators. Whether a
substance is classified as a conductor or an insulator depends on its interatomic bonding and on
how tightly the atoms of the substance hold their electrons. The interatomic bonding in some
materials, such as silicon, is intermediate between that of a good conductor and that of a good
insulator.
Fig 7.2
Silicon and germanium belong to group of materials called semiconductors. They are good
insulators in their pure crystalline form at very low temperature. Conductivity increases with
temperature or when they are exposed to light Conductivity can be increased tremendously when
even one atom in ten million is replaced with an impurity that adds or removes an electron from
the crystal structure. The chips used in electronics are made of semiconductor materials, and so
are photovoltaic cells. The most common semiconductor is silicon. Semiconductor materials
will also interact with light (see Figure 1). A photon hitting a silicon atom can give an electron
within the atom enough energy to leave it and move off through the structure. The negatively
charged electron leaves a positively charged hole (a position once occupied by an electron) in its
place; so the photon has created an electron/hole pair. An electron orbiting a surrounding atom
near to a hole can move into the hole leaving a new hole in its place; in this way the positively
charged holes can also move through the structure. In the presence of an electric field the
electrons move in one direction and the holes in the other, because they have opposite electric
charges with holes behaving in nearly all respects as positive particles. In semiconductor
materials, electric current is the flow of oppositely charged electrons and holes.
Rubber, glass, wood
Copper, iron,
aluminium, goldSilicon, germanium
Semi-conductorsPoor conductors
Good insulators
Good conductors
Poor insulators

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The Photovoltaic (PV) Effect
Without an electric field to separate the electrons and holes created by the light they would soon
recombine and there would be no net current. To avoid this a photovoltaic cell (PV cell) is a
wafer or thin film of semiconductor material which is arranged to have an internal electric field,
pointing from the top surface of the wafer or film to the bottom surface (or vice versa). An
electrical contact, usually aluminum, covers the bottom surface. The top surface also has an
electrical contact, but this one is transparent so as to let in the light. When the silicon (or other
semiconductor material) in the PV cell absorbs light, electron/hole pairs are generated. Because
of the internal electric field the electrons move to one contact and holes to the other thus building
up a voltage. The cell acts as a voltage source. If you connect the two contacts with a wire an
electric current will flow in the wire; this is known as the "short-circuit current" of the PV cell;
you can measure it with an ammeter. If you don't connect the contacts the electrons and holes
build up on opposite surfaces of the cell, producing a voltage between the contacts that you can
measure with a voltmeter; this is called the "open-circuit voltage" of the PV cell.
The internal field:
To produce the necessary internal electric field we make use of two types of "doped"
semiconductor material; these are called "n-type" and "p-type" material.
N-type silicon contains a small percentage of phosphorus atoms. These fit quite well into the
structure of the silicon, except that each has one more electron than each silicon atom. These
extra electrons escape from the phosphorus and are free to move round the structure; what they
leave behind are positively charged phosphorus ions, (which are fixed in the structure and can't
move). The phosphorus is called an n-type dopant because of the negative electrons it adds to
the silicon; the resulting material is called n-type silicon because of the electrons it contains
(though you should remember it contains an equal number of positive fixed charges).
P-type silicon contains boron atoms. These fit quite well into the structure of the silicon, except
that each has one fewer electrons than each silicon atom. They therefore grab electrons from the

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silicon, creating holes that are free to move round the structure; what the holes leave behind are
negatively charged boron ions, (because of the extra electron they've grabbed); the boron ions are
fixed in the structure and can't move. The material is called p-type because of the positive holes
it contains; it also contains an equal number of negative fixed charges. Boron is said to be a p-
type dopant in silicon.
Now consider a wafer of silicon that has excess boron in the top half (p-type silicon) and excess
phosphorus in the bottom half (n-type silicon). In the middle there is what is called a pn-
junction, where the material changes from p-type to n-type. On the n-type side of the junction
there will be electrons and fixed positive charge (phosphorus ions); on the p-type side there will
be holes and fixed negative charge (boron ions). Because there are many electrons in n-type and
very few in p-type material the electrons from the n-side will tend to spread into the p-side,
leaving some net positive charge on the n-side (because of the positive phosphorus ions); this
positive charge will stop the electrons diffusing too far into the p-type material and is further
increased by holes spreading from the p-side, (which also leaves negative charge on the p-side,
because of the negative boron ions). The result is fixed positive electric charges on the n-type
side of the junction and negative fixed charges on the p-type side. This produces an internal
electric field pointing across the junction, which is precisely what is needed for a PV cell.
This accelerates electrons from electron-hole pairs separated by light from the p-type material
into the n-type material where there are many electrons and few holes and so not much chance of
recombining. Similarly the junction accelerates holes from electron-hole pairs in the n-type
material to the p-type material where they are similarly unlikely to recombine.

26
Solarcells
A solar cell is a PV cell designed to convert sunlight to electricity. The simplest cells (Figure 1a)
consist of a circular silicon wafer with a pn-junction sandwiched in the middle, a metallic bottom
contact (e.g. aluminum) and a transparent top contact (either a transparent conducting oxide or a
grid-like metal structure). Solar panels with cells like this have played a vital role in space
technology since the late '50s, powering space satellites. They are expensive to produce because
silicon wafers are expensive to produce (mainly because they are high-purity single crystals) but
their cost was unimportant in the space race.
Fig 7.3
In recent years there has been a continuous search for cheaper forms of PV cell, economical
enough to be used in applications here on earth (terrestrial applications). Attempts have been
made to use cheaper forms of silicon, of lower quality than that used in computer chips, despite
the poorer cell efficiencies that result. One possibility has been to replace the single-crystal
wafer by polycrystalline squares, (consisting of many small grains of crystalline material). A
more radical approach is to use amorphous silicon, having no crystalline structure at all. This
material has the advantage of being much more light-absorbing than crystalline silicon: a thin
film on a suitable substrate only a few microns thick (a thousandth of a millimeter) absorbs most
of the sunlight falling on it; by contrast crystalline cells have to be about 100 microns and in
practice are 0.5mm thick. This means that you need far less amorphous silicon to make the cells,
and they can even be made flexible, whereas crystalline cells are very fragile. The electrons and
holes don't move so easily in amorphous silicon, but this is partly compensated for by the fact
Photon
BACK CONTACT PLATE
FRONT CONTACT GRID
SILICON CONTAINING BORON AS DOPANT
SILICON CONTAINING PHOSPHOROUS AS DOPANT
P-region
N-region
Hole
Electron
Hole
Electron
Photon
Photon





27
that they don't have to move as far (because the cell is so thin). Cell efficiencies are perhaps only
half those in crystalline silicon, but the amorphous cells potentially cost much less than half for
the same surface area, so they seem to be the most economical choice at the moment.
Manufacture of amorphous siliconsolarcells
The manufacture of amorphous silicon cells (e.g. by UNI-SOLAR) is very different from that
of crystalline cells. No wafers are involved. Instead the silicon is deposited as a thin film on a
substrate, usually either stainless steel or a glass sheet covered with a layer of tin oxide acting as
a transparent contact.
As shown in Figure 2, the substrate is placed in a steel chamber which is evacuated (i.e. all the
air is pumped out); a small amount of the gas saline (a gaseous compound of silicon and
hydrogen) is then bled in through a valve. Two metal plates within the chamber connect to a
radio-frequency power supply which sets up a purple-colored glow discharge (sometimes called
a plasma) in the saline gas; electrons collide with saline molecules and knock away the hydrogen
atoms, leading to the silicon atoms depositing in a thin amorphous film on the substrate (mixed
with some of the hydrogen atoms, which in fact turn out to be beneficial for the cell). Substrates
used are often 300 mm wide, but in principle they could be larger, limited only by the size of the
deposition chamber.
To make n-type amorphous silicon the same procedure is followed, except that the saline is
mixed with one or two per cent of the gas phosphine, a compound of phosphorus and hydrogen.
To make p-type amorphous silicon the saline is mixed with diorama, a compound of boron and
hydrogen. Either separate chambers or sequential gas streams are used for making each type.
Fig 7.4
Photon
SUPERSTRATE (not necessary if stainless steel back contact used)
N-layer
P-layer
INTRINSIC
LAYER
AMORPHOUS SILICON
AMORPHOUS SILICON CONTAINING BORON
AMORPHOUS SILICON CONTAINING PHOSPHOROUS
Transparent front contact (tin oxide or indium-tin oxide)
Aluminium back contact or stainless steel


Electron
Hole
Photon
Photon


Electron
Hole

28
Unfortunately electron-hole recombination of n- or p-type amorphous silicon to light is very
high. To get round this problem the cell is made mostly from undoped amorphous silicon (i.e.
using just saline): the thin film of undoped amorphous silicon is sandwiched between far thinner
layers of n- and p-type amorphous silicon, as shown in Figure 1b. The n- and p-layers serve to
produce the internal field across the undoped layer, but almost all the light is absorbed in the
undoped layer. (The undoped material is referred to as intrinsic, and the cell is said to have a p-
i-n structure, as opposed to the p-n structure of crystalline silicon cells).
The process used for depositing amorphous silicon lends itself well to mass production
techniques. The substrate (with its electrical contact layer if necessary) passes into a chamber
and receives the n-type deposition, then into a chamber receiving the undoped deposition, and
then to chamber receiving the p-type deposition. (This is simpler to automate than cutting and
polishing wafers).
The PV industry benefits from technological developments in other fields. The development of
silicon coated drums for colour photocopiers is now applied to the production of continuous
metal strips covered with amorphous silicon. If the substrate is flexible stainless steel (as with
Plugging into the Sun laminates) that can be wound into a large roll, it is possible to have a
continuous roll-to-roll production process for amorphous silicon solar cells, (Figure 3). The
stainless steel sheet unwinds from the supply roll and passes though cleaning procedures and the
chambers for n-type, intrinsic, and p-type deposition before reaching the take-up roll. The
resulting cells have the additional advantage of being flexible.
Many manufacturers base their cells on glass substrates. Normally tin-oxide-coated glass is used
since the tin oxide serves as a transparent contact. The p-layer is deposited, followed by the i-
layer and then the n-layer. Aluminum is deposited to form the back contact. In this form of
structure the cell is illuminated through the glass and is protected by it (it is therefore known as a
superstrate).
A single silicon solar cell produces an open-circuit voltage of about 0.5volt. There are
amorphous silicon solar modules that are in fact single cells, producing a low voltage and a
correspondingly high current. However, it is far more common for the module to be divided into
individual strip-shaped cells, which are arranged to be connected in series to produce a working
voltage of around 14 volts, suitable for charging 12-volt lead-acid batteries.

29
We have dealt with the main principles of amorphous silicon solar cell production. There is a
mass of subsidiary detail which is too extensive to cover here. Cell efficiencies can be increased
to some extent by including a second p-i-n structure under the first, using an alloy of amorphous
silicon with germanium. This absorbs a longer wavelength part of the solar spectrum. This is
called a tandem cell or multi-junction cell.
Fig 8.1
Spectrum-splitting
cell,constructed of
three separate p-i-n
type,amorphous
semiconductorsolar
sub-cells,eachwitha
differentspectral
response
characteristic.Inthis
way,the cell can
convertthe different
visible andnear
infraredwavelengths
of sunlightwith
optimal efficiency.

30
How a triple (three layer) UNI-SOLAR amorphous silicon PV cell is made.
Fig 8.2
Adding a third p-i-n structure forms a triple-junction cell. (In production terms this is just a
matter of additional chambers and their gas supplies; see Figure 3b). The right sort of
roughening of the cell surface leads to less reflection from the cell surface, and to corresponding
increases in cell efficiency. The front contact needs careful design, and the whole cell must be
suitably encapsulated and protected against the weather. If everything is done right there is no
reason why the cells should not last for thirty years or more.
N-layer chamber
P-layer chamber
Thicker intrinsic layer chamber
In Roll Out Roll
N-layer chamber
P-layer chamber
N-layer chamber P-layer chamber
N-layer chamber
P-layer chamber
P-layer
chamber
N-layer chamber
In Roll Out Roll

31
Substrate (stainless
steel or glass)
passing through
chamber
Electrode 1
Electrode 2
Excited molecules in a
gaseous state containing:
Silicon and either boron (p-
layer) or phosphorus (n-
layer)
Regular layer of
deposited silicon
and >1% doping
material





 

 
 









 



32
LASER Light:
Fig 8.3
A laseris a device that emits light through a process of optical amplification based on
the stimulated emission of electromagnetic radiation. The term "laser" originated as
an acronym for "light amplification by stimulated emission of radiation". The first laser was
built in 1960 by Theodore H. Mailman at Hughes Laboratories, based on theoretical work
by Charles Hard Townes and Arthur Leonard Schawlow. A laser differs from other sources of
light in that it emits light coherently. Spatial coherence allows a laser to be focused to a tight
spot, enabling applications such as laser cutting and lithography. Spatial coherence also allows a
laser beam to stay narrow over great distances (collimation), enabling applications such as laser
pointers. Lasers can also have high temporal coherence, which allows them to emit light with a
very narrow spectrum, i.e., they can emit a single color of light. Temporal coherence can be used
to produce pulses of light as short as a femtosecond.

33
Loud Speaker:
Fig 8.4
A loudspeaker (or loud-speaker or speaker) is an electroacoustic transducer; [1] a device which
converts an electrical audio signal into a corresponding sound.[2] The first crude loudspeakers
were invented during the development of telephone systems in the late 1800s, but electronic
amplification by vacuum tube beginning around 1912 made loudspeakers truly practical. By the
1920s they were used in radios, phonographs, public address systems and theatre sound systems
for talking motion pictures.
The most widely-used type of speaker today is the dynamic speaker, invented in 1925 by Edward
W. Kellogg and Chester W. Rice. The dynamic speaker operates on the same basic principle as
a dynamic microphone, but in reverse, to produce sound from an electrical signal. When an
alternating current electrical audio signal input is applied through the voice coil, a coil of wire
suspended in a circular gap between the poles of a permanent magnet, the coil is forced to move
rapidly back and forth due to Faraday's law of induction, which causes a diaphragm (usually
conically shaped) attached to the coil to move back and forth, pushing on the air to create sound

34
waves. Besides this most common method, there are several alternative technologies that can be
used to convert an electrical signal into sound.
PCB (Printed Circuit Board):
Fig 8.3
A printed circuit board (PCB) mechanically supports and electrically
connects electronic components using conductive tracks, pads and other features etched from
copper sheets laminated onto a non-conductive substrate. PCBs can be single sided (one copper
layer), double sided (two copper layers) or multi-layer (outer and inner layers). Multi-layer PCBs
allow for much higher component density. Conductors on different layers are connected with
plated-through holes called vias. Advanced PCBs may contain components - capacitors, resistors
or active devices - embedded in the substrate.
Processto DesignPCB:
 Front-end tooldata preparation
 The board designer has prepared his layout on a Computer Aided Design or CAD
system. Each CAD system uses its own internal data format, so the PCB industry has
developed a standard output format to transfer the layout data to the manufacturer.
 Preparing the photo tools.

35
 We use laser photo plotters in a temperature and humidity-controlled darkroom to make
the films we will use later to image the PCBs. The photo plotter takes the board data and
converts it into a pixel image. A laser writes this onto the film. The exposed film is
automatically developed and unloaded for the operator.
 Print inner layers.
 To produce the inner layers of our multilayer PCB, we start with a panel of laminate.
Laminate is an epoxy resin and glass-fibre core with copper foil pre-bonded onto each
side.
 Etch inner layers.
 We remove the unwanted copper using a powerful alkaline solution to dissolve (or etch
away) the exposed copper. The process is carefully controlled to ensure that the finished
conductor widths are exactly as designed. But designers should be aware that thicker
copper foils need wider spaces between the tracks. The operator checks carefully that all
the unwanted copper has been etched away.
 Registerpunch and Automatic Optical Inspection (AOI)
 The inner core of our multilayer is now complete. Next we punch the registration holes
we will use to align the inner layers to the outer layers. The operator loads the core into
the optical punch which lines up the registration targets in the copper pattern and
punches the registration holes.
 Lay-up and bond
 The outer layers of our multilayer consist of sheets of glass cloth pre-impregnated with
uncured epoxy resin (prepare) and a thin copper foil.
 Drilling the PCB
 Now we drill the holes for leaded components and the via holes that link the copper
layers together. First we use an X-ray drill to locate targets in the copper of the inner
layers. The machine drills registration holes to ensure that we will drill precisely through
the centre of the inner layer pads.
 Electrolysescopperdeposition

36
 The first step in the plating process is the chemical deposition of a very thin layer of
copper on the hole walls.
 Image the outer layers.
 We image the outer layers in a clean room to make sure that no dust gets onto the panel
surface where it could cause a short or open circuit on the finished PCB.
 Platedgold edge connectors.
 For edge-connectors we electroplate hard gold. First the operator puts protective tape on
the board above the connectors. Then he mounts the panel on a horizontal electroplating
bath.
Printed Circuit BoardLayout:

38
Fig 9.2
CONCLUSION
The possibilities are numerous and can be explored further. If his technology can be put
into practical use, every bulb can be used something like a Wi-Fi hotspot to transmit wireless
data and we will proceed toward the cleaner, greener, safer and brighter future. The concept of
Li-Fi is currently attracting a great deal of interest, not least because it may offer a genuine and
very efficient alternative to radio-based wireless. As a growing number of people and their many
devices access wireless internet, the airwaves are becoming increasingly clogged, making it more
and more difficult to get a reliable, high-speed signal. This may solve issues such as the shortage
of radio-frequency bandwidth and also allow internet where traditional radio based wireless isn’t
allowed such as aircraft or hospitals. One of the shortcomings however is that it only work in
direct line of sight.

39
References:-
Websites:-
1:- http://timesofindia.indiatimes.com/home/science/Now-just-light-a-bulb-to-
switch-on-your-broadband/articleshow/9713554.cms
2:-
http://oledcomm.com/lifi.html
3:-
http://en.wikipedia.org/wiki/Li-Fi
4:-
https://images.google.com/

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