Li-Fi stands for Light-Fidelity. Li-Fi is transmission of data using visible light by sending data through an LED light bulb that varies in intensity faster than the human eye can follow. If the LED is on, the photo detector registers a binary one; otherwise it’s a binary zero. The idea of Li-Fi was introduced by a German physicist, Harald Hass, which he also referred to as “Data through Illumination”. The term Li-Fi was first used by Haas in his TED Global talk on Visible Light Communication. According to Hass, the light, which he referred to as ‘DLight’, can be used to produce data rates higher than 1 Giga bits per second which is much faster than our average broadband connection. Here a practical circuit to transfer audio signal is implemented

1. (Light Fidelity)
Mini Project
Presenting By:
- Muhammed Anaz PK (27)
- Mahamood Salam Ali PM (25)
(S7 ECE -B)

2. What is Li-Fi…?
 Li-Fi is a form of wireless communication system in which Light is
used as Carrier Signal.
 It uses LED’s to Transmit Data wirelessly.
 Li-Fi is also Known as Visible Light Communication System (VLC).
 VLC uses Rapid Pulses of Light to Transmit Information Wirelessly
that cannot be detected by Human Eye.
 It is works by switching LED’s ON and OFF within Nanoseconds
(ns).
 Since light cannot penetrate through walls, so Li-Fi is currently used
in short range, even though it is more secure than Wi-Fi from
Hacking.
 Minimum speed of Li-Fi is 1Gbps.
 Reflected Light can give up to 70 mbps speed.
 Li-Fi has Higher Bandwidth than Wi-Fi (~10,000 Times).
 Currently Li-Fi is its initial stages, more advancement can be
seen as time proceeds.

3. How Li-Fi Works…?

4.  Electrical Signals Corresponding to Sound is fed to
Lamp Driver consist of Op-Amp and Transistor.
 Op amp acts as an comparator and output is Pulse
Signals.
 This signal is fed to the base of transistor, which act as
modulator and Amplifier.
 Modulated signal is send to the air as light (Stream of
Photons) using LED
 At the Receiver end Photo Detector is used to receive
transmitted signal
 Received data, after Processing and Amplification Fed
to Speaker.

5. Circuit Diagram
Transmitter Circuit

6. Circuit Description
 Circuit consist of an Op-Amp (µA 741), transistor BC548 and an
LED bulb with Resistors and capacitors of different values .
 The input Low Frequency signal is fed to the Pin 3 of op-amp
and it compares with the Pin 2,and Pulse signals are generated
at Pin 6 of Op-Amp
 BC 548 is a general purpose NPN BJT transistor used as a
switching/ Modulating circuit and amplifier, the output of op- Amp
is fed to the base of transistor, which makes transistor keep alive
and LED continues to glow
 Whenever signal at Pin 3 is interrupted, there will be low
fluctuation at Pin 6 and is amplified by Transistor, which gives
flickering effect to LED and makes Li-Fi to become Live.
 The flickering of LED Cannot be detected Human eye.

7. Components Details
µA-741
 A-741is general Purpose operational amplifier.
 It is ideal for Voltage follower applications
 The device exhibits high stability and is short
circuit protected.
 it can be configured in inverting and Non-Inverting Mode.
 It can be used to implement comparators, Astable,
Monostable Multvibrators. Amplifiers, etc..

8. BC 548 Transistor
 It is a general purpose silicon NPN BJT.
 It is used for Amplification and switching applications.
 The current gain is vary between 110 to 800.
 For Amplification applications it is used in common emitter
Configuration.
 For switching applications, Transistor is biased so that it is
fully ON if there is a signal at its base and OFF otherwise.

9. LED
 LEDs are special type of Diodes, which emit light only when it
is forward biased.
 The most important requirement of light source is its ability to
turn ON and OFF Repeatedly in very short intervals.
 LEDs have fast Switching Characteristics
 They can be used as a light source as well as communication
Transmitter.

10. Receiver Circuit

11. Circuit Description
 Circuit Consist of Photo detector, Amplifier,
Speaker.
 The light is received by photodiode and convert
it to electrical signal
 I is amplified by the transistor
 And fed to the Speaker.

12. Component Description
Photo Detector
 It is a semi conductor device that converts light in to current, it
is generated when photons are absorbed by the diode.
 It have usually slower time response as their area increases.
 Usually solar cell is used to generate electric signal as it is a
large area Photodiode.
 It works reverse biased mode.
Solar CellPhoto Diode

13. Speaker
 Speaker converts electrical signals to Audible
sound signals
 It converts using electro magnets present in
the speaker.

14. Advantages
 More Spectrum Than Radio Waves (~10,000 Times). So it could use
high data rates.
 Light Boxes are already available, so infrastructure is already available
and installed.
 Highly Efficient Since LED’s are cheap and Less Power Consuming.
 More speed compared to Wi-Fi.
 No License is required to use visible Light Frequency band, so it is
cheaper.
 Light can’t Pass through Objects.
 Interference from external sources like Sun, Bulbs, and opaque
materials in the path of transmission will cause interruption in the
communication (Slightly).
 Li-Fi Requires Line of Sight (LOS).
 Main problem is still persisting is How an receiving device will transmit
back to the transmitter.
Limitations

15. Applications.
 Street Lamps can be used as access points.
 Can be used in Airlines for communication. Since aircrafts
uses radio waves to communicate with the ATC, presently
communication inside the aircrafts are limited. this drawback
can be overcome by Light waves.
 Can be use in medical equipment's.
 Visible light is more safe than RF, so it can be used in places
where RF can’t be used. Such as Petrochemical Plants.
 It can be used in ocean Beds.
 Li-Fi is still in Infancy, so more applications can be found as
development of this Technology take boom.
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