International Journal of Advanced Engineering Research and Technology (IJAERT) Volume 4 Issue 5, May 2016, ISSN No.: 2348 8190

160

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Li-Fi Technology based Data Transciever System

C. Navin Kumar*, Abhinav Singh**, B. Premalatha*** *,** Third Year B.E Students, Department of ECE, Coimbatore Institute of Technology, Coimbatore-14.

***Assistant Professor, Department of ECE, Coimbatore Institute of Technology, Coimbatore-14.

ABSTRACT At present, enormous new technologies are participating

to satisfy the growing demands of wireless

communication environment for an end user. A new

technology proposed by the German physicist-Harald

Haas, named Li-Fi (Light-Fidelity) provides

transmission of data through illumination. Data can be

sent through an LED bulb in which the intensity gets

varied faster than the human eye could follow and at the

same time illuminating the room. As the number of users

increases everyday there is a need for an alternative

which does not depend on the current technology.

Visible light communication can be the solution. It

provides high security communication where the digital

data in the transmitter is encoded before being

transmitted by the LED. Microcontroller was used in

transmitter as well as in the receiver. The encoded digital

data is transmitted through LED bulbs using a

microcontroller and it is received by a photodiode where

it is decoded by another microcontroller.

Keywords LED, Li-Fi, Visible Light Communication

I. INTRODUCTION Li-Fi technology has been proposed to transmit digital

data through LED bulbs by varying its intensity very

faster which is too quick to be noticed by the human eye.

Amplitude modulation is done in which the LED bulbs

are switched ON and OFF million times per second

where light ON denotes logic 1 and light OFF

denotes logic 0. Li-Fi is an emerging branch of

wireless optical communication which can provide high

data transmission rate depending on the switching

characteristics of LEDs. Nowadays LED bulbs are used

everywhere for lighting purpose and data transmission

through the same makes it more advantageous.

Also RF waves produced by devices causes

Interference. i.e. Affects the operation of nearby

devices. For example, in Hospitals Wi-Fi is not used

because of the above reason. But visible light doesnt

have this effect. Also LEDs are made from Non-toxic

substances and has no effects on living tissues unlike

Wi-Fi. So it does not possess any biological threat. The

objective is to transmit any digital data to a particular

distance through visible light and at the same time

illuminate the room. In this project text messages were

transmitted through LED bulb to a particular distance

where the distance of transmission depends on the

intensity of the LED bulb used. Greater the power of

LED bulb, more will be the transmitted distance.

II. PROPOSED SYSTEM The entire project is covered in the block diagram as

shown in fig.1. In the transmitter section input data is

converted to digital form by an ADC in case of analog

input and for digital input ADC is not required. The

digital data is then given to the microcontroller where

encoding is done. The encoded data is sent to the LED

bulb through a driver circuit which is powered

separately. Intensity modulation is done in which light

OFF denotes logic 0 and light ON denotes logic 1. In

the receiver section, a photo detector receives the

encoded data sequence and it is decoded using another

microcontroller. In order to differentiate between 0s and

1s a threshold level is set in the controller. This level is

based on the intensity of the LED bulb used and the

ambient light falling on the photo diode. This setting

decreases the probability of wrong decision by the

receiver.

Fig.1 Block diagram of proposed system

Now by using DAC (only if ADC was used in

transmitter) analog output is obtained and thus original

data is retrieved.

III. ENCODING METHOD When a digital data sequence is transmitted there is a

possibility that the LED may flicker which could be

detected by the naked eye. This is not appreciable

because the objective is to brighten the room and at the

same time transmit the data. So encoding has to be done

to eliminate the flickering problem. The only alternate to

this problem is to encode the bit streams with maximum

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International Journal of Advanced Engineering Research and Technology (IJAERT) Volume 4 Issue 5, May 2016, ISSN No.: 2348 8190

161

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number of 1s possible (i.e. Reduce the number of zeros

to be transmitted) and at the receiver decode them to get

the original data back.

IV. HARDWARE REQUIREMENTS 4.1 ADC

The analog signal is converted to digital signal using

analog to digital convertor (ADC). The Microchip

Technology Inc. MCP3002 is a successive

approximation 10-bit Analog-to-Digital (A/D) Converter

used in this project. ADC is used only when the input

signal is analog and it is optional.

4.2 DAC

The digital data is converted back to analog signal at the

receiver using Digital to Analog convertor (DAC). The

MCP4716 are single channel 10-bit buffered voltage

output Digital-to Analog Converters (DAC) with

nonvolatile memory and an I2C serial interface is used

here. This is also optional.

4.3 Microcontroller Encoding of digital data is done through a

microcontroller and it is transmitted through an LED

bulb. This is done to eliminate the flickering problem. In

the receiver side the data is decoded by another

controller. ATmega328P is an 8-bit microcontroller from

ATMEL and is used in this project.

4.4 LED

High power DC LED bulb which is enough to brighten a

small room is used for data transmission too. Encoded

data stream is transmitted serially to the LED from the

controller.

4.5 LED Driver The output power from the controller is not sufficient to

drive the high power LED so driver circuit must be used.

L293D driver is used to serve for this purpose in this

project. Separate power supply is provided to the driver

to drive the LED.

4.6 Photo detector

To convert light signals to electrical signal photo diode

is used. BPW34S is a PIN photodiode with high speed

and high radiant sensitivity which is sensitive to visible

and near infrared radiation is used in this project.

V. EXPERIMENTAL RESULTS 5.1 Stage-1 Proof of Concept (PoC) The objective is to transmit digital data through LED. So

the initial step is to check whether data can be sent

through an LED or not. Therefore the primary focus was

to transmit and receive square wave (simple digital data)

and not on the distance of transmission. Square wave

was produced using microcontroller and the output was

given to the LED .The light signal captured by the photo

diode was displayed in a CRO after amplification.

Fig.2 Stage 1- Block diagram

Fig.3 Square wave transmission

Fig.4 amplification and buffer circuit

Fig.5 CRO output

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International Journal of Advanced Engineering Research and Technology (IJAERT) Volume 4 Issue 5, May 2016, ISSN No.: 2348 8190

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5.2 Stage-2 Stepping into Li-Fi In stage-2 two major changes were included in the

system:

Small sized LED was replaced by a high power LED

bulb and LED driver circuit was used to give necessary

power to the bulb. This was done to increase the distance

of transmission and also for brightening the room. Fig.6

and Fig.7 explains the experimental setup and its

description.

Fig.6 Stage 2- Block diagram

In this stage the only focus was on increasing the

distance of transmission while the data was still the same

square wave. Thus the actual concept of Li-Fi was

demonstrated in this stage.

Fig.7 Stage-2 Setup

5.3 Stage-3 Transmitting text messages The final stage of this project is to transmit TEXT

messages from one system to another.

Fig.8 Stage-3 Setup

Fig.9 Data transmission

Fig.10 Data at the transmitter side

Fig.11 Output at the Receiver Side

VI. CONCLUSION AND FUTURE WORK Thus the digital data was transmitted using LED bulb in

an efficient manner without much complication. The

desired output was obtained. Lighting the room and

simultaneous transmission of text messages were done

successfully. The distance of transmission depends on

the intensity of the bulb used. This work can be

extended even better by applying the same concept in

smart phones. By developing an android application to

control the LED flash light used for camera,

transmission of any files to the neighboring devices can

be achieved. The same hardware for flashing purpose

can also be used for data transmission at a very high rate.

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