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Audio Transmission via VLC
A Thesis
Submitted in Partial Fulfillment of the
Subject Requirements in Thesis II (ELE527)
Respectfully Submitted By:
Marc Anthony B. Gonzales
Renz Mark C. Rico
Researchers
Respectfully Submitted To:
Engr. Arlene C. Grate, ECE, MEng-ECE
Research Adviser
March 2016
ii
APPROVAL SHEET
In partial fulfillment of the requirements for the degree of Bachelor of Science in
Electronics Engineering, this thesis entitled “Audio Transmission via VLC” has been
prepared and submitted by Marc Anthony B. Gonzales and Renz Mark C. Rico who are
hereby recommended for oral examination.
ENGR. ARLENE CERICO-GRATE, ECE, MEng-ECE
Research Adviser
Approved in partial fulfillment of the requirements for the degree of Bachelor of
Science in Electronics Engineering by the Committee on Oral Examination.
ENGR. GREG MALLARI, ECE, PECE, REE, MEng-EE
Chairman
ENGR. NOEL YAP, ECE, MIT ENGR. SALLY C. CORPUS, ECE, MBA Critic/Member Member
Accepted in partial fulfillment of the requirements for the degree of Bachelor of
Science in Electronics and Communications Engineering.
ENGR. ARLENE CERICO-GRATE, ECE, MEng-ECE
Chairperson, Electronics Engineering Department
ENGR. GREG MALLARI, ECE, PECE, REE, MEng-EE
Dean, College of Engineering
iii
Acknowledgment
To the energetic, supportive, and beautiful professor of the proponents, Engr.
Arlene C. Grate, ECE, MEng-ECE for her undying guidance on the whole process of this
thesis. Her words of wisdom, motivational quotes and unending reminders of the
deadlines gave the proponents the courage and strength to pursue the project research and
accomplish the tasks on time. She has selflessly given her time and expertise to help the
proponents on their inquiries for the purpose of improving their study. Her encouraging
words made the proponents focus and consistent in completing this project research.
To the friends, classmates, and especially to the families of the proponents who
are always willing to help and give what they have without expecting anything in return.
Their contributions on this project research are priceless. The proponents are very lucky
to have generous, loving, and caring persons like them.
To the very helpful personnel of Electronics Engineering laboratory like Sir Luigi
Gayacao and Engr. Sally C. Corpus, ECE, MBA, who are always ready to give the
equipment and materials needed by the proponents on their experimentations. To the very
kind school Librarian, Mrs. Jocelyn C. David who always allows the researchers to see
other thesis works for their references. To the respondents who generously given their
time to evaluate the prototype made by the proponents.
And to the One and Almighty God who enlightened the path of the proponents
on their journey to the kingdom of knowledge and the One who helped them open the
door to see the brighter side of life.
THANK YOU!!!
iv
Dedication
This study is wholeheartedly dedicated
To researchers’ family
To researchers’ professor
To classmates and friends
To future researchers
The Researchers
v
ABSTRACT
Visible light communications is the emerging technology nowadays. Using visible
light to transmit information to the receiver is the basic principle of this technology.
Integrating communication to visible light is the main concern of this study. In this paper,
the researchers presented a wireless audio transmission using visible light. The system
consists of audio source (from microphone or portable devices), transmitter circuit (where
the visible light is connected), and a receiver circuit (an audio amplifier with solar cell
attached to it).The researchers aim to provide a two-way wireless communication using
visible light.
Keywords: Visible Light Communication, Wireless Audio Transmission
vi
TABLE OF CONTENTS
Page
TITLE PAGE…………………………………………………………….…….… I
APPROVAL SHEET ……..……………………………………………………… Ii
ACKNOWLEDGMENT ………..………………………………………..……… Iii
DEDICATION …………………………..……………………………….……… Iv
ABSTRACT ………………..…..…..……………………………….…………… V
TABLE OF CONTENTS ………………………..……………………….……… Vi
LIST OF TABLES ………………………………..………………………...…… Viii
LIST OF FIGURES ………………………………..………………………...…… Ix
CHAPTER
I. THE PROBLEM AND ITS BACKGROUND
Introduction ………………………………………….………………..… 1
Statement of the Problem ……………………………………………..… 2
Significance of the Study …………………………………………..…… 3
Scope and Delimitation of the Study ………………………..……...….. 3
II. THEORETICAL FRAMEWORK
Related Literature………………………………………………..……… 4
Related Studies…………………………………………………………..
Conceptual Framework …………………………………………..........
17
29
vii
Definition of Terms …………………………………………………… 30
III. METHODOLOGY
Project Research Design…..…………………..………………………… 31
Project Development ……………………...…………………………..... 33
Instruments and Techniques Used………………………………………. 52
Bill of Materials …………………………………………… …………. 64
Time Frame.…..…………………………………………… …………. 65
IV. RESULTS AND DISCUSSION
Project Technical Description …………..………………..…..……… 66
Project Limitations and Capabilities…………………….…………… 69
Project Evaluation………………….…………………….…………… 70
V. SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS
Summary ………………………………………..…………………….
Conclusion…………………………………………………………….
Recommendation……………………………………………………..
79
80
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REFERENCES……………………………………………………..…………
APPENDIX…..………………….…………………………………………….
CURRICULUM VITAE ………………….………….......................................
viii
LIST OF TABLES
Table Page
1 Timeline of VLC Deployment………………..…………………… 5
2 Table of Specification of LM2904D Op Amp…………………..... 56
3
4
5
6
7
8
Data Sheet of BC547 and BC548 Transistors……..………………
Bill of Materials……….……………………………………………
Time Frame………………………………………………………...
Mean Range Interpretation…………………………………………
Evaluation Instrument Analysis……………………………………
System Evaluation Summary………………………………………
58
64
65
72
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ix
LIST OF FIGURES
Figure Page
1 Illustration of Photophone Transmitter and Receiver………………. 4
2 Dispersion of White Light in Prism and Visible Light Spectrum……. 10
3 Visible Light Communications………………………………............ 11
4 Smart Lighting Systems……………………………………………… 12
5 VLC on Hospitals and Aircrafts……………………………………. 13
6 VLC for Mobile Connectivity……………………………………… 14
7 Vehicle-to-Vehicle Communications…..……………………………. 14
8 Underwater Communication via VLC……………………………… 15
9 Defense and Security Application of VLC...…………………......... 15
10 Block Diagram of VLC Transmitter Design……………………..… 17
11 Block Diagram of VLC Receiver Design……………………...……. 18
12 Layout of Moritz’s Project………………………………………….. 20
13 VLC Audio Transmitter and Receiver Block Diagram…………….. 22
14
15
16
17
18
Final Products of VLC Audio Transmitter and Receiver……………
Real Time Video/Audio VLC transmission System…………………
Laser Torch Based Transmitter and Receiver……………………….
Basic Circuit and Constructed Prototype for Airline Entertainment VLC
audio Transmission System…………………………………..
Conceptual Framework………………………………………………
22
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x
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Audio Transmitter Block Diagram………………………………….
Audio Receiver Block Diagram……………………………………..
Connecting a Small Solar Cell from Calculator to the Audio Jack Wire
of Mono Portable Speaker…………………………………….
First Audio Transmissions Using Ordinary White Light LED………..
First Transmission of Audio Signals Using Cellphone……………....
First Transmission of Audio Signals from Laptop and Cellphone with a
Distance of 5 Meters…………………………………………………..
Closer Look of Transmitter Circuit With Left and Right Audio
Signals………………………………………………………………….
Wireless Audio Transmissions Using Multiple Receivers………….....
Making of Electret Microphone Preamplifier Circuit………………….
Making of Audio Amplifier Circuit…………………………………….
Waveform at the Transmitter’s Output Terminal While Playing a Music
from a Cellphone…………………………………………….................
Waveform Generated by the Solar Cell while Transmitting Audio Signal
from a Cellphone……………………………………………..................
Output Waveform of the Electret Microphone Preamplifier
Circuit……………………………………………………………………..
Wireless Audio Transmission Using Visible Light at a Distance of 5
Meters…………………………………………………………………….
VLC Transmitter Circuit Diagram………………………………………
Electret Microphone Preamplifier Circuit Diagram…………………….
32
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xi
35
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VLC Receiver Circuit Diagram…………………………………………
Transmitter Circuit for Printing………………………………………..
Microphone Preamplifier Circuit on a Pre-synthesized PCB…………..
Audio Amplifier Circuit on a Pre-synthesized PCB……………………
Soldering of the Components………..…………………………………
Electret Microphone…………………………………………………….
Audio Jack Plug…………..…………………………………………….
Power Light Emitting Diode….…………………………………………
LM2904D Pin out Connections…………………………………………
BC547 and BC548 Transistors………………………………………….
Electrolytic and Ceramic Capacitors……………………………………
Generic Resistors and Potentiometer……………………………………
AC Adapter and 9 Volt Battery…………………………………………
Solar Cells……………………………………………………………….
Multimedia Speakers……………………………………………………
Printed Circuit Board……………………………………………………
Breadboard and Jumper Wires………………………………………….
Envelope Produced by Amplitude Modulation…………………………
System Evaluation Summary Graph……………………………………
49
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1
Chapter 1
The Problem and Its Background
Introduction
You will not lose your eyesight by looking at the bright side of life (Arlega,
2012). Looking at the bright side of visible light will lead you to the most advanced way
of communication, without being hurt of course. Technologies are not made to hurt
humankind but to help them live their lives to fullest.
Visible light is only a small portion of the electromagnetic spectrum that fall
within the visible range of humans (0.3PHz to 3PHz). Due to the electromagnetic
spectrum congestion nowadays, researchers from different parts of the world found a new
way of wireless optical communication by utilizing the visible light. Communication
using visible light is not harmful to humans because they can perceive it and can act to
protect their eyes. It is also not harmful when used in environments that prohibit the use
of wireless communication such as in hospitals, aircrafts, and gasoline stations. Visible
light has so many different applications that combine both illumination and
communication purposes.
Incandescent bulbs, fluorescent lamps, lasers, and especially LEDs are different
manmade visible light sources but LEDs are preferred and used to transmit different
information signals (data, voice, video, and audio) to the receiver in contrast to the
sunlight as the natural visible light source used by Alexander Graham Bell on his photo
phone way back 1880’s (Wikipedia). LEDs are now replacing the conventional
incandescent bulbs and fluorescent lamps because of its power efficiency, long life, and
eco-friendly characteristics. Because of its fast switching capability, it can be used as a
communication source by modulating the LED light with the information signal. With
2
LEDs, illumination and communication working at the same time is possible. Other
possible applications are just waiting to be discovered.
Statement of the Problem
Wireless transmission of information signals conventionally used radio signals
and this radio signals cause radiation that is somehow harmful to humans. Another thing
with wireless transmission of information signal is that it is prohibited in some
environments where there are devices operating at ISM radio bands for it can cause
interference to those devices.
The researchers want to contribute an alternative way of wireless transmission of
signals by utilizing the visible light portion of the spectrum. Transmission of information
signals using visible light is not hazardous and will not cause radiation that is why it is a
greener, cleaner, and safer way of wireless transmission. Another thing is that it will not
cause interference to any devices because this kind of transmission does not use radio
waves but light waves.
During the course of the study, the following specific objectives are expected to meet:
1. To transmit audio signals using visible light from mobile devices (cellphone,
laptop, tablet) to a loudspeaker
2. To transmit human voice signals using visible light from a microphone to a
loudspeaker
3. To use the principle of reflection in transmitting audio signals
4. To test the functionality, reliability, efficiency, and effectiveness of this
wireless transmission scheme
5. To promote visible light communication, especially to electronics engineering
students that will later engage in studies of new technologies.
3
Significance of the Study
The researchers came into this study because of its significance to the following:
The Students. The study is useful for students for better understanding the
principle of visible light communication for future references.
The School. The study can be applied in a classroom setup whenever there are
organizational meetings or activities.
The Community. The study is very economical and can be used conveniently for
it combines both illumination and communication purposes.
The Environment. The study is very timely because it wants to utilize the
unused portion of electromagnetic spectrum, the visible light. The study is very
applicable to any kind of environment because the kind of transmission is not the same
with those transmissions that uses radio frequencies that can cause interference to some
devices.
Scope and Delimitation
1. The study is limited only for the transmission of audio signals coming from
mobile devices and microphone using visible light.
2. Audio signals will be transmitted using power LED and the modulated signal will
be received by a solar cell.
3. The distance between the transmitter and receiver will tell the reliability (and
level of loudness) of the sound being transmitted; the farther the transmitter from
the receiver, the weaker the signal is being transmitted.
4. The transmitter and the receiver should be in a line of sight (with each other) and
there should be no obstruction between the two (for visible light cannot penetrate
solid objects).
4
Chapter II
Theoretical Framework
Review of Related Literature
History of Visible Light Communication
Revisiting the past and learning from it is the best step to move forward. Looking
to the history of visible light communication will reveal that it is invented as early as June
3,1880 in Bell’s laboratory at 1325 L street, Washington D.C. Visible light
communication was born, without noticing it, when the Scottish scientist Alexander
Graham Bell and his assistant Charles Sumner Tainter invented the photophone. This
invention of Alexander Graham Bell and his assistant was used to transmit wirelessly a
speech on modulated sunlight over several hundred meters. Photophone is said to be the
greatest achievement and the greatest invention of Bell greater than the telephone (G.
Povey, 2011).
(a) (b)
Figure 1. Illustration of Photophone (a) transmitter and (b) receiver (Google)
The illustration of transmitter in Figure 1 shows the path of reflected sunlight
before and after being modulated while the illustration of receiver shows the conversion
5
of modulated light to sound as well as its electrical source. Photophone has the same
principle with contemporary telephone but the only difference is the carrier of the
information. In telephone, the information relied on modulated electricity carried over a
conductive wire circuit while in photophone, the information relied on modulated light
which is propagated to free space (M. Bellis, about.com). Photophone worked by
projecting human voice through an instrument toward a mirror. The vibrations caused by
human voice caused oscillations in the shape of the mirror, which captured and projected
the oscillations toward a receiving mirror. Although it is a very important invention, the
importance of this invention was not fully realized during their time due to practical
limitations in technology for photophone is subjected to outside interferences, such as
cloud that easily disrupt the transmission of information. Photophone is said to be the
progenitor of the modern fiber optic telecommunications system.
After looking at the history of how visible light communication was started, the
timeline of visible light development will be shown on Table 1. The timeline will cover
the years after the invention of photophone to present.
Table 1. Timeline of VLC Development by Dr. Isaac Jamieson, 2015
Year Development of Visible light Communication
1931 Dr. Sergius P. Grace of the US Bell Telephone Laboratories discussed the
potential of using light for wireless communications to prevent the danger of
eavesdropping by others
1962 MIT Lincoln Labs built an experimental optical wireless communication link
using light emitting GaAs diode and was able to transmit TV signals over a
distance of 30 miles
1993 Infrared Data Association (IrDA) was formed with a brief of developing low cost
6
Continuation of Table 1
interoperable worldwide infrared technology
2001 Reasonable Optical Near Joint Access (RONJA) Free Space Optics device from
the Czech Republic became the first device to transmit wirelessly with a data rate
of 10 Mbps using beams of light within the range of 0.87 miles
2002 Dr. Stefan Spaarmann developed a visible light communication system but cannot
find a company to fund the building of prototype
2003 Visible Light Communication Consortium (VLCC) was established between
major Japanese companies to develop, plan, research , and standardize ubiquitous
high-speed biologically-friendly VLC LED systems
2004 VLCC demonstrated at Combined Exhibition of Advanced Technologies
(CEATEC) Japan how LED light systems can be used for high-speed transmission
of data to handheld and mobile devices
2005 Japan’s Ministry of Land trialed VLC communication technology to transmit
information to mobile phones in the Departure Lounge of Kansai Airport.
Throughput estimated at 10Kbps from fluorescent light units and several Mbps
from a LED
2006 Researchers from CICTR at Penn State proposed a combination of power line
communication (PLC) and white light LED to provide broadband access for
indoor applications. This research suggested that VLC could be deployed as a
perfect last-mile solution in the future
2007
VLC developed by NEC was showcased by Fuji Television at the International
Exhibition (Inter BEE) in Japan. In that demonstration a LED-backlit LCD
television operated whilst transmitting information to a PDA via light. The device
7
Continuation of Table 1
also enabled the information to be sent securely to chosen individuals
2008 EU funded OMEGA project in developing global standards for home networks,
including the use of optical wireless using infrared and VLC technology
2008 A joint-cooperative agreement covering complementary research and
development to advance the communication technology industry was announced
between VLCC and IrDA. The agreement allowed both organizations to undertake
vital complementary research, combining widely-used mobile phone IrDA
technology and new VLC technology, to further refine and develop existing and
proposed commercial applications of the optoelectronic spectrum, using infrared
and visible light frequencies, for items such as cameras, cars, indicator lights,
indoor lighting, mobile phones, printers, toll booths, traffic signals, and monitor
displays.
2009 Dr. Stefan Spaarmann, a German scientist, stated that the problem of light smog
can be avoided through the inclusion of the transmission signals within the optical
surrounding signals ( as with natural light ). He stressed the importance of
mimicking nature
2009 Continuous research in Japan in increasing viable communication distances for
VLC to hundred meters. Such work will allow the transmission of information by
light from billboards, and from new generations of traffic lights to automobiles
and trains
2009
VLCC issued their first Specification Standards which incorporates and expands
upon core IrDA specification and defined spectrum to allow for the use of visible
light wavelengths. By modifying the IrDA specifications, existing IrDA optical
8
Continuation of Table 1
modules can-with only minor alteration- be utilized for VLCC date transmission.
As a result, this specification change will lead to reduced development costs when
the IrDA specification is used widely in portable technology
2010 Center for Ubiquitous Communication by Light (UC-Light) at the University of
California seeks to develop VLC technology further to allow communication
between a wide variety of electronic products, such as HDTV, information kiosk,
PCs, PDAs, and smartphones
2010 Demonstration undertaken successfully in Japan showing the combination of VLC
with indoor Global Positioning System
2010 Data transmission speeds of VLC systems are shown to be rapidly improving,
with a frequency modulated white LED being shown by Siemens researchers and
the Heinrich Hertz Institute in Berlin to be capable of transmitting information
over 5 meters at a rate of 500 Mbps which is significantly faster than present Wi-
Fi technologies. The same researchers were also able to demonstrate that a system
using up to 5 LEDs could transfer data over greater distances at 100 Mbps with
direct line-of-sight. Reduced levels of transmission would have occurred using
diffused light from walls outside of line-of-sight
2010 VLC standardization process is conducted within IEEE Wireless Personal Area
Networks working group (802.15)
2010 St. Cloud Minnesota signed a contract with LVX Minnesota and became the first
to commercially deploy this technology
2011 Live demonstration of HDTV being transmitted from a standard LED lamp was
shown at TED Global
9
Continuation of Table 1
2011 Organic LEDs (OLED) have been used as optical transceivers to build up VLC
communication links up to 10 Mbps
2011 Li-Fi consortium, a non-profit organization, promoted the adoption of Light
Fidelity (Li-Fi) products
2014 Axrtek launched a commercial bidirectional RGB LED VLC system called
MOMO that transmits down and up at speeds of 300 Mbps within a range of 25
feet
2015 Philips collaborated with Carrefour to deliver VLC location-based services to
shopper’s smartphones in a hypermarket in Lille, France. Indoor positioning
systems based on VLC can be used in places such as hospitals, eldercare homes,
warehouses, and large, open offices to locate people and control indoor robotic
vehicles
2015 IEEE 802.15 has formed a task group to write a revision to IEEE 802.15.7-2011
that accommodates infrared and near ultraviolet wavelengths, in addition to
visible light, and adds options such as optical camera communications and LI-FI
Visible Light Spectrum
Visible light spectrum is a section of the electromagnetic radiation spectrum
which is visible to the human eye. Its wavelength ranges from 390nanometer to
700nanometer that corresponds to the frequency band from 430 terahertz to 770 terahertz.
The wavelength of the light determines the perceived color (A. Z. Jones, about.com). The
narrow band of visible light is affectionately known as ROYGBIV which stands for Red,
Orange, Yellow, Green, Blue, Indigo, and Blue.
10
Like the visible light communication, visible light spectrum has also its own
history. As early as 13th
century, Roger Bacon theorized that rainbows were produced by
a similar process to the passage of light through glass or crystal. During the 17th
century,
Isaac Newton showed that light shining through a prism will be separated into its
different wavelengths showing the different colors. The separation of visible light into its
different colors was known as dispersion. Figure 2 (b) shows the visible light spectrum
starting from the shorter wavelength which is violet to the longer wavelength which is red
and Figure 2 (a) shows the dispersion of white light through a prism. It is said that when
all the wavelengths of the visible light spectrum strike the eye at the same time, white is
perceived. This statement means that the combination of ROYGBIV colors produces
white light.
(a) (b)
Figure 2. (a) Dispersion of White Light in Prism, (b) Visible Light Spectrum (Google)
Visible Light Communication in the Modern World
Visible light communication in the modern world is now using the man made
light sources for the purpose of combined illumination and communication, thus visible
light communication has the formula:
VLC = Illumination + Communication
11
This formula of visible light communication does not cover the visible light
communication using infrared, laser, laser diode, and optical fibers for they do not give
the purpose of illumination. In VLC there should be a constant light source that can light
up a room and at the same time this light can be used as a transmitter of information as
what the image below is illustrating. Figure 3 shows that the information coming from
different sources is being received by a single device that is capable of receiving
information coming from different light sources.
Figure 3. Visible Light Communications (Google)
Optical Wireless Communication
Optical wireless Communication (OWC) is a general term referring to all types of
optical communications (VLC, Free Space Optics, Li-Fi, and infrared remote controls)
where cables or optical fibers are not used to transmit information. Free Space Optics
(FSO) is used in narrow beams of focused light for applications such as communication
links between buildings. FSO is similar to VLC but is not constrained to visible light,
meaning ultraviolet and infrared also fall into this category. Even though VLC and FSO
are under the same category and have the same purpose, to use light source to transmit
information, there are still big differences between them. In contrast to VLC, illumination
12
is not a requirement for FSO. Laser diodes are often used in FSO rather than LED for
illumination is not the purpose for FSO. In terms of distance for transmit and receive,
FSO can transmit in longer distances compared to VLC. The reason behind this
transmission distances is the light source used to transmit the information. VLC is
commonly used on indoor applications while FSO can be used on both inside and outside
applications but outside light interferences and other atmospheric interferences, such as
rain, fog, dust, and heat, are the main problems in FSO. Light Fidelity, coined by Prof.
Harald Haas on TED Global talk, is a term often used to describe high speed VLC
applications. Li-fi is similar to Wi-Fi but instead of radio waves, LI-Fi used light to
transmit high-speed data. This OWC has been proposed to solve the problems of radio
frequency bandwidth limitations. In contrast to VLC which can be used for wireless
communication without internet, Li-Fi is only used for internet connectivity.
General Applications of VLC
Figure 4. Smart Lighting Systems Google)
One of the best applications of VLC is smart lighting which combines the two
purposes, the lighting and communication within a building or any offices. Smart lighting
will greatly reduce wirings and energy consumptions within the building for there is no
13
need for separate device for communication. This technology is designed primarily for
energy efficiency. Figure 4 shows the smart lighting system which is the possible
application of VLC.
VLC can be applied to hazardous environments, such as mines, petro-chemical
plants, oil rigs, etc. It can also be applied to environments where radio waves are
prohibited, such as aircrafts and hospitals, where radio waves can cause interference to
devices on those environments. The reason behind this is the devices on hospitals and
aircrafts and the handheld devices like cellphones and other wireless devices are
operating on the same frequency band, commonly known as ISM (Industrial, Scientific,
and Medical) band. VLC can be used on those kinds of environments for VLC does not
use radio waves but light waves. Figure 5 shows the application of visible light
communication on hospitals and aircraft.
(a) (b)
Figure 5. (a) VLC on Hospitals, (b) VLC on Aircraft (Google)
VLC can also be used for mobile connectivity. Pointing a visible light at another
device can create a very high speed data link between devices. This application of VLC
overcomes the disadvantage of having to pair your device to another device and it also
14
provides a much higher data rate compared to Bluetooth and Wi-Fi. Figure 6 shows the
application of visible light communication for mobile devices connectivity.
Figure 6. VLC for Mobile Connectivity (Google)
Another promising application of VLC is for vehicle-to-vehicle communication
where vehicles can communicate with each other using their lights. The lights coming
from traffic signals and warning signs will guide the car on its way. This application of
VLC for vehicle-to-vehicle communication will lead to a lesser road accidents. Figure 7
shows how embedded visible light on every vehicle can be used for vehicle-to-vehicle
communication. Figure 7 is the illustration of vehicle-to-vehicle communication using
visible light.
Figure 7. Vehicle-to-Vehicle Communications (Google)
15
VLC can also be used for underwater communications. Visible light can support
high speed data transmission over short distances underwater while radio frequency will
not work on this kind of environment. This application of VLC will enable divers and
underwater vehicles to communicate with each other. The images in Figure 8 show how
communication takes place underwater. The figure on the left is for water vehicle
communications and on the right is for divers’ communication underwater using visible
light.
Figure 8. Underwater Communication via VLC (Google)
Figure 9. Defense and Security Application of VLC (Google)
16
Defense and security is another field that VLC can be applied. VLC is a much
secured communication compared to other communication system that uses radio waves
that can be detected and hacked by others. VLC is a more secured type of communication
because the visible light cannot be detected on the other side of the wall. It is best to
applied for defense and security where quick transmission and reception of information in
a secure way is needed. Figure 9 shows the defense and security application of VLC
which can be used in military operations.
Advantages and Disadvantages of VLC
Technologies are made by weighing its advantages and disadvantages. One of the
rules of technology is that there should be more advantages compared to disadvantages.
Visible light communication technology also has its own strengths and weaknesses.
The following are some of the advantages of VLC:
1. It will solve the spectrum scarcity of the current wireless communication system
2. It can provide both illumination and communication at the same time
3. It is energy efficient for communication devices is integrated with the light source
4. It will lessen the use of wires in buildings
5. It can be used in hazardous environments, underwater, and in environments where
radio waves are prohibited
6. It is a very fast and secure type of communication
The following are some of the disadvantages of VLC:
1. It is a communication for short distances.
2, It is subjected to external interference, such as other light sources
3. It cannot penetrate walls.
4. The super bright light can damage the eye of the user.
17
Review of Related Studies
The related studies that the researchers will discuss here are studies coming from
journals of various authors from different countries. Most of the related studies come
from open access journals on the internet. For the sake of the study, the researchers will
focus only on the principles, designs, and materials used for wireless audio transmission
using visible light for some of the journals did not focus on the audio transmission alone
but for video and alphanumeric data transmission also.
Way back 1999, the journal about Optical Wireless Based on High Brightness
Visible LEDs by Chi-Ho Chan and company, talked about the LEDs potential
applications on the field of wireless optical communication on the future. Their system
designs were very interesting for they explained well the different elements they used on
the circuit. Figure 10 is the block diagram of the transmitter designed by Chan et. al.
Figure 10. Block Diagram of the Transmitter Design (Chan et. al., 1999)
First of all they used an audio input coming from cassette tape or CD player and
fed it to the audio amplifier and level shifter to amplify the weak audio signal and to shift
the average voltage level of the audio signal to an appropriate level so that the signal is
within the capture range of the voltage controlled oscillator. They used a voltage
controlled oscillator to modulate the incoming audio signal variations from the audio
amplifier and to generate frequency modulated signal. Instead of a sine wave, they used a
18
square wave VCO for the reason LEDs have only two states; on and off. They have set
the carrier frequency at 100 KHz having a frequency deviation of 50 KHz and 50 KHz.
They used LEDs array as a light source which is also the same with the traffic light. The
frequency of LEDs switching was high enough making it unnoticeable by the human eye.
For the receiver circuit, they used a photo-detector, consisting of a photodiode and
a resistor. The signal captured by the photo-detector was fed to the limiting pre-amplifier,
consisting of two operational amplifiers together with some diodes and resistors. Diodes
were used by the authors to limit the input voltage level to a desired level. A comparator
was used to a rectangular signal pulses. Two pre-amplifiers with lower gain were used to
achieve a high gain but with reduced noise. The data reproducing circuit was used,
consisting of a resistor, operational amplifier, and two NAND Schmitt triggers, to
produce rectangular pulses from the amplified signal on the previous stage. Two NAND
Schmitt trigger gates were used to enhance the noise immunity, to correct edges from low
to high level due to the slew rate of amplifier, and to produce a non-inverted signal. A
differentiator circuit, consisting of a capacitor and resistor, was used to detect the leading
edges of the pulse with the trailing edges blocked by a diode. Schmitt trigger gate was
used as a pulse generator and the output was the inverted version of pulses from the
differentiator. An integrator and envelope detector were used to carry double integrations.
Figure 11 shows the receiver block diagram designed by Chan et. al.
Figure 11. Block Diagram of the Receiver Design (Chan et. al., 1999)
19
The first scenario is if the inverted pulses from the pulse generator contain high
frequency, the frequency of integration is higher and the voltage level of the output
would also be higher. Second thing is if the inverted pulses contain low frequency, the
frequency of integration is lower and the voltage level of the output would also be lower.
Band pass filter was used to filter out high frequency distortions caused by the integrator
and envelope detector. The output of the band pass filter was an audio signal fed to the
power amplifier connected to the loudspeaker.
After a long experimentations and studies, the authors came into results that the
bit error rate decreases as the power or light intensity of LED increases which means the
brighter the LED light, the smaller the bit error rate occurred at the receiver. They have
observed that other visible light sources contribute to a higher bit error rate at the
receiver. The authors concluded their study that visible LED light beam requires a clear
line of sight to make the transmission of information possible and it is suitable only for
short-range communication for the photo-detector current is proportional to the received
power. They also mentioned that the relationship between the radiant intensity and
distance from the receiver follows the inverse square law.
Even though the said study was conducted on 1999, the study is still helpful for
the researchers for it elaborated well the different components they have used on their
wireless audio transmission. Their results and observations were all helpful for the
researchers for it discussed some of the circumstances that the researchers should take
into considerations in designing the system. Their conclusions gave the researchers
knowledge about the principles of using visible LED light for communication.
The paper of Jason Moritz, Audio-to-Optical Conversion and Transmission, for
his senior project on 2011 is most concerned on the understanding of the free-space
20
optical transmission of signals in the application of transmitting audio signals. The study
of Moritz can be considered as experimentation for he uses two different light sources,
the LED and laser diode, and compared their strength and weaknesses in terms of power
and distance on actual application. The author wanted to know if the received signal is
affected by the conversion of audio signal to an optical signal and transmission of it
through free-space. In short, he wanted to know the quality of sound being transmitted
using two different light sources.
Figure 12 shows that Moritz used audio output from a computer as an audio
source to modulate an optical current source which provide power to a laser diode and
light emitting diode. The light waves generated by the light sources were propagated
through free-space. Lens was also used to concentrate the light, which resulted to a lower
attenuation in terms of distance. The light waves were received by a photo detector that
converted optical signal into electrical signal. The electrical signal was fed into an
amplifier which is connected to a loudspeaker. The audio signal coming from the speaker
was measured using a decibel meter.
Figure 12. Layout of Moritz’s Project (Moritz, 2011)
After a long experimentation and testing, Moritz came into conclusion that laser
diode is much better light source for any point-to-point communication system rather
than LED. This conclusion of him was supported by his experimentation results that LED
21
was able to transmit up to 10dB more power than laser diode at all frequencies however,
laser diode was able to transmit a more consistent power with respect to distance than the
LED. Results showed that LED had a higher average attenuation with respect to distance
of 5.8dB/cm compared to 5.2dB/cm for the laser diode, meaning laser diode would be
more effective on longer distance transmission rather than LED.
By reviewing the study of Moritz, the researchers can say that the work of Moritz
is for the transmission of audio signal alone. He is more concerned on the quality of
transmitted audio signal. Illumination may not be the concern of the author but his tests
and experiments can be a good reference for the researchers to consider the quality of
sound being transmitted.
On 2013, Lau Chih Yung designed and constructed visible light communication
system prototypes for audio and digital signal transmission. The main objective of the
author was to study the VLC system and to design a prototype that would demonstrate
the functionality of VLC system for audio and digital signal transmission through
modulated LED light beam. On his design for audio system, he used white light LED on
transmitter circuit and a photodiode on the receiver circuit. For the testing of the working
prototype, Yung used a computer as audio source. Results of the experiment of Yung’s
working prototype showed that the transmission speed was slow due to the sensitivity of
the photodiode and LED used. The author came into conclusion that higher sensitivity
photodiode and fast response LED was necessary for the system design in order to
achieve the higher transmission speed.
Figure 13 is the design system of wireless audio transmission and reception of
Yung. He also used the computer audio output as input of the system, like the previous
journal, and was fed also into a LED for transmission. The transmitted signal was then
22
captured by a photodiode on the receiver section and was fed to a Sonic Gear Tatoo 101
speaker.
Figure 13. VLC Audio Transmitter and Receiver Block Diagram (Yung, 2013)
Figure 14 was the final product of Yung’s proposed system. Yung used a battery
as a power supply on the receiver section and A-type male USB connector connected to a
USB port of a laptop which provided the power on the transmitter section.
Figure 14. Final Products of VLC Audio Transmitter and Receiver (Yung, 2013)
Another journal about The Development of Optical Wireless Audio System Using
Infrared Light Communications by N. F. Azmi and company was presented on 2013, but
now the source of light is coming from infrared device. The objective of the authors was
to increase the transmission distance and widen the effective signal coverage area of
23
infrared light. For their working prototype, they used a UM66 IC for the transmitter to
generate a continuous musical tone and fed it to the infrared light. The infrared light
flashing patterns followed the patterns generated by musical tones which were indications
that the audio signal is being modulated. On their receiver circuit design, they used 741
IC, the popular operational amplifier, and LM386 IC audio frequency amplifier along
with the photodiode. The authors said that a brighter infrared light or a lens that would
help to focus the light was needed to improve the transmission distance. Based on their
experiment results, they found out that communication system using infrared can work in
a distance of up to 10 meters and the sensitivity of the photodiode is up to 140 degrees.
Their experiments were successful but they recommend a laser diode as a light source in
the future for it can transmit the signals over a long distance with low noise.
This study about the development of optical wireless audio transmission using
infrared light has the same principle with the wireless audio transmission using LEDs or
laser diodes but the only drawback of using an infrared light is its distance limitation to
the receiver. Based on past studies, the farthest distance that an infrared light can travel is
about 1 to 10 meters only which makes it impractical for short-range wireless
communication.
Figure 15. Real-time Video/Audio VLC Transmission Systems (Ding et. al., 2013)
24
Figure 15 came from Real-Time Audio and Video Transmission System Based
on Visible Light Communication by Liwei Ding et.al on 2013. It was a proposed
prototype for real-time audio and video broadcast system using inexpensive
commercially available LED lamps. Video and audio signals coming from a video
camera were transmitted at the same time but in different channels using two LEDs
separated by a distance of 10 centimeters to avoid mutual interference caused by light
sources. Figure 15 was the proposed system designed by the authors showing two
different channels for video and audio signals coming from a video camera and received
by two photodiodes which detect light transmitted over two separate optical channels.
Video and audio capture module with USB interface was used to digitally convert the
captured analog video and audio signals, which is connected to a laptop to display in real
time the transmitted information
The LEDs used on their prototype provide a luminous flux of 107 lumens at a
current of 350mA. Reflection cups were mounted on each LED for the purpose of
focusing and concentrating the light straight to the photodiodes for better reception.
Results showed that without using a reflection cup the distance of 2 meters can be
achieved and this can be increased to 3 meters using a focusing lens. They have observed
that some distortions still exist by comparing the original to the received information.
They have stated that distortions maybe the result from the process of photoelectric
conversion, signal amplification or the introduction of background noise. They
recommend analog signal from the video camera should be converted first into digital
signal before transmitting to improve the system performance.
Low cost voice communication device design using ordinary laser torch and LDR
available in Bangladesh proposed by Md. Kayesar Ahmmed et.al was another study on
25
the year 2013. The study was most concerned about implementation of longer distance
LOS communication and yet economical. The said study can be used at conference room,
political assembly, class room, and general conversation between two houses. The design
of transmitter and receiver circuit was powered by a 9-volt fixed voltage power supply as
shown in Figure 16. One of the highlights of their design is the use light dependent
resistor or LDR as a receiver. They have compared LDR to photo transistor and other
light receiving devices and found out that LDR has some advantages compared to others.
They have said that although phototransistor response is better, its operation is frequency
sensitive. LDR then does not need proper biasing to work for the resistance is inversely
proportional to the intensity of the received light. Another advantage of the said system
was the use of laser torch which concentrates energy to extremely high intensities and
transmits a constant light over long distances because of low divergence. Figure 15 is the
laser torch transmitter and receiver circuit designed by Ahmmed et. al.
(a) (b)
Figure 16. Laser Torch based (a) transmitter and (b) receiver (Ahmmed et. al., 2013)
The said study aimed to implement an optical wireless communication over long
distances using low price devices. The goal of the researchers for their design was also to
use the lowest price components available. Even though the said study did not consider
26
the purpose of lighting combined with communication as compared to the objective of
the researchers, the study is still helpful for the researchers for it gave the researchers the
idea to explore what type of light receiver they should use on their design to achieve their
desired output.
When it comes to the journal of Boone-Wy Chan and company on May 2014,
Designs of VLC Transceiver Circuits for Reading Light Transmission of High-Quality
Audio Signals on Commercial Airliners, they designed a transmitter and receiver circuits
for high quality audio signals using the existing reading light on commercial airlines as a
light source. The main objective of the authors was to provide high quality sound for the
entertainment of the passengers of commercial airlines. They placed the receiver circuit
on headphones and integrated the transmitter circuit on LED reading lights above
passengers’ seats. Figure 17 shows the transmitter and receiver prototype for airline
entertainment.
Figure 17. Basic circuit and Constructed Prototype for Airline Entertainment VLC Audio
Transmission System (Chan et. al., 2014)
They built and tested three different designs of audio transmitter and receiver
circuits using different audio amplifier ICs. The ICs were compared to each other in
terms of its characteristics on slew rate, volume, power, gain, bass effect, and most
27
specially its sound quality. Using OPA2134 IC, the circuit produced a clear and
distinctive sound and provided the loudest volume compared to other circuits. When
LM833 IC was used, it exhibited a good rich bass and showed no dead band crossover
distortion, but it needed more power and gain to achieve the same volume of operation of
OPA2134 IC. Among all, LME49860 IC gave the best sound quality. It generated a bass
effect that is not as heavy as the operation of LM833 IC but is not as weak as compared
to the operation of OPA2134 IC.
The authors suggested exploring different types and brands of ICs to know what
will give the best performance. The authors concluded that wireless optical
communication using visible light has the largest potential when it comes to the
development of wireless airline entertainment systems for it can be easily integrated into
existing devices on the plane and it does not interfere with the aircraft’s control systems.
This journal of Chan and company gave the researchers a good basis for choosing
the right IC that should be used on the design of the circuit. Audio circuits should be the
first thing to consider as what the authors said on their work. Choosing the right elements
of the audio circuits will lead to a high quality wireless audio transmission and reception.
Another related study which also used light as a sender of the information was the
study about fiber optic communication. Future Trends in Fiber Optics Communication by
O. Hope et. al on 2014 was a study that gave an overview of fiber optic communication
system including their key technologies. The authors also discussed the technological
trend of fiber optic communication towards the next generation. The principle of fiber
optics communication was also the same with the principle of visible light
communication for fiber optic communication is a communication technology that uses
light pulses to transfer information from one point to another through an optical fiber.
28
The only difference between fiber optic communication and visible light communication
is the way of transmission of information where in fiber optics communication, the
information is sent through a transmission line while in visible light communication, the
information is sent wirelessly. It is said that fiber optic communication is definitely the
future of data communication but visible light communication, as what researchers are
saying on their studies, is also the future for wireless communication. In short, the future
of communication systems is the transmission of information using light sources.
Voice Transmission through Bluetooth by R. Deshmukh on 2014, was another
closely related study for audio transmission using visible light. The main goal of the
author was to establish a full duplex communication in the department and the college.
The design of the proposed study is there was an embedded Bluetooth protocol within the
computer and an android based mobile handset will communicate to it. The author aimed
to explore the utility of the android operating system for a full duplex communication
using Bluetooth. The study was about wireless transmission of voice which is also the
aim of the researchers but the only difference was the device used to transmit the
information. Bluetooth transmits information using radio waves while LED and other
optical devices transmit information using visible light waves but both are short-range
wireless transmissions.
In terms of wireless communication, VLC is also related with wireless
technologies like Wireless Fidelity (Wi-Fi) and Wireless Interoperability for Microwave
Access (WiMax). The Analysis of Wi-Fi and WiMax and Wireless Network Coexistence
by S. Song and B. Isaac on 2014 compared the two wireless technologies stated earlier.
The goals of the authors were to explore through simulation the wireless network
coexistence of Wi-Fi and WiMax and to discuss the future of WiMax in relation to Wi-Fi.
29
The authors concluded that using the two wireless technologies can achieved a better
coverage of the wireless networks. They also said that WiMax has moved into a
bottleneck position and this cannot be avoided for mobile operators are now gradually
moving into Long Term Evolution (LTE) market, however Wi-Fi is in the state of
continuous development. Even though WiMax has some advantages in some areas, it still
faced the risk of being acquired. The authors recommended that WiMax should pinpoint
its location, find the appropriate development of the market, and think of better
coexistence with Wi-Fi.
Conceptual Framework
Input Output
Process
Figure 18. Conceptual framework
As shown in Figure 18, the main concept of the study was to combine the
communication and illumination purposes. Using the light to transmit information was
the main purpose of the system. The audio input in this study came from mobile devices
(cellphone, tablet, or laptop) and from a microphone. The process includes the
amplification of the audio input signal, modulation of the information through a power
LED, and transmitting the information wirelessly. The process also includes the reception
Audio
Amplifier
Audio
Source
Op-Amp
Power
LED
Light
Detector
Loudspeaker
30
of the audio signal using light detector that will convert the light signals into current that
will be fed again to an amplifier. The output of the system was the audio that the
loudspeaker outputted.
Definition of Terms
Free Space Optical Communication. An optical communication technology that
uses light propagating in free space to wirelessly transmit data for telecommunication or
computer networking
ISM band. Radio band reserved intentionally for the use of radio frequency
energy for industrial, scientific, and medical purposes other than telecommunications
Laser. A device that emits light through a process of optical amplification based
on the stimulated emission of electromagnetic radiation
Laser Diode. An electrically pumped semiconductor laser in which the active
laser medium is formed by a p-n junction of a semiconductor diode
Light Emitting Diode. A two-lead semiconductor light source commonly used in
visible light communication
Light Fidelity. A bidirectional, high speed and fully networked wireless
communications that uses visible light communication and similar to Wireless Fidelity
Operational Amplifier. A DC-coupled high gain electronic voltage amplifier
with a differential input and usually a single-ended output
Optical Wireless Communication. A form of optical communication in which
unguided visible, infrared, or ultraviolet light is used to carry a signal
Visible Light. Electromagnetic radiation which is visible to the human eye
Visible Light Communication. A data communication medium which uses
visible light
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Chapter III
Research Designs and Methods
Project Research Design
The system wass all about wireless transmission of audio signal using visible
light. At the transmitter side, the input to the system will be a voice and this analog signal
will be converted by the electret microphone or condenser into electrical signal. Audio
coming from mobile devices, such as mobile phones, tablets, or laptops can also be used
as input to the system. The converted input audio signals will be fed to an operational
amplifier that will produce an output signal that will be passed to the base of the
transistor for amplification. The amplified signal will be taken from the emitter of the
transistor. The voltage and current output on the emitter will be used to light up the
power light emitting diode. The amplified audio signal will ride on the light produced by
the power LED for transmission. There will be a potentiometer that will control both the
intensity of signal and light. The intensity of light is directly proportional to the intensity
of the input signal meaning, the louder the audio source the brighter the power light
emitting diode.
At the receiver side, there will be a solar cell connected to the audio amplifier
circuit. As the intensity of light of the power light emitting diode varies according to the
intensity of the input signal, the electrical signal that the solar cell will produce at the
receiver will also vary according to the intensity of light being captured. The weak
electrical signal produced by the solar cell will now passed to the amplifier circuit for
further amplification before feeding it to the loudspeaker that will produce the desirable
audio signal. There will also a volume controller on the receiver side so that the receiver
can control and can adjust the desired loudness of the received audio signal.
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Audio Transmitter
Figure 19. Audio Transmitter Block Diagram
As shown in Figure 19, audio transmitter of the system was composed of the
microphone or audio output from mobile devices, operational amplifier, transistor, and
power light emitting diode. Super bright light power light emitting diode was chosen by
the researchers so that the light can be used also for illumination. As stated earlier the
input to the system is a voice or audio coming from mobile devices. The researchers will
use a microphone with preamplifier when human voice is the input and will use an audio
jack plug to connect the audio output of mobile devices to the audio transmitter. The
analog signals produced by voice will be converted to proportional electrical signals by
the microphone. The audio jack plug will also convert the audio signals from mobile
devices into electrical signals that will be interfaced to the audio transmitter. The
converted signals will now enter the operational amplifier inverting and non-inverting
input. The operational amplifier will pass the output signal to the transistor for
modulation and amplification. The modulated and amplified signal by the transmitter will
be fed to the power light emitting diode for transmission.
Audio Receiver
Figure 20. Audio Receiver Block Diagram
Microphone/
Audio from
Mobile Devices
Operational
Amplifier Transistor
1 Watt Power
LED
Solar Cell Audio Amplifier Loudspeaker
33
Figure 20 shows the concept of the audio receiver which was composed of solar
cell, amplifier, and loudspeaker. As stated earlier, the input to the audio receiver is the
modulated signal transmitted by the power LED. The modulated signal will be captured
by the solar cell. Solar cell will convert the captured intensity of light into electrical
signals proportional to it. The converted light signals will then enter the amplifier stage,
where it is divided into two; the pre-amplifier and the power amplifier. The signal will
enter the pre-amplifier section to remove the noise generated during the process of
transmission. After the removal of noise, the signal will now pass through the power
amplifier to further strengthen the weak signals. The amplified signal is now ready to be
fed to the speaker, where the electrical signals will be converted back to analog signals.
The output on the speaker is the voice or the audio from mobile devices.
Project Development
The journey of the researchers to the kingdom of knowledge began when the title
defense has been set. The researchers dig deeper in searching for three proposals that can
help the community and the environment when it is to be implemented. After researching
so many times about different topics and ideas, the researchers finally got the three
proposals that are interesting for them. All the three proposals seem to be all interesting,
but there was one proposal that the researchers are both interested with and this was the
concept of wireless transmission of information using visible light. After presenting the
three proposals to the panel, the researchers was given the right to choose what topic is
the best for them and the researchers chose the proposal about audio transmission via
visible light.
After the title defense, the researchers planned the tasks that they should
accomplish every month. The researchers began to work with the paper works two weeks
34
after the title defense. Searching for different related studies, theories, and literature led
the researchers into a deeper understanding of the concept that they are working with.
The researchers found out that the concept that they are studying has so many
applications which are all helpful to every human.
After knowing the related theories, studies, and literatures of the chosen proposal,
the researchers are now ready to design the system that they wanted to implement.
Designing of the system, includes designing of the schematic diagram, choosing the right
materials that should be used, and testing the reliability and effectiveness of the system.
The researchers were on the right track of accomplishing the task that they should take.
Following the right track will lead the researchers to a better outcome in achieving their
goals and objectives.
Before the researchers took experimentations, they studied first the concept of
their proposed system. They analyzed first how it works and what are the possible
components and materials that they should use during the experimentations. The
researchers were very lucky because the system they are working with has so many
tutorials and discussions on the internet. Those tutorials helped them to understand easily
the concept of their proposed system. The researchers knew that their proposed system
was not new but they wanted to know how it works so that they can somehow modify or
improve the system. After studying and analyzing the whole concept of the system, the
researchers listed all the components needed for their experimentations. During the
experimentations the researchers were surprised because the components needed are very
minimal, meaning the system was not that expensive to be implemented.
On the first day of experimentation, the researchers gathered all the components
needed for experimentation on the transmitter circuit. The researchers made the circuit
35
design posted by Tarun Shrivastava on the internet as reference. The circuit design used
LM741 operational amplifier but the op-amp that the researchers ordered on E-Gizmo
was replaced by LM2904D but E-Gizmo said that it is also the same as LM741 IC that is
why the researchers continue to work. The researchers followed the circuit diagram
including the connections on the pins of the op-amp and without looking at the true
output pins of LM2904D. After checking the connections, the researchers applied the
power source and fortunately the circuit worked. This was the day that the researchers
experienced on their own hands and proven on themselves that visible light can be used
in communication. On their first experimentation day, they used a small solar cell from a
calculator and connected it to the audio jack wire of a mono portable speaker. The
researchers tested to transmit audio coming from the laptop and it worked.
Figure 21. Connecting a Small Solar Cell from Calculator to the Audio Jack Wire of
Mono Portable Speaker
Figure 21 shows the idea of the researchers to connect a solar cell from calculator
to the audio input of the mono portable speaker. At first the researchers did not know if
this idea will work but when they implemented it to the system, fortunately it worked.
36
The transmitted sound was not that good in quality but the researchers did not look onto it
but they looked on the idea and the principle behind that experience. The researchers took
a video of this experience and shared it to their friends. After that experience, the
researchers started to think why the transmission of the audio was not that good in
quality. There were so many maybe reasons why the audio was not in good quality,
maybe because of the op-amp that they used, maybe because of the potentiometer or the
transistor, maybe because of the solar cell, maybe because of the portable speaker, maybe
because of other light sources, or maybe because of the light source that they used.
Figure 22. First Audio Transmissions Using Ordinary White Light LED
Figure 22 is the screenshot came from the video made by the researchers on their
first transmission of audio coming from the laptop. The audio jack terminal was
connected to the solar cell of a calculator. The portable speaker was charging at that time
that is why the speaker was also connected to the USB port of the laptop.
Because of not good quality audio transmission, the researchers investigated the
possible reason for this problem. Another problem that the researchers encountered, the
37
audio source was only operating on laptop but when the audio source was connected to a
cellphone, the light was not working. While investigating for those problems, they
decided to buy other light sources such as flash light and laser so that the distance of
transmission will increase. They have tested the flashlight and transmitted audio signals
for at least 3 meters with volume of the source and speaker at full volume. On that 3
meters the received audio was comparable to a low volume even though all volumes were
in its full. The researchers also tested the laser but the sound quality was not desirable
that is why they stick in using flashlight as light source.
Another problem came because there were times when the circuit was working
and there were times the circuit was not working even though the connections were fully
checked. This was the day where the researchers investigated on the components they’ve
used. They started first to search for the pins of LM2904 and found out that it was not the
same configuration as LM741. They found out that LM2904 was a dual input and output
operational amplifier and the pins are not the same with LM741. After knowing that,
there came a big question at the back of the mind of the researchers, how the circuit
worked during their first experimentation if the pin connection on the op-amp was not
actually correct? Setting aside that question, they decided to connect the right
connections of the pins of the op-amp to the circuit but now the light was not glowing.
The scenario was this, when the audio jack plug was being connected to the laptop, the
light was glowing but when the audio jack plug was being removed on the laptop, there
was no light. Another problem was the audio jack if fully connected, the circuit was not
working but when it was not the circuit is working. There were so many problems
encountered by the researchers but they did not stop in finding answers on their own.
They started again to speculate that maybe the audio jack was the problem that is why
38
they searched again about audio jacks and found out that most devices nowadays are
using TRS or TRRS audio jacks. The researchers decided to buy a stereo audio jack but
when they connected it to the system, the transmitter was transmitting but the received
signal was very low even though the distance was close enough. It felt like the transistor
was not amplifying that is why the researchers tried to replace the transistor but after the
replacement, the transmission was still the same. There was a time when the transmitter
circuit worked when cellphone was connected but on the other day it was not working
again.
Figure 23. First Transmission of Audio Signals Using Cellphone
Figure 23 is the first time ever the cellphone was used as audio source to transmit
audio signals. After that transmission, the circuit was not working again. The
development of the transmitter circuit was started when one of the researchers decided to
work alone on their house while the other was working on the microphone circuit. One of
the researchers aimed to accomplish the problems of the transmitter circuit in one day and
fortunately the transmitter circuit worked on laptop and cellphone after long hours of
39
tests and trial and error. The researcher had an idea that on the tutorial there was a mono
speaker receiver and the transmit signal was also mono because the op-amp used has a
single input and output only, that is why the idea to use the advantage of LM2904D, the
two input signals, the left and the right signals crossed the mind of the researcher. If the
transmitter has left and right audio signals, the receiver must also be a stereo speaker.
Those ideas helped the researchers a lot on moving forward on their experimentations.
After long hours of trial and error, the transmitter circuit worked and transmitted audio
signals for about 5 meters. The flashlight was very bright and the volumes of the sources
and the receiver were all on its peak. The received audio signal on that distance was still
clear and loud enough which made the researcher think that the design was good
compared to their first transmission with the distance of 3 meters.
Figure 24. First Transmission of Audio Signals from Laptop and Cellphone with a
Distance of 5 Meters
Figure 24 was the transmitter circuit with two signal inputs, the left and the right
audio signals. It was a good idea to use the two input and output pins of the LM2904D
40
op-amp having the same power source but even though the idea was good, the researcher
still not convinced with the circuit because one input cannot be controlled using the
potentiometer. The possible reason with this was wrong circuitry or wrong connections of
pins of the LM204D op-amp. Having this kind of design, the researcher found out that
there was only a certain point at the potentiometer to transmit in full power without
distortion of the signal. The researcher knew this because when the potentiometer was
being set at its maximum or even half-way, the transmitted signal was distorted and the
light seems to flicker which then produced noise at the receiver.
Figure 25. Closer Look of the Transmitter Circuit with Left and Right Audio Signals
Figure 25 shows the closer look of the transmitter circuit having two inputs and
outputs, the left and right audio signals. The problem with this circuit was the left signal
cannot be controlled by adjusting its potentiometer while the right signal can be
controlled and the inverting input of the right channel was connected to the non-inverting
pin of the LM2904D op-amp while the non-inverting of the right channel was connected
to the inverting input of the LM204D op-amp. The battery was connected in parallel for
the left and right channel and the output signal was also connected in parallel. In short the
41
circuit was a product of trial and error without referring on others’ works that is why the
researcher was not convinced by this kind of design but the idea of separating the left and
right audio signals was good. The good thing happened was the transmitter circuit was
used both in laptop and cellphone. The only problem was how to improve the circuit.
Setting aside the problem, the researchers started to make the electret microphone
preamplifier. The circuit that they followed came from the internet. After connecting all
the components, the microphone worked. When they tried to connect it to the transmitter
circuit, the transmitted sound was not audible, it seemed that the transistor again was not
amplifying and the output of the microphone was not that good. After that the researchers
started to make an audio amplifier for the receiver but again the problem was the output
signal was not good. While searching for good quality microphone preamplifier and
audio amplifier, the researchers tested the transmitter circuit on multiple receivers and the
good thing was it is possible for multiple receivers to receive the transmitted audio
signals as long as the receivers are within the range of the light.
Figure 26. Wireless Audio Transmissions Using Multiple Receivers
42
Figure 26 is the screenshot came from the video made by the researchers. The
researchers experimented to use multiple receivers while transmitting audio signals. They
successfully transmitted the signals to multiple receivers and the quality of received
signal was better than before. At the back of the solar panel there is a computer speaker
where its audio jack terminal was connected to the round solar cell. In front there is a
subwoofer system having a center bass and two satellite speakers on both sides where its
audio jack was connected to the rectangular solar cell.
After the experimentations of multiple receivers, the researchers decided to make
their microphone for they never tested yet the microphone as input to their system. The
researchers took advantage of the internet and searched for a good quality electret
microphone preamplifier tutorials. Fortunately, they got the best tutorial for this and
adopted it to the system that they are working with. The output quality of sound produced
by the electret microphone preamplifier was good when it was tested and connected
directly to the computer speaker and it seemed that there was no noise produced at the
output of the pre-amp.
Figure 27. Making of Electret Microphone Preamplifier Circuit
43
Figure 27 shows the making and testing of electret microphone preamplifier. The
circuit has no gain controller and has no operational amplifier, but the sound quality was
good. Some resistors, polymer capacitors, and especially the electret microphone were
the only components used on this preamplifier circuit. The circuit was powered by a 3
volt AAA battery for the purpose of portability. The output of this pre-amp will be
connected to the input terminal of the transmitter circuit once the system is implemented.
After finding out that the electret microphone preamplifier worked, the researchers
decided to interface it to their transmitter. Fortunately, the circuit worked well with some
feedback of course. The potentiometer on the transmitter circuit will be used to set the
microphone voice transmission on a less feedback possible.
After proving on their own that human voice can also be used as input to the
transmitter, the researchers decided to make their own small audio amplifier so that the
receiver can be placed on a small casing for the purpose of portability and cost
effectiveness also.
Figure 28. Making of Audio Amplifier Circuit
44
Figure 28 shows the making and testing of audio amplifier circuit. This audio
amplifier used capacitors, resistors, LM386 operational amplifier, and potentiometers
powered by a 9 volt battery. It has a bass booster and the output sound is fair.
After accomplishing all the circuits needed for the wireless audio transmission
system using visible light, the researchers planned to do the laboratory experimentation to
see the waveforms that the circuits produced using the oscilloscope. At first, they decided
to see the output waveform of the transmitter circuit. The positive of the probe was
connected at the emitter of the transistor and the negative to the ground. The researchers
started to play a music coming from a cellphone at the input side of the transmitter and
saw the following waveform.
Figure 29. Waveform at the Transmitter’s Output Terminal While Playing Music from a
Cellphone
It can be seen on the Figure 29 that the transmitter circuit is really amplifying the
input signal. As the volume of the cellphone increases, the amplitude of the waveform
also increases dramatically. The waveform on the transmitter circuit was the signal being
45
fed to the power LED for transmission. The electrical signal was converted into optical
signal by the power LED and the converted signal was received by a photo sensitive
device such as solar cell. The solar cell then converted the light impulses into electrical
signals and fed it to the audio amplifier circuit. The researchers also decided to see the
waveform received by the solar cell. Figure 30 is the waveform that the researchers
acquired when they connect the positive of the probe to the positive side of the solar cell
and the negative to the negative side of the solar cell.
Figure 30. Waveform Generated by the Solar Cell While Transmitting Audio Signal from
a Cellphone
It can be seen in Figure 30 that the waveform taken at the solar cell has two
signals. The darker color yellow was the signal of the transmitted audio signal while the
lighter color yellow was the signal from the fluorescent light on the ceiling of the room.
The researchers decided not to turn off the other light sources so that they will see the
waveform when the solar cell is subjected to other light sources and the noise effect was
very minimal. The noise on the amplifier made by other light sources was like a low level
46
continuous noise that can never be noticed when the transmitter is transmitting audio
signals. It was also evident on the figure that the maximum and minimum voltages were
in millivolts value, the reason with this is that the signal was not yet fed to the audio
amplifier circuit.
The researchers also decided to see the waveform produced by the electret
microphone preamplifier circuit using oscilloscope. The positive of the probe was
connected to the output ceramic capacitor and the negative was connected to the ground
of the circuit.
Figure 31. Output Waveform of the Electret Microphone Preamplifier Circuit
Figure 31 shows the output waveform of electret microphone preamplifier circuit
and it can be seen that the output waveform was not that big because the researchers set
the voltage per division to 100millivolts and the output maximum and minimum voltage
were all below the value of the voltage per division which made it suitable to be used as
input for the transmitter for further amplification. The frequency was in kilohertz because
voice signals must be on the range of 20Hz to 20kHz.
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After all the laboratory experimentations, the researchers started to test their
prototype with varying distances of transmission. As the distance of the transmission
increases the volume of the sound being received decreases dramatically. At first, the
researchers transmitted audio using microphone at a distance of 5 meters with the volume
of the audio amplifier at its maximum. The received audio was still audible that is why
they increase again the distance up to 7 meters and there still an audible sound on the
receiver side with reduced loudness. Figure 32 shows the setup for transmitting audio
signals using microphone at a distance of 5 meters.
Figure 32. Wireless Audio Transmissions Using Visible Light at a Distance of 5 Meters
At the transmitter side, there was a transmitter circuit with LED flashlight
connected to it and powered by a 9volt adapter. On the breadboard, there was an electret
microphone preamplifier powered by a 3volt AAA battery with the output connected to
the input terminal of the transmitter circuit. On the receiver side, there was a computer
speaker with audio jack connected to the solar cell and powered by the USB terminal of
the laptop. It is evident on the figure that the light made its way beyond the receiver setup
which means the receiver can extend on that distance and still be able to receive the audio
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signals. The distance from the transmitter circuit to the wall behind the whiteboard is 7
meters and the researchers successfully transmitted audio signals on that distance with
decrease in loudness while the computer speaker was at full power.
After testing and transmission distance measurement, the researchers started to
design the schematic diagram of the circuits for prototyping. The researchers used eagle
software in designing the schematic diagrams as shown in Figure 33. After designing the
schematic diagrams on eagle software it was converted into a circuit design for printing
purposes for the PCB.
Figure 33. VLC Transmitter Circuit Diagram
Figure 33 shows the transmitter which is composed of ceramic and electrolytic
capacitors, resistors and potentiometer, operational amplifier, transistor, power LED, and
power supply. For the input to the transmitter, the researchers will be using a 3.5mm TRS
audio jack when the input is coming from mobile devices and will be using an electret
microphone with preamp circuit when human voice is the input. Figure 34 shows the
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electret microphone preamplifier circuit design which is composed of electret
microphone, ceramic capacitors, resistors, transistor, and power supply.
Figure 34. Electret Microphone Preamplifier Circuit Diagram
Figure 35. VLC Receiver Circuit Diagram
Figure 35 shows the receiver circuit which is composed of solar cell, capacitors,
resistors, operational amplifier, speaker, and power source.
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After designing the schematic diagrams, the researchers started to make the PCB
layout of the microphone preamplifier, transmitter, and audio amplifier. The researchers
used Eagle software to design the PCB layout of the circuits. The dimensions of the
transmitter and the microphone preamplifier circuits are 1inch by 2 inches as shown.
Figure 36. Transmitter Circuit for Printing
Figure 36 is the converted schematic diagram from Eagle software. This is to be
printed to be placed on a pre-synthesized PCB to be able to have a cleaner prototype. The
transmitter circuit should look like the one shown below for the microphone preamplifier.
The researchers decided to make the PCBs as small as possible for the purpose of
portability and because the components used are only minimal.
Fig. 37. Microphone Preamplifier Circuit on Pre-synthesized PCB
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Figure 38. Audio Amplifier Circuit on Pre-synthesized PCB
Figure 37 and Figure 38 are the microphone preamplifier and audio amplifier
circuit placed on a pre-synthesized PCB having a dimension of 1.5 inches by 1.5 inches
for the microphone preamp and 1.5inches by 2inches for audio amplifier.
Figure 39. Soldering of the Components
After etching of the circuits for the transmitter, microphone preamplifier, and
audio amplifier, the researchers started to solder all the components. Figure 39 is the
soldering of components for the receiver circuit with the casing in front of the proponent.
Wearing a gas mask is a must when working with soldering lead.
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Instruments and Techniques Used
The researchers need the following components and materials in constructing
their working prototype. The researchers took into considerations the table of
specifications and most specially the prices of the components to have a cost effective
system design. Familiarizing with the components will help to know the capabilities and
effectiveness of the components when applied to the system.
Electret Microphone
Electret microphone is a type of electrostatic capacitor-based microphone, which
eliminates the need for a polarizing power supply by using a permanently charged
material. It is a stable dielectric material with a permanently embedded static electric
charge. The name electret comes from the words electrostatic and magnet, drawing
analogy to the formation of a magnet by alignment of magnetic domains in a piece of
iron. Electret microphone, as shown in Figure 40, was used by the researchers on their
prototype if the input to the system is human voice. A DC powered electret microphone
operating at 3 volts will be used by the researcher for the transmitter circuit.
Figure 40. Electret Microphone (Google)
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Audio Jack Plug
Audio jack plug also known as phone connector or phone jack, is a common
family of connector typically used for analog signals, primarily audio. It is cylindrical in
shape, typically with two (TS), three (TRS), or four (TRRS) contacts where T stands for
tip, R for ring, and S for sleeve. In its original configuration, the outside diameter of the
sleeve conductor is 6.35mm. The mini connector has a diameter of 3,5mm and the sub-
mini connector has a diameter of 2.5mm. Audio jack plug is often used to connect the
output audio terminal of mobile devices to an audio amplifier. A 3.5mm TRS stereo
audio jack plug, as shown in Figure 41, was used by the researchers to connect the audio
output terminal of mobile devices to the transmitter circuit.
Figure 41. Audio Jack Plug (Google)
Power Light Emitting Diode
Power LED, as shown in Figure 42, is a two-lead, high power semiconductor light
source. Low power LED commonly operates with a 20mA current while high power LED
can operate with a wide range of current, ranging from tens of mA to several hundreds of
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mA. Suitable amount of voltage is needed by the LED so that the electrons will be able to
combine with electron holes to release the energy in the form of photons with different
particular wavelengths. Different semiconductors used in the manufacture of LEDs will
result in different wavelengths (colors) of light emitted. Currently, the brightest
semiconductor materials are Aluminum Indium Gallium Phosphide (AlInGaP) for reds,
oranges, ambers, and yellows, and Indium Gallium Nitride (InGaN) for blues and greens.
A white LED is typically a blue LED coated in a yellow emitting phosphor, or
combination of phosphors which are excited by the blue light which is the reason why
LEDs appear yellow when they are in the off state. The source of light chosen by the
researchers to be used on the prototype is the 1 watt power LED because of limited
output voltage and current on the transmitter. 1 watt power LED has a voltage range of
3.2 to 3.6 volts and typical current rating of 300mA and has a luminous intensity of 80 to
90 lumens. It was chosen because of its inexpensiveness and portability. Its small size
and yet very bright light characteristics make it stand among other light sources.
Figure 42. Power Light Emitting Diode (E-Gizmo)
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Operational Amplifier
Operational amplifier is a DC-coupled high gain electronic voltage amplifier with
a differential input and usually has a single ended output. In this configuration, an
operational amplifier produces an output potential that is typically hundreds of thousands
of times larger than the potential difference between its input terminals. Due to negative
feedback, the characteristics of an operational amplifier 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 operational
amplifier itself. Operational amplifiers are among the most widely used electronic
devices today, being used in a vast array of consumer, industrial, and scientific devices.
The researchers used the LM2904D operational amplifier for the transmitter circuit.
LM2904D is a low power general purpose dual operational amplifier. It consists of two
independent high-gain frequency-compensated operational amplifiers designed to operate
from a single supply or dual supply over a wide range of voltages. The terminals of
LM2904D, as shown in Figure 43, include (1) output A, (2) inverting input A, (3) non-
inverting input A, (4) ground, (5) non-inverting input B, (6) inverting input B, (7) output
B, and (8) Vcc.
Figure 43. LM2904D Pin out Connections (Google)
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Table 2 is the specifications of LM2904D low power general purpose dual
operational. It can be seen that the data sheet came from Texas Instruments but the
researchers did not buy their operational amplifier from them but from other
manufacturer.
Table 2. Table of Specification of LM2904D Op-Amp (Texas Instruments)
Manufacturer Texas Instruments
Product Category Operational Amplifiers – Op Amps
Amplifier Type High Gain Amplifier
Package/Case SOIC-8
Supply Voltage Max 26 V
Output Current per Channel 30mA
Number of Channels 2 Channel
Gain Bandwidth Product 700kHz
Slew Rate 0.3V/us
Common Mode Rejection Ratio 50dB
Input Bias Current 250nA
Input Offset Voltage 7mV
Supply Voltage Min 3V
Operating Supply Current 12mA
Maximum Operating Temperature +125 degree Celsius
Minimum Operating Temperature -40 degree Celsius
Transistors
Transistors are three-terminal semiconductor devices used to amplify or switch
electronic signals and electrical power. The three terminals of transistor as stated earlier
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are the emitter, base, and collector. A voltage or current applied to one pair of the
transistor’s terminals changes the current through another pair of terminals. NPN and
PNP are the two types of bipolar junction transistors used for different applications. NPN
and PNP are current-controlled transistors that allow current amplification. The input
current on the base of the transistor will be amplified and become larger across the
emitter and collector terminals. The internal construction of the two types of bipolar
junction transistors is very different with each other meaning, there must be a correct
allocation of current and voltage in order for these two devices to work. The researchers
used two NPN transistors; BC547 for electret microphone preamplifier and BC548 for
the transmitter circuit as shown in Figure 44.
Figure 44. BC547 and BC548 Transistors (Google)
BC547 transistors are essentially the same as the BC548 transistors but selected
with higher breakdown voltages. BC548 is low cost and is available in most European
Union and many other countries. It is often the first type of bipolar transistor hobbyists’
encounter, and is often featured in designs in hobby electronics magazines where general
purpose transistor is required. The letters on the transistors indicates its gain. Letter A
indicates low gain (110 to 220 at 2mA), B indicates medium gain (200 to 450), and C
58
indicates high gain (420 to 800). Table 3 is the specifications of the transistors used by
the researchers.
Table 3. Datasheet of BC547 and BC548 Transistors (alltransistors.com)
BC547 and BC548 Transistor Datasheet. Parameters and Characteristics
Type Designator BC547 BC548
Material of Transistor Silicon Silicon
Polarity NPN PNP
Maximum Collector Power Dissipation 500mW 500mW
Maximum Collector-Base Voltage 50V 30V
Maximum Collector-Emitter Voltage 50V 30V
Maximum Emitter-Base Voltage 6V 5V
Maximum Collector Current 100mA 100mA
Maximum Temperature 150 degree Celsius 150 degree Celsius
Transition Frequency 300MHz 300MHz
Forward Current Transfer Ratio 110hFE 110hFE
Capacitors
Capacitors, as shown in Figure 45, originally known as condensers are passive
two-terminal electrical components used to store electrical energy temporarily in an
electric field. The forms of practical capacitors vary widely, but all contain at least two
electrical conductors or plates separated by a dielectric. The conductors can be thin films,
foils or sintered beads of metal or conductive electrolyte. The non-conducting dielectric
acts to increase the capacitor’s charge capacity. Materials commonly used as dielectrics
include glass, ceramic, plastic film, air, vacuum, paper, mica, and oxide layers. An ideal
59
capacitor does not dissipate energy but stores energy in the form of an electrostatic field
between its plates. Capacitors are widely used in electronic circuits for blocking direct
current while allowing alternating current to pass. Capacitors are often used as filters on
most circuits. For low power circuits, common values of capacitors used are in micro
Farads. Ceramic Capacitors do not have polarity while electrolytic capacitors have
polarity that is why when working with electrolytic capacitors, be sure to look at its
positive and negative terminals before connecting it to the circuit. The researchers used
electrolytic capacitors and some ceramic capacitors on their prototype.
Figure 45. Electrolytic Capacitors (Left) and Ceramic Capacitors (Right) (Google)
Resistors and Potentiometers
Resistors, as shown in Figure 46, are passive two-terminal devices used to limit
the flow of current and at the same time used to lower voltage levels in a circuit. Circuits
usually used resistors to complement active components such as integrated circuits,
operational amplifiers, and microcontrollers. Resistors have different sizes and values and
these should be considered in designing because the sizes and values depend upon the
application it is to be used. Aside from using generic resistors, the researchers also used
variable resistor or potentiometer, as shown also in Figure 46, for varying the resistance
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on one part of the circuit. Potentiometers are three terminal resistors with a rotating
contact that forms an adjustable voltage divider. It acts as variable resistor or rheostat if
only two terminals are used, one end and the rotating contact. Potentiometer is often used
as a volume controller.
Figure 46. Generic Resistors (Left) and Potentiometer (Right) (Google)
AC Adapter/Battery
AC adapter or AC to DC converter, as shown in Figure 47, is a type of external
power supply, often enclosed in a case similar to an AC plug. Adapters for battery
powered devices may be described as chargers or rechargers. Portability is the main
concern when it comes to choosing what type of power supply should be used for a
certain device. If the device will be installed only on a certain room, a battery is not a
good choice but rechargeable battery or AC adapter must be considered. The power
supply that the researchers used on their prototype is a 9-Volt battery or a 9- Volt AC
adapter.
Figure 47. AC Adapter (Left) and 9-Volt Battery (Right) (Google)
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Solar Cell
Solar Cell or photovoltaic cell is an electrical device that converts the energy of
light directly into electricity by the photovoltaic effect, which is physical and chemical
phenomenon. It is a form of photoelectric cell, defined as a device whose electrical
characteristics, such as current, voltage, or resistance, vary when exposed to light. Solar
cells are the building block of photovoltaic modules or solar panels.
Solar cells, as shown in Figure 48, are described as being photovoltaic
irrespective of whether the source is sunlight or an artificial light. They are used as a
photo-detector (for example infrared detectors), detecting light or other electromagnetic
radiation near the visible range, or measuring light intensity.
Figure 48. Solar Cells (Google)
Multimedia Speakers
Multimedia speakers or computer speakers, as shown in Figure 49, are
electroacoustic transducers that convert electrical audio signals into corresponding
sounds. Most such speakers have an internal amplifier, and consequently require a power
source, which may be by a mains power supply often via an AC adapter, batteries, or
62
USB port (able to supply no more than 2.5Watts DC, 500mA at 5Volts). The signal input
connector is often a 3.5mm jack plug but RCA connectors are sometimes used. The
researchers used a USB powered computer speakers with 3.5mm audio jack for their
prototype.
Figure 49. Multimedia Speakers (Google)
Printed Circuit Board
Figure 50. Printed Circuit Board (Google)
Printed Circuit Board (PCB), as shown in Figure 50, mechanically supports and
electrically connects electronic components using conductive tracks, pads, and other
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features etched from copper sheets laminated onto a non-conductive substrate. It can be a
single sided (one copper layer) double sided (two copper layer), or multi-layer (outer and
inner layers). The researchers used a pre synthesized printed circuit board for their
prototype so that the circuit design is tidy.
Breadboard and Jumper Wires
Breadboard, as shown in Figure 51, was also used by the researchers. It was used
for temporary mounting and testing of the prototype. Using breadboard is the easiest way
of accomplishing the circuit design with the help of jumper wires. Integrated circuits are
often placed in the middle of the breadboard so that the half of the legs is on one side and
the half on the other side for easier connections.
Figure 51. Breadboard and Jumper Wires (Google)
Casing
After designing the whole circuit for the transmitter and receiver circuits, the
researchers will design a casing that will keep all the circuits to make the prototype more
presentable. The researchers wanted to place their receiver circuit on a bamboo or on a
closed box. The researchers cannot decide where to put their transmitter circuit because
they wanted to implement it as table lamp but they also wanted to place it inside a bulb.
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Bill of Materials
The materials stated on table 4 are the major components that the researchers used
on their prototype. Other materials used on experimentations were not stated.
Table 4. Bill of materials (E-Gizmo)
Unit Values Quantity Total Price
Resistor 10ohms
80ohms
10Kohms
15Kohms
100Kohms
1
2
7
4
2
Php 8.00
Electrolytic Capacitor
Ceramic Capacitor
10uF
100uF
470uF
1000uF
0.1uF
0.47uF
2
1
2
3
9
1
Php 26.00
Transistor BC548
BC547
2
2
Php 12.00
Power LED w/ Heat
sink
1 Watt 2 Php 70.00
Operational
Amplifier
LM386
LM2904D
1
2
Php 36.00
Battery 9 Volts
1.5Volts AAA
2
4
Php 105.00
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Continuation of Table 4
Variable resistor 1Mohms and 10Kohms 7 Php 35.00
PCB 3x5 1 Php 90.00
Audio Jack TRS Male 3 Php 45.00
Total Php 427.00
Time Frame
The researchers plan the dates that they should work to accomplish the
requirements and to meet the deadlines. Table 5 shows the planned dates of the
researchers in accomplishing their study.
Table 5. Time frame
Planned Date Activities
Mid of August Planning and designing of the working prototype.
Making of the schematic diagram and determining
the components needed for the circuit design.
September to Mid of October Making of the thesis paper until chapter 3
Mid of October to November Canvass the prices of the components needed for the
circuit. Buying the parts needed. Testing of the
materials that will be used on the prototype.
November to December Continuing the making of the thesis paper
December to January Making of the working prototype.
January to February Testing the reliability and effectiveness of the
prototype.
February to March Finalizing the thesis paper and the working prototype
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Chapter IV
Results and Discussions
Project Technical Description
In line with the visible light communication technology, the proponents’ proposed
project about audio transmission via VLC seeks to be comparable to other existing
systems. The system used audio source coming from mobile devices such as laptop,
android phones, or tablets and from a microphone with preamplifier circuit. The
transmitter circuit used passive components such as capacitors, resistors, potentiometer
and active components such as operational amplifier, transistor, and LED. As the audio
source started to pass the very low signal, with 20 to 20 KHz frequency, to the transmitter
circuit, the signals started to flow through the 0.1uF ceramic capacitor where direct
current components are removed and through the 10kOhm resistor that limits the current
to the operational amplifier inverting input pin 6. The 1MOhm potentiometer was a
feedback gain controller that controls the signal output from operational amplifier pin 7
passing through the base of the transistor. The transistor worked as a modulator and
amplifier in the circuit. The electrolytic capacitors, 470uF and 1000uF, were used as
filters to reduce ac components spike in the circuit. Using a voltage divider, the 9 volts
supply voltage will be divided into half for powering the LED. A 9 volt battery or adapter
with a maximum of 800mA can be used as a power source for the transmitter circuit. The
transistor will modulate and amplify the signal and will pass it to the LED where the
signal was being carried by the photons. The arriving signal will be captured by the 6volt,
1.6 watts solar cell where the light will be converted into electrical signal and will be fed
to the audio amplifier circuit. To have a two-way wireless communication using visible
light, the proponents will provide two transmitters and two receiver circuits.
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The proponents used LED flashlights as light source which is comparable in
luminosity of a 1 watt power LED of about 80 to 100 lumens with beam angle of 30 to 50
degrees and a beam distance of about 7 to 10 meters. LED light was powered by 4.5 to 6
volts with 200 to 400mA current. The microphone preamplifier was powered by a two
AAA 1.5volts battery which added a little voltage to the output LED light when
connected as input.
When it comes to BC548B transistor, the collector and emitter current were
approximately equal to 80mA and the base current was approximately 222uA which gave
the total gain of 360 to 400. Based on the BC548B transistor specification the gain of this
transistor must be 110 to 450 which is true based on the calculations of the proponents.
The collector-emitter voltage was about 4.5 volts which gave a total collector power
dissipation of 360mV. All the specifications of the transistor were met by the proponents.
The researchers chose the solar cell as photo detector for their system instead
of photodiode or phototransistor because of its wide area coverage, sensitivity, and
response time. While solar cell can still deliver output even when the light is slightly
focused or dimmed, other photo detectors produce dark currents, currents generated
during absence of light, which lessen their sensitivity and response time. Using a solar
cell, the output can be delivered on real-time with good quality characteristics.
When it comes to the modulation of the audio signal, the proponents found out
that the modulation used on their system was amplitude modulation. As the volume of the
source increases, the amplitude of the sine wave also increases dramatically without
affecting the frequency of the signal. On the receiver side, the signal was also amplitude
modulated sine wave. In figure 52, the envelope made by amplitude modulation was very
evident.
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Figure 52. Envelope Produced by Amplitude Modulation
Figure 52 is a screenshot of the video made by the researchers during their
experimentation and it can be seen on the figure that the amplitude of the sine waves
were making its way up as the volume of the source increases.
For the receiver, the system can use a mono, stereo, or even multiple audio
amplifiers as long as the solar cell connected to their inputs must be covered by the LED
light source. For the mono audio amplifier, the positive terminal of the solar panel was
connected to the tip of the audio jack and the negative terminal connected to the sleeve of
the audio jack. For the stereo audio amplifier, there must be two connections for the
positive terminal of the solar panel to be connected to the tip and ring of the audio jack
and the negative must be connected to the sleeve of the audio jack. For multiple
receivers, multiple solar cells were also needed. Connecting in parallel the multiple audio
amplifiers to one solar cell is a bad idea because the current produced by the solar cell
will be divided on the connected audio amplifiers, thus resulting to a quieter output for all
the connected audio amplifiers. The researchers decided to use stereo speakers for their
prototype.
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Project Limitations and Capabilities
A wireless communication system using visible light was successfully developed
by the proponents with the purpose of integrating communication to lightings. All
systems are not perfect that is why there are limitations and capabilities to be considered.
There should be a balancing of the limitations and capabilities of a system before
deciding whether the system is advantageous or not.
After all the experimentations and testing done by the proponents, the capabilities
that they identified on their proposed system are as follows:
1. The system is capable of transmitting high quality audio signals wirelessly
coming from mobile devices and microphone using visible light and at the same
time can function as illuminator in small area.
2. The transmitter can transmit audio signals at a distance of 5 to 7 meters with
acceptable loudness at the receiver side.
3. When the transmitter and receiver are close to each other (at least 1 meter), the
transmitted sound is comparable to the sound when the speaker is directly
connected to the audio source.
4. The transmitter can also transmit by means of reflection, meaning using a mirror
the transmitter can transmit at different angles as long as the light can strike the
receiver.
5. The system can be used to any kind of environment especially on hospitals and
aircrafts where wireless devices are sometimes prohibited.
6. The system can be deployed by having a single transmitter with multiple
receivers.
7. The system is capable of producing consistent output on a real time basis.
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8. The system transmission can penetrate transparent blockings on the path of light
with a small effect on the received signal.
9. For full-duplex communication, the system is secured as long as the lights are
within the area of the communicating party.
On the other hand, the system is not that perfect and there are some situations that
can be identified as limitations of the system. The limitations that the proponents
identified on their system are as follows:
1. Big solid blockings on the path of light can disturb the communication.
2. The system is for short distance (1m to 7m) and point to point optical wireless
communication only.
3. The transmitter was not designed for simultaneous transmission of voice and
audio signals from mobile devices.
4. Ambient light or other light sources can cause interference to the captured signal
by the solar panel, producing unwanted noise on the audio amplifier circuit.
Project Evaluation
To prove the systems capabilities and limitations stated above are true, the system
should undergo the process of evaluation by allowing it to use by the respondents. The
respondents will serve as the end user of the system who will express their perception of
the system. The system was evaluated in terms of its functionality, reliability, efficiency,
effectiveness, and maintainability. Each criteria have different conditions under and will
be rated 1 to 5 where 5 stands for very good, 4 for good, 3 for fair, 2 for poor, and 1 for
very poor.
The system was evaluated by four faculty members of Electronics Engineering
Department, including the chairperson of ECE, to be able to have an exchange of
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knowledge with the professionals who have a better understanding of electronics and
communications systems. The system was also evaluated by three faculty members of
Computer Engineering Department for them to appreciate where the ECEs are heading in
terms of communication and technology.
The system was evaluated with different criteria for functionality, reliability,
efficiency and effectiveness, and maintainability. For the functionality criteria, the system
will be evaluated if it functions according to the intended purpose, if it can produce the
expected outputs in a given period of time, if it is comparable to the existing similar
system, if it is easy to use and operate, and if it gives convenience to the users every time
they use it. For the reliability criteria, the system will be graded if it can withstand the
intended operation, if it is reliable in terms of strength, capacity, and performance, if high
degree of security can be obtained when using the system, if there is consistency on
outputs, and if it can satisfy the needed outputs of the user. For the efficiency and
effectiveness criteria, the system will be graded if it meets the user’s objectives and
requirements, if it can be used to its maximum design capacity, if it can respond to the
needs of the end user, if it can contribute for the development of the same model of
technology, and if it can enhance the individual’s learning. For the maintainability
criteria, the system will be evaluated if it can operate accurately with minimum
maintenance, if it can be adapted to any changes in its working condition, and if
troubleshooting or repair can be done easily by the user. After grading the system, the
respondents should feel free to write comments, suggestions, or recommendations for the
improvement of the system.
Before the evaluation proper, the respondents should fill up the space provided for
their name, complete address, and profession or field of specialization. There was a letter
72
for the respondents asking for their kind evaluation of the system. There was also an
instruction that the respondents should follow while evaluating the system. After the
evaluation table, there was a space provided for comments, suggestions, or
recommendations if they feel that the system needs improvement or modification.
After all the chosen respondents finished the evaluation form, it was collected by
the proponents for data analysis. For the interpretation of gathered data, the proponents
used averaging technique on every criterion. For every criterion the computed mean was
interpreted as shown in Table 6.
Table 6. Mean Range Interpretation
Mean Range Interpretation
4.5 to 5 Very Good
3.5 to 4.4 Good
2.5 to 3.4 Fair
1.5 to 2.4 Poor
0.5 to 1.4 Very Poor
In the interpretation of data the proponents will know if their system is very good,
good, fair, poor, or very poor. The results will help the proponents to know if they need
improvement of the system or modification on some aspects. This evaluation should
reflect the objectives given by the proponents on the first chapter of this paper and the
capabilities and limitations of the system as stated earlier. After accomplishing the
evaluation instrument by the responders, the proponents gathered all the data for
interpretation. The following data are shown on Table 7 with every criterion having the
mean value using the averaging technique as stated earlier for computation.
73
Table 7. Evaluation Instrument Analysis
CRITERIA
Grade Interpretation
1 2 3 4 5 Mean(n=7)
FUNCTIONALITY
1. The system functions according to the
intended purpose.
0 0 0 1 6 4.857
2. The system can produce the expected
outputs in a given period of time.
0 0 0 1 6 4.857
3. The system is comparable to the
existing similar system.
0 0 0 0 7 5
4. The system is easy to use and to
operate.
0 0 0 1 6 4.857
5. The system gives convenience to the
users every time they use it.
0 0 0 1 6 4.857
Weighted Average 4.886
RELIABILTY
1. The system can withstand the intended
operation (continuous or intermittent).
0 0 0 3 4 4.571
2. The system is reliable in terms of
strength, capacity and performance.
0 0 0 4 3 4.429
3. High degree of security can be obtained
when using the system.
0 0 0 3 4 4.571
4. There is consistency on outputs. 0 0 0
2 5 4.714
74
Continuation of Table 7
5. The system can satisfy the needed
outputs of the user.
0 0 0 1 6 4.857
Weighted Average 4.628
EFFICIENCY AND EFFECTIVENESS
1. The system meets the user’s objectives
and requirements.
0 0 0 0 7 5
2. The system can be used to its
maximum design capacity.
0 0 0 1 6 4.857
3. The system can respond to the needs of
the end user.
0 0 0 1 6 4.857
4. The system can contribute for the
development of the same model of technology.
0 0 0 2 5 4.714
5. The system can enhance individual’s
learning.
0 0 0 0 7 5
Weighted Average 4.886
MAINTAINABILITY
1. The system can operate accurately with
minimum maintenance.
0 0 0 2 5 4.714
2. The system can be adapted to any
changes in its working condition.
0 0 0 4 3 4.429
3. Troubleshooting/repair can be done
easily by the user.
0 0 1 0 6 4.714
Weighted Average 4.619
75
The proponents let at least seven respondents, including the chairperson of ECE,
to evaluate their proposed system. The objectives of the proponents were shown on the
respondents and each criterion was clearly discussed. Table 7 shows the results of the
evaluation done by the respondents. Each interpretation on each criterion was a weighted
mean of the gathered data.
For the criteria for functionality, the system was graded very good and good. For
the statement the system functions according to the intended purpose was rated good and
very good but most of the respondents rated very good that is why the interpretation for
this was very good. The proponents agreed to this for they know that they made the
system according to its intended purpose based on their objectives stated on the first
chapter of this paper. Same those with the statements the system can produce the
expected outputs in a given period of time, the system is comparable to the existing
similar system, the system is easy to use and operate, and the system gives convenience
to the users every time they use it, were rated very good. These results were good
manifestation that the system performed well when it comes to its functionality. For the
proponents, they can say that the idea of the system was not theirs but the system can
stand as improvement or modification of other existing systems.
For the criteria about reliability, the system was graded very good and good also.
The statement the system is reliable in terms of strength, capacity, and performance was
interpreted as good. On the other hand, the system was interpreted as very good for the
statements the system can withstand the intended operation (continuous or intermittent),
the system can satisfy the needed outputs of the user, there is consistency on the outputs,
and high degree of security can be obtained when using the system. The proponents were
proud to say that their system is reliable enough based on the data that they gathered.
76
Some respondents never realized that the system is also capable of transmitting voice
signals that is why there is a security issue on this criterion. The system can be used by
two parties as a two-way voice communication which is very secured as long as the lights
are within the area of the two communicating parties in contrast with the RF signals
where any interested party can intercept the communication between the two
communicating parties.
When it comes to the efficiency and effectiveness criteria, the system was graded
very good and good. The researchers felt happy about the interpretation of the gathered
data under this criterion. The statements the system meets the user’s objectives and
requirements, the system can be used to its maximum design capacity, the system can
respond to the needs of the end user, the system can enhance individual’s learning, and
the system can contribute for the development of the same model of technology were all
interpreted as very good. The statement the system can enhance individual’s learning for
the proponents are really true because they can proudly say that they learned a lot while
doing their proposed system and they want to share it to everybody who are interested on
this kind of technology. Based on the results under this criterion, the system was very
efficient and very effective for the users given that the system has its own limitations.
Under the maintainability criteria, the system was graded good, very good, and
fair. Under this criterion, it is understood that the system troubleshooting or repair can
only be done by technicians or any other persons who have knowledge about simple
circuitry. The proponents were grateful of the interpretation of the gathered data under
this criterion. The statement the system can operate accurately with minimum
maintenance and troubleshooting/repair can be done easily by the user were interpreted as
very good maybe because the respondents have a broad knowledge about simple circuits
77
and at the same time the components used by the proponents were minimal that is why
the system can be easily repaired. On the other hand, the statement the system can be
adapted to any changes on its working condition was interpreted as good.
The portability criteria were not be able to include by the proponents on their
evaluation instrument but they can say that their system is portable enough to be carried
anywhere and can be easily installed because the system was only powered by a 9-volt
adapter or 9-volt battery. The system is compatible to any other devices with audio output
such as desktop, laptop, mobile phones, and tablets.
Table 8. System Evaluation Summary
Criteria Weighted Average
Functionality 4.886
Reliability 4.628
Efficiency and Effectiveness 4.886
Maintainability 4.619
Total Average : 4.755
Figure 53. System Evaluation Summary Graph
4.886
4.628
4.886
4.619
4.45
4.5
4.55
4.6
4.65
4.7
4.75
4.8
4.85
4.9
4.95
Functionality Reliability Efficiency andEffectiveness
Maintainability
Functionality
Relibility
Efficiency and Effectiveness
Maintainability
78
The system evaluation instrument analysis summary was used as the basis for the
overall performance of the system. Table 8 and Figure 53 show different criteria for
system evaluation with corresponding weighted averages. The weighted averages of the
criteria were also used again for computation of the total average which can be
interpreted as the total performance of the system. It can be seen on the table that the total
performance of the system was graded as 4.755 which can be interpreted as very good but
the grade clearly says that the system was not perfect or almost perfect. The proponents
knew that their proposed system has its own weakness that is why there were space
provided for comments, suggestions, and recommendations for them to know what are
the things that they should improve and enhance on the system. The chairperson of ECE
left it blank and let the proponents think what should be the recommendations because
they are the ones who knew the capabilities and limitations of their system. One of the
respondents made a comment that the system was an original concept and the first he had
ever seen so far in Columban College. Other respondents left the comments part blank
but they discussed to the proponents their comments on the system that can be used for
future enhancement of it.
The system finally underwent the respondents or end-users evaluation. The
system was graded very good, good, and fair on different criteria such as functionality,
reliability, efficiency and effectiveness, and maintainability. These results of the
evaluation were used by the proponents to know the strengths and weaknesses of their
system and were used as basis for improvement or modification of some aspects of the
system. Based on the results of gathered data, the proponents can proudly say that they
met their desired output of their proposed system which satisfied their given objectives
on the first chapter of this paper.
79
Chapter V
Summary, Conclusion, and Recommendation
Summary
Visible light communications is the emerging technology in the world of
communications nowadays with unimaginable possible applications. Every year there are
advancements on the studies about it which is the possible solution to the overcrowding
capacity on radio frequency spectrum used in communications. The frequency spectrum
of visible light is said to be 10,000 times larger than the radio waves frequency spectrum
and at the same time not regulated by the FCC which can be treated as free. Using
unguided visible light sources such as ordinary LED and laser can provide
communication.
Because of interesting applications and advantages of visible light
communication, the proponents proposed one of the possible applications of visible light
communication which is the audio transmission. The system was composed of audio
inputs from microphone or mobile devices, VLC transmitter, and VLC receiver. The
researchers aim to provide a two way wireless communication using visible light even
though their objective is only to be able to transmit audio signals from microphone and
mobile devices. The main objective of the proponents was to provide both
communication and illumination at the same time.
The proponents have gained many things after the long process of their
experimentations and they are very excited to share it to other students. The proponents
learned the concept and principle of their proposed system which is electrical signals
coming from source is carried out by the photons produced by the light and it will be
received by a photosensitive element that will convert those light intensity to proportional
80
electrical signals. They also learned the components that should be used to provide a
desirable output, the modulation technique which is amplitude modulation, and the
distance of transmission which is inversely proportional to the received signal. The
system is cost effective and yet can be used on any other applications involving both
illumination and communication purposes for audio and voice transmission.
The system outputs a high quality audio transmission which is comparable to a
wired transmission of audio or voice signals. To test the functionality, reliability,
efficiency and effectiveness, and maintainability of the system, it was subjected to
evaluation by the respondents who act as end users. The feedbacks of the respondents
were all good based on the results of the gathered data but there are some aspects that the
respondents were not completely convinced and the proponents will take that as their
recommendations for future studies.
Conclusion
The system being discussed on the whole part of this paper was all about audio
transmission by the use of visible light communication. The construction of the system
had undergone much experimentation before the proponents arrived to the best design
that can output the best and most desirable quality of transmitted signals. The system was
evaluated by the respondents who act as end users and their feedbacks on the system
were all good.
The first objective of the proponents was to transmit audio signals coming from
mobile devices using visible light and the proponents can say that this objective was
realized because they were able to transmit music wirelessly from mobile phones and
laptop using the visible light. Another objective was to transmit human voice signals
using visible light and for the proponents they were also able to accomplish this objective
81
for they transmitted human voice using microphone. The third objective of the
proponents was to use the principle of reflection to transmit audio signals and the
proponents were able to transmit audio signals using a mirror with small effect on the
intensity of light received by the receiver. To test the functionality, reliability, efficiency
and effectiveness of the system was also one of the objectives of the researchers and they
accomplish this with the help of the evaluation instrument provided to the respondents
who evaluated the system. To promote the system to ECE students who will later engage
in studies of new technologies was also an objective of the proponents and they
successfully accomplished this for some of their respondents came from fourth year ECE
students. Based on the results of the gathered data on evaluation instrument, the
proponents can therefore conclude that they accomplished all the objectives that they
cited on the first chapter of this paper.
Recommendation
The researchers can say that their proposed system has its own weaknesses and
limitations but these will be treated by the proponents as possible subjects for further
development of the system. The following recommendations are offered as possible ways
to further improve the proposed system. The recommendations will also cover
recommendations for research of other applications of visible light communication.
1. Using transistor and operational amplifier that can operate at higher voltage and
current to have a higher power output for much brighter LED lighting.
2. Using a more luminous LED lighting to increase the transmission distance and to
widen up the coverage area of transmission.
3. To improve the receiver circuit by making it stand alone receiver by making solar
panel the charger and at the same time receiver of the audio amplifier.
82
4. To explore other applications of visible light communication such as video and
data transmission.
5. To explore other modulation techniques such as pulse width modulation or pulse
position modulation.
6. To install the system on two different rooms to have a two way wireless
communication between rooms.
Appendix A
Letter of Permit to Conduct Study August 8, 2015 Engr. Greg C. Mallari, PECE, REE, MEng-EE Dean, College of Engineering Columban College Dear Engr. Mallari: The researchers would like to request permission from your good office to conduct a study in line with our thesis entitled: “Audio Transmission via VLC,” in compliance for the subject Practicum/Thesis 1 (ELE512). Thank you and God Bless. Very yours truly,
Marc Anthony B. Gonzales Researcher Renz Mark C. Rico Researcher
Noted and Approved by:
Engr. Arlene A. Cerico-Grate, ECE, MEng-ECE Research Adviser BSECE Chairperson
Appendix B
System Evaluation Instrument
Name of Respondent: ____________________________________________________
Complete Address: ____________________________________________________
Profession/ Field of Specialization: ________________________________________
Dear Respondent,
Kindly evaluate my system “Audio Transmission Via VLC” in terms of its
functionality, reliability, efficiency and effectiveness, and maintainability.
Please check or mark the appropriate box that corresponds to your assessment,
using the following scales:
5 – Very Good 4 – Good 3 – Fair 2 – Poor 1 – Very Poor
CRITERIA 1 2 3 4 5
A. FUNCTIONALITY
1. The system functions according to the intended
purpose.
2. The system can produce the expected outputs in a
given period of time.
3. The system is comparable to the existing similar
system.
4. The system is easy to use and to operate.
5. The system gives convenience to the users every
time they use it.
B. RELIABILTY
1. The system can withstand the intended operation
(continuous or intermittent).
2. The system is reliable in terms of strength,
capacity and performance.
3. High degree of security can be obtained when
using the system.
4. There is consistency on outputs.
5. The system can satisfy the needed outputs of the
user.
C. EFFICIENCY AND EFFECTIVENESS
1. The system meets the user’s objectives and
requirements.
2. The system can be used to its maximum design
capacity.
3. The system can respond to the needs of the end
user.
4. The system can contribute for the development of
the same model of technology.
5. The system can enhance individual’s learning.
D. MAINTAINABILITY
1. The system can operate accurately with minimum
maintenance.
2. The system can be adapted to any changes in its
working condition.
3. Troubleshooting/repair can be done easily by the
user.
Comments/Suggestions/Recommendations:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
References
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Bagal, N. and Pandita, S. (April 2015). A review: real-time wireless audio-video
transmission. IJETAE Vol. 5, Issue 4
Chan, C. et al. (October 1999). Optical wireless based on high brightness LEDs.
Phoenix, Arizona, USA.
Cho, E. et. al. (2013). Simultaneous transmission of udio and vSignals using
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Deshmukh, R. (May 2014). Voice transmission through bluetooth. International
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Engineering Vol. 2, Issue 5
Ding, L. et al. (June 2013). Real-time audio and video transmission system based
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http://www.scirp.org/journal/opj
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Fath, T.C.M. (October 2013). Evaluation of spectrally efficient indoor optical
wireless transmission techniques. University of Edinburgh
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Haruyama S. (February 2011). Visible light communications: recent activities in
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Hope, O. et al. (July 2014). Future trends in fiber optics communication. ISBN:
978-988-19252-7-5
Isaac, B. and Song, S. (November 2014). Analysis of Wi-Fi and WiMax and
wireless network coexistence. IJCNC Vol. 6, No. 6
Komine, t. (2005). Visible light wireless communications and its fundamental
study
Lee, C. G.(February 2011). Visible light communication. Chosun University,
South Korea.
Malhotra, H. (September 2014). Transmission of multiple audio signals using
laser communication system. Vol. 4, Issue 9 ISSN 2277 128X
Moritz, J. (2011). Audio-to-optical conversion and transmission. California
Polytechnic State University
Png, L. C. (June 2015). Design of VLC transceiver circuits for reading light
transmission of high-quality audio signals on commercial airlines.
http://www.researchgate.net/publication/275208935
Yung, L. (April 2013). Design and construction of visible light communication
system prototypes for Aadio and digital signal transmission. Universiti Tunku Abdul
Rahman
Curriculum Vitae
MARC ANTHONY BELLECA GONZALES
Address: #047 Del Pilar, Castillejos, Zambales
Contact No: 0912-796-0164
E-mail Address: [email protected]
PERSONAL INFORMATION
Date of Birth : August 26, 1993
Age : 22
Gender : Male
Civil Status : Single
Religion : Roman Catholic
Nationality : Filipino
Language : Tagalog, English
Height : 5'7”
Weight : 110 lbs.
EDUCATIONAL ATTAINMENT
Tertiary : Columban College
Address : Rizal St. Extension, Bo. Barretto, Olongapo City
Course : BS- ECE
Year Attended : 2011-2016
Secondary : St. Nicholas Academy
Address : San Juan, Castillejos, Zambales
Year Attended : 2006 - 2010
Curriculum Vitae
RENZ MARC C. RICO
Address: #13 Graham St. E.B.B.O.C
Contact No: 0927-500-1691
E-mail Address: [email protected]
PERSONAL INFORMATION
Date of Birth : January 10, 1992
Age : 23
Gender : Male
Civil Status : Single
Religion : Born Again Christian
Nationality : Filipino
Language : Tagalog, English
Height : 5'6”
Weight : 132 lbs.
EDUCATIONAL ATTAINMENT
Tertiary : Columban College
Address : Rizal St. Extension, Bo. Barretto, Olongapo City
Course : BS- ECE
Year Attended : 2008-2016
Secondary : San Pablo 2nd
High School
Address : Lubao, Pampanga
Year Attended : 2004 – 2008
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