Title:
“Voice and Data Transmission through an Optical Fiber”
Authors:

KARTIK K KAMRA*
VIT University
Vellore, India

LAKSHAY PARMAR
VIT University
Vellore, India

ASHWINI KUMAR
VIT University
Vellore, India

JABEENA A
VIT University
Vellore, India
*Address for correspondence: kartikk.kamra2012@vit.ac.in
ABSTRACT
The project involves voice and data transmission through an optical fiber. The Data that
will be transmitted is BCD data. For this Purpose UM 9121 B IC which commonly
generates DTMF signal has been used, and at the receiver part decoding of this signal
id done with help of IC CM 8870. IC CM 8870 will convert the DTMF signal to a BCD
signal then with the help of IC 7447 output can be seen on a seven segment display.
Voice is fed through a mike and at the receiver part can be easily heard with help of a
Speaker. This model is very useful for line to line or point to point communication.
KEYWORDS





optical fiber
data transmission
voice transmission
long distance communication
high bandwidth
INTRODUCTION
Fiber-optic communication is a method of transmitting information from one place to
another by sending pulses of light through an optical fiber. The light forms
an electromagnetic carrier wave that is modulated to carry information. Optical fiber
can be used as a medium for telecommunication and computer networking because it is
flexible and can be bundled as cables. It is especially advantageous for long-distance
communications, because light propagates through the fiber with little attenuation
compared to electrical cables. This allows long distances to be spanned with few
repeaters.
MATERIALS AND METHODS
In this project transmission of two signals takes place; one is recorded and the second
one is the signal from the mike. To change over the signals a switch has been deployed.
The major components used are:





IC UM9121B- DTMF Signal Generator
IC CM8870- DTMF Decoder
IC 7447- Seven Segment Display
IC 7805 – Power Regulator
IC 741- Operational Amplifier
(1) For Direct Audio Signal from a mike:
Data is fed from mike, mike converts the audio signal into an electrical signal and this
electrical signal is coupled in to pin number 2 at I.C 741. Here I.C 741 is being used as
a mike amplifier. Pin number 6 is the output pin, this is the amplified output. For
further amplification a Transistor circuit is used. Output of transistor is connected to a
LED. Data is super imposed on LED light and is focused on the receiver. When this
light is sensed by a photo sensor, it converts the light into PHOTO CURRENT and it is
later on converted into voltage, this small voltage is again fed to pin number 2 at I.C
741. Output is taken from pin 6 and given to a transistor circuit, where it is amplified
again, and given to a speaker, and so we hear the voice.
(2) For recorded BCD signal:
Transmitter section consists of 9-switches for the nine BCD numbers and receiver
section will consist of a seven segment display for numeric display. IC UM9121B
serves of best purpose as it generates DTMF (Dual Tone Multi Frequency) signal in
form of PWM (pulse width modulation). This IC is commonly used to generate DTMF
signals. All nine switches are connected to 9 inputs of this IC and acts as a MATRIX
NETWORK. Switches are divided in four rows(R-1 R-2 R-3 R-4) and three
columns(C-1 C-2 C-3). When we press switch number 1 the pins connected to R-1 and
C-1 gets activated. Output signal is available at pin 7 of this IC. Data is fed to pin
number 2 at I.C 741. Here I.C 741 is being used as an amplifier. Pin number 6 is the
output pin, this is the amplified output. For further amplification a Transistor circuit is
used. Two transistors are used NPN and PNP. Collector of NPN is connected to
positive supply and collector of PNP to negative supply. Output is available at emitter
from the transistor. Output of transistor is connected to a LED. Data is super imposed
on LED light and is focused on the receiver. When this light is sensed by a photo
sensor, it converts the light into PHOTO CURRENT and it is later on converted into
voltage, this small voltage is again fed to pin number 2 at I.C 741. Output is taken from
pin 6 and now it is connected to a DTMF decoder, so for this purpose we use IC
CM8870. Signal from operational amplifier is fed at pin number 2 and 3 of this IC.
This IC receives the signals and decodes it and output is available at pin number 11, 12,
13 and 14 in form of BCD signal. This signal is given to Seven Segment display and
numeric data is displayed.
(3) Circuit Diagram:
i.
For Transmitter part:
The Transmitter contains IC UM9121B which is connected to switches as can be
seen in the circuit diagram. UM9121B is connected by a Zener diode to regulate the
voltage and a resistance of 150 ohm to limit the current flow. It is also connected to
a Crystal Oscillator which operates at 3.579545 MHZ. A mike signal input is
present before a switch. A switch is connected to an operational amplifier and also
has 2 transistors to amplify the signal. A LED is present to convert signal into light
pulse.
Fig. 1. Circuit diagram of transmitter
ii.
For Receiver part:
The Receiver contains IC CM8870 which is connected to seven segment display
IC7447. IC CM8870 is connected by a IC 7805 which is a power regulator and is
used to regulate the voltage and a resistance of 470 ohm to limit the current flow. It
is also connected to a Crystal Oscillator which operates at 3.579545 MHZ. A
speaker is present and it has connections with operational amplifier and transistor
circuit. A photodiode is used to sense the light signal and convert it into an
electrical signal.
Fig. 2. Circuit diagram of receiver
(4) Flowchart:
3-WAY SWITCH IN
WHICH STATE (ON-1
/OFF/ON-2)
O
N
INPUT FROM MIKE
AND AMPLIFIED BY
OP-AMP AND
TRANSISTOR
O
N
2
Output to
DTMF
Decoder and
then to seven
segment
display
Output from mike
INPUT FROM
SWITCHES AND
GIVEN TO DTMF
GENERATOR
T
O
LE
CONVERT
ELECTRICAL TO
LIGHT SIGNAL
PHOTODIODE
SENSES AND
PRODUCES A
PHOTODIODE
CURRENT
AMPLIFIED
BY OP-AMP
(5) Working
Fig. 3. IC-CM8870 Pin Diagram
The 8870 DTMF decoder sheet shown in Figure 3 includes an example circuit as well
as a table showing how the binary output represents 1 of 16 possible DTMF tones.
There are actually five output pins used on the 8870 decoder - four of them represent
the binary data and a 5th pin toggles from low to high and then back to low every time
a valid DTMF signal has been decoded. This allows your receiving circuit or device to
know when a number has been repeated. Without this data receive pin, you would have
no way to know if the same key has been pressed multiple times as the last data on the
4 bit output will simply remain the same. So every time a new DTMF tone has been
decoded and sent to the 4 bit binary port, the data ready pin will toggle to high for a
short time. On my 8870 version, the binary data output pins are marked Q1, Q2, Q3,
Q4
and
the
data
ready
pin
is
marked
as
STD.
To get DTMF data into the 8870 decoder chip, pins 1, 2, 3, and 4 are set up as an
analog input as shown in the datasheet example. The audio signal is processed by a
robust signal processor inside the 8870 and any DTMF tones heard will be registered
on the data output port. The input is very versatile and can be directly connected to the
phone line or to any audio playback device such a computer sound card or digital
recording unit. Basically, and device capable of sending an audio signal can be fed into
the 8870 DTMF decoder, and as long as the signal quality is decent, the DTMF tones
can be decoded.
RESULT
The following figures 4, 5, 6, 7 depict the BCD values that are shown on the seven
segment display. The Voice signal also successfully gets transmitted through the
Optical fiber.
Fig. 4. Data output: number 3
Fig. 5. Data output: number 6
Fig. 6. Data output: number 8
Fig. 7. Data output: number 9
Fig. 8. Fabricated transmitter (left) and receiver (right)
CONCLUSION
The project involves the transmission of data and voice signal through an optical fiber.
Though the project is a successful one, but it is implemented for a short range of
distance in real time scenarios, the distances are usually long. Long distance
communication can also be implemented by increasing distance of the fiber but LOSS
factor also will increase so one has to keep in mind about both the Fiber loss and the
Distance of communication (REFERENCE-2). In place of LED a laser can also be used
which has its own advantages but will be more costly.
REFERNCES
1) http://www.iaeng.org/publication/WCE2014/WCE2014_pp438-442.pdf
2) http://www.ijetae.com/files/Volume3Issue5/IJETAE_0513_78.pdf
3) http://www.cisco.com/c/en/us/products/collateral/interfacesmodules/transceiver-modules/white_paper_c11-463661.pdf
4) http://www.coe.montana.edu/ee/rwolff/EE548/papers/ieee%2050th%20annivers
ary/01006983.pdf_isNumber=21724&prod=JNL&arnumber=1006983&arSt=13
8&ared=147&arAuthor=Ramaswami%252C+R.pdf
5) http://lucidscience.com/pro-phone%20number%20decoder-2.aspx