Implementation of FSO communication.

1. IMPLEMENTATION OF FREE SPACE
OPTICAL (FSO) COMMUNICATION
Guided By:
Dr. Sumanta Gupta
Prepared By:
Tulasi Chandan(1301EE42)

2. What Is Free Space optical
Communication?
 Wireless optical connections
through the atmosphere.
 Data modulated LASER beam is
transmitted through free space.
 Photodiode Receiver
 Directional, Long distance and
Secure form of Communication

3. Objective
Transmitting information via a laser beam
◦ Video
◦ Image
◦ Sound
010001100110
111011001111
001010000010
101110010001
111001011011

4. BASIC IDEA

5. Structural Design
Photo diode
Microcontroller
Laser driver
UART
Laser
Diode
Microcontroller
Transistor and Comparator
UART

6. COMPONENTS USED
❑ LASER DIODE
❑ LM317
❑ CAPACITORS
❑ RASBERRY PI
❑ PHOTO DIODE
❑ LM358
❑ RESISTORS
❑ LED

7. Light
Amplification by
Stimulated
Emission of
Radiation
Device that emits light through a
process of optical amplification
based on the stimulated emission of
electromagnetic radiation.
❑Stimulated Emission
❑Spontaneous Emission

8. CIRCUIT DIAGRAM

9. RECEIVING UNIT:
Photodiode:
❖ Photo means light and diode means a device consisting of two
electrodes.
❖ A photo diode is a light sensitive electronic device capable of
converting light into a voltage or current signal. It works on the
principle of photo generation.
❖ We can think of it as having a very high resistance when no light is
falling on it.
❖ As we increase the intensity of light incident on it, the current
through it gradually increases too. So, by increasing the incident light
on a photodiode, we convert it into a normal low value resistor, which
conducts current.

10. LM358:
❖ The LM358 series consists of two independent, high
gain, internally frequency compensated operational
amplifiers which were designed specifically to operate
from a single power supply over a wide range of
voltages.
❖ But in our experiment we are not using it as an
amplifier as such mainly, so basically, we use it as a
voltage comparator to compare two voltages, one is
fixed and the other varies with an environmental
parameter.
❖ If the parameter controlled voltage is higher than the
fixed voltage, then the IC should give one output, and
if it is lower than the fixed voltage, then it should give
another output. So, we see that the IC gives only two
types of outputs, which we design to be 5 Volts and 0
Volts. This makes our sensor digital.

11. WORKING OF RECEIVING CIRCUIT
❖ A photo diode is a light sensitive electronic device capable
of converting light into a voltage or current signal. It works
on the principle of photo generation.
❖ When the light emitted by laser or LED become incident on
the photodiode, the photodiode’s resistance comes down to a
finite value.
❖ Thus leading to generation of finite amount of of voltage or
current. If the voltage developed across the resistor is greater
than the threshold set by us, the output of the IC will be high,
else it will be low.
❖ Hence, if our reflected radiation is never strong enough to
be greater than the threshold and we have a constant low as
output, we can reduce the threshold voltage by turning the
“minus shaped” slit in the variable resistance towards its
terminal where we connected Gnd. In case our threshold is
very low and the output is always high in spite of no radiation
or if it is just too sensitive, then you can increase the
threshold by turning the slit the other way.

12. Pseudo Code: Transmitter
► Import related libraries
► ser = serial.Serial('/dev/ttyUSB3', 9600) #open serial comm
► x=glob.glob('*.jpg') #list of available images
► img= mp.imread(x[imno])
#x[imno] is user choosen image
► fimg= open(x[imno],'rb') #open image in binary format
► byte=fimg.read() #read image
► def Transmit(): #function to transmit data stream
► start= time.time();
► for i in range(len(byte)):
► ser.write(byte[i])
► time.sleep(0.005)
► ser.close() #stop serial
► delay = (time.time()-start) #calculate time and speed of tx
► speed=size*0.001/delay
► plt.imshow(img)
► plt.show()

13. Pseudo Code: Receiver
► Import related libraries
► port = serial.Serial('/dev/ttyUSB1', 9600)
#start serial comm
► f= open('received.jpg','wb') #create file for receiving
► while True: #keep on checking serial
► try:
► data = port.readline()
► if data:
► f.write(chr(int(data))) #store binary data in file
► time.sleep(0.001)
► except KeyboardInterrupt: #on CTRL+C come out
► f.close()
► break
► img= mp.imread('received.jpg') #read and display image
► plt.imshow(img)
► plt.show()

14. OUTPUT
FREQ:10Hz FREQ:100Hz FREQ:300Hz

15. ► High bandwidth of optical communication
► With increasing data size faster
communication is necessary
► Directional, Long Distance, Fast, Security
► Green technology
► License free
► Speed vs range trade-off
Advantages of FSO over
other

16. Current Applications
►Defense and sensitive areas.
►Medical devices
►Under water Systems
►Mines, Mountains
►Communication with ISS,
Satellites
Earth

17. Thank You!