Posted on Feb 6, 2014

Free-space optical (FSO) communication uses light as a medium to transmit data. We did communication between two computers using laser(without help of any existing means of communication). We sent texts from one PC to other(Laser Chat Messenger) just like what SMS do on mobile. We also sent different types of files(. txt, . png, . rar etc. ) like bluetooth file transfer. Thus now we have new mean of free-space

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optical communication. We are trying to transmit data via the medium of laser. Basically the data to be transmitted is obtained in digital format and then the voltage is varied with certain frequency across the laser diode according to 1`s or 0`s(low for 0 and high for 1). A photo diode is used to sense the high and low voltage on the receiver side along with a clock of the same frequency. This is free space, line of sight, serial data transmission method. The data is transmitte by blinking laser and receivd using photo diode at receiver. The received data is sampled along with a clock which has the same frequency as the sent data. The main problem faced was of finding the photodiode that would respond to the red light laser. The most of the photodiodes available in the market respond to the IR-region of spectrum of light. We tested our basic circuit(the one shown in circuit diagram). We blinked the laser at different frequencies and saw its graph on oscilloscope. It was working well upto a max. frequency = 1000000/175. We also tested different circuits, like we used schmitt trigger using LM324 and IC741 opamps. But we got best output using logical schmitt trigger on our basic circuit using arduino. Initially, there occurred unexpected garbage in between the data transfer if laptops with different clock frequencies were used. But the problem was solved later.

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