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Laser Communication

By | Jan. 2013
Page 1 of 19
Display for the Virginia Museum of Science
Digital Communications

Date Submitted: 6 October 2002
Independent Research Project EE 491
Digital Communications
Cadets: Joseph Wunder
Brian Holt

I. Introduction
Many electronic devices today communicate with each other externally and internally. The information in these devices can be numbers, words, sounds, and pictures. The simplest form of this information is digital one’s and zero’s. Sequences of one’s and zero’s are used by electronic devices to pass information back and forth as well as process the information. The concept of representing information with zero’s and one’s was devised in 1940 by Claude Shannon in his master thesis at MIT. He devised theorems that showed how digital one’s and zero’s (or bits) can be used to describe information. He then pioneered ways in which these bits can be manipulated or sent to other devices with little or no error.

To demonstrate, in simple terms, the concept of digital communication using bits, a museum display involving analog to digital conversion and laser bit communication was constructed. The exhibit also demonstrates how more bits can be used to communicate a more accurate signal. For this task, an audio information source (CD player) produces a signal that is converted to digital information. This information will then be sent to a receiver using laser light switching on and off to communicate zero’s and one’s. The receiver will pick up the laser light and convert the digital information back into an analogue signal for output to a speaker. See Figure 1 for a system block diagram. Covering some of the lasers (removing bits) will demonstrate that less bits result in a poorer signal and reduced audio quality.

Information
Source (CD
Player)
Speaker
Output

A/D
Conversion

D/A
Conversi
on

Transmitter
(8-Laser
Array)
Receiver
(8-Phototransistor
Array)

Figure 1: System block diagram for museum display

II. System Functionality
To...
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