How CD’s Work Speros Shepherd 2005. The Anatomy of a CD Piece of simple plastic- 4/100 of an inch...
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Transcript of How CD’s Work Speros Shepherd 2005. The Anatomy of a CD Piece of simple plastic- 4/100 of an inch...
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How How CD’s CD’s WorkWork
Speros ShepherdSperos Shepherd
20052005
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The Anatomy of a CDThe Anatomy of a CD• Piece of simple plastic- 4/100 of an inch
thick• Injection-molded, clear, polycarbonate
piece of plastic• Has microscopic bumps arranged in an
extremely long spiral track
Complex CD Layers
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The Anatomy of a CDThe Anatomy of a CD• Thin, reflective, aluminum layer
covers the bumps.
• Thin acrylic layer is used to protect the aluminum layer
Simple Layers of a CD
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The Spiral of the CDThe Spiral of the CD
• Spiral data track always starts in the center
• 0.5 microns wide• 1.6 microns
separating the individual tracks
• Micron= millionth of a meter
The Basic CD Spiral
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The Bumps on a CDThe Bumps on a CD
• Bumps make track long because of the small dimensions
• If stretched out track would be 0.5 microns wide and 3.5 miles long3.5 miles long
CD Bumps Magnified
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The Bumps on a CDThe Bumps on a CD• Bumps- 0.5
microns wide, 0.83 microns long, 125 nanometers high
• Nanometer- billionth of a meter
• Bumps look like pits on the aluminum side.
CD Bumps Magnified
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CD Player ComponentsCD Player Components• Drive motor
spins the CD
• Drive motor rotates between 200-500 rotations per minute
• Laser moves at micron resolutions
Parts of a CD Player
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CD Player ComponentsCD Player Components• Laser and
lens system focuses in on and reads the bumps
• The tracking mechanism moves the laser.
CD PlayerCD Player
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Laser Focus of a CD PlayerLaser Focus of a CD Player• The technology forms data into
understandable blocks (on an Audio or CD-ROM)
• CD player- focuses laser on the data track
Different Focuses of a CD Laser
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Laser Focus of a CD PlayerLaser Focus of a CD Player•“lands”- aluminum layer•opto-electronic sensor: detects change in reflectivity
CD Player Lasers
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Laser Focus of a CD PlayerLaser Focus of a CD PlayerThe electronics in the drive interpret the
reflectivity changes to read bits that make up the bytes. Laser stages: passes through polycarbonate layer, reflects off aluminum layer, hits opto-electronic device that detects changes in light.
How a Laser Focuses on a CD
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• spindle motor slows the speed of the CD so that the bumps travel past the laser at a constant speed. (data comes off at a constant rate)
CD Player TrackingCD Player Tracking•Laser beam centered on data track system continually moves the laser outwards.
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• 2 most common: CD-DA (audio CD), CD-ROM (computer data).These are both widely used. Data is converted into electrical pulses by laser reflections.
CD Data FormatsCD Data Formats
A CD-RW (can be edited)
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CD Data FormatsCD Data Formats
• modifications to the CD have to be made for you to burn data on it. (CD-RW have no bumps)
A CD-RW (can be edited)
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CD Data FormatsCD Data Formats
A clear dye layer covers the CD’s mirror.The laser that writes the data to the disc heats up the dye layer to make it opaque.
A CD-R (cannot be edited, just read)
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CD Data FormatsCD Data Formats• The dye layer
must become transparent for data to be written. The data can be changed or rewritten when heated or cooled.
A CD-R (cannot be edited, just read)
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SperosSperos• I am 13 years old
and in the seventh grade.
• I like playing and watching football
• I am Greek.
• I like going to parties, but NOT dancing.
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Bibliography Bibliography • Brain, Marshall. How CD’s Work. How Stuff
Works. 25 April 2005. <http://electronics.howstuffworks.com/cd1.htm>.
• How Do Cd’s Work. CDMan Disc Manufacturing. 28 April 2005. <http://www.cdman.com/technical/howdocdswork1.html>.
• How Do CD-RW’s Work? How Stuff Works. 2 May 2005 <http://electronics.howstuffworks.com/question655.htm