29-11-2012, 11:15 AM
OPTICAL DISC READER
[attachment=41609]
HISTORY
Sony first publicly demonstrated an optical digital audio disc in September 1976. In September 1978 they demonstrated an optical digital audio disc with a 150 minute playing time.
Sony released the world's first CD Player called the CDP-101 in 1982 utilising a slide-out tray design for the CD.
INTRODUCTION
An optical disc is used to store data in digital form.
An optical disc consists of five layers.
An optical disc is made from 1.2 millimetres thick, polycarbonate plastic and weighs 15–20 grams.
the center spindle hole is 15 mm diameter.
A spiral track moulded into the top of the polycarbonate layer.
CD data is stored as a series of tiny indentations known as "pits“.
The areas between pits are known as "lands".
Each pit is approximately 100 nm deep and 500 nm wide, and varies from 850 nm to 3.5 µm in length.
The distance between the tracks and the pitch is 1.6 µm.
Scanning velocity is 1.2–1.4 m/s constant linear velocity equivalent to approximately 500 rpm at the inside of the disc, and approximately 200 rpm at the outside edge.
A disc played from beginning to end slows down during playback.
CONSTRUCTION
Disc drive mechanism
The disc drive mechanism consists of a motor that will drive the disc in a circular motion.
The mechanism will also have a disc feed – a loading tray that is used to accept the DVD from the user.
Thus the entire disc drive is basically a spindle that holds the disc and a motor that is used to circle the disc.
The spindle is held in its position with the help of small gears and belts that are attached internally.
Some players have an automatic feed system in which, there will be no tray.
Optical system
The optical system mainly consists of the laser beam, lenses, prism, photo-detectors and also mirrors.
The output of this mechanism will be the input for the disc-drive.
The laser beam will be a red laser diode which works at a wavelength of 600 nanometers.
The optical system also requires a motor to drive it. The laser system and photo-detector is placed together on a single platform.
The laser diode as well as other diodes is made with the help of glass.
WORKING
The pits and bumps in the DVD are hit by the laser from the optical mechanism of the DVD player.
This laser will be reflected differently according to the change of pits and bumps.
Though the laser hits a single spot, the DVD moves in a circular motion so that the entire area is covered. Mirrors are also used to change the spot.
These reflected laser beams are then collected by a light sensor (eg. photo-detector) which converts the different signals into a binary code.
In short, the optical system helps in converting the data from the DVD into a digital code.
[attachment=41609]
HISTORY
Sony first publicly demonstrated an optical digital audio disc in September 1976. In September 1978 they demonstrated an optical digital audio disc with a 150 minute playing time.
Sony released the world's first CD Player called the CDP-101 in 1982 utilising a slide-out tray design for the CD.
INTRODUCTION
An optical disc is used to store data in digital form.
An optical disc consists of five layers.
An optical disc is made from 1.2 millimetres thick, polycarbonate plastic and weighs 15–20 grams.
the center spindle hole is 15 mm diameter.
A spiral track moulded into the top of the polycarbonate layer.
CD data is stored as a series of tiny indentations known as "pits“.
The areas between pits are known as "lands".
Each pit is approximately 100 nm deep and 500 nm wide, and varies from 850 nm to 3.5 µm in length.
The distance between the tracks and the pitch is 1.6 µm.
Scanning velocity is 1.2–1.4 m/s constant linear velocity equivalent to approximately 500 rpm at the inside of the disc, and approximately 200 rpm at the outside edge.
A disc played from beginning to end slows down during playback.
CONSTRUCTION
Disc drive mechanism
The disc drive mechanism consists of a motor that will drive the disc in a circular motion.
The mechanism will also have a disc feed – a loading tray that is used to accept the DVD from the user.
Thus the entire disc drive is basically a spindle that holds the disc and a motor that is used to circle the disc.
The spindle is held in its position with the help of small gears and belts that are attached internally.
Some players have an automatic feed system in which, there will be no tray.
Optical system
The optical system mainly consists of the laser beam, lenses, prism, photo-detectors and also mirrors.
The output of this mechanism will be the input for the disc-drive.
The laser beam will be a red laser diode which works at a wavelength of 600 nanometers.
The optical system also requires a motor to drive it. The laser system and photo-detector is placed together on a single platform.
The laser diode as well as other diodes is made with the help of glass.
WORKING
The pits and bumps in the DVD are hit by the laser from the optical mechanism of the DVD player.
This laser will be reflected differently according to the change of pits and bumps.
Though the laser hits a single spot, the DVD moves in a circular motion so that the entire area is covered. Mirrors are also used to change the spot.
These reflected laser beams are then collected by a light sensor (eg. photo-detector) which converts the different signals into a binary code.
In short, the optical system helps in converting the data from the DVD into a digital code.