CD/DVD player | Technical Characteristics | instrumentic.info

It's a drive optical drive that reads through a laser diode optical discs called CDs or CD
It's a drive optical drive that reads through a laser diode optical discs called CDs or CD

The CD player

It's a drive optical drive that reads through a laser diode optical discs called CDs or CD, be it CD or computer CD-ROM.

When it is used to listen to music CDs, the CD player can be integrated into various types of portable devices or servants, to a radio handset, etc. It can also be a separate, portable device or domestic, to connect to a channel Hi-Fi, an audio amplifier or headphones.

Computer, the CD player is either in the form of an internal device in the central unit, or an external device connected to the computer by a USB or FireWire port.

DVD player (or DVD player) is an optical disc drive used to exploit the digital data stored on DVDs. The arrival of the DVD Video (Digital Versatile Disc) revolutionized so this little world, which appeared in 17 aux √Čtats-Unis en 18 in Europe particularly in France.
Most DVD players can read several formats of optical discs.

Operation

Rotation of the disc

The disk rotates by a servo engine at variable speed. Indeed, whether the section of track1 is in the center or periphery, the length of the sectors is always the same, therefore, unlike the vinyl disc, the scrolling of the data in front of the playhead must be constant.
In simple speed, an area must be flown in 1/75th of a second. For a linear reading speed of 1.2 ms-1, the rotational speed varies from 458 tre min-1 to read the 50 mm diameter areas of the disk to 197 tr-min-1 to read the areas with a diameter of 116 mm (about)
For comparison, a drive with a speed 16 times higher (CD-Rom 16x player) will see the speed of its disc vary between 7,328 tre min-1 and 3,152 tremin-1.
Mechanical CD Philips with swivel arms.

Moving the head

The movement of the optical block is provided either by a swivel arm (Philips mechanics) or by a linear servo with very high precision because, on a possible total displacement of three centimeters4, it is able to adopt 600 different positions per millimeter.
A lens from a CD player.

Laser diode

The laser diode emits in the infrared and is used for both writing and reading; however, the power of the beam is different if it is a reader or an engraver (a few milliwatts in reading versus 24 mW for a quadruple-speed engraver), moreover, it varies according to the speed of engraving.

Optically directing beams

The laser diode emits a beam to a prism (which can be characterized as a semi-transparent mirror); this prism sends the beam back at right angles to direct it to the lenses. The beam reflected by the disk (in polycarbonate) passes through the prism to excite the photodiode.

Lenses

The optical focusing block is on a mobile device whose movements are controlled by electromagnets. This system allows the position adjustment (sliding setting) of the focusing lens (mounted on a moving coil) in relation to the disk. This package is the goal.
The lens, upstream of the lens, is used to concentrate the laser beam, so as to obtain a beam about one micrometer in diameter, in order to be able to read the microcuvettes (pits in English) of different lengths of the disc6.
Since the diameter of the beam is not significantly wider than the wavelength of the incident beam, the focus of the beam must therefore be extremely precise.
The manufacture of these lenses requires greater rigor but, unlike microscope lenses, for a single wavelength, that of the laser beam.

Photosensitive diode

This detects changes in reflected light. For a reader, this diode is used to read the disk information by detecting the variations of light received, characterized by the fronts generated by the succession of microcuvettes and intermediate smooth ranges (lands) of the disk.
The high-frequency signal picked up by this receptive cell is called an eye diagram.
Its decoding is used for several systems, including locating the position of the laser beam on the disk and assessing the speed of rotation of the disk, with a view to correcting it continuously (work of the enslavement circuits).
For an engraver, it is also used to control the engraving. For a CD, the captured binary rate is standardized at 4.3218 MHz.

DVD player


Computer, DVD players are a computer input devices. They may be internal, which is integrated in the housing, or external, installed in their own case and connected to the computer through USB or FireWire connector, and powered electricity sector.

DVD players can be used in the salon to reproduce video content. They are then connected to a TV through HDMI or SCART, S-Video, RCA, and audio amplification by outputs analog audio system or by an optical type S/PDIF for digital sound cable.
The DVD video frames are also able to read the CD audio type, or even VCD / SVCD and, for the most recent, CDs and data DVDs containing media files in various formats (especially MP3 music, JPEG for photos (, and DivX for video).