CD Basic Information.
CDs are transparent plastic disks that have a hole in the middle.
On top of a CD is a thin layer of aluminium. The plastic layer (it's scientific names is polycarbonate) is there to protect the aluminium layer where the data is written. This is why a scratch on the bottom of the disk is easier to repair, but a scratch on the top can easily ruin the CD. A very thin layer of Lacquer protects the aluminium but not too well.
The underside of the aluminium layer has a spiral track. This spiral track has either small pits in it if it's a manufactured CD, or small patches of dark ink in a computer-burned CD. All of these pieces of information together are assembled by the CD player into a song.
On top of a CD is a thin layer of aluminium. The plastic layer (it's scientific names is polycarbonate) is there to protect the aluminium layer where the data is written. This is why a scratch on the bottom of the disk is easier to repair, but a scratch on the top can easily ruin the CD. A very thin layer of Lacquer protects the aluminium but not too well.
The underside of the aluminium layer has a spiral track. This spiral track has either small pits in it if it's a manufactured CD, or small patches of dark ink in a computer-burned CD. All of these pieces of information together are assembled by the CD player into a song.
You will understand this diagram more as we move through.
The CD Player Itself
CD Players are quite complicated, they use refraction and reflection at the same time.
A CD player has a turntable like a record player, it holds the CD and spins it very quickly. There is a laser on an 'arm' which follows the grooves in the CD as it spins. The laser shines a light onto the CD, which bounces off the metal coating and into a light detector. When the laser hits a pit or a dark patch of ink, it lowers the level of light reflected back. The light detector records tens of thousands of flickers of the light every second based on the tiny pits or patches of ink. It sends this information to a computer, which decodes it, turning the digital signal into sound waves.
A CD player has a turntable like a record player, it holds the CD and spins it very quickly. There is a laser on an 'arm' which follows the grooves in the CD as it spins. The laser shines a light onto the CD, which bounces off the metal coating and into a light detector. When the laser hits a pit or a dark patch of ink, it lowers the level of light reflected back. The light detector records tens of thousands of flickers of the light every second based on the tiny pits or patches of ink. It sends this information to a computer, which decodes it, turning the digital signal into sound waves.
Binary Codes- 'A coding system used to represent letter, digit or character using 1s and 0s'
Data on CDs is stored digitally; after music has been
recorded, it is converted into numbers by a process called sampling.
A piece of electronic equipment measures the sound, turns the measurement into
a number, and stores it in binary format (a pattern of zeros and ones). So in reality there is no music on your CD- just millions of ones and zeros! It is done with only 8-14 pieces of encoding so it doesn't become too complicated.
In a factory- A CD is "burned" with a laser beam that etches microscopic bumps (pits) into its surface. The bump represents the number zero, so every time the laser burns a bump into the disc, a zero is stored there. A hill (when there is no bump) represents the number one. The information is held in a tight continuous spiral of approx 3-5 billion pits.
E.g.
A= 01000001 whereas a= 01100001
In a factory- A CD is "burned" with a laser beam that etches microscopic bumps (pits) into its surface. The bump represents the number zero, so every time the laser burns a bump into the disc, a zero is stored there. A hill (when there is no bump) represents the number one. The information is held in a tight continuous spiral of approx 3-5 billion pits.
E.g.
A= 01000001 whereas a= 01100001
Semiconductor diode laser (laser)
You will learn more about Refraction here and how it works with lasers-When you press play on your CD player, inside an electric motor makes the CD spin (at 500rpm). The laser turns on and starts to scan the disc with the photocell (electronic light detector). The pits on the CD scatter the light (deviates in different directions) and the hills (lands) reflect the light back. An electric current is sent to a circuit when it sees a land and generates the number one; if there is no land the photocell doesn't send anything- a number zero. This creates the binary code.
Refraction-
The Laser goes through a convex lens. The lens refracts the light, it focus it towards a point on the aluminium side of the CD. The lens moves slightly to check that there are no mistakes made and focuses on specific points (creates a focal point on CD). This helps the laser concentrate on the individual pits in the CD.
Refraction-
The Laser goes through a convex lens. The lens refracts the light, it focus it towards a point on the aluminium side of the CD. The lens moves slightly to check that there are no mistakes made and focuses on specific points (creates a focal point on CD). This helps the laser concentrate on the individual pits in the CD.
BEWARE
CD Players are designed you do not look at the laser! They could partially or fully blind you! Be careful!