Inpu and Output devices

Question 1

How Keyboard works

Answer 1

• Underneath each key on the keyboard there is a small peg, which sits inside a hole in the keyboard’s base.
• As you push down on the key, the peg pushes through the hole to touch the contact layers below.
• The contact layers consist of 2 conducting layers separated by an insulation layer which keeps them apart. A electrical signal is created when the peg pushes the layer together which tells us that a particular key has been pressed

Question 2

Computer mouse

Answer 2

A red LED light is reflected off a surface and any movement is picked up by sensors made up of an array of photo-sensitive diodes.

Question 3

Touch screen resistive

Answer 3

Pushing on the screen makes 2 conductive layers make that are separated by an insulating layer make contact which creates an electrical signal and we can figure out the position of the contact by a microprocessor.

Question 4

Touch screen capacitive

Answer 4

• Human bodies can act as an electrical conductor
• So when we touch the screen we distort its electrostatic field
• The position of the distortion can be interpreted by a microprocessor

Question 5

Touch screen infra-red

Answer 5

• They utilize an array of LED beams which have corresponding detectors
• So it can detect touch events

Question 6

Microphone

Answer 6

• Diaphragm vibrates when hit by sound waves
• Vibrations are detected and converted into an electrical signal using an ADC

Question 7

Digital camera

Answer 7

• When the shutter opens, light falls onto the charge-coupled device array which breaks it up into millions of pixels
• The sensor measures color and brightness of each pixel and stores it as a number
• Digital photographs are simply a file consisting of information about each pixel and meta-data about the file itself

Question 8

2D scanner

Answer 8

• It uses an array of light-sensitive diodes on a charge-coupled device sensor
• This converts light into an electrical charge
• Bright light illuminates the documents and a scan head goes across
• Mirrors and lenses reflect the documents onto the diodes and the varying electrical charges are converted into digital values