Input Devices

Question 1

What is the difference between analogue and digital data?

Answer 1

Analogue is the information as it is in nature, digital is the way that computers will represent that information.

Question 2

What is an analogue signal?

Answer 2

An analogue signal Analogue data is in a continuous form. It varies smoothly.
Analogue signals preserve all the information with no loss. It is, however, difficult and expensive to get a computer to work with analogue data.

Question 3

What is a digital signal?

Answer 3

A digital signal is a set of numbers that represent the exact strength of the signal at regular time intervals.
Analogue and Digital Signals, and Computers
You also need to understand that when a computer is dealing with a signal, it is dealing with an electrical signal that has a measurable voltage.

Question 4

How are analogue signals converted into digital signals?

Answer 4

Analogue to digital: an analogue to digital converter (ADC) converts a signal from analogue to digital by sampling. At set intervals (sampling frequency) the analogue signal is measured and a numerical value assigned. The result is a digital signal.

Question 5

How are digital signals converted to analogue signals?

Answer 5

Digital to analogue: a digital to analogue converter (DAC) converts a digital signal to an analogue signal by using the digital data to produce a corresponding voltage. DACs also look ahead - if the next sample has a higher level it starts increasing the output voltage to produce a smooth curve. Parameters affecting DACs are the same as for ADCs - a better digital signal will produce a better analogue signal.

Question 6

What are some examples of analogue devices?

Answer 6

Convential camera
most telephones
TV
Microphone
Speaker

Question 7

What are some examples of Digital devices?

Answer 7

Digital camera
GSM cellphones
Computer monitor
Keyboard
Printer

Question 8

How does a keyboard work?

Answer 8

Each key has its own circuit. It is allocated two scan codes: one for when it is pressed and the other for when it is released.
When pressed, a current flows through, or is changed, in the key’s circuit.
The keyboard’s own processor generates a scan code for the key and places it in the keyboard’s own buffer..
The keyboard’s own processor raises an interrupt (IRQ) with the CPU.
The scan code for the key is sent to the computer when the CPU is ready for it.
The CPU, using the BIOS, tells the keyboard to delete the scan code from its buffer.
The next action depends on which key was pressed
Special keys have a flag in a special area of memory:
Shift, control (CTRL), ALT or insert (INS) keys: the flag is set to 1 when the key is pressed and 0 when it is released.
Num lock, caps lock or scroll lock keys (the “toggle” keys): the flag is set to 1 when the key pressed and 0 when it is pressed again (i.e. pressing the key toggles the flag on or off).
Changes in flags are reported to the active application for action.
Any other key: the scan code is used to determine the ASCII code for the key. The ASCII code is reported to the active application.

Question 9

What are the different types of keys on a keyboard?

Answer 9

Metal Contact keyboard
Mechanical keyboard
Capacitive / flat keyboard

Question 10

How does a metal contact key work?

Answer 10

Each key is a switch. Pressing the key brings two metal contacts together to complete a circuit.
This method was standard on older keyboards, but nowadays used primarily in mechanical keyboards ($$$)

Question 11

How does a Capacitative (or Flat) Keyboard work?

Answer 11

A capacitative keyboard, also called a flat keyboard, uses capacitors to detect keypresses.
A capacitor is an electronic component that can store an electrical charge. It is made of two metal plates, separated by some material that does not conduct electricity.
Capacitance is the amount of electrical charge that can be stored in a capacitor.
A capacitive or flat keyboard has two metal plates separated by a rubber membrane (a capacitor) under each key. Pressing the key changes the capacitance; this change is detected as a keypress.

Question 12

Where is a capacitive flat keys found?

Answer 12

laptops
Calculators
EFTPOS
Cash registers

Question 13

What is the DVORAK keyboard layout?

Answer 13

Invented in 1930 by Albert Dvorak and William Dealy
Developed to be a more efficient layout
Allow typists to type faster (estimated 16 times more efficient than Qwerty)
Never became popular
More expensive to purchase than Qwerty

Question 14

Describe the QWERTY Keyboard layout?

Answer 14

Most common type of keyboard layout
Name from the first six keys in the first row of the keys with the alphabet on them Q, W, E, R, T and Y keys
Developed in 1868 by Christopher Sholes, also the inventor of the typewriter
Not the most efficient
Used today as it is the most familiar to users

Question 15

What is a pointing device?

Answer 15

Supplements the keyboard actions by doing tasks such as moving and pointing to onscreen objects
Tasks that the cursor is not able to do
Pointer starts with an arrow but changes if it is moved over certain parts of the screen
Actions can be performed using the different buttons on the mouse (or a combination of these)

Question 16

What are the three different types of mice?

Answer 16

Mechanical mouse
Opto-mechanical mouse
Optical mouse

Question 17

How does a mechanical mouse work?

Answer 17

Contains a hard rubber ball that sits against two rollers at a 90degree angle to each other.
One roller measures forward/backward movement whilst the other measures side to side movements.
Rollers are connected to disks with contacts on them
The mouse moves, the rollers turn, the disks turn.
Turning disks generate pulses of electricity, which are sent back to the computer via the mouse cable
These different circuit changes are interpreted by the mouse driver, in turn delivering its required output

Question 18

How does a opto-mechanical mouse work?

Answer 18

Same as the mechanical mice except:
The disks have slots in them with pairs of Light Emitting Diodes (LED) which generate light
As the mouse moves, the disks move, in turn creating pulses of light which are detected by the photo sensors, resulting in pulses of electricity
These pulses of electricity are sent back to the computer to be interpreted by the mouse driver in turn delivering its required output

Question 19

How does an optical mouse work?

Answer 19

No moving parts
Shines a small light mounted on its bottom side onto almost any type of surface
The light allows a CMOS digital camera to take an extreme close-up of the shapes, ripples, pits, bumps, etc.
The camera takes 1,500 of these pictures each second
A digital signal processor analyses consecutive pictures to calculate the direction and speed of the mouse

Question 20

How does a trackpad work?

Answer 20

Turn the mechanical mouse upside down.
A trackball is simply a mouse mounted so that the ball is rotated with your fingers instead of on the surface of your desk

Question 21

How does a touchpad work?

Answer 21

Beneath the top rubber layer lies two more layers each containing electrodes, one row horizontal and the other row vertical
When top layer is touched, the crossing electrode layers do not actually touch but a positive charge is generated in one row and a negative charge is generated in the other row creating an electrical field… “mutual capacitance”
The size and shape of this electrical field between the two layers influences the amount of capacitance.
The capacitance is most effected by the center of the finger
OS reads the capacitance of the adjoining intersections, in turn delivering its required output

Question 22

How does a pointing stick work?

Answer 22

Looks like a pencil eraser embedded among keys on a keyboard
When a finger applies lateral pressure to the eraser head, it does not move.
Force is passed to a combination of four force-sensing resistors placed to measure forward, backward, and sideways forces
Resistors are made of two electrical contacts separated by a film that resists the flow of electricity
Pressure from the users finger will push these contacts closer together so that more electricity flows between the contacts
Micro controller monitors the amount of electricity going through the resistors and uses this information to interpret where the cursor movement is on the screen