Transcript 6.1 Input Device

6.1 Input Device
 Input Device
 The hardware that allows users to enter
data into a computer and converts the data
into a computer-readable form.
mouse
microphone
keyboard
6.1 Input Device
 Keyboards
 Allow users to enter data or commands into
a computer and convert the pressed keys
into electrical signals
Letter key
Modifier key
6.1 Input Device
 Pointing Devices
 Allow users to control the cursor or pointer
on a graphical user interface and trigger an
action
 A pointer is a small symbol on the screen
an arrow
a pointing hand
an I-beam
 With a pointing device, you can position the
pointer to select or move an item on the
screen.
6.1 Input Device
Select an item in a menu.
Move an item from one
place to another.
6.1 Input Device
 Mouse
 Uses multidirectional
mechanism to register
its motion
 Mechanical mouse
Tracks rolling
direction of the ball
on its underside
 Optical mouse
Optical sensor tracks
its movement
buttons
scrolling
wheel
6.1 Input Device
 Mouse
Top view
Bottom
view
Mechanical
mouse
Top view
Bottom
view
Optical
mouse
6.1 Input Device
 Trackball
 It is like an inverted
mouse
 You move the pointer by rolling
the ball.
 The buttons next to the ball
works the same as those on a
mouse.
 Has the advantage of saving
space since it remains
stationary during operation.
6.1 Input Device
 Touchpad
 A touch-sensitive
plate usually found on
a notebook computer.
 You move the pointer by dragging fingertip
on touch pad.
 Tapping the pad is equivalent to clicking
buttons on a mouse.
6.1 Input Device
 Trackpoint
 A small stick usually
positioned
somewhere between
the keys.
 Pressure-sensitive, moving pointer in the
direction you push in.
6.1 Input Device
 Joystick
 A pointing device
designed for playing
computer games
 The vertical lever controls the movement of
the pointer.
 Most joysticks contain trigger buttons that
can be used to perform certain actions in a
computer game.
6.1 Input Device
 Touch Screen
 A video display device
that has a transparent,
touch-sensitive layer
 The user can interact with the computer by
pressing the icons or figures on the screen.
 Widely used in information kiosks, personal
digital assistants and notebook computers.
6.1 Input Device
 Digitizing Tablet
 Allows users to draw
and sketch directly
into a computer
 Detects the movements and pressure of
pen-like stylus and converts them into
digital signals
 Widely used in graphic design and
engineering
6.1 Input Device
 Scanners
 Create digital images of
source documents
 Operation:
Projects light
onto scanned
object
Captures the
reflected light
Converts the
signals into a
bitmap image
6.1 Input Device
 Scanners
 The quality of a scanned image is
determined by:
Resolution
• Determines
the sharpness
of picture
• Measured in
dots per inch
(dpi)
Color depth
• Determines
how many
colors are
used to
represent
each dot
Accuracy
• Depends on
the likeness
of the
scanned
image in
terms of color
and shape to
the original
object
6.1 Input Device
 Scanners
 Optical character recognition (OCR)
software can read a scanned image of text
document and translate it into a text file.
6.1 Input Device
 Optical Readers
 Read predetermined characters, marks or
codes and translate them into digital data
that a computer can use.
 Bar Code Readers
Captures images of bar codes and
translates them into numbers.
6.1 Input Device
 Optical Readers
 Optical Mark Readers
Used with optical mark
recognition (OMR)
software
OMR recognizes specific
hand-written marks.
Commonly applied on multiple choice
answer sheets.
6.1 Input Device
 Microphones
 Allows users to record
sound into a computer
 Usually connected to a
sound card installed on the
motherboard
 Can be used with speech recognition
software, which translates vocal speech into
text or commands.
6.1 Input Device
 Digital Cameras
 Uses a light-sensitive
processor chip to
capture scenes and
turn them into digital
image
 Image files are stored in a memory card.
 The amount of memory space taken by an
image depends on the compression ratio, the
file format and image resolution.
 The larger the number of light-sensitive
photosites in the processor chip, the higher
the resolution of the image.
6.1 Input Device
 Digital Camcorders
 Uses a light-sensitive
processor chip to
capture the moving
images and store
them as a sequence
of high-quality digital
images
 The digital images can be transferred to the
computer directly without quality loss.
6.1 Input Device
 Digital Camcorders
 Uses a light-sensitive
processor chip to
capture the moving
images and store
them as a sequence
of high-quality digital
images
 The digital images can be transferred to the
computer directly without quality loss.
6.2 Output Device
 Output Device
 The hardware that translates information
processed by the computer into a form that
humans can understand
Visual display
Printer
Speakers
6.2 Output Device
 Visual Display Unit (VDU)
 Allows a user to view computer output
instantly on a screen
Liquid crystal display
(LCD) monitor
Cathode ray tube
(CRT) monitor
6.2 Output Device
 Visual Display Units (VDU)
 Pixel
The smallest display unit of the monitor
screen
Represents one dot of an electronic
image by displaying a certain colour and
colour intensity
 Size of monitor
Determined by the diagonal length of the
screen
6.2 Output Device
 Visual Display Units
 Quality of a monitor’s display
Determined by:
Resolution
Dot Pitch
• The number of pixels
a monitor can display.
• At higher resolution,
a larger work area
can be displayed, but
the text and images
will appear smaller.
• The vertical distance
between each pixel
on a screen.
• The smaller the dot
pitch, the sharper
the displayed image.
6.2 Output Device
 Visual Display Units
Resolution
= 768 x 1024
768
pixels
1024 pixels
Dot pitch
6.2 Output Device
 Visual Display Units
Contrast Ratio
Refresh Rate
• The measurement
of the difference
between the
brightest white
and the darkest
black
• e.g. 600:1
• The rate for a
monitor to redraw
the display
• e.g. 75 Hz
6.2 Output Device
 Visual Display Units
 A comparison between LCD monitors and
CRT monitors
Advantages of
LCD monitors
 Slimmer and lighter
 Clearer display
 Lower radiation
emission
 Lower power
consumption
Advantages of
CRT monitors
 Cheaper
 Higher contrast
ratio
 Higher refresh rate
6.2 Output Device
 Speakers
 Used to produce audio signals for a
computer system
 The sound card converts digital audio
signals into analogue signals for output
through the speakers.
 Speakers with subwoofer produces better
base frequencies.
Speakers with
subwoofer
Speakers
6.2 Output Device
 Printers
 Allow users to produce text and graphics on
a physical medium such as paper or
transparency film
 The performance of a printer is mainly
determined by:
Printing Speed
Resolution
• Measured by the
number of dots per
inch (dpi)
• The higher the dpi,
the sharper the
image.
•Measured either by the
number of pages per
minute (ppm) or
characters per minute
(cps)
6.2 Output Device
 Printers
 Some common types of printers:
Dot-matrix printer
Laser printer
Ink-jet printer
Plotter
6.2 Output Device
 Printers
 Comparison of mechanism
Type of
printer
Dot-matrix
printer
Mechanism
 Strike pins on an ink ribbon to form a
dotted image on the paper.
Ink-jet
printer
 Form images by spraying tiny ink drops
onto paper.
Laser
printer
 Use a laser beam to produce an
electrostatic film on a drum.
 The toner stuck on the charged area is
then transferred and fused onto paper.
6.2 Output Device
 Printers
 Comparison of mechanism
Type of
printer
Thermal
printer
Plotter
Mechanism
 Produce a printed image by selectively
heating thermal paper when the paper
passes over the thermal print head.
 Similar to ink-jet printers
6.2 Output Device
 Printers
 Comparison of features
Type of
printer
Printing
quality
Printing
speed
Printing
Cost
Dot-matrix
printer
Low
Low
Low
Ink-jet
printer
High
Medium
High
Laser printer
High
High
Medium
Plotter
Similar to ink-jet printers
6.2 Output Device
 Printers
Type of
printer
Dot-matrix
printer
Other features


Ink-jet printer
Laser printer

Thermal printer

Plotter

Ideal for printing multi-part forms
Uses a black cartridge and one or
more colour cartridge to produce
high-quality color printouts
Has to store the whole image of the
page before printing process begins
Used in point of sale systems
Creates high-quality or large-format
printouts
6.2 Output Device
 Multifunction Printers
 Combines the functions of
 Printer
 Scanner
 Photocopier
 Fax machine
 Telephone
 Advantages
 Takes up less space
 Cheaper than buying all devices
separately
6.2 Output Device
 Data Projectors
 Used to project the computer display onto a
large screen
 The performance is mainly determined by
the panel resolution and the brightness
 Two common types of projectors
DLP projector
LCD projector
6.2 Output Device
 Data Projectors
 Comparison between LCD and DLP projector
Type of
projector
Mechanism
LCD
projector
Uses built-in light
source to project
the image on its
LCD panel onto
screen
DLP
projector
Builds images on
the screen by
digitally controlling
the reflections on
tiny mirrors
Consequence

Uses light less
efficiently
Uses light more
efficiently
 Can be seen
clearly even in
well-lit room
