IO Devices - SNGCE DIGITAL LIBRARY
IO Devices - SNGCE DIGITAL LIBRARY
What’s available for input…
touch - fingers, feet, breath
sound - voice, other sounds
visual images - photos, diagrams, icons
sounds - music, voice
by a person to communicate to a computer.
information from the computer to a person.
The most commonly used input device is the
keyboard on which data is entered by manually
keying in or typing certain keys. A keyboard typically
has 101 or 105 keys.
The keyboard allows the computer user to enter words, numbers, punctuation,
symbols, and special function commands into the computer’s memory.
Is a pointing device which is used to control the
movement of a mouse pointer on the screen to make
selections from the screen. A mouse has one to five
buttons. The bottom of the mouse is flat and contains
a mechanism that detects movement of the mouse.
Pointing devices - direct
used for applications with occasional
use, for example
Bank ATMs, Information Kiosks, etc.
No extra hardware - used for input and for
Can be precise to 1 pixel
Good for menu choice - not so good for other
Intuitive to use
if at wrong angle (needs to be
30-45% from horizontal)
Get greasy, jammy
Finger can obscure screen
Alternative - use stylus to touch screen,
Indirect Pointing Devices
Need more cognitive processing than
direct methods, but can be more
devices - other
Tracker ball, trackpad, trackpoint
Less space on desktop
Good in moving environments, e.g.
Indirect pointing devices other
The main use of a joystick is to
play computer games by
controlling the way that
something moves on the screen.
Microphones - Speech Recognition
•Use a microphone to talk to your
•Add a sound card to your computer
•Sound card digitizes audio
input into 0/1s
•A speech recognition program can
process the input and convert it into
machine-recognized commands or
Audio Input: Speech Recognition
Speech recognition is a type
of input in which the
computer recognizes words
spoken into a microphone.
Special software and a
microphone are required.
Latest technology uses
recognition where the user
does not have to pause
Microphones - Speech Recognition
A digital camera can store many more
pictures than an ordinary camera. Pictures
taken using a digital camera are stored inside
its memory and can be transferred to a
computer by connecting the camera to it. A
digital camera takes pictures by converting the
light passing through the lens at the front into a
A scanner can be used to input pictures and
text into a computer. There are two main types
of scanner; Hand-held and Flat-bed.
•A light pen is a small ‘pen-shaped’ wand,
which contains light sensors.
•It is used to choose objects or commands on
the screen either by pressing it against the
surface of the screen or by pressing a small
switch on its side.
•A signal is sent to the computer, which then
works out the light pen’s exact location on the
•The advantage of a light pen is that it doesn’t
need a special screen or screen coating.
•A bar code is a set of lines of different thicknesses
that represent a number
•Bar Code Readers are used to input data from bar
codes. Most products in shops have bar codes on
•Bar code readers work by shining a beam of light
on the lines that make up the bar code and
detecting the amount of light that is reflected back
2. Output Types
Output Devices: Engaging our Senses
Output devices are peripheral devices that enable us to
view or hear the computer’s processed data.
Visual output – Text, graphics, and video
Audio output – Sounds, music, and synthesized
A monitor is a peripheral device which displays
computer output on a screen.
Screen output is referred to as soft copy.
Types of monitors:
Cathode-ray tube (CRT)
Liquid Crystal Display (LCD or flat-panel)
electron gun shoots a stream of electrons at a specially
on impact, the phosphor flares up for a fraction of a second
electron gun sweeps across the screen many times a second
one of several types of “flat-panel” displays
forms output by solidifying crystals and “backlighting” the
image with a light source
sets are CRTs and many desktop monitors use this
is primarily used for laptops and other portable
Video Display Terminology
element (smallest unit of an
image, basically a single dot on the
of pixels in the image
resolution size is 1024x768
often a CRT’s electron gun rescans
The CRT electron gun
“shoots” 3 electrons at
the screen representing
the amount of red, green
and blue for the pixel
displays do not use an electron gun,
so do not perform refreshing
Ink Jet Printer
least expensive, color, slower with a
higher per page cost than laser printers
expensive, faster, lower per page
cost than ink jet,
A printer is a peripheral device that
produces a physical copy or hard copy
of the computer’s output.
Types of Printers
Inkjet printer, also called a
bubble-jet, makes characters
by inserting dots of ink onto
Cost of printer is inexpensive
but ink is costly
Laser printer works like a
Quality determined by dots
per inch (dpi) produced
Color printers available
Expensive initial costs but
cheaper to operate per page
A plotter is a printer that uses a pen that moves over a large revolving sheet of
It is used in engineering, drafting, map making, and seismology.
Audio Output: Sound Cards and
Audio output is the ability of the computer to output sound.
Two components are needed:
Sound card – Plays contents of digitized recordings
Speakers – Attach to sound card
As a computer technician, you may be required to purchase, repair, or
maintain a printer.
Printer selection criteria:
Capacity and Speed
Meat time between failures (MTNF)
Total Cost of Ownership (TCO)
Printer to Computer Interfaces
To access a printer, a computer must have an interface with it. The following
are common interface types:
Small Computer System Interface (SCSI)
Universal Serial Bus (USB)
A laser printer is a high-quality, fast printer that uses a laser beam to create
Laser printing process
WARNING: The primary corona wire or grid, or the conditioning roller, can be
very dangerous. The voltage runs as high as -6000 volts. Only certified
technicians should work on the unit. Before working inside a laser printer,
you should make sure that voltage is properly discharged.
Impact printers use a print head impacts a
printer tape or inked ribbon to create
There are two types:
They use inexpensive consumables and have
carbon copy printing ability. Unfortunately they
are also noisy, have lower graphic resolution
and limited color capabilities.
Use ink-filled cartridges that spray ink onto a
page through tiny holes, or nozzles. The ink is
sprayed in a pattern on the page, one column of
dots at a time.
Two types of inkjet nozzles:
They produce high quality print, are easy to use
and are less expensive than laser printers.
However the nozzles are prone to clogging and
the ink is wet after printing.
A feeding mechanism draws paper in and the
paper passes by the print head where ink is
sprayed onto it.
Use solid sticks of ink rather than toner or ink cartridges.
The printing process:
This type of printers produce
vibrant color prints and can use
many different paper types.
The printer and the ink used
are normally expensive and
they are slow to warm up.
A thermal printer uses chemically-treated paper that
becomes black when heated.
A thermal transfer printer uses heat-sensitive ribbon,
which the print head melts onto the paper.
Thermal printers have a longer life because there are few
•Paper is expensive
•Paper has a short shelf life
•Images are poor quality
•Paper must be stored at
Also called thermal dye printers
Usually used in producing photo-quality images for graphic
Uses solid sheets of ink that change directly from solid to gas
when heated, in a process called sublimating
•Very high quality images
•Overcoat layer reduces smearing, increases moisture resistance
•Media can be expensive
•They are better for color than for
grayscale (black and white)
Scanners typically create an RGB image that can be
converted into image formats such as JPEG, TIFF, Bitmap,
Some scanners can create text documents using optical character
Resolution of a scanner is measured in dots per inch (dpi).
Like printers, the higher the dpi, the better the quality of
Interfaces and cables used for scanners are typically the same as those
used for printers: Parallel, USB, SCSI, and Firewire.
An all-in-one device combines
the functionality of multiple into
one physical piece of hardware
(scanner, printer, copier and
Normally this type of devices
are not expensive and easy to
configure. Unfortunately they
are usually no designed for
heavy use and a single problem
can affect all the functionality.
Often used to scan books and photographs
Image is acquired by placing the document
face down on the glass. The scanner head
lies beneath the glass and moves along the
item, capturing the image.
The glass should be maintained clean and
protected from scratching.
A handheld scanner is small
Pass the scanner head across
the surface you want to
When you want to scan an
item larger than the head of
the handheld scanner, you
must make more than one
pass to capture the full image.
Drum scanners produce a high-quality scanned
image, but they are being replaced by lower
priced, high-quality flatbed scanners.
Still in use for high-end reproductions, such as
archiving photographs in museums.
To scan an image using a drum scanner you
should attach the image to a revolving drum or
load it into a supporting canister.