section 2: input and output devices input devices

section 2: input and output devices input devices
KEYBOARDS: A concept keyboard is a flat board which contains a grid of switches. Each
switch can be programmed to do
whatever you want. The computer
keyboard has over 100 keys on it.
When you press a key a number
(code) is sent to the computer to tell
it which key you have pressed. This
layout of keys is called QWERTY
because Q-W-E-R-T-Y is the order in which the letters occur on the top row
of the keyboard.
• NUMERIC KEYPAD: Applications where only numeric data is to be entered.
Inserting pin numbers for chip and pin credit/debit cards, or when using an
ATM machine to withdraw money or check a bank balance
MOUSE: Mouse: a hand-operated electronic device that
controls the coordinates of a cursor on your computer screen as you move it
around on a pad; on the bottom of the mouse is a ball that rolls on the surface of
the pad. The advantages are: you don’t need you to be using the keyboard, its
more easier to use the mouse.
The disadvantages are: when its broken, you have to buy another.
TOUCH PAD: A computer input device consisting of a flat
pad with a special pin and an electronically sensitive
grid. With a touchpad you use your finger to move the
cursor rather than your wrist. This technology is already
used on many laptop computers.
By moving a finger or other object along the pad, you
can move the pointer on the display screen. And you
click by tapping the pad.
TRACKER BALL: A trackball is a
computer cursor control device
used in many notebook and laptop
computers. A tracker ball: (or
trackball) is an alternative to a mouse. It works in the same way as a mouse
except that the ball is on top. Turning the ball with your hand moves the
pointer on the screen. It can be used for developing and moving around 3D environments. The advantages are: its more easier to use. The
disadvantages are that you could not know how to use it. Tracker balls are
common on CAD workstations for ease of use.
• TOUCH SENSITIVE SCREEN: A touch sensitive
screen is a special type of visual display unit.
When you touch the screen the computer senses where you have
pressed. Touch screens can be used to choose options which are
displayed on the screen. The main application for which touch
screens are used is the provision of public information systems. Touch
screen operated computers can be found in places such as travel
agents and airports. Touch screens are not used very often as they are
not very accurate, tiring to use for a long period and are more expensive than alternatives
like a mouse. The main advantage of the touch screen is that anyone can use it without
having to be trained.
• LIGHT PEN: A light pen looks like an ordinary pen apart from the fact that it
has a cable connecting it to the computer. Although it looks as though the
pen draws on the computer screen this is not in fact what is happening. An
electron beam, controlled by the computer, builds up the picture on the
screen. The light pen detects when this beam passes and sends a signal to
the computer. This input can be used as part of a drawing program with the
pen being used to select tools and to mark points on the drawing.
JOYSTICKS: A joystick is a physical device typically used to control
objects on a computer screen. It is frequently used for games and
sometimes used in place of a mouse. A lever that moves in all
directions and controls the movement of a pointer or some other
display symbol. A joystick is similar to a mouse, except that with a
mouse the cursor stops moving as soon as you stop moving the mouse.
With a joystick, the pointer continues moving in the direction the
joystick is pointing. To stop the pointer, you must return the joystick to its
upright position. Most joysticks include two buttons called triggers.
Joysticks are used mostly for computer games, but they are also used occasionally for
CAD/CAM systems and other applications. Joysticks are popular for playing computer games
and controlling computer simulations and assistive technology.
VIDEO DIGITISERS: A video digitiser takes an image from a video
camera or television and converts it so that it can be used by and
stored on a computer. Almost all video digitisers now work in colour.
Unlike scanners video digitisers can capture moving video
sequences as well as still images. When a video sequence is
captured the computer stores this as a sequence of still images
called frames. These images are displayed quickly one after the
other (rather like a flick-book) to create the illusion of a moving
picture. Video sequences captured using a video digitiser are often
used in multimedia presentations.
• REMOTE CONTROLS: Device used to perform monitoring,
controlling, and/or supervisory functions, at a distance. Refers to a program's or
device's ability to control a computer system from a remote location. Remotecontrol programs for PCs enable you to access data stored on your home system
even when you are travelling. The advantages are that if you are in a comfortable
place and you don’t want to move, you can use the control, you don’t need to be going
and returning.
MAGNETIC STRIPES: are built into many plastic cards such as cheque
credit 6
Magnetic stripes look like this :
The strip can contain up to 60 characters
(numbers or digits) of information which is
stored magnetically. Usually the information is put onto the stripe when the
card is made and is never changed. Magnetic stripe codes can also sometimes be found on
the back of railway tickets.
To be read the card is swiped through a machine which quickly and accurately reads the
pattern of magnetism. The information stored on the card can be destroyed by exposure to
magnetic fields, by scratching or by coming into contact with some liquids.
Magnetic stripes are commonly found on credit cards, bank debit cards, prepaid telephone
and vending cards, mass transit cards, drivers' licenses, employee ID badges, membership
cards, school lunch programs and library cards, gift certificates, loyalty cards and access
control cards. This well-established technology is used in industries with low- to medium-data
storage needs.
SCANNERS: A scanner can be used to input printed images such as photographs or pages of
text directly into the computer. A scanner works by "digitizing" an image and placing it on
the computer as a file.
There are two different types of scanner :
Flatbed Scanner : You place the image on top of the scanner. The scanner moves the light and
sensor itself and scans the whole image
automatically. Most flatbed scanners are A4
Handheld Scanner : You must manually
push the light/sensor along the image.
Handheld scanners are usually 5 inches
Flatbed scanners are better as they can
scan larger images and are more accurate
than handheld scanners. On the other hand
handheld scanners are cheaper and more portable. The price of flatbed scanners has fallen so
much in recent years that handheld scanners are rarely sold now.
DIGITAL CAMERAS: Digital cameras are used in the same way as
standard photographic cameras. Most digital cameras look just like
ordinary cameras. Unlike photographic cameras digital cameras do
not use film. Inside a digital camera is an array of light sensors. When a
picture is taken the array of sensors is used to input the image. The
image can then be stored either in the camera's RAM or on a floppy
disk or on the memory card. Later the pictures can be transferred onto
a computer for editing using a painting package. Some digital
cameras are available relatively cheaply.
GRAPHICS TABLET: A graphics tablet consists of a flat pad (the tablet) on which the user
"draws" with a special pen called a stylus. As the user "draws" on
the pad the image is created on the screen. The pad on which
the user draws can be any size from A5 to A1 (eight times as large
as an A4 page). Drawings created using a graphics tablet can
be accurate to within hundredths of an inch. Graphics tablets are
mainly used by professional graphics designers. Using a graphics
tablet a designer can produce much more accurate drawings
on the screen than he could with a mouse or other pointing
device. Graphics tablets are also known as graphics digitisers. The stylus that the user draws
with may have a button on it which will act like a mouse button. Sometimes instead of a
stylus a highly accurate mouse-like device called a puck is used to draw on the tablet.
Graphics tablets are often used to provide input to Computer Aided Design
SENSORS: A sensor is a device which measures a physical quantity such as the temperature
and then sends a voltage to the computer representing the quantity. Sensors can be either
analogue or digital :
Digital : Sensors are either on or off. For example a switch of pressure pad.
Analogue : Sensors can measure a range of values. The size of the voltage the sensor
produces is determined by the size of the quantity that the sensor has measured. For
example if a cold temperature is measured a small voltage will be sent, whilst if a hot
temperature is measured a larger voltage will be sent.
A sensor is any component that feeds raw data values into the ACS for purposes of model
estimation. There are multiple ways of sensing and estimating just about every physical attribute
of the earth, atmosphere, and aircraft. Physical sensors that provide the raw data vary in quality,
reliability, and the extent to which their values must be filtered and combined with others to
obtain useful estimates. Survivability and fault-tolerance constraints require that the system use
whatever data is actually available; the ACS cannot shut down just because a sensor goes out
of service.
There are lots of different sensors available, each of which is designed to measure a specific
quantity. Examples of sensors include :
Quantity Measured
Temperature sensor
Analogue How hot/cold it is.
Monitoring the temperature of a
science experiment.
Light sensor
Analogue How light/dark it is.
Turning street lights on when it is dark.
Pressure Pad
Detecting cars arriving at a car park
pH sensor
Analogue The acidity of a liquid.
Monitoring river pollution.
If the button is being pressed.
Obtaining a ticket at a car park entry
Light Gate
Detects an object passing
through the gate.
Measuring the speed or acceleration
of objects.
If a pad is being pressed.
Sensors are usually used in data logging and control systems.
MICROPHONES: Any electromechanical device designed to convert sound into
an electrical signal. Hardware peripheral that allows computer users to input
audio into their computers. Record voices or sounds and place them onto
computers, generally as a wav file. Microphones also can be used with other
applications such as a voice dictation program or a
voice conference program. When connecting the
microphone to the back of the computer the
microphone will be placed in the hole which
generally has Mic or microphone written next to it
as illustrated in the above illustration.
MIDI INSTRUMENTS: A standard for representing musical information in a
digital format. Software that conforms to this standard, used for
composing and editing electronic music. MIDI: Musical Instrument Digital
Interface, an industry-standard interface used on electronic musical
keyboards and PCs for computer control of musical instruments and
Is a set of specifications for describing music. Instead of capturing and
storing the sound of music, MIDI information describes the instruments, notes, and timing of the
music, which can then be recreated on MIDI-capable devices.
MICR: The Magnetic Ink Character Recognition (MICR) system reads characters printed in a
special magnetic ink into the computer. The main users of MICR are banks. They use it to
read information from cheques into their computers so that the cheques can be cashed.
Here is some information stored on a cheque using MICR :
The information printed on the cheque using MICR is :
A unique number for the cheque.
A code that identifies the bank and branch that issued the cheque (the sort code).
The number of the account that the cheque relates to.
MICR readers can only read one special font which can represent only numbers and a few
punctuation marks. They can read characters very quickly and with 100% accuracy. Information
printed in magnetic ink is also very secure. It is not possible to change the information by writing
over it with a pen and the printed numbers are not damaged by folding (as often happens with
cheques). Both the reader used by MICR and the special ink are expensive.
OMR: Optical mark recognition. An optical mark reader reads marks made by pencil on a
printed form into the computer. OMR systems are used by examination boards to collect the
answers to multiple
choice examinations
lottery tickets. Here is
an example answer
examination. :
drawing a line in pencil in the box that he/she thinks is the correct one. The answer grid is printed
in a special coloured ink called that the OMR system will ignore. Marks down the side of the form
are used to automatically line the form up in the reader so that it can be read. The reader
detects where the marks are placed by shining a light at the page and measuring the amount
of light reflected. Less light is reflected where the marks have been made. A pile of forms
collected at the end of an examination can be put into a tray (called a bin). The reader will go
through each form in turn and record the candidates’ marks.
Input using OMR is accurate and
very fast. Problems can occur if the
OMR forms get creased as the
reader may jam.
Recognition software can be
used to read printed text from an
image that has been scanned
and store it as text rather than an image. You can then edit the text using a word processor
or desktop publisher. OCR software is not yet sophisticated enough to read hand-written text
accurately. An optical character recognition system consists of a scanner and some
software. The scanner is used to scan an image of a page of text to be read into the
computer. The software then examines the page and extracts the text from it, storing it in a
form that can be processed.
BARCODE READER: Barcodes are often printed on products that you can buy and are used
by shops and supermarkets to produce bills for customers. A barcode is made up of a
sequence of bars of different widths. Different
groups of bars are used to represent different
numbers. A printed barcode is therefore simply a
way of representing a number. The number is often
printed above or below the barcode so that
humans can read it.
A barcode reader is used to read the code. The reader
uses a laser beam that is sensitive to the reflections
from the line and space thickness and variation. The reader translates the reflected light into
digital data that is transferred to a computer for immediate action or storage. Bar codes and
readers are most often seen in supermarkets and retail stores, but a large number of different
uses have been found for them. They are also used to take inventory in retail stores; to check
out books from a library; to track manufacturing and shipping movement; to sign in on a job; to
identify hospital patients; and to tabulate the results of direct mail marketing returns. Very small
bar codes have been used to tag honey bees used in research. Readers may be attached to a
computer (as they often are in retail store settings) or separate and portable, in which case they
store the data they read until it can be fed into a computer.
VIDEO CAMERA: A camera that captures light on chips that
convert light into electronic impulses (CCDs) and then fix the
electronic impulses onto tape. Identify suitable uses of the
input devices above, stating the advantages and
disadvantages of each. Capture an image of each one.
Digital Video is the format used when you record images and
sound with a Digital Video Camera. The Digital Video format
is newer than the analog (VHS, VHS-C, Super-VHS, Hi-8) format
and is superior in quality, ease-of-use, and features (usually).
CHIP READERS: A chip card reader is disclosed having a plugin-socket, an insertion slot for a chip card, and a housing according to a
PCMCIA format. The housing includes a base plate and a cover plate
extending between the plug-in socket and the insertion slot. The base
plate and the cover plate include a plastic part and a metallic part and
the metallic part of the base plate is directly welded to the metallic part
of the cover plate. AT ATMs to obtain cash and in retail stores for bill
PIN PAD: Uses for debit and other types of payment that require customers
to enter a personal identification number (PIN). At ATMs to obtain cash and
in retail stores for bill payments.
Almost all computers have a monitor. Monitors are also known as Visual Display Units (VDUs).
Most computers use this display as the main output device. There are two different types of
display :
CRT screen: A standard monitor screen is a
CRT (cathode ray tube)
• Liquid Crystal Displays (LCDs) : These displays
are completely flat and so can be used in
portable computers and other small devices
such as calculators. They are more
expensive to make than desktop monitors. A
technology for the ultimate LCD display. LCD
monitors, also called flat panel displays, are replacing the old style cathode ray tubes
(CRTs) as the displays of choice. Nearly all LCD monitors today use TFT technology.
The three most important features of a screen are its size, the colours it can display and its
resolution. There is more information about these features below. They apply to both desktop
monitors and LCDs.
Size : How big is the screen ? Typical sizes are 10" or 12" for LCDs and 14", 15" or 21" for
desktop monitors. The size is measured along the diagonal from the bottom left hand
corner to the top right hand corner of the screen.
Colour : Is the monitor colour or black & white ? Most new desktop computers have
colour screens as they are no longer that much more expensive than black & white ones
and modern computer applications work better with a colour monitor.
Resolution : An image displayed on the screen is made up of lots of dots called pixels. If
you look closely at the screen you may be able to see these pixels. The resolution of the
screen is how many pixels there are up and down and from left to right across the screen.
High resolution displays can show much more detail than low resolution ones and are
required for applications such as Computer Aided Design (CAD) and Multimedia.
Printers are usually divided into two different categories, impact printers and
This is a "family tree" of output devices that can produce hard copy :
Impact Printers
Dot Matrix Printers: Impact printers produce output by striking a
ribbon with a hammer. When the ribbon is hit a mark is made on the
paper behind it. If carbon paper is put into the printer then an
impact printer can print more than one copy of a document at a
time. This feature is often used by companies when they print
invoices, bills etc. Because of the hammering action impact printers are noisy when they
are printing. Dot matrix printers are cheap to purchase and have low operating costs.
Daisy Wheel Printers: Daisy wheel printers are rarely used any more. A daisy wheel printer
hammers character stamps (like those on typewriters) against a ribbon to produce high
quality text output. The character patterns are all arranged around the edge of a wheel.
When a letter is to be printed the wheel rotates so that the correct letter is against the
ribbon. A hammer then hits the letter against the ribbon to print it on the paper. Daisy
wheel printers are very slow and noisy. It is not possible to print graphics using a daisy
wheel printer.
Non-Impact Printers: Non-impact printers are very quiet
Laser Printer
Ink Jet Printer
but can not print multiple copies using carbon paper.
Laser Printers
Laser printers produce very high quality output, are very
quiet and very fast. The main disadvantage of this type
of printer is the high cost. Running costs are higher than
impact printers but lower than most ink jet printers.
Ink Jet Printers
Ink jet printers are the most popular type of printer for
use at home or in a small business. This is because they are relatively cheap to purchase and
can print in colour.
Thermal Printers
Thermal printers are no longer used as printers for PCs. They are however still used in some
computer control systems, tills and in many fax machines. These printers print on special heat
sensitive paper which is expensive. The image is produced from small dots which are made on
the paper by heating it up. The quality is reasonable and graphics can be printedFlatbed Plotter
: The paper is fixed and the pen moves left and right and up and down across the paper to
draw lines.
Plotter : A plotter is a vector graphics printing device that connects to a computer. The
pen moves up and down on the paper and the paper is moved left and right by rotating
a drum on which the paper is placed.
Plotters can automatically change their
pens and so can produce colour
output. The lines drawn by a plotter are
continuous and very accurate. Plotters
are very slow but produce high quality
output. They are usually used for
Computer Aided Design (CAD) and
Computer Aided Manufacturing (CAM)
applications such as printing out plans
for houses or car parts. The quality of the output produced by ink jet printers is now very
good and large format (big) ink-jet printers are steadily replacing plotters for most tasks.
An output device to reproduce sound. When computers were originally
released they had onboard speakers that generated a series of different
tones and beeps. As multimedia and games became popular higher
quality computers speakers began to be released for more higher
quality sound effects and music.
CONTROL DEVICES: Computers can also be used to control other devices such as switches,
lights, pumps and motors.
A computer control system is a computerised system designed to control a process.
MOTORS: Automatic washing machines, automatic cookers, central heating controllers,
computer-controlled greenhouses, microwave ovens, ropbototics, production line
BUZZERS: Automatic cookers, microwave ovens
HEATERS: Automatic washing machines, automatic cookers, central heating controllers,
computer-controlled greenhouses.
LIGHTS/LAMP: Computer controlled greenhouses.
Example Control Systems:
Traffic Light System : The computer controls the sequences of lights displayed at a crossroads to ensure that cars do not crash Additionally the computer operates a pedestrian
crossing to let pedestrians cross the road when a button is pressed.
Greenhouse : The computer controls the temperature in a greenhouse to maintain the
conditions required for the plants in it to grow. If the temperature gets too cold then the
computer turns on a heater to keep the plants warm.
Robot Arm : The computer controls the movement of a robot arm which sprays parts of a
car body. The arm must only spray when the body part is present and must then follow a
programmed spraying path. The arm must stop if any foreign object, such as a human
being, gets in its way.
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