Transcript INPUT devices - Beverley Grammar School

INPUT, OUTPUT & STORAGE
• INPUT: getting information and data into the
computer
• OUTPUT: getting information and data out of
the computer
• STORAGE: being able to hold/keep information
and data permanently even when the power is
switched off
• ROM & RAM …something to cover later!
INPUT devices
• Keyboards
A computer keyboard is an array of switches, each
sends the PC a unique signal when pressed.
The "Microsoft Natural
Elite" keyboard has become
the most popular choice for
an alternative keyboard
priced under $100.00.
The "Kinesis" ergonomic keyboard features
concave keypads and is designed to
minimize the effect of keyboard use on the
body. The design of the Kinesis keyboard
helps users achieve a more natural posture by
aligning the hands, arms and shoulders.
INPUT devices
• Mice
In the early 1980s the first PCs were equipped with
the traditional user input device - a keyboard. By
the end of the decade however, a mouse device
had become an essential for PCs running the GUI based Windows operating system.
GUI: Graphical User
Interface
INPUT devices
• Touch Sensitive Screens
A grid of light beams or fine wires cross the computer screen.
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.
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 applications 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.
INPUT only?? Is it?? What about an interactive whiteboard… input
or output?
INPUT devices
• Light Pen
A light pen is a special pen which you can point at any computer
monitor. When the pen is pointed at the screen the computer can
work out where the pen is pointing. Light pens can be used to
"draw" on the screen or to select options from menus presented
on the screen. Light pens are extremely poor input devices. They
are very inaccurate and tiring to use. Light pens are hardly ever
used today.
• Tracker Ball
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. Tracker
balls are used mainly when there is not enough space for a mouse.
e.g. in portable computers.
INPUT devices
• Joystick
Joysticks are used to play computer games.
You can move a standard joystick in any one of eight directions.
The joystick tells the computer in which direction it is being
pulled and the computer uses this information to e.g. move a
spaceship on screen. A joystick may also have several buttons
which can be pressed to trigger actions such as firing a missile.
The best joysticks, called analogue joysticks measure how far the
joystick is being moved in the direction it is being pulled. This
information is used to set how quickly the object on the screen
moves. The further you push the joystick the faster the object
moves.
Small joysticks called trackpoint devices are sometimes built into
the keyboards of portable computers and used instead of a mouse.
INPUT devices
• Graphics Tablet
Graphics tablets are used mainly 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. 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.
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.
INPUT devices
•Scanner
A scanner can be used to input
printed images such as
photographs or pages of text
directly into the computer. (Optical Character Recognition)
A scanner works by shining a light at the image being scanned and
measuring how much light is reflected back using an optical sensor.
The amount of light that is reflected back tells the computer how
light or dark the image is at each point.
The light and optical sensor reads information about one line of the image at a time.
They must be moved down the picture to input the whole image. 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 size.
Handheld Scanner : You must manually push the light/sensor along the image.
Handheld scanners are usually 5 inches wide.
INPUT devices
• 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. Later the pictures can be transferred onto a
computer for editing using a graphics package.
INPUT devices
• Video Digitiser
• A video digitiser takes an image from a video camera or television and converts
it so that it can 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.
• When you want to capture a video sequence you must tell the computer :
• Size : How big you want the image you capture to be. e.g. should it take up the
whole screen, 1/2 the screen, 1/8th of the screen ... ?
• Frame Rate : How frequently the frames should be captured from the video.
• If you want to capture large images you may have to settle for a slow frame rate
which will make the captured video film look jittery. If you want a fast frame
rate you may only be able to capture a small image size. Video sequences
captured using a video digitiser are often used in multimedia presentations.
INPUT devices
• Voice Recognition
• Voice recognition systems listen to what people are saying and carry out the
instructions given to them when people speak. A microphone is used to provide
input for a voice recognition system. Currently these systems are not very
sophisticated and are used only for certain applications. Existing voice
recognition systems come in two different types :
• Systems which recognise only a few words but can understand most peoples
voices. e.g. telephone banking computers.
• Systems which recognise a wide vocabulary but need to be trained to
understand each different voice. e.g. automatic dictation systems.
• In the last few years a number of voice dictation packages have been developed.
These packages let the user dictate text into a computer to appear in a word
processed document. Dictating like this can be much quicker than typing but the
computer still makes some mistakes especially with short words.
DDE INPUT devices
DDE: direct data entry
Direct data entry devices are used when large volumes of data must be entered
into the computer quickly
• Bar Code Readers
• Bar codes are often printed on products that we buy and are used by shops to
produce bills for customers. A bar code is made up of a sequence of bars of
different widths. Different groups of bars are used to represent different
numbers. A printed bar code is therefore simply a way of representing a number.
The number is often printed above or below the bar code so that humans can
read it.
• Bar codes are read into the computer using a wand or a fixed scanner. Bar codes
are not easily damaged and can normally still be read if they are creased or not
stuck onto a flat surface. They can be printed using a normal printer and ink and
so are cheap to produce. The information normally included on a bar code for a
product is country of origin, manufacturer and item code. The price is not
included in the bar code.
DDE INPUT devices
• Magnetic Stripe Codes & Readers
• Magnetic stripes are built into many plastic cards such as cheque
guarantee or credit cards. 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.
DDE INPUT devices
• Smart Cards & Readers
• Smart cards are often called input devices. In fact they are actually simple
storage devices. A smart card contains a small RAM chip. When the card is put
into a machine data can be read from the card or written onto it. A smart card
can store much more data than a magnetic stripe can. A popular card in use at
the moment can store 8k (about 8000 characters) of information.
• Petrol companies and supermarkets use smart cards to store information about
points that customers earn when they buy goods. Every time the customer buys
something the number of points stored on the card is increased. The customer
can then spend these points to buy goods.
• Satellite television companies also use smart cards in their receivers. The smart
card stores a code which is needed to let the receiver decode and display the
pictures coming from the satellite. The government is currently considering
introducing an identity card which could be based on a smart card. Many people
are worried about this as people would not be able to tell what information was
stored about them.
• A new generation of smart cards is now appearing which contain a small
microprocessor as well as memory. These cards are practically a complete
computer system on a card.
DDE INPUT devices
• Magnetic Ink Character Recognition (MICR)
• The 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 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.
DDE INPUT
devices
• Optical Mark Recognition (OMR)
• 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 and to purchase lottery tickets. The student
answers each question by 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.
DDE INPUT devices
• Turnaround Documents
A turnaround document is a document which :
• Has some information printed onto it by a computer.
• Has more information added to it by a human.
• Is fed back into a computer to transfer the added information into the computer.
• Here is a turnaround document that a gas company could use to record meter
readings
DDE INPUT devices
• Sensors
• Sensors can be used to measure physical quantities such as temperature, light
and pressure. The measurements can then be stored for later use (data logging)
or used to control devices such as heaters or fans (computer control).
DATA LOGGING can be taken a step further. MONITORING AND CONTROL:
this will be covered in another lesson.
On-line resources for you to look at
DATA LOGGING: click here
Test & Learn on the net – click here: http://www.school-resources.co.uk/data_logging_and_control_quiz.htm