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Input and Output Devices
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Input and Output Devices






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    Input and Output Devices Input and Output Devices Presentation Transcript

    • Keyboard • Common method of entering data • Often called the QWERTY keyboard • Consists of a rows of electronic switches encased in a plastic surround, which has a graphic that describes its function • Key stokes are combined to modify the input
    • Keyboard Advantage: • The most efficient way of entering numbers, text and commands into the computer, as each key has a specific function. • Inexpensive, as virtually every computer needs one.
    • Keyboard Disadvantage: • You have to learn to type! • There are 'arrow keys' but they are not as good as a mouse for controlling the screen cursor. • May cause sore wrists and arms
    • Alternative Keyboards • Designed to reduce repetitive strain • Hands fit in the molding and wrist need not have to move so much • Use key combinations to type letters and characters • Another type – more comfortable than the standard one
    • Keyboard for physical disabilities • Keyguard – plate fits over the keyboard with holes positioned over the keys • Keyguard – steel with wipe clean surface and held in place with dual lock • People with disabilities rest their hands on the keyguard – prevents accidental keystrokes
    • Mouse • Popular way of controlling the screen cursor through the use of on-screen ‘menus’ • Fits within the palm of your hand • Detects the back and forth movement and input the X-Y (left- right,forward-backward) data into the computer
    • • Switches – depressed to cause ‘click’ data to be input, ‘clicks’ control screen menus • Some have little wheel – to scroll within windows • Wireless mouse – use radio signals rather than wires to connect to computer • Two mechanisms to detect hand movements  ‘Roller ball’  ‘Optical’ mouse
    • Advantages: • One of the easiest way of translating. X-Y hand movements into the computer. • Excellent for controlling the cursor, menus and windows on screen. • Easy to use.
    • Disadvantage: • You have to have space next to the keyboard to move the mouse. • Prolonged use can give you sore wrists and arms. • Not as good as a graphics tablet for drawing straight lines and shapes on screen
    • Alternatives ‘Trackball Mouse’  reduce wrist movements, thus reduce repetitive strain  rolling the ball controls the cursor  switches – work in same way as standard mouse
    • Alternatives ‘Whale Mouse’ • Contoured palm rest encourages neutral wrist, hand and finger positions. • Promotes the use of the larger arm muscles relaxing the more delicate muscles • Minimizes sharp, quick wrist movements that can lead to injury. • Easily adjusts to fit any size hand - left or right.
    • Graphics Tablet • Excellent device for use with drawing or graphics package • Using pen – natural method of drawing lines and shapes • Allows X-Y data input same as mouse • Slide the stylus along the surface which inputs the movement to the computer
    • • Natural hand and arm movement than mouse for creating sweeping lines and curves • Can create thick and thin lines –by pressing harder or lighter on the stylus
    • Advantage: • Excellent for use with a drawing or graphics package to draw lines and shapes. • Can input pressure data for use in a graphics package  
    • Disadvantage: • More expensive than a mouse, especially in the larger sizes. • Not as precise as a mouse for menu control, so it tends to be an addition rather than a replacement- you can run both perfectly well by making sure the pen is off the tablet when you do not need it.  
    • Concept Tablet • Touch sensitive • Plastic sheet with various pictures and graphics is placed on the surface • Tapping the picture cause a command to input • Appropriate software is used to sense these commands
    • Advantages: • Can be used to issue specific commands to the computer. • Avoids staff having to know the price of everything. • Allows software to be controlled with a single touch of the tablet.
    • Disadvantage: • There has to be the right software running for the command to make sense. • Number of commands that can be issued is limited by the size of the device.
    • Touch Screen Uses: • Dusty, dirty or wet environments where a keyboard would be damaged • Hazardous environments where there must not be any chance of a spark • Constricted areas where there is no room for another input device • Hygienic environments where it must be simple to wipe clean
    • • Optical touch screen  LEDs along one vertical and horizontal edge and detectors on the other • Electrical touch panel  Two transparent plates one coated with conductive material and other resistive material separated by distance
    • • Acoustic touch panel  high frequency sound waves generated in horizontal and vertical directions across a glass plate  touching the screen reflects the wave from fingers to emitters  time interval between transmission and reflection gives the position of contact
    • Advantage: • No moving parts • Can use any number of menu levels • Can display large text to assist less- sighted people
    • Disadvantages: • Expensive compared to a standard keyboard or mouse. • Has to have specific software to make sense of the input. • Can be a problem seeing the screen in bright sunlight.
    • Scanner • Input graphic information • Input picture is laid flat, face down on the scanner surface with lid lowered to avoid stray light creeping in • Sensor sweeps along the picture – image is built up as a series of ‘pixels’
    • • A scanner can 1) Create a black and white image - handy for line drawings and text 2) Create a full color image - excellent for inputting photographs • Low resolution, black and white image  small file size with a few hundred kilobytes at most • High quality, high resolution image  huge file size with several megabytes
    • Advantage: • Scanners can convert photographs and flat documents into electronic images. • Both color and black & white images can be created. • Extremely high resolution if required. • Relatively inexpensive compared to a digital camera.
    • Disadvantages: • Cannot take 3 dimensional images. • Document has to fit on the glass • Relatively slow compared to taking a digital photograph.  
    • Space ball and Track ball • Trackball  ball rotated to produce screen cursor movement  potentiometers attached measure the amount and direction of rotation  mounted on keyboards or mouse
    • • Space ball  Trackball : 2D positioning devices whereas space ball provides 6 degrees of freedom  Simultaneously pan, zoom or rotate 3D models scene or camera datasets with the controller in one hand, while the other hand selects, inspects or edits with the mouse
    •  Eliminate tedious and repetitive steps that put unnecessary stress on mouse hand  Used for 3D positioning and selection operations in virtual reality systems, modeling, animation and CAD and other applications
    • Joysticks • Small, vertical stick mounted on a base used to steer the screen cursor around • Distance moved in any direction from center position corresponds to screen cursor movement • Some respond to stick movement and others to pressure
    • Joysticks • Potentiometers mounted at the base the measure the amount of movement • Springs return the stick back to center position • One or more buttons programmed to signal certain actions once screen position is selected
    • Optical Mark Reader Advantage: • Good for inputting large volume of data at low cost. • Very little training or instruction required to use the forms/card. • Good for multi-choice questionnaires.
    • Optical Mark Reader Disadvantage: • Can only input a limited data set • Poorly marked forms/cards cause errors. • Creased/folded forms cause errors.
    • Optical Character Reader • Combination of scanner and special software that converts printed text into electronic ASCII characters • Additional mechanisms to handle multiple sheets • Eg 1) Converting paper records into electronic files. 2) Scanning invoices into spreadsheets
    • • Advantage:  Allows paper records to be converted into electronic format • Disadvantage:  Conversion is often not perfect and so someone has to read the results and correct them.  Can be slow (unless an expensive system is used).  
    • Magnetic Stripe Reader • Information is simply encoded in magnetic form on the strip • The reader picks up the information by swiping the card through it and inputs it to the connected computer • Eg. Bank card, Credit Card, Security passes etc.
    • Advantage: • Inexpensive • Robust - not easily damaged • Simple to use • Fast Disadvantage: • A card can be copied fairly easily. • Sensitive to strong magnetic fields
    • • Quality of picture depends on dot size (spot size) and no. of dots per inch (addressability) • In high quality prints, adjacent dots overlap • Printers produce output by either impact or non impact methods  Impact: press character faces against inked ribbon onto the paper  Non Impact: use techniques like inkjet sprays, electrostatic method…
    • Dot-Matrix Printers • Print head of 7 to 24 pins • Each pin fired individually to strike a ribbon against the paper • Print head moves across the paper one step at a time and paper is advanced one line • Raster output device requires scan conversion
    • • Colored ribbon  produce color hard copy • Two approaches Multiple print heads: each with different color ribbon  Single print head with multicolored ribbon • More colors created by overstriking two different colors at the same dot on the paper • With 3 colors upto 8 colors can be created • Often true black is added to the ribbon
    • LASER PRINTERS • Positively charged rotating drum is coated with selenium • Areas of drum hit by laser beam lose charge • Positive charge remains only where the copy is to be black • A negatively charged powdered toner adhere to the positive areas and is then transferred to the paper
    • • In color xerography: this process is repeated three times, one for each primary color Selenium coated Laser drum beam LASER Deflection system
    • Ink-jet Printers • Two methods I method  Spray cyan, magenta, yellow and sometimes black ink onto the paper  Ink jets are mounted on a head  Head moves across page to draw one scan line, returns while paper advances
    • II method  Wrap paper around a drum  Drum rotates rapidly while print head moves slowly along the drum
    • Thermal transfer Printers • Finely spaced heating nibs transfer pigments from colored wax paper to plain paper • Wax and plain paper are drawn together over the strip of heating nibs, which are selectively heated to cause pigment transfer
    • • For color printing, the wax paper is on a roll of alternating cyan, magenta, yellow strips each of length = paper size • Nibs heat and cool rapidly, a single color hard copy image is created in less than a minute