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Chapter 2 - Lesson 2

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M
MLG College of Learning, Inc

This document discusses different types of input and output devices for computers. It describes various mouse types including mechanical mice that use balls and optical mice that detect light reflections. It also covers touchpads, trackballs, joysticks, touch screens, styli, and eye tracking. For displays it discusses CRT and LCD monitors as well as special displays like vector, plasma, and digital paper which can be updated electronically like an e-reader. It notes health concerns around extended CRT use and advantages of LCDs having no radiation.

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chapter 2 – The Computer Lesson 2 – Types of Mouse and display devices
Lesson Objectives: • At the end of the lesson the students can: • Identify and explain the types of mouse. • Differentiate the different display devices
How does it work? Two methods for detecting motion • Mechanical – Ball on underside of mouse turns as mouse is moved – Rotates orthogonal potentiometers – Can be used on almost any flat surface • Optical – light emitting diode on underside of mouse – may use special grid-like pad or just on desk – less susceptible to dust and dirt – detects fluctuating alterations in reflected light intensity to calculate relative motion in (x, z) plane
Even by foot … • some experiments with the footmouse – controlling mouse movement with feet … – not very common :-) • but foot controls are common elsewhere: – car pedals – sewing machine speed control – organ and piano pedals
Touchpad • small touch sensitive tablets • ‘stroke’ to move mouse pointer • used mainly in laptop computers • good ‘acceleration’ settings important – fast stroke • lots of pixels per inch moved • initial movement to the target – slow stroke • less pixels per inch • for accurate positioning
Trackball and thumbwheels Trackball – ball is rotated inside static housing • like an upsdie down mouse! – relative motion moves cursor – indirect device, fairly accurate – separate buttons for picking – very fast for gaming – used in some portable and notebook computers. Thumbwheels … – for accurate CAD – two dials for X-Y cursor position – for fast scrolling – single dial on mouse
Joystick and keyboard nipple Joystick – indirect pressure of stick = velocity of movement – buttons for selection on top or on front like a trigger – often used for computer games aircraft controls and 3D navigation Keyboard nipple – for laptop computers – miniature joystick in the middle of the keyboard
Touch-sensitive screen • Detect the presence of finger or stylus on the screen. – works by interrupting matrix of light beams, capacitance changes or ultrasonic reflections – direct pointing device • Advantages: – fast, and requires no specialised pointer – good for menu selection – suitable for use in hostile environment: clean and safe from damage. • Disadvantages: – finger can mark screen – imprecise (finger is a fairly blunt instrument!) • difficult to select small regions or perform accurate drawing – lifting arm can be tiring
Stylus and light pen Stylus – small pen-like pointer to draw directly on screen – may use touch sensitive surface or magnetic detection – used in PDA, tablets PCs and drawing tables Light Pen – now rarely used – uses light from screen to detect location BOTH … – very direct and obvious to use – but can obscure screen
Digitizing tablet • Mouse like-device with cross hairs • used on special surface - rather like stylus • very accurate - used for digitizing maps
Eyegaze • control interface by eye gaze direction – e.g. look at a menu item to select it • uses laser beam reflected off retina – … a very low power laser! • mainly used for evaluation (ch x) • potential for hands-free control • high accuracy requires headset • cheaper and lower accuracy devices available sit under the screen like a small webcam
Cursor keys • Four keys (up, down, left, right) on keyboard. • Very, very cheap, but slow. • Useful for not much more than basic motion for text- editing tasks. • No standardised layout, but inverted “T”, most common
Discrete positioning controls • in phones, TV controls etc. – cursor pads or mini-joysticks – discrete left-right, up-down – mainly for menu selection
display devices bitmap screens (CRT & LCD) large & situated displays digital paper
bitmap displays • screen is vast number of coloured dots
resolution and colour depth • Resolution … used (inconsistently) for – number of pixels on screen (width x height) • e.g. SVGA 1024 x 768, PDA perhaps 240x400 – density of pixels (in pixels or dots per inch - dpi) • typically between 72 and 96 dpi • Aspect ratio – ration between width and height – 4:3 for most screens, 16:9 for wide-screen TV • Colour depth: – how many different colours for each pixel? – black/white or greys only – 256 from a pallete – 8 bits each for red/green/blue = millions of colours
anti-aliasing Jaggies – diagonal lines that have discontinuities in due to horizontal raster scan process. Anti-aliasing – softens edges by using shades of line colour – also used for text
Cathode ray tube • Stream of electrons emitted from electron gun, focused and directed by magnetic fields, hit phosphor-coated screen which glows • used in TVs and computer monitors electron gun focussing and deflection electron beam phosphor- coated screen
Health hazards of CRT ! • X-rays: largely absorbed by screen (but not at rear!) • UV- and IR-radiation from phosphors: insignificant levels • Radio frequency emissions, plus ultrasound (~16kHz) • Electrostatic field - leaks out through tube to user. Intensity dependant on distance and humidity. Can cause rashes. • Electromagnetic fields (50Hz-0.5MHz). Create induction currents in conductive materials, including the human body. Two types of effects attributed to this: visual system - high incidence of cataracts in VDU operators, and concern over reproductive disorders (miscarriages and birth defects).
Health hints … • do not sit too close to the screen • do not use very small fonts • do not look at the screen for long periods without a break • do not place the screen directly in front of a bright window • work in well-lit surroundings  Take extra care if pregnant. but also posture, ergonomics, stress
Liquid crystal displays • Smaller, lighter, and … no radiation problems. • Found on PDAs, portables and notebooks, … and increasingly on desktop and even for home TV • also used in dedicted displays: digital watches, mobile phones, HiFi controls • How it works … – Top plate transparent and polarised, bottom plate reflecting. – Light passes through top plate and crystal, and reflects back to eye. – Voltage applied to crystal changes polarisation and hence colour – N.B. light reflected not emitted => less eye strain
special displays Random Scan (Directed-beam refresh, vector display) – draw the lines to be displayed directly – no jaggies – lines need to be constantly redrawn – rarely used except in special instruments Direct view storage tube (DVST) – Similar to random scan but persistent => no flicker – Can be incrementally updated but not selectively erased – Used in analogue storage oscilloscopes
large displays • used for meetings, lectures, etc. • technology plasma – usually wide screen video walls – lots of small screens together projected – RGB lights or LCD projector – hand/body obscures screen – may be solved by 2 projectors + clever software back-projected – frosted glass + projector behind
situated displays • displays in ‘public’ places – large or small – very public or for small group • display only – for information relevant to location • or interactive – use stylus, touch sensitive screem • in all cases … the location matters – meaning of information or interaction is related to the location
• small displays beside office doors • handwritten notes left using stylus • office owner reads notes using web interface Hermes a situated display small displays beside office doors handwritten notes left using stylus office owner reads notes using web interface
Digital paper • what? – thin flexible sheets – updated electronically – but retain display • how? – small spheres turned – or channels with coloured liquid and contrasting spheres – rapidly developing area appearance cross section

More Related Content

Chapter 2 - Lesson 2

  • 1. chapter 2 – The Computer Lesson 2 – Types of Mouse and display devices
  • 2. Lesson Objectives: • At the end of the lesson the students can: • Identify and explain the types of mouse. • Differentiate the different display devices
  • 3. How does it work? Two methods for detecting motion • Mechanical – Ball on underside of mouse turns as mouse is moved – Rotates orthogonal potentiometers – Can be used on almost any flat surface • Optical – light emitting diode on underside of mouse – may use special grid-like pad or just on desk – less susceptible to dust and dirt – detects fluctuating alterations in reflected light intensity to calculate relative motion in (x, z) plane
  • 4. Even by foot … • some experiments with the footmouse – controlling mouse movement with feet … – not very common :-) • but foot controls are common elsewhere: – car pedals – sewing machine speed control – organ and piano pedals
  • 5. Touchpad • small touch sensitive tablets • ‘stroke’ to move mouse pointer • used mainly in laptop computers • good ‘acceleration’ settings important – fast stroke • lots of pixels per inch moved • initial movement to the target – slow stroke • less pixels per inch • for accurate positioning
  • 6. Trackball and thumbwheels Trackball – ball is rotated inside static housing • like an upsdie down mouse! – relative motion moves cursor – indirect device, fairly accurate – separate buttons for picking – very fast for gaming – used in some portable and notebook computers. Thumbwheels … – for accurate CAD – two dials for X-Y cursor position – for fast scrolling – single dial on mouse
  • 7. Joystick and keyboard nipple Joystick – indirect pressure of stick = velocity of movement – buttons for selection on top or on front like a trigger – often used for computer games aircraft controls and 3D navigation Keyboard nipple – for laptop computers – miniature joystick in the middle of the keyboard
  • 8. Touch-sensitive screen • Detect the presence of finger or stylus on the screen. – works by interrupting matrix of light beams, capacitance changes or ultrasonic reflections – direct pointing device • Advantages: – fast, and requires no specialised pointer – good for menu selection – suitable for use in hostile environment: clean and safe from damage. • Disadvantages: – finger can mark screen – imprecise (finger is a fairly blunt instrument!) • difficult to select small regions or perform accurate drawing – lifting arm can be tiring
  • 9. Stylus and light pen Stylus – small pen-like pointer to draw directly on screen – may use touch sensitive surface or magnetic detection – used in PDA, tablets PCs and drawing tables Light Pen – now rarely used – uses light from screen to detect location BOTH … – very direct and obvious to use – but can obscure screen
  • 10. Digitizing tablet • Mouse like-device with cross hairs • used on special surface - rather like stylus • very accurate - used for digitizing maps
  • 11. Eyegaze • control interface by eye gaze direction – e.g. look at a menu item to select it • uses laser beam reflected off retina – … a very low power laser! • mainly used for evaluation (ch x) • potential for hands-free control • high accuracy requires headset • cheaper and lower accuracy devices available sit under the screen like a small webcam
  • 12. Cursor keys • Four keys (up, down, left, right) on keyboard. • Very, very cheap, but slow. • Useful for not much more than basic motion for text- editing tasks. • No standardised layout, but inverted “T”, most common
  • 13. Discrete positioning controls • in phones, TV controls etc. – cursor pads or mini-joysticks – discrete left-right, up-down – mainly for menu selection
  • 14. display devices bitmap screens (CRT & LCD) large & situated displays digital paper
  • 15. bitmap displays • screen is vast number of coloured dots
  • 16. resolution and colour depth • Resolution … used (inconsistently) for – number of pixels on screen (width x height) • e.g. SVGA 1024 x 768, PDA perhaps 240x400 – density of pixels (in pixels or dots per inch - dpi) • typically between 72 and 96 dpi • Aspect ratio – ration between width and height – 4:3 for most screens, 16:9 for wide-screen TV • Colour depth: – how many different colours for each pixel? – black/white or greys only – 256 from a pallete – 8 bits each for red/green/blue = millions of colours
  • 17. anti-aliasing Jaggies – diagonal lines that have discontinuities in due to horizontal raster scan process. Anti-aliasing – softens edges by using shades of line colour – also used for text
  • 18. Cathode ray tube • Stream of electrons emitted from electron gun, focused and directed by magnetic fields, hit phosphor-coated screen which glows • used in TVs and computer monitors electron gun focussing and deflection electron beam phosphor- coated screen
  • 19. Health hazards of CRT ! • X-rays: largely absorbed by screen (but not at rear!) • UV- and IR-radiation from phosphors: insignificant levels • Radio frequency emissions, plus ultrasound (~16kHz) • Electrostatic field - leaks out through tube to user. Intensity dependant on distance and humidity. Can cause rashes. • Electromagnetic fields (50Hz-0.5MHz). Create induction currents in conductive materials, including the human body. Two types of effects attributed to this: visual system - high incidence of cataracts in VDU operators, and concern over reproductive disorders (miscarriages and birth defects).
  • 20. Health hints … • do not sit too close to the screen • do not use very small fonts • do not look at the screen for long periods without a break • do not place the screen directly in front of a bright window • work in well-lit surroundings  Take extra care if pregnant. but also posture, ergonomics, stress
  • 21. Liquid crystal displays • Smaller, lighter, and … no radiation problems. • Found on PDAs, portables and notebooks, … and increasingly on desktop and even for home TV • also used in dedicted displays: digital watches, mobile phones, HiFi controls • How it works … – Top plate transparent and polarised, bottom plate reflecting. – Light passes through top plate and crystal, and reflects back to eye. – Voltage applied to crystal changes polarisation and hence colour – N.B. light reflected not emitted => less eye strain
  • 22. special displays Random Scan (Directed-beam refresh, vector display) – draw the lines to be displayed directly – no jaggies – lines need to be constantly redrawn – rarely used except in special instruments Direct view storage tube (DVST) – Similar to random scan but persistent => no flicker – Can be incrementally updated but not selectively erased – Used in analogue storage oscilloscopes
  • 23. large displays • used for meetings, lectures, etc. • technology plasma – usually wide screen video walls – lots of small screens together projected – RGB lights or LCD projector – hand/body obscures screen – may be solved by 2 projectors + clever software back-projected – frosted glass + projector behind
  • 24. situated displays • displays in ‘public’ places – large or small – very public or for small group • display only – for information relevant to location • or interactive – use stylus, touch sensitive screem • in all cases … the location matters – meaning of information or interaction is related to the location
  • 25. • small displays beside office doors • handwritten notes left using stylus • office owner reads notes using web interface Hermes a situated display small displays beside office doors handwritten notes left using stylus office owner reads notes using web interface
  • 26. Digital paper • what? – thin flexible sheets – updated electronically – but retain display • how? – small spheres turned – or channels with coloured liquid and contrasting spheres – rapidly developing area appearance cross section