Input & Output devices

1. Input & Output devices

2. Input Device :keyboard • a keyboard is an input device, partially modeled after the typewriter keyboard, which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches. • A keyboard is also used to give commands to the operating system of a computer. • Connectors to keyboard AT(DIN-5) PS2 andUSB. • XT with 83 keys,At with 84 keys, 104 keys by adding window keys. • Keys includes: Typing keys numeric keypad,function keys,control keys • Virtual Laser Keyboard(sensor,Signalsto computer)

3. Input Device :keyboard • Components of Keyboard • Keyboard switches • Keyboard processor or circuitry • Key matrix • Types of keySwitches • Capacitive switch • Hall effect switch • Opto electronic switch • Membrane switch • Mechnical switch

4. Input Device :keyboard • Key matrix: keyboard matrix is the arrangement of circuit connections between the keyboard controller and all the keys. • Key switch: The main component of any keyboard is the key switch. These switches generate typical codes of signal when they are depressed and it is used for interfacing with computer system

5. Input Device :keyboard

6. Input Device :keyboard

7. Input Device :keyboard • Key matrix: keyboard matrix is the arrangement of circuit connections between the keyboard controller and all the keys. • each key is placed at the intersection of a matrix row and a matrix column. The keyboard repeatedly applies current to each column in turn, and checks to see which rows output current. From this, the keyboard can deduce which keys in that column have been depressed.

8. Input Device :keyboard • Capcitive switch:two plates of the capacitor are brought closer when the key is pressed. • Change in capacitance of switch changes and change in capacitance is detected in terms of voltage. • Basedon the switch open/close voltage is recived thisvoltage is converted into proper signals to inform CPU. • Lifespan 20 millonkey strokes. • Hall effect switch: magnetic field is applied to any device the resistance of device will be increases or decresed(current starts flowing) • This allow current flow • Lifespan 100 million keystrokes

9. Input Device :keyboard

10. Input Device :keyboard • opto-electronic switch: have LED light generate light when electric power is applied.uses photo- transistor which allow current to flow in the circuit. • When key is pressed not pressed the light from LED falls onto photo-transistor • When key is pressed the value will be produced at the ouput Vout • membrane switch:it is multi layered plastic or rubberuses the row and colum conductor sheets. • Mechanical switch: it uses two metal pieces or contacts . • Rubber dome:madeup of polyester domes • Refered as direct switches.

11. Input Device :keyboard opto-electronic switch membrane switch

12. Input Device :keyboard Mechanical switch

13. Keyboard Interfaces • Connects to PC • KEYBOARD • KEYBOARD CONNECTOR • Inside keyboard a processor and circuit which carry information to or from that processor. • Keyboard controller is single chip contains memory RAM, processor ROM(control operations of keyboard) • Key matrix: row and columns made up wires and each key act like switch • Key matrix is grid of circuits when key is pressed the row wire makes contact with colmn wire and completes the circuit . KM passes current to keyboard controller . • Keyboard controller will detects the closed circuit and registers the key press and controller read the key pressed.

14. Keyboard Interfaces • KEYBOARD CONNECTOR • Interface between keyboard and pc • AT keyboard connector(DIN5) • PS2 keyboard connector or(MIN-DIN6) • USB connector • AT keyboard connector(DIN5) • Uses 5 pins: KBDCLK(provide clock pulse), KBDAT(send/recive data),KBRST (reset keyboardinternal buffer),GND(ground),VCC(+5v provides power to keyboard) PS2 keyboard connector or(MIN-DIN6): With 6 pins

16. USB keyboard connector: • USB keyboard connector: uses 4 pins VDC(+5V),DATA- carries -ve data signal,DATA+it carries +ve data Signal, • Keyboard working:key is pressed it pushes down the rubber dome • Dome tuches a pair of conductive lines on circuit • Allow current flow

17. Mouse: • Mechanical Mouse : Mechanical Mouse uses ball for the movement of cursor on thecomputer screen. When the ball is rolled in any direction, a sensor of the mouse detects it and also moves the mouse pointer in the same direction. • Optical Mouse : Optical Mouse uses Laser rays for the movement of cursor on the computer screen. It is an advanced pointing device. Movement is detected by sensing changes in the reflected light rather than the motion of a rolling sphere. • Cord-Less Mouse : Cord-Less Mouse is battery driven and does not need any wire for the physical connection with the motherboard. It transmits data through infrared or radio signal.

18. Mechanical mouse

19. Mouse types 1.Mechanical mouse: a rubber ball rolls as the mouse is moved across table top or mouse pad. The wheels are referred as encoders have tiny metal contact points on rims Location of mouse is identified by how many times the contact points have touched the bars. mouse moved across flat surface. As balls rotate it touches and turns two rollers inside the mouse Two rollers are used for vertical and horizontal movements of cursor 19

20. Mouse types • Each roller attached to encoder. • Each time a contact bar touches a point an electrical signal. • Signals generated are sent to PC over the mouse cables • And number of mouse time mouse button is clicked. 2. Optical-mechanical mouse: • When mouse moves the ball of mouse moves and two separate rollers fixed at 90 degree to each other one roller is for vertical and horizontal movement of cursor. • Each roller connected to wheel these rollers are rotated by movement of rollers. • Wheel rotate pair of LED and photo detectors • Signals sent to PC through mouse connectors 20

21. Mouse types • Optical mouse: • LED produces a red light that is emitted onto surface the light reflected back to CMOS sensor then to DSP(digital signal processor) for analysis • DSP analysis the signal and and patterns and determines mouse movements. • Along with coordinates are received by computer and will show mouse movement on screen.

22. Monochrome Monitor

23. Monochrome Monitors

24. Monochrome Monitors • Video processing unit: contains video signals from display adopter card to video Amplifier Circuit. • Video signal controls brightness of beam only two levels to set brightness ON and OFF. • Vertical Sync Processing:

25. Grayscale Monitors • A special type of monochrome monitor capable of displaying different shades of gray. • They are also known as black-and-white, are composed exclusively of shades of gray, varying from black at the weakest intensity to white at the strongest. • Early grayscale monitors can only show up to sixteen different shades

26. Grayscale Monitor

27. Color Monitors • A display monitor capable of displaying many colors. • Color Monitors works like a monochrome one, except that there are three electron beams instead of one. • The three guns represent additive colors (red, green and blue) although the beam they emit are colorless. • Each pixel includes three phosphors, red, green and blue, arranged in a triangle. • When the beam of each of these guns are combined and focused on a pixel, the phosphors light up.

28. Color Monitors • The monitors can display different colors by combining various intensities of three beams.

29. Mixing of Colors

30. What is being used today? • The most popular display today remains Color monitors CRT. • It has been available for more than 70 years. • CRT is used. • Cost less than LCD monitors.

31. History of the Cathode Ray • 1855- Heinrich Geissler creates the mercury pump, the first good vacuum tubes. Sir William Crookes uses these to produce the first cathode rays. • 1858- Julius Plücker bends cathode rays using a magnet • 1869- J.W. Hittorf establishes that the “rays” travel in straight lines • 1883- Heinrich Hertz concludes incorrectly that cathode rays are not made up of particles because they are not deflected by electrically charged metal plates • 1895- Jean-Baptiste Perrin shows that cathode rays are particles because they deposit a negative charge where they impact • 1897- J.J. Thomson discovers electrons using cathode rays

32. How Monitor Works? • Most use a cathode-ray tube as a display device. • CRT: Glass tube that is narrow at one end and opens to a flat screen at the other end.

33. How Monitor Works? • Electrons travel through a vacuum sealed container from the cathode (negative) to the anode (positive). • Because the electrons are negatively charged, they are repelled away from the cathode, and move across the tube to the anode. • The ray can be affected by a magnet because of its relation to positive and negative charges

34. Some Anatomy of the CRT • Anode- Positively Charged, Ray travels towards this • Cathode- Negatively Charged, Ray travels away from this

35. Cathode Ray Tube (CRT) Monitors • A CRT monitor contains millions of tiny red, green, and blue phosphor dots that glow when struck by an electron beam. Electron beam travels across the screen to create a visible image. • In a CRT monitor tube, the cathode is a heated filament. • The heated filament is in a vacuum created inside a glass tube. The electrons are negative and the screen gives a positive charge so the screen glows.

37. Basic Cathode Ray Tube • Electrons excite phosphor to glow • Electrons fired from the back • Phosphor is arranged in dots called pixels • Dot mask ensures proper pixel is lit

38. Phosphore • It is a semi-conducteur material which emits visible radiation in response to the impact of electrons. (i.e. when it absorbs energy from some source such as an electron beam, it releases a portion of this energy in the form of light). • In response to a sudden change in the electron beam(from on to off), the light emission does not fall instantaneously, there is a gradual reduction challed ‘fluorescence’ .

39. Scanning Pattern of CRT Electron Gun • The electron gun scans from left to right and • From top to bottom. • Refreshing every phosphor dot in a zig-zag pattern.

40. Advantages of CRT • The cathode rayed tube can easily increase the monitor’s brightness by reflecting the light. • They produce more colours • The Cathode Ray Tube monitors have lower price rate than the LCD display or Plasma display. • The quality of the image displayed on a Cathode Ray Tube is superior to the LCD and Plasma monitors. • The contrast features of the cathode ray tube monitor are considered highly excellent.

41. Disadvantages of CRT • They have a big back and take up space on desk. • The electromagnetic fields emitted by CRT monitors constitute a health hazard to the functioning of living cells. • CRTs emit a small amount of X-ray band radiation which can result in a health hazard. • Constant refreshing of CRT monitors can result in headache. • CRTs operate at very high voltage which can overheat system or result in an implosion • Within a CRT a strong vacuum exists in it and can also result in a implosion • They are heavy to pick up and carry around

42. CRT Monitor

43. Liquid Crystal Display - Monitor • It is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals (LCs). • LCs do not emit light directly .

44. LCD History • Liquid crystals were first discovered in 1888 by Austrian botanist Friedrich Reinitzer. • RCA, an American Laboratory made the first experimental LCD in (1968). • Manufacturers have been developing creative variations and improvements since on LCDs. • In 1997, manufactures began to offer full size LCD monitors as alternatives to CRT monitors. • Until recently, was only used on notebook computers and other portable devices.

45. LCD Technology • Used for displays in notebooks, small computers, pagers, phones and other instruments. • Uses a combination of fluorescent-based backlight, color filters, transistors, and liquid crystal to create and illuminate images. • Until recently, was only used on notebook computers and other portable devices.

46. From CRT to LCD • CRT • Bulky, heavy, use vacuum tube technology. • Using technology that was developed in the 19th century. • LCD • First LCD laptop monitors were very small due to manufacturing costs but now are available in a variety of sizes. • Light, sleek, energy-efficient, have sharp picture.

47. Liquid Crystal Display • There are mainly two categories of LCD. • The passive matrix LCD • The Active matrix LCD

48. Passive Matrix LCD • Monochrome passive-matrix LCDs were standard in most early laptops. • Still being used today for applications less demanding than laptops and TVs. • It consisting of a grid of horizontal and vertical wires. • At the intersection of each grid is an LCD element which constitutes a single pixel, either letting light through or blocking it. • Passive matrix LCD • Pixels arranged in a grid • Pixels are activated indirectly • Row and column are activated • Animation can be blurry

50. Passive Matrix Display