Input Output Devices

1. Input Output Devices

2. Input Devices is any hardware that takes input from the user.

3. Keyboard Enters data into computer by pressing one key at a time. Structure • Alphanumeric Keys : (A-Z),(0-9),(+,-,*,/) • Numeric Keypad : (0-9) on right hand side • Function Keys : F1 – F12 • Cursor Movement Keys : , , , 

4. How It Works? • When user press a key on keyboard, a tiny computer chip called Keyboard Controller, records that a key has been pressed. • Keyboard Controller places the code into a part of memory, called Keyboard Buffer, indicating the key has been pressed. • This code is called Key’s Scan Code. • Then keyboard sends an Interrupt request (special message to computer system in form of signals) to the system software when it receives a complete key stroke. • When system software receives an interrupt request, it evaluates the request to determine an appropriate response. • It passes the scan code to CPU then.

5. Keyboard Advantage • Faster in entering data than in positioning devices. • More reliable and produce fewer error than others. Disadvantage • Take a lot of time in practice to type quickly. • Typing speed is still very slow when compared with computer speed.

6. Mouse Mouse • Pointing device that translates the motion of mouse into signals.

7. Mechanical Mouse • Two rollers are placed attached to the mouse ball exactly at 90 degree to each other. • When mouse ball rotates, rollers also rotate. • On either side, there is an infrared emitter and on board chip read pulses (signal) from infrared sensors turns them into binary data. Drawback • Performance Degradation like ball takes dust and obstructs proper motion of shafts.

8. Optical Mouse

9. Optical Mouse • It uses small camera that takes 1500 pictures every second. • Light Emitting diode (LED) bounces off light of surface onto Complementary Metal Oxide Semiconductor (CMOS) Sensor. • CMOS sends each picture to digital to see how the image has changed since previous change. • The Digital Signal Processor operates at 18 million instructions per second. • By analyzing these images, processor determines the movement of cursor on screen.

10. Mouse Advantages • User friendly for computer beginner. • Easy and convenient to use GUI. • Selection and movement on screen is faster than using keyboard. Disadvantage • Not easy and convenient to input text. • Issuing command is slower than keyboard. • Needs practice. • Requires flat screen to operate.

11. Light Pen It is handheld input device that contains a light source or can detect light.

12. How it works? • Light Pen contains a lens that focuses light from computer monitor onto photoelectric cell. • As monitor’s electron beam passes through lens, cells emit an electric pulses. • Strengthen by an amplifier, pulse is sent as digital signal and computer determine location of pen on screen. • A touch of light pen’s control button tells computer to note this position for selection.

13. Pros and Cons Advantage • More direct and precise than mouse. • Convenient for application with limited desktop space. Disadvantage • It requires special designed monitors.

14. Touch Screen A monitor that has a touch sensitive panel on screen. You interact with the computer by touching areas of screen with fingers that acts as input device.

15. How it works? • Whenever user touches the screen, it disturbs the electrons emitted on screen and computer processor recognizes the area where the electron are being damaged and considers it as selection.

16. Pros and Cons Advantage • No extra peripherals are needed except monitor. • It allows easy access on commands. Disadvantage • It is not suitable for inputting a large amount of data. • Only items already on screen can be detected.

17. Scanners • An input device which translates paper document into an electronic format, which can be stored in computer. The input document can be text, picture, graphics. Types of Scanner • Flatbed scanners • Handheld scanner

18. Flatbed Scanner Like a copy machine, this consists of a box having a glass plate on the top, and a lid that cover the glass plate. WORKING The document is to be scanned is placed upside down on glass plate. Light source below plate moves horizontally from left to right. After scanning one line, light beam moves up a little and scan next line and process repeats for all lines.

19. Handheld Scanner It has set of LEDs placed in a small case, which conveniently held in hand during operation. WORKING To scan a document, a scanner is slowly dragged very steadily and carefully over document.

20. Output Devices Is any hardware component that can convey information to user.

21. Monitors It’s the most important output device • 2 common types • CRT • LCD • Featured by: • Refresh rate • Resolution • Visible screen size • Response time

22. CRT (Cathode Ray Tube) Monitors

23. CRT (Cathode Ray Tube) Monitors • CRT monitors a CRT is used as the picture of monitor. The screen is divided into rows and columns. Each cell of this screen is called Pixel. • This vacuum tube contains a negatively charged cathode which shoots electrons at the back of positively charged screen. • The screen is coated with phosphorous chemical. • When the electrons strike the back of the screen, phosphorous is excited and it provides a glow to individual pixels. • The distance between these pixels called as Dot Pitch and it is measured in millimeters. • The picture tube redraws the picture after a short interval. The number of times the electronic gun redraws the picture on screen is called as the Refresh Rate and it is measured in Hertz(Hz). • The number of pixels per unit area of the screen is called as Resolution. More the resolution, more clearer will be the picture.

24. ADVANTAGES OF CRT • Higher refresh rates. • Ability to adjust images. • Display full motion video better. • Significantly lower cost because the technology has matured. • Work better at multiple resolutions. • Modern version may include a sleep mode for energy efficiency. • Color fidelity, so essential for graphic artist, has not been matched by LCD’s. • Screen images viewed from side angle are as good as when viewed straight on.

25. DISADVANTAGES OF CRT • Larger size takes up more desk space, the bigger the screen, the bigger the foot print. • Heavy weight. • Heavier size limits easy and convenient movement. • Expands more energy and throws off heat.

26. Types of Flat Panel Displays

27. What is plasma? • Plasma is often called as forth state of matter other three being solid, liquid, gas. • Plasma is a distinct state of matter containing number of charged particle.

28. Construction • Plasma panels are two edge-sealed layers of glass separated by a thin layer of neon based gas. • There are horizontal conductors on one glass layer and vertical on the other glass layer.

29. How it works? • When the voltage is applied on the intersection of horizontal and vertical pair of conduction the gas at the intersection become ionized and emit a spot light. • All the conductor may have sustaining voltage applied to them that keeps the spot eliminated for several thousand times a second.

30. LED Panels • LED stands for light emitting diodes which are basically used in calculators, retail counters, large digital watches etc. • The first LED’s that were used deep red in color but other colors are also available now. • It is a type of emissive device.

31. LED Cont… • In this a matrix of diodes is arranged to form pixel positions in the display. • The picture definition is stored in the frame buffer. • As in scan lines refreshing of a CRT, information is read from the refresh buffer and converted to voltage levels that are applied to the diodes to produce light patterns on the display.

32. LCD Panels

33. How it works? • The screen used in computer devices is the LCD screen. The LCD screen produces images by aligning molecular crystals. • The LCD screen consists of twisted crystals. These crystals are present in twisted form like a spring and they untwist at varying angles when varying voltages are applied. • These crystals are packed in two screens. The front screen is transparent and back screen is reflective.

34. LCD Cont… • The back screen reflects light towards the front screen. The light gets deviated by these molecules. • This backed and deviated light produces images on front layer.

35. Advantages of LCD • Light weight. • Smaller foot print on desk leaving, freeing up work area on the user desk. • Flicker free screen. • More usable display area than on comparably sized CRTs. • Low frequency radiation is practically eliminated. • Easy adjustment storage and movement. • Efficient energy and they do not generate heat. • Good for basic web surfing. • Potentially less eyestrain due to reduced screen glare.

36. Disadvantage of LCD • Fragile screen may result in both screen and back light lamp damage if touched. Thus not recommended in environments where it may be handled roughly • Contrast ratio causes darkness to not be displayed true. Darkest area may be viewed as dark grey rather than black • Designed only for optimum resolution, can’t adjust images • The color accuracy of an LCD monitor does not match that of a CRT monitors. • These are more expensive than CRTs.

37. Printers • A printer is an output device that produces text and graphics on a physical medium such as paper. • Printed information is often called hard copy because the information exists physically and is a more permanent form of output than that presented on a VDU (Monitor). • Printers can be grouped into - impact and non-impact printers-

38. Impact Printers • An impact printer forms characters and graphics on a piece of paper by striking a mechanism against an ink ribbon that physically contacts the paper.

39. Non-Impact Printers • A non-impact printer forms characters and graphics on a piece of paper without actually striking the paper.

40. Characteristics of a printer • Speed of printer - The printing speed of a printer is usually expressed in pages per minute (ppm). • Resolution - Printer resolution is often expressed in dpi (dots per inch). The larger the number, the higher the resolution.

41. Advantages of printers • Information produced is permanent.

42. Disadvantages of printers • The time to get the printout is slow, when compared with display devices. • Paper is wasted for obtaining the output. • Printers are generally noisier than display devices.

43. Categories of printers

44. Dot Matrix Printes • The print head travels from side to side across the paper and is made up of numerous pins which are pushed out to form the shape of each character • The pins hit an ink ribbon against the paper so the characters are printed out. • The paper is usually continuous with holes down each side and perforations so the pages can be easily separated by tearing. • Because the pins make an impact against the paper the characters can be printed through several layers of self-carbonating paper to produce duplicate copies.

45. Suitable uses: • Limited to situations where duplicate copies are needed and the quality is not too important. • Typical uses might be in warehouses where duplicate copies of orders need to produce quickly and cheaply.

46. Advantages of Dot Matrix • The purchase cost is low and the running costs are very low. • They can print fairly quickly, particularly if you remember that multiple copies are being printed in one print run. • They are robust and can operate in harsh environments. • If several sheets of self-carbonating paper are placed into the printer then the impact will produce duplicate copies.

47. Disadvantages of Dot Matrix • The printing quality is low - these printers produce low to medium quality black and white printing and can only print low resolution graphics. • Because of the impact of the pins against the paper, these printers can be quite noisy.

48. Ink-Jet Printers • An ink-jet printer is a non-impact printer that forms characters and graphics by spraying tiny drops of liquid ink onto a piece of paper. Ink-jet printers can produce letter-quality text and graphics in both black-and-white and colors. • Some ink-jet printers can print photo-quality images on any type of paper. Printer resolution is measured in dots per inch (dpi). The speed of an ink-jet printer is measured in pages per minute (ppm).

49. How it works? • The print head contains tiny nozzles through which different colored inks can be sprayed onto the paper to form the characters or the graphic images. • The ink is forced out by heat or by tiny piezoelectric crystals which change shape when an electric current is applied across them.

50. Suitable uses • A popular choice for home use where small amounts of printing are done and photographic quality color printing is needed. • The speed over 150 ppm.