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Lecture 6

  1. M. Raihan Email:
  2. Output Devices Part-2
  3. Types of LCD 06-Aug-17 3 LCD element form the pixels in LCD screen.  The LCD elements are switched on and off by different techniques to display an image on the screen.  There are two types of LCD screens: passive-matrix and active-matrix.
  4. Passive Matrix LCD 06-Aug-17 4 Each LCD element in placed between two electrodes and arranged in rows and columns in X-Y matrix format. The bottom electrodes of each row elements are connected together and the top electrodes of each column elements are connected together. The elements in a row are controlled by a row-driver and the elements in a column by a column-driver. Activating a row-driver and a column driver results in a current through a specific LCD element.
  5. Passive Matrix LCD (continue) 06-Aug-17 5  An image is created on the screen by activating a row driver and activating the column drivers in sequence like scanning a line.  The drawback of this simple design is that if a current through a cell is large, then adjacent elements, often those in the same column, also get affected and this results in ghosting.  If the current through an element is too weak, the elements don’t switch on and off very quickly which results in poor contrast and losing detail in moving images.  The dual scan technique improves the performance.
  6. Active matrix LCD 06-Aug-17 6 AMLCDs use one transistor driver for each LCD element. The transistors are arranged in the matrix format.  It allows the current through individual elements to be switched on and off quickly with sufficient current to get good contrast. The electrodes for active matrix panels are also made of the transparent material. The transistor drivers are fabricated right on the panel substrate, using thin film technology. As the transistors are able to switch the elements more rapidly than the passive matrix scheme and adjacent elements are not affected, large currents can be used without ghosting. The higher currents provide higher contrast and sharper and brighter images.
  7. Techniques for solving Viewing Angle Problem 06-Aug-17 7 The simplest technique uses a diffusing film on the top layer of the display. It causes the light traveling in specific direction to divert in different directions. In the second technique, instead of passing the current from top through the liquid crystal to bottom The electrodes are arranged in such a way that the current flows from side to side. It causes the molecules to align in horizontal direction, which results in wider viewing angles. In the third technique, each liquid crystal element is divided into multiple regions The substrate is pre-tilt in different directions so that the molecules align in different directions. It causes the light to emerge different directions, which results in wider viewing angles.
  8. Printer 06-Aug-17 8 Printers are the primary output devices used to prepare permanent documents for human use.  Printing output is called hard copy output. There are two types of printers − Impact Printers Non-Impact Printers Three different types of printers are in use today. They are- Dot-Matrix printer Ink-Jet printer and Laser-Jet printer
  9. Impact Printers 06-Aug-17 9 Impact printers print the characters by striking them on the ribbon, which is then pressed on the paper. These printers are of two types- Character printers (Dot Matrix Printer(DMP), Daisy Wheel) Line printers (Drum Printer, Chain Printer) Characteristics of Impact Printers- Very low consumable costs Very noisy Useful for bulk printing due to low cost There is physical contact with the paper to produce an image
  10. Non-impact Printers 06-Aug-17 10 Non-impact printers print the characters without using the ribbon. These printers print a complete page at a time, thus they are also called as Page Printers. These printers are of two types- Laser Printers Inkjet Printers Characteristics of Non-impact Printers- Faster than impact printers They are not noisy High quality
  11. Dot-Matrix Printer 06-Aug-17 11 A dot matrix printer has a printer head, which contains an array of 7, 9, 14, 18 or 24 pins arranged in a vertical column.  While printing, the pins forming one column of dot pattern of the character matrix project from the print head and press the inked ribbon against a plain paper.  Only one column of dot pattern of character matrix is printed at a time.  As the print head moves across the line, series of vertical dot patterns representing the character are retrieved from the printer’s internal memory and printed.
  12. Dot-Matrix Printer (continue) 06-Aug-17 12
  13. Dot-Matrix Printer (continue) 06-Aug-17 13 The print head is mounted on a carriage and moved back and forth along a rail by a belt.  The dot-matrix printers receive stream of character from the computer, convert to series of column of dot patterns and print.  The print quality depends on the number of pins provided on the print head.  24-pin printers produce high quality printouts.
  14. Ink-Jet Printer 06-Aug-17 14 The operation of the ink-jet printer is similar to that of a dot-matrix printer. Ink-jet printers have tiny nozzles on the print head that spray ionized ink onto a plain paper in the pattern to form the characters and images. The print head cartridge has 50 or more nozzles and is mounted on a carriage that is carried back and forth along a rail by a belt that is driven by a motor. The print head is connected to the electronic control unit through a long, flat, flexible print head cable.
  15. Ink-Jet Printer (continue) 06-Aug-17 15
  16. Ink-Jet Printer (continue) 06-Aug-17 16  When the PC sends a character to be printed, a series of vertical dot patterns representing the character is retrieved from the printer’s internal memory and sent through a series of print nozzle driver circuits. The driver amplifies the signals into the fast, high-energy pulses needed to fire minute droplets of ink from each nozzle. As the pulse reaches the nozzle, it creates an intense surge of heat that literally creates a bubble. The nozzle cools down in a fraction of a second and becomes ready for another pulse. The print quality of ink-jet printer depends on the quality of paper also. They require periodic maintenance, as they use liquid ink. The ink may dry in the nozzles and clog them.
  17. Laser-jet printer 06-Aug-17 17 Laser-jet printers function like a plain paper copier. While a bright light source is used in a plain paper copier for generating the images, a laser is used in laser printer. The laser printer creates an electrostatic image of a text or graphics page on a photosensitive drum using the laser beam. When the drum is moved across the toner, it attracts the toner particles and deposits on the electrostatic image.
  18. Laser-jet printer (continue) 06-Aug-17 18
  19. Laser-jet printer (continue) 06-Aug-17 19 The drum is then pressed against a plain paper to transfer the image on to the paper. The paper is then passed between hot rollers to fuse the toner particles into the paper. The area of the drum is the same as that of the paper onto which the image is transferred. Every point on the drum corresponds to a point on the paper. Laser printers are very popular today because of their print quality and relatively low running cost.  The print quality is less sensitive to paper quality.
  20. Laser-jet printer (continue) 06-Aug-17 20  Laser printers get all the information about the page to be printed and keep them in their internal memory before starting the printing.  The amount of memory present in a printer determines its capability.
  21. Daisy Wheel Printer 06-Aug-17 21 Head is lying on a wheel and pins corresponding to characters are like petals of Daisy (flower) which is why it is called Daisy Wheel Printer. These printers are generally used for word-processing in offices that require a few letters to be sent here and there with very nice quality. Advantages: More reliable than Dot Matrix Printer (DMP) Better quality Fonts of character can be easily changed Disadvantages: Slower than DMP Noisy More expensive than DMP
  22. Daisy Wheel Printer(continue) 06-Aug-17 22
  23. Line Printers 06-Aug-17 23 The line printer is an impact printer that prints one entire line of text at a time. It is mostly associated with unit record equipment and the early days of digital computing, but the technology is still in use. Line printers are of two types −  Drum Printer  Chain Printer
  24. Drum Printer 06-Aug-17 24 This printer is like a drum in shape hence it is called drum printer. The surface of the drum is divided into a number of tracks. Total tracks are equal to the size of the paper, i.e. for a paper width of 132 characters, drum will have 132 tracks. Different character sets available in the market are 48 character set, 64 and 96 characters set. Drum printers are fast in speed and can print 300 to 2000 lines per minute. Advantages: Very high speed Disadvantages: Very expensive Characters fonts cannot be changed
  25. Drum Printer (continue) 06-Aug-17 25
  26. Chain Printer 06-Aug-17 26 In this printer, a chain of character sets is used, hence it is called Chain Printer. A standard character set may have 48, 64, or 96 characters. Advantages: Character fonts can easily be changed. Different languages can be used with the same printer. Disadvantages: Noisy
  27. Chain Printer (continue) 06-Aug-17 27
  28. Thank You 06-Aug-17 28