Various Output Devices:

Output Devices:

Output devices are hardware components, which are used to display or print the processed information. The processed data, presented to the user via the output devices could be text, graphics, audio or video. Common output devices include monitor, printer, plotter, speaker etc.

1. Printer

Printers   are  the  most  popular   output   devices   used  today   for  producing   hard-copy   output. The print quality of the printer is determined by the resolution of the printer. Resolution is measured in dots per inch (dpi). Printers with high resolution i.e. more dpi provide better image quality. Different   types  of printers  are described  below.

i. Dot Matrix Printer

Dot-matrix  printers  are character  printers  that print one character  at a time. They are the kind of impact printers that  form characters  and all kinds  of images as patterns  of dots. Since  dot matrix  printers  produce  printed  output  as patterns  of dots,  they  can print. any  shape  of character  that  a program  can describe.  They, therefore,  can print many special  characters,  different  sizes of print,  and also have the ability to print graphics  such as charts  and graphs. Dot-matrix  printers  are impact  printers  because  they print by hammering  the pins on the   inked ribbon  to leave ink impressions   on  a  paper.  Hence,   they  can  be  used  to  produce   multiple   copies   by  using  carbon  paper  or  Its equivalent.  Due to impact printing,  dot-matrix  printers  are noisy as compared  to non-Impact      printers. The speed of dot matrix printer lies between 200 and 600 characters per second (cps) an their resolution ranges from 72 to 360 dpi. Dot matrix printers normally come in two sizes – 80 column printer and 132 column printer.

ii. Drum Printers

They are  impact printers because they print by hammering on a paper and inked ribbon against the characters embossed on the drum. Due to impact printing, drum printers are noisy in operation and often use a cover to reduce the noise level. Printing speeds of drum printers are in the range of 300 to 2000 lines per minute.

iii. Inkjet Printers

Inkjet printers are character printers that form characters and all kind of images on a paper. They are non impact printers. The print head of an inkjet printer contains up to 64 tiny nozzles that  can be heated up selectively in a few microseconds by an integrated circuit resistor. When the resistor heats up, the ink near it vaporizes and is ejected through the nozzle making a dot on the paper placed in front of the print head. A high resolution  inkjet printer has as many as 64 nozzles within a height of 7mm providing print resolution of around 360 dots per inch.

iv. Laser Printers

Laser printer is a non-impact printer that creates latent image by means of a laser beam and then makes it visible by a toner, transfers and then fixes it on paper. The laser printer can print 5-24 pages of text per minute. The resolution of laser printers is 600 dpi . Some high model laser printers have resolution of 1200 dpi. The speed of laser printer is very high with a very low level of noise.

v. Chain/Band Printers

Chain/band printers are line printers that print one line at a time. It consists of a metallic chain/band on which all characters of the character set supported by the printer are embossed. A standard character set may have 48, 64 or 96 characters. The printer has a set of hammers mounted in front of the chain/band in a manner that an inked ribbon and paper can be placed between the hammers and chain/band. The total number of hammers is equal to the total number of print positions. Therefore, a printer supporting 132 print positions will have 132 hammers.

vi. Thermal Printer

In this printer, heat elements produce dot-matrix images on heat sensitive paper. The output of thermal printer fades quality when exposed to light.

vii. Electrostatic printer

Electrostatic printers are devices in which the parts of paper which are to be printed are electrostatically charged and attract a fine dust which is then focused to the paper by the application of heat.

2. Plotter

Dot  matrix,  inkjet,  and  laser  printers  are  capable  of producing   graphics  output.  However, many engineering  design  applications  like architectural  plan of a building,  design  of mechanical  components  of an aircraft  or a car, etc., often require  high-quality,  perfectly-proportioned    graphic  output  on large sheets. The various types  of  printers  discussed   above  are  not  suitable  for  meeting  this  output  requirement   of  such  applications.   A special  type  of  output  device,  called  plotters,   is used  for  this  purpose. Plotters are an ideal output device for architects, engineers, city planners and others who need to routinely generate high precision, hard copy, graphic output of widely varying sizes. They are mainly used for drawings in AUTOCAD (computer assisted drafting), Computer Aided Design (CAD) and Computer Aided Manufacturing (CAM) applications. Plotters are of two types:

i. Drum plotter

ii. Flatbed plotter

i. Drum Plotter

In  a drum  plotter,  the  paper  on which  the  design  is to  be  made  is placed  over  a drum  that  can  rotate  in both clockwise  and anti-clockwise.  directions  to produce  vertical  motion,  The mechanism  also  consists  of one or more penholders   mounted  perpendicular    to the  drum  s surface.  The  pen(s) clamped   in the  holder(s)  can  move  left to right or right to left to produce  horizontal  motion.  A graph-plotting   program  controls  the movements  of the drum and pens). That is, under  computer  control,  the drum and pen(s) move simultaneously   to draw designs  and graphs on the sheet placed on the drum. The plotter  can also annotate  the designs  and graphs  so drawn  by using the pen to draw characters  of various  sizes.  Since each  pen is program  selectable,  pens having  ink of different  colors  can be mounted  in different  holders  to produce  multi-colored  designs.

ii. Flatbed Plotter

A  flatbed   plotter   plots   a design   or  graph   on  a  sheet   of  paper   spread   and  fixed   over  a rectangular     flatbed   table.   In his  type   of  plotter,    normally     the   paper   does   not   move    and   the   pen   holding    mechanism     provides    all  types   of motions    necessary    to  draw   complex    designs    and  graphs.    That   is,  under   computer    control,   the  pen(s)   move   in the required   manner   to draw  designs   and  graphs   on  the  sheet   placed   on the  flatbed   table.   The  plotter   can  also  annotate the  designs   and  graphs   so  drawn   by  using   the  pen  to  draw   characters     of  various    sizes.   Provision    is also  there   to mount   more  than  one  pen  in the  pen(s) holding      mechanism.     Since   each  pen  is program    selectable,    pens  having   ink of different    colors   can  be mounted    in different    holders   to  produce   multi-colored     designs.   The  plot  size  is restricted by  the  area  of  the  bed.  Some   may   be  as  small   as  A4  size  (8″x  11″  page)   while   some   very   large   beds   used   in the design   of cars,  ships,   aircrafts,    buildings,    highways,    etc.  can  be  up to 20  ft. by  50 ft.  Some  plotters   can  also  etch  on plastic   or metal   plates.   in this  case,  the  plastic   or metal   sheet   is spread   on  the  bed  and  the  drawing   pen  has  a sharp- edged   needle.

3. Screen Image Projector

Screen   image   projector    is an output   device   used  to  project   information     from  a computer    on  a large  screen   (such   as a   cloth    screen    or   wall)    so  that   a  group    of   people    can   view    it  simultaneously.       It  is  very   useful    for   making presentations     to a group   of people   with  direct   use  of a computer. Before   such   an  output   device   was  available,    the  contents    of  a presentation     were   prepared    using   a computer.    The presentation     material    was  then   printed    on  a  printer   and  the  printout    was   next   reproduced     on  overhead    projector transparency     sheets   by  using  a copier   machine.    Finally,   the  presentation     was  made  by  using  an  overhead    projector. Special   marker   pens  had  to  be  used  for  marking    certain   portions    of  the  contents    on  the  transparency     sheets   during the presentation,                                .

4. Monitor

Commonly known as monitor, the visual display unit (VDU) is a very important output device. It is made up of tiny dots called pixels, which are arranged in a rectangular form. The resolution of the monitor, which is nothing but the sharpness of an image, depends upon these pixels. Inside the monitor, there is wither a cathode ray tube (CRT) or liquid crystal display (LCD) . Therefore, monitors are either CRT or LCD type.

Based on the quality of resolution, monitors are classified into the following six categories:

i. Colour graphic adapter (CGA)

It displays both text and graphics with graphics of resolution 320X250 (no. of pixels). Its text resolution s of fair quality.

ii. Monochrome display adapter (MAD)

It can display only text with good quality resolution.

iii. Enhanced graphic adapter (EGA)

It can display both text and enhanced graphics with graphics resolution of 640X350. Its text resolution is also of good quality.

iv. Hercules graphics adapter (HGA)

It can display both text and mono graphics with graphics resolution of 320X200. Its text resolution is of fair quality.

v. Video graphics adapter (VGA)

It can display both text and video graphics with graphics resolution of 640X480. Its text resolution is much better than all above discussed types.

vi. Super VGA (SVGA)

This is the most popularly used monitor, which can display both text and video graphics with graphics while a monochrome monitor displays it in single colour

The clarity of image on the computer screen depends on three factor:

i. Resolution of screen

The number of pixels in horizontal and vertical direction. More the number of pixels, the sharper is the image. The common resolution screen is 800X600 and 1024X768

ii. Dot pitch

The diagonal distance between two coloured pixels on a display screen.

iii. Refresh Rate

The number of times per second the pixels are recharged so that their glow remains bright.

Visual Display Terminal (VDA) A monitor and keyboard together are known as Visual Display Terminal.

5. Computer Output Microfilm (COM)

COM is a technique to produce output on a microfilm media (microfilm reel or microfiche card). A microfiche card is a 4by 6 inch film sheet, which can store several hundred pages. COM is used for storing output in banking and insurance applications, medical X rays etc.

6. Voice Response System

Just as  a  speech    recognition      system    allows    a  user   to  talk   to  a  computer,     a  voice    response     system    enables    a computer  to  talk   to   a     A  voice   response    system    has  an   audio-response       device   that   produces    audio   output. Obviously,                  the    output     is   temporary,   soft-copy     output.     Voice    response     systems     are   of   two    types    –   voice reproduction    system   and speech   synthesizer.     They   are  described    below.

Voice Reproduction  System

A  voice   reproduction      system   produces     audio   output   by  selecting    an  appropriate     audio   output   from   a  set  of  pre- recorded         audio   responses.     The   set  of  pre-recorded      audio    responses     may   include    words,    phrases,    or  sentences spoken    by  human    beings,    music    or  alarms    generated     by  musical    instruments,     or  any   other   type   of  sound., The actual    analog    recordings     of  the   pre-recorded      sounds    are   converted     into   digital    data   first    and   then   stored   on  a computer’s     disk,   or  in  its  memory    chip   permanently.     When   audio   output   is to  be  produced.         the  computer    selects the  appropriate     sound   from  the  set  of  pre-recorded     sounds.   The  selected    sound   is converted and  then  routed   to a speaker   to  produce   the  audio   output.   back   into  analog   form and  then  routed   to a speaker   to  produce   the  audio   output.

Voice   reproduction     systems   are  very  useful   in a wide  range   of applications.     Their   uses  include:

i. Audio help    for   guiding     how    to   operate     a   system.     For   example,      banking     industry     uses    voice reproduction systems    in  automatic     teller   machines    to  provide    systematic     guidance    to  customers     on how  to transact   with  the  bank  by  using  an  ATM.

ii. Automatic answering     machines.     For   example,     telephone     enquiries     for   new   telephone     numbers     in place   of  old  numbers,     or  vacancy    status   of  a  flight   or  train   is  often   taken   care   of  by  an  automatic answering         machine.

iii.  Video games   are  made   exciting    and   interesting     by  playing    an  event-based      sound   from   a  set  of  pre- recorded sounds.

iv. Talking alarm   clocks.   For  example,    every   hour  the  clock   speaks   out  what   is the  time   by  selecting    the appropriate  voice   message    corresponding     to that  hour  from  the  set  of  pre-recorded     voice   messages:    In addition,    the  clock   may  speak   “its  time  to wake   up”  at the  time  set  for  alarm.

v. Talking toys  and  home   appliances    also  use  a voice   reproduction     system.

vi. Often personal    computers    with  audio   facility   are  used  for  automated     multimedia     presentations     during exhibitions.

Speech Synthesizer

A speech  synthesizer  converts  text  information  into spoken  sentences.  To produce  speech,  these  devices  combine basic   sound   units  called  phonemes.    From  a  given   text   information,    sequence   of  words  are  combined   into phonemes,  amplified,  and output  through  a speaker  attached  to the system.  Speech  synthesizers   are still  in their infancy  because  currently  they  can  produce  only  limited  unique  sounds  with  only  limited  vocal  inflections  and phrasing.  However,  they are very useful  in a wide  range of applications.   Their uses include:

i. For reading  out  text  information   to  blind  persons.   For example,  a recently  published   book  may  be scanned  using a scanner,  converted  into text using OCR software,  and read out to blind persons  using a speech  synthesizer.  This allows  blind persons  to know the latest  information  published  in a book as soon as it is printed.

ii. For allowing  those  persons  who  cannot  speak,  to  communicate   effectively.   For example,  a person with  this type  of disability   simply  types  the  information   and  the  speech  synthesizer  converts  it into spoken  words.

iii. For translation   systems  that  convert  an  entered  text  into  spoken  words  in a selected  language.  For example,  a foreigner  coming  to  India may  enter a text he/she  wants to communicate  to an Indian, and the speech synthesizer  converts  it into spoken  words of the selected  Indian language.