Output devicesUnit-2-Chap3

Printers Plotters Computer output micro film Monitor Voice response system Projector Headphone and headset

contents

Output is data that have been processed into useful information.

It can be displayed or viewed on a monitor , printed with a help of printer, or hear with the help of speakers or headsets.

There are two categories of output◦ Hard copy◦ Soft copy

introduction

The physical form of output is known as hard copy.

It refers to the recorded information copied from a computer onto a paper or some other durable surface such as microfilm

It is permanent form of output Highly portable Paper is one of the widely used output

media Eg: printouts, whether text or graphics from

printers

Hard copy

The electronic version of output, which usually resides in computer memory and/or on disk is soft copy.

Not permanent form of output It is usually displayed on the screen. It is not tangible, cannot be touched. Includes audio and videos that is generated

by the computer. Includes textual or graphical form of

information

Soft copy

A printer prints information and data from the computer onto paper.

Printer prints 80 or 132 columns of characters in each line and prints each single sheets or continuous roll of paper, depending upon the printer itself.

The quality of printer depends on how clear the print is produced, I,e resolution

Resolution is used to describe the sharpness and clarity of image.

Higher the resolution, better the image.

printers

For printers the resolution is measured in dpi

The more dpi, the better quality print will be.

Printers are divided into two basics categories: impact printers and non-impact printers.

Impact printers work by physically striking a head or needle against an ink-ribbon to make a mark on paper.

Includes drum printers, daisy wheel printers, dot-matrix printers.

Non-impact printers are opposite to impact printers.

Eg: laser printers and ink-jet printers. They use techniques other than physically

striking the page to transfer ink to page. Different printers

◦ Dot matrix◦ Daisy wheel◦ Drum printer◦ Ink-jet◦ Laser◦ HYDRA

Also known as wire matrix printer Uses oldest printing technique. Prints one character at a time It prints a characters and images as patterns

of dots. The speed of dot matrix measures in cpi Varies from 200 to 500 cps The print quality is determined by the

number of pins, varies from 9 to 24. More pins per inch, more the resolution is.

Dot matrix printer

The best dot matrix printer (24 pins) can produce near letter-quality-type image.

Are inexpensive and low operating costs. They print bi-directional, they print characters

in both directions. Drawback is

◦ prints the data only in black and white color.◦ Image printing is limited.

Used in cash registers, used in situations where copies are required and quality is not important.

The paper is pressed against the rubber-coated cylinder and is pulled forward as printing progresses.

The printer consists of an electro-magnetically driven print head, which is made up many pins.

The character is formed by moving the electro-magnetically driven head across the paper, which strikes the printer ribbon situated between the paper and printpin head.

How does it works?

As the head stamps onto the paper through the inked ribbon, a character is produced that is made up of these dots

The drawback of dot matrix printer is that pattern of dots make up each character is visible on the print produced by it, making it to look unprofessional.

The print head of this printer resembles a daisy flower with printing arms that appear like the petals of the flower.

Commonly called as letter quality printers. Produces high quality resolution output. Have speed upto 90cps

Daisy wheel printer

Also called as smart printers, because their bi-directional printing and built-in microprocessor control features.

This gives only alphanumeric output. They cannot print graphics Cannot change font unless the wheel is

changed physically. Slower because it takes time to rotate the

wheel for required letter on the wheel. Slower but expensive than dot matrix

printers

The dot matrix and daisy wheel printers are character and serial printers i.e. one character at time.

Drum printer is line printer, can print one line of data in single operation.

It is used because of its speed as it uses a special tractor-fed paper with pre-punched holes along each side.

Speed varies from 300 to 2000 lines per min with 96-160 characters on 15 inch line.

Drum printers

It is faster than character printers but very noisy, have limited font-capability , produce lower quality printouts.

Used for heavy printing applications. Drum printers with high speed are

expensive The strike of the hammer should be precise. A single miss of strike can create a wavy

and slightly blurred printing.

Commonly used at homes Places extremely small droplets of ink onto the

paper to create an image. Non-impact printer Uses serials of nozzles to spray the ink onto

the paper. Originally manufactured for monochrome

printing i.e. black and white only. Now it comes for cyan, magenta, yellow, black Combination is called CMYK

Inkjet printers

Ink-jet printers are costlier than dot-matrix printers, quality is much better.

Printers can print any shape of character, which user specify.

Can print different sized prints, graphics such as graphs, charts.

Resolution is 600dpi or more They print high quality text and graphics

printouts Affordable, medium pace of printing (6 pages

per min)

Provides highest quality text and images for personal computers today.

Very fast printer that operates on the same principle as photocopy machine.

Also known as page printers because they process ,store and print in terms of pages.

Produce sharp, crisp images of both text and graphics

Resolution of 300 to 2400 dpi They are quite, fast (4- 32 text only pages per min)

for microcomputers 200 pages for mainframes

Laser printer

Can print different font, sizes and styles. Expensive than other printer and difficult to

maintain. Costs depends on the combination of

paper , toner replacement and drum replacement.

Useful when there is high volume printing because of their speed.

The core component is photoconductive drum. A rotating beam causes the beam of laser to

sweep across the photoconductive drum Initially the beam of laser charges the

photoconductive drum positively. When charged drum is exposed to an optical

image through a beam of light to discharge, invisible image is formed.

At the point when laser strikes the surface of drum, it creates a dot of positive charge.

How it works?

These points are represented as black dots which will be printed on paper.

After this, printer coats the drum with a black powder called toner.

This toner is negatively charged hence it clings to those areas of drum which is positively charged.

When the powder is fixed onto the drum, it is rotated onto a paper through a pressure roller

This pressure roller transfers the toner to paper.

Finally the paper passes through a fuser and a pair of heated rollers.

As the paper passes through these rollers, the loose powder gets melted and gets fused with fibers of the paper

Then the paper is brought out of the printer

Working of laser printer

Hybrid document reproduction apparatus printer, known as all-in-one printer.

Consolidates multiple machines into one. Includes devices like printer, scanner,

photocopier and fax machine. Some come with memory card slots , have

inbuilt wireless capabilities Used by small organization because of its

small size, less space requirement and cost effectiveness

Hydra printer

They save power to great extent, as only one outlet of power is required to run various machine

Easy to install and easy to use because of GUI that helps user to understand its functions easily

Is a pen-based output device that is attached to computer for making vector graphics, i.e. images created by series of many straight lines

Used to draw high definition charts, graphs, blueprints, maps , circuit diagrams and other line based diagrams.

Similar to printer but draws lines using a pen.

Multicolor plotter uses pens with different inked pens.

plotters

Color plots can be made by using four pens and no need of human intervention to change them.

Plotter draws a crisper lines and graphics The lines drawn by these are continuous and

very accurate. It is considered as slow output device because

it requires excessive mechanical movement to plot.

It is unable to produce solid fills and shading.

They are expensive than printers and produce more number of printouts than standard printers.

Used mainly for Computer Aided Design CAD, Computer Aided manufacturing CAM applications such as printing out plans for houses or car parts.

Used in AUTOCAD programs to draw graphics output.

There are two types of plotters: drum plotter (where paper moves) and flatbed plotter (where paper is stationary)

The paper on which the design is to be printed is placed over the drum.

These plotters contain one or more pens that are mounted over the carriage which is horizontally placed over the drum.

The drum can rotate in both direction i.e. clockwise or anticlockwise direction under the control of plotting instructions sent by the computer.

The curves are created by drawing very short straight lines.

Drum plotter

Drum plotter

Consists stationary, horizontal plotting surface on which paper is fixed.

The pen is mounted on the carriage, which can move leftwards, rightwards, horizontally or vertically to draw lines.

Paper does not move Can work on any size of paper from A4 to very

big sized sheets . They are used to design aircrafts, buildings,

ships. Disadvantage is it is slow device and takes

hours together to complete complex drawing.

Flatbed plotter

Flatbed plotter

It is an extremely high-speed , low cost process, which records computer-generated information directly from the computer tape or cartridge to miniaturized microflim media.

The microflim product is in roll format, which form at a highly significant speed from that of the paper printer.

Traditional microflim is 16 mm wide, with a film image i.e. 1/24 of the size of the original document , often called as 24x

Computer output microflim

There are two ways to create a microfilm◦ Photographic process◦ Non-photographic process

Photographic process◦ Oldest method of creating microfilms.◦ Is a form of miniature photography, which uses a

microfilm camera for producing microfilms.◦ When the original documents are fed through a

microfilm camera, it captures the document into reduced size photo.

◦ Once a photographs are taken, the rolls of films are removed from the camera for further processing and development.

◦ The processed images can be rolled on film rolls or cut into sections and loaded to flat microfiche holders.

Creating a microfilm

Non-photographic process◦ User can entirely avoid the film developing process.◦ This process uses a monitor and the computer output is

read onto the magnetic tape.◦ After this , data is printed on microfilm machine directly

to a computer recorder.◦ It is possible to couple a microfilm machine directly to

a computer◦ Recorder can directly receive information from the

computer.◦ Recorder projects the computer information onto the

screen, a high speed camera photographs the displayed information.

Also known as visual display unit, is the most frequently used output device for producing soft copy output.

Is a TV-like display attached to computer on which the output can be displayed and viewed.

A monochrome screen uses only one color to display text on contrasting background.

Monitors are available in various size like 14,15,17,19 and 21 inches.

monitor

The size of the display is described based on two parameters◦ Aspect ratio◦ Screen size

Aspect ratio is the ratio of the width of the display screen to the height.

Computer display have an aspect ratio of 4:3

Screen size is normally measured diagonally , the distance from one corner to the opposite corner.

The image produced by monitors are not solid but created by the configurations of dots.

These dots are known as picture elements or pixels.

More no. of pixels the sharper the picture. The screen clarity depends on three basic qualities:◦ Resolution◦ Dot pitch◦ Refresh rate

Refers to the no. of pixels in horizontal and vertical directions on the screen

In medium resolution graphics, pixels are large

In high resolution graphics, pixels are small. The average display is 800 X 600 or 1024 x

768 pixels. The more dots or pixels available to create

the image , sharper it will be

resolution

It is the measurement of the diagonal distance between two like-colored pixels on the display screen.

Measured in millimeters , common values are .51mm, .31 mm, .28mm, .27mm, .26mm, .25 mm

The smaller the dot pitch, sharper the image when displayed on the screen.

Dot pitch

Refresh rate is the no. of times per second the pixels are recharged so that their glow remains bright.

Screen pixels are made up phosphor. An electron beam strikes the phosphor and causes

it to emit light, resulting the display of image. The refresh rate is measured in Hz , varies from

60-75Hz. The higher the refresh rate, more solid the images

looks on the screen. The pixels don’t flicker.

Refresh rate

Cathode ray tube

Most of the monitors use CRT, which are glass vacuum tubes into which electron gun emits a flow of electrons guided by an electrical field towards a screen covered in small phosphorescent elements.

A beam of electrons emitted by an electron gun, passes through focusing and deflection systems that direct the beam towards specified positions on the phosphor-coated screen.

The phosphor then emits a small spot of the light at each position contacted by the beam.

When the electron beam strikes the phosphor , it continues to glow briefly, this condition is known as persistence.

Cathode ray tube (CRT) monitors

The primary components of an electron gun are the heated metal cathode and control grid.

Heat is supplied to the grid by directing a current through a coil of wire called the filament.

This causes the electron to be “boiled off” the hot cathode surface.

The negatively charged electrons are then accelerated towards phosphor coating by a highly positive voltage.

Before reaching the phosphor coated screen, the electrons have to be passed through the monitor’s focusing elements.

Focusing can be accomplished either by electric or magnetic fields.

The deflection plates create a magnetic fields, which control the direction of the electron beam, guiding them to strike the proper position on the screen.

When the electron in the beams collide with the phosphor coating , their kinetic energy is absorbed by the phosphor.

Some of this energy is converted into heat while rest of the energy causes the phosphor to move up to the higher energy levels.

When these electrons begin to return to the ground state, they emit the light at certain frequencies that is colors.

As a result the Image which is seen on the screen is the combination of the electron light emission.

The electron gun is made up of a cathode, a negatively charged metallic electrode, and one or more anodes

The cathode emits the electrons attracted by anode.

The anode acts as a accelerator and concentrator for the electrons, forming a flow of electrons aimed at the screen

LCD screen have long been used on notebook computers but are also becoming popular as desktop monitor

LCD screen is collection of multiple layers. A fluorescent light source, known as backlight

makes up the rearmost layer. Light passes through the first of the two

polarising filters. The polarised light then passes through the

layers that contain thousand of liquid crystal blobs aligned in tiny containers called cells.

Liquid crystal display

These cells are aligned in row across the screen, one or more cells make up a pixel.

Electric leads around the edge of the LCD create an electric field that twists the crystal molecule which lines the light up with the second polarising filter and allow it to pass through.

LCD monitor

SIZE: LCD is light weight and compact, which saves desktop space when compared to CRT.

RESOLUTION: LCD is designed to work in a single resolution while CRT is designed for many resolutions.

PIXEL DENSITY: LCD ‘s pixel density is not tight as dot pitch of CRT

BRIGHTNESS: the illuminated phosphor of CRT is not nearly as bright as what can produced with its florescent backlight.

Difference between LCD and CRT

POWER CONSUMPTION: LCD consumes less power when compared to CRT and has low emission risk.

FLICKERS: with CRT monitors the goal is to get a faster refresh rate of at least 85Hz, but LCD monitors are designed to run much slower refresh rate.

PIXEL RESPONSE TIME: the time taken by a pixel to change its state is called pixel response time.

VIEWING ANGLE: CRT can be viewed almost at any angle, but LCD is best viewed ‘head on’. Even when viewing a LCD head on, narrow viewing angles can appear to have inconsistent color and brightness

VIEWING AREA: the viewing area of CRT is usually less than its advertised area, LCD monitors are measured exactly.

COST: prices for LCD screens is quite high but they are coming down. They are still much more costlier than CRT.

The voice response system has an audio-response device that produces audio outputs.

These are pre-recorded in computer system. Each sound has a unique code. Whenever an enquiry is sought from the

system, the computer responds in digital form which is sent to voice devices that unscramble the digital information and produces sound messages to the requesting computer

Voice response system

There are two basic approaches to get a computer to talk to the user.

The first is synthesis by analysis, in which the devices analyzes the input of an actual human voice speaking words, stores, process the spoken sounds and reproduces them when needed.

The second approach is synthesis by rule, in which the device applies a complex set of linguistic rules to create artificial speech.

The standard computer system can provide audio output with the addition of two components:◦ Speech synthesizer that does the speaking◦ Screen reading software that tells the synthesizer

what to say. The synthesizer can be a computer card inserted

into the computer or the software that works with the computer’s sound card.

Screen reader is a software program that allows the user to control the synthesizer so that he can text, which is displayed on the computer monitor, with the combinations of keystrokes.

Some screen review software use the standard computer keyboard keys, some numeric keypad and some special external keypads.

A visual impaired user can use a screen reader to read anything on the screen.

The screen reading software can even notify a user about various computer messages that ‘pop up’ on the monitor from time to time.

Used in places like airlines, bus terminals , banks.

Also called screen. They have allowed the world to share greater

information pertaining to culture, technology, medicine and community.

Used to project information from a computer on to a large screen, so that it can be simultaneously viewed by a large group of people.

Commonly used for classrooms training or conference or multimedia presentation with large audience

projector

LCD Projectors◦ LCD- Liquid Crystal Display◦ Used by most of the technology◦ Most of the LCD’s contains three separate LCD

glass panels, one for each red, green and blue components of the image signal being fed into the projector.

◦ As light passes through the LCD panels, individual pixels can be opened to allow light to pass or closed to block the light.

◦ This activity modulates the light and produces the image that is projected onto the screen.

Types of projectors

DLP projectors◦ DLP- Digital Light Processing◦ It uses single DMD (digital micro-mirror device)

chip that has thousands of tiny mirrors, each representing a single pixel.

◦ These mirrors tilt back and forth, directing the light either into the lens path to turn pixel ON, or away from the lens path to turn it OFF and create the image.

◦ It handles images extremely well.

Headphone is an audio device equipped with a pair of speakers attached to a head strap worn by the users.

Comes with CD, DVD players, mp3 players, ipod etc.

Comprise high quality speakers, light weight and very comfortable to wear.

They can easily connect to a computer via a mini stereo plug.

Allows only to hear

Headphones and headset

Headset is used when we want to user to speak.

It is combination of one or two speaker and the microphone with both the speaker and the microphone attached to head strap.

The speakers allows the person to hear the conversation and the microphone allows the user to communicate with person on the other end.