INPUT DEVICES - · PDF fileWith this new ability, these devices came to be know as...

_______________________________________________________COMPUTER FUNDAMENTAL |2010

Prepared By, Mr. H.H.Parmar & R.P.Madhu(9662140014) Page No.: 1

COMPUTER PERIPHERALS

A computer peripheral is a device which can attach with computer to accomplish some

specific functions.

A computer system can be useful, only when it is able to communicate with external

environment. Peripheral devices provide the means of communication between the computer and

the outer world. Input Output (I/O) devices are a type of peripheral devices.

INPUT DEVICES: • An Input device is an electromechanical device, which accepts data from the outside world,

and translates them into a form, which the computer can interpret.

• We can broadly classify them into the following categories:

1. Keyboard

2. Point-and-Draw devices

3. Data scanning devices

Functioning of above devices & its applications are described below.

1 KEYBOARD:

• Keyboard is the most commonly used input device.

• Keyboard is quite similar to typewriter.

• In Keyboard there are many additional keys that handle control functions.

• They allow data entry into a computer system by pressing a set of keys (labeled button) which

are mounted on a keyboard.

• The most popular keyboard used today is the QWERTY keyboard.

• Keyboard is connected to the computer using wire or wireless technology.

• Generally today’s keyboard contains 104 keys & some keyboard contains 107 to 110 keys

which is some time called multimedia keyboard.

2 POINT-AND-DRAW DEVICES:

� Interaction with computer was initially restricted mainly to text mode. However, it was soon

realized that interacting with computer in text-mode is cumbersome and time-consuming.

Hence, a new type of interface, called Graphical User Interface (GUI) was devised for

interacting with computers.



� A GUI provides a screen full of graphic icons or menus to the user, and allows the user to make

a rapid selection from the displayed icons or menus to give instruction to the computer. For

which we required such input device which used to rapidly point to and select a particular

graphic icon or menu items from the multiple options displayed on the screen. Hence, research

efforts to find a suitable input device for GUI gave birth to several input devices as below :

2.1 Mouse 2.2 Trackball

2.3 Joystick 2.4 Light pen

2.5 Touch screen

Later it was realized that many of these devices like mouse and light pen, could also be

very effectively used to create graphic elements on the screen, such as lines, curves, freehand

shapes etc. With this new ability, these devices came to be know as point-and-draw devices

2.1 MOUSE:-

� Mouse is the most popular point-and-draw device.

� It can become a must-have input device on personal computers which have a GUI based user

interface.

� A mouse is a small hand-held device, which can comfortably fit in a user’s palm.

� When a user moves the mouse across a flat surface, the graphics cursor moves on the screen of

the visual display terminal in the direction of the mouse’s movement.

� The graphic cursor, which is used to point and draw, is displayed on the screen as an arrow.

� Depending on the application, the text and graphics cursor may be displayed on the screen at

the same time.

� Moving the graphics cursor at a menu item or an icon by moving the mouse is said to point to

that menu item or icon. With the click of the mouse’s button, the system can then be notified of

this choice. With the proper software, a mouse can also be used to draw pictures on the screen

and edit text.

� We can broadly classify mouse mainly in three types

1) Ball mouse (use rubber ball mechanism)

2) Optical Mouse (use optical technology-LED(Light Emulating Diodes) to illuminate

surface)

3) Laser Mouse (use laser technology)

Mouse is connected with computer through wire or wireless. Today’s mouse also contains scroll

wheel for scrolling screen up & down and other additional buttons for easy navigation.



2.2 TRACK BALL:-

� A trackball is a pointing device, similar to a mouse.

� The ball which is placed in the base of the mouse is placed on the top along with the buttons, in

case of track ball.

� To move the graphics cursor around the screen, the ball is rolled with the fingers. Because the

whole device is not moved for moving the graphics cursor, a trackball required less space than

a mouse for operation.

� Trackballs built into the keyboard are commonly used in laptop (notebook) computers.

Because the ball is fixed on the top, some people find it helpful to think of a trackball as an

upside-down mouse.

� A trackball comes in various shapes and forms with the same functionality. The three

commonly used shapes are a) ball, b) button and c) square. A trackball is a pointing device,

similar to a mouse.

� The ball which is placed in the base of the mouse is placed on the top along with the buttons, in

case of track ball.

� To move the graphics cursor around the screen, the ball is rolled with the fingers. Because the

whole device is not moved for moving the graphics cursor, a trackball required less space than

a mouse for operation.

� Trackballs built into the keyboard are commonly used in laptop (notebook) computers.

Because the ball is fixed on the top, some people find it helpful to think of a trackball as an

upside-down mouse.

a) Ball : In case of ball, the ball is rolled with the help of fingers to move the graphics cursor

as shown in picture.

b) Button : In case of a button, the button is pushed with a finger in the desired direction

of the graphics cursor movement.

c) Square: In case of square the finger is placed on top of it, and moved in the desired

direction of the graphics cursor movement.

2.3 JOYSTICK:- � A Joystick is a pointing device, which works on the same principle as a trackball.

� Spherical ball moves in a socket, on the stand. To make the movement of the ball (spherical

ball) easier a stick mounted on it.

� Instead of using the fingers in case of trackball, the user of a joystick moves the spherical

ball with the help of the stick with his/her hand.

� The stick can be moved forward or backward, left or right, to move and position the

graphics cursor at the desired position.



� Potentiometers are used to sense the movements. On most joysticks, a button on the top is

provided to select the option, which is currently pointed to by the cursor.

� The button is clicked to make this selection. Typical uses of a joystick include video games,

flight simulators, training simulators, and for controlling industrial robots.

2.4 LIGHT PEN:-

� This is a pen shaped device allowing natural movement on the screen.

� The pen contains the light receptor and is activated by pressing the pen against the display

screen.

� Receptor is the scanning beam which helps in locating the pen’s position. Suitable system

software is provided to initiate necessary action when we locate an area on the display

surface with the help of the light pen.

� It allows the user to point to displayed objects, or draw on the screen, in a similar way to a

touch screen but with greater positional accuracy.

� A light pen can work with any CRT-based monitor, but not with LCD screens, projectors or

other display devices.

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2.5 TOUCH SCREEN:-

� Touch screen is the most simple, intuitive and easiest to learn of all input devices.

� A touch screen enables the used to choose from available options by simply touching with

their finger the desired icon or menu item displayed on the computer’s screen.

� Touch screen are the most preferred human-computer interface devices used in

information kiosks.

� An information kiosk is an unattended system having no keyboard or mouse, which is used

to store information of public interest and allow common people to access the stored

information as per their requirement.

� It’s software provide all types of option needed to input data or searching information.

Main application of touch screen in information kiosks may be located

1) In bank ATM

2) At an airport or railway station to provide information

to passengers

3) At public utility services like Electricity office

to know consumer its account status & other

information. In large museums or zoos to guide the visitors

See the images of Touch Screen ----�



3 Data scanning Devices:

� Data scanning devices are input devices, which are used for direct data entry into the computer

system from source documents.

� Some of the data scanning devices are also capable of recognizing marks or characters. Data

scanning devices typically have the following characteristics

1) They eliminate some of the duplication of human effort required to get data into the

computer. Human beings do not have to manually enter the data.

2) The reduction in human intervention improved data accuracy

3) Speedily available data in electronic form

4) Since scanners are direct data entry devices, they demand high quality of input

documents. Documents that are poorly typed or have strikeovers or erasures are

normally rejected or not recognizing well.

5) With these devices, form design and ink specification may become more critical than is

the case when people key in the data from the forms.

� Data scanning devices are of many types as below:

3.1 Image scanner

3.2 OCR (Optical Character Recognition)

3.3 OMR (Optical Mark Reader)

3.4 MICR (Magnetic-Inc Character Recognition)

3.5 OBR (Optical Bar-code Reader)

3.1 IMAGE SCANNER:-

� An image scanner is an input device, which translates paper documents, into an electronic

format, which can be stores in a computer.

� The input documents may be types text, pictures, graphics or even hand written material.

� This input device has been found very useful in preserving paper documents in electronic form.

� The copy of a document stored in a computer in this manner will never deteriorate in quality

or become yellow with age, and can be displayed or printed, whenever desired.

� If the computer in which the scanned documents is stored has the right kind of software (called

image-processing software), the stored images can be altered and manipulated in interesting

ways.

� Image scanners come in various shapes and sizes. The two commonly used types are:

1) Flatbed Scanner

2) Hand-held Scanner

Flatbed Scanner :

� Flatbed scanner is like a copy machine, which consists of a box having a glass plate on its

top and a lid that covers the glass plate.

� The document to be scanned is placed upside down on the glass plate.

� The light source is situated below the glass plate and moves horizontally from left to right

when activated.



� After scanning one line, the light beam moves up a little and scans the next line. The process

is repeated for all the lines. It takes about 20 seconds to scan a document of size 21 cm x 28

cm.

Hand-held Scanner:

� A hand-held scanner has a set of LED encased in a small case, which can be conveniently

held in hand during operation.

� To scan a document, the scanner is slowly dragged from one end of the documents to its

other end, with its light on.

� The scanner has to be dragged very steadily and carefully over the document, otherwise the

conversion of the document into its equivalent bit map will not be correct. Due to this

reason, hand-held scanners are used only in cases where high accuracy is not needed.

� They are also used when the volume of documents to be scanned is low. They are also much

cheaper as compared to flatbed scanners.

Flatbed Scanner Hand held Scanner

3.2 OCR (Optical Character Recognition devices):-

When image scanners are used for inputting text documents they have the following two

limitations:

1) The input document is stored as an image, instead of text, it is not possible to do any

word processing of the document (the computer cannot interpret the stored document

as letters, numbers and special characters.

2) The storage required for storing the document as an image is much more than that

required for storing the same document as text (about 10 to 15 times more storage

required for image).

� The OCR technology is used to overcome these limitations. In this case, the scanner is

equipped with character recognition software (called OCR software), which converts the bit

map images of character to equivalent ASCII codes. That is, the scanner first create the bit

map image of the document, and then the OCR software translates the array of grid points

into ASCII text, which the computer can interpret as letters, numbers and special

characters.

� OCR software is extremely complex, because it is difficult to make a computer recognize an

unlimited number of typefaces and fonts. Hence, these software are designed to recognize

texts, which are written using standard type fonts (called OCR fonts). Two such standard

fonts are OCR-A (American standard) and OCR-B (European standard). Note that, if the



document contains italics or bold face letters, or fonts other than that for which the OCR

software has been designed, the OCR software will not work effectively.

3.3 OMR (Optical Mark Reader):-

� OMR is the scanning of paper to detect the presence or absence of a mark in a

predetermined position.

� These scanners are capable of recognizing a pre-specified type of mark made by pencil or

pen. Many students might have appeared in objective type tests, in which they had to mark

their answers to questions on a special pre-printed answer sheet by darkening a small

square, circular or oval shaped box by a pencil.

� In OCR to indicate their correct choice out of the various given option. These answer sheets

are directly fed to a computer for grading with the use of an optical mark reader.

Question paper

1. The binary equivalent of decimal 4 is:

a) 101

b) 111

c) 001

d) 100

2. The full form of CPU is:

a) Cursor Positioning Unit

b) Central Power Unit

c) Central Processing Unit

d) None of the above

Answer Sheet

1.

a b c d

2.

a b c d

3.4 MICR (Magnetic Ink Character Recognition):-

� MICR, a character recognition technology adopted mainly by the banking industry to

facilitate the processing of the large volume of cheques being handled every day.

� The process was demonstrated to the American Bankers Association in July 1956, and it

was almost universally employed by 1963. Banks, which employ MICR technology, use a

special type of cheque. The bank’s identification code (name, branch etc.), account number,

and the cheque number are pre-printed (encoded) by using characters from a special

character set on all these cheques with a special ink, which contains magnetizable particles

of iron oxide, before the cheques are given to the customer for use.

� When a customer presents a filled-in cheque at a bank, a bank employee manually enters

the amount written on the cheque, in the lower right corner of the cheque by using an MICR

inscriber, which prints the amount with the magnetic ink.

� The date of the transaction is automatically recorded for all cheques processed that day.

This cheque is then processed by using an MICR reader-sorter, which can recognize

magnetic ink characters. The MICR reader-sorter reads the data on the cheques, and sorts

the cheques for distribution to other banks or for further processing.

� The most commonly used character set by MICR devices is known as E13B font, which

consists of the numeral 0 to 9 and four special characters as shown below:

� Coded data in the form of these fonts are transferred from cheques to the computer by an

MICR reader-sorter. As the cheques enter the reading unit, they pass through a magnetic



field, which causes the particles in the ink to become magnetized. Read heads then interpret

these characters by examining their shapes. The sorter is used to sort the cheques into

different pockets, according to their identification code numbers.

� MICR technology speeds up data input for the banking industry, because cheques can be

directly fed into the input device, and automatically processed thereafter. Besides enabling

faster processing of cheques, this technology also ensures accuracy of data entry, because

most of the information is pre-printed on the cheque, and is directly fed to the computer.

� However, MICR has not been adopted by other industries, because the currently supported

character set has only 14 symbols. No alphabetic characters are available.

3.5 OBR (Optical Bar-code Reader):-

� Data coded in the form of small lines (bars) are known as bar codes.

� Bar codes represent alphanumeric data by a combination of adjacent vertical lines by

varying their width and the spacing between them.

� They are particularly used for unique identification of all types of goods, postal packages,

badges, tags etc.

� A optical bar-code reader is a device, which is used for reading (decoding) bar-coded data.

It may be a hand-held scanner or may be embedded in a stationary scanner.

� It scans a bar-coded image, and coverts it into an alphanumeric value, which is then fed to

the computer to which the bar-code reader is connected, just as though the alphanumeric

value had been typed on a keyboard.

� A OBR uses a laser-beam scanning technology. The laser beam is stroked across the pattern

of bars of a bar code. Different bar codes, having different patterns of bars, reflect the beam

in different ways, which is sensed by a light-sensitive detector. Reflected light patterns are

converted into electrical pulses, and then transmitted to recognition login circuits, which

convert it into an alphanumeric value.

Hand-held OBR

Example of Bar-code

� Just as there are a variety of internal bit encoding systems, there are a variety of bar-coding

systems. The most widely known bar-coding system is the Universal Product Code (UPC code),

which now appears on almost all retail packages in USA. The UPC, originally used for

supermarket items, is now being printed on other consumer goods also. The UPC bar-code

patterns are decoded as 10 digits. The first 5 of these digits identify the manufacturer or

supplier of the product, and the next 5 digits identify a special product of the manufacturer.

� OBR are commonly found in supermarkets and department stores. When a customer picks up a

product for purchasing and brings it to the cash counter for payment, the sales person at the

counter uses a bar-code reader to scan the bar-code printed on the product. The bar-code

reader converts the bar code into an alphanumeric value, and feeds it to the computer, which



looks up the price of the product, possibly updates inventory and sales records, and uses the

price and description information to prepare a purchase bill for the customer. Postal delivery

services also use bar code to identify and track each packet. For Example, Federal Express of

USA uses a unique bar-coding system, and their employees can usually tell a customer, within a

minute, the current location of any packet.

OUTPUT DEVICES

� “ An output device is an electromechanical device, which accepts data from a

computer and translates them into a form, which is suitable for use by the outside

world (the users).”

� Several output devices are available today. They can be broadly classified into the

following categories:

2.1.1 Monitor / VDU (Visual Display Unit)

2.1.2 Printer

2.1.3 Plotter

� Output devices generate computer output, which can be broadly classified into the

following two types:

1) Soft-copy output:-

� A soft copy output is an output, which is not produced on a paper or some material, which

can not be touched and carried for being shown to others.

� Soft-copy output may be temporary or permanent.

� Output displayed on a terminal screen or spoken out by a voice response system can say

soft-copy and temporary by nature while data stored in computer memory are also soft-

copy though it is not temporary by nature.

2) Hard-copy output:-

� A hard-copy output is an output, which is produced on a paper or some material, which can

be touched and carried for being shown to others.

� They are permanent in nature, and can be kept in paper files, or can be looked later, when

the person is not using the computer.

� For example, output produced by printers or plotters on paper are hard-copy output.

� Functioning of above devices & its applications are described below.

2.1. Monitors / Visual Display Unit (VDU)

� Monitors are the most popular output devices used today for producing soft-copy output.

� They display the generated output on a television like screen.

� A monitor is usually associated with keyboard, and together they form a video display

terminal (VDT).

� A VDT (often referred as terminal) is the most popular input/output (I/O) device used with

today’s computers. That is, it serves as both an input and an output device.

� The keyboard is used for input to the computer, and the monitor is used to display the

output from the computer.



� The name “terminal” comes from the fact that a terminal is at the terminal, or end, point of a

communication path.

� Graphic display is made up of a series of dots ‘pixels’ (picture elements) whose pattern

produces the image.

� Each dot on the screen is defined as a separate unit which can be directly addressed.

� There are many types of monitor available in market.

� We will see most famous three types as below:

1. CRT (Cathode Ray Tube) 2. L.C.D (Liquid Crystal Display) 3.PLASMA DISPLAY:

CRT (Cathode Ray Tube ) :-

� The cathode ray tube (CRT), invented by German physicist Karl Ferdinand in 1897.

� The main components of a CRT terminal are the electron gun (a source of electrons), the

electron beam controlled by an electromagnetic field and a fluorescent (phosphor coated)

display screen of glass. While electrons strike the fluorescent screen, light is emitted.

� The single electron beam can be processed in such a way as to display moving pictures in

natural colors.

� There are two types of CRT displays:

a) Vector CRT displays in which the electron beam is directed only to the places where the

image is to be created

b) Raster scan displays in which the image is projected on to the screen by directing the

electron beam across each row of picture elements (pixels) from the top to the bottom

of the screen. This type of display provides a high dynamic capability since image is

continuously refreshed and it allows for continual user input and output. It offers full

color display at a relatively low cost and is becoming very popular.

19" inch CRT computer

monitor

Close-up of a color PC CRT

LCD (Liquid Crystal Display)

� First introduced in watches and clocks in 1970s.

� A liquid crystal display (LCD) is a thin, flat display device made up of any number of color

or monochrome pixels arrayed in front of a light source or reflector.

� LCD Principles: LCD is works by letting through varying amounts of light from a permanent

backlight. Colors are achieved by selective filtering of white light. Two polarizer filters,

color filters and two alignment layers determine exactly how much light is allowed to pass

and which colors are created. The crystal layer is positioned between two glass panels.



� It uses very small amounts of electric power, and is therefore suitable for use in battery-

powered electronic devices, occupy less space, light weight, less emissive than CRT causes

less eyestrain. Due to all these benefits, LCD monitors have finally taken over CRTs in the

marketplace.

PLASMA DISPLAY:

� A plasma display panel (PDP) is a type of flat panel display now commonly used for large

TV displays (typically above 37-inch or 940 mm).

� Many tiny cells located between two panels of glass hold an inert mixture of noble gases

(neon and xenon). The gas in the cells is electrically turned into a plasma which then excites

phosphors to emit light.

� The largest plasma video display in the world was shown at the 2006 Consumer Electronics

Show in Las Vegas, Nevada, U.S.A, a 103-inch, unit manufactured by PANASONIC.

� The superior brightness, faster response time, greater color spectrum, and wider viewing

angle of color plasma video displays made them one of the most popular forms of display

for HDTV flat panel displays.

2.2. Printers:

� Printers are the most commonly used output devices today for producing hard-copy output

(output on paper).

� There are a large variety of printing devices which can be classified according to the printing

technology, print quality and printing speeds.

� By printing technology we can classify printers in mainly two categories; 1) Impact printers

and 2) non-impact printers.

� Impact printers : It use variations of standards typewriter printing mechanism where a

hammer strikes paper through inked ribbon. Example, Dot Matrix printer, Drum printer,

chain/band printer etc.



� Non-impact printers : It uses chemical, heat or electrical signals to etch or induce symbols on

paper. Many of there require special coated or treated paper. Example, Ink jet printer, laser

printer etc.

2.2.1. IMPACT PRINTERS

1. Dot-Matrix Printer :

� Dot-matrix printers are character printers, which print one character at a time.

� They form characters and all kinds of images as a pattern of dots.

� Figure 1 show how various types of characters can be formed as a pattern of dots.

� A dot-matrix printer has a print head, which can move horizontally across the paper. The print

head contains an array of pins, which can be activated independent of each other to extend and

strike against an inked ribbon to form a pattern of dots on the paper.

� To print a character, the printer activates the appropriate set of pins as the print head moves

horizontally.

� For faster printing, may dot matrix printers are designed to print both while the print head

moves from left to right, and while it moves from right to left, on return.

� Since dot-matrix printers produce printed output as patterns of dots, they can print any shape

of character, which a programmer can describe.

� This allows the printer to print many special characters, different sized of print, and the ability

to print graphics, such as charts and graphs.

� Dot-matrix printers are impact printer, because they print by hammering the pins on the inked

ribbon to leave ink impressions on the paper.

� Hence, they can be used to produce multiple copies by using carbon paper or its equivalent.

� However, due to impact printing, dot-matrix printers are noisy as compared to non-impact

printers.

� Dot-matrix printers are normally slow with speeds usually ranging between 30 to 600

characters per second.

� However, they are cheap in terms of both initial cost and cost of operation. Hence they are

preferred by individuals and organizations for generating printed outputs, if the speed and

quality of printing are not important factors.

� They are also used for applications, which require multicopy output, such as shipping forms

and invoices which rely on impact for generating multiple copies.

Figure 1 Figure 2

2. Drum Printers:

� Drum printers are line printers, which print one line at a time.



� The print mechanism of a drum printer is, It consists of a solid cylindrical drum with characters

embossed (raised characters) on its surface in the form of circular bands. Each band consists of

all the printing characters supported by the printer in its character set, and the total number of

bands is equal to the maximum number of character (print position) that can be printed on a

line. Hence, a drum printer with 132 characters per line, and supporting a character set of 96

characters, will have altogether 12,672 (132 x 96) characters embossed on its surface.

� In addition to the drum, the printer has a set of hammers mounted in front of the drum in a

manner that an inked ribbon and paper can be placed between the hammers and the drum.

� The total number of hammers is equal to the total number of bands on the drum, that is, one

hammer is located opposite to each band of the drum.

� The drum rotates at a high speed, and a character at a print position is printed by activating the

appropriate hammer, when the character embossed on the band at the print position passes

below it. Hence, the drum would have to complete one full revolution to print each line of

output. This means that all characters on a line are not printed at exactly the same time, but the

time required to print an entire line is so fast that it appears as if one line is printed at a time.

� The drum of a drum printer is expensive and cannot be changed often. Hence, drum printers

can only print a pre-defined set of characters, in a pre-defined style, which is embossed on the

drum. Due to this reason, drum printers do not have the ability to print any shape of

characters, different sizes of print, and graphics, such as charts and graphs.

� Drum printers are impact printers, because they print by hammering the paper and the inked

ribbon against the characters embossed on the drum. Hence they can be used to produce

multiple copies by using carbon paper or its equivalent. However, due to impact printing, drum

printers are noisy in operation, and often use a cover to reduce the noise level. Typical speeds

of drum printers are in the range of 300 to 2000 lines per minutes.

3. Chain/band Printers:

� Chain/band printers are line printers, which print one line at a time.

� It consists of a metallic chain/band on which all the characters of the character set supported

by the printer are embossed. A standard character set may have 48, 64 or 96 character.

� In order to enhance the printing speed, the characters in the character set are embossed

several times on the chain/band. For example, the chain/band of a 64-character set printer

may have 4 sets of 64 characters each embossed on it. In this case, the chain/band will have

altogether 256 (64 x 4) characters embossed on it.

� In addition to the chain/band, 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 the chain/band.

� The total number of hammers is equal to the total number of print positions. Therefore if there

are 132 print positions, the printer will have 132 hammers.

� Unlike the drum of a drum printer, the chain/band of a chain/band printer can be easily

changed. This allows the use of different fonts (styles of characters) and different scripts

(languages) to be used with the same printer.

� However, just like drum printers, chain/band printers can only print pre-defined sets of

characters, which are embossed on the chain/band used with the printer. Due to this reason,

chain/band printers do not have the ability to print any shape of characters, different sizes of

print, and graphics, such as charts and graphs.



� Chain/band printers are impact printers, because that print by hammering the paper and the

inked ribbon against the characters embossed on the chain/band. Hence, they can be used to

produce multiple copies by using carbon paper or its equivalent

� However, due to impact printing, that are noisy in operation, and often use a cover to reduce

the noise level. Typical speed of chain/band printers are in the range of 400 to 3000 lines per

minute.

2.2.2. NON-IMPACT PRINTERS

1. Inkjet Printers:

� Inkjet printers are character printers, which form characters and all kind of images by spraying

small drops of ink on the paper.

� Inkjet printer uses ink cartridge for printing which contain ink and head.

� You can get black-and-white printing using black cartridge and color printing using color

cartridge.

� The print head of an inkjet printer contain up to 64 tiny nozzles, which can be selectively

heated up in a few microseconds by an integrated circuit register.

� When the register heats up, the ink near it vaporizes, and is ejected through the nozzle, and

makes a dot on the paper placed in front of the print head.

� To print a character, the printer selectively heats the appropriate set of nozzles as the print

head moves horizontally.

� Since inkjet printers produce printed output as patterns of tiny dots, they can print any shape

of characters, which a programmer can describe.

� This allows the printer to print many special characters, different sizes of print, and the ability

to print graphics, such as charts and graphs.

� Inkjet printers are non-impact printers, because they print by spraying ink on the paper.

Hence, they are quiet in operation. However, like other non-impact printers, inkjet printers

cannot be used to produce multiple copies of a document in a single printing.

� Inkjet printers are slower than dot-matrix printers with speeds usually ranging between 4 to

300 characters per second.

� The printing cost per paper of inkjet printer is more than a dot-matrix printer. They are

preferred by individuals and organizations for producing colorful & quality printing.

2. Laser Printers:

� Laser printers are page printers, which print one page at a time.

� The main components of a laser printer are a laser bean source, a multi-sided mirror, a

photoconductive drum and toner (tiny particles of oppositely charged ink).



� To print a page of output, the laser beam is focused on the electro statically charges drum by

the spinning multisided mirror. The mirror focuses the laser beam on the surface of the drum

in a manner to create the patterns of characters/ images to be printed on the page. As the drum

is photoconductive, a difference in electric charge is created on those parts of the drum surface,

which are exposed to the laser beam. As a result, the toner, which is composed of oppositely

charges ink particles, sticks to the drum in the places, where the laser beam has charged the

drum surface. The toner is then permanently fused on the paper with hear and pressure to

generate the printer output. The drum is then rotated and cleaned with a rubber blade to

remove the toner sticking to its surface to prepare the drum for the next page printing.

� Laser printers produce very high quality output, because they form characters by very tiny ink

particles.

� The most common laser printers have resolution of 1200 dpi (dot per inch).

� Because of their high resolution these printers give excellent graphics art quality.

� Since laser printers produce printed output as patterns generated by laser beam, they can print

any shape of characters, which a programmer can describe.

� This allows the printer to print many special characters, different sizes of print, and the ability

to print graphics.

� Laser printers are faster in printing speed than other printers discussed before.

� Low speed laser printers can print 4 to 15 pages per minute.

� Very high-speed laser printers are also available, which can print 500 to 1000 pages per

minute.

� That is fast enough to print this entire book in about one minute. Because of their better print

quality and printing speed, laser printers are mo expensive than other printers.

Laser Printer

1) Applying a negative

charge to the

photosensitive drum

2) How the bitmap is

written to the

photosensitive drum.

3) Fusing Melting toner

into the paper using heat

and pressure.

2.3. PLOTTERS:

� We saw above that 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.

� Plotters are mainly use for 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 ideal output device for architects, engineers, city planners, and others who need to

routinely generate high-precision, hard-copy, and graphics output of widely varying sizes.

� The two commonly used types of plotters are drum & flatbed plotters as below:

2.3.1 Drum Plotter

� In a drum plotter the paper, on which the design has to be made is placed over a drum, which

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. The movement of the drum and the pen(s) are controlled by the graph-plotting

program. That is under computer control, the drum and the pen(s) move simultaneously to

draw the 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.

Drum Plotter Flatbed Plotter

2.3.2 Flatbed Plotter :-

� A flatbed plotter plots a design or graph on a sheet of paper, which that is spread and fixed over

a rectangular flatbed table.

� In this type of plotter, normally the paper does not move and the pen holding mechanism is

designed to provide 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 the designs and

graphs on the sheet placed on the flatbed table.

� The plotter can also annotate the designs and graphs so drawn by using pen to draw characters

of various sizes. Here also, provision is 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 while some

very large beds used in the design of cars, ships, aircrafts, buildings, highways, etc. can be upto

20 ft by 50 ft. Some plotters are also designed to etch 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.

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