UNIT-1 : INPUT-OUTPUT DEVICES

UNIT STRUCTURE

1.1 Learning Objectives 1.2 Introduction 1.3 Input Devices 1.3.1 Keyboard 1.3.2 Mouse 1.3.3 Light 1.3.4 1.3.5 Scanner 1.3.6 1.3.7 Web Camera 1.4 -1: Monitor 1.4.1 Block Diagram of Monitor 1.4.2 Pixel and Resolution 1.4.3 Basic Overview of CRT and TFT(LCD) monitor 1.5 Output Device-2: 1.6 Let Us Sum Up 1.7 Further Readings 1.8 Answers To Check Your Progress 1.9 Possible Questions

1.1 LEARNING OBJECTIVES

After going through the unit you will be able to- • Identify different types of Input devices. • Describe about the different output devices. • Distinguish between different types of monitors. • Describe about the different types of printers.

Elements of Hardware 7 m Unit-i Input-Output Devices 1,2 INTRODUCTION

This unit basically deals with the different types of input and output devices to a computer. These devices enable us to interact with the computer and get our required job done. In this unit you will learn about the different types of input-output devices and their applications. You will also know about their advantages, working principles and their interfacing with the com puter.

1,3 INPUT DEVICES

Input device is an electromechanical device that allows the user to feed information into the computer. It is used for analysis, storage, and to give commands to the computer. An captures information in hu man readable form and converts it into computer readable form (binary form).Examples of input devices include the Keyboard, Mouse, Modem, Joystick, Digitizing pen and tablet, . Touch screen. Scanner,

camera.

1.3.1 Keyboard

It is the main input device used in most of the computer systems. It has letter and number keys, and some function keys and computer specific task keys. That allows the user, to - use an English-like language to issue

instructions to an electronic environ ment. It uses a cursor to keep your place on the screen and to let you know where to begin typing. You are! able to input commands, type data into documents. Fig. 1.1 : Original View of a multimedia keyboard (Source:joey, ubuntu-rocks. org)

Elements of Input-Output Devices Unlt-1 compose documents, draw pictures with the use of certain keys, pull down menus, and respond to prompts issued by the computer. The keyboard contains special keys to manipulate the user inter face. When a key is touched, an eiectrical impulse is sent through the device which is picked up by the operating system software, and sent through the computer to be processed.

The keyboard operates as a typical typewriter and uses a standard "QWERTY" keyboard. QWERTY is the way the keyboard is set up for typing. If you look at the keyboard under the top number row, you will see that the alphabet top row begins with QWERTY.

1,3,2 Mouse

The mouse is a hand heid that iets you point to and selects items on your screen. It also enables you to move a cursor or pointer on a screen just by moving the mouse over a flat surface. In a PC mouse there are mostly 2-3 buttons. The mouse is included in almost every computer that is sold today. Besides becoming an important input tool, it has provided access to the computer for many individuals with disabilities that might not otherwise have the oppor tunity to use the computer.

Types of Mouse; Basically there are three types of mouse, viz.-

• Mechanical mouse • Optomecahnical mouse • Fig 1.2: Original view of a mouse (Source: lmgs.tootoo.com) A mechanical mouse consist a rubber or a metal ball under it, free to move in any direction. Mechanical sensors detect the movement of the ball and consequently move the cursor on the screen. Optomechanical mouse is similar to a mechanical mouse, only dif- ' ference is that it uses optical sensors to detect the movement of the Elements of Computer Hardware Unit-1 Input-Output Devices ball. Optical mouse uses a light emitting diode and a photodiode to

detect the movement of the mouse.

1.3.3 Light Pen

The pen lets you draw on what is cailed a digitizing tablet that mir rors the surface area of the computer screen. The pen can be used as a standard mouse (without wires connected to it) or aiso as a free flowing drawing device. The pen is usefui for drawing since draw ing graphics with a mouse tends to be somewhat difficult. A iight pen basically consists of light sensors. When it touches the digitizing tablet the computer detects the location of its touch and works ac cordingly.

1.3.4 Touch Screen

The touch screen lets the user touch the area to be activated by using the finger or hand. A touch screen can detect exactly the place where the screen is touched. It is most useful to people who are not experienced of using devices. The edge of a touch screen emits horizontal and vertical lines that criss-cross the screen. Whenever a finger touches the screen,the beams are inter rupted and detect location of touch.

1.3.5 Scanner

It allows a PC to convert a picture or object into digital code that al lows the computer to display and use an image. A scanner's sophi stication is the ability to translate <«( an unlimited number of analog Fig. 1.3: A scanner voltage levels to digital values. The (Sourcexen.wiki2buy. com)

10 Elements of Computer Hardware Input-Output Devices Unit-1 scanner takes the information it sees on a page and converts into code that the computer can use. A picture once scanned can be edited, printed, or used in an application. Scanners can come with specialized software called optical character recognition (OCR). This software can read text as printed or written. The information can then be manipulated in the computer.

1.3.6 Joystick

Joysticks are also a type of input device to a computer, it consist of a stick mounted on a base, the stick is movable to left, right, fonvard and backward and when released it comes to the centre again. The cursor on the computer screen moves according to the movements of the joystick. are mostly used while playing computer games as it allows the user to move quickly.

1.3.7 Web Camera

Web cameras are basically video and image capturing device just like a ordinary video camera or photo graphic camera. Here there is no photo film as in conventional camera. It contains mainly-a lens /^if for focussing, image sensor and / ' some electronic circuitry for digi- tizing the image sensed by the im- V age sensor. They are basically con- ^ nected to the computer through / " ^ \ USB port. The main use of the web- . % cam is in videophone or video conferencing system. Fig. 1.4: Web Camera (Source: www.buymebuyme.com)

Now a day, an advanced version of web camera is available which is known as IP camera and these camera can be controlled remotely with the help of LAN/WAN. Elements of Computer Hardware 11 Unit-1 Input-Output Devices

CHECK YOUR PROGRESS-1

J. State true or false: (i) Keyboard enables us to enter or type text on a computer. (ii) Mouse is one of the pointing devices.

2. Fill in the Blanks: (i) Light have sensors. (ii) Scanner are used for an image. (iii) Web cameras are basically and capturing device,

(iv) The edges of a _ emits horizontal and vertical lines that criss-cross the screen, (v) There are basically types of mouse.

14 OUTPUT DEVICE-1: MONITOR

The monitor is the common output device mostly used. It can be thought of as a high resolution TV set. The monitor can also determine if the dis play will be color, black and white, or include graphical objects (pictures).

The monitor displays text and images (pictures) converted to output from the video adapter. The video adapter is an that plugs into the . The adapter changes the instructions from the (CPU) into a way that the monitor can understand it.

Most computer monitors are based on Cathode Ray Tube(CRT) technol ogy. The basic operation of these tubes is similar to that in television sets. With the widespread use of smaller computers like PDAs and laptops PDA: Personal nowadays, a new type of display screen Liquid Crystal Display(LCD) has Digital Assistant. been used.

1.4.1 Block Diagram of Monitor

The following figures shows the block diagram (fig 1.5) of a CRT Monitor and the fig 1.6 shows a typical CRT monitor with cover re moved showing its internal parts.

12 Elements of Computer Hardware Input-Output Devices Unit-1

AUX AUX I AUX COMPOSITE VIDEO 1 I SOURCE j^MONITO^ Lrru

I 1 I— I AUX I TDS COMPOSITE VIDEO I DISPLAY CONSOLE I monitor'

CATHODE

VIDEO 1/2 SELECT VIDEO FILAMENT CONTROL TV BRIGHTNESS MONITOR FUNCTION CONTROL CONTRAST MONITOR COMPOSITE VIDEO PANEL CRT

+1&V\+15V' TO ALL V. FUNCTIONS POWER -15V 1, AND TV DISTRI MONITORS BUTION •tSV CONTROL HORIZONTAUVERTICAL BLANK

FUNCTION ¥ PANa SWEEP FLYBACK SYNC PULSE GENERATOR FUNCTION HORIZONTAL/VERTICAL YOKE,

Fig. 1.5: Block Diagram of CRT Monitor (Source: www.tpub.com)

CRT Mounting CRT HV Connector Screw (1 of 4) CRT Neck Board (Covered by Shield) DAG Costing on CRT

CRT HV Cable Access Holes for RGB Deflection Yoke Adjustments EC Power Purity/Static Connector Convergence Magnet Rings

Mainboard iorizontal Output Transistor (HOT) _ ^ Ferrite Core for Video Cable rpI Supression Mostly Behind Shield (Mostly Behind« i.* j Focus screen (G2) Heat Sink HniA ^vra PnnnprtnrConnector Heat Sink) Control Qgntjoi (porHOT) Fig. 1.6: inside of a Typical CRT Monitor

Elements of Computer Hardware 13 Unit-1 Input-Output Devices 1,4.2 Pixel and Resolution

The picture information is optical in character and may be thought of as a group of a large number of bright & dark areas representing picture details. These elementary areas into which the picture de tails may be broken up are known as picture details may be broken up are known as picture elements (PIXEL). Thus an image in a TV screen or photographic print composed of large number of pixel which may be observed by using a magnifying glass. For higher resolution the pixel should be very close to each other.

PIXEL

Pixel is the smallest unit forming a digital image and represents the light intensity variation or information content of the image. Each pixel is a sample of the original image where more samples typically pro vide more accurate representations of the original. In colour sys tems, each pixel has typically three or four components such as red, green, and blue, or cyan, magenta, yellow, and black. The number of pixels in an image is sometimes called the resolution, though reso lution has a more specific definition which will be taken up below.

The number of distinct colours that can be represented by a pixel depends on the number of bits per pixel(bpp). A1 bpp image uses 1 - bit for each pixel, so each pixel can be either on or off. It Is called a binary image. Each additional bit doubles the number of colours available, so a 2 bpp image can have 4 colours, and a 3 bpp Image

can have 8 colours:

1 bpp, 2^ = 2 colours(monochrome) 2 bpp, 22 = 4 colours 3 bpp, 2® = 8 colours 8 bpp, 2® = 256 colours 16 bpp, 2^® = 65,536 colours ("Highcolour") 24 bpp, 224 16.8 million colours ("Truecolour")

14 Elements of Computer Hardware Input-Output Devices Unlt-1 For colour depths of 15 or more bits per pixel, the depth is normally the sum of the bits allocated to each of the red, green, and blue components. Highcolour, usually meaning 16 bpp, normally has five bits for red and blue, and six bits for green, as the human eye is more sensitive to errors in green than in the other two primary colours. For applications involving transparency, the 16 bits may be divided into five bits each of red, green, and blue, with one bit left for trans parency. A 24-bit depth allows 8 bits per component. On some sys tems, 32-bit depth is available; this means that each 24-bit pixel has an extra 8 bits to describe its opacity (for purposes of combining with another image).

RESOLUTION

Resolution determines the visible detail of an image. It represents the density of gray levels or Information contained in an image. Higher resolution means more image detail. Image resolution can be mea sured in various ways. It quantifies how close points can be to each other and still be visibly resolved. Resolution units can be linked to physical sizes (e.g. lines per mm, lines per inch) or to the overall size of a picture (lines per picture height, also known simply as lines, or TV lines). Resolution is depended on two factors of a digital im age. These are- numbers of samples and gray levels. The more these two are present more closely the digitized array approximates the original image. But unfortunately, more are the samples and gray levels, more will be the storage space required and computational complexity.

RESOLUTION TYPES :

Pixel Resolution- This is used in case of images. Pixel resolution is expressed as a set of two positive numbers, where the first num ber is the number of pixel columns (width) and the second is the number of pixel rows (height). Example-640 by 480. Another popu lar convention is to cite resolution as the total number of pixels in the image, commonly referred as a number of megapixels, which can be calculated by multiplying pixel columns by pixel rows and dividing by Elements of Computer Hardware j 5 Unit-1 Input-Output Devices one million. Other conventions include describing pixel? per length unit or pixels per area unit, such as pixels per inch or per square inch (ppi). Spatial Resolution-It refers to the number of independent pixel val ues per unit iength. It is a measure of how ciosely lines can be re solved in an image. The spatiai resolution of some computer moni tors is stated as 72 to 100 lines per inch, corresponding to pixel reso lutions of 72 to 100 ppi. With scanners, optical resolution is some times used to distinguish spatiai resolution from the number of pix els per inch. Spectral resolution- It is associated with colour images to distin guish light of different spectra. Generaiiy it arises when the image spectra is referred to. Multi-spectral images resoive even finer differ ences of spectrum or wavelength than is needed to reproduce colour. It means that they can have higher spectral resolution. Temporal resolution- This is a type of resolution associated with time. Temporal resolution can be used to provide resolution distinc tion of motion picture sequences recorded with different rates in frames per second. Movie cameras and high-speed cameras can resolve events at different points in time. The time resolution used for movies is usually 15 to 30 frames per second (frame / s), while high-speed cameras may resolve 1 CO to 1000frame /s, or even more. Many cameras and displays offset the colour components relative to each other or mix up temporal with spatiai resolution:

Images can be of several types. These are:

> Black and white or gray level image > Binary or monochrome Image and > Colour Image

1.4.3 Basic Overview of CRT and LCD Monitor

The display units or Monitor mainly used with computers are basi cally of two types as mentioned earlier, viz.-

• CRT Monitor • LCD Monitor 16 Elements of Computer Hardware Input-Output Devices Unit-1

CRT MONITOR

CRT Monitor basically consists of a CRT or a Cathode Ray Tube. This type was the only display unit available for computers for many years before the LCD monitors came into play. The working of a cathode ray tube is as follows- it consist of a vacuum tube and elec tron guns and a florescent screen. The electrons released from the electron gun are accelerated by the use of a electric field. The elec trons released are allowed to pass through a narrow space sur rounded by the anode which generates a fine narrow beam of elec trons. This beam is being deflected by the application of magnetic and when the electrons strike the florescent screen illuminations are produced and we can see the display. Black and White CRT moni tors consist of a single electron gun whereas colour CRT monitors consist of three electron guns. So for a complete display of a any view on the monitor screen a large number of electrons are released from the electron guns and these are deflected according to the in formation to be displayed and the altogether strikes the smallest units of the florescent screen which are also known as pixels and the whole display appears on the screen.

Fig. 1.7: Schematic of a CRT tube (Source: www.wikipedia.com) 1. Three Electron guns(for red, green, and blue phosphor dots) 2. Electron beams 3. Focusing coils 4. Deflection coils 5. Anode connection 6. Mask for separating beams for red, green, and blue part of displayed image 7. Phosphor layer with red, green, and blue zones 8. Close-up of the phosphor-coated inner side of the screen

Elements of Computer Hardware 17 Unit-1 Input-Output Devices

LCD MONITOR

LCD monitors are now-a- day are mostly used dis PSIIfl play units with computers. ■. ':■ '■ i te»i ^ ;V ■ ■ I It's less power consump tion, high display resolution and slim design makes it - • " i ■i■ 1 ..i. - ^- i more advantageous over rj ; ■ . ■ ■ . ^ the CRT monitors. The ■ ■« ■ ■ - j; -■. ,."■7 ■ ■■■'■ -■ ^ LCD monitors mostly uses TFT-LCD (Thin Film Transistor-Liquid Crystal Display) technology for producing the display. The Fig. 1.8 : Pixel layout of TFT connections made to con (Source: www.wikipedia.com) trol the display through LCD or liquid crystal displays used in small calculator and mobile phones are not much complex but when the matter comes to a large display, the connections become much more complicated. To avoid this problem all the display units or pixel are connected in a matrix f order and each unit are made ON or OFF through a thin film transis tor. This arrangement makes the control much easier and the ar rangement can be extended for much smaller display units or pixels accordingly the resolution of the display increases.

CHECK YOUR PROGRESS-2

Fill in the Blanks ; (i) Pixel is the . of a image or a display. Resolution determines the discernible detail of an image. CRT basically consists of ,

(iv) TFT means (v) In LCD monitors each display unit is connected in Order.

18 Elements of Computer Hardware Input-Output Devices Unit-1 1.5 OUTPUT DEVICE-2: PRINTER

It is the widely used hard copy output device. A printer prints information and data from the computer onto a paper. Some printers can produce only textual information but some others can produce graphics also.

Printers are divided into two major categories: Impact printers : The printers that work by physically striking a head or needle against an ribbon to make mark.

Non impact printers :The printers that work by not physically striking a head or needle against an ink ribbon to make a mark.

Impact printers are divided into Dot matrix printers, Daisy-Wheel print ers and Drum printers.

Dot Matrix Printer : This printer is the cheapest but loudest of all the printers. This printer prints one character at a time. The printer uses a fine stripe of carbon and depending on what pin it is, will determine the quality of the printing. The pin sizes range from 9-24. The print head hits the ink ribbon with one of its many pins causing it to form a letter number or char

acter.

Fig. 1.9: A Dot-Matrix Printer

With the pins hitting the ribbon this printer becomes quite loud. The ppm (page per minute ranges from 1 to 3 but in new changes in technology it is becoming more and more used in offices today and also can print 3-6 ppm plus it is much more quite. The drawback in most dot matrix printers is the on-roll paper which has a track which feeds it through the printer. Also in most new dot matrix printers there is a paper feed which allows most forms of paper. Elements of Computer Hardware 19 Unit-1 Input-Output Devices Daisy Wheel Printer : Daisy-wheel printers operate in much the same fashion as a typewriter. A hammer strikes a wheel with petals (the daisy wheel), each petal containing a letter form at its tip. The letter form strikes a ribbon of ink, depositing the ink on the page and thus printing a character. By rotating the daisy wheel, different characters are selected for printing. You can change the daisy wheel to print different fonts. This printer is also called the letter quality printer.

Drum printer: Drum printer is one of the most commonly used line print

ers

Hammers(one for each band) Paper 1 Ribbon y tww w wwwwwwwwwwirAH vvvvvvvvvvvvvv uuuuuuuuuuuuuu

Sollc Cylindrical/^"* SSSSSSSSSS38SS drum with embossed RRRRHR R RRRR RRR characters QQQQQQQQQQQQQQ PPPPPPPPPPPPPP oooooooooooooo NNNNNNNN'NNNNN'N

V Total number of bands is equal to the maximum number of characters(print positions)on a line

Fig. 1.10: Printing Mechanism of a Drum Printer In a typical drum printer design, a fixed font character set is engraved onto the periphery of a number of print wheels, the number matching the number of columns (letters in a line) the printer could print. The wheels, joined to form a large drum (cylinder), spin at high speed and paper and an inked ribbon are stepped (moved) past the print position. As the desired character for each column passes the print position, a hammer strikes the paper from the rear and presses the paper against the ribbon and the drum, causing the desired character to be recorded on the continuous paper. Because the drum carrying the letterforms (characters) remains in constant motion, the strike-and-retreat action of the hammers had to be very fast. Typically, they were driven by voice coils mounted on the moving part of the hammer.

20 Elements of Computer Hardware Input-Output Devices Unit-1 The non impact printers commonly used are: Inkjet Printer: This printer is set at the standard for home use. It is a non impact printer and it does not touch the paper while printing. Instead, the print head sprays ink onto paper forming an image or text

For business letters an Inkjet printer is the most common one used for its high quality printing. The common speed on an ink jet printer is about 3 ppm and 300 dpi (dots per inch).

Fig. 1.11 :An ink Jet Printer

Laser Printer : Among the different types of printers, laser printers re main the fastest, and the most efficient way to reproduce text and images, offering high resolution and quick speeds at a relatively low cost. A laser printer uses an electrostatic process similar to a photocopier. The laser charges areas of a photosensitive image drum. Toner particles are then attracted to these areas of the drum. By rolling this drum against a piece of paper, the printer creates an image on a page. In the final stage, heat is used to fuse the toner to the paper. : A plotter is a hard copy output device used to draw high-resolu tion charts, graphs, maps, and other line based diagrams. It is a pen based output device, attached to a computer for making vector graphics, that is, images created by a series of many straight lines. A plotter is a very slow and expensive output device. They are mainly used for Computer Aided Design (CAD) and Computer Aided Manufacturing applications. are classified as Drum plotters and Flatbed plotters.

Elements of Computer Hardware 21 Unit'1 Input-Output Devices

Design drawn on the paper

Paper

Fig. 1.11 : A Flatbed Plotter

CHECK YOUR PROGRESS-3

Fill in the Blanks:

(i) Printers are of basically two types- and

(ii) Dot Matrix printers can print, character at a time. (iii) The common speed of ink jet printer is dpi. (iv) Among all the printers printer is the fastest.

1.6 LET US SUM UP

In this unit we have explained to you-

• Input device is an electromechanical device that allows the user to feed information into the computer for analysis, storage, and to give commands to the computer • The monitor displays text and images (pictures) converted to output from the video adapter. • These elementary areas into which the picture details may be bro ken up are known as picture details may be broken up are known as picture elements(PIXEL).

22 Elements of Computer Hardware Input-Output Devices Unit-1 • CRT consists of a vacuum tube and electron guns and a florescent

screen.

LCD monitors mostly uses TFT-LCD (Thin Film Transistor-Liquid Crystal Display) technology for producing the display.

Printers are divided into two major categories- Impact printers and non impact printers

1.7 FURTHER READINGS

• Fundamentals of Computer Hardware -Mandeep S. Bhatia (Khanna Book Publishing co(p) Ltd, Deihi) • Learning PC Hardware -Ramesh Bangia (Khanna Book Pubiish- ing CO. pvt Ltd) • Modern Colour Monitor Circuits -Manahar Lotia (BPB Publica tion)

1.8 ANSWERS TO CHECK YOUR PROGRESS

ANSWER TO CHECK YOUR PR06RESS-1 1. State true or false: (i) True, (ii) True 2. Fill in the Blanks : (i) light, (ii) digitizing, (iii) video, image, (iv) touch screen,(v) three

ANSWER CHECK YOUR PROGRESS-2

Fill in the Blanks : (i) smallest (ii) discemible. (iii) Vacuum tube, electron gun, florescent screen (iv) Thin film transistor (v) Matrix

ANSWER CHECK YOUR PROGRESS-3

Fill in the Blanks: (i) Impact, non impact (ii) One (iii) 300 (iv) Laser

Elements of Computer Hardware 23 Unit-1 Input-Output Devices 1.9 POSSIBLE QUESTIONS

1. Describe in brief about different input devices and their functions.

2. Write short notes on Pixel and Resolution. 3. Describe in short about the working of CRT and LCD monitor. 4. Write in short about the difference between Impact and Non-Impact printers. 5. Describe in brief about the different types of printers.

Elements of Computer Hardware 24