CHAPTER 3

INPUT AND OUTPUT DEVICES

Learning Objectives

Upon completion of this unit, you should be able to do the following:

1. Understand the importance of current input and output devices in a computer system.

2. Explain the functionality and mechanisms of several input and output devices.

3. Identify other areas of application for specific input and output devices.

4. Evaluate and choose appropriate input and output devices.

OverviewComputer input and output devices have undergone remarkable development since their existence. This chapter covers the different types of computer input and output devices.

The primary function of input devices is ‘getting’ data and instruction into the computer. Popular input devices are keyboard, mouse, scanner, microphone and webcam. An Output device is any hardware component that can convey information to a user. Common output devices are monitors, printers and sound speakers

3.0 IntroductionInput devices accept user commands or data and send them to the computer for processing. Typical input devices are keyboard, mouse, scanner and microphone. On the other hand, output devices accept results or information generated by the computer, and present this to the user in a variety of means (both audio and visual e.g. textual, image, video). Typical output devices are printers, monitors and speakers. Some special devices can be used for both input and output, such as floppy disks and hard drives. Computer input and output devices have undergone remarkable development with advances in technology.

3.1 Input devicesWith all the input devices available today, users may find it difficult to determine which one is best for entering data into their personal computer. The main function of input devices is to convert people-readable form of data into a machine-readable form that the computer can store and process. People readable form of data can be letters, numbers, visual codes and symbols. Machine-readable forms of data consist of electronic signals of 0's and 1's. A personal

computer is normally equipped with a mouse and keyboard as standard input devices. Input devices can fall under three categories, namely pointing, scanning and voice. Input can be made by keyboard or direct entry.

3.1.1 KeyboardMost modern computer keyboards are based on the QWERTY layout, and resemble a typewriter keyboard except that they have extra keys for certain special functions, such as:

Function keys: located at the top of the keyboard with prefix F, example F1, F2 and so on. However, these shortcuts on depends on the specific software used.

Numeric keypad: located on the right corner of the keyboard, is a separate set of number keys, like that of a calculator, for quick input of numbers and arithmetic operators.

Arrow keys or navigation keys: located between the main keypad and the numeric keypad, are used to move the cursor up, down, left, and right.

Insert, delete, page up, page down keys: located above the arrow keys, are used in word processing for performing insert, delete, page up, and page down.

Figure 3-1 Keyboard

In recent years, so called “Internet keyboards” have also become popular. These include extra buttons for specific applications or functions like e-mail client or browser.Ergonomic keyboard have features designed to reduce the effects of occupational overuse syndrome (formally known as Repetitive Strain Injury). An example is the split keyboard, illustrated in Figure 3-2, which offers infinitely adjustable positioning.

Figure 3-2 Split Keyboard

The trend now is wireless keyboard design that offers more freedom for the user. Rather than being tied to a computer, forced to sit perhaps in an uncomfortable position for hours sometimes, wireless keyboard can be placed comfortable anywhere on the table or on the lap.

3.1.2 MouseA mouse is a pointing device, as shown in Figure 3-3. It is used to move an electronic pointer called a cursor around the screen or click on an object or option on the screen to trigger it to respond. The mouse is now present in virtually every office environment because of the predominance of graphical user interface (GUI).

Figure 3-3 A mouse

Types of mouseA mechanical mouse has a rubber or metal ball on its underside. When the ball rolls in a certain direction, electronic circuits in the mouse translate the movement into signals that are sent to the computer.

An optical mouse has gained widespread adoption by eliminating the need for a special mouse pad. It has no moving parts; instead it uses light emitting diodes and photodiodes, that emit and sense light to detect the mouse’s movement. An optical mouse can be used on nearly all surfaces, is more precise than a mechanical mouse, and does not require cleaning.

A cordless mouse, or wireless mouse, is a battery-powered device that transmits data using wireless technology, such as radio waves or infrared light waves. A cordless mouse uses technology very similar to that of a wireless keyboard.Apart from the regular mouse that is operated by the hands, other mouse variants exist. These cater for people who may feel uncomfortable with traditional designs

The trackball is sometimes called an upside-down mouse. While a mouse employs a rolling ball on its underside, a trackball uses an exposed ball that the user manipulates with his or her fingers. Unlike a traditional mouse, a trackball does not require a horizontal pad on which to

move. Trackballs are a good choice for those with limited desk space, large monitors or poor gripping ability.

Figure 3-4 Trackball

Foot mouse (also called no hands mouse) is a mouse variant for those whose hands are injured due to Carpal Tunnel Syndrome or mouse overuse fatigue. It can eliminate stress related to the wrist, elbow and shoulder. These innovative “no hands” mouse uses two interchangeably foot pedals; one to move the cursor and the other one to click, drag and drop objects on the computer desktop. It is also a more productive mouse since users can keep typing without having to jump between the keyboard to the mouse and back.

Figure 3-5 Foot Mouse

3.1.3 TouchscreenA touchscreen is an intuitive computer input device that works by simply touching the display screen, either by a finger, or with a stylus, rather than typing on a keyboard or pointing with a mouse. A stylus is a "pen" that does not write! The stylus point is made of a firm but non-scratching plastic to "write" on screen. Touchscreen is a pointing input device that allows the

user to select actions and commands with the finger. It consists of a special type of visual display unit (VDU), which has a grid of light beams or fine wires criss-crossing the screen. When the screen is touched (usually to choose an on-screen option), the computer senses where on the screen it has been pressed to respond. The touch-sensing mechanisms can use optical, electrical or acoustical methods to determine the co-ordinates of the touch.

Any touchscreen system comprises the following three basic components:

a touchscreen sensor panel, that sits above the display and which generates appropriate voltages according to where, precisely, it is touched.

a touchscreen controller, that processes the signals received from the sensor and translates these into touch event data which is passed to the PC's processor, usually via a serial or USB interface.

a software driver, provides an interface to the PC's operating system and which translates the touch event data into mouse events, essentially enabling the sensor panel to "emulate" a mouse.

The touchscreen interface is simple, intuitive, and easiest to learn of all PC input devices. It is fast becoming the interface of choice for a wide variety of applications, such as Public Information Systems, Information kiosks, tourism displays, and other electronic displays are used by many people that have little or no computing experience. The user-friendly touchscreen interface can be less intimidating and easier to use than other input devices, especially for novice users, making information accessible to the widest possible audience.

One disadvantage of touchscreen is that using the finger to point is not always suitable for accurate selection of small regions and it can leave greasy marks on the screen.

Figure 3-6 Touchscreen

3.1.4 TouchpadA touch pad feels less mechanical than a mouse or trackball because the user simply moves a finger on the pad. A touch pad has two parts. One part acts as a button, while the other emulates a mouse pad on which the user traces the location of the cursor with a finger and striking over the surface. People with carpal tunnel syndrome find touch pads and trackballs easier to use than mice. Many portable computers have built-in trackballs or touch pads as input devices. However, even experienced users continue to report problems, if another finger accidentally touches the pad causing motion detection to become confused and the cursor to jump across the screen.

Figure 3.7 Touchpad of Laptop

3.1.5 Light penA lightpen is a pointing device that is held to point directly to items on the screen. This light sensitive pen addresses individual pixels for fine selection and drawing. Hence, it is much more accurate than the touchscreen. Some limitations of the fragile lightpen are that it may be tiring on the arm, can cause obstruction of sight on the monitor and varying background lighting often corrupts lightpen input.

Figure 3-8 Lightpen

3.1.6 Digitizing tablet or digitiserA Digitising tablet is a device that facilitates the accurate input of 2-D or 3-D drawings and designs. A drawing can be placed directly on the tablet, and the user traces outlines or inputs coordinate positions with a hand-held cursor or stylus. For digitizing tablets, each point on the tablet represents a point on the display screen in a fixed manner. This differs from mouse, in which all movement is relative to the current cursor position. The static nature of digitizing tablets makes them particularly effective for tracing complex drawings by designers, engineers and architects. Digitizing tablets are also called digitizers, graphics tablets, touch tablets, or simply tablets. Modern graphics tablets are widely considered to offer a very natural way to create computer graphics. They have stylus-based interface with ability to detect pressure, tilt and other attributed of the stylus and its interaction with the tablet

Figure 3-9 Digitising Tablet

3.1.7 ScannerA scanner is a device which scans documents containing text or graphics and converts them into a bitmap (digital picture image). Most scanners today are variations of the desktop or flatbed scanner that allows documents to be placed on a flat scanning surface.

Figure 3-10 A Flatbed Scanner

A flatbed scanner works as follows:

A light source illuminates the paper, and light is reflected off the paper down onto the scanning mechanism.

Blank or white spaces reflect more light than darker areas.

A motor moves the scanning head underneath the page along its length.

As the scan head moves down the page, it captures the reflected light bounced off the page.

3.1.8 Barcode readerAs illustrated in Figure 3-12, barcodes consists of different groups of vertical bars that can be

read by an optical scanner. They are printed on nearly every product. Supermarkets use barcode reader or scanner to read data from a product item barcode and transfer it to the processor to determine price and product details. They are cheap to produce and very durable.

Figure 3-12 Barcode(Left) and Barcode Reader(Right)

3.1.9 Image and video input devicesThe digital camera records and stores photographic images in digital form that can be fed to a computer for viewing and printing.

A web camera (or webcam) is a real-time camera whose images can be accessed using the PC video software application. The images can be uploaded to a web server, either continuously or at regular intervals. Videoconferencing applications can use a webcam connected directly to a PC.

Today there are thousands of webcams that provide views of homes, offices and other buildings as well as providing panoramic views of cities. Special webcams are used to monitor traffic, weather and even volcanoes. The video feeds obtained from webcams are uploaded to a computer where it can be processed using appropriate software.

3.1.10 Audio input deviceA microphone is a transducer that converts sound into an electrical signal for recording onto computers. It is very popular as a sound input device and is used with multimedia applications such as for voice recording; speech recognition, Iinternet telephony and teleconferencing. Microphones now come as headsets, USB microphones or Bluetooth and wireless headset.

(a)

(b)Figure 3-13 (a) Bluetooth wireless headset (b) USB microphone.

3.1.11 Wired glovesOne of the mainstays of the new virtual reality systems is the wired glove, a 3-D input device. It consists of a special lycra glove with sensors to determine the 3-D positional information. The potential for the wired glove is vast; gesture recognition and sign language interpretation are two main applications. Various sensor technologies are used to capture physical data such as bending of fingers. Wired gloves are often called “data gloves” or “cyber gloves”, but these two terms are trademarks.

Figure 3-14 A Data Glove

The fundamental task in computer input is to transfer information from the brain of the user to the computer. Progress in this discipline attempts to develop better human-computer interface by seeking faster, more natural and, convenient means for a user to transmit information to a computer.

3.2 Output DevicesOutput devices have evolved over time. They are not as numerous as input devices but their efficiency is much appreciated in the computer technology world. The basic function of an output device is to get information or any other response out of the computer.

3.2.1 Display devicesMonitor screens are devices used to display information from the computer. In fact, television

sets include monitor screens, though in general, the monitor screens used in computer systems are of a much higher quality.

Monitors come in various sizes, commonly starting at 14 inch, then 15 inch, as well as 17 and 19 inch. This is the size of the viewable screen measured across the diagonal from corner to corner. Resolution of the monitor screen refers to the number of dots, called pixels, displayed in the horizontal and vertical display area. Typical screens are capable of displaying 640 x 480 or 1024 x 768 pixels. The greater the pixel density, i.e. the number of pixels per unit area on the monitor screen, the better the resolution. Hence, higher resolution produces higher display quality.

Another term used with monitors is refresh rate. This refers to the number of times per second that the image is redrawn on the monitor screen. A refresh rate of 60Hz means the images is redrawn 60 times a second. Higher refresh rates are required for larger resolutions, else the viewer tend to see the image on the screen flicker. The images on the screen have to be refreshed at a reasonable rate (greater than 50Hz); otherwise the human eye perceives the image as flickering.

Another measurement of resolution is the dot pitch, the distance in millimeters between pixels. The smaller the dot pitch the better the resolution. The signal to a display screen comes from a video card or graphics card. This card converts digital output to analogue signals for the display. The Video Electronics Standards Association (VESA) develops standards for video displays. Most monitors are at least SVGA (Super Video Graphics Array) with 1280 x 1024 resolution and laptops with XGA (Extended Graphics Array) for higher resolution.

The number of colours that a video card can display is determined by its bit depth or colour depth. This is how many bits it uses to store the colour of one pixel. An 8-bit card will only allow 256 colours. Most cards today are at least 24-bit and can display 16.7 million colours.

3.2.2 Liquid Crystal Displays (LCD) and Cathode Ray Tube (CRT) MonitorsThere exist two types of monitors: Cathode Ray Tube (CRT) and Liquid Crystal Display (LCD). Modern laptop computers use LCDs similar to those used in calculators and watches. This type of display has also become popular in larger formats with desktop computers because of their compactness. They take up less space and are lighter than most CRT monitors. LCDs can be used in many places where a larger CRT monitor cannot fit. Other advantages of LCDs are the absence of electromagnetic waves, lower heat emission and power savings over the CRT. LCD monitors exist in monochrome or colour. The screen is perfectly flat, with no distortions due to a curved screen like CRTs. Most new LCDs connect to standard video cards, although a few require their own graphics adapters. Disadvantages of the LCD monitor are the higher cost, image dimness, small viewing angle and slower response times. All of these disadvantages are being addressed as new technology is applied.

LCD display is based on a totally different technology than CRTs. An electric current is passed through a liquid crystal solution between two sheets of polarizing material. As the current

passes through, it causes the crystals to align so that light cannot pass through them. The image appears as some crystals allow light to pass through and others do not.

(a) (b)Figure 3-15 (a) LCD and (b) CRT Monitor

3.2.3 PrintersBy far, paper is the single largest output from computers. A printer is a device that produces a hardcopy (permanent human-readable text and graphics, usually on paper or transparencies) from data stored in a computer connected to it. Modern printers come in a variety of types, with many capabilities.

Printer outputs are produced by impact or non-impact methods. Impact printers, such as dot-matrix, rely on the forcible impact of pins that presses against an inked ribbon onto paper to form a character or symbol, like a typewriter. Non-impact printers, like inkjet, laser and thermal printers, do not involve physical contact of mechanical device striking on the paper. Instead, they use ink spray or toner powder.

Dot-matrix printerDot Matrix printers rely on a matrix of pins or dots and they have survived the market changes in technology, due to their application as impact printers. This means that they are able to print on multipart paper using carbonless copy paper, which is used extensively in the accounting and auditing sector, and other businesses that need to keep accurate records and legal copies of documents. However, even for sales invoices or receipts printing, dot-matrix printers are now rapidly being superseded by other types of printers. Figure 3-16 shows a dot matrix printer used in office.

Figure 3-16 Dot Matrix Printer.

The main features of dot matrix are tabulated in Table 3-1.

Mechanism

It has a mechanical print head that travels across the paper. The head has a set of pins which are pushed out to form the shape of each character. The pins hit an ink ribbon against the paper as the print head moves along. Different coloured-ink ribbons can be used.

UsesLimited to situations where carbon copies are needed and the quality is not too important. Typical uses might be for very high volume applications like invoice printing.

Advantages

The purchase cost is low and the running costs are very low. They can print fairly quickly, when multiple copies are being printed in one print run. They are robust and can operate in harsh environments. If several sheets of self-carbonating paper are placed into the printer then the impact will produce multiple copies.

DisadvantagesThe printing quality is low - these printers produce low to medium quality black and white printing, and can only print low resolution graphics. These printers can be quite noisy.

Table 3-1 Dot Matrix Printer Features

Inkjet printers

Figure 3-17 Inkjet Printer

The main features of an Inkjet printer are tabulated in Table 3-2.

Mechanism

The print head contains tiny nozzles through which different coloured inks can be sprayed onto the paper to form the characters or the graphic images. The ink is forced out by heat or by tiny piezoelectric crystals which change shape when an electric current is applied across them.

Uses A popular choice for home and school use where small amounts of printing are done and colour printing is only occasionally needed.

AdvantagesThese printers are relatively inexpensive and produce high quality black and white or colour printing. Relatively quiet printing and better output compared to dot matrix.

DisadvantagesThe ink cartridges can be expensive so running costs can be high. The printing speed is slow compared to a laser printer. Ink can be smeared on paper.

Table 3-2 Inkjet Printer Features

Laser printers

Figure 3-18 Laser Printer

The main features of a Laser printer are tabulated in Table 3-3.

Mechanism

These print in the same way as photocopiers. The powdered ink (toner), is transferred to the paper and then fixed by heat and pressure.A school or business printer would have a typical speed of 10 to 20 pages per minute (ppm).

Uses Common wherever fast, high quality printing is required.

AdvantagesThey are quiet and fast and produce high quality printouts. Running cost are low because although toner cartridges are expensive to replace, they last a long time.

Disadvantages

Laser printers are more expensive than ink-jet printers (but the difference is narrowing). Toner cartridges are expensive to replace. (but their speed and high quality output means they are becoming more popular).

Table 3-3 Laser Printer Features

When buying a printer, users should evaluate relative purchase costs, running costs, quality and speed of different types of printers.

3.2.4 PlottersPlotters are devices, used by artists, designers or architects for producing multi-colour, high quality drawings such as architectural plans, charts and maps.

Pen plotters print their output by moving a pen across the surface on paper larger in size than used for printers. They can draw precise and complex line art, including text, but very slowly because of the mechanical movement of pens. Thermal and laser plotters are faster and

produce high density images. Plotters are used primarily in technical drawing and CAD (computer aided design) applications, where they have the advantage of working on very large paper sizes while maintaining high resolution.

Figure 3-19 A Plotter

3.2.5 Sound output deviceA speaker is an output device whose function is to output sounds when connected to a sound card installed on the computer motherboard. Computer speakers range from a basic pair of speakers (stereo speakers) to surround sound speakers with the finest sound for computer gaming. Voice output systems are used in public places such as airports to signal passengers of events and they are efficient means for assisting physically challenged people.

3.2.6 ProjectorsThe function of these devices is mainly to reproduce images or video frames on white screen. Some common types of projectors are video projectors, LCD projectors and handheld projectors.

Figure 3-20 LCD Projector

Video projectors accept a video signal as input, and the output is a corresponding picture frame on a projection screen using a lens system. They are commonly used in conference room presentations, classroom training as well as home cinema applications. LCD projectors, use liquid crystal display technology to produce images. In the trend of projector development there is a new craze of making it miniature. A pocket or handheld projector would enable projection of images whenever and wherever desired. The idea is to incorporate projectors in mobile phones, PDA’s (Personal Digital Assistant) and digital cameras.

3.3 Future of Input and Output DevicesGiven the current state of the art, computer input and output are quite asymmetric. The amount of information that is communicated from computer to user is typically far greater than that from user to computer.

Voice recognition software can be used as another means to supplement data input to the computer. A combination of voice, keyboard and mouse operations can be used for entering text information efficiently.With the emergence of virtual reality, the computer input and output is becoming more like interacting with the real world. For input, this means attempting to make the user’s input actions as close as possible to the user’s thoughts that motivated those actions. Graphics, animations, audio, and other media can output large amounts of information rapidly.

Exercises

Multiple Choice Questions

1. A device that allows one to enter data into the computer in the form of text is:

(a) keyboard (b) mouse (c) printer (d) modem (e) scanner

2. A device used for producing multi-colour, high quality drawings such as architectural plans, charts and maps is:

(a) laser printer(b) plotter(c) lightpen(d) digitizing tablet(e) touchscreen

3. In situations where carbon copies are needed and the quality is not too important, such as invoice sheets, we use:

(a) fast plotter(b) laser printer(c) dot matrix printer(d) inkjet printer(e) photocopy machine

4. Resolution is not a relevant criterion for a:

(a) monitor(b) digitiser(c) printer(d) scanner(e) microphone

5. One advantage of the dot matrix printer over the laser printer is :

(a) Dot matrix printer produces higher quality output. (b) Dot matrix printer prints more pages per minute.(c) Dot matrix printer can print carbon copies.(d) Dot matrix printer is portable.(e) Dot matrix printer has higher running cost.

6. A device used for 3-D positional information in virtual reality systems is the:

(a) optical mouse(b) split keyboard(c) trackball(d) data glove(e) touchscreen

7. The choice of input device for an application such as tourism or public information system is:

(a) digitising tablet(b) touchpad(c) touchscreen(d) keyboard(e) mouse

8. Which of the following is not a true characteristic of LCDs?

(a) LCD screens are perfectly flat.(b) LCDs have wide viewing angle.(c) LCDs are light and take up less space.(d) LCDs have low power consumption(e) LCDs do not produce electromagnetic waves.

9. The number of colours that a video card can display is determined by

(a) dot pitch(b) pixel density(c) refresh rate(d) power consumption(e) bit depth

10. Which of the following device is least prone to input errors:

(a) keyboard(b) touchscreen(c) lightpen

(d) mouse(e) touchpad

Open-Ended Questions

1. Describe the characteristics of CRT monitor and the factors that affect its quality.

2. Differentiate between an impact printer and a non-impact printer.

3. Explain how a flatbed scanner works.

4. State two applications where touchscreen interface is used and outline the advantages of using touchscreen.

5. Discuss the advantages and disadvantages of LCD and CRT monitors.

6. What are the factors you would consider before buying a printer?

7. Explain the importance and functionality of mechanical, optical and cordless mouse types.

8. Outline the merits and limitations of using touchpad and light-pen.

9. What is the difference between a plotter and a printer?

10. Discuss input and output systems that can assist physically challenged people.