12.1 Input Devices

An input device is the hardware that allows users to enter data into a computer and converts the data into a computer-readable form.

Examples: Keyboards Pointing devices Scanners Optical readers Microphones Digital cameras Digital video cameras

Keyboards Allow users to enter data or commands into a computer

by pressing its keys. Convert keystrokes into corresponding electrical signals

that the computer can understand. Contain keys for typing letters, numbers and punctuation

as well as modifier keys such as ‘Shift’, ‘Ctrl’ and ‘Alt’.

12.1 Input Devices

A MIDI keyboard for inputting musical instrument digital interface (MIDI) instructions

A keyboard

Pointing Devices Allow users to control a cursor of a pointer on a

graphical user interface (GUI). Trigger an action that sends a command to the

computer. A pointer is a small symbol on the screen.

Appear as an I-beam, a block arrow or a pointing hand

Select an item from a menu

Move an item from one place to another

Drag

12.1 Input Devices

Pointing Devices Mice

Use a multidirectional mechanism to register its motion. Control the movement of the screen pointer. The buttons on the top are used to issue commands. Scrolling wheel allows a user to move a document displayed

up and down rapidly when viewing a long computer file. Mechanical mouse has a ball on its underside and tracks

the direction in which the ball is rolling. Optical mouse has an optical sensor which detects its

movement accurately.

12.1 Input Devices

Pointing Devices Mice

Mechanical mouse Optical mouse

Top view Top view

Bottom view Bottom view

Scrolling wheel

12.1 Input Devices

Pointing Devices Trackballs

Like an inverted mouse Roll the ball with your finger to control the screen pointer. Base of a trackball remains stationary while operating Saving space

A trackball

12.1 Input Devices

Pointing Devices Touchpads

A touch-sensitive plate, usually found on a notebook computer

Drag your fingertip on the surface of the touchpad to control the movement of the screen pointer.

Tap the pad = click the buttons on a mouse

A touchpad

12.1 Input Devices

Pointing Devices Track Points

A small stick that looks like an eraser tip of a pencil Pressure-sensitive, allow users to move the pointer in the

direction it is pushed Usually positioned between the keys on the keyboard of a

notebook computer

A track point

12.1 Input Devices

Pointing Devices Joysticks

Designed for playing computer games Has a vertical lever that controls the movement of the

pointer Usually include trigger buttons for performing certain

actions in computer games

A joystick

12.1 Input Devices

Pointing Devices Touch screens

A video display device that has a transparent, touch-sensitive layer

Send an electrical signal to the computer to indicate the location at which a finger or a stylus touches.

Users can interact with a computer by pressing and dragging icons of figures on a screen.

12.1 Input Devices

A handheld game console

An information kiosk Applications of touch screen

Pointing Devices Touch screens

Widely used in: Information kiosks in airports Libraries Shopping centres Personal digital assistants (PDAs) Smart phones Handheld game consoles Notebook computers

12.1 Input Devices

Pointing Devices Digitizing Tablets

Also called a graphics tablet Allow users to draw and sketch directly into a computer. Detect the movements and pressure of a pen-like stylus and

converts the movements into digital signals. Widely used in graphic design and engineering

12.1 Input Devices

A digitizing tablet

Pointing Devices Handwriting Boards

Designed for Chinese character input Consist of a pressure-sensitive board and a pen-like stylus Must work with character recognition software to identify

the sketches and convert them into Chinese characters or symbols

Can also be used as a digitizing tablet

A handwriting board

12.1 Input Devices

Scanners Used to input text and graphics into computers Project light onto an object Capture the reflected light and interpret it as a pattern of

coloured dots

A pen scannerA scanner

12.1 Input Devices

Scanners Pattern of dots forms a bitmap image The resolution, measured in dots per inch (dpi),

determines the sharpness of the picture. The colour depth (or bit depth) of a scanner indicates the

number of colours used to represent each dot. The accuracy of a scanned image depends on its likeness

to the original object. Quality of scanned image is determined by:

Resolution Colour depth Accuracy

12.1 Input Devices

Scanners Can be used with optical character recognition (OCR)

software to convert the text on a printed document into an editable file

Scan a document by a scanner.

Import into OCR software. An editable file is created.

Using OCR software to convert text into an editable file

12.1 Input Devices

Optical Readers Read predetermined characters, marks or codes and

translate them into digital data. Examples:

Bar code readers Optical mark readers

12.1 Input Devices

Optical Readers Bar code readers

A mini-scanner which capture images of bar codes and translate them into digital data

The use of bar codes greatly increase the accuracy and efficiency of data entry.

A bar code reader

12.1 Input Devices

Optical Readers Optical Mark Readers

Used with optical mark recognition (OMR) software OMR software recognizes specific handwritten marks. Commonly applied to collect data from:

Multiple choice answer sheets Course registration forms Questionnaires Lottery tickets

An optical mark reader

12.1 Input Devices

Microphones Allow users to record sound into a computer. Usually connected to a sound card installed on the

motherboard Recorded sound can be saved as a digital file and played

back using a media-playing program. Can be used with speech recognition software which

translates vocal speech into text or commands

12.1 Input Devices

A microphone

Digital Cameras and Digital Video Cameras Digital cameras

Use a light-sensitive processor chip to capture scenes and turn them into digital images.

Images are stored in a memory card and the amount of memory space taken depends on the compression ratio, the file format and image resolution.

Usually contains an LCD display The larger the number of light-sensitive photosites in the

light-sensitive processor chip, the higher the resolution of the digital image.

12.1 Input Devices

A digital camera

Digital Cameras and Digital Video Cameras Web cam

Special type of digital cameras Usually connected to a computer Images captured can be stored in a computer. Commonly used for video conferencing and remote

surveillance via a computer network.

12.1 Input Devices

A web cam

Digital Cameras and Digital Video Cameras Digital video cameras

Also use a light-sensitive processor chip to capture the moving images

Store images as a sequence of high-quality digital images to form a video file.

Storage media can be DV tapes, DVDs or internal hard disks.

A digital video camera

12.1 Input Devices

Digital Cameras and Digital Video Cameras Digital video cameras

Also use a light-sensitive processor chip to capture the moving images

Store images as a sequence of high-quality digital images to form a video file.

Storage media can be DV tapes, DVDs or internal hard disks.

A digital video camera

12.1 Input Devices

12.2 Output Devices

Output Devices Hardware that translates computer processes and

information into a form that humans can understand Examples:

Visual display units Speakers Printers Video projectors

Visual Display Units (VDU) Also called monitor Allow a user to view a computer’s output instantly on a

screen Information on the screen is intangible. Examples:

Cathode ray tube (CRT) monitors Liquid crystal display (LCD) monitors

12.2 Output Devices

Visual Display Units (VDU) CRT monitor

Size = diagonal length of the screen The screen is divided into many dots known as pixels. A pixel is the smallest display unit of the monitor screen. Quality of a monitor’s display depends on its resolution, dot

pitch and contrast ratio.

A CRT monitor

Pixel

Dot pitch Pixels and dot pitch

12.2 Output Devices

Visual Display Units (VDU)

Resolution The number of pixels a monitor can display At a higher resolution, you can display a larger

working area, but the text and images will appear smaller.

Dot pitch The vertical distance between each pixel on a screen

The smaller the dot pitch, the sharper the displayed images is.

Contrast ratio

The measurement of the difference in light intensity between the brightest white and the darkest black

The higher the contrast ratio, the more levels of colour can be distinguished.

Resolution, dot pitch and contrast ratio of visual display units

12.2 Output Devices

Visual Display Units (VDU) LCD monitors

Slimmer Lighter Lower power consumption Better sharpness Lower radiation emission More expensive Lower contrast ratio Lower refresh rate Colour of images displayed on an LCD monitor varies

significantly at different angles. Unsuitable for graphic design and photo retouching.

An LCD monitor

12.2 Output Devices

Speakers Used to convert audio signals of a computer into sound Most personal computers have small built-in speakers

that produce warning sounds to alert users to certain events.

Essential output devices for multimedia computers. Connected to a sound card. Sound card will converts digital audio signals into

analogue signals for output through the speakers. Subwoofer can produce better base frequencies.

A pair of speakers with a subwoofer

12.2 Output Devices

Printers Produce text and graphics on a physical medium such as

paper or transparency film. Printed information is called a hard copy or a printout. Major factors of a printer’s performance:

Resolution Determine the sharpness of a printout Measured by number of dots per inch (dpi)

Printing speed Measured by number of pages per minute (ppm) or

characters per second (cps)

12.2 Output Devices

Printers Dot-matrix printers

Contain a print head made up of small pins. Produce printed images by striking those pins against an ink

ribbon to leave dots on the paper. Slow, noisy and incapable of producing high-quality

printouts Resolutions rarely exceed 480 dpi. Speeds vary from 200 cps to 600 cps. Ideal for printing multi-part forms

A dot-matrix printer

12.2 Output Devices

Printers Inkjet Printers

Form images by spraying tiny ink drops onto paper. Can use a black cartridge and one or more colour cartridges

to produce high-quality colour printouts. Typical inkjet printer provides a resolution of 600 dpi to

5,760 dpi. Speed: 1 ppm – 27 ppm

An inkjet printer

12.2 Output Devices

Printers Laser printers

Use a laser beam to produce an electrostatic film on a drum according to the dot pattern of the output image.

The toner sticks to the charged area when the drum rotates against the toner cartridge.

Toner is then transferred and fused on the paper as the drum presses against it.

A laser printer

12.2 Output Devices

Printers Laser printers

Can produce high resolution printouts at high speed Resolution: 600 dpi – 4,800 dpi Speed: 4 ppm – 50 ppm Has to store the whole image of the page before the printing

process begins More complicated graphics printed at high resolution

requires much more memory than a page with simple text only.

Colour laser print one page in four passes with four different colour toners.

12.2 Output Devices

Printers Thermal printer

Produces a printed image by selectively heating thermal paper when the paper passes over the thermal print head.

Coating of the thermal paper turns black in the areas where it is heated, producing an image.

Commonly used in point-of sale systems.

A thermal printer

12.2 Output Devices

Printers Plotters

Used to create high-quality or large-format printouts such as:

Blueprints Maps Posters

Mechanism of a plotter is similar to an inkjet printer.

Plotters

12.2 Output Devices

Multifunction Printers Include the functions of printing and communication. Example:

Printer Scanner Photocopier Fax machine Telephone

Suitable for small office home office (SOHO) Take up less space. Cheaper than buying all the devices separatelyA

multifunction printer

12.2 Output Devices

Video Projectors Project the computer display onto a large screen Use high intensity light bulb and a set of optical lenses Examples:

Liquid crystal display (LCD) projectors Digital light processing (DLP) projectors

12.2 Output Devices

Video Projectors LCD projector

Use a built-in light source to project the image on its LCD panel onto a screen

DLP projector Build images on the screen by digitally controlling the

reflection on tiny mirrors Quality of video projector:

Display resolution Standard: 1,024 x 768

Brightness Standard: 2,000 ANSI lumens

An LCD projector

12.2 Output Devices

Video Projectors LCD projector

Use a built-in light source to project the image on its LCD panel onto a screen

DLP projector Build images on the screen by digitally controlling the

reflection on tiny mirrors Quality of video projector:

Display resolution Standard: 1,024 x 768

Brightness Standard: 2,000 ANSI lumens

An LCD projector

12.2 Output Devices

12.3 Daily Applications of Input and Output Devices

Point-of-sale (POS) Terminal Widely used in supermarkets and chain stores Consists of the register itself and some various input

devices and output devices Input devices used:

Bar code reader Keyboard Readers for credit cards, Octopus cards and ATM cards

Output devices used: Thermal printers Monitors

A point-of-sale terminal in a supermarket

Cheque deposit Machine Equipped with a touch screen and an ATM card reader When cheques are inserted into the machine, the

machine scans the cheques one by one. Print receipt slips using a thermal printer.

A cheque deposit machine in a branch of Bank of China (Hong Kong) Limited

12.3 Daily Applications of Input and Output Devices

SOHO SOHO = small office home office Working space is a big concern Prefer to use a multifunction printer Prefer notebook computer to desktop computers

A SOHO office

12.3 Daily Applications of Input and Output Devices

Conference Room Most essential equipment for presentations: video

projector Wireless pointing devices

Allow the presenter to walk around the room during the presentation

May be equipped with a laser pointer, timer, buttons for slideshow controls, volume control and built-in flash memory

Wireless pointing devices for presentations in a conference room

12.3 Daily Applications of Input and Output Devices

Conference Room Most essential equipment for presentations: video

projector Wireless pointing devices

Allow the presenter to walk around the room during the presentation

May be equipped with a laser pointer, timer, buttons for slideshow controls, volume control and built-in flash memory

Wireless pointing devices for presentations in a conference room

12.3 Daily Applications of Input and Output Devices