Unit2-chap2-input devices

Unit2-chap2-input devices

contentsImportance of I/O devicesTypes of input devicesKeyboardPointing devicesSpeech recognitionDigital cameraWebcamScannersOCROMRMICRBar-code reader

introductionA computer system has four components: input devices, CPU, output devices and memory.An input device provides data to CPU fro processing.After processing , the input data is converted to meaning full information and this is sent to output devices.An input device is an electromechanical device that allows the user to feed information into the computer analysis , storage and give commands to the computer.

After processing the data from input devices the computer provides the results with the help of output devices.An output devices converts machine readable information into human readable form.

Importance of input/output devicesThree stepsStep1 : data input via an input devices.Step 2: processing the dataStep 3: data output via an output device.Input devices play a major role in the processing of any data via the computer system because the output is always based on the input provided.Generally the data provided from input devices is raw in natureHence the input device should manipulate this raw data and send for further processing.

Types of input devicesComputer accepts the data in two ways i.e. manually or directly.In case of manual data entry, the user enters data into the computer by hand using keyboard or mouseA user can enter the data directly by transferring information automatically from a source document into the computer. Some common input devices are keyboard, mouse, scanners, speech recognition etc

keyboardUsing keyboard user can give text and commands.Designed as regular typewriter with few additional keys.Data is entered into the computer by pressing the keys.The layout of keyboard has changed ever since it is been introduced. Variations are with additions of more keys that provide additional functionality.

Laptop keyboards are slightly different arranged from the desktop keyboards.Many system manufactures add some special buttons to standard keyboardIt is the easiest input device which does not require any special skill to operate or learn.The maintenance and operational cost of keyboard is very low.It is a slow process, inputting all data from the keyboardHard for people suffering from muscular disorders.

How does keyboard work?It is series of switches connected to a small keyboard microprocessor that monitors the state of each switch and initiate specific actions to a change in state.When the user presses the key , it causes change in the current flowing through the circuit The keyboard microprocessor detects this change in current flow.By doing this, the processor can tell when a key is pressed and when it is released.

Depending on which key is pressed, the processor generates the associative code called as scan code, of the key and sends it to operating system,A copy of this code is stored in the keyboards memory.When the operating system reads this scan code, it informs the keyboard and the scan code stored in keyboards memory

Pointing devicesA pointing device is used to communicate with the computer by pointing on the locations on the monitor screen.They dont need key of characters, instead the user can move the cursor and perform operations by clicking or dragging MouseTrackballJoystickLight penTouch screen

mouseA small hand-held pointing device with a rubber ball embedded at its lower side and buttons on the top.Mouse contains two or three buttons, which can be used to input the commands and information.Classified as mechanical mouse and optical mouse based on the technology used.A mechanical mouse uses a rubber ball at the bottom surface which rotates as the mouse is moved along a flat surface

Mouse (electromechanical )

Mouse (optical)

Commonly used and cheapest pointing deviceAn optical mouse uses a light beam instead if rotating ball to detect the mouse movement.As the user moves the mouse, the cursor on the screen also movesCostlier than mechanical mouse, does not need a mouse pad and always accurate.A mouse allows us to create graphic elements on screen such as lines , curves and freehand shapes.

No additional installing and cost is required, comes with the computer as keyboard.Requires a flat space near the computer to move itLaptops or palm tops do not have mouse, they use touch pad or trackball

How does mouse work?A mechanical mouse has rubber ball at the bottomWhen the user moves the ball over a flat surface , the ball rolls.The distance , direction and speed of the balls motion is tracked.The information measured is used to move the cursor inside the screen in the computer.There are three rollers.One of them, which is mounted at 45 to other two balls, is spring loaded.

Internal parts of mouse

This roller is the smallest of the three balls.The other two rollers are usually larger and different color.These rollers are mounted at 90 angle to another, one roller measures how fast the ball is turning horizontally, and other measures how fast the ball is turning in vertical direction.When the ball rolls, it turns these two rolls.These balls are connected to axles, which are connected to sensors that measures how fast the axle is turning.

There is a small processor present in the mouse, which consists more than one chip, which uses the information of how fast the mouse is moving and in what direction.This information is passed to computer via a mouse cord, where the operating system then moves the cursor accordingly.

The optical mouse uses an infrared light and special mouse pads with the fine grid lines to measure the rotation of the axle.The axle in the optical mouse is connected to a little photo interrupter wheel with a number of tiny holes in it.In front of this wheel, there is a light source on the other side of the wheel is a light metreAs the wheel turns, the light flashes occurs, the light sensor can measure how fast the wheel is turning and sends these values to the computer

The computer moves the cursor as per the values received from the mouse.This happens hundred of times per second, making the cursor appear on the screen to move very smoothly.

trackballA pointing device that reassembles a ball nestled in a square cradle and serves as an alternative to mouse.Similar to mouse turned upside down.It consists of a ball that is moved by fingers and the mouse moves accordingly.The size of the ball varies from large as cue ball to small as marbleIt comes in various shape commonly in three i.e. square, button and ball

trackball

Used to control the mouse movements and actions on the computer screen.By moving with fingers and not entire arm, user will be able to move the mouse pointer with a greater precision and accuracy.Used by graphics designers and gamers.Requires less space than mouseIn form of button, it can be reprogrammed according to the function.Does not comes with the computer, if user wants it , he should buy it separately, hence additional cost will apply.

joystickIt is a device that moves in all directions and controls the movement of the cursor.Basic design consists of a stick that is attached to a plastic base with a flexible rubber sheath.The electronic circuitry measures the movement of the stick from its central position and sends information for processingIt has buttons which can be programmed as the actions required.If offers the types of control: digital, glide and direct

Digital control allows movement in a limited number of directions such as top, down , left and rightGlide and direct control allows movements in all directions (360)Is used to control the velocity of the screen cursor movement rather than its absolute position.Used in computer games.Also used in flight simulators, training simulators , CAD/CAM systems , controlling industrial robots.

Light penAlso called mouse penIs a hand-held electro-optical pointing device which when touched to or aim closely at a connected computer monitor, will allow the computer to determine where at that screen the pen is aimed.Helps in drawing images and selects objects on the display screen just pointing into the objects.It does not emit any kind of light as in name, it has a light-sensitive diode which senses the light emitted by the screen.

The light emitted from the screen causes the photocell to respond by generating a pulse.This electric response is transmitted to the processor that identifies the position to which the light pen is pointing to.With the movement of the light pen , lines or images are drawn.Does not require a mouse pad or horizontal surface, behaves exactly like a mouse.Using light pen, users can interact with computers very easily like for selecting, drag and drop etc

It is pointed directly to the screen, does not require any special skill to use it.Perfect to use when user has less desk space, harsh work environments and situations where fast accurate inputs are required.It does not give any kind of information when pointed to blank part of the screen.Economical and requires little or no maintainance.

Touch screenSpecial kind of input device that allows the direct selection of menu item or the desired icon with the touch of finger.It registers the input when the user touches the menu item.Used when information has to be accessed with minimum effort.Not suitable for inputting large amount of data.Used in systems that provides information's such as hospitals, airlines, railways reservations, atm etc

TrackpadIs a stationary pointing device that works by sensing the movement of the fingers across a small sensitive surface and translating them into pointing movement in the screen.Used in laptops and can be used for PC by connecting it to it with help of cord.Present in PDAs, media playersHas two or three buttons which act same as mouse buttons.Many are strike sensitive, the user just has to tap the trackpad to perform the operations.

Speech recognitionOne of the most interactive systems to communicate with the computer.The user can simply instruct the computer with the help of microphone, to perform a task.It is technology in which sounds, words or phrases spoken by humans are converted to digital signals and hence converted into computer generated text or commands.Most of the system are speaker dependent so they must be separately trained for each individual user.

The recognition system learns the voice of the user, who speaks the words repeatedly, then these voiced words are used in future.Used by people with disabilities or travelers who record information for later transcription.The computer based recognition system can browse data on internet, letters or emails, navigate among applications by voice commands.They allow user to communicate with the computer without using a mouse or keyboard.

Speech recognition

The reliability of speech recognition system is lesser when compared to mouse or keyboard input devices.Disadvantage is that at times the recognition system will not differentiate between two similar voiced words such as sea and see etc.Not suitable for noisy places.

Digital cameraStores digitally rather than recording them on a filmOnce the picture is clicked, it can be transferred to the computer system then it can be manipulated with an image editing software and can be finally printed.The making photo is inexpensive as there is no film processing.

Digital camera

Web camShort form of web cameraIs a portable video camera, which captures live videos or images that may be viewed in real time over a network or the internet.Small digital camera that is either built in computer or can be connected through a USB portPlaced normally above monitor or laptop to capture images of the user while he or she is working in the computer.

Web cam

Wide variety of web cam are availableIn two categories they are classified, streaming and snapshotA streaming webcam captures moving images thus creating a streaming video- a web video plays on a computer immediately as its data arrive via network, the recipient need not download the video.High speed internet is required to transfer the video smoothly.

A snapshot camera only captures still images and refreshes it continuously.It produces a better quality images and is easier to configure than streaming videos.Webcam are used in video conferencing to provide real time communication where groups of people can see and interact with each otherUsed in various messengers such as yahoo, windows live messenger where videos are shared with somebody.

Webcams are cheap, compact and are easy to install and use.They are affordable because of their lower manufacturing cost.Disadvantage is they produce real time images only when they are plugged to PC, useless if they are not connected to a PCSome webcams come with special features such as automatic lighting controls, automatic face tracking and autofocus with increased cost.

scannersThe information on the paper is needed on the computer for further operation, then scanners are used.A scanner is an input device that converts a document into an electronic format that can be stored on the disk.The electronic image can be edited, manipulated, combined and printed by using an image editor.Scanners are also called optical scanners if they use light bean to scan the input data.

scanners

Scanners come with a utility program that allow them to communicate with the computer and save the scanned images as graphics files on the computerThey can store images in both grayscale and color modeTwo types are Hand-held scannersFlatbed scanners

Handheld scannerIt consists of LEDs which are placed over the document to be scannedThe scanner performs the scanning very slowly from top to the bottom of the document with its lights onAll documents scanned are converted into images.The scanner is scanned over the document slowly steadily and carefully over the document at constant speed without stopping or jerking in order to obtain better result.

Used where accuracy is not of that importance.Size of such scanners are small.Comes in resolutions upto 800 dpi, are available in grayscale or color.Used when the volume of documents to be scanned is low.Commonly used to read price tags, shipping labels , book ISBN and so on.

Handheld scanner

Flatbed scannerSimilar to photocopier machine.It consists of box containing a glass plate on its top and lid that covers the glass plateThe glass plate used for placing the document to be scanned.The light bean is placed below the glass plate and when it is activated, it moves horizontally from left to right.After scanning one line , the light beam moves in order to scan the next line and the procedure is repeated until all the lines are scanned.

Scanning an A4 page takes about 20 seconds.These scanners can scan black and white as well as color images.They are larger in size and more expensive than held-held scanners.They usually produce better quality images because they employ better scanning technology.

Flatbed scanner

Optical character recognitionA scanner converts an input document into an electronic format that can be stored on the disk.If the scanned document contains text, you need an optical character recognition software.When a scanner scans a document , the scanned document is stored in bitmap in the computer s memory.The OCR translates this bitmap image of text to ASCII codes that the computer can interpret as letters, numbers and special charecters.

Because of OCR , data entry becomes easier, error free and less time consuming.It is very expensive, if the document is not typed properly, it becomes OCR to recognize the characters.Paragraph marks and tabs or text formatting is lost during scanning.The output from a finished text scan will be a single column editable text file.

OCR

Optical mark recognitionIs a process the detecting the presence of the intended marked responses.Optical mark reading done by a device called optical mark reader.In order to be detected by the OMR reader, a mark has to be positioned correctly on the paper and should be significantly darker than surrounding paper.It enables a high speed reading large quantities of data and transferring this data to a computer without using a keyboard.

Used for reading answer scriptsSpecial printed forms/ documents are printed with boxes which can be marked with a dark pencil or inkThese forms are passed under a light source and presence of dark ink is transformed into electric pulses, which transformed to the computer.OMR has better recognition than OCR because fewer mistakes are made by machines to read marks than in reading handwritten characters.

Large volumes of data can be read quickly and easily without the need for specially trained staff.Can scan about 1500 to 10000 forms per hour.OMR readers are slow, the person writing the form should follow special instructions while filling it.If there is any dirt or any folding of the paper will make the OMR to read the data in wrong way.It requires alignment of printing forms and needs good quality

OMR (marks sheet)

Omr machine

Magnetic ink character recognitionThere are special characters written on cheque.The character are printed using a special ink, which contains iron particles that can be magnetized.In order to read this, there should be a device called Magnetic ink Character reader (MICR) is used.It reads the character by examining the shapes in matrix form and the information is then passed on to the computer

Banks prefer MICR as it provides extra security against forgeries.When the cheque are manipulated, they wont have magnetized particles hence codes produced by the MICR wont be same, or will produce incorrect code.The reading speed of the MICR is also higherThis is efficient and time saving for data processing.

MICR cheque

MICR reader

Bar code readerBar code is machine readable code in the form of group of parallel vertical lines of varying widths.Commonly used for labeling goods that are available in supermarkets and numbering books in libraries.This code is sensed by a bar code reader using a reflective light.The information recorded are fed into the computer, which recognizes the information from thickness and spacing of bars.

Bar code reader is hand held or fixed mountHand held bar code readers read the bar code of a stationary items.Fixed mount bar code readers, items are passed by the scanner by hand by the retail scanning applications or conveyor belt in industrial applications.Provides enormous benefits such as capturing the data faster and more accurateA bar code reader can record data 5-7 times faster than a skilled typist.

It has error rate of 1 in 3 millionIt reduces cost in terms of labor cost and revenue losses resulting due to data collection errors.Bar code readers are used in supermarkets, department stores, libraries and other places.Bar codes is commonly seen behind books , greeting cards.In grocery shops it is used to determine the item being sold and to retrieve the price from the system.

Bar code reader and bar code

Bar code reader