Input Devices

      An input device is any machine that is used to feed data into computer.  Some of them are general purpose, that is they are used by all computers where as some others are special purpose which are used to input data in a specific way.  Keyboard and mouse can be considered as general purpose and special purpose input devices are optical mark readers, optical character readers and track ball.  We will dicuss these different input hardwares. 

 1. Keyboard   

                 Keyboard  is  the most widely used device to input information in the form of words,  numbers,  etc.  It consists of type writer like keys that enable to enter data into a computer.  Keyboard come in variety of sizes and shapes.  There are 101 keys on a standard keyboard.  The keys on keyboard are often classified into standard typewriter keys, function keys, special purpose keys, cursor movement keys and numeric keys.  

                 The keyboard is an electro-mechanical device that is designed to create special sstandardised electronic codes when a key is pressed.  This code is transmitted to the computer through  the cable that connects keyboard to the computer. Here the incoming code is analysed and converted to appropriate computer usable code. 

 2. Mouse  

           Mouse is a pointing device, that controls the movement of the cursor,  or pointer on a display screen.  As the mouse is rolled along a flat surface the pointer on the display screen moves in the same direction.  

        The mouse has two or three buttons which have different functions depending on the program that is running.  The mouse is often used in graphic oriented computers.  When the mouse is moved and the cursor reaches the desired location,  the user can push the button on the mouse once or twice to signal a menu selection.               When the mouse moves on a flat surface the roller under the mouse moves.  This mechanical motion is converted into digital values that determines the magnitude and direction of the mouse movement using the electronic circuits in the mouse. 

 3. Optical Mark Reader (OMR) 

      Optical Mark Reader (OMR) is a

technology where the OMR device senses the presence or absence of a mark such asa pencil mark.

 

 OMR is commonly used in objective type tests and for inputting data recorded on questionnaires.In this method special pre-printed forms are designed with boxes which can be marked with dark pencil or ink. 

 The data recorded in this form is converted into computer-usable form using a high intensity beam in the Optical Mark Reader. The beam scans the marked forms and detects the number and location of the pencil marks. The data is then converted into electric signals for

computer. As the information is entered at its source, the possibility of errors is reduced. The disadvantage is the need for accurate. alignment of printing on forms and the need for good quality expensive paper.

 4. Magnetic  Ink Character Recognition

  (MICR) 

          Magnetic Ink Character Recognition

 (MICR) allows the computer to characters printed in a special font.

It is used in banks to read the numbers on the chegues directly, so that it reduces the errors.

The cheque is printed at the bottom with

the bank's identification number and depositor's account number. These numbersare printed with a special ink that contains magnetizable particles of iron oxide. When the cheque is received at the bank, the clerk prints the cheque amount using the magnetic ink. Now the cheque can be processed quickly using MICR with accuracy of data entry.

 5. Optical Character Recognition

(OCR) 

           Optical Character Recognition (OCR)

involves reading text from paper and

translating the images into a form that

computer can manipulate. An OCR enables

To feed a magazine directly into a computer.

All OCR systems include an optical scanner that uses a light and lens system for reading text and a sophisticated software for analysing images For OCR no special ink is

required. The OČR reader examines each

character as if it was made of minute spots.

Once the whole character is scanned, the

pattern is matched with a set of patterns stored in the computer to recognize the character. Patterns that are not identified are rejeeted.

 

  6. Bar code reafer 

             Bar Code Readers are photo electric scanners that read the bar codes or vertical zebra striped marks printed on product containers, A bar code is used to identify the description and price of a product to the super market's computer.

When the hand held scanner passes over
the bar code, it analyses the light and dark
bars for width and spacing, translating this into electrical signals for the computer.The
computer identifies the item and its price and informs it to the Point of Sales Terminal. In the case of a counter top scanning device the light source may be a laser  The super markets use a bar coding
scheme called the Universal Product Code
(UPC) which identifies data based on width
of bars and space between them.

 7. Joy Stick  

         Joy stick is a device that lets the user

move an object quickly on the screen It has

a lever that moves in all directions and controls the pointer or some other display symbols. Joysticks are used mostly for computer games. They are also used for CAD/CAM systems.

A joy stick is a stick set in two crossed

grooves with two buttons called triggers on

the top. As the stick is moved around the

socket the movements are translated into

binary instructions with the help of an electric contact in the base of the joy stick.

The pointer on the screen moves forward in the direction joy stick is pointing. To stop the pointer the joy stick has to be returned to its upright position.

 8.Track ball  

        A track ball is a pointing device in the

shape of a mouse lying on its back. To move the pointer, the ball is rotated. The three buttons provided next to the ball can be used like mouse buttons.

The advantage of track balls is that it

does not require much space to use as it is

stationaryIt can be kept on any surface. This is why track balls are popular pointing devices in porfable computers.

 9. Light pen  

               Light pen is an input device that utilizes a light sensitive detector to select objects directly on a display screen using a pen Light pen has a photocell placed in a smáll tube.

When the pen is moved over the screen

surface, it is able to detect the light coming

from the screen. The light from the screen

causes the photocell to respond, indicating X-Y screen co-ordinates to the computer. This bit locates the exact position on the screen.

Light pens are frequently used by

graphic designers, illustrators and drafting

engineers using Computer Aided Design

(CAD) to draw directly on the screen 

using the pen and key pad attached to a CADterminal or an engineering workstation userscan select colors, line thickness, reduce or enlarge drawing etc. very easily

  10. Scanner  

         Scanner is an input device that can read text or pictures printed on paper and translate the Information into computer usable form.

Most scanners use Charge Coupled Device

(CCD) arrays that consist of tightly packed

rows of light receptors that can detect variations in light intensity and frequencu

utery. A scanner works by dividing an image into a grid of boxes that represents each box with a zero or one depending on whether the box is filled in. Each box is represented by upto 24 bits. The resulting matrix of bits called bit map can be stored in a file and displayed on the screen. The denser the bit higher the resolution. The number of bits used to represent a pixel (picture element) is called bit depth. A higher bit depth can represent more colours.

 11. Digital Camera  

           Images can be input into a computer

using a digital camera. The digital camera

can take still photographs and store it. The

images can be transferred as digital input into the computer. The images are stored in the computer as digital files and can be

manipulated in many ways using the various imaging software's available.

 12. Web camera   

         A webcam is a video camera that feeds or streams an image or video in real time to or through a computer to a computer network, such as the Internet.

Webcams are typically small cameras that sit on a desk, attach to a user's monitor, or are built into the hardware. Webcams can be used during a video chat session involving two or more people, with conversations that include live audio and video.

  13. Voice Input Devices  

              A substantial amount of research is being done in voice recognition programming that can recognize spoken words and commands Voice input devices convert a person's speech into digital form These input devices, when combined with appropriate software, form voice recognition systems.

fig:various voice input  devices

  

These systems enable users to operate micro computers using voice commands.

Voice input devices convert spoken

words into electrical signals by comparing the electrical patterns produced with pre-recorded.The problems of voice input devices are the limitations of the size of computer's Vocabulary, pronunciation differences among, individuals and the inability to accept continuous speech. Voice input units are classified as single word recognition unit and continuous speech recognition unit. Single word recognition systems are used to control a micro computer's operations and to issue single word commands for special application programs.Continuous speech means, sentences spoken continuously is dictated directly into a computer using a microphone. The computer stores the sentences in a word processing file

which can be manipulated later.