Working of input devices.

Q1. Why is input unit needed in a computer? Discuss various types of input devices along with their working mechanism.

Ans. The input unit is responsible for taking input and converting it into computer understandable form (the binary code). Since a computer operates on electricity i.e., either ON and OFF or high voltage or low voltage. That means a computer can understand two states ON/OFF or High/Low voltage or the binary language that uses just two signals: 1 for ON and 0 for OFF.

Types of input devices along with their working mechanism are:

  1. The Keyboard: An important data entry device is the keyboard, which is a typewriter like device. Internally, a keyboard contains a matrix of switches (one switch per key) and a keyboard controller. When you press a key, its switch gets pressed and when you release a key, its switch gets released. Through pressing and releasing of switches, keyboard controller generates a scan code using a firmware look up table. This scan code is sent to PC. The PC (the computer) has another keyboard controller which converts the received scan code into a specific character.
  2. The Mouse: The mouse is a pointing device that fits under palm of a hand. Mouse controls movement of pointer (also called mouse pointer) on screen. When a mouse moves on a flat surface, the cursor on the screen also moves in the direction of mouse’s movement. A mouse generally has two or three buttons and it may or may not have a wheel. With its buttons and wheel, a mouse can perform any of these operations:
  3. Point
  4. Double Click
  5. Rotate Wheel
  6. Click
  7. Drag
  8. Press Wheel
  9. Right-Click
  10. Right Drag


There are three basic types of mice:

  1. Mechanical Mouse
  2. Opto-Mechanical Mouse
  3. Optical Mouse


  1. The Light Pen: A light pen is also a pointing device. The light pen consist of a photocell mounted in a pen-shaped tube. When the pen is brought in front of a picture element of the screen, it senses light coming from a limited field of view. The light coming from the screen causes the photon cell to respond by generating a pulse. This electric response is transmitted to a processor that identifies the pixel (graphic point) the light pen is pointing to. Clicking is performed by pressing the pen on screen. Thus, to identify a specific location, the light pen is very useful.
  2. Touch Screen: A type of display screen that has a touch-sensitive transparent panel covering the screen is known as touch screen. Instead of using a pointing device such as mouse or light pen, you can use your finger to point directly to objects on the screen.

In Touch Screen, a grid of light beams or fine wires criss-cross the compiler screen. When you touch the screen with your finger, the rays are blocked and the computer senses where you have pressed and identifies the object which you want to choose.

  1. Graphics Tablet: A graphic tablet or simply a tablet or digitizing tablet is an input device that enables you to enter drawing and sketches into a computer. A digitizing tablet consists of an electronic surface and a cursor or pen. A cursor (also called a puck) is similar to a mouse, except that it has a window with cross hairs for pinpoint placement, and it can have as many as 16 buttons. A pen (also called a stylus) looks like a simple ballpoint pen but uses an electronic head instead of ink. The tablet contains electronic circuitry that enables it to detect movement of the cursor or pen and translate the movements into digital signals that it sends to the computer.

A graphics tablet has a flat pad ( called the tablet) on which you can draw with a special pen (called stylus) or with a special device (called puck). As you draw on the pad, the image is created on screen. The drawings created in the manner are very accurate (generally up to hundredth of an inch).


  1. Joystick: The joystick is a device that lets user move an object on the screen. Children can play with computer in a simple way by the use of a joystick (or a trackball).

A joystick is a stick set in two crossed grooves and can be moved left or right, forward or backward. The movements of the stick are sensed by a potentiometer. As the stick is moved around, the movements are translated into binary instructions with the help of electrical contacts in its base.

A joystick is generally used to control the velocity of the screen cursors movement rather than its absolute position.

The tracker ball also does the same thing but is round in shape. Both joystick and the tracker ball allow you to move objects around the screen easily.

  1. Microphone (Mic): We can send sound input to computer through a special input device called microphone or mic in short.

The microphone works in tanden with a sound card. You can speak your words or input a sound through mic an the sound card translates the electrical signal from microphone into a digitized form that the computer can store and process.


  1. Magnetic Ink Character Reader (MICR): In this method, human readable characters are printed on documents (such as cheques) using a special magnetic ink.

Characters are printed using a special ink called magnetic ink (that contains iron oxide). MICR reads these characters by magnetizing the ink abd by examining the shape of the character. MICRs are mainly used in Banks.

  1. Scanner: A scanner is a device similar to a photocopier. A photocopier prints the gives printed image/page on a page. And a scanner creates an electronic form of the printed image, which can later be manipulated, changed and modified according to the requirements.

The scanners can convert any image into electronic form by shining light on to the image and sensing the intensity of the reflection at every point. Scanners come in variety of sizes from hand-held to desk top models as discussed below:

  1. Hand-held Scanners
  2. Flatbed Scanners
  3. Drum Scanners


  1. Optical Character Reader(OCR): OCRs are capable of reading/identifying hand written text also. The printed characters are examined by passing them under a strong light and a lens system, which differentiates light (no ink) from inked areas, and a logical system which attempts to determine which of the possible characters is being examined.
  2. Optical Mark Reader (OMR): In this method, special preprinted forms are designed with boxes which can be marked with a dark pencil or ink. Each box is annotated distinctly so that the user clearly understands what response she is marking. Such a document is read by a document reader, called optical mark reader (OMR) which transcribes the marks into electrical pulse which are transmitted to the computer.
  3. Smart Card Reader: The smart card contains a microprocessor that retains certain security and personal data in its memory at all times. The special reader machines that can read information in smart cards are called smart card readers.

The smart cards can hold more information, have some processing capability and are almost impossible to duplicate. Also, they can serve as multi-purpose card e.g., an ATM card, credit card, ID-card, electronic cash card etc.

  1. Bar Code Reader: A bar code reader emits a beam of light (generally a laser beam) which reflects off the bar code image. A light-sensitive detector in the bar code reader then identifies the bar code image by recognizing special bar at the both ends of the image. Once the bar code is identified, the bar pattern is converted into a numeric code that can be processed later in any manner.
  2. Biometric Sensors: Biometrics is a technology that verifies a person’s identity by measuring a unique-to-the-individual biological trait. Biometric Technologies includes dynamic signature verification, retinal/iris scanning, DNA identification, face-shape recognition, voice recognition and fingerprint identification. Biometric identification is superior to lower technology identification methods in common use today- namely passwords, PIN numbers, key cards and smartcards.
  3. Web Camera (WebCam): A webcam or web camera is the term used for any camera that generates images that can be accessed by and displayed on web browsers through a server. A webcam is essentially a camera that is connected to a computer either directly or wireless. A webcam gathers a series of digital images that can be displayed remotely on web browsers remotely.

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