computer input

8 Input Devices

8Through this device, a complete set of instructions and data is fed into the computer system and into the memory unit, to be stored until needed.

8 In short, the following functions are performed by an input device:

8 It accepts data and instructions in a form understandable to human beings from the outside world.

8 It converts these data and instructions into a computer acceptable form.

8 It supplies the converted instructions and data to the memory unit of the computer or register unit of CPU for further processing.

Category of Input Device

8 Direct-Entry Input Device

Example: keyboard

8 Pointing Devices

It is a kind of input device that enables the user to freely move an on-screen pointer and to select text, menu options, icons, and other on-screen objects. Some popular types of pointing devices are mouse, trackball, track pad, light pen etc.

8 Scanning Devices:

These are one kind of input devices that copy a printed page into the memory of computer and transform the image into digital data. Examples of scanning devices include scanner, OMR (Optical Mark Reader), OCR (Optical Character Recognition), Bar Code Reader etc.

8Audio Input Device

Example: microphone

88 Video Input Device

Example: Web camera, digital camera

Keyboard

8Keyboard is the primary input device for entering text and number.

8 A keyboard has 100/101 keys.

8 In a standard keyboard layout keys can divided into following category:

8 Alphanumeric keys

8 Modifier keys

8 Numeric keypad

8 Function keys

8 Cursor-movement keys

8 Special-purpose keys

Keyboard Layout

How the Computer Accepts Input from the Keyboard 

Mouse

˜ An input device that rolls around on a flat surface and controls the pointer

˜ Location

˜ Selection

Mouse operations

Pointing

Clicking

Double-clicking

Dragging

Right-clicking

Inside an optical computer mouse

Inside an optical computer mouse

1.     Click wheel.

2.     LED (obscured by click wheel).

3.     Switch detects when you press left mouse button. There's an identical switch on the right to detect the right mouse button and the whole click wheel is mounted on another switch so it doubles as a third, central button.

4.     Potentiometer (variable resistor) measures how much you turn the click wheel.

5.     LED.

6.     Resistor.

7.     Mica capacitor.

8.     Electrolytic capacitor.

9.     Prism bends light from LED through 90° down onto desk.

10. Light-detector chip measures light reflected from desk and sends details of mouse movements to computer.

11. Resistors.

12. USB cable connection to computer.

13. LED shines light down onto desk.

Mouse Variants

•        Trackball

•        Track pad

•        Integrated pointing device - Track point

•        Wheel mouse

•        Joysticks

•        Game pads

Optical Input Devices

• Image scanner

• Scanner is an input device that is used to convert any printed image into electronic form by shining light onto the image and sensing the intensity of light’s reflection at every point.

1. Handheld scanners

2. Flatbed scanners

3. Sheet-fed scanners

Audiovisual Input Devices

•  Microphones and Speech Recognition Software

> Dragon Naturally Speaking / Via Voice

> Unidirectional microphones

> Voice dependent vs. Voice independent

•  Video Input

> Digital Cameras

> Web cam