Tuesday, October 12, 2010

Input devices

Input devices 

The keyboard
A 'keyboard' is a human interface device which is represented as a layout of buttons. Each button, or key, can be used to either input a linguistic character to a computer, or to call upon a particular function of the computer. Traditional keyboards use spring-based buttons, though newer variations employ virtual keys, or even projected keyboards.
Keyboards usually have the following:
  • Keys for the letters of the alphabet.
  • Keys for punctuation symbols.
  • Numbered keys or a numeric keypad (or both).
  •  Keys to move the typing cursor and other text controls, such as Tab, Insert, Delete, Backspace, Enter, and so on.
  • Keys which change the function of other keys, such as Shift, Caps Lock, Alt, and Ctrl.
  • Function keys numbered from F1 to F12. The function of these keys is set by whichever program is running.

The Keyboard.

The pointing device
A pointing device is any human interface device that allows a user to input spatial data to a computer. In the case of mice and touch screens, this is usually achieved by detecting movement across a physical surface. Analog devices, such as 3D mice, joysticks, or pointing sticks, function by reporting their angle of deflection. Movements of the pointing device are echoed on the screen by movements of the cursor, creating a simple, intuitive way to navigate a computer's GUI.
  • A mouse is used by moving it across a mouse mat or other flat surface. This moves a ball on the bottom of the mouse. The movement of the ball sends a signal to the computer. Software interprets this signal and performs an operation, such as moving a cursor or drawing a line.
  • A mouse has two or more buttons on top of it, the function of which depend upon the software being used.

A computer mouse

The scanner

A scanner is a device that uses light to read an image or text and turn it into a digital message. This media can then be used to store, change and send the image or text. There are various types of scanners. The three most common are Drum, flatbed and hand. Drum scanners use photomultiplier tubes (PMT). Flatbed scanners use a glass pane and a bright light. Hand scanners are dragged across the image manually.

  • Hand-held scanners are dragged across the paper to scan it.
  • Flatbed scanners have the paper placed on top of them, in a similar way to a photocopier. These are more expensive than hand-held scanners but they are usually able to produce higher resolution images.
  • Companies needing to store paper records can transfer them to microfilm. A microfilm is a series of page images, miniaturised onto 35mm film. Special scanners are available to prepare and read microfilm using a computer.
  • If a scanner is used to scan a page of text, Optical Character Recognition (OCR) software can be used to convert the scanned image into text data that can be edited using word processing software.

The scanner

The trackball:

A trackball is a pointing device consisting of a ball held by a socket containing sensors to detect a rotation of the ball about two axes—like an upside-down mouse with an exposed protruding ball. The user rolls the ball with the thumb, fingers, or the palm of the hand to move a cursor. Large tracker balls are common on CAD workstations for easy precision. Before the advent of the touchpad, small trackballs were common on portable computers, where there may be no desk space on which to run a mouse. Some small thumb balls clip onto the side of the keyboard and have integral buttons with the same function as mouse buttons. The trackball was invented by Tom Cranston and Fred Long staff as part of the Royal Canadian Navy's DATAR system in 1952, eleven years before the mouse was invented. This first trackball used a Canadian five-pin bowling ball.
  • A trackball can be used as an alternative to a mouse. It has buttons, like a mouse, but the pointer is moved using a rotating ball set into the top of the device (basically an upside-down mouse).
  • Some people find a trackball easier to use than a mouse. One advantage is that it does not need a flat area to use it. For this reason, trackballs are sometimes included on laptop computers.


The TrackBall

The touchpad

A touchpad (also track pad) is a pointing device consisting of specialized surface that can translate the motion and position of a user's fingers to a relative position on screen. They are a common feature of laptop computers and also used as a substitute for a computer mouse where desk space is scarce. Touchpad vary in size but are rarely made larger than 40 square centimeters (6.3 x 6.3 cm or about 6 inch²). They can also be found on personal digital assistants (PDAs) and some portable media players, such as the iPod using the click wheel.

  • A touch pad is another device for moving the pointer. In this case, you use your finger or a pen-like instrument (or stylus) on a sensitive pad to move the screen pointer.
  • Because a touch pad is flat and does not require the user to push down a specific key (as with a keyboard) or grasp it (as with a mouse), it is often used as an input device for people with particular disabilities. Touch pads are also used on laptops and palmtop computers.
  • Another form of touch pad is the graphics tablet. This enables the user to create an image on the computer by drawing on the pad with a specially designed pen. Graphics tablets are used by graphic design artists and for children's drawing software.

The touchpad

The joystick
A joystick is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling. Joysticks are often used to control video games, and usually have one or more push-buttons whose state can also be read by the computer. A popular variation of the joystick used on modern video game consoles is the analog stick.
  • A joystick consists of a base and a stick perpendicular to the base. The stick can be moved in any direction, enabling the user to move an object around the computer screen. A joystick can perform a similar function to a mouse or trackball, but is only commonly used for playing games.

The joystick

The microphone
The microphone converts audio signals to electrical waves and these can be converted by electronic circuitry in the computer to digital from. What is difficult is the recognition by the computer, of the signal, so that it can be handle it in the same way as if it had been typed. Highly sophisticated speech-recognition software is required to be able to match the sound uttered by the user with a vocabulary of sound signals stored in the computer and to display the words on the screen as though they had been entered at the keyboard.

The microphone

The Digital Camera

Digital cameras take pictures in electronic format, providing convenience for users who want to preview, modify and delete photos immediately. A digital camera hooks up to your computer as an input device--typically via a USB cable. Drivers and digital camera software applications installed on your computer make it possible to transfer the digital photos to your system.

  • Digital cameras work in much the same way as normal cameras, except that the exposure from the subject is recorded onto light sensitive diodes not photographic film. The image is saved to a flash memory card (CompactFlash for example). Images can often be printed directly to a printer or displayed on a television or can be transferred to a computer (either by connecting the camera to a suitable port (such as a USB port) or by inserting the memory card into a card reader.
  • There are also devices to capture moving images. Web Cams can record low resolution video images. High resolution digital video cameras are available, but are still quite expensive. Some filmmakers are starting to record motion pictures entirely on digital video.

The Digital Camera

The Webcam

A web camera, or webcam, is an input imaging device that typically connects to a USB port on a computer. The device inputs live picture and image feeds, which can be connected to the Internet in real-time. Webcams have many uses, including connecting people to video conferences and displaying live weather and traffic conditions over the Internet.

Light pen
  • A light pen is a hand-held device (very similar to a standard ballpoint pen) that has a device at the tip, which either emits light or is light sensitive. The user is able to send information to the computer by touching the pen onto certain areas of a specially designed screen.
  • Light pens are not widely used because they require a lot of arm movement, making them tiring and uncomfortable to use.
  • Possible uses include engineering production lines and science laboratories where dirt or other environmental factors make the use of a keyboard or mouse impractical.


Light pen



  2. I like the Blog !!(: explain the meaning of the input and output divices