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Input devices


Revision Points:

Mouse
A typical modern computer mouseThe mouse is used to control the movement of a pointer on the screen when it is moved horizontally over a flat surface.

A ball under the mouse rotates when it is moved and turns two rods, one for left/right and one for up/down.

Buttons on the mouse let you select options  from menus and drag objects around the screen etc. Some models are now wireless.

Uses:
  • Movement - controlling a screen pointer
  • Buttons - selecting items / menus etc.
Advantages:
  • Ideal for use with desktop computers.
  • Usually supplied with a computer so no additional cost.
  • All computer users tend to be familiar with using them.
Disadvantages:
  • They need a flat space close to the computer.
  • The mouse cannot easily be used with laptop, notebook or palmtop computers. (These need a tracker ball or a touch sensitive pad called a touch pad).

Tracker ball
A Tracker BallA tracker ball is used in the same way as a mouse but it is useful where desk space is limited.

It is like an upside down mouse because the user rotates the ball and the main body part stays still. It has buttons like a standard mouse.

Advantages:
  • Ideal for use where flat space close to the computer is limited.
  • Can be useful with laptops as they can be built into the computer keyboard or clipped on.
Disadvantages:
  • Not supplied as standard so an additional cost and users have to learn how to use them.

Standard Keyboard (Further keyboards types)
An ergonomic keyboardA specialised keyboardThe standard QWERTY keyboard is the commonest way to enter text and numerical data into a computer.

Each individual key is a switch, which when pressed, sends a digital code to the computer.

For example, pressing the 'A' key produces the binary code 01100001 representing the lower case letter 'a'. Holding down the shift key at the same time produces the binary code 01000001 representing the upper case letter 'A'.

Advantages:
  • Reliable for data input of text and numbers.
  • Usually supplied with a computer so no additional cost.
  • Specialised keyboards are available.
Disadvantages:
  • Users may be slow for not very accurate typists.
  • Slow for accessing menus etc. and difficult to use if you want to move objects around the screen.
  • Difficult for people unable to use keyboards through paralysis or muscular disorder.

Digital camera
These are used to take photographs like a normal camera but produce digital images instead of using film.

The light passing through the lens is digitised by special light sensitive sensors. The image is stored on memory chips in the camera and can then be transferred to a computer.

The resolution of such cameras is increasing rapidly and professional models have become standard in photo-journalism. Images are usually compressed as jpeg's to save memory.

Removable memory cardAdvanced models have removable memory cards to increase the camera's storage capacity. Images can be transferred to a computer by cables or memory card readers.

Advantages:
  • No film is needed and there are no film developing costs
  • Unwanted images can be deleted straight away
  • Images are already digital and can easily be transferred to a computer and edited or transferred over the Internet
  • Special image editing software can allow a huge range of adjustments and special effects to be tried
Disadvantages:
  • Images often have to be compressed to avoid using up too much expensive memory.

Scanner
These are used to digitise images of pages or objects.

A light moves slowly over the surface of the picture or object to be scanned. The colours of the reflected light are detected and digitised to build up a digital image. The digital data can then be saved by a computer as an image file.

They can be used with OCR software to convert images of text into actual text data which can be edited by a word processor.

Advantages:
  • Flat-bed scanners are very accurate and can produce images with a far higher resolution than a digital camera
Disadvantages:
  • Can produce very large image files which need a lot of computer memory to view and edit

Magnetic Stripe Reader
Magnetic stripes are thin strips of magnetic tape which are usually found on the back of plastic credit and debit cards.

When the card is inserted into a reader (in an Automatic Teller Machine or ATM for example) the tapes slides past a playback head similar to that used in a tape recorder. This reads the data from the stripe and passes it to a computer.

Advantages:
  • Simple to use and cheap to produce. The data can be altered if necessary.
Disadvantages:
  • Very limited storage capacity. Data easily destroyed by strong magnetic fields.
  • Not very secure as thieves can obtain the readers and alter the data.

Joystick
A joystick-controlled wheelchairJoysticks are often used for playing computer games such as flight simulators. They can also be used to control the movement of a wheelchair or other machinery.

They input directional data like a mouse but work by switches being closed as the joystick is moved left or right and up or down.

Mini finger-controlled joysticks can be used to control a laptop cursor.

Advantages:
  • Easy to learn to use.  Very simple design so they can be inexpensive.
Disadvantages:
  • Control can be a bit crude as the directions in simple joysticks are limited to forward, backwards, left and right.  Better models offer diagonal movement or better.

Microphone
MicrophoneThis is used for the input of sound which is then digitised by the computer. The digital audio can be saved for playback later on.

The digital audio can also be used with voice-recognition software to control hardware, navigate a menu or input text into a word processor.  Voice recognition can also be used in security systems.

Advantages:
  • Voice recognition software can be used to convert your voice into text or to control menu options on a phone system.
Disadvantages:
  • Stored audio files can take up a lot of memory.
  • Voice commands can be difficult to recognise by the software.

Video digitiser
A digital video cameraA video digitiser is used to convert sequences of analogue images into a digital format.

The digitised images can then be saved as a file and played back on a monitor to produce a moving image.

Software will allow the video to be edited and special effects added, as well as individual still images to be captured and saved. Digital video cameras digitise the image inside the camera and save the video frames in a digital format. This data can then be transferred directly to the computer via a fast transfer cable and interface such as Firewire.

Advantages:
  • Digital video is easily edited.  Sections can easily be cut and pasted together and digital effects added.
  • The output can be rendered into a wide range of formats ranging from DVD quality down to streaming video suitable for the Internet.
Disadvantages:
  • Video files take up a great deal of memory.
  • Fast video capture cards may be needed to capture high quality video footage.
  • A powerful computer and graphics card is often needed to process video footage.

MIDI instruments
MIDI stands for Musical Instrument Digital Interface.  These are normal musical instruments which have a MIDI port for input into a MIDI interface in the computer.

The notes are converted into digital data and saved as a file on the computer.  This data can be converted back into notes or edited by computer software.

The software often has a wide range of special effects or stored sound data from real instruments.

Advantages:
  • Data from a musical instrument is easily captured and edited with a computer.
  • MIDI files are small.
  • MIDI files can be recorded on one type of instrument and played back on another.
Disadvantages:
  • Audio cannot be recorded directly as an audio files such as MP3.
  • The playback depends on the instrument/computer sound card so may not sound the same as the original.
  • Only the note and the timing are stored.

Sensors
These detect changes in the physical or chemical environment and convert them into electrical signals. These signals can then be digitised and used by the computer.

 Sensors are often used when data logging.

Advantages:
  • There are a huge range of possible sensors and they include: heat; light; sound; movement; magnetism; pressure; strain; acidity (pH); oxygen levels; liquid levels; humidity; pulse rates; salinity; water flow; speed and acceleration. Switch sensors can detect angles of tilt or whether something is open or closed.
Disadvantages:
  • Most sensors need an interface to convert analogue signals into the digital signals that a computer can understand.

 

Remote control
These emit a beam of infra-red light which carries digital data signals. They are often used to control TV's and VCR's.

More advanced models can be programmed to transmit a series of commands with one button press.

Advantages:
  • Each function can have its own button making them very simple to use.
Disadvantages:
  • Only advanced models can be have the buttons reprogrammed so they cannot be used to control anything other than the device they were designed for.

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