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 Input
devices
| Revision Points: |
- Candidates are expected to identify
the following input devices:
- keyboards, pointing devices (including
mouse, touch pad and tracker ball),
video digitisers, remote
controls, joysticks, magnetic
stripes, scanners, digital
cameras, microphones, sensors,
MIDI instruments.
- Candidates are expected to identify suitable
uses of the input devices in above, stating the advantages
and disadvantages of each.
|
|
Mouse |
 The
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 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) |
  The 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 or 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.
 Advanced
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: |
- Resolution is still not as good as film but is improving steadily
- 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 |
  Joysticks 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 |
 This 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.
|
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Disadvantages:
|
- Stored audio files can take up a lot of memory.
|
| Video digitiser |
 A
video digitiser is used to convert analogue
signals from a video camera or video cassette
recorder into a digital format.
The digitised video data can then be saved as a file
and played on a monitor.
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.
|
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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 is often needed to process video footage.
|
| Midi instruments |
  These are used to produce music and
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.
|
| Disadvantages:
|
- Audio cannot be recorded.
- 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 emits 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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