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 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.
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:
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.
Disadvantages:
Stored audio files can take up a lot of memory.
Voice commands can be difficult to recognise by the software.
Video digitiser
A
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.
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.
The
mouse is used to control the movement of a pointer on the screen when it is moved horizontally over a flat surface.
A
tracker ball is used in the same way
as a mouse but it is useful where desk
space is limited.
The standard QWERTY keyboard is the
commonest way to enter text and numerical data into a computer.
These
are used to take photographs like a normal camera but produce digital
images instead of using film.
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.
These
are used to digitise images of pages or objects.
Magnetic
stripes are thin strips of magnetic tape which are usually found on the back
of plastic credit and debit cards.
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.
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.
A
video digitiser is used to convert sequences of 
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.
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.
These emit a
beam of infra-red light which carries digital data signals. They are often
used to control TV's and VCR's.