1.3.3 Input Devices 2D scanners Scanners can be used to convert images or text on paper into a digital format that can be used by the computer. A scanner works by shining a beam of light onto the surface of the object that you are scanning. This light is then reflected back onto a sensor that detects the colour of the light. This is then used to build up the digital image. Items that are scanned are usually stored in an image format. However, special software - Optical Character Recognition - can be used to convert text on the paper into text which can be edited with a word processor. However, the text doesn't always get converted very well and you could end up with a lot of mistakes. There are three types of scanner: Flatbed scanners Handheld scanners Specialist scanners The most popular type is the flatbed scanner. This is shown in the picture which has its lid raised to show the glass surface where you place the item to be scanned. This is probably the one that you use at school. They can scan larger images and are more accurate than handheld scanners. Handheld scanners are usually only a few inches wide and are held in the hand whilst they are rolled across the document to be scanned. The images produced are generally not as large or as high quality as those captured with a flatbed scanner. Advantages of scanners Disadvantages of scanners Flatbed scanners are very accurate and can produce reasonably high quality images. Images produced by the scanner can take up a lot of memory space. Any image which is digitised by the scanner can then be included on electronic documents. Images lose some quality in the scanning and digitising process. Images once digitised can be enhanced with a graphics application. The quality of the final image is dependent on the quality of the original image.
Transcript
1.3.3 Input Devices
2D scanners
Scanners can be used to convert images or text on paper into a digital format that
can be used by the computer. A scanner works by shining a beam of light onto the surface of the object that you are scanning. This light is then reflected back onto a
sensor that detects the colour of the light. This is then used to build up the digital image. Items that are scanned are usually stored in an image format. However,
special software - Optical Character Recognition - can be used to convert text on the paper into text which can be edited with a word processor. However, the text doesn't always get converted very well and
you could end up with a lot of mistakes.
There are three types of scanner:
Flatbed scanners
Handheld scanners Specialist scanners
The most popular type is the flatbed scanner. This is shown in the picture which
has its lid raised to show the glass surface where you place the item to be scanned.
This is probably the one that you use at school. They can scan larger images and are more accurate than handheld scanners.
Handheld scanners are usually only a few inches wide and
are held in the hand whilst they are rolled across the document to be scanned. The images produced are generally
not as large or as high quality as those captured with a flatbed scanner.
Advantages of scanners Disadvantages of scanners
Flatbed scanners are very accurate and can produce reasonably high
quality images.
Images produced by the scanner can take up a lot of memory
space.
Any image which is digitised by the scanner can then be included
on electronic documents.
Images lose some quality in the
scanning and digitising process.
Images once digitised can be enhanced with a graphics
application.
The quality of the final image is dependent on the quality of the
original image.
3D Scanners
A 3D scanner is a device that analyses a real-world object or environment to collect
data on its shape and possibly its appearance (e.g. colour). The collected data can then
be used to construct digital three-dimensional models.
Many different technologies can be used to build these 3D-scanning devices; each
technology comes with its own limitations, advantages and costs. Many limitations in
the kind of objects that can be digitised are still present, for example, optical
technologies encounter many difficulties with shiny, mirroring or transparent objects
Collected 3D data is useful for a wide variety of applications. These devices are used
extensively by the entertainment industry in the production of movies and video
games. Other common applications of this technology include industrial design
The purpose of a 3D scanner is usually to create a point cloud of geometric samples on
the surface of the subject. These points can then be used to extrapolate the shape of
the subject (a process called reconstruction). If colour information is collected at each
point, then the colours on the surface of the subject can also be determined.
Bar code reader
Barcodes are used to represent information about products. A barcode is normally a pattern
of thick and thin dark and light lines. A form of scanner called a barcode reader is used to
read them. Some are handheld and some are built into the EPOS terminal. Like a flatbed
scanner, it consists of a light source, a lens and a light sensor translating optical impulses into electrical
ones. The different thicknesses of lines are converted by computer into a number.
They are used in all kinds of shops, wherever the details of products represented b code
numbers need to be input. In libraries they are used to input the book number and library
card number.
They are faster than typing the number in using a keypad and more accurate method of
data entry compared with typing the number in.
Digital cameras
A digital camera (or digicam) is a camera that encodes digital images and videos digitally and stores them for later reproduction. Most cameras sold today are digital, and digital cameras are incorporated into many devices ranging from PDAs
and mobile phones (called camera phones) to vehicles.
Digital and film cameras share an optical system, typically using a lens with a variable diaphragm to focus light onto an image pickup device. The diaphragm and
shutter admit the correct amount of light to the imager, just as with film but the image pickup device is electronic rather than chemical. However, unlike film cameras, digital cameras can display images on a screen immediately after being
recorded, and store and delete images from memory. Many digital cameras can also record moving videos with sound. Some digital cameras can crop and stitch pictures
and performs other elementary image editing.
Keyboard The most common input device it is used for inputting text,numbers,punctuation marks, symbols and instructions using a number of software applications. By
pressing down a key completes an electrical circuit. This circuit then transmits a binary signal (commonly using ASCII) to the computer to represent the key
pressed. Ergonomic or ergonometric keyboards are shaped so that the user is less likely to suffer from RSI (repetitive strain injury).
Overlay or concept keyboards consist of an A4-sized tray that can have an overlay
sheet in it. It is used by people who may have disabilities as it is easier to press a
large symbol than to press the key on the keyboard.
Laser mouse An optical computer mouse uses a light source, typically a light-emitting diode, and
a light detector, such as an array of photodiodes or an image sensor, to detect movement relative to a surface. It is an alternative to the mechanical mouse, which
uses moving parts to perform the same function. When a mouse is connected with the computer, a red LED starts glowing. This light is focused on the surface beneath the mouse by a special type of lens (HDNS-
2100). The reflected light falls back to the camera integrated in Optical Mouse Sensor. The camera takes images of the surface with a frequency in the range of
1500 to 6000 images per second to calculate the position of mouse. These images are processed by Digital Signal Processor (DSP) and resultant co-ordinates are sent to the PC. The driver of the mouse installed in the computer receives the co-
ordinates and makes the cursor move on the screen accordingly.
Touch screens
A touch screen is the only device which works as both an input and an output device. You view the options
available to you on the screen (output) and you then use your finger to touch the option that you have
chosen (input). Touch screens work particularly well with a menu
driven interface. For example, a cashpoint (ATM) at a bank would first of all ask which service you want. You touch the option 'withdraw cash' on the screen. You
are then presented with another choice, 'how much cash do you want to withdraw?’ Once you have chosen
how much, you then get other options such as 'do you want a receipt?’ Another major use of touch screens are on smart
phones and modern tablet computers. Each 'app' is accessed by an icon on the touch screen.
Touch screens are easy to use and are often found in public places such as cashpoints at banks, ticket collection terminals at theatres or airports,
information centres at museums. Touch screens are not commonly used to input large
amounts of data because they are not very accurate and they would be tiring on the hands to use for long periods of time.
Capacitive Infra-red resistive Made up of many layers
of glass that act like a
capacitor, creating
electric fields between
the glass plated in
layers
The electric current
changes when the top
glass layer is touched
which is determined by
a microprocessor.
Heat sensitive
It uses glass
as screen
material
which needs
a warm
object e.g
finger to
carry out
input
operation
Optical
It uses an
array of
sensors in
the form of
grid
The point
of contact
is based on
which
coordinated
is touched.
Consists of upper layer of
polyester and bottom layer
of glass.
When top layer is touched,
the top and bottom layer
complete a circuit.
Signals are sent out and
interpreted by a
microprocessor; the
calculations determine the
coordinates of where the
screen was touched. Advantages
Screen visibility is good
even in strong sunlight
Permits multi-touch
capability.
Screen is very durable
It is a medium cost
technology.
Advantages
Allow multi-touch capability
The optical system allows
bare finger, gloved or stylus
for input.
Both have good screen
durability, it takes a major
impact to break the glass
Both have fairly good visibility
in strong sunlight.
Advantages
Relatively inexpensive
technology
Can used bare finger,
gloved finger or a stylus to
carry out an input
operation
Disadvantages
It allows only bare
fingers as input but
latest screens
permit a special
stylus to be used
Disadvantages
Relatively expensive
technology
Heat-sensitive only
allow bare fingers to be
used for input.
Disadvantages
Screen visibility is poor in
strong sunlight.
Doesn’t permit multi-touch capability.
The screen durability is
only fair and vulnerable t
scratches and wears out
through time.
Microphones
Microphones are used to input sound, which can then be stored and manipulated.
The sound input to the microphone is converted into an analogue electrical signal,
which has to be converted in turn into a digital signal so that the computer can
process it. This is usually done by the computer’s sound card, which acts as an analogue to digital converter.
Sensor: A sensor is a device that detects events or changes in quantities and provides a
corresponding output, generally as an electrical or optical signal. They can produce a stream of input data automatically without any human intervention. Usually this is
an analogue signal so it needs to be converted into digital data for the computer to process. This is done using by an Analogue-to-Digital Converter (ADC). Sensors are used extensively in monitoring / measuring / data logging systems, and also in
computer control systems. Following is the list of commonly used sensors:
Temperature Magnetic Field Gas
Pressure Moisture
Humidity Ph/Acidity/Alkalinity
Motion/ Infra-Red Advantages of using sensors to collect data are:
1. They can collect data far more frequently than a person. 2. They are more reliable than a person, who may forget to take readings. 3. They are more accurate than a person who may misread the signal.
4. They can collect data from places where it is not possible for a person to go such as inside a chemical or nuclear reaction vessel.
The disadvantage of using sensors is that they may need a power supply to work and may need regular calibration to check their accuracy. Temperature Sensor:
A temperature sensor produces a signal that depends on the temperature of its surroundings. The computer process the digitize signal to display a measurement or
to control an appliance. We can use temperature sensor in many appliance such:
Automatic washing machine
Digital thermometer Controlling heating system in buildings, including greenhouses and chemical
reaction vessels.
Pressure sensor:
A pressure sensor produces a signal that depends on the pressure to which it is exposed. Pressure sensor can be used in many appliances such as automatic blood pressure monitor. Pressure sensor can also control the pressure of gases or liquids
in chemical reaction vessel.
Magnetic Field: The Magnetic Field Sensor can be used to study the field around permanent
magnets, coils, and electrical devices. This sensor uses a Hall effect transducer, and measures a vector component of the magnetic field near the sensor tip. It has two
ranges, allowing for measurement of relatively strong magnetic fields around permanent magnets and electromagnets, as well as measurement of weak fields such as the Earth’s magnetic field. The articulated sensor tip allows you to measure both transverse and longitudinal magnetic fields.
Gas:
A gas sensor produces a signal depending on the concentration of a particular gas or vapor. We can use gas sensor for an inflammable gas to monitor the atmosphere and sound an alarm if there is a leakage. We can use gas sensor in other
applications such as: Breathalyzer, which measure the concentration of alcohol vapour in a sample
of breath and estimate the concentration of alcohol in blood. Process control in chemical industry. Environment monitoring of air pollution
Moisture/ Humidity sensor A moisture sensor produces a signal that depends on the concentration of water
vapors in the atmosphere. A moisture sensor can control an irrigation system more efficiently only allow water when soil is dry. We can use moisture sensor in many
other application including: Controlling a heating system and air conditioning system. Maintaining sufficient humidity in the air in a greenhouse.
Measuring humidity for meteorological record and forecasting in a weather
station.
PH/acidity/alkalinity sensor:
.1 Input, output and storage devices PH Sensor measures the pH of aqueous solutions in industrial and municipal process applications. It is designed to perform in the harshest of environments,
including applications that poison conventional pH sensors. Typical activities using our pH sensor include:
Acid-base titrations
Studies of household acids and bases Monitoring pH change during chemical reactions or in an aquarium as a result
of photosynthesis Investigations of acid rain and buffering
Analysis of water quality in streams and lakes Infrared sensor: An infra (IR) sensor produces a signal that depends on the level of invisible IR
radiation falling on it. All objects (unless they are extremely cold) emit significant IR radiation. Security camera equips with lens and grid of IR sensors uses this IR radiation to form a
detector for a person.
Sensor Measures Where Used
Heat Temperature Living room for central heating system
Humidity Water vapour in the air Swimming pool, greenhouse
Infra-red Infra-red radiation e.g. body heat Security alarm systems
Light Light levels External security lights
PH Acid/alkali levels e.g. pH of soil Environmental experiments, river pollution
DLP is significantly more expensive than LCD, but requires less ongoing
maintenance.
LCD projectors are portable and lightweight.
DLP quality is superior to LCD (although LCD is sufficient for most usage).
Film, photography, highly detailed graphics and images, etc., will all appear
crisper and brighter with DLP technology as compared to LCD.
1.3.5 Memory, storage devices and media
Primary memory is computer memory that is accessed directly by the CPU. This
includes several types of memory, such as the processor cache and system ROM.
However, in most cases, primary memory refers to system RAM.
RAM, or random access memory, consists of one or more memory modules that
temporarily store data while a computer is running. RAM is volatile memory,
meaning it is erased when the power is turned off. Therefore, each time you start
up your computer, the operating system must be loaded from secondary
memory (such as a hard drive) into the primary memory, or RAM. Similarly,
whenever you launch an application on your computer, it is loaded into RAM.
The operating system and applications are loaded into primary memory, since RAM
can be accessed much faster than storage devices. In fact, the data can be
transferred between CPU and RAM more than a hundred times faster than between
the CPU and the hard drive. By loading data into RAM, programs can run
significantly faster and are much more responsive than if than constantly accessed
data from secondary memory.
NOTE: Primary memory may be called "primary storage" as well. However, this
term is somewhat more ambiguous since, depending on the context, primary
storage may also refer to internal storage devices, such as internal hard drives.
DVD RAM
DVD RAM is a recent addition to the optical media group. Unlike other CD and DVD
formats, DVD RAMs have several discrete concentric tracks rather than a single
spiral track. This gives them the advantage that writing and reading can occur at
the same time. This makes it possible to watch an already recorded television
program at the same time as different program is being recorded.DVD RAMs can
written to many times.DVD RAMs have a long life estimated to be 30 years and re-
write operation can be carried out over 100,000 times which is 100 times more
than RW formats.
Secondary memory refers to storage devices, such as hard drives and solid state
drives. Unlike primary memory; secondary memory is not accessed directly by
the CPU. Instead, data accessed from secondary memory is first loaded
into RAM and is then sent to the processor. The RAM plays an important
intermediate role, since it provides much faster data access speeds than secondary
memory. By loading software programs and files into primary memory, computers
can process data much more quickly.
While secondary memory is much slower than primary memory, it typically offers
far greater storage capacity. For example, a computer may have a
one terabyte hard drive, but only 16 gigabytes of RAM. Secondary memory is non-
volatile, meaning it retains its data with or without electrical power. RAM, on the
other hand, is erased when a computer is shut down or restarted. Therefore,
secondary memory is used to store "permanent data," such as the operating
system, applications, and user files.
Hard disk
A hard disk is really a set of
stacked "disks," each of
which, like phonograph
records, has data recorded
electromagnetically in
concentric circles or "tracks"
on the disk. A "head” records
(writes) or reads the
information on the tracks.
Two heads, one on each side
of a disk, read or write the data as the disk spins. Each read or write operation
requires that data be located, which is an operation called a "seek." (Data already
in a disk cache, however, will be located more quickly.)
A hard disk/drive unit comes with a set rotation speed varying from 4500 to 7200
rpm. Disk access time is measured in milliseconds. The physical location can be
identified with cylinder, track, and sector locations.
Solid state devices (SSDs)
Solid-state drives actually aren't hard drives in the traditional sense of the term, as
there are no moving parts involved. A traditional hard disk drive (HDD) consists of
a spinning disk with a read/write head on a mechanical arm. An SSD, on the other
hand, has an array of semiconductor memory organized as a disk drive, using
integrated circuits (ICs) rather than magnetic or optical storage media.
Off-line storage
Offline storage is any storage that is not currently online, live or connected to the
computer. The data stored in offline storage remains permanently in the storage
device even if it’s disconnected or unplugged from the computer after the data has been stored. Offline storage is generally portable in nature and can be used on
different computer systems. Common examples of offline storage include floppy
disks, compact disks and USB sticks.
Solid state memory
Solid state systems control the movements of electrons within the microchip. The
1s and 0s are stored in millions of miniature transistors within the microchip. If a
transistor conducts a current this is equivalent to a 1 otherwise 0.they consequently
have no moving parts, consume much less power and are extremely robust.
Memory sticks/pen drives
It uses solid state technology to store several GBytes of data. It is usually
connected to a computer through the USB port and power to operate them is drawn
from the host computer. They are small and very portable.
Memory sticks and pen drives are used for transporting files between computers or
as a backup store. They are used a security device, a dongle, to prevent software
piracy
Flash memory cards
These are a form of electrically erasable programmable
read only memory (EEPROM) and are another example of
solid state memory. They are used to store photos on
digital cameras. Mobile phones use them as memory
cards. They are also used in MP3 players to store music
