Chap2 input devices

contents
 Importance of I/O devices
 Types of input devices
◦ Keyboard
◦ Pointing devices
◦ Speech recognition
◦ Digital camera
◦ Webcam
◦ Scanners
◦ OCR
◦ OMR
◦ MICR
◦ Bar-code reader

introduction
 A computer system has four components:
input devices, CPU, output devices and
memory.
 An input device provides data to CPU fro
processing.
 After processing , the input data is
converted to meaning full information and
this is sent to output devices.
 An input device is an electromechanical
device that allows the user to feed
information into the computer analysis ,
storage and give commands to the
computer.

 After processing the data from input devices
the computer provides the results with the
help of output devices.
 An output devices converts machine
readable information into human readable
form.

Importance of input/output
devices
 Three steps
◦ Step1 : data input via an input devices.
◦ Step 2: processing the data
◦ Step 3: data output via an output device.
• Input devices play a major role in the processing of
any data via the computer system because the
output is always based on the input provided.
• Generally the data provided from input devices is
raw in nature
• Hence the input device should manipulate this raw
data and send for further processing.

Types of input devices
 Computer accepts the data in two ways i.e.
manually or directly.
 In case of manual data entry, the user
enters data into the computer by hand
using keyboard or mouse
 A user can enter the data directly by
transferring information automatically from
a source document into the computer.
 Some common input devices are keyboard,
mouse, scanners, speech recognition etc

keyboard
 Using keyboard user can give text and
commands.
 Designed as regular typewriter with few
additional keys.
 Data is entered into the computer by
pressing the keys.
 The layout of keyboard has changed ever
since it is been introduced.
 Variations are with additions of more keys
that provide additional functionality.

 Laptop keyboards are slightly different
arranged from the desktop keyboards.
 Many system manufactures add some special
buttons to standard keyboard
 It is the easiest input device which does not
require any special skill to operate or learn.
 The maintenance and operational cost of
keyboard is very low.
 It is a slow process, inputting all data from the
keyboard
 Hard for people suffering from muscular
disorders.

How does keyboard work?
 It is series of switches connected to a small
keyboard microprocessor that monitors the
state of each switch and initiate specific
actions to a change in state.
 When the user presses the key , it causes
change in the current flowing through the
circuit
 The keyboard microprocessor detects this
change in current flow.
 By doing this, the processor can tell when a
key is pressed and when it is released.

 Depending on which key is pressed, the
processor generates the associative code
called as scan code, of the key and sends it
to operating system,
 A copy of this code is stored in the
keyboards memory.
 When the operating system reads this scan
code, it informs the keyboard and the scan
code stored in keyboard’s memory

Pointing devices
 A pointing device is used to communicate
with the computer by pointing on the
locations on the monitor screen.
 They don’t need key of characters, instead
the user can move the cursor and perform
operations by clicking or dragging
 Mouse
 Trackball
 Joystick
 Light pen
 Touch screen

mouse
 A small hand-held pointing device with a
rubber ball embedded at its lower side and
buttons on the top.
 Mouse contains two or three buttons, which
can be used to input the commands and
information.
 Classified as mechanical mouse and optical
mouse based on the technology used.
 A mechanical mouse uses a rubber ball at
the bottom surface which rotates as the
mouse is moved along a flat surface

 Commonly used and cheapest pointing
device
 An optical mouse uses a light beam instead
if rotating ball to detect the mouse
movement.
 As the user moves the mouse, the cursor
on the screen also moves
 Costlier than mechanical mouse, does not
need a mouse pad and always accurate.
 A mouse allows us to create graphic
elements on screen such as lines , curves
and freehand shapes.

 No additional installing and cost is required,
comes with the computer as keyboard.
 Requires a flat space near the computer to
move it
 Laptops or palm tops do not have mouse,
they use touch pad or trackball

How does mouse work?
 A mechanical mouse has rubber ball at the
bottom
 When the user moves the ball over a flat
surface , the ball rolls.
 The distance , direction and speed of the
ball’s motion is tracked.
 The information measured is used to move
the cursor inside the screen in the
computer.
 There are three rollers.
 One of them, which is mounted at 45º to
other two balls, is spring loaded.

 This roller is the smallest of the three balls.
 The other two rollers are usually larger and
different color.
 These rollers are mounted at 90º angle to
another, one roller measures how fast the
ball is turning horizontally, and other
measures how fast the ball is turning in
vertical direction.
 When the ball rolls, it turns these two rolls.
 These balls are connected to axles, which
are connected to sensors that measures
how fast the axle is turning.

 There is a small processor present in the
mouse, which consists more than one chip,
which uses the information of how fast the
mouse is moving and in what direction.
 This information is passed to computer via
a mouse cord, where the operating system
then moves the cursor accordingly.

 The optical mouse uses an infrared light
and special mouse pads with the fine grid
lines to measure the rotation of the axle.
 The axle in the optical mouse is connected
to a little photo interrupter wheel with a
number of tiny holes in it.
 In front of this wheel, there is a light source
on the other side of the wheel is a light
metre
 As the wheel turns, the light flashes occurs,
the light sensor can measure how fast the
wheel is turning and sends these values to
the computer

 The computer moves the cursor as per the
values received from the mouse.
 This happens hundred of times per second,
making the cursor appear on the screen to
move very smoothly.

trackball
 A pointing device that reassembles a ball
nestled in a square cradle and serves as an
alternative to mouse.
 Similar to mouse turned upside down.
 It consists of a ball that is moved by fingers
and the mouse moves accordingly.
 The size of the ball varies from large as cue
ball to small as marble
 It comes in various shape commonly in
three i.e. square, button and ball

 Used to control the mouse movements and
actions on the computer screen.
 By moving with fingers and not entire arm, user
will be able to move the mouse pointer with a
greater precision and accuracy.
 Used by graphics designers and gamers.
 Requires less space than mouse
 In form of button, it can be reprogrammed
according to the function.
 Does not comes with the computer, if user
wants it , he should buy it separately, hence
additional cost will apply.

joystick
 It is a device that moves in all directions
and controls the movement of the cursor.
 Basic design consists of a stick that is
attached to a plastic base with a flexible
rubber sheath.
 The electronic circuitry measures the
movement of the stick from its central
position and sends information for
processing
 It has buttons which can be programmed as
the actions required.
 If offers the types of control: digital, glide
and direct

 Digital control allows movement in a limited
number of directions such as top, down , left
and right
 Glide and direct control allows movements in
all directions (360º)
 Is used to control the velocity of the screen
cursor movement rather than its absolute
position.
 Used in computer games.
 Also used in flight simulators, training
simulators , CAD/CAM systems , controlling
industrial robots.

Light pen
 Also called mouse pen
 Is a hand-held electro-optical pointing
device which when touched to or aim
closely at a connected computer monitor,
will allow the computer to determine where
at that screen the pen is aimed.
 Helps in drawing images and selects
objects on the display screen just pointing
into the objects.
 It does not emit any kind of light as in name,
it has a light-sensitive diode which senses
the light emitted by the screen.

 The light emitted from the screen causes the
photocell to respond by generating a pulse.
 This electric response is transmitted to the
processor that identifies the position to which
the light pen is pointing to.
 With the movement of the light pen , lines or
images are drawn.
 Does not require a mouse pad or horizontal
surface, behaves exactly like a mouse.
 Using light pen, users can interact with
computers very easily like for selecting, drag
and drop etc

 It is pointed directly to the screen, does not
require any special skill to use it.
 Perfect to use when user has less desk
space, harsh work environments and
situations where fast accurate inputs are
required.
 It does not give any kind of information
when pointed to blank part of the screen.
 Economical and requires little or no
maintainance.

Touch screen
 Special kind of input device that allows the
direct selection of menu item or the desired
icon with the touch of finger.
 It registers the input when the user touches
the menu item.
 Used when information has to be accessed
with minimum effort.
 Not suitable for inputting large amount of
data.
 Used in systems that provides information's
such as hospitals, airlines, railways
reservations, atm etc

Trackpad
 Is a stationary pointing device that works by
sensing the movement of the fingers across
a small sensitive surface and translating
them into pointing movement in the screen.
 Used in laptops and can be used for PC by
connecting it to it with help of cord.
 Present in PDA’s, media players
 Has two or three buttons which act same as
mouse buttons.
 Many are strike sensitive, the user just has
to tap the trackpad to perform the
operations.

Speech recognition
 One of the most interactive systems to
communicate with the computer.
 The user can simply instruct the computer
with the help of microphone, to perform a
task.
 It is technology in which sounds, words or
phrases spoken by humans are converted
to digital signals and hence converted into
computer generated text or commands.
 Most of the system are speaker dependent
so they must be separately trained for each
individual user.

 The recognition system learns the voice of
the user, who speaks the words repeatedly,
then these voiced words are used in future.
 Used by people with disabilities or travelers
who record information for later
transcription.
 The computer based recognition system
can browse data on internet, letters or
emails, navigate among applications by
voice commands.
 They allow user to communicate with the
computer without using a mouse or
keyboard.

 The reliability of speech recognition system
is lesser when compared to mouse or
keyboard input devices.
 Disadvantage is that at times the
recognition system will not differentiate
between two similar voiced words such as
sea and see etc.
 Not suitable for noisy places.

Digital camera
 Stores digitally rather than recording them
on a film
 Once the picture is clicked, it can be
transferred to the computer system then it
can be manipulated with an image editing
software and can be finally printed.
 The making photo is inexpensive as there is
no film processing.

Web cam
 Short form of web camera
 Is a portable video camera, which captures
live videos or images that may be viewed in
real time over a network or the internet.
 Small digital camera that is either built in
computer or can be connected through a
USB port
 Placed normally above monitor or laptop to
capture images of the user while he or she
is working in the computer.

 Wide variety of web cam are available
 In two categories they are classified,
streaming and snapshot
 A streaming webcam captures moving
images thus creating a streaming video- a
web video plays on a computer immediately
as its data arrive via network, the recipient
need not download the video.
 High speed internet is required to transfer
the video smoothly.

 A snapshot camera only captures still
images and refreshes it continuously.
 It produces a better quality images and is
easier to configure than streaming videos.
 Webcam are used in video conferencing to
provide real time communication where
groups of people can see and interact with
each other
 Used in various messengers such as
yahoo, windows live messenger where
videos are shared with somebody.

 Webcams are cheap, compact and are
easy to install and use.
 They are affordable because of their lower
manufacturing cost.
 Disadvantage is they produce real time
images only when they are plugged to PC,
useless if they are not connected to a PC
 Some webcams come with special features
such as automatic lighting controls,
automatic face tracking and autofocus with
increased cost.

scanners
 The information on the paper is needed on
the computer for further operation, then
scanners are used.
 A scanner is an input device that converts a
document into an electronic format that can
be stored on the disk.
 The electronic image can be edited,
manipulated, combined and printed by
using an image editor.
 Scanners are also called optical scanners
if they use light bean to scan the input data.

 Scanners come with a utility program that
allow them to communicate with the
computer and save the scanned images as
graphics files on the computer
 They can store images in both grayscale
and color mode
 Two types are
◦ Hand-held scanners
◦ Flatbed scanners

Handheld scanner
 It consists of LEDs which are placed over
the document to be scanned
 The scanner performs the scanning very
slowly from top to the bottom of the
document with its lights on
 All documents scanned are converted into
images.
 The scanner is scanned over the document
slowly steadily and carefully over the
document at constant speed without
stopping or jerking in order to obtain better
result.

 Used where accuracy is not of that
importance.
 Size of such scanners are small.
 Comes in resolutions upto 800 dpi, are
available in grayscale or color.
 Used when the volume of documents to be
scanned is low.
 Commonly used to read price tags,
shipping labels , book ISBN and so on.

Flatbed scanner
 Similar to photocopier machine.
 It consists of box containing a glass plate on its
top and lid that covers the glass plate
 The glass plate used for placing the document
to be scanned.
 The light bean is placed below the glass plate
and when it is activated, it moves horizontally
from left to right.
 After scanning one line , the light beam moves
in order to scan the next line and the procedure
is repeated until all the lines are scanned.

 Scanning an A4 page takes about 20
seconds.
 These scanners can scan black and white
as well as color images.
 They are larger in size and more expensive
than held-held scanners.
 They usually produce better quality images
because they employ better scanning
technology.

Optical character recognition
 A scanner converts an input document into
an electronic format that can be stored on
the disk.
 If the scanned document contains text, you
need an optical character recognition
software.
 When a scanner scans a document , the
scanned document is stored in bitmap in
the computer ‘s memory.
 The OCR translates this bitmap image of
text to ASCII codes that the computer can
interpret as letters, numbers and special
charecters.

 Because of OCR , data entry becomes
easier, error free and less time consuming.
 It is very expensive, if the document is not
typed properly, it becomes OCR to
recognize the characters.
 Paragraph marks and tabs or text
formatting is lost during scanning.
 The output from a finished text scan will be
a single column editable text file.

Optical mark recognition
 Is a process the detecting the presence of
the intended marked responses.
 Optical mark reading done by a device
called optical mark reader.
 In order to be detected by the OMR reader,
a mark has to be positioned correctly on the
paper and should be significantly darker
than surrounding paper.
 It enables a high speed reading large
quantities of data and transferring this data
to a computer without using a keyboard.

 Used for reading answer scripts
 Special printed forms/ documents are
printed with boxes which can be marked
with a dark pencil or ink
 These forms are passed under a light
source and presence of dark ink is
transformed into electric pulses, which
transformed to the computer.
 OMR has better recognition than OCR
because fewer mistakes are made by
machines to read marks than in reading
handwritten characters.

 Large volumes of data can be read quickly
and easily without the need for specially
trained staff.
 Can scan about 1500 to 10000 forms per
hour.
 OMR readers are slow, the person writing
the form should follow special instructions
while filling it.
 If there is any dirt or any folding of the
paper will make the OMR to read the data
in wrong way.
 It requires alignment of printing forms and
needs good quality

Magnetic ink character
recognition
 There are special characters written on
cheque.
 The character are printed using a special
ink, which contains iron particles that can
be magnetized.
 In order to read this, there should be a
device called Magnetic ink Character
reader (MICR) is used.
 It reads the character by examining the
shapes in matrix form and the information is
then passed on to the computer

 Banks prefer MICR as it provides extra
security against forgeries.
 When the cheque are manipulated, they
wont have magnetized particles hence
codes produced by the MICR wont be
same, or will produce incorrect code.
 The reading speed of the MICR is also
higher
 This is efficient and time saving for data
processing.

Bar code reader
 Bar code is machine readable code in the
form of group of parallel vertical lines of
varying widths.
 Commonly used for labeling goods that are
available in supermarkets and numbering
books in libraries.
 This code is sensed by a bar code reader
using a reflective light.
 The information recorded are fed into the
computer, which recognizes the information
from thickness and spacing of bars.

 Bar code reader is hand held or fixed mount
 Hand held bar code readers read the bar
code of a stationary items.
 Fixed mount bar code readers, items are
passed by the scanner by hand by the
retail scanning applications or conveyor belt
in industrial applications.
 Provides enormous benefits such as
capturing the data faster and more accurate
 A bar code reader can record data 5-7
times faster than a skilled typist.

 It has error rate of 1 in 3 million
 It reduces cost in terms of labor cost and
revenue losses resulting due to data
collection errors.
 Bar code readers are used in
supermarkets, department stores, libraries
and other places.
 Bar codes is commonly seen behind books
, greeting cards.
 In grocery shops it is used to determine the
item being sold and to retrieve the price
from the system.

Chap2 input devices

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Chap2 input devices