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Input & Output
devices
Input Device :keyboard
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a keyboard is an input device, partially modeled after the
typewriter keyboard, which uses an arrangement of buttons or
keys, to act as mechanical levers or electronic switches.
A keyboard is also used to give commands to the operating
system of a computer.
Connectors to keyboard AT(DIN-5) PS2 andUSB.
XT with 83 keys,At with 84 keys, 104 keys by adding window
keys.
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Keys includes: Typing keys numeric keypad,function
keys,control keys
Virtual Laser Keyboard(sensor,Signalsto computer)
Input Device :keyboard
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Components of Keyboard
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Keyboard switches
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Keyboard processor or circuitry
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Key matrix
Types of keySwitches
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Capacitive switch
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Hall effect switch
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Opto electronic switch
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Membrane switch
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Mechnical switch
Input Device :keyboard
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Key matrix: keyboard matrix is the arrangement of circuit
connections between the keyboard controller and all the keys.
Key switch: The main component of any keyboard is the key
switch. These switches generate typical codes of signal when
they are depressed and it is used for interfacing with computer
system
Input Device :keyboard
Input Device :keyboard
Input Device :keyboard
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Key matrix: keyboard matrix is the arrangement of circuit
connections between the keyboard controller and all the keys.
each key is placed at the intersection of a matrix row and a
matrix column. The keyboard repeatedly applies current to
each column in turn, and checks to see which rows output
current. From this, the keyboard can deduce which keys in
that column have been depressed.
Input Device :keyboard
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Capcitive switch:two plates of the capacitor are brought
closer when the key is pressed.
Change in capacitance of switch changes and change in
capacitance is detected in terms of voltage.
Basedon the switch open/close voltage is recived thisvoltage
is converted into proper signals to inform CPU.
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Lifespan 20 millonkey strokes.
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Hall effect switch:
magnetic field is applied to any device the resistance of device
will be increases or decresed(current starts flowing)
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This allow current flow
Lifespan 100 million keystrokes
Input Device :keyboard
Input Device :keyboard
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opto-electronic switch: have LED light generate light when
electric power is applied.uses photo- transistor which allow
current to flow in the circuit.
When key is pressed not pressed the light from LED falls onto
photo-transistor
When key is pressed the value will be produced at the ouput
Vout
membrane switch:it is multi layered plastic or rubberuses the
row and colum conductor sheets.
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Mechanical switch: it uses two metal pieces or contacts .
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Rubber dome:madeup of polyester domes
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Refered as direct switches.
Input Device :keyboard
opto-electronic
switch
membrane
switch
Input Device :keyboard
Mechanical
switch
Keyboard Interfaces
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Connects to PC
– KEYBOARD
– KEYBOARD CONNECTOR
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Inside keyboard a processor and circuit which carry information
to or from that processor.
Keyboard controller is single chip contains memory RAM,
processor ROM(control operations of keyboard)
Key matrix: row and columns made up wires and each key act
like switch
Key matrix is grid of circuits when key is pressed the row wire
makes contact with colmn wire and completes the circuit . KM
passes current to keyboard controller .
Keyboard controller will detects the closed circuit and registers
the key press and controller read the key pressed.
Keyboard Interfaces
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KEYBOARD CONNECTOR
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Interface between keyboard and pc
– AT keyboard connector(DIN5)
– PS2 keyboard connector or(MIN-DIN6)
– USB connector
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AT keyboard connector(DIN5)
– Uses
5
pins:
KBDCLK(provide
clock
pulse),
KBDAT(send/recive data),KBRST (reset keyboardinternal
buffer),GND(ground),VCC(+5v provides power to keyboard)
PS2 keyboard connector or(MIN-DIN6): With 6 pins
USB keyboard connector:
USB keyboard connector : uses 4 pins VDC(+5V),DATAcarries -ve data signal,DATA+it carries +ve data Signal,
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Keyboard working:key is pressed it pushes down the rubber
dome
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Dome tuches a pair of conductive lines on circuit
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Allow current flow
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Mouse:
Mechanical Mouse : Mechanical Mouse uses ball for the
movement of cursor on thecomputer screen. When the ball is
rolled in any direction, a sensor of the mouse detects it and also
moves the mouse pointer in the same direction.
Optical Mouse : Optical Mouse uses Laser rays for the
movement of cursor on the computer screen. It is an advanced
pointing device. Movement is detected by sensing changes in
the reflected light rather than the motion of a rolling sphere.
Cord-Less Mouse : Cord-Less Mouse is battery driven and does
not need any wire for the physical connection with the
motherboard. It transmits data through infrared or radio signal.
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Mechanical
mouse
Mouse types
1.Mechanical mouse: a rubber ball rolls as the mouse is moved
across table top or mouse pad.
The wheels are referred as encoders have tiny metal contact
points on rims
Location of mouse is identified by how many times the contact
points have touched the bars.
mouse moved across flat surface.
As balls rotate it touches and turns two rollers inside the mouse
Two rollers are used for vertical and horizontal movements of
cursor
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Mouse types
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Each roller attached to encoder.
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Each time a contact bar touches a point an electrical signal.
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Signals generated are sent to PC over the mouse cables
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And number of mouse time mouse button is clicked.
2. Optical-mechanical mouse:
When mouse moves the ball of mouse moves and two separate
rollers fixed at 90 degree to each other one roller is for vertical
and horizontal movement of cursor.
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Each roller connected to wheel these rollers are rotated by
movement of rollers.
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Wheel rotate pair of LED and photo detectors
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Signals sent to PC through mouse connectors
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Mouse types
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Optical mouse:
LED produces a red light that is emitted onto surface the
light reflected back to CMOS sensor then to DSP(digital
signal processor) for analysis
DSP analysis the signal and and patterns and
determines mouse movements.
Along with coordinates are received by computer and will
show mouse movement on screen.
Monochrome Monitor
Monochrome Monitors
Monochrome Monitors
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Video processing unit: contains video signals from display adopter
card to video Amplifier Circuit.
Video signal controls brightness of beam only two levels to set
brightness ON and OFF.
Vertical Sync Processing:
Grayscale Monitors
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A special type of monochrome monitor capable
of displaying different shades of gray.
They are also known as black-and-white, are
composed exclusively of shades of gray, varying
from black at the weakest intensity to white at
the strongest.
Early grayscale monitors can only show up to
sixteen different shades
Grayscale Monitor
Color Monitors
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A display monitor capable of displaying many colors.
Color Monitors works like a monochrome one, except
that there are three electron beams instead of one.
The three guns represent additive colors (red, green and
blue) although the beam they emit are colorless.
Each pixel includes three phosphors, red, green and
blue, arranged in a triangle.
When the beam of each of these guns are combined and
focused on a pixel, the phosphors light up.
Color Monitors
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The monitors can display different colors by combining
various intensities of three beams.
Mixing of Colors
What is being used today?
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The most popular display today remains
Color monitors CRT.
It has been available for more than 70 years.
CRT is used.
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Cost less than LCD monitors.
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History of the Cathode Ray
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1855- Heinrich Geissler creates the mercury pump, the first good
vacuum tubes. Sir William Crookes uses these to produce the first
cathode rays.
1858- Julius Plücker bends cathode rays using a magnet
1869- J.W. Hittorf establishes that the “rays” travel in straight lines
1883- Heinrich Hertz concludes incorrectly that cathode rays are not
made up of particles because they are not deflected by electrically
charged metal plates
1895- Jean-Baptiste Perrin shows that cathode rays are particles
because they deposit a negative charge where they impact
1897- J.J. Thomson discovers electrons using cathode rays
How Monitor Works?
Most use a cathode-ray tube as a display
device.
 CRT: Glass tube that is narrow at one end
and opens to a flat screen at the other
end.
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How Monitor Works?
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Electrons travel through a vacuum sealed
container from the cathode (negative) to the
anode (positive).
Because the electrons are negatively charged,
they are repelled away from the cathode, and
move across the tube to the anode.
The ray can be affected by a magnet because of
its relation to positive and negative charges
Some Anatomy of the CRT
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Anode- Positively Charged, Ray travels towards this
Cathode- Negatively Charged, Ray travels away from
this
Cathode Ray Tube (CRT) Monitors
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A CRT monitor contains millions of tiny red, green, and
blue phosphor dots that glow when struck by an electron
beam. Electron beam travels across the screen to create
a visible image.
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In a CRT monitor tube, the cathode is a heated filament.
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The heated filament is in a vacuum created inside a
glass tube. The electrons are negative and the screen
gives a positive charge so the screen glows.
Basic Cathode Ray Tube
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Electrons excite phosphor to glow
Electrons fired from the back
Phosphor is arranged in dots called pixels
Dot mask ensures proper pixel is lit
Phosphore
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It is a semi-conducteur material which emits visible
radiation in response to the impact of electrons.
(i.e. when it absorbs energy from some source such
as an electron beam, it releases a portion of this
energy in the form of light).
In response to a sudden change in the electron
beam(from on to off), the light emission does not fall
instantaneously, there is a gradual reduction challed
‘fluorescence’ .
Scanning Pattern of CRT Electron
Gun
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The electron gun scans from left to right and
From top to bottom.
Refreshing every phosphor dot in a zig-zag pattern.
Advantages of CRT
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The cathode rayed tube can easily increase the
monitor’s brightness by reflecting the light.
They produce more colours
The Cathode Ray Tube monitors have lower price rate
than the LCD display or Plasma display.
The quality of the image displayed on a Cathode Ray
Tube is superior to the LCD and Plasma monitors.
The contrast features of the cathode ray tube monitor
are considered highly excellent.
Disadvantages of CRT
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They have a big back and take up space on desk.
The electromagnetic fields emitted by CRT monitors
constitute a health hazard to the functioning of living
cells.
CRTs emit a small amount of X-ray band radiation which
can result in a health hazard.
Constant refreshing of CRT monitors can result in
headache.
CRTs operate at very high voltage which can overheat
system or result in an implosion
Within a CRT a strong vacuum exists in it and can also
result in a implosion
They are heavy to pick up and carry around
CRT Monitor
Liquid Crystal Display - Monitor
It is a flat panel display, electronic visual
display, or video display that uses the light
modulating properties of liquid crystals
(LCs).
 LCs do not emit light directly .
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LCD History
Liquid crystals were first discovered in 1888 by Austrian
botanist Friedrich Reinitzer.
 RCA, an American Laboratory made the first experimental
LCD in (1968).
 Manufacturers have been developing creative variations and
improvements since on LCDs.
 In 1997, manufactures began to offer full size LCD monitors
as alternatives to CRT monitors.
 Until recently, was only used on notebook computers and
other portable devices.
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LCD Technology
Used for displays in notebooks, small computers, pagers,
phones and other instruments.
 Uses a combination of fluorescent-based backlight, color
filters, transistors, and liquid crystal to create and
illuminate images.
 Until recently, was only used on notebook computers and
other portable devices.
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From CRT to LCD
CRT
 Bulky, heavy, use vacuum tube
technology.
 Using technology that was
developed in the 19th century.
 LCD
 First LCD laptop monitors were
very small due to manufacturing
costs but now are available in a
variety of sizes.
 Light, sleek, energy-efficient, have
sharp picture.
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Liquid Crystal Display
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There are mainly two categories of LCD.
 The
passive matrix LCD
 The Active matrix LCD
Passive Matrix LCD
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Monochrome passive-matrix LCDs were standard in
most early laptops.
 Still being used today for applications less demanding
than laptops and TVs.
It consisting of a grid of horizontal and vertical wires.
 At the intersection of each grid is an LCD element
which constitutes a single pixel, either letting light
through or blocking it.
Passive matrix LCD
 Pixels arranged in a grid
 Pixels are activated indirectly
 Row and column are activated
 Animation can be blurry
Passive Matrix Display
Active Matrix LCD
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Active-matrix LCDs depend on thin film
transistors (TFT).
 TFTs
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are tiny switching transistors and capacitors.
They are arranged in a matrix on a glass
substrate.
 Each
pixel is activated directly
 Pixels have 4 transistors
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One each for red, green, blue
One for opaqueness
 Animation
is crisp and clean
TFT LCD Screen
Advantages of LCD
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The sharpness of a LCD display is at maximum tweak
ness.
High peak intensity produces very bright images. Best for
brightly lit environments.
Screens are perfectly flat.
Thin, with a small footprint. Consume little electricity and
produce little heat
The LCD display unit is very light and can be put
anywhere or moved anywhere in the house.
Lack of flicker and low glare reduce eyestrain.
Disadvantages of LCD
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After a while the LCD display the some of the
pixels will die you will see a discoloured spot on
a black spot on the display.
The cost of a LCD is considerably at a high
price.
The LCD display will have slow response times.
The LCD display has a fixed resolution display
and cannot be changed.
The viewing angle of a LCD display is very
limited.
Other types of Monitors
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Paper-white displays
 High
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contrast between fore and background
Electro-luminescent displays (ELD)
 Similar
to LCD
 Uses phosphor to produce light
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Plasma monitor
 Gas
is excited to produce light
Paper White Display
NASA -Electroluminescent displays
Plasma Monitors
Monitor Specifications
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Monitor Specifications can be judged
through,
 Size
 Resolution
 Refresh
rate
 Dot pitch
Size
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A monitor’s size affect how well we can see images.
With a larger monitor, we can make the objects on the
screen appear bigger.
Monitors are measured diagonally, in inches, across the
front of the screen.
A 17 inch monitor measures 17 inches from the lower left
to the upper right corner.
CRT monitors viewing area is smaller than the monitor’s
overall size.
Resolution
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The images you see on your monitor are made of tiny
dots called pixels.
The term resolution refers to the sharpness and clarity of
an image.
A monitor resolution is determined by the number of
pixels on the screen. It is expressed as a Matrix.
The more pixels a monitor displays, higher will be its
resolution. Clearer will be images appear.
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For example 640 X 480 resolution means that there are 640
pixels horizontally across the screen and 480 pixels vertically
down the screen.
Resolution
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Actual resolution is determined by the video controller.
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Most monitors can operate at several different resolutions. They
are
640 X 480
800 X 600
1024 X 768
1152 X 864
1280 X 1024
As the resolution increases, image on the screen gets
smaller.
Resolution Settings
Standards
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There are various standards for monitor
resolution.
 Video
Graphics Array standard is 640 X 480
pixels.
 Super VGA is 800 x 600 and 1024 x 768.
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Today, nearly all color monitors can be set
to higher resolution.
Refresh Rate
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Monitor refresh rate is the number of times per second
that the electron guns scan every pixel on the screen.
Refresh rate is important because phosphor dots fade
quickly after the electron gun charges them with
electrons.
If the screen is not refreshed, it will appear to flicker.
Refresh rate is measured in Hz or Cycles per second.
 If the monitor refresh rate is 100 Hz, it means that it
refreshes its pixels 100 times every second.
Refresh Rate
Dot Pitch
It is the distance between the same color
dots
 Ranges between .15 mm and .40 mm
 Smaller creates a finer picture
 Should be less than .22
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Dot Pitch
Touch screen technologies
It is visual display that can detect the presence
and location of touch with in the display area
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Touch screen senses the passive object,finger,etc..
Components of touch screen
– Touch sensor
– Controller
– Software driver
 Touch sensor: Touch screen detects the location of
touches with in display area. It is touch sensor panel with a
touch responsive surface over display
 Sensor have electric current or signal which produces
voltage or signal to determine touch to screen.
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Touch screen technologies
Controller: It is printed circuit board connects
sensor and display, it carries information from
touch screen and translates to computer.
Software Driver: a program which allows
communication between OS and controller .
Different TS Technologies
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–
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Resistive
capacitive
Surface acoustic wave
Infrared
Resistive Touch screen technology
Flexible top layer polyethylene bottom layer of glass both
layers are coated with Indium Tin Oxide(ITO)Electric
current flows between the two layers.
 Change in electrical signal detected and coordinates are
calculated by controller and parsed into readable signals to
the OS.
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capacitive Touch screen technology
Most durable and coated with capacitive material (ITO)
Transmit 90% of light from monitor.
Surface CTS technology
– Large panels
– Transparent electrode film is placed above glass
– Voltage is applied to electrodes placed at four corners
– Generate low uniform voltage
– Simple structure , low cost.
– No multi-sense.
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CTS technology
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Projective CTS technology
– Small touch panels
– It includes IC chips over which layer of numerous
transparent electrodes are placed
SAW technology
Surface acoustic wave panels achieve bright touch panels
with high levels of visibility which refereed as surface wave
Two transducers
Waves
passes through glass and reflected back to
sensors. When it senses touch these waves are absorbed
and touch is sensed
– High surface durability
– Best optical quality
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Infrared/optical imaging technology
Based on infrared image sensors infrared LED on top
of panel and image sensor.
When
touch sensed by image sensor image is
captured . The image shadow formed by infrared light
hjgh
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Plasma display
gas discharge display
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Three cells make up one pixel (one cell has red
phosphor, one green, one blue).
 cells are sandwiched between x- and y-axis panels, and a
cell is selected by charging the appropriate x and y
electrodes.
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Plasma Pixels
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Each pixel is made up of three cells full of ionized gas
that are lined with red, green and blue phosphors. When
charged, the gas emits ultraviolet light that causes the
phosphors to emit their colors.
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Plasma display
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gas discharge display
Plasma display
Inside a Plasma unit sit hundreds and thousands of tiny
pixels which are cells filled with a mixture of neon and
xenon gases
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These cells are sandwiched between two glass panels
running parallel to each other.
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A single pixel is made up of three colored sub-pixels, one
sub pixel has a red light phosphor, one has a green light
phosphor and the third has a blue light phosphor.
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A plasma screen works by controlling each individual
phosphor.
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Visual Display Devices
Video Cards
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Interface between computer and a display device.
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Unless a computer has graphics capability built into the
motherboard, the video card is required.
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The CPU, working in conjunction with software
applications, sends information about the image to the
video card. The video card decides how to use the pixels
on the screen to create the image. It then sends that
information to the monitor through output interface.
Parts of Video Card
How Video card works?
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The CPU, working in conjunction with software
applications, sends information about the image
to the graphics card.
The graphics card decides how to use the pixels
on the screen to create the image.
It then sends that information to the monitor
through a cable.
It is capable of rendering 3D images.
Video Card - GPU
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Similar to CPU but designed specifically to
perform complex mathematical and geometric
calculations necessary for graphics rendering.
Less congestion on the system bus
Reduction in the workload of CPU
Graphics GPU
Video Card - GPU
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Operations: bitmap transfers, painting, window
resizing and repositioning, line drawing, font
scaling and polygon drawing etc.
Some GPUs have image enhancement
algorithms built-in.
Video Card - GPU
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Some of the latest GPUs
have more transistors
than average CPU and
produce a lot of heat.
Heat-sinking and fan
cooling are required
Video Card - Memory
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When a video card is connected within the
motherboard, it will use the computers random access
memory (RAM).
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If it is not connected to the motherboard though, the
video card often has its own memory known as Video
RAM (VRAM).
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The capacity of VRAM in modern video cards ranges
from 125 to almost 800 MB.
Video Card Memory
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In 2006, DDR technology was the base of the VRAM.
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The clock rate of the memory was between 300 MHz and
1.7 GHz.
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The Z-buffer is an important part of the video memory. It
takes care of the depth coordinates in 3D graphics
Modern cards have up to 512 MB RAM
Changing your computer’s display settings
Click Start button
Then, click
here to open
the Control
Panel
Opening “Display” window
Double-click on
“Display”
Re-setting Resolution
First, click
“Settings” tab
Next, move slider-bar to adjust
resolution to 1024 by 768 pixels
Getting to “Dots Per Inch”
Then, click the “Advanced”
button to set Dots Per Inch
Resetting Dots Per Inch (DPI)
Change DPI
setting to “Large
Size” (120 DPI)