Display devices and TOUCH SCREEN TECHNOLOGY

Display Devices
And
Touch Screen Technology

Presented By:-
Abhishek Pal

Outline
• Introduction of Display Devices
• Types of Display Devices
1. CRT(Cathode Ray Tube) Displays
2. LED Displays
3. LCD Displays
• Introduction of Touch Screen Technology
• Components of Touch Screen
• Types of Touch Screen Technology
1. Resistive Touchscreen
2. Capacitive Touchscreen
3. Saw Touchscreen
4. Infrared Touchscreen

Introduction of Display Devices
• A display device is an output device for presentation of
information in visual or tactical form

• One of the earliest electronic displays is the cathode ray tube
(CRT), which was made commercial in 1922

• Since then electronic display
devices based on various
principles are developed.

Types of Display devices
• Active display devices are based on luminescence.
• Luminescence
• Photo-luminescence
• Cathodo-luminescence
• Electro-luminescence

• Passive display devices reflect or modulate light.

Outline
1. CRT Displays
2. LED Displays
3. LCD Displays
3. Saw Touchscreen

CRT (Cathode Ray Tube) Displays
• The Cathode Ray Tube (CRT) was invented by German
physicist Karl Ferdinand Braun in 1897.

• Cathode Ray Tube (CRT) contains four basic parts:
• Electron gun,
• Evacuated glass
• Focusing and
accelerating systems,
• Deflecting systems,

CRT Displays Principles
• Display principle
• Raster Scan Display Principle
 In this system the screen is scan in vertically and
horizontally
• Random Scan Display Principle
 Here the electron gun of CRT illuminates point and/or
straight lines in any order
• The frequency at which a picture is redrawn on the screen is
referred to as the “Refresh Rate”.

• The maximum number of points that can be displayed on a
CRT is referred to as the “Resolution”.

LED Display
• An LED display is a flat panel display, which uses light-emitting
diodes as a video display.

• A cluster of red, green, and blue diodes is driven together to
form a full-color pixel, usually square in shape.

• Matrix of diodes is arranged to form pixels and picture definition
is stored in refresh buffer.

• Information is read from refresh buffer
and converted into voltage levels that
are provided to diodes, thus
producing light patterns in the display.

Techniques Used
Three techniques are used in making LED displays:-

1. Edge-Led :- It is done around the rim by using a special
diffusion panel to spread the light evenly behind the screen.

2. Full-array Led :- The are arranged behind the screen and
their brightness are not controlled individually.

3. Dynamic „Local Dimming‟ Led:- This type of back-lightning
allows dimming of specific areas of darkness on the screen.

LCD Displays
• George H. Heilmeier invented LCD in 1964

• The heart of all liquid crystal displays (LCDs) is a liquid crystal
itself.

• Produces pictures by passing polarized light through liquid-
crystal material.

• There are three basic types of
liquid crystals which are termed
1. Nematic
2. Chiral
3. Smetic

Working Principle
Off State
1. Surrounding light is polarized on the upper plate.

2. Light moves along with
liquid crystals and
twisted at right angle

3. Molecules and lights are
parallel to the lower
analyzer.

4. Light passes through the
plate and thus screen
appear transparent.

Working Principle
ON State
1. Surrounding light is polarized on the upper plate.

2. Light moves along with liquid crystals which moves straight
along the electric field.

3. Molecules and lights are
perpendicular to the lower analyzer.

4. Light cannot pass through.

5. Screen appear dark.

Comparison
CRT LCD LED

POWER High power is consumes 50-70% consumes 30-40%
CONSUMPTION consumed less energy as of less power than
compared to CRT LCD

PICTURE High contrast ratio Poor picture Superior than CRT
QUALITY quality than LED and LCD

COST Low cost High cost Very high cost
(~2 times of CRT) (~4 times of CRT)

Outline
1. CRT Displays
2. LCD Displays
3. LED Displays
3. Saw Touchscreen

Introduction
• First described by E.A Johnson in his work on capacitive
touchscreen in 1967.

• A Touchscreen is basically a input device
so it should be combined with a display
device and a computer.

• A Touchscreen basically includes:-
1. Touch Screen Sensor
2. Controller
3. Software Driver

Components
Touch Screen Sensor

• A touch screen sensor is a clear glass panel with a touch
responsive surface.
• The sensor generally has an electrical current or signal going
through it.
• Voltage change determine the point of touch.
21

Components
Controller

• The controller connects between the touch sensor and the PC.

• The controller determines what
type of connection you will
need on the PC.

• Controllers are available that
work with DVD players and
other devices.
22

Components
Software Driver

• The driver allows the touchscreen and computer to work
together.

• Most touch screen drivers today
are a mouse-emulation type driver.

• This allows the touchscreen
to work with existing software.

23

Introduction
• In 1971, the first "touch sensor" was developed by Doctor Sam
Hurst

• A touch screen is an Electronic
Visual Display.

• The touch screen is one of the
easiest to use and most intuitive
of all PC interfaces

• This touch screen works on the
principle of voltage dividers.
25

Resistive Technology

V=Voltage (Volts)
A difference in electrical potential
I=Current (Amps)
A flow of electric charge which (by convention) flows from a higher to
a lower voltage potential
R=Resistance (Ohms)
Resists the flow of electric current
I = V/R
Current flow proportional to Voltage and inversely proportional to
resistance

Potential Divider

V
I
R
R R1 R2
V
I
R1 R2
V V1 V2
V2 IR2
V
V2 R2
R1 R2
R2
V2 V
R1 R2

Potentiometer

V2 is proportional to
the position of the
arrow. At the top V2=V
and at the bottom V2=0

Resistive Touch Sensor
• The sensor panel consists of several layers, the most important
of which are two thin, transparent layers separated by thin
space.

• Top screen has coating on the
underside surface.
.
• Voltage is applied to one layer
and sensed by the other.

• Generally a 4-wire technology
is used.

4-Wire Technology
• It consists of 4 resistances arranged so indicate X and Y
Cartesian axis.

• When the screen is touched
the conductive coating on
the coversheet connects
with the coating on the
glass.

• The controller reads the
X and Y positions.

Calculation of Touch Position

Calculation of
Y-Position
X-Position

Advantages & Disadvantages
ADVANTAGES

• Force activated so can use finger even with a glove, stylus or
any other (non sharp) prodding device.
• Tolerates dust/dirt, rain and insects.

DISADVANTAGES

• Conductive coating reduces display brightness.
• Continual flexing of outer layer causes microscopic cracks so
affects linearity of resistance (other processes can overcome
this)

Capacitive Touch Screen
• It is an all glass touch screen with a transparent metallic
conductive coating.

• It is made up of
all-glass material
with transparent
conductive coating.

• The transparent
conductor used is
Indium Tin Oxide.

Working principle
• The basic idea is the consideration of human body to be
conducting.

• Whenever the screen is touched a small amount of current is
attracted by the finger
causing change in the
capacitance.

• These are of 2 types:-
1. Surface Capacitive
2. Projected Capacitive

Surface Capacitive Touchscreen

• It consists of uniform conductive coating on one side of the
glass panel.

• Electrodes around the panel edge evenly distribute a low
voltage around the conducting layer.

Surface Capacitive Touchscreen

Projected Capacitive Touchscreen

• It have front and protective glass to provide additional optical
and strength enhancements options.

• Its middle layer consists of laminated sensor grid of micro-fine
wires.

Projected Capacitive Touchscreen
• The screen is divided into small
grids of unit cell.

• Whenever a touch occurs, the
finger disturbs the electric field
projected by sensor by
conducting electric current.

• The location is calculated by
checking the capacitance at
each point on the grid regularly.

ADVANTAGES

• It has high resolution and Image clarity.
• Immune to surface contaminants like dirt, grease or moisture.
• Durable and resistant to scratches.

DISADVANTAGES

• Will work only when touched by a conductive device.
• Some capacitive touches can have erratic behavior when
touched by more than one input.

SAW Touchscreen Technology
• It have a glass overlay
with transmitting and
receiving piezoelectric
transducers.

• Transmitting transducer,
converts the electric
signal into ultrasonic
waves within the glass.

• These waves are reflected
across the screen by
reflectors.

Advantages and Disadvantages
ADVANTAGES
• It provides superior image clarity, resolution, and higher light
transmission.

• It has the highest durability factor.

DISADVANTAGES
• It must be touched only by finger, gloved hand, or soft-tip
stylus.

• It is not completely sealable, can be affected by large amounts
of dirt, dust, and / or water in the environment.

Infrared Touchscreen Technology

• In 1983, the computer manufacturing company, Hewlett-
Packard introduced the HP-150.

• The HP-150 had a built in grid of infrared beams across the
front of the monitor which detected finger movements.

ADVANTAGES
• It can detect essentially any input including a finger, gloved
finger, stylus or pen.

• It have better durability and optical clarity.

DISADVANTAGE
• It is sensitive to dirt/dust that can interfere with the IR beams.

• It suffer from parallax in curved surfaces and accidental press.

Display devices and TOUCH SCREEN TECHNOLOGY

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