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.


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”.


1. CRT Displays

2. LED Displays

3. LCD Displays




3. Saw Touchscreen


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.


1. CRT Displays

2. LED Displays

3. LCD Displays




3. Saw Touchscreen


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

Basic Design of LCD Display

Working PrincipleOff 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 PrincipleON 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.

ComparisonCRT LCD LED

POWER CONSUMPTION

High power is consumed

consumes 50-70% less energy as compared to CRT

consumes 30-40% of less power than LCD

PICTURE QUALITY

High contrast ratio Poor picture quality than LED

Superior than CRT and LCD

COST Low cost High cost(~2 times of CRT)

Very high cost(~4 times of CRT)


1. CRT Displays

2. LCD Displays

3. LED Displays




3. Saw Touchscreen


TOUCH SCREEN TECHNOLOGY

Introduction

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

• A Touchscreen is basically a input deviceso it should be combined with a displaydevice and a computer.

• A Touchscreen basically includes:-1. Touch Screen Sensor

2. Controller

3. Software Driver


1. CRT Displays

2. LCD Displays

3. LED Displays




3. Saw Touchscreen


21

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.

22

ComponentsController

• 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.

23

ComponentsSoftware 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.


1. CRT Displays

2. LCD Displays

3. LED Displays




3. Saw Touchscreen


25

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.

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

21

22

221

2

22

21

21

21

RR

RVV

RRR

VV

IRV

VVV

RR

VI

RRRR

VI

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 theunderside 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 touchedthe 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-PositionX-Position

5-Wire and 8-Wire Technology

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)


1. CRT Displays

2. LCD Displays

3. LED Displays




3. Saw Touchscreen


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 transparentconductor used is Indium Tin Oxide.

Working principle • The basic formula of capacitance is

Here;

C= capacitance; ; A= area of the platesd= distance between plates

• Hence , larger the area of plates greater is the capacitance and smaller the distance between them larger the capacitance.

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 thecapacitance.

• 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.


1. CRT Displays

2. LCD Displays

3. LED Displays




3. Saw Touchscreen


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.

Working Principle

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.


1. CRT Displays

2. LCD Displays

3. LED Displays




3. Saw Touchscreen


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.

Working Principle


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.

References

display devices and touch screen technology

Education

video display

basic design of lcd

flat panel display

random scan display

crt displays2

led displays3

lcd displays george

times of crt