TOUCH SCREEN TECHNOLOGY

Presented by: Shuchi Parashar B.Tech(EC)VIsem Roll no. : 6008

WHAT IS A TOUCHSCREEN???

A type of display screen that has a touch-sensitive transparent panel covering the screen. Instead of using a pointing device such as a mouse or light pen, you can use your finger or stylus to point directly to objects on the screen.

BASIC TOUCHSCREEN

A basic touch screen has three main components:1. Touch sensor2. Controller 3. Software driverThe touch screen is an input device, so it needs to be combined with a display and a PC or other device to make a complete touch input system.

HOW DOES A TOUCHSCREEN WORK? 

TOUCH SENSOR

A touchscreen sensor is a clear glass panel with a touch responsive surface. The touch sensor is placed over a display screen.

The sensor generally has an electrical current going through it and touching the screen can cause a voltage change. This change determines the location of the touch.

CONTROLLER

The controller connects between the touch sensor and the PC. It takes information from the touch sensor and translates it into information that PC can understand. The controller determines what type of interface you will need on the PC.

SOFTWARE DRIVER

It tells the computer's operating system how to interpret the touch event information that is sent from the controller. Most touch screen drivers today are a mouse-emulation type driver.

SENSING TOUCH

5V is applied to a column, and a voltage measurement circuit is attached to a horizontal sensing line. Other columns and sensing lines are set to high impedance and ground potential, respectively.

SENSING TOUCH

When there is no touch, the measured

voltage is zero. When there is touch, the column and

the sensing line are electrically connected and the measurement circuit detects an electrical potential.

TOUCH SCREEN TECHNOLOGY

Resistive touch screen Capacitive touch screen Infrared touch screen Surface acoustic wave (SAW) touch

screen

RESISTIVE TOUCH SCREEN

StructureResistive touch screens consist of a glass or acrylic panel that is coated with electrically conductive and uniform resistive layers made with indium tin oxide (ITO) .The thin layers are separated by invisible spacers.

RESISTIVE CIRCUIT DIAGRAM

4-WIRE RESISTIVE TOUCHSCREEN

DRAWBACKS Cause microscopic cracks in the ITO

coating, changing its electrical characteristics (resistance), degrading the linearity and accuracy of this axis.

4-wire touch screen are of less durability.

Accuracy can drift with environmental changes.

Four-wire touchscreen in applications is recommended with a display size of 6.4" or smaller. 

8-WIRE RESISTIVE TOUCHSCREEN

CHARACTERS: Eight-wire touchscreen are used to

stabilize the system. Reduce the drift caused by

environmental changes. Eight-wire systems are usually seen in

sizes of 10.4" or larger where the drift can be significant.

5-WIRE RESISTIVE TOUCHSCREEN

The construction is similar but all four bus bars are connected to the lower, non-flexible layer of the screen. The flexible layer is always used as a sense layer to read the voltage connection point to the bottom layer.

So, they would no longer cause non-linearities.

It is more accurate, durable and reliable.

5-WIRE RESISTIVE TOUCHSCREEN

Advantages: Good resolution Will operate with

any stylus Low parallax Not affected by

dirt, dust, moisture, water, or light

Affordable touchscreen technology

Disadvantages: It can be damaged

by using a sharp instrument

Hose down can cause unwanted activation of target areas

Lowest transmissivity of all touch technologies - 55%-65%

CAPACITIVE TOUCH SCREEN

Projected-capacitive touchscreen

Surface-capacitive touchscreen

PROJECTED-CAPACITIVE TOUCHSCREEN

StructureProjected capacitive touchscreen have front and back protective glassproviding optical and strength enhancement options.Its middle layer consists of a laminated sensor grid of micro-fine wires, andoptical enhancement options.

PROJECTED-CAPACITIVE TOUCHSCREEN

Working Principle: During a touch, capacitance forms between

the finger and the sensor grid. The embedded serial controller in the touchscreen calculates touch location coordinates and transmits them to the computer for processing.

SURFACE-CAPACITIVE TOUCHSCREEN

Structure: Surface capacitive technology consists of

a uniform conductive coating on a glass panel. Electrodes around the panel’s edge evenly distribute a low voltage across the conductive layer, creating a uniform electric field.

SURFACE-CAPACITIVE TOUCHSCREEN

Working principle:A human body is an electric conductor, so on touch a slight amount of current is drawn, creating a voltage drop. The current respectively drifts to the electrodes on the four corners. Theoretically, the amount of current that drifts through the four electrodes should be proportional to the distance from the touch point to the four corners. The controller precisely calculates the proportion of the current passed through the four electrodes and figures out the X/Y coordinate of a touch point.

SURFACE-CAPACITIVE TOUCHSCREEN

Advantages: High resolution –

better then resistive.

Low parallax with spherical screen

Impervious to dust, oils, grease, moisture

Impervious to scratching by all but the hardest materials

High transmissivity - >85%

Disadvantages: Will not respond to

gloved finger or any non-conductive stylus.

INFRARED TOUCHSCREEN Principle: Infrared (IR) technology relies on the

interruption of an IR light grid in front of the display screen.

Structure:

Row of IR-light emitting diode (LEDs) and photo transistors, each mounted on two opposite sides to create a grid of invisible infrared light.

The IR controller sequentially pulses the LEDs to create a grid of IR light beams.

INFRARED TOUCHSCREEN

INFRARED TOUCHSCREEN Working: When a stylus, such as a finger, enters

the grid, it obstructs the beams. One or more photo transistors from each axis detect the absence of light and transmit signals that identifies the x and y coordinates.

Advantages: Best image quality Impervious to

scratching Activates with

gloved or ungloved finger and any stylus that is large enough to break IR light beam (typically >.25")

Disadvantages: Low resolution Exhibits worst

parallax problem Pressure hose down

may cause unwanted target selection

Dust, oil or grease buildup on frame that hinder the light beam may cause malfunction.

SAW TOUCHSCREEN

Principle: It is based on sending acoustic waves

across a clear glass panel with a series of transducers and reflectors. When a finger touches the screen, the waves are absorbed, causing a touch event to be detected at that point. 

SAW TOUCHSCREEN

SAW TOUCHSCREEN

Working : The technology is based on two transducers

and reflector. The controller sends electrical signal to the transmitting transducer, and transducer converts the signal into ultrasonic waves and emits to reflectors. After reflectors refract waves to the receiving transducers, the receiving transducer converts the waves into an electrical signal and sends back to the controller. When a finger touches the screen, the waves are absorbed, causing a touch event to be detected at that point.

SAW TOUCHSCREEN

SAW TOUCHSCREEN

Advantages: High touch

resolution Highest image

clarity All glass panel, no

coatings or layers that can wear out or damage

Disadvantages: Must be touched by

finger, gloved hand, or soft-tip stylus. Something hard like a pen won't work

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

Technology Capacitive SAW Infrared Resistive

Transparence Very good >92%

Very good >92%

Very good >92%

75%~85%

Resolution Good Good Limited due tospacing of IRsensors

good

SurfaceContaminants/durability

Resistant tomoisture andother surfacecontaminants

Adversely affected bymoisture orSurfacecontaminants

Potential forFalse activationor dead zonesFrom SurfaceContaminants

Unaffected by Surfacecontaminants.Polyester topsheet is easilyscratched

Sensor substrate

Glass with ITO coating

Glass with ITO coating

Any substrate Polyester top sheet, glasssubstrate withITO coating

Display size 8.4"-21" 10.4"-30" 10.4"-60" up to 19"

Touch method Human touch finger, gloved

hand or soft tip Can use any pointing device

Can use any pointing device

APPLICATIONS: iPhone and mobile phones Military applications Railway Ticket Machines ATMs Banking and Financial Applications Public information kiosks High traffic indoor environments The concept of a Yuno coffee mug PC

REFERENCES

http://searchcio-midmarket.techtarget.com/sDefinition/0,,sid183_gci214510,00.html

http://www.sensoria.in/TU/knowledge-pool/34-electronics-and-communication/56-working-principle-behind-touchscreen-mobiles.html

http://en.wikipedia.org/wiki/Touchscreen http://en.wikipedia.org/wiki/

Resistive_touchscreen http://www.devicelink.com/mem/archive/

01/09/013.html

CONT…

http://www.touchscreens.com/intro-touchtypes-resistive.html

http://www.touchscreens.com/intro-touchtypes-saw.html

http://www.tvielectronics.com/Touch_Screen.html

http://www.norteng.com/pages/tchselgd.html

Thanks!!!