touchscreens ei presentation-1

8/8/2019 Touchscreens Ei Presentation-1

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By

Aditya Patil

TOUCHSCREENS


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yA touch screen is an electronic visual display that can detect

the presence and location of a touch within the display area.

y The term generally refers to touching the display of thedevice with a finger or hand.

y The display screen has a sensitive glass overlay placed on

it (touchpad)and we could give the desired input by touching

it.

WHAT ARE TOUCH SCREENS?


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Five basic elements make up a complete touchscreen system:

y The touchscreen itself.

y A computer (typically a PC) whose display is fitted with thetouchscreen.

y A controller card, which drives the touchscreen and converts eachtouch into coordinates.

y A software driver program, which communicates between the controllercard and the computer's operating system.

y

Application-development software, which enables developers of touchprograms to build their own applications and/or customize existingtouch applications.

HOW A TOUCHSCREEN SYSTEM WORKS


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Resistive

Capacitive

a. Surface capacitance

b. Projected capacitance

Surface acoustic wave

Scanning Infrared TS

Strain gauge TS

Types of touch screens


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y A resistive touchscreen panel is composed of several layers, the most

important of which are two thin, metallic, electrically conductive layers

separated by a narrow gap.

y When an object, such as a finger, presses down on a point on the

panel's outer surface the two metallic layers become connected at that

point: the panel then behaves as a pair of voltage dividers with

connected outputs.

y The two charged sheets are separated just enough to keep the

charges from touching each other.y This causes a change in the electrical current, which is registered as a

touch event and sent to the controller for processing.

RESISTIVE TOUCHSCREEN


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Working ofresistive

touchscreen


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AdvantagesCheap to make.

Any object can be used to make contact.

Accuracy is high so interface is ideal for note taking and character recognition.

They are very accurate and can be used for high resolutions up to 4096X4096dpi.

It can also be used in multiple touch screen pads.

DisadvantagesTop layer susceptible to damage.

Since there are many layers piled up on actual display, visibility is reduced.

Usually around 75% transmission is promised.

Over time tends to become less sensitive, accuracy decreases.

RESISTIVE TOUCHSCREEN


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A capacitive TS can be of two types

i) Surface Capacitive

ii) Projected Capacitive . In both cases top layer is usually of glass making it

more scratch resistant than resistive TS.

Core property used here is that of the capacitor twoconductors separated by an insulator.

CAPACITIVE TOUCHSCREEN


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y Glass coated with conductive layer indium tin oxide on underside.

y This technology is based on the capacitor coupling effects.

y Small amount of voltage is applied to uniformly charge the entire surface.

y There are electrodes on the four corners of the screen to check for voltage

changes.

y When a conducting object, like a human finger touches the screen the charge

is drained at that point(glass acts as insulator between conducting layer and

conducting object)and a voltage change is registered.

y Each electrode detects this change, to arrive at the point of contact.

SURFACE CAPACITIVE TOUCHSCREEN


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y Consists of two parallel layers of conducting material (ITO),similar to the setup

seen in Resistive TS.

y The difference being ,there are no flexible layers- both layers are glass, and

conducting material is etched on the proximal surfaces so as to form a grid ofelectrodes separated by a thin film of air(capacitors)

y Capacitance field is active above the surface of the top layer of glass bringing

conductive material like human finger close(2mm is enough) to the TS causes a

discharge and resultant voltage is picked by electrodes.

y i-Phone and other premium phones use this technology.

PROJECTED CAPACITIVE TOUCHSCREEN


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PROJECTED CAPACITIVE TOUCHSCREEN


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Advantagesy True touchscreens where mere touch generates input.

y Projected capacitive TS allows detection of multiple points of contact,allowing multitouch operations/gestures.

y Compared to resistive touchscreens ,these screens allow faster inputs.

y Since glass isn't easily scratched, this is more rugged than Resistive TS.

Disadvantagesy Needs a conducting object to register touch, so an ordinary stylus or even a finger

nail will not do.

y Scratches on the top layer can impact performance.

CAPACITIVE TOUCHSCREEN


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y This technology employs ultrasonic waves(USW) to form a grid above

the screen.

y Piezoelectric USW generators and reflectors are used to generate US

waves and stream them over the surface-usually glass.

y US waves are generate on both vertical and horizontal directions by

generators, while receivers placed at the opposite ends monitor them.

y Even when a finger or a object is placed near it ,some of the US waves

are blocked.

y This is detected by the receivers on both axes, and the location of thepoint of touch is calculated.

SURFACE ACCOUSTIC WAVE TS


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Made of a glass overlay with transmitting and receiving piezoelectrictransducers for both the X and Y axes.

When a touch occurs, the wave is absorbed shortening the echo timeit takes to reach the receivers



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Advantagesy Since there are no layers involved, just as glass sheet, visibility is high.

y Works with any object.

yFast Touch Response

y High Resolution

y The only TS technology that can also detect Z-axis or pressure if any.

Disadvantagesy

Since the network of US waves is above the surface,it is possible that falsetouches are registered if objects come close.

y Expensive



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Similar in concept and function as Surface acoustic wave TS,

here IR diodes and sensors are placed on opposite sides of the

bezel to generate and receive IR waves respectively.

The obstruction in the IR waves at the point where the object is

placed on the screen is reduced to X and Y coordinates

SCANNING INFRARED TS


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Advantagesy There is no need to overlay any screens ,just the bezel containing the IR

transmitters and receivers are needed.

y So visibility is maximum among TS types.

y

Since the circuitry can be completely sealed in bezel, this technology offersreliability even in the toughest environments.

y Most preferred TS technology for large screens

Disadvantagesy Since normal sunlight also contains IR rays ,these screens do not perform

optimally when placed in areas with abundant sunlight.

y The density of the IR diodes determines the sensitive areas of the screen anddetectable size of the object.

y Some of the narrow spread or newer technologies are touched next



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In a strain gauge configuration, also called force panel technology, the

screen is spring-mounted on the four corners and strain gauges are used

to determine deflection when the screen is touched.

Also called force panel technology.

This technology has been around since the 1960s, but new advances by

Vissumo andF-Origin have made the solution commercially viable.

It can also measure the Z-axis and the force of a person's touch. Such

screens are typically used in exposed public systems such as ticketmachines due to their resistance to vandalism.

STRAINGAUGE TS


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y Multi touch screens and collaborative software make a tough team.

y It is easy to picture a person using multi touch to rotate an image , but the

true power if multitouch is in having multiple people collaborating on the same

project.

y Two people collaborating on the same screen would be better. but nothingwould beat having a third person adding his inputs over the net.

y As the bandwidths expand and the internet connections speed up and

appropriate software is created, such an intercontinental brain storming

session would be possible causing an revolution in cloud computing

y TSs and gestures are predicted to make mice and keyboard redundant.y This is debatable.

THEFUTURE.


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BIBLIOGRAPHY

www.wikipedia.com

http://www.circuitstoday.com

http://www.seminarprojects.com


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touchscreens ei presentation-1

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