touch screen sensor matheen

8/7/2019 Touch Screen Sensor Matheen

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Touch Screen Sensor

Quanling zheng


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How Does a Touchscreen Work?

A basic touchscreen has three main components:

1 Touch sensor;

2 Controller;

3 Software driver.

The touchscreen is an input device, so it needs to becombined with a display and a PC or other device to make acomplete touch input system.


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Touch Sensor

A touch screen sensor is a clear glass panel with a touchresponsive surface. The touch sensor/panel is placed overa display screen so that the responsive area of the panelcovers the viewable area of the video screen. There areseveral different touch sensor technologies on the markettoday, each using a different method to detect touch input.The sensor generally has an electrical current or signalgoing through it and touching the screen can cause avoltage or signal change. This change is used to determinethe location of the touch to the screen.


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Controller

The controller connects between the touch sensor and thePC. It takes information from the touch sensor andtranslates it into information that PC can understand. Thecontroller determines what type of interface/connection you

will need on the PC. Controllers are available that canconnect to a Serial/COM port (PC) or to a USB port.Specialized controllers are also available that work withDVD players and other devices.


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Software Driver

The driver allows the touchscreen and computer to worktogether. It tells the computer's operating system how tointerpret the touch event information that is sent from thecontroller. Most touch screen drivers today are a mouse-emulation type driver. This makes touching the screen assame as clicking your mouse at the same location on thescreen. This allows the touchscreen to work with existingsoftware and allows new applications to be developedwithout the need for touchscreen specific programming.


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Touchscreen Technology

Resistive touchscreen

Capacitive touchscreen

Infrared touchscreenSurface acoustic wave (SAW) touchscreen

Strain gauge touchscreen

Optical imaging touchscreen

Dispersive signal technology touchscreen


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Structure

Resistive touch screensconsist of a glass or acrylic

panel that is coated withelectrically conductive andresistive layers made withindium tin oxide (ITO) .Thethin layers are separated by

invisible spacers.


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4-wire resistive touchscreen


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The construction of the panels are similarwith 4-wire technology, but for a 5-wiretouch screen all four bus bars are connected

to the lower, non-flexible layer of the screen.The flexible layer is always used as a senselayer to read the voltage connection point to

the bottom layer.


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Characters:

1. Cost effective solutions

2. Activated by a stylus, a finger or gloved hand

3. Not affected by dirt, dust, water, or light

4. 75%~85% clarify

5. resistive layers can be damaged by a very sharp object


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Projected-capacitive touchscreen

Structure

Projected capacitivetouchscreens have front and

back protective glassproviding optical and strengthenhancement options.

Its middle layer consists of a

laminated sensor grid of micro-fine wires, andoptical enhancement options.


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Projected-capacitive touchscreen

During a touch, capacitance forms between thefinger and the sensor grid.The embedded serialcontroller in the touchscreen calculates touch

location coordinates and transmits them to thecomputer for processing.


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Surface-capacitive touchscreen

Structure

Surface capacitive technology consists of auniform conductive coating on a glass panel.

Electrodes around the panels edge evenlydistribute a low voltage across the conductivelayer, creating a uniform electric field.


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Surface-capacitive touchscreen

Working principle

A human body is an electric conductor, so when you touch the screen witha finger, a slight amount of current is drawn, creating a voltage drop. Thecurrent respectively drifts to the electrodes on the four corners. Theoretically,the amount of current that drifts through the four electrodes should beproportional to the distance from the touch point to the four corners. Thecontroller precisely calculates the proportion of the current passed through the

four electrodes and figures out the X/Y coordinate of a touch point.


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Capacitive touchscreen

Characters:

1. Durable and resistant to scratches fordemanding applications

2. Faster and more responsive

3. Immune to surface contaminants

4. Superior optical clarity, brighter display and less

surface reflection

5. Must be touched by finger, will not work with anynon-conductive input


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Infrared touchscreen

Infrared (IR) technology relies on the interruption of an IRlight grid in front of the display screen. The touch framecontains a row of IR-light emitting diode (LEDs) and phototransistors, each mounted on two opposite sides to create

a grid of invisible infrared light.The IR controller sequentially pulses the LEDs to create agrid of IR light beams. When a stylus, such as a finger,enters the grid, it obstructs the beams. One or more phototransistors from each axis detect the absence of light and

transmit signals that identifies the x and y coordinates.


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Characters:

1. Clear as glass, improves reading ability

2. Most durable surface


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SAW touchscreen

PrincipleSurface waves are readily absorbed when

a soft object such as a fingertip touches thesubstrate.

SAW Touch Screenuse pure glass withtransmitting and receiving piezoelectric

transducers for both the X and Y axes.

The touch screen controller sends anelectrical signal to the transmitting transducer,which converts the signal into ultrasonicwaves within the glass.

When you touch the screen, you absorb a

portion of the wave traveling across it. Thereceived signal is then compared to the storeddigital map, the change recognized, and acoordinate calculate.


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SAW touchscreen


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SAW touchscreen

Characters:

1. Durable glass construction

2. High optical clarity3. Activated by a finger, gloved hand or soft

tip

4. Not completely sealable, can be affectedby large amounts of dirt, dust, and / orwater in the environment


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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

Adverselyaffected bymoisture orSurfacecontaminants

Potential forFalse activationor dead zonesFrom SurfaceContaminants

Unaffected bySurfacecontaminants.Polyester topsheet is easilyscratched

Sensor substrate Glass with ITOcoating

Glass with ITOcoating

Any substrate Polyester topsheet, glass

substrate 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 anypointing device

Can use anypointing device


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Multi-touch technology

Multi-touch denotes a set of interactiontechniques which allow computer users tocontrol graphical applications with several

fingers.Products:

Apple iPhone, iPod touch, MacBook Air, and

MacBook ProMicrosoft Surface

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