Touch Screen Sensors

Outline

What are touch screen sensorsDifferent types touch screen sensorsWorking principlesMajor applications References

What are Touch Screen Sensors?

“A Touchscreen is a display which can detect the location of touches within the display area. This allows the display to be used as an input device, removing the keyboard and/or the mouse as the primary input device for interacting with the display's content.”

Types of Touch Screen Sensors

External add on touch screens

Integrated Touch Screen Monitors

External Add On Touch Screen Sensor

Can be added to your home computerBrings touch screen technology to the

common user

Integrated Touch Screens

The sensor system is already integrated into the screen or monitor

Working Principles

•A clear touch sensor is placed over the viewable video screen

Working Principles

A controller (2) takes information from the touch screen (1)

The info is turned into information the computer can understand

• A software driver is needed to allow the touch screen and computer to work together (3)

Working PrinciplesMultiple Types of Touch Sensors

ResistiveSurface Acoustic WaveCapacitiveInfraredStrain Gage

Resistive

Composed of several layer including two metallic layers separated from each other

When metallic layers are connected (touched) they act as like 2 voltage dividers

Change in electric current is sent to controller and the location is determined

4-wire resistive touchscreen

Surface Acoustic Wave

•Uses Ultrasonic waves across the surface

•When the screen is touched part of the wave is absorbed

•This allows the controller to determine the position of the touch

Capacitive

Coated with a current conducting material

Sensor has a precisely controlled field of stored electrons in horizontal and vertical directions

Humans also exhibit capacititanceA controller detects when there is a

disturbance in the electric field (touch)The controller then determines the location

Surface-capacitive touchscreen

StructureSurface 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.

Projected-capacitive touchscreen

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 touchscreenWorking principle

A human body is an electric conductor, so when you touch the screen with a finger, a slight amount of current is drawn, creating a voltage.s 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.

Infrared

An array of infrared sensors are placed horizontally and vertically

The sensors send out pulses of lightThe sensors detect the interruption of the

lightThe location is then determined by the

controller

Strain Gage

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•Screen is mounted on four springs one at each corner

•Deflection of screen when touched is measured by all four strain gages

•Calculations are made based on each of the four deflections to determine the location of the touch

Typical Applications

Consumer ElectronicsPhonesTabDigital CamerasGPSetc

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Typical Applications

ATM

Interactive Kiosks and learningstations

Etc. Etc. Etc.

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