How touchscreens work

A touchscreen is a computer input device that enables users to make a selection by touching the screen, rather than typing on a keyboard or pointing with a mouse. Computers with touchscreens have a smaller footprint, can be mounted in smaller spaces, have fewer movable parts, and can be sealed.

09/01/1998


A touchscreen is a computer input device that enables users to make a selection by touching the screen, rather than typing on a keyboard or pointing with a mouse. Computers with touchscreens have a smaller footprint, can be mounted in smaller spaces, have fewer movable parts, and can be sealed. Touching a screen is more intuitive than using a keyboard or mouse, which translates into lower training costs.

3 components in common

All touchscreen systems have three components. To process a user's selection, a sensor unit and a controller sense the touch and its location, and a software device driver transmits the touch coordinates to the computer's operating system. Touchscreen sensors use one of five technologies: resistive, capacitive, infrared, acoustic wave, or near field imaging.

Resistive touchscreens typically include a flexible top sheet and a glass base separated by insulating dots. Each layer is coated with a transparent metal oxide on its inside surface. Voltage applied to the layers produces a gradient across each. Pressing the top sheet creates electric contact between resistive layers, essentially closing a switch in the circuit.

Capacitive touchscreens are also coated with a transparent metal oxide, but the coating is bonded to the surface of a single sheet of glass. Unlike resistive touchscreens, where any object can create a touch, capacitive touchscreens require contact with a bare finger or conductive stylus. The finger's capacitance, or ability to store an electric charge, draws some current from each corner of the touchscreen, where voltage has been applied.

Infrared touchscreens are based on light-beam interruption technology. Instead of placing a layer on the display surface, a frame surrounds it. The frame has light sources, or light-emitting diodes (LEDs), on one side, and light detectors, or photosensors, on the opposite side, creating an optical grid across the screen. When any object touches the screen, the invisible light beam is interrupted, causing a drop in the signal received by the photosensors.

Acoustic wave touchscreens use transducers mounted at the edge of a glass screen to emit ultrasonic sound waves along two sides. The ultrasonic waves are reflected across the screen and received by sensors. When a finger or other soft-tipped stylus touches the screen, the sound energy is absorbed, causing the wave signal to weaken. In surface acoustic wave (SAW) technology, waves travel across surface of the glass, while in guided acoustic wave (GAW) technology, waves also travel through the glass.

Near field imaging (NFI) touchscreens consist of two laminated glass sheets with a patterned coating of transparent metal oxide in between. An ac signal is applied to the patterned conductive coating, creating an electrostatic field on the surface of the screen. When a finger—gloved or ungloved—or other conductive stylus comes into contact with the sensor, the electrostatic field is disturbed.

Elizabeth Morse is communication coordinator at Dynapro (Vancouver, British Columbia, Canada), a hardware, software and touchscreen manufacturer.



Checklist for Touch Screen Selection

Besides price, consider the following before choosing a touchscreen technology:

How will the operator touch the screen? (Check one.)

_ Bare finger _ Gloved hand _ Other stylus

Describe the environment. (Circle all that apply.)

Moisture, dust, grease, chemicals, abrasives.

Temperature fluctuations, humidity fluctuations.

Vibration, shock.

Does the touchscreen require a NEMA seal? Yes No

Could it be vandalized? Yes No

Will it be used: Inside? Outside?

Is the environment protected? Yes No

Describe the stability required. (Check as needed.)

_ Periodic calibration to align the touchscreen to the display surface.

_ Drift-free alignment required.

Touchscreen attributes (Circle applicable number.)

Is low or high image clarity required? Low 1 2 3 4 5 High

How fine of resolution is required? Grainy 1 2 3 4 5 Fine

How fast does it respond to touches? Slow 1 2 3 4 5 Quick

How much force is needed to operate? Low force 1 2 3 4 5 High Force

How long is it expected to last? ___________________________

What are the power requirements? ______________________

Graphic by Cahners Business Information with data from Dynapro.



No comments
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by...
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
Controller programming; Safety networks; Enclosure design; Power quality; Safety integrity levels; Increasing process efficiency
Additive manufacturing benefits; HMI and sensor tips; System integrator advice; Innovations from the industry
Robotic safety, collaboration, standards; DCS migration tips; IT/OT convergence; 2017 Control Engineering Salary and Career Survey
Featured articles highlight technologies that enable the Industrial Internet of Things, IIoT-related products and strategies to get data more easily to the user.
This article collection contains several articles on how automation and controls are helping human-machine interface (HMI) hardware and software advance.
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Mobility as the means to offshore innovation; Preventing another Deepwater Horizon; ROVs as subsea robots; SCADA and the radio spectrum
Future of oil and gas projects; Reservoir models; The importance of SCADA to oil and gas
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me