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TouchScreens provide fast access to all forms of digital information

2005.04.20 - Using a touch interface increases operator accuracy, reduces training time, and improves overall operational efficiencies, thus keeping costs down. While many shy away from computer keyboards, mice, or trackballs, there is no hesitation when it comes to just touching a screen. Users instinctively understand how to use the interface and simply can't make a mistake. Companies across a broad spectrum of industries have successfully harnessed the power of touch for a limitless variety of applications. See below for a summary of specific touch screen technologies.

Technology Summary


Capacitive Touchscreens
 Capacitive touchscreens use a glass overlay with a thin metallic conductive coating over the surface of the screen. When touching the screen, the user becomes part of the electrical circuit, creating a capacitive coupling with the voltage field and drawing a small amount of current to the point of contact. Capacitive touchscreens cannot be used by anyone wearing gloves, and scratching the touchscreen surface will render these touchscreens inoperable. In addition, they require ongoing maintenance to ensure accurate calibration.

Four-Wire Resistive Touchscreens
Four-wire resistive touchscreens are typically constructed using a plastic-on-plastic configuration. The top piece of plastic has a hard coat on the outer side and a conductive coating on the inner side. The bottom piece of plastic has a conductive coating on the inner side and is usually laminated to a glass panel or thicker polycarbonate plastic for support. The primary drawback of the four-wire technology is that one coordinate axis (usually the Y-axis) uses the top coversheet as its uniform voltage gradient, while the bottom substrate acts as the voltage probe. The constant flexing that occurs on the outer coversheet will change its electrical characteristics (resistance) with use, degrading the linearity and accuracy of this axis. As you can imagine, four-wire touchscreens are not as durable.

Five-Wire Resistive Touchscreens
Five-wire resistive touchscreens use a glass panel with a uniform resistive coating. A polyester coversheet is tightly suspended over the top of the glass, separated from it by small, transparent insulating dots. The coversheet has a hard, durable coating on the outer side and a conductive coating on the inner side. When you touch the screen, the conductive coating makes electrical contact with the coating on the glass. The voltages produced are the analog representation of the position you touched. The controller digitizes these voltages and transmits them to the computer for processing. The result of this process is an accurate, durable, and reliable touchscreen.

Infrared Touchscreens
Infrared touchscreens rely on the interruption of an infrared (IR) light grid in front of the display screen. The touch frame contains a row of IR-light-emitting diodes (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. When a stylus, such as a finger, enters the grid, it obstructs the beams. One or more photo transistors detect the absence of light and transmit a signal that identifies the X and Y coordinates. IR touchscreens can be operated in direct sunlight and offer a built-in filter to protect the surface of the display and to further seal the unit.

Surface Wave Touchscreens
Surface wave touchscreens consist of two main components: a clear, solid piece of glass formed to match the shape of the monitor, and a controller. The controller uses surface waves on the glass to develop a map of the touchscreen surface. When the screen is touched, your finger absorbs a portion of the signal traveling across it. The resulting change in the wave is detected by the controller, which calculates X and Y coordinates. Surface wave touchscreens are the preferred kiosk technology because they are durable enough to last the lifetime of the kiosk. Because there is no coating to degrade, they are very clear and provide stable "drift-free" operation.

 

Choosing a Touch Screen Technology

 

Your application requirement: Touch Screen Technology:
When economy is key Four-Wire Resistive
Clerk or employee-activated applications Five-Wire Resistive
Rugged environments and other special applications Infrared
Public-access applications Surface Wave
 
Four-Wire Resistive: When economy is key
Specific Features

Form Factor Options

Five-Wire Resistive: Clerk or employee-activated applications
Example Applications Specific Features Form Factor Options
Surface Wave: Public-access applications
Example Applications Specific Features Form Factor Options
Surface Wave: public-access applications in a vandal-risk environment
Specific Features Form Factor Options
Infrared: Rugged environments and other special applications
Example Applications Specific Features Form Factor Options

 

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How Touch Screens Operate

Touch Screen Composition
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