We use touch screens everywhere: tourist kiosks, automatic teller machines, point-of-sale terminals, industrial controls. Half a dozen vendors, plus in-house departments at major manufacturers, produced $800 million worth in 2000. The market is growing because the interfaces are easy-to-use, durable and inexpensive.
Touch screens employ one of three physics principles for detecting the point of touch. Pressing a “resistive” design with a finger or other stylus raises a voltage. In “capacitive” models, a finger draws a minute current (this method is often used for cursor pads on notebook computers). In other designs, a finger or stylus interrupts a standing pattern of acoustic waves or infrared lights that blanket the surface.
Resistive screens are the oldest, most widely used and least expensive, and they work with any stylus (finger, pen). Capacitive screens must be touched by a finger or an electrically grounded stylus to conduct current. Wave screens are the newest and most expensive. Surface acoustic wave screens must be touched by a finger or a soft stylus such as a pencil eraser to absorb energy; infrared screens work with any stylus. The different technologies may be used in the same applications, although pros and cons lead to prevalent combinations: resistive screens for industrial controls and Palm Pilots; capacitive screens for slot machines; wave screens for ATMs and indoor kiosks.
Most people are unaware of the type of screen they are using. But tricks can help you tell, according to Frank Shen of Elo TouchSystems in Fremont, Calif., the largest U.S. maker. Push the screen lightly with your fingernail (not your skin). If it responds, it could be resistive or infrared. In this case, place two separated fingers against the screen at the same time. If the cursor moves beneath one finger, the unit is infrared (software registers the first touch); if the cursor moves between the fingers, it is resistive (the points are averaged). If the unit does not respond to your fingernail, again place two separated fingers against it. If the cursor moves beneath one finger, the unit is acoustic wave; if the cursor moves between the fingers, it is capacitive.
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