Appliance Design - February 2008 - (Page 16) CONTROLS & SENSORS Taking Charge This touch-control panel features a touch screen, wheel slider, and buttons. A capacitive system evolves and expands beyond traditional uses. C by larry adams 16 applianceDESIGN February 2008 apacitive touch-control technologies are considered by many to be the workhorses of the electronics industry, having been used in applications such as cash registers, kiosks, cooking appliances, medical equipment, consumer electronics, and more. The robustness and versatility of capacitive-based touch control has been under development for more than 80 years, and its uses continue to grow. A capacitive touch control with a touch screen uses a surface coated with a conductive material such as indium tin oxide that can store a charge. The material conducts an electrical current across the panel along the X- and Y-axes. When touched by something conductive, such as a finger, that controlled field is altered and the location of the touch along the horizontal and vertical axes can be determined. In an application with button-key touch locations, a discrete sensor is placed under that particular key location, and when the sensor’s field is disturbed, the system notes the touch and the location. Capacitive technologies have a number of advantages, including high-touch resolution and the ability to use touch surfaces that provide high image clarity, and resistance to dirt, grease or moisture. Of course, it is not necessarily a panacea for all touchcontrol applications. One disadvantage of capacitive technology is that to actuate the screen or panel, a finger must touch it. This is unlike some other technologies such as resistive controls or acoustic signal processing systems that can be activated with a pen, a stylus, a corner of a credit card or other item. Some experts also say that traditional capacitive systems are susceptible to electrostatic discharge and electromagnetic interference. The technology has traditionally also cost more to use than some alternatives. It has been expensive to use because of the complex signal processing electronics. For instance, when developing a human machine interface with multiple discrete touch points, each touch point has to be directly tied to a sensor. Ten www.applianceDESIGN.com http://www.appliancedesign.com
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