Appliance Design - February 2008 - (Page 17) CONTROLS & SENSORS QTouch sensors can drive single or multiple keys. QMatrix detects a touch using a scanned, passive matrix. buttons require 10 sensors. One of the early players in this field was the U.K.-based Quantum Research Group whose technology is based on the capacitance method, but whose technology has evolved to keep the advantages of the system while mitigating some of the disadvantages. Founded in 1996, the company’s technology has been successfully incorporated into a range of devices from home appliances to consumer electronics. In many of these applications, the touch controls can be subjected to moisture, temperature changes, chemicals, electrical noise, and a host of other things that have the potential to confuse a user-interface control system. “Capacitive sensing dates back to the 1920’s, but it has taken a long time to make it sufficiently robust and cost effective to the point where designers feel comfortable enough to use it,” says Chris Ard, director of business development for Quantum. “Over the last 10 years of our company, the technology has been perfected and now we are extending the technology and its applications.” Quantum has focused on developing integrated circuit technology that is based on charge-transfer capacitive sensing. The company’s earliest products were based on the QTouch™ system, which was patented in 1999. Among its first applications were touch and proximity controls for kitchen refrigerator water dispensers in the U.S., as well as biomedical equipment in www.applianceDESIGN.com the UK. QTouch ICs are designed to detect touch using a single connection between the sensor chip and a simple key electrode. These chips are best suited for low-key count applications of up to 10 keys. The QTouch devices work by charging a sense electrode of unknown capacitance to a known potential. The resulting charge is transferred into a measurement circuit. By measuring the charge after one or more charge-and-transfer cycles, the capacitance of the sense plate can be determined. Placing a finger on the touch surface introduces external capacitance that affects the flow of charge at that point. This registers as a touch. QTouch microcontrollers can also be programmed to detect the proximity of a finger, rather than absolute touch. Signal processing in the decision logic module makes QTouch robust and reliable, Ard says. False triggering due to electrostatic spikes or momentary unintentional touch or proximity is eliminated. QTouch sensors can drive single or multiple keys. Where multiple keys are used, each key can be set for an individual sensitivity level. Keys of different sizes and shapes can be used to meet both functional and aesthetic requirements. The Samsung microwave features Quantum’s touch scroll-wheel technology. applianceDESIGN February 2008 17 http://www.appliancedesign.com
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