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issue: May 2007 APPLIANCE European Edition

Switches and Switching Devices
A Touch of Design

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APPLIANCE Staff Feature

Slovenian kitchen appliance maker Gorenje made a conscious decision to move upmarket, and over the past 5 years it has worked to strengthen its image as a design and technology trendsetter.

Gorenje’s cooktop slider controls allow “direct access” temperature setting without the need for slew keys, which is said to create a highly desirable replacement for mechanical knobs.

A milestone of this effort was the launch of its Pininfarina series of kitchen appliances in 2005. In November 2006, this series received the prestigious Manufacturer’s Award from The Designer magazine—the third prize won by this product line after little more than 1 year in the market.

Key to this award-winning design is the use of touch controls from Quantum Research Group in Southampton, England. In a first-ever product design, Gorenje made use of Quantum’s QT401 QSlide sensing chip for three of its Pininfarina cooktop controls, along with Quantum QT1100A ten-key chips for discrete buttons. These spread-spectrum charge-transfer devices allowed Gorenje to develop user interfaces in a fresh way.

There were problems with the former switches, according to Hal Philipp, CEO of touch chip provider Quantum. “Mechanical switches were not consumer appealing or functional enough to do the job,” he says. “The product definition called for touch controls to enhance the product and make the product more upscale. Mechanical switches are not reliable enough, nor are they differentiating enough.”

The new chip is used in Pininfarina cooktops as a temperature setting mechanism, allowing “direct access” to the desired heat setting rather than the more traditional “slew” type control, which most users find tedious. The chip is a charge-transfer based capacitive sensor IC that detects finger position along a strip. The sensor’s fields can penetrate up to 5-mm thick glass panels.

The basis of this technology is the use of CMOS switches to charge the sensing electrode strip to a voltage, then transfer the electrode strip’s charge to a pair of fixed capacitors whose voltages are then measured. This 14-pin surface-mount device has a resolution of 127 positions across the sensing strip. The strip can be a resistive film or resistor ladder, or interleaved copper PCB electrodes. It uses spread spectrum burst modulation to suppress the effects of electrical noise. The interface is SPI, and the part operates over a 2.7-V to 5-V range. The chips include automatic drift compensation and automatic calibration.

Gorenje’s Pininfarina kitchen makes extensive use of touch controls to give it a sleek, stylish look with easy-to-use, intuitive user interfaces.

Up to 10 additional touch buttons come from the QT1100A 10-key chip that senses touch or proximity using capacitive charge-transfer technology. The basis of this technology is the use of CMOS switches to charge the sensing electrode to a voltage, then transfer the electrode’s charge to a fixed capacitor, whose voltage is then measured. This 48-pin surface-mount device also features patented Adjacent Key Suppression™ (AKS), used to resolve touch ambiguity when more than one key is touched unintentionally, such as in tightly spaced keypads.

This device uses spread spectrum burst modulation to suppress the effects of electrical noise on performance and offers three output interfaces: UART, SPI and scanport. It operates over a 3.3- to 5-V range. The 10-key chip includes automatic drift compensation and automatic calibration.

Both chips project a touch sense field through thick glass, including glass cooktops. “Gorenje’s choice of touch slider and button chips for its Pininfarina series allowed them to create distinctive, high-value designs not found elsewhere,” Philipp says. “Gorenje’s choice of controls was inspired, not only because it won them so many immediate design awards, but also because it allows intuitive non-mechanical user controls, easy wipe-down functionality, electrical robustness, and [more] importantly, a high degree of design flexibility simply not available with other control technologies.”

According to Joze Dermol, lead engineer of Gorenje’s R&D department, “The positive experiences customers report about these touch controls made us think, research and develop user interfaces in a different, fresh way. With these devices, we see that there are no longer problems for us to create any kind or shape of appliance front panel, solving a major design barrier. We realize now that touch-sensor-based user interfaces can meet any design demand, and the resulting modern design and user-friendly interface no longer needs to be an exclusive feature.”

Philipp says Quantum is working with Gorenje on next-generation user interfaces for kitchen appliances.

Suppliers mentioned in this article:
Quantum Research Group Ltd.

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