Touch sensors are on the button for HMIs

Novel charge-transfer digital sensor chips facilitate the manufacture of man-machine interfaces at a cost comparable to using electromechanical switches.

With a cost per key of around US $0.15 in high volume consumer applications, the QTouch QT220 and QT240 charge-transfer digital sensor chips facilitate the manufacture of human/machine interfaces at a cost comparable to using electromechanical switches.

They are capable of detecting near-proximity or touch on two or four electrodes, respectively, and allow these electrodes to project independent sense fields through any dielectric including glass, plastic, stone, ceramic or wood.

They can also turn metal-bearing objects into intrinsic sensors, making them responsive to proximity or touch.

This capability, together with a continuous self-calibration feature, can lead to entirely new product concepts, adding user appeal to the aesthetics and functionality of human interfaces.

Typical applications include control panels, appliances, gaming devices, lighting controls, or anywhere a mechanical switch or button might otherwise be used.

The devices can also be used for some material sensing and control applications.

No mechanical movement is needed for reliable sensing to occur and products designed with these devices can be totally sealed - factors that make them inherently more reliable than electromechanical counterparts.

Each of the key channels operates independently of the others, and each can be tuned for a unique sensitivity level by simply changing its sample capacitor value.

Two speeds are supported, one of which consumes only 90uA of typical current at 4V.

Both devices operate from a single 3.9 to 5.5V DC supply and use a 20-SSOP lead-free package.

The QT220 and QT240 feature sync pins for synchronisation with additional similar parts and/or to an external source to suppress interference.

This pin doubles as a drive pin for spread-spectrum modulation.

Option pins are provided which allow different timing and feature settings.

The RISC cores of these devices use signal processing techniques to meet numerous operating environment challenges, such as "stuck sensor" conditions, component ageing, moisture films and signal drift.

Unique among capacitance sensors, the devices incorporate spread spectrum modulation for EMC compliance.

Both devices are available now.

Prices for 100,000-unit quantities are under US $0.50 for the two-key QT220 and under US $0.60 for the four-key QT240.

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