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Touch sensor IC caters to mobile devices

Posted: 25 Mar 2009     Print Version  Bookmark and Share

Keywords:touch sensor  capacitive sensing  capacitive user interfaces  touch button 

Atmel Corp. has introduced an easy to implement, low-cost touch sensor IC, which brings capacitive user interfaces to price-sensitive consumer and mobile devices.

The AT42QT1040 is available in a 3mm x 3mm x 0.85mm VQFN 20 pin package, making it suitable for use in mobile phones and other handheld devices where PCB space is at a premium. In low power mode the AT42QT1040 draws only 31µA from a 1.8Vdc supply, allowing capacitive sensing to be added with minimal impact on battery lifetime.

The device is the latest solution from Atmel's touch sensor division, which develops capacitive touch button, slider, wheel and touchscreen controllers. The AT42QT1040 includes four digital output channels, enabling per-channel indication on touch detection. The IC can also be configured using one channel as a proximity sensor, enabling 'hidden-until-lit' user interfaces where the device detects the presence of a finger some distance away from the keypad.

The AT42QT1040 is based on Atmel's QTouch charge-transfer sensing method. The technology uses spread-spectrum modulation to achieve high immunity to electrical noise. Atmel's Adjacent Key Suppression, technology, essential for tight-pitched keys, is used to ensure that only the intended key is activated by the touch of a finger.

Long-term reliability is achieved because the device automatically calibrates on power-up and always stays calibrated even if there is a build-up of moisture or other contaminants on the touch surface or if the overall system is subject to ageing. Individual key sensitivity can be configured to support a range of front panel thicknesses and materials including glass or plastic up to several millimeters thick. Electrodes can be made from copper, silver, carbon, indium tin oxide or any other conductive material. Widely different electrode sizes and shapes are possible, giving the product designer great flexibility to tailor the user interface.

The device has two power modes: a low power mode, which is suitable for small, battery-driven devices and a fast response mode, which provides minimum response time for applications where low touch latency is essential. To aid product development, the AT42QT1040 has a debug mode in which internal data from the chip can be accessed. The ability to monitor the behaviour of the device in this way means that designs can quickly be evaluated and tuned resulting in a shorter product design time frame.

The AT42QT1040 is priced at Rs.17.40 ($0.35) in quantities of 100,000 units. An evaluation kit, EVK1040A, is also available, priced at Rs.1,242.98 ($25).

Click here for technical tutorials on capacitive sensors.

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