Freescale Touch Sensor Draws Less Current

A new low-power capacitive sensor could make it easier forengineers to employ touch-pad interfaces on products ranging from cell phonesto garage door openers.

Known as the MPR121 ultra-low power capacitive sensor, itbrings touch panel interfaces to a host of new electronic devices, largelybecause it offers a dramatic reduction in power consumption. As a result, itcould serve as a replacement for some mechanical on-off switches, which draw nopower, but don't easily allow for the creation of smart interfaces.

"The advantage of this sensor is it allows you to drop in anadvanced interface," says Bryce Osoinach, touch sensors systems andapplications engineer for FreescaleSemiconductor, maker of the sensor. "But you don't lose much in terms ofpower consumption."

Freescale engineers say the new 12-electrode sensor consumesfar less current than its predecessors. In contrast to similar 12-electrodecapacitive sensors, which typically draw between 50 and 200 muA, the MPR121consumes only 29 muA of current, Osoinach says.

Freescale predicts the new sensor will be employed inlighting controls, low-resolution touch screens, photo frames and GPS systems,as well as large- and small-appliance touch panel interfaces.

Along with the new sensor, Freescale has also rolled out atouch sensing software suite compatible with more than 300 of the company'seight-bit microcontrollers (MCUs). For customers who already use Freescaleeight-bit MCUs, the software suite provides an alternate solution by enablingthem to manipulate the MCU itself to act as a touch sensor.

Freescale engineers expect the new sensor to be ofparticular interest to makers of cell phone handsets. There, the sensor couldenable the phone to "know" when it is and isn't being used by employingcapacitive sensing. As a result, the phone could more easily determine when toshut off its backlighting, and therefore save on power consumption.

"We're definitely seeing a trend toward reducing powerconsumption of (electronic) devices," Osoinach says. "In that respect, theMPR121 can help."

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