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Freescale Touch Sensor Draws Less Current
Brings touchpad interfaces to cell phones, GPS systems and garage door openers
Charles J. Murray, senior technical editor -- Design News, October 12, 2009
A new low-power capacitive sensor could make it easier for engineers to employ touch-pad interfaces on products ranging from cell phones to garage door openers.
Known as the MPR121 ultra-low power capacitive sensor, it brings touch panel interfaces to a host of new electronic devices, largely because it offers a dramatic reduction in power consumption. As a result, it could serve as a replacement for some mechanical on-off switches, which draw no power, but don't easily allow for the creation of smart interfaces.
"The advantage of this sensor is it allows you to drop in an advanced interface," says Bryce Osoinach, touch sensors systems and applications engineer for Freescale Semiconductor, maker of the sensor. "But you don't lose much in terms of power consumption."
Freescale engineers say the new 12-electrode sensor consumes far less current than its predecessors. In contrast to similar 12-electrode capacitive sensors, which typically draw between 50 and 200 µA, the MPR121 consumes only 29 µA of current, Osoinach says.
Freescale predicts the new sensor will be employed in lighting 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 a touch sensing software suite compatible with more than 300 of the company's eight-bit microcontrollers (MCUs). For customers who already use Freescale eight-bit MCUs, the software suite provides an alternate solution by enabling them to manipulate the MCU itself to act as a touch sensor.
Freescale engineers expect the new sensor to be of particular interest to makers of cell phone handsets. There, the sensor could enable the phone to "know" when it is and isn't being used by employing capacitive sensing. As a result, the phone could more easily determine when to shut off its backlighting, and therefore save on power consumption.
"We're definitely seeing a trend toward reducing power consumption of (electronic) devices," Osoinach says. "In that respect, the MPR121 can help."
Drawing just 29 µA, the MPR121 offers lower-power capacitive touch sensing for electronic products, such as cell phones and MP3 players.
