PORTLAND, Ore.--New touchpad technology introduced by Freescale Semiconductor Inc. converts capacitive touch panel readings into reproducible functions of buttons, dials and sliders and other control surfaces.
Touch has become the expected modality for human-machine interfaces for everything from smartphones to washing machines. Touch-based control panels use touchpads with pictures demonstrating common functions that people already know how to do, virtually obsolescing mechanical switches.
Freescale (Austin, Texas) provides the artwork to make a variety of analog-like input devices by patterning copper traces behind a plastic control panel covered with pictures of those buttons, dials and sliders. By artfully crafting a pattern of copper traces to track the capacitance of up to 16 locations, original equipment manufacturers (OEMs) can create a control panel that is self-explanatory in how it controls their specific device, according to Freescale.
For a slider, for instance, dividing a rectangular copper pad into two right triangles allows you to change the differential capacitance between them by running your finger over its length. Other novel patterns allow ordinary controllers—like dials and switches—or an infinite variety of custom control surfaces to be defined.
"One thing that our customers do is create their own proprietary patterns ," said Eduardo Viramontes, touch sensing applications engineer at Freescale. "But we have boards you can start out with that have the most common patterns for buttons, dials and sliders."
Touch Sensing Software libraries (center) make use of touch-sensing modules (bottom) built into or added on to any Freescale microcontroller
The latest software iteration of Freescale's Touch Sensing Software (TSS) library—version three, free for use with its microcontrollers—adds robust auto-sensitivity calibration (ASC) based on noise level analysis that Freescale claims prevents false readings even in the presence of electrical noise, making touch control panels more reliable. So robust is the auto-calibration, according to Freescale, that it allows capacitive touchpanels to work even when they get wet, then return to normal calibration when dried.
"The software is always recalibrating so that it is always adjusts to the conditions where it's at," said Raul Hernandez Arthur, product marketing manager at Freescale.
Freescale's TSS was announced this week at the 2012 Freescale Technology Forum India (Bengaluru, India). TSS is a part of Freescale's portfolio of sensing solutions, including MEMS accelerometers, magnetometers and altimeters, but requires no extra hardware for many HCS08 devices, ColdFire+ MCUs and Kinetis MCU families built on the ARM Cortex-M4 processor.
It sounds like a nice way for designers to have the user interface be "touch" with simple (I hope) copper based PCB etch. Does the copper etch need to be on the surface or can it be below the printed outer layer? I could see flex circuit boards being used under a printed press on outer layer being easy to build and use.
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