#ALGORITHMS: "Touch sensing software gets robust"

Have you noticed that nothing comes with a manual anymore? The trend is to use commonly known symbols and functions with touch control being the newest way to make user interfaces self-explanatory. Touchscreens, of course, offer the ultimate in configurability, since you can change the image to redefine its buttons, but for the fixed functions of most devices a touchpad with stenciled legends and symbols is just as good and almost free. The easiest path is just etching traces on a printed circuit board that are then mounted behind a plastic control panel. The key to making them work, however, is the software that interprets the touches: R. Colin Johnson


Touch Sensing Software (TSS) offers a common set of algorithms for the touch panel functions of buttons, dials and sliders as well as allowing for innovative designers to define custom control surfaces for special purposes.

Here is what EETimes says about touch panels: 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.


Touch Sensing Software libraries (center) make use of touch-sensing modules (bottom) built into or added on to any Freescale microcontroller

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...

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