Capacitive Touch Sensors Sticking your finger into an electromagnetic field can be fun and useful! -By Jacob Hildebrandt

Controller of an Icon The iPod’s “click wheel” is one of the most recognizable user interfaces in the world, but what’s behind it? Capacitive touch sensors, of course!

How Capacitive Sensing Works Two electromagnetic fields are set up, by charging one “plate”, and grounding the other two. As finger moves…

How Capacitive Sensing Works Two electromagnetic fields are set up, by charging one “plate”, and grounding the other two. As finger moves… The EM fields change

Like an LVDT, the magnitude of these changes in EMFs are measured and compared to each other (as well as the previously measured values). From these values, direction and position can be easily computed. Unlike and LVDT, however, the fields can be manipulated by anything that can hold a charge—like human flesh.

iPod Click Wheel Alternating positive and negative electrodes—eight of each Chip provides 7-bit resolution—128 different positions can be read. Holes for traditional push-buttons

Signal Conditioning

Why Use Capacitive Sensing? Reliability No moving parts Virtually unaffected by changes in temperature, pressure, humidity, etc. EMF can effect it, but is easily compensated for Actual sensor array is virtually fail-proof User friendly Intuitive, works as you would expect Relatively cheap and simple to implement

Why Use Capacitive Sensing? cont. A lack of physical “buttons” allows for: Flat, sleek surfaces Easier manufacturing Weatherproof, easy to clean More freedom in design Thin profile Infinite resolution, number of buttons limited only by A-D hardware Can be defined by user though software No need for physical contact “Skins” and faceplates, cases, etc. can be installed without effecting performance Buttons can be placed behind LCD screens, embedded in plastic

Which iPods Use Cap. Sensing? Video, Photo 3G Mini Nano iPhone

Other Popular Devices that Use Cap. Touch Sensors UGOBE Pleo Apple Mighty Mouse Motorola KRZR Microsoft Ultimate Keyboard Laptop Touchpads