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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?.

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Capacitive touch sensors

Capacitive Touch Sensors

Sticking your finger into an electromagnetic field can be fun and useful!

-By Jacob Hildebrandt


Controller of an icon
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
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 works1
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


Capacitive touch sensors

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
iPod Click Wheel measured and compared to each other (as well as the previously measured values). From these values, direction and position can be easily computed.

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
Signal Conditioning measured and compared to each other (as well as the previously measured values). From these values, direction and position can be easily computed.


Why use capacitive sensing
Why Use Capacitive Sensing? measured and compared to each other (as well as the previously measured values). From these values, direction and position can be easily computed.

  • 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
Why Use Capacitive Sensing? measured and compared to each other (as well as the previously measured values). From these values, direction and position can be easily computed. 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
Which iPods Use Cap. Sensing? measured and compared to each other (as well as the previously measured values). From these values, direction and position can be easily computed.

Video, Photo

3G

Mini

Nano

iPhone


Other popular devices that use cap touch sensors
Other Popular Devices that Use Cap. Touch Sensors measured and compared to each other (as well as the previously measured values). From these values, direction and position can be easily computed.

UGOBE Pleo

Apple Mighty Mouse

Motorola KRZR

Microsoft Ultimate Keyboard

Laptop Touchpads