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

2. 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!

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

4. 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

5. 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.

6. 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

7. Signal Conditioning

8. 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

9. 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

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

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