Capacitive Touch Sensors

murmerlastUrban and Civil

Nov 16, 2013 (3 years and 6 months ago)

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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

Capacitive touch sensors, of course!


behind it?

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

Chip provides 7
-
bit
resolution

128
different positions can
be read.

Alternating positive and
negative electrodes

eight of each

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?

Mini

Video, Photo

iPhone

3G

Nano

Other Popular Devices that Use Cap.
Touch Sensors

UGOBE
Pleo

Microsoft
Ultimate Keyboard

Motorola
KRZR

Apple
Mighty Mouse

Laptop Touchpads