Researchers at the University of
Washington’s aptly named
Ubiquitous Computing Lab can turn
any LCD monitor in your house into a
touchscreen, with nothing more
than a $5 sensor that plugs into the
wall and some clever software.
The technology, called uTouch,
works by measuring the
electromagnetic interference (EMI)
caused by your hand when it moves
near or touches an LCD monitor.
This might sound a little bit crazy,
but I’ll explain.
Basically, the
electricity running through the wires
in your house has a unique
electromagnetic signature. There is
the “carrier wave,” provided by the
power company and your nearby
substation, and then every single
kink and switch along the way
modulates the EM signature until it
is quite unique. What most people
don’t realize, though, is that every
device that is plugged into a wall
outlet also changes your EM
signature. Your TV doesn’t just suck
power from your house — it’s a
two-way street, with the electronic
components in the TV producing
interference that change your
house’s EM signature.
An EMI noise graph, showing a
touch event on a standard LCD
monitor
Now, by plugging an EMI sensor into
any wall socket, you can read your
house’s EM signature — and if you
continue to listen, you can detect
changes in the signature. Obvious
changes occur when a device is
switched on or off, but it also turns
out that simply moving your hand
close to an LCD monitor also alters
your house’s EM signature. It might
sound a bit unbelievable, that a
single finger moving towards an LCD
monitor can be detected by a sensor
at the other end of the house, but
that’s exactly what the University of
Washington researchers have
accomplished.
As for how a finger moving towards
or touching an LCD monitor creates
additional EMI, the simple answer is:
It’s very similar to how a normal
touchscreen works. Basically, every
LCD monitor has a massive matrix of
wires connected to every single
pixel. These pixels are updated row
by row, at a speed that’s dictated by the monitor’s row rate. The row
rate is generated by a row driver,
which oscillates at a very specific
frequency (say, 60KHz). If
something touches the row wires, or even comes close to them, the
capacitance (voltage) changes — just
like the Galaxy S4′s Floating Touch
feature . This capacitance causes the monitor’s row driver to work harder, which produces more EMI at that specific (60KHz) frequency.
Using that $5 sensor, which is
attached to a PC running some
clever software, the University of
Washington researchers are able to
discern between five different
gestures: full-hand touch, five-finger touch, hovering above the screen, pushing, and pulling.
Two years ago, the same research
group used the same technology to
turn CFL bulbs into proximity
sensors. Again, it’s quite hard to
believe, but when you walk into a
room it causes a minute change in
the wires inside the CFL bulb, which
causes detectable EMI on your
house’s power lines. This system,
called LightWave [PDF], could even
detect hand gestures made near CFL
bulbs.
The ultimate goal of the Ubiquitous
Computing Lab, as the name
suggests, is to find cheap and easy
ways of making everything around
us interactive. The uTouch
technology would probably never be
used on a standard desktop monitor
or laptop, but it could be useful in
the living room, commercial spaces,
and museums, where large,
expensive displays that could be
turned into touchscreens. Throw
LightWave into the equation, and it’s
easy to imagine dumb, non-
interactive spaces suddenly
becoming richly interactive.
Sadly, the Ubiquitous Computing Lab doesn’t intend to commercialize
uTouch, but co-author Sidhant Gupta
tells Technology Review that the $5
sensor uses off-the-shelf parts, and
the algorithms are included in the
paper, so it would be fairly easy for
you — or a commercial entity — to
recreate the uTouch system.
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