Make: DIYSUPERHUMAN
ROCKING OUT HANDS FREE
You play air guitar, moving your
4 fingers
corresponding to the first 4 “note” buttons
on the Guitar Hero controller.
Electrodes on your arm detect tiny
electrical signals from the muscles that move
your fingers. These EMG signals are
boosted by amplifiers, each on their own
channel. The amplified signals are gathered
by the data acquisition board, which
sends them on to the laptop computer.
The USB video capture device pulls
the Guitar Hero video from the Wii
video game console into the computer, for
purposes of training the software.
The Air Guitar Hero software interprets
the mixture of EMG signals as one of the
4 button-pressing motions, then sends the
corresponding button command over to
the hacked GH controller which relays
it to the Wii. It sends the Strum command
automatically when you hit the note. You’re
rocking out!
NOTE: The hardest songs in GH require
you to stretch your little finger to hit the
fifth controller button. This motion is more
difficult to train and decode, so it isn’t used
in this tutorial, but it’s certainly possible to
train the Air Guitar Hero system to recognize
a fifth motion. Think of it as a challenge!
When a muscle contracts or flexes,
it produces electrical activity. While
faint (in the millivolt range), these
signals can be detected by placing
electrode sensors on the skin. The
technology to measure, evaluate,
and process muscular electricity is
called electromyography (EMG).
Air Guitar Hero uses EMG to send
signals to the Wii console to control
the game. But since the electrical
signal generated by twiddling your
fingers is very weak, additional
computation must be performed
to generate reliably accurate commands. The system uses pattern
recognition algorithms to identify
patterns in the EMG signals and
decide which colored button to
activate.
The algorithms require training
data to provide examples of what
signal characteristics to look for.
First, you must correctly play
on-screen notes with the guitar
while the electrodes record your
EMG signals.
Next, the recorded data is used
to train a model for recognition
the next time you make those
movement patterns.
Third, practice makes perfect!
Playing this type of video game
can be useful for building muscle
tone and dexterity.
Wii-Hab Lab: How the Air Guitar Hero system works.
Damien Scogin
46 Make: makezine.com/29
