FIGURE 2. Game screen shots showing
wobble board-controlled dot off target
(left) and on target (right).
plastic or wooden disc, typically 18
inches in diameter. A dome over a
pivot point in the center of the bottom
side allows 15 to 20 degrees of tilt.
OPTP is one of several vendors that
offers affordable models starting at
about $40 ( www.optp.com).
Physical therapists and sports
trainers use balance boards with their
clients to rehabilitate ankle injuries,
enhance range of motion, and for general motor skill training. Many runners
and martial artists incorporate wobble
boards in their training programs to
increase flexibility and reduce
incidence of injury. The downside of
working with a wobble board is that
there is no immediate feedback and
the routines quickly become boring —
hence the motivation for an exergame.
The on-screen view of the wobble
board-controlled exergame is shown
in Figure 2. After a series of countdown screens, the player is presented
with a constantly moving bull’s-eye
target. While standing on the wobble
board, the player attempts to adjust
the tilt of the board so that the white
dot constantly tracks the center of the
bull’s-eye. The goal of gameplay is to
track the bull’s-eye target as long as
possible within 100 seconds. Contact
time translates directly to score.
To move the dot up on the TV
display, the player tilts the wobble
board forward by pressing her toes
down while simultaneously adjusting
her body to maintain balance. Similarly,
moving the dot to the left involves the
player shifting her body weight, pressing her left leg down, and flexing her
ankles to the right. Intermediate players
can stand with their feet together.
Advanced players can stand on one
foot while holding their free knee to
their chest or performing a similarly
challenging maneuver. Based on personal use and feedback from several
users, the game succeeds in transforming a typically boring series of exercises
into a fun and slightly addictive activity.
The following sections describe
the Hydra Game System, including the
hardware and software, the characteristics of the Memsic 2125 accelerome-
FIGURE 3. Hydra board
with EEPROM card.
ter, and the software and
hardware required to
interface the accelerometer to the Hydra.
Hydra Game
System
The Hydra Game
System is aptly named,
in that it isn’t simply
another microcontroller board, but is
a complete system for game development. In addition to the Hydra board
and peripherals, the system includes a
CD-ROM filled with software and an
800+ page book that provides an
integrated explanation of the hardware environment in the context of
classic or retro game development.
Working with the Hydra board (see
Figure 3) and library of games, game
engines, and demos — including titles
inspired by Breakout, PacMan, Lock N
Chase, Q-bert, and Centipede — is like
taking a step back in time to the days of
the Atari and Commodore- 64. Although
VGA is supported, most of the demos
are written to composite NTSC video,
which accounts for the low resolution,
retro look of the exergame shown in
Figure 2.
nents are socketed for future upgrades
and experimentation. The Hydra also
sports a game card expansion port near
the center of the board, and ports for
RCA audio and video out, VGA out,
PS/2 mouse and keyboard, RJ- 11 serial
network, 9 VDC power in, mini-USB,
four-pin USB2USER, and a pair of
Nintendo NES gamepads.
The Hydra Game System includes
a blank experimentation card and a
128K EEPROM card, either of which
can be plugged in to the game card
expansion port. Additional cards can
be purchased from Parallax; 3V and 5V
power, eight I/O ports, serial network,
USB, and EEPROM lines are available
from the 20-pin game card expansion
port, and on the EEPROM and experimental card solder pads. To facilitate
Hardware
The main Hydra
board is populated with
an eight-core Propeller
chip clocked at 80 MHz,
a 128 KB EEPROM, and a
10 MHz crystal. All three
of these core compo-
FIGURE 4. 128K EEPROM
card with 2 x 10 header pins
soldered to the I/O pads.
June 2007 73
