Game Development Reference
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relates the ratio of the sum of the load values to the body weight of the user and the
position of the center of gravity to determine body orientation. For example, the Wii
can tell if both of the user's feet are on the board, or if the user is accelerating part of his
leg. The table provided in the Wii patent is reproduced in Table 23-3 .
Table 23-3. Motion-identifying condition table
Motion
Ratio of load value to body weight value
Position of the center of gravity
Right foot riding
25 to 75%
+0.01 to +1.0
Both feet riding
More than 95%
−0.7 to +0.7
Left foot riding
25 to 75%
−1.0 to −0.01
Left thigh lifting
More than 100%
+0.01 to +1.0
Right thigh lifting
More than 100%
−1.0 to −0.01
Both feet putting down
Less than 5%
Not considered
Barometers
Continuing our exploration of new user input methods, especially in the rapidly ma‐
turing mobile device gaming market, now we'll discuss an interesting inclusion in the
latest smartphones: a barometer. Unlike buttons and balance boards, whose pressure
sensors only indirectly handle pressure, barometers directly measure the fluid pressure
that the atmosphere exerts on the sensor.
The sensors used in mobile phones today are piezoresistive microelectromechanical
systems (MEMS) and are very accurate. As shown in Figure 23-6 , the sensors consist
of a void machined into a piece of silicon. The diaphragm is then bonded to a stiff
material such as steel or glass. As we are trying to measure absolute pressure , this bond
is airtight. Using a material called monocrystalline semiconductor silicon to form the
void ensures that the entire diaphragm acts much like a piezoresistive strain gauge.
Figure 23-6. MEMS piezoresistive pressure sensor
 
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