A Performance Analysis System for the Sport of Bowling

almost 27 times between the foul line and the head pin. The ball would also have
to be thrown at over 25 miles an hour for the rotational rate to reach 1000 rpms.
Those values are extreme, but they allow an upper limit of 1000 rpms (16.7 Hz) to
be set as the maximum angular velocity.
The vast majority of bowling establishments utilize fluorescent lighting.
Preliminary testing with the TSL251 revealed that the sensor is responsive enough
to detect the 120 Hz optical ripple of the overhead fluorescent lights. This ACinduced
ripple becomes part of the ambient light level, and could cause a
problem, since the pseudo-sinusoidal target waveform must be extracted from the
ambient light. However, the AC ripple is confined to a narrow band at 120 Hz,
while the desired fundamental waveform is of a much lower frequency.
Sampling the waveform at a frequency less than twice the 120 Hz ripple could
result in "aliasing" the 120 Hz content down into the frequencies of interest (< 20
Hz). And sampling at a frequency other than a harmonic multiple of 120 Hz
could introduce harmonic variations into the raw waveform that the module must
then deal with, since it certainly won't have the processing capabilities to digitally
filter the data. Sampling at a harmonic multiple of 120 Hz, such as 240 Hz, and
storing the average of two consecutive samples (yielding a net 120 Hz data rate),
averages out the AC ripple. The frequency of the AC ripple exceeds the target
waveform by at least a factor of 7 (in the extreme case), but is actually closer to a
factor of 15-20. Hence, the 120 Hz ripple should not interfere with data collection
as long as an appropriate sample frequency is chosen, allowing for a resolution of
at least 18°-24° of rotation.
• Ball Speed: The vast majority of bowlers, even at the 200+ average level,
generate an average ball speed of less than 20 mph (~30 fps). At 30 fps, it takes at
least 2 seconds for the ball to travel from the foul line to the head pin (60 feet).
For a ball speed of 30 fps and a net sampling frequency of 120 Hz, the ball travels
3" per sample period, good enough for 0.4% resolution over 60 feet. The vast
majority of bowlers generate ball speeds greater than 10 mph (15 fps), especially
those that average greater than 180. At 15 fps, it takes the ball 4 seconds to
completely traverse the lane, or 480 samples at 120 Hz.
• Data Memory: The hardware for the prototype SMARTDOT module was
originally specified in January of 1993. At that time, the highest serial memory
density readily available that was cheap enough to be practical was a 4096 bit
(512 x 8) chip. This size memory is only big enough to capture a single roll of the
ball. Affordable serial EEPROM memory density has increased dramatically
since the SMARTDOT module prototype was designed, and the "Sample Memory"
section details the implications of using a higher memory density.
For the prototype module, ambient light sample data is produced faster than it can
be consumed by single byte writes to the EEPROM. However, the EEPROM can
handle 8 samples at a time, with a 10 msec max write time. A sample is produced
every 8.333 msecs (120 Hz), and a circular sample buffer is used to accumulate 8
consecutive samples for writing to the EEPROM. The EEPROM performs the
actual write in the background, after the data has been input to its write buffer.
The 87C752 can continue collecting data in the circular buffer without having to
wait for the EEPROM to finish storing the data.
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