U.S. patent application number 10/689753 was filed with the patent office on 2005-04-21 for golf ball location system.
This patent application is currently assigned to Exelys LLC. Invention is credited to Barr, Keith E..
Application Number | 20050085316 10/689753 |
Document ID | / |
Family ID | 34521468 |
Filed Date | 2005-04-21 |
United States Patent
Application |
20050085316 |
Kind Code |
A1 |
Barr, Keith E. |
April 21, 2005 |
Golf ball location system
Abstract
A golf ball and golf ball search receiver is described. The golf
ball includes a transmitter and the search receiver includes a
receiver. The golf ball may be activated by an accelerometer that
causes the transmitter to produce an RF signal across a
predetermined frequency band for a duration of time, which may be
determined by a timer. The transmitter modulates an audio signal
and transmits the modulated signal within an output band of the
transmitter. The receiver tunes to a narrower band thereby
receiving and demodulating a fraction of the transmitted signal.
The receiver's input band halves an input bandwidth set to coincide
with a fraction of the output band, thereby alleviating adverse
effects due to variations in transmitter and receiver components,
as well as adverse effects due to localized noise within the output
band. Additionally, relative positioning of the receiver's input
band may cycle across the transmitter's output band to further
mitigate the adverse effects of localized noise.
Inventors: |
Barr, Keith E.; (Los
Angeles, CA) |
Correspondence
Address: |
MORRISON & FOERSTER LLP
755 PAGE MILL RD
PALO ALTO
CA
94304-1018
US
|
Assignee: |
Exelys LLC
645 N. Tigertail Road
Los Angeles
CA
90049
|
Family ID: |
34521468 |
Appl. No.: |
10/689753 |
Filed: |
October 20, 2003 |
Current U.S.
Class: |
473/353 |
Current CPC
Class: |
A63B 37/0088 20130101;
A63B 43/00 20130101; A63B 2220/40 20130101; A63B 37/0055 20130101;
A63B 2225/50 20130101; A63B 37/0003 20130101; A63B 2071/0625
20130101 |
Class at
Publication: |
473/353 |
International
Class: |
A63B 043/00 |
Claims
What is claimed is:
1. A system for locating a golf ball, the system comprising: the
golf ball having an encapsulated transmitter that modulates an
audible signal to an output band, wherein the output band defines
an output bandwidth; and a receiver having an input band defining
an input bandwidth wherein a center frequency of the input band of
the receiver is variable; wherein the input bandwidth is smaller
than the output bandwidth.
2. The system of claim 1, wherein the audible signal comprises a
saw-tooth wave.
3. The system of claim 1, wherein the audible signal has a period
defining a frequency between about 20 Hz and about 20 kHz.
4. The system of claim 1, wherein the audible signal has a period
defining a frequency between about 60 Hz and about 2 kHz.
5. The system of claim 1, wherein the audible signal has a period
defining a frequency between about 2 kHz and about 6 kHz.
6. The system of claim 1, wherein the audible signal comprises a
sequence of audible tones.
7. The system of claim 1, wherein the audible signal comprises a
sequence of audible tones and pauses between the tones.
8. The system of claim 1, wherein the transmitter further includes
a battery and the audible signal indicates a condition of the
battery.
9. The system of claim 1, wherein the transmitter includes a free
running oscillator.
10. The system of claim 9, wherein the free running oscillator
includes an LC tank circuit having an inductor and a capacitor.
11. The system of claim 10, wherein the inductor comprises an
antenna.
12. The system of claim 1, wherein the transmitter further includes
a variable capacitance.
13. The system of claim 12, wherein the variable capacitance is
provided by a bank of switched capacitors.
14. The system of claim 13, wherein the bank of switched capacitors
is controlled by an output of a counter.
15. The system of claim 1, wherein the center frequency of the
input band cycles across a range of the output band at a
sub-audible rate.
16. The system of claim 15, wherein the sub-audible rate is between
about 0 Hz and about 10 Hz.
17. The system of claim 15, wherein the sub-audible rate is between
about 1 Hz and about 2 Hz.
18. The system of claim 15, wherein the input band cycles across
the output band following a saw-tooth wave having a period defined
by the sub-audible rate.
19. The system of claim 15, wherein the input band cycles across
only a sub-portion of the output band thereby defining a guard band
at each end of the output band.
20. The system of claim 19, wherein the guard band is at least as
wide as the input bandwidth.
21. The system of claim 1, wherein an output bandwidth of the
output band is between about 4 MHz and about 5 MHz.
22. The system of claim 1, wherein the input bandwidth is between
about 0.1 MHz and about 0.3 MHz.
23. The system of claim 1, wherein an output bandwidth of the
output band is between about 4 MHz and about 5 MHz and the input
bandwidth is between about 0.1 MHz and about 0.3 MHz.
24. The system of claim 1, wherein the input bandwidth represents
less than 50. % of an output bandwidth of the output band.
25. The system of claim 1, wherein the input bandwidth represents
between about 5% and about 50% of an output bandwidth of the output
band.
26. The system of claim 1, wherein the input bandwidth represents
between about 2% and about 8% of an output bandwidth of the output
band.
27. The system of claim 1, wherein the receiver includes a
detector.
28. The system of claim 27, wherein the detector comprises an AM
detector.
29. The system of claim 1, wherein the receiver includes an
extendable antenna.
30. A golf ball comprising: an encapsulated transmitter that
modulates an audible signal to an output band; wherein the output
band defines an output bandwidth and the transmitter includes a
free running oscillator having an inductor and a capacitor.
31. The golf ball claim 30, wherein the free running oscillator
further has a variable capacitance.
32. The golf ball claim 31, wherein the variable capacitance is
provided by a bank of switched capacitors.
33. The golf ball claim 32, wherein the bank of switched capacitors
is controlled by an output of a counter.
34. A method to locate a golf ball using a golf ball location
system having a transmitter encapsulated in a golf ball and a
receiver, the method comprising: modulating an audible signal with
the transmitter; transmitting the modulated signal to an output
band; providing a receiver with an input band, wherein the input
band is narrower and within the output band; receiving an input
signal residing within the input band; and varying a center
frequency of the input band to traverse the output band.
35. The method of claim 34, wherein the act of varying the center
frequency comprises modulating the input band across the output
band at a sub-audible rate.
36. The method of claim 34, further comprising: extending an
antenna on the receiver to increase an input signal gain; moving
the receiver closer to the transmitter; and retracting the antenna
to decrease the input signal gain.
37. The method of claim 34, wherein the act of modulating the
audible signal comprises cycling a center frequency of the
transmitted signal across the output band at the audible rate.
Description
BACKGROUND
[0001] Attempts to successfully manufacture and market a golf ball
having an embedded radio transmitter for radio location of a lost
ball have been unsuccessful. The lack of success may be due to the
severe conditions under which golf balls are traditionally made
(high pressures and temperatures), and the severe conditions golf
balls endure during play (high impact G-forces). The production of
radio transmitters having closely controlled and stable center
frequencies that remain stable under ball construction and play
conditions may be extremely difficult.
[0002] Golf balls containing sensors to trigger radio frequency
transmitters may be useful in the game of golf, as a lost ball
constitutes a penalty in score, as well as the obvious loss of the
ball itself. Golf balls that emit radio signals for a few minutes
after being struck can be located with a simple radio receiver. The
integration of a radio transmitter with precise frequency control
into a golf ball is complicated by the extreme shock balls
encounter during play. Such harsh conditions make the use of
accurate but fragile components problematic.
[0003] A radio embedded in a golf ball may use either a quartz
crystal or a free running oscillator to accurately generate and
control the golf ball's transmitter center frequency. Incorporation
of a quartz crystal oscillator into a golf ball may be unfavorable
from both cost and durability points of view. Crystals typically
represent a sizable portion of the cost of the circuits that employ
them. Additionally, crystals are very susceptible to damage from
impact forces such as those applied to golf balls during
manufacturing and normal use. Solutions to protect a crystal from
damage (e.g., insulating circuitry from shock forces) may reduce
the probability of potential damage but may also significantly
increase the part and manufacturing costs of a golf ball.
Furthermore, the cost of a high-reliability quartz crystal
oscillator that is able to withstand the shock experienced during
play may be cost-prohibitive.
[0004] Therefore, it may be desired to have a durable, interference
resilient transmission and detection system contained within a golf
ball. Further, it may be desirable to operate such a system with a
free-running oscillator.
SUMMARY OF THE INVENTION
[0005] Embodiments of the present invention relate to a golf ball
and a golf ball location system that assists in the recovery of
golf balls lost during a game of golf. The golf ball may include a
transmitter circuit capable of transmitting within a determined
bandwidth, a bandwidth that is wide enough to negate frequency
drift of various transmitter components. In some embodiments, a
transmitter modulates a signal at an audible rate.
[0006] The location system may include a receiver circuit capable
of receiving a signal at or near a designed center frequency. In
some embodiments, a receiver has an input bandwidth that is
narrower than the transmitter's output bandwidth. In some
embodiments, a receiver has an input band that traverses a wider
band at a sub-audible rate.
[0007] In accordance with embodiments of the present invention, a
system for locating a golf ball comprises: the golf ball having an
encapsulated transmitter that modulates an audible signal to an
output band, wherein the output band defines an output bandwidth;
and a receiver having an input band defining an input bandwidth
wherein a center frequency of the input band of the receiver is
variable; wherein the input bandwidth is smaller than the output
bandwidth.
[0008] In accordance with some embodiments of the present
invention, a golf ball comprises: an encapsulated transmitter that
modulates an audible signal to an output band; wherein the output
band defines an output bandwidth and the transmitter includes a
free running oscillator having an inductor and a capacitor.
[0009] In accordance with other embodiments of the present
invention, a method to locate a golf ball using a golf ball
location system having a transmitter encapsulated in a golf ball
and a receiver, the method comprises: modulating an audible signal
with the transmitter; transmitting the modulated signal to an
output band; providing a receiver with an input band, wherein the
input band is narrower and within the output band; receiving an
input signal residing within the input band; and varying a center
frequency of the input band to traverse the output band.
[0010] In some embodiments of the present invention, a state of the
power source or battery of the golf ball is communicated by the
golf ball.
DESCRIPTION OF DRAWINGS
[0011] FIG. 1 shows a cutaway perspective view of a golf ball
containing an encapsulated transmitter, in accordance with
embodiments of the present invention.
[0012] FIGS. 2A through 2D graphically relate frequency tolerances
and bandwidths of a transmitter and receiver, in accordance with
embodiments of the present invention.
[0013] FIGS. 3A and 3B relate a transmitter's output band to an
example modulation waveform, in accordance with embodiments of the
present invention.
[0014] FIGS. 4A through 4C relate a transmitter's output band to a
receiver's input band and an example modulation waveform, in
accordance with embodiments of the present invention.
[0015] FIGS. 5A and 5B show block and schematic diagrams of a
transmitter in accordance with embodiments of the present
invention.
[0016] FIG. 6 shows a schematic diagram of an embodiment of a
receiver in accordance with the present invention.
[0017] FIG. 7 shows a plan view of a printed circuit board (PCB)
having an etched inductor in accordance with embodiments of the
present invention.
[0018] FIG. 8 shows a cross sectional view of a PCB according to
some embodiments of the present invention.
[0019] FIG. 9 shows a perspective view of transmitter module to be
encapsulated within the core of a golf ball in accordance with
embodiments of the present invention.
DESCRIPTION OF INVENTION
[0020] It is well-known that many golf balls are lost during play
when golf balls land in particularly overgrown areas of a golf
course. The loss can occur even though the ball may have been
visible during its entire flight and the approximate region of the
landing of the ball is known. The loss of a golf ball not only
entails financial loss to the player it also means that the player
is put at a disadvantage as far as game scoring is concerned. The
present invention aids in reducing the occurrence of lost golf
balls. Players employing golf balls that can be more readily
recovered are at an advantage both financially and by avoiding
unnecessary point loss.
[0021] To provide a locatable golf ball, a free running oscillator
having an inductor and a capacitor to set a transmitter's center
radio frequency may be used. Free running oscillators, however, may
suffer from excessive tolerance problems. Some free running
oscillators are constructed from tank circuits having a capacitor
and an inductor placed in parallel. Cost effective capacitors have
a wide range of acceptable tolerances in the order of .+-.5%.
Etched inductors similarly have a wide range of acceptable
tolerances in the range of .+-.2% due to variables of etching. Wire
wound coil inductors have an even wider range of acceptable
tolerances.
[0022] To improve accuracy, some components are tunable. Etched
inductors may utilize various tuning methods, such as, e.g., using
a conductive disk or a "tuning slug". Tuning slugs, however, may be
large, expensive and suffer the disadvantage of potentially being
disturbed during subsequent encapsulation. Tunable free running
oscillators typically require careful adjustment prior to
encapsulation and final ball molding. Even after careful
adjustment, components may drift due to the pressures and
temperatures of final manufacturing and molding, and due to the
ultimate abuse of play. Under such conditions a circuit may have an
ultimate operating frequency that can easily drift by several
percent from its factory set frequency. These variations may be far
outside the normal modulation input bandwidths of traditional
receivers.
[0023] One solution to combat the variations of free running
oscillators is to use a transmitter that masks the variations by
transmitting over a wide frequency bandwidth. Such a transmitter
may have an output bandwidth that is substantially larger the
potential frequency variation of the oscillator. A receiver may be
designed to operate over a similar substantially wide or wider
bandwidth. In such designs, even if the output band of the
transmitter and the input band of the receiver do not exactly
align, a majority of the transmitter's output bandwidth fall within
the receiver's input band.
[0024] Unfortunately, such receivers, which have an input bandwidth
nearly equal to or greater than the transmitter's output bandwidth,
leave the receiver open to interference from any strong signal that
falls within the receiver's input band. Furthermore, wide band
transmitters typically use more power than their narrower band
counterparts.
[0025] FIG. 1 shows a cutaway view of a golf ball 10 containing an
encapsulated transmitter region 20. The encapsulated transmitter 20
is surrounded by molded rubber 30 that is enclosed by a molded
cover 40. A transmitter 100 within the encapsulated transmitter
region 20 is positioned within the golf ball 10 during the
manufacturing process. Rather than including a transmitter
employing a fragile crystal, embodiments of the present invention
may use an inexpensive inductive-capacitive (LC) tank circuit,
which resonates at or near a desired carrier frequency. By
eliminating the crystal, the golf ball 10 may have improved
resiliency against impact damage and shock absorbing packaging may
be reduced or omitted.
[0026] According to some embodiments of the present invention, even
if the center frequencies of a transmitter and a receiver have
drifted from their designed center frequencies, for example, due to
manufacturing variations, environmental conditions and/or normal
wear, the transmitter-receiver pair utilizes a modulation technique
to overcome these frequency uncertainties. A transmitter 100
transmits within a wide band and a complementary receiver has an
input bandwidth that is narrower than the transmitter's output
bandwidth.
[0027] Some embodiments include a golf ball having a transmitter
that modulates a signal having audible frequencies. The transmitter
modulates the signal having audible frequencies across the
transmitter's output band. Frequencies between 20 Hz and 20 kHz are
called the audible frequencies. A signal having an audible
repetition rate includes periodic signals that repeat at an audible
frequency. A signal having an audible repetition rate forms a
signal having audible frequencies. A periodic signal having an
audible repetition rate between 20 Hz and 20 kHz repeats every 50
microseconds to 50 milliseconds. For example, a signal may be a
gradually rising or falling saw-tooth waveform repeating at an
audible rate between 20 Hz and 20 kHz, thereby repeating every 50
microseconds to 50 milliseconds. Alternatively, a signal having
audible frequencies may be formed by a signal having a changing
frequency. For example, the signal may be a waveform having a
center frequency that changes by incrementally increasing and/or
decreasing its center frequency among a set of values between 20 Hz
and 20 kHz.
[0028] In some embodiments, a transmitter's output band is greater
in spectral width than the receiver's input band. For example, the
transmitter's output band may span several MHz and the receiver's
input band may span several hundred kHz. By using a receiver with a
front-end having a narrower bandwidth that the full transmitter's
bandwidth, a receiver may substantially decrease the probability
that it receives unwanted signals that interfere with proper
detection of a golf ball's transmitted signal.
[0029] In some embodiments, the receiver's input bandwidth
represents between 2 and 8 percent of the transmitter's output
bandwidth. For example, a transmitter may have an output bandwidth
between 4 MHz to 5 MHz and a corresponding receiver may have an
input bandwidth between 100 KHz to 300 KHz. In some embodiments,
the receiver's input bandwidth represents less than 50 percent of
the transmitter's output bandwidth. In some embodiments, the
receiver's input bandwidth represents between 5 and 20 percent of
the transmitter's output bandwidth. In some embodiments, the
receiver's input bandwidth is less than 5 percent. In other
embodiments, the receiver's input bandwidth is greater than 50
percent of the transmitter's output bandwidth.
[0030] In some embodiments, a detection unit includes a receiver
that has a stationary input band or input window. In other
embodiments, the receiver has an input window that traverses at
least a part of the transmitter's output band at a sub-audible
rate. By sweeping a receiver's input band across a transmitter's
wider output band, a receiver is not permanently impaired by a
stationary interfering signal. As a result, precise frequency
alignment between the transmitter and receiver is not necessary
when using the present invention.
[0031] A sub-audible rate is a rate between 0 Hz and 20 Hz. For
example, a 20 Hz input window, which traverses a spectrum at a
sub-audible rate of 20 Hz, traverses the spectrum every 50
milliseconds. An input window that traverses a spectrum at 0.5 Hz
cycles through a spectrum every 2 seconds.
[0032] In some embodiments, a receiver traverses its input window
using a periodic waveform, e.g., a saw-tooth or triangular
waveform. In some embodiments, a receiver traverses its input
window with a periodic waveform having a period greater than or
equal to approximately 50 milliseconds, such as a period set
between 50 milliseconds and 10 seconds, or more particularly
between 200 milliseconds and 5 seconds, or even more particularly,
between one-half second and 2 seconds.
[0033] In some embodiments, the receiver has an input window that
traverses the entire designed output band of a transmitter. In
other embodiments, the receiver has an input window that is a
fraction as wide as the transmitter's output band and traverses
only a portion of the designed output band of a transmitter. The
portions of the transmitter's output band that the receiver does
not traverse form a guard band, which is used to insure that the
receiver's window falls within the transmitter's output window. A
larger guard band allows a design to use components with wider
tolerances and allows for drifts in component values over time and
use.
[0034] For example, a transmitter is designed with an output band
that is 5 MHz wide. A corresponding receiver traverses its input
window across only 2 to 3 MHz of the entire 5 MHz bandwidth of the
transmitter. A receiver having an input window that is 300 kHz wide
receives a signal from a transmitter that has a transmission band
that is 5 MHz wide. The receiver may slide its input window across
just the center 3 MHz of the 5 MHz wide transmission window. This
receiver may traverse its input window across the 3 MHz sub-window
once every second or equivalently at a sub-audible rate of 1 Hz.
This design forms a 1 MHz guard band at each end of the
transmitter's output window. The guard band allows for substantial
drift in component values.
[0035] Some embodiments include both a golf ball that modulates an
audible rate signal and a detection unit having an input window
that traverse a band at a sub-audible rate. The golf ball includes
a transmitter that modulates an audible signal to an output band.
The detection unit includes a receiver that has an input window
that traverses at least a portion of the transmitter's output band
periodically at a sub-audible rate.
[0036] In some embodiments, the ratio between the audible
repetition rate of the periodic signal and the sub-audible rate at
which the receiver's input window traverses the transmitter's
output window is set to a value between 20000-to-1 and 10-to-1, or
more particularly between 2000-to-1 and 50-to-1, or even more
particularly between 400-to-1 and 100-to-1.
[0037] In some embodiments, once activated, a golf ball 10
transmits a signal that sweeps between two frequencies about the
actual center frequency of the golf ball. The transmitted signal
sweeps across a transmit band. If a receiver has a narrower
bandwidth than the transmitter, the transmitter will eventually
transmit a signal that passes through the narrower input band of
the receiver.
[0038] In some embodiments, prior to encapsulating the transmitter
100, the transmitter 100 is adjusted to transmit with a
predetermined center frequency by modifying the inductor's
inductance. Etch inductors may be tuned using conductive disks.
Coil inductors may be tuned by bending the coil turns. Once tuned,
the inductor may be encapsulated.
[0039] The frequency modulation bandwidth of the transmitter may be
designed wide enough to account for: (1) the transmitter's expected
maximum center frequency deviation during molding, temperature and
service; (2) the expected maximum receiver frequency tolerance; and
(3) the width of the input band of the receiver.
[0040] In some embodiments, a receiver used to detect a golf ball
may use a receiver having at a fixed center frequency. In other
embodiments, a receiver has a varying center frequency. The varying
center frequency may oscillate between an upper bound and a lower
bound at a sub-audible rate, e.g. 1 Hz or 2 Hz. A window, which
represents the input band of the receiver, thereby cycles across
the output band of the transmitter at the sub-audible rate.
Embodiments that sweep or cycle the input window of the receiver
across the output band of the receiver help to reduce the adverse
effects of interfering signals and also reduce the need for well
tuned components in both the transmitter and receiver.
[0041] FIGS. 2A through 2D graphically relate center frequency
tolerances to output bandwidth BW.sub.Tx and input bandwidth
BW.sub.Rx of the transmitter 100 and receiver, respectively. Both
the transmitter 100 and receiver are designed to work at a center
frequency of f.sub.C=f.sub.designTxC=f.sub.designRxC. FIG. 2A shows
a designed center frequency f.sub.designTxC of a transmitter 100
may vary within a tolerance from a low of
f.sub.designTxC.sub..sub.--.sub.Low to a high of
f.sub.designTxC.sub..sub.--.sub.High. Drift and variations in a
transmitter's center frequency are due to several factors,
including component tolerances, manufacturing conditions, usual
ball wear, and operating conditions.
[0042] FIG. 2B illustrates an output band of a transmitter 100. The
transmitter 100 has a transmit bandwidth BW.sub.Tx that is centered
on f.sub.actualTxC. The actual transmitter output band low and high
frequency limits are f.sub.actualTxLow and f.sub.actualTxHigh,
respectively. The output bandwidth BW.sub.Tx is the difference
between f.sub.TxActualHigh and f.sub.TxActualLow:
BW.sub.Tx=f.sub.TxActualHigh-f.- sub.TxActualLow. A transmitter may
emit a signal anywhere within its output bandwidth.
[0043] FIG. 2C shows a center frequency of a receiver may vary from
a low of f.sub.designRxC.sub..sub.--.sub.Low to a high of
f.sub.desighRxC.sub..sub.--.sub.High. Again, the drift and
variations may be due several factors, including component
tolerances, manufacturing conditions and operating conditions.
[0044] FIG. 2D illustrates an input band determined by design of a
receiver. The receiver has an input bandwidth BW.sub.Rx that is
centered on f.sub.actualRxC. The actual receiver input band low and
high frequency limits are f.sub.actualRxLow and f.sub.actualRxHigh,
respectively. The input bandwidth BW.sub.Rx is the difference
between f.sub.RxActualHigh and f.sub.RxActualLow:
BW.sub.Rx=f.sub.RxActualHigh-f.sub.RxActualLow. A receiver may
detect signals anywhere within its input bandwidth.
[0045] A transmitter 100 is designed to transmit at a center
frequency of f.sub.designTxC but in fact has an actual transmitter
center frequency f.sub.actualTxC, which falls anywhere between
f.sub.designTxC.sub..sub.--- .sub.Low and
f.sub.designTxC.sub..sub.--.sub.High. Similarly, a receiver is
designed to receive at a center frequency of
f.sub.designRxC=f.sub.des- ignTxC but in fact may have an actual
receiver center frequency f.sub.actualRxC, which falls anywhere
between f.sub.actualRxLow and f.sub.actualRxHigh and may be
different from the actual transmitter center frequency.
[0046] In operation, a receiver's input band may be designed to
fall entirely within a transmitter's output band even when the
center frequency of the transmitter 100 has drifted. For example, a
transmitter 100 may have a center frequency that has drifted in one
direction and the receiver may have a center frequency that has
drifted in the other direction. To select an appropriate
transmitter output bandwidth BW.sub.Tx knowing that center
frequency variations are possible, one may consider the worst case
frequency drifts along with a predetermined receiver input
bandwidth BW.sub.Rx. The worst scenarios occur when the transmitter
100 and receiver have center frequencies that drift to extremes in
opposite directions. However, even when a portion of the receiver's
input band falls outside of the transmitter's output band, the
signal from the transmitter may still be detectable.
[0047] The lower boundary of the output band f.sub.actualTxLow of
the transmitter 100 may be determined by assuming the transmitter
100 has an actual center frequency f.sub.actualTxC that has drifted
up to an extreme center frequency
f.sub.designTxC.sub..sub.--.sub.High and the receiver has an actual
center frequency f.sub.actualRxC that has drifted down to an
extreme center frequency f.sub.designRxC.sub..sub.--.sub.Low. The
spectral distance between the transmitter's actual center frequency
f.sub.actualTxC and the receiver's actual center frequency
f.sub.actualRxC is: (f.sub.actualTxC-f.sub.actualRxC), and in this
extreme case is
(f.sub.designTxC.sub..sub.--.sub.High-f.sub.designRxC.sub-
..sub.--.sub.Low). The lower boundary of the output band
f.sub.actualTxLow is equal to the transmitter's actual center
frequency less this spectral distance less half the width of the
receiver's input bandwidth:
f.sub.actualTxLow={f.sub.actualTxC-(f.sub.designTxC.sub..sub.--.sub.High--
f.sub.designRxC.sub..sub.--.sub.Low)-0.5*(BW.sub.Rx)}.
[0048] Similarly, the upper boundary of the output band
f.sub.actualTxHigh of the transmitter 100 may be determined by
assuming the transmitter 100 has an actual center frequency
f.sub.actualTxC that has drifted down to the other extreme center
frequency f.sub.designTxC.sub..sub.--.sub.Low and the receiver has
an actual center frequency f.sub.actualRxC that has drifted up to
an opposite extreme center frequency
f.sub.designRxC.sub..sub.--.sub.High. The spectral distance between
the transmitter's actual center frequency f.sub.actualTxC and the
receiver's actual center frequency f.sub.actualRxC is:
(f.sub.actualRxC-f.sub.actual- TxC), and in this extreme case is
(f.sub.designRxC.sub..sub.--.sub.High-f.-
sub.designTxC.sub..sub.--.sub.Low). The upper boundary of the
output band f.sub.actualTxHigh is equal to the transmitter's actual
center frequency plus this spectral distance plus half the width of
the receiver's input bandwidth:
f.sub.actualTxHigh={f.sub.actualTxC+(f.sub.designRxC.sub..sub.-
--.sub.High-f.sub.designTxC.sub..sub.--.sub.Low)+0.5*(BW.sub.Rx)}.
[0049] The lower and upper boundary thereby defined the
transmitter's output bandwidth:
BW.sub.Tx=(f.sub.actualTxHigh-f.sub.actualTxLow), which equals
[{f.sub.actualTxC+(f.sub.designRxC.sub..sub.--.sub.High-f.sub.desi-
gnTxC.sub..sub.--.sub.Low)+0.5
(BW.sub.Rx)}-{f.sub.actualTxC-(f.sub.design-
TxC.sub..sub.--.sub.High-f.sub.designRxC.sub..sub.--.sub.Low)-0.5*(BW.sub.-
Rx)}], which simplifies to
[(f.sub.designTxC.sub..sub.--.sub.High-f.sub.de-
signTxC.sub..sub.--.sub.Low)+(f.sub.designRxC.sub..sub.--.sub.High-f.sub.d-
esignRxC.sub..sub.--.sub.Low)+BW.sub.Rx], or equivalently to the
variation in the transmitter plus the variation in the receiver
plus the receiver's input bandwidth.
[0050] If a transmitted signal sweeps across the full transmit
modulation bandwidth of the transmitter, that is from
f.sub.actualTxLow to f.sub.actualTxHigh, a receiver having a
narrower input band that falls within the transmitter's output band
will periodically receive the transmitted signal.
[0051] FIGS. 3A and 3B relate a transmitter's output band to an
example modulation waveform. FIG. 3A shows a transmitter's output
transmission band having a bandwidth of BW.sub.Tx. FIG. 3B shows
one possible modulation waveform of a transmitter 100. As time
progresses, the modulation waveform, shown as a saw-tooth wave, is
modulated by frequency modulation (FM). As the saw-tooth wave value
increases from a minimum value to a maximum valve, the FM
transmitter generates a peak that sweeps from frequency
f.sub.actualTxLow to frequency f.sub.actual TX High. Once the
maximum value is reached, the process repeats again starting from
the minimum value.
[0052] For example, a signal having frequency f.sub.1 is
transmitted at time t.sub.1. As time progresses from t.sub.1 to
t.sub.2, the frequency of the transmitted signal progresses from
f.sub.1 to f.sub.2. An ever increasing frequency is transmitted
until the upper end of the transmitter's output band is reached.
Once the saw-tooth wave reaches its maximum value and returns to
its minimum valve, the FM transmitter effectively generates a
signal that restarts from a frequency f.sub.actualTxLow. The cycle
of generating an increasing then resetting frequency signal
continues as long as the saw-tooth modulation signal persists.
[0053] FIGS. 4A through 4C relate a transmitter's output band to a
receiver's input band and provide an example modulation waveform.
FIG. 4A shows a transmitter's output band having a bandwidth of
BW.sub.TX. FIG. 4B shows a receiver's input band having a narrower
bandwidth of BW.sub.RX that falls within the transmitter's output
band. FIG. 4C shows ranges of time when a receiver detects a
transmitted signal within its input band. The receiver receives a
passing peak of energy as the transmitted signal sweeps through the
receiver's input band. Two durations of time during which the
receiver detects the transmitted waveform are shown. The first
duration occurs as the signal generated by the transmitter 100
sweeps between f.sub.actualTxLow and f.sub.actualTxHigh. During
this period the frequency transmitted falls within the actual
receiver input band. The second duration occurs as the transmitter
resets and sweeps again. During these durations of time, the
receiver detects the transmitted signal.
[0054] In the example illustrated, the transmitter modulates a
saw-tooth signal. Additionally, the center frequencies of the
transmitter and receiver may be slightly skewed. The resulting
demodulated signal, when converted to an audible signal, may be
masked by the monotonic nature of the saw-tooth waveform.
[0055] Alternatively, the transmitter could modulate a triangular
signal. If the center frequencies of the transmitter and receiver
are slightly skewed, the resulting demodulated signal, when
converted to an audible or visual signal, may be perceived as a
series of double bursts. By comparing the elapsed time between the
double bursts and between successive sets of double bursts, one can
determine the aggregate drift between the transmitter and receiver
center frequencies.
[0056] The saw-tooth waveform shown in FIGS. 3B and 4C may be
replaced by any number of modulation waveforms. A monotonic
waveform that simply increases from frequency f.sub.actualTxLow to
frequency f.sub.actualTxHigh then restarts increasing from
frequency f.sub.actualTxLow again, such as the saw-tooth waveform,
would also mask the effects of drift and differences between the
transmitter and receiver center frequencies. Alternatively, a
sinusoidal wave, triangular wave, a monotonically increasing
potentially periodic waveform or the like may be used.
Alternatively, other periodic waveforms (having a repetition rate
of, for example, 20 Hz to 20 kHz, or more particularly 60 Hz to 2
kHz) may be used. The frequency of the modulation waveform may be
intentionally set to a low frequency but below the upper limit of
the audio range. Modulated signals received by the receiver through
the receiver's input band are received at a rate within the audio
frequency range. An operator can "home in" on the lost golf ball by
listening for effects of the ball's modulation signal. A
retractable antenna on the detector unit may be used to adjust the
receiver's gain during the homing process.
[0057] Many RF environments might have one or more interfering
signals within the transmitter output band. If one of these
interfering signals exists within the receiver input band, a
receiver might not be able to detect a signal from a transmitting
golf ball. By varying the position of the receiver's input band, a
particular interfering signal may be periodically avoided.
[0058] In some embodiments, the receiver center frequency varies
within a band of frequencies that may be centered on the designed
transmitter center frequency. In some embodiments, the receiver
center frequency varies periodically at a sub-audible rate such
that the position of the receiver's input band appears to slide
across the transmitter's output band. The center frequency value
may step among several predetermined center frequency values.
Alternatively, the center frequency may sweep or traverse across a
range of frequencies. The range of frequencies that the center
frequency varies within may be limited such that the receiver input
band always falls within a part of the transmitter's output band.
By stepping or sweeping a receiver's center frequency at a
sub-audible rate, the input window of the receiver moves. An
interfering signal may momentarily interrupt reception while the
receiver's input band captures the interfering signal. Once the
input window moves past the interfering signal, however, the
receiver filters out and avoids the interfering signal.
[0059] As shown in FIGS. 4A and 4B, the receive window (defined by
the receiver bandwidth BW.sub.Rx) is narrower than the transmit
window (defined by the transmitter bandwidth BW.sub.Tx). Though the
receiver bandwidth BW.sub.RX might not substantially change, the
placement of the receive window (or received input band) changes as
the window follows the varying receiver center frequency. By
implementing a receiver with an input window that steps or sweeps
across a transmitter's output band, component tolerances may be
relaxed. Using components that have wider tolerances and components
that do not need tuning during the assembly process reduces the
manufacturing costs and decreases the effects of long term
component degradation.
[0060] An embodiment having a varying receiver center frequency
effectively steps or slides the receiver window up or down the
spectrum within the transmit window. In some embodiments, the
receiver center frequency steps or slides the input window of the
receiver up or down the transmit band at a sub-audible rate, e.g.,
1 or 2 Hz. In some embodiments, the receive window passes across a
majority of the transmitter's output window during one sub-audible
cycle. In some embodiments, a sub-audible cycle follows a saw-tooth
wave. For example, the input window starts at the low end of the
transmitter's output band and slowly steps or slides up to the high
end of the output band. Once the high end is reached, the input
window is repositioned at the low end to repeat the process.
[0061] In some embodiments, a receiver uses an FM demodulator. In
other embodiments, a receiver uses an AM demodulator. An AM
demodulator has the advantage of being less expensive to implement
than an FM demodulator. Additionally, a receiver designed with
intentionally varying center frequency may be more effectively
implemented with an AM demodulator than with an FM demodulator.
[0062] FIG. 5A shows a block diagram of an exemplary embodiment of
a transmitter 100. The golf ball's transmitter 100 consists of a
power source (e.g., a battery) electrically attached to circuitry
having an oscillator, sensor, modulator, modulation source, timer,
and antenna.
[0063] The oscillator may be an LC tank circuit having an inductor
L and a capacitor C. The LC tank circuit acts as a control
component of the transmitter and generates a resonant frequency
that may be used as an oscillator whose frequency is controlled by
individually tuning the inductor and/or the capacitor. The resonant
frequency of the LC tank circuit and the component values determine
the actual center frequency of the transmitter circuit. The
resonant frequency may be tuned by adjusting either the circuit's
inductance or capacitance by methods well known to those skilled in
the art.
[0064] The inductor L may be, for example, either an etched
inductor or a coil inductor. In some embodiments, the inductor is
etched onto a printed circuit board (PCB) thereby defining an
inductive strip. An inductive strip, such as a spiral inductive
strip, may be tuned by placing one or more conductive patches over
the inductor trace on the PCB. Additionally, the inductive strip or
coil inductor may double as an emitting antenna as shown in FIG.
5B. The inductor couples the resonant energy from the tuned circuit
to free space as propagating electromagnetic waves (radio waves).
Furthermore, as the radiating area of the inductor is necessarily
small, its efficiency as the transmitter may be improved by
operating the device at a rather high frequency, on the order of
hundreds of megahertz.
[0065] The transmitter's impact sensor may be any suitable sensor
component having the ability to indicate when a sufficient amount
of force has been placed on the golf ball. A sensor such as an
accelerometer, shock sensor, force sensor, acceleration sensor or
impact sensor may be used to indicate when the golfer has struck
the golf ball and thus the desire for golf ball detection may be
imminent. Alternatively, a user controllable switch may be
used.
[0066] The timer and switch are used in tandem to control the
ON-time of the transmitter. For example, once the sensor detects
sufficient force, such as that placed on the golf ball during its
launch, the timer closes the switch to initiate transmission of an
FM sweeping signal.
[0067] An integrated circuit (IC) may be used to combine multiple
elements of the transmitter circuitry. For example, the FM
modulator, modulation source and timer functions may be integrated
into a single IC chip. The IC chip may be conveniently mounted onto
the PCB holding the inductive strip.
[0068] A battery, one or more accelerometers, a wide band FM radio
transmitter and a timer may be integrated as a module 100 into the
core of a golf ball. In some embodiments, the accelerometer turns
the transmitter on, and simultaneously starts the timer when
sufficient shock is detected. Once the timer has expired, the
circuitry turns the transmitter off. The timer may be set to expire
after a sufficient time has passed that would allow a golfer to
find a wayward ball, however, it may be desired that the time not
be set to such a long duration that the power source prematurely
exhausts. Three to five minutes may be an appropriate length of
time for ball transmission.
[0069] In some embodiments, a carrier is modulated with a
modulation waveform by altering the capacitance of the LC tank
circuit.
[0070] FIG. 5B shows an LC tank circuit of a transmitter that is
modulated by varying the tank circuit's capacitance. The circuit
forms an oscillator comprised of a bank of capacitors having a
variable capacitance C.sub.1, a fixed capacitor having a
capacitance C.sub.2, and inductor having inductance L. The bank of
capacitors and the fixed capacitor combine to form a total
capacitance C=C.sub.1+C.sub.2. The bank of capacitors, which
provide a variable capacitance, is placed in parallel with the tank
circuit to modify the circuit's total capacitance. The resulting
resonant frequency of the circuit is 1 1 2 LC .
[0071] The bank of capacitors may be comprised of a number of
capacitors configured in parallel. As additional capacitance is
desired, capacitors with higher capacitances are switched into the
circuit. Each capacitor is associated with a MOS switch that is
configured to connect and disconnect the capacitor to and from the
circuit. An external control signal is used to open and close the
MOS switch, thereby electrically disconnecting and connecting the
capacitor to the tank circuit. A desired capacitance may be derived
from a signal proportional to the modulated waveform. The resulting
LC tank circuit thereby generates a modulate signal. If the
modulation waveform varies between two extremes, the transmitted
modulated carrier signal varies between an upper bound and a lower
bound of the transmitter output band.
[0072] In some embodiments, a bank of capacitors is controlled by a
digital signal supplied by an up/down counter. For example, a
counter counts from a low valve to a high value, then down to the
low value again. By repeating this pattern, a saw-tooth waveform
may be formed. In some embodiments, the pattern repeats at an
audible rate.
[0073] Some embodiments include a transmitter having a desired
transmitter output bandwidth of 5 MHz at a desired center frequency
of 226.25 MHz. The transmitter includes an inductor L of 22 nH and
a fixed capacitor of 20 pF in parallel with a bank of capacitors
that provides from 2 pF to 3 pF of capacitance. The bank of
capacitors has a 9-bit control input, thereby allowing the
capacitance to be controlled in steps of 2.sup.-9 pF. A 9-bit
control input may be used to individually switch in and out any one
of 512 capacitors. These component values resulted in an output
band that covers approximately 223.7 to 228.8 MHz. A clock stepping
the up/down counter at 25 kHz causes the total capacitance to vary
from 22 pF to 23 pF, then back down to 22 pF in 100 .mu.sec or
equivalently at an audible rate of 10 kHz.
[0074] In some embodiments, the user may manually "tune" the
detection unit. Manual tuning adjusts the receiver's center
frequency slightly higher or lower such that the user may search
for a clean spot on the spectrum with no substantial interference.
Once the receiver is tuned to a quiet range within the band, the
user may more easily detect the golf ball's transmitted signal.
This allows the user to operate a receiver in a band that is absent
significant interference when searching for the ball's transmitted
signal.
[0075] The modulated signal produced by the ball can be
characteristic, so that the ball's signal can be identified in the
presence of interfering noise. In some embodiments, the modulation
signal is a sequence of audible notes. For example, a transmitter
transmits a sequence of notes until the timer 100 expires. The
sequence of notes may repeat at a rate of approximately 3 cycles
per second. One possible sequence may be a 440 Hz tone followed by
a 660 Hz tone followed by an 880 Hz tone. Other possible signals
include a continuous 5 kHz tone and a sequence of 5 kHz tones.
[0076] In some embodiments, a transmitter 100 periodically
incorporates a pause in its transmission to aid in prolonging a
golf ball's power supply. For example, if the golf ball, when
active, transmitted with an ON-OFF duty cycle of 1:5, a golf ball's
battery could be extended substantially. In such a system, when a
ball has been detected, the receiver may demodulate a series of
audible tones followed by a pause. The pauses, which occur between
the series of audible tones, last five times as long as the audible
tones last if the duty cycle is 1:5.
[0077] As a further advantage in some embodiments, a transmitter
100 has the ability to communicate a signal indicative of the
energy remaining in the transmitter's power supply. The transmitter
may transmit an alternate pattern if the power supply's remaining
energy or voltage is low or lower than a threshold. For example, a
unique sequence, such as a 440 Hz tone followed by a 660 Hz tone,
could be repeated to indicate that a golf ball's battery is
substantially low. Alternatively, the rate at which the tones
change from one tone to the next tone may be used to indicate the
golf balls battery condition. For example, the sequence may repeat
at a rate of 1 cycle per second, rather than 3 cycles per second,
when the battery is low.
[0078] FIG. 6 shows a block diagram of a receiver. The receiver may
include an antenna, RF amplifier, mixer, sub-audible wave
modulator, oscillator, intermediate frequency amplifier (IF amp)
and detector circuit, audio amplifier, and indicator. In some
embodiments, the receiver uses an AM demodulator the. In other
embodiments, receiver uses an FM demodulator. In some embodiments,
the antenna is a retractable antenna thereby adjusting the
receiver's gain when the antenna is extracted or collapsed.
[0079] The RF amplifier receives a signal from the antenna and
provides a signal to the first input of a mixer. The mixer receives
a second input from an oscillator. In some embodiments, the
oscillator is a variable oscillator. The frequency produced by the
oscillator is varied at a sub-audible rate by a signal provided by
a sub-audible wave modulator. The sub-audible wave modulator may be
formed with a varactor (also known as a variable capacitance diode
or a varicap). The varactor provides an electrically controllable
capacitance, which may be used in adjust the frequency of the
oscillator at a sub-audible rate. By varying the second input into
the mixer, the input window of the receiver effectively moved
across a band at a sub-audible rate.
[0080] The mixer produces an intermediate frequency signal, which
is amplified and detected by the IF amp and detector circuit. The
detector circuit may be a logarithmic amplitude detector. The
signal from the detector may be amplified and provided to an
indicator, such as a speaker, an LED or the like. An optional audio
amplifier may be used to amplify the detected signal prior to
providing the signal to the indicator.
[0081] Radio location by homing in on a transmitter while listening
for audible signal strength may be very difficult using a
traditional FM receiver having a front-end limiting stage. A
limiting-stage automatically adjusts the amplitude of the received
signal. If a limiting stage is used, the audible signal strength
does not appreciably vary as the receiver approaches the
transmitter. The receiver used in this invention can benefit by
replacing the limiting stage with a user-controlled, variable gain
stage prior to the detector allowing the user to adjust the
receiver's sensitivity and overall receiver loudness.
Alternatively, the antenna may be a retractable antenna. The gain
of the receiver may be adjusted by adjusting the length of the
antenna. In addition, an operator's hand may cup the detection
unit, thereby reducing the overall effectiveness of the antenna. As
an operator nears the transmitting ball, retracting and/or cupping
of the antenna reduces the gain of the antenna, thereby allowing an
operator to detect a golf ball residing within a very short
radius.
[0082] FIG. 7 shows a plan view of a printed circuit board (PCB)
having an etched inductor in accordance with the present invention.
The inductor is connected by vias (or through holes) to the
component side of the PCB. Also shown is a metallic sticker that
may be attached with an insulating adhesive to the etched inductor
to tune or alter the inductor's inductance. Alternatively, the
etched inductor may be replaced with a coil of wire having a small
number of turns. Some coil inductors have as few as two to three
turns with a small diameter, such as 8 millimeters. The coil's
inductance may be tuned by bending the coil turns prior to
encapsulation.
[0083] In the production of the golf ball core circuitry, an
assembled printed circuit board, attached to its battery, may be
allowed to transmit while the natural frequency of the assembled LC
tank circuit is measured. Component values for the capacitor and
for the etched inductor may be intentionally chosen such that the
LC tank circuit resonates at a frequency that is slightly lower
than the intended frequency of operation.
[0084] FIGS. 8 and 9 show views of a printed circuit board (PCB).
FIG. 8 shows a cross sectional view of a PCB according to some
embodiments of the present invention. FIG. 9 shows a prospective
view of an embodiment of a transmitter 100 including its PCB
electrically connected to a battery. The etched inductor may face
away from the battery to aid in efficient radiation of the
transmitted signal.
[0085] Examples provided are meant to be exemplary and not
limiting. The following claims define the scope and limits of the
invention.
* * * * *