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An acoustic occupancy sensor includes and acoustic transmitter, acoustic receiver, variable bandpass filter and a controller. The acoustic transmitter transmits acoustic signals into a defined region and the acoustic receiver receives acoustic signals from the defined region. The received acoustic s

An acoustic occupancy sensor includes and acoustic transmitter, acoustic receiver, variable bandpass filter and a controller. The acoustic transmitter transmits acoustic signals into a defined region and the acoustic receiver receives acoustic signals from the defined region. The received acoustic signal is converted to an electrical signal. A pre-amplifier amplifies the electrical signal and the electrical signal is digitized. The digitized electrical signal is demodulated by a demodulator to remove the carrier signal. The digitized electrical signal is filtered by a bandpass filter that sweeps up along a range of frequencies and down along a range of frequencies. The amplitudes of the filtered signals are averaged and analyzed to determine the presence or absence of an occupant within the defined region.

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What is claimed is: 1. An occupancy sensor, comprising: an acoustic transmitter; an acoustic receiver; a variable bandpass filter operably coupled to the acoustic receiver comprising: a digital potentiometer, wherein the digital potentiometer controls a gain of the bandpass filter; a digital potent

What is claimed is: 1. An occupancy sensor, comprising: an acoustic transmitter; an acoustic receiver; a variable bandpass filter operably coupled to the acoustic receiver comprising: a digital potentiometer, wherein the digital potentiometer controls a gain of the bandpass filter; a digital potentiometer, wherein the digital potentiometer controls a tuning of the bandpass filter; and a digital potentiometer, wherein the digital potentiometer controls a ratio of a center frequency of the bandpass filter to a bandwidth of the bandpass filter; and a controller operably coupled to the acoustic transmitter, the acoustic receiver, and the variable bandpass filter; wherein the controller transmits acoustic signals using the acoustic transmitter, receives acoustic signals using the acoustic receiver, filters the acoustic signals using the variable bandpass filter, and processes the filtered acoustic signals to determine the presence or absence of an occupant within a defined region. 2. An occupancy sensor, comprising: an acoustic transmitter; an acoustic receiver comprising: an acoustic sensor; a pre-amplifier operably coupled to the acoustic sensor comprising a digital potentiometer, wherein the digital potentiometer controls the gain of the pre-amplifier to prevent clipping of signals received by the acoustic receiver; and an analog to digital converter operably coupled to the pre-amplifier; a demodulator operably coupled to the acoustic receiver; a variable bandpass filter operably coupled to the demodulator comprising: a digital potentiometer, wherein the digital potentiometer controls a gain of the bandpass filter; a digital potentiometer, wherein the digital potentiometer controls a tuning of the bandpass filter; and a digital potentiometer, wherein the digital potentiometer controls a ratio of a center frequency of the bandpass filter to a bandwidth of the bandpass filter; and a controller operably coupled to the acoustic transmitter, the acoustic receiver, the demodulator, and the variable bandpass filter comprising: a pre-amplifier engine, wherein the pre-amplifier engine controls the acoustic receiver; a bandpass filter engine, wherein the bandpass filter engine controls the variable bandpass filter; a doppler shift engine, wherein the doppler shift engine characterizes the signals filtered by the variable bandpass filter; and an occupancy sensing engine, wherein the occupancy sensing engine processes the characterized signals of the Doppler shift engine to determine the presence of absence of the occupant within the defined region; wherein the controller transmits acoustic signals using the acoustic transmitter, receives acoustic signals using the acoustic receiver, processes the received acoustic signals using the demodulator, filters the processed acoustic signals using the variable bandpass filter, and processes the filtered acoustic signals to determine the presence or absence of an occupant within a defined region. 3. The occupancy sensor of claim 2, wherein the bandpass filter engine comprises: a quiet bandwidth search engine for searching a range of frequencies for quiet bandwidth areas that do not include background noise; and wherein the doppler shift engine characterizes the signals filtered by the variable bandpass filter within the quiet bandwidth areas. 4. The occupancy sensor of claim 2, wherein the bandpass filter engine comprises: a noisy bandwidth search engine for searching a range of frequencies for noisy bandwidth areas that include background noise; and wherein the doppler shift engine characterizes the signals filtered by the variable bandpass filter that are not within the noisy bandwidth areas. 5. The occupancy sensor of claim 2, wherein the occupancy sensing engine comprises: a determination of possible noise engine for processing signals filtered by the variable bandpass filter to determine if they indicate a possible source of noise; a determination of possible occupancy engine for processing the signals filtered by the variable bandpass filter to determine if they indicate the possible presence of an occupant within the defined region; and a statistical processing engine for processing the indications of possible noise and occupants to determine if the defined region is occupied by an occupant, wherein the statistical processing engine determines that the defined region is occupied by an occupant based upon the frequency of the indications of occupants within the defined region. 6. The occupancy sensor of claim 2, wherein the occupancy sensing engine comprises: a determination of noise engine for processing a subset of signals filtered by the variable bandpass filter to determine if they indicate a source of noise; and a determination of occupancy engine for processing the subset of the signals filtered by the variable bandpass filter to determine the presence or absence of an occupant within the defined region. 7. The occupancy sensor of claim 2, wherein the occupancy sensing engine comprises: a determination of noise engine for processing the signals filtered by the variable bandpass filter within a predetermined time period to determine if they indicate a source of noise; and a determination of occupancy engine for processing the signals filtered by the variable bandpass filter within a predetermined time period to determine the presence or absence of an occupant within the defined region. 8. A method of operating an occupancy sensor, comprising: transmitting acoustic signals into a defined region; receiving acoustic signals from the defined region; filtering the received acoustic signals using a variable bandpass filter comprising: sweeping the variable bandpass filter upwardly along a range of frequencies; and sweeping the variable bandpass filter downwardly along a range of frequencies; determining if a filtered acoustic signal indicates a source of noise within the defined region; and determining if the filtered acoustic signals indicate a presence or absence of an occupant within a defined region. 9. A method of operating an occupancy sensor, comprising: transmitting acoustic signals into a defined region; receiving acoustic signals from the defined region; converting the acoustic signals into electrical signals; amplifying the electrical signals without clipping the electrical signals; filtering the received acoustic signals using a variable bandpass filter; controlling a ratio of a center frequency to a bandwidth of the variable bandpass filter; sweeping the variable bandpass filter upwardly along a range of frequencies; then sweeping the variable bandpass filter downwardly along a range of frequencies; time averaging an amplitude of the filtered acoustic signals; comparing the time averaged amplitudes of the filtered acoustic signals; determining if a filtered acoustic signal indicates a source of noise within the defined region; and determining if a filtered acoustic signal indicates a presence of an occupant within the defined region. 10. The method of claim 9, further comprising: searching for quiet bandwidth areas within a range of frequencies that do not include background noise; and time averaging an amplitude of the filtered acoustic signals within the quiet bandwidth areas. 11. The method of claim 9, further comprising: searching for noisy bandwidth areas within a range of frequencies that include background noise; and time averaging an amplitude of the filtered acoustic signals not within the noisy bandwidth areas. 12. The method of claim 9, further comprising: determining a possible presence of a source of noise within the defined region; determining a possible presence of an occupant within the defined region; and determining the presence of an occupant within the defined region as a function of a frequency of the determination of the possible presence of an occupant within the defined region. 13. The method of claim 9, further comprising: determining a possible presence of a source of noise within the defined region; determining a possible presence of an occupant within the defined region; and determining the presence of an occupant within the defined region as a function of a frequency of the determination of the possible presence of an occupant within the defined region relative to a frequency of the determination of the possible presence of a source of noise within the defined region. 14. The method of claim 9, further comprising: time averaging an amplitude of a subset the filtered acoustic signals. 15. The method of claim 9, further comprising: time averaging an amplitude of the filtered acoustic signals for a finite time period. 16. A system for operating an occupancy sensor, comprising: means for transmitting acoustic signals into a defined region; means for receiving acoustic signals from the defined region; means for filtering the received acoustic signals using a variable bandpass filter; means for controlling a ratio of a center frequency to a bandwidth of the variable bandpass filter; means for time averaging an amplitude of the filtered acoustic signals; means for comparing the time averaged amplitudes of the filtered acoustic signals; means for determining if a filtered acoustic signal indicates a source of noise within the defined region; and means for determining if the filtered acoustic signals indicate a presence or absence of an occupant within a defined region. 17. A system for operating an occupancy sensor, comprising: means for transmitting acoustic signals into a defined region; means for receiving acoustic signals from the defined region; means for converting the acoustic signals into electrical signals; means for amplifying the electrical signals without clipping the electrical signals; means for filtering the received acoustic signals using a variable bandpass filter; means for controlling a ratio of a center frequency to a bandwidth of the variable bandpass filter; means for sweeping the variable bandpass filter upwardly along a range of frequencies; means for then sweeping the variable bandpass filter downwardly along a range of frequencies; means for time averaging an amplitude of the filtered acoustic signals; means for comparing the time averaged amplitudes of the filtered acoustic signals; means for determining if a filtered acoustic signal indicates a source of noise within the defined region; and means for determining if a filtered acoustic signal indicates a presence of an occupant within the defined region. 18. The system of claim 17, further comprising: means for searching for quiet bandwidth areas within a range of frequencies that do not include background noise; and means for time averaging an amplitude of the filtered acoustic signals within the quiet bandwidth areas. 19. The system of claim 17, further comprising: means for searching for noisy bandwidth areas within a range of frequencies that include background noise; and means for time averaging an amplitude of the filtered acoustic signals not within the noisy bandwidth areas. 20. The system of claim 17, further comprising: means for determining a possible presence of a source of noise within the defined region; means for determining a possible presence of an occupant within the defined region; and means for determining the presence of an occupant within the defined region as a function of a frequency of the determination of the possible presence of an occupant within the defined region. 21. The system of claim 17, further comprising: means for determining a possible presence of a source of noise within the defined region; means for determining a possible presence of an occupant within the defined region; and means for determining the presence of an occupant within the defined region as a function of a frequency of the determination of the possible presence of an occupant within the defined region relative to a frequency of the determination of the possible presence of a source of noise within the defined region. 22. The system of claim 17, further comprising: means for time averaging an amplitude of a subset the filtered acoustic signals. 23. The system of claim 17, further comprising: means for time averaging an amplitude of the filtered acoustic signals for a finite time period. 24. A computer-readable means communicably coupled to an occupancy sensor, said means comprising computer-executable instructions for operating an occupancy sensor comprising: transmitting acoustic signals into a defined region; receiving acoustic signals from the defined region; filtering the received acoustic signals using a variable bandpass filter comprising sweeping the variable bandpass filter upwardly along a range of frequencies; and sweeping the variable bandpass filter downwardly along a range of frequencies; determining if a filtered acoustic signal indicates a source of noise within the defined region; and determining if the acoustic signals indicate a presence or absence of an occupant within a defined region. 25. A computer-readable means communicably coupled to an occupancy sensor, said means comprising computer-executable instructions for operating an occupancy sensor comprising: transmitting acoustic signals into a defined region; receiving acoustic signals from the defined region; converting the acoustic signals into electrical signals; amplifying the electrical signals without clipping the electrical signals; filtering the received acoustic signals using a variable bandpass filter; controlling a ratio of a center frequency to a bandwidth of the variable bandpass filter; sweeping the variable bandpass filter upwardly along a range of frequencies; then sweeping the variable bandpass filter downwardly along a range of frequencies; time averaging an amplitude of the filtered acoustic signals; comparing the time averaged amplitudes of the filtered acoustic signals; determining if a filtered acoustic signal indicates a source of noise within the defined region; and determining if a filtered acoustic signal indicates a presence of an occupant within the defined region. 26. The computer-readable means of claim 25, further comprising instructions for: searching for quiet bandwidth areas within a range of frequencies that do not include background noise; and time averaging an amplitude of the filtered acoustic signals within the quiet bandwidth areas. 27. The computer-readable means of claim 25, further comprising instructions for: searching for noisy bandwidth areas within a range of frequencies that include background noise; and time averaging an amplitude of the filtered acoustic signals not within the noisy bandwidth areas. 28. The computer-readable means of claim 25, further comprising instructions for: determining a possible presence of a source of noise within the defined region; determining a possible presence of an occupant within the defined region; and determining the presence of an occupant within the defined region as a function of a frequency of the determination of the possible presence of an occupant within the defined region. 29. The computer-readable means of claim 25, further comprising instructions for: determining a possible presence of a source of noise within the defined region; determining a possible presence of an occupant within the defined region; and determining the presence of an occupant within the defined region as a function of a frequency of the determination of the possible presence of an occupant within the defined region relative to a frequency of the determination of the possible presence of a source of noise within the defined region. 30. The computer-readable means of claim 25, further comprising instructions for: time averaging an amplitude of a subset the filtered acoustic signals. 31. The computer-readable means of claim 25, further comprising instructions for: time averaging an amplitude of the filtered acoustic signals for a finite time period. 32. A method of operating an occupancy sensor, comprising: transmitting acoustic signals into a defined region; receiving acoustic signals from the defined region; filtering the received acoustic signals using a variable bandpass filter; controlling a ratio of center frequency to a bandwidth of the variable bandpass filter; time averaging an amplitude of the filtered acoustic signals; comparing the time averaged amplitudes of the filtered acoustic signals to determine if the filtered acoustic signals indicate a presence or absence of an occupant within a defined region. 33. A method of operating an occupancy sensor, comprising: transmitting acoustic signals into a defined region; receiving acoustic signals from the defined region; filtering the received acoustic signals using a variable bandpass filter; controlling a ratio of center frequency to a bandwidth of the variable bandpass filter; processing the filtered acoustic signals to determine a presence or absence of an occupant within a defined region.