Low power motion detector

• US 7,216,053 B2
• Filed: 12/30/2004
• Issued: 05/08/2007
• Est. Priority Date: 12/30/2004
• Status: Active Grant

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Koli, Kimmo, Rakkola, Juha, Salminen, Jukka, Salo, Teemu
• Primary Examiner(s): Barlow; John
• Assistant Examiner(s): Moffat; Jonathan
• Application Number:
  US11/027,024
• Publication Number:
  US 20060161377A1
• Time in Patent Office: 859 Days
• Field of Search: 702/141
• US Class Current: 702/141
• CPC Class Codes: G01P 13/00 Indicating or recording presence, absence, or direction, of movement electric switches H01H; counting moving objects G06M7/00
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G06F 1/3215 Monitoring of peripheral devices
• CPC Class Codes: H04M 2250/12 including a sensor for measuring a physical value, e.g. temperature or motion telephones including GPS signal receivers H04M2250/10

Abstract

An energy-efficient acceleration measurement system is presented. The system includes an accelerometer, responsive to acceleration of the system, for providing an accelerometer output signal having a magnitude indicative of at least one component of the acceleration. A motion detector is responsive to the accelerometer output signal, and provides a processor interrupt signal, but only if the magnitude of acceleration reaches a threshold. The processor, responsive to the processor interrupt signal, measures the acceleration with higher accuracy than the motion detector is capable of, but in a way that consumes more power than was needed by the motion detector.

Claims

1. A system, comprising:

an accelerometer, responsive to acceleration of the system, configured to provide an accelerometer output signal having a magnitude indicative of at least one component of the acceleration;

a motion detector, responsive to the accelerometer output signal, configured to provide a processor interrupt signal if the magnitude reaches a threshold; and

a processor, responsive to the processor interrupt signal, configured to determine acceleration with higher accuracy than the motion detector is capable of

wherein the interrupt signal is for interrupting a power-saving state of the processor and for beginning a power-saving state of the motion detector, and

wherein the processor is responsive to the accelerometer output signal only when the processor interrupt signal has interrupted the processor.

2. The system of claim 1,

wherein the interrupt signal separates a motion detector mode from a full accuracy mode,

wherein, during the full accuracy mode, the processor is configured to utilize digital signal processing that includes low-pass filtering, a plurality of decimation stages, and a calibration algorithm, and

wherein the motion detector mode has a lower energy requirement than the full accuracy mode.

3. The system of claim 1,

wherein the system further comprises a converter for converting the accelerometer output signal from analog to digital.

4. The system of claim 1, wherein the processor is also configured to perform responses to the acceleration, but only if the processor has received the processor interrupt signal.

5. The system of claim 1, wherein the system is housed in a portable device that also includes a mobile communication terminal.

6. A method comprising:

setting a reference level for each axis, upon enabling a motion detector,

averaging acceleration data obtained from an accelerometer output signal, so as to accomplish low pass filtering results without a multiplier,

updating the reference level at periods that are sufficiently small to offset temperature drift, and

providing a processor interrupt signal if the motion detector concludes that an absolute difference between an average acceleration and a corresponding reference level exceeds at least one threshold

wherein the interrupt signal is for interrupting a power-saving state of the processor and for beginning a power-saving state of the motion detector, and

wherein the processor is responsive to the accelerometer output signal only when the processor interrupt signal has interrupted the processor.

7. The method of claim 6, further comprising the subsequent steps of the processor performing digital signal processing with low-pass filtering, a plurality of decimation stages, and a calibration algorithm.

8. The method of claim 7, wherein the subsequent steps are applied to further accelerometer output signals only if the processor confirms that the absolute difference between the average acceleration and the corresponding reference level exceeds the at least one threshold.

9. The method of claim 6,

wherein the at least one threshold is programmed for each axis independently, and

wherein exceeding at least one programmed combination of the at least one threshold is necessary for generating the interrupt signal.

10. A computer readable medium encoded with a software data structure sufficient for performing the method of claim 6.

11. A motion detector comprising:

at least one reference level register, configured to set and periodically update a reference level for each axis,

a summing register for each coordinate axis, configured to average acceleration data obtained from the accelerometer to yield an average acceleration,

an offsetting and compare unit, configured to offset the average acceleration using the reference level, and configured to provide an offset acceleration, and compare the offset acceleration to at least one threshold, and

an interrupt unit, configured to provide a processor interrupt signal if the at least one threshold is reached

wherein the interrupt signal is for interrupting a power-saving state of the processor and for beginning a power-saving state of the motion detector.

12. The motion detector of claim 11,

wherein the summing register is used instead of a multiplier,

wherein the reference level is set and updated independently of device orientation and gravitational direction, and

wherein the updating of the reference level is performed at intervals sufficient to offset temperature drift.

13. A method, comprising:

providing an accelerometer output signal, having a magnitude indicative of at least one component of acceleration, to a motion detector, in response to the acceleration;

providing a processor interrupt signal if the magnitude reaches a threshold, in response to the accelerometer output signal;

determining acceleration with higher accuracy than the motion detector is capable of, in response to the processor interrupt signal; and

providing instructions in response to determining the acceleration with higher accuracy;

wherein the interrupt signal is for interrupting a power-saving state of the processor and for beginning a power-saving state of the motion detector, and

wherein the processor is responsive to the accelerometer output signal only when the processor interrupt signal has interrupted the processor.

14. The method of claim 13, wherein the determining of the acceleration with higher accuracy utilizes low-pass filtering, a plurality of decimation stages, and a calibration algorithm.

15. A computer readable medium encoded with a software data structure the software comprising codes which, when executed, control the following:

providing an accelerometer output signal, having a magnitude indicative of at least one component of acceleration, to a motion detector, in response to the acceleration of the system;

providing a processor interrupt signal if the magnitude reaches a threshold, in response to the accelerometer output signal;

determining acceleration with higher accuracy than the motion detector is capable of, in response to the processor interrupt signal; and

providing instructions in response to determining the acceleration with higher accuracy;

wherein the interrupt signal is for interrupting a power-saving state of the processor and for beginning a power-saving state of the motion detector, and

wherein the processor is responsive to the accelerometer output signal only when the processor interrupt signal has interrupted the processor.

16. The computer readable medium of claim 15, wherein the determining of the acceleration with higher accuracy utilizes low-pass filtering, a plurality of decimation stages, and a calibration algorithm.

17. A system, comprising:

means for providing an accelerometer output signal, having a magnitude indicative of at least one component of acceleration, in response to the acceleration of the system;

means for providing an interrupt signal if the magnitude reaches a threshold, in response to the accelerometer output signal; and

means for determining acceleration with higher accuracy, in response to the interrupt signal,

wherein the interrupt signal is for interrupting a power-saving state of the means for determining acceleration with higher accuracy, and for beginning a power-saving state of the means for providing the interrupt signal, and

wherein the means for determining acceleration with higher accuracy is responsive to the accelerometer output signal only when the processor interrupt signal has interrupted the means for determining acceleration with higher accuracy.

18. Apparatus comprising:

a receiving unit configured to receive an accelerometer output signal having a magnitude indicative of at least one component of acceleration; and

an interrupt unit configured to provide a processor interrupt signal if the magnitude reaches a threshold,

wherein the apparatus is configured to enter a power-saving state if the magnitude reaches the threshold, and

wherein the processor interrupt signal is for making the processor responsive to the accelerometer output signal.

19. The apparatus fo claim 18, further comprising a housing which also contains other components of an electronic device, including the accelerometer, the processor, and a power source responsive to the processor.