Single axis earth magnetic field sensor for motion detection in TPMS application
First Claim
1. A sensor module comprising:
- a magnetic sensor configured to measure a magnitude of a magnetic field component of an Earth magnetic field projected on a sensing axis of the magnetic sensor and configured to generate a measurement signal based on the magnitude of the magnetic field component projected on the sensing axis, wherein the magnetic sensor is configured to rotate about an axis through the Earth magnetic field such that the measurement signal oscillates between a first extrema and a second extrema as the magnitude of the magnetic field component projected onto the sensing axis changes due to rotation of the magnetic sensor about the axis; and
a microcontroller configured to receive the measurement signal from the magnetic sensor, acquire a predetermined number of measurement samples from the measurement signal over a predetermined sampling period, calculate a variance value of a magnitude of the acquired measurement samples, and determine whether the magnetic sensor is rotating about the axis based on a threshold test of the variance value,wherein the predetermined number is three or more, and the microcontroller is configured to calculate the variance value based on all the measurement samples acquired over the predetermined sampling period.
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Abstract
A sensor module is provided that includes a magnetic sensor and a microcontroller. The magnetic sensor is configured to measure a magnitude of a magnetic field component of an Earth magnetic field projected on a sensing axis of the magnetic sensor and is configured to generate a measurement signal. The magnetic sensor is configured to rotate about an axis through the Earth magnetic field such that the measurement signal oscillates between a first and second extremas as the magnitude of the magnetic field component projected onto the sensing axis changes due to rotation of the magnetic sensor about the axis. The microcontroller is configured to receive the measurement signal, acquire a predetermined number of measurement samples over a sampling period, calculate a variance value of the acquired measurement samples, and determine whether the magnetic sensor is rotating about the axis based on a threshold test of the variance value.
17 Citations
30 Claims
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1. A sensor module comprising:
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a magnetic sensor configured to measure a magnitude of a magnetic field component of an Earth magnetic field projected on a sensing axis of the magnetic sensor and configured to generate a measurement signal based on the magnitude of the magnetic field component projected on the sensing axis, wherein the magnetic sensor is configured to rotate about an axis through the Earth magnetic field such that the measurement signal oscillates between a first extrema and a second extrema as the magnitude of the magnetic field component projected onto the sensing axis changes due to rotation of the magnetic sensor about the axis; and a microcontroller configured to receive the measurement signal from the magnetic sensor, acquire a predetermined number of measurement samples from the measurement signal over a predetermined sampling period, calculate a variance value of a magnitude of the acquired measurement samples, and determine whether the magnetic sensor is rotating about the axis based on a threshold test of the variance value, wherein the predetermined number is three or more, and the microcontroller is configured to calculate the variance value based on all the measurement samples acquired over the predetermined sampling period. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method of motion detection comprising:
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measuring a magnitude of a magnetic field component of an Earth magnetic field projected on a sensing axis of a magnetic sensor, wherein the magnetic sensor is configured to rotate about an axis through the Earth magnetic field; generating a measurement signal based on the magnitude of the magnetic field component projected on the sensing axis, wherein, as the magnetic sensor rotates about the axis through the Earth magnetic field, the measurement signal oscillates between a first extrema and a second extrema as the magnitude of the magnetic field component projected onto the sensing axis changes due to rotation of the magnetic sensor about the axis; acquiring a predetermined number of measurement samples from the measurement signal over a predetermined sampling period; calculating a variance value of a magnitude of the acquired measurement samples, wherein the predetermined number is three or more, and the variance value is calculated based on all the measurement samples acquired over the predetermined sampling period; and determining whether the magnetic sensor is rotating about the axis based on a threshold test of the variance value. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. A tire pressure monitoring system (TPMS) comprising:
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a tire having an axis of rotation; a magnetic sensor fixed to the tire and configured to monitor rotation of the tire by measuring a magnitude of a magnetic field component of an Earth magnetic field projected on a sensing axis of the magnetic sensor, wherein the magnetic sensor is configured to generate a measurement signal based on the magnitude of the magnetic field component projected on the sensing axis, wherein the magnitude of the magnetic field component projected on the sensing axis changes as the magnetic sensor rotates about the axis of rotation; a microcontroller configured to receive the measurement signal from the magnetic sensor, acquire a predetermined number of measurement samples from the measurement signal over a predetermined sampling period, calculate a variance value of a magnitude of the acquired measurement samples, and determine whether the tire is rotating about the axis of rotation based on a threshold test of the variance value, wherein the predetermined number is three or more, and the microcontroller is configured to calculate the variance value based on all the measurement samples acquired over the predetermined sampling period. - View Dependent Claims (25, 26, 27, 28, 29, 30)
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Specification