Time and frequency domain based step counter

A non-transitory computer readable medium having programming instructions stored thereon which, when executed by a processor, cause the processor to perform a method including:

• receiving an output from three-dimensional (3-D) accelerometer sensor-circuitry, including sensor circuits, configured and arranged to generate and output accelerometer data associated with three perpendicular axes;
• pre-processing the received output of the 3-D accelerometer sensor-circuitry, wherein the pre-processing includes removing a direct current (DC) component from the output of the 3-D accelerometer sensor-circuitry;
• determining a dominant component among vertical component data and horizontal component data in the output of the 3-D accelerometer sensor-circuitry after the pre-processing, wherein the output of the 3-D accelerometer sensor-circuitry is used to derive the vertical component data and the horizontal component data, the vertical component data is proportional to a vector inner product between a mean vector of a plurality of vector samples along the three perpendicular axes and each dynamic vector corresponding to a first difference between each of the plurality of vector samples and the mean vector, wherein the horizontal component data is related to a norm of a second difference between the first difference and the mean vector scaled by the vertical component data;
• and
• counting steps using the dominant component, wherein the counting includes performing a Fast Fourier Transform (FFT) and zero crossing detection.