LSM6DSV datasheet(4/187 Pages) STMICROELECTRONICS

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2.2

Pedometer algorithm

The pedometer algorithm is composed of a cascade of four stages:

Computation of the acceleration magnitude signal in order to detect the signal independently from device

orientation;

FIR filter to extract relevant frequency components and to smooth the signal by cutting off high frequencies;

Peak detector to find the maximum and minimum of the waveform and compute the peak-to-peak value;

Step count: if the peak-to-peak value is greater than the settled threshold, a step is counted.

Figure 1. Four-stage pedometer algorithm

The LSM6DSV embeds a dynamic internal threshold for step detection that is updated after each peak-to-peak

evaluation: the internal threshold is increased with a configurable speed if a step is detected or decreased with a

configurable speed if a step is not detected.

This approach ensures high accuracy when the user starts to walk and a false peak rejection when the user is

walking or running.

An internal configurable debounce algorithm can be also set to filter false walks: indeed, an accelerometer pattern

is recognized as a walk or run only if a minimum number of steps are counted.

The LSM6DSV has been designed to reject a false-positive signal inside the algorithm core.

On top of the mechanisms detailed above, the LSM6DSV allows enabling and configuring a dedicated false-

positive rejection block to further boost pedometer accuracy.

2.3

Tilt detection

The tilt function helps to detect activity change and has been implemented in hardware using only the

accelerometer to achieve targets of both ultra-low power consumption and robustness during the short duration of

dynamic accelerations.

The tilt function is based on a trigger of an event each time the device's tilt changes and can be used with

different scenarios, for example:

•

Triggers when phone is in a front pants pocket and the user goes from sitting to standing or standing to

sitting;

•

Doesn’t trigger when phone is in a front pants pocket and the user is walking, running or going upstairs.

2.4

Significant motion detection

The significant motion detection (SMD) function generates an interrupt when a ‘significant motion’, that could be

due to a change in user location, is detected. In the LSM6DSV device this function has been implemented in

hardware using only the accelerometer.

SMD functionality can be used in location-based applications in order to receive a notification indicating when the

user is changing location.

LSM6DSV

Pedometer algorithm

DS13476 - Rev 2

page 4/187

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