ISM330BX datasheet(8/150 Pages) STMICROELECTRONICS

8 / 150 page

2.7

Pedometer functions: step detector and step counters

The ISM330BX embeds an advanced pedometer with an algorithm running in an ultralow-power domain in order

to ensure extensive battery life in battery-constrained applications.

Leveraging on enhanced configurability, the advanced embedded pedometer is suitable for a large range of

wearable devices.

The algorithm processes and analyzes the accelerometer waveform in order to count the user's steps during

walking and running activities.

The pedometer works at 30 Hz and it is not affected by the selected device power mode (ultralow-power, low-

power, high-performance), thus guaranteeing an ultralow-power experience and extreme flexibility in conjunction

with other device functionalities.

The accelerometer operating mode can be changed at runtime and is based on user requirements without

impacting the performance of the pedometer.

The pedometer output can be batched in the device's FIFO buffer, in order to decrease overall system supply

current.

ST freely provides the support and the tools for easily configuring the device and tuning the algorithm

configuration for a best-in-class user experience.

2.8

Pedometer algorithm

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

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

orientation

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

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

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

Figure 4. Four-stage pedometer algorithm

The ISM330BX 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 ISM330BX has been designed to reject a false-positive signal inside the algorithm core.

On top of the mechanisms detailed above, the ISM330BX allows enabling and configuring a dedicated false-

positive rejection block to further boost pedometer accuracy.

ISM330BX

Embedded low-power features

DS14588 - Rev 2

page 8/150

ISM330BX Datasheet(PDF) 8 Page - STMicroelectronics