IIS328DQ Threshold Settings

[KTeng.1]

For IIS328DQ, if the threshold is set to 0.25g, does this mean that it will interrupt if either X, Y, or Z changes more than 0.25g? Our application is to detect a vehicle is moving or not. What is the best threshold to set for this application?

[Eleon BORLINI]

Hi @KTeng.1​ ,

you can set the direction of the threshold crossing by selecting the desired axis (x, y, z or a combination of them) in the INT1_CFG (30h) register (datasheet, p. 30).

For example, setting the INT1_CFG = 22h, you will receive an interrupt whenever the x axis data or the z axis data exceed the chosen threshold (that you can configure in the INT1_THS (32h) register).

A proper way to detect whether a vehicle is moving or not would be use 2 axis on INT1 and 1 on INT2: supposing the chip is planar, the x and y axis will detect the horizontal movement of the vehicle, and a reasonable threshold could be 200 or 250 mg as you suggested, while the z axis for monitoring the out-of-plane vibrations, and in this case the threshold could be a little higher, 300 or 350mg.

Please let me know if these suggestions can help you.

-Eleon

[KTeng.1]

So if I set the threshold for z-axis to 300 or 350mg, any difference of forces between time at t1 and at t2 more than 300 or 350mg, the interrupt event will occur?

[Eleon BORLINI]

Hi @KTeng.1​ ,

not exactly... I mean, along Z axis you have the 1g (=1000mg) gravity value, so you have to take it into account. The interrupt occurs when the absolute (and not the t2-t1 relative) value of the acceleration exceeds the defined threshold: for this reason, it is maybe better to configure the high pass filter in the CTRL_REG2 (21h) register (HPM1, HPM0 bits), specifically for the INT1 or the INT2 (HPen1 or HPen2 bits), depending where you have configured the z axis interrupt.

-Eleon

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