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

[KTeng.1]

Assuming the sensor is placed flat to a surface the Z axis will have 1g. If we want the interrupt event to happen if the vibration more than 350mg, we need to set the threshold to 1.35g? The device can be placed flat on a surface or it can be placed somewhere slope that Z axis will be no longer having 1g. Do you mean that we need to constantly update the threshold? I don't quite get the picture. If you can elaborate more with an example, it will be good.

[Eleon BORLINI]

>> If we want the interrupt event to happen if the vibration more than 350mg, we need to set the threshold to 1.35g?

If you apply an high pass filter on the z interrupt as suggested in my previous comment, it won't be necessary to set 1.350mg. The high pass filter applies only to the data that make the interrupt raise, and not to the acquired dataout.

Otherwise, if you don't want to filter the interrupt, you can set 1.350mg as stated by you.

-Eleon

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[KTeng.1]

If I did a dummy read of the X, Y, and Z value, does this mean that the high pass filter is set to the current acceleration value?

[Eleon BORLINI]

Hi @KTeng.1​ ,

yes, after configuring the internal HP filter, the data available in the output registers are already filtered.

-Eleon