How does the "reference" mode in the ADXL362 activity detection work?
In reference mode, the operation of the ADXL362 should be thought of this way. Here’s an example:
Let’s say you enable the activity interrupt (set threshold = 0.5g, samples number = 2, use AC mode or say the reference mode), then the first sample output while be: X = 0g, Y = 0g, Z = 1g.
This is the value the ADXL362 will use as the reference value. Let’s explore the following sample scenario where there are two continuous samples such that:
(X axis output – 0g > 0.5g or X axis output – 0g < -0.5g) OR (Y axis output – 0g > 0.5g or Y axis output – 0g < -0.5g) OR (Z axis output – 1g > 0.5g or Z axis output – 1g < -0.5g),
This will trigger the activity interrupt.
If you make activity time longer, or say they use more samples to trigger activity event, there is a risk that fast events will not be recorded.
One way to guard against this is to increase ODR.
If you look at the operation this way, then there is no risk to losing low frequency information based on how the ADXL362 reference mode works.
In reference mode the device is not using the difference in the sample output – last sample output but current sample output – fixed sample output (this is the sample just after you enable the activity interrupt).
By using this activity mode, you are not losing any low-frequency information away. On the contrary, it will can catch the low-frequency change.
Let’s look at one more example to clarify this. After you enable activity interrupt (set threshold = 0.5g, samples number = 2000, use the “AC mode” or say the reference mode), the first sample output is X = 0g, Y = -1g, Z = 0g.
You can rotate the board very slowly from position A to position B. For this case, let’s say, the shift is 0.00000000001 deg/hr.
At position B, the values will be X = 1g, Y = 0g, Z -0g, as 1g – 0g >, which Is greater than the 0.5g threshold; therefore, after 2000 samples, the activity interrupt will be triggered.
However, if you set the high pass filter, say to a cut off frequency = 0.1Hz, then the position change will not trigger the activity interrupt.
In summary, this is difference between ADXL362 reference mode and the high pass filter mode.
Retrieving data ...