Continuously varying output from MEMS Gyroscope

[Sharat_Rao]

We are using the X-STM32MP-GNSS2 (with the STM32 discovery board DK2), which has ISM330DHCX IMU. The accelerometer readings seem fine from the IMU, but the gyroscope gives enormously high and varying readings even when we are stationary. See below the varying output from the gyro

root@FAFUSION:/sys/bus/iio/devices/iio:device2# ls
buffer    in_anglvel_x_raw  sampling_frequency
buffer0    in_anglvel_y_raw  sampling_frequency_available
current_timestamp_clock     in_anglvel_z_raw  scan_elements
dev    name      subsystem
in_anglvel_scale    of_node      uevent
in_anglvel_scale_available  power      waiting_for_supplier
root@FAFUSION:/sys/bus/iio/devices/iio:device2# cat name
ism330dhcx_gyro
root@FAFUSION:/sys/bus/iio/devices/iio:device2# cat sampling_frequency
833.000000
root@FAFUSION:/sys/bus/iio/devices/iio:device2# cat in_anglvel_scale
0.000152716
root@FAFUSION:/sys/bus/iio/devices/iio:device2# cat in_anglvel_x_raw in_anglvel
_y_raw in_anglvel_z_raw
-19111
11246
-3500
root@FAFUSION:/sys/bus/iio/devices/iio:device2# cat in_anglvel_x_raw in_anglvel
_y_raw in_anglvel_z_raw
-18835
15691

-4096
root@FAFUSION:/sys/bus/iio/devices/iio:device2#
root@FAFUSION:/sys/bus/iio/devices/iio:device2# cat in_anglvel_x_raw in_anglvel
_y_raw in_anglvel_z_raw
-19119
-22581
-10041
root@FAFUSION:/sys/bus/iio/devices/iio:device2# cat in_anglvel_x_raw in_anglvel
_y_raw in_anglvel_z_raw
-19194
16978
-4096
root@FAFUSION:/sys/bus/iio/devices/iio:device2#

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Also, the scale here does not seem correct. For a 16-bit 2s-complement max of 32767 and a scaling factor of 0.000152716, the full-scale range is 32767 x 0.000152716 = 5 degrees/sec, which is not what the datasheet says. I would expect this to be 125 dps.

[Federica Bossi]

Hi @Sharat_Rao ,

Can you try to follow our examples on Github and let me know if you still have the same issue?

Thanks

[Sharat_Rao]

Hi @Federica Bossi ,

We are using the drivers from that link which is what is causing the device to get enumerated as an IIO device. The question here is more about the gyroscope itself. Even at rest, it is measuring extremely large angular rates. How can we debug and fix this?

[MZina.1]

We have same problem here: for example at range of 125 dps we are getting this results in full stop position:

raw data output: X: -29 Y: -98 Z: -86 which function "ism330dhcx_from_fs250dps_to_mdps" transates to: -87.500000 -542.500000 -437.500000 dps and this is not acceptable.