In the mainline kernel bma400 device driver, there are multiple-scale values for different acceleration ranges +-2g, +-4g, etc. root@raspberrypi:/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-0014/iio:device0# cat in_accel_scale_available 0.038357 0.076714 0.153428 0.306856 With +-4g range root@raspberrypi:/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-0014/iio:device0# cat in_accel_scale 0.076714 root@raspberrypi:/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-0014/iio:device0# cat in_accel_z_raw 519 root@raspberrypi:/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-0014/iio:device0# echo "0.076714 * 506" | bc 39.277568 With +- 2g range root@raspberrypi:/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-0014/iio:device0# echo 0.038357 > in_accel_scale root@raspberrypi:/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-0014/iio:device0# cat in_accel_scale 0.038357 root@raspberrypi:/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-0014/iio:device0# cat in_accel_z_raw 1012 root@raspberrypi:/sys/devices/platform/soc/3f804000.i2c/i2c-1/1-0014/iio:device0# echo "0.038357 * 1012" | bc 38.817284 The _raw value from the sensor is as per the datasheet but the final value for the Z axis after applying scale for all ranges is around 38.8 which is not expected. I tried by placing the sensor in a different position where the X-axis value should be approximately 9.8 m/s2 but In this case also the value is around 38.8 m/s2 Is the above method to calculate the acceleration in the Z-axis correct or am I missing something? For confirmation I also tested the mpu6050 IMU. root@raspberrypi:/sys/bus/iio/devices/iio:device1# cat in_accel_scale_available 0.000598 0.001196 0.002392 0.004785 root@raspberrypi:/sys/bus/iio/devices/iio:device1# cat in_accel_scale 0.000598 root@raspberrypi:/sys/bus/iio/devices/iio:device1# cat in_accel_z_raw 16706 root@raspberrypi:/sys/bus/iio/devices/iio:device1# echo "0.000598 * 16706" | bc 9.9801 With MPU6050 I am getting 9.9801 m/s2 which is near to earth's acceleration due to gravity 9.8 m/s2 For BMA400 I recalculated the scale values from sensitivity for different acceleration ranges https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bma400-ds000.pdf For +-2g - 1 LSB = 0.0095768 m/s2 For +-4g - 1 LSB = 0.0191536 m/s2 For +-4g - 1 LSB = 0.0383072 m/s2 Is the above method to calculate the scale values correct or am I missing something? Thank you Jagath
