How to set up the BBE Accelerometer and Gyro

How to set up the Accelerometer and Gyro of your BeagleBone Enhanced

1. First list the directory contents of all iio nodes
   
   

   To discover the iio device you need to first list the directory contents of all iio nodes:

   root@beaglebone:~# ls -l /sys/bus/iio/devices/
   total 0
   lrwxrwxrwx 1 root root 0 Dec 8 18:23 iio:device0 -> ../../../devices/platform/ocp/44e0b000.i2c/i2c-0/0-0068/iio:device0
   lrwxrwxrwx 1 root root 0 Dec 8 18:23 iio:device1 -> ../../../devices/platform/ocp/44e0b000.i2c/i2c-0/0-005c/iio:device1
   lrwxrwxrwx 1 root root 0 Dec 8 18:23 trigger0 -> ../../../devices/platform/ocp/44e0b000.i2c/i2c-0/0-0068/trigger0
   lrwxrwxrwx 1 root root 0 Dec 8 18:23 trigger1 -> ../../../devices/platform/ocp/44e0b000.i2c/i2c-0/0-005c/trigger1

   As you can see we have 2 iio devices 0 and 1.  Inspect the contents of the folders to see what the devices are.  e.g.:

   root@beaglebone:~# ls -l /sys/bus/iio/devices/iio\:device0/

2. For the MPU-6050 accelerometer and gyro you need the following contents:
   
   

   drwxr-xr-x 2 root root 0 Dec 8 18:24 buffer
   -r–r–r– 1 root root 4096 Dec 8 18:24 dev
   -r–r–r– 1 root root 4096 Dec 8 18:24 in_accel_matrix
   -rw-r–r– 1 root root 4096 Dec 8 18:24 in_accel_scale
   -r–r–r– 1 root root 4096 Dec 8 18:24 in_accel_scale_available
   -rw-r–r– 1 root root 4096 Dec 8 18:24 in_accel_x_calibbias
   -rw-r–r– 1 root root 4096 Dec 8 18:24 in_accel_x_raw
   -rw-r–r– 1 root root 4096 Dec 8 18:24 in_accel_y_calibbias
   -rw-r–r– 1 root root 4096 Dec 8 18:24 in_accel_y_raw
   -rw-r–r– 1 root root 4096 Dec 8 18:24 in_accel_z_calibbias
   -rw-r–r– 1 root root 4096 Dec 8 18:24 in_accel_z_raw
   -rw-r–r– 1 root root 4096 Dec 8 18:24 in_anglvel_scale
   -r–r–r– 1 root root 4096 Dec 8 18:24 in_anglvel_scale_available
   -rw-r–r– 1 root root 4096 Dec 8 18:24 in_anglvel_x_calibbias
   -rw-r–r– 1 root root 4096 Dec 8 18:24 in_anglvel_x_raw
   -rw-r–r– 1 root root 4096 Dec 8 18:24 in_anglvel_y_calibbias
   -rw-r–r– 1 root root 4096 Dec 8 18:24 in_anglvel_y_raw
   -rw-r–r– 1 root root 4096 Dec 8 18:24 in_anglvel_z_calibbias
   -rw-r–r– 1 root root 4096 Dec 8 18:24 in_anglvel_z_raw
   -r–r–r– 1 root root 4096 Dec 8 18:24 in_gyro_matrix
   -rw-r–r– 1 root root 4096 Dec 8 18:24 in_temp_offset
   -rw-r–r– 1 root root 4096 Dec 8 18:24 in_temp_raw
   -rw-r–r– 1 root root 4096 Dec 8 18:24 in_temp_scale
   -r–r–r– 1 root root 4096 Dec 8 18:24 name
   lrwxrwxrwx 1 root root 0 Dec 8 18:24 of_node -> ../../../../../../../firmware/devicetree/base/ocp/i2c@44e0b000/mpu6050@68
   drwxr-xr-x 2 root root 0 Dec 8 18:24 power
   -rw-r–r– 1 root root 4096 Dec 8 18:24 sampling_frequency
   -r–r–r– 1 root root 4096 Dec 8 18:24 sampling_frequency_available
   drwxr-xr-x 2 root root 0 Dec 8 18:24 scan_elements
   lrwxrwxrwx 1 root root 0 Dec 8 18:24 subsystem -> ../../../../../../../bus/iio
   drwxr-xr-x 2 root root 0 Dec 8 18:24 trigger -rw-r–r– 1 root root 4096 Dec 8 18:23 uevent

3. Check that you have the correct device by querying the name:
   
   

   root@beaglebone:~# cat /sys/bus/iio/devices/iio\:device0/name mpu6050

4. If you need to know the current axis acceleration you can simply cat the dev node to extract the reading:
   
   

   root@beaglebone:~# cat /sys/bus/iio/devices/iio\:device0/in_accel_x_raw 1940
   root@beaglebone:~# cat /sys/bus/iio/devices/iio\:device0/in_accel_scale 0.000598

   Reading the datasheet for the scaling it is the following calculation:

   in_accel_x_raw * in_accel_scale = g
   1940 * 0.000598 = 1.16012g

   You can use the same process for x, y & z

5. If you need to know the current axis angle you can simply cat the dev node to extract the reading:
   
   

   root@beaglebone:~# cat /sys/bus/iio/devices/iio\:device0/in_anglvel_x_raw -18
   root@beaglebone:~# cat /sys/bus/iio/devices/iio\:device0/in_anglvel_scale 0.001064724

   Reading the datasheet for the scaling it is the following calculation:
   in_anglvel_x_raw * in_anglvel_scale = rad
   -18 * 0.001064724 = -0.019165032 rad

   In order to convert to degrees you need to multiply the radians by 57.29577951307855 :
   -0.019165032 * 57.29577951307855 = -1.098075447833095 deg

   You can use the same process for x, y & z

   Remember that the reading you get from the gyro is the rate of change not absolute, so you need to accumulate fast readings if you want to get the absolute value.