BNO055 IMU

The BNO055 IMU or Intelligent 9-axis absolute orientation sensor as Bosch like to call it is a sensor that combines a 3 axis gyro, accelerometer and magnetometer in a single small package. In many respects this makes it similar to products like the Mindsensors AbsoluteIMU and the Dexter Industries dIMU, however the BNO055 has two features which make it more interesting:

• In addition to the raw sensor devices the BNO055 contains an on board processor that performs the computations needed to fuse the data from the 3 sensors. This processing allows the device to produce the following outputs Quaternion, Euler angles, Rotation vector, Linear acceleration, Gravity, Heading, at an update rate of 100Hz. In addition the processor performs automatic calibration of the sensors during operation reducing drift and providing very stable outputs.
• The sensor can like the others be accessed via i2c operations but in addition to this it also supports a 5V serial UART interface making it ideal for use with the EV3 when running leJOS. On the EV3, UART based sensors use hardware to perform the low level operations (unlike i2c which is software based) which reduces the cpu overhead considerably.

The device itself comes in a tiny 3.8×5.2mm package which is not easy for a hobbyist to use. Luckily a number of companies provide a breakout board for the device. I used the one produced by adafruit and available from Amazon for around £35. For a lot more details about the device see:

Click to access BST_BNO055_DS000_12.pdf

for a good overview of the device see:
https://learn.adafruit.com/adafruit-bno055-absolute-orientation-sensor/overview

The picture above shows the device alongside the LEGO Gyro sensor, as you can see it is pretty small. This picture also shows the additional wire (between the PS1 pin and the 3V output) needed to tell the device to use the UART interface (by default it uses i2c). With this wire in place all that is required is to hook up the gnd(pin 3 red), 5V(pin 4 green) and UART tx(pin 6 blue) and rx(pin 5 yellow) connections to a standard EV3 cable and you are ready to start talking to the device.

A search for “BNO055 java” turns up the following useful page BNO055 9DOF Java Class for FRC roboRio I used the code from the associated github project as the basis for a first pass at a driver. I had to modify the code to use the leJOS UART interface and I also added methods to allow loading and saving of calibration data. The updated driver can be found here. Note that this code does not follow the leJOS sensor framework conventions and is a little rough around the edges, I will clean this up and the driver will probably appear in a later (post 0.9.1) version of leJOS. So with this code we can now access the device.

 static void initIMU(BNO055 imu)
 {
     if(!imu.begin(BNO055.opmode_t.OPERATION_MODE_NDOF)) {
         /* There was a problem detecting the BNO055 ... check your connections */
         System.out.println("Ooops, no BNO055 detected ... Check your wiring!");
         System.exit(0);
     }

     Delay.msDelay(1000);

     /* Display the current temperature */
     System.out.println("Current Temperature: " + imu.getTemp() + " C");

     imu.setExtCrystalUse(true);
     Delay.msDelay(2000);
     double[] pos = new double[3]; // [x,y,z] position data

     while(true)
     {
         pos = imu.getVector(BNO055.vector_type_t.VECTOR_EULER);
         System.out.print("X: " + pos[0] + " Y: " + pos[1] + " Z: " + pos[2]);
         cal = imu.getCalibration();
         System.out.println(" CALIBRATION: Sys=" + cal.sys + " Gyro=" + cal.gyro + " Accel=" + cal.accel + " Mag=" + cal.mag);
         Delay.msDelay(1000);
     }
 
 }

The above code initializes the IMU and sets it into full fusion mode. It then loops printing out the 3 Euler angles and the state of the calibration for the three sensors.

If you would like to see how this sensor can be used take a look at the following article Improving position tracking of a mobile robot which shows how the BNO055 can be used to improve the odometry used to track the position of a robot and also compares the device to the LEGO gyro.