Get accelerometer values from BNO055 using adafruit's Unified Sensor Library

Question

If I understand correctly using the Adafruit_Sensor one can extract information from the sensor specific information. These sensors are currently mentioned in the README. I am using the BNO055 for two things:

1. Orientation values (Heading, pitch, roll)
2. Linear Acceleration values

My code is similar to the Example mentioned Adafruit_BNO055's bunny

Code

I tried the following in my loop()

void loop() {
  // put your main code here, to run repeatedly:
  sensors_event_t event;
  bno.getEvent(&event);

  Serial.print(F("Orientation: "));
  Serial.print((float)event.orientation.x);
  Serial.print(F(" "));
  Serial.print((float)event.orientation.y);
  Serial.print(F(" "));
  Serial.print((float)event.orientation.z);
  Serial.println(F(""));

  Serial.print(F("Acceleration: "));
  Serial.print((float)event.acceleration.x);
  Serial.print(F(" "));
  Serial.print((float)event.acceleration.y);
  Serial.print(F(" "));
  Serial.print((float)event.acceleration.z);
  Serial.println(F(""));

  delay(BNO055_SAMPLERATE_DELAY_MS);
}

Created sensors_event_t event and used the orientation and acceleration parameters to obtain the orientation and acceleration values in x, y, z directions.

output

The orientation and accleration values are the same:

Orientation: 105.50 -20.56 -101.00
Acceleration: 105.50 -20.56 -101.00
Orientation: 97.81 -14.69 -119.56
Acceleration: 97.81 -14.69 -119.56
Orientation: 93.81 -10.94 -125.56
Acceleration: 93.81 -10.94 -125.56
Orientation: 94.44 -12.25 -122.56

I tried adding another event event1 in the loop() but I still get the same results

sensors_event_t event;
  bno.getEvent(&event);

  Serial.print(F("Orientation: "));
  Serial.print((float)event.orientation.x);
  Serial.print(F(" "));
  Serial.print((float)event.orientation.y);
  Serial.print(F(" "));
  Serial.print((float)event.orientation.z);
  Serial.println(F(""));

  sensors_event_t event1;
  bno.getEvent(&event1);
  Serial.print(F("Acceleration: "));
  Serial.print((float)event1.acceleration.x);
  Serial.print(F(" "));
  Serial.print((float)event1.acceleration.y);
  Serial.print(F(" "));
  Serial.print((float)event1.acceleration.z);
  Serial.println(F(""));

  delay(BNO055_SAMPLERATE_DELAY_MS);

Can't the BNO055 along with the Adafruit_Sensor library not provide the acceleration and orientation values as events or is the library used only to obtain orientation values from the BNO055?

Answer 1

Findings

If I use the same sensors_event_t in the code and use event.acceleration and event.orientation within the loop() and they provide me exactly the same values. I in fact get the same values for heading, pitch, roll and acceleration in x, y, z direction.

sensors_event_t event;
  bno.getEvent(&event);

  Serial.print(F("Orientation: "));
  Serial.print((float)event.orientation.heading);
  Serial.print(F(" "));
  Serial.print((float)event.orientation.pitch);
  Serial.print(F(" "));
  Serial.print((float)event.orientation.roll);
  Serial.println(F(""));
 Serial.print((float)event.acceleration.x); // same as roll
 Serial.println(F(""));
 Serial.print((float)event.acceleration.y); // same as pitch
 Serial.println(F(""));
 Serial.print((float)event.acceleration.z); // same as heading
 Serial.println(F(""));

Sensor

I have a Blue Dot BNO055 sensor and it has marking on it for X, Y, Z directions as follows:

I crossed checked with the logic of Euler Angles from Wikipedia

If i rotate along the x Axis, I do in fact get roll (0 to 360) and so on.

Inference

The Adafruit_Sensor library provides only orientation values when used with BNO055 and Linear acceleration values need to be called separately using the Adafruit_BNO055.

code for Linear Acceleration and orientation

  sensors_event_t event;
  bno.getEvent(&event);

  Serial.print(F("Orientation: "));
  Serial.print((float)event.orientation.heading);
  Serial.print(F(" "));
  Serial.print((float)event.orientation.pitch);
  Serial.print(F(" "));
  Serial.print((float)event.orientation.roll);
  Serial.println(F(""));
//  Serial.print((float)event.acceleration.x); // same as roll
//  Serial.println(F(""));
//  Serial.print((float)event.acceleration.y); // same as pitch
//  Serial.println(F(""));
//  Serial.print((float)event.acceleration.z); // same as heading
//  Serial.println(F(""));

  imu::Vector<3> li_ac = bno.getVector(Adafruit_BNO055::VECTOR_ACCELEROMETER);
  Serial.print(F("Li. Acc.: "));
  Serial.print((float)li_ac.x());
  Serial.print(F(" "));

  Serial.print((float)li_ac.y());
  Serial.print(F(" "));

  Serial.print((float)li_ac.z());
  Serial.print(F(" "));
  Serial.println();

  delay(BNO055_SAMPLERATE_DELAY_MS);

Answer 2

You must set the operation mode from adafruit_bno055_opmode_t enum. Use bno.setMode.

For modes see section 3.3 in the datasheet.

The sensors_event_t is an union struct so the same memory is accessed with different member names.