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I'm trying to implement the "BNO055 9 Axes Motion Shield". There is an existing Arduino sketch GitHub that reads out the Euler data, I changed it a bit to print out quaternion data.

#include "NAxisMotion.h"        //Contains the bridge code between the API and the Arduino Environment
#include <Wire.h>

NAxisMotion mySensor;         //Object that for the sensor 
unsigned long lastStreamTime = 0;     //To store the last streamed time stamp
const int streamPeriod = 20;          //To stream at 50Hz without using additional timers (time period(ms) =1000/frequency(Hz))

void setup() //This code is executed once
{    
  //Peripheral Initialization
  Serial.begin(115200);           //Initialize the Serial Port to view information on the Serial Monitor
  I2C.begin();                    //Initialize I2C communication to the let the library communicate with the sensor.
  //Sensor Initialization
  mySensor.initSensor();          //The I2C Address can be changed here inside this function in the library
  mySensor.setOperationMode(OPERATION_MODE_NDOF);   //Can be configured to other operation modes as desired
  mySensor.setUpdateMode(MANUAL);   //The default is AUTO. Changing to MANUAL requires calling the relevant update functions prior to calling the read functions
  //Setting to MANUAL requires fewer reads to the sensor  
}

void loop() //This code is looped forever
{
  if ((millis() - lastStreamTime) >= streamPeriod)
  {
    lastStreamTime = millis();    
    mySensor.updateQuat();        //Update the Quat data into the structure of the object
    mySensor.updateCalibStatus();  //Update the Calibration Status

    Serial.print("Time: ");
    Serial.print(lastStreamTime);
    Serial.print("ms ");

    Serial.print(" W: ");
    Serial.print(mySensor.readQuatW()); 

    Serial.print(" X: ");
    Serial.print(mySensor.readQuatX());

    Serial.print(" Y: ");
    Serial.print(mySensor.readQuatY()); 

    Serial.print(" Z: ");
    Serial.print(mySensor.readQuatZ()); 

    Serial.println();
  }
}

Here is a snippet of the "NAxisMotion.h" header file:

    /*******************************************************************************************
    *Description: This function is used to return the w-axis of the quaternion data
    *Input Parameters: None
    *Return Parameter:
    *   int16_t:    W-axis quaternion data multiplied by 1000 (for 3 decimal places accuracy)
    *******************************************************************************************/
    int16_t readQuatW(void);

    /*******************************************************************************************
    *Description: This function is used to return the x-axis of the quaternion data
    *Input Parameters: None
    *Return Parameter:
    *   int16_t:    X-axis quaternion data multiplied by 1000 (for 3 decimal places accuracy)
    *******************************************************************************************/
    int16_t readQuatX(void);

    /*******************************************************************************************
    *Description: This function is used to return the y-axis of the quaternion data
    *Input Parameters: None
    *Return Parameter:
    *   int16_t:    Y-axis quaternion data multiplied by 1000 (for 3 decimal places accuracy)
    *******************************************************************************************/
    int16_t readQuatY(void);

    /*******************************************************************************************
    *Description: This function is used to return the z-axis of the quaternion data
    *Input Parameters: None
    *Return Parameter:
    *   int16_t:    Z-axis quaternion data multiplied by 1000 (for 3 decimal places accuracy)
    *******************************************************************************************/
    int16_t readQuatZ(void);

I understand that the output data type is signed integer, but what syntax do I need to use to store them in an array? Because it seems the only way to access them is through "mySensor.readQuatX()"

  • It would be better if you adopted the habit of including system libs first. The reason behind this is it is theoretically possible (very unlikely) that a header file will include a the system lib header and then redefine a pre-processor variable that the system library uses and so you might get different/conflicting header files for the library. Very very unlikely, unless you work with true coding cowboys. – Code Gorilla Jan 17 '18 at 15:50
  • Do you mean in this case Wire.h should come before NAxisMotion.h? – mascail Jan 18 '18 at 9:11
  • Yes #include <xxx> before #include "xxx". This also means if you get a duplicate definition int foo = 7 the error will be reported against the code you are more likely to have written rather than suggesting some system library is wrong. Others will argue I'm wrong, but it would be boring if we all thought the same. – Code Gorilla Jan 18 '18 at 10:21
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If I understand correctly you want to store a number of signed integers in an array. Arrays have fixed sizes so you need to know the number of values you want to store.

// Global declarations
enum QIndex {WAxis, XAxis, YAxi, ZAxis, MaxIndex};
int16_t qData[MaxValues] = {0};

// Code inside loop
qData[WAxis] = readQuatW();
qData[XAxis] = readQuatX();
qData[YAxis] = readQuatY();
qData[ZAxis] = readQuatZ();

// Pass the array  of values to another function with the declaration
// void SomeFunction (int *ar);
// or
// void SomeFunction (int ar[]);
SomeFunction (qData);

Is that what you mean?

  • So basically I tried it out and your code worked, thanks a lot. But now I my problem is, I can't convert the unsigned int sensor data to floats (which would also have to be unsigned) for further proccesing in the program "Processing" for visualization. Is there any way? – mascail Jan 16 '18 at 20:30
  • Yes, but it will only give you a whole number, because that's all you have. float fValue = (float)iValue; – Code Gorilla Jan 17 '18 at 8:11
  • I want to divide each element of the int16_t data-type array by 1000 and then convert them to float. It works but only gives me whole numbers like you said. What am I doing wrong? I need at least 2 decimal places. – mascail Jan 17 '18 at 8:41
  • You are doing integer division, you want float division. float result = ((float)input) / 1000.0f; You have to make both number floats and then divide. – Code Gorilla Jan 17 '18 at 14:57

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