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Topic: I2c on SAMD21  (Read 82 times) previous topic - next topic

Nathaniel_

I have a Sparkfun SAMD21 mini breakout that I want to use as a substitute for an arduino. I want to measure pitch and roll from an MPU6050. This has worked fine with an arduino nano (with Serial instead of SerialUSB), but with the SAMD21, I get weird values, It sometimes reads values like -395 degrees or 250 degrees. Past a certain angle, the output reads nan. Is there a difference between the Wire library for Arduino and the Wire library for the SAMD21 boards?

The code is modified from Broxxing's code: http://www.brokking.net/imu.html

Code: [Select]
///////////////////////////////////////////////////////////////////////////////////////
/*Terms of use
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//THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//THE SOFTWARE.


///////////////////////////////////////////////////////////////////////////////////////
//Support
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Website: http://www.brokking.net/imu.html
Youtube: https://youtu.be/4BoIE8YQwM8
Version: 1.0 (May 5, 2016)

///////////////////////////////////////////////////////////////////////////////////////
//Connections
///////////////////////////////////////////////////////////////////////////////////////
Power (5V) is provided to the Arduino pro mini by the FTDI programmer

Gyro - Arduino pro mini
VCC  -  5V
GND  -  GND
SDA  -  A4
SCL  -  A5

LCD  - Arduino pro mini
VCC  -  5V
GND  -  GND
SDA  -  A4
SCL  -  A5
*//////////////////////////////////////////////////////////////////////////////////////

//Include LCD and I2C library
//#include <LiquidCrystal_I2C.h>
#include <Wire.h>

//Declaring some global variables
int gyro_x, gyro_y, gyro_z;
long acc_x, acc_y, acc_z, acc_total_vector;
int temperature;
long gyro_x_cal, gyro_y_cal, gyro_z_cal;
long loop_timer;
int lcd_loop_counter;
float angle_pitch, angle_roll;
int angle_pitch_buffer, angle_roll_buffer;
boolean set_gyro_angles;
float angle_roll_acc, angle_pitch_acc;
float angle_pitch_output, angle_roll_output;

void setup() {
  Wire.begin();                                                        //Start I2C as master
  //Serial.begin(57600);                                               //Use only for debugging
  pinMode(LED_BUILTIN, OUTPUT);                                                 //Set output 13 (LED) as output
 
  setup_mpu_6050_registers();                                          //Setup the registers of the MPU-6050 (500dfs / +/-8g) and start the gyro

  digitalWrite(LED_BUILTIN, HIGH);                                              //Set digital output 13 high to indicate startup

  SerialUSB.begin(115200);    //Initialize the LCD
  SerialUSB.println("begin");
  for (int cal_int = 0; cal_int < 2000 ; cal_int ++){                  //Run this code 2000 times
    if(cal_int % 75 == 0) SerialUSB.print("*");                             //Print a dot on the LCD every 125 readings
    read_mpu_6050_data();                                              //Read the raw acc and gyro data from the MPU-6050
    gyro_x_cal += gyro_x;                                              //Add the gyro x-axis offset to the gyro_x_cal variable
    gyro_y_cal += gyro_y;                                              //Add the gyro y-axis offset to the gyro_y_cal variable
    gyro_z_cal += gyro_z;                                              //Add the gyro z-axis offset to the gyro_z_cal variable
    delay(3);                                                          //Delay 3us to simulate the 250Hz program loop
  }
  gyro_x_cal /= 2000;                                                  //Divide the gyro_x_cal variable by 2000 to get the average offset
  gyro_y_cal /= 2000;                                                  //Divide the gyro_y_cal variable by 2000 to get the average offset
  gyro_z_cal /= 2000;                                                  //Divide the gyro_z_cal variable by 2000 to get the average offset

  /*lcd.clear();                                                         //Clear the LCD
 
  lcd.setCursor(0,0);                                                  //Set the LCD cursor to position to position 0,0
  lcd.print("Pitch:");                                                 //Print text to screen
  lcd.setCursor(0,1);                                                  //Set the LCD cursor to position to position 0,1
  lcd.print("Roll :");   */                                              //Print text to screen
 
  digitalWrite(LED_BUILTIN, LOW);                                               //All done, turn the LED off
 
//  loop_timer = micros();                                               //Reset the loop timer
}

void loop(){

  read_mpu_6050_data();                                                //Read the raw acc and gyro data from the MPU-6050

  gyro_x -= gyro_x_cal;                                                //Subtract the offset calibration value from the raw gyro_x value
  gyro_y -= gyro_y_cal;                                                //Subtract the offset calibration value from the raw gyro_y value
  gyro_z -= gyro_z_cal;                                                //Subtract the offset calibration value from the raw gyro_z value
 
  //Gyro angle calculations
  //0.0000611 = 1 / (250Hz / 65.5)
  angle_pitch += gyro_x * 0.0000611;                                   //Calculate the traveled pitch angle and add this to the angle_pitch variable
  angle_roll += gyro_y * 0.0000611;                                    //Calculate the traveled roll angle and add this to the angle_roll variable
 
  //0.000001066 = 0.0000611 * (3.142(PI) / 180degr) The Arduino sin function is in radians
  angle_pitch += angle_roll * sin(gyro_z * 0.000001066);               //If the IMU has yawed transfer the roll angle to the pitch angel
  angle_roll -= angle_pitch * sin(gyro_z * 0.000001066);               //If the IMU has yawed transfer the pitch angle to the roll angel
 
  //Accelerometer angle calculations
  acc_total_vector = sqrt((acc_x*acc_x)+(acc_y*acc_y)+(acc_z*acc_z));  //Calculate the total accelerometer vector
  //57.296 = 1 / (3.142 / 180) The Arduino asin function is in radians
  angle_pitch_acc = asin((float)acc_y/acc_total_vector)* 57.296;       //Calculate the pitch angle
  angle_roll_acc = asin((float)acc_x/acc_total_vector)* -57.296;       //Calculate the roll angle
 
  //Place the MPU-6050 spirit level and note the values in the following two lines for calibration
  angle_pitch_acc -= -0.6;                                              //Accelerometer calibration value for pitch
  angle_roll_acc -= -2.7;                                               //Accelerometer calibration value for roll

  if(set_gyro_angles){                                                 //If the IMU is already started
    angle_pitch = angle_pitch * 0.9996 + angle_pitch_acc * 0.0004;     //Correct the drift of the gyro pitch angle with the accelerometer pitch angle
    angle_roll = angle_roll * 0.9996 + angle_roll_acc * 0.0004;        //Correct the drift of the gyro roll angle with the accelerometer roll angle
  }
  else{                                                                //At first start
    angle_pitch = angle_pitch_acc;                                     //Set the gyro pitch angle equal to the accelerometer pitch angle
    angle_roll = angle_roll_acc;                                       //Set the gyro roll angle equal to the accelerometer roll angle
    set_gyro_angles = true;                                            //Set the IMU started flag
  }
 
  //To dampen the pitch and roll angles a complementary filter is used
  angle_pitch_output = angle_pitch_output * 0.9 + angle_pitch * 0.1;   //Take 90% of the output pitch value and add 10% of the raw pitch value
  angle_roll_output = angle_roll_output * 0.9 + angle_roll * 0.1;      //Take 90% of the output roll value and add 10% of the raw roll value
 
  SerialUSB.print("Pitch: ");     
  SerialUSB.print(angle_pitch_output);
  SerialUSB.print("  roll: ");
  SerialUSB.println(angle_roll_output); //Write the roll and pitch values to the LCD display

}
 

pylon

Quote
Is there a difference between the Wire library for Arduino and the Wire library for the SAMD21 boards?
Yes, as the base processor uses a different architecture the two codes are completely different.  But the interface is kept compatible as long as the official API is used.

Keep in mind that a Nano runs with 5V levels while the SAMD21 runs on 3V3 levels. Did you adjust the hardware accordingly?

Where did you wire the signals? the wiring in the source code comments is not accurate for the SAMD21. Please post a wiring diagram.

Nathaniel_

So I should add level shifters between the mpu6050's I2C pins and the SAMD21's I2C pins?

pylon

Quote
So I should add level shifters between the mpu6050's I2C pins and the SAMD21's I2C pins?
No, the MPU6050 is running on 3V3. It might be something different if you don't use the chip directly but some unknown breakout board. In this case post the schematics of the board.

Nathaniel_

I did some more tests and it seems that the raw gyro Output is almost always in the 60000 to 65000 range, but ever so often while being rotated it jumps down to a value from 0-200, then right back to a value between 60000 and 650000.
This is the wiring:
SAMD21 GND to MPU6050 GND
SAMD21 VCC to MPU6050 VCC
SAMD21 SDA to MPU6050 SDA
SAMD21 SCL to MPU6050 SCL

On the SAMD21, Vcc is 3.3v right? Because the SAMD21 is connected to the computer's usb, which operates at 5v, so is Vcc the usb's Vcc or is it connected to the output of the 3.3v regulator?

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