Understanding values from an MPU6050

Question

I'm trying to understand the values that I'm getting from my MPU6050. I believe that there is a problem with my code. I'm not entirely sure how the code is supposed to look like. There doesn't seem to be very many examples on the MPU6050.

What is wrong?

After taking a look at the system print I found that the numbers that are written out is the time and not the values of the MPU6050. Why am I getting the zeros and nan for?

I also had a library problem thats fixed now.

I got the code from a site and I've modified it because it didn't run for me.

This is my code:

// collect readings
accelgyro.getMotion6(&ax, &ay, &az, &gx, &gy, &gz);

// apply gyro scale from datasheet
gsx = gx/gyroScale;   gsy = gy/gyroScale;   gsz = gz/gyroScale;

// calculate accelerometer angles
ary = -(180/3.141592) * atan(ax / sqrt(square(ay) + square(az))); 
arx =  (180/3.141592) * atan(ay / sqrt(square(ax) + square(az)));
arz = (180/3.141592) * atan(sqrt(square(ay) + square(ax)) / az);

// set initial values equal to accel values
if (i == 1) {
grx = arx;
gry = ary;
grz = arz;
}
// integrate to find the gyro angle
else{
grx = grx + (timeStep * gsx);
gry = gry + (timeStep * gsy);
grz = grz + (timeStep * gsz);
}  

// apply filter
rx = (0.1 * arx) + (0.9 * grx);
ry = (0.1 * ary) + (0.9 * gry);
rz = (0.1 * arz) + (0.9 * grz);

 Serial.print(ax);   Serial.print("\t");
 Serial.print(ay);   Serial.print("\t");
 Serial.print(az);   Serial.print("\t\t");
 Serial.print(gx);   Serial.print("\t");
 Serial.print(gy);   Serial.print("\t");
 Serial.print(gz);   Serial.print("\t\t");
 Serial.print(arx);   Serial.print("\t");
 Serial.print(ary);   Serial.print("\t");
 Serial.print(arz);   Serial.print("\t\t");
 Serial.print(grx);   Serial.print("\t");
 Serial.print(gry);   Serial.print("\t");
 Serial.print(grz);   Serial.print("\t\t");
 Serial.print(rx);   Serial.print("\t");
 Serial.print(ry);   Serial.print("\t");
 Serial.println(rz);

This is the output im getting

2   1.00    61.00   0.06000     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
3   61.00   139.00  0.07800     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
4   139.00  219.00  0.08000     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
5   219.00  300.00  0.08100     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
6   300.00  380.00  0.08000     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
7   380.00  462.00  0.08200     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
8   462.00  543.00  0.08100     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
9   543.00  624.00  0.08100     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
10  624.00  705.00  0.08100     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
11  705.00  788.00  0.08300     0   0   0       0   0   0       nan nan nan     

...

41  3223.00 3307.00 0.08400     0   0   0       0   0   0       nan nan nan nan nan nan     nan nan nan
42  3307.00 3392.00 0.08500     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
43  3392.00 3476.00 0.08400     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
44  3476.00 3560.00 0.08400     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
45  3560.00 3645.00 0.08500     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
46  3645.00 3729.00 0.08400     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
47  3729.00 3813.00 0.08400     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
48  3813.00 3897.00 0.08400     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
49  3897.00 3982.00 0.08500     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
50  3982.00 4066.00 0.08400     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
51  4066.00 4150.00 0.08400     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
52  4150.00 4234.00 0.08400     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
53  4234.00 4319.00 0.08500     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
54  4319.00 4403.00 0.08400     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
55  4403.00 4487.00 0.08400     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
56  4487.00 4571.00 0.08400     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
57  4571.00 4656.00 0.08500     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
58  4656.00 4740.00 0.08400     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan
59  4740.00 4824.00 0.08400     0   0   0       0   0   0       nan nan nan     nan nan nan     nan nan nan

Answer 1

I think the best choice for you is to read raw data from the sensor using Wire library.

1. First of all, you have to include the "Wire.h" library:

   #include "Wire.h"
   

2. Next step is to start the I2C communication by calling the following function in setup()

   Wire.begin();
   

3. Now that the master joined the I2C bus, all you have to do is to set the power mode of the module by setting the register 0x6B to 0x0. You can use the following function:

int sendCommand(int8_t register_address, int8_t register_value) {
Wire.beginTransmission(mpu_address);
Wire.write(register_address);
Wire.write(register_value);
int statusCommand = Wire.endTransmission(true);
Serial.print("I2C Address: "); Serial.print(mpu_address, HEX);
Serial.print(" Register address: "); Serial.print(register_address, HEX);
Serial.print(" Register value: "); Serial.print(register_value, HEX);
Serial.print(" Status command: "); Serial.println(statusCommand);

return statusCommand;
}

Please note that the default I2C address for the MPU6050 is 0x68. You can use the I2C Scanner to find its address.

To actually set the register 0x6B to 0x0 you have to call the sendCommand like below:

sendCommand(0x6B,0x0);

4. Request the raw data from the MPU6050. You can check the MPU6050 Register Map for additional information. Accelerometer can be found from 0x3B to 0x40, temperature from 0x41 and 0x42, and finally, the gyro from 0x43 to 0x48. IMPORTANT!!! Every register's value occupy 1 byte (int8_t), so you have to get the values of two registers (2 bytes) and store them in an int16_t.

Here is the full code to get the angles from the sensor:

#include "Wire.h"

int8_t mpu_address = 0x68;
int sendCommand(int8_t register_address, int8_t register_value) {
  Wire.beginTransmission(mpu_address);
  Wire.write(register_address);
  Wire.write(register_value);
  int statusCommand = Wire.endTransmission(true);
  Serial.print("I2C Address: "); Serial.print(mpu_address, HEX);
  Serial.print(" Register address: "); Serial.print(register_address, HEX);
  Serial.print(" Register value: "); Serial.print(register_value, HEX);
  Serial.print(" Status command: "); Serial.println(statusCommand);

  return statusCommand;
}

void setup() {
  //join the I2C bus
  Wire.begin();
  //start serial communication
  Serial.begin(115200);
  delay(1000);

  /* sendCommand can return 5 possile values:
   * -> 0:success
   * -> 1:data too long to fit in transmit buffer
   * -> 2:received NACK on transmit of address
   * -> 3:received NACK on transmit of data
   * -> 4:other error
   */
  while(sendCommand(0x6B,0x0) != 0){
    delay(1000);
  }

  Serial.println("MPU6050 started");
}

void convertRawDataToAngle(int16_t AcX, int16_t AcY, int16_t AcZ) {
  int minVal = 265; int maxVal = 402;
  int xAng = map(AcX, minVal, maxVal, -90, 90);
  int yAng = map(AcY, minVal, maxVal, -90, 90);
  int zAng = map(AcZ, minVal, maxVal, -90, 90);

  int x = RAD_TO_DEG * (atan2(-yAng, -zAng)+PI);
  int y = RAD_TO_DEG * (atan2(-xAng, -zAng) + PI);
  int z = RAD_TO_DEG * (atan2(-yAng, -xAng)+PI);

  Serial.print("X angle: "); Serial.print(x);
  Serial.print(" Y angle: "); Serial.print(y);
  Serial.print(" Z angle: "); Serial.print(z);
}

void readData(int8_t register_address) {

  int bytesReceived = -1;
  int statusCommand = -1;
  do {
    Wire.beginTransmission(mpu_address);
    Wire.write(register_address);
    statusCommand = Wire.endTransmission(false);
    bytesReceived = Wire.requestFrom(mpu_address, 6, true);
    Serial.print("I2C Address: "); Serial.print(mpu_address, HEX);
    Serial.print(" Register address: "); Serial.print(register_address, HEX);
    Serial.print(" Status command: "); Serial.print(statusCommand);
    Serial.print(" Bytes received: "); Serial.println(bytesReceived);
  } while (statusCommand != 0 && bytesReceived != 6);
  //check if MPU6050 sent all the requested data
  //in total 6 bytes, 2 bytes for each axis
  if (Wire.available() == 6) {
    int16_t AcX = Wire.read() << 8 ;
    AcX |= Wire.read();
    int16_t AcY = Wire.read() << 8 ;
    AcY |= Wire.read();
    int16_t AcZ = Wire.read() << 8 ;
    AcZ |= Wire.read();
    convertRawDataToAngle(AcX, AcY, AcZ);
  }
}
void loop() {
  //put your main code here, to run repeatedly:
  readData(0x3B);
  delay(100);
}

Answer 2

The output MPU 6050 does need filtering/processing before you can get any sense from it. I have used the library "MPU6050_6Axis_MotionApps20.h" with success, it is located here: MPU6050_6Axis_MotionApps20.h

I have written an example here: MPU 6050 for MicroView.