MPU 9250 IMU sensor reading

The MPU-9250 is a System in Package (SiP) that combines two chips: the MPU-6500, which contains a 3-axis gyroscope, a 3-axis accelerometer, and an onboard Digital Motion Processor (DMP) capable of processing complex MotionFusion algorithms; and the AK8963, the market leading 3-axis digital compass.

The sensor can be controlled via the I2C interface. The wiring between the sensor and the Arduino is as follow:

Image from: https://create.arduino.cc/projecthub/msana/mpu9250-data-visualization-153f84

Sensor reading implementation is pretty forward since library for Arduino is already available. Example:

#include <Wire.h>

#include <MPU9250.h>

// class default I2C address is 0x68
// specific I2C addresses may be passed as a parameter here
// AD0 low = 0x68 (default for SparkFun breakout and InvenSense evaluation board)
// AD0 high = 0x69
MPU9250 mpu;

void setup() 
{
    Wire.begin();
    Wire.setClock(400000); // 400kHz I2C clock.
    ...
    int status = mpu.initialize();
    status = mpu.initialize();
    if (status == MPU_OK)
    {
        log(LOG_INFO, "IMU is initialized. Calibrating accel + gyro. Dont move the robot");
        mpu.calibrateAccelGyro();
    }
    else
    {
        log(LOG_ERR, "Cannot initialize IMU device, status: 0", status);
    }
    ...
    
}

void loop()
{
    mpu.update();
    ...
    // read mpu raw data
    float gx = mpu.getGyro(0);
    float gy = mpu.getGyro(1);
   float gz = mpu.getGyro(2);

    float ax = mpu.getAcc(0);
    float ay = mpu.getAcc(1);
    float az = mpu.getAcc(2);

    float mx = mpu.getMag(0);
    float my = mpu.getMag(1);
    float mz = mpu.getMag(2);
}

Detail implementation can be found in the Arduino JETTY.ino code base. The IMU sensor data is a part of the 47 bytes COBS data frame which will be bring up to ROS for high level control.

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