Yifei Teng / FreeIMU Featured

10DOF FreeIMU port for FreeIMU v4 board and GY-86. This library was modified extensively to specifically suit the Mbed platform. Used threads and interrupts to achieve async mode.

Dependencies:   HMC58X3 AK8963 MS561101BA MODI2C MPU9250

Dependents:   MTQuadControl FreeIMU_serial FreeIMU_demo

Port of FreeIMU library from Arduino to Mbed

10DOF FreeIMU port for FreeIMU v4 board and GY-86. This library was modified extensively to specifically suit the Mbed platform. Maximum sampling rate of 500hz can be achieved using this library.

Improvements

Sensor fusion algorithm fast initialization

This library implements the ARHS hot start algorithm, meaning that you can get accurate readings seconds after the algorithm is started, much faster than the Arduino version, where outputs slowly converge to the correct value in about a minute.

Caching

Sensors are read at their maximum output rates. Read values are cached hence multiple consecutive queries will not cause multiple reads.

Fully async

Acc & Gyro reads are performed via timer interrupts. Magnetometer and barometer are read by RTOS thread. No interfering with main program logic.

Usage

Declare a global FreeIMU object like the one below. There should only be one FreeIMU instance existing at a time. 

#include "mbed.h"
#include "FreeIMU.h"
FreeIMU imu;

int main(){
    imu.init(true);
}

Then, anywhere in the code, you may call imu.getQ(q) to get the quarternion, where q is an array of 4 floats representing the quarternion structure.

You are recommended to call getQ frequently to keep the filter updated. However, the frequency should not exceed 500hz to avoid redundant calculation. One way to do this is by using the RtosTimer: 

void getIMUdata(void const *);     //method definition

//in main
RtosTimer IMUTimer(getIMUdata, osTimerPeriodic, (void *)NULL);
IMUTimer.start(2);     //1 / 2ms = 500hz

//getIMUdata function
void getIMUdata(void const *dummy){
    imu.getQ(NULL);
}

Diff: FreeIMU.cpp

Revision:
1:794e9cdbc2a0
Parent:
0:21840c01d3d7
Child:
2:5c419926dcd7
--- a/FreeIMU.cpp	Sat Nov 02 17:25:51 2013 +0000
+++ b/FreeIMU.cpp	Tue Nov 05 11:31:39 2013 +0000
@@ -40,12 +40,9 @@
 
 I2C i2c(I2C_SDA,I2C_SCL);
 
-FreeIMU::FreeIMU() {
+FreeIMU::FreeIMU() : accgyro(MPU6050(i2c)), magn(HMC58X3(i2c)), baro(MS561101BA(i2c)){
 
    i2c.frequency(400000);
-   accgyro = MPU6050(i2c); // I2C
-   magn = HMC58X3(i2c);
-   baro = MS561101BA(i2c);
 
   // initialize quaternion
   q0 = 1.0f;
@@ -59,7 +56,6 @@
   twoKi = twoKiDef;
   integralFBx = 0.0f,  integralFBy = 0.0f, integralFBz = 0.0f;
   
-  
   update.start();
   dt_us=0;
   /*
@@ -110,43 +106,26 @@
 
 void FreeIMU::init(int accgyro_addr, bool fastmode) {
 
-  wait_ms(5);
-  /*
-  // disable internal pullups of the ATMEGA which Wire enable by default
-  #if defined(__AVR_ATmega168__) || defined(__AVR_ATmega8__) || defined(__AVR_ATmega328P__)
-    // deactivate internal pull-ups for twi
-    // as per note from atmega8 manual pg167
-    cbi(PORTC, 4);
-    cbi(PORTC, 5);
-  #else
-    // deactivate internal pull-ups for twi
-    // as per note from atmega128 manual pg204
-    cbi(PORTD, 0);
-    cbi(PORTD, 1);
-  #endif
-  */
-  
-  /*
-  if(fastmode) { // switch to 400KHz I2C - eheheh
-    TWBR = ((F_CPU / 400000L) - 16) / 2; // see twi_init in Wire/utility/twi.c
-  }
-*/
-  //accgyro = MPU6050(false, accgyro_addr);
+  wait_ms(10);
+
   accgyro = MPU6050(0x68);
   accgyro.initialize();
   accgyro.setI2CMasterModeEnabled(0);
   accgyro.setI2CBypassEnabled(1);
-  accgyro.setFullScaleGyroRange(MPU6050_GYRO_FS_2000);
-  wait_ms(5);
+  accgyro.setFullScaleGyroRange(MPU6050_GYRO_FS_1000);
+  accgyro.setDLPFMode(1);
+  accgyro.setRate(0);
+  wait_ms(10);
 
 
   // init HMC5843
   magn.init(false); // Don't set mode yet, we'll do that later on.
+  magn.setGain(0);
   // Calibrate HMC using self test, not recommended to change the gain after calibration.
-  magn.calibrate(1); // Use gain 1=default, valid 0-7, 7 not recommended.
+  magn.calibrate(0, 8); // Use gain 1=default, valid 0-7, 7 not recommended.
   // Single mode conversion was used in calibration, now set continuous mode
   magn.setMode(0);
-  wait_ms(10);
+  wait_ms(20);
   magn.setDOR(6);
   
   baro.init(FIMU_BARO_ADDR);
@@ -195,19 +174,6 @@
           q[3] = q3;
   }
 }
-/*
-#ifndef CALIBRATION_H
-
-static uint8_t location; // assuming ordered reads
-
-void eeprom_read_var(uint8_t size, byte * var) {
-  for(uint8_t i = 0; i<size; i++) {
-    var[i] = EEPROM.read(location + i);
-  }
-  location += size;
-}
-*/
-
 
 /**
  * Populates raw_values with the raw_values from the sensors
@@ -245,7 +211,7 @@
         values[i] = (float) accgyroval[i];
       }
       else {
-        values[i] = ((float) accgyroval[i]) / 16.4f; // NOTE: this depends on the sensitivity chosen
+        values[i] = ((float) accgyroval[i]) / 32.8f; // NOTE: this depends on the sensitivity chosen
       }
     }