From 82ffa82cc0423ed83ab94def6d3295f424a7c03c Mon Sep 17 00:00:00 2001
From: Vegard Storheil Eriksen <zyp@jvnv.net>
Date: Mon, 11 Apr 2011 05:46:10 +0200
Subject: Test IMU filter.

---
 IMU.cpp | 92 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100755 IMU.cpp

(limited to 'IMU.cpp')

diff --git a/IMU.cpp b/IMU.cpp
new file mode 100755
index 0000000..8a4926c
--- /dev/null
+++ b/IMU.cpp
@@ -0,0 +1,92 @@
+//=====================================================================================================
+// IMU.c
+// S.O.H. Madgwick
+// 25th September 2010
+//=====================================================================================================
+// Description:
+//
+// Quaternion implementation of the 'DCM filter' [Mayhony et al].
+//
+// User must define 'halfT' as the (sample period / 2), and the filter gains 'Kp' and 'Ki'.
+//
+// Global variables 'q0', 'q1', 'q2', 'q3' are the quaternion elements representing the estimated
+// orientation.  See my report for an overview of the use of quaternions in this application.
+//
+// User must call 'IMUupdate()' every sample period and parse calibrated gyroscope ('gx', 'gy', 'gz')
+// and accelerometer ('ax', 'ay', 'ay') data.  Gyroscope units are radians/second, accelerometer 
+// units are irrelevant as the vector is normalised.
+//
+//=====================================================================================================
+
+//----------------------------------------------------------------------------------------------------
+// Header files
+
+#include "IMU.h"
+#include <math.h>
+#include <ch.h>
+
+//----------------------------------------------------------------------------------------------------
+// Definitions
+
+#define Kp 2.0f			// proportional gain governs rate of convergence to accelerometer/magnetometer
+#define Ki 0.005f		// integral gain governs rate of convergence of gyroscope biases
+#define halfT (0.5f / 100)		// half the sample period
+
+//---------------------------------------------------------------------------------------------------
+// Variable definitions
+
+float q0 = 1, q1 = 0, q2 = 0, q3 = 0;	// quaternion elements representing the estimated orientation
+float exInt = 0, eyInt = 0, ezInt = 0;	// scaled integral error
+
+//====================================================================================================
+// Function
+//====================================================================================================
+
+void IMUupdate(float gx, float gy, float gz, float ax, float ay, float az) {
+	float norm;
+	float vx, vy, vz;
+	float ex, ey, ez;         
+	
+	// normalise the measurements
+	norm = sqrt(ax*ax + ay*ay + az*az);       
+	ax = ax / norm;
+	ay = ay / norm;
+	az = az / norm;
+	
+	// estimated direction of gravity
+	vx = 2*(q1*q3 - q0*q2);
+	vy = 2*(q0*q1 + q2*q3);
+	vz = q0*q0 - q1*q1 - q2*q2 + q3*q3;
+	
+	// error is sum of cross product between reference direction of field and direction measured by sensor
+	ex = (ay*vz - az*vy);
+	ey = (az*vx - ax*vz);
+	ez = (ax*vy - ay*vx);
+	
+	// integral error scaled integral gain
+	exInt = exInt + ex*Ki;
+	eyInt = eyInt + ey*Ki;
+	ezInt = ezInt + ez*Ki;
+	
+	// adjusted gyroscope measurements
+	gx = gx + Kp*ex + exInt;
+	gy = gy + Kp*ey + eyInt;
+	gz = gz + Kp*ez + ezInt;
+	
+	// integrate quaternion rate and normalise
+	q0 = q0 + (-q1*gx - q2*gy - q3*gz)*halfT;
+	q1 = q1 + (q0*gx + q2*gz - q3*gy)*halfT;
+	q2 = q2 + (q0*gy - q1*gz + q3*gx)*halfT;
+	q3 = q3 + (q0*gz + q1*gy - q2*gx)*halfT;  
+	
+	// normalise quaternion
+	norm = sqrt(q0*q0 + q1*q1 + q2*q2 + q3*q3);
+	q0 = q0 / norm;
+	q1 = q1 / norm;
+	q2 = q2 / norm;
+	q3 = q3 / norm;
+}
+
+//====================================================================================================
+// END OF CODE
+//====================================================================================================
-- 
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