flix/flix/imu.ino

// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
// Repository: https://github.com/okalachev/flix

// Work with the IMU sensor

#include <SPI.h>
#include <FlixPeriph.h>
#include "vector.h"
#include "lpf.h"
#include "util.h"

MPU9250 imu(SPI);
Vector imuRotation(0, 0, -PI / 2); // imu orientation as Euler angles

Vector gyro; // gyroscope output, rad/s
Vector gyroBias;

Vector acc; // accelerometer output, m/s/s
Vector accBias;
Vector accScale(1, 1, 1);

void setupIMU() {
	print("Setup IMU\n");
	imu.begin();
	configureIMU();
}

void configureIMU() {
	imu.setAccelRange(imu.ACCEL_RANGE_4G);
	imu.setGyroRange(imu.GYRO_RANGE_2000DPS);
	imu.setDLPF(imu.DLPF_MAX);
	imu.setRate(imu.RATE_1KHZ_APPROX);
	imu.setupInterrupt();
}

void readIMU() {
	imu.waitForData();
	imu.getGyro(gyro.x, gyro.y, gyro.z);
	imu.getAccel(acc.x, acc.y, acc.z);
	calibrateGyroOnce();
	// apply scale and bias
	acc = (acc - accBias) / accScale;
	gyro = gyro - gyroBias;
	// rotate to body frame
	Quaternion rotation = Quaternion::fromEuler(imuRotation);
	acc = Quaternion::rotateVector(acc, rotation.inversed());
	gyro = Quaternion::rotateVector(gyro, rotation.inversed());
}

void calibrateGyroOnce() {
	static Delay landedDelay(2);
	if (!landedDelay.update(landed)) return; // calibrate only if definitely stationary

	static LowPassFilter<Vector> gyroBiasFilter(0.001);
	gyroBias = gyroBiasFilter.update(gyro);
}

void calibrateAccel() {
	print("Calibrating accelerometer\n");
	imu.setAccelRange(imu.ACCEL_RANGE_2G); // the most sensitive mode

	print("1/6 Place level [8 sec]\n");
	pause(8);
	calibrateAccelOnce();
	print("2/6 Place nose up [8 sec]\n");
	pause(8);
	calibrateAccelOnce();
	print("3/6 Place nose down [8 sec]\n");
	pause(8);
	calibrateAccelOnce();
	print("4/6 Place on right side [8 sec]\n");
	pause(8);
	calibrateAccelOnce();
	print("5/6 Place on left side [8 sec]\n");
	pause(8);
	calibrateAccelOnce();
	print("6/6 Place upside down [8 sec]\n");
	pause(8);
	calibrateAccelOnce();

	printIMUCalibration();
	print("✓ Calibration done!\n");
	configureIMU();
}

void calibrateAccelOnce() {
	const int samples = 1000;
	static Vector accMax(-INFINITY, -INFINITY, -INFINITY);
	static Vector accMin(INFINITY, INFINITY, INFINITY);

	// Compute the average of the accelerometer readings
	acc = Vector(0, 0, 0);
	for (int i = 0; i < samples; i++) {
		imu.waitForData();
		Vector sample;
		imu.getAccel(sample.x, sample.y, sample.z);
		acc = acc + sample;
	}
	acc = acc / samples;

	// Update the maximum and minimum values
	if (acc.x > accMax.x) accMax.x = acc.x;
	if (acc.y > accMax.y) accMax.y = acc.y;
	if (acc.z > accMax.z) accMax.z = acc.z;
	if (acc.x < accMin.x) accMin.x = acc.x;
	if (acc.y < accMin.y) accMin.y = acc.y;
	if (acc.z < accMin.z) accMin.z = acc.z;
	// Compute scale and bias
	accScale = (accMax - accMin) / 2 / ONE_G;
	accBias = (accMax + accMin) / 2;
}

void printIMUCalibration() {
	print("gyro bias: %f %f %f\n", gyroBias.x, gyroBias.y, gyroBias.z);
	print("accel bias: %f %f %f\n", accBias.x, accBias.y, accBias.z);
	print("accel scale: %f %f %f\n", accScale.x, accScale.y, accScale.z);
}

void printIMUInfo() {
	imu.status() ? print("status: ERROR %d\n", imu.status()) : print("status: OK\n");
	print("model: %s\n", imu.getModel());
	print("who am I: 0x%02X\n", imu.whoAmI());
	print("rate: %.0f\n", loopRate);
	print("gyro: %f %f %f\n", rates.x, rates.y, rates.z);
	print("acc: %f %f %f\n", acc.x, acc.y, acc.z);
	imu.waitForData();
	Vector rawGyro, rawAcc;
	imu.getGyro(rawGyro.x, rawGyro.y, rawGyro.z);
	imu.getAccel(rawAcc.x, rawAcc.y, rawAcc.z);
	print("raw gyro: %f %f %f\n", rawGyro.x, rawGyro.y, rawGyro.z);
	print("raw acc: %f %f %f\n", rawAcc.x, rawAcc.y, rawAcc.z);
}