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ardupilot/libraries/AP_IMU/AP_IMU.cpp

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/*
AP_IMU.cpp - IMU Sensor Library for Ardupilot Mega
Code by Doug Weibel, Jordi Muñoz and Jose Julio. DIYDrones.com
This library works with the ArduPilot Mega and "Oilpan"
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
Methods:
quick_init() : For air restart
init() : Calibration
gyro_init() : For ground start using saved accel offsets
get_gyro() : Returns gyro vector. Elements in radians/second
get_accel() : Returns acceleration vector. Elements in meters/seconds squared
*/
#include <AP_IMU.h>
#define A_LED_PIN 37 //37 = A, 35 = C
#define C_LED_PIN 35
// ADC : Voltage reference 3.3v / 12bits(4096 steps) => 0.8mV/ADC step
// ADXL335 Sensitivity(from datasheet) => 330mV/g, 0.8mV/ADC step => 330/0.8 = 412
// Tested value : 418
#define GRAVITY 418 //this equivalent to 1G in the raw data coming from the accelerometer
#define accel_scale(x) (x*9.80665/GRAVITY)//Scaling the raw data of the accel to actual acceleration in meters per second squared
#define ToRad(x) (x*0.01745329252) // *pi/180
#define ToDeg(x) (x*57.2957795131) // *180/pi
// IDG500 Sensitivity (from datasheet) => 2.0mV/º/s, 0.8mV/ADC step => 0.8/3.33 = 0.4
// Tested values : 0.4026, ?, 0.4192
#define _gyro_gain_x 0.4 //X axis Gyro gain
#define _gyro_gain_y 0.41 //Y axis Gyro gain
#define _gyro_gain_z 0.41 //Z axis Gyro
#define ADC_CONSTRAINT 900
// Sensor: GYROX, GYROY, GYROZ, ACCELX, ACCELY, ACCELZ
const uint8_t AP_IMU::_sensors[6] = {1,2,0,4,5,6}; // For ArduPilot Mega Sensor Shield Hardware
const int AP_IMU::_sensor_signs[] = { 1, -1, -1,
1, -1, -1};
// Temp compensation curve constants
// These must be produced by measuring data and curve fitting
// [X/Y/Z gyro][A/B/C or 0 order/1st order/2nd order constants]
const float AP_IMU::_gyro_temp_curve[3][3] = {
{1665,0,0},
{1665,0,0},
{1665,0,0}
}; // To Do - make additional constructors to pass this in.
void
AP_IMU::init(void)
{
init_gyro();
init_accel();
}
/**************************************************/
void
AP_IMU::init_gyro(void)
{
float temp;
int flashcount = 0;
int tc_temp = _adc->Ch(_gyro_temp_ch);
delay(500);
Serial.println("Init Gyro");
for(int c = 0; c < 200; c++){
digitalWrite(A_LED_PIN, LOW);
digitalWrite(C_LED_PIN, HIGH);
delay(20);
for (int i = 0; i < 6; i++)
_adc_in[i] = _adc->Ch(_sensors[i]);
digitalWrite(A_LED_PIN, HIGH);
digitalWrite(C_LED_PIN, LOW);
delay(20);
}
for(int i = 0; i < 200; i++){
for (int j = 0; j <= 2; j++){
_adc_in[j] = _adc->Ch(_sensors[j]);
// Subtract temp compensated typical gyro bias
_adc_in[j] -= gyro_temp_comp(j, tc_temp);
// filter
_adc_offset[j] = _adc_offset[j] * 0.9 + _adc_in[j] * 0.1;
//Serial.print(_adc_offset[j], 1);
//Serial.print(", ");
}
//Serial.println(" ");
delay(20);
if(flashcount == 5) {
Serial.print("*");
digitalWrite(A_LED_PIN, LOW);
digitalWrite(C_LED_PIN, HIGH);
}
if(flashcount >= 10) {
flashcount = 0;
digitalWrite(C_LED_PIN, LOW);
digitalWrite(A_LED_PIN, HIGH);
}
flashcount++;
}
Serial.println(" ");
save_gyro_eeprom();
}
void
AP_IMU::init_accel(void) // 3, 4, 5
{
float temp;
int flashcount = 0;
delay(500);
Serial.println("Init Accel");
for (int j = 3; j <= 5; j++){
_adc_in[j] = _adc->Ch(_sensors[j]);
_adc_in[j] -= 2025;
_adc_offset[j] = _adc_in[j];
}
for(int i = 0; i < 200; i++){ // We take some readings...
delay(20);
for (int j = 3; j <= 5; j++){
_adc_in[j] = _adc->Ch(_sensors[j]);
_adc_in[j] -= 2025;
_adc_offset[j] = _adc_offset[j] * 0.9 + _adc_in[j] * 0.1;
//Serial.print(j);
//Serial.print(": ");
//Serial.print(_adc_in[j], 1);
//Serial.print(" | ");
//Serial.print(_adc_offset[j], 1);
//Serial.print(", ");
}
//Serial.println(" ");
if(flashcount == 5) {
Serial.print("*");
digitalWrite(A_LED_PIN, LOW);
digitalWrite(C_LED_PIN, HIGH);
}
if(flashcount >= 10) {
flashcount = 0;
digitalWrite(C_LED_PIN, LOW);
digitalWrite(A_LED_PIN, HIGH);
}
flashcount++;
}
Serial.println(" ");
_adc_offset[5] += GRAVITY * _sensor_signs[5];
save_accel_eeprom();
}
void
AP_IMU::zero_accel(void) // 3, 4, 5
{
_adc_offset[3] = 0;
_adc_offset[4] = 0;
_adc_offset[5] = 0;
save_accel_eeprom();
}
/**************************************************/
// Returns the temperature compensated raw gyro value
//---------------------------------------------------
float
AP_IMU::gyro_temp_comp(int i, int temp) const
{
// We use a 2nd order curve of the form Gtc = A + B * Graw + C * (Graw)**2
//------------------------------------------------------------------------
return _gyro_temp_curve[i][0] + _gyro_temp_curve[i][1] * temp + _gyro_temp_curve[i][2] * temp * temp;
}
/**************************************************/
Vector3f
AP_IMU::get_gyro(void)
{
int tc_temp = _adc->Ch(_gyro_temp_ch);
for (int i = 0; i < 3; i++) {
_adc_in[i] = _adc->Ch(_sensors[i]);
_adc_in[i] -= gyro_temp_comp(i,tc_temp); // Subtract temp compensated typical gyro bias
if (_sensor_signs[i] < 0)
_adc_in[i] = (_adc_offset[i] - _adc_in[i]);
else
_adc_in[i] = (_adc_in[i] - _adc_offset[i]);
if (fabs(_adc_in[i]) > ADC_CONSTRAINT) {
adc_constraints++; // We keep track of the number of times
_adc_in[i] = constrain(_adc_in[i], -ADC_CONSTRAINT, ADC_CONSTRAINT); // Throw out nonsensical values
}
}
_gyro_vector.x = ToRad(_gyro_gain_x) * _adc_in[0];
_gyro_vector.y = ToRad(_gyro_gain_y) * _adc_in[1];
_gyro_vector.z = ToRad(_gyro_gain_z) * _adc_in[2];
return _gyro_vector;
}
/**************************************************/
Vector3f
AP_IMU::get_accel(void)
{
for (int i = 3; i < 6; i++) {
_adc_in[i] = _adc->Ch(_sensors[i]);
_adc_in[i] -= 2025; // Subtract typical accel bias
if (_sensor_signs[i] < 0)
_adc_in[i] = _adc_offset[i] - _adc_in[i];
else
_adc_in[i] = _adc_in[i] - _adc_offset[i];
if (fabs(_adc_in[i]) > ADC_CONSTRAINT) {
adc_constraints++; // We keep track of the number of times
_adc_in[i] = constrain(_adc_in[i], -ADC_CONSTRAINT, ADC_CONSTRAINT); // Throw out nonsensical values
}
}
_accel_vector.x = accel_scale(_adc_in[3]);
_accel_vector.y = accel_scale(_adc_in[4]);
_accel_vector.z = accel_scale(_adc_in[5]);
return _accel_vector;
}
/********************************************************************************/
void
AP_IMU::load_gyro_eeprom(void)
{
_adc_offset[0] = read_EE_float(_address );
_adc_offset[1] = read_EE_float(_address + 4);
_adc_offset[2] = read_EE_float(_address + 8);
}
void
AP_IMU::save_gyro_eeprom(void)
{
write_EE_float(_adc_offset[0], _address);
write_EE_float(_adc_offset[1], _address + 4);
write_EE_float(_adc_offset[2], _address + 8);
}
/********************************************************************************/
void
AP_IMU::load_accel_eeprom(void)
{
_adc_offset[3] = read_EE_float(_address + 12);
_adc_offset[4] = read_EE_float(_address + 16);
_adc_offset[5] = read_EE_float(_address + 20);
}
void
AP_IMU::save_accel_eeprom(void)
{
write_EE_float(_adc_offset[3], _address + 12);
write_EE_float(_adc_offset[4], _address + 16);
write_EE_float(_adc_offset[5], _address + 20);
}
void
AP_IMU::print_accel_offsets(void)
{
Serial.print("Accel offsets: ");
Serial.print(_adc_offset[3], 2);
Serial.print(", ");
Serial.print(_adc_offset[4], 2);
Serial.print(", ");
Serial.println(_adc_offset[5], 2);
}
void
AP_IMU::print_gyro_offsets(void)
{
Serial.print("Gyro offsets: ");
Serial.print(_adc_offset[0], 2);
Serial.print(", ");
Serial.print(_adc_offset[1], 2);
Serial.print(", ");
Serial.println(_adc_offset[2], 2);
}
/********************************************************************************/
float
AP_IMU::read_EE_float(int address)
{
union {
byte bytes[4];
float value;
} _floatOut;
for (int i = 0; i < 4; i++)
_floatOut.bytes[i] = eeprom_read_byte((uint8_t *) (address + i));
return _floatOut.value;
}
void
AP_IMU::write_EE_float(float value, int address)
{
union {
byte bytes[4];
float value;
} _floatIn;
_floatIn.value = value;
for (int i = 0; i < 4; i++)
eeprom_write_byte((uint8_t *) (address + i), _floatIn.bytes[i]);
}
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