ardupilot/libraries/AP_Math/chirp.cpp

93 lines
3.2 KiB
C++

/*
* chirp.cpp
*
* Copyright (C) Leonard Hall 2020
*
* This file is free software: you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This file is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
* See the GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/*
* This object generates a chirp signal based on the input variables. A chirp is
* a sine wave starting from the minimum frequency and ending at the maximum frequency.
* The progression in frequency is not linear but designed to increase exponentially.
* The chirp can be designed to dwell at the minimum frequency for a specified time
* before sweeping through the frequencies and also can fade in the magnitude at the
* beginning and fade out the magnitude at the end. This object can also generate
* constant frequency sine waves by setting the minimum and maximum frequency to the
* same value.
*/
#include <AP_Math/AP_Math.h>
#include "chirp.h"
// constructor
Chirp::Chirp() {}
// initializes the chirp object
void Chirp::init(float time_record, float frequency_start_hz, float frequency_stop_hz, float time_fade_in, float time_fade_out, float time_const_freq)
{
// pass in variables to class
record = time_record;
wMin = M_2PI * frequency_start_hz;
wMax = M_2PI * frequency_stop_hz;
fade_in = time_fade_in;
fade_out = time_fade_out;
const_freq = time_const_freq;
B = logf(wMax / wMin);
// Mark as incomplete
complete = false;
}
// determine chirp signal output at the specified time and amplitude
float Chirp::update(float time, float waveform_magnitude)
{
magnitude = waveform_magnitude;
if (time <= 0.0f) {
window = 0.0f;
} else if (time <= fade_in) {
window = 0.5 - 0.5 * cosf(M_PI * time / fade_in);
} else if (time <= record - fade_out) {
window = 1.0;
} else if (time <= record) {
window = 0.5 - 0.5 * cosf(M_PI * (time - (record - fade_out)) / fade_out + M_PI);
} else {
window = 0.0;
}
if (time <= 0.0f) {
waveform_freq_rads = wMin;
output = 0.0f;
} else if (time <= const_freq) {
waveform_freq_rads = wMin;
output = window * magnitude * sinf(wMin * time - wMin * const_freq);
} else if (time <= record) {
// handles constant frequency dwells and chirps
if (is_equal(wMin, wMax)) {
waveform_freq_rads = wMin;
output = window * magnitude * sinf(wMin * time);
} else {
waveform_freq_rads = wMin * expf(B * (time - const_freq) / (record - const_freq));
output = window * magnitude * sinf((wMin * (record - const_freq) / B) * (expf(B * (time - const_freq) / (record - const_freq)) - 1));
}
} else {
waveform_freq_rads = wMax;
output = 0.0f;
}
complete = time > record;
return output;
}