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