diff options
author | Andrew Tridgell <tridge@samba.org> | 2013-08-04 15:09:16 +1000 |
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committer | Lorenz Meier <lm@inf.ethz.ch> | 2013-08-04 19:12:41 +0200 |
commit | ac89322d74ac1f5a29a6665feb4220aba3025f82 (patch) | |
tree | 343d7affe4d774ddc0d1fe30ad72a3e375a762d3 /src/modules/mathlib/math/filter/LowPassFilter2p.cpp | |
parent | 36cca7a31b428408eb686df592f092ba5fc24006 (diff) | |
download | px4-firmware-ac89322d74ac1f5a29a6665feb4220aba3025f82.tar.gz px4-firmware-ac89322d74ac1f5a29a6665feb4220aba3025f82.tar.bz2 px4-firmware-ac89322d74ac1f5a29a6665feb4220aba3025f82.zip |
mathlib: added LowPassFilter2p object
used in gyro and accel drivers for better filtering
Diffstat (limited to 'src/modules/mathlib/math/filter/LowPassFilter2p.cpp')
-rw-r--r-- | src/modules/mathlib/math/filter/LowPassFilter2p.cpp | 77 |
1 files changed, 77 insertions, 0 deletions
diff --git a/src/modules/mathlib/math/filter/LowPassFilter2p.cpp b/src/modules/mathlib/math/filter/LowPassFilter2p.cpp new file mode 100644 index 000000000..efb17225d --- /dev/null +++ b/src/modules/mathlib/math/filter/LowPassFilter2p.cpp @@ -0,0 +1,77 @@ +// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*- + +/**************************************************************************** + * + * Copyright (C) 2012 PX4 Development Team. All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in + * the documentation and/or other materials provided with the + * distribution. + * 3. Neither the name PX4 nor the names of its contributors may be + * used to endorse or promote products derived from this software + * without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS + * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE + * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, + * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS + * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED + * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN + * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE + * POSSIBILITY OF SUCH DAMAGE. + * + ****************************************************************************/ + +/// @file LowPassFilter.cpp +/// @brief A class to implement a second order low pass filter +/// Author: Leonard Hall <LeonardTHall@gmail.com> + +#include "LowPassFilter2p.hpp" +#include "math.h" + +namespace math +{ + +void LowPassFilter2p::set_cutoff_frequency(float sample_freq, float cutoff_freq) +{ + _cutoff_freq = cutoff_freq; + float fr = sample_freq/_cutoff_freq; + float ohm = tanf(M_PI_F/fr); + float c = 1.0f+2.0f*cosf(M_PI_F/4.0f)*ohm + ohm*ohm; + _b0 = ohm*ohm/c; + _b1 = 2.0f*_b0; + _b2 = _b0; + _a1 = 2.0f*(ohm*ohm-1.0f)/c; + _a2 = (1.0f-2.0f*cosf(M_PI_F/4.0f)*ohm+ohm*ohm)/c; +} + +float LowPassFilter2p::apply(float sample) +{ + // do the filtering + float delay_element_0 = sample - _delay_element_1 * _a1 - _delay_element_2 * _a2; + if (isnan(delay_element_0) || isinf(delay_element_0)) { + // don't allow bad values to propogate via the filter + delay_element_0 = sample; + } + float output = delay_element_0 * _b0 + _delay_element_1 * _b1 + _delay_element_2 * _b2; + + _delay_element_2 = _delay_element_1; + _delay_element_1 = delay_element_0; + + // return the value. Should be no need to check limits + return output; +} + +} // namespace math + |