flight/libraries/math/butterworth.h

   1 /**
   2  ******************************************************************************
   3  * @addtogroup OpenPilot Math Utilities
   4  * @{
   5  * @addtogroup Butterworth low pass filter
   6  * @{
   7  *
   8  * @file       butterworth.h
   9  * @author     The OpenPilot Team, http://www.openpilot.org Copyright (C) 2014.
  10  * @brief      Direct form two of a second order Butterworth low pass filter
  11  *
  12  * @see        The GNU Public License (GPL) Version 3
  13  *
  14  *****************************************************************************/
  15 /*
  16  * This program is free software; you can redistribute it and/or modify
  17  * it under the terms of the GNU General Public License as published by
  18  * the Free Software Foundation; either version 3 of the License, or
  19  * (at your option) any later version.
  20  *
  21  * This program is distributed in the hope that it will be useful, but
  22  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  23  * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
  24  * for more details.
  25  *
  26  * You should have received a copy of the GNU General Public License along
  27  * with this program; if not, write to the Free Software Foundation, Inc.,
  28  * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  29  */
  30
  31 #ifndef BUTTERWORTH_H
  32 #define BUTTERWORTH_H
  33
  34 // Coefficients of second order Butterworth biquadratic filter in direct from 2
  35 struct ButterWorthDF2Filter {
  36     float b0;
  37     float a1;
  38     float a2;
  39 };
  40
  41 // Function declarations
  42 void InitButterWorthDF2Filter(const float ff, struct ButterWorthDF2Filter *filterPtr);
  43 void InitButterWorthDF2Values(const float x0, const struct ButterWorthDF2Filter *filterPtr, float *wn1Ptr, float *wn2Ptr);
  44 float FilterButterWorthDF2(const float xn, const struct ButterWorthDF2Filter *filterPtr, float *wn1Ptr, float *wn2Ptr);
  45
  46 #endif