93 lines
2.9 KiB
C++
93 lines
2.9 KiB
C++
// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
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//
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// This is free software; you can redistribute it and/or modify it under
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// the terms of the GNU Lesser General Public License as published by the
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// Free Software Foundation; either version 2.1 of the License, or (at
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// your option) any later version.
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//
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/// @file LowPassFilter.h
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/// @brief A class to implement a low pass filter without losing precision even for int types
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/// the downside being that it's a little slower as it internally uses a float
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/// and it consumes an extra 4 bytes of memory to hold the constant gain
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#ifndef LowPassFilter_h
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#define LowPassFilter_h
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#include <inttypes.h>
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#include <Filter.h>
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// 1st parameter <T> is the type of data being filtered.
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template <class T>
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class LowPassFilter : public Filter<T>
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{
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public:
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// constructor
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LowPassFilter(float gain);
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// apply - Add a new raw value to the filter, retrieve the filtered result
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virtual T apply(T sample);
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// reset - clear the filter - next sample added will become the new base value
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virtual void reset() {
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_base_value_set = false;
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};
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// reset - clear the filter and provide the new base value
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virtual void reset( T new_base_value ) {
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_base_value = new_base_value; _base_value_set = true;
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};
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private:
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float _gain; // gain value (like 0.02) applied to each new value
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bool _base_value_set; // true if the base value has been set
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float _base_value; // the number of samples in the filter, maxes out at size of the filter
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};
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// Typedef for convenience (1st argument is the data type, 2nd is a larger datatype to handle overflows, 3rd is buffer size)
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typedef LowPassFilter<int8_t> LowPassFilterInt8;
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typedef LowPassFilter<uint8_t> LowPassFilterUInt8;
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typedef LowPassFilter<int16_t> LowPassFilterInt16;
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typedef LowPassFilter<uint16_t> LowPassFilterUInt16;
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typedef LowPassFilter<int32_t> LowPassFilterInt32;
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typedef LowPassFilter<uint32_t> LowPassFilterUInt32;
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typedef LowPassFilter<float> LowPassFilterFloat;
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// Constructor //////////////////////////////////////////////////////////////
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template <class T>
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LowPassFilter<T>::LowPassFilter(float gain) :
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Filter<T>(),
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_gain(gain),
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_base_value_set(false)
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{
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// bounds checking on _gain
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if( _gain > 1.0) {
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_gain = 1.0;
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}else if( _gain < 0.0 ) {
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_gain = 0.0;
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}
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};
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// Public Methods //////////////////////////////////////////////////////////////
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template <class T>
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T LowPassFilter<T>:: apply(T sample)
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{
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// initailise _base_value if required
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if( !_base_value_set ) {
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_base_value = sample;
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_base_value_set = true;
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}
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// do the filtering
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_base_value = _gain * (float)sample + (1.0 - _gain) * _base_value;
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// return the value. Should be no need to check limits
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return (T)_base_value;
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}
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#endif |