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Dependencies: mbed
LowpassFilter.cpp@0:dfea4e0e064b, 2017-05-22 (annotated)
- Committer:
- beacon
- Date:
- Mon May 22 10:45:28 2017 +0000
- Revision:
- 0:dfea4e0e064b
k
Who changed what in which revision?
User | Revision | Line number | New contents of line |
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beacon | 0:dfea4e0e064b | 1 | /* |
beacon | 0:dfea4e0e064b | 2 | * LowpassFilter.cpp |
beacon | 0:dfea4e0e064b | 3 | * Copyright (c) 2016, ZHAW |
beacon | 0:dfea4e0e064b | 4 | * All rights reserved. |
beacon | 0:dfea4e0e064b | 5 | */ |
beacon | 0:dfea4e0e064b | 6 | |
beacon | 0:dfea4e0e064b | 7 | #include "LowpassFilter.h" |
beacon | 0:dfea4e0e064b | 8 | |
beacon | 0:dfea4e0e064b | 9 | using namespace std; |
beacon | 0:dfea4e0e064b | 10 | |
beacon | 0:dfea4e0e064b | 11 | /** |
beacon | 0:dfea4e0e064b | 12 | * Creates a LowpassFilter object with a default corner frequency of 1000 [rad/s]. |
beacon | 0:dfea4e0e064b | 13 | */ |
beacon | 0:dfea4e0e064b | 14 | LowpassFilter::LowpassFilter() { |
beacon | 0:dfea4e0e064b | 15 | |
beacon | 0:dfea4e0e064b | 16 | period = 1.0f; |
beacon | 0:dfea4e0e064b | 17 | frequency = 1000.0f; |
beacon | 0:dfea4e0e064b | 18 | |
beacon | 0:dfea4e0e064b | 19 | a11 = (1.0f+frequency*period)*exp(-frequency*period); |
beacon | 0:dfea4e0e064b | 20 | a12 = period*exp(-frequency*period); |
beacon | 0:dfea4e0e064b | 21 | a21 = -frequency*frequency*period*exp(-frequency*period); |
beacon | 0:dfea4e0e064b | 22 | a22 = (1.0f-frequency*period)*exp(-frequency*period); |
beacon | 0:dfea4e0e064b | 23 | b1 = (1.0f-(1.0f+frequency*period)*exp(-frequency*period))/frequency/frequency; |
beacon | 0:dfea4e0e064b | 24 | b2 = period*exp(-frequency*period); |
beacon | 0:dfea4e0e064b | 25 | |
beacon | 0:dfea4e0e064b | 26 | x1 = 0.0f; |
beacon | 0:dfea4e0e064b | 27 | x2 = 0.0f; |
beacon | 0:dfea4e0e064b | 28 | } |
beacon | 0:dfea4e0e064b | 29 | |
beacon | 0:dfea4e0e064b | 30 | /** |
beacon | 0:dfea4e0e064b | 31 | * Deletes the LowpassFilter object. |
beacon | 0:dfea4e0e064b | 32 | */ |
beacon | 0:dfea4e0e064b | 33 | LowpassFilter::~LowpassFilter() {} |
beacon | 0:dfea4e0e064b | 34 | |
beacon | 0:dfea4e0e064b | 35 | /** |
beacon | 0:dfea4e0e064b | 36 | * Resets the filtered value to zero. |
beacon | 0:dfea4e0e064b | 37 | */ |
beacon | 0:dfea4e0e064b | 38 | void LowpassFilter::reset() { |
beacon | 0:dfea4e0e064b | 39 | |
beacon | 0:dfea4e0e064b | 40 | x1 = 0.0f; |
beacon | 0:dfea4e0e064b | 41 | x2 = 0.0f; |
beacon | 0:dfea4e0e064b | 42 | } |
beacon | 0:dfea4e0e064b | 43 | |
beacon | 0:dfea4e0e064b | 44 | /** |
beacon | 0:dfea4e0e064b | 45 | * Resets the filtered value to a given value. |
beacon | 0:dfea4e0e064b | 46 | * @param value the value to reset the filter to. |
beacon | 0:dfea4e0e064b | 47 | */ |
beacon | 0:dfea4e0e064b | 48 | void LowpassFilter::reset(float value) { |
beacon | 0:dfea4e0e064b | 49 | |
beacon | 0:dfea4e0e064b | 50 | x1 = value/frequency/frequency; |
beacon | 0:dfea4e0e064b | 51 | x2 = (x1-a11*x1-b1*value)/a12; |
beacon | 0:dfea4e0e064b | 52 | } |
beacon | 0:dfea4e0e064b | 53 | |
beacon | 0:dfea4e0e064b | 54 | /** |
beacon | 0:dfea4e0e064b | 55 | * Sets the sampling period of the filter. |
beacon | 0:dfea4e0e064b | 56 | * This is typically the sampling period of the realtime thread of a controller that uses this filter. |
beacon | 0:dfea4e0e064b | 57 | * @param the sampling period, given in [s]. |
beacon | 0:dfea4e0e064b | 58 | */ |
beacon | 0:dfea4e0e064b | 59 | void LowpassFilter::setPeriod(float period) { |
beacon | 0:dfea4e0e064b | 60 | |
beacon | 0:dfea4e0e064b | 61 | this->period = period; |
beacon | 0:dfea4e0e064b | 62 | |
beacon | 0:dfea4e0e064b | 63 | a11 = (1.0f+frequency*period)*exp(-frequency*period); |
beacon | 0:dfea4e0e064b | 64 | a12 = period*exp(-frequency*period); |
beacon | 0:dfea4e0e064b | 65 | a21 = -frequency*frequency*period*exp(-frequency*period); |
beacon | 0:dfea4e0e064b | 66 | a22 = (1.0f-frequency*period)*exp(-frequency*period); |
beacon | 0:dfea4e0e064b | 67 | b1 = (1.0f-(1.0f+frequency*period)*exp(-frequency*period))/frequency/frequency; |
beacon | 0:dfea4e0e064b | 68 | b2 = period*exp(-frequency*period); |
beacon | 0:dfea4e0e064b | 69 | } |
beacon | 0:dfea4e0e064b | 70 | |
beacon | 0:dfea4e0e064b | 71 | /** |
beacon | 0:dfea4e0e064b | 72 | * Sets the corner frequency of this filter. |
beacon | 0:dfea4e0e064b | 73 | * @param frequency the corner frequency of the filter in [rad/s]. |
beacon | 0:dfea4e0e064b | 74 | */ |
beacon | 0:dfea4e0e064b | 75 | void LowpassFilter::setFrequency(float frequency) { |
beacon | 0:dfea4e0e064b | 76 | |
beacon | 0:dfea4e0e064b | 77 | this->frequency = frequency; |
beacon | 0:dfea4e0e064b | 78 | |
beacon | 0:dfea4e0e064b | 79 | a11 = (1.0f+frequency*period)*exp(-frequency*period); |
beacon | 0:dfea4e0e064b | 80 | a12 = period*exp(-frequency*period); |
beacon | 0:dfea4e0e064b | 81 | a21 = -frequency*frequency*period*exp(-frequency*period); |
beacon | 0:dfea4e0e064b | 82 | a22 = (1.0f-frequency*period)*exp(-frequency*period); |
beacon | 0:dfea4e0e064b | 83 | b1 = (1.0f-(1.0f+frequency*period)*exp(-frequency*period))/frequency/frequency; |
beacon | 0:dfea4e0e064b | 84 | b2 = period*exp(-frequency*period); |
beacon | 0:dfea4e0e064b | 85 | } |
beacon | 0:dfea4e0e064b | 86 | |
beacon | 0:dfea4e0e064b | 87 | /** |
beacon | 0:dfea4e0e064b | 88 | * Gets the current corner frequency of this filter. |
beacon | 0:dfea4e0e064b | 89 | * @return the current corner frequency in [rad/s]. |
beacon | 0:dfea4e0e064b | 90 | */ |
beacon | 0:dfea4e0e064b | 91 | float LowpassFilter::getFrequency() { |
beacon | 0:dfea4e0e064b | 92 | |
beacon | 0:dfea4e0e064b | 93 | return frequency; |
beacon | 0:dfea4e0e064b | 94 | } |
beacon | 0:dfea4e0e064b | 95 | |
beacon | 0:dfea4e0e064b | 96 | /** |
beacon | 0:dfea4e0e064b | 97 | * Filters a value. |
beacon | 0:dfea4e0e064b | 98 | * @param value the original unfiltered value. |
beacon | 0:dfea4e0e064b | 99 | * @return the filtered value. |
beacon | 0:dfea4e0e064b | 100 | */ |
beacon | 0:dfea4e0e064b | 101 | float LowpassFilter::filter(float value) { |
beacon | 0:dfea4e0e064b | 102 | |
beacon | 0:dfea4e0e064b | 103 | float x1old = x1; |
beacon | 0:dfea4e0e064b | 104 | float x2old = x2; |
beacon | 0:dfea4e0e064b | 105 | |
beacon | 0:dfea4e0e064b | 106 | x1 = a11*x1old+a12*x2old+b1*value; |
beacon | 0:dfea4e0e064b | 107 | x2 = a21*x1old+a22*x2old+b2*value; |
beacon | 0:dfea4e0e064b | 108 | |
beacon | 0:dfea4e0e064b | 109 | return frequency*frequency*x1; |
beacon | 0:dfea4e0e064b | 110 | } |