c22e30a4a6
New implementation of the heart rate sensor data processing using a frequency based PPG algorithm. The HRS3300 settings are fine-tuned for better signal to noise at 10Hz. The measurement delay is now set to 100ms. Enable and use the ambient light sensor. FFT implementation based on ArduinoFFT (https://github.com/kosme/arduinoFFT, GPLv3.0).
130 lines
5.6 KiB
Markdown
130 lines
5.6 KiB
Markdown
arduinoFFT
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==========
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# Fast Fourier Transform for Arduino
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This is a fork from https://code.google.com/p/makefurt/ which has been abandoned since 2011.
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~~This is a C++ library for Arduino for computing FFT.~~ Now it works both on Arduino and C projects. This is version 2.0 of the library, which has a different [API](#api). See here [how to migrate from 1.x to 2.x](#migrating-from-1x-to-2x).
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Tested on Arduino 1.6.11 and 1.8.10.
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## Installation on Arduino
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Use the Arduino Library Manager to install and keep it updated. Just look for arduinoFFT. Only for Arduino 1.5+
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## Manual installation on Arduino
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To install this library, just place this entire folder as a subfolder in your Arduino installation. When installed, this library should look like:
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`Arduino\libraries\arduinoFTT` (this library's folder)
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`Arduino\libraries\arduinoFTT\src\arduinoFTT.h` (the library header file. include this in your project)
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`Arduino\libraries\arduinoFTT\keywords.txt` (the syntax coloring file)
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`Arduino\libraries\arduinoFTT\Examples` (the examples in the "open" menu)
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`Arduino\libraries\arduinoFTT\LICENSE` (GPL license file)
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`Arduino\libraries\arduinoFTT\README.md` (this file)
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## Building on Arduino
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After this library is installed, you just have to start the Arduino application.
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You may see a few warning messages as it's built.
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To use this library in a sketch, go to the Sketch | Import Library menu and
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select arduinoFTT. This will add a corresponding line to the top of your sketch:
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`#include <arduinoFTT.h>`
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## API
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* ```ArduinoFFT(T *vReal, T *vImag, uint_fast16_t samples, T samplingFrequency, T * weighingFactors = nullptr);```
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Constructor.
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The type `T` can be `float` or `double`. `vReal` and `vImag` are pointers to arrays of real and imaginary data and have to be allocated outside of ArduinoFFT. `samples` is the number of samples in `vReal` and `vImag` and `weighingFactors` (if specified). `samplingFrequency` is the sample frequency of the data. `weighingFactors` can optionally be specified to cache weighing factors for the windowing function. This speeds up repeated calls to **windowing()** significantly. You can deallocate `vReal` and `vImag` after you are done using the library, or only use specific library functions that only need one of those arrays.
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```C++
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const uint32_t nrOfSamples = 1024;
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auto real = new float[nrOfSamples];
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auto imag = new float[nrOfSamples];
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auto fft = ArduinoFFT<float>(real, imag, nrOfSamples, 10000);
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// ... fill real + imag and use it ...
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fft.compute();
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fft.complexToMagnitude();
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delete [] imag;
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// ... continue using real and only functions that use real ...
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auto peak = fft.majorPeak();
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```
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* ```~ArduinoFFT()```
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Destructor.
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* ```void complexToMagnitude() const;```
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Convert complex values to their magnitude and store in vReal. Uses vReal and vImag.
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* ```void compute(FFTDirection dir) const;```
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Calcuates the Fast Fourier Transform. Uses vReal and vImag.
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* ```void dcRemoval() const;```
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Removes the DC component from the sample data. Uses vReal.
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* ```T majorPeak() const;```
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Returns the frequency of the biggest spike in the analyzed signal. Uses vReal.
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* ```void majorPeak(T &frequency, T &value) const;```
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Returns the frequency and the value of the biggest spike in the analyzed signal. Uses vReal.
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* ```uint8_t revision() const;```
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Returns the library revision.
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* ```void setArrays(T *vReal, T *vImag);```
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Replace the data array pointers.
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* ```void windowing(FFTWindow windowType, FFTDirection dir, bool withCompensation = false);```
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Performs a windowing function on the values array. Uses vReal. The possible windowing options are:
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* Rectangle
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* Hamming
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* Hann
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* Triangle
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* Nuttall
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* Blackman
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* Blackman_Nuttall
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* Blackman_Harris
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* Flat_top
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* Welch
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If `withCompensation` == true, the following compensation factors are used:
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* Rectangle: 1.0 * 2.0
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* Hamming: 1.8549343278 * 2.0
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* Hann: 1.8554726898 * 2.0
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* Triangle: 2.0039186079 * 2.0
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* Nuttall: 2.8163172034 * 2.0
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* Blackman: 2.3673474360 * 2.0
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* Blackman Nuttall: 2.7557840395 * 2.0
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* Blackman Harris: 2.7929062517 * 2.0
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* Flat top: 3.5659039231 * 2.0
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* Welch: 1.5029392863 * 2.0
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## Special flags
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You can define these before including arduinoFFT.h:
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* #define FFT_SPEED_OVER_PRECISION
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Define this to use reciprocal multiplication for division and some more speedups that might decrease precision.
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* #define FFT_SQRT_APPROXIMATION
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Define this to use a low-precision square root approximation instead of the regular sqrt() call. This might only work for specific use cases, but is significantly faster. Only works if `T == float`.
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See the `FFT_speedup.ino` example in `Examples/FFT_speedup/FFT_speedup.ino`.
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# Migrating from 1.x to 2.x
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* The function signatures where you could pass in pointers were deprecated and have been removed. Pass in pointers to your real / imaginary array in the ArduinoFFT() constructor. If you have the need to replace those pointers during usage of the library (e.g. to free memory) you can do the following:
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```C++
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const uint32_t nrOfSamples = 1024;
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auto real = new float[nrOfSamples];
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auto imag = new float[nrOfSamples];
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auto fft = ArduinoFFT<float>(real, imag, nrOfSamples, 10000);
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// ... fill real + imag and use it ...
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fft.compute();
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fft.complexToMagnitude();
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delete [] real;
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// ... replace vReal in library with imag ...
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fft.setArrays(imag, nullptr);
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// ... keep doing whatever ...
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```
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* All function names are camelCase case now (start with lower-case character), e.g. "windowing()" instead of "Windowing()".
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## TODO
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* Ratio table for windowing function.
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* Document windowing functions advantages and disadvantages.
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* Optimize usage and arguments.
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* Add new windowing functions.
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* ~~Spectrum table?~~
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