![](/media/cache/group/default_image.jpg.50x50_q85.jpg)
oldexamplecode
Dependencies: mbed
Diff: DFT.cpp
- Revision:
- 0:6863633bf8a4
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/DFT.cpp Fri Mar 24 11:22:30 2017 +0000 @@ -0,0 +1,148 @@ + +#include "DFT.h" + + +// Preprocesses the data array and performs a dft on it, ARRAY MUST BE 1024 LONG +void performFFT(float* datam, int datalength){ + if (datalength == 1024){ + // - Calculating and substracting the mean - Takes ~2N additions + subMean(datam, datalength); + // - Applying a hanning window - N multiplications + applyHanningTable(datam, datalength); + // - Re-indexing the array - 2N operations + reindexData(datam, datalength); + // It then applies a radix-2 Cooley Tukey FFT to create a DFT of the original signal + cooleyTukeyRadix2(datam, datalength); + // Remove the DC component and null everything above the nyquist + afterProcessing(datam, datalength); + } + // Thus preprocessing takes 5N operations + // FFT itself takes NlogN operations + // Calculating to complex is N operations + // Calulating the complex back to magnitude is ~4N operations + // Total operation time is thus ~10N + NlogN complex operations +} + +// Performs a radix-2 cooley tukey FFT on the data array +void cooleyTukeyRadix2(float* data, int datalength){ + + complex_num fftdata[1024]; + complex_num fftbuffer[512]; + complex_num twiddlebuffer; + + complex_num minusone; + minusone.real = -1; + minusone.imaginary = 0; + + // Convert data to complex data + for (int i = 0; i < datalength; i++){ + fftdata[i].real = data[i]; + fftdata[i].imaginary = 0; + } + + for (int stage = 0; stage < 10; stage++){ + + unsigned int step = 1<<(stage+1); + + for (unsigned int i = 0; i < 1024; i = i+step){ // Crack it up in parts, i.e. for stage0 -> 512, stage1 -> 256 , 2>128, 3>64, 4>32, 5>16, 6>8, 7>4, 8>2, 9>1 --> 1024/2^stage OR IN STEPS: stage0 -> 2, stage1 -> 4, 2>8, 3>16, 4,32, 5>64, ......... 9>512 --> 1024 - 1024/2^stage+1 + // Buffer the first 'half' of the thing, which is the first half step + for (unsigned int k = 0; k < step / 2; k++){ + fftbuffer[k].real = fftdata[i+k].real; + fftbuffer[k].imaginary = fftdata[i+k].imaginary; + } + + // Apply twiddle factors to the seconds half (half step) depending on stage and numbering + for (unsigned int k = 0; k < step / 2; k++){ + // Read in the correct twiddle factor + // Twiddle factor is recalculated with k*(1024 / 2^stage+1) which can be recalculated to 1<< + twiddlebuffer.imaginary = twiddleLookupTable_Imaginary[k * (1<<(9-stage))]; + twiddlebuffer.real = twiddleLookupTable_Real[k * (1 << (9 - stage))]; + + fftdata[i + k + step / 2] = complex_multiply(fftdata[i + k + step / 2], twiddlebuffer); + } + + // Recalculate the first half by addition of the first and recalculated half + for (unsigned int k = 0; k < step / 2; k++) + fftdata[i + k] = complex_add(fftdata[i+k], fftdata[i+k+step/2]); + + + // Multiply the second half with minus 1 + for (unsigned int k = 0; k < step / 2; k++) + fftdata[i + step / 2 + k] = complex_multiply(fftdata[i + step/2+k], minusone); + + // Add the buffered old values, with the new second half values + for (unsigned int k = 0; k < step / 2; k++) + fftdata[i + step / 2 + k] = complex_add(fftdata[i + step/2 + k], fftbuffer[k]); + } + } + + // Convert complex data back to magnitude data + for (int i = 0; i < 1024; i++) + data[i] = complex_magnitude(fftdata[i]); +} + +// Calculates and subtracts the signal mean - Takes ~2N operations +void subMean(float* data, int datalength){ + float mean = 0; + float total = 0; + // Because the data is between 0 and 1, we can just sum and then device by datalength + // Normally you would devide each data sample by the datalength and sum all of those (to prevent overflow), so this saves N times multiplications + for (int i = 0; i < datalength; i++) + total += data[i]; + + mean = total / datalength; + + for (int i = 0; i < datalength; i++) + data[i] = data[i] - mean; + +} + +// Reindexes the array in preperation of the FFT implemented using a LUT, 2N operations +void reindexData(float* data, int datalength){ + + float reordereddata[1024]; + + for (int i = 0; i < datalength; i++){ + reordereddata[reversebit_lut_i[i]] = data[i]; + } + + // Copy all the reorderddata to the original array (datalength*int size in bytes) + memcpy(data, reordereddata, datalength*4); +} + +// Removes the DC component and null everything above the nyquist frequency +void afterProcessing(float* data, int datalength){ + data[0] = 0; // Set DC component to 0 + + for (int i = datalength-1; i > datalength / 2; i--) // Null everything above the nyquist frequency + data[i] = 0; + + // FIlter 50hz + filterfreq(50, data, datalength); +} + +// Filters a frequency and its multiples +void filterfreq(int frequency, float* data, int datalength){ + int niggr = 512; + int freqperbin = 10; + // Calculate which bin contains the frequency + int bin = frequency / freqperbin; + + // Null bin frequencies and the two surrounding bins, plus its multiples adjecent + do{ + if (bin - 1 >= 0) // Negative elements = you gonna have a bad time + data[bin - 1] = 0; + data[bin] = 0; + data[bin + 1] = 0; // Since element 512-1024 also exist, we can null it even if it isnt really usefull + bin *= 2; + } while (bin<niggr); +} + +// Calculate total magnitude, frequency magnitude component integrating module (FMCIM) +int calcPSD(float* data, int datalength){ + float knoedel=0; + for (int i = 0; i < datalength; i++){ + knoedel += (float)data[i]; + } + return (int)knoedel; +} \ No newline at end of file