filter.cpp

00001 float lowPass(float sample)
00002 {
00003     static const float a[4] = {1.00000000e+00,-2.77555756e-16,3.33333333e-01,-1.85037171e-17};
00004     static const float b[4] = {0.16666667,0.5,0.5,0.16666667};
00005 // x array for holding recent inputs (newest input as index 0, delay of 1 at index 1, etc.
00006     static volatile float x[4] = {0};
00007 // x array for holding recent inputs (newest input as index 0, delay of 1 at index 1, etc.
00008     static volatile float y[4] = {0};
00009     x[0] = sample;
00010 // Calculate the output filtered signal based on a weighted sum of previous inputs/outputs
00011     y[0] = (b[0]*x[0]+b[1]*x[1]+b[2]*x[2]+b[3]*x[3])-(a[1]*y[1]+a[2]*y[2]+a[3]*y[3]);
00012     y[0] /= a[0];
00013 // Shift the input signals by one timestep to prepare for the next call to this function
00014     x[3] = x[2];
00015     x[2] = x[1];
00016     x[1] = x[0];
00017 // Shift the previously calculated output signals by one time step to prepare for the next call to this function
00018     y[3] = y[2];
00019     y[2] = y[1];
00020     y[1] = y[0];
00021     return y[0];
00022 }
00023 
00024 float boxcar(float sample)
00025 {
00026     static const int boxcarWidth = 30; // Change this value to alter boxcar length
00027     static float recentSamples[boxcarWidth] = {0}; // hold onto recent samples
00028     static int readIndex = 0; // the index of the current reading
00029     static float total = 0; // the running total
00030     static float average = 0; // the average
00031 // subtract the last reading:
00032     total = total - recentSamples[readIndex];
00033 // add new sample to list (overwrite oldest sample)
00034     recentSamples[readIndex] = sample;
00035 // add the reading to the total:
00036     total = total + recentSamples[readIndex];
00037 // advance to the next position in the array:
00038     readIndex = readIndex + 1;
00039 // if we're at the end of the array...
00040     if (readIndex >= boxcarWidth) {
00041 // ...wrap around to the beginning:
00042         readIndex = 0;
00043     }
00044 // calculate the average:
00045     average = total / boxcarWidth;
00046 // send it to the computer as ASCII digits
00047     return average;
00048 }
00049 float complement(float x, float y , float ratio)
00050 {
00051     return (ratio*x + (1 - ratio)*y);
00052 }