I forgot to mention that 

http://www.piclist.com/techref/uk/ac/york/cs/www-users/http/~fisher/mkfilter
/index.htm

Is actually working now.. It will generate C code for 

Infinite Impulse Response (IIR) 

- Butterworth / Bessel / Chebyshev 

- Resonator 

- Proportional-Integral 


Finite Impulse Response (FIR) 

- Raised Cosine 

- Hilbert Transformer 


For example:

Makeing a Butterworth filter of order 1 for Lowpass to process 10000 samples
per second with the corner at 1000 Hertz 

Digital filter designed by mkfilter/mkshape/gencode   A.J. Fisher
   Command line: mkfilter.exe -Bu -Lp -o 1 -a 0.1 -l */

#define NZEROS 1
#define NPOLES 1
#define GAIN   4.077683537e+000

static float xv[NZEROS+1], yv[NPOLES+1];

static void filterloop()
  { for (;;)
      { xv[0] = xv[1]; 
        xv[1] = `next input value' / GAIN;
        yv[0] = yv[1]; 
        yv[1] =   (xv[0] + xv[1])
                     + (  0.5095254495 * yv[0]);
        `next output value' = yv[1];
      }
  }



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