Convert online calculator to Excel format

[artz]

Hi,

I need to filter some time series data gathered during an experiment. Column A is Time starting at 0 increasing in 0.1s increments. Column B is voltage data. The number of data rows varies.

I found an online program that calculates digital filter coefficients for a selected filter type, cutoff frequency, and filter order.

My input parameters were filter type= Butterworth highpass, cutoff frequency= 0.1Hz, and filter order = 3. The calculator returned a generic output:

Recurrence relation:

 y[n] = ( -1 * x[n- 3])
     + (  3 * x[n- 2])
     + ( -3 * x[n- 1])
     + (  1 * x[n- 0])

     + (  0.9875122361 * y[n- 3])
     + ( -2.9749461327 * y[n- 2])
     + (  2.9874336501 * y[n- 1])

Also, is the following C code from the output:

/* Digital filter designed by mkfilter/mkshape/gencode   A.J. Fisher
   Command line: /www/usr/fisher/helpers/mkfilter -Bu -Hp -o 3 -a 1.0000000000e-03 0.0000000000e+00 -l */

#define  NZEROS 3
#define  NPOLES 3
#define  GAIN   1.006302976e+00

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

static void filterloop()
  { for (;;)
      { xv[0] = xv[1]; xv[1] = xv[2]; xv[2] = xv[3]; 
        xv[3] = next input value / GAIN;
        yv[0] = yv[1]; yv[1] = yv[2]; yv[2] = yv[3]; 
        yv[3] =   (xv[3] - xv[0]) + 3 * (xv[1] - xv[2])
                     + (  0.9875122361 * yv[0]) + ( -2.9749461327 * yv[1])
                     + (  2.9874336501 * yv[2]);
        next output value = yv[3];

Can anyone in the Forum convert either of these outputs to either Excel formulas or VBA?

Any help is appreciated.

Thanks,

-Art