Point by Point Filters

[shellie]

I wish to take in a signal and bandpass it using a pt by pt filter between 0.5Hz and 5Hz.

The Butterworth I seem to be unable to get working at all. In the current set-up it slightly works when fs=10, but if I set it to 100 or 1000 it does nothing. Even when it slightly works it is not producing the results expected. It doesn't even return errors when the Nyquist criterion is not fulfilled.

The equi-ribble filter works to an extent, but again if I change fs it fails to work, and it requires that I allow there to be a considerable gap between the pass band values and stop band values - which in turn allows unwanted frequency value to corrupt my signal.

In both cases I have tried different values for the cut-off points, sampling values, taps, and order, but have failed to come to a configuration that suits. I have not found sufficent documentation on pt by pt filters that can aid in my understanding of them - this could be a major source of my problem!!!

Any help at all would be much appreciated.

Thank you

[rpursley8]

Looks to me like you are only feeding one out of every 100 points to the filter. The rest are just thrown away. If you are acquiring 100 points with the A/D then you need to send all 100 points to the filter. Instead of indexing the Y data, put a for/next loop around the filter and feed the Y data into the loop where all 100 points will be indexed and fed to the filter and the results will be indexed and put back out as shown in attached bmp file.