FPGA: Butterworth Filter Express with no output

[gerardpc]

Hello,

I'm trying to use a Butterworth filter express in my FPGA (7852R), but I'm apparently getting no output. I suspect it has something to do with data types (fixed point vs I16), but I believe I have tried all the possible combinations, so I must be doing something wrong.

The idea is to implement a very simple derivative and then apply a low pass filter (order 2 or 4) to get rid of the high frequency components. The code works well without the filter, but when I try to insert it between the red and blue dots, I don't get anything. How should I wire it, and what should I consider?

[MichaelBalzer]

How have you configured the Butterworth Filter? Does your loop rate match the configured expected sample rate?

What value is being returned by the Butterworth Filter VI - is it always zero?