Simulink to see Fourier

I have a very simple task but am not being successful.

I have a PWM generator in simulike runing at a certain frequency and certain duty cycle.

I want to take the fourier analysis of it and plot it in a scope.

What i expect to see is the DC component of the perioid signal... (i think?)

So if i have a period signal PWM signal with a magnitude of say 5 and duty cycle of .5 i expect to see a DC of 2.5 out on my scope.

How can i acomplish this? I have tried a few different blocks in simulink but im not getting what im expecting.

Perhaps my expecatations are wrong.

Answer 1

[Pat Gipper]

I put it in a Matlab Fcn block and it seems to work. See the attached file for details.

[Robert Scott]

What are those blocks providing the feedback called?

[Pat Gipper]

The memory block on the bottom, "io" retains a pointer into the top memory block, "buffer", where the latest sample of the input "u" is stored. "buffer" is a circular memory for storing the block of data for calculating the FFT. I tried to store this information within the Matlab function, but it was extremely unhappy with this attempt. I also wanted to make the FFT length a variable, and this was also problematical. I gave up on this for now and am just using a 32 (or was it 64, I forget?) point fixed length FFT.

You can find memory in the discrete selection of Simulink.

[Pat Gipper]

Were you able to open the attached file "fft_fcn.slx"? It was written using Matlab/Simulink 2024a build.