How to plot FFT Output(Computed using HDL node) on the Labview Host VI?

[sathya123]

I need the plot the 64 complex outputs of a 64pt FFT computed using the HDL node.  Frequency Spectrum??

[Mark M]

Hi,

Could you explain in more details about your system please? What type of data are you trying to pass to the host VI for plotting?

Thanks,

[sathya12]

My hdl node performs the 64pt FFT and the complex outputs are written in a file. Now, i want to plot those outputs on a graph.

So, what should i need to plot them on a graph?

[Mark M]

Hi,

How are you doing!

Could you explain more about the syntax and format your FFT results are written into your file? Also do you have both real and imaginary magnitudes or just a single complex magnitude with frequencies? Does it contain phase as well?

 
A typical routine for off-line processing will be:

1. Understand the syntax and format of the file.

2. Read the file in LabVIEW and extract interested information.

3. Seperate and store magnitudes, phase and frequencies into two or three arrays.

4. If real and imaginary magnitudes, write an algorithm in LabVIEW and calculate the complex magnitudes.

5. Plot the graph using Waveform Graph VI in LabVIEW.

[sathya12]

Fine  Mark M..

FFT outputs are only Complex numbers(32-bit) with 16-bit real and 16-bit imaginary.

Corresponding Frequencies for the Outputs are calculated on the HOST VI based on the formula.(depends on the SR,Base frequency and number of points)

Can u help me out with an example of similar type ??

[Mark M]

Hi there,

Apologies for the confusion. I think you can use a DMA FIFO to transfer your FFT outputs from the HDL node to the host VI.

Please take a look at a portion of code attached as "Host VI.png" that may help you to build the host VI.

On the other hand, the VI running on the FPGA may look like the one in the second attachment "FPGA.png". As I don't have your HDL node so I only used a FFT node here that comes standard with LabVIEW 8.6.

There is a developer's article that you may also find it helpful: Using DMA FIFO to Develop High-Speed Data Acquistion Applications for Reconfigurable I/O Devices

Hope it helps,

[Nghtcrwlr]

Hello

I have a similar problem. I have an image of size M X N (pixel).

Fisrt of all i have read the image from the path location. Then I used Unflatten Pixmap VI to convert the image to array. Now i need to find the 2 D FFT. I have to do the FFT by fist computing the transforms of the rows in parallel and then the transforms of the columns of the result. For that i extracted the N Resolution value and gave it to ta for loop ( since there are N rows for the image.) Then I calculated the FFT for these rows. The resulting array is transposed to do the FFT for the columns. Is the VI i made  correct? Please see the attchement for the image.

How can i get the 2D- FFT plot ?

Thankss

[Shur]

To plot your 2D data, different options can be used in LabVIEW, like Intensity Graph or Surface Plot.

Anuj Bhansali

AE NI INDIA 

[Nghtcrwlr]

Hello Anuj

I have an NXN image. I made the 2D Fast Fourier Transform of this one. Now i need to binearly interpolate the Fourier complex spectrum in a polar raster. How is this possible.? This is what i need.

Thanks