How to run an FFT on a PDA

[calistra]

Moving from LV Express to LV for PDA has been a bit of a nightmare.

I wrote an app in LV Express and expected it to be easy to migrate it to LV 4 PDA.

To avoid overruns, I am doing start/read/stop each iteration of the while loop.

I am reading in a waveform which I passed straight into an FFT / power spectrum
later I tried filtering it.

For testing, I am generating the input sine wave with a PCI-6014 on a PC.

Sampling at 2048 Hz, 2048 Samples.

I have managed to get the frequency reasonably accurately (OK up to 180 Hz, Higher frequencies get about a +10 Hz error).

I cannot interpret the amplitude at all. Any clues?

[Ankita]

Hi,

When you say that you are not able to interpret the amplitude , do you mean that you can interpret the amplitude in LV Express for PC but cannot do so in LV for PDA? If so, are you having problems even before downloading the program on the PDA or after it. Please elaborate more on your application or better still post  a small VI that demonstrates it. Also, are you using a Pocket PC or Palm?

Please provide the requested information and I will do my best to help.

Ankita

[calistra]

Yes - When I built an LV Express VI the amplitude coming out of the FFT made sense.

Problem 1 - I am getting buffer errors that I have so far solved by doing a start/acquire/stop/analyse inside the while loop.

Problem 2 - for some reason, the FFT in express always gives positive values, in PDA it has real & complex, real goes negative.

I use power spectrum and the max intensity seem a bit unrelated. Also - even on inserting a better waveform, my freuency is a bit out.

[Ankita]

Hi Calistra,

I tried your vi on LV 7.1 for Windows and PocketPC emulator. To me the results appeared similar. I am attaching the modified version of your vi that I used for both cases.

Please try the attached vi and provide me with some more information on the differences.

Thanks,

Ankita Agarwal