How to FFT signal practically (urgent)

[angeline]

I am a bit confused and only study FFT in theory . I never did it in practical before . If I have a 50Hz sine wave measured as current waveform , FFT the signal I have read that I need to sample it at at least 2*50Hz ... which is a minimum of 100 Hz . How do I do it practically as in sampling at 100Hz ? and do I need to do any filter ?

I will FFT this signal using the dsPIC30F which I know I need to perform ADC to the signal but before that on my hardware part ... I got a little confuse as I have stated above. Hope to get some advice.

 

[muralicrl]

Hi,

You are confusing. Once you sample at 100 Hz, you will be having two samples for each cycle of the signal. To extract the frequency you have to perform minimum 128 point FFT, so that your frequency resolution is around 1 Hz.

If you need more information, contact me,

Regards,

N. Muralidhara

CRL-BEL

 

[jossion]

dsPIC30F-- I think a microcontroller. Now if not wrong you has got confused with sampling and the ADC. ADC is one device which used for sampling . There is not else to do with your 50Hz sine wave before connecting to ADC. Just set the sampling frequency of ADC at 100Hz and read the samples coming out of it with microcontroller or any processor and then do FFT.

 

[angeline]

Thanks for your advice got a clearer picture ... manage to do the ADC part now trying the FFT which is kind of confusing ... anyone do it before that could give me an advice ?

 

[jossion]

Some keywords you have to search for implementation is Butterfly FFT, radix algorithms etc. Most computer aided DSP books are give the implementation. Or visit some xilinx or altera website and see how they doing the FFT. Big documentations are there in those site.

 

[engkhaled]

this is avery good book in DSP

https://www.dspguide.com/pdfbook.htm

explaining DFt and FFt using FORTRAN