Hi,

I try to make an analyzer of frequency with a DSP (blackfin 533).

Frequency band: 50Hz in 5000Hz.

I try to make a program which calculates the FFT of any signal in this frequency band. As first test, I use a sinusoidal signal generated by a waveform generator, this signal is sent to a CAN to sample it to be able to calculate this FFT.

What I shall want to know, it is : which frequency of sampling do I have to use?

It is what counts it of point which it is necessary to use, of such way of having a FFT of a step of 1.

That is be able to calculate a FFT for every frequency: 50, 51,52 .. 5000Hz.

Software: VisualDSP ++ 5

DSP: ADSP BF 533 EZ-KIT LITE

ADC: AD7980 (can have a frequency of maxi sampling of 1MHz)

thanks

Hi,

The sampling frequency for FFT has to be atleast twice the highest signal component. So, you can go for a Fs of 10kHz since your signal bandwidth is 5kHz.You can choose any proper FFT size(power of 2). Since the FFT size and frequency resolution are directly related, to increase the frequency resolution for a given frequency range, increase the number of points acquired at the same sampling frequency. If the sampling rate is doubled, the FFT Size also needs to be doubled to get the same frequency resolution.Therefore, set the sampling rate as high as necessary for the highest frequency that you want to measure, but not higher because a higher sampling rate means lower frequency resolution for the same FFT size. You can choose 10KHz sampling frequency with a FFT size of say, 1024 and check the frequency resolution. You can then modify the FFT size accordingly to increase or decrease the frequency resolution.

Thanks,

Vinod