How to get main frequency from digital signal I have sampled digital signal with noise. I want to get main frequency of this signal how to do it?
Currently it is smoothed by moving average. Is good way to make Fourier Transform an take the highest peak? Or the first peak?

Thanks.
Generally, yes, you should perform FFT and take the highest peak from the first half of the transformed signal. However, if the frequency your are looking for is constant (or close to constant), i.e. doesn't change (much) throughout the observation time, I would recommend using Welch's method instead of a simple FFT.
If the accuracy is not good enough you can perform interpolation around the peak, or on the entire signal using zero-padding.