MATLAB: Convert time to frequency domain

fft

I have a time domain signal and want to convert to frequency domain using FFT. I would be very grateful if someone could help me plot frequency vs normalised FFT amplitude. I have attached my time domain file and a photo of how i would like my plot to be. Any help would be much appreciated.

Best Answer

To normalise it to a maximum value of 1, divide the Fourier transformed data by the maximum of the Fourier transformed data: 
D = load('time_domain.txt');
t = D(:,1);
s = D(:,2);
L = numel(t);                                                   % Vector Length
Ts = mean(diff(t));                                             % Sampling Interval
Fs = 1/Ts;                                                      % Sampling Frequency
Fn = Fs/2;                                                      % Nyquist Frequency
FTs = fft(s)/L;                                                 % Fourier Transform
Fv = linspace(0, 1, fix(L/2)+1)*Fn;                             % Frequency Vector
Iv = 1:numel(Fv);                                               % Index Vector
FTs_plot = abs(FTs(Iv))/max(abs(FTs(Iv)));                      % Normalised Fourier Transform
figure
plot(Fv, FTs_plot)
grid
xlim([0 0.5])
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