Time domain to Frequncy domain signal conversion

This is my program to generate time-amplitde ECG signal, now i want to convert this output signal into frequency-amplitude domain. I tried using FFT technique but it is invalid taking fft(x,y). Please Help

A=dlmread('samples (7).csv',',',2,0);

x= A(2:1:14761 ,1);

y= A(2:1:14761 ,2);

figure;

%z=f(x,y);

hold on;

z=plot(x,y);

xlabel('Time(sec)')

ylabel('Amplitude(mV)')

axis tight;

grid on;

Answer 1

[Star Strider]

Use the Signal Processing Toolbox spectrogram (link) function to do time-frequency analysis.

[vandana sharma]

i do not want to do the time-frequency analysis, i want to convert/plot the same time-ampltude domain signal into frequency-amplitude domain.

[Star Strider]

Try this:

filename = 'samples (7).csv';
[D,S] = xlsread(filename);

t = D(:,1);
EKG = D(:,2);

figure
plot(t, EKG)
grid

L = numel(t);                                                       % Data Row Size
QF = std(diff(t));                                                  % Check For Non-Uniform Sampling
tr = linspace(min(t), max(t), L);                                   % Time Vector For Resampling
EKGr = resample(EKG, tr);                                           % Resampled EKG
Ts = mean(diff(t));                                                 % Sampling Interval (s)
Fs = 1/Ts;                                                          % Sampling Frequency (Hz)
Fn = Fs/2;                                                          % Nyquist Frequency (Hz)
FT_EKG = fft(EKGr-mean(EKGr))/L;                                    % Fourier Transform (Offset Corrected)
Fv = linspace(0, 1, fix(L/2)+1)*Fn;                                 % Frequency Vector
Iv = 1:numel(Fv);                                                   % Index Vector

figure
plot(tr(1:500), EKGr(1:500))
grid

figure
plot(Fv, abs(FT_EKG(Iv)))
grid
xlim([0 50])
xlabel('Frequency (Hz)')
ylabel('Amplitude (mV)')