Matlab fft plot axes

% 

clc;

clear;

close all;

%% Visualization loop for raw EMG signal

% Parameters

sampling_frequency = 1000; % Sampling frequency in Hz

duration = 5; % Duration of signal acquisition in seconds

num_samples = sampling_frequency * duration;

% Initialize variables

time = (0:num_samples-1)/sampling_frequency;

frequency = linspace(0, sampling_frequency/2, num_samples/2);

x = zeros(1, num_samples);

a = arduino();

%figure('Name', 'Signal from EMG sensor');

%grid on;

%title('Signal from EMG sensor');

%xlabel('Time (s)');

%ylabel('Voltage');

% Plot frequency spectrum

figure('Name', 'Frequency Spectrum');

grid on;

title('Frequency Spectrum of EMG Signal');

xlabel('Frequency (Hz)');

ylabel('Magnitude');

% Start loop to acquire signal

for i = 1:num_samples

% Read voltage

voltage = readVoltage(a, 'A0');

% Store voltage

x(i) = voltage;

% Update plot

plot(time(1:i), x(1:i));

xlim([0, duration]); % Adjust xlim as needed

drawnow;

end

% Calculate Fourier Transform

X = fft(x);

X_magnitude = 2*abs(X(1:num_samples/2))/num_samples;

% Plot frequency spectrum

figure('Name', 'Frequency Spectrum');

plot(frequency, X_magnitude);

title('Frequency Spectrum of EMG Signal');

xlabel('Frequency (Hz)');

ylabel('Magnitude');

xlim([0, max(frequency)]); % Adjust xlim as needed

I have this code in MATLAB. I want to acquire EMG signal from Arduino and i tried FFT, but i want the y axis to have magnitude values and the x axis to have the frequency values. how do I do that?

Answer 1

[Star Strider]

This would be my approach —

Fs = 1000;
Fn = Fs/2;
L = 60;
t = linspace(0, Fs*L, Fs*L+1).'/Fs;                                 % Time Vector
EMG = sum(sin(2*pi*t*(1:50:450)),2);                                % Signal Vector

slen = size(EMG,1);
NFFT = 2^nextpow2(slen);
FTEMG = fft((EMG-mean(EMG)).*hann(slen), NFFT)/sum(hann(slen));
Fv = linspace(0, 1, NFFT/2+1)*Fn;                                   % Frequency Vector
Iv = 1:numel(Fv);                                                   % Index Vector

figure
plot(Fv, abs(FTEMG(Iv))*2)
grid
xlabel('Frequency')
ylabel('Magnitude')

There are other ways to do this. This code is my usual approach.

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