Matlab fft plot axes

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Iro Liontou
Iro Liontou on 11 Apr 2024
Answered: Star Strider on 11 Apr 2024
%
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?

Answers (1)

Star Strider
Star Strider on 11 Apr 2024
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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