My codes won't show in the plots.

%% I wrote this program, it runs but doesn't show in the plot. Can someone help me ?
% FFT Coding Practice
clear all
clc
A = arduino('COM3', 'Mega2560');

n = 10;
for i =0:n;
    vo1 = readVoltage(A,'A0');
    vo2 = readVoltage(A,'A1');
    vo3 = readVoltage(A,'A2');
end
Vx = vo1*1000;
Vy = vo2*1000;
Vz = vo3*1000;
Ax = (Vx - 2496.2)/333.7;
Ay = (Vy - 2533.9)/ 346.4;
Az = (Vz - 2492.5)/334.1;


X = Ax;
Y=  Ay;
Z = Az;
fprintf(' X %d, Y %d , Z %d  \n',X,Y,Z);


% for a = 1:n-1

fs = 1/0.050; % sampling frequency
L1 = length(X)
N=1024;  % Block size
f = fs/2*linspace(0,1,N/2+1);  % Frequency values
subplot(311)
XX = fft(X,N)/L1; % Accel. along X axis
plot(f,2*abs(XX(1:N/2+1)));  grid on; 
title('One-sided Amplitude Spectrum');
subplot(312)
YY = fft(Y,N)/L1;          % Accel. along Y axis    
plot(f, 2*abs(YY(1:N/2+1)));  grid on; 
subplot(313)
ZZ = fft(Z,N)/L1;         % Accel. along Z axis 
plot(f,2*abs(ZZ(1:N/2+1)));  grid on; 
figure(2)
plot(f, 2*abs(XX(1:N/2+1)), 'r',f,2*abs(YY(1:N/2+1)), 'g',f,2*abs(ZZ(1:N/2+1)), 'b');  grid on; 
xlabel('f, frequency, [Hz]')
legend('Acc X ','Acc Y','Acc Z')
title('One-sided Amplitude Spectrum')  

[DGM]

If nothing shows up, have you verified that X, Y, and Z are actually valid?

X = rand(10,1);
Y = rand(10,1);
Z = rand(10,1);

fs = 1/0.050; % sampling frequency
L1 = length(X);
N=1024;  % Block size
f = fs/2*linspace(0,1,N/2+1);  % Frequency values
subplot(311)
XX = fft(X,N)/L1; % Accel. along X axis
plot(f,2*abs(XX(1:N/2+1)));  grid on; 
title('One-sided Amplitude Spectrum');
subplot(312)
YY = fft(Y,N)/L1;          % Accel. along Y axis    
plot(f, 2*abs(YY(1:N/2+1)));  grid on; 
subplot(313)
ZZ = fft(Z,N)/L1;         % Accel. along Z axis 
plot(f,2*abs(ZZ(1:N/2+1)));  grid on; 

figure(2)
plot(f, 2*abs(XX(1:N/2+1)), 'r',f,2*abs(YY(1:N/2+1)), 'g',f,2*abs(ZZ(1:N/2+1)), 'b');  grid on; 
xlabel('f, frequency, [Hz]')
legend('Acc X ','Acc Y','Acc Z')
title('One-sided Amplitude Spectrum')  

Otherwise, you'll have to provide example response data. I can't shake your arduino from here.

[Emmanuel Iroulor]

Thanks DGM

Answer 1

[Walter Roberson]

for i =0:n;
    vo1 = readVoltage(A,'A0');
    vo2 = readVoltage(A,'A1');
    vo3 = readVoltage(A,'A2');
end

Every time through the loop, you overwrite all of vo1, vo2, vo3. After the loop, vo1 will have only the value that it got when i == n, likewise vo2 and vo3 are going to hold only the last values they were assigned.

fprintf(' X %d, Y %d , Z %d  \n',X,Y,Z);

That line would not have worked properly if X, Y, Z were not scalars because you had saved all of the vo* entries. You would need

fprintf(' X %d, Y %d , Z %d  \n',[X(:),Y(:),Z(:)].');

Then

XX = fft(X,N)/L1; % Accel. along X axis

X is a scalar as it is constructed from the vo1 values and you only saved one vo1 value. The output of the fft is going to have the (scalar) value of X in the first entry, and be effectively 0 in the other entries.

You need to save all of the vo* entries. For example,

n = 10;
vo1 = zeros(n+1, 1);
vo2 = zeros(n+1, 1);
vo3 = zeros(n+1, 1);
for i = 0:n;
    vo1(i+1) = readVoltage(A,'A0');
    vo2(i+1) = readVoltage(A,'A1');
    vo3(i+1) = readVoltage(A,'A2');
end

I recommend that you add comments documenting your design decision to count from 0 to n instead of counting from 1 to n+1, or making n one less and counting 1 to n.

[Emmanuel Iroulor]

Thank you Walter Roberson. Your response was helpful.