How to plot square wave in Matlab?
Joey W
i have done analysis on simple sine wave x[n]=sin(2*pi*fo*n*(Ts)) , and by perfoming fft(x) I can get the frequency content of the signal..Now, i need to do spectral analysis on some other waveforms, such as square/rectangular wave..thats why i need to know the programming code or the Function Equation for square wave.. I have no idea how to write coding to represent a square wave, hope you can help me..thankyou..
In Matlab Help-> Signal Processing toolbox->waveform generation only show
x=Square(t);
however i fail to generate a square plot with this 1 line of coding, actually how to define t? how can I input the frequency to this plot? and also sampling frequency?
can u show me a sample coding to help me understand it?
Regards,
Joey
Toby
Is this what you are looking for? A definition of x and y.
x = [0 1 2 2 3 4 5 5 6 7 8]
y = [0 0 0 5 5 5 5 0 0 0 0]
plot(x,y,'-x')
"Joey W" <joey...@hotmail.com> wrote in message <hgq853$fs7$1...@fred.mathworks.com>...
Wayne King
Hi Joey, did you read
>>doc square
?
The square wave works just like sin(t) and cos(t) except that it takes value +1 and -1.
a 100 Hz square wave
t = 0:0.001:0.1; % Sampling frequency 1 kHz
y = square(2*pi*100*t);
plot(t,y);
axis([0 0.1 -1.5 1.5]);
xlabel('Seconds');
ylabel('Amplitude');
Hope that helps,
Wayne
Joey W
Dear Wayne,
Thanks so so so much!! it really helps.. i can understand already..
if there is a sum of signals, it will be y= square(2*pi*100*t)+ square(2*pi*2000*t); ?
is it correct? if i want to show combination of frequencies..
How to see the above example is taking 1KHz as sampling frequency?
thank you so much!
Regards,
Joey
Wayne King
You can certainly create a superposition of square waves, but you should keep in mind:
1.) that square waves are not sine waves so you won't just be contributing a single frequency component per square wave. In fact, you should see that you get odd harmonics, e.g. a square wave of 100 Hz will have peaks at 100, 300, 500, Hz
2.) you have to increase your sampling rate, decrease your sampling interval, if you want a square wave at 2 kHz as you've written above. You can't do that if you keep your sampling interval at 0.001.
Hope that helps,
Wayne
Joey W
Dear Wayne,
Really thanks for your explanation..I have got better understanding on the square wave.
As u said a square wave of 100 Hz will have peaks at 100, 300, 500, Hz, so just now i tried to plot "amplitude versus frequency" to visualize it myself, but the coding i wrote ,cant generate the output as what we want, can you please correct my coding?
t = 0:0.001:0.1;
f= 100;
y = square(2*pi*f*t);
plot(t,y);
axis([0 0.1 -1.5 1.5]);
xlabel('Seconds');
ylabel('Amplitude');
X=fft(y);
subplot (2,1,2), plot (f,abs(X));
xlabel('Frequency');
ylabel('amplitude');
Wayne King
You need a proper frequency vector. You have declared f as a scalar and used it as the frequency of the square wave and then you try to use the same variable as a frequency vector in plotting the absolute value of the Fourier transform, but you need a vector of frequencies in the latter case.
Wayne