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Generate Square Wave

Asked by Onur Öçalan on 16 Dec 2011
Hi everybody;
I want to create a rectangular wave with a specific function. For example,
the wavelength of the wave = 20 milliseconds
the wave width = 1.2 milliseconds
How do I do with Matlab ?
Please help...
Thanks.

  3 Comments

I am a bit confused as to what you are calling the "wavelength" and "width" of the wave... in my mind the wavelength should be an equivalent way of saying the width of a single wave. See my answer below for providing a "wavelength" equal to 1.2 milliseconds, a "signal length" of 20 milliseconds, and an amplitude of 0.75.
http://imageshack.us/photo/my-images/714/20111217100355.jpg/
I want just like it...
Thanks.
And I cann't put this value to Nidaq 6008 digital out line ??

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3 Answers

Answer by Paulo Silva
on 16 Dec 2011

Here's my crazy way to do it, I'm assuming some values for example the sampling time. This way doesn't require any toolboxes, another way to do it easily would be to use the Control System Toolbox™ gensig function that I usually use.
l=20e-6;
w=1.2e-6;
Ts=1e-9;
t=0:Ts:l; %generate the time vector
s=0:Ts:w; %generate a piece of the wave, the one with zeros
s0=s*0;
%generate another piece of the wave, the one with ones
s1=s*0+1;
s=[s s1]; %combine them for one period of the wave
s=repmat(s,1,round(l/(2*w)+1)); %create the entire wave from that first piece
%view the wave
plot(t,s((1:size(t,2))))
ylim([-0.5 1.5])

  3 Comments

certainly works!
http://imageshack.us/photo/my-images/714/20111217100355.jpg/
I want just like it...
Thanks.
l=20e-6;
w=1.2e-6;
Ts=1e-9;
t1=0:Ts:w;
t0=w+Ts:Ts:l-Ts;
s1=ones(size(t1));
s0=zeros(size(t0));
s=[s1 s0];
N=2; %How many repetitions of the wave
ss=repmat(s,1,N);
t=0:Ts:N*l-Ts;
plot(t,ss)
ylim([-0.5 1.5])

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Answer by Dr. Seis
on 17 Dec 2011

signal_length = 20e-6; % length of signal in seconds
wave_length = 1.2e-6; % wavelength of rectangle pulse in seconds
amplitude = 0.75; % amplitude of wave
dt = 1e-9; % time increment in seconds
time = 0:dt:signal_length; % time samples in seconds
% Define the rectangle signal timeseries
rectsignal = sign(sin(2*pi*time/wave_length)).*ones(size(time))*amplitude;
% Plot the timeseries
plot(time,rectsignal,'r-');

  2 Comments

The above basically provides a squared-off sine wave. Is this what you want?
http://imageshack.us/photo/my-images/714/20111217100355.jpg/
I want just like it...
Thanks.

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Answer by Dr. Seis
on 18 Dec 2011

This should work:
dt = 1e-9; % time increment (in seconds)
maxtime = 200e-6; % maximum length of signal (in seconds)
time = 0:dt:maxtime; % time samples (in seconds)
wavelength = 20e-6; % distance between beginning of each pulse
wavewidth = 1.2e-6; % width of each pulse
rectpulse = ones(1,round(wavewidth/dt)); % Define width of rectangle pulse
operator = zeros(size(time)); % Set operator to zeros
operator(mod(time,wavelength)==0) = 1; % Place 1 at each pulse location
rectsignal = conv(operator,rectpulse); % Convolve rectpulse w/ operator
rectsignal = rectsignal(1,1:length(time)); % Remove any extra traces
plot(time,rectsignal); % Plot the signal

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