Generate Square Wave

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.

[Dr. Seis]

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.

[Onur Öçalan]

http://imageshack.us/photo/my-images/714/20111217100355.jpg/

I want just like it...

Thanks.

[Onur Öçalan]

And I cann't put this value to Nidaq 6008 digital out line ??

Answer 1

[Paulo Silva]

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])

[Sean de Wolski]

certainly works!

[Onur Öçalan]

http://imageshack.us/photo/my-images/714/20111217100355.jpg/

I want just like it...

Thanks.

[Paulo Silva]

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])

Answer 2

[Dr. Seis]

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-');

[Dr. Seis]

The above basically provides a squared-off sine wave. Is this what you want?

[Onur Öçalan]

http://imageshack.us/photo/my-images/714/20111217100355.jpg/

I want just like it...

Thanks.

Answer 3

[Dr. Seis]

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