Need to make a square pulse w/o a special function

hi everyone,

really stuck here, need to make a periodic square (step pulse) that turns on to a certain value at a time, and turns off again. I need to make a code for it as i cant use a prebuilt function like square etc. Preferably use for loops and if statements etc.

can someone help me

[Saurabh Sakpal]

heres a sample photo

Answer 1

[Star Strider]

No loops needed. Just use the repmat funciton.

See if this does what you want:

LP = 10;                                        % Pulse Length
IP = 10;                                        % Inter-Pulse Interval
NC =  3;                                        % Number Of Cycles

PT = repmat([ones(1,LP) zeros(1,IP)], 1, NC);   % Complete Pulse Train

TV = 0:length(PT)-1;                            % Time Vector

figure(1)
plot(TV, PT, 'LineWidth',1.5)
hold on
plot(xlim, [0 0], '-k')
hold off
axis([0  length(TV)    -1.25  1.25])
set(gca, 'YTick', [-1 0 1], 'YTickLabel',{'-a', '', 'a'})
ylabel('Volts')

Experiment to get the result you need. The ‘PT’ assignment is the actual pulse train. You can use it in any subsequent code, such as fft or others. I plotted it here because that seems to be what you want.

[Image Analyst]

repmat() might be banned by the instructor also.

http://www.mathworks.com/matlabcentral/answers/38787-what-can-be-programmed-without-any-built-in-functions

And a "for" loop is so trivial that I don't even think we need to give an example for a for loop. Same for "if" statements. If he can't even do a for loop or if block, then this link might be helpful: http://www.mathworks.com/matlabcentral/answers/8026-best-way-s-to-master-matlab

[Star Strider]

Possibly. We may not know everything we need to about this problem.

If repmat is not allowed, the repmat call could easily be replaced by a single for loop with a serial horizontal concatenation at every iteration.

Answer 2

[Geoff Hayes]

Saurabh - why not use the sine and sign functions to do this? You could try something like

 % create an array of 10000 elements linearly spaced from 0 to 10
 % (can consider this a time vector of then seconds)
 t = linspace(0,10,10000);

 % set the amplitude
 a = 2.0;

 % create the square pulse
 y = (a/2)*sign(sin(2*pi*t)) + (a/2);

 plot(t,y);

As the result of

 sign(sin(2*pi*t))

is an array of values between -1 and +1, then in order to get the range as shown in your figure (which is the interval [0 a]) we just multiply the result by a/2 and then add a/2. Try the above and see what happens!

[Saurabh Sakpal]

I want it to be "Aperiodic" and unsymettrical as well. Like o for 20 seconds, off for 80 seconds.

Is there any function that does this?

Answer 3

[Saurabh Sakpal]

Sorry i want to apologise, i AM allowed to use function. I just wanted to avoid them as it is easier to modify parts of the code rather than a pre built fucntion. But feel free to use functions.

Answer 4

[Saurabh Sakpal]

Hey guys its not working, as i the repmat function doesnt go as a function of time. I need to pass the pulse as a function of time. Still Stuck.

[Star Strider]

What does ‘its not working’ mean? We cannot guess what you want. You must tell us as specifically as you can.

My repmat code produces a single string of 1s and 0s of whatever length and ratio you want for as many periods as you want. You can specify them individually.

To define it as a function of time, define a time vector for it. The linspace function is perfect for this.