# Plot square wave

Yigit Turgut y.turgut at gmail.com
Wed Jan 18 09:41:48 EST 2012

```Hi all,

I am trying to generate a pseudo pwm signal, low-high transition will
take place when screen goes from black to white and high-low
transition when white to black. As a result I am trying to plot the
signal. Here is my code;

import time, pylab, numpy, scipy, pygame

def _func1():
global end
global white
global k
global t
global i
k = numpy.arange(4)
t = numpy.arange(4)
i = 0
f = open("test.txt", "w")
white = True
start = time.time()
end = time.time() - start
screen = pygame.display.set_mode((0, 0), pygame.FULLSCREEN)
timer = pygame.time.Clock()
test = repr(time.time())
while(end<8.00):
end = time.time() - start
if white:
screen.fill((255, 255, 255))
time.sleep(1)
k[i] = 0
t[i] = end
f.write(str(t[i]) + "\t" + str(k[i]) + "\n")
i = i + 1
print repr(end)

else:
screen.fill((0, 0, 0))
time.sleep(1)
k[i] = 1
t[i] = end
f.write(str(t[i]) + "\t" + str(k[i]) + "\n")
i =  i+ 1
print repr(end)

white = not white
pygame.display.update()
pygame.quit()

if __name__ == "__main__":
_func1()
print k
print t
print i
pylab.plot(time,data)
pylab.show()

Problem is I get a sawtooth instead of a square wave. I know that I
need to define points between 0,1,2 time integer values to achieve
this. But I hope there is a python trick that will yield this
time,data plot to a square wave?

```