Plotting A Square Wave Using Matplotlib, Numpy And Scipy

Overview:

  • Square waves are period waveforms.

 

  • However, Square waves are non-sinusoidal. The transition between the peak values is instantaneous in a square wave.

 

  • The period of the square wave that is starting from a position like zero crossing the time it takes to return to the same position again.

 

  • The period of the square wave is also called the pulse width.

 

  • To draw a square wave using matplotlib, scipy and numpy following details are required
    • Frequency of the square wave - Say 10 Hz - That is 10 cycles per second

 

  • The sampling frequency - That is how many data points with which the square wave is being constructed - higher the data points smoother the square is.

 

  • Square waves have a duty cycle of 50%. That is, the percentage of the waveform that occurs above zero axes is 50% for a square wave.

 

  • By default the signal.square() function of scipy takes a duty value of 0.5.

 

Example:

from scipy import signal

import matplotlib.pyplot as plot

import numpy as np

 

# Sampling rate 1000 hz / second

t = np.linspace(0, 1, 1000, endpoint=True)

 

# Plot the square wave signal

plot.plot(t, signal.square(2 * np.pi * 5 * t))

 

# Give a title for the square wave plot

plot.title('Sqaure wave - 5 Hz sampled at 1000 Hz /second')

 

# Give x axis label for the square wave plot

plot.xlabel('Time')

 

# Give y axis label for the square wave plot

plot.ylabel('Amplitude')

 

plot.grid(True, which='both')

 

# Provide x axis and line color

plot.axhline(y=0, color='k')

 

# Set the max and min values for y axis

plot.ylim(-2, 2)

 

# Display the square wave drawn

plot.show()

Output:

Square wave


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