Python Pyserial Readline Example

Introduction

Python Open Readline

This example only exports a raw socket connection. The next example below gives the client much more control over the remote serial port. The serial port settings are set on the command line when starting the program. There is no possibility to change settings from remote. All data is passed through as-is. examples: Examples Miniterm Miniterm is now available as module instead of example. See:ref:`miniterm` for details.

To use Python as a graphical interface for an Arduino powered robot, programmatically read the USB with the pySerial library. However, waiting for input from pySerial's Serial object is blocking, which means that it will prevent your GUI from being responsive. The process cannot update buttons or react to input because it is busy waiting for the serial to say something.

The first key is to use the root.after(milliseconds) method to run a non-blocking version of read in the tkinter main loop. Keep in mind that when TkInter gets to the root.mainloop() method, it is running its own while loop. It needs the things in there to run every now and then in order to make the interface respond to interactions. If you are running your own infinite loop anywhere in the code, the GUI will freeze up. Alternatively, you could write your own infinite loop, and call root.update() yourself occasionally. Both methods achieve basically the same goal of updating the GUI.

Python

However, the real issue is making sure that reading from serial is non-blocking. Normally, the Serial.read() and Serial.readline() will hold up the whole program until it has enough information to give. For example, a Serial.readline() won't print anything until there is a whole line to return, which in some cases might be never! Even using the after() and update() methods will still not allow the UI to be updated in this case, since the function never ends. This problem can be avoided with the timeout=0 option when enitializing the Serial object, which will cause it to return nothing unless something is already waiting in the Serial object's buffer.

Code

It’s useful to be able to read and plot serial data in real time (for example, you might want to monitor the output of a laser scanner or IMU). While this is a trivial task in MATLAB or LabVIEW, I wondered if there was a low effort way to do it for free.

I’ve known for a while that Python has an easy-to-use serial library, but I wasn’t sure what kinds of plotting/graphing options might exist for Python. A quick search turned up Matplotlib – a MATLAB-like plotting API for Python. As it turns out, Matplotlib includes an animation API and a function called FuncAnimation, which can be used to animate data over time (or update a graph with some sensor data over time).

Python Pyserial Readline Example Python

I’m using this page to document my attempt(s) to use Matplotlib to create a real time graph of data read from a serial port. For a proper introduction to Matplotlib, I’d recommend sentdex’s Matplotlib video series.

Items used

Pyserial Write Example

  • Laptop or PC running Ubuntu 18
  • Python 3.x
  • Matplotlib
  • pyserial
  • Arduino (or any programmable device with a serial port)

Installing matplotlib and pyserial on Ubuntu 18

Generating some fake serial data with an Arduino

To test my code, I used an Arduino to put some data on the serial port. In the example code below, the arduino simulates a coin toss using the function random.

On each iteration of the main loop, a random integer between 0 and 1 is generated, and the relative frequency of getting one side of the coin or the other is updated. This data is then sent to the serial port as comma delimitted line, where the termination character is ‘/n’. That is, the serial data looks like this:

The idea is that I’m putting some data on a serial port over time, and now I can write a python script to read and plot it.

Creating the real time plot

Pyserial Readline Example

References

Pyserial Example Code

  • https://pythonhosted.org/pyserial/shortintro.html
  • https://www.youtube.com/watch?v=ZmYPzESC5YY
  • https://matplotlib.org/
  • https://matplotlib.org/api/_as_gen/matplotlib.animation.FuncAnimation.html#matplotlib.animation.FuncAnimation