python realtime plot using pyqtgraph

Question

I need to plot in realtime a series floating point numbers from the serial port. These values are sepparated by the '\n' character, so the data sequence is something like this: x1 x2 x3 ...

How would you plot the data? I am using an Arduino board, the data rate is 200 samples/s, and my PC is running on Windows7 64 bits. I think a good choice is use the pyqtgraph library. I started to use the Plotting.py example in pyqtgraph (plenty more examples available after installing pyqtgraph and then running python3 -m pyqtgraph.examples), but I don't know how to adapt this code for my needs (see below). Thank you very much in advance.

from pyqtgraph.Qt import QtGui, QtCore
import numpy as np
import pyqtgraph as pg

# Set graphical window, its title and size
win = pg.GraphicsWindow(title="Sample process")
win.resize(1000,600)
win.setWindowTitle('pyqtgraph example')

# Enable antialiasing for prettier plots
pg.setConfigOptions(antialias=True)

# Random data process
p6 = win.addPlot(title="Updating plot")
curve = p6.plot(pen='y')
data = np.random.normal(size=(10,1000)) #  If the Gaussian distribution shape is, (m, n, k), then m * n * k samples are drawn.

# plot counter
ptr = 0 

# Function for updating data display
def update():
    global curve, data, ptr, p6
    curve.setData(data[ptr%10])
    if ptr == 0:
        p6.enableAutoRange('xy', False)  ## stop auto-scaling after the first data set is plotted
    ptr += 1

# Update data display    
timer = QtCore.QTimer()
timer.timeout.connect(update)
timer.start(50)


## Start Qt event loop unless running in interactive mode or using pyside.
if __name__ == '__main__':
    import sys
    if (sys.flags.interactive != 1) or not hasattr(QtCore, 'PYQT_VERSION'):
        QtGui.QApplication.instance().exec_()

Answer 1

Here is the code that works fine. The main process is contained in the update() function. It reads the input value from the serial port, updates the array Xm (that contains the input values) and then updates its associated curve.

This code was posted for the sake of simplicity and works just for low data rates (less than 100 samples/s). For higher data rates, it should be modified inside the update() function as follows. A set of values (instead of a single one) should be read from the serial port. Then, such set should be appended to the array Xm

I hope this answer is useful for you, and thank you very much for your help!

# Import libraries
from numpy import *
from pyqtgraph.Qt import QtGui, QtCore
import pyqtgraph as pg
import serial

# Create object serial port
portName = "COM12"                      # replace this port name by yours!
baudrate = 9600
ser = serial.Serial(portName,baudrate)

### START QtApp #####
app = QtGui.QApplication([])            # you MUST do this once (initialize things)
####################

win = pg.GraphicsWindow(title="Signal from serial port") # creates a window
p = win.addPlot(title="Realtime plot")  # creates empty space for the plot in the window
curve = p.plot()                        # create an empty "plot" (a curve to plot)

windowWidth = 500                       # width of the window displaying the curve
Xm = linspace(0,0,windowWidth)          # create array that will contain the relevant time series     
ptr = -windowWidth                      # set first x position

# Realtime data plot. Each time this function is called, the data display is updated
def update():
    global curve, ptr, Xm    
    Xm[:-1] = Xm[1:]                      # shift data in the temporal mean 1 sample left
    value = ser.readline()                # read line (single value) from the serial port
    Xm[-1] = float(value)                 # vector containing the instantaneous values      
    ptr += 1                              # update x position for displaying the curve
    curve.setData(Xm)                     # set the curve with this data
    curve.setPos(ptr,0)                   # set x position in the graph to 0
    QtGui.QApplication.processEvents()    # you MUST process the plot now

### MAIN PROGRAM #####    
# this is a brutal infinite loop calling your realtime data plot
while True: update()

### END QtApp ####
pg.QtGui.QApplication.exec_() # you MUST put this at the end
##################