ComPlotter – a graphical serial port data logger

I’m working on a simple data logger application called ComPlotter that opens a serial port and reads an incoming plain text data stream, plotting one or more signals in realtime in a scrolling window. The incoming data is assumed to be in plain text with the same number of integers (currently assumed to be three) on each line, separated by spaces. The incoming text is printed in a log window and the data values from each line are parsed and plotted in the graph area.

ComPlotter is still very much a work in progress, but it’s starting to come together and I have a reasonable looking screenshot, so I thought I’d post a little bit about it. Here’s the screenshot of the application as it currently looks. The signals displayed in the plot in this screenshot are from a simple accelerometer circuit that I had connected to my PC. The three signals visible in the plot are the x, y and z axes of the accelerometer.

ComPlotter tries serial port numbers in descending order, starting with COM30. The idea of this is that a USB-to-serial adapter may be assigned a different COM port number each time it is plugged into the PC, but it is likely to have the highest numbered port each time. In my experience, this is a pretty reliable way of accessing the type of USB-to-serial adapter that I usually use to connect my dsPIC microcontroller circuits to my PC.

ComPlotter is written in Python using the wxPython GUI toolkit. Here’s the complete source code (all 130 lines of it).

#
# ComPlotter.py - wxPython data logger GUI
#
# Written by Ted Burke
# Last updated 11-5-2012
#

import serial

import wx
import numpy
import matplotlib
matplotlib.use('WXAgg')
from matplotlib.backends.backend_wxagg import FigureCanvasWxAgg
from matplotlib.figure import Figure
import matplotlib.pyplot as plt

class DataLoggerWindow(wx.Frame):
	def __init__(self):
		wx.Frame.__init__(self, None, -1, "ComPlotter", (100,100), (640,480))

		self.SetBackgroundColour('#ece9d8')

		# Flag variables
		self.isLogging = False

		# Create data buffers
		self.N = 100
		self.n = range(self.N)
		self.M = 3
		self.x = []
		for m in range(self.M):
			self.x.append(0 * numpy.ones(self.N, numpy.int))

		# Create plot area and axes
		self.fig = Figure(facecolor='#ece9d8')
		self.canvas = FigureCanvasWxAgg(self, -1, self.fig)
		self.canvas.SetPosition((0,0))
		self.canvas.SetSize((640,320))
		self.ax = self.fig.add_axes([0.08,0.1,0.86,0.8])
		self.ax.autoscale(False)
		self.ax.set_xlim(0, 99)
		self.ax.set_ylim(-100, 1100)
		for m in range(self.M):
			self.ax.plot(self.n,self.x[m])

		# Create text box for event logging
		self.log_text = wx.TextCtrl(
			self, -1, pos=(140,320), size=(465,100),
			style=wx.TE_MULTILINE)
		self.log_text.SetFont(
			wx.Font(12, wx.DEFAULT, wx.NORMAL, wx.NORMAL, False))

		# Create timer to read incoming data and scroll plot
		self.timer = wx.Timer(self)
		self.Bind(wx.EVT_TIMER, self.GetSample, self.timer)

		# Create start/stop button
		self.start_stop_button = wx.Button(
			self, label="Start", pos=(25,320), size=(100,100))
		self.start_stop_button.SetFont(
			wx.Font(14, wx.DEFAULT, wx.NORMAL, wx.NORMAL, False))
		self.start_stop_button.Bind(
			wx.EVT_BUTTON, self.onStartStopButton)

	def GetSample(self, event=None):
		# Get a line of text from the serial port
		sample_string = self.ser.readline()

		# Add the line to the log text box
		self.log_text.AppendText(sample_string)

		# If the line is the right length, parse it
		if len(sample_string) == 15:
			sample_string = sample_string[0:-1]
			sample_values = sample_string.split()

			for m in range(self.M):
				# get one value from sample
				value = int(sample_values[m])
				self.x[m][0:99] = self.x[m][1:]
				self.x[m][99] = value

			# Update plot
			self.ax.cla()
			self.ax.autoscale(False)
			self.ax.set_xlim(0, self.N - 1)
			self.ax.set_ylim(-100, 1100)
			for m in range(self.M):
				self.ax.plot(self.n, self.x[m])
			self.canvas.draw()

	def onStartStopButton(self, event):
		if not self.isLogging:
			self.isLogging = True
			self.ser = serial.Serial()
			self.ser.baudrate = 38400
			self.ser.timeout=0.25
			# Try serial ports one by one starting
			# with COM30 and working downwards
			for m in range(29, 0, -1):
				self.ser.port = m
				try:
					# Try this port number
					self.ser.open()
					# We only get to here if port opened
					self.log_text.AppendText(
						'Opened COM' + str(m+1) + '...\n')
					break
				except:
					# We end up here if this port number
					# failed to open
					pass
			if self.ser.isOpen():
				# We successfully opened a port, so start
				# a timer to read incoming data
				self.timer.Start(100)
				self.start_stop_button.SetLabel("Stop")
		else:
			self.timer.Stop()
			self.ser.close()
			self.isLogging = False
			self.start_stop_button.SetLabel("Start")

if __name__ == '__main__':
	app = wx.PySimpleApp()
	window = DataLoggerWindow()

	window.Show()
	app.MainLoop()

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