Controlling a serial device with Python

This program to sends a command to serial device, receives data from the device, converts it to numeric format, and graphs the data in real time. It is written in Python using wxPython for the display.

The device is connected to /dev/ttyS0 with a baud rate of 19200, 8-bit data, no parity, and 1 stopbit. You need to edit the line 'serial.Serial' with the relevant parameters to use this code for your device. Editing 'DATA_LENGTH' will change the rate at which the graph scrolls forward. Also, you'd need to change the 'command' that the device understands as 'send me data' (here it is the s character - line 'input'). Knowledge of the format of the returned data is also essential (here I turn ascii into 2 integers) line 'struct.unpack' - see here for help). Otherwise this should work with any device. Tested on Ubuntu 9.10 and 10.4 using serial port and USB-serial converters.

	import os
	import pprint
	import sys
	import wx
	# use wx with mpl is with the WXAgg backend
	import matplotlib
	matplotlib.use('WXAgg')
	from matplotlib.figure import Figure
	from matplotlib.backends.backend_wxagg import FigureCanvasWxAgg as FigCanvas, NavigationToolbar2WxAgg as NavigationToolbar
	import numpy as npy
	import pylab
	import serial
	import time
	import struct
	# set connection:
	ser = serial.Serial('/dev/ttyUSB0', 19200, bytesize=serial.EIGHTBITS, parity=serial.PARITY_NONE, stopbits=1, timeout=0.1, xonxoff=1, rtscts=0)
	ser.open() # open connection
	ser.isOpen() # should be true
	DATA_LENGTH = 120 #seconds
	REDRAW_TIMER_MS = 60 # milliseconds
	def getData():
	input = 's'
	# send 's' the character to the device
	ser.write(input)
	out = ''
	# give device time to answer
	time.sleep(0.02)
	while ser.inWaiting() > 0:
	out += ser.read(1) #request data (serial.read() only returns 8 bit ASCII strings)
	#out += ser.read(ser.inWaiting())
	if out != '':
	# read in a length-2 string of 8-bit characters and then use the struct module to convert the strings into integers
	response=struct.unpack(">bb", out)
	# use only first integer in tuple (2nd is empty)
	print response[0]
	return response[0]
	class GraphFrame(wx.Frame):
	# the main frame of the application
	def __init__(slf):
	wx.Frame.__init__(slf, None, -1, "Sensor response", size=(800,600))
	slf.Centre()
	slf.data = []
	slf.create_main_panel()
	slf.redraw_timer = wx.Timer(slf)
	slf.Bind(wx.EVT_TIMER, slf.on_redraw_timer, slf.redraw_timer)
	slf.redraw_timer.Start(REDRAW_TIMER_MS)
	def create_main_panel(slf):
	slf.panel = wx.Panel(slf)
	slf.init_plot()
	slf.canvas = FigCanvas(slf.panel, -1, slf.fig)
	slf.hbox1 = wx.BoxSizer(wx.HORIZONTAL)
	slf.vbox = wx.BoxSizer(wx.VERTICAL)
	slf.vbox.Add(slf.canvas, 1, flag=wx.LEFT | wx.TOP | wx.GROW)
	slf.panel.SetSizer(slf.vbox)
	def init_plot(slf):
	slf.dpi = 100
	slf.fig = Figure((3.0, 3.0), dpi=slf.dpi)
	slf.axes = slf.fig.add_subplot(111)
	slf.axes.set_axis_bgcolor('black')
	slf.axes.set_title('My data', size=12)
	slf.ymin = -50000 # initalise with large values
	slf.ymax = 50000
	pylab.setp(slf.axes.get_xticklabels(), fontsize=8)
	pylab.setp(slf.axes.get_yticklabels(), fontsize=8)
	# plot the data as a line series, and save the reference
	# to the plotted line series
	slf.plot_data = slf.axes.plot(
	slf.data,
	linewidth=2,
	color="white",
	)[0]
	#count=count+1
	#if count>120:
	# slf.Destroy()
	def draw_plot(slf):
	# redraws the plot
	xmax = len(slf.data) if len(slf.data) > DATA_LENGTH else DATA_LENGTH
	xmin = xmax - DATA_LENGTH
	ymin = slf.ymin # ymin and ymax set based on previous entries
	ymax = slf.ymax #50000
	slf.axes.set_xbound(lower=xmin, upper=xmax)
	slf.axes.set_ybound(lower=ymin, upper=ymax)
	pylab.setp(slf.axes.get_xticklabels(), visible=True)
	slf.plot_data.set_xdata(npy.arange(len(slf.data)))
	slf.plot_data.set_ydata(npy.array(slf.data))
	slf.canvas.draw()
	def on_redraw_timer(slf, event):
	newData = getData()
	slf.data.append(newData)
	slf.draw_plot()
	data=slf.data
	if len(data)>=6:
	# get last 5 values
	datanew=[data[len(slf.data)-5],data[len(slf.data)-4],data[len(slf.data)-3],data[len(slf.data)-2],data[len(slf.data)-1]]
	slf.ymin = (min(datanew))-(min(datanew)*10)/100 # min of last 5, minus 10%
	slf.ymax = (max(datanew))+(max(datanew)*10)/100 # max of last 5, plus 10%
	else:
	slf.ymin = (min(data))-(min(data)*10)/100 # min minus 10%
	slf.ymax = (max(data))+(max(data)*10)/100 # max plus 10%
	def on_exit(slf, event):
	slf.Destroy()
	def flash_status_message(slf, msg, flash_len_ms=1500):
	slf.statusbar.SetStatusText(msg)
	slf.timeroff = wx.Timer(slf)
	slf.Bind(
	wx.EVT_TIMER,
	slf.on_flash_status_off,
	slf.timeroff)
	slf.timeroff.Start(flash_len_ms, oneShot=True)
	def on_flash_status_off(slf, event):
	slf.statusbar.SetStatusText('')
	if __name__ == '__main__':
	app = wx.PySimpleApp()
	app.frame = GraphFrame()
	app.frame.Show()
	app.MainLoop()

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