Unable to get arduino serial communication working in wxpython GUI - user-interface

Question

This is the definition which is used to update the labels in the GUI:
def updateV(self, event):
""""""
global v
ser = serial.Serial( port='COM3', baudrate=9600)
x = ser.read() # read one byte
ser.close()
print x
if v>3:
self.labelOne.SetBackgroundColour('red')
self.labelOne.SetLabel('Battery Voltage : ' + x)
else:
self.labelOne.SetBackgroundColour('white')
self.labelOne.SetLabel('Battery Voltage : ' + str(v))
self.Refresh()
This is the simple arduino code i have been using:
int a;
void setup() {
Serial.begin(9600);// put your setup code here, to run once:
}
void loop() {
a=5;
Serial.println(a);
delay(10);
}
I have been using this definition to update my labels for my GUI. I recently started to set up serial communication on my GUI using that code. Logically using the mainloop() of the wx library, i thought i could update the 'x' value and get it printed on the GUI. But all the GUI window shows in 0.0 even though the python console prints 5 regularly. Please help! I am pretty new to this.

Answer 1

Your issue is that ser.read() will block. Even if you tweak the timeout of your serial.Serial instance, it still will keep the GUI busy. In that situation I do not know a method to "force" a refresh/wx.Yield(), it simply will not work. The standard solution for blocking calls is to spin up a thread
or poll regularily (e. g. with wx.Timer). However, I was only able to make threading work. The example is based on wxTerminal in pyserial.
# -*- coding: utf-8 -*-
import wx
import serial
from threading import Thread
ARDUINO_NEWLINE = '\r\n'
class serial_reader(object):
def __init__(self, callback=None):
"""Creates serial reader.
:param callback: callable, gets called when byte on serial arrives.
"""
self.callback = callback
self.thread = None
# Signal if serial is alive and should be read
self.alive = False
def start_reader(self, serial_cfg):
"""Start the receiver thread.
:param serial_cfg: dictionary, gets unpacked to parameters for :class:`serial.Serial`
"""
self.ser_cfg = serial_cfg
self.serial = serial.Serial(**serial_cfg)
# set != None so it will not block for longer than timeout on shutdown
self.serial.timeout = 0.1
self.alive = True
self.thread = Thread(target=self.serial_read)
self.thread.daemon = True
self.thread.start()
def stop_reader(self):
"""Stop the receiver thread, wait util it is finished."""
if self.thread is not None:
# signal no more reads
self.alive = False
# wait until thread has finished
self.thread.join()
self.thread = None
# cleanup
self.serial.close()
def serial_read(self):
"""Thread that handles the incoming traffic."""
while self.alive:
try:
text = self.serial.read()
if text and self.callback:
# return value to main loop in thread-safe manner
wx.CallAfter(self.callback, text)
except serial.serialutil.SerialException:
# will happen when Windows goes in sleep mode
print 'serial.serialutil.SerialException'
class ser_frm(wx.Frame):
def __init__(self, *args, **kwds):
wx.Frame.__init__(self, *args, **kwds)
self.txt = wx.TextCtrl(self, -1, '', style=wx.TE_MULTILINE)
class serial_controller(object):
def __init__(self, app):
self.app = app
# buffer for serial data
self.ser_buf = ''
self.frm = ser_frm(None, -1, 'testfrm')
# setup serial configuration
self.serial_cfg = {'port': 'COM4', 'baudrate': 9600}
# When parameter dsrdtr is set to True, the Arduino
# will not reset on serial open, for details see
# http://playground.arduino.cc/Main/DisablingAutoResetOnSerialConnection
self.serial_cfg['dsrdtr'] = True
self.ser_rd = serial_reader(callback=self.on_serial)
tit = 'Arduino on port {port} at baudrate {baudrate}'.format(**self.serial_cfg)
self.frm.SetTitle(tit)
self.ser_rd.start_reader(self.serial_cfg)
self.frm.Show()
self.frm.Bind(wx.EVT_CLOSE, self.on_close)
def on_close(self, evt):
"""Shutdown serial read thread before closing."""
if self.ser_rd.alive:
self.ser_rd.stop_reader()
evt.Skip()
def on_serial(self, text):
"""Handle input from the serial port."""
self.ser_buf += text
if self.ser_buf.endswith(ARDUINO_NEWLINE):
if self.frm.txt.GetInsertionPoint() > 1000:
self.frm.txt.SetValue('')
self.frm.txt.AppendText(self.ser_buf)
self.ser_buf = ''
if __name__ == "__main__":
app = wx.App(redirect=False)
serialctr = serial_controller(app)
app.MainLoop()
EDIT: It is not necessary to tinker with DSR/DTR on Arduinos with USB on chip (e.g. the Arduino micro), so delete the line
self.serial_cfg['dsrdtr'] = True
and it will still work properly.