PyQT4, Python27 - Serial connection and global variables

Question

I think my issue is simple, but I have hit a brick wall. I am not a programmer but needed a program to control a laser engraver via Arduino. My Original code was mostly working, but I wanted the ability to select a serial port with a QComboBox so I can make it software available for everyone.

I figured out how to do that with the code below:

import sys
import serial
import time
import serial.tools.list_ports
from PyQt4 import QtGui
from window_test import Ui_MainWindow


class Main(QtGui.QMainWindow):
    def __init__(self):
        QtGui.QMainWindow.__init__(self)
        self.ui = Ui_MainWindow()
        self.ui.setupUi(self)
        self.ui.btn_laser_poweron.clicked.connect(self.btnFIRE)
        self.ui.btn_laser_poweroff.clicked.connect(self.btnOFF)
        self.ui.btn_lig_power.clicked.connect(self.btnLIG)
        self.ui.btn_cutting_power.clicked.connect(self.btnCUT)
        self.ui.btn_power_meter.clicked.connect(self.btnTEST)
        self.ui.spinBox.valueChanged.connect(self.PwrLevel)
        self.ui.comboBox.activated.connect(self.srlprt)


    def srlprt(self):
        serial.Serial(str(self.ui.comboBox.currentText()))
    def btnFIRE(self):
        ser.write("a" + chr(255))
    def btnOFF(self):
        ser.write("b" + chr(0))
    def btnTEST(self):
        ser.write("c" + chr(0))
        time.sleep(59.5)
        ser.write("d" + chr(255))
    def btnLIG(self):
        ser.write("e" + chr(29))
    def btnCUT(self):
        ser.write("f" + chr(160))
    def PwrLevel(self):
        val = self.ui.spinBox.value()
        ser.write("g" + chr(val))



if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    window = Main()
    window.show()
    sys.exit(app.exec_())

Now my problem is that none of my buttons work because "ser" is not globally defined. I understand that I broke that when I removed "ser = serial.Serial(port=COM3)" when it was above the class definition, but I don't know how to fix it. Any help would be greatly appreciated.

Cheers!

Answer 1

A simple solution would be to just set ser as attribute of your Main instance. Also it couldn't hurt to close the serial connection if it is open before opening a new one, e.g:

import sys
import serial
import time
import serial.tools.list_ports
from PyQt4 import QtGui
from window_test import Ui_MainWindow


class Main(QtGui.QMainWindow):
    def __init__(self):
        QtGui.QMainWindow.__init__(self)
        self.ser = None
        self.ui = Ui_MainWindow()
        self.ui.setupUi(self)
        self.ui.btn_laser_poweron.clicked.connect(self.btnFIRE)
        self.ui.btn_laser_poweroff.clicked.connect(self.btnOFF)
        self.ui.btn_lig_power.clicked.connect(self.btnLIG)
        self.ui.btn_cutting_power.clicked.connect(self.btnCUT)
        self.ui.btn_power_meter.clicked.connect(self.btnTEST)
        self.ui.spinBox.valueChanged.connect(self.PwrLevel)
        self.ui.comboBox.activated.connect(self.srlprt)


    def srlprt(self):
        if self.ser:
            self.ser.close()
        self.ser = serial.Serial(str(self.ui.comboBox.currentText()))
    def btnFIRE(self):
        self.ser.write("a" + chr(255))
    def btnOFF(self):
        self.ser.write("b" + chr(0))
    def btnTEST(self):
        self.ser.write("c" + chr(0))
        time.sleep(59.5)
        self.ser.write("d" + chr(255))
    def btnLIG(self):
        self.ser.write("e" + chr(29))
    def btnCUT(self):
        self.ser.write("f" + chr(160))
    def PwrLevel(self):
        val = self.ui.spinBox.value()
        self.ser.write("g" + chr(val))



if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    window = Main()
    window.show()
    sys.exit(app.exec_())