exampleQT.py

from PyQt4 import QtCore, QtGui
from mainui import MainUI
import time 
from hardware_controller import Hardware_Controller

class Worker(QtCore.QThread):

    update_text_signal = QtCore.pyqtSignal(str) #have to pass the type str
    
    def __init__(self, hdwr_ctrl, update_rate):

        QtCore.QThread.__init__(self)
        self.hdwr_ctrl = hdwr_ctrl
        self.update_rate = update_rate
        self.running = True 
        self.controller_num = 1

    def run(self):

        while(self.running):

            text = self.hdwr_ctrl.get_important_text(self.controller_num)
            update_text_signal.emit(text)
            time.sleep(self.update_rate)

    @QtCore.pyqtSlot(int)
    def change_controller_num(self,i):
        """
        Change the controller number from the spin box in the UI.
        """
        self.controller_num = i



class MainWindow(QtGui.QMainWindow):

    def __init__(self, parent=None):

        QtGui.QMainWindow.__init__(self,parent)
        self.ui = MainUI # contains a bunch of widget definitions we don't care about
        self.ui.setUpUi(self) 
        self.__connect()

    def __connect(self):

        self.hdwr_ctrl = Hardware_Controller()

        self.worker = Worker(self.hdwr_ctrl,1)

        self.worker.update_text_signal.connect(self.update_text)

        QtCore.QObject.connect(self.ui.spinbox, QtCore.SINGAL("valueChanged(int)"), self.worker.change_controller_num)
        self.worker.start()

        # so we can close the program
        self.connect(self, QtCore.SIGNAL('triggered()'), self.closeEvent)

    def update_text(self, text):
        """
        Callback for the worker.update_text_signal pyqtSignal
        """
        self.ui.textBox.setText(text)

    def closeEvent(self):
        """
        Safely shut down worker threads.
        """
        self.worker.running = False 
        self.worker.quit()
        self.worker.wait()



if __name__ == '__main__':
    
    app = QtGui.QApplication(sys.argv)
    GUI = MainWindow()
    GUI.show()
    sys.exit(app_exec_())    

Thanks to Paul for syntax correction in the closeEvent method.