import sys
import serial


from PyQt5.QtWidgets import QMainWindow, QApplication
from PyQt5.QtCore import QThread, pyqtSignal
from PyQt5.uic import loadUi


ser = serial.Serial('/dev/tty.usbmodem14201', 9600, timeout=1)

class TestThread(QThread):
    serialUpdate = pyqtSignal(str)
    def run(self):
        while ser.is_open:
            QThread.sleep(1)
            value = ser.readline().decode('ascii')
            self.serialUpdate.emit(value)
            ser.flush()

class MainWindow(QMainWindow):
    def __init__(self):
        super(MainWindow, self).__init__()
        loadUi('/Users/bogdanvesa/P2A_GUI/mainwindow.ui', self)
        self.thread = TestThread(self)
        self.thread.serialUpdate.connect(self.handleSerialUpdate)

        self.connect_btn.clicked.connect(self.connectSer)
        self.lcd_EBtn.clicked.connect(self.startThread)

    def startThread(self):
        self.thread.start()

    def handleSerialUpdate(self, value):
        print(value)
        self.lcd_lineEdit.setText(value)


def main():

    app = QApplication(sys.argv)
    form = MainWindow()
    form.show()
    sys.exit(app.exec_())

if __name__ == "__main__":
    main()

from PyQt5 import QtCore, QtWidgets, QtSerialPort

class Widget(QtWidgets.QWidget):
    def __init__(self, parent=None):
        super(Widget, self).__init__(parent)
        self.message_le = QtWidgets.QLineEdit()
        self.send_btn = QtWidgets.QPushButton(
            text="Send",
            clicked=self.send
        )
        self.output_te = QtWidgets.QTextEdit(readOnly=True)
        self.button = QtWidgets.QPushButton(
            text="Connect",
            checkable=True,
            toggled=self.on_toggled
        )
        lay = QtWidgets.QVBoxLayout(self)
        hlay = QtWidgets.QHBoxLayout()
        hlay.addWidget(self.message_le)
        hlay.addWidget(self.send_btn)
        lay.addLayout(hlay)
        lay.addWidget(self.output_te)
        lay.addWidget(self.button)

        self.serial = QtSerialPort.QSerialPort(
            '/dev/tty.usbmodem14201',
            baudRate=QtSerialPort.QSerialPort.Baud9600,
            readyRead=self.receive
        )

    @QtCore.pyqtSlot()
    def receive(self):
        while self.serial.canReadLine():
            text = self.serial.readLine().data().decode()
            text = text.rstrip('rn')
            self.output_te.append(text)

    @QtCore.pyqtSlot()
    def send(self):
        self.serial.write(self.message_le.text().encode())

    @QtCore.pyqtSlot(bool)
    def on_toggled(self, checked):
        self.button.setText("Disconnect" if checked else "Connect")
        if checked:
            if not self.serial.isOpen():
                if not self.serial.open(QtCore.QIODevice.ReadWrite):
                    self.button.setChecked(False)
        else:
            self.serial.close()

if __name__ == '__main__':
    import sys
    app = QtWidgets.QApplication(sys.argv)
    w = Widget()
    w.show()
    sys.exit(app.exec_())