serial_sample.py

import serial


def main():
    ser: serial.Serial
    with serial.Serial() as ser:
        ser.baudrate = 4800
        ser.port = '/dev/ttyUSB0'
        ser.open()
        sent = False
        while ser.isOpen():
            try:
                x = ser.readline()
                s = x.decode('utf8')
                print(s)

                if s.startswith('$WAIT'):
                    continue

                if not sent:
                    print("SENDING START COMMAND")
                    ser.write(b'$START\r\n')
                    sent = True

            except Exception as e:
                ser.write(b'$RESET\r\n')
                print(e)
                pass


if __name__ == '__main__':
    main()