diff --git a/arduino_timetable/gui.py b/arduino_timetable/gui.py
new file mode 100644
index 0000000..4cc5abf
--- /dev/null
+++ b/arduino_timetable/gui.py
@@ -0,0 +1,403 @@
+''' A Tkinter Gui Application for running scheduled commands '''
+
+# library imports
+import asyncio
+import os
+import serial
+import tkinter as tk
+import tkinter.ttk as ttk
+
+from enum import Enum
+from datetime import timedelta
+from multiprocessing import Process, Lock
+from tkinter import filedialog
+from tkinter import messagebox
+
+# local imports
+from .timetable import parse_excel_file, find_arduino_port
+
+# delay for checking if commands are running on the Arduino
+CHECK_DELAY = 100
+# delay after connecting to the arduino before a programm can be run
+CONNECT_DELAY = 2500
+
+
+class ArduinoState(Enum):
+    ''' State of the current Arduino setup '''
+    not_initialized = 'not_initialized'
+    connected = 'connected'
+    running = 'running'
+    finished = 'finished'
+
+
+def arduino_subprocess(lock, com_port, scheduled_commands, **kwargs):
+    ''' connecting to the Arduiono and running the scheduled commands
+
+    lock:
+        Separaion controll between establishing connection and running
+        commands. Must be of class multiprocessing.Lock
+    com_port:
+        port where the Arduino is connected
+    scheduled_commands:
+        list of .timetable.TimedCommands to run
+    **kwargs:
+        arguments used to open serial connection
+        the most importent one is 'baudrate', defaults to 9600
+
+    To run the scheduled commands a separate process is used. Otherwise the
+    execution of the gui would stop until the commands finish. This would
+    lead to an unresponsive gui programm.
+
+    The serial connection is not pickable and therfore the connection to the
+    arduino and running the commands must be made in the same process. To
+    have a separation between establishing the connection and running the
+    commands, a simple lock is used. Before starting the subprocess, the lock
+    will be acquired by the main programm and releasing the lock will start
+    the commands.
+    '''
+    # get a custom baudrate or use the default 9600
+    baudrate = kwargs.pop('baudrate', 9600)
+    with serial.Serial(com_port, baudrate=baudrate, **kwargs) as connection:
+        # use a fresh asyncio event loop every time
+        loop = asyncio.new_event_loop()
+        # wait until the lock is released to start the commands
+        lock.acquire()
+        try:
+            # schedule the commands for execution
+            for scheduled_command in scheduled_commands:
+                loop.call_later(
+                    scheduled_command.delta.total_seconds(),
+                    connection.write,
+                    scheduled_command.cmd
+                    )
+            # loop should stop one second after last command in list
+            timed_loop_stop = scheduled_command.delta + timedelta(seconds=1)
+            loop.call_later(timed_loop_stop.total_seconds(), loop.stop)
+            # run the loop
+            try:
+                loop.run_forever()
+            except KeyboardInterrupt:
+                loop.stop()
+            loop.close()
+        finally:
+            lock.release()
+
+
+def timedelta_as_str(timedelta):
+    ''' a nice string output for a timedelta
+
+    shamlessly copied from the original timedelta implementation, but the
+    original implementation displays the microseconds always with six
+    characters.
+    '''
+    mm, ss = divmod(timedelta.seconds, 60)
+    hh, mm = divmod(mm, 60)
+    s = "%d:%02d:%02d" % (hh, mm, ss)
+    if timedelta.days:
+        def plural(n):
+            return n, abs(n) != 1 and "s" or ""
+        s = ("%d day%s, " % plural(timedelta.days)) + s
+
+    # microseconds are stored as int between 0 and 999999 inclusive
+    s = s + ".%d" % (timedelta.microseconds / 10**5)
+
+    return s
+
+
+class FilePanel(tk.Frame):
+    ''' Tkinter Panel for selecting files '''
+
+    def __init__(self, parent):
+        tk.Frame.__init__(self, parent.master)
+        self._parent = parent
+        self.btn_files = tk.Button(
+            self,
+            text="Select Excel File",
+            command=self._parent.select_files
+            )
+        self.btn_files.pack(pady=5, padx=5)
+        sep = ttk.Separator(self, orient=tk.HORIZONTAL)
+        sep.pack(side=tk.BOTTOM, fill=tk.X)
+        self.pack(side=tk.TOP, fill=tk.X)
+
+
+class ParsedCommandsPanel(tk.Frame):
+    ''' Tkinter Panel displaying the scheduled commands to be run '''
+
+    def __init__(self, parent):
+        tk.Frame.__init__(self, parent.master)
+        self._parent = parent
+        self.label = tk.Label(self)
+        self.label.pack(fill=tk.X, pady=5, padx=5)
+        self.messages = tk.Message(self, text='', font=("Courier", 8))
+        self.messages.pack(fill=tk.X, pady=5, padx=5)
+        self.pack(side=tk.TOP, fill=tk.X)
+
+    def set_schedule_text(self, text):
+        ''' display the scheuled commands to run '''
+        self.messages.config(text=text)
+        self.messages.update_idletasks()
+
+    def set_label_text(self, text):
+        ''' display the filename of the scheduled commands '''
+        self.label.config(text=text)
+        self.label.update_idletasks()
+
+    def clear_text(self):
+        ''' clear all text in this panel '''
+        self.set_schedule_text('')
+        self.set_label_text('')
+
+    def show_schedule(self, command_list):
+        ''' transformes the command list to a textual representation '''
+        times = [timedelta_as_str(cmd.delta) for cmd in command_list]
+        commands = [cmd.command for cmd in command_list]
+        # search for the longest time text
+        max_len_limes = max(len(time_str) for time_str in times)
+        # template for each command line
+        template = '{delta:<{size}}   {cmd}'
+        # assemble all lines
+        lines = [
+            template.format(delta=delta, size=max_len_limes, cmd=cmd)
+            for delta,cmd
+            in zip(times, commands)
+            ]
+        # return the text for the command list
+        self.set_schedule_text('\n'.join(lines))
+
+
+class ActionPanel(tk.Frame):
+    ''' Tkinter Panel for the action buttons '''
+
+    def __init__(self, parent):
+        tk.Frame.__init__(self, parent.master)
+        self._parent = parent
+        # different configurations for the 'run' button
+        self.btn_config_disabled = {
+            'text': 'Run Commands',
+            'background': 'SystemButtonFace',
+            'activebackground': 'SystemButtonFace',
+            'state': 'disabled'
+            }
+        self.btn_config_wait = {
+            'text': 'Connecting',
+            'background': 'SystemButtonFace',
+            'activebackground': 'SystemButtonFace',
+            'state': 'disabled'
+            }
+        self.btn_config_ready = {
+            'text': 'Run Comands',
+            'background': 'green',
+            'activebackground': 'green',
+            'state': 'normal'
+            }
+        self.btn_config_running = {
+            'text': 'Stop Comands',
+            'background': 'red',
+            'activebackground': 'red',
+            'state': 'active'
+            }
+        ttk.Separator(self, orient=tk.HORIZONTAL).pack(side=tk.TOP, fill=tk.X)
+        self.btn_go = tk.Button(
+            self,
+            command=self._parent.go_button_clicked,
+            **self.btn_config_disabled
+            )
+        self.btn_go.pack(side=tk.LEFT, pady=5, padx=5)
+        self.btn_quit = tk.Button(self, text="Quit", command=self._parent.quit)
+        self.btn_quit.pack(side=tk.RIGHT, pady=5, padx=5)
+        self.pack(side=tk.BOTTOM, fill=tk.X)
+
+    def update_button_state(self):
+        ''' update the button state reflecting the state of the Arduino '''
+        if self._parent.arduino_state == ArduinoState.running:
+            self.btn_go.config(**self.btn_config_running)
+        elif self._parent.arduino_state == ArduinoState.not_initialized:
+            self.btn_go.config(**self.btn_config_disabled)
+        else:
+            # establishing the connection takes some time, show a 'connecting'
+            # state and after some time show the 'ready' state
+            self.btn_go.config(**self.btn_config_wait)
+            self.after(CONNECT_DELAY, self._enable_button)
+        self.btn_go.update_idletasks()
+
+    def _enable_button(self):
+        ''' shows the 'ready' state of the button '''
+        self.btn_go.config(**self.btn_config_ready)
+        self.btn_go.update_idletasks()
+
+
+class Application(tk.Frame):
+    ''' The Tkinter application containing the buisiness logic '''
+
+    def __init__(self, master, available_commands):
+        ''' initialization
+
+        master:
+            tkinter root object
+
+        available_commands:
+            list of available commands for the Arduino
+        '''
+        master.minsize(height=330, width=300)
+        tk.Frame.__init__(self, master)
+        self._master = master
+        self.pack(fill=tk.BOTH)
+
+        # the layout sections
+        self.file_panel = FilePanel(self)
+        self.program_panel = ParsedCommandsPanel(self)
+        self.action_panel = ActionPanel(self)
+
+        # properties for the buisiness logic
+        self.available_commands = available_commands
+        self.scheduled_commands = []
+        self.arduino_process = None
+        self.arduino_lock = None
+        self._arduino_state = ArduinoState.not_initialized
+        self.reset()
+
+    @property
+    def arduino_state(self):
+        ''' property for the current state of the arduino '''
+        return self._arduino_state
+
+    @arduino_state.setter
+    def arduino_state(self, new_state):
+        ''' setter for the arduino state property
+
+        as soon as the property changes, the 'go'-button will be updated
+        '''
+        self._arduino_state = new_state
+        self.action_panel.update_button_state()
+
+    def select_files(self):
+        ''' selecting a new excel file with scheduled_commands '''
+        # open the file selection dialog
+        opts = {
+            'initialdir': '~/',
+            'filetypes': [('Excel Files', '.xlsx')],
+            'multiple': False}
+        excel_file = tk.filedialog.askopenfilename(**opts)
+        # if no excel file is selected, do nothing
+        if not excel_file:
+            return
+        # reset the application
+        self.reset()
+        # try to parse the excel file
+        self.scheduled_commands = parse_excel_file(
+            excel_file,
+            self.available_commands
+            )
+        if self.scheduled_commands:
+            # if parsing resultet in a schedule, prepare everything to run
+            self.arduino_prepare_process()
+            self.program_panel.set_label_text(os.path.basename(excel_file))
+            self.program_panel.show_schedule(self.scheduled_commands)
+
+    def reset(self):
+        ''' reset the application state '''
+        # stop any connection to the Arduino
+        if self.arduino_state in (ArduinoState.running, ArduinoState.connected):
+            self.arduino_stop_process()
+        self.action_panel.update_button_state()
+        self.program_panel.clear_text()
+
+    def go_button_clicked(self):
+        ''' start scheduled commands or stop the execution '''
+        if self.arduino_state == ArduinoState.running:
+            # 'Stop Commands' clicked.
+            self.arduino_stop_process()
+            self.arduino_prepare_process()
+        else:
+            # 'Run Commands' clicked.
+            # the connection is already established, we just need to release
+            # the lock
+            self.arduino_lock.release()
+            self.arduino_state = ArduinoState.running
+        # regular check if the scheduled commands finished
+        self.after(CHECK_DELAY, self._check_process)
+
+    def _check_process(self):
+        ''' checks if the scheduled commands have already finished '''
+        if self.arduino_process:
+            if self.arduino_process.is_alive():
+                # still running, recheck after a short delay
+                self.after(CHECK_DELAY, self._check_process)
+            else:
+                # commands finished
+                self.arduino_stop_process()
+                self.arduino_prepare_process()
+
+    def arduino_stop_process(self):
+        ''' stops a connected Arduino '''
+        if self.arduino_state != ArduinoState.not_initialized:
+            # only do this if a connection was established
+            loop = asyncio.get_event_loop()
+            loop.stop()
+            loop.close()
+            self.arduino_process.terminate()
+            self.arduino_process = None
+            self.arduino_lock = None
+            self.arduino_state = ArduinoState.not_initialized
+
+    def arduino_prepare_process(self):
+        ''' open a subprocess setting up the arduino '''
+        # find the com port of the Arduino
+        try:
+            com_port = find_arduino_port()
+        except IOError as e:
+            messagebox.showerror('COM Port', 'No Arduino found')
+            return
+        except serial.SerialException:
+            messagebox.showerror('COM Port', 'Could not talk to Arduino')
+            return
+        # Create a lock and acquire it. This will put the subprocess on hold
+        # after establishing the connection. As soon as the lock is released,
+        # the scheduled commands will be run
+        self.arduino_lock = Lock()
+        self.arduino_lock.acquire()
+        # start the subprocess for the Arduino connection
+        self.arduino_process = Process(
+            target=arduino_subprocess,
+            args = (
+                self.arduino_lock,
+                com_port,
+                self.scheduled_commands
+                )
+            )
+        self.arduino_process.start()
+        self.arduino_state = ArduinoState.connected
+
+    def quit(self):
+        ''' stop the programm '''
+        self.arduino_stop_process()
+        self._master.destroy()
+
+
+def run_application(available_commands, title='Arduino Scheduled Commands'):
+    ''' run the gui application
+
+    available_commands:
+        list of available commands for the Arduino
+
+    title:
+        window title bar text
+    '''
+
+    # create the Tkinter root and instantiate the application
+    root = tk.Tk()
+    root.wm_title(title)
+    app = Application(master=root, available_commands=available_commands)
+
+    # use app.quit() as callback if the window is closed (with the 'X' button)
+    # if an Arduino connection is established, the standard callback does not
+    # stop the subprocess and therfore the application would not quit
+    root.protocol("WM_DELETE_WINDOW", app.quit)
+
+    # start the application
+    app.mainloop()
+    try:
+        root.destroy()
+    except tk.TclError:
+        pass