[Python] Python to Arduino serial communication

I'm making an interface in Tkinter where you have several options and a send button. When you click the send button it sends a value over serial connection to an Arduino Mega who puts a pin low/high and connects through optocouplers to an external device.

When I send my commands via the serial monitor to my Arduino everything is working flawless. When I try to send the commands via my Python app I see the led blinking that my Arduino receives something but nothing happens.

I've installed an LCD, when I send stuff from the serial line I see it on the screen. When it comes from Python I only see "Wachten op data".

I think the problem will have to do with some kind of carriage return character but I've tried everything I could.

Thanks!

PS: the lcd is not important, it's just to debug at the moment.

Arduino Code

#include <Arduino.h>
#include <LiquidCrystal.h>

const int ledPin = 12;

// LCD-instellingen: (RS, E, D4, D5, D6, D7)
LiquidCrystal lcd(7, 6, 5, 4, 3, 2);

void setup() {
Serial.begin(9600);
pinMode(ledPin, OUTPUT);

lcd.begin(16, 2); // 16 kolommen, 2 rijen
lcd.print("Wachten op data...");
}

void loop() {
if (Serial.available() > 0) {
delay(100); // Wacht kort om data volledig binnen te krijgen
String command = Serial.readString();
command.trim(); // Verwijder spaties en nieuwe regels

if (command.length() > 0) {
// Laat ontvangen bericht zien op het LCD
lcd.clear();
lcd.setCursor(0, 0);
lcd.print("Ontvangen:");
lcd.setCursor(0, 1);
lcd.print(command);

// Debug output naar seriële monitor
Serial.print("Ontvangen: [");
Serial.print(command);
Serial.println("]");

// Controleer op "1" of "2" voor LED aan/uit
if (command == "1") {
digitalWrite(ledPin, HIGH);
Serial.print("LED Aan");
} else if (command == "2") {
digitalWrite(ledPin, LOW);
Serial.print("LED Uit");
}

// Controleer op "Aanwezig" en "Uitgeschakeld"
if (command.indexOf("Aanwezig") != -1) {
digitalWrite(ledPin, HIGH);
Serial.println("LED Aanwezig AAN");
}
else if (command.indexOf("Uitgeschakeld") != -1) {
digitalWrite(ledPin, LOW);
Serial.println("LED Uitgeschakeld UIT");
}
}
}
}


Code Python

import tkinter as tk
import serial
import serial.tools.list_ports
from tkinter import messagebox

class ParameterRow(tk.Frame):
def __init__(self, master, label_text, options, default_value, send_function):
super().__init__(master)
self.label = tk.Label(self, text=label_text, anchor="w")
self.label.grid(row=0, column=0, sticky="w")
self.var = tk.StringVar(value=default_value)
self.radio_buttons = []
for i, option in enumerate(options):
rb = tk.Radiobutton(self, text=option, variable=self.var, value=option)
rb.grid(row=0, column=i + 1, sticky="w")
self.send_button = tk.Button(self, text="Verzenden", command=send_function)
self.send_button.grid(row=0, column=len(options) + 1, sticky="w")

class ArduinoInterface:
def __init__(self, master):
self.master = master
master.title("Arduino Parameters")

# COM-poort selectie
self.com_label = tk.Label(master, text="COM-poort:")
self.com_label.grid(row=0, column=0, sticky="w")
self.com_var = tk.StringVar()
available_ports = self.get_available_ports()
if available_ports:
self.com_var.set(available_ports[0])
self.com_dropdown = tk.OptionMenu(master, self.com_var, *available_ports)
self.com_dropdown.grid(row=0, column=1, sticky="w")
else:
messagebox.showerror("Fout", "Geen COM-poorten beschikbaar.")
return

# Bakje toevoerwater
self.toevoerwater_row = ParameterRow(master, "Bakje toevoerwater:", ["2", "1"], "2", self.send_toevoerwater)
self.toevoerwater_row.grid(row=1, column=0, sticky="w")

# Bakje condenswater
self.condenswater_row = ParameterRow(master, "Bakje condenswater:", ["aanwezig", "afwezig"], "aanwezig", self.send_condenswater)
self.condenswater_row.grid(row=2, column=0, sticky="w")

# Niveau toevoerwater
self.niveau_row = ParameterRow(master, "Niveau toevoerwater:", ["hoog", "laag"], "hoog", self.send_niveau)
self.niveau_row.grid(row=3, column=0, sticky="w")

# Deur
self.deur_row = ParameterRow(master, "Deur:", ["open", "dicht"], "dicht", self.send_deur)
self.deur_row.grid(row=4, column=0, sticky="w")

# Extra Aan/Uit optie
self.extra_aan_uit_row = ParameterRow(master, "Extra Aan/Uit:", ["Aan", "Uit"], "Uit", self.send_extra_aan_uit)
self.extra_aan_uit_row.grid(row=5, column=0, sticky="w")

self.ser = None

def get_available_ports(self):
ports = [p.device for p in serial.tools.list_ports.comports()]
return ports

def send_toevoerwater(self):
value = self.toevoerwater_row.var.get()
self.send_data(value)

def send_condenswater(self):
self.send_data(f"condenswater,{self.condenswater_row.var.get()}")

def send_niveau(self):
self.send_data(f"niveau,{self.niveau_row.var.get()}")

def send_deur(self):
self.send_data(f"deur,{self.deur_row.var.get()}")

def send_extra_aan_uit(self):
value = self.extra_aan_uit_row.var.get()
self.send_data(value) # Verzend alleen Aan of Uit.

def send_data(self, data):
com_port = self.com_var.get()
try:
self.ser = serial.Serial(com_port, 9600)
self.ser.write((data + "\n").encode())
print(f"Sent data to {com_port}: {data}")
self.ser.close()
except serial.SerialException as e:
messagebox.showerror("Fout", f"Kan COM-poort {com_port} niet openen.")

root = tk.Tk()
my_gui = ArduinoInterface(root)
if my_gui.com_var.get() != "":
root.mainloop()

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