Python & Arduino communication with serial port

Projects Programming
1

I have a small project to show how to communicate between Arduino and python project. The idea is to create python ap to control the traffic light. Arduino (UNO) part is just a small traffic light with only 3 LEDs (red - 2, yellow-3,green-4). Also the Python part is a simple tkinter app with 2 buttons: set 10 sec delay, and set 5 sec delay. They are communicating with serial port. All codes (py and arduino parts) will be below. An issue is when i press 'set 5 sec' button, in the next loop iteration, delay becomes 5 sec. But when i press 'set 10 sec' button, nothing happens. I am noob at arduino and c++, but know python very well. Also english is not my native language, so dont scold me for some mistakes.

python:

import serial
from time import sleep
import tkinter
from tkinter import ttk

# Укажите порт, к которому подключена Ваша плата Arduino.
ARDUINO_PORT = 'COM4'
BAUDRATE = 9600

def on():
    command = '10'
    arduino.write(command.encode())
    sleep(0.1)  # Добавляем небольшую задержку для обработки

def off():
    command = '5'
    arduino.write(command.encode())
    sleep(0.1)  # Добавляем небольшую задержку для обработки

main_window = tkinter.Tk()
main_window.title('Управление arduino')
main_window.geometry('800x600')

button1 = ttk.Button(text='Задержка 10 сек.', command=on)
button0 = ttk.Button(text='Задержка 5 сек.', command=off)
buttons = [button1, button0]

for button in buttons:
    button.pack()

status_label = ttk.Label()
status_label.pack()

try:
    arduino = serial.Serial(ARDUINO_PORT, BAUDRATE, timeout=1)
    sleep(2)
    status_label.config(text='Подключено к Arduino')
except serial.SerialException:
    status_label.config(text='Не удается подключиться')

main_window.mainloop()

arduino:

int main_delay = 10000;
int sign_delay = main_delay - 3000;
int yellow_delay = 3000;
int green_morg_delay = 1000;

void setup() {
    pinMode(2, OUTPUT);
    pinMode(3, OUTPUT);
    pinMode(4, OUTPUT);
    Serial.begin(9600);
}

void loop() {
    if (Serial.available() > 0) {
        char command = Serial.read();
        if (command == '10') {
            main_delay = 10000;
        } else if (command == '5') {
            main_delay = 5000;
        }
    }

    digitalWrite(2, HIGH);
    digitalWrite(3, LOW);
    digitalWrite(4, LOW);
    delay(main_delay);
    
    digitalWrite(2, HIGH);
    digitalWrite(3, HIGH);
    digitalWrite(4, LOW);
    delay(yellow_delay);
    
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
    digitalWrite(4, HIGH);
    delay(main_delay);
    
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
    digitalWrite(4, LOW);
    delay(green_morg_delay);
    
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
    digitalWrite(4, HIGH);
    delay(green_morg_delay);
    
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
    digitalWrite(4, LOW);
    delay(green_morg_delay);
    
    digitalWrite(2, LOW);
    digitalWrite(3, HIGH);
    digitalWrite(4, HIGH);
    delay(yellow_delay);
}

I already tried to talk with chat-gpt but it cant help me. Also all hardware is working correctly.

2

Multiple character commands are more difficult to use because of the timing of serial data transfer. If you change your “10” command into a single character (‘a’ perhaps?) it should work.

If you really need multiple character parsing look for the “serial input basics” tutorial.

1 Like
3

First off, thank you for posting your code inside code tags! +1.

Using single quotes in C/C++ specifies a single char and you are using 2 in that expression. If you change your preferences inside the IDE and increase your warning level, the compiler would have told you about that.

As @DaveX pointed out, it is much easier to just have each command be a single character.

2 Likes
4

Thank you! I can't make all commands be only 1 character, because in future, I want to let user choose any delay they want, just with entry. I made buttons just to test how it works.

5

Thank you!

6

You can send and parse numbers a character at a time, like "12345d" for a delay of 12345.

Look at the pcRead example:

and some of the linked Wokwi simulations:

This does a lot with single character-at-a-time processing:

1 Like
7

Why can't I just do something like that:

int main_delay = 10000;
int sign_delay = main_delay - 3000;
int yellow_delay = 3000;
int green_morg_delay = 1000;

void setup() {
    pinMode(2, OUTPUT);
    pinMode(3, OUTPUT);
    pinMode(4, OUTPUT);
    Serial.begin(9600);
}

void loop() {
    if (Serial.available() > 0) {
        int command = Serial.read();
        main_delay = command;
    }

    digitalWrite(2, HIGH);
    digitalWrite(3, LOW);
    digitalWrite(4, LOW);
    delay(main_delay);
    
    digitalWrite(2, HIGH);
    digitalWrite(3, HIGH);
    digitalWrite(4, LOW);
    delay(yellow_delay);
    
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
    digitalWrite(4, HIGH);
    delay(main_delay);
    
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
    digitalWrite(4, LOW);
    delay(green_morg_delay);
    
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
    digitalWrite(4, HIGH);
    delay(green_morg_delay);
    
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
    digitalWrite(4, LOW);
    delay(green_morg_delay);
    
    digitalWrite(2, LOW);
    digitalWrite(3, HIGH);
    digitalWrite(4, HIGH);
    delay(yellow_delay);
}

No, characters, no problems!
python:

import serial
from time import sleep
import tkinter
from tkinter import ttk

# Укажите порт, к которому подключена Ваша плата Arduino.
ARDUINO_PORT = 'COM4'
BAUDRATE = 9600

def test_delay():
    command = str(int(delay_entry.get())*1000)
    arduino.write(command.encode())

main_window = tkinter.Tk()
main_window.title('Управление arduino')
main_window.geometry('800x600')

delay_entry = ttk.Entry()
button_test = ttk.Button(text='Задать задержку', command=test_delay)
delay_entry.pack()
button_test.pack()

status_label = ttk.Label()
status_label.pack()

try:
    arduino = serial.Serial(ARDUINO_PORT, BAUDRATE, timeout=1)
    sleep(2)
    status_label.config(text='Подключено к Arduino')
except serial.SerialException:
    status_label.config(text='Не удается подключиться')

main_window.mainloop()

But in this case, nothing happens at all. WHY

8

look this over

const byte PinLeds [] = { 13, 12, 11, 10 };
const int  Nled       = sizeof(PinLeds);

enum { Off = HIGH, On = LOW };

// -----------------------------------------------------------------------------
void loop ()
{
    if (Serial.available ())  {
        char buf [90];
        int  n = Serial.readBytesUntil ('\n', buf, sizeof(buf)-1);
        buf [n] = '\0';     // terminate string with nul

        char cmd [10];
        int  val1;
        int  val2;

        sscanf (buf, "%s %d %d", cmd, &val1, &val2);

        Serial.println (cmd);
        if (! strcmp (cmd, "ledOn"))
            digitalWrite (PinLeds [val1], On);
        else if (! strcmp (cmd, "ledOff"))
            digitalWrite (PinLeds [val1], Off);
    }
}

// -----------------------------------------------------------------------------
void setup ()
{
    Serial.begin (9600);

    for (int n = 0; n < Nled; n++)
        pinMode (PinLeds [n], OUTPUT);
}
9

Because this Serial.read() reads one character at a time.

main_delay will be in the 0-255 range unless there was no character to read(), in which case (obviated by the availiable()>0) the returned -1 would cause a 2^32-1ms delay.

Did you read @Robin2's discussion of how the arduino is so much faster than 9600 baud?

Also, this bit makes the number into a string of characters:

10

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