无法将字符串从python发送到arduino

Question

So I am trying to create a simple program that allows me to control the colors of a RGB LED with my computer. I created a little window with tkinter on python 3 in order to control the color, but the problem is that when I try to change the color it simply doesn't respond. I have no idea what is going on. I tried to put the string in the arduino code and it worked out, but it simply doesn't respond when I send through a serial communication.

Arduino code

//pin layout
int   red = 12;
int green = 11;
int  blue = 10;

//string that will receive
String    data;
String subData;

//Color values
int value[3];

void setup() {
  Serial.begin(9600);
  pinMode(red,OUTPUT);
  pinMode(green,OUTPUT);
  pinMode(blue,OUTPUT);  
  }

void loop() {
  while(Serial.available() == 0);
    data = Serial.readString();

    int initialVal =0;
    int val;

    int pos = 0;

    do{
    val = data.indexOf(',',initialVal);
    subData = data.substring(initialVal,val);
    value[pos] = subData.toInt();
    pos = pos + 1;
    initialVal = val + 1;
    }while(val != -1);
    Serial.println(data);
    analogWrite(red,value[0]);
    analogWrite(green,value[1]);
    analogWrite(blue,value[2]);  


  }

And here is the python code:

from tkinter import *
from serial import *


window = Tk()
#all definitions for the window
window.title("RGB LED control Panel")
window.geometry("300x180")
window.resizable(False,False)

Title = Label(window, text = "RGB control", width = 15)
Title.grid(row = 0, column = 0, columnspan = 3)

Explanation = Label(window, text = "  This window controls the \ncolor of an RGB LED. Have \n fun!!!")
Explanation.grid(row =1 , column = 3)

RedTitle = Label(window, text = "Red", width = 5, bg = "Red")
RedTitle.grid(row = 1, column = 0)

GreenTitle = Label(window, text = "Green", width = 5, bg = "Green")
GreenTitle.grid(row = 1, column = 1)

BlueTitle = Label(window, text = "Blue", width = 5, bg = "Blue")
BlueTitle.grid(row = 1, column = 2)


RedScale = Scale(window, from_ = 0, to = 255, orient = VERTICAL)
RedScale.grid(row = 2, column = 0)

GreenScale = Scale(window, from_ = 0, to = 255, orient = VERTICAL)
GreenScale.grid(row = 2, column = 1)

BlueScale = Scale(window, from_ = 0, to = 255, orient = VERTICAL)
BlueScale.grid(row = 2, column = 2)

#now the serial com with the arduino

arduino = Serial()
arduino.baudrate = 9600
arduino.port = "COM3"
arduino.open()

while 1:
    window.update_idletasks()
    window.update()

    RED = str(RedScale.get())
    GREEN = str(GreenScale.get())
    BLUE = str(BlueScale.get())

    finalString = RED + "," + GREEN + "," + BLUE

    arduino.write(finalString.encode("utf-8"))
    print(finalString)
    print("\n")

Update

So changing the arduino code (at the part that receives the string) for this:

  while(Serial.available() == 0);
  data = Serial.readStringUntil('\n');
  Serial.setTimeout(0.01);

And the part of the python code which sends the string to this: while 1: window.update_idletasks() window.update()

    RED = str(RedScale.get())
    GREEN = str(GreenScale.get())
    BLUE = str(BlueScale.get())

    finalString = RED + "," + GREEN + "," + BLUE + "\n"
    if lastMsg != finalString:
        finalString= finalString.encode("utf-8")
        arduino.write(finalString)
        lastMsg = finalString

    print(finalString)

The LED changes it's color, but it, sometimes, changes to other colors and the the python program crashes!!!! Is there anything missing in Serial.readStringUntil("\\n") or in the arduino.write(finalString)?

Answer 1

You are sending just too many messages one after another to Arduino , so what happens is that when it invokes readString() it takes a very long string , and increments pos past the legitimate interval 0..2 , which means that you are corrupting the memory stack and from there anything can happen.

---

Proposed fixes:

1. Replace Serial.readString() with Serial.readStringUntil('\\n') , the former returns when it times out , whereas the latter returns when it matches a newline character or it times out . The default timeout is 1 second .

2. Change

    finalString = RED + "," + GREEN + "," + BLUE 

   to

    finalString = RED + "," + GREEN + "," + BLUE + "\\n" 

   and remove print("\\n")

3. Change your python code so that it sends a message to Arduino only when the content of the message has changed wrt. the last one that was sent:

    last_msg = "" while 1: window.update_idletasks() window.update() RED = str(RedScale.get()) GREEN = str(GreenScale.get()) BLUE = str(BlueScale.get()) finalString = RED + "," + GREEN + "," + BLUE + "\\n" if finalString != last_msg: arduino.write(finalString.encode("utf-8")) last_msg = finalString print(finalString) 

---

Note 01: even after you fixed it, consider posting your Arduino code to code review for some feedback on code styling and strong design .

Note 02: Even with the proposed fixes, the source code remains vulnerable to wrong behaviours given the right set of circumstances (eg: what happens if readStringUntil() timeouts before \\n is matched? how do you deal with partial input?)

---

EDIT 1: The python code crashes due to the fact that you do not check for the validity of objects RedScale , GreenScale and BlueScale before accessing them with get() , and this obviously fails right after the tk window is closed .

A naive solution would be the following:

import sys
import time

global exitFlag
exitFlag = False

...

def endProgram():
    global exitFlag
    exitFlag = True
    window.destroy()

window.protocol("WM_DELETE_WINDOW", endProgram)

...

last_msg = ""
finalString = ""
while 1:
    if not exitFlag:
        window.update_idletasks()

    if not exitFlag:
        window.update()

    if not exitFlag:
        RED = str(RedScale.get())
        GREEN = str(GreenScale.get())
        BLUE = str(BlueScale.get())

        finalString = RED + "," + GREEN + "," + BLUE + "\n"

    if finalString != last_msg:
        arduino.write(finalString.encode("utf-8"))
        last_msg = finalString

        print(finalString)

     if exitFlag:
         sys.exit()

Note that, although stackoverflow is overcrowded with people suggesting this solution, i think that it is bad design and I suspect still buggy . A proper solution would be to override the event listener for the adjustment of the Scale instances, so that the value of the Scale is only read and sent when it is actually changed by the user. I'll let you work out the details.