无法将字符串从 python 发送到 arduino

Question

所以我正在尝试创建一个简单的程序，让我可以用我的计算机控制 RGB LED 的颜色。我在 python 3 上用 tkinter 创建了一个小窗口以控制颜色，但问题是当我尝试更改颜色时它根本没有响应。我不知道发生了什么。我试图将字符串放入 arduino 代码中，它成功了，但是当我通过串行通信发送时它根本没有响应。

Arduino 代码

//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]);  


  }

这里是python代码：

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")

更新

因此，为此更改 arduino 代码（在接收字符串的部分）：

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

以及将字符串发送到此的 python 代码部分： 而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)

LED 会改变它的颜色，但有时它会变成其他颜色，python 程序会崩溃！！！！ Serial.readStringUntil("\n") 或 arduino.write(finalString) 中是否缺少任何内容？

Answer 1

您只是一个接一个地向 Arduino 发送 太多 消息，所以当它调用 readString() 时会发生一个很长的字符串，并增加pos 超过合法间隔0..2，这意味着您正在破坏memory stack，从那里任何事情都可能发生。

---

建议的修复：

1. 将Serial.readString()替换为Serial.readStringUntil('\n')，former在超时时返回，而后者在匹配换行符字符时返回strong>或它超时。 默认超时时间是1秒。

2. 改变

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

   到

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

   并删除print("\n")

3. 更改您的 python 代码，使其仅在消息内容已更改 wrt 时才向 Arduino 发送消息。最后发送的：

   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)
   

---

注意 01： 即使在您修复它之后，也请考虑将您的 Arduino 代码发布到 code review，以获取有关 代码样式 和 的反馈em>强大的设计。

注意 02：即使有建议的修复，源代码仍然容易受到错误行为的影响，因为正确的情况（例如：如果在\n 匹配之前readStringUntil() 超时会发生什么？你如何处理部分输入？）

---

编辑 1： python 代码 崩溃是因为您之前没有检查对象 RedScale、GreenScale 和 BlueScale 的有效性使用get() 访问它们，这显然在 tk 窗口 关闭之后失败。

天真的解决方案如下：

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()

请注意，虽然 stackoverflow 人满为患 有人建议这种解决方案，但我认为这是 糟糕的设计，我仍然怀疑 越野车。一个合适的解决方案是覆盖 事件监听器 来调整 Scale 实例，这样 Scale 的值只会被读取并在用户实际更改时发送。我会让你弄清楚细节。