为什么我的 python 串行代码不起作用，而从 arduino 串行监视器发送相同的数据呢？

Question

I have an arduino that reads in two ints over a serial connection when I send the data from the arduino serial monitor it works as it should, but no matter what I do I can't get it to work when I send the same data from python using pySerial, I have been at this hours and have gotten nowhere

I have tried encoding the data as utf8, different encodings flushing the output buffer and have read too many other similar stackoverflow Q&As to count

I am using python 3.7.1 in Windows 10 but the code will untimately be running on a Rpi

import os
import time
import serial
ser = serial.Serial('COM7', baudrate=9600, parity=serial.PARITY_NONE, stopbits=serial.STOPBITS_ONE, bytesize=serial.EIGHTBITS, timeout=5)
print("writting")
time.sleep(0.5)
ser.write(b'4,5')
ser.write(b'\r\n')
time.sleep(0.5)
ser.flushOutput()
ser.close()

#include <SoftwareSerial.h>
byte buttonPin = 9;
const int pin_led = LED_BUILTIN; // Pin for indication LED
int sensorPin = A0;
int sensorValue = 0;
int remotePower = 0;  

SoftwareSerial mySerial(11, 12); // RX, TX

void setup()
{
  pinMode(pin_led, OUTPUT); // Set LED pin as output
  Serial.begin(9600);
  mySerial.begin(9600);
  pinMode(buttonPin, INPUT_PULLUP);
}

int oldremotePower = 0; 

void loop()
{
  // if there's any serial available, read it:
  while (Serial.available() > 0) {
    Serial.println("theres Data");
    // look for the next valid integer in the incoming serial stream:
    int mode = Serial.parseInt();
    // do it again:
    int action = Serial.parseInt();
    // do it again:
    //int blue = Serial.parseInt();

    // look for the newline. That's the end of your sentence:
    if (Serial.read() == '\n') {
      // constrain the values to 0 - 255 and invert
      // if you're using a common-cathode LED, just use "constrain(color, 0, 255);"
      mode = constrain(mode, 1, 4);
      action =  constrain(action, 0, 100);

      mySerial.print(mode);
      mySerial.print(",");
      mySerial.println(action);
    }
  }


    oldremotePower = remotePower;
    sensorValue = analogRead(sensorPin);
    remotePower = map(sensorValue, 0, 1023, 1, 100);
    if (oldremotePower != remotePower){
      //Serial.println(oldremotePower);
      //Serial.println(remotePower);
        }

  if (digitalRead(buttonPin) == LOW) {
    mySerial.println(remotePower);
  }
}

I send "1,100" from the arduino serial monitor and the uno responds with "theres Data" and on the software serial it prints the values it was just sent this works but when I try to send "1,100\\r" from my python script nothing happens the script runs without error the Rx led on the uno flashes but there is no output on the software serial port It must be something wrong with my python serial code.

Answer 1

You are missing the part where you read from the port.

Contrary to the terminal or serial monitor, where everything that arrives to the port is immediately and automatically displayed, with pyserial you need to explicitly read bytes from the RX buffer:

incoming = ser.read()     #Read one byte
incoming = ser.read(n)    #Read n bytes, whit n and INT
incoming = ser.readline() #Read everything until a \n is received
incoming = ser.read(ser.inWaiting()) #Read everything in the buffer

You need to choose one of those and add it to your code.

To make sure you read everything you can add a loop to read until nothing else is waiting in the buffer and maybe a certain amount of time elapses:

timeout=time.time()+1.0
while ser.inWaiting() or time.time()-timeout<0.0:
    if ser.inWaiting()>0:
        data+=ser.read(ser.inWaiting())
        timeout=time.time()+1.0
print(data)

This will keep reading for 1 second after the buffer is detected to be empty. I took it from here .

EDIT: As you say in the comments, you were indeed missing the read commands but that was on purpose.

Your other potential problem is the way you handle Serial.parseInt() on your Arduino code.

Serial.parseInt() reads integer values up to the delimiter (in your case the colon) but you need to explicitly call Serial.read() to swallow the delimiter itself. So just try calling Serial.read() after every Serial.parseInt() and your code should work.

One other thing you can do is to compare the result of Serial.parseInt() with 0 to check if you got a timeout.

Answer 2

So I have managed to make it work. (for now, I think) I put back a 2 sec wait (which I had when I first wrote this code) after opening the port in my python code and changed my write command to ser.write(bytes(b'4,5\\n')) I also removed the ser.flushOutput() and it seems to be working okay. I didn't need to make any changes to the arduino code. I have no real idea why all of a sudden it now works as the code I now have is almost identical to what I started with before I started debugging it and trying to make it work, which is infuriating to me as I have no clue what I did to fix it :<

Thanks All