Communication between my arduino and my Python code doesn't seem to work

Question

I need to use data collected from a sensor connected to an arduino Uno in a Python code. It's a basic question of getting the state of the digitalPin to my Python code. I first wanted to try my hand at just making a communication going both ways, from Python to Arduino, and after from Arduino to Python.

So I tried doing a ping-pong with Python sending a command, and Arduino sending back 0 if it didn't reach or 1 if it worked. The thing is: I can see the command test in Arduino, but the back data is not working.

Here's my Arduino code :

void setup() {
  Serial.begin(9600);
  delay(1000);
}

void loop() {
  
    if (Serial.available() > 0) {  // check if there's data from python
    String command = Serial.readStringUntil('\n');  // read python command
    Serial.println(command);  // show command in Arduino monitor
    Serial.write("command\n");
      if (command == "test") {  // if command is "test"
        Serial.write(1);}  // Envoie 1 en tant que byte
      else {
        Serial.write(0);}  // Envoie 0 en tant que byte
      Serial.flush();
  }
}

And here's my Python code:

import serial
import time

capt = serial.Serial('COM5',9600,timeout=5)

def testcomm(test):  
    out = 0
    com = (test + '\n').encode()  # Send test command with end ligne indicator \n
    print(f"Commande envoyée : {com}")
    capt.write(com)  # send command to Arduino
    time.sleep(4)  
    # Check if there's data
    if capt.in_waiting > 0 :
        testout = capt.readline()  # read
        print(f'testout val (raw): {testout}')  # show raw
        if testout:
            out = testout.strip()  # clean answer
        print(f'testout val (cleaned): {out}')
    else:
        print("Doesn't work")
    
    return out

test1 = testcomm('test')
capt.close()

And here's the result in my Python console:

Commande envoyée : b'test\n'
Doesn't work

I checked whether the command line in itself worked inside the Arduino monitor, it does, and it sends back 1, but really, I can't read it in Python.

I also tried read(), readline() and readlines() just in case. I tried a lot of different things, but I didn't keep track, and I was also learning the pyserial library in parallel, so a lot of my tries were just weird. What can I try next?

Kovy Jacob · Accepted Answer · 2025-01-10 01:15:53Z

1

So, after looking a bit more into it, again, I played with time.sleep(). The problem was that I was sending a command too quickly after I opened the port, so it was unable to catch the command. The solution was to add a time.sleep() after the port was opened (in my case I put it before the capt.write() command).

edited Jan 10 at 1:15

Kovy Jacob

1,18911 silver badges26 bronze badges

answered Jan 8 at 15:30

Tsuyo

292 bronze badges

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