How to send data with arduino Uno with the help of broker?

[iuliana_ast]

I need to create a connection between arduino and python with the help of mqtt. I want to make the arduino the server and to get the data in python.
I found online a code and worked on it for my ip connection and mac address, but somehow the serial monitor ouputs that the connection is not successful. How can I debug the code to send data from arduino?

#include <SPI.h>
#include <Ethernet.h>
#include <PubSubClient.h>

// Function prototypes
void subscribeReceive(char* topic, byte* payload, unsigned int length);
 
// Set your MAC address and IP address here
byte mac[] = { 0x90, 0x61, 0xAE, 0xEE, 0x10, 0x29 };
IPAddress ip(192, 168, 0, 138);

// Make sure to leave out the http and slashes!
//const char* server = "test.mosquitto.org";
const char* server = "broker.emqx.io";

// Ethernet and MQTT related objects
EthernetClient ethClient;
PubSubClient mqttClient(ethClient);


void setup()
{
  // Useful for debugging purposes
  Serial.begin(9600);
  
  // Start the ethernet connection
  Ethernet.begin(mac, ip);              
  
  // Ethernet takes some time to boot!
  delay(3000);                          
 
  // Set the MQTT server to the server stated above ^
  mqttClient.setServer(server, 1883);   
 
  // Attempt to connect to the server with the ID "myClientID"
  if (mqttClient.connect("myClientID")) 
  {
    Serial.println("Connection has been established, well done");
 
    // Establish the subscribe event
    mqttClient.setCallback(subscribeReceive);
  } 
  else 
  {
    Serial.println("Looks like the server connection failed...");
  }
}


void loop()
{
  mqttClient.loop();
 
  // Ensure that we are subscribed to the topic "MakerIOTopic"
  mqttClient.subscribe("MakerIOTopic");
 
  // Attempt to publish a value to the topic "MakerIOTopic"
  if(mqttClient.publish("MakerIOTopic", "Hello World"))
  {
    Serial.println("Publish message success");
  }
  else
  {
    Serial.println("Could not send message :(");
  }
 
  delay(4000);
}

void subscribeReceive(char* topic, byte* payload, unsigned int length)
{
  Serial.print("Topic: ");
  Serial.println(topic);
 
  Serial.print("Message: ");
  for(int i = 0; i < length; i ++)
  {
    Serial.print(char(payload[i]));
  }
 
  Serial.println("");
}

In python, I would need afterwards to subscribe to the connection.

What am I doing wrong in the arduino sketch?

I attach the screenshots with the ip and mac address:

[pylon]

@iuliana_ast

byte mac[] = { 0x90, 0x61, 0xAE, 0xEE, 0x10, 0x29 };

You must not use the MAC address of your notebook for the Ethernet Shield of your Arduino. MAC addresses have to be unique among the complete network, usually that address should be globally unique to ensure that.
It also must use a different IP address.

As you're using an MQTT broker on the Internet you have to ensure both the notebook and the Arduino have access to the Internet.