Source Code Hello World MQTT

/********************************************
 * 18 Mar 2021 FG
 * 
 * Code für das Senden von MQTT Nachrichten mittels
 * client.publish("mein Topic", "meine Nachricht")
 * Wobei "mein Topic" für unser Demo "workshop" lauten
 * sollte
 * 
 *********************************************/


#include <ESP8266WiFi.h>
#include <PubSubClient.h>
byte ledPin=D8; 
long timestamp = 0;



// KONFIGURATION DES INTERNET-ZUGANGS
// ============================================
const char* ssid = "FRITZ!Box Fon WLAN 7360";
const char* password = "...";
String clientId = "ESP8266Client-Box01-";
// ============================================


const char* mqtt_server = "62.75.187.126";
const char* myTobic = "workshop";


WiFiClient espClient;
void callback(char* topic, byte* payload, unsigned int length) {
}

PubSubClient client(espClient);
unsigned long lastMsg = 0;
#define MSG_BUFFER_SIZE  (50)
char msg[MSG_BUFFER_SIZE];
int value = 0;

void setup_wifi() {
  delay(10);
  // We start by connecting to a WiFi network
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);

  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  randomSeed(micros());
  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}


void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    if (client.connect(clientId.c_str())) {
      Serial.println("connected. now subscribing...");
      client.subscribe("LED");
      String sendThis = clientId + ": connecting...";
      client.publish(myTobic, sendThis.c_str());
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}

void setup() {
  clientId += String(random(0xffff), HEX);
  pinMode(D3, INPUT_PULLUP); // Hier den Taster anschließen
  pinMode(D8, OUTPUT);
  digitalWrite(D8, LOW);
  Serial.begin(9600);
  setup_wifi();
  client.setServer(mqtt_server, 1883); 
  client.setCallback(callback);
}

/*********************************************************
 * 
 * Code oberhalb der Loop-Funktion bitte nicht verändern bis
 * auf die Konfigurationsparameter des Internets
 * 
 **********************************************************/

void loop() {


  if (!client.connected()) {
    reconnect();
  }
  client.loop();
}