E11. MQTT Publish and Subscribe

#include <WiFi.h>                         // the Wi-Fi commands
#include <PubSubClient.h>                 // the MQTT commands

String ssid = "YOUR_WIFI_SSID";           // your Wi-Fi network name
String password = "YOUR_WIFI_PASSWORD";   // your Wi-Fi password

WiFiClient wifiClient;                    // the network connection MQTT uses
PubSubClient mqtt(wifiClient);            // the MQTT client
int count = 0;                            // the number we send

void setup() {                            // runs once
  Serial.begin(115200);                   // start Serial at the ESP32 speed

  WiFi.begin(ssid, password);             // start joining the network
  Serial.print("Connecting");             // tell the user we are trying
  while (WiFi.status() != WL_CONNECTED) { // repeat until we have joined
    delay(500);                           // wait half a second
    Serial.print(".");                    // print a dot each time
  }
  Serial.println(" connected");           // we are on the network

  mqtt.setServer("test.mosquitto.org", 1883); // the broker's address and port
}

void loop() {                             // runs over and over
  if (mqtt.connected() == false) {        // not connected to the broker?
    Serial.println("Connecting to MQTT"); // say so
    mqtt.connect("wilteq-yourname-1");    // connect with a name no one else uses
  }
  mqtt.loop();                            // keep the connection alive

  count = count + 1;                      // add one to the count
  String message = String(count);         // turn the number into text
  mqtt.publish("wilteq/yourname/count", message.c_str()); // send it to the topic
  Serial.print("Sent ");                  // a label
  Serial.println(message);                // what we sent
  delay(5000);                            // wait 5 seconds
}

#include <WiFi.h>                         // the Wi-Fi commands
#include <PubSubClient.h>                 // the MQTT commands

String ssid = "YOUR_WIFI_SSID";           // your Wi-Fi network name
String password = "YOUR_WIFI_PASSWORD";   // your Wi-Fi password
const int ledPin = 2;                     // the LED is on GPIO 2

WiFiClient wifiClient;                    // the network connection MQTT uses
PubSubClient mqtt(wifiClient);            // the MQTT client

// the library runs this when a message arrives (copy the first line as it is)
void messageArrived(char* topic, byte* message, unsigned int length) {
  if (message[0] == '1') {                // first character of the message is 1?
    digitalWrite(ledPin, HIGH);           // LED on
  }
  if (message[0] == '0') {                // first character of the message is 0?
    digitalWrite(ledPin, LOW);            // LED off
  }
}

void setup() {                            // runs once
  Serial.begin(115200);                   // start Serial at the ESP32 speed
  pinMode(ledPin, OUTPUT);                // the LED pin is an output

  WiFi.begin(ssid, password);             // start joining the network
  Serial.print("Connecting");             // tell the user we are trying
  while (WiFi.status() != WL_CONNECTED) { // repeat until we have joined
    delay(500);                           // wait half a second
    Serial.print(".");                    // print a dot each time
  }
  Serial.println(" connected");           // we are on the network

  mqtt.setServer("test.mosquitto.org", 1883); // the broker's address and port
  mqtt.setCallback(messageArrived);       // run messageArrived when a message comes
}

void loop() {                             // runs over and over
  if (mqtt.connected() == false) {        // not connected to the broker?
    Serial.println("Connecting to MQTT"); // say so
    mqtt.connect("wilteq-yourname-2");    // connect with a name no one else uses
    mqtt.subscribe("wilteq/yourname/led"); // ask for messages on this topic
  }
  mqtt.loop();                            // keep the connection alive and get messages
}