ESP MQTT

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/*********
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  Rui Santos
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  Complete project details at https://randomnerdtutorials.com  
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*********/
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​
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#include <WiFi.h>
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#include <PubSubClient.h>
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#include <Wire.h>
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#include <Adafruit_BME280.h>
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#include <Adafruit_Sensor.h>
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​
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// Replace the next variables with your SSID/Password combination
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const char* ssid = "REPLACE_WITH_YOUR_SSID";
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const char* password = "REPLACE_WITH_YOUR_PASSWORD";
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​
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// Add your MQTT Broker IP address, example:
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//const char* mqtt_server = "192.168.1.144";
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const char* mqtt_server = "YOUR_MQTT_BROKER_IP_ADDRESS";
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​
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WiFiClient espClient;
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PubSubClient client(espClient);
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long lastMsg = 0;
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char msg[50];
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int value = 0;
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​
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//uncomment the following lines if you're using SPI
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/*#include <SPI.h>
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#define BME_SCK 18
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#define BME_MISO 19
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#define BME_MOSI 23
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#define BME_CS 5*/
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​
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Adafruit_BME280 bme; // I2C
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//Adafruit_BME280 bme(BME_CS); // hardware SPI
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//Adafruit_BME280 bme(BME_CS, BME_MOSI, BME_MISO, BME_SCK); // software SPI
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float temperature = 0;
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float humidity = 0;
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​
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// LED Pin
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const int ledPin = 4;
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​
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void setup() {
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  Serial.begin(115200);
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  // default settings
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  // (you can also pass in a Wire library object like &Wire2)
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  //status = bme.begin();  
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  if (!bme.begin(0x76)) {
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    Serial.println("Could not find a valid BME280 sensor, check wiring!");
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    while (1);
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  }
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  setup_wifi();
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  client.setServer(mqtt_server, 1883);
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  client.setCallback(callback);
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​
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  pinMode(ledPin, OUTPUT);
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}
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​
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void setup_wifi() {
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  delay(10);
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  // We start by connecting to a WiFi network
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  Serial.println();
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  Serial.print("Connecting to ");
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  Serial.println(ssid);
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​
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  WiFi.begin(ssid, password);
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​
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  while (WiFi.status() != WL_CONNECTED) {
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    delay(500);
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    Serial.print(".");
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  }
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​
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  Serial.println("");
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  Serial.println("WiFi connected");
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  Serial.println("IP address: ");
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  Serial.println(WiFi.localIP());
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}
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​
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void callback(char* topic, byte* message, unsigned int length) {
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  Serial.print("Message arrived on topic: ");
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  Serial.print(topic);
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  Serial.print(". Message: ");
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  String messageTemp;
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  for (int i = 0; i < length; i++) {
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    Serial.print((char)message[i]);
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    messageTemp += (char)message[i];
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  }
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  Serial.println();
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​
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  // Feel free to add more if statements to control more GPIOs with MQTT
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​
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  // If a message is received on the topic esp32/output, you check if the message is either "on" or "off". 
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  // Changes the output state according to the message
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  if (String(topic) == "esp32/output") {
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    Serial.print("Changing output to ");
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    if(messageTemp == "on"){
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      Serial.println("on");
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      digitalWrite(ledPin, HIGH);
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    }
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    else if(messageTemp == "off"){
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      Serial.println("off");
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      digitalWrite(ledPin, LOW);
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    }
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  }
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}
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​
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void reconnect() {
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  // Loop until we're reconnected
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  while (!client.connected()) {
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    Serial.print("Attempting MQTT connection...");
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    // Attempt to connect
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    if (client.connect("ESP8266Client")) {
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      Serial.println("connected");
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      // Subscribe
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      client.subscribe("esp32/output");
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    } else {
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      Serial.print("failed, rc=");
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      Serial.print(client.state());
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      Serial.println(" try again in 5 seconds");
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      // Wait 5 seconds before retrying
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      delay(5000);
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    }
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  }
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}
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void loop() {
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  if (!client.connected()) {
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    reconnect();
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  }
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  client.loop();
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​
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  long now = millis();
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  if (now - lastMsg > 5000) {
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    lastMsg = now;
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    // Temperature in Celsius
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    temperature = bme.readTemperature();   
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    // Uncomment the next line to set temperature in Fahrenheit 
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    // (and comment the previous temperature line)
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    //temperature = 1.8 * bme.readTemperature() + 32; // Temperature in Fahrenheit
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    // Convert the value to a char array
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    char tempString[8];
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    dtostrf(temperature, 1, 2, tempString);
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    Serial.print("Temperature: ");
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    Serial.println(tempString);
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    client.publish("esp32/temperature", tempString);
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​
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    humidity = bme.readHumidity();
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    // Convert the value to a char array
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    char humString[8];
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    dtostrf(humidity, 1, 2, humString);
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    Serial.print("Humidity: ");
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    Serial.println(humString);
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    client.publish("esp32/humidity", humString);
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  }
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}
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​
Subscribing to MQTT topics
In the reconnect() function, you can subscribe to MQTT topics. In this case, the ESP32 is only subscribed to the esp32/output:
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client.subscribe("esp32/output");
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In the callback() function, the ESP32 receives the MQTT messages of the subscribed topics. According to the MQTT topic and message, it turns the LED on or off:
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// If a message is received on the topic esp32/output, you check if the message is either "on" or "off". 
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// Changes the output state according to the message
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if (String(topic) == "esp32/output") {
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  Serial.print("Changing output to ");
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  if (messageTemp == "on") {
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    Serial.println("on");
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    digitalWrite(ledPin, HIGH);
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  }
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  else if (messageTemp == "off") {
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    Serial.println("off");
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    digitalWrite(ledPin, LOW);
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  }
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}
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Publishing MQTT messages
In the loop(), new readings are being published every 5 seconds:
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if (now - lastMsg > 5000) { ... }
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By default the ESP32 is sending the temperature in Celsius, but you can uncomment the last line to send the temperature in Fahrenheit:
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// Temperature in Celsius
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temperature = bme.readTemperature(); 
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// Uncomment the next line to set temperature in Fahrenheit 
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// (and comment the previous temperature line)
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//temperature = 1.8 * bme.readTemperature() + 32; // Temperature in Fahrenheit
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You need to convert the temperature float variable to a char array, so that you can publish the temperature reading in the esp32/temperature topic:
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// Convert the value to a char array
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char tempString[8];
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dtostrf(temperature, 1, 2, tempString);
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Serial.print("Temperature: ");
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Serial.println(tempString);
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client.publish("esp32/temperature", tempString);
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The same process is repeated to publish the humidity reading in the esp32/humidity topic:
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humidity = bme.readHumidity();
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// Convert the value to a char array
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char humString[8];
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dtostrf(humidity, 1, 2, humString);
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Serial.print("Humidity: ");
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Serial.println(humString);
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client.publish("esp32/humidity", humString);
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