ESP-MQTT-client-temp/ESP-MQTT-client-temp.ino

#include <WiFi.h>
#include <PubSubClient.h>
#include <Wire.h>

#define O_LED 2
int PIN_ANALOG_IN = 39;

const char* ssid = "BFKBYOD";
const char* password = "bfkskoleelev";
const char* mqtt_broker = "109.74.205.66";
int mqtt_port = 443;

WiFiClient espClient;

PubSubClient mqtt_client(espClient);

String lastMsg;

#define MSG_BUFFER_SIZE (50)
char msg[MSG_BUFFER_SIZE];

void setup_wifi() {
  delay(10);

  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);

  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println("");
  Serial.println("WiFi connected");
  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());
}

void callback(char* topic, byte* payload, unsigned int length) {
  Serial.print("Message arrived [");
  Serial.print(topic);
  Serial.print("] ");

  lastMsg = "";

  for (int i = 0; i < length; i++) {
    Serial.print((char)payload[i]);
    lastMsg += (char)payload[i];
  }
  Serial.println();
  
  if ((String)topic == "sebastian/control" && lastMsg == "on") {
    digitalWrite(O_LED, HIGH);
  } else if ((String)topic == "sebastian/control" && lastMsg == "off") {
    digitalWrite(O_LED, LOW);
  }
}

void reconnect () {
  while (!mqtt_client.connected()) {
    Serial.print("Attempting MQTT connection...");

    String clientId = "ESP32Client-";
    clientId += String(random(0xffff), HEX);

    if (mqtt_client.connect(clientId.c_str())) {
      Serial.println("connected");

      mqtt_client.publish("ClientAnnouncements", "Sebastian");

      mqtt_client.subscribe("inTopic");
      mqtt_client.subscribe("sebastian/control");
    } else {
      Serial.print("failed, rc=");
      Serial.print(mqtt_client.state());
      Serial.println(" trying again in 5 seconds");
      delay(5000);
    }
  }
}

void setup() {
   pinMode(O_LED, OUTPUT);

   Serial.begin(9600);

   setup_wifi();

   mqtt_client.setServer(mqtt_broker, mqtt_port);
   mqtt_client.setCallback(callback);
}

void loop() {
  if (!mqtt_client.connected()) {
    reconnect();
  }

  int adcValue = analogRead(PIN_ANALOG_IN);                       //read ADC pin
  double voltage = (float)adcValue / 4095.0 * 3.3;                // calculate voltage
  double Rt = 10 * voltage / (3.3 - voltage);                     //calculate resistance value of thermistor
  double tempK = 1 / (1 / (273.15 + 25) + log(Rt / 10) / 3950.0); //calculate temperature (Kelvin)
  double tempC = tempK - 273.15;                                  //calculate temperature (Celsius)
  //Serial.printf("ADC value : %d,\tVoltage : %.2fV, \tTemperature : %.2fC\n", adcValue, voltage, tempC);

  char CharArrTemp[6];
  dtostrf(tempC, 5, 2, CharArrTemp);

  mqtt_client.publish("sebastian/temp", CharArrTemp);

  delay(500);

  mqtt_client.loop();
}