Arduino sketch for ESP8266 - Wemos D1 Mini. Read temperature from BMP180 via I2C and publish value to MQTT topic.

mqttSensor2.ino

#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include <Adafruit_BMP085.h>

Adafruit_BMP085 bmp;

const char* ssid = "ArduinoSensor";
const char* password = "ArduinoSensorNetwork";
const char* mqttServer = "192.168.1.1";
const int sleepTimeS = 60;

WiFiClient espClient;
PubSubClient client(espClient);

char valTemperature[5];
char valPressure[5];

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

  Serial.begin(115200);
  setup_wifi();

  client.setServer(mqttServer, 1883);

  if (!bmp.begin()) {
    Serial.println("BMP085 not found");
    while (1) {}
  }
}

void setup_wifi() {

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


void reconnect() {
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    if (client.connect("esp2", "arduino", "arduino")) {
      Serial.println("connected");
      client.publish("sensors/esp2", "hello world");
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}

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

  // read temperature
  dtostrf(bmp.readTemperature(), 3, 1, valTemperature);
  String payload;
  payload = "sensor2 temperature=";
  payload += valTemperature;
  // publish temperature
  client.publish("sensors/node2/temperature", (char*) payload.c_str());

  // read pressure
  dtostrf(bmp.readPressure(), 3, 1, valPressure);
  payload = "sensor2 pressure=";
  payload += valPressure;
  // publish pressure
  client.publish("sensors/node2/pressure", (char*) payload.c_str());

  // fall into sleep
  ESP.deepSleep(sleepTimeS * 1000000);
}