OLED-MQTT.ino

# oled screen off a esp8266 will display via mqtt temp and humidity
#
#

#include Wire.h
#include Arduino.h
#include U8g2lib.h
#include ESP8266WiFi.h
#include PubSubClient.h

U8G2_SSD1306_128X32_UNIVISION_F_HW_I2C u8g2(U8G2_R0, /* reset=*/ U8X8_PIN_NONE, /* clock=*/ 2, /* data=*/ 0);   // pin remapping with ESP8266 HW I2C

const char* ssid = "SSID";      // ssid
const char* password = "PW";  // password
const char* mqtt_server = "192.168.X.X";  // mqtt server
const char* inTopic = "/";                  // topic esp will subscribe to
const char* clientId = "esp";               // id of the esp

WiFiClient espClient;
PubSubClient client(espClient);
long lastMsg = 0;
char msg[50];
int value = 0;

void setup()
{
  u8g2.begin();
  u8g2.enableUTF8Print();
  Serial.begin(9600);
  setup_wifi();
  client.setServer(mqtt_server, 1883);
  client.setCallback(callback);
}

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

 void callback(char* topic, byte* payload, unsigned int length) {
    Serial.print("Message arrived [");
    Serial.print(topic);
    Serial.print("] ");
  for (int i = 0; i < length; i++) {
    payload[length] = '\0';
    Serial.print((char)payload[i]);
}
    Serial.println();

    String message = String((char*)payload);


    if ((char)payload[0]) {
//    if ((char)payload[0] == '1') {
    u8g2.clearBuffer();
    u8g2.setFont(u8g2_font_ncenB10_tr);
    u8g2.setCursor(0, 24);
    u8g2.print(message);
//  u8g2.drawStr(0,24,"Turning ON");
    u8g2.sendBuffer();
    delay(5000);
     } else if ((char)payload[0] == '0') {
    u8g2.clearBuffer();
    u8g2.print(message);
//  u8g2.drawStr(0,24,"Turning OFF");
    u8g2.sendBuffer(); 
     }
}

void reconnect() {
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    if (client.connect(clientId)) {
      Serial.println("connected");
      client.subscribe(inTopic);
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      delay(5000);
    }
  }
}

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