Basic ESP8266 MQTT example

    This sketch demonstrates the capabilities of the pubsub library in combination
    with the ESP8266 board/library.

    It connects to an MQTT server then:
    - publishes "hello world" to the topic "outTopic" every two seconds
    - subscribes to the topic "inTopic", printing out any messages
    it receives. NB - it assumes the received payloads are strings not binary
    - If the first character of the topic "inTopic" is an 1, switch ON the ESP Led,
    else switch it off

    It will reconnect to the server if the connection is lost using a blocking
    reconnect function. See the 'mqtt_reconnect_nonblocking' example for how to
    achieve the same result without blocking the main loop.

    To install the ESP8266 board, (using Arduino 1.6.4+):
    - Add the following 3rd party board manager under "File -> Preferences -> Additional Boards Manager URLs":
    - Open the "Tools -> Board -> Board Manager" and click install for the ESP8266"
    - Select your ESP8266 in "Tools -> Board"


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

// Update these with values suitable for your network.

const char* ssid = "SepehrNet";
const char* password = "orangecoffee";
const char* mqtt_server = "test.mosquitto.org";

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

void setup_wifi() {

    // We start by connecting to a WiFi network
    Serial.print("Connecting to ");

    WiFi.begin(ssid, password);

    while (WiFi.status() != WL_CONNECTED) {


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

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

    // Switch on the LED if an 1 was received as first character
    if ((char)payload[0] == '1') {
        digitalWrite(BUILTIN_LED, LOW);   // Turn the LED on (Note that LOW is the voltage level
        // but actually the LED is on; this is because
        // it is active low on the ESP-01)
    } else {
        digitalWrite(BUILTIN_LED, HIGH);  // Turn the LED off by making the voltage HIGH


void reconnect() {
    // Loop until we're reconnected
    while (!client.connected()) {
        Serial.print("Attempting MQTT connection...");
        // Create a random client ID
        String clientId = "ESP8266Client-";
        clientId += String(random(0xffff), HEX);
        // Attempt to connect
        if (client.connect(clientId.c_str())) {
            // Once connected, publish an announcement...
            client.publish("sepehr.ghasem.helloxxx", "hello world");
            // ... and resubscribe
        } else {
            Serial.print("failed, rc=");
            Serial.println(" try again in 5 seconds");
            // Wait 5 seconds before retrying

void setup() {
    pinMode(BUILTIN_LED, OUTPUT);     // Initialize the BUILTIN_LED pin as an output
    client.setServer(mqtt_server, 1883);

void loop() {

    if (!client.connected()) {

    long now = millis();
    if (now - lastMsg > 2000) {
        lastMsg = now;
        snprintf (msg, 50, "hello world #%ld", value);
        Serial.print("Publish message: ");
        client.publish("outTopic", msg);

enter image description hereI'm beginner at IOT and I'm using NodeMcu ESP8266 board and I want to control it with Arduino IDE so I install everything necessary and also using PubSubClient library for that. I used example file of PubSub in arduino. The NodeMcu first connects to internet and after a second disconnects. I also switched the server(I don't know internet connection) from home modem to my mobile internet but it doesn't worked. I installed MQTT android application and want to connect to test server"test.mosquitto.org" and publish a meassage from NodeMcu to MQTT dashboard on my android mobile. what is the problem with this standard sample code?

  • I don't know how to add my sketch in a properly way. does anyone know? – sepehr Apr 2 at 21:02
  • 1
    One line: three back-apostrophes. Then paste your sketch. Then three back-apostrophes again on another line. – Majenko Apr 2 at 21:07
  • FYI: Return code -4 means: MQTT_CONNECTION_TIMEOUT - the server didn't respond within the keepalive time. It looks like your NodeMCU connects to your Wifi but cannot reach the MQTT broker. Can you ping test.mosquitto.org from your PC? – StarCat Apr 3 at 14:25
  • @jsotola, this looks like the mqtt_esp8266 example sketch that's part of the PubSubClient library – StarCat Apr 3 at 15:26
  • @sepehr, Your code connected and ran without problems on one of my NodeMCUs (with my Wifi credentials). The problem is not in your code. – StarCat Apr 3 at 15:31

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