#include
#include

const char* ssid = “Your wifi”;
const char* password = “password”;
const char* mqtt_server = “broker.emqx.io”;// Your server IP address
const char* mqtt_user = “ioctrl”;
const char* mqtt_password = “1234”;

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

void setup() {
pinMode(LED_BUILTIN, OUTPUT); // Initialize the BUILTIN_LED pin as an output
Serial.begin(115200);
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++) {
Serial.print((char)payload[i]);
}
Serial.println();

if ((char)payload[0] == ‘1’) {
digitalWrite(BUILTIN_LED, LOW); 
} else {
digitalWrite(BUILTIN_LED, HIGH); 
}

}

void reconnect() {
// Loop until we’re reconnected
while (!client.connected()) {
Serial.print(“Attempting MQTT connection…”);

if (client.connect(“ESP8266Client”, mqtt_user , mqtt_password)) {
Serial.println(“connected”);

client.subscribe(“led_topic”);
} 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();

long now = millis();
if (now – lastMsg > 2000) {
lastMsg = now;
value=analogRead(A0);
snprintf (msg, 1000, “%ld”, value/10);
Serial.print(“Publish message: “);
Serial.println(msg);
client.publish(“sensor_data”, msg);
}
}

• Open the serial monitor and check your wifi connections with ESP8266.
• Check the broker connection and ESP8266 connection with MQTT Broker.
• Check the message publishing to MQTT Broker is correct on specified Topic.