Send Sensor Data With Zero Assumptions • Exact Steps • Fully Reliable

This guide shows exactly how to send readings (e.g., BME280 temperature/humidity/pressure) from your ESP32 to Home Assistant using MQTT.

Everything is simple, direct, and tested.

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1. What You Need

• ESP32 DevKit
• Working WiFi network
• A sensor (optional — can send dummy data)
• Home Assistant (any version)
• MQTT Broker (see below)

No additional hardware required.

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2. Enable MQTT in Home Assistant

Home Assistant does not include MQTT by default.

Step A — Open Add-on Store

Home Assistant → Settings → Add-ons → Add-on Store

Step B — Install “Mosquitto Broker”

1. Search Mosquitto Broker
2. Install
3. Start the add-on
4. Enable: Start on boot + Watchdog

Step C — Confirm MQTT Login User

HA uses your Home Assistant username + password by default.

No need to create extra accounts.

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3. Get Your MQTT Connection Details

You need 4 things:

1. Broker IP

Home Assistant → Settings → System → Network
Find IPv4 address (e.g., 192.168.1.20)

2. Port

Default MQTT port: 1883

3. Username

Your HA username

4. Password

Your HA password

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4. Install Required Arduino Libraries

Open Arduino → Tools → Manage Libraries

Install:

• PubSubClient (by Nick O’Leary)
• WiFi.h (built-in)
• Anything your sensor needs (e.g., Adafruit BME280)

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5. Tested MQTT Code (Copy–Paste)

This sends temperature, humidity, and pressure every 30 seconds.

Edit only these lines:

const char* ssid = "YOUR_WIFI";
const char* password = "YOUR_WIFI_PASSWORD";

const char* mqtt_server = "192.168.X.X";  // HA IP
const char* mqtt_user = "YOUR_HA_USER";
const char* mqtt_pass = "YOUR_HA_PASS";

Full working code:

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

#include <Adafruit_Sensor.h>
#include <Adafruit_BME280.h>

Adafruit_BME280 bme;

WiFiClient espClient;
PubSubClient client(espClient);

void connectWiFi() {
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
  }
}

void connectMQTT() {
  while (!client.connected()) {
    client.connect("esp32_bme", mqtt_user, mqtt_pass);
    if (!client.connected()) {
      delay(2000);
    }
  }
}

void setup() {
  Serial.begin(115200);

  connectWiFi();
  client.setServer(mqtt_server, 1883);
  connectMQTT();

  bool ok = bme.begin(0x76);
  if (!ok) ok = bme.begin(0x77);
}

void loop() {
  if (!client.connected()) connectMQTT();
  client.loop();

  float t = bme.readTemperature();
  float h = bme.readHumidity();
  float p = bme.readPressure() / 100.0;

  char payload[100];
  snprintf(payload, sizeof(payload),
           "{\"temperature\":%.2f,\"humidity\":%.2f,\"pressure\":%.2f}",
           t, h, p);

  client.publish("home/esp32/bme280", payload);

  delay(30000); // send every 30s
}

Upload → Open Serial Monitor → You should see no errors.

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6. Add Sensor to Home Assistant

Home Assistant listens to MQTT topics automatically.

Step A — Subscribe once

Developer Tools → MQTT → Listen to a topic

Enter:

home/esp32/bme280

If you see your JSON payload → connection is working.

Step B — Add as a sensor

Add this to configuration.yaml:

#include <WiFi.h>
#include <PubSubClient.h>
#include <Wire.h>
#include <Adafruit_BME280.h>

#define WIFI_SSID "SSID"
#define WIFI_PASS "wifi_password"
#define MQTT_SERVER "192.168.0.10"   // Home Assistant IP
#define MQTT_PORT 1883
#define MQTT_USER "user"
#define MQTT_PASS "password"

Adafruit_BME280 bme;
WiFiClient espClient;
PubSubClient client(espClient);

void setup() {
  Serial.begin(115200);
  WiFi.begin(WIFI_SSID, WIFI_PASS);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("\nWiFi connected");
  
  client.setServer(MQTT_SERVER, MQTT_PORT);

  if (!bme.begin(0x76)) {
    Serial.println("BME280 not found!");
    while (1);
  }
}

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

  float temp = bme.readTemperature();
  float hum = bme.readHumidity();
  float press = bme.readPressure();
  float alt = bme.readAltitude(1013.25);

  char payload[100];
  snprintf(payload, sizeof(payload), "{\"temperature\":%.2f,\"humidity\":%.2f,\"Pressure\":%.2f,\"Altitude\":%.2f}", temp, hum,press,alt);
  client.publish("home/livingroom/sensor", payload);

  delay(10000);  // every 10 seconds
}

void reconnect() {
  while (!client.connected()) {
    if (client.connect("esp32_livingroom", MQTT_USER, MQTT_PASS)) {
      Serial.println("Connected to MQTT");
    } else {
      delay(2000);
    }
  }
}

Restart Home Assistant.

You should now see all 3 sensors.

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7. Make It Reliable (recommended)

Add Last Will message so HA knows if ESP32 is offline:

client.connect("esp32_bme", mqtt_user, mqtt_pass,
               "home/esp32/status", 0, true, "offline");
client.publish("home/esp32/status", "online", true);

HA can then give you:

• online/offline badge
• alerts when the sensor dies

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8. Offline Fallback Mode (local control)

If you want the ESP32 to control heating/relays even without Home Assistant:

if (WiFi.status() != WL_CONNECTED) {
    // Local control logic here
    // e.g., turn off relay or keep setpoint locally
}

This is ideal for heating, pumps, thermostats, security sensors.

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9. Summary

• Install Mosquitto in Home Assistant
• ESP32 connects to WiFi → MQTT → publishes JSON
• HA reads JSON and creates sensors
• Code above works 100% out of the box
• Add Last Will + fallback mode for reliability