An ESP32 can easily replace five separate smart sensors with a single multi-sensor node that sends everything to Home Assistant:

• 🌡️ Temperature
• 💧 Humidity
• 🚶 Motion (PIR)
• 💡 Ambient light (LDR)
• 💦 Water leak (probe)

All fully local, no cloud, and powered from a single USB supply.

This guide shows how to build an all-in-one ESP32 multi-sensor, using:

• ESPHome (automatic integration), and
• MQTT with Arduino code (manual but flexible)

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1. Hardware Overview

Suggested sensor combination (cheap and easy to source):

• ESP32 DevKit
• BME280 (temperature, humidity, pressure – I²C)
• PIR motion sensor (AM312 or HC-SR501)
• LDR (photoresistor) + 10 kΩ resistor (light level)
• Water leak sensor (leak probe board or two stainless wires)
• USB power supply and cable
• Wires, small enclosure with holes/vents

You can swap BME280 with SHT45 or SHT31 – wiring and concept remain the same.

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2. Pin Assignments (All Sensors on One ESP32)

Recommended mapping (easy to remember and avoids conflicts):

• BME280 (I²C)
  • SDA → GPIO 21
  • SCL → GPIO 22
• PIR motion
  • OUT → GPIO 27
• LDR (light sensor)
  • LDR + 10 kΩ voltage divider → GPIO 34 (ADC)
• Water leak sensor
  • OUT / probe input → GPIO 32

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METHOD 1 – ESPHome Multi-Sensor Node

This is the simplest way: one ESPHome YAML file, auto-discovered by Home Assistant.

3. ESPHome YAML (All Sensors in One File)

esphome:
  name: esp32-multisensor
  platform: ESP32
  board: esp32dev

wifi:
  ssid: "YOUR_WIFI"
  password: "YOUR_PASSWORD"

logger:
api:
ota:

# -----------------------
# I2C bus for BME280
# -----------------------
i2c:
  sda: 21
  scl: 22
  scan: true

# -----------------------
# Environment: BME280
# -----------------------
sensor:
  - platform: bme280
    address: 0x76
    temperature:
      name: "Node Temperature"
      oversampling: 16x
    pressure:
      name: "Node Pressure"
    humidity:
      name: "Node Humidity"
    update_interval: 10s

  # Light sensor on ADC (LDR + 10k divider on GPIO34)
  - platform: adc
    pin: 34
    name: "Node Light Level"
    attenuation: 11db       # 0–3.3V
    update_interval: 5s
    filters:
      - multiply: 100.0     # scale to 0–100 (%-like)

# -----------------------
# Motion & Leak: binary sensors
# -----------------------
binary_sensor:
  # PIR motion sensor on GPIO27
  - platform: gpio
    name: "Node Motion"
    pin:
      number: 27
      mode:
        input: true
        pullup: true
    device_class: motion
    filters:
      - delayed_off: 2s

  # Water leak sensor on GPIO32
  - platform: gpio
    name: "Node Water Leak"
    pin:
      number: 32
      mode:
        input: true
        pullup: true
    device_class: moisture
    filters:
      - delayed_on: 200ms
      - delayed_off: 10s

After flashing this to the ESP32:

• Home Assistant detects esp32-multisensor automatically
• Entities appear for:
  • sensor.node_temperature
  • sensor.node_humidity
  • sensor.node_pressure
  • sensor.node_light_level
  • binary_sensor.node_motion
  • binary_sensor.node_water_leak

---

4. Example Home Assistant Dashboard

A simple Lovelace card grouping all sensors:

type: entities
entities:
  - entity: sensor.node_temperature
  - entity: sensor.node_humidity
  - entity: sensor.node_light_level
  - entity: binary_sensor.node_motion
  - entity: binary_sensor.node_water_leak

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METHOD 2 – MQTT Multi-Sensor Node (Your Style)

In this method, the ESP32 sends MQTT messages and Home Assistant reads them via mqtt: in configuration.yaml.

We’ll use:

• One JSON topic for environment data
• Separate topics for motion and leak

5. Home Assistant configuration.yaml (MQTT Sensors)

mqtt:
  sensor:
    - name: "Node Temperature"
      state_topic: "home/multisensor/env"
      value_template: "{{ value_json.temperature }}"
      unit_of_measurement: "°C"

    - name: "Node Humidity"
      state_topic: "home/multisensor/env"
      value_template: "{{ value_json.humidity }}"
      unit_of_measurement: "%"

    - name: "Node Pressure"
      state_topic: "home/multisensor/env"
      value_template: "{{ value_json.pressure }}"
      unit_of_measurement: "hPa"

    - name: "Node Light Level"
      state_topic: "home/multisensor/env"
      value_template: "{{ value_json.light }}"
      unit_of_measurement: "%"

  binary_sensor:
    - name: "Node Motion"
      state_topic: "home/multisensor/motion"
      payload_on: "1"
      payload_off: "0"
      device_class: motion

    - name: "Node Water Leak"
      state_topic: "home/multisensor/leak"
      payload_on: "LEAK"
      payload_off: "DRY"
      device_class: moisture

Topics used:

• home/multisensor/env → JSON with temp/hum/pressure/light
• home/multisensor/motion → "1" or "0"
• home/multisensor/leak → "LEAK" or "DRY"

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6. ESP32 Arduino MQTT Code (All Sensors Together)

This sketch reads:

• BME280 over I²C
• PIR on GPIO27
• LDR on GPIO34 (scaled 0–100)
• Leak on GPIO32

…and publishes to the topics defined above.

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

#define WIFI_SSID   "YOUR_WIFI"
#define WIFI_PASS   "YOUR_PASSWORD"
#define MQTT_SERVER "192.168.0.10"

#define PIR_PIN   27
#define LDR_PIN   34
#define LEAK_PIN  32

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

int lastMotion = -1;
int lastLeak = -1;

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

  pinMode(PIR_PIN, INPUT_PULLUP);
  pinMode(LEAK_PIN, INPUT_PULLUP);
  analogReadResolution(12); // 0–4095 on ESP32

  Wire.begin(21, 22);
  if (!bme.begin(0x76)) {
    Serial.println("BME280 not found!");
  }

  WiFi.begin(WIFI_SSID, WIFI_PASS);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
  }

  client.setServer(MQTT_SERVER, 1883);
}

void loop() {
  if (!client.connected()) {
    while (!client.connected()) {
      client.connect("ESP32_Multisensor");
    }
  }

  // ---------- Environment: BME280 + LDR ----------
  float temp = bme.readTemperature();
  float hum  = bme.readHumidity();
  float press = bme.readPressure() / 100.0F; // Pa → hPa

  int rawLdr = analogRead(LDR_PIN);          // 0–4095
  float lightPercent = (rawLdr / 4095.0) * 100.0;

  String envJson = "{";
  envJson += "\"temperature\":" + String(temp, 2) + ",";
  envJson += "\"humidity\":" + String(hum, 1) + ",";
  envJson += "\"pressure\":" + String(press, 1) + ",";
  envJson += "\"light\":" + String(lightPercent, 1);
  envJson += "}";

  client.publish("home/multisensor/env", envJson.c_str());

  // ---------- Motion ----------
  int motion = digitalRead(PIR_PIN);
  if (motion != lastMotion) {
    lastMotion = motion;
    if (motion == HIGH)
      client.publish("home/multisensor/motion", "1");
    else
      client.publish("home/multisensor/motion", "0");
  }

  // ---------- Leak ----------
  int leak = digitalRead(LEAK_PIN); // LOW when water present if wired to GND
  if (leak != lastLeak) {
    lastLeak = leak;
    if (leak == LOW)
      client.publish("home/multisensor/leak", "LEAK");
    else
      client.publish("home/multisensor/leak", "DRY");
  }

  client.loop();
  delay(2000);
}

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7. Example Automations

Motion-based light only when dark (using this node only)

automation:
  - alias: "Hallway Light On (Motion & Dark)"
    trigger:
      - platform: state
        entity_id: binary_sensor.node_motion
        to: "on"
    condition:
      - condition: numeric_state
        entity_id: sensor.node_light_level
        below: 40
    action:
      - service: light.turn_on
        target:
          entity_id: light.hallway

  - alias: "Hallway Light Off After No Motion"
    trigger:
      - platform: state
        entity_id: binary_sensor.node_motion
        to: "off"
        for: "00:02:00"
    action:
      - service: light.turn_off
        target:
          entity_id: light.hallway

Leak alarm

automation:
  - alias: "Node Leak Alarm"
    trigger:
      - platform: state
        entity_id: binary_sensor.node_water_leak
        to: "on"
    action:
      - service: notify.mobile_app
        data:
          message: "Water leak detected by multisensor node!"

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8. Placement Tips

For a single multi-sensor box:

• Mount high on a wall or shelf for good Wi-Fi, PIR field of view, and realistic room temperature
• Add side/bottom vents for airflow to the BME280
• Run leak probes via wires to floor level (under sink, behind appliance)
• Keep PIR away from direct sun and hot appliances
• Avoid placing the LDR where it sees direct lamp glare (unless that’s desired)

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