ESP32 Motion + Light Sensor (PIR + LDR) with Home Assistant – ESPHome & MQTT Guide

A motion sensor that only turns lights on when it’s dark is one of the most useful smart home automations.
By combining a PIR motion sensor with a simple LDR (light-dependent resistor) and an ESP32, it’s easy to build a local, fast, and cloud-free “smart presence + ambient light” node for Home Assistant.

This guide shows how to connect:

PIR sensor → detects motion
LDR + resistor → measures ambient light level

and integrate them into Home Assistant using:

ESPHome (auto-discovery)
MQTT (manual YAML configuration)

1. Hardware Required

ESP32 DevKit
PIR sensor (HC-SR501, AM312, or similar)
LDR (light-dependent resistor/photoresistor)
10kΩ resistor (for LDR voltage divider)
Jumper wires
Breadboard (optional)
USB cable

2. Wiring the PIR and LDR to ESP32

2.1 PIR Motion Sensor Wiring

Most PIR modules have three pins:

VCC (3.3V or 5V depending on module)
GND
OUT (digital motion signal)

Example wiring (3.3V-compatible PIR like AM312):

ESP32 → PIR
3.3V  → VCC
GND   → GND
GPIO27 → OUT

2.2 LDR + Resistor Voltage Divider

The ESP32 cannot read resistance directly, so the LDR is wired as a voltage divider with a fixed resistor.

3.3V ── LDR ── A0 (GPIO34, analog in)
A0 (GPIO34) ── 10kΩ ── GND

When it is bright, LDR resistance is low → higher voltage at A0
When it is dark, LDR resistance is high → lower voltage at A0

3. Method 1 – ESPHome Integration

ESPHome makes it easy to define both a motion binary sensor and a light-level sensor.

3.1 ESPHome YAML for PIR + LDR

esphome:
  name: esp32-motion-light
  platform: ESP32
  board: esp32dev

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

logger:
api:
ota:

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

# LDR on GPIO34 (analog read)
sensor:
  - platform: adc
    pin: 34
    name: "Hallway Light Level"
    update_interval: 5s
    attenuation: 11db          # allows 0–3.3V range
    filters:
      - multiply: 100.0        # optional scaling to 0–100 range

This exposes two entities in Home Assistant:

binary_sensor.hallway_motion
sensor.hallway_light_level

These can then be used in automations.

4. Method 2 – MQTT Integration (PIR + LDR)

For MQTT-based setups, the ESP32 publishes motion and light-level data via MQTT, and Home Assistant reads them via mqtt: sensors.

4.1 Home Assistant `configuration.yaml` – MQTT Sensors

mqtt:
  binary_sensor:
    - name: "Hallway Motion"
      state_topic: "home/hallway/pir"
      payload_on: "1"
      payload_off: "0"
      device_class: motion

  sensor:
    - name: "Hallway Light Level"
      state_topic: "home/hallway/light"
      unit_of_measurement: "%"
      value_template: "{{ value | float }}"

home/hallway/pir → receives "1" or "0"
home/hallway/light → receives a numeric value (0–100, for example)

4.2 ESP32 Arduino MQTT Code (PIR + LDR)

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

#define PIR_PIN 27
#define LDR_PIN 34

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

WiFiClient espClient;
PubSubClient client(espClient);

int lastPirState = -1;

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

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

  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_Motion_Light");
  }

  // PIR state
  int pirState = digitalRead(PIR_PIN);
  if (pirState != lastPirState) {
    lastPirState = pirState;
    if (pirState == HIGH)
      client.publish("home/hallway/pir", "1");
    else
      client.publish("home/hallway/pir", "0");
  }

  // LDR reading → convert 0–4095 to 0–100
  int raw = analogRead(LDR_PIN);
  float level = (raw / 4095.0) * 100.0;
  char buf[8];
  dtostrf(level, 1, 1, buf);
  client.publish("home/hallway/light", buf);

  client.loop();
  delay(500);
}

5. Home Assistant Dashboard Example

A simple card showing motion and light level:

type: entities
entities:
  - entity: binary_sensor.hallway_motion
  - entity: sensor.hallway_light_level

6. Example Automations (Only Turn Lights On When Dark)

The real power of combining PIR + LDR is conditional lighting: only turn lights on when motion is detected and it is dark.

6.1 Turn on light when motion is detected AND it’s dark

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

6.2 Turn off light after no motion for 2 minutes

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

7. Calibration Tips for the LDR

Because LDRs are not calibrated lux meters, it’s best to think of the reading as a relative light level:

Note the sensor value when the room is bright
Note the value when the room is too dark
Choose a threshold roughly in between (e.g. 40%)

If using ESPHome, the raw ADC reading (0–1.0 or 0–3.3V) can be scaled or mapped using filters.

Example scaling filter in ESPHome:

filters:
  - multiply: 100.0

This converts 0–1.0 to 0–100 for easier comparisons.

8. Troubleshooting

Motion is detected all the time

PIR pointed at hot objects (radiators, TVs)
PIR sensitivity too high (adjust trimmer on HC-SR501)
Warm-up period not completed (PIR modules often require 30–60 seconds after power-on)

LDR readings are unstable

Use an analog pin from ADC1 (GPIO32–GPIO39, not used by WiFi)
Use shielded or short wires
Apply a longer update_interval (5–10 seconds)

Light level seems inverted

If high values appear when it’s dark, swap the position of LDR and fixed resistor in the divider, then adjust logic or invert mapping.

9. Typical Use Cases

Hallway / staircase automatic lighting
Closet or pantry light that only turns on when it’s dark
Garage entrance lighting
Night lighting in children’s rooms
Entryway lights that don’t turn on during daytime

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