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Smart Home 18 min read • Updated: March 2025

Smart Lighting with Alexa & Google Home

Build a complete voice-controlled smart lighting system using NodeMCU ESP8266, relay modules, and Home Assistant. Control your lights with Alexa and Google Assistant.

1. Project Overview

In this project, we'll build a complete smart lighting system that integrates with both Amazon Alexa and Google Home. You'll be able to control your lights with voice commands like "Alexa, turn on the living room lights" or "Hey Google, dim the bedroom lights to 50%".

This system is expandable - start with one light and add more channels as needed. You can control lamps, ceiling lights, LED strips, or any AC appliance safely.

2. Required Components

3. Understanding Relay Modules

A relay is an electrically operated switch. It allows low-voltage DC (from NodeMCU) to control high-voltage AC (your lights) safely through electromagnetic isolation.

Relay Module Pinout

DC Side (Low Voltage)          AC Side (High Voltage)
┌─────────────────┐           ┌──────────────────────┐
│ VCC  ─── 5V     │           │ COM  ─── Live In    │
│ GND  ─── GND    │           │ NO   ─── Live Out  │
│ IN1  ─── GPIO   │           │ NC   ─── (Unused)   │
└─────────────────┘           └──────────────────────┘
    Control Side                  Load Side

Relay Types

Type	Active	Description
Active HIGH	3.3V/5V	Relay turns ON when GPIO is HIGH
Active LOW	GND	Relay turns ON when GPIO is LOW (more common)

4. Hardware Setup

NodeMCU ESP8266 Pinout:
┌─────────────────┐
│  VIN   GND      │  VIN = 5V power in
│  D0    D1       │  D1 = GPIO 5 (relay control)
│  D2    D3       │  D0 = GPIO 16
│  D4    D5       │  D4 = GPIO 2 (built-in LED)
│  D6    D7       │
│  D8    RX       │
│  TX    RST      │
└─────────────────┘

5. NodeMCU Programming

Option 1: Arduino IDE with MQTT

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

// WiFi credentials
const char* ssid = "YOUR_WIFI_SSID";
const char* password = "YOUR_WIFI_PASSWORD";

// MQTT Broker
const char* mqtt_server = "192.168.1.100";  // Your broker IP
const int mqtt_port = 1883;

// Relay pin
#define RELAY_PIN D1  // GPIO 5

// MQTT Topics
const char* lightTopic = "home/livingroom/light";
const char* lightStateTopic = "home/livingroom/light/state";

WiFiClient espClient;
PubSubClient client(espClient);

void setup_wifi() {
  delay(10);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
  }
}

void reconnect() {
  while (!client.connected()) {
    String clientId = "NodeMCU-" + String(random(0xffff), HEX);
    if (client.connect(clientId.c_str())) {
      client.subscribe(lightTopic);
    } else {
      delay(5000);
    }
  }
}

void callback(char* topic, byte* payload, unsigned int length) {
  String message;
  for (int i = 0; i < length; i++) {
    message += (char)payload[i];
  }
  
  if (message == "ON") {
    digitalWrite(RELAY_PIN, LOW);  // Active LOW
    client.publish(lightStateTopic, "ON");
  } else if (message == "OFF") {
    digitalWrite(RELAY_PIN, HIGH);  // Active LOW
    client.publish(lightStateTopic, "OFF");
  }
}

void setup() {
  pinMode(RELAY_PIN, OUTPUT);
  digitalWrite(RELAY_PIN, HIGH);  // Start OFF (Active LOW)
  
  setup_wifi();
  client.setServer(mqtt_server, mqtt_port);
  client.setCallback(callback);
}

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

Option 2: ESPHome (Recommended for Home Assistant)

ESPHome is the easiest way to integrate with Home Assistant:

# living_room_light.yaml
esphome:
  name: living_room_light
  platform: ESP8266
  board: nodemcuv2

wifi:
  ssid: "YOUR_WIFI_SSID"
  password: "YOUR_WIFI_PASSWORD"

# Enable Home Assistant API
api:
  password: "your_api_password"

ota:
  password: "your_ota_password"

# Relay configuration
switch:
  - platform: gpio
    name: "Living Room Light"
    pin: D1
    id: living_room_relay
    restore_mode: ALWAYS_OFF
    
# Optional: Status LED
status_led:
  pin:
    number: D4
    inverted: true

Upload to NodeMCU:

# Install ESPHome
pip install esphome

# Compile and upload
esphome living_room_light.yaml run

6. Home Assistant Setup

Install Home Assistant

Choose one of these installation methods:

• Home Assistant OS: Complete OS for Raspberry Pi or VM
• Home Assistant Container: Docker installation
• Home Assistant Supervised: On existing Linux

# Docker installation example
docker run -d \
  --name homeassistant \
  --privileged \
  --restart=unless-stopped \
  -e TZ=MY_TIME_ZONE \
  -v /path/to/config:/config \
  --network=host \
  ghcr.io/home-assistant/home-assistant:stable

Add ESPHome Integration

1. Open Home Assistant UI
2. Go to Settings → Devices & Services
3. Click Add Integration
4. Search for ESPHome
5. Your NodeMCU should appear automatically
6. Click Submit and enter API password

Configure MQTT Light (Alternative)

Add to your configuration.yaml:

mqtt:
  switch:
    - name: "Living Room Light"
      state_topic: "home/livingroom/light/state"
      command_topic: "home/livingroom/light"
      payload_on: "ON"
      payload_off: "OFF"
      qos: 1
      retain: true

7. Alexa Integration

Option 1: Home Assistant Cloud (Nabu Casa) - Easiest

1. In Home Assistant, go to Settings → Home Assistant Cloud
2. Click Start Free Trial ($6.99/month after 1 month free)
3. Create account and log in
4. Enable Alexa integration
5. Say: "Alexa, discover devices"
6. Your lights will appear in Alexa app

Option 2: HA-Bridge (Free, More Complex)

HA-Bridge emulates Philips Hue bridge for Alexa:

# Docker installation
docker run -d \
  --name ha-bridge \
  --net=host \
  -v /path/to/config:/config \
  bwssytems/ha-bridge

1. Access HA-Bridge at http://your-ip:80
2. Add new device with MQTT commands
3. Set On/Off URLs to publish MQTT messages
4. In Alexa app: Devices → + → Add Device
5. Say: "Alexa, discover devices"

Option 3: Home Assistant Skill (Legacy)

Use the official Home Assistant skill in Alexa app (requires port forwarding or Duck DNS).

8. Google Home Integration

Home Assistant Cloud (Recommended)

1. In Home Assistant Cloud, enable Google Assistant
2. Link your Home Assistant account in Google Home app
3. Say: "Hey Google, sync my devices"
4. Control lights with: "Hey Google, turn on living room light"

Manual Configuration

Expose specific entities to Google:

# configuration.yaml
google_assistant:
  project_id: YOUR_PROJECT_ID
  service_account:
    key_file: /config/google_credentials.json
  expose_by_default: false
  exposed_domains:
    - switch
    - light
  entity_config:
    switch.living_room_light:
      expose: true
      room: Living Room
      aliases:
        - Main Light
        - Ceiling Light

9. Voice Commands & Routines

Basic Voice Commands

Alexa	Google Home	Action
"Turn on living room light"	"Turn on living room light"	Switch ON
"Turn off living room light"	"Turn off living room light"	Switch OFF
"Dim living room light to 50%"	"Set living room light to 50%"	Dim (if supported)
"Brighten living room light"	"Brighten living room light"	Increase brightness

Creating Routines

Alexa Routine - "Good Morning":

1. Open Alexa app → More → Routines
2. + → When: Voice → "Good morning"
3. Add action: Smart Home → Turn on living room light
4. Add action: Smart Home → Turn on kitchen light
5. Add action: Music → Play morning news

Google Routine - "Good Night":

1. Open Google Home app → Routines
2. + → Starter: "Hey Google, good night"
3. Add action: Turn off all lights
4. Add action: Set thermostat to 68°F
5. Add action: Play sleep sounds

Home Assistant Automations

# Automations in configuration.yaml
automation:
  - alias: "Sunset - Turn on lights"
    trigger:
      platform: sun
      event: sunset
    action:
      service: switch.turn_on
      target:
        entity_id: switch.living_room_light
        
  - alias: "Motion - Turn on hallway light"
    trigger:
      platform: state
      entity_id: binary_sensor.hallway_motion
      to: "on"
    action:
      service: switch.turn_on
      target:
        entity_id: switch.hallway_light
      data:
        duration: 60  # Turn off after 60 seconds

10. Safety Considerations

Best Practices

• Use LED bulbs (lower power, less heat)
• Label all wires before disconnecting
• Take photos of original wiring
• Test with low voltage first
• Keep DC and AC wiring separated
• Use strain relief on all cables
• Ground metal enclosures

11. Troubleshooting

Problem: NodeMCU Won't Connect to WiFi

• Check SSID and password (case-sensitive)
• Ensure 2.4GHz network (ESP8266 doesn't support 5GHz)
• Move closer to router
• Check MAC filtering on router
• Try static IP configuration

Problem: Relay Clicks But Light Doesn't Turn On

• Check AC wiring connections
• Verify light bulb works
• Test relay with multimeter (continuity between COM and NO)
• Ensure relay is rated for your voltage/current

Problem: Home Assistant Can't Find Device

• Ensure NodeMCU and HA are on same network
• Check API password matches
• Verify mDNS is working
• Try static IP for NodeMCU
• Check firewall settings

Problem: Alexa/Google Can't Discover Devices

• Ensure entities are exposed to cloud
• Check Home Assistant Cloud status
• Try "Alexa/Google, sync my devices"
• Verify entity has unique name
• Check entity is not disabled