Light Application Control (ESP32 + Android MQTT)

This project demonstrates controlling a light state via MQTT between an ESP32 (Arduino) device and an Android application.

• ESP32 firmware is in main.ino. It connects to Wi‑Fi, subscribes to esp32/light_control on HiveMQ public broker, and reacts to commands: ON, OFF, STATUS.
• Android app (Kotlin) is in App/LightControlApplication/. It uses Eclipse Paho MQTT to publish/subscribe on the same topic and display or control the state.

Features

• MQTT communication over public broker (broker.hivemq.com:1883)
• Commands: ON, OFF, STATUS
• Status messages from ESP32: STATUS_ON or STATUS_OFF
• Auto-reconnect for ESP32 when MQTT connection is lost

Repository Structure

• main.ino — ESP32 Arduino sketch
• App/LightControlApplication/ — Android app module (Gradle/Kotlin)
• LICENSE — License for this repository
• .gitignore — Git ignore rules for Android + Arduino

Prerequisites

Hardware

• ESP32 development board
• USB cable

Software

• Arduino IDE (or Arduino CLI)
• Android Studio (Arctic Fox or newer)

Arduino Libraries

• WiFi.h (bundled with ESP32 board support)
• PubSubClient (by Nick O'Leary)

Install ESP32 board support in Arduino IDE via Boards Manager, and install PubSubClient via Library Manager.

ESP32 Setup and Upload

1. Open main.ino in Arduino IDE.
2. Configure your Wi‑Fi:
   • Edit ssid and password in main.ino to match your network.
3. Select Board and Port:
   • Tools → Board → ESP32 Arduino → your ESP32 model
   • Tools → Port → your device port
4. Upload the sketch.
5. Open Serial Monitor at 115200 baud to see connection logs and status messages.

The sketch:

// Topic used by both ESP32 and Android app
const char* topic = "esp32/light_control";
// Commands expected from Android: ON | OFF | STATUS
// Status published by ESP32: STATUS_ON | STATUS_OFF

Android App Setup (Kotlin)

1. Open App/LightControlApplication/ in Android Studio.
2. Let Gradle sync. Ensure internet permission exists in the app manifest if you add UI activities.
3. The MQTT service is implemented in app/src/main/java/com/demo/lightcontrolapplication/MqttService.kt using Eclipse Paho client.
4. Run the app on a device/emulator with internet access.

MQTT Details

• Broker: broker.hivemq.com
• Port: 1883
• Topic: esp32/light_control
• Client IDs: Randomized for both ESP32 and Android to avoid conflicts.

Usage

• From the Android app, publish ON or OFF to toggle the ESP32 light state.
• Publish STATUS to request the current state.
• ESP32 publishes STATUS_ON or STATUS_OFF whenever state changes or upon status request.

Security Notes

• Replace the default Wi‑Fi credentials in main.ino before committing code to any public repository.
• Public brokers are for testing only. For production, host your own MQTT broker with TLS and authentication.
• Do not commit secrets (keystores, API keys). .gitignore is configured to help avoid accidental commits.

Troubleshooting

• If ESP32 fails to connect to Wi‑Fi: verify SSID/password and 2.4GHz availability.
• If MQTT connect fails: public brokers can rate‑limit; wait and retry or use your own broker.
• Ensure both ESP32 and Android use the exact same topic esp32/light_control.
• Check that corporate/VPN/firewall does not block port 1883.

License

This project is licensed under the terms in LICENSE.