Concept:  The project aims to control a four LED using Bluetooth communication between an Android smartphone and an Arduino board. The LED can be turned on or off remotely from the smartphone app.

Working Method:

1.            The Bluetooth module is connected to the Arduino board, and the LED is connected to one of the Arduino's digital pins.

2.            The Arduino board is programmed to receive commands via Bluetooth from the smartphone app.

3.            The smartphone app sends a signal to the Bluetooth module on the Arduino board to turn the LED on or off.

4.            The Arduino board receives the signal and sets the digital pin connected to the LED to HIGH or LOW to turn the LED on or off, respectively.

5.            The LED will remain in the state specified by the last command received until a new command is sent.