How can an Android phone send a targeted message through Bluetooth to an Arduino HC-05 module?

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To send a targeted message through Bluetooth from an Android phone to an Arduino HC-05 module, follow these steps:

1. Connect the HC-05 module to the Arduino and upload a sketch to initialize the module.

2. Pair the Android phone with the HC-05 module. This can be done by enabling Bluetooth on both devices and searching for available devices on the Android phone. Once the HC-05 module is detected, select it and enter the default password "1234" if prompted.

3. Install a Bluetooth serial terminal app on the Android phone, such as Bluetooth Terminal or Serial Bluetooth Terminal. Open the app and connect to the HC-05 module by selecting it from the list of available devices.

4. Once connected, use the app to type a message in the terminal window. The message should follow a specific format that the Arduino sketch can parse and process. For example, you could use a comma-separated format where the first value represents the command to execute and the second value contains the data to use. For example, "LED,1" could indicate turning on an LED connected to the Arduino.

5. In the Arduino sketch, read the incoming data from the HC-05 module using the Serial.read() function. Parse the data to extract the command and data values, then execute the corresponding action using the appropriate pin or component on the breadboard.

6. Send a response message back to the Android phone if needed, indicating whether the command was successful or not. This can be done using the Serial.write() function to send back a message in the same format as the incoming message.

With these steps, you should be able to send targeted messages from an Android phone to an Arduino HC-05 module over Bluetooth, allowing for remote control of various components and sensors.