Build an nRF52 BLE GATT Heart Rate Monitor with Android Kotlin App

Implementing an nRF52-based BLE GATT Server for Heart Rate Monitoring with a Companion Android App Using Kotlin

This tutorial will guide you through the process of implementing a Bluetooth Low Energy (BLE) GATT server using the nRF52 series microcontroller for heart rate monitoring. We will also cover creating a companion Android application using Kotlin to interact with the GATT server. By the end of this guide, you will have a functioning heart rate monitor that communicates with an Android device.

Prerequisites

• Basic knowledge of C programming and Kotlin.
• Familiarity with BLE concepts.
• Access to an nRF52 development kit (e.g., nRF52832 or nRF52840).
• Android Studio installed on your computer.
• Nordic SDK installed and configured for your development environment.

Parts/Tools

• nRF52 Development Kit
• Heart Rate Sensor (optional)
• Android Studio
• Nordic SDK
• Smartphone with Android 4.3 or later

Steps

1. Set Up the nRF52 BLE GATT Server
   1. Install the Nordic SDK and set up your development environment.
   2. Create a new project based on the BLE GATT server template.
   3. In your project, configure the heart rate service.

   
   #define HR_SERVICE_UUID 0x180D
   #define HR_MEASUREMENT_CHAR_UUID 0x2A37
   
   ble_gatts_char_md_t char_md;
   ble_gatts_attr_md_t attr_md;
   ble_gatts_attr_t attr_char_value;
               

   4. Implement the heart rate measurement characteristic in your code.
2. Write the GATT Server Code
   1. Create the heart rate service instance.

   
   void heart_rate_service_init() {
       // Implementation details...
   }
               

   2. Handle BLE events to notify connected devices of heart rate updates.

   
   void on_ble_event(ble_evt_t const *p_ble_evt) {
       // Handle notifications...
   }
               

3. Compile and Flash the Code
   1. Compile the project using your IDE.
   2. Connect your nRF52 development kit to your computer.
   3. Flash the compiled binary to the development kit.
4. Create the Companion Android App
   1. Open Android Studio and create a new project.
   2. Add the necessary Bluetooth permissions to your AndroidManifest.xml.

   
   <uses-permission android:name="android.permission.BLUETOOTH" />
   <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
               

   3. Implement the Bluetooth scanning functionality to discover the nRF52 device.

   
   val bluetoothAdapter: BluetoothAdapter = BluetoothAdapter.getDefaultAdapter()
   val filter = IntentFilter(BluetoothDevice.ACTION_FOUND)
   registerReceiver(receiver, filter)
               

   4. Create the UI to display heart rate data.
5. Connect and Test the Application
   1. Run the Android application on your smartphone.
   2. Scan for BLE devices and connect to your nRF52 GATT server.
   3. Request heart rate notifications from the server.

   
   bluetoothGatt.setCharacteristicNotification(characteristic, true)
               

   4. Display the heart rate data in the app.

Troubleshooting

• Device Not Found: Ensure that Bluetooth is enabled on your Android device and that it is in range of the nRF52 development kit.
• No Data Received: Verify that the heart rate characteristic is configured correctly and that notifications are enabled on the GATT server.
• Application Crashes: Check your logcat logs in Android Studio for any runtime exceptions and ensure all permissions are granted.

Conclusion

In this tutorial, you have successfully implemented an nRF52-based BLE GATT server for heart rate monitoring and created a companion Android app using Kotlin. With this foundation, you can expand the functionality to include additional features or integrate different sensors. Happy coding!