ble-nrf52-multi-device-connection (BLE-Nordic---NRF52)

BLE multi-device connection system using Nordic nRF52. An Android app that connects to multiple wearable devices simultaneously and integrates sensor data for real-time visualization.

요약

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Purpose

Meaningful services from wearable devices require data from multiple devices to be unified and analyzable in one place. The goal was to go beyond single-device BLE connections and build simultaneous multi-device connectivity with integrated data visualization.

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Core technical challenge

Implementing BLE multi-connection on Android Android's BLE API is fundamentally designed for single-device connections. Implemented multi-device connectivity by repeating the BluetoothDevice.connectGatt() + BluetoothGattCallback.onConnectionStateChange() sequence for each device independently. Redesigned the callback structure with per-device variables so each device can be accessed and managed independently.

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System architecture

Nordic nRF52DK (hardware)
  + Heart rate sensor
    ↓
BLE GATT Profile (custom service/characteristic definitions)
    ↓
Android app (Java)
  — BLE scan and multi-device connection
  — Real-time data reception
  — SQLite storage + CSV export
  — Real-time and time-range graph visualization

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Features

1. Device scan & connection

• BLE device scanning and listing
• Simultaneous multi-device connection

2. Data collection & storage

• Real-time heart rate sensor data reception
• SQLite database storage
• CSV export (Bit field based data structure)

3. Data visualization

• Real-time line graph rendering
• Time-range data query and graph display
• Simultaneous visualization of multiple connected devices

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Design artifacts

• System architecture diagram
• BLE GATT profile design
• Use case diagram
• Sequence diagrams (data usage / device management)
• Class diagrams (Bluetooth / visualization / data)
• DB modeling / CSV modeling

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Stack

Java Android BLE (Bluetooth Low Energy) Nordic nRF52DK GATT Profile SQLite

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Structure

ble-nrf52-multi-device-connection/ ├── app/ │ └── src/main/java/ │ — BLE connection management │ — Real-time data reception │ — DB / CSV handling │ — Visualization (LineGraph, RealtimeData, SelecttimeData) └── build.gradle

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설계

1. 기본설계

2. 프로파일 구조

3. Use Case

4. functional requirement 4-1. 데이터 사용 기능

4-1-1. Suquence Diagram

4-2. WD 관리기능

4-2-1. Suquence Diagram

기능구현

1. UI

• 홈

• 기기 스캔 및 연결

• 데이터보기

2. 하드웨어

• Nordic nRF52DK

• 심박센서 연결

3. Visuallizaion

• 시각화 Diagram

• Point class

• Linegraph classDiagram

• SelecttimeDataActivity ClassDiagram

• RealtimeDataActivity ClassDiagram

4. Bluetooth

• Bluetooth ClassDiagram

• multiconnect BluetoothDevice # connectGatt ()를 한후 BluetoothGattCallback # onConnectionStateChange () 를 완료하고, 다른 기기 또한 이 과정을 반복하면서 진행해서 다중 연결을 한다. 기존의 함수에 새로운 변수들을 추가해서 각각의 함수에 접근할 때의 방법을 바꿔주었다.

5. Database & CSV

• DB 모델링

• CSV 모델링

• Bit field

6 Profile

• BLE GATT Profile

• 클래스 다이어그램

참고 (결과)

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그래프 출력 / 다중연결

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