MetaWearHandler.java

Purpose

The MetaWearHandler class in the Android layer manages communication between the HealthyWear Flutter app and MetaWear BLE sensors. It handles device discovery, connection, sensor initialization, data reading, and file writing.

Responsibilities

  • Scans for and connects to MetaWear devices (up to 2 devices simultaneously).

  • Initializes sensor fusion (IMU), temperature, and ambient light sensors.

  • Collects and processes telemetry.

  • Compresses and writes data to .gz files.

  • Sends real-time updates to Flutter via EventChannel.

Key Functionalities

1. Sensor Management

  • setupSensors: Initializes all active sensor modules (IMU, temperature, ambient light).

  • startSensorFusion, startTemperature, startAmbientLight: Start individual modules with callbacks.

  • stopAllSensors(): Graceful cleanup and stopping of streams.

2. Data Collection

Each reading is stored in buffer queues and written to file periodically:

Queue<String> bufferSensorFusion;
Queue<String> bufferTemperature;
Queue<String> bufferAmbientLight;

3. File Handling

  • Data is compressed using GZIPOutputStream.

  • Stored using dynamic filenames based on timestamps and device.

4. Bluetooth Communication

  • Uses Android BLE APIs to scan for MetaWear devices.

  • Maintains a list of bonded devices.

  • Maps device index to status and connection flags.

5. Status Mapping

public String getSensorStatus(int deviceIndex)

  • Returns sensor status as a JSON string.

  • Indicates connection, latest reading timestamps, and write-time.

Integration

  • Interfaced with Flutter through MethodChannel and EventChannel.

  • Used in MainActivity.java for initializing and managing BLE sensor logic.

  • Designed to work concurrently with another handler for multi-device support.

Best Practices

  • Separates scan logic and sensor management cleanly.

  • Ensures decoupled queues per device and sensor.

  • Buffered I/O reduces write frequency to storage, improving performance.

Dependencies

  • Android BLE

  • MetaWear SDK

  • Gson for JSON formatting

  • Java utility classes for Queues and file management

Additional Notes

  • Timestamps for each type of sensor are maintained individually for better diagnostics.

  • Code includes checks for board.isConnected() to ensure communication reliability.

  • Sensor fusion data is time-synchronized across multiple sensors.