Polar BLE SDK

The Polar BLE SDK is the official library for connecting to Polar sensors and watches via Bluetooth LE on Android (minSdk 24) and iOS (14.0+). It allows developers to stream real-time data such as heart rate, ECG, accelerometer, and PPG.

Key Technical Detail: The SDK API utilizes ReactiveX for handling asynchronous operations.

The Polar OH1 optical heart rate sensor provides the following data streams via the SDK:

• Heart rate: Measured in beats per minute (BPM).
• Heart rate broadcast: Standard BLE heart rate broadcasting.
• Photoplethysmography (PPG): Raw PPG values.
• PP interval: Cardiac pulse-to-pulse interval (in milliseconds) extracted from the PPG signal.
• Accelerometer data: 3-axis acceleration data with a 50Hz sampling rate and an 8G range. Axis-specific acceleration is provided in mG.

The Polar H9 heart rate chest strap provides the following features through the Polar BLE SDK:

• Heart rate: Available as beats per minute (BPM) and RR Interval in milliseconds (ms).
• Heart rate broadcast: Supports heart rate broadcasting.

NOTE

Unlike the Polar H10, the Polar H9 does not support streaming over the BLE Polar Measurement Data (PMD) service.

SDK Mode is a device state that provides access to a wider range of raw stream capabilities, such as higher sampling rates and adjustable sensor ranges.

Important Trade-offs:

• Algorithms Disabled: When SDK Mode is enabled, all on-device algorithms are disabled. You will no longer receive computed data like heart rate, PP intervals, or RR intervals.
• Passive Data Disabled: Passive data gathering, such as activity or sleep tracking, is suspended.
• Sensor Management: All sensors (accelerometer, gyroscope, PPG, etc.) are shut down by default when entering SDK Mode. They are only enabled when you explicitly request them for streaming or offline recording.
• Battery Life: Using SDK Mode with low sampling rates for specific sensors can be a way to extend device lifetime.

The iOS Communications library provides three distinct levels of functionality for interacting with Polar devices over Bluetooth LE:

1. iOS Communications: The base layer providing core connection and communication logic. Used primarily by Polar's own applications.
2. Polar BLE SDK: A wrapper around the base library designed specifically for 3rd party developers. This is the primary entry point for most external integrations. It includes targets for both iOS (PolarBleSdk) and watchOS (PolarBleSdkWatchOs).
3. Polar BLE SDK PROPRIETARY: An internal-only version for Polar development, maintained on a separate branch (sdk-proprietary).

Note that the PolarBleSdk and PolarBleSdkWatchOs targets depend on the iOSCommunications base target.

Pulse-to-Pulse interval (PPI) is the signal between two main peaks of the Photoplethysmography (PPG) signal obtained from optical heart rate sensors (e.g., Polar wrist devices, Verity Sense, OH1).

Key Differences from ECG (R-R intervals):

• PPI is derived from optical PPG signals, whereas R-R intervals are derived from ECG (e.g., H9/H10).
• PPI is significantly more sensitive to noise such as movement or light leaking.

Critical Usage Constraint: PPI cannot be measured accurately during activity. It should only be used when the user is at complete rest.

Replace RxJava Schedulers with Kotlin Coroutine Dispatchers. While the SDK handles much of its own threading, you should use Dispatchers.Main for UI updates and withContext(Dispatchers.IO) or .flowOn(Dispatchers.IO) for background work.

// Launch on Main for UI
lifecycleScope.launch(Dispatchers.Main) {
    // Switch to IO for background work
    withContext(Dispatchers.IO) {
        // background task
    }
}

// Using flowOn for Flows
flow.flowOn(Dispatchers.IO)
    .collect { /* runs on caller's dispatcher */ }

Polar 360 battery levels dictate available functionality:

Charging Events (Firmware 2.0.8+, SDK 6.4.0+):

• CHARGING: Device is connected to a power source and charging.
• DISCHARGING ACTIVE: Device is operating and discharging.

Note on Storage Mode: When the device is turned off, it enters storage mode where the battery circuit is disconnected. Timekeeping is disabled in this mode. It is recommended to sync with the app and reset the time when the device is turned back on.