RRStreamer

Android client that streams heart rate and beat-to-beat interval data from a BLE heart-rate band to the network as Lab Streaming Layer marker streams. Two band families are supported, with the right protocol picked automatically at connect time:

• ECG bands (Polar H10, Wahoo TICKR, Garmin HRM-Pro, Coospo, Decathlon Kalenji, Suunto Smart Sensor, and any band advertising the standard BLE Heart Rate service 0x180D with R-R intervals) — streams HR + true R-R intervals from the standard Heart Rate Measurement characteristic 0x2A37.
• Optical (PPG) bands (Polar Verity Sense, Polar OH1, Polar OH1+) — streams HR + PP (peak-to-peak) intervals via Polar's proprietary Polar Measurement Data (PMD) service.

Behaviour matches the Python and Rust references at HRBand-LSL on the HR side; the PP path is unique to this client.

Project page (with screenshots and architecture): abcsds.github.io/RRStreamer · Source: github.com/abcsds/RRStreamer

Install

The easiest way to get the app is the prebuilt APK from the latest release:

1. On your Android phone, allow installs from your browser (Settings → Apps → Special access → Install unknown apps).
2. Download RRStreamer-vX.Y.Z.apk from the release page.
3. Open the file. Android will prompt for confirmation; tap Install.

Min Android version: 8.0 (API 26). Tested on Android 15 (API 35).

Build from source

The project ships a Nix flake that provisions JDK 17, Gradle 8, the Android SDK + NDK, adb, and Python with pylsl. The phone needs developer mode with USB debugging enabled and connected over adb.

git clone https://github.com/abcsds/RRStreamer.git
cd RRStreamer

nix run                   # build APK, install on connected device, launch (preferred)
nix run .#build           # just build APK; output ends up at app/build/outputs/apk/release/
nix build                 # ./result/bin/{rrstreamer-build,rrstreamer-run} wrappers
nix develop               # drop into a shell with gradle, adb, JDK, NDK, sdkmanager

nix build produces wrapper scripts rather than a packaged APK because Gradle fetches its dependencies from Maven Central during the build and pure Nix derivations can't access the network. Run result/bin/rrstreamer-build (or just nix run .#build) to get the APK at app/build/outputs/apk/release/app-release.apk.

Using the app

1. Grant Bluetooth (and on Android 13+, notification) permissions.
2. Tap Scan, wait a few seconds, then tap a device (e.g. Polar H10 ABC12345).
3. The app connects, picks the right BLE protocol, and pushes samples to two LSL outlets. The HR outlet is always the same; the second outlet swaps RR ↔ PP based on what the band can give you:

Outlet	Stream Name	Type	Channels	Format	Source ID
HR	HR <devicename>	Markers	1	int32	HR_markers_<devicename>
RR (ECG bands)	RR <devicename>	Markers	1	int32	RR_markers_<devicename>
PP (PPG bands)	PP <devicename>	Markers	1	int32	PP_markers_<devicename>

Both intervals are pushed as milliseconds (rounded int). A foreground service keeps the connection alive when the screen is off.

Protocol selection

On every connect the app subscribes to the standard 0x2A37 first; on the first notification it inspects the RR-intervals flag bit. If RR is present it stays there (ECG path); if it isn't and the device exposes the Polar PMD service (FB005C80-…), the app unsubscribes, requests MTU 232, chains through the PMD CCCD writes, and finally writes a start PPI request to the PMD control point. Subsequent samples come back as PPI frames on the PMD data characteristic and surface as the PP <devicename> outlet.

A note on PP-derived HRV

RMSSD, the short-term HRV indicator shown in the UI, is technically an RR-domain metric. From PP samples it's an approximation — the PPG waveform smooths out the sharp R-peak and adds optical-path latency. The UI flags this with a ≈ prefix on the RMSSD label and an "approx" qualifier on the 100-beat graph; the approximation is still useful for relative comparisons (rest vs. exertion within one session) but should not be treated as ECG-grade.

Verify the stream

On any machine on the same network:

pip install pylsl
python scripts/verify_lsl.py

The script resolves HR … and RR … / PP … streams and prints each sample as it arrives. Inside nix develop it's already available as python3 scripts/verify_lsl.py.

How LSL is bundled

• Native liblsl.so (v1.16.2) for arm64-v8a, armeabi-v7a, x86, x86_64 is fetched from mvidaldp/liblsl-android-builder via Nix; Gradle reads the path from RRSTREAMER_LSL_JNILIBS and uses it directly without mutating the source tree.
• libjnidispatch.so ships with the JNA Android AAR (net.java.dev.jna:jna:5.13.0@aar).
• The Java bindings (edu.ucsd.sccn.LSL) are vendored from liblsl-Java with two small upstream-bug patches noted in the file header.

License

MIT — see LICENSE.

Author: Alberto Barradas (@abcsds)