PolarBLE is a C# .NET 8 WinForms application that connects to a Polar H10 ECG sensor over Bluetooth Low Energy (BLE) and streams raw ECG and accelerometer data in real time to LabStreamingLayer (LSL).
This project is a port of my previous PolarBand2lsl Python/Kivy implementation. I took info from the project Dont-hold-your-breath by Kieran Brennan. Look it up!
- Scan for nearby Polar straps via BLE
- Connect and start the Polar Measurement Data (PMD) ECG and accelerometer streams
- Decode and stream 130 Hz ECG data to LSL
- Decode and stream 200 Hz accelerometer data to LSL, including delta-compressed frames
- Live sample-count telemetry for both streams
- Battery level, updated live for the duration of the recording
Two outlets are advertised. <device> is the strap's advertised name, e.g. Polar H10 12345678, and <address> is its Bluetooth address in hex.
| Stream name | Type | Channels | Unit | Rate | source_id |
|---|---|---|---|---|---|
<device>_ECG |
ECG |
ECG |
microvolts | 130 Hz | PolarBLE:<address>:ECG |
<device>_ACC |
Accelerometer |
X, Y, Z |
milli-g | 200 Hz | PolarBLE:<address>:ACC |
The source_id is derived from the Bluetooth address, so a recorder can re-bind to the same physical strap after a dropout, and two straps recorded simultaneously never collide.
Each stream also carries an acquisition metadata block naming the manufacturer, model, device address and the exact PMD settings that were requested — sample rate, resolution, and for the accelerometer the ±8 g range.
PolarBLE does not compute timestamps itself. Each burst of decoded samples is pushed to LSL in one push_chunk call with no timestamp argument, so liblsl stamps it at push time — the same thing it has always done for a single-sample push, just called once per BLE notification instead of once per sample.
- Windows 10 (build 17763) or later
- .NET 8 Desktop Runtime to run a release build, or the .NET SDK 8.0 or newer to build from source
- Bluetooth LE–capable adapter (internal or external)
- Polar H10 ECG sensor
Download the latest release from the GitHub repository, unzip and run.
- Press Scan. Nearby Polar straps appear in the list. The strap has to be worn, or its electrodes moistened, before it advertises.
- Select a strap and press Connect, or double-click it. Connecting can take up to a minute.
- Once connected, the window shows the measured sample rate of both streams. Dropped frames and timing gaps are counted and shown in red.
- Press Disconnect, or close the window, to stop the measurement cleanly. This matters: without it the strap keeps streaming and draining its battery.
If the strap refuses a configuration, or a required service is missing, the reason is reported in the window instead of leaving an empty stream advertised on the network.
git clone https://github.com/markspan/PolarBLE.git
cd PolarBLE
dotnet build PolarBLE.sln -c Release
dotnet test PolarBLE.sln
Or open PolarBLE.sln in Visual Studio 2022 and press F5.
| Path | Purpose |
|---|---|
src/PolarBLE.Core |
Platform-free core: PMD protocol codec, sample timing, the LSL sink. Targets plain net8.0 so it can be tested without a radio. |
src/PolarBLE.App |
Windows shell: WinRT Bluetooth and the WinForms user interface. |
tests/PolarBLE.Core.Tests |
xUnit tests for the codec and the sample clock. No hardware required. |
third_party/liblsl |
Vendored, unmodified liblsl C# binding and its native lsl.dll. |
The separation is deliberate: every byte-level decoding rule is a pure function over a ReadOnlySpan<byte>, so the places where a silent data-corruption bug could hide are covered by tests rather than by hoping a recording looks plausible.
Distributed under the GNU Lesser General Public License v2.1. See LICENSE.
The vendored liblsl binding in third_party/liblsl is covered by its own upstream licence.