PulseRelay

日本語版は README.ja.md をご覧ください。

PulseRelay is a local bridge between Bluetooth LE heart-rate devices and OSC-compatible applications. It connects directly to any tracker that implements the standard Bluetooth Heart Rate Service (0x180D) — no phone, no cloud, no vendor API in the real-time path — and forwards BPM to a local OSC endpoint over UDP (for example VRChat).

Current status: desktop app + CLI probe. The Avalonia desktop app streams live BPM from a real tracker on Windows 11 and forwards it over OSC; this has been verified on hardware with a Fitbit Charge 6. Linux builds include an experimental BlueZ/D-Bus BLE backend. macOS builds run with a simulated source.

Quick start (Windows 11)

If you just want to use PulseRelay and do not plan to work on the source code, install the Microsoft Store version. The commands below are for running from source.

dotnet run --project src/PulseRelay.Desktop -f net10.0-windows10.0.19041.0

1. Start heart-rate sharing on your device first (see the Charge 6 steps below).
2. Click Start in PulseRelay. The dashboard shows the device, live BPM, and OSC state.
3. OSC output is on by default and sends to 127.0.0.1:9000 at /avatar/parameters/VRCOSC/Heartrate/Value.

Using a Fitbit Charge 6 (example device)

The tracker side cannot be automated — PulseRelay can never press Share for you. Each session:

1. On the tracker, open the HR on equipment tile and keep its screen awake.
2. Tap Share, then Start on the tracker when it asks to share heart rate.
3. Click Start in PulseRelay.
4. Keep sharing active on the tracker for the whole session — leaving the Share screen stops the broadcast (PulseRelay will auto-reconnect once you start sharing again).

Note: the Charge 6 connects to one app or piece of equipment at a time. Close other connections (other PCs, gym equipment, the CLI probe) before starting.

Any other tracker that exposes the standard Heart Rate Service should work the same way; use its own "broadcast/share heart rate" feature and set the device name filter in PulseRelay's settings if several BLE devices are nearby.

OSC output

Setting	Default
Host	127.0.0.1
Port	9000
Address	/avatar/parameters/VRCOSC/Heartrate/Value (int)

All configurable in the app's settings (and via CLI flags for the probe). See docs/vrchat-osc.md.

Troubleshooting

• The app can't find the device — make sure the device is actually sharing (Charge 6: the "HR on equipment" screen must be open with Share started), Bluetooth is on, and the device is near the PC. If several BLE devices are around, set the device name filter (e.g. Charge 6) in settings.
• The device line shows a generic name — the UI shows the device's advertised name once connected (e.g. BLE Charge 6), falling back to your device name filter or "Bluetooth LE device". It should never show BLE <unknown> while connected; if it does, please report it.
• OSC isn't received — check the receiving app listens on the configured host/port (VRChat: enable OSC in the action menu; default port 9000) and that the OSC address matches what your avatar/receiver expects. The Output card shows send errors.
• "Device disconnected" right after connecting — the device is probably still connected to another app or equipment. Disconnect it everywhere else, restart sharing, and Start again.
• No data after ~10 s — the dashboard flags stale data and reconnects automatically after 30 s of silence. First readings can take ~20 s on some trackers; that is normal. If no first measurement arrives for 60 seconds after connecting, PulseRelay creates a fresh connection.
• Started without enabling sharing — if no BLE connection is established for 30 continuous minutes, PulseRelay stops the bridge to avoid scanning indefinitely. The app and tray stay open so you can enable sharing and press Start again. Once a connection has been established, this 30-minute limit is disabled; active streaming has no time limit.
• Closing the main window — by default the window hides to the tray and the bridge keeps running. This can be disabled in Settings. Use Quit in the tray menu for an orderly shutdown.

Layout

Project	Target	Purpose
src/PulseRelay.Core	net10.0	Platform-neutral models, 0x2A37 parser, source interfaces, mock source
src/PulseRelay.Osc	net10.0	Minimal OSC 1.0 encoder + UDP sender
src/PulseRelay.WindowsBle	net10.0-windows10.0.19041.0	WinRT GATT client (scan, pair, subscribe)
src/PulseRelay.App	net10.0	Bridge session/supervisor, settings, localization
src/PulseRelay.Desktop	both	Avalonia desktop app (dashboard)
src/PulseRelay.Probe	both	CLI: scan / connect / mock
tests/PulseRelay.Tests	net10.0	xunit unit + headless UI tests

See docs/architecture.md for the design.

Building

Any platform (macOS/Linux/Windows), .NET 10 SDK required (pinned via global.json):

dotnet build PulseRelay.CrossPlatform.slnf   # cross-platform projects + tests
dotnet test  PulseRelay.CrossPlatform.slnf
dotnet build PulseRelay.sln                  # full solution incl. Windows BLE (compiles anywhere, runs BLE only on Windows)

Running the CLI probe

On any platform — synthetic heart rate, optionally forwarded over OSC:

dotnet run --project src/PulseRelay.Probe -f net10.0 -- mock --osc
dotnet run --project src/PulseRelay.Probe -f net10.0 -- mock --interval-ms 1 --sample-count 1

On Windows 11 — real BLE (see docs/charge6-verification.md for the full checklist):

dotnet run --project src/PulseRelay.Probe -f net10.0-windows10.0.19041.0 -- scan --service 180D --verbose
dotnet run --project src/PulseRelay.Probe -f net10.0-windows10.0.19041.0 -- connect --name "Charge 6" --verbose

On Linux with BlueZ running on the system bus — experimental real BLE:

dotnet run --project src/PulseRelay.Probe -f net10.0 -- scan --service 180D --verbose
dotnet run --project src/PulseRelay.Probe -f net10.0 -- connect --name "Charge 6" --verbose

PulseRelay deliberately does not use the Fitbit Web API, Google Health API, or any cloud service for real-time BPM, and never persists Bluetooth addresses (tracker addresses are rotating RPAs, not stable identities).

License

MIT — see LICENSE.