Claudelk

Drive an ELK-BLEDOM Bluetooth LED strip from .NET, and (optionally) wire it to Claude Code lifecycle hooks so the strip reflects whatever Claude is doing — colour, blink, off, whatever you map it to.

Inspired by claude-lamp (MIT, bobek-balinek). Claudelk targets the cheap ELK-BLEDOM strips that ship on AliExpress, runs on Windows, and is implemented in C# on .NET 10.

Status: CLI and Claude Code integration both shipped. The integration runs without a long-running daemon — each hook fires the published exe with async: true so Claude never blocks on the ~1.6 s BLE write.

Solution layout

Claudelk.slnx
└── src/
    ├── Claudelk.Core/    BLE + protocol library (reusable)
    └── Claudelk.Cli/     claudelk.exe — command-line interface

Requirements

• Windows 10 build 1809 (17763) or later — needed for the WinRT BLE stack that 32feet.NET wraps.
• .NET 10 SDK.
• An ELK-BLEDOM (or compatible: ELK-BLE, LEDBLE, MELK, ELK-BULB, ELK-LAMPL) strip, powered, in range, and not currently connected to the vendor mobile app.

Build & publish

# Dev build (use 'dotnet run' afterwards):
dotnet build Claudelk.slnx

# Production exe used by Claude Code hooks (~1.6 s cold per command):
dotnet publish src/Claudelk.Cli -c Release
# Default output: .build\bin\Claudelk.Cli\Release\<tfm>\publish\
#
# To install elsewhere (e.g. so Claude Code hooks can invoke a stable path),
# create `src/Claudelk.Cli/Claudelk.Cli.csproj.user` — gitignored, picked up
# automatically by MSBuild — with:
#   <Project>
#     <PropertyGroup>
#       <PublishDir>C:\Path\To\Install\</PublishDir>   <!-- pick any path -->
#     </PropertyGroup>
#   </Project>

Use

The examples below assume your publish directory is on PATH so claudelk resolves directly. Otherwise substitute the full exe path.

# 1. Discover nearby strips.
claudelk scan              # add --debug to see all BLE adverts

# 2. Save a device as the default target. This also runs Windows pair so
#    subsequent commands skip the advert scan and connect in ~1 s.
claudelk pair <device-id>

# 3. Drive it.
claudelk ensure                                # verify connection (re-pair / power-on if needed), then white
claudelk on
claudelk color "#ff8800"
claudelk blink "#ff0000"                       # default 4×250ms, holds colour
claudelk blink "#ff0000" 10 250 --end "#ffffff" # 5s pulse, ends white
claudelk brightness 60
claudelk effect 0x87
claudelk off

Every command accepts --device <id> to override the default. The saved device id lives at %APPDATA%\Claudelk\config.json.

Claude Code integration

The integration is purely lifecycle hooks in your user-level ~/.claude/settings.json — no daemon process. Each event invokes claudelk.exe with "async": true and "shell": "powershell" so Claude Code returns immediately while the strip catches up in the background.

How loud you want the strip to be is entirely up to you. Below are two example configurations to crib from — neither is mandatory.

Example A — "ambient white, blink when Claude wants me"

The strip glows white whenever Claude Code is open, blinks red for 5 s on permission prompts, blinks yellow for 3 s when Claude finishes and is waiting for your next message. Never turns off.

Event	Matcher	Strip state
SessionStart	—	solid white #ffffff
Notification	permission_prompt	red #ff0000, 5 s blink, ends on white
Notification	idle_prompt	yellow #ffff00, 3 s blink, ends on white

ensure is used instead of plain color so a fallen-out Windows pairing or a powered-off strip is repaired on session start (reconnect → idempotent re-pair → power-on → set white).

"SessionStart": [{
  "hooks": [{
    "type": "command", "shell": "powershell", "async": true,
    "command": "& 'C:\\path\\to\\claudelk.exe' ensure"
  }]
}],
"Notification": [
  {
    "matcher": "permission_prompt",
    "hooks": [{
      "type": "command", "shell": "powershell", "async": true,
      "command": "& 'C:\\path\\to\\claudelk.exe' blink '#ff0000' 10 250 --end '#ffffff'"
    }]
  },
  {
    "matcher": "idle_prompt",
    "hooks": [{
      "type": "command", "shell": "powershell", "async": true,
      "command": "& 'C:\\path\\to\\claudelk.exe' blink '#ffff00' 6 250 --end '#ffffff'"
    }]
  }
]

Example B — strip mirrors every lifecycle phase

The strip changes colour on every event. Closer to claude-lamp's behaviour but produces a lot of BLE traffic (PreToolUse fires on every tool call).

Event	Strip state
SessionStart	amber #ffaa00 (ready)
UserPromptSubmit	cyan #00ccff (thinking)
PreToolUse (*)	orange #ff8800 (acting)
Stop	green #00ff44 (idle)
Notification	blink red #ff0000
SessionEnd	off

Notification matcher values

The Notification event fires for several distinct reasons. Useful matchers:

Matcher	Meaning
permission_prompt	Claude is asking you to approve a tool call
idle_prompt	Claude finished its turn and is waiting on your reply
elicitation_dialog	An MCP server is asking you for structured input

Combine with \| for regex alternation, e.g. "matcher": "permission_prompt|idle_prompt".

After editing settings.json, open /hooks in Claude Code once to reload the config (or start a fresh session).

Protocol summary

Every command is a 9-byte BLE GATT write to 0000fff3-0000-1000-8000-00805f9b34fb on service 0000fff0-...:

Action	Bytes
Power on	7e 00 04 01 00 00 00 00 ef
Power off	7e 00 04 00 00 00 00 00 ef
Brightness %	7e 00 01 NN 00 00 00 00 ef
RGB colour	7e 00 05 03 RR GG BB 00 ef
Effect speed	7e 00 02 NN 00 00 00 00 ef
Built-in fx	7e 00 03 CC 03 00 00 00 ef (CC = 0x80–0x9f)
Temperature	7e 00 03 NN 02 00 00 00 ef

Brightness is only honoured in solid-RGB mode — built-in effects and grayscale modes ignore it. See NOTICE.md for the upstream sources that documented these byte formats.

Performance

Path	Time
dotnet run --project ...	~6 s
claudelk.exe <cmd> (paired, cold)	~1.6 s
Within one process (e.g. blink's 8 writes)	~30 ms each

Dispatcher.ResolveDeviceAsync calls Bluetooth.GetPairedDevicesAsync() first and only falls back to a 3 s advert scan if the device is unknown to Windows — pairing once during claudelk pair is what keeps every later command sub-2-second. Going below the ~1.6 s floor needs a daemon that holds the GATT connection open across invocations; that work is not done.

Roadmap

1. ✅ Standalone CLI to scan, pair, and drive an ELK-BLEDOM strip.
2. ✅ Claude Code hooks for SessionStart, UserPromptSubmit, PreToolUse, Stop, Notification, and SessionEnd.
3. ⏳ Optional long-running daemon to push per-command latency from ~1.6 s to <100 ms. Not needed for the hook flow above; only relevant if you want sub-second feedback on every individual tool call.

Credits

See NOTICE.md for full attribution.

License

MIT — see LICENSE.