Quick Introduction and Small Disclaimer

I really hope you find this guide helpful. I am no authority on this protocol and you should treat this all with a grain of salt, and assume that any of this could change at any time. I did my best to document what I found.

At the time of writing (07-13-2025) my Elegoo Centauri Carbon is on Firmware version 1.1.29

What is SDCP

SDCP, specifically SDCP 3.0, from what I could tell is an MQTT over WebSockets protocol developed by cbd-tech; a Chinese manufacturer of 3D printer mainboards as well as the company behind ChituBox, the popular slicing software for resin printers.

Elegoo appears to have partnered with cbd-tech on most likely the mainboard, and has thus landed on using SDCP for their latest and greatest...the Elegoo Centauri Carbon.

SDCP implementation varies

Just because a printer uses SDCP doesn't mean it will use the same cmd codes, status codes, or payloads. This is a per-printer specification. So Cmd code 129 might mean pause the print on the Elegoo Centauri Carbon but might mean start on some other printer.

Connecting To your Printer

The Centauri Carbon's websocket server is available at your printers local IP ws://192.168.XX.XX/websocket, it requires no handshake or authentication so you can imediatly start sending events via something like postman.

Keeping the Connection open

By default the websocket connection will get closed after 60 seconds of nothing from the client. From my experience any cmd will work to reset but you can also send a simple "ping" message body.

Known Commands and what they do...

Cmd	Function	Description	Example
0	Request Status Update	Prompts the printer to send its current status immediately.	View
1	Get Device Attributes	Returns printer name, firmware, capabilities, IP, MAC, supported features, and other device metadata.	View
128	Start Print Job	Begins printing a selected G-code file with optional start layer and toggles.	View
129	Pause Print	Pauses the active print job.	View
130	Cancel Print	Cancels the current print and returns the printer to an idle state.	View
131	Resume Print	Resumes a paused print.	View
134	Unknown / No-op	Returns Ack, but no side effects observed.	View
258	List Files	Retrieves G-code files from a specified directory, e.g., /local.	View
320	Get Print History	Returns UUIDs for historical prints.	View
386	Get Camera Stream URL	Enables the printer's camera and returns MJPEG video URL.	View
403	Toggle Light	Turns second light on/off. RGB appears unsupported.	View

---

Status Message Example

{
  "Status": {
    "CurrentStatus": [0],
    "TimeLapseStatus": 0,
    "PlatFormType": 0,
    "TempOfHotbed": 67.49338678423711,
    "TempOfNozzle": 115.34388355923741,
    "TempOfBox": 26.42958339525779,
    "TempTargetHotbed": 0,
    "TempTargetNozzle": 0,
    "TempTargetBox": 0,
    "CurrenCoord": "202.00,264.50,24.59",
    "CurrentFanSpeed": {
      "ModelFan": 0,
      "AuxiliaryFan": 0,
      "BoxFan": 0
    },
    "ZOffset": 0.00000000000001,
    "LightStatus": {
      "SecondLight": 1,
      "RgbLight": [0, 0, 0]
    },
    "PrintInfo": {
      "Status": 8,
      "CurrentLayer": 0,
      "TotalLayer": 165,
      "CurrentTicks": 0,
      "TotalTicks": 9749,
      "Filename": "",
      "TaskId": "",
      "PrintSpeedPct": 100,
      "Progress": 0
    }
  },
  "MainboardID": "608715130105041800009c0000000000",
  "TimeStamp": 1752339395,
  "Topic": "sdcp/status/608715130105041800009c0000000000"
}

Status codes I've observed in PrintInfo.Status

Code	Meaning	Description
0	Idle	No print in progress. Default state after power-on or when print is canceled/finished.
5	Pausing	Print job is in the process of pausing.
8	Preparing to Print	Print job accepted, beginning warm-up or calibration routines.
9	Starting Print	Print has begun — may be homing, priming, or performing initial G-code steps.
10	Paused	Print is paused by user or error.
13	Printing (Active)	Actively printing layer-by-layer; heaters, motion, and timers engaged.
20	Resuming	Print job is preparing to print after being paused.

ACK Message Example

{
  "Id": "979d4C788A4a78bC777A870F1A02867A",
  "Data": {
    "Cmd": 128,
    "Data": { "Ack": 2 },
    "RequestID": "3333",
    "MainboardID": "608715130105041800009c0000000000",
    "TimeStamp": 1752339218
  },
  "Topic": "sdcp/response/608715130105041800009c0000000000"
}

Ack Code	Meaning	Description
0	Success	Command was received and executed successfully.
1	Failure/Error	Command failed (e.g., invalid operation or unsupported parameter).
2	File Not Found	Saw when attempting to start a print job with a non-existent file.

🔍 Examples

Cmd: 0 — Request Status Update

{
  "Id": "",
  "Data": {
    "Cmd": 0,
    "Data": {},
    "RequestID": "abc123",
    "MainboardID": "",
    "TimeStamp": 1752333800479,
    "From": 1
  }
}

Cmd: 1 — Get Device Attributes

{
  "Id": "",
  "Data": {
    "Cmd": 1,
    "Data": {},
    "RequestID": "e4518e17dc004ae3b1cd88fc01ec3c72",
    "MainboardID": "",
    "TimeStamp": 1752333800479,
    "From": 1
  }
}

Cmd: 128 — Start Print Job

{
  "Id": "",
  "Data": {
    "Cmd": 128,
    "Data": {
      "Filename": "/local/some_file.gcode",
      "StartLayer": 0,
      "Calibration_switch": 0,
      "PrintPlatformType": 0,
      "Tlp_Switch": 0
    },
    "RequestID": "bc6990ec21c94b9694f7e0be31b99514",
    "MainboardID": "",
    "TimeStamp": 1752338967263,
    "From": 1
  }
}

Cmd: 129 — Pause Print

{
  "Id": "",
  "Data": {
    "Cmd": 129,
    "Data": {},
    "RequestID": "25d142c593774914aeaa658f5e9397b1",
    "MainboardID": "",
    "TimeStamp": 1752338252077,
    "From": 1
  }
}

Cmd: 130 — Cancel Print

{
  "Id": "",
  "Data": {
    "Cmd": 130,
    "Data": {},
    "RequestID": "490f5d7547294bb2a35ebbce2de1e5df",
    "MainboardID": "",
    "TimeStamp": 1752338652034,
    "From": 1
  }
}

Cmd: 131 — Resume Print

{
  "Id": "",
  "Data": {
    "Cmd": 131,
    "Data": {},
    "RequestID": "b5a7c589bb6842eca994a66c02ebac8a",
    "MainboardID": "",
    "TimeStamp": 1752338355217,
    "From": 1
  }
}

Cmd: 134 — Unknown / No-op

{
  "Id": "",
  "Data": {
    "Cmd": 134,
    "Data": {},
    "RequestID": "420451207d6e44ec9131bdba6afb5991",
    "MainboardID": "",
    "TimeStamp": 1752335529,
    "From": 1
  }
}

Cmd: 258 — List Files

{
  "Id": "",
  "Data": {
    "Cmd": 258,
    "Data": {
      "Url": "/local"
    },
    "RequestID": "83fe754d9e654b51b7de04a68fa6258f",
    "MainboardID": "",
    "TimeStamp": 1752335626,
    "From": 1
  }
}

Cmd: 320 — Get Print History

{
  "Id": "",
  "Data": {
    "Cmd": 320,
    "Data": {},
    "RequestID": "d6a3fbc59ddd43c089156d274ddbbd81",
    "MainboardID": "",
    "TimeStamp": 1752335377,
    "From": 1
  }
}

Cmd: 386 — Get Camera Stream URL

{
  "Id": "",
  "Data": {
    "Cmd": 386,
    "Data": {
      "Enable": 1
    },
    "RequestID": "d40d5619eb2441f1ac1881b70c47d768",
    "MainboardID": "",
    "TimeStamp": 1752335729,
    "From": 1
  }
}

Cmd: 403 — Toggle Light

{
  "Id": "",
  "Data": {
    "Cmd": 403,
    "Data": {
      "LightStatus": {
        "SecondLight": true,
        "RgbLight": [0, 0, 0]
      }
    },
    "RequestID": "78bb6259e2f94a4ea9c13beee3a5b109",
    "MainboardID": "",
    "TimeStamp": 1752337353254,
    "From": 1
  }
}

Sources and Acknowledgements

• cassini CLI tool — Python CLI lib by Vladimir Vukicevic, appears to be no longer supported.
• SDCP-Smart-Device-Control-Protocol-V3.0.0 — SDCP spec from CBD Tech
• sdcpapi By Bushvin — Most complete example of a lib for interacting with SDCP, specifically good resource for the Elegoo flavor.