Jarvis desk

Jarvis Desk Controller

Control a Jarvis/Jiecang standing desk via the RJ-12 port using the reverse-engineered serial protocol from phord/Jarvis.

Two platforms are supported:

Hardware Required

Arduino Uno

• Arduino Uno
• RJ-12 breakout / socket
• 2× 1kΩ resistors (signal protection)
• Hookup wire

ESP32-C6

• DFRobot Beetle ESP32-C6 (or any ESP32-C6 board)
• RJ-12 breakout / socket
• 1× 1kΩ + 1× 2kΩ resistor (voltage divider for RX line)
• Hookup wire

Wiring

The RJ-12 port is the 6-pin telephone-style jack on the desk controller (used for the optional Bluetooth add-on). Only the center 4 pins are needed.

 RJ-12 Jack (front view, tab down)
 ┌──────────┐
 │ 1 2 3 4 5 6 │
 └──┬─┬─┬─┬─┬─┬──┘
    │ │ │ │ │ │
    NC│ │ │ │ NC
      │ │ │ │
      │ │ │ └── Pin 5: HTX (to desk) ──[1kΩ]── Arduino Pin 3
      │ │ └──── Pin 4: VCC (5V out)    (see power notes below)
      │ └────── Pin 3: DTX (from desk) ──[1kΩ]── Arduino Pin 2
      └──────── Pin 2: GND ──────────── Arduino GND

Connections Summary

Why series resistors?

The 1kΩ resistors protect both the Arduino and the desk controller from shorts, voltage spikes during hot-plugging, and current surges. They don't affect signal integrity at 9600 baud.

Power Options

For development (recommended): Power the Arduino via USB. Leave RJ-12 Pin 4 (VCC) disconnected.

For standalone deployment: You can power the Arduino from the desk's 5V supply on RJ-12 Pin 4 → Arduino 5V pin. However:

⚠️ Never connect both USB and desk 5V simultaneously — this back-powers the USB host and can damage your computer or the desk controller. Use a diode or power switch if you need both.

ESP32-C6 Wiring (Desk-Powered)

The ESP32 can be powered directly from the desk's 5V supply — no USB needed after the first firmware upload (use OTA for updates).

                    DFRobot Beetle ESP32-C6
                    ┌─────────────────────┐
                    │                     │
RJ-12              │  VIN ←── 5V power   │
┌──────┐           │  GND ←── Ground     │
│1    6│           │                     │
│ NC  NC│           │  GPIO17 (RX) ←─┐   │
│      │           │                 │   │
│2 GND─┼──────────→│  GND            │   │
│      │           │                 │   │
│3 DTX─┼──[1kΩ]──┬─┼─────────────────┘   │
│      │         │ │                     │
│      │       [2kΩ]                     │
│      │         │ │                     │
│      │        GND│                     │
│      │           │                     │
│4 VCC─┼──────────→│  VIN (5V)           │
│      │           │                     │
│5 HTX─┼──────────→│  GPIO18 (TX)        │
│      │           │                     │
│6  NC │           └─────────────────────┘
└──────┘

Parts needed: 1× 1kΩ resistor, 1× 2kΩ resistor (or 2× 1kΩ in series)

Why the Voltage Divider?

The desk sends data at 5V. The ESP32-C6 GPIOs are rated for 3.3V max. Without a divider, 5V goes straight into a 3.3V pin — this will damage the chip.

Two resistors drop the voltage: 5V × 2kΩ / (1kΩ + 2kΩ) = 3.33V ✅

The TX line (ESP32→desk) doesn't need this because the ESP32 outputs 3.3V, which the desk's 5V logic reads as HIGH (above the ~2.5V threshold).

⚠️ Never connect USB and desk 5V at the same time — this back-powers the USB host. Disconnect the RJ-12 before plugging in USB, or use OTA for all updates after the first upload.

Current budget: The desk provides ~300mA at 5V. The ESP32-C6 draws ~120-180mA during WiFi activity — well within budget.

Serial Signal Notes

Live testing on a Jiecang JCB36N2CA (Fully Jarvis) confirmed normal UART polarity — standard 9600/8N1 with no inversion needed. Earlier documentation suggested inverted logic, but this was not the case on the tested controller.

The code uses SoftwareSerial with inverse_logic = false (standard polarity). If you get garbage data, try toggling this flag — some controller models may differ.

Building & Uploading (PlatformIO)

This project uses PlatformIO for build/upload/serial monitoring.

Setup

1. Install the PlatformIO IDE extension in VSCode (platformio.platformio-ide)
2. Open this folder in VSCode — PlatformIO detects platformio.ini automatically

Build, Upload & Monitor

Use the PlatformIO toolbar at the bottom of VSCode, or:

# Arduino Uno
pio run -e uno
pio run -e uno --target upload

# ESP32-C6
pio run -e esp32c6
pio run -e esp32c6 --target upload

# Tests
pio test -e native

# Open serial monitor (115200 baud)
pio device monitor

# Build + upload + monitor in one shot
pio run -e uno --target upload && pio device monitor

ESP32-C6 Setup

1. Copy include/config.example.h to include/config.h
2. Edit config.h with your WiFi SSID/password and MQTT broker IP
3. Build: pio run -e esp32c6
4. Upload: pio run -e esp32c6 --target upload
5. Monitor: pio device monitor

Home Assistant Integration

The ESP32 firmware publishes MQTT auto-discovery messages. After connecting:

• A "Jarvis Desk" device appears automatically in Home Assistant
• Entities: height sensor (cm), target height (number), presets 1–4 (buttons), up/down/stop (buttons)
• Requires an MQTT broker (e.g., Mosquitto) configured in Home Assistant

MQTT Topics

OTA Updates

After the first upload via USB, subsequent updates can use OTA:

pio run -e esp32c6 --target upload --upload-port jarvis-desk.local

Alternative: Arduino IDE

If you prefer the Arduino IDE, copy files from src/ and include/ into a single folder named jarvis-desk-controller/, rename main.cpp → jarvis-desk-controller.ino, and open it in the Arduino IDE.

Usage

Open the Serial Monitor at 115200 baud. Type commands and press Enter:

What you'll see

=== Jarvis Desk Controller ===
Type 'help' for commands

Waking desk...
[DESK] HEIGHT (05 06 07)  height=1286
> Moving to preset 1
[DESK] HEIGHT (03 CA 07)  height=970

Protocol Reference

• UART: 9600 baud, 8N1, normal polarity (not inverted)
• Packets: [addr][addr][cmd][len][params...][checksum][0x7E]
• Handset address: 0xF1 0xF1
• Controller address: 0xF2 0xF2
• Checksum: Low byte of (cmd + len + params...), i.e. & 0xFF

Full protocol documentation: https://github.com/phord/Jarvis

Protocol Discoveries (Live Testing)

Tested on a Jiecang JCB36N2CA (Fully Jarvis, RJ-12 port). The RJ-12 interface works standalone — no handset required.

Confirmed Commands (Handset → Desk)

Controller Responses

Key Observations

• Normal UART polarity — standard 9600/8N1, no inversion needed.
• GOTO_HEIGHT (0x1B) is the cleanest move method — desk handles acceleration, deceleration, and auto-stop.
• STOP (0x2B) halts movement immediately. ESPHome uses wake + stop as an init sequence.
• Preset values are raw encoder positions, not display millimeters.
• Height offset: Display height has a ~2.4 cm offset from physical (tape-measure) height.
• Physical limits on tested unit: 76.5–125.3 cm reported, ~74.1–122.9 cm actual.
• No-response commands: 0x0E (UNITS), 0x19 (MEM_MODE), 0x1D (COLL_SENS) — these are setters that likely need parameters, or are RJ-45 only.

RJ-12 vs RJ-45

This project uses the RJ-12 interface (6-pin, Bluetooth add-on port). The larger RJ-45 port (8-pin, handset port) has additional button mux lines (HS0-HS3) not available on RJ-12.

On RJ-12, some responses differ:

• SETTINGS returns fewer response packets
• LIMIT_STOP and REP_PRESET are not sent

Troubleshooting

License

This project is for personal/educational use. The protocol was reverse-engineered by phord.