Velxio: Arduino Emulator

Live at velxio.dev

A fully local, open-source Arduino emulator. Write Arduino code, compile it, and simulate it with real AVR8 CPU emulation and 48+ interactive electronic components — all running in your browser.

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Support the Project

Velxio is free and open-source. Building and maintaining a full Arduino emulator takes a lot of time — if it saves you time or you enjoy the project, sponsoring me directly helps keep development going.

Platform	Link
GitHub Sponsors (preferred)	github.com/sponsors/davidmonterocrespo24
PayPal	paypal.me/odoonext

Your support helps cover server costs, library maintenance, and frees up time to add new boards, components, and features. Thank you!

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Try it now

https://velxio.dev — no installation needed. Open the editor, write your sketch, and simulate directly in the browser.

To self-host with Docker (single command):

docker run -d -p 3080:80 ghcr.io/davidmonterocrespo24/velxio:master

Then open http://localhost:3080.

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Screenshots

Raspberry Pi Pico simulation — ADC read test with two potentiometers, Serial Monitor showing live output, and compilation console at the bottom.

Arduino Uno driving an ILI9341 240×320 TFT display via SPI — rendering a real-time graphics demo using Adafruit_GFX + Adafruit_ILI9341.

Library Manager loads the full Arduino library index on open — browse and install libraries without typing first.

Component Picker showing 48 available components with visual previews, search, and category filters.

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Features

Code Editing

• Monaco Editor — Full C++ editor with syntax highlighting, autocomplete, minimap, and dark theme
• Multi-file workspace — create, rename, delete, and switch between multiple .ino / .h / .cpp files
• Arduino compilation via arduino-cli backend — compile sketches to .hex / .uf2 files
• Compile / Run / Stop / Reset toolbar buttons with status messages
• Compilation console — resizable output panel showing full compiler output, warnings, and errors

Multi-Board Support

• Arduino Uno (ATmega328p) — full AVR8 emulation via avr8js
• Arduino Nano (ATmega328p) — full AVR8 emulation
• Arduino Mega (ATmega2560) — full AVR8 emulation
• Raspberry Pi Pico (RP2040) — full RP2040 emulation via rp2040js, compiled with arduino-pico core
• Board selector in the toolbar — switch boards without restarting

AVR8 Simulation (Arduino Uno / Nano / Mega)

• Real ATmega328p emulation at 16 MHz using avr8js
• Full GPIO support — PORTB (pins 8-13), PORTC (A0-A5), PORTD (pins 0-7)
• Timer0/Timer1/Timer2 peripheral support (millis(), delay(), PWM via analogWrite())
• USART (Serial) — full transmit and receive support
• ADC — analogRead() on pins A0-A5, voltage injection from UI components
• SPI — hardware SPI peripheral (enables ILI9341, SD card, etc.)
• I2C (TWI) — hardware I2C with virtual device bus
• ~60 FPS simulation loop with requestAnimationFrame

RP2040 Simulation (Raspberry Pi Pico)

• Real RP2040 emulation via rp2040js at 133 MHz
• UART0 serial output displayed in Serial Monitor
• ADC — 12-bit, 3.3V reference on GPIO 26-29 (A0-A3)

Serial Monitor

• Live serial output — characters as the sketch sends them via Serial.print()
• Auto baud-rate detection — reads hardware registers, no manual configuration needed
• Send data to the Arduino RX pin from the UI
• Autoscroll with toggle

Component System (48+ Components)

• 48 electronic components from wokwi-elements
• Component picker with search, category filters, and live previews
• Drag-and-drop repositioning on the simulation canvas
• Component rotation in 90° increments
• Property dialog — pin roles, Arduino pin assignment, rotate & delete

Wire System

• Wire creation — click a pin to start, click another pin to connect
• Orthogonal routing — no diagonal paths
• 8 signal-type wire colors: Red (VCC), Black (GND), Blue (Analog), Green (Digital), Purple (PWM), Gold (I2C), Orange (SPI), Cyan (USART)
• Segment-based wire editing — drag segments perpendicular to their orientation

Library Manager

• Browse and install the full Arduino library index directly from the UI
• Live search, installed tab, version display

Auth & Project Persistence

• Email/password and Google OAuth sign-in
• Project save with name, description, and public/private visibility
• Project URL — each project gets a permanent URL at /project/:id
• Sketch files stored on disk per project (accessible from the host via Docker volume)
• User profile at /:username showing public projects

Example Projects

• 8 built-in examples (Blink, Traffic Light, Button Control, Fade LED, Serial Hello World, RGB LED, Simon Says, LCD 20×4)
• One-click loading into the editor

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Self-Hosting

Option A: Docker (single container, recommended)

# Pull and run
docker run -d \
  --name velxio \
  -p 3080:80 \
  -v $(pwd)/data:/app/data \
  ghcr.io/davidmonterocrespo24/velxio:master

Open http://localhost:3080.

The /app/data volume contains:

• velxio.db — SQLite database (users, projects metadata)
• projects/{id}/ — sketch files per project

Option B: Docker Compose

git clone https://github.com/davidmonterocrespo24/velxio.git
cd velxio
cp backend/.env.example backend/.env   # edit as needed
docker compose -f docker-compose.prod.yml up -d

Environment variables (backend/.env)

Variable	Default	Description
SECRET_KEY	(required)	JWT signing secret
DATABASE_URL	sqlite+aiosqlite:////app/data/velxio.db	SQLite path
DATA_DIR	/app/data	Directory for project files
FRONTEND_URL	http://localhost:5173	Used for OAuth redirect
GOOGLE_CLIENT_ID	—	Google OAuth client ID
GOOGLE_CLIENT_SECRET	—	Google OAuth client secret
GOOGLE_REDIRECT_URI	http://localhost:8001/api/auth/google/callback	Must match Google Console
COOKIE_SECURE	false	Set true when serving over HTTPS

Option C: Manual Setup

Prerequisites: Node.js 18+, Python 3.12+, arduino-cli

git clone https://github.com/davidmonterocrespo24/velxio.git
cd velxio

# Backend
cd backend
python -m venv venv && source venv/bin/activate  # Windows: venv\Scripts\activate
pip install -r requirements.txt
uvicorn app.main:app --reload --port 8001

# Frontend (new terminal)
cd frontend
npm install
npm run dev

Open http://localhost:5173.

arduino-cli setup (first time):

arduino-cli core update-index
arduino-cli core install arduino:avr
# For Raspberry Pi Pico:
arduino-cli config add board_manager.additional_urls \
  https://github.com/earlephilhower/arduino-pico/releases/download/global/package_rp2040_index.json
arduino-cli core install rp2040:rp2040

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Project Structure

velxio/
├── frontend/                    # React + Vite + TypeScript
│   └── src/
│       ├── pages/               # LandingPage, EditorPage, ProjectByIdPage, ...
│       ├── components/          # Editor, simulator canvas, modals, layout
│       ├── simulation/          # AVRSimulator, RP2040Simulator, PinManager
│       ├── store/               # Zustand stores (auth, editor, simulator, project)
│       └── services/            # API clients
├── backend/                     # FastAPI + Python
│   └── app/
│       ├── api/routes/          # compile, auth, projects, libraries
│       ├── models/              # User, Project (SQLAlchemy)
│       ├── services/            # arduino_cli, project_files
│       └── core/                # config, security, dependencies
├── wokwi-libs/                  # Local clones of Wokwi repos
│   ├── wokwi-elements/
│   ├── avr8js/
│   └── rp2040js/
├── deploy/                      # nginx.conf, entrypoint.sh
├── Dockerfile.standalone        # Single-container production image
├── docker-compose.yml           # Development compose
└── docker-compose.prod.yml      # Production compose

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Technologies

Layer	Stack
Frontend	React 19, Vite 7, TypeScript 5.9, Monaco Editor, Zustand, React Router 7
Backend	FastAPI, SQLAlchemy 2.0 async, aiosqlite, uvicorn
Simulation	avr8js (AVR8), rp2040js (RP2040), wokwi-elements (Web Components)
Compiler	arduino-cli (subprocess)
Auth	JWT (httpOnly cookie), Google OAuth 2.0
Persistence	SQLite + disk volume (/app/data/projects/{id}/)
Deploy	Docker, nginx, GitHub Actions → GHCR + Docker Hub

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Troubleshooting

arduino-cli: command not found — install arduino-cli and add to PATH.

LED doesn't blink — check port listeners in browser console; verify pin mapping in the component property dialog.

Serial Monitor shows nothing — ensure Serial.begin() is called before Serial.print().

Compilation errors — check the compilation console; verify the correct core is installed.

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Community

Join the Discord server to ask questions, share projects, and follow updates:

discord.gg/rCScB9cG

Contributing

Suggestions, bug reports, and pull requests are welcome at github.com/davidmonterocrespo24/velxio.

If you'd like to support the project financially, see the Support the Project section above or sponsor directly at github.com/sponsors/davidmonterocrespo24.

Note: All contributors must sign a Contributor License Agreement (CLA) so that the dual-licensing model remains valid. A CLA check runs automatically on pull requests.

License

Velxio uses a dual-licensing model:

Use case	License	Cost
Personal, educational, open-source (AGPLv3 compliant)	AGPLv3	Free
Proprietary / closed-source product or SaaS	Commercial License	Paid

The AGPLv3 is a certified Open Source license. It is free for all uses — including commercial — as long as any modifications or network-accessible deployments make their source code available under the same license. Companies that cannot comply with that requirement can purchase a Commercial License.

For commercial licensing inquiries: davidmonterocrespo24@gmail.com

See LICENSE and COMMERCIAL_LICENSE.md for full terms.

References

• Wokwi — Inspiration
• avr8js — AVR8 emulator
• wokwi-elements — Electronic web components
• rp2040js — RP2040 emulator
• arduino-cli — Arduino compiler
• Monaco Editor — Code editor