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Velxio — Introduction

Velxio is a fully local, open-source multi-board emulator and electronics simulator that runs entirely in your browser.

Write Arduino C++ or MicroPython, compile it with a real arduino-cli / ESP-IDF backend, and simulate it with true CPU emulation — AVR8, RP2040, Xtensa, RISC-V, and ARM — plus a full ngspice analog circuit engine for op-amps, transistors, diodes, and passive components.

19+ boards, 5 CPU architectures, 590+ electronic components, custom-chip SDK, and a desktop app — without installing anything on your machine.

Why Velxio?

  • No installation required — runs in the browser, or as a native desktop app for offline work.
  • Real CPU emulation — avr8js, rp2040js, QEMU (Xtensa LX6/LX7, RISC-V RV32IMC, ARM Cortex-A53/A72/A76). Not toy simulators.
  • Digital + analog — every digital pin is fed into a co-simulated SPICE netlist, so you get true voltages, currents, and waveforms (not just HIGH/LOW).
  • 590+ interactive components — LEDs, displays, sensors, transistors, op-amps, logic gates, motors, e-paper panels, instruments, and more.
  • Custom chips — write your own chip in C, compile to WebAssembly, drop on the canvas, wire it up.
  • Multi-board canvases — mix an Arduino, an ESP32, and a Raspberry Pi 3 on the same canvas and bridge them over UART.
  • Open-source (AGPLv3) — inspect, modify, and self-host with Docker.

Supported Boards

19 boards across 5 CPU architectures:

Family Boards Engine
AVR8 (browser) Arduino Uno, Nano, Mega 2560, ATtiny85 avr8js
RP2040 (browser) Raspberry Pi Pico, Pico W rp2040js
Xtensa LX6/LX7 (QEMU backend) ESP32 DevKit V1, ESP32 DevKit C V4, ESP32-CAM, Wemos Lolin32 Lite, ESP32-S3 DevKit, XIAO ESP32-S3, Arduino Nano ESP32 QEMU lcgamboa fork
RISC-V RV32IMC (QEMU backend) ESP32-C3 DevKit, XIAO ESP32-C3, ESP32-C3 SuperMini QEMU lcgamboa fork
ARM Cortex-A (QEMU backend) Raspberry Pi Zero, Pi 1B+, Pi 2B, Pi 3B, Pi 4B, Pi 5 QEMU virt / raspi3b

Languages supported: Arduino C++ on every board, MicroPython on Pico / Pico W / all ESP32 / ESP32-S3 / ESP32-C3 variants, Python 3 on every Raspberry Pi.

See Supported Boards for the full table with CPU clock speeds and FQBNs.

What you can build

  • Digital sketches — blink an LED, read a button, talk over Serial, drive an LCD, run a servo. The classic Arduino workflow, faster than flashing a real board.
  • Analog circuits — 5V/GND rails, voltage dividers, op-amp filters, RC networks, transistor amplifiers. Probe with the on-canvas voltmeter, ammeter, and oscilloscope, or inject signals with the function generator.
  • Mixed-signal designs — an ATmega reading a sensor through an op-amp buffer, an ESP32 driving a NeoPixel ring, a Pi 3 over UART to an Arduino acting as a slave. All co-simulated in one canvas.
  • Custom silicon — model a 4-bit Intel 4004, a Z80, a 74HC595 shift register, or a 24LC256 EEPROM as a custom chip in C.
  • IoT prototypes — ESP32 WiFi (SLIRP NAT), HTTP servers, MQTT, BLE advertising — all without a real radio.

Documentation

Getting Started

  • Getting Started — Hosted, Docker, manual setup, desktop app
  • Roadmap — What's implemented, in progress, planned

Architecture & Internals

Boards & Emulation

Components & Examples

Custom Chips Deep-Dive

Electrical Simulation Deep-Dive

Apps & Integrations

  • Desktop App — Tauri-based offline desktop build (Pro)
  • MCP Server — Model Context Protocol — drive Velxio from Claude / Cursor
  • Analytics — Self-hosted plausible / GA bridge

Infrastructure

Community & Links