Velxio 3.0 — Retro CPUs, MicroSD, ePaper & Multi-Board Embedded Simulator

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Velxio

Offline Arduino, RP2040 & ESP32 simulator

Starting local backend…

Free online circuit + microcontroller simulator — SPICE-accurate analog wired to Arduino, ESP32, RP2040, ATtiny85 & more

Velxio is a free, open-source online circuit simulator with hybrid digital + analog co-simulation. Real-time SPICE analysis (ngspice-WASM) wired to 19 supported boards across 5 CPU architectures. Build custom chips in C, Rust, or AssemblyScript. 100+ interactive components, live oscilloscope, voltmeter, ammeter, Monaco Editor, Serial Monitor, arduino-cli compiler, and Library Manager — no cloud, no latency, no account required.

What's new in Velxio 2.5

Real-time SPICE analog simulation in your browser via ngspice-WASM (eecircuit-engine) — Modified Nodal Analysis at ~60 Hz, not a linear approximation

Hybrid digital + analog co-simulation — GPIO pins drive SPICE nets as voltage sources; analogRead() reads solved node voltages back into firmware

100+ SPICE-accurate parts : resistors, capacitors, inductors, BJTs, MOSFETs, op-amps (LM358/741/TL072), regulators (7805/7812/LM317), Zener/Schottky diodes, optocouplers, relays

Live instruments : oscilloscope (multi-channel), voltmeter, ammeter, signal generator (sine/square/DC)

40+ new analog & hybrid examples : voltage divider, RC filter, full-wave rectifier, Schmitt trigger, op-amp amplifier, Wheatstone bridge, H-bridge motor driver

Features

Real AVR8 emulation: Arduino Uno (ATmega328p), Nano, Mega 2560, ATtiny85, Leonardo, Pro Mini at 16 MHz via avr8js

Raspberry Pi Pico & Pico W (RP2040, ARM Cortex-M0+ at 133 MHz) via rp2040js

ESP32-C3 / XIAO ESP32-C3 / SuperMini / CH32V003 (RISC-V RV32IMC/EC) — via QEMU lcgamboa (libqemu-riscv32)

ESP32 / ESP32-S3 / ESP32-CAM / Arduino Nano ESP32 (Xtensa LX6/LX7 at 240 MHz) via QEMU lcgamboa

Raspberry Pi 3B (ARM Cortex-A53, full Linux) via QEMU raspi3b — runs Python scripts with RPi.GPIO

Custom Chips — author your own integrated circuits in C, Rust, or AssemblyScript using the Wokwi Custom Chips API; reuse them across projects

48+ wokwi interactive electronic components (LEDs, resistors, buttons, sensors, TFT displays, NeoPixel…)

Monaco Code Editor with full C++ / Python syntax highlighting

arduino-cli compilation backend — produces real .hex / .uf2 / .bin files

Serial Monitor with auto baud-rate detection and send

Library Manager for Arduino libraries

Multi-file workspace (.ino, .h, .cpp, .py)

Wire system with orthogonal routing

ILI9341 TFT display simulation

I2C, SPI, USART, ADC, PWM support

Multi-board canvas: mix Arduino + ESP32 + Raspberry Pi + analog circuits in one simulation

Supported Boards

Arduino Uno (ATmega328P) — full AVR8 emulation at 16 MHz

Arduino Nano (ATmega328P) — full AVR8 emulation at 16 MHz

Arduino Mega 2560 (ATmega2560) — 256 KB flash, 54 digital pins, 4 serial ports

ATtiny85 — AVR, 8 KB flash, DIP-8, all 6 I/O pins emulated

Arduino Leonardo (ATmega32u4) — USB HID capable AVR

Arduino Pro Mini (ATmega328P) — 3.3 V / 5 V variants

Raspberry Pi Pico (RP2040) — ARM Cortex-M0+ at 133 MHz

Raspberry Pi Pico W (RP2040) — ARM Cortex-M0+ + WiFi

ESP32-C3 DevKit (RISC-V RV32IMC) — 160 MHz, QEMU libqemu-riscv32

Seeed XIAO ESP32-C3 (RISC-V RV32IMC) — compact, QEMU libqemu-riscv32

ESP32-C3 SuperMini (RISC-V RV32IMC) — mini form factor

CH32V003 (RISC-V RV32EC) — 48 MHz, ultra-compact DIP-8

ESP32 DevKit V1 / C V4 (Xtensa LX6) — 240 MHz, WiFi, QEMU

ESP32-S3 (Xtensa LX7) — 240 MHz, dual-core, QEMU

ESP32-CAM (Xtensa LX6) — camera module, QEMU

Seeed XIAO ESP32-S3 (Xtensa LX7) — compact, QEMU

Arduino Nano ESP32 (Xtensa LX6) — Arduino form factor, QEMU

Raspberry Pi 3B (ARM Cortex-A53) — full Linux OS via QEMU raspi3b, runs Python

Get Started

Open the Editor — no installation needed.

Self-host with Docker: docker run -d -p 3080:80 ghcr.io/davidmonterocrespo24/velxio:master

Documentation

Browse the full Velxio documentation to learn how to set up, configure, and extend the emulator:

Frequently Asked Questions

Is Velxio free?<br>Yes. Velxio is free and open-source under the GNU AGPLv3 license. A commercial license is available for proprietary integrations.<br>Does Velxio work offline?<br>The SPICE analog solver and the browser-side CPU emulators (AVR8 via avr8js, RP2040 via rp2040js) run entirely in the browser. Xtensa and RISC-V boards (ESP32 / ESP32-S3 / ESP32-C3 / CH32V003) and Raspberry Pi 3 Linux run through QEMU lcgamboa, which is bundled in the self-hosted Docker image. Compilation requires the local arduino-cli backend. Self-hosted deployments work fully offline once running.<br>Can Velxio simulate analog circuits like SPICE?<br>Yes. Velxio 2.5 includes real-time SPICE analog simulation via ngspice compiled to WebAssembly. It runs full Modified Nodal Analysis on every tick — non-linear devices (diodes, BJTs, MOSFETs, op-amps with saturation) behave like real silicon, not idealised models.<br>Can I co-simulate Arduino code...