I built a small emulator project called Velxio.

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. GitHub: https://github.com/davidmonterocrespo24/velxio

The goal of this project was to learn more about how emulators work internally: CPU instructions, memory management, and low-level architecture.

It's still experimental, but it already runs basic instructions and I'm continuing to improve it.

Hi HN!

I built Velxio to explore how microcontroller emulators work internally.

It's an Arduino environment that runs entirely in the browser. You can write sketches, compile them with arduino-cli, and simulate circuits using a real AVR8 CPU emulator.

Features: - Arduino Uno / Nano support - Raspberry Pi Pico (RP2040) - GPIO, SPI, I2C, UART, ADC peripherals - interactive electronic components

The goal is to create an open-source environment for experimenting with embedded systems without installing anything.

I'd love feedback from embedded developers!

Thanks for the share, it looks great! Can I load my own OS in rpi?

Did you see that it's an rpi pico, which doesn't really run OSes in the traditional sense?

You are right, when I skimmed through I thought it’s an sbc one. Still very cool, would try it later.

Yeah exactly ,the Pico (RP2040) is a microcontroller rather than a full SBC, so it doesn't run a traditional OS like Linux.

In the future I'd like to support more low-level experimentation though (bare-metal programs, custom runtimes, etc.).

Thanks for checking it out!

What parts have you exactly built?

All I see are dependencies that are glued together with claude.

Can you clearify exactly what you have developed?

I built specifically:

The browser-based IDE (editor, project handling, UI)

The circuit simulation layer that connects components to the emulator

The glue between the AVR8 emulator and the virtual peripherals (GPIO, UART, SPI, etc.)

The component interaction system (buttons, LEDs, displays, etc.)

The architecture that lets compiled Arduino sketches run and interact with the simulated hardware

Some parts like the AVR CPU emulation and the compiler toolchain obviously come from existing projects, but the goal of Velxio wasn't to re-implement an AVR core from scratch. It was to build a usable environment where all of these pieces work together in the browser.

I'm still having trouble connecting the cables and components properly. I'm looking for a better algorithm. I'm also trying to create a real-world electronics simulator in JavaScript using an engine like CircuitJS1.

what do you mean with "The browser-based IDE (editor ...)

You use Monaco Editor for that.

Yes, the editor itself uses Monaco. That dependency is listed in the README

When I said "browser-based IDE", I meant the environment around it: project handling, compilation with arduino cli, the UI, the serial monitor, and the integration with the emulator and circuit simulation

Monaco is just the editing component

This is amazing!

Thanks! I'm glad you like it

Very cool. I can't wait to play around with this!

Thanks! Hope you enjoy trying it out. feedback is always welcome.

See also: https://wokwi.com (ESP32 equivalent)

[Edit] Which also does Arduino.

Yes! Wokwi is great and definitely served as inspiration for Velxio. My goal with this project was mainly to explore how microcontroller emulators work internally and experiment with building parts of that stack myself.

If anyone wants a quick thing to try in the simulator, here's a simple LED blink example with Serial output:

void setup() { pinMode(13, OUTPUT); Serial.begin(9600); }

void loop() { digitalWrite(13, HIGH); Serial.println("LED ON"); delay(500);

  digitalWrite(13, LOW);
  Serial.println("LED OFF");
  delay(500);

}

In Velxio you can connect an LED to pin 13 and watch it blink, while the Serial Monitor prints the messages in the terminal.

*Arduino emulator front end, using the AVR emulation from https://github.com/wokwi/avr8js

If it also uses screen emulation, SPI protocols, IC2, and sensors, it's built from scratch. It also integrates the Arduino CLI for compiling the project and using external libraries. I created an algorithm for the wiring (currently working on it). I've also integrated more Arduino models and the Raspberry Pi Pico. I plan to integrate ESP32, but I haven't been able to finish the emulator using QEMU as a base. It's not just an avr8js frontend

If anyone wants to try it quickly, there's a live demo available here:

https://velxio.dev/editor

What a great project, thanks for sharing.

Thanks!