A free, open-source emulator for 19 embedded boards: Arduino, ESP32, Raspberry Pi, RISC-V , running real compiled code in your browser.
The best part: it's fully local.
No cloud dependency. No student accounts. No data leaving your network. Self-hostable with a single Docker container.
Universities and bootcamps can deploy it on their own servers and give every student access to a complete embedded development environment, for free.
I've been working on this for over a year, and just shipped v2.0 with ESP32 emulation (via QEMU), a custom RISC-V core, and Raspberry Pi 3 support that runs real Python
Yes,peripherals are fully emulated, not just the CPU. LEDs blink, buttons respond to clicks, Serial Monitor works, servos rotate, displays render (ILI9341 TFT), and we have 48 o more components from the wokwi-elements library. The Blink example should show the built-in LED toggling on pin 13. If it didn't blink for you, it might be a compilation issue
try the example Traffic Light : Simulate a traffic light with red, yellow, and green LEDs
Is it easy to feed an elf or bin and run that (esp32c3)? I see compilation available, but I'm playing with asm and have my toolchain figured out already and would just like to emulate the firmware.
Another +1 for this one as this is what turns this tool from a toy environment with basic sketches into something that's actually useful for larger projects with a full toolchain, libraries, and so forth.
A lot of simulators stop at simple sketches, but the goal with Velxio is to support more realistic workflows , multiple boards interacting, real toolchains, and more complex setups
Still early, but definitely moving in that direction
Hey HN, I posted Velxio here a while back and got great feedback. Since then I've shipped a major update
What's new in v2:
- 19 boards across 5 CPU architectures (AVR8, Xtensa, RISC-V, ARM Cortex-M0+, ARM Cortex-A53)
- ESP32 emulation via QEMU (lcgamboa fork) — real flash images, ROM function emulation, GPIO/ADC/timers
- ESP32-C3 and CH32V003 run on a custom RISC-V core written in TypeScript, entirely in the browser
- Raspberry Pi 3B via QEMU raspi3b — boots real Pi OS, runs Python
- Realistic sensor simulation: DHT22 (40-bit protocol timing), HC-SR04 (trigger/echo), WS2812B NeoPixel (GRB decoding)
- 48+ electronic components from wokwi-elements
Architecture:
- AVR, RP2040, and RISC-V emulation runs client-side (avr8js, rp2040js, custom TS core)
- ESP32 Xtensa and Pi 3 run on backend QEMU
- Compilation via real arduino-cli
- React + Vite frontend, FastAPI backend
- Self-hostable via Docker, no account needed
When I try to visit velxio.dev, a CrowdSec page shows up and says I am not allowed to view it. I am a pretty normal android user on firefox mobile, so that is surprising.
I look forward to trying this out though, great project!
I often write a bunch of Esphome ‘code’ , which I then use with various esp32 based devices (mostly from M5stack) via esphome/HomeAssistant.
Can this project help me in any way during dev stage before uploading the code to device just to see it doesn’t work ? Eg could I use this to somehow compile&run those esphome yamls via this emulator?
Really impressive - browser-based hardware emulation is a brutal WebAssembly performance problem. Curious what you're doing for the rendering layer: are the circuit visualizations on canvas/WebGL, or DOM-based? I've been hitting similar render-loop problems with a deck.gl mapping project (realtime vessel positions, thousands of points updating simultaneously) and the pattern I found that helped most was batching state updates on a fixed 2s interval before diffing the render layer - prevents the WebGL context from recomposing faster than the data actually changes meaningfully. Does Velxio have a similar throttle, or does it redraw on every emulation tick?
The container instructions has -d in it, but note that after booting the container it downloads another, I don't know, 300+mb more (its still downloading as I write), so if you can't connect that's why.
Might be better to not include -d in the instructions?
One suggestion: The main splash screen image is nearly 8MB big. It takes a noticeable time to download on my connection. I'm not sure what bandwidth costs these days, but seems like that could be something to optimize.
Nice work! One minor point for me: it wasn’t immediately clear that you need to press Compile before Play gets enabled (e.g. Arduino IDE let's you upload right away and compiles if needed)
That looks awesome, thank you for your hard work! I would love tinker with it, but I'm not sure how to abstract things connected to those supported u_controller boards? Example, 7x16 Pico unicorn hat is driven by RP2040 PIO.
From what I can see, I cannot give it an ESP32-C6 firmware binary to execute, I have to compile my source code (C only) and the source has to use Arduino APIs. Under the hood it's still QEMU.
Isn't the problem with these emulations that they are not realtime and therefore will never give true feedback? As in the simulation will unlikely to translate to real world behaviour.
58 comments
A free, open-source emulator for 19 embedded boards: Arduino, ESP32, Raspberry Pi, RISC-V , running real compiled code in your browser.
The best part: it's fully local.
No cloud dependency. No student accounts. No data leaving your network. Self-hostable with a single Docker container.
Universities and bootcamps can deploy it on their own servers and give every student access to a complete embedded development environment, for free.
I've been working on this for over a year, and just shipped v2.0 with ESP32 emulation (via QEMU), a custom RISC-V core, and Raspberry Pi 3 support that runs real Python
Does your editor do this? I tried the example but didn't see e.g. LEDs blinking
try the example Traffic Light : Simulate a traffic light with red, yellow, and green LEDs
A lot of simulators stop at simple sketches, but the goal with Velxio is to support more realistic workflows , multiple boards interacting, real toolchains, and more complex setups
Still early, but definitely moving in that direction
What's new in v2:
- 19 boards across 5 CPU architectures (AVR8, Xtensa, RISC-V, ARM Cortex-M0+, ARM Cortex-A53) - ESP32 emulation via QEMU (lcgamboa fork) — real flash images, ROM function emulation, GPIO/ADC/timers - ESP32-C3 and CH32V003 run on a custom RISC-V core written in TypeScript, entirely in the browser - Raspberry Pi 3B via QEMU raspi3b — boots real Pi OS, runs Python - Realistic sensor simulation: DHT22 (40-bit protocol timing), HC-SR04 (trigger/echo), WS2812B NeoPixel (GRB decoding) - 48+ electronic components from wokwi-elements
Architecture:
- AVR, RP2040, and RISC-V emulation runs client-side (avr8js, rp2040js, custom TS core) - ESP32 Xtensa and Pi 3 run on backend QEMU - Compilation via real arduino-cli - React + Vite frontend, FastAPI backend - Self-hostable via Docker, no account needed
Source: https://github.com/davidmonterocrespo24/velxio (AGPLv3)
Happy to discuss the emulation architecture — particularly the trade-offs between in-browser vs. backend QEMU emulation
I look forward to trying this out though, great project!
Can this project help me in any way during dev stage before uploading the code to device just to see it doesn’t work ? Eg could I use this to somehow compile&run those esphome yamls via this emulator?
-din it, but note that after booting the container it downloads another, I don't know, 300+mb more (its still downloading as I write), so if you can't connect that's why.Might be better to not include
-din the instructions?One suggestion: The main splash screen image is nearly 8MB big. It takes a noticeable time to download on my connection. I'm not sure what bandwidth costs these days, but seems like that could be something to optimize.
Things are more stable now, but still tuning performance under load
If anyone finds it useful, the source is here: https://github.com/davidmonterocrespo24/velxio
Always happy to get feedback or contributions.