Arduino, running the sketch you wrote
arduino-cli compiles it, an AVR8 core executes it instruction by instruction, and the LCD shows what the ATmega328P actually put on the bus. Uno, Nano, Mega and ATtiny85, no board on your desk.
Arduino, ESP32 & Raspberry Pi.
Right in your browser.
Hardware is all about iteration. Velxio lets you wire a circuit, program the board and run it in seconds, real firmware on a real solver, right in the browser.
- 35boards
- 2.6k+stars on GitHub
- AGPLv3open source
Hardware partners
Real silicon. Real physics. One canvas.
Nothing on this page is a scripted animation: the firmware is compiled and executed, and the circuit around it is solved.
Your firmware, on an emulated CPU
arduino-cli or ESP-IDF compiles the sketch, then AVR8, RP2040, RISC-V, Xtensa or ARM executes it instruction by instruction. What the OLED draws and what the serial monitor prints is what the chip actually did.
Analog that is solved, not faked
ngspice compiled to WebAssembly runs a full nodal analysis about 60 times a second. GPIO pins drive real nets, ADC inputs read solved node voltages, and probes report RMS, DC and current wherever you drop them.
Digital logic, gate by gate
Adders, comparators, decoders, flip-flops and a 1-bit ALU slice: no microcontroller anywhere, just gates, switches and LEDs solved as a real net. The classroom half of electronics, without the breadboard.
The partner boards, emulated for real
The M5Stack Cardputer with its keyboard, Seeed's round display keeping time, Pimoroni's Badger 2350 driving e-paper, and DFRobot's UNIHIKER M10 in the catalogue alongside them. Their makers sent the hardware so the emulation could be checked against the real thing.
Supported HardwareEvery architecture.
Every architecture.
One tool.
35 boards across 6 CPU architectures — AVR8, ARM Cortex-M, ARM Cortex-A, RISC-V, Xtensa, and Linux. Including partner boards from Pimoroni, M5Stack, Seeed Studio and DFRobot. All running locally, no cloud needed.
avr8jsArduino · AVR8 · ATmega
rp2040js · rp2350jsRaspberry Pi Pico · RP2040 / RP2350 · ARM + RISC-V
QEMU · in-browser JSESP32 · Xtensa & RISC-V · WiFi + BLE
M5Stack CoreESP32 · 320×240 LCDOpen example
M5 Cardputer ADVESP32-S3 · keyboardOpen example
QEMU · ARMSTM32 · ARM Cortex-M3 / M4
QEMU · ARMSingle-board computers · ARM Cortex-A · Linux
QEMU lcgamboaOther RISC-V
CH32V003RISC-V · 48 MHz · 16 KB
Classroom
Bring Velxio into your course.
One institution contract gives every student in the class a full Pro account. No per-seat checkout, no card details in a classroom.
Pro for every student
Private projects, BOM and schematic exports, GitHub Sync and the offline desktop app, for everyone enrolled.
One predictable bill
Billed once to your institution, per semester or per year. Volume pricing on request for large cohorts.
The tools they will use at work
Arduino, ESP32, RP2040, STM32, ATtiny and Raspberry Pi, with SPICE analog solved alongside the firmware. Not a sandboxed mock.
Pricing
Free to run circuits. Pay for the AI.
The simulator stays free forever. Paid plans raise the daily AI quota and unlock the Linux boards, private projects and the offline desktop app.
Free
$0/ month
Discover the simulator + light AI help.
- Basic AI chat: help, explanations and code answers (50 messages/day, own pool)
- 20 daily AI credits (up to 600/month)
- 30+ boards: Arduino, ESP32, RP2040 (incl. Pico W), RISC-V, M5Stack, XIAO
- 48+ components on the canvas
- Real CPU emulation in the browser
- Custom chips and programmable sensors: write them in C, compile to WASM, drive them with live sliders
- Library Manager + arduino-cli compilation (100 MB library storage)
- Save unlimited public projects
- STM32, Raspberry Pi Linux and UNIHIKER: 3 free 15-minute trial sessions per family (unlimited on Maker and up)
- Agent + Tutor modes: the AI builds and teaches on your canvas (Maker and up)
- Upload custom Arduino libraries (.zip)
- Unlimited ESP32 run time (free runs are time-capped)
- Private projects
- Desktop offline app
- Priority compile queue
Maker
$5.75/ month
$69 billed annually
For makers shipping real circuits with AI help.
- Agent mode: the AI builds circuits on your canvas from a prompt
- Tutor mode: step-by-step teaching over your own circuit
- Create with AI: describe a part and the agent writes, compiles and places the chip for you
- 500 daily AI credits (up to 15,000/month)
- Everything in Free, plus:
- STM32 and Raspberry Pi Linux boards, with unlimited simulation time
- Desktop offline app (Linux · Windows · macOS)
- Unlisted projects (share by link, hidden from gallery)
- Premium components (advanced sensors, displays, ICs)
- Upload custom Arduino libraries (.zip) + 500 MB library storage
- Private IoT gateway
- Custom WiFi access points: your own SSIDs on the simulated air
- Local network gateway: the board reaches your LAN and localhost
- Priority compile queue
- Cancel anytime
Most popular
Pro
$15.75/ month
$189 billed annually
Private projects, GitHub Sync and BOM exports.
- Connect AI agent: drive the project from Claude Code or Codex over MCP
- My Chips library: save your custom chips on the server and reuse them in every project
- 2,000 daily AI credits (up to 60,000/month)
- Everything in Maker, plus:
- Private projects (only you can access)
- 2 GB library storage (4x Maker) for custom .zip libraries
- BOM export (CSV → Mouser / Digi-Key)
- Schematic PNG export
- GitHub Sync
- Direct support from the maintainer
- Cancel anytime
Connect with the open source community
Questions, bugs and ideas: the Discord and the issue tracker are open, and so is every line of the simulator.