Velxio
Offline Arduino, RP2040 & ESP32 simulator
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Velxio
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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.

Try Simulator Free Online →View on GitHub
  • 35boards
  • 2.6k+stars on GitHub
  • AGPLv3open source

Hardware partners

DFRobotEspressifM5StackSeeed StudioPimoroni

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.

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.

Open the editor→
Arduino, running the sketch you wrote

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.

Open the editor→
Your firmware, on an emulated CPU

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.

SPICE simulator→
Analog that is solved, not faked

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.

Digital examples→
Digital logic, gate by gate

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.

See every board→
Arduino, running the sketch you wrote
Your firmware, on an emulated CPU
Analog that is solved, not faked
Digital logic, gate by gate
Supported Hardware

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
Arduino Uno
Arduino UnoATmega328p · 32 KBOpen example
Arduino Nano
Arduino NanoATmega328p · 32 KBOpen example
Arduino Mega 2560
Arduino Mega 2560ATmega2560 · 256 KBOpen example
ATtiny85AVR · 8KB · DIP-8
ATtiny85AVR · 8 KB · DIP-8Open example
rp2040js · rp2350jsRaspberry Pi Pico · RP2040 / RP2350 · ARM + RISC-V
Raspberry Pi Pico
Raspberry Pi PicoRP2040 · Cortex-M0+Open example
Raspberry Pi Pico W
Raspberry Pi Pico WRP2040 · WiFiOpen example
XIAO RP2040
XIAO RP2040Seeed · RP2040Open example
Pimoroni Pico Plus 2 WRP2350B · WiFiOpen example
Pimoroni Badger 2350RP2350 · 2.9" e-paperOpen example
Galactic UnicornRP2350 · 53×11 LEDOpen example
QEMU · in-browser JSESP32 · Xtensa & RISC-V · WiFi + BLE
ESP32 DevKit V1
ESP32 DevKit V1Xtensa LX6 · 240 MHzOpen example
ESP32 DevKit C V4
ESP32 DevKit C V4Xtensa LX6 · 240 MHzOpen example
ESP32-CAM
ESP32-CAMXtensa LX6 · OV2640Open example
ESP32-S3 DevKit
ESP32-S3 DevKitXtensa LX7 · USB OTGOpen example
XIAO ESP32-S3
XIAO ESP32-S3Seeed · Xtensa LX7
XIAO ESP32-S3 Sense
XIAO ESP32-S3 SenseSeeed · camera + micOpen example
Arduino Nano ESP32
Arduino Nano ESP32ESP32-S3 · Nano form
ESP32-C3 DevKit
ESP32-C3 DevKitRISC-V RV32IMCOpen example
XIAO ESP32-C3
XIAO ESP32-C3Seeed · RISC-V
ESP32-C3 SuperMini
ESP32-C3 SuperMiniRISC-V · tiny form
ESP32-C6
ESP32-C6RISC-V · WiFi 6 · BLE 5Open example
XIAO ESP32-C6
XIAO ESP32-C6Seeed · WiFi 6Open example
M5Stack CoreESP32 · 320×240 LCDOpen example
M5 Cardputer ADVESP32-S3 · keyboardOpen example
QEMU · ARMSTM32 · ARM Cortex-M3 / M4
STM32 Blue Pill
STM32 Blue PillSTM32F103 · Cortex-M3Open example
STM32 Black Pill
STM32 Black PillSTM32F411 · Cortex-M4Open example
Black Pill F401
Black Pill F401STM32F401 · Cortex-M4Open example
STM32F4 Discovery
STM32F4 DiscoverySTM32F407 · Cortex-M4Open example
Netduino Plus 2
Netduino Plus 2STM32F405 · Cortex-M4Open example
Olimex H405
Olimex H405STM32F405 · Cortex-M4Open example
QEMU · ARMSingle-board computers · ARM Cortex-A · Linux
Raspberry Pi 3B
Raspberry Pi 3BCortex-A53 · 1.2 GHzOpen example
Raspberry Pi 4B
Raspberry Pi 4BCortex-A72 · 1.5 GHzOpen example
Raspberry Pi 5
Raspberry Pi 5Cortex-A76 · 2.4 GHzOpen example
UNIHIKER M10
UNIHIKER M10DFRobot · Cortex-A35Open example
QEMU lcgamboaOther RISC-V
CH32V003RV32EC · 48 MHz
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.

From $34 per student per year after the education discount. 5-student minimum, and we answer quote requests within 2 business days.See classroom plans →
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
Get started
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
Start Maker
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
Subscribe to Pro

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.

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Velxio
GitHubDocumentationExamplesEditorPricingFor schoolsAbout

Velxio is a free, open-source circuit and microcontroller simulator that runs entirely in your browser. Arduino, ESP32, RP2040 and ATtiny85, with SPICE-accurate analog co-simulation. Built for makers, students and embedded engineers learning by doing. AGPLv3.