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.

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.
DFRobot · M5Stack links on this page are affiliate links: a purchase through them earns Velxio a small commission at no extra cost to you.
Nothing on this page is a scripted animation: the firmware is compiled and executed, and the circuit around it is solved.
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-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.

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.

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 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.




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.
One institution contract gives every student in the class a full Pro account. No per-seat checkout, no card details in a classroom.
Private projects, BOM and schematic exports, GitHub Sync and the offline desktop app, for everyone enrolled.
Billed once to your institution, per semester or per year. Volume pricing on request for large cohorts.
Arduino, ESP32, RP2040, STM32, ATtiny and Raspberry Pi, with SPICE analog solved alongside the firmware. Not a sandboxed mock.
The simulator stays free forever. Paid plans raise the daily AI quota and unlock the Linux boards, private projects and the offline desktop app.
Discover the simulator + light AI help.
For makers shipping real circuits with AI help.
Private projects, GitHub Sync and BOM exports.
Questions, bugs and ideas: the Discord and the issue tracker are open, and so is every line of the simulator.
An interactive Esp32 Devkit C V4 circuit simulation you can run free in your browser on Velxio, by zhao.
/*
* ============================================================================
* Adaptive Health Lighting System v1.0 - ESP32 Edition
* ============================================================================
*
* Hardware (Plan B: DevKitC + 2x19 pin-header socket):
* - ESP32 DevKitC development board (WROOM-32, WiFi + BT)
* inserted into J1 2x19 female header on PCB
* - VEML7700 ambient light sensor (I2C 0x10, +/-5%)
* - SHT30 temperature/humidity sensor (I2C 0x44)
* - PIR motion sensor (GPIO27)
* - 2x AO3400 MOSFET (dual-channel LED driver, SOT-23)
* - Warm white LED strip 2700K (GPIO25 HW / GPIO27 SIM, LEDC ch0)
* - Cool white LED strip 6500K (GPIO26, LEDC ch1)
* - PCB Type-C: power-only (no data)
* - Program download: via DevKitC onboard USB (CP2102)
*
* Simulation Mode (Velxio):
* Uncomment #define SIMULATION_MODE below to use:
* - Potentiometer on GPIO34 (ADC1_CH6) -> simulated light 0-500 lux
* - Potentiometer on GPIO35 (ADC1_CH7) -> simulated temperature 0-50 C
* - Push button on GPIO14 (INPUT_PULLUP) -> simulated PIR
* - Yellow LED + 68-100R on GPIO27 -> warm white (GPIO25=DAC1 stuck HIGH in Velxio)
* - White LED + 68-100R on GPIO26 -> cool white
* - Black button on GPIO0 (BOOT) -> mode switch
* LED output: SOFTWARE PWM via digitalWrite, 50Hz / 32-step + 100uF cap (Velxio's
* QEMU hangs on ledcWrite in the main-firmware context; digitalWrite verified OK.
* Frequency evolution: 25Hz flickered, 1kHz lost duty info, 100-120Hz had beat-
* frequency aliasing. 50Hz + 100uF smoothing capacitor (Drain->GND) = no flicker
* + SPICE resolves duty. Gamma correction SKIPPED in sim (2.2 crushes low duty).)
* WiFi/MQTT/NTP/OTA/WebServer/NVS are skipped in simulation (compile-isolated)
*
* Libraries required:
* Adafruit_VEML7700, Adafruit_SHT31, ArduinoJson, PubSubClient
*
* Author: HealthLight Project
* Date: 2026-08-13
* ============================================================================
*/
// ============================================================================
// SECTION 0: SIMULATION TOGGLE
// ============================================================================
// ★ DEFAULT ON: simulation mode for Velxio / Wokwi (uses potentiometers +
// push buttons instead of real VEML7700 / SHT30 / PIR sensors).
// Velxio does NOT have the Adafruit_VEML7700 / Adafruit_SHT31 libraries,
// so leaving this ON is REQUIRED for the online simulator to compile.
// >>> For REAL HARDWARE (breadboard / PCB with actual sensors), COMMENT
// THIS LINE BACK OUT so the I2C sensor drivers get compiled. <<<
#define SIMULATION_MODE
// ============================================================================
// SECTION 1: PIN DEFINITIONS (ESP32 DevKit V1 silkscreen labels)
// ============================================================================
// Layout strategy: LEFT side = inputs/sensors/PWM outputs; RIGHT side = I2C/status.
// See ES