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.
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 circuit simulation you can run free in your browser on Velxio, by lavanyaavala1729.
#include <Arduino.h>
#include <SPI.h>
#include <Wire.h>
#include <SD.h>
#include <Adafruit_GFX.h>
#include <Adafruit_ILI9341.h>
#include <Adafruit_SSD1306.h>
#include <RTClib.h>
#include <TinyGPS++.h>
#include <math.h>
// =====================================================
// PIN DEFINITIONS
// =====================================================
// ---------- GPS ----------
#define GPS_RX 16
#define GPS_TX 17
// ---------- I2C ----------
#define I2C_SDA 21
#define I2C_SCL 22
// ---------- SPI ----------
#define SPI_SCK 18
#define SPI_MISO 19
#define SPI_MOSI 23
// ---------- MICRO SD ----------
#define SD_CS 13
// ---------- TFT ----------
#define TFT_CS 5
#define TFT_DC 26
#define TFT_RST 27
// ---------- BUTTONS ----------
#define START_BUTTON 32
#define END_BUTTON 33
// ---------- BUZZER ----------
#define BUZZER 25
// =====================================================
// OLED SETTINGS
// =====================================================
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_ADDRESS 0x3C
// =====================================================
// FARE SETTINGS
// =====================================================
const float RATE_PER_KM = 2.0;
const float MINIMUM_FARE = 10.0;
// =====================================================
// DEMO MODE
// =====================================================
// TRUE = Velxio simulation
// FALSE = actual GPS
const bool DEMO_MODE = true;
// Demo starting location
const double DEMO_START_LAT = 16.9891;
const double DEMO_START_LON = 82.2475;
// Demo destination
const double DEMO_END_LAT = 17.0050;
const double DEMO_END_LON = 82.2600;
// =====================================================
// OBJECTS
// =====================================================
HardwareSerial GPS_Serial(2);
TinyGPSPlus gps;
RTC_DS3231 rtc;
Adafruit_ILI9341 tft(
TFT_CS,
TFT_DC,
TFT_RST
);
Adafruit_SSD1306 oled(
SCREEN_WIDTH,
SCREEN_HEIGHT,
&Wire,
-1
);
// =====================================================
// VARIABLES
// =====================================================
unsigned long passengerID = 1001;
bool journeyStarted = false;
bool sdOK = false;
bool rtcOK = false;
bool oledOK = false;
bool tftOK = false;
// GPS coordinates
double startLatitude = 0.0;
double startLongitude = 0.0;
double destinationLatitude = 0.0;
double destinationLongitude = 0.0;
// Trip data
double distanceKm = 0.0;
double totalFare = 0.0;
// =====================================================
// BUZZER
// =====================================================
void beep(int duration)
{
digitalWrite(BUZZER, HIGH);
delay(duration);
digitalWrite(BUZZER, LOW);
}
// =====================================================
// HAVERSINE DISTANCE
// =====================================