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 Arduino Uno circuit simulation you can run free in your browser on Velxio, by frank-oenings.
#include <Wire.h>
#include "RTClib.h"
#include <Adafruit_NeoPixel.h>
#define LED_PIN 8 // Der Daten-Pin, an dem die Matrix hängt
#define MATRIX_WIDTH 16 // Physikalische Breite der Matrix
#define MATRIX_HEIGHT 16 // Physikalische Höhe der Matrix
#define NUM_LEDS (MATRIX_WIDTH * MATRIX_HEIGHT)
Adafruit_NeoPixel matrix(NUM_LEDS, LED_PIN, NEO_GRB + NEO_KHZ800);
RTC_DS3231 rtc;
// Farbdefinition (RGB)
const uint32_t FARBE_AN = matrix.Color(0, 0, 50); // Blau (nicht max. Helligkeit wegen Stromverbrauch)
const uint32_t FARBE_AUS = matrix.Color(0, 0, 0);
// Hilfsfunktion: Schaltet einen Buchstaben im 16x8 Raster ein (x: 0-15, y: 0-7)
void schalteBuchstabeEin(int x, int y) {
// Da jeder Buchstabe 2 Pixel hoch ist, betrifft das zwei physikalische Y-Zeilen
int physY1 = y * 2;
int physY2 = (y * 2) + 1;
int ledIndex1, ledIndex2;
// Berechnung für das typische Zick-Zack-Layout der Matrix
// Reihe 1 (physY1)
if (physY1 % 2 == 0) {
ledIndex1 = physY1 * MATRIX_WIDTH + x; // Von links nach rechts
} else {
ledIndex1 = physY1 * MATRIX_WIDTH + (MATRIX_WIDTH - 1 - x); // Von rechts nach links
}
// Reihe 2 (physY2)
if (physY2 % 2 != 0) {
ledIndex2 = physY2 * MATRIX_WIDTH + x;
} else {
ledIndex2 = physY2 * MATRIX_WIDTH + (MATRIX_WIDTH - 1 - x);
}
// Beide LEDs für diesen Buchstaben einschalten
matrix.setPixelColor(ledIndex1, FARBE_AN);
matrix.setPixelColor(ledIndex2, FARBE_AN);
}
// Hilfsfunktion: Schaltet ein ganzes Wort anhand von Start-X, End-X und der Y-Reihe ein
void schalteWort(int startX, int endX, int y) {
for (int x = startX; x <= endX; x++) {
schalteBuchstabeEin(x, y);
}
}
void setup() {
Serial.begin(9600);
matrix.begin();
matrix.show(); // Alle LEDs initial aus
if (!rtc.begin()) {
while (1); // Stoppen, wenn keine RTC gefunden wurde
}
if (rtc.lostPower()) {
rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));
}
}
void loop() {
DateTime now = rtc.now();
int stunde = now.hour();
int minute = now.minute();
aktualisiereWortuhr(stunde, minute);
delay(1000); // Alle 10 Sekunden prüfen
}
void aktualisiereWortuhr(int h, int m) {
matrix.clear(); // Zuerst alle LEDs ausschalten
// IMMER AN: "ES IST" (Beispieldaten: Reihe 0, Plätze 0-1 und 3-5)
schalteWort(0, 1, 0); // ES
schalteWort(3, 5, 0); // IST
int gerundeteMinute = (m / 5) * 5;
bool stundeErhoehen = false;
// MINUTEN
switch (gerundeteMinute) {
case 5: schalteWort(0, 3, 2); schalteWort(12, 15, 2); break; // FÜNF NACH
case 10: schalteWort(12, 15, 1); schalteWort(12, 15, 2); break; // ZEHN NACH
case 15: schalteWort(4, 10, 2); schalteWort(12, 15, 2); break; // VIERTEL NACH
case 20: schalteWort(0, 6, 1); schalteWort(12, 15, 2); break; // ZWANZIG NACH
case 25: schalteWort(0, 3, 2); schalteWort(0, 2, 3); schalteWort(4, 7, 3); stundeErhoehen = true; break; // FÜNF VOR HALB
case 30: schalteWort(4, 7, 3); stundeErhoehen = true; break; //