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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.

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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.




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An interactive Arduino Uno circuit simulation you can run free in your browser on Velxio, by dave.
// Semáforo con LEDs y display 7 segmentos (2 dígitos)
// Pines LEDs: Rojo=8, Amarillo=9, Verde=10
// Pines 7 segmentos UNIDADES: A=2, B=3, C=4, D=5, E=6, F=7, G=11
// Pines 7 segmentos DECENAS: A=A0, B=A1, C=A2, D=A3, E=A4, F=A5, G=13
// Definición de pines para segmentos UNIDADES
#define SEG_A 2
#define SEG_B 3
#define SEG_C 4
#define SEG_D 5
#define SEG_E 6
#define SEG_F 7
#define SEG_G 11
// Definición de pines para segmentos DECENAS
#define SEG_A2 A0
#define SEG_B2 A1
#define SEG_C2 A2
#define SEG_D2 A3
#define SEG_E2 A4
#define SEG_F2 A5
#define SEG_G2 13
// Pines de LEDs del semáforo
#define LED_ROJO 8
#define LED_AMARILLO 9
#define LED_VERDE 10
// Pin del botón de parada
#define BOTON_PARADA 12
// Variable para controlar si el semáforo está detenido
bool detenido = false;
// Tiempos por fase (en milisegundos)
const unsigned long TIEMPO_ROJO = 5000;
const unsigned long TIEMPO_ROJO_AMARILLO = 1000;
const unsigned long TIEMPO_VERDE = 5000;
const unsigned long TIEMPO_AMARILLO = 1000;
// Variables para el cronómetro
unsigned long tiempoInicio = 0;
unsigned long tiempoActual = 0;
unsigned long tiempoRestante = 0;
int estadoActual = 0; // 0=Rojo, 1=Rojo+Amarillo, 2=Verde, 3=Amarillo
unsigned long duracionEstado[] = {TIEMPO_ROJO, TIEMPO_ROJO_AMARILLO, TIEMPO_VERDE, TIEMPO_AMARILLO};
// Función para mostrar un dígito en un display específico
void mostrarDigitoEnDisplay(int digito, bool esDecenas) {
// Patrón para mostrar dígitos 0-9 (segmentos A-G)
// Formato: {A, B, C, D, E, F, G}
const bool digitos[10][7] = {
{HIGH, HIGH, HIGH, HIGH, HIGH, HIGH, LOW}, // 0
{LOW, HIGH, HIGH, LOW, LOW, LOW, LOW}, // 1
{HIGH, HIGH, LOW, HIGH, HIGH, LOW, HIGH}, // 2
{HIGH, HIGH, HIGH, HIGH, LOW, LOW, HIGH}, // 3
{LOW, HIGH, HIGH, LOW, LOW, HIGH, HIGH}, // 4
{HIGH, LOW, HIGH, HIGH, LOW, HIGH, HIGH}, // 5
{HIGH, LOW, HIGH, HIGH, HIGH, HIGH, HIGH}, // 6
{HIGH, HIGH, HIGH, LOW, LOW, LOW, LOW}, // 7
{HIGH, HIGH, HIGH, HIGH, HIGH, HIGH, HIGH}, // 8
{HIGH, HIGH, HIGH, HIGH, LOW, HIGH, HIGH} // 9
};
if (esDecenas) {
// Segundo display (decenas)
digitalWrite(SEG_A2, digitos[digito][0]);
digitalWrite(SEG_B2, digitos[digito][1]);
digitalWrite(SEG_C2, digitos[digito][2]);
digitalWrite(SEG_D2, digitos[digito][3]);
digitalWrite(SEG_E2, digitos[digito][4]);
digitalWrite(SEG_F2, digitos[digito][5]);
digitalWrite(SEG_G2, digitos[digito][6]);
} else {
// Primer display (unidades)
digitalWrite(SEG_A, digitos[digito][0]);
digitalWrite(SEG_B, digitos[digito][1]);
digitalWrite(SEG_C, digitos[digito][2]);
digitalWrite(SEG_D, digitos[digito][3]);
digitalWrite(SEG_E, digitos[digito][4]);
digitalWrite(SEG_F, digitos[digito][5]);
digitalWrite(SEG_G, digitos[digito][6]);
}
}
// Función para mostrar un número de 2 dígitos (0-15)
void mostrarNumero(int numero) {
if (numero > 15) numero = 15; // Limitar a 15
if (numero < 0) numero =