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.
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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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Arduino, ESP32, RP2040, STM32, ATtiny and Raspberry Pi, with SPICE analog solved alongside the firmware. Not a sandboxed mock.
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An interactive ATtiny85 circuit simulation you can run free in your browser on Velxio, by ian7171.
#define F_CPU 8000000UL // Is slower than the CPU but for this is fine
#include <avr/io.h>
#include <avr/pgmspace.h>
#include <util/delay.h>
#include <stdint.h>
#include "functions.h"
const uint8_t glyph_H[5] PROGMEM =
{
0x7F, 0x08, 0x08, 0x08, 0x7F
};
const uint8_t glyph_E[5] PROGMEM =
{
0x7F, 0x49, 0x49, 0x49, 0x41
};
const uint8_t glyph_L[5] PROGMEM =
{
0x7F, 0x40, 0x40, 0x40, 0x40
};
const uint8_t glyph_O[5] PROGMEM =
{
0x3E, 0x41, 0x41, 0x41, 0x3E
};
/* =========================================================
PRINT ONE GLYPH
========================================================= */
static void oled_glyph(const uint8_t *glyph)
{
oled_data_start();
for (uint8_t i = 0; i < 5; i++)
{
uint8_t b =
pgm_read_byte(&glyph[i]);
usi_write_byte(b);
}
usi_write_byte(0x00);
oled_data_stop();
}
//static void oled_putc(char c)
//{
// if (c < 32 || c > 126)
// c = '?';
// uint16_t offset = ((uint8_t)c - 32) * 5;
// oled_data_start();
// for (uint8_t i = 0; i < 5; i++)
// {
// uint8_t b = pgm_read_byte(&font5x7[offset + i]);
// usi_write_byte(b);
// }
/* one blank column between characters */
// usi_write_byte(0x00);
// oled_data_stop();
//}
//static void print_to_oled(const char *format)
//{
// char c;
// while ((c = pgm_read_byte(format++)))
// {
// oled_putc(c);
// }
//}
int main(void)
{
usi_i2c_init(); // Set up AT85 SCL and SDA to USI
oled_init(); // Init the OLED
oled_clear(); // Clear the screen
oled_cursor(10, 2); // Set the display position on the oled column, page
// oled_putc('H');
//print_to_oled(PSTR("Ian")); // PSTR means the fixed text is stored in FLASH rather than consuming SRAM.
oled_glyph(glyph_H);
oled_glyph(glyph_E);
oled_glyph(glyph_L);
oled_glyph(glyph_L);
oled_glyph(glyph_O);
while (1)
{
}
return 0;
}