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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.

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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An interactive Arduino Mega circuit simulation you can run free in your browser on Velxio, by juliwicksmancay.
/*
* SERVER UTAMA MONITORING KANDANG AYAM - Arduino Mega 2560
* VERSI: kipas per node (relay di tiap node ESP32), LCD 16x2 I2C
*
* Koneksi UART:
* Node 1 -> Serial1 (RX1=19, TX1=18)
* Node 2 -> Serial2 (RX2=17, TX2=16)
* Node 3 -> Serial3 (RX3=15, TX3=14)
* Node 4 -> tergantung pengaturan NODE4_PAKAI_RX0TX0 di bawah
*
* LCD 16x2 I2C: SDA = pin 20, SCL = pin 21, alamat 0x27 (atau 0x3F)
* Buzzer: pin 8 | LED hijau/kuning/merah: pin 22/23/24
* (Relay kipas TIDAK lagi di Mega; relay ada di tiap node ESP32.)
*
* Protokol:
* Mega -> node : "?F1\n" (kipas ON) atau "?F0\n" (kipas OFF)
* Node -> Mega : $<id>,<suhu>,<rh>,<status_sensor>,<status_kipas>*<checksum>\n
*
* Logika kipas per node (dihitung Mega):
* - Sensor node error : kipas node itu ON (fail-safe)
* - Selain itu : kipas node ON jika suhu node ITU >= T_KIPAS_NODE_ON
* (histeresis 1 derajat). Node lain tidak ikut menyala.
* - Node offline : Mega tidak bisa memerintah; node mengatur kipasnya sendiri
* - Status global (AMAN/WASPADA/BAHAYA) hanya memengaruhi LED, buzzer, dan LCD.
* Opsi KIPAS_SEMUA_SAAT_BAHAYA = 1 membuat semua kipas ikut menyala saat BAHAYA.
*
* Library: LiquidCrystal I2C (Frank de Brabander).
*/
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
// 1 = Node 4 di Serial0 (pin 0 = RX0, pin 1 = TX0). Tidak ada log ke Serial Monitor.
// Cabut kabel pin 0/1 saat upload ke board asli.
// 0 = Node 4 di SoftwareSerial (RX = pin 10, TX = pin 11). Serial Monitor tetap aktif.
#define NODE4_PAKAI_RX0TX0 1
#if !NODE4_PAKAI_RX0TX0
#include <SoftwareSerial.h>
SoftwareSerial serialNode4(10, 11); // RX, TX
#endif
#define JUMLAH_NODE 4
Stream* portNode[JUMLAH_NODE]; // diisi di setup()
LiquidCrystal_I2C lcd(0x27, 16, 2); // 16 kolom x 2 baris
const byte PIN_BUZZER = 8;
const byte PIN_LED_HIJAU = 22;
const byte PIN_LED_KUNING = 23;
const byte PIN_LED_MERAH = 24;
// ======================= AMBANG BATAS =======================
const float THI_WASPADA = 75.0;
const float THI_BAHAYA = 82.0;
const float T_NODE_WASPADA = 30.0;
const float T_NODE_BAHAYA = 33.0;
const float HISTERESIS = 1.0;
const float T_KIPAS_NODE_ON = 28.0; // kipas node ON jika suhu node itu >= ini (OFF jika <= ini - histeresis)
// 0 = kipas HANYA ditentukan suhu node masing-masing (status global tidak memengaruhi kipas)
// 1 = saat status BAHAYA, semua kipas ikut menyala
#define KIPAS_SEMUA_SAAT_BAHAYA 0
const unsigned long INTERVAL_POLLING = 2500;
const unsigned long TIMEOUT_BALASAN = 1000; // ms (hardware asli: 300 cukup; simulator lebih lambat)
const unsigned long INTERVAL_HALAMAN = 3000; // ganti halaman LCD tiap 3 detik
const byte JUMLAH_HALAMAN = 4;
// ======================= VARIABEL GLOBAL =======================
float suhu[JUMLAH_NODE];
float lembab[JUMLAH_NODE];
bool valid[JUMLAH_NODE];
byte nodeState[JUMLAH_NODE] = {2, 2, 2, 2}; // 0=OK, 1=