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 ESP32 circuit simulation you can run free in your browser on Velxio, by sabharish3434.
// ============================================================
// DISASTER MONITORING SYSTEM - GATEWAY
// ============================================================
// NODE 1 -> FLOOD
// NODE 2 -> FIRE
// NODE 3 -> AIR POLLUTION
//
// Gateway displays latest status of ALL 3 nodes.
// No raw packets.
// No UNKNOWN PACKET.
// ============================================================
#define LORA_RX 16
#define LORA_TX 17
HardwareSerial LoRaSerial(2);
// ============================================================
// NODE DATA
// ============================================================
String node1Status = "WAITING";
String node1Reason = "Waiting for sensor data";
String node2Status = "WAITING";
String node2Reason = "Waiting for sensor data";
String node3Status = "WAITING";
String node3Reason = "Waiting for sensor data";
bool node1Received = false;
bool node2Received = false;
bool node3Received = false;
// ============================================================
// GET VALUE
// ============================================================
String getValue(String packet, String key)
{
int start = packet.indexOf(key);
if (start == -1)
return "";
start += key.length();
int end = packet.indexOf(',', start);
if (end == -1)
end = packet.length();
String value = packet.substring(start, end);
value.trim();
return value;
}
// ============================================================
// CONVERT STATUS
// ============================================================
String convertStatus(String status)
{
status.toUpperCase();
if (status.indexOf("CRITICAL") >= 0)
return "RISK";
if (status.indexOf("DANGER") >= 0)
return "RISK";
if (status.indexOf("WARNING") >= 0)
return "WARNING";
if (status.indexOf("SAFE") >= 0)
return "SAFE";
return "CHECK";
}
// ============================================================
// NODE 1 - FLOOD
// ============================================================
void processNode1(String packet)
{
node1Received = true;
String status = getValue(packet, "STATUS=");
// ------------------------------------------
// STATUS DETECTION
// ------------------------------------------
if (status != "")
{
node1Status = convertStatus(status);
}
else if (packet.indexOf("DANGER") >= 0 ||
packet.indexOf("CRITICAL") >= 0)
{
node1Status = "RISK";
}
else if (packet.indexOf("WARNING") >= 0)
{
node1Status = "WARNING";
}
else
{
node1Status = "SAFE";
}
// ------------------------------------------
// REASON
// ------------------------------------------
if (packet.indexOf("RAIN_STATUS=HEAVY") >= 0)
{
node1Reason = "Heavy rainfall detected";
}
else if (packet.indexOf("WATER=DANGER") >= 0)
{
node1Reason = "High water level detected";
}
else if (packet.indexOf("WATER=CRITICAL") >= 0)
{
node1Reason = "Critical water level detected";
}
else if (packet.indexOf("WA