Board
ESP8266 NodeMCU simulator, with the WiFi simulated and said to be
Mokxi models the NodeMCU V1.0: an ESP-12E with its Xtensa LX106 at 80 MHz, the GPIO block, IO_MUX, the RTC pin that is D0, UART0 and the TOUT converter. The radio is not modeled (WiFi here is simulated, the Arduino API over a network of ours), and neither is a PWM peripheral, because the chip has none.
- 9peripheral areas modeled
- 5projects ready to run
- Real timeon your own machine
Click to open it in the editor
The board is running real firmware right now. Click it to open the circuit in the editor.
The model
What is modeled
Taken from the board's own contract document and put in plain words, with what is missing listed underneath.
Core
Xtensa LX106 in the call0 ABI (sixteen registers, no window), one instruction per cycle at 80 MHz
Memory
32 KB of instruction RAM at 0x4010_0000 and 80 KB of data RAM at 0x3FFE_8000, the two segments every ESP8266 linker script names
GPIO and IO_MUX
Sixteen ordinary pins at the real offsets, with the pull-up that is the only pull this part has
GPIO 16
D0 is the RTC’s pin, in none of the GPIO registers, with a pull-down instead of a pull-up and no interrupt at all
UART0
Paced at the configured baud rate, wired to the serial monitor
The clock
CCOUNT and CCOMPARE0, which are core registers rather than a peripheral address anyone had to guess, behind millis(), micros() and a delay() that parks the core
analogRead
Ten bits of the real voltage on A0, behind the board’s own 220k/100k divider, so the header’s full scale is 3.2 V where the chip’s is 1.0
analogWrite
Software PWM from a timer handler, eight pins at once, 0 to 1023, the same range the Arduino ESP8266 core uses
WiFi, simulated
WiFi.h, HTTPClient.h and WebServer.h over a network written in software: no radio, no 802.11, no real internet
Not in the model
- A radio of any kind. No 802.11, no PHY, no channel, no WPA2. WiFi here is simulated (WiFi.h, HTTPClient.h and WebServer.h over a network written in software, with no real internet behind it), and on this chip, whose whole reason to exist is the radio, that is said first rather than last.
- Flash and the cache that maps it, so no PROGMEM read from flash, no SPIFFS, no LittleFS and no OTA.
- FRC1 and FRC2, the two hardware timers, and both watchdogs. Deep sleep and the RTC. SPI, I2S and the hardware UART1.
- The ADC’s registers are this model’s own. Espressif has never published the ESP8266’s SAR interface (system_adc_read() lives inside the SDK blob), so rather than invent an address and let a reader assume it is the chip’s, the contract says plainly that analogRead is the one call here that would need changing for real hardware.
Start here
Open one and press Run
Each of these opens in the editor exactly as it is drawn here.
Projects
Every built-in project on the ESP8266 NodeMCU V1.0
Each has its own page with the circuit running, the code and a parts list.
Questions
Is it free?
Yes. Every board and every part is on the free plan, with no account needed.
Does it do WiFi?
Simulated WiFi, yes, and it is worth being blunt about which half is which. Your sketch uses the real Arduino calls (WiFi.begin, WiFi.status, HTTPClient, WebServer), and the board joins a network, fetches a page and serves one. Underneath there is no radio, no 802.11 and no real internet: four made-up addresses under .mokxi exist and nothing a sketch does leaves this tab.
Why is digitalWrite(2, HIGH) the wrong pin?
Because D0 to D8 are not GPIO numbers. D4 is GPIO 2, D2 is GPIO 4 and D3 is GPIO 0. The runtime defines D0 to D8, so you can write the name on the silkscreen and mean the pin you are looking at.
Why does my LED light when I write LOW?
Because both on-board LEDs are wired from 3V3 to the pin, so LOW lights them. That is the real board, and it is the mistake this one is best at provoking.
Why is analogWrite(pin, 255) dim?
Because the range here is 0 to 1023, which is what the Arduino ESP8266 core does, so 255 is a quarter. analogWriteRange(255) makes an Uno sketch behave.
Can I compile my own sketch for it?
Yes. Edit the sketch and press Run: it compiles in the tab with clang for Xtensa, and the build panel shows every step. Nothing is uploaded.
Will my firmware run on a real NodeMCU?
Everything but analogRead, which talks to registers this model invented because the chip’s are not public. Section 6 of the contract sorts every other address into as-real-as-this-part-gets and believed.
Also here
The other boards
Every one of these runs today, and every one is free.
Looking for the shorter introduction? See the ESP8266 simulator page.
ESP32-C3-DevKitM-1
runs nowA RISC-V core at 160 MHz with GPIO, UART, the SYSTIMER, a twelve-bit ADC on GPIO 0 to 4 and LEDC PWM on any pin, on the real memory map.
Firmware for the modeled peripherals uses the board’s memory map. The contract also marks register addresses inside the SAR ADC and LEDC that are still unverified.
Open the board page
Arduino Uno R3
runs nowA complete ATmega328P, with three timers in every mode, USART0, the ADC, interrupts and sleep.
Blink, serial, a held button and a hardware PWM fade, at 16 MHz and real time.
Open the board page
Arduino Nano
runs nowThe Uno's ATmega328P on a board 45 by 18 mm, so it pushes into the breadboard instead of standing beside it.
Two more analog inputs than an Uno, and the same firmware runs on both.
Open the board page
Arduino Mega 2560
runs nowThe big Arduino: fifty-four digital pins, sixteen analog inputs and four serial ports, on the ATmega2560.
Everything an Uno sketch knows how to do, with enough pins left over to do it to twelve things at once.
Open the board page
Arduino Leonardo
runs nowAn Uno-shaped board whose USB goes to the chip itself: Serial is a USB CDC endpoint and Serial1 is pins 0 and 1.
The ATmega32U4 with its ten-bit timer, fourteen ADC channels and five external interrupts, at 16 MHz.
Open the board page
ESP32-C6-DevKitC-1
runs nowA second RISC-V board: thirty-one GPIOs, 512 KB of SRAM in one window, UART0, the SYSTIMER, a twelve-bit ADC on GPIO 0 to 6 and LEDC PWM on any pin.
The contract says plainly which addresses come from the manual, which are believed rather than verified, and what is not modeled at all.
Open the board page
ESP32 DevKit V1
runs nowThe classic ESP32 on an Xtensa LX6 at 240 MHz: the GPIO matrix, UART0, timer group 0, a twelve-bit ADC1 and the eight LEDC PWM channels, on the real memory map.
One core where the chip has two, no radio and no FPU. Your own sketch compiles in the tab.
Open the board page
ESP32-S3-DevKitC-1
runs nowThe ESP32-S3 on an Xtensa LX7 at 240 MHz: GPIO matrix, UART0, USB serial, ADC1, LEDC PWM and the RMT driving the RGB LED, on the real memory map.
One core where the chip has two, no radio and no FPU. Your own sketch compiles in the tab.
Open the board page
Raspberry Pi Pico
runs nowRP2040 on our own ARMv6-M core, with SIO GPIO, the 1 MHz timer and alarms, UART0 and eight PWM slices.
Blink, a button, serial and a fade at real time, with sleep parked on WFI.
Open the board page
Raspberry Pi Pico W
runs nowThe same RP2040 and the same forty pins as the Pico, so the same ELF runs on it.
The CYW43439 is not modeled. WiFi uses a simulated network, and the on-board LED is driven through the board runtime rather than GP25.
Open the board page
Seeed XIAO SAMD21
runs nowA thumbnail-sized Cortex-M0+ at 48 MHz: eleven pads, every one of them an analog input, with PWM on ten of them.
Serial is the chip’s own USB, modeled as a byte pipe with no stack above it, and Serial1 is a real USART on D6 and D7.
Open the board page
BBC micro:bit V2
runs nowThe nRF52833 on our own Cortex-M4 core at 64 MHz, with GPIO, GPIOTE, three TIMERs, RTC0 and UARTE0 on the real register map.
The 5x5 LED matrix scanned as the hardware scans it, buttons A and B, the speaker and three rings on the edge connector.
Open the board page
ATtiny85
runs nowA whole microcontroller in an 8-pin DIP, straight into the breadboard: six I/O, two timers, an ADC and a USI.
Blink, a button on INT0, a knob on the ADC and a serial port it bit-bangs for itself.
Open the board page
STM32F411 Black Pill
runs nowCortex-M4 with Thumb-2, NVIC and SysTick at 84 MHz, with GPIO, TIM2 to TIM5 and USART1 on the real register map.
Blink on PC13, a button, serial and a PWM fade, all at real time.
Open the board page
STM32 Blue Pill (F103)
runs nowCortex-M3 at 72 MHz, with GPIO on the F1’s CRL and CRH, TIM1 to TIM4, USART1 and a twelve-bit ADC.
Blink on PC13, a button, serial with a live reading, and a PWM fade, all at real time.
Open the board page
Arduino Uno R4 Minima
runs nowRenesas RA4M1, Arm Cortex-M4 at 48 MHz, in an Uno’s shape and on an Uno’s 5 V pins. Modeled: the PFS port block, GPT PWM on the six tilde pins, SCI2 as Serial1 on D0 and D1, and a fourteen-bit ADC that analogRead reads ten bits of.
Not modeled: a USB stack (Serial is a byte pipe with no enumeration behind it), the ICU, so there is no attachInterrupt, and the AGT. The contract says plainly which addresses come from the manual and which are believed rather than verified.
Open the board page
Arduino Pro Mini
runs nowThe Uno’s ATmega328P on the smallest Arduino there is, with no USB on it, in both builds: 5 V at 16 MHz and 3.3 V at 8 MHz.
The 3.3 V board really runs at 8 MHz, so a sketch built for 16 MHz keeps half time on it, as it does on the bench.
Open the board page
Arduino Micro
runs nowThe Leonardo’s ATmega32U4 on a board that pushes into a breadboard, with the L LED on pin 13 and the SPI pins on holes of their own.
Serial is the chip’s own USB and Serial1 is pins 0 and 1, and the Leonardo’s programs run on it unchanged.
Open the board page
SparkFun Pro Micro
runs nowThe ATmega32U4 in a Pro Mini’s footprint with a USB socket on the end, running the Leonardo’s programs.
No LED on pin 13: its lamps are RX and TX, lit by pulling their pins low.
Open the board page
Wemos D1 mini
runs nowThe NodeMCU’s ESP8266 on a board a third the size, with the same D0 to D8 names and only the holes that do something.
WiFi on a simulated network, and your own sketch compiles in the tab.
Open the board page
ESP-01S
runs nowAn ESP8266 with eight pins, four of them GPIO, and a blue LED that lights when its pin is low.
Wired with jumpers, because its two rows will not sit in a breadboard. WiFi is simulated.
Open the board page
Seeed XIAO ESP32-C3
runs nowThe ESP32-C3 at 160 MHz on the XIAO’s thumbnail outline: fourteen pads, and D0 to D10 that are the XIAO’s numbers, not GPIOs.
No user LED to blink, WiFi on a simulated network, and sketches that compile in the tab.
Open the board page
ESP32-C3 SuperMini
runs nowThe smallest ESP32-C3 board in common use, sixteen pins named by GPIO, at 160 MHz.
Its blue LED on GPIO 8 lights when the pin is LOW, the other way around from the DevKit’s.
Open the board page
Arduino Uno R4 WiFi
runs nowThe Uno R4’s RA4M1 with a 12 x 8 LED matrix to draw on through Arduino_LED_Matrix.h.
WiFi through WiFiS3.h on a simulated network: no radio, no ESP32-S3 in the model, no real internet.
Open the board page
Try it on your own firmware
What you build here runs on the board on your desk, unchanged. Nothing to install and no account needed.