ESP8266 NodeMCU

An open-source Wi-Fi development board built around the Espressif ESP8266EX, pairing a 32-bit microcontroller with 802.11 b/g/n networking on a breadboard-friendly module.

Try it in the simulator

ESP8266 NodeMCU: Wi-Fi development board

What is the ESP8266 NodeMCU?

NodeMCU is a low-cost, open-source development board built around the Espressif ESP8266EX system-on-chip, carried here on the ESP-12E/12F module used by the LoLin V3 variant. It bundles a microcontroller and a 2.4 GHz Wi-Fi radio in a single package, so a single board can read sensors, run logic, and talk to the network without a separate shield.

At its core is a Tensilica Xtensa 32-bit LX106 RISC processor running at 80 MHz (configurable up to 160 MHz), backed by 4 MB of SPI flash and roughly 80 KB of usable RAM. The ESP8266EX implements a full 802.11 b/g/n WLAN MAC and TCP/IP stack. On the board, an AMS1117 regulator drops the 5 V USB/Vin rail to the 3.3 V the chip needs, and a USB-to-serial bridge (CH340 on LoLin units) handles programming and the serial console over micro USB.

Makers program it with the Arduino IDE (ESP8266 core), MicroPython, or Lua. The header layout exposes 11 usable GPIO, one 10-bit ADC channel, and hardware SPI, I2C, and UART, all on a 0.1 in pitch that straddles a breadboard. Its combination of price, size, and built-in Wi-Fi makes it a default choice for IoT sensor nodes, web-controlled gadgets, and cloud data logging.

ESP8266 NodeMCU pin reference

Pin	Function	Type
`A0` A0 (ADC0)	Analog single 10-bit ADC (TOUT), 0–1.0 V	Digital input
`RSV` RSV	No connect	No connect
`RSV2` RSV	No connect	No connect
`SD3` SD3 (GPIO10)	Digital · PWM · SPI flash SDIO — usable as GPIO in DIO/QIO-safe modes	Bidirectional (GPIO)
`SD2` SD2 (GPIO9)	Digital · PWM · SPI flash SDIO — usable as GPIO in DIO/QIO-safe modes	Bidirectional (GPIO)
`SD1` SD1 (MOSI)	Digital GPIO8 · SPI flash MOSI (SDD1) — reserved	Bidirectional (GPIO)
`CMD` CMD (CS)	Digital GPIO11 · SPI flash CS (SDCMD) — reserved	Bidirectional (GPIO)
`SD0` SD0 (MISO)	Digital GPIO7 · SPI flash MISO (SDD0) — reserved	Bidirectional (GPIO)
`CLK` CLK (SCLK)	Digital GPIO6 · SPI flash SCLK (SDCLK) — reserved	Bidirectional (GPIO)
`GND` GND	Power	Power in
`3V3` 3V3	Power	Power out
`EN` EN	Digital chip enable (active-high); leave pulled up for normal run	Digital input
`RST` RST	Digital active-low reset	Digital input
`GND_2` GND	Power	Power in
`VIN` Vin (5V)	Power	Power in
`D0` D0 (GPIO16)	Digital GPIO16 — read/write + deep-sleep wake only; no interrupt/PWM/I²C/OneWire	Bidirectional (GPIO)
`D1` D1 (GPIO5)	Digital · PWM · I²C SCL (default Wire)	Bidirectional (GPIO)
`D2` D2 (GPIO4)	Digital · PWM · I²C SDA (default Wire)	Bidirectional (GPIO)
`D3` D3 (GPIO0)	Digital · PWM · Strapping FLASH button — hold LOW at reset to enter flash mode; HIGH for normal boot	Bidirectional (GPIO)
`D4` D4 (GPIO2)	Digital · PWM · UART TXD1 (debug) · Strapping on-module blue LED (active-low); must be HIGH at reset	Bidirectional (GPIO)
`3V3_2` 3V3	Power	Power out
`GND_3` GND	Power	Power in
`D5` D5 (GPIO14)	Digital · PWM · SPI HSPI SCLK (default SPI SCK)	Bidirectional (GPIO)
`D6` D6 (GPIO12)	Digital · PWM · SPI HSPI MISO (default SPI MISO)	Bidirectional (GPIO)
`D7` D7 (GPIO13)	Digital · PWM · SPI HSPI MOSI (default SPI MOSI) · UART RXD2	Bidirectional (GPIO)
`D8` D8 (GPIO15)	Digital · PWM · SPI HSPI CS (default SPI SS) · UART TXD2 · Strapping must be LOW at reset for normal boot	Bidirectional (GPIO)
`D9` D9 (GPIO3/RX)	UART RXD0 (Serial RX) · Digital	Bidirectional (GPIO)
`D10` D10 (GPIO1/TX)	UART TXD0 (Serial TX) · Digital	Bidirectional (GPIO)
`GND_4` GND	Power	Power in
`3V3_3` 3V3	Power	Power out

Specifications

Operating voltage: 3.3 V (max 5.5 V)
Interface: gpio
Clock speed: 80 MHz
Flash: 4 MB
RAM: 80 KB
GPIO pins: 11
ADC: 1 channels · 10-bit
PWM channels: 8
Dimensions: 58 × 31.5 × 14 mm

Verified from the Tinkered component library · LoLin.

Circuit requirements

Power the board over micro USB or by feeding 5 V into the Vin pin; the onboard AMS1117 regulator steps either source down to 3.3 V for the module.
As an alternative, a clean regulated 3.3 V can be fed directly into the 3V3 pin, but do not also drive Vin or USB at the same time, since that back-feeds the regulator.
Logic level is 3.3 V and the GPIO pins are not 5 V tolerant. Any 5 V sensor or signal line must go through a level shifter or divider before reaching a pin.
The single analog input A0 is rated for 0 to 1.0 V per the verified pin spec. Use an external voltage divider to read higher voltages, and never apply the 3.3 V rail directly to it.
The 3V3 pin can only supply what the onboard regulator allows, and Wi-Fi transmit bursts draw sharp current spikes, so keep peripheral loads modest and add a bulk capacitor near power-hungry parts.
GPIO0 (D3), GPIO2 (D4), and GPIO15 (D8) are strapping pins whose levels at reset select the boot mode. Avoid wiring them to anything that pulls them the wrong way during power-up.
GPIO16 (D0) is limited to plain digital read/write and deep-sleep wake; it has no PWM, interrupt, or I2C. Tie it to RST if you want the board to wake itself from deep sleep.

Common ESP8266 NodeMCU mistakes

Feeding 5 V into GPIO pins

The ESP8266 I/O is 3.3 V and is not 5 V tolerant. Wiring a 5 V logic output, sensor, or the Vin rail straight to a GPIO can permanently damage the pin or the chip. Level-shift or divide any 5 V signal first.

Confusing D-labels with GPIO numbers

The silkscreen D-numbers do not match the GPIO numbers. D1 is GPIO5, D2 is GPIO4, D3 is GPIO0, and so on. Mixing them up in code (for example calling pinMode on the GPIO number instead of the Arduino D constant) drives the wrong pin.

Using strapping pins in a way that blocks boot

GPIO0 (D3), GPIO2 (D4), and GPIO15 (D8) must be at the correct level at reset. Holding GPIO0 low, pulling GPIO2 low, or pulling GPIO15 high at power-up puts the board into flash mode or stops it booting. Reserve these pins for signals that idle in the safe state.

Overloading the 3V3 pin or the regulator

The AMS1117 regulator and the 3V3 rail have limited headroom, and Wi-Fi activity causes current spikes. Powering several sensors, a display, and a radio module all from 3V3 can cause brownouts and random resets. Budget the current and add decoupling capacitors.

Exceeding the A0 analog input range

The ADC input is rated to a low full-scale voltage (0 to 1.0 V on the bare chip). Applying more than the rated voltage to A0 gives clipped readings or damages the input. Scale higher voltages down with a divider sized for the actual range.

Popular ESP8266 NodeMCU projects

Wi-Fi weather station

Read a DHT22 or BME280 for temperature, humidity, and pressure, then push the values to a cloud dashboard like ThingSpeak or Blynk over Wi-Fi.

Web-controlled relay and home automation

Run a small HTTP server on the board so a phone browser can switch a relay, controlling lights or appliances from anywhere on the local network.

MQTT sensor node for Home Assistant

Publish sensor readings and subscribe to commands over MQTT, letting the board join a Home Assistant or Node-RED setup as a low-cost wireless endpoint.

Deep-sleep battery sensor

Wire GPIO16 (D0) to RST and use deep sleep so the board wakes periodically, takes a reading, transmits it, and sleeps again to stretch battery life for weeks.

REST API GPIO controller

Expose the board's pins through a simple JSON REST API so other devices or scripts can read inputs and toggle outputs remotely.

OTA-updatable IoT firmware

Use the ESP8266 Arduino OTA library to push new firmware over Wi-Fi, so a deployed board can be reprogrammed without a USB cable.

Build with the ESP8266 NodeMCU.

Drop the ESP8266 NodeMCU into a circuit, write firmware, and simulate it in your browser, then deploy to real hardware. All in one editable Tinkered project.

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