Microcontroller Pinout Reference

About this tool

A searchable pin reference for the microcontroller boards you're most likely to reach for — Arduino Uno, Nano, and Mega, ESP32, ESP8266 (NodeMCU), and the STM32 "Blue Pill". Pick a board and filter by pin name or function (SPI, I2C, PWM, ADC, etc.) to quickly find which physical pin does what, without digging through a datasheet.

Frequently asked questions

Are these pinouts complete?

They cover the pins and functions most people actually look up day-to-day — primary UART/SPI/I2C, PWM-capable pins, ADC channels, and notable strapping/boot pins. For a full electrical reference (alternate function mappings, current limits, exact timing), always cross-check your board's datasheet before finalizing a design.

Why do some ESP32/ESP8266 pins have warnings?

Both chips have pins tied to boot-mode selection or internal flash that can prevent the board from booting (or cause unpredictable behavior) if pulled the wrong way at power-on — those are flagged in the notes so you don't accidentally wire something to them.

Do pin numbers match the silkscreen labels on my board?

For Arduino boards, yes — the labels match what's printed on typical boards. For ESP32/ESP8266/STM32, labels follow the common GPIO/port naming used on most breakout boards (e.g. NodeMCU's D0–D8 labels, or STM32's PA/PB/PC port names) — silkscreens can vary slightly between manufacturers, so double-check against your specific board if it looks different.