Arduino, ESP32, Pico & ESP8266 Pinout Reference
Searchable pin functions, PWM/ADC/I²C/SPI pins and boot-strapping warnings for popular boards · free, no signup
See Arduino, ESP32, Pico & ESP8266 Pinout Reference in action
Free Microcontroller Pinout Reference
Picking pins is where microcontroller projects quietly go wrong: an ESP32 that will not boot because a sensor pulls GPIO12 high, an Arduino whose serial upload fails because D0/D1 are in use, a Pico I²C bus on the wrong pins, an ADC that stops working when Wi-Fi starts. This reference lists the pins of four popular boards — Arduino Uno/Nano, ESP32 DevKit (38-pin), Raspberry Pi Pico and NodeMCU/Wemos D1 (ESP8266) — with what each can do (PWM, ADC, DAC, touch, I²C, SPI, UART, interrupts) and the traps to avoid.
Filter by function (for example 'I2C' or 'ADC') or search for a pin name, and boot-strapping pins, input-only pins, flash pins and USB-serial pins are highlighted. The notes also remind you of the logic level of each board — the ESP32, Pico and ESP8266 are 3.3 V only and not 5 V tolerant — and typical per-pin current limits. It is compiled from the manufacturers' datasheets; check your own board's silkscreen, because clones differ.
Key features
Four boards
Arduino Uno/Nano, ESP32 DevKit, Raspberry Pi Pico, NodeMCU ESP8266.
Filter by function
PWM, ADC, DAC, touch, I²C, SPI, UART, interrupts, power.
Warnings built in
Strapping, input-only, flash, USB-serial and boot-state notes.
Voltage and current notes
3.3 V vs 5 V logic and typical pin current limits.
How to use it
- Choose your board.
- Filter by the function you need or search for a pin.
- Read the notes for each pin before wiring.
- Pick pins that avoid the highlighted warnings.
Worked example
Example
On an ESP32, pick GPIO32–39 for analog input if Wi-Fi is used (ADC1), keep GPIO34–39 for inputs only, avoid GPIO0/2/12/15 for devices that pull them at boot, and use GPIO21/22 for the default I²C bus.
Who uses this tool
Hobbyists
Choose safe pins for sensors, displays and motors.
Students
Learn what each pin can do.
Makers
Debug boot and Wi-Fi problems caused by pin choice.
Tips for the best results
- Prefer pins with no special boot behaviour for outputs.
- Use level shifters between 5 V devices and 3.3 V boards.
- Check ADC2 vs ADC1 on the ESP32 when using Wi-Fi.
- Read your board's own schematic for on-board LED and button pins.
Common mistakes to avoid
- Wiring a 5 V sensor directly to an ESP32 or Pico.
- Using GPIO6–11 on an ESP32 (flash).
- Pulling a strapping pin high or low with a peripheral.
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Frequently asked questions
Are clone boards the same?
Often yes, but always check the silkscreen and schematic.
Does it include the Mega or STM32?
Not yet — the most-used four boards are covered.
Which pins are safe on the ESP32?
GPIO4, 13, 14, 16–19, 21–23, 25–27, 32, 33 for general use.
Is it free?
Yes.