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Arduino Micro

Category: Arduino
Manufacturer: Arduino
SKU: A000053
Status: Active
Release Year: 2012
Form Factor: Arduino Micro
Read Time: ~8 min read

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Arduino Micro top view
Arduino Micro bottom view
Arduino Micro pinout
Arduino Micro top view
Arduino Micro bottom view
Arduino Micro pinout

Overview

The Arduino Micro is a compact, breadboard-friendly microcontroller board built on the ATmega32U4 — the same MCU used in the Arduino Leonardo. At 48 × 18 mm, it is small enough to fit inside enclosures, embed in wearables, and mount directly onto a standard solderless breadboard using its 0.1-inch-spaced through-hole pins.

Like the Leonardo, the Micro's ATmega32U4 integrates the USB controller directly on-chip, enabling native USB HID support. The board can enumerate as a USB keyboard, mouse, MIDI device, or other HID class without any additional bridge hardware. This makes it a popular choice for custom USB input devices, macro pads, game controllers, and automation tools in compact packages.

Released in 2012 in collaboration with Adafruit, the Micro targets applications where the Leonardo's larger footprint is impractical but the HID capability is still required.

Quick Overview

Property Value
Microcontroller ATmega32U4 (8-bit AVR)
Clock Speed 16 MHz
Operating Voltage 5V
Input Voltage (recommended) 7–12V
Digital I/O Pins 20 (7 with PWM)
Analog Input Pins 12
Flash Memory 32 KB (4 KB used by bootloader)
SRAM 2.5 KB
EEPROM 1 KB
Hardware UART 1 (Serial1 on D0/D1)
USB micro-USB (native HID — ATmega32U4 integrated)
Form Factor Breadboard compatible (0.1" pin spacing)
Dimensions 48 × 18 mm

Key Features

  • Same ATmega32U4 as the Arduino Leonardo — native USB HID without a bridge chip
  • Compact breadboard-compatible design (fits standard 0.1" solderless breadboards)
  • 20 digital I/O pins (7 with PWM) in a small footprint
  • 12 analog input channels for versatile sensor reading
  • Native USB keyboard, mouse, MIDI, and joystick emulation
  • Simultaneous USB CDC serial (Serial) and hardware UART (Serial1) on D0/D1
  • Micro-USB connector for programming and power
  • On-board power LED and user LED on pin 13
  • Compatible with the Keyboard, Mouse, and MIDIUSB Arduino libraries

Technical Specifications

Specification Value
Microcontroller ATmega32U4
Architecture 8-bit AVR
Clock Speed 16 MHz
Operating Voltage 5V
Recommended Input Voltage 7–12V
Maximum Input Voltage 20V
Digital I/O Pins 20
PWM Pins 7 (D3, D5, D6, D9, D10, D11, D13)
Analog Input Pins 12 (A0–A5 + A6–A11 on digital pins)
DC Current per I/O Pin 40 mA
DC Current for 3.3V Pin 50 mA
Flash Memory 32 KB (4 KB bootloader)
SRAM 2.5 KB
EEPROM 1 KB
Hardware UART 1 (Serial1, D0=RX1, D1=TX1)
USB Serial (CDC) Serial (USB virtual port)
I2C 1 (D2 SDA, D3 SCL)
SPI 1 (ICSP header)
USB micro-USB (native, ATmega32U4)
On-Board LED Pin 13
Dimensions 48 × 18 mm

Pinout

Arduino Micro top view

Digital I/O

The Micro exposes its pins on two rows of through-hole pads along its long edges, designed to straddle a standard breadboard.

Pin Function Notes
D0 (RX1) Hardware Serial1 RX Also digital I/O
D1 (TX1) Hardware Serial1 TX Also digital I/O
D2 Digital I/O / SDA I2C data
D3 Digital I/O / SCL / PWM I2C clock, PWM
D4 / A6 Digital I/O / Analog Dual-function
D5 Digital I/O / PWM PWM output
D6 / A7 Digital I/O / Analog / PWM Dual-function, PWM
D7 Digital I/O
D8 / A8 Digital I/O / Analog Dual-function
D9 / A9 Digital I/O / Analog / PWM Dual-function, PWM
D10 / A10 Digital I/O / Analog / PWM Dual-function, PWM
D11 Digital I/O / PWM PWM
D12 / A11 Digital I/O / Analog Dual-function
D13 Digital I/O / PWM / LED Built-in LED, PWM

Analog Pins

Pin Notes
A0–A5 Dedicated analog input pins on separate header pads
A6–A11 Shared with D4, D6, D8, D9, D10, D12

Power Pins

Pin Description
VIN 7–12V external input
5V Regulated 5V output
3.3V 3.3V output (50 mA max)
GND Ground
RESET Pull LOW to reset
AREF Analog reference for ADC

Power

The Arduino Micro is powered via:

  1. micro-USB: 5V from the connected computer or USB charger — the most common power source.
  2. VIN Pin: 7–12V from an external supply, regulated to 5V on-board.
  3. 5V Pin: Direct 5V supply (bypasses the regulator — ensure the source is stable and clean).

The compact size means the on-board regulator has limited thermal headroom for high-current loads. For power-intensive applications, supply regulated 5V directly to the 5V pin from an external source.

HID Support

The Arduino Micro supports the same native USB HID capabilities as the Arduino Leonardo, since both use the ATmega32U4.

HID Class Library Example Use
USB Keyboard Keyboard.h Key presses, text automation, macros
USB Mouse Mouse.h Cursor movement, button clicks, scroll
USB MIDI MIDIUSB.h MIDI note and control messages
USB Joystick Joystick.h (third-party) Game controller input

HID Keyboard Example

#include <Keyboard.h> const int buttonPin = 4; void setup() { pinMode(buttonPin, INPUT_PULLUP); Keyboard.begin(); } void loop() { if (digitalRead(buttonPin) == LOW) { Keyboard.press(KEY_LEFT_CTRL); Keyboard.press('c'); delay(100); Keyboard.releaseAll(); // Copy keystroke delay(300); } }

HID Mouse Example

#include <Mouse.h> void setup() { Mouse.begin(); } void loop() { // Move cursor right by 10 pixels every 500ms Mouse.move(10, 0, 0); delay(500); }

Upload Consideration with HID Sketches

When a HID sketch causes the Micro to enumerate without a CDC serial port, the COM port disappears from the host OS. To upload a new sketch, press the RESET button on the Micro once while the IDE attempts to upload — this interrupts the HID sketch and briefly re-activates the bootloader.

Getting Started

What You Need

  • Arduino Micro
  • Micro-USB cable
  • Solderless breadboard (optional but useful for the Micro's form factor)
  • Computer with Arduino IDE installed

Steps

  1. If desired, insert the Micro into a breadboard — its pins span the central gap on a standard 5-row breadboard.
  2. Connect via micro-USB cable to your computer.
  3. Open the Arduino IDE.
  4. Select Tools > Board > Arduino AVR Boards > Arduino Micro.
  5. Select the correct COM port under Tools > Port.
  6. Upload the Blink sketch.

Blink Example

// Blink the built-in LED on pin 13 of the Arduino Micro void setup() { pinMode(13, OUTPUT); } void loop() { digitalWrite(13, HIGH); delay(1000); digitalWrite(13, LOW); delay(1000); }

Serial Note

Like the Leonardo, Serial on the Micro is the USB CDC virtual port. Hardware serial on D0/D1 is Serial1. Always wait for the USB connection when using Serial in setup:

void setup() { Serial.begin(9600); while (!Serial) { ; } // Wait for USB serial to open Serial.println("Arduino Micro ready"); } void loop() {}

Programming

  • Bootloader: Caterina bootloader (1200-baud USB CDC touch reset)
  • Upload method: 1200-baud touch on the CDC serial port triggers reset into bootloader
  • Manual reset: Press RESET button when "Uploading…" appears if auto-reset fails
  • Board package: Arduino AVR Boards (included with Arduino IDE by default)
  • No bridge chip: The ATmega32U4 manages USB directly at all times

Package Contents

Item Quantity
Arduino Micro board 1

The Micro is sold with or without pre-soldered headers. A micro-USB cable is not included. For breadboard use, break-away 0.1" male headers are recommended if the board is supplied without them.

Applications

  • Custom USB macro keypads and shortcut controllers
  • Compact USB MIDI instruments and controller pads
  • Embedded HID automation devices (fits inside keyboard cases, enclosures)
  • Wearable electronics requiring USB connectivity
  • Breadboard-based HID prototyping
  • Custom USB game controllers and simulation inputs
  • Space-constrained robotics and rover control boards
  • USB-powered sensor logging with serial output

Where to Buy

Equivalent Boards

Board Key Difference
Arduino Leonardo Same ATmega32U4 and HID capability, larger Uno form factor, not breadboard-friendly
Arduino Nano Similar compact size, ATmega328P (no native HID), has USB via CH340/FT232 bridge
Arduino Pro Mini Even smaller, no USB connector at all, no HID, requires FTDI adapter

Documentation

Notes

  • The Arduino Micro is electrically nearly identical to the Arduino Leonardo. Sketches written for the Leonardo run on the Micro without modification, and vice versa.
  • The Micro's small size makes it ideal for permanent installs inside project enclosures. Its 0.1" pin spacing means it can also be soldered directly to custom PCBs.
  • Third-party ATmega32U4-based boards (Pro Micro, etc.) are common clones. They may use different pin mappings or bootloaders — verify before swapping with official Micro boards.
  • Pin A6–A11 are only available as analog inputs on the digital pin pads; they do not have separate labeled analog header pins like A0–A5.
  • Power consumption is low enough for operation from a USB host's 500 mA port, but add up all peripheral loads before assuming this headroom is sufficient.

Community

Revision History

Version Date Notes
v1.0 2026-06 Initial entry