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A-Star 32U4 Micro

A-Star 32U4 Micro
A-Star 32U4 Micro
A-Star 32U4 Micro
A-Star 32U4 Micro
A-Star 32U4 Micro
A-Star 32U4 Micro
A-Star 32U4 Micro

Supplier : Pololu
Arduino Compatible

Our PriceHK$102.00
Stock 10
Weight 5
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The A-Star 32U4 Micro is a tiny programmable module featuring Atmel’s ATmega32U4 microcontroller. It packs a Micro-USB interface and 15 digital input/output pins (of which 7 can be used as PWM outputs and 8 as analog inputs) onto a board measuring only 1″×0.6″ and comes preloaded with an Arduino-compatible bootloader.


The Pololu A-Star 32U4 Micro is a general-purpose programmable module based on Atmel’s ATmega32U4 AVR microcontroller, which has 32KB of flash program memory, 2.5KB of RAM, and built-in USB functionality. Onboard features of the A-Star (abbreviated A*) include a 16MHz resonator, a USB Micro-B connector, an in-system programming (ISP) header, and a pair of indicator LEDs. A voltage regulator and power selection circuit allow the board to be powered from either USB or an external 5.5V to 15V source, while a resettable PTC fuse on the USB VBUS supply and reverse protection on VIN help protect it from accidental damage.

The A-Star 32U4 Micro breaks out 15 general-purpose I/O lines along two rows of pins, including 7 usable as PWM outputs and 8 usable as analog inputs. It fits all this into a 20-pin dual in-line package (DIP) measuring only 1″×0.6″ (even smaller than competing ATmega32U4 boards like the Teensy 2.0 and Pro Micro), and its 0.1″ pin spacing makes the A* easy to use with solderless breadboards, perfboards, and 0.1″-pitch connectors.

Our comprehensive user’s guide provides the basics you need to get started with the A-Star as well as detailed technical information for advanced users.

This product requires a USB A to Micro-B cable (not included) to connect to a computer.

Arduino compatibility

The A-Star 32U4 ships with a preloaded Arduino-compatible bootloader (which uses 4KB of flash memory, leaving 28KB available for the user program). We provide a software add-on that enables the board to be easily programmed from the Arduino environment.

The A-Star 32U4 uses the same microcontroller as the Arduino Leonardo and Arduino Micro and runs at the same frequency, making it just as powerful. Although the larger boards offer a few more I/O pins, the A-Star 32U4 Micro fits in an area half that of the Arduino Micro, and it takes up only 11% as much area as a standard full-size Arduino!

Pololu A-Star 32U4 Micro, Arduino Micro, and Arduino Leonardo.



  • Dimensions: 1″×0.6″ (1.05″×0.6″ including USB Micro-B connector)
  • Programmable 16MHz Atmel ATmega32U4 AVR microcontroller
    • 32KB flash (4KB used by bootloader, leaving 28KB available for user program by default)
    • 2.5KB SRAM
    • 1KB EEPROM
    • Native full-speed USB (12Mbps)
  • Preloaded with Arduino-compatible bootloader (no external programmer required)
  • Many I/O lines in a small package
    • 15 general-purpose I/O pins available along the sides of the board
    • 3 additional I/O pins available on ISP header
    • 7 pins can be configured as hardware PWM outputs
    • 8 pins can be configured as analog inputs
  • 2 user-controllable LEDs
  • Can be powered from USB or external 5.5V to 15V source on VIN
  • PTC fuse on VBUS supply
  • Reverse-voltage protection on VIN supply
  • 6-pin ISP header for use with an external programmer
  • Comprehensive user’s guide



This diagram identifies the I/O and power pins on the A-Star 32U4 Micro; yellow labels represent digital I/O pins and green labels represent analog input channels. Light text on a dark background indicates Arduino digital and analog pin numbering, while dark text on a light background indicates a name or function of the pin as defined in the ATmega32U4 datasheet. For more information about the ATmega32U4 microcontroller on this board, see Atmel’s ATmega32U4 documentation.

Printed on the A* circuit board are indicators that you can use to quickly identify each pin’s capabilities: a triangle next to the pin means it can be used as an analog input, and a square wave symbol under the pin number means it can be used as a PWM output.

The board can either be powered directly from the USB 5V supply or from a separate 5.5V to 15V source on the VIN pin, which is reduced to 5V by a 100mA low-dropout (LDO) regulator; you can access this 5V supply through the 5V power output pin. Additionally, the ATmega32U4 contains an internal 3.3V regulator whose output is available on the 3V3 pin. Current drawn from the 3V3 output should not exceed about 50mA, and when the board is being powered through VIN, the sum of the 5V output current, 3V3 output current, GPIO output current, and current used by the board itself (typically about 25mA) should not exceed 100mA.

Included hardware

A 1×20-pin breakaway 0.1″ male header is included with the A-Star 32U4 Micro, which can be soldered in to use the board with perfboards, breadboards, or 0.1″ female connectors. (The headers might ship already separated into two 1×10 pieces.) Also included is a 2×3 header that can be installed to allow external programming of the microcontroller through the AVR ISP interface, such as with our USB AVR programmer.

A-Star 32U4 Micro with included optional headers.
A-Star 32U4 Micro with soldered headers and connected USB cable.


Size: 0.6″ × 1.05″ × 0.18″1
Weight: 1.3 g2

General specifications

Processor: ATmega32U4 @ 16 MHz
RAM size: 2560 bytes
Program memory size: 32 Kbytes3
Motor channels: 0
User I/O lines: 154
Minimum operating voltage: 5.5 V
Maximum operating voltage: 15 V
Reverse voltage protection?: Y5
External programmer required?: N


Without included optional headers. This measurement includes the USB Micro-B connector, which extends 0.05″ past the edge of the PCB.
Without included optional headers.
Note that 4 KB of the MCU's 32 KB of flash memory is used by the pre-installed USB bootloader. All 32 KB is available when programming via the ISP header rather than the bootloader.
All 15 can be used as digital I/O and 8 can be used as analog inputs. An extra 3 digital I/O lines are accessible through the ISP header.

Documentation and other information

Pololu A-Star 32U4 Micro User’s Guide (Printable PDF: pololu_a-star_32u4_micro.pdf)

User’s manual for the Pololu A-Star 32U4 Micro.

File downloads

Pololu A-Star Software and Drivers (version 1.0.1) (98k zip)
This download contains the Windows drivers for the A-Star, the add-on for the Arduino IDE, the source code and compiled version of the bootloader, and a configuration file that some Linux users will need.
Pololu A-Star 32U4 Micro schematic diagram (253k pdf)
Printable schematic diagram of the A-Star 32U4 Micro.
Pololu A-Star 32U4 Micro dimension drawing (116k pdf)
Detailed dimension drawing of the A-Star 32U4 Micro.

Recommended links

A-Star repository on GitHub
This repository contains the A-Star Arduino add-on files, the Windows drivers, and the source code of the bootloader.
Arduino Software
Arduino integrated development environment (IDE) software
ATmega32U4 documentation
Atmel’s product page for the ATmega32U4.
AVR Libc Home Page
The web site for AVR Libc, which is the standard library of functions that you can use with C and C++ on the AVR.
Pololu A-Star and Orangutan Forum Section
The A-Star and Orangutan discussion section of the Pololu Robotics Forum.
AVR Freaks
AVR community with forums, projects, and AVR news.
AVRDUDE is a cross-platform command-line utility for programming the flash memory on AVR microcontrollers.
LUFA – the Lightweight USB Framework for AVRs
LUFA is an embedded software library written in C that can be used to create USB applications on USB-capable AVRs. It comes with a large library of example USB applications and bootloaders.
Atmel Studio 6
Atmel’s free integrated development environment (IDE) for AVRs.
A free, open-source suite of development tools for the AVR family of microcontrollers, including the GNU GCC compiler for C/C++.
LPS331 Arduino library
This is a library for the Arduino that interfaces with the Pololu LPS331AP pressure/altitude sensor carrier as well as the pressure sensor IC on the AltIMU-10 v3 (it also works with the original AltIMU-10). It makes it simple to read the raw pressure data from the sensor, and it provides functions to help calculate altitude based on the measured pressure.
Arduino library for addressable RGB LED strips from Pololu
This library allows you to control an arbitrary number of addressable LED strips with an arbitrary number of LEDs from an Arduino.


LSM303 Arduino library
This is a library for the Arduino that interfaces with our LSM303D, LSM303DLHC, and LSM303DLM 3D compass and accelerometer carriers as well as the compass and accelerometer ICs on the MinIMU-9 v3 and AltIMU-10 v3 (it also works with older versions of those boards, some of which used the LSM303DLH and LSM303DLHC). It makes it simple to configure the device and read the raw accelerometer and magnetometer data, and it has a function for computing the tilt-compensated heading for those looking to use the LSM303 as a tilt-compensated compass.
L3G Arduino library
This is a library for the Arduino that interfaces with our L3GD20H and L3GD20 3-axis gyro carriers as well as the gyros on the MinIMU-9 v3 and AltIMU-10 v3 (it also works with older versions of those boards, some of which used the L3G4200D and the L3GD20). It makes it simple to configure the device and read the raw gyro data.
Arduino Library for the Pololu QTR Reflectance Sensors
This guide explains how to use the QTRSensors library to read Pololu QTR reflectance sensors and QTR sensor arrays with Arduinos and Arduino-compatible devices like the Pololu Orangutan robot controllers.

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