A-Star 32U4 Micro

Overview

The Pololu A-Star 32U4 Micro is a general-purpose programmable module based on the ATmega32U4 AVR microcontroller from Microchip (formerly Atmel), which has 32 KB of flash program memory, 2.5 KB of RAM, and built-in USB functionality. Onboard features of the A-Star (abbreviated A*) include a 16 MHz 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 5.5 V to 15 V 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; another three GPIO pins can be accessed through the 6-pin ISP header. It fits all this into a 20-pin dual in-line package (DIP) measuring only 1" x 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.

A-Star 32U4 Micro, bottom view with U.S. quarter for size reference.

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.

Features

• Dimensions: 1" x 0.6" (1.05" x 0.6 including USB Micro-B connector)

• Programmable 16 MHz ATmega32U4 AVR microcontroller

○ 32 KB flash (4 KB used by bootloader, leaving 28 KB available for user program by default)

○ 2.5 KB SRAM

○ 1 KB EEPROM

○ Native full-speed USB (12 Mbps)

• 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 5.5 V to 15 V 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

Arduino compatibility

The A-Star 32U4 ships with a preloaded Arduino-compatible bootloader (which uses 4 KB of flash memory, leaving 28 KB available for the user program).

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

Pinout

This diagram identifies the I/O and power pins on the A-Star 32U4 Micro; it is also available as a printable PDF (409k pdf). For more information about the ATmega32U4 microcontroller on this board, see Microchip’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 5 V supply or from a separate 5.5 V to 15 V source on the VIN pin, which is reduced to 5 V by a 100 mA low-dropout (LDO) regulator; you can access this 5 V supply through the 5V power output pin. Additionally, the ATmega32U4 contains an internal 3.3 V regulator whose output is available on the 3V3 pin. Current drawn from the 3V3 output should not exceed about 50 mA, 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 25 mA) should not exceed 100 mA.

The A-Star family

From top to bottom: A-Star 328PB Micro, 32U4 Micro, 32U4 Mini SV, and 32U4 Prime SV.

Specifications

Dimensions

General specifications

Notes:

1 Without included optional headers. This measurement includes the USB Micro-B connector, which extends 0.05" past the edge of the PCB.
2 Without included optional headers.
3 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.
4 All 18 can be used as digital I/O and 8 can be used as analog inputs. 15 of the 18 are available along the sides for use in a breadboard; the remaining three are accessible through the ISP header.
5 On VIN.

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