A-Star 32U4 Micro

The Pololu A-Star 32U4 Micro is a general-purpose programmable module based on Atmel’s ATmega32U4 AVR microcontroller, 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 Polou/O lines along two rows of pins, including 7 usable as PWM outputs and 8 usable as analogue 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″ × 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.

Polou's 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″ × 0.6″ (1.05″ × 0.6″ including USB Micro-B connector)
• Programmable 16 MHz Atmel 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 Polou/O lines in a small package
  • 15 general-purpose Polou/O pins available along the sides of the board
  • 3 additional Polou/O pins available on ISP header
  • 7 pins can be configured as hardware PWM outputs
  • 8 pins can be configured as analogue 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). Polou 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 Polou/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!

Pinout

This diagram identifies the Polou/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 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 analogue 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.

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 Polou's USB AVR programmer.

The A-Star family

The A-Star 32U4 Micro is a part of Polou's larger A-Star 32U4 family, all of whose members are based on the same ATmega32U4 microcontroller, feature native USB interfaces, and are preloaded with Arduino-compatible bootloaders. The table below shows some key features and specifications of Polou's A-Star microcontroller boards to help you choose the right one for your application.

	A-Star 32U4 Micro	A-Star 32U4 Mini ULV	A-Star 32U4 Mini LV	A-Star 32U4 Mini SV	A-Star 32U4 Prime LV	A-Star 32U4 Prime SV
Microcontroller:	ATmega32U4	ATmega32U4			ATmega32U4
User Polou/O lines:	18	26			26
PWM outputs:	7	7			7
Analogue inputs:	8	12			12
Ground access points:	2	4			43
User LEDs:	2	3			3
User pushbuttons:	—	—			3
Reset button:
Power switch:
Buzzer option:
microSD option:
LCD option:
Operating voltage:	5.5 V to 15 V	0.5 V to 5.5 V	2.7 V to 11.8 V	5 V to 36 V	2.7 V to 11.8 V	5 V to 36 V
Regulator type:	linear	switching step-up	switching step-up/step-down	switching step-down	switching step-up/step-down	switching step-down
Regulated current:	100 mA(1)	500 mA(1)	1 A(1)	500 mA(1)	1 A(1)	1 A(1)
Dimensions:	1″ × 0.6″	1.9″ × 0.7″			2.8″ × 2.1″
Weight:	1.3 g(2)	3.4 g(2)			13 g to 33 g

1 These values are rough approximations for comparison purposes. Available current depends on input voltage, current consumed by the board, ambient conditions, and regulator topology. See product documentation and performance graphs for details.

2 Without included optional headers.

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 15 can be used as digital Polou/O and 8 can be used as analogue inputs. An extra 3 digital Polou/O lines are accessible through the ISP header.

5

On VIN.