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The A-Star 32U4 Mini LV is a programmable module based on the ATmega32U4 from Atmel. Unlike competing products, it has an onboard switching step-up/step-down regulator that allows it to be powered efficiently from a 2.7 V to 11.8 V supply. This compact 1.9″ × 0.7″ board breaks out all 26 of the microcontroller’s I/O pins (of which 7 can be used as PWM outputs and 12 as analog inputs), and loading programs is made easier by a Micro-USB interface and a preloaded Arduino-compatible bootloader.

A robust power selection circuit enables seamless transitions between regulator power and USB power, and overcurrent and reverse-voltage protection help safeguard the board against accidental damage.

All 26 general-purpose I/O lines on the ATmega32U4 are accessible on the A* 32U4 Mini; 7 of these are usable as PWM outputs and 12 are usable as analog inputs. The board measures 1.9″ × 0.7″, the same size as an Arduino Micro, and features a pair of mounting holes sized for #2 or M2 screws (not included). Its 0.1″ pin spacing makes the A* easy to use with solderless breadboards, perfboards, and 0.1″-pitch connectors.

This version, the A-Star Mini LV, can be powered from a 2.7 V to 11.8 V external source. The input voltage is regulated to 5 V by a TPS63061 switching step-up/step-down (buck-boost) converter from Texas Instruments. The regulator’s flexibility in input voltage is especially well-suited for battery-powered applications in which the battery voltage begins above 5 V and drops below 5 V as the battery discharges.

Without the typical restriction on the battery voltage staying above 5 V throughout its life, a wider range of battery types can be considered. For example:
A 4-cell battery holder, which might have a 6 V output with fresh alkalines or a 4.0 V output with partially discharged NiMH cells, can be used to power this A*.A disposable 9 V battery powering the board can be discharged to under 3 V instead of cutting out at 6 V, as with typical linear or step-down regulators.

Dimensions: 1.9″ × 0.7″ (1.95″ × 0.7″ 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
  • Native full-speed USB (12 Mbps)

Preloaded with Arduino-compatible bootloader (no external programmer required)
All I/O lines from the ATmega32U4 broken out in a compact package

  • 26 general-purpose I/O pins available along the sides of the board
  • 7 pins can be configured as hardware PWM outputs
  • 12 pins can be configured as analog inputs

3 user-controllable LEDs

Reset button
Switching regulator enables efficient low-power operation
Power selection circuit with seamless switching between power sources and overcurrent protection
Reverse-voltage protection on external power inputs
Precision 16 MHz crystal

Size: 0.7″ × 1.95″ × 0.23″
Weight: 3.4 g

General Specifications:

  • Processor: ATmega32U4 @ 16 MHz
  • RAM size: 2560 bytes
  • Program memory size: 32 Kbytes3
  • Motor channels: 0
  • User I/O lines: 26
  • Input voltage range: 2.7 V to 11.8 V (LV)
  • Minimum operating voltage: 2.7 V
  • Maximum operating voltage: 11.8 V
  • Maximum output current: 1.5 A4
  • Logic voltage: 5 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.
  • Available current depends on input voltage, current consumed by the board, ambient conditions, and regulator topology. See product documentation and performance graphs for details.
  • On Bat+ (LV, SV) or Bat- (ULV).