A-Star 32U4 Prime LV, bottom view.

The Pololu A-Star 32U4 Prime is a general-purpose programmable board based on Atmel’s ATmega32U4 AVR microcontroller and arranged in the common Arduino form factor exemplified by the Uno R3 and Leonardo. As such, the A-Star Prime (abbreviated A* Prime) is compatible with many Arduino shields, including all of the Arduino shields we carry. All 26 of the microcontroller’s GPIO lines are accessible on the board, including seven than can be used as PWM outputs and twelve that can be used as analog inputs. The ATmega32U4 is capable of native full-speed USB, which makes it more versatile than similar boards that rely on USB-to-serial adapters: in addition to supporting a virtual (CDC) serial/COM port interface, the A-Star can appear to a connected computer as a mouse and keyboard. The A-Star’s USB interface can be accessed through its USB Micro-B connector.

The A* Prime supports the on-board microcontroller with many additional features and improvements over competing products, including enhanced connectivity and superior power management. The Prime is available in two main versions: LV, which features a blue solder mask and a step-up/step-down voltage regulator that allows operation from 2.7 V to 11.8 V, and SV, which features a green solder mask and a switching step-down regulator that allows operation from 5 V to 36 V. Each version is available in several different configurations: with or without preinstalled through-hole components like standard Arduino female headers and with or without microSD support. There is also a configuration available for each version with an 8×2 character LCD.

A-Star 32U4 Prime LV microSD with LCD.

A-Star 32U4 Prime LV (2.7 V to 11.8 V) configurations:

A-Star 32U4 Prime SV microSD with LCD.

A-Star 32U4 Prime SV (5 V to 36 V) configurations:

We carry an A-Star Prime accessory pack that contains an assortment of parts you might want when assembling the configurations without preinstalled headers (items #3105, #3106, #3111, and #3112).

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.

A-Star 32U4 Prime pinout diagram.

A-Star 32U4 Prime power distribution diagram.


  • Programmable ATmega32U4 MCU with 32 KB flash, 2.5 KB SRAM, 1 KB EEPROM, and native full-speed USB (clocked by precision 16 MHz crystal oscillator)
  • Preloaded with Arduino-compatible bootloader (no external programmer required)
  • All 26 general-purpose I/O lines from the ATmega32U4 are broken out (including PB0, PD5, and PE2); 7 of these can be used as hardware PWM outputs and 12 of these can be used as analog inputs
  • Convenient 0.1″-spaced power, ground, and signal connection points
  • Buzzer option for simple sounds and music
  • microSD support (microSD version only)
  • HD44780-based character LCD option
  • 3 user-controllable LEDs
  • 3 user pushbuttons
  • Reset button
  • Power features:
    • Can be powered from USB or from an external source (with several access points for connecting external power)
      • LV operating range: 2.7 V to 11.8 V
      • SV operating range: 5 V to 36 V
    • Switching 5 V regulator enables efficient operation
    • 3.3 V rail supplied by 300 mA linear regulator
    • Power switch for external power inputs
    • Reverse-voltage protection on external power inputs
    • Power selection circuit allows for seamless switching between power sources while providing overcurrent protection and feedback about which power source is selected
  • 6-pin ISP header for use with an external programmer
  • Comprehensive user’s guide

Details for item #3108

A-Star 32U4 Prime LV microSD.

This configuration of the A-Star 32U4 Prime LV includes microSD support and is assembled with through-hole components as shown in the picture above so that all the basic features can be used without any additional soldering. The standard female headers common to many Arduinos are preinstalled, as is the 2×3 male ISP header, buzzer, DC power jack, and shorting block headers for enabling the microSD hardware, buzzer, and battery voltage monitor. This is the LV version of the A-Star Prime, which operates from 2.7 V to 11.8 V.

A-Star 32U4 Prime LV 5 V regulator

A major feature of the A* Prime LV is its power system, which allows it to efficiently operate from a 2.7 V to 11.8 V external source. Like on the smaller A-Star 32U4 Mini LV, the input voltage is regulated to 5 V by a TPS63061 switching step-up/step-down (buck-boost) converter from Texas Instruments. (We also make a standalone regulator based on this integrated circuit.) 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.

As shown in the left graph below, the LV’s 5 V switching regulator has an efficiency – defined as (Power out)/(Power in) – of 80% to 90% for most combinations of input voltage and load.

The A-Star’s components, including the microcontroller and LEDs, draw 30 mA to 40 mA in typical applications (without the buzzer, microSD card, or an LCD). The rest of the regulator’s achievable output current, which depends on input voltage as well as ambient conditions, can be used to power other devices. The blue line in the right graph above shows output currents at which the voltage regulator’s over-temperature protection typically kicks in after a few seconds. These currents represent the limit of the regulator’s capability and cannot be sustained for long periods; under typical operating conditions, a safe limit for the maximum continuous regulator output current is 60% to 70% of the values shown in the graph.

Arduino compatibility

The A-Star 32U4 Prime ships with a preloaded Arduino-compatible bootloader (which uses 4 KB of flash memory, leaving 28 KB available for the user program). We provide a software add-on that enables the board to be easily programmed from the Arduino environment and an Arduino library to make it easy to use the additional on-board hardware. The A-Star 32U4 has the same microcontroller and form factor as the Arduino Leonardo, and it runs at the same frequency, so we generally expect it to work with shields that are compatible with the Leonardo and similar boards. Note that the Prime has additional components and connection points, so you should make sure these do not physically interfere with any shield you are considering using. The following table shows how the Prime compares to the Leonardo and Uno:

Arduino Uno R3

Arduino Leonardo

A-Star 32U4 Prime LV

A-Star 32U4 Prime SV
Microcontroller: ATmega328P ATmega32U4 ATmega32U4
Clock: 16 MHz resonator 16 MHz crystal 16 MHz crystal
User I/O lines: 20 23 26
PWM outputs: 6 7 7
Analog inputs: 6 12 12
Ground access points: 4 4 43
User LEDs: 3 3 3
User pushbuttons: 3
Reset button: yes yes yes
Power switch:     yes
Buzzer option:     yes
microSD option:     yes
LCD option:     yes
yes yes yes
USB connector: B Micro-B Micro-B
power selection:
partial partial TPS2113A
input voltage:
7 V to 12 V 7 V to 12 V 2.7 V to 11.8 V 5 V to 36 V
Regulator type (5 V): linear linear switching
5 V
at 3 V in 0.75 A
at 5 V in 1.5 A 0.2 A
at 7 V in 1.0 A 1.0 A 1.5 A 1.0 A
at 9 V in 0.5 A 0.5 A 1.5 A 1.0 A
at 11 V in 0.35 A 0.35 A 1.5 A 1.0 A
at 24 V in 1.0 A
via USB
0.5 A(1) 0.5 A(1) 1.5 A(1) 1.5 A(1)
Weight: 28 g 20 g 13 g to 33 g

1 With sufficiently capable USB power supply.

Side-by-side comparison of the A-Star 32U4 Prime LV microSD to the Arduino Leonardo.

The A-Star family

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

The A-Star 32U4 Prime is a part of our 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 our 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
A-Star 32U4 Robot Controller LV

A-Star 32U4 Robot Controller SV
Microcontroller: ATmega32U4 ATmega32U4 ATmega32U4 ATmega32U4
User I/O lines: 18 26 26(1) 26(1)
PWM outputs: 7 7 7 7(1)
Analog inputs: 8 12 12 12(1)
Ground access points: 2 4 43 44
User LEDs: 2 3 3 3
User pushbuttons: 3 3
Reset button:   yes yes yes
Power switch:     yes yes
Buzzer option:     yes yes
microSD option:     yes  
LCD option:     yes  
Motor drivers:       yes
Operating voltage: 5.5 V to 15 V ULV: 0.5 V to 5.5 V
LV: 2.7 V to 11.8 V
SV: 5 V to 36 V
LV: 2.7 V to 11.8 V
SV: 5 V to 36 V
LV: 2.7 V to 11 V
SV: 5.5 V to 36 V
Regulator type: linear switching

ULV: step-up
LV: step-up/step-down
SV: step-down

LV: step-up/step-down
SV: step-down

LV: step-up/step-down
SV: step-down
Regulated current:(2) 100 mA ULV: 500 mA
LV: 1 A
SV: 500 mA
1 A LV: 1 A
SV: 1.5 A
Dimensions: 1″ × 0.6″ 1.9″ × 0.7″ 2.8″ × 2.1″ 2.6″ × 2.2″
Weight: 1.3 g(3) 3.4 g(3) 13 g to 33 g 14 g to 23 g

1 Some microcontroller resources are used by on-board hardware.

2 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.

3 Without included optional headers.



Size: 2.8″ × 2.1″ (common Arduino form factor)
Weight: 20 g

General specifications

Processor: ATmega32U4 @ 16 MHz
RAM size: 2560 bytes
Program memory size: 32 Kbytes1
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 A2
Logic voltage: 5 V
Reverse voltage protection?: Y
External programmer required?: N


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.


Documentation and other information

Pololu A-Star 32U4 User’s Guide (Printable PDF)

User’s manual for the Pololu A-Star 32U4 family of user-programmable boards.

File downloads

A-Star 32U4 Prime pinout and power distribution diagrams (1MB pdf)
Printable pinout and power distribution diagrams of the A-Star 32U4 Prime (applies to both LV and SV versions).
Pololu A-Star 32U4 drivers for Windows (version (7k zip)
This download contains the Windows drivers for the A-Star 32U4 and the rest of our 32U4 family of boards.
A-Star 32U4 Prime LV schematic diagram (1MB pdf)
Printable schematic diagram of the A-Star 32U4 Prime LV.
Dimension diagram of the A-Star 32U4 Prime LV (4MB pdf)
A-Star 32U4 Prime LV drill guide (197k dxf)
This DXF drawing shows the locations of all of the board’s holes.


SKU PL-3108
Brand Pololu

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