Pololu A-Star 32U4 Series User manual

A-Star 32U4 Mini LV
Overview
The Pololu A-Star 32U4 Mini boards are general-purpose programmable modules 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. The A-Star (areviated A*) adds a number of onboard features
to support the microcontroller and make it easier to work with, including a 16 MHz crystal, a USB
Micro-B connector, an in-system programming (ISP) header, a reset button, and three indicator
LEDs.
A-Star 32U4 Mini ULV, LV, and SV.
Each A-Star 32U4 Mini contains a switching regulator that efficiently produces 5 V from an external
voltage source to power the microcontroller. Three different versions are available, covering a wide
range of input voltages:
A-Star 32U4 Mini ULV: 0.5 V to 5.5 V
A-Star 32U4 Mini LV: 2.7 V to 11.8 V
A-Star 32U4 Mini SV: 5 V to 36 V
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.
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: 1.9″ × 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
1 KB EEPROM
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
Can be powered from USB or from an external source:
ULV: 0.5 V to 5.5 V
LV: 2.7 V to 11.8 V
SV: 5 V to 36 V
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
6-pin ISP header for use with an external programmer
Comprehensive user’s guide
Details for item #3103

A-Star 32U4 Mini LV, bottom view with
dimensions.
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. (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 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. 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 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; a good estimate for the maximum continuous regulator output current is
60% to 70% of the values shown in the graph.
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). We provide a software add-on that enables
the board to be easily programmed from the Arduino environment.
The A-Star 32U4 Mini boards use the same microcontroller as the Arduino Leonardo and Arduino
Micro and run at the same frequency, and they are the same size as the Arduino Micro, but they
offer a number of advantages over these other ATmega32U4-based boards. Most notably, their
efficient switching regulators cover a wide range of input voltages, opening up new possibilities for
powering projects built around Arduino-compatible microcontroller boards. Another advantage is
the power selection circuit based on the TPS2113A power multiplexer from Texas Instruments,
which allows safe, seamless power switching between USB and an external source without losses
from passive components like fuses or diodes along with the ability to monitor and control the
selected power source. Additionally, the A* 32U4 Mini breaks out a few additional pins from the
ATmega32U4 microcontroller that are not exposed on the Arduino Micro or Leonardo, and it
features larger, more convenient mounting holes than the Arduino Micro.

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 Mini (even though it shows the
ULV version, it applies to all three A-Star Mini boards); it is also available as a printable PDF (269k
pdf). For more information about the ATmega32U4 microcontroller and its peripherals, 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 A-Star 32U4 Mini can either be powered directly from the USB 5 V supply or from an external
voltage source, which is regulated to 5 V by its onboard regulator, and the board’s power selection
circuit enables automatic, uninterrupted transitions between the two power sources. When the A-
Star is powered through an external power supply connected to the BAT+ and BAT- pins, its
reverse-voltage protection circuit helps prevent it from being damaged by accidentally-reversed

power connections, and the VIN pin can be used as an output to supply reverse-protected power to
other devices. Alternatively, the external supply can be connected directly between VIN and GND,
bypassing the reverse-voltage protection.
The A-Star 32U4 user’s guide discusses the board’s features in more detail.
Included hardware
A pair of 1×17-pin breakaway 0.1″ male headers 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. 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. The board has two
mounting holes that work with #2 and M2 screws (not included).
A-Star 32U4 Mini LV with included optional
headers. A-Star 32U4 Mini SV with soldered headers
and connected USB cable.
The A-Star family
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
Microcontroller: ATmega32U4 ATmega32U4
User I/O lines: 151 26
PWM outputs: 7 7
Analog inputs: 8 12
User LEDs: 2 3
Reset button:
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
Regulator type: linear switching step-up switching step-up/step-
down switching step-down
Regulated
current2: 100 mA 500 mA 1000 mA 500 mA
Dimensions: 1″ × 0.6″1.9″ × 0.7″
Weight3: 1.3 g 3.4 g
1 Three extra digital I/O lines are accessible through the ISP header.
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.
Documentation on producer website.