Pololu A-Star 32U4 Series User manual

Pololu A-Star 32U4 User’s
Guide
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
https://www.pololu.com/docs/0J61/all Page 1 of 59

1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Supported operating systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Contacting Pololu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. A-Star 32U4 Micro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. A-Star 32U4 Micro pinout and components . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. A-Star 32U4 Micro schematic and dimensions . . . . . . . . . . . . . . . . . . . . . . . 9
4. A-Star 32U4 Mini . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. A-Star 32U4 Mini pinout and components . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.2. A-Star 32U4 Mini ULV regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.3. A-Star 32U4 Mini LV regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.4. A-Star 32U4 Mini SV regulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.5. A-Star 32U4 Mini schematic and dimensions . . . . . . . . . . . . . . . . . . . . . . . 20
5. A-Star 32U4 Prime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.1. A-Star 32U4 Prime configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.2. A-Star 32U4 Prime pinout and components . . . . . . . . . . . . . . . . . . . . . . . . 24
5.3. A-Star 32U4 Prime LV regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.4. A-Star 32U4 Prime SV regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
5.5. A-Star 32U4 Prime schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
5.6. A-Star 32U4 Prime demo program . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
6. Getting started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.1. Installing Windows drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.2. Programming using the Arduino IDE . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.3. Programming using avr-gcc and AVRDUDE . . . . . . . . . . . . . . . . . . . . . . . 46
7. A-Star 32U4 Arduino library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
8. The A-Star 32U4 USB interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
9. The A-Star 32U4 Bootloader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
10. Reviving an unresponsive A-Star . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
10.1. Reviving using the Arduino IDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
10.2. Reviving using AVRDUDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
11. Related Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
Page 2 of 59

From top to bottom: A-Star 32U4 Micro, Mini SV,
and Prime SV.
1. Overview
The Pololu A-Star 32U4 microcontroller 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. Each A-Star (abbreviated A*)
adds onboard components and connectors that
support the microcontroller and make it easier to
use. The boards feature USB interfaces and ship
with a preloaded Arduino-compatible bootloader,
and we provide a software add-on that enables
them to be easily programmed from the Arduino
environment. The following sections of this
user’s guide discuss each A-Star in more detail.
AUSB A to Micro-B cable [https://www.pololu.com/
product/2072] (not included) is required to connect
an A-Star 32U4 to a computer.
Features
• 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
• Can be powered from USB or external source regulated to 5 V by onboard regulator
• Reverse-voltage protection on external power input
• 6-pin ISP header for use with an external programmer [https://www.pololu.com/product/3172]
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
1. Overview Page 3 of 59

A-Star comparison table
A-Star 328PB
Micro
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: ATmega328PB ATmega32U4
User I/O lines: 24 18 26 26(1) 26(1)
PWM outputs: 9 7 7 7 7(1)
Analog inputs: 8 8 12 12 12(1)
Ground access
points: 6 2 4 43 44
User LEDs: 1 2 3 3 3
User
pushbuttons: — — — 3 3
USB interface:
Reset button:
Power switch:
Buzzer option:
microSD option:
LCD option:
Motor drivers:
Operating
voltage:
3.3V VCC: 3.8 V to
15 V
5V VCC: 5.5 V to
15 V
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 40 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: 3.3 V or 5 V l near 5 V l near
5 V sw tch ng
ULV: step-up
LV: step-up/step-
down
SV: step-down
5 V sw tch ng
LV: step-up/step-
down
SV: step-down
5 V sw tch ng
LV: step-up/step-down
SV: step-down
Regulated
current:(2) 100 mA 100 mA
ULV: 500 mA
LV: 1 A
SV: 800 mA
1 A LV: 1 A
SV: 1.5 A
Dimensions: 1.3″ × 0.7″ 1″ × 0.6″ 1.9″ × 0.7″ 2.8″ × 2.1″ 2.6″ × 2.2″
Weight: 1.5 g(3) 1.3 g(3) 3.4 g(3) 13 g to 33 g 14 g to 23 g
1Some m crocontroller resources are used by on-board hardware.
2These values are rough approx mat ons for compar son purposes. Ava lable current depends on nput voltage, current consumed
by the board, amb ent cond t ons, and regulator topology. See product documentat on and performance graphs for deta ls.
3W thout ncluded opt onal headers.
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
1. Overview Page 4 of 59

1.1. Supported operating systems
The A-Star 32U4 boards can be programmed using any operating system that supports the Arduino
environment. We have tested the A-Stars, our Arduino software add-on, and the Arduino IDE on
Microsoft Windows 10, 8.1, 8, 7, Vista, XP (with Service Pack 3), Linux, and Mac OS X.
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
1. Overview Page 5 of 59

2. Contacting Pololu
We would be delighted to hear from you about any of your
projects and about your experience with the Pololu A-Stars. You
can contact us [https://www.pololu.com/contact] directly or post on
our forum [http://forum.pololu.com/]. Tell us what we did well, what
we could improve, what you would like to see in the future, or
anything else you would like to say!
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
2. Contacting Pololu Page 6 of 59

3. A-Star 32U4 Micro
A-Star 32U4 Micro,
top view.
3.1. A-Star 32U4 Micro pinout and components
Pinout
The diagram above identifies the I/O and power pins on the A-Star 32U4 Micro; it is also available
as a printable PDF [https://www.pololu.com/file/0 796/a-star-32u4-micro-pinout.pdf] (409k pdf). or more
information about the ATmega32U4 microcontroller on this board, see Atmel’s ATmega32U4
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
3. A-Star 32U4 Micro Page 7 of 59

documentation [https://www.microchip.com/wwwproducts/en/ATmega32u4].
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.
LEDs
The A-Star 32U4 Micro has two indicator LEDs.
The yellow LED is connected to Arduino pin 13, or PC7. You can drive this pin high in a user program
to turn this LED on. The A-Star 32U4 Bootloader [https://www.pololu.com/docs/0 61/9] fades this LED on
and off while it is waiting for a sketch to be loaded.
The green LED is connected to PD5 and lights when the pin is driven low. While the board is running
the A-Star 32U4 Bootloader or a program compiled in the Arduino environment, it will flash this LED
when it is transmitting data via the USB connection.
Connectors
The A-Star 32U4 includes a USB Micro-B connector that can be used to connect to a computer’s
USB port via a USB A to Micro-B cable [https://www.pololu.com/product/2072] (not included). The USB
connection can be used to transmit and receive data from the computer, and a preloaded USB
bootloader makes it possible to program the board over USB. The USB connection can also provide
power to the A-Star.
The board also has a 6-pin ISP header that allows it to be programmed with an external programmer,
such as our USB AVR programmer v2.1 [https://www.pololu.com/product/3172]. Pin 1 of the header is
indicated with a small white dot and has an octagonal shape. Three of the pins on this header can
be used as an SPI interface or as general-purpose digital I/O, as shown in the pinout diagram. In
the Arduino environment, you can refer to these three pins using either their pin numbers or the
names of their SPI functions (which are defined as aliases); for example, digitalRead(15) and
digitalRead(SCK) are equivalent.
Power
The A-Star 32U4 Micro can either be powered directly from the USB 5 V supply or from a separate
source on the VIN pin. The board features a power selection circuit that allows both USB and VIN to
be connected at the same time; if this is done, the A-Star will draw power from VIN.
USB power input: The A-Star can be powered from the USB 5 V bus voltage (VBUS) if it is connected
to a USB cable. It will draw power from USB only if VIN is disconnected. A resettable PTC fuse on
VBUS makes it less likely for the A-Star (and the connected computer or other device) to be damaged
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
3. A-Star 32U4 Micro Page 8 of 59

if too much current is drawn from the USB connection.
VIN power input: The A-Star can be powered from VIN if you connect a 5.5 V to 15 V power
supply (such as a battery or wall power adapter) to the VIN and GND pins, with the positive terminal
connected to VIN.
When powering the A-Star 32U4 Micro from VIN, a minimum voltage of 5.5 V is required
to ensure that the board’s 5 V supply is stable. Even if power is being provided to the
A-Star via USB, connecting a voltage higher than 0 V but lower than 5.5 V to VIN is not
recommended, as this can interfere with the power selection circuit and cause the 5 V line
to drop (potentially triggering a brown-out reset).
5V power output: This pin provides access to the board’s 5 V supply, which comes from either the
USB 5 V bus voltage or a low-dropout (LDO) regulator on VIN, depending on which power source is
connected. The regulator can supply up to 100 mA, although some of this is used by the board itself
(typically about 25 mA) or used to provide current for the GPIO pins or 3.3 V power output (see below).
3V3 power output: This pin gives access to the output of the internal 3.3 V regulator inside the
ATmega32U4. The microcontroller uses this regulated voltage for USB signaling, but up to about
50 mA is available for powering external circuits or devices.
When the A-Star 32U4 Micro 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 should not exceed the 100
mA that the regulator can provide.
3.2. A-Star 32U4 Micro schematic and dimensions
Schematic diagram
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
3. A-Star 32U4 Micro Page 9 of 59

Pololu A-Star 32U4 Micro schematic diagram.
This schematic is also available as a PD : A-Star 32U4 Micro schematic diagram
[https://www.pololu.com/file/0 742/pololu-a-star-32u4-micro-schematic-diagram.pdf] (253k pdf).
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
3. A-Star 32U4 Micro Page 10 of 59

Dimension diagram
A dimension diagram of the A-Star 32U4 Micro is available as a PD : A-Star 32U4 Micro dimension
diagram [https://www.pololu.com/file/0 747/pololu-a-star-32u4-micro-dimension-diagram.pdf] (255k pdf).
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
3. A-Star 32U4 Micro Page 11 of 59

4. A-Star 32U4 Mini
A-Star 32U4 Mini ULV, LV, and SV.
4.1. A-Star 32U4 Mini pinout and components
Pinout
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
4. A-Star 32U4 Mini Page 12 of 59

This diagram identifies the I/O and power pins on the A-Star 32U4 Mini (ULV, LV, and SV versions);
it is also available as a printable PDF [https://www.pololu.com/file/0 1515/a-star-32u4-mini-pinout.pdf] (223k
pdf). or 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.
LEDs
The A-Star 32U4 Mini has three indicator LEDs.
The yellow LED is connected to Arduino pin 13, or PC7. You can drive this pin high in a user program
to turn this LED on. The A-Star 32U4 Bootloader [https://www.pololu.com/docs/0 61/9] fades this LED on
and off while it is waiting for a sketch to be loaded.
The green LED is connected to the pin labeled TXL, or PD5, and lights when the pin is driven
low. While the board is running the A-Star 32U4 Bootloader or a program compiled in the Arduino
environment, it will flash this LED when it is transmitting data via the USB connection.
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
4. A-Star 32U4 Mini Page 13 of 59

The red LED is connected to the pin labeled RXL (usable as Arduino pin 17), or PB0, and lights when
the pin is driven low. While the board is running the A-Star 32U4 Bootloader or a program compiled in
the Arduino environment, it will flash this LED when it is receiving data via the USB connection.
Connectors
The A-Star 32U4 includes a USB Micro-B connector that can be used to connect to a computer’s
USB port via a USB A to Micro-B cable [https://www.pololu.com/product/2072] (not included). The USB
connection can be used to transmit and receive data from the computer, and a preloaded USB
bootloader makes it possible to program the board over USB. The USB connection can also provide
power to the A-Star.
The board also has a 6-pin ISP header that allows it to be programmed with an external programmer,
such as our USB AVR programmer v2.1 [https://www.pololu.com/product/3172]. Pin 1 of the header is
indicated with a small dot and has an octagonal shape.
Power
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 switching regulator.
The board’s power selection circuit uses the TPS2113A power multiplexer [https://www.pololu.com/
product/2596] from Texas Instruments to choose whether its 5 V supply is sourced from USB or an
external supply via the regulator, allowing both sources to be connected at the same time and enabling
the A-Star to safely and seamlessly transition between them. The TPS2113A is configured to select
external power unless the regulator output falls below about 4.5 V. If this happens, it will select the
higher of the two sources, which will typically be the USB 5 V bus voltage if the A* is connected to
USB. The currently selected source is indicated by the STAT pin in the middle of the board; this pin
is an open-drain output that is low if the external power source is selected and high-impedance if the
USB supply is selected. The current limit of the TPS2113A is set to about 1.9 A. or more information
about the power multiplexer, see the TPS2113A datasheet [https://www.pololu.com/file/0 771/tps2113a.pdf]
(1MB pdf).
In some situations, it might be undesirable for the A-Star 32U4 Mini to draw power from an external
source when it is connected to USB. If this is the case, the regulator can be disabled by driving the
regulator shutdown pin, SHDN, high; this shuts down the regulator and causes the power mux to fall
back to USB power. or example, this could allow a battery-powered device to turn off the regulator
and avoid draining its battery while it is connected to a computer.
The input voltage range of the regulator depends on the particular version of the A-Star 32U4 Mini:
•ULV: 0.5 V to 5.5 V (see Section 4.2 for regulator details)
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
4. A-Star 32U4 Mini Page 14 of 59

•LV: 2.7 V to 11.8 V (see Section 4.3 for regulator details)
•SV (see Section 4.4 for regulator details):
◦ original ac02c version: 5 V to 36 V
◦ newer ac02f version: 5 V to 40 V
Reverse-protected power inputs: The BAT+ and BAT- pins are power inputs with reverse-voltage
protection. These are the recommended pins to use when connecting an external power supply
because they allow the A-Star’s reverse-voltage protection circuit to help prevent it from being
damaged by accidentally-reversed power connections.
VIN power output (or alternative input):When power is supplied through the BAT pins, 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.
5V power output: This pin provides access to the board’s 5 V supply, which comes from either the
USB 5 V bus voltage or the onboard switching regulator, depending on which power sources are
connected and enabled. Note that some of the available current on the 5 V line is used by the board
itself (typically about 30 mA) or used to provide current for the GPIO pins or 3.3 V power output (see
below).
3V3 power output: This pin gives access to the output of the internal 3.3 V regulator inside the
ATmega32U4. The microcontroller uses this regulated voltage for USB signaling, but up to about
50 mA is available for powering external circuits or devices.
When the A-Star 32U4 Mini 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 should not exceed the
maximum current that the regulator can provide; see the following sections for details about the
regulator on each version.
4.2. A-Star 32U4 Mini ULV regulator
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
4. A-Star 32U4 Mini Page 15 of 59

A-Star 32U4 Mini ULV, bottom view with
dimensions.
The A-Star 32U4 Mini ULV can be powered from a
0.5 V to 5.5 V external source. The input voltage is
regulated to 5 V by a TPS61202 switching step-up
(boost) converter from Texas Instruments. (We also
make a standalone regulator [https://www.pololu.com/
product/2562] based on this integrated circuit.)
The regulator’s low minimum input voltage makes it
possible to power this A* with 1 to 3 NiMH, NiCd, or
alkaline cells or from a single lithium cell. Unlike
standard boost regulators, the TPS61202 also features
a linear down-regulation mode that is automatically
enabled when the input voltage exceeds 5 V, allowing
it to handle input voltages as high as 5.5 V.
As shown in the left graph below, the ULV’s switching
regulator has an efficiency – defined as
(Power out)/(Power in) – of 70% 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.
4.3. A-Star 32U4 Mini LV regulator
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
4. A-Star 32U4 Mini Page 16 of 59

A-Star 32U4 Mini LV, bottom view with
dimensions.
The A-Star 32U4 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
[https://www.pololu.com/product/2123] 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. or 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
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
4. A-Star 32U4 Mini Page 17 of 59

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.
4.4. A-Star 32U4 Mini SV regulators
There have been two versions of the A-Star 32U4 Mini SV: the original ac02c version
and its replacement, the newer ac02f version. The ac02f version uses an improved
5 V regulator that can deliver more current (800 mA vs 500 mA) and operates to 40 V
instead of 36 V. The easiest way to distinguish between the two versions is via the
silkscreen on the side of the board opposite the USB connector, where the original
version is labeled ac02c and the new version is labeled ac02f. The new version also
uses an ENIG finish, so the plating on the exposed copper looks gold, and it has
unplated mounting holes. See the picture below for a side-by-side comparison:
A-Star 32U4 Mini SV: comparison of
original ac02c version (left) to newer
ac02f version (right).
The A-Star 32U4 Mini SV (ac02c) is the original version of the Mini SV, and it can be powered from
a5 V to 36 V external source. The input voltage is regulated to 5 V by a 500 mA ISL85415 switching
step-down (buck) converter from Renesas (which acquired Intersil). (We also make a standalone
regulator [https://www.pololu.com/product/2843] based on this integrated circuit.)
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
4. A-Star 32U4 Mini Page 18 of 59

The A-Star 32U4 Mini SV (ac02f) is the newest version of the Mini SV, and it can be powered from a
5 V to 40 V external source. The input voltage is regulated to 5 V by an 800 mA ISL85418 switching
step-down converter, which is part of the same family as the ISL85415. (We also make a standalone
regulator based on the 1 A version [https://www.pololu.com/product/2831] of this integrated circuit.)
The graphs below show the efficiency of the two SV versions, where efficiency is defined as
(Power out)/(Power in):
Typical efficiency of the regulator on
the A-Star 32U4 Mini SV (original ac02c
version).
Typical efficiency of the regulator on
the A-Star 32U4 Mini SV (newer ac02f
version).
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 green lines in the graph below
show the output currents where the regulator’s output voltage drops below 4.75 V. These currents
are close to the limits of the regulator’s capability and generally cannot be sustained for long periods;
under typical operating conditions, a safe limit for the maximum continuous regulator output current is
approximately 500 mA for ac02c and 800 mA for ac02f.
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
4. A-Star 32U4 Mini Page 19 of 59

The dropout voltage of a step-down regulator is defined as the minimum amount by which the input
voltage much exceed the regulator’s target output voltage in order to assure the target output can be
achieved. As can be seen in the graphs below for the two versions of the Mini SV, the dropout voltages
of the Mini SV’s regulators increase approximately linearly with the output current. or light loads
where the dropout voltage is small, the boards can operate down to 5 V. However, for larger loads, the
dropout voltage should be taken into consideration when selecting a power supply; operating above
6 V will ensure the full output current is available.
Typical dropout voltage of the 5V
regulator on the A-Star 32U4 Mini SV
(original ac02c version).
Typical dropout voltage of the 5V
regulator on the A-Star 32U4 Mini SV
(newer ac02f version).
Note: Batteries can have much higher voltages than their nominal voltages when fully
charged, so be careful with nominal voltages above 24 V. A 36 V battery is not appropriate
for this product.
4.5. A-Star 32U4 Mini schematic and dimensions
Schematic diagram
The schematic diagram for the A-Star 32U4 Minis is available as a PD : A-Star 32U4 Mini schematic
diagram [https://www.pololu.com/file/0 780/a-star-32u4-mini-schematic.pdf] (243k pdf).
Dimension diagrams
Dimension diagrams for the A-Star 32U4 Minis are available as PD s:
•A-Star 32U4 Mini ULV dimension diagram [https://www.pololu.com/file/0 781/ac02a-
dimensions.pdf] (274k pdf)
•A-Star 32U4 Mini LV dimension diagram [https://www.pololu.com/file/0 782/ac02b-
dimensions.pdf] (292k pdf)
Pololu A-Star 32U4 User’s Guide © 2001–2018 Pololu Corporation
4. A-Star 32U4 Mini Page 20 of 59