a
[https://www.pololu.com/product/1459]
to supply power through the control
board’s USB connector, although we have sometimes observed AVR brown-out resets occurring when
a board powers the Raspberry Pi this way. A typical computer USB port might not be able to supply
enough current to properly power the Balboa 32U4 control board and an attached Raspberry Pi.
Power provided to the Raspberry Pi can be switched off by driving the Raspberry Pi shutdown pin,
RPISHDN
, to 5 V.
An ideal diode circuit on the control board makes it safe to have a different power supply connected to
the Raspberry Pi (for example, through the Raspberry Pi’s USB Micro-B receptacle) while the control
board is connected and powered. (In other words, it is safe to have any combination of control board
USB power, battery power, and Raspberry Pi USB power connected to the system.)
Note that the diode circuit prevents power from being shared in the reverse direction: the Raspberry
Pi cannot supply 5 V logic power to the control board through the 40-pin connector.
Power distribution
•
VBAT
is connected to the battery contact labeled
BAT+
and provides a direct connection to
the battery supply.
•
VSW
is the battery voltage after reverse-voltage protection and the power switch circuit.
•
VREG
is the output of the on-board 5 V regulator.
•
5V
is the output of the TPS2113A power multiplexer circuit which is connected to VREG by
default, but switches to 5 V USB power if VREG is too low.
•
3V3
is the output of the 3.3 V LDO regulator.
See
for a diagram of the board’s power access points.
3.7. Expansion headers
The Balboa 32U4 control board has expansion headers on its four edges that break out several
free general-purpose I/O lines from the ATmega32U4 microcontroller along with a few power pins.
Various power inputs, outputs, and control pins are also accessible elsewhere on the board. The
following diagrams identify the locations of these pins and the hardware associated with them; they
are also available as a
[https://www.pololu.com/file/0J1268/balboa-32u4-control-board-pinout-
(2MB pdf). For more information about the ATmega32U4 microcontroller and its peripherals,
see Atmel’s ATmega32U4 documentation.
Pololu Balboa 32U4 Balancing Robot User’s Guide
© 2001–2019 Pololu Corporation
3. Balboa 32U4 in detail
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