Digilent Cerebot Plus Board - Manual (Page 3)

Digilent Cerebot Plus Reference Manual Digilent, Inc.
www.digilentinc.com page 3 of 13
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The Cerebot Plus is rated for external power
from 3.6 to 9 volts DC. Using voltage outside
this range could damage the Cerebot Plus and
connected devices.
There are three different dedicated power
supply connectors on Cerebot Plus for board/
processor power: J7, J8, and J9.
The barrel connector, J7, is useful for desktop
development and testing where use of
batteries is cost- or time-prohibitive. J7 is the
connector used by the AC supply adapter
available from Digilent. J7 is a 2.5mm x 5.5mm
coaxial connector wired with the center
terminal as the positive voltage.
J8 is a two-pin male header that provides easy
battery or battery-pack connection. Digilent has
both two-cell and four-cell AA battery holders
with two pin connectors available for
connection to J8.
J9 is a screw terminal connector for an
alternative battery supply or bench top power
supply connection.
Connectors J7, J8, and J9 are wired in parallel
and connect to one terminal of the power
switch, SW1. The other terminal of SW1
connects to the main unregulated power bus
VU. The VU power bus connects to the center
terminal of the voltage regulator input jumper
JP1 and also connects to the VU terminal of
the power select jumper associated with each
Pmod connector.
Jumper JP1 is used to select the voltage for
the main board power bus VCC. When JP1 is
in the ‘normal’ position, the VCC power bus is
powered by the output of the on-board 3.3V
regulator. When JP1 is in the ‘bypass’ position,
the on-board voltage regulator is bypassed and
the VCC bus is connected directly to the VU
bus. In this case, the AVR microcontroller and
other on-board electronics are powered directly
from the voltage supply connected to VU. In
this case, the input voltage must be in the
range 2.7V – 3.3V. A supply voltage outside
this range can permanently damage the board.
You can also power the Cerebot Plus from any
Pmod connector. Place the power select
jumper associated with the Pmod connector in
the VU position to supply power to the VU bus,
or the VCC position to supply power to the
VCC bus. If power is being supplied to the VU
bus, JP1 should be in the ‘normal’ position so
that the on-board regulator will be able to
regulate the supplied voltage to the 3.3V board
operating voltage. If the Pmod connector
power routing jumper is in the VCC position,
the shorting block on JP1 should be placed in
the ‘bypass’ position or removed.
The Cerebot Plus has a second screw terminal
connector, J10, that supplies power to the
servo power bus, VS, to power the RC hobby
servo connectors. This allows servos to be
powered from a separate power supply than
the one powering the electronics on the
Cerebot Plus. This can be useful when using
servos that draw large amounts of power.
The Cerebot Plus can provide power to any
peripheral modules attached to the Pmod
connectors and to TWI devices powered from
the TWI power daisy chain connectors, J4 and
J5. Each Pmod connector provides power pins
that can be powered by either unregulated
voltage, VU, or regulated voltage, VCC, by
setting the voltage jumper block to the desired
position. The TWI power connectors only
provide regulated voltage, VCC.
The regulated voltage on the VCC bus is
provided by an on-board voltage regulator.
This regulator is capable of providing a
maximum of 500mA of current. The
ATmega2560 microcontroller will use
approximately 15mA when running at 8MHz.
The external SRAM memory uses
approximately 90mA when operating and 1mA
when in standby mode. The remaining current
is available to provide power to attached Pmod
and TWI devices. The regulator is on the
bottom of the board, near the power
connectors, and will get warm when the
amount of current being used is close to its
limit.