Digilent MX4cK - Manual (Page 7)

Cerebot MX4cK Reference Manual
www.digilentinc.com page 7 of 35
Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.
Connector J14 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 J14.
Connector J18 is a screw terminal connector
for an alternative power supply connection for
use with higher current battery packs, bench
supplies or other power sources where use of
a hard wired power supply is desirable.
Connectors J13, J14, and J18 are wired in
parallel and connect to the “External Power”
position on the Power Select jumper block J12.
A shorting block should be placed on the “EXT”
position of J12 when using this option for board
power. Only one of these three power
connectors should be used at a time. If
multiple power supplies are connected
simultaneously, damage to the board or the
power supplies may occur.
The Cerebot MX4cK has a second screw
terminal connector, J5 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 MX4cK. This can be useful when
using servos that draw large amounts of
power.
Jumper JP1 can be used to connect the
Cerebot MX4cK unregulated power bus
BRD_VU to the servo power bus, VS. When
no shorting block is installed on JP1, the
BRD_VU and VS busses are separate. When
a shorting block is on JP1, the two busses are
joined and the BRD_VU bus can be powered
in any of the previously indicated ways, or from
connector J5.
The Cerebot MX4cK can provide power to any
peripheral modules attached to the Pmod
connectors and to I
2 C devices powered from
the I 2 C daisy chain connectors, J2 and J6.
Each Pmod connector provides power pins
that can be powered by either unregulated
voltage, BRD_VU, or regulated voltage,
BRD_3V3, by setting the voltage jumper block
to the desired position. The I
2 C power
connectors only provide regulated voltage,
BRD_3V3.
The PIC32 microcontroller and on-board I/O
devices operate at a supply voltage of 3.3V
provided by the BRD_3V3 bus. The PIC32
microcontroller will use approximately 55mA
when running at 80MHz. The remaining
current is available to provide power to
attached Pmod and I
2 C devices.
Power Supply Monitor Circuit
The Cerebot MX4cK microcontroller can
measure the power supply voltage on the
BRD_VU and VS power busses using the
provided power supply monitor circuits. This
feature is especially useful when using
batteries because it allows the microcontroller
firmware to determine the charge state of the
battery and potentially notify the user when a
battery supply is low.
Each power supply monitor circuit is made up
of a voltage divider that divides the power bus
voltage by four, and a filter capacitor to
stabilize the voltage. Jumper JP4 enables the
supply monitor circuit for BRD_VU power bus,
and jumper JP2 enables the supply monitor
circuit for the VS power bus. The analog to
digital converter built into the PIC32
microcontroller is used to measure the power
supply voltages. ADC channel 8 is used to
measure BRD_VU and ADC channel 9 is used
to measure VS.
When using the Cerebot MX4cK with the
chipKIT MPIDE, these are accessed using the
analogRead() function using analog input A6 to
read BRD_VU and A7 to read VS.