Kauai Labs VMX-pi User manual
Hardware Reference Manual
Version 1.10
Figure 1 VMX-pi configured with Raspberry Pi 3
VMX-pi Hardware Reference Manual (version 1.10) 2
Contents
Feature Summary......................................................................................................................................3
Technical Specifications ............................................................................................................................ 5
I/O Summary.............................................................................................................................................8
I/O Resource Summary ...........................................................................................................................10
Channel/Resource Routing .................................................................................................................10
I/O Channel Types/Numbers .................................................................................................................. 11
High Current DIO Input/Output Selection Jumper .............................................................................12
Power Management Scheme..................................................................................................................13
VMX-pi Power Management...............................................................................................................14
External Device Power/Signal Voltage Configuration.............................................................................16
Signal Voltage Select Jumpers.............................................................................................................16
Power Voltage Select Jumpers............................................................................................................16
VMX-pi I/O Signal/Logic Levels ...............................................................................................................16
Board-edge Connectors ..........................................................................................................................18
FlexDIO Connectors (VMX Channels 0-7)............................................................................................18
FlexDIO Header (VMX Channels 8-11) ................................................................................................19
High-Current DIO Header (VMX Channels 12-21)...............................................................................19
Analog Input Header (VMX Channels 22-25) ......................................................................................20
CommDIO Connectors (VMX Channels 26-33) ...................................................................................21
CAN Connector....................................................................................................................................21
CAN Termination Jumper....................................................................................................................21
Micro-USB Connector .........................................................................................................................22
Input Power Connector.......................................................................................................................22
Battery & Real-time Clock.......................................................................................................................22
40-pin Raspberry Pi Connector ...............................................................................................................23
Optional 5V Fan Connector..................................................................................................................... 23
LEDs.........................................................................................................................................................23
Buttons....................................................................................................................................................24
Physical Dimensions................................................................................................................................25
VMX-pi Hardware Reference Manual (version 1.10) 3
Feature Summary
VMX-pi is designed to control a reliable, intelligent robot that is tele-operated, semi-autonomous or
fully-autonomous when combined with an inexpensive Raspberry Pi-based processor. VMX-pi is also
usable as a Vision/Motion co-processor when paired with another robot controller.
The current recommended Raspberry Pi model 3(shown in picture on the cover
page of this document); the Raspberry Pi Zero W may also be used although it provides only a subset of
the Raspberry Pi 3 capabilities.
1GB DDR
RAM
4-core 1.2Ghz
64-bit ARM
Cortex-A53
Bluetooth
4.1 HDMI
Ethernet
Networking
2.4Ghz
802.11 Wifi
Broadcom
VideoCore IV
GPU (400Mhz)
Raspberry Pi 3
4 USB 2.0
Ports
SD Card
VMX-pi + Raspberry Pi 3 Key Components
CSI Camera
Interface
USB
Data/
Config
Port
100Mhz 32-
bit ARM
Cortex-M4 w/
FPU
9-axis Inertial
Sensor/
Motion
Processor
Voltage Regulator
w/5 and 3.3V
Outputs
VMX-pi
Barometer
(optional)
Battery-backed
Realtime Clock
30 Digital I/Os
4 Analog I/Os;
SPI, I2C, TTL
UART
CAN
Interface External Device
Current-limiting
Figure 2 VMX-pi & Raspberry Pi Key Components
VMX-pi Hardware Reference Manual (version 1.10) 4
Component
Function
Key Attributes
Voltage Regulator
w/wide input
voltage range
Converts unregulated 6-16VDC to 5V & 3.3V,
up to a maximum of 3A; includes real-time
under-voltage management
Can provide 2.1A to Raspberry
Pi and .5A to external devices at
input voltages as low as 6VDC
External Device
Current Limiting
Switch & Short-
circuit protection
External 5/3.3V supplies are current limited at
.5A, to ensure full power is always provided
to the Raspberry Pi processor and VMX-pi
microcontroller
Processors continue running
even when external devices
draw excessive power or when
short-circuits occur
5/3.3V Voltage
Translation
Flexibly supports signaling with 5V and 3.3V
external devices
Eliminates need for external
voltage translation devices
Battery-backed
Real-time Clock
(RTC)
When VMX-pi is used in environments
without Network Time Server access,
provides real-time clock for distributed sensor
data alignment and accurate log timestamps
Includes CR2032 battery
w/expected life of 5 years
before replacement
100Mhz 32-bit
ARM-M4 w/FPU
Microcontroller
(STM32F411)
Implements real-time IO and timer functions,
IMU sensor data fusion, CAN bus message
buffering and Power/Brownout Management
Field-upgradable firmware can
be updated w/new features and
bugfixes
30 Digital I/Os
with overvoltage
protection
Flexible digital IO support including PWM
Generation on outputs, PWM Capture, Quad
Encoder decode, Interrupt Generation on
inputs
•PWM Generation on all
outputs
•PWM Capture o
inputs
•Interrupt Generation on all
inputs
•Quadrature Encoder decode
4 Analog I/Os with
overvoltage
protection
12-bit ADC providing 46.5k samples/sec on
each channel
Over-sampling and Averaging
Engine; Analog Triggering
supporting Interrupt generation
on Analog Inputs
CAN Interface
CAN 2.0b transceiver and controller
supporting message transmission/reception
and filtering
1 mbps bus data rate supported
9-axis Inertial
Sensor/Motion
Processor
Generates Yaw/Pitch/Roll measures as well as
Quaternions and raw gyro/accelerometer/
magnetometer data; also includes automatic
calibration software w/flash-based storage of
calibration data
Invensense MPU-9250 and
navX-Technology Kauai Labs
firmware
I2C Support
2 Comm DIO Channels can be configured for
I2C communication w/built-in pullup resistors
400Khz I2C communication
supported
TTL UART Support
2 Comm DIO Channels can be configured for
TTL UART communication
115.2 kbps UART
communication supported
VMX-pi Hardware Reference Manual (version 1.10) 5
Table 1 VMX-pi Component Functions & Attributes
Technical Specifications
VMX-pi Technical Specifications are summarized in the table below. Note that certain specifications
may be improved over time due to firmware updates. For the most up-to-date technical specifications,
-pi.kauailabs.com.
ELECTRICAL SPECIFICATIONS
Input Voltage:
6-16V DC
Output Voltages:
5V, 3.3V for External Devices
5V for Raspberry Pi
Protection Features:
Input Power Under-voltage Management
Output Power Current Limiting/Short-circuit Protection
Input Signal Over-voltage Protection
Communications Interface:
USB, I2C, SPI, CAN, UART
Power Connector:
2-Pin JST VH Connector
USB Connector:
USB Micro-B (can provide standalone power to VMX-
pi microcontroller)
IMU PERFORMANCE SPECIFICATIONS
Note: Certain IMU performance specifications are only valid after a start-up gyroscope/accelerometer calibration
period, during which time the VMX-pi circuit board must be held still.
SPI Support
4 Comm DIO Channels can be configured for
SPI communication
8Mhz SPI communication
supported
Locking
Connectors
Locking Power, FlexDIO and CAN connectors
Helps ensure electrical circuits
are not affected by vibration
Micro-USB
external interface
Additional dedicated USB interface on VMX-pi
Enables remote access to IMU
data, and VMX-pi
configuration/firmware update
VMX-pi Hardware Reference Manual (version 1.10) 6
Startup Calibration Period:
15 seconds
Gyro Sensitivity:
+/- 2000 degrees/sec
Accel Sensitivity:
+/- 2 g
Magnetometer Sensitivity:
1.3 Gauss
Yaw angle accuracy:
~1 degree of drift/minute
Yaw angle accuracy (when still):
~.25 degree of drift/minute
Orientation Data Update Rate:
4-200 Hz
Magnetometer Raw Update Rate:
4 Hz
Magnetometer Angular Accuracy:
+/- 2 degrees
Pitch/Roll Angular Accuracy:
+/- 1.5 degrees
ANALOG INPUT SPECIFICATIONS
Number of Channels:
4
Resolution:
12 bits
Per-channel Sampling Rate:
46.5K samples/sec
DIGITAL IO SPECIFICATIONS
Total Number of Channels:
30
Number of Input-capable & Interrupt-capable Channels:
26
Number of Output-capable & PWM-capable Channels:
28
VMX-pi Hardware Reference Manual (version 1.10) 7
Number of Quadrature Encoder Channel Pairs
(Hardware-decode):
5
Number of PWM Capture Inputs
6
DIGITAL COMMUNICATION SPECIFICATIONS
CAN Protocol (2.0b)
1mbps
SPI Protocol
8 Mhz
I2C Protocol
400 kHz
USB Protocol
12 mbps
UART Protocol
115,200 bps
VMX-pi Hardware Reference Manual (version 1.10) 8
I/O Summary
High-
Current DIO
(PWM/Relay/
Digital Output
or Input)
[5 or 3.3V]
10
Analog
Inputs
(12-bit
resolution)
[5 or 3.3V]
CAN I2C
(or 2 DO or 2DI
w/pullups)
SPI
(or 3 DO, 1DI)
TTL UART
(or 1 DO, 1DI)
HW Quadrature Decode (Max 5 Pair [10 pins])
PWM/Digital IOs (Max 12)
150mA Analog
Supply Up to 400mA Digital Supply
FlexDIO
12
4
VMX-pi I/O Summary
3.3 V (5V Tolerant
inputs)
• 30 Digital I/O Channels
-FlexDIOsPWM-capable, H/W decode of 5 Quadrature Encoders
-High Current DIOseither all inputs or all PWM-capable outputs
-Comm DIOsPWM-capable outputs, 4 inputs) supporting SPI, I2C
and UART or Digital I/O functions
• 4 Analog Input Channels
• Dedicated CAN Interface
Comm DIO [5 or 3.3V]
Figure 3 VMX-pi IO Summary
FlexDIO Channels: These channels drive 3.3V, are 5V tolerant when used as inputs, and each channel is
individually software configurable as input or output channel. FlexDIO channels have a lower output
current drive than other channel types, and support advanced timer functions including decoding of
signals from quadrature encoders.
High-Current DIO Channels: These channels drive 3.3V or 5V (jumper-configurable), and are jumper-
configurable to be either all inputs or all outputs. High-Current DIO channels provided enhanced
current-drive capabilities allowing them to be used to drive relays as well as motor controllers.
Analog Input Channels: These channels accept 3.3V or 5V input signals.
Comm DIO Channels: These channels drive 3.3V or 5V (jumper-configurable); some are fixed as input
channels, and some are as fixed output channels. These channels support a medium-current drive
capability to support communication across extended distances, subject to the restrictions of each
protocol; these channels are designed to support high-bandwidth communication rates.
VMX-pi Hardware Reference Manual (version 1.10) 9
CAN Interface: The CAN interface supports a positive and negative differential signal pair. NOTE: The
two CAN -pi Channel
below.
Table 2 VMX I/O Channel Type Summary
Type
Count
S/W
Direction
Select
High
Current/Jumper
Direction Select
Analog
Input
Digital
Comm
FlexDIO
12
Yes
HiCurrDIO
10
Yes
CommDIO
8
Yes
AnalogIn
4
Yes
VMX-pi Hardware Reference Manual (version 1.10) 10
I/O Resource Summary
Each VMX-pi channel can be used for multiple functions. This flexibility functionality is provided by a set
of I/O Resources. Each VMX-pi channel may be routed (under software control) to different I/O
resources, depending upon the VMX-pi application requirements.
Type
Description
Typical Use
Digital Input
Detects current signal digital level
(high/low)
Reading state of a button
Digital Output
Transmits current signal digital level
(high/low)
Triggering a Relay
PWM Generator
Transmits periodic pulses with
configurable period and pulse-width
Controlling a motor or servo
PWM Capture
Measures pulse with (frequency and duty
cycle) of periodic pulses
Reading current pulse width
from servo controller
Interrupt
Generates Interrupts on selected signal
edge transitions
of an ultrasonic
distance sensor
Accumulator
Performs Oversampling/Averaging on an
Analog Input
Noise-removal and resolution
enhancement on inputs from an
analog potentiometer
Analog Trigger
Generates Interrupts on analog input
high/low level transitions
sensor input
UART
TX/RX line data transceiver
Communication with an
external GPS
SPI
CLK/MOSI/MISO/CS line data transceiver
Communication with an
external IMU sensor
I2C
SCL/SDA line data transceiver
Communication with an
external LIDAR sensor
Table 3 VMX-pi Resource Summary
Many I/O Resource Types support a single I/O Channel; certain Resource Types may support more than
1 channel (e.g., a Quadrature Encoder Resource supports two I/O Channels, one for the A signal and
another for the B signal).
Channel/Resource Routing
To use an I/O Resource, one or more I/O Channels must be routed to the resource. Each I/O Channel
Type may be routed to the following I/O Resources:
Type
DIO/
PWM
Encoder
PWM
Capture
Interrupt
Accumulator
Analog
Trigger
UART
SPI
I2C
# Chan
per
Resource
1
2
1
1
1
1
2
4
2
FlexDIO
Yes
Yes
Yes
Yes
HiCurrDIO
Yes
Yes
VMX-pi Hardware Reference Manual (version 1.10) 11
CommDIO
Yes
Yes
Yes
Yes
Yes
AnalogIn
Yes
Yes
Yes
I/O Channel Types/Numbers
VMX-pi follows a Channel-numbering scheme for all I/O connectors (except the signals on the CAN
connector), allowing application software to address and reconfigure the functions on each channel.
Note that all Channel Numbers start from 0, and begin with FlexDIO connectors on the bottom-right of
the below diagram and increase in a counter-clockwise direction.
01234567
8910 11 12 13 14 15 16 17 18 1920 21 22 23 24 25
2627 2829 30313233
FlexDIO Connectors
FlexDIO Header HighCurrentDIO Header AnalogInput Header
CommDIO Connectors
I2C UART SPI
(ch. 8-11)
(ch. 0-7)
(ch. 26-33)
(ch. 12-21) (ch. 22-25)
HighCurrentDIO Input/
Output Selection Jumper
Figure 4 VMX-pi Channel Types and Numbers
I/O Channel Type
Connector
Type
Channel
Numbers
Location
Flex DIO Connectors
Connector
0-7
Bottom-right
Flex DIO Header
Header
8-11
Left-side Top
High Current DIO
Header
12-21
Left-side mid
Analog Input
Header
22-25
Left-side bottom
Comm DIO
Connector
26-33
Bottom-left
VMX-pi Hardware Reference Manual (version 1.10) 12
High Current DIO Input/Output Selection Jumper
The entire bank of High Current DIOs can be either all inputs, or all outputs. This selection is performed
in hardware via the High Current DIO Input/Output Selection Jumper. If the jumper is present, all High
Current DIOs function as outputs, otherwise they function as inputs.
VMX-pi Hardware Reference Manual (version 1.10) 13
Power Management Scheme
To minimize the number of system components, VMX-pi provides integrated voltage regulators; the
input power source may be a wide range of DC input voltages (e.g., from a battery) and outputs 5VDC to
the Raspberry Pi, as well as 5VDC and 3.3V DC External Devices.
Buck Regulator
(3A)
6-16VDC
(unregulated)
RPi-3
5VDC
CAN
Controller/
Transceiver
Max 2.1A
Max 120mA
(CANL Short condition)
Internal 3.3V
Digital LDO
(200mA Limt) uC
Max 180mA
Onboard
Sensors
Max 25mA
Max 50mA
Current
Limiting Switch
(Max 500mA)
Max
500mA
Internal Analog
LDO/OpAmp
(3.3V, 30 mA)
External I/O
Voltage LDO
(3.3V, Max
500mA)
ADC
Max 10mA
Current
Fault
Indicator
3.3VDC
(Max 500mA
Combined)
VMX-pi Power Tree
(Max Power Consumption: 15W)
LEDs
Max 35mA
Max 48mA External IOs
VMX-pi is powered by a single 6-16VDC unregulated voltage source, and the devices it powers may
consume up to 3 Amps (15 Watts). The VMX-pi voltage regulators are designed to output the following
maximum current levels:
Max. Current
Purpose
2.1 Amps
Raspberry Pi Processor & USB peripheral power
.4 Amps
VMX-pi microcontroller and onboard circuitry
power (including IMU, CAN and signal-driving
circuitry)
.5 Amps
VMX-pi External Device power
VMX-pi Hardware Reference Manual (version 1.10) 14
VMX-pi Power Management
VMX-pi Power Management ensures reasonable system behavior in exceptional events including Input
Power under-voltage, and also external device power over-current and short-circuit conditions.
External Device Over-current and short-circuit management
When the VMX-pi 5V and 3.3V regulators that provide power to External Devices detect a current draw
from those external devices exceeding the maximum current level (.5A), current is either limited to the
maximum, or alternatively the current is completely removed, depending upon software configuration.
This design ensures that sufficient power is reserved for proper operation of the VMX-pi microcontroller
and the Raspberry Pi processor and its USB peripherals - even when External Device short-circuit
conditions occur.
Input Power under-voltage management
In Input Power under-voltage situations, VMX-pi is designed to preserve power to the VMX-pi
microcontroller and the Raspberry Pi processor, at the expense of any peripherals which may be
attached. Specifically, VMX-
first, then the VMX-pi microcontroller second, and lowest priority is given to any External Devices. This
design ensures that critical components are able to maintain state (e.g., software algorithms, IMU
calibration coefficients, or buffers of recently received CAN packets).
Figure 5 VMX-pi power supply voltage regulator dropout curve
As shown in the VMX-pi voltage regulator dropout curve above, the VMX-pi voltage regulator can
guarantee the full 3A (15W) power output as long the Input Power voltage is above 5.75V.
The Raspberry Pi 3 USB power supply which is designed to power external USB devices - will brown out
when the VMX-pi 5V voltage regulator output drops below 4.75V. At the maximum 3A load, this
corresponds to a VMX-pi input voltage of 5.75V. For a more typical lightly-loaded Raspberry Pi
consuming 1A, this corresponds to a minimum input voltage of 5V. Note also that the Raspberry Pi
processor will continue to function until the VMX-pi input voltage reaches 4.5V, and the VMX-pi
VMX-pi Hardware Reference Manual (version 1.10) 15
microcontroller will continue to function until the VMX-pi input voltage reaches 4V however these
extremely low voltages are insufficient to support fully-operational scenarios, and can only main
processor life-support. Therefore, the minimum required voltage is 5.75V.
To manage low Input Power voltage situations typically occurring in battery-operated scenarios, when
VMX-pi detects Input Power voltage levels below 5.75V, the External Device power supply output (e.g.,
power supplied to power pins on FlexDIO, HighCurrentDIO, AnalogInput and CommDIO
headers/connectors) is temporarily disabled until the input voltage rises again to approximately 5.85V.
This ensures the full 3A output current remains available to the Raspberry Pi and the VMX-pi
microcontroller.
The system behavior at various Input Power voltage levels is summarized below:
Input Power
Voltage
VMX-pi external
devices
Raspberry Pi
external USB
devices
Raspberry Pi
Processor
VMX-pi
Microcontroller
5.75V and
above (at
full 3A load)
OK
OK
OK
OK
Below
5.75V
External device
Power rail disabled
OK
OK
OK
Below
4.75V
External device
Power rail disabled
Insufficient Power
OK
OK
Below 4.5V
External device
Power rail disabled
Insufficient Power
Insufficient Power
OK
Below 4V
External device
Power rail disabled
Insufficient Power
Insufficient Power
Insufficient Power
VMX-pi Hardware Reference Manual (version 1.10) 16
External Device Power/Signal Voltage Configuration
VMX-pi provides flexibility in the voltage used to power and exchange signals with External Devices.
Several onboard jumpers allow various configurations to address many system configurations, typically
eliminating the need for external voltage translation devices.
High Current
DIO Power/
Signal
Voltage
Select
Analog Input
Power
Voltage
Select
COMM/DIO
Power/Signal
Voltage
Select
FlexDIO
Power
Voltage
Select
Figure 6 VMX-pi Signal/Power Voltage Select Jumpers
Signal Voltage Select Jumpers
Either 5 or 3.3V output signal levels may be selected for High Current and Comm DIOs.
Note 1: Flex DIOs are fixed at 3.3V output levels.
Note 2: All inputs are tolerant of higher voltages, see Table 5 below.
Power Voltage Select Jumpers
Either 5 or 3.3V power output for external devices may be selected for Flex, High Current and Comm
DIOs and also for power pins on the Analog Input block
VMX-pi I/O Signal/Logic Levels
VMX-pi Analog and Digital I/O channels are designed to support nominal signal levels in both 3.3V and
5V systems, and also include circuit protection circuitry to handle cases when input signal levels exceed
the expected range.
VMX-pi Hardware Reference Manual (version 1.10) 17
Table 4 Digital Channel output signal drive current summary
Channel Type
Max. Drive Current
FlexDIO
4mA (@3.3V)
High-Current DIO
12mA (@5V)
CommDIO
10mA (@3.3V)
CAN
45mA
Table 5 Analog/Digital Input Channel signal over-voltage protection summary
Channel Type
Vmax(DC)
FlexDIO
12V
High-Current DIO
12V
Analog Inputs
12V (Vmin = -12V)
CommDIO
6V
CAN
58V
Table 6 Digital Channel signal Logic Level summary
Channel Type
Input/Output
Logic Levels
Output V maxLow/minHigh
FlexDIO
3.3V TTL/CMOS
0.4V, 2.4V @4mA [3.3V]
High-Current DIO
3.3V/5V CMOS
0.24V, 4.75v @1mA [5V
mode]
CommDIO
3.3V/5V CMOS
1.5V, 3.3V @4mA [5V mode]
.8V, 2V @4mA [3.3V mode]
Table 7 Digital Channel Pull-up/Pull-down resistance summary
Channel Type
Pull Direction
Resistance
FlexDIO
Up, Down or Floating (s/w
selectable)
50k-ohm
High-Current DIO
Pull-down
40k-ohm
CommDIO I2C (when used as
input)
Pull-up
2.2k-ohm
CommDIO (UART when used as
a digital input channel)
Floating
n/a
CommDIO SPI (when used as a
digital input channel)
Floating
n/a
Note that CommDIO input signals are floating in support of high-bandwidth communications. In certain
applications, external pull-up resistors may be used but are not typically required.
VMX-pi Hardware Reference Manual (version 1.10) 18
Board-edge Connectors
VMX-pi connectors are oriented at right-angles to the circuit board. Many of the connectors use locking
connectors to ensure reliable connectivity.
Flex DIO
4*No Power/Gnd on
SPI connector
CAN
1
Power
1
VMX-pi External IO Connector Summary
(NOTE: All connectors exit at right-angle from board)
I2C, UART,
4QuadEnc
(or DIO)
6
SPI*
(or DIO)
1
3-pin PWM Header
(.1" pitch)
High-
Current
DIO
10
Analog In
4
JST VH locking connector
(2-wire, 16-22 AWG [max
10 Amp], 3.5mm pitch)
Weidmuller 2-pin Push-in
Direct Insert lock
connector (3.5mm pitch)
L H
JST GH locking connector (4-wire,
26-30 AWG [max 1 Amp], 1.25mm
pitch)
CommDIOFlex DIO
Note: Power cables and JSG GH cables and associated breakout boards are available at the Kauai Labs
online store (www.kauailabs.com/store).
FlexDIO Connectors (VMX Channels 0-7)
FlexDIO Connectors are a set of four locking JST GH connectors (4 pins each) with power, ground, signal
A and signal B on each connector. These connectors are designed to support Quadrature Encoders, but
may also be configured for use as Digital Inputs, Interrupts, Digital Outputs, PWM Generation or PWM
Capture.
VMX-pi Hardware Reference Manual (version 1.10) 19
Figure 7 FlexDIO GH Connector (VMX Channels 0-7) pinout
FlexDIO Header (VMX Channels 8-11)
The FlexDIO Header provides 4 sets of power, ground, and a single signal channel. The signals may be
configured to support Quadrature Encoders, Digital Inputs, Interrupts, Digital Outputs, PWM Generation
or PWM Capture.
Figure 8 FlexDIO Header (VMX Channels 8-11) pinout
High-Current DIO Header (VMX Channels 12-21)
The High-Current DIO Header provides 10 sets of power, ground, and a single signal channel. The signals
may be configured to support Digital Inputs, Interrupts, Digital Outputs, or PWM Generation.
VMX-pi Hardware Reference Manual (version 1.10) 20
Figure 9 HighCurrentDIO Header (VMX Channels 12-21) pinout
Analog Input Header (VMX Channels 22-25)
The Analog Input Header provides 4 sets of power, ground, and a single signal channel. The signals may
be configured to support Analog Accumulation or Analog Interrupts.
Figure 10 Analog Input Header (VMX Channels 22-25) pinout
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