Momentum: GNSS, 9-DOF IMU, Barometer Sensor Shield

This document also applies to Momentum Lite which the same board design, with reduced components (no GNSS).

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Table of Contents

• Momentum: GNSS, 9-DOF IMU, Barometer Sensor Shield
  • 1 Overview
    • 1.1 Bill of Materials (BOM)
    • 1.2 Block Diagram
  • 2 Board Specifications
    • 2.1 Connectors
    • 2.2 Switches & Jumpers
    • 2.3 Batteries
    • 2.4 LEDs
    • 2.5 Test Pads
    • 2.6 Power Supply
      • 2.6.1 5 V Power OR Switch
      • 2.6.2 Optional 5 V Pin Supply Protection
      • 2.6.3 3.3 V LDO Supply
    • 2.7 SPI Interface
    • 2.8 Level Shifter
    • 2.9 STM32L432KC Flashing
    • 2.10 USB-C Serial Interface
  • 3 Schematics
  • 4 CAD 3D Model

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1 Overview

1.1 Bill of Materials (BOM)

Manufacturer Part Number	Manufacturer	Description	Quantity	Notes
STM32L432KC	STMicroelectronics	32-bit MCU	1
CP2102N-A02-GQFN24R	Silicon Labs	USB 2.0 to UART Interface	1
BNO086	CEVA Technologies, Inc.	9-DOF IMU	1
BMP390	Bosch Sensortec	Barometric Pressure Sensor	1
TJA1057BTK	NXP USA Inc.	CAN Bus Transceiver	1
SAM-M10Q	u-blox	RF Receiver Galileo, GLONASS, GPS	1
WS2812B	(Various)	PWM Addressable RGB LED	1

Note: Momentum was originally designed for the BNO085, however hardware files were updated to reflect use of the newer BNO086. Firmware is cross compatible for both the BNO085/6, however source files maintain the use of the "BNO085" naming.

1.2 Block Diagram

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2 Board Specifications

2.1 Connectors

Connectors fixed by hardware (PCB traces or the connector itself).

Connector	Ref	Description
Tag-Connect TC2050	J1	SWD programming/debug connector
BOOT0 jumper	J2	Open for run flash memory (pull-down on open)
USB-C	J3	USB-to-serial programming/debug, secondary 5 V source
CAN1	J4	Pin 1: CAN1 High, Pin 2: CAN1 Low

2.2 Switches & Jumpers

User controllable hardware and/or firmware driven inputs.

Switch/Jumper	Ref	Description
Sensor Hub MCU reset button	SW1	Generic 6 mm TH button, push to reset
5 V bypass	JP1	Closed = Short protection (schottky) diode pads, open = enforce schottky diode
Level shifter V IO	JP2	1 + 2 closed = 5 V, 2 + 3 closed = 3.3 V
BOOT0 DTR bridge	JP3	Closed = CP2102N DTR BOOT0 control, open = Manual BOOT0
BNO086 clock select	JP4	Open = crystal, closed = external/internal
BMP390 I2C address	JP5	Open = 0x76, closed = 0x77
Interface SPI CS pin select	JP6	1 + 2 closed = CS1 (D10), 2 + 3 closed = CS2 (D8)
Interface 3.3 V output	JP7	Open = no output, closed = 3.3 V LDO output bridged
Interface NRESET output	JP8	Open = no output, closed = STM32 NRST bridged

2.3 Batteries

Onboard battery supplies.

Battery	Ref	Description
CR1220 battery cell	BT1	u-blox GNSS RTC and ephemeris RAM

2.4 LEDs

LEDs used to show board status and/or user controllable.

Test Point	Mark	Description
UART TX	Silkscreen: "TX"	Green LED: blinking = transmitting data
UART RX	Silkscreen: "RX"	Amber LED: blinking = receiving data
5 V Supply	Silkscreen: Lighting bolt	Amber LED: on = 5V pin, off = (only) USB-C
WS2812B LED	None	RGB addressable LED

2.5 Test Pads

Test Point	Ref	Description
GNSS NRST	TP1	u-blox GNSS NRST net
GNSS RX	TP2	u-blox GNSS RX net
GNSS TX	TP3	u-blox GNSS TX net
WS2812B LED PWM	TP4	DOUT from onboard WS2812B

2.6 Power Supply

The board can be powered by either of the following methods:

1. 5V pin via the Uno-style interface.
2. Onboard USB-C connector.

2.6.1 5 V Power OR Switch

The 5 V supply is controlled by an OR-ing power switch (TPS2116DRL).

• The Uno-style 5V pin has priority: if ~1 V or higher is present, it is used as the source.
• If this condition is not met, the board automatically switches to the USB-C 5 V supply.

2.6.2 Optional 5 V Pin Supply Protection

The 5V pin supply can be optionally protected with diodes (not installed by default). To enable protection, follow these steps:

• Cut the 5 V bypass jumper to remove the short across the schottky diode pads, ensuring use of the schottky diode.
• Schottky diode required (designator D1, footprint SMA).
  • Intended to provide reverse polarity protection.
• TVS diode required (designator D2, footprint SMB).
  • Intended to provide short transient over-voltage clamping.

2.6.3 3.3 V LDO Supply

The 3.3 V supply is managed onboard by a dedicated 5 V to 3.3 V LDO, independent of any connected board.

If the user wishes to use the Momentum dev board's 3.3 V supply as an output supply for low current applications, the Interface 3.3 V output jumper can be bridged, allowing for 3.3 V to be supplied from the onboard LDO.

Warning: This modification should be evaluated for each specific application. Many development boards provide their own regulated 3.3 V output on the Uno-style 3.3V pin. Connecting this pin in parallel with another 3.3 V supply can cause contention between the two outputs, potentially resulting in damage or unstable operation.

2.7 SPI Interface

All SPI pins interfacing with external boards are level-shifted. By default, the SPI bus is shifted to 5 V. However, it can also be shifted to 3.3 V via the Level shifter V IO 3-pad jumper.

See section 2.8 Level Shifter for details.

The SPI CS pin can be reassigned between Uno-style pins D10 (default) and D8 via the Interface SPI CS pin select jumper, allowing flexibility in resolving pin conflicts.

2.8 Level Shifter

Note the level shifter interfaces with the SPI singals (CIPO, COPI, SCK and CS) as well as the WS2812B PWM data line. Adjusting the Level shifter V IO 3-pad jumper selects between 3.3 V and 5 V.

When set to 3.3 V, note that the WS2812B LED may become unstable. According to the WS2812B datasheet:

1. DIN high >= 0.7 * VDD
2. DIN low <= 0.3 * VDD

A 3.3 V logic-high signal may not satisfy the DIN high threshold, potentially causing reduced or unreliable functionality in this configuration.

2.9 STM32L432KC Flashing

The official STM32L432KC Momentum firmware is managed here: momentum.

The STM32L432KC can be flashed in 3 different ways:

1. SWD via Tag-Connect TC2050 interface.
2. Hands-free UART bootloader via USB-C (CP2102N USB-to-UART).
3. Manual BOOT0 jumper with UART bootloader via USB-C (CP2102N USB-to-UART).

For use of the USB-C UART bootloader interface, the custom flashing software pyblasher is highly recommended.

All three options are available by default, however it is suggested to use options 1 and 2 based on user preference.

Option 3 is applicable for users who wish to use the USB-C for as both a serial and UART bootloader interface. In this method, the through-hole BOOT0 jumper must be manually bridged to assert BOOT0.

See section 2.10 USB-C Serial Interface for details.

2.10 USB-C Serial Interface

The USB-C interface connected via the CP2102N USB-to-UART is primarily designed as a UART bootloader flashing interface, however it can also be used as a serial interface for simple communication to a desktop computer.

Due to the design for hands-free flashing, the STM32's BOOT0 is controlled by the CP2102N's DTR pin. Consequently, when a serial port is established BOOT0 will be raised high, entering the bootloader. To prevent this behaviour, the BOOT0 DTR bridge jumper must be cut, allowing for USB-C serial communication without triggering the bootloader.

If the user wishes to still use the UART bootloader with this modification, the BOOT0 must be asserted manually to enter the bootloader via the 2-pin through-hole BOOT0 jumper.

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3 Schematics

Download PDF: momentum_pcb-schematic.pdf.

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4 CAD 3D Model

Download STEP: momentum_pcb-3D.step.