...

Measure environmental data throughout the car, including relative humidity, airflow, and temperature (see data acquisition Data Acquisition SRR for more rationale)

Physical Design

• Each node consists of a main environment board + sensor breakout board

• Main environment board - interfaces with a PSOM (Peripheral System on Module) to provide ADC, I2C, and CAN functionality; connects to breakout board via short (TODO: absolute wire size/constraints after testing) wire

• Sensor breakout board - implements exposed humidity, airflow, and temperature sensors with all passive components and connectors a connector to interface with the main environment board

• Modularity - can pick and choose which sensors to use on each breakout board during assembly

  • Doesn’t require Not all sensors need to be present at every node

Rationale

• Sensor The sensor breakout board needs to be as small as possible to not disrupt airflow in the intake, exhaust, battery box, etc. (according to Cooling/Emech)

• Main The main board has to be at least the size of PSOM + any connector footprints, which is too large to place in the cooling system

  • Decided to break out sensors onto a separate board to balance airflow and data integrity

• Airflow sensor needs an uninterrupted flow of air to measure accurately - no other components can be placed in the line of measurement

• Humidity/Temperature sensors must also be exposed to the environment that’s being monitored

Interface

• Main environment boardwill send all environment

  • Sends environmental data to the

  main Environment Leaderboard

  • Data Acquisition leader board via internal

  Data Acq.

  • EnvironmentCAN

  • Will then be sent over TelemetryCAN to the telemetry module??

  • TODO:

  breakout system

  • TVS for i2c, fuse, connectors

  • pinouts for connectors on board silkscreen if also using for logic analzer debug points

  • possibly need i2c repeater: Need clarification on this

• Sensor breakout board

  • Receives sensor power and ground from the main board

    • All power connections are fused on the main board using PTC (resettable) fuses for overcurrent protection

  • Sends/receives I2C and Analog signals to/from the main board

    • Each I2C line on the main board is protected from ESD (transient voltage spikes) using TVS diodes

• I2C Repeater - https://www.nxp.com/products/interfaces/ic-spi-i3c-interface-devices/ic-bus-repeaters-hubs-extenders/level-translating-ic-bus-smbus-repeater:PCA9509

  • May be needed to reduce noise on I2C signal lines due to a large distance between the main board and the breakout

Context

Location of the board: Several boards Boards will be located utilized by several systems throughout the car as outlined below

• Cooling

  • Nose Intake, Tail Exhaust, Battery box intake/exhaust, internally in battery box multiple locations

• any TODO: Any other systems needing environmental sensing TBD

Connection List

PeripheralSOM Daughterboard Connection List

...

Sensor Schematics

...

Protection for Breakout Board

...

Main Board

...

Connectors

...

Breakout Connector

...

List of Circuit Components

...

• Description: Digital relative humidity and temperature sensor

• Justification for selection of specific part: DataAcq chose it

• Datasheet link: https://sensirion.com/media/documents/33FD6951/662A593A/HT_DS_Datasheet_SHT4x.pdf

• Associated passives/components:

  • 100nF capacitor

  • 2x 10k resistors

• Interface: I2C

• Footprint: Non-standard QFN

  • Breakout: https://www.adafruit.com/product/5665

• Notes:

  • 3.3v supply voltage

  • Maximal power-up time = 1ms

  • Also measures temperature – not using this functionality due to modular nature of board

  • Heater functionality provided for high humidity (>90%RH) conditions

  • Accurate to ±1.0 %RH

Airflow Sensor – https://www.mouser.com/ProductDetail/Renesas-Electronics/FS3000-1005?qs=xZ%2FP%252Ba9zWqYVrq1uDYsQug%3D%3D

• Description: Air velocity sensor module with 12-bit digital output

• Justification for selection of specific part: DataAcq chose it

• Datasheet link: https://www.mouser.com/datasheet/2/698/REN_FS3000_DST_20230207-3075780.pdf

• Associated passives/components:

  • 3x 0.1uF capacitors

  • 1uF capacitor

• Interface: I2C

• Footprint: Non-standard QFN

  • Breakout: https://www.sparkfun.com/products/18768

• Notes:

  • 3.3v supply voltage

...

• Description: Analog temperature sensor with Class-AB output

• Justification for selection of specific part: DataAcq chose it

• Datasheet link: https://www.ti.com/lit/ds/symlink/lmt87.pdf?ts=1728144032765&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLMT87

• Associated passives/components:

  • 0.01uF capacitor connected between Pin 4 (VDD) and GND

  • Other VDD pins connect to PWR plane

• Interface:

  • Analog - output voltage is inversely proportional to temperature as shown below

    

• Footprint: SOT(5)

  • Breakout Board

• Notes:

  • 2.7v to 5.5v supply voltage

  • 0.7ms power-on time

TVS Diodes - https://www.mouser.com/ProductDetail/863-ESD9B3.3ST5G

• Description: Transient voltage suppressor (TVS) diode to protect sensitive components from ESD

• Justification for selection of specific part: Sufficient working peak reverse voltage and breakdown voltage to protect broken-out I2C devices (sensors)

• Datasheet link: https://www.onsemi.com/pub/Collateral/ESD9B-D.PDF

Description:

• Footprint: SOD-923

• Notes:

  • V_RWM (Working Peak Reverse Voltage) of 3.3v

  • V_BR (Breakdown Voltage) of 5v

PTC Fuses - https://www.mouser.com/ProductDetail/530-0ZCM0010FF2G

• Description:

...

Connectors (WIP)

• PSOM (53307-2471 connector)

• Power from CAN

• EnvironmentCAN

  • TODO

Layout (WIP)

...

• Positive temperature coefficient (PTC) resettable fuses

• Justification for selection of specific part: Sufficient hold current and trip current for broken-out sensors

• Datasheet link: https://www.mouser.com/datasheet/2/643/ds_cp_0zcm_series-1313124.pdf

• Footprint: 0603

• Notes:

  • Hold current of 100mA

  • Trip current of 250mA

Layout

Dimensions: 59mm x 53mm (Main board), 27.2mm x 19.4mm (Breakout board)

Requirements/Constraints: As described in the rationale above.

Design Choices (WIP)

PCB

...

3D Models

...

section.

PCB

...

3D Models

...

Firmware (WIP)

Test setup: Nucleo-F429ZI

• Pinout reference - https://os.mbed.com/platforms/ST-Nucleo-F429ZI/

• SHT45 Breakout

  • Sensor - Nucleo

  • VCC - 3V3

  • GND - GND

  • I2C1_SDA - PB_9

  • I2C1_SCL - PB_8

TODO: add documentation for the following

• CRC calculation for SHT45

• checksum calculation for FS3000

• drivers for SHT45, FS3000, LMT87

• CAN package information

• build/test instructions