Project Ownership: Ravi Shah

Github Link (Main Board): https://github.com/lhr-solar/DataAcq-EnvironmentBoard

Github Link (Breakout): https://github.com/lhr-solar/DataAcq-EnvBreakoutPCB

BOM Link: https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=8fef7b51e5

Description/Purpose

Measure environmental data throughout the car, including relative humidity, airflow, and temperature (see 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 a connector to interface with the main environment board

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

  • Not all sensors need to be present at every node

Rationale

• 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)

• 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 board

  • Sends environmental data to the Data Acquisition leader board via internal EnvironmentCAN

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

  • TODO: 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: Boards will be 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

• TODO: Any other systems needing environmental sensing

Connection List

PeripheralSOM Daughterboard Connection List

Main

Sensor Schematics

Protection for Breakout Board

Main Board Connectors

Breakout Connector

List of Circuit Components

Humidity Sensor – https://sensirion.com/products/catalog/SHT45

• 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

Temperature Sensor – https://www.ti.com/product/LMT87

• 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

• 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: 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 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