Project Ownership: @Ravi Shah

Github Link (Main Board): GitHub - lhr-solar/DataAcq-EnvironmentBoard

Github Link (Breakout): GitHub - lhr-solar/DataAcq-EnvBreakoutPCB: Breakout Board for Data Acquisition's environment breakout PCB

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 - 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

Open

Humidity Sensor

Open

Airflow Sensor

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: Adafruit Sensirion SHT45 Precision Temperature & Humidity Sensor

• 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 – Renesas Electronics FS3000-1005

• 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 – 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 - onsemi 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 - Bel 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