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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
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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
# | Name | Type | Ideal Voltage | Notes |
---|---|---|---|---|
U4 | Daughterboard PSOM Connector | 53307-2471 (PSOM) | N/A | 3.65mm tall |
J2 | CAN Output | 1x4xP3.00mm_PolarizingPeg_Vertical | +12V | 6.98mm tall |
J3 | CAN Input | 1x4xP3.00mm_PolarizingPeg_Vertical | +12V | 6.98mm tall |
J6 | Breakout Connector | 2x05_P2.50mm_Vertical | +3.3V | 9.05mm tall |
PeripheralSOM Daughterboard Connection List
Pin # | Net Name | Notes |
---|---|---|
2, 9 | +3.3V | General 3.3V source for SHT45 humidity sensor and FS3000 airflow sensor |
4, 11 | GND | Ground associated with general 3.3V source |
6 | I2C2_SDA | I2C data signal for FS3000 airflow sensor |
8 | I2C2_SCL | I2C clock signal for FS3000 airflow sensor |
10 | VDDA (3.3V) | Isolated 3.3V analog voltage source for LMT87 temperature sensor |
12 | GNDA | Isolated analog ground for LMT87 temperature sensor |
14 | I2C1_SCL | I2C clock signal for SHT45 humidity sensor |
16 | I2C1_SDA | I2C data signal for SHT45 humidity sensor |
20 | PA1 (ADC) | STM32 analog-to-digital converter input on PSOM; connected to analog output of LMT87 temperature sensor |
21 | CAN_L | CAN Bus Low; connected to other Environment boards and Leader board over EnvironmentCAN |
22 | +12V_In | 12V input from CAN I/O connector |
23 | CAN_H | CAN Bus High; connected to other Environment boards and Leader board over EnvironmentCAN |
24 | GNDPWR | Ground associated with 12V from CAN I/O connector |
Note |
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I2C2 jumpers on Peripheral SOM PeripheralSOM must be closed for pull-up functionality (default is open for GPIO) |
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Sensor Schematics
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Note |
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R1 and C7 values were chosen arbitrarily due to lack of documentation, need to test/verify |
Protection for Breakout Board
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Main Board
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Connectors
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Breakout Connector
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List of Circuit Components
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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
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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)
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:
VRWM (Working Peak Reverse Voltage) of 3.3v
VBR (Breakdown Voltage) of 5v
PTC Fuses - https://www.mouser.com/ProductDetail/530-0ZCM0010FF2G
Description:
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Connectors (WIP)
PSOM (53307-2471 connector)
Power from CAN
EnvironmentCAN
TODO
Layout (WIP)
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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 abovesection.
Design Choices (WIP)
PCB
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3D Models
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PCB
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3D Models
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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