Sensor Device BOM Design
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Schematic Implementation Notes — EU Smart Environmental Sensor Node
Status
Schematic-stage implementation has been created using approved compatible substitutions. Electrical Rule Checks currently return no ERROR or WARNING results after fixing the real schematic connectivity issues found during validation.
Design Rule Check airwires are expected at this stage because the PCB layout has not yet been sized, placed, or routed. Do not treat DRC airwires as schematic failures before layout.
Implemented Architecture
Power tree
- J3: 14.4 V smart Li-ion battery power input placeholder.
- U1 ST1S14PHR: battery to 5V buck rail.
- U2 ST1S14PHR: battery to 3V3 buck rail.
- U3 LDK130M18R: 3V3 to 1V8 LDO for radar and PDM microphone domains.
- Rails:
BAT_PLUS,5V,3V3,1V8,GND.
MCU / wireless
- IC1 STM32WBA55UGI6 substituted for STM32WBA65PII7.
- SWD debug: PA13 / PA14 / NRST to J2.
- BOOT0 pulled down for normal boot.
- RF pin routed to J4 antenna placeholder. Replace this with a datasheet-matched RF matching network and antenna before layout/manufacturing.
Sensors and interfaces
- I2C 3.3 V bus on PB6/PB7 with 4.7 kΩ pull-ups:
- U4 BME280, address 0x76.
- U5 BME688, address 0x77.
- U6 LIS2DW12 accelerometer.
- U7 TSL25911FN light sensor.
- U8 SCD41 CO2 substitute.
- J1 camera/control placeholder.
- SPI bus on PA5/PA6/PA7:
- U11 BGT60TR13C radar substitute.
- J1 camera data placeholder.
- UART on PA2/PA3:
- U9 PMS5003 particulate sensor substitute.
- PDM microphone:
- MK1 IM69D130 substitute on PB13 clock and PB14 data.
- Analog gas sensing:
- U10 MiCS-6814 NH3/RED/OX analog substitute on PA0, PA1, PA11.
Actuation / illumination
- Four SFH 4045N IR LEDs are current-limited and switched by Q1 AO3400A low-side MOSFET from MCU PWM pin PA4.
USB-C debugging update
- Added J5 USB-C 2.0 receptacle as a service/debug port.
- Added U16 CP2102N USB-to-UART bridge for a dedicated debug console.
- Added U15 USBLC6-2P6 for USB D+/D- ESD protection.
- Added USB-C CC pull-down resistors for sink-mode detection, USB D+/D- series resistors, VBUS/VDD decoupling, and two debug LEDs.
- Debug UART uses PA9/PA10 so the existing PMS5003 UART on PA2/PA3 remains dedicated to the PM sensor.
- Added LED1 power indicator and LED2 MCU status indicator on PA8.
Key Substitutions and Caveats
Table
| Original BOM item | Implemented substitute / placeholder | Caveat |
|---|---|---|
| STM32WBA65PII7 | STM32WBA55UGI6 | Same STM32WBA family, not exact memory/package equivalent. |
| L6982N50DR / L6981N33DR | ST1S14PHR adjustable bucks | Not pin-compatible; feedback network set for 5 V and 3.3 V rails. |
| Senseair Sunrise | Sensirion SCD41-D-R1 | Functional CO2 substitute, not drop-in mechanical/electrical replacement. |
| Bosch BMV080 | PMS5003 | Much larger, fan-based UART PM module; power/mechanical behavior differs. |
| EC Sense I2C NH3 module | MiCS-6814 | Analog raw sensor substitute; requires calibration and is not a calibrated I2C NH3 module. |
| BGT60LTR11AIP | BGT60TR13C | Same vendor/radar family but different interface, pinout, and RF behavior. |
| IM69D127 | IM69D130 | PDM microphone substitute; not same IP57 part. |
| VD55G4 camera | J1 camera placeholder | Exact camera symbol/footprint still required before manufacturing. |
| RRC2054-2 pack/connector | J3 placeholder | Exact smart-battery connector/SMBus pinout still required. |
Known Engineering Risks Before Layout
- RF network is placeholder only: J4 must be replaced with the STM32WBA reference RF matching/antenna network.
- Camera is placeholder only: exact VD55G4 connector, power sequencing, timing, and signal integrity need manufacturer CAD/datasheet confirmation.
- MiCS-6814 is not a drop-in NH3 module: analog front-end and calibration need a dedicated review.
- Radar supply filtering is simplified: BGT60TR13C normally benefits from per-domain low-noise filtering and careful RF layout.
- **STM32WBA SMPS/VDD11 support should be reviewed against the exact selected STM32WBA package datasheet before layout.
Validation Snapshot
- ERC: clean after remediation, including USB-C debug additions.
- Board was reduced to 80 mm × 100 mm with a 4-layer stackup.
- Components have been re-placed on the reduced board with USB-C and debug hardware included.
- DRC airwires remain because routing has not started; no placement overlap/out-of-bounds issues were reported by the placement pass.
- Next gated step: confirm placement, then proceed to routing.
Status
Implemented Architecture
Power tree
MCU / wireless
Sensors and interfaces
Actuation / illumination
USB-C debugging update
Key Substitutions and Caveats
Known Engineering Risks Before Layout
Validation Snapshot
