Temperature and Humidity Sensor Node Design

flux

Yes — C5 should stay in the decoupling network.
Why:
  • In the current schematic, C5 is a 100 nF capacitor connected directly from U3 VDD to GND, and its role is already tagged as “Decoupling for HDC3020 VDD pin.”
  • That matches standard local bypass practice for IC supplies: 100 nF MLCC is the normal value for a local decoupling capacitor
Updated list treatment
Move C5 out of the vague “sensor power and decoupling” bucket and call it out explicitly as:
Sensor local decoupling
  • C5 — 100 nF local bypass capacitor for U3, connected from VDD to GND
  • Keep it physically close to U3, since decoupling caps should stay near the IC they support; supporting components should move with their IC during placement
Corrected section for the add-and-wire list

Table

NetConnect
3V3U3 VDD, C5 P1
GNDU3 GND, EPAD, C5 P2
I2C_SCLESP1 IO8, U3 SCL, R6 P2
I2C_SDAESP1 IO10, U3 SDA, R5 P2
3V3R5 P1, R6 P1
Net 1U3 *RESET tied high as currently implemented
Bottom line
  • Keep C5 in the decoupling list
  • Treat it specifically as U3’s local supply bypass capacitor
  • It is not optional if you want a complete, sensible sensor supply network
If you want, I can now rewrite the entire add-and-wire list into one cleaned-up final version with no ambiguities.
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Project Specification
Design Summary
Status: Draft
Manufacturing target: Prototype
Software / firmware: TBD
Scope
Purpose
Design a low-power automotive temperature and humidity sensor node powered from USB-C 5 V input, with protected power entry, regulated 3.3 V rail, dual-radio Wi-Fi/BLE processing, and digital environmental sensing.
In scope
  • USB-C 5 V sink power input
  • Input protection for reverse polarity, over-voltage, under-voltage, and over-current
  • Power-path and 3.3 V regulation for low-power embedded operation
  • Dual-radio 2.4 GHz Wi-Fi plus BLE MCU/module integration
  • Digital temperature and relative humidity sensing over I2C
  • Debug, reset, RF support passives, decoupling, and PCB-layout preparation
Out of scope
  • Battery charging and battery backup
  • Cellular, GNSS, or sub-GHz radios
  • Full enclosure and harness design
  • Final routed PCB manufacturing package in this step
System context
This board is a compact automotive-oriented environmental sensing node intended to monitor local temperature and humidity and report data wirelessly over Wi-Fi or BLE. It is powered from a protected USB-C 5 V input and internally regulates logic power for the MCU/module and digital sensor.
Key interfaces
  • Power input: USB-C 5 V sink
  • Main comms interfaces: 2.4 GHz Wi-Fi, BLE, I2C
  • Debug/programming: UART and reset/boot access or native USB if supported by selected MCU
  • Critical external devices: digital temperature/relative humidity sensor
Architecture
Diagram



  
    
  
  
    
  



""Power and Protection""


""Wireless Control""


""Sensing""














USB-C node_5V Input
Protection and Power Path
3.3V Regulation and Filtering
Ultra low power WiFi BLE MCU
Programming and Reset
Digital Temp RH Sensor
I2C Bus
Requirements
Functional
  • The board shall accept power from a USB-C connector as a 5 V sink.
  • The board shall protect the input path against reverse polarity, over-voltage, under-voltage, and over-current conditions.
  • The board shall provide a regulated rail for the wireless MCU and digital sensor.
  • The board shall measure temperature and relative humidity using a digital sensor.
  • The board shall support 2.4 GHz 802.11 b/g/n Wi-Fi and BLE 5.x wireless connectivity.
Electrical
  • Input power: 5 V nominal from USB-C sink connection
  • Input protection current range: 0.5 A to 3 A
  • Main logic rail: 3.3 V nominal
  • Critical interfaces: I2C sensor bus, debug/programming interface, RF feed/antenna region
  • The design shall include local decoupling and bulk filtering for stable operation during wireless transmit bursts.
Mechanical / environmental
  • Intended for automotive-oriented use and robust operation in electrically noisy environments.
  • PCB layout shall reserve space and keepout for the USB-C connector and RF section.
  • Components should favor wide operating-range and robust sourcing where practical.
Key constraints
  • Low standby power is required.
  • RF layout must respect antenna and keepout requirements.
  • USB-C shall be used in default 5 V sink mode without requiring USB Power Delivery negotiation.
  • Protection architecture must cover reverse polarity, OVP, UVLO, and OCP on the input path.
Dependencies and risks
Dependencies
  • Firmware support for Wi-Fi/BLE stack and sensor polling
  • Final mechanical/layout decisions for antenna placement and connector orientation
  • Final component selection subject to library availability
Key risks
  • Wi-Fi transmit current bursts can destabilize a weak 3.3 V rail if regulation and decoupling are undersized.
  • RF performance can degrade if antenna keepout and grounding are not preserved in layout.
  • Automotive fault tolerance depends strongly on the selected protection IC capabilities and ratings.
Validation
Success criteria
  • Protected 5 V USB-C input is fully implemented in the schematic.
  • Dual-radio MCU/module and digital temperature/humidity sensor are integrated with correct support circuitry.
  • I2C, reset/boot, decoupling, and RF support requirements are represented in the schematic.
  • The design is ready for PCB layout setup with stackup and placement constraints.
Planned checks
  • Schematic connectivity review
  • Datasheet-based support circuit verification
  • ERC review and missing support-passive review
  • Layout setup and placement preparation
Release-facing notes
Expected deliverables
  • Schematic
  • PCB layout setup
  • BOM with selected major parts
  • Design notes for protection and power choices
Special release notes
  • USB-C is power-only in default sink configuration.
  • RF section requires antenna keepout and careful placement.
  • Protection thresholds and current limit should be tuned around selected protection IC capabilities.
Change notes / open questions
Changes in this revision
  • Defined initial architecture and project requirements.
  • Established three main functional blocks: power/protection, wireless control, and sensing.
  • Fixed the design target to USB-C 5 V input with protected 3.3 V internal regulation.
Open questions
  • Final MCU/module choice from available library parts.
  • Final protection IC combination to best satisfy reverse polarity, OVP, UVLO, and OCP requirements.
  • Final sensor choice balancing automotive suitability, power, and availability.

  • Design Summary

  • Scope

  • System context

  • Requirements

  • Functional

  • Electrical

  • Mechanical / environmental

  • Key constraints

  • Dependencies and risks

  • Validation

  • Release-facing notes

  • Change notes / open questions