USB-C Sensor Node

flux

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Completed so far:
  • Created and named the project: USB-C WiFi BLE Environmental Sensor Node.
  • Updated the project description/properties.
  • Created the initial project specification: Project Specification — USB-C WiFi BLE Environmental Sensor Node.
  • Defined the intended architecture: USB-C 5 V sink, protected VBUS path, 3.3 V regulator, ESP32-C3 Wi‑Fi/BLE module, digital T/RH sensor, USB programming, boot/reset, status LED, and test pads.
Remaining work:
  • Select library-backed components for the ESP32-C3 module, T/RH sensor, USB-C connector, eFuse/protection, buck regulator, ESD/TVS, buttons, LED, and test points.
  • Add and wire the schematic.
  • Run ERC/design review and fix issues.
  • Create firmware, bring-up, and FCC/CE compliance notes once the schematic exists.
    I’m blocked from continuing execution because this workspace has no available ACUs right now, so AI design actions are unavailable.
Completed so far:
  • Created and named the project: USB-C WiFi BLE Environmental Sensor Node.
  • Updated the project description and project-level properties.
  • Created the initial project specification: Project Specification — USB-C WiFi BLE Environmental Sensor Node.
  • Defined the intended architecture: USB-C 5 V sink, protected VBUS path, 3.3 V regulator, ESP32-C3 Wi‑Fi/BLE module, digital T/RH sensor, USB programming, boot/reset, status LED, and test pads.
Remaining work:
  • Select library-backed parts for the ESP32-C3 module, T/RH sensor, USB-C connector, eFuse/protection, buck regulator, ESD/TVS, buttons, LED, and test points.
  • Add and wire the schematic.
  • Run ERC/design review and fix any issues.
  • Create firmware, board bring-up, and FCC/CE compliance notes once the schematic exists.
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Project Specification — USB-C WiFi BLE Environmental Sensor Node
Project Overview
Status: Draft schematic in progress.
A consumer indoor environmental sensor node powered from USB-C 5 V. It measures ambient temperature and relative humidity and reports data over Wi-Fi and/or Bluetooth Low Energy.
Intended Use
  • Indoor consumer environmental monitoring node.
  • Prototype-to-consumer-intent hardware baseline.
  • Powered from a standard USB-C 5 V source such as a charger, hub, PC, or power bank.
What the Device Should Do
  • Measure temperature and relative humidity with a digital T/RH sensor.
  • Connect over 2.4 GHz Wi-Fi 802.11 b/g/n.
  • Support Bluetooth Low Energy 5.x.
  • Operate from USB-C default 5 V power.
  • Include input protection: reverse blocking, over-voltage protection, under-voltage lockout, over-current protection, and inrush/soft-start behavior.
  • Remain compatible with 0.5 A to 3 A USB-C sources by designing the load below a conservative default-current budget unless future firmware adds CC current sensing.
Main Features
  • ESP32-C3 module with integrated antenna for Wi-Fi + BLE.
  • Digital I2C temperature/humidity sensor.
  • USB-C receptacle for 5 V power and native USB programming/debug.
  • Protected 5 V power path and 3.3 V rail.
  • Boot/reset controls, status LED, and bring-up test points.
System Architecture
Diagram



  
    
  
  
    
  


















USB-C 5 V sink
VBUS TVS + eFuse OVP UVLO OCP reverse blocking
USB D+/D- ESD
ESP32-C3 Wi-Fi BLE MCU module
3.3 V buck regulator
SHT4x T/RH sensor
Status LED
Test pads
Hardware Subsystems
  • Power input: USB-C sink-only configuration with independent CC pull-down resistors.
  • Protection: VBUS transient suppression plus eFuse/load-switch class IC providing OVP, UVLO, OCP/current limiting, reverse blocking, and soft start.
  • Regulation: 5 V to 3.3 V buck regulator sized for ESP32 radio bursts.
  • Compute/radio: ESP32-C3 module for Wi-Fi b/g/n and BLE 5.x.
  • Sensor: SHT4x-family I2C temperature/humidity sensor with local decoupling and shared I2C pull-ups.
  • Debug/programming: USB native interface, boot/reset buttons, UART fallback pads, and rail/signal test points.
Interfaces and Connections
  • USB-C receptacle: VBUS, GND, CC1/CC2 Rd, D+/D- to MCU native USB, shield to board ground strategy.
  • I2C: MCU SDA/SCL to T/RH sensor with one pair of pull-ups.
  • GPIO: status LED, eFuse fault/power-good where supported, BOOT and EN/RESET.
  • Test points: 5V_PROT, 3V3, GND, EN, BOOT, UART TX/RX, I2C SDA/SCL.
Power and Runtime Expectations
  • USB-C powered only; no battery runtime target in this revision.
  • Low-power firmware should duty-cycle Wi-Fi and LED activity where possible.
  • Device current is intended to remain safely below default USB current in normal operation.
Power Tree and Power Budget
Diagram



  
    
  
  
    
  
















USB-C source 5 V, 0.5 A to 3 A capable
eFuse current limit target 0.6 A to 1.0 A
Protected 5 V rail
3.3 V buck, 1 A class
3.3 V rail
ESP32-C3 module peak radio bursts
SHT4x sensor
Status LED
Preliminary budget:

Table

3.3 V LoadSleepTypical activePeak
ESP32-C3 module<1 mA firmware-dependent80–250 mA radio-active400–500 mA burst
SHT4x sensor<1 uA idle<1 mA measuring<2 mA
Status LED0 mA off1–5 mA5 mA
Pull-ups / leakage<1 mA<1 mA<1 mA
Total design target<5 mA<260 mA<510 mA
Use a 1 A-class 3.3 V buck and set VBUS current limiting conservatively around 0.6–1.0 A unless CC current sensing is added.
Manufacturing and Assembly Expectations
  • Surface-mount consumer prototype board.
  • Use a pre-certified wireless module to reduce RF design risk.
  • Add test points for production/bring-up.
  • Sensor placement must support airflow and thermal isolation.
Firmware-Relevant Hardware Requirements
  • ESP-IDF or Arduino support for ESP32-C3.
  • I2C sensor polling and Wi-Fi/BLE telemetry.
  • USB native flashing/debug path plus BOOT/RESET access.
  • Status LED should be firmware-disableable.
  • If eFuse fault output is available, route it to a GPIO/test pad.
Physical Design Expectations
  • ESP32-C3 antenna at board edge with no copper/components/traces in antenna keepout on all layers.
  • T/RH sensor near board edge or airflow opening, away from ESP32, regulator, LED, and USB connector heat.
  • Keep buck switch node compact and away from sensor and antenna.
  • USB ESD/TVS close to connector.
Important Design Decisions
  • Use ESP32-C3 module rather than bare RF chip for certified antenna/matching and simpler layout.
  • Use conservative USB-C sink behavior with 5.1 kΩ CC pull-downs; do not draw 3 A by assumption.
  • Use eFuse-class input protection rather than only a polyfuse/TVS.
  • Use 1 A-class 3.3 V buck for Wi-Fi burst margin.
Assumptions
  • Consumer indoor device, not outdoor/weatherproof.
  • USB-C is 5 V only; no USB Power Delivery negotiation.
  • No battery charging or backup supply in this revision.
  • Normal system load remains below default USB current.
Change Notes
  • Initial specification created from user request on 2026-07-15.

  • Project Overview

  • Intended Use

  • What the Device Should Do

  • Main Features

  • System Architecture

  • Hardware Subsystems

  • Interfaces and Connections

  • Power and Runtime Expectations

  • Power Tree and Power Budget

  • Manufacturing and Assembly Expectations

  • Firmware-Relevant Hardware Requirements

  • Physical Design Expectations

  • Important Design Decisions

  • Assumptions

  • Change Notes