USB-C Sensor Node

flux

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/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.
Search library parts
Recommend component MPNs
Draft schematic plan
Add compliance constraints
No schematic yet

Talk to Flux to get started.

Refine this doc
Ask about this doc
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

USB-C WiFi BLE Environmental Sensor Node

USB-C WiFi BLE Environmental Sensor Node thumbnail
Low-power USB-C powered temperature/humidity sensor node with ESP32-C3 WiFi/BLE, protected 5V input, and digital T/RH sensor.

Properties

IoT

USB-C

FCC/CE

WiFi

5

V

Pricing & Availability

See prices from popular manufacturers for your project.

Controls