USB-C Sensor Node

flux

Implemented the schematic for the USB-C powered Wi‑Fi/BLE temperature/humidity node. It uses a SiWG917 Wi‑Fi/BLE 5.4 module, SHT41 T/RH sensor, USB-C sink input, TPS25940 true reverse-blocking eFuse with OVP/UVLO/OCP/soft-start, MP28301 3.3 V buck regulator, ESD protection, reset/ISP/SWD debug, I2C pull-ups, and status LED.
Created project files:
Open items:
  • PCB layout/routing is not done yet, so airwire DRC errors are expected.
  • Generic passives still need final manufacturer MPNs before manufacturing export.
  • Layout must enforce the SiWG917 antenna keepout and thermal isolation around the SHT41.
Suggested next steps:
  1. Set board size/stackup and move into PCB placement.
  2. Place U1 at the board edge with antenna keepout and U4 away from heat sources.
  3. Route power, buck, I2C, SWD/UART, and USB-C protection paths.
  4. Assign final passive MPNs and run full DRC/manufacturing checks.

flux

The schematic is complete with 46 components and 31 nets: SiWG917 Wi‑Fi/BLE, SHT41 sensor, protected USB‑C input, TPS25940 reverse-blocking eFuse, MP28301 3.3 V buck, ESD protection, controls, and debug access. Documentation for requirements, firmware, bring-up, and regulatory planning was also created.
Remaining work:
  • PCB outline, stackup, placement, and routing
  • SiWG917 antenna keepout and SHT41 thermal isolation
  • Final passive MPN assignment
  • PCB DRC and manufacturing validation
  • Review the attached text and apply any requested changes
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Review attached requirements
Set up board placement
Finalize passive BOM
Plan critical placement
Check design issues
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Project Specification — USB-C WiFi BLE TH Sensor
Project Overview
Status: Draft schematic in progress.
A consumer USB-C powered temperature and relative humidity sensor node with Wi-Fi and Bluetooth Low Energy connectivity. The board uses a protected USB-C 5 V sink input, local 3.3 V regulation, a low-power Wi-Fi/BLE MCU module, and a digital I2C T/RH sensor.
Intended Use
  • Indoor consumer environmental monitoring node.
  • Powered from USB-C 5 V chargers, hubs, or ports.
  • Designed for prototype-to-production learning; not medical, industrial safety, or outdoor/weatherproof use unless later specified.
What the Device Should Do
  • Measure ambient temperature and relative humidity.
  • Connect over 2.4 GHz 802.11 b/g/n Wi-Fi.
  • Support BLE 5.x provisioning or local telemetry.
  • Power from USB-C default 5 V sources.
  • Survive common consumer input faults with reverse-current, overvoltage, undervoltage, and overcurrent protection.
Main Features
  • USB-C receptacle configured as sink-only with independent CC1/CC2 5.1 kΩ Rd resistors.
  • Protected 5 V input sized for 0.5–3 A capable sources, while the node itself is expected to draw well below 500 mA average.
  • 3.3 V logic rail for MCU and sensor.
  • Native USB data/programming path where supported by the selected MCU.
  • Boot/reset controls, debug/programming access, and status LED.
System Architecture
Diagram



  
    
  
  
    
  









I2C

USB D+/D-






USB-C Receptacle node_5V Sink
VBUS Protection OVP UVLO OCP Reverse Blocking
3.3V Regulator
WiFi/BLE MCU Module
Digital T/RH Sensor
Status LED
Hardware Subsystems
  • Power input: USB-C receptacle, CC pull-downs, VBUS ESD/TVS, protected power switch/eFuse or load switch with OVP/UVLO/OCP/reverse-current blocking.
  • Regulation: 5 V to 3.3 V rail sized for Wi-Fi transmit current peaks.
  • Compute/radio: certified ESP32-family module preferred to avoid custom RF matching and simplify regulatory work.
  • Sensor: digital I2C temperature/humidity sensor with local decoupling and one shared I2C pull-up pair.
  • User/debug: reset and boot controls, status LED, USB programming, optional exposed test/debug header.
Interfaces and Connections
  • External: USB-C 5 V power and USB 2.0 D+/D- for programming/debug.
  • Internal: 3.3 V rail, GND, I2C SDA/SCL, boot/reset, status LED GPIO.
  • RF: integrated 2.4 GHz antenna module; PCB layout must provide the module antenna keepout.
Power and Runtime Expectations
  • Source: USB-C 5 V default power only; no battery in this revision.
  • Source capability planning: tolerate 0.5 A, 1.5 A, and 3 A capable USB-C sources. Do not assume the device may draw 3 A unless CC current advertisement is measured/implemented.
  • Low-power behavior: firmware should sleep between samples and radio transmissions, but USB-powered operation makes absolute sleep current less critical than thermal and regulatory behavior.
Power Tree and Power Budget

Table

RailLoadSleepTypical activePeak
3.3 VWi-Fi/BLE MCU module~10–100 µA deep sleep~80–240 mA radio active~500 mA short Wi-Fi TX burst
3.3 VT/RH sensor<1 µA standby~0.5–1 mA measuring~1 mA
3.3 VStatus LED0 mA off~2 mA on~5 mA configured max
3.3 VPull-ups/leakage~1–2 mA worst when lines lownegligible average~1.4 mA for two 4.7 kΩ pull-ups low
Estimated 3.3 V rail sizing target: 250 mA typical active, 510 mA transient peak. For an LDO from 5 V, input current is approximately output current; thermal at 250 mA is about (5.25 V - 3.3 V) × 0.25 A = 0.49 W, so a small SOT-23 LDO may be marginal during sustained Wi-Fi. Preferred choices are a high-current low-Iq regulator in a thermally capable package or a quiet buck regulator if sustained radio current/thermal limits demand it.
Manufacturing and Assembly Expectations
  • Default assembly: SMD, production-intent consumer PCB.
  • Use stocked, non-EOL parts where available.
  • Add test points for 5 V protected rail, 3.3 V, GND, reset/boot, and I2C if space permits.
Firmware-Relevant Hardware Requirements
  • Define actual GPIO pins for I2C SDA/SCL and status LED.
  • Provide USB programming or serial/JTAG path.
  • Support Wi-Fi + BLE provisioning, periodic sensor reads, and telemetry output.
  • Include boot/reset access for field recovery.
Physical Design Expectations
  • ESP32 module antenna must be placed at board edge with no copper/traces/components in the keepout on all layers.
  • Sensor should be isolated from regulator/MCU heat sources and exposed to ambient airflow.
  • USB-C connector should be board-edge mounted and mechanically reinforced.
Important Design Decisions
  • Use an ESP32-family certified module rather than a bare RF SoC.
  • Use a digital I2C humidity/temperature sensor.
  • Use USB-C sink-only 5 V; no USB-PD negotiation in this revision.
  • Include a protected VBUS front end instead of relying on a fuse alone.
Assumptions
  • Indoor consumer use, ambient operating range roughly 0–50 °C unless later expanded.
  • No enclosure dimensions or board size provided yet.
  • No cloud protocol specified; firmware examples will print readings and include Wi-Fi/BLE placeholders.
Change Notes
  • Initial requirements captured from user request on 2026-07-17.

  • 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 TH Sensor

USB-C WiFi BLE TH Sensor thumbnail
Consumer USB-C powered environmental sensor node with Wi-Fi, BLE 5.x, digital temperature/humidity sensing, protected 5 V input, and a 3.3 V low-power MCU/sensor rail.

Properties

WiFi

USB-C

Consumer IoT

5

V

Bluetooth

Pricing & Availability

Distributor

Qty 1

Arrow

$4.10–$6.66

Digi-Key

$0.00

HQonline

$3.72–$3.82

LCSC

$5.53–$5.70

Mouser

$26.56

TME

$1.03

Verical

$5.53–$8.26

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