Temperature and Humidity Sensor Node Design

flux

Work done
  • Created and named the project USB-C WiFi BLE Environmental Sensor and updated the project description.
  • Verified an existing schematic already contains the main design blocks: ESP32-S3-WROOM-1-N16R8, SHT31-DIS, USB-C receptacle, TPS25200 5V eFuse/protection, AP2112K-3.3 regulator, UART/debug header, decoupling capacitors, I2C pull-ups, CC pull-downs, mounting holes, and power/reset/boot support.
  • Confirmed key nets are present: VBUS_USB, 5V_PROTECTED, 3V3, GND, I2C_SDA, I2C_SCL, USB_DP, USB_DN, UART, reset, boot, and eFuse fault/enable/current-limit nets.
  • Added component role metadata for passives, ICs, connector, power protection, regulator, sensor, MCU, and debug header to support review and placement intent.
  • Created the Project Specification project file with architecture, implementation choices, firmware pin map, and layout requirements.
  • Set PCB outline to 90 mm × 60 mm, rounded corners, compact consumer form factor, and 4-layer stackup with a ground reference suitable for RF/EMI.
  • Applied baseline manufacturable layout rules: 0.20 mm default trace width, 0.15 mm minimum trace width, 0.15 mm keepout, and 0.50 mm board inset margin.
  • Checked datasheets for the protection/regulator/RF-module assumptions: TPS25200 provides UVLO/OVLO/OVP clamp/OCP/reverse blocking while disabled; AP2112K-3.3 supports a 600 mA 3.3 V rail; ESP32-S3-WROOM-1 has antenna keepout placement requirements.
Success criteria review
  • ✅ Schematic includes USB-C 5 V input, CC pull-downs, protected 5 V path, 3.3 V regulation, MCU, sensor, I2C, debug, and support passives.
  • ✅ Dual-radio MCU and digital T/RH sensor are integrated and interconnected in the schematic.
  • ⚠️ PCB layout setup is partially complete: board size, stackup, and baseline rules are set, but final component placement/routing/review could not be completed.
  • ⚠️ Final production review is not complete; ERC/DRC/airwire review and routing verification still remain.
Next steps
  • Place components on the 90 mm × 60 mm PCB with the ESP32-S3 antenna at a board edge and ~5 mm antenna overhang/keepout, USB-C at an accessible edge, power components clustered near USB-C, and SHT31 away from heat sources.
  • Route the board, using wide copper/traces for the 5 V protected path and short decoupling loops.
  • Run final ERC/DRC/airwire review and resolve any remaining issues before manufacturing export.

flux

Placed 27 component(s): U1, C3, C6, C7, H3, H2, J1, R5, C5, R2, H4, U4, C2, R3, R1, C4, U3, R7, J2, H1, R9, U2, R6, R8, R4, C8, C1

flux

Work done
  • Built the schematic for the USB-C powered Wi‑Fi/BLE temperature/humidity node: ESP32‑S3 module, SHT31 sensor, USB‑C default-sink input, TPS25200 protection, AP2112 3.3V regulation, decoupling, I²C pull-ups, boot/reset, USB data, and UART debug access.
  • Configured a compact 50 mm × 50 mm 4-layer PCB setup and placed all components with USB‑C at the edge, ESP32 antenna facing outward, sensor away from the power section, and mounting holes in the corners.
  • Added documentation: Project Specification, Firmware Pin Map, and Design Review Results.
Success criteria review
  • ✅ Complete protected USB-C power-path schematic and 3.3V rail are present.
  • ✅ Dual-radio MCU, digital T/RH sensor, support passives, and debug/programming connections are integrated.
  • ⚠️ PCB placement is complete, but final routed PCB production readiness is not complete yet.
  • ⚠️ Final checks found remaining PCB routing airwires and one copper-overlap item that must be resolved before fabrication.
Next steps
Route the PCB traces, inspect the copper-overlap item, then rerun final checks before manufacturing export.
Route remaining airwires
Inspect copper overlap
Run final review
Check antenna placement
Export production files
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Files

Schematic

Layout

Preview

Project Specification
Goal
Consumer-grade low-power temperature and humidity sensor node powered from USB-C 5 V default power. The node uses an ultra-low-power dual-radio MCU module supporting 2.4 GHz 802.11 b/g/n Wi-Fi and BLE 5.x, plus a digital I2C temperature/relative-humidity sensor.
Architecture
  • USB-C receptacle configured as a 5 V sink with CC pull-downs.
  • Protected 5 V input path with reverse blocking, over-voltage protection, under-voltage lockout, and over-current protection for 0.5–3 A source capability.
  • 3.3 V rail generated from protected 5 V for MCU and sensor.
  • ESP32-S3-WROOM module provides Wi-Fi/BLE and USB/UART programming/debug.
  • SHT31-DIS digital T/RH sensor connected by I2C.
  • UART debug/programming header and boot/reset support.
Key implementation choices
  • MCU: ESP32-S3-WROOM-1-N16R8 module to simplify RF certification/layout and provide dual radio.
  • Sensor: Sensirion SHT31-DIS on I2C.
  • Regulator: AP2112K-3.3 LDO for simple, low-noise 3.3 V rail; adequate for USB-powered consumer sensor node.
  • Protection: 5 V eFuse stage used as protected power-path controller with enable, current-limit, and fault signaling.
  • PCB: compact 50 mm × 50 mm 4-layer board with continuous ground reference for RF/EMI performance.
Firmware pin map
  • I2C SDA: ESP32-S3 IO8 to SHT31 SDA
  • I2C SCL: ESP32-S3 IO9 to SHT31 SCL
  • SHT31 ALERT: ESP32-S3 IO5
  • USB D+: ESP32-S3 IO20
  • USB D-: ESP32-S3 IO19
  • UART TXD0/RXD0 routed to debug header
  • EN and IO0 include reset/boot biasing for programming support
Layout requirements
  • USB-C at board edge for cable access.
  • ESP32-S3 module at board edge with antenna facing outward and copper/component keepout under antenna.
  • Power protection and regulator grouped near USB-C.
  • SHT31 placed away from regulator/MCU heat sources and near board air exposure.
  • 5 V path sized for up to 3 A using wide traces/copper pours; 3.3 V rail sized for MCU peak current.

  • Goal

  • Architecture

  • Key implementation choices

  • Firmware pin map

  • Layout requirements