USB-C Temperature Humidity Sensor Node
Worked for 6 mins 35 sec
I renamed the project to USB-C WiFi BLE Environmental Node and updated the description. I also created a project specification file capturing the requirements, architecture, assumptions, and initial power budget: Project Specification.
I selected and researched likely core parts:
- MCU/radio: ESP32-C3-WROOM-02-N4 — Wi‑Fi 2.4 GHz 802.11 b/g/n + BLE 5, integrated PCB antenna, native USB pins.
- Sensor: SHT40-AD1B-R2 — low-power I2C temperature/RH sensor.
- USB-C connector: USB4105-GF-A / USB-C 2.0 receptacle.
- Input protection candidate: MP5036AGJ-P eFuse/load switch, but its datasheet text was not accessible in this run, so wiring was not started.
- Regulator: AP2114H-3.3TRG1 3.3 V / 1 A LDO; datasheet confirmed 4.7 µF input/output capacitors, EN behavior, 1 A rating, and thermal limits.
- USB data ESD: USBLC6-2SC6.
- VBUS ESD: TPD1E05U06DPYR.
- Reset/boot buttons and status LED candidates were found.
Initial power sizing:
- ESP32-C3 rail should be designed for at least 500 mA peak.
- SHT40 is sub-mA during measurement, unless heater is used.
- 3.3 V rail target is about 510 mA peak minimum, so the 1 A AP2114 LDO has current margin, but layout copper/thermal handling will matter.
No schematic components were added or wired yet because execution credits ran out before the build step. Remaining work is to add components, wire the USB-C protection/regulator/ESP32/SHT40/support passives, create firmware notes, run schematic review, and fix any violations.
Add core parts
Find eFuse
USB-C input schematic
Run ERC
Document assumptions
No schematic yet
Talk to Flux to get started.
Refine this doc
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Project Specification
Project Overview
Status: Draft.
USB-C powered consumer environmental sensor node measuring temperature and relative humidity, with 2.4 GHz Wi-Fi 802.11 b/g/n and BLE 5.x connectivity.
Intended Use
Indoor consumer/IoT environmental monitoring node powered from USB-C 5 V adapters, hubs, or ports. Intended as a compact prototype/production-intent reference design.
What the Device Should Do
- Accept 5 V from USB-C in default sink mode.
- Measure temperature and relative humidity using a digital sensor.
- Communicate over Wi-Fi and Bluetooth Low Energy.
- Support low-power firmware modes when not actively transmitting.
- Survive common USB input faults using reverse/OVP/UVLO/OCP protection.
Main Features
- USB-C receptacle, 5 V default sink, planned for 0.5–3 A advertised sources.
- Protected 5 V input path.
- 3.3 V rail for MCU and sensor.
- Wi-Fi + BLE MCU module.
- I2C temperature/RH sensor.
- Boot/reset controls and programming/debug access through native USB where supported.
System Architecture
Diagram
Hardware Subsystems
- Power input: USB-C sink with CC pull-downs.
- Protection: current limiting/fuse, surge/ESD protection, reverse-current blocking, OVP/UVLO load-switch/eFuse behavior.
- Regulation: 5 V to 3.3 V rail sized for Wi-Fi transmit peaks.
- Compute/radio: integrated MCU module with Wi-Fi 802.11 b/g/n and BLE 5.x.
- Sensing: digital I2C temperature/humidity sensor.
- User/debug: boot/reset buttons, USB programming, status LED.
Interfaces and Connections
- USB-C VBUS/GND/CC1/CC2/D+/D-.
- 3.3 V rail.
- I2C SDA/SCL between MCU and sensor.
- EN/reset and boot straps.
Power and Runtime Expectations
USB powered only. Firmware should use modem sleep/light sleep between measurements where practical. No battery runtime target in this revision.
Power Tree and Power Budget
Initial estimate:
- ESP32-class Wi-Fi/BLE module: about 240 mA active Wi-Fi typical, design for 500 mA short peaks.
- Digital T/RH sensor: <1 mA active, microamp sleep.
- Status LED/debug overhead: up to 5 mA.
- 3.3 V rail design target: 510 mA peak minimum; select regulator/protection with margin.
- USB-C input path should tolerate 0.5–3 A source capability, but firmware/hardware should not assume 3 A without Type-C current detection or fixed product limits.
Manufacturing and Assembly Expectations
Consumer-use prototype with SMD components. Use module-based RF design to avoid custom RF matching and certification complexity.
Firmware-Relevant Hardware Requirements
- I2C sensor polling.
- Wi-Fi + BLE stack support.
- USB serial/programming if using native USB MCU/module.
- Boot and reset controls.
- Low-power sleep strategy.
Physical Design Expectations
Place radio module antenna at board edge with antenna keepout. Keep input protection near USB-C. Place decoupling capacitors close to IC power pins.
Important Design Decisions
- Use an ESP32-C6/S3-class module rather than bare chip for integrated certified RF path.
- Use a high-efficiency 3.3 V regulator or thermally adequate LDO after checking current/thermal budget.
- Use an I2C digital humidity/temperature sensor such as SHT4x-class for low-power consumer sensing.
Assumptions
- USB-C Power Delivery negotiation is not required; device operates from 5 V only.
- Consumer indoor temperature range unless later specified.
- No battery charging in this revision.
Change Notes
- Initial specification created from user requirements.
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
