USB-C Smart Sensor Node Design
Worked for 2 mins 30 sec
I ran out of execution credits before I could finish wiring and validating the schematic.
Completed so far:
- Renamed the project to USB-C ESP32 Environmental Sensor Node and updated the description.
- Created project files:
- Project Specification
- Power Budget
- Selected and added the main schematic components:
- ESP32-C3-MINI-1-N4 Wi-Fi/BLE MCU module
- SHT40 temperature/humidity sensor
- TPS25940 eFuse for reverse/OVP/UVLO/OCP protection
- TPS62840 750 mA ultra-low-IQ buck regulator
- USB-C receptacle
- USB data ESD protection
- VBUS TVS diode
- Reset and boot buttons
- Status LED
- Buck inductor
- Consulted datasheets for ESP32-C3, SHT40, TPS25940, USB ESD, and VBUS TVS.
Remaining work:
- Fetch/verify the TPS62840 datasheet using a corrected URL.
- Add all required support passives: buck caps/VSET parts, eFuse ILIM/OVP/UVLO/dVdT parts, USB-C CC resistors, I2C pull-ups, MCU/sensor decoupling, EN RC, LED resistor.
- Wire all nets.
- Mark unused ESP32/module pins correctly.
- Run schematic review/ERC and fix violations.
- Create firmware starter and board bring-up project files.
- After schematic is clean, ask for confirmation before moving to layout.
Finish schematic wiring
Calculate buck passives
Complete USB-C input
Run design review
Add firmware notes
Refine this doc
Ask about this doc
Project Specification
Project Overview
Status: Draft
USB-C powered consumer environmental sensor node measuring temperature and relative humidity, with Wi-Fi and Bluetooth Low Energy connectivity.
Intended Use
Indoor consumer environmental monitoring node powered from a 5 V USB-C source. Intended for prototype-to-consumer design direction with production-oriented SMD parts.
What the Device Should Do
- Accept 5 V from a USB-C receptacle using default USB-C sink behavior.
- Measure temperature and relative humidity using a digital sensor.
- Communicate over 2.4 GHz Wi-Fi 802.11 b/g/n and BLE 5.x.
- Operate from a protected 5 V input and regulated 3.3 V rail.
- Support low-power operation when not actively transmitting.
Main Features
- ESP32-class dual-radio MCU module with integrated antenna.
- Digital I2C temperature/humidity sensor.
- USB-C 5 V sink input with CC pull-downs.
- Reverse/OVP/UVLO/OCP input protection sized for 0.5–3 A USB-C sources.
- Efficient 3.3 V regulator for Wi-Fi peak current.
- Boot/reset controls and status LED.
System Architecture
USB-C 5V -> input protection/eFuse -> 3.3V regulator -> Wi-Fi/BLE MCU
-> T/RH sensor
MCU I2C <-> T/RH sensor
USB-C CC1/CC2 -> 5.1k sink pull-downs
Hardware Subsystems
- Power input: USB-C receptacle, sink CC resistors, VBUS ESD/transient protection, protected 5 V path.
- Power protection: reverse/overvoltage/undervoltage/overcurrent protection for variable USB-C source capabilities.
- Regulation: 5 V to 3.3 V efficient regulator sized for radio transmit peaks.
- Compute/radio: Wi-Fi + BLE MCU module with integrated RF front end and antenna.
- Sensor: digital I2C temperature/humidity sensor with local decoupling.
- User/debug: reset/boot controls and status LED; firmware prepared for serial logging.
Interfaces and Connections
- USB-C: VBUS, GND, CC1, CC2; USB data optional for firmware if MCU pinout supports it.
- I2C: SDA/SCL with one shared pull-up pair to 3.3 V.
- GPIO: status LED, boot button, reset/enable button.
Power and Runtime Expectations
USB-C powered only. Low-power firmware should use sleep between readings, but Wi-Fi transmit peaks dominate power sizing.
Power Tree and Power Budget
Initial sizing assumptions:
- MCU Wi-Fi TX peak: up to ~500 mA on 3.3 V for short bursts.
- MCU active typical: ~80–250 mA depending on Wi-Fi/BLE state.
- T/RH sensor: sub-mA average, low peak.
- Status LED: configurable, ~2–5 mA target.
- 3.3 V regulator target: at least 600 mA peak capability, preferably >=750 mA.
- USB-C input protection target: compatible with 0.5 A, 1.5 A, and 3 A-capable sources; firmware/hardware should not assume 3 A is always available without CC current detection.
Manufacturing and Assembly Expectations
SMD production-oriented consumer design. Use module-based RF to avoid custom antenna matching.
Firmware-Relevant Hardware Requirements
- Configure Wi-Fi and BLE radio.
- Poll T/RH sensor over I2C.
- Support low-power sleep between samples.
- Drive status LED.
- Provide boot/reset access for programming and recovery.
Physical Design Expectations
ESP32 module antenna must be placed at a PCB edge with keepout under and in front of antenna on all copper layers.
Important Design Decisions
- Use an ESP32-C3/S3-class module rather than bare RF SoC.
- Use an efficient buck regulator rather than a small LDO to reduce heat during Wi-Fi peaks.
- Use an I2C digital humidity/temperature sensor.
Assumptions
- USB-C is sink-only, 5 V default, no USB Power Delivery negotiation.
- Consumer indoor environment, not industrial temperature unless later requested.
- Compact SMD assembly is acceptable.
Change Notes
- Initial specification created from user request.
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
