USB-C Sensor Node
Worked for 7 mins 9 sec
Created 5 project docs
Project Specification — USB-C WiFi BLE T-RH Sensor
Status: Draft schematic complete / ready for review. A consumer USB-C powered environmental sensor node measuring temperature and relative h...
Design Notes and Power Budget — USB-C WiFi BLE T-RH Sensor
USB-C receptacle in 5 V sink/device mode. TPS25940LRVCR eFuse for OVP, UVLO, overcurrent, inrush control, fault telemetry, current monitor, ...
Firmware Starter — ESP32-C3-WROOM-02-N4
MCU/module: ESP32-C3-WROOM-02-N4 Framework: Arduino on PlatformIO
Board Bring-Up Plan — USB-C WiFi BLE T-RH Sensor
Equipment: USB current-limited bench supply or USB power meter, DMM, oscilloscope, USB-C cable, PlatformIO host. Firmware: see Firmware Star...
Show 1 More
I added project documentation: specification, power/design notes, firmware starter, bring-up plan, and FCC/CE notes. I’m running checks now and will fix any real schematic issues found.
Worked for 2 mins 54 sec
Implemented the schematic for the USB-C powered Wi‑Fi/BLE temperature/humidity sensor node with ESP32-C3, SHT40, TPS25940 input protection, TPS62840 3.3 V buck, USB programming, CC current sensing, boot/reset, and status LED. ERC/passive checks are clean; remaining reported errors are expected pre-layout airwires and generic-passive MPNs to resolve before manufacturing.
Project files created:
- Project Specification
- Design Notes and Power Budget
- Firmware Starter
- Board Bring-Up Plan
- Regulatory FCC/CE Notes
Suggested next steps:
- Do PCB placement with ESP32 antenna keepout and SHT40 thermal isolation.
- Route USB D+/D−, buck power loop, and sensitive sensor/ADC nets.
- Assign production MPNs to generic passives.
- Run full DRC/manufacturing checks after layout.
Place, route, assign MPNs
Start PCB placement
Route critical nets
Assign passive MPNs
Run full checks
Review USB-C compliance
Refine this doc
Ask about this doc
Project Specification — USB-C WiFi BLE T-RH Sensor
Project Overview
Status: Draft schematic complete / ready for review.
A consumer USB-C powered environmental sensor node measuring temperature and relative humidity and reporting data over Wi-Fi and BLE 5.x. The design uses a pre-certified Espressif ESP32-C3 wireless module, Sensirion SHT40 I2C T/RH sensor, protected 5 V USB-C input, and an ultra-low-IQ 3.3 V buck regulator.
Intended Use
- Indoor consumer environmental monitoring node.
- Powered from USB-C 5 V adapters, hosts, or hubs.
- Designed to operate within a conservative sub-500 mA input budget while detecting Type-C current advertisement for firmware policy.
What the Device Should Do
- Accept 5 V over USB-C in sink/device mode.
- Protect downstream electronics against overcurrent, overvoltage, undervoltage, reverse-current/backfeed, ESD, and inrush.
- Measure temperature and relative humidity digitally.
- Connect using 2.4 GHz Wi-Fi 802.11 b/g/n and BLE 5.x.
- Support firmware flashing/debug over native ESP32-C3 USB Serial/JTAG.
Main Features
- ESP32-C3-WROOM-02-N4 Wi-Fi + BLE module with integrated PCB antenna.
- SHT40-AD1B-R3 I2C temperature/humidity sensor, address 0x44.
- USB4105-GF-A USB-C receptacle with separate 5.1 kΩ Rd resistors on CC1/CC2.
- CC1/CC2 ADC sensing through 100 kΩ resistors to classify default / 1.5 A / 3 A Type-C source advertisements.
- TPS25940LRVCR eFuse input protection with adjustable UVLO/OVP/OCP and true reverse-current blocking.
- TPS62840DLCR 3.3 V, 750 mA, 60 nA-IQ buck regulator.
- Reset and boot buttons, status LED, eFuse PGOOD/FLT monitoring, eFuse IMON ADC telemetry.
System Architecture
Diagram
Hardware Subsystems
USB-C Input and Protection
- USB-C sink role via R1/R2 = 5.1 kΩ from CC1/CC2 to GND.
- D2 protects raw VBUS; D1 protects D+/D−; D4/D5 protect CC1/CC2.
- U3 TPS25940 provides protected VBUS, inrush control, current limit, adjustable UVLO/OVP, fault output, current monitor, and reverse-current blocking.
3.3 V Power
- U4 TPS62840 buck converts protected 5 V to 3.3 V.
- L1 = 2.2 µH, C7 = 4.7 µF input, C8 = 10 µF output, R20 = 267 kΩ for 3.3 V.
- MODE pulled low for automatic power-save mode; STOP pulled low so the converter runs by default.
Wireless MCU
- U1 ESP32-C3-WROOM-02-N4 powered from 3.3 V.
- EN has 10 kΩ pull-up and 1 µF reset delay capacitor; reset button pulls EN low.
- GPIO9 has 10 kΩ pull-up and boot button to GND for download mode.
- GPIO2 and GPIO8 have 10 kΩ pull-ups for valid boot/download strapping.
- USB D−/D+ route to GPIO18/GPIO19 through 22 Ω series resistors.
Sensor
- U2 SHT40 powered at 3.3 V with 100 nF local decoupling.
- I2C on GPIO4/GPIO5 with one 4.7 kΩ pull-up pair to 3.3 V.
- Layout must place the sensor away from ESP32, buck regulator/inductor, eFuse, USB-C shell, and LED heat.
Interfaces and Connections
Table
| Interface | Nets / Pins | Notes |
|---|---|---|
| USB-C VBUS | VBUS_RAW → TPS25940 → VBUS_PROT | 5 V only; no PD negotiation |
| USB-C CC | USB_CC1/USB_CC2 | 5.1 kΩ Rd plus ADC current advertisement sense |
| USB 2.0 FS | USB_DN_CONN/USB_DP_CONN → 22 Ω → USB_DN_MCU/USB_DP_MCU | Native ESP32-C3 USB Serial/JTAG |
| I2C | I2C_SDA GPIO4, I2C_SCL GPIO5 | SHT40 address 0x44 |
| eFuse status | EFUSE_PGOOD GPIO7, EFUSE_FLT_N GPIO10 | Pulled up to 3.3 V |
| Analog telemetry | VBUS_IMON GPIO3, CC1_SENSE GPIO0, CC2_SENSE GPIO1 | ADC inputs |
| User controls | ESP_EN, ESP_BOOT | Reset and boot buttons |
Power and Runtime Expectations
- USB-C 5 V input only; no battery.
- Target conservative operation below default USB current. CC sensing allows firmware to adapt behavior for default / 1.5 A / 3 A sources.
- Worst-case 3.3 V load target: <= 750 mA regulator capability; normal operation expected far lower.
Power Tree and Power Budget
Diagram
See the Design Notes file for calculations and threshold values.
Manufacturing and Assembly Expectations
- SMT assembly, consumer product orientation.
- Keep ESP32 antenna at board edge with full antenna keepout.
- Keep SHT40 exposed to airflow and isolated from heat sources; avoid contamination and conformal coating over sensor.
- Add test access in layout for 5 V raw, protected VBUS, 3V3, GND, EN, BOOT, I2C, and USB if possible.
Firmware-Relevant Hardware Requirements
- Platform: Arduino or ESP-IDF on ESP32-C3.
- Firmware should read CC1/CC2 ADC at startup and limit high-current behaviors when default current is detected.
- Firmware should avoid sustained SHT40 heater operation; SHT40 heater duty cycle must remain below datasheet limit.
- USB Serial/JTAG flashing via USB-C with BOOT/RESET buttons.
Physical Design Expectations
- Small 2-layer or 4-layer PCB; 4-layer recommended for RF/USB cleanliness.
- ESP32 antenna at edge with no copper, traces, screws, enclosure metal, or components in keepout.
- Buck inductor and eFuse away from ESP32 antenna and SHT40.
- SHT40 near an airflow opening, with thermal relief/slots if enclosure allows.
Important Design Decisions
- Use ESP32-C3-WROOM-02-N4 module instead of bare SoC to reduce RF design/certification risk.
- Use TPS25940 eFuse instead of a simple polyfuse to satisfy OVP/UVLO/OCP/reverse-current requirements.
- Use TPS62840 buck instead of LDO to avoid 0.5–0.85 W LDO heating during Wi-Fi peaks.
- Use passive USB-C sink plus CC ADC sensing, not USB-PD, because product only needs 5 V.
Assumptions
- USB-C source provides 5 V only; no power delivery voltage negotiation required.
- Device target current remains below USB default current in normal operation.
- Consumer indoor environmental range, not industrial/outdoor sealed operation.
- BLE means BLE 5.x only, not Bluetooth Classic.
Change Notes
- Initial schematic created with MCU, sensor, USB-C, eFuse protection, buck regulator, boot/reset, USB programming, CC sensing, and documentation.
Project Overview
Intended Use
What the Device Should Do
Main Features
System Architecture
Hardware Subsystems
USB-C Input and Protection
3.3 V Power
Wireless MCU
Sensor
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
