USB C Sensor Node
Worked for 1 min 56 sec
Built the schematic for a USB-C powered Wi‑Fi/BLE temperature + humidity sensor node using ESP32‑C3‑MINI‑1‑N4, SHT40, TPS25940 eFuse protection, MP28301 3.3 V buck regulation, USB-C CC pull-downs, USB data ESD, VBUS TVS, reset/boot controls, status LED, and test pads. I also created the key project files: Project Specification, Power Budget and Design Notes, Firmware Starter, Board Bring-Up Plan, and Technical Construction File.
Open items:
- I’m blocked from continuing because your account currently has no available ACUs, so AI tools are unavailable.
- Full check results show expected PCB airwires because layout/routing has not been done yet.
- Several generic passives/testpoints still need final manufacturer part numbers before manufacturing export.
- Layout still needs antenna keepout, SHT40 thermal isolation, USB-C ESD placement, and buck-regulator power-loop placement.
Suggested next steps:
- Refill/enable ACUs, then ask me to finish verification and clean remaining manufacturing metadata.
- Proceed to PCB placement with ESP32 antenna edge keepout and isolated SHT40 placement.
- Route the board, then run DRC/ERC again.
- Lock exact passive/inductor MPNs and generate manufacturing files.
Verify, layout, export
Finish verification
Place components
Route and review
Lock MPNs
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Project Specification — USB-C WiFi T-RH Sensor Node
Project Overview
Status: Draft schematic complete / pre-layout.
USB-C powered consumer environmental sensor node measuring temperature and relative humidity, with Wi-Fi 2.4 GHz 802.11 b/g/n and BLE 5.x connectivity using an ESP32-C3 module.
Intended Use
- Indoor consumer environmental monitoring.
- Powered from USB-C 5 V default sources.
- Intended for prototype-to-consumer-product development; final enclosure, airflow, labeling, and compliance testing remain open.
What the Device Should Do
- Accept 5 V power from a USB-C receptacle as a sink-only device.
- Protect the downstream electronics against overvoltage, undervoltage, overcurrent/short circuit, reverse current, ESD, and controlled inrush.
- Regulate protected 5 V down to 3.3 V for the radio MCU and sensor.
- Measure temperature and relative humidity with a digital I2C sensor.
- Provide Wi-Fi and BLE connectivity for reporting data.
- Provide USB native debug/programming plus reset/boot controls and manufacturing test pads.
Main Features
- ESP32-C3-MINI-1-N4 Wi-Fi/BLE module with integrated antenna.
- Sensirion SHT40-AD1B-R2 temperature/RH sensor on I2C.
- USB4215-03-A USB-C receptacle with independent 5.1 kΩ Rd pull-downs on CC1/CC2.
- TPS25940LRVCR input eFuse for OVP/UVLO/OCP/reverse-current protection.
- MP28301GG-P low-IQ synchronous buck for 3.3 V rail.
- USB D+/D− ESD protection and VBUS TVS.
- Reset/BOOT buttons, status LED, UART and power test pads.
System Architecture
Table
| Block | Implementation | Notes |
|---|---|---|
| USB-C input | J1 USB4215-03-A | 5 V sink-only; no USB-PD negotiation. |
| Input protection | D1 VBUS TVS, D2 USB ESD, U3 TPS25940 | OVP/UVLO/OCP/reverse current/inrush. |
| 3.3 V rail | U4 MP28301 buck, L1 2.2 µH | CTRL1/2/3 tied high for 3.3 V OUT1. |
| Wireless MCU | U1 ESP32-C3-MINI-1-N4 | USB D− GPIO18, USB D+ GPIO19. |
| Sensor | U2 SHT40 | I2C address 0x44, SDA GPIO5, SCL GPIO6. |
| UI/debug | LED1, S1/S2, TP1–TP5 | Status LED GPIO3, reset EN, BOOT GPIO9. |
Power/data flow: USB-C 5 V → VBUS ESD → TPS25940 eFuse → 5V_PROT → MP28301 buck → 3V3 → ESP32-C3 + SHT40. USB D+/D− route through ESD to ESP32-C3 native USB pins.
Hardware Subsystems
Power and Protection
- J1 VBUS_A/VBUS_B tied to VBUS_RAW.
- CC1/CC2 each use independent 5.1 kΩ pull-downs to GND for USB-C sink attach.
- U3 TPS25940 settings:
- R10 = 88.7 kΩ sets ~1 A current limit.
- R11/R12/R13 = 768 kΩ / 68.1 kΩ / 160 kΩ sets approximately UVLO 4.33 V and OVP 6.16 V.
- C5 = 10 nF sets controlled output ramp, roughly 4 ms at 5 V.
- U4 MP28301 buck:
- 5V_PROT feeds VIN1/VIN2.
- CTRL1/CTRL2/CTRL3 high selects 3.3 V OUT1.
- CTRL4/CTRL5 low disables unused LDO output.
MCU / Wireless
- U1 ESP32-C3-MINI-1-N4 on 3V3.
- EN has 10 kΩ pull-up, 1 µF RC delay, and reset button to GND.
- GPIO9 has 10 kΩ pull-up and BOOT button to GND.
- GPIO8 and GPIO2 have 10 kΩ pull-ups for safe boot strapping.
- USB native debug: GPIO18 = USB_D−, GPIO19 = USB_D+.
Sensor
- U2 SHT40 powered from 3V3.
- SDA on GPIO5, SCL on GPIO6.
- One pair of 4.7 kΩ I2C pull-ups to 3V3.
- 100 nF local VDD decoupling.
- Exposed pad intentionally not soldered/connected per Sensirion recommendation to avoid heat-sink effects.
Interfaces and Connections
Table
| Interface | Nets | Components | Notes |
|---|---|---|---|
| USB-C power | VBUS_RAW, 5V_PROT, GND | J1, D1, U3 | 5 V only, sink role. |
| USB data | USB_DP, USB_DM | J1, D2, U1 | Native ESP32-C3 USB Serial/JTAG. |
| I2C | I2C_SDA, I2C_SCL | U1, U2, R7, R8 | SHT40 at 0x44. |
| Reset/boot | ESP_EN, ESP_BOOT_GPIO9 | S1, S2, U1 | Manual recovery/programming. |
| Test pads | 3V3, GND, UART_TXD0, UART_RXD0, ESP_BOOT_GPIO9 | TP1–TP5 | Bring-up and manufacturing access. |
Power and Runtime Expectations
- Power source: USB-C 5 V default, compatible with default-current, 1.5 A, and 3 A sources.
- The design does not negotiate USB-PD and must not assume 3 A is available.
- Target peak input current is below 500 mA for default-current compatibility.
- Low-power behavior depends heavily on firmware Wi-Fi duty cycle and disabling status LED when idle.
Power Tree and Power Budget
See
Power Budget and Design Notes for detailed calculations. Summary:- 3V3 rail peak design load: about 602 mA with ESP32 radio peak + SHT40 heater + LED.
- Buck rating: 700 mA; adequate but heater should not be run continuously during sustained Wi-Fi TX.
- USB/eFuse current limit: about 1 A; normal operating peak estimated below 500 mA input.
Manufacturing and Assembly Expectations
- SMD assembly assumed.
- Generic passives assigned 0603 or 0805 footprints; inductor assigned SMD_MAPI-3012.
- RF module antenna keepout and sensor thermal isolation are layout-critical.
- Final manufacturing export requires PCB layout, DRC, and enclosure/mechanical review.
Firmware-Relevant Hardware Requirements
- Arduino/PlatformIO starter firmware targets ESP32-C3.
- GPIO5/GPIO6 I2C bus reads SHT40.
- GPIO3 drives status LED.
- GPIO0 reads eFuse IMON analog output.
- GPIO4 reads eFuse PGOOD.
- GPIO7 reads buck PG1.
- USB CDC/JTAG available via USB-C.
Physical Design Expectations
- Place ESP32-C3 antenna at board edge with no copper/components in keepout on all layers.
- Place SHT40 away from ESP32, buck regulator, USB connector, LED, and hot copper. Prefer an enclosure vent and optional thermal moat/slot.
- Place ESD devices close to USB-C connector.
- Keep buck power loop compact and away from sensor/antenna.
Important Design Decisions
- Chose ESP32-C3-MINI-1-N4 module instead of bare IC to reduce RF design/certification risk.
- Chose buck regulator instead of LDO to avoid ~0.85 W heat at 500 mA peaks.
- Chose true eFuse TPS25940 for robust input protection instead of a simple load switch.
- Routed USB D+/D− for programming/debug, not just power.
- Did not add USB-PD controller; product remains 5 V-only USB-C sink.
Assumptions
- Indoor consumer use, plastic enclosure, no battery.
- USB-C is for 5 V power plus USB 2.0 device/debug data.
- Default-current compatibility is more important than drawing 3 A.
- Wi-Fi current bursts are around 500 mA on 3V3.
- SHT40 heater use is occasional and firmware-limited.
Change Notes
- Initial schematic created with power/protection, MCU, sensor, debug, and documentation.
Project Overview
Intended Use
What the Device Should Do
Main Features
System Architecture
Hardware Subsystems
Power and Protection
MCU / Wireless
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
