Reading schematic details for J1, U1, U2 and 8 more.
Thought for a moment
Considering debug options
I'm thinking about the UART ISP on GPIO_8/9 not being connected for debugging. Maybe we could add test points, but right now we don’t have any. I'm considering using J2 pins 7/8 instead, but I wonder if SWD would be enough as it typically suffices for debugging. Skill suggests including UART updates, and datasheet backs that up. I’ll probably go with J2 pin 7 for UART_TX and pin 8 for UART_RX instead of using TDI, since SWD might cover it.
Evaluating GPIO Connections
I’m considering wiring for the U1 pins and determining which should be set to "no connect." The pins I've used include JTAG_TMS, JTAG_TCK, GPIO_8, and others. I need to list all unused GPIO that should not connect, possibly including the RF pins for the built-in antenna. I’m also thinking about the USB connector pins and whether certain capacitors might be necessary. Should I mark OUT2 as NC and remove C8 if LDO is disabled? I'll need to check the datasheet as well.
Considering pin configuration
I want to avoid a single-pin output, but using a capacitor could be okay. I’m thinking if CTRL4
I want to design a compact PCB for my NCS wearable monitoring system using an ESP32, AD8232 ECG, MAX30102 PPG, MPU6050 IMU, FSR pressure sensor, and microSD module. Use GPIO34 for ECG output, GPIO32/33 for LO+/LO−, GPIO21/22 for I2C, GPIO35 for FSR, and GPIO5/23/19/18 for microSD SPI. Power the system using a 3.7 V Li-Po battery with TP4056 charging, an ON/OFF switch, and a suitable voltage regulator. Please verify all connections and power requirements, add necessary protection/filtering components, minimize ECG noise, and create the schematic and compact 2-layer PCB layout.
No changes were made to the NCS wearable design. The current project still contains parts from the earlier USB‑C Wi‑Fi/BLE sensor concept.
Remaining: create and verify the ESP32 wearable schematic, Li‑Po charging/protection and regulation, ECG filtering/noise controls, then place and route the compact 2‑layer PCB. Execution is currently unavailable because your account has no ACUs.
A consumer USB-C powered temperature and relative humidity sensor node with Wi-Fi and Bluetooth Low Energy connectivity. The board uses a protected USB-C 5 V sink input, local 3.3 V regulation, a low-power Wi-Fi/BLE MCU module, and a digital I2C T/RH sensor.
Intended Use
Indoor consumer environmental monitoring node.
Powered from USB-C 5 V chargers, hubs, or ports.
Designed for prototype-to-production learning; not medical, industrial safety, or outdoor/weatherproof use unless later specified.
What the Device Should Do
Measure ambient temperature and relative humidity.
Connect over 2.4 GHz 802.11 b/g/n Wi-Fi.
Support BLE 5.x provisioning or local telemetry.
Power from USB-C default 5 V sources.
Survive common consumer input faults with reverse-current, overvoltage, undervoltage, and overcurrent protection.
Main Features
USB-C receptacle configured as sink-only with independent CC1/CC2 5.1 kΩ Rd resistors.
Protected 5 V input sized for 0.5–3 A capable sources, while the node itself is expected to draw well below 500 mA average.
3.3 V logic rail for MCU and sensor.
Native USB data/programming path where supported by the selected MCU.
Boot/reset controls, debug/programming access, and status LED.
System Architecture
Diagram
Hardware Subsystems
Power input: USB-C receptacle, CC pull-downs, VBUS ESD/TVS, protected power switch/eFuse or load switch with OVP/UVLO/OCP/reverse-current blocking.
Regulation: 5 V to 3.3 V rail sized for Wi-Fi transmit current peaks.
Compute/radio: certified ESP32-family module preferred to avoid custom RF matching and simplify regulatory work.
Sensor: digital I2C temperature/humidity sensor with local decoupling and one shared I2C pull-up pair.
User/debug: reset and boot controls, status LED, USB programming, optional exposed test/debug header.
Interfaces and Connections
External: USB-C 5 V power and USB 2.0 D+/D- for programming/debug.
Internal: 3.3 V rail, GND, I2C SDA/SCL, boot/reset, status LED GPIO.
RF: integrated 2.4 GHz antenna module; PCB layout must provide the module antenna keepout.
Power and Runtime Expectations
Source: USB-C 5 V default power only; no battery in this revision.
Source capability planning: tolerate 0.5 A, 1.5 A, and 3 A capable USB-C sources. Do not assume the device may draw 3 A unless CC current advertisement is measured/implemented.
Low-power behavior: firmware should sleep between samples and radio transmissions, but USB-powered operation makes absolute sleep current less critical than thermal and regulatory behavior.
Power Tree and Power Budget
Table
Rail
Load
Sleep
Typical active
Peak
3.3 V
Wi-Fi/BLE MCU module
~10–100 µA deep sleep
~80–240 mA radio active
~500 mA short Wi-Fi TX burst
3.3 V
T/RH sensor
<1 µA standby
~0.5–1 mA measuring
~1 mA
3.3 V
Status LED
0 mA off
~2 mA on
~5 mA configured max
3.3 V
Pull-ups/leakage
~1–2 mA worst when lines low
negligible average
~1.4 mA for two 4.7 kΩ pull-ups low
Estimated 3.3 V rail sizing target: 250 mA typical active, 510 mA transient peak. For an LDO from 5 V, input current is approximately output current; thermal at 250 mA is about (5.25 V - 3.3 V) × 0.25 A = 0.49 W, so a small SOT-23 LDO may be marginal during sustained Wi-Fi. Preferred choices are a high-current low-Iq regulator in a thermally capable package or a quiet buck regulator if sustained radio current/thermal limits demand it.