Temperature and Humidity Sensor Node Design

flux

0:00

Work done
  • Power + protection path confirmed and labeled: J1 (USB-C) -> U2 (eFuse) -> U3 (LDO) with rails VBUS_5V, VPROT_5V, 3V3, and 3V3_DECOUP.
  • Fixed bulk capacitor values on the 5 V and 3.3 V rails: C7, C8, C9, C10 set to 10uF.
  • Implemented analog front end connectivity:
    • Howland pump: U4 with matched network R3, R4, R5, R6, routed to electrode connector J2 (I+ and I-).
    • INA front end: U5 inputs wired to J2 (V_SENSE_P/V_SENSE_N), output wired to MCU ADC pin U1 PA0 (net ECG_AMP_OUT).
  • I2C bus completed with required 4.7 kΩ pull-ups: R8 on I2C_SDA, R9 on I2C_SCL, shared by U6, U7, and IC1.
  • Debug + comms nets labeled and connected: J3 (SWDIO/SWCLK/NRST) and J4 (UART_TX/UART_RX), with Wi-Fi placeholder ESP1 powered from 3V3.
  • Added floorplanning guidance (Power / Analog / Digital-RF partition, antenna keepout, guard/return guidance) as a project property, and updated the project description.
Success criteria review
  • ✅ The 3.3 V rail and power nets are defined, labeled, and decoupled (bulk + 0.1 uF network present on 3V3_DECOUP).
  • ✅ Howland pump and INA128 front end are wired and the INA output is connected to an MCU ADC pin (U1 PA0).
  • ✅ 4.7 kΩ pull-ups are placed on the I2C bus (R8, R9).
  • ✅ Key nets (SWD, UART, sensor interrupts) are labeled, and floorplanning notes include antenna keepout + guard ring guidance.
  • ✅ Schematic is partitioned at the documentation level (power / analog / digital-RF) suitable for bioimpedance mixed-signal layout.
Next steps If you want, I can do a Stage-2 pass next: assign Net Type properties (Power/Analog/Ground/etc.), pick a 4-layer stackup, and start converting remaining generic passives to real MPNs per .
69 days
varshars1711

varshars1711

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69 days

flux

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Yelling Lime Memory Implanter thumbnail
Bioimpedance + ECG/PTT node (USB-C protected 5V in, Howland pump, INA128 front end, STM32WB55 BLE, I2C sensors, SWD)

Properties

flowchart TD subgraph Power [Power] USB[USB-C 5V] --> Prot[Reverse OV UVLO OCP] Prot --> Reg33[3.3V Regulation] end subgraph Electrodes [Electrodes] EConn[Tetrapolar Electrode Connector\nI+ I- V+ V-] end subgraph Injection [Bioimpedance Injection] DAC[MCU DAC/PWM->Filter] --> Howland[Howland Current Pump\nOP07 + Matched R] Howland --> EConn end subgraph Sensing [Analog Sensing] EConn --> INA[Instrumentation Amplifier] INA --> ADC[MCU ADC] ECG[ECG/PTT Front End] --> ADC end subgraph Sensors [Digital Sensors] PPG[MAX30102 PPG] --> I2C[I2C] IMU[IMU] --> I2C SHT[SHT3x Temp/RH] --> I2C end subgraph MCU_RF [MCU and RF] Reg33 --> MCU[STM32WB55 BLE MCU] MCU --> I2C MCU --> BLE[2.4GHz Antenna\nKeepout] MCU --> OptionalWiFi[Optional Wi-Fi Module] end Power --> Injection Power --> Sensing Power --> Sensors Power --> MCU_RF

Partition PCB into 3 zones: (1) Power entry/regulation: J1 USB-C, U2 eFuse, input bulk C9/C10, LDO U3, bulk C7/C8/C11/C12. Keep high di/dt loops tight, place TVS/fuse as needed. (2) Analog: Howland current pump U4 + R3/R4/R5/R6 matched network, electrode connector J2, INA128 U5 + RG resistor R7, guard ring around INA inputs, route V_SENSE_P/V_SENSE_N as tightly-coupled pair with GND guard, keep away from SWD/UART/I2C. Star/quiet analog return to main GND near U5 and keep injection return away from sense return. (3) Digital/RF: U1 STM32WB5MMG, I2C sensors U6/U7/IC1 with pullups R8/R9, ESP1 placeholder. Antenna keepout: no copper/ground pour/components under U1 ANT area and at least 15 mm clearance in front of antenna. Keep RF path short, solid GND reference around RF except keepout. Stitch ground vias at zone boundaries.

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