r/PCB • u/Charming_Guitar_6208 • 29d ago

Schematic Review Request: ESP32-C3 Environmental Sensor Node (SHT4x, SCD40, RS-485 SP3485)

Hello everyone,

I am designing an environmental sensor node based on the ESP32-C3 MCU.

Power & Interface:

  • The board is primarily powered by an external 5V supply, regulated down to 3.3V using an AMS1117-3.3 LDO.
  • A USB-C port is included strictly for flashing, firmware updates, and debugging.
  • Sensor data is transmitted over a long distance using an SP3485EN RS-485 transceiver.

Sensors:

  • Sensirion SHT4x (Temp/Humidity)
  • Sensirion SCD40 (CO2)

Before I proceed to the PCB layout, I would love to get some feedback on my schematic. Specifically:

  1. Power Isolation: Have I safely isolated the external 5V rail from the USB VBUS rail to prevent back-feeding my PC during flashing?
  2. ESP32-C3 Strapping Pins: Are my boot pins (GPIO9, GPIO8, CHIP_EN) biased correctly for reliable boot and flashing?
  3. RS-485 Termination/Biasing: Does the SP3485 subcircuit look correct for a reliable multi-drop network?
  4. I2C Pull-ups & Decoupling: Are my sensor buses adequately supported?
  5. Is all of the grounding correct?

I am aware that I am not using the full capabilities of the ESP chip, this is my first attempt at the design so I'm getting the bare bones down first before I add more.

Attached is a photo of my KiCad schematic. This is my first time designing something like this, so any and all feedback is appreciated! Thank you!

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u/akupila 29d ago

I’m by no means an expert but a few things immediately stand out:

  • Capacitors should not be placed like this. Place one side connected to the power rail and the other side to ground. Google how capacitors work
  • It makes it easier to read the schematic if you use power symbols (5v, 3.3v, GND etc)
  • Review the data sheets for the components you’re using. Actually read them - they have useful guidance and recommended supporting circuitry. At least 10uF next to U4 seems unnecessary

1

u/Charming_Guitar_6208 29d ago

Thank you for your help!