Stm32-field node

STM32 Field Node

A compact STM32G031-based microcontroller board with USB-C power, 3.3 V regulation, SWD debugging, and a 2-layer PCB.

Status

Hardware revision: Rev A
Fabrication: Gerber and drill files generated
Assembly: Not assembled
Validation: Not electrically validated

KiCad ERC passes cleanly. PCB DRC has no connectivity or manufacturing-rule violations; the intentional local USB-C footprint override is excluded from the library-mismatch check.

Hardware

MCU

• STM32G031K8T6
• ARM Cortex-M0+
• LQFP-32
• 3.3 V operation

Power

Power is supplied through USB-C.

USB-C 5 V
    |
    v
TLV75533 LDO
    |
    v
3.3 V
    |
    v
STM32G031

The board uses:

• TLV75533 3.3 V LDO
• 1 µF input capacitor
• 4.7 µF output capacitor
• 100 nF MCU decoupling
• 4.7 µF local bulk capacitance

USB-C

USB-C is used for 5 V power input only. Firmware programming and debugging are provided through the SWD header.

• 5 V VBUS
• 5.1 kΩ Rd resistors on CC1 and CC2
• D+ and D− not connected
• TVS protection on VBUS
• Shield connected to GND

Debug

The board exposes an SWD programming/debug header:

This can be connected to an ST-Link or compatible SWD debugger.

Key Components

PCB

• 2-layer PCB
• Components placed on the front side
• F.Cu used primarily for signal and power routing
• B.Cu maintained primarily as a continuous GND plane
• SMD passive components
• LQFP-32 MCU
• USB-C receptacle
• Dedicated GND vias for local decoupling and power circuitry

The PCB includes custom front silkscreen artwork and board identification.

Design Notes

Decoupling

The STM32 supply uses a local 100 nF decoupling capacitor placed close to the MCU VDD/VSS pins.

Additional 4.7 µF bulk capacitance is provided on the 3.3 V rail.

LDO

The TLV75533 converts USB VBUS from 5 V to 3.3 V.

Input and output capacitors are placed close to the regulator to minimize local power-loop impedance.

Ground

The bottom copper layer is used as a GND plane.

Critical ground connections, including MCU decoupling, regulator bypass, and VBUS transient protection, use short connections to nearby vias into the ground plane.

USB-C Footprint

The GCT USB4105 footprint is locally overridden to increase NPTH-to-copper clearance.

The four affected GND pads were reduced from 0.60 mm × 1.15 mm to 0.60 mm × 1.00 mm.

The modification applies to A1, A12, B1, and B12.

This local override intentionally differs from the KiCad library footprint, and the corresponding library-mismatch DRC warning is excluded.

Repository Layout

hardware/
├── fab/
│   ├── drill/
│   │   ├── stm32-field-node-NPTH.drl
│   │   └── stm32-field-node-PTH.drl
│   └── gerber/
│       ├── stm32-field-node-B_Cu.gbr
│       ├── stm32-field-node-B_Mask.gbr
│       ├── stm32-field-node-Edge_Cuts.gbr
│       ├── stm32-field-node-F_Cu.gbr
│       ├── stm32-field-node-F_Mask.gbr
│       ├── stm32-field-node-F_Silkscreen.gbr
│       └── stm32-field-node-job.gbrjob
├── reports/
│   └── DRC.rpt
├── stm32-field-node.kicad_pcb
├── stm32-field-node.kicad_pro
└── stm32-field-node.kicad_sch

Fabrication

Gerber and Excellon drill files are available under hardware/fab/.

The fabrication package contains:

• Front copper
• Back copper
• Front solder mask
• Back solder mask
• Front silkscreen
• Board outline
• Plated through-hole drill data
• Non-plated through-hole drill data
• Gerber job file

The generated files have been inspected using KiCad Gerber Viewer.

Before ordering a new revision, regenerate the fabrication files from the current PCB source and run DRC again.

Bring-Up

Recommended first power-up procedure:

1. Check resistance between 3V3 and GND.
2. Check resistance between USB_5V and GND.
3. Apply USB power with current limiting if available.
4. Verify USB_5V.
5. Verify +3V3.
6. Check the LDO for unexpected heating.
7. Connect ST-Link.
8. Verify that the MCU can be detected over SWD.
9. Read the MCU device ID.
10. Flash minimal test firmware.
11. Verify reset operation.
12. Verify basic GPIO operation.

Revision History

Rev A

Initial hardware revision.

• STM32G031K8T6 MCU
• USB-C 5 V power input
• TLV75533 3.3 V regulation
• VBUS transient protection
• SWD programming and debugging interface
• 2-layer PCB with bottom GND plane
• Initial fabrication package