STPM34 Breakout

STPM33 Breakout

KiCad 10 open-hardware breakout for the STMicroelectronics STPM33 metering ASIC. It measures one isolated voltage channel and two current-transformer channels, making it useful for phase/neutral comparison, tamper detection, and two-current experiments sharing one voltage reference.

Front end

• Supply: 3.3 V.
• Voltage input: isolated 9 VAC transformer secondary only.
• Current inputs: two 100 A:50 mA CTs.
• Current burdens: 2.4 ohm differential, giving 120 mV RMS at 100 A.
• Current filters: 100 ohm series resistors and 330 nF capacitors.
• Voltage divider: symmetric 200 kohm / 2.49 kohm legs.
• Voltage filters: 1 kohm series resistors and 33 nF capacitors.
• Clock: 16 MHz crystal.
• Grounding: separate GNDA and DGND pours joined through NT1. NT1 is a copper net tie; no component is fitted there.

This is not an isolated mains-input board. Connect only isolated low-voltage sources and follow applicable electrical-safety practices.

J1 pin map

Underside pads expose INT1, INT2, LED1, LED2, and CLKOUT/ZCR.

SPI/UART selector

STPM33 supports SPI or UART, not I2C. SJ1 biases SCS through R14 at power-up:

• Pads 1-2 are closed by default, selecting SPI with a DGND bias.
• For UART, cut pads 1-2 and bridge pads 2-3 to bias SCS to +3V3.
• Press SW1 after changing SJ1 so EN is asserted low and the interface mode is sampled again.

Rebuilding

Run the scripts from the repository root:

python .\scripts\build_stpm33_schematic.py
python .\scripts\apply_stpm33_bom.py
& "C:\Program Files\KiCad\10.0\bin\python.exe" .\scripts\build_stpm33_pcb.py

Routing uses Freerouting with Java 25:

$env:JAVA25 = "C:\Program Files\Eclipse Adoptium\jre-25.0.4.101-hotspot\bin\java.exe"
$env:FREEROUTING_JAR = "C:\path\to\freerouting-2.4.1.jar"
& "C:\Program Files\KiCad\10.0\bin\python.exe" .\scripts\route_stpm33.py
& "C:\Program Files\KiCad\10.0\bin\python.exe" .\scripts\finalize_stpm33_pcb.py

The checked-in routed PCB is the production source. Reconstruction scripts capture the schematic, mechanical envelope, placement, routing workflow, ground pours, markings, and project-local 3D/logo assets.

Manufacturing outputs

python .\scripts\apply_stpm33_bom.py
python .\scripts\render_stpm33.py
python .\scripts\generate_stpm33_gerbers.py

The Elecrow BOM is written to manufacturing. Gerbers, separate PTH/NPTH drills, Gerber job data, front/rear position CSVs, and the upload ZIP are written to gerber. The BOM contains 16 grouped unique parts and 33 fitted components.

Validation

KiCad 10 ERC and DRC are mandatory before fabrication export. The Gerber generator enforces zero ERC/DRC violations and zero unconnected items before creating the package.