Senfusion

PyFusion — RP2040 Sensor Fusion Board

A compact, custom-fabricated two-layer sensor fusion PCB built around the Raspberry Pi RP2040. Integrates a 6-axis IMU, 3-axis magnetometer, and barometric pressure sensor on a single board — programmable natively in MicroPython.

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Hardware

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PCB Design

The board is a two-layer design captured in KiCad 9.0. Layout decisions were driven primarily by the sensitivity requirements of the three MEMS sensors.

Layer Stack

• Top layer — signal routing and 3.3V power polygon pour
• Bottom layer — continuous ground plane for low-impedance return paths and shielding, with minimal routing tracks

Sensor Placement

IMU (IAM-20680HV) Placed on a mechanically stable region of the board, away from mounting holes and connectors. Requires a solid ground plane beneath it for noise reduction — copper fill is maintained under this device. The exposed ground pad is connected to the ground plane via multiple vias.

Magnetometer (IIS2MDCTR) Highly sensitive to magnetic fields from nearby copper currents. Ground plane and copper pours are cleared on both layers in the region surrounding this device. High-current traces and switching components are kept at a distance.

Barometer (BMP581) Isolated from large copper regions on both layers to prevent thermal gradients and mechanical stress from influencing pressure readings.

Key Layout Decisions

Decoupling — All bypass capacitors placed within 1–2mm of their associated VDD pins, with short via stubs to the ground plane, in accordance with each sensor's datasheet.

Crystal — ABM8-272-T3 placed as close as practical to the RP2040 XIN/XOUT pins. Load capacitors are inline. A copper pour guard ring tied to GND prevents switching-noise coupling into the oscillator.

USB differential pair — USBDP/USBDM routed as a 90Ω differential pair (0.8mm track width, 0.15mm gap on a 1mm substrate) per the RP2040 hardware design guide.

GPIO header — 23 pins expose selected RP2040 GPIO signals for external interfacing via UART, SPI, or I2C, making the board extensible rather than a closed system.

BOOTSEL and RESET — dedicated push-buttons for bootloader entry and manual reset.

KiCad Footprint Note

The IAM-20680HV KiCad footprint files were not available at the time of design. The ICM-20602 footprint was used as a drop-in substitute — the two devices share an identical package and pin layout. The assembled board uses the IAM-20680HV component on the ICM-20602 footprint without modification.

Design Verification

Before manufacture the following checks were completed in KiCad:

• Electrical Rules Check (ERC) — no unconnected pins or conflicting power nets
• Design Rules Check (DRC) — cleared against manufacturer minimums (trace width, clearance, via drill, annular ring)
• Footprint verification — each land pattern cross-checked against the manufacturer datasheet
• Gerber preview — layer stack-up, drill file, and copper patterns confirmed

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Firmware

All firmware is written in MicroPython and runs directly on the RP2040. The board was developed and flashed using Thonny IDE.

File Overview