Kingfisher hat

Kingfisher Sensor HAT (rev 0.3)

Custom HAT for the extra-tall GPIO header above the M.2 HAT+. It replaces the cabin SparkFun NEO-M9N and ICM-45686 breakouts. The schematic netlist is checked. The board is routed on JLCPCB stackup JLC04161H-7628. Gerbers and drills are in fab/. Confirm header engagement, the CR2032 against the lid, and that the GNSS antenna is active before ordering.

Outline is the official Pi HAT (65 × 56.5 mm, M2.5 on 58 × 49 mm).

The GPS circuit follows UBX-19014285 and UBX-19014286: V_USB grounded, UART pull-up on D_SEL, 33 Ω on TX/RX, ML414H directly on V_BCKP charged through an LM4040-3.0 and 34 kΩ, and a 27 nH / 100 nF bias-T into the antenna. The CR2032 does not back up the GPS and has no charge path. There is no UPS on this board. See docs/DESIGN.md.

Open in KiCad

KiCad 9 (generated against 9.0.2).

kicad hardware/hat/kingfisher-hat.kicad_pro

Libraries:

• libs/Kingfisher.kicad_sym — ICM-45686, BMP581, NEO-M9N
• libs/Kingfisher.pretty — ICM-45686 (TDK pin numbers), BMP581, ML414H

Regenerate with system Python, not a uv venv. pcbnew comes from python3-pcbnew.

python3 hardware/hat/scripts/build_libs.py
python3 hardware/hat/scripts/build_sch.py
kicad-cli sch export netlist -o /tmp/kingfisher-hat.net hardware/hat/kingfisher-hat.kicad_sch
python3 hardware/hat/scripts/check_netlist.py /tmp/kingfisher-hat.net
python3 hardware/hat/scripts/place_pcb.py
python3 hardware/hat/scripts/route_pcb.py

check_netlist.py is the schematic check. It passed for rev 0.3 (69 nets). place_pcb.py keeps the template socket and mounting holes and deletes tracks. route_pcb.py restores the route and the 4-layer stackup.

Status

Done:

• Schematic for the GPS replica, TDK IMU land, BMP581, RV-3028, both backup cells, X1200 header, test points, and the GPS power LED
• Netlist check against datasheet pin numbers
• Parts placed on the HAT outline, clear of the notch, the slot, the mounting holes, and the header
• Routed, including the 0.32 mm U.FL microstrip (bare Z0 about 50.2 Ω at the pressed 7.1 mil / Er 4.4 height). Soldermask pulls that down about 1–2 Ω
• JLC04161H-7628 stackup filled in. Error-level DRC is clean
• Gerbers and drills in fab/

Still to confirm on the aircraft, and still open in software:

• Female-header engagement, lid clearance over the CR2032, pin 1 against the real extender, and whether the GNSS antenna is active
• i2c-rtc for the RV-3028, a cabin BMP581 reader, and an AHRS mount matrix measured from this board's silk

Attribution

• Outline and GPIO socket: KiCad Raspberry Pi HAT template
• BMP581 pads: SparkFun Qwiic BMP581 hardware, CC-BY-SA 4.0
• ML414H pads and the GPS power circuit: SparkFun NEO-M9N SMA / SparkFun-Batteries
• NEO-M9N symbol: derived from the KiCad NEO-M8N symbol
• ICM-45686 pad centers: IPC LGA-14. Pin numbers and axes: TDK DS-000577