Stitch candidate

USB-C microSD reader prototype

A custom RP2040 board intended to expose a removable microSD card as a USB drive. It uses 2 MiB external firmware flash, a 12 MHz crystal, USB-C, and a switched SPI card interface.

Status: design stage. No board has been assembled or bench tested. Hardware file checks pass. UART bring-up firmware is included; SD and USB Mass Storage firmware still need implementation.

The design

• 55 × 30 mm, four layers, components on both sides.
• USB full speed at 12 Mb/s; storage throughput has not been measured.
• An initial qualification target of 8–32 GB SDHC cards over SPI.
• A switched card supply and Nexperia Ioff buffer to limit back-power.
• BOOT and RESET buttons, activity LED, SWD pads, UART, and supply test points.

The external flash stores firmware. User files would live on the removable card, with the host owning its filesystem while USB storage is active.

What has been checked

The root A1 files were checked with KiCad 10.0.6 on 2026-10-01 after correcting the issues found in the initial review.

Current check logs, publication changes, and the original review provide the evidence and limits. The firmware build record is included with the current evidence.

These results establish file consistency and selected design rules. USB signal quality, enumeration, storage behavior, connector fit, current, temperature, and suspend behavior still need physical tests. The documented USB reference-plane discontinuities remain an open prototype qualification issue; there is no controlled-impedance or compliance claim.

Files to use

The local libraries resolve through ${KIPRJMOD}. Standard KiCad 10 models are needed for the 3D view. revisions/A2/ is an archived preparation workspace, not a completed revision. work/ contains historical generation scripts and intermediate layouts; regenerating can overwrite reviewed routing.

Next steps

1. Confirm remaining exact-part sources and the fabricator's actual stackup. Review the USB route and two-sided QFN assembly before ordering a small prototype batch.
2. Inspect the assembled board, measure its supplies with current-limited power, and check ROM recovery and UART diagnostics.
3. Implement SD initialization and USB Mass Storage, including the current, suspend, removal, and errata policies.
4. Test disposable-card write/readback, both USB plug orientations, temperature, and interrupted writes. Publish photos and measurements when those tests exist.

An enclosure and debug fixture have not been designed. The RP2040 exposed-pad QFN needs reflow assembly.

The project uses scripted generation, local autorouting, and AI-assisted drafting and review. Library sources and terms identify upstream material. Original work has no broader reuse license selected; the included KiCad library collection retains its upstream license.