GitHub - florolf/apu-m2: M.2 NVMe SSD adapter for PC Engines APU2 boards

This repo contains the hardware design for an adapter/holder combination that allows installing a 2280 M.2 NVMe SSD into a PC Engines APU2 board.

(This picture shows an older version of the design with some bodges applied, the version released here should just work out of the box, see below)

The original apu2 board only allows SD cards/mSATA SSDs for storage. The former is not very performant/durable and the latter is getting rarer/more expensive per GB. There's also a regular SATA connector, but regular SATA SSDs don't fit well into the standard enclosure.

Conversely, M.2 SSDs are a staple piece of hardware nowadays. PCIe/NVMe is also a nicer interface compared to SATA (although raw throughput is approximately the same here, since we are trading SATA 3.0 for 1× PCIe Gen 2).

Version 1.0 of the adapter PCB had the RX/TX lanes swapped because the mPCIe spec and the M.2 spec use different perspectives for describing the data transfer direction. Version 1.1, published here, fixes this and also adds some more assembly options for handshaking signals and additional decoupling. None of those are strictly necessary though, so the DNP annotations in the schematic reflect the electrical behavior of v1.0 (except for the RX/TX crossover), which has been working well in practice.

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