Mehrdad Majzoobi Releases an Open-Hardware PCIe M.2 Adapter Board for the Raspberry Pi 5
If you fancy building your own Hardware Attached on the Bottom (HAB) M.2 adapter, grab this KiCad project and get to it.
Maker Mehrdad Majzoobi has released yet another open-hardware Raspberry Pi 5 accessory, developed as part of the Ubo Pod project — this time a Hardware Attached on the Bottom (HAB) PCI Express M.2 adapter.
"Even though similar boards are widely available for purchase under $10 nowadays, I have had issues with some causing interference with Wi-Fi, lacking LED indicators, FPC [Flexible Printed Circuit] cable blocking microSD Card reader, etc.," Majzoobi explains of the reason for going the DIY route over buying off-the-shelf. "Since I am designing a whole system with enclosure, I needed more control over board dimensions and flex cable positioning and length."
The Raspberry Pi 5 launched last year as the first mainstream model in the popular single-board computer range to offer access to a PCI Express Gen. 2 lane — the performance of which can be boosted to Gen. 3 rates, if you don't mind running outside official specifications. Delays in the launch of an official adapter to take the in-house flat flexible circuit (FFC) connector to an M.2 slot saw third-parties pop up with their own designs — many of which flip the classic Hardware Attached on Top (HAT) concept and instead sit underneath the single-board computer as a Hardware Attached on the Bottom (HAB) device.
It's this latter style that Majzoobi picked, basing his board design on the work of George Smart who was the first to build an adapter by reverse-engineering the Raspberry Pi 5 FFC pinout — even before Raspberry Pi had released official specifications. It also comes hot on the heels of Majzoobi's release of a passive M.2 A/E-key adapter board, designed to make it easier to swap between high-speed Non-Volatile Memory Express (NVMe) modules and accelerators for machine learning and artificial intelligence workloads.
"This was my first experience with high-speed PCIe and I learned a lot about PCIe standard," Majzoobi says of the project. "I also designed the flex cable that goes with this board."
More information is available in Majzoobi's Reddit post; KiCad project files have been published to the Ubo Pod GitHub repository under the reciprocal GNU General Public License 3, along with an FFC for connecting it to the Raspberry Pi 5. "I am working on V2 of this board," he notes of this latter design, "that incorporates several improvements."