We’ve just written about Will Whang’s RPI5-SDexpress-Hat board, which adds a microSD Express slot to the Raspberry Pi 5, but it’s not that small, and it’s using the 40-pin GPIO for power, so it’s not convenient if you want to install another Raspberry Pi HAT+.
Vassily Petrov’s “microSD-express Pi Adapter” is a much smaller microSD Express adapter on a flexible PCB that plugs directly into the PCIe FFC connector and nothing else, driving power from the PCIe connector only.
There’s not much on the PCB itself besides a microSD Express card slot and a Microchip MIC2230 800mA/800mA step-down DC/DC regulator. We’re told speeds of up to 800 MB/s are achievable, limited by the PCIe Gen3 x1 interface on the Pi 5 itself. For reference, the RPI5-SDexpress-Hat was tested at about 600 MB/s for sequential reads and under 200MB/s for sequential writes using a 256GB Samsung microSD Express card.
A worry I initially had was whether there was enough power through PCIe at all times. In theory, a microSD Express card can consume up to 1.8 Watts on a PCIe Gen3 x1 interface, and the two 5V pins on the PCIe interface of the Pi 5 are rated at 500mA (for 1A total current), so it should be enough at 5V (5 Watts in total).
The microSD-express Pi Adapter is open-source hardware with KiCad schematics and PCB layout, PDF schematics, BoM, and Gerber files all released on GitHub, but without any clear license. If you plan to make one yourself, Vassily explains that “controlled impedance is critical for good PCIe performance. The files are designed for 50μm PI dielectric and 0.5oz copper”.
There’s no indication that Vassily plans to sell the adapter, but I would not be surprised if it eventually shows up for a few dollars on AliExpress or eBay.
Thanks to Tom for the tip.
Jean-Luc started CNX Software in 2010 as a part-time endeavor, before quitting his job as a software engineering manager, and starting to write daily news, and reviews full time later in 2011.
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This comes off the back of the Switch 2 and it’s general requirement to use a more expensive type of card. If it could become popular in the Pi 5 too then it might drive up adoption and drive down pricing.
So well worth showing the concept and for something that seems very quick and easy to install, whilst the read and write speeds are not comparable with many an M.2 SSD in a hat, likely capable enough to give users a boost that could well be worth it, if all that is required is a tiny outlay and 60 seconds on installation time.
I’d be willing to bet that the next microSD card slot on the Pi 6 will be of this type.
Perhaps we will see come November.
This seems to be missing the microcontroller to tell the uSD card to go into pci-e mode. Are they relying on the current cards on the market which default to that mode (possibly in violation to the spec?) Not sure I want to bet my future on that, but for the price, it’s not that big of a risk.
I do love the design mechanically, though. Putting the whole thing on an flex PCB is just :chefskiss: