With the recent teardown of the Raspberry Pi 500, there were immediately questions raised about the unpopulated M.2 pad and related traces hiding inside. As it turns out, with the right parts and a steady hand it only takes a bit of work before an NVMe drive can be used with the RP500, as [Jeff Geerling] obtained proof of. This contrasts with [Jeff]’s own attempt involving the soldering on of an M.2 slot, which saw the NVMe drive not getting any power.
The missing ingredients turned out to be four PCIe coupling capacitors on the top of the board, as well as a source of 3.3 V. In a pinch you can make it work with a bench power supply connected to the pads on the bottom, but using the bottom pads for the intended circuitry would be much neater.
This is what [Samuel Hedrick] pulled off with the same AP3441SHE-7B as is used on the Compute Module 5 IO board. The required BOM for this section which he provides is nothing excessive either, effectively just this one IC and required external parts to make it produce 3.3V.
With the added cost to the BOM being quite minimal, this raises many questions about why this feature (and the PoE+ feature) were left unpopulated on the PCB.
Featured image: The added 3.3v rail on the Raspberry Pi 500 PCB. (Credit: Samuel Hedrick)
Looking forward to seeing the complete list of parts and a set of instructions on how to do this. I’d like to have a Pi500, but I’m done with SD card onboard storage. There are 100’s of makerspaces that have the solder level skills to help the average consumer make this a possibility.
I’ll guess that after the Holidays that TEMU will be full of NVME PI500’s
The author of that mod posted the BOM on his Twitter profile.
I’d rather insert the Pi500 widthways into an intimate orifice than use Xitter but I’m sure it’ll soon be available on places that aren’t sewers of hatred.
Why those features were left unpopulated is pretty obvious: It raises the BOM and manufacturing costs enough that another $5 or $10 would have to be added to the price. And Raspberry Pi really does try to keep these things affordable. We’ll just hope that the plus/pro module does show up before much longer.
I don’t really see how it would even add $5 to the BoM. It’s the 4 pictured capacitors, a 3V3 buck IC, a couple more capacitors, and an inductor. At quantity that can’t be more than $3, even with a 10W buck PMIC.
I had already decided to stay away from rpi products, I’m just not their target audience anymore, but the unusable m.2 slot seems bizarre to me.
The DC/DC’s literally 18 cents at qty 1000 from a distributor, they’d be able to get it cheaper. The additional BOM cost is without a doubt sub-dollar. Maaaybe if they weren’t clever it’d be what, 4 extra line items at most (forgot the inductor and likely a feedback resistor that’s probably unique).
Could be testing issues, but I’d guess with that clip-together design it’s the extra effort needed to make it so that it doesn’t need to be opened.
I was feeling the same way about the regulator, but then remembered that some drives can pull shocking amounts of power. Anecdotally, it seems like 10W is roughly the most you can expect, and when I checked Digikey it looked like, through them, 3A 3V3 bucks cost just over $2 at quantity.
But wait! I was looking on my phone so filtering was clunky. You can get a fully featured (soft-start, high-frequency, PFM mode) TI 3V3 3.7A buck converter for 29c. So yeah, <$1 BoM cost. Obviously, that was enough to make someone flinch, but I think it’s ridiculous.
“It raises the BOM and manufacturing costs enough that another $5 or $10”
Yeah, no. The parts in total are sub-dollar in large quantity and it’s two line items.
I think it’s more they don’t want to encourage people to take it apart, and avoiding that would require an opening of some sort, and that would likely add to the price enough.
A dollar on the BOM is multiple dollars on the sales price.
It’s also more than two lines, there’s a regulator, the ancillary parts (6 if they’re using the datasheet example), the socket, the coupling caps.
They already have the socket on the BoM.
Wouldn’t this just mean that they couldn’t get the nvm slot work reliably in all circumstances? That’s what I would first think of when it’s not populated at all.
Seems logical.
The article seems to imply the SSD has its own regulator so I doubt it’s run off the main 3.3V rail
Is it possible that there is not enought power on the 3V3 rail for some additional hardware?