[dragontamer]

Really?

The most critical portion of the connector is MicroSD, which is just simple SPI signaling. (This is how the Rasp. Pi CM4 seems to boot up from).

There's "difficult" portions: PCIe 2.0, HDMI, Ethernet, and USB 2.0 are all differential pairs. But all of them seem optional and can be left disconnected. I don't expect the differential pair to be especially hard to do in KiCAD if you need one of these features though.

Looking through the manual, I can see that Rasp. Pi CM4 requires 3x power rails (5V, 3.3V, and 1.8V), as well as a startup sequence wherein enable-pins come up at the right timing. But a few MOSFETs and a few capacitors in the right places solve that problem (and maybe a couple hours of simulation in LTSpice).

In my experience though, popular parts will have power-up sequences figured out somewhere. There's probably a chip that just automatically starts up a Rasp. Pi CM4 by now (and if not, at least a premade design that we can copy/paste from the internet).

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What looks difficult to you about the Rasp. Pi CM4??

[jacquesm]

I've put together some small scale SMD stuff. My hands are no longer steady enough to be able to do this stuff reliably, a USB connector is about the limit of what I can manage (under a microscope, at that) manually so that rules out simply connecting to the module directly.

So any kind of use of this device starts off with PCB design whereas the most obvious uses for me would be to use them to create computing fabrics so I'd like to be able to just send power and networking to them but then I'm suddenly back at the regular raspberry pi. I don't see the point of having 400 lines into and out of a compute node. I'd simply like a denser version of the Pi that still has enough RAM to make it count.

The Pico with castellated i/o is about my comfort zone, but it is hard to use that for any kind of networked solution (or you'd have to go wireless).

Of course you could use a breakout board and just wire up power and ethernet but then you're already back to the same price of a regular Pi and you lose the density advantage.

[dragontamer]

Fair enough. 0.4mm pitch is definitely looking difficult from a physical assembly perspective.

I guess I thought you were talking about the difficulty of the PCB design, not necessarily the physical tweezers + soldering iron needed to assemble this.

[jacquesm]

Between failing eyesight (+3.5 now) and unsteady hands this stuff is way out of my league right now and I don't think I have to hope for a reversal on either. Maybe I could train one of my kids ;) Of course I could design a board and order that but that sort of negates the whole advantage. I liked the SODIMM edge connector format much better (and at 0.6 mm pitch it too is probably outside of my comfort zone, but not nearly as far and with some tricks I can probably do that).

The real reason I think I'm a bit disappointed is that Raspberry Pi stuff tends to the end of the hobbyist market where a low barrier to entry is what gets people into the devices and this one breaks that pattern it is simply an industrial intermediary product, not something aimed at end users.