It’s Almost A New Raspberry Pi Compute Module 4. But Not Quite

We know that readers are familiar with the global chip shortage and its effects on product availability. The Raspberry Pi folks haven’t escaped its shadow, for even though they’ve managed to preserve availability of their RP2040 microcontroller, it’s fair to say that some of their flagship Linux-capable boards have been hard to find. All of this has had an unlikely effect in the form of a new Raspberry Pi, but unexpectedly it’s one which few end users are likely to get their hands on.

The Raspberry Pi Compute Module has been part of the range since the early days, and in its earlier versions took a SODIMM form factor. The last SODIMM Compute Module had a Pi 3 processor, and this unexpected new model is reported as having a very similar hardware specification but featuring the Pi 4 processor. It seems that the chip shortage has affected supplies of the earlier SoC, and to keep their many industrial customers for the SODIMM Compute Modules in business they’ve had to produce this upgrade. As yet it’s not surfaced for sale on its own and there’s a possibility it will stay only in the realm of industrial boards, but as the story develops there’s a Raspberry Pi forum topic about it for the latest and you can find the pertinent info in the video below the break.

Of course, the Compute Module of the moment remains the CM4 in its newer form factor, which we see as possibly the most exciting of all the Pi products of the moment. Meanwhile this is not the first custom industrial Raspberry Pi to be seen in the wild.

21 thoughts on “It’s Almost A New Raspberry Pi Compute Module 4. But Not Quite

      1. Of course they don’t, the use cases for low temp are much smaller than high temp. I just happen to work with one. The real frustrating thing is that when you spec something commercial (0 to 70) it *might* work from -40 to 0. Spec it -20 to +85, much stronger chance it doesn’t.

    1. i’m having some comprehension problems. do you mean how long until pi foundation drops broadcom?

      i looked around a little bit at pi alternatives and it looks like it’s nationalized. pine64 (China) mostly sells chips from chinese companies Allwinner and Rockchip. Hardkernel aka Odroid (South Korea) mostly sells chips from Samsung (South Korea), and of course Pi Foundation (UK) uses Broadcom (US).

      i don’t have any data yet but from looking at open source support online for them, i honestly suspect pi is at the back of the pack.

      what i’m saying is if you want to ditch the broadcom tax you don’t have to wait for pi to do it, you can just use a different vendor.

      1. The Pi4 blows current Allwinner and RK offerings out of the water, at least for desktop usability experience. Now, they’re catching quick, but it’ll be a few years yet before they’ll match the Pi4. No idea on Odroid, though.

      2. I’m more talking about the flagship smartphone SoC availability in the near future. After the shortage recovery, any flagship Qcom chip from 2020+ would be a real desktop contender.

  1. The CM4 is a very nice module with lots of capability and at a great price… if you can find them. For me the negative is the silly mating connectors. The connectors themselves are not an issue… but that there are no alignment pins to ensure PCB placement is accurate. This creates all sorts of problems, as you have two 100-pin connectors with 0.4mm pitch that have to maintain a fixed separation distance to properly mate with the CM4… what could go wrong? argh…

    1. I haven’t heard of any issues… I’d imagine with how long they are and how much wetted area they have, they’d self-align pretty well.

      Also, alignment between processes (milling and copper in this case) can be one of the most difficult things of fabbing PCBs, I’ve seen values for misalignment tolerance that would get close to that pitch. It might be actively detrimental to try and locate with pins.

      1. Self alignment can be fine and is done for QFP, BGA, etc to certain degree, but in these cases the attachments are all part of the same package and so all pins, etc can move in unison. In this application there are two separate connectors and so if one shifts a bit then then this places stress on the CM4’s mating connector which could cause connectivity issues… over time, vibration, etc. In fact because of this it is important to use the CM’4 mounting holes to ensure that the module is securely fastened to the PCB.

        As for alignment pins… not an issue, as these can be easily added to the connector ends and so have no impact to the pin areas. Alignment pins are used on a lot of fine pitch connectors by the same Manufacturer (Hirose) and others and so it is surprising that a version is not offered on this one.

        On my test PCB the alignment was less than optimal and so some level of rework was necessary which was a pain. I designed an alignment jig to ensure that both connectors are properly spaced and oriented during reflow. I have not tested the jig, but will do so once I have some spare time.

        1. I believe hirose themselves in their ‘DF40 Series Guideline’ document now states “please avoid the use of more than one set of connector receptacle and plug on single board”

          I haven’t had an issue with the boards I’ve used, but it is unnecessarily annoying to deal with in production as well as in end user applications—the so-dimm form factor seems less prone to issues if it ever needs swapping out.

      2. I personally do not understand what was driving decision to change the form factor. I would love to understand what was reason behind this decision. It seems to me that SODIMM socket is so common, robust, proven etc. that on the first look it was not necessary. Well, I understand that world is colorful sometimes and there might have been nontechnical reasons a well. I do not consider myself to judge it but on my subjective feeling I kind of do feel it was mistake.

    1. Hmmm… I beg to differ in a general sense. Perhaps compared to the PiZ it is more expensive, but it has far more capabilities and is targeted towards different applications. As for the CM4’s price… For mere mortals you could not buy the parts alone for what the CM4 sells for… let alone the PCB, manufacturing, test, etc. I say this, as even the volumes I deal with with (100’s ) there is no way that I could build a comparable module for the CM4’s price… and I spent a lot of hours at doing something similar with a number of other similar processors.

    2. The Pi Zero is sold at cost or discount (I forgot which) so it can get in the hands of more people, but I remember they said if you want to buy them in bulk for commerical use it’s more expensive per unit

      1. “at cost”. Pretty sure you can’t buy _anything_ new “at cost” or even “at MSRP” these days. The MSRP for a Pi Zero is $5. $10 for Zero W.

        You can get one for $50 on ebay, and not even get free shipping. We are in the worst timeline for electronics tinkerers, for sure.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.