from the what-will-they-think-of-next? dept.
Ras Pi foundation announces a new product: the compute module.
The compute module contains the guts of a Raspberry Pi (the BCM2835 processor and 512Mbyte of RAM) as well as a 4Gbyte eMMC Flash device (which is the equivalent of the SD card in the Pi). This is all integrated on to a small 67.6x30mm board which fits into a standard DDR2 SODIMM connector (the same type of connector as used for laptop memory). The Flash memory is connected directly to the processor on the board, but the remaining processor interfaces are available to the user via the connector pins.
While not yet what I imagined by only the name i.e a unit to build a shoebox-sized Beowolf cluster of 1K-RasPi-cores the new form factor and pin-out should make this endeavour easier (ahem... for someone skilled in PCB design, EE practician, and a soldering-fu master that has achieved enlightenment... not quite my profile).
(Score: 1) by meisterister on Thursday April 10 2014, @12:10AM
...welcome our new Slot 3 overlords!
(May or may not have been) Posted from my K6-2, Athlon XP, or Pentium I/II/III.
(Score: 1) by crutchy on Thursday April 10 2014, @09:43AM
my heart started beating like crazy when i saw the first photo... i think i'm in love!
(Score: 2) by edIII on Thursday April 10 2014, @12:15AM
I'm not that deep into hardware apparently.
Is this connected into a memory slot on laptop motherboards or something? Or does it mention the laptop memory just to indicate profile and pins?
If you are adding to this to an existing system I guess I am really confused as to why it would be in the memory slot specifically.
Probably a stupid question, but I'm definitely missing something here from the article.
Technically, lunchtime is at any moment. It's just a wave function.
(Score: 3, Informative) by BsAtHome on Thursday April 10 2014, @12:27AM
It is simply a form-factor. It does not emulate a RAM-DIMM. It is the same connector as SODIMM uses because that is "cheap".
The better question would be: what will it cost?
(Score: 2) by aristarchus on Thursday April 10 2014, @01:05AM
Granted it is not RAM, but before I worry about what it costs, what does a raspberry Pi _do_ in a slot?
(Score: 3, Interesting) by tftp on Thursday April 10 2014, @02:17AM
It is the same connector as SODIMM uses because that is "cheap".
Perhaps, if you buy in volume. However in quantity one it costs $10 [newark.com].
Also note that the PCB pads are 0.35 mm wide, and the pad to pad clearance is only 0.25 mm. This connector is very expensive to put onto a PCB. Even an experienced tech with a benchtop reflow machine and solder paste may have hard time. A guy at home, with a $20 soldering iron? Forget it.
I think I understand what R-Pi people are tryng to do here. They are not after a hobbyist. They want to be a component provider; they want to sell R-Pi modules as parts, in millions. This is not an entirely bad idea. I am interested.
(Score: 2, Interesting) by NoMaster on Thursday April 10 2014, @04:41AM
Cool. I'll remember that while I'm hand-soldering the handful of VSSOP & TSSOP chips on the board I just made.
It's not for the faint-hearted or blind, but it can be done with a bit of practice. It's a certainly not "forget it"...
Live free or fuck off and take your naïve Libertarian fantasies with you...
(Score: 1) by tftp on Thursday April 10 2014, @05:05AM
I hope you aren't using a cheap soldering iron for that. I have a Metcal soldering station with a good assortment of tips, and a microscope. Just those two cost more than $1K together. You also may need a hot air pencil and some solder paste (though it does not play nicely with hot air.) Perhaps some hobbyists can afford good tools, but generally the costs are paid by some business.
A week ago I hand-soldered three W5100 ICs [digikey.com]; they have pin spacing of 0.40 mm. This is more dense than the SODIMM connector that we are discussing (0.6 mm.) This was hard. I will need to install two more. Perhaps IR reflow would be wiser... but I have no time to order the stencil, and there are no thermal pads underneath.
As SMT goes, I would say that TQFP/TSSOP with 1 mm pin spacing, and anything >= 0805, are reasonably easy to install with an inexpensive soldering iron. Quality of installation of smaller parts degrades quickly, unless professional technologies are used. Those boards with W5100s are populated with 0402s - and I am not happy about the amount of solder that ended up on the pads. But I can't do much about that - I'd have to use solder paste to deposit less solder, or find a 5-10 mil solder. (I was using 16 mil.)
(Score: 1) by NoMaster on Friday April 11 2014, @04:29AM
Late back, but:
It's perfectly possible with a cheap setup; you don't need $1000's worth of gear. I normally use an Ersa analogue station (don't like the balance of the Metcals) & an old modified Olympus stereo dissection microscope, but just for giggles I did one of the boards with my old gear - a cheap Atten station with T18-05C & 08D tips, working under a maggylamp from the hardware store. Total cost AU$100.
Working distance was as crap as you'd imagine (I ended up coming in from the side & using the corner of the 0.8mm D tip, as I couldn't get the face of the C tip square onto the joint), and you need plenty of flux, a steady hand, a good eye, and the experience to know what the solder is doing while the joint is hidden by the tip - but, soldering the 0.5mm & 0.65mm pitch TSSOP & VSSOPs, the results are as good as any hand-soldered SOT-223 or SOIC.
And that was hand-soldering every pin individually - I'm old-school enough that I can't bring myself to do the typical "flood 'em with solder & wick up the excess" method everyone seems to favour, and it doesn't work well on home-made boards without soldermask anyway...
Live free or fuck off and take your naïve Libertarian fantasies with you...
(Score: 1) by tftp on Friday April 11 2014, @05:36AM
Yes, that was a difficult job. My microscope is currently one of those Omano things [microscope.com]. It works fine, and the lens is protected from smoke with a clear filter. I never work under a magnifying lamp - just not my thing. I don't even have such a lamp.
One of big concerns with "flood them and wick them" is overheating of the part. I try to avoid such a method.
With regard to homemade boards without a soldermask... is it worth it if you can order three boards made, with SM and silkscreen, for $33 each [4pcb.com]? Or such a service is not available in .au? A 2-layer board would be pretty horrible in terms of EMC, but a hobbyist isn't likely to try for CISPR 22 Class B. Given the minimum trace/space that they accept, one can build a copy of IBM/360 on one board without making even a single jumper (as long as you put power rails on top, as they used to do :-)
(Score: 1) by NoMaster on Friday April 11 2014, @09:30AM
Very nice at that price! I'm off to investigate it further. The (lack of) DoF on my old Olympus is an issue...
Agreed, and that's another reason I don't do it (the first two being that basically it makes me cringe, and by the time you wick up the excess it doesn't seem any faster than pin-by-pin...)
True - but if you send them out you can't have prototypes in your hand by lunchtime ;). The ones I did yesterday are built and functionally tested already; I'm about to rejig the design a bit and will send them out to be made while I finish the software.
Since getting out of the trade I mostly do small low-speed data & sub-VHF radio stuff (e.g. those boards are I2C + interface logic, 4MHz signal amp/buffer, programmable silicon oscillator, & associated passives), so can usually get away with predominantly single-sided (the other side is left mostly as groundplane, except for the odd jumper track & where it has to be pulled back e.g. for amp stability).
As you say, EMC compliance rarely raises its head for home-built stuff (although I sometimes think it should, particulaly with the rise of switchmode supplies designed by hobbyists!), and all my commercial experience is with telco stuff (serial 56 under the Aus regs). I also sometimes think things like the RPi are a bit of a sneaky end-run around the regs - the RPi itself has passed but, given that they're starting to appear as a component of at least semi-commercial gear, I wonder how much of that is being tested (& would pass)?
Is it still CISPR 22 Part B in most of the world? Aus seems to have already started transitioning to CISPR 32; I'll have to look up the differences sometime...
Live free or fuck off and take your naïve Libertarian fantasies with you...
(Score: 2) by anubi on Thursday April 10 2014, @08:08AM
As far as soldering this thing, I would use lots of rosin-type flux and solder wick. The idea is to wet everything with solder ( yes, you will get lots of bridging ), then use the solder wick to remove the excess solder. Kinda like spilling a whole pail of water on the floor then mopping it up. When you get enough solder wicked back up, there is enough left on the pad to make a secure wetted contact, but not enough excess left to make a bridge. Anyway, that is the way I get those tiny parts I can barely see ( let alone see the leads to ) soldered. Then clean off the board with lots of alcohol. Personally, I like to use a bowl of "dirty" alcohol and a paint brush to remove most of the flux, then finish off with pure alcohol from a spray bottle interspersed with bursts of compressed air for a final cleaning. I have successfully soldered some really tiny parts doing this using some rather antique soldering tools. I prefer denatured ethanol if I can get it, but I have also used isopropyl sold in drug stores with good results.
The most important thing seems to make darned sure your part is positioned over the pads squarely, which means you gotta use your tweezers and microscope. First, position your part. Apply solder only to an end pin first first, as you will use it as an anchor to hold the part. When you have it positioned accurately, drop another anchor with the opposing pin. Make sure you get your part exactly placed. You get several do-overs if your iron is not too hot and you use a good low-temp solder and lots of extra rosin flux ( you can get it in little vials at many electronic stores ).
I cannot stress enough to make sure your part is centered on the pads. Once you apply solder to the whole thing, it is darned near impossible to move it around anymore without damaging something unless you have the proper reworking tools. A non-centered part's leads will bridge the pads making a solder job nearly impossible.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
(Score: 1) by tftp on Thursday April 10 2014, @08:49AM
Here's what I found in China.... There are lots of pics of the connector here.
That sounds very reasonable. My link was about the original TE part, but this is a no-name production. I am not brave enough to enable JavaScript on that Web site, though, so I can't see much of pictures. Those SODIMM connectors also come in several variants, but I'm sure the right one is available.
As far as soldering this thing, I would use lots of rosin-type flux and solder wick.
Yes, that's what one has to do if the part has pin spacing under 1 mm. It's possible, but highly unlikely to solder the part without bridging simply because the tip of the iron is larger than several pins - and that is even if you use the smallest tip that there is. (Otherwise it won't transfer enough heat. It's already a concern with small tips.) Professionals use preheating of the board.
Another possibility is to spread low-temp solder paste onto the pads (but the amount has to be just right) and then heat the area. This is hard to do with a hot air pencil because the solder paste will produce droplets of solder that will ruin your circuit. You need IR, but for that it would be better to begin with this method. A toaster oven and a multimeter with a thermocouple will do just fine.
I would strongly advise against using any alcohol that is sold in drug stores. It contains too much water. Water does not evaporate fast enough, and it interferes with cleaning (does not dissolve rosin.) I bought a gallon of ethyl alcohol in a chemical supply store for $40. This will be enough for me nearly forever. It is denatured with a tiny amount of methyl alcohol, but it won't harm you unless you drink it in quantity :-) In professional environment a water-soluble flux is used (I have some, it's cheap) but then you need to wash it off with deionized water [puretecwater.com]. In mass production this is a significant advantage over using the expensive ethanol and then dealing with pollution.
The most important thing seems to make darned sure your part is positioned over the pads squarely, which means you gotta use your tweezers and microscope.
If you use solder paste then this problem becomes a non-problem. Solder paste is sold in small tubes for about $15; mine comes from a nearby store, but there are other sources [digikey.com]. It has to be stored in a refrigerator, but still it won't last more than a year or two - then it dries up and does not print well through the stencil.
Professional stencils are cut with laser from a sheet of stainless steel foil. They are pretty expensive ($300 for a set.) Hobbyists (and small time professionals) can use stencils that Pololu makes [pololu.com] from plastic. I had ordered some, and they were quite OK for the task at hand. Not good for mass production, of course, but they are fine for a few boards.
A hobbyist probably will not manage the two-sided SMT IR reflow assembly. This requires a machine that can maintain the exact temperature profile on each side of the board individually.
I cannot stress enough to make sure your part is centered on the pads. Once you apply solder to the whole thing, it is darned near impossible to move it around anymore
Two-pin parts, like passives, can be easily moved around with two soldering irons. I have one cheap Chinese soldering station that is not as good as Metcal, but it is handy when I need to remove a resistor. Removal of larger ICs is impossible without some sort of rework station [zeph.com]. I have one (not Zephyrtronics,) but it's very old and cannot reach the melting temperature of RoHS solders. You also need a whole bunch of nozzles for it, and they are expensive - and you need many of them, since there are so many different IC packages. If you simply want to remove a part, you can use a heat gun (that painters use to strip paint.) However its airflow is extremely high, so you have a good chance of desoldering about a hundred 0201 parts around the IC that you need to remove - and all of them will be blown away. Still, I have seen it done.
Otherwise - yes, parts need to be properly centered. This is not hard with passives. But TQFP packages, with pins on all sides, require careful placement before you commit. Do not accept any skew because it eats into the clearance between pins. Usually it's enough to tack one pin to position two sides, and then tack another on the opposite end. Once you are happy, solder the rest. But... do not neglect to check where the pin #1 is :-)
(Score: 2) by anubi on Friday April 11 2014, @01:43AM
I can tell for sure you have been around the bush a few times! ;)
I have even used your heat gun trick to remove boardfuls of components at a time, with the exact result you reported: blown away. But I did get some SMD parts recovered to use on other things.
Love your warning about pin#1. Done that a couple of times myself. Sure made me mad when I realized what I had done wrong.
About the wide tip and bridging... that's what the rosin-soaked solder wick is for. The wick will absorb the excess solder so there isn't enough material left to make a bridge, but there will be ample left to wet the area between pin and pad. With my older iron, typically the end of the iron covers darned near a dozen pins. The solder itself is several pins wide. So I run my iron and wick along the part after I have soldered it down and its full of bridges ( sometimes a solid bridge ), using the wick to remove the bridges. The solder that wicked up between the pin and pad stays there. The remaining pins hold the part in place while I am wicking up the excess.
Thanks for the stencil link. I have really got to learn about how do do this.
You are so right about the drug store isopropyl.... I do not like to use the drug store stuff for the exact reason you stated... its got too much water in it. The best stuff I got was some stuff from the hardware store that was marked I believe as lacquer thinner and came in a gallon can.
As far as the China link to AliExpress: I have used them a few times and found them to be a decent supplier, albeit you have to watch your descriptions and shipping/pricing closely. My own findings were that buying consumer items was tricky, as my experience has shown I would have come out better just going to a retail store where I could personally inspect the thing before purchase. The expense of shipping often is more than the price of the item ( even if the merchant offers free shipping from China; if you get the item and it fails to meet your expectations, you are expected to return it at your expense. Fair enough I guess. Order a couple of samples and be prepared to just "eat it" if they are not what you thought.)
I have used their dispute arbitration system ( and in all cases I called on it, they ruled in my favor ), however I used it only as a last resort before calling on VISA to reverse the charges - also knowing I would forever be barred from any future transactions through Ali. So far, I have had pretty good experiences buying parts and assemblies such as Arduino compatibles, power converters, and LED assemblies. I have presently got an order with them for a lot of IRF510, which I intend to use in building another power supply for my METCAL. I have always wanted a small 12-volt soldering iron, and I was lucky enough to get a dozen handpieces for these at a surplus house ( the power supplies were all blown ). Being I have worked in RF a lot, to me these looked just like a 13.56 MHz CCFL ( cold-cathode fluorescent lamp ) driver to me. No biggie.
A little offtopic: I understand your reluctance to enable JavaScript. I have noted that it is darned near impossible for me to go to Amazon anymore, and I cannot help but think I am infected with something that interferes with Amazon, yet my own virus scanners tell me I am clean. I hardly ever buy from Amazon anymore, as I do not know whether or not Amazon just got a new script-crazy webmaster, or did I pick up something from China that is inhibiting Amazon. For me, the AliExpress site works, Alibris works, Amazon is slow as all getout and is apt to simply lock up at the oddest moment. I am running a WIN7 box with Firefox/NoScript.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
(Score: 2) by egcagrac0 on Thursday April 10 2014, @12:05PM
I, personally, would look at brushing the component leads with solder paste, then carefully aligning the part, then sticking it in a toaster oven.
(Score: 2) by anubi on Friday April 11 2014, @12:46AM
I have heard about this method but I have never tried it. I heard about it in Circuit Cellar. Even collected several old toaster ovens to try doing it this way. I always thought I would have problems with cooking the board as well as its components, but have no practical experience to back up that belief.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
(Score: 1) by lentilla on Friday April 11 2014, @01:10AM
Now all we need is a SO-DIMM socket that fans the connections into a wider pinout.
(Score: 1) by tftp on Friday April 11 2014, @01:30AM
Now all we need is a SO-DIMM socket that fans the connections into a wider pinout.
I am not sure how would that be more useful than the standard R-Pi. But if enough people want it, there is nothing stopping them to make such a breakout board. I certainly could lend a hand, considering that I work with this stuff day and night for fun and profit. The only catch is that I have no easily accessible manufacturing contacts in China. So either the boards are made in the USA, with appropriate premium, or a SN member in China volunteers to shake a tree on that side of the planet.
(Score: 1) by timbim on Thursday April 10 2014, @06:22AM
And also: will it blend?
(Score: 4, Funny) by egcagrac0 on Thursday April 10 2014, @12:30AM
I heard you liked computers, so we put a computer in your computer so you can compute while you compute.
(Score: 1) by Ethanol-fueled on Thursday April 10 2014, @12:47AM
In the dystopic future, due to increased recognition of hardware signatures and NWO control of the internet and the access regulations thereof, inexpensive and disposable self-contained computers will be your only way to get your rocks off getting away with posting that first-post troll on Soylent News...again.
(Score: 2) by egcagrac0 on Thursday April 10 2014, @12:52AM
This sounds like a job for virtualization.
(Score: 1) by lajos on Thursday April 10 2014, @01:47AM
(offtopic)
Ethanol-fueled your posts are amusing. You should put your blog in your signature, or if you don't have one, you should start one and then put it in your signature.
Maybe you'll have a picture of yourself on your blog, too. Until then, I'll imagine you as late 1940s, mid baby-bloomer, cranky, cigar smoker dude typing away on a 1990s mechanical keyboard.
(/offtopic)
(Score: 0) by Anonymous Coward on Thursday April 10 2014, @02:24AM
(offtopic) I'm not going to shove myself [tinypic.com] up your ass farther than I already do. (/offtopic)
(Score: 2) by Kilo110 on Thursday April 10 2014, @01:10AM
Can someone educate me why this form factor is preferable to the existing one?
Who would find this useful and for what reason?
(Score: 3, Insightful) by egcagrac0 on Thursday April 10 2014, @01:28AM
The new form factor is smaller. The connector on the compute module is (almost) cheap-as-free (card edge connectors are), the mating connector is ubiquitous and similarly cheap.
Since almost everything is stripped off, there are more I/O lines available.
This isn't so much targeted at hobbyist users as people in industry who might embed it into something else, and only have to design a much simpler interface board, instead of a whole system.
(Score: 4, Interesting) by iwoloschin on Thursday April 10 2014, @01:58AM
Hi, EE/Hardware Engineer here.
I just finished designing a board with a similar "Computer On Module", but the one I picked has a Texas Instruments AM335X processor, the same family as the BeagleBone Black. I picked it due to some familiarity with BBB, and the fact that it's super easy to get Linux running on it now. Designing a board isn't necessarily hard, but it's not something most people will be doing. You can actually use KiCAD to do all of the design work, it's F/OSS, and it's not much compared to some of the really fancy packages, but it gets the job done. Even if you spent the time to design a board, I don't know anyone who's going to happily hand solder a SO-DIMM 200 connector. I goofed one of my prototype boards and had to hand solder half of a SO-DIMM 204 connector, and let me tell you, it sucked. A lot. These connectors are designed for automated placement and reflow, not home users with a $20 soldering iron.
So, basically, I'm confused by this. It's a neat idea, simple to implement, but who's going to use it? This space is saturated with CoM vendors, using more open ARM processors, with more features built onto the CoM, though many of them are in the $100-$500 range, not $30. So maybe companies can use this, but I know that I'm not going to bother, since there's other options that are better for me. Home users might use it, but they're not making their own one-off boards for this. I could maybe see companies making daughter-expansion boards that provide more features, but I'm not sure that's a very lucrative market. Then again, maybe I should go design a few boards and throw them on Kickstarter and see what happens.
(Score: 2) by c0lo on Thursday April 10 2014, @02:30AM
From the comments of TFA (a blog post really): ---
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https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 1) by tftp on Thursday April 10 2014, @02:53AM
Yes, it would. As James says, you'll need to design your own PCB, though.
I used those connectors before, and their footprint is in the CAD. It would cost me about 1 hour to produce Gerbers. A few more if you want additional breakout connectors. The catch is in cost, though. Even if the design is free, the manufacturing of the PCB won't be. As a bare minimum you are looking at $66/each (in small quantity) or about $25 each in quantity 25-50. Cheaper boards can be had only in even higher volume, in China. It remains to be seen if the same PCB can satisfy enough people. They may be better off with the original R-Pi that already has all the connectors, even if from all sides of the board.
However if someone is interested in a design that would be of use for many (such as an outdoor, zero-lux HD camera that can be assembled under $100) then it's very much possible. It's a trivial breakout board for anyone who ever made a PCB.
(Score: 1) by tftp on Thursday April 10 2014, @02:34AM
You have answered your own question. I also use COM boards (from Kontron.) But they are relatively expensive, so you cannot just buy one and slap it onto an inexpensive relay board, or something. However a $30 module, and a connector that will cost you $5 in volume, is something else entirely - it may be now suddenly viable if you don't need Atom or other x86.
Personally, when I aim for the lowest cost I use Atmel AVRs - these days that would be AVR32, for my own convenience. if I need Ethernet I drop a W5100 in. This combination covers pretty much everything, except the LCD/HDMI/DP. If those are needed then you need a bigger gun. This product might be very viable, especially considering the time to market. You, as a hardware guy, just connect all wires to all pins (as we do with FPGAs, modulo clocks and bank power) and call it a day. The rest is software - and with R-Pi it can be modularized. If all you want is {Ethernet,USB,RS232,SPI,I2C} to discretes, with soft real time requirements, then R-Pi might work just fine.
(Score: 0) by Anonymous Coward on Thursday April 10 2014, @08:40AM
A lot of those COM boards are also designed for industrial apps with extended temperature range and such like. Many of them also guarantee their availability and support for many years, as well as having different options with pin compatibility e.g. faster CPU, more RAM or other peripheral choices.
I think it is this in part that pushes the price up.
It will be interesting to see if the Pi So-DIMM offers these assurances too. At $30 it could be quite disruptive.
(Score: 0) by Anonymous Coward on Thursday April 10 2014, @08:28PM