For those of you interested in the chumby One, the schematics and gerbers are now posted on chumby’s wiki in the hardware section. Hopefully, over time some of the hacks we’ve done will be documented on the wiki. Or, you could contribute and document your hacks there as well…it is a public wiki after all!
I think a short reminder is due about the hardware license attached to the schematics and gerbers. The topic of Open Source licensing is certainly one that has spawned many Holy Wars, with True Believers on all sides. Many accuse me of not being a “true” open source person, an opinion for which they are entitled to. I have always had my own opinion about open source that in some places run contrary to the popular opinion; for example, I find the GPL to be a bit burdensome at times, and the weight that comes with GPL code some times prevents me from using it or linking against it; instead, I have to find code that uses a “lighter”, less-restrictive license. However, I do firmly believe that both the company and the community are well served by sharing schematics for devices, and quite often these get out there regardless of the intentions of the maker. Oh and — in case it wasn’t clear, this blog is my personal, independent expression, so my opinions and views don’t necessarily reflect those of chumby Industries.
So, the first question many people ask is, why not GPL or CC? Originally, I thought I could attach any of the common, popular F/OSS licenses to these documents, but actually, they don’t apply, because hardware is a different beast than software. CC can’t protect functional works, and GPL is not a good match with hardware. The most important issue is that in hardware, patents are de rigueur, whereas software works are typically copyrighted. Patents are actually a fairly good match to hardware and they don’t have the same ridiculous shelf life that a copyright may have. As defined, patents grant limited rights to inventors of a “useful process, machine, article of manufacture, or composition of matter, or any new and useful improvement thereof” — a hardware-oriented legal mechanism drafted in a time before software existed.
Thus, the most important provision of the chumby HDK license is that in exchange for chumby sharing our technology with you, it requires you, under certain conditions, to share your technology with chumby. Simply put, it protects all of us from, for example, someone taking the chumby design, adding a GPS, patenting that combination, and thereby potentially preventing anyone else (including chumby) from creating a chumby with a GPS in it. I think this is a very reasonable provision, because essentially it creates a pool of cross-licensed patents within the chumby ecosystem. This pool is important because if a troll comes along and decides to threaten the ecosystem by asserting their patent rights to chumby or chumby-derivative products, then the entire pool of created patents are available to fight the troll.
That being said, it’s not a perfect license, so there’s a note in there asking you to reach out to us in case you need something different. In particular, there is an exclusion in there that prevents people from manufacturing chumby devices (you can modify and extend them, but not make them from scratch) based on these plans. Personally, I don’t like that exclusion — I’d love it if some university or non-profit felt free to use these plans to make cheap linux computers for teaching and/or bridging the digital divide — but I’m reminded by many people, both from the Open Source community and from the corporate interests of chumby, that there is a lot more to making a chumby than just the schematics. There are other issues, such as trademark, media licenses (such as MP3, On2 VP6, etc.), and code licenses (Adobe Flash) that need to be properly addressed to create a chumby product, and we haven’t figured out a good way to deal with all of the potential scenarios in a uniform fashion. So for now, it’s basically a friendly request to “contact us” and we’ll figure it out together.
And, now that I’ve made you suffer through reading that, the answer to the question that’s burning on the minds of almost one hundred submitters to the via-guessing contest:
The number of vias on that particular revision of the circuit board is 785 total. There are 298 8-mil vias, 350 10-mil vias, 8 12-mil vias, 14 13-mil vias, and 115 15-mil vias. A mil is 1/1000th of an inch, or 25.4 microns. The 8-mil vias are used selectively underneath the i.MX233 CPU, and I try to use them sparingly because they are the most difficult to manufacture (each via is individually drilled by a mechanical drill, one at a time, with a very tiny drill bit — the car-sized machine that does this is quite impressive, the whole floor trembles as it runs). The 350 10-mil vias are used elsewhere on the board for general signal routing. The 8 and 14 via counts are vias that are part of package layouts, such as QFN’s, that recommend specially-sized vias according to the manufacturer’s datasheets. And the 115 15-mil vias are primarily used to create the ring of vias around the PCB that form an EMI shield so that we can pass FCC without requiring an expensive metal shield over the PCB.
Some of you asked what a via is, and basically, it’s a vertical plug of metal that allows signals from one layer of a PCB to connect to signals of a another layer of a PCB. Below is a 3-D rendering of the chumby One PCB, cut-away, to reveal one layer of traces and the vias connected to it (click on the image for a larger version).
The region you are looking at is the back side of the CPU/memory region of the PCB, and the top-layer metal traces connected to them, as well as the vias that extend through the board. Five other metal layers are hidden from this view to emphasize the via locations.
The image above is generated by my PCB design tool, Altium Designer. Among other things, the tool unifies schematic, 2-D layout, and 3-D mechanical views in a single framework. It’s not a cheap piece of software, but in the context of a commercial project like this it easily pays for itself through the mistakes you avoid using the powerful analysis and visualization tools bundled into the package. Actually, in the spectrum of CAD tools, it’s quite reasonably priced; the really expensive tools are used for chip design, with licenses for a complete design kit costing upwards of $1 million/year (and trust me, for the price you’re paying, the software quality is utter crap). However, for people who are used to getting all their software for free, or at the price of a couple hundred bucks maximum, the idea of paying even a couple thousand dollars for a tool seems expensive, until you balance that off against the cost of a prototype run and a last-minute ticket to China to fix a mistake you didn’t catch at design time because you couldn’t visualize the problem adequately.
Below is an animation I had previously posted of a real PCB, as viewed in an X-ray machine. You can see the bobbin-shaped vias in the animation as the board rocks back and forth.
I wasn’t actually thinking anyone would try to count all the visible vias — kudos to those who put in that effort (omg follower I can’t believe you did that!) — but there are also many vias obscured by components on both sides of the PCB. I wanted to make sure there was some element of luck and chance involved, to give a bit of a disadvantage to people who happened to have access to AOI systems that can automatically count the number of vias using image-recognition algorithms.
The median guess was 463 vias, and the average guess was 495 vias. The closest guess was by “Clever_Screen_Name” at 781 vias (who, ironically, asked what a via was…just a lucky guess? or being ironic?), just an error of 4 vias from the actual count of 785. Congrats, email me to claim your chumby One!
Thanks to everyone else for playing the game — quite an overwhelming response, it took me a while to go through all the comments and tally the guesses. For those who didn’t win, you can still buy one at the chumby store. Remember, the launch promotion is ending soon, and the price will go up to $119 from $99.
Happy hacking!
