Winner, Name that Ware December 2020

January 31st, 2021

The Ware for December 2020 was an Intellivision game console by Mattel. It used the CP1610 CPU, whose architecture was based on the PDP-11, and it had a whole kilobyte of RAM! Congrats to Chris on nailing it rather quickly; e-mail me to claim your prize!

Name that Ware, December 2020

December 31st, 2020

The Ware for December 2020 is shown below.

This one should be much easier to guess than last month; click for a larger image that has more context. This was one of my first attempts at repairing a thing; it obviously didn’t end well, as my solder-fu was clearly not up to snuff some 30 years ago.

This is the last ware for 2020! I really had to dig through the archives for the last couple of wares. With travel restrictions still in place, I haven’t gone further than a 5km radius now in 9 months — probably a lifetime record for me. I might have a few more interesting pieces of gear from around the home I could share, but especially these days, I welcome guest entries!

Winner, Name that Ware November 2020

December 31st, 2020

The Ware for November 2020 was from a Cimlinc (originally Cadlinc) “turnkey system in mechanical CAD/CAM applications” (see page 268). Here is an excerpt of a market analysis report from the Computer History Museum:

Cimlinc’s competitive advantages include a good working knowledge of the manufacturing process, a wide library of machine tool post processors, and aggressive pricing. The Company has long-time ties to metalworking industries and sells its products primarily to discrete parts manufacturing companies that need to automate their factory processes. Cimlinc emphasizes factory floor links and interfaces to data from other CAD vendors rather than mechanical design and analysis.

The Company manufactures its own line of 68020-based computers; Cimlinc’s aim is to make its workstation appear indistinguishable from Sun and Apollo workstations. Although Cimlinc is able to offer a low-cost workstation today, continuing with this approach would require that the Company maintain parity with developments in computer hardware technology—a near impossibility for a small company [200 employees].

They sold at least 1600 units of purpose-built workstations similar to the one shown, at a list price of $20,995 in 1986 ($49,515 in 2020), and the systems required a maintenance contract of $335/month ($790 in 2020).

In some ways, we’ve made a lot of progress since then; but in other ways, we’re right back where we started — returning to purpose-built mainframes packed full of graphics accelerators listing at $199,000, costing hundreds if not thousands of dollars a month for rental access, but branded as “cloud computing” so we don’t all roll our eyes and sigh “OK boomer” about the business model.

There were some fairly close-ish guesses, but none quite close enough that I’d call a winner for this month. Thanks for playing!

What’s the Value of Hackable Hardware, Anyway?

December 11th, 2020

There is plenty of skepticism around the value of hackable products. Significantly, hackability is different from openness: cars are closed-source, yet support vibrant modding communities; gcc is one of the “real OG”s of open source, but few users find it easy to extend or enhance. Is it better to have a garden planted by the most knowledgeable botanists and maintained by experienced gardeners, or an open plot of land maintained by whoever has the interest and time?


Above left: Walled garden of Edzell Castle; above right: Thorncliffe Park community garden.

In the case of hardware products, consumer behavior consistently affirms a strong preference for well-curated gardens. Hardware is hard – not only is it difficult to design and validate, supply chains benefit from economies of scale and predictable user demand. The larger a captive audience, the more up-front money one can invest into developing a better hardware product. However, every decision to optimize comes with inherent trade-offs. For example, anytime symmetry is broken, one must optimize for either a right-handed or a left-handed version.


Above: touching the spot indicated by the red arrow would degrade antenna performance on an iPhone 4. This spot would naturally rest on the palm of a left-handed user. Image adapted from “iPhone 4” by marc.flores, licensed under CC BY 2.0.

Some may recall a decade ago when the iPhone 4 was launched, left-handed people noticed the phone would frequently drop calls. It turned out the iPhone 4 was designed with a critical antenna element that would fail when held naturally by a left-handed person. The late Steve Jobs responded to this problem by telling users to “just avoid holding it that way”. Even if he didn’t mean it, I couldn’t help but feel like he was saying the iPhone 4 was perfect and left-handers like me were just defective humans who should be sent to re-education camps on how to hold things.

Of course, as a hardware engineer, I can also sympathize with why Steve Jobs might have felt this way – clearly, a huge amount of effort and thought went into designing a technical masterpiece that was also of museum-quality construction. It’s frustrating to be told, after spending years and billions of dollars trying to build “the perfect product” that they somehow got it wrong because humans aren’t a homogeneous population. Rumors have it Apple spent tens of millions of dollars building micron-precision production jigs out of injection-molding grade tooling to ensure the iPhone4 was simply perfect in terms of production tolerances; duplicating all of those to make a mirror-image version for left-handers that make up 10% of the market size just made no business sense. It proved to be cheaper and easier, ultimately, to take full refunds or to give out rubber bumpers to the users who requested them.

I do think there is such a thing as “over-designing” a product. For example, contemporary “high concept” smartphone design is minimalist – phone companies have removed headphone jacks, hidden the front camera, and removed physical buttons. There is clearly no place for screws in this world; the love affair of smartphones and adhesives has proven to be … sticky. Adhesives, used in place of screws in modern smartphones, are so aggressive that removing them either requires additional equipment, such as a hot plate and solvents, or simply destroying the outer bezel by breaking the outer case off in pieces and replacing it with an entirely new bezel upon re-assembly. In other words, hacking a modern smartphone necessarily implies the destruction or damage of adhesive-bound parts.

With Precursor, I’m bringing screws back.

Precursor’s screws are unapologetic – I make no attempt to hide them or cover them with bits of tape or rubber inserts. Instead, I’ve sourced custom-made Torx T3 metric screws with a black oxide finish that compliments the overall color scheme of Precursor. Six of them line the front, as a direct invitation for users to remove them and see what’s inside. I’ve already received ample criticism for the decision to show screws as “primitive”, “ugly”, “out of touch with modern trends” — but in the end, I feel the visual clutter of these six screws is a small price to pay for the gain in hackability.

Of course, the anti-screw critics question the value of hackability. Surely, I am sacrificing mass-market appeal to enable a fringe market; if hackability was so important, wouldn’t Apple and Google already have incorporated it into their phones? Wouldn’t we see more good examples of hackability already?

This line of questioning is circular: you can’t get good examples of hacks until you have made hackable products wide-spread. However, the critics are correct, in a way: in order to bootstrap an ecosystem, we’re going to need some good examples of why hackability matters.

In the run-up to crowdfunding Precursor, I was contemplating a good demo hack for Precursor. Fortuitously, a fellow named Matt Campbell opened a GitHub issue requesting a text-to-speech option for blind users. This led me to ask what might be helpful in terms of a physical keyboard design to assist blind people. You can read the thread for yourself, but I’ll highlight that even the blind community itself is divided on whether or not there is such a thing as the “blind ghetto” — an epithet applied by some users who feel that blindness-specific products tend to lag behind modern smartphones, tablets, and laptops. However, given that most modern gadgets struggle to consider the needs of 10% of the population that’s left-handed, I’m readily sympathetic to the notion that gadgets make little to no concession to accommodate the even smaller number of blind users.

Matt was articulate in specifying his preferred design for a pocketable keyboard. He referred me to the “Braille ‘n Speak” (shown above) as an example of an existing braille keyboard. Basically, it takes the six dots that make up braille, and lines them up horizontally into three left and three right sets of buttons, adding a single button in the middle that functions as a space bar. Characters are entered by typing chords that correspond to the patterns of the six dots in the braille alphabet. Not being a braille user myself, I had to look up what the alphabet looked like. I made the guide below based on a snippet from Wikipedia to better understand how such a keyboard might be used.

Ironically, even though Matt had linked me to the picture of the Braille n’ Speak, it still took a while to sink in that a braille variant of Precursor did not need a display. I’m a bit ashamed to admit my first sketches involved trying to cram this set of switches into the existing keyboard area of the Precursor, without first removing the display entirely. I had to overcome my own prejudice about how the world should look and it took me time and empathy to understand this new perspective.

Once I had a better grasp of Matt’s request, I set about designing a customized braille variant. Precursor was designed for this style of hacking: the keyboard is a simple 2-layer PCB that’s cheap and easy to re-design, and the front bezel is also a PCB, which is a bit more expensive to redesign. Fortunately, I was able to amortize setup costs by bundling the braille front bezel variant with another variant that I had to fabricate anyways for the crowdfunding campaign. Beyond that, I also had to come up with some custom key caps to complement the switches.

The major challenge in designing any type of mobile-friendly keyboard is always a trade-off between the hand feel of the switches, versus thinness of the overall design. On one side of the spectrum, full-travel mechanical switches have a wonderful hand feel, but are thicker than a sausage. On the other side of the spectrum, dome switches and printed carbon ink patterns are thinner than a credit card, but can feel mushy and have a limited “sweet spot” — the region of a key switch with optimal tactile feedback and operational force curves. The generally well-regarded Thinkpad keyboards go with a middle-ground solution that’s a few millimeters thick, using a “scissor” mechanism to stabilize the key caps over a silicone dome switch, giving individual keys a bit of travel while ensuring that the “sweet spot” covers the entire key cap. Optimizing key switch mechanisms is hard: some may recall the controversy over Apple’s re-design of the MacBook’s keyboard to use a “butterfly” mechanism, which shaved a couple mm of thickness, but led to lawsuits over a defect where the keyboard allegedly stopped working when small bits of dust or other particles got trapped under it.

Given the short time frame and a shoestring budget, I decided to use an ultra-thin (0.35mm) tactile switch that I could buy off-the-shelf from Digikey and create custom key caps with small dimples to assist users in finding the relatively small sweet spots typical of such switches. I have sincere hopes this is a pretty good final solution; while it lacks a scissor mechanism to spread off-centered force, the simple mechanism meant I didn’t have to stick with a square key cap and could do something more comfortable and ergonomic to focus forces into the sweet spot. At the very least, the mechanism would be no worse than the current mechanism used in Precursor’s existing keyboard for sighted users, which is similarly a dome switch plus a hybrid-polymer key film.

Next, I had to figure out where to place the switches. To assist with this, I printed a 1:1 scale version of the Precursor case, dipped my fingertips in ink, and proceeded to tap on the printout in what felt like a natural fashion.

I then took the resulting ink spots and dimensioned their centers, to place the centroid of each key cap. I also asked my partner, who has smaller hands, to place her fingers over the spots and noted the differences in where her fingers lay to help shape the final key caps for different-sized hands.

Next, using the “master profile” discussed in the previous post on Precursor’s mechanical design, I translated this into a sketch to help create a set of key caps based on splines that matched the natural angle of fingers.

Above, you can see an early sketch of the key caps, showing the initial shape with dimples for centering the fingers.

Before moving ahead and spending a few hundred dollars to build a functional prototype, I decided to get Matt’s feedback on the design. We submitted the design to Shapeways and had a 3D print sent to Matt, which he graciously paid for. After receiving the plastic dummy, his feedback was that the center space bar should be a single key, instead of two separate keys, so I merged the two separate key caps of the space bar together into a single piece, while retaining two separate switches wired in parallel under the space bar. I felt this was a reasonable compromise that would allow for a “sweet spot” that serviced lefties as well as righties.

I then re-designed the keyboard PCB, which was a fairly simple task, because the braille keyboard consists of only eight switches. I just had to be careful to pick row/column pairs that would not conflict during chording and be sure to include the row/column pairs necessary to turn Precursor on after being put to sleep. I also redesigned the bezel; eliminating the display actually makes manufacturing a little bit easier because it also removes a beveling step in the manufacturing process. I kept the RF antenna in exactly the same location, as its design was already well-characterized and it takes a lot of effort to tune the antenna. Finally, I decided to manufacture the key switches out of aluminum. The switches have a lot of fine features and I needed a stiff material that could translate off-target force to the key switches to enlarge the sweet spot as much as possible.


Above: The prototype of Precursor with braille keyboard.

About three weeks later, all the parts for the braille keyboard had arrived. I decided to use purple anodization for the key switches which, combined with the organic key shapes, gives the final design a bit of a Wakanda-esque “Black Panther” aesthetic, especially when mounted in a brass case. The key switch feel is about in line with what I imagined, with the caveat that one of the switches feels a little less nice than the rest, but I think that’s due to a bad solder job on the switch itself. I haven’t had a chance to trace it down because…well, I’ve had to write a bunch of posts like this to fund Precursor. I have also been working with Xobs to refactor Xous in hopes of putting together enough code to send Matt a prototype he can evaluate without having to write gobs of embedded hardware driver code himself.

Above is a quick photo showing the alignment of fingers to keys. Naturally, it’s perfect for my hand because it was designed around it. I’m looking forward to hearing Matt’s opinion about the feel of the keys.

Above is a photo of the custom parts for the braille keyboard. At the top, you can see the custom bezel with key caps and the RF antenna matching circuitry on the top right. On the bottom, you can see the custom keyboard PCB mounted onto a Precursor motherboard. The keyboard PCB is mostly blank and, because of the small number of keys and the flexibility of the FPGA, there’s an option to mount more peripherals on the PCB.

Despite not being yet finalized, I hope this exercise is sufficient to demonstrate the potential value of hackable products. The original design scope for Precursor (née Betrusted) did not explicitly include a braille keyboard option, but thanks to modular design principles and the use of accessible construction materials, I was able to produce a prototype in about a month that has a similar fit and finish as the mainstream product.

As long as humans choose to embrace diversity, I think hackability will have value. A notional “perfect” product implies there’s such a thing as a “perfect” user. However, in reality, even the simple conundrum of left- or right-handedness challenges the existence of a singular “perfect” product for all of humanity. Fortunately, accommodating the wonderfully diverse, quirky, and interesting range of humanity implicates just a few simple engineering principles, such as embracing screws over adhesives, openness, and modularity. That we can’t hack our products isn’t a limitation of physics and engineering. Precursor demonstrates one can build something simultaneously secure and hackable, while being compact and pocketable. This suggests the relative lack of hackable products on the market isn’t a fundamental limitation. Maybe we just need a little more imagination, maybe we need to be a little more open-minded about aesthetics, and maybe companies need to be willing to take brave steps toward openness and inclusivity.

For Apple, true “courage to move on and do something new that betters all of us” was to remove the headphone jack, which resulted in locking users deeper into a walled-garden ecosystem. For hackers like myself, our “courage” is facing blunt criticisms for making “ugly” products with screws in order to facilitate mods, such as braille keyboards, in order to expand the definition of “all of us” beyond a set of privileged, “perfect” users.

I hope this braille keyboard is just the first example of many mods for Precursor that adapt the product for unique end-users, bucking the trend of gaslighting users to mold their behavior and preferences to fit the product. If you’ve got an itch to develop your own yet-to-be-seen feature in a mobile device, please visit our crowdfunding campaign page to learn more about Precursor. We’re close to being funded, but we’ve only a few days left in the campaign. After the campaign concludes on December 15th, the limited edition will no longer be available, and pricing of the standard model goes up. If you like what you see, please consider helping us to bring Precursor to life!

Precursor’s Mechanical Design

December 7th, 2020

“Pocketability” is the difference between Precursor and naked PCB FPGA development platforms. We hope Precursor’s pocketability helps bring more open hardware out of the lab and into everyday use. Thus, the mechanical design of Precursor is of similar importance to its electrical, software, and security design.

We always envisioned Precursor as a device that complements a smartphone. In fact, some of the earliest sketches had Precursor (then called Betrusted) designed into a smartphone’s protective case. In this arrangement, Precursor would tether to the phone via WiFi and the always-on LCD for Precursor could then be used to display static data, such as a shopping list or a QR code for a boarding pass, giving Precursor a bit of extra utility as a second screen that’s physically attached to your phone. However, there are too many types of smartphones out there to make “Precursor as a phone case” practical, so we realized it would make more sense to make Precursor a “stand-alone device”.

As such, we wanted Precursor to be unobtrusive and thin in order to lighten the burden of carrying a secondary security device. Our first-draft EVT design had Precursor at just 5.7 mm thick, placing it among the ranks of the thinnest phones. Unfortunately, the EVT device had no backlight on the LCD, which made it unusable in low-light conditions. Increasing the final thickness to 7.2 mm allowed us to introduce a backlight, while still being slimmer than every iPhone since the iPhone 8.

To minimize the thickness of Precursor, I first divided the design into major zones, such as the main electronics area, the battery compartment, the vibration motor, and the speaker. I then estimated the overall thickness of components in each zone and optimized the thickest one by either re-arranging components or making component substitutions until another zone dominated the overall thickness.


A cross-section view of the final Precursor design, calling out the dimensions of the various vertical height zones of the design.

After considering about a dozen or so mechanical layout scenarios, we arrived at the design shown above. Like every modern mobile device, when viewed by size and weight, Precursor is basically a battery attached to a display.

The practical limit on battery thickness is driven by the overhead of the protective wrapping around the battery. Lithium-polymer “pouch” batteries rapidly decline in energy density with decreasing thickness as the protective wrapper around the battery starts to factor appreciably into its overall thickness. The loss of energy density becomes appreciable below 3.5mm, and so this fixed the battery’s thickness at 3.5mm, plus about 0.2mm allowance for any swelling that might happen plus adhesive films.


Teardown view of Precursor’s LCD with backlight attached. Note that to inspect the transistors inside the LCD, the backlight module needs to be removed.

Display thickness is limited by the thickness of the liquid crystal (LC) “cell”, plus backlight. Fortunately, LC cells are extremely thin, as they are basically just the glass sheets used to confine a microscopic layer of liquid crystal material, plus some polarizer films – in Precursor’s case, the LC cell is just 0.705mm thick. The backlight is substantially thicker, as it requires a waveguide plus a film stack that consists of two brightness enhancing films, a diffuser sheet, adhesives, and its own protective case to hold the assembly together, leading to a net thickness increase of roughly 1.3mm. The backlight itself is actually a full-custom assembly that we designed just for Precursor; it’s not available as an off-the-shelf part.

With the display and battery thicknesses defined, the final thickness of the product is determined by the material selection of the protective case. We use aluminum for the bottom case and FR-4 for the bezel (we discuss the bezel in a previous post).

Using aluminum for the bottom case allows us to shave about 1 mm (~15%) of thickness relative to using a polymer like ABS or PC at the expense of a fairly substantial increase in per-unit manufacturing costs. Although polymers are about twice the cost of aluminum by weight, an aluminum case costs about 10x as much to produce. This is because polymers can be molded in a matter of seconds, with very little waste material, whereas aluminum must be CNC’d out of a slab in a time-consuming process that scraps 80% of the original material. Surprisingly, the 10x cost-up isn’t the waste material; there is an efficient market for buying and recycling post-machining aluminum. Most of the extra cost is due to the labor required to machine the case which is orders of magnitude longer than the time required for injection molding.

Thus, while we could have made Precursor cheaper, we felt it would both be more pocketable, as well as more desirable, with the machined aluminum case: it would look more like a high-end mobile device, instead of a cheap plastic toy or remote control.

Using aluminum also allows us to play some fun tricks with the fit and finish of the product, thanks in part to the transformative effect Apple had on the mobile phone industry. Their adoption of CNC machining as a mass production process sparked a huge investment in CNC capability, making once-exotic processes more affordable for everyone. A good example of this is the single-crystal diamond cutting process for making shiny beveled edges. This used to be a fairly expensive specialty process, which you can read more about in this great thesis on “Precision and Techniques for Designing Precision Machines” by Layton Carter Hale which, on page 27, describes the Large Optics Diamond Turning Machine (LODTM). The LODTM relies on the raw precision achievable with a diamond bit to create geometries for mirrors without the need for post-polishing.


A single-crystal diamond bit, courtesy of Victor from Jiada

I first learned about this technique in 2017, when I brought a Xiaomi aluminum mouse pad with a mirror-finish bevel.


Bevel on the Xiaomi mousepad

Despite a sub-$20 price tag, the mirror-finish bevel gave it quite an expensive look. Polishing to a mirror finish is a time consuming task, so I became curious about how this could be economical on a humble mouse pad. I bought another mouse pad, and brought it to Prof. Nadya Peek, and asked her how she thought it was fabricated. Readers who are familiar with our Novena laptop may recall her name as the designer of the Peek Array for mounting accessories inside the Novena. I’ve been lucky to have her mentorship and advice on all things mechanical engineering for many years now. So many of my products are better thanks to her!

She took one look at the bevel and immediately guessed it was cut by a single-crystal diamond bit, but she could do even better than making a guess. At the time, she was still a graduate student at the MIT Center for Bits and Atoms, where she had a Hitachi FlexSEM 1000 II equipped with the X-ray composition analysis option at her disposal. So, she took the mouse pad to the machine shop, chopped a corner off with a band saw, and loaded it into the SEM.


Viewing the output of the composition analysis.

If you zoom into the screen on the right, you can see the X-ray composition analysis reveals an unusually high amount of carbon on the aluminum surface (~10% by weight). Unlike iron, carbon is not commonly used in alloying aluminum. In this case, the chief alloying element seems to be magnesium, implying that the mousepad is probably a 5000-series alloy (perhaps 5005 or 5050). Given this, it seemed reasonable to conclude that the carbon residue on the beveled surface is direct evidence of a diamond cutting bit.


The shiny beveled edge on Precursor is brought to you by a single-crystal diamond milling bit.

Armed with this knowledge, I was able to work with Victor, the owner of Jiada – the primary CNC provider for Precursor – to specify a diamond-bit beveling process that brings you the nice edge finish on the final Precursor product. I also count Victor as one of my many mechanical design mentors; he’s one of those practicing-engineer-as-CEO types who has applied his extensive knowledge of mechanical engineering to open his own CNC and injection molding business. He always seems up for the challenge of developing new and interesting fabrication processes. That’s why I’ve been working closely with Victor to develop the campaign-only omakase version of Precursor.

Because Precursor’s case is CNC, we’re not limited to aluminum as the base material. It’s primarily a matter of cost and yield to manufacture with other materials. We could, for example, machine the case out of titanium, but the difficulty of machining titanium means we would likely have to machine two or three cases to yield a single one that passes all of our quality standards. This, combined with the high cost of raw titanium, would have added about a thousand dollars on to the final price of the omakase Precursor and we felt that would be just too expensive. Thus, Victor and I are currently evaluating two material candidates: one is physical vapor deposition (PVD)-finished stainless steel, the other is naval brass. These material choices were heavily influenced by Prof. Peek’s opinions. (It’s a coincidence the recently launched iPhone 12 uses PVD stainless steel for its case, as we have been working on this project since well before the details of iPhone 12 were publicly known.)

While both the PVD steel and naval brass are much more expensive than aluminum, they have a terrific hand feel and excellent machinability. Aesthetically, the main difference between the two is the color: for the stainless steel PVD, we’d be going with a high-gloss, polished black look, and for the naval brass we’re considering a brushed finish. The naval brass is more distinctive, but the soft metal is easy to scratch; a highly polished brass surface starts to look much less nice after a week or two of banging around in your pocket. A brushed finish hides such scratches and fingerprints better and over the course of years it should develop a handsome patina.

The major downside of the naval brass is that it’s highly conductive. Both the PVD stainless steel and anodized aluminum inherently have a tough, non-conductive surface layer; the naval brass does not. This is particularly concerning because if any of the internal battery connections get frayed, it could lead to a fire hazard. I’m currently working to see if I can find a surface coating that adequately protects the inside of the naval brass case from short circuits, but if I can’t find one, that may definitively rule out the naval brass option, leaving us with a PVD stainless steel case for the omakase version.

While good looks and a nice hand feel are significant benefits of going with a CNC process, another important reason I picked CNC over injection molding is anyone could build a full-custom version of a Precursor case in single quantities, with no compromise on finish quality or durability. Unlike the situation of injection molding versus 3D printing, which either use radically different base materials (for SLA 3D printing) or processes (for FDM 3D printing), your custom case can be made in single quantities with the exact same metal alloys and the exact same processes used in production Precursors.

This trait is particularly important for a mobile device and not just because the design works better when it’s built using its originally intended material system. It’s also because mobile devices don’t have a lot of extra space to devote to expansion headers and breakout boards. While it is beyond the level of a weekender hobby project to make a custom case, it’s probably within the scope of an undergraduate-level research project to undertake the necessary revisions to, for example, thicken the case and incorporate a novel medical sensor or a new kind of radio. In order to facilitate easier modifications to the case’s native Solidworks design file, I use a “master profile” to define the case body, bezel, and “ribbon” (the outer band that defines the height of the case). Helena Wang, another friend to whom I turn to for advice on mechanical design, taught me about the general technique of top-down modeling and using master profiles. Top-down modeling pushes a lot of design work into the up-front structure and planning of the 3D body in exchange for being able to revise the model without having to resolve dozens of conflicting downstream mechanical constraints. For example, when I realized I had to modify the case to be 1.5mm thicker to accommodate the backlight for the LCD, I was able to make the necessary change by just adjusting a single dimension in the ribbon height master profile, followed up by perhaps a half hour of cleaning up the offsets on structures which were defined outside of the master profile, such as the mounting points used to support the keyboard and the polymer radome that allows the WiFi signal out from the metal case.


A screenshot of the CAD tool view of the Precursor case, highlighting the master profile that defines the outer dimensions of the case.

Of course, making edits to the master profile requires access to a copy of Solidworks, which is not an open source tool; but FreeCAD users are welcome to redraw the design in their native format! I’ve heard good things about FreeCAD, but I just haven’t had the time to learn a new design tool. For smaller modifications that don’t involve changing major dimensions of the case – such as adding some extra through-holes for sensors or internal mounts for additional circuit boards – the case design is also available in a tool-neutral STEP format. Every CAD tool I know of can accept STEP format and, since it is actually the format used for CNC fabrication, it’s by definition sufficient for creating copies of the case.

If you’ve read my posts over the years, you may have noticed that I’ve never taken a formal course on mechanical engineering. Everything I know has been either gleaned from taking things apart, touring factories, scouring the Internet, and perhaps most importantly receiving advice from friends and mentors like Nadya, Victor, and Helena. It’s been a wonderful journey learning how things are made, I hope posts like this and the associated design files will aid anyone who wants to learn about mechanical design, so they may have an easier time of it than I did. Most of all, I’m hoping applying my experience and making Precursor pocketable and hackable will enable more open source technology to make it out of the lab and into everyday use, without requiring anyone to learn about mechanical design.

Thanks again to all our backers for bringing us closer to our funding goal! At the time of posting, we’re just at 90% funded, but we’re also getting down to the last week to wrap things up. We need your support to get us over the 100% mark. We recognize that these are difficult, trying times for everyone, but even small $10 donations inch us toward a successful campaign. Perhaps more importantly, if you know someone who might be interested in Precursor, we’d appreciate your help in spreading the word and letting them know about our campaign. With your help, hopefully we’ll blow past our funding goal before the campaign ends, and we can begin the hard but enjoyable work of building and delivering the first run of Precursor devices.