WiFi, PWM Backlight, And Graphics On Updated Chumby Kernel

August 29, 2023 by 5 Comments

For some, the Chumby was a peek at what could have been. That vision never died for [Doug Brown], and he has been working tirelessly on bringing mainline Linux kernel support to the customizable smart display. He has posted several updates but recently got graphics and the PWM backlight working.

Of course, we covered when [Doug] first started working on the new kernel, so it’s high time we revisited the progress. The WiFi hardware uses a Marvell 88W8686 chipset, which talks over the SDIO bus, so it’s a matter of convincing the libertas driver to talk to it. With a USB to Ethernet adapter, [Doug] could boot new kernels over NFS, so he didn’t have to walk over to swap the SD card. After dealing with an unhandled fault when trying to read the SDHCI_HOST_VERSION register, [Doug] had access points showing up in NetworkManager but could not connect. As a nasty hack, he temporarily removed the interrupts and switched to polling in the driver. While that worked, it would never get upstreamed. A critical interrupt was being dropped, and commands went out of sequence. A second, perhaps ugly hack, read a register after acknowledging an SDIO interrupt, which seemed to work. But it was still a hack, and [Doug] wanted something cleaner. In a blind stroke of luck, he found the errata online and noticed that it mentioned that an interrupt could be missed when a signal was asserted. After following the workaround with a lot of head-scratching and deep diving, he had a fully working WiFi driver.

Graphics were a more straightforward endeavor compared to WiFi. He enabled the simpledrm driver (similar to simplefb) but using Direct Rendering Manager. He had a working panel that could run Qt apps by adding the frame buffer to the device tree with the correct compatible string, registers, and data. However, there was a Vivante GC300 graphics accelerator onboard that he wanted to use. A driver for Vivante GPUs already exists in the kernel, but after enabling it, the driver detects the GC300 and then starts complaining. He discovered that older revisions of the GC300 (like the ones found in Chumbys) mapped registered at different addresses and didn’t set some bits in their idle registers. Of course, just loading a GPU driver isn’t quite enough. He modified an x11 server that supported Vivante accelerators to support the GC300.

For hacking purposes, [Doug] set the backlight GPIO high. While easy to see, perhaps not the best for a device meant to blend in. The PAX166 comes with PWM hardware, though confusingly, it has two PWM modes for pin 84. PWM1 and PWM2 share some common clock and reset bits in a decidedly undocumented way. PWM2 doesn’t work until you configure and then turn off PWM1. However, the backlight turned off once out of UBoot and into Linux. Linux re-initialized the hardware too quickly, causing the device to freak out. This was solved using the abrupt shutdown register.

It’s a journey through debugging, Linux internals, and device tree hackery. Perhaps the most incredible thing is that these changes are submitted for upstreaming to the Linux kernel, with many landing in Linux 6.2. While it’s a shame new Chumbys aren’t being made, making your own smart display has never been easier.

The 2003 Northeast Blackout And The Harsh Lessons Of Grid Failures

August 29, 2023 by 87 Comments

The grid failure in 2003 which reverted much of the eastern US and Canada back to a pre-electrification era may be rather memorable, yet it was not the first time that a national, or even international power grid failed. Nor is it likely that it will be the last. In August of 2023 we mark the 20th anniversary of this blackout which left many people without electricity for up to three days, while costing dozens of  people their lives. This raises the question of what lessons we learned from this event since then.

Although damage to transmission lines and related infrastructure is a big cause of power outages – especially in countries where overhead wiring is the norm – the most serious blackouts involve the large-scale desynchronization of the grid, to the point where generators shutdown to protect themselves. Bringing the grid back from such a complete blackout can take hours to days, as sections of the grid are reconnected after a cascade scenario as seen with the 2003 blackout, or the rather similar 1965 blackout which affected nearly the same region.

With how much more modern society relies today on constant access to electrical power than it did twenty, let alone fifty-eight years ago, exactly how afraid should we be of another, possibly worse blackout?

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Blame It On The Sockets: Forensic Analysis Of The Arecibo Collapse

August 29, 2023 by 58 Comments

Nearly three years after the rapid unplanned disassembly of the Arecibo radio telescope, we finally have a culprit in the collapse: bad sockets.

In case you somehow missed it, back in 2020 we started getting ominous reports that the cables supporting the 900-ton instrument platform above the 300-meter primary reflector of what was at the time the world’s largest radio telescope were slowly coming undone. From the first sign of problems in August, when the first broken cable smashed a hole in the reflector, to the failure of a second cable in November, it surely seemed like Arecibo’s days were numbered, and that it would fall victim to all the other bad luck we seemed to be rapidly accruing in that fateful year. The inevitable finally happened on December 1, when over-stressed cables on support tower four finally gave way, sending the platform on a graceful swing into the side of the natural depression that cradled the reflector, damaging the telescope beyond all hope of repair.

The long run-up to the telescope’s final act had a silver lining in that it provided engineers and scientists with a chance to carefully observe the failure in real-time. So there was no real mystery as to what happened, at least from a big-picture perspective. But one always wants to know the fine-scale details of such failures, a task which fell to forensic investigation firm Thornton Tomasetti. They enlisted the help of the Columbia University Strength of Materials lab, which sent pieces of the failed cable to the Oak Ridge National Laboratory’s High Flux Isotope reactor for neutron imaging, which is like an X-ray study but uses streams of neutrons that interact with the material’s nuclei rather than their electrons.

The full report (PDF) reveals five proximate causes for the collapse, chief of which is “[T]he manual and inconsistent splay of the wires during cable socketing,” which we take to mean that the individual strands of the cables were not spread out correctly before the molten zinc “spelter socket” was molded around them. The resulting shear stress caused the zinc to slowly flow around the cable strands, letting them slip out of the surrounding steel socket and — well, you can watch the rest below for yourself.

As is usually the case with such failures, there are multiple causes, all of which are covered in the 300+ page report. But being able to pin the bulk of the failure on a single, easily understood — and easily addressed — defect is comforting, in a way. It’s cold comfort to astronomers and Arecibo staff, perhaps, but at least it’s a lesson that might prevent future failures of cable-supported structures.

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It’s A Sander! No, It’s A Toothbrush! Relax, Relax, It’s Both

August 29, 2023 by 11 Comments

We always enjoy a project that transforms some common object into something useful for us. [Modelkitsdeluxe] fits the bill by modifying a power toothbrush into a miniature sander. If you want to practice your Spanish, you can watch the video below. Or you can try the automatically translated captions.

As you can guess from the user name, he is mainly interested in working with small models, but it struck us that this might also be useful for general 3D printing. Honestly, once you have the idea, there isn’t much to it. You mutilate a brush head that fits the toothbrush to accept a small sanding disk.

There are probably a dozen ways to attach your sandpaper or emery cloth to the head. [Modelkitdeluxe] used double-sided tape and Velcro. While we applaud the upcycling, we’ll probably stick with a hobby tool. Our toothbrush makes an annoying buzz every 30 seconds or so to remind you to move to another part of your mouth. That doesn’t seem like a great feature when doing precision sanding. On the other hand, you could probably yank the controller out of the toothbrush and use it for the motor, drive, and batteries to avoid that.

If you want to tackle that, here’s something to get you started. If sanding doesn’t turn your crank, maybe you can try turning your deadbolt.

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This CRT Luggable Makes Sense

August 28, 2023 by 3 Comments

There was a time when portable computing meant not a svelte laptop but a suitcase-sized machine that was really a slimmed-down desktop with a small CRT incorporated int he same box. They were heavy and unwieldy, but the computing compromises of using one at the time were less than with what served for more portable machinery. It’s a form factor which understandably has long ago disappeared, but that hasn’t stopped [Sdomi] from reviving it with a machine that packs plenty of modern computing power.

It’s a project that started with a monitor, a diminutive green-screen model which had previously adorned a CNC machine. It’s a composite model, so it’s driven from a VGA-to-composite converter. The computing power comes from a thin-client board that packs an up-to-date AMD Ryzen processor and 32 GB of memory, and the case is manufactured from oriented strand chipboard.

The result is a chunky but definitely practical and usable take on a portable cyberdeck, with the caveat that a composite monitor will not deliver the resolution some of us might be used to. We have to admit rather liking it, there’s nothing like the curved glass of a CRT.

It’s by no means the only up to date luggable we’ve seen, though more often now they feature an LCD.

Microelectrode (Utay) array and the decoding of the corresponding actions. (Francis R. Willet et al., 2023)

Restoring A Person’s Voice Using A Brain-Computer Interface

August 28, 2023 by 5 Comments

Being able to vocalize is one of the most essential elements of the human experience, with infants expected to start babbling their first words before they’re one year old, and much of their further life revolving around interacting with others using vocalizations involving varying degrees of vocabulary and fluency. This makes the impairment or loss of this ability difficult to devastating, as is the case with locked-in syndrome (LIS), amyotrophic lateral sclerosis (ALS) and similar conditions, where talking and vocalizing has or will become impossible.

In a number of concurrent studies, the use of a brain-computer interface (BCI) is investigated to help patients suffering from LIS (Sean L. Metzger et al., 2023) and ALS (Francis R. Willett et al., 2023) to regain their speaking voice. Using the surgically implanted microelectrode arrays (Utah arrays) electrical impulses pertaining to the patient’s muscles involved in speaking are recorded and mapped to phonemes, which are the elements that make up speech. Each of these phonemes requires a specific configuration of the muscles of the vocal tract (e.g. lips, tongue, jaw and larynx), which can be measured with a fair degree of accuracy. Continue reading “Restoring A Person’s Voice Using A Brain-Computer Interface” →

Making An Injection Mold For Yourself

August 28, 2023 by 29 Comments

Injection molding is the obvious onward step from 3D printing when the making of a few plastic parts becomes their series manufacture. The problem with injection molding is though, that making a mold can be prohibitively expensive. Has the advent of affordable CNC machining changed that? [Teaching Tech] takes a look, and machines a mold for part of a bicycle bracket.

With a diversion into home-made silicone seals for the injection molding machine, he proceeds to machine the mold itself from a block of aluminium. It’s a basic introduction to mold construction for those of us who’ve never ventured in this direction before, and it provides some interesting lessons. As we’d expect he does a rough machining pass before returning with a ball-end tool to smooth off those curves, but there’s a lesson in measuring rather than believing the paperwork. The tool he used was a bit smaller then the spec, so his path left some rough edges that had to be returned to. Otherwise the use of a removable pair of bolts to form holes in the finished part is we guess obvious after watching the video, but it’s something we learned as injection molding newbies.

This video follows on from a previous one we also covered, in which we’re introduced to the machine itself.

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