Raspberry Pi Server Cluster In 1U Rack-Mount Case

[Paul Brown] wants to take advantage of off-site server colocation services. But the providers within [Paul]’s region typically place a limit of 1A @ 120V on each server. Rather than search out commercial low-power solutions, [Paul] embraced the hacker spirit and built his own server from five Raspberry Pi 4b single board computers.

The task involves a little bit more than just mounting five Pi4s in a chassis and calling it done. There is an Ethernet switch connecting all the modules to the network, and each Pi has a comparatively bulky SSD drive + enclosure attached. By far the most annoying part of the assembly is the power supply and distribution cabling, which is further complicated by remote controlled power switching relays (one of the computers is dedicated to power management and can shut the other four modules on and off).

Even if you’re not planning on building your own server, check out the thoroughly documented assembly process and parts list — we particularly liked the USB connector to screw terminal breakout connector that he’s using for power distribution. For all the detailed information, assembly instructions and photos, we think a top-level block diagram / interconnection drawing would be very helpful for anyone trying to understand or replicate this project.

There are a lot of connections in this box, and the final result has a messy look-and-feel. But in fairness to [Paul]’s craftsmanship, there aren’t many other ways to hook everything together given the Raspberry Pi form-factor. Maybe a large and costly PCB or using CM4 modules instead of Raspberry Pi boards could help with cable management? In the end, [Paul] reckons he shelled out about $800 for this unit. He compares this expense with some commercial options in his writeup, which shows there are some cheaper and more powerful solutions. But while it may be cheaper to buy, we understand that strong urge to roll your own.

We’ve written about many Pi cluster projects in the past, including this one which contains a whopping 750 Raspberry Pis. Have you ever used a colocation service, and if so, did you use a DIY or an off-the-shelf server?

Miller (Effect) Time

While the Miller effect might sound like fun, it is actually the effect of parasitic capacitance in amplifiers. What do you do about it? Watch the video below the break from [All Electronics] and find out. We like how the test circuit it uses has a switch to put the mitigation circuitry in and out of the test for comparison purposes.

Actually, the Miller effect can refer to any impedance but in practice that is most often parasitic capacitance because of the construction used for tubes and transistors. The sometimes tiny capacitance gets multiplied by the inverting gain of the stage and increases the amplifier’s input impedance. This, in turn, reduces the bandwidth of the stage.

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A New Spin On 360 Degree Displays

Back in 2018, [Salah] created a prototype display that seems to defy logic using little more than a Pringles can and a fast motor. While not volumetric, this hack does show the same 2D image from any vantage point in 360 degrees around it.

How can cardboard create this effect? Somewhat like a zoetrope uses slits to create a shutter effect, this display uses a thin slit to limit the view of the image within to one narrow vertical slice at a time. When moving fast enough, Persistence of Vision kicks in to assemble these slices into a complete image. What we think is so cool about this hack is that the effect is the same from any angle and by multiple viewers simultaneously.

The project page and video demonstration after the break are light on details, though the idea is so simple as to not require additional explanation. We assume the bright LED seen in the video below was added to overcome the relatively dim appearance of the image when viewed through the narrow slit and isn’t strictly required.

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Clever PCB Brings Micro USB To The Arduino Uno

Even with more and more devices making the leap to USB-C, the Arduino Uno still proudly sports a comparatively ancient Type-B port. It wouldn’t be a stretch to say that many Hackaday readers only keep one of these cables around because they’ve still got an Uno or two they need to plug in occasionally.

Looking to at least move things in the right direction, [sjm4306] recently set out to create a simple board that would let him mount a micro USB connector in place of the Uno’s original Type-B. Naturally there are no components on the PCB, it simply adapts the original through-hole footprint to the tight grouping of surface mount pads necessary to mount a female micro USB port.

Making castellated holes on the cheap.

The design is straightforward, but as [sjm4306] explains in the video below, there’s actually more going on here than you might think. Looking to avoid the premium he’d pay to have the board house do castellated holes, he cheated the system a bit by having the board outline go right through the center of the standard pads.

Under a microscope, you can see the downside of this approach. Some of the holes got pretty tore up as the bit routed out the edges of the board, with a few of them so bad [sjm4306] mentions there might not be enough of the pad left to actually use. But while they may not be terribly attractive, most of them were serviceable. To be safe, he says anyone looking to use his trick with their own designs should order more boards than they think they’ll actually need.

Of course you could go all the way and retrofit the Uno with a USB-C port, as we’ve seen done with devices in the past. But the latest-and-greatest USB interface can be a bit fiddly, especially with DIY gadgets, so we can’t blame him for going with the more reliable approach.

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ZeroBug: From Simulation To Smooth Walking

Thanks to 3D printing and cheap hobby servos, building you’re own small walking robot is not particularly difficult, but getting them to walk smoothly can be an entirely different story. Knowing this from experience, [Max.K] tackled the software side first by creating a virtual simulation of his ZeroBug hexapod, before building it.

Learning from his previous experience building a quadruped, ZeroBug started life in Processing as a simple stick figure, which gradually increased in complexity as [Max.K] figured out how to make it walk properly. He first developed the required movement sequence for the tip of each leg, and then added joints and calculated the actuator movements using reverse kinematics. Using the results of the simulations, he designed the mechanics and pulled it back into the simulation for final validation.

Each leg uses three micro servos which are controlled by an STM32F103 on a custom PCB, which handles all the motion calculations. It receives commands over UART from a python script running on a Raspberry Pi Zero. This allows for user control over a web interface using WiFi, or from a gamepad using a Bluetooth connection. [Max.K] also added a pincer to the front to allow it to interact with its environment. Video after the break.

The final product moves a lot smoother than most other servo-driven hexapods we’ve seen, and the entire project is well documented. The electronics and software are available on GitHub and the mechanics on Thingiverse.

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Retrotechtacular: Nuvistor, Vacuum’s Last Gasp

In 2021 all our electronics are solid state, in that they exclusively use semiconductor devices as their active components. Some of us may experiment with vacuum tubes, but only for curiosity or aesthetic purposes. Semiconductors have overtaken vacuum devices in all but the rarest of niche applications due to their easier design requirements, greater reliability, lower cost, and increased performance.

It was not always this way though, and there was a period at the start of the semiconductor era when transistors and vacuum tubes existed together side-by-side and competed directly. Vacuum tube manufacturers continued to create new devices into the 1970s, and in doing so they pushed the boundaries of their art in unprecedented directions. [David W Knight] has a page dedicated to the Nuvistor, something his calls the “final evolution of the thermionic valve”. His comparison photo seen above shows a Nuvistor on the left — a miniature vacuum tube you’ve likely never seen before.

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Precise Sundial Tells Time To The Minute

We’re always a fan of an interesting or unique clock build around here, which often use intricate pieces of technology to keep time such as weights and gears, crystal oscillators, or even a global network of satellites in the case of GPS. While these are all interesting methods of timekeeping, the original method of tracking the sun is often forgotten. With this clock, the sun is the main method of keeping track of time, but unlike traditional sundials it has a number of advancements that let it keep surprisingly accurate time. (Google Translate from German)

While most sundials can only show hours, this one from [leon andrĂ©], a retired physicist, has a method for displaying minutes as well. It uses pinholes instead of shadows to keep track of the position of the sun, with the pinhole casting a bright spot of sunlight onto a diagram below. The diagram keeps track of the minutes, and consists of curved lines which help account for the sun’s changing path throughout a typical year. The dial keeps track of local solar time, as any sundial would, but by rotating it along its vertical axis it can be calibrated for the timezone that it’s in regardless of its position.

As far as clock builds go, one that is completely passive like this semi-digital sundial is fairly unique, especially for its accuracy. And, when set to local solar time, it will be the most reliable method of keeping time long-term than possibly any other clock we’ve seen before, as long as it’s not too cloudy outside. On the other hand, it is possible to augment a sundial with some modern technology as well.

Thanks to [Adrian] for the tip!