A Minicomputer Tape Drive Receives Some Love

Taking on a refrigerator-sized minicomputer  is not for the faint-hearted, but [Usagi Electric] has done it with a DEC PDP-11/44. He’s not doing it in half measures either, for his machine is tricked out with an impressive array of upgrades. Among them however is no storage, and with two co-processors there’s a meager 3U of rack space left. The plan is to fit a period 8″ hard drive in the space alongside a TU50 tape dive, and it’s this final component that’s the subject of his latest video.

DEC never did anything by halves, and a DECTape II cartridge is more than a simple container for tape reels. Instead it has a capstan of its own that engages with one in the drive, and an internal drive belt that moves the reels. All the rubber parts in both tapes and drive are thoroughly perished, and it’s impressive that he manages to find inexpensive modern polymer alternatives. The original drive is probably intended for a VAX system, thus it has the interesting feature of a second drive mechanism out of sight to hold a tape containing microcode.

Having reconditioned the drive, it goes in behind a custom front panel, and though there’s no useful data to test it with on the tapes he has, it appears all working. You can see it all in the video below the break, and if you’re interested further we’ve covered this machine in the past.

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Reshaping Eyeballs With Electricity, No Lasers Or Cutting Required

Glasses are perhaps the most non-invasive method of vision correction, followed by contact lenses. Each have their drawbacks though, and some seek more permanent solutions in the form of laser eye surgeries like LASIK, aiming to reshape their corneas for better visual clarity. However, these methods often involve cutting into the eye itself, and it hardly gets any more invasive than that.

A new surgical method could have benefits in this regard, allowing correction in a single procedure that requires no lasers and no surgical cutting of the eye itself. The idea is to use electricity to help reshape the eye back towards greater optical performance.

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The site controller board

Homebrew Dam Control System Includes All The Bells And Whistles

Over on brushless.zone, we’ve come across an interesting write-up that details the construction of a dam control system. This is actually the second part, in the first, we learn that some friends purchased an old dysfunctional 80 kW dam with the intention of restoring it. One friend was in charge of the business paperwork, one friend the mechanical side of things, and the other was responsible for the electronics — you can probably guess which ones we’re interested in.

The site controller is built around a Nucleo-H753 featuring the STM32H753ZI microcontroller, which was selected due to it being the largest single-core version of the dev board available. This site controller board features a dozen output light switches, sixteen front-panel button inputs, dual 24 V PSU inputs, multiple non-isolated analog inputs, atmospheric pressure and temperature sensors, multiple analog multiplexers, a pair of SSD1309 OLED screens, and an ESP32 for internet connectivity. There’s also fiber optic TX and RX for talking to the valve controller, a trio of isolated hall-effect current sensors for measuring the generator phase current, through current transformers, four contactor outputs (a contactor is a high-current relay), a line voltage ADC, and the cherry on top — an electronic buzzer.

The valve controller has: 48 V input from either the PSU or battery, motor phase output, motor field drive output, 8 kV rated isolation relay, limit switch input, the other side of the optical fiber TX and RX for talking to the site controller board, and connectors for various purposes.

If you’re interested in seeing this dam control system being tested, checkout the video embedded below.

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Just a simple Lego bouncy DVD logo screensaver mechanism. (Credit: Grant Davis, YouTube)

Building The DVD Logo Screensaver With LEGO

The completed Lego DVD screensaver. (Credit: Grant Davis, YouTube)
The completed Lego DVD screensaver. (Credit: Grant Davis, YouTube)

There’s something extremely calming and pleasing about watching a screensaver that merely bounces some kind of image around, with the DVD logo screensaver of a DVD player being a good example. The logical conclusion is thus that it would be great to replicate this screensaver in Lego, because it’d be fun and easy. That’s where [Grant Davis]’s life got flipped upside-down, as this turned out to be anything but an easy task in his chosen medium.

Things got off on a rocky start with figuring out how to make the logo bounce against the side of the ‘screen’, instead of having it merely approach before backing off. The right approach here seemed to be Lego treads as used on e.g. excavators, which give the motion that nice pause before ‘bouncing’ back in the other direction.

With that seemingly solved, most of the effort went into assembling a functional yet sturdy frame, all driven by a single Lego Technic electromotor. Along the way there were many cases of rapid self-disassembly, ultimately leading to a complete redesign using worm gears, thus requiring running the gears both ways with help from a gearbox.

Since the screensaver is supposed to run unattended, many end-stop and toggle mechanisms were tried and discarded before settling on the design that would be used for the full-sized build. Naturally, scaling up always goes smoothly, so everything got redesigned and beefed up once again, with more motors added and multiple gearbox design changes attempted after some unfortunate shredded gears.

Ultimately [Grant] got what he set out to do: the DVD logo bouncing around on a Lego ‘TV’ in a very realistic fashion, set to the noise of Lego Technic gears and motors whirring away in the background.

Thanks to [Carl Foxmarten] for the tip.

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Diagram of C99 designated initializers.

Tips For C Programming From Nic Barker

If you’re going to be a hacker, learning C is a rite of passage. If you don’t have much experience with C, or if your experience is out of date, you very well may benefit from hearing [Nic Barker] explain tips for C programming.

In his introduction he notes that C, invented in the 70s by Dennis Ritchie, is now more than 50 years old. This old language still appears in lists of the most popular languages, although admittedly not at the top!

He notes that the major versions of C, named for the year they were released, are: C89, C99, C11, and C23. His recommendation is C99 because it has some features he doesn’t want to live without, particularly scoped variables and initializing structs with named members using designated initializers. Also C89 is plagued with non-standard integer types, and this is fixed by stdint.h in C99. Other niceties of C99 include compound literals and // for single-line comments.

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Building A Diwheel To Add More Tank Controls To Your Commute

It’s often said that one should not reinvent the wheel, but that doesn’t mean that you cannot change how the use of said wheel should be interpreted. After initially taking the rather zany concept of a monowheel for a literal ride, [Sam Barker] decided to shift gears, did a ‘what if’ and slapped a second monowheel next to the first one to create his diwheel vehicle. Using much thicker steel for the wheels and overall much more robust construction than for his monowheel, the welding could commence.

It should be said here that the concept of a diwheel, or dicycle, isn’t entirely new, but the monowheel – distinct from a unicycle – is much older, with known builds at least as far back as the 19th century. Confusing, self-balancing platforms like Segways are also referred to as ‘dicycles’, while a diwheel seems to refer specifically to what [Sam] built here. That said, diwheels are naturally stable even without gyroscopic action, which is definitely a big advantage.

The inner frame for [Sam]’s diwheel is built out of steel too, making it both very robust and very heavy. High-tech features include suspension for that smooth ride, and SLS 3D-printed nylon rollers between the inner frame and the wheels. After some mucking about with a DIY ‘lathe’ to work around some measurement errors, a lot more welding and some questionable assembly practices, everything came together in the end.

This is just phase one, however, as [Sam] will not be installing pedals like it’s an old-school monowheel. Instead it’ll have electrical drive, which should make it a bit less terrifying than the Ford Ka-based diwheel we featured in 2018, but rather close to the electric diwheel called EDWARD which we featured back in 2011. We hope to see part two of this build soon, in which [Sam] will hopefully take this beast for its first ride.

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