Dry Ice From Seashells, The Hard (But Cheap) Way

December 6, 2023 by 11 Comments

[Hyperspace Pirate] wants to make his own dry ice, but he wants it to be really, really cheap. So naturally, his first stop is… the beach?

That’s right, the beach, because that’s where to find the buckets of free seashells that he turned into dry ice. Readers may recall previous efforts at DIY dry ice, which used baking soda and vinegar as a feedstock. We’d have thought those were pretty cheap materials for making carbon dioxide gas, but not cheap enough for [Hyperspace Pirate], as the dry ice he succeeded in making from them came out to almost ten bucks a pound. The low yield of the process probably had more to do with the high unit cost, in truth, so cheaper feedstocks and improved yield would attack the problem from both ends.

With a supply of zero-cost calcium carbonate from the beach and a homemade ZVS-powered induction heater tube furnace at the ready, [Hyperspace Pirate] was ready to make quicklime and capture the CO2 liberated in the process. That proved to be a little more difficult than planned since the reaction needed not just heat but a partial vacuum to drive the CO2 off. An oil-free vacuum pump helped, yielding a little CO2, but eventually he knuckled under and just doused the shells in vinegar. This had the fun side effect of creating calcium acetate, which when distilled not only corrodes the copper still plumbing but also makes a lousy but still flammable grade of acetone. Once enough CO2 was stored in a couple of beach balls, the process of cooling and condensing it into dry ice was pretty much the same as the previous method, except for taking advantage of the Joule-Thomson cryocooler he built a while back.

The result is a hundred or so grams of dry ice snow, which isn’t great but still shows promise. [Hyperspace Pirate] feels like the key to improving this process is more heat to really drive the calcination reaction. Might we suggest a DIY tube furnace for that job?

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Directional Antenna Stands Tall

December 5, 2023 by 7 Comments

When you think of directional ham radio antennas, you probably think of a Yagi, cubical quad, or a log-periodic antenna. These antennas usually are in a horizontal configuration up on a high tower. However, it is possible to build beams with a vertical orientation and, for some lower frequencies, it is far more practical than mounting the elements on a boom. [DXCommander] shows us his 40 meter two-element vertical antenna build in the video below.

A typical Yagi is just a dipole with some slightly longer or shorter elements to direct or reflect the signal. A normal vertical, however, is nothing more than half of a dipole that uses the ground as the other half. So it is possible to create reflectors and directors with a vertical-driven element.

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Inside A Rubidium Frequency Standard

December 5, 2023 by 14 Comments

We think of crystals as the gold standard of frequency generation. However, if you want real precision, you need something either better than a crystal or something that will correct for tiny errors — often called disciplining the oscillator. [W3AXL] picked up a rubidium reference oscillator on eBay at a low cost, and he shows us how it works in the video you can see below. He started with a GPS-disciplined oscillator he had built earlier and planned to convert it to discipline from the rubidium clock.

The connector looks like a D-shell connector superficially, but it has a coax connector in addition to the usual pins. The device did work on initial powerup, and using a lissajous pattern to compare the existing oscillator with the new device worked well.

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This Pogo Pin Test Fixture Keep Your SMDs From Taking Flight

December 5, 2023 by 12 Comments

There’s no denying how useful surface mount technology is, and how enabling the ability to make really small circuits has become. It comes at a price, though; most of us probably know what it’s like for the slightest wrong move to send a part the size of a grain of sand into another dimension.

To help make testing these parts a little easier, [IMSAI Guy] has come up with this clever little SMD test fixture. It’s designed to hook up to another custom board, which in turn connects to a wonderful old Hewlett-Packard 4275A LCR meter. The jig is based on two pogo pins mounted directly across from each other on a scrap of single-clad PCB. The spring-loaded contacts, which short together when not in use, are pulled apart to load an SMD part, like the 1-μH inductors shown in the video below. The pins hold the component firmly and make good electrical contact, allowing hands-free testing without the risk of an errant touch of the test probes sending it flying.

While the test fixture works well for larger SMDs, we could see this being a bit fussy for smaller parts. That would be easy enough to fix with perhaps some 3D-printed arms that retract the pogo pins symmetrically, holding them open until the part is loaded. A centering fixture might help too, as would a clear shield to contain any parts that get the urge to go for a ride. But, for the tactical application [IMSAI Guy] has in mind, this sure seems like enough.

Just getting into surface mount? If so, you might want to check out this handy guide to the often cryptic markings used on SMD parts.

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Affordable Networking For Your Classic Mac

December 5, 2023 by 1 Comment

The Mac SE and in particular the Mac SE/30 number among the more sought-after of the classic all-in-one Apple computers, and consequently their peripherals including network cards are also hard to find and pricey. Even attempts at re-creating them can be expensive, usually because the chips used back in the day are now nearly unobtainable. But if the search is widened to other silicon it becomes possible to create substitutes, as [Richard Halkyard] is doing with a modern version of the SE Ethernet card.

The chip which makes this possible is the Microchip ENC624J600, an embedded 10/100 Ethernet controller with an impressively configurable interface that can be easily mated to the 68k bus. For The SE it’s mapped to a memory area, while for the /30 there can be a declaration ROM which informs the machine where it is.

This is an as yet unfinished project, a work in progress. But it deserves to succeed, and if we can provide encouragement by featuring it here then it’s definitely worth a look. Or course, this is by no means the only replacement for an original board.

SE/30 picture: Cornellanense, CC BY-SA 4.0.

Retrotechtacular: The Gunsmith Of Williamsburg

December 5, 2023 by 11 Comments

A modern firearm is likely to be mass-produced using high-precision machine tools, and with a uniformity to the extent that parts from one can be interchanged with those from another. This marks a progression of centuries of innovation, in gunsmithing, in machine tooling, and in metallurgy. In the 18th century there was little of the innovations found in a modern weapon, and a rifle would have been made entirely by hand through the work of a master gunsmith. The video below the break is a fascinating 1969 film following Wallace Gusler, the gunsmith at the museum town of Williamsburg, Virginia, as he makes an 18th-century muzzle-loading flintlock rifle from raw materials. It’s a long video, but it leaves nothing out and has a really informative commentary we’re told from the gunsmith himself.

The film opens with a piece of wrought iron being forged into a long strip. We’ve talked about wrought iron as a difficult-to-find blacksmith’s material before here, so this immediately makes us curious as to what material the current Williamsburg gunsmiths use. The strip is formed round a mandrel and laboriously forge-welded to form a rough tube, before being bored with a series of drills and then rifled with a toothed slug. The finishing is done by had with a file, with the rough tube being filed to an octagonal shape. Continue reading “Retrotechtacular: The Gunsmith Of Williamsburg” →

A Single Board Computer, With Vacuum Tubes

December 5, 2023 by 8 Comments

We have occasionally featured vacuum tube computers here at Hackaday and we’ve brought you many single board computers, but until now it’s probable we haven’t brought you a machine that combined both of these things. Now thanks to [Usagi Electric] we can see just such a board, in the form of his UE-0.1, a roughly 260 by 210 mm PCB with 24 6AU6 pentodes on board that implements a simple one-bit CPU.

The architecture starts with the MC14500B 1-bit microcontroller, which was the subject of a previous vacuum tube computer. People found the unusual architecture difficult to understand, so this board is an even simpler take. It doesn’t have all the features of the Motorola original but it is (just) enough to be a CPU.

The tubes are arranged in groups of four with heaters in series from a 24 V supply, while the inputs and clock come in the form of on-board suitably retro-looking switches. The final touch is a VFD of the type used in bar graphs, were used to show the state of the various bits. It’s a fully working computer in the simplest sense, and definitely worth a look in the video below the break.

It would be interesting to see whether the tube count could be reduced further, or is this a record. The number of physical devices could be cut by using tubes with more than one device in them such as double-triodes, but perhaps that would be cheating.

Meanwhile, if you think vacuum computing is all about the old stuff, perhaps you should look at the state of the art.

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