Lost Foam Casting In Action

May 19, 2024 by Jenny List 19 Comments

Even though not all of us will do it, many of us are interested in the art of casting metal. It remains a process that’s not out of reach, though, especially for metals such as aluminium whose melting points are reachable with a gas flame. The video below the break takes us through the aluminium casting process by showing us the lost-foam casting of a cylinder head for a BSA Bantam motorcycle.

The foam pattern is CNC milled to shape, and the leftover foam swarf is removed with a hot wire. The pattern is coated with a refractory coating of gypsum slurry, and the whole is set up in a tub packed with sand. We get the impression that the escaping gasses make this a tricky pour without an extra sprue, and indeed, they rate it as not perfect. The cooling fins on the final head are a little ragged, so it won’t be the part that goes on a bike, but we can see with a bit of refining, this process could deliver very good results.

For this pour, they use a gas furnace, but we’ve seen it done with a microwave oven. Usually, you are losing wax, not foam, but the idea is the same.

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A Tiny Tuner For The Low Power Ham

May 18, 2024 by Jenny List 10 Comments

Something that all radio amateurs encounter sooner or later is the subject of impedance matching. If you’d like to make sure all that power is transferred from your transmitter into the antenna and not reflected back into your power amplifier, there’s a need for the impedance of the one to match that of the other. Most antennas aren’t quite the desired 50 ohms impedance, so part of the standard equipment becomes an antenna tuner — an impedance matching network. For high-power hams these are big boxes full of chunky variable capacitors and big air cored inductors, but that doesn’t exclude the low-power ham from the impedance matching party. [Barbaros Aşuroğlu WB2CBA] has designed the perfect device for them: the credit card ATU.

The circuit of an antenna tuner is simple enough, two capacitors and an inductor in a so-called Pi-network because of its superficial resemblance to the Greek letter Pi. The idea is to vary the capacitances and inductance to find the best match, and on this tiny model it’s done through a set of miniature rotary switches. There are a set of slide switches to vary the configuration or switch in a load, and there’s even a simple matching indicator circuit.

We like this project, in that it elegantly provides an extremely useful piece of equipment, all integrated into a tiny footprint. It’s certainly not the first ATU we’ve brought you.

Thanks [ftg] for the tip!

How Italians Got Their Power

May 18, 2024 by Jenny List 28 Comments

We take for granted that electrical power standards are generally unified across countries and territories. Europe for instance has a standard at 230 volts AC, with a wide enough voltage acceptance band to accommodate places still running at 220 or 240 volts. Even the sockets maintain a level of compatibility across territories, with a few notable exceptions.

It was not always this way though, and to illustrate this we have [Sam], who’s provided us with a potted history of mains power in Italy. The complex twists and turns of power delivery in that country reflect the diversity of the power industry in the late 19th and early 20th century as the technology spread across the continent.

Starting with a table showing the impressive range of voltages found across the country from differing power countries, it delves into the taxation of power in Italy which led to two entirely different plug standards, and their 110/220 volt system. Nationalization may have ironed out some of the kinks and unified 220 volts across the country, but the two plugs remain.

Altogether it’s a fascinating read, and one which brings to mind that where this is being written you could still find a few years ago some houses with three sizes of the archaic British round-pin socket. Interested in the diversity of plugs? We have a link for that.

Raspberry Pi Files Paperwork With The London Stock Exchange

May 17, 2024 by Jenny List 27 Comments

If you’re a regular visitor to the Raspberry Pi website and you have a sharp eye, you may have noticed during the last few days a new link has appeared in their footer. Labelled “Investor relations“, it holds links to the documents filed with the London Stock Exchange of their intention to float. In other words, it’s confirmation of their upcoming share offering.

It has been interesting to watch the growth of Raspberry Pi over the last twelve years, from cottage industry producing a thousand boards in China, to dominating the SBC market and launching their own successful silicon. Without either a crystal ball or a window into Eben Upton’s mind, we’re as unreliable as anyone else when it comes to divining their future path. But since we’re guessing that it will involve ever more complex silicon with a raspberry logo, it’s obvious that the float will give them the investment springboard they need.

For those of us who have been around for a long time this isn’t the first company in our corner of the technology world we’ve seen burn brightly. It’s not even the first from Cambridge. Appointing ourselves as pundits though, we’d say that Raspberry Pi’s path to this point has been surprisingly understated, based upon the strength of its products rather than hype, and while Eben is undoubtedly a well-known figure, not based upon a cult of personality. There is already a significant ecosystem around Raspberry Pi, we’d like to think that this move will only strengthen it. We may not be looking at the British Microsoft, but we don’t think we’re looking at another Sinclair either.

Autochrome For The 2020s

May 12, 2024 by Jenny List 2 Comments

For all intents and purposes, photography here in 2024 is digital. Of course chemical photography still exists, and there are a bunch of us who love it for what it is, but even as we hang up our latest strip of negatives to dry we have to admit that it’s no longer mainstream. Among those enthusiasts who work with conventional black-and-white or dye-coupler colour film are a special breed whose chemistry takes them into more obscure pathways.

Wet-collodion plates for example, or in the case of [Jon Hilty], the Lumière autochrome process. This is a colour photography process from the early years of the twentieth century, employing a layer of red, green, and blue grains above a photosensitive emulsion. Its preparation is notoriously difficult, and he’s lightened the load somewhat with the clever use of CNC machinery to automate some of it.

His web site has the full details of how he prepares and exposes the plates, so perhaps it’s best here to recap how it works. Red, green, and blue dyed potato starch grains are laid uniformly on a glass plate, then dried and pressed to form a random array of tiny RGB filters. The photographic emulsion is laid on top of that, and once it is ready the exposure is made from the glass side do the light passes through the filters.

If the emulsion is then developed using a reversal process as for example a slide would be, the result is a black and white image bearing colour information in that random array, which when viewed has red, green, and blue light from those starch filters passing through it. To the viewer’s eye, this then appears as a colour image.

We can’t help being fascinated by the autochrome process, and while we know we’ll never do it ourselves it’s great to see someone else working with it and producing 21st century plates that look a hundred years old.

While this may be the first time we’ve featured such a deep dive into autochrome, it’s certainly not the first time we’ve looked at alternative photographic chemistries.

Tweeze Your Way To Soldering Success!

May 12, 2024 by Jenny List 25 Comments

Soldering, for those of us who spend a lot of time at an electronics bench, is just one of those skills we have, in the way that a blacksmith can weld or a tailor can cut clothing. We have an uncommon skill with hot metal and can manipulate the tiniest of parts, and incidentally our chopstick skills aren’t that bad as a consequence, either.

But even the best with a soldering iron can find useful tips from an expert, and that’s where [Mr SolderFix] comes in. His channel is chock-full of soldering advice, and in his latest video he takes a look at tweezers. They’re a part of the solderer’s standard kit and we all have several pairs, but it’s fair to say that we don’t always have the right pair to hand.

It was refreshing to hear him confirm that a good pair of tweezers, once a certain quality threshold has been met, need not necessarily be the most expensive set. We’ve certainly seen expensive tweezers with suspiciously bendy ends, and have found random AliExpress purchases which have stood the test of time. He also makes the point about which situations a set of tweezers with serrated heads might be more useful, and he demonstrates with a crystal oscillator.

As with photography though, we’d observe that sometimes the best set of tweezers to rectify a mishap are the ones in your hand. If you’re interested in more from [Mr SolderFix], we’ve featured his work more than once in the past. When he showed us how to lift SMD pins, for example.

The Impossible Repair: Ribbon Cables

May 11, 2024 by Jenny List 32 Comments

It’s a problem that faces many a piece of older equipment that ribbon cables of the type used on membrane keyboards start to fail as they become older. These cables are extremely difficult to repair as they can’t be soldered to, and since they are usually custom to the device in question. All is not lost, though, as [Spare Time Repair] shows us with the cable on a Honeywell heating controller broken by a user attempting to remove the battery with a screwdriver.

The whole process can be seen in the video below the break, and it involves the use of a vinyl cutter to cut the pattern of tracks in aluminium tape stuck on a sheet of acetate. This makes a new piece of ribbon cable, however it’s still a step short of being part of the circuit. His challenge is to make a clip tight enough to attach it to the intact part of the broken cable and maintain contact, then to hope that the new piece of cable bent back on itself can make enough contact for the device to work.

At the end of it all, he has a working Honeywell controller, though as he points out, it’s a device he has little interest in. Instead, this opens a window on an extremely useful technique that should be of relevance far beyond the world of heating. There’s one machine close to home for us that could use this technique, for example.

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