In the movie Conan the Barbarian, we hear a great deal about “the riddle of steel.” We are never told exactly what that riddle is, but in modern times, it might be: What’s the difference between 4150 and 1020 steel? If you’ve been around a machine shop, you’ve probably heard the AISI/SAE numbers, but if you didn’t know what they mean, [Jason Lonon] can help. The video below covers what the grade numbers mean in detail.
The four digits are actually two separate two-digit numbers. Sometimes, there will be five digits, in which case it is a two-digit number followed by a three-digit number. The first two digits tell you the actual type of steel. For example, 10 is ordinary steel, while 41 is chromium molybdenum steel. The last two or three digits indicate how much carbon is in the steel. If that number is, say, 40, then the steel contains approximately 0.40% carbon.
It isn’t just a spy movie trope: secret messages often show up as microdots. [The Thought Emporium] explores the history of microdots and even made a few, which turned out to be — to quote the video you can see below — “both easier than you might think, and yet also harder in other ways.”
If you want to hide a secret message, you really have two problems. The first is actually encoding the message so only the recipient can read it. However, in many cases, you also want the existence of the message to be secret. After all, if an enemy spy sees you with a folder of encrypted documents, your cover is blown even if they don’t know what the documents say.
Today, steganography techniques let you hide messages in innocent-looking images or data files. However, for many years, microdots were the gold standard for hiding secret messages and clandestine photographs. The microdots are typically no bigger than a millimeter to make them easy to hide in plain sight.
Have you ever heard of Fordite? It was a man-made agate-like stone that originated from the Ford auto factories in the 1920s. Multiple layers of paint would build up as cars were painted different colors, and when it was thick enough, workers would cut it, polish it, and use it in jewelry. [SheltonMaker] uses a similar technique to create artwork using a laser engraver and shares how it works by showing off a replica of [Van Gogh’s] “Starry Night.”
A piece of Fordite on a pendant
The technique does have some random variation, so the result isn’t a perfect copy but, hey, it is art, after all. While true Fordite has random color layers, this technique uses specific colors layered from the lightest to the darkest. Each layer of paint is applied to a canvas. Only after all the layers are in place does the canvas go under the laser.
The first few layers of paint are white and serve as a backer. Each subsequent layer is darker until the final black layer. The idea is that the laser will cut at different depths depending on the desired lightness. A program called ImagR prepared the image as a negative image. Adjustments to the brightness, contrast, and gamma will impact the final result.
Of course, getting the exact power settings is tricky. The best result was to start at a relatively low power and then make more passes at an even lower power until things looked right. In between, compressed air cleared the print, although you have to be careful not to move the piece, of course.
There are pictures of each pass, and the final product looks great. If art’s not your thing, you can also do chip logos. While the laser used in this project is a 40-watt unit, we’ve noted before that wattage isn’t everything. You could do this—probably slower—with a lower-powered engraver.
[Mellow_Labs] wanted an Everything Presence Lite but found it was always out of stock. Therefore, he decided to create his own. The kit uses a millimeter wave sensor as a super-sensitive motion tracker for up to three people. It can even read your heart rate remotely. You can see a video of the project below.
There are a few differences from the original kit. Both use the C4001 24 GHz human presence detection sensor. However, the homebrew version also includes a BME680 environmental sensor.
Some old computer languages are destined to never die. They do, however, evolve. For example, Fortran, among the oldest of computer languages, still has adherents, not to mention a ton of legacy code to maintain. But it doesn’t force you to pretend you are using punched cards anymore. In the 1970s, if you wanted to crunch numbers, Fortran was a good choice. But there was another very peculiar language: APL. Turns out, APL is alive and well and has a thriving community that still uses it.
APL has a lot going for it if you are crunching serious numbers. The main data type is a multidimensional array. In fact, you could argue that a lot of “modern” ideas like a REPL, list types, and even functional programming entered the mainstream through APL. But it did have one strange thing that made it difficult to use and learn.
[Kenneth E. Iverson] was at Harvard in 1957 and started working out a mathematical notation for dealing with arrays. By 1960, he’d moved to IBM and a few years later wrote a book entitled “A Programming Language.” That’s where the name comes from — it is actually an acronym for the book’s title. Being a mathematician, [Iverson] used symbols instead of words. For example, to create an array with the numbers 1 to 5 in it and then print it, you’d write:
⎕←⍳5
Since modern APL has a REPL (read-eval-print loop), you could remove the box and the arrow today.
What Key Was That?
Wait. Where are all those keys on your keyboard? Ah, you’ve discovered the one strange thing. In 1963, CRTs were not very common. While punched cards were king, IBM also had a number of Selectric terminals. These were essentially computer-controlled typewriters that had type balls instead of bars that were easy to replace.
In a recent video, [Joel] of 3D Printing Nerd interviews a researcher at University of California, Berkeley about their work with glass 3D printing technology. A resin is impregnated with tiny glass nanoparticles and produces green parts. An oven burns away the resin and then another heating step produces the actual silica glass part. You can see a video about the process below.
As you might expect with glass, the temperatures are toasty. The first burn is at 1100 C and the fusing burn is at 1300 C. The nanoparticles are about 40 nanometers across. The resulting parts are tiny with very small feature sizes. The technology to do this has been around for a few years, and the University continues researching this form of computed axial lithograph (CAL) 3D printing. These parts are so small that it uses an adaptation called microCAL that produces much smaller parts at high precision. However, the equipment available today won’t produce very large objects. The video talks about the uses for some of these small glass items.
We wonder how much the firings in the ovens change the tiny tolerances. They obviously work, so either they account for that or it doesn’t shrink much.
We live in a time where there’s virtually no excuse not to have some kind of oscilloscope. As [IMSAI Guy] shows in a recent video, for what you might expect to pay for a decent meter, you can now get one that includes a scope. There are several options out there but it is hard to know how much to spend to get the best possible product. The Zoyi ZT-702S that he looks at costs under $80. But is it worth it?
Scopes that connect to your PC are often very inexpensive. You can also find little toy scopes that use a microcontroller and a little LCD screen. Even though the specs on these are usually appalling, they will still let you visualize what’s happening in a circuit. Sure, you want an expensive bench scope with lots of channels sometimes, but often, you just need to see a signal in broad strokes. Having a scope and a meter together is very handy.
