Author: Al Williams

4263 Articles

Reverse Engineering STL Files With FreeCAD

October 21, 2025 by No comments

If you think about it, STL files are like PDF files. You usually create them using some other program, export them, and then expect them to print. But you rarely do serious editing on a PDF or an STL. But what if you don’t have anything but the STL? [The Savvy Engineer] has a method to help you if you need to reverse engineer an STL file in FreeCAD. Check it out in the video below.

The problem is, of course, that STLs are made up of numerous little triangles. The trick is to switch workbenches and create a shape from mesh. That gets you part of the way.

Once you have a shape, you can convert it to a solid. At that point, you can create a refined copy. This gives you a proper CAD file that you can export to a STEP file. From there, you can use it in FreeCAD or nearly any other CAD package you like to use.

Once you have a proper object, you can easily use it like any other solid body in your CAD program. This is one of those things you won’t need every day, but when you do need it, it’ll come in handy.

Want to up your FreeCAD game? We can help. There are other ways to hack up STL files. You can even import them into TinkerCAD to do simple things, but they still aren’t proper objects.

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Word Processing: Heavy Metal Style

October 20, 2025 by 10 Comments

If you want to print, say, a book, you probably will type it into a word processor. Someone else will take your file and produce pages on a printer. Your words will directly turn on a laser beam or something to directly put words on paper. But for a long time, printing meant creating some physical representation of what you wanted to print that could stamp an imprint on a piece of paper.

The process of carving something out of wood or some other material to stamp out printing is very old. But the revolution was when the Chinese and, later, Europeans, realized it would be more flexible to make symbols that you could assemble texts from. Moveable type. The ability to mass-produce books and other written material had a huge influence on society.

But there is one problem. A book might have hundreds of pages, and each page has hundreds of letters. Someone has to find the right letters, put them together in the right order, and bind them together in a printing press’ chase so it can produce the page in question. Then you have to take it apart again to make more pages. Well, if you have enough type, you might not have to take it apart right away, but eventually you will.

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Don’t Believe Planck’s Constant? Measure It Yourself

October 20, 2025 by 8 Comments

We aren’t sure if [Looking Glass Universe] didn’t trust the accepted number for Planck’s constant, or just wanted the experience of measuring it herself. Either way, she took some LEDs and worked out the correct figure. Apparently, it hasn’t changed since we first measured it in 1916. But it’s always good to check.

The constant, if you need a refresher, helps explain things like why the color of light changes how the photoelectric effect manifests, and is at the root of quantum physics. LEDs are perfect for this experiment because, of course, they come in different colors. You essentially use a pot to tune down the LED until it just reaches the point where it is dark. Presuming you know the wavelength of the LED, you can estimate Planck’s constant from that and the voltage across the virtually ready-to-light LED. We might have used the potentiometer in a voltage divider configuration, but it should work either way.

The experiment showed that even a disconnected LED emits a few stray photons. But it was still possible to interpret the results. The constant is very tiny, so you’ll want your scientific calculator get do the math or, as she used, Wolfram Alpha.

The first result was off by the alarming amount of 1 x 10-40. No, that’s not alarming at all. That number is amazingly small.

This is a fairly common home physics experiment. You can do it quick, like [Looking Glass] did, or you can build something elaborate.

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Decoding A 350 Year Old Coded Message

October 19, 2025 by 2 Comments

Usually, a story about hacking a coded message will have some computer element or, at least, a machine like an Enigma. But [Ruth Selman] recently posted a challenge asking if anyone could decrypt an English diplomatic message sent from France in 1670. Turns out, two teams managed it. Well, more accurately, one team of three people managed it, plus another lone cryptographer. If you want to try decoding it yourself, you might want to read [Ruth’s] first post and take a shot at it before reading on further here: there are spoilers below.

No computers or machines were likely used to create the message, although we imagine the codebreakers may have had some mechanized aids. Still, it takes human intuition to pull something like this off. One trick used by the text was the inclusion of letters meant to be thrown out. Because there were an odd number of Qs, and many of them were near the right margin, there was a suspicion that the Qs indicated a throw-away character and an end of line.

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Radio Astronomy In The Palm Of Your Hand

October 17, 2025 by 4 Comments

When you think of a radio telescope, you usually think of a giant dish antenna pointing skyward. But [vhuvanmakes] built Wavy-Scope, a handheld radio telescope that can find the Sun and the Moon, among other things.

The build is relatively straightforward, using a commercial LNB to detect signals in the 10-12 GHz range. The detector is a simple satellite finder, although you could also connect it to a software-defined radio, if you wanted something more sophisticated.

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DIY Telescope Uses Maker Tools

October 17, 2025 by 12 Comments

You’ve got a laser cutter. You’ve got a 3D printer. What do you make? [Ayushmaan45] suggests a telescope. The modest instrument isn’t going to do serious astronomy with only 8X worth of optics, but it would make a fine spyglass for a youngster.

The body is cut from MDF, and there are only a few 3D printed parts. The only other things you need are rubber bands and a pair of lenses. You don’t even need glue. We might have spray painted the inside of the scope black or used some black contact paper to cut down on reflections, although it probably wouldn’t make much difference.

Of course, depending on your lenses, you may have to make some changes. Or find new lenses, for that matter. We like that it doesn’t take any exotic parts. We also appreciate that it is easy for kids to take apart and put back together. It would be interesting to see how a motivated kid might alter the design, as well.

If a kid gets interested, you could move on to a more sophisticated telescope. Or maybe you’d prefer a nice microscope.

Positive Results With Negative Resistance

October 16, 2025 by 18 Comments

Try an experiment. Next time you are in a room with someone, ask them to name everything in the room. Only certain kinds of people will say “air” or “light.” For most people, those are just givens, and you don’t think about them unless, for some reason, you don’t have them. Resistance is like that in electronics. You use it constantly, but do you ever think much about what it is? For a resistor, the value in ohms really represents the slope of the line that describes the amount of voltage you’ll see across the component when it carries a certain amount of current. For resistors, that slope is — at least in theory — constant and positive. But [Void Electronics] made a video exploring negative resistance, and it is worth watching, below.

If you haven’t seen negative resistance before, you might wonder how that is possible. Ohm’s law is just a shorthand for calculating the slope of a graph with voltage on the Y axis and current on the X axis. It works because the voltage and current are always zero at the same time, so the slope is (V-0)/(I-0), and we just shorten that to the normal Ohm’s law equation.

But not everything has a linear response to current. Some devices will have different slopes over different current regions. And sometimes that slope can be negative, meaning that an increase in current through the device will cause it to drop less voltage. Of course, this is usually just over a narrow range and, as [Void] points out, most devices don’t specify that parameter on their data sheets. In fact, some transistors won’t even work in the circuit.

The circuit in question in the video below the break is an odd one. It uses two resistors, an LED, and a transistor. But the transistor’s base is left disconnected. No 555 needed. How does it work? Watch the video and you’ll see. There’s even a curve tracer if you don’t like to see hand-drawn graphs.

We’ve looked at negative resistance more than once. There are a few exotic devices, like tunnel diodes, that are explicitly used for the negative resistance property. When the gas in a neon bulb breaks down, you get the same effect. Continue reading “Positive Results With Negative Resistance” →