Hackaday Europe 2026 – Build A Cable Modem For Your Arduino

July 16, 2026 by Zoe Skyforest 17 Comments

Even for those of us that are quite technically minded, we spend precious little time thinking about the cables that carry our signals and do all the important work we need them to do on a daily basis. A great deal of theory and engineering goes into making things like telephone lines and HDMI cables work, but we mostly just plug them in and get on with whatever we’re doing.

If this is your experience, you might find the Hackaday Europe talk from [Michael Wiebusch] to be particularly interesting. He dives into transmission line theory from an accessible standpoint, explaining how two disparate signals can go in opposite directions on the very same wire. Then he demonstrates the theory by building a cable modem… well, sort of!

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An Introduction To Analog Filtering

December 4, 2025 by Bryan Cockfield 8 Comments

One of the major difficulties in studying electricity, especially when compared to many other physical phenomena, is that it cannot be observed directly by human senses. We can manipulate it to perform various tasks and see its effects indirectly, like the ionized channels formed during lightning strikes or the resistive heating of objects, but its underlying behavior is largely hidden from view. Even mathematical descriptions can quickly become complex and counter-intuitive, obscured behind layers of math and theory. Still, [lcamtuf] has made some strides in demystifying aspects of electricity in this introduction to analog filters.

The discussion on analog filters looks at a few straightforward examples first. Starting with an resistor-capacitor (RC) filter, [lcamtuf] explains it by breaking its behavior down into steps of how the circuit behaves over time. Starting with a DC source and no load, and then removing the resistor to show just the behavior of a capacitor, shows the basics of this circuit from various perspectives. From there it moves into how it behaves when exposed to a sine wave instead of a DC source, which is key to understanding its behavior in arbitrary analog environments such as those involved in audio applications.

There’s some math underlying all of these explanations, of course, but it’s not overwhelming like a third-year electrical engineering course might be. For anyone looking to get into signal processing or even just building a really nice set of speakers for their home theater, this is an excellent primer. We’ve seen some other demonstrations of filtering data as well, like this one which demonstrates basic filtering using a microcontroller.

Dream Projects Face Reality

August 20, 2022 by Elliot Williams 26 Comments

Do you ever get a project stuck in your mind? An idea so good you just keep thinking about it? Going over iterations and options and pros and cons in the back of your mind, or maybe on paper, but having not yet subjected it to the hard work of pulling it into reality? I’ve had one of those lurking around for the last couple weeks, and it’s time for me to get building.

And I’ve got to get started soon, because it’s rare that any project makes the leap from thought to reality unscathed, and when I hold on to the in-thought project too long, I become far too fond of some of the details and nuances that just might not make the cut, or might get in the way of getting a first pass finished. When I really like a (theoretical) solution to a (theoretical) problem, I’ll try to make it work a lot longer than I should, and I can tell I’m getting attached to this one now.

The only cure to this illness is to get prototyping. When the rubber hits the road, and the bolts are tightened, either the solution is a good one or it’s not, and no amount of dreaming is going to change that. Building is a great antidote to the siren song of a dream project. Although it feels now like I don’t want the fantasy to have to adapt to reality, as it inevitably will, I know that getting something working feels a lot better. And it frees me up to start dreaming on the next project… To the workshop!

The Real World Strikes Back

February 12, 2022 by Elliot Williams 17 Comments

My son was into “Secret Coders“, a graphic novel series wherein a pair of kids discover and thwart a plot to take over the world by learning to program in the LOGO computer language. When I told him that these “turtle bots” were originally actually real physical things, he wanted one. So we built one out of some nice geared DC motors I had lying around.

A turtle bot has essentially three jobs: move forward in a straight line a controlled distance, turn a given number of degrees, and raise and lower a pen. If you’re already screaming “use stepper motors!” at your screen, well, you’re probably right. But I had these nice Faulhaber/Micromo geared motors with encoders that were just collecting dust in the closet, so I used ’em. And because of that, the robot stumbles on two of its three goals in life — the servo pen lifter works just fine.

Perfectly matched DC motors don’t exist. Of course I knew this, because I’ve built bots with DC motors before. But they’ve all had complex control mechanisms and/or feedback that made it moot. Not here. This bot needs to drive perfectly straight without any lines to guide it or more interesting navigation algorithms.

We spent a good half hour driving it around in not-quite-but-almost squares, tweaking each side’s PWMs, running the motors backwards for short bursts to brake the wheels, and generally trying to map degrees of rotation to milliseconds of motor drive. And you know what, my son enjoyed it. The concepts were simple enough for a second grader, and guessing the right PWM values was like a game. When we finally got it good enough, there was a small celebration.

Of course I know that what it really needs is encoder feedback. I installed those encoder gearmotors on purpose after all. But dealing with quadrature and probably a PID loop to control and sync the two sides is not for my son, at least not for another couple years. (They do learn closed-loop control theory in fourth grade these days, right?) I’ll have to do that all offline some night while he’s sleeping.

But I hope he’ll remember the lessons learned from stabbing at it the naive way. Abstractions are great, but no two motors are ever perfectly alike. You’d think you could just calibrate it out, but the motors differ in driven and coasting behavior, so you’ve got a lot more calibrating to do than you think at first. The real world is tough, and although it’s important to have theory and ideas and abstractions to guide you, you’re going to have to tweak to make it work when the wheels hit the floor. But also that it’s fun to do so, and super rewarding when it finally draws a wonky square.

The Devil Is In The Details

July 3, 2021 by Elliot Williams 28 Comments

If you’ve taken a physics class, you’ve doubtless heard tales of mythical beasts like the massless string, the frictionless bearing, and the perfect sphere. And if you’re designing something new, it’s not always wrong to start by thinking in terms of these abstractions, just to get the basic framework laid and a first-order handle on the way things go. But once you start building, you’d better be ready to shed your illusions that a 6 mm peg will fit into a 6 mm hole.

Theory and practice are the same thing, in theory. But as soon as you step into practice, your “weekend build” can easily turn into a 500-hour project, full of hurdles, discoveries, experimentation, and eventual success. I’m not going to rehash [Scott Rumschlag]’s project here — you should really watch his detailed video — but suffice it to say that when building a sub-millimeter precision 3D measuring device, bearings do have friction and string does have non-zero mass, and it all matters.

When you start working on a project that “looked good on paper” or for whatever reason just doesn’t turn out as precisely as you’d wished, you could do worse than to follow [Scott’s] example: start off by quantifying your goals, and then identify where every error along the way accumulates to keep you from reaching them. Doing precise work isn’t easy, but it’s not impossible either if you know where all the errors are coming from. You at least have a chain of improvements that you can consider, and if you’ve set realistic goals, you also know when to stop, which is almost as important.

And if anyone out there has an infinite sheet of perfectly conductive material, I’m in the market.

The Imperfect Bipolar Transistor

April 16, 2021 by Al Williams 15 Comments

We like to pretend that our circuit elements are perfect because, honestly, it makes life easier and it often doesn’t matter much in practice. For a normal design, the fact that a foot of wire has a tiny bit of resistance or that our capacitor value might be off by 10% doesn’t make much difference. One place that we really bury our heads in the sand, though, is when we use bipolar transistors as switches. A perfect switch would have 0 volts across it when it is actuated. A real switch won’t quite get there, but it will be doggone close. But a bipolar transistor in saturation won’t be really all the way on. [The Offset Volt] looks at how a bipolar transistor switches and why the voltage across it at saturation is a few tenths of a volt. You can see the video below.

To understand it, you’ll need a little bit of math and some understanding of the construction of transistors. The idea of using a transistor as a switch is that the transistor is saturated — that is, increasing base current doesn’t make much change in the collector current. While it isn’t perfect, it is good enough to switch a relay or do other common switching tasks.

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Don’t Fret Over The Ukulele

March 27, 2021 by Bryan Cockfield 17 Comments

A ukulele is a great instrument to pick to learn to play music. It’s easy to hold, has a smaller number of strings than a guitar, is fretted unlike a violin, isn’t particularly expensive, and everything sounds happier when played on one. It’s not without its limited downsides, though. Like any stringed instrument some amount of muscle memory is needed to play it fluidly which can take time to develop, but for new musicians there’s a handy new 3D printed part that can make even this aspect of learning the ukulele easier too.

Called the Easy Fret, the tool clamps on to the neck of the ukulele and hosts a series of 3D printed “keys” that allow for complex chord shapes to be played with a single finger. In this configuration the chords C, F, G, and A minor can be played (although C probably shouldn’t be considered “complex” on a ukulele). It also makes extensive use of compliant mechanisms. For example, the beams that hit the chords use geometry to imitate a four-bar linkage. This improves the quality of the sound because the strings are pressed head-on rather than at an angle.

While this project is great for a beginner learning to play this instrument and figure out the theory behind it, its creator [Ryan Hammons] also hopes that it can be used by those with motor disabilities to be able to learn to play an instrument as well. And, if you have the 3D printer required to build this but don’t have an actual ukulele, with some strings and tuning pegs you can 3D print a working ukulele as well.