Misc Hacks

4100 Articles

Long-tail pair waves

Current Mirrors Tame Common Mode Noise

March 17, 2025 by 12 Comments

If you’re the sort who finds beauty in symmetry – and I’m not talking about your latest PCB layout – then you’ll appreciate this clever take on the long-tailed pair. [Kevin]’s video on this topic explores boosting common mode rejection by swapping out the old-school tail resistor for a current mirror. Yes, the humble current mirror – long underestimated in DIY analog circles – steps up here, giving his differential amplifier a much-needed backbone.

So why does this matter? Well, in Kevin’s bench tests, this hack more than doubles the common mode rejection, leaping from a decent 35 dB to a noise-crushing 93 dB. That’s not just tweaking for tweaking’s sake; that’s taking a breadboard standard and making it ready for sensitive, low-level signal work. Instead of wrestling with mismatched transistors or praying to the gods of temperature stability, he opts for a practical approach. A couple of matched NPNs, a pair of emitter resistors, and a back-of-the-envelope resistor calculation – and boom, clean differential gain without the common mode muck.

If you want the nitty-gritty details, schematics of the demo circuits are on his project GitHub. Kevin’s explanation is equal parts history lesson and practical engineering, and it’s worth the watch. Keep tinkering, and do share your thoughts on this.

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You Know Pi, But Do You Really Know E?

March 14, 2025 by 28 Comments

Pi Day is here! We bet that you know that famous constant to a few decimal points, and you could probably explain what it really means: the ratio of a circle’s circumference to its diameter. But what about the constant e? Sure, you might know it is a transcendental number around 2.72 or so. You probably know it is the base used for natural logarithms. But what does it mean?

The poor number probably needed a better agent. After all, pi is a fun name, easy to remember, with a distinctive Greek letter and lots of pun potential. On the other hand, e is just a letter. Sometimes it is known as Euler’s number, but Leonhard Euler was so prolific that there is also Euler’s constant and a set of Euler numbers, none of which are the same thing. Sometimes, you hear it called Napier’s constant, and it is known that Jacob Bernoulli discovered the number, too. So, even the history of this number is confusing.

But back to math, the number e is the base rate of growth for any continually growing process. That didn’t help? Well, consider that many things grow or decay through growth. For example, a bacteria culture might double every 72 hours. Or a radioactive sample might decay a certain amount per century. Continue reading “You Know Pi, But Do You Really Know E?” →

The Mysterious And Important Work Of Prop Design On Severance

March 13, 2025 by 28 Comments

Have you seen Severance? Chances are good that you have; the TV series has become wildly popular in its second season, to the point where the fandom’s dedication is difficult to distinguish from the in-universe cult of [Kier]. Part of the show’s appeal comes from its overall aesthetic, which is captured in this description of the building of one of the show’s props.

A detailed recap of the show is impossible, but for the uninitiated, a mega-corporation called Lumon has developed a chip that certain workers have implanted in their brains to sever their personalities and memories into work and non-work halves. The working “Innies” have no memory of what their “Outies” do when they aren’t at work, which sounds a lot better than it actually ends up being. It’s as weird as it sounds, and then some.

The prop featured here is the “WoeMeter” from episode seven of season two, used to quantify the amount of woe in a severed worker — told you it was weird. The prop was built by design house [make3] on a short timeline and after seeing only some sketches and rough renders from the production designers, and had to echo the not-quite-midcentury modern look of the whole series. The builders took inspiration from, among other things, a classic Nagra tape recorder, going so far as to harvest its knobs and switches to use in the build. The controls are all functional and laid out in a sensible way, allowing the actors to use the device in a convincing way. For visual feedback, the prop has two servo-operated meters and a string of seven-segment LED displays, all controlled by an ESP-32 mounted to a custom PCB. Adding the Lumon logo to the silkscreen was a nice touch.

The prop maker’s art is fascinating, and the ability to let your imagination run wild while making something that looks good and works for the production has got to be a blast. [make3] really nailed it with this one.

Thanks to [Aaron’s Outie] for the tip.

Fixing An Unpleasant SD Card Slot Issue In A NanoVNA

March 9, 2025 by 9 Comments

SD cards & the much smaller microSD cards are found on many devices, with the card often accessible from outside the enclosure. Unfortunately there’s a solid chance that especially small microSD cards will find their way past the microSD card reader slot and into the enclosure. This is what happened to [Rob] of the SevenFortyOne Radios and Repairs channel on YouTube with a NanoVNA unit. While shaking the unit, you can clearly hear the microSD card rattling inside, courtesy of the rather large gap above the card slot.

After a quick teardown and extracting the lost microSD card, the solution to prevent this is a simple bit of foam stuck on top of the microSD card slot, so that the too large opening in the enclosure is now fully blocked. It’s clearly a bit of a design fail in this particular NanoVNA unit, worsened by the tiny size of the card and having to use a fingernail to push the card into the slot as it’s so far inside the enclosure.

While [Rob] seems to blame himself for this event, we’d chalk it mostly up to poor design. It’s an issue that’s seen with certain SBC enclosures and various gadgets too, where losing a microSD card is pretty much a matter of time, and hugely fiddly at the best of times. That said, what is your preferred way of handling microSD card insertion & removal in devices like these?

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A 3D-printed, hand-cranked, toy conveyor belt designed after the transporter belts in Factorio.

Designing A Toy Conveyor Belt For Fun And Profit

March 5, 2025 by 4 Comments

[Hope This Works] wants to someday build a tiny factory line in the garage, with the intent of producing some simple widget down the line. But what is a tiny factory without tiny conveyor belts? Not a very productive one, that’s for sure.

As you may have noticed, this is designed after the transporter belts from the game Factorio. [Hope This Works] ultimately wants something functional that’s small enough to fit in one hand and has that transporter belt aesthetic going. He also saw this as a way to level up his CAD skills from approximately 1, and as you’ll see in the comprehensive video after the break, that definitely happened.

And so [Hope This Works] started by designing the all-important sprockets. He found a little eight-toothed number on McMaster-Carr and used the drawing for reference. From there, he designed the rest of the parts around the sprockets, adding a base so that it can sit on the desk or be held in the hand.

For now, this proof-of-concept is hand-cranked. We especially love that [Hope This Works] included a square hole for the crank handle to stand in when not in use. Be sure to check out the design/build video after the break to see it in action.

How happy would you be to see Factorio come up in a job interview?

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Haptic Displays Bring Sports To The Vision Impaired

March 5, 2025 by 3 Comments

When it comes to the majority of sports broadcasting, it’s all about the visual. The commentators call the plays, of course, but everything you’re being shown at home is on a screen. Similarly, if you’re in the stadium, it’s all about getting the best possible view from the best seats in the house.

Ultimately, the action can be a little harder to follow for the vision impaired. However, one company is working hard to make sports more accessible to everyone. Enter OneCourt, and their haptic sports display technology.

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“Some Assembly Required” Makes Us Love Things More

March 2, 2025 by 36 Comments

For the maker looking to turn their project into a business, trying to price your widget can be a bit of a conundrum. You want to share your widget with the world without going broke in the process. What if you could achieve both, letting the end user finish assembly? [PDF]

While over a decade has passed since Harvard Business School released this study on what they dub “The IKEA Effect,” we suspect that most of it will still be relevant given the slow pace of human behavior change. In short, when you make someone become part of the process of manufacturing or assembling their stuff, it makes them value it more highly than if it was already all put together in the box.

Interestingly, the researchers found “that consumers believe that their self-made products rival those of experts,” and that this is true regardless of whether these people consider themselves to be DIY enthusiasts or not. This only holds if the person is successful though, so it’s critical to have good instructions. If you have a mass market item in the works, you probably don’t want to require someone with no experience to solder something, but as IKEA has shown, nearly anybody can handle some hex screws and Allen wrenches.

If you’re looking for more advice on how to get your invention in people’s hands, how about this Supercon talk by Carrie Sundra about manufacturing on a shoestring budget or this video from Simone Giertz on her experiences with manufacturing from idea to finished product. You might want to steer clear of people promising patents for pennies on commercials, though.