Hackaday Podcast Episode 327: A Ploopy Knob, Rube-Goldberg Book Scanner, Hard Drives And Power Grids Oscillating Out Of Control

July 4, 2025 by 7 Comments

It’s Independence Day here in the USA, but if you’re not a fan of fireworks and hot dogs, Elliot and Dan’s rundown of the best hacks of the week is certainly something to celebrate. Rest easy, because nothing exploded, not even the pneumatic standing desk that [Matthias] tore into, nor the electroplated 3D prints that [H3NDRIK] took a blowtorch to. We both really loved the Ploopiest knob you’ve ever seen, which would be even Ploopier in anodized aluminum, as well as an automatic book scanner that takes its job very seriously. We looked into the mysteries of the Smith chart, another couple of fantastic student projects out of Cornell, the pros and cons of service loops, and what happened when the lights went out in Spain last Spring. And what does Janet Jackson have against laptops anyway?

 

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Ploppy knob

Open-Source Knob Packed With Precision

June 28, 2025 by 61 Comments

The world of custom mechanical keyboards is vibrant, with new designs emerging weekly. However, keyboards are just one way we interact with computers. Ploopy, an open-source hardware company, focuses on innovative user interface devices. Recently, [Colin] from Ploopy introduced their latest creation: the Ploopy Knob, a compact and thoughtfully designed control device.

At first glance, the Ploopy Knob’s low-profile design may seem unassuming. Housed in a 3D-printed enclosure roughly the size of a large wristwatch, it contains a custom PCB powered by a USB-C connection. At its core, an RP2040 chip runs QMK firmware, enabling users to easily customize the knob’s functions.

The knob’s smooth rotation is achieved through a 6705ZZ bearing, which connects the top and bottom halves and spans nearly the device’s full width to eliminate wobble. Unlike traditional designs, the Ploopy Knob uses no mechanical encoder or potentiometer shaft. Instead, an AS5600 magnetic encoder detects movement with remarkable precision. This 12-bit rotary encoder can sense rotations as fine as 0.088 degrees, offering 4096 distinct positions for highly accurate control.

True to Ploopy’s philosophy, the Knob is fully open-source. On its GitHub Page, you’ll find everything from 3D-printed case files to RP2040 firmware, along with detailed guides for assembly and programming. This transparency empowers users to modify and build their own versions. Thanks to [Colin] for sharing this innovative device—we’re excited to see more open-source hardware from Ploopy. For those curious about other unique human-machine interfaces, check out our coverage of similar projects. Ploopy also has designs for trackballs (jump up a level on GitHub and you’ll see they have many interesting designs).

Look! It’s A Knob! It’s A Jack! It’s Euroknob!

April 28, 2025 by 25 Comments

Are your Eurorack modules too crowded? Sick of your patch cables making it hard to twiddle your knobs? Then you might be very interested in the new Euroknob, the knob that sports a hidden patch cable jack.

Honestly, when we first saw the Euroknob demo board, we thought [Mitxela] had gone a little off the rails. It looks like nothing more than a PCB-mount potentiometer or perhaps an encoder with a knob attached. Twist the knob and a row of LEDs on the board light up in sequence. Nice, but not exactly what we’re used to seeing from him. But then he popped the knob off the board, revealing that what we thought was the pot body is actually a 3.5-mm audio jack, and that the knob was attached to a mating plug that acts as an axle.

The kicker is that underneath the audio jack is an AS5600 magnetic encoder, and hidden in a slot milled in the tip of the audio jack is a tiny magnet. Pop the knob into the jack, give it a twist, and you’ve got manual control of your module. Take the knob out, plug in a patch cable, and you can let a control voltage from another module do the job. Genius!

To make it all work mechanically, [Mitxela] had to sandwich a spacer board on top of the main PCB. The spacer has a large cutout to make room for the sensor chip so the magnet can rotate without hitting anything. He also added a CH32V003 to run the encoder and drive the LEDs to provide feedback for the knob-jack. The video below has a brief demo.

This is just a proof of concept, to be sure, but it’s still pretty slick. Almost as slick as [Mitxela]’s recent fluid-motion simulation pendant, or his dual-wielding soldering irons.

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Android Head Unit Gets Volume Knob Upgrade

January 17, 2025 by 22 Comments

Touch screen head units are pretty much the norm these days. Many compromise with annoying on-screen volume controls or tiny buttons. If you find yourself with such a unit, you  might like to hack in a real volume knob. [Daniel Ross] shows us how to do just that.

The build uses an ATMega328 as the heart of the operation, though [Daniel] notes an Arduino Uno or Mini would have done just fine. It’s set up with a 74HC14 hex Schmitt trigger, and a CD4066 quad bilateral switch on a custom PCB. As for the volume knob itself, it’s not a real analog pot, instead it’s using a rotary encoder with a center push button. The way it works is that the Arduino reads the encoder, and figures out whether you’re trying to turn the volume up or down based on the direction you’re turning it. It then sends commands to the CD4066 to switch resistors in and out of circuit with lines going to the stereo to emulate the action of volume buttons on the steering wheel.

[Daniel’s] guide explains how everything works in greater detail, and how you can calibrate your head unit to accept these signals while preserving the function of your actual steering wheel volume buttons. Then you just have to find a neat way to integrate the knob into your existing dashboard.

We don’t see as many car stereo hacks in this era when infotainment systems rule all, but we’ve seen some great stuff from older vehicles over the years. Video after the break.

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Turn A Mouse Into An Analogue Tuning Knob

September 27, 2024 by 4 Comments

The software defined radio has opened up unimaginable uses of the radio spectrum for radio enthusiasts, but it’s fair to say that there’s one useful feature of an old-fashioned radio they lack when used via a computer. We’re talking of course about the tuning knob, because it represents possibly the most intuitive way to move across the bands. Never fear though, because [mircemk] has a solution. He’s converted a mouse into a tuning dial.

The scroll wheel on a mouse is nothing more than a rotary encoder, and can easily be used as a sort of tuning knob. Replacing it with a better encoder gives it a much better feel, so that’s what he’s done. An enclosure has the guts of a mouse, with the front-mounted encoder wired into where the scroll wheel would have been. The result, for a relatively small amount of work, is a tuning knob, and a peripheral we’re guessing could also have a lot of uses beyond software defined radio.

It’s not the first knob we’ve seen, for that you might want to start with the wonderfully named Tiny Knob, but it’s quite possibly one of the simplest to build. We like it.

Steel Reinforcement Toughens Cracked Vintage Knobs

September 21, 2024 by 8 Comments

Nothing can ruin a restoration project faster than broken knobs. Sure, that old “boat anchor” ham rig will work just fine with some modern knobs, but few and far between are the vintage electronics buffs that will settle for such aesthetic affrontery. But with new old stock knobs commanding dear prices, what’s the budget-conscious restorationist to do? Why, fix the cracked knobs yourself, of course.

At least that’s what [Level UP EE Lab] tried with his vintage Heahkit DX60 ham transmitter, with pretty impressive results. The knobs on this early-60s radio had all cracked thanks to years of over-tightening the set screws. To strengthen the knobs, he found some shaft collars with a 1/4″ inside diameter and an appropriate set screw. The backside of the knob was milled out to make room for the insert, which was then glued firmly in place with everyone’s go-to adhesive, JB Weld. [Level UP] chose the “Plastibonder” product, which turns out not to be an epoxy but rather a two-part urethane resin, which despite some initial difficulties flowed nicely around the shaft collar and filled the milled-out space inside the knob. The resin also flowed into the channels milled into the outside diameter of the shaft collars, which are intended to grip the hardened resin better and prevent future knob spinning.

It’s a pretty straightforward repair if a bit fussy, but the result is knobs that perfectly match the radio and still have the patina of 60-plus years of use. We’ll keep this technique in mind for our next restoration, or even just an everyday repair. Of course, for less demanding applications, there are always 3D printed knobs.

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A Tiny Knob Keeps You In Control

August 11, 2024 by 35 Comments

There are many forms of human interface device beyond the ubiquitous keyboard and mouse, but when it comes to fine-tuning a linear setting such as a volume control there’s nothing quite like a knob. When it comes to peripherals it’s not the size that matters, as proven by  [Stefan Wagner] with the Tiny Knob. It’s a very small PCB with a rotary encoder and knob, an ATtiny85, a USB port, and not much else.

It uses the V-USB software implementation of USB HID, and should you have a need for a Tiny Knob of your own you can find all the files for it in a GitHub repository. There’s even a very professional-looking 3D-printed enclosure for the finishing touch. We like this project for its simplicity, and we think you might too.

Over the years we’ve brought you more than one knob, they appear to be a popular subject for experimentation. If you’re up for more, have a look at this one.