Open-Source Knob Packed With Precision

June 28, 2025 by Matt Varian 59 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).

Modern Tech Meets Retro 7-Segment

June 23, 2025 by Matt Varian 7 Comments

At one point in time mechanical seven segment displays were ubiquitous, over time many places have replaced them with other types of displays. [Sebastian] has a soft spot for these old mechanically actuated displays and has built an open-source 7-segment display with some very nice features.

We’ve seen a good number of DIY 7-segment displays on this site before, the way [Sebastian] went about it resulted in a beautiful well thought out result. The case is 3D printed, and although there are two colors used it doesn’t require a multicolor 3d printer to make your own. The real magic in this build revolves around the custom PCB he designed. Instead of using a separate electromagnets to move each flap, the PCB has coil traces used to toggle the flaps. The smart placement of a few small screws allows the small magnets in each flap to hold the flap in that position even when the coils are off, greatly cutting down the power needed for this display. He also used a modular design where one block has the ESP32 and RTC, but for the additional blocks those components can remain unpopulated.

The work he put into this project didn’t stop at the hardware, the software also has a great number of thoughtful features. The ESP32 running the display hosts a website which allows you to configure some of the many features: the real-time clock, MQTT support, timer, custom API functions, firmware updates. The end result is a highly customizable, display that sounds awesome every time it updates. Be sure to check out the video below as well as his site to see this awesome display in action. Also check out some of the other 7-segment displays we’ve featured before.

Continue reading “Modern Tech Meets Retro 7-Segment” →

Casting Time: Exploded Watch In Resin

June 23, 2025 by Matt Varian 12 Comments

We’ve all seen the exploded view of complex things, which CAD makes possible, but it’s much harder to levitate parts in their relative positions in the real world. That, however, is exactly what [fellerts] has done with this wristwatch, frozen in time and place.

Inspired by another great project explaining the workings of a mechanical watch, [fellerts] set out to turn it into reality. First, he had to pick the right watch movement to suspend. He settled on a movement from the early 1900s—complex enough to impress but not too intricate to be impractical. The initial approach was to cast multiple layers that stacked up. However, after several failed attempts, this was ruled out. He found that fishing line was nearly invisible in the resin. With a bit of heat, he could turn it into the straight, transparent standoffs he needed.

Even after figuring out the approach of using fishing line to hold the pieces at the right distance and orientation, there were still four prototypes before mastering all the variables and creating the mesmerizing final product. Be sure to head over to his site and read about his process, discoveries, and techniques. Also, check out some of the other great things we’ve seen done with epoxy in the past.

Cube Teeter Totter: One Motor, Many Lessons

June 16, 2025 by Matt Varian 5 Comments

Balancing robots are always fun to see, as they often take forms we’re not used to, such as a box standing on its corner. This project, submitted by [Alexchunlin], showcases a cool single motor reaction cube, where he dives into many lessons learned during its creation.

At the outset, [Alexchunlin] thought this would be a quick, fun weekend project, and while he achieved that, it took longer than a weekend in the end. The cube’s frame was a simple 3D print with provisions to mount his MotorGo AXIS motor controller. This motor controller was initially designed for another project, but it’s great to see him reuse it in this build.

Once the parts were printed and assembled, the real work began: figuring out the best way to keep the cube balanced on its corner. This process involved several steps. The initial control code was very coarse, simply turning the motor on and off, but this didn’t provide the fine control needed for delicate balancing. The next step was implementing a PID control loop, which yielded much better results and allowed the cube to balance on a static surface for a good amount of time. The big breakthrough came when moving from a single PID loop to two control loops. In this configuration, the PID loop made smaller adjustments, while another control loop focused on the system’s total energy, making the cube much more stable.

By the end of the build, [Alexchunlin] had a cube capable of balancing in his hand, but more importantly, it was a great learning experience in controls. Be sure to visit the project page for more details on this build and check out his video below, which shows the steps he took along the way. If you find this project interesting, be sure to explore some of our other featured reaction wheel projects.

Continue reading “Cube Teeter Totter: One Motor, Many Lessons” →

LED Probe: A Smart, Simple Solution For Testing LEDs

June 14, 2025 by Matt Varian 13 Comments

If you’ve worked on a project with small LEDs, you know the frustration of determining their polarity. This ingenious LED Probe from [David] packs a lot of useful features into a simple, easy-to-implement circuit.

Most multimeters have a diode test function that can be used to check LEDs; however, this goes a step further. Not only will the probe light up an LED, it will light up no matter which side of the LED the leads are touching. A Red/Green LED on the probe will indicate if the probe tip is on the anode or cathode.

The probe is powered by a single CR2032 battery, and you may notice there’s no on/off switch. That’s because the probe enters a very low-current sleep mode between uses. The testing intelligence is handled by either an ATtiny85 or, in the newest version, an ATtiny202, though the basic concept and design are compatible with several other chips. All the design files for the PCB, the ATtiny code, a parts list, and a detailed explanation of how it works are available on [David]’s site, so be sure to check them out. Once you build one of these probes, you’ll want something to test it on, so explore some of the LED projects we’ve featured in the past.

2025 Pet Hacks Contest: Cat At The Door

June 12, 2025 by Matt Varian 14 Comments

This Pet Hacks Contest entry from [Andrea] opens the door to a great collaboration of sensors to solve a problem. The Cat At The Door project’s name is a bit of a giveaway to its purpose, but this project has something for everyone, from radar to e-ink, LoRa to 3D printing. He wanted a sensor to watch the door his cats frequent and when one of his cats were detected have an alert sent to where he is in the house

There are several ways you can detect a cat, in this project [Andrea] went with mmWave radar, and this is ideal for sensing a cat as it allows the sensor to sit protected inside, it works day or night, and it doesn’t stop working should the cat stand still. In his project log he has a chapter going into what he did to dial in the settings on the LD2410C radar board.

How do you know if you’re detecting your cat, some other cat, a large squirrel, or a small child? It helps if you first give your cats a MAC address, in the form of a BLE tag. Once the radar detects presence of a suspected cat, the ESP32-S3 starts looking over Bluetooth, and if a known tag is found it will identify which cat or cats are outside waiting.

Once the known cat has been identified, it’s time to notify [Andrea] that his cat is waiting for his door opening abilities. To do this he selected an ESP32 board that includes a SX1262 LoRa module for communicating with the portable notification device. This battery powered device has a low power e-paper display showing you which cat, as well as an audio buzzer to help alert you.

To read more details about this project head over to the GitHub page to check out all the details. Including a very impressive 80 page step-by-step guide showing you step by step how to make your own. Also, be sure to check out the other entries into the 2025 Pet Hacks Contest.

Continue reading “2025 Pet Hacks Contest: Cat At The Door” →

Bringing A Father Ted Joke To Life

June 8, 2025 by Matt Varian 8 Comments

Inspired by a gag from a mid-90s sitcom Father Ted, [Stephen] decided to create his own talking tape dispenser.

This project is a actually a follow-up to the first version of the dispenser he built back in 2022, and [Stephen] has documented the process thoroughly for anyone wanting to build their own. In the first version, he modified a tape dispenser to house a Raspberry Pi, enabling voice functionality. In the new version, he replaced the Raspberry Pi with a cheaper ESP8266 and designed an entirely 3D printed dispenser that looks closer to the screen-used version.

A clever change was replacing the rotary encoder with a custom encoder embedded in the printed parts. Using a photodiode and an LED, it measures the tape pulled from the spool. As you pull the tape, the encoder calculates the length and announces it through the speaker, just like in the show.

If you’re into prop recreations like this, be sure to check out the winners of our 2022 Sci-Fi Contest.

Continue reading “Bringing A Father Ted Joke To Life” →