4-bit Relay Logic Counter Begs To Have Its Buttons Pushed

May 31, 2026 by Donald Papp 4 Comments

What’s one to do with some nice little relays of questionable pinout, and prototyping board? How about a quietly clicky 4-bit counter using relay logic with tons of buttons?

The register with LEDs and buttons is on the top board, the incrementer on the bottom board.

[Agatha Mallett] made the counter after finding herself in possession of a quantity of relays burdened by terrible documentation (the datasheet shockingly lacks a pinout, and doesn’t even mention the coil being unidirectional). But since the relays are also small and of decent quality, they were a good candidate for a small relay logic-based project.

The key to the build is implementing D-type flip-flops using relays. This is done by holding the coil voltage of each relay between its set and release voltage levels. A small voltage bump will energize the coil, closing the relay and leaving it closed. Conversely, a small negative spike releases the coil, leaving it open. This forms the basis of the counter, and [Agatha] has a separate write-up all about the details of using relays in this way.

Implementing this was rather less straightforward than it may sound because it relies on balancing the coils of many relays on a figurative knife-edge of voltage, but not every component is perfectly identical. A tweaked resistor or capacitor here and there was needed before things settled into reliability.

The end product has indicator LEDs, buttons to increment or clear the current count, and it even has buttons to set or clear individual bits. This is a project that begs to be interacted with, and there’s a short video on the project page so you can watch it go through its paces.

Thanks to [Jess] for the tip!

DIY Potentiometer Is A Great Teaching Aid

May 20, 2026 by Zoe Skyforest 16 Comments

A potentiometer is a simple electrical device that allows resistance to be varied at will. Most everyone in the electronics field is intimately familiar with how they work on a fundamental level. Of course, we all had to be taught once, though, and a great way to do that would be with a teaching tool like the one [DiscoLapy] built.

What you’re looking at here is a very simple potentiometer that bares its function for all to see. It consists of a 3D printed base and knob, which form the mechanical part of the device. A paper track is then laid on top to act as the main resistive element, once properly covered with graphite from a regular old pencil. From there, it’s as simple as adding the necessary contacts and wiper to the device, and you’ve got a potentiometer sitting in front of you.

What’s great about this build is that it’s very intuitive. Just by looking at it or putting it together, you get a straightforward understanding of everything that’s going on. By drawing the resistive trace, and by turning the knob, particularly if hooked up to an LED or something like in the demonstration, it’s easy to see how the potentiometer varies its resistance and affects a circuit.

We’ve featured some other fantastic teaching tools in the past, too. If you’ve got your own educational gems, be sure to let us know.

Qualcomm’s New QCC74x Appears To Target The ESP32 MCUs

May 17, 2026 by Maya Posch 38 Comments

These days wireless microcontrollers featuring built-in WiFi and Bluetooth are all the rage, with Espressif’s range of ESP32 MCUs being the default option for commercial and hobbyist projects alike. This makes Qualcomm’s recently released QCC74x MCU rather interesting, as specification-wise it would seem to be placed firmly in ESP32 territory.

On the radio side you get 1×1 WiFi 6, Bluetooth 5.4, and IEEE 802.15.4 (e.g. Thread and Zigbee), coupled with a single-core 352 MHz RISC-V CPU with FPU and DSP features and 484 kB of SRAM. The SDK for this MCU is hosted on Codelinaro, featuring the typical FreeRTOS-based stack, though confusingly Bluetooth and Zigbee support are currently marked as ‘not supported’. This might still be in progress.

Where the competition with Espressif feels clear is in the pricing, with the highest-performance evaluation board (QCC748M EVK, pictured above) listed for $13 (before taxes/tariffs). This gets you 8 MB of PSRAM built-in with unspecified link speed, but likely the same QSPI as used for the NOR Flash. USB support is available on this higher-end tier, while absent on the QCC743. Development documentation is also available, and looks fairly complete based on first glance.

Overall the QCC74x looks to be an upgrade to the older and significantly less powerful QCC730 MCU. Depending on software support and final pricing it could make for an interesting competitor to some of Espressif’s modules like its ESP32-C series or ESP32-S2, though the upcoming ESP32-S31 would seem to have it matched or beat on all metrics.

Y-zipper: 3D Printing Flexible–Rigid Transition Mechanism For Rapid And Reversible Assembly

May 13, 2026 by Maya Posch 20 Comments

Along with Velcro, zippers have become an integral part of every day life, being a quick and easy way to usually temporarily join fabric together. Which isn’t to say that you cannot do more with the basic zipper concept, including using them to turn floppy 2D shapes into rigid 3D ones, such as with the Y-zipper concept proposed and demonstrated by [Jiaji Li] et al.

Although not a fully new idea, the Y-zipper is compared with a range of similar mechanisms that do not feature the same abilities, including the standard zipper ease of zipping up, the possibility of having curved geometry and automatic actuation.

Plus there is that the Y-zipper is designed from the start to be 3Dprinted, while still following the same basic pattern of interlocking teeth that the slider mechanism alternately pushes together or pulls apart.

By modifying the basic straight design of the flat strips, the resulting zipped-up form can take on a distinct bend, as well as turn into a coil or a screw. With a demonstrated joint design it is then possible to join multiple Y-zipper rods together, which could make for an interesting alternative to traditional pop-up tent supports, for example.

Also demonstrated is the use of TPU to create compliant bridges, as well as the direct integration of fabric, to show the versatility of the technology. With the used materials (PLA, TPU) the researchers estimate a maximum viable length of about 3 meters before the printed structures begin to disintegrate.

This Random Number Generator Does It With Neon

May 12, 2026 by Donald Papp 16 Comments

The quest for true randomness has roots in cryptography and is a rabbit hole that gets surprisingly deep with alarmingly rapidity. Still, the generation of random-enough numbers is a popular hacker project. Part of the appeal is the way these devices strive to incorporate physical phenomena, and in [Joshua Coleman]’s case, his Neon Entropy (Pseudo) Random Number Generator uses a trio of vintage neon lamps.

Neon lamps discharge at rates that vary unpredictably. They’re also pretty to look at.

[Joshua] chose neon lamps in part because the discharge rate of an energized lamp is a variable, physical process that makes a good source of entropy. They also have an attractive visual appeal that fits the concept [Joshua] had in mind. Unlike random number generators that kick off by measuring radiation or some other imperceptible thing, it’s possible — at least in a sense — to see this one working.

The small variations in the three neon lamps are measured optically by three TEPT4400 ambient light sensors (isolated from the neon lamps themselves) and turned into analog signals. A Raspberry Pi Pico W reads these signals, then uses them in a process that culminates in SHA-256 64-bit values that can be used as random seeds.

There’s also a web dashboard that shows everything live, furthering the “watch it work” concept [Joshua] is aiming for. The video below shows the project in action if you want to see how the sausage gets made.

Earlier we mentioned how random number generators are popular projects among hackers, and here are a few selected ones. Don’t miss the stylish glow and slick enclosure of this Nixie tube RNG, or the lava lamp RNG which is in fact not a gimmick. And while it is commonly understood that meaningful randomness must come from outside a digital chip, uninitialized internal volatile RAM — if accessed correctly — can be a remarkably good source of entropy.

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Squeezing Fluids With The Right Peristaltic Pump For The Task

May 3, 2026 by Maya Posch 6 Comments

Peristaltic pumps are a very simple and effect device for transferring fluids without said fluid ever coming into contact with any part of the pump mechanism. At their core they involve a mechanism squeezing fluids through compressible tubing, but there are various implementations of such a mechanism that all have their pros and cons. In a recent article by [T. K. Hareendran] over at EDN these types are discussed and when you’d want to pick one over the other.

Also known as a roller pump, these positive displacement pumps have been known since the 19th century, finding uses in industrial, medical, research, agriculture and many other fields. Each of these fields have different requirements with the use of a peristaltic pump as a dosing pump being a specific application whereby e.g. a stepper motor can be used to provide exact dosing.

For industrial settings the typical rollers that compress the tube are replaced with shoes that provide higher pressures and endurance, with overall a bewildering number of motor types and tubing materials available. Depending on what your project needs, you may opt for continuous flow, fine control over dosing, the ability to reverse the flow, etc.

Unless your project is particularly rugged, a roller-based mechanism should be fine, while silicone tubing is great for biocompatibility and PVC is a cheaper tube material option. If you intend to transfer certain kinds of chemicals that will react with each of these there are some more exotic tubing options available as well.

We have previously covered projects that use a peristaltic pump for rather interesting things, such as DIY pharmaceutics, in a home-grown flow battery, not to mention creating DIY peristaltic pumps from first principles.

Five Different Styles Of Cardboard Hinges

April 30, 2026 by Maya Posch 5 Comments

One doesn’t generally associate cardboard with structural components like hinges, but [Itoshige Studio] assures us that you can absolutely create hinges out of this ubiquitous material. In total the video covers five different designs, ranging from the simple and straightforward to an interlocking tab design that approximates a typical steel hinge with paper rod to keep both sides of the hinge together.

Simple paper hinge. (Credit: Itoshige Studio, YouTube)

The most simplistic hinge is unsurprisingly just a strip of craft paper, which is also demonstrated as the hinge for a wooden box in lieu of the typical metal hinge. This same principle is then demonstrated for a fancy cardboard box.

From here the designs get increasingly more involved. First a seamless hinge variation, and then a kamichoban hinge design that’s inspired by traditional Japanese room dividers and furniture, using panels that are interconnected with overlapping sections to create a fascinatingly flexible hinge that can fully fold either way.

The flush hinge design is somewhat like the craft paper hinge, but significantly fancier and probably sturdier, while also looking pretty good on something like a cabinet. Finally the interlocking tab hinge is effectively a cardboard version of the hinge design that’s found on every room’s door, with a similar level of flexibility. This is obviously the trickiest one to assemble and get right, but it has its own charm.

Considering that all of these examples use regular corrugated cardboard that we get shipped to our homes by the truckload, the cost to try these examples is your time plus some basic tools and glue. The author also sells a book that contains templates – in addition to digital versions – for these hinges and other designs, if you’d like to enjoy the 100% paper experience.

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