How Pulse Oximetry Figures Out Your Blood Oxygen Levels

May 19, 2026 by No comments

If you’ve ever had a medical team investigating cardiac issues, you’ve probably had a bunch of electrodes stuck all over your chest and been hooked up to an electrocardiogram. This is the gold standard when it comes to understanding electrical activity in the heart and can diagnose a great many conditions. However, sometimes doctors just need the basic information—your pulse rate, and whether or not there’s actually any oxygen in your blood.

Thankfully, there’s a cheap and simple device that can offer that exact information. It’s the pulse oximeter, and it’s a key piece of equipment that’s just about vital for monitoring vitals. Let’s learn how it works!

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Biofeedback Butterfly Beats With A Pulse

May 19, 2026 by No comments

Biofeedback is the idea of making one conscious of a biological process or feature, and then using this to try and exert control over the very same. [Mariia Hruntes] demonstrates this ably with a fluttering build of her own design.

In this case, the biological process being made clear is that of the user’s heartbeat. This is tracked with a MAX30102 pulse oximetry sensor, which can be used to measure both heart rate and blood oxygen levels if so desired. It’s hooked up to an Arduino Uno, which polls for pulse rate data, and then actuates an SG90 micro servo in turn. This operates the wings of a 3D printed butterfly, such that they flap in pace with the wearer’s pulse. The goal is to observe this, and then try and calm one’s self to relax and slow the flapping through the power of the mind.

It’s a simple build, but one that clearly demonstrates the concepts of biofeedback in action. We’ve seen similar principles applied to everything from aiding sleep to improving the practice of mediation. If you’re working on your own neat biofeedback project, be sure to let us know on the tipsline.

How Search Engines Enabled Finding Needles In A WWW-Sized Haystack

May 19, 2026 by 2 Comments

When the World Wide Web surged into existence during the 1990s, we were introduced to the problem of how to actually find something in this ever-ballooning construction zone that easily outpaced even the fastest post-WW2 urban sprawl. Although domain names provided a way to find servers using DNS rather than having to mash in IP addresses, you still somehow had to know the relevant URL.

A range of solutions were thought up over time, ranging from printed Yellow Pages type guides, to online curated lists of resources, as well as things like web rings where one website would link to a relevant similar website. This was the time when word-of-mouth was also very relevant, with people proudly announcing their own website on Geocities or other hosting service.

Search engines already existed long before the WWW became the hot new thing during the 1990s, but it was the WWW that would really push them to their limits. As anyone who used search engines for the WWW can attest, they had many issues. Often you’d end up using multiple search engines to find something, and despite fierce competition between web search engines to become the starting page for their browser, actually finding things on the WWW remained a tough problem.

Since a web search engine ‘just’ has to index the WWW and match a search query against the results, why was this such a hard problem that persisted until Google apparently cracked the code?

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Remembering The Tech We Lost With A Virtual Graveyard

May 19, 2026 by 14 Comments

Although 1999 might still feel like yesterday for some of us, in the world of technology the intervening years are practically an eternity. New websites, applications and devices pop up all the time, only to die off just as fast again for a variety of reasons. Amidst such chaos it’s always good to take a breather and reflect on all that we have lost, such as on the virtual graveyard that [Burak Ozdemir] created with hand-written obituaries and only the classiest of 90s-era web design.

Remembered are everything from instant messengers and social networks to web hosts and devices. Who still remembers their ICQ number? There was a good chance that you were also on GeoCities or similar web host back then too. Maybe you weren’t really into Google+, but some of us still have fond memories of its virtual hangouts that provided a connection to people around the world in a way not since replicated.

Not all of the entries are as well-known, of course, with not everyone remembering or ever having heard about services like Songza. A few rare entries on the list have punched a zombified hand through six feet of soil and shambled back into the daylight, such as the Pebble devices. Some entries are quite more recent, with many probably remembering Microsoft’s short-lived Tay that made clear that public chatbots need a lot of safety rigging, a lesson that was mostly remember by subsequent chatbots.

Although some things like forum signatures and personal homepages arguably still live on, the death of Clippy will definitely be mourned by many.

Digital Organizer Given Modern Upgrade

May 18, 2026 by 8 Comments

Remember digital organizers? They were like the lower-spec version of a PDA that couldn’t really do much more than store a few phone numbers and calendar entries. [TundraLegendZ] recently grabbed such a device from 1995 and set about transforming it into something a little more capable.

The device in question is a Casio Business Organizer Scheduling System SF-5580. The original guts have been replaced , though, with the power of a Raspberry Pi Zero. The single-board computer is hooked up to a small color LCD screen with a resolution of 480 x 800, which is tucked neatly into the spot where the original display lived. There’s also a Raspberry Pi Pico on board, which is charged with interfacing all 82 keys of the original keyboard. Power is courtesy of a 6000 mAh battery which should last a good few hours on a single charge. Hearing the buzzer hacked is fun, too. It’s more mobile phone ringtone than outright chiptune, but we still enjoyed listening to the results. Screencaps of the software show just what this setup can do with better hardware and a nicer screen than 1995 could provide. Future work is planned to give the build more capabilities with a HackRF upgrade.

We’re not convinced anyone ever got much use out of these diminutive digital organizers, but a great many were sold in the 1990s.

Prolog Via Pokémon

May 18, 2026 by 8 Comments

Like many people who read Hackaday, we are fairly fluent in a number of computer languages, but we have to admit it is easier to pick up languages that look like they group with things like Fortran. Sure, modern languages have all sorts of features, but the idea that you have a text file that executes in some order, variables, statements, and so on runs through most popular languages, but not all of them. Lisp and its variants are a different way of looking at things. And then there’s Prolog. [Alexander Petros] has an interesting way of explaining Prolog as a Pokémon game.

Prolog was “the next big thing” when AI meant expert systems. It is more of a specialized database where you define facts and rules that the computer can infer answers to queries. For example, if the facts say that Paul and Anna both have Mary as a parent, and a rule says that people with the same parent are siblings, then a query asking whether Paul and Anna are siblings will indicate that they are.

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Electroplating 3D Prints Without Requiring A Big Vat

May 18, 2026 by 19 Comments

Electroplating 3D prints is a good way to get a pretty nice coating on even a basic PLA part, but generally you’re expected to dunk the entire part into a big vat with electrolyte after coating it with the requisite conductive paint layer. This is great for small parts, like a ring you’d put on a finger, but gets rather silly when it’s a much larger part, such as the one in [Hendrik]’s recent video. Out of curiosity he tried to see whether rotating the part through a much smaller vat would still get you an even coating, or not.

Perhaps ironically this process required building a custom vat out of acrylic, as well as an entire rig to hold up the part and gently rotate it. This highlights the main disadvantage of this approach, in that unless you’re doing a small production run or otherwise get to re-use the rig a lot it’s a lot of extra effort.

That said, the rotation is controlled by an ESP32 and a stepper motor along with a requisite stepper driver, with the most exotic part being the whole custom PCB and enclosure, all of which can be used repeatedly. With all of that tested and confirmed working, the part to be plated was sanded, sprayed with conductive paint and hooked up to the rotating rig for an overnight run.

Following that the part’s new copper coating was polished before more layers of electroplating were applied to get the desired two different colors from different metals. Along the way no issues were found with this method of rotating electroplating, so if you regularly struggle with oversized parts to electroplate, this would seem to be a viable method.

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