Making Liquid Oxygen: Far From Easy But Worth The Effort

April 9, 2025 by Dan Maloney 26 Comments

Normally, videos over at The Signal Path channel on YouTube have a certain vibe, namely teardowns and deep dives into high-end test equipment for the microwave realm. And while we always love to see that kind of content, this hop into the world of cryogenics and liquid oxygen production shows that [Shahriar] has other interests, too.

Of course, to make liquid oxygen, one must first have oxygen. While it would be easy enough to get a tank of the stuff from a gas supplier, where’s the fun in that? So [Shahriar] started his quest with a cheap-ish off-the-shelf oxygen concentrator, one that uses the pressure-swing adsorption cycle we saw used to great effect with DIY O₂ concentrators in the early days of the pandemic. Although analysis of the machine’s output revealed it wasn’t quite as capable as advertised, it still put out enough reasonably pure oxygen for the job at hand.

The next step in making liquid oxygen is cooling it, and for that job [Shahriar] turned to the cryocooler from a superconducting RF filter, a toy we’re keen to see more about in the future. For now, he was able to harvest the Stirling-cycle cryocooler and rig it up in a test stand with ample forced-air cooling for the heat rejection end and a manifold to supply a constant flow of oxygen from the concentrator. Strategically placed diodes were used to monitor the temperature at the cold end, a technique we can’t recall seeing before. Once powered up, the cryocooler got down to the 77 Kelvin range quite quickly, and within an hour, [Shahriar] had at least a hundred milliliters of lovely pale blue fluid that passed all the usual tests.

While we’ve seen a few attempts to make liquid nitrogen before, this might be the first time we’ve seen anyone make liquid oxygen. Hats off to [Shahriar] for the effort.

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Implantable Battery Charges Itself

April 25, 2024 by Bryan Cockfield 18 Comments

Battery technology is the major limiting factor for the large-scale adoption of electric vehicles and grid-level energy storage. Marginal improvements have been made for lithium cells in the past decade but the technology has arguably been fairly stagnant, at least on massive industrial scales. At smaller levels there have been some more outside-of-the-box developments for things like embedded systems and, at least in the case of this battery that can recharge itself, implantable batteries for medical devices.

The tiny battery uses sodium and gold for the anode and cathode, and takes oxygen from the body to complete the chemical reaction. With a virtually unlimited supply of oxygen available to it, the battery essentially never needs to be replaced or recharged. In lab tests, it took a bit of time for the implant site to heal before there was a reliable oxygen supply, though, but once healing was complete the battery’s performance leveled off.

Currently the tiny batteries have only been tested in rats as a proof-of-concept to demonstrate the chemistry and electricity generation capabilities, but there didn’t appear to be any adverse consequences. Technology like this could be a big improvement for implanted devices like pacemakers if it can scale up, and could even help fight diseases and improve healing times. For some more background on implantable devices, [Dan Maloney] catches us up on the difficulties of building and powering replacement hearts for humans.

Implant Fights Diabetes By Making Insulin And Oxygen

October 10, 2023 by Dan Maloney 13 Comments

Type 1 diabetes remains a problem despite having an apparently simple solution: since T1D patients have lost the cells that produce insulin, it should be possible to transplant those cells into their bodies and restore normal function. Unfortunately, it’s not actually that simple, and it’s all thanks to the immune system, which would attack and destroy transplanted pancreas cells, whether from a donor or grown from the patient’s own stem cells.

That may be changing, though, at least if this implantable insulin-producing bioreactor proves successful. The device comes from MIT’s Department of Chemical Engineering, and like earlier implants, it relies on encapsulating islet cells, which are the insulin-producing cells within the pancreas, inside a semipermeable membrane. This allows the insulin they produce to diffuse out into the blood, and for glucose, which controls insulin production in islet cells, to diffuse in. The problem with this arrangement is that the resource-intensive islet cells are starved of oxygen inside their capsule, which is obviously a problem for the viability of the implant.

The solution: electrolysis. The O₂-Macrodevice, as the implant is called, uses a tiny power-harvesting circuit to generate oxygen for the islet cells directly from the patient’s own interstitial water. The circuit applies a current across a proton-exchange membrane, which breaks water molecules into molecular oxygen for the islet cells. The hydrogen is said to diffuse harmlessly away; it seems like that might cause an acid-base imbalance locally, but there are plenty of metabolic pathways to take care of that sort of thing.

The implant looks promising; it kept the blood glucose levels of diabetic mice under control, while mice who received an implant with the oxygen-generating cell disabled started getting hyperglycemic after two weeks. What’s really intriguing is that the study authors seem to be thinking ahead to commercial production, since they show various methods for mass production of the cell chamber from standard 150-mm silicon wafers using photolithography.

Type 1 diabetics have been down the “artificial pancreas” road before, so a wait-and-see approach is clearly wise here. But it looks like treating diabetes less like a medical problem and more like an engineering problem might just pay dividends.

Printable Portable Mask Gives You The Numbers On Your Workout

January 16, 2022 by Dan Maloney 7 Comments

We’re currently in the midst of New Year’s Resolutions season, which means an abundance of spanking new treadmills and exercise bikes. And one thing becomes quickly obvious while using those machines: the instruments on them are, at best, only approximately useful for measuring things like your pulse rate, and in the case of estimating the calories burned by your workout, are sometimes wildly optimistic.

If precision quantification of your workout is your goal, you’ll need to monitor your “VO₂max”, a task for which this portable, printable mask is specifically designed. This is [Robert Werner]’s second stab at a design that senses both pressure differential and O₂ concentration to calculate the maximum rate of oxygen usage during exercise. This one uses a commercially available respirator, of the kind used for painting or pesticide application, as the foundation for the build. The respirator’s filter elements are removed from the inlets to provide free flow of air into the mask, while a 3D printed venturi tube is fitted to its exhaust port. The tube houses the pressure and O₂ sensors, as well as a LiPo battery pack and an ESP32. The microcontroller infers the volume of exhaled air from the pressure difference, measures its O₂ content, and calculates the VO₂ max, which is sent via Bluetooth to a smartphone running an exercise tracking app like Zwift or Strava.

[Robert] reports that his $100 instrument compares quite well to VO₂ max measurements taken with a $10,000 physiology lab setup, which is pretty impressive. The nice thing about the design of this mask is how portable it is, and how you can take your exercise routine out into the world — especially handy if your fancy exercise bike gets bricked.

Two views of the M19O2 oxygen concentrator

Design Improvements Make DIY Oxygen Concentrator Even Better

August 18, 2021 by Dan Maloney 8 Comments

A lot of projects we feature on these pages are of the “one and done” variety — tactical builds that serve a specific purpose with little need for further development. Some projects, though, come out as rough prototypes and then go through multiple rounds of refinement, a process we really enjoy tracking down and following. And when the project is something as important as an oxygen concentrator that can be built and maintained easily, all the better.

The need for cheap oxygen concentrators stems directly from the COVID-19 pandemic, which suggested that high-flow oxygen therapy was a better choice than invasive intubations and mechanical ventilation. But medical-grade oxygen isn’t always easy to come by in all parts of the world, so easily built oxygen concentrators, which rely on the nitrogen-adsorbing properties of the mineral zeolite, are meant to fill the gaps. Early versions of the M19O2 and the related OxyKit concentrator, had a very homebrew feel to them, built on wooden frames as they were. And while the rustic nature of the early builds didn’t detract from their utility, the hackers behind them, including our own [Anool Mahidharia], have been making incremental improvements aimed at not only making the devices work better, but also making them easier to build.

The hackers at Maker’s Asylum have done a fantastic job at documenting their work, with everything posted to a GitHub repo so that anyone can undertake a build. And really, for something as important as making oxygen when it’s needed, there’s really no reason not to give this a try.

Building An Oxygen Concentrator: It Isn’t Rocket Science

May 10, 2021 by Jenny List 40 Comments

Back at the start of the pandemic, a variety of hacker designs for life-saving machinery may have pushed the boundaries of patient safety. There are good reasons that a ventilator must pass extensive safety testing and certification before it can be attached to a patient, because were it to in some way fail, the patient would die. A year later, we have many much safer and more realistic ways to use our skills as part of the effort.

Probably one of the most ambitious projects comes from a coalition of Indian hackerspaces who are adapting a proven oxygen concentrator for local manufacture. Among them is Hackaday’s own [Anool Mahidharia], who hosts a Maker’s Asylum video (embedded below) explaining how the oxygen concentrator works and how they can be made safely.

The team have proven their ability in manufacturing over the past year, here showing off the M19 motorised air purifying respirator.

An oxygen concentrator is both surprisingly simple and imbued with a touch of magic. At its center are two columns of zeolite, a highly porous aluminosilicate mineral that performs the task of a molecular sieve. When air is pumped into the column, the zeolite traps nitrogen, leaving the oxygen-enriched remnant to be supplied onwards. There are two such columns to allow each to be on an alternate cycle of enrichment or purging to remove the accumulated nitrogen.

The point of the video is to show that such a device can be constructed from readily available parts and with common tools; as the title says it isn’t rocket science. Concentrators produced by the hackerspace coalition won’t save the world on their own, but as a part of the combined effort they can provide a useful and reliable source of oxygen that will make a significant difference in a country whose oxygen distribution network is under severe strain.

We previously covered the Indian oxygen concentrator effort when they launched the project. Their website can be found on the Maker’s Asylum website, and their crowdfunding campaign can be found on the Indian crowdfunding platform, Ketto. They have already proved their ability to coordinate large-scale manufacturing with their previous PPE and respirator projects, so please consider supporting them if you can. Meanwhile, we can’t help a twinge of space envy, from the fleeting glimpse of Maker’s Asylum in the video.

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Open-Source Oxygen Hack Chat

May 3, 2021 by Dan Maloney 22 Comments

Join us on Wednesday, May 5 at noon Pacific for the Open-Source Oxygen Hack Chat with Maher Daoudi and the OxiKit Team!

In such tumultuous times, it may be hard to remember last week, let alone last year. But if you dig back a bit, you may recall what a panic the world was in at this point in 2020 about the ventilator crisis. With COVID-19 cases on the rise and the potential for great numbers of patients needing intensive care, everyone and their brother was hacking together makeshift ventilators, in the well-intentioned belief that their inventions would help relieve the coming shortage of these lifesaving medical mechanical miracles.

As it came to pass, though, more COVID-19 patients have benefited from high-flow oxygen therapy than from mechanical ventilation. That’s great news in places where medical oxygen is cheap and easily available, but that’s always the case. We’ve seen recent reports of hospitals in India running out of oxygen, and even rural and remote areas of the developed world can find themselves caught without enough of the vital gas.

To meet the world’s increasing demand for high-flow oxygen therapy, the team at OxiKit has developed an open-source oxygen concentrator that can be built for far less than what commercial concentrators cost. By filtering the nitrogen out of the air, the concentrator provides oxygen at 90% or higher purity, at a flow of up to 25 liters per minute.

Oxikit founder Maher Daoudi and some of the technical team will join us for this Hack Chat to discuss the details of making oxygen concentrators. We’ll learn about how they work, what the design process for their current concentrator was like, and how they got past the obstacles and delivered on the promise of high-flow oxygen for the masses.

Our Hack Chats are live community events in the Hackaday.io Hack Chat group messaging. This week we’ll be sitting down on Wednesday, May 5 at 12:00 PM Pacific time. If time zones have you tied up, we have a handy time zone converter.

Click that speech bubble to the right, and you’ll be taken directly to the Hack Chat group on Hackaday.io. You don’t have to wait until Wednesday; join whenever you want and you can see what the community is talking about.
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