Clever Gas Mixer Gets Just The Right Blend For Homebrew Laser Tubes

[Lucas] over at Cranktown City on YouTube has been very busy lately, but despite current appearances, his latest project is not a welder. Rather, he built a very clever gas mixer for filling his homemade CO2 laser tubes, which only looks like a welding machine. (Video, embedded below.)

We’ve been following [Lucas] on his journey to build a laser cutter from scratch — really from scratch, as he built his own laser tube rather than rely on something off-the-shelf. Getting the right mix of gas to fill the tube has been a bit of a pain, though, since he was using a party balloon to collect carbon dioxide, helium, and nitrogen at measuring the diameter of the ballon after each addition to determine the volumetric ratio of each. His attempt at automating the process centers around a so-called AirShim, which is basically a flat inflatable bag made of sturdy material that’s used by contractors to pry, wedge, lift, and shim using air pressure.

[Lucas]’ first idea was to measure the volume of gas in the bag using displacement of water and some photosensors, but that proved both impractical and unnecessary. It turned out to be far easier to sense when the bag is filled with a simple microswitch; each filling yields a fixed volume of gas, making it easy to figure out how much of each gas has been dispensed. An Arduino controls the pump, which is a reclaimed fridge compressor, monitors the limit switch and controls the solenoid valves, and calculates the volume of gas dispensed.

Judging by the video below, the mixer works pretty well, and we’re impressed by its simplicity. We’d never seriously thought about building our own laser tube before, but seeing [Lucas] have at it makes it seem quite approachable. We’re looking forward to watching his laser project come together.

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Scratch-Built CO2 Laser Tube Kicks Off A Laser Cutter Build

When we see a CO2 laser cutter build around these parts, chances are pretty good that the focus will be on the mechatronics end, and that the actual laser will be purchased. So when we see a laser cutter project that starts with scratch-building the laser tube, we take notice.

[Cranktown City]’s build style is refreshingly informal, but there’s a lot going on with this build that’s worth looking at — although it’s perhaps best to ignore the sourcing of glass tubing by cutting the ends off of an old fluorescent tube; there’s no mention of what became of the mercury vapor or liquid therein, but we’ll just assume it was disposed of safely. We’ll further assume that stealing nitrogen for the lasing gas mix from car tires was just prank, but we did like the rough-and-ready volumetric method for estimating the gas mix.

The video below shows the whole process of building and testing the tube. Initial tests were disappointing, but with a lot of tweaking and the addition of a much bigger neon sign transformer to power the tube, the familiar bluish-purple plasma made an appearance. Further fiddling with the mirrors revealed the least little bit of laser output — nowhere near enough to start cutting, but certainly on the path to the ultimate goal of building a laser cutter.

We appreciate [Cranktown City]’s unique approach to his builds; you may recall his abuse-powered drill bit index that we recently covered. We’re interested to see where this laser build goes, and we’ll be sure to keep you posted.

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A Simple But Effective High-Flow Oxygen Concentrator From Hardware Store Parts

To say that a lot has happened in the year since the COVID-19 pandemic started is an understatement of epic proportions, so much so that it may be hard to remember how the hardware hacking community responded during those early days, with mass-produced PPE, homebrew ventilators and the like. But we don’t recall seeing too many attempts to build something like this DIY oxygen concentrator during that initial build-out phase.

Given the simplicity and efficacy of the design, dubbed OxiKit, it seems strange that we didn’t see more of these devices. OxiKit uses zeolite, a porous mineral that can be used as a molecular sieve. The tiny beads are packed into columns made from hardware store PVC pipes and fittings and connected to an oil-less air compressor through some solenoid-controlled pneumatic valves. After being cooled in a coil of copper pipe, the compressed air is forced through one zeolite column, which preferentially retains the nitrogen while letting the oxygen pass through. The oxygen stream is split, with part going into a buffer tank and part going into the outlet of the second zeolite column, where it forces the adsorbed nitrogen to be released. An Arduino controls the valves that alternate the gas flow back and forth, resulting in 15 liters per minute of 96% pure oxygen.

OxiKit isn’t optimized as a commercial oxygen concentrator is, so it’s not particularly quiet. But it’s a heck of a lot cheaper than a commercial unit, and an easy build for most hackers. OxiKit’s designs are all open source, but they do sell kits and some of the harder-to-source parts and supplies, like the zeolite. We’d be tempted to build something like this just because the technology is so neat; having a source of high-flow oxygen available isn’t a bad idea, either.

The Devil Is In The Details For This Open Air Laser

Normally, we think of lasers as pretty complex and fairly intimidating devices: big glass tubes filled with gas, carefully aligned mirrors, cooling water to keep the whole thing from melting itself, that sort of thing. Let’s not even get started on the black magic happening inside of a solid state laser. But as [Jay Bowles] shows in his latest Plasma Channel video, building a laser from scratch isn’t actually as difficult as you might think. Though it’s certainly not easy, either.

The transversely excited atmospheric (TEA) laser in question uses high voltage passed across a a pair of parallel electrodes to excite the nitrogen in the air at standard atmospheric pressure, so there’s no need for a tube and you don’t have to pull a vacuum. The setup shakes so many UV photons out of the nitrogen that it doesn’t even need any mirrors. In fact, you should be able to get almost all the parts for a TEA laser from the hardware store. For example, the hexagonal electrodes [Jay] ends up using are actually 8 mm hex keys with the ends cut off.

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No Doorknobs Needed For This Nitrogen Laser Build

Sometimes the decision to tackle a project or not can boil down to sourcing parts. Not everything is as close as a Digi-Key or Mouser order, and relying on the availability of surplus parts from eBay or other such markets can be difficult. Knowing if and when a substitute will work for an exotic part can sometimes be a project all on its own.

Building lasers is a great example of this, and [Les Wright] recently looked at substitutes for hard-to-find “doorknob” capacitors for his transversely excited atmospheric lasers. We took at his homebrew TEA lasers recently, which rely on a high voltage supply and very rapid switching to get nitrogen gas to lase. His design uses surplus doorknob caps, big chunky parts rated for very high voltages but also with very low parasitic inductance, which makes them perfect for the triggering circuit.

[Les] tried to substitute cheaper and easier-to-find ceramic power caps with radial wire leads rather than threaded lugs. With a nominal 40-kV rating, one would expect these chunky blue caps to tolerate the 17-kV power supply, but as he suspected, the distance between the leads was short enough to result in flashover arcing. Turning down the pressure in the spark gap chamber helped reduce the flashover and prove that these caps won’t spoil the carefully engineered inductive properties of the trigger. Check out the video below for more details.

Thanks to [Les] for following up on this and making sure everyone can replicate his designs. That’s one of the things we love about this community — true hackers always try to find a way around problems, even when it’s just finding alternates for unobtanium parts.

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How About A Nice Cuppa TEA Laser?

If lasers are your hobby, you face a conundrum. There are so many off-the-shelf lasers that use so many different ways of amplifying and stimulating light that the whole thing can be downright — unstimulating. Keeping things fresh therefore requires rolling your own lasers, and these DIY nitrogen TEA and dye lasers seem like a fun way to go.

These devices are the work of [Les Wright], who takes us on a somewhat lengthy but really informative tour of transversely excited atmospheric (TEA) lasers. The idea with TEA lasers is that a gas, often carbon dioxide in commercial lasers but either air or pure nitrogen in this case, is excited by a high-voltage discharge across long parallel electrodes. TEA lasers are dead easy to make — we’ve covered them a few times — but as [Les] points out, that ease of construction leads to designs that are more ad hoc than engineered.

In the video below, [Les] presents three designs that are far more robust than the typical TEA laser. His lasers use capacitors made from aluminum foil with polyethylene sheets for dielectric, sometimes with the addition of beautiful “doorknob” ceramic caps too. A spark gap serves as a very fast switch to discharge high voltage across the laser channel, formed by two closely spaced aluminum hex bars. Both the spark gap and the laser channel can be filled with low-pressure nitrogen. [Les] demonstrates the power and the speed of his lasers, which can even excite laser emissions in a plain cuvette of rhodamine dye — no mirrors needed! Although eye protection is, of course.

These TEA lasers honestly look like a ton of fun to build and play with. You might not be laser welding or levitating stuff with them, but that’s hardly the point.

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Arduino Nitrox Analyzer For The Submarine Hacker

For Hackaday readers who don’t spend their free time underwater, nitrox is a blend of nitrogen and oxygen that’s popular with scuba divers. Compared to atmospheric air, nitrox has a higher concentration of oxygen; which not only allows divers to spend more time underwater but also reduces the risk of decompression sickness. Of course when fiddling with the ratio of gases you breathe there’s a not inconsequential risk of dying, so nitrox diving requires special training and equipment to make sure the gas mixture is correct.

Divers can verify the ratio of oxygen to nitrogen in their nitrox tanks with a portable analyzer, though as you might expect, they aren’t exactly cheap. But if you’re confident in your own hacking skills, [Eunjae Im] might have the solution for divers looking to save some cash. He’s come up with an Arduino based nitrox analyzer that can be built for considerably less than the cost of a commercial unit.

Now before you get the torches lit up, we should be clear: ultimately the accuracy, and therefore safety, of this device depends on the quality of the oxygen sensor used. [Eunjae] isn’t suggesting you get a bottom of the barrel sensor for this build, and in fact links to a replacement sensor that’s intended for commercial nitrox analyzers as a way to verify the unit is up to the task. The downside is that the sensor alone runs $80. If you want to go with something cheaper, you do so at your own risk.

With a suitable sensor in hand, the project really boils down to building up an interface and enclosure for it. [Eunjae] is using an Arduino Nano, a 128×64 OLED screen, and a battery inside of a rugged waterproof case. He also added an ADS1115 16 Bit DAC between the oxygen sensor and the Arduino for fast and accurate readings over I2C. With the hardware assembled, calibrating the device is as simple as taking it outside and making sure you get an oxygen reading of 20.9% (the atmospheric normal).

While [Eunjae] is happy with his analyzer on the whole, he does see a few areas which could be improved in future revisions. The case is bulky and rather unattractive, something that could be addressed with a custom 3D printed case (though waterproofing it might be an issue). He also says the only reason he used a 9V alkaline battery was because he had it on hand, a small rechargeable battery pack would be a much more elegant solution.

We’ll go out on a limb and say that most Hackaday readers aren’t avid scuba divers. For better or for worse, we’re the sort of folks who stay in the shallow end of the pool. But when one of our ilk does dip below the waves, they really seem to go all out.

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