While the “should have used a 555” meme is strong around these parts, we absolutely agree with [Kelvin Brammer]’s decision to make this 555-shaped plug-in replacement for the 555 timer chip using discrete parts, rather than just a boring old chip.
As [Kelvin] relates, this project started a while back as an attempt to both learn EDA and teach students about the inner workings of the venerable timer chip. The result was a 555-equivalent circuit on a through-hole PCB, with the components nicely laid out into the IC’s functional blocks. As a bonus, the PCB was attached to an 8-pin header which could be plugged right in as a direct replacement for the chip.
Fast forward a few years, and [Kelvin] needed to learn yet another EDA package; what better way than to repeat the 555 project? It was also a good time to step into SMD design, as well as add a little zazzle. While the updated circuit isn’t as illustrative of the internal arrangement of the 555, the visual celebration of the “triple nickel” is more than worth it. And, just like the earlier version, this one has a header so you can just plug and chug — with style.
The Earth’s oceans are a vast frontier that brims with possibilities for the future of medicine, ocean conservation, and food production. They remain largely unexplored because of the physical limits of scuba diving. Humans can only dive for a few hours each day, and every minute spent breathing compressed air at depth must be paid for with a slower ascent to the surface. Otherwise, divers could develop decompression sickness from nitrogen expanding in the bloodstream.
An illustration of the Conshelf 3 habitat. Image via Medium
In the 1960s, world-famous oceanographer Jacques Cousteau built a series of small underwater habitats to extend the time that he and other researchers were able to work. These sea labs were tethered to a support ship with a cable that provided air and power.
Cousteau’s first sea lab, Conshelf 1 (Continental Shelf Station) held two people and was stationed 33 feet deep off the coast of Marseilles, France. Conshelf 2 sheltered six people and spent a total of six weeks under the Red Sea at two different depths.
Conshelf 3 was Cousteau’s most ambitious habitat design, because it was nearly self-sufficient compared to the first two. It accommodated six divers for three weeks at a time and sat 336 feet deep off the coast of France, near Nice. Conshelf 3 was built in partnership with a French petrochemical company to study the viability of stationing humans for underwater oil drilling (before we had robots for that), and included a mock oil rig on the nearby ocean floor for exercises.
Several underwater habitats have come and gone in the years since the Conshelf series, but each has been built for a specific research project or group of tasks. There’s never really been a permanent habitat established for general research into the biochemistry of the ocean.
How cool would it be if there was a material that couldn’t be cut or drilled into? You could make the baddest bike lock, the toughest-toed work boots, or the most secure door. Really, the list of possibilities just goes on and on.
Proteus chews through an angle grinder disc in seconds.
The material is made of aluminium foam that’s embedded with a bunch of small ceramic spheres. It works by inducing retaliatory vibrations into the cutting tools, which turns the tools’ force back on themselves and quickly dulls their edges.
The creators have named the material Proteus after the elusive and shape-shifting prophet of Greek mythology who would only share his visions of the future with those who could get their arms around him and keep him still. It sounds like this material could give Proteus a run for his money.
The ceramic spheres themselves aren’t indestructible, but they’re not supposed to be. Abrading the spheres only makes Proteus stronger. As the cutting tool contacts them, they’re crushed into dust that fills the voids in the aluminium foam, strengthening the material’s destructive vibratory effect. The physical inspiration for Proteus comes from protective hierarchical structures in nature, like the impact-resistant rind of grapefruit and the tendency of abalone shells to resist fracture under the impact of shark teeth.
How It’s Made
Proteus recipe in pictures.
At this point, Proteus is a proof of concept. Adjustments would likely have to be made before it can be produced at any type of scale. Even so, the recipe seems pretty straightforward. First, an aluminium alloy powder is mixed with a foaming agent. Then the mixture is cold compacted in a compressor and extruded in dense rods. The rods are cut down to size and then arranged along with the ceramic spheres in a layered grid, like a metallurgical lasagna.
The grid is spot-welded into a steel box and then put into a furnace for 15-20 minutes. Inside the furnace, the foaming agent releases hydrogen gas, which introduces voids into the aluminium foam and gives it a cellular structure.
Effects of cutting into a cylinder of Proteus with an angle grinder.
According to their paper, the researchers tried to penetrate the material with an angle grinder, a water jet cutter, and a drill. Of these, the drill has the best chance of getting through because the small point of contact can find gaps more easily, so it’s less likely to hit a ceramic sphere. The researchers also made cylindrical samples without steel cladding which they used to test the compressive strength and prove Proteus’ utility as a structural material for beams and columns. It didn’t fare well initially, but became less compressible as the foam matrix collapsed.
The creation process lends some leeway for customization, because the porosity of the aluminium foam can be varied by changing the bake time. As for the drill bit problem, tightening up security is as easy as adjusting the size and/or density of the ceramic spheres.
In the video after the break, you can watch a chunk of Proteus eat up an angle grinder disc in under a minute. Some may argue about the tool wielder’s technique, but we think there’s something to be said for any material that can destroy a cutting disc that fast. They don’t claim that Proteus is completely impenetrable, but it does look impressive. We wish they would have tried more cutting tools like a gas torch, or experimented with other destructive techniques, like plastic explosives, but we suppose that research budgets only go so far.
This constant resistance dummy load has not yet been tested in the real world. [YS] was inspired to come up with the circuit after reading Wednesday’s Re:load dummy load post. That was a constant current load, not a constant resistance load. [YS] started with the schematic for the Re:load and made his changes to arrive at this.
For him the exercise was just to alter the design to achieve constant resistance. He didn’t actually build and test the hardware because he doesn’t really have a need for it. This image was exported from Proteus, which includes a ProSPICE circuit emulator. His slides run through test voltages from 5V to 50V, maintaining a constant 10 Ohm resistance.
When studying this project we needed a little refresher on the different varieties of dummy loads. We found this post very informative about the differences and uses of Constant Current, Constant Power, and Constant Resistance (Impedance) loads.
