The Thermochromic Display You Didn’t Know You Needed

We love unique ways of displaying data here at Hackaday, and this ingenious thermochromic display created by [Moritz v. Sivers] more than fits the bill. Using sheets of color changing liquid crystals and careful temperature control of the plates they’re mounted on, he’s built a giant seven-segment display that can colorfully (albeit somewhat slowly) show the current temperature and humidity.

The sheets of temperature sensitive liquid crystals are a bit like flattened out Mood Rings; they starts out black, but as heat is applied, their color cycles through vibrant reds, greens, and blues. The sheets are perhaps best known as the sort of vaguely scientific toys you might see in a museum gift shop, but here [Moritz] has put their unique properties to practical use.

To achieve the effect, he first cut each segment out of copper. The crystal sheets were applied to the segments, thanks to their handy self-stick backing, and the excess was carefully trimmed away. Each segment was then mounted to a TES1-12704 Peltier module by way of thermally conductive epoxy. TB6612FNG motor controllers and a bevy of Arduino Nano’s are used to control the Peltier modules, raising and lowering their temperature as necessary to get the desired effect.

You can see the final result in the video after the break. It’s easily one of the most attractive variations on the classic seven-segment display we’ve ever seen. In fact, we’d go as far as to say it could pass for an art installation. The idea of a device that shows the current temperature by heating itself up certainly has a thoughtful aspect to it.

This actually isn’t the first display we’ve seen that utilized this concept, though it’s by far the largest. Back in 2014 we featured a small flexible display that used nichrome wires to “print” digits on a sheet of liquid crystals.

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Kitty Litter And Broken Light Bulbs Power This Homebrew Gas Chromatograph

We’re always on the lookout for unexpected budget builds here at Hackaday, and stumbling across a low-cost, DIY version of an instrument that sells for tens of thousands of dollars is always a treat. And so when we saw a tip for a homebrew gas chromatograph in the tips line this morning, we jumped on it. (Video embedded below.)

For those who haven’t had the pleasure, gas chromatography is a chemical analytical method that’s capable of breaking a volatile sample up into its component parts. Like all chromatographic methods, it uses an immobile matrix to differentially retard the flow of a mobile phase containing the sample under study, such that measurement of the transit time through the system can be made and information about the physical properties of the sample inferred.

The gas chromatograph that [Chromatogiraffery] built uses a long stainless steel tube filled with finely ground bentonite clay, commonly known as kitty litter, as the immobile phase. A volatile sample is injected along with an inert carrier gas – helium from a party balloon tank, in this case – and transported along the kitty litter column by gas pressure. The sample interacts with the column as it moves along, with larger species held back while smaller ones speed along. Detection is performed with thermal conductivity cells that use old incandescent pilot lamps that have been cracked open to expose their filaments to the stream of gas; using a Wheatstone bridge and a differential amp, thermal differences between the pure carrier gas and the eluate from the column are read and plotted by an Arduino.

The homebrew GC works surprisingly well, and we can’t wait for [Chromatogiraffery] to put out more details of his build.

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An All-Iron Battery Isn’t Light, But It’s Cheap

Rechargeable batteries are a technology that has been with us for well over a century, and which is undergoing a huge quantity of research into improved energy density for both mobile and alternative energy projects. But the commonly used chemistries all come with their own hazards, be they chemical contamination, fire risk, or even cost due to finite resources. A HardwareX paper from a team at the University of Idaho attempts to address some of those concerns, with an open-source rechargeable battery featuring electrode chemistry involving iron on both of its sides. This has the promise of a much cheaper construction without the poisonous heavy metal of a lead-acid cell or the expense and fire hazard of a lithium one.

A diagram of the all-iron cell.
A diagram of the all-iron cell.

The chemistry of this cell is split into two by an ion-exchange membrane, iron (II) chloride is the electrolyte on the anode side where iron is oxidised to iron 2+ ions, and Iron (III) chloride on the cathode where iron is reduced to iron hydroxide. The result is a cell with a low potential of only abut 0.6V, but at a claimed material cost of only $0.10 per kWh Wh of stored energy. The cells will never compete on storage capacity or weight, but this cost makes them attractive for fixed installations.

It’s encouraging to see open-source projects coming through from HardwareX, we noted its launch back in 2016.

Thanks [Julien] for the tip.

Etching Large Brass Sheets Is Harder Than You Think

One of my favorite ways to think of engineering is that a glass is not half empty or half full, only twice as large as it needs to be. As useful as that idea is, it also means that I rarely put any effort into the aesthetics of my projects – I learn or accomplish what I need, desolder and recycle the components, then move on. Few of my projects are permanent, and custom cases tend to be non-reusable, so I skip the effort and expense.

Once in a while though, I need to make a gift. In that case form and function both become priorities. Thankfully, all that glitters is not gold – and over the last year I’ve been learning to etch the copper alloys commonly classified as ‘brass’. We’ve covered some truly excellent etched brass pieces previously, and I was inspired to try and etch larger pieces of metal (A4 and larger) without sacrificing resolution. I thought this would be just like etching circuits. In fact, I went through several months of failed attempts before I produced anything halfway decent!

Although I’m still working on perfecting my techniques, I’ve learned enough in the meantime to give a report. Read on if you’re feeling the need for more fancy brass signs in your life.

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Perovskites: Not Just For Solar Cells Anymore

If you’ve been around long enough, you’ll know there’s a long history of advances in materials science that get blown far out of proportion by both the technical and the popular media. Most of the recent ones seem to center on the chemistry of carbon, particularly graphene and nanotubes. Head back a little in time and superconductors were all the rage, and before that it was advanced ceramics, semiconductors, and synthetic diamonds. There’s always some new miracle material to be breathlessly and endlessly reported on by the media, with hopeful tales of how one or the other will be our salvation from <insert catastrophe du jour here>.

While there’s no denying that each of these materials has led to huge advancements in science, industry, and the quality of life for billions, the development cycle from lab to commercialization is generally a tad slower than the press would have one believe. And so when a new material starts to gain traction in the headlines, as perovskites have recently, we feel like it’s a good opportunity to take a close look, to try to smooth out the ups and downs of the hype curve and manage expectations.

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Loads Of Testing Yields New, Reliable, And Cheap Leather Hardening Technique

Leather hardening has been around for such a long time that one might think that there was little left to discover, but [Jason F. Timmermans] certainly showed that is not the case. Right around the end of 2018 he set up experiments to compare different techniques for hardening leather, and empirically determine the best options. After considerable effort, he crafted a new method with outstanding results. It’s part of his exhaustive testing of different techniques for hardening leather, including some novel ones. It was a considerable amount of work but [Jason] says that he gathered plenty of really useful information, which we’re delighted that he took the time to share it.

According to [Jason], the various methods of hardening can be separated into four groups:

  1. Thermal: heat-treating at 180 ºF or higher, usually via some kind of boiling or baking process.
  2. Chemical: soaking in a substance that causes changes in the leather. Some examples include ammonia, vinegar, acetone, brine, and alcohol.
  3. Mechanical: hammering the leather.
  4. “Stabilizing” methods: saturating the leather with a substance to add rigidity and strength without otherwise denaturing the leather itself. Examples include beeswax, pine pitch, stearic acid, and epoxy.

We recommend making the time to follow the link in the first paragraph and read the full results, but to summarize: heat-treating generally yields a strong but brittle product, and testing revealed stearic acid  — which resembles a kind of hard, dense wax at room temperature — was an early standout for overall great results. Stearic acid has many modern uses and while it was unclear from [Jason]’s reasearch exactly when in history it became commonplace, at least one source mentioned it as a candidate for hardening leather.

But the story doesn’t stop there. Unsatisfied with simply comparing existing methods, [Jason] put a lot of work into seeing if he could improve things. One idea he had was to combine thermal treatment with a stabilizer, and it had outstanding results. The winning combination (named X1 in his writeup) was to preheat the leather then immerse it in melted stearic acid, followed by bringing the temperature of the combination to 200 ºF for about a minute to heat treat the leather at the same time. [Jason]’s observation was that this method “[B]lew the rest out of the water. Cutting the sample to view the cross section was like carving wood. The leather is very rigid and strong.”

The world may not revolve around leather the way it used to, but there’s still stuff to learn and new things to discover. For example, modern tools can allow for novel takes on old techniques, like using 3D printing to create custom leather embossing jigs.

Decap ICs Without The Peril

There can be few of us who haven’t gazed with fascination upon the work of IC decappers, whether they are showing us classic devices from the early years of mass semiconductor manufacture, or reverse-engineering the latest and greatest. But so often their work appears to require some hardcore scientific equipment or particularly dangerous chemicals. We’ve never thought we might be able to join the fun. [Generic Human] is out to change all that, by decapping chips using commonly available chemicals and easy to apply techniques. In particular, we discover through their work that rosin — the same rosin whose smell you will be familiar with from soldering flux — can be used to dissolve IC packaging.

Of course, ICs that dissolved easily in the face of soldering wouldn’t meet commercial success, so an experiment with flux meets little success. Pure rosin, however, appears to be an effective decapping agent. [Generic Human] shows us a motherboard voltage regulator boiled in the stuff. When the rosin is removed with acetone, there among the debris is the silicon die, reminding us just how tiny these things are. We’re sure you’ll all be anxious to try it for yourselves, now, so take a while to look at the video below showing their CCC Congress talk.

The master of chip decapping is of course [Ken Shirriff], whose work we’ve featured many times. Our editor [Mike Szczys] interviewed him last year, and it’s well worth a look.

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