Polymer Skins That Change Color and Texture When Exposed to Water

Researchers at Stanford University recently came up with an interesting way (Phys.org summary) to create patterns and colors that emerge when a polymer is exposed to water. Although the paper itself is sadly paywalled with no preprint available, it’s fairly easily summarized and illustrated with details from the Supplementary Data section. The polymer used is poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), which when exposed to an electron beam (electron-beam lithography) undergoes certain changes that become apparent when said water is added.

The polymer is hygroscopic, but the electron beam modifies the extent to which a specific area swells up, thus making it possible to create patterns that depend on the amount of electron beam exposure. In order to ‘colorize’ the polymer, complex cavities are created that modify the angular distribution of light, as illustrated in the top image from the Supplemental Data docx file.

By varying the concentration of IPA versus water, the intermediate swelling states can be controlled. Although this sounds pretty advanced, if you look at the supplementary videos that are already sped up a lot, you can see that it is a very slow process. Compared to an octopus and kin whose ability to alter their own skin texture and coloring is legendary and directly controlled by their nervous system, this isn’t quite in the same ballpark yet, even if it’s pretty cool to watch.

hackaday.com/2026/01/23/polyme…

Lead Acid Battery Upgraded to Lithium Iron Phosphate

Lithium batteries have taken over as the primary battery chemistry from applications ranging from consumer electronics to electric vehicles and all kinds of other things in between. But the standard lithium ion battery has a few downsides, namely issues operating at temperature extremes. Lead acid solves some of these problems but has much lower energy density, and if you want to split the difference with your own battery you’ll need to build your own lithium iron phosphate (LiFePO4) pack.

[Well Done Tips] is building this specific type of battery because the lead acid battery in his electric ATV is on the decline. He’s using cylindrical cells that resemble an 18650 battery but are much larger. Beyond the size, though, many of the design principles from building 18650 battery packs are similar, with the exception that these have screw terminals so that bus bars can be easily attached and don’t require spot welding.

With the pack assembled using 3D printed parts, a battery management system is installed with the balance wires cleverly routed through the prints and attached to the bus bars. The only problem [Well Done Tips] had was not realizing that LiFePO4 batteries’ voltages settle a bit after being fully charged, which meant that he didn’t properly calculate the final voltage of his pack and had to add a cell, bringing his original 15S1P battery up to 16S1P and the correct 54V at full charge.

LiFePO4 has a few other upsides compared to lithium ion as well, including that it delivers almost full power until it’s at about 20% charge. It’s not quite as energy dense but compared to the lead-acid battery he was using is a huge improvement, and is one of the reasons we’ve seen them taking over various other EV conversions as well.

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hackaday.com/2026/01/23/lead-a…

PLA Mold To Plaster Bust, No Silicone Needed

3D printing is wonderful, but sometimes you just don’t want to look at a plastic peice. Beethoven’s bust wouldn’t look quite right in front of your secret door if it was bright orange PLA, after all. [Denny] over at “Shake the Future” on YouTube is taking a break from metal casting to show off a quick-and-easy plaster casting method— but don’t worry, he still uses a microwave.

Most people, when they’re casting something non-metallic from a 3D print are going to reach for castable silicone and create a mold, first. It works for chocolate just as easily as it does plaster, and it does work well. The problem is that it’s an extra step and extra materials, and who can afford the time and money that takes these days?

[Denny]’s proposal is simple: make the mold out of PLA. He’s using a resin slicer to get the negative shape for the mold, and exporting the STL to slice in PrusaSlicer, but Blender, Meshmixer and we’re pretty sure Cura should all work as well. [Denny] takes care when arranging his print to avoid needing supports inside the mold, but that’s not strictly necessary as long as you’re willing to clean them out. After that, it’s just a matter of mixing up the plaster, pouring it into the PLA, mold, and waiting.

Waiting, but not too long. Rather than let the plaster fully set up, [Denny] only waits about an hour. The mold is still quite ‘wet’ at this point, but that’s a good thing. When [Denny] tosses it in his beloved microwave, the moisture remaining in the plaster gets everything hot, softening the PLA so it can be easily cut with scissors and peeled off.

Yeah, this technique is single-use as presented, which might be one advantage to silicone, if you need multiple copies of a cast. Reusing silicone molds is often doable with a little forethought. On the other hand, by removing the plaster half-cured, smoothing out layer lines becomes a simple matter of buffing with a wet rag, which is certainly an advantage to this technique.

Some of you may be going “well, duh,” so check out [Denny]’s cast-iron benchy if his plasterwork doesn’t impress. We’ve long been impressed with the microwave crucibles shown off on “Shake the Future”, but it’s great to have options. Maybe metal is the material, or perhaps plain plastic is perfect– but if not, perchance Plaster of Paris can play a part in your play.

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hackaday.com/2026/01/23/pla-mo…

Hackaday Podcast Episode 354: Firearms, Sky Driving, and Dumpster Diving

Hackaday Editors Elliot Williams and Al Williams took a break to talk about their favorite hacks last week. You can drop in to hear about articulated mirrors, triacs, and even continuous 3D-printing modifications.

Flying on an airplane this weekend? Maybe wait until you get back to read about how the air traffic control works. Back home, you can order a pizza on a Wii or run classic Basic games on a calculator.

For the can’t miss articles, the guys talked about very low Earth orbit satellites and talked about readers who dumpster dive.

Check out the links below if you want to follow along, and don’t be shy. Tell us what you think about this episode in the comments!

html5-player.libsyn.com/embed/…

As always, this episode is available in DRM-free MP3.

Where to Follow Hackaday Podcast

Places to follow Hackaday podcasts:

• iTunes
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• RSS
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• Check out our Libsyn landing page

Episode 354 Show Notes:

What’s that Sound?

• Congratulations to [Spybob42], who guessed last week’s sound. Come back next week to take your shot at a coveted Hackaday Podcast T-Shirt.

News

• Washington State Bill Seeks To Add Firearms Detection To 3D Printers

Interesting Hacks of the Week:

• How To Use Tiny Open Loop Actuators For A Living Mirror
  
  • Making A Wooden Multi-Mirror Display Device
  • Daniel Rozin Wooden Mirror

  
  

• A Guide To Using Triacs For Switching AC
• Testing A Continuous Printing Mod For The Bambu Lab A1 Mini
  
  • swapmod A1m kit – SWAP SYSTEMS
  • 3D Printer Add On Makes Sharp(ie) Colors

  
  

• Accurately Aiming Audio With An Ultrasonic Array
  
  • Acoustic Mirrors: How To Find Planes Without RADAR
  • A Phased-Array Ultrasonic 3D Scanner From Scratch
  • Supercon 2024: Killing Mosquitoes With Freaking Drones, And Sonar
  • Build A Parametric Speaker Of Your Own

  
  

• Self-Powered Top Spins For Hours
• Inside Air Traffic Control

Quick Hacks:

• Elliot’s Picks:
  
  • The Windows Interface You Didn’t Like, For Linux
  • Binary And Digital Gradients For Telling Time
  • Ordering Pizza On The Nintendo Wii (Again)

  
  

• Al’s Picks:
  
  • BASIC On A Calculator Again
    
    • github.com/ctosullivan/Python-…

    
    

  • Robot Sees Light With No CPU
  • Flux And Solder Paste Dispenser Looks Good While Doing It

  
  

Can’t-Miss Articles:

• Skimming Satellites: On The Edge Of The Atmosphere

• Ask Hackaday: Do You Curb Shop Components?

hackaday.com/2026/01/23/hackad…

Size (and Units) Really Do Matter

We miss the slide rule. It isn’t so much that we liked getting an inexact answer using a physical moving object. But to successfully use a slide rule, you need to be able to roughly estimate the order of magnitude of your result. The slide rule’s computation of 2.2 divided by 8 is the same as it is for 22/8 or 220/0.08. You have to interpret the answer based on your sense of where the true answer lies. If you’ve ever had some kid at a fast food place enter the wrong numbers into a register and then hand you a ridiculous amount of change, you know what we mean.

Recent press reports highlighted a paper from Nvidia that claimed a data center consuming a gigawatt of power could require half a million tons of copper. If you aren’t an expert on datacenter power distribution and copper, you could take that number at face value. But as [Adam Button] reports, you should probably be suspicious of this number. It is almost certainly a typo. We wouldn’t be surprised if you click on the link and find it fixed, but it caused a big news splash before anyone noticed.

Thought Process

Best estimates of the total copper on the entire planet are about 6.3 billion metric tons. We’ve actually only found a fraction of that and mined even less. Of the 700 million metric tons of copper we actually have in circulation, there is a demand for about 28 million tons a year (some of which is met with recycling, so even less new copper is produced annually).

Simple math tells us that a single data center could, in a year, consume 1.7% of the global copper output. While that could be true, it seems suspicious on its face.

Digging further in, you’ll find the paper mentions 200kg per megawatt. So a gigawatt should be 200,000kg, which is, actually, only 200 metric tons. That’s a far cry from 500,000 tons. We suspect they were rounding up from the 440,000 pounds in 200 metric tons to “up to a half a million pounds,” and then flipped pounds to tons.

Glass Houses

We get it. We are infamous for making typos. It is inevitable with any sort of writing at scale and on a tight schedule. After all, the Lincoln Memorial has a typo set in stone, and Webster’s dictionary misprinted an editor’s note that “D or d” could stand for density, and coined a new word: dord.

So we aren’t here to shame Nvidia. People in glass houses, and all that. But it is amazing that so much of the press took the numbers without any critical thinking about whether they made sense.

Innumeracy

We’ve noticed many people glaze over numbers and take them at face value. The same goes for charts. We once saw a chart that was basically a straight line except for one point, which was way out of line. No one bothered to ask for a long time. Finally, someone spoke up and asked. Turns out it was a major issue, but no one wanted to be the one to ask “the dumb question.”

You don’t have to look far to find examples of innumeracy: a phrase coined by [Douglas Hofstadter] and made famous by [John Allen Paulos]. One of our favorites is when a hamburger chain rolled out a “1/3 pound hamburger,” which flopped because customers thought that since three is less than four, they were getting more meat with a “1/4 pound hamburger” at the competitor’s restaurant.

This is all part of the same issue. If you are an electronics or computer person, you probably have a good command of math. You may just not realize how much better your math is than the average person’s.

Gimli Glider

“Air Canada 143 after landing” from the FAA
Even so, people who should know better still make mistakes with units and scale. NASA has had at least one famous case of unit issues losing an unmanned probe. In another famous incident, an Air Canada flight ran out of fuel in 1983. Why?

The plane’s fuel sensors were inoperative, so the ground crew manually checked the fuel load with a dipstick. The dipstick read in centimeters. The navigation computer expected fuel to be in kg. Unfortunately, the fuel’s datasheet posted density in pounds/liter. This incorrect conversion happened twice.

Unsurprisingly, the plane was out of fuel and had to glide to an emergency landing on a racetrack that had once been a Royal Canadian Air Force training base. Luckily, Captain Pearson was an experienced glider pilot. With reduced control and few instruments, the Captain brought the 767 down as if it were a huge glider with 61 people onboard. Although the landing gear collapsed and caused some damage, no one on the plane or the ground were seriously hurt.

What’s the Answer?

Sadly, math answers are much easier to get than social answers. Kids routinely complain that they’ll never need math once they leave school. (OK, not kids like we were, but normal kids.) But we all know that is simply not true. Even if your job doesn’t directly involve math, understanding your own finances, making decisions about purchases, or even evaluating political positions often requires that you can see through math nonsense, both intentional and unintentional.

[Antoine de Saint-Exupéry] was a French author, and his 1948 book Citadelle has an interesting passage that may hold part of the answer. If you translate the French directly, it is a bit wordy, but the quote is commonly paraphrased: “If you want to build a ship, don’t herd people together to collect wood and don’t assign them tasks and work, but rather teach them to long for the endless immensity of the sea.”

We learned math because we understood it was the key to building radios, or rockets, or computer games, or whatever it was that you longed to build. We need to teach kids math in a way that makes them anxious to learn the math that will enable their dreams.

How do we do that? We don’t know. Great teachers help. Inspiring technology like moon landings helps. What do you think? Tell us in the comments. Now with 285% more comment goodness. Honest.

We still think slide rules made you better at math. Just like not having GPS made you better at navigation.

hackaday.com/2026/01/23/size-a…

Wired to Wireless: ESP32 Gives Your USB Keyboard Bluetooth

Few things rival the usability and speed of a full-sized keyboard for text input. For decades, though, keyboards were mostly wired, which can limit where you use your favorite one. To address this, [KoStard]’s latest project uses an ESP32 to bridge a USB keyboard to BLE devices.

The ESP32-S3 packs a ton of fantastic functionality into its small size and low price—including USB-OTG support, which is key here. Taking advantage of this, [KoStard] programmed an ESP32-S3 to host a keyboard over its USB port while connecting via BLE to devices like cellphones.

There are some slick tricks baked in, too: you can pair with up to three devices and switch between them using a key combo. Some of you might be wondering how you can just plug a microcontroller into a keyboard and have it work. The truth is, it doesn’t without extra hardware. Both the keyboard and ESP32-S3 need power. The simplest fix is a powered USB hub: it can be battery-powered for a truly mobile setup, or use a wired 5V supply so you never have to charge batteries.

We love seeing a simple, affordable microcontroller extend the usefulness of gear you already have. Let us know in the comments about other hacks you’ve used to connect keyboards to devices never designed for them.

youtube.com/embed/dVUMYTfJw0s?…

hackaday.com/2026/01/23/wired-…

The Defunct Scooter Company, and the Default Key

Äike were an Estonian scooter company, which sadly went bust last year. [Rasmus Moorats] has one, and since the app and cloud service the scooter depends on have lost functionality, he decided to reverse engineer it. Along the way he achieved his goal, but found a vulnerability that unlocks all Äike scooters.

The write-up is a tale of app and Bluetooth reverse engineering, ending with the startling revelation of a hardcoded key that’s simply “ffffffffffffffff”. From that he can unlock and interact with any Äike scooter, except for a subset that were used as hire scooters and didn’t have Bluetooth. Perhaps of more legitimate use is the reverse engineering of the scooter functionality.

What do you do when you find a vulnerability in a product whose manufacturer has gone? He reported to the vendor of the IoT module inside the scooter, who responded that the key was a default value that should have been changed by the Äike developers. Good luck, should you own one of these machines.

Meanwhile, scooter hacking is very much a thing for other manufacturers too.

hackaday.com/2026/01/23/the-de…

Embedded TPM: Watch Out!

Today’s PCs are locked up with Trusted Platform Module (TPM) devices so much so that modern Windows versions insist on having a recent TPM to even install. These have become so prevalent that even larger embedded boards now have TPM and, of course, if you are repurposing consumer hardware, you’ll have to deal with it, too. [Sigma Star] has just the primer for you. It explains what TPM does, how it applies to embedded devices, and where the pitfalls are.

The TPM is sometimes a chip or sometimes secure firmware that is difficult to tamper with. They provide secret storage and can store boot signatures to detect if something has changed how a computer starts up. The TPM can also “sign off” that the system configuration is the same to a remote entity. This allows, for example, a network to prevent a hacked or rogue computer from communicating with other computers.

Embedded systems, usually, aren’t like PCs. A weather station at a remote location may have strangers poking at it without anyone noticing. Also, that remote computer might be expected to be working for many more years than a typical laptop or desktop computer.

This leads to a variety of security concerns that TPM 2.0 attempts to mitigate. For example, it is unreasonable to think a typical attacker might connect a logic analyzer to your PC, but for an embedded system, it is easier to imagine. There is a session-based encryption to protect against someone simply snooping traffic off the communication bus. According to the post, not all implementations use this encryption, however.

Motherboard has a slot for TPM, but no board? We’ve seen people build their own TPM boards.

Title image by [Raimond Spekking] CC BY-SA-4.0

hackaday.com/2026/01/23/embedd…