Thermal Earring Tracks Body Temperature

If you want to constantly measure body temperature to track things like ovulation, you usually have to wear something around your wrist or finger in the form of a smartwatch or ring. Well, what if you can’t or don’t want to adorn yourself this way? Then there’s the thermal earring.

Developed at the University of Washington, the thermal earring is quite small and unobtrusive compared to a smartwatch. Sure, it dangles, but that’s so it can measure ambient temperature for comparison’s sake.

You don’t even need to have pierced ears  — the earring attaches to the lobe magnetically. And yeah, the earring can be decorated to hide the circuitry, but you know we would rock the bare boards.

The earring uses BLE to transmit readings throughout the day, and of course goes into sleep mode between transmissions to save power. Coincidentally, it runs for 28 days per charge, which is the length of the average menstrual cycle. While the earring at this time merely “shows promise” as a means of monitoring stress and ovulation, it did outperform a smartwatch at measuring skin temperature while the wearers were at rest.

This is definitely not the only pair of earrings we’ve got around here. These art deco earrings use flexible PCBs, and this pair will light up the night.

An image of a cave drawing of horned cow. There is another one coming up behind it as well. There are four dots as described by the researchers on the main cow's back.

Writing – So Easy A Caveperson Could Do It

We modern humans tend to take writing for granted, and often forget that like any other technology, somebody had to invent it. Researchers from Cambridge believe they’ve determined the purpose of one of the earliest writing beta-tests.

Examining a database of images taken in caves throughout Europe and dated to the Upper Paleolithic, the researchers found “three of the most frequently occurring signs—the line <|>, the dot <•>, and the <Y>—functioned as units of communication.”

It appears the <|> and <.> symbols when “in close association with images of animals” denote time relating to lunar months of the year, starting with spring as the new year. The <Y> symbol appears to carry the meaning <To Give Birth> allowing early people a way to tell others information about the prey of a region, which would be pretty handy when hunting and gathering are your only options for food.

We’ve covered other ancient technologies like storytelling and abrasives. If you’re curious what the climate was like for our ancestors, perhaps paleoclimatology will tickle your fancy.

Tool Changing? Bah! Just Add A Second Gantry

What’s a dual gantry 3D printer? It’s a machine with two completely independent XY motion systems, with two independent hot ends, sharing the same build platform. That might be a little hard to visualize, so head over to [Zruncho 3D]’s Dueling Zero project and get a good look at what what a dual gantry machine looks like.

Dual gantry differs from IDEX, which doubles the amount of moving mass on an axis.

Let’s take a moment to quickly cover the different ways to create multi-filament prints before we dive into what’s different with Dueling Zero. One way to print in multiple filaments (for example, multiple colors) is to swap filaments between a single print head, which is what the Prusa MMU and the Bambu AMS do. However, the main tradeoff is that the filament swapping process can be time-consuming. Another option is IDEX (Independent Dual EXtruder) which has two separate hot ends on the same axis. The main downside there is that an IDEX printer has essentially doubled the moving mass on the axis, which limits speed and can affect print quality. Then there’s toolchanging printers like the Prusa XL, which swap entire heads as needed but have a much higher cost.

The Dueling Zero instead adds a completely independent second gantry, so it has two print heads (like an IDEX) but thanks to the mechanical design it acts much more like a single-extruder 3D printer in terms of print quality and motion control. Speed and acceleration aren’t limited by added mass, either, which is good because slow printers are rapidly falling out of style.

We love how clean and finished the design is. At its core, [Zruncho 3D]’s dual gantry mod (designated D0) is based on the Voron Zero design. Dueling Zero is, to our knowledge, the only open-source and fully documented dual gantry printer out there, which is pretty wild. Watch it in action in the short video, embedded below.

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Memory Box Shows Photos Based On Fingerprint

With his young son’s birthday coming up in a few weeks, [Mike Buss] wanted to build him something fun that the boy could hold on to all his life. After doing some sketching, [Mike] arrived at the idea to make a memory box uses a fingerprint scanner to show different pictures based on the fingerprint.

[Mike] started by rendering the box in Blender and then cutting a sizable hole in the lid for the E-ink screen. That’s around the time the first problem came up — there were weird vertical lines in the display. Sure enough, that screen was broken. Then he added the SD card reader, but the SD card wouldn’t work, and was heating up besides. Finally, the fingerprint scanner was causing issues, but it turned out that the power supply was at fault.

After all of that, [Mike] switched from an ESP32 to a Raspi Zero W to simplify the whole process of finding a photo tagged with the person’s fingerprint. [Mike] added a Python script that listens for new memories over Wi-Fi. A memory in this case consists of a picture, a description, a list of people tagged in the picture, and some additional metadata.

One important lesson [Mike] learned was that of balancing planning vs. just taking action. If he had taken the time to consider the complexity of the tagged-photo retrieval system, he would have arrived at an SBC solution much sooner. Be sure to check out the build video after the break.

You can have all sorts of fun with fingerprint scanners, like this one that opens a secret bookcase door.

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A Clock Made Out Of Electromechanical Relays

Electromechanical circuits using relays are mostly a lost art these days, but sometimes you get people like [Aart] who can’t resist to turn a stack of clackity-clack relays into a functional design, like in this case a clock (article in Dutch, Google Translate).

It was made using components that [Aart] had come in possession of over the years, with each salvaged part requiring the usual removal of old solder, before being mounted on prototype boards. The resulting design uses the 1 Hz time signal from a Hörz DCF77 master clock which he set up to drive a clock network in his house, as he describes in a forum post at Circuits Online (also in Dutch).

The digital pulses from this time signal are used by the relay network to create the minutes and hours count, which are read out via a resistor ladder made using 0.1% resistors that drive two analog meters, one for the minutes and the other for the hours.

Sadly, [Aart] did not draw up a schematic yet, and there are a few issues he would like to resolve regarding the meter indicators that will be put in front of the analog dials. These currently have weird transitions between sections on the hour side, and the 59 – 00 transition on the minute dial happens in the middle of the scale. But as [Aart] says, this gives the meter its own character, which is an assessment that is hard to argue with.

Thanks to [Lucas] for the tip.

Have A Ball With This 3D Printed Sphere-Making Machine

Alright, everyone has 30 seconds to get all the jokes out of their system before we proceed with a look at this 3D printed wooden ball polisher.


Theoretically, making a sphere out of any material should be easy. All you need to do is pick a point in space inside the material and eliminate everything more than a specified distance from that point. But in practice, sphere-making isn’t quite so simple. The machine [Fraens] presents in the video below is geared more toward the final polish than the initial forming, with a trio of gear motors set 120 degrees apart driving cup-shaped grinding pads.

Constant pressure on the developing sphere is maintained with a clever triangular frame with springs that pre-load the arms and pull them in toward the workpiece, but stop at the desired radius. The three grinding pads are fitted with sandpaper and constantly turn, wearing down the rough piece until it reaches the final diameter. The machine also supports more aggressive tooling, in the form of hole saws that really get to work on the rough blank. Check it out in the video below.

While we appreciate the fact that this is 3D printed, watching the vibrations it has to endure while the blank is still rough, not to mention all the dust and chips it creates, makes us think this machine might not stand up for long. So maybe letting this circular saw jig cut out a rough ball and using this machine for the final polish would be a good idea. Continue reading “Have A Ball With This 3D Printed Sphere-Making Machine”

Sprint: The Mach 10 Magic Missile That Wasn’t Magic Enough

Defending an area against incoming missiles is a difficult task. Missiles are incredibly fast and present a small target. Assuming you know they’re coming, you have to be able to track them accurately if you’re to have any hope of stopping them. Then, you need some kind of wonderous missile of your own that’s fast enough and maneuverable enough to take them out.

It’s a task that at times can seem overwhelmingly impossible. And yet, the devastating consequences of a potential nuclear attack are so great that the US military had a red hot go anyway. In the 1970s, America’s best attempt to thwart incoming Soviet ICBMs led to the development of the Sprint ABM—a missile made up entirely of improbable numbers.

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