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The Different Ways To Look at Negative Resistance

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[lcamtuf] has an in-depth look at the concept of negative resistance that goes somewhat further than one might expect. Normally, as voltage across a resistance increases so too does the current. Negative resistance is the concept of current decreasing as voltage increases. But beyond the raw concept, there are a few other ways to look at this idea. The usual way to think about it is negative differential resistance (NDR) . Not everything has a linear relationship between voltage and current, and for a device to exhibit NDR means that in certain ranges the I–V curve actually slopes downward; increasing one of voltage or current decreases the other. This kind of thing occurs in neon lamps. Once they are glowing, increasing current can result in decreasing voltage. True negative resistance, that of a literal -100 Ω resistor, does not exist. Not in the sense of a passive component, anyway. Such a device would supply power into a circuit rather than dissipating it, and would therefore ...
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Anti-Doomscroll Tamagotchi Only Lives if You Do

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The odds are, you have a device deliberately designed to be addictive in your pocket or on the table next to you if you aren’t staring at it right now– your smartphone. We’ve seen a number of projects that try and help people control or moderate their phone usage using a variety of techniques; this vitual pet by [brenpoly] does it by weponizing human empathy, and our bizzare ability to pack-bond with literally anything. The virtual pet itself is based on an ESP32 in a cutesy 3D-printed case, and we think it would probably work well enough if it just had hard-coded behaviors based on hooks in what you’re doing on your phone– the “my little buddy is sick because I’m doomscrolling” should be effective enough on its own, and that part is hardcoded on the ESP32 along with the regular virtual pet behaviour–but this is the year of our Llama 2026, so there has to be an LLM in there somewhere, right? Some people would leave this part out,...
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Are Desktop PC-ABS Prints Outperformed by Industrial FDM? Not Really

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[Igor] of [My Tech Fun] set out to discover what differences, if any, can be found between parts printed in PC-ABS filament on an industrial 3D printer, and those from prosumer-grade machines and filament. His video is full of his usual attention to detail as he compares a test suite of parts printed at home in Polymaker PC-ABS with those from a Stratasys Fortus 450mc using proprietary PC-ABS filament. PC-ABS is a filament that strives to deliver the benefits of both polycarbonate and ABS. It’s durable and has fantastic impact resistance, but it costs a bit more than either PC or ABS and requires a heated chamber. In the end, PC-ABS from a home printer compares favorably to an industrial system, at a fraction of the price. [Igor] has previously compared industrial ABS with comsumer ABS , but what made him curious about PC-ABS in particular was the large difference in print temperatures between Polymaker PC-ABS, and Stratasys’s own proprietary PC-ABS. [Igor] prints Polym...
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Fixing a 1990s LEGO Electric Train Speed Regulator

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Before LEGO train sets moved to battery-powered locomotives with plastic rails, all of them worked pretty much like any other train set of the era. This meant metal rails that the locomotive’s wheels would use to pick up power from and a central controller that would inject said power and also regulate the train’s speed and direction. The LEGO 2868b Electric Train Speed Regulator is one such example, and [Nonsense Wars] recently had one under the knife to repair it . The single PCB inside is quite straightforward, with the 9-12 VAC supply input from an external power adapter, and a variable voltage regulator that sees its target voltage switched by a bank of resistors. It are these resistors that the big yellow control switches between when you operate it, changing the output voltage and also output polarity you cross the midway point. Effectively this means that there is just one non-passive component on the PCB, in the form of the TO-220 package strapped to the big heat...
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How Bats Prevent Doppler Acoustic Interference

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Lesser horseshoe bat. (Credit: Lylambda, Wikimedia ) As great as echolocation is, things can get rather messy once it’s not just you chirping away, but also hundreds of your buddies in roughly the same area. This is the scenario that the typical colonies of bats have to deal with. In a recent study by [Haruhito Matsumoto] et al. in Journal of Comparative Physiology they investigated how colonies of greater Japanese horseshoe bats deal with this issue. Echolocation in animals can use a variety of methods, including frequency modulation (FM, varying the pitch) or constant frequency (CF), with both having their uses during hunting as well as obstacle avoidance. One big advantage of CF is that it can be used for Doppler shift, giving very precise information about location and velocity of objects in the environment, but if used in a busy colony the acoustic interference would effectively render them blind. What researchers have found is that the CF component frequencies differ p...
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Kelvin–Helmholtz Instabilities Found to Drive Plasma Mixing on the Sun

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As easy as the Sun is to observe, it’s simultaneously very hard to study due to how extreme the conditions are, even on the surface of a rather unassuming star. One of these study topics is the interaction between the Sun’s plasma and magnetic field, as this drives much of the dynamism of the Sun’s surface layer (i.e., the photosphere). Recent observations by the 4-meter solar telescope in Hawaii have now led to interesting new findings, as detailed in a paper in  Nature by [David Kuridze] et al. Despite popular portrayal, this photosphere is not a boiling liquid, but rather pockets of plasma at various temperatures. The plasma moves within the magnetic field and convective movements that create the ‘boiling’ pattern, which gives the illusion of a boiling liquid surface. Within this photosphere, [Kuridze] et al. were able to observe Kelvin-Helmholtz instabilities , which are fluid instabilities caused by velocity shearing in either a continuous fluid or...
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ESP32-P4 Powers Video Alarm Clock

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Once upon a time, you had the option of waking up to a bell, a harsh buzzer, or whatever happened to be on the radio that morning. Now that it’s the 21st century, we’ve gotten used to being able to set our alarms to whatever sound or song we want, but what if you don’t just want to wake up to sound? Enter [Impossible_Agent1436] a.k.a. [brunokeymolen]’s Video Alarm Clock that will wake you up to whatever clip you want, as long as it fits on the 720 pixel square display. That display is a pre-built Waveshare module powered by an ESP32-P4, which looks like a handy bit of kit aside from being out of stock at the moment. The dev board makes this almost entirely a software project– the only hardware [bruno] had to come up with was the 3D-printed stand to hold it on his bedside. That’s not a slight to [bruno]; it was a good choice in the spirit of “work smarter, not harder”. Sometimes you want to reinvent the wheel, and sometimes you just want a...
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