[My Ham Radio Journey] wanted to see if a “common person” (in his words) could build an effective vertical ham radio antenna. If you look at the video below, the answer is apparently yes.
He started with a 24-foot fishing rod and a roll of 22 gauge wire. The height of the antenna wire is just over 20 feet long and he has several ground radials, as you might expect for a vertical antenna.
[Dale Cook] has cats, and as he readily admits, cats are jerks. We’d use stronger language than that, but either way it became a significant impediment to making progress with an RFID-based sensor to allow his cats access to their litterbox. Luckily, though, he was able to salvage the project enough to give a great talk on RFID from first principles and learn about a potentially tragic mistake.
If you don’t have 20 minutes to spare for the video below, the quick summary is that [Dale]’s cats are each chipped with an RFID tag using the FDX-B protocol. He figured he’d be able to build a scanner to open the door to their playpen litterbox, but alas, the read range on the chip and the aforementioned attitude problems foiled that plan. He kept plugging away, though, to better understand RFID and the electronics that make it work.
To that end, [Dale] rolled his own RFID reader pretty much from scratch. He used an Arduino to generate the 134.2-kHz clock signal for the FDX-B chips and to parse the returned data. In between, he built a push-pull driver for the antenna coil and an envelope detector to pull the modulated data off the carrier. He also added a low-pass filter and a comparator to clean up the signal into a nice square wave, which was fed into the Arduino to parse the Differential Manchester-encoded data.
Although he was able to read his cats’ chips with this setup, [Dale] admits it was a long road compared to just buying a Flipper Zero or visiting the vet. But it provided him a look under the covers of RFID, which is worth a lot all by itself. But more importantly, he also discovered that one cat had a chip that returned a code different than what was recorded in the national database. That could have resulted in heartache, and avoiding that is certainly worth the effort too.
Continue reading “RFID From First Principles And Saving A Cat”
[Japhy Riddle] was tired of creating pixel art. He went to subpixel art. The idea is that since each color pixel is composed of three subpixels, your display is actually three times as dense as you think it is. As long as you don’t care about the colors, of course.
Is it practical? No, although it is related to the Bayer filter algorithm and font antialiasing. You can also use subpixel manipulation to hide messages in plain sight.
When you tear into an old piece of test equipment, you’re probably going to come up against some surprises. That’s especially true of high-precision gear like oscilloscopes from the time before ASICs and ADCs, which had to accomplish so much with discrete components and a lot of engineering ingenuity.
Unfortunately, though, those clever hacks that made everything work sometimes come back to bite you, as [Void Electronics] learned while bringing this classic Tektronix 466 scope back to life. A previous video revealed that the “Works fine, powers up” eBay listing for this scope wasn’t entirely accurate, as it was DOA. That ended up being a bad op-amp in the power supply, which was easily fixed. Once powered up, though, another, more insidious problem cropped up with the vertical attenuator, which failed with any setting divisible by two.
With this curious symptom in mind, [Void] got to work on the scope. Old analog Tek scopes like this use a bank of attenuator modules switched in and out of the signal path by a complex mechanical system of cams. It seemed like one of the modules, specifically the 4x attenuator, was the culprit. [Void] did the obvious first test and compared the module against the known good 4x module in the other channel of the dual-channel scope, but surprisingly, the module worked fine. That meant the problem had to be on the PCB that the module lives on. Close examination with the help of some magnification revealed the culprit — tin whiskers had formed, stretching out from a pad to chassis ground. The tiny metal threads were shorting the signal to ground whenever the 4x module was switched into the signal path. The solution? A quick flick with a sticky note to remove the whiskers!
This was a great fix and a fantastic lesson in looking past the obvious and being observant. It puts us in the mood for breaking out our old Tek scope and seeing what wonders — and challenges — it holds.
Continue reading “Close Shave For An Old Oscilloscope Saved With A Sticky Note”
Boats normally get around with propellers or water jets for propulsion. Occasionally, they use paddles. [Engineering After Hours] claims he is “changing the boat game forever” with his new 3D printed boat design that uses a tank tread for propulsion instead. Forgive him for the hyperbole of the YouTuber. It’s basically a modified paddle design, but it’s also pretty cool.
The basic idea is simple enough—think “floating snowmobile” and you’re in the ballpark. In the water, the chunky tank track provides forward propulsion with its paddle-like treads. It’s not that much different from a paddle wheel steamer. However, where it diverges is that it’s more flexible than a traditional paddle wheel.
The tracked design is actually pretty good at propelling the boat in shallow water without getting stuck. In fact, it works pretty well on dirt, too! The video covers the basic concept, but it also goes into some detail regarding optimizing the design, too. Getting the float and track geometry right is key to performance, after all.
If you’re looking to build an oddball amphibious craft, maybe working with the snowmobile concept is worth your engineering time. Continue reading “3D Printed Boat Uses Tank Tracks For Amphibious Propulsion”
The open-source hardware business landscape is no doubt a tough one, but is it actually tougher than for closed-source hardware? That question has been on our minds since the announcement that the latest 3D printer design from former open-source hardware stalwarts Prusa Research seems like it’s not going to come with design files.
Ironically, the new Core One is exactly the printer that enthusiasts have been begging Prusa to make for the last five years or more. Since seeing hacker printers like the Voron and even crazy machines like The 100 whip out prints at incredible speed, the decade-old fundamental design of Prusa’s i3 series looks like a slow and dated, if reliable, workhorse. “Bed slinger” has become a bit of a pejorative for this printer architecture in some parts of the 3DP community. So it’s sweet to see Prusa come out with the printer that everyone wants them to make, only it comes with the bitter pill of their first truly closed-source design.
Is the act of not sharing the design files going to save them? Is it even going to matter? We would argue that it’s entirely irrelevant. We don’t have a Core One in our hands, but we can’t imagine that there is anything super secret going on inside that couldn’t be reverse engineered by any other 3DP company within a week or so. If anything, they’re playing catch up with other similar designs. So why not play to one of their greatest strengths – the engaged crowd of hackers who would most benefit from having the design files?
Of course, Prusa’s decision to not release the design files doesn’t mean that they’re turning their backs on the community. They are also going to offer an upgrade package to turn your current i3 MK4 printer into the new Core One, which is about as hacker-friendly a move as is possible. They still offer kit versions of the printers at a discount, and they continue to support their open-source slicer software.
But this one aspect, the move away from radical openness, still strikes us as bittersweet. We don’t have access to their books, of course, but we can’t imagine that not providing the design files gains them much, and it will certainly damage them a little in the eyes of their most devoted fans. We hope the Core One does well, but we also hope that people don’t draw the wrong lesson from this – that it does well because it went closed source. If we could run the experiment both ways, we’d put our money on it doing even better if they released the design files.
Tiling a space with a repeated pattern that has no gaps or overlaps (a structure known as a tessellation) is what led mathematician [Gábor Domokos] to ponder a question: how few corners can a shape have and still fully tile a space? In a 2D the answer is two, and a 3D space can be tiled in shapes that have no corners at all, called soft cells.
These shapes can be made in a few different ways, and some are shown here. While they may have sharp edges there are no corners, or points where two or more line segments meet. Shapes capable of tiling a 2D space need a minimum of two corners, but in 3D the rules are different.
A great example of a natural soft cell is found in the chambers of a nautilus shell, but this turned out to be far from obvious. A cross-section of a nautilus shell shows a cell structure with obvious corners, but it turns out that’s just an artifact of looking at a 2D slice. When viewed in full 3D — which the team could do thanks to a micro CT scan available online — there are no visible corners in the structure. Once they knew what to look for, it was clear that soft cells are present in a variety of natural forms in our world.
[Domokos] not only seeks a better mathematical understanding of these shapes that seem common in our natural world but also wonders how they might relate to aperiodicity, or the ability of a shape to tile a space without making a repeating pattern. Penrose Tiles are probably the most common example.
