In our surface-mount age, it’s easy to be jaded about miniaturization. We pretty much expect every circuit to be dimensionally optimized, something that’s easy to do when SMDs that rival grains of sand are available. But dial the calendar back half a century or so and miniaturization was a much more challenging proposition.
Challenging, perhaps, but by no means unachievable, as [Helge Fyske (LA6NCA)] demonstrates with this ultra-compact regenerative vacuum tube receiver. It’s a companion to his recent “spy transmitter,” a two-tube radio built in — or on, really — an Altoids tin. The transmitter was actually a pretty simple circuit, just a crystal-controlled oscillator and an RF amplifier really, but still managed about 1.5 Watts output on the 80-meter ham band.
The receiver circuit ended up being much more complicated, as receivers do, and therefore harder to cram into the allotted space. [Helge]’s used a three-tube regenerative design, with one tube each devoted to the RF amp, detector/mixer, and audio amplifier stages. As in the transmitter, the receiver tubes are mounted on the outside of the box, with the inside crammed full of components. [Helge] had to be quite careful about component positioning, to prevent interstage coupling and other undesirable side effects of building in such close quarters.
Was it worth it? Judging by the video below, absolutely! We’ve rarely heard performance like that from even a modern receiver with all the bells and whistles, let alone from a homebrew design under such constraints. It sounds fantastic, and hats off to [Helge] for completing his spy radio suite in style.
The build begins with small cut sections of plastic water pipe. These are used as housings to hold tennis balls, which are pressed in with a unique tool of [The Q]’s own construction. The individual ball assemblies are then bolted into a standard bicycle wheel, and a tread from a regular bike tire is stretched around the outside for grip.
It goes without saying that these tires won’t offer the same quality of ride as regular pneumatic bike tires. Nor will the performance be as good, due to the significant extra unsprung weight. They are eye-catching and fun, however. Plus, if you live in an area with tons of nails or prickles, you might find these are just the ticket. Maybe.
Some things remain classics, even after centuries, and chess and watches have certainly stood the test of time. [W&M Levsha] decided to combine them both in this “Chess Club” watch containing a miniature chess game frozen in time.
[W&M Levsha] used an off-the-shelf wristwatch for the mechanism and case, but rearranged the parts and built a custom watchface that’s much nicer than the original. The new watchface was cut and etched on a fiber laser after disassembly of the original watch.
The real magic happens when [W&M Levsha] turns those teeny little chess pieces on the lathe. The knight was a two piece affair with the horse head being laser cut out of brass sheet and then soldered onto a turned base. As you can see from the video embedded below, all of the chess pieces inside the watch could fit on the maker’s fingernail! It’s probably a good thing that this tiny set isn’t playable since trying to play on a board that size would be an exercise in patience.
As any radio amateur will tell you, the world of radio abounds with exciting possibilities. Probably the simplest pursuit of them all is that of the SWL, or short wave listener, who scours the airwaves in search of interesting stations. SWLs will often have fully-featured setups with high-end general-coverage communications receivers and tuned antenna arrays, but it can start with the cheapest of radios at its bottom end. Such a radio is the subject of this review, the XHDATA D-219 is a miniature portable receiver that costs under ten dollars, yet is currently the talk of the town in SWL circles. This interest is in no small amount due to its being an especially low-price way to get your hands on a shortwave radio using one of the SIlicon Labs integrated software-defind radio receiver chips. We don’t often review a consumer radio here at Hackaday, but with an avid eye for unexpected gems at the cheaper end of the market this one’s worth a second look.
What Do You Get For Your Tenner?
I ordered my D-219 from the XHDATA website, spending about £10 including the postage from China. The usual wait ensued before the package landed on my doormat, and inside was the radio in its box with an instruction leaflet. It’s a small unit about 135 mm x 75 mm x 30 mm, and it follows closely the form factor of other similar radios.
On the top is the extensible antenna with an on-off switch and sockets for headphone and 5 V power, on the side are side-on knobs for tuning and volume, while on the front is the speaker and old-style multi-band tuning display.
On the back is a flip-up stand and a hatch for a pair of AA cells. There’s a band switch covering AM, nine different shortwave bands from 4.75 MHz to 22 MHz, the east Asian FM band from 64 MHz to 87 MHz, and the international FM band from 87 MHz to 108 MHz. The tuning indicator is very old-school, a vertical bar that moves across a frequency scale with the tuning knob. Continue reading “Review: XHDATA D-219 Short Wave Radio Receiver”→
[3D Honza] has been sharing progress pictures and videos on his Twitter account, and just recently released the first version of his design. Version 1.0 is just the mechanics, but he’s already at work on version 2.0 which includes the ability to attach servos to drive the treads. At this writing, the design is currently downloadable directly from his site and includes CAD files, which is great to see.
One part of the design we’d like to draw your attention to is the chunky hinge that doubles as a kind of axial structure making up the body. This allows the tank to print in an unfolded state with the treads and wheels flat on the print bed. After printing, the tank gets folded up a bit like a taco to attain its final form. It’s a clever layout that allows the unit to be printed according to a filament-based 3D printer’s strengths, printing as a single piece that transforms into a small tank chassis, complete with working treads, in a few seconds.
The nutcracker is manufactured out of 17-4 PH stainless steel, heat treated to the H900 condition. A flexural spring section at the top of the nutcracker takes the place of the usual hinge, allowing the handles to be squeezed together and the teeth of the cracker to open the nut. Machining the flexural section is first achieved with a series of CNC drill operations on the billet stock, before regular milling is used to shape the rest of the spring section and tool. The video dives deep into the finer points of the CNC operations that produce such a great finish on the final part. It even covers the use of a tiny scissor jack to help hold the handles still during machining.
The result is a highly attractive and desirable nutcracker that looks far more special than the regular fare you might pick up at Walgreens. The all-billet tool is a nutcracker very much fit for a sci-fi set. We’ve seen some other kitchen tools around here before, too, albeit of more questionable utility.
This week, Editor-in-Chief Elliot Williams and Assignments Editor Kristina Panos decided against using one of Kristina’s tin can microphones to record the podcast, though that might be a cool optional thing to do once (and then probably never again).
After a brief foray into the news that the Chaos Communications Congress will be decentralized once again this year, as COVID restrictions make planning this huge event a complete headache (among other notable symptoms), we discuss the news that the EU is demanding replaceable batteries in phones going forward.
After that, it’s time for another What’s That Sound results show, and despite repeated listens, Kristina fails to guess the thing. Even if she’d had an inkling as to what it was, she probably would have said ‘split-flap display’ instead of the proper answer, which is ‘flip-dot display’, as a few people responded. Finally, it’s on to the hacks, where we talk about uses for ferrofluid and decide that it’s one of those things that’s just for fun and should not be applied to the world as some sort of all-purpose whacking device.
Check out the links below if you want to follow along, and as always, tell us what you think about this episode in the comments!