Even if you never want to generate hydrogen, [Maciej Nowak’s] video (embedded below) is interesting to watch because of the clever way the electrode is formed from stainless steel washers. You’ll need heat shrink tubing, but you ought to have that hanging around anyway. Building the electrode using the techniques in the video results in a lot of surface area which is important for an electrochemical reaction.
A standard rechargeable cell provides power for the generator which resides in a modified plastic bottle. The overall build looks good even though it is all repurposed material.
Many films use a similar trope when it comes to poisoning. The aspiring murderer ingests a drink poured from the same vessel as that given to their intended victim to indicate the liquid is safe to imbibe. The Assassin’s Teapot is a way one could achieve such a ruse, allowing two different liquids to be poured from what is seemingly a regular teapot, as shown by [Steve Mould]. (Video after the break.)
The trick is simple. Two separate cavities exist within the teapot, exiting via their own paths in the same spout. Each cavity also has an air hole in the top. If the hole for a given cavity is blocked by the pourer’s thumb, the liquid will not flow.
Each cavity can be filled with its own liquid. For example, one can be filled with tea, the other with poisoned tea. The murderer blocks the hole for the poison cavity when pouring their own beverage, delivering tea to their own glass. Then, when pouring for the enemy, the hole for the tea cavity is blocked, and poison is allowed to flow into the glass of one’s target.
The workings are simple; if air cannot flow into the cavity of the teapot to replace liquid flowing out, air pressure will stop the liquid flowing at all. The concept is demonstrated ably by [Steve]’s 2D recreation, letting us visualize the workings of the teapot quite easily.
It also shows a minor flaw in the design, which should be accounted for – if the spout isn’t designed carefully, sometimes flow from one cavity can dribble into the other. Between this and the chance of getting confused about which hole to cover to pour the poison, it would pay to keep some antidote on hand. Or, alternatively, just pour your guests tea instead – they’ll appreciate it!
Typical concrete work relies on a form often made with wood, steel, or plastic. That’s easy to do, but hard to make complex shapes. However, if you can create complex shapes you can easily put material where it adds strength and omit material where it doesn’t carry load. Using a robotic-arm 3D print technique, the researchers can lay out prefabricated blocks of foam that create forms with highly complex shapes. Continue reading “Concrete With 3D Printed Foam Forms”→
You asked for it, and now you’ve got it. It’s taken more than a decade of accumulated complaining, but this gigantic 555 timer IC has finally gathered enough psychokinetic energy to take corporeal form and demand fealty from the readers of Hackaday.
Or not. The less exciting explanation is that creator [Rudraksha Vegad] was looking for a way to combine his interests in discrete electronic components and woodworking. The result is an incredible build that’s more than just a conversation starter; this desktop-sized version of the iconic integrated timer circuit is fully functional. You can even hook it up to a breadboard, assuming you’ve got some alligator clips handy.
Lifting the lid on this wooden “chip” uncovers an intricate hand-wired array of discrete components that stand in for the microscopic goings on inside the real thing. He’s even gone through the trouble of recreating the symbols for the comparators and flip-flops that you’d see in a diagram of a 555 using wooden shapes to elevate their respective components. It might not fit the classical definition, but surely this must count as some form of circuit sculpture.
For those who love travelling around the world, life hasn’t been great for the past two years. World-wide lockdowns and travel restrictions have kept many people stuck inside their own homes when they would rather be jetting off to distant cities. If you’re one of those bothered by Wanderlust, [Alex Shakespeare] might have a solution for you: a window that shows a live image from another location around the world.
To make the experience as lifelike as possible, [Alex] used an actual window in his London home and mounted a large TV behind it. A wall-mounted map enables him to choose any of five locations by moving a little magnetic plane across the map. LEDs show the available spots, while magnetometers detect the motion of the aircraft. An ESP8266 then instructs a media server to connect to the appropriate livestream, which is subsequently displayed on the TV screen.
All of this is clever enough already, but [Alex] decided to go one step further and added a thermal sensor that detects the location of any persons standing near the display and shifts the image a little when they move. This simulates the perspective of looking out a real window, and should give the image a more life-like quality than if it were simply static.
The whole design is available on [Alex]’s GitHub page, ready to be replicated by anyone who wants to look out over some exotic location. If, instead, you want a way to reminisce about the places you’ve visited in the past, check out this cool souvenir globe. We’ve also seen a neat Google Maps based one a few years back.
In our no-nonsense journey through the world of audio technology we’ve so far have looked at digital audio and the vinyl disk recording. What’s missing? Magnetic tape, the once-ubiquitous recording medium that first revolutionised the broadcast and recording industries in the mid-20th-century, and went on to be a mainstay of home audio before spawning the entire field of personal audio. Unless you’re an enthusiast or collector, it’s likely you won’t have a tape deck in your audio setup here in 2021 and you’ll probably be loading your 8-bit games from SD card rather than cassette, but surprisingly there are still plenty of audio cassettes released as novelties or ephemeral collectables.
The Device That Made The Sound Of The Latter Half Of The 20th Century
The first magnetic recordings were made directly on metal wires, but metal fatigues as it bends. By coating a flexible plastic tape in ferrous particles, the same simple technique of laying down an audio signal as variations in the magnetic field could be made smaller, lighter, and more robust. But the key to the format’s runaway success is the technical advancements that differentiate those 1950s machines from their wire recorder ancestors.
Whether it is a humble cassette recorder or a top-end studio multitrack, all tape recorders are very similar. There are two reels that hold the tape: the playback reel that houses the recording, and the take-up reel that stores the tape as it plays in the machine. The take-up reel is lightly driven to run faster than the tape speed, and the playback reel has a slight braking force to keep the tape under tension at all times. Continue reading “Know Audio: Mixtapes, Tape Loops, And Razor Blades”→
Building a complete operating system by compiling its source code is not something for the faint-hearted; a modern Linux or BSD distribution contains thousands of packages with millions of lines of code, all of which need to be processed in the right order and the result stored in the proper place. For all but the most hardcore Gentoo devotees, it’s way easier to get pre-compiled binaries, but obviously someone must have run the entire compilation process at some point.
What’s true for modern OSes also holds for ancient software such as MS-DOS. When Microsoft released the source code for several DOS versions a couple of years ago, many people pored over the code to look for weird comments and undocumented features, but few actually tried to compile the whole package. But [Michal Necasek] over at the OS/2 Museum didn’t shy away from that challenge, and documented the entirely-not-straightforward process of compiling DOS 2.11 from source.
The first problem was figuring out which version had been made available: although the Computer History Museum labelled the package simply as “MS-DOS 2.0”, it actually contained a mix of OEM binaries from version 2.0, source code from version 2.11 and some other stuff left from the development process. The OEM binaries are mostly finished executables, but also contain basic source code for some system components, allowing computer manufacturers to tailor those components to their specific hardware platform.
Compiling the source code was not trivial either. [Michal] was determined to use period-correct tools and examined the behaviour of about a dozen versions of MASM, the assembler likely to have been used by Microsoft in the early 1980s. As it turned out, version 1.25 from 1983 produced code that most closely matched the object code found in existing binaries, and even then some pieces of source code required slight modifications to build correctly. [Michal]’s blog post also goes into extensive detail on the subtle differences between Microsoft-style and IBM-style DOS, which go deeper than just the names of system files (MSDOS.SYS versus IBMDOS.COM).
The end result of this exercise is a modified DOS 2.11 source package that actually compiles to a working set of binaries, unlike the original. And although this does not generate any new code, since binaries of DOS 2.11 have long been available, it does provide a fascinating look into software development practices in an age when even the basic components of the PC platform were not fully standardized. And don’t forget that even today some people still like to develop new DOS software.