We don’t think of computers as something you’d find in the 17th century. But [Levi McClain] found plans for one in a book — books, actually — by [Athanasius Kirker] about music. The arca musarithmica, a machine to allow people with no experience to compose church music, might not fit our usual definition of a computer, but as [Levi] points out in the video below, there are a number of similarities to mechanical computers like slide rules.

Apparently, there are a few of these left in the world, but as you’d expect, they are quite rare. So [Levi] decided to take the plans from the book along with some information available publicly and build his own.

The computer is a box of wooden cards — tablets — with instructions written on them. Honestly, we don’t know enough about music theory to quite get the algorithm. [Kirker] himself had this to say in his book about the device:

Mechanical music-making is nothing more than a particular system invented by us whereby anyone, even the ἀμουσος [unmusical] may, through various applications of compositional instruments compose melodies according to a desired style. We shall briefly relate how this mechanical music-making is done and, lest we waste time with prefatory remarks, we shall begin with the construction of the Musarithmic Ark.

If you want to try it yourself, you won’t need to break out the woodworking tools. You can find a replica on the web, of course. Let us know if you set any Hackaday posts to music.

We know not everyone thinks something mechanical can be a computer, but we disagree. True, some are more obvious than others.

It is hard to imagine that it has been more than four decades since two of the original designers of the Sinclair ZX Spectrum broke off to market the Jupiter Ace. [Nemanja Trifunovic] remembers the tiny computer in a recent post, and we always love to recall the old computers that used TVs for screens and audio tape recorders for mass storage.

One thing we always loved about the Jupiter Ace is that while most computers of the era had Basic as their native tongue, the Ace used Forth. As the post points out, while this may have given it great geek cred, it didn’t do much for sales, and the little machine was history within a year. However, the post also proposes that Forth wasn’t the real reason for the machine’s lack of commercial success.

Why did they pick Forth? Why not? It is efficient and interactive. The only real disadvantage was that Basic was more familiar to more people. Books and magazines of the day showed Basic, not Forth. But, according to the post, the real reason for its early demise was that it was already using outdated hardware from day one.

The Ace provided only 3K of RAM and did not offer color graphics. While this may sound laughable today, it wasn’t totally out of the question in 1978. Unfortunately, the Ace debuted in 1982. There were options that offered much more for just a little less. There is also the argument that as users became less technical, they just wanted to load pre-programmed tapes or cartridges and didn’t really care what language was running the computer.

Maybe, but we did and we can’t help but imagine a future where Forth was the language of choice for personal computers. Given how few of these were made, we see a lot of projects around them or, at least, replicas. Of course, these days that can be as simple as a single chip.

Is a bicycle like a motorcycle? Of course, the answer is it is and it isn’t. Saying something is “like” something else presupposes a lot of hidden assumptions. In the category “things with two wheels,” we have a winner. In the category “things that require gasoline,” not so much. We’ve noticed before that news stories about astronomy often talk about “sun-like stars” or “Earth-like planets.” But what does that really mean? [Paul Gilster] had the same questions, if you want to read his opinion about it.

[Paul] mentions that even textbooks can’t agree. He found one that said that Centauri A was “sun-like” while Centauri B was sometimes considered sun-like and other times not. So while Paul was looking at the examples of press releases and trying to make sense of it all, we thought we’d just ask you. What makes a star like our sun? What makes a planet like our planet?

Part of the problem is we don’t really know as much as we would like about other planets and their stars. We know more than we used to, of course. Still, it would be like wondering if the motorcycle was like that distant point of light. Maybe.

This is one of those things that seems deceptively simple until you start thinking about it. Is a planet Earth-like if it is full of water? What if it is totally covered in water? What if there’s no life at all? But life isn’t it, either. Methane-breathing silicon-based life probably doesn’t live on Earth-like planets.

Maybe Justice Potter Stewart was on to something when he said, “I know it when I see it!” Unfortunately, that’s not very scientific.

So what do you think? What’s a sun-like star? What’s an Earth-like planet? Discuss in the comments.

Don’t even get us started on super-earths, whatever they are. We are learning more about our neighbors every day, though.

[BorisDigital] was mesmerised by a modern elevator. He decided to see how hard it would be to design his own elevator based on Raspberry Pis. He started out with a panel for the elevator and a call panel for the elevator lobby. Of course, he would really need three call panels since he is pretending to have a three-floor building.

It all looks very professional, and he has lots of bells and whistles, including an actual alarm. With the control system perfected, it was time to think about the hydraulics and mechanical parts to make a door and an actual lift.

It is still just a model, but he does have 10A AC switches for the pumps. Everything talks via MQTT over WiFi. There’s also a web-based control dashboard. We didn’t count how many Pi boards are in the whole system, but it is definitely more than three.

If you are wondering why this was built, we are too. But then again, we never really need an excuse to go off on some project, so we can’t throw stones.

Want to see a more practical build? Check it out. Perhaps he’ll start on an escalator next.

If you want to get started in microfluidic robotics, [soiboi soft’s] salamander is probably too complex for a first project. But it is impressive, and we bet you’ll learn something about making this kind of robot in the video below.

The pneumatic muscles are very impressive. They have eight possible positions using three sources of pressure. This seems like one of those things that would have been nearly impossible to fabricate in a home lab a few decades ago and now seems almost trivial. Well, maybe trivial isn’t the right word, but you know what we mean.

The soft robots use layers of microfluidic channels that can be made with a 3D printer. Watching these squishy muscles move in an organic way is fascinating. For right now, the little salamander-like ‘bot has a leash of tubes, but [soiboi] plans to make a self-contained version at some point.

If you want something modular, we’ve seen Lego-like microfluidic blocks. Or, grab the shrinky dinks.

IBM mainframes are known for very unusual terminals. But IBM made many different things, including the IBM 3151 ASCII terminal, which uses a cartridge to emulate a VT220 terminal. [Norbert Keher] has one and explains in great detail how to connect it to a mainframe.

It had the 3151 personality cartridge for emulating multiple IBM and DEC terminals. However, the terminal would not start until he unplugged it. The old CRT was burned in with messages from an IBM 3745, which helped him work out some of the configuration.

If you’ve only used modern ASCII terminals, you might not realize that many terminals from IBM and other vendors used to use a block mode where the computer would dump a screen to the terminal. You could “edit” the screen (that is, fill in forms or enter lines). Then you’d send the whole screen back in one swoop. This is “block” mode, and some of the terminals the 3151 can emulate are character mode, and others are block mode, which explains its odd keyboard and commands.

[Norbert] gets the terminal running with a virtual mainframe, but along the way, he explains a lot about what’s going on. The video is about an hour long, but it is an hour well spent if you are interested in mainframe history.

Of course, you can always get the real deal to connect. If you don’t have your own virtual mainframe, you are missing out.

The RTL-SDR dongles get most of the love from people interested in software-defined radio, but the Pluto is also a great option, too. [FromConceptToCircuit] shares code to turn one of these radios into a spectrum analyzer that sweeps up to 6 GHz and down to 100 MHz. You can see a video of how it works below.

While it may seem that 100 MHz is a bit limiting, there’s plenty of activity in that range, including WiFi, Bluetooth, radio systems, both commercial and amateur, and even cell phones.

The system uses a lock-in amplifier technique for best performance. The Python code is straightforward. You simply scan all frequencies and determine the signal strength at each point. Of course, the devil is in the details.

We covered using Pluto with GNU Radio a while back. We like how it connects like a network adapter, among other things. Spectrum analysis is a common project for one of these SDRs.

[Georges Gagnerot] has been trying to emulate iOS and run iPhone software in a virtual environment. There were a few choices, and qemu-t8030 had a number of interesting features that you can check out in his post.

The project requires a patched QEMU, and [Georges] did some basic jailbreaking techniques. The real problem, of course, was not having the Apple Silicon GPU. Older versions of iOS let you select software rendering, but that option is gone on newer versions. However, it was possible to patch the phone to still use software rendering. There are still apps that directly use Metal or OpenGL that won’t run, but that’s another problem.

There is a plan to explore forwarding GPU calls to a real device. However, that seems difficult so it will have to wait for now.

That wasn’t the last problem, of course. But the post gives you a great view into the detective work. There is still work to go, but it looks like a lot of progress.

You can find the t8030 code on GitHub. Most of the iPhone hacking we see is hardware even if it means cutting the screen.

If you think of records as platters, you are of a certain age. If you don’t remember records at all, you are even younger. But there was a time when audio records were not flat — they were drums, which was how the original Edison phonograph worked. [Our Own Devices] did a video earlier showing one of these devices, but since it was in a museum, he didn’t get to open it up. Lucky for us, he now has one of his own, and we get to see inside in the video below.

Ironically, Edison was deaf yet still invented the phonograph. While he did create the working phonograph — his self-identified most important invention — the original invention wasn’t commercially viable. You could record and playback audio on tin foil wrapped around a drum. But you couldn’t remove the foil without destroying it.

Edison was busy, but another inventor related to Bell created a similar system that used wax cylinders instead of foil. Edison’s vision for his invention didn’t include popular music, which hurt sales.

If you want to skip the history lesson — although it is well worth watching — you can skip to the 9-minute mark. You can hear the machine play and then see the box come off.

Oddly, people were recording things before they were able to play them back. Keeping a machine like this running can be quite a challenge.

Usually when we talk about retrocomputing, we want to look at — and in — some old hardware. But [Z→Z] has a different approach: dissecting MacPaint, the Apple drawing program from the 1980s.

While the program looks antiquated by today’s standards, it was pretty hot stuff back in the day. Things we take for granted today were big deals at the time. For example, being able to erase a part of something you drew prompted applause at an early public demo.

We enjoyed the way the program was tested, too. A software “monkey” was made to type keys, move things, and click menus randomly. The teardown continues with a look inside the Pascal and assembly code with interesting algorithms like how the code would fill an area with color.

The program has been called “beautifully organized,” and [Z→Z] examines that assertion. Maybe the brilliance of it has been overstated, but it did work and it did influence many computer graphics programs over the years.

We love digging through old source code. Even old games. If you do your own teardowns, be sure to send us a tip.

We remember when the transputer first appeared. Everyone “knew” that it was going to take over everything. Of course, it didn’t. But [Oscar Toledo G.] gives us a taste of what life could have been like with a JavaScript emulator for the transputer, you can try in your browser.

If you don’t recall, the transputer was a groundbreaking CPU architecture made for parallel processing. Instead of giant, powerful CPUs, the transputer had many simple CPUs and a way to chain them all together. Sounds great, but didn’t quite make it. However, you can see the transputer’s influence on CPUs even today.

Made to work with occam, the transputer was built from the ground up for concurrent programming. Context switching was cheap, along with simple message passing and hardware scheduling.

The ersatz computer has a lot of messages in Spanish, but you can probably muddle through if you don’t hablar español. We did get the ray tracing example to work, but it was fairly slow.

Want to know more about the CPU? We got you. Of course, these days, you can emulate a transputer with nearly anything and probably outperform the original. What we really want to see is a GPU emulation.

You don’t see them as often as you used to, but it used to be common to see “electronics trainers” which were usually a collection of components and simple equipment combined with a breadboard, often in a little suitcase. We think [Pro Maker_101’s] portable electronics workstation is in the same kind of spirit, and it looks pretty nice.

The device uses a 3D printed case and a custom PC board. There are a number of components, although no breadboard. There is a breakout board for Raspberry Pi GPIO, though. So you could use the screw terminals to connect to an external breadboard. We were thinking you could almost mount one as a sort of lid so it would open up like a book with the breadboard on one side and the electronics on the other. Maybe version two?

One thing we never saw on the old units? An HDMI flat-screen display! We doubt you’d make one exactly like this, of course, but that’s part of the charm. You can mix and match exactly what you want and make the prototyping station of your dreams. Throw in a small portable soldering iron, a handheld scopemeter, and you can hack anywhere.

We’d love to see something like this that was modular. Beats what you could build in 1974.

There seems to be nothing a 555 can’t do. We’ve seen it before, but [electronzapdotcom] reminds us you can use a 555 and a few parts to make a reasonable touch switch in this video, embedded below.

The circuit uses some very large resistors so that noise from your body can overcome the logic level on the trigger and threshold inputs. You can easily adapt this idea if you need a simple touch switch. Though we imagine this circuit wouldn’t work well if you were in a quiet environment. We suspect 50 or 60 Hz hum is coupling through your finger and triggering the pins, but it could be a different effect.

How reliable is it? Beats us. The circuit is a bistable, so essentially your finger pumps a signal into a flip-flop. This is old trick, but could be useful. Of course, if you really need a touch switch, you have plenty of options. You can get little modules. Or, directly measure skin resistance.

We are always fascinated by bubble memory. In the late 1970s, this was the “Next Big Thing” that, as you may have guessed, was, in fact, not the next big thing at all. But there were a number of products that used it as non-volatile memory at a time when the alternative was tape or disk. [Smbakeryt] has a cool word processor with an acoustic coupler modem made by Teleram. Inside is — you guessed it — bubble memory.

The keyboard was nonfunctional, but fixable. Although we wouldn’t have guessed the problem. Bubble memory was quite high tech. It used magnetic domains circulating on a thin film of magnetic material. Under the influence of a driving field, the bubbles would march past a read-write head that could create, destroy, or read the state of the bubble.

Why didn’t it succeed? Well, hard drives got cheap and fairly rugged. The technology couldn’t compete with the high-density hard drives that could be reached with improved heads and recording strategies. Bubble memory did find use in high-vibration items, but also wound up in things like this terminal, at least one oscilloscope, and a video game.

Bubble memory evolved from twistor memory, one of several pre-disk technologies. While they are hard to come by today, you can find the occasional project that either uses some surplus or steals a part off of a device like this one.

How do you get images downlinked from 30 km up? Hams might guess SSTV — slow scan TV — and that’s the approach [desafloinventor] took. If you haven’t seen it before (no pun intended), SSTV is a way to send images over radio at a low frame rate. Usually, you get about 30 seconds to 2 minutes per frame.

The setup uses regular, cheap walkie-talkies for the radio portion on a band that doesn’t require a license. The ESP32-CAM provides the processing and image acquisition. Normally, you don’t think of these radios as having a lot of range, but if the transmitter is high, the range will be very good. The project steals the board out of the radio to save weight. You only fly the PC board, not the entire radio.

If you are familiar with SSTV, the ESP-32 code encodes the image using Martin 1. This color format was developed by a ham named [Martin] (G3OQD). A 320×256 image takes nearly two minutes to send. The balloon system sends every 10 minutes, so that’s not a problem.

Of course, this technique will work anywhere you want to send images over a communication medium. Hams use these SSTV formats even on noisy shortwave frequencies, so the protocols are robust.

Hams used SSTV to trade memes way before the Internet. Need to receive SSTV? No problem.

Surely by now you’ve at least heard of RTL-SDR — a software project that let’s cheap TV tuner dongles work as a software-defined radios. A number of projects and tools have spun off the original effort, but in his latest video, [Tech Minds] shows off a particularly unique take. It’s a Web browser-based radio application that uses WebUSB, so it doesn’t require the installation of any application software. You can see the program operating in the video below.

There are a few things you should know. First, you need the correct USB drivers for your RTL-SDR. Second, your browser must support WebUSB, of course. Practically, that means you need a Chromium-type browser. You may have to configure your system to allow raw access to the USB port, too.

Watching the video, you can see that it works quite well. According to the comments, it will work with a phone, too, which is an interesting idea. The actual Web application is available as open source. It isn’t going to compete with a full-fledged SDR program, but it looked surprisingly complete.

These devices have grown from a curiosity to a major part of radio hacking over the years. Firefox users can’t use WebUSB — well, not directly, anyway.

Ever heard of VENIX? There were lots of variants of Unix back in the day, and VENIX was one for the DEC Professional 380, which was — sort of — a PDP 11. The 1982 machine normally ran the unfortunately (but perhaps aptly) named P/OS, but you could get VENIX, too. [OldVCR] wanted to put one of these back online and decided the ST-506 hard drive was too risky. A solid-state drive upgrade and doubling the RAM to a whole megabyte was the plan.

It might seem funny to think of a desktop workstation that was essentially a PDP-11 minicomputer, but in the rush to corner the personal computer market, many vendors did the same thing: shrinking their legacy CPUs. DEC had a spotty history with small computers. [Ken Olsen] didn’t think anyone would ever want a personal computer, and the salespeople feared that cheap computers would eat into traditional sales. The Professional 350 was born out of DEC’s efforts to catch up, as [OldVCR] explains. He grabbed this one from a storage unit about to be emptied for scrap.

The post is very long, but you get a lot of history and a great look inside this vintage machine. Of course, the PDP-11 couldn’t actually handle more than 64K without tricks and you’ll learn more about that towards the end of the post, too.

Just as a preview, the story has a happy ending, including a surprising expression of gratitude from the aging computer. DEC didn’t enjoy much success in the small computer arena, eventually being bought by Compaq, which, in turn, was bought by Dell. During their heyday, this would have been unthinkable.

The PDP/11 did have some success because it was put on a chip that ended up in several lower-end machines, like the Heathkit H11. Ever wonder how people programmed the PDP computers with switches and lights?

If you do FDM 3D printing, you know one of the biggest problems is sensing the bed. Nearly all printers have some kind of bed probing now, and it makes printing much easier, but there are many different schemes for figuring out where the bed is relative to the head. [ModBot] had a Voron with a clicky probe but wanted to reclaim the space it used for other purposes. In the video, also linked below, he reviews the E3D PZ probe which is a piezoelectric washer, and the associated electronics to sense your nozzle crashing into your print bed.

There are many options, and it seems like each has its pros and cons. We do like solutions that actually figure out where the tip is so you don’t have to mess with offsets as you do with probes that measure from a probe tip instead of the print head.

Of course, there are other piezo probes we’ve seen. There are also many other kinds of sensors available. The version from E3D is available as a kit you can add to anything, assuming you can figure out how. Or you can do like [ModBot] did and opt for an E3D heatsink with the washer already in place which, presumably, will best fit E3D products.

From the printer’s point of view, the device looks like a normal end stop, so it is simple to configure the printer. There are other ways to sense a head crash, of course. We keep meaning to install one of the “real time” sensors you can get now, but our CR Touch works well enough that we never find the time.

We know how [Techmoan] feels. In the 1980s we had a bewildering array of oddball gadgets and exciting new tech. But as kids we didn’t have money to buy a lot of what we saw. But he had a £5 note burning a hole in his pocket from Christmas and found a Casio RD-10 “card radio” on sale and grabbed it. He’s long-ago lost that one, but he was able to find a new old stock one and shows us the little gadget in the video below.

The card-thin (1.9 mm) FM radio had many odd features, especially for the 1980s. For one thing, it took a coin cell, which was exotic in those days. The headphones had a special flat connector that reminded us of an automotive fuse. Even the idea of an earbud was odd at that time.

It was a good idea not to lose the earbud, as it had that strange connector. The earbud worked as the antenna and power switch, too. Oddly enough, you could get a slightly fatter AM radio version, and they even made one that was AM and FM. Unsurprisingly, Casio even made a version with a calculator built-in. It had a solar cell, but that only powers the calculator. You still needed the coin cell for the radio.

The sound? Meh. But what did you expect? There was a stereo version, too. However, that one had a rechargeable battery, which was not in good health after a few decades. He also shows a Sony card radio that is a bit different. We were hoping for a teardown, especially of the rechargeable since it was toast, anyway, but for now, we’ll have to imagine what’s inside.

We love nostalgic radios, although usually they are a little older. We miss the days when a kid might think it was cool to see an ad touting: “Oh boy! We’re radio engineers!”