Reverse engineering a payphone doesn’t sound like a very interesting project, at least in the United States, where payphones were little more than ruggedized versions of residential phones with a coin mechanism attached. Phones in other parts of the world were far more interesting, though, as this look at the mysteries of a payphone from Israel reveals (in Hebrew; English translation here.)

This is a project [Inbar Raz] worked on quite a while ago, but only got around to writing up recently. The payphone in question was sourced from the usual surplus market channels, and appears to have been removed from service by Israeli telecommunications company Bezeq only shortly before he found it. It was in pretty good shape, and was even still locked tight, making some amateur locksmithing the first order of the day. The internals of the phone are surprisingly complex, with a motherboard that looks more like something from a PC. Date codes on the chips and through-hole construction date the device to the early- to mid-1990s.

With physical access gained, [Inbar] turned to the firmware. An Atmel flash chip seemed a good place to look, and indeed he was able to pull code off the chip. That’s where things took a turn thanks to the CPU the code was written for — the CDP1806, a later version of the more popular but still fringe CDP1802. This required [Inbar] to fall down the rabbit hole of writing a new processor definition file for Ghidra so that the firmware could be reverse-engineered. This got him to the point of understanding 1806 assembly well enough that he was able to re-flash the phone to print debugging messages on the built-in 16×2 LCD screen, which allowed him to figure out which routines were being called under various error conditions.

It doesn’t appear that [Inbar] ever completed the reverse engineering project, but as he points out, what does that even mean? He got inside, took a look around, and made the phone do some cool things it couldn’t do before, and in the process made things easier for anyone working with 1806 processors in Ghidra. That’s a pretty complete win in our books.

For some reason, we never tire of stories highlighting critical infrastructure that’s running outdated software, and all the better if it’s running on outdated hardware. So when we learned that part of the San Francisco transit system still runs on 5-1/4″ floppies, we sat up and took notice. The article is a bit stingy with the technical details, but the gist is that the Automatic Train Control System was installed in the Market Street subway station in 1998 and uses three floppy drives to load DOS and the associated custom software. If memory serves, MS-DOS as a standalone OS was pretty much done by about 1995 — Windows 95, right? — so the system was either obsolete before it was even installed, or the 1998 instance was an upgrade of an earlier system. Either way, the San Francisco Municipal Transportation Agency (SFMTA) says that the 1998 system due to be replaced originally had a 25-year lifespan, so they’re more or less on schedule. Replacement won’t be cheap, though; Hitachi Rail, the same outfit that builds systems that control things like the bullet train in Japan, is doing the job for the low, low price of $212 million.

We don’t know who needs to here this, but we got a tip from Clem Mayer about upcoming changes to EU regulations that might affect the maker community. It concerns the General Product Safety Regulations, or GPSR, which appears to be an extension of current rules that will impose additional compliance burdens on anyone selling products to the EU market on online marketplaces. We won’t pretend to know the intricacies of GPSR, or even the basics, but Smander.com has a brief summary of the rules and how best to comply, which seems to amount to retaining the services of a company to take care of the compliance paperwork. We also took a look at the official EU information page for GPSR, which is pretty thin on information but at least it’s a primary source. If you’re selling kits or other products into the EU market, chances are good that you’re going to need to figure this out, and soon — seems like the rules go into effect December 13th.

You’ve got to feel for the authors of open-source software. As if developing, maintaining, and supporting the software that keeps the Internet running wasn’t a thankless enough job, you can actually get doxxed by your own creation. A case in point is Daniel Stenberg, the original author and lead developer on curl and libcurl. His name and email address are often found in the documentation for products using his software, so frustrated users who find his contact information tend to reach out to him after being ignored by the product’s support team. It seems annoying, and we sympathize with Daniel and others like him, but then again, it’s a measure of your impact that your contact information is literally everywhere.

If you’re in the market for a unique gift for the geek in your life and have an extra $230 to spread around, check out this custom Lego kit of the ASML TWINSCAN EXE:500 extreme UV lithography machine. Actually, strike that; now that we look at the specs, this kit is tiny. It’s only 851 pieces and 13.9″ (35 cm) wide when assembled, and isn’t exactly a richly detailed piece. Sure, Lego kits are fun, but there seem to be much better choices out there; we had a blast putting together the Apollo 11 Lunar Module Eagle kit a few years back, and that was only about $70.

And finally, Festo fans will want to check out this literal air guitar from the automation company’s “Experience Center” in Lupfig, Switzerland. Festo engineers bedazzled an acoustic guitar with pneumatic cylinders and control valves and programmed the system to pluck out the intro riff from AC/DC’s “Thunderstruck.” It’s actually pretty good, and we especially appreciate the pneumatic party whistle that chips in from time to time. There’s a missed opportunity here, though; we really expected a pneumatic cylinder to do the characteristic double rap on the body of the guitar when you get to the “Thun-der!” part. Too bad — maybe for version two.

What do scanning electron microscopes and satellites have in common? On the face of things, not much, but after seeing [Zachary Tong]’s latest video on liquid metal ion thrusters, we see that they seem to have a lot more in common than we’d initially thought.

As you’d expect with such a project, there were a lot of false starts and dead ends. [Zach] started with a porous-emitter array design, which uses a sintered glass plate with an array of tiny cones machined into it. The cones are coated in a liquid metal — [Zach] used Galinstan, an alloy of gallium, indium, and tin — and an high voltage is applied between the liquid metal and an extraction electrode. Ideally, the intense electric field causes the metal to ionize at the ultra-sharp tips of the cones and fling off toward the extraction electrode and into the vacuum beyond, generating thrust.

Getting that working was very difficult, enough so that [Zach] gave up and switched to a slot thruster design. This was easier to machine, but alas, no easier to make work. The main problem was taming the high-voltage end of things, which seemed to find more ways to produce unwanted arcs than the desired thrust. This prompted a switch to a capillary emitter design, which uses a fine glass capillary tube to contain the liquid metal. This showed far more promise and allowed [Zach] to infer a thrust by measuring the tiny current created by the ejected ions. At 11.8 μN, it’s not much, but it’s something, and that’s the thing with ion thrusters — over time, they’re very efficient.

To be sure, [Zach]’s efforts here didn’t result in a practical ion thruster, but that wasn’t the point. We suspect the idea here was to explore the real-world applications for his interests in topics like electron beam lithography and microfabrication, and in that, we think he did a bang-up job with this project.

If there’s anything more frustrating than mounting holes that don’t line up with the thing you’re mounting, we don’t know what it could be. You measure as carefully as possible, you drill the holes, and yet at least one hole ends up being just out of place. Sometimes you can fudge it, but other times you’ve got to start over again. It’s maddening.

Getting solid measurements of the distance between holes would help, which is where these neat snap-on attachments for digital calipers come in. [Chris Long] came up with the 3D printed tools to make this common shop task a little easier, and they look promising. The extensions have cone-shaped tips that align perfectly with the inside edge of the caliper jaws, which lines the jaws up with the center of each hole. You read the center-to-center distance directly off the caliper display, easy peasy.

Of course, there’s also the old machinist’s trick (last item) about zeroing out the calipers after reading the diameter of one of the holes and then measuring the outside-to-outside distance between the two holes. That works great when you’ve got plenty of clearance, but the shorter inside jaws might make measuring something like a populated PCB with this method tricky. For the price of a little filament and some print time, these might be just the tool to get you out of a bind.

What do cats get up to in the 30 minutes or so a day that they’re awake? Being jerks, at least in our experience. But like many hackers, [Brent] wanted to quantify the activity of his cat, and this instrumented cat exercise wheel was the result.

To pull this off, [Brent] used what he had on hand, which was an M5Stack ESP32 module, a magnetic reed switch, and of course, the cat exercise wheel [Luna] seemed to be in the habit of using at about 4:00 AM daily. The wheel was adorned with a couple of neodymium magnets to trip the reed switch twice per revolution, with the pulse stream measured on one of the GPIOs. The code does a little debouncing of the switch and calculates the cat’s time and distance stats, uploading the data to OpenSearch for analysis and visualization. [Brent] kindly includes the code and the OpenSearch setup in case you want to duplicate this project.

As for results, they’re pretty consistent with what we’ve seen with similar cat-tracking efforts. A histogram of [Luna]’s activity shows that she does indeed hop on the wheel at oh-dark-thirty every day, no doubt in an effort to assassinate [Brent] via sleep deprivation. There’s also another burst of “zoomies” around 6:00 PM. But the rest of the day? Pretty much sleeping.

Getting every detail perfectly right is often the goal in automotive restorations, and some people will go to amazing lengths to make sure the car looks and acts just like it did when it rolled off the dealer’s lot all those decades ago. That ethos can be pushed a little too far, though, especially with practical matters like knowing how much gas is left in the tank. Get that wrong and you’ll be walking.

Unwilling to risk that cruel fate with his restoration of 1978 Volkswagen Bus, [Pegork] came up with a replacement fuel gauge that looks identical to the original meter, but actually works. The gas gauges on ’60s and ’70s VWs were notoriously finicky, and when they bothered to work at all they were often wildly inaccurate. The problem was usually not with the sender unit in the tank, but the gauge in the dash, which used a bimetallic strip heated by a small coil of wire to deflect a needle. [Pegor]’s “SmoothBus” modification replaces the mechanical movement with a micro servo to move the needle. The variable voltage coming back from the fuel sender is scaled through a voltage divider and read by an analog input on an ATtiny85, which does a little algorithmic smoothing to make sure the needle doesn’t jump around too much. A really nice addition is an LED low fuel indicator, a feature that would have saved us many walks to the gas station back in our VW days. Except for the extra light, the restored gauge looks completely stock, and it works far better than the original.

Hats off to [Pregor] for this fantastic restomod. As we’ve noted before, classic VWs are perhaps the most hackable of cars, and we applaud any effort to keep these quirky cars going.

We’ve got mixed feelings about a new video from [AndysMachines] that details how he makes custom ball screws. On the one hand, there’s almost zero chance that we’ll ever have an opportunity to put this information to practical use. But on the other hand, the video gives a fantastic look at the inner workings and design considerations for ball screws, which is worth the price of admission alone

The story behind these ball screws is that [Andy] is apparently in cahoots with SkyNet and is building a T-800 Terminator of his own. Whatever, we don’t judge, but the build requires a short-throw linear drive mechanism that can be back-driven, specs that argue for a ball screw. [Andy] goes through the challenges of building such a thing, which mainly involve creating threads with a deep profile and wide pitch. The screw itself wasn’t too hard to cut, although there were some interesting practical details in the thread profile that we’d never heard of before.

The mating nut was another. Rather than try to cut deep internal threads, [Andy] took a sort of “open-face sandwich” approach, creating half-nuts in a single piece of brass using a CNC machine and a ball-nose mill. The threads were completed by cutting the two halves apart and bolting them together — very clever! [Andy] also showed how the balls recirculate in the nut through channels cut into one of the half-nuts.

Whether the results were worth the effort is up to [Andy], but we were just glad to be along for the ride. And if you want a little more detail on lead screws and ball screws, we’ve got just the article for that.

The crystal radio is a time-honored build that sadly doesn’t get much traction anymore. Once a rite of passage for electronics hobbyists, the classic coil-on-an-oatmeal-carton and cat’s whisker design just isn’t that easy to pull off anymore, mainly because the BOM isn’t really something that you can just whistle up from DigiKey or Mouser.

Or is it? To push the crystal radio into the future a bit, [tsbrownie] tried to design a receiver around standard surface-mount inductors, and spoiler alert — it didn’t go so well. His starting point was a design using a hand-wound air-core coil, a germanium diode for a detector, and a variable capacitor that was probably scrapped from an old radio. The coil had three sections, so [tsbrownie] first estimated the inductance of each section and sourced some surface-mount inductors that were as close as possible to their values. This required putting standard value inductors in series and soldering taps into the correct places, but at best the SMD coil was only an approximation of the original air-core coil. Plugging the replacement coil into the crystal radio circuit was unsatisfying, to say the least. Only one AM station was heard, and then only barely. A few tweaks to the SMD coil improved the sensitivity of the receiver a bit, but still only brought in one very local station.

[tsbrownie] chalked up the failure to the lower efficiency of SMD inductors, but we’re not so sure about that. If memory serves, the windings in an SMD inductor are usually wrapped around a core that sits perpendicular to the PCB. If that’s true, then perhaps stacking the inductors rather than connecting them end-to-end would have worked better. We’d try that now if only we had one of those nice old variable caps. Still, hats off to [tsbrownie] for at least giving it a go.

Note: Right after we wrote this, a follow-up video popped up in our feed where [tsbrownie] tried exactly the modification we suggested, and it certainly improves performance, but in a weird way. The video is included below if you want to see the details.

Unless you’ve got a shop with a well-stocked hardware bin, it’s a trip to the hardware store when you need a special screw. But [Sanford Prime] has a different approach: he prints his hardware, at least for non-critical applications. Just how much abuse these plastic screws can withstand was an open question, though, until he did a little torque testing to find out.

To run the experiments, [Sanford]’s first stop was Harbor Freight, where he procured their cheapest digital torque adapter. The test fixture was similarly expedient — just a piece of wood with a hole drilled in it and a wrench holding a nut. The screws were FDM printed in PLA, ten in total, each identical in diameter, length, and thread pitch, but with differing wall thicknesses and gyroid infill percentages. Each was threaded into the captive nut and torqued with a 3/8″ ratchet wrench, with indicated torque at fastener failure recorded.

Perhaps unsurprisingly, overall strength was pretty low, amounting to only 11 inch-pounds (1.24 Nm) at the low end. The thicker the walls and the greater the infill percentage, the stronger the screws tended to be. The failures were almost universally in the threaded part of the fastener, with the exception being at the junction between the head and the shank of one screw. Since the screws were all printed vertically with their heads down on the print bed, all the failures were along the plane of printing. This prompted a separate test with a screw printed horizontally, which survived to a relatively whopping 145 in-lb, which is twice what the best of the other test group could manage.

[Sanford Prime] is careful to note that this is a rough experiment, and the results need to be taken with a large pinch of salt. There are plenty of sources of variability, not least of which is the fact that most of the measured torques were below the specified lower calibrated range for the torque tester used. Still, it’s a useful demonstration of the capabilities of 3D-printed threaded fasteners, and their limitations.

Solderless breadboards are a fantastic tool for stirring the creative juices. In a few seconds, you can go from idea to prototype without ever touching the soldering iron. Unfortunately, the downside to this is that projects tend to expand to occupy all the available space on the breadboard, and the bench surrounding the project universally ends up cluttered with power supplies, meters, jumpers, and parts you’ve swapped in and out of the circuit.

In an attempt to tame this runaway mess, [Raph] came up with this neat modular breadboard system. It hearkens back to the all-in-one prototyping systems we greatly coveted when the whole concept of solderless breadboards was new and correspondingly unaffordable. Even today, combination breadboard and power supply systems command a pretty penny, so rolling your own might make good financial sense. [Raph] made his system modular, with 3D-printed frames that lock together using clever dovetail slots. The prototyping area snaps to an instrumentation panel, which includes two different power supplies and a digital volt-amp meter. This helps keep the bench clean since you don’t need to string leads all over the place. The separate bin for organizing jumpers and tidbits that snaps into the frame is a nice touch, too.

Want to roll your own? Not a problem, as [Raph] has thoughtfully made all the build files available. What’s more, they’re parametric so you can customize them to the breadboards you already have. The only suggestion we have would be that making this compatible with [Zack Freedman]’s Gridfinity system might be kind of cool, too.

If you’re used to thinking about 3D printing in Cartesian terms, prepare your brain for a bit of a twist with [Joshua Bird]’s 4-axis 3D printer that’s not quite like anything we’ve ever seen before.

The printer uses a rotary platform as a build plate, and has a linear rail and lead screw just outside the rim of the platform that serves as the Z axis. Where things get really interesting is the assembly that rides on the Z-axis, which [Joshua] calls a “Core R-Theta” mechanism. It’s an apt description, since as in a CoreXY motion system, it uses a pair of stepper motors and a continuous timing belt to achieve two axes of movement. However, rather than two linear axes, the motors can team up to move the whole print arm in and out along the radius of the build platform while also rotating the print head through almost 90 degrees.

The kinematic possibilities with this setup are really interesting. With the print head rotated perpendicular to the bed, it acts like a simple polar printer. But tilting the head allows you to print steep overhangs with no supports. [Joshua] printed a simple propeller as a demo, with the hub printed more or less traditionally while the blades are added with the head at steeper and steeper angles. As you can imagine, slicing is a bit of a mind-bender, and there are some practical problems such as print cooling, which [Joshua] addresses by piping in compressed air. You’ll want to see this in action, so check out the video below.

This is a fantastic bit of work, and hats off to [Joshua] for working through all the complexities to bring us the first really new thing we’ve seen in 3D printing is a long time.

Thanks to [Keith Olson], [grythumn],  [Hari Wiguna], and [MrSVCD] for the near-simultaneous tips on this one.

Spoiler alert: almond butter isn’t phosphorescent. But powdered milk is, at least to the limit of detection of this homebrew phosphorescence detector.

Why spend a bunch of time and money on such a thing? The obvious answer is “Why not?”, but more specifically, when [lcamtuf]’s son took a shine (lol) to making phosphorescent compounds, it just seemed natural for dad to tag along in his own way. The basic concept of the detector is to build a light-tight test chamber that can be periodically and briefly flooded with UV light, charging up the putatively phosphorescent compounds within. A high-speed photodiode is then used to detect the afterglow, which can be quantified and displayed.

The analog end of the circuit was the far fussier end of the design, with a high-speed transimpedance amplifier to provide the needed current gain. Another scaling amp and a low-pass filter boosts and cleans up the signal for a 14-bit ADC. [lcamtuf] went to great lengths to make the front end as low-noise as possible, including ferrite beads and short leads to prevent picking up RF interference. The digital side has an AVR microcontroller that talks to the ADC and runs an LCD panel, plus switches the 340 nm LEDs on and off rapidly via a low gate capacitance MOSFET.

Unfortunately, not many things found randomly around the average home are all that phosphorescent. We’re not sure what [lcamtuf] tried other than the aforementioned foodstuffs, but we’d have thought something like table salt would do the trick, at least the iodized stuff. But no matter, the lessons learned along the way were worth the trip.

If you’ve been tearing electronic devices apart for long enough, you’ll know that the old gear had just as many mysteries within as the newer stuff. The parts back then were bigger, of course, but often just as inscrutable as the SMD parts that populate boards today. And the one part that always baffled us back in the days of transistor radios and personal cassette players was those little silver boxes with a hole in the top and the colorful plug with an inviting screwdriver slot.

We’re talking about subminiature intermediate-frequency transformers, of course, and while we knew their purpose in general terms back then and never to fiddle with them, we never really bothered to look inside one. This teardown of various IF transformers by [Unrelated Activities] makes up somewhat for that shameful lack of curiosity. The video lacks narration, relying on captions to get the point across that these once-ubiquitous components were a pretty diverse lot despite their outward similarities. Most had a metal shell protecting a form around which one or more coils of fine magnet wire were wrapped. Some had tiny capacitors wired in parallel with one of the coils, too.

Perhaps the most obvious feature of these IF transformers was their tunability, thanks to a ferrite cup or slug around the central core and coils. The threaded slug allowed the inductance of the system to be changed with the turn of a screwdriver, preferably a plastic one. [Unrelated] demonstrates this with a NanoVNA using a nominal 10.7-MHz IFT, probably from an FM receiver. The transformer was tunable over a 4-MHz range.

Sure, IFTs like these are still made, and they’re not that hard to find if you know where to look. But they are certainly less common than they used to be, and seeing what’s under the hood scratches an itch we didn’t even realize we had.

If you think your job sucks, be grateful you’re not this homebrew sewer inspection robot.

Before anyone gets upset, yes we know what [Stargate System] built here isn’t a robot at all; it’s more of a remotely operated vehicle. That doesn’t take away from the fact that this is a very cool build, especially since it has to work in one of the least hospitable and most unpleasant environments possible. The backstory of this project is that the sewer on a 50-year-old house kept backing up, and efforts to clear it only temporarily solved the problem. The cast iron lateral line was reconfigured at some point in its history to include a 120-degree bend, which left a blind spot for the camera used by a sewer inspection service. What’s worse, the bend was close to a joint where a line that once allowed gutters and foundation drains access to the sewer.

To better visualize the problem, [Stargate] turned to his experience building bots to whip up something for the job. The bot had to be able to fit into the pipe and short enough to make the turn, plus it needed to be — erm, waterproof. It also needed to carry a camera and a light, and to be powered and controlled from the other end of the line. Most of the body of the bot, including the hull and the driving gear, was 3D printed from ABS, which allowed the seams to be sealed with acetone later. The drive tracks were only added after the original wheels didn’t perform well in testing. Controlling the gear motors and camera was up to a Raspberry Pi Zero, chosen mostly due to space constraints. An Ethernet shield provided connectivity to the surface over a Cat5 cable, and a homebrew PoE system provided power.

As interesting as the construction details were, the real treat is the down-hole footage. It’s not too graphic, but the blockage is pretty gnarly. We also greatly appreciated the field-expedient chain flail [Stargate] whipped up to bust up the big chunks of yuck and get the pipe back in shape. He did a little bit of robo-spelunking, too, as you do.

And no, this isn’t the only sewer bot we’ve ever featured.

We received belated word this week of the passage of Ward Christensen, who died unexpectedly back in October at the age of 78. If the name doesn’t ring a bell, that’s understandable, because the man behind the first computer BBS wasn’t much for the spotlight. Along with Randy Suess and in response to the Blizzard of ’78, which kept their Chicago computer club from meeting in person, Christensen created an electronic version of a community corkboard. Suess worked on the hardware while Christensen provided the software, leveraging his XMODEM file-sharing protocol. They dubbed their creation a “bulletin board system” and when the idea caught on, they happily shared their work so that other enthusiasts could build their own systems.

BBSs were the only show in town for a long time, and the happy little modem negotiation tones were like a doorbell you rang to get into a club where people understood your obsession. Perhaps it’s just the BBS nostalgia talking, but despite the functional similarities to today’s social media, the BBS experience seemed a lot more civilized. It’s not that people were much better behaved back then; any BBS regular can tell you there were plenty of jerks online then, too. But the general tone of BBS life was a little more sedate, probably due in part to the glacial pace of dial-up connections. Even at a screaming 2,400 baud, characters scrolled across your screen slower than you could read them, and that seemed to have a sedating effect on your passions. By the time someone’s opinion on the burning issues of the day had finally been painted on your monitor, you’d had a bit of time to digest it and perhaps cool down a bit before composing a reply. We still had our flame wars, of course, but it was like watching slow-motion warfare and the dynamic was completely different from today’s Matrix.

Speaking of yearning for a probably mythical Golden Age, Casio has announced a smart ring that looks like a miniature version of their classic sports chronograph wristwatch. The ring celebrates Casio’s 50th anniversary of making watches, and features a stainless steel case made by metal injection molding. The six-digit LCD is pretty limited in what it can display, and the ring doesn’t do much other than tell the time and date and sound alarms. So we’re not sure where the smarts are here, except for the looks, of course.

We got a tip recently on a series of really interesting videos that you might want to check out, especially if you’re into EMC simulations. Panire’s channel is chock full of videos showing how to use openEMS, the open-source electromagnetic field solver, with KiCad EDA software to simulate the RF properties of high-speed circuits. He’s got some in-depth videos on getting things set up plus some great tutorials on creating simulations that let you see how your PCB designs are radiating, allowing you to make changes and see the results right away. Very useful stuff, and pretty fun to look at, too.

Here at Hackaday, we get a surprising and disappointingly regular stream of projects that claim to finally have beaten the laws of thermodynamics. So the words “Perpetual Motion” are especially triggering to us, but we instantly put that aside when we saw the title card on this video about the Atmos Clock. No, it’s not perpetual motion, but since as the name suggests, being powered by atmospheric pressure and temperature changes, it’s about as close as you can get. We remember one of these beautiful timepieces on the mantle in our grandparents’ house, gifted to “Grampy” for years of faithful service by his employer. It was a delicate machine and fascinating to watch work, which it only briefly did once we grandkids got near it. Still, watching how the mechanism worked is pretty interesting stuff.

And finally, if you haven’t checked out The Analog, you really should. It’s a weekly newsletter written by our friend Mihir Shah and is full of interesting tidbits from the world of electronics and technology. This time around he gifted us with a video that looks inside optical sorting in food processing. You’ve probably seen these in action before, where cascades of objects — grapes in this case, obviously in a winery — are spread out on a high-speed conveyor belt under the watchful gaze of a computer vision system, which spots the bad grapes and yeets them into oblivion with a precisely controlled jet of compressed air. The mind boggles on the control loops needed to get the jet and the bad grape to meet up at just the right time so that good grapes stay in the game.

These days, oscilloscope hacking is all about enabling features that the manufacturer baked into the hardware but locked out in the firmware. Those hacks are cool, of course, but back in the days of analog scopes, unlocking new features required a decidedly more hardware-based approach.

For an example of this, take a look at this oscilloscope beam splitter by [Lockdown Electronics]. It’s a simple way to turn a single-channel scope into a dual-channel scope using what amounts to time-division multiplexing. A 555 timer is set up as an astable oscillator generating a 2.5-kHz square wave. That’s fed into the bases of a pair of transistors, one NPN and the other PNP. The collectors of each transistor are connected to the two input signals, each biased to either the positive or negative rail of the power supply. As the 555 swings back and forth it alternately applies each input signal to the output of the beam splitter, which goes to the scope. The result is two independent traces on the analog scope, like magic.

More after the break…

If you’re wondering how this would work on a modern digital scope, so was [Lockdown Electronics]. He gave it a go with his little handheld scope meter and the results were surprisingly good and illustrative of how the thing works. You can clearly see the 555’s square wave on the digital scope sandwiched between the two different input sine waves. Analog scopes always have trouble showing these rising and falling edges, which explains why the beam splitter looks so good on the CRT versus the LCD.

Does this circuit serve any practical purpose these days? Probably not, although you could probably use the same principle to double the number of channels on your digital scope. Eight channels on a four-channel scope for the price of a 555? Sounds like a bargain to us.

[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.

Thanks for the tip, [Gustavo].

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.

When electronics release the Magic Smoke, more often than not it’s a fairly sedate event. Something overheats, the packaging gets hot enough to emit that characteristic and unmistakable odor, and wisps of smoke begin to waft up from the defunct component. Then again, sometimes the Magic Smoke is more like the Magic Plasma, as was the case in this absolutely smoked Omron programmable logic controller.

Normally, one tasked with repairing such a thing would just write the unit off and order a replacement. But [Defpom] needed to get the pump controlled by this PLC back online immediately, leading to the somewhat unorthodox repair in the video below. Whatever happened to this poor device happened rapidly and energetically, taking out two of the four relay-controlled outputs. [Defpom]’s initial inspection revealed that the screw terminals for one of the relays no longer existed, one relay enclosure was melted open, its neighbor was partially melted, and a large chunk of the PCB was missing. Cleaning up the damaged relays revealed what the “FR” in “FR4” stands for, as the fiberglass weave of the board was visible after the epoxy partly burned away before self-extinguishing.

With the damaged components removed and the dangerously conductive carbonized sections cut away, [Defpom] looked for ways to make a temporary repair. The PLC’s program was locked, making it impossible to reprogram it to use the unaffected outputs. Instead, he redirected the driver transistor for the missing relay two to the previously unused and still intact relay one, while adding an outboard DIN-mount relay to replace relay three. In theory, that should allow the system to work with its existing program and get the system back online.

Did it work? Sadly, we don’t know, as the video stops before we see the results. But we can’t see a reason for it not to work, at least temporarily while a new PLC is ordered. Of course, the other solution here could have been to replace the PLC with an Arduino, but this seems like the path of least resistance. Which, come to think of it, is probably what caused the damage in the first place.