Author: Dan Maloney

3283 Articles

Homebrew Phosphorescence Detector Looks For The Glow In Everyday Objects

November 28, 2024 by 8 Comments

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.

A Look Under The Hood Of Intermediate Frequency Transformers

November 27, 2024 by 11 Comments

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.

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DIY Pipe Inspector Goes Where No Bot Has Gone Before

November 27, 2024 by 7 Comments

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.

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Retrotechtacular: The Deadly Shipmate

November 27, 2024 by 33 Comments

During World War II, shipboard life in the United States Navy was a gamble. No matter which theater of operations you found yourself in, the enemy was all around on land, sea, and air, ready to deliver a fatal blow and send your ship to the bottom. Fast forward a couple of decades and Navy life was just as hazardous but in a different way, as this Navy training film on the shipboard hazards of low-voltage electricity makes amply clear.

With the suitably scary title “115 Volts: A Deadly Shipmate,” the 1960 film details the many and various ways sailors could meet an untimely end, most of which seemed to circle back to attempts to make shipboard life a little more tolerable. The film centers not on the risks of a ship’s high-voltage installations, but rather the more familiar AC sockets used for appliances and lighting around most ships. The “familiarity breeds contempt” argument rings a touch hollow; given that most of these sailors appear to be in their 20s and 30s and rural electrification in the US was still only partially complete through the 1970s, chances are good that at least some of these sailors came from farms that still used kerosene lamps. But the point stands that plugging an unauthorized appliance into an outlet on a metal ship in a saltwater environment is a recipe for being the subject of a telegram back home.

The film shows just how dangerous mains voltage can be through a series of vignettes, many of which seem contrived but which were probably all too real to sailors in 1960. Many of the scenarios are service-specific, but a few bear keeping in mind around the house. Of particular note is drilling through a bulkhead and into a conduit; we’ve come perilously close to meeting the same end as the hapless Electrician’s Mate in the film doing much the same thing at home. As for up-cycling a discarded electric fan, all we can say is even brand new, that thing looks remarkably deadly.

The fact that they kept killing the same fellow over and over for each of these demonstrations doesn’t detract much from the central message: follow orders and you’ll probably stay alive. In an environment like that, it’s probably not bad advice.

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Hackaday Links: November 24, 2024

November 24, 2024 by 6 Comments

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.

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Double Your Analog Oscilloscope Fun With This Retro Beam Splitter

November 24, 2024 by 18 Comments

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…

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RFID From First Principles And Saving A Cat

November 23, 2024 by 5 Comments

[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.

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