Hackaday Podcast Episode 295: Circuit Graver, Zinc Creep, And Video Tubes

November 8, 2024 by Dan Maloney 1 Comment

With Superconference 2024 in the books, Dan joined Elliot, fresh off his flight back from Pasadena, to look through the week (or two) in hacks. It was a pretty good crop, too, despite all the distractions and diversions. We checked out the cutest little quadruped, a wireless antenna for wireless communications, a price-tag stand-in for paper calendars, and a neat way to test hardware and software together.

We take the closest look yet at why Arecibo collapsed, talk about Voyager’s recent channel-switching glitch, and find out how to put old Android phones back in action. There’s smear-free solder paste application, a Mims-worthy lap counter, and a PCB engraver that you’ve just got to see. We wrap things up with a look at Gentoo and pay homage to the TV tubes of years gone by — the ones in the camera, for the TV sets.

Download the zero-calorie MP3.

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Mechanisms: Tension Control Bolts

November 7, 2024 by Dan Maloney 54 Comments

If there’s an enduring image of how large steel structures used to be made, it’s probably the hot riveting process. You’ve probably seen grainy old black-and-white films of a riveting gang — universally men in bib overalls with no more safety equipment than a cigarette, heating rivets to red heat in a forge and tossing them up to the riveters with a pair of tongs. There, the rivet is caught with a metal funnel or even a gloved hand, slipped into a waiting hole in a flange connecting a beam to a column, and beaten into submission by a pair of men with pneumatic hammers.

Dirty, hot, and dangerous though the work was, hot riveted joints were a practical and proven way to join members together in steel structures, and chances are good that any commercial building that dates from before the 1960s or so has at least some riveted joints. But times change and technology marches on, and riveted joints largely fell out of fashion in the construction trades in favor of bolted connections. Riveting crews of three or more men were replaced by a single ironworker making hundreds of predictable and precisely tensioned connections, resulting in better joints at lower costs.

Bolted joints being torqued to specs with an electric wrench might not have the flair of red-hot rivets flying around the job site, but they certainly have a lot of engineering behind them. And as it turns out, the secret to turning bolting into a one-person job is mostly in the bolt itself.

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Clever Circuit Makes Exercise Slightly Less Boring

November 6, 2024 by Dan Maloney 11 Comments

We say this with the greatest respect, but [Joel] — your exercise routine is horrible! Kudos for getting up and doing something, but 108 trips up and down the stairs? That sounds like torture, not exercise. Even [Joel] admits that it’s so boring that he loses count, and while we’d bet that he isn’t likely to restart the routine when that happens, it’s still annoying enough that he built this clever little lap counter to automate the task.

We kid, of course; any exercise is better than no exercise, and the stairs offer few excuses for skipping the daily workout. To bust the boredom problem, [Joel] toyed with a couple of ideas for toting up his laps before landing on a beam-break optical system with sensors at the top and the bottom of the stairs. Worried about the potential for false triggering by swinging arms and legs, he searched for ideas for bounceless switch circuits in the old “Engineer’s Notebook” by [Forrest Mims] and found a circuit close enough to modify for his needs. Each sensor setup has a high-output red LED and a phototransistor on one side of the stairwell, and a retroreflector on the opposite wall. Breaking the beam switches off the LED on that sensor and switches the other one on, to save on battery power.

The sensor’s flips and flops are counted and displayed on a three-digit seven-segment LED; [Joel] offers no detail on the counter itself, but with [Mims] as his muse, we suspect it’s something like the three-digit BCD counter circuit a few pages on from the bounceless switch circuit. The lap counter is shown in action in the brief video below.

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Zinc Creep And Electroplasticity: Why Arecibo Collapsed

November 5, 2024 by Dan Maloney 33 Comments

It’s been nearly four years since the Arecibo Telescope collapsed, an event the world got to witness in unprecedented detail thanks to strategically positioned drones. They captured breathtaking video of one of the support cables pulling from its socket as well as the spectacularly destructive results of 900 tons of scientific instruments crashing into the 300-meter primary reflector. But exactly why did those cable sockets fail?

A new report aims to answer that question, and in the process raises some interesting questions of its own. The proximate causes of the collapse have been known for a while, including the most obvious and visible one, the failure of the zinc “spelter sockets” that were cast around the splayed ends of the wire ropes to hold them in place. The new report agrees with this conclusion, at least in part, implicating “zinc creep,” or the tendency for zinc to deform over time under load. Where it appears to differ, though, is with the quality of workmanship on the sockets, finding no issues with the way the individual wires in the failed support cable were manually splayed within the socket before the molten zinc was poured. The report also points out that the collapse probably started when Hurricane Maria swept over Puerto Rico 39 months before the collapse, after which zinc creep in the sockets seemed to accelerate.

But why did the sockets fail? As the report points out, spelter sockets are commonly used to anchor cables that support heavy loads under conditions similar to the tropical climate at Arecibo. After ruling out every other cause, the committee was left with the conclusion that Arecibo itself may have been to blame for the accelerated zinc creep, thanks to electrical currents induced in the cables and sockets when the telescope’s powerful transmitters were used. They call this “long-term, low-current electroplasticity.” Electroplastic effects have been observed since the 1950s, and while far from certain that’s what happened here, the thought is that skin-effect currents induced in the support cables flowed to ground through the zinc sockets, increasing the plasticity of the metal and accelerating the zinc creep that ultimately led to collapse.

Case closed? Hardly. The electroplasticity mechanism for the Arecibo collapse offered by this report is almost a “diagnosis of exclusion” situation. It makes sense, though; since no other spelter sockets have ever failed this way in a century of use, there’s a good chance that the root cause was specific to Arecibo, and since it was once the world’s most powerful radio transmitter, it seems like a red flag that bears further investigation.

A Lesson In RF Design Thanks To This Homebrew LNA

November 4, 2024 by Dan Maloney 7 Comments

If you’re planning on working satellites or doing any sort of RF work where the signal lives down in the dirt, you’re going to need a low-noise amplifier. That’s typically not a problem, as the market is littered with dozens of cheap options that can be delivered in a day or two — you just pay your money and get to work. But is there a case to be made for rolling your own LNA?

[Salil, aka Nuclearrambo] thinks so, and he did a nice job showing us how it’s done. The first step, as always, is to define your specs, which for [Salil] were pretty modest: a low noise figure, moderate gain, and good linearity. He also wanted a bandpass filter for the 2-meter amateur radio band and for weather satellite downlinks, and a bias-tee to power the LNA over the coax feedline. The blog post has a detailed discussion of the electrical design, plus some good tips on PCB design for RF applications. We also found the discussion on bias-tee design helpful, especially for anyone who has ever struggled with the idea that RF and DC can get along together on a single piece of coax. Part 2 concentrates on testing the LNA, mostly using hobbyist-grade test gear like the NanoVNA and tiny SA spectrum analyzer. [Salil]’s tests showed the LNA lived up to the design specs and more, making it more than ready to put to work with an RTL-SDR.

Was this more work than buying an LNA? Absolutely, and probably with the same results. But then again, what’s to learn by just getting a pre-built module in the mail?

Hackaday Links: November 3, 2024

November 3, 2024 by Dan Maloney 22 Comments

“It was the best of times, it was the blurst of times?” Perhaps not anymore, if this Ig Nobel-worthy analysis of the infinite monkey theorem is to be believed. For the uninitiated, the idea is that if you had an infinite number of monkeys randomly typing on an infinite number of keyboards, eventually the complete works of Shakespeare or some other famous writer would appear. It’s always been meant to be taken figuratively as a demonstration of the power of time and randomness, but some people just can’t leave well enough alone. The research, which we hope was undertaken with tongue firmly planted in cheek, reveals that it would take longer than the amount of time left before the heat death of the universe for either a single monkey or even all 200,000 chimpanzees in the world today to type the 884,647 words of Shakespeare’s complete works in the proper order.

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Measuring Temperature Without A Thermometer

November 2, 2024 by Dan Maloney 21 Comments

If you need to measure the temperature of something, chances are good that you could think up half a dozen ways to do it, pretty much all of which would involve some kind of thermometer, thermistor, thermocouple, or other thermo-adjacent device. But what if you need to measure something really hot, hot enough to destroy your instrument? How would you get the job done then?

Should you find yourself in this improbable situation, relax — [Anthony Francis-Jones] has you covered with this calorimetric method for measuring high temperatures. The principle is simple; rather than directly measuring the temperature of the flame, use it to heat up something of known mass and composition and then dunk that object in some water. If you know the amount of water and its temperature before and after, you can figure out how much energy was in the object. From that, you can work backward and calculate the temperature the object must have been at to have that amount of energy.

For the demonstration in the video below, [F-J] dangled a steel ball from a chain into a Bunsen burner flame and dunked it into 150 ml of room-temperature water. After a nice long toasting, the ball went into the drink, raising the temperature by 27 degrees. Knowing the specific heat capacity of water and steel and the mass of each, he worked the numbers and came up with an estimate of about 600°C for the flame. That’s off by a wide margin; typical estimates for a natural gas-powered burner are in the 1,500°C range.

We suspect the main source of error here is not letting the ball and flame come into equilibrium, but no matter — this is mainly intended as a demonstration of calorimetry. It might remind you of bomb calorimetry experiments in high school physics lab, which can also be used to explore human digestive efficiency, if you’re into that sort of thing.

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