Author: Dan Maloney

3373 Articles

Quick And Very Dirty Repair Gets Smoked PLC Back In The Game

November 21, 2024 by 11 Comments

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.

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Simple Stack Of Ferrites Shows How Fluxgate Magnetometers Work

November 20, 2024 by 8 Comments

Have you ever wondered how a magnetometer works? We sure have, which was why we were happy to stumble upon this article on simple homebrew fluxgate magnetometers.

As [Maurycy] explains, clues to how a fluxgate magnetometer works can be found right in the name. We all know what happens when a current is applied to a coil of wire wrapped around an iron or ferrite core — it makes an electromagnet. Wrap another coil around the same core, and you’ve got a simple transformer.

Now, power the first coil, called the drive coil, with alternating current and measure the induced current on the second, or sense coil. Unexpected differences between the current in the drive coil and the sense coil are due to any external magnetic field. The difference indicates the strength of the field. Genius!

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Junk Box Build Helps Hams With SDR

November 20, 2024 by 5 Comments

SDRs have been a game changer for radio hobbyists, but for ham radio applications, they often need a little help. That’s especially true of SDR dongles, which don’t have a lot of selectivity in the HF bands. But they’re so darn cheap and fun to play with, what’s a ham to do?

[VK3YE] has an answer, in the form of this homebrew software-defined radio (SDR) helper. It’s got a few features that make using a dongle like the RTL-SDR on the HF bands a little easier and a bit more pleasant. Construction is dead simple and based on what was in the junk bin and includes a potentiometer for attenuating stronger signals, a high-pass filter to tamp down stronger medium-wave broadcast stations, and a series-tuned LC circuit for each of the HF bands to provide some needed selectivity. Everything is wired together ugly-style in a metal enclosure, with a little jiggering needed to isolate the variable capacitor from ground.

The last two-thirds of the video below shows the helper in use on everything from the 11-meter (CB) band down to the AM bands. This would be a great addition to any ham’s SDR toolkit.

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Hackaday Links: November 17, 2024

November 17, 2024 by 18 Comments

A couple of weeks back, we covered an interesting method for prototyping PCBs using a modified CNC mill to 3D print solder onto a blank FR4 substrate. The video showing this process generated a lot of interest and no fewer than 20 tips to the Hackaday tips line, which continued to come in dribs and drabs this week. In a world where low-cost, fast-turn PCB fabs exist, the amount of effort that went into this method makes little sense, and readers certainly made that known in the comments section. Given that the blokes who pulled this off are gearheads with no hobby electronics background, it kind of made their approach a little more understandable, but it still left a ton of practical questions about how they pulled it off. And now a new video from the aptly named Bad Obsession Motorsports attempts to explain what went on behind the scenes.

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Schooling ChatGPT On Antenna Theory Misconceptions

November 17, 2024 by 39 Comments

We’re not very far into the AI revolution at this point, but we’re far enough to know not to trust AI implicitly. If you accept what ChatGPT or any of the other AI chatbots have to say at face value, you might just embarrass yourself. Or worse, you might make a mistake designing your next antenna.

We’ll explain. [Gregg Messenger (VE6WO)] asked a seemingly simple question about antenna theory: Does an impedance mismatch between the antenna and a coaxial feedline result in common-mode current on the coax shield? It’s an important practical matter, as any ham who has had the painful experience of “RF in the shack” can tell you. They also will likely tell you that common-mode current on the shield is caused by an unbalanced antenna system, not an impedance mismatch. But when [Gregg] asked Google Gemini and ChatGPT that question, the answer came back that impedance mismatch can cause current flow on the shield. So who’s right?

In the first video below, [Gregg] built a simulated ham shack using a 100-MHz signal generator and a length of coaxial feedline. Using a toroidal ferrite core with a couple of turns of magnet wire and a capacitor as a current probe for his oscilloscope, he was unable to find a trace of the signal on the shield even if the feedline was unterminated, which produces the impedance mismatch that the chatbots thought would spell doom. To bring the point home, [Gregg] created another test setup in the second video, this time using a pair of telescoping whip antennas to stand in for a dipole antenna. With the coax connected directly to the dipole, which creates an unbalanced system, he measured a current on the feedline, which got worse when he further unbalanced the system by removing one of the legs. Adding a balun between the feedline and the antenna, which shifts the phase on each leg of the antenna 180° apart, cured the problem.

We found these demonstrations quite useful. It’s always good to see someone taking a chatbot to task over myths and common misperceptions. We look into baluns now and again. Or even ununs.

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Classic LED Bubble Displays Ride Again

November 17, 2024 by 17 Comments

Hewlett-Packard used to make some pretty cool LED displays, many of which appeared in their iconic pocket calculators back in the 1970s and 1980s. [Upir] tracked down some of these classic bubble displays and used them with a microcontroller. We love the results!

The displays featured here, the HPDL-1414, aren’t quite what would have been found in an HP-35, of course. These displays have 16 segments for reasonably legible approximations of most of the ASCII character set. Also, these aren’t just the displays; rather, a pair of the bubble-topped displays, each with four characters, is mounted to a module that provides a serial interface. [Upir] found these modules online, but despite the HP logo on the PCB silkscreen, it’s not really clear who made them. The documentation was a bit thin, to say the least, but with a little translation help from Google, he figured out the serial parameters and the character encoding. The video below shows him putting these modules through their paces.

Unusually for [upir], who has made a name for himself hacking displays to do things they weren’t designed to do, he stuck with the stock character set baked into this module. We think it would be fun to get one of these modules and hack the firmware to provide alternative character sets or even get a few of the naked displays and build a custom interface. Sounds like a fun rainy-day project.

This reminded us of another HP display project we saw a while back. Or, roll your own displays.

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Homebrew PH Meter Uses Antimony Electrode

November 15, 2024 by 11 Comments

Understanding the nature of pH has bedeviled beginning (and not-so-beginning) chemistry students for nearly as long as chemistry has had students. It all seems so arbitrary, being the base-10 log of the inverse of hydrogen ion concentration and with a measurement range of 0 to 14. Add to that the electrochemical reactions needed to measure pH electronically, and it’s enough to make your head spin.

Difficulties aside, [Markus Bindhammer] decided to tackle the topic and came up with this interesting digital pH meter as a result. Measuring pH electronically is all about the electrode, or rather a pair of electrodes, one of which is a reference electrode. The potential difference between the electrodes when dipped into the solution under test correlates to the pH of the solution. [Markus] created his electrode by drawing molten antimony into a length of borosilicate glass tubing containing a solid copper wire as a terminal. The reference electrode was made from another piece of glass tubing, also with a copper terminal but filled with a saturated solution of copper(II) sulfate and plugged with a wooden skewer soaked in potassium nitrate.

In theory, this electrode system should result in a linear correlation between the pH of the test solution and the potential difference between the electrodes, easily measured with a multimeter. [Marb]’s results were a little different, though, leading him to use a microcontroller to scale the electrode output and display the pH on an OLED.

The relaxing video below shows the build process and more detail on the electrochemistry involved. It might be worth getting your head around this, since liquid metal batteries based on antimony are becoming a thing.

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