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

November 21, 2024 by Dan Maloney 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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Making PCB Strip Filter Design Easy To Understand

October 28, 2024 by Dan Maloney 4 Comments

We’ve always been fascinated by things that perform complex electronic functions merely by virtue of their shapes. Waveguides come to mind, but so do active elements like filters made from nothing but PCB traces, which is the subject of this interesting video by [FesZ].

Of course, it’s not quite that simple. A PCB is more than just copper, of course, and the properties of the substrate have to be taken into account when designing these elements. To demonstrate this, [FesZ] used an online tool to design a bandpass filter for ADS-B signals. He designed two filters, one using standard FR4 substrate and the other using the more exotic PTFE.

He put both filters to the test, first on the spectrum analyzer. The center frequencies were a bit off, but he took care of that by shortening the traces slightly with a knife. The thing that really stood out to us was the difference in insertion loss between the two substrates, with the PTFE being much less lossy. The PTFE filter was also much more selective, with a tighter pass band than the FR4. PTFE was also much more thermostable than FR4, which had a larger shift in center frequency and increased loss after heating than the PTFE. [FesZ] also did a more real-world test and found that both filters did a good job damping down RF signals across the spectrum, even the tricky and pervasive FM broadcast signals that bedevil ADS-B experimenters.

Although we would have liked a better explanation of design details such as via stitching and trace finish selection, we always enjoy these lessons by [FesZ]. He has a knack for explaining abstract concepts through concrete examples; anyone who can make coax stubs and cavity filters understandable has our seal of approval.

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Homebrew TEM Cell Lets You EMC Test Your Own Devices

November 2, 2023 by Dan Maloney 14 Comments

Submitting a new device for electromagnetic compatibility (EMC) testing seems a little like showing up for the final exam after skipping all the lectures. You might get lucky and pass, but it really would have been smarter to take a few of the quizzes to see how things were going during the semester. Similarly, it would be nice to know you’re not making any boneheaded mistakes early in the design process, which is what this DIY TEM cell is all about.

We really like [Petteri Aimonen]’s explanation of what a TEM cell, or transverse electromagnetic cell, is: he describes it as “an expanded coaxial cable that is wide enough to put your device inside of.” It basically a cage made of conductive material that encloses a space for the device under test, along with a stripline going down its center. The outer cage is attached to the outer braid of a coaxial cable, while the stripline is connected to the center conductor. Any electric or magnetic field generated by the device inside the cage goes down the coax into your test instrument, typically a spectrum analyzer.

[Petteri]’s homebrew TEM is made from a common enough material: copper-clad FR4. You could use double-sided material, or even sheet copper if you’re rich, but PCB stock is easy to work with and gets the job done. His design is detailed in a second post, which goes through the process of designing the size and shapes of all the parts as well as CNC milling the sheets of material. [Petteri] tried to make the joints by milling part-way through the substrate and bending the sheet into shape, but sadly, the copper didn’t want to cooperate with his PCB origami. Luckily, copper foil tape and a little solder heal all wounds. He also incorporated a line impedance stabilization network (LISN) into the build to provide a consistent 50-ohm characteristic impedance.

How does it work? Pretty well, it seems; when connected to a TinySA spectrum analyzer, [Petteri] was able to find high-frequency conductive noise coming from the flyback section of a switch-mode power supply. All it took was a ferrite bead and cap to fix it early in the prototyping phase of the project. Sounds like a win to us.

Illustrated Kristina with an IBM Model M keyboard floating between her hands.

Keebin’ With Kristina: The One With The Music Typewriter

April 20, 2023 by Kristina Panos 4 Comments

This edition’s community build comes from the Yes They Could, But Should They Have? file. Well, I ultimately say yes, this is intriguing. Redditor [dj_edit] looked at the venerable Model M and thought, this buckling-spring masterpiece can yet be improved upon. Yeah! Well, to each their own. I must say that it does sound great, especially with the solenoid feedback enabled via rotary encoder. Just check out the typing test.

To be clear, this is essentially a new keyboard that fits inside a Model M case, but that alone is quite a feat, especially if you consider the curvature of the backplate. Because of this hurdle, [dj_edit] went with 1 mm FR4 for the switch PCB, which is a nice compromise of sturdiness and flexibility.

Underneath those stunning reproduction keycaps are Kailh box white switches, which are pretty chonky-sounding on their own. But turn on that sweet solenoid action and you really get noisy.

Those box whites are sitting in hot-swap sockets, a design decision that kind of made things difficult because of the curvature. [dj_edit] ended up using an acrylic plate that gets bent to match the curvature by the switches themselves.

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Shot of CubeTouch, a six sided cube built out of PCBs with each of the top PCB allowing for diffusion of the LEDs on the inside to shine through

Keyboard Shortcuts At The Touch Of A Planetary Cube

September 19, 2022 by Abe Connelly 3 Comments

[Noteolvides] creates the CubeTouch, a cube made of six PCBs soldered together that creates a functional and interactive piece of art through its inlaid LEDs and capacitive touch sensors.

The device itself is connected through a USB-C connector that powers the device and allows it to send custom keyboard shortcuts, depending on which face is touched.

The CubeTouch is illuminated on the inside with six WS2812 LEDs that take advantage of the diffusion properties of the underlying FR4 material to shine through the PCBs. The central microprocessor is a CH552 that has native USB support and is Arduino compatible. Each “planet” on the the five outward facing sides acts as a capacitive touch sensor that can be programmed to produce a custom key combination.

Assembling the device involves soldering the connections at two joints for each edge connecting the faces.

We’re no strangers to building enclosures from FR4, nor are we strangers to merging art and functionality. The CubeTouch offers a further exploration of these ideas in a sweet package.

The CubeTouch is Open Source Hardware Certified with all documentation, source code and other relevant digital artifacts available under a libre/free license.

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PCB Microsurgery Puts The Bodges Inside The Board

December 14, 2021 by Dan Maloney 23 Comments

We all make mistakes, and there’s no shame in having to bodge a printed circuit board to fix a mistake. Most of us are content with cutting a trace or two with an Xacto or adding a bit of jumper wire to make the circuit work. Very few of us, however, will decide to literally do our bodges inside the PCB itself.

The story is that [Andrew Zonenberg] was asked to pitch in debugging some incredibly small PCBs for a prototype dev board that plugs directly into a USB jack. The six-layer boards are very dense, with a forest of blind vias. The Twitter thread details the debugging process, which ended up finding a blind via on layer two shorted to a power rail, and another via shorted to ground. It also has some beautiful shots of [Andrew]’s “mechanical tomography” method of visualizing layers by slowly grinding down the surface of the board.

[Andrew] has only tackled one of the bodges at the time of writing, but it has to be seen to be believed. It started with milling away the PCB to get access to the blind via using a ridiculously small end mill. The cavity [Andrew] milled ended up being only about 480 μm by 600 μm and only went partially through a 0.8-mm thick board, but it was enough to resolve the internal short and add an internal bodge to fix a trace that was damaged during milling. The cavity was then filled up with epoxy resin to stabilize the repair.

This kind of debugging and repair skill just boggles the mind. It reminds us a bit of these internal chip-soldering repairs, but taken to another level entirely. We can’t wait to see what the second repair looks like, and whether the prototype for this dev board can be salvaged.

Thanks to [esclear] for the heads up on this one.

RGB Glasses Built From PCBs

January 16, 2021 by Lewin Day 8 Comments

Shutter shades were cool once upon a time, but if you really want to stand out, it’s hard to go past aggressively bright LEDs right in the middle of your face. A great way to achieve that is by building a pair of RGB glasses, as [Arnov Sharma] did.

The design intelligently makes use of PCBs to form the entire structure of the glasses. One PCB makes up the left arm of the glasses, carrying an ESP12F microcontroller and the requisite support circuitry. It’s fitted to the front PCB through a slot, and soldered in place. The V+, GND, and DATA connections for the WS2812B LEDs also serve as the mechanical connection. The right arm of the glasses is held on in the same way, being the same as the left arm PCB but simply left unpopulated. A little glue is also used to stiffen up the connection.

It’s a tidy build, and one that can be easily controlled from a smartphone as the ESP12F runs a basic webserver which allows the color of the glasses to be changed. It’s not the first time we’ve seen a flashy pair of LED shades either! Video after the break.

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