Do You Trust Your Cheap Fuses?

April 11, 2024 by Jenny List 33 Comments

When a fuse is fitted in a power rail, it gives the peace of mind that the circuit is protected. But in the case of some cheap unbranded fuses of the type that come in kits from the usual online suppliers that trust can be illusory, as they fail to meet the required specification.

[Andreas Spiess] has used just these fuses for protection for years as no doubt have many of you, so it was something of a shock for him to discover that sometimes they don’t make the grade. He’s taken a look at the issue for himself, and come up with an accessible way to test your fuses if you have any of those cheap ones.

It’s an interesting journey into the way fuses work, as we’re reminded that the value written on the fuse isn’t the current at which it blows but the maximum it’s intended to take. The specification for fuses should have a graph showing how quickly one should blow at what currents above that level, and the worry was that this time would be simply too long for the cheap ones.

In the video below the break, he looks at the various set-ups required to test a fuse, and instead of a bank of large power supplies, he came up with a circuit involving an 18650 cell and three one ohm resistors in parallel. The resulting 1/3 ohm resistor should pass in the region of 10 A when connected across the 18650, so with a 5 A fuse in that circuit and a storage ‘scope he’s able to quickly test a few candidates. He found that the cheap fuses he had were slower to blow than a Bosch part but weren’t as worrisome as he’d at first thought. If you have any of these parts, maybe you should take a look at them too?

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Op-Amp Drag Race Turns Out Poorly For 741

February 23, 2024 by Dan Maloney 32 Comments

When it was first introduced in 1968, Fairchild’s 741 op-amp made quite a splash. And with good reason; it packed a bunch of components into a compact package, and the applications for it were nearly limitless. The chip became hugely popular, to the point where “741” is almost synonymous with “op-amp” in the minds of many.

But should it be? Perhaps not, as [More Than Electronics] reveals with this head-to-head speed test that compares the 741 with its FET-input cousin, the TL081. The test setup is pretty simple, just a quick breadboard oscillator with component values selected to create a square wave at approximately 1-kHz, with oscilloscope probes on the output and across the 47-nF timing capacitor. The 741 was first up, and it was quickly apparent that the op-amp’s slew rate, or the rate of change of the output, wasn’t too great. Additionally, the peaks on the trace across the capacitor were noticeably blunted, indicating slow switching on the 741’s output stage. The TL081 fared quite a bit better in the same circuit, with slew rates of about 13 V/μS, or about 17 times better than the 741, and nice sharp transitions on the discharge trace.

As [How To Electronics] points out, comparing the 741 to the TL081 is almost apples to oranges. The 741 is a bipolar device, and comparing it to a device with JFET inputs is a little unfair. Still, it’s a good reminder that not all op-amps are created equal, and that just becuase two jelly bean parts are pin compatible doesn’t make them interchangeable. And extra caution is in order in a world where fake op-amps are thing, too.

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Mapping The Nintendo Switch PCB

February 20, 2024 by Bryan Cockfield 22 Comments

As electronics have advanced, they’ve not only gotten more powerful but smaller as well. This size is great for portability and speed but can make things like repair more inaccessible to those of us with only a simple soldering iron. Even simply figuring out what modern PCBs do is beyond most of our abilities due to the shrinking sizes. Thankfully, however, [μSoldering] has spent their career around state-of-the-art soldering equipment working on intricate PCBs with tiny surface-mount components and was just the person to document a complete netlist of the Nintendo Switch through meticulous testing, a special camera, and the use of a lot of very small wires.

The first part of reverse-engineering the Switch is to generate images of the PCBs. These images are taken at an astonishing 6,000 PPI and as a result are incredibly large files. But with that level of detail the process starts to come together. A special piece of software is used from there that allows point-and-click on the images to start to piece the puzzle together, and with an idea of where everything goes the build moves into the physical world.

[μSoldering] removes all of the parts on the PCBs with hot air and then meticulously wires them back up using a custom PCB that allows each connection to be wired up and checked one-by-one. With everything working the way it is meant to, a completed netlist documenting every single connection on the Switch hardware can finally be assembled.

The final documentation includes over two thousand photos and almost as many individual wires with over 30,000 solder joints. It’s an impressive body of work that [μSoldering] hopes will help others working with this hardware while at the same time keeping their specialized skills up-to-date. We also have fairly extensive documentation about some of the Switch’s on-board chips as well, further expanding our body of knowledge on how these gaming consoles work and how they’re put together.

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.

Hackaday Prize 2023: Circuit Scout Lends A Hand (Or Two) For Troubleshooting

August 11, 2023 by Dan Maloney 13 Comments

Troubleshooting a circuit is easy, right? All you need is a couple of hands to hold the probes, another hand to twiddle the knobs, a pair of eyes to look at the schematic, another pair to look at the circuit board, and, for fancy work, X-ray vision to see through the board so you know what pads to probe. It’s child’s play!

In the real world, most of us don’t have all the extra parts needed to do the job right, which is where something like CircuitScout would come in mighty handy. [Fangzheng Liu] and [Thomas Juldo]’s design is a little like a small pick-and-place machine, except that instead of placing components, the dual gantries place probes on whatever test points you need to look at. The stepper-controlled gantries move independently over a fixture to hold the PCB in a known position so that the servo-controlled Z-axes can drive the probes down to the right place on the board.

As cool as the hardware is, the real treat is the software. A web-based GUI parses the PCB’s KiCAD files, allowing you to pick a test point on the schematic and have the machine move a probe to the right spot on the board. The video below shows CircuitScout moving probes from a Saleae logic analyzer around, which lets you both control the test setup and see the results without ever looking away from the screen.

CircuitScout seems like a brilliant idea that has a lot of potential both for ad hoc troubleshooting and for more formal production testing. It’s just exactly what we’re looking for in an entry for the Gearing Up round of the 2023 Hackaday Prize.

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A Deep Dive On Battery Life

July 28, 2023 by Bryan Cockfield 12 Comments

There are all kinds of old wives’ tales surrounding proper battery use floating around in the popular culture. Things like needing to fully discharge a battery every so often, unplugging devices when they’re fully charged, or keeping batteries in the fridge are all examples that have some kernel of truth to them but often are improperly applied. If you really want to know the truth about a specific battery, its behavior, and its features, it helps to dig in and actually take some measurements directly like [Tyler] has done with a vast array of embedded batteries in IoT devices.

[Tyler] is a firmware engineer by trade, so he is deeply familiar with this type of small battery. Battery performance can change dramatically under all kinds of scenarios, most important among them being temperature. But even the same type of battery can behave differently to others that are otherwise identical, which is why it’s important to have metrics for the batteries themselves and be able to measure them to identify behaviors and possible problems. [Tyler] has a system of best practices in place for monitoring battery performance, especially after things like firmware upgrades since small software changes can often have a decent impact on battery performance.

While working with huge fleets of devices, [Tyler] outlines plenty of methods for working with batteries, deploying them, and making sure they’re working well for customers. A lot of it is extremely useful for other engineers looking to develop large-scale products like this but it’s also good knowledge to have for those of us rolling out our own one-off projects that will operate under battery power. After all, not caring for one’s lithium batteries can have disastrous consequences.

How Hardware Testing Got Plugged Into A Continuous Integration Framework

June 26, 2023 by Donald Papp 5 Comments

The concept of Continuous Integration (CI) is a powerful tool in software development, and it’s not every day we get a look at how someone integrated automated hardware testing into their system. [Michael Orenstein] brought to our attention the Hardware CI Arena, a framework for doing exactly that across a variety of host OSes and microcontroller architectures.

The Hardware CI Arena allows testing software across a variety of hardware boards such as Arduino, RP2040, ESP32, and more.

Here’s the reason it exists: while in theory every OS and piece of hardware implements things like USB communications and device discovery in the same way, in practice that is not always the case. For individual projects, the edge cases (or even occasional bugs) are not much of a problem. But when one is developing a software product that aims to work seamlessly across different hardware options, such things get in the way. To provide a reliable experience, one must find and address edge cases.

The Hardware CI Arena (GitHub repository) was created to allow automated testing to be done across a variety of common OS and hardware configurations. It does this by allowing software-controlled interactions to a bank of actual, physical hardware options. It’s purpose-built for a specific need, but the level of detail and frank discussion of the issues involved is an interesting look at what it took to get this kind of thing up and running.

The value of automatic hardware testing with custom rigs is familiar ground to anyone who develops hardware, but tying that idea into a testing and CI framework for a software product expands the idea in a useful way. When it comes to identifying problems, earlier is always better.