Hardware Bug In Raspberry Pi’s RP2350 Causes Faulty Pull-Down Behavior

August 28, 2024 by Maya Posch 51 Comments

Erratum RP2350-E9 in the RP2350 datasheet, detailing the issue.

The newly released RP2350 microcontroller has a confirmed new bug in the current A2 stepping, affecting GPIO pull-down behavior. Listed in the Raspberry Pi RP2350 datasheet (page 1340) as erratum RP2350-E9, it involves a situation where a GPIO pin is configured as a pull-down with input buffer enabled. After this pin is then driven to Vdd (e.g. 3.3V) and then disconnected, it will stay at around 2.1 – 2.2 V for a Vdd of 3.3V. This issue was discovered by [Ian Lesnet] of [Dangerous Prototypes] while working on an early hardware design using this MCU.

The suggested workaround by Raspberry Pi is to enable the input buffer before a read, and disable it again immediately afterwards. Naturally, this is far from ideal workaround, and the solution that [Ian] picked was to add external pull-down resistors. Although this negates the benefits of internal pull-down resistors, it does fix the issue, albeit with a slightly increased board size and BOM part count.

As for the cause of the issue, Raspberry Pi engineer [Luke Wren] puts the blame on an external IP block vendor. With hindsight perhaps running some GPIO validation tests involving pull-up and pull-down configurations with and without input buffer set could have been useful, but we’re guessing they may be performed on future Pi chips. Maybe treating the RP2350 A0 stepping as an ‘engineering sample’ is a good idea for the time being, with A3 (or B0) being the one you may want to use in actual production.

In some ways this feels like déjà vu, as the Raspberry Pi 4 and previous SBCs had their own share of issues that perhaps might have been caught before production.

(Note: original text listed A0 as current stepping, which is incorrect. Text has been updated correspondingly)

DEC’s LAN Bridge 100: The Invention Of The Network Bridge

August 27, 2024 by Maya Posch 13 Comments

DEC’s LAN Bridge 100 was a major milestone in the history of Ethernet which made it a viable option for the ever-growing LANs of yesteryear and today. Its history is also the topic of a recent video by [The Serial Port], in which [Mark] covers the development history of this device. We previously covered the LANBridge 100 Ethernet bridge and what it meant as Ethernet saw itself forced to scale from a shared medium (ether) to a star topology featuring network bridges and switches.

Featured in the video is also an interview with [John Reed], a field service network technician who worked at DEC from 1980 to 1998. He demonstrates what the world was like with early Ethernet, with thicknet coax (10BASE5) requiring a rather enjoyable way to crimp on connectors. Even with the relatively sluggish 10 Mbit of thicknet Ethernet, adding an Ethernet store and forward bridge in between two of these networks required significant amounts of processing power due to the sheer number of packets, but the beefy Motorola 68k CPU was up to the task.

To prevent issues with loops in the network, the spanning tree algorithm was developed and implemented, forming the foundations of the modern-day Ethernet LANs, as demonstrated by the basic LAN Bridge 100 unit that [Mark] fires up and which works fine in a modern-day LAN after its start-up procedure. Even if today’s Ethernet bridges and switches got smarter and more powerful, it all started with that first LAN Bridge.

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3D Printed Electronics Breadboard

August 25, 2024 by Maya Posch 9 Comments

The printed breadboard cover, seen from the bottom. (Credit: CHEP, YouTube) — The printed breadboard cover as seen from the bottom. (Credit: CHEP, YouTube)

Does it make sense to make your own breadboards rather than purchasing off the shelf ones? As [Chuck Hellebuyck] notes in a recent video on DIY, 3D-printed breadboards, there’s a certain charm to making a breadboard exactly the size you need, which is hard to argue with. The inspiration came after seeing the metal breadboard spring clips on sale by [Kevin Santo Cappuccio], who also has a 3D printable breadboard shell project that they fit into. This means that you can take the CAD model (STEP file) and modify it to fit your specifications before printing it, which is what [Chuck] attempts in the video.

The models were exported from TinkerCAD to Bambu Lab Studio for printing on a Bambu Lab A1 Mini FDM printer. After a failed first print (which the A1 Mini, to its credit, did detect), a model was printed on a Creality K1 Max instead. Ultimately [Chuck] traced this back to the Bambu Lab Studio slicer failing to add the inner grid to the first layer, which the Creality slicer did add, caused by the ‘wall generator’ setting in the Bambu Lab slicer being set to ‘Classic’ rather than ‘Arachne,’ which can vary line width.

After this, the models printed fine and easily fit onto the spring clips that [Chuck] had soldered down on some prototyping board. A nice feature of these spring clips is that they have a bit of space underneath them where an SMD LED can fit, enabling functional (or just fancy) lighting effects when using a custom PCB underneath the contraption. As for whether it’s worth it depends on your needs. As [Chuck] demonstrates, it can be pretty convenient for a small breadboard on an add-on card (with or without custom lighting) like this, but it’s unlikely to replace generic breadboards for quick prototyping. We can, however, imagine a custom breadboard with mounting points for things like binding posts, switches, or potentiometers.

If we had that kind of custom breadboard, we wouldn’t need these. People were making custom breadboards back in 1974, but they didn’t look like these.

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Charles Duke during his interview with Jack Gordon. (Credit: Jack Gordon, YouTube)

Lunar Landing Lunacy: Charles Duke Confronted With Reality-Deniers

August 24, 2024 by Maya Posch 104 Comments

Lunar Module pilot Charles Duke saluting the US flag during Apollo 16. (Credit: NASA)

Imagine: you spent years training for a sojourn to the Moon, flew there on top of a Saturn V rocket as part of Apollo 16, to ultimately land on the lunar surface. You then spend the next few days on the surface, walking and skipping across the lunar regolith while setting up experiments and exploring per your mission assignments. Then, you pack everything up and blast off from the lunar surface to the orbiting command module before returning to Earth and a hero’s welcome. Then, decades later, you are told to your face that none of that ever happened. That’s the topic of a recent interview which [Jack Gordon] recently did with astronaut [Charles Duke].

None of these ‘arguments’ provided by the reality-denying crowd should be too shocking or feel new, as they range from the amount of fuel required to travel to the moon (solved by orbital mechanics) to the impossibility of lighting on the Moon (covered by everyone and their dog, including the Mythbusters in 2008).

Of course, these days, we have lunar orbiters (LRO and others) equipped with powerful cameras zoomed in on the lunar surface, which have photographed the Apollo landing sites with the experiments and footsteps still clearly visible. Like today’s crowd of spherical Earth deniers, skeptics will denounce anything that doesn’t fit their ill-conceived narrative as ‘faked’ for reasons that only exist in their fevered imaginations.

A common objection we’ve heard is that if we went to the moon back then, why haven’t we been back? The reason is obvious: politics. The STS (Shuttle) project sucked up all funding and the USSR collapsed. Only recently has there been a new kind of ‘space race’ in progress with nations like China. That doesn’t keep countless individuals from dreaming up lunar landing conspiracy theories to file away with their other truth nuggets, such as how microwaved and genetically engineered foods cause cancer, vaccines are another government conspiracy to control the population, and nuclear power plants can explode like nuclear bombs.

Perhaps the best takeaway is that even if we have not found intelligent life outside Earth yet, for at least a few years, intelligent life was the only kind on Earth’s Moon. We wish [Charles Duke] many happy returns, with maybe a casual return to the Moon in the near future as well, to frolic once more on the lunar surface.

Not that there hasn’t been a moon hoax, just not lately. If you want to watch the old Apollo video, it has been improved in recent years.

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Meta Cancels Augmented Reality Headset After Apple Vision Pro Falls Flat

August 24, 2024 by Maya Posch 50 Comments

The history of consumer technology is littered with things that came and went. For whatever reason, consumers never really adopted the tech, and it eventually dies. Some of those concepts seem to persistently hang on, however, such as augmented reality (AR). Most recently, Apple launched its Vision Pro ‘mixed reality’ headset at an absolutely astounding price to a largely negative response and disappointing sale numbers. This impending market flop seems to now have made Meta (née Facebook) reconsider bringing a similar AR device to market.

To most, this news will come as little of a surprise, considering that Microsoft’s AR product (HoloLens) explicitly seeks out (government) niches with substantial budgets, and Google’s smart glasses have crashed and burned despite multiple market attempts. In a consumer market where virtual reality products are already desperately trying not to become another 3D display debacle, it would seem clear that amidst a lot of this sci-fi adjacent ‘cool technology,’ there are a lot of executives and marketing critters who seem to forego the basic question: ‘why would anyone use this?’

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Comparing AliExpress Vs LCSC-Sourced MOSFETs

August 24, 2024 by Maya Posch 26 Comments

The fake AliExpress-sourced IRFP460 MOSFETs (Credit: Learn Electronics Repair, YouTube)

These days, it’s super-easy to jump onto the World Wide Web to find purported replacement parts using nothing but the part identifier, whether it’s from a reputable source like Digikey or Mouser or from more general digital fleamarkets like eBay and AliExpress. It’s hardly a secret that many of the parts you can buy online via fleamarkets are not genuine. That is, the printed details on the package do not match the actual die inside. After AliExpress-sourced MOSFETs blew in a power supply repair by [Learn Electronics Repair], he first tried to give the MOSFETs the benefit of the doubt. Using an incandescent lightbulb as a current limiter, he analyzed the entire PSU circuit before putting the blame on the MOSFETs (IRFP460) and ordering new ones from LCSC.

Buying from a distributor instead of a marketplace means you can be sure the parts are from the manufacturer. This means that when a part says it is a MOSFET with specific parameters, it almost certainly is. A quick component tester session showed the gate threshold of the LCSC-sourced MOSFETs to be around 3.36V, while that of the AliExpress ‘IRFP460’ parts was a hair above 1.8V, giving a solid clue that whatever is inside the AliExpress-sourced MOSFETs is not what the package says it should be.

Unsurprisingly, after fitting the PSU with the two LCSC-sourced MOSFETs, there was no more magic smoke, and the PSU now works. The lesson here is to be careful buying parts of unknown provenance unless you like magic smoke and chasing weird bugs.

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Intuitive Explanation Of Arithmetic, Geometric & Harmonic Mean

August 24, 2024 by Maya Posch 8 Comments

The simple definition of a mean is that of a numeric quantity which represents the center of a collection of numbers. Here the trick lies in defining the exact type of numeric collection, as beyond the arithmetic mean (AM for short, the sum of all values divided by their number) there are many more, with the other two classical Pythagorean means being the geometric mean (GM) and harmonic mean (HM).

The question that many start off with, is what the GM and AM are and why you’d want to use them, which is why [W.D.] wrote a blog post on that topic that they figure should be somewhat intuitive relative to digging through search results, or consulting the Wikipedia entries.

Compared to the AM, the GM uses the product of the values rather than the sum, which makes it a good fit for e.g. changes in a percentage data set. One thing that [W.D] argues for is to use logarithms to grasp the GM, as this makes it more obvious and closer to taking the AM. Finally, the HM is useful for something like the average speed across multiple trips, and is perhaps the easiest to grasp.

Ultimately, the Pythagorean means and their non-Pythagorean brethren are useful for things like data analysis and statistics, where using the right mean can reveal interesting data, much like how other types using something like the median can make a lot more sense. The latter obviously mostly in the hazy field of statistics.

No matter what approach works for you to make these concepts ‘click’, they’re all very useful things to comprehend, as much of every day life revolves around them, including concepts like ‘mean time to failure’ for parts.

Top image: Cycles of sunspots for the last 400 years as an example data set to apply statistical interpretations to. (Credit: Robert A. Rohde, CC BY-SA 3.0)