Month: October 2025

All Hail The OC71

October 29, 2025 by 46 Comments

Such are the breadth of functions delivered by integrated circuits, it’s now rare to see a simple small-signal transistor project on these pages. But if you delve back into the roots of solid state electronics you’ll find a host of clever ways to get the most from the most basic of active parts.\

Everyone was familiar with their part numbers and characteristics, and if you were an electronics enthusiast in Europe it’s likely there was one part above all others that made its way onto your bench. [ElectronicsNotes] takes a look at the OC71, probably the most common PNP germanium transistor on the side of the Atlantic this is being written on.

When this device was launched in 1953 the transistor itself had only been invented a few years earlier, so while its relatively modest specs look pedestrian by today’s standards they represented a leap ahead in performance at the time. He touches on the thermal runaway which could affect germanium devices, and talks about the use of black silicone filling to reduce light sensitivity.

The OC71 was old hat by the 1970s, but electronics books of the era hadn’t caught up. Thus many engineers born long after the device’s heyday retain a soft spot for it. We recently even featured a teardown of a dead one.

Continue reading “All Hail The OC71” →

The winning entry, a photo of a fly on a grain of rice.

Nikon Small World Competition Announces 2025 Winners

October 28, 2025 by 3 Comments

They say that, sometimes, less is more. That would certainly apply to photomicrography, where you want to take pictures of tiny things. Nikon agrees, and they sponsor the Small World contest every year. The 2025 winners are a big — or not so big, maybe — deal.

This photomicrography competition dates back to 1975, so this is the 51st set of winners. First place went to [Zhang You] for his photograph of a rice weevil (sitophilus oryzae) on a grain of rice.

[You] is an entomologist from the Entomological Society of China. He says, “It pays to dive deep into entomology: understanding insects’ behaviors and mastering lighting, a standout work blends artistry with scientific rigor, capturing the very essence, energy, and spirit of these creatures.” We can’t argue with the results.

If you’re interested in Nikon and photography, you might also be interested in repairing a broken lens or a Nikon D3.

Web Development In… Pascal?

October 28, 2025 by 27 Comments

If you were asked to make an e-commerce website in 2025, what language would you reach for? Show of hands: JavaScript? Go? Pascal? Well, there was at least one taker for that last one: [jns], and he has an hour-long tutorial video showing you how he made it happen. 

The site in question is the web store for his personal business, Photronic Arts, so you cannot say [jns] does not have skin in the game. From the front end, this is HTML and could be anything upto and including Shopify under the hood. It’s not, though: it’s a wholly custom backend [jns] put together in FreePascal, using the Lazarus IDE.

There’s a case to be made for Pascal in the modern day, but when we wrote that we weren’t expecting to get tips about web development.  Ironically enough [jns] spends so much time giving the technical details in this video he doesn’t delve that deeply into why he chose FreePascal, especially when it’s clear he’s very familiar with C and C++. In his associated writeup on his Gopher page (link though Floodgap) [jns] simply declares it’s a language he’s quite fond of, which is reason enough of us. The source code is available, though on request, to avoid AI scraping. It’s a sad but understandable response to these modern times.

If you’re not into web development and want to see a deep-dive into how the backend works, this video is worth watching even if you don’t particularly care for Pascal. It’s also worth watching if you do know backend development, and are Pascal-curious. If neither of those things interest you, what about this Pascal Library for Arduino?

Thanks to [jns] for the tip! If you’re doing modern work with questionably-modern tools, we call that a hack and would love to hear from you.

 

Testing Cheap DC Breakers And How To Not Start Fires

October 28, 2025 by 11 Comments

One characteristic of adding PV solar to homes is a massive increase in high-voltage and high-current DC installations. With this comes a need for suitable breakers, but without the requisite knowledge it can be easy to set up a fire hazard. There is also the issue of online shopping platforms making it easy to get fuses and breakers that may not be quite as capable as they claim, never mind being rated for DC use.

Recently [Will Prowse] had a poke at a range of common purportedly DC-rated breakers from everyone’s favorite US-based seller of tat, to see whether they should be bought or avoided at all cost. Perhaps unsurprisingly the cheap breakers are about as dodgy as you’d imagine. With a hundred plus amps flowing through them they get surprisingly crispy, even if they generally did their job. Minus the few that arrived in a broken condition, of course.

Ultimately [Will] found that the molded case circuit break (MCCB) by one ‘DIHOOL’ performed the best. Compared to the competition, it is much larger and has sizeable terminals that avoid the quaint heat-soaking issues seen with the cheap-and-cheerful rest. At a mere $34 for the 125A-rated version, it’s still a fraction of the cost of a comparable Eaton MCCB, but should upset your insurance company significantly less than the alternatives.

Don’t forget to add in fuses, with [Will] testing a range of cheapo 12V DC fuses, to see which one will prevent fires, and which one cause them. Unsurprisingly, some of them like the Bojack-branded ones ran very hot, making them more of a liability than an asset.

As for what makes DC breakers so different from AC one is that the extinguishing point of a DC arc is much steeper, which means that an AC breaker is likely to fail to extinguish the arc when used for DC applications. This is why a properly rated and ideally certified breaker is essential, and also not really the point where you want to start saving money.

Continue reading “Testing Cheap DC Breakers And How To Not Start Fires” →

Original E39 Head Unit Modernized

October 28, 2025 by 24 Comments

Although most modern cars have moved to using proprietary components nearly everywhere, especially when it comes to infotainment systems, for a brief moment which peaked in the 90s and 00s most cars shipped with radios that fit in a standard size opening called a DIN slot. If you wanted a new Pioneer or Kenwood stereo it was usually a simple matter to slide the factory radio out and put your choice of aftermarket head unit in its place. [Stefan] has an E39 BMW from this era and wanted to upgrade the factory radio but use the original hardware instead of replacing it.

This isn’t just a simple stereo upgrade either. [Stefan] has gone all-out for this build which he started in 2020. Beginning with a Kotlin/Jetpack Compose Linux application to handle control input from the vehicle’s various knobs and buttons he moved on to a map application and an on-screen keyboard. From there he implemented VGA to send video to the OEM screen, and now has a fully functional system based on a Raspberry Pi. It does everything the original unit can do including playing music and showing the feed from the backup camera, plus adds plenty of new, modern features like Bluetooth.

For a certain classic car enthusiast, this build hits a sweet spot of modernizing a true classic like the E39 without removing or permanently modifying any OEM components. The amount of work that went into it is pretty staggering as well, with [Stephan] putting in over 100 hours of work just to get the video signal timing correct. We also like it because it reminds us of the flash-in-the-pan “carputer” trend from the late 00s where people in the pre-smartphone age were shoving all kinds of computing horsepower in their trunks.

2025 Component Abuse Challenge: A Bistable Flip-Flop With A Fuse

October 28, 2025 by 8 Comments

The flip-flop, in whichever of its several forms you encounter it, is a staple of logic design. Any time that you need to hold onto something, count, or shift bits, out it comes. We expect a flip-flop to be an integrated circuit if we use one, but most of us could knock one together with a couple of transistors.

You aren’t restricted to transistors of course, a relay will do just as well, but how about a fuse? [b.kainka] has made a functioning set/reset flip-flop using a pair of PTC self-resetting fuses.

The circuit is simplicity itself, a pair of incandescent bulbs in series, each in turn in parallel with a momentary action switch and a PTC fuse. On start-up both fuses are conducting, so one or other of them will do its job as a fuse and go high impedance. At that point its bulb will light and the other fuse will remain low impedance so its bulb will stay dark. Press the switch across the lit bulb for a few seconds however, and the circuit resets itself. The other fuse goes high impedance while the first fuse returns to low impedance, and the other bulb lights.

We’re not sure we can see much in the way of practical application for this circuit, but sometimes merely because you can is reason enough. It’s part of our 2025 Component Abuse Challenge, for which you just about still have time to make an entry yourself if you have one.

2025 Hackaday Component Abuse Challenge

Know Audio: Lossy Compression Algorithms And Distortion

October 28, 2025 by 29 Comments

In previous episodes of this long-running series looking at the world of high-quality audio, at every point we’ve stayed in the real world of physical audio hardware. From the human ear to the loudspeaker, from the DAC to measuring distortion, this is all stuff that can happen on your bench or in your Hi-Fi rack.

We’re now going for the first time to diverge from the practical world of hardware into the theoretical world of mathematics, as we consider a very contentious topic in the world of audio. We live in a world in which it is now normal for audio to have some form of digital compression applied to it, some of which has an effect on what is played back through our speakers and headphones. When a compression algorithm changes what we hear, it’s distortion in audio terms, but how much is it distorted and how do we even measure that? It’s time to dive in and play with some audio files. Continue reading “Know Audio: Lossy Compression Algorithms And Distortion” →