Identifying Fake Small-Signal Transistors

October 25, 2025 by 46 Comments

It’s rather amazing how many electronic components you can buy right now are not quite the genuine parts that they are sold as. Outside of dedicated platforms like Mouser, Digikey and LCSC you pretty much enter a Wild West of unverifiable claims and questionable authenticity. When it comes to sites like eBay and AliExpress, [hjf] would go so far as to state that any of the power transistors available for sale on these sites are 100% fake. But even small-signal transistors are subject to fakes, as proven in a comparison.

Found within the comparison are a Mouser-sourced BC546C, as well as a BC547C, SN3904 and PN2222A. These latter three all sourced from ‘auction sites’. As a base level test all transistors are put in a generic component tester, which identifies all of them correctly as NPN transistors, but the ‘BC547C’ and ‘PN2222A’ fail the test for having a much too low hFE. According to the generic tester at least, but it’s one red flag, along with the pin-out for the ‘BC547C’ showing up as being inverted from the genuine part.

Next is a pass through the HP4145B curve tracer, which confirms the fake BC547C findings, including the abysmal hFE. For the PN2222A the hFE is within spec according to the curve tracer, defying the component tester’s failing grade.

What these results make clear is that these cheap component testers are not a realistic ‘fake’ tester. It also shows that some of the fake transistors you find on $auction_site are clearly fake, while others are much harder to pin down. The PN2222A and 2N3904 used here almost pass the sniff test, but have that distinct off-genuine feeling, while the fake BC547C didn’t even bother to get its pinout right.

As always, caveat emptor. These cheapo transistors can be a nice source for some tinkering, just be aware of possibly wasting hours debugging an issue caused by an off-nominal parameter in a fake part.

Teaching Math With 3D Printers

October 25, 2025 by 10 Comments

We’ve often thought that 3D printers make excellent school projects. No matter what a student’s interests are: art, software, electronics, robotics, chemistry, or physics, there’s something for everyone. A recent blog post from [Prusa Research] shows how Johannes Kepler University is using 3D printing to teach math. You can see a video with Professor [Zsolt Lavicza] explaining their vision below.

Instead of relying on abstract 3D shapes projected on a 2D screen, GeoGebra, educational math software, creates shapes that you can produce on a 3D printer. Students can physically handle and observe these shapes in the real world instead of on a flat screen.

One example of how the 3D printer finds use in a math class is producing “Genius Square,” a multilevel tic-tac-toe game. You can find the model for that and other designs used in the classes, on Printables. Some prints are like puzzles where students assemble shapes from pieces.

Putting 3D printers in school isn’t a new idea, of course. However, machines have become much simpler to use in recent years, so maybe the time is now. If you can’t find money for printers in school, you can always teach robotics using some low-tech methods.

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Avoid Missed Connections With The Connectorbook’s Web Tool

October 24, 2025 by 25 Comments

Connectors are wonderful and terrible things. Wonderful, in that splicing wires every time you need to disassemble something is really, really annoying. Terrible in that it can be just such an incredible pain-in-the-assets to find the right one if you’re stuck with just a male or a female for some unfortunate reason. We’ve all been there, and all spent time growing increasingly frustrated poring over the DigiKey catalog (or its local equivalent) trying to figure out what the heck we were dealing with. That’s why [Davide Andrea]’s The Connectorbook exists–and even better, the free web service they call Identiconn.

The tool isn’t super new–the Wayback Machine has snapshots of it dating back to 2021–but it’s still very much worth highlighting. There’s a “quick pick” option that lets you narrow it down with photos, or if you want to get specific there are dozens of filters to try and help you find your exact part. You can filter based on everything from the pitch and geometry of the connectors, to how it terminates, attachments, latches, et cetera. While we can’t guarantee the database is fully exhaustive, it looks pretty darn big, and using it is going to be a lot less exhausting than pouring through catalogs hoping that particular vendor or manufacturer lists the matching part.

Some might argue that this database is not a hack, but it’s certainly going to enable a certain amount of hacking. That’s why we’re grateful to [Alex] for the tip! If you’ve got a know tool you think we all should know about that hasn’t been shared yet, please let us know.

The Great ADS1115 Pricing And Sourcing Mystery

October 24, 2025 by 6 Comments
The AdaFruit ADS1115 board hooked up for testing. (Credit: James Bowman)
The AdaFruit ADS1115 board hooked up for testing. (Credit: James Bowman)

Following up on the recent test of a set of purported ADS1115 ADCs sourced from Amazon [James Bowman] didn’t just test a genuine Ti part, but also dug into some of the questions that came up after the first article. As expected, the AdaFruit board featuring a presumed genuine Ti ADS1115 part performed very well, even performing significantly better on the tested parameters than the datasheet guarantees.

Thus we can confirm that when you get the genuine Ti part, you can expect very good and reliable performance for your ADC purposes. Which leaves the unaddressed questions about what these cheapo Amazon-sourced ADS1115 ICs are, and how it can be that LCSC has what should be the same parts for so much cheaper than US distributors?

As far as LCSC pricing is concerned, these are likely to be genuine parts, but also the subject of what is known as price discrimination. This involves pricing the same product differently depending on the targeted market segment, with e.g. Digikey customers assumed to be okay with paying more to get the brand name assurance and other assumed perks. Continue reading “The Great ADS1115 Pricing And Sourcing Mystery” →

Making A Cardboard Airplane Wing

October 24, 2025 by 20 Comments

Ideally, an aircraft would be made of something reasonably strong, light, and weather resistant. Cardboard, is none of those things. But that did not stop [PeterSripol] from building an ultralight wing out of cardboard.

Firstly, he wanted to figure out the strongest orientation of the cardboard flutes for the wing spars. He decided on a mix of horizontal and vertical flutes for the wing spar, with the horizontal flutes resisting vertical deformations and the vertical flutes resisting chord wise deformations.

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Tiny UPS Keeps WiFi Online

October 24, 2025 by 29 Comments

For any mission-critical computer system, it’s a good idea to think about how the system will handle power outages. At the very least it’s a good idea to give the computer enough time to gracefully shut down if the power outage will last for an indefinite time. But for extremely critical infrastructure, like our home Wi-Fi, we might consider a more long-term battery backup that can let us get through the longest of power outages.

Part of why this project from [Next Builder] works so well is that most off-the-shelf routers don’t actually use that much energy. Keeping that and a modem online when the power is out only requires a few lithium batteries. To that end, three lithium ion cells are arranged in series to provide the router with between 9 and 12 volts, complete with a battery management system (BMS) to ensure they aren’t over- or under-charged and that they are balanced. The router plugs directly into a barrel jack, eliminating any switching losses from having to use an inverter during battery operation.

While [Next Builder] is a student who lives in an area with frequent interruptions to the electricity supply, this does a good job of keeping him online. If you’re planning for worse or longer outages, a design like this is easily adapted for more batteries provided the correct BMS is used to keep the cells safely charged and regulated. You can also adapt much larger UPS systems to power more of your home’s electrical system, provided you can find enough batteries.

The Isetta TTL Computer Makes Some Noise

October 24, 2025 by 5 Comments

Our Hackaday colleague [Bil Herd] is known for being the mind behind the Commodore 128, a machine which famously had both a 6502 and a Z80 processor on board. The idea of a machine which could do the job of both those processors in hardware while containing neither would have blown the mind of any 1980s computer enthusiast, yet that’s exactly what [Roelh]’s Isetta TTL computer does. It’s an extremely clever design whose targeted microcode allows the processor-swap trick, and since he’s brought it from prototype to production and has it running SymbOS since we last saw it, it’s time we gave it another look.

A diagram showing chip placement on the Isetta PCB.
All the functions on what is a surprisingly compact board.

The video below the break shows the machine in action, with the Windows 95-like SymbOS GUI running a series of sound tests in the emulated AY-3-8910 sound generator, as well as a Lemmings-like game. It also runs Sinclair ZX Spectrum software, giving it access to a huge library.

We were lucky enough to see some of this in person when we encountered it for a second time on our travels during the summer — and it’s just as impressive in the real as it looks in the video. The feeling really hits you of how this would have blown away anything on the 8-bit market in 1985, made more impressive by the silicon in use being not too far from what was available at the time.

We’re told you can now buy one for yourself as a kit, and we’re looking forward to seeing it generate an ecosystem. We’re particularly curious as to whether that retargetable microcode could allow it to support other archetctures of the day.

Our original coverage can be read here, and we’ve also touched upon SymbOS.

Continue reading “The Isetta TTL Computer Makes Some Noise” →