Inside A Germanium Transistor

October 10, 2025 by Jenny List 9 Comments

The first transistors were point contact devices, not far from the cats-whiskers of early radio receivers. They were fragile and expensive, and their performance was not very high. The transistor which brought the devices to a mass audience through the 1950s and 1960s was the one which followed, the alloy diffusion type. [Play With Junk] has a failed OC71 PNP alloy diffusion transistor, first introduced in 1957, and has cracked it open for a closer look.

Inside the glass tube is a small wafer of germanium crystal, surrounded by silicone grease. It forms the N-type base of the device, with the collector and emitter being small indium beads fused into the germanium. The junctions were formed by the resulting region of germanium/indium alloy. The outside of the tube is pained black because the device is light-sensitive, indeed a version of this transistor without the paint was sold as the OCP71 phototransistor.

These devices were leaky and noisy, with a low maximum frequency and low gain. But they were reliable and eventually affordable, so some of us even cut our electronic teeth on them.

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Qualcomm Introduces The Arduino Uno Q Linux-Capable SBC

October 7, 2025 by Maya Posch 89 Comments

Generally people equate the Arduino hardware platforms with MCU-centric options that are great for things like low-powered embedded computing, but less for running desktop operating systems. This looks about to change with the Arduino Uno Q, which keeps the familiar Uno formfactor, but features both a single-core Cortex-M33 STM32U575 MCU and a quad-core Cortex-A53 Qualcomm Dragonwing QRB2210 SoC.

According to the store page the board will ship starting October 24, with the price being $44 USD. This gets you a board with the aforementioned SoC and MCU, as well as 2 GB of LPDDR4 and 16 GB of eMMC. There’s also a WiFi and Bluetooth module present, which can be used with whatever OS you decide to install on the Qualcomm SoC.

This new product comes right on the heels of Arduino being acquired by Qualcomm. Whether the Uno Q is a worthy purchase mostly depends on what you intend to use the board for, with the SoC’s I/O going via a single USB-C connector which is also used for its power supply. This means that a USB-C expansion hub is basically required if you want to have video output, additional USB connectors, etc. If you wish to run a headless OS install this would of course be much less of a concern.

Blocky tread, yellow hub-- yep, it looks like LEGO

10″ LEGO Tyre Is Practical Nostalgia

September 29, 2025 by Tyler August 6 Comments

If there’s one thing that has come to define the generations after the baby boom, it’s probably nostalgia. It’s heavily marketed and weaponized by the market: yearning for better, simpler times seems to be a core thread of the consumer economy these days. [Makerneer] combined his xilennial love of LEGO bricks with the flat tires on his log splitter to produce a 10″ TPU tyre will never go flat, and provide a dopamine release every time he sees it.

The tyre is a custom model to fit his particular rims, but he does provide STEP and F3D files if you’d like to try modifing it for your own purpose — they’re at Step 6 of the Instructable. Props to [Makerneer] for truly open-sourcing the design instead of just tossing STL files online. His build log also takes the time to point out the ways he had to modify the LEGO tyre profile to make it amenable to 3D printing: notably chamfering some of the tread pattern to eliminate bridging, which is a bit of a no-no with TPU.

As you can see in the (unfortunately vertical) demo video below, it’s a bit quite a bit squishier than a regular run-flat tyre, but that was part of [Makerneer]’s design goal. He didn’t like how rigid the non-pneumatic tyres he’d tried were, so endevoured to design something himself; the whole LEGO thing was just for fun. If you wanted to replicate this tyre with a bit less skoosh, you need only tune the infill on your print.

While only time will tell how long this LEGO-inspired add-on will continue adding whimsy to [Makerneer]’s log-splitting, we have tests to show it will outperform any other plastic he might have printed. This project is probably more practical than a 3D printed bicycle tyre, which doesn’t even have the side benefit of whimsy. Continue reading “10″ LEGO Tyre Is Practical Nostalgia” →

Whither The Chip Shortage?

September 27, 2025 by Elliot Williams 40 Comments

Do you remember the global chip shortage? Somehow it seems so long ago, but it’s not even really been three years yet. Somehow, I had entirely forgotten about it, until two random mentions about it popped up in short succession, and brought it all flooding back like a repressed bad dream.

Playing the role of the ghost-of-chip-shortage-past was a module for a pair of FPV goggles. There are three versions of the firmware available for download at the manufacturer’s website, and I had to figure out which I needed. I knew it wasn’t V1, because that was the buggy receiver PCB that I had just ordered the replacement for. So it was V2 or V3, but which?

Digging into it, V2 was the version that fixed the bug, and V3 was the redesign around a different microcontroller chip, because they couldn’t get the V2 one during the chip shortage.

I saw visions of desperate hackers learning new toolchains, searching for alternative parts, finding that they could get that one chip, but that there were only 20 of them left and they were selling for $30 instead of $1.30. I know a lot of you out there were designing through these tough couple years, and you’ve all probably got war stories.

And yet here we are, definitively post-chip-shortage. How can you be sure? A $30 vape pen includes a processor that we would have killed for just three years ago. The vape includes a touchscreen, just because. And it even has a Bluetooth LE chip that it’s not even using. My guess is that the hardware designers just put it in there hoping that the firmware team would get around to using it for something.

This vape has 16 MB of external SPI Flash! During the chip shortage, we couldn’t even get 4 MB SPI flash.

It’s nice to be on the other side of the chip shortage. Just order whatever parts you want and you get them, but don’t take for granted how luxurious that feels. Breathe easy, and design confidently. You can finally use that last genuine STM32F103 blue pill board without fear of it being the last one on earth.

(Featured image is not an actual photo of the author, although he does sometimes have that energy.)

Play Capacitor Cupid With The Matchmaker

September 23, 2025 by Donald Papp 5 Comments

Occasionally a design requires capacitors that are much closer to being identical in value to one another than the usual tolerance ranges afford. Precision matching of components from parts on hand might sound like a needle-in-a-haystack problem, but not with [Stephen Woodward]’s Capacitor Matchmaker design.

The larger the output voltage, the greater the mismatch between capacitors A and B.

The Matchmaker is a small circuit intended to be attached to a DVM, with the output voltage indicating whether two capacitors (A and B) are precisely matched in value. If they are not equal, the voltage output indicates the degree of the mismatch as well as which is the larger of the two.

The core of the design is complementary excitation of the two capacitors (the CD4013B dual flip-flop achieves this) which results in a measurable signal if the two capacitors are different; nominally 50 mV per % of mismatch. Output polarity indicates which of the capacitors is the larger one. In the case of the two capacitors being equal, the charges cancel out.

Can’t precision-matched capacitors be purchased? Absolutely, but doing so is not always an option. As [Stephen] points out, selection of such components is limited and they come at an added cost. If one’s design requires extra-tight tolerances, requires capacitor values or types not easily available as precision pairs, or one’s budget simply doesn’t allow for the added cost, then the DIY approach makes a lot more sense.

If you’re going to go down this road, [Stephen] shares an extra time-saving tip: use insulated gloves to handle the capacitors being tested. Heating up a capacitor before testing it — even just from one’s fingers — can have a measurable effect.

[Stephen]’s got a knack for insightful electronic applications. Check out his PWMPot, a simple DIY circuit that can be an awfully good stand-in for a digital potentiometer.

It’s A Variable Capacitor, But Not As We Know It

September 17, 2025 by Jenny List 22 Comments

Radio experimenters often need a variable capacitor to tune their circuits, as the saying goes, for maximum smoke. In decades past these were readily available from almost any scrap radio, but the varicap diode and then the PLL have removed the need for them in consumer electronics. There have been various attempts at building variable capacitors, and here’s [radiofun232] with a novel approach.

A traditional tuning capacitor has a set of meshed semicircular plates that have more of their surface facing each other depending on how far their shaft is turned. The capacitor presented in the first video below has two plates joined by a hinge in a similar manner to the covers of a book. It’s made of tinplate, and the plates can be opened or closed by means of a screw.

The result is a capacitor with a range from 50 to 150 picofarads, and in the second video we can see it used with a simple transistor oscillator to make a variable frequency oscillator. This can form the basis of a simple direct conversion receiver.

We like this device, it’s simple and a bit rough and ready, but it’s a very effective. If you’d like to see another unusual take on a variable capacitor, take a look at this one using drinks cans.

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A photo of the air-wired circuit, with one LED on and the other off.

The Magic Of The Hall Effect Sensor

September 9, 2025 by John Elliot V 22 Comments

Recently, [Solder Hub] put together a brief video that demonstrates the basics of a Hall Effect sensor — in this case, one salvaged from an old CPU fan. Two LEDs, a 100 ohm resistor, and a 3.7 volt battery are soldered onto a four pin Hall effect sensor which can toggle one of two lights in response to the polarity of a nearby magnet.

If you’re interested in the physics, the once sentence version goes something like this: the Hall Effect is the production of a potential difference, across an electrical conductor, that is transverse to an electric current in the conductor and to an applied magnetic field perpendicular to the current. Get your head around that!

Of course we’ve covered the Hall effect here on Hackaday before, indeed, our search returned more than 1,000 results! You can stick your toe in with posts such as A Simple 6DOF Hall Effect ‘Space’ Mouse and Tracing In 2D And 3D With Hall Effect Sensors.

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