Is A Cheap Frequency Standard Worth It?

January 6, 2025 by 26 Comments

In the quest for an accurate frequency standard there are many options depending on your budget, but one of the most affordable is an oven controlled crystal oscillator (OCXO). [RF Burns] has a video looking at one of the cheapest of these, a sub ten dollar AliExpress module.

A crystal oven is a simple enough device — essentially just a small box containing a crystal oscillator and a thermostatic heater. By keeping the crystal at a constant temperature it has the aim of removing thermal drift from its output frequency, meaning that once it is calibrated it can be used as a reasonably good frequency standard. The one in question is a 10 MHz part on a small PCB with power supply regulator and frequency trimming voltage potentiometer, and aside from seeing it mounted in an old PSU case we also are treated to an evaluation of its adjustment and calibration.

Back in the day such an oscillator would have been calibrated by generating an audible beat with a broadcast standard such as WWV, but in 2024 he uses an off-air GPS standard to calibrate a counter before measuring the oven crystal. It’s pretty good out of the box, but still a fraction of a Hertz off, thus requiring a small modification to the trimmer circuit. We’d be happy with that.

For the price, we can see that one of these makes sense as a bench standard, and we say this from the standpoint of a recovering frequency standard nut.

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No Frills PCB Brings USB-C Power To The Breadboard

January 6, 2025 by 30 Comments

At this point, many of us have gone all-in on USB-C. It’s gotten to the point that when you occasionally run across a gadget that doesn’t support being powered USB-C, the whole experience seems somewhat ridiculous. If 90% of your devices using the same power supply, that last 10% starts feeling very antiquated.

So why should your breadboard be any different? [Axiometa] has recently unveiled a simple PCB that will plug into a standard solderless breadboard to provide 3.3 and 5 VDC when connected to a USB-C power supply. The device is going to start a crowdfunding campaign soon if you want to buy a completed one — but with the design files and Bill of Materials already up on GitHub, nothing stops you from spinning up your own version today.

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Schematic for progress of 3D integration. a, Schematic showing conventional 3D integration by TSV through wafers. b, M3D integration of single-crystalline Si devices by transfer, c, Growth-based M3D integration of polycrystalline devices. d, Growth-based seamless M3D integration of single-crystalline devices. (Credit: Ki Seok Kim et al., 2024, Nature)

Growing Semiconductor Layers Directly With TMDs

January 6, 2025 by 5 Comments

Transition-metal dichalcogenides (TMDs) are a class of material that’s been receiving significant attention as a possible successor of silicon. Recently, a team of researchers has demonstrated the use of TMDs as an alternative to through-silicon-vias (TSV), which is the current way that multiple layers of silicon semiconductor circuitry are stacked, as seen with, e.g., NAND Flash ICs and processors with stacked memory dice. The novelty here is that the new circuitry is grown directly on top of the existing circuitry, removing the need for approaches like TSV to turn 2D layers into 3D stacks.

As reported in the paper in Nature by [Ki Seok Kim] and colleagues (gift article), this technique of monolithic 3D (M3D) integration required overcoming a number of technological challenges, most of all enabling the new TMD single-crystals to grow at low enough temperatures that it doesn’t destroy the previously created circuitry. The progress is detailed in the paper’s schematic (pictured above): from TSV to M3D by transfer of layers and high- and low-temperature growth of single-crystal layers.

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Before GPS There Was LORAN

January 6, 2025 by 37 Comments

We found it nostalgic to watch [ve3iku] fire up an old Loran-A receiver and, as you can see in the video below, he got it working. If you aren’t familiar with LORAN, it was a common radio navigation technique before GPS took over everything.

LORAN — an acronym for Long Range Navigation — was a US byproduct of World War II and was similar in many ways to Britain’s Gee system. However, LORAN operated at lower frequencies to improve its range. It was instrumental in helping convoys cross the Atlantic and also found use in the Pacific theater.

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Cassette Tape Plays MP3s

January 6, 2025 by 65 Comments

Cassette tapes were a major way of listening to (and recording) music througout the 1980s and 1990s and were in every hi-fi stereo, boom box, and passenger vehicle of the era. Their decline was largely as a result of improvements in CD technology and the rise of the MP3 player, and as a result we live in a world largely absent of this once-ubiquitous technology. There are still a few places where these devices crop up, and thanks to some modern technology their capabilities as a music playback device can be greatly enhanced.

The build starts, as one might expect, by disassembling the cassette and removing the magnetic tape from the plastic casing. With the interior of the cassette empty it’s capable of holding a small battery, USB-C battery charger, and a Bluetooth module. The head of an old tape deck can be wired to the audio output of the Bluetooth module and then put back in place in the housing in place of the old tape. With the cassette casing reassembled, there’s nothing left to do but pair it to a smartphone or other music-playing device and push play on the nearest tape deck.

As smartphones continue to lose their 3.5 mm headphone jacks, builds like this can keep lots of older stereos relevant and usable again, including for those of us still driving older vehicles that have functioning tape decks. Of course, if you’re driving a classic antique auto with a tape technology even older than the compact cassette, there are still a few Bluetooth-enabled options for you as well.

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One Small Step: All About Stepper Motors

January 6, 2025 by 12 Comments

The primary feature of stepper motors is listed right within their name: their ability to ‘step’ forwards and backwards, something which they (ideally) can do perfectly in sync with the input provided to their distinct coils. It’s a feature that allows the connected controller to know the exact position of the stepper motor, without the need for any sensor to provide feedback after a movement, saving a lot of hardware and effort in the process.

Naturally, this is the optimal case, and there are a wide number of different stepper motor configurations in terms of coil count,  types of rotors and internal wiring of the coils, as well as complications such as skipped steps due to mechanical or driver issues. Despite this, in general stepper motors are quite reliable, and extremely versatile. As a result they can be found just about anywhere where accurate, step-based movement is desirable, such as (3D) printers and robotics.

For each application the right type of stepper motor and driving circuit has to be determined, of course, as they also have many reasons why you’d not want to use them, or just a particular type. When diving into a new stepper motor-based project, exactly what are the considerations to pay attention to?

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Turns Out Humans Are Terrible At Intuiting Knot Strength

January 6, 2025 by 36 Comments

We are deeply intuitively familiar with our everyday physical world, so it was perhaps a bit of a surprise when researchers discovered a blind spot in our intuitive physical reasoning: it seems humans are oddly terrible at judging knot strength.

One example is the reef knot (top) vs. the grief knot (bottom). One is considerably stronger than the other.

What does this mean, exactly? According to researchers, people were consistently unable to tell when presented with different knots in simple applications and asked which knot was stronger or weaker. This failure isn’t because people couldn’t see the knots clearly, either. Each knot’s structure and topology was made abundantly clear (participants were able to match knots to their schematics accurately) so it’s not a failure to grasp the knot’s structure, it’s just judging a knot’s relative strength that seems to float around in some kind of blind spot.

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