Inside A Vintage Oven Controlled Crystal Oscillator

February 1, 2025 by Maya Posch 8 Comments

Crystal oscillators are incredibly useful components, but they come with one little snag: their oscillation is temperature-dependent. For many applications the relatively small deviation is not a problem, but especially for precision instruments this is a deal breaker. Enter the oven controlled crystal oscillator, or OCXO. These do basically what it says on the tin, but what’s inside them? [Kerry Wong] took apart a vintage Toyocom TCO-627VC 10 MHz OCXO, revealing a lot more complexity than one might assume.

Inside the insulated enclosure there is of course the crystal oscillator itself, which has a heating coil wrapped around it. Of note is that other OCXOs that [Kerry] took apart had more insulation, as well as other ways of providing the thermal energy. In this particular unit a thermistor is attached to the crystal’s metal case to measure its temperature and provide feedback to the heating circuit. The ICs on the PCB are hard to identify due to the conformal coating, but at least one appears to be a 74LS00, alongside a 78L05 voltage regulator which reduces the 12V input voltage.

As an older OCXO it probably is a lot chunkier than newer units, but the basic principle remains the same, with a heating loop that ensures that the crystal inside the unit remains at the same temperature.

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Using Microwave Heating To Locally Anneal CNT-Coated FDM Prints

February 1, 2025 by Maya Posch 19 Comments

The CNT coating between the layers is heated with microwaves to locally anneal. (Credit: Sweeney et al., Science Adv., 2017)

Layer adhesion is one of the weak points with FDM 3D printing, with annealing often recommended as a post-processing step. An interestingly creative method for this was published in Science Advances back in 2017, featuring the work of researchers at Texas A&M University and citing previous work by other teams. In the paper by [Charles B. Sweeney] et al, they describe how they coated PLA filament with carbon nanotubes (CNTs), resulting in this CNT being distributed primarily between the individual layers of polymer.

This is useful because CNTs are quite sensitive to microwave radiation, resulting in the conversion to thermal energy, i.e. heat. Compared to traditional annealing where the entire part is placed into an oven or similar, this microwave-based heating – or locally induced RF (LIRF) as they call this method – localizes the heat to the interface between two layers.

The advantages of this approach are that it doesn’t change the dimensions of the part noticeably, it’s faster and more efficient, and the annealing between layers approaches the strength of traditional manufacturing. Unfortunately not too much seems to have happened with this approach since then, but considering that both CNTs (single & double-walled) and microwaves are readily available, there’s not much standing in the way of replicating these results.

Taking A $15 Casio F91W 5,000 Meters Underwater

February 1, 2025 by Maya Posch 42 Comments

When considering our favorite spy movies and kin that involve deep-sea diving, we’d generally expect to see some high-end watch that costs thousands of dollars and is specially engineered to withstand the immense pressures kilometers below the ocean’s surface. Yet what about a humble Casio F91W that can be bought for about $15 if it’s the genuine article and not one of the millions of fakes? Over at the Watches of Espionage site they figured that they’d dress up one of these famous watches to give it the best possible shot at surviving the crushing pressures at a depth of 5 km.

The actual modification to the F91W was pretty mild, involving nothing but a ‘hydro-mod’ whereby oil is used to replace the air inside the watch case. Since oil is incompressible, nothing bad should happen to the watch. Theoretically at least. The Watch-Under-Test (WUT) was strapped to a US Navy’s CURV 21 remotely operated vehicle and dunked into the ocean before starting its descend into the inky darkness of the deep sea.

Although only hitting a measly 4,950 m, the watch survived just fine, showing that even if you’re a secret US operative on a deep-dive espionage mission, all you really need is one of these Casio watches.

Electroplating DIY PCB Vias At Home Without Chemical Baths

January 31, 2025 by Maya Posch 20 Comments

Although DIY PCB making has made great strides since the early days of chemical etching, there’s one fly in the ointment: vias. These connect individual layers of the board with a conductive tube, and are essential for dual-layer PCBs, never mind boards with a larger layer stack. The industry standard way of producing them is rather cumbersome and doesn’t scale well to a hobby or prototyping context. Might there be a better way? This is the question that [Levi Janssen] set out to answer with a new home PCB manufacturing project.

The goal here is to still electroplate the vias as with the commercial solution, just without having to use chemical baths. This way it should be suitable for an automated setup, with a tool head that performs the coating of the via with a high-resistance conductive ink before the electroplating step, all without submerging the entire PCB. After an initial experiment showed promising results, [Levi] committed to a full prototype.

This turned out to be a bridge too far, so the prototype was scaled down to a simpler machine. This is where the main issue with electroplating one via at a time became clear, as a standard 0.3 mm via takes easily 10 minutes to electroplate, even with an increase in voltage. At that point ordering a PCB from China becomes the faster option if you have enough vias in the design. Fortunately [Levi] figures he may have some solutions there, so we’ll have to wait and see what those are in the next installment. The video is below the break.

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Patching Up Failing Hearts With Engineered Muscle Tissue

January 30, 2025 by Maya Posch 3 Comments

As the most important muscle in our body, any serious issues with our heart are considered critical and reason for replacement with a donor heart. Unfortunately donor hearts are rather rare, making alternatives absolutely necessary, or at the very least a way to coax the old heart along for longer. A new method here seems to be literally patching up a patient’s heart with healthy heart tissue, per the first human study results by [Ahmad-Fawad Jebran] et al. as published in Nature (as well as a partially paywalled accompanying article).

Currently, simple artificial hearts are a popular bridging method, which provide a patient with effectively a supporting pump. This new method is more refined, in that it uses induced pluripotent stem cells (iPS) from an existing hiPSC cell line (TC1133) which are then coaxed into forming cardiomyocytes and stromal cells, effectively engineered heart muscle (EHM). After first testing this procedure on rhesus macaque monkeys, a human trial was started involving a 46-year old woman with heart failure after a heart attack a few years prior.

During an operation in 2021, 10 patches of EHMs containing about 400 million cells each were grafted onto the failing heart. When this patient received a donor heart three months later, the removed old heart was examined and the newly grafted sections found to be healthy, including the development of blood vessels.

Although currently purely intended to be a way to keep people alive until they can get a donor heart, this research opens the tantalizing possibility of repairing a patient’s heart using their own cells, which would be significantly easier than growing (or bioprinting) an entire heart from scratch, while providing the benefit of such tissue patches grown from one’s own iPS cells not evoking an immune response and thus mitigating the need for life-long immune system suppressant drugs.

Featured image: Explanted heart obtained 3 months after EHM implantation, showing the healthy grafts. (Credit: Jebran et al., 2025, Nature)

Comparing Adhesives For Gluing PETG Prints

January 30, 2025 by Maya Posch 31 Comments

Testing every kind of glue with PETG, including wood glue. (Credit: Cosel, YouTube)

PETG is a pretty great material to print 3D models with, but one issue with it is that gluing it can be a bit of a pain. In a recent video by [Cosel] (German language, with English auto-dub) he notes that he found that with many adhesives the adhesion between PETG parts would tend to fail over time, so he set out to do a large test with just about any adhesive he could get his hands on. This included everything from epoxy to wood glue and various adhesives for plastics

TL;DR: Some superglues seem to weaken PETG, and a construction polyurethane glue is the absolute winner.

For the test, two flat surfaces were printed in PETG for each test, glued together and allowed to fully dry over multiple days. After about a week each sample was put into a rig that tried to pull the two surfaces apart while measuring the force required to do so.

With e.g. two-part epoxy and super glue the parts would break rather than the glue layer, while with others the glue layer would give way first. All of these results are noted in the above graphic that has the force listed in Newton. The special notes and symbols stand for strong smell (‘Geruch’), the PETG itself breaking (‘Substrat gebrochen’) and high variability (‘hohe Streuung’) between the multiple samples tested per adhesive.

Interesting is that multiple superglues (‘Sekundenkleber’) show different results, while MMA (Methyl Methacrylate) and similar score the highest. The Bostik P580 is a polyurethane construction adhesive, usually used for gluing just about anything to anything in interior and exterior applications, so perhaps its high score isn’t so surprising. Trailing at the end are the wood glue in last place, with the UHU general adhesive also scoring rather poorly.

Clearly there are many options for gluing PETG parts, but some are definitely more sturdy than others.

Thanks to [Risu no Kairu] for the tip.

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The Guanella 1:1 balun. (Credit: Steve Arar)

Using Guanella Baluns As Impedance Transformers

January 29, 2025 by Maya Posch 2 Comments

Guanella Impedance Transformer. (Credit: FesZ Electronics)

Even before entering the mystical realms of UHF design, radio frequency (RF) circuits come with a whole range of fun design aspects as well. A case in point can be found in transmission line transformers, which are commonly used in RF power amplifiers, with the Guanella transformer (balun) being one example. Allowing balanced and unbalanced (hence ‘balun’) systems to interface without issues, they’re both very simple and very complex. This type of transformer and its various uses is explained in a video by [FesZ Electronics], and also the subject of an article by [Dr. Steve Arar] as part of a larger series, the latter of which is recommended to start with you’re not familiar with RF circuitry.

Transmission line transformers are similar to regular transformers, except that the former relies on transmission line action to transfer energy rather than magnetic flux and provides no DC isolation. The Guanella balun transformer was originally described by Gustav Guanella in 1944. Beyond the 1:1 balun other configurations are also possible, which [Dr. Arar] describes in a follow-up article, and which are also covered in the [FesZ] video, alongside the explanation of another use of Guanella transformers: as an impedance transformer. This shows just how flexible transformers are once you can wrap your mind around the theory.

We have previously covered RF amplifier builds as well as some rather interesting balun hacks.

Heading image: The Guanella 1:1 balun. (Credit: Steve Arar)

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