Making A Copper-Oxide Photodetector From Scratch

September 20, 2026 by Maya Posch 4 Comments

Photodetectors come in a wide variety of constructions and materials, with the Cu₂O-based photodetector that [Mad Scientist Creations] demonstrates in a recent video being a good example of a photodetector that can be created at home using nothing but some copper and a heat source.

Of the two copper elements in a salt water cell, one element is heated to the point where a copper oxide layer forms, specifically Cu₂O, which acts as a semiconductor and provides the photosensitive layer. Even a fairly crude sensor created with a regular gas stove produces enough of a current that it can be used in a simple light detection circuit.

Although copper-oxide photodetectors may seem quaint, they are getting a lot of interest as they feature a very narrow bandgap at 1.2 eV. In a 2019 study by [Hyeon-Joo Song] et al. as published in Scientific Reports such a sensor is enhanced with an optimized grain structure that improves its performance, with much higher sensitivity and faster response times.

As demonstrated by [Andrzej Kwiatkowski] et al. in a 2024 paper in Solar Energy Materials and Solar Cells these copper-oxide sensors can also be used for gas detectors, though they used advanced gas deposition to produce the thin films instead of sticking a bit of copper tape into a natural gas flame.

Even if DIY copper-oxide sensors aren’t quite as exciting as what one can do with access to a well-equipped (semiconductor) lab, it’s still a pretty accessible material that lends itself for easy experimentation.

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Teardown And Repair Of An Insoma Water Timer

September 19, 2026 by Maya Posch 5 Comments

Water timers are nifty devices that can water the lawn at set times or keep that vegetable garden from turning into a dustbowl. When [electronupdate] timer refused to output water on any of its three outlets, he did the right thing. Instead of angrily checking the warranty on the sodding thing, he tore it apart to attempt a repair.

As expected, the design of these devices is quite straightforward. Three solenoids control whether an outlet is open or closed. A control board also handles the user controls and display.

There was no obvious sign of damage, and the PCB was potted in a white substance that should have kept out any moisture. A quick check with a battery revealed that the three solenoids also worked just fine, so the cause likely was somewhere on the — potted — PCB.

These solenoids are rated for 6VDC and take about 20 ms to act, but on an oscilloscope capture it was plain to see that the board was only putting out around 2V. This wasn’t enough to drive the solenoid, raising the question of what had gone wrong on the controller board and setting the stage for some fun epoxy potting compound scraping.

A good bit of elbow grease revealed the control ICs, the H-bridges that drive the solenoids, and the rest of the circuitry, including a power boost circuit with a big electrolytic capacitor. The latter had a bit of suspicious liquid near its base, which turned out to be the culprit. Perhaps the most annoying thing here is that this electrolytic capacitor had the temerity to fail after only four months of use, but at least it was an easy enough fix.

If we had been in there, we might have been tempted to avoid many future battery changes. Impractical, but we wonder if anyone ever built a water timer with a water clock?

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Using Azo Photoisomerization To Alter Semiconductor Film Properties

September 19, 2026 by Maya Posch 2 Comments

Generally semiconductor devices like transistors have fixed properties, but using an azobenzene (Azo) compound it’s possible to optically alter these properties by exposing them to UV light. This is demonstrated in a recent paper by [Jaehoon Ji] et al., as published in Science Advances, with accompanying coverage by Princeton University.

Building on previous research on e.g. flakes of MoS₂ with photochromic Azo molecules, a functional semiconductor device was created. This uses a transition metal dichalcogenide (TMD) monolayer combined with the Azo compound, with the latter altering the electrical and optical properties of the structure.

In both n- and p-type FET semiconductors it was demonstrated using visible and UV light that this can alter the carrier densities in the material, effectively altering the FET’s behavior.

While this is of course just a proof of concept, it does show that by using (Azo) molecules that can respond to certain electromagnetic radiation frequencies, electric fields, temperature, etc. semiconductor devices can be created whose behavior dynamically changes with these factors. This could potentially provide new ways to make programmable circuits and sensors.

Making A Digital Music Player For Cassette Decks

September 18, 2026 by Maya Posch 32 Comments

In the cross-over between the era of tapes into that of MP3s, you’d see quite a few of those special cassette tapes that were actually digital music players inside. Some simply provided a 3.5 mm input, while others were complete MP3 players or Bluetooth receivers that just happened to also output to the magnetic read head of a cassette player. Recently [Jonathan Rowny] decided to make his own version of the latter.

Although getting the actual audio signal into the read head is easy enough – requiring little more than its equivalent being used as a write head on the cassette side – actually interfacing with the player’s mechanisms like auto-stop, reverse and so on requires the use of some gearing that detect motion on what would be the tape spools, as well as transfer the motion from the take-up spool to the other spool so that features like the auto-stop mechanism don’t get triggered.

A lot of inspiration here can be found in e.g. the videos made by [Clint] of [Lazy Game Reviews] who looked at a number of examples – including their internals – over the years, with various levels of functionality. For this particular implementation an ESP32-S3 module is used for the brains, along with a microSD card reader for music and a PCM5102 I2S audio codec to create the analog audio signal.

The gears were printed using an SLA printer and seem to work all right. Unfortunately he didn’t realize the importance of the capstan as the mechanism that actually transports the tape, so its motion was not measured as is done in the better cassette adapters. This will likely be corrected in a future iteration, however.

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Reconstructing A Pin On A Pin Grid Array Package

September 18, 2026 by Maya Posch 14 Comments

Before moving to land grid array (LGA) packaging whereby each pin on the substrate is just a copper pad, processors commonly used pin grid array (PGA) packaging, including the still highly relevant AMD AM4 socket. With PGA you get a pin soldered onto the copper pad which inserts into the ZIF socket, rather than a fragile pin on the mainboard side. Repairing a damaged PGA pin can be easy if just the pin broke off at the solder joint, or rough if the pad was destroyed, as in the case of this Pentium III CPU that [Bits und Bolts] recently tried to fix.

In the case of something like a ground pin or similarly unimportant pin you can ignore the damage, but in this case it concerned an important pin for this 1.2 GHz Tualatin PIII core, with the damage consisting of a well and truly destroyed pad. The first step to repair the damage is thus to try and rebuild the pad, which was done using solder mask and solder.

Although a PIII-era Celeron CPU is definitely not a high-value CPU, since they have so few and such large pins they do make for useful test subjects when it comes to PGA repair practicing. In this case the affected data pad and pin appears to have been repaired successfully, with it running overclocked to 1.6 GHz and crushing similarly or higher clocked Pentium 4 and AMD Athlon CPUs of the era.

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Why Wave Energy Is The Final Frontier Of Renewable Energy

September 17, 2026 by Maya Posch 50 Comments

With the Earth’s atmosphere being effectively just a less dense fluid than the oceans around us, it’s reasonable to ask why we got wind turbines and wind mills quite literally everywhere across the globe to harvest the power in the wind, whereas ocean waves and currents aren’t being exploited quite as much. In a recent video by [Giordano Scarciotti] this issue with wave power is addressed, in particular the massive engineering challenges involved.

Internal view of the CorPower Ocean wave turbine buoy. (Credit: CorPower Ocean)

One of the main problems is simply one of cost, with wind energy having converged on a single design involving effectively the same three-bladed rotor, gondola and tower design that has been optimized for decades now. For wave energy there’s no such one-design-fits-all solution, with each attempted design having its own advantages and disadvantages that may prevent it from working in various sites, or incur high maintenance costs in the highly abusive marine environment.

Having more energy in waves than in wind is also both a benefit and a curse, as wave turbines have to work with the waves and not get demolished every time there’s a storm. Even wind turbines regularly fail in windy weather when e.g. the brakes fail, under conditions that would be considered mild in a marine context.

Also covered in the video is a new contender, in the form of CorPower Ocean’s new buoy-like design that bobs up and down on the surface. Here you need to carefully tune the turbine mechanism to work with the wave motion to extract the most energy. Their current design is be 19 meters tall, 9 meters wide and claimed to be capable of being installed in >40 meter deep water, producing power with a 40-60% capacity factor at 300 kW.

As yet another attempt at making wave energy turbines work, the most exciting aspect of it will be to see whether it can survive adverse weather, when careful tuning gets tossed out of the window and chaotic waves pummel what is essentially a very big hollow buoy. The single prototype has so far survived bad weather off the coast of Portugal during a year of testing, but the real test is long-term survival, as losing half your wave turbine farm to a really bad storm every five-odd years would quickly scuttle the project like it has previous commercial contenders.

Although not addressed in the video, the commercial challenge here is also not so much making the power generated over its lifetime (LCoE) economically attractive, but also its system integration cost in terms of required transmission lines, grid-level energy storage and backup power generators like baseload and standby power plants. Without equipping these wave power farms with grid-forming converters as TSOs are asking, dealing with reactive power to absorb and generate it, any resulting grid oscillations exacerbated by grid-following converters risk causing another expensive blackout as recently on the Iberian peninsula.

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Introducing The Periodic Table Of US Electrical Receptacles

September 16, 2026 by Maya Posch 57 Comments

Although things may seem simple on the North American grid as an end-user if you limit yourself to just 120 VAC and NEMA 1-15 and 5-15 connectors, there is a veritable zoo of different voltages and receptacles out there in the NEMA connector catalogue. Recently [Practical Engineering] decided to not only take a look at how many of these defined standards are actually used, but also put them in a nice periodic table style graphic.

Responsible for these standards is the National Electrical Manufacturers Association (NEMA), which as the name says is a collection of manufacturers. Founded in 1926, this US trade association also affects outlet standards in countries like Canada, Mexico, Japan and so on. The caveat here is that compatibility between e.g. a similar looking Japanese 1-15-style plug and a US 1-15 outlet is not guaranteed, even if you ignore voltage and grid frequency differences.

In an ideal world everyone would agree on a set of reasonable connector designs and we could move on, but we live in a world where even today designing your own national connector instead of picking something like the ubiquitous Type F is considered to be reasonable. At least it’s not susceptible to the ‘penny challenge‘ flaw that the NEMA 5-15 connector suffers from, but that’s small comfort.

NEMA connectors are also unique in that they are often polarized, while Type E/F and others rarely are, putting the onus of dealing with AC polarity on the device. This already shows why the NEMA connector diversity exists, as this trade association wanted to have specific connectors for different polarities, different current limits and also the nearly half a dozen of different voltages commonly used throughout the US.

This ‘one connector for a specific combination’ approach means that quite a few of them are not really used in real life, though from a European perspective where you deal with Type C (‘euro plug’) and Type E/F (‘Schuko’) on ~240 VAC and triple-phase 440 VAC connectors if you run a heavy machine shop or want to fast-charge an EV at home, it’s still a bewildering number of active combinations.

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