Author: Aaron Beckendorf

81 Articles

A microscope objective is sitting on a spool of solder in a metal tin, in front of a circuit board which has wires running away from it.

Watching Radioactive Decay With A Homemade Spinthariscope

November 17, 2025 by 2 Comments

Among the many science toys that have fallen out of fashion since we started getting nervous around things like mercury, chlorinated hydrocarbons, and radiation is the spinthariscope, which let people watch the flashes of light on a phosphor screen as a radioactive material decayed behind it. In fact, they hardly expose their viewers to any radiation, which makes [stoppi]’s homemade spinthariscope much safer than it might first seem.

[Stoppi] built the spinthariscope out of the eyepiece of a telescope, a silver-doped zinc sulfide phosphor screen, and the americium-241 capsule from a smoke detector. A bit of epoxy holds the phosphor screen in the lens’s focal plane, and the americium capsule is mounted on a light filter and screwed onto the eyepiece. Since americium is mainly an alpha emitter, almost all of the radiation is contained within the device.

After sitting in a dark room for a few minutes to let one’s eyes adjust, it’s possible to see small flashes of light as alpha particles hit the phosphor screen. The flashes were too faint for a smartphone camera to pick up, so [stoppi] mounted it in a light-tight metal box with a photomultiplier and viewed the signal on an oscilloscope, which revealed many small pulses.

Continue reading “Watching Radioactive Decay With A Homemade Spinthariscope” →

A circuit board in the shape of a business card is shown. The circuitry is confined to the left side of the board, and the rest is used for text.

(Neural) Networking With A Business Card

November 15, 2025 by 9 Comments

A PCB business card is a great way for electrical engineers to impress employers with their design skills, but the software they run can be just as impressive as the card itself. As a programmer with an interest in embedded machine learning, [Dave McKinnon] wanted a card that showcased his skills, so he designed one that runs voice recognition.

[Dave] specifically wanted to run a neural network on his card, but needed to make it small enough to run on a microcontroller. Voice recognition looked like a good fit for this, since audio can be represented with relatively little data, a microphone is cheap and easy to add to a circuit board, and there was already an example of someone running such a voice recognition network on an Arduino. To fit the neural network into 46 kB, it only distinguishes the words “one” through “nine,” and displays its guess on an LED seven-segment display. [Dave] first prototyped the system with an Arduino, then designed the circuit board around an RP2040.

Continue reading “(Neural) Networking With A Business Card” →

A man's hands are shown holding a microphone capsule with a 3D-printed part on top of it, with a flared metal tube protruding from the plastic.

2025 Component Abuse Challenge: Playing Audio On A Microphone

November 10, 2025 by 5 Comments

Using a speaker as a microphone is a trick old enough to have become common knowledge, but how often do you see the hack reversed? As part of a larger project to measure the acoustic power of a subwoofer, [DeepSOIC] needed to characterize the phase shift of a microphone, and to do that, he needed a test speaker. A normal speaker’s resonance was throwing off measurements, but an electret microphone worked perfectly.

For a test apparatus, [DeepSOIC] had sealed the face of the microphone under test against the membrane of a speaker, and then measured the microphone’s phase shift as the speaker played a range of frequencies. The speaker membrane he started with had several resonance spikes at higher frequencies, however, which made it impossible to take accurate measurements. To shift the resonance to higher frequencies beyond the test range, the membrane needed to be more rigid, and the driver needed to apply force evenly across the membrane, not just in the center. [DeepSOIC] realized that an electret microphone does basically this, but in reverse: it has a thin membrane which can be uniformly attracted and repelled from the electret. After taking a large capsule electret microphone, adding more vent holes behind the diaphragm, and removing the metal mesh from the front, it could play recognizable music.

Replacing the speaker with another microphone gave good test results, with much better frequency stability than the electromagnetic speaker could provide, and let the final project work out (the video below goes over the full project with English subtitles, and the calibration is from minutes 17 to 34). The smooth frequency response of electret microphones also makes them good for high-quality recording, and at least once, we’ve seen someone build his own electrets. Continue reading “2025 Component Abuse Challenge: Playing Audio On A Microphone” →

A central circular element is releasing steel ball bearings into a complex nest of eight intertwined plastic paths.

Mesmerizing Marble Runs From Procedural Generation

November 9, 2025 by 10 Comments

There are few things that can keep a certain kind of mechanically-inclined mind entranced as well as a marble run, and few structures that look as interestingly organic as procedurally-generated designs – combine the two and you get [Will Morrison]’s Marble Fountain.

[Will]’s first approach to generating a marble run was to have a script randomly place some points, generate a path following a spline through those points, and give that path a constant slope. This worked, but the paths it generated were a bit too simple to take full advantage of a 3D printer’s capabilities, so he next wrote a path solver to generate more complicated runs. The solver starts by generating a series of random line segments connecting the top and bottom of the run, then iteratively moves the segments into position. Each segment has to stay within the print volume, be evenly spaced with the others, maintain a constant slope, avoid segments from other tracks, and avoid distant segments of its own track. The result is a complicated network of tracks that keeps the marbles in motion without letting them fly out in fast sections. Continue reading “Mesmerizing Marble Runs From Procedural Generation” →

A drone is shown hovering in the sky, with two bright lights shining from its underside.

2025 Component Abuse Challenge: Overdriven LEDs Outshine The Sun

November 6, 2025 by 13 Comments

Tagging wildlife is never straightforward in the best of times, but it becomes a great deal more complicated when you’re trying to track flying insects. Instead of trying to use a sensor package, [DeepSOIC] attached tiny, light retroreflectors to bees and hornets, then used a pulsed infrared light mounted on a drone to illuminate them. Two infrared cameras on the drone track the bright dot that indicates the insect, letting the drone follow it. To get a spot bright enough to track in full sunlight, though, [DeepSOIC] had to drive some infrared LEDs well above their rated tolerances.

The LEDs manage to survive because they only fire in 15-µs pulses at 100 Hz, in synchrony with the frame rate of the cameras, rather like some welding cameras. The driver circuit is very simple, just a MOSFET switch driven by an external pulse source, a capacitor to steady the supply voltage, and a current-limiting resistor doing so little limiting that it could probably be removed. LEDs can indeed survive high-current pulses, so this might not really seem like component abuse, but the 5-6 amps used here are well beyond the rated pulse current of 3 amps for the original SFH4715AS LEDs. After proving the concept, [DeepSOIC] switched to 940 nm LEDs, which provide more contrast because the atmosphere absorbs more sunlight around this wavelength. These new LEDs were rated for 5A, so they weren’t being driven so far out of spec, but in tests they did survive current up to 10A.

We’ve seen a similar principle used to drive laser diodes in very high-power pulses a few times before. For an opposite approach to putting every last bit of current through an LED, check out this low-power safety light.

Continue reading “2025 Component Abuse Challenge: Overdriven LEDs Outshine The Sun” →

An aluminium box is visible on the left side of the image, with a power supply on the right side, and a lamp ballast in the middle. A man's hand is holding the end of an optical fiber in the lower left corner, and it is emitting a white light.

Building A Xenon Lamp For Spectroscopy

November 2, 2025 by 29 Comments

Before a spectrometer can do any useful work, it needs to be calibrated to identify wavelengths correctly. This is usually done by detecting several characteristic peaks or dips in a well-known light source and using these as a reference to identify other wavelengths. The most common reference for hobbyists is the pair of peaks produced by a mercury-vapor fluorescent light, but a more versatile option is a xenon-bulb light source, such as [Markus Bindhammer] made in his latest video.

A xenon gas discharge produces a wide band of wavelengths, which makes it a useful illumination source for absorbance spectroscopy. Even better, Xenon also has several characteristic spikes in the infrared region. For his light source, [Markus] used an H7 xenon bulb meant for a vehicle headlight. The bulb sits in the center of the source, with a concave mirror behind it and a pair of converging lenses in front of it. The converging lenses focus the light onto the end of an optical cable made of PMMA to better transmit UV. A few aluminum brackets hold all the parts in place. The concave mirror is made out of a cut-open section of aluminum pipe. The entire setup is mounted inside an aluminum case, with a fan on one end for cooling. To keep stray light out of the case, a light trap covers the fan’s outlet.

[Markus] hadn’t yet tested the light source with his unique spectrometer, but it looks as though it should work nicely. We’ve seen a wide variety of amateur spectrometers here, but it’s also illuminating to take a look at commercial scientific light sources.

Two colored plastic films are loosely tied over the entrances to two plastic containers.

Cooking Up Plastics In The Kitchen

October 28, 2025 by 3 Comments

The earliest useful plastics were made out of natural materials like cellulose and casein, but since the Bakelite revolution, their use has dwindled away and left them mostly as curiosities and children’s science experiments. Fortunately, though, the raw materials for bioplastics are readily available in most grocery stores, and as [Ben] from NightHawkInLight demonstrates, it’s still possible to find new uses for them.

His first recipe was for a clear gelatine thermoplastic, using honey as a plasticizer, which he formed into the clear packet around some instant noodles: simply throw the whole packet into hot water, and the plastic dissolves away. With some help from the home bioplastics investigator [Giestas], [Ben] next created a starch-based plastic out of starch, vinegar, and glycerine. Starch is a good infrared emitter in the atmospheric window, and researchers have made a starch-plastic aerogel that radiates enough heat to become cooler than its surroundings. Unfortunately, this requires freeze-drying, and while encouraging freezer burn in a normal freezer can have the same effect, it’ll take a few months to get a usable quantity of the material.

The other problem with starch-based plastics is their tendency to absorb water, at least when paired with plasticizers like glycerine or honey. Bioplastics based on alginate, however, are easy to make waterproof. A solution of sodium alginate, derived from seaweed, reacts with calcium ions to make a cross-linked waterproof film. Unfortunately, the film forms so quickly that it separates the solutions of calcium ions from the alginate, and the reaction stops. To get around this, [Ben] mixed a sodium alginate solution with powdered calcium carbonate, which is insoluble and therefore won’t react. To make the plastic set, he added glucono delta lactone, which slowly breaks down in water to release gluconic acid, which dissolves the calcium carbonate and lets the reaction proceed.

The soluble noodle package reminded us of a similar edible package, which included flavoring in the plastic. We’ve also seen alginate used to make conductive string, and rice used to make 3D printer filament. It’s worth some caution, though – not all biologically-derived plastics are healthier than synthetic materials.

Continue reading “Cooking Up Plastics In The Kitchen” →