Author: Aaron Beckendorf

50 Articles

A pink sine wave is seen against the black background of an oscilloscope display.

Coping With Disappearing Capacitance In A Buck Converter

August 10, 2025 by 19 Comments

Designing a circuit is a lot easier on paper, where components have well-defined values, or lacking that, at least well-defined tolerances. Unfortunately, even keeping percentage tolerances in mind isn’t always enough to make sure that circuits work correctly in the real world, as [Tahmid] demonstrates by diagnosing a buck converter with an oddly strong voltage ripple in the output.

Some voltage ripple is an inherent feature of the buck converter design, but it’s inversely proportional to output capacitance, so most designs include a few smoothing capacitors on the output side. However, at 10 V and a 50% duty cycle, [Tahmit]’s converter had a ripple of 0.75 V, significantly above the predicted variation of 0.45 V. The discrepancy was even greater at 20 V.

The culprit was the effect of higher voltages on the ceramic smoothing capacitors: as the voltage increases, the dielectric barrier in the capacitors becomes less permittive, reducing their capacitance. Fortunately, unlike in the case of electrolytic capacitors, the degradation of ceramic capacitors performance with increasing voltage is usually described in specification sheets, and doesn’t have to be manually measured. After finding the reduced capacitance of his capacitors at 10 V, [Tahmid] calculated a new voltage ripple that was only 14.5% off from the true value.

Anyone who’s had much experience with electronics will have already learned that passive components – particularly capacitors – aren’t as simple as the diagrams make them seem. On the bright side, they are constantly improving.

A filament extruder is shown on a workbench. On the front is a knob and the display of a PID controller. A black geared spool is mounted on the top of the extruder, and on the right, a clear plastic bottle is positioned over a metal rod.

Turning Waste Plastic Into Spools Of Filament

August 1, 2025 by 26 Comments

Despite being a readily-available source of useful plastic, massive numbers of disposable bottles go to waste every day. To remedy this problem (or take advantage of this situation, depending on your perspective) [Igor Tylman] created the PETmachine, an extruder to make 3D printer filament from PET plastic bottles.

The design of the extruder is fairly standard for such machines: a knife mounted to the frame slices the bottle into one long strip, which feeds through a heated extruder onto a spool which pulls the plastic strand through the system. This design stands out, though, in its documentation and ease of assembly. The detailed assembly guides, diagrams, and the lack of crimped or soldered connections all make it evident that this was designed to be built in a classroom. The filament produced is of respectable quality: 1.75 mm diameter, usually within a tolerance of 0.05 mm, as long as the extruder’s temperature and the spool’s speed were properly calibrated. However, printing with the filament does require an all-metal hotend capable of 270 ℃, and a dual-drive extruder is recommended.

One issue with the extruder is that each bottle only produces a short strand of filament, which isn’t sufficient for printing larger objects. Thus, [Igor] also created a filament welder and a spooling machine. The welder uses an induction coil to heat up a steel tube, inside of which the ends of the filament sections are pressed together to create a bond. The filament winder, for its part, can wind with adjustable speed and tension, and uses a moving guide to distribute the filament evenly across the spool, avoiding tangles.

If you’re interested in this kind of extruder, we’ve covered a number of similar designs in the past. The variety of filament welders, however, is a bit more limited.

Thanks to [RomanMal] for the tip!

A rough, pixelated outline of a bird is shown in white in the top of the image. A red replica of this image is shown in a spectrogram in the lower half of the image. A smaller picture-in-picture display in the bottom right of the image shows a man sitting in a studio.

AVIF: The Avian Image Format

July 29, 2025 by 35 Comments

Humans have long admired the sound of birdsong, but to fully appreciate how technically amazing it is, you need an ultrasonic microphone. [Benn Jordan] recently created a video about using these microphones to analyze a collection of bird calls, even training a starling to repeat an image encoded in sound, and has some recommendations for amateurs wanting to get started in computational ornithology.

In the first part of the video, [Benn] set up automated ultrasonic recorders at home, made recordings in Florida and rural Georgia, and visited a starling named “The Mouth,” famous for his ability to mimic human sounds. As a demonstration of his abilities, [Benn] drew a simple bird shape in a spectrogram, converted it into sound, and played it for The Mouth several times. Initially, it didn’t seem that the starling would repeat it, but while he was analyzing his recordings later, [Benn] found the characteristic bird shape. The Mouth had been able to repeat it almost pitch-perfectly. It was in this analysis that the ultrasonic microphones showed their worth, since they were able to slow down the birds’ complex vocalizations enough to detect their complex structures without losing audio quality. Continue reading “AVIF: The Avian Image Format” →

A man’s hand is shown holding a polished metal billet. The billet has a few voids in the surface, and the surface shows a pattern of lighter lines against the darker metal background.

Casting Meteorite-like Materials

July 29, 2025 by 3 Comments

From the outside, iron meteorites tend to look like formless, rusted lumps of metal, which is why museums often polish and etch sections to show their interior structure. This reveals their Widmanstätten patterns, a latticework structure of parallel iron-nickel intermetallic crystals which forms over millions of years of very slow solidification. Inspired by this, [Electron Impressions] created his own metal composition which forms similar patterns on a much-faster-than-geological time scale.

Witmanstätten patterns form when a meteorite colliding with a planet launches molten iron and nickel into space, where they very slowly solidify. As the mixture cools, it first forms a stable phase called Taenite, then begins to precipitate another phase called Kamacite. Kamacite forms needle-shaped crystals, which when polished show up against the Taenite background. However, such needle-shaped growth only becomes noticeable at a cooling rate of a few degrees per million years, so it’s not really a practical way to make the pattern. Continue reading “Casting Meteorite-like Materials” →

The bed of a small CNC machine is shown. A plastic tub is on the bed, and in the tub is a sheet of metal under a pale green solution. In place of the spindle of the CNC, there is a rectangular orange tube extending down into the solution. A red wire runs to this tube, and a black wire runs to the sheet of metal in the tub.

Painting In Metal With Selective Electroplating

July 24, 2025 by 5 Comments

Most research on electroplating tries to find ways to make it plate parts more uniformly. [Ajc150] took the opposite direction, though, with his selective electroplating project, which uses an electrode mounted on a CNC motion system to electrochemically print images onto a metal sheet (GitHub repository).

Normally, selective electroplating would use a mask, but masks don’t allow gradients to be deposited. However, electroplating tends to occur most heavily at the point closest to the anode, and the effect gets stronger the closer the anode is. To take advantage of this effect, [ajc150] replaced the router of an inexpensive 3018 CNC machine with a nickel anode, mounted an electrolyte bath in the workspace, and laid a flat steel cathode in it. When the anode moves close to a certain point on the steel cathode, most of the plating takes place there.

To actually print an image with this setup, [ajc150] wrote a Python program to convert an image into set of G-code instructions for the CNC. The darker a pixel of the image was, the longer the electrode would spend over the corresponding part of the metal sheet. Since darkness wasn’t linearly proportional to plating time, the program used a gamma correction function to adjust times, though this did require [ajc150] to recalibrate the setup after each change. The system works well enough to print recognizable images, but still has room for improvement. In particular, [ajc150] would like to extend this to a faster multi-nozzle system, and have the algorithm take into account spillover between the pixel being plated and its neighbors.

This general technique is reminiscent of a metal 3D printing method we’ve seen before. We more frequently see this process run in reverse to cut metal.

A red, cuboid electrochemical cell is in the center of the picture, with a few wires protruding from the front. Tubes run from each side of the cell to a peristaltic pump and tank on each side. The frame holding the pumps and tanks is white 3D printed plastic.

An Open Source Flow Battery

July 23, 2025 by 29 Comments

The flow battery is one of the more interesting ideas for grid energy storage – after all, how many batteries combine electron current with fluid current? If you’re interested in trying your hand at building one of these, the scientists behind the Flow Battery Research Collective just released the design and build instructions for a small zinc-iodide flow battery.

The battery consists of a central electrochemical cell, divided into two separated halves, with a reservoir and peristaltic pump on each side to push electrolyte through the cell. The cell uses brass-backed grafoil (compressed graphite sheets) as the current collectors, graphite felt as porous electrodes, and matte photo paper as the separator membrane between the electrolyte chambers. The cell frame itself and the reservoir tanks are 3D printed out of polypropylene for increased chemical resistance, while the supporting frame for the rest of the cell can be printed from any rigid filament.

The cell uses an open source potentiostat to control charge and discharge cycles, and an Arduino to control the peristaltic pumps. The electrolyte itself uses zinc chloride and potassium iodide as the main ingredients. During charge, zinc deposits on the cathode, while iodine and polyhalogen ions form in the anode compartment. During discharge, zinc redissolves in what is now the anode compartment, while the iodine and polyhalogen ions are reduced back to iodides and chlorides. Considering the stains that iodide ions can leave, the researchers do advise testing the cell for leaks with distilled water before filling it with electrolyte.

If you decide to try one of these builds, there’s a forum available to document your progress or ask for advice. This may have the clearest instructions, but it isn’t the only homemade flow cell out there. It’s also possible to make these with very high energy densities.

A cylindrical red furnace is in the center of the image. To the left of it is a black power supply. A stand is in front of the furnace, with an arm extending over the furnace. To the right of the furnace, a pair of green-handled crucible tongs sit on an aluminium pan.

The Hall-Héroult Process On A Home Scale

July 22, 2025 by 8 Comments

Although Charles Hall conducted his first successful run of the Hall-Héroult aluminium smelting process in the woodshed behind his house, it has ever since remained mostly out of reach of home chemists. It does involve electrolysis at temperatures above 1000 ℃, and can involve some frighteningly toxic chemicals, but as [Maurycy Z] demonstrates, an amateur can now perform it a bit more conveniently than Hall could.

[Maurycy] started by finding a natural source of aluminium, in this case aluminosilicate clay. He washed the clay and soaked it in warm hydrochloric acid for two days to extract the aluminium as a chloride. This also extracted quite a bit of iron, so [Maurycy] added sodium hydroxide to the solution until both aluminium and iron precipitated as hydroxides, added more sodium hydroxide until the aluminium hydroxide redissolved, filtered the solution to remove iron hydroxide, and finally added hydrochloric acid to the solution to precipitate aluminium hydroxide. He heated the aluminium hydroxide to about 800 ℃ to decompose it into the alumina, the starting material for electrolysis.

To turn this into aluminium metal, [Maurycy] used molten salt electrolysis. Alumina melts at a much higher temperature than [Maurycy]’s furnace could reach, so he used cryolite as a flux. He mixed this with his alumina and used an electric furnace to melt it in a graphite crucible. He used the crucible itself as the cathode, and a graphite rod as an anode. He does warn that this process can produce small amounts of hydrogen fluoride and fluorocarbons, so that “doing the electrolysis without ventilation is a great way to poison yourself in new and exciting ways.” The first run didn’t produce anything, but on a second attempt with a larger anode, 20 minutes of electrolysis produced 0.29 grams of aluminium metal.

[Maurycy]’s process follows the industrial Hall-Héroult process quite closely, though he does use a different procedure to purify his raw materials. If you aren’t interested in smelting aluminium, you can still cast it with a microwave oven.