A lead box with a small aperture sits on a desk. A ruler leads away from it. A small disk on a stand is held in front of the aperture.

Testing The Wave-Particle Duality With Gamma Rays

April 6, 2026 by Aaron Beckendorf 14 Comments

Everything on the electromagnetic spectrum has some properties of both waves and particles, but it’s difficult to imagine a radio wave, for example, behaving like a particle. The main evidence for a particle-like nature is quantization, the bundling of electromagnetic energy into discrete packets. One way around this is to theorize that quantization is due to the specific interaction between the electromagnetic field and matter, not intrinsic to the field itself. To investigate this theory, [Huygens Optics] conducted several experiments with gamma rays, including Compton scattering.

For these experiments, he used a Radiacode 110 X-ray and gamma ray detector, which uses a photodetector to detect radiation’s passage through a scintillation crystal. By summing the energy contained in the light emitted by one ray, it can measure the ray’s energy and, over time, create an energy spectrum. [Huygens Optics] used the americium capsule from an old smoke detector as a radiation source, and cast a lead enclosure to shield the Radiacode from most background radiation, with a small opening for measurements.

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A booted foot is seen descending on a foot pedal attached to a lever underneath a three-legged stand. Three levers extend from the legs, each with a wheel on it, and attach to the central foot plate.

Building A Vise Stand With Pen-Like Retracting Wheels

April 5, 2026 by Aaron Beckendorf 12 Comments

Old shop tools have a reputation for resilience and sturdiness, and though some of this is due to survivorship bias, some of it certainly comes down to an abundance of cast iron. The vise which [Marius Hornberger] recently restored is no exception, which made a good stand indispensable; it needed to be mobile for use throughout the shop, yet stay firmly in place under significant force. To do this, he built a stand with a pen-like locking mechanism to deploy and retract some caster wheels.

Most of the video goes over the construction of the rest of the stand, which is interesting in itself; the stand has an adjustable height, which required [Marius] to construct two interlocking center columns with a threaded adjustment mechanism. The three legs of the stand were welded out of square tubing, and the wheels are mounted on levers attached to the inside of the legs. One of the levers is longer and has a foot pedal that can be pressed down to extend all the casters and lock them in place. A second press on the pedal unlocks the levers, which are pulled up by springs. The locking mechanism is based on a cam that blocks or allows motion depending on its rotation; each press down rotates it a bit. This mechanism, like most parts of the stand, was laser-cut and laser-welded (if you want to skip ahead to its construction, it begins at about 29:00).

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An overlay is shown on a topographical map. High points are highlighted in blue. The letters "A" and "B" are shown in red text at two points.

Using A Scientific Satellite For Passive Radar

March 30, 2026 by Aaron Beckendorf 5 Comments

The basic principle of radar systems is simple enough: send a radio signal out, and measure the time it takes for a reflection to return. Given the abundant sources of RF signals – television signals, radio stations, cellular carriers, even Wi-Fi – that surround most of us, it’s not even necessary to transmit your own signal. This is the premise of passive radar, which uses passive RF illumination to form an image. The RF signal doesn’t even need to come from a terrestrial source, as [Jean Michel Friedt] demonstrated with a passive radar illuminated by the NISAR radar-imaging satellite (pre-print paper).

NISAR is a synthetic-aperture radar satellite jointly built by NASA and ISRO, and it completes a pass over the world every twelve days. It uses an L-band chirp radar signal, which can be picked up with GNSS antennas. One antenna points up towards the satellite, and has a ground plane blocking the signal from directly reaching the second antenna, which picks up reflections from the landscape under observation. Since the satellite would illuminate the scene for less than a minute, [Jean-Michel] had to predict the moment of peak intensity, and achieved an accuracy of about three seconds.

The signals themselves were recorded with an SDR and a Raspberry Pi. High-end, high-resolution SDRs such as the Ettus B210 gave the best results, but an inexpensive homebuilt MAX2771-based SDR also produced recognizable images. This setup won’t be providing any particularly detailed images, but it did accurately show the contours of the local geography – quite a good result for such a simple setup.

If you’re more interested in tracking aircraft than surveying landscapes, check out this ADS-B-synchronized passive radar system. Although passive radar doesn’t require a transmitter license, that doesn’t mean it’s free from legal issues, as the KrakenSDR team can testify.

A 3D printer is shown, with the print bed pitched sharply toward the camera. The hotend is depositing plastic on a model at a sharp angle to the print bed.

Multicolor 5-Axis 3D Printing

March 29, 2026 by Aaron Beckendorf 8 Comments

Usually, when we see non-planar 3D printers, they’re rather rudimentary prototypes, intended more as development frames than as workhorse machines. [multipoleguy]’s Archer five-axis printer, on the other hand, breaks this trend with automatic four-hotend toolchanging, a CoreXY motion system, and print results as good-looking as any Voron’s.

The print bed rests on three ball joints, two on one side and one in the center of the opposite side. Each joint can be raised and lowered on an independent rail, which allows the bed to be tilted on two axes. The dimensions of the extruders’ motion system limit how much the bed can be angled when the extruder is close to the bed, but it can reach sharp angles further out.

The biggest difficulty with non-planar printing is developing a slicer; [multipoleguy] is working on a slicer (MaxiSlicer), but it’s still in development. It looks as though it’s already working rather well, to the point that [multipoleguy] has been optimizing purge settings for tool changes. It seems that when a toolhead is docked, the temperature inside the melt chamber rises above the normal temperature in use, which causes stringing. To compensate for this, the firmware runs a more extensive purge when a hotend’s been sitting for a longer time. The results speak for themselves: a full three-color double helix, involving 830 tool changes, could be printed with as little as six grams of purge waste.

As three-axis 3D printers become consumer products, hackers have kept looking for further improvements to make, which perhaps explains the number of non-planar printing projects appearing recently, including a few five-axis machines. Alternatively, some have experimented with non-planar print ironing.

A man's hand is shown holding a 3D-printed structure. The structure is hollow and has a fiber-optic cable leading to it. Blue light shines from a hole in the structure. In the background, a laser module is coupled to a fiber-optic cable.

Building A Laser-Driven Photoacoustic Speaker

March 22, 2026 by Aaron Beckendorf 8 Comments

An MRI scan is never a pleasant occasion – even if you aren’t worried about the outcome, lying still in a confined, noisy space for long periods of time is at best an irksome experience. For hearing protection and to ameliorate boredom or claustrophobia, the patient wears headphones. Since magnets and wires can’t be used inside an MRI machine, the headphones have to literally pipe the sound in through tubes, which gives them poor sound quality and reduces the amount of noise they can block. [SomethingAboutScience], however, thinks that photoacoustic speakers could improve on these, and built some to demonstrate.

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An oscilloscope display is seen in lower left corner. In the rest of the image, two purple circuit boards are connected by SMA RF cables. A wire antenna is connected to one board.

Building A $50 SDR With 20 MHz Bandwidth

March 22, 2026 by Aaron Beckendorf 9 Comments

Although the RTL-SDR is cheap, accessible, and capable enough for many projects, it does have some important limitations. In particular, its bandwidth is limited to about 3.2 MHz, and the price of SDRs tends to scale rapidly with bandwidth. [Anders Nielsen], however, is building a modular SDR with a target price of $50 USD, and has already reached a bandwidth of almost 20 MHz.

If this project looks familiar, it’s because we’ve covered an earlier iteration. At the time, [Anders] had built the PhaseLoom, which filters an incoming signal, mixes it down to baseband, and converts it to I/Q signals. The next stage is the PhaseLatch, a board housing a 20-MHz, 10-bit ADC, which samples the in-phase and quadrature signals and passes them on to a Cypress FX2LP microcontroller development board. [Anders] had previously connected the ADC to a 6502 microprocessor instead of the FX2LP, but this makes it a practical SDR. The FX2LP was a particularly good choice for this project because of its USB 2.0 interface, large buffers for streaming data, and parallel interface. It simply reads the data from the SDR and dumps it to the computer.

Continue reading “Building A $50 SDR With 20 MHz Bandwidth” →

A blue frontplate to a circuit board is shown. On the left side is an OLED screen displaying "4.35 µH". To the right of this are a red and a black socket, with an inductor between them.

Building An LC Meter With A Franklin Oscillator

March 18, 2026 by Aaron Beckendorf 10 Comments

Although it dates back to the early days of the Marconi Company in the 1920s, the Franklin oscillator has remained a relatively obscure circuit, its memory mostly kept alive by ham radio operators who prize its high stability at higher frequencies. At the core of the circuit is an LC tank circuit, a fact which [nobcha] used to build quite a precise LC meter.

The meter is built around two parts: the Franklin oscillator, which resonates at a frequency defined by its inductance and capacitance, and an Arduino which counts the frequency of the signal. In operation, the Arduino measures the frequency of the original LC circuit, then measures again after another element (capacitor or inductor) has been added to the circuit. By measuring how much the resonant frequency changes, it’s possible to determine the value of the new element.

Before operation, the meter must be calibrated with a known reference capacitor to determine the values of the base LC circuit. In one iteration of the design, this was done automatically using a relay, while in a later version a manual switch connects the reference capacitor. Because the meter measures frequency differences and not absolute values, it minimizes parasitic effects. In testing, it was capable of measuring inductances as low as 0.1 µH.

We’ve seen a few homebrew LC meters here, some battery-powered and some rather professional.