Magic Eye tubes were popular as tuning guides on old-school radio gear. However, the tubes, the 6U5 model in particular, have become rare and remarkably hard to come by of late. When the supply dried up, [Bjørner Sandom] decided to build a digital alternative instead.

The build relies on a small round IPS display, measuring an inch in diameter and with a resolution of 128×115 pixels. One can only presume it’s round but not perfectly so. It was then fitted with a 25mm glass lens in order to give it a richer, deeper look more akin to a real Magic Eye tube. In any case, a STM32F103CBT was selected to drive the display, with the 32-bit ARM processor running at a lovely 72 MHz for fast and smooth updates of the screen.

The screen, controller, and supporting circuitry are all built onto a pair of PCBs and installed in a 3D-printed housing that lives atop a tube base. The idea is that the build is a direct replacement for a real 6U5 tube. The STM32 controller receives the automatic gain control voltage from the radio set it’s installed in, and then drives the screen to behave as a real 6U5 tube would under those conditions.

By virtue of the smart design, smooth updates, and that nifty glass lens, the final product is quite a thing to behold. It really does look quite similar to the genuine article. If you’ve got a beloved old set with a beleagured magic eye, you might find this a project worth replicating. Video after the break.

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Here at Hackaday, we take pride in presenting the freshest hacks and the best of what’s going on today in the world of hardware hacking. But sometimes, we stumble upon a hack from the past so compelling that we’ve got to bring it to you, so we can all marvel at what was possible in the Before Times.

This one, a completely homebrewed automatic photometric telescope, was designed and built by the father-son team of [Jack Ells] and [Peter Ells]. From the elder [Ells]’ field notes, the telescope saw its first light in 1988, giving us some idea of the scale of problems that had to be overcome to get this wonderful machine working. The optics are straightforward, as least as telescopes go — it’s an f-4.0 Newtonian reflector with an 8.5″ (221 mm) primary mirror on an equatorial mount. The telescope is very rugged-looking indeed, and even stands on brick piers for stability. The telescope’s mount is controlled by a BBC Micro running custom BASIC software.

For the photometric parts, the [Ells] boys installed a photo-multiplier tube at the focus of the telescope. More precisely, they used a liquid light guide to connect the eyepiece to a rack full of equipment, which included the PM tube, its high-voltage power supply, and a series of signal conditioners and counter circuits. The idea was to view a single star through a pinhole mask over the objective of the telescope and count the rate of photons received over time. Doing so would reveal periodic changes in the star’s brightness. Today we’d use similar data to search for exoplanet transits; while we don’t think that was a thing back in 1988, it looks like this telescope could easily have handled the job.

Sadly, [Jack Ells] died only two years after finishing the telescope. But he left it with his son, who eventually moved it to a location with better seeing conditions, where it gathered data for another eight years. The quality of the work is amazing, and as father-son projects go, this one is tough to beat.

In the 60’s and 70’s there were many ways to display numeric data. Nixie tubes, Vacuum Florescent Displays (VFD), micro projection systems, you name it. All of them had advantages and drawbacks. One of the simplest ways to display data was the RCA Numitron. [Alec] at Technology Connections has a bit of a love/hate relationship with these displays.

The Numitron is simply a seven-segment display built from light bulb filaments. The filaments run at 5 V, and by their nature are current limited.  Seven elements versus the usual ten seen in Nixie tubes reduced the number of switching elements (transistors, relays, or tubes) needed to drive them, and the single low-voltage supply was also much simpler than Nixie or even VFD systems.

Sounds perfect, right? Well, [Alec] has a bone to pick with this technology. The displays were quite dim, poorly assembled, and not very pleasing to look at. RCA didn’t bother tilting the “8” to fit the decimal point in! Even the display background was gray, causing the numbers to wash out in ambient light. Black would have been much better. In [Alec]’s words, the best way to describe the display would be “Janky,” yet he still enjoys them. In fact, he built a fancy retro-industrial-themed clock with them.

The Numitron was not a failure, though — we know variants of this display ended up in everything from gas pumps to aircraft cockpit gauges. You can even build an LED-based replica clock — no glowing filaments necessary.