Linux Fu: UPNP A Port Mapping Odyssey

March 23, 2026 by 5 Comments

If you’ve ever run a game server or used BitTorrent, you probably know that life is easier if your router supports UPnP (Universal Plug and Play). This is a fairly old tech — created by a standards group in 1999 — that allows a program to open an incoming port into your home network. Of course, most routers let you do this manually, but outside of the Hackaday universe, most people don’t know how to log into their routers, much less how to configure an open UDP port.

I recently found myself using a temporary setup where I could not access the router directly, but I needed some open ports. That got me thinking: if a program can open a port using UPnP, why can’t I? Turns out, of course, you can. Maybe.

Caveats

The first thing, of course, is that you need your firewall open, but that’s true no matter how you open up the router. If the firewall is in the router, then you are at the mercy of the router firmware to realize that if UPnP opens something up, it needs to open the firewall, too.

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A Simple Switch For Simply Too Much Current

March 23, 2026 by 27 Comments

A switch is simple: connect two pieces of metal together and bam! Except, it’s not that simple at high currents. How much current? Just about 400 car batteries worth would certainly cause some issues. This is the issue that [Technology Hobby] hoped to fix with his clever switch design.

While many content creators are great at finding or making high-current sources (looking at you, Styropyro), their switches can’t always hold up to the abuse. [Technology Hobby] found that many of the switches used by these creators had issues based on an inconsistent and limited contact area. Making a bigger contact patch is always fairly easy; keeping those contacts from skipping can be a bit more difficult.

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The Zero-Power Flight Computer

March 23, 2026 by 19 Comments

In the early days of aviation, pilots or their navigators used a plethora of tools to solve common navigation and piloting problems. There was definitely a need for some kind of computing aid that could replace slide rules, tables, and tedious dead-reckoning computations. This would become even more important during World War II, when there was a massive push to quickly train young men to be pilots.

The same, but different. A Pickett slide rule (top) and an E6B slide rule (bottom). (Own Work).

Today, we’d whip up some sort of computer device, but in the 1930s, computers weren’t anything you’d cram on a plane, even if they’d had any. For example, the Mark 1 Fire Control Computer during WW2 was 3,000 pounds of gears and motors.

The computer is made to answer flight questions like “how many pounds of fuel do I need for another hour of flying time?” or “How do I adjust my course if I have a particular crosswind?”

History

There were a rash of flight computers starting in the 1920s that were essentially specialized slide rules. The most popular one appeared in the late 1930s. Philip Dalton’s circular slide rule was cheap to produce and easy to use. As you’ll see, it is more than just an ordinary slide rule. Keep in mind, these were not computers in the sense we think of today. They were simple slide rules that easily did specialized math useful to pilots.

Dalton actually developed a number of computers. The popular Model B appeared in 1933, and there were refinements leading to additional models. The Mark VII was very popular. Even Fred Noonan, Amelia Earhart’s navigator, used a Mark VII. Continue reading “The Zero-Power Flight Computer” →

Stream Deck Radio Controller Built With Cheap Yellow Display

March 23, 2026 by 4 Comments

Stream decks are pretty useful in all kinds of contexts, but commercial models can feel a bit pricy for what is effectively a bunch of buttons. [WhiskeyTangoHotel] has whipped up one of their own on the cheap using some readily available parts.

The build came about due to the use of Stream Decks as a common way to control the Flex-6400 software-defined radio. [WhiskeyTangoHotel] figured that using a full-priced Elgato Stream Deck was overkill for this purpose, and that a cheaper interface could be put together for less. Enter the Cheap Yellow Display—a combination of the ESP32 microcontroller with a 2.8-inch touchscreen LCD. It was simple enough to code the device such that it had four big touch buttons to control RIT-, RIT+, XIT-, and XIT+ on the Flex-6400. Plus, with the ESP32 having WiFi onboard, it’s able to control the radio wirelessly—you just need to feed the unit 5 volts, and you’re up and running.

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Better Faux-Analog VU Meters

March 23, 2026 by 3 Comments

One of the coolest things about old hi-fi hardware is that it often came with flickety needles that danced with the audio level. You can still buy these if you want, or you can simulate the same look on a screen, as [mircemk] demonstrates.

It isn’t [mircemk]’s first rodeo in this regard. An earlier project involved creating simulated VU meters on round displays, but they were somewhat limited. Using the Adafruit GFX library on an ESP32 netted a working setup, but it was jerky and very jagged and digital-looking. It was more akin to a fake needle display running on an 8-bit computer than something that looked like a real vintage VU meter.

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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 6 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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The 3DFX Voodoo Lives Again In An FPGA

March 22, 2026 by 35 Comments

The 3DFX Voodoo was not the first dedicated 3D graphics chipset by any means, but it became the favourite for gamers among the early mass-market GPUs. It would be found on a 3D-processing-only PCI card that sat on the feature connector of your SVGA card. The Voodoo took any game that supported its Glide API into the world of (for the time) smooth and beautiful 3D. They’re worth a bit now, but if you don’t fancy forking out for mid-’90s silicon in 2026, there’s another option. [Francisco Ayala Le Brun] has implemented the 3DFX Voodoo 1 in SpinalHDL for FPGAs.

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