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3D Printed Air Raid Siren Sounds Just Like The Real Thing

February 14, 2025 by 11 Comments

Air raid sirens have an important job to do, and have been a critical piece of public safety infrastructure in times of geopolitical turmoil. They sound quite unlike anything else, by virtue of their mechanical method of generating an extremely loud sound output. They’re actually remarkably simple to build yourself, as [MarkMakies] demonstrates.

[Mark’s] build relies almost entirely on 3D printed components and ex-RC gear. The sound itself is generated by a rotor which spins inside a stator. Each is designed with special slots, such that as the rotor turns at speed, it creates spikes of air pressure that generate a loud wail. The rotor and stator are fitted inside a housing with a horn for output, which helps direct and amplify the sound further.

To spin the rotor, [Mark] used a powerful brushless motor controlled by a common hobby speed controller. The actual speed is determined by a potentiometer, which generates pulses to command the speed controller via a simple 555 circuit. By ramping the speed of the motor up and down, it’s possible to vary the pitch of the siren as is often done with real air raid sirens. This action could be entirely automated if so desired.

If you do decide to build such a siren, just be wary about how you use it. There’s no need to go around agitating the townsfolk absent an actual air raid. It’s worth noting that sirens of this type aren’t just used for air raids, either. They’re often used for tornado warnings, too, such as in Dallas, for example. But why not for music?

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A 3D Printed Camera You Can Now Download, Shutter And All

February 13, 2025 by 16 Comments

A couple of years ago we were excited to read news of an entirely 3D printed camera, right down to the shutter. We wrote it up back then but sadly the required STL files were not yet available. Now after time away with his family, its creator [Mark Hiltz] is back. The medium-format Pioneer Camera can now be downloaded for printing in its entirety under a Creative Commons licence.

Looking at the design, it appears to be a relatively straightforward build. The shutter is extremely simple, as far as we can see, relying on magnets to ensure that the open part of its rotation is at an unstable repulsing point between stable magnetic poles. The images aren’t perfect because he’s using a very simple lens, but this is part of the charm of a camera like this one. We hope that people will take it and produce refinements to the design making for a cheap and good entry to medium format photography.

While you’re printing your own Pioneer, take a look at our original coverage.

Google FindMy Tools Run On An ESP32

February 11, 2025 by 43 Comments

As of about a day ago, Google’s reasonably new Find My network just got more useful. [Leon Böttger] released his re-implementation of the Android tracker network: GoogleFindMyTools. Most interestingly for us, there is example code to turn an ESP32 into a trackable object. Let the games begin!

Everything is in its first stages here, and not everything has been implemented yet, but you are able to query devices for their keys, and use this to decrypt their latest location beacons, which is the main use case.

The ESP32 code appears not to support MAC address randomization just yet, so it’s possibly more trackable than it should be, but if you’re just experimenting with the system, this shouldn’t be too much of a problem. The README also notes that you might need to re-register after three days of use. We haven’t gotten to play with it just yet. Have you?

If you’re worried about the privacy implications of yet another ubiquitous tracking system out there, you’re not alone. Indeed, [Leon] was one of the people working on the Air Guard project, which let iPhone users detect trackers of all sorts around them. Anyone know if there’s something like that for Android?

Thanks [Lars] for the hot tip!

 

Jeff Dunham next to a Philco Predicta TV

Jeff Dunham Finds A NOS 1958 Philco Predicta

February 8, 2025 by 14 Comments

When you see a ventriloquist like [Jeff Dunham], you probably expect to see him with a puppet. This time – spoilers ahead – you won’t. Besides his fame on stage, [Dunham] is also a collector of vintage tech and a die-hard television enthusiast. In the video below, [Dunham] has gotten his hands on a rarity: an unboxed 1958 Philco Predicta TV. The original tape was still on the box. We get to follow along on his adventure to restore this sleek, retro-futuristic relic!

[Dunham]’s fascination with the Predicta stems from its historical significance and bold design. At a time when television was making its way into American homes, the Predicta dared to be different with its swivel-mounted picture tube and early printed circuit boards. Despite its brave aesthetics, the Predicta’s ambition led to notorious reliability issues. Yet, finding one in pristine condition, sealed and untouched for over six decades, is like unearthing a technological time capsule.

What makes this story unique is [Dunham]’s connection to both broadcasting and his craft. As a ventriloquist inspired by Edgar Bergen — whose radio shows captivated America — [Dunham] delights in restoring a TV from the same brand that first brought his idol’s voice to airwaves. His love for storytelling seamlessly translates into this restoration adventure.

After unboxing, [Dunham’s] team faces several challenges: navigating fragile components, securing the original shipping brace, and cautiously ramping up voltage to breathe life into the Predicta. The suspense peaks in the satisfying crackle of static, and the flicker of a 65-year-old screen finally awakened from slumber.

Have you ever come across an opportunity like this? Tell us about your favorite new old stock find in the comments. Buying these can be a risk, since components have a shelf life. We appreciate when these old TVs play period-appropriate shows. Who wants to watch Game of Thrones on a Predicta?

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Soviet Wired Radio, How It Worked

January 25, 2025 by 42 Comments

At the height of the Cold War, those of us on the western side of the wall had plenty of choice over our radio listening, even if we stuck with our country’s monolithic broadcaster. On the other side in the Soviet Union, radio for many came without a choice of source, in the form of wired radio systems built into all apartments. [Railways | Retro Tech | DIY] grew up familiar with these wired radios, and treats us to a fascinating examination of their technology, programming, and ultimate decline.

In a Soviet apartment, usually in the kitchen, there would be a “Radio” socket on the wall. Confusingly the same physical dimension as a mains socket, it carried an audio signal. The box which plugged into it was referred to as a radio, but instead contained only a transformer, loudspeaker, and volume control. These carried the centralised radio station, piped from Moscow to the regions by a higher voltage line, then successively stepped down at regional, local, and apartment block level. A later refinement brought a couple more stations on separate sub-carriers, but it was the single channel speakers which provided the soundtrack for daily life.

The decline of the system came over the decades following the end of communism, and he describes its effect on the mostly older listenership. Now the speaker boxes survive as affectionate curios for those like him who grew up with them.

You probably won’t be surprised to find twisted-wire broadcasting in use in the West, too.

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This QR Code Leads To Two Websites, But How?

January 23, 2025 by 45 Comments

QR codes are designed with alignment and scaling features, not to mention checksums and significant redundancy. They have to be, because you’re taking photos of them with your potato-camera while moving, in the dark, and it’s on a curved sticker on a phone pole.  So it came as a complete surprise to us that [Christian Walther] succeeded in making an ambiguous QR code.

Nerd-sniped by [Guy Dupont], who made them using those lenticular lens overlays, [Christian] made a QR code that resolves to two websites depending on the angle at which it’s viewed. The trick is to identify the cells that are different between the two URLs, for instance, and split them in half vertically and horizontally: making them into a tiny checkerboard. It appears that some QR decoders sample in the center of each target square, and the center will be in one side or the other depending on the tilt of the QR code.

Figuring out the minimal-difference QR code encoding between two arbitrary URLs would make a neat programming exercise. How long before we see these in popular use, like back in the old days when embedding images was fresh? QR codes are fun!

Whether it works is probably phone- and/or algorithm-dependent, so try this out, and let us know in the comments if they work for you.

Thanks [Lacey] for the tip!

 

A Ribbon Microphone Is Harder Than You Think

January 22, 2025 by 21 Comments

There’s a mystique around ribbon microphones due to their being expensive studio-grade items, which has led more than one experimenter down the rabbit hole of making one. [Catherine van West] has posted her experiments in the field, and it makes for an interesting read.

The recipe for a ribbon microphone is very simple indeed — suspend a corrugated ribbon of foil in a magnetic field, and take the voltage across the ribbon. But that simplicity hides some significant issues, as the foil is much thinner than the stuff you might roast your turkey under. Such lightweight foil is extremely fragile, and the signwriters leaf used here proved to be difficult to get right.

Then when the microphone is built there’s still the exceptionally low impedance and small voltage across the ribbon to contend with. The choice here is a transformer rather than a FET preamp, which surprised us.

The result is by all accounts a decent sounding microphone, though with some hum pickup due to difficulty with shielding. Should you give one a try? Maybe not, but that hasn’t stopped others from giving it a go.