Rotating Plasma Vortex Speaker

[Anthony Garofalo] has made a fancier plasma speaker. Not content with a simple spark, he uses a plasma vortex. To make the vortex, the spark gap is swapped out for an electrode placed in the centre of a ring magnet. The Lorentz force experienced by the arc causes it to rotate rapidly enough round the arc of the magnet’s centre to appear as a continuous sheet of plasma.

The speaker gets its power from an inverter using a flyback transformer driven through a MOSFET by a 555-based pulse width modulator. You can see the result in the video below the break, it’s very impressive to look at but probably not quite ready to sit in your hi-fi stack. The resulting sound isn’t quite as good as that from a stationary arc, but it looks a lot cooler.

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This TARDIS Is An Infrasonic Subwoofer

If you’re a fan of action movies or dance music, you’ll probably be familiar with sub-bass. The moment in those James Bond explosions that thuds through your chest in the movie theatre? That’s the product of a large subwoofer, a tuned pipe housing a speaker working somewhere just above the lower limit of human hearing, in the tens of Hz.

[Mike's] TARDIS final build
[Mike’s] TARDIS final build
But what about sound below the range of human hearing, below 20Hz? You can’t directly hear infrasound, but its presence can have a significant effect on the experience of the listener. [Mike Michaud] was interested in this phenomenon for his home movie setup so built himself an infrasonic subwoofer tuned to 17Hz. Since the resulting cabinet was rather large he disguised it as a vintage UK police telephone box that you’d hardly notice in his basement theater. 

A resonant 17Hz speaker horn is a rather inconvenient size for a home theatre, at about 25 feet long. Fortunately there is no need for the horm to be straight, it can be folded into a more convenient enclosure, and that is what [Mike] has done. He used a design published by [lilmike], which folds the horn three times into a more manageable size.

Speaker cabinet construction requires attention to the choice of materials as well as to the driver unit itself, so [Mike] goes into detail on the materials he rejected and his selection of a particular brand of subfloor ply.

He rates the resulting speaker as incredible. His driver is rated for 500 watts but he only has an amplifier capable of serving 100, even with that power he fears for his basement windows. He describes the noise made by the feet of the robots in War Of The Worlds as “little earthquakes” and the general effect as very menacing.

We’ve featured quite a few subwoofers on Hackaday over the years, though with the exception of this rotary device they have mostly been for more conventional sub-bass applications. Here for example is another folded horn. So if sub has become rather run-of-the-mill for you all, how about using it to be entertained by this vortex cannon?

My Most Obsolete Skill: Delta-Gun Convergence

In a lifetime of working with electronics we see a lot of technologies arrive, become mighty, then disappear as though they had never been. The germanium transistor for instance, thermionic valves (“tubes”), helical-scan video tape, or the CRT display. Along the way we pick up a trove of general knowledge and special skills associated with working on the devices, which become redundant once the world has moved on, and are suitable only reminiscing about times gone by.

When I think about my now-redundant special skills, there is one that comes to the fore through both the complexity and skill required, and its complete irrelevance today. I’m talking about convergence of the delta-gun shadow mask colour CRTs that were the height of television technology until the 1970s, and which were still readily available for tinkering purposes by a teenager in the 1980s.
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Pimped out 70’s Home Intercom System, Now with More Pi

If you own a house that was built in the 1970’s, you might still have the remnants of a home intercom system on the walls of each room. They were consider the end-all-be-all of “home automation” back in the day. Now, they look dated and out of place (but still kind of retro-cool at the same time).  [Cpostier] decided that he wanted to keep his old intercom system, but give it an update with a Rasperry Pi and a 7 inch touch screen, and the results are totally groovy, man.

The original unit served two functions, as an intercom system, and also as a whole house music player.  [Cpostier] wasn’t interested in the intercom feature, and so he started with the traditional gutting of the 70’s dried up electronics. Each room received a new $7 speaker (from Amazon), and the main control panel was fitted with a Pi, TFT touch screen, and new amplifier. The Pi is running Kodi (formerly know as XBMC) and along with it being a great media player, it can also show weather data, or what ever else you would like.

Something magical happens when you blend new tech with old tech – we totally dig it.

A Power Switch for the Chromecast

Chromecasts are fantastic little products, they’re basically little HDMI sticks you can plug into any monitor or TV, and then stream content using your phone or computer as the controller. They are powered by a micro USB port in the back, and if you’re lucky, your TV has a port you can suck the juice off. But what if you want to turn it off while you use a different input on your TV so that your monitor will auto-sleep? You might have to build a power switch.

Now in all honesty, the Chromecast gets hot but the amount of power it draws when not in use is still pretty negligible compared to the draw of your TV. Every watt counts, and [Ilias] took this as an opportunity to refine his skills and combine a system using an Arduino, Bluetooth, and Android to create a robust power switch solution for the Chromecast.

The setup is rather simple. An HC-05 Bluetooth module is connected to an Attiny85, with some transistors to control a 5V power output. The Arduino takes care of a bluetooth connection and uses a serial input to control the transistor output. Finally, this is all controlled by a Tasker plugin on the Android phone, which sends serial messages via Bluetooth.

All the information you’ll need to make one yourself is available at [Ilias’] GitHub repository. For more information on the Chromecast, why not check out our review from almost three years ago — it’s getting old!

Home Made Half Life 2 Turret Powered By Pi

To help expand his inter-dimensional empire, [Solderchips] has decided to build his own Half Life 2 turret. This, he hopes, will automatically track and shoot anyone who hinders the work of Our Benefactors. He’s documenting the process, and has just published his first step: creating a 3D model of the turret and printing it out. The final project will use a Raspberry Pi and a webcam to track rebels and fire on them automatically, especially those with crowbars.

He’s made a promising start, using a papercraft model of the turret to build the 3D model, then modifying it to accommodate the brains (the Raspberry Pi) and the brawns, a couple of small servos that will move the top of the turret around. The next step will perhaps be to add a tilt switch so that the whole thing falls asleep if it falls over. The thing to learn from this project, is that at some point you just have to stop thinking about it and actually make something. This paper model is a big step toward success compared to carrying around the dream in your head.

We’ve seen a few Portal Turret builds and a very nice Wheatley build, but not a decent Half Life 2 turret build, so hopefully [Solderchips] will see this through to completion and release all of his files.

Netflix and Chill – and Socks?

Waking up to spoilers in the last episode after falling asleep during the first episode of a Netflix binge-watching session ranks right up there on the list of first-world problems. Luckily there’s a solution in the form of a pair of Netflix enabled socks, which looks like a pretty neat wearable IoT project.

To be sure, calling these socks Netflix enabled is a bit of a stretch. Aside from the sock designs, which are based on popular Netflix original series, there’s nothing about the electronics that’s specific to the popular streaming service. These socks, with their Arduino Pro Trinket and accelerometer, detect when you stop moving and send an IR signal to do your bidding – pause the movie, kill the TV, or whatever. The electronic side of the build is pretty approachable – it’s just a couple of modules soldered together. The fiber arts side of the project might be a little outside the wheelhouse of the typical hardware hacker, but you can either team up with someone who knits – an experienced knitter, as socks are not a beginner’s pattern – or just slip the felt-clad hardware into your favorite comfy socks. We’d be a bit concerned about ESD protection for the hardware in the wooly environment, though.

“Netflix and chill” is the current version of last century’s “Watching the submarine races,” and as such the need for special socks or a custom Netflix switch for the occasion is a bit puzzling. Still, the underlying wearables idea is pretty good, with plenty of possibilities for expansion and repurposing.

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