Putting out Fires with a Dubstep Drop

Two engineering students from George Mason University have built a rather unorthodox fire extinguisher. It uses a subwoofer to send sound waves powerful enough to extinguish small fires.

Similar in concept to a giant smoke-ring canon, the device uses a subwoofer with a tube that has a smaller aperture opening at the end. When the bass drops (literally), this causes an intense wave of sound (well, air), to be expelled from the device. And as you can see in the video below, it’s quite effective at putting out small fires.

They use a small frequency generator and amplifier to power the system, and throughout extensive testing found 30-60Hz to work best. It’s not actually one big blast of air, but a pressure wave that goes back and forth — agitating the air, and separating it from the fire. There is a catch though.

One of the problems with sound waves is that they do not cool the fuel,” Isman said. “So even if you get the fire out, it will rekindle if you don’t either take away the fuel or cool it.

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Robotic Glockenspiel Crunches “Popcorn”

[James] sent us a video of his latest creation: a robotic glockenspiel that’s currently set up to play “Popcorn”. It uses eight servos to drive mallets that strike the tone bars with fast, crisp movements. The servos are driven with a 16-channel I²C servo driver and MIDI shield, which are in turn controlled with an Arduino Uno. The previous incarnation of his autoglockenspiel employed solenoids, dowels, and elastic bands.

[Gershon Kingsley]’s 1969 composition for synthesizer “Popcorn” has been covered by many artists over the years, though perhaps the most popular cut was [Hot Butter]’s 1972 release. Check it out after the break, and dig that lovely cable management. We’d love to see [James]’s autoglockenspiel play “Flight of the Bumblebee” next.

If you’re hungry for more electro-acoustic creations, have a gander at [Aaron Sherwood]’s Magnetophone.

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Robotic Player Guitar Rocks Out on Its Own

Back in 1988 [Ben Reardon] walked through the Japanese pavilion at the World Expo held in Brisbane, Australia. He saw a robot playing a classical guitar, and was in awe. Later in his life, he decided to learn guitar, and always thought back to that robot. After going to SIGGRAPH 2014 and being inspired by all the creative makers out there, he realized the technology was here — to build his own Robot Guitar.

He started small though — with a prototype robotic Tambourine. It helped flush out some of the ideas for coding that he would eventually employ on the Robot Guitar. The guitar features both an Arduino and a Raspberry Pi, along with six RC servos — one for each string. The biggest challenge with the project was getting the servos mounted just right — stiff, but with adjustment so each pick could be tuned for identical timing. He ended up using aluminum extrusion to mount the servos, three per side in order to leave space for the picks.

Once the mechanical portion was done — onto the coding…

In the end, it ended up being only 460 lines of code. Python and a bit of Bash for the Raspberry Pi — and of course a few sketches for the Arduino. But enough talking about it — let’s hear it!

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Logic Noise: More CMOS Cowbell!

Logic Noise is an exploration of building raw synthesizers with CMOS logic chips. This session, we’ll tackle things like bells, gongs, cymbals and yes, cowbells that have a high degree of non-harmonically related content in them.

Metallic Sounds: The XOR

I use the term “Non-harmonic” in the sense that the frequencies that compose the sound aren’t even integer multiples of some fundamental pitch as is the case with a guitar string or even our square waves. To make these metallic sounds, we’re going to need to mess things up a little bit, and the logic function we’re introducing today to do it is the exclusive-or (XOR).

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Guitar Speaker Cabinet Actually Belongs In Garbage Can

[Dano] builds a lot of guitar pedals and amps. He needed a speaker cabinet dedicated to this task in order to be a consistent reference when checking out his electronic creations. He ordered a couple of 10″ guitar speakers…. and they sat around for a while.

Then one day at the craft store, he stumbled on an inexpensive wooden trash can. It had a tapered design and came with a lid. As would any normal person, [Dano] immediately thought these would make a perfect speaker cabinet so he bought two of them.

The trash cans would be used in an upside-down orientation. The intended lid makes for a well fitting bottom of the cabinet. Holes were cut for the speaker and two terminal blocks. Since these cabinets would be used for testing a bunch of different amps, two different terminal blocks were used to permanently have multiple connector types available.

A pair of modern kitchen cabinet handles were used as carrying handles for each of the two cabinets. If a speaker cabinet one speaker tall is cool, a cabinet two speakers tall must be twice as cool. To get there, the two cabinets were bolted together using electrical conduit as an industrial looking spacer. Those brackets bolted to the sides of the bottom cabinet are actually Ikea shelf brackets that [Dano] had bought and never used. The Ikea brackets support casters making for easy moving around the studio.

Overall, [Dano] is happy with how his cabinets sound. They are very unique and interesting at the least. We’d be happy to play some riffs through them!

Logic Noise: Filters and Drums

Filters and Drums

Logic Noise is an exploration of building raw synthesizers with CMOS logic chips. This session, we continue to abuse the 4069UB as an amplifier. We’ll turn the simple unity-gain buffer of last session into a single-pole active lowpass filter with a single part. (Spoiler: it’s a capacitor.)

While totally useful, this simple filter is a bit boring and difficult to make dynamic. So we’ll look into an entirely different filter, the Twin-T notch filter, that turns out to be sharp enough to build a sine-wave oscillator on, and tweakable enough that we’ll make a damped-oscillator drum sound out of it.

Here’s a quick demo of where we’re heading. Read on to see how we get there.

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3D Spectrum Analyzer uses 1280 LEDs

One of [Dooievriend]’s friends recently pressed him into service to write software for a 3d spectrum analyzer/VU that he made. The VU is a fairly complex build: it’s made up of 1280 LEDs in a 16x16x5 matrix controlled by a PIC32 clocked at 80MHz. [Dooievriend] wrote some firmware for the PIC that uses a variation on a discrete Fourier transform to create a 3D VU effect.

j6v2i When [Dooievriend] set out to design the audio analyzing portion of the firmware, his mind jumped to the discrete Fourier transform. This transform calculates the amplitude in a series of frequency bins in the audio—seemingly perfect for a VU. However, after some more research, [Dooievriend] decided to implement a constant Q transform. This transform is very similar to a Fourier transform, but it takes into account the logarithmic way that the human ear interprets sound.

[Dooievriend] started implementing the constant Q transform using an interrupt-based sampler, but he quickly ran into issues with slow floating-point math on his PIC32 (which doesn’t have a hardware floating-point unit). Thankfully he rewrote his code using fixed-point math, and the transform runs nearly real-time. Check out the video after the break to see the VU in action, and a second video that gives some details on the hardware build.

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