Bela: Real-Time BeagleBone Audio/Analog Cape

Bela is a cape for the BeagleBone Black that’s aimed at artists and musicians. Actually, the cape is much less than half of the story — the rest is in some clever software and a real-time Linux distribution. But we’re getting ahead of ourselves. Let’s talk hardware first.

First off, the cape has stereo input and output as well as two amplified speaker outs. It can do all of your audio stuff. It also has two banks of analogue inputs and outputs, each capable of handling eight signals. In our opinion, this is where the Bela is cool. In particular, the analog outputs are not Arduino-style “analog outputs” where it’s actually a digital output on which you can do PWM to fake an analog signal. These are eight 16-bit outputs from an AD5668 DAC which means that you can use the voltages directly, without filtering.

Then there’s the real trick. All of these input and output peripherals are hooked up to the BeagleBone’s Programmable Realtime Units (PRUs) — a hardware subsystem that’s independent of the CPU but can work along with it. The PRU is interfaced with the real-time Linux core to give you sub-microsecond response in your application. This is a big deal because a lot of other audio-processing systems have latencies that get into the tens of milliseconds or worse, where it starts to be perceptible as a slight lag by humans.

The downside of this custom analog and audio I/O is that it’s not yet supported by kernel drivers, and you’ll need to use their “Heavy Audio Tools” which compiles Pd programs into C code, which can then drive the PRUs. Of course, you can write directly for the PRUs yourself as well. If you just want to play MP3s, get something you have a bunch of simpler, better options. If you need to do responsive real-time audio installations, Bela is a way to go.

The project is open-source, but we had to do a bunch of digging to find what we were looking for. The hardware is in zip files here, and you’ll find the software here. The demo projects look/sound pretty cool and their Kickstarter is long over-funded, so we’re interested to see what folks make with these.

Automatic Pneumatic Harmonica

A wise man once said “If all you’ve got is a cute desktop compressor and some solenoid valves, everything looks like a robotic harmonica.” Or maybe we’re paraphrasing. Regardless, [Fabien-Chouteau] built a pneumatic, automatic harmonica music machine.

It’s actually an offshoot of his other project, a high-speed candy sorting machine. There, he’s trying to outdo the more common color-sensor-and-servo style contraptions by using computer vision for the color detection and a number of compressed-air jets to blow the candy off of a conveyor belt into the proper bins.

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EP Composes a New Chiptune Each Time

[Captain Credible] is a chiptune music artist. He wanted to release an EP, but a regular old em-pee-three was too lame for him, so he made a tiny board with a coin cell, an ATtiny85, and a 3.5mm socket on it.

Rather than just writing some code to generate the tones for a pre-composed song, his “Dead Cats” EP generates the music itself. Using the arduino-tiny library, which adds the tone() function to the ATtiny, he has the chip pick its own time signature, key, subdivisions, and tempo. The melody and drum beat is randomly generated into an array. In addition to that, there are some code “one-liners” which insert unique sounds. After that the code just loops through the music.

If you don’t like the song, simply unplug the audio cable and plug it back in. The 3.5mm jack he chose has a built-in micro-switch, so the board is only powered up if someone is listening. If you’d like to see the circuit diagram, purchase the EP, or take a look at the code, all of that is available on his site.

ARM Board Transmits FM

There is more than a casual link between computer people and musicians. Computers have created music since 1961 when an IBM7094 sang the song Daisy Bell (later inspiring another computer, the HAL 9000, to do the same).

[Vinod.S] wanted to create music on an STM32F407 Discovery board, but he also wanted it to play on his FM radio. He did it, and his technique was surprising and straightforward. The key is that the ARM processor on the Discovery board uses an 8MHz crystal, but internally (using a phase-locked loop, or PLL) it produces a 100MHz system clock. This happens to be right in the middle of the FM radio band. Bringing that signal back out of the chip on a spare output pin gives you the FM carrier.

That’s simple, but a carrier all by itself isn’t sufficient. You need to FM modulate the carrier. [Vinod.S] did the music playback in the usual way and fed the analog signal via a resistor to the crystal. With some experimentation, he found a value that would pull the crystal frequency enough that when multiplied up to 100MHz, it would produce the desired amount of FM deviation. You can see a video of the whole thing in action, below.

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Incredible Marble Music Machine

We tried to figure out how to describe the band [Wintergatan]. It took a lot of googling, and we decided to let their really incredible music machine do it for them. The best part? Unlike some projects like this that come our way, [Wintergatan] documented the whole build process in an eight part video series.

The core of the machine is a large drum with two tracks of alternating grey and black Lego Technic beams and pins. The musician sequences out the music using these. The pins activate levers which in turn drop ball bearings on the various sound producing devices in the machine. The melody is produced by a vibraphone. At first we thought the drum kit was electronic, but it turns out the wires going to it were to amplify the sound they made when hit. At the end of their travel the bearings are brought up to the hopper again by a bucket conveyor.

The final part count for the machine sits at 3,000 not including the 2,000 ball bearings rolling around inside of it. If you’ve ever tried to make a marble machine, then you’ll be just as impressed as we were that the machine only appeared to lose a few marbles in the course of a three minute song. Aside from the smoothness of the machine, which is impressive, we also enjoyed the pure, well, hackiness of it. We can spy regular wood screws, rubber bands, plywood, bits of wire, and all sorts of on-the-spot solutions. Just to add bonus cool, the whole project appears to have been built with  just a bandsaw, a drill press, and a few hand power tools.

The machine is great, but we also really appreciate the hacker spirit behind it. When a commenter on a YouTube video told him he was a genius, he replied, “Thank you for that! But I do think, though, that it is mostly about being able to put in the time! I mean the talent of being stubborn and able to see things through are more important than the abilities you have to start with. If you work hard on anything, you will learn what you need and success! Its my idea anyway! So happy people like the machine!”. Which we think is just as cool as the machine itself. Video of the machine in action and part one of the build series after the break!

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Drawn in by the Siren’s Song

When I say “siren” what do you think of? Ambulances? Air raids? Sigh. I was afraid you were going to say that. We’ve got work to do.

You see, the siren played an important role in physics and mathematics about 150 years ago. Through the first half of the 1900s, this fine apparatus was trivialized, used for its pure noise-making abilities. During the World Wars, the siren became associated with air raids and bomb shelters: a far cry from its romantic origins. In this article, we’re going to take the siren back for the Muses. I want you to see the siren in a new light: as a fundamental scientific experiment, a musical instrument, and in the end, as a great DIY project — this is Hackaday after all.

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The Hovalin: Open Source 3D Printed Violin Sounds Great

[Matt and Kaitlin Hova] have created The Hovalin, an open source 3D-printed violin. Yes, there have been 3D-printed instruments before, but [The Hovas] have created something revolutionary – a 3D printed acoustic instrument that sounds surprisingly good. The Hovalin is a full size violin created to be printed on a desktop-sized 3D printer. The Hovas mention the Ultimaker 2, Makerbot Replicator 2 (or one of the many clones) as examples. The neck is one piece, while the body is printed in 3 sections. The Hovalin is also open source, released under the Creative Commons Attribution Non-Commercial Share Alike license.

A pure PLA neck would not be stiff enough counter the tension in the strings, so [The Hovas] added two carbon fiber truss rods. A handful of other components such as tuners, and of course strings, also need to be purchased. The total price is slightly higher than a $60 USD starter violin from Amazon, but we’re betting the Hovalin is a better quality instrument than anything that cheap.

The Hovalin was released back in October. There are already some build logs in the wild, such as this one from [Emulsifide]. Like any good engineering project, the Hovalin is a work in progress. [Matt and Kaitlin] have already released version 1.0.1, and version 2.0 is on the horizon. Hearing is believing though, so click past the break to hear [Kaitlin] play her instrument.

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