Peek Into This Synth’s Great Design (And Abandoned Features)

March 9, 2021 by Donald Papp 30 Comments

[Tommy]’s POLY555 is an analog, 20-note polyphonic synthesizer that makes heavy use of 3D printing and shows off some clever design. The POLY555, as well as [Tommy]’s earlier synth designs, are based around the 555 timer. But one 555 is one oscillator, which means only one note can be played at a time. To make the POLY555 polyphonic, [Tommy] took things to their logical extreme and simply added multiple 555s, expanding the capabilities while keeping the classic 555 synth heritage.

The real gem here is [Tommy]’s writeup. In it, he explains the various design choices and improvements that went into the POLY555, not just as an instrument, but as a kit intended to be produced and easy to assemble. Good DFM (Design For Manufacturability) takes time and effort, but pays off big time even for things made in relatively small quantities. Anything that reduces complexity, eliminates steps, or improves reliability is a change worth investigating.

For example, the volume wheel is not a thumbwheel pot. It is actually a 3D-printed piece attached to the same potentiometer that the 555s use for tuning; meaning one less part to keep track of in the bill of materials. It’s all a gold mine of tips for anyone looking at making more than just a handful of something, and a peek into the hard work that goes into designing something to be produced. [Tommy] even has a short section dedicated to abandoned or rejected ideas that didn’t make the cut, which is educational in itself. Want more? Good news! This isn’t the first time we’ve been delighted with [Tommy]’s prototyping and design discussions.

POLY555’s design files (OpenSCAD for enclosure and parts, and KiCad for schematic and PCB) as well as assembly guide are all available on GitHub, and STL files can be found on Thingiverse. [Tommy] sells partial and complete kits as well, so there’s something for everyone’s comfort level. Watch the POLY555 in action in the video, embedded below.

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A Sympathetic Nail Violin

March 3, 2021 by Matthew Carlson 5 Comments

As a hacker community, we are no strangers to beautiful and unique musical instruments. A sympathetic nail violin built by [Nicolas Bras] is a welcome addition to the eclectic family. Working up from the simple idea of a nail in a piece of wood and adjusting the pitch by hammering the nail farther into the wood, [Nicolas] expanded the idea. With careful planning and tuning, the nails can have sympathetic properties. These properties mean that when one nail is played via a bow, it causes other nails to sound, creating harmonies and sustains.

With a bit of careful woodworking and a scant touch of metalwork, an instrument was crafted. It offers vast flexibility as it can be played by bow, by plucking with your finger, or by strumming. There are several levels of nails, each level having a paired sympathetic nail. This allows for a diverse and versatile instrument.

Here at Hackaday, we seem to have a thing for tiny violins, whether physical or virtual. While the nail violin may not look like your traditional violin, we can certainly appreciate the wonderful music it creates.

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An Homage To Daft Punk In Fan-Made Helmets Through The Years.

March 2, 2021 by Jenny List 32 Comments

It’s with sadness that we note the end to an end. The French dance music duo Daft Punk have split up, announced in a video that’s has already clocked 22 million views.The band have inspired hardware geeks across the world not just with their music but the way they present themselves. A perennial project has been to replicate in some way their iconic robot helmets.

Ben Heck's 2009 take on the helmet — Harrison Krix’s 2009 take on Guy-Manuel de Homem-Christo’s helmet.

The artists themselves have been reticent about the exact technology that powers their headgear, but while this is a source of endless mystery and speculation to the music press it’s safe to assume from our perspective that their designers have the same parts at their disposal as we have. Microcontrollers, EL wire, and LEDs are universal, so the challenge lies in artistic expression with the helmet design rather than in making the effects themselves. We’ve reached into the archives for a bit of Daft Punk helmet nostalgia, so stick on Harder Better Faster and lets take a look at them, er, one more time.

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Audio Out Over A UART With An FTDI USB-To-TRS Cable

February 24, 2021 by Maya Posch 41 Comments

What is the easiest way to get audio from a WAV file into a line-level format, ready to be plugged into the amplifier of a HiFi audio set (or portable speaker)? As [Konrad Beckmann] demonstrated on Twitter, all you really need is a UART, a cable and a TRS phono plug. In this case a USB-TTL adapter based around the FTDI FT232R IC: the TTL-232R-3V3-AJ adapter with 12 Mbps USB on one end, and a 3 Mbps UART on the other end.

[Konrad] has made the C-based code available on GitHub. Essentially what happens underneath the hood is that it takes in a PCM-encoded file (e.g. WAV). As a demonstration project, it requires the input PCM files to be a specific sample rate, as listed in the README, which matches the samples to the baud rate of the UART. After this it’s a matter of encoding the audio file, and compiling the uart-sound binary.

The output file is the raw audio data, which is encoded in PDM, or Pulse-Density Modulation. Unlike Pulse-Code Modulation (PCM), this encoding method does not encode the absolute sample value, but uses binary pulses, the density of which corresponds to the signal level. By sending PDM data down the UART’s TX line, the other side will receive these bits. If said receiving device happens to be an audio receiver with an ADC, it will happily receive and play back the PDM signal as audio. As one can hear in the video embedded in the tweet, the end result is pretty good.

If we look at at the datasheet for the TTL-232R-3V3-AJ adapter cable, we can see how it is wired up:

When we compare this to the wiring of a standard audio TRS jack, we can see that the grounds match in both wirings, and TX (RX on the receiving device) would match up with the left channel, with the right channel unused. A note of caution here is also required: this is the 3.3V adapter version, and it lists its typical output high voltage as 2.8V, which is within tolerances for line-level inputs. Not all inputs will be equally tolerant of higher voltages, however.

Plugging random TRS-equipped devices into one’s HiFi set, phone or boombox is best done only after ascertaining that no damage is likely to result. Be safe, and enjoy the music.

PVC Pipes Play “Popcorn” Perfectly

February 22, 2021 by Kristina Panos 16 Comments

There are all sorts of fun ways to make music with empty jugs and other things that resonate with a popping sound when poked with a finger. Should you ever get stuck on that proverbial desert island, you can entertain yourself by making cheerful, staccato music with nothing but a fingertip and the inside of your cheek. At the very least, it will keep your spirits up until you can fashion an ocarina from a coconut.

[Nicolas Bras] loves to make homemade instruments. When he saw all the scrap pieces of perfectly finger-sized PVC tubing piling up around the workshop, he decided to make an instrument specifically to play the effervescent synth tune “Popcorn”. (Video, embedded below.) He plays it by plugging and quickly unplugging wood-capped pipes with his fingers, and using another PVC tube to blow across the tops of them to fill out the orchestration.

[Nicolas] started by making a two-octave chromatic scale with 25 pipes ranging from C4 to C6. He kept building on it from there in both directions, ultimately ending up with a poppin’ 68-note pipe organ that sounds fantastic. If you’re interested in getting the sound samples, [Nicolas] has those and the instrument plans available through Patreon.

Be sure to check out the build and demo video below — it’s a joy to see it come together, and the whole thing clocks in under six minutes. Take our word for it and don’t jump to the “Popcorn” cover, because the build-up is necessary for maximum enjoyment.

Hungry for more “Popcorn”? Here’s a robotic glockenspiel busting out a striking cover.

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Stochastic Markov Beats

February 20, 2021 by Matthew Carlson 7 Comments

[Attoparsec] has been building intriguing musical projects on his YouTube channel for a while and his latest is no exception. Dubbed simply as “Node Module”, it is a rack-mounted hardware-based Markov chain beat sequencer. Traditionally Markov chains are software state machines that transition between states with given probabilities, often learned from a training corpus. That same principle has been applied to hardware beat sequencing.

Each Node Module has a trigger input, four outputs each with a potentiometer, and a trigger out. [Attoparsec] has a wonderful explanation of all the different parts and theories that make up the module at the start of his video, but the basic operation is that a trigger input comes in and the potentiometers are read to determine the probabilities of each output. One is randomly selected and fired. As you can imagine, there are loops and even dead-end nodes and for some musical pieces there is a certain number of beats expected, so a clever reset signal can be sent to pull the chain back to the initial starting state at a regular interval. The results are interesting to listen to and even better to imagine all the possibilities.

The module itself is an Arduino-based custom PCB that is laid out quite cleanly. The BOM, code, and KiCad files are available on GitHub if you want to make one yourself. This isn’t the first instrument we’ve seen [Attoparsec] make, and we’re confident it won’t be the last.

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12-Note Polyphony On An Arduino Synth

February 19, 2021 by Lewin Day 9 Comments

When synthesizers first hit the scene back in the mid-20th century, many were monophonic instruments, capable of producing just one pitch at a time. This was a major limitation, and over time polyphonic synthesizers began to flood into the scene, greatly expanding performance possibilities. [Kevin] decided to build his own polyphonic synthesizer, but far from taking the easy route, he built it around the Arduino Uno – not a platform particularly well known for its musical abilities!

[Kevin]’s build manages 12-note polyphony, an impressive feat for the ATmega328 at the heart of the Arduino Uno. It’s done by running an interrupt on a timer at a steady rate, and implementing 12 counters, one per note. When a counter overflows, a digital IO pin is flipped. This outputs a square wave at a certain pitch on the IO pin, producing the given note. The outputs of 12 digital IO pins are mixed together with a simple resistor arrangement, producing a basic square wave synth. Tuning isn’t perfect, but [Kevin] notes a few ways it could be improved down the line.

[Kevin] has added features along the way, expanding the simple synth to work over several octaves via MIDI, while also building a small tactile button keyboard, too. It’s a project that serves as a great gateway into basic synthesis and music electronics, and we’re sure [Kevin] learned a lot along the way. We’ve seen other microcontroller synths before too, like this tiny device that fits inside a MIDI plug. Video after the break.

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