Solving Grounding Issues On Switch Audio

Grounding of electrical systems is an often forgotten yet important design consideration. Issues with proper grounding can be complicated, confusing, and downright frustrating to solve. So much so that engineers can spend their entire careers specializing in grounding and bonding. [Bsilvereagle] was running into just this sort of frustrating problem while attempting to send audio from a Nintendo Switch into a PC, and documented some of the ways he attempted to fix a common problem known as a ground loop.

Ground loops occur when there are multiple paths to ground, especially in wires carrying signals. The low impedance path creates oscillations and ringing which is especially problematic for audio. When sending the Switch audio into a computer a loop like this formed. [Bsilvereagle] set about solving the issue using an isolating transformer. It took a few revisions, but eventually they settled on a circuit which improved sound quality tremendously. With that out of the way, the task of mixing the Switch audio with sources from other devices could finally proceed unimpeded.

As an investigation into a nuisance problem, this project goes into quite a bit of depth about ground loops and carrying signals over various transforming devices. It’s a great read if you’ve ever been stumped by a mysterious noise in a project. If you’ve never heard of a ground loop before, take a look at this guide to we featured a few years ago.

Upgrading A MIDI Controller With An FPGA

While the “M” in MIDI stands for “musical”, it’s possible to use this standard for other things as well. [s-ol] has been working on a VJ setup (mixing video instead of music) using various potentiometer-based hardware and MIDI to interface everything together. After becoming frustrated with drift in the potentiometers, he set out to outfit the entire rig with custom-built encoders.

[s-ol] designed the rotary-encoder based boards around an FPGA. It monitors the encoder for changes, controls eight RGB LEDs per knob, and even does capacitive touch sensing on the aluminum knob itself. The FPGA communicates via SPI with an Arduino master controller which communicates to a PC using a serial interface. This is [s-ol]’s first time diving into an FPGA project and it looks like he hit it out of the park!.

Even if you’re not mixing video or music, these encoders might be useful to any project where a standard analog potentiometer isn’t accurate or precise enough, or if you just need something that can dial into a specific value quickly. Potentiometers fall short in many different ways, but if you don’t want to replace them you might modify potentiometers to suit your purposes.

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The Teensy Audio Library

There are a few ways of playing .WAV files with a microcontroller, but other than that, doing any sort of serious audio processing has required a significantly beefier processor. This isn’t the case anymore: [Paul Stoffregen] has just released his Teensy Audio Library, a library for the ARM Cortex M4 found in the Teensy 3 that does WAV playback and recording, synthesis, analysis, effects, filtering, mixing, and internal signal routing in CD quality audio.

This is an impressive bit of code, made possible only because of the ARM Cortex M4 DSP instructions found in the Teensy 3.1. It won’t run on an 8-bit micro, or even the Cortex M3-based Arduino Due. This is a project meant for the Teensy, although [Paul] has open sourced everything and put it up on Github. There’s also a neat little audio adapter board for the Teensy 3 with a microSD card holder, a 1/8″ jack, and a connector for a microphone.

In addition to audio recording and playback, there’s also a great FFT object that will split your audio spectrum into 512 bins, updated at 86Hz. If you want a sound reactive LED project, there ‘ya go. There’s also a fair bit of synthesis functions for sine, saw, triangle, square, pulse, and arbitrary waveforms, a few effects functions for chorus, flanging, envelope filters, and a GUI audio system design tool that will output code directly to the Arduino IDE for uploading to the Teensy.

It’s really an incredible amount of work, and with the number of features that went into this, we can easily see the quality of homebrew musical instruments increasing drastically over the next few months. This thing has DIY Akai MPC/Monome, psuedo-analog synth, or portable effects box written all over it.

HDDJ: Hard Drive As Rotary Input


[nvillar] wanted a relatively cheap way to make a rotary input device for audio mixing. After looking at several options including turn tables and professional audio scrubbers, they decided on the hard drive due to its size, price, and the feel of the disk. The geek factor of using a hard drive as an input device probably didn’t hurt either. They provide schematics and details on how to make it all work. There’s a video after the break of the unit sending signals to a computer. No performances though, sorry.

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Aurora Mixer Now Available

It’s been a long time coming but that highly sought after open source mixer, the aurora224 is now available for purchase on the company’s website. The aurora mixer is a fully programmable USB mixer complete with 24 back lit knobs, 2 faders, and a single crossfader.

While the instructions on how to assemble your own mixer from scratch have been available for sometime now, many wanted a kit complete with everything needed to avoid having to source the parts themselves.

The aurora mixer is available in 2 versions, a fully assembled turn key deck and a DIY kit that requires the use of a soldering iron and the ability to follow directions.

So, if you’ve wanted to build your own aurora mixer but never knew where to start, this may be your lucky day. Don’t wait too long as you have until September 1st to get your order in.

Fnordlicht: RGB Mixing LED Light

While [Will] goes and hides in his offshore datashelter, Hack-A-Day is happy to welcome back our veteran foreign correspondent [fbz]. She promises future posts will have far less ‘German by example’. -[Eliot]

The Fnordlicht is a color mixing LED platform with free hardware schematics and open source firmware initially started by [fd0]. The system is dynamically controllable (via RS-485) and can also work as a standalone with pre-loaded color mixing. I have one of these soldered up and working at home; the circuits come in a stack of three boards with an optional serial level shifter board add-on. There are project pages in German about the Fnordlicht as well, which include some photos of the first prototype. Full kits (“Fnordlicht Bausatz” means “Fnordlicht kit”) and printed circuit boards (“Fnordlicht Platinensatz ohne Bauteile” means “Fnordlicht circuit board set without parts”) can be purchased from their shop, but be sure to ask them first about shipping prices to your location. I love this project, I fire it up and stick it in a corner of my hack room to add some color-changing atmosphere.

A while ago [Eliot] covered the MoMolight, a color changing led project controlled by the colors playing on your monitor.