Logic Noise: Ping-pong Stereo, Mixers, and More

So far on Logic Noise, we’ve built up a bunch of sound-making voices and played around with sequencing them. The few times that we’ve combined voices together, we’ve done so using the simplest possible passive mixer — a bunch of resistors. And while that can work, we’ve mostly just gotten lucky. In this session, we’ll take our system’s output a little bit more seriously and build up an active mixer and simple stereo headphone driver circuit.

For this, we’ll need some kind of amplification, and our old friend, the 4069UB, will be doing all of the heavy lifting. Honestly, this week’s circuitry is just an elaboration of the buffer amplifiers and variable overdrive circuits we looked at before. To keep things interesting we’ll explore ping-pong stereo effects, and eventually (of course) put the panning under logic-level control, which is ridiculous and mostly a pretext to introduce another useful switch IC, the 4066 quad switch.

At the very end of the article is a parts list for essentially everything we’ve done so far. If you’ve been following along and just want to make a one-time order from an electronics supply house, check it out.

klangoriumIf you’re wondering why the delay in putting out this issue of Logic Noise, it’s partly because I’ve built up a PCB that incorporates essentially everything we’ve done so far into a powerhouse of a quasi-modular Logic Noise demo — The Klangorium. The idea was to take the material from each Logic Noise column so far and build out the board that makes experimenting with each one easy.

Everything’s open and documented, and it’s essentially modular so you can feel free to take as much or as little out of the project as you’d like. Maybe you’d like to hard-wire the cymbal circuit, or maybe you’d like to swap some of the parts around. Copy ours or build your own. If you do, let us know!

OK, enough intro babble, let’s dig in.

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DIY Concrete Mixing Wheelbarrow Made from Recycled Parts

[Dan] had a bunch of concrete mixing to do. Sure, it was possible to stand there and mix concrete and water in a wheelbarrow for hours and hours but that sounds like a tedious task. Instead, [Dan] looked around the shop to see if he had parts available to make a concrete mixer. As you may have guessed, he did. Instead of stopping at just a concrete mixer, he decided to make a concrete mixing wheelbarrow!

The frame is built out of plywood left over from a past canoe project. The frame holds a mixing barrel that was also hanging around the shop. From the photo, the drive system looks simple but it is not. First, the small motor pulley spins a larger pulley that is in-line with the barrel. Gearing down the drive this way increases torque available to spin the barrel, and that gear reduction is necessary to spin the heavy concrete slowly. What you can’t see is a planetary gear system that gears down the drive train again. The gears are cut out of plywood and were designed in this Gear Generator program. The sun (center) gear of the planetary setup is supported by another scavenged part, a wheel bearing from a Chevy minivan.

Now [Dan] can mix all the concrete he wants, wheel it over and dump it wherever he needs it. With the exception of the drive belt and some miscellaneous hardware, all the parts were recycled.

Digital to Analog to Digital to Analog to Digital Conversion

[Andy] had the idea of turning a mixing desk into a MIDI controller. At first glance, this idea seems extremely practical – mixers are a great way to get a lot of dials and faders in a cheap, compact, and robust enclosure. Exactly how you turn a mixer into a MIDI device is what’s important. This build might not be the most efficient, but it does have the best name ever: digital to analog to digital to analog to digital conversion.

The process starts by generating a sine wave on an Arduino with some direct digital synthesis. A 480 Hz square wave is generated on an ATTiny85. Both of these signals are then fed into a 74LS08 AND gate. According to the schematic [Andy] posted, these signals are going into two different gates, with the other input of the gate pulled high. The output of the gate is then sent through a pair of resistors and combined to the ‘audio out’ signal. [Andy] says this is ‘spine-crawling’ for people who do this professionally. If anyone knows what this part of the circuit actually does, please leave a note in the comments.

The signal from the AND gates is then fed into the mixer and sent out to the analog input of another Arduino. This Arduino converts the audio coming out of the mixer to frequencies using a Fast Hartley Transform. With a binary representation of what’s happening inside the mixer, [Andy] has something that can be converted into MIDI.

[Andy] put up a demo of this circuit working. He’s connected the MIDI out to Abelton and can modify MIDI parameters using an audio mixer. Video of that below if you’re still trying to wrap your head around this one.

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Mixer for Korg Volcas

Korg, everyone’s third or fourth favorite synth company, but one of the only ones that still in business, recently put out a new line of synths, drum machines, and groove boxes. They’re called Volcas, and they’re cheap, analog, and very cool. [Jason] has a few of these Volcas, and while he enjoys the small form factor, using an off-the-shelf mixer to dump send the audio from these machines to his computer takes up too much space. He created a passive mini mixer to replace his much larger Mackie unit.

The circuit for this tiny passive mixer is an exercise in simplicity, consisting of just a few jacks, pots, and resistors. [Jason] overbuilt this; even though the Volcas only have mono out, he wired the entire mixer up for stereo.

The enclosure – something that looks to be a standard Hammond die cast aluminum enclosure – was drilled out, and a lovely laser cut acrylic laminate placed on top. It looks great, and for anyone interested in learning soldering, you couldn’t come up with a better first project.

A mixer (re)built to travel

[Toby Cole] likes to mix tunes whenever he gets a chance. But the size of his DJ equipment made it a real bother to lug around with him. He does own a Behringer portable mixer but without cross faders it’s not really all that usable, and most of the other offerings don’t get good reviews. He ended up replacing the enclosure of a proper mixer in order to make it light and small. The growing availability of affordable laser-cut parts made this project possible.

Build Brighton, [Toby’s] local Hackerspace, has a laser cutter. So he knew that if he could figure out a smaller case design it would be a snap to get his parts made. He cracked open the heavy metal case on the KMX 100 mixer and found it had a ton of extra room inside. He designed all of the plates using a digital calipers to properly space the holes and text labels. These designs were combined with BoxMaker to produce the files the laser cutter needed. The first prototype was cut from cardboard, with the finished product cut from 3mm plywood.

Cocktail machine minces words

For those living in a magical land of candy, with orange-faced helpers to do their bidding, the ability to taste your words is nothing new. But for the rest of us, the ability to taste what you type in cocktail form is a novelty. [Morskoiboy] took some back-of-the-envelope ideas and made them into a real device that uses syringes as keys, and facilitates the injection of twenty-six different flavorings into a baseline liquid. He figures that you can make each letter as creative as you want to, like representing different alcohols with a letter (T for tequila) or matching them to colors (R for red). Check out the video after the break to see an ‘Any Word’ cocktail being mixed.

This setup is entirely mechanical, and makes us wonder if [Morskoiboy] works in the medical equipment design industry. Each letter for the keyboard is affixed to the plunger on a syringe. When depressed, they cause the liquid in an external vessel (not seen above) to travel through tubing until it fills the proper cavities on a 15-segment display to match the letter pressed. From there the additive is flushed out by the gravity-fed base liquid into the drinking glass. We can’t imagine the time that went into designing all of the plumbing!

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Convert an old busted phone into a voice-altering prank machine

phone_mixer

Have you ever wanted to be someone else, at least over the phone? Do you dream of turning the tables on telemarketers, making them hurry to get off the line instead of you? If so, [Brad] over at LucidScience has the project for you.

A bit of a prankster at heart, he walks through the conversion of a normal telephone into a Data Access Arrangement device (DAA), allowing you to interface it with either hardware or software-based audio mixers.

The process can be completed in a relatively short time period, and doesn’t require much more than an old telephone, a handful of tools, and some miscellaneous switches and jacks. He disassembled a telephone and trimmed off all of the unnecessary circuitry while retaining most of the original functionality. Line in and out jacks were then installed in place of the handset microphone and speakers, respectively. The final result is a compact box that relays altered audio from any kind of mixing device to person at the other end of the call. Since the majority of the phone remains intact, your calls still sound natural as they pass through the phone’s existing voice filter and preamp circuitry.

Once the DAA is complete, you can use any number of effects on your voice, limited only by your audio mixer. [Brad] says he has long-time friends that don’t even recognize his voice after he has run it through his effects machine, so get started on yours before April Fool’s day arrives!