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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Logic Noise: Sequencing in Silicon

In this session of Logic Noise, we’ll combine a bunch of the modules we’ve made so far into an autonomous machine noise box. OK, at least we’ll start to sequence some of these sounds.

A sequencer is at the heart of any drum box and the centerpiece of any “serious” modular synthesizer. Why? Because you just can’t tweak all those knobs and play notes and dance around at the same time. Or at least we can’t. So you gotta automate. Previously we did it with switches. This time we do it with logic pulses.

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Logic Noise: Sawing Away with Analog Waveforms

Today we’ll take a journey into less noisy noise, and leave behind the comfortable digital world that we’ve been living in. The payoff? Smoother sounds, because today we start our trip into analog.

If you remember back to our first session when I was explaining how the basic oscillator loads and unloads a capacitor, triggering the output high or low when it crosses two different thresholds. At the time, we pointed out that there was a triangle waveform being generated, but that you’d have a hard time amplifying it without buffering. Today we buffer, and get that triangle wave out to our amplifiers.


But as long as we’re amplifying, we might as well overdrive the amps and head off to the land of distortion. We’ll do just that and build up a triangle-wave oscillator that can morph into a square wave, passing through a rounded-over kinda square wave along the way. The triangle sounds nice and mellow, and the square wave sounds bright and noisy. (You should be used to them by now…) And we get everything in between.

And while we’re at it, we might as well turn the triangle wave into a sawtooth for that nice buzzy-bass sound. Then we can turn the fat sawtooth into a much brighter sounding pulse wave, a near cousin of the square wave above.

What’s making all this work for us? Some dead-boring amplification with negative feedback, and the (mis-)use of a logic chip to get it. After the break I’ll introduce our Chip of the Day: the 4069UB.

If you somehow missed them, here are the first three installments of Logic Noise:

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Logic Noise: The Switching Sequencer Has the Beat

Logic Noise is all about using logic circuits to make sounds. Preferably sound that will be enjoyable to hear and useful for making music. This week, we’ll be scratching the surface of one of my favorite chips to use and abuse for, well, nearly anything: the 4051 8-way analog switch. As the name suggests, you can hook up eight inputs and select one from among them to be connected up to the output. (Alternatively, you can send a single input to one of eight destinations, but we won’t be doing that here.)

Why is this cool? Well, imagine that you wanted to make our oscillator play eight notes. If you worked through our first installment, you built an abrasive-sounding but versatile oscillator. I had you tapping manually on eight different resistors or turning a potentiometer to eight different positions. This week, we’ll be letting the 4051 take over some of the controls, leaving us to do the more advanced knob twiddling.

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Logic Noise: 8-bits of Glorious Sounds

Logic Noise is all about using analog circuits to make sounds. Preferably sound that will be enjoyable to hear and useful for making music. Now, the difference between music, sound, and noise is certainly in the ear of the behearer, but you must admit that last installment’s simple square wave lacked a little something. (Although the sync oscillator circuit extension was kinda cool.)

This week, we’ll take our single wimpy square-wave oscillator and beef it up by adding a bunch of sub-octaves to the mix. And we’ll do it using a chip that’ll be really useful for us in the future as well: the 4040 binary counter chip.

Counters (binary or decimal) are going to be fertile ground for more musical noise experiments. Why so? Because octaves are just doublings or halvings of frequencies, and because a lot of rhythmic patterns have factors of two underlying them.  Just think about the most basic drum pattern you know: bass drum on the one, snare on one and three, and hi-hats on one, two, three, and four. Each different instrument fires off twice as frequently as the one before it.

But for now, enough blabber. We’ve got an oscillator to build.

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Clocked 8-Bit Random Pattern Generator For a CMOS Synth

A random noise generator is pretty handy when working with music, and building one using a micro-controller can be pretty trivial. So it’s nice when someone comes along and builds it from a few analog and digital parts. [acidbourbon] built his Clocked 8-BIT Random Pattern Generator for  CMOS Synth  inspired and motivated by the recent article Logic Noise: Sweet, Sweet Oscillator Sounds by [Elliot Williams]. It’s 8-bit output can be used as a random sequencer for DIY CMOS synths.
This pattern generator is suited to to be used in combination with a 4051 8-channel analog multiplexer. But it sounds quite interesting on it’s own (best enjoyed in stereo, check out the video after the break). After building some CMOS synth circuits, [acidbourbon] moved on to make some sequencers and multiplexers which then let him to devise this random pattern generator which could be gated using a clock signal.

The basic principle is straight forward – generate noise, amplify it, apply a clock to get the gated noise output. His design choices for the various sections are well explained, based on constraints that he had to work with. Everything needs to work at 5V, but his noise generator circuit requires 12V to work. He choose to use a charge pump to generate -5V, resulting in a 10V supply, which was barely enough, but worked. A boost regulator might probably have served better to generate 12V, but maybe he already had the ICL7660 charge pump IC lying around in his parts bin. The rest of the circuit uses standard CMOS/TTL devices, and [acidbourbon] provides all of the design files for what looks like a neat, single sided PCB that can easily be made using the toner-transfer method.

Video below.

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Hacklet #8: The Animals


This week on the Hacklet we’re looking at Hackaday.io projects that are all about animals! Hackers and makers are well-known animal lovers, in fact many a hacker can be found with a pet curled up at their feet, or on their keyboard!

catWater[Brian’s] cat Roger loves drinking from the bathtub faucet. Unfortunately Roger hasn’t learned how to operate the faucet himself, so it gets left on quite a bit. To keep Roger happy while saving water, [Brian] created the Snooty Cat Waterer. Cat’s still don’t have thumbs, so [Brian] turned to capacitive sensing in the form of a Microchip MTCH10 capacitive proximity sensor chip. Coupled with a home etched PC board, the waterer can detect a cat at 3 inches. A valve and water feed teed off the toilet provide the flow. The project is moving along well, though Roger has been slow to warm up to this new water source.


catWater2[Jsc] has the opposite problem. His cat has decided that bathtubs are the perfect litter boxes. [Jsc] is taking aim at this little problem with his Cat Dissuader. After a servo controlled squirt bottle proved too anemic for his needs, [Jsc] turned to the Super Soaker Hydrostorm. These electric water guns can be had for as little as $16 on sale. [JSC] didn’t want to permanently modify the gun, so he 3D printed a switchable battery pack.The replacement pack is actually powered by a simple wall wart. Power to the gun is controlled by an Arduino, which senses his cat with a passive infrared sensor. Since the dissuader was installed, [Jsc’s] cat has been a model citizen!


doggieBowlCat’s don’t get all the love though, plenty of engineers and hackers have dogs around the house. [Colin] loves his dog, but he and his family were forgetting to feed it. He created Feed the Dog to help the household keep its four-legged member from going hungry. [Colin] tried a microcontroller, but eventually settled on implementing the circuit with old-fashioned 4000 series CMOS logic chips. He used a 4060 (14-stage ripple counter w/ internal oscillator) as an 8 hour timer, and 4013 dual flip-flop. Operation of Feed the Dog is as simple as wagging your tail. Once the dog is feed, the human presses a button. A green “Just fed” LED will glow for 30 minutes, then go dark. After about 6 hours, a red LED turns on. After 8 hours, the red LED starts blinking, letting everyone know that it’s time to feed the dog.



[Steve] has outdoor pets. Chooks to be exact, or chickens for the non Australians out there. He loves watching his birds, especially Darth Vader, who is practicing to become a rooster. To keep track of the birds, he’s created What the Chook?, a sensor suite for the hen-house. He’s using a GCDuiNode with a number of sensors. Temperature, humidity, even a methane detector for when the bedding needs to be replaced. An OV528 JPEG camera allows [Steve] to get pictures of his flock. The entire project connects via WiFi. Steve hopes to power it from a couple of AA batteries. [Steve] also entered What the Chook? in The Hackaday Prize. If he wins, this will be the first case of flightless birds sending a human to space!



Hey – Did you know that Hackaday is building a Hackerspace in Pasadena California? We’re rounding up the local community while our space is being built out. Join us at a Happy Hour Show & Tell Meetup Event hosted by our own [Jasmine Brackett] August 18th! It’s an informal show and tell, so you don’t have to bring a hack to attend. If you’re local to Pasadena, come on down and say hello!