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A project log for DrumKid: aleatoric drum machine

A lo-fi digital drum machine which uses randomness to create unpredictable beats. Runs on Arduino, with audio provided by the Mozzi library.

Matt BradshawMatt Bradshaw 05/06/2019 at 17:020 Comments

I'm reaching a tricky point in the development process. Skills-wise, I'm someone with a fairly good grasp of coding, but only a patchy (if gradually improving) grasp of electronics. This means that, while I'm pretty capable of solving weird software problems, things like grounding issues or noisy power supplies send me into a cold sweat.

I've never really had to worry about problems like this before this project, because I could always avoid them. My previous musical instrument builds were one-offs, and I could choose a platform that didn't require me to do much "real" electronics. For instance, a lot of my recent instruments have used a Teensy 3.X (£20+) with a Teensy audio adaptor (£13), which instantly gives lovely clean audio and plenty of processing power. I also power most of my projects with a USB power supply rather than batteries, which simplifies things.

DrumKid, though, is my first attempt at a real-world "product", and developing it is a very different process. I've used a £2 Atmega328 chip to try and keep costs down, but doing so is causing me all sorts of problems that I wouldn't hit with a Teensy. I can't just put £33 of extra components in there, though, because I'll then have to put the price up by that amount. Then again, with the better components, it's probably a better instrument and probably worth more, so maybe that's okay. And by using a Teensy instead of an Atmega328, I would probably save myself a bunch of time and money on the development process.

The problem is, I have no idea how to do the calculations that would tell me whether my current strategy of trying to be as cheap as possible is the right one. I've also sunk a lot of time into this design, and I don't want to change tack, which I know is bad logic.

Anyway, my current problem is this: DrumKid works nicely when using a proper Arduino and a nice clean 5V power supply for testing, although the audio is a little quiet. I can boost the audio with an LM386 amplifier, but then it becomes really important to have a clean power supply. The finished product will be powered by batteries, run through a boost converter to get to 5V, and it's quite hard (but possible) to get that power supply clean enough for good audio. Basically, everything should work fine together, but when I try all the elements together on a breadboard, I get horrendous, unacceptable amounts of noise. Now, I know that a solderless breadboard is probably not the best way to test a fairly sensitive circuit like this, but I don't know what else to try. Is it worth spending time making a stripboard version? Do I have to resort to doing another iteration of the PCB, knowing that it probably won't be the final one, and might not even work?

I think I'm starting to see the difference between being a "hacker" and a "designer"...

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