I set out to build a synth. I ended up building a platform.

Rodeo started around April 2026 with a simple, slightly selfish question: could I build a real synth?

Not a toy, not a mini synth that fits in a pocket. A full-size desktop instrument with proper knobs spaced far enough apart that you can actually play it.

Where I was coming from

This wasn’t my first time with electronics. Last year I built a small five-module Eurorack system: VCO, VCA, filter, envelope and sequencer. I’d also designed a few boards of my own, including a Pomodoro timer, and I’d been deep in another project, Buddy System, which had just reached a working prototype.

Rodeo began as a break from Buddy System. I wanted to work on something different and finally build an instrument. It didn’t stay a side project for long. It became the main thing.

I never seriously considered buying a synth instead. Buying one was never the point. This was a DIY project, and I was doing it because building things is fun.

The problem with “full-size”

As soon as you say “full-size desktop synth”, you run into a cost problem. A board big enough to hold every knob and jack of a real instrument is an expensive board. Most of that area is just there to keep the controls apart, and you pay for every square centimetre of it.

The usual answer is panel-mounted controls: a small main board, with pots, encoders and buttons mounted to the enclosure and wired back to it. That works, but it means a lot of soldering and point-to-point wiring, and honestly I don’t enjoy that part. Hand-wiring twenty-odd pots is tedious, and every joint is another place for a fault to hide.

So the first version of the idea was small. Instead of wiring every control by hand, each control would sit on its own little satellite board, and every satellite would plug into a central hub with a standard JST cable. No soldering at the panel. Just plug them in.

The moment it turned into something else

I knew from the start that the Daisy Seed (more on that in the next log) couldn’t read as many knobs as I wanted on its own. So I started designing a carrier board around it with two extra ADC chips. Then, because they were basically free to add, I broke out a bank of digital signals too. Then expansion headers.

About halfway through that design I realised what I actually had. It wasn’t a board for my synth. It was a board for any synth, or a pedal, or anything else that takes audio in, turns some knobs and sends audio out. The hub didn’t care what was plugged into it. The satellites didn’t care which instrument they ended up in.

That’s when “one synth” became a motherboard, a family of plug-in control boards, and instruments built by combining them. The synth I set out to build became the first instance, called rodeo-001, rather than the whole project.

What Rodeo is

The one-sentence pitch hasn’t changed since then:

Rodeo is a flexible, plug-and-play modular platform for building digital audio devices.

It’s for the synth DIY community, for pedal builders, and for anyone who wants to experiment with digital audio. I especially want it to work for people who aren’t comfortable with a soldering iron yet, or who are new to electronics. If you can plug in a cable, you should be able to build an instrument.

The rules I set myself

I set myself one main rule early on, and everything else follows from it: the user experience matters. Rodeo should be:

• Intuitive. You shouldn’t need the manual to get a sound out of it.
• Predictable. The same control does the same thing, every time.
• Well-documented. If something isn’t obvious, it’s written down.

Each instrument also gets its own design rules on top of that. rodeo-001’s rule, for example, was no hidden controls: every parameter has its own knob. But those three are the platform’s rules.

Oh, and the name

I was building a portfolio site and needed a cheap domain. derek.rodeo was the cheapest one I could find. I’ve been calling things Rodeo ever since.

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Next: choosing the brain. Why the Daisy Seed, and why I started on one version of it and switched to another partway through.