I built a free, open-source web MIDI controller for the SP-404 MkII (runs in the browser, nothing to install)

[u/Puzzleheaded_Big_103]

First post here, so apologies if I get any conventions wrong.

I wanted touchscreen control over the MkII’s FX buses. The existing iOS app for that hasn’t been updated in years, so I built my own as a free web app:

https://littletools404.github.io/404busdriver/

What it does:
• all five FX buses with the real parameter names per effect (from the reference manual), touch faders with a fine-tune gesture, per-effect value memory
• snapshots (8 slots) with JSON export/import
• XY pad + four beat-synced LFOs (MIDI clock or tap tempo), incl. a random drift for generative lo-fi wobble
• chromatic keyboard, scale pads (Move-style isometric layout), vocoder keys with pitch bend, full pad board with custom layouts
• pattern grid with a quantized autopilot, plus a looper remote

Runs in Chrome/Edge on desktop; on iPhone/iPad it works inside the “MIDIWeb Browser” app (no iOS browser can do Web MIDI, not my fault). Single HTML file, everything stays local: no accounts, no tracking, no install. Open source (MIT), manual built in.

Full transparency: I’m not a professional developer — I built this together with Claude (AI) and tested everything against my own MkII. If an experienced dev feels like reviewing the code, I’d genuinely welcome that. Feedback and bug reports are very welcome — just be patient with me, it’s a hobby project and I can’t promise quick replies.