Something else

The device does not care what is listening. Anything that can open a MIDI port gets the same three bytes. These are the routes George has used. The examples for them are not cleaned up yet; the talks they were built for link to what exists.

Plain JavaScript, no p5

Web MIDI is a browser API, not a p5 one. navigator.requestMIDIAccess() and an onmidimessage handler is the whole thing. The 2019 CSS-Tricks article walks through it: Dip Your Toes Into Hardware With WebMIDI. The p5 helper's MIDI plumbing, MidiCore inside midi-helpers.js, is plain JavaScript too and runs without p5 on the page.

Two libraries George has used for the plain-JavaScript demos: WebMidi.js, which wraps the API with named notes and events, and MIDIVal, written in TypeScript. The browser support table is at caniuse.com/midi. The shims and plugins from the 2017 talks, which stood in for browsers without Web MIDI, are not needed for Chrome, Edge or Firefox now.

Node

The demos from the 2017 talks ran Node servers next to the browser, reading the device with the midi and easymidi packages from npm. They are listed, as given, under Talks and workshops.

Python outside Processing

CPython reads MIDI with mido. Nothing here yet beyond the Python Mode helpers, which are Jython and will not import into CPython as they are.

Building the device

The other direction: a board that reads a sensor and sends the three bytes itself. That is Make your own.