This complete Arduino C++ sketch turns any RP2040 board (such as the Raspberry
Pi Pico, RP2040-Zero, or QT Py RP2040) into a native USB-MIDI device. It
receives incoming NoteOn, NoteOff, and ControlChange (CC) commands to light up
addressable LED strips with real-time color and brightness control.

Required Libraries (Install via Arduino Library Manager)

Adafruit_TinyUSB_Arduino (Enables native class-compliant USB-MIDI on RP2040)

MIDI Library by FranC'ois Best (Provides the MIDI state machine parser)

Adafruit_NeoPixel (Drives WS2812B or SK6812 strips via hardware PIO)

Arduino IDE Configuration

Board: Raspberry Pi Pico or Generic RP2040 (using the Raspberry Pi Pico/RP2040
core by Earle F. Philhower).

USB Stack: Go to Tools > USB Stack and select Adafruit TinyUSB.

Arduino Sketch (rp2040_midi_leds.ino)

#include <Adafruit_TinyUSB.h> #include <MIDI.h> #include <Adafruit_NeoPixel.h>
// =========================================================================
// HARDWARE CONFIGURATION // ==================================================
======================= #define LED_PIN 2 // GPIO pin connected to the LED
data line #define NUM_LEDS 144 // Number of LEDs on your strip #define
START_MIDI_NOTE 36 // First MIDI note mapped to LED index 0 (36 = C2) //
Choose LED type: // NEO_GRB + NEO_KHZ800 -> 3-channel WS2812B / WS2811 //
NEO_GRBW + NEO_KHZ800 -> 4-channel SK6812 RGBW (Recommended for dimming)
#define LED_TYPE (NEO_GRB + NEO_KHZ800) // ====================================
===================================== // GLOBAL OBJECTS & VARIABLES //
========================================================================= //
Initialize TinyUSB MIDI interface Adafruit_USBD_MIDI usb_midi;
MIDI_CREATE_INSTANCE(Adafruit_USBD_MIDI, usb_midi, MIDI); // Initialize
NeoPixel strip Adafruit_NeoPixel strip(NUM_LEDS, LED_PIN, LED_TYPE); //
Control states uint8_t masterBrightness = 128; // Default global brightness (0
- 255) uint16_t currentHueOffset = 0; // Color wheel shift via CC 12 (0 -
65535) // =====================================================================
==== // MIDI CALLBACK HANDLERS // =============================================
============================ // Called when a MIDI Note On message is received
void handleNoteOn(byte channel, byte note, byte velocity) { // MIDI standard:
Note On with velocity 0 is functionally a Note Off if (velocity == 0) {
handleNoteOff(channel, note, velocity); return; } int ledIndex = note -
START_MIDI_NOTE; // Ensure the note falls within the physical LED bounds if
(ledIndex >= 0 && ledIndex < NUM_LEDS) { // Generate dynamic HSV color: // Hue
spreads across the spectrum per note, shifted by CC 12 uint16_t hue =
(currentHueOffset + (note * 500)) % 65536; uint8_t sat = 255; // Full
saturation uint8_t val = map(velocity, 1, 127, 40, 255); // Scale brightness
to velocity // Convert HSV to
 32-bit RGB color value uint32_t rgbColor = strip.ColorHSV(hue, sat, val);
strip.setPixelColor(ledIndex, rgbColor); strip.show(); } } // Called when a
MIDI Note Off message is received void handleNoteOff(byte channel, byte note,
byte velocity) { int ledIndex = note - START_MIDI_NOTE; if (ledIndex >= 0 &&
ledIndex < NUM_LEDS) { strip.setPixelColor(ledIndex, 0); // Turn off specific
LED strip.show(); } } // Called when a Control Change (CC) message is received
void handleControlChange(byte channel, byte number, byte value) { switch
(number) { case 7: // CC 7: Master Volume / Brightness (0 - 127)
masterBrightness = map(value, 0, 127, 0, 255); strip.setBrightness(masterBright
ness); strip.show(); break; case 12: // CC 12: Global Color/Hue Offset (0 -
127) currentHueOffset = map(value, 0, 127, 0, 65535); break; case 120: // CC
120: All Sound Off case 123: // CC 123: All Notes Off strip.clear();
strip.show(); break; default: break; } } // ===================================
====================================== // INITIALIZATION & MAIN LOOP //
========================================================================= void
setup() { // Initialize USB descriptor names USBDevice.setManufacturerDescripto
r("DIY Instruments"); USBDevice.setProductDescriptor("RP2040 LED Visualizer");
// Start MIDI processing MIDI.begin(MIDI_CHANNEL_OMNI); MIDI.turnThruOff(); //
Prevent mirroring received messages back out // Register callback functions
MIDI.setHandleNoteOn(handleNoteOn); MIDI.setHandleNoteOff(handleNoteOff);
MIDI.setHandleControlChange(handleControlChange); // Initialize NeoPixel strip
strip.begin(); strip.setBrightness(masterBrightness); strip.clear();
strip.show(); // Wait until USB stack is mounted by the host PC while
(!TinyUSBDevice.mounted()) { delay(10); } } void loop() { // Continuously
parse incoming USB-MIDI packets MIDI.read(); } 

How Control Commands Map

Note On / Velocity: Striking a key lights the corresponding LED (N -
\text{StartNote}). Striking harder increases the individual LED's brightness
(V = 1127).

CC 7 (Master Brightness): Controls global strip dimming from 0 to 255 without
distorting current note colors.

CC 12 (Hue Offset): Shifts the entire color spectrum across the strip,
allowing you to switch palettes on the fly.

CC 123 (All Notes Off): Instantly clears all active LEDs.

For a demonstration of building a physical setup around an RP2040 board and
NeoPixel strip, see this MIDI NeoPixel Visualizer with RP2040. This video
provides a helpful visual reference for how an RP2040 microcontroller drives
NeoPixel strips directly in response to incoming MIDI note triggers. YouTube
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