RP2040 MIDI Tracker

A simple MIDI step sequencer using a Raspberry Pi Pico (or Pico W), an OLED display, a rotary encoder, and an 8x8 NeoPixel matrix.

Software Requirements

• Board Core: This project uses the Raspberry Pi Pico/RP2040 core by Earle F. Philhower, III.
  1. Add this URL to your Additional Boards Manager URLs in Preferences:
     https://github.com/earlephilhower/arduino-pico/releases/download/global/package_rp2040_index.json
  2. Go to Tools > Board > Boards Manager, search for "pico", and install Raspberry Pi Pico/RP2040.
  3. Select Raspberry Pi Pico (or Pico W) from the board menu.
• Libraries: Install via Library Manager:
  • Adafruit GFX Library, Adafruit SSD1306, Adafruit NeoPixel

Connections & Wiring

Properly wiring the components is crucial, especially for power.

Power

The project is best powered in two parts:

1. Raspberry Pi Pico W: Power the Pico via its Micro-USB port from a computer or a USB wall adapter.
2. NeoPixel 8x8 Matrix: This component is power-hungry and requires a separate, external 5V power supply. A power supply capable of delivering at least 2A is recommended.

Warning

: Do NOT power the NeoPixel matrix from the Pico's 3.3V or VBUS pins. VBUS is connected directly to the USB port, which is typically limited to 500mA. The matrix can draw over 2A, which could overload and damage your host computer's USB port.

Component Wiring

Make sure to establish a common ground by connecting the ground from your external 5V power supply to one of the GND pins on the Pico.

Component	Pico Pin	Description
SSD1306 OLED
VCC	3V3 (OUT) (Pin 36)	3.3V Power
GND	GND (Pin 38)	Ground
SDA	GP4 (Pin 6)	I2C Data
SCL	GP5 (Pin 7)	I2C Clock
Rotary Encoder
+ (VCC)	3V3 (OUT) (Pin 36)	3.3V Power
GND	GND (Pin 33)	Ground
CLK	GP12 (Pin 16)	Encoder Clock
DT	GP13 (Pin 17)	Encoder Data
SW	GP14 (Pin 19)	Encoder Switch
WS2812B 8x8 Matrix
DIN (Data In)	GP16 (Pin 21)	NeoPixel Data
5V / VCC	External 5V Supply +	External 5V Power
GND	External 5V Supply -	External Power Ground
	GND (Pin 18)	Common Ground with Pico
MIDI DIN (Serial)
TX (MIDI OUT)	GP0 (Pin 1)	To DIN Pin 5 (via 220Ω)

MIDI Hardware Note:

• MIDI OUT: Connect GP0 to DIN Pin 5 via a 220Ω resistor. Connect DIN Pin 4 to +5V via a 220Ω resistor. Connect DIN Pin 2 to GND.

Once everything is wired up, you can upload the code and your tracker should be ready to go!

Making it Portable

To run this project without being tethered to a computer, you'll need a portable power source that can supply both the Pico and the power-hungry NeoPixel matrix.

Option 1: Using a USB Power Bank (Easiest)

This is the simplest and safest method.

• What you'll need: A standard USB power bank with at least two outputs, capable of supplying a total of 2.5A or more.
• Pico Power: Connect a standard Micro-USB cable from one of the power bank's outputs to the Pico's USB port.
• Matrix Power: Use a second USB cable to power the NeoPixel matrix. You will likely need to cut the end of a USB cable and connect the 5V (usually red) and GND (usually black) wires to the matrix's power input.
• Common Ground: The common ground is handled automatically through the USB connections to the same power bank. However, it is still best practice to run a dedicated wire from the matrix's GND to one of the Pico's GND pins.

Option 2: LiPo Battery with a 5V Booster (More Compact)

For a more integrated build that can fit inside an enclosure, you can use a Lithium Polymer (LiPo) battery and a voltage-boosting board.

• What you'll need:
  • A single-cell (3.7V) LiPo battery.
  • A 5V booster board, such as the Adafruit PowerBoost 1000C. These boards can charge the LiPo battery and provide a stable 5V output.

LIPO BATTERY WARNING: LiPo batteries are powerful but require careful handling.

• Never use a LiPo battery without a dedicated protection circuit, which prevents over-charge, over-discharge, and short-circuits. Boards like the PowerBoost series have this built-in.
• Do not puncture, bend, or short-circuit a LiPo battery.
• Always charge them with a proper LiPo charger.

• Wiring:
  1. Connect the LiPo battery to the battery input terminals on the PowerBoost board.
  2. Connect the PowerBoost's 5V output to the NeoPixel Matrix's 5V/VCC input.
  3. Connect the PowerBoost's 5V output to the Pico's VBUS pin (Pin 40). This will power the Pico.
  4. Connect the PowerBoost's GND to both the NeoPixel Matrix's GND and one of the Pico's GND pins. This creates the essential common ground.

Usage

• Navigation: Rotate the encoder to move between steps.
• Edit Mode: Short press the encoder button to toggle Edit Mode. Rotate to change the note.
• Playback: Long press the encoder button (> 0.6s) to Start/Stop playback.
• MIDI: The device sends MIDI notes via the Hardware Serial (DIN) port on GP0.