nils
afb07dd1c0
- Power budget (BLE-only, never WiFi TX) with concrete mA table. - Bipolar CV section: ±12V rails (boost + inverter), DAC 0-4.096V -> ±10V via difference amp with 2.048V mid-ref, per-channel gain/offset trim, OPA4192 on ±12V, bidirectional TVS. Function+polarity decides mapping (pitch stays 0..+10V standard on a bipolar output). - Concrete BOM table (part numbers, packages, alternates). - Risks updated for bipolar calibration + ±12V rail noise. - Build order updated.
pico-pi-midi (Rust)
BLE-MIDI keypad firmware for the Raspberry Pi Pico W (RP2040 + CYW43439), written in Rust using embassy, the cyw43 driver (Bluetooth), and the TrouBLE BLE host.
This is the Rust port of the original C/BTstack firmware (now kept separately as pico-pi-midi-c). It talks BLE-MIDI 1.0 to iOS / macOS Core MIDI, turning the Pimoroni Pico RGB Keypad into a 16-pad wireless MIDI controller.
What it does
- 16-pad keypad (Pimoroni RGB Keypad Base): reads buttons over I²C (GPIO expander @ 0x20) and drives APA102 RGB LEDs over SPI (CS=17, SCK=18, MOSI=19).
- BLE-MIDI 1.0 GATT server (MIDI Service
03B80E5A-…), advertised so Core MIDI discovers it as a MIDI device. Pad presses → Note On/Off over Bluetooth; incoming Note On lights the pad. - Octave display: the BOOTSEL button cycles the keypad's note offset by +12 and flashes the active octave as a digit on the 4×4 grid for 500 ms.
- Onboard LED heartbeat (driven via the CYW43 chip — the Pico W's LED is on the wireless chip, not an RP2040 pin).
- USB serial logging via
embassy-usb-logger— connect and read withscreen /dev/cu.usbmodem* 115200to see boot/advertising logs.
Roadmap
This is v1: a BLE-MIDI keypad. The goal is a flexible MIDI router — MIDI over USB, BLE, keypad, TRS, and 4 stereo CV outputs, with channels configurable at runtime via an LCD. See the architecture notes (kept in the session memory) for the plan.
Building
Requires Rust stable (≥1.93) and the thumbv6m-none-eabi target:
rustup target add thumbv6m-none-eabi
cargo build --release
The CYW43 firmware blobs (cyw43-firmware/*.bin) are committed here so no network access is needed at build time. They are redistributable under the permissive binary license in the upstream embassy cyw43-firmware directory.
Flashing
cargo build --release
elf2uf2-rs convert target/thumbv6m-none-eabi/release/rgb-keypad target/uf2/rgb-keypad.uf2
# hold BOOTSEL + plug in the Pico W, then:
picotool load target/uf2/rgb-keypad.uf2 -x
License
GPL-3.0-or-later (see LICENSE).
src/codec.rs is a Rust port of the BLE-MIDI 1.0 packet codec from
rppicomidi/pico-w-ble-midi-lib,
which is MIT-licensed; that attribution is retained in the file header. MIT is
GPL-3.0-compatible, so the repository as a whole is GPL-3.0-or-later while that
file preserves its MIT provenance.