metronome/pico-cp

PM_K‑1 "Kit" — CircuitPython edition (USB drive + editor)

The CircuitPython firmware for the 52Pi EP‑0172 Pico kit. Unlike the MicroPython version (../pico/main.py), this makes the Pico mount as a USB drive (CIRCUITPY) that carries the firmware and your tracks — so you can edit on the web and reprogram it without Thonny. It runs the same program‑string language as https://metronome.varasys.io.

Status: experimental, phase 1. This drives the screen/touch/joystick/buzzer and reads your grooves from programs.json. The editor's one‑click "Save to device" and USB‑MIDI audio‑to‑computer are landing in later phases. The simpler MicroPython firmware (../pico/main.py) remains the rock‑solid fallback — and the Pico can't be bricked (BOOTSEL → drag a MicroPython .uf2 back).

Install

1. Flash CircuitPython: hold BOOTSEL, plug in, and drop the CircuitPython .uf2 for your board onto the RPI‑RP2 drive (https://circuitpython.org/board/raspberry_pi_pico/ — or the Pico 2 / W build). It reboots and a CIRCUITPY drive appears.
2. Copy everything from the bundle onto CIRCUITPY (drag‑and‑drop — it's a normal drive now):
   • code.py (this firmware — runs on boot)
   • programs.json (your grooves)
   • font_s.bin, font_m.bin, font_l.bin (the anti‑aliased fonts — kept as files to save RAM)
   • editor.html (an offline copy of the web editor, so the drive carries its own programmer)
3. It starts immediately. Editing programs.json (or re‑saving it from the editor) makes CircuitPython auto‑reload with the new tracks.

Play through the computer's speakers (USB-MIDI)

The board also shows up as a USB-MIDI device and sends a note on every click (a GM drum note per lane, velocity by accent). Open the editor in Chrome/Edge, click 🎹 Device audio, grant MIDI access, then press play on the device — the editor voices the groove through its full synth, out your computer's speakers, locked to the device's clock. The button shows the connected device's name and pulses green on each note; set MUTE_BUZZER = True in code.py if you'd rather silence the on-board buzzer while doing this.

If the editor says no MIDI input is connected, copy boot.py onto CIRCUITPY too and power-cycle the Pico (boot.py only runs on a full reset). It frees a USB endpoint (drops the unused HID interface) so the MIDI port is guaranteed to appear alongside the drive.

Protect the firmware (so end users only see the editor + their tracks)

To stop someone accidentally deleting the firmware, hide it — the files keep running and "Save to device" still works, but only editor.html + programs.json show in the file browser. On the host, with the drive mounted, run the included helper (needs fatattr):

./protect-firmware.sh /media/$USER/CIRCUITPY      # hides code.py, boot.py, font_*.bin, README, itself

(Reveal again with fatattr -h <file>.) For a hard lock — nothing on the drive can be changed from the computer at all — put storage.remount("/", readonly=True) in boot.py; but then the editor's Save to device can't write either, so you'd reprogram by temporarily removing that line (or gating it behind a held button at power-on). Hiding is usually the right balance.

Controls (same as the MicroPython build)

• Touch: on‑screen ◀◀ / ▶ / ▶▶ (prev · play/stop · next) and − / TAP / +.
• Joystick: up/down = tempo, left/right = previous/next groove.
• Button A (GP15) play/stop · Button B (GP14) tap tempo.
• RGB LED flashes each beat; buzzer clicks (accent/normal/ghost).

programs.json

{ "title": "PolyMeter",
  "programs": [ { "name": "Four on the floor", "prog": "t120;kick:4;snare:4=.x.x;hatClosed:4/2" } ] }

Each prog is a program string from the web editor. Add/replace entries and save — the device reloads.

Easiest way to (re)program it: in the editor (the web app, or the editor.html on the drive), build a set list, then the set‑list ⋯ menu → 📟 Save to device → pick the CIRCUITPY drive. In Chrome/Edge it writes programs.json straight onto the drive (the Pico auto‑reloads); elsewhere it downloads the file to drag on. 📥 Load from device reads a programs.json back into a new set list.

Calibration (flip flags at the top of code.py)

• Red/blue swapped: flip MADCTL between 0x48 (default) and 0x40.
• Colours look negative: toggle INVERT_COLORS.
• Taps land wrong: set TOUCH_DEBUG = True, watch the serial output, then set TOUCH_SWAP_XY / TOUCH_INVERT_X / TOUCH_INVERT_Y.
• Joystick reversed: toggle JOY_INVERT_X / JOY_INVERT_Y.
• Computer audio: MIDI_ENABLED (default on) sends the MIDI notes; MUTE_BUZZER silences the buzzer.
• LED too bright / too dim: change LED_BRIGHTNESS (0..1, default 0.15).
• Screen tearing: the SPI panel has no tearing-effect sync; SPI_BAUD (default 62.5 MHz) is pushed fast to minimise it — lower it only if the display is unstable.
• Screen blank / garbled: the panel lot may differ; drop SPI_BAUD, and if it's a 240×320 ILI9341 instead of the 320×480 ST7796, the init/size need changing (this targets the 320×480 you have).
• RGB LED is driven by the core neopixel_write module — no library to install. If it stays dark, your CircuitPython build is unusually missing that module (everything else still works).

If code.py ever errors, CircuitPython prints the traceback on the screen and over USB serial — copy that to me and I'll fix it.

The fonts are the same baked anti‑aliased blobs as the MicroPython build (see ../pico/gen_font.py).