metronome/pico

PM_K‑1 "Kit" — VARASYS PolyMeter firmware for the Raspberry Pi Pico

MicroPython firmware that turns a Raspberry Pi Pico on the 52Pi EP‑0172 "Pico Breadboard Kit Plus" into a touchscreen polymeter metronome. It runs the same program strings as https://metronome.varasys.io — design a groove in the web editor, copy its program string, paste it into PROGRAMS in main.py, and it plays here.

Everything is in one file: main.py (ST7796 display driver, GT911 touch, WS2812 RGB, buzzer, joystick, the polymeter engine — no external libraries).

The board (EP‑0172) — fixed pinout

Component	Pico pins
3.5″ ST7796 320×480 display	SPI0 — SCK GP2, MOSI GP3, CS GP5, DC GP6, RST GP7
GT911 capacitive touch	I2C0 — SDA GP8, SCL GP9 (addr 0x5D)
WS2812 RGB LED	GP12
Buzzer	GP13
Button A / Button B	GP15 / GP14
PSP joystick	X = ADC0/GP26, Y = ADC1/GP27

The components are wired on the board — you don't breadboard anything; just seat the Pico.

Flash it

1. MicroPython: hold BOOTSEL, plug the Pico into USB, and copy the MicroPython UF2 onto the RPI-RP2 drive that appears:
   • Pico / Pico W → https://micropython.org/download/RPI_PICO/
   • Pico 2 / Pico 2 W → https://micropython.org/download/RPI_PICO2/
2. The firmware: open main.py in Thonny (or rshell/mpremote) and save it to the Pico as main.py.
   • Thonny: open the file → File ▸ Save as… ▸ Raspberry Pi Pico → name it main.py.
   • mpremote: mpremote cp main.py :main.py
3. Reset (replug). It boots straight into the metronome.

Controls

• Touch: on‑screen << / >|| / >> (prev · play/stop · next) and − / TAP / +.
• Joystick: up/down = tempo (push far for ±5), left/right = previous/next groove.
• Button A (GP15): play / stop. Button B (GP14): tap tempo.
• RGB LED flashes each beat (amber = accent, cyan = normal, violet = ghost); the buzzer clicks with matching pitch.

Add your own grooves

Edit the PROGRAMS list near the top of main.py — each entry is ("Name", "program string"). Get program strings from the web editor's program box (e.g. v1;t120;kick:4;snare:4=.X.X;hat:4/2). Supported: tempo t<bpm>, lanes sound:grouping[/sub][=pattern][~][!], pattern chars X accent · x normal · g ghost · . - _ rest, grouped meters like 3+3+2, polymeter ~. (Per‑lane dB gain @n is parsed but ignored — the buzzer is mono.)

If something looks off — calibration

All the knobs are flags in the CONFIG block at the top of main.py:

• Colours look negative / washed out: toggle INVERT_COLORS.
• Red and blue swapped: set SWAP_RB = True.
• Taps land in the wrong place: set TOUCH_DEBUG = True, reset, watch the raw coordinates over the USB serial (Thonny shell) as you tap the corners, then set TOUCH_SWAP_XY / TOUCH_INVERT_X / TOUCH_INVERT_Y to match.
• Joystick reversed: toggle JOY_INVERT_X / JOY_INVERT_Y; widen JOY_DEADZONE if it drifts.
• Screen stays black: the backlight is hardwired on, so this usually means the SPI init didn't take — drop SPI_BAUD to 24_000_000 and retry.
• Garbled / wrong size image: your panel lot may be a 240×320 ILI9341 instead of the 320×480 ST7796. This firmware targets the ST7796 you have (you said 320×480); if a unit ever ships ILI9341, set WIDTH,HEIGHT = 240,320 and use an ILI9341 init sequence.

Notes

• Audio is a single passive buzzer, so coincident lane hits play one click at the highest priority (accent > normal > ghost); the RGB + screen still show the combined activity.
• The scheduler is non‑blocking and timed off time.ticks_us(), so tempo stays steady while the screen and inputs update.

Hardware reference: 52Pi EP‑0172 wiki · vendor code. VARASYS — Simplifying Complexity.