PM‑µ — Micro
The smallest possible polymeter unit for daily practice: one dial and a red LED, nothing to learn. Spin for tempo, press to start/stop, hold & spin to flip through grooves — that's it.
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Designed for
The practice desk. No screen to read, no menus — a single depressable scroll‑encoder does everything (spin = tempo, press = start/stop, hold + spin = switch track) and a bright 7‑segment LED shows the BPM (or the track number while you switch). It runs off any USB‑C charger, plays through a small built‑in speaker, and ships with the editor's grooves built in. Synth voices only — no analog audio path.
Bill of materials
Rough parts list — a USB‑C‑powered RP2040 practice unit. Ballpark one‑off prices (USD); cheaper at volume.
| Part | Qty | ~$ |
|---|---|---|
| Brain & display | ||
| RP2040 board, USB‑C — e.g. Waveshare RP2040‑Zero | 1 | 4 |
| 3‑digit 7‑segment LED (red) + driver — MAX7219 / shift register, or direct GPIO | 1 | 3 |
| Control | ||
| Detented push encoder (EC11) + knob — tempo / press / hold‑spin | 1 | 2 |
| Audio | ||
| MAX98357A I²S amp + 8 Ω 2 W speaker — synth click (no analog in) | 1 | 4 |
| Power & build | ||
| USB‑C bus power (on the board) + PWR LED | 1 | 1 |
| Custom PCB (or perfboard) | 1 | 4 |
| Passives, headers, wire | — | 2 |
| Small aluminium enclosure — bead‑blasted, matte‑black anodised | 1 | 8 |
| Total (one‑off) | ≈ $28 | |