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.
+ +A long, narrow practice bar you patch into your signal: instrument in one end, amp or + headphones out the other, the click mixed in. One clickable thumb‑roller does everything, an amber + 14‑segment display shows tempo and track names, and it runs off USB‑C or 2×AA.
Live widget (embedded). Open the full Micro page ↗ · embed this
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.
+Practising plugged in — at the desk or on the go. It sits inline in your signal chain: a 1/4″ TRS input on + one end, USB‑C and a 1/4″ TRS output on the other, with the metronome click summed into your signal in the + analog domain (and a small monitor speaker). No menus — a single clickable thumb‑roller does it all + (roll = tempo, press = start/stop, hold + roll = switch track), and the amber 14‑segment display shows the + BPM or the track name. Powered from USB‑C or 2×AA for portability; ships with the editor's grooves built in.
Bill of materials
-Rough parts list — a USB‑C‑powered RP2040 practice unit. Ballpark one‑off prices (USD); cheaper at volume.
+Rough parts list — a portable RP2040 inline bar (USB‑C or 2×AA) with analog click injection. + 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 |
| 4‑char 14‑segment alphanumeric LED + I²C driver — amber; HT16K33. Shows BPM & track names | 1 | 4 |
| 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 |
| Clickable thumb‑roller — EC11 encoder + roller wheel · roll / press / hold‑roll | 1 | 2 |
| Audio — analog click injection | ||
| PCM5102A I²S DAC — line‑level click | 1 | 3 |
| Dual op‑amp, NE5532 / OPA2134 — hi‑Z instrument buffer + summing mixer | 1 | 1 |
| PAM8302A mono Class‑D + 8 Ω speaker — monitor | 1 | 4 |
| Connectors & power | ||
| 1/4″ jack — Inst In (TS) · Out (TRS) | 2 | 2 |
| USB‑C bus power (5 V) + PWR LED — also carries config | 1 | 1 |
| 2×AA holder + boost/management + battery gauge — AA → 3.3/5 V for portable use | 1 | 3 |
| Build | ||
| Custom PCB (or perfboard) | 1 | 4 |
| Passives, headers, wire | — | 2 |
| Small aluminium enclosure — bead‑blasted, matte‑black anodised | 1 | 8 |
| Total (one‑off) | ≈ $28 | |
| Passives, headers, wire — R/C for the analog stage + decoupling | — | 2 |
| Extruded aluminium bar enclosure + end caps — bead‑blasted, matte‑black anodised | 1 | 8 |
| Total (one‑off) | ≈ $38 | |
Like the Stage, the click is summed in the analog domain: a high‑impedance + buffer of the 1/4″ instrument input is mixed with the DAC's click and sent to the 1/4″ output and the monitor + amp — your instrument is never re‑digitised (no added latency).