PM‑µ — Micro
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.
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Designed for
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 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 |
| 4‑char 14‑segment alphanumeric LED + I²C driver — amber; HT16K33. Shows BPM & track names | 1 | 4 |
| Control | ||
| 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 — 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).