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# PM_P‑1 Practice

A long, narrow inline practice bar — patch it into your signal, drive everything from one clickable thumb‑roller, and read tempo and track names off an amber 14‑segment display.

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## What it is

Hardware Inline practice bar~$35 one‑off

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 (roll = tempo, press = start/stop, hold + roll = switch track), and an amber 14‑segment display shows tempo and track names.

The click is summed into your signal in the analog domain (plus a small monitor speaker). Powered over USB‑C — a wall adapter for a permanent practice‑space install, or a pocket power bank when you're mobile (no internal battery to wear out); ships with the editor's grooves built in.

Dimensions & layout — ≈ 6.3 × 1.4 × 1.0 in (160 × 36 × 26 mm), an extruded bar

↕ 1.4 in
(36 mm)
Front (top face)
14‑seg display
thumb‑roller
↔ 6.3 in (160 mm) long
Left end
TRS In (instrument)
Right end
USB‑C · TRS Out
↕ ends ≈ 1.0 in (26 mm) deep
Spec & bill of materials

Rough parts list — a USB‑C‑powered RP2040 inline bar 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 — wall adapter or power bank; also carries config | 1 | 1
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) |  | ≈ $35

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