echoPi build log #1 — the detent: a steel ball, two springs, a 3.33 mm pitch
What it is. A pocket slider. Every push, in any direction, plays the next note of a preset song. The song is the instrument; you just keep pushing.
Where it stands. A closed-source consumer product, in development. Not for sale yet.
This log: how one "click" is made
Each click is a 3 mm steel ball, pushed by two small springs (about 1 N each), dropping into a cone-shaped pit in the sliding plate. The pits are 2.59 mm across, 45° cones, 0.8 mm deep, and sit 3.33 mm apart. That pitch is fixed: if the travel gets longer, you get more clicks, not wider ones.
Section through the ball centre: the plate's row of 45° pits, the 3 mm ball, its cup and the two springs. Housing material and outer dimensions are still being decided, so they are not shown.
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And the board
Functional zone plan, layout in progress.
Follow along / get a note when it launches: https://echopi.ai/?utm_source=devlog
Correction, 7 Nov 2026: an earlier version of this log said a 4 mm ball and 3.0 mm wide, 1.0 mm deep pits. The design uses a 3 mm ball and 2.59 mm wide, 0.8 mm deep pits; the drawing has been updated.
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