Build a hardware focus timer with firmware, app, PCB and enclosure

u/RamonvanDijk wanted to see how Claude Code copes when the output is a physical object rather than software. Over about a month it built every part of Grained, a digital hourglass for focus blocks: MicroPython firmware for an ESP32-C3 with an accelerometer, OLED, BLE and NFC stickers as an unlock key; an Expo and React Native iPhone app that uses Screen Time APIs to block apps per phase and talks to the device over BLE; a 4-layer board with 211 LEDs laid out in KiCad; an enclosure modelled in Blender for 3D printing; and a waitlist site. It also edited the launch video through a Blender MCP, wrote the voice-over script and generated the voice with the ElevenLabs API.

The breadboard prototype works end to end with the real phone app. The v4 board passed its design checks and a review by a second model, but has not been ordered. Real hardware exposed bugs no test caught, such as BLE advertising quietly stopping after a while. Pick-and-place rotations from KiCad did not match JLCPCB's convention, and neither the poster nor Claude noticed until the preview was checked by hand. The poster still watched every video render, since the agent cannot judge whether a cut feels right.

With hardware the feedback loop runs through the person, so most of the effort went into shortening it with simulators, on-board logs and a test script per hardware phase. Files that look correct can still be wrong for the fab house. Left to itself the agent picked a generic look, so the poster now hands it a design system and strict rules. Writing down decisions helped more than prompt tricks.