Project Logbook
A running record of design decisions, builds and testing, organized by stage.
Started sketching layouts for a six-dial split-flap display. Settled on a 4-digit time readout plus a dedicated two-character AM/PM pair, rather than folding AM/PM into a seventh dial. Matte black housing with exposed side panels to show the mechanism was the early front-runner for the case design.
Locked in the final dial arrangement and overall footprint (300 x 150 x 80mm). Each dial will use its own stepper rather than a shared cam-driven mechanism, trading some mechanical simplicity for independent control and easier debugging later on.
Printed the first single-dial prototype to test flap tolerances and flip motion. The flap catch needed a 0.3mm clearance increase to stop binding at the top of the rotation.
Adjusted the gear ratio between the stepper and dial shaft to smooth out the flip motion and cut down on audible motor whine. This slowed the flip slightly but made the click noticeably more satisfying, which felt like the right trade-off.
Got all six stepper drivers talking to the STM32L476 over a shared SPI bus with individual chip-select lines. Current draw at idle was higher than expected, so added per-driver current scaling once a dial reaches its target position.
Wired up the DS3231 RTC module and confirmed the clock now survives a power cycle without losing time. Drift over a two-week test was under 5 seconds, comfortably within the ±10s/month target.
All six dials assembled into the case for the first time. First power-on had two dials flipping out of sync due to a firmware indexing bug, fixed by resetting each dial's home position individually on boot rather than assuming a shared zero point.