ClearNote

A digital notepad built around E‑Ink, for studying without a glowing rectangle begging for attention. One device, one job: paper that remembers. It is also my research vehicle — ClearNote investigates how firmware architecture and hardware design choices affect responsiveness and power efficiency in a low-power E‑Ink system.

CoreESP32‑S3

Stack‑up4L rigid + 2L flex

Passives0402 / 0603

FirmwareFreeRTOS

FabricationPending

Sponsor slot — open

Fig. CN‑02 · Exploded assembly · ClearNote.glbScroll — the assembly opens

I — Turn 360°II — Fold on the flexIII — Extract

Loading geometry

A — E‑Ink panel

Paper, but programmable. Slow by nature; the whole design is about refusing to accept that.

B — The flex bridge

Panel and keyboard are one board. The flex is the hinge, so there is no connector to fail. I sized the bend from IPC‑2223: 50× the flex thickness, 0.45% copper strain, after reconciling three standards that disagreed by 7.5×.

C — Power

Budget targeted in weeks, not hours, and measured at bring‑up. Deterministic FreeRTOS tasks keep the radio and the panel out of each other’s way.

D — Case & hinge

Does not exist yet, and the drawing says so. Mechanical design comes after the board earns it.

The problem, stated plainly

E‑Ink is slow and the ESP32‑S3’s shared buses bottleneck easily. The whole project is about refusing to accept that: a 4‑layer rigid‑flex board drawn across seven schematic sheets (USB‑C power path, buck‑boost and LDO rails, an SGTL5000 codec, a 33‑key matrix, microSD, a TMR lid sensor) and a deterministic FreeRTOS firmware strategy, so latency is something I design, not something I get.

Where it stands, honestly

Rev B fixes what my mentor and I caught in review — a missing inductor, thin via stitching, a power-button circuit I was not proud of. A datasheet audit has caught more than twenty defects before fabrication, including a buck‑boost feedback divider that would have overvolted the 3.3 V rail. It orders after this semester’s exams; bring-up follows: power-on, E‑Ink boot, SD card, and the headphone-jack logic for audio studying.

ClearNote rev B rigid-flex board, rendered from the Altium export — Fig. CN‑01 · Rev B · rigid‑flexRendered from the Altium export

Protocols are a machine agreeing with itself. The next one had to agree with a network that was never asked. Mega‑CAN →