Reverse-Engineering the LCD Display Interface of the Nest 2nd Gen Thermostat

I reverse-engineered the Nest 2nd‑gen thermostat’s circular 320×320 LCD (TM025ZDZ01), built a 41‑pin 0.3 mm FPC breakout, and drove it over 3‑wire 9‑bit SPI with an ESP32‑C6 using Toit—covering the initialization sequence, partial‑window writes, SPI performance limits, and an MT3608 backlight boost. This work feeds into Sett, an open‑source, enclosure‑compatible replacement that reuses the Nest…