The Mijia MHO-C201 (also sold as  Xiaomi Miaomiaoce MMC-C201) is thermometer and hygrometer display with a segmented e-ink screen. A multimeter in con

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2024-12-14 10:30:03

The Mijia MHO-C201 (also sold as Xiaomi Miaomiaoce MMC-C201) is thermometer and hygrometer display with a segmented e-ink screen.

A multimeter in continuity mode was used to trace the connections between the stock MCU (a Holtek HT66F0182) and the display controller (a Holtek HT16E07). A schematic was created using Kicad.

To determine the purpose of each connection, a logic analyzer was used to capture the signals (see ./captures) between the MCU and display controller. The captures were compared to the HT16E07 datasheet which confirmed the display controller behaves like a HT16E07.

The MCU was then removed (using flush cutters but would have been nicer to desolder) and thin, 30-awg wires were soldered to the now-empty MCU pads. The other end of the wires connected to a NodeMCU ESP8266.

Based on observation, BUSY_N is pulled down by the display when busy, and floating when idle so the MCU pin connected to BUSY_N should have a pull-up resistor.

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