Matrix Hexpansion: Subway

Status: this is a concept; the schematics and layout are done but it has not yet been produced, assembled, and tested.

A daughter board for the Matrix Hexpansion containing up to 72 LEDs to be driven by a CH32V003 processor.

Optionally, the processor (and power supply) can be fitted to the back of this board for use without the adapter and badge. There are test pads for GND, SCL, SDA, and 3V3 so it could be controlled over I2C from a cheap ESP32 module or some such (perhaps it could show real-time status if SPT provided an API for train running information).