https://www.olimex.com/Products/ARM/ST/STM32-H407/open-source-hardware https://www.olimex.com/Products/ARM/ST/STM32-H407/open-sourc... The alternative that I w

https://www.olimex.com/Products/ARM/ST/STM32-H407/open-source-hardware https://www.olimex.com/Products/ARM/ST/STM32-H407/open-sourc... The alternative that I would suggest you consider is I/O expander chips so you can use any mcu with a handful of pins. MCP23 seems popular, see e.g. https://www.abelectronics.co.uk/p/54/io-pi-plus https://www.abelectronics.co.uk/p/54/io-pi-plus https://eu.mouser.com/Semiconductors/Interface-ICs/Interface-I-O-Expanders/_/N-aq4ec https://eu.mouser.com/Semiconductors/Interface-ICs/Interface...