This boards should provide SPI I/O expansion based on the MCP23S17.
The boards should be stackable since the layout of the SPI connector is the same for all boards.
The Digital Input and the Digital Relay Output are galvanically isolated.
Prototype has been tested with a Teensy 3.2 but any other SPI capable processor should work.
All In and Out power supply must be provided by external power suppl...