Erik,

I indeed don't bring the PCF8574 pins to the outside. Taking into account a previous recommendation from you, this wouldn't be that clever of me.

The pins won't see the 'border of the PCB', if I might say so. There will be at least buffers foreseen. And even more: to avoid damages from outside, all in/outputs will be decoupled via optocouplers.

Hope this is a correct choice?

Best regards,

-- Geert