Thanks for the explanations. I had already converted the Eagle files to Altium as I’m designing using Altium Dsigner.
The question I asked because I thought to use my OS 3.0 without the MOSFET drivers, but with an additional ESP32 board with optoisolated inputs and relay outputs.
I’m thinking to use this combination because I have to manage filling the water tanks from a well. This needs constant monitoring of the tank levels and the well water level.
I have already tried to drive opto isolated relays ( active low ) using the OS baseboard, but as the optocouplers accept 5V, I used a bit different approach as you can see from the attached drawing. I’m using VIN power instead COM.
But anyway, it looks like I can remove the OS baseboard without any problems and use the PCF8575 expander board to drive outputs from 9 to 24 without using zones 0-8. Correct?