The current version of the OSPi hardware can be found at https://github.com/OpenSprinkler/OpenSprinkler-Hardware/tree/master/OSPi/1.52. I don't need the analog inputs. So my simulation circuit is just a 74HC595 connected to the raspi as in the schematic (however, I powered it from the 3V3 rail) and LEDs at some of the output channels instead of the triacs.

Running the "Run Once Program" shows that everything works fine.

For the sensor inputs I provided 10k pull-up resistors to be on the safe side.

I assigned them to soil moisture sensors and when I connected an input to ground it was correctly recognized as wet soil which does not need irrigation. (The irrigation program was not executed.)