The saga continues. I’ve left my setup running for > 6 hours on the bench. The Pi appears to be operating as expected. Running the demo programs ospi.py and ospi_manual.py results in some pretty strange behavior. The expansion unit is attached. I haven’t tested every pair of zones but I’m seeing some strange interaction when turning on zones 1 & 16. For example, when running ospi_manual I turn on zone 1 but don’t measure a voltage change. I then turn on zone 16; zone 1 now measures 24vac. Then some clicking on/off between zone 1 and 16 will ultimately result in one or both zones turning off. No rhyme or reason that I can discern. Is there a way to “reset” the “shift registers”? Other ideas on how to debug or proceed?