OK, found a solution that takes a little work, but is cheap. I’m still waiting on one of the parts, so I’ll update to confirm that it works and post a circuit diagram.
I was interested in running two drains, which means two zones that need to run when the low temp threshold is reached, at the same time as the master is closed. The solution is to use a relay to close the master valve whenever the controller opens it when the zones connected to the drain valves are run.
While the Rachio is itself 24v DC, what I didn’t realize is that the common valves are 24V AC. For this reason, my initial solution to use the power wire from the drain zone to turn off the master didn’t work; 24 V AC didn’t flip my 24v DC relay (of course). I only thought to check out what the power requirements were for the valves after I figured out that my relay was never closing.The solution to that is to use a bridge rectifier to convert the AC to DC, so that the relay works. The relay is actually two in one, which lets you shut down the master if either of the two inputs is high, and will take the 12v output of the rectifier with a jumper setting.
Here are the parts I’m using:
AC-DC Converter 6/12/24V to 12V Full-bridge Rectifier Filter Power Supply Module
DC 24V 2-Channel Relay Moudle High/Low level Trigger
Another challenge of course is that the Rachio on IFTTT doesn’t let you start and stop individual zones or even a routine, so more challenges…