The short story is I would like to automate my irrigation system using my Elk M1, but I'd like the ability to flip a switch that would revert control back to the current controller. I know this can be done, but I want to make sure I am not over, or under, thinking this.
My initial thought is to have a secondary 24VAC power supply that will supply the power to the irrigation valves when in "automation mode". I would use DPDT relays controlled by the ELK to switch between power sources and switch the valves from their current loop to the automation loop. I'd wire the "automation" side normally closed so this is the default state and controller side to normally open. I would then have SPST relays to individually operate each valve. All of this would be controlled from outputs on my elk. The switch would use an input on the Elk to switch states so that a maintenance person can use the controller.
I guess my question is, am I thinking correctly with the use of DPDT relays or is there a simpler way to achieve what I am looking to do? If this seems correct, can you recommend a place to purchase said relays?