EtherRain together with Rainbird STP-6 irrigation controller

At this moment I use a Rainbird STP-6 irrigation controller to control the irrigation of my garden with 4 valves. I am interested in the EtherRain to be able to control my irrigation via Vera Lite. But I also want to keep on using my Rainbird controller (to just manually start irrigation when I am in the shed where it is installed). Is this possible ? How should I connect both the Rainbird and the EtherRain to the valves ?

Yes, this is possible.

Just connect the zone wires from one controller to the other: Zone 1 to Zone 1; Zone 2 to Zone 2; Zone 3 to Zone 3; and Zone 4 to Zone 4. Then connect the common wire(s) to both. You only need one common wire to any common terminal on the EtherRain.

Next: (Just in case they both turn on at the same time) You need to make sure the power phases are aligned: make sure that the same transformer wire is connected to the ground or common power pin on each controller.

On EtherRain the right-most power pin (when looking at the front panel of EtherRain) is the power pin that is connected to common. On your RainBird controller you might need an ohmmeter to find it, or it might be labeled. The common power pin will have 0 ohms resistance between itself and the common terminal (on the RainBird or on the EtherRain)