Off to the garage to do some more thinking and planning…

Found a more suitable US Robotics modem (remember them) 20V AC power adaptor so cracked open the case to pull out the actual transformer.

Going to use this plastic hobby case to hold the components.

A bit more thinking…

The sensor wiring is straight forward, Active, Neutral & Load – which powers the transformer.

Planning something like this – the transformer will mount inside the box directly below the sensor. Power lead will come in on one side. The irrigation solenoid will be mounted at the other end (or bottom) with hose connections – tap in sprinkler out.