Apparatus 11 and 13 for interfacing two AC sources with two AC loads 17a 17b in the form of solenoid operated valves over a single conductor 25, with a return conductor 19 in an irrigation system is disclosed. The apparatus has an encoder circuit 11 with two inputs 21a 21b for connection to the two AC sources, and an output 23 for connection to the single conductor 25, and a decoder circuit 13 having an input 27 for connection to the conductor 25, and two outputs 29a 29b for connection to loads 17a 17b respectively. When the first input 21 a is powered, the first load 17a will be switched on, and when the second input 21b is powered, the second load 17b will be switched on. The decoder portion 13 incorporates switching circuits 43a 43b, interfaced with turn on delay timers 45a 45b respectively, to delay operating the loads at switch on, and turn-off delay timers 47a 47b to hold the loads on after switch off.