A system 1 for controlling a plurality of irrigation valves 21, 22 . . . 2n is shown. The system receives 110 or 240 volts, mains voltage, electricity from the mains. This is applied to a 28 volt square wave generator 3, whose output is modulated in a modulator 4 under control of a control circuit 5. The modulated output is applied to a live line 6, receiving modulated positive and negative pulses of 28 volts with respect to a neutral line 7. At each valve 21, 22 . . . 2n, a respective decoder 81, 82 . . . 8n is provided. Live and neutral lines 10,11 pass from the decoders to the valves. Each decoder 8n has an input connector 21 for the live and neutral pair 6,7 powering it and an output connector 22 for the further live and neutral pair 10,11 to the respective valve 2n.