Abstract: A method and apparatus for the control of a number of valves in an irrigation system utilizing only two lines between a central encoder and a number of remotely located decoders. An alternating-current signal on the lines is used both to transmit power to the decoders and valves, and to convey control information in the form of decoder addresses and on/off signals represented in binary form by selectively clipping the alternating-current signal. The encoder includes timing and switching circuitry to effect temporary interruptions of the alternating-current signal, and to detect feedback signals transmitted from the decoders during the interruptions. At each decoder, the received control signals are recovered from the power lines, and each received decoder address is compared with one which identifies the decoder. When a match is found, the received on/off signal is employed to switch a valve and to initiate transmission of a confirmatory feedback signal.

Abstract: Apparatus, and a related method, for proportionately varying from a master unit the durations of irrigation at a plurality of valve stations controlled by a number of satellite units, and for transmitting over a single pair of wires control signals for starting a programmed sequence of valve operations at all of the satellites in a selected one of two groups of satellites, or for resetting all of the satellites to a "home" position. One disclosed embodiment includes adjustable timing circuitry in the master unit to generate a timing signal which is transmitted to the satellite units over a separate wire, and is utilized to vary the duty cycle of a station timing motor which measures the durations of irrigation. In an alternate embodiment, station timing at each satellite is measured by means of a digital pulse counter, and the irrigation times at all of the stations can be varied to the same degree by adjustment of a variable-frequency pulse generator at the master unit.