Abstract: A plurality of addressable transducers at remote locations are connected to a home station by a pair of transmission lines which carry power as well as address signals to the transducers, and carry response signals from the transducers, when addressed, to the home station. Each transducer carries a decoder which is programmed to recognize a particular code, and a response circuit comprising a current sink oscillator to modulate the transmission line current at a frequency corresponding to the measured parameter. The response circuit operates on an analog voltage representing the measured condition by an A/D converter to generate a corresponding digital number, a clock provides a fixed frequency, and a divider divides the fixed frequency by the digital number to provide a resultant frequency, which in turn is divided by a flip-flop to yield a square wave output.