Abstract: A circuit for serial data communication and power transmission between a main controller and a sub-station along two balanced transmission lines. The circuit includes a power supply for providing a DC voltage to the sub-station along the transmission lines. A main controller sending circuit generates two data signals of substantially equal magnitude and opposite polarity and supplies the data signals to the transmission lines. A sub-station receiving circuit detects the data signals, on the transmission lines and converts the data signals into a serial format output data signal.