Abstract: A system is disclosed for conversion of information from a preselected switching array to serial digital data utilizing conventional audio grade communications equipment such as a radio, recorder, and the like. An encoding scheme is utilized which involves amplitude modulation of the information superimposed upon a clock signal. Distortion of the digital signal due to any direct current component is avoided by using a clock signal symmetric about a zero reference. The information portion of the signal is not dependent upon variations in speed of recording media. While not limited thereto, one use of the present invention is to selectively activate any one or more of a number of system components remotely located from a centralized system control station. A series of digital pulses is generated, each one representing the desires status of each remote system component. The series of digital pulses is generated by a series of two position switches.