Abstract: An external signal processor is provided for use with a personal computer. The signal processor incorporates hardware components for receiving external analog or frequency signals and for converting the signals to digital form for retrieval by the computer in nibble mode. Interconnection with the personal computer is through the parallel printer port, with the signal processor installed between the computer and an external printer. Normal printer functions are available when a transparent mode is enabled. The signal processor can also monitor one or more external digital signals and output one or more digital control signals. An example of programmable control software is also provided.