Digital time interval sensor using a free running counter and a cycle counter with only the latter being reset at each event

摘要

Intervals between zero crossings of tone signals on two incoming lines are measured by a clock driven, free running binary counter common to the two lines and by an overflow counter individual to each line. The overflow counter is reset by the reception of the zero crossing of the tone signal and is then advanced by each overflow and recycle of the common counter. The common count number, produced when the zero crossing at the start of the interval is received, is processed with the common count number and the overflow number, produced when the zero crossing at the end of the interval is received, to calculate the duration of the interval and thereby determine the frequency of the tone.