Emergency signal warning system

A system for detecting the presence of sound signals varying in frequency in a predetermined manner over a predetermined frequency range, said system including in combination:

• a source of input signals representative of said sound signals;
• frequency selective sampling means coupled with the output of said source of input signals for sampling the output thereof at a sampling rate substantially greater than the rate of variation of said input signals for producing a first sample output signal from said frequency selective sampling means when an input signal representative of a sound signal in one of a plurality of different portions of said predetermined frequency range is present on the output of said source of input signals a predetermined number of times during a sampling interval of a predetermined unit of time, and for producing a second output signal therefrom when an input signal representative of a sound signal is present on the output of said source of input sound signals less than said predetermined number of times during such predetermined unit of time;
• first counter means responsive to the output of said frequency selective sampling means for counting the number of successive shifts in frequency from one of said different portions of said predetermined frequency range to another as represented by successive first sample output signals to produce an operating signal in response to a predetermined number of successive frequency shifts in the same direction;
• second counter means coupled to the output of said first counter means and responsive to successive operating signals from said first counter means for producing an output signal on the output of said second counter means in response to a count of a predetermined number of said operating signals by said second counter means;
• interval timing means having a timing interval of "N" seconds coupled with said first and second counter means for continuously resetting first and second counter means to an initial count every "N" seconds;
• means coupled with the output of said first counter means and responsive to said operating signals for resetting said first counter means a predetermined time interval after each such operating signal is produced by said first counter means;
• and
• means coupled to the output of said second counter means for producing an indicator in response to the attainment of a predetermined count by said second counter means.