Sequential two tone detector

DETAILED DESCRIPTION It is an object of the invention, therefore, to provide a high security method and means for determining the presence of a two tone command signal.
It is a further object of the invention to provide the above described high security system further comprising a method and means for determining the ordered sequence of the input tones to thereby control corresponding output functions.
Briefly, according to the invention, a method is described for detecting the presence of a first frequency signal followed by a second frequency signal.
The steps of this method include first determining that the first frequency signal is present for a predetermined minimum time interval.
Second, a determination is made that the second frequency signal begins within a predetermined time interval referenced to the conclusion of the first frequency signal.
Finally, it is determined that the second frequency signal is present for a predetermined minimum time interval following the conclusion of the first frequency signal.
Thus, a high security two tone detection method is accomplished.
Wherein the first frequency signal is one of the signals A and B and the second frequency signal is the other of the signals A and B, a method is further described for detecting the tone sequence and thereby activating a first output in response to a A-B sequence and a second output in response to a B-A sequence.
Corresponding apparatus is described which performs the above methods.