Abstract: A system is provided for the detection and recognition of pre-established sound patterns such as the various patterns produced by the sirens of emergency vehicles. The system includes a microprocessor which programmed with pre-established sequence detection algorithms corresponding to the different types of emergency vehicles sirens signal patterns which are to be recognized. A first omnidirectional microphone is coupled through a bandpass circuit to a trigger circuit to produce square wave signals representative of analog signals in the band of interest. At least two directional microphones are coupled through similar bandpass amplifier circuits to analog digital converters which produce a digital output representative of the strength of the signals received by the directional microphones. This directional information along with the output of the Schmitt trigger is supplied to the microprocessor which is used to control the signal lights at an intersection in response to the detected siren.

Abstract: A system for the detection and recognition of a particular sound pattern including an initial frequency discrimination circuit comprising either band pass filters of pre-selected frequency or IC phase-locked loop tone decoders. A sequence detection circuit is responsive to the frequency discrimination circuit to successively enable paired timers upon detection of audio tones in the proper sequence and frequency. Out-of-sequence tones disable the circuit. A trigger pulse is then sent to a counter chain and successive pulse must be received by the counter chain in a predetermined time period to actuate a traffic signal control relay. The system used for a traffic signal control further includes a direction differentiation circuit to cause red lights in one direction and green lights in another as determined by the direction of the source of the sound pattern.