Patent ID: 7675431
Filing Date: 2010-03-09
Classification: G08G

Abstract:
1. An apparatus to detect a sound frequency signal emitted by a warning device of vehicles comprising: a sensor to sense a selected sound frequency signal spectrum is in communication with an initial detection stage to detect a frequency of approximately 600 Hz and frequency of approximately 1400 Hz within a specified time interval; a signal identification stage in communication with said initial detection stage wherein said signal identification stage has a digital signal processor programmed to identify a wail and a yelp warning signal and to compare said wail and said yelp warning signal to a histogram stored in a memory to estimate the distance from said sound frequency signal; wherein said signal identification stage is placed in a power save mode on application of electrical power and is maintained in said power save mode until activated by said initial detection stage to process a gain output signal upon detection of said frequency of approximately 600 Hz and said frequency of approximately 1400 Hz within said specified time interval; sampling said gain output signal in 0.5 second increments for processing by a fast fourier transform algorithm and for conversion to a polar coordinate output representation; filtering the polar coordinate output representation for removal of background noise and storing the filtered signal in a memory in the form of a histogram; scanning the stored histogram on a first-in-last-out basis and comparing the histogram to a siren sound characteristic signal stored in the memory to identify a siren sound; and a user warning indicator controlled by said digital signal processor and an electronic power source.