Automotive rear safety detection system

Claim 1

A safety detection system for attachment to an automobile, said safety detection system comprising: a constant frequency ultrasonic isosceles wave generating generator connected to be energized from the automobile; first and second outputs from said constant frequency isosceles wave generating generator; an ultrasonic radiator for mounting on the automobile and connected to said first output for generating ultrasonic acoustic waves adjacent the automobile so that obstructions adjacent the automobile reflect ultrasonic waves back toward the automobile; an ultrasonic receiver for mounting on the automobile, said ultrasonic receiver receiving ultrasonic waves and converting them to corresponding electrical signals; means for subtracting said second output from said constant frequency isosceles wave ultrasonic wave generator from the received signal to produce a resultant isosceles triangle wave train which has a frequency corresponding to the difference in frequency between the transmitted ultrasonic signal and the received ultrasonic signal, a low pass filter, said wave train being connected through said low pass filter to filter out substantially all ultrasonic signal so that the resultant wave train has a frequency and amplitude which is a direct function of the difference between the frequency of the radiated signal and the frequency of the received signal; and a counter for counting the frequency of the wave train from said low pass filter and an alarm connected to said counter so that when said counter detects a frequency of said wave train above a reference frequency, said alarm is energized.