Vehicle ostacle detector and alarm system

An obstacle detector and alarm system comprising:

• a) at least one flexible obstacle detector assembly having means for producing electrical oscillations when said assembly touches or scrapes against an obstacle where said detector assembly comprises:
• (1) an impact head having a back projecting cavity,
• (2) a piezoelectric element having an outer electrode and an inner electrode, where the outer electrode of said element is tightly fitted against the cavity wall and forward end of said cavity in a prestressed condition to maintain said element in its maximum sensitivity, where when said impact head touches or scrapes against an obstacle, said piezoelectric element produces electrical oscillations, and
• (3) a flexible housing having a front end that is sized to tightly fit into said back cavity behind the back end of said piezoelectric element, said housing comprising a coaxial cable that includes an inner electrical conductor and an outer shield conductor, where at the front end of the cable the inner conductor is attached to the inner electrode and the outer conductor is attached to the outer electrode of said piezoelectric element, where from said obstacle detector, via said coaxial cable, are emitted the electrical oscillations.
• b) an electronics control unit that is solely powered from a vehicle battery and having means for receiving and processing the electrical oscillations from said obstacle detector assembly and for providing an alarm when said assembly has encountered an obstacle, said unit comprising:
• (1) an amplifier circuit having a first operational amplifier and means for receiving, processing and amplifying the electrical oscillations from said assembly and for producing an output signal,
• (2) a comparator circuit having a second operational amplifier and means for comparing the output signal from said amplifier circuit with a preset threshold voltage that when equalled or exceeded, produces corresponding digital signals,
• (3) a retriggable multivibrator circuit having a third operational amplifier and means for receiving the digital signals from said comparator circuit and for producing a signal consisting of a series of time dependent output pulses,
• (4) an audio generator circuit having a fourth operational amplifier and means for producing a series of audio frequency pulses, and
• (5) an alarm circuit that receives the output pulses from said multivibrator circuit and the audio frequency pulses from said audio generator circuit, said alarm circuit having means for converting the two inputs into visual and audio alarm signals that indicate when said obstacle detector assembly has encountered an obstacle.