sorry for the poor explanation. actually i making an ultrasonic sensor that would help the visually impaired through sounds transmitted through earphones. the output i get form my sensors would be would be amplified using an op amp before i feed the circuit to a VCO to get my frequency. but the ulltrasonic sensor would give me a low voltage for detecting a near object and thus the frequency given by the VCO would be low. but ill would like a high frequency for detecting a a near object. lets say the input voltage to the VCO ranges for 1-5volts but ill would like to get a high freq for a low voltage input and a low freq for a high voltage input. any suggestions??