215 so as to achieve the desired number of echo reflections the controller 400 performs this function by increasing or decreasing the number and or amplitude of resonant voltage pulses applied to the temperature dependent transducer the number of resonant pulses applied to the transducer typically ranges from a low of 1 pulse to a high of 16 or more pulses although other numbers of pulses may be applied a switched capacitor charge pump is preferably used to increase or decrease the amplitude of the transducer drive voltage applied to the driver 410 under the control of controller 400 the drive voltage typically varies from low of 2 volts to a high of 30 volts the number and amplitude of drive pulses is selected based on the number of echo reflections that are received if the number of echo reflections falls below a preset quantity calculated based on the relative distance being discerned the controller 400 increases the amplitude and or number of drive pulses conversely if the number of echo reflections is greater than the preset quantity the controller 400 decreases the amplitude and or number of drive pulses applied to the transducer 115 210 reducing unwanted distortion and noise thus a closed loop gain control is created for the transmission and detection of the ultrasonic sound wave 130 215 echo reflections the.