Re: Ultrasonic sensors
Two ways to do it. First you can measure travel time, second you can measure reflected signals amplitude.
Travel time measurement is explained by the message above.For amplitude measurement, reflected signals amplitude is measured to determine distance. But you need and ADC, you need to calibrate system, plus reflection coefficent can be different for materials.
There is tranceivers around for robotics, usually working around at 40KHz. You can use them. Take a look at digikey.com and other mail order component sellers' calalogues.