i once started to build such a thing, but it's still unfinished. i use a free running oscillator at about 40khz, which may be enabled/disabled from the pic. on the other side, i use an amplifier/limiter/schmitt-trigger combination to detect incoming signal. after enabling the oscillator, you have to measure the time until the schmitt-trigger goes active. my circuit worked within about 3..8feet. if you need a wider range, i think you have to use an agc to reduce level for short distance, and completely isolated mounting of tx and rx device for longer distances, to avoid crosstalk over mounting brackets. (or if you know within which range you are measuring, you can supress all pulses outside this timing window. tino Tim Thompson Gesendet von: pic microcontroller discussion list 27.02.02 11:28 Bitte antworten an pic microcontroller discussion list An: PICLIST@MITVMA.MIT.EDU Kopie: Thema: [OT]: ultra sonic range finder Hello all.. Was wondering if anyone out there has ever done a simple ultra sonic range finder? I specificly want to make a PIC controlled ranger that is capable of doing a distance range of around 5 inches to atleast 10 feet, with a fair degree of acuracy. The pic will also interface a small LCD, but that part i have done before so its not an issue.. My only new venture would be into the hardware and software required to make the ranger, and a routine for converting the result to feet/inches for display would also be a big plus.. I have a pair of ~44Khz ultrasonic transmitter/recievers that would do the job nicely, but am at a loss in how to implement the range finder hardware.. Any suggestions? Thanks in advance, Tim Thompson -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics