On Wed, 22 Oct 1997 16:53:30 -0400 Andy Kunz writes: >At 11:09 AM 10/22/97 -0200, you wrote: >>Hi to All, >> >>I'm trying to do a ultrasound distance measurement with PIC, I don't >want >>to use the Polaroid module. Does anyone has some experience to share? >>I know how to generate the transmition pulse but I need help in the >>receiver part. >>The range will be from 20 to 200 inches. The Polaroid module is quite well-done, an excellent example of USA engineering in the early 1970's. If you're needing the full range the stepped increasing gain of the receiver will be necessary. As someone else said, there is nothing in that module that isn't necessary. I doubt you can buy the receiver chip seperately anymore. > >Why not optically? Since light travels much faster than sound, resolving a distance would require wider signal processing bandwidth. The target must also reflect light to some degree (at long range, must reflect quite well). This does seem to be the preferred solution for modern autofocus cameras though. Some use a CCD to look for optimum fine detail in the picture. Others have a couple of infrared windows in the front. Do those use the main lens too, or is it an independent distance- measuring system? How does it work?