On 24 October 2010 17:00, John Gardner wrote: > That's cool. Why could'nt you do that acoustically? > >> they linearly > slewed the transmitter frequency at a given rate and then heterodyned > the current =A0tx =A0signal with the reflected signal. The difference in > frequency between tx and rx signals gave the time delay and hence > distance... If you use phase comparisons on tx and > rx rather than just frequency you can deal with slower to much slower > slew rates. > > Jack > -- You can.When I was at university there was a big project that used this technique to assist the blind. I wasn't involved but remember there were a variety of implementations including a cane and spectacles with the transducers attached. I also remember a project that reversed the output frequency so that the more distant objects produced a lower frequency tone which as somehow more intuitive. I think a lot of the magic was getting the transducers to work effectively over a sufficiently wide frequency range. RP --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .