On Jan 9, 2008 4:56 PM, peter green wrote: > Water and metal (cans/foil/metalised plastic packages) are all very bad > for propogation of radio signals and are all found in substatial > ammounts in random arrangements within a typical shopping trolly load. > Theese are almost certain to block out some of the tags meaning those > items won't be accounted for. True, but RFID is more a magnetic field than a radio field, though many of the same problems remain. A redesign of the shopping carts (narrower, plastic, shelf-like, ?) might also help. Of course, a redesign requirement would raise the initial cost to very high. Would work better in a clothing store where little metal is problematic, and with some additional sensing metal can be detected and a cashier alerted that a particular load needs personal attention. But yes, it is largely impractical, especially now. Who knows what might change in the future that may make it possible. -Adam -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Moving in southeast Michigan? Buy my house: http://ubasics.com/house/ Interested in electronics? Check out the projects at http://ubasics.com Building your own house? Check out http://ubasics.com/home/ -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist