About a week or two ago there was a discussion about how to read a dip
     switch or something similar with a single pin to allow uniquely
     addressing a particular model railway engine. In case anyone didn't
     mention this one, how about using a Dallas DS2401 Silicon Serial
     Number chip?

     This is a true one pin solution, even the chip power can be fed from
     the same pin used to read the serial #, if desired. This device is
     programmed with a serially readable 48 bit guaranteed unique id
     number. Best of all, these devices are tiny, the largest package is a
     TO92, with SOT-223 and TSOC surface mount versions that are even
     smaller. I recall that the original poster stated that size was a
     critical issue.

     Of course, these devices do not allow the serial number to be set, you
     take what you get and the ability to change the id sent via the track
     signal must be done on the controller end, not the engine end as was
     originally suggested, but these handy chips seem tailor made for the
     job the original poster asked about.


     CIAO - Martin.