On 2/5/2010 6:19 PM, dpharris@telus.net wrote: > Yes, that's a good suggestion. Alternately, if you have a lead screw, then the > slider could activate a set of microswitches, which should give excellent > longevity, and be quite eay to construct and be eraltively inexpensive. > > David > > with a crankQuoting Bob Ammerman: > >> Well if you have a brass crank, why not just a rotary encoder on its shaft >> and a zero position sensor at one end of the travel of the pointer. >> >> -- Bob Ammerman Davids solution hits at the heart of the matter - you are digitizing the position into discrete points (and not many of them) so although you described an analog approach initially, thinking digitally makes some sense. If a leadscrew nut travels along activating microswitches as it passes them, you will always know where the contraption is set to. The only hurdle is power up out in the middle somewhere and knowing where you are. This could be handled by remembering the last place (nvram) or at power up, always travel a bit until a microswitch gets activated and then back up to where you just started from. Plus requiring people to operate the hand-crank will slow their enthusiasm for ripping back and forth on the system. It sounds like a fun project so if possible, let us know what you final system solution is and perhaps photos? -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist