> On Olin's page there is a cool spinning row of LEDs that show text. > In this application, how does the PIC know the exact position of the > motor/row of led's? > > http://www.embedinc.com/ourportfolio.asp#eyeball Only Olin can tell you the specific of this example - he mentions "... an index pulse once per revolution." But the general principle is to provide some external reference to allow both rotational timing and position synchronisation. This could be a magnet plus reed switch or hall sensor, a mechanical contact (unlikely), an opto interrupter, a magnetic pulse to a coil (possibly also used for power or signal transfer) or some similar arrangement. This is one of the nice and less usual applications where, at least for a simple version, the result is more impressive than difficult. It is surprisingly easy to get a basic strobed display of this sort working, although you can spend as much effort as you wish refining it. Russell McMahon -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist