Blind faith my son. Actually, blind faith in engineers' specifications. Stepper motors .have well defined conditions under which they will "follow" the "move-along-now" signals given to them. As long as the stepping signals stay within the speed range specified for the applied load then you can confidently expect the motor to revolve at the stepping rate. In this application the load is (or should be) a well balanced and quite light weight (hence low inertia) disk so the loading is almost purely inertial. As long as the disk is "light" (which is relative to the power of the motor used) then it will track properly. Acceleration rates need not be vast in this application and can, if necessary be limited to ensure lock is not lost. -----Original Message----- From: TONY NIXON 54964 To: PICLIST@MITVMA.MIT.EDU Date: Monday, 9 March 1998 21:23 Subject: Re: Optical Tachometer >>There is a method which may be simpler than building a >>frequency counter per se with a PIC. Briefly, don't measure >>what the motor is doing - instead, tell the user what YOU >>are MAKING the motor do. > >How does the controller know if the stepper is actually turning >at 'any' speed ;-) > >Tony > > > >PicNPoke Multimedia 16F84 Beginners PIC Tools. > >PicNPoke - PicNPlay - PicNPlan - PicNPrep - PicNPost >Plus DT type saver. >New addition - PicNPort I/O Tutor. > >http://www.dontronics.com/picnpoke.html >