While this isn't a CNC question, exactly, it is related.

I am looking at building a PC controlled focuser for a telescope using a small stepper motor and pulleys. What has me scratching my head is how to tell the software where "home" is.

The scope is a Maksutov Cassegrain and its focused by turning a knob which moves the primary mirror. The knob rotates but it does not move in and out. In fact there are no moving parts to which I can attach any kind of switch to detect when the mirror is at the limits of travel.

So I'm trying to figure out how to "home" the focuser so that the software can reliably move to a position to repeat a previously found perfect focus.

The best would be hardware limit switches so the software could find its own travel limits during initial setup and do a "home" at each startup thereafter. However, I can't really think of a method of doing this..

Anyone have any ideas?