[epineh]

I would think using software limits would be the best option unless you want to take the scope apart and stick a limit/homing switch in there somehow.

Can you manually put the mirror in the same position at the start then switch the stepper drive on and tell it that it is homed straight away ? And possibly when you power it down leave it in the homed position so at restart you can do the same thing...

Also what software do you intend to control this with ? I would think if it is simply moving at a constant speed you could just use a 555 timer to generate step pulses to send to the stepper driver, though you would have to include some kind of brain so it knows when to stop. Seems overkill to hook up a PC and monitor to control this...but I guess a second hand PC is practically free these days.

Cheers.

Russell.

[wildwestpat]

Hi Rhodan

To focus the scope the priamry to corrector plate reflector distance is being changed. I guess your problem is that the optical system is 'sealed' and this precludes the mounting of mechanical switches to home the separation of the mirrors. What happens when the focus control is turned to the extreems of its travel? Is the focus continuous but changes sign ie.e. is some form of cam operated mechanism? If so then it might be worth investigating using a colimated beam of light bounced off the primary mirror from a slit source mounted on the corrector frame using a photo transitor or diode on the oposite side arranged to be triggered whrn the distance is at its greatest. You will have to look at the geometary involved as it might even be possible to bounce the beam off the corrector plate as well as the extra reflections add to the accuracy.

Hope this gives you some other ideas as the microswitch may not be the most appropriate sensor for homing a folded optical system. Also could you use the diffusion to detect sharpness of a known star using a CCD pinched from a defunct autofocus camera?!!!! Can the change in drive torque (motor current) be used?

Regards

Pat