Re: know your limits

["William Scalione" <wscalione-at-nc.rr.com>]

Ian,

Hi, Well I'm no expert, but since you asked,  here goes. I didn't use
a pull up resistor on my setup. I simply wired the home pin through
a N/O switch and back to one of the parallel port ground pins (18-25??)
A pull up is probably a good idea, but maybe you should get it working
without it first. Then if that works add the pull up later. I suppose my
parallel port has pull ups built in, as I have no problems running it this
way.

If the numbers turn green as soon as you hit home it means the switch
is made, or the porarity is wrong in the ini file. Since you tried to swap
the polarity maybe there is a problem with the ground.Are you using the
parallel port ground or some other ground?

Also, in re reading your original post, I see you have the switches in
series?
Change to parallel as all switches must be closed in order for series to
work.
In the ascii art below || represents a switch



                   |----------||----------|
Pin 12 ---------|----------||----------|-------to parallel port ground
                   |----------||----------|

Bill

ps others more knowledgable, feel free to jump in here.


>
> Hi Bill,
>
> Can you tell me a bit more about your home switches please? I have tried
> putting a +5v supply onto pin 12 via a 5K6 current limiting resistor and
> then connecting the home switch from this to ground but I can't get any
> response from EMC. If I set the 'homing switch polarity' to '0' in the
.ini
> file, pressing the 'home' button turns the relevant axis display green but
> there is no movement from the machine. If I set it to '1', then pressing
the
> 'home' button sends the machine off in a positive direction along the axis
> but it never stops - the switch has no effect whatsoever. What am I doing
> wrong?
>
>
> >
> > Ian,
> >
> > I had the same question about this when I first hooked up my home
switches
> >
> > When you home in EMC each axis is homed separately, and yes, you must
> > either use the offset function or move that axis off the switch to home
> any
> > other
> > axis. I believe you can also use one of the limit switches as a home
> switch
> > although I have not done this.
> >
> > Once an axis is homed, then the software limits work well. Suppose you
> > set up an axis with 10" of total travel, with zero at one end of that
> > travel.
> >  If you now move to 5" and set that point to zero you will be able to
move
> > -5" to +5". It will not let you move to +6"
> >
> > Bill
> >
> >
> >
> > > Hi,
> > >
> > > Having now got bits of mechanism moving back and forth under EMC
> control,
> > I
> > > am turning my attention to adding switches to the axes etc.
> > >
> > > What use are home and limit switches using the EMC program? I can't
work
> > out
> > > in my own mind how three home or limit switches in series can possibly
> > give
> > > any usable output. Presumably the first to trip will just bring the
> > machine
> > > to a complete stop and, since it would be physically impossible to get
> all
> > > three to trip at the same instant, this would mean that two axes will
be
> > at
> > > an unpredicatable position. If you use the 'home offset' feature, does
> > this
> > > mean that the first axis will close its switch, back off by the offset
> > > amount and then stop, and that the second axis will then continue to
> move
> > > until its switch closes and then back off and stop to allow the third
to
> > do
> > > likewise? I had considered just relying on the software 'maximum
> distance'
> > > option to limit travel but, if you reset zero along the way, this
> > presumably
> > > becomes ineffective. Any advice would be appreciated. Thanks,
> > >
> > > Ian
> > > --
> > > Ian W. Wright
> > > Sheffield  UK
> > > www.iw63.freeserve.co.uk
> > >
> > >
> >
> >
> >
>
>