Re: Limit switch problems..observations (Shelby)

>
> Hello Caudlet,
>
> I am lost as to why the X and Y axis had been working perfectly for
> several weeks on the original wiring set up and just by connecting

Z

> axis it has now killed all the axis's.
>
> One thought, what if the resistor was sold to me as 10k but was not
> say if lower or higher in value? I do remember I had replaced the Y
> and Z axis resistor this time as well.
>
> Regards
> Shelby

Regardless of the resistor value(s) It's not good practice to tie
parallel port pins to each other (unless you want to loopback inputs
and outputs but that's another story). It's ok to put switches in
parallel but they need to be diode isolated so that trying them
together does not short across port pins. I can't explain why things
worked oaky but you have to troubleshoot it like this:

It worked before...what changed. Whatever was changed is the first
place to look.

BTW 10K resisitor is Brn-Blk-Org. 1K is Brn-blk-red. Putting more
pins in parallel each with pull-ups, places pull-ups in parallel and
decreases total resistance.

Normally each Home switch is tied to a separate parallel port input
and the limit switches are wired in series (like christmas tree
lights) and are tied to another separate pin. If you want to use the
same switch as home and limit, a good controller package will allow
that just in software. Still need a separate pin for each switch but
they perform doubleduty depending on what you have asked for.

In MACH2 you just map limit and home to the same pin (switch) and
depending on weather you command a "reference" move (to home) or are
just moving in code or jogging, a switch trip does different things.
During a reference move the machine moves slowly towards the home
position and once the switch is activated the software stops the move
and backs up a constant distance to come back off the switch.

I still want to go on record as saying that table limit switches
should be part of a failsafe design that mechanically turns off power
to the machine. The software needs to be notified after the fact that
an e-stop condition has occurred. Don't rely on telling the software
first and depending on it to stop the motion...it might not. Simple
Physics: motors won't produce motion without applied voltage.

Home switches are REAL nice to have especially if something happens
and you loose reference during a run. You just tell it to "home" and
it goes back to a known spot (I have mine set at table 0,0) and
rewind the code and start the cut where you left off. I use the
reference command a lot. In MACH there is a g-code (G28.1 XYZ) that
will let you reference a single axis or any combination in the
program. I built a custom screen that has a button to reference X &
Y but not Z.