Re: "att caudlet" Limit switch problems

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "shelbyshepherd2002"
<cabrillo_shepherd@m...> wrote:

>
> Hi Caudlet,
>
>
> Thanks for your thoughts on this problem.
>
> Correction these are Home and Limit for the X and Y
> switches......and only a Home for the Z axis.
> All the wiring is correct as X and Y were working perfectly prior

to

> setting up the Z axis
> The X and Y home and limit are wired parallel and shared the same
> pin.
>
>
> This is the wiring I have used X and Y:
>
> (1)Ground goes to one of the Home and limit switch term.
>
> (2)5volt ---> 10k resistor ----> X and Y axis wire from parallel

port

> |
> |
> |---> other Home switch terminal.
> |
> |
> ----> Limit switch terminal.
>
>
> This is the wiring I have used Z:
>
> (1) Ground goes to one of the Home switch term.
>
> (2) 5volt --->10k resistor ----> Z axis wire from parallel port
> |
> |
> ----> other Home switch terminal.
>
>
>
>
>
> I tried another computer box that had a perfect parallel port
> (printer was working on it)and it also did not go.
>
>
>
> Shelby
>
>
>

If I am reading your "schematic" correctly you have 10K resistors in
series with the parallel port pins. While this will limit the
current when the pin goes low the parallel port will not source very
much current on an input anyway. Technically you should be able to
short an input pin to the pc ground with no harm to the port. There
exists pullup resistors (or constant current source) on the parallel
port pins. Measure the voltage at the port pin with the switch
activated. If it is over 2.4VDC your computer may not see that as
a "low". I would think that if you want to use a series resistor a
1K would be more appropriate (limit to 5ma). One thing you will find
is that this configuration with a series resistor will make the line
more susceptable to noise. Pulling the pins up to a good solid +5
through a 1K (reduce noise in non-activate condition) and pulling the
pin directly to pc ground (not table or motor ground) would give the
best signal with the lowest possibility of false triggering.

I am curious. Where did you get the circuit you are using? Is it
not a PITA to get things reset after moving to "Home" and tripping
the limit? On my machines the limits are hardwired to a relay
through normally closed switches in series. The switch have to ALL
be closed to pull in the relay coil. The relay is a 12V varity; its
NO contacts (closed when energized) pull in a large contactor that is
the DC supply to all of the motors. A panic switch is in series with
the limit switches so if any of the switches are tripped even
momentarily the big contactor falls out and latches in that condition
requiring a manual push of a button to reset everything.

I don't trust software to keep my machine from moving. My motors
will not move unless the big green lamp on the console is
on...period. None of that is controlled by the software. I use an
opto to feedback a stop condition to the e-stop input so the software
will stop.