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Limit switch problems.

Discussion in 'Controller Boards' started by Ian Parr, Nov 17, 2014.

  1. Ian Parr

    Ian Parr New
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    Hi, I've nearly completed my OX 4 x 2 machine, and have installed the electronics. I am using a 5 axis breakout board and 4 steppers from E Bay bought from Xories.
    After initial setup problems I have got the electronics working the machine. The problems have arisen when I tried to wire up the limit switches. The instructions recommended that the switches be connected NO (normally open) but general advice is that normally closed is the safest option. The emergency E stop functions, and initially limit switches on the X and Y axis worked also. When I came to install the Z axis limit switch Mach3 refused to re-set with the massage "limit switch triggered". I have tried both NO and NC options on the switches, obviously resetting the active low and high accordingly, with no success. I thought maybe there was some electrical interference and used shielded cable, again no success. Now even if I disable the limit switches the same reset alert is given. Mach3 initially resets, often after several attempts, but the reset seems unstable and after a few moments the reset alert appears again.

    Looking on the diagnostics menu, the yellow limit switch LED does not show when the alert is given. When the switches are triggered manually all is as should be and the lights show.

    Just about to throw the whole thing in the skip!!

    Any help much appreciated

    Ian
     
  2. Tweakie

    Tweakie OpenBuilds Team
    Staff Member Moderator Builder

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    Hi Ian,

    Sounds very much like your limit switch wiring is picking up enough electrical noise to trigger the E-Stop.
    The way in which the screen / shield (of the switch wiring) is connected to Earth is also important - please take a look at Electronics 101 which, hopefully, will be of assistance http://openbuilds.com/threads/electronics-101.693/

    Tweakie.
     
  3. Zootalaws

    Zootalaws Veteran
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    Were they the limit switches sold by openbuilds?
     
  4. DistortedDesigns

    DistortedDesigns Journeyman
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    I would run NO as it is much safer. There is a de-bounce setting so it ignores a certain amount of noise and you usually have to a resistor on the line as well. Go to cnczone.com. There is a huge forum there for Mach3.
     
  5. dddman

    dddman Master
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    NO isn't safer... If you have a broken cable, you want the system to recognise it as a trigger and stop the system. If you use NO, the system can't detect broken cables.

    BTW, send us a picture of your Mach3 settings we may find something in there. Meanwhile, short them one by one to see which one is problematic.
     
    Hytech2k and Nick W like this.
  6. Hytech2k

    Hytech2k Master
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    I agree NC is a much better way to wire limit switches and Estops.. If there is a loose connection or break in the wire you'll know about it before a problem arises.

    Under settings make sure Auto Override is ticked and be sure when the Z zeros it backs off enough to un trip the z limit switch. Send a screen shot of your Input signals screen showing your limit switches under Ports and Pins. Z Home and Z++ should be checked off, Z always homes to the + all other axis home to -.

    Also like Distorted said you can raise the debounce setting, that sometimes helps when using manual limit switches.


    Gerald
     
    #6 Hytech2k, Feb 5, 2015
    Last edited: Feb 5, 2015
  7. DistortedDesigns

    DistortedDesigns Journeyman
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    Sorry NC is what i meant. I have a large cnc that i have been working on for too long. I had the same issue with limits triggering. I changed my limits to NC and wired them in a large loop. You don't have to do that but i only had 1 open port for limits. I hooked up one my limits with a 1 inch piece of wire and they still triggered. So that told me it was mach3 and not anything else. You still need to run shielded wire because steppers and power supplies will add noise. You have to have a resistor on the line i don't remember the size, you have to tell mach if your limits trigger on low or high and then you can change the debounce. Too much debounce and your limits may not trigger. Goto the cnczone and search for mach3 limit switch settings.
     

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