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Multiple Limit Switchs per Axis only one Input on Controller

Discussion in 'CNC Mills/Routers' started by eleethesontai, Mar 7, 2018.

  1. eleethesontai

    eleethesontai Journeyman
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    I forgot to factor in Limit Switches in my planning of my build. I have a dual y axis cnc with the panucat gradus m1 pro. the controllers only has 1 input for each access for limit switchs. problem is i need 8 total 2 for x, 2 for z and 4 for y i was wondering can you chain the limit switchs so that they go into one input on the controller?

    from what i understand there are two types of limit switchs always on or always off which one of these types is the limit switch that is sold in the openbuilds store and also does anyone know what type the gradus is designed to work with?
     
  2. Ranga

    Ranga Well-Known
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    Most limit switches are actually made as both normally open (NO) and normally closed (NC), which is the same kind that's available on the openbuilds store. The way that they are wired determines if they are NO or NC.

    Here's a post (#13) from cnczone that explains an NO/NC switch and how to wire it. Need Help - Final steps before movement - Page 2

    Edit: looks like I was wrong as shown below, I didn't know you could chain together limit switches as long as they were for the same axis. I've edited out the info so that there's no wrong info floating around out there.
     
    #2 Ranga, Mar 7, 2018
    Last edited: Mar 8, 2018
  3. eleethesontai

    eleethesontai Journeyman
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    Thank for the response the explanation of no/nc clears up some of my confusion. I am not really about the homing usage of the limit switches but the limit use. even if I treat the y axis as one I still need at least two switches to cover the forward and backwards limits. what I meant by chaining was can I link two y axis limits then put one cord into the connection on the gradus.
     
  4. Scotty Orr

    Scotty Orr Master
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    Yes, you can chain limit switches! Depending on whether they are n.c. or n.o., you would chain either in series or in parallel (respectively). You set which way in GRBL. Take a look at the info and wiring diagrams at Wiring Limit Switches · gnea/grbl Wiki · GitHub (These show connected to arduino, but the wiring to the Gradus would be similar.)
     
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  5. JustinTime

    JustinTime Master
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    What Scotty said is the correct answer. The machine knows which direction is home and which direction is just limit (home and limit are the same at the zero point). If the machine didn't know which direction is home then giving the command G1 X0, for example, would mean nothing to the machine but it does mean something to it and it goes to the zero point (where ever you've set the zero point). That is why you can connect all the limit/home switches, of one axis, in parallel and to one input terminal if they are Normally Open (NO or n.o.) and in series when the are Normally Closed (NC or n.c.).
     
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  6. eleethesontai

    eleethesontai Journeyman
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    what is meant by in parallel and in sequence?
     
  7. Giarc

    Giarc Master
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    Those are the two types of circuits for limit switches as shown in the link listed a couple posts above. By the way, everyone new to GRBL should very thoroughly read that entire GRBL Wiki because it will answer most questions. Anyways, back to Parallel circuits and Series (not sequence) circuits. On normally closed switches, you want series so when one is switched it opens the circuit letting the controller know a limit has been reached. Parallel is for normally open switches. If either is closed, the signal is sent to the controller. Google those terms to learn more, hey are the most basic of electrical circuits. Your home is full of them.
     
  8. Kevon Ritter

    Kevon Ritter Master
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    I actually made my own breakout board based on the circuit below. Each axis has a positive as well as a negative input. They are connected in parallel and have no effect on the opposing switch, which means that you don't need both of them installed. Plus it's filtered and grounded.

    X +/-
    Y +/-
    Z +/-
    5v power
    switch ground
    chassis ground (shielding)
     

    Attached Files:

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  9. eleethesontai

    eleethesontai Journeyman
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    that is awesome, I will have to copy that one day. On the gradus for each of the inputs there is the input then a ground. on this mockup there is one ground input then 1 for each of the axis. do I need to run a ground to each one?
     
  10. Kevon Ritter

    Kevon Ritter Master
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    My ninja edit wasn't so ninja. Check my post again. The 6 pin connector was also missing from that pic.

    You only need one ground for them all. If you look at the copper picture, the second from the left on the big board (T looking bit) is the shared ground for all limits.
     
  11. eleethesontai

    eleethesontai Journeyman
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    yea the Arduino diagram and yours only has one ground. Thats why I was confused why the gradus has a ground for each axis? do I just use one of them and leave the other two empty?
     
  12. Kevon Ritter

    Kevon Ritter Master
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    Looking at the wiring diagram for the Gradus shows that each axis has it's own ground. Ultimately, ground is ground. It doesn't matter if you have 50 switches or just one. As long as the connector can handle the current, it's all the same.
     

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