# Limit Switch Wiring Problems - Again!



## TomS (Sep 22, 2016)

When I built my mill a couple of years ago I struggled with wiring my limit switches in series.  My intent was to use one input on the BoB so I would have a couple for future expansion.  That didn't work out so I ended up wiring each switch to and individual input.  It's been working just fine until yesterday when I decided I wanted a Z axis zero tool setter.  This is where my problems begin.  

Here's a picture of my limit switch/tool setter terminal block.  The three wires on the upper left are the X, Y and Z plus (+) wires from the limit switches.  Each of the four upper right terminals are jumpered with one wire going to an input terminal on the BoB (pin 10 on the Input Signal tab in Ports and Pins).  I checked continuity and all is good.  You will note that the tool setter plus (+) wire is not connected nor is it connected at the BoB.  One step at a time.

The four wires on the lower left are ground wires (-) for the X, Y, and Z axis and the E-Stop circuit.  The E-Stop plus (+) is wired to pin 13 on the BoB.  The wires on the lower right are also jumpered with one wire going to the ground terminal on the BoB.  Checked continuity and it is good across all terminals.



I enabled all limit and home switches on the Input Signal screen and set them to pin 10.  As I said above the E-Stop is set to pin 13.  The E-Stop works.  I checked and am getting 5VDC across pin 10 and the BoB ground terminal but nothing at the terminal block.  As a reality check I unwired all the switches and wired in just one and it worked.  I can trip the circuit and home the one axis.  

All this being said what am I missing or doing wrong?  I'd like to get this problem solved so I can continue with wiring in the tool setter.

Tom S.


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## Boswell (Sep 22, 2016)

From your description and the picture it looks like you have them all wired in parallel not Series. Is that what you intended?    You would need Normally Open limit switches for a Parallel setup and Normally Closed limit switches for a Series strategy. Best practice is for Limit Switches to be Normal Closed and wired in Series so any wiring fault will trigger the limit circuit.   So the question is, are your limit switches Normally Open or Normally Closed?   You mentioned that you tried it with one limit swtch connected and it worked. Did you then go straight to all three or did you try it with just two?  what was the result?  Are you 100% sure your jumper wires are working as expected? It is hard to tell from the photo. You can test this by leaving the jumper wires in place and then using just one limit switch (you said that works) and move it to each of the 3 positions. If it does not work in each position, then your jumpers or wiring block is not working as expected.. If it does work in each position then try adding a second limit switch.


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## TomS (Sep 23, 2016)

Boswell said:


> From your description and the picture it looks like you have them all wired in parallel not Series. Is that what you intended?    You would need Normally Open limit switches for a Parallel setup and Normally Closed limit switches for a Series strategy. Best practice is for Limit Switches to be Normal Closed and wired in Series so any wiring fault will trigger the limit circuit.   So the question is, are your limit switches Normally Open or Normally Closed?   You mentioned that you tried it with one limit swtch connected and it worked. Did you then go straight to all three or did you try it with just two?  what was the result?  Are you 100% sure your jumper wires are working as expected? It is hard to tell from the photo. You can test this by leaving the jumper wires in place and then using just one limit switch (you said that works) and move it to each of the 3 positions. If it does not work in each position, then your jumpers or wiring block is not working as expected.. If it does work in each position then try adding a second limit switch.



Thanks for your response and questions.  My switches are NC so that being said I need to wire them in series.  I connected one switch only.  Didn't try two.  Jumped right to three and got no where.  

I hear what your are saying about parallel vs. series wiring.  Bear with me.  I'm electrically challenged but I think I grasp the concept.  I'm out of town for the next five days but will give it a try when I get back.  I'll post how it works out. 

Tom S.


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## Boswell (Sep 23, 2016)

I am also out of town for a few days but with NC switches you must wire them series. so  the ground goes into one switch, then out of that switch into the next, our of that switch into the third, and then finally into the BOB. there will be NO common GRD connection as each switch is daisy chained from one to the next.


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## TomS (Sep 23, 2016)

Boswell said:


> I am also out of town for a few days but with NC switches you must wire them series. so  the ground goes into one switch, then out of that switch into the next, our of that switch into the third, and then finally into the BOB. there will be NO common GRD connection as each switch is daisy chained from one to the next.



Thanks.  Can't wait to get back in the shop and get my mill running again.

Tom S.


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## TomS (Sep 28, 2016)

Back at it today.  Wired the switches in series, or so I thought.  Obviously I'm not getting it because I'm not getting lights on the Mach 3 Diagnostics screen when I actuate a switch.  Here's a picture of my terminal block and an explanation on how I wired it.




Starting at the upper right is the wire from pin 10 on my BoB.  The COM wire from the X axis switch which is connected to the upper left terminal which is jumpered to the second terminal from the upper left.  The X axis NC wire is connected to the terminal second from the top on the right side.  The Y axis switch is wired in series, or so I thought, from the X axis switch to the Z axis switch with the last terminal on the lower left going to the ground terminal on the BoB.  Pins and Ports is setup with pin 10 designated for all switches.  

I'm a reasonably intelligent person but for some reason I have a mental block when it comes to electricity and wiring.  Any input is appreciated.

Thanks,

Tom S.


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## JimDawson (Sep 28, 2016)

I'm sorry Tom, I don't understand your explanation, but try this:

First make sure all of your limit switches are wired Normally Closed. Check this with a Multimeter ohms setting.

Then with the power off, again use the the Multimeter to follow the path.  Put one lead on the wire going to pin 10, then check at the X switch with the other lead, then make sure that you have the signal at your terminal block, then make sure you have the signal at the Y com terminal at the switch, then check to make sure that toggling the switches causes a state change and so on.  Trace through the circuit one connection point at a time until you get back to the Bob Com terminal.  Then if all is well, it should work as desired.

It also helps sometimes to draw the circuit out on a piece of paper, just to help troubleshoot.


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## TomS (Sep 28, 2016)

JimDawson said:


> I'm sorry Tom, I don't understand your explanation, but try this:
> 
> First make sure all of your limit switches are wired Normally Closed. Check this with a Multimeter ohms setting.
> 
> ...



Thanks Jim.  Below is the diagram I used (limit switch circuit only).  My BoB is powered through a USB hub so the DC power supply shown on the diagram is not applicable.  I'll do the test procedure you laid out and see if I can find the problem.

Tom S.


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## Boswell (Sep 28, 2016)

Tom,

The C from the Limit Z should probably go to the +VDC not -VDC.   The typical circut is that the BOB is looking for +5v or +Vdc to indicate that all is well and nothing to indicate that there is a problem.
So if you connect C (common) from the Limit Z and then through all of the limit switches as indicated to the BOB then with all of the switches in their Normal postion it will allow the +Vdc to get to the BOB. If any switch actuates then it will break the circuit and prevent the +Vdc from getting to the BOB.

BTW, I would expect the same for the E-STOP as most E-STOP switches are Normally Closed


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## TomS (Sep 28, 2016)

I followed the procedure Jim laid out in his post above.  First checked continuity across the NC terminals on each of the limit switches.  Then checked each for a state change when activated.  All is good with the switches.  Connected wire from Pin 10 terminal to the terminal block and checked continuity.  Did a continuity check at each connection point as I assembled the wiring up to and including the last wire going to the ground terminal on the BoB.  Again all is good.  

Fired up the computer and set the input pin for all limit/home switches to pin 10.  Z setter is set to pin 11 and E-stop is pin 12.  Verified the E-stop and Z setter functions correctly.  Limit switches still not working.  Checked voltage across pin 10 and ground terminal and it was zero.  Shouldn't it be 5VDC?

Boswell - If I understand what you are saying I should swap the pin 10 wire and ground wire on the terminal block.  

Tom S.


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## JimDawson (Sep 28, 2016)

TomS said:


> Checked voltage across pin 10 and ground terminal and it was zero. Shouldn't it be 5VDC?



It should be 0 V with the switches connected and closed.  Check again with a switch activated, then it should read 5 V

Is the pin set properly in Mach3, I think it should be Active High,, but try Active Low also


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## TomS (Sep 28, 2016)

JimDawson said:


> It should be 0 V with the switches connected and closed.  Check again with a switch activated, then it should read 5 V
> 
> Is the pin set properly in Mach3, I think it should be Active High,, but try Active Low also



I'll check it in the morning.  Each of the switches are set active low which is the setting they were at when I had the switches wired to separate inputs.  I'll set them active high and see what happens.  Thanks again for your help.

Tom S.


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## Boswell (Sep 28, 2016)

to be sure, you would need to know if the BOB you are using has built in pull-up resistors. If so then the way you have wired it should work and as Jim says, with no switches activated it should read ZERO volts at Pin 10 and with any one of the three activated it should read +Vdc at pin 10. However if the BOB does not have internal pull-up resistors then you will need to move the wire that goes from the Z-Limit switch from the -Vdc terminal to the +Vdc terminal. Then measure again and you should get +Vdc with no switches are activated and Zero volts when any one or more limit switches are activated.  Once you verify that it works with an volt meter then you you can set Mach3 to Active Hi or Active Lo depending on which of the two configurations that you are determ that you have. My guess from your symptoms is that you need to use the second configuration where you have the last switch in the chain (Z-Limit) connected to +Vdc and not -Vdc like you show in the schematic.


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## TomS (Sep 29, 2016)

Boswell said:


> to be sure, you would need to know if the BOB you are using has built in pull-up resistors. If so then the way you have wired it should work and as Jim says, with no switches activated it should read ZERO volts at Pin 10 and with any one of the three activated it should read +Vdc at pin 10. However if the BOB does not have internal pull-up resistors then you will need to move the wire that goes from the Z-Limit switch from the -Vdc terminal to the +Vdc terminal. Then measure again and you should get +Vdc with no switches are activated and Zero volts when any one or more limit switches are activated.  Once you verify that it works with an volt meter then you you can set Mach3 to Active Hi or Active Lo depending on which of the two configurations that you are determ that you have. My guess from your symptoms is that you need to use the second configuration where you have the last switch in the chain (Z-Limit) connected to +Vdc and not -Vdc like you show in the schematic.



I thought about your response and realized I might not have been clear in my explanation when I posted the wiring diagram.  My BoB is powered through a USB hub which means I don't have +Vdc or -Vdc terminals.  I'll post my wiring diagram in the next couple of hours.

Again, thaks for your help.

Tom S.


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## Boswell (Sep 29, 2016)

I am making all my comments off of the schematic that you shared above where you clearly show a -Vdc and a -Vdc.  I just read your text to say that you did not implement a power supply like the diagram shows. So you will have to find a +Vdc somewhere.  What is the Brand and model of your BOB?


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## TomS (Sep 29, 2016)

Here is my wiring diagram and my BoB manual.  My limit/home switches worked when they were wired to separate inputs.  That's why I'm confused as to why they don't work when wired in series.

Tom S.


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## Boswell (Sep 29, 2016)

ok, let take a look at this. I think we can get this figured out but it will be this evening before I can look into it.


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## JimDawson (Sep 29, 2016)

I see the problem, you are shorting the switches with the jumpers.  

try it like this


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## jbolt (Sep 29, 2016)

It has been a while since I went through this but I recall if you gang all the Home switches together you have to Home each axis individually and not use the Ref All Home button.


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## TomS (Sep 29, 2016)

JimDawson said:


> I see the problem, you are shorting the switches with the jumpers.
> 
> try it like this
> 
> View attachment 136783



Right on.  I was driving back from town and the light went on.


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## TomS (Sep 29, 2016)

JimDawson said:


> I see the problem, you are shorting the switches with the jumpers.
> 
> try it like this
> 
> View attachment 136783



Success!!  It worked and my mill is up and running.  Now I have an extra input for my next headache, aka tool setter.

Thanks to everyone for their input.  I'd be lost without the support I get from this forum.

Tom S.


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## JimDawson (Sep 29, 2016)

Happy to hear you got it!


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## TomS (Sep 29, 2016)

JimDawson said:


> Happy to hear you got it!



Thanks for your help.  

Tom S.


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