Wiring Limit, Home and E-Stop Switches

[gpraceman]

I found this diagram, mentioned in an old thread, that seems to be a good way to wire up limit, home and E-Stop switches.

My question, is if I can just put the E-Stop switch in series with the limit switches and free up a parallel port input? I assume so.

Also, should the home switches be in the same location as X--, Y-- and Z++ limit switches or offset from each other?

I am using Mach3, if that matters.

[Crevice Reamer]

Hi Race man!

NO! Wire the Estop to its own separate input.

If you want to save inputs, just wire ALL of the switches NC in one big series loop, connect one end to PSU ground and the other end to one input. Mach3 knows what switch is what. You can use 3 of the switches as both home and limit switches.

CR.

[gpraceman]

NO! Wire the Estop to its own separate input.

OK. Help me understand the reasoning behind that.

If you want to save inputs, just wire ALL of the switches NC in one big series loop, connect one end to PSU ground and the other end to one input. Mach3 knows what switch is what. You can use 3 of the switches as both home and limit switches.

I guess that I wanted to leave one free for some future use.

I know that 3 of the switches can be used as both limit and home switches with Mach3, but I assume that you cannot wire them in series to do so. Seems that I can put the X++, Y++ and Z-- switches in series and tie those to one parallel port input, but leave the combo home/limit switches as separate inputs.

[Crevice Reamer]

Nope! Wire all six Normally Closed switches in series and forget about it. Three of them will also be combo. Mach3 will know which switch is which and for what.

CR.

[gpraceman]

Nope! Wire all six Normally Closed switches in series and forget about it. Three of them will also be combo. Mach3 will know which switch is which and for what.

I guess that I am having a hard time grasping that. If all 6 limit switches are wired to the same parallel port pin, how does Mach3 really know it is in the home position and not at some other limit?

I'm a noob to Mach3 and CNC in general, so it helps if I have a little more explanation of things for me to understand. I just got my first CNC machine this past week.

[Crevice Reamer]

Mach3 knows where all the switches are. During a cutting operation, if it encounters a switch, it assumes it to be a limit and shuts down. During homing, it first moves the Z until encountering a switch, recognizes home, and backs off a trifle to close the switch. Then it will home the X, and then the Y. Because limits and homes are used in two completely separate operations, it has no trouble doing this.

Limit/home/Estop switches use very low Voltages and are easily subject to crosstalk from other wires nearby. You MUST use shielded wire and try to route it not close to other wires.

Combining Estop with the homes/limits just multiplies the chances of having spurious signals interupting your CNC program.

You may find some of this info to be helpful:

http://crevicereamer.com/Page_2.html

CR.

[gpraceman]

OK, I believe that I understand now. So, I can simplify that diagram and just use two parallel port inputs. One for E-Stop and the other for all of the limit switches in series (3 of those doing double duty as home switches).

Can I get the +5V off of one of the other parallel port pins?

[Fastest1]

That is correct about the switches. Regarding the 5v, I believe you want to keep the power on the pc side seperate from the machine sides power. A cheap wall wart will supply the 5v (most cell phone chargers are 5v, check first). You could try the 5v from the PP and if it starts throwing faults get power elsewhere. I have had many problems with grounds and such. Nothing causing any release of the magic smoke but tripping estops and such. In fact it has happened every time I have added something new and electrical in the system, such as probes, relays and limit switches. Good luck and enjoy. Btw when you see it home the first time it is too cool. It works exactly like CR said.

OK, I believe that I understand now. So, I can simplify that diagram and just use two parallel port inputs. One for E-Stop and the other for all of the limit switches in series (3 of those doing double duty as home switches).

Can I get the +5V off of one of the other parallel port pins?

[gpraceman]

Regarding the 5v, I believe you want to keep the power on the pc side seperate from the machine sides power. A cheap wall wart will supply the 5v (most cell phone chargers are 5v, check first). You could try the 5v from the PP and if it starts throwing faults get power elsewhere.

I was hoping to avoid yet another external wire to deal with. So far, it seems I have a spaghetti factory going on and haven't yet added the limit switches or the E-Stop, which will add to it. If I can get that +5V off the parallel port, is there a specific pin or is there something that I need to do in Mach3 to turn on an output pin?

You MUST use shielded wire and try to route it not close to other wires.

I guess that precludes bundling them with stepper motor wires, even if using shielded wire, correct?

[Crevice Reamer]

I was hoping to avoid yet another external wire to deal with. So far, it seems I have a spaghetti factory going on and haven't yet added the limit switches or the E-Stop, which will add to it. If I can get that +5V off the parallel port, is there a specific pin or is there something that I need to do in Mach3 to turn on an output pin?

Ah, how simple life becomes when you use a G540 and avoid all of this spaghetti.

I guess that precludes bundling them with stepper motor wires, even if using shielded wire, correct?

YES, if motor wires are unshielded, Not necessarily if motor wires ARE shielded. Either way, the drain wire of the shielding must be grounded at the BOB end only.

CR.

[Crevice Reamer]

Now, if you want to cut down some of the wiring complexity:

I don't USE limit switches with steppers. IMO they are unnecessary. Worst case if you exceed a limit, steppers will just stall harmlessly. Soft limits set in Mach3 work just fine to prevent this though.

I consider HOME switches to be mandatory though.

CR.

[gpraceman]

Ah, how simple life becomes when you use a G540 and avoid all of this spaghetti.

That is a very nice controller and something that I considered. I'm not sure that I would have less of a spaghetti issue with it though. I went with the control box that Zenbot offered. Most of the spaghetti is actually all of the cords and cables for the computer and monitor that I am using. I was considering a SmoothStepper so I could use my laptop, but thought that I'd give the desktop a try. I had a recently retired XP machine within easy reach.

I don't USE limit switches with steppers. IMO they are unnecessary. Worst case if you exceed a limit, steppers will just stall harmlessly. Soft limits set in Mach3 work just fine to prevent this though.

I consider HOME switches to be mandatory though.

I appreciate all of your assistance. I guess I'm a bit paranoid of messing up the machine as I am learning to use it. I'll just worry about the home switches, make sure the wires are shielded and not run them with the stepper motor wires.

Do I really even need to worry about an E-Stop?

I do have some soft limits set in Mach3, at least for X and Y (until I get the replacement for the Z head that was damaged during shipment).