Wiring limit switches in series?

[PapaSierra]

Hi,

I'm nearly done building a desktop CNC from scratch and I'm stuck at a silly problem. I fitted 5 limit switches - two each on axis X and Y and one on Z.

The switches are MakerBot design, with a build in LED. There's a good description of them here: https://reprap.org/wiki/Mechanical_Endstop
CNC controller I use is a DLC32 board with RGBL f/w. "Invert limit pins" is activated in the f/w configuration.

Z axis is basically wired directly, Vcc to Vcc, GND to GND, Signal to Signal. It works fine, so normally the signal pin is HIGH and the LED on the switch PCB light stays off. When the switch activates, the LED light comes ON, and the signal pin changes to LOW. Stepper stops as a result.

The problem is on X and Y axes as they only activate when BOTH switches on a given axis are pressed. Obviously that's to do with the way I wired them. What I did is, on each axis, I connected together both switches in parrallel. I understand this is wrong since the circuit operates in NC logic (for an extra layer of safety), so rather then parallel, I need to wire them in series but I'm not sure exactly how.

Could anyone sketch a simple diagram, please?

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[machinehop5]

...there are other Options maybe...one is there should be an enable/disable + (plus) and an enable/disable - (minus) direction Inputs on each Axis drive amp module. Wiring switches at both ends of travel this way and it's easy and failsafe way to stop overtravel and still be able to Jog off the switch when overtraveled.

DJ

[PapaSierra]

...there are other Options maybe...one is there should be an enable/disable + (plus) and an enable/disable - (minus) direction Inputs on each Axis drive amp module. Wiring switches at both ends of travel this way and it's easy and failsafe way to stop overtravel and still be able to Jog off the switch when overtraveled.

DJ

Thanks for your tips DJ. I attached a drawing of my stepper motor controller board. Could you tell me which inputs you are thinking about?

[PapaSierra]

Sorry, I don't think the attachment worked in my last post.

[CNCMAN172]

Wire all the switches in parallel

[phomann]

Wire all the switches in parallel

Unless I’m missing something that won’t work as when one switch is pressed it will pull the input to 0v, while the other switches are still pulling the input to 5v.

According your limit switch schematic what you need to do is:
1. For the 1st limit switch, connect pin 1 to 5v, pin 2 to 0v.
2. For the 2nd limit switch, connect pin 1(pwr) to pin4 (output) of the 1st limit switch ,pin2 to 0v.
3. For the 3rd limit switch, connect pin 1(pwr) to pin4 (output) of the 2nd limit switch ,pin2 to 0v.
4. Continue this for all intermediate limit switches.
5. For the last limit switch, connect pin 1(pwr) to pin4 (output) of the preceding limit switch ,pin2 to 0v AND connect pin4 to the input on your breakpoint board.

So each limit switch is powered from the output of the preceding switch. If any of the preceding switches is pressed, the power line is set to 0v, resulting in the final output being set to 0v.

Cheers
Peter


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[PapaSierra]

Thanks a lot phomann for a detailed explanation. In case of two switches on one axis, is this what you mean (see attachement)?

EDIT: I just tried it, works flawlessly
Thanks a lot man(n)!

[phomann]

Yes, that’s correct. Glad that you understood and that it worked. I wrote it on my phone during lunch.

You can just keep daisy chaining all your limit/ home switches so they all use a single input.
Doing it this way means that you can only home 1 axis at a time so it knows which home switch is hit.
For limit switches, the control software doesn’t need to know which switch is hit as an error has occurred.

Cheers
Peter.


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[PapaSierra]

Thanks again, I really appreciate you spent time on your lunch helping me out.

I have them all wired and tested now. Since my board has three separate limit switch inputs, I wired them separately so the software reports which axis hit the switch.

This is my final wiring in the attachement in case anybody else needs it.