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Author Topic: LImit and home switches  (Read 4655 times)

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LImit and home switches
« on: November 27, 2014, 04:25:19 AM »
Still learning but help required.

1/  Can you use Mach3 with normally open limit switches, i cannot find a reference to this in the manual unless i have missed it.

2/  How can i use 24Vdc for my limit and home switches.

Any help appreciated, please keep it simple i am a lay person when it coms to electrics

Thanks Cheryl.

Offline Tweakie.CNC

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Re: LImit and home switches
« Reply #1 on: November 27, 2014, 07:33:08 AM »
Hi Cheryl,

1) If you wish - Mach3 allows normally open or normally closed switches to be used (selecting Active Low / Active High as appropriate). Most prefer to use normally closed switches - supposedly it makes if 'fail-safe' if a wire falls off ( n.b. I use normally open switches and have never had a problem yet  :) ).

2) You will need to use a Break Out Board or Controller that accepts 24 Volt input signals.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: LImit and home switches
« Reply #2 on: November 27, 2014, 08:55:48 AM »
Why i asked th questions is that i have built a controller that drives the machine ok apart from having random limit and e-stop activations.
I have used shielded cable for limit and e-stop wiring and stepper motor wiring but i still get the random activations.

I have been told by a local electrical engineer who works on manufacturing machinery, mainly servo drives, that they always use at least 24Vdc to their control circuits which eliminated any stray signals.

How can i stop these random activations.
Oh, i have switched off WatchDogs and have Debounce set at 1000.

Offline ger21

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Re: LImit and home switches
« Reply #3 on: November 27, 2014, 09:03:22 AM »
The easy way is to set debounce higher. Try 3000.

Otherwise, make sure all your components are properly grounded using the star grounding method.
Gerry

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Re: LImit and home switches
« Reply #4 on: November 27, 2014, 09:05:13 AM »
Thanks Gerry,
What exactly is star grounding method, any diagram.
Thanks Cher

Offline stirling

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Re: LImit and home switches
« Reply #5 on: November 27, 2014, 09:06:33 AM »
2) you could use a simple 2 resistor potential divider to drop 24V switch network to 5V
Re: LImit and home switches
« Reply #6 on: November 27, 2014, 09:10:17 AM »
Thanks stirling,
I am not an electrical person, so i do not know what this is.
Any pics or description/circuit diagram.
Thanks,
Cher

Offline ger21

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Re: LImit and home switches
« Reply #7 on: November 27, 2014, 09:14:49 AM »
star grounding is where every component has it's own ground wire, all tied to a single point in the control box. If you google it, you'll find tons of examples.
Gerry

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Re: LImit and home switches
« Reply #8 on: November 27, 2014, 09:32:52 AM »
Hi Gerry,
I`ll do that, thank very much for you help.

Cher

Offline stirling

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Re: LImit and home switches
« Reply #9 on: November 27, 2014, 09:34:28 AM »
if you look here. On the diagram you see a simple potential divider.

Vin would be your 24V

suitable values for the resistors Z1 and Z2 would be 18K and 4.7K respectively

Vout would then be connected to a Mach input and would be at 5V

You'd put your switches in parallel between the 24V source and Z1

With all switches open, the 4.7K resistor would pull the input down to 0V

With any switch closed the input would be at 5V