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Author Topic: Limit Switch Problems - BAFFLING!  (Read 10159 times)

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Limit Switch Problems - BAFFLING!
« on: February 11, 2007, 04:16:05 PM »
I have my limit switches (3 sets 2-x,2-y,and 1-z) wired in series. All are set to be
normally closed and therefore return a ground to their respective parallel port pins.
The measured voltage at the controller is 2.5 millivolts closed and
4.5 volts when active (open) for each of the three signals. The diagnostics panel
sees these activations and responds with the appropriate LEDs lit when switches
are activated. The switches are lever activated microswitches so there is no external
voltage or active circuitry present, just pull up resistors to +5 and ground.

My problem is that when the pins are set up in MACH3, it tells me that there
is a limit switch active and refuses to reset. The odd thing about all this is that
if I make all the switches normally open, this works. Obviously I had to change
the sense of the switches in Mach 3 to make this happen. I really don't
want to run this in a normally open switch configuration. Can anyone offer
a little light on this problem?

I wouldn't be so perplexed if the darn diagnostic panel didn't say one thing while
the main page said something else ( i.e. limit switch activated.

Offline Chip

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Re: Limit Switch Problems - BAFFLING!
« Reply #1 on: February 11, 2007, 05:59:27 PM »
Hi, moonlightmedia

Have you changed the state of "Active Low" in Config, Ports and Pins, Inputs, for your switch inputs.

This will change the way Mach looks at the switch "NO" "NC",  click on the X or Check mark it will change state, then Apply.

Hope this Helps, Chip
« Last Edit: February 13, 2007, 02:24:26 PM by afn09556 »

Offline skaha

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Re: Limit Switch Problems - BAFFLING!
« Reply #2 on: February 11, 2007, 07:14:12 PM »
Hi, I have exactly the same setup on my machine, works well, have you checked for a  faulty switch with an ohm meter, sounds like one is not opening to complete the circuit.
Terry
Re: Limit Switch Problems - BAFFLING!
« Reply #3 on: February 13, 2007, 10:07:52 AM »
I know the set up and switches are working because the Diagnostic Panel Lights go on and off
correctly when the switches are tripped. No lights on and I can't reset.

Offline Scott

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Re: Limit Switch Problems - BAFFLING!
« Reply #4 on: February 13, 2007, 10:55:43 AM »
It still sound like the switches are set backwards in Config/Ports and Pins/Input Signals.  I think you should have a red X in the 'Active Low' column.

Also check the settings page for 'Manual Override Limits' or 'Auto Override'.  If on, then you should be able to reset and move off the switches.
Scott
Re: Limit Switch Problems - BAFFLING!
« Reply #5 on: February 13, 2007, 11:00:56 AM »
Also add a bit of debounce and see if that helps... 2000 should help if it is a noise problem
Fixing problems one post at a time ;)

www.newfangledsolutions.com
www.machsupport.com

Offline Tarak

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Re: Limit Switch Problems - BAFFLING!
« Reply #6 on: February 17, 2007, 06:09:22 AM »
Hi Brian, I'm having a similar problem, I'm wondering if the Debounce will fix my problem, which field should I enter a value into DEBOUNCE INTERVAL or INDEX DEBOUNCE?

Hood

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Re: Limit Switch Problems - BAFFLING!
« Reply #7 on: February 17, 2007, 12:51:19 PM »
Debounce Interval is the one you need to use for limits etc. The Index Debounce is for the spindle speed sensor if you have such a thing fitted.
Hood

Offline Tarak

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Re: Limit Switch Problems - BAFFLING!
« Reply #8 on: February 17, 2007, 03:03:45 PM »
Thanks, I'll give it a try.
Re: Limit Switch Problems - BAFFLING!
« Reply #9 on: February 18, 2007, 04:24:15 PM »
This has still got me stumped. I tried to set up a simpler scenario so I could troubleshoot this problem.
I took everything down to just one switch which is normally close. All switches are disabled with the
exception of this one switch on pin 10 of the parallel port and set to active high. The meter agrees
at .6 ohms across the contacts with the closure being to ground. Mach 3 is set to be active high.

1- Nothing is moving and the switch is STATIC at ground.
2- Switches that are not being switched, don't bounce in my humble opinion.
3- Mach 3 diagnostic panel shows NO LIGHTS ON. In effect this means
   that Mach 3 agrees that it also sees a ground from the port.
4- The main page in Mach 3 will not do a reset and reports that a limit switch is tripped.

Steps one thru four are in CONFLICT. Mach 3 sees a ground (no limit switch active) and yet
reports a limit switch is tripped. This is the part that I don't get !!!!!

What I am beginning to suspect is that the Diagnostic Panel and the operational structure of
Mach 3 are looking at two different places - This is the only way I can explain why it might act
this way.

I'm not looking to criticize Mach 3, I love the software. I just want to figure out whats going on
so my router will run correctly.


Even more bizarre is that if you set the switch (resolder) to be normally open and the
corresponding signal on pin 10 to be active low, this all works ! Unfortunately this is not
the best way to wire this (active low) since a broken connection will give no indication.
« Last Edit: February 18, 2007, 04:28:03 PM by moonlightmedia »