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Author Topic: hooking up limits  (Read 8307 times)

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hooking up limits
« on: May 03, 2008, 05:29:20 PM »
i'm using optical limits as my home and limit switches for my mill.  the switch when triggered sends a +5volt signal to the computer.  however, pins 10, 11,12, 13 have 4.5 volts on them when the optical switches aren't connected.  my optical switches are wired to send 5 volts to the computer to create a trigger event.  i thought that pins 10-13 were input pins?  what am i doing wrong?

Offline Chip

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Re: hooking up limits
« Reply #1 on: May 03, 2008, 05:46:22 PM »
Hi, SDConcepts

Change the Active Low state on the Inputs should do it.

Hope this Helps, Chip

Offline Greolt

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Re: hooking up limits
« Reply #2 on: May 03, 2008, 06:38:52 PM »
To send a signal to Mach you must make the input change state. 

So if it is high (5v) you must pull it low (0v) and vice versa.

Input pins on a standard LPT are high when not connected. 

Some BOBs pull the inputs low with on board resistors. So they are now low when not connected.

Can your optical limits be wired to pull the pin to ground (0v) when active ?

Or you may be able to install a pulldown resistor of the appropriate value so that the pin is low until the switch becomes active and pulls it high.

You need to refer to the documentation of your BOB.

Greg
Re: hooking up limits
« Reply #3 on: May 04, 2008, 07:40:58 AM »
I'm not using a BOB, i'm wired directly to the parallel port.  my last adventures try to cnc through a bob were useless. do i need to add a resistor parrallel with the input to pull the parallel port pin down to 0?
Re: hooking up limits
« Reply #4 on: May 09, 2008, 01:00:57 PM »
OK, i got the limits all hooked up and they work on the diagnostic screen.  however, i still get an e-stop trigger and it tells me a limit is triggered.  how do you trace something like this when nothing is showing up in the diagnostics?

Offline Hood

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Re: hooking up limits
« Reply #5 on: May 09, 2008, 01:32:56 PM »
Sounds like noise, try setting the Debounce Interval to 2000, if that works reduce it until you have problems again then step up slightly. Make sure your limits have shielded cables grounded only at the control end.
Hood
Re: hooking up limits
« Reply #6 on: May 09, 2008, 02:17:07 PM »
Hood,

thanks for the tip.  i tried that and it worked for a while but ended up triggering the limits sooner or later on its own again.  any other tips other than shielding the cables? 

Offline Hood

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Re: hooking up limits
« Reply #7 on: May 09, 2008, 02:41:10 PM »
If you are still getting problems with 2000 then shielding is the way to go, in fact shielding is a must in my opinion, its the first thing that should be done to any wire carrying 5v signals. The difference between Hi and Lo is so close it is very easy for electrical interference to cause false triggers. I have 24V on things such as limit switches and then convert the 24V signal to 5V as near to the computer as possible and still have all the 5v signals shielded. The reason is the difference betwen Hi and Lo in a 24V system is much greater than a 5v system and so noise is hardly ever an issue.
Hood
Re: hooking up limits
« Reply #8 on: September 04, 2008, 11:31:14 AM »
Great tip on the 24v signals...

Offline Kristin D

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Re: hooking up limits
« Reply #9 on: September 04, 2008, 12:10:28 PM »
I have 24V on things such as limit switches and then convert the 24V signal to 5V as near to the computer as possible and still have all the 5v signals shielded. The reason is the difference betwen Hi and Lo in a 24V system is much greater than a 5v system and so noise is hardly ever an issue.
Hood

Hood,

Very interesting can you post a schematic or description of how you do the 24v to 5 v ?

Kristin