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Changing the Sensitivity of Limit Switches?
« on: February 07, 2008, 04:43:13 PM »
Hi folks,

I'd like to make my limit switches less sensitive if thats possible...does anyone have any idea how?

I'm using Mach3, HobbyCnc 4 Axis Pro, and my 4 switches are wired parallel.

Any suggestions are appreciated. Thanks. ???

Offline Hood

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Re: Changing the Sensitivity of Limit Switches?
« Reply #1 on: February 07, 2008, 05:07:54 PM »
If you mean you are getting false triggering then the debounce may well help. You will find it from the Config menu then General config. It is at the top right of that page. Try a seeting of 2000 and if that works lower until your problem starts again then nudge back up.
Hood
Re: Changing the Sensitivity of Limit Switches?
« Reply #2 on: February 07, 2008, 05:20:16 PM »
Thanks Hood,

Should I change the "Debounce Interval" or "Index Debounce" ?

Offline Chip

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Re: Changing the Sensitivity of Limit Switches?
« Reply #3 on: February 07, 2008, 05:22:57 PM »
Hi, Thkoutsidthebox

"Limit switches less sensitive", Can you expand on this a little, Are thy tripping on there own ?

Thanks, Chip

Offline Hood

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Re: Changing the Sensitivity of Limit Switches?
« Reply #4 on: February 07, 2008, 05:23:13 PM »
Debounce Iterval is for general stuff like limits, the Index is solely for the Index pulse for spindle.
Hood
Re: Changing the Sensitivity of Limit Switches?
« Reply #5 on: February 07, 2008, 05:53:56 PM »
Chip, every so often I get a Limit Switch Triggered during cutting with the Z carriage in the center of the cutting area (Not near the sides). I look at all the limits and none have been triggered by anything that I can see, sides, hanging wires, extractor tube etc. Anyway, I reset, run from here, cycle start and continue.

This seems to happen at random during jobs. It might not happen for days, then it might happen a few times in as many hours. I think the problem is that my wires are not soldered to the limits, just wrapped around the terminals, and that when the Z carriage moves sometimes the wires pull/push up/down/sideways, and the bare ends rub the terminals on a switch, thus causing the error.

I have tried testing the sensitivity of my limits, and I can trigger them by almost an imperceptible brush with my finger against the touch plate, without actually puching in the button behind the plate until it clicks. I only want them to trigger if the button behind the plate is actually pushing in (It goes in about 1.5mm before clicking) enough to click. Hence I think that I need them to be less sensitive.

I hope that all makes sense..... ?

Hood, I will try editing the Debounce Interval tomorrow. Thanks.

Offline Chip

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Re: Changing the Sensitivity of Limit Switches?
« Reply #6 on: February 07, 2008, 06:25:02 PM »
Hi, Thkoutsidthebox

The Debounce setting should help, It will delay Mach a little on responding to the switch closing.

Most use NC switch's in series, That way your system won't reset unless it confirms continuity of the switch's.

The non soldered raped connections need to be soldered, You no.

Hope this Helps, Chip

Re: Changing the Sensitivity of Limit Switches?
« Reply #7 on: February 08, 2008, 04:12:23 AM »
Solder or clamp those connections! If they use blade terminals you could use corresponding crimp connectors, that would work well.

The other thing is, your machine sounds fairly new so this probably won't be an issue but large old machines like mine often suffer from earth leakage from old wires, splashy coolant etc. I've got all my limits relayed to counteract this - they need a good current of 30mA or so to operate. It takes very little current to drag a port pin down to logic 0, earth leakage or fortuitous contact with earthed parts will easily do this.

Offline jimpinder

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Re: Changing the Sensitivity of Limit Switches?
« Reply #8 on: February 08, 2008, 11:38:59 AM »
Reading all this I seem to think that you must (1) solder all your connections (2) if your limits are all connected in series, then make sure that the wire round them all is shielded and earthed.(3) The way to make your switches less sensitive is to up (or down) your pull up, or pull down resistors. This is a bit difficult because I don't know which way you have wired up your limits, or, indeed, what switches your are using to trigger them.

If you are saying that merely touching one of your switches causes it to trigger, then that suggests to me it is the capacitance of your body that is triggering it and not the physical switching of the switch. This also suggests that your wiring is a bit suspect as well.
Not me driving the engine - I'm better looking.
Re: Changing the Sensitivity of Limit Switches?
« Reply #9 on: February 08, 2008, 02:58:36 PM »
Thanks for the replies all.  :)

I set the debounce to 100 and the problem is gone! The limits still work fine but they have to be pressed in fully.  ;D Thankyou.

It may have had something to do with my body capacitance, but I just don't think so, I really think the switch was just too sensitive.....I know that the connections should be done properly....they are blade terminals and I have plenty of crimp connectors but unfortunately not enough time!  ::)

I've had this machine about four or five months. I designed and built it myself. Its made of wood, and is mounted in a wooden enclosure 3 feet from the ground inside a wooden shed, so I don't think earth leakage is a problem...yet!  ;)

If you would like you can see my build thread at the link below, but it hasn't been updated with pics since I moved, so the new enclosure, new gantry and Z carriage, and new workshop are not shown. :) Thanks again.
http://www.cnczone.com/forums/showthread.php?t=35211
« Last Edit: February 08, 2008, 03:00:23 PM by thkoutsidthebox »