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IndustryArena Forum > OpenSource CNC Design Center > Arduino > Bad Limit Switches causing random behaviour
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  1. #1
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    Bad Limit Switches causing random behaviour

    Hi

    I have been struggling with my Mill-Router hybrid´s end switches for a couple of days and after trying a lot of different tricks ended up pulling apart one of the switches I planned to use. What I found was extremely poor build quality.

    I tried to understand why GRBL couldn´t clear X ahis limit switch even though I had a lot of extra pull off distance. I tried configuring things in all sort of weird ways when running out of ideas, and it didn´t pop in my mind that it could just be the inconsistent behaviour of the switches themselves that causes the problem. They are chinese really sweet looking "industrial" limit switches from Amazon. Mechanically they are hopeless.

    My multimeter gives really random readings that are hard to explain by anything other than dirty contacts (cleaned one with acetone and it got better but not good) and misalignment of the contactors. Pull down resistors didn´t help at all ( I tried many sizes, from 10K down to 3,3K). Akll the cables are shielded.

    Is arduino based control electronics especially delicate in this sense? I mean do people have similar issues? I ordered real branded switches and am hoping them to clear the problem, but at the same time am afraid that there is something else too in it.

    -Propeller

  2. #2
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    Re: Bad Limit Switches causing random behaviour

    I tried to understand why GRBL couldn´t clear X ahis limit switch even though I had a lot of extra pull off distance.
    Your limit switch must clear when the actuator doesn't touch it any more. If not, it may be influenced by magnetic fields like a stepper motor moving towards the switch. Increase the pull off until the switch is clear from the actuator and the switch level is HIGH again.
    Pull down resistors didn´t help at all
    Arduino processors (your RPI has an ATMEGA328) have build in pullup resistors. Your Z-axis works fine that shows extra resistors are not needed.
    Is arduino based control electronics especially delicate in this sense
    No, all processors will response in a similar way. It is the switch that causes this problem.

    I assume you use high voltage switches (230 V) for these low level signals (as most of us do). If money doesn't matter, you could use low voltage switches. As an alternative, you could use proximity switches like LJ12A3-4-Z / TL-W5MC1 / NJK-5001C / etc. Your RPI controller needs a 5 volt version but most (cheaper) 6..24V versions also work on 5V.

  3. #3
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    Re: Bad Limit Switches causing random behaviour

    OK, thanks. I am looking for Telemechanique psn - det 61 11 switches now, 1 ordered and tomorrow I can try it out. If it´s no good I´ll probably do 3D printer sort of flingy but precise solution with Omron´s micro switches.

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