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  1. #1
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    Default Hall Effect Limit Switches

    I finally got the router back in service today....yay! ( all 3 axis are as smooth as silk now )

    I decided to start cutting out some acrylic housings for some Hall Effect Limit Switches.
    I saw the thread on CNCZONE ( Electronic home switches made easy! )
    and was going to use the same IC but my machine uses a AKZ250 Motion Control Card and I can't get them to work in Mach3. They use Gekko drives. Can't imagine them being different, but I couldn't get them to work. I tested 44E's and the inbuilt SMD led DID work but the IC would not work with Mach3.

    I did find that 49E's do work, but cant get a led to operate from it, so I'm just going to use the IC without any led indication.
    I bought some 10 mm Acrylic off Ebay and drew up a simple housing. Its deep enough that I can rotate the IC 90( if I need to ) and it will still fit. Bonus.
    Going to fill the cavity with epoxy once I confirm the mounting point on the machine. I may need to adjust the position of the slots yet...will see.

    20160724_142640 (Small).jpg

  2. #2
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    Thumbs up Limit Switches

    Hi Steve,

    Interesting use of plastic there. I need to make some limit switches for my camper electric step. It hadn't occurred to me to use a hall device. I've used ordinary single pole change over microswitches, switching the motor directly. However they are prone to damage from water, dirt and other road nasties thrown up by the front wheels. Hall devices and a relay would be the perfect solution here.

    Thanks for the idea.

    PS. Old computer fans are a good source for hall switches. ON/OFF types rather than variable resistance ones.
    Best Regards:
    BaronJ.

  3. #3
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    Default

    Thanks Baron,
    yes, Hall Effect IC's are very handy. You have to use a magnet for the source though.
    You might be able to use proximity switches instead, if your steps are steel. Save you messing with magnets.

    Never thought of computer fans as a source.
    I just buy them in lots of 10 or so from Ebay out of China. Cheap and have spares....

  4. #4
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    Default

    As far as I know, all Hall Effect switches are binary - on/off - and can't do variable.
    Another type of binary switch is optical emitter/receiver. Lots of those in printers and such.

  5. #5
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    Default

    There are variable output Hall Effect IC's but I don't think that is important for this application. I don't know the requirements of my Motion Card but the 49E IC seems to work well.
    I'm waiting for some more IC's to arrive and some magnets with a mounting hole, that will make fitting very easy.
    Stay tuned...lol

  6. #6
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    Default

    Hi Guys,

    Jordan, there are many variants of both Hall Effect devices and Opto couplers that you referred to. Most often their use in electronic equipment is as a switch rather than a variable output device. Some of those that are specifically intended as a switch usually have a Schmitt Trigger output to ensure a logic high or low.

    Steve, I have cheated a little on my limit switches I found some normally closed reed switches in a draw and have used a couple with magnets super glued to the moving part of the step. The reeds use a tiny magnet to keep them closed and the big magnet forces them to open. I placed them into some heat shrink tube and glued it to the stationary part of the frame.
    Best Regards:
    BaronJ.

  7. #7
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    Default

    Quote Originally Posted by BaronJ View Post
    Hi Guys,

    Jordan, there are many variants of both Hall Effect devices and Opto couplers that you referred to. Most often their use in electronic equipment is as a switch rather than a variable output device. Some of those that are specifically intended as a switch usually have a Schmitt Trigger output to ensure a logic high or low.

    Steve, I have cheated a little on my limit switches I found some normally closed reed switches in a draw and have used a couple with magnets super glued to the moving part of the step. The reeds use a tiny magnet to keep them closed and the big magnet forces them to open. I placed them into some heat shrink tube and glued it to the stationary part of the frame.

    Reed switches are a nice solution. I considered them but thought I may use my limits for zeroing so didn't use them. They may introduce some very small variations of stopping point but that won't be a problem for you. Probably not for me either, but I've started down this road already...lol

    I cut some modified housing to suit the X Axis....a bit smaller and shorter mounting slots so the cable can enter from the side, so its neater.

    Steve

    20160728_134930 (Small).jpg

  8. #8
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    Default

    I got some time to do a quick test today. The test Limit switch seems to work fine. The machine stops very quickly and I cannot see any variation in stopping position when changing the jogging speeds, which is good. ( I assume this IS but I can't see it with the naked eye...)

    One thing I have look at is Mach 3 trips the machine when it hits the limit, but I then cannot back away from it. I have manually wind the stepper off the limit and then reset Mach 3. I would like to be able to drive the axis off the limit electrically. Anyone come across this?

    Steve

    20160829_172521 (Small).jpg 20160829_172529 (Small).jpg

  9. #9
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    Default

    Hi Steve,

    Nice work there. I like the setup.
    I see two possibilities, (1) the magnet is saturating the hall device, unlikely but possible, (2) the software is not allowing the motor feed to be reversed. There should be two inputs for the limit switches, one for each direction, its maybe that you are feeding "Dead stop", particularly since you say you have to reset the software.

    Disclaimer: I don't know Mach 3, only my experience with other CNC stuff.
    HTH.
    Best Regards:
    BaronJ.

  10. #10
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    Default

    Hi Baron,
    The limit does appear to switch later than in my earlier tests, but I hadn't used these particular magnets before. I suspect the magnets are mean't to be orientated 90 to the way I'm using them, but I can't help that. They work well enough.
    I have the "driving off the limit" problem sorted. I found a setting in Mach3 that allows the machine to drive OFF the limit after the software is reset. Its called 'Auto Limit Override' and appears on the settings tab.
    Unfortunately it also allow one to drive though the limit so one must be careful...lol

    I'm using ONE input for all of the limits switches and wiring all the switches in parallel, as per someones recommendation on the Net.

    Now to start fitting the switches and running the cables.

    Steve

    Quote Originally Posted by BaronJ View Post
    Hi Steve,

    Nice work there. I like the setup.
    I see two possibilities, (1) the magnet is saturating the hall device, unlikely but possible, (2) the software is not allowing the motor feed to be reversed. There should be two inputs for the limit switches, one for each direction, its maybe that you are feeding "Dead stop", particularly since you say you have to reset the software.

    Disclaimer: I don't know Mach 3, only my experience with other CNC stuff.
    HTH.

  11. #11
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    Default

    Hi Steve,

    I can envisage that the software knows which direction it was running when a limit was tripped and that it should be able to record that and prevent any further movement in that direction only allowing movement to take place in the opposite direction. But if you are resetting the software then it seems that you are loosing that information. To me that would not be acceptable.
    Best Regards:
    BaronJ.

  12. #12
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    Default

    After taking doing some re-work, I'm finally moving forward again....
    I have the Y axis complete and the the Z Axis completed today. I had a brain fart with the Z Axis switches and mixed up the wiring at BOTH ends ( doh ) so that took some time to sort out.
    I am not entirely happy with the sensing distance. I would like a couple more mm. I don't know why its so low. I experimented with the orientation of the neodymium magnets but nothing made any difference.
    Maybe the thickness of the acrylic is affecting it. I tried to keep it to a minimum but its still about 1.5mm.
    I tried packing the magnet away from the Aluminium frame but that did not affect it. I also tried overhanging the magnets...no go either.
    I have ordered some thicker magnets so that is the last resort. If they do not give me more clearance, I will have to live with it.
    I tried to find a way to mount he switches so the magnets travel across the front instead of travelling directly at the switch but could not work out a neat solution. Never mind....
    Just the X Axis to go and they should be a lot simpler to fit.
    Steve

    20160907_160345_001 (Small).jpg 20160907_160328 (Small).jpg

    PS Pics WERE orientated correctly when I uploaded them....sigh....

  13. #13
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    Thumbs up Hall Data

    Hi Steve,

    HALL_EFFECT_SENSING_AND_APPLICATION.pdf
    SS49e_Hall_Sensor_Datasheet.pdf
    Hall_Switch-3122.pdf

    Attached are two data sheets and a copy of the Honeywell application notes.
    The latter is a 1.6Mb file. I hope that these are useful to you.

    I suspect that the device you are using is not suitable for use with Mach 3 since its output is a linear one rather than a logic switch.
    Best Regards:
    BaronJ.

  14. #14
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    Default

    Hi Baron,
    Thanks for the info.
    My approach to choosing a IC was not very scientific. I should have put more thought into it. I did know the device was linear. i just thought it would not be a problem, as long as the flux density was high enough.
    I tested a few until I found one that worked with my motion card. I thought an analog device would be ok. It still might be...
    I read though your first document and it confirms partially what I suspected. The flux strength increases with an increase in cross sectional area as well as length.
    I have ordered thicker magnets to try. Longer magnets are feasible but not considered yet.... I can also try to reduce the distance between the sensor and the outer side of the enclosure.

    If I could have used magnets passing across the sensor, then I would not have this problem....never mind...lol

    it's all good fun.....

    Steve

  15. #15
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    Default

    Hi Steve,

    I have some hall switches salvaged from computer fan motors, I can't remember off hand what the part No: is but I'll try and find out later.
    Best Regards:
    BaronJ.

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