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Thread: Hall Effect Limit Switches
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25th Jul 2016, 01:55 AM #1Diamond Member
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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.
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25th Jul 2016, 02:32 AM #2
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:
Baron J.
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25th Jul 2016, 11:44 PM #3Diamond Member
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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....
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3rd Aug 2016, 07:36 PM #4Mechanical Butcher
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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.
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3rd Aug 2016, 09:26 PM #5Diamond Member
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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
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5th Aug 2016, 03:56 AM #6
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:
Baron J.
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5th Aug 2016, 10:35 PM #7Diamond Member
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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
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29th Aug 2016, 11:13 PM #8Diamond Member
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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
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30th Aug 2016, 03:01 AM #9
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:
Baron J.
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30th Aug 2016, 08:17 PM #10Diamond Member
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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
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31st Aug 2016, 07:32 AM #11
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:
Baron J.
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7th Sep 2016, 10:51 PM #12Diamond Member
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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
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PS Pics WERE orientated correctly when I uploaded them....sigh....
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8th Sep 2016, 07:16 AM #13
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:
Baron J.
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8th Sep 2016, 01:45 PM #14Diamond Member
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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
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8th Sep 2016, 06:56 PM #15
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:
Baron J.
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