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Encoder using Hall-Effect Switches — Parallax Forums

Encoder using Hall-Effect Switches

MacGeek117MacGeek117 Posts: 747
edited 2005-06-15 03:59 in Robotics
How would I mount the Hall-Effect switch on my Boe-Bot to track rotations of the wheel?
bugg

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So many projects, so little time.

Comments

  • allanlane5allanlane5 Posts: 3,815
    edited 2005-01-27 15:08
    Mount a small magnet on the wheel, mount the sensor on the side of the 'bot?
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-01-27 19:25
    I would recommend several small magnets for precision...A single magnet will only give you limited precision, as it will only count a full rotation of each wheel.· Interestingly enough you could probably find magnets that will fit in the holes of many of the BOE-Bot wheels I have seen.

    But, a simpler ready-made solution that would have the same effect would be:

    http://www.parallax.com/detail.asp?product_id=28107



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    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    Designs Page:··· http://www.lightlink.com/dream/designs
    ·
  • MacGeek117MacGeek117 Posts: 747
    edited 2005-01-27 23:51
    Thanks guys, but what I'm really asking is how far away can a Hall-Effect switch detect
    a magnet?
    bugg

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    So many projects, so little time.
  • MacGeek117MacGeek117 Posts: 747
    edited 2005-01-28 00:28
    I'm also wondering, what is the parallel-in serial-out brther of the 74HC595?
    bugg

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    So many projects, so little time.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-01-28 01:18
    bugg said...
    I'm also wondering, what is the parallel-in serial-out brther of the 74HC595?
    bugg
    74HC165

    http://www.parallax.com/detail.asp?product_id=602-00010



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    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    Designs Page:··· http://www.lightlink.com/dream/designs
    ·
  • Jon WilliamsJon Williams Posts: 6,491
    edited 2005-01-28 02:32
    StampWorks shows how to use the '165 alone and daisy-chained.

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    Jon Williams
    Applications Engineer, Parallax
    Dallas, TX· USA
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2005-01-30 16:08
    A word of caution.

    There are two main types of Hall effect switches.

    One is latching and the other is not.
    Be sure that you get the type you want (If I recall correctly, the non-latching is what you want) or you will find that you have to do some additional engineering to get operational.

    Incidentally, Hall Effect switches are about the same prices as regular switchs and eliminate any and all bounce. This can be useful if you want to use them a on/off pressure or positon sensors in various parts of a robot. The only draw back is that they require +5 volts, but then again all de-bounce schemes require this much or more.

    More magnets are only useful for reasonably slow rotation where you might want to exactly position a wheel (I think a stepper motor can do this better) or for sensing parts of a circle (such as a direction indicator for wind). In either case, you have the option to have more magnets on the spinning shaft (which may be hard to place) or more Hall-Effect sensors positioned around the outside.

    It seems to me that more sensors is the way to go.

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    G. Herzog in Taiwan
  • MacGeek117MacGeek117 Posts: 747
    edited 2005-01-30 17:02
    Kramer, I'm not sure what I'm getting. They are from www.goldmine-elec.com
    -products-sensors.confused.gif
    bugg

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    So many projects, so little time.
  • JavalinJavalin Posts: 892
    edited 2005-02-01 10:48
    Hi,

    I have been using latching hall effect sensors with small magnets for a similar task. The problem I have found is getting a strong-enough magnet to toggle the hall-effect with a 2-3mm range.

    Need to see what the guass of the magnet and hall-effect sensor are to work this out...

    James
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-02-03 20:06
    http://www.wondermagnets.com/cgi-bin/edatcat/WMSstore.pl?user_action=list&category=Magnets_and_Magnetism%3BPermanent_Magnets%3BNeodymium

    Has practically any size you could want, and they are rare earth magnets, they'll trigger a hall effect from a fair distance. A large enough magnet held in your hand near a filing cabinet or fridge will break the bones in your hand! (like this one http://www.wondermagnets.com/cgi-bin/edatcat/WMSstore.pl?user_action=detail&catalogno=0072·thats 12,100 gauss multiplied by its surface area, more than enough·to yank the jumperwires right off your bot·devil.gif·)· And good luck getting the thing to come free, it will likely become a permanent fridge magnet.

    ·Paul

    Post Edited (Paul Baker) : 2/3/2005 8:18:38 PM GMT
  • JED1JED1 Posts: 17
    edited 2005-06-15 03:59
    You would want to mount the Hall effect close to the wheels inner surface but attached it to the body of the robot. On the wheel you will want to mount
    your magnets (if more than one make sure they are spaced evenly). The magnet will need to pass in close proximity to the sensor for it work so check that alignment
    prior to making the attachmnet premanent. Also watch out and make sure that the magnets don't interfear with the normal rotation of the wheel. For the sensor
    pay attention to its orientation (see your application notes).
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