<div dir="ltr">There are different kinds of hall effect sensors. Some need to have alternate poles to turn on/off and some do not.<br><br>With the HE sensor I am using I only need one magnet.<br><br>The HE sensors are a bit more expensive than optical forks, but they are so much simpler to use and don't need any supporting electronics.<br>
<br>I bought the tiny magnets from a place in USA by mail order, but might end up using something I bought from Natures Discovery.<br><br>Interestingly, that flexible fridge magnet stuff is made up of alternate bands of north and south magnet and would make an effective linear encoder.<br>
<br>Quite a few DC motor encoders use HE sensors because they are far more robust against dust etc than optical sensors.<br> <br><br><div class="gmail_quote">On Thu, Sep 4, 2008 at 8:34 AM, Richard Jones <span dir="ltr"><<a href="mailto:rjtp@ihug.co.nz">rjtp@ihug.co.nz</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Thanks Charles,<br>
<br>
The UGN3141 Hall effect sensor from South Island Components does look<br>
interesting, a little more expensive than optical.<br>
<br>
To ensure that the hall effect sensors get low enough gauss to release do<br>
magnets need to be alternated N S N S? That would mean an even number so to<br>
detect direction of rotation you need 90 degree separation between hall<br>
effect devices rather than 180 degree that works with an odd number. Where<br>
do you get your tiny magnets?<br>
<br>
I wonder if you might be able to place the hall effect sensor somewhere<br>
inside a brushed DC motor?<br>
<br>
Richard<br>
<br>
On Thu, 4 Sep 2008 07:38:10 +1200, "Charles Manning" <<a href="mailto:cdhmanning@gmail.com">cdhmanning@gmail.com</a>><br>
wrote:<br>
<div><div></div><div class="Wj3C7c">> Hi Richard<br>
> There's an alternative that we are dabbling with using a Hall Effect<br>
> sensor<br>
> that is probably a lot easier to do than shaft encoders.<br>
> The Hall Effect sensor is just a 3-pin transistor like device that<br>
detects<br>
> a<br>
> magnetic field (eg. UGN3141 from South Island Components). The magnet can<br>
> be<br>
> one of those tiny 2.5mm Neodymium magnets embedded in a gear (Drill a<br>
hole<br>
> and glue it in). Since some of gears inside the gearbox rotate quite fast<br>
> you can get pretty good resolution.<br>
><br>
><br>
> On Wed, Sep 3, 2008 at 10:06 PM, Richard Jones <<a href="mailto:rjtp@ihug.co.nz">rjtp@ihug.co.nz</a>> wrote:<br>
><br>
>> I came across this shaft encoder arrangement for the Tamiya Twin-Motor<br>
>> Gearbox: <a href="http://www.noplabs.com/twinmotor/twinmotor.html" target="_blank">http://www.noplabs.com/twinmotor/twinmotor.html</a><br>
>> This came via the HBRC mailing list. Andrew showed something along these<br>
>> lines at one of our robotics meetings several years back.<br>
>><br>
>> Richard<br>
>><br>
>><br>
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>><br>
<br>
<br>
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