support/bracket for sensor on PCB

Discussion in 'The Projects Forum' started by ebeowulf17, Aug 12, 2014.

  1. ebeowulf17

    Thread Starter Active Member

    Aug 12, 2014
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    I’m working on designing a circuit board which will use a hall effect sensor to detect the position of a magnet on a rotating arm. The limited available space has led me to a design which has the hall effect sensor coming straight out of the board (through-hole mounting) with its sensor plane perpendicular to the PCB. When left unsupported, the sensor is pretty easy to knock around and bend out of shape, so I’d like something more secure to hold it in the right orientation.

    Once the prototypes are worked out, the goal is to have these boards mass-produced. Our electronics manufacturer can't ensure consistent sensor orientation without some sort of physical support. Also, we may be getting the boards potted, so if the orientation is wrong, it would get stuck that way forever before we could manually fix it (we'd rather not spend time hand-tweaking them all anyway, even if we could.)

    I’m imagining a bracket that would be quite similar to the heat sinks available for small transistors, but I can’t find anything that seems quite right for this sensor. Ideally, I'd like something that can be assembled as part of the board, that holds the sensor perpendicular to the PCB, and that's straightforward enough that our electronics manufacturer won't have any trouble consistently using it.

    The sensor is a Honeywell SS494B (same package as the entire SS490 series: SIP-3 with pins 0.05” apart from each other, and NOT a TO-92 package as at least one vendor website claims!) If anyone can help me find what I’m looking for or suggest another way to support the sensor in a tight space, I’d appreciate it.

    Here are the sensor specs:
    https://drive.google.com/file/d/0B21hjJ3dWyi7Vmd3SXdzSnFOenc/edit?usp=sharing

    And here's a really rough pic of the sensor soldered (badly) onto a tiny PCB to test the geometry of our current setup:
    https://drive.google.com/file/d/0B21hjJ3dWyi7MmRaRXdIUWE1Rk0/edit?usp=sharing

    Thanks,
    Eric
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Is there some compelling reason the board cannot be rotated 90° so the surface mount version can be surface mounted?

    Otherwise a block of most anything can be epoxied into place. Finding some standard bracket will be a daunting task.
     
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  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    How critical is the mounting anyways..
    Can't it just be mounted with the base (where the leads come out) flush to the board?

    What about a reed switch vs hall effect?

    Frankly if your board house can't orientate it then find another.. I just can't see how that would really be a problem?

    bivar "might" have something..
    keystone electronics maybe?
    maybe this http://www.rapidonline.com/electron...-98-transistor-mounting-pad-converters-531326
     
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  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I would have thought that would have worked also?
    Max.
     
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  5. ebeowulf17

    Thread Starter Active Member

    Aug 12, 2014
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    Thanks for the feedback!

    Probably should've mentioned up front (although it may be obvious) that I'm pretty new to most of this. I've been experimenting with electronics on a hobby level and learning just fast enough to make things work the way I want, but I know next to nothing about manufacturing and what is reasonable to expect from our suppliers.

    Rotating the board and going SMT would be pretty difficult because of the tight space we have to work in, and it would require a more complicated mounting scheme - our current plan is very elegant and simple, but only works for a horizontal board with the sensor perpendicular to it. It certainly does look like the surest way to get consistent sensor mounting. If all else fails, we can re-design around SMT, but I'd rather not.

    As for through-hole mounting with the base all the way flush to the PCB, I'm not sure why I was thinking we couldn't/shouldn't. Maybe I just forgot it was an option because I was prototyping on boards with 0.1" spacing and couldn't go flush on the prototype? Anyway, certainly seems like an improvement, and it should make the height consistent, although I'm still not sure it would guarantee a consistently square placement.

    On the reed vs. hall question, we definitely want hall effect here, because we're using it for position sensing in two different directions, taking the analog signal and using it to trigger multiple outputs based on position. We could achieve the same effect with multiple reed switches, but not with one.

    I do have a follow-up question about SMT possibilities: we've considered the idea of keeping our main board flat and mounting the SMT sensor on a tiny daughter-board, soldered perpendicular to the main board to keep within our space requirements. Do any of you have experience with non-parallel daughter-boards? Do you think that might be a more reliable way to get the sensor consistently oriented the way we want?

    Thanks for all your help!
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I would think that you would still run into structural and rigidity problems that would still not be as positive as mounting thro-hole flush to the board.
    Max.
     
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  7. BMorse

    Senior Member

    Sep 26, 2009
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    We use some hall effect sensors in most of our machinery for motor positioning and such, in one application we had the same issue, what I ended up doing is mounting the sensor flat on the PCB, then when it was potted a piece of ferrous metal was placed on top of the sensor to act as a "conduit" for the magnet.
     
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  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Seconded. Getting a SMD on a daughter board means a 2nd PCB plus some sort of interconnect, 90 degree pins or such.

    That is many more parts then just using a thru hole device. Put a height spec (min and max) on the part, and if your board stuffer can’t do that call the next guy and the next guy until you find the house that can do the job correctly.

    It’s not rocket soldering anyway.
     
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  9. ebeowulf17

    Thread Starter Active Member

    Aug 12, 2014
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    Thanks for all the great insights! For now, I've built a second test board holding the sensor flush to the PCB and mounting it in [what we think will be] the way that the final product should work. There will be more testing and tweaking in the near term, and then eventually we'll have a qualified EE look at where we're at and make it right before going into production - this is all just proof-of-concept and mechanical testing stuff for now.

    I'll update as things develop. For now, here are two pics of the current test rig (when the bar magnet swings left and right, the sensor/circuit combo detects the position and activates one of two outputs.)

    https://drive.google.com/file/d/0B21hjJ3dWyi7RnhYM1VINnUyUFE/edit?usp=sharing


    https://drive.google.com/file/d/0B21hjJ3dWyi7R3gtVFJCcUticjQ/edit?usp=sharing
    [​IMG]
     
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  10. ebeowulf17

    Thread Starter Active Member

    Aug 12, 2014
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    Just writing to say thanks again for the great insights, and to update everyone on the status of this project.

    After a lot of testing with hand made prototypes, I ended up going away from my original idea of using a single sensor perpendicular to the board to sense magnet movement in two different directions, and changing it to a system using two separate sensors near the outside edges of the magnet's travel. I was a little disappointed at first, because I had thought the single sensor with bi-directional capability was pretty clever, but in the end I'm just glad to have a system that works well. The difference between the weakest "on" signal and the strongest "off" signal with the original single-sensor arrangement was small enough that the odds of doing mass production without needing some amount of per-unit physical calibration was looking dubious. With two separate sensors, the difference is much clearer and manufacturing tolerances shouldn't be an issue. The new arrangement also means flat SMT sensor mounting instead of perpendicular mounting, so board manufacturing is more straightforward as well.

    After testing a hand made version of the new dual-sensor circuit, I went ahead with my first PCB design attempt and we had a short run of units produced for testing. This phase was rather nerve-racking for me because I have no previous PCB design experience and I was really worried about making a very expensive mistake. I did tons of reading and research and tried to make sure I was doing everything right, and I seem to have gotten away with it. It probably helps that this is a really simple, fairly forgiving circuit (no extreme voltages, no RF, etc.)

    We've got two of the test units installed on our R&D machine right now and everything is working exactly as planned. Assuming there are no surprises, we should be producing machines with the new circuit in the next few months.

    Thanks again to everyone on this forum. I really couldn't have made this work without the help I found here, both in terms of reading other people's questions and answers, and in terms of the questions I asked directly, from which I got lots of great feedback. I wish I could share more details about the final design, but my employer doesn't want to make this too terribly easy for competitors to copy, so I'm including a few pics, but nothing super-detailed (otherwise I would have done a more complete write-up in the Completed Projects forum.)

    IMG_0412_sharing.jpg IMG_0382_sharing.jpg
     
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