looking for N.O. mini reed switch

Discussion in 'The Projects Forum' started by coeng, Nov 3, 2009.

  1. coeng

    Thread Starter Member

    Oct 29, 2009
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    I am looking for something like the Velleman HAA28 mini reed switch, but one that is normally open. I tried using the HAA27 but there is just not enough clearance, I need something low-profile.
     
  2. BMorse

    Senior Member

    Sep 26, 2009
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    Is this low enough profile for your needs?? >>>http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=HE509-ND < normally open contacts...

    Can't get any smaller than the glass body reed switches.......

    My .02
     
  3. coeng

    Thread Starter Member

    Oct 29, 2009
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    Sorry, I should have been more specific. This is for a garage door monitor application. The switch indicates when a garage door has been opened. I wouldn't know how to mount/use the switches you referenced.
     
  4. BMorse

    Senior Member

    Sep 26, 2009
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    The switches I referenced are used the same way as any reed switch, you just use a magnet to close the switch......

    You can search for Reed Switch at Digikey and it will give you a whole bunch of filters you can apply, to get to the right one you need >>http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=1114199&k=REED


    My. 02
     
  5. coeng

    Thread Starter Member

    Oct 29, 2009
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    Lions and Tigers and Bears, oh my. I don't know much about the search filter criteria for these switches. All I know is that I need it to be similar to the Velleman HAA28.

    Series: ?
    Type: ?
    Circuit: SPST-NO
    Switching Current: ? (my circuit is 11mA)
    Switching Voltage ? (my transformer puts out 15.6V)
    Must Operate ?
    Must Release ?
    Magnet ?
    Mounting Type ?
    Termination Style ?
    Packaging?
     
  6. BMorse

    Senior Member

    Sep 26, 2009
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  7. coeng

    Thread Starter Member

    Oct 29, 2009
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    Great. Now just three more questions...

    1) What specifically do the specs MUST OPERATE and MUST RELEASE refer to? In the first switch the numbers are 4.44mm/20.32mm. In the second switch they are 25.40mm/33.02mm.

    2) Can the switch and magnet be oriented at right angles? I need to mount the switch to the wall but I need to mount the magnet on top of the garage door (from the inside of course).

    3) I wanted to compare physical dimensions between these and the Velleman switch. Why doesn't Digikey carry these?
     
  8. BMorse

    Senior Member

    Sep 26, 2009
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    That is the distance the magnet has to be to the reed switch for it to operate.....

    velleman probably does not produce the switch, it could have been manufactured by some other company...

    yes they can be oriented in different ways, as long as when they are close together, the magnet can still activate the switch....
     
  9. coeng

    Thread Starter Member

    Oct 29, 2009
    32
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    I figured that but I still don't understand the numbers. Is it referring to maximum switch/magnet separation in order for the circuit to be open and minimum switch/magnet separation for the switch to be closed?

    So if MUST OPERATE is 4.44mm and MUST RELEASE is 20.32mm, that means that I should mount the magnet on the garage door (in the closed position) such that there is no more than 4.44mm separation between the magnet and the sensor? Furthermore does it mean that when the garage door begins to open, when the separation between the sensor and the magnet exceeds 20.32mm, it will close the circuit?

    Or am I totally off?
     
  10. BMorse

    Senior Member

    Sep 26, 2009
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    When the magnet is close to the sensor(4.44mm) it will close the circuit since it is normally open, and when it separates more than 20.32mm then the circuit will open.....


    so if you want to detect when the door opens (LED lights when open):

    With the door in the open position, attach sensor and magnet to where they are within 4.4mm of each other (or when ever you hear a really faint "click" from the reed switch, or if you have a multimeter, set it to continuity and attach a probe on each lead of the sensor, when the magnet comes close enough to close the switch you will hear a tone from your meter). This way when the door is open, the LED will light.

    If you want to detect when door is closed, do the opposite, and close the garage door and place the sensor and magnet near each other.....
     
    Last edited: Nov 3, 2009
  11. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Wait a minute...
    Before you go ordering a NO reed switch, post your circuit diagram.

    Usually for "door open" indicators, you'd want a NC switch. When the magnet is near, the switch contacts open; when it's further away, the contacts close.
     
  12. coeng

    Thread Starter Member

    Oct 29, 2009
    32
    0
    Put it this way...when I wired my two garage door sensors the other day, I connected both NO terminals to the positive side of my power source. I then connected both COM terminals of the sensors to the anode of the first of two LEDs (the LEDs are wired in series). When the garage door is in the closed position, the magnets are right next to their respective switches...LEDs are off. When either garage door is opened, a magnet separates from its sensor, closing the respective circuit and lighting up the LED. This is called NO, right?

    The problem I am having is that the garage doors don't always close in the same exact position (like a house window would for example). There door lifter can be jerky from time to time and because the sensor and magnet need to be close to each other (in order to turn the LED off), they sometimes bump into each other when the door opens and/or closes. What I really need is a switch/magnet pair that can be separated by about 1" (for the door to be considered closed) and several inches for the doors to be considered opened. This would account for any garage door misalignment on the way down.

    I've decided to upload some photos with comments. This should make it easier to understand my problem.

    [​IMG]



    [​IMG]



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    [​IMG]
     
  13. coeng

    Thread Starter Member

    Oct 29, 2009
    32
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    Two more photos (continued from previous post):

    [​IMG]


    [​IMG]
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    It looks like you've mounted the magnet on the top of the door, and the switch above it. When the door opens, it'll smack right into it.

    Why don't you mount the magnet on the edge (side) of the door vertically, and the switch on the frame next to it?
     
  15. coeng

    Thread Starter Member

    Oct 29, 2009
    32
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    Its not a problem when the door opens. The door opener actually pulls the door away from the switch (toward the inside of the garage) before it starts to provide an upward lift. Its on the way down where the problem is....there is contact made half the time.

    I already tried mounting the magnet vertically on the side of the doors. The problem is that the magnet gets caught in the tracking. There's just not enough clearance.
     
  16. SgtWookie

    Expert

    Jul 17, 2007
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    OK. So, mount a flexible plate on top of the door, and the magnet on top of that. It should pull the magnet away from the switch on opening even faster due to the increased length from the pivot point. On closing, the plate should ride over the top of the switch before the magnet drops in below it.
     
  17. coeng

    Thread Starter Member

    Oct 29, 2009
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    Maybe I should just give up on the reed switches. There is just too much play in the garage door and it won't end up in the same exact position every time. What I do know is that when the garage door opens fully it always ends up at the end of the track, so I guess I should start looking into mounting a momentary contact switch on an L bracket. Unless someone has another idea????
     
  18. BMorse

    Senior Member

    Sep 26, 2009
    2,675
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    Try using different magnets, possibly a neodymium magnet with more power, then you can mount it further away from the reed switch.... You don't necessarily need to use the magnets that come with the sensor.... or a cherry switch with a lever actuator >>> http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=CH344-ND

    Or you can go with a photoelectric sensor (more costly than cherry switches or reeds)....


    My .02
     
  19. coeng

    Thread Starter Member

    Oct 29, 2009
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    You mean something like this ? How far away do you think I can mount it? Because of its shape I can't mount on the top of the garge door. Do you think it will work if I mount it on the inside of the garage door just at the very edge where it meets the top? Because the door is metal and has thickness to it, this may not work. I wish the top the of garage door was flat, but as you can see in the photos, it is not. It has a raised ridge in the middle.

    Actually this may work if I move the sensor to the side of the door and mount it (and the magnet) vertically. This way the magnet (since its only 1/4 in thick) will easily clear the track.

    How different is the magnet above from the original magnet? Do I need to modify my circuit in any way?
     
  20. BMorse

    Senior Member

    Sep 26, 2009
    2,675
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    That magnet would work, although it is pretty big maybe a smaller one would about 1/2" x 1" x 1/4".... but the one you show should work just fine, even if it was an 1" or so from the reed switch...

    The original magnet is probably just a standard magnet, the neodymium ones are VERY powerfull, 9 of those you show, can lift a compact car! Be very carefull in playing with 2 or more, they can snap together very quick and damage themselves or anything cought in between.....

    No changes to your circuit is necessary.....


    My .02
     
    Last edited: Nov 4, 2009
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