How do Ifind the most sensitive reed switch?

Discussion in 'The Projects Forum' started by tikiguy, May 26, 2007.

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  1. tikiguy

    Thread Starter New Member

    May 26, 2007
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    Hello,

    I am working on a project that will use a reed switch. I have been trying to find the most sensitive reed switch on the market, but have been confused.

    Basically I am making a device that will open a door using a solenoid, and I want to trigger it from as far away as possible using a neo magnet about the size of 3 nickels stacked together.

    I have found some sites that sell reed switches, but couldn't tell what to get for my needs. I will need a switch that is normally open.

    Also, is there anything else besides a reed switch that you could suggest that would allow me to have something tiny that could trigger a switch that is not magnetic?

    Any help is greatly appreciated.

    Thanks,

    Tikiguy
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    If the idea is to provide a curent path for a solenoid latch, a reed relay is pretty good. Just about anything else will require a power supply and a box holding the circuitry.

    You may be able to find specs for sensitivity, but the current handling capacity is most important. Don't know if you can still get the kind that are mercury wetted, but they just lasted forever. Reeds are more sensitive to what part is exposed to the magnetic field - you have to experiment to find the best spot. Some are a bit more sensitive to one pole than the other.
     
  3. hgmjr

    Moderator

    Jan 28, 2005
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    Have you considered a Hall-Effect Switch? Unlike the reed switch you will need to power the Hall-Effect device but it may provide you the additional magnetic sensitivity you need.

    If you are interested you can google using keyword phrase "hall-effect sensor".

    hgmjr (1700)
     
  4. cumesoftware

    Senior Member

    Apr 27, 2007
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  5. mrmeval

    Distinguished Member

    Jun 30, 2006
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    You could make a magnetic switch. Consider a large piece of metal just balanced enough not to pull a switch closed. Then wave your magnet near it.

    You could use a chunk of metal on a pendulum.

    Etc
     
  6. thingmaker3

    Retired Moderator

    May 16, 2005
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    Reed switch sensitivity is measured in Ampere Turns. The smaller the coil required to activate the reed switch, the lower the AT number. (And the smaller or farther away the permanant magnet needed.) About 10 to 15 AT is as sensitive as the reed switches come.
     
  7. tikiguy

    Thread Starter New Member

    May 26, 2007
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    Thanks for the tip about the AT number. That was exactly what I was trying to figure out.

    Lincoln
    PS - thanks to everyone else for their suggestions as well.
     
  8. kender

    Senior Member

    Jan 17, 2007
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    You can make any reed switch more sensitive, if you permanently attach a small magnet to it. The small magnet should be too weak to close the switch by itself, but the 2 magnets (small one and the one that the user has) should be strong enough to close the switch. I've used this method in the past successfully.

    BTW, the same approach can be used to make a normally-closed reed switch from a normally open one.
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
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    There is a problem with the above suggestion. The magnetic field constantly present will magnetize the reeds, and they will not open after some time.

    I used to work on a disk file that ran the heads in and out with linear motors. The null point in the motor coil was selected with reed relays. They became magnetized and stuck on after a couple of years. If they will do it in intermittent use, a permanent field will just hurry the process.

    Every few days, we had to pull one of the reed relay boards and bang it on the floor to open up the stuck contacts.
     
  10. Gompers

    Member

    Feb 21, 2007
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    I think you need a strain gauge
     
  11. ludwig

    New Member

    Nov 17, 2008
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    You could make a magnetic switch. Consider a large piece of metal just balanced enough not to pull a switch closed. Then wave your magnet near it.
     
  12. mcj74

    New Member

    Jan 10, 2007
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    Interesting...

    Curious, do you think this behavior has changed with modern reed switches? I was considering trying this, as I need just a little bit more sensitivity
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,542
    2,369
    An old thread!
    There are compact reed switches and companion magnet made by Hamlin, they are similar to the type used in burglar alarms but generally smaller.
    There is also the bare glass discrete reed switches that can be obtained in various sensitivities on the Digikey site.
    Max.
     
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