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I am working on an Arduino project that should be sealed, with the possibility to switch off when the user wants. A solution I have seen on commercial products is the use of a Reed switch, normally closed. When there is no magnet, the board is powered on. When the user adds a magnet at a given location on the box containing the electronics, the board is powered off.

I have been looking for such components online, but I have a hard time finding tutorials / explanations for Reed switch n00bs like me. So what I need is some help understanding a datasheet / understanding if what I think about will work.

My speccing needed:

  • range of operating temperatures: -40C to 30C (this is important, polar environment use! -60C would be even better, but that seems hard to find).
  • switching on and off electronics working at 3.3V
  • max power draw by the electronics: up to around 200mA
  • way to close the reed switch: by using a small rare earth magnet (these are surprisingly strong, but I do not have a spec available), through a plastic wall of approximately 1.5mm thickness.

After searching online I am considering this switch: MDRR-DT Series https://www.littelfuse.com/products/magnetic-sensors-and-reed-switches/reed-switches/mdrr-dt.aspx .

I like it better formed (i.e. F version, less risk to have the 2 legs getting in contact). I am quite unsure about which sensitivity to use though. I want to be sure that it is not too sensitive and does not close unexpectedly, but I still want to be able to close with my quite powerful rare earth magnet. Should I go for something like 25-30AT then? That would be like this: https://no.mouser.com/ProductDetail/Littelfuse/MDRR-DT-25-30-F/?qs=nyo4TFax6New9CGWZwJeTA%3D%3D .

Anything I am not thinking about that is important when considering using Reed switches for such applications?

Edit 1:

What I am confused about is in part why AT is given as a range. Does AT 15-25 well mean that the switching is happening somewhere between 15 and 25, or that at above 25 weird things happen?

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The AT rating is given as a range because that's as good as this vendor is willing to specify. It's always a balancing act. Too sensitive and it could get triggered inadvertently. Too insensitive and it takes too much power to switch it.

You should plan in your design to give it something ABOVE the maximum so that you are 100% sure it will switch when you want it to. If you are in the middle, it's not guaranteed to switch. It might, but then it might not.

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