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Getting the right reed switches and magnets

I have a setup in mind, which involves a magnet put next to a reed switch, times 2. So it should work so that a reed switch is only activated when two magnets are stuck together and next to a reed switch, and deactivate once there's only one magnet next to it.

So I have found a couple of products from this at Sparkfun:




But the thing is that I don't know how to figure out what kind of magnets to get, or whether they're too strong or too weak for the reed switch. All I've found out is that the magnetic field is measured in Teslas, but there is no info on the reed switch, and how much pull it needs to activate.

Furthermore I'm going to need a touchscreen, and I've been thinking about buying this:



But the problem is that I will need to attach my magnet right behind the touchscreen, so I need to get a magnet that's weak enough, that it doesn't ruin or distort the touch screen, if at all possible.


So can anyone give me some pointers to this?

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Thanks, rik. Yeah, I had found the wikipedia article on Tesla, and later checked the article for Gauss. Well, what do you know.

I'm not quite sure what you mean by brute magnet, but I suspect it just means a big magnet. So yeah, I wanna get as small a magnet as possible, so that 0,25" magnet would suit me fine sizewise. But considering that I want the reed switch to only be activated by 2 magnets, and magnets have many different strengths, I was hoping someone knew how much strength a reed switch needs. Then I can hopefully calculate what kind of magnet I need, instead of having to buy many different ones, since I ideally want one that's not too strong, nor too weak.


And thanks, g_code. That's good to hear. So I think I'll go ahead and buy those things and do some experimenting with them.

If Spark Fun says their little magnet is good for their reed switch, I would take their word for it. My experience with these switches (30 years ago, so there may have been improvements since) is that a brute magnet will cause the contacts in the switch to "kling" to each other. With unwanted results. So smaller is better. Tune the distance from magnet to switch to suit your needs.

I do believe that lcd screens are not affected by magnets.

I may be wrong but I just touched my laptop screen and a calculator screen with a neodymium magnet with no effect

Magnets are measured in gauss, not teslas.
"One billionth of a tesla is a nanotesla, equivalent to 0.01 milligauss (mG) and it is in nanoteslas that common metric home measurements are made to determine local magnetic field levels."