Would be much easier to go to any home improvement or hardware store and buy some Magnetic Door and Window sensors. This way everything comes neatly packaged and ready to easily mount. Here in the US any Home Depot, Lowes or True Value Hardware should have them in stock. If the factory packaging is too large just bust the reed switches out of the plastic housing, likewise the magnets.

Ron

Thanks for that suggestion Ron.... Have you used any of these things and would they satisfy the limited movement I described previously?

 

Would be much easier to go to any home improvement or hardware store and buy some Magnetic Door and Window sensors. This way everything comes neatly packaged and ready to easily mount. Here in the US any Home Depot, Lowes or True Value Hardware should have them in stock. If the factory packaging is too large just bust the reed switches out of the plastic housing, likewise the magnets.

Ron

Both the magnets and the switches used in those are rather large even without the plastic cases.

 

Below are links to reed switches and a suitable magnet. I would expect the operate-release distance to be in the 1-2cm range but I can't say exactly what it would be. I don't think the fridge magnet strips would would be strong enough to work the switches reliably.
Switch Magnet

 

Thanks for that suggestion Ron.... Have you used any of these things and would they satisfy the limited movement I described previously?

Years ago I was involved using quite a few reed switches including testing them. They were used in a device called a RPI (Rod Position Indicator). The process when complete involves soldering reed switches in a staggered formation having 1/2" centers. A circular magnet with a known gauss would travel the rod. We could resolve 0.5" or about 12.7mm based on switch closures over about 80 inches.

Yes, the switches I mentioned earlier may be too large even busted out of their enclosures. Thanks Albert for pointing that out. However you can look at buying small reed switches from any number of suppliers. When I was involved with them they were Hamlin who I believe is now Little Fuse. I did find this data sheet which may prove useful in switch selection.

Ron

 

I would expect the operate-release distance to be in the 1-2cm range but I can't say exactly what it would be.

Thanks for those links..... is there not a process for determining a magnet strength rating for a particular required switch when designers use these items in their product?

BTW.... Digikey sure is pricey!

 

The switches generally give an At rating - the number of ampere-turns needed to operate it. This is very useful if you are winding a coil for it but not so useful if you are intending to use a bar magnet

 

The switches generally give an At rating - the number of ampere-turns needed to operate it. This is very useful if you are winding a coil for it but not so useful if you are intending to use a bar magnet

Correct again Mr. Hall..... Ron and yourself are helping me quite a bit, but I still have not found out how to match up a particular magnet based on it's Gauss rating to a switch based on it's AT sensitivity for my required operational distance.

I'm still looking around..... :b

 

Correct again Mr. Hall..... Ron and yourself are helping me quite a bit, but I still have not found out how to match up a particular magnet based on it's Gauss rating to a switch based on it's AT sensitivity for my required operational distance.

I'm still looking around..... :b

Some magnets are sold with a known gauss but really, short of some very expensive equipment your best bet is look for a switch that physically meets your needs and just try a few inexpensive store bought magnets. The reed switches, in my experience are pretty repeatable and last for tens of thousands of cycles. The Hamlin switches I worked with long ago were subjected to a very hot environment and were proven very reliable. Matter of fact testing involved placing racks of them in an oven inside a large coil running at 60 Hz. where they ran for about four hours or more. Anyway, I would get several switches to play around with and see how they react to various magnets.

Ron

 

. Anyway, I would get several switches to play around with and see how they react to various magnetsRon

After reading much more on this subject than I thought I might, including two PDF files where both authors finally spit it out that designing a Reed Switch system might just require a lot of experimentation...... I agree with you completely Ron.....

Pictures at 11:00

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