N\C Magnetic switch

[dino40]

Good day All,
I am looking for a normally closed magnetic switch that is both very small and will turn on the circuit when the magnet is removed the whole assembly must be watertight. Any suggestions or other ideas will be helpful.

 

[VEBill]

The hardest part of your search might be getting past the alarm vendors that have it backwards:

"N/C (NORMALLY CLOSED CIRCUIT WHEN MAGNET IS NEXT TO IT)"

This is Alarm System nomenclaturism.

Many years ago, Radio Shack sold both types of reed switches. The majority were the type that closed the contacts when the magnet was nearby (I'd call them NO), but they also sold the reed switches that opened the contacts when the magnet was brought nearby (I'd call them NC).

 

[TurboXS]

For a change over type try;

http://www.rsaustralia.com/cgi-bin/...rchType=quick&viewType=text&SearchText=339752

regards
Pete

 

[itsmoked]

As VE1BLL is saying you need a reed switch. Google for hermetic or water proof reed switches.

Keith Cress
Flamin Systems, Inc.- <

http://www.flaminsystems.com>

 

[VEBill]

By the way (in what seems to be a common theme...).

Dollar Stores (bless 'em) sells cute little alarms that have a built-in magnet reed switch, some button cell batteries, a slide swicth, and a piezo alarm. The gadget comes with the complete package including the magnet and batteries ARE included.

Cdn$1.00 each (about US$0.85).

Point being - since the alarm sounds when the magnet goes away, I suspect that they're probably using a N/C reed switch (contacts closed when the magnet goes away). It's less likely that they're using any circuitry to invert a oh-so-very-slightly cheaper N/O reed switch.

If you're making a prototype or other one-off, check the Dollar Stores.

 

[Madcow]

VE1BLL
Is that a dollar store Canadian or
an 85 cents store U.S.?

 

[VEBill]

Yes.

 

[zeitghost]

In Ripoff Britain, that's a Pound store... it was ever thus...

 

[OperaHouse]

If I remember correctly (my mind does exist in a Foggy Time Warp)all two pin reed switches are normally open and the normally closed ones just have a little magnet in them to bias them closed. I prefer external circuits to reverse this. Believe there are three pin NO/NC where the NC contacts are non magnetic.

 

[Comcokid]

SPDT reed switches are made - You can use the NC contacts to meet your needs.

I assume you are using this as some kind of power or activation switch. I have seen products with a micro that remains in sleep if a reed switch is closed (magnet present) and actives when the contacts are open (magnet removed). The proper micro will only require a few microamps in sleep.

 

[BSMAN]

http://www.reedswitchdevelopments.com/index.html