Make a Magnetic Reed Switch Work Backwards (sort of)

A reed switch normally goes ON when a moving magnet is near.
Adding a second non-moving magnet to balance the field will make it OPEN when the moving magnet is in the right spot.

Step 1: The Norths and The Souths of it

The magnet with the north pole at the top is adjusted until the switch turns OFF with the other moving magnet in it's 'special' position.

When the moving magnet moves either closer or farther, the switch turns ON.

Comments

[VIRON]

I used to have some reeds with magnets on them that did that. It seems that I unglued the magnets and put them in the adjacent drawer. But, what do ya know, I also have some 3-pin reed switches that work both ways. Maybe useful for... magnetic key or combination lock or solenoid deadbolt.

[flxforce]

The 3-pin reed switches may work a little different,they are many work ways like :Closed Loop = When a magnet is in close proximity to the switch the switch is closed.
• Open Loop = When a magnet is in close proximity to the switch, the switch is open.
• SPDT = This switch has a common, closed & open side.
• DPDT = This switch has two SPDT reeds in the same switch housing, each having it's own common, closed, and open side.
• Dual Single Pole Single Throw = Two closed loop reeds in one switch housing

[penixnet]

Recently I ordered the wrong parts,
thanks to you I was able to complete my project.

GOOD WORK!

[manicmonday]

The purpose of this kind of switch is as an alarm. The NC switch is actually NO, because it sits next to the magnet. When the door or window is opened the switch moves away from the magnet, and closes, then the alarm goes off.

[Handsome-Ryan]

How hard is it to keep the magnets 'balanced'? I've never needed a normally closed reed switch but I'll keep this technique in mind for future projects.

[leevonk]

all you need is to use a transistor as an inverter, see diagram below

[pinski1]

Actually it's quite useful, sometimes you want a normally open switch instead of a normally closed, or visa versa. So this is quite nice.

[ikarias]

Lol. I like it. Its the kind of stuff i cant imagene anyone would have a purpose for, but i like how ingenious mankind can be, in the simpelest of things.