Instructables

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.
 
Remove these adsRemove these ads by Signing Up

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.
shinojmahe2 months ago

i need to make a toy, that the magnet will keep 3 to5 Inches away from this circuit, still this circuit should start,

what type of reed i have to use with?? pls guide me

VIRON7 years ago
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 VIRON2 years ago
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
penixnet4 years ago
Recently I ordered the wrong parts,
thanks to you I was able to complete my project.

GOOD WORK!
manicmonday6 years ago
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.
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.
leevonk7 years ago
all you need is to use a transistor as an inverter, see diagram below
invert.gif
pinski17 years ago
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.
ikarias7 years ago
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.