DIYbanter - View Single Post - Define "Normally Open" vs. "Normally Closed"

Bitzer

hr(bob) wrote:
On Apr 29, 9:07 am, Bitzer wrote:
I'm replacing a broken surface mount magnetic switch mounted on my
garage door that controls a signal light in the house that comes on when
the door is open.

Thus, I need a switch that is OPEN (meaning no current flows) when the
magnet is near the switch and CLOSED (meaning current flows) when the
magnet is removed from the switch.

So do I need a normally open switch or a normally closed one? Different
manufacturers/vendors seem to use the terms differently. Is it "normal"
when the magnet is near the switch-- or away from it?

You use a reed switch, with TWO magnets. When the door is down, place
the two magnets so they oppose each other, the reed switch will stay
open if you position the magnets correctly. one magnet on the door,
one on the frame next to the reed relay/switch. When the door goes
up, the one magnet will move away from the reed relay/switch and the
remaining magnet will close the switch and turn on your alarm/light
bulb/whatever. This is high-school 9th grade stuff, not rocket
science!!!!

If I recall, the first thing they taught back in 9th grade was to answer
the question that was asked, not tell the inquirer how to build a
convoluted Rube Goldberg device ;-)