On Thu, 29 Apr 2010 13:49:12 -0700 (PDT), DerbyDad03
wrote:

On Apr 29, 11:56*am, Bitzer wrote:
Existential Angst wrote:
"MLD" wrote in message
...
"Bitzer" wrote in message
...
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?
Forget current flows or doesn't flow--that is confusing. *Instead, do you
have to close the switch in order to turn on the light? *If so, then you
need a normally open switch. *Conversely, if the switch is open when the
light is on, then you need a normally closed switch. *From what you
describe, I would think that you need a normally open switch---light off
when door is closed.
MLD

Actually, not correct, either in analogy or in answer.

The answer is normally closed -- as others have said, the state with no
outside force acting on it.
Same thing with relays -- IF the relay is "single throw".
If the relay is "double throw", then again, NO or NC doesn't apply, as both
states can be wired in as normal.

A toggle light switch also has two "normal" states, even tho it single
throw -- because the "outside force" is, well, you, so there is no natural
"return position"..
Ditto with any rotary-type multi-position switch, for fan speeds, etc.:
every position is normal.

To the OP, curious as to where you would get this kind of switch -- oem,
from the garage door mfr??
How much $$?? *Wouldn't they be able to just supply the right part, or are
you kluging your own solution?

Remarkably, Stormin brought up a good point semantically: *"closed" in
switching has the opposite meaning to a valve, ito flow. *Go figger -- both
the semantic snafu, and that Stormin actually grokked it.

I bought the switch for about two bucks 15-20 years ago at Radio Shack--
along with the wire, transformer and LED indicator light i needed for my
custome designed system. A contractor bashed the existing switch so I've
been to a few Radio Shack stores around town but the clerks didn't know
wht I was talking about. I showed the broken one to one clerk who
thought it was a doorbell. RS seems to mainly sell cell phones and
electronic toys these days-- no more electronic components.

I see lots of them on line and on Ebay for around $10 or *so-- but it's
really unclear if they will keep the circuit open when the magnet is
near or away. I guess I'll just buy one of each kind-- an NO and an NC--
and toss the one I don't need.- Hide quoted text -

- Show quoted text -

"Radio Shack seems to mainly sell cell phones and electronic toys
these days-- no more electronic components."

Well, since you brought it up...

I was working at an event this weekend and somebody broke the 1/4 mono
jack for one of the loudspeakers.

I went over to the nearest Radio Shack to get a new jack. Since the
young lady was nice enough to approach me and ask if she could help, I
started to explain to her what I needed - quickly noticing the glaze
that was coming over her eyes.

Her response was "You'll have to speak to one of those guys. I know a
lot about cell phones, but not much about that kind of stuff."

So what's the deal? Does Radio Shack *expect* that everyone that walks
into the store wants a cell phone? If not, why would someone who knows
nothing about their other products approach me?

Radio Shack should expect everyone to buy a cellphone.

They left me with a bad taste in my mouth when I bought my first
compute from them.

I used to buy everything at Radio Shack. I can't remember the last
time I have been in one of their stores. Several years.

I know your situation was that you needed something that day. I let
Newegg bring the stuff to my door.