Can anyone point me towards a phone or online supplier for an
inexpensive, cylindrical, enclosed reed switch, Normally Closed, for
use as door sensors in a burglar alarm circuit please.

I'm still googling but so far without success and want to place an
order for delivery Monday. Thought I'd found one but it's a Normally
Open type. (BTW, I was surprised how many don't specify that crucial
detail.)

--
Terry, East Grinstead, UK

On Sat, 07 Feb 2009 11:35:45 +0000, Terry Pinnell
wrote:

Can anyone point me towards a phone or online supplier for an
inexpensive, cylindrical, enclosed reed switch, Normally Closed, for
use as door sensors in a burglar alarm circuit please.

I'm still googling but so far without success and want to place an
order for delivery Monday. Thought I'd found one but it's a Normally
Open type. (BTW, I was surprised how many don't specify that crucial
detail.)


Not being funny but do you really want a NC switch ? That would infer, when the
door is closed, the switch would be open.

Normally, the switch would be closed when the door is closed. i.e. a NO switch.
Sorry if that's incorrect.

In message , Terry Pinnell
writes
Can anyone point me towards a phone or online supplier for an
inexpensive, cylindrical, enclosed reed switch, Normally Closed, for
use as door sensors in a burglar alarm circuit please.

I'm still googling but so far without success and want to place an
order for delivery Monday. Thought I'd found one but it's a Normally
Open type. (BTW, I was surprised how many don't specify that crucial
detail.)


When you say Nc do you mean when the door is closed? This would be
typical as it then goes open when the door is opened.

Most are No until the magnet is placed near them.


Maybe?

http://www.maplin.co.uk/Module.aspx?ModuleNo=4767



Perhaps?

http://uk.rs-online.com/web/search/s...?method=retrie
veTfg&Ne=4294922322&Ntt=reed&Nr=AND(avl%3auk%2csea rchDiscon_uk%3aN)&Ntk=I
18NAll&Ntx=mode%2bmatchallpartial&N=4294954000+429 4917138&Ns=stockPolicy_
uk|1||new_uk|1&Nty=1&binCount=235#breadCrumb



http://www.screwfix.com/prods/39061/...er-Alarm-Compo
nents/Honeywell-Door-Wired-Recess-Mount-Contact

--
Bill

On Sat, 07 Feb 2009 11:35:45 +0000, Terry Pinnell wrote:

Can anyone point me towards a phone or online supplier for an
inexpensive, cylindrical, enclosed reed switch, Normally Closed, for
use as door sensors in a burglar alarm circuit please.

I'm still googling but so far without success and want to place an
order for delivery Monday. Thought I'd found one but it's a Normally
Open type. (BTW, I was surprised how many don't specify that crucial
detail.)

Normally closed (i.e. closed when the door is open) would be more likely.
Maplin lists alarm reed switches he

http://www.maplin.co.uk/Search.aspx?...itch&source=15

....even some change-over types, albeit bare reeds.

In message , Frazer Jolly
Goodfellow writes

Normally closed (i.e. closed when the door is open) would be more likely.
Maplin lists alarm reed switches he

Eh?
To quote Maplin:-

"The reed makes contact when subjected to a magnetic field."

i.e. when the door is closed and the reed next to the magnet.

So that you can have a number of them wired in series and any one
opening will be detected.


http://www.maplin.co.uk/Search.aspx?...itch&source=15

...even some change-over types, albeit bare reeds.

--
Bill

In article ,
Terry Pinnell wrote:
Can anyone point me towards a phone or online supplier for an
inexpensive, cylindrical, enclosed reed switch, Normally Closed, for
use as door sensors in a burglar alarm circuit please.

I'm still googling but so far without success and want to place an
order for delivery Monday. Thought I'd found one but it's a Normally
Open type. (BTW, I was surprised how many don't specify that crucial
detail.)

Two options. Replace the reed switch in a normal one with what you want -
changeover types are available. Or since most alarm cables have 12 volts
available for powering sensors, use a transistor to swap the action.

--
*Why doesn't glue stick to the inside of the bottle?

Dave Plowman London SW
To e-mail, change noise into sound.

On Sat, 7 Feb 2009 13:05:16 +0000, Bill wrote:

In message , Frazer Jolly
Goodfellow writes

Normally closed (i.e. closed when the door is open) would be more likely.
Maplin lists alarm reed switches he

Eh?
To quote Maplin:-

"The reed makes contact when subjected to a magnetic field."

i.e. when the door is closed and the reed next to the magnet.

So that you can have a number of them wired in series and any one
opening will be detected.


http://www.maplin.co.uk/Search.aspx?...itch&source=15

...even some change-over types, albeit bare reeds.

Eh? indeed. Invert everything I said.
Also means that snipping the wire will trip the alarm.

In article ,
Terry Pinnell writes:
Can anyone point me towards a phone or online supplier for an
inexpensive, cylindrical, enclosed reed switch, Normally Closed, for
use as door sensors in a burglar alarm circuit please.

I'm still googling but so far without success and want to place an
order for delivery Monday. Thought I'd found one but it's a Normally
Open type. (BTW, I was surprised how many don't specify that crucial
detail.)

http://cpc.farnell.com/unbranded/a40...als/dp/SR00148

They're all normally closed when the door is closed.
That's what burglar alarms normally expect (although
some can be programmed to work the other way around).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Feb 7, 4:35*pm, Terry Pinnell
wrote:
Can anyone point me towards a phone or online supplier for an
inexpensive, cylindrical, enclosed reed switch, Normally Closed, for
use as door sensors in a burglar alarm circuit please.

I'm still googling but so far without success and want to place an
order for delivery Monday. Thought I'd found one but it's a Normally
Open type. (BTW, I was surprised how many don't specify that crucial
detail.)

--
Terry, East Grinstead, UK

i dont know much about it but i think http://www.dashmeshheaters.com
might help you in solving there problem
thanks

Thanks all. I was indeed wrong about the type, of course. In
mitigation, there's some ambiguity IMO over the meaning of 'normally
open'. I'd forgotten that the magnet was (normally!) keeping it
closed! I was regarding 'normality' as the state when my doors are
closed ;-)

I did realise my mistake soon after posting and duly ordered a few
from Rapid Electronics
http://www.rapidonline.com/Electroni...354/kw/78-0797

--
Terry, East Grinstead, UK

On Sat, 07 Feb 2009 11:35:45 +0000, Terry Pinnell
wrote:

Can anyone point me towards a phone or online supplier for an
inexpensive, cylindrical, enclosed reed switch, Normally Closed, for
use as door sensors in a burglar alarm circuit please.

Seems you've found the solution.
However I've used these NC devices in the past and they consist of a
standard reed switch with an attached 'slave' magnet which holds the
contacts closed. The actuating magnet has to be correctly positioned
to cancel the field of the slave when the two come together.

As might be expected, not straightforward to set up.

GrahamC

In article ,
Graham C writes:
On Sat, 07 Feb 2009 11:35:45 +0000, Terry Pinnell
wrote:

Can anyone point me towards a phone or online supplier for an
inexpensive, cylindrical, enclosed reed switch, Normally Closed, for
use as door sensors in a burglar alarm circuit please.

Seems you've found the solution.
However I've used these NC devices in the past and they consist of a
standard reed switch with an attached 'slave' magnet which holds the
contacts closed. The actuating magnet has to be correctly positioned
to cancel the field of the slave when the two come together.

As might be expected, not straightforward to set up.

If someone really needed a magnetic switch which worked the other
way around, there are changeover reed switches available, so you
have a NO and NC contact. (They aren't used in burglar alarms
though.)

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]