UK source for this magnetic switch?

[Terry Pinnell]

Can anyone point me towards a UK source (phone or online) for an
inexpensive cylindrical, enclosed reed switch, N/C, for use in a
burglar alarm circuit please.

I'm still googling but so far without success and want to place an
order for delivery Monday.

 

[William Sommerwerck]

Aren't there any electronic-parts distributors in the UK that consumers can
purchase from?

 

[Adrian C]

Aren't there any electronic-parts distributors in the UK that consumers can
purchase from?

"electronic-parts distributor" in the UK implies a trade only source
with limited interest in selling to retail customers. Those that do,
typically charge exorbitant delivery, minimun order and service charges
- leaving the only real alternative to be a toy shop called Maplin. Or eBay.

 

[IanM]

Aren't there any electronic-parts distributors in the UK that consumers can
purchase from?

Plenty, but he's looking for the wrong thing.

There is no such thing as a NC reed switch. The induced magnetism in the
reeds *always* attracts them together when you bring the magnet up, and
never repels them so all two terminal bare reed switches are NO.
It is possible to put an additional non-magnetic reed in the capsule, so
that one of the magnetic reeds is in contact with it until an external
magnetic field is applied, but as the reeds have to be brought out
through the pinch of the glass capsule to support them, this provides a
SPDT switch, not a NC one although it can be used as such.

If he googles 'SPDT reed switch' (without the quotes), both Rapid and
Maplin stock them. but for alarm use, I'm fairly sure he wants a
complete reed sensor and magnet pair for a NC loop, NOT a bare reed capsule.

If he's looking for a switch/magnet pair he can mount in the edge of a
door and its frame in drilled holes, googling 'recessed reed switch'
will find plenty, all NC in the presence of their magnet (i.e. with the
door closed). Again Maplin have some.

If he wants a true NC action, he's either going to have to stick a bare
SPDT reed in a cylindrical housing e.g a plastic tube from a biro with a
dab of hot glue or mess around with a biasing magnet to cancel out the
field of the actuating magnet as it approaches. Enclosed SPDT reed
switches, although nearly as rare as hens teeth, are available but
apparently not in a cylindrical recessed format.

 

[PeterD]

Can anyone point me towards a UK source (phone or online) for an
inexpensive cylindrical, enclosed reed switch, N/C, for use in a
burglar alarm circuit please.

I'm still googling but so far without success and want to place an
order for delivery Monday.

No Radio Shack there? Try an alarm company then... They were commonly
used in the big dish satellite systems on the positioning motor, but
since big dishes are uncommon now, that's not a good source, but some
satellite dish companies may have a few sitting on the shelf.

 

[Phil Allison]

"Ian Massive Pedant "

There is no such thing as a NC reed switch.

** It's a better than even money bet Terry wants the switch to be closed
with a magnet nearby.

Which IS the NORMAL situation in an alarm installation.



...... Phil

 

[Adrian C]

Who could forget CPC/Farnell? Deal with them once and they'll keep your
letter box well fed for the rest of your life!

Yeah, but they are trade.

You can deal as an individual but on small quantities you pay postage,
don't get free technical support etc.. Basically 2nd class treatment and
they make you feel that. Attempts at getting trade registration for my
credit worthy limited company failed at Farnell without an explanation
why :-(

It takes a bit longer, but I find eBay works for me. If it's urgent,
then Maplin, Cricklewood Electronics or me turning up at an RS trade
counter with my VAT registration certificate (yes really).

BTW Radio Shack pulled out years ago. Now that was a toy shop...

 

[IanM]

"Ian Massive Pedant "




** It's a better than even money bet Terry wants the switch to be closed
with a magnet nearby.

Which IS the NORMAL situation in an alarm installation.



..... Phil

You snipped the bit where I gave a usable search term and suggestion for
a retail supplier for exactly that! Here, I've put it back:

Thanks for not swearing ;-)

 

[Jasen Betts]

"electronic-parts distributor" in the UK implies a trade only source
with limited interest in selling to retail customers. Those that do,
typically charge exorbitant delivery, minimun order and service charges
- leaving the only real alternative to be a toy shop called Maplin. Or eBay.

Find one where you can walk in off the street during business hours
if you demonstrate posession of atleast half a clue when you walk in
and pay cash they'll treat you ok.

 

[Baron]

The only one in the UK which has trade counters in several cities is
RS Components - and they won't serve someone walking in off the
street. And rightly so - a genuine client shouldn't have to wait while
an amateur asks for advice, etc.

Maplin is the place for that sort of thing.

Actally B&Q, Focus, Wikkes, Aldi, Morrisons, Even Asda have or have had
similar devices on their shelves !

 

[Baron]

But not a N/C one. You'll need to obtain the correct reed switch
elsewhere and fit it to the housing. Or just use a transistor to
invert the output as I suggested earlier.

All the ones I referred to were standard reeds with an actuating magnet
in a separate housing. Ak for burglar alarm systems.
I've never seen a normally closed one used for those, although I have
seen change over, SPCO, reeds used in electronic equipment.

 

[Terminal Crazy]

The only one in the UK which has trade counters in several cities is RS
Components - and they won't serve someone walking in off the street. And
rightly so - a genuine client shouldn't have to wait while an amateur
asks for advice, etc.

CPC have counters and served me, but i have registered an account on their
web site . It was No problem and the parts were waiting for pick up.

 

[Adrian C]

Farnell also will hapily sell to the public via their website - The
Farnell organisation own CPC btw, I`ve also had good dealings with Rapid
Online.

Happily, that's a laugh.. :-(

The word is grudgingly. Both CPC and Farnell technical support is free
for account holders, and there is no minimum order for trade customers.
Other companies even have free post for trade customers on any order
size. Because on things like internet sales they have to agree to
"distance selling regulations" and similar, they end up losing money
dealing with consumers. Maplin is the only UK national choice for
hobbyists and small time repairers like me.

Never mind, if it works for you. Good

eBay and purchasing outside the UK works for me and yes; I know what a
scam fest eBay can sometimes be, but not in this case.

For example I recently had to replace a shot schottky SMD diode in a HP
printer SMPS. Per part, 20p each from Farnell. Minimun order charge £20.
Post and packing £4.25.

From an eBay seller in the states, £8 including postage for 500 diodes.
They were delivered within the week.

If it's urgent I jump in the car and find something in a shop closer. Or
risk a dodgy substitute for the part, which I really shouldn't do if
it's critical ....

 

[Adrian C]

Yeah they are happy to take your money whoever you are,

wrong. They have to discriminate.

the days of the

'trade only' wholesalers is more or less over.

wrong. They have to discriminate.

You fill in the order

form, authorise the credit card and the goods arrive next day, what`s so
dificult to understand about that?

I understand their terms and conditions perfectly.

That`s because Farnell are in business to make money not cater for
hobbyists who want one diode.

Exactly

Do you want them to lose money so that you

can fix your printer on the cheap?

I know they do. That is my point. They have to discriminate.

If you don't like CPC or Farnell, I suggest you try Rapid Electronics.

I go elsewhere as I have stated.

 

[John G.]

Can anyone point me towards a UK source (phone or online) for an
inexpensive cylindrical, enclosed reed switch, N/C, for use in a
burglar alarm circuit please.

I'm still googling but so far without success and want to place an
order for delivery Monday.

Dragging this discussion back from the trading pinciples of some companies.

I do not know about the UK but in Australia and I suspect the USA this sort
of thing is easy to find at DIY stores like Bunnings (here) or Home
Depot/Lowes (in the US) in the build your self a burgular alarm aisle.

There are at least three layman's electronic suppliers in Aus, DSE (about
equiv to Radio Shack), Jaycar (a bit better) and Altronics. All have walk
in, chose for yourself, super market type shops. Surley the UK has
equivelents.

John G.

 

[IanM]

Dragging this discussion back from the trading pinciples of some companies.

I do not know about the UK but in Australia and I suspect the USA this sort
of thing is easy to find at DIY stores like Bunnings (here) or Home
Depot/Lowes (in the US) in the build your self a burgular alarm aisle.

There are at least three layman's electronic suppliers in Aus, DSE (about
equiv to Radio Shack), Jaycar (a bit better) and Altronics. All have walk
in, chose for yourself, super market type shops. Surley the UK has
equivelents.

John G.

Unfortunately Maplin have nearly turned into Rat Shack. No blister
packed resistors at three for a pound (80's pricing, it would be 3 for
five pounds now) but they've got the piles of consumer tat and now have
branches without a parts counter. Where they still do parts, their
standard stock level for any store stocked semiconductor (and that's not
many from their vastly reduced range) is 3 with long restocking
intervals. Bit awkward if you are assembling a bridge from discrete
diodes or want enough bicolour LEDs to monitor a bi-directional serial
link with handshake lines. They are better than nothing but not by a
lot. I am not aware of any other chain of retail electronic component
stockists, but hopefully someone knows of some alternatives.

 

[David Nebenzahl]

Can anyone point me towards a UK source (phone or online) for an
inexpensive cylindrical, enclosed reed switch, N/C, for use in a
burglar alarm circuit please.

I'm still googling but so far without success and want to place an
order for delivery Monday.

Sorry, I can't help, being in the US where things like this are
trivially easy to get.

Just one thing: did someone here say that switches like this were
typically N/O rather than N/C? And that such could be used for an alarm
circuit?

Think about it: if you have a N/O switch as an alarm sensor, all the bad
guy has to do to get in is to cut it out of the circuit. There's a
reason alarm switches are normally closed.

Hard to believe a N/C reed switch wouldn't be easy to buy somewhere in
England.


--
Personally, I like Vista, but I probably won't use it. I like it
because it generates considerable business for me in consulting and
upgrades. As long as there is hardware and software out there that
doesn't work, I stay in business. Incidentally, my company motto is
"If this stuff worked, you wouldn't need me".

- lifted from sci.electronics.repair

 

[John G.]

Sorry, I can't help, being in the US where things like this are trivially
easy to get.

Just one thing: did someone here say that switches like this were
typically N/O rather than N/C? And that such could be used for an alarm
circuit?

Think about it: if you have a N/O switch as an alarm sensor, all the bad
guy has to do to get in is to cut it out of the circuit. There's a reason
alarm switches are normally closed.

Hard to believe a N/C reed switch wouldn't be easy to buy somewhere in
England.

N/O reed switches are the simlest to build and in alarm systems are useually
held closed by a magnet on the other side of the door etc. so it will
activate the alarm if the door opens or the wire is cut.
But like you I find it hard to believe they are hard to get.

Terry, If you only need one I will post it from Australia if you are
desperate.

John G.

 

[Nobody]

Just one thing: did someone here say that switches like this were
typically N/O rather than N/C? And that such could be used for an alarm
circuit?

Think about it: if you have a N/O switch as an alarm sensor, all the bad
guy has to do to get in is to cut it out of the circuit. There's a
reason alarm switches are normally closed.

Phil Allison said:

** It's a better than even money bet Terry wants the switch to be closed
with a magnet nearby.

Which IS the NORMAL situation in an alarm installation.

IOW, it's a question of how you define "normally".

Reed switches are open in the absence of a magnetic field, and closed when
one is present.

For a relay, you would call such contacts "normally open".

But for a burglar alarm, the "normal" situation is for the magnetic field
to be present, from a permanent magnet in a door or window which is
"normally" adjacent to the reed switch. In this situation, the contacts
will be held closed.

 

[David Nebenzahl]

Phil Allison said:


IOW, it's a question of how you define "normally".

Reed switches are open in the absence of a magnetic field, and closed when
one is present.

For a relay, you would call such contacts "normally open".

But for a burglar alarm, the "normal" situation is for the magnetic field
to be present, from a permanent magnet in a door or window which is
"normally" adjacent to the reed switch. In this situation, the contacts
will be held closed.

Ah, so. That makes sense.


--
Personally, I like Vista, but I probably won't use it. I like it
because it generates considerable business for me in consulting and
upgrades. As long as there is hardware and software out there that
doesn't work, I stay in business. Incidentally, my company motto is
"If this stuff worked, you wouldn't need me".

- lifted from sci.electronics.repair