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UK source for this magnetic switch?

Discussion in 'Electronic Repair' started by Terry Pinnell, Feb 7, 2009.

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  1. 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.
     
  2. Aren't there any electronic-parts distributors in the UK that consumers can
    purchase from?
     
  3. Adrian C

    Adrian C Guest

    "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.
     
  4. IanM

    IanM Guest

    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.
     
  5. PeterD

    PeterD Guest

    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.
     
  6. Phil Allison

    Phil Allison Guest

    "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
     
  7. Adrian C

    Adrian C Guest

    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...
     
  8. IanM

    IanM Guest

    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 ;-)
     
  9. Jasen Betts

    Jasen Betts Guest

    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.
     
  10. Baron

    Baron Guest

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

    Baron Guest

    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.
     
  12. 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.
     
  13. Adrian C

    Adrian C Guest

    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 ....
     
  14. Adrian C

    Adrian C Guest

    wrong. They have to discriminate.

    the days of the
    wrong. They have to discriminate.

    You fill in the order
    I understand their terms and conditions perfectly.
    Exactly

    Do you want them to lose money so that you
    I know they do. That is my point. They have to discriminate.
    I go elsewhere as I have stated.
     
  15. John G.

    John G. Guest

    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.
     
  16. IanM

    IanM Guest

    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.
     
  17. 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
     
  18. John G.

    John G. Guest

    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.
     
  19. Nobody

    Nobody Guest

    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.
     
  20. 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
     
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