Idiots guide to using reed switches (wanted)

Wobbleboxer

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Have seen a few posts recently about the use of reed switches to automate points. Having never used such magic in all my years of railroading I'm looking for some idiot proof guidance.

Am I right in thinking that a reed is just a momentary switch controlled by a magnet and therefore the wiring diagrams I have in my head should work the same as if they had trackside switches?

Where's the best/cheapest place to get them, somewhere like Maplins?

Thanks.
 

bobg

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Wobbleboxer said:
Am I right in thinking that a reed is just a momentary switch controlled by a magnet and therefore the wiring diagrams I have in my head should work the same as if they had trackside switches?
Certainly is! It's held on (or off) by the presence of the magnet.

Wobbleboxer said:
Where's the best/cheapest place to get them, somewhere like Maplins?

I fink I'd like to know that too.
 

whatlep

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bobg said:
Wobbleboxer said:
Am I right in thinking that a reed is just a momentary switch controlled by a magnet and therefore the wiring diagrams I have in my head should work the same as if they had trackside switches?
Certainly is! It's held on (or off) by the presence of the magnet.

Wobbleboxer said:
Where's the best/cheapest place to get them, somewhere like Maplins?

I fink I'd like to know that too.

Depends on what sort of reed switch you need and whether it's going to be used outdoors or not. If indoors, the bare reed switches (glass tube with two wires coming out of it to which you can solder) often used in OO or N gauge will do just fine. There are innumerable sources of those, including Maplin and RS components.

For outdoors I'd strongly recommend that you go for "fully encapsulated" reed switches. That's a conventional reed switch fully enclosed in a weatherproof, sealed plastic case which has two screw holes for attaching the switch to the track. They invariable come with two Teflon coated wires about 1 foot long pre-attached to the switch (with the solder connections also in the plastic case). This is a good example of the type and the one I use on my own line: http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0338743
 

minimans

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One word of caution is to make sure the amp rating is sufficient for the device you are controlling.
 

Wobbleboxer

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minimans said:
One word of caution is to make sure the amp rating is sufficient for the device you are controlling.
For a couple of LGB point motors, I'm guessing fairly small, 1 amp max?

Second question, I assume they need to be offset from the track centre to enable two way running without triggering the wrong thing, does that mean I won't be able to run bunker first any more?
 

pugwash

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I use LGB reed switches, they are readily available and will definitely fit / work.
:D
 

stockers

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Neil Robinson said:
but the £4.95 +vat p&p ay be ofputting for small orders.
You would burn more than that in petrol!
 

whatlep

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Wobbleboxer said:
minimans said:
One word of caution is to make sure the amp rating is sufficient for the device you are controlling.
For a couple of LGB point motors, I'm guessing fairly small, 1 amp max?

Second question, I assume they need to be offset from the track centre to enable two way running without triggering the wrong thing, does that mean I won't be able to run bunker first any more?
All the reed switches mentioned in previous posts will handle up to 10 amps momentary contact, far more than needed.

To achieve directional selection you'd need to be very accurate in placement of both reed switch and magnet on the stock. mine simply trigger every time something passes over them, irrespective of direction.
 

nicebutdim

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I just used normal standard reed switches, then heatshrinked over them and the connecting wire. Been working ok for nearly a year now. Maplin can be quite expensive for components, I (carefully) shop for most bits from ebay.
 

tramcar trev

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DO NOT BUY THE RECONDIONED ONES ON SALE....
Also I encpsulated mine in a small resin block made to look like some sort of inspection pit, see the thread on model tramway signals. The magnets are the tricky bit I found and I bought rare earth magnets from a model aeroplane shop, they use them to keep canopies closed and a re very strong and quite small..... I also have a small Vero board circuit that controls signals and has an output to a relay that could be used to throw points as well....
 

dumpy

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Wobbleboxer said:
Second question, I assume they need to be offset from the track centre to enable two way running without triggering the wrong thing, does that mean I won't be able to run bunker first any more?
Would it not be possible with a bit of lateral thinking to place a second reed switch before of after the one you have to reverse the points for reverse running. I have a number of switches activating points and signals and whereas they activate whenever a magnet goes over them, I have others to counter them to change points back, of alter signals again.
 

Bram

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Interesting thread, what type of magnets do you use and what strenght is required to trip the reed switch
 

dumpy

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On the garden railway I use the flat LGB magnets which fit in the recess under the engines. These are split into N and S. However if something goes wrong I trip the reed switches with an old bar magnet I have to hand. Just "swipe" the reed.
On my 00 gauge I just fasten a small bar magnet under any convenient coach or truck that has some metal. You can tell if the magnet works because if listen carefully you can hear the switch click.
 

Bram

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That sounds fine, but what if you have the reed switch mounted on a wagon/carriage and the magnet on the track? The distance between the two will then be greater, hence the the need for a beefy magnet. Which type do you guys use?
 

dumpy

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Ah! I see more lateral thinking required.
I presume the reeds are inside the wagon/coach rather than stuck underneath. If latter no problem, if former then a number of variables come into play. Obviously reed needs mounting as low down as possible and where floor is thinest. Most powerful, easily available magnets are Neodymium ones. (Lots on E-bay) Get bar not circular which have poles on opposite sides so will not activate reed. Finally the magnets have to be positioned such that they pass over the reed parallel to it.
That's about the limit of my experience in these matters. Hope it helps.
 

Bram

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Thanks for that info, the reeds are mounted on the outside, which should make it easier but I note your comment on the circular magnets
 

Bram

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That's a useful link Ross, many thanks
 

dumpy

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Interesting page on reed switches.
I have incorporated both ordinary relays and latched relays in my layout. Ordinary relays for the points. i.e. Momentary contact, and latched relays for signals when require the light to stay on.
 

minimans

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I just remembered I have a genuine idiots guide to reed switches and operation! It's in German but I'll see if I can find it and get you the details I seem to remember it has lots of different uses for reeds and what type are best.........................Paul