A further experiment in coach lighting.

Discussion in 'Other Electronic Interfaces' started by Keith M, Aug 25, 2018.

  1. Keith M

    Keith M Staff Member Moderator

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    I liked the idea of magnetically switched coach lighting as fitted in my recently bought LNER Dynamometer car so much that I've decided to experiment myself. I could always buy 'Function only' DCC decoders, but with a stock of about 35 coaches, that could work out quite a pricey option, so instead, I'm going for the magnetically operated reed switch method. There are a number of sellers of 3 pin NC/NO (Normally Closed/Normally Open) small glass reed switches quite cheaply (£3-£4 for 10) on that certain auction site, so with that in mind, I've ordered 15 to start with and we'll see how it goes. I'll hopefully be able to use the 'Magic wand' that came with the Dynamometer coach to do the switching, although I could easily make more up if needed as I have a stock of 3x3x3mm Neodymium magnets, and the reed switches themselves are easily capable of switching the low currents of the coach lighting, and it'll be useful to be able to switch the lighting off on coaches 'parked' in sidings etc and it will also reduce the total current load drawn from the DCC rail supply when coaches are not in use. I anticipate using small sections of Veroboard (stripboard) to mount the reed switches onto, gluing them into each coach roof so that I can just wave the "Magic Wand" over each coach roof to operate as needed. I'll likely do a "How-To" as and when I receive the switches, so 'Watch this space'.
    Keith.
     
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  2. Toto

    Toto Staff Member Founder Administrator

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    Great Keith. should be interesting.

    toto
     
  3. jakesdad13

    jakesdad13 Staff Member Moderator

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    I will look forward to this thread, I've got a few reed switches from an abandoned project and half a dozen coaches to build so it would be nice to install lighting as they are assembled.

    Pete.
     
  4. Keith M

    Keith M Staff Member Moderator

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    Standard 2 pin reed switches won't do the job Pete, as they change when the magnet is near, then revert back to the previous state after the magnet is removed. You'll need the 'changeover' type so that for example, in the 'Normally Open' state the circuit is not connected, wave the magnet over the switch and it will change to 'normally Closed', close the circuit and stay in that state until the magnet is waved over it again. This type of reed switch will usually have 3 pins, common, normally open and normally closed so it works in a similar way to an electro-mechanical latching relay. You could use the Normally Open type in conjunction with a latching relay I guess, but that's just adding to cost, space (in 00 gauge) and complication, so probably not worth it, easier to stick with the 3 pin reed switch I reckon.
    Keith.
     
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  5. jakesdad13

    jakesdad13 Staff Member Moderator

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    Cheer's Keith, to be fair it had crossed my mind but being a tech luddite I will go with the three pin type once I've clocked your method!

    Pete.
     
  6. TimberSurf

    TimberSurf Full Member

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    I will follow with interest, but I have a mind to use LDR's myself.
     
  7. Keith M

    Keith M Staff Member Moderator

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    It's been a while since I posted on further progress regarding using reed switches to switch coach lighting, basically because I've been unable to source suitable switches at a sensible price. I'm aware that layouts4u list suitable switches, but at £3 a pop, and with about 40 coaches to do, that's not gonna happen, so I've spent some time on the internet researching and found that the way these switches work is with a weak magnet attached to the side of a standard switch (layouts4u switch appears to have a 'wrap-around' weak magnet), the idea being that the magnet just holds the reed in place in the 'Off' position, but moving a stronger magnet alongside causes the reed to change over to the 'On' position, and the weak magnet is not strong enough to pull the reed back to it's original position. To change the reed back to it's original position, all that's needed is to apply the opposite pole of the strong magnet to the reed, thus changing it over to be held by the weak magnet again until the stronger magnet is again applied. I'm thinking that using maybe a small section of flexible magnet, such as is often used in refrigerator door seals, might do the job (these door seals are usually encased in the plastic sleeve that seals the door to the casing when it's closed) so I need to look at this further. I also had a look at maybe using electronics to switch the lighting, using the reed switch purely to switch the electronics, but cost and physical size make this unappealing, so it's back to experimenting with the reed switches again. More 'dabbling' required, unless other members have had success with other methods, if so, do tell!:giggle:

    Keith.
     
  8. TimberSurf

    TimberSurf Full Member

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    Keith
    I did a little research a while back and found these, but never got any further. We need to find an accessible supplier.
    The best I found was £2.04 each if 100 bought (but they are also very big)

    From my research I found out that they are a reed switches with a weak magnet attached to them. It is not strong enough to close the contacts until the correct polarity external magnet is placed close by. Then the contacts close and the built-in magnet is just strong enough to keep the contact closed. To open the contact, the external magnet has to be applied with the poles reversed. That weakens the magnetic flux of the weak magnet allowing the contacts to open.

    https://www.reed-sensor.com/reed-sensors/biased-smd/standard-latching-reed-sensors/
    2000 at 85p ea from https://www.digikey.co.uk/products/en/switches/magnetic-reed-switches/193?k=latching reed switc

    I can find expensive ones, or cheap by the thousand! Hence I gave up!
     
    Last edited: Nov 27, 2018
  9. Keith M

    Keith M Staff Member Moderator

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    As luck would have it, layouts4u had a stall at the Peterborough show last weekend, so I bit the bullet and bought 3 of the latching reed switches from them. I've had a chance to try one and it seems to work ok, so am building it into one of my Birdcage coaches, currently waiting for glue to dry, but the pic below shows the difference between a standard reed switch (ignoring the fact that this is a changeover 3 pin type) and the 2 pin 'latching' type. As can be seen, it has a tiny red weak bar magnet heat shrink sleeved to the side of the switch, which holds the reed until a stronger magnet is moved near to it. All I need now is a source of tiny weak magnets!
    Keith.

    IMG_1351.JPG
     
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  10. paul_l

    paul_l Staff Member Administrator

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    How about a logic OR gate latch - a quad 2 input orgate can be had for less than a pound, I've seen on ebay 35 for a tenner.

    Circuit

    upload_2018-12-11_23-53-21.png

    The reed feeds gate 1, once the output goes live the the latch back to the second output keeps the led on.

    Paul
     
  11. Keith M

    Keith M Staff Member Moderator

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    Interesting Paul, but what is the physical size of these gates and what other (if any) components are required ? (don't forget, I'm on 00 Gauge!). I understand that the reed switch closing would trigger the gate, but as it's normally open, would a second momentary closing then switch the gate off? If not, then how would the gate be switched off?
    Keith.
     
  12. Keith M

    Keith M Staff Member Moderator

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    Well, I found I already had in stock some of the flexible magnet I previously mentioned, so I did a few experiments, but all to no avail, so gave up and bought a further 7 of the latching reed switch from 'layouts4u', set to and did some installs as detailed, first candidates were the 3 coach "Birdcage" set I bought recently. Having removed the body, first job was to clean up and tin the tag ends of the bogie pickups, since the metal is plated and doesn't accept solder. It makes sense since both bogies are fitted with pickups, to electrically link the tags on the bogies together, thus reducing the chance of losing electrical contact on points or dirty rails, so this was done, leaving a small wire loop to allow for bogie swivelling. The loose wire ends will be passed through a suitable hole in the interior seating unit to connect to the rectifier PCB fitted into whatever space is available, usually toilet or Guards compartment. Wires were superglued in place on the chassis to avoid being trapped on reassembly.

    IMG_1352.JPG
     
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  13. Keith M

    Keith M Staff Member Moderator

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    Once this was done, the wires were passed through into the seating unit. Extra weight in the form of small sections of lead flashing were glued into the pockets formed in the underside of seats, since despite the metal weight, these coaches (as are many) were still on the light side.

    IMG_1353.JPG
     
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  14. Keith M

    Keith M Staff Member Moderator

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    At this point, the prepared PCB was 'Blu-tacked' to the chassis, input wiring from the pickups having been connected. Red/Black wires will go (red via reedswitch) to the LED strip glued into the coach roof. This pic shows the centre coach chassis, which you'll note has a different setup, toilet compartments being near to the coach centre. There were even moulded in toilet pans (can't imagine why, as the toilet compartment windows are opaque, so you can't see them anyway!) with an angled division between the 2 compartments. This and the pans were cut out to give sufficient room for the PCB, this particular one being a 'slimline' version of my usual standard fit type, constructed on a 5 strip wide board instead of my usual 6 wide one as there ain't much room here. You can see in this pic, the added weights glued under the seat mouldings. IMG_1355.JPG
     
  15. Keith M

    Keith M Staff Member Moderator

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    Now with passengers in place and the seating unit back in place, wiring ready for connection to the roof/body section.

    IMG_1356.JPG
     
  16. Keith M

    Keith M Staff Member Moderator

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    These last 2 pics are taken using one of my Bachmann Mk1 coaches which have a separate roof rather than the "Birdcage" set which has roof/sides/ends as a single unit. Reason for this is that it's clearer photographically with just a roof section, though the setup is exactly the same for both types. I use SMD LED strips with a thin aluminium backing for my coach lighting, more compact than standard LED's soldered to a Veroboard strip, but no reason why either can't be used, it's just personal choice. I glue the LED strip in place, then solder the reed switch into the +ve line, supergluing it to the coach roof to ensure it stays put, connect the supply wires from the PCB, keeping them as short as is reasonably practicable (you don't really want to be able to see the wiring through the coach windows unless absolutely unavoidable).

    IMG_1358.JPG
     
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  17. Keith M

    Keith M Staff Member Moderator

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    The previous pic shows the reed switch itself in position, tiny magnet heat shrink sleeved to the side of the switch itself. They aren't cheap at £3 each, and I doubt I'll retro-fit all my coaching stock of about 40 at this price, but as with most things, "Yer pays yer money and takes yer choice!" If I do eventually manage to find a cheaper supply of these switches, then I may reconsider, and of course, it's useful to be able to switch off coach lighting as it all adds up to extra electrical load on your DCC track supply. At this point in reassembly, it's best to get out your operating magnet, drop the coach onto powered track and check lighting and switch operation before refitting the roof. Here's what mine looks like before roof refitting.

    IMG_1357.JPG
     
  18. Keith M

    Keith M Staff Member Moderator

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    So that about wraps it up, 10 coaches down, 30 to go (if I bother with all of them!). An easy job to fit, inexpensive, unless you're tempted to go for the ESU coach lighting kits which are priced at about £18 a coach........think how many coaches you could DIY fit out yourself for that kind of money!!! As they say in Yorkshire, "Ow much???":giggle:
    (With apologies to our Yorkshire members!)
    Keith.
     
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  19. York Paul

    York Paul Staff Member Moderator

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    WHAT HOW MUCH !!!:avatar:
     
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  20. Keith M

    Keith M Staff Member Moderator

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    "Tightwad Alert!!!"
    Yes, I'm STILL trying to find a cheap/easy way of being able to switch coach lighting on/off as needed on a DCC layout like mine, so ever alert to a simple and cheap way to do this, rooting about on that well-known auction site, I came across these rather small "Mini-torch push button On/Off switches" at the princely sum of £2.40 for 10 (and that includes postage!!!). The brain cells came up with the idea of gluing one into the coach end so that the 'button' part just fits through a hole drilled through the coaches moulded end 'corridor connection'. I use home-made bellows type connectors, fitted only at one end of each coach and glued to the corridor bellows frame which most coaches already have so my thinking is to fit a switch into the coach end which doesn't have a bellows attached, the switch itself then being covered (but not operated by) the bellows on the adjoining coach. I appreciate that this would mean uncoupling a coach to switch on or off as needed, but that's surely better than the alternative (which some coaches come already fitted with) a switch on the underside, but a lot better than having to take each coach off the track to do the switching operation. The switches are so shallow that the button would be too deeply set into a coach end to be operated by the pressure of the bellows onto the button. Here's the switch I'm referring to.

    IMG_1365.JPG
     
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