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Magnetic Reed Switch

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Magnetic Reed Switch
Posted by scott018 on Friday, February 10, 2012 10:49 AM

Wanted to put a magnetic reed switch like the ones that Kato used on the Easy Peeze pass light kit in a N scale car. Wave a mag over it ...light on, wave it again ....light off. But am having a tough time finding them anybody have a source for them.......Thanks Much

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Posted by BroadwayLion on Friday, February 10, 2012 11:47 AM

All Electronics has them, but they are not the ones you need.

You should check with Mouser, I got some there that worked for what I wanted, but they only pull in the presence of the magnet. I want to turn the lights off, I put the magnet on top of the train. I want them on, I take it away.

Are you using DCC with power on all the time? Then the lights will be on all of the time.

Are you using battery powered car lights? I tried that but was not happy with what I built.

What I am doing now is to use a rectifier, a regulator, capacitors and LEDs The lights will stay on after the train stops, but then after a while the capacitors will be fully discharged and the lights will be off.

ROAR

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Here there be cats.                                LIONS with CAMERAS

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Posted by St Francis Consolidated RR on Friday, February 10, 2012 12:27 PM

scott018

 Wave a mag over it ...light on, wave it again ....light off. ..Thanks Much

I am also interested in this, and a resource. So if anybody knows a resource I will be watching. LION's response may be interesting in some way, but it has nothing to do with the question, pretty much as usual. LION needs to ROAR in time out again!!!!

The St. Francis Consolidated Railroad of the Colorado Rockies

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Posted by MisterBeasley on Friday, February 10, 2012 1:03 PM

The keyword to search for is "latching."  That's the industry term for something that stays where you put it until you tell it to go back the other way.  As I recall, though, I had a hard time finding these, too.

It takes an iron man to play with a toy iron horse. 

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Posted by Motley on Friday, February 10, 2012 3:23 PM

St Francis Consolidated RR

 

 scott018:

 

 Wave a mag over it ...light on, wave it again ....light off. ..Thanks Much

 

 

I am also interested in this, and a resource. So if anybody knows a resource I will be watching. LION's response may be interesting in some way, but it has nothing to do with the question, pretty much as usual. LION needs to ROAR in time out again!!!!

But wait, we're missing the random photo of a cat? The would fully explain his response.

ROOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOAAAAAAAAAAAAAAAAAAAAAAAAARHHHHHHHHH!!!

Michael


CEO-
Mile-HI-Railroad
Prototype: D&RGW Moffat Line 1989

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Posted by Motley on Friday, February 10, 2012 3:56 PM

Actually I forgot. I have a couple of Walthers P2K locomotives that have the QSI decoder. And it has a reed switch in it to reset the decoder.

Try to contact Walthers?

Michael


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Posted by MisterBeasley on Friday, February 10, 2012 4:53 PM

Motley

Actually I forgot. I have a couple of Walthers P2K locomotives that have the QSI decoder. And it has a reed switch in it to reset the decoder.

Those, however, are momentary, non-latching switches.  MIniatronics carries those, and they're very inexpensive.  But, they won't do the job that the OP wants.

It takes an iron man to play with a toy iron horse. 

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Posted by St Francis Consolidated RR on Friday, February 10, 2012 5:02 PM

Gentlemen....is this what we are looking for?

[View:http://www.meder.com/switch_ksk-1e66_us.html?&tx_jppageteaser_pi1[backId]=2864:550:0]

p.s.....I set this to open in a separate window, I hope it works that way! I find it annoying personally to click on something that takes me off the original page.

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Posted by BATMAN on Friday, February 10, 2012 6:29 PM

Rapido also uses them in there coaches. They work well. I want to rig one of their magnets down from a signal arch and route the train on the track that passes under it to turn them on or off as the train leaves or enters the yard or station. You don't have to touch the coach to turn them on, just get within about a quarter inch or so.

Email Rapido, they may be able to point you in the right direction of where you can buy them.

                BrentCowboy

Brent

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Posted by BroadwayLion on Friday, February 10, 2012 7:43 PM

Motley

 

 

 

But wait, we're missing the random photo of a cat? The would fully explain his response.

ROOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOAAAAAAAAAAAAAAAAAAAAAAAAARHHHHHHHHH!!!

The animal control officer keeps deleting my cats. If you want cats click the link in my signature. Mischief

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Here there be cats.                                LIONS with CAMERAS

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Posted by hon30critter on Friday, February 10, 2012 9:43 PM

St Francis

I can't get your posted link to work, and I'm not sure how to fix it. I know others have done this before when a link won't work. Perhaps someone can step in to save the day.

Dave

I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!

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Posted by JSperan on Friday, February 10, 2012 10:09 PM

This link should work.

From what I could gather from the documentation & data sheets a magnetic coil is required in addition to the Reed switch with latching function.

 

Meder Electronic-Reed Switches


 

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Posted by St Francis Consolidated RR on Friday, February 10, 2012 10:16 PM

hon30critter

St Francis

I can't get your posted link to work, and I'm not sure how to fix it. I know others have done this before when a link won't work. Perhaps someone can step in to save the day.

Dave

Now it works Dave....I didn't originally use the little chain link deal at the top to insert the website. Geez!

But I still don't know if the switch is what we're looking for. The post below mentions that it needs a coil magnet, but I'm a little embarrassed to say I don't know what that means.

 

The St. Francis Consolidated Railroad of the Colorado Rockies

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Posted by kstrong on Friday, February 10, 2012 10:58 PM

If I'm reading the .pdf file that covers the latching function, you still need a secondary magnet in association--one that's not strong enough to close the switch on its own, but can hold it closed after a magnet of the same polarity passes over. When a magnet of opposite polarity passes over, it separates it--if I'm reading correctly (no gaurantees that I am).

I think for purposes of turning lights on and off, you'd perhaps want to use a "normal" magnetic reed switch in conjunction with a latching relay. This is a relay that when energized with a pulse of electricity, throws one way, then when energized with a pulse again, throws itself back the other way. that would allow you to use a magnet to turn the lights on and off. The magnet would momentarilty close the circuit to energize the relay coil. The output of the relay would be used to route power from the track to the lights.

Probably no trouble to hook that up in HO scale, but fitting a relay inside an N-scale coach may be a bit problematic.

Later,

K

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Posted by Alantrains on Saturday, February 11, 2012 4:20 AM

You can make any magnetic reed switch latching by placing a weak magnet near it. It needs to be placed such that it won't cause the reed to operate by itself. Placing a strong magnet near it will cause it to operate and the weak magnet (if in the right place) will hold it in and cause the latching. Turning the strong magnet in the opposite direction will cancel the magnetic field and the reed will release. It requires a little fiddling to get the right strength magnet in the right place. It's best to do this trial and error process at the workbench with the lights connected so you can tell if the reed is operated or released.

cheers

Alan Jones in Sunny Queensland (Oz)

 

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Posted by hdtvnut on Saturday, February 11, 2012 5:11 AM
I was buying Meder glass tube latching reeds fron Demar until Meder decided to wholesale them in large lots only - now Demar does not sell them, nor anyone else I could find. However, the Meder MK06-10-E is the same thing with an added plastic housing. They don't require an external magnet or coil. I was able to get ten at $4 each, double the price of the unhoused version, from, I seem to remember, Digikey. Hal
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Posted by JSperan on Saturday, February 11, 2012 9:56 AM

Yes, Digikey has them.  Looks like the price is $7+ for one though.

The E at the end designates the latching function.  These do not require a magnet to assist in closing the circuit, but a two pole magnet is required to cycle them on and off.

Meder  #MK06-10-E

I've been looking for something like this too.  The price however, does not make me feel warm and fuzzy.  I think I could figure out a magnetically operated, transistorized, latching switch, for less than $7.

Thanks for pointing me in the right direction to find these all the same!

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Posted by rrinker on Saturday, February 11, 2012 11:09 AM

 If the lights are being powered by a battery or some other continuous power supply (absolutely no drop outs), then yes, a basic standard reed switch could be used as the trigger to a simple transistor flip-flop circuit so that the lights would go on the first time you bring the magnet near, and the lights would go off if you brought the magnet near again. The transistor portion of the circuit would always be drawing power though, even with the lights off, so it wouldn't last forever in storage, you'd have to remove the batteries. Since the lights, even if using LEDs, would be the lion's share of the load, it would be better than not turning off the lights.

                   --Randy


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by scott018 on Saturday, February 11, 2012 12:33 PM

Yes it sounds like I am looking for the latching ones, the same that are in the Rapido passinger car lighting units 

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Posted by JSperan on Saturday, February 11, 2012 1:20 PM

rrinker

The transistor portion of the circuit would always be drawing power though, even with the lights off, so it wouldn't last forever in storage, you'd have to remove the batteries. Since the lights, even if using LEDs, would be the lion's share of the load, it would be better than not turning off the lights.

                   --Randy

Randy,

Thanks for joining this discussion.  I've linked a schematic below.  In the circuit transistors are used to latch a momentary push button.  The text mentions the capacitor charging when the circuit is powered up but the transistors don't "turn on" until the momentary contacts are closed.

Latching a Push-button

Are the transistors drawing power in the off state with this circuit?  Once the cap charges fully will it continue to consume power if the momentary contacts are not closed, turning on the transistors?

Thanks.

JS

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Posted by rrinker on Saturday, February 11, 2012 2:15 PM

 Yes, that circuit will always draw power, not a lot, but it's not 0. Depending on the on or off state, either Q1 or Q2 is conducting to hold that state. Current draws are miniscule, with the 10K and 470K resistors used for biasing, but again, it's not 0. It will take a long time to drain the batteries when off.

 Can't really be avoided, the only zero current draw option is the latching reed switch (and after a long enough time the bias magnet would loose enough of its magnatism to not work any more - like old motor magnets get weak. But we're talking 40-50+ years here, hardly worth worrying about.

 As for this circuit, I didn't look up the limits on the BC547 to see what kind of load it can handle. Probably NOT 5-6 30ma light bulbs.

 BTW that's a great site with lots of information and useful circuits. The section on H-bridges, that's how DCC decoders drive the motor. ANd there are a pair of nice simple CDU power supplies for those using twin coil switch motors.

                     --Randy


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by JSperan on Saturday, February 11, 2012 2:40 PM

rrinker

 Yes, that circuit will always draw power, not a lot, but it's not 0. Depending on the on or off state, either Q1 or Q2 is conducting to hold that state. Current draws are miniscule, with the 10K and 470K resistors used for biasing, but again, it's not 0. It will take a long time to drain the batteries when off.

Ahh, OK I see now.

rrinker

 As for this circuit, I didn't look up the limits on the BC547 to see what kind of load it can handle. Probably NOT 5-6 30ma light bulbs.

No, the BC547 has a maximum 100 mA current capability.  Substituting a 2N2222 (800mA max) for higher current loads should do the trick though, not?

rrinker

 BTW that's a great site with lots of information and useful circuits. The section on H-bridges, that's how DCC decoders drive the motor. ANd there are a pair of nice simple CDU power supplies for those using twin coil switch motors.

                     --Randy

Yes, lots of great circuit ideas.  Thanks again Randy!

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Posted by rrinker on Saturday, February 11, 2012 5:38 PM

 The 2N2222 should work. It's possible the resistors would need to be adjusted, but the BC547 is a common substitute the opposite way.

              --Randy


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by JSperan on Sunday, February 12, 2012 3:24 AM

rrinker

 The 2N2222 should work. It's possible the resistors would need to be adjusted, but the BC547 is a common substitute the opposite way.

              --Randy

Thanks Randy,

Just picking this electronic stuff up mostly by teaching myself over the last 40 years, so still learning.  I bought that Forest Mimms book from Radio Shack when I was a kid and understood about a tenth of it, Huh? but came back to it later in life and it made more sense.  Anyway, I'm rambling now.

I wondered myself if you would advise possible adjustment of the resistors.

I'm also wondering if the 2222 would need more power to turn on?  Changing the charging resistor or the cap?

I'll have to look closer at the datasheets.  While those are helpful, some of the specs are like a foreign language, again Huh?

It's a circuit I want to breadboard and take to a proto-board once it's solid.

If I have issues I might look you up again.

Thanks for the know-how as always!

Thinking about latching reed switches;

If one took a normal reed switch and carefully wrapped and secured a coil of magnet wire around the tube then fed the coil from the reed switch through an appropriate resistor, when you used a magnet to initiate the circuit, would the coil be able to latch the relay until an opposite pole magnet was used to open the circuit again?

JS

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Posted by rrinker on Sunday, February 12, 2012 9:43 AM

 That might work, but getting the right number of turns so the coil wouldn't draw too much power might be tricky. The other option would be two reed switches and a relay wired to latch, one reed switch bypaases the latching contacts to pull the relay in, ther other would be a NC reed switch which would interrupt the relay power and allow it to drop out. Magnet to the frotn of the car turns on the lights, magnet to the rear turns them off.

                     --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by steamnut on Tuesday, February 14, 2012 5:24 PM

As others have pointed out you are looking for a latching magnetic reed switch. I have used them for caboose interior lighting with great success. An Austrian company used to sell them through Walthers but they haven't been listed in Walthers for years now. There must be sources because they are used today for passenger lighting in some of the high end passneger car runs.

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