Author Topic: "Bistable" ("Latching") Reed Switch Source?  (Read 1737 times)

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Maletrain

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"Bistable" ("Latching") Reed Switch Source?
« on: December 29, 2017, 12:52:35 PM »
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I would like to make some "EZ Peezy" type, battery powered lighting for some short passenger cars, and turn it on and off by waving a magnet over it, like the commercial product functions.

But, I have not been able to find a source for magnetic reed switches that stay on after the magnet is taken away, but turn off when the magnet is used again.  That type is sometimes called "latching" and sometimes called "bistasble", as compared to "normally open" and "normally closed".

Apparently, a company named "Accurate Lighting" once sold them to the model railroad market, but now seems to be gone.

Searches on Mouser give thousands of results that are not actually bistable items, even when that is the first word in the search, and "customer support" finally answered my e-mail to say that none of what they sell are actually bistable.

So, does anybody know of a source for these?

C855B

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peteski

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Re: "Bistable" ("Latching") Reed Switch Source?
« Reply #2 on: December 29, 2017, 01:28:50 PM »
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EZ Peasy lights use a standard reed switch (not bi-stable) and an electronic chip which is always powered by the battery to toggle the lights on and off.  True bi-stable latching reeds are rare and expensive.  I looked for those once and gave up.

From my research I found out that those are regular 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, external magnet has to be applied with the poles reversed. That weakens the magnetic flux of the weak magnet allowing the contacts to open.   That is the (unscientific) gist of how those work.
« Last Edit: December 29, 2017, 01:33:56 PM by peteski »
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Maletrain

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Re: "Bistable" ("Latching") Reed Switch Source?
« Reply #3 on: December 29, 2017, 05:45:05 PM »
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Mike,

Thanks for the link, but with its size (1.125" L x 0.150" W x 0.225" H (28.58mm x 3.81mm x 5.72mm), it is a bit large, compared to what I am looking for.  Price isn't too terrible, at $52.80 for 10, but also much more expensive than what I had in mind.

Peteski,

I understand how the bistable version works with an internal "latching" magnet.  From what I have read, using an external "latching chip" uses battery capacity while the car just sits there.  That might mean that the batteries run down fast enough that trains in staging tracks could not just be left there between operating sessions without losing lighting function for the next session (or the one after?).  I really would like a "solution" that doesn't have me changing batteries inside the cars too often.  (But I am still trying to figure an unobtrusive way to put a battery holder under the car, maybe in a model of a battery box.)

Do you know how long the batteries in an EZ Peezy last just sitting there with the lights off?


peteski

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Re: "Bistable" ("Latching") Reed Switch Source?
« Reply #4 on: December 29, 2017, 06:51:33 PM »
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Peteski,

I understand how the bistable version works with an internal "latching" magnet.  From what I have read, using an external "latching chip" uses battery capacity while the car just sits there.  That might mean that the batteries run down fast enough that trains in staging tracks could not just be left there between operating sessions without losing lighting function for the next session (or the one after?).  I really would like a "solution" that doesn't have me changing batteries inside the cars too often.  (But I am still trying to figure an unobtrusive way to put a battery holder under the car, maybe in a model of a battery box.)

Do you know how long the batteries in an EZ Peezy last just sitting there with the lights off?

I have not tested the battery longevity in those light circuits, but I would venture a guess that in the off state the battery would last for years. The chip in question is most likely using typical CMOS technology and the current drain is in fractions of a micro-Amp in the off state. Not something I could even measure with my ammeter. I would not worry about the battery life in the off state.

Personally I'm not a fan of battery operated illumination in models. Not only it requires battery replacements (since the lights do get turned on and consume power), the batteries often leak and corrode the terminals. They are messy.  And you have to take the model apart to change the batteries. I much rather get get the power from the track and use a de-flicker circuit.  Of course I'm talking about DCC (since that provides a full track voltage during operation).  To me occasional wheel cleaning is much easier to deal with than replacing leaky batteries.
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Maletrain

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Re: "Bistable" ("Latching") Reed Switch Source?
« Reply #5 on: December 29, 2017, 08:29:03 PM »
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Battery leakage is definitely a bummer, when it happens.  But, it really should not happen.  Lately, battery brands that I used to count on to not leak have leaked, sometimes in less than a year, without beng discharged, first.  I guess that means that the manufacturing was transferred to China.  Duracell AAs seem to be the worst culprits in my recent experience. 

I would suggest that we start a thread on the best batteries (in sizes that we use for model railroading), but, with the unannounced changes in actual manufacturers these days, I don't think that would be meaningful, at least not for long.

So, batteries under the floor sound best to me.

With DCC, I hate to waste that expensive track power on lights that do not need to change function while in operation.  Sound is already taking additional power.  And, there is the complexity of taking power off the rails and getting it into the roofs of passenger cars.  There are not that many types of low-frictin power pickup trucks around, and putting wipers on standard trucks can cause a lot of drag that I don't want.

SOOO, does anybody have a good link to one of those electroninc chips that toggles power every time it sees a connection from a normally-open reed switch?

MK

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Re: "Bistable" ("Latching") Reed Switch Source?
« Reply #6 on: December 29, 2017, 08:38:49 PM »
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Battery leakage is definitely a bummer, when it happens.  But, it really should not happen.  Lately, battery brands that I used to count on to not leak have leaked, sometimes in less than a year, without beng discharged, first.  I guess that means that the manufacturing was transferred to China.  Duracell AAs seem to be the worst culprits in my recent experience. 

Me too!  I thought I was the only one noticing this.  Luckily they started leaking inside the package and not in the device.  But now I can't really trust them.  I don't use Energizers enough to see if they have similar problems.  Not for anything, the supposedly inferior RayOVac's do much better in the leakage department (no leaks so far).

peteski

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Re: "Bistable" ("Latching") Reed Switch Source?
« Reply #7 on: December 29, 2017, 09:49:51 PM »
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With DCC, I hate to waste that expensive track power on lights that do not need to change function while in operation.  Sound is already taking additional power.  And, there is the complexity of taking power off the rails and getting it into the roofs of passenger cars.  There are not that many types of low-frictin power pickup trucks around, and putting wipers on standard trucks can cause a lot of drag that I don't want.

SOOO, does anybody have a good link to one of those electroninc chips that toggles power every time it sees a connection from a normally-open reed switch?

Is that really *THAT* much of a problem (especially in N scale)? There are 0 scale layouts running under DCC with high-current boosters. N scale current consumption pales in comparison. A realistically lit N scale passenger car will probably would consume no more than 20mA of current (or even less). Especially if the LEDs are wired in series (3-per chain). Even the "nuclear glow" illuminated car will probably not use more than 50mA.  So a 20-car train with "nuclear glow" would use up 1A of current.  That is probably about the same as 2 sound equipped locos. A realistically lit 20-car train would use less than 400mA  (that is less than half of one Amp)!  Is that excessive?

Today's high-amperage boosters are plentiful and affordable. To me it makes sense to use track power.

The chip you are asking for is most likely custom manufactured for Rapido. They might have more info (if they are willing to reveal it).
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mmagliaro

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Re: "Bistable" ("Latching") Reed Switch Source?
« Reply #8 on: December 30, 2017, 03:01:20 AM »
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What you need is a basic "latch" circuit, to which you connect a standard reed switch.

Here's one:
http://www.discovercircuits.com/DJ-Circuits/Low-Voltage-Latching.htm

And I like this one (above) because it's designed to operate on very very low voltages.