Good source for latching magnetic Rees switch, or how make it latching?

[craigolio1]

Hello all. I need some latching magnetic switches to turn the markers on and off on the two end cars on my dinner train. This is the last step before its done.

I bought a bunch off of eBay and was super excited when they arrived today, only to find they were not latching. That was my fault for not knowing there is a difference.

So I still need some. Or, is there a very simple circuit to make the power latch using my momentary switches. They are normally open. These cars already have anti-flicker circuits with bridge rectifiers and will run off DCC. I think a function only decoder is over kill.

I looked on eBay again for the latching switches but they seemed a bit expensive. If someone knows a good source please share. I'm considering harvesting two from a couple of Rapido passenger cars just to get it done.

Thanks.

Craig

[peteski]

IIRC, the Rapido light boards use a solid-state (Hall-effect) electronic switch.  Reed switches themselves are not latching - they are just simple mechanical contacts closed when magnetic field is present. To make them latching there has to be a weak magnet placed next to them.  It is weak enough not to close the contacts but if if an additional external magnetic field is applied (using a stronger magnet), it then closes the contact and the constant weak magnetic field will keep them closed.  To open, you apply reverse polarity external magnetic field which then nullifies the weak holding field, opening the switch.

I have never shopped for one but, I'm sure that someone does sell latching reed switch (basically a reed switch and a weak magnet in a single housing).

[craigolio1]

Yes I did see them. $40 shipped for 10 seemed a bit much. I was just curious if anyone had a better idea or maybe I could make a simple circuit incorporating the switches I bought. I may crack open my Rapido CN caboose and see how easy it is to duplicate that circuit.

Thanks for the input.

Craig.

[peteski]

Rapido uses an electronic (Hall Effect) "switch".  To duplicate you would have to find the component they use.  They  work from 4.5V but I think that the Hall Effect switch will work from up to 15V.   The way they have that switch wired, it has constant battery voltage supplying power. If your models do not receive power when you are not running them on your layout I'm not sure of the Hall Effect switch will power up in off, on, or in a random state (if that matters).

I dug up the Easy-Peasy unit I bought for experimenting. (I'm not a fan of battery-powered lights).

It uses 3V to power the LEDs. It has an ordinary (non-latching) reed switch.  It also has a custom-made integrated circuit chip (IC) embedded on the circuit board (the IC die is bonded directly to the circuit board and encapsulated by a drop of black epoxy).  The reed switch is hooked up directly to the IC and it simply is used to toggle some flip-flop inside the IC. One momentary closure of the reed switch (by waving the magnet by it), turns the LEDs on, another momentary closure turns them off and so on.

There are no external resistors on the board so the LED current is either internally limited by the IC, or since the battery voltage is 3V, there is not current limiting (since the Vf of white LEDs is around 3V).

Since that IC cannot be identified, it would be difficult to find for purchase (it might be specifically made for that circuit).

[craigolio1]

Thanks very much for that analysis. So much for my plan. What to do.  Maybe a function only decoder is the easiest way.

[peteski]

How about installing a micro-miniature on-off slide or push button switch in the floor of the car?  I suppose that you would prefer just waving a magnetic wand over the car.   

But if the marker is track powered then why is there a need to turn it off?

[craigolio1]

It's a dinner train that ran in two directions and the loco ran around it. It had a car with markers at either end.

I'd like to be able to turn them on and off based on the direction.

Craig

[peteski]

Here is a link to couple of latching reed switches. http://www.meder.com/bistable-switches6.html .  You can contact that company to see if they'll send you s free sample (since you only  need couple) or point you to their distributor who carries these.

I think I found one at Digikey http://www.digikey.com/product-search/en?vendor=0&keywords=374-1062-ND
http://www.digikey.com/Web%20Export/Supplier%20Content/Meder_374/PDF/MEDER_Reedswitch_used_with_permanent_magnet.pdf?redirected=1

EDIT:  Ngineering also sells very small on-off slide switches.
http://www.ngineering.com/Switch.pdf

[craigolio1]

Thanks for the effort Peteski!  I contacted them to inquire about samples and a local distributor.

Craig