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33374 Views 8 Replies Latest reply: Jul 29, 2013 7:04 PM by TonyStewart RSS
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Feb 10, 2012 9:23 AM

Remote switch & white LEDs

Sorry, this is actually two questions.


Question 1.  I have a model train that has LED lighting in the cars.  The lights are activated by waving a magnetic wand over one end of the car.


Took one car apart and found a magnetic reed switch, some sort of an IC (three lead, SMD potted in epoxy) and 2 - 1.5V batteries as the only components on the circuit board (besides the LEDs - no resistors, no capacitors, no nuthin!).


Since I broke the glass reed switch taking the board out, I have obtained replacements (100V, 1A), soldered one in and it works fine.  Trouble is, the IC is potted with dark green epoxy so I can't tell what it is.  I know if I scrape off the epoxy I will probably destroy the printing on the IC.


I think it may be a low-voltage SCR, but am not sure.  It obviously acts as a latch since the reed switch is normally open except when the magnet pulses it, which grounds one lead of the IC to the negative pole of the batteries for a short time and the LEDs go on.  When you pass the magnet over it again, the lights go off.  This works much better than any other kind of switch since it is hidden inside the car (nothing shows outside).


Any ideas as to what the potted component is?  (All the latching IC I have found are low-current CMOS Hall-effect ICs - don't think they would be able to drive two high-intensity LEDs).  I would like to order replacements for that IC (either SMD or through-hole), since I am bound to screw one up eventually and the manufacturer isn't forthcoming with part numbers (not surprising).



Second question.  I am looking for warm white LEDs in 3mm TO-1 size (through hole mount).  LEDtronics makes exactly what I am looking for, but I don't want to order lots of 500, 1,000 or more!!! (Digi-Key doesn't stock them, either).


The color I am looking for is around 3,000K or slightly below.  Ordered some 4,000K white LEDs from DigiKey (special order - still waiting) but think they might end up being too cool (and cost around $1 each).  Any suggestions???  I want an LED that looks like an incadescent light color-wise.


-- John

  • Novice 1 posts since
    Feb 10, 2012
    Currently Being Moderated
    Feb 10, 2012 11:51 PM (in response to John63)
    Remote switch & white LEDs

    Hi John,


    I sell a small latching circuit that might work for you. It was designed for movie prop makers. It's called a "pushbutton latch" on my web-site



  • Novice 15 posts since
    Dec 28, 2011
    Currently Being Moderated
    Feb 22, 2012 10:07 PM (in response to John63)
    Remote switch & white LEDs

    Do you want single SMD LED ?     Try to buy a white LED strip light and  cut one down and then you can still use the strip light mormally ! and you can try ,maybe there is what you want(i bought 10 7watt light bulbs 3 months ago,they are  really high quality) , good luck !

  • MarcMa Novice 1 posts since
    May 18, 2013
    Currently Being Moderated
    May 18, 2013 2:39 AM (in response to John63)
    Remote switch & white LEDs

    Hi,Buddy, I do not know whether your are still in need. Now , I know a website , I think you can go there and have a look,Maybe you can find one that you are looking for, Good luck, I bought a sample from them , Excellent. You can have a try.

  • brightchoicelighting_ Novice 3 posts since
    Jul 15, 2013
    Currently Being Moderated
    Jul 15, 2013 6:10 AM (in response to John63)
    Remote switch & white LEDs

    No !dea though i found your experiment interesting, can you also build some setup like this for me.?

  • Tim17543 Novice 1 posts since
    Jul 22, 2013
    Currently Being Moderated
    Jul 22, 2013 8:43 AM (in response to John63)
    Remote switch & white LEDs

    Dim LED's: most white LED's need 3.2V to 3.8V to operate.  As for an SCR: gate will trigger it on, but you'll need the load current to drop below the specified holding current (10 mA or so) or voltage across the SCR to reverse.

  • TonyStewart Novice 1 posts since
    Jul 29, 2013
    Currently Being Moderated
    Jul 29, 2013 7:04 PM (in response to John63)
    Remote switch & white LEDs

    Many Hall sensors can certainly drive LEDs



    ATS177-PG-A-B  is one such sensor.  However you may want a latch instead of a momentary switch, 


    They probably used an edge triggered flip flop with Qbar to D feedback and with an RC filter on the input to reduce noise.

    A Schmitt trigger would be better to drive an edge triggered FLip Flop ( /2 counter has Qbar to D feedback) and can be obtained in a single SMD package.


    Train Lights for N scale are best done with a light pipe using glass or plastic fibre optic or thick fishing line bonded to a hole in the lens of 3 or 5mm part with clear epoxy and black heat shrink around the whole part to block stray light.  THgere are tons of warm White 5mm and 3mm is too big for N scale. Not sure what scale you use.



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