all  led"s  are one color or the other, but too achieve what you want use a white  led and a red led and just put a diode in series so as one direction of the dc current will turn on red led and other direction of the other diode will turn on the white  . that will be the simplest way to do what you want!

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Red/White bi-color LED's are fairly rare.  It may be because they seem to be somewhat fragile.  I had some that I used in a project, and several of them died for no apparent reason.  I still have a few, but I'm a bit spooked about using them.

In my search I found some odd ones on eBay: 10 Pcs Flashing Leds 0 3/16in Red/White Clear Flash Indicator Bicolor

Not exactly what I was looking for, but kinda' neat.

If your rear light already has a lens and you are comfortable assembling small components, another option is to use 2 pre-wired surface-mount LEDs.  For less than 50 cents each, here are some 0402 size LED (0.04" x 0.02") or about 1mm on the longest dimension. 

0402 pre wired leds in white and red

So you could fit 2 of these LEDs within the "footprint" of a typical 3mm sized LED popular in O gauge.  If you have a lens in place you won't be able to tell the light is coming from two different bulbs. I don't know how prototypical dual color backup lights worked but they might have been implemented with 2 different bulbs too?  Or was it a red lens that rotated into place over a white bulb sort of like a semaphore signal?  

In any case having the wiring separate (rather than a 2-pin bi-color LED) allows you to wire it up for 3-wire common-anode or common-cathode operation which could simplify hookup depending on your electronics.

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bicolor red-green 5mm LED backlit green

What he said (sort of).   Above photo from this OGR thread.  Obviously use an outward facing white surface mount LED instead of green!  

Above photo shows a 3-terminal common-anode configuration that was required for the application discussed there.  However, if you need a 2-terminal bipolar configuration you could simply straddle the surface mount LED between the 2 terminals of the leaded LED.

If red-white bicolor LEDs are as rare as suggested, at $3.50 each (plus shipping?) wouldn't it be a hoot if that red-white LED is fabricated as above!  

 

 

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riki posted:

Thanks Stan. John.  

I ordered some so I'll see.  But also may try yours guys suggestions.

 

Could you let us know (photos would be great...hint...hint) what it looks like?  3mm?  5mm? pre-wired?  any instructions or technical info on DC operating voltage range?  from the link provided earlier, all I can tell is it's a bipolar bi-color LED costing $3.50 (plus shipping).

red white LED for over 3 bucks

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So is that the $3.50 red/white LED in your last photo?  Did it come with any technical specs on voltage range?  I see what appears to be some components under heat-shrink.  Since it's 2-wires it would require positive or negative DC...where is this voltage coming from (that presumably flips polarity when direction changes)?

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